Heavy Metal Index
Ask the IndexAboutIndex Pro

Mechanisms of Hexavalent Chromium-Induced Lung Carcinogenesis: DNA Double-Strand Breaks and DNA Repair Inhibition in a Guinea Pig Model

Cite this pageVersion history

This mechanistic study translated the established mechanism of hexavalent chromium Cr(VI)-induced lung carcinogenesis (DNA double-strand breaks via gamma-H2AX, inhibition of homologous recombination repair via RAD51) to a guinea pig animal model. Guinea pigs were chosen because, unlike mice and rats, they lack endogenous ascorbic acid (vitamin C) synthesis and have a dichotomous bronchiole branching pattern similar to humans, making them more physiologically relevant for Cr(VI) inhalation carcinogenesis research.

Key numbers

Acute exposure (oropharyngeal aspiration, 24 h):

  • Saline, 0.2, 0.4, 0.8 mg/kg zinc chromate led to 948.8, 1282.5, 1212.7, and 1092.6 total gamma-H2AX foci (DNA double-strand breaks) in 100 bronchiolar epithelial cells respectively; lowest dose (0.2 mg/kg) induced statistically significant increase versus control in bronchioles.
  • Alveolar gamma-H2AX foci: 271.7, 366.6, 329.4, and 306.9 total at the same doses; not statistically significant.
  • RAD51 foci (DNA repair marker) in bronchioles: 177.1, 369.9, 379.2, and 259.9 for saline and three doses; low and middle doses significantly increased RAD51 in bronchioles (not in alveoli).

Subchronic exposure (90-day, all three zinc chromate doses):

  • All three doses significantly induced gamma-H2AX foci (DNA double-strand breaks) in bronchioles but not alveoli (1163.4, 1139.7, 1191.1 versus saline 800.5 total gamma-H2AX foci per 100 bronchiolar cells).
  • Subchronic exposure inhibited RAD51 foci in bronchioles (DNA repair inhibition), consistent with the established carcinogenic mechanism of Cr(VI).
  • Males had overall higher DNA double-strand break levels than females in both bronchioles and alveoli.

Methods (brief)

Formalin-fixed paraffin-embedded guinea pig lung tissue; gamma-H2AX (DNA double-strand break marker) and RAD51 (homologous recombination repair marker) quantified by confocal microscopy using immunofluorescence (cytokeratin used to identify epithelial cells); 100 cells counted per region per animal; gamma-H2AX/RAD51 ratio calculated as repair index. Statistical analysis: n = 7 males and 7 females per group; p or q values reported; q values used for FDR-corrected multiple comparisons.

Evidence fitness

Supports: establishing that Cr(VI) induces DNA double-strand breaks and inhibits DNA repair specifically in bronchiolar epithelial cells (the site of Cr(VI)-induced tumors in humans), and that this mechanism is reproduced in a human-relevant guinea pig model. This paper is specifically about hexavalent chromium carcinogenesis, not arsenic. It is contextual evidence for inhalation pathway metal carcinogenesis in lungs.

Limitations

Animal model only (guinea pigs); oropharyngeal aspiration route differs from occupational inhalation; Cr(VI) as zinc chromate does not capture all Cr(VI) compound speciation; no long-term tumor endpoint measured; sex differences noted but not fully explained.

Update history

No substantive edit history is available in this build. The full commit record is available in git.

Referenced by