Evaluation of morphological changes of the skin after radiation-induced injury in Wistar rats

The cancer covers a heterogeneous group of more than 100 diseases with different etiology and prognosis. Radiotherapy is one of the most commonly used treatment modalities, aiming at the destruction of cancer cells, using ionizing radiation. One of the limiting factors of radiotherapy is that radiation promotes the death of tumor cells in addition to injure healthy tissue neighboring the tumor, and may cause their death. Irradiation of the skin, accidental or for therapeutic purposes can trigger many injuries culminating in fibrosis, which implies functional alteration of the body. The evaluation of morphological effects associated with skin irradiation becomes essential to develop more effective radiation strategies and decreased morbidity; and in case of accidents, proper handling of the victim.Evaluate radio-induced dermal changes using a Wistar rats model irradiated with 10, 40 and 60Gy. Male Wistar rats, aged approximately three months, were pre-anesthetized with midazolam and xylazine and anesthetized with sodium pentobarbital, shaved in the back, immobilized on polystyrene support in the prone position and irradiated with doses of 10, 40 and 60 Gy, with 4MeV nominal energy electron beams. The skin was irradiated in a 3cm2 field, and used 0.5cm of tissue equivalent material, to obtain a homogeneous dose distribution. After irradiation, the animals remained on constant evaluation, and the lesions were recorded photographically. The animals were divided into groups and were killed on the irradiation day, 5, 10, 15, 25 and 100 days after irradiation. The skin was fixed in 10% formaldehyde; the samples were embedded in paraffin and cut. The sections were stained with hematoxylin-eosin, picrosirius red and immuno stained with antibody anti-TGF beta1. Another part of the tissue was fixed in 2.5% glutaraldehyde and processed for scanning electron microscopy. It was observed macroscopically the appearance of skin lesions similar to burns on the entire irradiated area. The optical microscope verified the early development of lesions in the 5 days group. After 10 days of irradiation it was already possible to see evidences of epidermal healing under the crust formed by the lesion. At 15 days after irradiation the tissue beneath the lesion had reconstructed epidermis. It was also observed the characteristics of tissue healing. It was also seen a significant polymorphonuclear cells infiltration. After 25 days at the higher doses the lesions remained, which did not occur at the lower dose, where the irradiated area of the animals were already completely healed. After 100 days of irradiation at 40Gy dose the wound was healed with the emergence of a well defined healed tissue. At the 60Gy dose, the lesion persisted in some animals, and in those that healing occurred the epidermis was a hypertrophied (acanthosis). It was visualized a tissue with their morphological aspect completely mis characterized, where it's possible to view a necrotic tissue. The results of the scanning electron microscopy analysis corroborate with the in optical microscopy findings, where it's possible to visualize the distortion of collagen fibers at the higher dosages. The results indicate that the used doses induced an important skin inflammatory process, activating the immune system. This fact leads to an increase in the expression of TGF beta1, one of the responsible for the increased production of extracellular matrix (ECM) by various cell types, mainly fibroblasts in injured tissues. Besides the increased expression of ECM, the TGF beta1 also promotes the inhibition of the degradation processes of the same. The intense expression of cytokines in irradiated skin can trigger the fibrosis process; consequently, affect the homeostasis of this organ due to the accumulation of ECM. (author)