The influence of chronic low-level cadmium and/or lead feeding on myocardial contractility related to phosphorylation of cardiac myofibrillar proteins

Cardiac Myosin and Thin Filament as Targets for Lead and Cadmium Divalent Cations

Lead and cadmium are heavy metals widely distributed in the environment and contribute significantly to cardiovascular morbidity and mortality. Using Leadmium Green dye, we have shown that lead and cadmium enter cardiomyocytes, distributing throughout the cell. Using an in vitro motility assay, we have shown that sliding velocity of actin and native thin filaments over myosin decreases with increasing concentrations of Pb2+ and Cd2+. Significantly lower concentrations of Pb2+ and Cd2+ (0.6 mM) were required to stop sliding of thin filaments over myosin compared to the stopping actin sliding over the same myosin (1.1-1.6 mM). Lower concentration of Cd2+ (1.1 mM) needed to stop actin sliding over myosin compared to the Pb2++Cd2+ combination (1.3 mM) and lead alone (1.6 mM). There were no differences found in the effects of lead and cadmium cations on relative force developed by myosin heads or number of actin filaments bound to myosin. Sliding velocity of actin over myosin in the left atrium, right and left ventricles changed equally when exposed to the same dose of the same metal. Thus, we have demonstrated for the first time that Pb2+ and Cd2+ can directly affect myosin and thin filament function, with Cd2+ exerting a more toxic influence on myosin function compared to Pb2+.

A systematic review and meta-analysis of human population studies on the association between exposure to toxic environmental chemicals and left ventricular dysfunction (LVD)

BACKGROUND

Exposure to environmental chemicals has been associated with an elevated risk of heart failure (HF). However, the impact on early markers of HF, such as left ventricular dysfunction (LVD), remains limited.

OBJECTIVE

To establish a foundation of evidence regarding early HF markers and their association with environmental pollutants, a systematic review and meta-analysis was conducted.

METHODS

The search, conducted on October 13th, 2023, encompassed PubMed, Embase, and Web of Science without filters, focusing on observational studies reporting myocardial geometrical, structural, or functional alterations in individuals without a history of heart disease. This included the general adult population, workers, young people, and the elderly. The risk of bias was assessed using the ROBINS-I tool at both study and item levels.

RESULTS

The systematic review included 17 studies involving 43.358 individuals exposed to air pollution and 2038 exposed to heavy metals. Approximately 41% of the effect measures of associations reported significant abnormalities in myocardial structure or function. The metanalyses by pollutants categories indicated positive associations between LV systolic and diastolic abnormalities and exposure to PM2.5 [-0.069 (-0.104, -0.033); -0.044 (-0.062, -0.025)] and PM10 [-0.055 (-0.087, -0.022); -0.030 (-0.050, -0.010)] and NO2 [-0.042 (-0.071, -0.013); -0.021 (-0.037, -0.004)], as well as positive associations between lead exposure and LV systolic abnormalities [-0.033 (-0.051, -0.016)].

CONCLUSIONS

Existing evidence shows that specific early markers of HF may be associated with exposure to chemical pollutants. It is recommended to include such endpoints in new longitudinal and case-control studies to confirm further risk associations. These studies should consider co-exposures, account for vulnerable groups, and identify cardiotoxic compounds that may require regulation. When examining the link between myocardial abnormalities and environmental exposure, it is also advisable to explore the supportive use of Adverse Outcome Pathway (AOP) approaches to confirm a causal relationship.

Direct Effects of Toxic Divalent Cations on Contractile Proteins with Implications for the Heart: Unraveling Mechanisms of Dysfunction

The binding of calcium and magnesium ions to proteins is crucial for regulating heart contraction. However, other divalent cations, including xenobiotics, can accumulate in the myocardium and enter cardiomyocytes, where they can bind to proteins. In this article, we summarized the impact of these cations on myosin ATPase activity and EF-hand proteins, with special attention given to toxic cations. Optimal binding to EF-hand proteins occurs at an ionic radius close to that of Mg²⁺ and Ca²⁺. In skeletal Troponin C, Cd²⁺, Sr²⁺, Pb²⁺, Mn²⁺, Co²⁺, Ni²⁺, Ba²⁺, Mg²⁺, Zn²⁺, and trivalent lanthanides can substitute for Ca²⁺. As myosin ATPase is not a specific MgATPase, Ca²⁺, Fe²⁺, Mn²⁺, Ni²⁺, and Sr²⁺ could support myosin ATPase activity. On the other hand, Zn²⁺ and Cu² significantly inhibit ATPase activity. The affinity to various divalent cations depends on certain proteins or their isoforms and can alter with amino acid substitution and post-translational modification. Cardiac EF-hand proteins and the myosin ATP-binding pocket are potential molecular targets for toxic cations, which could significantly alter the mechanical characteristics of the heart muscle at the molecular level.

Cadmium exposure and growth differentiation factor-15 (GDF-15) levels in non-smoking older adults

BACKGROUND

Cadmium (Cd) exposure is a risk factor for cardiovascular disease (CVD); however, understanding the effects of Cd at the cellular level remains incomplete. Since growth differentiation factor-15 (GDF-15) is a cytokine produced in many cell types in response to tissue injury and inflammation that may capture several pathways between Cd and CVD, this study examined the relationship between blood Cd levels and serum GDF-15 concentrations in community-dwelling older adults.

METHODS

Cd and GDF-15 were measured in 1942 non-smoking individuals aged 65+ with no previous history of CVD. The association of Cd with GDF-15 was evaluated in linear regression models that adjusted for sociodemographic, lifestyle and biological risk factors, inflammatory biomarkers (IL-6, C-reactive protein and neutrophil to lymphocyte ratio), and markers of vascular damage (NTproBNP and cTnT-hs).

RESULTS

Geometric mean Cd exposure was 0.11 μg/L (0.09 in never- and 0.15 in former-smokers) and geometric mean GDF-15 was 1186.21 pg/mL (1182.67 in never- and 1191.66 in former-smokers). In multivariable analyses, we found a dose-response association between Cd levels and GDF-15: adjusted mean percentage differences in GDF-15 (95% confidence interval) per 2-fold increase in Cd concentrations in the overall non-smoking population and in never smokers were, respectively, 2.54% (1.01, 4.06) and 2.50% (0.47, 4.54). In spline regression, the dose-response relationship was progressive over the range of Cd concentrations with no significant departures from linearity.

CONCLUSIONS

Cd exposure may be related to enhanced GDF-15 expression. Future studies with repeated GDF-15 measurements should confirm the present findings to better understand the biological mechanisms underlying this association.

Urinary Cadmium and Incident Heart Failure: A Case-Cohort Analysis Among Never-Smokers in Denmark

BACKGROUND

Epidemiologic studies suggest cadmium exposure is associated with cardiovascular disease risk, including heart failure. However, prior findings may be influenced by tobacco smoking, a dominant source of cadmium exposure and risk factor for heart failure. The present study leverages up to 20 years of follow-up in the Danish Diet, Cancer and Health cohort to examine the relationship between urinary cadmium and incident heart failure among people who never smoked.

METHODS

Between 1993 and 1997, 19,394 never-smoking participants (ages 50-64 years) enrolled and provided a urine sample. From this sample, we randomly selected a subcohort of 600 men and 600 women and identified 958 incident heart failure cases occurring between baseline and 2015. Using a case-cohort approach, we estimated adjusted hazard ratios (aHR) for heart failure in Cox proportional hazards models with age as the time scale.

RESULTS

Participants had relatively low concentrations of urinary cadmium, as expected for never smokers (median = 0.20; 25th, 75th = 0.13, 0.32 μg cadmium/g creatinine). In adjusted models, we found that higher urinary cadmium was associated with a higher rate of incident heart failure overall (aHR = 1.1 per interquartile range difference [95% CI = 1.0, 1.2). In sex-stratified analyses, the association seemed restricted to men (aHR = 1.5 [95% CI = 1.2, 1.9]).

CONCLUSIONS

In this cohort of people who never smoked tobacco, environmental cadmium was positively associated with incident heart failure, especially among men.

Force-velocity characteristics of isolated myocardium preparations from rats exposed to subchronic intoxication with lead and cadmium acting separately or in combination

This investigation continues our study of the effects of Pb-Cd poisoning on the heart, extending the enquiry from isometric to auxotonic contractions, thereby examining the effect on the ability of myocardial tissues to perform mechanical work. Different shifts were revealed in myocardial force-velocity relations following subchronic exposure of rats to lead acetate and cadmium chloride acting separately, in combination, or in combination with a bioprotective complex (BPC). The experiments were conducted on isolated preparations of trabecules and papillary muscles of the right ventricle in physiological loading conditions and on isolated heart muscle contractile proteins examined by the in vitro motility assay. The results of the latter correlate with the shifts in the ratio of cardiac myosin isoforms. The amount of work performed by the myocardium was calculated on the basis of the tension-shortening loop area and was found to be similar in the preparations from all experimental groups. This fact presumably reflects adaptive capacity of the myocardial function even when contractility is damaged due to the metallic intoxication of a moderate severity. Some characteristics of rat myocardium altered by the impact of lead-cadmium intoxication became fully or partly normalized if intoxication developed against background administration of a bioprotective complex (BPC). Together with previously reported results obtained in the isometric mode of contractility, all these results strengthen the scientific foundations of risk assessment and risk management projects in the occupational and environmental conditions characterized by human exposure to lead and/or cadmium.

A Rare Case of Lead-Induced Cardiomyopathy

A 39-year-old man, painter by profession, presented with symptoms of heart failure. His work up was unrevealing except for elevated blood lead levels (BLL). He was started on guideline-directed medical therapy and was referred to occupational therapy. No improvement in his ejection fraction was noted until his BLL decreased. (Level of Difficulty: Intermediate.)

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.

Further verification of some postulates of the combined toxicity theory: New animal experimental data on separate and joint adverse effects of lead and cadmium

Outbred male rats were repeatedly injected intraperitoneally two-level sub-lethal doses of lead acetate and/or cadmium chloride solutions 3 times a week during 6 weeks. The animals developed explicit, even if moderate, subchronic intoxication characterized by a large number of indices, both common to both metals (including increased DNA fragmentation coefficient) and lead-specific. Special attention was paid to hemodynamic and electrocardiographic effects. The combined action of lead and cadmium was modeled with the help of the Response Surface Methodology to obtain additional support for the previously substantiated postulates of combined toxicity's typological ambiguity. This is dependent on which particular effect comes under consideration, on its level, and on the acting dose ratio. For one and the same toxic combination, the type of combined toxic action can vary from synergistic to contra-directional. In particular, the actions of lead and cadmium on blood pressure were found to be opposite in direction. Furthermore, it is shown once again that the systemic toxic effects of a metal combination, its in vivo genotoxicity included, can be more or less attenuated by background administration of a theoretically justified composition of biologically active agents.

Further analysis of rat myocardium contractility changes associated with a subchronic lead intoxication

A moderate subchronic lead intoxication was observed in male rats after repeated intraperitoneal injections of lead acetate. Right ventricular trabeculae and papillary muscles were isolated for in vitro studying of the contraction-relaxation cycle under isotonic and physiological loading. The contractile function of the myocardium was also assessed by measuring the velocity of thin filament movement over myosin. Lead intoxication led in papillary muscles to a decrease in the maximal rate of isotonic shortening for all afterloads and a decrease in the thin filament sliding velocity. Papillary muscles from lead-exposed rats displayed marked changes in most of the main characteristics of afterload contraction-relaxation cycles, but in trabeculae these changes were less pronounced. The reported changes were attenuated to some extent in rats treated with a Ca-containing bioprotector. The amount of work produced by both types of heart muscle preparations was not changed by lead. Only in papillary muscles the load-dependent relaxation index was significantly increased in the lead-treated groups. Thus subchronic lead intoxication affects the peak rate of force development and relaxation properties of cardiac muscle contracting in isotonic/physiological regimes rather than the total amount of mechanical work, which may reflect adaptive changes in the myocardial function under decreased contractility.

Effects of subchronic lead intoxication of rats on the myocardium contractility

Outbred male rats were repeatedly injected IP with sub-lethal doses of lead acetate 3 times a week during 5 weeks. They developed an explicit, even if moderate, lead intoxication characterized by typical hematological and some other features. The next day after the last injection the heart of each animal was excised, and the trabecules and papillary muscles from the right ventricle were used for modeling in vitro isometric (with varying starting length of the preparation) regimes of the contraction-relaxation cycle with different preloads. Several well-established parameters of this model were found changed compared with the preparations taken from the hearts of healthy control rats. Background in vivo calcium treatment attenuated both systemic and cardiotoxic effects of lead to an extent. We show for the first time that subchronic intoxication with lead caused myocardial preparations in a wide range of lengths to respond by a decrease in the time and speed parameters of the isometric contraction while maintaining its amplitude and by a decrease in the passive stiffness of trabecules. The responses of the various heart structures are outlined, and the isomyosin ratio is shown to have shifted towards the slow isoform. Mechanistic and toxicological inferences from the results are discussed.

Left Ventricular Structure and Function in Relation to Environmental Exposure to Lead and Cadmium

Background

Experimental studies have demonstrated that lead and cadmium have direct toxic effects on the myocardium, but the few human studies are limited by design, assessment of exposure, and use of heart failure as a late‐stage endpoint.

Methods and Results

In a prospective population study, we studied the association of left ventricular (LV) function with blood lead (BPb) and 24‐hour urinary cadmium (UCd). In 179 participants randomly recruited from a Flemish population (50.3% women; mean age 39.1 years), geometric mean BPb and UCd at enrollment (1985‐2000) were 0.20 μmol/L and 6.1 nmol, respectively. We assessed systolic and diastolic LV function 11.9 years (median) later (2005‐2010) by using Doppler imaging of the transmitral blood flow and the mitral annular movement and speckle tracking. In multivariable‐adjusted linear regression, LV systolic function decreased with BPb. For a doubling of exposure, estimates were −0.392% for global longitudinal strain (P=0.034), −0.618% and −0.113 s⁻¹ for regional longitudinal strain (P=0.028) and strain rate (P=0.008), and −0.056 s⁻¹ for regional radial strain rate (P=0.050). Regional longitudinal strain rate (−0.066 s⁻¹, P=0.009) and regional radial strain (−2.848%, P=0.015) also decreased with UCd. Models including both exposure indexes did not allow differentiating whether LV dysfunction was predominately related to BPb or UCd. Diastolic LV function was not associated with BPb or UCd (P≥0.159).

Conclusions

Although effect sizes were small, our results suggest that environmental exposure to lead, cadmium, or both might be a risk factor for systolic LV dysfunction, a condition often proceeding to heart failure.

Effects of Low-Level Cadmium Intake on the Contractility and Morphology of the Rat Aorta

Female Long Evans hooded rats with an initial mean (± SE) weight of 85.7 ± 1.2 g were exposed to 5 ppm cadmium (Cd) in drinking water for 6 months. Rats which received no Cd in the drinking water served as untreated controls. Weights, systolic blood pressures (tail cuff method), several aspects of aortic ultrastructure, and isolated aortic contractile responses to epinephrine, angiotensin, and potassium chloride at 0, 1, 2, 3, and 6 months were observed in both groups. At none of the testing times was there a significant difference between the weights or systolic blood pressures of the control and Cd-treated groups. Analysis of variance indicated that aortas from control and Cd-treated rats showed similar age-related changes in maximum tension development (contractility) and similar threshold doses. However, Cd-treated aortas developed significantly less maximum tension than control aortas when compared at the same time intervals in response to all of the vasoconstrictors tested. This decreased contractility was apparent at one month and persisted at about the same level (20%) at 2, 3, and 6 months. There were also expected age-related changes in aortic ultrastructure of both groups, and although the 6-month Cd-treated aortas showed more degenerating endothelial cells, differences that might explain the consistent decreases in contractility of the Cd-treated aortas were not observed. The results of this study indicate that chronic low-level Cd treatment causes decreases in aortic contractility, as have previously been reported for acute exposure to Cd, but that this change is not associated with the development of hypertension or with structural changes in the aorta.

Combination of cadmium and high cholesterol levels as a risk factor for heart fibrosis

The deleterious effects of increased cadmium (Cd) serum levels on the cardiovascular system are proven by epidemiological and basic science studies. Cd exposure of animals and humans is known to impair myocardial function, possibly leading to heart failure. This study aims at investigating the effect of Cd treatment on the cardiac system with emphasis on the combined effect of Cd and high serum cholesterol levels as an important cardiovascular risk factor. Detailed analyses of Cd-induced effects on the heart of ApoE-/- mice fed a high fat diet (HFD), ApoE-/- mice fed a normal diet (ND), and C57BL/6J mice fed a ND revealed proinflammatory and fibrotic changes in the presence of cellular hypertrophy but in the absence of organ hypertrophy. Hypercholesterolemia in ApoE-/- mice alone and in combination with Cd treatment resulted in significant cardiomyocyte cell death. Based on further analyses of heart sections, we conclude that severe hypercholesterolemia in combination with ApoE-/- genotype as well as Cd treatment results in necrotic cardiomyocyte death. These data were supported by in vitro experiments showing a Cd-induced depolarization of the mitochondrial membrane and the permeabilization of the plasma membrane arguing for the occurrence of Cd-induced necrotic cell death. In summary, we were able to show for the first time that the combination of high cholesterol and Cd levels increase the risk for heart failure through cardiac fibrosis. This observation could in part be explained by the dramatically increased deposition of Cd in the hearts of ApoE-/- mice fed a HFD.

Six interaction profiles for simple mixtures

The Agency for Toxic Substances and Disease Registry (ATSDR) has a program for chemical mixtures that encompasses research on chemical mixtures toxicity, health risk assessment, and development of innovative computational methods. ATSDR prepared a guidance document that instructs users on how to conduct health risk assessment on chemical mixtures (Guidance Manual for the Assessment of Joint Toxic Action of Chemical Mixtures). ATSDR also developed six interaction profiles for chemical mixtures. Two profiles were developed for persistent environmental chemicals that are often found in contaminated fish and also can be detected in human breast milk. The mixture included chlorinated dibenzo-p-dioxins, hexachlorobenzene, dichlorodiphenyl dichloroethane, methyl mercury, and polychlorinated biphenyls. Two profiles each were developed for mixtures of metals and mixtures of volatile organic chemicals (VOCs) that are frequently found at hazardous waste sites. The two metal profiles dealt with (a) lead, manganese, zinc, and copper; and (b) arsenic, cadmium, chromium, and lead; the two VOCs mixtures dealt with (a) 1,1,1-trichloroethane, 1,1-dichloroethane, trichloroethylene, and tetrachloroethylene; and (b) benzene, ethylbenzene, toluene, and xylenes (BTEX). Weight-of-evidence methodology was used to assess the joint toxic action for most of the mixtures. Physiologically based pharmacokinetic modeling was used for BTEX. In most cases, a target-organ toxicity dose modification of the hazard index approach is recommended for conducting exposure-based assessments of noncancer health hazards.

A review of persistent, low-grade lead challenge: neurological and cardiovascular consequences

Although acute toxicity following heavy intake of lead (Pb) is a well-established clinical entity, the harmful effects of persistent, low-dose challenge, a situation commonly found among the general population, is uncertain. The major dangers of persistent, low-dose challenge that have been hypothesized are controversial: first, mentation and behavioral perturbations and second, development of hypertension with its consequences on the cardiovascular system. Accordingly, one cannot exclude some contributions from persistent Pb exposure to chronic disease and the aging process. Despite these potential adversities, many sources for Pb contact still remain with us. Current estimates are that 10-50% of American children (over 3-4 million) harbor unsafe levels according to present-day standards. Therefore, it is reasonable to conclude that more work is needed in this area. Clearcut evidence concerning the deleterious influence of Pb on the nervous and/or cardiovascular-renal systems would lead to greater attempt to lessen exposure, to ameliorate symptomatology by providing supplemental agents which obviate the unwanted effects of Pb (iron, calcium, zinc), and to consider therapy with binding agents, like CaNa2EDTA, in the afflicted.

Cardiotoxicity and hypertension in rats after oral lead exposure

The rats were exposed to lead (0.25, 0.5 and 1.0 per cent lead acetate through drinking water) for 90 days to study its effect on some physiological and morphological parameters of the cardiovascular system. Blood lead levels increased in a dose dependent manner but heart tissue showed rise at only two higher doses in exposed animals. The two higher doses of lead resulted in an increased arterial blood pressure and calcium influx in atrial trabeculae and papillary muscles. No marked pathological or histochemical changes were observed in heart tissue excepting congestion and slightly reduced activity of succinic dehydrogenase in the highest dosed group. It was concluded that lead exposure through drinking water may produce increased arterial blood pressure and minor changes in the myocardium. Whether these changes are mediated through the effect of lead on the calcium transport needs further investigation.

The persistent threat of lead: medical and sociological issues

Lead exposure is an ancient malady. Its history serves as a useful paradigm through which to understand many other pollutants that our technological society has inserted into the human environment and may guide preventive steps for other agents. Lead poisoning was first recognized in workers exposed to high doses. The discovery of childhood toxicity occurred a century ago in Australia, when children with striking symptoms of paralysis, ophthalmoplegia, or meningitis were found to be highly lead exposed. Encephalopathy generally occurs at blood lead levels of 80 micrograms/dL or more, but unequivocal brain damage has been demonstrated at doses well below this level. At lower doses, the neurocognitive effects of lead are expressed as diminished psychometric intelligence, attention deficits, conduct problems, alterations in the electroencephalogram, school failure, and increased referral rates for special needs. Careful epidemiologic studies, which have controlled for the important confounders, have set the effect level at 10-15 micrograms/dL. Elegant animal studies in which confounding is not an issue have confirmed these findings. Although blood lead levels in the population have dropped over time for a number of reasons, there are some 3-4 million American children with blood lead levels of more than 15 micrograms/dL. Biochemical and functional changes have been demonstrated in the heme biosynthetic pathway and in the renal, cardiovascular, endocrine, immune, and nervous systems. The threshold for effect depends on the sensitivity of the methods used. A no-effect level has not been found. Further, this is not a disease of the poor alone. But the poor are exposed to much more lead than are the more economically favored. Deficiencies in body calcium, zinc, iron, and protein stores are associated with increased uptake. Optimizing nutrition enhances the resistance to lead. All children should be screened for lead at regular intervals, especially those with anemia, growth failure, and developmental or behavioral problems. Treatment protocols are well worked out, but chelation is only part of the therapy. Controlling the environment, strengthening the family's supports, enhancing nutrition, and offering remedial education are essential to a successful therapeutic outcome. Lead control has involved a continuing struggle between vested economic interests and regulatory agencies. In one area, the control of airbone lead, science, and public health have prevailed. In the past decade, the amount of alkyl lead consumed in gasoline additives has been reduced by 99%. Body lead burdens have dropped in close correspondence.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of selenium on blood pressure, urinary sodium excretion and plasma aldosterone in cadmium-treated male rats

The present study was carried out to help elucidate the possible mechanisms underlying the effect of Cd and the interaction of Se with Cd on blood pressure. Male Wistar rats were divided into four groups: control, Cd-treated, Se-treated, Se-and Cd-treated. Cd and Se were administered at doses of 1.0 mg/kg body weight by subcutaneous injection of aqueous solutions of CdCl2 X 2 X 1/2 H2O and Na2SeO3, respectively. Injections were made either alone or in the Cd + Se treated group, simultaneously at 12-h intervals for 7 consecutive days. All animals were then maintained without further treatment for an additional period of 18 days. Treatment with Cd and Se separately lowered the blood pressure on days 3 and 8, but these levels increased and were significantly higher than that in control rats by day 26. Plasma aldosterone concentrations increased and urinary Na excretion decreased from day 1 to 3 in rats treated with Cd and Se separately. Thereafter, increased water retention precedes the onset of increased blood pressure. From these findings, we suggest that in rats treated with Cd and Se separately the increase in plasma aldosterone is a main factor for decreased urinary Na excretion and increased retention of water, and these factors may be associated with an increase in blood pressure. The treatment with Cd and Se simultaneously decreased urinary Na excretion and increased the plasma aldosterone concentration and water retention before the onset of increased blood pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Bioaccumulation of cadmium: toxicity in Mugil cephalus

A series of 12 lethal and sublethal concentrations of Cd were applied in seawater to determine LC50 for two sizes of fish. Fries were found to be more sensitive to Cd toxicity than juveniles. During 2, 4, 6 and 8 week exposure periods to graded Cd concentrations, mortality increased but no significant effect on growth occurred. From subacute experiments, the MATC for fries and juveniles were 0.05-0.02 ppm Cd2+/1 and 2-0.1 ppm Cd2+/1, respectively. Liver was found to accumulate the highest concentration of Cd followed by gill, muscle, alimentary canal and finally the heart.

Calcium-dependent effects of cadmium on energy metabolism and function of perfused rat heart

Postequilibrated isolated rat hearts were perfused for 60 min with a standard supporting electrolyte buffer containing one of the following calcium concentrations: 0.9, 1.8, 3.5, or 5.0 mM, either with or without added cadmium. Doses of cadmium which proved to be minimally (0.03 microM Cd)--and maximally (3.0 microM Cd)--effective at 0.9 mM Ca were studied at all other calcium concentrations. A dose-dependent positive inotropy that persisted throughout the 60-min perfusion period was induced by the graded increases in the perfusate calcium concentration throughout the range from 0.9 to 5.0 mM. Atrioventricular node conductivity was prolonged significantly in hearts perfused with 0.9 mM Ca as compared to hearts perfused with higher calcium concentrations. Increasing the perfusate calcium concentration caused a dose-dependent increase in heart glycerol 3-phosphorylcholine (GPC) content. The other measured phosphatic metabolites of the heart were not altered significantly by varying the perfusate calcium level. In contrast, cadmium (3.0 microM Cd) induced extensive functional and metabolic aberrations which varied in magnitude as an inverse function of the perfusate calcium concentration. Contractile tension, rate of tension development (dT/dt), heart rate, coronary flow rate, and atrioventricular node conductivity were decreased significantly in response to cadmium perfusion. Moreover, these hearts characteristically had significantly elevated low energy phosphate (inosine monophosphate and inorganic phosphate) and decreased high energy phosphate (ATP, PCr) levels relative to their respective calcium controls. Furthermore, various phosphorylated intermediates of glycolysis (glucose 6-phosphate, fructose 6-phosphate, glucose 1-phosphate), as well as glycerol 3-phosphate, and uridine diphosphoglucose accumulated significantly in hearts perfused with cadmium at certain calcium concentrations below 5.0 mM. The calcium-activated increase in heart GPC was inhibited completely by 3 microM cadmium. At the minimally effective dose of cadmium (0.03 microM), demonstrable changes were apparent only at the lowest perfusate calcium concentration examined (0.9 mM). These findings are consistent with the hypothesis that cadmium interferes with calcium-activated and calcium-mediated physiologic and biochemical processes of the mammalian heart. The primary mechanistic basis for the action of cadmium appears to be linked to a competition with calcium for membrane and possibly intracellular binding and activation sites.

Cardiac physiologic and tissue metabolic changes following chronic low-level cadmium and cadmium plus lead ingestion in the rat

Female Long-Evans hooded rats received Schroeder's rye-based diet and 0 or 1 microgram/ml cadmium, or cadmium plus lead in mineral fortified drinking water from weaning to 18 months. The heavy metal-fed rats were normal with respect to control, including growth rates and final body weights. Rats receiving added cadmium and cadmium plus lead in the diet were characterized by a persistent hypertension which was evident after 2 months. Cardiac conduction system excitability was depressed preferentially in cadmium-(atrioventricular nodal region) and cadmium plus lead-(His-Purkinje system) fed rats. Although heart rates were comparable to control, myocardial contractile activity (peak active tension and dT/dt) was significantly decreased in intact perfused heart preparations from both heavy metal-treated groups. In conjunction with the observed physiologic changes, various tissue-specific metabolic alterations were detected in heart, kidney, and liver. Generally, prolonged heavy-metal ingestion at these levels resulted in impaired energy metabolism (e.g., decreased ATP, PCr; increased Pj, ADP concentrations) and altered essential mineral composition (e.g., calcium, magnesium, zinc, and to a lesser extent, sodium and potassium; copper levels were unaffected) that varied in severity according to the tissue. The addition of lead to the cadmium diet had little additive effect on the cardiovascular system; however, renal and hepatic tissues did exhibit apparent additive effects further suggesting that cadmium and lead actions and interactions may be tissue dependent. These experimental findings and the biologic inferences derived are consonant with the hypothesis that chronic, life-long cadmium exposure approximating environmental levels may have significant adverse effects on mammalian systems, that include effects on cardiovascular tissues.

Does cadmium contribute to human hypertension

In 1962 Schroeder reported marked hypertension in rats chronically fed a very low cadmium diet and 5 ppm cadmium in water, but subsequently he reported only moderate hypertension. Using Schroeder's food and water, but a slightly less cadmium-free environment, we repeatedly induced mild hypertension with 5 ppm cadmium, mild because control pressures were higher not because cadmium-fed animals had lower pressures. Seven laboratories have observed hypertension after feeding cadmium; six have not. Thus, chronically fed cadmium can induce hypertension in rats, but conditions are important. Additional observations on cadmium-induced hypertension indicate that: (1) concentrations from 0.1 to 5 ppm cadmium in water are pressor; (2) sex, strain, and age of animals are apparently not limiting factors; (3) there is associated sodium retention; (4) there is a concomitant decrease in the high energy phosphate content of tissues. Rats with cadmium-induced hypertension have renal cadmium concentrations which bracket those of the average environmentally exposed American or European. Finally, renal cadmium concentrations in man were significantly higher (p less than 0.05) for "hypertensives" than for normotensive "matches" in five of nine reported series, lower in one, and similar in three, with all series being small and suboptimal in subject selection.

Additive statistical effects of cadmium and lead on heart-related disease in a North Carolina autopsy series

The association of heart-related mortality with tissue cadmium and lead in a study of autopsies performed on persons who resided in a soft-water, leached-soil area of North Carolina was examined. Liver cadmium concentrations and aortic lead level were indices of these elements. Both cadmium and lead levels had statistically significant correlations with cause of death (heart-related disease vs. non-heart-related disease, excluding cancer). Although cause of death was significantly associated with age, the association with cadmium and lead persisted after statistical adjustment for the effect of age. The combined effects of cadmium and lead provided sufficient information in an additive model to predict cause of death correctly for 80% of the cases, with age contributing insignificantly. These findings indicate the intimate relation of these two trace metals with increased risk of heart-related mortality, even in light of known conventional causes of such deaths.