Semen quality of men employed at a lead smelter

Lead toxicity and potential therapeutic effect of plant-derived polyphenols

BACKGROUND

Due to its unique physical and chemical properties, lead is still used worldwide in several applications, especially in industry. Both environmental and industrial lead exposures remain a public health problem in many developing and rapidly industrializing countries. Plant polyphenols are pleiotropic in their function and have historically made a major contribution to pharmacotherapy.

PURPOSE

To summarize available pre-clinical and limited clinical evidence on plant polyphenols as potential antidotes against lead poisoning and discuss toxic mechanisms of lead.

METHOD

A comprehensive search of peer-reviewed publications was performed from core collections of electronic databases such as PubMed, Web of Science, Google Scholar, and Science Direct. Articles written in English-language from inception until December 2022 were selected.

RESULTS

In this review, we review key toxic mechanisms of lead and its pathological effects on the neurological, reproductive, renal, cardiovascular, hematological, and hepatic systems. We focus on plant polyphenols against lead toxicity and involved mechanisms. Finally, we address scientific gaps and challenges associated with translating these promising preclinical discoveries into effective clinical therapies.

CONCLUSION

While preclinical evidence suggests that plant polyphenols exhibit bioprotective effects against lead toxicity, scant and equivocal clinical data highlight a need for clinical trials with those polyphenols.

Association of peripubertal blood lead levels with reproductive hormones and semen parameters in a longitudinal cohort of Russian men

STUDY QUESTION

Are peripubertal blood lead levels (BLLs) associated with semen parameters and serum reproductive hormones among young Russian men?

SUMMARY ANSWER

We observed a suggestion of lower ejaculate volume with higher peripubertal BLL but no associations of BLLs with reproductive hormones measured throughout adolescence or with other sperm parameters measured at adulthood.

WHAT IS KNOWN ALREADY

Lead is a known reproductive toxicant and endocrine disruptor. Previous literature has shown associations between high lead exposure and poorer semen quality both in occupationally and environmentally exposed men. However, to our knowledge, no longitudinal studies have explored the association of childhood lead exposure with semen parameters and reproductive hormones in young men.

STUDY DESIGN, SIZE, DURATION

The Russian Children's Study is a prospective cohort study that enrolled 516 boys at age 8-9 years in 2003-2005 and followed them annually for 10 years. BLLs were measured at entry and lifestyle and health questionnaires were completed. Reproductive hormones were measured in blood samples collected every 2 years.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Among the 516 boys enrolled, 481 had BLLs measured at entry. Of these, 453 had at least one measurement of serum testosterone, follicle stimulating hormone (FSH) or luteinizing hormone (LH) (median = 5 samples per boy) and 223 had semen samples collected ∼10 years after enrolment. Semen assessment included ejaculated volume, sperm concentration, progressive motility and total sperm count, and parameters were categorized using published andrology standards for low semen quality based on sperm count and motility. Linear mixed models were used to examine the associations of log-transformed BLLs (and BLL categories) with reproductive hormones and semen parameters, adjusting for potential confounders.

MAIN RESULTS AND THE ROLE OF CHANCE

Among the 223 young men with peripubertal BLLs and at least one semen sample (total samples = 438), the median (interquartile range) BLL was 3 (2, 5) µg/dl and 27% had BLL ≥5 µg/dl. Overall, 49% of the semen samples fell below reference levels for sperm count and/or motility. Men with peripubertal BLL ≥5 µg/dl had significantly lower ejaculated volume than those with BLL <5 µg/dl (mean = 2.42 vs 2.89 ml, P = 0.02), but this difference was attenuated in adjusted models (mean = 2.60 vs 2.83 ml, P = 0.25). No associations were observed between BLL measured at age 8-9 years and reproductive hormone levels or sperm parameters, including sperm concentration, total count, progressive motility and total progressive motile sperm count, or with the probability of having low semen quality based on sperm count/motility.

LIMITATIONS, REASONS FOR CAUTION

Only a subset of the original cohort participated in the semen quality portion of the study, although inverse probability weighting was used to account for possible selection bias. BLLs were only measured at a single time in peripuberty, and other exposure time periods, including later or longer-term childhood exposure, may be more predictive of semen quality. The young men were also exposed to other chemical contaminants before and during pubertal development.

WIDER IMPLICATIONS OF THE FINDINGS

While semen volume often receives less attention than other sperm parameters, it is an important component of male fertility. Additional prospective studies covering different exposure windows and including other seminal plasma biomarkers are warranted to explore our finding of potentially lower ejaculated volume with higher BLLs and to confirm the lack of associations for other semen parameters among youth exposed to environmental BLLs.

STUDY FUNDING/COMPETING INTEREST(S)

Funding was provided through grants R01ES0014370 and P30ES000002 from the National Institute of Environmental Health Sciences, grant R82943701 from the U.S. Environmental Protection Agency, and grant 18-15-00202 from the Russian Science Foundation (O.S and Y.D.). All authors report no competing interests.

TRIAL REGISTRATION NUMBER

N/A.

Metal(loid)s and human semen quality: The LIFE Study

Multiple studies have demonstrated a global population-wide decline in semen quality, with sperm concentrations having fallen 50 % over the past 50 years. Several metal and metalloid ("metal(loid)") compounds are known to have testicular toxicity, raising concerns about their contribution to rising infertility. In the male reproductive tract, metal(loid)s can reduce semen quality and disturb function both directly, by inducing tissue damage, and indirectly, by disrupting hormone production and secretion. This study assessed associations between 15 creatinine-adjusted metal(loid)s and 7 measures of semen quality among 413 reproductive-aged men recruited from 16 U.S. counties between 2005-2009. Multi-metal(loid) multivariable linear regression models estimated associations between semen quality endpoints and urinary concentrations of chromium, cobalt, copper, molybdenum, selenium, zinc, antimony, arsenic, barium, cadmium, lead, thallium, tin, tungsten, and uranium. LASSO regression was employed to select model variables and account for multicollinearity of the metal(loid)s. A positive association was observed between tin and sperm morphology (β = 4.92 p = 0.045). Chromium (β = 1.87, p = 0.003) and copper (β= -1.30, p = 0.028) were positively and negatively associated with total sperm count, respectively. With respect to DNA fragmentation, cadmium (β = 12.73, p = 0.036) was positively associated and chromium was negatively associated (β = -5.08, p = 0.001). In this cohort of U.S. population-based men, there was evidence of both positive and negative associations between specific metal(loid)s and semen quality. Additional research is needed to determine interactions between metal(loid)s within a mixture, consistent with typical human exposure, and identify sperm effects resulting from cumulative metal(loid) exposures.

Antioxidant, anti-inflammatory and anti-apoptotic effects of hydro-ethanolic extract of Cyperus esculentus L. (tigernut) on lead acetate-induced testicular dysfunction in Wistar rats

AIM

Lead acetate impairs testicular function by enhancing testicular oxidative stress and apoptosis. Cyperus esculentus possesses antioxidants and has shown great improvement of testicular function. This study investigated the protective effect of hydro-ethanolic extract of Cyperus esculentus on lead acetate-induced testicular dysfunction in Wistar rats.

MATERIALS AND METHODS

Twenty-five male Wistar rats (180-195 g) were randomly divided into 5 groups (n = 5) namely: Normal control (NC), Lead control (PbC) (20 mg/kg b.w. i.p.), C. esculentus-treated (CE) (500 mg/kg b.w p.o.), Pb + CE(500) (20 mg/kg of lead and 500 mg/kg of extract) and Pb + CE(1000) (20 mg/kg of lead and 1000 mg/kg of extract). Administration lasted for 21 days.

RESULTS

Sperm count, motility, viability, serum testosterone and follicle stimulating hormone, Johnsen's score, Leydig cell count, Sertoli cell count, testicular testosterone, B-cell lymphoma protein-2 (Bcl-2), steroidogenic acute regulatory protein, cytochrome P450 A1, 3β-hydroxysteroid dehydrogenase (HSD), 17β-HSD, enzymatic antioxidant activities and total antioxidant capacity were significantly (p < 0.05) decreased in PbC compared with NC. These parameters however increased significantly (p < 0.05) in Pb + CE(500) and Pb + CE(1000) compared with PbC. Lead acetate upregulated (p < 0.05) testicular malondialdehyde, nitric oxide, glucose, lactate, lactate dehydrogenase, C-reactive protein, tumor necrosis factor-α, interleukin (IL)-6, IL-1β, Bcl-2 associated X (Bax), Bax/Bcl-2 and cleaved caspase-3 levels. All these parameters were downregulated (p < 0.05) in Pb + CE(500) and Pb + CE(1000) in comparison with PbC.

CONCLUSION

C. esculentus exhibited a dose-dependent mitigation of lead acetate-induced testicular dysfunction in Wistar rats via its antioxidant, anti-inflammatory and anti-apoptotic effects.

The Impact of the Flint Water Crisis on Fertility

Flint switched its public water source in April 2014, increasing exposure to lead and other contaminants. We compare the change in the fertility rate and in health at birth in Flint before and after the water switch to the changes in other cities in Michigan. We find that Flint fertility rates decreased by 12 % and that overall health at birth decreased. This effect on health at birth is a function of two countervailing mechanisms: (1) negative selection of less healthy embryos and fetuses not surviving (raising the average health of survivors), and (2) those who survived being scarred (decreasing average health). We untangle this to find a net of selection scarring effect of 5.4 % decrease in birth weight. Because of long-term effects of in utero exposure, these effects are likely lower bounds on the overall effects of this exposure.

The effects of Pb on sperm parameters and sperm DNA fragmentation of men investigated for infertility

Background Lead (Pb) is one of the metals most prevalent in the environment and is known to cause infertility and deoxyribonucleic acid (DNA) fragmentation. This study aimed to determine the association between seminal plasma Pb and sperm DNA fragmentation in men investigated for infertility. Methods Male partners (n = 300) of couples investigated for infertility were recruited after informed consent was obtained. Sperm parameters were assessed according to the World Health Organization (WHO) guidelines. Seminal plasma Pb was estimated by atomic absorption spectrophotometry after digestion with nitric acid. Results In Pb-positive and -negative groups the sperm parameters and sperm DNA fragmentation were compared using independent sample t-test and the Mann-Whitney U-test, respectively. The mean [standard deviation (SD)] age and duration of infertility were 34.8 (5.34) years and 45.7 (35.09) months, respectively, and the mean Pb concentration was 15.7 μg/dL. In Pb positives compared to Pb negatives the means (SD) of sperm count, progressive motility viability and normal morphology were lower (p > 0.05) but the DNA fragmentation was significantly higher 39.80% (25.08) than Pb negatives 22.65% (11.30). Seminal plasma Pb concentration and sperm DNA fragmentation had a positive correlation (r = 0.38, p = 0.03). A negative correlation was observed between sperm DNA fragmentation and sperm concentration, progressive motility, total motility and viability. When the DNA fragmentation was ≥30% sperm concentration and viability decreased (p < 0.05). Conclusions Pb in seminal plasma had a significant effect on sperm DNA fragmentation but not with other sperm parameters.

Low-level lead exposure is associated with aberrant sperm quality and reproductive hormone levels in Chinese male individuals: Results from the MARHCS study low-level lead exposure is associated with aberrant sperm quality

Studies in animals suggest an adverse effect of high-level lead exposure on male reproductive outcomes. However, evidence of the effects of low-level lead exposure is inconsistent. The purpose of our study was to explore the relationship between low-level lead exposure from daily environmental contaminants and semen quality in a community population without occupational exposure. We recruited 751 students in the Male Reproductive Health in Chongqing College Students (MARHCS) study and 190 community males from Bishan, Chongqing. Eight urinary metals (Pb, Cd, As, Cu, Zn, Ni, Mn, and Cr), semen quality, and serum sex hormones were detected. Even if the blood lead concentration was below the US lead poisoning standard for children (100 μg/L), a significant dose-response relationship was found between lead exposure and a decrease in semen quality. Multilinear regression showed that urinary Pb was negatively associated with sperm concentration, total sperm count, progressive motility and total sperm motility (regression coefficient: -0.074, -0.103, -0.024, and -0.014, respectively; p: <0.001, <0.001, 0.007, and <0.001, respectively), accompanied by decreased serum follicle-stimulating hormone, serum testosterone and the testosterone/luteinizing hormone ratio (β coefficient: -0.090, -0.082, and -0.020, respectively; p: 0.002, <0.001, and 0.021, respectively). Logistic regression also indicated that the risk of having abnormal semen quality was higher in the high Pb group (OR: 2.501, 95% CI: 1.411, 4.435, p = 0.002) than in the low Pb group after adjusting for confounders, with a dose-response relationship in the trend test (p = 0.007). Our results revealed an inverse association between Pb exposure at low levels and semen quality.

The effects of exposure to lead, cadmium and mercury on follicle-stimulating hormone levels in men and postmenopausal women: data from the Second Korean National Environmental Health Survey (2012-2014)

Background

Follicle-stimulating hormone (FSH), a gonadotropin secreted by the pituitary gland, is a representative secondary sex hormone and an important indicator of reproductive function. The effects of heavy metals such as lead, cadmium, and mercury on humans have been studied, but reports on their effects on sex hormone levels are lacking. Therefore, we investigated the relationship between heavy metal exposure and FSH levels in Korean men and postmenopausal women.

Methods

A total of 4,689 adults (2,763 men and 1,926 postmenopausal women aged 50 years or over) who participated in the Second Korean National Environmental Health Survey (2012–2014) were included. We compared differences in serum FSH levels by demographic characteristics using the t-test and analysis of variance. Multiple linear regression analysis was used to determine the relationship between the blood levels of lead and mercury and the urine cadmium level, and serum FSH levels.

Results

On multiple linear regression analysis, lead exposure was positively associated with serum FSH concentrations in postmenopausal women (β = 2.929, p = 0.019). However, we found no significant association between serum FSH concentration and blood lead and mercury levels, or urine cadmium level, in men.

Conclusions

This study suggests that lead exposure can affect the FSH level in postmenopausal women. Further studies are needed to evaluate the effects of low-dose long-term exposure to heavy metals on sex hormones.

Genomic instability in adult men involved in processing electronic waste in Northern China

BACKGROUND

Managing and recycling electronic waste (e-waste), while useful and necessary, has resulted in significant contamination of several environments in China. The area around Tianjin, China has become one of the world's largest e-waste disposal centers, where electronics are processed by manually disassembly or burning, which can result in serious exposure of workers to a multitude of toxicants.

OBJECTIVE

The present study assessed potential genomic damage in workers involved in recycling e-waste.

METHODS

To detect cytogenetic and DNA damage, chromosomal aberrations (CA), cytokinesis blocking micronucleus (CBMN) and the comet assay were performed. Concentrations of some trace elements, markers of oxidative stress and polychlorinated biphenyls (PCBs) in whole blood or serum were measured, and relationships among the markers described above, age, and duration of exposure were analyzed. The profiles of expression of genes in lymphocytes in peripheral blood were assessed to determine the status of the regulation of genes involved in genome stability.

RESULTS

Concentrations of 28 PCB congeners in the whole blood of the exposed group were significantly (P<0.001) greater than those in the control individuals. Frequency of CA (8.01%) and CBMN (26.3‰) in lymphocytes and the level of DNA damage in the lymphocytes and spermatozoa of the exposed men were also significantly (P<0.0001) greater than those of the controls. There were significant relationships between CA, CBMN, DNA damage and duration of exposure. Concentrations of malondialdehyde (MDA) and lead (Pb) in the blood serum were significantly greater, but activities of superoxide dismutase (SOD), glutathione (GSH) and concentrations of calcium (Ca) and magnesium (Mg) were lower in the serum of the exposed men. MDA, Pb, Ca and Mg were associated with the duration of exposure to handling e-waste. In males involved in handling of e-waste, there were 13 genes - ATM, ATR, ABL1, CHEK1, CHEK2, GADD45A, CDK7, GTSE1, OGG1, DDB1, PRKDC, XRCC1 and CCNH - for which expression of mRNA was up-regulated and 7 genes - BRCA1, GTF2H1, SEMA4A, MRE11A, MUTYH, PNKP and RAD50 - for which the expression of mRNA was down-regulated.

CONCLUSIONS

A strong correlation between indicators of damage of DNA, which could result in instability of the genome, and duration of processing e-waste was observed. If proper procedures are not followed, there are significant risks to the health of the individuals involved in such activities.

Lead exposure reduces sperm quality and DNA integrity in mice

Toxicity of lead on male reproductive functions has raised wide public concern as environmental lead contamination remains common worldwide. Conflicting and controversial data are available regarding effects of lead on male fertility. More importantly, our knowledge on effects of lead on sperm DNA integrity is significantly limited. Thus, further studies should focus on this issue. In the current study, adult male mice were exposed to a series of lead acetate concentrations in drinking water for six weeks. Following administration, lead levels in blood, testicles, and epididymis were measured, and potential changes in morphology of testis and epididymis due to lead exposure were identified. We also analyzed sperm parameters, including sperm density, viability, motility, and morphology, to evaluate quality of sperm collected from epididymis. Especially, hypothetical influence of lead on sperm DNA integrity was also evaluated by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling, alkaline comet assay, and sperm chromatin structure assay. Lead exposure possibly exerted no effect on growth of mice because these animals acquired similar body weight gain during the experimental period. However, high lead concentrations (0.5% and 1%) in drinking water affected sperm motility and increased percentage of spermatozoa with abnormal morphology. In groups treated with 0.25%, 0.5%, and 1% lead acetate, percentages of sperm cells showing DNA breaks and chromatin structure damage significantly increased. Altogether, lead exposure not only exhibits adverse effects on sperm physiological parameters, but also impairs DNA structure and integrity. These effects may lead to significant decline in male fertility.

Human health risk assessment of lead, manganese and copper from scrapped car paint dust from automobile workshops in Nigeria

The economic downturn in Nigeria and Structural Adjustment Programme led to the flooding of Nigerian market with imported used automobiles. Most of these vehicles needed refurbishing and reworking. The present study is a human health risk assessment of metal exposure resulting from reworking of imported used vehicles in Nigeria. Scrap paint dusts from 56 Japanese made cars were collected from 8 different mechanic villages (workshops A-H] in Southeastern Nigeria. Scrap paints were homogenized, mixed, divided into fine particles and digested by standard method. The filtrates were assayed of lead, manganese and copper with atomic absorption spectrophotometry (AAS). Workshop B has the highest concentration of Pb (4.26 ± 0.93). Manganese in workshops A and F were (3.31 ± 0.85) and (3.04 ± 0.47) respectively and were higher than the levels from workshops C, B, D, G and H. Copper in workshop D (7.11 ± 0.21) was significantly greater than the other workshops. The highest hazard quotient (HQ) through ingestion, inhalation and dermal exposures in adults were 9.44E-05 (workshop B), 4.20E-01 (workshop B) and 1.08E-05 (workshop D) respectively. The highest values for HQ through ingestion, inhalation and dermal in children were 8.82E-04, 7.61E-01 and 2.86E-05 all in workshop B respectively. For children, the highest carcinogenic risk levels were 7.05E-08, 6.09E-05 and 2.29E-10 for ingestion, inhalation and dermal exposures respectively. In adults, the carcinogenic risk levels were 7.55E-09, 3.39E-05 and 8.67E-10 for ingestion, inhalation and dermal exposures respectively. Chronic exposure to scrap car paint dusts may be of significant public health importance in Nigeria as this may add to the body burden of some heavy metals.

Can Half-Day Trainings Motivate Small Contractors to Address Lead Safety?

There is a real need to educate small painting and remodeling contractors about lead-safe work practices to protect the health of occupants (especially small children) and employees. From 1996 to 2000, 34 half-day lead awareness trainings were held throughout California to increase contractors’ use of lead-safe practices. Educational methods included focusing on best practices, utilizing a peer educator, and working with stakeholders to do outreach to this hard-to-reach audience. We report on the evaluation of 18 of these seminars where we found that 30% to 49% of the interviewed contractors began doing many of the lead-safe work practices after attendance. We conclude that this program can have a modest impact in areas that contractors are more familiar with; new areas not part of their experience do not fare as well. However, without a more integrated public health educational and enforcement strategy, educational efforts such as ours can have only a limited impact.

Biomonitoring of blood heavy metals and reproductive hormone level related to low semen quality

Reproductive hormones and exposure to environmental metals are correlated with low-quality semen. The aim of this study was to evaluate the levels of heavy metals and reproductive hormones in the blood in addition to other relevant factors to clarify the relationship between these factors and semen quality. We recruited 154 male participants from a reproductive medical center. All participants were provided with a questionnaire on lifestyle implementation. The levels of metals in the blood were determined using inductively coupled plasma-mass spectrometry. The levels of hormones in the blood were determined using an automatic gamma counter. Multiple logistic regression analyses were conducted to predict the effects of statistically significant risk factors on semen quality by adjusting for relevant confounders and modifiers. After adjusting for the age, education level, and related factors in the multiple logistic regression analyses, we observed that the increased blood Pb levels were significantly and positively associated with low semen quality. High blood Pb levels (>50 μg/L) had an 11-fold risk of low semen quality. Our results suggest that progressive motility sperm may be a sensitive indicator of the semen quality among all the semen parameters in Taiwan.

Human health risk assessment related to contaminated land: state of the art

Exposure of humans to contaminants from contaminated land may result in many types of health damage ranging from relatively innocent symptoms such as skin eruption or nausea, on up to cancer or even death. Human health protection is generally considered as a major protection target. State-of-the-art possibilities and limitations of human health risk assessment tools are described in this paper. Human health risk assessment includes two different activities, i.e. the exposure assessment and the hazard assessment. The combination of these is called the risk characterization, which results in an appraisal of the contaminated land. Exposure assessment covers a smart combination of calculations, using exposure models, and measurements in contact media and body liquids and tissue (biomonitoring). Regarding the time frame represented by exposure estimates, biomonitoring generally relates to exposure history, measurements in contact media to actual exposures, while exposure calculations enable a focus on exposure in future situations. The hazard assessment, which is different for contaminants with or without a threshold for effects, results in a critical exposure value. Good human health risk assessment practice accounts for tiered approaches and multiple lines of evidence. Specific attention is given here to phenomena such as the time factor in human health risk assessment, suitability for the local situation, background exposure, combined exposure and harmonization of human health risk assessment tools.

Biomarkers of exposure to molybdenum and other metals in relation to testosterone among men from the United States National Health and Nutrition Examination Survey 2011-2012

OBJECTIVE

To examine the potential associations between biomarkers of metal exposure and serum testosterone in men of reproductive age in the general US population.

DESIGN

Cross-sectional epidemiology study with adjustment for potential confounders.

SETTING

Not applicable.

PATIENT(S)

Men recruited in the United States National Health and Nutrition Examination Survey (NHANES).

INTERVENTION(S)

Metal concentrations measured in whole blood, urine, and/or serum samples collected from 484 men.

MAIN OUTCOME MEASURE(S)

Serum T concentration.

RESULT(S)

Concentrations of the metals were detected in 69%-100% of the samples. In adjusted analyses where metals were modeled as a continuous variable, we found significant inverse associations between urinary molybdenum and serum copper and serum T, whereas there were significant positive associations between blood lead and cadmium and serum T. When metals were categorized into quartiles, analyses for serum copper and blood lead and cadmium produced significant associations in the same direction as the continuous measures. A suggestive inverse association was observed between quartiles of urinary molybdenum and serum T, but the association was statistically significant when molybdenum was categorized into quintiles. Significant positive associations were also observed for quartiles of blood Se and serum Zn and serum T.

CONCLUSION(S)

These findings add to the limited human evidence that exposure to molybdenum and other metals is associated with altered T in men, which may have important implications for male health. More research is needed to confirm the findings of our study.

Occupation exposures and sperm morphology: a case-referent analysis of a multi-centre study

OBJECTIVE

We examined occupational exposures and sperm morphology to establish whether exposures implicated differed from those affecting motile sperm concentration.

METHODS

Computer aided sperm morphometric assessment was undertaken on morphology slides obtained as part of a multi-centre study in 1999-2002 of occupational factors in male infertility. Men attending 14 fertility clinics across the UK were recruited and gave a semen sample. Before results of the semen analysis were known, the men completed detailed questionnaires about their employment and lifestyle. Occupational exposures were assessed by occupational hygienists. Data were analysed using an unmatched case-referent design, allowing for clustering and for confounders. Three case definitions were used: poor morphology (normal morphology <4%), low motile sperm count (MSC) (<4.8×10(6)) and either condition.

RESULTS

Morphology results were available for 1861/2011 men employed at the time of recruitment. Of these 1861, 296 (15.9%) had poor morphology; of the 2011with sperm count, 453 (22.5%) had low MSC; 654/1981 (33.0%) had either condition. Poor morphology, adjusted for confounding, was related to self-reported lifetime exposure to lead (OR=1.33; 95% CI 1.00 to 1.75). Low MSC was also related to self-reported lead and to hygienist-assessed glycol ether exposure. Self-reported use of paint stripper (OR=1.47; 95% CI 1.07 to 2.03) and lead, but not glycol ether, were significantly related to the combined case definition.

CONCLUSIONS

While this study did not identify any occupational exposure uniquely related to sperm morphology, the capacity of the study to detect risk was increased by including morphology with sperm concentration and motility.

Culture, Urbanism and Changing Human Biology

Anthropologists have long known that human activity driven by culture changes the environment. This is apparent in the archaeological record and through the study of the modern environment. Perhaps the largest change since the paleolithic era is the organization of human populations in cities. New environments can reshape human biology through evolution as shown by the evolution of the hominid lineage. Evolution is not the only process capable of reshaping our biology. Some changes in our human biology are adaptive and evolutionary while others are pathological. What changes in human biology may be wrought by the modern urban environment? One significant new change in the environment is the introduction of pollutants largely through urbanization. Pollutants can affect human biology in myriad ways. Evidence shows that human growth, reproduction, and cognitive functioning can be altered by some pollutants, and altered in different ways depending on the pollutant. Thus, pollutants have significance for human biologists and anthropologists generally. Further, they illustrate the bio-cultural interaction characterizing human change. Humans adapt by changing the environment, a cultural process, and then change biologically to adjust to that new environment. This ongoing, interactive process is a fundamental characteristic of human change over the millennia.

The accumulation and efflux of lead partly depend on ATP-dependent efflux pump-multidrug resistance protein 1 and glutathione in testis Sertoli cells

Since lead accumulation is toxic to cells, its excretion is crucial for organisms to survive the toxicity. In this study, mouse testis sertoli (TM4) and Mrp1 lower-expression TM4-sh cells were used to explore the lead accumulation characteristics, and the role of ATP-dependent efflux pump-multidrug resistance protein 1 (Mrp1) in lead excretion. TM4 cells possess Mrp-like transport activity. The expression levels of mrp1 mRNA and Mrp1 increased after lead treatments at first and then decreased. The maximum difference of relative mRNA expression reached 10 times. In the presence of lead acetate, the amount of cumulative lead in TM4-sh was much higher than that in TM4. After the treatment with lead acetate at 10-40 μM for 12h or 24h, the differences were about 2-8 times. After with the switch to lead-free medium, the cellular lead content in TM4-sh remains higher than that in TM4 cells at 1,3, 6, and 9h time points (P<0.01). Energy inhibitor sodium azide, Mrp inhibitors MK571 and glutathione (GSH) biosynthesis inhibitor BSO could block lead efflux from TM4 cells significantly. These results indicate that lead excretion may be mediated by Mrp1 and GSH in TM4 cells. Mrp1 could be one of the important intervention points for lead detoxification.

Relationships of polychlorinated biphenyls and dichlorodiphenyldichloroethylene (p,p'-DDE) with testosterone levels in adolescent males

BACKGROUND

Concern persists over endocrine-disrupting effects of persistent organic pollutants (POPs) on human growth and sexual maturation. Potential effects of toxicant exposures on testosterone levels during puberty are not well characterized.

OBJECTIVES

In this study we evaluated the relationship between toxicants [polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (p,p´-DDE), hexachlorobenzene (HCB), and lead] and testosterone levels among 127 Akwesasne Mohawk males 10 to < 17 years of age with documented toxicant exposures.

METHODS

Data were collected between February 1996 and January 2000. Fasting blood specimens were collected before breakfast by trained Akwesasne Mohawk staff. Multivariable regression models were used to estimates associations between toxicants and serum testosterone, adjusted for other toxicants, Tanner stage, and potential confounders.

RESULTS

The sum of 16 PCB congeners (Σ16PCBs) that were detected in ≥ 50% of the population was significantly and negatively associated with serum testosterone levels, such that a 10% change in exposure was associated with a 5.6% decrease in testosterone (95% CI: -10.8, -0.5%). Of the 16 congeners, the more persistent ones (Σ8PerPCBs) were related to testosterone, whereas the less persistent ones, possibly reflecting more recent exposure, were not. When PCB congeners were subgrouped, the association was significant for the sum of eight more persistent PCBs (5.7% decrease; 95% CI: -11, -0.4%), and stronger than the sum of six less persistent congeners (3.1% decrease; 95% CI: -7.2, 0.9%). p,p´-DDE was positively but not significantly associated with serum testosterone (5.2% increase with a 10% increase in exposure; 95% CI: -0.5, 10.9%). Neither lead nor HCB was significantly associated with testosterone levels.

CONCLUSIONS

Exposure to PCBs, particularly the more highly persistent congeners, may negatively influence testosterone levels among adolescent males. The positive relationship between p,p´-DDE and testosterone indicates that not all POPs act similarly.

CITATION

Schell LM, Gallo MV, Deane GD, Nelder KR, DeCaprio AP, Jacobs A; Akwesasne Task Force on the Environment. 2014. Relationships of polychlorinated biphenyls and dichlorodiphenyldichloroethylene (p,p´-DDE) with testosterone levels in adolescent males. Environ Health Perspect 122:304-309; http://dx.doi.org/10.1289/ehp.1205984.

Influence of lead-doped hydroponic medium on the adsorption/bioaccumulation processes of lead and phosphorus in roots and leaves of the aquatic macrophyte Eicchornia crassipes

In this study, lead bioaccumulation by the living free-floating aquatic macrophyte Eicchornia crassipes in different hydroponic conditions with variations in phosphorus and lead concentrations was investigated. A set of growth experiments in hydroponic media doped with lead and phosphorus within a wide concentration range was performed for 32 days in a greenhouse. All experiments were carried out with periodic replacement of all nutrients and lead. The concentration of lead and nutrients in biomass was determined by synchrotron radiation-excited total reflection X-ray fluorescence. By increasing the lead concentration in the medium, a reduction in biomass growth was observed, but a higher phosphorus retention in roots and leaves was shown at lower lead concentrations. In addition, an increase in the amount of bioaccumulated lead and phosphorus in roots was observed for higher lead and phosphorus concentrations in the medium, reaching saturation values of 4 mg Pb g(-1) and 7 mg P g(-1), respectively. Four non-structural kinetic models were tested, to represent the bioaccumulation of lead and phosphorus in roots. Pseudo-second order and irreversible kinetic models described the lead bioaccumulation data well, however, an irreversible kinetic model better fitted phosphorus uptake in roots.

Genomic and proteomic analyses of 1,3-dinitrobenzene-induced testicular toxicity in Sprague-Dawley rats

1,3-Dinitrobenzene (DNB) is an industrial intermediate and testicular toxicant that has been shown to target Sertoli cells. The mechanism of action of DNB in the testis, however, is unclear. To investigate global alterations in gene or protein expression during testicular toxicity, testes from rats treated orally with DNB were subjected to microarray and two-dimensional gel electrophoresis (2-DE) analyses. Histopathological abnormalities were detected in the testes of the DNB-treated rats. Microarray analysis revealed that, during early testicular toxicity, several genes involved in apoptosis, germ cell/Sertoli cell junction, and tight junction signaling pathways were differentially expressed. Based on 2-DE analysis, 36 protein spots showing significantly different expression during early testicular toxicity were selected and identified. Network analysis of the identified proteins revealed that these proteins are associated with cellular development or reproductive system diseases. Collectively, these data will help clarify the molecular mechanism underlying testicular toxicity in DNB-exposed rats.

What should it take to describe a substance or product as 'sperm-safe'

BACKGROUND

Male reproductive potential continues to be adversely affected by many environmental, industrial and pharmaceutical toxins. Pre-emptive testing for reproductive toxicological (side-)effects remains limited, or even non-existent. Many products that come into direct contact with spermatozoa lack adequate testing for the absence of adverse effects, and numerous products that are intended for exposure to spermatozoa have only a general assumption of safety based on the absence of evidence of actual harm. Such assumptions can have unfortunate adverse impacts on at-risk individuals (e.g. couples who are trying to conceive), illustrating a clear need for appropriate up-front testing to establish actual 'sperm safety'.

METHODS

After compiling a list of general areas within the review's scope, relevant literature and other information was obtained from the authors' personal professional libraries and archives, and supplemented as necessary using PubMed and Google searches. Review by co-authors identified and eliminated errors of omission or bias.

RESULTS

This review provides an overview of the broad range of substances, materials and products that can affect male fertility, especially through sperm fertilizing ability, along with a discussion of practical methods and bioassays for their evaluation. It is concluded that products can only be claimed to be 'sperm-safe' after performing objective, properly designed experimental studies; extrapolation from supposed predicate products or other assumptions cannot be trusted.

CONCLUSIONS

We call for adopting the precautionary principle, especially when exposure to a product might affect not only a couple's fertility potential but also the health of resulting offspring and perhaps future generations.

Reproductive toxicity of metals in men

A combination of genetic, environmental and lifestyle factors contributes to adverse effects on the reproductive health in men. Metals are pervasive in food, water, air, tobacco smoke, and alcoholic beverages. Experimental studies suggest that many metals have adverse effects on the male reproductive function. However, information about reproductive effects of human exposure to metals is scarce and/or inconsistent. This review summarises the information from epidemiological studies of the effects of metal exposure on reproductive function in men. Factors capable of affecting these relationships were identified and discussed. A particular attention is given to the studies considering influence of concomitant exposure to various metals. These studies have generally confirmed that even moderate- to low-level exposure to lead affects certain reproductive parameters, and that exposure to cadmium affects the prostate function and serum testosterone levels. Adverse effects of mercury, manganese, chromium and arsenic on semen quality and altered serum hormone are less well documented. There is no clear evidence that boron exposure may impair reproductive health in men. Only a few studies have investigated reproductive effects of concomitant exposure to several metals and controlled for potential confounders. Future studies should consider the contribution of combined exposure to various metals and/or other factors that may influence individual susceptibility to reproductive health impairment in men.

Lead level in seminal plasma may affect semen quality for men without occupational exposure to lead

BACKGROUND

Infertility affects approximately 10-15% of reproductive-age couples. Poor semen quality contributes to about 25% of infertile cases. Resulting from the direct effect on testicular function or hormonal alterations, heavy metals exposure has been related to impaired semen quality. The objective of this study was to assess the level of lead in the seminal plasma in men without occupational exposure to lead, and to determine the relationship between semen quality and lead concentration in the semen.

METHODS

This is a prospective and nonrandomized clinical study conducted in University infertility clinic and academic research laboratory. Three hundred and forty-one male partners of infertile couples undergoing infertility evaluation and management were recruited to the study. Semen samples collected for the analyses of semen quality were also used for the measurement of lead concentrations. Semen samples were evaluated according to the WHO standards.

RESULTS

All subjects were married and from infertile couples without occupational exposure to lead. There is a significant inverse correlation between the lead concentration in seminal plasma and sperm count. A higher semen lead concentration was correlated with lower sperm count, but not with semen volume, sperm motility or sperm morphology as assessed by simple linear regression.

CONCLUSIONS

We found that semen lead concentration was significantly higher among the patients with lower sperm count. To our knowledge, this is the first study to demonstrate that a high level of lead accumulation in semen may reduce the sperm count contributing to infertility of men without occupational exposure to lead.

Clinical relevance of vitamin C among lead-exposed infertile men

AIMS AND OBJECTIVES

A cross-sectional study was designed by targeting 120 male workers occupationally exposed to lead from a battery-manufacturing industry situated at the Patancheru industrial area, Hyderabad, Andhra Pradesh, India, to see the impact of lead on testicular dysfunction with reference to infertility. Further, the study was designed to see the in vivo effect of an antioxidant in the form of vitamin C, prophylactically administered at the dose of 1000 mg/day for five consecutive days in a week for 3 months.

METHODOLOGY

Blood samples and semen samples were collected from 120 men in the study group exposed to lead, and 120 healthy human subjects, who have no history of exposures to chemicals, were selected as controls for comparison. The mean age of the workers who participated in this study falls in the range of 25-55 years. The semen samples were collected with due consent of the industrial workers to perform the conventional semen analysis and the measure of sperm DNA fragmentation by the comet assay.

RESULTS

Industrial workers showed a statistically significant increase in sperm motility (p<0.001), sperm total count (p<0.001), and a statistically significant decrease in abnormal sperm morphology (p<0.001) after vitamin C prophylaxis. The comet assay also showed similar results, where there is a statistically significant decrease in alkaline-labile sites and a statistically significant decrease in the mean tail length of the comet when compared to the control group (p<0.001) after vitamin C prophylaxis.

CONCLUSION

This study leads us to conclude that the lead compound interferes with the testicular function, inducing its activity and also by exerting its effect on sperm DNA, leading to fragmentation. Further, the prophylaxis with antioxidant treatment may offer protection against the reactive oxygen species (ROS)-induced DNA damage, which is a major cause in the etiology of male infertility.

Semen quality and reproductive endocrinal function related to blood lead levels in infertile painters

Lead causes male reproductive impairment among painters, but information is still limited. Therefore, the effect of lead on semen quality and reproductive endocrinal function in those patients was investigated. A case series of 27 infertile painters were subjected to semen analysis, measuring of blood lead level (PbB) and serum levels of endocrinal parameters including follicle-stimulating hormone (FSH), luteinising hormone (LH), testosterone (T) and prolactin (PRL). Significantly lower sperm count and motility were found in those with duration of exposure (≥ 15 years), but no significant difference was found for PbB and serum levels of FSH, LH, PRL and T. A significant negative correlation between PbB and spermatic count and motility was observed, while there was no significant correlation between PbB and all endocrinal parameters. Patients with PbB ≥ 20 μg dl(-1) showed a significant decrease in sperm motility and increase in testosterone alone among all measured hormones. But the observed decrease in sperm count did not reach a significant level. It is concluded that infertile painters are at risk of lead-related influence on semen quality, especially sperm motility and increased testosterone level without significant affection of other reproductive endocrinal parameters.

Protective role of Centella asiatica on lead-induced oxidative stress and suppressed reproductive health in male rats

Centella asiatica has been mentioned in ancient ayurvedic text of the Indian system of medicine for its properties to promote intelligence. The objective of the present study was to investigate the beneficial effects of C. asiatica on lead-induced oxidative stress and suppressed reproductive performance in male rats. Significant decrease in the weights of testes and epididymis were observed in lead treated animals. Exposure to lead acetate significantly increased malondialdehyde levels with a significant decrease in the superoxide dismutase and catalase activities in the liver, brain, kidneys and testes of rats. Epididymal sperm count, viable sperms, motile sperms and HOS-tail coiled sperms decreased significantly in lead-exposed rats. Testicular steroidogenic enzyme activities also decreased significantly in lead-exposed rats. No significant changes in the selected reproductive variables were observed in the plant extract alone treated rats. Whereas, co-administration of aqueous extracts of C. asiatica to lead exposed rats showed a significant increase in the weights of reproductive organs, reduction in lead-induced oxidative stress in the tissues and improvement in selected reproductive parameters over lead-exposed rats indicating the beneficial role of C. asiatica to counteract lead-induced oxidative stress and to restore the suppressed reproduction in male rats.

Exposure sources and reasons for testing among women with low blood lead levels

Previous research has focused on highly elevated blood lead (PbB). This study examined reasons for testing and potential sources of exposure among women with PbBs less than 0.72 μmol/l (15 μg/dl). A questionnaire was mailed to 18- to 49-year-old women in upstate New York, USA, who were PbB tested in 2007. The most common testing reason was pregnancy among 125 women who returned the questionnaire. Among women tested for PbB during pregnancy, doctors ordered approximately 80% of tests regardless of lead level. Few women with PbBs less than 0.24 μmol/l (5 μg/dl) reported a potential source of lead exposure. However, among women with PbBs of 0.24-0.71 μmol/L (5-14.9 μg/dl), 29.2% had a job and 21.2% had a hobby with potential lead exposure. There are systematic differences in reasons for testing and exposure sources among women with PbBs less than 0.72 μmol/l and these differences have implications for screening.

Disturbances of energetic metabolism in rat epididymal epithelial cells as a consequence of chronic lead intoxication

Adult male Wistar rats were intoxicated with 1% lead acetate (PbAc) administered in drinking water for nine months, which amounts to a period five times longer than the duration of one spermatogenesis. There were mitochondrial ultrastructure disorders of epididymal epithelial cells observed in PbAc-treated rats; also a significant lead-induced decrease in ATP concentration in epididymal epithelial cells (by 32%, P < 0.05), Adenylate Energy Charge value (AEC) (by 8%, P < 0.05) and an increase in ADP (28.5%, P < 0.05), AMP (27%, P < 0.05) and adenosine (by 56%, P < 0.05). The results were measured using high performance liquid chromatography (HPLC) and detected even at low lead concentrations in whole blood (M:7.03 μg/dL; Q1-Q3: 2.99-7.65). The function of mitochondria in cultured epididymal epithelial cells of control and PbAc-treated animals were evaluated using fluorophores: Mitotracker Green FM and JC-1. After incubation with Mitotracker Green FM, we observed active mitochondria producing bright green fluorescence in the cytoplasm of cultured epididymal epithelial cells, both in the control group and the Pb-treated animals. Incubation of cultured epididymal epithelial cells of animals from both groups produced red-orange fluorescence with the mitochondrial JC-1 probe indicating mitochondria with high membrane potential (ΔΨm > 80-100 mV) and green fluorescence in the mitochondria with low membrane potential (ΔΨm < 80 mV). The results showed that a chronic low-level exposure to lead, even without severe clinical symptoms of contamination, disrupted the ultrastructure and energy metabolism of mitochondria in epididymal epithelial cells.

Environmental chemical mediated male reproductive toxicity: Drosophila melanogaster as an alternate animal model

Industrialization and indiscriminate use of agrochemicals have increased the human health risk. Recent epidemiological studies raised a concern for male reproduction given their observations of reduced sperm counts and altered semen quality. Interestingly, environmental factors that include various metals, pesticides and their metabolites have been causally linked to such adversities by their presence in the semen at levels that correlate to infertility. The epidemiological observations were further supported by studies in animal models involving various chemicals. Therefore, in this review, we focused on male reproductive toxicity and the adverse effects of different environmental chemicals on male reproduction. However, it is beyond the scope of this review to provide a detailed appraisal of all of the environmental chemicals that have been associated with reproductive toxicity in animals. Here, we provided the evidence for reproductive adversities of some commonly encountered chemicals (pesticides/metals) in the environment. In view of the recent thrust for an alternate to animal models in research, we subsequently discussed the contributions of Drosophila melanogaster as an alternate animal model for quick screening of toxicants for their reproductive toxicity potential. Finally, we emphasized the genetic and molecular tools offered by Drosophila for understanding the mechanisms underlying the male reproductive toxicity.

Relationships between heavy metal concentrations in three different body fluids and male reproductive parameters: a pilot study

BACKGROUND

Animal studies have shown the reproductive toxicity of a number of heavy metals. Very few human observational studies have analyzed the relationship between male reproductive function and heavy metal concentrations in diverse biological fluids.

METHODS

The current study assessed the associations between seminal and hormonal parameters and the concentration of the 3 most frequent heavy metal toxicants (lead, cadmium and mercury) in three different body fluids. Sixty one men attending infertility clinics that participated in a case-control study to explore the role of environmental toxins and lifestyles on male infertility were analyzed. Concentration of lead, cadmium and mercury were measured in blood and seminal plasma and whole blood using anodic stripping voltammetry and atomic absorption spectrophotometry. Serum samples were analyzed for follicle-stimulating hormone, luteinizing hormone and testosterone. Semen analyses were performed according to World Health Organization criteria. Mann-Whitney test and Spearman's rank correlations were used for unadjusted analyses. Multiple linear regression models were performed controlling for age, body mass index and number of cigarettes per day.

RESULTS

There were no significant differences between cases and controls in the concentrations of heavy metals in any of the three body fluids. In multivariate analyses using all subjects no significant associations were found between serum hormone levels and metal concentrations. However there was a significant positive association between the percentage of immotile sperms and seminal plasma levels of lead and cadmium.

CONCLUSIONS

Our results suggest that the presence of lead and cadmium in the reproductive tract of men may be related to a moderate alteration of their seminal parameters.

How does lead induce male infertility?

An important part of male infertility of unknown etiology may be attributed to various environmental and occupational exposures to toxic substances, such as lead. The reproductive effects of lead are complex and appear to involve multiple pathways, not all of which are fully understood. It is still unclear, for example, if male reproductive issues in lead-exposed persons are mostly related to the disruption of reproductive hormones, whether the problems are due to the lead's direct effects on the gonads, or both? This question has been difficult to answer, because lead, especially at high levels, may adversely affect many human organs. Although lead can potentially reduce male fertility by decreasing sperm count and motility, inducing abnormal morphology and affecting functional parameters; not all studies have been able to clearly demonstrate such findings. In addition, research has shown that the blood-testis barrier can protect testicular cells from direct exposure to high levels of blood lead. For these reasons and considering the wide spectrum of lead toxicity on reproductive hormones, the present review suggests that lead's main influence on male reproduction probably occurs by altering the reproductive hormonal axis and the hormonal control on spermatogenesis, rather than by a direct toxic effect on the seminiferous tubules of the testes. As blood lead concentrations below the currently accepted worker protection standard may still adversely affect male fertility, future studies should aim to establish more concrete links between lead exposure (especially at low levels) and subsequent male infertility. Research should also pay more attention to lead's effects on reducing male fertility rates based on not only hormonal axis alteration, but also on the changes in sperm characteristic among exposed subjects.

Opacification of lenses cultured in the presence of Pb

PURPOSE

Occupational and environmental Pb-exposure is associated with protein aggregation diseases which typically present in elderly populations (Parkinsons and cataract). Post-translational processing of crystallins, the major structural proteins of the lens, is altered with short-term Pb-exposure in Fisher 344 rats. In addition, lenses from aged rats become opaque upon long-term exposure to Pb in organ culture. To explore the route to lens opacification in the presence of Pb, cultured lenses from young rats which exhibit higher metabolic activity in lens culture and are more susceptible to experimental cataract in vivo and in vitro were exposed to Pb and evaluated for morphological and biochemical alterations.

METHODS

Following culture in Pb (as lead nitrate) for four days (in the presence/absence of oxidative challenge), lenses were examined for clarity, integrity of epithelial layer, and molecular stability including crystallin post-translational modification and choline transport. Clarity of lenses cultured with/without Pb for up to 8 days was assessed to determine if Pb exposure would accelerate opacification.

RESULTS

Lenses cultured in Pb for four days exhibited epithelial abnormalities including epithelial cell multilayering and nuclei abnormalities with extension of the nucleated epithelial cells past the bow region. Alterations in crystallin post-translational modifications and decreased membrane transport of choline were noted without corresponding lens opacification or altered α-crystallin chaperone activity. Lenses treated with Pb according to the same exposure protocol with subsequent challenge by hydrogen peroxide became opaque while the contralateral control lenses did not. Lenses which were cultured in the presence of Pb for longer periods with no subsequent oxidative insult exhibited lens failure at earlier time points than did the controls.

CONCLUSIONS

These data indicate that Pb-exposure can accelerate the degradation of the cultured lens through induction of epithelial cell abnormalities, induce structural protein modifications before opacity, and predispose the lens to opacification with subsequent oxidant challenge.

Environmental exposure to metals and male reproductive hormones: circulating testosterone is inversely associated with blood molybdenum

OBJECTIVE

To explore associations between exposure to metals and male reproductive hormone levels.

DESIGN

Cross-sectional epidemiology study with adjustment for potential confounders.

SETTING

University Medical Center.

PATIENT(S)

Men recruited through two infertility clinics in Michigan.

INTERVENTION(S)

Metal concentrations and reproductive hormone levels were measured in blood samples collected from 219 men.

MAIN OUTCOME MEASURE(S)

Serum FSH, LH, inhibin B, T, and sex hormone-binding globulin levels.

RESULT(S)

Cadmium, copper, and lead were all significantly or suggestively positively associated with T when modeled individually, findings that are consistent with limited previous human and animal studies. Conversely, molybdenum was associated with reduced T. A significant inverse trend between molybdenum and T remained when additionally considering other metals in the model, and a positive association between T and zinc was also found. Finally, in exploratory analysis there was evidence for an interaction between molybdenum and zinc, whereby high molybdenum was associated with a 37% reduction in T (relative to the population median level) among men with low zinc.

CONCLUSION(S)

Although reductions in T and reproductive toxicity after molybdenum exposure have been previously demonstrated in animal studies, more research is needed to determine whether molybdenum poses a risk to human reproductive health.

The role of MAPK and FAS death receptor pathways in testicular germ cell apoptosis induced by lead

The aim of the present study is to investigate gene expression involved in the signal pathway of MAPK and death signal receptor pathway of FAS in lead-induced apoptosis of testicular germ cells. First, cell viabilities were determined by MTT assay. Second, using single cell gel-electrophoresis test (comet assay) and TUNEL staining technique, apoptotic rate and cell apoptosis localization of testicular germ cells were measured in mice treated with 0.15%, 0.3%, and 0.6% lead, respectively. Third, the immunolocalization of K-ras, c-fos, Fas, and active caspase-3 proteins was determined by immunohistochemistry. Finally, changes in the translational levels of K-ras, c-fos, Fas, and active caspase-3 were further detected by western blot analysis. Our results showed that lead could significantly induce testicular germ cell apoptosis in a dose-dependent manner (P<0.01). The mechanisms were closely related to the increased expressions of K-ras, c-fos, Fas, and active caspase-3 in apoptotic germ cells. In conclusion, K-ras/c-fos and Fas/caspase-3 death signaling receptor pathways were involved in the lead-induced apoptosis of the testicular germ cells in mice.

The effect of lead intoxication on endocrine functions

Studies on the effects of lead on the endocrine system are mainly based on occupationally lead-exposed workers and experimental animal models. Although evidence is conflicting, it has been reported that accumulation of lead affects the majority of the endocrine glands. In particular, it appears to have an effect on the hypothalamic-pituitary axis causing blunted TSH, GH, and FSH/LH responses to TRH, GHRH, and GnRH stimulation, respectively. Suppressed GH release has been reported, probably caused by reduced synthesis of GHRH, inhibition of GHRH release or reduced somatotrope responsiveness. Higher levels of PRL in lead intoxication have been reported. In short-term lead-exposed individuals, high LH and FSH levels are usually associated to normal testosterone concentrations, whereas in long-term exposed individuals' low testosterone levels do not induce high LH and FSH concentrations. These findings suggest that lead initially causes some subclinical testicular damage, followed by hypothalamic or pituitary disturbance when longer periods of exposure take place. Similarly, lead accumulates in granulosa cells of the ovary, causing delays in growth and pubertal development and reduced fertility in females. In the parenchyma of adrenals histological and cytological changes are demonstrated, causing changes in plasma basal and stress-mediated corticosterone concentrations and reduced cytosolic and nuclear glucocorticoid receptor binding. Thyroid hormone kinetics are also affected. Central defect of the thyroid axis or an alteration in T4 metabolism or binding to proteins may be involved in derangements in thyroid hormone action. Lead toxicity involves alterations on calcitropic hormones' homeostasis, which increase the risk of skeletal disorders.