Inhibition of DNA methylation attenuates low-dose cadmium-induced cardiac contractile and intracellular Ca(2+) anomalies

Heavy Metal Exposure and Cardiovascular Disease

Heavy metals are harmful environmental pollutants that have attracted widespread attention due to their health hazards to human cardiovascular disease. Heavy metals, including lead, cadmium, mercury, arsenic, and chromium, are found in various sources such as air, water, soil, food, and industrial products. Recent research strongly suggests a connection between cardiovascular disease and exposure to toxic heavy metals. Epidemiological, basic, and clinical studies have revealed that heavy metals can promote the production of reactive oxygen species, which can then exacerbate reactive oxygen species generation and induce inflammation, resulting in endothelial dysfunction, lipid metabolism distribution, disruption of ion homeostasis, and epigenetic changes. Over time, heavy metal exposure eventually results in an increased risk of hypertension, arrhythmia, and atherosclerosis. Strengthening public health prevention and the application of chelation or antioxidants, such as vitamins and beta-carotene, along with minerals, such as selenium and zinc, can diminish the burden of cardiovascular disease attributable to metal exposure.

Cadmium-induced global DNA hypermethylation promoting mitochondrial dynamics dysregulation in hippocampal neurons

Environmental cadmium exposure during pregnancy or adolescence can cause neurodevelopmental toxicity, lead to neurological impairment, and reduce cognitive abilities, such as learning and memory. However, the mechanisms by which cadmium causes neurodevelopmental toxicity and cognitive impairment are still not fully elucidated. This study used hippocampal neurons cultured in vitro to observe the impact of cadmium exposure on mitochondrial dynamics and apoptosis. Exposure to 5 μM cadmium causes degradation of hippocampal neuron cell bodies and axons, morphological destruction, low cell viability, and apoptosis increase. Cadmium exposure upregulates the expression of mitochondrial fission proteins Drp1 and Fis1, reduces the expression of mitochondrial fusion-related proteins MFN1, MFN2, and OPA1, as well as reduces the expression of PGC-1a. Mitochondrial morphology detection demonstrated that cadmium exposure changes the morphological structure of mitochondria in hippocampal neurons, increasing the number of punctate and granular mitochondria, reducing the number of tubular and reticular mitochondria, decreasing mitochondrial mass, dissipating mitochondrial membrane potential (ΔΨm), and reducing adenosine triphosphate (ATP) production. Cadmium exposure increases the global methylation level of the genome and upregulates the expression of DNMT1 and DNMT3α in hippocampal neurons. 5-Aza-CdR reduces cadmium-induced genome methylation levels in hippocampal neurons, increases the number of tubular and reticular mitochondria, and promotes cell viability. In conclusion, cadmium regulates the expression of mitochondrial dynamics-related proteins by increasing hippocampal neuron genome methylation, changing mitochondrial morphology and function, and exerting neurotoxic effects.

The Role of Trace Elements in Cardiovascular Diseases

Essential trace elements play an important role in human physiology and are associated with various functions regulating cellular metabolism. Non-essential trace elements, on the other hand, often have well-documented toxicities that are dangerous for the initiation and development of diseases due to their widespread occurrence in the environment and their accumulation in living organisms. Non-essential trace elements are therefore regarded as serious environmental hazards that are harmful to health even in low concentrations. Many representatives of these elements are present as pollutants in our environment, and many people may be exposed to significant amounts of these substances over the course of their lives. Among the most common non-essential trace elements are heavy metals, which are also associated with acute poisoning in humans. When these elements accumulate in the body over years of chronic exposure, they often cause severe health damage in a variety of tissues and organs. In this review article, the role of selected essential and non-essential trace elements and their role in the development of exemplary pathophysiological processes in the cardiovascular system will be examined in more detail.

Use of an Exposome Approach to Understand the Effects of Exposures From the Natural, Built, and Social Environments on Cardio-Vascular Disease Onset, Progression, and Outcomes

Obesity, diabetes, and hypertension have increased by epidemic proportions in recent years among African Americans in comparison to Whites resulting in significant adverse cardiovascular disease (CVD) disparities. Today, African Americans are 30% more likely to die of heart disease than Whites and twice as likely to have a stroke. The causes of these disparities are not yet well-understood. Improved methods for identifying underlying risk factors is a critical first step toward reducing Black:White CVD disparities. This article will focus on environmental exposures in the external environment and how they can lead to changes at the cellular, molecular, and organ level to increase the personal risk for CVD and lead to population level CVD racial disparities. The external environment is defined in three broad domains: natural (air, water, land), built (places you live, work, and play) and social (social, demographic, economic, and political). We will describe how environmental exposures in the natural, built, and social environments "get under the skin" to affect gene expression though epigenetic, pan-omics, and related mechanisms that lead to increased risk for adverse CVD health outcomes and population level disparities. We also will examine the important role of metabolomics, proteomics, transcriptomics, genomics, and epigenomics in understanding how exposures in the natural, built, and social environments lead to CVD disparities with implications for clinical, public health, and policy interventions. In this review, we apply an exposome approach to Black:White CVD racial disparities. The exposome is a measure of all the exposures of an individual across the life course and the relationship of those exposures to health effects. The exposome represents the totality of exogenous (external) and endogenous (internal) exposures from conception onwards, simultaneously distinguishing, characterizing, and quantifying etiologic, mediating, moderating, and co-occurring risk and protective factors and their relationship to disease. Specifically, it assesses the biological mechanisms and underlying pathways through which chemical and non-chemical environmental exposures are associated with CVD onset, progression and outcomes. The exposome is a promising approach for understanding the complex relationships among environment, behavior, biology, genetics, and disease phenotypes that underlie population level, Black: White CVD disparities.

Changes in rat myocardium contractility under subchronic intoxication with lead and cadmium salts administered alone or in combination

Subchronic intoxications induced in male rats by repeated intraperitoneal injections of lead acetate and cadmium chloride, administered either alone or in combination, are shown to affect the biochemical, cytological and morphometric parameters of blood, liver, heart and kidneys. The single twitch parameters of myocardial trabecular and papillary muscle preparations were measured in the isometric regime to identify changes in the heterometric (length-force) and chronoinotropic (frequency-force) contractility regulation systems. Differences in the responses of these systems in trabecules and papillary muscles to the above intoxications are shown. A number of myocardium mechanical characteristics changing in rats under the effect of a combined lead-cadmium intoxication and increased proportion of α-myosin heavy chains were observed to normalize fully or partially if such intoxication was induced against background administration of a proposed bioprotective complex. Based on the experimental results and literature data, some assumptions are suggested concerning the mechanisms of the cardiotoxic effects produced by lead and cadmium.

Gender Differences in Cardiac Remodeling Induced by a High-Fat Diet and Lifelong, Low-Dose Cadmium Exposure

Childhood obesity, which is prevalent in developed countries, is a metabolic risk factor for cardiovascular disease. Cadmium (Cd), a ubiquitous environmental toxic metal, also has deleterious effects on the cardiovascular system. However, the combined effects of a high-fat diet (HFD) and lifelong, low-dose Cd exposure on cardiac remodeling remain unclear. This study aims to determine the effects of combined HFD and Cd exposure on cardiac remodeling, as well as gender-specific differences in the response. C57BL/6J mice were exposed to Cd at a low dose (L-Cd, 0.5 ppm) or high dose (H-Cd, 5 ppm) via drinking water from conception to sacrifice. After being weaned, the offspring mice were fed with a HFD (42% kcal from fat) for an additional 10 weeks. H-Cd exposure significantly increased Cd accumulation in the hearts of both parents and their offspring; a HFD showed no added effects on cardiac Cd content. H-Cd exposure increased cardiac metallothionein protein levels only in female mice, regardless of dietary intake. Histological analysis revealed that H-Cd exposure combined with a HFD induced cardiac hypertrophy and fibrosis only in female mice. This was further supported by elevated expression of ANP and COL1A1 protein levels along with COL1A1, COL1A2, and COL3A1 mRNA levels. Profibrotic markers PAI-1, CTGF, and FN were also elevated in HFD/H-Cd-exposed female mice. Levels of the oxidative stress marker 3-NT significantly increased in the hearts of HFD-fed female mice, whereas Cd exposure showed no additional effects. Of all the antioxidant markers examined, levels of CAT significantly increased in mice fed a HFD, regardless of gender and Cd exposure. In summary, a HFD combined with lifelong, low-dose Cd exposure induces cardiac hypertrophy and fibrosis in female but not male mice, a response that is independent of oxidative stress.

DNA methylation regulated gene expression in organ fibrosis

DNA methylation is a major epigenetic mechanism to regulate gene expression. Epigenetic regulation, including DNA methylation, histone modifications and RNA interference, results in heritable changes in gene expression independent of alterations in DNA sequence. Epigenetic regulation often occurs in response to aging and environment stimuli, including exposures and diet. Studies have shown that DNA methylation is critical in the pathogenesis of fibrosis involving multiple organ systems, contributing to significant morbidity and mortality. Aberrant DNA methylation can silence or activate gene expression patterns that drive the fibrosis process. Fibrosis is a pathological wound healing process in response to chronic injury. It is characterized by excessive extracellular matrix production and accumulation, which eventually affects organ architecture and results in organ failure. Fibrosis can affect a wide range of organs, including the heart and lungs, and have limited therapeutic options. DNA methylation, like other epigenetic process, is reversible, therefore regarded as attractive therapeutic interventions. Although epigenetic mechanisms are highly interactive and often reinforcing, this review discusses DNA methylation-dependent mechanisms in the pathogenesis of organ fibrosis, with focus on cardiac and pulmonary fibrosis. We discuss specific pro- and anti-fibrotic genes and pathways regulated by DNA methylation in organ fibrosis; we further highlight the potential benefits and side-effects of epigenetic therapies in fibrotic disorders.

The Impact of Environmental Factors in Influencing Epigenetics Related to Oxidative States in the Cardiovascular System

Oxidative states exert a significant influence on a wide range of biological and molecular processes and functions. When their balance is shifted towards enhanced amounts of free radicals, pathological phenomena can occur, as the generation of reactive oxygen species (ROS) in tissue microenvironment or in the systemic circulation can be detrimental. Epidemic chronic diseases of western societies, such as cardiovascular disease, obesity, and diabetes correlate with the imbalance of redox homeostasis. Current advances in our understanding of epigenetics have revealed a parallel scenario showing the influence of oxidative stress as a major regulator of epigenetic gene regulation via modification of DNA methylation, histones, and microRNAs. This has provided both the biological link and a potential molecular explanation between oxidative stress and cardiovascular/metabolic phenomena. Accordingly, in this review, we will provide current insights on the physiological and pathological impact of changes in oxidative states on cardiovascular disorders, by specifically focusing on the influence of epigenetic regulation. A special emphasis will highlight the effect on epigenetic regulation of human's current life habits, external and environmental factors, including food intake, tobacco, air pollution, and antioxidant-based approaches. Additionally, the strategy to quantify oxidative states in humans in order to determine which biological marker could best match a subject's profile will be discussed.

Blood Cadmium Levels and Incident Cardiovascular Events during Follow-up in a Population-Based Cohort of Swedish Adults: The Malmö Diet and Cancer Study

BACKGROUND

Cadmium exposure may increase the risk of cardiovascular disease. The only published longitudinal study on cadmium and incident cardiovascular disease was performed in American Indians with relatively high cadmium exposure.

OBJECTIVES

Our aim was to examine the association between blood cadmium at baseline and incident cardiovascular events in a population-based study of Swedish men and women with cadmium levels similar to those of most European and U.S.

METHODS

A Swedish population-based cohort (n = 6,103, age 46-67 years) was recruited between 1991 and 1994. After we excluded those with missing data on smoking, 4,819 participants remained. Acute coronary events, other major cardiac events, stroke, and cardiovascular mortality were followed until 2010. Associations with blood cadmium (estimated from cadmium in erythrocytes) were analyzed using Cox proportional hazards regression including potential confounders and important cardiovascular risk factors.

RESULTS

Hazard ratios for all cardiovascular end points were consistently increased for participants in the 4th blood cadmium quartile (median, 0.99 μg/L). In models that also included sex, smoking, waist circumference, education, physical activity, alcohol intake, serum triglycerides, HbA1c, and C-reactive protein, the hazard ratios comparing the highest and lowest quartiles of exposure were 1.8 (95% CI: 1.2, 2.7) for acute coronary events, and 1.9 (1.3, 2.9) for stroke. Hazard ratios in never-smokers were consistent with these estimates.

CONCLUSIONS

Blood cadmium in the highest quartile was associated with incident cardiovascular disease and mortality in our population-based samples of Swedish adults. The consistent results among never-smokers are important because smoking is a strong confounder. Our findings suggest that measures to reduce cadmium exposures are warranted, even in populations without unusual sources of exposure.

CITATION

Barregard L, Sallsten G, Fagerberg B, Borné Y, Persson M, Hedblad B, Engström G. 2016. Blood cadmium levels and incident cardiovascular events during follow-up in a population-based cohort of Swedish adults: the Malmö Diet and Cancer Study. Environ Health Perspect 124:594-600; http://dx.doi.org/10.1289/ehp.1509735.

Association Between Blood Cadmium Levels and Mortality in Peritoneal Dialysis

The negative impact of environmental exposure of cadmium has been well established in the general population. However, the effect of cadmium exposure in chronic peritoneal dialysis (PD) patients remains uncertain.A total of 306 chronic PD patients were included in this 36-month observational study. Patients were stratified into 3 groups by the tertile of baseline blood cadmium levels (BCLs): high (>0.244 μg/L, n = 101), middle (0.130-0.244 μg/L, n = 102), and low (<0.130 μg/L, n = 103) for cross-sectional analyses. Mortality rates and cause of death were recorded for longitudinal analyses.Patients in the high-BCL group were older, more likely to have diabetes mellitus, had lower levels of serum albumin and lower percentage of lean body mass than patients in the low-BCL group. A multivariate logistic regression analysis revealed that logarithmic transformed BCL was independently associated with a higher risk of low turnover bone disease (odds ratio = 3.8, P = 0.005). At the end of the 36-month follow-up, 66 (21.6%) patients died. Mortality rates increased with higher BCLs (P for trend = 0.005). A Cox multivariate analysis showed that, using the low-BCL group as the reference, the high-BCL group had increased hazard ratios (HR) for all-cause mortality in chronic PD patients after adjusting for related variables (HR = 2.469, 95% confidence interval = 1.078-5.650, P = 0.043).In conclusion, BCL showed significant association with malnutrition and low turnover bone disease in chronic PD patients. Furthermore, BCL is an important determinant of mortality. Our findings suggest that avoiding environmental exposure to cadmium as much as possible is warranted in chronic PD patients.

Epigenetics and the overhealing wound: the role of DNA methylation in fibrosis

Fibrosis is a progressive and potentially fatal process that can occur in numerous organ systems. Characterised by the excessive deposition of extracellular matrix proteins such as collagens and fibronectin, fibrosis affects normal tissue architecture and impedes organ function. Although a considerable amount of research has focused on the mechanisms underlying disease pathogenesis, current therapeutic options do not directly target the pro-fibrotic process. As a result, there is a clear unmet clinical need to develop new agents. Novel findings implicate a role for epigenetic modifications contributing to the progression of fibrosis by alteration of gene expression profiles.

This review will focus on DNA methylation; its association with fibroblast differentiation and activation and the consequent buildup of fibrotic scar tissue. The potential use of therapies that modulate this epigenetic pathway for the treatment of fibrosis in several organ systems is also discussed.

Environmental pollution and DNA methylation: carcinogenesis, clinical significance, and practical applications

Environmental pollution is one of the main causes of human cancer. Exposures to environmental carcinogens result in genetic and epigenetic alterations which induce cell transformation. Epigenetic changes caused by environmental pollution play important roles in the development and progression of environmental pollution-related cancers. Studies on DNA methylation are among the earliest and most conducted epigenetic research linked to cancer. In this review, the roles of DNA methylation in carcinogenesis and their significance in clinical medicine were summarized, and the effects of environmental pollutants, particularly air pollutants, on DNA methylation were introduced. Furthermore, prospective applications of DNA methylation to environmental pollution detection and cancer prevention were discussed.

Cadmium exposure and incidence of heart failure and atrial fibrillation: a population-based prospective cohort study

OBJECTIVES

Cadmium is a non-essential toxic metal with multiple adverse health effects. Cadmium has been shown to be associated with cardiovascular diseases, but few studies have investigated heart failure (HF) and none of them reported atrial fibrillation (AF). We examined whether cadmium exposure is associated with incidence of HF or AF.

DESIGN

A prospective, observational cohort study with a 17-year follow-up.

SETTING

The city of Malmö, Sweden.

PARTICIPANTS

Blood cadmium levels were measured in 4378 participants without a history of HF or AF (aged 46-67 years, 60% women), who participated in the Malmö Diet and Cancer (MDC) study during 1992-1994.

PRIMARY AND SECONDARY OUTCOME MEASURES

Incidence of HF and AF were identified from the Swedish hospital discharge register.

RESULTS

143 participants (53% men) were diagnosed with new-onset HF and 385 individuals (52% men) were diagnosed with new-onset AF during follow-up for 17 years. Blood cadmium in the sex-specific 4th quartile of the distribution was significantly associated with incidence of HF. The (HR, 4th vs 1st quartile) was 2.64 (95% CI 1.60 to 4.36), adjusted for age, and 1.95 (1.02 to 3.71) after adjustment also for conventional risk factors and biomarkers. The blood cadmium level was not significantly associated with risk of incident AF.

CONCLUSIONS

Blood cadmium levels in the 4th quartile were associated with increased incidence of HF in this cohort with comparatively low exposure to cadmium. Incidence of AF was not associated with cadmium.

Heart failure: advanced development in genetics and epigenetics

Heart failure (HF) is a complex pathophysiological syndrome that arises from a primary defect in the ability of the heart to take in and/or eject sufficient blood. Genetic mutations associated with familial dilated cardiomyopathy, hypertrophic cardiomyopathy, and arrhythmogenic right ventricular cardiomyopathy can contribute to the various pathologies of HF. Therefore, genetic screening could be an approach for guiding individualized therapies and surveillance. In addition, epigenetic regulation occurs via key mechanisms, including ATP-dependent chromatin remodeling, DNA methylation, histone modification, and RNA-based mechanisms. MicroRNA is also a hot spot in HF research. This review gives an overview of genetic mutations associated with cardiomyopathy and the roles of some epigenetic mechanisms in HF.