色素调节剂对体外培养的人表皮黑素细胞的影响

目的 观察几种色素调节剂对体外培养的人表皮黑素细胞形态及功能的影响.方法 体外培养正常表皮黑素细胞,分别加入合适浓度的表没食子儿茶素没食子酸酯(EGCG)、氢醌(HQ)、烟酰胺(NAA)、α-黑素细胞刺激素(α-MSH)和维生素C磷酸酯镁(AP-Mg)干预细胞72h,测定酪氨酸酶活性和黑素生成量.用黑素体相关蛋白单克隆抗体(NKI-beteb)染色鉴定黑素细胞,观察并摄片.结果 3mmol/L EGCG,0.5mmol/L HQ,6mmol/L AP-Mg与黑素细胞共同孵育72h后,其细胞酪氨酸酶活性及黑素生成受到抑制,但只有EGCG组细胞形态发生变化;50nmol/L α-MSH干预后,细胞酪氨酸酶活性及黑素生成显著增加,形态改变较显著.1mg/mL NAA组细胞酪氨酸酶活性无改变,而黑素生成减少,细胞异形化.结论 EGCG,HQ,NAA,AP-Mg和α-MSH对黑素细胞都有显著的影响,虽然作用于黑素细胞的机制有所不同,但也有一些相似的地方,其具体机理有待于进一步研究.     

UVB致成纤维细胞损伤及两种中药的保护作用研究

目的观察中波紫外线(UVB)辐射后成纤维细胞(FB)DNA光产物环丁烷嘧啶二聚体(CPD s)产生和清除情况及表没食子儿茶素没食子酸酯(EGCG)和黄芩甙的干预作用。方法以30,60,90 m J/cm2UVB照射FB并予EGCG及黄芩甙干预处理,采用免疫细胞化学法在照光后不同时间检测CPD s的产生和清除情况。结果细胞损伤程度随照光剂量加大而加重;30 m J/cm2UVB照射后细胞CPD s生成量在辐射后1 h左右达到高峰,同时细胞也开始清除CP-D s,辐射后4 h内清除速率较快,4 h后清除速率逐渐降低,至24 h基本清除CPD s;EGCG和黄芩甙处理UVB辐射的细胞CPD s少于单纯照光组(P<0.05)。结论UVB辐射可以导致FB的DNA损伤而产生光产物CPD s;细胞损伤程度显示剂量依赖性;细胞自身有修复能力;EGCG和黄芩甙均可降低UVB辐射所致的光产物水平。     

阿魏酸对黑素细胞增殖、黑素合成、酪氨酸酶活性及c-kit、ERK蛋白表达的影响北大核心CSCD

目的 探讨阿魏酸对体外培养的正常人表皮黑素细胞增殖、黑素合成、酪氨酸酶活性及c-kit、ERK蛋白表达的影响.方法 以不同浓度的阿魏酸干预体外培养的正常人表皮黑素细胞,用MTS法分别检测培养24、48、72 h后黑素细胞的增殖活性.用NaOH裂解法检测培养72 h后黑素细胞的黑素合成.用多巴氧化反应法测定培养72 h后黑素细胞酪氨酸酶活性.用Western印迹法测定培养72 h黑素细胞c-kit蛋白及ERK1/2蛋白表达水平.结果 与对照组相比,0.01、0.1、1 mg/ml阿魏酸在作用24、48、72 h后,抑制黑素细胞增殖作用的差异有统计学意义（均P＜ 0.05）,其中1 mg/ml阿魏酸作用72 h抑制黑素细胞活性最高.0.01、0.1、1 mg/ml阿魏酸均能显著影响黑素合成和酪氨酸酶活性,并可降低黑素细胞中c-kit蛋白及ERK1/2蛋白表达水平,与对照组相比,差异有统计学意义（均P＜ 0.05）.结论 阿魏酸可抑制培养的人表皮黑素细胞增殖、黑素合成及酪氨酸酶活性,并可下调黑素细胞c-kit蛋白及ERK蛋白的表达.     

与黑素结合的羟氯喹对长波紫外线诱导HaCaT细胞死亡的光保护机制研究

目的:观察与黑素结合的羟氯喹(HCQ)对细胞内活性氧基(ROS)的清除以及对长波紫外线(UVA)诱导人角质形成细胞(HaCaT细胞)凋亡和坏死的保护.方法:自一株产黑素的嗜麦芽假单胞菌AT18的培养液中分离纯化获得细菌衍生黑素,在体外与不同浓度HCQ结合后处理培养的HaCaT细胞,随后给予半数致死剂量(30 J/cm2)的UVA照射.照射12 h后,以四甲基偶氮唑蓝(MTT)比色法测定细胞存活率;碘化丙啶(PI)染色结合流式细胞仪检测细胞凋亡率;采用二氯荧光素二酯(DCFH-DA)标记法测定细胞内ROS水平.结果:低浓度(10、50 μmol/L)HCQ与黑素结合后能明显保护HaCaT细胞抵抗半数致死剂量(30 J/cm2)UVA照射,尤其是50 μmol/L HCQ 50 mg/L黑素处理组细胞存活率较单纯黑素和单纯HCQ组显著增高(P＜0.05);相反,用高浓度(250 μmol/L)HCQ与黑素结合处理细胞,细胞存活率较单纯黑素和单纯HCQ组减低.与单纯黑素和单纯HCQ组相比,10 μmol/L HCQ与黑素结合还能显著提高细胞内ROS的清除能力和抑制UVA'诱导HaCaT细胞凋亡.结论:低浓度HCQ与黑素结合能协同增强黑素对细胞内ROS的清除,抑制UVA诱导的皮肤细胞凋亡,这些作用很可能关系到治疗皮肤型红斑狼疮时抗疟药的抗光敏机制.     

内皮素拮抗剂对中波紫外线诱导豚鼠色素沉着的观察

目的 探讨内皮素拮抗剂对紫外线诱导豚鼠色素沉着的治疗作用.方法 用中波紫外线(UVB)照射豚鼠皮肤制作色素沉着模型.模型制作成功后,模型动物分为空白对照组(生理氯化钠溶液)、内皮素拮抗剂组及熊果苷组(阳性对照).分别于中波紫外线(UVB)照射前、15 d后及30 d后,用Mexameter(R) MX 18检测豚鼠背部皮肤的黑素指数.连续治疗30 d后比较黑素指数、表皮内黑素细胞数目和黑素含量等指标.结果 UVB照射30 d时,豚鼠背部9块UVB照射区域的黑素指数显著高于照射前(P＜ 0.000 1).外涂1‰内皮素拮抗剂的照射区域30 d后的黑素指数值明显降低,和熊果苷组比较,差异有统计学意义(P＜ 0.000 1).内皮素拮抗组黑素含量指数1明显低于空白对照组(P＜0.05).而3组间黑素含量指数2差异无统计学意义(P＞ 0.05).结论 外涂内皮素拮抗剂对UVB照射诱导豚鼠的色素沉着有一定治疗作用.     

甲氧沙林对培养人表皮黑素细胞黑素合成的影响及信号转导的研究

目的：观察甲氧沙林(8-甲氧补骨脂素，8-MOP)对体外培养的人表皮黑素细胞黑素合成和酪氨酸酶活性的影响，并初步探讨8-MOP诱导表皮黑素细胞分化的信号转导途径。方法：采用4种浓度(10～500μmol／L）的8-MOP作用于体外培养的人表皮黑素细胞，观察不同浓度、不同时间8-MOP对黑素细胞的形态、增殖、酪氨酸酶活性、黑素含量的影响，并用放射免疫法测定8-MOP对细胞内环磷腺苷酸(cAMP)含量的影响。结果：100μmol／L 8-MOP作用黑素细胞120h能显著促进酪氨酸酶的活性，提高黑素细胞的黑素含量，8-MOP抑制黑素细胞增殖和提高细胞内cAMP的水平呈浓度依赖性。结论：8-MOP在体外能直接刺激表皮黑素细胞的黑素合成，上述变化可能通过cAMP依赖的蛋白激酶(PK)A信号通路发挥作用。     

黄芩苷对中波紫外线诱导后BALB/c小鼠表皮光产物形成的干预作用

目的 观察中波紫外线（UVB）诱导BALB/c小鼠皮肤表皮细胞光产物的形成和清除情况,以及黄芩苷的干预作用。方法 将黄芩苷（1 mg/cm2）连续3 d外用于BALB/c小鼠表皮24 h后,采用免疫组织化学法及免疫印迹法检测180 mJ/cm2 UVB辐射后1 h、24 h和48 h小鼠表皮内环丁烷嘧啶二聚体（CPD）的产生和清除情况。结果 CPD仅在接受UVB辐射的小鼠皮肤内出现。相对于UVB辐射后1 h光产物的平均值,UVB辐射组1 h、24 h和48 h,CPD的信号强度分别为（100 ± 5.22）％、（75.34 ± 8.22）％和（42.11 ± 3.24）％;经过黄芩苷处理后的小鼠接受UVB辐射后1 h、24 h和48 h,CPD的信号强度分别为（81.45 ± 5.22）%、（32.14 ± 6.33）%和（5.21 ± 3.15）%;而丙酮处理后的小鼠接受UVB辐射后1 h、24 h和48 h,CPD的信号强度分别为（106 ± 8.21）%、（70.23 ± 4.13）%和（41.22 ± 4.21）%。结论 外用黄芩苷能抑制UVB辐射诱导光产物的形成,并在48 h内加速光产物的清除。黄芩苷是一种有效的紫外线防护剂。     

不同浓度阿魏酸溶液对人表皮黑素细胞增殖的影响

目的:观察不同浓度阿魏酸溶液对体外培养的正常人表皮黑素细胞增殖的影响。方法:采用L-DOPA染色法鉴定正常人表皮黑素细胞;分别用0.01、0.1、1 mg/m L的阿魏酸溶液处理正常人表皮黑素细胞24 h、48 h、72 h,采用MTS法测定黑素细胞增殖活性。结果:与未用阿魏酸溶液处理的对照组相比,0.01、0.1、1 mg/m L阿魏酸在作用24、48、72 h后,黑素细胞增殖作用均受到抑制,差异均有统计学意义(P值均0.05);不同浓度与时间有交互作用(F=2.48,P=0.034),随着阿魏酸溶液浓度的增加及作用时间的延长,对黑素细胞的抑制作用增强。结论:阿魏酸溶液可以抑制正常人表皮黑素细胞的增殖,提示其在治疗黄褐斑等疾病方面具有良好的前景。     

EGCG对中波紫外线诱导HaCaT细胞p53基因和蛋白表达的实验研究

目的:研究表没食子儿茶素没食子酸酯(EGCG)对中波紫外线(UVB)照射诱导永生化角质形成细胞株-HaCaT细胞的p53 mRNA和p53蛋白表达的影响。方法:以一定剂量UVB照射HaCaT细胞,并以200μg/mL EGCG处理照射后的HaCaT细胞,分别用RT-PCR法和Western blot方法检测各处理条件下p53 mRNA和/或p53蛋白的表达水平。结果:30 mJ/cm2的UVB照射后HaCaT细胞的p53 mR-NA和p53蛋白表达逐渐增加,4 h达到峰值,4 h后随照射剂量增加而增加,24 h后有所恢复;加入EGCG可下调UVB诱导的表达作用。结论:UVB照射对HaCaT细胞p53 mRNA和p53蛋白的诱导表达有时效性与量效性,EGCG可下调UVB照射的这种诱导作用。     

芦荟素抑制人表皮黑素细胞酪氨酸酶的最佳浓度选择

目的:研究抑制人表皮黑素细胞酪氨酸酶的芦荟素最佳浓度。方法:选择不同浓度的中药单体芦荟素(分别为0.010、0.001、0.100、1.000和10.000mmol/L),作用于体外培养的人表皮黑素细胞,测定黑素细胞增殖率、酪氨酸酶活性和黑素含量。结果:10.000mmol/L芦荟素组导致黑素细胞死亡;与正常对照组相比,芦荟素浓度大于0.100mmol/L的黑素细胞增殖率明显下降(P<0.05);所有实验组黑素细胞的酪氨酸酶活性和黑素含量都显著降低(P<0.001)。结论:低浓度的芦荟素(0.001～0.010mmol/L)在不影响黑素细胞增殖的情况下可以显著抑制酪氨酸酶活性和黑素的合成。     

Polydeoxyribonucleotide promotes cyclobutane pyrimidine dimer repair in UVB-exposed dermal fibroblasts

BACKGROUND: DNA is the main cellular chromophore for ultraviolet B (UVB). Its absorption leads to the generation of typical photoproducts. The most frequent types (about 80%) are cyclobutane pyrimidine dimers (CPDs). Several studies have suggested that treatment with deoxyribonucleosides can protect some cell types from DNA damage. The aim of this work was to evaluate the ability of the polydeoxyribonucleotide (PDRN) to protect human dermal fibroblasts from UVB-induced DNA damage. METHODS: Human dermal fibroblasts were irradiated with 600 mJ/cm(2) of UVB radiation. Cells were analyzed at increasing time points from irradiation to study the recovery from UVB-induced DNA photodamage. Damage repair was subsequently assessed by immunocytochemical analysis of CPDs levels and by measurement of p53 protein expression. RESULTS: The extracellular addition of 100 microg/ml PDRN immediately after irradiation caused a strong activation of p53 protein in the first 24 h. This signal was accompanied by an increase in CPDs repair rates at early time points of recovery. CONCLUSIONS: The addition of PDRN to the culture medium supports CPDs repair probably providing a faster supply of precursors for the deoxyribonucleotide triphosphates pool necessary to UVB-damaged cells. This condition could promote the action of the salvage pathway, thereby accelerating DNA repair, but other inducible responses linked to increased p53 expression could be involved.     

Baicalin protects human fibroblasts against ultraviolet B-induced cyclobutane pyrimidine dimers formation

Exposure to ultraviolet B (UVB) irradiation is a major risk factor for the development of skin cancer. Therefore, it is important to identify agents that can offer protection against UVB-caused DNA damage. Photocarcinogenesis is caused largely by mutations at the sites of incorrectly repaired DNA photoproducts, of which the most common are the cyclobutane pyrimidine dimers (CPDs). In this study, a DNA damage model of UVB irradiation-induced fibroblasts was established. The immunocytochemical staining, immuno dot blotting and Western blotting were employed in the study. We demonstrated that pre-treatment of fibroblasts with Baicalin dose-dependently reduced the amount of UVB-generated CPDs. Compared with UVB irradiated cells, UVB-induced p53 accumulation was less pronounced in Baicalin-treated cells. Taken together, these results suggest that Baicalin prevent CPDs formation induced by UVB. Baicalin is therefore a promising protective substance against UVB radiation.     

紫外线对皮肤角质形成细胞和成纤维细胞产生MMP-1和MMP-3的影响

目的:研究中波紫外线辐射对体外培养的表皮角质形成细胞和真皮成纤维细胞产生基质金属蛋白酶-1(MMP-1)和MMP-3的直接和间接影响,研究绿茶中的主要活性成分表没食子儿茶酚没食子酸酯(EGCG)对此影响的保护作用。方法:体外培养角质形成细胞株HaCaT和真皮成纤维细胞,中波紫外线辐射、不同浓度IL-6刺激及EGCG处理后,ELISA方法测定上清液中Pro-MMP-1和MMP-3蛋白含量,半定量RT-PCR方法测细胞中mRNA含量。结果:UVB30mJ/cm2辐射后角质形成细胞分泌的pro-MMP-1和MMP-3并未增加(P>0.05),真皮成纤维细胞合成和分泌MMP-1和MMP-3mRNA含量和蛋白水平均显著增加(P<0.05),IL-6(8、16、24pg/mL)可显著增加成纤维细胞产生MMP-1和MMP-3(P<0.05)。EGCG(0.15、0.3mM)能够显著抑制紫外线诱导成纤维细胞产生MMP含量的增加(P<0.05),但IL-6刺激成纤维细胞所产生的MMP-1和MMP-3的增加不受EGCG的影响(P>0.05)。结论:中波紫外线辐射并不能直接导致角质形成细胞分泌MMP-1和MMP-3增加,但紫外线辐射后角质形成细胞分泌的IL-6可促进成纤维细胞产生MMP。EGCG对IL-6刺激成纤维细胞产生MMP增加没有影响,但它可以显著抑制紫外线辐射直接导致的成纤维细胞产生MMP-1和MMP-3的增加,对防治皮肤光老化可能有一定作用。     

High levels of 8-hydroxy-2'-deoxyguanosine appear in normal human epidermis after a single dose of ultraviolet radiation

Major photoproducts induced by carcinogenic ultraviolet (UV) radiation are the cylobutane pyrimidine dimers (CPDs) and pyrimidine-pyrimidone (6-4) photoproducts (6-4 PPs). 8-Hydroxy-2 -deoxyguanosine (8-OHdG) is also a DNA base-modified product generated by reactive oxygen species in conditions of ultraviolet stress, Although UVB-induced CPDs and 6-4 PPs have been investigated in animal and human skin, little is known about the role of 8-OHdG in UVB-induced human skin damage or carcinogenesis. Normal human skin from three volunteers was exposed to UV radiation, and the time course of induction and removal of 8-OHdG was examined by immunohistochemical analysis with catalysed signal amplification on formalin-fixed paraffin sections. Formation of CPDs and 6-4 PPs was also examined by immunostaining on the same skin specimens. Control epidermis with no exposure to UV radiation showed little nuclear staining of 8-OHdG, but an increased level of 8-OHdG was clearly observed in epidermis biopsied after irradiation. Induced 8-OHdG can rapidly be removed from nucleus during the first 24-48 h, as the staining intensity diminished gradually, almost reaching the control level by 72-96 h after irradiation. Staining for CPDs or 6-4 PPs revealed induction of these photoproducts in human skin, although 6-4 PP-positive cells disappeared more rapidly than those that stained for CPDs or 8-OHdG. Together with protective effect of antioxidants, our results indicate that not only CPDs and 6-4 PPs but also 8-OHdG may play a significant part in UV carcinogenesis.     

Photoadaptation to ultraviolet (UV) radiation in vivo: photoproducts in epidermal cells following UVB therapy for psoriasis

BACKGROUND: Ultraviolet (UV) radiation is mutagenic and induces specific DNA lesions in human skin that are often found at dipyrimidine sites. These photoproducts are likely to be biologically relevant regarding skin carcinogenesis, as p53 mutations in skin tumours are most often found at these UV radiation-specific sites within DNA. Psoriasis patients receiving long-term phototherapy are at an increased risk of non-melanoma skin cancers. OBJECTIVES: The aim of this study was to quantify DNA photoproducts in human epidermis in vivo following consecutive doses of UVB and to investigate variations in DNA damage according to skin type, UVB dose and age. METHODS: Eleven psoriasis patients receiving UVB phototherapy three times a week were recruited and underwent skin biopsies on a non-sun-exposed site before starting phototherapy and after three, nine and 18 UVB exposures. A biopsy was also taken at least 4 weeks after stopping phototherapy. DNA was extracted from separated epidermis and three types of photoproducts were quantified using a novel 32P high-performance liquid chromatographic technique. RESULTS: The mean level of cyclobutane dipyrimidine dimers (CPDs) after three doses of UVB (dose range 0.03-0.15 J cm-2) was 3.2 (range 0.8-8.9) photoproducts per 106 normal nucleotides for TT=T dimers and 4.5 (range 0-14) per 106 normal nucleotides for TT=C dimers. The mean levels of TT-C 6-4 photoproducts after three doses of UVB were very low (0.2, range 0-1.8). Overall, the levels of TT=T and TT=C reached a plateau at three exposures and were found to decrease for subsequent exposures despite increasing UVB doses. Skin type was negatively associated with mean levels of CPDs. However, significant differences in levels of photoproducts were seen between individuals, even after adjusting for skin type. No association was found between challenge dose of UVB and photoproduct yield in this study. CONCLUSIONS: This study showed a great individual variation in the accumulation of DNA photoproducts following exposure to repetitive doses of UVB. Photoadaptive responses of human skin involving DNA repair, tanning and epidermal thickening are likely to explain the overall lack of increase in DNA lesions throughout phototherapy. This in vivo study confirms that psoriasis patients produce a significant amount of DNA photolesions at suberythemal doses of UVB. Further work is needed to investigate which host factors are most likely to predict susceptibility to UV radiation-induced DNA damage.     

Photoprotective potential of Cordyceps polysaccharides against ultraviolet B radiation-induced DNA damage to human skin cells

Summary Background Ultraviolet (UV) radiation causes DNA damage resulting in photoageing and skin cancer. UVB (290–320 nm) interacts directly with DNA, inducing two major photoproducts: cyclobutane‐pyrimidine dimers (CPDs) and (6‐4) pyrimidine‐pyrimidone photoproducts. Cordyceps sinensis (Berk.) Sacc. is a medicinal fungus with reported anticancer and cytoprotective effects. Objectives To investigate genoprotective effects of polysaccharide‐rich Cordyceps mycelial components against UVB‐induced damage in normal human fibroblast cells. Methods Cultured human fibroblasts (BJ cells) were treated for 30 min and, separately, for 24 h with hot water extract of Cordyceps fungal mycelia or exopolysaccharides. Cells were washed, irradiated with UVB (302 nm), and immediately lysed, after which DNA damage, as strand breaks, was measured using an enzyme‐assisted comet assay that detects CPDs. Results DNA damage in UVB‐irradiated cells was significantly lowered (P < 0·01) with Cordyceps pretreatment. Similar results were seen with 30 min and 24 h pretreatment. Specifically, and in comparison with irradiated cells with no Cordyceps pretreatment, there was a 27% reduction in CPDs in irradiated cells with 24 h pretreatment with 200 μg mL^?1 of the hot water Cordyceps extract, and a 34% reduction with 24 h pretreatment with 200 μg mL^?1 of the exopolysaccharide extract. Conclusions Clear evidence of protection against UVB‐induced CPDs was seen with Cordyceps mycelial extracts. Results indicate that Cordyceps may offer photoprotection and lower the risk of basal cell carcinoma, the main skin cancer caused by CPDs. Further study is needed to identify protective mechanisms.     

黄芩甙对紫外线诱导人正常黑素细胞黑素合成的抑制作用研究

体外培养黑素细胞（MC）分别经隔日长波紫外线（UVA）或中波紫外线（UVB）照射和（或）黄芩处理后，观察细胞增殖情况，测定酪氨酸酶活性和黑素含量。结果：（1）UVA使细胞增殖增快，但剂量较大时增殖减发电量；UVB使细胞增殖减慢。二者均可使细胞酪氨酸酶活性和黑素含量高于对照组。（2）黄芩具有抑制UVA和UVB诱导的MC增殖、酪氨酸酶活性及黑素合成改变的作用。提示黄芩能抑制UVA和UVB诱导的细胞反应，还可通过抑制酪氨酸酶减少MC黑素合成。     

黄芪甲苷对HaCaT细胞的光保护效能及其机制

目的 观察黄芪甲苷对于中波紫外线（UVB）损伤的人表皮细胞的保护作用,探讨其相关机制。方法 将培养的永生化人皮肤角质形成细胞（HaCaT细胞）分为对照组、UVB组、黄芪甲苷组和UVB + 黄芪甲苷组,其中UVB组和UVB + 黄芪甲苷组细胞接受50 mJ/cm2 UVB照射,加药组加入不同浓度的黄芪甲苷（10、20、50、100、200 mg/L）进行干预,24 h后CCK8法检测细胞活性。根据CCK8法检测结果选择最佳药物浓度（20 mg/L）进行后继实验。照光后继续培养24 h,流式细胞仪检测细胞内活性氧（ROS）水平,Western印迹法检测HaCaT细胞中p53、p38、基质金属蛋白酶9（MMP-9）和高迁移率族蛋白A1（HMGA-1）的表达。 结果 与对照组相比,10 mg/L和20 mg/L黄芪甲苷组对HaCaT细胞的增殖活性无明显影响（F = 1.32,P > 0.05）,50、100和200 mg/L黄芪甲苷对细胞增殖活性有一定抑制作用（F = 20.20,P < 0.05）;UVB组与对照组比较,HaCaT细胞增殖活性显著下降（F = 99.00,P < 0.01）。与UVB组相比,UVB + 黄芪甲苷（10 ~ 200 mg/L）组HaCaT细胞增殖活性不同程度升高（F = 19.08,P < 0.01）,其中UVB + 20 mg/L黄芪甲苷组升高程度最高。进一步实验表明,与UVB组相比,UVB + 20 mg/L黄芪甲苷组ROS产生受到明显抑制（t = 21.12,P < 0.01）。Western印迹结果表明,与对照组比较,UVB组p53、p38、MMP-9和HMGA-1蛋白的表达升高（均P < 0.01）,而UVB + 20 mg/L黄芪甲苷组细胞内p53、p38、MMP-9和HMGA-1蛋白的表达水平较UVB组显著降低（P < 0.01）。 结论 黄芪甲苷可有效抑制UVB引起的表皮细胞光损伤。