Effects of L-carnitine over-supplementation on spermatogenesis and sperm function in healthy NMRI mice.

L-carnitine (LC) plays a key role in lipid metabolism by transporting fatty acids from the cytosol into mitochondria for energy production. Beyond its metabolic function, LC exhibits significant antioxidant, anti-cytokine, and anti-apoptotic properties, contributing to cellular protection. This study investigates the potential adverse effects of four weeks of LC supplementation (20, 100, and 500 mg/kg body weight, n = 10) on spermatogenesis and sperm function in healthy NMRI male mice. Sperm parameters-motility, concentration, and morphology-were assessed alongside sperm and testicular oxidative status. Sperm chromatin and DNA integrity were evaluated through histone persistence (Aniline Blue staining), protamine deficiency (CMA3 staining), and DNA fragmentation (Acridine Orange staining). Pregnancy outcomes were also investigated. After four weeks, the LC500 group exhibited significantly higher liver weight than the controls. However, sperm parameters, reactive oxygen species (ROS) production, lipid peroxidation, and testicular malondialdehyde and total antioxidant capacity levels showed no significant differences among groups. Notably, the LC500 group demonstrated a significant decline in sperm DNA and chromatin integrity (P < 0.05). Alongside, liver sections from LC500-treated mice showed a marked increase in lipid droplets, while controls maintained normal hepatic morphology. Despite these alterations, male fertility indices remained unchanged. Our findings suggest that while LC is essential for metabolism, over-supplementation may compromise male fertility by inducing sperm chromatin damage and DNA fragmentation. Furthermore, high-dose LC intake may contribute to inflammation and non-alcoholic fatty liver disease (NAFLD), emphasizing the need for cautious LC supplementation to safeguard reproductive health.