Assessment of the male reproductive system in the preweanling rat following Mn3O4 exposure

Manganese-induced effects on testicular trace element levels and crucial hormonal parameters of Hyline cocks

Manganese (Mn) is an essential element required for normal development and reproduction. However, little is known about the reproductive toxicity of Mn in birds. To investigate the Mn-induced toxicity on testicular trace element levels and crucial hormonal parameters on male reproduction in birds, 50-day-old male Hyline cocks were fed either a commercial diet or a Mn-supplemented diet. The changes in contents of copper (Cu), iron (Fe), zinc (Zn), and calcium (Ca) in testis were detected. Hormonal parameters were evaluated including the levels of testosterone (T), luteinizing hormone (LH), follicle-stimulating hormone (FSH), thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) in the serum. The mRNA levels of luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR) were determined in this study. The results showed that Mn was accumulated in testis, and the content of Cu, Fe, Zn, and Ca decreased. Exposure to Mn significantly lowered the content of T, LH, FSH, and the mRNA expression levels of LHR and FSHR. Levels of T3 and T4 appeared with a decreased tendency, and TSH presented no obvious regularity. It indicated that Mn exposure resulted in the disbalance of testicular trace elements and influenced hormone levels in the molecular level, which may be possible underlying reproductive toxicity mechanism induced by Mn.

Tissue Manganese Concentrations in Young Male Rhesus Monkeys following Subchronic Manganese Sulfate Inhalation

High-dose human exposure to manganese results in manganese accumulation in the basal ganglia and dopaminergic neuropathology. Occupational manganese neurotoxicity is most frequently linked with manganese oxide inhalation; however, exposure to other forms of manganese may lead to higher body burdens. The objective of this study was to determine tissue manganese concentrations in rhesus monkeys following subchronic (6 h/day, 5 days/week) manganese sulfate (MnSO(4)) inhalation. A group of monkeys were exposed to either air or MnSO(4) (0.06, 0.3, or 1.5 mg Mn/m(3)) for 65 exposure days before tissue analysis. Additional monkeys were exposed to MnSO(4) at 1.5 mg Mn/m(3) for 15 or 33 exposure days and evaluated immediately thereafter or for 65 exposure days followed by a 45- or 90-day delay before evaluation. Tissue manganese concentrations depended upon the aerosol concentration, exposure duration, and tissue. Monkeys exposed to MnSO(4) at > or = 0.06 mg Mn/m(3) for 65 exposure days or to MnSO(4) at 1.5 mg Mn/m(3) for > or = 15 exposure days developed increased manganese concentrations in the olfactory epithelium, olfactory bulb, olfactory cortex, globus pallidus, putamen, and cerebellum. The olfactory epithelium, olfactory bulb, globus pallidus, caudate, putamen, pituitary gland, and bile developed the greatest relative increase in manganese concentration following MnSO(4) exposure. Tissue manganese concentrations returned to levels observed in the air-exposed animals by 90 days after the end of the subchronic MnSO(4) exposure. These results provide an improved understanding of MnSO(4) exposure conditions that lead to increased concentrations of manganese within the nonhuman primate brain and other tissues.

The mechanism of manganese-induced inhibition of steroidogenesis in rat primary Leydig cells

In previous studies in cultured primary rat Leydig cells, manganese was shown to inhibit hCG-stimulated steroidogenesis of Leydig cells, and the data showed that while the inhibition of StAR protein expression and/or function and mitochondrial dysfunction contribute to the acute reduction of steroidogenesis (2 and 4h manganese treatment), the enzyme activities of P450scc and 3beta-HSD were only reduced after 24h manganese treatment, we hypothesize that there were different mechanisms for its effect at later stage (24 and 48 h manganese treatment). We further our study by examining StAR mRNA level in cultured primary rat Leydig cells to understand if inhibition of StAR protein expression occurs at the level of transcription of StAR mRNA. The cellular ATP content was measured to determine the extent that manganese altered mitochondrial function. Since mitochondria are regulators of Ca(2+) homeostasis, and there are indications that manganese affects intracellular Ca(2+) levels, [Ca(2+)]i was also tested. The effects of manganese on Leydig cell apoptosis and cell cycle distribution were studied to see whether these effects contribute to the reduction of steroidogenesis by manganese at later stage of manganese treatment. In the present study, we demonstrated that manganese could increase [Ca(2+)]i and reduced ATP contents in primary Leydig cells after 4h treatment, while the effects on StAR mRNA level appeared later (24h). Manganese could also induce arrest at the G(0)/G(1) phase cell cycle after 24h manganese treatment and subsequently increased in the sub-G(1) phase DNA contents, indicating induction of apoptosis. Combined with our previous studies, the results indicate that inhibition of StAR protein expression and/or function, mitochondrial dysfunction and disturbance of calcium homeostasis contribute to the adverse effects of manganese on the Leydig cells at the early/immediate stage after treatment (2 and 4h). However, at later stages (24 and 48 h) manganese could arrest the cell cycle and induce apoptosis of primary Leydig cells, StAR mRNA and enzyme activities of P450scc and 3beta-HSD were also reduced, leading to reduced level of steroidogenesis in cultured primary Leydig cells.

The inhibitory effects of manganese on steroidogenesis in rat primary Leydig cells by disrupting steroidogenic acute regulatory (StAR) protein expression

Manganese 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, the effects of manganese on the biosynthesis of testosterone by primary rat Leydig cells were examined. Primary Leydig cells were exposed to various concentrations of manganese chloride for different periods of time. Dose and time-dependent reductions of human chorionic gonadotropin (hCG)-stimulated testosterone level were observed in the culture medium. The expression of Steroidogenic Acute Regulatory (StAR) protein and the activities of P450 side-chain cleavage (P450scc) and 3beta-hydroxysteroid dehydrogenase (3beta-HSD) enzymes were also detected. The expression of StAR protein stimulated by hCG was suppressed by manganese chloride at all concentrations (0.01, 0.1, 1.0 mM) and time points (2, 4, 24, 48 h) tested. Progesterone productions treated with 22R-hydroxycholesterol or pregnenolone were reduced after treated by manganese chloride for 24 or 48 h, respectively. The manganese exposure effect on cell viability was significant at 1.0 and 1.5 mM at 24 h, while at 48 h it was significant at every concentration tested. The decreasing effect of manganese on mitochondrial membrane potential was significant at every concentration measured and every time point tested. These data suggest that manganese exposure for 2 and 4 h inhibited rat primary Leydig cell steroidogenesis by decreasing StAR protein expression while 24 and 48 h exposure of manganese chloride caused adverse effects on both StAR protein and P450scc and 3beta-HSD enzyme activity to reduce steroidogenesis. Manganese may also disrupt StAR expression and/or function secondary to mitochondrial dysfunction.

Effects of oral administration of manganese on the kidneys and urinary bladder of Sprague-Dawley rats

The purpose of this study was to investigate the effect of oral administration of manganese acetate on the kidneys and urinary bladder of Sprague-Dawley (SD) rats. Male and female SD rats (150 to 175 g), 6 weeks old, were administered varying doses of manganese acetate for 63 days by oral gavage. At the end of 63 days, 50% of the animals were sacrificed and kidney tissue was isolated and fixed for histopathological studies (study A). The remaining 50% were cross-mated and dosing ceased. Animals were sacrificed after 2 weeks (study B). Male treated animals were noted to have viscous, gritty urine in the urinary bladder, and the high-dose groups had urinary bladder stones (uroliths). Histopathologically, the most striking lesions were observed in the kidneys and prostate glands of male animals. Mild-to-moderate tubulointerstitial nephritis with tubular proteineous and glomerulosclerosis was observed in animals of all treatment groups. Urolithiasis in the urinary bladder was confirmed in 33% to 66% of treated animals. Female animals did not show a significant difference above controls in renal tissues. Results of this study suggest that male rats are more sensitive to the effects of high levels of manganese given orally than female rats and that the genitourinary structures represent target organs of toxicity.

Effects of long-term exposure to manganese chloride on fertility of male and female mice

The effect of long-term ingestion of manganese (II) chloride tetrahydrate was investigated on fertility of male and female Swiss mice. Adult male or female mice ingested a solution of manganese chloride along with drinking water at concentrations of 1000, 2000, 4000 and 8000 mg/l for 12 weeks. Fertility was significantly reduced in male mice exposed to manganese chloride solution at a concentration of 8000 mg/l, but not at the other concentrations. There were no treatment-related effects on the number of implantation sites, viable fetuses or the number of resorptions in female rats impregnated by males who had ingested manganese chloride. Fertility was not significantly reduced in female mice exposed to manganese chloride solution at all concentrations used in this study. However, the numbers of implantations and viable fetuses were significantly reduced in females exposed to manganese chloride solution at a concentration of 8000 mg/l. There was no significant effect on the number of resorbed fetuses in females exposed to manganese chloride solution compared to their control counterparts. Absolute body weight was not significantly affected in females exposed to manganese chloride solutions. However, ovarian weight was significantly increased in females exposed to manganese chloride solution at concentrations of 4000 and 8000 mg/l. A significant increase in the uterine weight was also observed at all concentrations used in the study. These results indicate that ingestion of manganese chloride by adult male and female mice causes some adverse effects on fertility and reproduction.

Bioaccumulation of manganese and its toxicity in feral pigeons (Columba livia) exposed to manganese oxide dust (Mn3O4)

Manganese tetroxide (Mn3O4) is a product from the combustion of methylcyclopentadienyl manganese tricarbonyl. Exposure to high levels of manganese can lead to serious health effects especially to the central nervous and respiratory systems. Very few studies on the effects of long-term low level exposure to Mn3O4 have been reported. The present study was therefore conducted to examine the bioaccumulation and toxicity of manganese in various organs of feral pigeons (Columba livia) when exposed to low levels of Mn3O4 via inhalation and hence to find any possible relationship between these two parameters. A total of 22 pigeons was exposed to 239 micrograms/m3 of manganese for 7 h/day, 5 days/week for 5, 9, and 13 consecutive weeks. Manganese concentrations in various tissues, e.g., brain (mesencephalon), lung, liver, intestine, pancreas, kidney, muscle, bone, and whole blood, were measured by neutron activation analysis. Various biochemical parameters in blood, e.g., hematocrit, total proteins, glucose, uric acid, alanine aminotransferase, total iron, blood urea nitrogen and triglycerides, were also measured. Manganese concentrations in brain, lung, and bone were significantly higher in Mn3O4-exposed pigeons (0.59, 0.58, and 3.02 micrograms wet tissue, respectively) than in the control group (0.46, 0.19, 1.74 micrograms/g wet tissue, respectively). However, except for total proteins such exposure did not produce any changes in various biochemical parameters which were within the normal values. Thus these results have shown that, despite significant bioaccumulation of manganese in some tissues, no significant toxic effects could be seen.

Occupational hazards for the male reproductive system

The etiology of male infertilities is largely undetermined, and our knowledge of exogenous factors affecting the male reproductive system is still limited. In particular, the role of specific environmental and occupational factors is incompletely elucidated. Various occupational (physical and chemical) agents have been shown to affect male reproductive functions in animals, but large differences in reproductive function and/or xenobiotic handling between species limit extrapolation to humans. When available, human data are often conflicting and, except in a few instances, usually refer to broad and heterogenous occupational categories or to groups of agents (e.g., solvents). It is often difficult to elucidate the role of a single agent because occupational exposure conditions are often complex and various confounding factors related to lifestyle (smoking, alcohol, and diet) or socioeconomic state may also affect sperm quality, fertility, or pregnancy outcomes. The objective of this work is to summarize the main epidemiological and, where relevant, experimental findings pertaining to agents (physical and chemical) encountered in the occupational environment that might affect the male reproductive system (sperm count, motility and morphology, libido, and fertility) and/or related pregnancy outcomes (spontaneous abortion, stillbirth, low birth weight, and birth defects and childhood malignancy in offspring). Some methodological issues related to research on the reproductive effects of toxicants are also discussed briefly.

Effect of cadmium and other metal cations on in vitro Leydig cell testosterone production

In vivo assessment of toxicant action on Leydig cell function is subject to homeostatic mechanisms which make it difficult to determine whether any changes seen in serum testosterone (T) concentration are due to extragonadal endocrine alterations or to a direct effect on the Leydig cell. For example, metal cations administered in vivo have been shown to depress serum T concentration and alter serum concentrations of pituitary hormones in laboratory animals. The studies reported here use a testicular cell culture technique to evaluate Leydig cell testosterone biosynthesis in the presence of several metal cations. To determine the site of toxic action, the Leydig cells were stimulated to produce testosterone by using human chorionic gonadotrophin (hCG), dibutyl cyclic adenosine monophosphate (db-cAMP), or several substrates required for the biosynthesis of testosterone. hCG was chosen because resultant T production requires an intact membrane receptor and db-cAMP was used to test for post LH receptor defects caused by the metals. The other substrates were chosen to isolate the effect of metals on enzymatic pathways. Collagenase dispersed testicular cells (15% Leydig cells) were incubated with metal cations (1 to 5000 microM) for 3 hr in the absence and presence of maximally stimulating concentrations of hCG, db-cAMP, 20 alpha-hydroxycholesterol (HCHOL), or pregnenolone (PREG), and T concentration was determined by radioimmunoassay. In one separate experiment we also tested the effect of the substrates progesterone, 17 alpha-hydroxy-progesterone, and androstenedione on Cd2(+)-treated Leydig cells. The results show no change in Leydig cell viability with any metal cation treatment during the 3-hr incubation. Ca2+, Cr3+, Fe3+, Mg2+, Na+, or Pb2+ had no effect on stimulated testosterone. Dose-response depression in both hCG- and db-cAMP-stimulated T production were seen with Cd2+, Co2+, Cu2+, Hg2+, Ni2+, and Zn2+ treatment. Surprisingly, Cd2+, Co2+, Ni2+, and Zn2+, which caused a depression in hCG- and db-cAMP-stimulated T production, caused significant increases in HCHOL- and PREG-stimulated T production over untreated and similarly stimulated cultures. This indicates that these cations may act at multiple sites within the Leydig cell.

Serum chemistries of Coturnix coturnix japonica given dietary manganese oxide (Mn3O4)

1. Plasma creatinine and inorganic phosphorus were increased in manganese oxide (Mn3O4)-treated adult male Coturnix quail, but BUN, BUN/creatinine ratio, uric acid, and total calcium were decreased. 2. Serum enzymes (alkaline phosphatase, glutamic oxaloacetic transaminase, glutamic pyruvic transaminase, and lactic dehydrogenase) were elevated in Mn3O4-treated adult male Coturnix quail, but creatine phosphokinase was not affected. 3. Dietary Mn3O4 at 5000 ppm did not produce overt signs of toxicosis.