Dose-effect Relationship Of Q-switch Laser On Skin Pigmentation In Guinea Pigs

Background: Many Skin diseases that break down the cosmetic appearance are more closely related to skin pigmentation, such as post-inflammatory hyperpigmentation (post-inflammatory hyperpigmentation, PIH), freckles and melasma, etc. They are very common clinical diseases, but the methods to treat them was difficult and the effect is uncertainty. Drug therapy is a main choice for traditional treatment, and its basic principles are to inhibit the activity and proliferation of melanocytes, block the formation of black pigment particles and accelerate their degradation. Chemical peel agents, alone or in combination skin bleaching agents, retinoic alcohol and corticosteroids, vitamin C and its derivatives, and chinese herbal drugs are the topical medication for external application. The onset of these drug therapy is often slow, and their efficacy is poor, with more adverse reactions, such as skin irritation, allergies, and even cause a risk of new pigmentation. Therefore, how to find the discipline of skin pigmentation, and treat them effectively and rapidly, has become a difficulty and a interest of dermatologists.Based on "selective photothermolysis theory", Q-switched laser technique reduces heat damage to normal skin, and improve the safety, with less pain and scar. Many patients who have freckles, melasma, post inflammatory hyperpigmentation or other skin hyperpigmentation have been successfully treated by Q-switched laser at home and abroad. However, Q-switched laser technique is an "double edged sword". On one hand, the technique can treat skin pigmentation effectively, on the other hand, in the Asian ethnic group (the Fitzpatrickâ…¢-â…¤type), Q-switched laser in the regular or higher energy parameters, are very easy to trigger a new pigmentation (commonly known as "laser spot response"), so that controversy has raged among pros and cons of such laser treatment technology for skin pigmentation. In recent years, some of the foreign scholars tried low energy of Q-switched laser to treat skin pigmentation and achieved some effect. But this technique is lack of relevant animal experiments and theoretical support, especially dose-effect relationship research. Therefore, research in this area is very important.Objective: To investigate the effect of fluence on the treatment of UVB-induced hyperpigmentation of the brown guinea pig skin using different energy in different Q-switched laser and observe the change of melanin granules and melanocytes of skin. To develop a new"low-energy treatment"model that can be used as reference standard in laser studies, by analyzing the relationship between the effect and the dose.Objects and methods: Ten brown guinea pigs(Zhejiang Chinese Medical University Experimental Animal Center, China),â‘ induced a animal model of pigmentation using ultraviolet B (UVB) radiation;â‘¡Select the Q switched Nd: YAG laser (1064nm) and the Q switched ruby laser (694 nm) in different parameters of treatment respectively to irradiate the guinea pigs'pigmented shin, and evaluate the effect of fluence on the treatment of UVB-induced hyperpigmentation of the brown guinea pig skin;â‘¢Visual, skin multi-functional detector's, confocal laser scanning microscopy(CLSM)'s and histological analyses were accomplished before, during a nd after laser treatment to evaluate the efficacy in the treatment and dose-effect relationship of Q-switch Laser on skin pigmentation in Guinea Pigs.â‘£Data from the study were analyzed with analysis of variance and t test by SPSS(13.0) to determine the relationship between therapeutic effect. p <0.05 was considered statistically significant.Results:â‘ Comparison between the efficacy of different laser: the amount of melanin after Q-694 treatment is less than that of Q-1064 treatment, which meant Q-694 more effective than Q-1064 in the treatment of UVB-induced hyperpigmentation of the brown guinea pig skin.â‘¡Comparison between the efficacy of different doses of the same laser: the optimal effect was obtained at lowest dose group: complete clearance of hyperpigmentation was achieved, with no recurrence in a loner time than other groups; melanin content index (MCI) decreased significantly compared with other groups(F=4.2, P <0.05); the CLSM images showed a drastic decrease in the reflection from epidermal-basal keratinocytes, dendritic melanocytes became invisible, and the staining intensity significantly decreased in basal layers. On the contrary, other groups all developed rebound hyperpigmentation.Conclusions: The histological effect of Q-switched laser on pigmented skin of guinea pigs is closely related to the pulse energy and the frequency, lower energy while relatively more times of treatment may be a better way to get optimal effects. Compared to Q-1064, Q-694 has better efficacy for treating epidermal pigmentation. The confocal laser scanning microscopy might directly observe the melain of the melanocyte.