delta-aminolevulinic acid (ALA) promotes the generation of reactive oxygen species (ROS). Accumulation of ALA, as occurs in acute intermittent porphyria (AIP), is a potential endogenous source of ROS, which can then exert oxidative damage to cell structures. In this work we investigated the role of pharmacological concentrations of melatonin on the deleterious effect of ALA and its effect on porphyrin biosynthesis. Rat cerebellum incubations were carried out with either ALA (1.0 mM) together with increasing concentrations of melatonin (0.1-2.0 mM) or 2.0 mM melatonin together with varying ALA concentrations (0.05-2.0 mM) for different times (1-4 hr). ALA-induced lipid peroxidation was significantly diminished by melatonin in a concentration-dependent manner. In all conditions 2.0 mM melatonin restored malondialdehyde levels to control values. In incubations without ALA, melatonin markedly reduced (36-40%) the basal levels of lipid peroxidation when compared with the corresponding controls. ALA uptake and porphyrin accumulation were increased 30% in incubations with 1.0-2.0 mM ALA for 4 hr in the presence of 2.0 mM melatonin, providing evidence for the involvement of ALA-promoted ROS in the damage of enzymes related to porphyrin biosynthesis. These results are further support for the protective role of melatonin against oxidative damage induced by ALA; this protective action of melatonin is probably due to melatonin's antioxidant and free radical scavenger properties. The development of a new therapeutic approach for AIP patients employing melatonin alone or in combination with conventional treatments should be considered.
Summary Tetrapyrrole synthesis in CNCM-1221 cells exposed to 0.6 mm aminolaevulinic acid (ALA) was found to be approximately linear over a 6-h period of incubation. The rate was not significantly affected by cell density over a range of 0.015 to 0.15 x 106 cells cm-2 (final cell density). Tetrapyrrole synthesis was not affected by GABA or glutamic acid in concentrations up to 6 mm and 2.72 mm respectively, suggesting that these amino acids, which are similar in structure to ALA, do not competitively inhibit the ALA uptake pathway in these cells. Pre-exposure to haem arginate (up to 100 gM) was inhibitory, presumably by suppression (through the inhibition of ALA synthase) of an endogenous component of the response. The ALA-stimulated response was not modified by co-exposure to AIA (up to 100 mg ml-'). Despite significant reduction of protein synthesis, the porphyrinogenic response of cells exposed to ALA was unaffected by cycloheximide (10 gg ml-') or actinomycin D (10 gg ml-') even when cells were preincubated with these agents for 3 h before ALA exposure. Fetal bovine serum (10%) inhibited tetrapyrrole synthesis by 30% but increased the rate of porphyrin export by cells by a factor of 1.5. The uptake of [14C]ALA was shown to be strongly influenced by the density of the cultures. In dense cultures (final cell density of approximately 0.15 x 106 cells cm-2), the ALA uptake rate was less than 0.8 compared with a maximum rate of 4.2 fmol per cell h-' at a cell density of 0.02 x 106 cells cm-2. Since tetrapyrrole synthesis is less affected than ALA uptake by cell density, the resultant discrepancy in ALA incorporation occurrng in dense cultures implies that endogenous ALA synthesis is induced in these cells. ALA uptake was not affected by cycloheximide or actinomycin D in serum-free conditions. However, fetal bovine serum decreased external ALA uptake by about 50%. This effect was abrogated by preincubation with cycloheximide.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.