The effect of age of exposure on lead-induced testicular toxicity

Quercetin as a Dietary Supplementary Flavonoid Alleviates the Oxidative Stress Induced by Lead Toxicity in Male Wistar Rats

Quercetin is a naturally existing plant pigment belonging to the flavonoid group; it is contained in a wide range of vegetables and fruits. The accumulated evidence points to the potential uses of quercetin in protection of some disease conditions. Lead is one of the highly toxicant heavy metals that are widely spread in the environment and implicated in a wide spectrum of industries. No previous study has been reported to evaluate the effect of quercetin on lead toxicity. Therefore, the present study was conducted to elucidate some aspects of quercetin bioactivities in regard to its ability to combat the oxidative stress induced by lead toxicity. For this purpose, a total of sixty male Wistar rats were randomly and equally divided into three groups of 20 animals each; untreated control animals (group 1), lead-exposed animals (group 2; exposed to lead daily by oral gavage at the dose of 80 mg/Kg b.w.), and group 3 of animals, which were exposed to lead and daily received quercetin (10 h gap time between lead exposure and the receiving of quercetin) by oral gavage at the dose of 350 mg/Kg b.w. The experiment period was 8 weeks. All the assayed hematological and biochemical parameters of animals exposed to lead were significantly altered compared with the untreated control levels. Animals exposed to lead (group 2) exhibited significant decrements of the erythrocytic and total leucocytic counts, hemoglobin concentration, packed cell volume percent, total proteins, albumin and globulin. These animals also disclosed significantly decreased levels of antioxidant markers including total thiols, catalase and glutathione. On the other hand, these animals demonstrated significant increments in the levels of bilirubin, urea, creatinine, BUN, serum enzymes, H₂O₂ and MDA. Animals exposed to lead and given quercetin (group 3) exhibited improvement of these parameters, which were brought back at varying degrees toward the untreated control levels. Basing on the improvements of the assayed hematological and biochemical parameters, it was concluded that quercetin as a dietary supplement can act efficiently as an antioxidant to counteract the oxidative stress induced by lead toxicity and to maintain the oxidant antioxidant balance.

Structure-Activity Relationship of Lanthanide-Incorporated Nano-Hydroxyapatite for the Adsorption of Fluoride and Lead

The growing demand for water purification provided the initial momentum to produce lanthanide-incorporated nano-hydroxyapatite (HAP) such as HAP·CeO2, HAP·CeO2·La(OH)3 (2:1), and HAP·CeO2·La(OH)3 (3:2). These materials open avenues to remove fluoride and lead ions from contaminated water bodies effectively. Composites of HAP containing CeO2 and La(OH)3 were prepared using in situ wet precipitation of HAP, followed by the addition of Ce(SO4)2 and La(NO3)3 into the same reaction mixture. The resultant solids were tested for the removal of fluoride and lead ions from contaminated water. It was found that the composite HAP·CeO2 shows fluoride and lead ion removal capacities of 185 and 416 mg/g, respectively. The fluoride removal capacity of the composite was improved when La(OH)3 was incorporated and it was observed that the composite HAP·CeO2·La(OH)3 (3:2) has the highest recorded fluoride removal capacity of 625 mg/g. The materials were characterized using scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) spectrometry, Fourier transform infrared (FT-IR) spectrometry, X-ray powder diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) surface area analysis. Analysis of results showed that Ce and La are incorporated in the HAP matrix. Results of kinetic and leaching analyses indicated a chemisorptive behavior during fluoride and lead ion adsorption by the composites; meanwhile, the thermodynamic profile shows a high degree of feasibility for fluoride and lead adsorption.

Low dose of fire retardant, 2,2',4,4'-tetrabromodiphenyl ether (BDE47), stimulates the proliferation and differentiation of progenitor Leydig cells of male rats during prepuberty

2,2',4,4'-Tetrabromodiphenyl ether (BDE47), a flame retardant, is extensively distributed in the food chain. However, whether BDE47 affects Leydig cell development during prepuberty remains unclear. BDE47 was daily gavaged to 21-day-old Sprague-Dawley male rats with 0 (corn oil), 0.1, 0.2, and 0.4 mg/kg for 14 days. BDE47 did not affect the body weight or testis weight of rats. It significantly increased serum testosterone level at 0.4 mg/kg, but decreased luteinizing hormone (LH) level without affecting estradiol level. BDE47 induced Leydig cell hyperplasia (the number of CYP11A1-positive Leydig cells increased), and up-regulated the expression of Scarb1, Star, Hsd11b1, Pcna, and Ccnd1 in the testis. BDE47 significantly reduced p53 and p21 levels but increased CCND1 level. It also markedly increased the phosphorylation of AKT1, AKT2, ERK1/2, and CREB. BDE47 significantly up-regulated the expression of Scarb1, Star, and Hsd11b1 and stimulated androgen production by immature Leydig cells from rats under basal, LH, and 8Br-cAMP stimulated conditions at 100 nM in vitro. In conclusion, BDE47 increased Leydig cell number and up-regulated the expression of Scarb1 and Star, thereby leading to increased testosterone synthesis.

The Effect of Lead Acetate and Quercetin on the Tight and Gap Junctions in the Mouse Testis

Environmental pollutant effects on fertility sometime are irretrievable. The aim of this study was to investigate the effect of lead acetate and quercetin on tight (claudin 11 and occludin) and gap junctional (connexin 43) proteins and the integrity of the blood-testis barrier status. Experimental groups, including the lead acetate (Pb), quercetin (QE), lead acetate with quercetin (Pb + QE), and control mice, were treated at least one spermatogenic cycle. Gene expression of claudin 11 and occludin decreased in Pb + QE, Pb, and QE compared with the control group. Connexin 43 (Cx43) expression in the control and Pb groups was lower than in Pb + QE and QE. The immunohistochemical data were generally in line with these findings. In conclusion, the results showed that Pb exposure led to disorders in cellular interactions that affect testicular function; however, simultaneous treatment with quercetin did not alleviate these effects. Graphical Abstract.

In utero and peripubertal metals exposure in relation to reproductive hormones and sexual maturation and progression among girls in Mexico City

There is increasing evidence that several metals are endocrine disrupting chemicals (EDCs). In utero development and adolescence are critical windows of susceptibility to EDC exposure. With the exception of a few heavy metals, few human studies have evaluated the impact of metal exposure on pubertal development. Our aim was to investigate measures of in utero and peripubertal metal exposure in relation to reproductive hormone levels and sexual maturation and progression among girls from the Early Life Exposure in Mexico to Environmental Toxicants (ELEMENT) cohorts. We measured urinary concentrations of aluminum (Al), arsenic (As), barium (Ba), cadmium (Cd), cobalt (Co), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), nickel (Ni), antimony (Sb), selenium (Se), and zinc (Zn) in samples collected from women during their third trimester of pregnancy and from their female children at 8-13 years (n = 132). We measured serum testosterone, estradiol, dehydroepiandrosterone sulfate (DHEA-S), inhibin B, and sex hormone-binding globulin (SHBG) at age 8-13, and assessed Tanner stages for sexual maturation (breast, pubic hair development, and menarche status), at two time points (8-13, 14-18 years). We used linear regression to independently examine in utero and peripubertal metal concentrations as predictors of peripubertal hormones. In a longitudinal analysis using generalized estimation equations, we evaluated Tanner stage and menarche progression in relation to individual in utero and peripubertal metal concentrations. We found that higher in utero Zn was associated with increased inhibin B. Several metals at 8-13 years were associated with higher DHEA-S and estradiol, while Ni was positively but Cu was negatively associated with testosterone. In utero Ni, Al, and Cd were associated with slower progression of breast development after adjustment for child age and BMI z-score. For example, an IQR increase in in utero Al exposure was associated with 0.82 times lower odds of progressing to a higher Tanner stage for breast development per year (95% CI: 0.68, 0.99). Peripubertal concentrations of Ba and Al were also associated with being at a higher pubic hair Tanner stage and menarche at 8-13, but lower odds of progressing to the next stage at 14-18 years. We used Bayesian kernel machine regression (BKMR) to model the joint effect of multiple metals while accounting for correlated exposures, as well as potential non-linear relationships between metals and outcomes of interest, which yielded results similar to individual analyses. These findings suggest that female reproductive development may be vulnerable to the effects of metal exposure, and using both Tanner stages and hormone levels may provide clues about underlying mechanisms in two sensitive periods of development.

Environmental Chemical Contaminants in Food: Review of a Global Problem

Contamination by chemicals from the environment is a major global food safety issue, posing a serious threat to human health. These chemicals belong to many groups, including metals/metalloids, polycyclic aromatic hydrocarbons (PAHs), persistent organic pollutants (POPs), perfluorinated compounds (PFCs), pharmaceutical and personal care products (PPCPs), radioactive elements, electronic waste, plastics, and nanoparticles. Some of these occur naturally in the environment, whilst others are produced from anthropogenic sources. They may contaminate our food-crops, livestock, and seafood-and drinking water and exert adverse effects on our health. It is important to perform assessments of the associated potential risks. Monitoring contamination levels, enactment of control measures including remediation, and consideration of sociopolitical implications are vital to provide safer food globally.

Lead toxicity: a review

Lead toxicity is an important environmental disease and its effects on the human body are devastating. There is almost no function in the human body which is not affected by lead toxicity. Though in countries like US and Canada the use of lead has been controlled up to a certain extent, it is still used vehemently in the developing countries. This is primarily because lead bears unique physical and chemical properties that make it suitable for a large number of applications for which humans have exploited its benefits from historical times and thus it has become a common environmental pollutant. Lead is highly persistent in the environment and because of its continuous use its levels rise in almost every country, posing serious threats. This article reviews the works listed in the literature with recent updates regarding the toxicity of lead. Focus is also on toxic effects of lead on the renal, reproductive and nervous system. Finally the techniques available for treating lead toxicity are presented with some recent updates.

Age-related testicular toxicity of mGluR5 negative allosteric modulators appears to be unrelated to testis drug transporter maturity

Testicular degeneration was observed in exploratory toxicity studies in Wistar rats treated with several mGluR5 negative allosteric modulators. To determine if these testis effects were influenced by animal age, these compounds were administered to male Wistar rats of different ages (8, 10, and 12 weeks old) for 2 weeks followed by evaluation of male reproductive organ weights, testis histopathology, and inhibin B levels. Overall, seminiferous tubule degeneration was observed in 2/15, 5/15, and 0/15 compound treated rats from the 8, 10, and 12 week old cohorts and inhibin B was decreased in 8 and 10 week old animals, but not in 12 week old rats, suggesting that there is an age-related component to this testis toxicity. The gene expression profiles of drug transporters in the testis of rats aged PND 38 through PND 91 were very similar, indicating that immaturity of these transporters is an unlikely factor contributing to the age-related toxicity.

Cross-species coherence in effects and modes of action in support of causality determinations in the U.S. Environmental Protection Agency's Integrated Science Assessment for Lead

The peer-reviewed literature on the health and ecological effects of lead (Pb) indicates common effects and underlying modes of action across multiple organisms for several endpoints. Based on such observations, the United States (U.S.) Environmental Protection Agency (EPA) applied a cross-species approach in the 2013 Integrated Science Assessment (ISA) for Lead for evaluating the causality of relationships between Pb exposure and specific endpoints that are shared by humans, laboratory animals, and ecological receptors (i.e., hematological effects, reproductive and developmental effects, and nervous system effects). Other effects of Pb (i.e., cardiovascular, renal, and inflammatory responses) are less commonly assessed in aquatic and terrestrial wildlife limiting the application of cross-species comparisons. Determinations of causality in ISAs are guided by a framework for classifying the weight of evidence across scientific disciplines and across related effects by considering aspects such as biological plausibility and coherence. As illustrated for effects of Pb where evidence across species exists, the integration of coherent effects and common underlying modes of action can serve as a means to substantiate conclusions regarding the causal nature of the health and ecological effects of environmental toxicants.

Perspectives in endocrine toxicity of heavy metals--a review

An attempt has been made to review the endocrine/hormonal implications of a few environmentally significant metals, viz, lead, mercury, cadmium, copper, arsenic and nickel, in man and animals. Special emphasis has been given to the adrenals, thyroid, testis, ovary and pancreas. Toxic metals can cause structural and functional changes in the adrenal glands. Their effects on steroidogenesis have been reviewed. It has been reported that thyroid hormone kinetics are affected by a number of metallic compounds. Occupational exposure to a few of these metals can cause testicular injury and sex hormone disturbances. Protective effects of a few antioxidants on their reproductive toxicity have also been discussed. Information gathered on female reproductive toxicity of heavy metals shows that exposure to these metals can lead to disturbances in reproductive performance in exposed subjects. Certain metals can cause injury to the endocrine pancreas. Exposure to them can cause diabetes mellitus and disturb insulin homeostasis. The need to develop molecular markers of endocrine toxicity of heavy metals has been suggested. Overall information described in this review is expected to be helpful in planning future studies on endocrine toxicity of heavy metals.

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.

Effect of long-term dietary lead exposure on some maturation and reproductive parameters of a female Prussian carp (Carassius gibelio B.)

Lead is reported to be an endocrine disruptor. In the current study, we exposed female Prussian carp to artificial feed, supplemented with five doses of dietary Pb (0, 1 (control), 8, 13, 24, and 49 mg/kg) over either a 24-month period or a 12-month period, followed by further 12 months where the fish were fed the control diet. Periodically, oocyte maturation, gonadosomatic index (GSI), ability to secret luteinizing hormone (LH) as well as gonad Pb concentrations were measured. It was found that the reproductive system of the female Prussian carp is not indifferent to chronic exposure to lead. The negative effect was manifested by a decrease in the GSI after 12 months despite the fact that a higher proportion of oocytes at more advanced maturity stages were concurrently observed. After 12 months of exposure, the effect on LH secretion varied according to the dose. In the group exposed to the lowest dose (8 mg/kg), LH decreased spontaneously, and in the groups exposed to the highest two doses (24 and 48 mg/kg), a significantly higher LHRH-A-stimulated LH secretion was observed. After 24 months of lead exposure, the effects on oocyte maturation and size and on GSI values were not pronounced. Analysis of the effect of lead exposure on LH secretion showed that the relationships were similar to those observed after 12 months but nonsignificant. During chronic a 24-month period exposure to Pb, Prussian carp female appears to acclimate to Pb doses used in the experiment. After 12 months of exposure and 12 months of depuration, the levels of spontaneous and stimulated LH secretion observed in all the groups were similar to the control, which is evidence that depuration eliminates the previously observed effects of exposure to lead. Lead is easily accumulated in the ovary, reaching a fivefold higher level (0.8 mg/kg tissue) compared to the control(0.15 mg/kg tissue), but after discontinuation of exposure, this organ is quickly depurated. The results indicate that environmental Pb can be a potent endocrine disruptor affecting ovarian steroidogenesis, gametogenesis, and ovulation, which may lead to adverse impacts on fish reproduction and population density and that female Prussian carp become resistant to the negative effects of lead with advancing age, and their organs cope by reaching a state of homeostasis.

In vivo distribution of lead in male and female rats after intraperitoneal and oral administration

The resultant effects of lead exposure are seen in almost all the systems of the body and results in toxicity to many organs. Since toxicity depends on its degree of uptake, distribution and metabolism, the authors investigated the differential uptake, accumulation and distribution of lead in organs of males and female Wistar rats following various routes of administration. Group 1 served as control male and control female; group 2 males and females received 5 mg/kg body weight of lead intraperitoneally for 8 days while group 3 males and female rats were administered drinking water containing 100 ppm of lead acetate for 18 days. Tissues were collected for analysis of the lead content using atomic absorption spectroscopy. The relative retention of lead by the tissues was greater in rats exposed to lead by the i.p. route varying in the order of accumulation / uptake in males as lungs > spleen > stomach > kidney > blood > heart and in females as spleen > stomach > heart > kidney > blood > lungs (i.p. route) and (oral route) as for males kidney > lungs > stomach > blood > heart > spleen, and females as kidney > lungs > stomach > blood > heart > spleen. Male Wistar rats showed more accumulation with oral exposure in lungs, spleen and blood with values for kidney and stomach being significantly ( p < 0.05) higher when compared with females. Female Wistar rats showed more accumulation with i.p. exposure for spleen and stomach tissues while values for the heart was significantly ( p < 0.05) higher than the males. Our findings suggest that lead retention and the organ distribution varied depending upon the sex and route of lead administration.

Lead acetate induced reproductive and paternal mediated developmental toxicity in rats

Lead was administered orally to adult male rats at exposure level of 273 or 819 mg/L (0.05% or 0.15% lead acetate, respectively) for 45 days via drinking water. At the end of the exposure period, control and experimental males were mated with untreated females. Of the females mated with treated males, 73.3% in the 0.05% group and 53.33% in the 0.15% group showed copulatory plugs. Significant decrease in number of implantations and pre- and post-implantation loss was also observed in females mated with treated males. Significant decrease in the weight of the reproductive organs, reduction in epididymal sperm count, motile sperm and viable sperm were observed in lead-exposed rats indicating decreased sperm production and deteriorated sperm quality. Significant decrease in serum testosterone levels were also observed in treated rats indicating decreased steroidogenesis. The decreased serum testosterone levels and deteriorated sperm quality might be responsible for the suppressed reproduction in rats after exposure to lead.

INHIBITORY ACTIONS OF LEAD ON STEROIDOGENESIS IN MA-10 MOUSE LEYDIG TUMOR CELLS

The inhibitory actions of Pb on StAR protein expression and steroidogenic enzymes on steroidogenesis were analyzed by both linear and 2nd order polynomial models in MA-10 mouse Leydig tumor cells. Lead acetate, ranging from 10(-8) M to 10(-5) M, caused inhibitory effects on StAR protein expression and steroidogenic enzymes. The correlation coefficients R2 (linear vs. 2nd order polynomial) were 0.93 vs. 0.96 for human chorionic gonadotropin-stimulated progesterone production, 0.38 vs. 0.79 for dibutyryl cAMP-stimulated progesterone production, 0.03 vs. 0.99 for the expression of StAR protein, 0.6 vs. 0.92 for P450 side-chain cleavage enzyme activity, and 0.52 vs. 0.96 for 3beta-hydroxysteroid dehydrogenase activity. Thus, 2nd order polynomial model showed higher correlation coefficients than the linear model for predicting inhibitory actions of Pb on StAR protein expression and the activities of steroidogenic enzymes after exposure of Pb on steroidogenesis in MA-10 cells.

The effects of metals as endocrine disruptors

This review reports current knowledge regarding the roles that cadmium (Cd), mercury (Hg), arsenic (As), lead (PB), manganese (Mn), and zinc (Zn) play as endocrine-disrupting chemicals (EDCs). The influence of these metals on the endocrine system, possible mechanisms of action, and consequent health effects were correlated between experimental animals and humans. Analysis of the studies prompted us to identify some critical issues related to this area and showed the need for more rigorous and innovative studies. Consequently, it was recommended that future studies need to: (1) identify the mechanisms of action, because at the present time only a few have been elucidated-in this context, the possible presence of hormesis need to be determined, as currently this was reported only for exposure Cd and As; (2) study the possible additive, synergistic, or antagonistic effects on the endocrine system following exposure to a mixture of metals since there is a lack of these studies available, and in general or occupational environments, humans are simultaneously exposed to different classes of xenobiotics, including metals, but also to organic compounds that might also be EDCs; (3) assess the potential adverse effects on the endocrine system of low-level exposures to metals, as most of the information currently available on EDCs originates from studies in which exposure levels were particularly high; and (4) assess the effects on the endocrine and reproductive systems of other metals that are present in the general and occupational environment that have not yet been evaluated.

Chronic effects of low lead levels on sperm quality, gonadotropins and testosterone in albino rats

The current study evaluates the impact of low or moderate levels of lead acetate (PbAc) on sperm parameters, gonadotropins (FSH, LH) and testosterone. Adult albino wistar male rats were allocated to five groups and given 0%, 0.025%, 0.05%, 0.1% and 0.3% PbAc in distilled drinking water for 24 weeks. There was no change in body weight gain and in absolute or relative weight of testes, epididymides and seminal vesicles. The ventral prostate weight was decreased in groups exposed to 0.05%, 0.1% and 0.3% PbAc without statistically significant differences. Sperm velocity was decreased in all treated groups while reduction of sperm motility was observed in rats exposed to 0.05%, 0.1% and 0.3% PbAc without statistically significant differences compared to the control group. However, there was a significant increase greater than 100% in the total percentage of abnormal sperm in groups treated with 0.1% (p<0.01) and 0.3% PbAc (p<0.05).The frequency of dead sperm was significantly increased only in the 0.3% PbAc group (p<0.01). Significant increases in frequencies of amorphous head sperm (p<0.01) and abnormal tails (p<0.01) were found in the group exposed to 0.1% PbAc, while the frequency of neck abnormalities was increased in the high-lead-exposed group (p<0.01). The levels of LH and FSH were not significantly affected after lead treatment and significant increase in serum testosterone level was noted only in animals administered 0.05% PbAc (p<0.01). In conclusion, our results reveal that some sperm parameters were altered at low or moderate lead concentrations with no obvious alteration of hypothalamic-pituitary function. The increase of testosterone level observed suggests that lead may target testicular function.

Effects of lead exposure on sperm concentrations and testes weight in male rats: a meta-regression analysis

The correlation between exposure to lead (PB) and sperm concentrations and testes weight are important in risk assessment of metal toxicity to male reproductive functions. The authors carried out two systematic reviews and meta-analyses of rats. In addition, a meta-regression analysis was taken to explore a dose-response relationship between the mean difference of testes weight (MD(testes)) and available confounding factors. Data were obtained from computerized literature searches of several databases from their inception through December 2005. The reference lists of identified articles were examined further for relevant articles. The authors identified 6 and 12 studies, separated into 16 and 28 subgroups, in the two meta-analyses. The authors conducted random- or fixed-effect models toward the effect size. Heterogeneity between study results was explored through chi-square tests and meta-regression. Results showed that a decrease in sperm concentrations was found as low as mean difference of sperm concentrations (MD(sperm)) = 30.9 and 95%CI = (25.43-36.37) in a fixed-effect model or MD(sperm) = 35.47 and 95%CI = (15.27-55.68) in a random-effect model after Pb exposure. Similarly, a significantly lower testes weight was also evident: MD(testes) = 0.033 and 95%CI = (0.021-0.046) in a fixed-effect model or MD(testes) = 0.047 and 95%CI = (0.0044-0.089) in a random-effect model. In the meta-regression analysis, two confounders, age and body weight, explained part of the observed heterogeneity. The body weight after Pb exposure was inversely associated with MD(testes). These findings support the notion that Pb exposure produced decreased sperm concentrations and testes weight in rats.

Reproductive potential of male Portan rats exposed to various levels of lead with regard to zinc status

The present study was designed to elucidate the mechanisms accounting for disruption of the normal function of the testis exposed to various levels of Pb. Three different doses of Pb (10, 50, 200mg Pb/kg body weight per d) were given orally to male Portan rats (groups 2, 3, 4). Zn (1mg Zn/kg body weight per d) was also given with Pb (50mg Pb/kg body weight per d) in group 5. Treatments continued for 3 months. Plasma luteinizing hormone and follicle-stimulating hormone concentrations were found to be decreased in Pb-exposed rats. This was in turn reflected in the appreciable decline in fertility status. In cell kinetic studies, significant declines in various cell populations (preleptotene, pachytene, young (step 7) spermatids and mature (step 19) spermatids) were seen. However, in group 5 after Zn supplementation, hormone levels, cell numbers and fertility status were found to be close to normal. It is concluded that Pb might act at maturation level to cause conspicuous degenerative changes in the testis; Zn supplementation protected against these effects.

Inhibitory mechanisms of lead on steroidogenesis in MA-10 mouse Leydig tumor cells

Lead can directly influence Leydig cell steroidogenesis, which results in reduction of testosterone and causes low sperm counts in human beings and animals. This study investigated the effect of 6 h incubation time of lead on steroidogenesis in MA-10 mouse Leydig tumor cells. Lead acetate, ranging from 10(-8) to 10(-5) M, caused profounder inhibitory effects on human chorionic gonadotropin (hCG)- and dibutyryl cAMP (dbcAMP)-stimulated progesterone production for 6 h in MA-10 mouse Leydig tumor cells. Lead acetate significantly inhibited hCG- and dbcAMP-stimulated progesterone production from 20 to 35% in MA-10 cells at 6 h. Lead suppressed the expression of steroidogenesis acute regulatory (StAR) protein from 30 to 55%. Moreover, the activities P450 side-chain cleavage (P450scc) enzyme and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) were reduced by lead from 15 to 25%. Thus, after 6 h exposure to lead caused profounder inhibitory effects on StAR protein expression and steroidogenic enzymes and then progesterone production compared to 2- or 3-h lead treatments in MA-10 mouse Leydig tumor cells.

Concentration dependency in lead-inhibited steroidogenesis in MA-10 mouse Leydig tumor cells

Lead acetate (Pb) decreases the expression of steroidogenic acute regulatory (StAR) protein and the enzymatic activities of cytochrome P-450 side-chain cleavage (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) in a concentration-dependent manner in Leydig cells at 2 h, the duration of submaximal inhibition. This study was undertaken at 3 h of Pb incubation to compare the effects at maximal metal inhibition of steroidogenesis. Quantitatively a 3-h Pb incubation with MA-10 cells resulted in higher decreases in human chorionic gonadotropin (hCG)-stimulated progesterone production, expression of StAR protein, and the activity of 3beta-HSD compared to 2 h. In contrast, lead inhibited dibutyryl cAMP (dbcAMP)-stimulated progesterone production but lacked this effect at 2 h. Surprisingly, Pb at 3 h of incubation did not affect P450scc enzyme activity, yet this enzymatic activity was inhibited at 2 h. Data indicate that incubation time is a factor in Pb-induced alterations in MA- 10 cell steroidogenesis.

Role of early GnRH administration in sexual behavior disorders of rat pups perinatally exposed to lead

The effects of maternal exposure to lead (Pb) during the perinatal (1% and 0.1% Pb) periods of sexual brain differentiation were studied in adult male offspring. Maternal Pb levels were measured after treatment. Behavioral (open field and sexual behavior), physical (sexual maturation, body and organ weights), and biochemical (testosterone levels and hypothalamic monoamine and respective metabolite levels) data were assessed in perinatally exposed offspring. The effects of gonadrotopin-releasing hormone (GnRH) administration to pups at birth on puberty and sexual behavior were also investigated in offspring postnatally exposed to the metal. Results showed that perinatal administration of the two Pb concentrations did not modify maternal weight gain; 1% Pb exposure reduced offspring body weight during the 7 days of treatment while no changes were observed after 0.1% Pb exposure; neither Pb concentration altered offspring sexual maturation; the higher Pb concentration improved sexual behavior while the 0.1% concentration reduced it; exposure to 0.1% Pb caused decrease in testis weight, an increase in seminal vesicle weight and no changes in plasma testosterone levels; hypothalamic VMA levels were increased compared to the control group; GnRH administration reversed the effects of 0.1% Pb administration on male sexual behavior. These results show that perinatal exposure to Pb had a dose-dependent effect on the sexual behavior of rats and that a decrease in GnRH source in the offspring was probably involved in the reduction of their sexual performance.

Effect of lead on Sertoli-germ cell coculture of rat

Mixed cultures of Sertoli and germ cells were prepared from rat testes and their response to lead (Pb) was studied. Cultures consisted of a monolayer of Sertoli cells to which clusters of germ cells were attached. The effect of Pb added as lead acetate was tested at 0.0, 0.4, 4.0 and 40.0 microM for 24 and 48 h intervals. Addition of Pb to the culture medium caused germ cells to progressively detach from the Sertoli cell monolayer into the medium in a concentration and duration dependent manner Viability of the detached cells as judged by trypan blue exclusion test showed a decrease with increase in time and concentration of Pb. Significant leakage of lactate dehydrogenase (LDH) was recorded in the culture media only at the higher concentrations of 4.0 and 40.0 microM. Thus Pb at the doses tested induced cytotoxicity in rat Sertoli-germ cell coculture.

Endocrine-disrupting chemicals: prepubertal exposures and effects on sexual maturation and thyroid function in the male rat. A focus on the EDSTAC recommendations. Endocrine Disrupter Screening and Testing Advisory Committee

Puberty in mammalian species is a period of rapid interactive endocrine and morphological changes. Therefore, it is not surprising that exposure to a variety of pharmaceutical and environmental compounds has been shown to dramatically alter pubertal development. This concern was recognized by the Endocrine Disrupter Screening and Testing Advisory Committee (EDSTAC) that acknowledged the need for the development and standardization of a protocol for the assessment of the impact of endocrine-disrupting compounds (EDC) in the pubertal male and recommended inclusion of an assay of this type as an alternative test in the EDSTAC tier one screen (EPA, 98). The pubertal male protocol was designed to detect alterations of pubertal development, thyroid function, and hypothalamic-pituitary-gonadal (HPG) system peripubertal maturation. In this protocol, intact 23-day-old weanling male rats are exposed to the test substance for 30 days during which pubertal indices are measured. After necropsy, reproductive and thyroid tissues are weighed and evaluated histologically and serum taken for hormone analysis. The purpose of this review was to examine the available literature on pubertal development in the male rat and evaluate the efficacy of the proposed protocol for identifying endocrine-disrupting chemicals. The existing data indicate that this assessment of puberty in the male rat is a simple and effective method to detect the EDC activity of pesticides and toxic substances.

Chelation therapy in aluminum-loaded rats: influence of age

The influence of age at which aluminum (Al) exposure was initiated on the efficacy of chelation therapy in mobilizing Al was investigated in two groups of male rats exposed to this element at two different stages of the life cycle. Young (21 days old) and old (18 months) rats were exposed to 0 and 50 mg Al/kg/day administered as Al nitrate in drinking water for a preliminary period of 14 days followed by a period of 100 days, in which Al-exposed animals received 100 mg Al/kg/day. At the end of the period of exposure, Al-loaded rats in each age group were given one of the following treatments: s.c. deferoxamine (DFO), oral 1,2-dimethyl-3-hydroxypyrid-4-one (L1) and 1-(p-methylbenzyl)-2-ethyl-3-hydroxypyrid-4-one (MeBzEM) at doses of 0.89 mmol/kg/day for 5 consecutive days. Another group of Al-exposed rats received a concurrent administration of s.c. DFO and oral L1 both at 0.45 mmol/kg/day. During chelation therapy urines were collected daily. Control groups included rats exposed and unexposed to Al. Oral administration of L1 was the most effective treatment in enhancing urinary Al excretion in both age groups of Al-loaded rats. This beneficial effect was similar for old and young animals. Concurrent administration of DFO and L1 had no advantages over the use of either single agent, while MeBzEM was not effective in mobilizing Al from Al-exposed rats.

Assessment of aggression, sexual behavior and fertility in adult male rat following long-term ingestion of four industrial metals salts

1. The effect of long-term ingestion of the industrial metals salts, manganese sulfate, aluminum chloride, lead acetate and copper chloride was investigated on aggression, sexual behavior and fertility in male rat. Adult male rats ingested solutions of these salts along with drinking water at a concentration of 1000 p.p.m. for 12 weeks. 2. Male rat sexual behavior was suppressed after the ingestion of manganese sulfate, aluminum chloride, lead acetate and copper chloride. The ingestion of solutions of these salts markedly prolonged the intromission and ejaculation latencies. Aluminum chloride and copper chloride reduced the copulatory efficiency. 3. Male rat aggression was also abolished after the ingestion of manganese sulfate, aluminum chloride, lead acetate and copper chloride. The ingestion of solutions of these salts markedly suppressed lateralizations, boxing bouts, fight with stud male and ventral presenting postures. 4. Fertility was reduced in male rats ingested with lead acetate. The total number of resorptions was increased in female rats impregnated by males ingested with manganese sulfate and lead acetate. 5. Body, absolute or relative testes, seminal vesicles weights were dropped in adult male rats ingested with manganese sulfate, aluminum chloride, lead acetate and copper chloride. However, the absolute or relative preputial gland weights were not affected. Collectively, these results suggest that the long-term ingestion of manganese sulfate, aluminum chloride, lead acetate and copper chloride would have adverse effects on sexual behavior, territorial aggression, fertility and the reproductive system of the adult male rat.

Effects of vitamin E and/or C on reactive oxygen species-related lead toxicity in the rat sperm

This study was undertaken to investigate whether treatment with vitamin E (VE) and/or vitamin C (VC) protects rat sperm by inhibiting reactive oxygen species generation induced by lead (Pb) exposure. Male Sprague-Dawley rats were assigned to the following five groups: vitamin-unsupplemented; 150 mg VE/kg chow supplemented; 300 mg VE/kg chow supplemented; 500 mg VC/l drinking water supplemented and 150 mg VE/kg chow + 500 mg VC/l drinking water supplemented group. Rats in each group were divided into Pb-unexposed and Pb-exposed subgroups, received weekly intraperitoneal injection of 10 mg sodium acetate or 10 mg Pb acetate/kg for 6 weeks, respectively. The blood and sperm Pb levels were analyzed by graphite furnace atomic absorption spectrophotometer. Chemiluminescence was measured to evaluate the generation of sperm reactive oxygen species (ROS). Motility and sperm-oocyte penetration rate (SOPR) were measured. In Pb-unexposed rats, epididymal sperm counts, motility, ROS, and SOPR were not different in the five supplemented groups. Lead exposure might decrease the defense capacity of sperm to the oxidative stress and therefore elevate the ROS generation, reduce sperm motility, and reduce SOPR. Supplementation with VE and/or VC reduced ROS generation, prevented loss of motility and capacity of oocyte penetration in Pb-exposed rats. This study suggests that supplementation with VE and/or VC inhibits Pb-related ROS generation, protects spermatozoa from loss of motility and oocyte penetration capability.

Male reproductive toxicity of lead in animals and humans. ASCLEPIOS Study Group

OBJECTIVE

To critically review the literature on male reproductive toxicity of lead in animals and humans.

METHODS

A systematic literature search identified a total of 32 experimental studies in animals and 22 epidemiological studies, one case report on humans and five review articles or documents. The studies were evaluated by paying attention mainly to sample size, study design, exposure, and dose characterisation, analytical method standardisation, and quality assurance.

RESULTS

Several studies on rats and other rodents indicated that blood lead concentrations > 30-40 micrograms/dl were associated with impairment of spermatogenesis and reduced concentrations of androgens. However, other animal studies, mainly about histopathological, spermatozoal, and hormonal end points, indicated that certain species and strains were quite resistant to the reproductive toxicity of lead and that different testicular lead concentrations could account for these differences. The human studies focused mainly on semen quality, endocrine function, and birth rates in occupationally exposed subjects, and showed that exposure to concentrations of inorganic lead > 40 micrograms/dl in blood impaired male reproductive function by reducing sperm count, volume, and density, or changing sperm motility and morphology. No relevant effects were detected on endocrine profile.

CONCLUSION

Several factors make it difficult to extrapolate the animal data to the human situation. The difficulties are mainly due to differences between species in reproductive end points and to the level of exposure. Concentrations of blood lead > 40 micrograms/dl seemed to be associated with a decrease in sperm count, volume, motility, and morphological alterations and a possible modest effect on endocrine profile. Dose-response relation, in particular at a threshold level, is poorly understood, and site, mode, or mechanism of action are unknown. Also, the effects were not always the same or associated in the same on sperm count and concentration. Some methodological issues and indications for future studies are discussed.

Effects of lead exposure on GnRH and LH secretion in male rats: response to castration and alpha-methyl-p-tyrosine (AMPT) challenge

Animal and clinical studies suggest that lead exposure disrupts the hypothalamic-pituitary axis. To define more precisely the toxic action of lead on the hypothalamic-pituitary unit, a series of in vivo and in vitro experiments were performed. The first experiment was designed to determine whether lead exposure exerts an inhibitory effect on GnRH secretion as reflected by an enhanced inhibition of luteinizing hormone (LH) secretion in response to the tyrosine hydroxylase inhibitor methyl-p-tyrosine (AMPT). In the control animals, the AMPT dose had no significant effect on LH secretion, whereas LH fell significantly in the lead-treated animals. In experiments designed to evaluate the effects of lead exposure on the pattern of pulsatile release of gonadotropins castrated control and lead-dosed animals were cannulated, and serial blood sampling was performed. Baseline LH and follicle-stimulating hormone values were not statistically different between the control and lead-treated group. There were no significant differences noted in pulsatile patterns when the data were analyzed as groups. Pituitary cells harvested from lead-treated animals released significantly more LH that did the control animals. These data are consistent with the hypothesis that the signals between the hypothalamus and pituitary gland are disrupted by lead exposure in the intact animal. However, the lead-exposed castrated rat's hypothalamic-pituitary unit is able to adapt to the toxic effects of lead.

The effect of age on aluminum retention in rats

The present study was designed to assess potential changes in aluminum (Al) retention during advanced age. Young (21 day old), adult (8 months), and old (16 months) rats were exposed to 0, 50, and 100 mg Al/kg/day administered as aluminum nitrate in drinking water for a period of 6.5 months. Urinary Al levels were measured after 3 and 6.5 months of Al exposure. Organ weights and tissue Al concentrations were examined at 6.5 months of Al administration. Differences in the tissue accumulation of Al with age included higher liver, kidneys, spleen, bone and testes levels in old rats than in tissues of both young or adult animals. In contrast, brain concentrations were higher in young rats. Urinary Al levels of young, adult or old Al-exposed rats showed different trends at 6.5 months of Al exposure: compared with young values adult values declined, while those of old rats tended to increase further. The current results show that tissue Al retention patterns may be significantly altered depending on the age at Al exposure. This finding may be of concern for future investigations on the potential role of Al in certain neurological disorders.

Lead affects steroidogenesis in rat Leydig cells in vivo and in vitro

Lead is known to impede the male reproductive function, however, the mechanisms through which the adverse effects are mediated are not clearly elucidated. In order to get insight into those mechanisms, we have examined the effects of lead on the biosynthesis of steroid hormones by Leydig cells in the rat. To determine whether lead has a direct action on Leydig cells, we have compared the concentrations of testosterone secreted by Leydig cells in ex vivo experiments after animals had been injected with high doses of lead and in vitro experiments with Leydig cells from normal rats maintained in culture in presence or absence of lead. In ex vivo experiments male Spargue-Dawley rats were injected i.p. with lead acetate (8 mg lead/kg/day, 5 days a week for 5 weeks) or with sodium acetate. Testosterone production by Leydig cells isolated and maintained in culture for 48 h was then assessed under basal conditions or after stimulation by human chorionic gonadotrophin (hCG). Both basal and hCG-stimulated testosterone production dropped by 59% and 37%, respectively, with Leydig cells from lead-exposed rats. For in vitro experiments, cultures of Leydig cells from control rats were exposed to various concentrations of lead acetate for different periods. Dose and time-dependent reductions of testosterone level were observed in the culture medium. The effective doses of hCG for maximal and half-maximal testosterone production did not change, indicating that the sensitivity of Leydig cells to hCG was not impaired by exposure to lead in vitro. Progesterone production was also decreased after this exposure. The negative effect of lead on testosterone and progesterone production was correlated with the lower expression of the enzymes cytochromes P450scc (CYP11A1) and P450c17 (CYP17) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) involved in steroid hormone biosynthesis, as shown by immunohistochemistry. Ultrastructural alterations of the smooth endoplasmic reticulum observed after lead administration might be correlated with the lower expression of the microsomal enzymes P450c17 and 3 beta-HSD. Our results indicate that lead can adversely affect the Leydig cell function by impairing directly steroidogenesis.

Impairment of testicular endocrine function after lead intoxication in the adult rat

To clarify the mechanism of the action of lead on male reproductive function, adult male rats were injected intraperitoneally (i.p.) with lead acetate (8 mg/kg/day of lead), 5 days a week for 35 days. Despite this high dose, germ cells and Sertoli cells did not appear to be major targets of lead. However, lead determination in the reproductive organs showed that the accessory sex glands are such a target. Epididymal function was unchanged. In lead-exposed rats, plasma and testicular testosterone dropped by about 80%, but plasma luteinizing hormone (LH) only dropped by 32%. After luteinizing hormone releasing hormone (LHRH) stimulation of the pituitary, the plasma LH level reached the control one, but plasma testosterone remained significantly reduced by 37%. The sharp decrease in the testosterone:LH ratio in lead-exposed rats, combined with the significant reduction of intertubular tissue volume in the testes, indicate impaired Leydig cell function.

Destruction of preantral follicles in adult rats by 4-vinyl-1-cyclohexene diepoxide

4-vinyl-1-cyclohexene diepoxide (VCD) is known to destroy oocytes in ovaries of immature rats. Since ovaries functionally differ between immature and adult animals, we examined the effect of VCD on oocytes in adult rats. Adult (58 days) and immature (28 days) rats were injected daily (30 days) with vehicle or VCD. Each group contained 10 rats. During this time, cyclicity was determined daily by vaginal cytology. Animals were terminated on day 31 and tissues were collected. Oocytes were counted; livers, spleens, and uteri were weighed. VCD reduced the number of regular estrous cycles/30 days in adults, but not immature rats (n = 20, P < 0.05). VCD reduced the number of oocytes in adult and immature rats (n = 20, P < 0.05). Liver, spleen, or ovarian weights were not affected by VCD in either group. VCD reduced uterine weight in adult (n = 20, P < 0.05) but not in immature rats. These results demonstrate that VCD decreases uterine weight in adult rats and as with immature rats, selectively destroys oocytes in ovaries of adults.

Effects of lead poisoning of rats during pregnancy on the reproductive system and fertility of their offspring

1. The effects of lead poisoning during pregnancy were tested on female Sprague-Dawley rats that inhaled 5 mg m-3 lead oxide for 13 days during gestation. At the end of gestation, the respective blood lead levels of dams and fetuses were 71.1 and 83.2 micrograms 100 ml-1, indicating lead poisoning. 2. In the 90 day-old male offspring of the exposed dams, testis weight and histology, and epididymal weight and sperm reserve, were all similar to those of control males. Spermatozoa mobility and morphology were normal. 3. Also similar to control values were the pituitary weight in these male offspring, their plasma FSH, LH and testosterone levels, and the weight of their ventral prostate and seminal vesicles, the targets of the sexual hormones. 4. When male and female offspring of exposed dams were mated, their fertility was normal, with no increase in prenatal death or malformations, and no changes in the size or sex ratio of litters. 5. These results indicate that, under our experimental conditions, lead oxide inhalation by rats during pregnancy did not perturb reproductive function in their male offspring.

Effect of ingestion and inhalation of lead on the reproductive system and fertility of adult male rats and their progeny

Ninety-day-old Sprague-Dawley rats were intoxicated for 70 d with lead, given either as 0.3% lead acetate in drinking water or by inhalation as 5 mg m-3 lead oxide. Direct or transmitted lead toxicity for the male reproductive system was assessed in the rats and their offspring from pituitary and genital organ weights after exposure, the numbers of Sertoli and germ cells, the number, motility and morphology of epididymal spermatozoa, the levels of plasma testosterone, LH and FSH and fertility tests. Whole blood lead levels were similar after lead ingestion and after inhalation (58.0 +/- 1.7 micrograms dl-1 vs. 51.1 +/- 1.8 micrograms dl-1). Lead acetate ingestion did not affect the reproductive system or fertility of rats. Inhalation of lead oxide did not affect fertility either, but seminal vesicle weight dropped significantly, which might suggest an alteration in the pattern of testosterone secretion. In the male progeny of sires that inhaled lead, the number of epididymal spermatozoa decreased but this did not interfere with fertility. Our results show that for the doses studied, lead inhalation and lead ingestion do not produce strikingly different effects on the male rat's reproductive system. Differences between the present findings and those of others might be due to difference of rat strain or of age at exposure.