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

The effects of hexachloronaphthalene on selected parameters of heme biosynthesis and systemic toxicity in female wistar rats after 90-day oral exposure

Hexachloronaphthalenes (HxCNs) are the most toxic congeners of polychlorinated naphthalenes, a group of compounds lately included into the list of persistent organic pollutants (POPs). This study presents the effects of 90-day intragastric administration of HxCN to female Wistar rats at doses of 0.03, 0.1, and 0.3 mg/kg body weight. The study examined selected parameters of the heme synthesis pathway, oxidative stress, hepatic cytochromes level, and basic hematology indicators. A micronucleus test was also performed. The subchronic exposure of rats to HxCN resulted in disruption of heme biosynthesis, hematological disturbances, and hepatotoxicity. The highest dose of HxCN inhibited aminolevulinic acid dehydratase (ALA-D) and uroporphyrinogen decarboxylase (URO-D). Accumulation of higher carboxylated porphyrins in the liver and increased excretion of 5-aminolevulinic acid in the urine was observed after a dose of 0.1 mg/kg body weight. The most sensitive effect of HxCN in rats was very strong induction of hepatic CYP1A1 activity, which was observed after the lowest dose. The highest dose of HxCN induced significant thrombocytopenia, thymic atrophy and hepatotoxicity, expressed as hepatomegaly and hepatic steatosis.

Effect of an oral iron chelator or iron-deficient diets on uroporphyria in a murine model of porphyria cutanea tarda

Porphyria cutanea tarda is a liver disease characterized by elevated hepatic iron and excessive production of uroporphyrin (URO). Phlebotomy is an effective treatment that probably acts by reducing hepatic iron. Here we used Hfe(-/-) mice to compare the effects on hepatic URO accumulation of two different methods of hepatic iron depletion: iron chelation using deferiprone (L1) versus iron-deficient diets. Hfe(-/-) mice in a 129S6/SvEvTac background were fed 5-aminolevulinic acid (ALA), which results in hepatic URO accumulation, and increasing doses of L1 in the drinking water. Hepatic URO accumulation was completely prevented at low L1 doses, which partially depleted hepatic nonheme iron. By histological assessment, the decrease in hepatic URO accumulation was associated with greater depletion of iron from hepatocytes than from Kupffer cells. The L1 treatment had no effect on levels of hepatic cytochrome P4501A2 (CYP1A2). L1 also effectively decreased hepatic URO accumulation in C57BL/6 Hfe(-/-) mice treated with ALA and a CYP1A2 inducer. ALA-treated mice maintained on defined iron-deficient diets, rather than chow diets, did not develop uroporphyria, even when the animals were iron-supplemented either directly in the diet or by iron dextran injection.

CONCLUSION

The results suggest that dietary factors other than iron are involved in the development of uroporphyria and that a modest depletion of hepatocyte iron by L1 is sufficient to prevent URO accumulation.

Pro-oxidant and antioxidant factors in acute intermittent porphyria: family studies

Given the crucial role of iron and porphyrins in oxidative cellular damage in the chronic porphyrias, we undertook an extensive study in families with acute porphyrias to evaluate the possible role of similar oxidative damage in these diseases, whose natural history is often also complicated by neoplastic evolution. Four unrelated patients with acute intermittent porphyria (AIP) were studied together with 37 members of four different families. Aminolevulinic acid and porphobilinogen were measured in urine, and porphyrins in urine, plasma and stools. The activity of the congenitally deficient enzyme, porphobilinogen deaminase, and the concentrations of plasma iron, transferrin, ferritin, and various antioxidants (ascorbic acid, retinol, tocopherol, alpha- and beta-carotene, by a personal HPLC method) and the urinary and plasma metabolites of nitrous oxide were also assayed. The results showed no relationship between the observed increase of porphyrin metabolites and the presence of markers of oxidative damage or the decrease of circulating antioxidants: however, when such a decrease was registered, it depended on spontaneous or iatrogenic iron accumulation. We conclude that family screening, recommended for the identification of AIP carriers, must also include evaluation of iron stores with a view to preventing the oxidative damage and in order to forestall the neoplastic evolution of the disease.

Experimental hepatic uroporphyria induced by the diphenyl-ether herbicide fomesafen in male DBA/2 mice

Hepatic uroporphyria can be readily induced by a variety of treatments in mice of the C57BL strains, whereas DBA/2 mice are almost completely resistant. However, feeding of the protoporphyrinogen oxidase-inhibiting herbicide fomesafen (0.25% in the diet for 18 weeks) induced hepatic uroporphyria in male DBA/2N mice (liver porphyrin content up to 150 nmol/g, control animals 1 nmol/g), whereas fomesafen-treated male C57BL/6N mice displayed only a slight elevation of liver porphyrins (approximately 5 nmol/g). The profile of accumulated hepatic porphyrins in fomesafen-treated DBA/2N mice resembled the well-characterised uroporphyria induced by polyhalogenated aromatic hydrocarbons, while histological examination confirmed the presence of uroporphyria-specific cytoplasmic inclusions in the hepatocytes. Uroporphyrinogen decarboxylase activity decreased to about 30% of control values in fomesafen-treated DBA/2N mice; microsomal methoxyresorufin O-dealkylase activity was slightly reduced. The amount of CYP1A1 and CYP1A2 mRNA, as determined by real-time PCR, was not significantly changed; mRNA encoding the housekeeping 5-aminolevulinic acid synthase was elevated 10-fold. Total liver iron was slightly increased. A similar uroporphyria was induced by the herbicide formulation Blazer, containing a structurally related herbicide acifluorfen, when fed to DBA/2N mice at a dose corresponding to 0.25% of acifluorfen in the diet. Since DBA/2 mice are almost completely resistant to all well-characterised porphyrogenic chemicals, the results suggest the possible existence of a yet unknown mechanism of uroporphyria induction, to which the DBA/2 mouse strain is more sensitive than the C57BL strain.

Isolation and characterization of extragenic mutations affecting the expression of the uroporphyrinogen decarboxylase gene (HEM12) in Sacharomyces cerevisiae

Uroporphyrinogen decarboxylase (Uro-d; EC 4.1.1.37), the fifth enzyme in the heme biosynthetic pathway, which catalyzes the sequential decarboxylation of uroporphyrinogen to coproporphyrinogen, is encoded by the HEM12 gene in Saccharomyces cerevisiae. The HEM12 gene is transcribed into a major short mRNA and a minor longer one, approximately 1.35 and 1.55 kb, respectively, in size, and that differ in the 5' untranslated region. "Uroporphyric" mutants, which have no mutations in the HEM12 gene but accumulate uroporphyrinogen, a phenotype characteristic of partial Uro-d deficiency, were investigated. Genetic analysis showed that the mutant phenotype depends on the combined action of two unlinked mutations, udt1 and either ipa1, ipa2, or ipa3. ipa1 is tightly linked to HEM12. The mutation udt1 apparently acts specifically on the HEM12 gene, and causes a six to tenfold decrease in the levels of the short HEM12 mRNA, in the beta-galactosidase activity of a HEM12-lacZ fusion, in immunodetectable protein and enzyme activity. But heme synthesis is normal and porphyrin accumulation was modest. The mutations ipa1, ipa2, and ipa3 had no phenotype on their own, but they caused an increase in porphyrin accumulation in a udt1 background. This multiplicity of genetic factors leading to uroporphyric yeast cells closely resembles the situation in human porphyria cutanea tarda.

Uroporphyrinogen decarboxylase

Uroporphyrinogen decarboxylase (EC 4.1.1.37) catalyzes the decarboxylation of uroporphyrinogen III to coproporphyrinogen III. The amino acid sequences, kinetic properties, and physicochemical characteristics of enzymes from different sources (mammals, yeast, bacteria) are similar, but little is known about the structure/function relationships of uroporphyrinogen decarboxylases. Halogenated and other aromatic hydrocarbons cause hepatic uroporphyria by decreasing hepatic uroporphyrinogen decarboxylase activity. Two related human porphyrias, porphyria cutanea tarda and hepatoerythropoietic porphyria, also result from deficiency of this enzyme. The roles of inherited and acquired factors, including iron, in the pathogenesis of human and experimental uroporphyrias are reviewed.

Effect of the protoporphyrinogen oxidase-inhibiting herbicide fomesafen on liver uroporphyrin and heptacarboxylic porphyrin in two mouse strains

The effect of the protoporphyrinogen oxidase-inhibiting herbicide fomesafen on liver porphyrin accumulation was studied in long-term high-dose experiments. Fomesafen caused liver accumulation of uroporphyrin and heptacarboxylic porphyrin when fed at 0.25% in the diet to male ICR mice for 5 months (fomesafen-treated mice: 52 nmol uroporphyrin, 21 nmol heptacarboxylic porphyrin/g liver; control mice: traces of uroporphyrin, heptacarboxylic porphyrin not detected). Uroporphyrinogen decarboxylase activity was depressed to about 25% of control values. Iron treatment accelerated the development of this porphyria cutanea tarda-like experimental porphyria both in ICR and C57B1/6J mice. In contrast to other uroporphyrinogen decarboxylase inhibitors, fomesafen treatment did not increase the cytochrome P450IA-related activities and the amount of P450IA2 protein was shown to be significantly decreased by Western immunoblotting. Thus, fomesafen is a unique chemical that inhibits both the oxidation of protoporphyrinogen as well as the conversion of uroporphyrinogen to coproporphyrinogen. However, the accumulation of highly carboxylated porphyrins is evident only after prolonged treatment with high doses of the herbicide.