Promoting effect of total nymphaea candida polyphenols on skin ulcer healing in diabetic rats

To observe the effect of total polyphenols from Nymphaea candida (NCTP) on ulcer wound healing in diabetic rats and to explore its potential mechanism. A total of 75 male Sprague-Dawley (SD) rats were randomly divided into a normal control group (n = 15) and a diabetic modeling group (n = 60). Diabetic rats were induced by a high-fat diet combined with intraperitoneal injection of streptozotocin (STZ), followed by creation of a full-thickness skin defect on the back to establish a diabetic ulcer model. Successfully modeled diabetic rats were further randomized into four subgroups: a diabetic control group, a 0.5% NCTP group, a 1% NCTP group, and a 2% NCTP group. Wounds in the normal control and diabetic control groups were treated with normal saline, while those in the NCTP groups were topically applied with corresponding concentrations of NCTP solution once daily. Wound healing was observed and the healing rate was calculated on days 0, 3, 7, 14, and 21 after treatment. Granulation tissues were collected on days 7, 14, and 21. Histopathological changes were examined by hematoxylin and eosin (HE) staining. Protein expression levels of tumor necrosis factor-α (TNF-α), transforming growth factor-β1 (TGF-β1), and vascular endothelial growth factor (VEGF) were detected by immunohistochemistry. At days 3, 7, 14, and 21, wound healing rates in the normal control, 0.5% NCTP, 1% NCTP, and 2% NCTP groups were significantly higher than those in the diabetic control group (P < 0.01). Moreover, the healing rate in the 2% NCTP group was significantly higher than those in the 0.5% and 1% NCTP groups (P < 0.01). HE staining showed dense inflammatory cell infiltration, extremely low numbers of newly formed capillaries and fibroblasts, and loose, edematous tissue in the diabetic control group. In contrast, the normal control and 2% NCTP groups exhibited obvious proliferation of fresh granulation tissue, accelerated capillary neovascularization, markedly increased fibroblast counts, and significantly reduced inflammatory cell infiltration. These improvements were milder in the 1% and 0.5% NCTP groups. Immunohistochemical results revealed that TNF-α protein expression was significantly higher in the diabetic control and all NCTP-treated groups than in the normal control group (P < 0.01). Compared with the diabetic control group, TNF-α expression was significantly downregulated in all NCTP-treated groups (P < 0.01), and the 2% NCTP group showed a significantly lower level than the 0.5% and 1% NCTP groups (P < 0.01). Conversely, VEGF and TGF-β1 protein expression was significantly lower in the diabetic control and all NCTP-treated groups than in the normal control group (P < 0.05 or P < 0.01). However, compared with the diabetic control group, VEGF and TGF-β1 expression was significantly upregulated in all NCTP-treated groups (P < 0.05). Furthermore, the 2% NCTP group presented significantly higher VEGF and TGF-β1 expression than the 0.5% and 1% NCTP groups (P < 0.01).