Lipid profile and peripheral vascular disease in arseniasis-hyperendemic villages in Taiwan

Role of Environmental Toxicants in the Development of Hypertensive and Cardiovascular Diseases

The incidence of hypertension with diabetes mellitus (DM) as a co-morbid condition is on the rise worldwide. In 2000, an estimated 972 million adults had hypertension, which is predicted to grow to 1.56 billion by 2025. Hypertension often leads to diabetes mellitus that strongly puts the patients at an increased risk of cardiovascular, kidney, and/or atherosclerotic diseases. Hypertension has been identified as a major risk factor for the development of diabetes; patients with hypertension are at two-to-three-fold higher risk of developing diabetes than patients with normal blood pressure (BP). Causes for the increase in hypertension and diabetes are not well understood, environmental factors (e.g., exposure to environmental toxicants like heavy metals, organic solvents, pesticides, alcohol, and urban lifestyle) have been postulated as one of the reasons contributing to hypertension and cardiovascular diseases (CVD). The mechanism of action(s) of these toxicants in developing hypertension and CVDs is not well defined. Research studies have linked hypertension with the chronic consumption of alcohol and exposure to metals like lead, mercury, and arsenic have also been linked to hypertension and CVD. Workers chronically exposed to styrene have a higher incidence of CVD. Recent studies have demonstrated that exposure to particulate matter (PM) in diesel exhaust and urban air contributes to increased CVD and mortality. In this review, we have imparted the role of environmental toxicants such as heavy metals, organic pollutants, PM, alcohol, and some drugs in hypertension and CVD along with possible mechanisms and limitations in extrapolating animal data to humans.

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Rising incidence of hypertension may be linked to chronic exposure with environmental toxicants.

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Urban lifestyle and alcohol intake may be responsible for increased incidence of hypertension among urbanites.

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Exposure with organic solvent, heavy metals and pesticides could also be contributing to the rise in blood pressure.

Effects of arsenic exposure on lipid metabolism: a systematic review and meta-analysis

Lipid metabolism dysfunction is a risk factor for cardiovascular diseases. Reportedly, arsenic exposure could affect lipid metabolism, but this finding remains controversial. Herein, we updated and reevaluated evidence regarding the relationship between arsenic exposure and lipid metabolism. Electronic and manual searches were performed to determine the effect of arsenic exposure on lipid metabolism from inception up to 30 November 2019. Overall, five studies were included in our meta-analysis. Two reviewers independently extracted information. Standardized mean difference (SMD) and 95% confidence intervals (CI) were used to analyze the combined effects of four indicators related to lipid metabolism (total cholesterol [TC], triglyceride [TG], high-density lipoprotein [HDL], low-density lipoprotein [LDL]). Afterwards, subgroup and sensitivity analyses were performed to explore the source of heterogeneity. Publication bias was tested using funnel plots and Begg's test. In this study, we observed that arsenic exposure can affect lipid metabolism by reducing serum HDL levels and increasing serum LDL levels. Following subgroup analysis, the arsenic concentration appeared to affect lipid metabolism. Funnel plot and Begg's test suggested no asymmetry. In conclusion, we recommend that potential influencing factors, including age, exposure time, and multiple concentration gradients, should be considered to further explore the relationship between arsenic exposure and lipid metabolism.

Association of apolipoprotein levels with peripheral arterial disease: a meta-analysis of literature studies

AIMS

Lower limb peripheral artery disease (PAD) is a leading cause of atherosclerotic cardiovascular disease (ASCVD). Discordant data are available on the association between apolipoprotein and PAD. We performed a meta-analyses on the association between apolipoprotein (apo)B, apoA-I, and apoB/apoA-I ratio with PAD.

METHODS AND RESULTS

PubMed, Web of Science, Scopus databases were systematically searched. Studies providing data about apoB, apoA-I, apoB/apoA-I ratio in PAD subjects and non-PAD controls were included. Differences between PAD and non-PAD subjects were expressed as mean difference (MD) with pertinent 95% confidence intervals (95%CI). Twenty-two studies were included. Peripheral artery disease subjects showed higher apoB (MD: 12.5 mg/dL, 95%CI: 2.14, 22.87) and lower apoA-I levels (MD: -7.11 mg/dL, 95%CI: -11.94, -2.28) than non-PAD controls. Accordingly, ApoB/ApoA-I ratio resulted higher in PAD subjects than non-PAD controls (MD: 0.11, 95% CI: 0.00, 0.21). Non-HDL-C showed a direct association with the difference in apoB (z-value: 4.72, P < 0.001) and an inverse association with the difference of apoA-I (z-value: -2.43, P = 0.015) between PAD subjects and non-PAD controls. An increasing BMI was associated with an increasing difference in apoA-I values between PAD subjects and non-PAD controls (z-value: 1.98, P = 0.047).

CONCLUSIONS

Our meta-analysis suggests that PAD subjects exhibit increased apoB and reduced apoA-I levels, accompanied by an increased apoB/apoA-I ratio as compared with non-PAD controls.

Early-life arsenic exposure promotes atherogenic lipid metabolism in adolescence: A 15-year birth cohort follow-up study in central Taiwan

BACKGROUND

Inorganic arsenic (iAs) exposure potentially causes diabetes and cardiovascular diseases in adults. However, its effect on glucose and lipid metabolism in early life remains unknown.

OBJECTIVE

We evaluated the associations between early-life arsenic exposure and profiles of glucose and lipids in a 15-year birth cohort in central Taiwan.

METHODS

We studied 237 adolescents through 5 waves of follow-up interviews and examinations at ages of approximately 2, 5, 8, 11, and 14 y. We obtained at least one follow-up urine measurement for arsenic species and blood sample collection up to 14 y of age and identified group-based trajectories of serial iAs by semiparametric mixture modeling. Multiple linear and logistic regressions were performed to assess the effect of the arsenic exposure trajectory on serum fasting glucose, total cholesterol (TCHO), triglycerides (TGs), low-density lipoprotein cholesterol (LDL), and high-density lipoprotein cholesterol (HDL).

RESULTS

Three trajectories of postnatal arsenic exposure were identified, namely stable-low (31.4%), stable-high (48.2%), and rising-high (20.4%) groups. Compared with the stable-low trajectory group, the percent changes in TCHO and LDL was 14% (95% confidence interval 4-24%) and 23% (9-38%) for the group with "rising-high" trajectory and was 8% (-1-16%) and 16% (4-29%) for the group with "stable-high" trajectory. The rising-high group was also associated with an increase in the TCHO/HDL ratio by 14% (95% CI 3%-25%). The adjusted odds ratios of high developmental trajectories of TCHO, TG, LDL, and non-HDL levels were 4.0 (95% CI 1.2-13.7), 12.2 (2.2-67), 7.3 (1.8-30), and 3.6 (0.9-14.6), respectively, in the rising-high group (reference: stable-low group).

CONCLUSION

Our findings suggest that conversion to an atherogenic lipid profile in adolescents may be associated with early-life exposure to environmental arsenic, particularly during the pre-adolescent period. An environmental modification approach for preventing As-related cardiovascular disease is recommended to begin early in life.

Arsenic Exposure and Subclinical Endpoints of Cardiovascular Diseases

Mechanistic evidence suggests that arsenic exposure from drinking water increases the production of reactive oxygen species and influences inflammatory responses and endothelial nitric oxide homeostasis. These arsenic-induced events may lead to endothelial dysfunction that increases the risk of atherosclerosis and cardiovascular disease. We reviewed accumulating epidemiologic evidence that evaluated the association between arsenic exposure and intermediate markers and subclinical measures that predict future cardiovascular risk. Cross-sectional studies have indicated positive associations between high or low-to-moderate levels of arsenic exposure with indices of subclinical atherosclerosis, QT interval prolongation, and circulating markers of endothelial dysfunction. The evidence is limited for other intermediate endpoints such as markers of oxidative stress and inflammation, QT dispersion, and lipid profiles. Prospective studies are needed to enhance the causal inferences of arsenic's effects on subclinical endpoints of cardiovascular disease, especially at lower arsenic exposure levels.

Interaction between arsenic exposure from drinking water and genetic susceptibility in carotid intima-media thickness in Bangladesh

Epidemiologic studies that evaluated genetic susceptibility for the effects of arsenic exposure from drinking water on subclinical atherosclerosis are limited. We conducted a cross-sectional study of 1078 participants randomly selected from the Health Effects of Arsenic Longitudinal Study in Bangladesh to evaluate whether the association between arsenic exposure and carotid artery intima-media thickness (cIMT) differs by 207 single-nucleotide polymorphisms (SNPs) in 18 genes related to arsenic metabolism, oxidative stress, inflammation, and endothelial dysfunction. Although not statistically significant after correcting for multiple testing, nine SNPs in APOE, AS3MT, PNP, and TNF genes had a nominally statistically significant interaction with well-water arsenic in cIMT. For instance, the joint presence of a higher level of well-water arsenic (≥ 40.4 μg/L) and the GG genotype of AS3MT rs3740392 was associated with a difference of 40.9 μm (95% CI = 14.4, 67.5) in cIMT, much greater than the difference of cIMT associated with the genotype alone (β = -5.1 μm, 95% CI = -31.6, 21.3) or arsenic exposure alone (β = 7.2 μm, 95% CI = -3.1, 17.5). The pattern and magnitude of the interactions were similar when urinary arsenic was used as the exposure variable. Additionally, the at-risk genotypes of the AS3MT SNPs were positively related to the proportion of monomethylarsonic acid (MMA) in urine, which is indicative of arsenic methylation capacity. The findings provide novel evidence that genetic variants related to arsenic metabolism may play an important role in arsenic-induced subclinical atherosclerosis. Future replication studies in diverse populations are needed to confirm the findings.

Arsenic exposure from drinking water, arsenic methylation capacity, and carotid intima-media thickness in Bangladesh

We conducted a cross-sectional study to evaluate the interrelationships between past arsenic exposure, biomarkers specific for susceptibility to arsenic exposure, and carotid intima-media thickness (cIMT) in 959 subjects from the Health Effects of Arsenic Longitudinal Study in Bangladesh. We measured cIMT levels on average 7.2 years after baseline during 2010-2011. Arsenic exposure was measured in well water at baseline and in urine samples collected at baseline and during follow-up. Every 1-standard-deviation increase in urinary arsenic (357.9 µg/g creatinine) and well-water arsenic (102.0 µg/L) concentration was related to a 11.7-µm (95% confidence interval (CI): 1.8, 21.6) and 5.1-µm (95% CI: -0.2, 10.3) increase in cIMT, respectively. For every 10% increase in monomethylarsonic acid (MMA) percentage, there was an increase of 12.1 µm (95% CI: 0.4, 23.8) in cIMT. Among participants with a higher urinary MMA percentage, a higher ratio of urinary MMA to inorganic arsenic, and a lower ratio of dimethylarsinic acid to MMA, the association between well-water arsenic and cIMT was stronger. The findings indicate an effect of past long-term arsenic exposure on cIMT, which may be potentiated by suboptimal or incomplete arsenic methylation capacity. Future prospective studies are needed to confirm the association between arsenic methylation capacity and atherosclerosis-related outcomes.

A prospective study of arsenic exposure, arsenic methylation capacity, and risk of cardiovascular disease in Bangladesh

BACKGROUND

Few prospective studies have evaluated the influence of arsenic methylation capacity on cardiovascular disease (CVD) risk.

OBJECTIVE

We evaluated the association of arsenic exposure from drinking water and arsenic methylation capacity with CVD risk.

METHOD

We conducted a case-cohort study of 369 incident fatal and nonfatal cases of CVD, including 211 cases of heart disease and 148 cases of stroke, and a subcohort of 1,109 subjects randomly selected from the 11,224 participants in the Health Effects of Arsenic Longitudinal Study (HEALS).

RESULTS

The adjusted hazard ratios (aHRs) for all CVD, heart disease, and stroke in association with a 1-SD increase in baseline well-water arsenic (112 µg/L) were 1.15 (95% CI: 1.01, 1.30), 1.20 (95% CI: 1.04, 1.38), and 1.08 (95% CI: 0.90, 1.30), respectively. aHRs for the second and third tertiles of percentage urinary monomethylarsonic acid (MMA%) relative to the lowest tertile, respectively, were 1.27 (95% CI: 0.85, 1.90) and 1.55 (95% CI: 1.08, 2.23) for all CVD, and 1.65 (95% CI: 1.05, 2.60) and 1.61 (95% CI: 1.04, 2.49) for heart disease specifically. The highest versus lowest ratio of urinary dimethylarsinic acid (DMA) to MMA was associated with a significantly decreased risk of CVD (aHR = 0.54; 95% CI: 0.34, 0.85) and heart disease (aHR = 0.54; 95% CI: 0.33, 0.88). There was no significant association between arsenic metabolite indices and stroke risk. The effects of incomplete arsenic methylation capacity--indicated by higher urinary MMA% or lower urinary DMA%--with higher levels of well-water arsenic on heart disease risk were additive. There was some evidence of a synergy of incomplete methylation capacity with older age and cigarette smoking.

CONCLUSIONS

Arsenic exposure from drinking water and the incomplete methylation capacity of arsenic were adversely associated with heart disease risk.

Arsenic exposure from drinking water and mortality from cardiovascular disease in Bangladesh: prospective cohort study

OBJECTIVE

To evaluate the association between arsenic exposure and mortality from cardiovascular disease and to assess whether cigarette smoking influences the association.

DESIGN

Prospective cohort study with arsenic exposure measured in drinking water from wells and urine.

SETTING

General population in Araihazar, Bangladesh.

PARTICIPANTS

11,746 men and women who provided urine samples in 2000 and were followed up for an average of 6.6 years.

MAIN OUTCOME MEASURE

Death from cardiovascular disease.

RESULTS

198 people died from diseases of circulatory system, accounting for 43% of total mortality in the population. The mortality rate for cardiovascular disease was 214.3 per 100,000 person years in people drinking water containing <12.0 µg/L arsenic, compared with 271.1 per 100,000 person years in people drinking water with ≥ 12.0 µg/L arsenic. There was a dose-response relation between exposure to arsenic in well water assessed at baseline and mortality from ischaemic heart disease and other heart disease; the hazard ratios in increasing quarters of arsenic concentration in well water (0.1-12.0, 12.1-62.0, 62.1-148.0, and 148.1-864.0 µg/L) were 1.00 (reference), 1.22 (0.65 to 2.32), 1.35 (0.71 to 2.57), and 1.92 (1.07 to 3.43) (P = 0.0019 for trend), respectively, after adjustment for potential confounders including age, sex, smoking status, educational attainment, body mass index (BMI), and changes in urinary arsenic concentration since baseline. Similar associations were observed when baseline total urinary arsenic was used as the exposure variable and for mortality from ischaemic heart disease specifically. The data indicate a significant synergistic interaction between arsenic exposure and cigarette smoking in mortality from ischaemic heart disease and other heart disease. In particular, the hazard ratio for the joint effect of a moderate level of arsenic exposure (middle third of well arsenic concentration 25.3-114.0 µg/L, mean 63.5 µg/L) and cigarette smoking on mortality from heart disease was greater than the sum of the hazard ratios associated with their individual effect (relative excess risk for interaction 1.56, 0.05 to 3.14; P = 0.010).

CONCLUSIONS

Exposure to arsenic in drinking water is adversely associated with mortality from heart disease, especially among smokers.

Association between arsenic exposure from drinking water and proteinuria: results from the Health Effects of Arsenic Longitudinal Study

BACKGROUND

Proteinuria has been recognized as a marker for an increased risk of chronic renal disease. It is unclear whether arsenic (As) exposure from drinking water is associated with proteinuria.

METHODS

We evaluated the association between As exposure from drinking water and proteinuria in 11,122 participants in the Health Effects of Arsenic Longitudinal Study (HEALS). Proteinuria was detected by urinary dipstick tests at baseline and at 2-year intervals. As exposure variables included baseline well As and changes in urinary As during follow-up modelled as time-dependent variables in the analyses.

RESULTS

At baseline, well As was positively related to prevalence of proteinuria; prevalence odds ratios (PORs) for proteinuria in increasing quintiles of well As (≤ 7, 8-39, 40-91, 92-179 and 180-864 µg/l) were 1.00 (ref), POR 0.99 [95% confidence interval (CI) 0.77-1.27], POR 1.23 (95% CI 0.97-1.57), POR 1.50 (95% CI 1.18-1.89) and POR 1.59 (95% CI 1.26-2.00) (P for trend <0.01). Hazard ratios for incidence of proteinuria were POR 0.83 (95% CI 0.67-1.03) and POR 0.91 (95% CI 0.74-1.12) for participants with a decreasing level of >70 and 17-70 µg/l in urinary As over time, respectively, and were POR 1.17 (95% CI 0.97-1.42) and POR 1.42 (95% CI 1.16-1.73) for participants with an increasing level of 16-68 and >68 µg/l in urinary As over time, respectively, compared with the group with relatively little changes in urinary As as the reference group (urinary As -16 to 15 µg/l).

CONCLUSION

The findings suggest that there are adverse effects of As exposure on the risk of proteinuria and the effects are modifiable by recent changes in As exposure.

Arsenic induces apoptosis of human umbilical vein endothelial cells through mitochondrial pathways

To clarify the molecular mechanisms through which arsenic causes injuries to blood vessels, we analyzed the effects of sodium arsenite (NaAsO(2)) on the apoptosis of human umbilical vein endothelial cells (HUVECs), mitochondrial membrane potential (Delta Psi m), intracellular reactive oxygen species (ROS), and the expression of the related genes. HUVECs apoptosis increased and Delta Psi m decreased in a dose-dependent manner following arsenic treatment. Intracellular ROS showed 2 phase alterations: a slight decrease with low levels of arsenic (5 and 10 microM) treatment; but a sharp increase at higher concentrations (>or=20 microM). The arsenic-induced cell apoptosis and intracellular ROS were blocked by the addition of the antioxidant N-acetyl-L-cysteine (NAC). The mRNAs of superoxide dismutase 2 (SOD2) and NAD(P)H:quinone oxidoreductase 1 (NQO1) increased strikingly when cells were treated with a low concentration of NaAsO(2) (5 microM) and the level of induction was decreased with higher concentrations of arsenic treatment. Based on the results, we suggest that the decrease of Delta Psi m caused by arsenic and the resulting cell apoptosis may contribute to the injuries of blood vessel in arsenism. The decrease in intracellular ROS and the increase in SOD2 and NQO1 expressions observed when HUVECs were treated with low concentration of NaAsO(2), suggest the role of the two enzymes in protecting HUVECs from injuries of arsenic exposure.

Evaluation of biochemical changes in chronic arsenic poisoning among Bangladeshi patients

An estimated 40 million people in Bangladesh have been suffering from arsenic toxicity-related diseases because of drinking water contamination with high levels of naturally occurring arsenic. To evaluate the biochemical changes in chronic arsenic exposure, a total of 115 exposed subjects diagnosed as arsenicosis patients were examined and interviewed, and 120 unexposed volunteers were enrolled in this study. Drinking water, urine and peripheral blood samples were collected from all participants and analyzed. The average levels of arsenic in the drinking water and spot urine samples of the arsenicosis patients were 218.1 microg/L and 234.6 microg/L, respectively, and duration of exposure was 7.6 +/- 5.2 yrs that ranged from 1-25 yrs. Prevalence of diabetes mellitus among chronic arsenic-exposed subjects was about 2.8 times higher than the unexposed subjects. The activities of alkaline phosphatase were significantly elevated in the patients, 197 U/L compared to 149 U/L in the controls, but alanine transaminase and aspartate transaminase were mostly normal. The patients had significantly lower levels of serum creatinine, 0.97 mg/dL compared to 1.15 mg/dL in the controls; but had significantly elevated levels of total protein, 84 g/L and 77 g/L respectively. The mean level of inorganic phosphate in the serum of arsenicosis patients was 6.4 mg/dL compared to 4.6 mg/dL in the unexposed subjects and the level was significantly higher, indicating substitution of the pentavalent arsenate for the phosphate ion causing underutilization of the latter. Evaluation of the lipid profiles showed while the levels of triacylglycerol were not much different, the patients had significantly lower levels of cholesterol, HDL-cholesterol and LDL-cholesterol compared to the unexposed subjects. These findings suggest significant changes in biochemical parameters in human arsenic toxicity.

Examination of the effects of arsenic on glucose homeostasis in cell culture and animal studies: development of a mouse model for arsenic-induced diabetes

Previous epidemiologic studies found increased prevalences of type 2 diabetes mellitus in populations exposed to high levels of inorganic arsenic (iAs) in drinking water. Although results of epidemiologic studies in low-exposure areas or occupational settings have been inconclusive, laboratory research has shown that exposures to iAs can produce effects that are consistent with type 2 diabetes. The current paper reviews the results of laboratory studies that examined the effects of iAs on glucose metabolism and describes new experiments in which the diabetogenic effects of iAs exposure were reproduced in a mouse model. Here, weanling male C57BL/6 mice drank deionized water with or without the addition of arsenite (25 or 50 ppm As) for 8 weeks. Intraperitoneal glucose tolerance tests revealed impaired glucose tolerance in mice exposed to 50 ppm As, but not to 25 ppm As. Exposure to 25 and 50 ppm As in drinking-water resulted in proportional increases in the concentration of iAs and its metabolites in the liver and in organs targeted by type 2 diabetes, including pancreas, skeletal muscle and adipose tissue. Dimethylarsenic was the predominant form of As in the tissues of mice in both 25 and 50 ppm groups. Notably, the average concentration of total speciated arsenic in livers from mice in the 50 ppm group was comparable to the highest concentration of total arsenic reported in the livers of Bangladeshi residents who had consumed water with an order of magnitude lower level of iAs. These data suggest that mice are less susceptible than humans to the diabetogenic effects of chronic exposure to iAs due to a more efficient clearance of iAs or its metabolites from target tissues.

A review and rationale for studying the cardiovascular effects of drinking water arsenic in women of reproductive age

Drinking water arsenic has been shown to be associated with a host of adverse health outcomes at exposure levels >300 microg of As/L. However, the results are not consistent at exposures below this level. We have reviewed selected articles that examine the effects of drinking water arsenic on cardiovascular outcomes and present a rationale for studying these effects on women of reproductive age, and also over the course of pregnancy when they would potentially be more susceptible to adverse cardiovascular and reproductive outcomes. It is only recently that reproductive effects have been linked to drinking water arsenic. However, there is a paucity of information about the cardiovascular effects of drinking water arsenic on women of reproductive age. Under the cardiovascular challenge of pregnancy, we hypothesize that women with a slightly elevated exposure to drinking water arsenic may exhibit adverse cardiovascular outcomes at higher rates than in the general population. Studying sensitive clinical and sub-clinical indicators of disease in susceptible sub-populations may yield important information about the potentially enormous burden of disease related to low-level drinking water arsenic exposure.

Arsenic methylation capability and hypertension risk in subjects living in arseniasis-hyperendemic areas in southwestern Taiwan

BACKGROUND

Cumulative arsenic exposure (CAE) from drinking water has been shown to be associated with hypertension in a dose-response pattern. This study further explored the association between arsenic methylation capability and hypertension risk among residents of arseniasis-hyperendemic areas in Taiwan considering the effect of CAE and other potential confounders.

METHOD

There were 871 subjects (488 women and 383 men) and among them 372 were diagnosed as having hypertension based on a positive history or measured systolic blood pressure >or=140 mm Hg and/or diastolic blood pressure >or=90 mm Hg. Urinary arsenic species were determined by high-performance liquid chromatography-hydride generator and atomic absorption spectrometry. Primary arsenic methylation index [PMI, defined as monomethylarsonic acid (MMA(V)) divided by (As(III)+As(V))] and secondary arsenic methylation index (SMI, defined as dimethylarsinic acid divided by MMA(V)) were used as indicators for arsenic methylation capability.

RESULTS

The level of urinary arsenic was still significantly correlated with cumulative arsenic exposure (CAE) calculated from a questionnaire interview (p=0.02) even after the residents stopped drinking the artesian well water for 2-3 decades. Hypertensive subjects had higher percentages of MMA(V) and lower SMI than subjects without hypertension. However, subjects having CAE >0 mg/L-year had higher hypertension risk than those who had CAE=0 mg/L-year disregard a high or low methylation index.

CONCLUSION

Inefficient arsenic methylation ability may be related with hypertension risk.

Arsenic methylation, urinary arsenic metabolites and human diseases: current perspective

Arsenic can cause cancerous and non-cancerous human diseases. Inorganic arsenic from drinking water is the most common source of human exposure. Pentavalent arsenate can be reduced to trivalent arsenite in the blood, which is taken up mainly in the liver and metabolized by a sequence of reduction and oxidative methylation. A proportion of the inorganic arsenicals together with methylated metabolites are excreted in urine. Analyses of the urinary arsenic profile can give a hint to the methylation capacity of exposed individuals. All studies evaluating the association between urinary arsenic profiles and human diseases nowadays measure mainly the inorganic arsenate and arsenite and the two organic forms of methylated metabolites: the pentavalent form of monomethylarsonic acid (MMAV) and dimethylarsinic acid (DMAV). A review of the current literature suggests that reduced methylation capacity with increased MMAV percentage, decreased DMAV percentage, or decreased DMAV/MMAV is associated with skin lesions, skin cancer, bladder cancer, peripheral vascular disease, muscle cramps and structural chromosome aberrations in peripheral lymphocytes obtained from exposed subjects. The detection of the recently identified more toxic trivalent forms of methylated metabolites in urine awaits further confirmation.

Association between arsenic exposure from drinking water and anemia during pregnancy

OBJECTIVE

Arsenic is associated with numerous health effects. We investigated the association between arsenic exposure from drinking water and anemia during pregnancy.

METHODS

We conducted a prospective cohort pregnancy study in two Chilean cities with contrasting drinking water arsenic levels: 40 microg/L versus <1 microg/L. This analysis included 810 women who gave birth to live, singleton infants and had at least one hemoglobin determination during pregnancy.

RESULTS

Arsenic exposed women were more likely to be anemic during pregnancy after adjusting for other factors. Furthermore, as pregnancy progressed, the prevalence of anemia rose more sharply among those in the exposed versus unexposed city: 49% versus 17%.

CONCLUSION

This study suggests an association between moderate arsenic in drinking water and anemia during pregnancy. Further research is needed to identify the specific types of anemia underlying the association.

Arsenite induces endothelial cytotoxicity by down-regulation of vascular endothelial nitric oxide synthase

Epidemiological studies have demonstrated a high association of inorganic arsenic exposure with vascular diseases. Recent research has also linked this vascular damage to impairment of endothelial nitric oxide synthase (eNOS) function by arsenic exposure. However, the role of eNOS in regulating the arsenite-induced vascular dysfunction still remains to be clarified. In our present study, we investigated the effect of arsenite on Akt1 and eNOS and its involvement in cytotoxicity of vascular endothelial cells. Our study demonstrated that arsenite decreased the protein levels of both Akt1 and eNOS accompanied with increased levels of ubiquitination of total cell lysates. We found that inhibition of the ubiquitin-proteasome pathway by MG-132 could partially protect Akt1 and eNOS from degradation by arsenite together with a proportional protection from the arsenite-induced cytoxicity. Moreover, up-regulation of eNOS protein expression significantly attenuated the arsenite-induced cytotoxicity and eNOS activity could be significantly inhibited after incubation with arsenite for 24 h in a cell-free system. Our study indicated that endothelial eNOS activity could be attenuated by arsenite via the ubiquitin-proteasome-mediated degradation of Akt1/eNOS as well as via direct inhibition of eNOS activity. Our study also demonstrated that eNOS actually played a protective role in arsenite-induced cytoxicity. These observations supported the hypothesis that the impairment of eNOS function by arsenite is one of the mechanisms leading to vascular changes and diseases.

Depletion of Securin Increases Arsenite-Induced Chromosome Instability and Apoptosis via a p53-Independent Pathway

Arsenic is a pathologic factor of cardiovascular diseases and cancers; nevertheless, it also acts as an anticancer agent effective on acute promyelocytic leukemia and multiple myeloma. Securin, a proposed proto-oncogene, regulates cell proliferation and tumorigenesis. However, roles of securin on the arsenic-induced cell cycle arrest and apoptosis remain unknown. In this study, the effects of sodium arsenite on the expression of securin in two tissue types of cell lines, the vascular endothelial and colorectal epithelial cells, were investigated. Arsenite (8-16 microM, 24 h) increased the cytotoxicity, apoptosis, and growth inhibition in both endothelial and epithelial cells. The levels of phospho-CDC2 (threonine-161), CDC2, and cyclin B1 proteins were decreased, and the G2/M fractions were increased by arsenite. Concomitantly, arsenite markedly diminished the securin protein expression and induced the abnormal sister chromatid separation. The depletion of securin proteins increased the induction of mitotic arrest, aberrant chromosome segregation, and apoptosis after arsenite treatment. p53, a tumor suppressor protein, balances the cell survival and apoptosis. Arsenite raised the levels of phospho-p53 (serine-15) and p53 (DO-1) proteins in both the securin-wild-type and -null cells. The p53-functional cells were more susceptible than the p53-mutational cells to arsenite on the cytotoxicity and apoptosis. Besides, arsenite decreased the levels of securin proteins to a similar degree in both the p53-functional and -mutational cells. Together, it is the first time to demonstrate that the inhibition of securin expression induced by arsenite increases the chromosomal instability and apoptosis via a p53-independent pathway.

Arsenite enhances tumor necrosis factor-α-induced expression of vascular cell adhesion molecule-1

Epidemiological studies demonstrated a high association of vascular diseases with arsenite exposure. We hypothesize that arsenite potentiates the effect of proinflammatory cytokines on vascular endothelial cells, and hence contributes to atherosclerosis. In this study, we investigated the effect of arsenite and its induction of glutathione (GSH) on vascular cell adhesion molecule-1 (VCAM-1) protein expression in human umbilical vein endothelial cells (HUVECs) in response to tumor necrosis factor-alpha (TNF-alpha), a typical proinflammatory cytokine. Our study demonstrated that arsenite pretreatment potentiated the TNF-alpha-induced VCAM-1 expression with up-regulations of both activator protein-1 (AP-1) and nuclear factor-kappaB (NF-kappaB). To elucidate the role of GSH in regulation of AP-1, NF-kappaB, and VCAM-1 expression, we employed l-buthionine (S,R)-sulfoximine (BSO), a specific gamma-glutamylcysteine synthetase (gamma-GCS) inhibitor, to block intracellular GSH synthesis. Our investigation revealed that, by depleting GSH, arsenite attenuated the TNF-alpha-induced VCAM-1 expression as well as a potentiation of AP-1 and an attenuation of NF-kappaB activations by TNF-alpha. Moreover, we found that depletion of GSH would also attenuate the TNF-alpha-induced VCAM-1 expression with a down-regulation of the TNF-alpha-induced NF-kappaB activation and without significant effect on AP-1. On the other hand, the TNF-alpha-induced VCAM-1 expression could be completely abolished by inhibition of AP-1 or NF-kappaB activity, suggesting that activation of both AP-1 and NF-kappaB was necessary for VCAM-1 expression. In summary, we demonstrate that arsenite enhances the TNF-alpha-induced VCAM-1 expression in HUVECs via regulation of AP-1 and NF-kappaB activities in a GSH-sensitive manner. Our present study suggested a potential mechanism for arsenite in the induction of vascular inflammation and vascular diseases via modulating the actions of proinflammatory cytokines.

Inhibition of α7-nicotinic acetylcholine receptor expression by arsenite in the vascular endothelial cells

The alpha7-nicotinic acetylcholine receptor (alpha7-nAChR), expressed in the neuronal and non-neuronal cells, has been shown to regulate cell proliferation. However, the expression and function of the alpha7-nAChR in the proliferation of the vascular endothelial cells remain unclear. In this study, we investigated the expression of the alpha7-nAChR in the arsenite-exposed vascular endothelial cells. The vascular endothelial cells SVEC4-10 and porcine aorta endothelial cells (PAEC) expressed the alpha7-nAChR proteins. Moreover, the location of the alpha7-nAChR proteins on cell membrane of the vascular endothelial cells was identified by the alpha7-nAChR binding to a tetramethylrhodamine-labeled alpha-bungarotoxin (alpha-BTX). Arsenite (20 microM, 24 h) significantly induced the cytotoxicity, cell growth inhibition, and apoptosis in the vascular endothelial cells. The level of alpha7-nAChR proteins was concentration dependently decreased in the arsenite-treated endothelial cells. Furthermore, a specific alpha7-nAChR antagonist, alpha-BTX, inhibited the cell viability in the vascular endothelial cells. Nevertheless, alpha-BTX, and a alpha7-nAChR agonist, nicotine, did not significantly alter the cytotoxicity in the arsenite-treated endothelial cells. In addition, arsenite decreased the level of endothelial nitric oxide synthase proteins but did not alter choline acetyltransferase proteins in the SVEC4-10 endothelial cells. Together, our results indicate that arsenite can inhibit the alpha7-nAChR protein expression and cause the cell injury in the vascular endothelial cells.

Arsenic exposure, urinary arsenic speciation, and peripheral vascular disease in blackfoot disease-hyperendemic villages in Taiwan

Long-term exposure to ingested inorganic arsenic is associated with peripheral vascular disease (PVD) in the blackfoot disease (BFD)-hyperendemic area in Taiwan. This study further examined the interaction between arsenic exposure and urinary arsenic speciation on the risk of PVD. A total of 479 (220 men and 259 women) adults residing in the BFD-hyperendemic area were studied. Doppler ultrasound was used to diagnose PVD. Arsenic exposure was estimated by an index of cumulative arsenic exposure (CAE). Urinary levels of total arsenic, inorganic arsenite (As(III)) and arsenate (As(V)), monomethylarsonic acid (MMA(V)), and dimethylarsinic acid (DMA(V)) were determined. Primary methylation index [PMI = MMA(V)/(As(III) + As(V))] and secondary methylation index (SMI = DMA(V)/MMA(V)) were calculated. The association between PVD and urinary arsenic parameters was evaluated with consideration of the interaction with CAE and the confounding effects of age, sex, body mass index, total cholesterol, triglycerides, cigarette smoking, and alcohol consumption. Results showed that aging was associated with a diminishing capacity to methylate inorganic arsenic and women possessed a more efficient arsenic methylation capacity than men did. PVD risk increased with a higher CAE and a lower capacity to methylate arsenic to DMA(V). The multivariate-adjusted odds ratios for CAE of 0, 0.1-15.4, and >15.4 mg/L x year were 1.00, 3.41 (0.74-15.78), and 4.62 (0.96-22.21), respectively (P < 0.05, trend test); and for PMI < or = 1.77 and SMI > 6.93, PMI > 1.77 and SMI > 6.93, PMI > 1.77 and SMI < or = 6.93, and PMI < or = 1.77 and SMI < or = 6.93 were 1.00, 2.93 (0.90-9.52), 2.85 (1.05-7.73), and 3.60 (1.12-11.56), respectively (P < 0.05, trend test). It was concluded that individuals with a higher arsenic exposure and a lower capacity to methylate inorganic arsenic to DMA(V) have a higher risk of developing PVD in the BFD-hyperendemic area in Taiwan.

Blackfoot disease and arsenic: a never-ending story

Blackfoot disease (BFD) is an endemic peripheral vascular disease confined to the southwestern coast of Taiwan. This article reviews the epidemiology, clinical manifestations and diagnosis, pathology, etiology and pathogenesis of this disease. Sporadic cases of BFD occurred as early as in the early 20th century, and peak incidence was noted between 1956 and 1960, with prevalence rates ranging from 6.51 to 18.85 per 1,000 population in different villages. Typical clinical symptoms and signs of progressive arterial occlusion mainly found in the lower extremities, but in rare cases, the upper extremities might also be involved. Ulceration, gangrene and spontaneous or surgical amputation were typical fate. An extensive pathological study concluded that 30% of the BFD patients had histologic lesions compatible with thromboangiitis obliterans and 70% showed changes of arteriosclerosis obliterans. Epidemiologic studies carried out since mid-20th century revealed that BFD was associated with the consumption of inorganic arsenic from the artesian wells. Recent studies confirmed the existence of preclinical peripheral vascular disease, subclinical arterial insufficiency and defects in cutaneous microcirculation in the residents of the endemic villages. A more recent study suggested that the methylation capacity of arsenic can interact with arsenic exposure in the development of peripheral vascular disease among residents of BFD-endemic areas. The incidence of BFD decreased dramatically after the implementation of tap water in these villages over the past 2-3 decades. The atherogenicity of arsenic could be associated with its effects of hypercoagulability, endothelial injury, smooth muscle cell proliferation, somatic mutation, oxidative stress, and apoptosis. However, its interaction with some trace elements and its association with hypertension and diabetes mellitus could also explain part of its higher risk of developing atherosclerosis. Although humic substances have also been suggested as a possible cause of BFD, epidemiologic studies are required to confirm its etiologic role.

Protective effect of methionine supplementation on arsenic-induced alteration of glucose homeostasis

Short term exposure of arsenic produces carbohydrate depletion and hypoglycemia. Dietary deficiency of methionine causes impaired biotransformation of arsenic which has been attributed to the pathogenesis of different diseases induced by arsenic. Accordingly, the effects of methionine supplementation on the altered glucose homeostasis induced by arsenic were studied. Arsenic (as sodium arsenite) treatment (i.p) of male Wistar rats (weighing 80-100 g) at a dose of 5.55 mg kg(-1) body weight (equivalent to 35% LD50) per day for a period of 21 days caused a significant diminution in blood glucose level and fall in liver glycogen and pyruvic acid contents. The free amino acid nitrogen content of liver was elevated while that of kidney was decreased after arsenic treatment. Transaminase activities in liver and kidney were not significantly altered except that glutamate-pyruvate transaminase activity of kidney decreased significantly after arsenic treatment. Methionine supplementation reversed the above changes except decreased liver glycogen due to arsenic treatment. It may be suggested that hypoglycemia with associated decreased glycolytic activity induced by arsenic treatment at the present dose and duration can be partially counteracted by dietary methionine supplementation.

Lipoprotein(a) is an independent risk factor for peripheral arterial disease in Chinese type 2 diabetic patients in Taiwan

OBJECTIVE

To examine the association between lipoprotein(a) [Lp(a)] and peripheral arterial disease (PAD) and determine the optimal cutoff in Chinese type 2 diabetic patients in Taiwan.

RESEARCH DESIGN AND METHODS

Serum Lp(a) was determined in 557 type 2 diabetic patients (243 men and 314 women) recruited consecutively from a diabetes clinic at the National Taiwan University Hospital. Ankle-brachial index (ABI) <0.9 was diagnosed as PAD (n = 45) and <0.8 as severe PAD (n = 20). Potential confounders included age, sex, BMI, waist-to-hip ratio (WHR), diabetes duration, insulin usage, smoking, hypertension, systolic and diastolic blood pressure, fasting plasma glucose (FPG), total cholesterol, triglycerides, and HDL and LDL cholesterol.

RESULTS

The distribution of Lp(a) was right skewed and no significant differences for sex, WHR, insulin usage, smoking, hypertension, and systolic and diastolic blood pressure were observed. In men, log[Lp(a)] was correlated positively with age, duration, and total and LDL cholesterol (borderline significant, P < 0.1) and negatively with BMI, triglycerides, and FPG (P < 0.1). In women, log[Lp(a)] was correlated positively with total and LDL cholesterol and negatively with triglycerides and BMI (P < 0.1). ABI was significantly correlated with log[Lp(a)], especially in men or in patients with PAD. The optimal cutoff determined by discriminant analysis was 13.3 mg/dl. Patients with Lp(a) above this value had a 2.7-fold higher risk of PAD after multivariate adjustment. Lp(a) also significantly increased from no PAD to mild and severe PAD (17.1 +/- 14.4, 23.7 +/- 20.3, and 36.9 +/- 22.8 mg/dl, respectively, P < 0.001).

CONCLUSIONS

Lp(a) is an independent risk factor for PAD in type 2 diabetic patients in Taiwan. The optimal cutoff is 13.3 mg/dl.

The protective role of NF-kappaB and AP-1 in arsenite-induced apoptosis in aortic endothelial cells

Arsenite (NaAsO(2)) has been shown to produce vascular dysfunction in many studies. Arsenite-induced damage to vascular endothelial cells represents one of the possible mechanisms causing leakage of the vascular endothelial barrier. To explore arsenite-induced vascular endothelial damage, we used primary porcine aortic endothelial cells (PAECs) as an in vitro system to test the effects of arsenite on signal transduction pathways and apoptosis. Here we demonstrated that arsenite exposure induced apoptosis accompanied by the occurrence of apoptotic signals including degradation of poly(ADP-ribose) polymerase (PARP) and CPP32 (cleavage/activation) and DNA ladder formation. By using the luciferase reporter assay, we demonstrated that arsenite exposure differentially activated two redox-sensitive transcription factors, NF-kappaB and AP-1. Lower levels of arsenite exposure (25 microM NaAsO(2), 24 h) induced co-activation of NF-kappaB and AP-1, accompanied by 9% total apoptosis. In contrast, higher levels of arsenite exposure (40 microM NaAsO(2), 24 h) induced higher levels of AP-1 activation, accompanied by 45% total apoptosis. Blockade of NF-kappaB or JNK activity further enhanced arsenite-induced apoptosis. Upregulation of JNK activity showed no effect on arsenite-induced apoptosis. Based on these data, we propose that activation of redox-sensitive transcription factors, NF-kappaB and AP-1, plays a very important role in the protection of PAECs from arsenite-induced apoptosis.

A potential mechanism for the impairment of nitric oxide formation caused by prolonged oral exposure to arsenate in rabbits

We have recently found evidence for impairment of nitric oxide (NO) formation and induction of oxidative stress in residents of an endemic area of chronic arsenic poisoning in Inner Mongolia, China. To investigate the underlying mechanisms responsible for these phenomena, a subchronic animal experiment was conducted using male New Zealand White rabbits. After 18 weeks of continuous exposure of rabbits to 5 mg/l of arsenate in drinking water, a significant decrease in systemic NO production occurred, as shown by significantly reduced plasma NO metabolites levels (76% of control) and a tendency towards decreased serum cGMP levels (81.4% of control). On the other hand, increased oxidative stress, as shown by significantly increased urinary hydrogen peroxide (H(2)O(2)) (120% of control), was observed in arsenate-exposed rabbits. In additional experiments measuring aortic tension, the addition of either the calcium ionophore A23187 or acethylcholine (ACh) induced a transient vasoconstriction of aortic rings prepared from arsenate-exposed rabbits, but not in those prepared from control animals. This calcium-dependent contractility action observed in aorta rings from arsenate-exposed rabbits was markedly attenuated by the superoxide (O2(.-)) scavenging enzyme Cu, Zn-SOD, as well as diphenyleneiodonium (DPI) or N(G)-nitro-L-arginine methyl ester (L-NAME), which are inhibitors for nitric oxide synthase (NOS). However, the cyclooxygenase inhibitor indomethacin or the xanthine oxidase blocker allopurinol had no effect on this vasoconstriction. These results suggest that arsenate-mediated reduction of systemic NO may be associated with the enzymatic uncoupling reaction of NOS with a subsequent enhancement of reactive oxygen species such as O2(.-), an endothelium-derived vasoconstricting factor. Furthermore, hepatic levels of (6R)-5,6,7,8-tetrahydro-L-biopterin (BH(4)), a cofactor for NOS, were markedly reduced in arsenate-exposed rabbits to 62% of control, while no significant change occurred in cardiac L-arginine levels. These results suggest that prolonged exposure of rabbits to oral arsenate may impair the bioavailability of BH(4) in endothelial cells and, as a consequence, disrupt the balance between NO and O2(.-) produced from endothelial NOS, such that enhanced free radicals are produced at the expense of NO.

Prevalence and risk factors of peripheral arterial obstructive disease in Taiwanese type 2 diabetic patients

The aim of this study was to evaluate the prevalence and risk factors of peripheral arterial obstructive disease (PAD) in Taiwanese type 2 diabetic patients. A total of 610 patients (268 men and 342 women), aged 63.3 +/- 10.8 years, were recruited from a diabetic clinic in a teaching hospital. PAD was diagnosed by an ankle-brachial index (ABI) < 0.9 on either leg. Risk factors studied were age, sex, body mass index (BMI), smoking, diabetes duration, hypertension, insulin therapy, systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting plasma glucose (FPG), serum total cholesterol (TC), and triglyceride (TG). Overall prevalence of PAD was 10.0% without significant sexual difference. Univariate analyses disclosed age, BMI (inverse association), diabetes duration, hypertension, insulin therapy, and SBP as significant risk factors. In stepwise logistic regression, age, SBP, BMI, and insulin therapy were independent risk factors with respective odds ratios (95% confidence intervals, CI) of 1.09 (1.05-1.13), 1.02 (1.01-1.04), 0.88 (0.80-0.96), and 3.37 (1.83-6.19). In conclusion, prevalence of PAD in Taiwanese type 2 diabetic patients was 10.0% and the major risk factors were older age, lower BMI, higher SBP, and insulin therapy. The inverse association between PAD and BMI is contradictory to the general impression that obesity is a risk factor for PAD.

Long-term arsenic exposure and ischemic heart disease in arseniasis-hyperendemic villages in Taiwan

The association between long-term arsenic exposure and peripheral vascular disease has been well documented in our previous epidemiologic studies. The purpose of this study was to evaluate whether long-term arsenic exposure could be associated with ischemic heart disease (IHD). A total of 462 subjects living in the blackfoot disease-hyperendemic villages along the southwestern coast of Taiwan and characterized by long-term arsenic exposure from drinking artesian well water was studied. The subjects were recruited from an epidemiologic cohort who participated in a health examination. IHD was diagnosed by coding the resting electrocardiograms with the Minnesota code. History of arsenic exposure was estimated through information obtained from a personal interview according to a structured questionnaire and the arsenic content in artesian well water of the villages. Cumulative arsenic exposure (CAE) was calculated as the sum of the products multiplying the arsenic concentration in artesian well water (mg/l) by the duration of drinking the water (years) in consecutive periods of living in the different villages. Among the subjects, 78 cases (16.9%) were diagnosed as having IHD. The prevalence rates of IHD for the age groups of 30-39, 40-49, 50-59, and >/=60 years were 4.9, 7.5, 16.8, and 30.7%, respectively (P<0.001). For those with CAE of 0, 0.1-14.9 and >/=15 mg/l-years, the prevalence rates of IHD were 5.2, 10.9 and 24.1%, respectively (P<0.001). The odds ratios (95% confidence intervals) for IHD were 1.60 (0.48, 5.34), and 3.60 (1.11, 11.65), respectively, for those with CAE of 0.1-14.9 and >/=15.0 mg/l-years, when compared with those lacking drinking water exposure to arsenic after multivariate adjustment. It is concluded that IHD in the arseniasis-hyperendemic villages in Taiwan was associated with long-term arsenic exposure.

Lack of association between angiotensin-converting enzyme gene polymorphism and peripheral vascular disease in type 2 diabetic patients in Taiwan

A total of 361 Chinese patients with type 2 diabetes were studied for the association between peripheral vascular disease (PVD) and the insertion/deletion polymorphism involving a 287-bp alu repeat sequence at intron 16 of the angiotensin-converting enzyme (ACE) gene. The patients were divided into PVD (+) (n=45) and PVD (-) (n=316) based on an ankle-brachial index <0.9 and > or =0.9, respectively. Polymerase chain reaction was used to identify gene polymorphism. Results showed that D allele frequency in the patients without and with PVD was 31.8% and 33.3%, respectively (p=NS). The prevalence rates of II, ID and DD genotypes in the PVD (-) group were 45.6%, 45.3% and 9.2%, respectively; and the respective values for the PVD (+) group were 44.4%, 44.4% and 11.1% (p=NS). Prevalence rates of PVD in genotypes II, ID, and DD were 12.2%, 12.3% and 14.7%, respectively (p=NS). In logistic regression analyses, the unadjusted and adjusted odds ratios for DD vs II and ID vs II genotypes for PVD were not statistically significant. The respective adjusted odds ratios were 1.88 (0.56-6.29) and 1.33 (0.63-2.80). In conclusion, there was not a significant association between the ACE genotype and PVD in Chinese type 2 diabetic patients. However, a type 2 error can not be ruled out.

An overview on peripheral vascular disease in blackfoot disease-hyperendemic villages in Taiwan

The arsenic-related peripheral vascular disease found to be endemic along the southwestern coast of Taiwan is reviewed. In the early 20th century a strange disease involving the lower extremities characterized by typical clinical symptoms and signs of progressive arterial occlusion was reported in a confined area located along the southwestern coast of Taiwan. The disease was locally called "blackfoot disease" because of its gangrenous appearance involving the feet of the patients. The prevalence of this disease ranged from 6.51 to 18.85 per 1,000 population in different villages. Epidemiologic studies revealed that blackfoot disease was associated with the consumption of artesian well water containing high levels of arsenic. High co-occurrence of blackfoot disease and arsenic-related skin lesions such as hyperpigmentation, hyperkeratosis, and skin cancer was also observed. Recent studies also confirmed the association of preclinical peripheral vascular disease with arsenic exposure in a dose-response pattern. Subclinical arterial insufficiency and defects in cutaneous microcirculation can also be demonstrated in seemingly normal subjects living in the endemic villages. The incidence of clinical manifestation of blackfoot disease decreased dramatically after the implementation of tap water in these villages over the past 2-3 decades. The atherogenicity of arsenic could be associated with its effects on hypercoagulability, endothelial injury, smooth muscle cell proliferation, somatic mutation, oxidative stress, and apoptosis. However, its interaction with some trace elements and its association with hypertension and diabetes mellitus could also explain part of its higher risk of developing atherosclerosis.

Epidemiologic evidence of diabetogenic effect of arsenic

It is well documented that arsenic can lead to skin lesions, atherosclerotic diseases and cancers. The association between arsenic exposure and diabetes mellitus is a relatively new finding. Up to now, there are six epidemiologic reports linking diabetes mellitus with arsenic exposure from environmental and occupational sources. Two reports in Taiwan carried out in the blackfoot disease-hyperendemic villages, one cross-sectional and one prospective follow-up of the same cohort, indicate that arsenic exposure from drinking artesian well water is associated with prevalence and incidence of diabetes mellitus in a dose-responsive pattern. The observation of the relation between arsenic exposure and diabetes mellitus is further supported by studies carried out in Sweden and Bangladesh. In Sweden, case-control analyses of death records of copper smelters and glass workers revealed a trend of increasing diabetes mellitus with increasing arsenic exposure from inhalation. In Bangladesh, prevalence of diabetes mellitus among arsenic-exposed subjects with keratosis was about five times higher than unexposed subjects. Increasing trends of diabetes mellitus with indices of arsenic exposure in drinking water seems to be independent of the presence of skin lesions associated with arsenic exposure. Although these studies consistently show an association between arsenic exposure and diabetes mellitus, the weak study designs of cross-sectional or case-control, the use of glucosuria or diabetes death as diagnostic criteria and the lack of adjustment for possible confounders in some studies, are major limitations that may reduce the strength of the evidence.

The cellular metabolism and systemic toxicity of arsenic

Although it has been known for decades that humans and many other species convert inorganic arsenic to mono- and dimethylated metabolites, relatively little attention has been given to the biological effects of these methylated products. It has been widely held that inorganic arsenicals were the species that accounted for the toxic and carcinogenic effects of this metalloid and that methylation was properly regarded as a mechanism for detoxification of arsenic. Elucidation of the metabolic pathway for arsenic has changed our understanding of the significance of methylation. Both methylated and dimethylated arsenicals that contain arsenic in the trivalent oxidation state have been identified as intermediates in the metabolic pathway. These compounds have been detected in human cells cultured in the presence of inorganic arsenic and in urine of individuals who were chronically exposed to inorganic arsenic. Methylated and dimethylated arsenicals that contain arsenic in the trivalent oxidation state are more cytotoxic, more genotoxic, and more potent inhibitors of the activities of some enzymes than are inorganic arsenicals that contain arsenic in the trivalent oxidation state. Hence, it is reasonable to describe the methylation of arsenic as a pathway for its activation, not as a mode of detoxification. This review summarizes the current knowledge of the processes that control the formation and fate of the methylated metabolites of arsenic and of the biological effects of these compounds. Given the considerable interest in the dose-response relationships for arsenic as a toxin and a carcinogen, understanding the metabolism of arsenic may be critical to assessing the risk associated with chronic exposure to this element.

Effect of arsenite on the induction of CYP1A4 and CYP1A5 in cultured chick embryo hepatocytes

We had reported previously that 2.5-5 microM sodium arsenite decreased the phenobarbital-mediated induction of CYP2H activity and protein but not CYP2H1 mRNA in chick-embryo hepatocyte cultures. Induction of a CYP1A activity and protein by 3-methylcholanthrene was also decreased by low arsenite concentrations; however, CYP1A mRNAs were not measured in those studies. We report here that low concentrations of arsenite decreased induction of activities and mRNAs of two chicken cytochromes P450, CYP1A (1A4 and 1A5), by 3-methylcholanthrene in chick-embryo hepatocyte cultures. Arsenite treatment did not affect the turnover of either mRNA, nor did it decrease the superinduction of each mRNA caused by treatment with cycloheximide in addition to 3-methylcholanthrene. Glutathione depletion enhanced the effect of arsenite to decrease induction of CYP1A4. These results indicate the induction of CYP1A4 and 1A5 is inhibited by sodium arsenite at the level of transcription, suggesting that the Ah receptor complex may be involved.

The incidence of type 2 diabetes mellitus in Taiwan

Currently, diabetes mellitus is the fifth leading cause of death in Taiwan. The trends of diabetes mortality is increasing steadily. Epidemiologic studies also showed increasing prevalence of diabetes mellitus over the past few decades. The incidence of diabetes mellitus in Taiwan has only been studied in recent 10 years. The areas that have been included as study areas for diabetes incidence are Kin-Chen (Kinmen), Chu-Dung, Pu-Tzu, Pu-Li and Pu-Tai. The reported incidence rates ranged from 1.0 to 4.0% per year for people with varying degrees of baseline plasma glucose levels not reaching the diagnosis of diabetes mellitus according to the criteria of the World Health Organization. Age, baseline glucose level, and obesity are important predictors for the development of diabetes mellitus. In the Pu-Tai study, which was aimed at following a group of people who had been living in the hyperendemic villages of blackfoot disease and had been exposed to arsenic from drinking artesian well water, the incidence of diabetes mellitus was calculated to be 27.4 per 1000 person years. The incidence of diabetes mellitus in these arseniasis-hyperendemic villages correlated with age, body mass index and cumulative arsenic exposure.

Stimulation of reactive oxygen, but not reactive nitrogen species, in vascular endothelial cells exposed to low levels of arsenite

Elevated levels of arsenite, the trivalent form of arsenic, in drinking water correlates with increased vascular disease and vessel remodeling. Previous studies from this laboratory demonstrated that environmentally relevant concentrations of arsenite caused oxidant-dependent increases in nuclear transcription factor levels in cultured porcine vascular endothelial cells. The current studies characterized the reactive species generated in these cells exposed to levels of arsenite that initiate cell signaling. These exposures did not deplete 5'-triphosphate, nor did they affect basal or bradykinin-stimulated intracellular free Ca2+ levels, indicating that they were not lethal. Electron paramagnetic resonance (EPR) spectroscopy, including spin trapping with carboxy-PTIO (cPTIO), demonstrated that 5 microM or less of arsenite did not increase *NO levels over a 30-min period relative to *NO release stimulated by bradykinin. However, these same levels of arsenite rapidly increased both oxygen consumption and superoxide formation, as measured by EPR oximetry and spin trapping with 5,5-dimethyl-1-pyrroline N-oxide (DMPO), respectively. Pretreatment of the cells with DPI, apocynin, or superoxide dismutase abolished arsenite-stimulated DMPO-OH adduct formation. Finally arsenite increased extracellular accumulation of H2O2, measured as oxidation of homovanillic acid, with the same time and dose dependence, as seen for superoxide formation. These data suggest that superoxide and H2O2 are the predominant reactive species produced by endothelial cells after arsenite exposures that stimulate cell signaling and activate transcription factors.

Low levels of arsenic trioxide stimulate proliferative signals in primary vascular cells without activating stress effector pathways

Chronic human exposure to low levels of inorganic arsenic increases the incidence of vascular diseases and specific cancers. Exposure of endothelial cells to environmentally relevant concentrations of arsenic trioxide (arsenite) induces oxidant formation, activates the transcription factor NF-kappaB, and increases DNA synthesis (Barchowsky et al., Free Radic. Biol. Med. 21, 783-790, 1996). We show, in the current study, that arsenite induces concentration-dependent cell proliferation or death in primary porcine aortic endothelial cells. Low concentrations caused cell proliferation and were associated with increased superoxide and H(2)O(2) accumulation, cSrc activity, H(2)O(2)-dependent tyrosine phosphorylation, and NF-kappaB-dependent transcription. These concentrations were insufficient to activate MAP kinases. However, the MAP kinases, extracellular signal-regulated kinase and p38, were activated in response to levels of arsenite that caused cell death. These data suggest that arsenite-induced oxidant accumulation and subsequent activation of tyrosine phosphorylation represent a MAPK-independent pathway for phenotypic change and proliferation in vascular cells.

Low serum carotene level and increased risk of ischemic heart disease related to long-term arsenic exposure

To elucidate the association between arsenic-related ischemic heart disease (ISHD) and serum antioxidant micronutrient level, residents aged 30 or older living in arseniasis-hyperendemic villages in Taiwan were recruited in a community-based health survey. A structured questionnaire was used to obtain a history of long-term exposure to arsenic through consuming artesian well water and fasting serum samples were also collected at the recruitment. A total of 74 patients affected with ISHD, who were diagnosed through both electrocardiography and Rose questionnaire interview, and 193 age-sex-matched healthy controls were selected for the examination of serum levels of micronutrients by high performance liquid chromatography (HPLC). There was a significant biological gradient between the risk of ISHD and the duration of consuming high-arsenic artesian well water. A significant reverse dose-response relationship with arsenic-related ISHD was observed for serum level of alpha- and beta-carotene, but not for serum levels of retinol, lycopene and alpha-tocopherol. Multivariate analysis showed a synergistic interaction on arsenic-related ISHD between duration of consuming artesian well water and low serum carotene level. An increased risk of arsenic-related ISHD was also associated with hypertension and elevated body mass index, but not with serum lipid profile, cigarette smoking and alcohol drinking. The findings seem to suggest that arsenic-related ISHD has a pathogenic mechanism which is at least partially different from that of ISHD unrelated to long-term exposure to arsenic.