ASSESSMENT IN THE RAT MODEL OF THE EFFECTS OF 830 nm DIODE LASER IRRADIATION IN A DIACHRONIC WOUND HEALING STUDY

Abstract

This study examined the effects of 830nm GaAlAs laser therapy on wound-healing processes in the rat skin to demonstrate possible diachronic alterations of cytokines, particularly interleukin-6 (IL-6), following laser irradiation, as IL-6 is one of the most typical, multifunctional cytokines and is moreover easy to detect. Two full-thickness incisional wounds (10 cm long) were made parallel to and 2 cm from the midline of the dorsum with a scalpel in 20 male Wistar rats. Immediately after incision the wounds were closed. The animals were separated into two groups of 10 animals each. Group A served as the unirradiated control group, and experimental group B received 20 seconds of LLLT along the right wound only with an 830 nm 60 mW GaAlAs diode laser, approximately 5 sec per point with the probe head 5 mm from the wound at the four points midway on each quarter of the wound giving a total dose per session of 24 J/cm2. The left hand wound was unirradiated to test for possible systemic reactions. Laser therapy was repeated daily until the 7th postoperative day. Immediately before wounding and daily thereafter until the 8th postoperative day, 6 mm punch biopsies were obtained from skin between the line of the wound and the midline bilaterally on both groups. Biopsies were taken before laser irradiation on days 1 to 7. The specimens were examined histochemically for IL-6 and histologically to follow the morphological wound healing response. IL-6 was measured using a solid-phase ELISA kit employing the multiple antibody sandwich principle. Significant differences were demonstrated between group A (unirradiated control) and specimens from both the irradiated (B1) and unirradiated (B2) sides in group B with higher levels of IL-6 seen on postoperative days 2 (B1: p < 0.001; B2: p < 0.05); 4 (B1 and B2: P < 0.05); 6 (Bl: p < 0.05; B2: p < 0.01); and 8 (B1 and B2: p < 0.01). Histologically, a more controlled inflammatory response was seen in both B1 and B2 specimens compared to the unirradiated control group A, although B1 showed a speedier response than B2 specimens. A greater number of neutrophils appeared earlier and disappeared earlier in the subcutaneous tissues of group B animals, suggesting that both wounds in group B animals finished the inflammatory phase and were entering the proliferative phase of wound healing earlier than those in control group A. These data suggest that 830 nm diode LLLT at the parameters in the present study can increase the levels of IL-6 in healing tissue, and can induce an earlier proliferative phase of wound healing. The data also strongly suggest a systemic response to laser therapy which should be carefully considered in any trial using contralateral unirradiated controls in the same animal to prove or disprove the efficacy of laser therapy.