Transgenerational Effects of Periconception Heavy Metal Administration on Adipose Weight and Glucose Homeostasis in Mice at Maturity

Transgenerational inheritance of methylmercury and vitamin A-induced toxicological effects in a Wistar rats environmental-based model

Mercury (Hg) and vitamin A (VitA) are two environmental factors with potential health impacts, especially during pregnancy and early childhood. Fish and seafood may present elevated levels of methylmercury (MeHg), the major Hg derivative, and VitA. This study aimed to evaluate the transgenerational effects of exposure to MeHg and/or VitA on epigenetic and toxicological parameters in a Wistar rat model. Our findings revealed persistent toxicological effects in generations F1 and F2 following low/mild doses of MeHg and/or VitA exposure during dams' (F0) gestation and breastfeeding. Toxicological effects observed in F2 included chronic DNA damage, bone marrow toxicity, altered microglial content, reduced neuronal signal, and diminished male longevity. Sex-specific patterns were also observed. Co-exposure to MeHg and VitA showed both synergistic and antagonistic effects. Additionally, the study demonstrated that MeHg and VitA affected histone methylation and caused consistent effects in F2. While MeHg exposure has been associated with transgenerational inheritance effects in other organisms, this study provides the first evidence of transgenerational inheritance of MeHg and VitA-induced toxicological effects in rodents. Although the exact mechanism is not yet fully understood, these findings suggest that MeHg and VitA may perpetuate their impacts across generations. The study highlights the need for remedial policies and interventions to mitigate the potential health problems faced by future generations exposed to MeHg or VitA. Further research is warranted to investigate the transgenerational effects beyond F2 and determine the matrilineal or patrilineal inheritance patterns.

Association of maternal metals exposure, metabolites and birth outcomes in newborns: A prospective cohort study

BACKGROUND

Maternal exposure to metals may pose a risk to the health of newborns, however, the underlying mechanisms remain ambiguous. Herein, we aimed to investigate the influence of metals exposure on birth outcomes and reveal the importance of metabolites in the exposure-outcomes association by using metabolomics methods.

METHODS

In our study, 292 mother-pairs were included who were recruited from the affiliated hospitals of Nanjing Medical University between 2006 and 2011. We measured fifteen metals (mercury, lead, vanadium, arsenic, zinc, cadmium, rubidium, copper, cobalt, iron, molybdenum, strontium, thallium, magnesium and calcium) and metabolites in maternal second trimester serums by using inductively coupled plasma mass spectrometry and ultra-high performance liquid chromatography high resolution accurate mass spectrometry, respectively. A multi-step statistical analysis strategy including exposome-wide association study (ExWAS) model, variable selection models and multiple-exposure models were performed to systematically appraise the associations of individual and mixed metals exposure with birth outcomes. Furthermore, differential metabolites that associated with metals exposure and birth outcomes were identified using linear regression models.

RESULTS

Metal's levels in maternal serums ranged from 0.05 μg/L to 1864.76 μg/L. In the ExWAS model, maternal exposure to arsenic was negatively associated with birth weight (β = 188.83; 95% CI: -368.27, -9.39), while maternal mercury exposure showed a positive association (β = 533.65; 95%CI: 179.40, 887.90) with birth weight. Moreover, each unit increase in mercury (1 ng/mL-log transformed) was associated with a 1.82 week-increase (95%CI: 0.85, 2.79) in gestational age. These findings were subsequently validated by variable selection models and multiple exposure models. Metabolomic analysis further revealed the significant role of 3-methyladenine in the relationship between arsenic exposure and birth weight.

CONCLUSION

This study provides new epidemiological evidence indicating the associations of metals exposure and neonatal birth outcomes, and emphasizes the potential role of metabolite biomarkers and their importance in monitoring adverse birth outcomes.

Combinatorial pathway disruption is a powerful approach to delineate metabolic impacts of endocrine disruptors

The prevalence of metabolic diseases, such as obesity, diabetes, metabolic syndrome and chronic liver diseases among others, has been rising for several years. Epidemiology and mechanistic (in vivo, in vitro and in silico) toxicology have recently provided compelling evidence implicating the chemical environment in the pathogenesis of these diseases. In this review, we will describe the biological processes that contribute to the development of metabolic diseases targeted by metabolic disruptors, and will propose an integrated pathophysiological vision of their effects on several organs. With regard to these pathomechanisms, we will discuss the needs, and the stakes of evolving the testing and assessment of endocrine disruptors to improve the prevention and management of metabolic diseases that have become a global epidemic since the end of last century.

Transgenerational inheritance and its modulation by environmental cues

The epigenome plays an important role in shaping phenotypes. However, whether the environment can alter an organism's phenotype across several generations through epigenetic remodeling in the germline is still a highly debated topic. In this chapter, we briefly review the mechanisms of epigenetic inheritance and their connection with germline development before highlighting specific developmental windows of susceptibility to environmental cues. We further discuss the evidence of transgenerational inheritance to a range of different environmental cues, both epidemiological in humans and experimental in rodent models. Doing so, we pinpoint the current challenges in demonstrating transgenerational inheritance to environmental cues and offer insight in how recent technological advances may help deciphering the epigenetic mechanisms at play. Together, we draw a detailed picture of how our environment can influence our epigenomes, ultimately reshaping our phenotypes, in an extended theory of inheritance.

Potential benefits of egg white hydrolysate in the prevention of Hg-induced dysfunction in adipose tissue

Aim: To investigate the effects of egg white hydrolysate (EWH) on the lipid and glycemic metabolism disruption in the white adipose tissue (WAT) dysfunction induced by mercury (Hg). Experimental: Wistar rats were treated for 60 days: control (saline, intramuscular - i.m.); hydrolysate (EWH, gavage, 1 g kg^-1 day^-1); mercury (HgCl₂, i.m., 1^st dose 4.6 μg kg^-1, subsequent doses 0.07 μg kg^-1 day^-1) and hydrolysate-mercury (EWH-HgCl₂). Hg level and histological analyses were performed in epididymal WAT (eWAT), pancreas and liver. GRP78, CHOP, PPARα, PPARγ, leptin, adiponectin, and CD11 mRNA expressions were analyzed in eWAT. The plasma lipid profile, glucose, and insulin levels were measured. Antioxidant status was also evaluated in the plasma and liver. Results: EWH intake prevented the reduced eWAT weight, adipocyte size, insulin levels, and antioxidant defenses and the increased glucose and triglyceride levels induced by Hg exposure; hepatic glutathione levels were higher in rats co-treated with EWH. The increased mRNA expression of CHOP, PPARα, and leptin induced by Hg was reduced in co-treated rats. EWH did not modify the elevated mRNA expression of GRP78, PPARγ and adiponectin in Hg-treated rats. Increased levels of Hg were found in the liver; the co-treatment did not alter this parameter. EWH prevented the morphological and metabolic disorder induced by Hg, by improving antioxidant defenses, inactivating pro-apoptotic pathways and normalizing the mRNA expression of PPARs and adipokines. Its effects enabled an increase in insulin levels and a normal balance between the fat storage and expenditure mechanisms in WAT. Conclusions: EWH may have potential benefits in the prevention and management of Hg-related metabolic disorders.

Developmental Exposure to Endocrine Disrupting Chemicals and Its Impact on Cardio-Metabolic-Renal Health

Developmental origin of health and disease postulates that the footprints of early life exposure are followed as an endowment of risk for adult diseases. Epidemiological and experimental evidence suggest that an adverse fetal environment can affect the health of offspring throughout their lifetime. Exposure to endocrine disrupting chemicals (EDCs) during fetal development can affect the hormone system homeostasis, resulting in a broad spectrum of adverse health outcomes. In the present review, we have described the effect of prenatal EDCs exposure on cardio-metabolic-renal health, using the available epidemiological and experimental evidence. We also discuss the potential mechanisms of their action, which include epigenetic changes, hormonal imprinting, loss of energy homeostasis, and metabolic perturbations. The effect of prenatal EDCs exposure on cardio-metabolic-renal health, which is a complex condition of an altered biological landscape, can be further examined in the case of other environmental stressors with a similar mode of action.

The effects of cadmium on the development of Drosophila and its transgenerational inheritance effects

A new focus in toxicology research is the impact of parental exposure to environmental toxic substances on the characteristics of offspring. In the present study, newly produced eggs of Drosophila melanogaster were treated with different concentrations of cadmium (0, 1, 2, 4, 8 mg/kg) to study the effects of development. The results showed that cadmium changed the larval body length and weight, prolonged the pupation and eclosion time, and changed the relative expression levels of development-related genes (baz, β-Tub60D, tj). Furthermore, the parental Drosophila (F₀) were treated with cadmium (4.5 mg/kg) from egg stage, and when grows to adults, they mated in standard medium to produce the de-stressed offspring (F₁-F₄) to assess the transgenerational effects of developmental delay. The results showed that the delayed effects of the pupation and eclosion time could be maintained for two generations, and the inhibiting effects of juvenile hormone (JH) and ecdysone (20-hydroxyecdysone, 20E) could be maintained for two or three generations. More importantly, cadmium increased the expression of DNA methylation-related genes (dDnmt2, dMBD2/3) in the ovaries (F₀-F₂) and testicles (F₀ and F₁). In addition, cadmium accumulated in parental Drosophila (F₀) was not transmitted to offspring through reproductive pathway. These results demonstrate that the developmental toxicity caused by cadmium could be transmitted to the de-stressed offspring, and the observed transgenerational inheritance effects may be associated with epigenetic regulation, underscoring the need to consider fitness of future generations in evaluating the toxicity and environmental risks of cadmium.

Exploring the evidence for epigenetic regulation of environmental influences on child health across generations

Environmental exposures, psychosocial stressors and nutrition are all potentially important influences that may impact health outcomes directly or via interactions with the genome or epigenome over generations. While there have been clear successes in large-scale human genetic studies in recent decades, there is still a substantial amount of missing heritability to be elucidated for complex childhood disorders. Mounting evidence, primarily in animals, suggests environmental exposures may generate or perpetuate altered health outcomes across one or more generations. One putative mechanism for these environmental health effects is via altered epigenetic regulation. This review highlights the current epidemiologic literature and supporting animal studies that describe intergenerational and transgenerational health effects of environmental exposures. Both maternal and paternal exposures and transmission patterns are considered, with attention paid to the attendant ethical, legal and social implications.

Adipotropic effects of heavy metals and their potential role in obesity

Epidemiological studies demonstrated an association between heavy metal exposure and the incidence of obesity and metabolic syndrome. However, the particular effects of metal toxicity on adipose tissue functioning are unclear. Therefore, recent findings of direct influence of heavy metals (mercury, cadmium, and lead) and metalloid (arsenic) on adipose tissue physiology are discussed while considering existing gaps and contradictions. Here, we provide a literature review addressing adipose tissue as a potential target of heavy metal toxicity. Experimental in vivo studies demonstrated a significant influence of mercury, cadmium, lead, and arsenic exposure on body adiposity. In turn, in vitro experiments revealed both up- and downregulation of adipogenesis associated with aberrant expression of key adipogenic pathways, namely CCAAT/enhancer-binding protein (C/EBP) and peroxisome proliferator-activated receptor gamma (PPARγ). Comparison of the existing studies on the basis of dose and route of exposure demonstrated that the effects of heavy metal exposure on adipose tissue may be dose-dependent, varying from increased adipogenesis at low-dose exposure to inhibition of adipose tissue differentiation at higher doses. However, direct dose-response data are available in a single study only for arsenic. Nonetheless, both types of these effects, irrespective of their directionality, contribute significantly to metabolic disturbances due to dysregulated adipogenesis. Particularly, inhibition of adipocyte differentiation is known to reduce lipid-storage capacity of adipose tissue, leading to ectopic lipid accumulation. In contrast, metal-associated stimulation of adipogenesis may result in increased adipose tissue accumulation and obesity. However, further studies are required to reveal the particular dose- and species-dependent effects of heavy metal exposure on adipogenesis and adipose tissue functioning.

Epigenetic Transgenerational Inheritance of Obesity Susceptibility

The prevalence of obesity and associated diseases has reached pandemic levels. Obesity is often associated with overnutrition and a sedentary lifestyle, but clearly other factors also increase the susceptibility of metabolic disease states. Ancestral and direct exposures to environmental toxicants and altered nutrition have been shown to increase susceptibility for obesity and metabolic dysregulation. Environmental insults can reprogram the epigenome of the germline (sperm and eggs), which transmits the susceptibility for disease to future generations through epigenetic transgenerational inheritance. In this review, we discuss current evidence and molecular mechanisms for epigenetic transgenerational inheritance of obesity susceptibility. Understanding ancestral environmental insults and epigenetic transgenerational impacts on future generations will be critical to fully understand the etiology of obesity and to develop preventative therapy options.

Methylmercury Epigenetics

Methylmercury (MeHg) has conventionally been investigated for effects on nervous system development. As such, epigenetic modifications have become an attractive mechanistic target, and research on MeHg and epigenetics has rapidly expanded in the past decade. Although, these inquiries are a recent advance in the field, much has been learned in regards to MeHg-induced epigenetic modifications, particularly in the brain. In vitro and in vivo controlled exposure studies illustrate that MeHg effects microRNA (miRNA) expression, histone modifications, and DNA methylation both globally and at individual genes. Moreover, some effects are transgenerationally inherited, as organisms not directly exposed to MeHg exhibited biological and behavioral alterations. miRNA expression generally appears to be downregulated consequent to exposure. Further, global histone acetylation also seems to be reduced, persist at distinct gene promoters, and is contemporaneous with enhanced histone methylation. Moreover, global DNA methylation appears to decrease in brain-derived tissues, but not in the liver; however, selected individual genes in the brain are hypermethylated. Human epidemiological studies have also identified hypo- or hypermethylated individual genes, which correlated with MeHg exposure in distinct populations. Intriguingly, several observed epigenetic modifications can be correlated with known mechanisms of MeHg toxicity. Despite this knowledge, however, the functional consequences of these modifications are not entirely evident. Additional research will be necessary to fully comprehend MeHg-induced epigenetic modifications and the impact on the toxic response.