Tissue responses to postoperative laser therapy in diabetic rats submitted to excisional wounds.

In a previous study about low-level laser therapy biomodulation on a full-thickness burn model we showed that single and fractionated dose regimens increased wound healing and leukocyte influx similarly when compared with untreated control. In order to verify if this finding would be similar in an impaired wound model, we investigated the effect of single and multiple irradiations on wound closure rate, type of inflammatory infiltrate, myofibroblasts, collagen deposition, and optical retardation of collagen in diabetic rats. Female Wistar rats in the same estrous cycle had diabetes induced with streptozotocin and an 8-mm excisional wound performed with a punch. The experimental groups were: control group--untreated ulcer; single-dose group--ulcer submitted to single dose of diode laser therapy (λ = 660 ± 2 nm; P = 30 mW; energy density: 4 J/cm2) and fractionated-dose group--ulcer submitted to 1 J/cm2 laser therapy on Days 1, 3, 8, and 10. The ulcers were photographed on the experimental days and after euthanasia tissue samples were routinely processed for histological and immunohistochemistry analyses. Independently of the energy density, laser therapy accelerated wound closure by approximately 40% in the first three days in comparison to the control group. Laser therapy increased acute inflammatory infiltrate until Day 3. Both laser groups exhibited more myofibroblasts and better collagen organization than the control group. The findings demonstrate that low-level laser therapy in the immediate postoperative period can enhance the tissue repair process in a diabetes model. Similar effects were achieved with laser therapy applied a single time with an energy density of 4 J/cm2 and applied four times with an energy density of 1 J/cm2. The application of laser therapy in the inflammatory phase was the most important factor to the enhancement of the tissue repair process

Percentage of normalized wound closure throughout experiment demonstrating the effect of laser therapy in the early tissue repair process.

<p>(mean ± SEM, <i>p</i><0.05)</p

Histological examination of healing tissue—Day 3: all groups in inflammatory phase of tissue repair (A, B, C), with a crust over the ulcer and an intense inflammatory infiltrate (*); Day 8: wounds in proliferative phase with granulation tissue (D, E, F); Some samples in FDG exhibited acute inflammatory infiltrate at this time (*).

<p>hematoxilyn & eosin staining; original magnification: 200 x</p

Morphology of wound healing on Day 22, showing similarity among experimental groups (hematoxilyn and eosin—A, C, E; Picrosirius Red—B D, F)

<p>Morphology of wound healing on Day 22, showing similarity among experimental groups (hematoxilyn and eosin—A, C, E; Picrosirius Red—B D, F)</p

Optical retardation analysis of collagen on Day 22, showing most organized collagen in SDG, followed by uninjured skin, FDG and CG

<p>Optical retardation analysis of collagen on Day 22, showing most organized collagen in SDG, followed by uninjured skin, FDG and CG</p

Wound healing in different groups throughout experiment (D = Day, CG = Control Group, SDG = Single Dose Group, FDG = Fractionated Dose Group).

<p>Original magnification 10x)</p

Inflammatory infiltrate score—SDG exhibited more leukocytes than other groups through to Day 10.

<p>Inflammatory infiltrate score—SDG exhibited more leukocytes than other groups through to Day 10.</p

Experimental groups and treatment parameters.

<p>Experimental groups and treatment parameters.</p