Abstract
Background: Infertility, defined as the failure to conceive after one year of regular, unprotected intercourse, affects 50–80 million people worldwide. A male factor is involved in approximately 20–30% of cases. In the etiology of male infertility, the association between poor semen quality and oxidative stress (OS) is well known. High levels of reactive oxygen species (ROS) allow the oxidation of DNA, proteins, and lipids of sperm cells, modifying their vitality, motility, and morphology. Methods: To evaluate the effects of antioxidants on sperm in infertile men, we queried the MEDLINE database (via the PubMed interface) for published studies in the last 10 years (2011–2021). The following keywords were used: “infertility” and -“inositol”, -“alpha-lipoic acid”, -“zinc”, -“folate”, -“coenzyme Q10”, -“selenium”, and -“vitamin”. Results: Inositol regulates OS levels in sperm cells thanks to its role in mitochondrial reactions and is involved in several processes favoring sperm–oocyte interactions. Alpha-lipoic acid (ALA) reduces ROS damage and improves semen parameters in terms of spermatozoa’s motility, morphology, and count. Poor zinc nutrition may be related to low quality of sperm. Supplementation of folate plus zinc has a positive effect on the sperm concentration and morphology. Supplementation with CoQ10 increases sperm concentration, total and progressive motility. Selenium (Se) supplementation improves the overall semen quality and is related to a higher ejaculated volume. Among vitamins, only vitamin B12 shows a positive effect on semen quality; it increases sperm count and motility and reduces sperm DNA damage. Conclusions: In men showing low-quality semen, diet supplementation with antioxidants may improve the sperm quality by alleviating OS-induced sperm damage and enhancing hormone synthesis and spermatozoa concentration, motility, and morphology. Future clinical trials should be focused on the possible association of several antioxidants to take advantage of combined mechanisms of action.
Highlights
World Health Organization (WHO) statistics reveal that infertility affects 50–80 million people worldwide, and male factors account for approximately 20–30% of all infertility cases [2]
Serum myoIns cannot cross the tight junctions at the testicular level and is transported into cells by a sodium/myo-Ins cotransport protein, whose expression is sensitive to osmolar changes [24]
Normal spermatozoa production, function, and vitality requires a balance between reactive oxygen species (ROS) and antioxidants
Summary
Sperm cells are extremely sensitive to damage caused by high ROS levels because of the large amounts of unsaturated fatty acids in their membranes, which are essential for sperm capacitation, acrosome reaction and sperm/oocyte interaction. Oxidative peroxidation of unsaturated fatty acids mediated by ROS represents the main mechanism of ROS-induced sperm damage, leading to infertility [16]. Due to the high concentration of plasma membrane polyunsaturated fatty acids and the lack of cytoplasmic defense mechanisms [17], high levels of ROS can increase OS by triggering the oxidation of sperm cell DNA, proteins, and lipids, and modifying sperm vitality, motility, and morphology [18]. Sperm DNA fragmentation is caused by extrinsic factors (e.g., smoking, heat exposure, chemotherapeutics, and environmental pollutants) and intrinsic factors (e.g., abortive apoptosis, defective germ cell maturation, and OS) [21]. The current narrative review aims to evaluate the updates on the roles and mechanisms of action of the antioxidants most commonly used in nutrition supplementation as a strategy to improve sperm quality
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