Abstract 1579: Induction of cytotoxicity by soluble chromium (VI) compounds in cultured C3H/10T1/2 Cl 8 mouse embryo cells effects of ascorbate and dehydroascorbate
Authors: Shahin Sophia A. , Liao William , Tran Laureen , Akinwumi Qasim A. , Tseng Farn-shuan , Mathew-Joseph Alyssa , Landolph Joseph R. 
Published: May 2015

Abstract
Hexavalent chromium [Cr(VI)]-containing compounds are human carcinogens. They cause cancers in the respiratory system when inhaled, and stomach/other internal cancers when ingested. Soluble and insoluble hexavalent chromium [Cr(VI)] compounds induced base substitution, deletion, addition, and frameshift mutations. Cr(VI) compounds also induce DNA-DNA cross links and DNA-protein cross-links in mammalian cells. We examined the ability of the soluble chromium compounds, sodium chromate (Na2CrO4), calcium chromate (CaCrO4) and potassium chromate (K2CrO4) to induce cytotoxicity and morphological transformation in C3H/10T½ Cl 8 (10T1/2) mouse embryo cells. We tested the hypothesis that the intracellular reductants, ascorbate and dehydroascorbate, can reduce Cr(VI) to Cr(V), Cr(IV), and Cr(III) intracellularly, making it a strong cytotoxin in mammalian cells. Ascorbate is present in serum at concentrations in the mM range under physiological conditions in humans, but is only present in the μM range in mouse embryo cells grown in BME cell culture medium plus 10% fetal calf serum. We hypothesized the relatively weak responses for induction of morphological transformation of mammalian cells by Cr(VI) compounds in culture (dose-dependent but weak induction of foci by lead chromate, and no induction of foci by calcium chromate, potassium chromate, and sodium chromate) is due to the small amounts of ascorbate in cultures of mammalian cells that are insufficient to reduce Cr(VI) to Cr(V), Cr(IV), and Cr(III). Therefore, we investigated the cytotoxic effects of ascorbate on 10T½ mouse embryo cells, and the effects of the highest non-cytotoxic concentrations of ascorbate on Cr(VI)-induced cytotoxicity in 10T½ cells, using reduction in plating efficiency as our cytotoxicity assay. Cell survival data showed that ascorbate itself exerted significant cytotoxic effects at concentrations of 0.00625 mM and higher on 10T½ mouse embryo cells. Furthermore, when 10T½ cells were treated with both Cr(VI) and ascorbate, ascorbate played dual roles. It served as a pro-oxidant (enhancer of the cytotoxicity of chromate) at concentrations up to 0.1 mM, and as an anti-oxidant (reducer of the cytotoxicity of chromate) at concentrations of 0.25 mM and higher. This information is important for our ongoing and future experiments, where we designed a protocol to incorporate ascorbate into our assays assessing the cytotoxicity and cell transforming activity of Cr(VI) compounds. We project that at concentrations of 0.1 mM and lower, ascorbate will enhance the cell transforming activity of Cr(VI) compounds. Supported by undergraduate fellowships from the Provost's Office at the University of Southern California (USC) (P. I., JRL), by funding from the M. S. Program in Molecular Microbiology and Immunology to JRL, by discretionary funding to JRL, and by prior grant ES03341 from NIEHS/NIH (P. I., JRL).
Citation Format: Sophia A. Shahin, William Liao, Laureen Tran, Qasim A. Akinwumi, Farn-shuan Tseng, Alyssa Mathew-Joseph, Joseph R. Landolph. Induction of cytotoxicity by soluble chromium (VI) compounds in cultured C3H/10T1/2 Cl 8 mouse embryo cells effects of ascorbate and dehydroascorbate. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1579. doi:10.1158/1538-7445.AM2014-1579