Duodenal crypt health following exposure to Cr(VI): Micronucleus scoring, γ-H2AX immunostaining, and synchrotron X-ray fluorescence microscopy.

Abstract

Lifetime exposure to high concentrations of hexavalent chromium [Cr(VI)] in drinking water results in intestinal damage and an increase in duodenal tumors in B6C3F1 mice. To assess whether these tumors could be the result of a direct mutagenic or genotoxic mode of action, we conducted a GLP-compliant 7-day drinking water study to assess crypt health along the entire length of the duodenum. Mice were exposed to water (vehicle control), 1.4, 21, or 180 ppm Cr(VI) via drinking water for 7 consecutive days. Crypt enterocytes in Swiss roll sections were scored as normal, mitotic, apoptotic, karyorrhectic, or as having micronuclei. A single oral gavage of 50mg/kg cyclophosphamide served as a positive control for micronucleus induction. Exposure to 21 and 180 ppm Cr(VI) significantly increased the number of crypt enterocytes. Micronuclei and γ-H2AX immunostaining were not elevated in the crypts of Cr(VI)-treated mice. In contrast, treatment with cyclophosphamide significantly increased numbers of crypt micronuclei and qualitatively increased γ-H2AX immunostaining. Synchrotron-based X-ray fluorescence (XRF) microscopy revealed the presence of strong Cr fluorescence in duodenal villi, but negligible Cr fluorescence in the crypt compartment. Together, these data indicate that Cr(VI) does not adversely effect the crypt compartment where intestinal stem cells reside, and provide additional evidence that the mode of action for Cr(VI)-induced intestinal cancer in B6C3F1 mice involves chronic villous wounding resulting in compensatory crypt enterocyte hyperplasia.

• Authors: Chad M Thompson, Jeffrey C Wolf, Reem H Elbekai, Madhav G Paranjpe, Jennifer M Seiter, Mark A Chappell, Ryan V Tappero, Mina Suh, Deborah M Proctor, Anne Bichteler, Laurie C Haws, Mark A Harris
• Journal: Mutation research. Genetic toxicology and environmental mutagenesis (Mutat Res Genet Toxicol Environ Mutagen) Vol. 789-790 Pg. 61-6 (Aug 2015) ISSN: 1879-3592 [Electronic] Netherlands
• PMID: 26232259 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)
• Copyright: Copyright © 2015 The Authors. Published by Elsevier B.V. All rights reserved.

Chemical References

• Drinking Water
• Histones
• gamma-H2AX protein, mouse
• Chromium
• chromium hexavalent ion

Topics

• Animals
• Chromium (administration & dosage, toxicity)
• Dose-Response Relationship, Drug
• Drinking Water
• Duodenum (drug effects, metabolism)
• Enterocytes (drug effects, metabolism)
• Female
• Histones (metabolism)
• Immunohistochemistry
• Male
• Mice, Transgenic
• Micronuclei, Chromosome-Defective (chemically induced, statistics & numerical data)
• Microscopy, Fluorescence (instrumentation, methods)
• Mitotic Index
• Synchrotrons
• X-Rays