Irisin in patients with nonalcoholic fatty liver disease.

OBJECTIVE: Irisin is a recently discovered myokine proposed to increase thermogenesis-related energy expenditure and improve metabolism. We aimed to comparatively evaluate serum irisin levels in patients with biopsy-proven nonalcoholic fatty liver disease (NAFLD) vs. controls and study their association with disease severity.

METHODS: Fifteen and 16 consecutively enrolled patients with biopsy-proven nonalcoholic simple steatosis (NAFL) and steatohepatitis (NASH), respectively, and 24 lean and 28 obese controls without NAFLD were recruited. Irisin, established adipokines and biochemical tests were measured.

RESULTS: Serum irisin levels were statistically different in obese controls (33.7±2.7 ng/mL; p<0.001) and patients with NAFL (30.5±1.5 ng/mL; p<0.001) and NASH (35.8±1.9 ng/mL; p=0.001) compared with lean controls (47.7±2.0 ng/mL), but were similar among patients with NAFL, NASH and obese controls. This difference remained significant after adjustment for body mass index (or waist circumference), gender, age, insulin resistance (assessed by HOMA-IR or QUICKI), exercise and time since blood collection. Serum leptin and adiponectin, but not irisin, levels were independently from BMI correlated with insulin resistance and cardiometabolic factors. Serum irisin tended to be higher in patients with (36.7±2.4 ng/mL) than without (30.8±1.2 ng/mL; p=0.02) portal inflammation and independently associated with the latter; these data need to be confirmed by future studies.

CONCLUSIONS: Serum irisin levels differ between lean controls and obese controls or NAFLD patients. Despite similar circulating irisin levels between NAFL and NASH groups, irisin may be independently and positively associated with the presence of portal inflammation. Future clinical and mechanistic studies are needed to confirm and extend these data.