**4. Conclusion**

*Free Radical Medicine and Biology*

Carnitines [L-carnitine (LC) and L-acetyl carnitine (LAC)] are water-soluble antioxidants involved in spermatozoa metabolism, fuelling important activities like spermatozoa motility [138]. The carnitine and acetylcarnitine can significantly improve spermatozoa motility or kinetics in patients with asthenozoospermia [120, 139]. In vitro studies of spermatozoa cultured in media containing carnitines had higher motility and viability. They exhibit their antioxidant activities through scavenging superoxide anions and hydrogen peroxide radicals, thereby inhibiting lipid peroxidation. A combined treatment of LC (2 g) and LAC (1 g) for 2 months' duration to placebo in men with OAT showed significant improvement in all semen parameters; however, the most significant increase was in spermatozoa motility. Low-grade varicocele and idiopathic infertility patients treated with LC and LAC in comparison with placebo had significant improvement in all semen parameters [140]. On the contrary, LC (1000 mg) and LAC (500 mg) daily treated asthenozoospermic men for 12 weeks and failed to show any significant improvement in spermatozoa motility [141].

CoQ10 is a vital antioxidant omnipresent in almost all body tissues. It is particularly present at high concentrations in spermatozoa mitochondria involved in cellular respiration and plays an integral role in energy production [142]. This contribution rationalizes its use as a promotility and antioxidant molecule. Furthermore, CoQ10 inhibits superoxide formation, delivering protection against OS-induced spermatozoa dysfunction. A significant negative correlation between CoQ10 levels and hydrogen peroxide has been reported, and a linear correlation between CoQ10 levels in seminal plasma spermatozoa count and motility was detected [115]. 300 mg CoQ10 for 26 weeks obtained a significant increase in sperm density and motility [143]. A systemic review of clinical trials on 332 infertile men revealed that treatment with CoQ10 (200–300 mg daily) resulted in a

Antioxidant properties of selenium are thought to stem from its ability to augment the function of glutathione. More than 25 selenoproteins exist, such as phospholipid hydroperoxide glutathione peroxidase (PHGPX) [145] and spermatozoa capsular selenoprotein glutathione peroxidase [146], to maintain spermatozoa structural integrity [147]. Selenium deficiency has been most commonly associated with morphological spermatozoa midpiece abnormalities and impairment of spermatozoa motility [148]. A significant increase (74%) in total normal spermatozoa concentration was noted amongst the subfertile group receiving combined therapy [116] with a combination of both folic acid and zinc for 26 weeks of treatment. Selenium has been less frequently investigated for the treatment of subfertile men. As previously noted, with selenium (200 mg) supplements for 26 weeks, results showed a significant improvement in all semen parameters. A strong correlation was seen between the sum of the selenium and mean spermatozoa concentration, motility and percentage normal morphology [149]. Furthermore, the combination of selenium with vitamin E resulted in an increase in spermatozoa motility [124, 150]. But in the contrary report, treatment with selenium (300 mg) daily for 48 weeks did not result in a significant influence on semen param-

Zinc plays a vital role in the metabolism of RNA and DNA, signal transduction, gene expression and regulation of apoptosis. Its antioxidant properties are thought to result from its ability to decrease production of hydrogen peroxide and hydroxyl radicals through antagonizing redox-active transition metals, such as iron and copper [151]. Zinc concentrations of seminal plasma were found to be significantly lower in subfertile men [152]. Spermatozoa flagellar abnormalities, such as hypertrophy and hyperplasia of the fibrous sheath, axonemal disruption, defects of the inner microtubular dynein arms and abnormal or absent midpiece, are all associated with zinc deficiency [153]. Zinc given for 3 months in men with asthenozoospermia obtained a significant improvement in spermatozoa concentration, progressive motility and fertilizing capacity and a reduction in the incidence of anti-spermatozoa antibodies [153]. Oral zinc supplementation

significant increase in spermatozoa concentration and motility [144].

eters of a group of normozoospermic men [122].

**82**

Spermatozoa possess an inherent but limited capacity to generate ROS which may help the fertilization process. Antioxidants improve the motility and fertilizing ability of spermatozoa. A balance between the benefits and risks from ROS and antioxidants appears to be necessary for the survival and normal functioning of spermatozoa. Antioxidants in extenders may minimize the detrimental effect of ROS and improve the quality of frozen–thawed spermatozoa in animals and human. From the other point of view, the divergent effect of each antioxidant supplementation, improving different parameters of frozen–thawed sperm quality, is attributed to animal species, extender medium and type of molecule and concentration used for each species. Although a beneficial influence was generally observed for antioxidants in reversing ROS-induced spermatozoa dysfunction and in improving pregnancy rates, evaluation of ROS and the use of antioxidants are not routine in clinical practice. The dose and duration of these antioxidants should also be determined and standardized. There should be an effort to develop optimum combinations of antioxidants to supplement spermatozoa media. Finally, this study suggests that further research should be done to determine the appropriate antioxidant compounds as well as certain dose of antioxidants whether used clinical practices or cryopreservation. Moreover the future studies should concern the spermatozoa fertilization and pregnancy rate as a research emphasis.
