Cardiovascular disease in African American and white physicians: the Meharry Cohort and Meharry-Hopkins Cohort Studies

Differences in cardiovascular disease (CVD) were studied in a cohort of medical students from the classes of 1958-65 of Meharry Medical College (n = 435), all African Americans, and the classes of 1957-64 of Johns Hopkins University (n = 580), all white. At baseline, African Americans were older (27 vs. 24 years, p = 0.001), more likely to smoke (71 vs. 47 percent), had greater body mass index (24 vs. 23 kg/m), and had higher systolic blood pressure (120 vs. 116 mmHg). At follow-up (23-35 years later), African American physicians had higher CVD risk (RR = 1.65, 95% CI = 1.3-2.41), higher incidence of coronary artery disease (1.4 times), and much higher case fatality (51.5 vs. 9.4 percent). Risk factor levels in youth can predict CVD events several years later; predictors may differ between racial groups. Best predictors were cigarette smoking, cholesterol, and paternal history in white physicians, and blood pressure in African American physicians.

Gout and risk for subsequent coronary heart disease. The Meharry-Hopkins Study

BACKGROUND

Patients with gout are encountered frequently in clinical practice. Previous studies have suggested that hyperuricemia and gout may represent risk factors for coronary heart disease (CHD), the most common cause of death in American men.

METHODS

Prospectively collected data from 2 longitudinal cohort studies of former medical students--371 black men in the Meharry Cohort Study and 1181 white men in the Johns Hopkins Precursors Study--were analyzed. The development of gout and of CHD was determined by physician self-report, and validated by using published criteria. The risk for CHD associated with gout was evaluated using Cox proportional hazards analysis.

RESULTS

During a median follow-up of 30 years, there were 38 gout cases and 44 CHD events among the Meharry men, and 68 gout cases and 138 CHD events among the Hopkins men. Prior gout was not associated with an increased risk for incident CHD (relative risk = 1.20; 95% confidence interval, 0.37-3.92) among the Meharry men or among the Hopkins men (relative risk = 0.66; 95% confidence interval, 0.24-1.79). Multivariate analysis adjusted for known CHD risk factors did not alter these findings.

CONCLUSION

These results, in black and white male physicians, do not suggest a role in men for targeting gout identification in the primary prevention of CHD.

Comparative inhibition of yeast glutathione reductase by arsenicals and arsenothiols

Tri(gamma-glutamylcysteinylglycinyl)trithioarsenite (AsIII(GS)3) is formed in cells and is a more potent mixed-type inhibitor of the reduction of glutathione disulfide (GSSG) by yeast glutathione (GSH) reductase than either arsenite (AsIII) or GSH. The present work examines the effects of valence and complexation of arsenicals with GSH or L-cysteine (Cys) upon potency as competitive inhibitors of the reduction of GSH disulfide (GSSG) by yeast GSH reductase. Trivalent arsenicals were more potent inhibitors than their pentavalent analogs, and methylated trivalent arsenicals were more potent inhibitors than was inorganic trivalent As. Complexation of either inorganic trivalent As or methylarsonous diiodide (CH3As(III)I2) with Cys or GSH produced inhibitors of GSH reductase that were severalfold more potent than the parent arsenicals. In contrast, dimethylarsinous iodide ((CH3)2As(III)I) was a more potent inhibitor than its complexes with either GSH or Cys. Complexes of CH3AsIII with GSH (CH3-AsIII(GS)2) or with Cys (CH3AsIII(Cys)2) were the most potent inhibitors, with Ki's of 0.009 and 0.018 mM, respectively. Inhibition of GSH reductase by arsenicals or arsenothiols was prevented by addition of meso-2,3-dimercaptosuccinic acid (DMSA) to a mixture of enzyme, GSSG, and inhibitor before addition of NADPH. DMSA added to the reaction mixture after NADPH reversed inhibition by (CH3)2As(III)I but had little effect on inhibition by CH3As(III)I2, Ch3AsIII(GS)2, CH3AsIII(Cys)2, or AsIII(GS)3. Partial redox inactivation of the enzyme with NADPH increased the inhibitory potency of CH3As(III)I2 and (CH3)2As(III)I and changed the mode of inhibition for CH3As(III)I2 from competitive to noncompetitive. The greater potency of methylated trivalent arsenicals and arsenothiols than of inorganic trivalent As suggests that biomethylation of As could yield species that inhibit reduction of GSSG and alter the redox status of cells.

Benefits and risks of hormone/estrogen replacement

Menopause is a natural event, yet almost 25% of postmenopausal women are taking some form of hormone replacement (HRT). Women can expect to live one-third of their lives postmenopausal. There is a plethora of conflicting literature about estrogen, and women faced with the decision whether or not to take HRT are confused. This article outlines the risks and benefits of hormone/estrogen replacement based on a comprehensive review of the current literature so that health care providers can give their patients the best information for making informed decisions about HRT.

The prediction of protein contacts from multiple sequence alignments

We have studied the question of how much extra predictive power the correlated mutational behaviour of pairs of amino acid residues separated along a sequence has concerning the likelihood of those residues being in contact in the folded protein. The mutational behaviour is deduced from multiple sequence alignments. Our findings are that there is, indeed, some valuable information available from this source and that it is sufficient to make a significant improvement in our ability to predict contacts, when compared with earlier methods that do not take into account the correlations between the mutations. This improvement is approximately twice as large as can be obtained by the more economical method of simply averaging pair preferences over the same sequence alignment. Even when using a method based on pair preferences, a further significant improvement can be made by penalizing more variable regions (on the reasonable assumption that invariant residues are relatively more likely to be in contact), though we have found no way of improving the pair preference method to the extent that it matches the method based on correlated behaviour. Our new method is thought to be the best data-based method of contact prediction developed so far, achieving, on average, an improvement over a random (i.e. information-free) prediction of a factor of five when the number of contacts predicted is chosen to match the number that actually occur.

Returning to work after liver transplant: experiencing the roadblocks

Liver transplant has been the treatment of choice for people with end-stage liver disease since the mid-1980s. The theme of returning to work after liver transplantation emerged from the data of a phenomenological study examining the lived experience of people with liver transplants. Thirteen liver recipients were interviewed using a semistructured approach. Only one of the first nine participants was able to return to work after the transplant; therefore, the last four participants were purposely chosen because they had been able to return to work. The possibility of losing health insurance benefits and disability benefits prevented many participants from working. Those able to return to work had professional careers that afforded them flexibility in their work schedule. Some implications for health professionals lie in the area of healthcare and health insurance policy change. Avenues for health insurance reform could be explored in an effort to empower the transplant recipient.

Liberation and analysis of protein-bound arsenicals

Protein-bound arsenicals were liberated from binding sites on liver cytosolic proteins by exposure to 0.1 M CuCl at pH 1. This method released greater than 90% of the arsenicals associated with biological matrices. Ultrafiltrates of CuCl-treated cytosols were subjected to thin-layer chromatography to speciate and quantify inorganic and methylated arsenicals. For rat liver cytosol in an in vitro methylation assay and for liver and kidney cytosols from arsenite-treated mice, most inorganic arsenic was protein bound. Appreciable fractions of the organoarsenical metabolites present in these cytosols were also protein bound. Therefore, CuCl treatment of cytosols releases protein-bound arsenicals, permitting more accurate estimates of the pattern and extent of arsenic methylation in vitro and in vivo.

Mono- and dimethylation of arsenic in rat liver cytosol in vitro

Production of methylarsonate and dimethylarsinate from radiolabelled [73 As]arsenite and [73 As]arsenate was examined in an assay system that contained cytosol prepared from a 20% homogenate (w/v) of livers from 8- 10-week-old male Fischer 344 rats. After a 60-min incubation at 37 degrees C with added S-adenosylmethionine and glutathione, up to 50% of carrier-free [73As]arsenite and about 15% of carrier-free [73As]arsenate were methylated. Incubation of cytosol at 100% degrees C for 1 min before addition to the assay system completely abolished methylation of arsenite. Production of methylarsonate increased in proportion to the arsenite concentration in the assay system; however, 50 microM arsenite inhibited production of dimethylarsinate. Methylarsonate production from carrier-free [73-As]arsenite was not dependent on addition of exogenous S-adenosylmethionine to the assay system. Addition of 0.1 mM S-adenosylmethionine maximized dimethylarsinate production. Addition of 0.1 or 1.0 mM S-adenosylhomocysteine decreased methylation of arsenite, especially dimethylarsinate production. Omission of glutathione from the assay system nearly abolished the methylation of arsenite. Addition of exogenous glutathione to the assay system (up to 20 mM) decreased protein binding of arsenic and increased the production of methylarsonate and dimethylarsinate. The effects of sodium selenite, mercuric chloride, EDTA, p-anisic acid and 2,3-dichloro-alpha-methylbenzylamine on the methylation of arsenite were determined. Addition of 10 microM selenite to the assay system nearly abolished the formation of either methylated species. Addition of 1 or 10 microM mercuric chloride inhibited dimethylarsinate production in a concentration-dependent manner but had little effect on methylarsonate yield. Addition of 10 mM EDTA to the assay system inhibited formation of both methylated metabolites, suggesting that an endogenous divalent cation might be involved in enzymatic methylation of arsenic. Neither p-anisic acid, an inhibitor of cytosolic methyltransferases, nor 2,3-dichloro-alpha-methylbenzylamine, an inhibitor of microsomal methyltransferases, inhibited the conversion of inorganic arsenic to mono- or dimethylated metabolites.

Myasthenia gravis presenting with stridor

The case is described of a 72 year old woman who presented with a two year history of exertional stridor in whom the diagnosis of myasthenia gravis was delayed. Although an uncommon cause, myasthenia gravis should be included in the differential diagnosis of stridor.

Comparative in vitro methylation of trivalent and pentavalent arsenicals

The time course and extent of methylation of 1 microM arsenite (iAsIII), arsenate (iAsV), methylarsenite (MeAsIII), methylarsenate (MeAsV), and MeAsIII-diglutathione complex (MeAsIII(GS)2) were examined in an in vitro assay system that contained rat liver cytosol. Precursor arsenicals and methylated metabolites were analyzed by thin-layer chromatography (TLC) or by hydride generation-atomic absorption spectrophotomoetry (HG-AAS). More than 90% of iAsIII was converted to a dimethylated species (Me2As) during a 90-min incubation at 37 degrees C; the amount of monomethylated metabolite was maximal at 15 min. In contrast, only 40% of iAsV was dimethylated during a 90-min incubation. Comparison of the yields of methylated species in the whole in vitro assay system as determined by HG-AAS and in an ultrafiltrate prepared from the in vitro assay system as determined by TLC indicated that nearly 70% of the dimethylated metabolite (possibly Me2AsIII) that was produced during a 90-min incubation was bound to proteins (> 10 kDa). The percentage of protein-bound arsenic in the assay system incubated at 0 degree C with trivalent arsenicals was three-to fivefold greater than the binding of corresponding pentavalent species. This indicated that both iAsIII and trivalent organoarsenicals interact avidly with proteins. Both MeAsIII prepared by metabisulfite-thiosulfate reduction of MeAsV and a MeAsIII(GS)2 were quantitatively converted to Me2As during 90-min incubation. In contrast, only 3% of MeAsV was dimethylated during this interval. These results suggest that trivalent arsenicals are preferred substrates for methylation reactions and that the reduction of As from pentavalent to trivalent states may be a critical step in the control of the rate of metabolism of As.

The folding and stability of titin immunoglobulin-like modules, with implications for the mechanism of elasticity

Titin (first known as connectin) is a vast modular protein found in vertebrate striated muscle. It is thought to assist myofibrillogenesis and to provide a passive elastic restoring force that helps to keep the thick filaments properly centered in the sarcomere. We show that representative titin modules do indeed fold independently, and report their stabilities (i.e., delta G of unfolding and melting temperature) as measured by circular dichroism, fluorescence, and nuclear magnetic resonance spectroscopies. We find that there is a region-dependent variation in stability, although we find no evidence to support a proposed elastic mechanism based on a molten-globular-like equilibrium folding intermediate, nor do our calculations support any mechanism based on the configurational entropy of the molecule itself; instead we suggest a model based on hydrophobic hinge regions that would not be strongly dependent on the precise folding pattern of the chain.

Time dependence of accumulation and binding of inorganic and organic arsenic species in rabbit erythrocytes

The uptake by rabbit erythrocytes of 0.4 mM arsenate, As(V), monomethylarsinate, MMA(V) and dimethylarsonate, DMA(V) were compared over 24 h. In membrane-free hemolysate, the distribution of As between proteins (10 kDa) and ultrafiltrate was determined by ultrafiltration and arsenic species in the ultrafiltrate were identified by thin layer chromatography methods. 1H spin-echo Fourier transform NMR was used to follow the binding of these arsenic species to glutathione (GSH). 31P-NMR was used to observe their effects on high-energy adenine nucleotide levels (ATP, ADP). These results demonstrate that As(III) readily accumulates in cells, reaches a quasi-plateau at 78% of the total As in the incubation after 1 h and 88% of the total As after 24 h. On average, 20% of the total erythrocyte As(III) burden is associated with the protein fraction, particularly with hemoglobin (Hb). About 68% of the erythrocyte As(III) burden is bound to GSH. As(III) has no effect on ATP levels during a 5-h incubation. By comparison, As(V) enters erythrocytes more slowly (53% of the total As after 5 h). Erythrocytes take up 81% of the As(V) in the reaction system after a 24 h incubation. Of the total As burden in As(V)-exposed erythrocytes, 22% was associated with the proteins (10 kDa) and possibly reduced to As(III) and 59% was in the ultrafiltrate (8% as As(III) and 51% as As(V)). This finding indicates that, over a 24 h incubation period, the reduction of As(V) to As(III) may account for 30% of the total As in rabbit erythrocytes. As(V) present in the erythrocytes enters the phosphate pool and depletes ATP. In comparison, about 65% of the total MMA(V) or about 44% of the total DMA(V) in the incubation system is taken up by rabbit erythrocytes during a 24 h incubation. Neither organoAs species perturbed the Hb signals observed by spin-echo Fourier transform NMR and the binding to GSH was minimal. Unlike As(V), MMA(V) and DMA(V) do not perturb phosphate metabolism, showing that, despite their pentavalent oxidation state, these arsenic species are not analogs for phosphate.

Factors affecting flow cytometric detection of apoptotic nuclei by DNA analysis

Apoptotic thymocyte nuclei normally appear on a flow cytometric DNA histogram as a subdiploid peak. We observed that addition of a specific RNase A preparation to the detergent-based lysing buffer increased the fluorescence of toxicant-induced apoptotic nuclei to the level of untreated diploid nuclei. The chelating agent EDTA partially inhibited the RNase effect, suggesting contaminating divalent cations may have been involved. Moreover, spectrofluorometric analysis revealed that addition of RNase or divalent cations decreased the amount of DNA present in the lysate. This suggested that the upscale fluorescence shift was due to a decrease in the ability of the lysing buffer to extract DNA, possibly as a result of cation-induced chromatin condensation, rather than increased accessibility of fluorochrome binding sites due to apoptotic degeneration. Moreover, during a 16-h culture, we observed a similar, but time-dependent, upscale shift in the fluorescence of thymocytes undergoing apoptosis either spontaneously or as a result of exposure to 1 microM tributyltin methoxide (TBT), 2% ethanol, 2% methanol, or 1 microM dexamethasone phosphate (DEX). This commonality of effect suggests that a similar magnitude of chromatin reorganization occurs in apoptotic cells in prolonged culture regardless of the method of apoptotic induction. These findings should alert investigators to potential inaccuracies in the flow cytometric quantitation of apoptosis in in vitro systems employing prolonged toxicant exposures or complex lysing cocktails that may contain active contaminants.

Genetic modification and selection of microorganisms for growth on Mars

Genetic engineering has often been suggested as a mechanism for improving the survival prospects of terrestrial microoganisms when seeded on Mars. The survival characteristics that these pioneer microorganisms could be endowed with and a variety of mechanisms by which this can be achieved are discussed, together with an overview of some of the potential hurdles that must be overcome. Also, a number of biologically useful properties for these microorganisms are presented that could facilitate the initial human colonisation and ultimately the planetary engineering of Mars.

NFATc3, a lymphoid-specific NFATc family member that is calcium-regulated and exhibits distinct DNA binding specificity

Signals transduced by the T cell antigen receptor (TCR) regulate developmental transitions in the thymus and also mediate the immunologic activation of mature, peripheral T cells. In both cases TCR stimulation leads to the assembly of the NFAT transcription complex as a result of the calcium-dependent nuclear translocation of cytosolic subunits, NFATc, and the Ras/protein kinase C-dependent induction of a nuclear subunit, NFATn. To further understand the diverse roles of antigen receptor signaling throughout T cell development, we have identified a new NFATc family member, NFATc3, that is expressed at highest levels in the thymus. NFATc3 is the product of a gene on murine chromosome 8 that is not linked to the other NFATc genes. NFATc3, like other NFATc family members, contains a conserved rel similarity domain, and also defines a region conserved among NFATc family members, the SP repeat region, characterized by the repeated motif SPxxSPxxSPrxsxx (D/E)(D/E)swl. NFATc3 activates NFAT site-dependent transcription when overexpressed, yet exhibits a pattern of DNA site specificity distinct from other NFATc proteins. Additionally, thymic NFATc3 undergoes modifications in response to agents that mimic T cell receptor signaling, including a decrease in apparent molecular mass upon elevation of intracellular calcium that is inhibited by the immunosuppressant FK506. Given the preferential expression of NFATc3 in the thymus, NFATc family members may regulate distinct subsets of genes during T cell development.

Biomechanics of skull fracture

This study was conducted to determine the biomechanics of the human head under quasistatic and dynamic loads. Twelve unembalmed intact human cadaver heads were tested to failure using an electrohydraulic testing device. Quasistatic loading was done at a rate of 2.5 mm/s. Impact loading tests were conducted at a rate of 7.1 to 8.0 m/s. Vertex, parietal, temporal, frontal, and occipital regions were selected as the loading sites. Pathological alterations were determined by pretest and posttest radiography, close-up computed tomography (CT) images, macroscopic evaluation, and defleshing techniques. Biomechanical force-deflection response, stiffness, and energy-absorbing characteristics were obtained. Results indicated the skull to have nonlinear structural response. The failure loads, deflections, stiffness, and energies ranged from 4.5 to 14.1 kN, 3.4 to 16.6 mm, 467 to 5867 N/mm, and 14.1 to 68.5 J, respectively. The overall mean values of these parameters for quasistatic and dynamic loads were 6.4 kN (+/- 1.1), 12.0 mm (+/- 1.6), 812 N/mm (+/- 139), 33.5 J (+/- 8.5), and 11.9 kN (+/-0.9), 5.8 mm (+/- 1.0), 4023 N/mm (+/- 541), 28.0 J (+/- 5.1), respectively. It should be emphasized that these values do not account for the individual variations in the anatomical locations on the cranium of the specimens. While the X-rays and CT scans identified the fracture, the precise direction and location of the impact on the skull were not apparent in these images. Fracture widths were consistently wider at sites remote from the loading region. Consequently, based on retrospective images, it may not be appropriate to extrapolate the anatomical region that sustained the impact forces. The quantified biomechanical response parameters will assist in the development and validation of finite element models of head injury.

Identification of methylated metabolites of inorganic arsenic by thin-layer chromatography

TLC on cellulose plates was used to identify methylated products of inorganic arsenic metabolism (monomethylarsonate and dimethylarsinate) in biological samples. Two solvent systems were tested: methanol-ammonium hydroxide (8:2) and isopropanol-acetic acid-water (10:1:2.5). The latter solvent system produced the most satisfactory separation of radiolabelled methylated arsenic compounds in aqueous solution, in rat liver cytosol incubated with carrier-free or 1 microM [73As]arsenite and in urine of mice given carrier-free [73As]arsenate or 5 mg of [73As]arsenate/kg per os. Oxidation of samples by hydrogen peroxide improved the separation and quantitation of monomethylarsonate in both biological matrices.

Chaos in protein folding: a simple one-dimensional model

A highly simplified one-dimensional model of protein folding has been developed in which the driving force is the attempt to achieve uniform internal density. The polypeptide chain is described as point-like beads on a polynomial curve, and the local density of beads is represented using wavefunctions. Despite the physical and mathematical simplicity of the model, it nonetheless displays chaotic behaviour, and analogies can be drawn to the molten-globular state, the transition state and the correctly folded state. The results support a more random view of protein folding than is often seen in the literature.

Becker muscular dystrophy presenting with complete heart block in the sixth decade

Becker muscular dystrophy may be associated with myocardial abnormalities which are usually diagnosed after the onset of weakness. We present a patient who developed complete heart block 6 years before the onset of muscle weakness which occurred unusually late at the age of 62 years.

Racial differences in the incidence of gout. The role of hypertension

OBJECTIVE

To estimate the incidence of and examine risk factors for the development of gout in black and white male physicians.

METHODS

Data from 2 cohorts of former medical students, 352 black men in the Meharry Cohort Study and 571 white men in the Johns Hopkins Precursors Study, were analyzed. Cases of gout were identified by self-report. Baseline variables and incident hypertension were examined as risk factors for the development of gout in both cohorts.

RESULTS

The incidence of gout was 3.11 and 1.82 per 1,000 person-years in the black men and the white men, respectively (P < 0.05); the cumulative incidence was 10.9% and 5.8%, respectively (P = 0.04). The relative risk (RR) for gout among the black men was 1.69 (95% confidence interval [95% CI] 1.02-2.80). This excess risk persisted after adjustment for baseline systolic blood pressure (adjusted RR = 1.96 [95% CI 1.14-3.38]). Incident hypertension was independently associated with the development of gout in univariate analysis (RR = 3.78 [95% CI 2.18-6.58]); when this variable was included as a time-dependent covariate in a Cox model, the excess risk for gout in black men was reduced and no longer significant (adjusted RR = 1.30 [95% CI 0.77-2.19]).

CONCLUSION

The approximately 2-fold excess risk for gout among black men is explained, in part, by a greater risk of incident hypertension.

In vitro inhibition of glutathione reductase by arsenotriglutathione

Arsenotriglutathione, a product of the reaction of arsenate or arsenite with glutathione, is a mixed-type inhibitor (Ki = 0.34 mM) of the in vitro reduction of glutathione disulfide by purified yeast glutathione reductase. Notably, arsenotriglutathione was a 10-fold more potent inhibitor than either arsenite or glutathione. The inhibition of glutathione reductase by arsenotriglutathione was partly reversed by the addition of meso-2,3-dimercaptosuccinic acid (DMSA). However, high concentrations of DMSA also inhibited the reduction of glutathione disulfide by the yeast enzyme (IC50 of 7 mM with 0.1 mM glutathione disulfide). Ultrafiltration of the enzyme-arsenotriglutathione complex recovered about 74% of the original (non-inhibited) activity, suggesting that the inhibition of glutathione reductase by arsenotriglutathione had both reversible and irreversible components. The relatively high potency of arsenotriglutathione as an inhibitor of glutathione reductase may alter the reduction of glutathione disulfide and affect the availability of glutathione that is required for the reduction of arsenate to arsenite and for the formation of the arsenotriglutathione complex.

Cloning and chromosomal localization of the human and murine genes for the T-cell transcription factors NFATc and NFATp

The nuclear factor of activated T cells (NFAT) is a transcription factor complex involved in the activation of cytokines and cell surface molecules associated with coordinating the actions of different cells required for an immune response. Two different genes have recently been cloned that encode proteins capable of functioning as the pre-existing (p) and cytosolic (c) component of the NFAT transcription complex, NFATc of human and NFATp of murine origin (Northrop et al., 1994; McCaffrey et al., 1993b). We report here the partial cDNA cloning of the murine homolog of NFATc and the human homolog of NFATp, and the chromosomal localization of both genes in both species to conserved syntenic regions. Through the use of mapping panels of human x Chinese hamster and mouse x rodent cells hybrids, the NFATc genes were mapped to human and mouse chromosomes 18. By analyzing a chromosome 18 radiation hybrid panel, the human NFATc gene was localized to the q terminus, closely linked to STS marker D18S497. The murine Nfatc gene was sublocalized to chromosome band 18E4 by FISH. The NFATp genes were mapped by somatic cell hybrid analysis to human chromosome 20 and mouse chromosome 2. Human NFATp was assigned to chromosome region 20q13.2-->q13.3 by FISH. Based on the conserved syntenic region on human chromosome 20 and mouse chromosome 2, murine Nfatp is predicted to reside in the vicinity of a mutant locus wasted. Homozygous wst/wst mice display a phenotype reminiscent of severe combined immune deficiency or ataxia telangiectasia, disorders that could therefore be considered candidates for NFATp mutations.

Arsenic toxicity in humans: Research problems and prospects

The disposition and toxicity of the metalloid, arsenic, is affected by its oxidation state and on the extent to which it is converted to methylated species. Given that these chemical modifications influence the fate and action of arsenic, new research efforts should be directed both towards elucidating the molecular processes involved in the metabolism of arsenic and in characterising interindividual variation in capacity for processes such as the methylation of arsenic. This information will contribute to a better understanding of the mechanisms of arsenic toxicity and carcinogenicity and to a better assessment of the hazards associated with chronic exposure to this agent.

Complexation of arsenic species in rabbit erythrocytes

The binding of arsenite, As(III), and arsenate, As(V), by molecules in the intracellular compartment of rabbit erythrocytes has been studied by 1H- and 31P-NMR spectroscopy, uptake of 73As, and ultrafiltration experiments. For intact erythrocytes to which 0.1-0.4 mM arsenite was added, direct evidence was obtained for entry of 76% within 1/2 h and subsequent binding of As(III) by intracellular glutathione and induced changes in the hemoglobin structure (NMR), likely due to binding of As(III). These results were compared with the effect of addition of As(V) on intact erythrocytes and revealed that a smaller amount of As(V) (approximately 25%) enters the cells; the main fraction of As(V) enters the phosphate pathway, depletes ATP, and increases Pi. In contrast, As(III) did not affect the ATP level. Both 1H- and 31P-NMR data indicated striking differences between As(III) and As(V) behavior when incubated with rabbit erythrocytes. These differences were confirmed by 73As uptake and binding experiments. meso-2,3-Dimercaptosuccinic acid (DMSA), a dithiol ligand, released glutathione from its arsenite complexes in erythrocytes.