Multiple roles of haem in cystathionine β-synthase activity: implications for hemin and other therapies of acute hepatic porphyria (original) (raw)
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Journal of pharmacological methods, 1981
Rat liver tryptophan pyrrolase plays a versatile and unique role among hepatic hemoproteins in relation to heme utilization. The depletion of pyrrolase heme in the experimental porphyria produced by 3,5-diethoxycarbonyl-1,4-dihydrocollidine is potentiated by joint administration of any one of 19 drugs known to exacerbate the human disease, but not by any of 13 nonexacerbators. These findings form the basis of a screening test for drug exacerbation of hepatic porphyrias; the conditions, details, and requirements of which are described.
PLoS ONE, 2012
Chronic kidney disease is a long-term complication in acute intermittent porphyria (AIP). The pathophysiological significance of hepatic overproduction of the porphyrin precursors aminolevulinate acid (ALA) and porphobilinogen (PBG) in chronic kidney disease is unclear. We have investigated the effect of repetitive acute attacks on renal function and the effect of total or five-sixth nephrectomy causing renal insufficiency on hepatic heme synthesis in the porphobilinogen deaminase (PBGD)-deficient (AIP) mouse. Phenobarbital challenge in the AIP-mice increased urinary porphyrin precursor excretion. Successive attacks throughout 14 weeks led to minor renal lesions with no impact on renal function. In the liver of wild type and AIP mice, 5/6 nephrectomy enhanced transcription of the first and rate-limiting ALA synthase. As a consequence, urinary PBG excretion increased in AIP mice. The PBG/ALA ratio increased from 1 in sham operated AIP animals to over 5 (males) and over 13 (females) in the 5/6 nephrectomized mice. Total nephrectomy caused a rapid decrease in PBGD activity without changes in enzyme protein level in the AIP mice but not in the wild type animals. In conclusion, high concentration of porphyrin precursors had little impact on renal function. However, progressive renal insufficiency aggravates porphyria attacks and increases the PBG/ALA ratio, which should be considered a warning sign for potentially life-threatening impairment in AIP patients with signs of renal failure.
Stimulation of liver heme oxygenase in hexachlorobenzene-induced hepatic porphyria
Archives of Toxicology, 1998
We have measured liver heme oxygenase, a heat shock protein known to be increased under conditions of oxidative stress, to obtain additional evidence for an oxidative stress mechanism in hepatic uroporphyria induced by hexachlorobenzene (HCB). We have studied heme oxygenase at dierent times during HCB treatment and in two strains of rats (Agus and Wistar strains), which are known to dier in their sensitivity to the porphyria-inducing properties of HCB, in order to ascertain whether the same time course and genetic dierences known to exist for the induction of porphyria also apply to hepatic oxidative stress. HCB induced heme oxygenase and accumulation of porphyrins in the liver of rats of both strains; no signi®cant dierence was found between the two strains in the HCB-induced heme oxygenase activity. The increased activity of the enzyme was ®rst detected during the early phases of treatment, when a modest increase in liver porphyrins was observed; heme oxygenase remained at induced levels for several weeks during HCB treatment, and was still raised when an increase in total liver iron content and the onset of marked porphyria were also found. In contrast to the eects of HCB, phenobarbitone sodium (given in the drinking water for up to 4 weeks) produced similar elevations of total liver cytochrome P450 as HCB, but did not stimulate heme oxygenase or increase the total liver content of either iron or porphyrins. These results are compatible with an oxidative stress mechanism in HCB-induced liver toxicity and porphyria, but also suggest the existence of successive stages in the induction of hepatic porphyria, with more than one mechanism contributing to the marked accumulation of uroporphyrin.
Regulation of heme synthesis in the regenerating rat liver
Biochemical Medicine and Metabolic Biology, 1990
Various aspects of heme metabolism in the regenerating rat liver have been documented (l-9), but no clear-cut picture has emerged giving an overview of the regulation of heme synthesis in regenerating rat liver. The activity of 6aminolevulinic acid synthase (ALAS) (EC 2.3.1.37) (2,5,6,9) and the concentrations of cellular heme and of P450 (1,2,5,9) were both reported to be reduced. One may, therefore, assume that in the postoperative state, ALAS activity is not under the control of its end product heme. However, changes in cellular heme, as measured by the "hot oxalic" method or by employment of pyridine hemochromogen, do not necessarily reflect the concentration of the "free heme" in the regulatory heme pool (10). The latter, which constitutes only a small percentage of intracellular heme, is considered, rather than total heme content, to be the regulator of ALAS (1 l-l 3). This work was carried out in order to provide data concerning the "regulatory heme pool" in regenerating rat liver and to further investigate whether the control of ALAS in this system differs from that of normal liver. MATERIALS AND METHODS Methods Ruts. Male Wistar rats, bred at random and weighing 140-160 g, were subjected either to sham operation (laparatomy only) or to two-thirds hepatectomy as described by Higgins and Anderson (14). On the appropriate days, rats were killed, livers were removed, and the various determinations were carried out. Experimental porphyria was induced by two ip injections (24-hr interval between injections) of either diethoxycarbonyl dihydrocollidine (DDC) or allylisopropylacetamide (AIA), 400 mg/kg/day dissolved in dimethyl sulfoxide (DMSO) (0.2 ml of 350 mg/ml). Operations were performed on the first or second day of drug administrations. Animals were fasted from 24 hr before the first injection until 24 hr after the second injection. Control rats were injected with DMSO only.
Journal of Internal Medicine, 2018
BackgroundAcute intermittent porphyria (AIP) is an inherited disorder of haem metabolism characterized by life‐threatening acute neurovisceral attacks due to the induction of hepatic δ‐aminolevulinic acid synthase 1 (ALAS1) associated with hydroxymethylbilane synthase (HMBS) deficiency. So far, the treatment of choice is hemin which represses ALAS1. The main issue in the medical care of AIP patients is the occurrence of debilitating recurrent attacks.ObjectiveThe aim of this study was to determine whether chronic hemin administration contributes to the recurrence of acute attacks.MethodsA follow‐up study was conducted between 1974 and 2015 and included 602 French AIP patients, of whom 46 had recurrent AIP. Moreover, we studied the hepatic transcriptome, serum proteome, liver macrophage polarization and oxidative and inflammatory profiles of Hmbs−/− mice chronically treated by hemin and extended the investigations to five explanted livers from recurrent AIP patients.ResultsThe introd...
IUBMB Life, 1999
Porphyrinogen carboxy-lyase is an enzyme that sequentially decarboxylates uroporphyrinogen III (8-COOH) to yield coproporphyrinogen III (4-COOH). In mammals this enzyme activity is impaired by hexachlorobenzene treatment, through generation of an enzyme inhibitor. The interaction of porphyrinogen carboxy-lyase inhibitor, extracted from the liver of hexachlorobenzene-treated rats, with substrate decarboxylation sites on the enzyme, was studied using four different carboxylated substrates belonging to the isomeric III series of naturally-formed porphyrinogens containing 8-,7-,6-and 5-COOH. Similar inhibitor effects were elicited against all the substrates assayed, with the exception of pentacarboxyporphyrinogen III in which decarboxylation was not inhibited to same extent. Enzyme protection assays in the presence of the different substrates, indicated that each porphyrinogen protects its own decarboxylation from inhibitor action. Preincubation of the inhibitor with normal enzyme increased its inhibitory effect. On the other hand, preineubation of both enzyme and inhibitor with superoxide dismutase or mannitol, did not alter inhibitory activity. Preincubation of the inhibitor with a number of aminoacids showed that only arginine and its derivative N~-Benzoyl-L-Arginine ethyl ester interact with the inhibitor, noticeably reducing its ability to inhibit porphyrinogen earboxy-lyase. Albumin, histidine, serine, cysteine and imidazol, were unable to quench inhibitor activity. The present results indicate that the inhibitor acts at the binding site of each porphyrinogen. Taking into account that arginine is related to enzyme activity, and that histidine is found at the binding site of the substrates, the results suggest that the inhibitor could bind to arginine residues, blocking the access of substrates to histidine and altering the adequate orientation for decarboxylation by masking the positively charged active site necessary for porphyrinogen binding to the enzyme. In addition an indirect effect of the inhibitor mediated through free radicals could be discarded.
PloS one, 2016
The aims of the present study were to explore the expression pattern of haem biosynthesis enzymes in circulating cells of patients affected by two types of porphyria (acute intermittent, AIP, and variegate porphyria, VP), together with the antioxidant enzyme pattern in AIP in order to identify a possible situation of oxidative stress. Sixteen and twelve patients affected by AIP and VP, respectively, were analysed with the same numbers of healthy matched controls. Erythrocytes, neutrophils and peripheral blood mononuclear cells (PBMCs) were purified from blood, and RNA and proteins were extracted for quantitative real time PCR (qRT-PCR) and Western-blot analysis, respectively. Porhobilinogen deaminase (PBGD) and protoporphyrinogen oxidase (PPOX) gene and protein expression was analysed. Antioxidant enzyme activity and gene expression were additionally determined in blood cells, together with protein carbonyl content in plasma. PBMCs isolated from AIP patients presented low mRNA level...
The EMBO journal, 2001
Cystathionine beta-synthase (CBS) is a unique heme- containing enzyme that catalyzes a pyridoxal 5'-phosphate (PLP)-dependent condensation of serine and homocysteine to give cystathionine. Deficiency of CBS leads to homocystinuria, an inherited disease of sulfur metabolism characterized by increased levels of the toxic metabolite homocysteine. Here we present the X-ray crystal structure of a truncated form of the enzyme. CBS shares the same fold with O-acetylserine sulfhydrylase but it contains an additional N-terminal heme binding site. This heme binding motif together with a spatially adjacent oxidoreductase active site motif could explain the regulation of its enzyme activity by redox changes.