van Den Boogert J, van Staveren H J, Edixhoven-Bosdijk A, Siersema P D, van Hillegersberg R
Laboratory for Experimental Surgery, Erasmus University, Rotterdam, The Netherlands.
J Photochem Photobiol B. 2000 Jun;56(1):53-60. doi: 10.1016/s1011-1344(00)00059-2.
Administration of 5-aminolevulinic acid (ALA) induces accumulation of the photosensitive compound protoporphyrin IX (PpIX) in certain tissues. PplX can be used as photosensitizer in photodynamic therapy (PDT). More selective or higher PpIX accumulation in the area to be treated could optimize the results of ALA-PDT. Porphobilinogen deaminase (PBGD) is rate-limiting in PpIX formation whereas ferrochelatase converts PpIX into haem by chelation of ferrous iron into PpIX. This results in a moment of close interaction (ferrochelatase binding to PpIX) during which ferrochelatase could selectively be destroyed resulting in an increased PpIX concentration. The aim of the present study was to investigate whether illumination before PDT can selectively destroy ferrochelatase. and whether this results in higher PpIX accumulation and thereby increases the PDT effect. Furthermore, the effect of a second ALA dose was tested.
STUDY DESIGN/MATERIALS AND METHODS: Oesophageal tissue of 60 rats were allocated to 2 groups of 30 animals each. In one group, enzyme and PpIX measurements were performed after ALA administration (200 mg/kg orally, n=20), or a second dose of 200 mg/kg ALA at 4 h (n=10), half of each group with and without illumination at 1 h with 12.5 J/cm diffuser length. In the second group, PDT was performed. Ten animals were illuminated at 3 h after ALA administration with 20 (n=5) or 32.5 J/cm (n=5), 10 animals were illuminated at 1 h (12.5 J/cm) and received intra-oesophageal PDT treatment (20 J/cm) at 3 h (n=5) or 4 h (n=5) after ALA. Additionally, 10 animals received a second dose of 200 mg/kg ALA at 4 h and were illuminated (20 J/cm) at 7 h after the first dose of ALA with (n=5) or without (n=5) illumination at 4 h (12.5 J/cm).
Illumination with 12.5 J/cm at 1 h after ALA administration caused inhibition of the activity of ferrochelatase at 3 and 4 h after ALA (P=0.02 and P<0.001, respectively), but not at 7 h (P=0.3). In animals sacrificed at 4 h the ratio PBGD:ferrochelatase was higher in animals illuminated at 1 h compared to non-illuminated animals (P<0.001). PpIX concentration was highest (42.7 +/- 3.2 pmol/mg protein) at 3 h after ALA administration and did not increase by illumination at 1 h. Administration of a second dose of ALA did not result in higher PpIX accumulation. After PDT, no difference in epithelial or muscular damage was found between the various groups.
Illumination at 1 h after ALA administration can cause selective destruction of ferrochelatase, resulting in a higher ratio of PBGD:ferrochelatase. This does not result in accumulation of more porphyrins, even when a second dose of ALA is given. Therefore, under the conditions used in this study fractionated illumination does not enhance ALA-PDT-induced epithelial ablation of the rat oesophagus.
给予5-氨基乙酰丙酸(ALA)可诱导某些组织中光敏化合物原卟啉IX(PpIX)的积累。PpIX可作为光动力疗法(PDT)中的光敏剂。在待治疗区域实现更具选择性或更高的PpIX积累可优化ALA-PDT的效果。胆色素原脱氨酶(PBGD)在PpIX形成过程中起限速作用,而亚铁螯合酶通过将亚铁离子螯合到PpIX中使其转化为血红素。这会导致一个紧密相互作用的时刻(亚铁螯合酶与PpIX结合),在此期间亚铁螯合酶可能被选择性破坏,从而导致PpIX浓度升高。本研究的目的是探究PDT前的光照是否能选择性地破坏亚铁螯合酶,以及这是否会导致更高的PpIX积累,进而增强PDT效果。此外,还测试了第二次给予ALA剂量的效果。
研究设计/材料与方法:将60只大鼠的食管组织分为两组,每组30只动物。一组在给予ALA(口服200mg/kg,n = 20)后,或在4小时给予第二剂200mg/kg ALA(n = 10)后进行酶和PpIX测量,每组各有一半在1小时时接受12.5J/cm漫射长度的光照,另一半不光照。另一组进行PDT。10只动物在给予ALA后3小时接受20(n = 5)或32.5J/cm(n = 5)的光照,10只动物在1小时接受光照(12.5J/cm),并在给予ALA后3小时(n = 5)或4小时(n = 5)接受食管内PDT治疗(20J/cm)。另外,10只动物在4小时接受第二剂200mg/kg ALA,并在第一剂ALA后7小时接受光照(20J/cm),其中5只在4小时接受光照(12.5J/cm),5只不接受光照。
给予ALA后1小时用12.5J/cm光照导致ALA后3小时和4小时亚铁螯合酶活性受到抑制(分别为P = 0.02和P < 0.001),但7小时时未受抑制(P = 0.3)。在4小时处死的动物中,与未光照动物相比,1小时光照动物的PBGD:亚铁螯合酶比值更高(P < 0.001)。ALA给药后3小时PpIX浓度最高(42.7±3.2pmol/mg蛋白),1小时光照并未使其增加。给予第二剂ALA并未导致更高的PpIX积累。PDT后,各实验组之间在上皮或肌肉损伤方面未发现差异。
给予ALA后1小时光照可导致亚铁螯合酶的选择性破坏,使PBGD:亚铁螯合酶比值升高。即使给予第二剂ALA,这也不会导致更多卟啉的积累。因此,在本研究使用的条件下,分次光照并不能增强ALA-PDT诱导的大鼠食管上皮消融。