What’s the evidence that certain foods and supplements can help manage osteoarthritis?

Can we recommend our clients use food to help medically manage osteoarthritis in their dogs? There are many food-derived supplements on the market nowadays for veterinary patients with osteoarthritis,^1-14 and using diet and supplements to manage the condition is a growing area of interest in both human and veterinary nutrition. Since nutrition is the foundation of health, it is natural for clients to inquire if specific foods can be used to improve mobility in osteoarthritic dogs. Therefore, the practitioner should be able to evaluate therapeutic foods and supplement claims so he or she can make specific nutritional recommendations to complement the medical management of osteoarthritis.

Food-derived supplements can be found in pet diets, treats, and as tablets or chews, often with suggested therapeutic or beneficial effects for canine osteoarthritis. Very few have been evaluated in a controlled manner, and even fewer have been evaluated in dogs with osteoarthritis. This is a brief review of scientific evidence and research for use of these food-derived supplements in dogs with osteoarthritis.

1. Avocado/soybean unsaponifiables (ASU): Composed of the unsaponifiable fractions of avocado and soybean oils in a 1/3 to 2/3 proportion.^15,16 ASU offers anti-osteoarthritic properties by inhibiting interlukin-1 and stimulating collagen synthesis in cartilage cultures.^16-18

In one study of dogs, osteoarthritis was induced by anterior cruciate ligament transection. The dogs received placebo or ASU (10 mg/ kg/24h).¹⁹ The size of macroscopic lesions of the tibial plateau, severity of cartilage lesions, synovial cellular infiltration, and inducible nitric oxide synthase were all significantly decreased. There was also a reduced loss of subchondral bone volume and calcified cartilage thickness in the group receiving ASU.¹⁹

In 14 dogs, surgery was performed to create two osteochondral defects in the lateral aspect of the trochlear groove of the knee joint. The dogs were randomly assigned to either a treatment group given 300 mg of ASU every three days, or a control group fed a normal diet. Exercise was not restricted and in 15 weeks the dogs were euthanized. Morphometric analysis of cartilage tissue revealed more immature repair tissue with greater collagen and chondral tissue content in the regenerated tissue in the ASU-treated dogs as compared to the untreated dogs. The ASU-treated tissues also showed markedly more immunostaining of transforming growth factor β (TGF- β).²⁰

2. Blueberries: Flowering plants of the genus Vaccinium, which includes cranberries and bilberries. They may have anti-oxidative and anti-inflammatory actions because they contain pterostilbene, anthocyanins, proanthocyanidins, resveratrol, flavonols, and tannins.²¹ In a study of sled dogs, those receiving a blueberry supplement had higher antioxidant status than those not receiving the supplement; however, there was no difference in creatinine kinase activity and isoprostane levels (a measure of oxidative stress) between dogs that received blueberries and those that did not.²²
   
3. New Zealand green-lipped mussel (Perna canaliculus): A rich source of glycosaminoglycans and has anti-inflammatory effects.²³ In a randomized controlled clinical study of 31 dogs with arthritis, green-lipped mussel powder (0.3%) was added to the diet during processing for one group of dogs.²⁴ Compared to the control group, which was fed the same diet without added green-lipped mussel powder, the treated group showed significant improvement in subjective arthritis scores, joint swelling, and joint pain.

However, this data must not be over-interpreted. In a randomized, double-controlled and double-blinded clinical trial, 45 dogs with osteoarthritis were evaluated. Dogs receiving green-lipped mussel experienced improvement in mobility when compared with placebo; however, it was not as effective as Carprofen.²⁵

In a study of 81 dogs with presumptive osteoarthritis, clinical signs improved in both the green-lipped mussel and placebo-treated groups when compared with baseline. On day 56 of the study, dogs receiving green-lipped muscle had improved clinical signs but not musculoskeletal scores.²⁶ An uncontrolled study of 85 dogs fed a green-lipped mussel supplemented diet for 50 days showed reduction of  a composite arthritic score when compared with baseline scores on various diets dogs were consuming.²⁷ In systematic reviews of agents used to treat canine osteoarthritis, the data regarding the benefits of green-lipped mussel extract in dogs was promising, but the scientific quality of the data is questionable and no definitive relationship has been proven between clinical improvements and therapy.^{28, 29}

4. Special milk protein concentrate: Prepared from the milk of hyperimmunized cows. Milk contains a number of biologically active compounds including immunoglobulins, cytokines, enzymes, hormones and growth factors. The milk protein concentrate exerts anti-inflammatory properties;³⁰ they do not appear to be due to the inhibition of arachidonic acid metabolism, but to the suppression of neutrophil migration from the vascular space.³¹

A randomized, controlled clinical trial evaluating special milk protein concentrate (Microlactin, Stolle Milk Biologics, Cincinnati, OH) in dogs with naturally-occurring osteoarthritis resulted in an improvement in subjective clinical signs and owner global assessment when compared with dogs receiving placebo.³²

5. Tumeric – curcumin and P54FP: P54FP is an extract of Indian and Javanese turmeric (Curcuma domestica and Curcuma xanthorrhiza) that contains a mixture of active ingredients possessing anti-inflammatory activity, including curcuminoids and essential oils.³³ Specifically, curcumin has been shown to inhibit PGE2, COX-2 and nuclear factor β, and upregulate MMP-3 and IL-1β induced proteoglycan degradation.34-36

One randomized, blinded study in dogs with osteoarthritis found no difference in objective ground reaction forces, but did see some improvements in certain subjective outcome measures.³³ In another study, 18 dogs with OA were randomly assigned to three groups:  the test group received a curcumin supplement at 4mg/kg; the positive control received oral Fibrocoxib at 5mg/kg; and a negative control group of healthy dogs was untreated. Data analysis of gene expressions was compared between these three groups of six dogs at Day 0 and Day 20. After 20 days, gene markers for inflammatory response and connective tissue development and function decreased in the curcumin and Fibrocoxib groups compared to the non-treated dogs. Specific molecular targets identified in the curcumin group, not observed in the NSAID group, were the TNRF-1 signaling pathway down-regulating TNFβ and IL-18 while upregulating 1kB. In addition, inhibition of macrophage proliferation and activation of fibrinolysis were noted in the curcumin group and not the NSAID group.

These results suggest that oral curcumin may have a complementary anti-inflammatory effect in OA that differs from a NSAID’s.³⁷

Conventional medical management of OA in dogs is dominated by NSAIDs, but adverse side effects can occur and there is concern about long term administration of these drugs. They have not been shown to slow the progression of the disease, or have a positive impact on joint degradation. Diet and dietary supplements are being increasingly studied since the economics of osteoarthritis in the aging human population is a growing concern. Pet owners will also be questioning practitioners on the use of dietary supplements in animals. Understanding the current literature allows you to understand the evidence, application, mechanism of action, and potential use of dietary supplements in the medical management of the osteoarthritic dog.