Trace elements and cardioprotection: increasing endogenous glutathione peroxidase activity by oral selenium supplementation in rats limits reperfusion-induced arrhythmias

The role of iron overload and ferroptosis in arrhythmia pathogenesis

Ferroptosis is a newly discovered form of programmed cell death triggered by intracellular iron overload, which leads to the accumulation of lipid peroxides in various cells. It has been implicated in the pathogenesis and progression of various diseases, including tumors, neurological disorders, and cardiovascular diseases. The intricate mechanism underlying ferroptosis involves an imbalance between the oxidation and antioxidant systems, disturbances in iron metabolism, membrane lipid peroxidation, and dysregulation of amino acid metabolism. We highlight the key molecular mechanisms governing iron overload and ferroptosis, and discuss potential molecular pathways linking ferroptosis with arrhythmias.

Micronutrient deficiencies and new-onset atrial fibrillation in a community-based cohort: data from PREVEND

AIM

Malnutrition has been linked to cardiovascular diseases. Both selenium and iron deficiency have been associated with worse prognosis in patients with heart failure (HF). Yet, little is known about the role of micronutrients in the development of atrial fibrillation (AFib). In this study, we aimed to elucidate the association of micronutrient deficiencies with new-onset AFib.

METHODS

Selenium, magnesium, and iron parameters were measured in a well-characterized prospective cohort study (N = 5452). Selenium deficiency was defined as serum selenium < 70 μg/L, iron deficiency as serum ferritin < 30 μg/L, and magnesium deficiency as plasma magnesium < 0.85 mmol/L. New-onset AFib was the primary outcome. Additionally, we tested for previously reported effect-modifiers where applicable.

RESULTS

Selenium, iron, and magnesium deficiency was observed in 1155 (21.2%), 797 (14.6%), and 3600 (66.0%) participants, respectively. During a mean follow-up of 6.2 years, 136 (2.5%) participants developed new-onset AFib. Smoking status significantly interacted with selenium deficiency on outcome (p = 0.079). After multivariable adjustment for components of the CHARGE-AF model, selenium deficiency was associated with new-onset AFib in non-smokers (HR 1.69, 95% CI 1.09-2.64, p = 0.020), but not in smokers (HR 0.78, 95% CI 0.29-2.08, p = 0.619). Magnesium deficiency (HR 1.40, 95% CI 0.93-2.10, p = 0.110) and iron deficiency (HR 0.62, 95% CI 0.25-1.54, p = 0.307) were not significantly associated with new-onset AFib.

CONCLUSION

Selenium deficiency was associated with new-onset AFib in non-smoking participants. Interventional studies that investigate the effects of optimizing micronutrients status in a population at risk are needed to assess causality, especially in those with selenium deficiency. Micronutrients deficiencies (selenium, iron, and magnesium) have been associated with cardiovascular diseases and mitochondrial dysfunction in human cardiomyocytes. However, it is not known whether these deficiencies are associated with atrial fibrillation. To investigate this question, we measured all three micronutrients in 5452 apparently healthy individuals. After a mean follow-up of 6.2 years, there were 136 participants who developed atrial fibrillation. Participants with selenium deficiency had a significant increased risk to develop atrial fibrillation, as did the participants with two or more deficiencies.

Selenium concentration is associated with occurrence and diagnosis of three cardiovascular diseases: A systematic review and meta-analysis

BACKGROUND

Selenium (Se) is a vital trace element playing its biological functions through selenoprotein, which has been implicated in various physiological and pathological processes. A growing number of studies indicate that low Se increases the risk of cardiovascular diseases (CVDs). This meta-analysis aimed to compare and analyze differences in Se levels between patients with heart failure (HF), myocardial infarction (MI), coronary heart disease (CHD), and healthy people. This will provide ideas with the potential to improve clinical intervention and prevention of CVDs.

METHODS

The PubMed, Embase, Chinese National Knowledge Infrastructure (CNKI) and Chinese Biomedical databases were systematically searched for relevant publications until November 20, 2020. The following combination keywords were used: "(heart failure disease OR myocardial infarction OR coronary heart disease) AND (selenium OR Se)". The identified studies were screened against inclusion and exclusion criteria and extracted data were analyzed using RevMan5.3 and State 16.0 software.

RESULTS

A total of 49 eligible studies (including 61 cohorts) were obtained. Results of the meta-analysis showed that there was a significant difference in Se levels between HF, MI, CHD patients and healthy people. The standard mean difference (SMD) level of Se in HF patients [SMD = -0.98, 95 % CI (-1.34, -0.62)], MI patients [MI: SMD = -3.46, 95 % CI (-4.43, -2.85)], and CHD patients [CHD: SMD = -0.47, 95 % CI (-0.64, -0.28)] were all significantly lower compared to healthy controls. Analysis of the correlation between Se level and publication year showed that SMD of Se levels in HF and controls was positively correlated with time. Se level was found to be a good diagnostic marker of MI (AUC = 0.7107, P = 0.0167, Sensitivity = 77.27 %, Specificity = 72.73 %).

CONCLUSIONS

This meta-analysis shows that Se levels in patients with HF, MI, and CHD are generally lower compared with healthy controls. However, due to the small number of included studies, further studies are needed to confirm the present results.

Therapeutic Potential of Selenium as a Component of Preservation Solutions for Kidney Transplantation

Selenium has strong antioxidant properties and diverse effects on the immune system. The aim of the study was to analyse the protective effect of selenium as a component of a kidney preservation solution on the prevention of ischemia-reperfusion injury of nephrons. The solution was modified by the addition of Se (1 µg/L), prolactin (0.1 µg/L) and Se with prolactin (1 µg/L Se + 0.1 µg/L PRL). The study used a model for storing isolated porcine kidneys in Biolasol^® (modified Biolasol^®), which minimizes ischemia-reperfusion injury of grafts. The introduction of Se⁴⁺ ions at a dose of 1 µg/L into the Biolasol^® preservation solution in the form of Na₂SeO₃ caused an increase in the activity/concentration of the analysed biochemical parameters: aspartate transaminase, alanine transaminase, urea and protein. This suggests an adverse effect of Se⁴⁺ on nephron function during ischemia-reperfusion. The best graft protection was obtained by using Biolasol^® modified with the addition of selenium (IV) at a dose of 1 µg/L and prolactin at a concentration of 0.1 µg/L. We proposed the mechanism of prolactin action in the metabolic reduction of selenite (SO₃²⁻) during ischemia/reperfusion.

Cardiomyopathy in Children: Classification and Diagnosis: A Scientific Statement From the American Heart Association

In this scientific statement from the American Heart Association, experts in the field of cardiomyopathy (heart muscle disease) in children address 2 issues: the most current understanding of the causes of cardiomyopathy in children and the optimal approaches to diagnosis cardiomyopathy in children. Cardiomyopathies result in some of the worst pediatric cardiology outcomes; nearly 40% of children who present with symptomatic cardiomyopathy undergo a heart transplantation or die within the first 2 years after diagnosis. The percentage of children with cardiomyopathy who underwent a heart transplantation has not declined over the past 10 years, and cardiomyopathy remains the leading cause of transplantation for children >1 year of age. Studies from the National Heart, Lung, and Blood Institute-funded Pediatric Cardiomyopathy Registry have shown that causes are established in very few children with cardiomyopathy, yet genetic causes are likely to be present in most. The incidence of pediatric cardiomyopathy is ≈1 per 100 000 children. This is comparable to the incidence of such childhood cancers as lymphoma, Wilms tumor, and neuroblastoma. However, the published research and scientific conferences focused on pediatric cardiomyopathy are sparcer than for those cancers. The aim of the statement is to focus on the diagnosis and classification of cardiomyopathy. We anticipate that this report will help shape the future research priorities in this set of diseases to achieve earlier diagnosis, improved clinical outcomes, and better quality of life for these children and their families.

Seleno-l-methionine and l-ascorbic acid differentiate the biological activity of doxorubicin and its metal complexes as a new anticancer drugs candidate

The most important problems of anti-cancer therapy include the toxicity of the drugs applied to healthy cells and the multi-drug cells resistance to chemotherapeutics. One of the most commonly used anticancer drugs is doxorubicin (DOX) used to treat certain leukemias and non-Hodgkin's lymphomas, as well as bladder, breast, stomach, lung, ovarian, thyroid, multiple myeloma and other cancers. Preliminary studies showed that metal complex with DOX improve its cytostatic activity with changes in their molecular structure and distribution of electrons, resulting in a substantial change of its biological activity (including antitumor activity). Thus, there is a chance to receiving derivatives of DOX with low toxicity for the healthy body cells, thus increasing its therapeutic selectivity. In the present study we examined the influence of Mn, Mg, Fe, Co and Ni, seleno-l-methionine and vitamin C on biological activity of DOX in prokaryotic model - Escherichia coli RFM443, with plasmid transcriptional fusion of recA promoter and luxCDABE as a reporter gene. Cytotoxic potency of tested chemicals was calculated on the basis of the bacteria culture growth inhibition (GI%) values. Genotoxic properties were calculated on the basis of the fold increase (FI) of relative luminescence units (RLU) values compared to control. Obtained results showed that doxorubicin metal complexes particularly with Ni, Co and Fe increased the cyto- and genotoxic activities of DOX. Bacteria culture supplemented with SeMet and vitamin C differentiate the DOX and its metal complexes toxicity. It seems, that DOX-Ni, DOX-Fe and DOX-Co complexes could be potent cytostatic drug candidates. Moreover, we noticed different sensitivity of recA::luxCDABE for 3 h and 24 h cultures of bacteria strain. It suggests, that the potency of genetic construct reactivity- recA::luxCDABE in E. coli depends on the growth-phase of bacterial culture.

An overview of the ongoing insights in selenium research and its role in fish nutrition and fish health

In the present review, the ongoing researches about selenium research in fish nutrition have been comprehensively discussed. Selenium research is getting popularity in fish nutrition as it is required for the normal growth and proper physiological and biochemical functions in fish. Its deficiency or surplus amounts create severe problems in fish. It is available as inorganic form, organic form, and nano form. In fish, most of the previous research is about the selenium requirements for fish by using only one selenium source mainly the inorganic one. Selenium shows maximum biological activity and bioavailability when it is supplied in proper form. However, to differentiate the more bioavailable and less toxic form of selenium, sufficient information is needed about the comparative bioavailability of different selenium forms in different fish species. In fish, important data about the new forms of selenoproteins is still scarce. Therefore, it is necessary to focus on the determination and elucidation of the new selenoproteins in fish through the utilization of recent approaches of molecular biology and proteomics. The adaptation of these new approaches will replace the old fashioned methodologies regarding the selenium research in fish nutrition. Moreover, the use of molecular biology and proteomics-based new approaches in combination with selenium research will help in optimizing the area of fish nutrition and will improve the feed intake, growth performance, and more importantly the flesh quality which has a promising importance in the consumer market.

Selenium and its supplementation in cardiovascular disease--what do we know?

The trace element selenium is of high importance for many of the body’s regulatory and metabolic functions. Balanced selenium levels are essential, whereas dysregulation can cause harm. A rapidly increasing number of studies characterizes the wide range of selenium dependent functions in the human body and elucidates the complex and multiple physiological and pathophysiological interactions of selenium and selenoproteins. For the majority of selenium dependent enzymes, several biological functions have already been identified, like regulation of the inflammatory response, antioxidant properties and the proliferation/differentiation of immune cells. Although the potential role of selenium in the development and progression of cardiovascular disease has been investigated for decades, both observational and interventional studies of selenium supplementation remain inconclusive and are considered in this review. This review covers current knowledge of the role of selenium and selenoproteins in the human body and its functional role in the cardiovascular system. The relationships between selenium intake/status and various health outcomes, in particular cardiomyopathy, myocardial ischemia/infarction and reperfusion injury are reviewed. We describe, in depth, selenium as a biomarker in coronary heart disease and highlight the significance of selenium supplementation for patients undergoing cardiac surgery.

Interaction between selenium and mercury in biological samples of Pakistani myocardial infarction patients at different stages as related to controls

It has been speculated that trace elements may a play role in the pathogenesis of heart diseases. In the present study, we aimed to assess the levels of selenium (Se) and mercury (Hg) in biological samples (whole blood, urine, and scalp hair) of myocardial infarction (MI) patients of both genders (age range 45-60 years) at the first, second, and third heart attack (n = 130), hospitalized in a cardiac ward of a civil hospital of Hyderabad City (Pakistan). For comparison, healthy age-matched referent subjects (n = 61) of both genders were also selected. Se and Hg in biological samples were measured by electrothermal atomic absorption spectrometry and cold vapor atomic absorption spectrometry, prior to microwave acid digestion, respectively. The validity of the methodology was checked by biological certified reference materials. During this study, 78 % of the 32 registered patients of third MI attack (aged >50 years) died. The concentration of Se was decreased in scalp hair and blood samples of MI patients, while Hg was higher in all biological samples as compared to referent subjects. Se concentration was inversely associated with the risk of MI attacks in both genders. These results add to an increasing body of evidence that Se is a protective element for cardiovascular health.

Biological effects of selenium compounds with a particular attention to the ontogenetic development

Selenium is a trace element that is essential for living organism. Its beneficial effect is, however, expressed in a very narrow dosage range: the high and low doses of selenium are connected with pathological manifestations. The toxicity depends on the chemical form of selenium, state of organism, interactions with heavy metals and on the stage of ontogenetic development. Whereas one dose of sodium selenite (20 micromol/kg b.w.) is lethal in adult rats, suckling rats are entirely resistant. However, within one week after administration of the same dose, cataract of eye lens developed. The highest incidence of cataract was observed in 10-day-old animals and it decreased until day 20. From postnatal day 20 to day 40 the rats were resistant to both the lethal and cataractogenic effects of selenium. The incidence of cataract may be suppressed by premature weaning, lower hydration of suckling, change of water soluble/water insoluble lens protein ratio, thyroxine treatment, and by interaction with mercury. By means of its oxidative and reduction properties, selenium is involved in the maintenance of the cell redox homeostasis. Typical example is its possible cardioprotective effect: selenium decreased number of arrhythmias, reduced infarct size and improved the contractile recovery after ischemia/reperfusion injury. Selenium supplementation may thus increase cardiac tolerance to ischemic damage.

Impact of dietary selenium intake on cardiac health: experimental approaches and human studies

Selenium, a dietary trace mineral, essential for humans and animals, exerts its effects mainly through its incorporation into selenoproteins. Adequate selenium intake is needed to maximize the activity of selenoproteins, among which glutathione peroxidases have been shown to play a major role in cellular defense against oxidative stress initiated by excess reactive oxygen species. In humans, a low selenium status has been linked to increased risk of various diseases, including heart disease. The main objective of this review is to present current knowledge on the role of selenium in cardiac health. Experimental studies have shown that selenium may exert protective effects on cardiac tissue in animal models involving oxidative stress. Because of the narrow safety margin of this mineral, most interventional studies in humans have reported inconsistent findings. Major determinants of selenium status in humans are not well understood and several nondietary factors might be associated with reduced selenium status. In this review, we discuss recent studies regarding the role of selenoproteins in the cardiovascular system, the effect of dietary intake on selenium status, the impact of selenium status on cardiac health, and the cellular mechanisms that can be involved in the physiological and toxic effects of selenium.

Radiation protection following nuclear power accidents: a survey of putative mechanisms involved in the radioprotective actions of taurine during and after radiation exposure

There are several animal experiments showing that high doses of ionizing radiation lead to strongly enhanced leakage of taurine from damaged cells into the extracellular fluid, followed by enhanced urinary excretion. This radiation-induced taurine depletion can itself have various harmful effects (as will also be the case when taurine depletion is due to other causes, such as alcohol abuse or cancer therapy with cytotoxic drugs), but taurine supplementation has been shown to have radioprotective effects apparently going beyond what might be expected just as a consequence of correcting the harmful consequences of taurine deficiency per se. The mechanisms accounting for the radioprotective effects of taurine are, however, very incompletely understood. In this article an attempt is made to survey various mechanisms that potentially might be involved as parts of the explanation for the overall beneficial effect of high levels of taurine that has been found in experiments with animals or isolated cells exposed to high doses of ionizing radiation. It is proposed that taurine may have radioprotective effects by a combination of several mechanisms: (1) during the exposure to ionizing radiation by functioning as an antioxidant, but perhaps more because it counteracts the prooxidant catalytic effect of iron rather than functioning as an important scavenger of harmful molecules itself, (2) after the ionizing radiation exposure by helping to reduce the intensity of the post-traumatic inflammatory response, and thus reducing the extent of tissue damage that develops because of severe inflammation rather than as a direct effect of the ionizing radiation per se, (3) by functioning as a growth factor helping to enhance the growth rate of leukocytes and leukocyte progenitor cells and perhaps also of other rapidly proliferating cell types, such as enterocyte progenitor cells, which may be important for immunological recovery and perhaps also for rapid repair of various damaged tissues, especially in the intestines, and (4) by functioning as an antifibrogenic agent. A detailed discussion is given of possible mechanisms involved both in the antioxidant effects of taurine, in its anti-inflammatory effects and in its role as a growth factor for leukocytes and nerve cells, which might be closely related to its role as an osmolyte important for cellular volume regulation because of the close connection between cell volume regulation and the regulation of protein synthesis as well as cellular protein degradation. While taurine supplementation alone would be expected to exert a therapeutic effect far better than negligible in patients that have been exposed to high doses of ionizing radiation, it may on theoretical grounds be expected that much better results may be obtained by using taurine as part of a multifactorial treatment strategy, where it may interact synergistically with several other nutrients, hormones or other drugs for optimizing antioxidant protection and minimizing harmful posttraumatic inflammatory reactions, while using other nutrients to optimize DNA and tissue repair processes, and using a combination of good diet, immunostimulatory hormones and perhaps other nontoxic immunostimulants (such as beta-glucans) for optimizing the recovery of antiviral and antibacterial immune functions. Similar multifactorial treatment strategies may presumably be helpful in several other disease situations (including severe infectious diseases and severe asthma) as well as for treatment of acute intoxications or acute injuries (both mechanical ones and severe burns) where severely enhanced oxidative and/or nitrative stress and/or too much secretion of vasodilatory neuropeptides from C-fibres are important parts of the pathogenetic mechanisms that may lead to the death of the patient. Some case histories (with discussion of some of those mechanisms that may have been responsible for the observed therapeutic outcome) are given for illustration of the likely validity of these concepts and their relevance both for treatment of severe infections and non-infectious inflammatory diseases such as asthma and rheumatoid arthritis.

Effect of dietary selenium on the progression of heart failure in the ageing spontaneously hypertensive rat

Oxidative stress has been directly implicated in hypertension and myocardial remodelling, two pathologies fundamental to the development of chronic heart failure. Selenium (Se) can act directly and indirectly as an antioxidant and a lowered Se status leads to a higher risk of cardiovascular disease. This study examined the role of Se on the development of hypertension and subsequent progression to chronic heart failure in spontaneously hypertensive rats (SHR). Three dietary groups were studied: (i) Se-free; (ii) normal Se (50 μg Se/kg food); and (iii) high Se (1000 μg Se/kg food). Systolic blood pressure and echocardiography were used to detect cardiac changes in vivo. At study end, cardiac tissues were assayed for glutathione peroxidase activity, thioredoxin reductase activity, and protein carbonyls. The major finding of this study was the high heart failure-related mortality rate in SHRs fed an Se-free diet (70%). Normal and high levels of dietary Se resulted in higher survival rates of 78 and 100%, respectively. Furthermore, high dietary Se was clearly associated with lower levels of cardiac oxidative damage and increased antioxidant expression, as well as a reduction in disease severity and mortality in the SHR.

Dietary selenium intake influences Cx43 dephosphorylation, TNF-α expression and cardiac remodeling after reperfused infarction

SCOPE

Post-infarct left ventricular dysfunction and cardiac remodeling are the primary causes of chronic heart failure in industrialized countries. In the present study, we examined the influence of dietary selenium intake on cardiac remodeling after reperfused myocardial infarction and explored one of the possible mechanisms.

METHODS AND RESULTS

Rats were fed a diet containing either 0.05 mg/kg (Low-Se, group of rats receiving the low-selenium diet) or 1.50 mg/kg (group of rats receiving the high-selenium diet) selenium. At the end of the 5th week of the diet, rats were subjected to transient (1 h) coronary ligation followed by 8 days of reperfusion. Infarct size and cardiac passive compliance were increased in the Low-Se group compared with group of rats receiving the high-selenium diet. Similarly, indices of cardiac remodeling (thinning index and expansion index) were more altered in Low-Se hearts. These adverse effects of the Low-Se diet on cardiac remodeling were accompanied by an increase in cardiac TNF-α content, a decreased activity of antioxidant seleno-enzymes and an increase in connexin-43 dephosphorylation.

CONCLUSION

Dietary selenium intake influences post-infarct cardiac remodeling even when provided within the range of physiological values. Our data suggest that the cardioprotective effect of selenium might be mediated by a reduced oxidative stress, a lower connexin-43 dephosphorylation, and a decreased TNF-α expression.

Simulated urban carbon monoxide air pollution exacerbates rat heart ischemia-reperfusion injury

Myocardial damages due to ischemia-reperfusion (I/R) are recognized to be the result of a complex interplay between genetic and environmental factors. Epidemiological studies suggested that, among environmental factors, carbon monoxide (CO) urban pollution can be linked to cardiac diseases and mortality. The aim of this work was to evaluate the impact of exposure to CO pollution on cardiac sensitivity to I/R. Regional myocardial I/R was performed on isolated perfused hearts from rats exposed for 4 wk to air enriched with CO (30-100 ppm). Functional variables, reperfusion ventricular arrhythmias (VA) and cellular damages (infarct size, lactate dehydrogenase release) were assessed. Sarcomere length shortening and Ca(2+) handling were evaluated in intact isolated cardiomyocytes during a cellular anoxia-reoxygenation protocol. The major results show that prolonged CO exposure worsens myocardial I/R injuries, resulting in increased severity of postischemic VA, impaired recovery of myocardial function, and increased infarct size (60 +/- 5 vs. 33 +/- 2% of ischemic zone). The aggravating effects of CO exposure on I/R could be explained by a reduced myocardial enzymatic antioxidant status (superoxide dismutase -45%; glutathione peroxidase -49%) associated with impaired intracellular Ca(2+) handling. In conclusion, our results are consistent with the idea that chronic CO pollution dramatically increases the severity of myocardial I/R injuries.

Serum selenium and prognosis in cardiovascular disease: results from the AtheroGene study

OBJECTIVE

Experimental data suggest a protective role of the essential trace element selenium against cardiovascular disease (CVD), whereas epidemiological data remains controversial. We aimed to investigate the impact of serum selenium concentration in patients presenting with stable angina pectoris (SAP) or acute coronary syndrome (ACS) on long term prognosis.

METHODS

Baseline selenium concentration was measured in 1731 individuals (852 with SAP, and 879 with ACS). During a median follow-up of 6.1 years, 190 individuals died from cardiovascular causes.

RESULTS

In those ACS patients who subsequently died of cardiac causes, selenium levels were lower compared to survivors (61.0microg/L versus 71.5microg/L; P<0.0001). In a fully adjusted model, patients in the highest tertile of selenium concentration had a hazard ratio of 0.38 (95% CI: 0.16-0.91; P=0.03) as compared with those in the lowest. No association between selenium levels and cardiovascular outcome was observed in SAP.

CONCLUSIONS

Low selenium concentration was associated with future cardiovascular death in patients with ACS.

Protective role of selenium supplementation against cardiac lesions induced by the combination of levomepromazine and risperidone in the rabbit

Neuroleptics are a suspected cause of sudden death in psychiatric patients, especially in those with pre-existing cardiac lesions. As these lesions were previously shown to be associated with selenium (Se) deficiency, the aim of the present study was to evidence the possible protective effect of Se supplementation against cardiac lesions induced by the combination of the neuroleptic drugs levomepromazine and risperidone in the rabbit. Two groups of 6 rabbits were treated with 3 mg/kg of levomepromazine daily intramuscularly combined with 1 mg/kg of risperidone intramuscularly every other week for 3 consecutive months, and one group additionally received a solution of sodium selenite (2 μg/kg/day) intramuscularly during the whole treatment period. Furthermore, one group of six untreated animals was given the Se supplementation and another group of six control animals received saline daily. Blood samples were drawn before and at the end of the treatment period for the measurement of serum Se levels. At the end of the study, all animals were sacrificed and their hearts were removed for the measurement of tissue Se concentrations. In addition, the hearts were prepared for histopathological examination. A variety of cardiac lesions was found in the neuroleptics-treated animals without supplementation and to a lesser extent in the control and Se-supplemented untreated animals. Importantly, only rare cardiac lesions were observed in neuroleptics-Se-treated animals. The most striking differences in Se concentrations were noted in the myocardium: as compared to controls, there was a 43% reduction in neuroleptics-treated, but non-Se-supplemented animals (p < .01), at the end of the treatment period, whereas only a 14% reduction (p < .05) was noted in the neuroleptics-Se-treated animals. These results confirm that neuroleptics induce cardiac lesions associated with Se deficiency. Selenium supplementation markedly decreased the incidence and severity of neuroleptics-induced cardiac lesions and these findings may serve as a basis for further evaluation of the protective role of Se supplementation in neuroleptics-treated patients. However, Se supplementation in normal animals without Se deficiency was also shown to be cardiotoxic.

Fish, mercury, selenium and cardiovascular risk: current evidence and unanswered questions

Controversy has arisen among the public and in the media regarding the health effects of fish intake in adults. Substantial evidence indicates that fish consumption reduces coronary heart disease mortality, the leading cause of death in developed and most developing nations. Conversely, concerns have grown regarding potential effects of exposure to mercury found in some fish. Seafood species are also rich in selenium, an essential trace element that may protect against both cardiovascular disease and toxic effects of mercury. Such protective effects would have direct implications for recommendations regarding optimal selenium intake and for assessing the potential impact of mercury exposure from fish intake in different populations. Because fish consumption appears to have important health benefits in adults, elucidating the relationships between fish intake, mercury and selenium exposure, and health risk is of considerable scientific and public health relevance. The evidence for health effects of fish consumption in adults is reviewed, focusing on the strength and consistency of evidence and relative magnitudes of effects of omega-3 fatty acids, mercury, and selenium. Given the preponderance of evidence, the focus is on cardiovascular effects, but other potential health effects, as well as potential effects of polychlorinated biphenyls and dioxins in fish, are also briefly reviewed. The relevant current unanswered questions and directions of further research are summarized.

The effects of selenium on oxidative stress biomarkers in the freshwater characid fish matrinxã, Brycon cephalus (Günther, 1869) exposed to organophosphate insecticide Folisuper 600 BR (methyl parathion)

Methyl parathion (MP), an organophosphate widely applied in agriculture and aquaculture, induces oxidative stress due to free radical generation and changes in the antioxidant defense system. The antioxidant roles of selenium (Se) were evaluated in Brycon cephalus exposed to 2 mg L(-1) of Folisuper 600 BR (MP commercial formulation - MPc, 600 g L(-1)) for 96 h. Catalase (CAT), glutathione peroxidase (GPx), superoxide dismutase (SOD), glutathione S-transferase (GST), reduced glutathione (GSH) and lipid peroxidation (LPO) levels in the gills, white muscle and liver were evaluated in fish fed on diets containing 0 or 1.5 mg Se kg(-1) for 8 weeks. In fish treated with a Se-free diet, the MPc exposure increased SOD and CAT activities in all tissues. However, the GPx activity decreased in white muscle and gills whereas no alterations were observed in the liver. MPc also increased GST activity in all tissues with a concurrent decrease in GSH levels. LPO values increased in white muscle and gills and did not change in liver after MPc exposure. A Se-supplemented diet reversed these findings, preventing increases in LPO levels and concurrent decreases in GPx activity in gills and white muscle. Similarly, GSH levels were maintained in all tissue after MPc exposure. These results suggest that dietary Se supplementation protects cells against MPc-induced oxidative stress.

Role of selenium in heart lesions produced by neuroleptics in the rabbit

Organic and/or functional heart lesions sometimes resulting in sudden death have been described in psychiatric patients treated with neuroleptics. As selenium has been suggested previously to play a role in the development of such lesions, the present study was undertaken to determine whether a correlation could be found between heart lesions induced by neuroleptics and changes in blood selenium as well as myocardial tissue concentrations in the rabbit. Twelve NZW adult rabbits were treated intramuscularly with both levomepromazine (3 mg kg(-1) day(-1)) and risperidone (1 mg kg(-1) once every other week) for 3 months, and compared with 12 saline-treated controls. Blood samples were drawn before and at the end of the study. Tissue samples from the heart, liver and kidneys were obtained at the end of treatment, and the hearts were examined histologically. Heart lesions including disorganization of cardiac fibers, myolysis, interstitial and endocardial fibrosis, and necrosis were noted in treated animals, but not in controls. There was a 20% decrease in selenium blood levels and a 50% decrease in selenium myocardial tissue levels in treated animals compared with controls (P < 0.001). In contrast, no differences in selenium levels in liver and kidneys were found across the experimental groups. These results suggest a possible correlation between selenium depletion and neuroleptics-induced heart lesions.

Counteraction of adriamycin-induced oxidative damage in rat heart by selenium dietary supplementation

Many reports indicate that dietary selenium, potentially increasing the activity of glutathione peroxidase, could offer protection against free-radical-induced damage. The effects of diets moderately enriched in selenium, as sodium selenite or as a lyophilized selenium-rich food, were studied in rats. Adriamycin, an anticancer drug causing a free-radical-mediated cardiotoxicity, was administered intraperitoneally to some rats. The onset of an oxidative damage was indicated by the increase in the plasma level of reactive oxygen metabolites coupled to a decrease in the total antioxidant activity but without modification of glutathione peroxidase activity, which were observed in all rats, independent of the dietary treatment. On the contrary, in the heart, selenium supplementation caused an increase in the total antioxidant activity, glutathione concentration, and glutathione peroxidase and catalase activities leading to a decreased generation of reactive oxygen metabolites. These results clearly indicate that a moderate Se dietary supplementation counteracts adriamycin-induced cardiotoxicity by preservation of endogenous antioxidants.

Selenium status as determinant of connexin-43 dephosphorylation in ex vivo ischemic/reperfused rat myocardium

Recent studies have demonstrated that electrical uncoupling at gap junctions during ischemia is associated with cardiac Connexin-43 (Cx43) dephosphorylation. Whether oxidative stress is involved in this phenomenon still remains unclear. In the present study, we examined the influence of selenium intake on reperfusion-induced Cx43 dephosphorylation. Male Wistar rats were fed a diet containing either 0.05 mg/kg (Low-Se, n = 13) or 1.5 mg/kg (High-Se, n = 11) selenium for 8 weeks. At the end of this diet, hearts were isolated and subjected to 10 min regional ischemia followed by 10 min reperfusion. The level of dephosphorylated Cx43 was determined in tissue samples from ischemic/reperfused and non-ischemic regions of the hearts. At the end of the experiemental diet, the activity of the antioxidant enzyme glutathione peroxidase (GSH-Px) was increased in high-Se hearts compared with low-Se hearts (+ 13%; p < 0.05). After ischemia/reperfusion, in low-Se hearts, Cx43 dephosphorylation appeared significantly increased in the left ventricle compared to the non-ischemic right ventricle (+ 149%; p < 0.05). The high-Se diet significantly reduced Cx43 dephosphorylation in the left ventricle (p < 0.05 vs. low-Se diet). In conclusion, our results suggest that oxidative stress may be involved in Cx43 dephosphorylation during myocardial ischemia/reperfusion, thereby contributing to arrhythmogenesis.

The impact of cardiopulmonary bypass on selenium status, thyroid function, and oxidative defense in children

Selenium has important functions for oxidative defense and thyroid hormone metabolism. Selenium-dependent enzymes include 5'-iodothyronine deiodinase and glutathione peroxidase (GPX). The objective of this study was to investigate the relationship between plasma selenium, GPX activity, and thyroid hormone status in pediatric cardiac surgical patients. Plasma concentrations of selenium, free triiodothyronine (fT3), free thyroxin (fT4), and c-reactive protein as well as plasma activity of GPX were prospectively evaluated at anesthetic induction and 48 hours postoperatively in 59 children requiring cardiopulmonary bypass (CPB). GPX was measured at additional time points at 6, 12, and 24 hours postoperatively. There was a significant reduction in the plasma selenium concentration after cardiopulmonary bypass with obtained median measurements of 0.61 micromol/L (induction) and 0.51 micromol/L (48 hours postoperatively). The fT3/fT4 ratio decreased significantly from 0.28 at anesthetic induction to 0.22 at 48 hours postoperatively. There were no significant changes of GPX activity. 48 hours fT3 concentration, fT3/fT4 ratio, and selenium concentration were significantly negatively correlated with the time spent in intensive care. The concentration of plasma selenium in children undergoing cardiopulmonary bypass significantly decreases, resulting in diminished deiodinase activity, and a subsequent reduction in the conversion of T4 to T3.

Preischemic selenium status as a major determinant of myocardial infarct size in vivo in rats

Prospective epidemiological studies have shown that the incidence of numerous cardiovascular pathologies is correlated with body selenium status. However, it remains unclear whether selenium status also influences the outcome of myocardial infarction. The aim of the present study was to test whether dietary selenium intake affects myocardial necrosis induced by transient regional ischemia in vivo in rats. For this purpose, male Wistar rats received either a high-selenium (High-Se: 1.5 mg of Se/kg) or a low-selenium (Low-Se: 0.05 mg of Se/kg) diet for 10 weeks. Animals were subjected to 30 min of myocardial ischemia induced by coronary artery ligation followed by 60 min of reperfusion. Pre- and postischemic blood samples were collected for glutathione (GSH and GSSG) determination and for glutathione peroxidase (GSH-Px) assessment. Our results show that high-selenium intake reduces myocardial infarct size (High-Se: 25.16 +/- 1.19% versus Low-Se: 36.51 +/- 4.14%, p < 0.05), preserves postischemic GSH/GSSG ratio (High-Se: 1.37 +/- 0.37 versus Low-Se: 0.47 +/- 0.10, p < 0.05), increases plasma GSH-Px activity, and improves postischemic mean arterial pressure. In conclusion, preischemic body selenium status is a major determinant of the outcome of myocardial ischemia in vivo in rats probably because it influences the cellular redox status.

Effects of dietary selenium on glutathione peroxidase and thioredoxin reductase activity and recovery from cardiac ischemia-reperfusion

Glutathione peroxidase and thioredoxin reductase are selenocysteine-dependent enzymes that protect against oxidative injury. This study examined the effects of dietary selenium on the activity of these two enzymes in rats, and investigated the ability of selenium to modulate myocardial function post ischemia-reperfusion. Male wistar rats were fed diets containing 0, 50, 240 and 1000 microg/kg sodium selenite for 5 weeks. Langendorff perfused hearts isolated from these rats were subjected to 22.5 min global ischemia and 45 min reperfusion, with functional recovery assessed. Liver samples were collected at the time of sacrifice, and heart and liver tissues assayed for thioredoxin reductase and glutathione peroxidase activity. Selenium deficiency reduced the activity of both glutathione peroxidase and thioredoxin reductase systemically. Hearts from selenium deficient animals were more susceptible to ischemia-reperfusion injury when compared to normal controls (38% recovery of rate pressure product (RPP) vs. 47% recovery of RPP). Selenium supplementation increased the endogenous activity of thioredoxin reductase and glutathione peroxidase and resulted in improved recovery of cardiac function post ischemia reperfusion (57% recovery of RPP). Endogenous activity of glutathione peroxidase and thioredoxin reductase is dependent on an adequate supply of the micronutrient selenium. Reduced activity of these antioxidant enzymes is associated with significant reductions in myocardial function post ischemia-reperfusion.

Selenium status in Saudi Arabia

Selenium (Se) is a naturally occurring trace element that is essential for animal and human nutrition, but the range between dietary requirements and toxic levels is relatively narrow. In this review, we are interested in the beneficial effects of selenium and we report on a number of studies of the selenium status of different populations in Saudi Arabia. The Status reflects the geographical area inhabited by the populations. Apart from the few available studies reviewed here, no data on the human status of Se in Saudi Arabia has been obtained. A further objective of this paper is throw some the light on the direction of future studies.

Effects of selenium deficiency on the response of cardiac tissue to ischemia and reperfusion

Over a 10-week period, female Wistar rats received a diet containing a low level of selenium, cofactor of the antioxidant enzyme glutathione peroxidase (GPx) in order to examine the influence of deficiency of this trace element (i) on tissue antioxidant enzyme defence systems, and (ii) on the susceptibility of the myocardium to ischemia-reperfusion injury. At the end of the dietary treatment, hearts were perfused at constant flow (11 ml/min) before being subjected to 15 min of global normothermic ischemia, followed by 30 min of reperfusion. The effects of selenium deficiency were estimated by studying functional recovery of various cardiac parameters (left ventricular developed pressure LVDevP, heart rate HR, and the product HR x LVDevP), as well as ultrastructural tissue characteristics. Furthermore, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were measured at the end of the reperfusion period. Results suggest that: (a) the activity of GPx is decreased by selenium deficiency while SOD activity remains unchanged, (b) the recovery of cardiac function and myocardial ventricular ultrastructure during reperfusion are altered in the selenium-deficient group compared to controls. These results illustrate the crucial role that selenium, the co-factor of one of the major antioxidant enzymes of the myocardium, plays in determining the vulnerability of the heart to ischemia and reperfusion.

The importance of selenium to human health

The essential trace mineral, selenium, is of fundamental importance to human health. As a constituent of selenoproteins, selenium has structural and enzymic roles, in the latter context being best-known as an antioxidant and catalyst for the production of active thyroid hormone. Selenium is needed for the proper functioning of the immune system, and appears to be a key nutrient in counteracting the development of virulence and inhibiting HIV progression to AIDS. It is required for sperm motility and may reduce the risk of miscarriage. Deficiency has been linked to adverse mood states. Findings have been equivocal in linking selenium to cardiovascular disease risk although other conditions involving oxidative stress and inflammation have shown benefits of a higher selenium status. An elevated selenium intake may be associated with reduced cancer risk. Large clinical trials are now planned to confirm or refute this hypothesis. In the context of these health effects, low or diminishing selenium status in some parts of the world, notably in some European countries, is giving cause for concern.

Modulation of endogenous glutathione availability

Glutathione is quantitatively the most important antioxidant and scavenger. In addition it has a number of important functions in amino acid transport across membranes, in protein synthesis and degradation, in gene regulation and in cellular redox regulation. It becomes more and more evident that depletion of glutathione is associated with states of severe diseases. From this perspective, the possibility of manipulating the availability of glutathione becomes a very attractive form of treatment. In this review, new insights into pathophysiology and the regulation of glutathione metabolism, in addition to effects of precursors to and stimulants of glutathione synthesis, are covered. It is very likely that glutathione precursors will soon be an important pharmacological tool for treatment in a number of diseased states.