A key role for the mitochondrial benzodiazepine receptor in cellular photosensitisation with δ-aminolaevulinic acid

• Published in: European journal of pharmacology 2000-10, Vol.406 (2), p.171-180
• Main Authors: Mesenhöller, Maike, Matthews, E.Keith
• Format: Article
• Language: English
• Subjects: Aciflourfen; Aminolevulinic Acid - pharmacology; Animals; Benzodiazepine receptor, mitochondrial; Biological and medical sciences; Chromatography, High Pressure Liquid; Dose-Response Relationship, Drug; Drug toxicity and drugs side effects treatment; Fluorescence; Heme - biosynthesis; Humans; Medical sciences; Miscellaneous; Mitochondria - physiology; Pharmacology. Drug treatments; Photosensitizing Agents - pharmacology; Protoporphyrin IX; Protoporphyrinogen oxidase; Protoporphyrins - metabolism; Radiotherapy. Instrumental treatment. Physiotherapy. Reeducation. Rehabilitation, orthophony, crenotherapy. Diet therapy and various other treatments (general aspects); Rats; Receptors, GABA-A - physiology; Toxicity: skin, dermoskeleton; Tumor Cells, Cultured; Zinc protoporphyrin IX; δ-Aminolaevulinic acid
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/S0014-2999(00)00646-4

The aim of this study was to determine the part played by the mitochondrial benzodiazepine receptor in cellular photosensitisation with the protoporphyrin IX precursor, δ-aminolaevulinic acid. Evaluation of the δ-aminolaevulinic acid-concentration dependence and kinetics of fluorescent protoporphyrin IX accumulation in monolayers of rat AR4 2J pancreatoma cells established a basis for assessing pharmacological modulation of the biosynthetic pathways for protoporphyrin IX production and photocytotoxicity. Iron chelation enhanced the accumulation of photo-active protoporphyrin IX whereas 1-(2-chlorophenyl)- N-methyl- N-(1-methylpropyl)-3-isoquinolinecarboxamide (PK11195), dipyridamole, or 7-(dimethylcarbamoloxy)-6-phenylpyrrolo-[2,1- d]benzothiazepine (DPB), competitive ligands of the mitochondrial benzodiazepine receptor, all diminished protoporphyrin IX accumulation, as did acifluorfen, a mitochondrial protoporphyrinogen oxidase inhibitor. In addition to protoporphyrin IX (Em max: 630 nm), δ-aminolaevulinic acid-treated cells also generated a fluorophore of Em max 580 nm; this compound was identified as Zn-protoporphyrin IX. Mitochondrial benzodiazepine receptor ligands increased the formation of the zinc porphyrin whilst decreasing that of protoporphyrin IX. The involvement of the mitochondrial benzodiazepine receptor in the translocation of porphyrins and the formation of Zn-protoporphyrin IX have wide implications for the use of δ-aminolaevulinic acid in photodynamic therapy.