Osteoarthritis is best described as an end-stage disease resulting from many potential causes. The hallmark features of the disease are inflammation of the synovium and changes in cartilage metabolism resulting in breakdown of matrix. Synovial mediation of inflammation is seen very early in osteoarthritis and may precede cartilage degeneration.
Inflammatory cytokines produced by cells in the synovium (and also by chondrocytes) are top candidates for therapeutic intervention. These cytokines cause two main adverse effects: they act directly to decrease matrix synthesis by chondrocytes, and they induce expression and secretion of matrix-degrading protease enzymes.
Nutritional therapies aimed at targeting inflammation
Arachidonic acid from cell membranes is a precursor to the proinflammatory cytokines prostaglandins and leukotrienes, the concentrations of which are increased in osteoarthritis. A diet rich in omega-3 fatty acids (specifically eicosapentaenoic acid, or EPA) alters the fatty makeup of cell membranes and reduces the presence of arachidonic acid as an inflammatory precursor.1
Incubation of chondrocytes with omega-3 fatty acids has resulted in decreased production of proinflammatory cytokines.2 Dogs fed a diet rich in omega-3 fats and vitamin E have showed objective improvements in lameness secondary to osteoarthritis.3,4
The recommended intake of EPA is between 40 and 100 mg/kg in order to achieve systemic anti-inflammatory effects. Supplementing the diet with the precursor molecule of omega-3 fatty acids, alpha-linolenic acid, does not show the same anti-inflammatory and analgesic benefit for dogs since dogs have limited ability to synthesize omega-3s from the precursor molecule.5
Evidence for anti-inflammatory or disease-modifying effects of oral glucosamine and chondroitin sulfate is equivocal in dogs and cats,6 but chondroitin sulfate has been demonstrated in other species and in vitro to control aspects of synovial membrane inflammation—cell infiltration and activity and mediator release.7,8 Glucosamine is also active on both cellular and molecular aspects of the inflammatory reaction.7,8
Human studies emphasize the importance of the quality of tested compounds for achieving high-quality clinical trials, and this needs to be pursued in veterinary research.7 Avocado and soybean unsaponifiables have been shown to reduce prostaglandin production in inflammation-stimulated chondrocytes when combined with glucosamine and low-molecular-weight chondroitin sulfate.9-11
Green-lipped mussel is rich in omega-3 fatty acids and also contains chondroitin sulfate. In one study, feeding arthritic dogs a diet enriched with green-lipped mussel (which also contained glucosamine) elevated blood concentrations of the omega-3 fats along with improving lameness based on force-plate analysis.12 In another study, elk velvet antler (which contains chondroitin sulfate) was shown to improve subjective and objective signs of osteoarthritis in dogs.13
The resin from Boswellia serrata has been shown to inhibit leukotriene biosynthesis from endogenous arachidonic acid in intact peripheral mononuclear neutrophils through the inhibition of 5-lipooxygenase (LOX) and to inhibit tumor necrosis factor alpha production.14 An appropriate dosage has not been fully established in dogs or cats, but a clinical trial giving 40 mg/kg of a resin extract to dogs with osteoarthritis had a positive subjective effect on pain and lameness.15
Management of obesity is part of managing the pain of existing arthritis, but overnutrition as a cause of arthritis may be overlooked. About 22 to 40 percent of dogs and cats are reportedly overweight or obese.16 In a lifespan study of Labrador retrievers, dogs that had increased body condition score (overweight) at the age of 2 years had a 25 percent prevalence of hip arthritis compared with 4 percent of restricted-fed dogs (ideal body condition score).17 By 6 years of age, the overweight dogs had 1.5 times the incidence of shoulder arthritis compared with restricted-fed dogs.18 Adipose tissue can produce systemic mediators of inflammation, and this may be part of the pathogenesis of osteoarthritis in obese individuals.19
Building muscle to support an arthritic joint can help to improve mobility and comfort. Therapeutic exercises provide stimulus for improvement in muscle strength and mass,20 but adequate protein intake is important for muscle building. This is especially true for older pets because they lose muscle as they age and actually require increased protein in their diets to offset this loss (or to build muscle). Restricted-protein diets are no longer recommended in senior diets for pets with healthy kidneys.21
Nutritional supplements can help modulate the inflammatory aspect of osteoarthritis and may also help improve cartilage metabolism, but the impact of reaching or maintaining a healthy weight and lean body mass on ameliorating clinical signs of osteoarthritis should not be underestimated.
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