Serum Irisin Concentrations in Severely Inflamed Patients

Irisin is a recently discovered exercise-induced myokine that has been attributed the role of favoring white-to-brown adipose tissue trans-differentiation. We confirmed in a population-based cohort that irisin serum concentrations are independently correlated with the habitual level of physical activity, but we also observed an independent correlation with serum concentrations of high-sensitivity C-reactive protein (hs-CRP), thus suggesting that inflammation may influence irisin production. In order to investigate the association between irisin and inflammation, we measured serum irisin concentrations in a group of inflamed inpatients. We hypothesized that if an association between irisin and inflammation exists, severely inflamed patients, even though physically inactive, might also exhibit high serum irisin levels. We recruited 40 consecutive markedly inflamed inpatients on the basis of serum CRP levels. Their irisin serum concentrations (Phoenix Europe, Germany) were compared with those obtained in the population-based cohort of the ABCD_2 study (Alimentazione, Benessere Cardiovascolare e Diabete) (ISRCTN15840340). The inflamed patients exhibited higher serum irisin concentrations (median: 6.77 ng/ml; 95% CI for the median: 5.97-7.23) than those observed in the ABCD cohort (median: 5.21 ng/ml; 95% CI for the median: 5.08-5.30; p <0.001). Irisin concentrations were significantly correlated with age (r=-0.44; p <0.001), creatinine (r=-0.35; p <0.05), and fibrinogen (r=0.40; p <0.05) concentrations. No association was observed between irisin, interleukine-6 and tumor necrosis factor alpha. This study confirms the association between inflammation and irisin concentrations. Further studies are needed to understand the mechanisms underlying this association and its possible clinical implications.