Effects of metalloporphyrins on hemoglobin formation in mouse Friend virus-transformed erythroleukemia cells. Stimulation of heme biosynthesis by cobalt protoporphyrin

Mouse Friend virus-transformed erythroleukemia cells in culture undergo erythroid differentiation when treated with a variety of compounds including iron protoporphyrin IX, i.e. hemin. Exogenous hemin is not only incorporated into hemoglobin in these cells but also stimulates heme biosynthesis (Granick, J. L., and Sassa, S. (1978) J. Biol. Chem. 253, 5402-5406). In this study, we examined whether metalloporphyrins other than hemin can also induce differentiation, and if so, whether they can also be incorporated into hemoglobin. Among eight metalloporphyrins examined in culture of these cells, i.e. Co, Mn, Cu, Mg, Ni, Zn, Sn, and Cd protoporphyrin IX, only Co protoporphyrin (10(-4) M) was found to significantly increase the biosynthesis of heme and hemoglobin. In contrast to hemin-mediated induction of erythroid differentiation, Co protoporphyrin was not incorporated into hemoglobin in Friend cells. These data indicate that Co protoporphyrin induces the formation of heme and hemoglobin in Friend cells and that these increases are due to the enhancement of heme biosynthetic activity.

Degradation of hemin IX and synthetic hemins to alpha-bilirubins and their conjugates in the isolated perfused rat liver

Hemin IX was perfused through rat liver of a normal, untreated animal. Its degradation products, collected in the bile fluid over a period of 90 min, were found to consist of the bilirubin IX-alpha diglucuronide (56%), the mixture of bilirubin IX-alpha monoglucuronides (42%), and free bilirubin IX-alpha (2%). When the synthetic hemin XIII 2 was perfused with the same technique, it was found to be degraded in the same way. The bile fluid contained the diglucuronide of bilirubin XIII-alpha 10 (55%), the monoglucuronide of bilirubin XIII-alpha 9 (43%) and the free bilirubin XIII-alpha 8 (2%). Similar results were obtained when the iron 1,4-di(beta-hydroxyethyl)-2,3,5,8-tetramethyl-6,7-di(beta-carboxyethyl) porphyrin 3 was perfused; the diglucuronide of the alpha-bilirubin 11 comprised 65% of the excreted bile bilirubins, the monoglucuronide was 25% of the total and the free alpha-bilirubin 11 10% of the total. Perfusion of hematohemin gave 58% of the diglucuronide of alpha-hematobilirubin, as well as 40% of the monoglucuronides, and 2% of the free alpha-hematobilirubin. The simultaneous perfusion of hematohemin and of hemin IX produced an inhibition of the degradation of the hemin IX, while hematohemin was degraded as described above. It was concluded that the normal rat liver is prepared to dispose of exogenously added hemins by their oxidation to alpha-biliverdins, reduction of the latter to the corresponding alpha-bilirubin and excretion of their conjugated derivatives through the bile duct.

Haem and drug-metabolizing enzymes in regenerating rat liver

Various parameters of haem and drug metabolism were measured during the course of liver regeneration after two-thirds hepatectomy. Partial hepatectomy produced a significant depression in delta-ALA synthetase and delta-ALA dehydratase, and induction in haem oxygenase at an early stage of regeneration. The values returned to normal within 7-14 days. These changes were also accompanied by a marked decline in benzo(a)pyrene hydroxylase and aminopyrene demethylase. The level of glutathione and the activity of glutathione reductase also increased during the early stage of proliferation. The increased level of glutathione with concomitant decrease in drug-metabolizing enzymes and induction in haem oxygenase could be considered as a protective mechanism for the detoxication process, although a contribution from other biotransforming mechanisms cannot be excluded.

Spectral and other studies on the intestinal haem receptor of the pig

We recently demonstrated the presence of a Triton-solubilized high-affinity haem binder on the pig duodenal brush border membrane. The association of haem to the binding factor was determined using radioactive haem and is now studied by a spectrophotometric technique. The binding alters the Soret absorption band of haem from 395 nm to 413 nm. The dissociation constant for the binding of haem to the solubilized binding factor was estimated to be about 10(-9) M by difference spectroscopy. Human serum albumin could not prevent the solubilized binding factor from binding haem. Trypsin digestion destroyed the binder.

Metal induction of haem oxygenase without concurrent degradation of cytochrome P-450. Protective effects of compound SKF 525A on the haem protein

The induction of hepatic haem oxygenase (EC 1.14.99.3) by a series of metals, organometals and metalloporphyrins was examined in vivo in the presence of compound SKF 525A, which is known to complex with the prosthetic group of cytochrome P-450. Concurrent administration of SKF 525A and an inducing metal did not affect the extent and time course of haem oxygenase induction. The decrease in cytochrome P-450 content normally associated with metal administration was, however, prevented, indicating that haem oxygenase induction by metals can proceed without the significant labilization of the haem moiety of cytochrome P-450. In addition, the integrity of this haem protein can be maintained by chemical means in the presence of sustained high activities of haem oxygenase.

Control of delta-aminolaevulinate synthase and haem oxygenase in chronic-iron-overloaded rats

The hepatic porphyrias are inborn errors of porphyrin and haem biosynthesis characterized biochemically by excessive excretion of delta-aminolaevulinate (ALA), porphobilinogen and other intermediates in haem synthesis. Clinical evidence has implicated iron in the pathogenesis of several types of genetically transmitted diseases. We investigated the role of iron in haem metabolism as well as its relationship to drug-mediated induction of ALA synthase and haem oxygenase in acute and chronic iron overload. Acute iron overload in rats resulted in a marked increase in hepatic haem oxygenase that was associated with a decrease in cytochrome P-450 and an increase in ALA synthase activity. Aminopyrine N-demethylase and aniline hydroxylase activities, which are dependent on the concentration of cytochrome P-450, were also decreased. In contrast, in chronic-iron-overloaded rats, there was an adaptive increase in haem oxygenase activity and an increase in ALA synthase that was associated with normal concentrations of microsomal haem and cytochrome P-450. The induction of ALA synthase in chronic iron overload was enhanced by phenobarbital and allylisopropylacetamide, in spite of the fact that these agents did not increase haem oxygenase activity. Small doses of Co2+ were potent inducers of the haem oxygenase in chronic-iron-overloaded, but not in control, animals. We conclude that increased hepatic cellular iron may predispose certain enzymes of haem synthesis to induction by exogenous agents and thereby affect drug-metabolizing enzyme activities.

Prevention of neonatal hyperbilirubinemia by tin protoporphyrin IX, a potent competitive inhibitor of heme oxidation

The effects of various metalloporphyrins on hepatic heme oxygenase (EC 1.14.99.3) activity were examined in order to identify compounds that could inhibit heme degradation to bile pigment and might therefore be utilized to suppress the development of hyperbilirubinemia in the newborn. Among nine metal-protoporphyrin IX chelates (i.e., metal-hemes) studied, Sn-heme, Mn-heme, and Zn-heme substantially diminished heme oxygenase activity in vivo in the rat. These metalloporphyrins act as competitive inhibitory substrates in the heme oxygenase reaction but are not themselves oxidatively degraded. Sn-heme was the most potent enzyme inhibitor (Ki = 0.011 microM) in liver, spleen, kidney, and skin. Sn-heme administered to newborn animals within the first 72 hr after birth blocked the postnatal increase in heme oxygenase activity that occurs in various tissues. Its effect on the enzyme levels was prompt and protracted. Sn-heme administration also entirely prevented the development of hyperbilirubinemia that normally occurs postnatally. The effect of the metalloporphyrin in lowering the increased concentrations of serum bilirubin in neonates was prompt (within 1 day) and persisted throughout the 42 days after birth. No deleterious effects of Sn-heme treatment of the newborn were observed. This demonstrates that a synthetic metalloporphyrin that is a potent competitive inhibitor of heme oxidation can, when administered to the newborn, also prevent the hyperbilirubinemia that normally develops postnatally. The potential clinical implications of these findings are evident, and it is suggested that the pharmacological properties of Sn-heme and related synthetic metalloporphyrins merit further study.

Specificity of heme oxygenase: a study with synthetic hemins

A large number of synthetic iron porphyrins were enzymatically oxidized by a microsomal heme oxygenase preparation from rat liver. They all had in common two vicinal propionic acid residues at C6 and C7. Iron porphyrins of type I were not substrates of the enzyme. Iron porphyrins that carried electron-withdrawing substituents (acyl residues) at C2 and C4 were substrates of heme oxygenase, although the product yields were reduced. Several iron porphyrins, such as hemin XIII (4) and hem III (5), were better substrates of heme oxygenase than the natural substrate hemin IX (1). The enzymatic oxidation was selective for the alpha-methine bridge, and the alpha-biliverdins obtained were reduced by Biliverdin reductase to the corresponding alpha-bilirubins. Preincubation of the enzymatic system with hemin IX (1) and hemin XIII (4) in the absence of NADPH resulted in an inhibition of their oxidation. The iron-free porphyrins which carried two vicinal propionic acid residues at C6 and C7 were also found to be inhibitors of the enzymatic system when preincubated with the latter. The presence of hematochemin IX (18) suppressed the enzymatic oxidation of hemin IX (1).

[Activity of key enzymes of heme synthesis and degradation and contents of cytochromes b5 and P-450 in rat liver]

The relation between the delta-aminolevulinate-synthase and heme-oxygenase activities and the contents of cytochromes b5 and P-450 in rat liver after phenobarbital and CoCl2 injections was studied. Two hours after a single injection of phenobarbital the delta-aminolevulinate-synthase activity is increased, showing a further rise after 24 hrs. The content of cytochrome b5 is not changed, while that of cytochrome P-450 is increased 24 hrs after the injection. The heme-oxygenase activity remains unaffected thereby. The increase in the enzyme activity and cytochrome P-450 content induced by phenobarbital is eliminated by a preliminary administration of actinomycin D. The administration of CoCl2 is accompanied by a decrease in the delta-aminolevulinate-synthase activity after 2 hrs and its further increase after 24 hrs. The heme-oxygenase activity shows a sharp rise 24 hrs after the injection. The rise in the delta-aminolevulinate-synthase activity induced by CoCl2 is removed by actinomycin D. CoCl2 decreases the content of cytochromes b5 and P-450 24 hrs after the injection. It is assumed that the correlation between the delta-aminolevulinate-synthase activity and cytochrome P-450 content is observed only in the case when the heme-oxygenase activity is not increased. The cytochrome b5 content is independent of the changes in the activity of the key enzyme of heme synthesis and depends to a certain extent on the rate of heme degradation by heme-oxygenase.

Degradation of mesoheme and hydroxymesoheme catalyzed by the heme oxygenase system: involvement of hydroxyheme in the sequence of heme catabolism

Mesoheme bound to heme oxygenase protein was easily degraded to mesobiliverdin by incubation with NADPH-cytochrome c reductase and NADPH. The features of mesoheme degradation were very similar to those of protoheme degradation catalyzed by the heme oxygenase system; an intermediate compound having its absorption maximum at 660 nm appeared in the couse of mesoheme degradation and this compound is presumably equivalent to the 688 nm compound which appears in the course of protoheme degradation. Hydroxymesoheme was chemically prepared and a complex of hydroxymesoheme and heme oxygenase was prepared. The complex was fairly stable in air, but when the complex was incubated with the NADPH-cytochrome c reductase system, the hydroxymesoheme bound to heme oxygenase was readily converted to mesobiliverdin through the 660 nm compound as an intermediate. It is evident that hydroxyheme is a real intermediate of heme degradation in the heme oxygenase reaction and that the 688 nm compound (or the 660 nm compound in the mesoheme system) is located between hydroxyheme and the biliverdin-iron chelate. The ferrous state of heme-iron may also be necessary for the onset of further oxidation of hydroxyheme.

Hepatic cytochrome P-450 and microsomal heme oxygenase in copper-deficient rats

Copper deficient and control rats were pair-fed from weaning a milk-based diet. Each animal received 25 mg of iron parenterally. After 6 weeks of dietary manipulations the animals were killed. As expected, rats fed the copper-deficient diet were anemic. Copper-dependent enzyme activities and copper content of plasma and liver confirmed that copper deficiency was present in these rats. Hepatic microsomal cytochrome P-450 specific contents were similar in control and copper-deficient animals in the uninduced state and following induction of cytochrome P-450 by treatment with phenobarbital. However, microsomal heme oxygenase was increased in copper-deficient animals compared with controls whether they were treated with phenobarbital or not. No differences were observed in splenic microsomal heme oxygenase between dietary groups. These studies suggest that hepatic heme catabolism is enhanced in copper deficiency. The explanation for this enhancement may be related to increased hepatic iron accumulation in copper-deficient animals or to the associated defect of selenium metabolism in copper deficiency.

Acute effect of methamphetamine on heme oxygenase activity and on cytochrome P-450 content in the liver of female rats

After a single treatment with d-methamphetamine (philopon) at a dose of 8 mg/kg in 10 weeks old female Wistar rats, heme oxygenase activity was enhanced at 3 hr and reached it peak level at 12 hr, whereas cytochrome P-450 content showed the lowest level at 12 hr. However, activity of delta-aminolevulinic acid synthetase was not affected. Twenty-four hr later, all measured parameters returned to nearly initial levels at zero time. The pretreatment with cycloheximide blocked the increase of heme oxygenase activity in philopon-treated animals.

Trace metals and hemoglobin metabolism

Hemoglobin is composed of two pairs of globin chains to which are attached four iron-containing metalloporphyrins. Factors regulating hemoglobin synthesis include the availability of iron and the presence of heme. Heme production occurs by enzymatic synthesis and includes a step mediated by aminolevulinic acid dehydrase, which is zinc-dependent and, thus, susceptible to the toxic effects of other metals. The intake of iron, copper, zinc, cobalt, manganese, cadmium or lead may affect hemoglobin levels by an influence on availability of iron or heme.

Effects of chlorinated benzenes of the activities of delta-aminolevulinic acid synthetase and heme oxygenase and on the content of hemoprotein in the liver of rats

Effects of chlorinated benzenes on the activities of delta-aminolevulinic acid (delta-ALA) synthetase and heme oxygenase, the rate-limiting enzyme in heme biosynthesis and degradation respectively, and on the incorporation of 3H-delta-ALA into hemoprotein in the liver of male rats were investigated. Monochlorobenzene (MCB) and 1,2,4-trichlorobenzene(TRCB) stimulated significantly the activities of above both hepatic enzymes. After a single injection of 200 mg/kg, heme oxygenase activity was enhanced rapidly and sustained markedly for at least 48 hr by MCB treatment, while that was also enhanced but restored nearly to control levels at 48 hr by TRCB. delta-ALA synthetase activity was once decreased at 6 hr and restored within 12 hr and then reached peak levels (about 2--3 times to control levels) at 24 hr by MCB or TRCB treatment. However, this activity was sustained for 48 hr by TRCB treatment, whereas returned again to nearly control levels by MCB at 48 hr. Cytochrome P-450 content at 48 hr was significantly decreased by MCB (63% to control), in contrast, increased by TRCB (200% to control). When MCB or TRCB injected once daily throughout the study, biphasic disappearance of radioactivity incorporated into CO-binding particles was shown in control and MCB- or TRCB-treated rats. The half-life of the fast phase was about 8 hr in control and about 6 or 13 hr in MCB- or TRCB-treated rats respectively.

Hepatic metabolism of heme in rats after exposure to benzene, gasoline and kerosene

delta-Aminolevulinic acid (ALA) synthetase, delta-ALA dehydratase and heme oxygenase activities were studied in the liver of albino rats, 3 and 20 h after i.p. administration of benzene, gasoline, and kerosene. delta-ALA synthetase activity was increased markedly after benzene administration, while gasoline and kerosene treated groups showed decreased enzyme activity. Inhibition of delta-ALA dehydratase activity was observed in all three groups, but heme oxygenase activity was unchanged.

Regional distribution of the enzymes of haem biosynthesis and the inhibition of 5-aminolaevulinate synthase by manganese in the rat brain

The activity of 5-aminolaevulinate synthase, the rate-limiting enzyme of haem biosynthesis, is differentially distributed in various regions of the rat brain. The cerebellum possessed the highest enzyme activity of the eight regions studied. The cerebral cortex and the midbrain also exhibited high 5-aminolaevulinate synthase activity; the septum, hypothalamus, thalamus, amygdala and the hippocampus possessed much lower enzyme activity. However, the total porphyrin and haem contents of the different brain segments did not vary greatly. Mn(2+), when administered subcutaneously to rats, effectively inhibited the activity of 5-aminolaevulinate synthase in the cerebellum, midbrain and cerebral cortex; however, repeated injections of the metal ion neither decreased the haem and porphyrin contents of the brain nor induced haem oxygenase activity. Mn(2+) was not an effective inhibitor of 5-aminolaevulinate synthase activity in vitro. On the other hand, studies carried out with the liver in vivo suggested that Mn(2+) may alter the turnover rate of cellular haem and haemoproteins. In that event, it is likely that the inhibition of 5-aminolaevulinate synthase by Mn(2+) was in part a result of the inhibition of protein synthesis by the metal ion. It is postulated that the haem and porphyrin contents of the brain are maintained at a steady-state level, due in part to the refractoriness to inducers of the regulatory mechanism for haem catabolic enzymes and in part to the ability of the organ to utilize haem precursors derived from extraneuronal sources.

Activity of microsomal heme oxygenase in liver and spleen of ascorbic acid-deficient guinea pigs

Hepatic heme oxygenase activity was significantly altered in vitamin C-deficient guinea pigs. It was increased two-fold after 14 days and was decreased by 20% after 21 days of deprivation of the vitamin (always in comparison with the control value). The apparent Km of the enzyme was also altered in the course of ascorbic acid deficiency. The data of hepatic heme oxygenase activity correspond to previous results on the metabolism of hepatic cytochrome P-450 in different stages of ascorbic acid deprivation. Splenic heme oxygenase activity decreased progressively arriving at 50% of the control value after 21 days of vitamin C omission, its apparent Km remained unaltered.

Degradation of cytochrome P-450 haem by carbon tetrachloride and 2-allyl-2-isopropylacetamide in rat liver in vivo and in vitro. Involvement of non-carbon monoxide-forming mechanisms

Degradation of intrinsic hepatic [(14)C]haem was analysed as (14)CO formation in living rats and in hepatic microsomal fractions prepared from these animals 16h after pulse-labelling with 5-amino[5-(14)C]laevulinic acid, a precursor that labels bridge carbons of haem in non-erythroid tissues. NADPH-catalysed peroxidation of microsomal lipids in vitro (measured as malondialdehyde) was accompanied by loss of cytochrome P-450 and microsome-associated [(14)C]haem (largely cytochrome P-450 haem), but little (14)CO formation. No additional (14)CO was formed when carbon tetrachloride and 2-allyl-2-isopropylacetamide were added to stimulate lipid peroxidation and increase loss of cytochrome P-450 [(14)C]haem. Because the latter effect persisted despite inhibition of lipid peroxidation with MnCl(2) or phenyl-t-butylnitrone(a spin-trapping agent for free radicals), it was concluded that carbon tetrachloride, as reported for 2-allyl-2-isopropylacetamide, may promote loss of cytochrome P-450 haem through a non-CO-forming mechanism independent of lipid peroxidation. By comparison with breakdown of intrinsic haem, catabolism of [(14)C]methaemalbumin by microsomal haem oxygenase in vitro produced equimolar quantities of (14)CO and bilirubin, although these catabolites reflected only 18% of the degraded [(14)C]haem. This value was increased to 100% by addition of MnCl(2), which suggests that lipid peroxidation may be involved in degradation of exogenous haem to products other than CO. Phenyl-t-butylnitrone completely blocked haem oxygenase activity, which suggests that hydroxy free radicals may represent a species of active oxygen used by this enzyme system. After administration of carbon tetrachloride or 2-allyl-2-isopropylacetamide to labelled rats, hepatic [(14)C]haem was decreased and haem oxygenase activity was unchanged; however, (14)CO excretion was either unchanged (carbon tetrachloride) or decreased (2-allyl-2-isopropylacetamide). These changes were unaffected by cycloheximide pretreatment. From the lack of parallel losses of cytochrome P-450 [(14)C]haem and (14)CO excretion, one may infer that an important fraction of hepatic [(14)C]haem in normal rats is degraded by endogenous pathways not involving CO. We conclude that carbon tetrachloride and 2-allyl-2-isopropylacetamide accelerate catabolism of cytochrome P-450 haem through mechanisms that do not yield CO as an end product, and that are insensitive to cycloheximide and independent of haem oxygenase activity.

Stimulation of heme oxygenase in macrophages and liver by endotoxin

In rat peritoneal macrophages, engaged in erythrophagocytosis in vitro, endotoxin stimulated heme oxygenase (HO) activity, which was additive to the substrate-mediated enzyme induction produced by the ingested erythrocyte hemoglobin. Endotoxin neither appeared to injure the erythrocytes, nor did it enhance the rate of erythrophagocytosis. In intact rats, HO activity in both parenchymal and sinusoidal cells of the liver was increased after treatment with endotoxin. It is likely that endotoxin directly stimulates HO activity, a process which may account for the reported rise in bilirubin formation in endotoxin-treated animals. The effect of endotoxin on HO may represent part of the general activation of phagocytic cells by endotoxin.