In utero arsenic exposure increases DNA damage and gene expression changes in umbilical cord mesenchymal stem cells (UC-MSCs) from newborns as well as in UC-MSC differentiated hepatocytes.

Prenatal exposure to arsenic is associated with an increased risk of disease development such as liver cancer in adulthood. Increasing evidence suggests that fetal stem cells are key targets during transplacental chemical exposure. Our earlier study reported that in utero arsenic exposure caused various types of DNA damage in newborns. In this study, we further investigated the effects of prenatal arsenic exposure on mutagenic DNA damage in umbilical cord mesenchymal stem cells (MSCs) that represent fetal stem cells from the same birth cohort. DNA damage measured as 8-hydroxydeoxyguanine (8-OHdG) and 8-nitroguanine was increased in umbilical cord MSCs of newborns in relation to maternal arsenic levels in a dose-dependent manner. Levels of 8-OHdG and 8-nitroguanine were significantly (p < 0.05) and positively associated with arsenic levels in cord blood and maternal toenails. In vitro studies confirmed that arsenite treatment alone (0-5 µM, 24 h) significantly increased the levels of 8-OHdG and 8-nitroguanine in an MSC cell line derived from umbilical cord tissue (UC-MSCs). When UC-MSCs were allowed to differentiate into hepatocytes in the presence of arsenite (0.5 µM, 21 days), there were significant increases (p < 0.05) in 8-OHdG and 8-nitroguanine compared to those observed in undifferentiated UC-MSCs. Moreover, in these arsenite-exposed differentiated hepatocytes, expression of inflammatory genes (CXCL6 and CXCL8) and an oxidative stress response gene (NFE2L2) was increased, while that of a DNA repair gene (OGG1) was decreased. Arsenite treatment also increased cell transformation ability of hepatocytes differentiated from UC-MSCs. These results suggest that arsenic exposure increases mutagenic DNA damage in fetal stem cells which continued when these cells differentiated to become hepatocytes which have increased cell transformation ability. This study highlights the potential risk of in utero arsenic exposure, which may lead to liver disease and cancer development later in life.

SAM and folic acid prevent arsenic-induced oxidative and nitrative DNA damage in human lymphoblast cells by modulating expression of inflammatory and DNA repair genes.

Growing evidence suggests that arsenic exposure increases the risk of developing a variety of inflammation-associated chronic diseases and cancers. Our previous study revealed that increased transcript levels of inflammatory genes (i.e. COX2, EGR1, and SOCS3) coupled with hypomethylation of the promoter regions of these genes was associated with increased DNA damage in arsenic-exposed newborns through their early childhood. This study further investigated the ability of the methyl group donors, S-adenosyl methionine (SAM) and folic acid, to prevent promoter hypomethylation that results in decreased mRNA expression of inflammatory genes (COX2, EGR1, and SOCS3), and a reduction in arsenic-induced oxidative and nitrative DNA damage in human lymphoblast cells. Pretreatment with SAM (100 nM, 2 days) increased promoter methylation, reduced the mRNA levels of these inflammatory genes, and decreased both 8-hydroxydeoxyguanosine (8-OHdG) and 8-nitroguanine levels by 50% (p < 0.01) in arsenic-treated cells. In addition, pretreatment with folic acid (10 µM, 7 days), a micronutrient, led to a significant increase in promoter methylation associated with the reduction in mRNA levels of these inflammatory genes and decreased levels of 8-OHdG and 8-nitroguanine by 80% and 90% (p < 0.01), respectively, compared with arsenic treatment alone. Moreover, pretreatments with these methyl group donors increased mRNA expression of an antioxidant defense regulator (Nrf2) and DNA repair genes (hOGG1, XRCC1, and PARP1). This study shows for the first time that SAM or folic acid supplementation can prevent arsenic-induced oxidative and nitrative DNA damage. This suggests the potential use of SAM or folic acid for prevention of arsenic toxicity in human populations.

Exposure to arsenic in utero is associated with various types of DNA damage and micronuclei in newborns: a birth cohort study.

BACKGROUND: Growing evidence indicates that in utero arsenic exposures in humans may increase the risk of adverse health effects and development of diseases later in life. This study aimed to evaluate potential health risks of in utero arsenic exposure on genetic damage in newborns in relation to maternal arsenic exposure. METHODS: A total of 205 pregnant women residing in arsenic-contaminated areas in Hanam province, Vietnam, were recruited. Prenatal arsenic exposure was determined by arsenic concentration in mother's toenails and urine during pregnancy and in umbilical cord blood collected at delivery. Genetic damage in newborns was assessed by various biomarkers of early genetic effects including oxidative/nitrative DNA damage (8-hydroxydeoxyguanosine, 8-OHdG, and 8-nitroguanine), DNA strand breaks and micronuclei (MN) in cord blood. RESULTS: Maternal arsenic exposure, measured by arsenic levels in toenails and urine, was significantly increased (p <  0.05) in subjects residing in areas with high levels of arsenic contamination in drinking water. Cord blood arsenic level was significantly increased in accordance with maternal arsenic exposure (p <  0.001). Arsenic exposure in utero is associated with genotoxic effects in newborns indicated as increased levels of 8-OHdG, 8-nitroguanine, DNA strand breaks and MN frequency in cord blood with increasing levels of maternal arsenic exposure. Maternal toenail arsenic level was significantly associated with all biomarkers of early genetic effects, while cord blood arsenic levels associated with DNA strand breaks and MN frequency. CONCLUSIONS: In utero arsenic exposure is associated with various types of genetic damage in newborns potentially contributing to the development of diseases, including cancer, later in life.

Decreased argininosuccinate synthetase expression in Thai patients with cholangiocarcinoma and the effects of ADI-PEG20 treatment in CCA cell lines.

Cholangiocarcinoma (CCA) is a severe cancer with poor prognosis. The aim of the present study was to explore the expression of argininosuccinate synthetase (ASS), as well as the possibility of using pegylated arginine deiminase (ADI-PEG20) for the treatment of CCA. ASS expression was determined in CCA specimens from 40 patients in Thailand. Immunohistochemical detection of ASS and determination of the proliferative index, Ki-67, were carried out in paraffin-embedded sections of these specimens, as well as in two CCA cell lines, HuCCA and RmCCA-1, derived from CCA samples from patients in Thailand. In total, ~45% of the CCA specimens had low ASS expression, and the level of expression was significantly negatively associated with cell differentiation (P<0.05) and Ki-67 expression (P<0.05). The level of ASS expression in tumor cells was significantly lower than that in non-tumor cells (1.3-fold, P<0.05). The HuCCA cell line had significantly lower levels (P<0.05) of ASS expression at the mRNA and protein levels relative to those of normal human immortalized fibroblast cells (BJ-1). By contrast, the RmCCA-1 cell line showed no significant difference. In addition, the effects of ADI-PEG20 on growth inhibition, apoptosis and cell cycle arrest were determined in HuCCA and RmCCA-1 cells. ADI-PEG20 treatment reduced cell viability and cell proliferation in the two CCA cell lines, though it had no effect in immortalized BJ-1 cells. Furthermore, ADI-PEG20 treatment significantly increased G0/G1 cell cycle arrest in HuCCA, though not in RmCCA-1 cells. ASS silencing in the RmCCA-1 cell line significantly enhanced its sensitivity to ADI-PEG20 treatment. Results from the in vitro study demonstrated that ADI-PEG20 has antitumor activity against CCA with low ASS expression.

The Combination of Arginine Deprivation and 5-Fluorouracil Improves Therapeutic Efficacy in Argininosuccinate Synthetase Negative Hepatocellular Carcinoma.

Argininosuccinate synthetase (ASS), a key enzyme to synthesize arginine is down regulated in many tumors including hepatocellular carcinoma (HCC). Similar to previous reports, we have found the decrease in ASS expression in poorly differentiated HCC. These ASS(-) tumors are auxotrophic for arginine. Pegylated arginine deiminase (ADI-PEG20), which degrades arginine, has shown activity in these tumors, but the antitumor effect is not robust and hence combination treatment is needed. Herein, we have elucidated the effectiveness of ADI-PEG20 combined with 5-Fluorouracil (5-FU) in ASS(-)HCC by targeting urea cycle and pyrimidine metabolism using four HCC cell lines as model. SNU398 and SNU387 express very low levels of ASS or ASS(-) while Huh-1, and HepG2 express high ASS similar to normal cells. Our results showed that the augmented cytotoxic effect of combination treatment only occurs in SNU398 and SNU387, and not in HepG2 and Huh-1 (ASS(+)) cells, and is partly due to reduced anti-apoptotic proteins X-linked inhibitor of apoptosis protein (XIAP), myeloid leukemia cell differentiation protein (Mcl-1) and B-cell lymphoma-2 (Bcl-2). Importantly, lack of ASS also influences essential enzymes in pyrimidine synthesis (carbamoyl-phosphate synthetase2, aspartate transcarbamylase and dihydrooratase (CAD) and thymidylate synthase (TS)) and malate dehydrogenase-1 (MDH-1) in TCA cycle. ADI-PEG20 treatment decreased these enzymes and made them more vulnerable to 5-FU. Transfection of ASS restored these enzymes and abolished the sensitivity to ADI-PEG20 and combination treatment. Overall, our data suggest that ASS influences multiple enzymes involved in 5-FU sensitivity. Combining ADI-PEG20 and 5-FU may be effective to treat ASS(-)hepatoma and warrants further clinical investigation.

Health risk evaluation in a population exposed to chemical releases from a petrochemical complex in Thailand.

Emissions from petrochemical industries may contain toxic and carcinogenic compounds that can pose health risk to human populations. The scenario may be worse in developing countries where management of such exposure-health problems is typically not well-implemented and the public may not be well-informed about such health risk. In Thailand, increasing incidences of respiratory diseases and cancers have been reported for the population around a major petrochemical complex, the Map Ta Phut Industrial Estate (MTPIE). This study aimed to systematically investigate an exposure-health risk among these populations. One-hundred and twelve healthy residents living nearby MTPIE and 50 controls located approximately 40km from MTPIE were recruited. Both external and internal exposure doses to benzene and 1,3-butadiene, known to be associated with the types of cancer that are of concern, were measured because they represent exposure to industrial and/or traffic-related emissions. Health risk was assessed using the biomarkers of early biological effects for cancer and inflammatory responses, as well as biomarkers of exposure for benzene and 1,3-butadiene. The exposure levels of benzene and 1,3-butadiene were similar for both the exposed and control groups. This was confirmed by a non-significant difference in the levels of specific urinary metabolites for benzene (trans,trans-muconic acid, t,t-MA) and 1,3-butadiene (monohydroxy-butyl mercapturic acid, MHBMA). Levels of 8-hydroxydeoxyguanosine (8-OHdG) and DNA strand breaks between the two groups were not statistically significantly different. However, functional biomarkers, interleukin-8 (IL-8) expression was significantly higher (p<0.01) and DNA repair capacity was lower (p<0.05) in the exposed residents compared to the control subjects. This suggests that the exposed residents may have a higher risk for development of diseases such as cancer compared to controls. However, the increased expression of IL-8 and lower DNA repair capacity were not associated with recent and excessive exposure to benzene and 1,3-butadiene, which were at the similar levels as those in the controls. The data would indicate that previous exposure to the two chemicals together with exposure to other toxic chemicals from the MTPIE may be responsible for the elevated functional biomarkers and health risk. Further studies are required to determine which other pollutants from the industrial complex could be causing these functional abnormalities.

Low level occupational exposure to styrene: its effects on DNA damage and DNA repair.

The present study aimed to evaluate the effects of styrene exposure at levels below the recommended standards of the Threshold Limit Value (TLV-TWA(8)) of 20 ppm (ACGIH, 2004) in reinforced-fiberglass plastics workers. Study subjects comprised 50 exposed workers and 40 control subjects. The exposed workers were stratified by styrene exposure levels, i.e. group I (<10 ppm, <42.20 mg/m(3)), group II (10-20 ppm, 42.20-84.40 mg/m(3)), and group III (>20 ppm, >84.40 mg/m(3)). The mean styrene exposure levels of exposed workers were significantly higher than those of the control workers. Biomarkers of exposure to styrene, including blood styrene and the urinary metabolites, mandelic acid (MA) and phenylglyoxylic acid (PGA), were significantly increased with increasing levels of styrene exposure, but were not detected in the control group. DNA damage, such as DNA strand breaks, 8-hydroxydeoxyguanosine (8-OHdG), and DNA repair capacity, were used as biomarkers of early biological effects. DNA strand breaks and 8-OHdG/10(5)dG levels in peripheral leukocytes of exposed groups were significantly higher compared to the control group (P<0.05). In addition, DNA repair capacity, determined by the cytogenetic challenge assay, was lower in all exposed groups when compared to the control group (P<0.05). The expression of CYP2E1, which is involved in styrene metabolism, in all styrene exposed groups, was higher than that of the control group at a statistically significant level (P<0.05). Levels of expression of the DNA repair genes hOGG1 and XRCC1 were significantly higher in all exposed groups than in the control group (P<0.05). In addition to styrene contamination in ambient air, a trace amount of benzene was also found but, the correlation between benzene exposure and DNA damage or DNA repair capacity was not statistically significant. The results obtained from this study indicate an increase in genotoxic effects and thus health risk from occupational styrene exposure, even at levels below the recommended TLV-TWA(8) of 20 ppm.