Associations Between Environmental Levels Of Exposure To Polycyclic Aromatic Hydrocarbons And Male Reproductive Health

In recent years,the effect of environmental pollutants on male reproductive health has been raised concern by an increasing number of studies.Some studies have shown a global decline of human sperm quality during the past decades.Environmental pollution has been considered to be one of the major causes of declined semen quality.Polycyclic aromatic hydrocarbons(PAHs)are one of the ubiquitous classes of environmental pollutants that are mainly produced by incomplete combustion of organic substances.PAHs in environment derived from artificial and natural sources.The general people can be exposed to PAHs through multiple routes such as ingestion,inhalation,and dermal absorption.Toxicology studies have shown that PAHs and their metabolites can cause testicular toxicity,reduce sperm quality,and damage sperm DNA.However,epidemiological evidence on the association between PAH exposure and male reproductive health is limited and inconsistent.Furthermore,the potential molecular mechanism involved in decresed semen quality after exposure to PAHs remains unclear.In this study,we conducted a hospital-based cross-sectional study to examine the relationship between environmental levels of exposure to PAHs and male reproductive health in a Chinese population.We measured 10 PAH metabolites in urine as biomarkers of environmental exposure to PAHs,and examined the associations between urinary PAH metabolites and semen quality parameters(traditional semen quality parameters and sperm motion parameters).Moreover,we measured sperm DNA damage,sperm apoptosis parameters,and reproductive hormones as sensitive makers of male reproductive health,and examined the associations of urinary PAH metabolites with sperm function and reproductive hormones.Further,we analysed the expressions of 3 candidate spermatogenesis-related miRNAs in seminal plasma,and examined the associations of these miRNAs with urinary PAH metabolites and semen quality.Also,we explored the mediating role of seminal plasma miRNAs in the associations between urinary PAH metabolites and semen quality.Our results contributed to the evidence and potential molecular mechanism for adverse reproductive health exerted by exposure to environmental PAHs in male populationPart One Urinary PAH Metabolites and Semen Quality?Objectives?Our goal was to investigate the relationships between environmental levels of exposure to PAHs and semen quality.?Methods?We recruited 933 men who sought for semen quality analysis in an infertility clinic in Wuhan,China.We analyzed 10 urinary PAH metabolites by gas chromatography-mass spectrometry(GC/MS).The semen quality parameters were analysed by the World Health Organization guidelines(WHO,2010).Associations with semen quality were assessed using a multivariable linear regression.Restricted cubic splines were used to further explore the dose-response relationships between urinary PAH metabolites and semen quality.?Results?We observed inverse associations between urinary 1-hydroxynaphthalene(1-OHNa)and sperm count,sperm concentration,and percentage of normal morphology(All P for trends<0.05),as well as between urinary?OHNa(Sum of 1-OHNa and 2-OHNa)and sperm concentration(P for trend=0.04).Additionally,we found inverse associations between urinary 9-hydroxyphenanthrene(9-OHPh)and semen volume and sperm straight-line velocity(Both P for trends<0.05),as well as between urinary?OHPh(Sum of 1-,2-,3-,4-,and 9-OHPh)and sperm count(P for trend=0.04).These dose-response relationships were further confirmed in the curves of the restricted cubic splines.?Conclusions?Our results suggest that exposure to environmental naphthalene and phenanthrene is associated with decreased semen quality.Part Two Urinary PAH Metabolites,Sperm DNA Damage,Spermatozoa Apoptosis,and Reproductive Hormones?Objectives?Our goal was to assess the assocaitions of environmental levels of exposure to PAHs with sperm function and reproductive hormones.?Methods?We used the comet assay,Annexin V/PI assay,and direct chemiluminescence assay for analysis of sperm DNA damage,spermatozoa apoptosis,and serum reproductive hormones,respectively.The multivariable linear models were used to estimate the associations of urinary PAH metabolites with sperm DNA damage,spermatozoa apoptosis,and reproductive hormones.The dose-response relationships of exposure measurements with outcomes were further evaluated by restricted cubic splines.?Results?We found that urinary 9-hydroxyfluorene(9-OHFlu)was associated with increased tail length and comet length(Both P for trends<0.05),and that urinary 9-OHPh and urinary?OHFlu were associated with increased comet length(Both P for trends<0.05).We also found that urinary 9-OHFlu and 9-OHPh with decreased percentage of Annexin V~-/PI~-spermatozoa were observed(All P for trends<0.05);and that urinary 2-OHPh with decreased percentage of Annexin V~-/PI~-spermatozoa and increased percentage of Annexin PI~+spermatozoa were observed(All P for trends<0.05).In addition,we found that urinary 2-OHNa was associated with decreased serum free testosterone,and that 9-OHFlu,9-OHPh,and 1-OHP were associated with decreased serum estradiol(All P for trends<0.05).Further,these dose-dependent associations were confirmed in restricted cubic splines.Moreover,a U-shaped association was observed across urinary 4-OHPh levels,with lower levels of serum sex hormone-binding globulin(SHBG)at median concentrations compared with 5th and95th percentile concentrations.?Conclusions?Our results suggest that environmental exposure to fluorene and phenanthrene are associated with declined sperm function and altered reproductive hormones.Part Three Urinary PAH Metabolites,Seminal Plasma microRNAs,and Semen Quality?Objectives?Our goal was to evaluate the mediating role of spermatogenesis-related miRNAs in seminal plasma in the associations between urinary PAH metabolites and semen quality.?Methods?We detected 3 candidate spermatogenesis-related miRNAs(miRNA21?miRNA34c,and miRNA106a)in seminal plasma by real-time quantitative PCR.Multivariable linear regression model was used to test the associations of seminal plasma miRNAs with urinary PAH metabolites and semen quality.We further performed a mediation analysis to test the mediating role of seminal plasma miRNAs in the assocaitions between urinary PAH metabolites and semen quality.?Results?Compared to those in the low levels of urinary 2-OHFlu and 2-OHPh,men in the high levels of urinary 2-OHFlu and 2-OHPh had mean decrease of 1.49%(95%CI:-2.97%,-0.01%)and 1.60%(95%CI:-3.08%,-0.11%)in seminal plasma miRNA34c.In comparison to those in the low levels of urinary 9-OHPh,men in the high levels of urinary 9-OHPh had mean decrease of 1.08%(95%CI:-2.02%,-0.14%)in seminal plasma miR106a.We also found that seminal plasma miR106a was associated with decreased sperm concentration,serpm count,sperm total motility,and progressive sperm motility(All P for trends<0.05).Further,we found that seminal plasma miR106a mediated 43.8%(?=-8.55%;95%CI:-16.15%,-0.26%)of estimated effect in the association between urinary 9-OHPh and decreased sperm concentration.?Conclusions?Our results suggest that altered seminal plasma miRNAs is associated with environmental exposure to PAHs,and that the changes in miR106a expression may play a mediating role in the assocaitions between environmental exposure to phenanthrene and decreased semen quality.