Effect of reactive oxygen species promoted by delta-aminolevulinic acid on porphyrin biosynthesis and glucose uptake in rat cerebellum.

1. delta-Aminolevulinic acid (ALA) has been reported to promote reactive oxygen species (ROS). Overproduction and accumulation of ALA, as it occurs in acute intermittent porphyria (AIP), can be the origin of an endogenous source of ROS, which can then exert their oxidative damage to cell structures. 2. To investigate the induction of lipid peroxidation by ALA, thiobarbituric acid reactive substances and conjugated diene formation were measured by using minimal tissue units (MTUs) obtained from rat cerebellum. Malondialdehyde levels increased with ALA concentration and incubation time (72% at 1.0 mM ALA and 127% at 4.0 mM ALA for 4 hr), and conjugated diene formation was enhanced 50% in incubations with 1.0 mM ALA for 4 hr. 3. ALA-promoted ROS by exposure of cerebellum MTUs to 1.0 mM ALA during different intervals (1-4 hr) was partly reduced by the addition of antioxidants such as superoxide dismutase (SOD; 50 U/ml), catalase (4.5 microM) and dimethylsulfoxide (150 mM), demonstrating the involvement of O2-., H2O2 and OH. in ALA autooxidation. 4. Porphobilinogen biosynthesis was 170% increased when cerebellum MTUs were incubated with 1.0 mM ALA for 4 hr in the presence of SOD, suggesting that protein damage was promoted by ALA autooxidation. 5. These findings provide the first experimental evidence of the involvement of ALA-promoted ROS in the damage of proteins related to porphyrin biosynthesis, specially ALA-D. Oxidation of this enzyme would lead to further accumulation of ALA in AIP patients, which may be the origin of the well-known neuropsychiatric manifestations.

In vivo protection by melatonin against delta-aminolevulinic acid-induced oxidative damage and its antioxidant effect on the activity of haem enzymes.

Accumulation of delta-aminolevulinic acid (ALA), as it occurs in acute intermittent porphyria, is a potential endogenous source of reactive oxygen species (ROS) which can then produce oxidative damage to cell structures and macromolecules. This in vivo study investigated whether melatonin could prevent the deleterious effects of ALA. Rats were injected i.p. for 2 weeks with ALA (40 mg/kg on alternate days) and/or with melatonin (50 microg/kg or 500 microg/kg daily). Administration of pharmacological doses of melatonin reduced and/or prevented ALA-induced lipid peroxidation (LPO) in both cerebral cortex and cerebellum, providing further evidence of melatonin's action as a ROS scavenger. Administration of pharmacological concentrations of melatonin to ALA-injected rats showed the protective properties of melatonin on the activities of both porphobilinogen-deaminase and delta-aminolevulinate dehydratase (ALA-D) in the cerebral cortex; the effect on ALA-D activity was unexpectedly high (at least 6-fold), indicating that, besides acting as a scavenger of hydroxyl radicals, melatonin may exert its protection on ALA-D through other mechanisms, such as increasing mRNA levels of antioxidant enzymes or/and inducing glutathione peroxidase activity. The possibility that changes in the expression of antioxidant enzymes could affect the expression of other proteins, even those not related to the cellular ROS homeostasis, should also not be discarded. The potential use of melatonin as an antioxidant and for its reactivating properties in the treatment of acute porphyrias is considered.

Rat harderian gland porphobilinogen deaminase: characterization studies and regulatory action of protoporphyrin IX.

Properties of purified porphobilinogen deaminase (PBG-D; EC 4.3.1.8) from rat harderian gland are here presented. The enzyme behaves as a monomer of Mr 38 +/- 2 kDa and is optimally active at pH 8.0-8.2. Its activation energy, determined by an Arrhenius plot, is 76.1 kJ/mol. Initial velocity studies showed a linear progress curve for uroporphyringen I formation and a hyperbolic dependence of the initial rate on substrate concentration, indicating the existence of a sequential displacement mechanism. Apparent kinetic constants, Km and Vm, calculated at 37 degrees C and pH 8.0 were 1.1 microM and 170 pmol/min mg, respectively. The pH dependence of the apparent kinetic parameters revealed the ionization of residues with pKAES and pKBES of 7.4 +/- 0.1 and 8.6 +/- 0.1, respectively, and a pKE value of 8.0 +/- 0.1. Incubation of PBG-D with 5.0 mM N-ethylmaleimide and 5.0 mM 5,5'-dithiobis(2-nitrobenzoic acid) at pH 8.0 led to inhibitions of 70 and 50%, respectively. The effect of pH, as well as the effect of thiol reagents, on enzyme activity strongly suggests the involvement of cysteine residue(s) in the mechanism of uroporphyrinogen I biosynthesis, in both the catalytic reaction and the substrate binding. Rat harderian gland PBG-D activity decreased with increasing concentrations of protoporphyrin IX, reaching a 40% inhibition at the in vivo concentration of the porphyrin and 7 microM PBG. Even at saturating concentrations of substrate, inhibition by protoporphyrin was not completely reversed. So, accumulated porphyrin may act as an regulator of PBG-D activity in rat harderian gland.

Melatonin's antioxidant protection against delta-aminolevulinic acid-induced oxidative damage in rat cerebellum.

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.

Porphyrinogenesis in rat cerebellum. Effect of high delta-aminolevulinic acid concentration.

1. delta-Aminolevulinic acid (ALA) uptake as well as precursor accumulation and porphyrin biosynthesis were investigated in rat cerebellum, using as experimental approach minimal tissue units called particles. 2. ALA was shown to be taken up into cerebellum particles by a non saturable process up to 4.0 mM ALA whereas PBG and porphyrin formation exhibited a hyperbolic response reaching the plateau at about 1.0 and 1.5 mM ALA respectively. 3. Exposure of cerebellum particles to high exogenous ALA amounts (0.01-4.0 mM) indicated that ALA can be accumulated in relatively high concentrations in the cells (40 nmol/mg protein). Under these experimental conditions, PBG-D presented a low activity (3.25 pmol/mg protein/4 hr) showing to be a secondary control step in heme biosynthesis. 4. Incubation of cerebellum particles in the presence of a physiological concentration of glucose revealed that 1.0 mM ALA decreased glucose uptake by the cells (87% during 1 hr incubation), being consistent with the fact that acute attacks are precipitated by fasting and that sugar administration appeared to be an efficient treatment of AIP crisis. 5. These findings provide the basis for a useful model to study the nature of the metabolic mechanism underlying the acute attack.