Prolactin changes as a consequence of chemical exposure

Lead, Arsenic, and Manganese Metal Mixture Exposures: Focus on Biomarkers of Effect

The increasing exposure of human populations to excessive levels of metals continues to represent a matter of public health concern. Several biomarkers have been studied and proposed for the detection of adverse health effects induced by lead (Pb), arsenic (As), and manganese (Mn); however, these studies have relied on exposures to each single metal, which fails to replicate real-life exposure scenarios. These three metals are commonly detected in different environmental, occupational, and food contexts and they share common neurotoxic effects, which are progressive and once clinically apparent may be irreversible. Thus, chronic exposure to low levels of a mixture of these metals may represent an additive risk of toxicity. Building upon their shared mechanisms of toxicity, such as oxidative stress, interference with neurotransmitters, and effects on the hematopoietic system, we address putative biomarkers, which may assist in assessing the onset of neurological diseases associated with exposure to this metal mixture.

Methylmercury inhibits prolactin release in a cell line of pituitary origin

Heavy metals, such as methylmercury, are key environmental pollutants that easily reach human beings by bioaccumulation through the food chain. Several reports have demonstrated that endocrine organs, and especially the pituitary gland, are potential targets for mercury accumulation; however, the effects on the regulation of hormonal release are unclear. It has been suggested that serum prolactin could represent a biomarker of heavy metal exposure. The aim of this study was to evaluate the effect of methylmercury on prolactin release and the role of the nitrergic system using prolactin secretory cells (the mammosomatotroph cell line, GH3B6). Exposure to methylmercury (0-100 μM) was cytotoxic in a time- and concentration-dependent manner, with an LC₅₀ higher than described for cells of neuronal origin, suggesting GH3B6 cells have a relative resistance. Methylmercury (at exposures as low as 1 μM for 2 h) also decreased prolactin release. Interestingly, inhibition of nitric oxide synthase by N-nitro-L-arginine completely prevented the decrease in prolactin release without acute neurotoxic effects of methylmercury. These data indicate that the decrease in prolactin production occurs via activation of the nitrergic system and is an early effect of methylmercury in cells of pituitary origin.

Protective effect of prolactin against methylmercury-induced mutagenicity and cytotoxicity on human lymphocytes

Mercury exhibits cytotoxic and mutagenic properties as a result of its effect on tubulin. This toxicity mechanism is related to the production of free radicals that can cause DNA damage. Methylmercury (MeHg) is one of the most toxic of the mercury compounds. It accumulates in the aquatic food chain, eventually reaching the human diet. Several studies have demonstrated that prolactin (PRL) may be differently affected by inorganic and organic mercury based on interference with various neurotransmitters involved in the regulation of PRL secretion. This study evaluated the cytoprotective effect of PRL on human lymphocytes exposed to MeHg in vitro, including observation of the kinetics of HL-60 cells (an acute myeloid leukemia lineage) treated with MeHg and PRL at different concentrations, with both treatments with the individual compounds and combined treatments. All treatments with MeHg produced a significant increase in the frequency of chromatid gaps, however, no significant difference was observed in the chromosomal breaks with any treatment. A dose-dependent increase in the mitotic index was observed for treatments with PRL, which also acts as a co-mitogenic factor, regulating proliferation by modulating the expression of genes that are essential for cell cycle progression and cytoskeleton organization. These properties contribute to the protective action of PRL against the cytotoxic and mutagenic effects of MeHg.

Hyperprolactinemia and prolactinomas

Any process interfering with dopamine synthesis, its transport to the pituitary gland, or its action at the level of lactotroph dopamine receptors can cause hyperprolactinemia. As described in this article, considering the complexity of prolactin regulation, many factors could cause hyperprolactinemia, and hyperprolactinemia can have clinical effects not only on the reproductive axis. Once any drug effects are excluded, prolactinomas are the most common cause of hyperprolactinemia. The most frequent symptom is hypogonadism in both genders. Medical and surgical therapies generally have excellent results, and most prolactinomas are well controlled or even cured in some cases.

From lead to manganese through mercury: mythology, science, and lessons for prevention

BACKGROUND

Lead (Pb), mercury (Hg), and manganese (Mn) are well-known neurotoxic metals. The knowledge of toxicity was developed through an extensive amount of research, starting with lead and mercury and proceeding today with manganese. Unfortunately, the consequent implementation of preventive measures was generally delayed, causing important negative effects to the exposed populations.

METHODS

A review and historical reconstruction of the research development that yielded modern understanding of lead and mercury neurotoxicity was conducted to derive useful lessons for the prevention of manganese neurotoxicity.

RESULTS

Medieval alchemists named planets and metals from gods since they were already aware of the toxicity and the adverse effects caused by lead and mercury. Historical lessons learned from these two metals may help to avoid the repetition of further mistakes regarding other neurotoxic metals like manganese. The knowledge and experience on the toxicokinetics and toxicodynamics of lead and mercury is useful and valuable to identify a proper approach to "safe" exposure levels for manganese.

CONCLUSIONS

Further information is still needed on the early neurotoxic and neurobehavioral effects after prolonged exposure to very low doses of lead, mercury, and manganese. Nevertheless, according to the precautionary principle, effective preventive measures should be already undertaken to prevent the onset of more severe health effects in the population. This is the most important lesson to be learned and applied from more than 30 years of occupational and environmental neurotoxicology of metals.