Safety and efficacy of percutaneous nephrolithotomy for the treatment of paediatric urolithiasis

INTRODUCTION

Paediatric percutaneous nephrolithotomy (PCNL) has revolutionised the treatment of paediatric nephrolithiasis. Paediatric PCNL has been performed using both adult and paediatric instruments. Stone clearance rates and complications vary according to the technique used and surgeon experience. We present our experience with PCNL using adult instruments and a 28Fr access tract for large renal calculi in children under 18 years.

METHODS

All patients undergoing PCNL at our institution between 2000 and 2009 were reviewed. Demographics, surgical details and post-operative follow-up information were obtained to identify stone clearance rates and complications.

RESULTS

PCNL was performed in 32 renal units in 31 patients (mean age: 10.8 years). The mean stone diameter was 19mm (range: 5-40mm). Twenty-six cases required single puncture and six required multiple tracts. Overall, 11 staghorn stones, 10 multiple calyceal stones and 11 single stones were treated. Twenty-seven patients (84%) were completely stone free following initial PCNL. Two cases had extracorporeal shock wave lithotripsy for residual fragments, giving an overall stone free rate of 91% following treatment. There was no significant bleeding or sepsis encountered either during the operation or in the post-operative setting. No patient required or received a blood transfusion.

CONCLUSIONS

Paediatric PCNL can be performed safely with minimal morbidity using adult instruments for large stone burden, enabling rapid and complete stone clearance.

Methylation of arsenic by recombinant human wild-type arsenic (+3 oxidation state) methyltransferase and its methionine 287 threonine (M287T) polymorph: Role of glutathione

Arsenic (+3 oxidation state) methyltransferase (AS3MT) is the key enzyme in the pathway for methylation of arsenicals. A common polymorphism in the AS3MT gene that replaces a threonyl residue in position 287 with a methionyl residue (AS3MT/M287T) occurs at a frequency of about 10% among populations worldwide. Here, we compared catalytic properties of recombinant human wild-type (wt) AS3MT and AS3MT/M287T in reaction mixtures containing S-adenosylmethionine, arsenite (iAs(III)) or methylarsonous acid (MAs(III)) as substrates and endogenous or synthetic reductants, including glutathione (GSH), a thioredoxin reductase (TR)/thioredoxin (Trx)/NADPH reducing system, or tris (2-carboxyethyl) phosphine hydrochloride (TCEP). With either TR/Trx/NADPH or TCEP, wtAS3MT or AS3MT/M287T catalyzed conversion of iAs(III) to MAs(III), methylarsonic acid (MAs(V)), dimethylarsinous acid (DMAs(III)), and dimethylarsinic acid (DMAs(V)); MAs(III) was converted to DMAs(III) and DMAs(V). Although neither enzyme required GSH to support methylation of iAs(III) or MAs(III), addition of 1mM GSH decreased K(m) and increased V(max) estimates for either substrate in reaction mixtures containing TR/Trx/NADPH. Without GSH, V(max) and K(m) values were significantly lower for AS3MT/M287T than for wtAS3MT. In the presence of 1mM GSH, significantly more DMAs(III) was produced from iAs(III) in reactions catalyzed by the M287T variant than in wtAS3MT-catalyzed reactions. Thus, 1mM GSH modulates AS3MT activity, increasing both methylation rates and yield of DMAs(III). AS3MT genotype exemplified by differences in regulation of wtAS3MT and AS3MT/M287T-catalyzed reactions by GSH may contribute to differences in the phenotype for arsenic methylation and, ultimately, to differences in the disease susceptibility in individuals chronically exposed to inorganic arsenic.

An in vitro assessment of bioaccessibility of arsenicals in rice and the use of this estimate within a probabilistic exposure model

In this study, an in vitro synthetic gastrointestinal extraction protocol was used to estimate bioaccessibility of different arsenicals present in 17 rice samples of various grain types that were collected across the United States. The across matrix average for total arsenic was 209 ng/g±153 (\[xmacr]±2σ). The bioaccessibility estimate produced an across matrix average of 61%±19 (\[xmacr]±2σ). The across matrix average concentrations of inorganic arsenic (iAs) and dimethylarsinic acid (DMA) were 81 ng/g±67.7 and 41 ng/g±58.1 (\[xmacr]±2σ), respectively. This distribution of iAs concentrations in rice was combined with the distribution of consumption patterns (from WWEIA) in a Stochastic Human Exposure and Dose Simulator model to estimate population-based exposures. The mean consumption rate for the population as a whole was 15.7 g per day resulting in a 0.98 μg iAs per day exposure. The mean consumption rate for children 1-2 years old was 7 g per day resulting in a 0.48 μg iAs per day exposure. Presystemic biotransformation of DMA in rice was examined using an in vitro assay containing the anaerobic microbiota of mouse cecum. This assay indicated that DMA extracted from the rice was converted to dimethylthioarsinic acid, although a second oxygen-sulfur exchange to produce DMDTA was not observed.

Tumors and proliferative lesions in adult offspring after maternal exposure to methylarsonous acid during gestation in CD1 mice

Developmental exposure to inorganic arsenic is carcinogenic in humans and mice, and adult offspring of mice exposed to inorganic arsenic can develop tumors of the lung, liver, adrenal, uterus, and ovary. It has been suggested that methylarsonous acid (MMA3+), a product of the biological methylation of inorganic arsenic, could be a key carcinogenic species. Thus, pregnant CD1 mice were provided drinking water containing MMA3+ at 0 (control), 12.5, or 25 parts per million (ppm) from gestational days 8 to 18. Tumors were assessed in groups of male or female (initial n = 25) offspring up to 2 years of age. In utero treatment had no effect on survival or body weights. Female offspring exhibited increases in total epithelial uterine tumors (control 0%; 12.5 ppm 26%; 25 ppm 30%), oviduct hyperplasia (control 4%; 12.5 ppm 35%; 25 ppm 43%), adrenal cortical adenoma at 25 ppm (control 0%; 12.5 ppm 9%; 25 ppm 26%), and total epithelial ovarian tumors (control 0%; 12.5 ppm 39%; 25 ppm 26%). Male offspring showed dose-related increases in hepatocellular carcinoma (control 0%; 12.5 ppm 12%; 25 ppm 22%), adrenal adenoma (control 0%; 12.5 ppm 28%; 25 ppm 17%), and lung adenocarcinoma (control 17%; 12.5 ppm 44%). Male offspring had unusual testicular lesions, including two rete testis carcinomas, two adenomas, and three interstitial cell tumors. Overall, maternal consumption of MMA3+ during pregnancy in CD1 mice produced some similar proliferative lesions as gestationally applied inorganic arsenic in the offspring during adulthood.

Alterations in physical state of silver nanoparticles exposed to synthetic human stomach fluid

The bioavailability of ingested silver nanoparticles (AgNPs) depends in large part on initial particle size, shape and surface coating, properties which will influence aggregation, solubility and chemical composition during transit of the gastrointestinal tract. Citrate-stabilized AgNPs were exposed to synthetic human stomach fluid (SSF) (pH 1.5) and changes in size, shape, zeta potential, hydrodynamic diameter and chemical composition were determined during a 1h exposure period using Surface Plasmon Resonance (SPR), High Resolution Transmission Electron Microscopy/Energy Dispersive X-ray Spectroscopy (TEM/EDS), Dynamic Light Scattering (DLS) and X-ray Powder Diffraction (XRD) combined with Rietveld analysis. Exposure of AgNPs to SSF produced a rapid decrease in the SPR peak at 414nm and the appearance of a broad absorbance peak in the near infrared (NIR) spectral region. During exposure to SSF, changes in zeta potential, aggregation and morphology of the particles were also observed as well as production of silver chloride which appeared physically associated with particle aggregates.

Analysis of arsenical metabolites in biological samples

Quantitation of iAs and its methylated metabolites in biological samples provides dosimetric information needed to understand dose-response relations. Here, methods are described for separation of inorganic and mono-, di-, and trimethylated arsenicals by thin layer chromatography. This method has been extensively used to track the metabolism of the radionuclide [(73)As] in a variety of in vitro assay systems. In addition, a hydride generation-cryotrapping-gas chromatography-atomic absorption spectrometric method is described for the quantitation of arsenicals in biological samples. This method uses pH-selective hydride generation to differentiate among arsenicals containing trivalent or pentavalent arsenic.

Relative bioavailability and bioaccessibility and speciation of arsenic in contaminated soils

BACKGROUND

Assessment of soil arsenic (As) bioavailability may profoundly affect the extent of remediation required at contaminated sites by improving human exposure estimates. Because small adjustments in soil As bioavailability estimates can significantly alter risk assessments and remediation goals, convenient, rapid, reliable, and inexpensive tools are needed to determine soil As bioavailability.

OBJECTIVES

We evaluated inexpensive methods for assessing As bioavailability in soil as a means to improve human exposure estimates and potentially reduce remediation costs.

METHODS

Nine soils from residential sites affected by mining or smelting activity and two National Institute of Standards and Technology standard reference materials were evaluated for As bioavailability, bioaccessibility, and speciation. Arsenic bioavailability was determined using an in vivo mouse model, and As bioaccessibility was determined using the Solubility/Bioavailability Research Consortium in vitro assay. Arsenic speciation in soil and selected soil physicochemical properties were also evaluated to determine whether these parameters could be used as predictors of As bioavailability and bioaccessibility.

RESULTS

In the mouse assay, we compared bioavailabilities of As in soils with that for sodium arsenate. Relative bioavailabilities (RBAs) of soil As ranged from 11% to 53% (mean, 33%). In vitro soil As bioaccessibility values were strongly correlated with soil As RBAs (R² = 0.92). Among physicochemical properties, combined concentrations of iron and aluminum accounted for 80% and 62% of the variability in estimates of RBA and bioaccessibility, respectively.

CONCLUSION

The multifaceted approach described here yielded congruent estimates of As bioavailability and evidence of interrelations among physicochemical properties and bioavailability estimates.

Arsenic exposure and toxicology: a historical perspective

The metalloid arsenic is a natural environmental contaminant to which humans are routinely exposed in food, water, air, and soil. Arsenic has a long history of use as a homicidal agent, but in the past 100 years arsenic, has been used as a pesticide, a chemotherapeutic agent and a constituent of consumer products. In some areas of the world, high levels of arsenic are naturally present in drinking water and are a toxicological concern. There are several structural forms and oxidation states of arsenic because it forms alloys with metals and covalent bonds with hydrogen, oxygen, carbon, and other elements. Environmentally relevant forms of arsenic are inorganic and organic existing in the trivalent or pentavalent state. Metabolism of arsenic, catalyzed by arsenic (+3 oxidation state) methyltransferase, is a sequential process of reduction from pentavalency to trivalency followed by oxidative methylation back to pentavalency. Trivalent arsenic is generally more toxicologically potent than pentavalent arsenic. Acute effects of arsenic range from gastrointestinal distress to death. Depending on the dose, chronic arsenic exposure may affect several major organ systems. A major concern of ingested arsenic is cancer, primarily of skin, bladder, and lung. The mode of action of arsenic for its disease endpoints is currently under study. Two key areas are the interaction of trivalent arsenicals with sulfur in proteins and the ability of arsenic to generate oxidative stress. With advances in technology and the recent development of animal models for arsenic carcinogenicity, understanding of the toxicology of arsenic will continue to improve.

Mouse arsenic (+3 oxidation state) methyltransferase genotype affects metabolism and tissue dosimetry of arsenicals after arsenite administration in drinking water

Arsenic (+3 oxidation state) methyltransferase (As3mt) catalyzes methylation of inorganic arsenic (iAs) producing a number of methylated arsenic metabolites. Although methylation has been commonly considered a pathway for detoxification of arsenic, some highly reactive methylated arsenicals may contribute to toxicity associated with exposure to inorganic arsenic. Here, adult female wild-type (WT) C57BL/6 mice and female As3mt knockout (KO) mice received drinking water that contained 1, 10, or 25 ppm (mg/l) of arsenite for 33 days and blood, liver, kidney, and lung were taken for arsenic speciation. Genotype markedly affected concentrations of arsenicals in tissues. Summed concentrations of arsenicals in plasma were higher in WT than in KO mice; in red blood cells, summed concentrations of arsenicals were higher in KO than in WT mice. In liver, kidney, and lung, summed concentrations of arsenicals were greater in KO than in WT mice. Although capacity for arsenic methylation is much reduced in KO mice, some mono-, di-, and tri-methylated arsenicals were found in tissues of KO mice, likely reflecting the activity of other tissue methyltransferases or preabsorptive metabolism by the microbiota of the gastrointestinal tract. These results show that the genotype for arsenic methylation determines the phenotypes of arsenic retention and distribution and affects the dose- and organ-dependent toxicity associated with exposure to inorganic arsenic.

Preabsorptive metabolism of sodium arsenate by anaerobic microbiota of mouse cecum forms a variety of methylated and thiolated arsenicals

The conventional scheme for arsenic methylation accounts for methylated oxyarsenical production but not for thioarsenical formation. Here, we report that in vitro anaerobic microbiota of mouse cecum converts arsenate into oxy- and thio- arsenicals. Besides methylarsonic acid (MMA(V)), arsenate was transformed into six unique metabolites: mono-, di-, and trithio-arsenic acid, monomethyldithio- and monomethyltrithio-arsonic acid, and dimethyldithioarsonic acid. Thioarsenicals were found in soluble and particulate fractions of reaction mixtures, suggesting interactions with anaerobic microbiota. Metabolism of ingested arsenate to oxy- and thio-arsenicals before absorption across the gastrointestinal barrier could affect bioavailability, systemic distribution, and resulting toxicity.

Effect of sodium arsenite dose administered in the drinking water on the urinary bladder epithelium of female arsenic (+3 oxidation state) methyltransferase knockout mice

The enzyme arsenic (+3 oxidation state) methyltransferase (As3mt) catalyzes reactions converting inorganic arsenic to methylated metabolites, some of which are highly cytotoxic. In a previous study, female As3mt knockout (KO) mice treated with diet containing 100 or 150 ppm arsenic as arsenite showed systemic toxicity and significant effects on the urothelium. In the present study, we showed that the cytotoxic and proliferative effects of arsenite administration on the urothelium are dose dependent. Female wild-type C57BL/6 mice and As3mt KO mice were divided into five groups (n = 7) with free access to drinking water containing 0, 1, 10, 25, or 50 ppm arsenic as arsenite for 4 weeks. At sacrifice, urinary bladders of both As3mt KO and wild-type mice showed hyperplasia by light microscopy; however, the hyperplasia was more severe in the As3mt KO mice. Intracytoplasmic granules were detected in the urothelium of As3mt KO and wild-type mice at arsenic doses ≥ 10 ppm but were more numerous, more extensive, and larger in the KO mice. A no effect level for urothelial effects was identified at 1 ppm arsenic in the wild-type and As3mt KO mice. In As3mt KO mice, livers showed mild acute inflammation and kidneys showed hydronephrosis. The present study shows a dose-response for the effects of orally administered arsenite on the bladder urothelium of wild-type and As3mt KO mice, with greater effects in the KO strain but with a no effect level of 1 ppm for both.

Purification of arsenic (+3 oxidation state) methyltransferase from rat liver cytosol

Demonstrating the enzymatic basis of arsenic methylation is critical to further studies of the pathway for the conversion of inorganic arsenic into a variety of methylated metabolites. This protocol describes a procedure for the purification of an arsenic methyltransferase from rat liver cytosol. Purification of this enzyme and subsequent cloning of its gene has permitted studies of enzyme structure and function, and has lead to the identification of orthologous genes in genomes of organisms ranging in complexity from sea urchins to humans. These proteins are referred to as arsenic (+3 oxidation state) methyltransferases.

Manipulation of expression of arsenic (+3 oxidation state) methyltransferase in cultured cells

Methylation of inorganic arsenic to produce mono-, di-, or trimethylated products is the central process in the cellular metabolism of arsenic. Identification of arsenic (+3 oxidation state) methyltransferase (As3mt) as the enzyme that could catalyze all the steps in the pathway for arsenic methylation suggests that expression of this enzyme could be a useful target for manipulation. Here, methods are described for heterologous expression of the rat As3mt gene in a human urothelial cell line that normally does not express this enzyme and for silencing of the AS3MT gene by RNA interference in a human hepatoma cell line. These tools can be applied to elucidating the role of methylation in the toxic and carcinogenic effects of arsenicals.

Arsenic (+3 oxidation state) methyltransferase genotype affects steady-state distribution and clearance of arsenic in arsenate-treated mice

Arsenic (+3 oxidation state) methyltransferase (As3mt) catalyzes formation of mono-, di-, and tri-methylated metabolites of inorganic arsenic. Distribution and retention of arsenic were compared in adult female As3mt knockout mice and wild-type C57BL/6 mice using a regimen in which mice received daily oral doses of 0.5mg of arsenic as arsenate per kilogram of body weight. Regardless of genotype, arsenic body burdens attained steady state after 10 daily doses. At steady state, arsenic body burdens in As3mt knockout mice were 16 to 20 times greater than in wild-type mice. During the post dosing clearance period, arsenic body burdens declined in As3mt knockout mice to ~35% and in wild-type mice to ~10% of steady-state levels. Urinary concentration of arsenic was significantly lower in As3mt knockout mice than in wild-type mice. At steady state, As3mt knockout mice had significantly higher fractions of the body burden of arsenic in liver, kidney, and urinary bladder than did wild-type mice. These organs and lung had significantly higher arsenic concentrations than did corresponding organs from wild-type mice. Inorganic arsenic was the predominant species in tissues of As3mt knockout mice; tissues from wild-type mice contained mixtures of inorganic arsenic and its methylated metabolites. Diminished capacity for arsenic methylation in As3mt knockout mice prolongs retention of inorganic arsenic in tissues and affects whole body clearance of arsenic. Altered retention and tissue tropism of arsenic in As3mt knockout mice could affect the toxic or carcinogenic effects associated with exposure to this metalloid or its methylated metabolites.

Arsenolysis and thiol-dependent arsenate reduction

Conversion of arsenate to arsenite is a critical event in the pathway that leads from inorganic arsenic to a variety of methylated metabolites. The formation of methylated metabolites influences distribution and retention of arsenic and affects the reactivity and toxicity of these intermediates. Indeed, some of the toxic and carcinogenic effects associated with exposure to arsenate or arsenite are probably mediated by methylated arsenicals. Recent work has demonstrated a biologically plausible role for phosphorolytic-arsenolytic enzymes in a reaction scheme in which an "activated" arsenate ester is readily reduced by thiols to arsenite. Thiol-dependent reduction of arsenate esters formed by arsenolysis may be one of several functionally reductant processes that control the flux of arsenic into the cellular pathway for arsenic methylation. Integrating these reductive processes into a conceptual model for arsenic metabolism may provide new insights into the cellular machinery for handling this toxic metalloid.

In vitro assays of inorganic arsenic methylation

Inorganic arsenic is extensively metabolized to produce mono-, di-, and trimethylated products. The formation of these metabolites produces a variety of intermediates that differ from inorganic arsenic in terms of patterns of distribution and retention and in toxic effects. In order to elucidate the pathway for arsenic methylation, it was necessary to develop a reliable in vitro assay system in which the formation of methylated metabolites could be monitored. Here, in vitro assay system that uses the postmicrosomal supernate from rat liver is used as the source of the enzymatic activity that catalyzes methylation reactions. This system can be used to study the requirements for methylation reactions (e.g., identifying the donor of methyl groups) and for screening of compounds as potential activators or inhibitors of arsenic methylation.

Interspecies differences in metabolism of arsenic by cultured primary hepatocytes

Biomethylation is the major pathway for the metabolism of inorganic arsenic (iAs) in many mammalian species, including the human. However, significant interspecies differences have been reported in the rate of in vivo metabolism of iAs and in yields of iAs metabolites found in urine. Liver is considered the primary site for the methylation of iAs and arsenic (+3 oxidation state) methyltransferase (As3mt) is the key enzyme in this pathway. Thus, the As3mt-catalyzed methylation of iAs in the liver determines in part the rate and the pattern of iAs metabolism in various species. We examined kinetics and concentration-response patterns for iAs methylation by cultured primary hepatocytes derived from human, rat, mice, dog, rabbit, and rhesus monkey. Hepatocytes were exposed to [(73)As]arsenite (iAs(III); 0.3, 0.9, 3.0, 9.0 or 30 nmol As/mg protein) for 24 h and radiolabeled metabolites were analyzed in cells and culture media. Hepatocytes from all six species methylated iAs(III) to methylarsenic (MAs) and dimethylarsenic (DMAs). Notably, dog, rat and monkey hepatocytes were considerably more efficient methylators of iAs(III) than mouse, rabbit or human hepatocytes. The low efficiency of mouse, rabbit and human hepatocytes to methylate iAs(III) was associated with inhibition of DMAs production by moderate concentrations of iAs(III) and with retention of iAs and MAs in cells. No significant correlations were found between the rate of iAs methylation and the thioredoxin reductase activity or glutathione concentration, two factors that modulate the activity of recombinant As3mt. No associations between the rates of iAs methylation and As3mt protein structures were found for the six species examined. Immunoblot analyses indicate that the superior arsenic methylation capacities of dog, rat and monkey hepatocytes examined in this study may be associated with a higher As3mt expression. However, factors other than As3mt expression may also contribute to the interspecies differences in the hepatocyte capacity to methylate iAs.

Disruption of the arsenic (+3 oxidation state) methyltransferase gene in the mouse alters the phenotype for methylation of arsenic and affects distribution and retention of orally administered arsenate

The arsenic (+3 oxidation state) methyltransferase (As3mt) gene encodes a 43 kDa protein that catalyzes methylation of inorganic arsenic. Altered expression of AS3MT in cultured human cells controls arsenic methylation phenotypes, suggesting a critical role in arsenic metabolism. Because methylated arsenicals mediate some toxic or carcinogenic effects linked to inorganic arsenic exposure, studies of the fate and effects of arsenicals in mice which cannot methylate arsenic could be instructive. This study compared retention and distribution of arsenic in As3mt knockout mice and in wild-type C57BL/6 mice in which expression of the As3mt gene is normal. Male and female mice of either genotype received an oral dose of 0.5 mg of arsenic as arsenate per kg containing [(73)As]-arsenate. Mice were radioassayed for up to 96 h after dosing; tissues were collected at 2 and 24 h after dosing. At 2 and 24 h after dosing, livers of As3mt knockouts contained a greater proportion of inorganic and monomethylated arsenic than did livers of C57BL/6 mice. A similar predominance of inorganic and monomethylated arsenic was found in the urine of As3mt knockouts. At 24 h after dosing, As3mt knockouts retained significantly higher percentages of arsenic dose in liver, kidneys, urinary bladder, lungs, heart, and carcass than did C57BL/6 mice. Whole body clearance of [(73)As] in As3mt knockouts was substantially slower than in C57BL/6 mice. At 24 h after dosing, As3mt knockouts retained about 50% and C57BL/6 mice about 6% of the dose. After 96 h, As3mt knockouts retained about 20% and C57BL/6 mice retained less than 2% of the dose. These data confirm a central role for As3mt in the metabolism of inorganic arsenic and indicate that phenotypes for arsenic retention and distribution are markedly affected by the null genotype for arsenic methylation, indicating a close linkage between the metabolism and retention of arsenicals.

Arsenic (+ 3 oxidation state) methyltransferase and the methylation of arsenicals in the invertebrate chordate Ciona intestinalis

Biotransformation of inorganic arsenic (iAs) involves methylation catalyzed by arsenic (+ 3 oxidation state) methyltransferase (As3mt) yielding mono-, di-, and trimethylated arsenicals. To investigate the evolution of molecular mechanisms that mediate arsenic biotransformation, a comparative genomic approach focusing on the invertebrate chordate Ciona intestinalis was used. Bioinformatic analyses identified an As3mt gene in the C. intestinalis genome. Constitutive As3mt RNA expression was observed in heart, branchial sac, and gastrointestinal tract. Adult animals were exposed to 0 or 1 ppm of iAs for 1 or 5 days. Steady-state As3mt RNA expression in the gastrointestinal tract was not modulated significantly by 5 days of exposure to iAs. Tissue levels of iAs and its methylated metabolites were determined by hydride generation-cryotrapping-gas chromatography-atomic absorption spectrometry. At either time point, exposure to iAs significantly increased concentrations of iAs and its methylated metabolites in tissues. After 5 days of exposure, total speciated arsenic concentrations were highest in branchial sac (3705 ng/g), followed by heart (1019 ng/g) and gastrointestinal tract (835 ng/g). At this time point, the sum of the speciated arsenical concentrations in gastrointestinal tract and heart equaled or exceeded that of iAs; in branchial sac, iAs was the predominant species present. Ciona intestinalis metabolizes iAs to its methylated metabolites, which are retained in tissues. This metabolic pattern is consistent with the presence of an As3mt ortholog in its genome and constitutive expression of the gene in prominent organs, making this basal chordate a useful model to examine the evolution of arsenic detoxification.

Impact of life stage and duration of exposure on arsenic-induced proliferative lesions and neoplasia in C3H mice

Epidemiological studies suggest that chronic exposure to inorganic arsenic is associated with cancer of the skin, urinary bladder and lung as well as the kidney and liver. Previous experimental studies have demonstrated increased incidence of liver, lung, ovary, and uterine tumors in mice exposed to 85 ppm (approximately 8 mg/kg) inorganic arsenic during gestation. To further characterize age susceptibility to arsenic carcinogenesis we administered 85 ppm inorganic arsenic in drinking water to C3H mice during gestation, prior to pubescence and post-pubescence to compare proliferative lesion and tumor outcomes over a one-year exposure period. Inorganic arsenic significantly increased the incidence of hyperplasia in urinary bladder (48%) and oviduct (36%) in female mice exposed prior to pubescence (beginning on postnatal day 21 and extending through one year) compared to control mice (19 and 5%, respectively). Arsenic also increased the incidence of hyperplasia in urinary bladder (28%) of female mice continuously exposed to arsenic (beginning on gestation day 8 and extending though one year) compared to gestation only exposed mice (0%). In contrast, inorganic arsenic significantly decreased the incidence of tumors in liver (0%) and adrenal glands (0%) of male mice continuously exposed from gestation through one year, as compared to levels in control (30 and 65%, respectively) and gestation only (33 and 55%, respectively) exposed mice. Together, these results suggest that continuous inorganic arsenic exposure at 85 ppm from gestation through one year increases the incidence and severity of urogenital proliferative lesions in female mice and decreases the incidence of liver and adrenal tumors in male mice. The paradoxical nature of these effects may be related to altered lipid metabolism, the effective dose in each target organ, and/or the shorter one-year observational period.