Lead (Pb) exposure is associated with changes in the expression levels of circulating miRNAS (miR-155, miR-126) in Mexican women

The role of exosome-shuttled miRNAs in heavy metal-induced peripheral tissues and neuroinflammation in Alzheimer's disease

Heavy metal-induced neuroinflammation is a significant pathophysiologic mechanism in Alzheimer's disease (AD). Microglia-mediated neuroinflammation plays a crucial role in the pathogenesis of AD. Multiple miRNAs are differentially expressed in peripheral tissues after heavy metal exposure, and increasing evidence suggests that they are involved in AD progression by regulating microglial homeostasis. Exosomes, which are capable of loading miRNAs and crossing the bloodbrain barrier, serve as mediators of communication between peripheral tissues and the brain. In this review, we summarize the current evidence on the link between miRNAs in peripheral tissues and neuroinflammation in AD after heavy metal exposure and propose a role for miRNAs in the microglial neurodegenerative phenotype (MGnD) of AD. This study will help to elucidate the link between peripheral tissue damage and MGnD-mediated neuroinflammation in AD after heavy metal exposure. Additionally, we summarize the regulatory effects of natural compounds on peripheral tissue-derived miRNAs, which could be potential therapeutic targets for natural compounds to regulate peripheral tissue-derived exosomal miRNAs to ameliorate heavy metal-induced MGnD-mediated neuroinflammation in patients with AD after heavy metal exposure.

Genetic and epigenetic modulations in toxicity: The two-sided roles of heavy metals and polycyclic aromatic hydrocarbons from the environment

This study emphasizes the importance of considering the metabolic and toxicity mechanisms of environmental concern chemicals in real-life exposure scenarios. Furthermore, environmental chemicals may require metabolic activation to become toxic, and competition for binding sites on receptors can affect the severity of toxicity. The multicomplex process of chemical toxicity is reflected in the activation of multiple pathways during toxicity of which AhR activation is major. Real-life exposure to a mixture of concern chemicals is common, and the composition of these chemicals determines the severity of toxicity. Nutritional essential elements can mitigate the toxicity of toxic heavy metals, while the types and ratio of composition of PAH can either increase or decrease toxicity. The epigenetic mechanisms of heavy metals and PAH toxicity involves either down-regulation or up-regulation of some non-coding RNAs (ncRNAs) whereas specific small RNAs (sRNAs) may have dual role depending on the tissue and circumstance of expression. Similarly, decrease DNA methylation and histone modification are major players in heavy metals and PAH mediated toxicity and FLT1 hypermethylation is a major process in PAH induced carcinogenesis. Overall, this review provides the understanding of the metabolism of environmental concern chemicals, emphasizing the importance of considering mixed compositions and real-life exposure scenarios in assessing their potential effects on human health and diseases development as well as the dual mechanism of toxicity via genetic or epigenetic axis.

The interaction between miRNAs and hazardous materials

Toxic agents are broadly present in the environment, households, and workplaces. Contamination of food and drinking water with these agents results in entry of these materials to the body. The crosstalk between these agents and microRNAs (miRNAs) affects pathoetiology of several disorders. These agents can influence the redox status, release of inflammatory cytokines and mitochondrial function. Altered expression of miRNA is involved in the dysregulation of several pathophysiological conditions and signaling pathways. These molecules are also implicated in the adaption to environmental stimuli. Thus, the interactions between miRNAs and toxic materials might participate in the hazardous effects of these materials in the body. This review describes the effects of the toxic materials on miRNAs and the consequences of these interactions on the human health.

Derivation of benchmark doses for male reproductive toxicity in a subacute low-level Pb exposure model in rats

The objectives of the study were to simulate low-level Pb exposure scenario in an animal model and to examine reproductive adverse effects. Based on obtained data, we have performed Benchmark dose (BMD)-response modelling. Male Wistar rats were randomized in seven groups (n = 6): one control and six treated with: 0.1, 0.5, 1, 3, 7, and 15 mg Pb/kg body weight, daily for 28 days by oral gavage. The rats were sacrificed and the blood and testes were used for further analysis of testosterone levels in serum, testicular essential metal levels and histological analysis. The Pb treatment led to a dose-dependent decrease of serum testosterone levels with a negative trend (BMDI 0.17-6.13 mg Pb/kg). Increase of Zn (dose-dependent, BMDI 0.004-19.7 mg Pb/kg) and Cu and a decrease of Mn testicular levels were also detected with unscathed histology of the testes. The presented results might be used in further evaluation of the point of departure in human health risk assessment for Pb.

A critical review on biochar-assisted free radicals mediated redox reactions influencing transformation of potentially toxic metals: Occurrence, formation, and environmental applications

Potentially toxic metals have become a viable threat to the ecosystem due to their carcinogenic nature. Biochar has gained substantial interest due to its redox-mediated processes and redox-active metals. Biochar has the capacity to directly adsorb the pollutants from contaminated environments through several mechanisms such as coprecipitation, complexation, ion exchange, and electrostatic interaction. Biochar's electron-mediating potential may be influenced by the cyclic transition of surface moieties and conjugated carbon structures. Thus, pyrolysis configuration, biomass material, retention time, oxygen flow, and heating time also affect biochar's redox properties. Generally, reactive oxygen species (ROS) exist as free radicals (FRs) in radical and non-radical forms, i.e., hydroxyl radical, superoxide, nitric oxide, hydrogen peroxide, and singlet oxygen. Heavy metals are involved in the production of FRs during redox-mediated reactions, which may contribute to ROS formation. This review aims to critically evaluate the redox-mediated characteristics of biochar produced from various biomass feedstocks under different pyrolysis conditions. In addition, we assessed the impact of biochar-assisted FRs redox-mediated processes on heavy metal immobilization and mobility. We also revealed new insights into the function of FRs in biochar and its potential uses for environment-friendly remediation and reducing the dependency on fossil-based materials, utilizing local residual biomass as a raw material in terms of sustainability.

Lead-induced neurodevelopmental lesion and epigenetic landscape: Implication in neurological disorders

Lead (Pb) was implicated in multiple genotoxic, neuroepigenotoxic, and chromosomal-toxic mechanisms and interacted with varying synaptic plasticity pathways, likely underpinning previous reports of links between Pb and cognitive impairment. Epigenetic changes have emerged as a promising biomarker for neurological disorders, including cognitive disorders, Alzheimer's disease (AD), and Parkinson's disease (PD). In the present review, special attention is paid to neural epigenetic features and mechanisms that can alter gene expression patterns upon environmental Pb exposure in rodents, primates, and zebrafish. Epigenetic modifications have also been discussed in population studies and cell experiment. Further, we explore growing evidence of potential linkage between Pb-induced disruption of regulatory pathway and neurodevelopmental and neurological disorders both in vivo and in vitro. These findings uncover how epigenome in neurons facilitates the development and function of the brain in response to Pb insult.

Early-Life Pb Exposure Might Exert Synapse-Toxic Effects Via Inhibiting Synapse-Associated Membrane Protein 2 (VAMP2) Mediated by Upregulation of miR-34b

Background: Early-life Pb exposure can cause behavioral and cognitive problems and induce symptoms of hyperactivity, impulsivity, and inattention in children. Studies showed that blood lead levels were highly correlated with neuropsychiatric disorders, and effects of neurotoxicity might persist and affect the incidence of neurodegenerative diseases, for example Alzheimer’s disease (AD). Objective: To explore possible mechanisms of developmental Pb-induced neuropsychiatric dysfunctions. Methods: Children were divided into low blood lead level (BLL) group (0–50.00μg/L) and high BLL group (>  50.00μg/L) and blood samples were collected. miRNA array was used to testify miRNA expression landscape between two groups. Correlation analysis and real-time PCR were applied to find miRNAs that altered in Pb and neuropsychiatric diseases. Animal models and cell experiments were used to confirm the effect of miRNAs in response to Pb, and siRNA and luciferase experiments were conducted to examine their effect on neural functions. Results: miRNA array data and correlation analysis showed that miR-34b was the most relevant miRNA among Pb neurotoxicity and neuropsychiatric disorders, and synapse-associated membrane protein 2 (VAMP2) was the target gene regulating synapse function. In vivo and in vitro studies showed Pb exposure injured rats’ cognitive abilities and induced upregulation of miR-34b and downregulation of VAMP2, resulting in decreases of hippocampal synaptic vesicles. Blockage of miR-34b mitigated Pb’s effects on VAMP2 in vitro. Conclusion: Early-life Pb exposure might exert synapse-toxic effects via inhibiting VAMP2 mediated by upregulation of miR-34b and shed a light on the underlying relationship between Pb neurotoxicity and developmental neuropsychiatric disorders.