Avaliação de alterações morfológicas da pele após lesão radioinduzida em ratos Wistar

Abstract

Radiation therapy is one of the most commonly used therapeutic modalities in cancer treatment, aiming the destruction of neoplastic cells using ionizing radiation. A limiting factor is the radiation damage in healthy tissues neighboring the tumor. The irradiation of the skin, accidentally or for therapeutic purposes, can trigger a series of injuries culminating in fibrosis, causing functional alterations in this organ. The morphological evaluation of the effects associated with skin irradiation becomes essential to establish more effective strategies for irradiation and decreased morbidity, and in case of accidents, proper handling of the victim. The aim of this study was to evaluate the radiation-induced dermal changes, using a rats model. Male Wistar rats, three months old, had their skin irradiated, in a 3cm2 field, with single doses of 10, 40 and 60 Gy of electrons with nominal energy of 4MeV. After irradiation, the animals were kept under constant observation, lesions were recorded photographically. The animals were divided into groups and euthanized: on the day of irradiation, 5, 10, 15, 25 and 100 days after irradiation. Part of the skin was fixed in formaldehyde, embedded in paraffin and subjected to microtomy. Sections were stained with hematoxylin-eosin, picrosirius red and immunostained with anti-TGF-beta1. Another part of the tissue was fixed in glutaraldehyde and processed for scanning electron microscopy. It was observed macroscopic skin lesions similar to burns throughout the irradiated area. It was verified, by optical microscopy, the early development of lesions 5 days after irradiation. After 10 days of irradiation there was evidence of epidermal wound healing under the crust formed by the injury. At the day 15 days the tissue below the lesion was reconstructed and had characteristics of healing, displaying a significant polymorphonuclear cells infiltration. After 25 days, at the higher doses, the lesions persisted, which did not occur at the lowest dose, which the irradiated area was already completely healed. After 100 days of irradiation with 40 Gy the wound was healed. With 60 Gy, in some animals, the lesion persisted. In the animals which the healing took place there was a hypertrophy of the epidermis (acanthosis). It was observed a tissue totally morphological mischaracterized, and necrotic. The results obtained by scanning electron microscopy analysis corroborate with the optical microscopy findings, where the higher doses collagen fibers were mischaracterized. The results indicate that the doses used induced a significant inflammation in the skin, activating the immune system. This fact promoted an increased expression of TGFbeta1, which is responsible for an increased production of extracellular matrix (ECM) by various cell types, mainly fibroblasts in injured tissues. Besides the increased expression of ECM, the TGFbeta1 also promotes the inhibition of the degradation processes of the same. The intense expression of this cytokines in irradiated skin can trigger the process of fibrosis and, consequently, affect the homeostasis of the body due to accumulation of ECM.