De Rosa Fernanda Scarmato, Lopez Renata Fonseca Vianna, Thomazine José Antônio, Tedesco Antônio Cláudio, Lange Norbert, Bentley Maria Vitória Lopes Badra
Department of Pharmaceutical Sciences, Faculty of Pharmaceutical Sciences of Ribeirão Preto, University of São Paulo, São Paulo, Ribeirão Preto, Brazil.
Pharm Res. 2004 Dec;21(12):2247-52. doi: 10.1007/s11095-004-7677-3.
In topical photodynamic therapy, 5-ALA and its esters are enzymatically converted in the endogenous photosensitizing compounds such as, for example, protoporphyrin IX (PpIX). In order to elucidate in more detail their enzymatic fate, we have determined in vitro the enzymatic degradation of methyl, butyl, hexyl, and octyl-5-ALA ester derivatives in skin homogenate. Furthermore, in vivo porphyrin accumulation was measured in healthy hairless mice skins.
Hairless mouse skins were homogenized in isotonic phosphate buffer pH 7.4. 5-ALA esters were added, and aliquots were colleted for HPLC-fluorimetric determinations of remaining content of 5-ALA esters. Furthermore, oil-in-water emulsions containing esters were topically applied to mice skin for 6 h, and the amount of accumulated PpIX in the treated areas was determined by quantitative extraction and confocal fluorescence microscopy.
The enzymatic degradation of esters follows pseudo first-order kinetics. The octyl ester had the largest rate constant for enzymatic degradation, followed by hexyl-, butyl-, and methyl-ALA. The long-chained 5-ALA esters, butyl-, hexyl-, and octyl ester, induced significantly more porphyrins than 5-ALA and 5-ALA methyl ester as shown by confocal microscopy and quantitative extraction studies.
5-ALA derivatives differ widely with respect to their enzymatic degradation. The presence of alkyl chains in 5-ALA esters significantly influences the in vitro enzymatic metabolism and the in vivo PpIX formation in healthy hairless mice skins.
在局部光动力疗法中，5-氨基乙酰丙酸（5-ALA）及其酯类会被酶转化为内源性光敏化合物，例如原卟啉IX（PpIX）。为了更详细地阐明它们的酶促命运，我们在体外测定了皮肤匀浆中甲基、丁基、己基和辛基-5-ALA酯衍生物的酶促降解情况。此外，还测量了健康无毛小鼠皮肤中体内卟啉的积累情况。
将无毛小鼠皮肤在pH 7.4的等渗磷酸盐缓冲液中匀浆。加入5-ALA酯，收集等分试样用于高效液相色谱-荧光法测定5-ALA酯的剩余含量。此外，将含有酯类的水包油乳液局部涂抹于小鼠皮肤6小时，通过定量提取和共聚焦荧光显微镜测定处理区域中积累的PpIX量。
酯类的酶促降解遵循准一级动力学。辛酯的酶促降解速率常数最大，其次是己酯、丁酯和甲基-ALA。共聚焦显微镜和定量提取研究表明，长链5-ALA酯，即丁酯、己酯和辛酯，比5-ALA和5-ALA甲酯诱导产生的卟啉明显更多。
5-ALA衍生物在酶促降解方面差异很大。5-ALA酯中烷基链的存在显著影响健康无毛小鼠皮肤中的体外酶促代谢和体内PpIX的形成。
