Porfiria hepato eritropoyética asociada a diabetes mellitus tipo 1: a propósito de un caso clínico / A clinical case of hepato-erythropoietic porphyria associated with type 1 diabetes mellitus / Relato de caso de porfiria hepato-eritropoiética associada a diabetes mellitus tipo 1

Las porfirias son un grupo complejo y heterogéneo de defectos en la vía de la síntesis del hemo. La porfiria hepato eritropoyética es un subtipo muy poco frecuente y de presentación en la infancia, con compromiso cutáneo predominante. Describimos el caso clínico de una paciente de 5 años, que se presenta con lesiones cutáneas e hipertricosis, se confirma el diagnóstico por elevación de uroporfirinas en orina y secuenciación del gen UROD.

Porphyria is a complex and heterogeneous group of heme synthesis disorder. Hepato-erythropoietic porphyria is a very rare subtype that onsets in childhood, and shows predominant skin involvement. We describe the clinical case of a 5-year-old patient who showed skin lesions and hypertrichosis and whose diagnosis was confirmed due to increased uroporphyrins in urine and UROD gene sequencing

A porfiria é um grupo complexo e heterogêneo de distúrbios da síntese do grupo heme. A porfiria hepato-eritropoiética é um subtipo muito raro que se inicia na infância e mostra envolvimento predominante da pele. Descrevemos o caso clínico de uma paciente de 5 anos que apresentou lesões cutâneas e hipertricose e cujo diagnóstico foi confirmado por aumento de uroporfirinas na urina e sequenciamento do gene UROD.

Characterization of the apicoplast-localized enzyme TgUroD in Toxoplasma gondii reveals a key role of the apicoplast in heme biosynthesis.

Apicomplexan parasites such as Toxoplasma gondii possess an unusual heme biosynthesis pathway whose enzymes localize to the mitochondrion, cytosol, or apicoplast, a nonphotosynthetic plastid present in most apicomplexans. To characterize the involvement of the apicoplast in the T. gondii heme biosynthesis pathway, we investigated the role of the apicoplast-localized enzyme uroporphyrinogen III decarboxylase (TgUroD). We found that TgUroD knockdown impaired parasite proliferation, decreased free heme levels in the parasite, and decreased the abundance of heme-containing c-type cytochrome proteins in the parasite mitochondrion. We validated the effects of heme loss on mitochondrial cytochromes by knocking down cytochrome c/c1 heme lyase 1 (TgCCHL1), a mitochondrial enzyme that catalyzes the covalent attachment of heme to c-type cytochromes. TgCCHL1 depletion reduced parasite proliferation and decreased the abundance of c-type cytochromes. We further sought to characterize the overall importance of TgUroD and TgCCHL1 for both mitochondrial and general parasite metabolism. TgUroD depletion decreased cellular ATP levels, mitochondrial oxygen consumption, and extracellular acidification rates. By contrast, depletion of TgCCHL1 neither diminished ATP levels in the parasite nor impaired extracellular acidification rate, but resulted in specific defects in mitochondrial oxygen consumption. Together, our results indicate that the apicoplast has a key role in heme biology in T. gondii and is important for both mitochondrial and general parasite metabolism. Our study highlights the importance of heme and its synthesis in these parasites.

Direct assay of enzymes in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry. Uroporphyrinogen decarboxylase and coproporphyrinogen III oxidase.

We report new assays of enzymes uroporphyrinogen decarboxylase (UROD) and coproporphyrinogen III oxidase (CPO) in the heme biosynthetic pathway. The assays were developed for use in clinical diagnostics of inherited disorders porphyria cutanea tarda and hereditary coproporphyria, respectively. Electrospray ionization tandem mass spectrometry is used to monitor the decarboxylation of pentaporphyrinogen I or uroporphyrinogen III catalyzed by UROD and to determine the enzyme activity in human erythrocytes by measuring the production of coproporphyrinogen I or III. The Km value for pentaporphyrinogen I was measured as 0.17 +/- 0.03 microM. A mass spectrometric assay was also developed for the two-step decarboxylative oxidation of coproporphyrinogen III to protoporphyrinogen IX catalyzed by CPO in mitochondria from human lymphocytes (Km = 0.066 +/- 0.009 microM). The assays show good reproducibility, use simple workup by liquid-liquid extraction of enzymatic products, and employ commercially available substrates and internal standards.

Comparison of two assay methods for activities of uroporphyrinogen decarboxylase and coproporphyrinogen oxidase.

Uroporphyrinogen decarboxylase (UROD) and coproporphyrinogen oxidase (copro'gen oxidase) are two of the least well understood enzymes in the heme biosynthetic pathway. In the fifth step of the pathway, UROD converts uroporphyrinogen III to coproporphyrinogen III by the decarboxylation of the four acetic acid side chains. Copro'gen oxidase then converts coproporphyrinogen III to protoporphyrinogen IX via two sequential oxidative decarboxylations. Studies of these two enzymes are important to increase our understanding of their mechanisms. Assay comparisons of UROD and copro'gen oxidase from chicken blood hemolysates (CBH), using a newly developed micro-assay, showed that the specific activity of both enzymes is increased in the micro-assay relative to the large-scale assay. The micro-assay has distinct advantages in terms of cost, labor intensity, amount of enzyme required, and sensitivity.

A mouse model of familial porphyria cutanea tarda.

Approximately one-third of patients with porphyria cutanea tarda (PCT), the most common porphyria in humans, inherit a single mutant allele of the uroporphyrinogen decarboxylase (URO-D) gene. PCT associated with URO-D mutations is designated familial PCT. The phenotype is characterized by a photosensitive dermatosis with hepatic accumulation and urinary excretion of uroporphyrin and hepta-carboxylic porphyrins. Most heterozygotes for URO-D mutations do not express a porphyric phenotype unless hepatic siderosis is present. Hemochromatosis gene (HFE) mutations are frequently found when the phenotype is expressed. We used homologous recombination to disrupt one allele of murine URO-D. URO-D(+/-) mice had half-wild type (wt) URO-D protein and enzymatic activity in all tissues but did not accumulate hepatic porphyrins, indicating that half-normal URO-D activity is not rate limiting. When URO-D(+/-) mice were injected with iron-dextran and given drinking water containing delta-aminolevulinic acid for 21 days, hepatic porphyrins accumulated, and hepatic URO-D activity was reduced to 20% of wt. We bred mice homozygous for an HFE gene disruption (HFE(-/-)) to URO-D(+/-) mice, generating mice with the URO-D(+/-)/HFE(-/-) genotype. These animals developed a porphyric phenotype by 14 weeks of age without ALA supplementation, and URO-D activity was reduced to 14% of wt. These data indicate that iron overload alone is sufficient to reduce URO-D activity to rate-limiting levels in URO-D(+/-) mice. The URO-D(+/-) mouse serves as an excellent model of familial PCT and affords the opportunity to define the mechanism by which iron influences URO-D activity.

Measurement of uroporphyrinogen decarboxylase activity.

Uroporphyrinogen decarboxylase (UROD) catalyzes decarboxylation of the four acetate side chains of urophyrinogen to form coproporphyrinogen. Activity of UROD can be measured using an enzymatically prepared substrate or a chemically prepared one. For the former, bacterial porphobilinogen deaminase is prepared and used to prepare the porphyrinogen substrate for the enzymatic assay. Erythrocyte lysates can be used to measure hemoglobin content as an indicator of UROD activity.

[Acquired characteristics of porphyria cutanea tarda in patients infected with hepatitis C virus]. / Carácter adquirido de la porfiria cutánea tarda en pacientes infectados con virus C de la hepatitis.

BACKGROUND: Porphyria cutanea tarda (PCT) is due to a partial defect of hepatic uroporphyrinogen decarboxylase (URO-D). In the hereditary form, both hepatic and erythrocytic enzymes are altered, whereas in the acquired form, only the hepatic enzyme fails. There is a high prevalence of hepatitis C virus infection in patients with PCT, specially in those without family history of the disease. AIM: To study erythrocytic URO-D activity in order to find out whether hepatitis C virus infection is associated to the acquired form of PCT or unveils an inactive hereditary form. PATIENTS AND METHODS: URO-D activity was measured in red blood cells of normal controls, hepatitis C virus carriers without symptoms of PCT and patients with PCT, with and without family history of the disease, with and without anti hepatitis C virus antibodies. RESULTS: URO-D activity was similar in normal controls, patients with chronic liver disease associated to hepatitis C virus, and in patients with PCT without family history of the disease with and without hepatitis C virus antibodies. URO-D activity was lower in patients with PCT and family history of the disease, with and without hepatitis C virus antibodies. CONCLUSIONS: PCT in patients with hepatitis C virus infection is due to an acquired alteration of hepatic URO-D. Hepatitis C virus does not modify erythrocytic URO-D.

The effect of desferrioxamine on iron metabolism and lipid peroxidation in hepatocytes of C57BL/10 mice in experimental uroporphyria.

The effects of the iron chelator desferrioxamine (DFx) on liver iron accumulation, malondialdehyde (MDA) production, porphyrin accumulation and uroporphyrinogen decarboxylase (URO-D; EC 4.1.1.37) activity were investigated over a period of 14 weeks in C57BL/10 mice, made porphyric by the administration of hexachlorobenzene (HCB) and iron-dextran (Imferon, IMF) or IMF alone. In addition, we measured the amount of low molecular weight (LMW) iron in liver tissue to determine a possible correlation with MDA production. These experiments showed that combined treatment with HCB + IMF, as well as IMF alone, resulted in porphyrin accumulation, increased MDA production and reduced URO-D activity, whereas HCB alone had no effect. DFx caused a reduction in hepatic porphyrins, this reduction being more distinct in the IMF group than in the HCB + IMF group. The effect of DFx on MDA production and URO-D activity was in agreement with the results on porphyrin accumulation. LMW iron pool measurements at 11 weeks correlated well with data on MDA production in all treated groups in that period (r2 = 0.84), suggesting both variables are interdependent. In conclusion, these results suggest an important role for iron in porphyrin accumulation, probably through its catalytic role in the generation of oxygen-related free radicals, resulting in direct damage to URO-D. The effectiveness of DFx in reducing porphyrin accumulation is probably the result of a reduction in LMW iron, thus diminishing the amount of iron available for a catalytic role in the generation of oxygen-related free radicals.

The role of ALA-S and ALA-D in regulating porphyrin biosynthesis in a normal and a HEM R+ mutant strain of Saccharomyces cerevisiae.

Catabolite repression and derepression on delta-aminolevulinate synthase (ALA-S) and delta-aminolevulinate dehydratase (ALA-D) in a normal yeast strain, D27, and its derived D27/C6 (HEM R+) were investigated. ALA-S and ALA-D activities and intracellular ALA (I-ALA) at different physiological states of the cells were measured. In YPD medium, under conditions of repression and when glucose was exhausted, both strains behaved identically as if the mutation was not expressed. In YPEt medium, however, both ALA-S and ALA-D activities were higher than in YPD, but the I-ALA content and the enzymic activity profiles shown by the two strains were quite different. It appears, therefore, that the mutation causes a deregulation of ALA-S, so that its activity is kept at a high level throughout the cell cycle. This would explain the increased levels of cytochromes present in the mutant. This mutation may affect some regulatory aspect of ALA formation and renders an ALA-S of high activity; moreover, this enzyme species seems to be more stable than in the normal strain.

Development of hexachlorobenzene porphyria in rats: time sequence and relationship with lipid peroxidation.

The relationship between the development of porphyria and free-radical formation induced by hexachlorobenzene was studied in iron-overloaded rats. The first sign of porphyria, an increase in porphyrins in the liver, was detected at day 22. Liver malondialdehyde was also increased at day 22. During the following weeks, liver porphyrins and malondialdehyde increased simultaneously, accompanied by a decrease in uroporphyrinogen decarboxylase activity and glucose-6-phosphate activity in liver, and a high excretion of porphyrins in the urine. In the rats given hexachlorobenzene, changes were detected in the pattern of lipids in the liver microsomes. In comparison with the controls, there were decreases in C20:4 and C22:5 fatty acids, whereas the fatty acid C20:3w6 was increased. In this study of hexachlorobenzene-induced liver damage there was no difference in the time course of the development of porphyria and that of lipid peroxidation.

Uroporphyrin accumulation in cultured chick embryo hepatocytes: comparison of 2,3,7,8-tetrachlorodibenzo-p-dioxin and 3,4,3',4'-tetrachlorobiphenyl.

Uroporphyrin (URO) accumulation caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 3,4,3',4'-tetrachlorobiphenyl (TCB) in cultured chick embryo hepatocytes was found to depend on the concentration of the added polyhalogenated aromatic compound, and on either the addition of 5-aminolevulinic acid or the induction of 5-aminolevulinic acid synthase. TCDD alone did not cause more than a slight increase in uroporphyrin, whereas TCB alone caused considerable uroporphyrin accumulation associated with increased 5-aminolevulinic acid synthase activity. However, in the presence of exogenous 5-aminolevulinic acid, TCDD was more potent than TCB in causing uroporphyrin accumulation. The concentrations of TCDD or TCB which maximally induced ethoxyresorufin deethylase activity, an indicator of induced cytochrome P450 activity, were lower than those required for maximal uroporphyrin accumulation. Furthermore, ethoxyresorufin deethylase activity was found to decline at concentrations of TCDD or TCB which caused maximum uroporphyrin accumulation. Pretreatment with 3-methylcholanthrene enhanced uroporphyrin accumulation, whereas addition of inhibitors of cytochrome P450 decreased uroporphyrin accumulation. Uroporphyrin accumulation occurred without a decrease in uroporphyrinogen decarboxylase activity, and was unrelated to the degree of conversion of the polyhalogenated aromatic compounds to water-soluble metabolites. Our results indicate that URO accumulation caused by TCDD and TCB requires two separate actions; (1) induction of cytochrome P450 which occurs at low concentrations of the halogenated chemicals, and (2) increased uroporphyrinogen oxidation which is catalyzed by the induced cytochrome P450 and which occurs at higher concentrations of the halogenated chemicals.

Uroporfirinogeno decarboxilasa eritrocitaria y hepatica en porfiria cutanea tardia / Erythrocytic and hepatic uroporphyrinogen decarboxylase in late cutaneous porphyria

- Se han estudiado 16 pacientes con diagnóstico de PCT sintomática, 12 hereditarios y 4 adquiridos, y un caso de PCT latente. - Se llevó a cabo, en todos, un estudio bioquímico completo acerca de la excreción urinaria y fecal de porfirinas, medición de las actividades enzimáticas de Aminolevúlico Dehidrasa, Porfobilinogenasa, Deaminasa y Uroporfirinógeno Decarboxilasa en eritrocitos. De 9 de esos pacientes se obtuvieron biopsias hepáticas, en las cuales se determinaron porfirinas endógenas y actividad de URO-D. - Se estableció una correlación entre los niveles de porfirinas urinarias y hepáticas. - En todos los pacientes, independientemente de que pertencieran al tipo hereditario o no, la actividad de ALA-D se encontró dentro del rango normal, en tanto que PBG-asa y Deaminasa estaban ligeramente aumentadas, confirmendo datos anteriores de este mismo laboratorio. - La actividad de la URO-D en sangre de pacientes con PCT hereditaria estaba notablemente reducida con respecto a los controles, en tanto que los valores de actividad en PCT adquiridas fueron normales. - La URO-D eritrocitaria disminuye su actividad al incrementarse la concentración de porfirinas urinarias y hepáticas en la PCT hereditaria, no así en la adquirida. - Tanto en PCT hereditaria como adquirida, la URO-D hepática se encuentra significativamente inhibida y esta inhibición es mayor cuanto mayores son los niveles de porfirinas hepáticas y urinaria. - La determinación de la URO-D eritrocitaria permite diferenciar claramente una PCT hereditaria de una adquirida (AU)

Uroporfirinogeno decarboxilasa eritrocitaria y hepatica en porfiria cutanea tardia / Erythrocytic and hepatic uroporphyrinogen decarboxylase in late cutaneous porphyria

- Se han estudiado 16 pacientes con diagnóstico de PCT sintomática, 12 hereditarios y 4 adquiridos, y un caso de PCT latente. - Se llevó a cabo, en todos, un estudio bioquímico completo acerca de la excreción urinaria y fecal de porfirinas, medición de las actividades enzimáticas de Aminolevúlico Dehidrasa, Porfobilinogenasa, Deaminasa y Uroporfirinógeno Decarboxilasa en eritrocitos. De 9 de esos pacientes se obtuvieron biopsias hepáticas, en las cuales se determinaron porfirinas endógenas y actividad de URO-D. - Se estableció una correlación entre los niveles de porfirinas urinarias y hepáticas. - En todos los pacientes, independientemente de que pertencieran al tipo hereditario o no, la actividad de ALA-D se encontró dentro del rango normal, en tanto que PBG-asa y Deaminasa estaban ligeramente aumentadas, confirmendo datos anteriores de este mismo laboratorio. - La actividad de la URO-D en sangre de pacientes con PCT hereditaria estaba notablemente reducida con respecto a los controles, en tanto que los valores de actividad en PCT adquiridas fueron normales. - La URO-D eritrocitaria disminuye su actividad al incrementarse la concentración de porfirinas urinarias y hepáticas en la PCT hereditaria, no así en la adquirida. - Tanto en PCT hereditaria como adquirida, la URO-D hepática se encuentra significativamente inhibida y esta inhibición es mayor cuanto mayores son los niveles de porfirinas hepáticas y urinaria. - La determinación de la URO-D eritrocitaria permite diferenciar claramente una PCT hereditaria de una adquirida

Enzymatic and immunological studies of uroporphyrinogen decarboxylase in familial porphyria cutanea tarda and hepatoerythropoietic porphyria.

Uroporphyrinogen decarboxylase activity was measured in hemoglobin-free lysates from two patients with hepatoerythropoietic porphyria (HEP) and from 12 unrelated patients with familial porphyria cutanea tarda (PCT). In HEP patients, enzyme activities were 5% of normal, and familial studies clearly confirmed that patients with HEP are cases of homozygous PCT. Immunoreactive uroporphyrinogen decarboxylase was measured by developing a direct and noncompetitive enzyme immunoassay (EIA). For the 12 familial PCT patients, we found an immunoreactive protein decreased (51%) to the same extent as the catalytic activity (48%) [cross-reactive immunological material ( CRIM ) negative]. The children from the HEP family were also CRIM negative, contrasting with another HEP family previously described as CRIM positive; our data support the hypothesis of a heterogeneity in familial uroporphyrinogen decarboxylase deficiency.

Assay of mouse liver uroporphyrinogen decarboxylase by reverse-phase high-performance liquid chromatography.

A method for the estimation of hepatic uroporphyrinogen decarboxylase activity employing reverse-phase HPLC is described. Mouse liver homogenate in 0.25 M sucrose was pretreated with a suspension of cellulose phosphate and then centrifuged to remove hemoglobin and debris. The supernatant was used as the enzyme source. Incubations were acidified, oxidized, and centrifuged only before analysis of the porphyrins formed, using a Spherisorb ODS column and a gradient solvent system constructed from methanol/lithium citrate mixtures. Coproporphyrinogen formation by BALB/c mouse liver supernatant was estimated as about 5.0 and 9.1 pmol/min/mg protein from uroporphyrinogens I and III, respectively, at 10 microM substrate concentration and pH 6.8. Decarboxylation of pentacarboxyporphyrinogens (the last step in coproporphyrinogen formation) proved to be easily measured. Coproporphyrinogen formation from pentacarboxyporphyrinogen III abd (20 microM) at pH 6.8 was about 109 pmol/min/mg protein. Pentacarboxyporphyrinogen I was not as good a substrate as III abd but was decarboxylated faster at pH 5.4 than at 6.8, and at the lower pH and at 10 microM concentration of substrate 42 pmol of coproporphyrinogen was formed/min/mg protein. These results compared favorably with those obtained by previously published procedures involving time-consuming extraction and esterification steps.