Clinical and metabolic characterization of obese subjects without non-alcoholic fatty liver: A targeted metabolomics approach

As a small proportion of obese individuals do not develop metabolic complications and non-alcoholic fatty liver disease (NAFLD), this study aimed to provide a comprehensive clinical, metabolic and genetic description of obese subjects with healthy livers. A total of 183 subjects were stratified, according to BMI, presence of metabolic syndrome, biochemical liver tests and hepatic steatosis on ultrasound, into: (i) lean controls (n = 69); (ii) obese healthy (n = 50); and (iii)obese NAFLD (n = 62) groups. Detailed clinical, genetic and metabolic evaluations were then performed. Obese healthy subjects did not differ in glucose parameters from lean controls, and had a lower rate of minor TM6SF2 gene variants compared with obese NAFLD (2/49 vs. 11/60, respectively; P = 0.035) and lean controls (13/64; P = 0.035), but significantly higher leptin concentrations than lean controls (P < 0.001); they also higher adiponectin concentrations (P < 0.001), and lower TNF-α and IL-6 concentrations (P = 0.01 and P < 0.001, respectively), than obese NAFLD subjects. Also, metabolomic studies identified ether- and ester-containing phospholipids [PC ae C44:6, PC ae C42:5, PC aa C40:4; P < 0.001, corrected by the false discovery rate (FDR) method] and found that the amino-acids lysine, glycine and isoleucine (FDR < 0.001) differed between the two obese groups, but not between lean controls and obese healthy subjects. Obese people with healthy livers are characterized by intact glucose homoeostasis, lower pro-inflammatory cytokine levels, and higher adiponectin and leptin concentrations compared with obese people with NAFLD. In addition, the major allele of TM6SF2, a set of phosphatidylcholines and several amino acids are associated with healthy livers in obesity.