Biochemical effects of copper nanomaterials in human hepatocellular carcinoma (HepG2) cells

In dose-response and structure-activity studies, human hepatic HepG2 cells were exposed for 3 days to nano Cu, nano CuO or CuCl2 (ions) at doses between 0.1 and 30 ug/ml (approximately the no observable adverse effect level to a high degree of cytotoxicity). Various biochemical parameters were then evaluated to study cytotoxicity, cell growth, hepatic function, and oxidative stress. With nano Cu and nano CuO, few indications of cytotoxicity were observed between 0.1 and 3 ug/ml. In respect to dose, lactate dehydrogenase and aspartate transaminase were the most sensitive cytotoxicity parameters. The next most responsive parameters were alanine aminotransferase, glutathione reductase, glucose 6-phosphate dehydrogenase, and protein concentration. The medium responsive parameters were superoxide dismutase, gamma glutamyltranspeptidase, total bilirubin, and microalbumin. The parameters glutathione peroxidase, glutathione reductase, and protein were all altered by nano Cu and nano CuO but not by CuCl2 exposures. Our chief observations were (1) significant decreases in glucose 6-phosphate dehydrogenase and glutathione reductase was observed at doses below the doses that show high cytotoxicity, (2) even high cytotoxicity did not induce large changes in some study parameters (e.g., alkaline phosphatase, catalase, microalbumin, total bilirubin, thioredoxin reductase, and triglycerides), (3) even though many significant biochemical effects happen only at doses showing varying degrees of cytotoxicity, it was not clear that cytotoxicity alone caused all of the observed significant biochemical effects, and (4) the decreased glucose 6-phosphate dehydrogenase and glutathione reductase support the view that oxidative stress is a main toxicity pathway of CuCl2 and Cu-containing nanomaterials.

Differential genomic effects of four nano-sized and one micro-sized CeO2 particles on HepG2 cells

The objective of this research was to perform a genomics study of five cerium oxide particles, 4 nano and one micrometer-sized particles which have been studied previously by our group with respect to cytotoxicity, biochemistry and metabolomics. Human liver carcinoma HepG2 cells were exposed to between 0.3 to 300 ug/ml of CeO2 particles for 72 hours and then total RNA was harvested. Fatty acid accumulation was observed with W4, X5, Z7 and less with Q but not Y6. The gene expression changes in the fatty acid metabolism genes correlated the fatty acid accumulation we detected in the prior metabolomics study for the CeO2 particles named W4, Y6, Z7 and Q, but not for X5. In particular, the observed genomics effects on fatty acid uptake and fatty acid oxidation offer a possible explanation of why many CeO2 particles increase cellular free fatty acid concentrations in HepG2 cells. The major genomic changes observed in this study were sirtuin, ubiquitination signaling pathways, NRF2-mediated stress response and mitochondrial dysfunction. The sirtuin pathway was affected by many CeO2 particle treatments. Sirtuin signaling itself is sensitive to oxidative stress state of the cells and may be an important contributor in CeO2 particle induced fatty acid accumulation. Ubiquitination pathway regulates many protein functions in the cells, including sirtuin signaling, NRF2 mediated stress, and mitochondrial dysfunction pathways. NRF2-mediated stress response and mitochondrial were reported to be altered in many nanoparticles treated cells. All these pathways may contribute to the fatty acid accumulation in the CeO2 particle treated cells.

Effects of Silver Nanoparticles and Silver Nitrate on mRNA and microRNA Expression in Human Hepatocellular Carcinoma Cells (HepG2)

In order to understand toxicity of nano silver, human hepatocellular carcinoma (HepG2) cells were treated either with silver nitrate (AgNO₃) or with nano silver capped with glutathione (Ag-S) at various concentration. Differentially expressed genelists for mRNA and microRNA were obtained through Illumina RNA sequencing and DEseq data analyses. Both treatments showed non-linear dose response relationships for mRNA and microRNA. Gene expression analysis showed signaling pathways common to both nano Ag-S and AgNO₃, such as cell cycle regulation, DNA damage response and cancer related pathways. But, nano Ag-S caused signaling pathway changes that were not altered by AgNO₃ such as NRF2-mediated oxidative stress response inflammation, cell membrane signaling, and cell proliferation. Nano Ag-S also affected p53 signaling, survival, apoptosis, tissue repair, lipid synthesis, angiogenesis, liver fibrosis and tumor development. Several of the pathways affected by nano Ag-S are hypothesized as major contributors to nanotoxicity. MicroRNA target filter analysis revealed additional affected pathways that were not reflected in the mRNA expression response alone, including DNA damage signaling, genomic stability, ROS, cell cycle, ubiquitination, DNA methylation, cell proliferation and fibrosis for AgNO₃; and cell cycle regulation, P53 signaling, cell proliferation, survival, apoptosis, tissue repair and so on for nano Ag-S. These pathways may be mediated by microRNA repression of protein translation.Our study clearly showed that the addition of microRNA profiling increased the numbers of signaling pathways discovered that affected by the treatments on HepG2 cells and gave US a better picture of the effects of these reagents in the cells.

Effects of Copper Nanoparticles on mRNA and Small RNA Expression in Human Hepatocellular Carcinoma (HepG2) Cells

With the advancement of nanotechnology, nanoparticles are widely used in many different industrial processes and consumer products. Copper nanoparticles (Cu NPs) are among the most toxic nanomaterials. We investigated Cu NPs toxicity in Human Hepatocellular carcinoma (HepG2) cells by examining signaling pathways, and microRNA/mRNA interactions. We compared the effects of exposures to Cu NPs at various concentrations and CuCl₂ was used as a control. The number of differentially expressed mRNA did not follow a linear dose-response relationship for either Cu NPs or CuCl₂ treatments. The most significantly altered genes and pathways by Cu NPs exposure were NRF2 (nuclear factor erythroid 2 related factor 2)-mediated oxidative stress response, protein ubiquitination, Tumor protein p53 (p53), phase I and II metabolizing enzymes, antioxidant proteins and phase III detoxifying gene pathways.Messenger RNA-microRNA interaction from MicroRNA Target Filter Analyses revealed more signaling pathways altered in Cu NPs treated samples than transcriptomics alone, including cell proliferation, DNA methylation, endoplasmic reticulum (ER) stress, apoptosis, autophagy, reactive oxygen species, inflammation, tumorigenesis, extracellular matrix/angiogenesis and protein synthesis. In contrast, in the control (CuCl₂) treated samples showed mostly changes in inflammation mainly through regulation of the Nuclear Factor Kappa-light-chain-enhancer of Activated B-cells (NFκB). Further, some RNA based parameters that showed promise as biomarkers of Cu NPs exposure including both well and lesser known genes: heme oxygenase 1 (HMOX1), heat shock protein, c-Fos proto-oncogene, DNA methyltransferases, and glutamate-cysteine ligase modifier subunit (GCLM, part of the glutathione synthesis pathway). The differences in signaling pathways altered by the Cu NPs and CuCl₂ treatments suggest that the effects of the Cu NPs were not the results of nanomaterial dissolution to soluble copper ions.

Biochemical Effects of Silver Nanomaterials in Human Hepatocellular Carcinoma (HepG2) Cells

In dose-response and structure-activity studies, human hepatic HepG2 cells were exposed to between 0.01 and 300 ug/ml of different silver nanomaterials and AgNO₃ for 3 days. Treatment chemicals included a custom synthesized rod shaped nano Ag, a glutathione capped nano Ag, polyvinylpyrrolidone (PVP) capped nano Ag (75 nm) from Nanocomposix and AgNO₃. Various biochemical parameters were then evaluated to study cytotoxicity, cell growth, hepatic function and oxidative stress. Few indications of cytotoxicity were observed between 0.1 ug/ml and 6 ug/ml of any nano Ag. At 10 ug/ml and above, Ag containing nanomaterials caused a moderate to severe degree of cytotoxicity in HepG2 cells. Lactate dehydrogenase and aspartate transaminase activity alterations were the most sensitive cytotoxicity parameters. Some biochemical parameters were altered by exposures to both nano Ag and AgNO₃ (statistically significant increases in alkaline phosphatase, gamma glutamyltranspeptidase, glutathione peroxidase and triglycerides; in contrast both glutathione reductase and HepG2 protein concentration were both decreased). Three parameters were significantly altered by nano Ag but not by AgNO₃ (decreases in glucose 6-phosphate dehydrogenase and thioredoxin reductase and increases in catalase). Cytotoxicity per se did not appear to fully explain the patterns of biological responses observed. Some of the observations with the three nano Ag (increases in alkaline phosphatase, catalase, gamma glutamyltranspeptidase, as well as decreases in glucose 6-phosphate dehydrogenase and glutathione reductase) are in the same direction as HepG2 responses to other nanomaterials composed of TiO₂, CeO₂, SiO₂, CuO and Cu. Therefore, these biochemical responses may be due to micropinocytosis of nanomaterials, membrane damage, oxidative stress and/or cytotoxicity. Decreased G6PDH (by all three nano Ag forms) and GRD activity (only nano Ag R did not cause decreases) support and are consistent with the oxidative stress theory of Ag nanomaterial action.

Metabolomic effects of CeO2, SiO2 and CuO metal oxide nanomaterials on HepG2 cells

BACKGROUND

To better assess potential hepatotoxicity of nanomaterials, human liver HepG2 cells were exposed for 3 days to five different CeO₂ (either 30 or 100 μg/ml), 3 SiO₂ based (30 μg/ml) or 1 CuO (3 μg/ml) nanomaterials with dry primary particle sizes ranging from 15 to 213 nm. Metabolomic assessment of exposed cells was then performed using four mass spectroscopy dependent platforms (LC and GC), finding 344 biochemicals.

RESULTS

Four CeO₂, 1 SiO₂ and 1 CuO nanomaterials increased hepatocyte concentrations of many lipids, particularly free fatty acids and monoacylglycerols but only CuO elevated lysolipids and sphingolipids. In respect to structure-activity, we now know that five out of six tested CeO₂, and both SiO₂ and CuO, but zero out of four TiO₂ nanomaterials have caused this elevated lipids effect in HepG2 cells. Observed decreases in UDP-glucuronate (by CeO₂) and S-adenosylmethionine (by CeO₂ and CuO) and increased S-adenosylhomocysteine (by CuO and some CeO₂) suggest that a nanomaterial exposure increases transmethylation reactions and depletes hepatic methylation and glucuronidation capacity. Our metabolomics data suggests increased free radical attack on nucleotides. There was a clear pattern of nanomaterial-induced decreased nucleotide concentrations coupled with increased concentrations of nucleic acid degradation products. Purine and pyrimidine alterations included concentration increases for hypoxanthine, xanthine, allantoin, urate, inosine, adenosine 3',5'-diphosphate, cytidine and thymidine while decreases were seen for uridine 5'-diphosphate, UDP-glucuronate, uridine 5'-monophosphate, adenosine 5'-diphosphate, adenosine 5'-monophophate, cytidine 5'-monophosphate and cytidine 3'-monophosphate. Observed depletions of both 6-phosphogluconate, NADPH and NADH (all by CeO₂) suggest that the HepG2 cells may be deficient in reducing equivalents and thus in a state of oxidative stress.

CONCLUSIONS

Metal oxide nanomaterial exposure may compromise the methylation, glucuronidation and reduced glutathione conjugation systems; thus Phase II conjugational capacity of hepatocytes may be decreased. This metabolomics study of the effects of nine different nanomaterials has not only confirmed some observations of the prior 2014 study (lipid elevations caused by one CeO₂ nanomaterial) but also found some entirely new effects (both SiO₂ and CuO nanomaterials also increased the concentrations of several lipid classes, nanomaterial induced decreases in S-adenosylmethionine, UDP-glucuronate, dipeptides, 6-phosphogluconate, NADPH and NADH).

A critique of the use of hormesis in risk assessment

There are severe problems and limitations with the use of hormesis as the principal dose-response default assumption in risk assessment. These problems and limitations include: (a) unknown prevalence of hormetic doseresponse curves; (b) random chance occurrence of hormesis and the shortage of data on the repeatability of hormesis; (c) unknown degree of generalizability of hormesis; (d) there are dose-response curves that are not hormetic, therefore hormesis cannot be universally generalized; (e) problems of post hoc rather than a priori hypothesis testing; (f) a possible large problem of ‘false positive’ hormetic data sets which have not been extensively replicated; (g) the ‘mechanism of hormesis’ is not understood at a rigorous scientific level; (h) in some cases hormesis may merely be the overall sum of many different mechanisms and many different dose-response curves - some beneficial and some toxic. For all of these reasons, hormesis should not now be used as the principal dose-response default assumption in risk assessment. At this point, it appears that hormesis is a long way away from common scientific acceptance and wide utility in biomedicine and use as the principal default assumption in a risk assessment process charged with ensuring public health protection.

Differential Genomic Effects on Signaling Pathways by Two Different CeO2 Nanoparticles in HepG2 Cells

To investigate genomic effects, human liver hepatocellular carcinoma (HepG2) cells were exposed for three days to two different forms of nanoparticles both composed of CeO2 (0.3, 3 and 30 μg/mL). The two CeO2 nanoparticles had dry primary particle sizes of 8 nanometers {(M) made by NanoAmor} and 58 nanometers {(L) made by Alfa Aesar} and differ in various other physical-chemical properties as well. The smaller particle has stronger antioxidant properties, probably because it has higher Ce3+ levels on the particle surface, as well as more surface area per unit weight. Nanoparticle M showed a normal dose-response pattern with 363, 633 and 1273 differentially expressed genes (DEGs) at 0.3, 3 and 30 μg/mL, respectively. In contrast, nanoparticle L showed a puzzling dose-response pattern with the most DEGs found in the lowest exposure group with 1049, 303 and 323 DEGs at 0.3, 3 and 30 μg/mL, respectively. This systems biological genomic study showed that the major altered pathways by these two nano cerium oxides were protein synthesis, stress response, proliferation/cell cycle, cytoskeleton remodeling/actin polymerization and cellular metabolism. Some of the canonical pathways affected were mTOR signaling, EIF2 signaling, fatty acid activation, G2/M DNA damage checkpoint regulation, glycolysis and protein ubiquitination. These two CeO2 nanoparticles differed considerably in their genomic effects. M is more active than L in respect to altering the pathways of mitochondrial dysfunction, acute phase response, apoptosis, 14-3-3 mediated signaling, remodeling of epithelial adherens junction signaling, actin nucleation by ARP-WASP complex, altered TCA cycle and elevated fatty acid concentrations by metabolomics. However, L is more active than M in respect to the pathways of NRF2-mediated stress response and hepatic fibrosis/hepatic stellate cell activation. One major difference in the cell response to nano M and L is that nano M caused the Warburg effect while nano L did not.

Pharmacokinetic and Genomic Effects of Arsenite in Drinking Water on Mouse Lung in a 30-Day Exposure

The 2 objectives of this subchronic study were to determine the arsenite drinking water exposure dependent increases in female C3H mouse liver and lung tissue arsenicals and to characterize the dose response (to 0, 0.05, 0.25, 1, 10, and 85 ppm arsenite in drinking water for 30 days and a purified AIN-93M diet) for genomic mouse lung expression patterns. Mouse lungs were analyzed for inorganic arsenic, monomethylated, and dimethylated arsenicals by hydride generation atomic absorption spectroscopy. The total lung mean arsenical levels were 1.4, 22.5, 30.1, 50.9, 105.3, and 316.4 ng/g lung tissue after 0, 0.05, 0.25, 1, 10, and 85 ppm, respectively. At 85 ppm, the total mean lung arsenical levels increased 14-fold and 131-fold when compared to either the lowest noncontrol dose (0.05 ppm) or the control dose, respectively. We found that arsenic exposure elicited minimal numbers of differentially expressed genes (DEGs; 77, 38, 90, 87, and 87 DEGs) after 0.05, 0.25, 1, 10, and 85 ppm, respectively, which were associated with cardiovascular disease, development, differentiation, apoptosis, proliferation, and stress response. After 30 days of arsenite exposure, this study showed monotonic increases in mouse lung arsenical (total arsenic and dimethylarsinic acid) concentrations but no clear dose-related increases in DEG numbers.

Oxidative stress studies of six TiO₂ and two CeO₂ nanomaterials: immuno-spin trapping results with DNA

Six TiO₂ and two CeO₂ nanomaterials with dry sizes ranging from 6-410 nm were tested for their ability to cause DNA centered free radicals in vitro in the concentration range of 10-3,000 ug/ml. All eight of the nanomaterials significantly increased the adduction of the spin trap agent 5,5-dimethyl-1-pyroline N-oxide (DMPO) to DNA as measured by the experimental technique of immuno-spin trapping. The eight nanomaterials differed considerably in their potency, slope, and active concentration. The largest increase in DNA nitrone adducts was caused by a TiO₂ nanomaterial (25 nm, anatase) from Alfa Aesar. Some nanomaterials that increased the amount of DNA nitrone adducts at the lowest exposure concentrations (100 ug/ml) were Degussa TiO₂ (31 nm), Alfa Aesar TiO₂ (25 nm, anatase) and Nanoamor CeO₂ (8 nm, cerianite). At exposure concentrations of 10 or 30 ug/ml, no nanomaterials showed significant in vitro formation of DNA nitrone adducts.

Arsenic-induced carcinogenesis--oxidative stress as a possible mode of action and future research needs for more biologically based risk assessment

Exposure to inorganic arsenic (iAs) induces cancer in human lungs, urinary bladder, skin, kidney, and liver, with the majority of deaths from lung and bladder cancer. To date, cancer risk assessments for iAs have not relied on mechanistic data, as we have lacked sufficient understanding of arsenic's pharmacokinetics and mode(s) of carcinogenic action (MOA). Furthermore, while there are vast amounts of toxicological data on iAs, relatively little of it has been collected using experimental designs that efficiently support development of biologically based dose-response (BBDR) models and subsequently risk assessment. This review outlines an efficient approach to the development of a BBDR model for iAs that would reduce uncertainties in its cancer risk assessment. This BBDR-based approach is illustrated by using oxidative stress as the carcinogenic MOA for iAs but would be generically applicable to other MOAs. Six major research needs that will facilitate BBDR model development for arsenic-induced cancer are (1) MOA research, which is needed to reduce the uncertainty in risk assessment; (2) development and integration of the pharmacodynamic component (MOA) of the BBDR model; (3) dose-response and extrapolation model selection; (4) the determination of internal human speciated arsenical concentrations to improve physiologically based pharmacokinetic (PBPK) models; (5) animal models of arsenic carcinogenesis; and (6) the determination of the low dose human relationship for death from cancer, particularly in lungs and urinary bladder. The major parts of the BBDR model are arsenic exposure, a physiologically based pharmacokinetic model, reactive species, antioxidant defenses, oxidative stress, cytotoxicity, growth factors, transcription factors, DNA damage, chromosome damage, cell proliferation, mutation accumulation, and cancer. The BBDR model will need to be developed concurrently with data collection so that model uncertainties can be identified and addressed through an iterative process of targeted additional research.

Oncogene expression profiles in K6/ODC mouse skin and papillomas following a chronic exposure to monomethylarsonous acid

We have previously observed that a chronic drinking water exposure to monomethylarsonous acid [MMA(III)], a cellular metabolite of inorganic arsenic, increases tumor frequency in the skin of keratin VI/ornithine decarboxylase (K6/ODC) transgenic mice. To characterize gene expression profiles predictive of MMA(III) exposure and mode of action of carcinogenesis, skin and papilloma RNA was isolated from K6/ODC mice administered 0, 10, 50, and 100 ppm MMA(III) in their drinking water for 26 weeks. Following RNA processing, the resulting cRNA samples were hybridized to Affymetrix Mouse Genome 430A 2.0 GeneChips(R). Micoarray data were normalized using MAS 5.0 software, and statistically significant genes were determined using a regularized t-test. Significant changes in bZIP transcription factors, MAP kinase signaling, chromatin remodeling, and lipid metabolism gene transcripts were observed following MMA(III) exposure as determined using the Database for Annotation, Visualization and Integrated Discovery 2.1 (DAVID) (Dennis et al., Genome Biol 2003;4(5):P3). MMA(III) also caused dose-dependent changes in multiple Rho guanine nucleotide triphosphatase (GTPase) and cell cycle related genes as determined by linear regression analyses. Observed increases in transcript abundance of Fosl1, Myc, and Rac1 oncogenes in mouse skin support previous reports on the inducibility of these oncogenes in response to arsenic and support the relevance of these genomic changes in skin tumor induction in the K6/ODC mouse model.

Transcriptional changes associated with reduced spontaneous liver tumor incidence in mice chronically exposed to high dose arsenic

Exposure of male C3H mice in utero (from gestational days 8-18) to 85ppm sodium arsenite via the dams' drinking water has previously been shown to increase liver tumor incidence by 2 years of age. However, in our companion study (Ahlborn et al., 2009), continuous exposure to 85ppm sodium arsenic (from gestational day 8 to postnatal day 365) did not result in increased tumor incidence, but rather in a significant reduction (0% tumor incidence). The purpose of the present study was to examine the gene expression responses that may lead to the apparent protective effect of continuous arsenic exposure. Genes in many functional categories including cellular growth and proliferation, gene expression, cell death, oxidative stress, protein ubiquitination, and mitochondrial dysfunction were altered by continuous arsenic treatment. Many of these genes are known to be involved in liver cancer. One such gene associated with rodent hepatocarcinogenesis, Scd1, encodes stearoyl-CoA desaturase and was down-regulated by continuous arsenic treatment. An overlap between the genes in our study affected by continuous arsenic exposure and those from the literature affected by long-term caloric restriction suggests that reduction in the spontaneous tumor incidence under both conditions may involve similar gene pathways such as fatty acid metabolism, apoptosis, and stress response.

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.

Tissue levels of arsenicals and skin tumor response following administration of monomethylarsonous acid and arsenite to K6/ODC mice

The effects of monomethylarsonous acid (MMA[III]) and arsenite, administered in drinking water on tissue levels of arsenicals, cytogenetics, and mouse skin tumorigenicity were determined. A low-methionine diet modified the pattern of arsenical tissue concentrations and decreased the tissue arsenical concentrations, particularly in kidney and urinary bladder, less so in liver, and had little effect in the lungs. In mice given 75 ppm arsenite and a low-methionine diet, the urinary bladder tissue levels were only 29%, 26%, and 38% of the inorganic arsenic (iAs), MMA, and dimethylarsinic acid (DMA) concentrations found in mice eating the control diet. In K6/ODC transgenic mice that consumed a normal diet (Purina 5002), a 26-week drinking water exposure to 10 ppm arsenite resulted in 5% of the treated animals having squamous skin tumors. Exposure to 10, 50, 75, or 150 ppm MMA(III) caused 5%, 6.7%, 5%, or 0% tumor-bearing animals. A low-methionine diet did not markedly change the incidence of skin tumors--10 ppm arsenite led to 10% tumors. With a low-methionine diet, 10 and 50 ppm, MMA(III) caused 5% and 6.7% tumor-bearing animals. In comparing the frequency of tumors in the concurrent control groups (1/70, 1.4%) with the frequency of tumors in the pooled arsenical-treated responsive groups (8/122, 6.6%), there is an excess of 6 mouse skin tumors observed in the pooled arsenical-responsive treatment groups compared to the expected number of tumors based on frequency of tumors observed in concurrent control mice. In summary, studies with MMA(III) and arsenite-treated K6/ODC transgenic mice showed (1) a low-methionine diet substantially altered mouse tissue arsenical levels and (2) numerically elevated incidence of mouse skin tumors following arsenical exposures.

Measurement of oxidative stress parameters using liquid chromatography-tandem mass spectroscopy (LC-MS/MS)

There is increasingly intense scientific and clinical interest in oxidative stress and the many parameters used to quantify the degree of oxidative stress. However, there remain many analytical limitations to currently available assays for oxidative stress markers. Recent improvements in software, hardware, and instrumentation design have made liquid chromatography and tandem mass spectroscopy (LC-MS/MS) methods optimal choices for the determination of many oxidative stress markers. In particular, LC-MS/MS often provides the advantages of higher specificity, higher sensitivity, and the capacity to determine multiple analytes (e.g. 4-11 oxidative stress markers per LC run) when compared to other available methods, such as gas chromatography-MS, immunoassays, spectrophotometric or fluorometric assays. LC-MS/MS methods are also compatible with cleanup and sample preparation methods including prior solid phase extraction or automated two dimensional LC/LC chromatography followed by MS/MS. LC-MS/MS provides three analytical filtering functions: (1) the LC column provides initial separation as each analyte elutes from the column. (2) The first MS dimension isolates ions of a particular mass-to-charge (m/z) ratio. (3) The selected precursor ion is fragmented into product ions that provide structural information about the precursor ion. Quantitation is achieved based on the abundances of the product ions. The sensitivity limits for LC-MS/MS usually lie within the range of fg-pg of analyte per LC on-column injection. In this article, the present capabilities of LC-MS/MS are briefly presented and some specific examples of the strengths of these LC-MS/MS assays are discussed. The selected examples include methods for isoprostanes, oxidized proteins and amino acids, and DNA biomarkers of oxidative stress.

Research approaches to address uncertainties in the risk assessment of arsenic in drinking water

Inorganic arsenic (iAs), an environmental drinking water contaminant, is a human toxicant and carcinogen. The public health community has developed recommendations and regulations that limit human exposure to iAs in drinking water. Although there is a vast amount of information available to regulators on the exposure, disposition and the health-related effects of iAs, there is still critical information about the toxicology of this metalloid that is needed. This necessary information includes identification of the chemical species of arsenic that is (are) the active toxicant(s), the mode(s) of action for its various toxicities and information on potentially susceptible populations. Because of these unknown factors, the risk assessment of iAs still incorporates default assumptions, leading to uncertainties in the overall assessment. The characteristics of a scientifically defensible risk assessment for iAs are that it must: (1) quantitatively link exposure and target tissue dose of active metabolites to key events in the mode of action for major health effects and (2) identify sources of variation in susceptibility to arsenic-induced health effects and quantitatively evaluate their impact wherever possible. Integration of research to address these goals will better protect the health of iAs-exposed populations.

Dissociation of arsenite-peptide complexes: Triphasic nature, rate constants, half-lives, and biological importance

We determined the number and the dissociation rate constants of different complexes formed from arsenite and two peptides containing either one (RVCAVGNDYASGYHYGV for peptide 20) or three cysteines (LECAWQGK CVEGTEHLYSMKCK for peptide 10) via radioactive 73As-labeled arsenite and vacuum filtration methodology. Nonlinear regression analysis of the dissociation of both arsenite-peptide complexes showed that triphasic fits gave excellent r2 values (0.9859 for peptide 20 and 0.9890 for peptide 10). The first phase of arsenite-peptide dissociation had the largest span (decrease in binding), and the rate was too fast to be measured using vacuum filtration methods. The dissociation rate constants of arsenite-peptide complexes for the second phase were 0.35 and 0.54 min(-1) and for the third phase were 0.0071 and 0.0045 min(-1) for peptides 20 and 10, respectively. For peptide 20, the three spans of triphasic decay were 85%, 9%, and 7% of the total binding of 16.1 nmol/mg protein. For peptide 10, which can bind in both an intermolecular and intramolecular manner, the three spans of triphasic decay were 59%, 16%, and 25% of the total binding of 43.7 nmol/mg protein. Binding of trivalent arsenicals to peptides and proteins can alter their structure and function and contribute to adverse health outcomes such as toxicity and carcinogenicity.

Arsenite binding to synthetic peptides: The effect of increasing length between two cysteines

We utilized radioactive 73As-labeled arsenite and vacuum filtration methodology to determine the binding affinity of arsenite to eight synthetic peptides ranging from 13 to 24 amino acids long and containing one or two cysteines separated by 0-17 intervening amino acids. Six of the eight peptides were highly similar in amino acid sequence and were based on cysteine containing regions of the hormone-binding site of the human estrogen receptor-alpha (e.g., the sequence of peptide 28 is LEGAWCGKGVEGTEHLYSMKCKNV). The peptides with 0-14 intervening amino acids between two cysteines bound arsenite with Kd values of 2.7-20.1 uM and with Bmax values from 36 to 103 nmol/mg protein (from 0.083 to 0.19 nmol/nmol of protein). Thus, increasing the number of intervening amino acids from 0 to 14 made very little difference in the observed Kd values for arsenite, a surprising finding. Therefore, these peptides are flexible in solution and effectively contain a dithiol high affinity binding site for arsenite. Peptide 17 with two C separated by 19 amino acids bound arsenite with a Kd of 123 uM and a Bmax of 41.8 nmol/mg. The monothiol peptide 19 bound arsenite with a Kd of 124 uM and a Bmax of 26 nmol/mg protein. All experimental binding curves fit well to a one site binding model.

Arsenite binding to synthetic peptides based on the Zn finger region and the estrogen binding region of the human estrogen receptor-alpha

We selected the estrogen receptor protein for study because of prior results indicating that arsenite is a "potential nonsteroidal environmental estrogen". We utilized radioactive (73)As-labeled arsenite and vacuum filtration methodology to determine the binding affinity of arsenite to synthetic peptides. A zinc finger region containing four free sulfhydryls and the hormone binding region containing three free sulfhydryls based on the human estrogen receptor-alpha were studied. Peptide 15 (RYCAVCNDYASGYHYGVWSCEGCKA) bound arsenite with a K(d) of 2.2 microM and B(max) (maximal binding capacity) of 89 nmol/mg protein. Peptide 10 (LECAWQGKCVEGTEHLYSMKCKNV) had a K(d) of 1.3 microM and B(max) of 59 nmol/mg protein. In contrast, the monothiol peptide 19 (LEGAWQGKGVEGTEHLYSMKCKNV) bound arsenite with a higher K(d) of 124 microM and a B(max) of 26 nmol/mg protein. In our studies, amino acids other than cysteine (including methionine and histidine) did not bind arsenite at all. Peptides modeled on the estrogen receptor with two or more nearby free sulfhydryls (two or five intervening amino acids) had low K(d) values in the 1-4 microM range. Peptides containing single sulfhydryls or two sulfhydryls spaced 17 amino acids apart had higher K(d) values in the 100-200 microM range, demonstrating lower affinity. With the exception of peptide 24 which had an unusually high B(max) value of 234 nmol/mg, the binding capacity of the studied peptides was proportional to the number of free cysteines. Binding of trivalent arsenicals to peptides and proteins can contribute to arsenic toxicity and carcinogenicity via altered peptide/protein structure and enzyme function.

An integrated pharmacokinetic and pharmacodynamic study of arsenite action2. Heme oxygenase induction in mice

Heme oxygenase (HO) is the rate-limiting enzyme in heme degradation and its activity has a significant impact on intracellular heme pools. Rat studies indicate that HO induction is a sensitive, dose-dependent response to arsenite (As(III)) exposure in both liver and kidney. The objective of this study was to evaluate the relationship of HO induction to administered As(III) dose, and concentrations of inorganic arsenic (iAs) in tissues and urine. Levels of iAs, mono- (MMA) and dimethylated arsenic (DMA) as well as HO activity were determined in liver, lung and kidney over time in female B6C3F1 mice given a single oral dose of 0, 1, 10, 30 or 100 micromol/kg As(III). Increased HO activity was a time and dose-dependent response in liver and kidney, but not in lung. Activity peaked in the 4-6 h time range in liver and kidney with the responsiveness in liver being approximately 2- to 3-fold greater than kidney. The lowest observed effect levels (LOELs) in this study for HO induction are 30 and 100 micromol/kg, respectively, in liver and kidney. The predominant form of arsenic (As) was iAs in liver at all doses, whereas DMA was the predominant form of As in kidney at all doses. Three- to four-fold higher levels of iAs were achieved in liver compared to kidney. MMA was the least abundant form of As in liver and kidney, never exceeding more than 20% of the total As present. The concentration of iAs in tissue or urine demonstrated the strongest correlation with HO activity in both liver and kidney. Results of this study suggest that HO induction is a biomarker of effect that is specific for tissue iAs because a high, but nontoxic, acute dose of DMA (5220 micromol/kg) did not induce HO in mice. Thus, HO induction has potential for use as a biomarker of effect for inorganic arsenic exposure and may be used as an indicator response to further the development of a biologically-based dose response model for As.

Do arsenosugars pose a risk to human health? The comparative toxicities of a trivalent and pentavalent arsenosugar

Seafood frequently contains high concentrations of arsenic (approximately 10-100 mg/kg dry weight). In marine algae (seaweed), this arsenic occurs predominantly as ribose derivatives known collectively as arsenosugars. Although it is clear that arsenosugars are not acutely toxic, there is a possibility of arsenosugars having slight chronic toxicity. In general, trivalent arsenicals are more toxic than their pentavalent counterparts, so in this work we examine the hypothesis that trivalent arsenosugars might be significantly more toxic than pentavalent arsenosugars in vitro. We compared the in vitro toxicity of (R)-2,3-dihydroxypropyl-5-deoxy-5-dimethylarsinoyl-beta-D-riboside, a pentavalent arsenosugar, to that of its trivalent counterpart, (R)-2,3-dihydroxypropyl-5-deoxy-5-dimethylarsino-beta-D-riboside. The trivalent arsenosugar nicked plasmid DNA, whereas the pentavalent arsenosugar did not. The trivalent arsenosugar was more cytotoxic (IC50 = 200 microM, 48 h exposure) than its pentavalent counterpart (IC50 > 6000 microM, 48 h exposure) in normal human epidermal keratinocytes in vitro as determined via the neutral red uptake assay. However, both the trivalent and the pentavalent arsenosugars were significantly less toxic than MMA(III), DMA(III), and arsenate. Neither the pentavalent arsenosugar nor the trivalent arsenosugar were mutagenic in Salmonella TA104. The trivalent arsenosugar was readily formed by reaction of the pentavalent arsenosugar with thiol compounds, including, cysteine, glutathione, and dithioerythritol. This work suggests that the reduction of pentavalent arsenosugars to trivalent arsenosugars in biology might have environmental consequences, especially because seaweed consumption is a significant environmental source for human exposure to arsenicals.

Plasmid DNA damage caused by stibine and trimethylstibine

Antimony is classified as "possibly carcinogenic to humans" and there is also sufficient evidence for antimony carcinogenicity in experimental animals. Stibine is a volatile inorganic antimony compound to which humans can be exposed in occupational settings (e.g., lead-acid battery charging). Because it is highly toxic, stibine is considered a significant health risk; however, its genotoxicity has received little attention. For the work reported here, stibine was generated by sodium borohydride reduction of potassium antimony tartrate. Trimethylstibine is a volatile organometallic antimony compound found commonly in landfill and sewage fermentation gases at concentrations ranging between 0.1 and 100 microg/m3. Trimethylstibine is generally considered to pose little environmental or health risk. In the work reported here, trimethylstibine was generated by reduction of trimethylantimony dichloride using either sodium borohydride or the thiol compounds, dithioerythritol (DTE), L-cysteine, and glutathione. Here we report the evaluation of the in vitro genotoxicities of five antimony compounds-potassium antimony tartrate, stibine, potassium hexahydroxyantimonate, trimethylantimony dichloride, and trimethylstibine-using a plasmid DNA-nicking assay. Of these five antimony compounds, only stibine and trimethylstibine were genotoxic (significant nicking to pBR 322 plasmid DNA). We found stibine and trimethylstibine to be about equipotent with trimethylarsine using this plasmid DNA-nicking assay. Reaction of trimethylantimony dichloride with either glutathione or L-cysteine to produce DNA-damaging trimethylstibine was observed with a trimethylantimony dichloride concentration as low as 50 microM and L-cysteine or glutathione concentrations as low as 500 and 200 microM, respectively, for a 24 h incubation.

Dimethylarsine and trimethylarsine are potent genotoxins in vitro

The mechanism of arsenic carcinogenesis is unclear. A complicating factor receiving increasing attention is that arsenic is biomethylated to form various metabolites. Eleven different arsenicals were studied for in vitro genotoxicity to supercoiled DNA (pBR 322 and phiX174). Five arsenicals showed various degrees of positivity-monomethylarsonous acid, dimethylarsinous acid, monomethylarsine, dimethylarsine, and trimethylarsine. Supercoiled DNA, blotted on nitrocellulose filter paper, was exposed to gaseous arsines by suspending the filter paper above aqueous reaction mixtures of sodium borohydride and an appropriate arsenical. All three methylated arsines damaged DNA; inorganic arsine did not. Arsines were generated in situ in reaction mixtures containing DNA by reaction of sodium borohydride with arsenite, monomethylarsonous acid, dimethylarsinous acid, and trimethylarsine oxide, at pH 8.0. Both dimethylarsine and trimethylarsine (generated from 200 micro M dimethylarsinous acid and trimethylarsine oxide, respectively) damaged DNA in less than 30 min. Under certain conditions, the two most potent genotoxic arsines, trimethylarsine and dimethylarsine, are about 100 times more potent than dimethylarsinous acid (the most potent genotoxic arsenical previously known). There was no evidence to suggest that anything other than the arsines caused the DNA damage. Possible models for the biological production of arsines were examined. The coenzymes, NADH and NADPH, are biological hydride donors. When NADH or NADPH (5 mM) were incubated with dimethylarsinous acid (0-2 mM) for 2 h, DNA damage was increased by at least 10-fold. A possible explanation for this result is that these compounds react with dimethylarsinous acid to generate dimethylarsine. DNA was incubated with a dithiol compound, dithioerythritol (5 mM), and trimethylarsine oxide (0.5 mM) for 2 h, and the reduction of trimethylarsine oxide to trimethylarsine resulted in DNA damage.

Oxidative stress as a possible mode of action for arsenic carcinogenesis

Many modes of action for arsenic carcinogenesis have been proposed, but few theories have a substantial mass of supporting data. Three stronger theories of arsenic carcinogenesis are production of chromosomal abnormalities, promotion of carcinogenesis and oxidative stress. This article presents the oxidative stress theory along with some supporting experimental data. In the area of which arsenic species is causually active, recent data have suggested that trivalent methylated arsenic metabolites, particularly monomethylarsonous acid (MMA(III)) and dimethylarsinous acid (DMA(III)), have a great deal of biological activity. Some evidence now indicates that these trivalent, methylated, and relatively less ionizable arsenic metabolites may be unusually capable of interacting with cellular targets such as proteins and even DNA. Thus for inorganic arsenic, oxidative methylation followed by reduction to trivalency may be a activation, rather than a detoxification pathway. This would be particularly true for arsenate. In forming toxic and carcinogenic arsenic species, reduction from the pentavalent state to the trivalent state may be as or more important than methylation of arsenic.

Plasmid DNA damage caused by methylated arsenicals, ascorbic acid and human liver ferritin

Both dimethylarsinic acid (DMA(V)) and dimethylarsinous acid (DMA(III)) release iron from human liver ferritin (HLF) with or without the presence of ascorbic acid. With ascorbic acid the rate of iron release from HLF by DMA(V) was intermediate (3.37 nM/min, P<0.05) and by DMA(III) was much higher (16.3 nM/min, P<0.001). No pBR322 plasmid DNA damage was observed from in vitro exposure to arsenate (iAs(V)), arsenite (iAs(III)), monomethylarsonic acid (MMA(V)), monomethylarsonous acid (MMA(III)) or DMA(V) alone. DNA damage was observed following DMA(III) exposure; coexposure to DMA(III) and HLF caused more DNA damage; considerably higher amounts of DNA damage was caused by coexposure of DMA(III), HLF and ascorbic acid. Diethylenetriaminepentaacetic acid (an iron chelator), significantly inhibited DNA damage. Addition of catalase (which can increase Fe(2+) concentrations) further increased the plasmid DNA damage. Iron-dependent DNA damage could be a mechanism of action of human arsenic carcinogenesis.

Defining, explaining and understanding hormesis

A problem that hormesis has in being more scientifically accepted is (1) proving that only one mechanism accounts for both the 'beneficial' and 'toxic' parts of the biphasic dose-response curve and (2) giving substantial evidence against the interpretation that 'hormesis' is the sum of many different mechanisms which add up to either 'beneficial' or 'toxic' in two different parts of the dose-response curve. Hormesis may consist of a initial beneficial dose region where several mechanisms are operating (just for the sake of argument let us say 3 mechanisms) and the overall sum of these 3 mechanisms is 'beneficial' to the organism. At higher, toxic, doses, many more mechanisms are operating (just for the sake of argument let us say 8 mechanisms) and the sum of all these 8 mechanisms puts the organism in the 'toxic' part of the biphasic dose-response curve.

Recent advances in arsenic carcinogenesis: modes of action, animal model systems, and methylated arsenic metabolites

Recent advances in our knowledge of arsenic carcinogenesis include the development of rat or mouse models for all human organs in which inorganic arsenic is known to cause cancer-skin, lung, urinary bladder, liver, and kidney. Tumors can be produced from either promotion of carcinogenesis protocols (mouse skin and lungs, rat bladder, kidney, liver, and thyroid) or from complete carcinogenesis protocols (rat bladder and mouse lung). Experiments with p53(+/-) and K6/ODC transgenic mice administered dimethylarsinic acid or arsenite have shown some degree of carcinogenic, cocarcinogenic, or promotional activity in skin or bladder. At present, with the possible exception of skin, the arsenic carcinogenesis models in wild-type animals are more highly developed than in transgenic mice. Recent advances in arsenic metabolism have suggested that methylation of inorganic arsenic may be a toxification, rather than a detoxification, pathway and that trivalent methylated arsenic metabolites, particularly monomethylarsonous acid and dimethylarsinous acid, have a great deal of biological activity. Accumulating evidence indicates that these trivalent, methylated, and relatively less ionizable arsenic metabolites may be unusually capable of interacting with cellular targets such as proteins and even DNA. In risk assessment of environmental arsenic, it is important to know and to utilize both the mode of carcinogenic action and the shape of the dose-response curve at low environmental arsenic concentrations. Although much progress has been recently made in the area of arsenic's possible mode(s) of carcinogenic action, a scientific concensus has not yet been reached. In this review, nine different possible modes of action of arsenic carcinogenesis are presented and discussed-induced chromosomal abnormalities, oxidative stress, altered DNA repair, altered DNA methylation patterns, altered growth factors, enhanced cell proliferation, promotion/progression, gene amplification, and suppression of p53.

An ELISA assay for heme oxygenase (HO-1)

A double antibody capture ELISA for the HO-1 protein has been developed to separately quantitate HO-1 protein. The use of 2.5% NP40 detergent greatly assists in freeing HO-1 protein from membranes and/or other cellular entities and increased the amount of HO-1 protein found in rat liver whole homogenates as well as the nuclear, mitochondrial and microsomal fractions. Use of the detergent NP40 did not substantially change HO-1 protein standard curves. The ELISA assay for HO-1 has been shown to be reproducible over (i) a 4-day trial period as well as (ii) almost 1 year of general laboratory use. Excellent specificity for the HO-1 isoform is shown by the failure of either the human HO-2 protein or HO-2 peptide (at concentrations as high as 1000 ng/ml) to generate any signal above background. At least a 300-fold greater signal comes from HO-1 protein as compared to the HO-2 protein. The EC(50) is about 200 ng/ml for HO-1, and the minimum detectable level of the HO-1 protein is about 1 ng/ml. The ELISA assay for the HO-1 protein requires a total of 6 h to complete. Of the total cellular HO-1 protein, 20, 19, 9 and 3% appeared in the nuclear, microsomal, mitochondrial and high speed supernatant fractions, respectively. As expected, the highest concentration of HO-1 protein per total protein in a subcellular fraction was found in the microsomes. For many research projects utilizing this ELISA assay for HO-1 protein concentration, use of the whole homogenate will be an excellent choice, rather than use of the postmitochondrial or microsomal fractions. Much higher HO-1 protein levels were found in tissues of rats rather than mice. This may be because the capture antibody and secondary antibody were both raised against the rat and not the mouse forms of the HO-1 protein. In rats the HO-1 concentrations were 1067, 364, 194, 31, 28 19, 5 and 2 ng/g tissue in whole homogenates from testes, brain, liver, lung, spleen, kidney, small intestines and urinary bladder, respectively. The ELISA assay for HO-1 described here will be useful for HO-1 research studies in tissues and cell cultures of rats and mice. This ELISA for HO-1 may also work with human tissues and cells.

Arsenic species that cause release of iron from ferritin and generation of activated oxygen

The in vitro effects of four different species of arsenic (arsenate, arsenite, monomethylarsonic acid, and dimethylarsinic acid) in mobilizing iron from horse spleen ferritin under aerobic and anaerobic conditions were investigated. Dimethylarsinic acid (DMA(V)) and dimethylarsinous acid (DMA(III)) significantly released iron from horse spleen ferritin either with or without the presence of ascorbic acid, a strong synergistic agent. Ascorbic acid-mediated iron release was time-dependent as well as both DMA(III) and ferritin concentration-dependent. Iron release from ferritin by DMA(III)) alone or with ascorbic acid was not significantly inhibited by superoxide dismutase (150 or 300 units/ml). However, the iron release was greater under anaerobic conditions (nitrogen gas), which indicates direct chemical reduction of iron from ferritin by DMA(III), with or without ascorbic acid. Both DMA(V) and DMA(III)) released iron from both horse spleen and human liver ferritin. Further, the release of ferritin iron by DMA(III)) with ascorbic acid catalyzed bleomycin-dependent degradation of calf thymus DNA. These results indicate that exogenous methylated arsenic species and endogenous ascorbic acid can cause (a) the release of iron from ferritin, (b) the iron-dependent formation of reactive oxygen species, and (c) DNA damage. This reactive oxygen species pathway could be a mechanism of action of arsenic carcinogenesis in man.

Dimethylarsinic acid treatment alters six different rat biochemical parameters: relevance to arsenic carcinogenesis

In a previous study, we found that sodium arsenite increased hepatic ornithine decarboxylase (ODC) activity and hepatic heme oxygenase (HO) activity, but did not cause any DNA damage in adult female rat liver or lung, suggesting that arsenite may be a promoter of carcinogenesis. In this study sodium arsenate, monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) were administered orally in equitoxic doses to adult female rats at 21 and 4 h prior to sacrifice. DNA damage (DD), cytochrome P450 content (P450), glutathione content (GSH), ODC, serum alanine aminotransferase (ALT) and HO were measured in liver and/or lung tissue. At 60 mg/kg in rat liver, sodium arsenate increased hepatic HO fivefold. MMA decreased ALT at 226 mg/kg, decreased ALT and GSH at 679 mg/kg and also increased P450 at 679 mg/kg in rat liver. DMA decreased ALT and hepatic GSH and increased hepatic HO at 387 mg/kg. In the lung, DMA decreased ODC at both 129 and 387 mg/kg. DD in lung tissue was significantly higher at 387 mg/kg DMA, demonstrating organ specific DNA damage. The biochemical effects and the inferred oncologic potential of the four major forms of arsenic (arsenate, arsenite, MMA and DMA) differ dramatically. The inorganic forms (arsenate and arsenite) are similar to each other (both good HO inducers); the methylated organic forms of arsenic (MMA and DMA) also share a similar pattern of biochemical effects (decreased GSH and ALT, increased P450). All six of the biochemical parameters studied were altered by DMA in either rat liver or lung.

An integrated pharmacokinetic and pharmacodynamic study of arsenite action. 1. Heme oxygenase induction in rats

Rat heme oxygenase (HO) activity was used as a specific (among forms of arsenic) and sensitive biomarker of effect for orally administered sodium arsenite in rats. Time course studies showed that HO was induced in rat liver from 2 to 48 h in both rat liver and kidney. Hepatic and renal inorganic arsenic (iAs) concentrations were high at times preceding a high degree of HO induction. At times following pronounced HO induction, tissue dimethylarsinic acid concentrations were high. Dose-response studies of arsenite showed substantial HO induction in liver at doses of 30 micromol/kg and higher and in the kidney at doses of 100 micromol/kg and higher. Doses of 10 (in liver) and of 30 micromol/kg (in kidney) sodium arsenite given by gavage did not significantly induce rat HO activity. Speciation of tissue total arsenic into iAs, methylarsonic acid (MMA), and dimethylarsinic acid (DMA) permits us to link tissue iAs and HO enzyme induction. There was a linear relationship between tissue inorganic arsenic (iAs) concentration and tissue HO in individual rats (r(2) = 0.780 in liver and r(2) = 0.797 in kidney). Nonlinear relationships were observed between administered arsenite dose and either liver or kidney iAs concentration. Overall, there was a sublinear relationship between administered arsenite and biological effect in rats. Teratogenesis Carcinog. Mutagen. 19:385-402, 1999. Published 1999 Wiley-Liss, Inc.

Dimethylarsinic acid effects on DNA damage and oxidative stress related biochemical parameters in B6C3F1 mice

Adult female B6C3F1 mice were given 720 mg/kg of DMA by oral gavage at one of three times (2 h, 15 h, or at both 21 and 4 h) before sacrifice. Significant (P < 0.05) decreases in liver GSH and GSSG contents (15-37%) were observed. Some evidence of DMA-induced hepatic DNA damage (at the P < 0.10 level only) was observed. Pulmonary and hepatic ODC activities were reduced (19-59%) by DMA treatment. Overall, these biochemical studies show that mice are much less responsive to DMA than rats.

Quantitative analysis of alachlor protein adducts by gas chromatography-mass spectrometry

This study examined the potential use of hemoglobin (Hb)- and serum-protein adducts of alachlor as potential biomarkers of alachlor exposure, a genotoxic and carcinogenic herbicide. The method developed was based on the observation that cleavage of S-cysteinyl alachlor-protein adducts by methanesulfonic acid gave the rearrangement product 3-(2',6'-diethylphenyl)-1, 3-thiazolidine-4-one (TZO). The structure of TZO was confirmed by mass spectroscopy, NMR spectroscopy, and independent synthesis. In the assay, treatment of alachlor-cysteinyl protein adducts by methanesulfonic acid was followed by extraction and analysis. TZO was detected and quantitated by electron-impact GC/MS in the single ion-monitoring mode. [ring-13C6]Alachlor-N-acetylcysteine was added as an internal standard prior to treatment and was converted to [ring-13C6]TZO, allowing response factors to be used to quantitate TZO concentrations. Incubations of alachlor (0-1000 microM) with human albumin and bovine serum albumin (BSA) resulted in linear adduct formation with both proteins. Maximal adduction levels of 613-1130 pmol alachlor-albumin adducts/mg protein were observed, with BSA binding close to twice that of human albumin. A linear concentration response of alachlor-Hb adducts was observed when whole blood from female CD rats was incubated with alachlor in vitro at concentrations up to 300 microM. Maximal binding was 1860 pmol alachlor-Hb adducts/mg globin. Male CD rats treated with alachlor at 150 mg/kg body wt/day ip for 0, 1, 2, and 3 days were sacrificed 4 days after final dosing. A maximal binding of 2250 pmol alachlor-Hb adducts/mg globin was observed. This assay provides a new approach for biomonitoring alachlor levels in experimental animals and has the potential for use in humans.

Simultaneous purification of human albumin and hemoglobin for use as environmental biomarkers

A combination of known biochemical techniques (binding of bromocresol green to human albumin, nondenaturing electrophoresis and electroelution) have been utilized in a novel purification of human albumin. This paper reports (a) purification of intact, nondenatured human albumin, (b) simultaneous purification of albumin and hemoglobin from a human plasma and red blood cell lysate mixture, (c) development of a purification method for the two most commonly employed protein biomarkers in human environmental epidemiology and (d) demonstration of the general technique of protein purification of colored ligand-protein complexes by nondenaturing electrophoresis. The noncovalent binding between a protein (albumin) and a colored ligand (bromocresol green) is the biochemical characteristic exploited in this novel purification scheme. This general purification method may be useful for other colored ligand or fluorescent ligand binding proteins. For small-scale electrophoresis, the amount of protein isolated, percentage yield and protein purity (estimated by SDS-PAGE) were 270 micrograms, 80% yield and > 99% purity for albumin and 217 micrograms, 54% yield and > 99% purity for hemoglobin, respectively. For large-scale electrophoresis the comparable data was 38.3 mg, 57% yield and 98% purity for albumin and 17.2 mg, 57% yield and 99% purity for hemoglobin, respectively.

Dose-response relationship for rat liver DNA damage caused by 1,2-dimethylhydrazine

An experimental approach was taken to the question of dose-response curves for chemical carcinogenesis, using DNA damage as a biomarker. Female rats were give 13 different doses of 1,2-dimethylhydrazine (from 1.4 to 135,000 micrograms/kg) and the subsequent hepatic DNA damage was determined by the alkaline elution technique. DMH doses below 450 micrograms/kg did not significantly damage DNA; all DMH doses of 1000 micrograms/kg or higher damaged rat hepatic DNA (P < 0.05). In this study the x values (dose) ranged over five orders of magnitude and the y values (DNA damage) ranged 30-fold. Ten different regression models (linear, quadratic, cubic, power, and six nonlinear transition models) were compared in their ability to fit the experimental data. With respect to log transformed dose, the six nonlinear transition equations fit the data considerably better than the four power type of equations. A sigmoid model fit to the log transformed dose of 1,2-dimethylhydrazine had an r2 of 0.9979, a degree of freedom adjusted r2 of 0.9969, a F-statistic of 1,457, and a fit standard error of 0.50. With respect to untransformed dose, only three equations (sigmoid, cascade and gaussian cumulative) could creditably fit the DMH data. The experimental results are interpreted with respect to hormesis, use of log transformed dose, sigmoid dose-response models, thresholds of biological response and cancer risk assessment.

Arsenite, but not cadmium, induces ornithine decarboxylase and heme oxygenase activity in rat liver: relevance to arsenic carcinogenesis

Sodium arsenite and cadmium chloride, were administered orally to adult female rats at 21 and 4 h prior to sacrifice. Liver, lung, skin and urinary bladder were the tissues studied. DNA damage, cytochrome P450, glutathione content (GSH), ornithine decarboxylase (ODC), serum alanine aminotransferase and heme oxygenase activity were measured. Sodium arsenite increased rat hepatic ODC activity at 1.6 and 24.6 mg/kg and hepatic heme oxygenase activity at 8.2 and 24.6 mg/kg, but did not cause any DNA damage. Cadmium chloride did not affect any of the six parameters tested. These findings suggest that sodium arsenite may be a promoter rather than an initiator of carcinogenesis.

Incorporation of 5-iodo-2'-deoxyuridine and 5-bromo-2'-deoxyuridine into rodent DNA as determined by neutron activation analysis

Using 5-iodo-2'-deoxyuridine (IdU) and 5-bromo-2'-deoxyuridine (BrdU) as DNA precursors, neutron activation analysis (NAA) of iodine and Br was developed as a quantitative method for determining DNA synthesis. Endogenous rodent tissue concentrations of bromine (Br) and iodine ranged 100-fold from a low of 0.06 microgram of iodine/g of rat gastrointestinal tract (GIT) to a high of 5.99 micrograms of Br/g of rat kidney. All 10 rodent tissues had concentrations of Br 4 to 76 times higher than those of iodine. Rat hepatic Br concentrations could be reduced 17-fold by dietary and pharmacological methods. Female Fischer 344 rats and male C57BL/6 mice were given 4-8 intraperitoneal injections of either IdU or BrdU as a DNA precursor. Tissue clearance of iodine in IdU-treated rodents was both faster and more complete (in mice 4 and in rats 17 h or less) than Br clearance from BrdU-treated rodents (at 162 h nonincorporated Br label still remains). In rat liver, lung, and kidney, the iodine label incorporated from IdU into DNA was stable for at least 162 h. The incorporation ratio is defined as the microgram halogen/tissue for either IdU- or BrdU-treated rodents divided by the microgram halogen/g tissue of untreated rodents. NAA-based studies of DNA synthesis gave high incorporation ratios in rat liver (5.3), rat lung (6.7), rat GIT (19.0), rat spleen (24.0), mouse GIT (10.1), and mouse spleen (25.8).

Dose-response relationship for rat liver DNA damage caused by 49 rodent carcinogens

An experimental approach was taken to the question of dose-response curves for chemical carcinogenesis. DNA damage in female rat liver was chosen as the experimental parameter because all chemicals found to damage hepatic DNA were rodent carcinogens. The lowest dose causing DNA damage was determined for the 12 active chemicals (1,2-dibromoethane, 1,2-dibromo-3-chloropropane, 1,2-dichloroethane, 1,4-dioxane, methylene chloride, auramine O, Michler's ketone, selenium sulfide, 1,3-dichloropropene, 1,2-dimethylhydrazine, N-nitroso-piperidine and butylated hydroxytoluene). The resulting dose-response curves for rat hepatic DNA damage were plotted versus log of the molar dose (all activity was in five orders of magnitude) and versus percent of chemicals' oral rat LD50 (most of the activity was in only two orders of magnitude). Dose-response studies of the active chemicals were analyzed by regression methods. With the exception of butylated hydroxytoluene, the dose-response curves fit a linear model well (r2 = 0.886) and a quadratic model even better (r2 = 0.947). Based on experimental data from 11 DNA-damaging carcinogens (a dose range of 6 orders of magnitude), an equation and graph of the dose-response relationship of an 'average DNA-damaging carcinogen' is presented over the x-axis dose range of eight orders of magnitude.

Complementarity of genotoxic and nongenotoxic predictors of rodent carcinogenicity

Twenty-one chemicals carcinogenic in rodent bioassays were selected for study. The chemicals were administered by gavage in two dose levels to female Sprague-Dawley rats. The effects of these 21 chemicals on four biochemical assays [hepatic DNA damage by alkaline elution (DD), hepatic ornithine decarboxylase activity (ODC), serum alanine aminotransferase activity (ALT), and hepatic cytochrome P-450 content (P450)] were determined. Available data from seven cancer predictors published by others [the Ames test (AMES), mutation in Salmonella typhimurium TA 1537 (TA 1537), structural alerts (SA), mutation in mouse lymphoma cells (MOLY), chromosomal aberrations in Chinese hamster ovary cells (ABS), sister chromatid exchange in hamster ovary cells (SCE), and the ke test (ke)] were also compiled for these 21 chemical carcinogens plus 28 carcinogens and 62 noncarcinogens already published by our laboratory. From the resulting 111 (chemicals) by 11 (individual cancer predictors) data matrix, the five operational characteristics (sensitivity, specificity, positive predictivity, negative predictivity, and concordance) of each of the 11 individual cancer predictors (four biochemical parameters of this study and seven cancer predictors of others) are presented. Two examples of complementarity or synergy of composite cancer predictors were found. To obtain maximum concordance it was necessary to combine both genotoxic and nongenotoxic cancer predictors. The composite cancer predictor (DD or [ODC and P450] or [ODC and ALT]) had higher concordance than did any of the four individual cancer predictors from which it was constructed. Similarly, the composite cancer predictor (TA 1537 or DD or [ODC and P450] or [ODC and ALT]) had higher concordance than any of its five individual constituent cancer predictors. Complementarity or synergy has been demonstrated both 1) among genotoxic cancer predictors (DD and TA 1537) and 2) between nongenotoxic (ODC, P450, and ALT) and genotoxic cancer predictors (TA 1537 and DD).

Dose-response relationship in multistage carcinogenesis: promoters

Published dose-response curves of promoters of multistage carcinogenesis were selected that met the combined criteria of long study times, multiple doses, and low doses. In rat liver, 12 dose-response studies of 7 different promoters (phenobarbital, 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], clophen A-50 (a polychlorinated biphenyl), alpha-, beta-, and gamma-hexachlorocyclohexane [HCH], and chloroform) were selected. These promoters were studied for 7-86 weeks and either altered hepatic foci or hepatic cancer were determined. The doses ranged from 1 ng (TCDD) to 400 mg (chloroform). In mouse skin, 10 dose-response studies of 4 promoters (12-O-tetradecanoylphorbol-13-acetate [TPA], anthralin, chrysarobin, and 2,6-di-tert-butyl-4-hydroperoxyl-2,5-cyclohexadienone [BHTOOH]) were selected. In these mouse skin studies the doses ranged from 0.425 nmole (TPA) to 20,000 nmole (BHTOOH) per mouse. The length of time promoters were applied to the skin varied between 15 and 60 weeks. Either skin papillomas or carcinomas were determined. The dose-response relationships are presented on the basis of moles of promoter, percentage of the fully effective promoting dose, or percentage of the acute oral rat LD50. The degree of concavity of the dose-response curves was determined. The available dose-response data are critiqued and discussed on the basis of future research needs for biologically based cancer risk assessment models.

Predicting rodent carcinogenicity of Ames test false positives by in vivo biochemical parameters

28 chemicals known to be mutagenic in the Ames test but not carcinogenic in rodent bioassays were selected for study. The chemicals were administered by gavage in 2 dose levels to female Sprague-Dawley rats. The effects of these 28 chemicals on 4 biochemical assays (hepatic DNA damage by alkaline elution (DD), hepatic ornithine decarboxylase activity (ODC), serum alanine aminotransferase activity (ALT), and hepatic cytochrome P-450 content (P450)) were determined. The scientific approach taken was to either experimentally find individual cancer predictors of high specificity or to mathematically create composite predictors of high specificity. Composite predictive parameters are defined as follows: CP = [ODC and P450], CT = [ALT and ODC], and TS = [DD or CP or CT]. The specificity (percent of rodent noncarcinogens which test negative) of DD, ODC, ALT, P450, CP, CT and TS was 100%, 46%, 89%, 86%, 93%, 93% and 86%, respectively. For these 28 mutagenic noncarcinogens, the specificity of structural alerts (SA) 13%, mutation in mouse lymphoma cells (MOLY) 0%, chromosomal aberrations in Chinese hamster ovary cells (ABS) 13%, and sister-chromatid exchange in Chinese hamster ovary cells (SCE) 0% were much lower. The ke test, an experimental measure of electron attachment, had a specificity of 33%. DD was the only DNA related parameter to predict well the noncarcinogenic rodent bioassay result of Ames false-positive chemicals. 5 nongenotoxic parameters (ALT, P450, CP, CT and [CP or CT]) predicted the rodent bioassay result well. Depending on the prevalence of chemicals carcinogenic to humans, the problem of Ames test false positives for predicting human cancer may be either small or large.