Hydrogen sulphide in liver glucose/lipid metabolism and non-alcoholic fatty liver disease.

BACKGROUND: For a long time, hydrogen sulphide (H2 S) was considered only as a toxic gas, inhibiting mitochondrial respiration at the level of cytochrome c oxidase, and an environmental pollutant. Nowadays, H2 S is recognized as the third mammalian gasotransmitter, playing an important role in inflammation, septic shock, ischaemia reperfusion events, cardiovascular disease and more recently in liver physiology and chronic liver diseases such as non-alcoholic fatty liver disease (NAFLD). METHODS: This narrative review is based on literature search using PubMed. RESULTS: From a bioenergetic perspective, H2 S is a very unique molecule, serving as a mitochondrial poison at high concentrations or as an inorganic mitochondrial substrate at low concentrations. By using transgenic animal models to specifically modulate liver H2 S biosynthesis or exogenous compounds that release H2 S, several studies demonstrated that H2 S is a key player in liver glucose and lipid metabolism. Liver H2 S content and biosynthesis were also altered in NAFLD animal models with the in vivo administration of H2 S-releasing molecules preventing the further escalation into non-alcoholic-steatohepatitis. Liver steady-state levels of H2 S, and hence its cell signalling properties, are controlled by a tight balance between its biosynthesis, mainly through the transsulphuration pathway, and its mitochondrial oxidation via the sulphide oxidizing unit. However, studies investigating mitochondrial H2 S oxidation in liver dysfunction still remain scarce. CONCLUSIONS: Since H2 S emerges as a key regulator of liver metabolism and metabolic flexibility, further understanding the physiological relevance of mitochondrial H2 S oxidation in liver energy homeostasis and its potential implication in chronic liver diseases are of great interest.

Glucose and glutamine handling in the Sertoli cells of transgenic rats overexpressing regucalcin: plasticity towards lactate production.

Sertoli cells (SCs) possess the unparalleled ability to provide the germ line with growth factors and nutrients. Although SCs can oxidize amino acids, e.g., glutamine, they mostly metabolize glucose, producing high amounts of lactate, the germ cells preferential substrate. Regucalcin (RGN) is a calcium-binding protein that has been indicated as a regulator of cell metabolism. In this study, we investigated glucose and glutamine handling in the SCs of transgenic rats overexpressing RGN (Tg-RGN) comparatively with wild-type (Wt) littermates. Primary SCs isolated from adult Tg-RGN animals and maintained in culture for 24 hours, produced and exported more lactate, despite consuming less glucose. These observations were underpinned by increased expression of alanine transaminase, and augmented glutamine consumption, suggesting that alternative routes are contributing to the enhanced lactate production in the SCs of Tg-RGN rats. Moreover, lactate seems to be used by germ cells, with diminished apoptosis being detected in the seminiferous tubules of Tg-RGN animals cultured ex vivo. The obtained results showed a distinct metabolism in the SCs of Wt and Tg-RGN rats widening the roles assigned to RGN in spermatogenesis. These findings also highlighted the plasticity of SCs metabolism, a feature that would be exploited in the context of male infertility.