Naringin, a flavanone glycoside, promotes angiogenesis and inhibits endothelial apoptosis through modulation of inflammatory and growth factor expression in diabetic foot ulcer in rats

•Diabetes wound was caused in SD rats on the dorsal surface of hind paw.•Naringin improved wound area, glycated Hb, serum glucose level and insulin.•Naringin up-regulated IFG-1, TGF-β, VEGF-c, Ang-1 and collagen-1 mRNA expression.•TNF-α, IL-1β and IL-6 mRNA expression were down-regulated by naringin.•Naringin induced angiogenesis via inflammatory mediator & growth factor modulation.

Chronic, unhealed diabetic foot ulcer (DFU) is one of the most severe complications of diabetes mellitus (DM). Naringin, a flavanone glycoside antioxidant, was reported to have antidiabetic and anti-apoptotic properties. In the present study DM was induced experimentally by streptozotocin (STZ, 55 mg/kg, i.p.). In surgically introduced wounds on the dorsal surface of the hind paw of rats, the healing potential of naringin was investigated. Rats were treated with naringin (20, 40 and 80 mg/kg, p.o.), insulin (10 IU/kg, s.c.) and tetrachlorodecaoxide (TCDO) (1 drop, twice a day, topically) for 16 days. The wound area was measured every second day, and on day 17 various biochemical parameters were determined in serum, wound tissue, and histopathological examination of the wound was performed. Naringin (40 and 80 mg/kg) significantly (P < 0.05) improved wound area, serum glucose level, glycated Hb and serum insulin. Naringin treatment at 40 and 80 mg/kg resulted in significant (P < 0.05) up-regulation of mRNA expression of growth factor (IFG-1, TGF-β and VEGF-c), Ang-1 and collagen-1 whereas mRNA expression of inflammatory mediators (TNF-α, IL-1β and IL-6) was down-regulated. Furthermore, naringin significantly (P < 0.05) attenuated STZ-induced apoptosis and stimulated angiogenesis in the wound tissue. Further results suggest that angiogenesis was improved via naringin-mediated inhibition of hyperglycemia, oxidative stress, down-regulation of inflammatory mediator expression and up-regulation of growth factor expression, leading to improved wound healing of DFU.

Graphical abstractPossible molecular mechanisms through which naringin may improve diabetic wound healing. In the cascade of a normal wound healing process, activation of platelets after injury causes release of pro-inflammatory cytokines like TNF-α, IL-1β that activate macrophages. Further release of TNF-α, IL-1β and IL-6 results in inhibition of fibroblast as well as keratinocytes proliferation and migration, which delays epithelization and granulation. In the diabetic condition, hyperglycemia causes oxidative stress, which inhibits IGF-1 expression, leading to increased apoptosis. Inhibition of fibroblast proliferation results in decreased VEGF-c synthesis and thus in down-regulation of TGF-β1 and Ang-1 expression. This cascade leads to decreased endothelial cell proliferation and thus to delayed neoangiogenesis and vasculogenesis. Decreased collagen synthesis due to down-regulation of Ang-1 synthesis, results in turn in decreased epithelization. Together, these phenomena cause delayed wound healing.Naringin reduces the STZ-induced elevated blood glucose level thus decreasing oxidative stress and modulating the expression of growth factors (IFG-1, VEGF-c and TGF-β1) and inflammatory mediators (TNF-α, IL-1β and IL-6) thereby up-regulating Ang-1 and collagen-1 expression, which prevents delayed healing of chronic diabetic foot ulcers. (Black line reflects the delayed diabetic wound healing process whereas blue lines indicate the proposed mechanism of naringin-mediated attenuation of delay in diabetic wound healing.)Figure optionsDownload full-size imageDownload as PowerPoint slide