Methods

We measured fasting serum visfatin, total and HDL-cholesterol, triglycerides (TG), alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP), and γ-glutamyltransferase (γ-GT). Breath test was performed by measuring 13 CO2-enrichment in breath before and after the oral administration of 2-keto [1-13C] isocaproate by using isotope ratio mass spectrometry [4]. After bivariate correlation analysis, linear regression analysis was conducted to examine the association of NAMPT/visfatin with the percentage of 2-keto [1-13C] isocaproate oxidized and biochemical variables controlling for age and BMI.

Results

NAMPT/visfatin was significantly associated with ALT (β=− 0.352, P= 0.013) and 2-keto [1-13C] isocaproate oxidized percentage (β= 0.583, adjusted P= 0.023). NAMPT/visfatin was not associated with BMI or FM (P> 0.2), whereas there were borderline associations between NAMPT/visfatin and HDL-cholesterol (β= 0.650) and γ-GT (β= 0–0.284)(both adjusted P< 0.06). The percentage of 2-keto [1-13C] isocaproate oxidized was inversely correlated with serum levels of gamma-GT (r=− 0.535, P= 0.001), ALT (r=− 0.431, P= 0.008) and ALP (r=− 0.447; P= 0.006).

Discussion

The present study showed an inverse association between circulating NAMPT/visfatin levels and liver mitochondrial function, as estimated by the 2-keto [1-13C] isocaproate breath test, in obese women. Though these findings should be taken as preliminary due to the small sample size of our study, we believe that the results are of clinical interest and provide further insights regarding the potential role of NAMPT/visfatin in the pathogenesis of NAFLD, insulin resistance and cardiovascular disease.