| In recent years, with the theory of selective photothermolysis having beenproposed, medical laser technology has developed very rapidly in the field of theclinical treatment and skin cosmetic. Q-switched Nd:YAG 1064nm laser hasachieved satisfactory results in the treatment of pigmentation disorders,such asnevus of Ota, melasma, freckles.However,the there is a certain side-effects inthis treatment.There could be two reasons,one is complex cause which exsits inthe pigmentation disorders,the other is that the mechanism of which Q-switchedNd:YAG 1064nm laser is still uncertain.So the wild application of Q-switchedNd:YAG 1064nm laser is limited.Now the understanding of the principle of QswitchedNd:YAG laser is confined in the selective photothermolysis,and somephotobiological effects is still not clear.Object: we adopted a preliminary experimental study to explore the effect ofQ-switched Nd:YAG 1064nm laser irradiation on the biology and melanogenesisof epidermal melanocytes . MethodMethod: In this study, we chosen the most advanced Q-switched Nd:YAG1064nm laser which was used in clinical treatment frequently at present.And thecultured human epidermal melanocytes in vitro were irradiated. Treatmentparameters were: wavelength 1064nm, spot diameter 6mm, frequency 2Hz. Weused optical microscope to observe morphology changes of epidermalmelanocytes;Cell viability of epidermal melanocytes was detected by MTTassay. Cell cycle and apoptosis were tested by flow cytometry; The number andthe length of epidermal melanocytes were measured by dopa stain; The activityof tyrosinase (Tyr) were detected by dopa oxidation assay; The mRNAexpression and protein level of Tyr,TRP-1 and TRP-2 were tested by fluorescentquantitative real-time RT-PCR and westen blot respectively.Results:1. The effects of Q-switched Nd:YAG 1064nm laser irradiation on humanepidermal melanocytes activity by different energy densities:①MTT resultssuggested that only when the energy density of Q-switched Nd:YAG 1064nmlaser irradiation increased to a certain threshold, the melanocytes could bedestroyed. In this experiment, the threshold point of laser energy density was3J/cm2. On this basis we divided melanocytes into control group,1J/cm2 groupand 5J/cm2 group to continue the following experiment.②Melanocyte activity inthe timeliness analysis results indicated that compared with control group therewere no significant differences of activity of the 1J/cm2 group melanocytes invarious time points(P＞0.05).While the activity of the 5J/cm2 group melanocyteswas significantly lower (P＜0.05). After the irradiation of 5J/cm2 energyidensity,the proliferation curve of melanocytes escalated to the bottom within48h,then it raised suddenly.③Under the optical microscopy,We observed thatthe shap of melanocytes of each group did not changed after the laser irradiation immediately. However, the melanocytes of the 3J/cm2 group were more smallerwith fewer dendrites,the length of the dendrites shortened at 24h after irradiation.2. The effects of Q-switched Nd:YAG 1064nm laser irradiation on cell cycleand apoptosis of human epidermal melanocytes:①Within the energy densitywhich did not affect the cell survival, we divided the experiment into controlgroup, 1 J/cm2 group and 3J/cm2 group.②The results of cell cycle suggestedthat the number of cells in S phase increased slightly in the 1J/cm2 group. Whileit was significantly reduced in the 3J/cm2 group. Compared with the controlgroup the differences of each group were statistically significant(P＜0.05).③The results of cell apoptosis suggested that compared with the control group therate of apoptosis of the 1J/cm2 group has no significant difference (P＞0.05),butthe rate of apoptosis of the 3J/cm2 group increased obviously(P＜0.05).3. The effects of Q-switched Nd:YAG 1064nm laser irradiation onmelanogenesis:①Within the energy range which did not affect cell survival,theQ-switched Nd:YAG 1064nm laser irradiation of 1J/cm2 could stimulate theactivity of Tyr, increase the number and the length of dendrites and enhancemRNA expression of Tyr and TRP-1.But there was no change of TRP-2. Thechange of protein level coincided with mRNA expression.②Also within theenergy range which did not affect cell survival,the Q-switched Nd:YAG 1064nmlaser irradiation of 3J/cm2 inhibited the activity of Tyr and decreased the numberand the length of dendrites obviously.It also decreased mRNA expression andprotein level of Tyr,TRP-1 and TRP-2 in varying degrees.Major conclusions:1. There is a certain threshold of energy density on the damage ofmelanocytes. When the energy density greater than the threshold value, theinhibition on melanocyte activity by the Q-switched Nd:YAG 1064nm laser irradiation may increase gradually with the increasing of the energy density.However, inhibition of lethal irradiation is not a continuing nature. Melanocyteactivity can enhance reboundly at some point in time.2. Within the energy range which not affects the cell viability, the Q-switchedNd:YAG 1064nm laser irradiation of the lower energy density can stimulateDNA synthesis of epidermal melanocytes mildly.But the irradiation of the higherenergy density can inhibit DNA synthesis and promote apoptosis of epidermalmelanocytes significantly.3. Within the energy range which not affects the cell viability, the Q-switchedNd:YAG 1064nm laser irradiation could impact melanogenesis.The irradiationof lower energy density could stimulate melanogenesis,while the irradiation ofthe higher energy density has inbibitional effect on melanogenesis.4. Within the energy range which not affects the cell viability, the Q-switchedNd:YAG 1064nm laser irradiation could impact the formation of dendrites.5. There are special photobiological effects on hunman epidermalmelanocytes by Q-switched Nd:YAG 1064nm laser irradiation.
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