Effects of mercury on the arterial blood pressure of anesthetized rats

An Unusual Cause of Complete Heart Block

Mercury poisoning is most frequently associated with multiorgan toxicity involving the brain, lungs, and kidneys. Cardiotoxic effects of mercury are rare and often overlooked. We demonstrate mercury poisoning-induced cardiotoxicity through a case study and then provide a review of the incidence, pathophysiology, and associated management plans. This case illustrates the importance of thorough history-taking to promote early recognition of toxicity.

Interaction of mercury species with proteins: towards possible mechanism of mercurial toxicology

The nature of the binding of mercurials (organic and inorganic) and their subsequent transformations in biological systems is a matter of great debate as several different hypotheses have been proposed and none of them has been conclusively proven to explain the characteristics of Hg binding with the proteins. Thus, the chemical nature of Hg-protein binding through the possible transportation mechanism in living tissues is critically reviewed herein. Emphasis is given to the process of transportation, and binding of Hg species with selenol-containing biomolecules that are appealing for toxicological studies as well as the advancement of environmental and biological research.

Associations between mercury exposure with blood pressure and lipid levels: A cross-sectional study of dental professionals

Mercury (Hg) exposure is a public health problem worldwide that is now being addressed through the Minamata Convention on Mercury. Fish containing methylmercury and dental amalgam containing elemental Hg are the major sources of exposure for most populations. There is some evidence that methylmercury impacts cardiovascular and metabolic health, primarily in populations with high exposure levels. Studies of elemental Hg and these outcomes are relatively rare. We aimed to examine associations between Hg exposure (both elemental and methylmercury) and blood pressure, as well as cholesterol and triglyceride levels. In 2012, we recruited dental professionals attending the Health Screening Program at the American Dental Association (ADA) Annual Session in California. Total Hg levels in hair and blood samples were analyzed as indicators of methylmercury exposure and in urine as an indicator of primarily elemental Hg exposure (n = 386; mean ± sd age 55 ± 11 years). We measured blood pressure (systolic and diastolic) and lipid profiles (total cholesterol, high-density lipoprotein cholesterol [HDL], low-density lipoprotein cholesterol [LDL] and triglycerides). The geometric means (geometric standard deviations) for blood, hair, and urine Hg were 3.64 (2.39) μg/L, 0.60 (2.91) μg/g, and 1.30 (2.44) μg/L, respectively. For every one μg/L increase in specific gravity-adjusted urine Hg, LDL increased by 2.31 mg/dL (95% CI = 0.09, 4.54), in linear regression adjusting for BMI, race, sex, polyunsaturated fatty acid intake from fish consumption, smoking status, and use of cholesterol-lowering medication. No significant associations between Hg biomarkers and blood pressure or hair or blood Hg with lipid levels were observed. Results suggest that elemental Hg exposure may influence LDL concentrations in adults with low-level exposure, and this relationship merits further study in other populations.

Total arsenic, dimethylarsinic acid, lead, cadmium, total mercury, methylmercury and hypertension among Asian populations in the United States: NHANES 2011-2018

BACKGROUND

Non-Hispanic Asians (NHA) in USA have been reported with higher arsenic (As), lead (Pb), cadmium (Cd), mercury (Hg) and their specific species levels, comparing with non-NHA. This study aimed to investigate the associations of these metal/metalloid levels with blood pressure levels and prevalence of hypertension among general NHA using the 2011-2018 National Health and Nutrition and Examination Survey (NHANES) data.

METHODS

The study included participants aged 20 years and older with determinations of As, Dimethylarsinic acid (DMA), Pb, Cd, Hg and methyl-Hg (MeHg) in blood (n = 10, 177) and urine (n = 5, 175). These metals/metalloid levels were measured by inductively coupled plasma mass spectrometry. Systolic (SBP) and diastolic blood pressure (DBP) levels were examined through a standardized protocol. Censored normal regression model and logistic regression model were employed to explore the associations of As, DMA, Pb, Cd, Hg and MeHg levels with blood pressure levels and prevalence of hypertension respectively, and potential confounders were adjusted in these regression models. Quantile-based g-computation approach was used to analysis joint effect of metals mixture on blood pressure level and hypertension.

RESULTS

For NHA, urinary As and Hg levels were associated with increased DBP level; Higher blood Hg and MeHg levels were related to increased blood pressure levels and hypertension; However, negative association was observed between urinary Cd and SBP level; Blood metals mixture (including blood Pb, Cd and Hg) was associated with increased DBP level, but not for hypertension. For non-NHA, urinary As and DMA levels were associated with increased SBP level, but not DBP level and prevalence of hypertension; Urinary Pb level was associated with decreased DBP level; Nevertheless, positive associations were observed between blood Pb levels and SBP and prevalence of hypertension; Blood Hg level was associated with decreased DBP level and prevalence of hypertension; Furthermore, blood MeHg level was associated with decreased DBP level; Positive association was observed between blood metals mixture and increased SBP level among non-NHA.

CONCLUSIONS

Highly exposed to Hg level among NHA was associated with increased blood pressure levels and prevalence of hypertension. Urinary As level was associated with increased DBP level among NHA. Furthermore, blood metals mixture was related to increased DBP level among NHA. Further prospective studies with larger sample size should be performed to warrant the results.

Association of Seafood Consumption and Mercury Exposure With Cardiovascular and All-Cause Mortality Among US Adults

IMPORTANCE

Although seafood is known to contain heart-healthy omega-3 fatty acids, many people choose to limit their seafood consumption because of fear of mercury exposure from seafood. It is imperative to clarify the potential health effects of current mercury exposure in contemporary populations.

OBJECTIVE

To examine the association of seafood consumption and mercury exposure with all-cause and cardiovascular disease (CVD)-related mortality in the US general population.

DESIGN, SETTING, AND PARTICIPANTS

This prospective cohort study included adults 20 years or older who participated in the 2003 to 2012 cycles of the National Health and Nutrition Examination Survey; data were linked to mortality records through December 31, 2015. Data analysis was performed from January to March 10, 2021.

EXPOSURES

Seafood consumption was assessed through two 24-hour dietary recalls, and mercury exposure was assessed by blood mercury levels.

MAIN OUTCOMES AND MEASURES

All-cause and CVD-related mortality. Multivariable Cox proportional hazards regression was used to estimate hazard ratios (HRs) and 95% CIs of mortality associated with usual seafood consumption and blood mercury concentration quartiles.

RESULTS

This study included 17 294 participants (mean [SD] age, 45.9 [17.1] years; 9217 [53.3%] female) with a mean (SD) blood mercury concentration of 1.62 (2.46) μg/L. During 131 276 person-years of follow-up, 1076 deaths occurred, including 181 deaths from CVD. The multivariable-adjusted HR for an increase in seafood consumption of 1 oz equivalent per day and all-cause mortality was 0.84 (95% CI, 0.66-1.07) and for CVD-related mortality was 0.89 (95% CI, 0.54-1.47). Blood mercury level was not associated with all-cause or CVD-related mortality. Comparing the highest with the lowest quartile of blood mercury concentration, the multivariable-adjusted HRs were 0.82 (95% CI, 0.66-1.05) for all-cause mortality and 0.90 (95% CI, 0.53-1.52) for CVD-related mortality.

CONCLUSIONS AND RELEVANCE

In this cohort study of US adults, seafood consumption and mercury exposure with the current seafood consumption level were not significantly associated with the risk of all-cause or CVD-related mortality. These findings may inform future public health guidelines regarding mercury exposure, seafood consumption, and cardiovascular health promotion.

Bioactive Peptides and Hydrolysates from Egg Proteins as a New Tool for Protection Against Cardiovascular Problems

The aim of the present work is to review the potential beneficial effects of dietary supplementation with bioactive egg protein hydrolysates or peptides on cardiometabolic changes associated with oxidative stress. The development of nutritionally improved food products designed to address specific health concerns is of particular interest because many bioactive food compounds can be potentially useful in various physiological functions such as for reducing oxidative stress. The results presented suggest that egg hydrolysates or derived peptides could be included in the diet to prevent and/or reduce some cardiometabolic complications associated with oxidative stress-related diseases.

Relationship between low-level lead, cadmium and mercury exposures and blood pressure in children and adolescents aged 8-17 years: An exposure-response analysis of NHANES 2007-2016

This study investigated whether low-level blood and urinary lead, cadmium and mercury exposures were associated with blood pressure (BP) in children and adolescents. Data from National Health and Nutrition Examination Survey (NHANES) between 2007 and 2016 for children and adolescents aged 8-17 years (n = 7076) were analyzed. Outcome variables were systolic BP, diastolic BP and high BP status. High BP was defined as: self-reported antihypertensive medication usage or a diagnosis of hypertension; classified as having elevated BP/hypertension according to 2017 AAP guidelines. Multivariable linear and logistic regressions models were performed and stratified by race/ethnicity and gender. Blood lead was negatively associated with diastolic BP among blacks, and positively associated with diastolic BP among whites. For a two-fold increase of blood lead concentration, the change in diastolic BP was -1.59 mm Hg (95% CI: -3.04 to -0.16 mm Hg) among blacks and 1.38 mm Hg (95% CI: 0.40 to 2.36 mm Hg) among whites. No significant associations between either systolic BP or diastolic BP with urinary lead were observed. The inverse associations between blood lead and high BP were found in females, Mexican Americans and other Hispanics. No associations between blood cadmium and BP were observed, except in other Hispanics. Urinary cadmium levels were inversely correlated with systolic BP, diastolic BP and high BP in all participants and in men. When compared to the lowest quartile of urinary cadmium levels, participants with a urinary cadmium level ≥ 0.12 μg/L had 0.48 (95% CI: 0.29-0.78) times and 0.53 (95% CI: 0.30-0.94) times reduced odds of having high BP in all participants and in men, respectively. No associations between either blood mercury or urinary mercury with systolic BP were observed. Significant inverse associations were found between blood total mercury and methyl mercury with diastolic BP in all participants and in men. Future prospective studies are warranted to confirm these findings.

Effects of Chronic Exposure to Mercury on Angiotensin-Converting Enzyme Activity and Oxidative Stress in Normotensive and Hypertensive Rats

BACKGROUND

Mercury's deleterious effects are associated with increased cardiovascular risk.

OBJECTIVE

To determine whether chronic exposure to inorganic mercury increases the activity of angiotensin-converting enzyme and its relationship with oxidative stress in several organs and tissues.

METHODS

We studied male Wistar and spontaneously hypertensive rats (SHR) (3-month-old) exposed or not to HgCl2 for 30 days. At the end of treatment, we investigated the following: changes in body weight, hemodynamic parameters, angiotensin-converting enzyme (ACE) activity and oxidative stress in the heart, aorta, lung, brain and kidney in hypertensive compared to normotensive animals. A value of p < 0.05 was considered significant.

RESULTS

Chronic exposure to HgCl2 did not affect weight gain in either group. Systolic blood pressure, measured weekly, did not increase in Wistar rats but showed a small increase in SHR rats. We also observed increases in left ventricular end-diastolic pressure and ACE activity in the plasma and hearts of normotensive rats. In the SHR+Hg group, ACE activity increased in plasma but decreased in kidney, lung, heart, brain and aorta. Oxidative stress was assessed indirectly by malondialdehyde (MDA) production, which increased in Hg-treated rats in both plasma and heart. In the SHR+Hg group, MDA increased in heart and aorta and decreased in lungs and brain.

CONCLUSION

These results suggest that chronic exposure to inorganic mercury aggravates hypertension and produces more expressive changes in ACE activity and oxidative stress in SHRs. Such exposure affects the cardiovascular system, representing a risk factor for the development of cardiovascular disorders in normotensive rats and worsening of pre-existing risks for hypertension.

Methylmercury exposure develops atherosclerotic risk factors in the aorta and programmed cell death in the cerebellum: ameliorative action of Celastrus paniculatus ethanolic extract in male Wistar rats

Methylmercury (MeHg) is a bioaccumulative global environmental contaminant present in fishes and seafood. MeHg is the methylated form of mercury emitted from diverse anthropogenic and natural sources. MeHg is accumulated in the aquatic environment and eventually reaches human system via food chain by biomagnification. We have reported previously that the neurotoxic effect of MeHg in rat cerebellum is mitigated by the administration of an ayurvedic medicinal plant, Celastrus paniculatus ethanolic extract. The present study has focussed to further explore the mechanism of action of Celastrus paniculatus against MeHg-induced neurotoxicity in the cerebellum. We have also inspected the effect of Celastrus paniculatus (CP) against MeHg-induced atherosclerotic risk factors like alterations in antioxidant levels, aortic lipid profile, and aortic histology by MeHg in the largest vasculature, aorta, which are the initiating factors of cardiovascular diseases. Male Wistar rats were divided as (i) control, (ii) MeHg (5 mg/kg b.w.), (iii) MeHg + CP (200 mg/kg b.w.), and (iv) CP alone (200 mg/kg b.w.). All were given orally for 21 days. In cerebellum Celastrus paniculatus, there were increased mitochondrial electron transport chain (p < 0.05) activity, reduced cytochrome c release (p < 0.05), and caspase 3 mRNA expression (p < 0.05). In the aorta, MeHg-induced oxidative stress, lipid profile changes, and endothelial denudation were ameliorated by Celastrus paniculatus. Hence, we conclude that Celastrus paniculatus protects against MeHg toxicity by inhibiting mitochondrial cytochrome c/caspase 3 apoptotic pathway in the cerebellum and reducing the development of atherosclerotic risk factors in the aorta.

Vulnerability associated with "symptoms similar to those of mercury poisoning" in communities from Xingu River, Amazon basin

The Brazilian Amazon is known to be a region with high levels of mercury (Hg) in the environment and studies point to an association between high levels of natural mercury in the mother rock and the vast number of clandestine gold mines. Other studies already report the contamination of fish in this region, as well as high levels of Hg in biological material from environmentally exposed populations. On the other hand, this is one of the least developed regions of the planet and it is necessary to understand the vulnerability factors in these populations that may be intoxicated by this element. The purpose of the present study was to investigate the vulnerability factors in communities from Xingu River-Amazon basin probably exposed to Hg. A cross-selection study in two cities localized in Xingu River was conducted, and the sample contained was 268 individuals. sociodemographic questions, lifestyle, diet habits and health conditions were collated. The majority of the sample was female, between 30 and 59 years old, had less than 3 years of educational level and lived in the local of study more than 240 months. There was regular fish consumption (95.9%), principally carnivorous species (80.5%). The visual problem has a highest prevalence (43.3%) between the health problems and about the symptoms of Hg intoxication, memory loss (42.9%), weakness (35.1%), fatigue (34.3%), mood changes (28.7%) and difficulties in concentration (27.2%) was most reported. The female sex, age over 60, educational level below 3 years of study, did not had flush toilet, smoke and least one chronic non-communicable disease represent higher probability to had symptoms of Hg intoxication. Lack of access to health services, low education level and income evidence the susceptibility of this community to diseases and injuries. The vulnerable groups identified in this study should be a priority in public health and environmental health policies.

Mercury-induced vascular dysfunction is mediated by angiotensin II AT-1 receptor upregulation

Low doses of mercury (Hg) promote deleterious effects on cardiovascular system, but the mechanisms implicated remain unclear. This study analyzed whether angiotensin II AT-1 receptors are involved in the vascular dysfunction caused by chronic exposure to low HgCl₂ doses. For this, rats were divided into four groups and untreated (saline by im injections and tap water by gavage) or treated for 30 days as follows: Mercury (HgCl₂im, first dose of 4.6 µg kg^-1 and subsequent doses of 0.07 µg kg^-1 day^-1, and tap water by gavage); Losartan (saline im and losartan, 15 mg kg^-1 day^-1, by gavage); Losartan-Mercury (HgCl₂im and Losartan by gavage). Systolic blood pressure was measured by tail plethysmography, vascular reactivity in aorta by isolated organ bath, oxidative stress by measuring the levels of reactive oxygen species (ROS), malondialdehyde (MDA) and antioxidant capacity (FRAP) and protein expression of AT-1 receptors by Western Blot. As results, co-treatment with losartan prevented the increased aortic vasoconstrictor responses to phenylephrine (Phe), the involvement of ROS and prostanoids on the response to Phe and the reduced negative endothelial modulation by nitric oxide on these responses. Moreover, this co-treatment avoided the increase in plasmatic and vascular oxidative stress and AT-1 protein expression in aorta. In conclusion, these results suggest that AT-1 receptors upregulation might play a key role in the vascular damage induced by Hg exposure by increasing oxidative stress and probably by reducing NO bioavailability.

The cessation of the long-term exposure to low doses of mercury ameliorates the increase in systolic blood pressure and vascular damage in rats

This study aimed to verify whether a prolonged exposure to low-level mercury promotes haemodynamic disorders and studied the reversibility of this vascular damage. Rats were divided into seven groups: three control groups received saline solution (im) for 30, 60 or 90 days; two groups received HgCl₂ (im, first dose, 4.6μg/kg, subsequent doses 0.07μg/kg/day) for 30 or 60 days; two groups received HgCl₂ for 30 or 60 days (im, same doses) followed by a 30-day washout period. Systolic blood pressure (SBP) was measured, along with analysis of vascular response to acetylcholine (ACh) and phenylephrine (Phe) in the absence and presence of endothelium, a nitric oxide (NO) synthase inhibitor, an NADPH oxidase inhibitor, superoxide dismutase, a non-selective cyclooxygenase (COX) inhibitor and an AT1 receptor blocker. Reactive oxygen species (ROS) levels and antioxidant power were measured in plasma. HgCl₂ exposure for 30 and 60 days: a) reduced the endothelium-dependent relaxation; b) increased the Phe-induced contraction and the contribution of ROS, COX-derived vasoconstrictor prostanoids and angiotensin II acting on AT1 receptors to this response while the NO participation was reduced; c) increased the oxidative stress in plasma; d) increased the SBP only after 60 days of exposure. After the cessation of HgCl₂ exposure, SBP, endothelium-dependent relaxation, Phe-induced contraction and the oxidative stress were normalised, despite the persistence of the increased COX-derived prostanoids. These results demonstrated that long-term HgCl₂ exposure increases SBP as a consequence of vascular dysfunction; however, after HgCl₂ removal from the environment the vascular function ameliorates.

Egg white-derived peptides prevent male reproductive dysfunction induced by mercury in rats

Oxidative stress in known to contribute to the male reproductive dysfunction induced by mercury (Hg). Our study tested the hypothesis that the egg white hydrolysate (EWH), a potent antioxidant in vitro, is able to prevent the effects of prolonged Hg exposure on male reproductive system in rats. For this, rats were treated for 60 days with: a) Untreated - saline solution (i.m.); b) Hydrolysate - EWH (1 g/kg/day, gavage); c) Mercury - HgCl₂ (1st dose 4.6 μg/kg, subsequent doses 0.07 μg/kg/day, i.m.); d) Hydrolysate-Mercury. At the end of the treatment, sperm motility, count and morphological studies were performed; Reactive Oxygen Species (ROS) levels, lipid peroxidation, antioxidant capacity, histological and immunohistochemical assays on testis and epididymis were also carried out. As results, HgCl₂-treatment decreased sperm number, increased sperm transit time in epididymis and impaired sperm morphology. However, these harmful effects were prevented by EWH. HgCl₂-treatment also increased ROS levels, lipid peroxidation and antioxidant capacity in testis and epididymis as well as promoted testicular inflammation and histological changes in epididymis. EWH improved histological and immunohistochemical alterations, probably due to its antioxidant property. In conclusion, the EWH could represent a powerful natural alternative to protect the male reproductive system against Hg-induced sperm toxicity.

Human exposure and risk assessment associated with mercury pollution in the Caqueta River, Colombian Amazon

Mercury (Hg) is a global contaminant posing severe risks to human health worldwide. The aim of this study was to assess the levels of total Hg (T-Hg) in human hair and fish in the Caqueta River, at the Colombian Amazon, as well as to determine fish consumption-based risks for T-Hg ingestion. T-Hg levels were measured using a direct mercury analyzer. The overall mean T-Hg level in hair for humans in the Caqueta River sample (n = 200) was 17.29 ± 0.61 μg/g (1.2 to 47.0 μg/g). Ninety-four percent of the individuals had hair T-Hg concentrations greater than the WHO threshold level (5 μg/g), and 79 % displayed levels higher than 10 μg/g. Average Hg concentrations in fish varied between 0.10-0.15 μg/g and 0.10-1.60 μg/g, for noncarnivorous and carnivorous species, respectively. Based on the maximum allowable fish consumption rate for adults, most carnivorous species should be avoided in the diet, as their target hazard quotient ranged from 2.96 up to 31.05, representing a risk for Hg-related health problems. In the light of existing evidence for elevated Hg levels in the indigenous population of the Colombian Amazon, carnivorous fish should be restricted as part of the diet, and breastfeeding should be reduced to protect children health. Most importantly, gold mining activities directly on rivers demand immediate attention from the national government to avoid extensive damage on the environment and human health.

Environment-Wide Association Study of Blood Pressure in the National Health and Nutrition Examination Survey (1999-2012)

Identifying environmental exposures associated with blood pressure is a priority. Recently, we proposed the environment-wide association study to search for and replicate environmental factors associated with phenotypes. We conducted the environment-wide association study (EWAS) using the National Health and Nutrition Examination Surveys (1999–2012) which evaluated a total of 71,916 participants to prioritize environmental factors associated with systolic and diastolic blood pressure. We searched for factors on participants from survey years 1999–2006 and tentatively replicated findings in participants from years 2007–2012. Finally, we estimated the overall association and performed a second meta-analysis using all survey years (1999–2012). For systolic blood pressure, self-reported alcohol consumption emerged as our top finding (a 0.04 increase in mmHg of systolic blood pressure for 1 standard deviation increase in self-reported alcohol), though the effect size is small. For diastolic blood pressure, urinary cesium was tentatively replicated; however, this factor demonstrated high heterogeneity between populations (I² = 51%). The lack of associations across this wide of an analysis raises the call for a broader search for environmental factors in blood pressure.

An Investigation of Organic and Inorganic Mercury Exposure and Blood Pressure in a Small-Scale Gold Mining Community in Ghana

There is increasing concern about the cardiovascular effects of mercury (Hg) exposure, and that organic methylmercury and inorganic Hg²⁺ may affect the cardiovascular system and blood pressure differentially. In small-scale gold mining communities where inorganic, elemental Hg exposures are high, little is known about the effects of Hg on blood pressure. In 2011, we assessed the relationship between Hg exposure and blood pressure (BP) in a cross-sectional study of adults from a small-scale gold mining community, Kejetia, and subsistence farming community, Gorogo, in Ghana’s Upper East Region. Participants’ resting heart rate and BP were measured, and hair and urine samples were provided to serve as biomarkers of organic and inorganic Hg exposure, respectively. Participants included 70 miners and 26 non-miners from Kejetia and 75 non-miners from Gorogo. Total specific gravity-adjusted urinary and hair Hg was higher among Kejetia miners than Kejetia non-miners and Gorogo participants (median urinary Hg: 5.17, 1.18, and 0.154 µg/L, respectively; hair Hg: 0.945, 0.419, and 0.181 µg/g, respectively). Hypertension was prevalent in 17.7% of Kejetia and 21.3% of Gorogo participants. Urinary and hair Hg were not significantly associated with systolic or diastolic BP for Kejetia or Gorogo participants while adjusting for sex, age, and smoking status. Although our results follow trends seen in other studies, the associations were not of statistical significance. Given the unique study population and high exposures to inorganic Hg, the work contained here will help increase our understanding of the cardiovascular effects of Hg.

Mercury Exposure and Endothelial Dysfunction: An Interplay Between Nitric Oxide and Oxidative Stress

Vascular endothelium plays a vital role in the organization and function of the blood vessel and maintains homeostasis of the circulatory system and normal arterial function. Functional disruption of the endothelium is recognized as the beginning event that triggers the development of consequent cardiovascular disease (CVD) including atherosclerosis and coronary heart disease. There is a growing data associating mercury exposure with endothelial dysfunction and higher risk of CVD. This review explores and evaluates the impact of mercury exposure on CVD and endothelial function, highlighting the interplay of nitric oxide and oxidative stress.

A review of metal-catalyzed molecular damage: protection by melatonin

Metal exposure is associated with several toxic effects; herein, we review the toxicity mechanisms of cadmium, mercury, arsenic, lead, aluminum, chromium, iron, copper, nickel, cobalt, vanadium, and molybdenum as these processes relate to free radical generation. Free radicals can be generated in cells due to a wide variety of exogenous and endogenous processes, causing modifications in DNA bases, enhancing lipid peroxidation, and altering calcium and sulfhydryl homeostasis. Melatonin, an ubiquitous and pleiotropic molecule, exerts efficient protection against oxidative stress and ameliorates oxidative/nitrosative damage by a variety of mechanisms. Also, melatonin has a chelating property which may contribute in reducing metal-induced toxicity as we postulate here. The aim of this review was to highlight the protective role of melatonin in counteracting metal-induced free radical generation. Understanding the physicochemical insights of melatonin related to the free radical scavenging activity and the stimulation of antioxidative enzymes is of critical importance for the development of novel therapeutic strategies against the toxic action of these metals.

Chronic exposure to low doses of HgCl2 avoids calcium handling impairment in the right ventricle after myocardial infarction in rats

Right ventricle systolic dysfunction is a major risk factor for death and heart failure after myocardial infarction (MI). Heavy metal exposure has been associated with the development of several cardiovascular diseases, such as MI. The aim of this study was to investigate whether chronic exposure to low doses of mercury chloride (HgCl2) enhances the functional deterioration of right ventricle strips after MI. Male Wistar rats were divided into four groups: Control (vehicle); HgCl2 (exposure during 4 weeks- 1st dose 4.6 µg/kg, subsequent dose 0.07 µg/kg/day, i.m. to cover daily loss); MI surgery induced and HgCl2-MI groups. One week after MI, the morphological and hemodynamic measurements and isometric tension of right ventricle strips were investigated. The chronic HgCl2 exposure did not worsen the injury compared with MI alone in the morphological or hemodynamic parameters evaluated. At basal conditions, despite similar maximum isometric force at L-max, relaxation time was increased in the MI group but unaffected in the HgCl2-MI compared to the Control group. Impairment of the sarcoplasmic reticulum (SR) function and reduction in the sarcolemmal calcium influx were observed in MI group associated with SERCA2a reduction and increased PLB protein expression. Induction of MI in chronic HgCl2 exposed rats did not cause any alteration in the developed force at L-max, lusitropic function or -dF/dt except for a tendency of a reduction SR function. These findings could be partially explained by the normalization in the sarcolemmal calcium influx and the increase in NCX protein expression observed only in this group. These results suggest that chronic exposure to low doses of HgCl2 prevents the impaired SR function and the reduced sarcolemmal calcium influx observed in MI likely by acting on NCX, PLB and SERCA2a protein expression.

Modulation of vasodilator response via the nitric oxide pathway after acute methyl mercury chloride exposure in rats

Mercury exposure induces endothelial dysfunction leading to loss of endothelium-dependent vasorelaxation due to decreased nitric oxide (NO) bioavailability via increased oxidative stress. Our aim was to investigate whether acute treatment with methyl mercury chloride changes the endothelium-dependent vasodilator response and to explore the possible mechanisms behind the observed effects. Wistar rats were treated with methyl mercury chloride (5 mg/kg, po.). The methyl mercury chloride treatment resulted in an increased aortic vasorelaxant response to acetylcholine (ACh). In methyl-mercury-chloride-exposed rats, the % change in vasorelaxant response of ACh in presence of N_ω-Nitro-L-arginine methyl ester hydrochloride (L-NAME; 10⁻⁴ M) was significantly increased, and in presence of glybenclamide (10⁻⁵ M), the response was similar to that of untreated rats, indicating the involvement of NO and not of endothelium-derived hyperpolarizing factor (EDHF). In addition, superoxide dismutase (SOD) + catalase treatment increased the NO modulation of vasodilator response in methyl-mercury-chloride-exposed rats. Our results demonstrate an increase in the vascular reactivity to ACh in aorta of rats acutely exposed to methyl mercury chloride. Methyl mercury chloride induces nitric oxide synthase (NOS) and increases the NO production along with inducing oxidative stress without affecting the EDHF pathway.

Associations of blood and urinary mercury with hypertension in U.S. adults: the NHANES 2003-2006

BACKGROUND

Few studies have examined the association between hypertension and mercury exposure in the general population. We examined cross-sectional associations between blood (mainly methylmercury) or urinary mercury (mainly inorganic mercury) and hypertension in representative U.S. adults and effect modifications by dietary omega-3 fatty acids and serum selenium.

METHODS

We examined 6607 adults aged 20 years or older, using the National Health and Nutrition Examination Survey (NHANES) from 2003/2004 to 2005/2006 (2201 adults were available for urinary mercury from NHANES 2003-2006; 2117 available for serum selenium from NHANES 2003-2004 aged 40 years or older). The average of omega-3 fatty acids from two 24-h recalls was calculated.

RESULTS

The weighted prevalence of hypertension was 32.2%. The geometric means (95% confidence intervals) of blood total and urinary mercury were 1.03 (0.95, 1.11)μg/L and 0.51 (0.47, 0.54)μg/L, respectively. The adjusted odds ratios for a doubling increase in blood mercury and urinary mercury were 0.94 (0.87 to 1.01) and 0.87 (0.78 to 0.99), respectively, after adjusting for potential confounders. The associations remained similar, even after adjusting for either omega-3 fatty acids or selenium or both. No significant effect modification by either omega-3 fatty acids or selenium was observed.

CONCLUSIONS

In this cross-sectional study of the U.S. general population, we found no association of hypertension with blood mercury but a suggestive inverse association with urinary mercury. Future prospective studies are warranted to confirm these findings.

Methylmercury and elemental mercury differentially associate with blood pressure among dental professionals

Methylmercury-associated effects on the cardiovascular system have been documented though discrepancies exist, and most studied populations experience elevated methylmercury exposures. No paper has investigated the impact of low-level elemental (inorganic) mercury exposure on cardiovascular risk in humans. The purpose of this study was to increase understanding of the association between mercury exposure (methylmercury and elemental mercury) and blood pressure measures in a cohort of dental professionals that experience background exposures to both mercury forms. Dental professionals were recruited during the 2010 Michigan Dental Association Annual Convention. Mercury levels in hair and urine samples were analyzed as biomarkers of methylmercury and elemental mercury exposure, respectively. Blood pressure (systolic, diastolic) was measured using an automated device. Distribution of mercury in hair (mean, range: 0.45, 0.02-5.18 μg/g) and urine (0.94, 0.03-5.54 μg/L) correspond well with the US National Health and Nutrition Examination Survey. Linear regression models revealed significant associations between diastolic blood pressure (adjusted for blood pressure medication use) and hair mercury (n=262, p=0.02). Urine mercury results opposed hair mercury in many ways. Notably, elemental mercury exposure was associated with a significant systolic blood pressure decrease (n=262, p=0.04) that was driven by the male population. Associations between blood pressure and two forms of mercury were found at exposure levels relevant to the general population, and associations varied according to type of mercury exposure and gender.

Toxic effects of mercury on the cardiovascular and central nervous systems

Environmental contamination has exposed humans to various metal agents, including mercury. This exposure is more common than expected, and the health consequences of such exposure remain unclear. For many years, mercury was used in a wide variety of human activities, and now, exposure to this metal from both natural and artificial sources is significantly increasing. Many studies show that high exposure to mercury induces changes in the central nervous system, potentially resulting in irritability, fatigue, behavioral changes, tremors, headaches, hearing and cognitive loss, dysarthria, incoordination, hallucinations, and death. In the cardiovascular system, mercury induces hypertension in humans and animals that has wide-ranging consequences, including alterations in endothelial function. The results described in this paper indicate that mercury exposure, even at low doses, affects endothelial and cardiovascular function. As a result, the reference values defining the limits for the absence of danger should be reduced.

Exposure to low mercury concentration in vivo impairs myocardial contractile function

Increased cardiovascular risk after mercury exposure has been described but cardiac effects resulting from controlled chronic treatment are not yet well explored. We analyzed the effects of chronic exposure to low mercury concentrations on hemodynamic and ventricular function of isolated hearts. Wistar rats were treated with HgCl₂ (1st dose 4.6 μg/kg, subsequent dose 0.07 μg/kg/day, im, 30 days) or vehicle. Mercury treatment did not affect blood pressure (BP) nor produced cardiac hypertrophy or changes of myocyte morphometry and collagen content. This treatment: 1) in vivo increased left ventricle end diastolic pressure (LVEDP) without changing left ventricular systolic pressure (LVSP) and heart rate; 2) in isolated hearts reduced LV isovolumic systolic pressure and time derivatives, and β-adrenergic response; 3) increased myosin ATPase activity; 4) reduced Na+-K+ ATPase (NKA) activity; 5) reduced protein expression of SERCA and phosphorylated phospholamban on serine 16 while phospholamban expression increased; as a consequence SERCA/phospholamban ratio reduced; 6) reduced sodium/calcium exchanger (NCX) protein expression and α-1 isoform of NKA, whereas α-2 isoform of NKA did not change. Chronic exposure for 30 days to low concentrations of mercury does not change BP, heart rate or LVSP but produces small but significant increase of LVEDP. However, in isolated hearts mercury treatment promoted contractility dysfunction as a result of the decreased NKA activity, reduction of NCX and SERCA and increased PLB protein expression. These findings offer further evidence that mercury chronic exposure, even at small concentrations, is an environmental risk factor affecting heart function.

Protective role of melatonin in myocardial oxidative damage induced by mercury in murine model

This study was designed to investigate the electrophysiological, hemodynamic and biochemical parameters of mercuric chloride and methylmercury exposure on cardiovascular functions and its modulation by melatonin in vivo. Wistar albino rats were divided into six group containing 10 animals each. Mercuric chloride (3.75 µM/L) in drinking water and methylmercury (0.5 mg/kg/day) through gavage, given for 1 month, induced a statistically significant increase ( p < 0.001) in left ventricular end diastolic pressure, blood and cardiac tissue mercury content and myocardial lipid peroxides compared to control. Significant attenuation ( p < 0.05) of baroreflex sensitivity and depletion of myocardial endogenous antioxidants ( p < 0.001) viz. Reduced glutathione (GSH) and superoxide dismutase (SOD) were also found in the mercury-exposed groups as compared to control group. Mercury exposure followed by subacute treatment with melatonin (4 µg/mL/day) in drinking water for 1 month significantly lowered ( p < 0.01) left ventricular end diastolic pressure and lipid peroxide levels and increased baroreceptor sensitivity ( p < 0.001) and also levels of GSH and SOD ( p < 0.001) as compared to mercury-exposed rats. The results of our study provide clear evidence that elevated oxidative stress and altered baroreflex mechanisms caused by mercury intoxication may be the contributing factors responsible for impairment of cardiovascular functions and melatonin may exhibit cardioprotective property against subacute heavy metal intoxication and enhance the antioxidant defense against mercury-induced oxidative myocardial injury in rats.

Low mercury concentrations cause oxidative stress and endothelial dysfunction in conductance and resistance arteries

Increased cardiovascular risk after mercury exposure has been described, but the underlying mechanisms are not well explored. We analyzed the effects of chronic exposure to low mercury concentrations on endothelium-dependent responses in aorta and mesenteric resistance arteries (MRA). Wistar rats were treated with mercury chloride (1st dose 4.6 μg/kg, subsequent dose 0.07 μg·kg−1·day−1im, 30 days) or vehicle. Blood levels at the end of treatment were 7.97 ± 0.59 ng/ml. Mercury treatment: 1) did not affect systolic blood pressure; 2) increased phenylephrine-induced vasoconstriction; 3) reduced acetylcholine-induced vasodilatation; and 4) reduced in aorta and abolished in MRA the increased phenylephrine responses induced by either endothelium removal or the nitric oxide synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 100 μM). Superoxide dismutase (SOD, 150 U/ml) and the NADPH oxidase inhibitor apocynin (0.3 mM) decreased the phenylephrine-induced contraction in aorta more in mercury-treated rats than controls. In MRA, SOD did not affect phenylephrine responses; however, when coincubated with l-NAME, the l-NAME effect on phenylephrine response was restored in mercury-treated rats. Both apocynin and SOD restored the impaired acetylcholine-induced vasodilatation in vessels from treated rats. Endothelial NOS expression did not change in aorta but was increased in MRA from mercury-treated rats. Vascular O2−production, plasmatic malondialdehyde levels, and total antioxidant status increased with the mercury treatment. In conclusion, chronic exposure to low concentrations of mercury promotes endothelial dysfunction as a result of the decreased NO bioavailability induced by increases in oxidative stress. These findings offer further evidence that mercury, even at low concentrations, is an environmental risk factor for cardiovascular disease.

Low nanomolar concentration of mercury chloride increases vascular reactivity to phenylephrine and local angiotensin production in rats

Exposure to mercury at nanomolar level affects cardiac function but its effects on vascular reactivity have yet to be investigated. Pressor responses to phenylephrine (PHE) were investigated in perfused rat tail arteries before and after treatment with 6 nM HgCl2 during 1 h, in the presence (E+) and absence (E-) of endothelium, after L-NAME (10(-4) M), indomethacin (10(-5 )M), enalaprilate (1 microM), tempol (1 microM) and deferoxamine (300 microM) treatments. HgCl2 increased sensitivity (pD2) without modifying the maximum response (Emax) to PHE, but the pD2 increase was abolished after endothelial damage. L-NAME treatment increased pD2 and Emax. However, in the presence of HgCl2, this increase was smaller, and it did not modify Emax. After indomethacin treatment, the increase of pD2 induced by HgCl2 was maintained. Enalaprilate, tempol and deferoxamine reversed the increase of pD2 evoked by HgCl2. HgCl2 increased the angiotensin converting enzyme (ACE) activity explaining the result obtained with enalaprilate. Results suggest that at nanomolar concentrations HgCl2 increase the vascular reactivity to PHE. This response is endothelium mediated and involves the reduction of NO bioavailability and the action of reactive oxygen species. The local ACE participates in mercury actions and depends on the angiotensin II generation.

Small doses of mercury increase arterial pressure reactivity to phenylephrine in rats

Mercury reduces cardiac contractility and arterial pressure at micromolar concentrations. We investigated the actions of 680ng/kg HgCl(2) on arterial pressure, heart rate (HR) and on the pressor reactivity to phenylephrine (PHE) in rats before and 1h after HgCl(2) administration and after hexametonium, verapamil and tempol treatments. HgCl(2) increased baseline systolic (SAP) and diastolic pressure (DAP) and HR, sensitivity (pD(2)) and maximal response (E(max)) to PHE pressor reactivity. Hexametonium and verapamil reduced baseline pressures and HR that increased after HgCl(2) treatment. Hexametonium did not change pD(2) or E(max) to PHE but verapamil reduced them. These parameters increased after HgCl(2) administration. Tempol did not alter baseline pressures, HR or PHE reactivity before and after HgCl(2). Results suggest that HgCl(2) increases SAP, DAP, HR and PHE reactivity; autonomic reflexes reduces HgCl(2) action; baseline pressure level do not interfere on HgCl(2) pressor effects but free radicals seems to be involved.

Small concentrations of mercury enhances positive inotropic effects in the rat ventricular myocardium

Small concentrations of mercury reduce the force development of the rat right myocardium and inhibit the sodium pump. This inhibition might increase the amount of activator Ca(2+) in the sarcoplasmic reticulum available upon activation. We further investigated whether this action could potentiate positive inotropic effects produced by Ca(2+) increment (0.62-1.25mM) and isoproterenol (20nM). Right ventricular strips contracting isometrically were treated with 0.1 and 1μM HgCl(2). Results showed that after HgCl(2) treatment the magnitude of both inotropic interventions was increased. Considering that Hg(2+) amongst its effects induces hypertension and might be associated with cardiovascular diseases these potentiating effects might have hazardous consequences.

Fish consumption, mercury exposure, and heart diseases

There is increasing concern regarding methylmercury exposure in populations that consume large amounts of fish. This situation poses a dilemma for those who choose to consume fish for its beneficial effects on heart disease risk. Recent evidence suggests that high mercury content in fish may diminish the cardioprotective effect of fish intake. We explore the current knowledge of Hg toxicity on the heart and evaluate the epidemiologic evidence to date.

Nitric oxide-dependent vasorelaxation and endothelial cell damage caused by mercury chloride

Mercury and its derivatives are known to constrict vascular smooth muscle cells. However, little is known about the role of endothelial cells in mercury-induced vasoreactivity. Using isolated, norepinephrine preconstricted rat aorta and pulmonary artery rings with intact endothelium, we demonstrate that mercury chloride (HgCl2) induces an endothelial-dependent vasorelaxation which was totally blocked by the nitric oxide inhibitor L-NAME. Besides this vasorelaxant effect, treatment with HgCl2 resulted in functional and morphological alterations of the endothelial cells. On aortic rings, endothelial cells were partly lifted from the basal membrane when incubated for 20 min in HgCl2 (10(-7) M)-containing buffer. At a concentration of 10(-6) M, the endothelial cells were completely denuded and acetylcholine vasorelaxation was abolished. Endothelial cell structure and function was preserved by incubating the vessels in HgCl2-containing rat blood instead of buffer. We conclude that HgCl2 induces an endothelial-dependent vasorelaxation and alters structure and function of vascular endothelial cells.

Effects of small concentrations of mercury on the contractile activity of the rat ventricular myocardium

Personal exposure to mercury vapor and the release of mercury from or during removal of amalgam dental fillings increases its blood and plasma concentration. However, it is not known if these very small amounts affect cardiac function. The effects of continuous exposure to 5 and 20 nM of HgCl(2) on the cardiac contractility were investigated in isometric and tetanic contractions of right ventricular strips and in Langendorff perfused rat hearts. The continuous exposure for 2 h produced a small but significant reduction of the isometric twitch force and time to peak tension shortened. Relative post-rest potentiation was not affected by this concentration of HgCl(2) suggesting a lack of action of the metal on the sarcoplasmic reticulum activity. Tetanic tension, in contrast to twitch force, was intensively reduced suggesting an important depressant action on the activity of contractile proteins. In perfused hearts beating spontaneously, isovolumic systolic pressure reduced progressively and the diastolic pressure increased. Although occurring heart rate reduction, it was similar for both controls and mercury treated hearts. Also, time dependent changes in coronary perfusion pressure were similar to controls. Results suggested that cardiac effects may be observed after continuous exposure to very small concentrations of mercury, probably as a result of the cell capacity to concentrate mercury. These results also indicate that continuous professional exposure to mercury followed by its absorption might have toxicological consequences affecting cardiac function, and being considered hazardous.