Reduction of sperm motility in a male laboratory worker exposed to solvents: a case study

Blood trihalomethane concentrations in relation to sperm mitochondrial DNA copy number and telomere length among 958 healthy men

BACKGROUND

In animal and human studies, exposure to trihalomethanes (THMs) has been associated with reduced semen quality. However, the underlying mechanisms remain poorly understood.

OBJECTIVE

To investigate the associations of blood THM concentrations with sperm mitochondrial DNA copy number (mtDNAcn) and telomere length (TL) among healthy men.

METHODS

We recruited 958 men who volunteered as potential sperm donors. A single blood sample was collected from each participant at recruitment and measured for chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM) concentrations. Within a 90-day follow-up, the last semen sample provided by each participant was quantified for sperm mtDNAcn and TL. We used multivariable linear regression models to assess the associations between blood THM concentrations and sperm mtDNAcn and TL. We also performed stratified analyses according to the time intervals between baseline blood THM determinations and semen collection (i.e., 0-9, 10-14, 15-69, or >69 days) to explore potential windows of susceptibility.

RESULTS

After adjusting for potential confounders, we found inverse associations between quartiles (or categories) of blood TBM, brominated THM (Br-THM, the sum of BDCM, DBCM, and TBM), and total THM (TTHM, the sum of all four THMs) concentrations and sperm mtDNAcn (all P for trend≤0.03). Besides, we found inverse associations between quartiles of blood TCM, Br-THM, chlorinated THM (Cl-THM, the sum of TCM, BDCM, and DBCM), and TTHM concentrations and sperm TL (all P for trend<0.10). Stratified analyses showed stronger associations between Br-THM concentrations and sperm mtDNAcn determined 15-69 days since baseline exposure determinations, and between blood TCM and TTHM concentrations and sperm TL determined >69 days since baseline exposure determinations.

CONCLUSION

Exposure to THMs may be associated with sperm mitochondrial and telomeric dysfunction.

Associations of blood trihalomethanes with semen quality among 1199 healthy Chinese men screened as potential sperm donors

BACKGROUND

Trihalomethanes (THMs) have demonstrated adverse effects on male reproductive systems in experimental animals, but human evidence has been inconsistent. Prior researches have been limited by small sample sizes and inadequate exposure assessment.

OBJECTIVES

To investigate the association between blood THMs and repeated measurements of semen quality parameters among 1199 healthy men screened as potential sperm donors.

METHODS

We recruited healthy men presenting to the Hubei Province Human Sperm Bank from April to December 2017. At study entry, each participant provided a spot blood sample which was used to quantify blood concentrations of four THMs: chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM) and bromoform (TBM). The summary measures of exposure for brominated THMs (Br-THMs; molar sum of BDCM, DBCM and TBM) and total THMs (TTHMs; molar sum of TCM and Br-THMs) were also calculated. We used multivariable linear regression models to estimate the cross-sectional associations of tertiles of blood THM concentrations with semen quality parameters measured at study entry, and mixed-effect models to estimate the longitudinal associations accounting for repeated measures of semen quality, adjusting for relevant confounding factors.

RESULTS

In the cross-sectional analysis, several inverse dose-response relationships were observed across tertiles of blood TCM concentrations and sperm count, total motility and progressive motility, and between blood DBCM, and Br-THMs, and TTHMs and sperm count and concentration. The inverse associations of blood TCM, DBCM, Br-THMs and TTHMs with sperm count were confirmed in the longitudinal, repeated measure analysis.

CONCLUSION

Our results suggest that exposure to THMs from drinking water may be related to decreased semen quality in young healthy men.

Effects of environmental contaminants on fertility and reproductive health

Recent research indicates that the human infertility rate is increasing. Although various reasons have been hypothesized for the growing infertility rate, environmental contaminants are potentially important causal agents associated with this change. Chemical contaminants are widespread throughout our environment and human exposure is virtually unavoidable. The overall contribution of environmental exposure to infertility is unknown, but studies involving occupational exposure, together with results from animal experiments, suggest that environmental contaminants may adversely affect fertility. We reviewed the adverse effects of environmental exposure on fertility and related reproductive outcomes. Environmental contaminants covered in this review include heavy metals, organic solvents, pesticides and endocrine disrupting chemicals. It is hoped that this review will highlight the need for further research in this area.

Impact of chloroform exposures on reproductive and developmental outcomes: A systematic review of the scientific literature

AIMS

We assessed the animal and epidemiological data to determine if chloroform exposure causes developmental and/or reproductive toxicity.

RESULTS AND DISCUSSION

Initial scoping identified developmental toxicity as the primary area of concern. At levels producing maternal toxicity in rats and mice, chloroform caused decrements in fetal weights and associated delays in ossification. In a single mouse inhalation study, exposure to a high concentration of chloroform was associated with small fetuses and increased cleft palate. However, oral exposure of mice to chloroform at a dose 4 times higher was negative for cleft palate; multiple inhalation studies in rats were also negative. Epidemiologic data on low birth weight and small for gestational age were generally equivocal, preventing conclusions from being drawn for humans. The animal data also show evidence of very early (peri-implantation) total litter losses at very high exposure levels. This effect is likely maternally mediated rather than a direct effect on the offspring. Finally, the epidemiologic data indicate a possible association of higher chloroform exposure with lower risk of preterm birth (<37 weeks gestation).

CONCLUSIONS

The available animal data suggest that exposures lower than those causing maternal toxicity should be without developmental effects in the offspring. Also, most studies in humans rely on group-level geographic exposure data, providing only weak epidemiologic evidence for an association with development outcomes and fail to establish a causal role for chloroform in the induction of adverse developmental outcomes at environmentally relevant concentrations.

In vitro effects of zinc, D-aspartic acid, and coenzyme-Q10 on sperm function

Reactive oxygen species favor reproductive processes at low concentrations, but damage spermatozoa and decrease their fertilizing capacity at high concentrations. During infection and/or inflammation of the accessory sex glands reactive oxygen species overproduction may occur which, in turn, may negatively impact on sperm motility, sperm DNA fragmentation, and lipid peroxidation. A number of nutraceutical formulations containing antioxidant molecules have been developed to counteract the deleterious effects of the oxidative stress. A recent formulation containing zinc, D-aspartic acid, and coenzyme-Q10 is present in the pharmaceutical market. Based on these premises, the aim of the present study was to evaluate the effects of this combination on spermatozoa in vitro. The study was conducted on 24 men (32.2 ± 5.5 years): 12 normozoospermic men and 12 asthenozoospermic patients. Spermatozoa from each sample were divided into two control aliquots (aliquot A and B) and an aliquot incubated with zinc, D-aspartic acid, and coenzyme-Q10 (aliquot C). After 3 h of incubation, the following parameters were evaluated: progressive motility, number of spermatozoa with progressive motility recovered after swim-up, lipid peroxidation, and DNA fragmentation. Incubation with zinc, D-aspartic acid, and coenzyme-Q10 maintained sperm motility in normozoospermic men (37.7 ± 1.2 % vs. 35.8 ± 2.3 % at time zero) and improved it significantly in asthenozoospermic patients (26.5 ± 1.9 % vs. 18.8 ± 2.0 % at time zero) (p < 0.01). This resulted in a significantly higher (p < 0.01) number of spermatozoa with progressive motility recovered after swim-up in both normozospermic men (4.1 ± 0.9 vs. 3.3 ± 1.0 millions) and asthenozooseprmic patients (3.2 ± 0.8 vs. 1.6 ± 0.5 millions). Finally, a statistically significant lower sperm lipid peroxidation was found after incubation with zinc, D-aspartic acid, and coenzyme-Q10 (p < 0.05) in both normozospermic men (1.0 ± 0.4 % vs. 2.4 ± 0.9 %) and asthenozooseprmic patients (0.2 ± 0.1 % vs. 0.6 ± 0.2 %). No statistically significant effect was observed on sperm DNA fragmentation. This nutraceutical formulation may be indicated in vitro during the separation of the spermatozoa in the assisted reproduction techniques, during which the spermatozoa undergo an increased oxidative stress.

Parenteral paradichlorobenzene exposure reduces sperm production, alters sperm morphology and exhibits an androgenic effect in rats and mice

Rats and mice (8 animals per species per group) were injected subcutaneously or intraperitoneally with paradichlorobenzene (PDCB) at doses of 0, 100, 200 and 400 mg/kg/day, 4-5 days a week, for 8 weeks (for rats) and either 2 or 6 weeks (for mice). Prostate and seminal vesicle weights were significantly increased in PDCB-treated rats but not in mice. Major histopathologic injuries were not found in testis and epididymis of both species. Daily sperm production was depressed in both species in a dose-response manner. Serum testosterone levels were not significantly changed in both species. Sperm morphology was evaluated in rats intraperitoneally administered PDCB at a dose of 800 mg/kg. Abnormal sperms with reduced hook, bent neck, coiled flagellum, bent flagellum and bent flagellum tip were significantly increased in treated rats. In Hershberger assay, PDCB administration increased weights of ventral prostate gland, seminal vesicle, levator ani/bulbocavernosus muscle and glans penis in castrated rats, and also weights of ventral prostate gland and glans penis in castrated mice. PDCB and 2,5-dichlorophenol (the major metabolite) did not bind androgen receptor (AR) up to 10 mM. In conclusion, PDCB affects sperm production and morphology but is somewhat androgenic independently from AR binding in rats and mice.

Impact of exposure to endocrine disrupters in utero and in childhood on adult reproduction

Recent reports have demonstrated a decline in human male reproductive health: high and probably increasing prevalence of cryptorchidism and hypospadias, low and probably decreasing semen quality, a rising incidence of testicular cancer and a growing demand for assisted reproduction. These changes seem to be interrelated and may be symptoms of a common underlying entity, the testicular dysgenesis syndrome, with foundations in fetal life due to adverse environmental influences. Wildlife experience and animal studies have provided evidence that fetal or perinatal exposure to endocrine disrupters results in disturbed sexual differentiation and urogenital malformations followed by decreased reproductive health in adult life. This chapter reviews existing evidence for a connection between (i) exposure to endocrine disrupters in fetal life and childhood and (ii) adult reproductive health in humans. This topic is not only relevant to basic scientists but also to clinical endocrinologists, who should also be encouraged to participate in research concerning this problem.