Short- and Long-Term Effects of Suboptimal Selenium Intake and Developmental Lead Exposure on Behavior and Hippocampal Glutamate Receptors in a Rat Model

Lead exerts a depression of neurotransmitter release through a blockade of voltage dependent calcium channels in chromaffin cells

The present work, using chromaffin cells of bovine adrenal medullae (BCCs), aims to describe what type of ionic current alterations induced by lead (Pb2+) underlies its effects reported on synaptic transmission. We observed that the acute application of Pb2+ lead to a drastic depression of neurotransmitters release in a concentration-dependent manner when the cells were stimulated with both K+ or acetylcholine, with an IC50 of 119,57 μM and of 5,19 μM, respectively. This effect was fully recovered after washout. Pb2+ also blocked calcium channels of BCCs in a time- and concentration-dependent manner with an IC50 of 6,87 μM. This blockade was partially reversed upon washout. This compound inhibited the calcium current at all test potentials and shows a shift of the I-V curve to more negative values of about 8 mV. The sodium current was not blocked by acute application of high Pb2+ concentrations. Voltage-dependent potassium current was also shortly affected by high Pb2+. Nevertheless, the calcium- and voltage-dependent potassium current was drastically depressed in a dose-dependent manner, with an IC50 of 24,49 μM. This blockade was related to the prevention of Ca2+ influx through voltage-dependent calcium channels coupled to Ca2+-activated K+-channels (BK) instead a direct linking to these channels. Under current-clamp conditions, BCCs exhibit a resting potential of -52.7 mV, firing spontaneous APs (1-2 spikes/s) generated by the opening of Na+ and Ca2+-channels, and terminated by the activation of K+ channels. In spite of the effect on ionic channels exerted by Pb2+, we found that Pb2+ didn't alter cellular excitability, no modification of the membrane potential, and no effect on action potential firing. Taken together, these results point to a neurotoxic action evoked by Pb2+ that is associated with changes in neurotransmitter release by blocking the ionic currents responsible for the calcium influx.

Lead exposure induced transgenerational developmental neurotoxicity by altering genome methylation in Drosophila melanogaster

Heavy metal toxicity is a significant global health concern, with particular attention given to lead (Pb) exposure due to its adverse effects on cognitive development, especially in children exposed to low concentrations. While Pb neurotoxicity has been extensively studied, the analysis and molecular mechanisms underlying the transgenerational effects of Pb exposure-induced neurotoxicity remain poorly understood. In this study, we utilized Drosophila, a powerful developmental animal model, to investigate this phenomenon. Our findings demonstrated that Pb exposure during the developmental stage had a profound effect on the neurodevelopment of F0 fruit flies. Specifically, we observed a loss of correlation between the terminal motor area and muscle fiber area, along with an increased frequency of the β-lobe midline crossing phenotype in mushroom bodies. Western blot analysis indicated altered expression levels of synaptic vesicle proteins, with a decrease in Synapsin (SYN) and an increase in Bruchpilot (BRP) expression, suggesting changes in synaptic vesicle release sites. These findings were corroborated by electrophysiological data, showing an increase in the amplitude of evoked excitatory junctional potential (EJP) and an increase in the frequency of spontaneous excitatory junctional potential (mEJP) following Pb exposure. Importantly, our results further confirmed that the developmental neurotoxicity resulting from grandparental Pb exposure exhibited a transgenerational effect. The F3 offspring displayed neurodevelopmental defects, synaptic function abnormalities, and repetitive behavior despite lacking direct Pb exposure. Our MeDIP-seq analysis further revealed significant alterations in DNA methylation levels in several neurodevelopmental associated genes (eagle, happyhour, neuroglian, bazooka, and spinophilin) in the F3 offspring exposed to Pb. These findings suggest that DNA methylation modifications may underlie the inheritance of acquired phenotypic traits resulting from environmental Pb exposure.

Maternal suboptimal selenium intake and low-level lead exposure affect offspring's microglial immune profile and its reactivity to a subsequent inflammatory hit

Micronutrients such as selenium (Se) are essentials since prenatal life to support brain and cognitive development. Se deficiency, which affects up to 1 billion people worldwide, can interact with common adverse environmental challenges including (Pb), exacerbating their toxic effects. Exploiting our recently validated rat model of maternal Se restriction and developmental low Pb exposure, our aims were to investigate: (i) the early consequences of suboptimal Se intake and low-Pb exposure on neuroinflammation in neonates' whole brains; (ii) the potential priming effect of suboptimal Se and low-Pb exposure on offspring's glial reactivity to a further inflammatory hit. To these aims female rats were fed with suboptimal (0.04 mg/kg; Subopt) and optimal (0.15 mg/kg; Opt) Se dietary levels throughout pregnancy and lactation and exposed or not to environmentally relevant Pb dose in drinking water (12.5 µg/mL) since 4 weeks pre-mating. We found an overall higher basal expression of inflammatory markers in neonatal brains, as well as in purified microglia and organotypic hippocampal slice cultures, from the Subopt Se offspring. Subopt/Pb cultures were highly activated than Subopt cultures and showed a higher susceptibility to the inflammatory challenge lipopolysaccharide than cultures from the Opt groups. We demonstrate that even a mild Se deficiency and low-Pb exposure during brain development can influence the neuroinflammatory tone of microglia, exacerbate the toxic effects of Pb and prime microglial reactivity to subsequent inflammatory stimuli. These neuroinflammatory changes may be responsible, at least in part, for adverse neurodevelopmental outcomes.

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.