Porphobilinogen and delta-amino levulinic acid in acute porphyria

Melatonin protects against lipid peroxidation induced by delta-aminolevulinic acid in rat cerebellum, cortex and hippocampus

The in vitro and in vivo effect of melatonin on delta-aminolevulinic acid-induced lipid peroxidation in rat cerebellum, cortex and hippocampus was determined. The concentration of malonaldehyde and 4-hydroxyalkenals was assayed as an index of induced membrane oxidative damage. The rise in malonaldehyde+4-hydroxyalkenals concentrations induced by delta-aminolevulinic acid in cerebellar homogenates was concentration-dependent (P < 0.001) and also time-dependent in cerebellar, cortical and hippocampal homogenates (P < 0.01). In vitro melatonin and vitamin E protected, in a concentration-dependent manner, against delta-aminolevulinic acid-induced lipid peroxidation in cortical, cerebellar and hippocampal homogenates. In in vivo experiments it was demonstrated that delta-aminolevulinic acid-induced lipid peroxidation (40 mg/kg) in cerebellum and hippocampus was reduced by acute melatonin (10 mg/kg) treatment (P < 0.05). The results show that both in vitro and in vivo melatonin confers protection against delta-aminolevulinic acid-induced oxidative toxicity in brain regions. The findings suggest that melatonin may be useful in reducing neural damage in individuals suffering from acute intermittent porphyria.

delta-Aminolevulinic acid effects on neuronal and glial tumor cell lines

Acute intermittent porphyria (AIP) or precursor syndrome is a well described neuropathic clinical entity with incompletely known etiology. The most prominent biological abnormalities associated with this syndrome are elevations in serum and hepatic delta-aminolevulinic acid (ALA) and porphobilinogen (PBG). We determined the impact of ALA and PBG on human neuroblastoma and glioblastoma tumor cell survival as measured by the MTT assay. ALA proved to be cytotoxic in neuroblastoma cells, while PBG lacked cytotoxic effects. This cytotoxic effect of ALA could be enhanced by deferoxamine and diminished by heme, presumably through modulation of ALA synthesis. In conclusion, ALA excess may prove to be associated with the development of neuropathy in AIP.

Endogenous protoporphyrin IX, a clinically useful photosensitizer for photodynamic therapy

The tissue photosensitizer protoporphyrin IX (PpIX) is an immediate precursor of heme in the biosynthetic pathway for heme. In certain types of cells and tissues, the rate of synthesis of PpIX is determined by the rate of synthesis of 5-aminolevulinic acid (ALA), which in turn is regulated via a feedback control mechanism governed by the concentration of free heme. The presence of exogenous ALA bypasses the feedback control, and thus may induce the intracellular accumulation of photosensitizing concentrations of PpIX. However, this occurs only in certain types of cells and tissues. The resulting tissue-specific photosensitization provides a basis for using ALA-induced PpIX for photodynamic therapy. The topical application of ALA to certain malignant and non-malignant lesions of the skin can induce a clinically useful degree of lesion-specific photosensitization. Superficial basal cell carcinomas showed a complete response rate of approximately 79% following a single exposure to light. Recent preclinical studies in experimental animals and human volunteers indicate that ALA can induce a localized tissue-specific photosensitization if administered by intradermal injection. A generalized but still quite tissue-specific photosensitization may be induced if ALA is administered by either subcutaneous or intraperitoneal injection or by mouth. This opens the possibility of using ALA-induced PpIX to treat tumors that are too thick or that lie too deep to be accessible to either topical or locally injected ALA.

Light-microscopic and microspectrofluorometric characterization of porphyrin-containing astrocytes in mouse optic nerve

Fluorescence spectroscopy has been employed to investigate the emission spectrum of unusual orange-red fluorescence found in the mouse optic nerve. Comparison of the spectra obtained with those of a number of porphyrins used as standards (protoporphyrin, uroporphyrin, and coproporphyrins) shows that the autofluorescence excited at about 400 nm (Soret band) is due to the presence of a mixture of these or other porphyrins in the nerve. Phase contrast, dark-field, and light-microscopy techniques demonstrated that the fluorescence is emitted by dense, coarse inclusions in the cytoplasm of astrocytes. The inclusions also exhibit high activity of endogenous peroxidase, a heme (porphyrin)- containing enzyme, characteristic for process of phagocytosis. A possible participation of these astrocytes in phagocytosis is delineated.

Experimental porphyric neuropathy: a preliminary report

An experimental model for the study of porphyric neuropathy is presented. Injection of either tetraphenyl-porphinesulfonate (TPPS), hematoporphyrin derivative (HpD), or delta-amino-levulinic acid (ALA) into mice resulted in markedly decreased motor nerve conduction velocity (MNCV). THe MNCV returned to normal within one week following the injection of large doses of ALA, and within three weeks following the injection of close to lethal doses of HpD, but there was no recovery of nerve function within 50 days following injection of substantially smaller doses of TPPS. Ultrastructural examination of motor nerves at various times following TPPS injection revealed the gradual development of structural abnormalities. Ultrastructural examination of the same nerves after a single dose of either ALA or HpD failed to demonstrate any abnormalities. The present observations call for precaution as to the use of TPPS as photosensitizer in human cancer treatment.