Avaliação dos efeitos da prata nanocristalina e da papaína sobre o processo cicatricial em ratos

Abstract

Wound healing represents a dynamic physiological process initiated and influenced by many factors. Nanocrystalline silver have been demonstrated to have antimicrobial and anti-inflammatory properties, whereas papain is a proteolytic enzyme, which has been used in different formulations for wound treatment in clinics. Objectives This study was conducted to further evaluate the wound healing activity of nanocrystalline silver dressings as compared to that obtained with 2% papain gel, for the treatment of acute wounds in rats and the impact on VEGF expression. Forty-eight male Wistar rats were randomly divided into four groups. Group 1: treated with saline solution (NaCl 0.9%); group 2: treated with nanocrystalline silver; group 3: treated with the excipient gel; group 4: treated with 2% papain gel. A full-thickness wound of 1.5 x 1.5 cm² was excised from the back of the rats, under aseptic conditions and were anesthetized by a mixture of ketamine and xylazine. All the animals were evaluated on the 3rd, 6th, 9th, 12th and 15th days for wound-healing rating and histological evaluation and imunohistochemistry for VEGF. The statistical analysis was performed ANOVA, followed by Bonferroni s test. The group treated with the nanocrystalline silver dressing, showed a healing ratio superior, in all periods, when compared to control group and was the unique showing complete wound healing at 15 days of evaluation. The 2% papain gel group, a significantly higher wound healing rate was observed only at the 3th and the 6th days, but the wound showed a bleeding and decrease of wound healing ratio from the 9th day on. Histological evaluation showed a fully matured and compact granulation tissue on the nanocristaline silver group. The others groups displayed thickned epidermis, with extensive areas of inflammation. Evident immunopositivity for VEGF was also seen in the granulation tissue layer at the 9th day, the nanocrystalline silver group showed a higher VEGF expression in blood vessels, epidermal cells and granulation tissue. In this work, based on both the qualitative and the quantitative analysis, the nanocrystalline silver group showed a better wound healing effect in view of a rapid contraction of wound, compared with the others groups. Furthermore, we show for the first time that pro-healing activities of nanocrystalline silver dressings are likely associated to the modulation of VEGF expression.