Studies in porphyria. IV. Expression of the gene defect of acute intermittent porphyria in cultured human skin fibroblasts and amniotic cells: prenatal diagnosis of the porphyric trait

Enzyme abnormalities in the porphyrias

Evidence is presented that each of the porphyrias represents a different inborn error of metabolism in haem biosynthesis. Control of the pathway takes place by feedback repression and inhibition by haem of delta-aminolaevulinic-acid synthase. It is suggested that insituations where the activity of this enzyme is derepressed, prophobilinogen deaminase represents a secondary control step.

Levels of delta-aminolevulinate dehydratase, uroporphyrinogen-I synthase, and protoporphyrin IX in erythrocytes from anemic mutant mice

Levels of erythrocyte delta-aminolevulinate dehydratase [ALA-dehydratase; porphobilinogen synthase; 5-aminolevulinate hydro-lyase (adding 5-aminolevulinate and cyclizing), EC 4.2.1.24], UROPORPHYRINOGEN-I synthase [Uro-synthase; porphobilinogen ammonia-lyase (polymerizing), EC 4.3;1.8], AND PROTOPORPHYRIN IX (Proto) were measured by sensitive semimicroassays using 2-5 mul of whole blood obtained from normal and anemic mutant mice. The levels of erythrocyte ALA-dehydratase and Uro-synthase showed marked developmental changes and ALA-dehydratase was influenced by the Lv gene. Mice with overt hemolytic diseases (ja/ja, sph/sph, nb/nb, ha/ha) had 10- to 20-fold increases in ALA-dehydratase, Uro-synthase, and Proto compared with their normal controls. Mice with an iron deficiency (mk/mk) and mice with hypoplastic anemias (W/Wv, Sl/Sld, an/an) had mild to moderate increases in these parameters. Elevated enzyme activities and Proto correlated well with the number of reticulocytes. Because all mice with anemias possessed elevated levels of ALA-dehydratase, Uro-synthase, and Proto independent of differences in their genotypes, the increase in these parameters is not likely to be the result of a specific gene defect. The increased enzyme activities and Proto concentration probably reflect increased frequency of young red cells that are still active in heme biosynthesis.

Studies in porphyria. VI. Biosynthesis of porphyrins in mammalian skin and in the skin of porphyric patients

Porphyrin biosynthesis in mammalian skin and in skin obtained from patients with selected types of porphyria has been studied. Cutaneous porphyrinogenesis required the precursor delta-aminolevulinic acid (ALA) which, when added to murine, rat, and human skin in vitro, was rapidly converted to porphyrins. Total porphyrin content was quantitated by fluorescence assay, and spectral studies indicated that more than 80% of the porphyrin produced was protoporphyrin. The majority of skin porphyrinogenesis occurrred in epidermis or in epidermal derivatives such as hair roots. Known inducers of hepatic delta-aminolevulinic acid synthetase (ALAS), the rate-limiting enzyme for heme biosynthesis, were not inducers when added to skin in vitro. Skin from patients with acute intermittent porphyria demonstrated a 43% decrease in cutaneous porphyrin production as compared to unaffected normals. This is consistent with the known deficiency of uroporphyrinogen synthetase that has been previously demonstrated in the liver and red blood cells of these patients. Porphyrinogenesis in skin of patients with porphyria cutanea tarda was not different from controls. These studies demonstrate that skin has the enzymatic capacity to synthesize porphyrins from added ALA and that cutaneous porphyrinogenesis from ALA is deficient in patients with acute intermittent porphyria.

Induction of a deficiency of steroid delta 4-5 alpha-reductase activity in liver by a porphyrinogenic drug

The hepatic enzymes that catalyze drug oxidations and the reductive metabolism of steroid hormones to 5alpha-derivatives are localized in membranes of the endoplasmic reticulum. Phenobarbital, which exacerbates acute intermittent porphyria in man, induces drug-oxidizing enzymes in liver. Additionally, patients in whome the primary gene defect (uroporphyrinogen-I-synthetase deficiency) of acute intermittent porphyria has become clinically expressed have low levels of hepatic steroid delta4-5alpha-reductase activity. This 5alpha-reductase deficiency in acute intermittent porphyria leads to the disproportionate generation of 5beta-steroid metabolites from precursor hormones; such steroid metabolites have significant porphyria-inducing action experimentally. In this study the effects of phenobarbital on drug oxidation and steroid 5alpha-reduction in man were examined to determine if this drug could produce changes in steroid 5alpha-reductase activity which mimicked those seen in patients with acute intermittent porphyria. Metabolic studies with [14C]-testosterone and 11beta-[3H]hydroxyandrostenedione were carried out in five normal volunteers. In all five subjects phenobarbital administration (2 mg/kg/per day for 21 days) enhanced plasma removal of the test drugs antipyrine and phenylbutazone as expected; but in four subjects phenobarbital also substantially depressed 5alpha-metabolite formation from [14C]testosterone and resulted in a pattern of hormone biotransformation characterized by a high ratio of 5beta/5alpha-metabolite formation. Studies with 11beta-[3H]hydroxy-androstenedione in three subjects confirmed that phenobarbital produced this high 5beta/5alpha ratio of steroid metabolism by depressing 5alpha-reductase activity for steroid hormones in liver. The high ratio of 5beta/5alpha-metabolites formed in normals after drug treatment mimicks the high 5beta/5alpha-steroid metabolite ratio formed from endogenous hormones in acute intermittent porphyria. The proximate mechanism by which phenobarbital induces reciprocal changes in activities of the microsomal enzymes which catalyze drug oxidations and steroid 5alpha-reductions is not known. This action of phenobarbital raises the possibility, however, that certain drugs which provoke exacerbations of human porphyria may do so, in part, by producing deleterious shifts in the patterns of endogenous steroid hormone metabolism.

Sequential induction of heme pathway enzymes during erythroid differentiation of mouse Friend leukemia virus-infected cells

The process of erythroid differentiation in mouse Friend leukemia virus transformed cells (T3-C1-2) was examined by following changes in several enzyme activities of the heme biosynthetic pathway and in heme concentration while the cells were undergoing erythroid differentiation after treatment with dimethylsulfoxide. Untreated cells on the one hand, have a limited capacity for spontaneous differentiation. On the other hand, dimethylsulfoxide(DMSO)-treated cells showed an increase in the activities of delta-aminolevulinic acid (ALA) synthetase, ALA dehydratase, uroporphyrinogen-I synthetase, ferrochelatase, and heme concentration by days 1, 1.5, 2, and 4, respectively. The increase of the heme pathway enzymes and heme concentration followed the order of these enzymes or products as they are arranged in the heme biosynthetic pathway. These changes induced by DMSO were effectively inhibited by treatment with actinomycin D, suggesting that continued RNA synthesis is required for the differentiation process. 5-bromo-2'-deoxyuridine (BrdU) (10(-5) M) inhibited the DMSO-induced changes of the heme pathway enzymes. BrdU was most effective when it was present during the first 2 days of cell culture. It gradually lost its inhibitory effect when added after the 3rd day or later. The BrdU-mediated inhibition was completely overcome by the addition of thymidine (7 x 10(-5) M), but not by uridine (7 x 10(-5) M). All these data suggest that a sequential induction of the heme pathway enzyme takes place during erythroid differentiation of Friend leukemia cells, and that the sequential induction of the enzymes may be due to a sequential activation of genes coding for these enzyme activities.