Metabolic patterns in insulin-sensitive male hypogonadism

Abstract

Male hypogonadism is a disorder characterised by low levels of the hormone testosterone. At beginning subjects with low levels of testosterone do not show insulin resistance (insulin-sensitive patients), which develops over time (insulin-resistance patients). To analyse the metabolic alterations mainly related to decreased testosterone, we performed metabolomics investigations on the plasma of males with hypogonadism who showed normal insulin levels. Plasma from patients with low testosterone (<8 nmol/l) and homeostatic model assessment for insulin-resistance-index (HOMAi) < 2.5, as well as matched controls, was analysed by UHPLC and mass spectrometry. Then metabolites were then subjected to multivariate statistical analysis and grouped by metabolic pathways. Glycolysis was not altered, as expected for the presence of insulin activity, but imbalances in several other pathways were found, such as the pentose phosphate pathway (PPP), glycerol shuttle, malate shuttle, Krebs cycle (TCA) and lipid metabolism. The PPP was significantly upregulated. Moreover, while the first steps of the Krebs cycle were downregulated, 2-oxoglutarate was replenished via glutaminolysis. Since glutaminolysis leads to an activation of the malate aspartate cycle, greater amounts of NADH and ATP with respect to the control were recorded. The activation of the glycerol shuttle was also recorded, with consequent lower triglyceride production and downregulation of beta-oxidation. This explained the moderately increased dyslipidaemia, as well as the mild increase in body mass index (BMI) observed in insulin-sensitive hypogonadism. Finally, a significant decrease in carnosine was recorded, explaining the muscle weakness commonly observed.