INTRODUCTION

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With 15% of all child-bearing age couples facing infertility, up to 80 million people are currently affected worldwide[1]. One in two of these cases can be attributed to malefactors[1]. Pathologies, such as varicocele, cryptorchidism, and hypogonadism, are often easily identifiable causes; however, in approximately a quarter of the cases, no definable source is found[1]. This idiopathic infertility is often categorized by abnormalities in sperm morphology, motility, and concentration[1]. These irregular findings are characterized as teratospermia, asthenospermia, and oligospermia, respectively.

Despite ongoing research, the pathogenesis of sperm dysfunction has yet to be completely elucidated. Current hypotheses suggest that elevated reactive oxidative species (ROS) may contribute abnormal semen profiles. Physiologic concentrations of ROS are vital for normal spermatozoa functioning in processes, such as capacitation, activation, acrosome reaction, and fusion2. The main sources of ROS include immature spermatozoa and leukocytes[2]. Developing sperm is exceptionally susceptible to the detrimental effects of ROS[2]. Comparison of semen from fertile and infertile men revealed that infertile men have high levels of ROS[2]. To counteract the effects of ROS, human ejaculate contains antioxidant sources, which protect developing sperm[1].

Due to this, the use of antioxidant supplementation has emerged as a therapy for idiopathic male infertility. However, there is controversy surrounding this treatment. Due to the physiological role of ROS in sperm function, antioxidant supplementation has the potential to further hinder normal sperm processes. Despite this possibility, multiple antioxidant supplementation trials have shown promising results with improvement in at least one sperm parameter[1]. The objective of this study is to describe causes of ROS-mediated infertility and examine the role of common antioxidants in this condition.

SPERM FUNCTION

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As previously described, ROS have a role in normal sperm development. These ROS are mainly produced as by-products of oxidative metabolism in sperm cells and aid maturation. Agarwal et al. described seminal leukocytes and immature spermatozoa as the major contributors of ROS[2]. The mechanism of ROS-mediated sperm damage is hypothesized to be lipid peroxidation. Lipid peroxidation is the process by which free radicals interact with polyunsaturated lipids of the cell membrane to form bioactive compounds[3]. These radical molecules not only affect the integrity of the lipid bilayer but also can affect DNA structure. Changes in DNA structure can target cells for premature apoptosis, impair fertilization, and affect embryo formation, leading to unsuccessful conception, and pregnancies. Of the two ROS-producing components, leukocytes, such as polymorphonuclear lymphocytes and macrophages, cause three-fold more ROS production[2].

Especially during episodes of infection, leukocytes increase superoxide concentrations, which can easily cause excessive ROS accumulation[2]. In a 2016 systemic review of 11 randomized controlled trials centered on the treatment of leukocytospermia, Jung et al. found that eight of these studies reported resolution of leukocytospermia after antibiotic treatment[4]. Although only one study showed a statistically significant increase in pregnancy rate, all four studies that reported pregnancy rates did have overall higher numbers of pregnancies in the treated group in comparison those to the untreated group[4]. From this work, antibiotic therapy appeared successful with limited adverse events, which included gastrointestinal issues and hypersensitivity[4]. However, current literature also suggests that reactive leukocytosis and ROS-production can occur due to pathologies other than infection.

CAUSES OF MALE INFERTILITY

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In addition to infection, Asadi et al. reviewed other potential causes of infertility[5]. Asadi et al. discussed factors that increase testicular oxidative stress, disturbing the physiological antioxidant balance[5]. This review examined the impact of testicular torsion, varicocele, diabetes, and hyperthyroidism[5]. These conditions have all been reported to increase ROS production through various mechanisms, leading to sperm damage and subsequent infertility. These findings are further described in Table 1[5]. In addition to defects in physiological processing caused by these pathologies, extrinsic factors, such as temperature, radiation exposure, and drug exposure, can also impact ROS-production[5]

. Table 1

Even components of foods prominently featured in the American diet can increase ROS. In rabbit model, El et al. demonstrated that exposure to N-nitrosamine, a common environmental toxin found in smoked or barbecued meat products, increase radical levels, and decreased antioxidant levels in testes of rabbits.[6] In addition, histological analysis of seminiferous tubules of exposed rabbits showed deterioration, nuclear atypia, and basement membrane dysfunction[6]. Finally, as a result of harmful diets, body habitus (body mass index [BMI] 25 and more) can also enhance lipid peroxidation.[3] In a 2015 case-control study, the dietary fat intake of infertile and fertile men was compared. The findings showed that increased dietary fat was directly related to sperm dysfunction, particularly affecting sperm motility[7]. Weight loss in patients with BMI of 25 or greater showed beneficial changes in sperm volume and motility[8]. Because many of these internal and external contributors are relatively common in the US population, the prevalence of male infertility could potentially increase dramatically without appropriate intervention, leading to more thought and consideration to antioxidant therapy as a viable solution.

ANTIOXIDANT SUPPLEMENTATION

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To combat the negative effects of ROS, antioxidant supplementation has become an important treatment option for idiopathic male infertility. Current literature on this topic is centered on the efficacy of antioxidant supplementation and its effect on sperm parameters. Antioxidants form two distinct categories: Enzymatic compounds and non-enzyme molecules[9]. Enzymatic compounds are often found physiologically within the cell. These include proteins, such as catalase, glutathione, and superoxide dismutase. These endogenous compounds cannot typically be supplemented; however, supplementation of non-enzymatic compounds often enhances the activity and effectiveness of the enzymes. Non-enzymatic compounds include certain vitamins, metals, non-metallic chemicals, and commercial homeopathic formulations. These have shown promise in improving and restoring sperm functioning with short-term use (< 1 year) in infertile men. While there is limited data on the sustained long-term effect of this type of antioxidant use, sperm characteristics do statistically significantly improve. The results of these studies are summarized in Table 2(in PDF File).

VITAMINS

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Commonly used vitamin supplements include fat-soluble vitamins, including Vitamin A, Vitamin C, Vitamin E, and non-fat soluble vitamins, such as Vitamin B12 and Vitamin B9. While broadly, these vitamins increase the likelihood of normal spermatic growth, each of them utilizes a different mechanism to enact this outcome. For example, retinol, a major component of Vitamin A, aids with the differentiation and maturation of many cell types, including gonadal cells. In a comparison study of men with either normospermia or idiopathic infertility, infertile men had lower levels of retinol and high rates of sperm DNA fragmentation[10]. Vitamin E, however, works by preventing lipid peroxidation of spermatic membranes; thereby, improving sperm motility[9]. Elsheikh et al. studied the effects of 6-month supplementation of Vitamin E (400 mg/day) in men with oligoasthenozoospermia[11].

Due to its synergistic effect with Vitamin E, Vitamin C also prevents oxidative damage of DNA and has important roles in sperm morphology. 3- month supplementation of Vitamin C (1000 mg/daily) for 5 days a week showed statistically significant improvement in sperm motility, total count, and morphology in the control group (n = 120), and the lead -exposed experimental group (n = 120)[12]. Given the size of this study, it offered promising results on the effect of Vitamin C on sperm parameters. However, it appears that the consistency of Vitamin C use is important for this effect. In a 6-month study, 50 control patients and 100 experimental patients were given 1000 mg of Vitamin C every other day.[8] Although there was an improvement in sperm motility, there were no significant findings in either sperm volume or morphology in this study[8]. Like fat-soluble vitamins, B vitamins also have potent effects on sperm development. Folic acid or Vitamin B9 is important for DNA and protein synthesis throughout multiple cell types; however, it is hypothesized to also have vital effects on spermatogenesis[9]. 16-week treatment of folic acid (5 mg) showed an increase in sperm concentration in the small study of 21 patients[13].

Microminerals
Like vitamins, microminerals, such as selenium and zinc, also improve sperm processing. Selenium is known to maintain sperm structure and functions synergistically with Vitamin E, much like Vitamin C. 25 crossbred rams were treated with 1 mg of selenium daily and/or gossypol, a toxic agent to the reproductive agent[14]. Four groups were created as the following: Group 1 (control), Group 2 (9 mg/kg gossypol), Group 3 (14 mg/kg gossypol), and Group 4 (9 mg/kg gossypol and 1 mg of selenium)[14]. In this study, selenium improved libido, sperm motility, and sperm output regardless of gossypol levels[14]. Reduction of oxidative stress can be achieved by zinc as well. Zinc maintains sperm structure, and supplementation with 220 mg of zinc daily can decrease abnormalities in chromatin integrity of sperm[14].

AMINO ACIDS AND DERIVATIVES

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In 2015 study of 47 patients with oligoasthenozoospermia, supplementation therapy included L-Arginine, along with pycnogenol, a nitric oxide synthase activator and synergist of L-Arginine[15]. In this study, the combination therapy statistically improved sperm volume, concentration, and motility showing that amino acids can have a role in antioxidant management [15].Methionine, a precursor amino acid for glutathione, has been shown to prevent ROS and can improve antioxidant defense system. Three groups of male Wistar albino rats were treated with placebo, reproductively toxic anti-tuberculosis drugs, and a combination of anti-tuberculosis drugs and methionine, respectively. Shayakhmetova et al. found that sperm count was significantly increased with the supplementation of methionine regardless of the presence of anti-tuberculosis drugs[16]. Another precursor of glutathione, N-acetylcysteine can also increase glutathione and contribute to more effective antioxidative defense[17]. Finally, L-carnitine, an amino acid derivative, protects sperm DNA and prevents ROS-induced apoptosis[17].

CAROTENOIDS

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Carotenoids are organic colored pigments that are derived from plants, algae, bacteria, and fungi. In these organisms, they function by absorbing light energy and simultaneously protect chlorophyll structure from photodamage caused by ROS. This functionality can be applied to protecting sperm from ROS-damage. Commonly studied carotenoids include astaxanthin, lycopene, and ubidecarenone (or ubiquinol). Astaxanthin, an algae-derived extract, was utilized in a combination antioxidant regimen for patients with oligozoospermia and/or asthenozoospermia[18]. Along with astaxanthin, patients were given ubidecarenone, L-carnitine, zinc, and lycopene for 3 months. Although the effectiveness of astaxanthin itself cannot be interpreted from these results, the combination therapy of three carotenoids, 1 amino acid, and 1 micromineral offered improvements to sperm count and motility and reduction of malondialdehyde (a ROS by-product)[18].

As a synergist with Vitamin E and selenium, lycopene, a common carotenoid found in tomatoes, improved sperm motility and reduced seminal leukocytosis in a tomato juice supplementation study[19]. Lycopene may also affect fatty acid profiles in the sperm membrane bi-layer. The main components affected include arachidonic acid (AA) and docosahexaenoic acid (DHA). Historically, high AA/DHA ratios in blood and sperm were associated with infertility[20,21]. After 3-month supplementation with 10 mg of lycopene twice a day, 44 patients had a decrease in seminal AA/DHA ratios.[20]

Finally, ubidecarenone has been one of the most commonly studied carotenoids. It is suggested to be increase sperm motility and count[9]. Thakur et al. studied the effect of ubiquinol (150 mg/day) on testosterone level, sperm count, and motility in oligospermic patients[22]. Although there was no change in testosterone level, total sperm count and motility were 53% and 35% improved from baseline in these 60 patients[22]. Similar improvement in motility secondary to 200 mg daily ubiquinol was confirmed in a larger study of 114 patients[21].

FATTY ACIDS AND PHENOLS

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Fatty acids are carboxylic acid components of fats and lipids and are important parts of the membrane bi-layers of cells. Fatty acid supplementation with alpha-lipoic acid (ALA) has also been seen to reduce ROS and chelate harmful transitional metals that can increase ROS. Haghighian et al. discovered a statistically significant improvement in multiple sperm characteristics, including sperm count, concentration, and motility, and seminal antioxidant balance with a 12-week ALA program for 44 asthenozoopermic patients[23]. In the seminal fluid, there was not only an increase in total antioxidant capacity but also a decrease in malondialdehyde (P = 0.001 and P = 0.002, respectively)[23].

Like fatty acids, phenols have beneficial effects. They possess antioxidant properties, showing success in research studies. Resveratrol, a phytochemical found in the wine, skin of grapes and other fruits, has been shown to boost sperm motility in male albino mice that were treated with resveratrol 1 mg/kg for 28 days[24]. While resveratrol in wine offers these benefits, punicalagin (PU) in pomegranate juice has shown promise. It caused a rise in the levels of glutathione, a major component of the antioxidant defense system, in adult mice treated with lead and those treated with lead and PU[24]. While the lead caused reproductive damage through ROS, PU use was shown to improve antioxidant balance[24].

COMMERCIAL ANTIOXIDANT PRODUCTS

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With the success of antioxidant therapy in studies, the market for antioxidant supplements has increased dramatically. Formulations of multiple ROS-fighting substances have been compounded to create daily antioxidant supplements. Such therapies include Zingiber officinale (ginger) tablets, Jurinea dolomiaea, Royal JellyTM, Shengling capsule, and Wuzi Yanzong pill (WZYZP). Many of these homeopathic medications are derived from Eastern medicine practices and have shown success in research studies.

Z. officinale (ginger) has antioxidant and anti-inflammatory properties[25]. Within 3 months of daily 500 mg of ginger powder use, DNA fragmentation, a key cause of sperm dysfunction, was decreased (P < 0.001)[25]. A perennial herb, J. dolamaiaea also has similar functioning. Although antioxidant levels in the treated rat were increased, these findings were not significant in male rats[26]. More commercialized products, such as Royal JellyTM, Shengling capsule, and WZYZP showed some results in improving catalase activity and sperm parameters in mouse and rat models, but there is limited randomized control trial data in humans for Chinese herbal medications[27,28]. Yao et al. summarized existing human data on these two therapies, the Shengling capsule and WZYZP[29]. The Shengling (decoction for generating sperm) capsule improved sperm concentration, motility, and reduced antisperm antibodies[29]. This formulation was found to be more effective than WZYZPs (pills for reproduction) in terms of improving sperm parameters[29]. No studies on the effect of WZYZPs on antisperm antibodies were discussed[29]. Although these medications appeared effective, there is no regulating body for drug manufacturing, making standardized testing for these supplements difficult.

Finally, FDA-approved selective estrogen receptor modulators (SERM), such as clomiphene citrate (CC) and tamoxifen, had some improvement in sperm health. CC is an antiestrogen steroid that is indicated in the treatment of polycystic ovarian disease and subsequent anovulatory infertility. Patients with oligoasthenozoospermia were treated with 6-month supplementation with either Vitamin E, CC, or both[11]. Outcome measures of mean sperm concentration and total sperm motility were analyzed, showing that CC alone and CC with Vitamin E therapy offered more benefits than Vitamin E therapy alone[11]. Another SERM, tamoxifen, is currently used in the US for idiopathic male infertility. Guo et al. showed improvement in total sperm count and antioxidant enzyme activity with daily 20 mg tamoxifen use in 41 men[30]. Due to the availability of these drugs on the US market, these medications can easily be utilized to improve infertility.

CONCLUSION

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As a better understanding of the pathogenesis of idiopathic male infertility emerges, treatments targeted for ROS reduction appear to have success in improving sperm stability. Although some amount of ROS is needed for proper functioning, excessive levels can easily accumulate due to certain pathologies and extrinsic factors that hasten the production of ROS through ineffective oxidative metabolism. In sperm, the accumulation of harmful ROS causes devastating damage to sperm structure. It is hypothesized that ROS targets cell membranes, DNA, and tissue structure, rendering germ cells incapable of normal function. The findings in the current literature suggest that vitamins, certain micro-molecules, herbal supplements, and medications can offer some therapeutic options. Although the data on the efficacy of these treatments are limited, strides in this field of research have validated the usefulness of some of these substances. These results can help augment existing treatment methods of weight loss, diet modification, and smoking cessation to better address the growing problem of male infertility.

AUTHOR'S CONTRIBUTION

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Author, Annika Sinha, completed the literature review and the manuscript. Author, Sajal Gupta, MD, served as the advising primary investigator of this work.

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