Development of a histological grading system for assessing microplastic-induced structural damage in rat aorta, trachea, and bladder tissues following acute exposure.

INTRODUCTION: Microplastic (MP) exposure has increasingly been associated with tissue-level impact in toxicology studies, including inflammatory changes and histopathological injury in aquatic and mammalian models. However, there is currently no consistently developed histological scoring approach for assessing the structural damage across different tissue types induced by MPs following acute exposure. This study aimed to develop and apply a semi-quantitative histological scoring framework to investigate the histological alterations of polyethylene terephthalate (PET) MPs in Sprague-Dawley rat aorta, trachea, and bladder ex vivo. MATERIALS AND METHODS: Rat tissues were excised and incubated for 22 to 24 hours at 4°C with different concentrations of PET particles (0.3 - 5.0 mg/mL). Trachea and bladder tissues were processed for haematoxylin and eosin staining, whereas aorta sections were stained using CD31 immunohistochemistry to assess the endothelial integrity. Images were randomised and scored independently by three blinded observers using tissue-specific grading criteria for aorta endothelium, tracheal epithelium, and bladder urothelium. RESULTS: Across the three tissues, the scoring system suggests organ-specific differences in terms of sensitivity to acute exposure, with bladder urothelium appearing as the most structurally vulnerable under the tested conditions. CONCLUSION: This method provides a structured framework for screening MPs-induced tissue damage and may improve reproducibility in histological evaluation of tissue structural integrity.