Body mass index and body fat content correlate similarly with synovial leptin

Abstract

Purpose: Obesity appears to play a role in the development of knee osteoarthritis (OA) and has been shown to influence pain and disease progression. Leptin is an adipokine involved in body weight regulation and known to show inflammatory effects in high concentrations and has also been implicated in OA physiopathology and pain. Objective: To evaluate the correlation between different body weight measurements (body mass index (BMI), waist-to-hip ratio (WTHr) and percentage of body fat (PBF)) and synovial fluid leptin and a surrogate marker of inflammation such as the amount of synovial fluid. Methods: Patients aged 50 years or more with symptomatic knee OA and joint effusion, Kellgren-Lawrence II-III. Demographics, disease duration and body mass index (BMI), waist-to-hip radio (WTHr) and percentage of body fat (PBF) were assessed. Percentage of body fat was determined by bio-electrical impedance. Knee ultrasound (US) was performed evaluating and measuring the presence of effusion and at the suprapatellar midline. After US measurement joint aspiration was performed; all patients were evaluated approximately at the same time of the day. Synovial leptin levels were analyzed using a Human leptin ELISA kit (Biocompare, California, USA). Results: Seventy consecutive female patients with symptomatic knee OA and Kellgren-Lawrence II-III were included, age 65 ±7.8 (50-79) years, disease duration of symptoms 66 ±49.5 mo (12-200). Mean BMI was 31.5 ±5.1 kg, mean WTHr 0.94 ±0.082 and mean BFP 42.34 ±5.11%. Mean synovial fluid measurement was 9.59 ±2.79 mm. Mean levels of leptin in synovial fluid were 76.76 ±38.66 ng/mL. None of the different types of body weight measurement showed any correlation with the amount of synovial fluid on US. On the other hand BMI and BFP showed similar moderate positive correlation with synovial fluid levels of leptin (r= 0.4626 and r= 0.4610, respectively), whereas no correlation was found between WTHr and leptin synovial levels (r= 0.059). Conclusions: Both BMI and the percentage of body fat were moderately correlated with synovial levels of leptin in a similar degree. Thus, synovial leptin may be associated in a similar way with a measure of relative weight as BMI or with a measure reflecting relative fat content. On the contrary, severity of obesity did not appear to correlate with a marker of inflammation such as synovial effusion.