Chu E S M, Wu R W K, Yow C M N, Wong T K S, Chen J Y
Biomedical Science Section, School of Nursing, Hong Kong Polytechnic University, China.
Cancer Chemother Pharmacol. 2006 Sep;58(3):408-14. doi: 10.1007/s00280-005-0169-2. Epub 2006 Jan 12.
5-aminolevulinic acid (ALA) and its hexylester (ALA-H) are the drugs currently used in photodynamic therapy (PDT). The side effect, especially the long-term side effect of these drugs is a problem of concern in this field, which has not been clearly understood yet.
The normal lymphocytes and nasopharyngeal carcinoma (NPC) cells were used as the cell models to evaluate the side effects of ALA or ALA-H in the absence of light or under sub-lethal doses of light.
The cytotoxic and DNA-damaging effects of ALA or ALA-H on lymphocytes and NPC cells were studied by means of the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and the alkaline comet assay. ALA at 0.75 mM concentration and ALA-H at 10-microM concentrations were selected in the studies. This is because under these concentrations, ALA- or ALA-H-mediated PDT can destroy most NPC cells in vitro. The intracellular distributions of the protoporphyrin IX (PpIX), induced by the ALA or ALA-H, were measured by the confocal laser scanning microscope to provide more information for understanding the DNA damage.
The incubation of 0.75 mM ALA or 10 microM ALA-H alone (without light) did not cause DNA damage as well as the considerable cytotoxic effect on NPC cells. However, after ALA (0.75 mM) incubation and without light irradiation, the serious cytotoxicity and remarkable DNA damage were found in lymphocytes. When the lymphocytes were incubated with ALA-H (10 microM) alone (in the absence of light), no DNA damage could be detected and a slight cytotoxic effect was found. Both ALA and ALA-H induced PpIX in the lymphocytes. The fluorescence images of PpIX intracellular localization demonstrated that the PpIX diffused into the nuclear region in ALA-(0.75 mM)-incubated lymphocytes but not existed in the nucleus of ALA-H(10 microM)- incubated lymphocytes, providing an explanation for the facts that ALA (0.75 mM) induced the DNA damage while ALA-H (10 microM) did not.
These results suggested that the genotoxic potential of lymphocytes seems high for ALA (0.75 mM) and could be excluded for ALA-H (10 microM).
5-氨基酮戊酸（ALA）及其己酯（ALA-H）是目前光动力疗法（PDT）中使用的药物。这些药物的副作用，尤其是长期副作用，是该领域一个备受关注但尚未完全清楚的问题。
以正常淋巴细胞和鼻咽癌（NPC）细胞为细胞模型，评估ALA或ALA-H在无光或亚致死剂量光照条件下的副作用。
采用3-(4,5-二甲基噻唑-2-基)-2,5-二苯基四氮唑溴盐法和碱性彗星试验，研究ALA或ALA-H对淋巴细胞和NPC细胞的细胞毒性及DNA损伤作用。研究中选择0.75 mM浓度的ALA和10 μM浓度的ALA-H。这是因为在这些浓度下，ALA或ALA-H介导的光动力疗法可在体外破坏大多数NPC细胞。通过共聚焦激光扫描显微镜测量ALA或ALA-H诱导产生的原卟啉IX（PpIX）的细胞内分布，为理解DNA损伤提供更多信息。
单独孵育0.75 mM ALA或10 μM ALA-H（无光）对NPC细胞未造成DNA损伤及明显的细胞毒性作用。然而，在孵育ALA（0.75 mM）且无光照射后，淋巴细胞出现严重的细胞毒性和明显的DNA损伤。当淋巴细胞单独与ALA-H（10 μM）孵育（无光）时，未检测到DNA损伤，仅发现轻微的细胞毒性作用。ALA和ALA-H均可在淋巴细胞中诱导产生PpIX。PpIX细胞内定位的荧光图像显示，在孵育ALA（0.75 mM）的淋巴细胞中，PpIX扩散至核区域，而在孵育ALA-H（10 μM）的淋巴细胞细胞核中未出现，这为ALA（0.75 mM）诱导DNA损伤而ALA-H（10 μM）未诱导提供了解释。
这些结果表明，对于ALA（0.75 mM），淋巴细胞的遗传毒性潜力似乎较高，而对于ALA-H（10 μM）则可排除。
