Background: Oxidative stress is characterized by an imbalance between the production of reactive oxygen species and antioxidant defense systems and is a potential factor in male infertility. The main sources of oxidative stress in vitro are endogenous and exogenous factors. To minimize the activity of free radicals, it is necessary to use antioxidants. Alpha-lipoic acid (ALA) is known as a universal antioxidant. ALA destroys hydroxyl radicals, hydrogen peroxide, superoxide anion, peroxynitrite, and nitric oxide in vitro and in vivo, reducing oxidative stress. ALA can also protect the mitochondria and, as a coenzyme in the Krebs cycle, can help produce ATP, which is very important for sperm motility. Objective: This study aimed to investigate the effect of ALA on the motility, viability, and mitochondrial membrane potential of sperm in vitro. Materials and Methods: In this lab trial study, normal semen samples were collected from 30 fertile men. After semen analysis according to World Health Organization criteria, each sample was divided into 3 groups: fresh, control, and ALA (treated with 0.02 mM ALA for 1 hr). In this study, sperm motility was evaluated with light microscopy, sperm viability was determined by eosin-nigrosin staining, and mitochondrial activity was assessed by rhodamine-123 staining. Results: A significant increase (p < 0.001) was seen in the mean sperm motility (67.80 ± 4.75) compared to the fresh group (65.13 ± 5.45) and the control group (61.50 ± 5.23). The mean percentage of viability in the group incubated with ALA (71.67 ± 3.57) compared to the control group (68.10 ± 3.26) showed a significant increase (p < 0.001). A significant increase in mitochondrial membrane potential was also seen in the group treated with ALA (62.53 ± 5.50) compared to the fresh and the control groups (61.37 ± 5.20, 57.83 ± 5.33), respectively (p < 0.05). Conclusion: Our data indicated that adding ALA to sperm samples creates a strong shield around the sperm membrane and protects sperm against reactive oxygen species. ALA also prevented mitochondrial inactivation by increasing mitochondrial enzymes, thereby increasing sperm motility and viability.
