Oxidative stress in experimental hepatic porphyria triggered by succinylacetone - an inhibitor of 5-aminoluvulinic acid dehydratase

Author(s)

Vanessa Eid da Silva Cardoso

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ)
• Defense date: 2010-01-28

Examining board members

Etelvino Jose Henriques Bechara; Ana Maria da Costa Ferreira; Alicia Juliana Kowaltowski; Paulo Euripedes Marchiori; Janice Onuki

• Advisor: Etelvino Jose Henriques Bechara

Abstract

To optimize an experimental model for studying redox imbalance in porphyrias related to 5-aminolevulinic acid (ALA) accumulation through the inhibition of ALA dehydratase (ALA-D), rats were treated with methyl ester of succinylacetone (SAME), a tyrosine catabolite that strongly inhibits ALA-D, what mimics the metabolic state observed in patients suffering from porphyrías and tyrosinemias. Models of acute treatment were established during 36 and 18 h. In the first model, animals received 3 injections of SAME (10, 40 or 80 mg/kg, groups Ali-IV). In the second model, animals received 3 injections of 40 mg/kg SAME, ALA or methyl ester of ALA (groups BII-IV), ALA:SAME (30:10 mg/kg, group BV), or 10 mg/kg SAME (group BVI). Concomitantly, we evaluated if the neurologic symptoms characteristics of porphyrias were a consequence of the oxidative mitochondrial impairment. For this, an optical technology for the measurement of cortical spreading depression was applied. This techonology determined the cerebral oxygenation and the redox state of cit c in mitochondria of the cerebral cortex of rats submitted to a chronic treatment with ALA (40 mg/kg), SAME (10 and 40 mg/kg) and ALASAME (30:10 mg/kg), alternate days, during 30 days. Acute treatment/36 h: ALA levels in plasma, liver and urine and clearance of renal ALA increased in treated groups. ALA-D activities and urinary coproporphyrin were found to be decreased. Liver and brain proteins carbonyl, iron and ferritin were higher in the liver of treated groups, especially in All. Liver malondialdehyde levels were higher in group AIV. Cerebral GSH/GSH+GSSG ratio and GPx activities increased in groups AIV and AIII, respectively. Consistently with these data indicating SAME-induced oxidative imbalance, mitochondrial and cytosolic ultrastructural changes were revealed, especially in the liver. Acute treatment/18 h: Plasma ALA levels increased in all treated groups but BIV. Group BII showed increased hepatic ALA levels. Interestingly, inhibition in ALA-D activities was not evidenced. Plasma iron content increased in group BII. For the groups treated with 10 and 40 mg SAME/kg, liver SOD activities reduced ~50% by extending the treatment from 18 to 36 h, suggesting that the latter is more effective in ALA-induced oxidative damage. Chronic treatment /30 days: Despite no changes in the redox state of treated animals were observed, the treatment with ALA reduced the cerebral blood flow (CBF) and the consumption of oxygen (CMRO2), suggesting a vasoconstriction mediated by ALA. This effetc was confirmed by vascular reactivity assay performed in aortic rings of rats incubated with ALA. The treatment with ALA:SAME recovered the CBF and CMRO2 levels. Interestingly, the availability of superoxide radical (O2•-) was reduced in the aortic rings incubated with ALA. Altogether, these data a) validate the model of acute treatment/36 h for studying biochemical and possibly physiological effects induced by ALA, and b)suggest that the changes mediated by exogenous ALA lead to vasoconstriction. (AU)