# Histological and Inflammatory Changes in Thyroid Glands and Early Growth Outcomes in Offspring of Rats Exposed to Ambient Air Pollution near a Petrochemical Complex: A Preliminary Study

## TL;DR

Exposure to air pollution near a petrochemical complex in Brazil caused thyroid changes and stunted growth in rat offspring.

## Contribution

This preliminary study links air pollution near a petrochemical complex to thyroid inflammation and developmental delays in rat offspring.

## Key findings

- Thyroid glands of offspring near the CPC showed follicular heterogeneity and increased inflammatory cytokines TNFα, IL-6, and IL-10.
- Offspring near the CPC had significantly lower body weights and shorter craniocaudal lengths compared to controls.
- SS2 group showed more pronounced deficits in birth weight and thyroid inflammation than the SS1 group.

## Abstract

Background: Environmental agents can disrupt thyroid function at several levels, including the synthesis, action, and excretion of thyroid hormones, and an inadequate concentration of thyroid hormones affects almost all organs and systems. Objective: The present study aimed to evaluate the histology and presence of the cytokines TNFα, IL-6, and IL-10 in the thyroid gland by immunohistochemical labeling, as well as the body weight and craniocaudal length of pups of Wistar rats exposed to ambient air in the vicinity of the Capuava Petrochemical Complex (CPC), located in the Santo André and Mauá cities, at São Paulo State, Brazil. Methods: This study used Wistar rats between 14 and 16 weeks of age, distributed in couples, that were exposed to pollution from the CPC located in the regions of Santo André and Mauá, Sao Paulo State, Brazil. One couple was positioned 600 m (SS1), and another was 1000 m (SS2) from the CPC, while the control group was kept at the animal research facility of the Physiology Laboratory of the FMABC University Center, Santo André. After mating, the resulting offspring were monitored for four weeks, with their body weight and craniocaudal length measured weekly. Subsequently, the offspring’s thyroid glands were histologically analyzed using H&E staining and immunohistochemistry to detect the presence of inflammatory cytokines (TNF-α, IL-6, and IL-10). Results: In the SS1 group, the thyroid glands showed follicular heterogeneity with macrofollicles and numerous microfollicles without colloid, lined by flattened epithelial cells. In these thyroid follicles, there was intense TNFα (p = 0.002) staining, slight IL-6 staining (p = 0.042), and significantly stronger staining for IL-10 (p = 0.013) compared to that in the control group. This group also had a significantly lower body weight than the control animals on the 6th, 13th, and 20th days of life. In the SS2 group, the thyroids presented an architecture dominated by microfollicles without colloid as well as inflammatory cells in the colloid of some follicles. Immunohistochemistry revealed intense pan-follicular TNFα (p = 0.002) staining, with additional cytoplasmic staining of IL-6 (p = 0.040) and IL-10 (p = 0.006). The SS2 group also showed a more pronounced deficit compared to the SS1 group in terms of birth weight. The cranial–caudal length was shorter on the 13th and 20th days of life in the SS1 and SS2 groups compared to the control group. Conclusions: The results indicate that proximity of rats to the CPC was a determining factor in the development of histological abnormalities and increases in inflammatory cytokine markers in the thyroid glands of the offspring. In addition, the offspring born near the CPC had lower birth weights and shorter craniocaudal lengths compared to the animals in the control group.