Osteoarthritis (OA) is a chronic, painful, degenerative and inflammatory disease that affects the synovial joints. This disease has a progressive course and is related to chronic pain, lameness, functional disability and reduced quality of life, leading finally to the loss of joint function and mobility. It is highly prevalent in dogs with 20 % of the canine population over 1 year old affected.
The management of OA in dogs is typically multimodal (drugs and dietary supplements). The main recommendation is to control clinical signs by reducing pain, improving mobility and hence quality of life. Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to decrease pain and inflammation whereas steroid injection is usually reserved for severe end-stage OA. It has been demonstrated the ability of several dietary supplements to prevent cartilaginous degradation, as well as their anticatabolic and anti-inflammatory properties.
The US Food and Drug Administration recognized the term “dietary supplements” and did not endorse the term nutraceutical (which comes from the combination of the words nutrition and pharmaceutical). The dietary supplements are defined as a food or food product, devoid of adverse effects, that provides health benefits, including prevention of a disease onset or progression. No official evidence of efficacy is necessary to market dietary supplements. Therefore, the market access is easier for dietary supplement than for drug. Moreover, dietary supplements have no treatment claim. Nevertheless, they could be good candidates, for management multimodal of OA combining several advantages. Firstly, since OA is a chronic disease, the long-term use of anti-inflammatory may be associated with detrimental effects. It has been shown that, in dogs, the use of anti-inflammatory can be reduced when their food is enriched regularly and conscientiously with dietary supplements devoid of adverse effects. Their good safety also explains that these compounds are added in pet food, to prevent OA in elderly dogs. Finally, food supplements are remarkably simple to use, since they can be added to dog food during the production process. It means that dog owners do not have to administer inconvenient pills to their pets, but they simply must feed their dogs normally with kibbles enriched with some dietary supplements.
Omega-3, chondroitin sulphate, glucosamine, curcumin, undenatured type II collagen, avocadosoya bean unsaponifiables and Boswellia resin were studied in dog OA and therefore discussed.
OMEGA-3
Omega-3 fatty acids are polyunsaturated fatty acids (PUFAs), in which the last double bond is located between the third and fourth carbon atom from the methyl end of chain. The main dietary omega-3 fatty acids are: linolenic acid (ALA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Omega-3 fatty acids are mainly present in fish oils, flaxseeds and walnuts. These compounds are metabolised by COXs and lipoxygenases (LOXs) into eicosanoids which tend to be anti-inflammatory. Several studies have evaluated the in vivo efficacy of omega-3 in dogs. For example, it has been shown that the carprofen using was reduced in client-owned dogs with chronic stable OA when their food was enriched for 12 weeks with fish oil omega-3 fatty acids. Moreover, the progression of arthritis was also limited in dogs that have received a diet with omega-3 fatty acids. Other researchers observed a reduction in inflammatory markers plasma concentrations (arachidonic acid, IL-1, IL-6 and PGE2) in dogs receiving diet with fish oil (containing omega-3 PUFAs) compared to dogs receiving diet with low omega-3 PUFAs content.
CHONDROITIN SULPHATE AND GLUCOSAMINE
Chondroitin sulphate (CS) and glucosamine sulphate (GS) are aminosaccharides that act as a preferred substrate for the biosynthesis of glycosaminoglycans (GAG) chains. They also exert anti-inflammatory and anticatabolic effects through the inhibition of nuclear factor kB (NF-kB). Several studies have shown that dogs administered per os with GS o glucosamine hydrochloride (G-HCl) and CS have significantly improved clinical signs and pain scores, compared to dogs treated with carprofen. However, during GS/CS treatment, pain relief has been delayed compared to carprofen.
CURCUMIN
The major polyphenol of turmeric, Curcumin derives from the roots of the plant Curcuma Longa and it has long been used in traditional Chinese and Ayurvedic medicine. In vitro, anticatabolic, anti-apoptotic and anti-inflammatory effects of curcumin have been largely described. Curcumin also had capacity to increase type II collagen synthesis. However, the bioavailability of natural curcumin is known to be low. Several attempts have been made to solve this problem: curcumin was dissolved in oil; it was also co-administered whith piperine or it was entrapped in micro-emulsions formed by turmeric essential oil and polysorbate 80. The latter possibility was soon abandoned because polysorbate 80 can cause serious hypersensitivity reactions in dogs. In vivo, in 2012, it has been shown that, in white blood cells from 12 OA dogs, gene expression involved in inflammatory response decreased more in dogs fed with curcumin than in dogs receiving NSAIDs. Curcumin also inhibited macrophages proliferation. In this study, curcumin was administered in phytosome, a complex of curcumin and phospholipids, to enhance its bioavailability.
UNDENATURATED TYPE II COLLAGEN
Undenatured type II collagen (UC-II) has an amino acid composition such as to provide high levels of glycine and proline which are essential amino acids for the stability and regeneration of cartilage. It has been shown that UC-II as dietary supplement reduced pain, lameness and stiffness in dogs suffering from OA.
AVOCADO SOYBEAN UNSAPONIFIABLES
Avocado – soybean unsaponifiables (ASU) are plant compound derived from unsaponifiable residues of avocado and soya bean oils, commonly mixed at a ratio of one-third to two-thirds, respectively. In vitro, ASU showed anticatabolic and anti-inflammatory effects, but few studies have evaluated the in vivo efficacy. Moreover, there is a lack of data concerning concentrations of ASU components achieved in blood.
BOSWELLIA
Boswellia resin is a natural resin extract of Boswellia serrata. Its 6 weeks administration in dogs with manifestations of chronic joint and spinal disease, reduces lameness, local pain and stiff gait.
In conclusion, the pharmacological management of OA in dogs remains dominated by NSAIDs, but these can cause adverse side effects and have no disease-modifying effect and cannot positively interfere with cartilage degradation. Food supplements are increasingly studied and open new and great horizons for the multimodal management of OA in dogs. First, they offer anti-inflammatory and chondroprotective effects. Second, the administration of food supplements is associated only with minor side effects, suggesting that they can be administered over the long term. However, further serious and well-designed in vivo studies are needed that could provide reliable data on the safety and efficacy of these compounds.