Study Of Low-Level Laser Therapy Facilitates Cutaneous Wound Healing In Diabetic Rats

Objects:To study the effects of low intensity630nm semiconductor laser irradiation on the wound healing of STZ induced diabetes of male Wistar rats. To analyse the the relationship between power density and the therapeutic outcomes of low-level laser therapy (LLLT), which would necessarily contribute to not only the discovery of rules controlling LLLT and its mechanisms, but also setting directions for clinical applications.Methods:Diabetes was chemically induced using STZ and administered as tail vein injection in36male Wistar rats. Two dorsal excisional wounds(10mm×10mm square) were made on the dorsum of each rat. Thirty-six rats were divided into three LLLT groups and a control group randomly,9rats per group. The three LLLT groups were irradiated with power density of5,10and20mW/cm2respectively. LLLT was started immediately after surgery and repeated5times/week for two weeks. The LLLT was performed using a630nm continuous semiconductor laser system at the same energy density of3.6J/cm2. Before surgery and14days after wounding, the blood glucose level of each rat was checked. At3,6,9and12days after wounding, the areas of wounds on all rats were recorded with standardized photography, and calculated the percentage of wound closure by ImageJ. At4,8and14days after wounding,3rats were chosen from each group randomly and killed. The tissue specimens were assessed by histopathological semi-quantitative evaluation(stained with HE and Masson) and immunohistochemical quantification(bFGF, TGF-β1and VEGF).Results:Blood glucose remained at similar levels throughout the experiment, with no significant difference between values before and after LLLT (P>0.05). At3days after wounding, only wounds of20mW/cm2group closed significantly faster than control group (P<0.05). At6and9days after wounding, wounds of all three LLLT groups closed significantly faster than control group (P<0.05). The histopathological study found that attenuated inflammation, greater re-epithelization, mature granulation tissue and extensive collagen deposition can be observed in LLLT groups at8days after wounding, especially in20mW/cm2group. At4days after wounding, there were significant differences in the creation of new collagen fibers between control group and10mW/cm2group (P<0.05) or20mW/cm2group (P<0.05). bFGF and TGF-β1expression in all LLLT groups increased significantly compared with the control group (P<0.05). At8days after wounding, the histological evaluation score of re-epithelization, numbers of PMNLs, fibroblasts and new collagen fibers, except for new vessels, shown significant differences between control group and20mW/cm2group (P<0.05). There were significant differences in extensive fibroblasts and new collagen fibers between control group and10mW/cm2group (P<0.05).5mW/cm2group had a significant bFGF increase in comparison to control group(P<0.05). VEGF expression in all LLLT groups increased significantly compared with the control group (P<0.05). At14days after wounding, there were significant differences in the evaluation score of new vessels between control group and5mW/cm2group or20mW/cm2group(P<0.05), except10mW/cm2group. VEGF expression in20mW/cm2group increased significantly compared with the control group (P<0.05).Conclusions:LLLT have auxiliary effects in the early and middle phases of wound healing of male Wistar rats with STZ induced diabetes. LLLT could obviously promote wound contraction, fibroblasts proliferation and collagen synthesis, alter growth factors production, and reduce inflammatory reaction. The optimum intensity among the three power densities we used was20mW/cm2.