Ultrastructural changes in epithelial tissues caused by exposure to heavy metals

Document Type : Research Paper

Authors

1 Department of Biology, Kazakh National Womens Teacher Training University, Almaty, Kazakhstan

2 Department of botany and agroecology, Faculty of Biology and Biotechnology, Al-Farabi Kazakh National University, Almaty, Kazakhstan

3 Department of Oncology, Asfendiyarov Kazakh National Medical University, Almaty, Kazakhstan

10.22124/cjes.2026.9503

Abstract

Heavy metal exposure is an environmental and occupational concern that threatens the health of the integumentary tissues, the body's first line of defense. This study aimed to investigate and compare the microstructural changes induced by three common heavy metals, including cadmium (Cd), hexavalent chromium [Cr(VI)], and lead (Pb), in lung (A549) and intestinal (Caco-2) epithelial cell lines. Cells were treated with subtoxic and toxic concentrations of these metals for 24 and 48 hours and then evaluated using transmission electron microscopy (TEM) and numerical image analysis. The results revealed distinct, dose- and time-dependent pathological patterns for each metal. Cadmium and chromium predominantly induced severe mitochondrial swelling and crystallolysis, with the percentage of swollen mitochondria reaching 68.5 ± 8.3% in A549 cells treated with 20 μM cadmium. In contrast, lead mainly caused mitochondrial matrix condensation (45.6 ± 9.2% at 50 μM). At the nuclear level, cadmium caused severe chromatin marginalization (index 2.8 ± 0.4) and chromium caused diffuse condensation and indentation of the nuclear membrane in 22% of the cells. All metals also significantly induced endoplasmic reticulum stress and autophagy activation. The number of cytoplasmic vacuoles in cadmium-treated cells increased to 15.2 ± 3.4 per cell. Comparison of the two cell lines showed that intestinal Caco-2 cells were more vulnerable to vacuole formation induced by cadmium and chromium than lung A549 cells. Overall, each metal produced a unique micromorphological “signature” that reflects its specific mechanisms of toxicity.

Keywords

References

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Caspian Journal of Environmental Sciences
Volume 24, Issue 1
January 2026
Pages 117-124

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