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

UNLABELLED: 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.

Effect of iron and ascorbate on uroporphyria in ascorbate-requiring mice as a model for porphyria cutanea tarda.

UNLABELLED: Excess hepatic iron is known to enhance both porphyria cutanea tarda (PCT) and experimental uroporphyria. Since previous studies have suggested a role for ascorbate (AA) in suppressing uroporphyria in AA-requiring rats (in the absence of excess iron), the present study investigated whether AA could suppress uroporphyria produced by excess hepatic iron. Hepatic URO accumulation was produced in AA-requiring Gulo(-/-) mice by treatment with 3,3',4,4',5-pentachlorbiphenyl, an inducer of CYP1A2, and 5-aminolevulinic acid. Mice were administered either sufficient AA (1000 ppm) in the drinking water to maintain near normal hepatic AA levels or a lower intake (75 ppm) that resulted in 70 % lower hepatic AA levels. The higher AA intake suppressed hepatic URO accumulation in the absence of administered iron, but not when iron dextran (300-500 mg Fe/kg) was administered. This effect of iron was not due to hepatic AA depletion since hepatic AA content was not decreased. The effect of iron to prevent AA suppression of hepatic URO accumulation was not observed until a high hepatic iron threshold was exceeded. At both low and high AA intakes, hepatic malondialdehyde (MDA), an indicator of oxidative stress, was increased three-fold by high doses of iron dextran. MDA was considerably increased even at low iron dextran doses, but without any increase in URO accumulation. The level of hepatic CYP1A2 was unaffected by either AA intake. CONCLUSION: In this mouse model of PCT, AA suppresses hepatic URO accumulation at low, but not high hepatic iron levels. These results may have implications for the management of PCT.

Chemopreventive activity of selenocysteine prodrugs against tobacco-derived nitrosamine (NNK) induced lung tumors in the A/J mouse.

Prodrugs of L-selenocysteine have potential utility in cancer chemoprevention. This study reports the efficacy of three selenazolidine-4(R)-carboxylic acids, (2-unsubstituted, 2-oxo, and 2-methyl derivatives; SCA, OSCA, and MSCA, respectively) against tobacco-related lung tumorigenesis in a mouse model. Seven days after initiation of an AIN-76A diet supplemented with sodium selenite (5 ppm Se), L-selenomethionine (3.75 ppm Se), Se-methyl-L-selenocysteine (3 ppm Se), L-selenocystine (15 ppm Se), SCA (15 ppm Se), OSCA (15 ppm Se), or MSCA (15 ppm Se), mice received 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK; 10 micromol, i.p.). After an additional 16 weeks on the diets, two compounds, OSCA and selenocystine, significantly reduced lung adenoma multiplicity from 7.2 tumors per mouse in the NNK group to 4.5 and 4.6 tumors per mouse, respectively. Neither selenium concentration nor glutathione peroxidase activity in either RBCs or liver served as surrogate indicators of tumor reduction. Hepatic selenium levels were significantly elevated by all selenium-containing compounds except Se-methyl-L-selenocysteine and SCA; RBC selenium levels by all except sodium selenite and MSCA. With the exception of L-selenomethionine, RBC glutathione peroxidase activity was increased along with the elevated selenium levels. Hepatic glutathione peroxidase activity was elevated by all Se-compounds except SCA. The two compounds showing significant tumor reduction (OSCA and selenocystine) were the only two compounds that showed ubiquity of changes, elevating both selenium levels and GPx activity in both liver and RBC.

Characteristics of selenazolidine prodrugs of selenocysteine: toxicity, selenium levels, and glutathione peroxidase induction in A/J mice.

We have previously reported the synthesis and characterization of two new classes of selenazolidine-4(R)-carboxylic acids (2-oxo and 2-methyl-SCAs) (OSCA and MSCA, respectively), as well as the "parent" compound, selenazolidine-4(R)-carboxylic acid (SCA, selenaproline). These compounds were designed as prodrugs of L-selenocysteine with potential application in cancer chemoprevention or other clinical uses. We will be exploring the chemopreventive activity of the new compounds in the well-established A/J mouse model of tobacco-induced lung carcinogenesis. The objectives of the present study were to investigate several fundamental biochemical endpoints after selenazolidine administration compared with other selenium-containing agents. Groups of mice were fed either AIN-76A diet alone or the diet supplemented with the following selenium compounds (ppm Se): sodium selenite (5), L-selenomethionine (3.75), L-selenocystine (15), Se-methyl-L-selenocysteine (3), MSCA (5, 10, or 15), OSCA (5, 10, or 15), or SCA (5, 10, or 15). After 28 days of supplementation, toxicity of the selenazolidines was not evident, as measured by outward appearance and behavior, body and organ weight changes, and histological evaluation of liver and lung tissue. Select treatment groups showed significant increases in selenium levels in blood and tissues. Increased activity of selenium-dependent glutathione peroxidase (GPx) in blood and liver illustrated that the selenazolidines provided a source of biologically-available selenium.