Stimulators and inhibitors of hepatic porphyrin formation in human sera

Porphyria cutanea tarda and pregnancy

Porphyria cutanea tarda is the most common disorder of porphyrin metabolism in Europe and North America. The disorder is characterized by specific cutaneous lesions, associated systemic findings, and excessive accumulation and excretion of uroporphyrin and coproporphyrins. Reports of this condition associated with pregnancy are scarce in the literature. In this review, we present the case of a patient with porphyria cutanea tarda to illustrate the natural progression and complications of the disorder during pregnancy. Based in this report and a review of the published cases, pregnancy may exacerbate the cutaneous lesions of porphyria cutanea tarda during the first trimester. The incidence of diabetes, antinuclear antibodies, and hepatitis B and C are increased among them, making glucose tolerance and antibody testing mandatory. Newborns should be tested for the disorder during the neonatal period. Genetic counseling is advisable as well as teaching avoidance of provocative factors in affected children.

Acute intermittent porphyria--an unusual cause of "surgical" abdomen. Response to propranolol therapy

We report a case of Acute Intermittent Porphyria which presented with acute abdominal distress, autonomic dysfunction and laboratory abnormalities. The treatment is discussed with special emphasis on the effect of large doses of Propranolol.

New developments in the regulation of heme metabolism and their implications

Various endogenous and exogenous chemicals, such as hormones, drugs, and carcinogens and other environmental pollutants are enzymatically converted to polar metabolites as a result of their oxidative metabolism by the mixed-function oxidase system. This enzyme complex constitutes the major detoxifying system of man and utilizes the hemoprotein--cytochrome P-450--as the terminal oxidase. Recent studies with trace metals have revealed the potent ability of these elements to alter the synthesis and to enhance the degradation of heme moiety of cytochrome P-450. An important consequence of these metal actions is to greatly impair the ability of cells to oxidatively metabolize chemicals because of the heme dependence of this metabolic process. In this report the effects of exposure to trace metals on drug oxidations is reviewed within the framework of metal alterations of heme metabolism, including both its synthesis and degradation, since these newly discovered properties of metals have made it possible to define a major dimension of metal toxicity in terms of a unified cellular mechanism of action.

Treatment of hemodialysis-related porphyria cutanea tarda with plasma exchange

A patient with hemodialysis-related porphyria cutanea tarda was treated with plasma exchange. A rapid clinical response occurred coincidentally with a significant fall in the plasma porphyrin level. The level fell further over the following few months without additional therapeutic intervention, whereafter a slow rise occurred without recurrence of skin disease. We suggest that this form of treatment may be ideal for the patient with porphyria cutanea tarda and chronic renal failure in whom no alternative therapy is available for the cutaneous problem.

Differential responses to inducers of delta-aminolaevulinate synthase and haem oxygenase during pregnancy

The responses of hepatic delta-aminolaevulinate synthase and microsomal haem oxygenase to inducers were examined in pregnant rats. 2-Allyl-2-isopropylacetamide-mediated induction of delta-aminolaevulinate synthase was greatly decreased during pregnancy and in the early post-partum period. Administration of allylisopropylacetamide to pseudopregnant rats induced delta-aminolaevulinate synthase normally. Treatment of pregnant rats with cortisol failed to restore the drug-mediated induction of delta-aminolaevulinate synthase. Microsomal cytochrome P-450 content and the activities of drug-metabolizing enzymes such as aniline hydroxylase and ethylmorphine. N-demethylase were significantly lowered during pregnancy. In contrast with the greatly impaired induction of delta-aminolaevulinate synthase, the induction of haem oxygenase in response to CoCl2 remained unaltered in pregnant rats. The normal perturbations of delta-aminolaevulinate synthase, consisting of an initial inhibition followed by a rebound increase in the enzyme activity associated with CoCL2 treatment, were observed during pregnancy. These findings indicate that hormones and metabolic factors associated with gestation exert significant but differential controls on the induction patterns of delta-aminolaevulinate synthase and haem oxygenase.

The effect of ethanol on heme and porphyrin synthesis

Despite the inherent difficulties in interpreting in vivo data on the effects of alcohol, it appears quite evident that ethanol itself alters the metabolism of the porphyrins and in so doing directly influences heme and hemoglobin synthesis. The mechanism of ethanol-induced iron overload remains elusive but, through observing the effects of phlebotomies and rechallenge with iron, the relationships of iron and alcohol to porphyria cutanea tarda are being more clearly defined. The control mechanisms of porphyrin synthesis by endogenous factors may be part of a more general red blood cell regulatory apparatus.

Study of factors causing excess protoporphyrin accumulation in cultured skin fibroblasts from patients with protoporphyria

The activity of heme synthetase, which catalyzes the chelation of ferrous iron to protoporphyrin to form heme, is deficient in sonicates of skin fibroblasts cultured from patients with protoporphyria. During culture in Eagle's medium supplemented with fetal calf serum, these cells do not accumulate protoporphyrin, however. This may be due to a minimal requirement for heme synthesis, since glycine is incorporated into heme at a low rate which is similar to that in normal fibroblasts. In addition, the activity of delta-aminolevulinic acid (ALA) synthetase, the first and rate-limiting enzyme of heme biosynthesis which catalyzes the formation of ALA from glycine, is normal in lysates of the fibroblasts. Cultured fibroblasts were therefore incubated with ALA in order to bypass the rate-limiting step of heme biosynthesis. In the presence of 25 muM iron, protoporphyrin was detected in protoporphyria cell lines when the concentration of ALA in the medium reached 50 muM, but not in normal lines. As the concentration of ALA was increased above 50 muM, all lines accumulated protoporphyrin. However, the amount was 2-3 times more in cultured fibroblasts from patients with protoporphyria, reflecting their deficiency of heme synthetase activity. When iron was not added to the medium, protoporphyrin accumulated to a similar degree in normal and protoporphyria fibroblasts; this was significantly more than that in the presence of iron. These studies indicate that excessive protoporphyrin accumulation in protoporphyria, which is due principally to deficient heme synthetase activity, may be modified by the rate of ALA formation in heme-producing tissues, and by the availability of iron.

On the obligatory role of the hypophysis in sexual differentiation hepatic metabolism in rats

The hepatic metabolism of 4-[4-14C]androstene-3,17-dione and 5alpha-[4-14C]androstane-3alpha,17beta-diol was studies in castrated and hypophysectomized male rats with a transplanted pituitary under the kidney capsule. The effects of testosterone propionate and estradiol benzoate on liver metabolism were also studied in these experimental animals. It was found that the autonomous pituitary secreted a "feminizing factor" that transformed the male type of steroid metabolism characteristic of hypophysectomized rats into a female type of metabolism Hypophysectomized rats were unresponsive towards androgen action on the liver and did not respond with feminized hepatic metabolism after treatment with estradiol benzoate. It is concluded that estrogenic action on liver enzymes is mediated via modulation of the secretion of a central (probably hypothalamic) "feminizing factor inhibiting factor" and the sex hormonal effects of hepatic metabolism only occur in the presence of a pituitary in situ.

Study of the developmental pattern of heme catabolism in liver and the effects of cobalt on cytochrome P-450 and the rate of heme oxidation during the neonatal period

The comparative development patterns of heme oxidation andof cytochrome P-450 dependent drug oxidation in rat liver were examined. High levels of heme oxygenase activity were present in whole embryo preparations at day 13 of gestation. At birth this enzyme activity in liver was approximately equal to that of normal adult liver. In the immediate postnatal period the rate of hepatic heme oxidation increased sharply, reaching levels 3-5 times normal during the first week postpartum. Thereafter, this enzyme activity progressively decreased and returned to normal adult levels by the 28th postpartum day. The development of microsomal heme oxidation and of P-450 dependent drug oxidation exhibited reciprocal patterns, with the latter being at low levels of activity during the immediate postnatal period and reaching adult activity only 4 or more wk after birth. Cobalt injected into pregnant animals or in to nursing mothers did not induce heme oxygenase in the fetus or suckling neonate. However, when treated directly with the metal, 4-day old neonates exhibited a small induction response of this enzyme; and the inducibility of heme oxygenase increased gradually to fully adult levels by the end of the 4th postpartum week. Cobalt at all postnatal developmental stages was capable of diminishing hepatic contents of total microsomal heme and P-450; however this effect of the metal was small in the immediate period after birth and increased progressively with maturation. These findings demonstrate that the patterns of development of hepatic capacity for carrying out the oxidation of heme and the P-450 dependent oxidation of drugs are different and thus provide further evidence that these microsomal enzyme systems are distinct from each other and under separate regulatory mechanisms. The degree of induction response for hepatic heme oxygenase evoked by the trace metal, cobalt, was also shown to have developmental determinants as did the susceptibility of hepatic cytochrome P-450 to degradation by this metal. The very high levels of hepatic heme oxygenase activity which characterize neonates during the first week of life indicate that over-production of bilirubin contributes significantly to the mechanism of neonatal jaundice.