Effect of body mass index on serum urate and renal uric acid handling responses to an oral inosine load: experimental intervention study in healthy volunteers

BACKGROUND: High body mass index (BMI) is strongly associated with hyperuricaemia. It is unknown whether overweight and obesity influences serum urate primarily through increased urate production or reduced renal clearance of uric acid. The aim of this study was to determine the influence of BMI on the response to inosine, a purine nucleoside that functions as an intermediate in the purine salvage and degradation pathways. METHODS: Following an overnight fast, 100 healthy participants without gout attended a study visit. Blood and urine samples were taken prior to and over 180 min after 1.5 g oral inosine. Serum urate and fractional excretion of uric acid (FEUA) were analysed according to high BMI (≥ 25 kg/m(2)) and low/normal BMI (< 25 kg/m(2)) groups, and according to BMI as a continuous variable. RESULTS: Participants in the high BMI group (n = 52, mean BMI 30.8 kg/m(2)) had higher serum urate concentrations at baseline (P = 0.002) compared to those with low/normal BMI (mean BMI 21.8 kg/m(2)). However, the high BMI group had a smaller increase in serum urate following the inosine load (P = 0.0012). The two BMI groups had a similar FEUA at baseline (P = 0.995), but those in the high BMI group had a smaller increase in FEUA following the inosine (P = 0.0003). Similar findings were observed when analysing BMI as a continuous variable. Those with high BMI had a smaller increase in FEUA per increase in serum urate, compared to those with low BMI (P = 0.005). CONCLUSIONS: In a fasting state, people with high BMI have elevated serum urate levels but similar FEUA values compared with those with low/normal BMI. Following a purine load, those with high BMI have an attenuated renal excretion of uric acid. These data, using an experimental method to dynamically assess human urate handling, suggest that people with high BMI have a higher renal capacity for uric acid reabsorption when fasted and following a dietary purine intake have reduced renal clearance. TRIAL REGISTRATION: Australia and New Zealand Clinical Trials Registry, ACTRN12615001302549, date of registration 30 November 2015.