Morbidly Obese Subjects Show Increased Serum Sulfide in Proportion to Fat Mass

Background and objectives The importance of hydrogen sulfide is increasingly recognized in the pathophysiology of obesity and type 2 diabetes in animal models. Very few studies have evaluated circulating sulfides in humans, with discrepant results. Here, we aimed to investigate serum sulfide levels according to obesity. Subjects and methods Serum sulfide levels were analyzed, using a selective fluorescent probe, in two independent cohorts [cross-sectionally in discovery ( n = 139) and validation ( n = 71) cohorts, and longitudinally in 82 participants from discovery cohort]. In the validation cohort, blood gene expression of enzymes contributing to H 2 S generation and consumption were also measured. Results In the discovery cohort, serum sulfide concentration was significantly increased in subjects with morbid obesity at baseline and follow-up, and positively correlated with BMI and fat mass, but negatively with total cholesterol, haemoglobin, serum ferritin, iron and bilirubin after adjusting by age, gender and fat mass. Fat mass ( β = 0.51, t = 3.67, p < 0.0001) contributed independently to age-, gender-, insulin sensitivity- and BMI-adjusted serum sulfide concentration variance. Importantly, receiver operating characteristic analysis demonstrated the relevance of fat mass predicting serum sulfide levels, which was replicated in the validation cohort. In addition, serum sulfide concentration was decreased in morbidly obese subjects with impaired compared to those with normal fasting glucose. Longitudinally, weight gain resulted in increased serum sulfide concentration, whereas weight loss had opposite effects, being the percent change in serum sulfide positively correlated with the percent change in BMI and waist circumference, but negatively with bilirubin. Whole blood CBS, CTH, MPST, SQOR, TST and MPO gene expression was not associated to obesity or serum sulfide concentration. Conclusions Altogether these data indicated that serum sulfide concentrations were increased in subjects with morbid obesity in proportion to fat mass and inversely associated with circulating markers of haem degradation.