Associations Between Exposure To Phenols At Environmental Levels And Male Reproductive Health

Over the past few decades,a decline in human semen quality has become a major public health problem that has attracted widespread attention worldwide.Studies have shown that environmental pollution caused by rapid industrialization and urbanization is an important risk factor for male reproductive health,and phenols are one of the common environmental pollutants.Toxicological and epidemiological studies have found that exposure to higher concentrations of phenols can cause reduced testosterone levels,impaired sperm formation and sperm DNA damage in experimental animals,as well as adverse effects such as reduced sperm motility,decreased total sperm count and reduced sperm concentration in men.Sperm mitochondrial DNA copy number and sperm telomere length are important genetic characteristics of sperm DNA,and any alterations can affect normal sperm function;and it has been reported that increased sperm mitochondrial DNA copy number are associated with decreased sperm motility,sperm concentration and total sperm count;and increased sperm telomere length can affect spermatogenesis.Humans are usually exposed to multiple phenols simultaneously in daily life,rather than individually.And previous studies generally focused on the relationship between a single class of phenols and male reproductive health.In addition,it is noted that previous studies generally measured urinary phenol levels and sperm quality parameters at a single time point,which could overlook the high within-individual variability.Another factor likely contributing to inconsistent results across studies is the relatively small sample size,which may be underpowered to generate precise risk estimates.Therefore,by employing repeated measurements in a group of healthy young men who volunteered as potential sperm donors at the Hubei Province Human Sperm Bank,the present study repeatedly collected urine and semen samples from individuals at baseline and the following 90 days.Concentrations of bisphenols,benzophenones and parabens in within-individual pooled urine were measured to reflect the average exposure during spermatogenesis,while semen quality parameters were examined and sperm DNA were extracted to measure sperm mitochondrial copy number and telomere length.Objectives: The present study aimed to explore the associations of urinary concentrations of bisphenols,benzophenones and parabens with semen quality parameters,sperm mitochondrial copy number and sperm telomere length in Parts 1,2 and 3,respectively,and the overall effect of mixed exposure to phenols on semen quality parameters,sperm mitochondrial copy number and sperm telomere length in Part 4.Methods: Between April 2017 and July 2018,1487 men were recruited,and after excluding 484 men due to illness or insufficient samples to complete laboratory determination,a total of 1003 men were ultimately included in this study,who provided5948 repeated semen samples.Urinay concentrations of phenols were determined by an ultra-performance liquid chromatography coupled with a triple quadrupole mass spectrometer.Semen analyses were performed according to the 5th World Health Organization laboratory manual.Real-time quantitative polymerase chain reaction was used to measure sperm mitochondrial DNA copy number and sperm telomere length.907 of 1003 participants completed sperm mitochondrial copy number and sperm telomere length determination.Urinary concentrations of bisphenols,benzophenones and parabens were divided into four groups according to their quartiles,and the lowest quartile group was used as the reference group.Mixed-effect models were used to examine the associations of urinary concentrations of bisphenols,benzophenones and parabens with semen quality parameters.General linear models were applied to explore the associations of urinary concentrations of bisphenols,benzophenones and parabens with sperm mitochondrial DNA copy number and sperm telomere length.We further applied restricted cubic spline(RCS)functions to explore potential non-linear dose-response relationships.Weighted quantile sum(WQS)regression,Bayesian kernel machine regression(BKMR)model and Quantile g-computation(QG-C)were used to evaluate the relationship between phenol mixture exposure and male reproductive health indicators.Results: In Part 1,the detection rates of bisphenol A(BPA),bisphenol F(BPF)and bisphenol S(BPS)were 96.41%,70.49%,and 98.40% in 1003 pooled urine,respectively.Their geometric mean(95%CI)of BPA,BPF,and BPS concentrations were 2.79(2.58,3.01),0.90(0.75,1.07)and 0.51(0.48,0.55)ng/m L,respectively.After adjusting for age,body mass index(BMI),abstinence period,urinary creatinine,number of pooled urine samples,education levels,smoking,drinking,monthly income,marital status,and semen sampling season in mixed-effect model,compared with men in the first quartile of BPA,those in the fourth quartile had a lower progressive sperm motility,total motility,and semen volume of 6.46%(95%CI:-12.01%,-0.56%),6.24%(95%CI:-11.35%,-0.83%)and 10.26%(95%CI:-16.83%,-3.15%),respectively;Compared with men in the lowest quartile of BPS,those in the highest quartile had a lower progressive sperm motility and total motility of 6.82%(95%CI:-12.24%,-1.07%)and 6.20%(95%CI:-11.22%,-0.89%),respectively.After adjusting for urinary creatinine and potential confounders in general linear model,compared with men in the first quartile of BPF,those in the fourth quartile had a higher sperm mitochondrial DNA copy number of 18.39%(95%CI: 2.86%,36.27%).The abovementioned associations were further confirmed in RCS.In Part 2,the detection rates of benzophenone-1(BP-1),benzophenone-4(BP-4),benzophenone-6(BP-6)and 4-hydroxy benzophenone(4-OH-BP)were 99.60%,89.03%,90.43% and 97.46%,respectively.Their geometric mean(95%CI)of BP-1,BP-4,BP-6and 4-OH-BP were 0.20(0.18,0.22),4.17(3.70,4.70),2.09(1.89,2.31)and 0.10(0.09,0.11)ng/m L,respectively.In mixed-effect model,compared with men in the first quartile of BP-6,those in the fourth quartile had a lower progressive sperm motility and total motility of 6.99%(95% CI:-12.68%,-0.93%)and 6.24%(95% CI:-11.52%,-0.64%),respectively.In general linear model,compared with men in the first quartile of BP-4 and4-OH-BP,those in the fourth quartile had a higher sperm telomere length of 10.31%(95%CI: 3.92%,17.08%)and 6.98%(95% CI: 0.62%,13.75%),respectively.In Part 3,the detection rates of methyl paraben(Me P),ethyl paraben(Et P)and propyl paraben(Pr P)were 100%,99.80% and 99.20%,respectively.Their geometric mean(95%CI)of Me P,Et P and Pr P were 13.26(12.05,14.58),1.21(1.08,1.35)and 0.86(0.75,0.99)ng/m L.In mixed-effect model,no significant associations between Me P,Et P and Pr P and semen quality parameters were found;We just found men in the fourth quartile of Me P had a lower progressive sperm motility and total motility of 5.33%(95%CI:-10.93%,0.61%;P=0.078)and 4.75%(95%CI:-9.93%,0.73%;P=0.088),compared to men in the first quartile.In general linear model,compared with men in the first quartile of Pr P,those in the highest quartile had a higher sperm mitochondrial DNA copy number of 15.12%(95%CI:-0.27%,32.88%;P=0.055).In Part 4,after adjusting for urinary creatinine and potential confounders in WQS regression model,one quartile increase in the WQS index was associated with a lower progressive sperm motility and total motility of 2.88%(95%CI:-5.77%,0.10%;P=0.058)and 2.65%(95%CI:-5.31%,0.09%;P=0.058),respectively;while BPS was the most heavily weighted chemicals(weights 0.34 and 0.32,respectively);and one quartile increase in the WQS index was associated with a higher sperm mitochondrial DNA copy number and sperm telomere length of 11.72%(95%CI:-1.20%,26.33%;P=0.078)and5.08%(95%CI: 0.75%,9.60%;P=0.021),respectively;while BPF and BP-4 were the most heavily weighted chemicals for sperm mitochondrial DNA copy number and sperm telomere length(weights 0.49 and 0.31,respectively).In the BKMR model,sperm mitochondrial copy number and sperm telomere length showed an increasing trend,while progressive sperm motility showed a decreasing trend when the phenol mixtures was at the 60 th percentile or above compared to their 50 th percentile.When all the other phenols were fixed at the median exposure level,BPF and Pr P showed a positive exposure-response relationship with sperm mitochondrial copy number,and BP-4 and4-OH-BP showed a positive exposure-response relationship with sperm telomere length.In QG-C,one quartile increase in phenol mixtures was associated with a lower progressive sperm motility and total motility of 3.94%(95%CI:-7.98%,0.28%;P=0.067)and 3.58%(95%CI:-7.19%,0.18%;P=0.062),respectively;and suggested that BPF and BP-4 were the main risk factors for sperm mitochondrial DNA copy number and sperm telomere length.Conclusion: The joint effect of phenol mixtures was associated with decreased progressive sperm motility and total motility,and increased sperm mitochondrial DNA copy number and sperm telomere length.BPS,BPF and BP-4 were identified as the most important risk factors with sperm motility,sperm mitochondrial DNA copy number and sperm telomere length,respectively.However,further studies are needed to confirm these results and explore the underlying biological mechanisms.