K₂CrO₄ reduces the viability of human cells deficient in certain DNA repair pathways at Cr(VI) levels detected in U.S. city water.

<p>HeLa cells (A) and TK6 cells (B) transiently or stably knocked down with shRNA against <i>RAD54</i>, <i>BRCA1</i>, or <i>POLD3</i> were exposed to K₂CrO₄ for ~3 days to determine their survival rate. (C) Point of departure analysis of TK6 indicated significant differences (p<0.0001) for TK6 control (log10(BMD) = 1.53, exponential model) vs. <i>POLD3</i> shRNA knock down (log10(BMD) = 0.99 (9.8 μg/L), polynomial model). The black arrow indicates the maximum contaminant levels (MCL) set by the U.S. EPA. The open arrow shows the highest Cr(VI) levels detected in US city water.</p

The genotoxicity of K₂CrO₄ in human and DT40 cells is drastically decreased when K₂CrO₄ incubation time is reduced.

<p>(A) <i>REV1</i> ko DT40 cells were incubated with K₂CrO₄ for 10 min to 8 hours followed by extensive washing. The cells were further cultivated for 3 days in fresh medium without addition of K₂CrO₄ to determine cell survival. (B) The exposure times (hours) were multiplicatively inversed followed by log transformation (x-axis). LC₅₀ data for each exposure time were log transformed (y-axis). Linear regression analysis was performed to determine the relationship between exposure time and LC₅₀ values (p<0.0001). (C) TK6 <i>POLD3</i> knock-down cells and TK6 mock shRNA-treated cells were incubated with K₂CrO₄ for 10 min followed by extensive washing. The cells were further cultivated for 3 days in fresh medium without addition of K₂CrO₄ to determine cell survival. The survival curves were compared between 10-min and 3-day exposure groups (p<0.0001). The green arrow indicates the Cr(VI) concentration (172,000 μg/L) that causes an increase in oral cancer, a finding that was previously shown in an NTP rodent study [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167503#pone.0167503.ref007" target="_blank">7</a>].</p

K₂CrO₄ reduces viability of human cells as well as DT40 cells deficient in certain DNA repair pathways at the maximum contaminant levels (MCL) set by the U.S. EPA.

<p>Various human cells (A) and DT40 parental cells and their mutant cells (B) deficient in <i>REV1</i>, <i>BRCA1</i>, or <i>RAD54</i> were exposed to K₂CrO₄ for ~3 days to determine their survival rates. Survival data were log-transformed giving approximate normality using Prism 5. Each LC₅₀ value was then calculated. The black arrow indicates the maximum contaminant levels (MCL) set by the U.S. EPA, while the open arrow shows the highest Cr(VI) levels detected in U.S. city water (12.9 μg/L). (C) Point-of-departure analysis showed a significant difference (p<0.0001) in DT40 (log10(BMD) = 1.98 by the Hill model) vs. <i>REV1</i>-deficient cells (log10(BMD) = 1.28 (19.2 μg/L) by the Hill model). (D) DT40 cell-based DNA damage response analysis was performed for K₂CrO₄ using a series of DT40 mutants. Relative LC₅₀ values were normalized according to the LC₅₀ value of the parental (wild type) DT40 cells. Error bars represent standard deviation from at least three independent experiments. Student’s t-test was used to test for significance in mean LC₅₀ values between DT40 parental cells and each mutant. Columns shaded in gray indicate significant differences (p<0.05) between parental DT40 cells and each mutant. Columns shaded in black show the cell lines (<i>REV1</i>, <i>RAD54</i>, <i>POLD3</i>, and <i>BRCA1</i> mutants) that are markedly sensitive to K₂CrO₄. (p<0.05 for all four cell lines after Bonferroni adjustment for 32 tests).</p