cute intermittent porphyria causes hepatic mitochondrial energetic ailure in a mouse model

Acute intermittent porphyria (AIP), an inherited hepatic disorder, is due to a defect of hydroxymethylbilane synthase (HMBS), an enzyme involved in heme biosynthesis. AIP is characterized by recurrent, life-threatening attacks at least partly due to the increased hepatic production of 5-aminolaevulinic acid (ALA). Both the mitochondrial enzyme, ALA synthase (ALAS) 1, involved in the first step of heme biosynthesis, which is closely linked to mitochondrial bioenergetic pathways, and the promise of an ALAS1 siRNA hepatic therapy in humans, led us to investigate hepatic energetic metabolism in Hmbs KO mice treated with phenobarbital. The mitochondrial respiratory chain (RC) and the tricarboxylic acid (TCA) cycle were explored in the Hmbs−/− mouse model. RC and TCA cycle were significantly affected in comparison to controls in mice treated with phenobarbital with decreased activities of RC complexes I (−52%, ** p < 0.01), II (−50%, ** p < 0.01) and III (−55%, * p < 0.05), and decreased activity of -ketoglutarate dehydrogenase (−64%, * p < 0.05), citrate synthase (−48%, ** p < 0.01) and succinate dehydrogenase (−53%, * p < 0.05). Complex II-driven succinate respiration was also significantly affected. Most of these metabolic alterations were at least partially restored after the phenobarbital arrest and heme arginate administration. These results suggest a cataplerosis of the TCA cycle induced by phenobarbital, caused by the massive withdrawal of succinyl-CoA by ALAS induction, such that the TCA cycle is unable to supply the reduced cofactors to the RC. This profound and reversible impact of AIP on mitochondrial energetic metabolism offers new insights into the beneficial effect of heme, glucose and ALAS1 siRNA treatments by limiting the cataplerosis of TCA cycle. © 2014 Elsevier Ltd. All rights reserved. Abbreviations: KGDH, alpha-ketoglutarate dehydrogenase; AIP, acute intermittent ynthase; ATP, Adenosine triphosphate; CoASH, coenzyme A; COX, cytochrome oxidase; henol indophenol; DNTB, dinitrothiocyanobenzene; EDTA, ethylenediaminetetraacetic a nsulin-like growth factor 1; KCl, potassium chloride; KCN, potassium cyanid; KGDH, cet denine dinucleotide; ND, NADH dehydrogenase; OXPHOS, oxidative phosphorylation; GC1, peroxisome proliferator-activated receptor coactivator 1; RC, respiratory ch pecies; SDH, succinate dehydrogenase; SiRNA, small interfering RNA, TCA cycle, tricarbo ∗ Corresponding author at: CHU d’Angers, Département de Biochimie et Génétique, 4 ru E-mail address: pareynier@chu-angers.fr (P. Reynier). 1 Contributed equally to this work. ttp://dx.doi. org/10.1016/j.biocel. 2014.03. 032 357-2725/© 2014 Elsevier Ltd. All rights reserved. porphyria; ALA, 5-aminolaevulinic acid; ADP, adenosine diphosphate; ALAS, ALA CS, citrate synthase; CuZnSOD, CuZn, superoxide dismutase; DCPIP, 2,6-Dichlorocid; EGTA, ethylene glycol tetraacetic acid; ICDH, isocitrate deshydrogenase; IGF-1, oglutarate deshydrogenase; MnSOD, Mn superoxide dismutase; NAD, nicotinamide PBG, porphobilinogen; HMBS, hydroxymethylbilane synthase; PB, phenobarbital; ain; RCR, respiratory control ratio; RNAi, RNA interfering; ROS, reactive oxygen xylic acid cycle; WT, wild type. e Larrey, F-49933 Angers, France. Tel. : +33 2 41355542; fax: +33 2 41354017.