Scheme 1
Envisaged mechanism of ALA-driven redox imbalance in SAME-treated rats.66 Bechara, E. J.; Dutra, F.; Cardoso, V. E.; Sartori, A.; Olympio, K. P.; Penatti, C. A.; Adhikari, A.; Assunção, N. A.; Comp. Biochem. Physiol., Part C: Toxicol. Pharmacol.
2007, 146, 88 and references therein. SA strongly inhibits (Ki = 30 nM) ALA-dehydration to porphobilinogen (PBG) in the heme biosynthetic pathway leading to ALA accumulation in the rat liver and other organs. Excess ALA undergoes enolization and further metal-catalyzed oxidation by molecular oxygen yielding ammonium ion and 4,5-dioxovaleric acid (DOVA), a multistep reaction mediated by superoxide, hydrogen peroxide and hydroxyl radical. These reactive oxygen species may reportedly cause oxidative damage to protein, DNA, lipids and other biomolecules.
Figure 1
Localization of iron (A, E, I), ferritin (B, F, J) and DNP (C, G, K) in the liver of control (A-D) or SAME treated rats (10 mg, E-H; 40 mg I-L; 80 mg, insert of Figures I-K). Stainable iron is observed as irregular dark granules in liver cell cytoplasm (arrows). The density of granules in the liver parenchyma varied with the animals' treatment (A, E, I and insert). By contrast, DNP immunoreactivity shows differences (C, G, K and insert) in intensity, but is uniformly distributed in liver cells. In general, immunoreaction for ferritin is weak in liver cells except in 10 mg SAME-treated samples (B, F, J). v: portal vein; s: sinusoid; h: hepatocyte columns; p: portal area. Figures D, H and L are representative of the immunoreaction controls in which the primary antibody was replaced by non-immune rabbit serum, respectively, for anti-ferritin in the control group, anti-DNP in the 10 mg SAME treated group, and anti-DNP reaction in the 40 mg SAME treated group. The liver sections were counterstained with Mayer hematoxylin or methyl green solution.
Scheme 2
Free radical hypothesis of inherited hepatic porphyrias related to the accumulation of ALA, the first precursor of the heme biosynthetic pathway. ALA is reportedly overproduced in the liver of AIP patients due to PBG deaminase deficiency and in HT1, owing to excess SA, a tyrosine catabolite that acts as a strong inhibitor of ALA dehydratase. Model studies with rat-administered SAME or ALA66 Bechara, E. J.; Dutra, F.; Cardoso, V. E.; Sartori, A.; Olympio, K. P.; Penatti, C. A.; Adhikari, A.; Assunção, N. A.; Comp. Biochem. Physiol., Part C: Toxicol. Pharmacol.
2007, 146, 88 and references therein. have revealed: (i) increased plasma ALA and urinary ALA clearance, accompanied by decreased urinary COPRO (references 44 Sassa, S.; Br. J. Haematol.
2006, 135, 281., 4343 Karim, Z.; Lyoumi, S.; Nicolas, G.; Deybach, J. C.; Gouya, L.; Puy, H.; Clin. Res. Hepatol. Gastroenterol.
2015, 39, 412. and this work); (ii) liposome and membrane lipoperoxidation (reference 30 and this work); mitochondrial permeabilization and impaired functions (reference 7 and this work); elevated carbonyl proteins (this work); increased liver chemiluminescence;3636 Demasi, M.; Costa, C. A.; Pascual, C.; Llesuy, S.; Bechara, E. J.; Free Radical Res.
1997, 26, 235. DNA strand breaks, 2'-deoxyguanosine (dGuo) oxidation and DOVA adduction;4444 Onuki, J.; Medeiros, M. H. G.; Bechara, E. J. H.; Di Mascio, P.; Biochim. Biophys. Acta
1994, 1225, 259.
45 Fraga, C.; Onuki, J.; Lucesoli, F.; Bechara, E. J. H.; Di Mascio, P.; Carcinogenesis
1994, 15, 2241.-4646 Douki, T.; Onuki, J.; Medeiros, M. H. G.; Bechara, E. J. H.; Cadet, J.; Di Mascio, P.; Chem. Res. Toxicol.
1998, 11, 150. and apoptosis (this work). In vivo or post-mortem studies of AIP patients have shown increased SOD activities;4040 Pereira, B.; Curi, R.; Kokubun, E.; Bechara, E. J.; J. Appl. Physiol.
1992, 72, 226.,4545 Fraga, C.; Onuki, J.; Lucesoli, F.; Bechara, E. J. H.; Di Mascio, P.; Carcinogenesis
1994, 15, 2241. ALA overload and porphyrin diminution44 Sassa, S.; Br. J. Haematol.
2006, 135, 281. plus deformed mitochondria, elevated iron deposits and lipid droplets.1515 Biempica, L.; Kosower, N.; Ma, M. H.; Goldfisher, S.; Arch. Pathol.
1974, 98, 336. A bulk of data advocate the implication of these ALA-triggered biochemical changes in the hemodynamic, hepatic, social behavior and psychiatric manifestations of AIP and HT1.44 Sassa, S.; Br. J. Haematol.
2006, 135, 281. Accordingly, we have also reported oxidative damage to γ-aminobutyric acid (GABA) receptors in cerebral structures of rat-chronically exposed to ALA or SAME.4747 Medeiros, M. H. G.; Marchiori, P. E.; Bechara, E. J. H.; Clin. Chem.
1982, 28, 242.
48 Demasi, M.; Penatti, C. A. A.; DeLucia, R.; Bechara, E. J. H.; Free Radical Biol. Med.
1996, 20, 291.-4949 Adhikari, A.; Penatti, C. A. A.; Resende, R. R.; Ulrich, H.; Britto, L. R. G.; Bechara, E. J. H.; Brain Res.
2006, 1093, 95.
