Targeting Mitochondria in MASLD: Comparative Evaluation of MitoQ and SS-31 (Elamipretide) in Aged Female Mice under Nutritional Stress

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is a major cause of cirrhosis, liver cancer, and cardiovascular disease. Early mitochondrial dysfunction drives lipid imbalance, inflammation, and fibrosis. Given the lack of approved pharmacological treatments, this study compares the mitochondria-targeted agents MitoQ and SS-31 for their effects on mitochondrial function, oxidative stress, apoptosis, and inflammation in aged, nutritionally stressed mice with MASLD. Aged female C57BL/6 mice (12-14 months) were fed a high-fat, high-fructose diet for 16 weeks to induce MASLD. Mice were randomized into four groups: (i) control diet, (ii) MASLD, (iii) MASLD + MitoQ (25 mg/kg/day, oral), and (iv) MASLD + SS-31 (3 mg/kg/day, i.p.). Liver tissues were analyzed by western blotting for mitochondrial biogenesis and dynamics markers (PGC-1?, NRF1, and TFAM), oxidative stress regulators (SOD2, Nrf2, 4-HNE), apoptosis-related proteins (Bax, and Bcl-2), inflammatory and fibrotic mediators (NF-?B, and NLRP3), and insulin signaling proteins (p-Akt, and GLUT2). Both MitoQ and SS-31 significantly improved mitochondrial protein expression and overall liver health compared with untreated MASLD mice. MitoQ primarily enhanced mitochondrial antioxidant defenses by upregulating SOD2 and Nrf2 while decreasing 4-HNE adduct formation, reflecting reduced oxidative damage. SS-31, in contrast, more effectively preserved mitochondrial structural integrity. Both compounds attenuated inflammation by suppressing NF-?B and NLRP3 activation. They also improved insulin sensitivity by increasing p-Akt and GLUT2 expression. Histological analysis using H&E staining revealed marked reductions in hepatic steatosis. Mitochondrial dysfunction drives MASLD progression. In aged MASLD mice, MitoQ enhances antioxidant defense, SS-31 preserves integrity, and both improve insulin signaling and reduce fibrosis, supporting mitochondrial therapy for MASLD.