Involvement of SIRT3 downstream targets ANT1, VDAC, CYPD, and Drp1 in a rat model of hepatic encephalopathy: Therapeutic role of thymoquinone.

OBJECTIVES: Hepatic encephalopathy (HE) is a brain disorder linked to hyperammonemia from liver injury. Elevated ammonia levels are known to impair mitochondrial function, the primary energy source for cells. Therefore, this study aimed to evaluate energy-related signaling pathways enhancing mitochondrial biogenesis using thymoquinone (TQ) in an HE model. MATERIALS AND METHODS: Wistar rats were randomly divided into three groups: sham, HE (200 mg/kg thioacetamide (TAA) in 2ml saline, administered intraperitoneally (IP) once every 48 hr for 14 consecutive days), and HE + TQ (20 mg/kg, IP, in 2 ml DMSO 5% administered once daily for seven consecutive days). Mitochondrial biomarkers (membrane potential [MMP], oxidative stress), gene expression (AMPK, PGC-1α), and protein expression (AMPK, P-AMPK, SIRT3, ANT1, CYPD, DRP1, VDAC, and P53) were measured in brain tissue. Additionally, electroencephalogram (EEG) recordings were obtained from the dentate gyrus (DG). RESULTS: Our findings indicate that TQ was associated with a significant increase in MMP and a concomitant decrease in mitochondrial oxidative stress. Furthermore, TQ appeared to augment the AMPK/PGC-1α/SIRT3 signaling pathway, and was associated with the reversal of HE-induced down-regulation of ANT1 and VDAC, as well as up-regulation of CYPD, DRP1, and P53. Besides, TQ treatment was also linked to increased power recorded in the EEG from the DG region of the rat hippocampus. CONCLUSION: The AMPK/PGC-1α/SIRT3 signaling pathway appears to function as a key energy sensor that may help revitalize the metabolic machinery in mitochondria, potentially facilitating metabolic exchanges and energy production, particularly in response to neurodegenerative diseases such as HE.