Behavioral and neurochemical effects in mice after one-generation exposure to low doses of manganese: Focus on offspring development.

The risk of exposure to toxic metals is a known concern to human populations. The overexposure to Mn can lead to a pathological condition, with symptoms similar to Parkinson's disease. Although toxicity of Mn has been reported, studies in neonates are scarce but necessary, as Mn can cross biological barriers. The present study evaluated if chronic perinatal exposure to Mn at low doses lead to neurotoxic effects in mice, after direct and indirect exposure. Couples of mice were exposed to Mn (0.013, 0.13, and 1.3 mg kg-1.day-1) for 60 days prior to mating, as well as during gestation and lactation. The offspring was distributed into two groups: animals that were not exposed after weaning - parental exposure only (PE); and animals subject to additional 60-day exposure through gavages after weaning - parental and direct exposure (PDE). Neurological effects were evaluated by Mn quantification, behavior tests and biochemical markers in the brain. PDE animals had alterations in short/long-term memory and increased anxiety-like behavior. Exposure to Mn triggered a decrease of glutathione-s-transferase and increase of cholinesterase activity in different regions of the brain. These findings highlight the risk of exposure to low doses of Mn over a generation and at early stages of development.

Evaluation of testicular structure in mice after exposure to environmentally relevant doses of manganese during critical windows of development.

Despite being an essential trace element with great importance for vital metabolic activities, the manganese (Mn) can also cause damage to organ systems. However, data on the effect of this metal on the male reproductive system are limited, especially using relevant doses to human exposure. The present study aimed to evaluate and compare the effects of Mn exposure on the testicular structure of mice. Three experiments were conducted: (I) direct exposure to realistic doses (0.013, 0.13, and 1.3 mg/kg/day of MnCl2); (II) parental and direct exposure to realistic doses (as in experiment I), where the animals were exposed during intrauterine development and from lactation until reproductive maturity; (III) direct exposure to high doses (15, 30, and 60 mg/kg/day of MnCl2). Biometric, histopathological, histomorphometric and stereological parameters of the testis were evaluated, in addition to sperm morphology. Bioinformatic analyses were performed to identify potential Mn binding sites in 3ß-HSD and P450ssc, as well as their protein-protein interaction network. The results obtained were compared using the integrated biomarker response index (IBR). There was an increase of seminiferous tubules pathologies in all experimental conditions tested, with effects on tubular volume, as well as a reduction in tubular diameter. The IBR analyses showed that parental and direct exposure had a significant negative effect on the testicular structure due to the exposure of this metal to sensitive periods of animal development. This study suggests that Mn has the potential to alter the morphological parameters of the testes, affecting the spermatogenesis in mice.

Evaluation of Mn exposure in the male reproductive system and its relationship with reproductive dysfunction in mice.

Manganese (Mn) is essential for animal development and homeostasis. However, anthropogenic activities increase the concentration of Mn in the environment and lead to increased risk of exposure to high doses of the metal. Thus, this study aimed to evaluate the effect of high doses of Mn on the male reproductive system of swiss mice. The 22-day old mice were randomly sorted into four groups and exposed to 0 (control), 15, 30 and 60 mg of MnCl2/kg/day, via daily gavages for 45 days. After the exposure, the mice were euthanized and sperm, hormonal and oxidative stress endpoints were evaluated in the testis, seminal vesicle and hypothalamus. Exposure to Mn promoted weight reduction of androgen-dependent organs, as well as alteration of the levels of fecal androgenic metabolites. Sperm parameters were drastically affected in all treated groups and the antioxidants tested (catalase and glutathione-disulfide reductase activities, and non-protein thiols content) decreased in the testis. However, only a few endpoints were altered in the seminal vesicle. For the hypothalamus, there was a reduction in acetylcholinesterase activity, suggesting a neurotoxic potential of Mn. In conclusion, Mn may affect the hypothalamic-gonadal axis by impairing the development of androgen-dependent organs, testicular redox status and Leydig cell maturation.

Multigenerational analysis of the functional status of male reproductive system in mice after exposure to realistic doses of manganese.

The present study aimed to analyze the effect of multigenerational exposure to Mn at realistic doses on the functional quality of the male reproductive system of mice. Females and males (generation F0) were treated for 60 days with MnCl2, via gavage, at the doses of 0, 0.013, 0.13, and 1.3 mg/kg/day. Treatment of F0 dams continued throughout gestation and lactation periods. At the time of weaning, the offspring (F1 generation) was divided into: animals that were not exposed after weaning - parental exposure (PE); and those exposed via parental generation and directly (PDE) for additional 60 days, at the same dose of F0 generation. F0 and F1 males were euthanized for assessment of sperm parameters and redox changes in the reproductive system. There was a decrease in the sperm concentration of the F0 generation. In addition, the sperm parameters of F1 generation were drastically affected. The activity of antioxidant enzymes was significantly reduced in PE animals. It was possible to verify that the biochemical damages were higher in the PE individuals, as demonstrated by the integrated biomarker response index. Our results show that Mn, even at low doses, is able to promote a reduction in sperm quality over a generation.