Silk fibroin and Nettle extract promote wound healing in a rat model: A histological and morphometrical study

Considering the anti-inflammatory, antimicrobial ability, and antioxidant effects besides stimulating ability of silk fibroin (SF) in cell migration and proliferation of Nettle, the current study aimed to investigate the effect of Nettle leaf extract (NLE) and SF on histology, morphometrical parameters and apoptosis on the wound in the rat model.

Wistar rats are divided into 5 groups, including 1-control (rats with healthy skin and no treatment); 2-wound (without any treatment); 3-SF (administration of silk fibroin solution for 14 consecutive days); 4- Nettle (administration of Nettle ointment for 14 consecutive days), and 5- Eucerin group (administration of Eucerin substance for 14 consecutive days) and then assessed wound area by photography, angiogenesis, inflammation, and thickness of epidermis using hematoxylin and eosin (H&E) staining, collagen deposition, and structure of dermis layers evaluated by Masson's trichrome staining and the apoptosis index determined by tunnel assay on days 7, 14 and 21.

photographic illustrations showed that the wound surface environment on the seventh day in group 4 was significantly different from group 2 (p < 0.002). The rate of wound healing on the fourteenth day was higher in groups 3 and 4 than in group 2 (p < 0.001). Also, at this time, group 4 was significantly different from group 3 and group 5 (p = 0.003 and p = 0.000, respectively). There was a significant difference in epidermal thickness between the wound group and other experimental groups (p < 0.05). The number of apoptotic cells at the wound edges on the seventh day in both group 3 and group 4 had a significant decrease compared to other groups of wounds (p = 0.000), but there was a significant increase on the fourteenth day. Also, on the 21st day, a significant decrease in apoptotic cells was observed in both group 3 and group 4 compared to other wound groups (p = 0.000).

Nettle and SF maintain cell homeostasis and accelerate wound closure by reducing cell apoptosis and enhancing cell proliferation on the seventh day, but by increasing the apoptosis of fibroblast cells on the fourteenth day, they lead to remodeling and keratinocytes migration to epidermis formation. Increased apoptosis also seems to be one of the pathophysiological mechanisms to prevent the formation of keloid and hypertrophic scar tissue. SF and Nettle extract, by increasing cell proliferation and migration of different cell types to the site of injury, control the remodeling process by inducing and regulating apoptosis in the first two weeks of wound healing and accelerating the process of collagen deposition and epithelialization.