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Best CBD Oil for Arthritis: Benefits & Uses for Rheumatoid Arthritis

As many as 54 million Americans are diagnosed with arthritis every year. According to NHIS data, it’s the leading cause of work disability leave in the United States.

Arthritis can be a real pain — literally and figuratively. The disorder often brings a lowered quality of life for those affected, forces people to take time off work, and makes it difficult to exercise and remain in good shape. Many people are therefore looking for an effective form of pain management to help with the disorder.

One of the most popular arthritis-supportive supplements being used today is cannabidiol (CBD) — one of the primary active ingredients in the cannabis plant.

Can CBD really help with arthritis? What’s the best CBD oil for arthritis?

We’ll explore these questions in detail in the article below. I’ll give you my top 5 CBD oils for arthritis pain, and give you some valuable insight into how to choose the best CBD oils for the job on your own.

This is a big topic so let’s dig in.

Best CBD Oils for Arthritis: Our Top 5 Brands of 2022

If you’re reading this article, you’re probably interested in finding a CBD product that can help you with your arthritis symptoms.

For those of you who want to understand how CBD works for arthritis, and what else you can do to make the effects of CBD even better, keep reading the sections below. If you’re simply looking for the best CBD oil to take, here’s a list of my top five CBD oils — including a breakdown of why I think it’s such a strong option.

Let’s dig into the list.

1. Royal CBD (Most Potent)

Get 15% off all Royal CBD products. Use code “CFAH” at checkout.

Technical Details:
Total CBD Content 250 – 2500 mg
Available Flavors Natural, Peppermint, Vanilla, Berry
Potency 8.3 – 83.3 mg/mL
What We Like About Royal CBD Oil:

A newcomer to the scene, Royal CBD is a premium manufacturer opting for high-grade organic ingredients in all its CBD products — including this full-spectrum hemp oil. The company’s product range is pretty simple, featuring only CBD oil, capsules, gummies, and some CBD-infused topicals.

The oil and capsules are full-spectrum extracts, while the gummies are made with a 99% pure CBD isolate. This oil has a few different options — you can choose between flavors like mint, berry, vanilla, or unflavored, and three separate potencies — 250 mg, 500 mg, 1000 mg, and 2500 mg of CBD per 30 milliliters (1 ounce) bottle. The strongest option carries 83.3mg of CBD in each milliliter.

For the best value, I recommend you aim for the higher potency option. This product has a higher initial cost than the others, but comes at a slight discount and will last a very long time — even if you use CBD on a daily basis. Only a few drops are needed to get a healthy dose of CBD.

If you don’t like the taste of natural CBD oil you can get their capsules instead. These come in an easy-to-swallow soft gel form and contain 25 mg per capsule.

All Royal CBD products are tested in third-party laboratories to ensure each batch is clean, has consistent levels of CBD, and is free from any potential contaminants.

  • Made with organic Colorado-grown hemp
  • All products are made with supercritical CO2 extraction
  • You can buy both full-spectrum and CBD isolate products
  • The highest potency bottle delivers 83.3 mg/mL
  • Every batch of product has been tested by a third-party laboratories
  • These products are priced on the higher end, although well justified

2. Gold Bee (Best Organic Formula)

Pros:
  • Made from US-grown, organic hemp
  • Contains full-spectrum CBD
  • 1200 mg of CBD per bottle (40 mg/mL)
  • Extracted with supercritical CO2
  • Delicious Kiwi flavor
  • Sweetened with organic honey
  • Third-party tested for cannabinoid content and purity
Cons:
  • Only one concentration available
  • Limited flavor options
What We Like About Royal CBD Oil:

When it comes to arthritis, the quality of ingredients is paramount, as any pro-inflammatory compound can actually worsen your symptoms. With Gold Bee, this isn’t a problem, as the brand sells all-organic CBD oils formulated with full-spectrum hemp extracts. The hemp used by the company comes from organic farms in Colorado and is gently extracted with supercritical CO2 to provide the highest purity and consistent potency.

The full-spectrum of cannabinoids means you’re getting the synergistic effects from all naturally-occurring compounds in hemp, including the supportive cannabinoids and terpenes. As a result, you need less CBD to achieve the desired results than you would with CBD isolate. The Gold Bee CBD oil packs 1200 mg of CBD in a 30-mL bottle, translating into 40 mg of CBD daily. The dosage fits within the most common range for daily use.

Gold Bee also doesn’t use artificial flavorings and sweeteners in its products. The kiwi version of the CBD oil is infused with natural terpenes and sweetened with organic honey from Brazillian rainforests. The entire Gold Bee product line is rigorously tested in third-party laboratories for potency and purity.

3. CBDPure

Technical Details:
Total CBD Content 100 – 600 mg
Available Flavors None
Potency 1.6 – 10 mg/mL
What We Like About CBDPure Hemp Oil:

CBDPure was founded in 2016 by cannabis aficionados from Colorado. The company has a simple mission — to make high-quality CBD oils made from organic hemp.

Although the company only sells CBD oil and capsules, it’s perfected both of these products. These extracts are made with supercritical CO2 and tested in third-party laboratories for quality assurance.

When it comes to CBDPure hemp oil, it isn’t as potent as those offered by Royal CBD — so if you’re looking for something high potency CBDPure may not be the best option available. However, if you want something cheap that maintains a high level of quality — CBDPure is an excellent choice.

CBDPure has an incredible return policy — which suggests the founders truly stand by their products. If you don’t like the product you can return it for 100% money back within 90 days. Most other CBD companies only offer this deal for 14 or 30 days, so this says a lot about the integrity of CBDPure as a company.

  • CBDPure products are sourced from organic hemp grown in Colorado
  • The company uses supercritical CO2 to make its extracts
  • 100% Satisfaction Guaranteed program (full refund within 90 days)
  • Narrow product range
  • The oil is slightly less potent than Royal CBD

4. Hemp Bombs

Technical Details:
Total CBD Content 300 – 5000 mg
Available Flavors Unflavored, Acai Berry, Orange Creamsicle, Peppermint, Watermelon
Potency 10 – 1166.6 mg/mL
What We Like About Hemp Bombs:

Hemp Bombs are one of the longest-standing companies in the CBD space. They’ve been around for years now, dating back before the CBD boom. As a result, the company has had a chance to become well-established in the industry, and have a loyal customer base as a result.

Although the branding makes these oils resemble a gas station brand of an energy drink — the oil contained inside is nothing to scoff at.

Hemp Bombs is able to use its large presence in the industry to source some of the best hemps in the country. They process all the hemp within the United States in GMP-certified labs. The company chose to use a CBD isolate for this oil rather than a full-spectrum extract. Using CBD isolate is cheaper and more accurate than full-spectrum products, but lacks the synergistic benefits of the entire cannabinoid and terpene profile — a concept referred to as the entourage effects.

The real benefit of using a CBD isolate is that this is the only way to guarantee the product contains no THC — which is the psychoactive cannabinoid responsible for producing the high from marijuana plants.

Hemp Bombs, like the others on this list, conducts extensive third-party testing on every batch of hemp extract that comes out of its facilities. This is the only way to ensure complete transparency and build trust with consumers. Hemp Bombs publishes these test results on the website for anybody to see — and includes the entire gamut of testing (heavy metals, cannabinoid profile, residual solvents, and microbial contaminant testing).

  • Made from high-grade CBD distillate
  • Comes in all different flavors and potencies
  • Third-party tested for transparency
  • Lacks the benefits of the entourage effect
  • Flavored with synthetic flavoring agents

5. Nuleaf Naturals

Technical Details:
Total CBD Content 240 – 4850 mg
Available Flavors None
Potency 48.5 mg/mL
What I Like About Nuleaf Naturals:

Nuleaf Naturals has the simplest product lineup I’ve ever seen. The company only offers one oil — a 48 mg/mL full-spectrum hemp extract. They use this same oil for every product offering.

When you go to the company website, you’ll find you can buy this oil in all different bottle sizes — but the oil itself is exactly the same. Even the pet oil options the company sells use this exact same extract.

The benefit of using just one oil is that Nuleaf Naturals can put all their attention and energy into this one product — doing everything they can to make it as top-notch as possible. And that’s exactly what they’ve done.

This oil is one of the best tastings and has some incredibly powerful effects compared to many of the other oils I’ve tried.

In order to even qualify for my top 5 list, the company has to offer third-party testing. I can’t trust the test results from a company doing their own testing. Nuleaf Naturals remains up to date with ordering third-party tests for every batch produced by the company. You’ll find a new test uploaded to the company website every two or three months as they release new batches of products. I have a look at these tests every time I order a bottle and have yet to find anything that stands out.

Every test I’ve seen from Nuleaf Naturals proves the oil is free from contaminants like heavy metals or pesticides, and the potency is almost always exactly the advertised potency. Occasionally a batch will come out that’s 2-5% off the advertised amount — which is expected for full-spectrum extracts.

  • Simple product lineup
  • Offers oils for both humans and pets
  • CBD oil comes in all different bottle sizes to support any budget
  • No flavor options available
  • All products use the same hemp oil

6. Medterra

Technical Details:
Total CBD Content 1000 – 2000 mg
Available Flavors Citrus
Potency 33.3 – 66.6 mg/mL
What I Like About Medterra:

This is a new product offered by the CBD giant Medterra. This company specializes in making broad-spectrum hemp extracts. This means the oil contains CBD, and most of the other supplemental cannabinoids like CBC, CBG, CBN, and THCV — but all traces of the psychoactive THC have been removed.

Medterra is intimately involved in the cultivation process for the hemp they use to make this oil — which allows the company to control the amount of pesticide used, and the timing of the harvest. These factors play a big role in the overall quality of the oil. Most other CBD companies buy hemp from farms located around the United States or Canada and have little control over the growing process.

Like any high-end CBD oil, this product has been thoroughly tested by both Medterras analysis lab, and independent laboratories.

Medterra sells a lot more than just CBD oils — you can also buy topicals, capsules, and pet treats.

  • Medterra has complete control of the entire manufacturing process from seed to bottle
  • Extensive third-party testing
  • Broad-spectrum THC-free hemp oil
  • Limited bottle sizes and flavor options
  • This oil is heavily processed

What is Arthritis?

Arthritis is one of the most common causes of disability in the United States. Millions of people in the United States alone suffer from debilitating joint pain and inflammation from arthritis.

The disease causes severe inflammation and pain, as well as swelling and loss of function in the joints.

There are two main types of arthritis:

  1. Rheumatoid arthritis — This form of arthritis is an autoimmune disease. This means that the cause of inflammation is triggered by our own immune systems. White blood cells mistakenly attack and destroy our own joint tissue, causing a cascade of inflammatory processes in the joints — causing them to swell up and feel hot and sore. This form of arthritis can affect any joint but tends to focus on the larger joints such as the knee, hips, elbows, and knuckles.
  2. Osteoarthritis — This form of arthritis is caused by physical trauma and wear and tear rather than the immune system. This form of arthritis is common in athletes and older people. The condition begins with a low-grade inflammation in the joint itself, which causes the degeneration of protective cartilage and synovial fluid (lubrication for the joints). As the joint tissue becomes damaged, inflammation and pain worsen and reduce the mobility of the joint. This condition is degenerative — which means it tends to worsen over time.

All forms of arthritis have the same basic symptoms — pain, inflammation, and reduced mobility of one or more joints. Despite having radically different underlying causes, CBD has become extremely popular among arthritis sufferers in recent years.

CBD Oil & Arthritis: Can it Help?

Let’s explore how CBD works, and why it’s become so popular among arthritis patients.

CBD is one of the active ingredients in hemp plants (Cannabis sativa). This phytochemical is completely non-psychoactive, which means it won’t cause the user to feel high. A related cannabinoid (THC) not found in high amounts in hemp plants is what causes marijuana users to feel high.

When CBD enters your bloodstream, it interacts with the endocannabinoid system — a complex neurochemical network responsible for maintaining various homeostatic functions in the body. This includes pain perception, immune response, temperature control, memory, mood, hunger, fertility, inflammation, and much more.

While research on CBD and arthritis is in the early stage, current evidence coming from animal studies and several human trials suggests it may alleviate the symptoms of arthritis while resulting in virtually no side effects.

Animal Studies on CBD & Arthritis

  1. A 2011 study discovered that CBD was able to reduce inflammatory pain in rats by changing the way pain receptors react to stimuli.
  2. A 2014 review of the existing animal-based studies concluded that CBD may be effective for relieving osteoarthritis.
  3. In a 2016 study, researchers found that CBD may relieve inflammation linked to arthritis in problematic areas when applied topically.
  4. A 2017 research paper suggested that CBD was a safe and effective treatment option for osteoarthritis joint pain.

The big question is whether these results can be replicated in actual human trials. Interestingly, this seems to be the case!

Clinical Trials on CBD & Arthritis

  1. In 2006, the first study on cannabinoids and rheumatoid arthritis concluded that a pharmaceutical CBD-enriched cannabis extract called Sativex had a “significant analgesic effect” in arthritis patients. Researchers reported that pain and inflammation were significantly reduced throughout the treatment despite having almost no reported side effects.
  2. A 2008 study involving cannabinoids in the management of chronic pain discovered that CBD offered effective pain relief and improved sleep quality in the test group.
  3. A 2016 analysis of human trials for rheumatoid arthritis, osteoarthritis, and fibromyalgia also found that CBD resulted in a reduction in joint pain and improvement in irregular sleep patterns caused by chronic pain.

CBD Oil For Sale: Where To Find High-Grade CBD Oil

Most people look for CBD oils online — myself included. Don’t get me wrong, it’s possible to find high-quality CBD oil in a local dispensary, but I’ve found online to offer a greater range of products, and quite frankly, better prices.

I recommend you check out the company websites listed in the section at the top of this article, or do your own research using the tips listed in the section below to find other reputable CBD brands online. Read reviews, and look for third-party testing before you buy the product to make sure it’s going to deliver on its promises.

Must-Know Details for People Buying CBD Oil for Arthritis

Knowing what to look for in the best CBD oil for arthritis will save you a lot of hassle — there are a lot of fly-by-night companies currently offering CBD oils with questionable quality, to say the least.

CBD is an emerging market, so it’s no wonder many companies want to capitalize on the booming trend before the dust settles and the industry stabilizes.

With such an abundance of different brands selling CBD in various forms, it’s important to find a trusted manufacturer who will ensure high standards for their products.

Here’s what you should pay attention to when shopping for CBD oil to help with your arthritis symptoms.

1. Hemp Source: Where is the Hemp Sourced?

Hemp plants are unique in that they will absorb and accumulate virtually any and all elements in the soil and air in which it’s grown — this includes both the good stuff and the bad stuff.

Plants grown in contaminated soils will often contain harmful levels of heavy metals like cadmium, lead, or mercury. For this reason, it’s important you look for products that have been grown in regions with little contamination — such as America or Canada.

Some companies source cheap hemp from India or China to cut costs — which are notoriously high in toxic heavy metal contaminants.

See also  Is cbd oil safe for your liver

I prefer oils made from American-grown hemp because of the high standards here that prevent farmers from growing food or supplementing crops in contaminated soils or polluted air.

The best hemp comes from USDA-certified organic farms — but these are hard to come by at the moment.

2. Extraction Method: Did The Company Use Toxic Solvents to Make the Oil?

Most reputable companies use CO2 for making their CBD oil. Pressurized CO2 works as a solvent that pulls CBD and other compounds from the plant material. When the pressure is released, the CO2 evaporates completely, leaving no trace of harmful chemical solvents in the final product.

This is in opposition to the conventional extraction methods — which use toxic solvents to strip the cannabinoids from the plant material such as hexane, propane, butane, or ether. If these solvents are used they need to be evaporated out. Oftentimes, small amounts of these chemicals will remain in the final product which can cause many unwanted side effects to people using the oil.

3. Cannabinoid Spectrum: Could There be any THC in the Final Product?

The next thing to look at is the cannabinoid profile of the oil. This refers to the amount of CBD and other cannabinoids in the final product.

There are three main categories here:

  1. Full-spectrum extracts — these oils contain many different cannabinoids aside from just CBD
  2. Broad-spectrum extracts — these oils contain many cannabinoids with the exception of THC
  3. CBD isolates — these oils contain only one cannabinoid — CBD

Many experts argue that full-spectrum CBD oil is better for arthritis-related inflammation. A 2016 Israeli study found that unlike pure CBD isolate, full-spectrum extracts offered more reliable benefits for arthritis sufferers. However, there are benefits to using broad-spectrum or isolate-based products as well.

4. Route of Administration: How is the Oil Intended to be Used?

CBD comes in a few different forms and can be used in several different ways:

  1. Sublingual — placed under the tongue for fast absorption
  2. Edibles — helps mask the flavor of hemp oil bit has a slower onset of effects
  3. Vape liquids — used in vape pens to inhale the CBD for absorption via the lungs
  4. Topicals — applied directly to the skin for localized relief

Generally, the best CBD products for arthritis are going to be a combination of topical CBD and oral CBD. I rub CBD-infused joint cream on the affected area first and then use CBD oil sublingually for the fastest onset of effects. I know a few other people that prefer to use a CBD-infused vape pen and CBD topicals to relieve arthritis.

5. Third-Party Testing: Does the Company Provide Transparency for its Claims?

Every company has the option to send a batch of their product to a third-party laboratory for content analysis. In order to be considered a third-party lab, it needs to have no affiliation with the manufacturer — allowing for a completely unbiased assessment of the products in question.

These laboratories measure the potency of CBD, scan the entire cannabinoid profile of the product, and can detect over 200 common contaminants.

This form of testing offers transparency on the quality and potency of the product. If you can’t find third-party testing to confirm the CBD oil you’re looking at contains exactly what the company says it does — I recommend you look elsewhere until you find a company that publishes this data publicly. It’s the only way to ensure the product you’re buying is going to be safe and effective.

What’s the Ideal CBD Dosage for Arthritis?

There is actually no one-size-fits-all dosage of cannabidiol when it comes to inflammatory pain caused by arthritis. The dose will vary a lot from one person to the next.

However, information gathered from CBD users suggests that most arthritis sufferers take around 25 mg of CBD in the form of an oil twice a day. You may need to increase or decrease this dose depending on how you respond to the oil. Most people shouldn’t expect any improvement in the first couple of days.

If you don’t feel any difference, gradually increase the amount of CBD oil until you find an effective dose.

Final Thoughts on Using CBD Oil for Arthritis

So far, research investigating the benefits of CBD oil for arthritis shows promising results. More research is needed to fully understand the role CBD and other cannabinoids play in alleviating arthritis-related pain and inflammation.

Although a large share of the studies currently available come from animal models. There are only a handful of good-quality clinical trials (double-blind and randomized). Of the few we have available in the scientific literature, all have shown notably positive results from the treatment group using CBD rather than placebo.

With all that said, it’s important to remember that CBD isn’t an overnight fix to all your problems, and in more serious cases, it may need some time to make the impact you’re looking for.

If you’re planning to use CBD oil for arthritis, consult your doctor first to discuss any potential interactions with other underlying health conditions or medications you may be taking.

Have you used CBD oil for arthritis symptoms? Post your results in the comment section below!

References:

  1. Schuelert, N. & Mcdougall, J.J. (2011). the Abnormal Cannabidiol Analogue O-1602 Reduces Nociception in a Rat Model of Acute Arthritis Via the Putative Cannabinoid Receptor Gpr55., Neuroscience Letters, 500(1), 72–76.
  2. La Porta, C., Bura, S.A., Negrete, R., Maldonado, R. (2014). Involvement of the Endocannabinoid System in Osteoarthritis Pain. The European Journal of Neuroscience, 39(3), 485–500.
  3. Philippot, H.T., O’Brien, M., McDougall, J.J. (2017). Attenuation of Early Phase Inflammation By Cannabidiol Prevents Pain and Nerve Damage in Rat Osteoarthritis. Pain, 158(12), 2442–2451.
  4. Blake, D.R., Robson, P., Ho, M., Jubb, R.W., McCabe, C.S. (2006) Preliminary Assessment of the Efficacy, Tolerability and Safety of a Cannabis-based Medicine (Sativex) in the Treatment of Pain Caused by Rheumatoid Arthritis. Rheumatology (Oxford), 45(1), 50–52.
  5. Russo E. B. (2008). Cannabinoids in the Management of Difficult to Treat Pain. Therapeutics and Clinical Risk Management, 4(1), 245–259.
  6. Fitzcharles, M.A., Baerwald, C., Ablin, J., Hauser, W. (2016). Efficacy, Tolerability and Safety of Cannabinoids in Chronic Pain Associated With Rheumatic Diseases (fibromyalgia Syndrome, Back Pain, Osteoarthritis, Rheumatoid Arthritis): a Systematic Review of Randomized Controlled Trials. Schmerz (Berlin, Germany), 30(1), 47–61.
  7. Gallily, R., Yekhtin, Z., Lumir, O.H. (2015). Overcoming the Bell-Shaped Dose-Response of Cannabidiol by Using Cannabis Extract Enriched in Cannabidiol. Pharmacology & Pharmacy, 6, 75–85.
Nina Julia

Nina created CFAH.org following the birth of her second child. She was a science and math teacher for 6 years prior to becoming a parent — teaching in schools in White Plains, New York and later in Paterson, New Jersey.

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Attenuation of early phase inflammation by cannabidiol prevents pain and nerve damage in rat osteoarthritis

* Corresponding author. Address: Departments of Pharmacology and Anaesthesia, Pain Management and Perioperative Medicine, Dalhousie University, 5850 College St, Halifax, NS B3H 4R2, Canada. Tel.: (902) 494-4066; fax: (902) 494-1388. E-mail address: [email protected] (J. J. McDougall).

Copyright © 2017 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the International Association for the Study of Pain.

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-No Derivatives License 4.0 (CCBY-NC-ND), where it is permissible to download and share the work provided it is properly cited. The work cannot be changed in any way or used commercially without permission from the journal.

Abstract

Osteoarthritis (OA) is a multifactorial joint disease, which includes joint degeneration, intermittent inflammation, and peripheral neuropathy. Cannabidiol (CBD) is a noneuphoria producing constituent of cannabis that has the potential to relieve pain. The aim of this study was to determine whether CBD is anti-nociceptive in OA, and whether inhibition of inflammation by CBD could prevent the development of OA pain and joint neuropathy. Osteoarthritis was induced in male Wistar rats (150-175 g) by intra-articular injection of sodium monoiodoacetate (MIA; 3 mg). On day 14 (end-stage OA), joint afferent mechanosensitivity was assessed using in vivo electrophysiology, whereas pain behaviour was measured by von Frey hair algesiometry and dynamic incapacitance. To investigate acute joint inflammation, blood flow and leukocyte trafficking were measured on day 1 after MIA. Joint nerve myelination was calculated by G-ratio analysis. The therapeutic and prophylactic effects of peripheral CBD (100-300 μg) were assessed. In end-stage OA, CBD dose-dependently decreased joint afferent firing rate, and increased withdrawal threshold and weight bearing (P < 0.0001; n = 8). Acute, transient joint inflammation was reduced by local CBD treatment (P < 0.0001; n = 6). Prophylactic administration of CBD prevented the development of MIA-induced joint pain at later time points (P < 0.0001; n = 8), and was also found to be neuroprotective (P < 0.05; n = 6-8). The data presented here indicate that local administration of CBD blocked OA pain. Prophylactic CBD treatment prevented the later development of pain and nerve damage in these OA joints. These findings suggest that CBD may be a safe, useful therapeutic for treating OA joint neuropathic pain.

1. Introduction

The most prominent form of synovial joint disease, osteoarthritis (OA), is characterised by joint degeneration, pain, and in some patients, articular neuropathy. 21 Chronic pain associated with OA is a major concern for which there are few viable treatments. The first-line therapy used to treat OA pain is nonsteroidal anti-inflammatory drugs; however, with long-term use their efficacy declines and they can lead to major adverse gastrointestinal and cardiovascular events. Historically, OA has been classified as noninflammatory arthritis; however, there is now overwhelming evidence that synovitis can occur in response to pro-inflammatory mediators being released into the joint. 10,11,13,29,32 It is believed that this low-level inflammation contributes to degenerative changes that affect the entire joint leading to the development of peripheral sensitisation and nociceptive pain. 18,22,37 In addition to structural defects, there is growing evidence to suggest that approximately 30% of patients with OA have neuropathic pain. 1,34 Thus, a therapeutic which can block inflammation, neuropathy, and pain is sorely needed.

The endocannabinoid system (ECS) plays an important physiological role in the regulation of tissue inflammation and pain. 23,38 A functional ECS has been demonstrated in the joints of animals 36 and humans, 31 which acts tonically to maintain joint homeostasis. Immunohistological and pharmacological evidence confirm that cannabinoid 1 (CB1) and cannabinoid 2 (CB2) receptors are expressed on the neurones and microvasculature that supply rat knee joints. 23,24,36 In addition, CB2 receptors are colocalized with pronociceptive transient receptor potential vanilloid-1 (TRPV1) channels where, through common intra-cellular pathways, they act together to modulate joint pain. 23,24,36 This suggests that drugs which target the ECS have the potential to regulate painful arthritis and inflammatory joint disease.

Cannabidiol is the main noneuphoria producing component of the cannabis plant. 26 Pharmacologically, CBD has a complex signalling mechanism whereby it can both activate and silence classical cannabinoid receptors as well as modulate noncanonical cannabinoid receptor pathways. In in vitro studies, CBD has been shown to be an inverse agonist at CB2 receptors, 40 and a full antagonist at CB1 receptors 40 and G protein-coupled receptor-55 (GPR55). 33 In vitro, CBD was found to be an agonist at TRPV1 3 and transient receptor potential ankyrin 1 (TRPA1), 9 which play a central role in the development of OA. 27 In musculoskeletal disease models, systemic administration of CBD suppressed the progression of collagen-induced arthritis by reducing inflammatory cytokine production. 20 Although these preliminary findings indicate a possible role for CBD in relieving joint inflammation, the local effect of articularly applied CBD on OA and joint pain has not been investigated.

The initial aim of this study was to assess the effect of locally administered CBD on joint pain in animals with end-stage OA. Since acute inflammation can contribute to the long-term development of OA joint pain, 32 the ability of CBD to reduce acute OA synovitis and prevent the subsequent progression of persistent OA pain was also investigated. Finally, the effect of prophylactic CBD treatment on OA joint neuropathy was assessed.

2. Methods

2.1. Animals

Male Wistar rats (150-175 g; Charles River Laboratories, Senneville, QC, Canada) were housed in ventilated racks at 22°C ± 2°C on a 12:12 hours light:dark cycle (light-on from 7:00 to 19:00). After arrival at the animal care facility, all rats were permitted at least 1 week to acclimate to their environment. Animals were housed in pairs, cages were lined with woodchip bedding, and animals were provided with environmental enrichment. Standard laboratory chow and water were provided ad libitum. All experimental protocols were approved by the Dalhousie University Committee on the Use of Laboratory Animals, which acts in accordance with Animal Research: Reporting of In Vivo Experiments (ARRIVE) and the standards put forth by the Canadian Council for Animal Care.

2.2. Sodium monoiodoacetate model of osteoarthritis

Animals were deeply anaesthetised (2%-4% isoflurane; 100% oxygen at 1 L/min) until cessation of all sensory reflexes. The right knee joint was shaved, swabbed with 100% ethanol and 50 μL of sodium monoiodoacetate (MIA) (3 mg in saline) was injected into the joint space (intra-articular; i.artic.). The knee was then manually extended and flexed for 30 seconds to disperse the solution throughout the joint.

2.3. Electrophysiological recording of joint afferents

After OA development (14-19 days after MIA), animals were deeply anaesthetised using urethane (25% solution; 2 g/kg i.p.). Core body temperature was measured by a rectally inserted thermometer and maintained at 37°C ± 1°C by a thermostatically controlled heating blanket (CWE Inc, Ardmore, PA). After loss of the pedal withdrawal reflex, the trachea was cannulated to allow for artificial ventilation with a Harvard rodent respiratory pump (Harvard Apparatus, Holliston, MA) with 100% O2 (stroke volume: 2.5 mL; breath frequency: 52 breaths/min). The left carotid artery was cannulated to allow for continuous measurement of the mean arterial blood pressure. The cannula was attached to an in-line pressure transducer (Kent Scientific Corp, Torrington, CT) attached to a differentially amplified blood pressure monitor (World Precision Instruments, Sarasota, FL). The jugular vein was cannulated for administration of the muscle relaxant gallamine triethiodide (50 mg/kg), which eliminated neural interference from hind limb musculature, and the distal saphenous artery was cannulated for close intra-arterial (i.a.) administration of CBD or vehicle to the knee joint (100 μL injection volume). A specialised clamp was fixed to the mid-shaft of the isolated right femur and attached to a stereotaxic frame to prevent movement of the proximal aspect of the rat hind limb. The right hind paw was then placed in a shoe-like holder that was connected to a force transducer and torque meter (Data Track 244-1-R; Intertechnology, ON, Canada) to standardise the amount of rotational force being applied to the knee joint. A longitudinal skin incision was made along the medial aspect of the hind limb and the reflected skin was sutured to a metal “O” ring to create a pool which was filled with warm mineral oil to prevent tissue desiccation. The medial articular branch of the saphenous nerve was isolated and transected in the inguinal region to prevent spinal reflexes. The epineurium was removed and the nerve teased to isolate fine neurofilaments which were then placed on a platinum recording electrode to measure single-unit activity. To identify a joint afferent fibre and its receptive field, the knee joint was gently probed with a blunt glass rod. The mechanical threshold of each recorded joint afferent was determined by gradually increasing the torque applied to the joint until the fiber elicited an action potential. The conduction velocity of the fibres were determined by electrically stimulating the receptive field with a pair of silver bipolar stimulating electrodes (0.6 Hz, 2 ms pulse width, 1-15 V). The mechanosensitivity of the joint fibre was assessed by applying noxious outward rotations to the knee and counting the number of action potentials elicited during the rotation. Noxious rotation refers to torque occurring outside the normal range but not severe enough to cause soft tissue injury.

2.3.1. Experimental timeline

On day 14 post-MIA induction, 3 sets of noxious rotations, each lasting 5 seconds, were applied 5 minutes apart as a baseline measurement of afferent activity. After close i.a. infusion of CBD (100, 200, or 300 μg in 100 μL) or vehicle (100 μL), joint mechanosensitivity was assessed for an additional 15 minutes. To minimise the use of animals, multiple doses of CBD or vehicle were assessed in each fibre. A washout period of at least 50 minutes was observed between the administration of varying doses of CBD or vehicle to allow afferent firing to return to baseline levels. The percentage change in afferent activity before and after administration of CBD or vehicle was calculated offline using Spike2 software (Cambridge Electronic Design, Cambridge, United Kingdom). All recorded fibres fired in response to close i.a. administration of potassium chloride (KCl; 1 mM, 0.1 mL) at the conclusion of the experiment, confirming that administered drugs had reached the mechanosensory nerve endings and that the recorded fibre was still viable.

2.4. Behavioural pain measurements

2.4.1. Von Frey hair mechanosensitivity

Von Frey hair mechanosensitivity was used as a measure of secondary allodynia. Alert, unanaesthetised animals were placed in a Plexiglas chamber with a metal mesh flooring which allowed access to the plantar surface of each hind paw. After allowing the animal to acclimate until exploratory behaviour ceased (approximately 10 minutes), ipsilateral hind paw mechanosensitivity was assessed using a modification of the Dixon up–down method. 5 A von Frey hair was applied perpendicular to the plantar surface of the ipsilateral hind paw (avoiding the toe pads) until the hair flexed; the filament was then held in place for 3 seconds. If there was a positive response (ie, withdrawal, shaking, or licking of the hind paw), the next lower strength hair was applied; if there was a lack of response, the next higher strength hair was applied up to a cut-off of 15 g bending force. The 50% withdrawal threshold was determined using the following formula: 10 (Xf + kδ) /10,000; where Xf = value (in log units) of the final von Frey hair used, k = tabular value for the pattern of the last 6 positive and/or negative responses, and δ = mean difference (in log units) between stimuli.

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2.4.2. Hind limb incapacitance

To perform dynamic weight bearing (DWB) measurements, animals were placed in a Perspex chamber (model BIO-DWB-AUTO-R; Bioseb, Boulogne, France) with a pressure-sensitive floor and allowed to move freely. Hind limb weight bearing was tracked and recorded over a 3-minute period. Weight borne on the ipsilateral hind paw was calculated as a percentage of the total weight borne on the hind limbs.

2.4.3. Experimental timeline

Animals underwent baseline von Frey hair mechanosensitivity and DWB testing. Separate cohorts were treated on day 14 post-MIA with an i.artic. injection of either vehicle (50 μL) or CBD (100-300 μg/50 μL). In other experimental cohorts, day 14 OA rats were treated with the highest dose of CBD (300 μg/50 μL) and either the CB1 receptor antagonist, AM281 (75 μg/50 μL), the CB2 receptor antagonist, AM630 (75 μg/50 μL), or the TRPV1 receptor antagonist, SB-366791 (30 μg/50 μL) administered locally (subcutaneously; s.c.) over the joint 10 minutes before i.artic. CBD administration. Behavioural pain measurements for these experiments were conducted at 30, 60, 120, 180, and 240 minutes after drug administration. To investigate the prophylactic effects of CBD on OA pain and peripheral neuropathy, a separate cohort of rats was treated with CBD (300 μg/50 μL) or vehicle (50 μL) s.c. over the knee joint 30 minutes before i.artic. injection of MIA (3 mg/50 μL) and once daily on each of the subsequent 3 days; behavioural pain measurements were conducted on days 0, 1, 2, 3, 7, 10, and 14.

2.5. Inflammation measures

Animals were deeply anaesthetised by an intraperitoneal injection of urethane (25% solution; 2g/kg i.p.). A longitudinal incision was made along the ventral skin of the neck to expose the trachea which was cannulated with PE-200 tubing to permit unrestricted breathing. The right carotid artery was also cannulated with PE-30 tubing filled with heparinised saline (1 U/mL) to allow for continuous monitoring of the mean arterial pressure (MAP).

2.5.1. Intravital microscopy

Both hind limbs were immobilised and the capsule of the ipsilateral knee was exposed by surgically removing a small ellipse of the overlying skin and superficial fascia. Physiological buffer (37°C ± 1°C) was immediately and continuously perfused over the exposed joint.

Intravital microscopy was used to assess leukocyte-endothelial interactions within the microcirculation of the knee joint, as described previously. 2 The synovial microcirculation was visualised under incident fluorescent light using a Leica DM2500 microscope with a HCX APO L 20X objective and an HC Plan 10X eyepiece giving a final magnification of ×200. In vivo leukocyte staining was achieved by intravenous administration of 0.05% rhodamine 6G (in saline). Straight, unbranched postcapillary venules (15-50 μm in diameter) were chosen for visualisation and 3 fluorescent videos (per time point) were captured for 1 minute each by a Leica DFC 3000 camera (Leica Microsystems Canada Inc, Richmond Hill, ON, Canada). Two measures of leukocyte-endothelial interactions were used to assess articular inflammation: (1) the number of rolling leukocytes to pass an arbitrary line perpendicular to the venule in 1 minute were counted and (2) the number of adherent leukocytes within a 100-μm portion of the venule. Rolling leukocytes were defined as positively stained blood cells travelling slower than the surrounding blood flow, and adherent leukocytes were defined as positively stained cells that remained stationary for a minimum of 30 seconds.

2.5.2. Laser speckle contrast analysis

In the same animals, knee joint blood flow was measured by laser speckle contrast analysis (LASCA) using a PeriCam PSI System (Perimed Inc, Ardmore, PA). At each time point, 1-minute recordings of the exposed knee joint were taken at a working distance of 10 cm with a frame capture rate of 25 images per second. Using dedicated software (PIMSoft, Version 1.5.4.8078), images were averaged to generate 1 perfusion image per second. At the end of the experiment, rats were euthanised and a dead scan of the knee was taken. This “biological zero” value was subtracted from all measurements to account for any Brownian motion in the tissue. Images were analysed offline where mean blood perfusion (perfusion units) in a defined region of interest approximating the knee joint was calculated.

2.5.3. Experimental timeline

Inflammation measures were conducted on day 1 post-MIA induction, which corresponds to the peak of inflammation in this OA model. After baseline intravital microscopy and LASCA recordings (1 minute) a 50-μL bolus of CBD (300 μg) or vehicle (separate cohort) was applied topically over the exposed knee joint. Subsequent recordings were taken at 5, 15, 30, 60, 120, and 180 minutes after drug administration. In separate cohorts, day 1 MIA rats were treated with the highest dose of CBD (300 μg/50 μL) and either the CB1 receptor antagonist, AM281 (75 μg/50 μL), the CB2 receptor antagonist, AM630 (75 μg/50 μL), or the TRPV1 receptor antagonist, SB-366791 (30 μg/50 μL) administered topically over the joint 10 minutes before CBD administration.

2.6. G-ratio analysis of the saphenous nerve

A segment of the saphenous nerve was isolated proximal to the ipsilateral knee joint and placed in 2.5% glutaraldehyde (diluted with 0.1 M sodium cacodylate buffer), and stored at 4°C for at least 1 week. The nerve samples were then removed from the fixative and rinsed 3 times with 0.1 M sodium cacodylate buffer. The samples were fixed in 1% osmium tetroxide for 2 hours, rinsed with distilled water, and then placed in 0.25% uranyl acetate (4°C) overnight. The samples were then dehydrated in a graduated series of acetone (50%, 70%, 95%, and finally 100%). The samples were then dried in 100% acetone for 10 minutes. Epon–araldite resin was used to mount the samples. The samples were placed in a 3:1 ratio of dried 100% acetone to resin for 3 hours, followed by a 1:3 ratio of dried 100% acetone to resin overnight. Next the samples were placed in 100% Epon–araldite resin for 3 hours and cured in an oven at 60°C for 48 hours. Finally, using an LKB Huxley ultramicrotome with a diamond knife, the samples were sectioned into 100 nm thick slices. Cross-sectional slices of nerves were placed onto a copper wire grid consisting of 300 individual squares per inch (each square measuring 83 × 58 μm) and then stained with 2% aqueous uranyl acetate for 10 minutes and finally lead citrate for 4 minutes.

The copper wire grids containing the saphenous nerve sections were inserted into a JEOL JEM 1230 transmission electron microscope (JEOL Corp Ltd, Tokyo, Japan). The microscope was set at a voltage of 80.0 kV, and images were captured at ×2500 using a Hamamatsu ORCA-HR digital camera (Hamamatsu Photonics, Hamamatsu City, Japan). One nerve cross-section image was visually partitioned into 9 quadrants and 3 images were captured (from quadrants 1, 5, and 9). All fibres were assessed using the G-ratio plugin in ImageJ processing software. The G-ratio was calculated using the equation where, a is the internal axonal area and A is the total axonal area of the fibre. The higher the G-ratio the higher the degree of demyelination.

2.7. Drugs and reagents

Cannabidiol (2-[(1R,6R)-3-methyl-6-(1-methylethenyl)-2-cyclohexen-1-yl]-5-pentyl-1,3-benzenediol) was obtained from Tocris Bioscience (Bio-Techne, Abingdon, United Kingdom). AM281 (CB1 receptor antagonist; 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide) and AM630 (CB2 receptor antagonist; 6-iodo-2-methyl-1-(2-morpholin-4-ylethyl)indol-3-yl]-(4-methoxyphenyl)methanone) were obtained from Cayman Chemicals (Ann Arbor, MI). SB-366791 (N-(3-methoxyphenyl)-4-chlorocinnamide), rhodamine 6G, cremophor, dimethyl sulphoxide (DMSO), urethane, and MIA were obtained from Sigma-Aldrich (St. Louis, MO). Solutions of CBD, AM281, AM630, and SB-366791 were prepared in vehicle (1:1:18; DMSO:cremophor:saline) on the day of use. Rhodamine 6G (0.05%) and MIA were dissolved in saline. Physiological buffer (135 mM NaCl, 20 mM NaHCO3, 5 mM KCl, 1 mM MgSO4*7H2O, pH = 7.4) was prepared in the laboratory.

2.8. Statistical analysis

All data were expressed as mean ± SEM. Data were tested for Gaussian distribution by the Kolmogorov–Smirnov test. All data were normally distributed and were therefore analysed using parametric statistics (2-way analysis of variance (ANOVA), 1-way ANOVA, unpaired 2-tailed Student t test, and paired 2-tailed Student t test). A P value less than 0.05 was considered statistically significant.

3. Results

3.1. Effect of acute administration of cannabidiol on joint afferent mechanosensitivity

A total of 17 afferent fibres were recorded in this study. Fibres were characterised based on mechanical and electrical threshold, and conduction velocity (summarised in Table ​ Table1 1 ).

Table 1

Characterisation of the recorded fibres in the electrophysiology experiments.

3.2. Effect of acute administration of cannabidiol on sodium monoiodoacetate–induced pain

Intra-articular injection of MIA produced secondary allodynia and weight-bearing deficits in the ipsilateral hind paw and hind limb, respectively, 14 days after injection (P < 0.0001; n = 24; Fig. ​ Fig.2A 2 A and P < 0.0001; n = 24; Fig. ​ Fig.2 2 B).

When compared with vehicle control, low dose CBD (100, 200 μg) had no effect on withdrawal threshold or hind limb weight bearing (P > 0.05; n = 8; Figs. ​ Figs.2A 2 A and B). The 300 μg dose of CBD, however, significantly increased hind paw withdrawal threshold and hind limb weight bearing over the time course tested (P < 0.0001; n = 8; Figs. ​ Figs.2A 2 A and B). All subsequent experiments used the 300 μg dose of CBD.

To determine whether CBD was acting locally, 300 μg of the drug was injected into the contralateral knee and the withdrawal threshold was assessed in the ipsilateral joint 1 hour later and hind limb weight bearing was assessed in the ipsilateral joint 3 hour later. It was found that the high dose of CBD administered to the contralateral knee had no effect on ipsilateral hind paw withdrawal thresholds indicating that CBD was not acting centrally in this pain test (P < 0.01; n = 8-10; Fig. ​ Fig.3A). 3 A). However, in the hind limb weight-bearing test, contralateral CBD was not statistically different from the ipsilateral CBD group (P > 0.05; n = 8-22; Fig. ​ Fig.3 3 B).

Effect of contralaterally administered CBD on ipsilateral pain behaviour. The improvement in hind paw withdrawal threshold seen with ipsilateral CBD was not observed when CBD (300 μg i.artic.) was administered to the contralateral knee (A). Contralateral CBD did not significantly decrease hind paw weight bearing (B) when compared with ipsilateral CBD. (*P < 0.05, **P < 0.01 1-way ANOVA with Fisher post hoc test; n = 8-9). Data are mean values ± SEM. ANOVA, analysis of variance; CBD, cannabidiol; VEH, vehicle.

The cannabinoid receptor antagonists AM281 and AM630 had no effect on CBD-induced analgesia (P > 0.05; n = 6-8; Figs. ​ Figs.4A 4 A and B). Conversely, the TRPV1 antagonist, SB-366791, significantly inhibited the analgesic effect of CBD (P < 0.05; n = 6-8; Fig. ​ Fig.4A) 4 A) with respect to the hind paw withdrawal threshold, but did not have a significant effect on hind limb weight bearing at 3 hours after injection (P > 0.05; n = 6-22; Fig. ​ Fig.4 4 B).

Contribution of cannabinoid and noncannabinoid receptors to the analgesic effects of CBD. Both hind paw withdrawal threshold (A) and hind limb weight bearing (B) were unaltered compared with control after local administration of the CB1 receptor antagonist AM281 (75 μg) or CB2 receptor antagonist AM630 (75 μg). Hind paw withdrawal threshold (A) was reduced compared with control after local administration of the TRPV1 antagonist SB-366791 (30 μg), but hind limb weight bearing (B) was unaffected. (*P < 0.05, **P < 0.01 1-way ANOVA with Fisher post hoc test; n = 6-8). Data are mean values ± SEM. ANOVA, analysis of variance; CBD, cannabidiol; VEH, vehicle.

3.3. Effect of acute administration of cannabidiol on sodium monoiodoacetate–induced inflammation

Anti-inflammatory action of CBD on day 1 MIA-induced inflammation. When compared with naïve controls, intra-articular MIA significantly increased rolling (A) and adherent (B) leukocytes, and caused synovial hyperaemia (C) (****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05, P > 0.05, unpaired t test; n = 6-12). Over a 3-hour time course, CBD (300 μg) significantly decreased leukocyte rolling (A) leukocyte adherence (B) and knee joint blood flow (C) when compared to vehicle. (****P < 0.0001, **P < 0.01, *P < 0.05 2-way ANOVA with Bonferroni post hoc test; n = 6). Data are mean values ± SEM. ANOVA, analysis of variance; CBD, cannabidiol; MIA, sodium monoiodoacetate; PU, perfusion unit; VEH, vehicle.

Contribution of cannabinoid and noncannabinoid receptors to the anti-inflammatory effects of CBD. The anti-rolling effect of CBD at 30 minutes was blocked (A) by CB2 receptor antagonist AM630 (75 μg) and TRPV1 antagonist SB-366791 (30 μg), but not CB1 receptor antagonist AM281 (75 μg). The anti-adherence effect of CBD in day 1 MIA joints was blocked by SB-366791 (B). (****P < 0.0001, ***P < 0.001 1-way ANOVA with Fisher LSD post hoc test; n = 60). Data are mean values ± SEM. ANOVA, analysis of variance; CBD, cannabidiol; MIA, sodium monoiodoacetate; VEH, vehicle.

3.4. Prophylactic effect of cannabidiol on sodium monoiodoacetate–induced osteoarthritis pain

Prophylactic treatment of MIA-injected knee joints with CBD (on days 0–3 of MIA) significantly attenuated the development of MIA-induced tactile allodynia during both the acute and late phase of OA development (P < 0.0001; n = 8; Fig. ​ Fig.7A). 7 A). Conversely, early treatment with CBD had no effect on hind limb weight bearing, when compared with vehicle-treated animals (P > 0.05; n = 8; Fig. ​ Fig.7 7 A).

Effect of prophylactic CBD administration on the development of pain over 14 days post-MIA injection. Treating MIA knee joints with CBD (300 μg; s.c.; days 0–3) significantly improved von Frey hair withdrawal threshold over the 14-day development of OA when compared with vehicle (A). Pretreatment of MIA knee joints with CBD had no significant effect on hind limb weight bearing (B) (****P < 0.0001, ***P < 0.001, **P < 0.01, *P < 0.05 2-way ANOVA with Bonferroni post hoc test; n = 8). Data are mean values ± SEM. ANOVA, analysis of variance; CBD, cannabidiol; MIA, sodium monoiodoacetate; OA, osteoarthritis; s.c., subcutaneous; VEH, vehicle.

3.5. Cannabidiol prophylaxis and sodium monoiodoacetate–induced peripheral nerve damage

Treatment of OA knees with CBD during the acute inflammatory phase of the MIA model (days 0–3 of MIA) inhibited saphenous nerve demyelination on day 14 compared with vehicle-treated knees (P < 0.05; n = 6-8; Fig. ​ Fig.8 8 B).

Prophylactic CBD reduces joint nerve demyelination in MIA-induced OA. Representative sections of electron micrographs of axons found in saphenous nerves taken at day 14 from MIA treated with vehicle (A) (days 0–3), or CBD (300 μg; days 0–3). (B) G-ratio calculations showing that MIA-induced axonal demyelination is prevented by CBD treatment. Scale bar is 6 μm. (*P < 0.05 unpaired t test; n = 6 = 8). Data are presented as mean values ± SEM. CBD, cannabidiol; MIA, sodium monoiodoacetate; OA, osteoarthritis; VEH, vehicle.

4. Discussion

Pain and disease progression are poorly managed in many patients with OA because of the multifactorial nature of the disease. Intra-articular injection of MIA produces monoarthritis with several features that resemble human OA, including joint pain, intermittent inflammation, and joint nerve damage. This study aimed to address, for the first time, whether the inflammatory and neuropathic pain associated with MIA could be blocked by local administration of the noneuphoria producing phytocannabinoid CBD.

It has previously been shown that the pain associated with the MIA model of OA is mediated in part by the sensitisation of joint afferent fibres. 35,37 Peripheral administration of CBD dose-dependently decreased joint afferent firing on day 14 after MIA injection. These electrophysiology data confirm that CBD has a peripheral site of action in knee joints. Because all recordings were made from Aδ or C fibres during noxious movement of the knee, this suggests that CBD can inhibit the mechanosensitivity of joint nociceptors.

In end-stage OA, intra-articular injection of 300 μg of CBD improved unrestrained hind limb weight bearing and hind paw withdrawal threshold (Fig. ​ (Fig.2). 2 ). These observations, along with our electrophysiology data, assert that CBD acts locally in the joint to reduce joint mechanical pain as revealed by improved weight bearing as well as a reduction in centrally mediated secondary allodynia as determined by hind paw withdrawal threshold. Contralateral injection of CBD had no discernible effect on ipsilateral secondary allodynia confirming that the analgesic effect of intra-articular CBD was localised to the site of administration for this pain test. The anti-nociceptive effect of low dose CBD (100 and 200 μg) observed with electrophysiology was not seen in the behavioural pain assessments. This may be because electrophysiology is a highly sensitive technique that detects subtle response to test agents in the periphery, whereas pain behaviours are more complex and encompass the entire pain pathway. The rationale for using two pain behavioural tests in this study was to interrogate different aspects of the pain pathway. Dynamic incapacitance is a measure of spontaneous pain that is associated with joint degeneration or inflammation arising from peripheral sensitisation. 4,28 In contrast, von Frey hairs were used to investigate evoked, reflexive responses (ie, paw withdrawal, shake, and lick) at a site distal to the injured joint. 28 This secondary allodynia is a consequence of central sensitisation in late stages of the MIA model, 16 and can be indicative of nerve injury. Thus, it seems that local injection of CBD is effective at reducing direct nociceptive and inflammatory pain in the joint as well as ameliorating neuropathic features of OA pain.

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Both CB1 and CB2 receptor antagonists failed to block the CBD-mediated improvements in hind paw withdrawal threshold and weight bearing. Although CBD has been shown to act as an inverse agonist at CB2 receptors and a full antagonist at CB1 receptors, 40 it has also been shown to act through GPR55, serotonin receptors (eg, 5-HT1A), and various transient receptor potential ion channels. Transient receptor potential vanilloid-1 is known to be involved in MIA-induced peripheral sensitisation, 17 therefore, antagonist experiments were performed to test the involvement of this ion channel in CBD-mediated analgesia. Here, the TRPV1 antagonist SB-366791 attenuated the secondary allodynia imparted by CBD in established OA. This mechanism of action has been previously reported in in vitro studies using human embryonic kidney (HEK 293) cells and using cell membranes from mouse and rat brains. 3 In vivo, TRPV1 antagonism has also been shown to block the pain-relieving effect of CBD in a model of carrageenan-induced paw oedema 7 and in the chronic constriction injury model of neuropathic pain. 6 Although these data show that the action of CBD is mediated in part by TRPV1, it remains unclear if CBD is acting directly on TRPV1 or if there is an indirect mechanism occurring in the joint. Cannabidiol has been shown to inhibit fatty acid amide hydrolase (FAAH) and the uptake of anandamide. 3 Inhibition of FAAH and anandamide reuptake would elevate anandamide levels in the joint which if high enough could ultimately lead to the activation of TRPV1. 3

Intra-articular injection of MIA produced an acute inflammatory response on day 1 after injection. This acute phase of inflammation was evinced by an increase in leukocyte trafficking and a moderate increase in joint blood flow. Local application of CBD significantly reduced these acute, inflammatory changes corroborating what has previously been reported in other inflammatory models. 8,12,20 Oral administration of CBD, for example, has been shown to be anti-inflammatory and anti-hyperalgesic in the carrageenan model of plantar oedema. 8 Malfait et al., showed that systemic administration of CBD, both intraperitoneally and orally, suppressed disease severity and decreased serum inflammatory cytokine levels in the collagen model of rheumatoid arthritis. 20 Moreover, CBD administered by a transdermal gel reduced joint swelling, immune cell infiltration, synovial membrane thickening, and the synthesis of pro-inflammatory biomarkers in the Freund complete adjuvant model of inflammatory arthritis. 12 The data presented here demonstrate for the first time that CBD has the capacity to reduce the inflammatory flares associated with OA.

The inhibitory effect of CBD on leukocyte trafficking was blocked by the TRPV1 antagonist SB-366791. Opening of TRPV1 ion channels causes the peripheral release of inflammatory neuropeptides which promote neurogenic inflammation and enhanced leukocyte trafficking in joints. 19,41 Thus, the anti-inflammatory effects of CBD observed here could be due to desensitisation of TRPV1 ion channels as has been shown elsewhere. 14 The anti-rolling effect of CBD on joint leukocytes was also blocked by AM630 suggesting that CB2 receptors may be involved in opposing leukocyte capture in day 1 MIA joints. Zhao et al. showed that activation of CB2 receptors can inhibit the expression of P-selectin which is the adhesion molecule responsible for leukocyte rolling. 43 Whether CBD inhibits joint P-selectin activity by a CB2 receptor mechanism requires further investigation.

A central hypothesis of this study was that early inhibition of OA-related inflammation with CBD would reduce the development of persistent joint pain. Prophylactic treatment of OA joints with CBD on days 1 to 3 after MIA induction prevented secondary allodynia at day 14, but had no effect on hind limb weight bearing. Inflammation associated with MIA diminishes by day 7, 4 therefore the pain associated with end-stage OA in this model is largely due to joint degeneration and peripheral neuropathy. Thus, by abolishing early inflammation with prophylactic treatment, CBD attenuates central sensitisation and neuropathic pain development in OA.

Previous studies have shown that MIA-induced OA causes peripheral nerve damage. 25,39 Demyelination of the ipsilateral saphenous nerve was confirmed by an increase in G-ratio, purporting MIA-induced peripheral neuropathy compared with saline control animals. 25 This study showed that prophylactic treatment with CBD during the early inflammatory phase of MIA prevented this loss of nerve myelin 14 days later, suggesting that blockade of inflammatory flares during OA could protect against joint nerve damage. The G-ratio data would benefit from future studies examining the expression of a biomarker for peripheral nerve damage to further support this finding.

The findings presented here and elsewhere support the concept that MIA recapitulates the neuropathic aspect of OA pain, which is found in approximately 30% of patients. 1,34 CBD treatment may be a beneficial therapeutic for the population of patients who experience neuropathic arthritis, and are refractory to currently used first- and second-line analgesics. Several cannabis compounds, including CBD, have been shown to be neuroprotective in other musculoskeletal disorders. In a preclinical model of multiple sclerosis, CBD was shown to improve clinical recovery and rotarod scores in animals, correlating with and indicative of a neuroprotective effect. 30 In addition, CBD and ∆ 9 -tetrahydrocannabinol have both been implicated in slowing the progression and promoting the survival of neurones in a preclinical model of amyotrophic lateral sclerosis. 15,42 These studies, in addition to the results presented here, highlight the potential utility of CBD as an analgesic and neuroprotective agent in OA.

Cannabidiol is a noneuphoria producing compound and has a more desirable side effect profile compared with other cannabinoid compounds and commonly prescribed analgesics. Animal studies where CBD was administered systemically showed that the animals had no signs of adverse side effects. 12,20 For example, exploratory behaviour in rats was not altered by systemic CBD, indicating limited central effects of treatment. 12 Our study shows for the first time that CBD is an effective anti-nociceptive and anti-inflammatory agent when administered locally around the joint. Successful relief of OA symptoms by peripherally administered CBD suggests a therapeutic option that has a low chance of adverse effects which is more desirable for patients.

5. Conclusions

This study showed for the first time that local CBD administration inhibited pain and peripheral sensitisation in established OA. Topical treatment with CBD reduced leukocyte trafficking and joint hyperaemia during the early stages of MIA. By attenuating this initial inflammatory response with CBD, end-stage OA pain and peripheral neuropathy were abrogated. Thus, CBD may be a safe therapeutic to treat OA pain locally as well as block the acute inflammatory flares that drive disease progression and joint neuropathy.

Conflict of interest statement

The authors have no conflicts of interest to declare.

This work was supported by an operating grant provided by The Arthritis Society.

Ethics: All experimental protocols were approved by the Dalhousie University Committee on Laboratory Animals, which acts in accordance with the standards put forth by the Canadian Council for Animal Care.

Availability of data and materials: The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Acknowledgements

The technical assistance of Allison Reid is gratefully acknowledged.

Author contributions: H. T. Philpott conducted the pain behaviour experiments, the inflammation measurements (IVM and LASCA), performed the G-ratio measurements, analysed data, and helped draft the manuscript. M. O’Brien conducted all electrophysiology experiments, analysed the data, and helped draft the manuscript. J. J. McDougall conceived the study, participated in its design and coordination, helped analyse data, and helped draft the manuscript. All authors read and approved the final manuscript.

Footnotes

Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.

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