Redox-Dependent Modulation of Cardiac Mitochondrial F₁F_O-ATPase and Respiratory Function by N-Acetylcysteine and...

Oxidative stress is closely associated with mitochondrial dysfunction and contributes to the development of several human diseases. Among antioxidant compounds, ASC and NAC are widely used for their cytoprotective and redox-regulating properties; however, their direct effects on specific aspects of mitochondrial bioenergetics are only partially characterized. In the present study, we investigated the effects of ASC and NAC, individually and combined, on Mg²⁺-dependent F₁F_O-ATPase hydrolysis, mitochondrial free thiol content and respiration in isolated swine heart mitochondria. ASC significantly stimulated F₁F_O-ATPase activity in a concentration-dependent manner, whereas kinetic analysis indicated a mixed uncompetitive activation mechanism. In contrast, NAC alone did not significantly affect F₁F_O-ATPase activity but abolished the stimulatory effect of ASC when the two compounds were combined. Both ASC and NAC increased mitochondrial free thiol content, although no change was observed under combined treatment conditions. Mitochondrial oxygen consumption analysis revealed substrate-dependent effects of the two antioxidants on electron transport. Overall, ASC and NAC exerted distinct direct actions on isolated mitochondria, and their combination did not produce additive or synergistic effects. These findings provide new insights into the direct modulation of mitochondrial function by antioxidant compounds and may contribute to expanding understanding of their potential therapeutic and dietary supplement applications, particularly when combined.