Hepatic Porphyrin Research Articles

225) - Comparative toxicity of polychlorinated biphenyls(PCB) and polychlorinated dibenzofurans(PCDF) in rats — Effect of PCB and PCDF on hepatic porphyrin biosynthesis —

225) - Comparative toxicity of polychlorinated biphenyls(PCB) and polychlorinated dibenzofurans(PCDF) in rats — Effect of PCB and PCDF on hepatic porphyrin biosynthesis —

Different patterns of hepatic microsomal enzyme activity produced by administration of pure hexachlorobiphenyl isomers and hexachlorobenzene

Three hexachlorobiphenyl isomers, 2,2′,4,4′,5,5′-hexachlorobiphenyl (I), 2,2′,3,3′,4,4′-hexachlorobiphenyl (II) and 2,2′,3,4,4′,5′-hexachlorobiphenyl (III), have been administered to rats and the effects of these three compounds upon hepatic microsomal drug metabolism and upon hepatic porphyrins have been studied. Comparisons have been made with hexachlorobenzene and a commercial polychlorinated biphenyl mixture, Aroclor 1254. From measurements of activities of microsomal drug oxidations in vitro, the durations of pharmacological actions of certain drugs in vivo and spectral shifts associated with cytochrome P-450 it is shown that the three pure hexachlorobiphenyl isomers initially produce changes in hepatic microsomal activity which resemble those seen after treatment with phenobarbitone (PB). In contrast, following chronic feeding of the isomers, compounds II and III but not I produce a pattern of hepatic microsomal enzyme activity which shows some characteristics of the 3-methylcholanthrene (3-MC) and some characteristics of the phenobarbitone classes of inducer. Also, compounds II and III, but not I, cause accumulation in the liver of porphyrins containing either seven or eight carboxyl groups. These two responses are similar to those observed following hexachlorobenzene treatment and suggest that a relationship may exist between the mixed pattern of enzyme induction and the onset of hepatic porphyrin accumulation.

Toxicological assessment of hexachlorobiphenyl isomers and 2,3,7,8-tetrachlorodibenzofuran in chicks: II. Effects on drug metabolism and porphyrin accumulation

Pure hexachlorobiphenyl (HCB) isomers induce a number of changes in parameters of drug metabolism in the chick including changes in cytochrome P-450, liver weight, and p-nitrophenol glucuronyl transferase, but not in testosterone glucuronyl transferase activity. The most active inducers of drug metabolism were 2,3,4,2′,3′,4′-HCB and 2,4,6,2′,4′,6′-HCB, while 2,4,5,2′,4′,5′-HCB produced intermediate effects and 2,3,6,2′,3′,6′-HCB was a poor inducer. All HCBs caused uroporphyrin accumulation and increased δ-aminolevulinic acid (ALA) synthetase activity, but only 3,4,5,3′,4′,5′-HCB, 2,3,4,2′,3′,4′-HCB, and 2,4,5,2′,4′,5′-HCB produced gross accumulation of hepatic porphyrins. Tissue HCB concentrations correlated well with hepatic effects. 2,3,7,8-Tetrachlorodibenzofuran (TCDF), a contaminant of commercial polychlorinated biphenyl (PCB) mixtures, had no effects on hepatic ALA synthetase activity, porphyrin accumulation, or glucuronyl transferase. TCDF did produce a slight increase in cytochrome P-450, but the increase was smaller than that produced by HCBs. Also, the cytochrome induced by TCDF appeared qualitatively different from the cytochrome induced by TCBs, differing by a shift in the peak of the CO-difference spectrum from 450 to 449 nm and by the ratio of absorbance at 455 to 430 nm of the ethyl isocyanide difference spectrum.

Erythropoietic protoporphyria: porphyrin content of a gall-stone (author's transl)

In the case of a 48 year old woman with characteristic signs of erythropoetic protoporphyria, a solitary gall-stone which had persisted over a period of 10 years was removed. Porphyrin-concentration of this gall-stone was found to be 22.6 mcg/g, which is almost twenty times the concentration of other cholestrol-stones. Besides protoporphyrin, porphyrins with a higher degree of carboxylation were discovered in four different samples by thin layer chromatography. It is postulated that the increased bile-concentration of protoporphyrin in the liver causes the cristallisation of cholestrol and the formation and growth of gall-stones. The biochemical finding of porphyrins with a higher degree of carboxylation indicates that the porphyrins of the gall-stone may not only come from hemolysed erythrocytes but possibly also from metabolites of disturbed hepatic porphyrin biosynthesis.

Editorial: Hematin and porphyria.

The discovery that hematin represses induction of δ-aminolevulinic acid synthetase (ALA-S), the rate-limiting enzyme for hepatic porphyrin and heme synthesis,1 is central to recent studies seeking to provide a means of terminating or ameliorating the acute attack of acute intermittent porphyria, porphyria variegata or hepatic coproporphyria. The induction of ALA-S in the acute attack of AIP, acute intermittent porphyria, porphyria variegata or hepatic coproporphyria markedly increases the porphyrin precursors, ALA and porphobilinogen (PBG), in liver, blood plasma and urine. The enzyme is induced because of heme deficiency in the liver secondary to the genetic partial lack of uroporphyrinogen synthetase (UPG-S) . . .

Hepatic porphyrin synthesis in rats after pretreatment with polychlorinated biphenyls (PCBs).

Abstract: A single dose of polychlorinated biphenyls caused an increase of δ‐aminolevulinic acid synthetase activity and porphyrin content in rat liver. δ‐aminolevulinic acid dehydratase activity was not altered significantly. A maximum effect was obtained 24 hrs after treatment, and the rate limiting enzyme of porphyrin synthesis returned to a normal level of activity at the third day after treatment. On the contrary the porphyrin content of the liver remained elevated up to 4 weeks after a single injection of polychlorinated biphenyls. After administration of polychlorinated biphenyls the kinetic properties of δ‐aminolevulinic acid synthetase of rat liver were found to be altered: an increase of Vmax was accompanied by a decrease of Km. The threshold dose for an increase of δ‐aminolevulinic acid synthetase activity and porphyrin content of rat liver after a single dose of polychlorinated biphenyls was about 0.019 mmol/kg body weight for starved animals. At this dose range no significant differences in response of the parameters examined were seen when polychlorinated biphenyls with variable chlorine contents were administrated. A maximum effect for δ‐aminolevulinic acid synthetase was obtained by a threefold dose, and no further increase was obtained by much higher doses, whereas increasing response up to these high doses was seen for the porphyrin content of the liver. At high doses the activity of δ‐aminolevulinic acid synthetase increased with increasing chlorine content of the polychlorinated biphenyls.

Stimulators and inhibitors of hepatic porphyrin formation in human sera.

Human sera were found to contain factors that stimulate and factors that inhibit porphyrin formation by cultured avian liver cells. The capacity of sera to stimulate or inhibit porphyrin formation varied in different hormonal states and in the porphyrias. Sera from 31 post partum women, eight of whom were not lactating, inhibited porphyrin formation to a mean level 30% below the level in control cultures and also inhibited drug and steroid stimulation of porphyrin formation. In contrast, mean porphyrin formation compared to control cultures was increased between 9 and 21% by sera from 52 normal subjects, 16 women on oral contraceptives, and 11 pregnant women. It was increased 193% by sera from nine subjects with acute intermittent porphyria and 172% by sera from 13 subjects with porphyria cutanea tarda. Heated sera or ethanol extracts of sera from all groups of subjects further increased the mean porphyrin stimulation by sera and, for the post partum subjects, eliminated the inhibitory effect. Ethanol extracts of sera from 28 oral contraceptive-treated women caused significantly greater mean stimulation of porphyrin formation than did extracts of sera from 30 normal women. While sera from 17 out of 22 porphyric subjects contained both stimulatory and inhibitory factors, 5 out of 22 had no evidence of an inhibitory component. There appeared to be heterogeneity in the occurrence of the factors among porphyrics.The factor(s) in sera responsible for porphyrin stimulation were heat-stable and insensitive to trypsin; were present in the supernates after ethanol precipitation of plasma proteins; were extractable in ethyl acetate and nondialyzable; and they migrated with the albumincontaining fraction of serum during electrophoresis. The factor(s) responsible for porphyrin inhibition were heat labile, sensitive to trypsin, and resistant to neuraminidase; were present in the ethanol precipitates of sera and were nondialyzable; and they migrated with the gamma globulin fraction of serum during electrophoresis. Inhibition of porphyrin formation was not attributable to heme, free or bound as hemoglobin, hemopexin, or hemalbumin.

Drug-induced porphyrin biosynthesis. 8. Investigation of the importance of an allyl group for activity in substituted acetamides.

Allylisopropylacetamide (AIA) was found to be considerably more potent than propylisopropylacetamide (PIA) in inducing hepatic δ-aminolevulinic acid (ALA) synthetase activity and hepatic porphyrin accumulation in the 17-day-old chick embryo, chickens, and mice of the CBA/J strain. AIA and PIA were shown to be approximately equipotent in inducing ALA synthetase activity and porphyrin accumulation in chick embryo liver cell culture. It is likely that the unusual responsiveness of chick embryo liver cell culture to PIA is not due to species or developmental differences but to the large amount of PIA available to the cultured liver cells.

The Molecular Basis of the Action of Chloroquine in Porphyria Cutanea Tarda

A single therapeutic dose of chloroquine, a 4 aminoquinoline, administered to patients with porphyria cutanea tarda (PCT) results in a massive porphvrinuria with subsequent remission at the disease. In the present investigation, an experimental animal model of porphyria was utilized to elucidate the initial biochemical events involved in the therapeutic response of patients with PCT to chloroquine. Rats were made chemically porphyria by treatment with 3.5 dicarbethoxy 1.4 dihydro 2,4,6, trimethyl pyridine (DDC) and subsequently treated with chloroquine. As in patients with PCT, chloroquine caused a massive porphyrinuria in the experimental animals. The increased excretion of porphyrin was associated with a marked decrease in hepatic porphyrin content without changing the activity of δ-aminoleyulinic acid synthetase. The rate controlling enzyme of porphyrin biosynthesis. In addition, there was no biochemical evidence of hepatotoxicity in the experimentally porphyric animals during chloroquine treatment. The validity of the present model system for the study of the effects of chloroquine in PCT is supported by the similarity of the response of the chemically porphyric animals and PCT patients to primaquine, an 8-aminoquinoline. In both instances, primaquine has no effect on porphyrin excretion. In vitro data based on spectrophotometric and gel filtration studies demonstrated that porphyrins form a unique molecular complex with chloroquine. Further equilibrium dialysis studies demonstrate that chloroquine causes the release of tissue-bound prophyrins. The in vitro studies, in association with the results from the animal model, suggest that the initial event following chloroquine administration to patients with PCT is a release of bound hepatic porphyrin and its rapid elimination.

Cycloheximide enhanced porphyrin synthesis in chick embryo liver: Association with an increase in the hepatic glycine pool

Cycloheximide 3 μ g injected into eggs with 15 day chick embryos prior to the administration of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) 2 caused a twofold increase in the hepatic porphyrin within 5 hr as compared with embryos given DDC alone. A corresponding increase in the level of δ-aminolevulinic acid (ALA) synthetase did not occur, nor was the conversion of exogenous ALA into porphyrin enhanced by the presence of cycloheximide. Glycine loading of chick embryos treated with DDC also raised the hepatic porphyrin level above that obtained when DDC alone was given. No further increase in porphyrin accompanied the use of cycloheximide at the time of glycine loading. A cycloheximidemediated rise in the hepatic glycine pool was demonstrated and it is proposed that this in turn caused an increase in the production of ALA, which was reflected in an enhanced porphyrin level.

Studies on low dose chloroquine therapy and the action of chloroquine in symptomatic porphyria.

Summary.— Eight patients with symptomatic porphyria (porphyria cutanea tarda symptomatica, PCT) were treated with small doses of chloroquin sulphate over periods ranging from 2 to 16 weeks. A good clinical and biochemical response was obtained in all but one patient, who relapsed after initial improvement. Manifestations of acute untoward reaction were seen in one patient only. It is concluded that low dose chloroquine therapy is both safe and effective in PCT. Studies in porphyric rats indicate that the mechanism of action of chloroquine in PCT is probably not related, as has been suggested, to the formation of a chloroquine-porphyrin complex which damages liver cells and thereby leads to a reduction in hepatic porphyrin stores. Chloroquine therapy led to increased urinary iron excretion and an increase in the desferrioxamine-chelatable iron in patients with PCT. It is suggested that the prolonged beneficial effects of chloroquine treatment may be related to reduction in a specific pool of liver iron.

Drug-induced porphyrin biosynthesis. VII. Species, sex, and developmental differences in the generation of experimental porphyria.

The following drugs have been shown to induce hepatic porphyrin accumulation in 5- to 7-weekold chickens: glutethimide, methsuximide, secobarbital, methyprylon, and mephenytoin, Since these drugs are inactive when administered to mice it is clear that a species difference exists in response to these drugs. Administration of 5β-pregnan-3α, 17α-diol-11, 20-dione to 17-day-old chick embryos results in a large increase in δ-aminolevulinic acid synthase (ALA-synthase) activity accompanied by a very small increase in hepatic porphyrin levels. A drug should therefore be screened for its effects on hepatic ALA-synthase activity as well as porphyrin accumulation prior to administration to porphyric patients. Although it has been reported that ALA-synthase activity cannot be induced by drugs in the livers of newborn rats and rabbits, this enzyme is readily induced by drugs in the livers of newborn chickens.

Suggested pathobiochemical development of chronic hepatic porphyrias

A working hypothesis concerning the development of acquired chronic hepatic porphyrias in liver diseases is proposed, based on biochemical differentiation of these metabolic disturbances. A stepwise progression appears to exist from the secondary porphyrinurias through the asymptomatic chronic hepatic porphyrias of the Types A, B, and C to porphyria cutanea tarda. It is attempted to diagnose chronic disturbances in hepatic porphyrin synthesis while they are still clinically inapparent.

Biochemical effects of chloroquine therapy in porphyria cutanea tarda

Three patients with porphyria cutanea tarda and evidence of liver disease on biopsy were treated with chloroquine in doses of 0.5 gm daily for eight days. In each instance an initial febrile episode was followed by evidences of hepatocellular injury, which soon reverted to pretreatment status. Associated with this was an increased excretion of delta-aminolevulinic acid, uroporphyrin, coproporphyrin and protoporphyrin in the urine and feces. In two of three patients the proportion of type I porphyrin isomers was not influenced by therapy. Porphyrin excretion became normal following therapy, and the patients experienced prolonged remissions, free of skin manifestations. These findings for the most part support the thesis that the responses are secondary to a reduction in hepatic porphyrins rather than interference of chloroquine in the porphyrin biosynthetic pathway. In one patient transient ascites and a hemolytic episode developed following administration of chloroquine.

The pattern of porphyrin isomer accumulation and excretion in symptomatic porphyria.

1. Thin-layer chromatography of porphyrin methyl esters provides a useful and rapid technique for resolving mixtures of porphyrins from biological samples. 2. Application of this technique to urinary, faecal and hepatic porphyrins from patients with symptomatic porphyria revealed five porphyrins of interest which could be identified by mass spectrometry as the methyl esters of porphyrins with 8-, 7-, 6-, 5- and 4-carboxyl groups. Millimolar extinction coefficients at the Soret absorption maxima for these porphyrin methyl esters in chloroform solution were measured. 3. A consistent pattern of urinary porphyrin excretion in symptomatic porphyria was seen with 8-, 7-, 6-, 5- and 4-carboxyl porphyrins constituting approximately 60%, 25%, 3%, 3% and 9% of the total respectively. Uroporphyrin (73%), hepta-carboxylic porphyrin (26%) and hexa-carboxylic porphyrin (1%) were the only porphyrins detected in the liver of one patient. 4. Isomer analysis of excreted and hepatic porphyrins revealed that uroporphyrin was approximately 35% isomer III, hepta- and hexa-carboxylic porphyrins almost all isomer III and penta-carboxylic and coproporphyrin approximately 50% isomer III. 5. To explain these findings it is suggested that there are two metabolic pathways for the handling of δ-aminolaevulic acid (ALA) in the liver.

The effects of certain barbiturates on the hepatic porphyrin metabolism of rats

(1) Some barbiturates when given to rabbits cause a rise in urinary coproporphyrin excretion while others, suspected of provoking acute attacks of porphyria in man, do not. To investigate this anomaly, the levels of hepatic enzymes occurring early in the biosynthetic pathway have been examined in rats, treated with these barbiturates. (2) Of the nine barbiturates tested all significantly raised the hepatic level of ALA. synthetase activity in the rat. (3) These barbiturates may be classified into four significantly different groups, which correspond to the groups of the earlier classification based on urinary coproporphyrin excretion. (4) It is suggested that these results show a direct reason for contraindication of any barbiturates in porphyria. (5) The mechanism of this elevation of enzyme activity by barbiturates is discussed.

Porphyrin metabolism in experimental hepatic siderosis in the rat.

Summary. Experimental hepatic siderosis in the rat due to dietary iron overload produced increased urinary excretion of uro‐ and coproporphyrin which was further aggravated by concurrent drinking of alcohol. On the basis of these findings it is considered very likely that the invariable presence of hepatic siderosis in symptomatic porphyria is more than incidental and that the presence of excessive iron in the liver cells is an important factor determining the development of symptomatic porphryia. Liver ALA synthetase activity was increased in the alcohol‐consuming animals but iron overload alone had no effect on the activity of this enzyme. The mechanism whereby siderosis influences hepatic porphyrin metabolism is unknown. No effect on hepatic mitochondrial coproporphyrinogen oxidase was found. It is suggested that in the siderotic animals and in patients with symptomatic porphyria there is interference with a normal disposal route for excessive haem precursors.

The quantitative regulation of the biosynthesis of porphyrins by intracellular ATP concentration

Protoporphyrin IX (PP) and N-methylprotoporphyrin IX (N-MePP) added in vitro to liver membranes reduced dose-dependently the affinity of [3H]PK 11195 for the mitocnondrial benzodiazepine receptors (MBRs), the latter being about 20 times more potent (Ki 4.5 and 0.25 muM). Preincubation of these two porphyrins with liver homogenates for 120 min at 4° resulted in significant inhibition of [3H]-PK 11195 binding even after repeated washings of the membranes due to the residual presence in the membranes of about 35 and 5% of PP and N-MePP, respectively. Thus, the hypothesis that an in vivo increase in the hepatic porphyrin content modifies the binding of the isoquinoline PK 11195 to the MBRs was investigated in an experimental model of protoporphyria. PP and N-MePP were allowed to accumulate in vivo through treatment with 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) (100 mg/kg i.p., once), and rats were killed 5 h after treatment when hepatic porphyrin accumulation was marked (10-fold increase), PP predominating. In the liver, treatment reduced the affinity (Kd) of [3H]PK 11195 for MBRs (from 3.56 to 15.37 nM, P < 0.01) and the maximum number of binding sites (Bmax) (55% decrease, P < 0.05); the affinity (Ki) of RO 5-4864 for [3H]PK 11195 binding sites was also reduced (from 23.9 to 72.99 nM, P < 0.05). No significant differences were found in the brain cortex. Liver and brain diazepam binding inhibitor levels and plasma corticosterone levels were unchanged. The reduction in [3H]PK 11195 binding to MBRs in the liver of DDC-treated rats thus appears to be attributable to a specific effect of the DDC-induced formation of the two protoporphyrins; this conclusion suggests that in hepatic protoporphyria processes modulated by MBRs may be altered.

Biliary iron excretion in normal and iron-loaded rats after desferrioxamine and CaDTPA.

ARTICLESBiliary iron excretion in normal and iron-loaded rats after desferrioxamine and CaDTPAWG Figueroa, and JH ThompsonWG Figueroa, and JH ThompsonPublished Online:01 Oct 1968https://doi.org/10.1152/ajplegacy.1968.215.4.807MoreSectionsPDF (806 KB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByEnhanced biliary iron excretion with amphiphilic diethylenetriaminepentaacetic acidHepatology, Vol. 14, No. 6Mechanisms of Metal Transport Across Liver Cell Plasma Membranes22 September 2008 | Drug Metabolism Reviews, Vol. 23, No. 1-2Solid phase immunoradiometric assay for porcine serum ferritinComparative Biochemistry and Physiology Part B: Comparative Biochemistry, Vol. 89, No. 2Deferoxamine-enhanced fecal losses of aluminum and iron in a patient undergoing continuous ambulatory peritoneal dialysisThe American Journal of Medicine, Vol. 82, No. 2Effect of desferrioxamine on the development of hexachlorobenzene-induced porphyriaBiochemical Pharmacology, Vol. 35, No. 14Effects of iron overload on bile secretion and hepatic porphyrin metabolism in ethinyl extradiol-treated ratsToxicology, Vol. 38, No. 2Excretion MechanismsBiliary Iron Excretion in Rats following Pyridoxal Isonicotinoyl HydrazoneBritish Journal of Haematology, Vol. 45, No. 2Haptoglobin-mediated transfer of haemoglobin from serum into bile12 November 2001 | FEBS Letters, Vol. 112, No. 2Decreased cytochrome p450 and increased porphyrin concentrations in the livers of rats on a low iron diet given a single dose of desferrioxamineBiochemical Pharmacology, Vol. 27, No. 6Pharmacology and therapeutic applications of agents used in heavy metal poisoningPharmacology & Therapeutics. Part A: Chemotherapy, Toxicology and Metabolic Inhibitors, Vol. 1, No. 1Biliary Excretion of Metals22 September 2008 | Drug Metabolism Reviews, Vol. 5, No. 2The Enterohepatic CirculationEnterohepatic circulation of 64Cu, 52Mn and 203Hg in ratsArchiv f�r Toxikologie, Vol. 31, No. 1Quantitative measurement of iron stores with diethylenetriamine penta-acetic acidGut, Vol. 11, No. 11Differential ferrioxamide test in haemochromatosis and liver diseaseGut, Vol. 10, No. 9 More from this issue > Volume 215Issue 4October 1968Pages 807-810 Copyright & PermissionsCopyright © 1968 by American Physiological Societyhttps://doi.org/10.1152/ajplegacy.1968.215.4.807PubMed5676381History Published online 1 October 1968 Published in print 1 October 1968 Metrics

The nonerythropoietic component of early bilirubin.

The early labeled bilirubin consists of two primary components. The more rapidly synthesized of the two is independent of erythropoiesis (nonerythropoietic), whereas the second fraction is related to red cell production (erythyropoietic). The present studies concern the origin of the nonerythropoietic component. The nonerythropoietic, early labeled bilirubin was studied in bile fistula rats with (delta ALA)-4-(14)C delta aminolevulinic acid and glycine-2-(14)C as precursors. That nephrectomy did not reduce the size of this component despite the large and rapidly turning over pool of renal heme suggests that this pool may be of minor importance in its production. Intoxication with lead to a level that reduced hepatic heme synthesis was associated with a decrease in early bilirubin formation. The synthesis of this bilirubin was assessed in animals with phenobarbital-induced heme protein and cycloheximide-suppressed protein synthesis. Rats pretreated with phenobarbital at a dose level of 60 mg/kg with induction of cytochrome P-450 synthesis showed a minor increase in early labeling when glycine-2-(14)C but not when delta ALA-4-(14)C was used as precursor. Rats given cycloheximide at a dose level that markedly reduced hepatic protein and cytochrome P-450 synthesis but allowed heme synthesis to continue at 60% of its pretreatment level synthesized normal or increased amounts of early bilirubin from delta ALA-4-(14)C. Allylisopropylacetamide intoxication caused little change in early bilirubin formation, whereas aminotriazole given at a time after maximal hepatic heme labeling produced a small but significant increase in the appearance of labeled bilirubin. These findings indicate that early bilirubin production is little influenced by increased hepatic porphyrin synthesis or by changes in the rapidly turning over heme protein P-450. A minimal increase attends catalase inactivation by aminotriazole. Normal or increased synthesis takes place in the presence of suppression of protein synthesis. This finding suggests that the nonerythropoietic early bilirubin may itself consist of two subcomponents. The first of these may arise from free tissue heme or its precursors, and the second may derive from the turnover of the heme proteins. The first subcomponent may serve as a regulatory mechanism for the removal of heme synthesized in excess of its protein acceptor. A composite scheme is proposed for the origin of the total early bilirubin from heme compartments in tissue and marrow.