Evaluation of the effects of a supplementary diet containing chicken comb extract on symptoms and cartilage metabolism in patients with knee osteoarthritis.

We aimed to investigate whether a supplementary diet containing chicken comb extract (CCE) rich in hyaluronic acid (HA) has an effect on pain and other symptoms, as well as cartilage type II collagen (CII) metabolism in patients with knee osteoarthritis (OA). A randomized double-blind placebo-controlled study was conducted in 43 subjects with knee OA (Kellgren/Lawrence grade, mainly 1-2) comprising 22 patients receiving concurrent exercise therapy (ET) and 21 without ET (referred as ET-receivers and ET-unreceivers, respectively). Subjects were randomized to a CCE-containing diet (active diet) group administered a dose of 1,800 mg/day (containing 630 mg of CCE and approximately 60 mg of HA) and a placebo group, and the intervention was continued for 16 weeks. Symptomatic efficacy was evaluated based on the Japanese Orthopaedic Association clinical trials response criteria (JOA response criteria) and Visual analog scales (VAS) before (baseline) and during the intervention. To further examine its effect on CII metabolism, the levels of two degradation biomarkers (CTX-II and C2C) and one synthesis biomarker (CPII) were measured using urine or serum samples. Nineteen subjects (10 ET-receivers and 9 ET-unreceivers) in the active diet group and 21 subjects (10 ET-receivers and 11 ET-unreceivers) in the placebo group were finally included in the study. Compared to the baseline, subscale scores of the JOA response criteria, i.e., 'pain/walking function', 'pain/step-up and -down function' and 'aggregate total symptoms' were more intensely improved in the active diet group than in the placebo group. Moreover, subgroup analyses of ET-receivers and ET-unreceivers indicated that significant improvements were restricted to ET-receivers of the active diet group. Furthermore, VAS assessment indicated that the 'pain on pressing' subscale was significantly improved in ET-receivers of the active diet group. In addition, analysis of CII biomarkers revealed that serum C2C and CPII levels, but not the urinary CTX-II level, were increased in the active diet group. Notably, both urinary CTX-II/serum CPII and serum C2C/serum CPII ratios were reduced in the active diet group (particularly ET-unreceivers), suggesting that CII synthesis was relatively increased compared to CII degradation in the active diet group. Finally, no diet-related side effects were observed. The CCE-containing diet is likely to be effective in relieving symptoms in patients with knee OA. In addition, it has the potential to improve the balance of CII degradation/synthesis in knee OA.