Currently, male factor infertility is a primary or contributing cause for ~50% of couples with infertility (Agarwal et al. 2021). In recent years, microcystins (MCs), a group of cyanobacterial toxins, have gained widespread attention given the global worsening of environmental water pollution (Svircev et al. 2019). MCs exert multiorgan toxicity in both wildlife and humans (Li et al. 2021). Indeed, toxicological studies have found that exposure to MCs can induce male infertility as reviewed by Chen et al. (Chen et al. 2016). Although previous analysis supports the notion that the testis is the second most important target organ of MCs (Chen and Xie 2005), to our knowledge, there have been no epidemiological studies regarding the effects of MCs on male reproductive health. Therefore, we conducted a cross-sectional study to assess the association between MC exposure and male reproductive quality.
Male partners of couples were enrolled at their visit to the Reproductive Medical Center, the Affiliated Drum Tower Hospital of Nanjing University Medical School, Nanjing, China. The study population was heterogeneous, including infertile men and healthy men whose partners suffered from female factor infertility. The criteria for subject selection were minimal: a) being 20-40 y old at the time of recruitment; b) living for over 3 y in the Jiangsu or Anhui area, where frequent water blooms have been observed; and c) no potential occupational exposure to MCs. From June 2020 to January 2021,2,588 eligible men were invited to join our study and complete the questionnaire under the guidance of a trained nurse. Of the 2,588 men, 873 were excluded as follows: 384 reported that the abstinence time was <2 or >7 d; 439 had chromosomal abnormality or experienced inflammation or surgery of the reproductive or urological system, sexually transmitted diseases, azoospermia, or a varicocele; 50 semen samples were missing. Thus, the final sample size was 1,715 in our study. We defined "cigarette smoker" as those individuals who smoked more than one cigarette per day for more than 6 consecutive months. Participants who had quit smoking for less than 6 months prior were still classified as "current smoker." We defined "alcohol drinker" as those who consumed alcohol at least once (or 50 g) per week for more than 6 consecutive months. Participants who had quit drinking for less than 6 months prior were still defined as "current alcohol drinker." Each participant provided a semen sample by masturbation. In addition, a total of 1,251 study participants provided venous blood samples for the measurement of inhibin B (924 samples) and other reproductive hormones [649 samples, including follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), total testosterone (T), and estradiol (E2)], respectively. The work was approved by the Ethical Committee of Drum Tower Hospital affiliated with Nanjing University Medical School. Written informed consent was provided by each participant in this study.
MCs contained in the semen samples were examined using an enzyme-linked immunosorbent assay (ELISA) kit (Beacon Analytical Systems, Inc.) as described in a previous study (Zheng et al. 2017). A...