Phlebotomy and iron-overload in porphyria cutanea tarda

The clinical manifestations of chronic iron overload

Primary or genetic haemochromatosis is an inherited disease characterized by an inappropriate degree of iron absorption with accumulation of excessive amounts of tissue iron. Parenchymal iron accumulation results in the typical clinical features of the disease including hepatic cirrhosis, diabetes, testicular atrophy and skin pigmentation. The disease is inherited in an autosomal recessive manner. The gene for the disease has not been identified but is tightly linked to the A locus of the histocompatibility complex on chromosome 6. The approximate homozygote frequency in Caucasians is 0.3% with an equal sex ratio. Excessive body iron stores have been described in a number of other conditions, particularly alcoholic liver disease. There is increasing evidence that many of these individuals are in fact also suffering from genetic haemochromatosis. Diagnostic tests including serum iron, transferrin saturation, serum ferritin and liver iron concentration make it possible to detect sufferers of the disease. Screening relatives of affected individuals with these tests allows a diagnosis to be made before permanent tissue damage has occurred. Removal of excess iron stores by repeated phlebotomy is the primary treatment. If iron is removed before significant tissue damage has occurred, the complications and natural course of the disease will be prevented provided reaccumulation of iron does not occur. Excessive iron accumulation with resultant organ damage also occurs in anaemias associated with ineffective erythropoiesis and after excessive parenteral iron administration or repeated blood transfusions. Similar clinical features may be seen. Chelation therapy is the mainstay of treatment in these cases where long-term venesection is not possible.

Association between alcoholism and increased hepatic iron stores

Although alcoholic liver disease is often associated with some increase in hepatic iron stores, it is now established that when gross iron overload is present, this is due to genetic hemochromatosis. Furthermore, there appears to be a critical iron concentration necessary for the induction of hepatic fibrosis. Lipid peroxidation induced by ethanol and/or iron would appear to play a major role in hepatic damage in both humans and experimental animals. Although the exact mechanism(s) of induction of lipid peroxidation by ethanol and iron remains to be elucidated, both toxins can exert a synergistic effect upon hepatic lipid peroxidation. Iron overload has also been shown to stimulate directly hepatocyte and hepatic procollagen mRNA expression, which is further stimulated by ethanol. The observed synergism between iron and alcohol with respect to both hepatic lipid peroxidation and collagen biosynthesis offers a possible explanation of the apparent early onset of fibrosis and cirrhosis in patients with iron overload who have an excessive alcohol intake.

Structural and functional properties of rat liver mitochondria in hexachlorobenzene induced experimental porphyria

A possible link between changes in iron and porphyrin content in liver mitochondria, from rats treated with either hexachlorobenzene, iron, or hexachlorobenzene plus iron, as a function of treatment time and their structural-functional properties, has been investigated. Normal oxidative phosphorylation in mitochondria from rats treated with iron has been shown. By contrast a significant and constant uncoupling of the phosphorylative process, fully reversed by albumin, in mitochondria from rats treated with hexachlorobenzene and hexachlorobenzene plus iron has been presented. A possible involvement of pentachlorophenol in causing these abnormalities has been proposed.

Effects of hexachlorobenzene and iron loading on rat liver mitochondria

The effects of hexachlorobenzene treatment and simultaneous iron-overload on the iron and porphyrin content of rat liver and rat liver mitochondria have been examined. In order to assess damages to the mitochondrial membrane occurring with these treatments, the content of malondialdehyde and selected functional properties of mitochondria were compared with those from control animals. Prolonged intake of hexachlorobenzene (8 weeks) resulted in a strikingly increased level of porphyrins together with a moderate increase in iron concentration. Simultaneous administration of hexachlorobenzene and iron-dextran caused the porphyrin level to reach 25% of the amount induced by hexachlorobenzene alone. The iron concentrations in liver as well as in liver mitochondria are also decreased under these conditions, as compared to the effect of iron-dextran. In contrast, the effects of hexachlorobenzene combined with iron-dextran on mitochondrial oxidative phosphorylation and malondialdehyde content are greater than those of either hexachlorobenzene or iron-dextran. These data suggest that porphyrin accumulation per se causes little deleterious effect and that both agents administered together act synergistically in causing damage to the mitochondrial membrane.

Iron metabolism in porphyria cutanea tarda

The iron metabolism has been studied in 11 patients with porphyria cutanea tarda. Despite significantly increased amounts of iron in the serum and liver, the porphyria patients absorb not less but significantly more radioiron than normal controls. Whereas phlebotomy-induced iron deficiency stimulates the absorption in controls, no further stimulation is found in the porphyria patients. The plasma iron turnover is high in the porphyria patients, and some of this iron is probably deposited in the liver. The relationship between the high iron absorption, high plasma iron turnover, high liver iron, liver damage and uroporphyrin production in the liver is discussed. It is suggested that two concurrent genetic defects may cause porphyria cutanea tarda, one in iron absorption and one in porphyrin synthesis by damaged liver cells. The absorption of inorganic iron was higher than that of hemaglobin iron. The possible damage which fortification with inorganic iron could cause to the very small group of porphyria patients is discussed.

The role of iron in the pathogenesis of porphyria cutanea tarda. An in vitro model

Porphyria cutanea tarda (PCT) is characterized biochemically by excessive hepatic synthesis and urinary excretion of uroporphyrin I. Clinical evidence has implicated iron in the pathogenesis of PCT. The synthesis of the normally occurring isomer of uroporphyrin, namely uroporphyrin III, from porphobilinogen (PBG) requires two enzymes; uroporphyrinogen I synthetase and uroporphyrinogen III cosynthetase (COSYN). In the absence of COSYN only uroporphyrinogen I is formed. These experiments were designed to study the effect of iron on porphyrin biosynthesis in porcine and human crude liver extracts and to measure COSYN activity in the presence of iron.Mitochondria-free crude liver extracts were prepared in 0.25 m sucrose at pH 7.4 by centrifugation at 37,000 g. Preparations were incubated with either 0.2 mm amino-levulinic acid (ALA) or 0.1 mm PBG. The addition of ferrous ion (either from ferritin iron [4 mug/ml] and cysteine [6.7 mm] or ferrous ammonium sulfate [0.3 mm Fe] and cysteine) significantly increased the rate of uroporphyrin synthesis from either ALA or PBG. The predominant porphyrin synthesized in the presence of ferrous ion was uroporphyrin I whereas coproporphyrin III predominated in its absence. Orthophenanthroline blocked these effects of ferrous ion.To investigate the effect of ferrous ion on COSYN, crude liver extracts were incubated with ferrous ammonium sulfate (0.3 mm Fe) and cysteine (6.7 mm) and the COSYN activity of the incubates was assayed directly. In both porcine and human extracts ferrous ion caused marked inhibition of COSYN activity. Orthophenanthroline blocked the inhibitory effect.Inactivation of COSYN by heating resulted in marked enhancement of porphyrin synthesis from PBG. The sole product was uroporphyrin I.Thus, inactivation of COSYN results in accelerated synthesis of uroporphyrin I. This effect of ferrous ion provides a possible biochemical explanation for the excess production and excretion of uroporphyrin I in patients with PCT and the reversal of this defect by phlebotomy.