The Dual Role of Exogenous Hydrogen Sulfide (H2S) in Intestinal Barrier Mitochondrial Function: Insights into Cytoprotection and Cytotoxicity Under Non-Stressed Conditions

Hydrogen sulfide (H₂S) is a critical gasotransmitter that plays a dual role in physiological and pathological processes, particularly in the gastrointestinal tract. While physiological levels of H₂S exert cytoprotective effects, excessive concentrations can lead to toxicity, oxidative stress, and inflammation. The aim of this study was to investigate the dose-dependent effects of exogenous H₂S on mitochondrial functions and biogenesis in intestinal epithelial cells under non-stressed conditions. Using a Caco-2 monolayer model, we evaluated the impact of sodium hydrosulfide (NaHS) at concentrations ranging from 1 × 10^-7 M to 5 × 10^-3 M on mitochondrial metabolism, redox balance, antioxidant defense, inflammatory responses, autophagy/mitophagy, and apoptosis. Our results demonstrated a biphasic response: low-to-moderate H₂S concentrations (1 × 10^-7 M-1.5 × 10^-3 M) enhance mitochondrial biogenesis through PGC-1α activation, upregulating TFAM and COX-4 expression, and increasing the mtDNA copy number. In contrast, higher concentrations (2 × 10^-3-5 × 10^-3 M) impair mitochondrial function, induce oxidative stress, and promote apoptosis. These effects are associated with elevated reactive oxygen species (ROS) production, dysregulation of antioxidant enzymes, and COX-2-mediated inflammation. H₂S-induced autophagy/mitophagy is a protective mechanism at intermediate concentrations but fails to mitigate mitochondrial damage at toxic levels. This study underscores the delicate balance between the cytoprotective and cytotoxic effects of exogenous H₂S in intestinal cells, helping to develop new therapeutic approaches for gastrointestinal disorders.