PNNL

Abstract

Gene expression changes in primary human uroepithelial cells exposed to arsenite and its methylated metabolites were evaluated to identify cell signal pathway perturbations potentially associated with bladder carcinogenicity. Uroepithelial cells from multiple individuals were treated in culture with mixtures of inorganic arsenic and its pentavalent or trivalent metabolites for 24 hours at relative proportions typically observed in the urine of individuals exposed to arsenic in drinking water. Total arsenic concentrations ranged from 0.06 µM to 18 µM, which includes the range of concentrations measured in the urine of populations exposure to arsenite in the drinking water. Two series of in vitro exposures were conducted with human bladder samples to measure changes in gene or protein expression: one (five samples) with arsenite and pentavalent methylated metabolites and a second (ten samples) with arsenite and trivalent methylated metabolites. Similar gene expression responses were obtained for mixtures containing pentavalent or trivalent metabolites. Principal component analysis indicated that interindividual variation was greater than changes in expression elicited by arsenic treatment. A common suite of gene changes, however, was consistently identified across individuals that reflect effects on a number of key signaling pathways: oxidative stress, protein folding, growth regulation, metallothionine regulation, DNA damage sensing, thioredoxin regulation, and immune response. Gene expression for certain genes, including those for DNA damage sensing and immune response, were suggestive of a non-monotonic response. BMDLs for the eight most common gene biomarkers across individuals ranged from 0.12 – 12 µM for the trivalent arsenical mixture. NOSTASOT results indicated NOAELs ranging from 0.2 – 0.3 µM expressed as arsenite concentration only. This study is the first to examine gene expression response in primary uroepithelial cells from multiple individuals and to identify no adverse effect levels for arsenical-induced cell signaling perturbations in normal human cells exposed to a biologically plausible concentration range.