Baseline Levels of Seminal Reactive Oxygen Species Predict Improvements in Sperm Function Following Antioxidant Therapy in Men With Infertility

Wayne Vessey; Shaghayegh Saifi; Aditi Sharma; Cassandra McDonald; Paula Almeida; Monica Figueiredo; Suks Minhas; Ashraf Virmani; Waljit S. Dhillo; Jonathan W. Ramsay; Channa N. Jayasena


Clin Endocrinol. 2021;94(1):102-110. 

In This Article


Semen ROS is a novel potential marker of sperm function with increasing evidence of its aetiological role in male infertility.[17] Oxidative stress may negatively affect fertility by adversely affecting sperm membrane lipid peroxidation, sperm motility, the acrosome reaction, chromatin maturation and subsequent sperm DNA fragmentation,[18] resulting in defective paternal DNA passage to the offspring.[19] With nearly 30%-80% of infertile men with high ROS, high oxidative stress is associated with reduced sperm function in men with idiopathic infertility and in cases of recurrent miscarriage. Subsequently, 'male oxidative stress infertility' or MOSI is a new proposed term by Agarwal et al to describe men with idiopathic infertility who have raised semen OS.[20] However currently, there is no consensus on which patients to select to test for ROS and lack of standardized method of ROS assessment and which patients would benefit from treatment.[21] Furthermore, although useful, these tests are expensive, time-consuming and require technical training.[15]

Men taking antioxidants have an associated significant increase in sperm parameters and in live-birth rates.[7,8,22] Cavallini et al assessed the effect of antioxidant therapy on idiopathic and varicocele-associated oligoasthenospermia patients with improvement in sperm parameters and pregnancy rate compared to placebo.[8] Furthermore, a recent Cochrane review indicated that there may be an increase in live-birth rate for those couples with the male partners taking antioxidants; however, the overall quality of evidence was low from only seven small randomized controlled trials.[22]

Antioxidants may represent a popular empirical therapy for male infertility; however, previous evidence underpinning their efficacy has been controversial. Consequently, many primary care and specialist clinicians remain sceptical about the proposed benefits of antioxidant therapy for infertile men. Our study suggests for the first time that a commercially available LAL preparation improves sperm count, total and progressive motility while dramatically reducing semen ROS levels in men with infertility. However, we report that LAL therapy is only effective for infertile men with reduced sperm function in whom semen ROS levels are abnormally elevated at baseline.

To date, twelve randomized, double-blinded placebo-controlled studies have reported that carnitine administration improves at least one aspect of sperm function in men with infertility:[9,32] one, three and ten of these studies reported increases in semen volume, sperm concentration, total sperm motility and progressive sperm motility respectively. Lenzi et al (2003) reported that L-carnitine therapy improved sperm motility and concentration in men with infertility, but only after the exclusion of five outlier patients with spontaneous increase of sperm motility during the second treatment period or spontaneous decrease of sperm motility during the washout period.[26] However, other studies failed to observe any improvements in sperm function following L-carnitine administration to men with infertility.[11,12] Sigman et al (2006) failed to show any significant improvement in sperm motility or total motile sperm count following daily treatment with L-carnitine (1000 mg) and L-acetyl-carnitine (500 mg) of men with idiopathic asthenospermia.[12] Conversely, we observed that 3 months of LAL supplementation increased sperm concentration significantly by over 50%, and total and progressive motility both increased by approximately 30% when compared with baseline in the elevated ROS group. Furthermore, supplementation with carnitines significantly reduced semen ROS levels by fivefold in the elevated ROS group. However, LAL had no significant effect on sperm function or semen ROS levels in infertile men with normal semen ROS levels ≤ 10 RLU/SEC/106. Results of our study may partially explain the inconsistency in the previously observed effects of carnitine therapy on male reproductive function when not stratified by baseline semen ROS levels. We also provide important mechanistic data supporting the hypothesis that LAL improves male reproductive function by reducing oxidative stress in semen of men with infertility. Our data suggest that semen ROS measurement has potential clinical utility for predicting and monitoring improvements in sperm function following LAL therapy in men with infertility.

ROS have a critical physiological role in oxidative metabolism and mitochondrial function. It is therefore plausible that excessive suppression of ROS could impair cellular function. Accordingly, it has recently been proposed that indiscriminate antioxidant therapy may be detrimental to sperm function in men with infertility by inducing a state of reductive stress.[33] Our published study is the first to investigate whether L-carnitine can worsen sperm function without elevated ROS at baseline. We did not observe any significant impairment in sperm volume, count, total or progressive motility men with infertility and normal baseline semen ROS levels. Our data therefore provide important preliminary safety data by suggesting that men without elevated semen ROS could take carnitines therapy without impairment of sperm function.

Compared with empirical hormonal therapies such as aromatase inhibitors and selective oestrogen receptor modulators, antioxidant therapy is relatively safe, inexpensive and widely available.[34] None of the patients in this study had any observed side effects from the antioxidant therapy. However, clinical guidelines are needed to avoid indiscriminate overuse of antioxidants.

Hypothesizing that carnitines are likely to affect sperm function by reducing semen ROS levels, we explored the relationship between changes in ROS and changes within individual markers of sperm function in men with infertility. We observed for the first time that during carnitines therapy, reductions in semen ROS are significantly associated with increase in sperm count, total and progressive motility. These data provide biological plausibility to the hypothesis[23,29] that novel drugs targeted to reduce semen ROS could be used to treat men with infertility.

The study is not without its limitations. The normal (<10) and high (>10) ROS levels in our study were arbitrary cut-offs in men who had abnormal baseline semen parameters. There is lack of standardization and inconsistencies in establishing a reference range. Furthermore, the established reference ranges attempt to define physiological levels of seminal ROS as opposed to high and low ROS levels within men with abnormal baseline semen parameters or infertility. In addition, sexual abstinence duration may influence ROS levels. A recent study showed that a group of men with > 4 days of abstinence duration had higher seminal oxidative stress compared with men with sexual abstinence of 4 days or less, albeit using different ROS assays.[35] All semen samples in our study were collected between 2 to 7 days of sexual abstinence as per the WHO 2010 guidelines;[14] therefore, this variation in abstinence duration may have influenced the ROS levels. In addition, it was a small sample size, requiring future larger studies to confirm these findings. Furthermore, a placebo group could not be included in this study of routine clinical practice; however, we consider this would have provided limited additional benefit to the study given that the included control group (infertile men with normal ROS) did not respond to LAL therapy. Published studies suggest that mean sperm counts would not change significantly during serial measurements in the absence of L-carnitine therapy.[33,36] We also acknowledge that the antioxidant supplement contains other ingredients other than LAL; therefore, the effects observed cannot be attributed only to the LAL ingredient. In addition, we did not measure reproductive hormones or paternity outcomes in this cohort.

In summary, we have performed a prospective study reflecting real-world practice with important implications for the use of antioxidants to treat men with infertility. Three months of over the counter LAL therapy improved sperm function in some but not all men with infertility. Critically, our data suggest LAL therapy only improves sperm function in men with elevated semen ROS. Our data therefore suggest that LAL administration has clinical utility to improve sperm function in men with infertility, but only benefits a subset of patients. Furthermore, LAL did not impair sperm function in infertile men without elevated semen ROS levels. Future studies are warranted to investigate if LAL therapy can improve pregnancy and live-birth outcomes in couples affected by male infertility.