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Biomedical subjects

A Kappas

Publications and source records attributed to A Kappas.

At least 145 records · Page 8Linked to original sources
PubMed1987

Drug metabolism by the human hepatoma cell, Hep G2.

The human liver-derived cell line, Hep G2, has aryl hydrocarbon hydroxylase and 7-ethoxycoumarin o-de-ethylase activities. Partial purification of cytochrome P-450 from Hep G2 cells provided spectral evidence of this hemeprotein in the purified fraction. These results suggest that Hep G2 cells will be useful for the study of cytochrome P-450 and the regulation of mixed function oxidase activities in liver cells of human origin.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1987

Porphyria cutanea tarda associated with the acquired immune deficiency syndrome.

Three male subjects with cutaneous symptoms and biochemical signs typical of porphyria cutanea tarda (PCT) developed acquired immune deficiency syndrome (AIDS). All three were in a classic high risk group for the latter disease and developed a typical progressive illness. Two patients succumbed to opportunistic infections; the third is alive but critically ill. The symptomatic prodrome of AIDS developed concurrently with or followed the onset of symptoms of PCT in all three individuals. PCT and AIDS are both uncommon disorders; their association in three patients is thus of inherent clinical interest. If this association is not coincidental, it raises the possibility that the occurrence of photosensitivity, skin lesions, and evidence of biochemical changes characteristic of PCT may, in certain patients at risk for AIDS, presage the subsequent full clinical expression of the latter disease.

Acquired Immunodeficiency Syndrome↗
PubMed1987

The absence of significant biliary excretion of antipyrine or its metabolites in humans.

Three patients with complete bile duct obstructions requiring a percutaneous biliary fistuala were given an oral dose of antipyrine. Drug elimination was assessed through plasma t1/2 studies and urine and bile excretion of both antipyrine and its metabolites. Urine metabolite patterns were in agreement with reference standards, but analysis of bile revealed no antipyrine metabolites and minimal parent compound (mean of total administered dose excreted from the bile fistulas was 4%). This finding was not predicted from previous experiments in the bile-cannulated rat and suggests caution regarding interspecies extrapolation of data concerning the hepatic disposition of certain commonly used test drugs in clinical pharmacologic studies.

Animals↗
PubMed1987

Dual control mechanism for heme oxygenase: tin(IV)-protoporphyrin potently inhibits enzyme activity while markedly increasing content of enzyme protein in liver.

Tin(IV)-protoporphyrin (Sn-protoporphyrin) potently inhibits heme degradation to bile pigments in vitro and in vivo, a property that confers upon this synthetic compound the ability to suppress a variety of experimentally induced and naturally occurring forms of jaundice in animals and humans. Utilizing rat liver heme oxygenase purified to homogeneity together with appropriate immunoquantitation techniques, we have demonstrated that Sn-protoporphyrin possesses the additional property of potently inducing the synthesis of heme oxygenase protein in liver cells while, concurrently, completely inhibiting the activity of the newly formed enzyme. Substitution of tin for the central iron atom of heme thus leads to the formation of a synthetic heme analogue that regulates heme oxygenase by a dual mechanism, which involves competitive inhibition of the enzyme for the natural substrate heme and simultaneous enhancement of new enzyme synthesis. Cobaltic(III)-protoporphyrin (Co-protoporphyrin) also inhibits heme oxygenase activity in vitro, but unlike Sn-protoporphyrin it greatly enhances the activity of the enzyme in the whole animal. Co-protoporphyrin also acts as an in vivo inhibitor of heme oxygenase; however, its inducing effect on heme oxygenase synthesis is so pronounced as to prevail in vivo over its inhibitory effect on the enzyme. These studies show that certain synthetic heme analogues possess the ability to simultaneously inhibit as well as induce the enzyme heme oxygenase in liver. The net balance between these two actions, as reflected in the rate of heme oxidation activity in the whole animal, appears to be influenced by the nature of the central metal atom of the synthetic metalloporphyrin.

Animals↗
PubMed1987

Cobalt-protoporphyrin suppresses thyroid and testicular hormone concentrations in rat serum: a novel action of this synthetic heme analogue.

Treatment of rats with Co-protoporphyrin, a synthetic metalloporphyrin which produces a marked and sustained induction of hepatic heme oxygenase and decline in cellular cytochrome P-450 content, caused a significant reduction in serum testosterone, serum thyroxine (T4) and 3,5,3'-triiodothyronine (T3) levels. These endocrine changes were not accompanied by reciprocal elevations in either serum luteinizing hormone (LH) or thyroid-stimulating hormone (TSH) concentrations. Seminal vesicles from Co-protoporphyrin-treated animals were atrophic. The pituitary response to luteinizing hormone-releasing hormone (LHRH) in Co-protoporphyrin-treated animals was moderately attenuated (approximately equal to 50%) but the response to thyrotropin-releasing hormone (TRH) was normal. These findings suggest that at least part of the effects of the metalloporphyrin are mediated at the level of the hypothalamus, such that suppression of serum levels of testosterone, T4 and T3 fails to elicit compensatory pituitary outputs of the respective trophic hormones. It is not known whether these effects are due to direct actions of Co-protoporphyrin on the endocrine system or whether they are secondary consequences of other metabolic derangements, such as those related to the pronounced cellular depletion of heme and cytochrome P-450 caused by the synthetic metalloporphyrin.

Animals↗
PubMed1987

Relationship of suppression of the androgenic axis by cobalt-protoporphyrin to its effects on weight loss and hepatic heme oxygenase induction.

Cobalt-protoporphyrin administration to adult male rats results in an intense induction of hepatic heme oxygenase, a pronounced decline of cytochrome P-450 content in liver and associated metabolic abnormalities, including a dose-dependent decrease in weight gain and a marked decline in serum concentrations of testosterone without a compensatory increase in serum luteinizing hormone levels. These abnormalities persist for at least 5-6 weeks after a single subcutaneous dose of the metalloporphyrin (25 mumol/kg b.w.). Experiments with pair-fed control and metalloporphyrin-treated rats indicated that the androgenic dysfunction produced by cobalt-protoporphyrin is not causally related to the associated weight loss produced by the compound. Hepatic heme oxygenase activity was markedly induced by cobalt-protoporphyrin as expected; the enzyme activity was not altered in hypothalami of treated rats but was elevated (approximately 5-fold) in pooled pituitaries. However, despite the expected decrease in hepatic cytochrome P-450 content, no changes were noted in cytochrome P-450 content of hypothalami or pituitaries. In experiments in which the enhanced heme oxygenase activity produced in liver by cobalt-protoporphyrin was completely antagonized by tin-protoporphyrin, a competitive inhibitor of the enzyme, neither the endocrine suppression nor the weight loss produced by cobalt-protoporphyrin was altered. These phenomena were thus clearly dissociated from the effects of cobalt-protoporphyrin on heme oxygenase. Whether or not cobalt-protoporphyrin acts centrally to impair both appetite and endocrine control mechanisms could not be determined in these experiments, but remains a possible explanation of the novel actions of this synthetic heme analogue.

Androgens↗
PubMed1987

Immunochemical study of uroporphyrinogen decarboxylase in a patient with mild hepatoerythropoietic porphyria.

Hepatoerythropoietic porphyria (HEP) is due to a marked deficiency of uroporphyrinogen (URO) decarboxylase, a cytosolic enzyme in the heme biosynthetic pathway. Using a radioimmunoassay method, we determined the concentration of URO decarboxylase protein in erythrocytes from a patient with mild HEP and found that the enzyme protein concentration had markedly decreased to less than 7% of the normal controls. This finding, however, was in contrast to the enzyme activity in the patient's erythrocytes, which was 16% of normal control levels and different from previously reported HEP cases in that erythrocytes in our patient contained disproportionately elevated URO decarboxylase activity in comparison to its immunoreactive material. Our findings suggests the possibility of a mutant isozyme in this patient that is not immunoreactive with an antibody raised against the normal enzyme.

Adult↗
PubMed1987

Enzymatic defect in a child with hereditary hepatic porphyria due to homozygous delta-aminolevulinic acid dehydratase deficiency: immunochemical studies.

Immunochemical studies of the enzyme defect in the first reported child with acute hepatic porphyria due to homozygous delta-aminolevulinic acid dehydratase deficiency are described. This enzyme activity was markedly decreased (approximately 2% of the normal control level) in the proband, a 3-year-old boy, and intermediately decreased (23% to 57%) in both parents, in both grandfathers, and in a sister, but it was normal in two siblings and in both grandmothers. In contrast to the profound decrease in delta-aminolevulinic acid dehydratase activity, the immunoreactive enzyme protein in the child's erythrocytes was decreased to only 28% of the normal control level, suggesting the presence of positive cross-reactive material. In other family members with abnormally decreased delta-aminolevulinic acid dehydratase activity, and in the proband immediately after transfusion of normal RBCs, the positive cross-reactive material was not detectable. The immunochemical and enzyme activity data support the idea that delta-aminolevulinic acid dehydratase deficiency in this porphyric child is associated with the production of a catalytically abnormal enzyme protein.

Blood Proteins↗
PubMed1986

Induction of haem synthesis in Hep G2 human hepatoma cells by dimethyl sulphoxide. A transcriptionally activated event.

Exposure of cultured human hepatoma cells (Hep G2) to medium containing 2% (v/v) dimethyl sulphoxide resulted in an approximate doubling in the activity of delta-aminolaevulinate dehydratase, an increase in the haem content and a decreased growth rate; induced enzyme activity was decrease by 50% after treatment with alpha-amanitin. The findings are strikingly similar to those seen in murine Friend-virus-transformed erythroleukaemia cells.

Amanitins↗
PubMed1986

Studies of the influence of chloro-substituent sites and conformational energy in polychlorinated biphenyls on uroporphyrin formation in chick-embryo liver cell cultures.

Treatment of cultured chick-embryo liver cells with polychlorinated biphenyls (PCB) results in decreased uroporphyrinogen decarboxylase activity and increased uroporphyrin accumulation. In the present study we examined the effect of the chloro- or bromo-substituent sites in biphenyls (BP) on uroporphyrin accumulation in cultured hepatocytes and the three-dimensional structure of these congeners determined by molecular orbital calculations using a MNDO ('modified neglect of diatomic overlap') method. Among 20 congeners examined, those which were effective in stimulating porphyrin accumulation contained at least two Cl or Br atoms at the lateral adjacent positions in each phenyl ring, e.g. 3,4,3',4'-tetrachloro-, 2,4,3',4'-tetrachloro-, 3,4,5,3',4',5'-hexachloro- and 3,4,5,3',4',5'-hexabromobiphenyl, whereas those which contained less than two halogen atoms or more than three halogen atoms in each phenyl ring or those which contained halogen atoms at 2,2'-positions were not effective. On the basis of the conformational energy (delta E, difference from the most stable conformational energy), which is calculated as a function of the dihedral angle (theta) between the two phenyl rings, biphenyl congeners can be classified into four groups with different conformations. The conformation of active PCB was relatively flexible, whereas inactive species had a rigidly angulated conformation. Furthermore, the calculated probability of the conformation distribution for each congener indicated that the probability of co-planarity was higher for active biphenyls than for inactive congeners. These structural characteristics suggest the significance of both the chloro-substituent sites and the conformational energy reflecting the phenyl-ring twist angles in determining the inhibitory effect of PCB on uroporphyrinogen decarboxylase activity.

Animals↗
PubMed1986

Biochemical properties of the heme oxygenase inhibitor, Sn-protoporphyrin. Interactions with apomyoglobin and human serum albumin.

Sn-protoporphyrin is a strong competitive inhibitor of heme oxygenase and a potential pharmacological agent for the treatment of neonatal hyperbilirubinemia. Little is otherwise known about the biochemistry of tin porphyrins. We have investigated aspects of the chemistry of tin-protoporphyrin in aqueous solution and of its interactions with heme-binding proteins other than heme oxygenase, specifically apomyoglobin and human serum albumin. In the pH region 7-10, Soret region absorption studies of unbound Sn-protoporphyrin demonstrate a pH-dependent monomer-dimer equilibrium (KD congruent to 10(6) M-1 at pH 7) with little higher aggregation. Dissociation of the dimer is relatively slow at neutral pH, permitting interaction of protein ligands with monomeric and dimeric species to be distinguished and providing insights into kinetic mechanisms of porphyrin binding by heme-binding proteins. In the present study, the kinetics of interaction of Sn-protoporphyrin with apomyoglobin are presented as novel evidence that this binding proceeds by an induced fit mechanism. Binding of Sn-protoporphyrin to both apomyoglobin and serum albumin is unexpectedly weak. Between pH 7 and 9, the apparent affinity of Sn-protoporphyrin for apomyoglobin is less than 1/200 that of heme and, at pH 9, is also significantly less than that of protoporphyrin. The apparent affinity of Sn-protoporphyrin for human serum albumin is less than 1/1000 that of heme and 1/30 to 1/100 that of protoporphyrin. Competition studies between heme and Sn-protoporphyrin and between bilirubin and Sn-protoporphyrin indicate that Sn-protoporphyrin distributes differently among porphyrin-binding sites on serum albumin than does heme and that it is also not an effective competitor with bilirubin for bilirubin-binding sites. These results argue that Sn-protoporphyrin should not significantly alter normal mechanisms for the binding and transport of heme or of preformed bilirubin by serum albumin. From a more general perspective, the results indicate potentially unusual binding site selectivity by tin chelates; possible origins of this selectivity are discussed.

Apoproteins↗
PubMed1986

Disposition of tin-protoporphyrin and suppression of hyperbilirubinemia in humans.

Tin (Sn4+)-protoporphyrin, a potent competitive inhibitor of heme degradation to bile pigment, was cleared rapidly from plasma in normal subjects (t1/2 approximately 4 hours for plasma levels greater than 5 nmol/ml, with evidence of dose-dependent pharmacokinetics at lower plasma concentrations). Small amounts were excreted promptly in urine (0.1% to 5.6%) and more gradually in feces (3.7% to 11.3%). The only dose-limiting (greater than 1.0 mumol/kg, single dose) side effect was mild sensitivity to sunlight and long-wave ultraviolet light. Absorption after intramuscular administration was rapid, but there was no absorption after oral dosing. In bile duct-ligated rats treated with Sn-protoporphyrin, there was a substantial (approximately 50%) reduction in plasma bilirubin levels compared with levels in ligated control animals. Seven studies were carried out in four women with moderate to severe cholestasis secondary to primary biliary cirrhosis and in two men with Gilbert's syndrome. In these studies Sn-protoporphyrin (total doses of 0.25 to 2.0 mumol/kg body weight) reduced plasma bilirubin levels to a varying degree (7% to 43%) promptly after its intravenous administration.

Absorption↗
PubMed1986

Tallysomycin-induced mitotic aneuploidy and point mutations in Aspergillus nidulans.

Tallysomycin is an antibiotic compound structurally related to bleomycin, and like bleomycins and phleomycins also shows antitumour activity. We have investigated the genetic activity of tallysomycin in the ascomycete Aspergillus nidulans for malsegregation of chromosomes at mitosis and for point mutations. We found that the antibiotic at very low concentrations from 0.025 to 0.2 micrograms/ml had an inhibitory effect on colonial growth of up to 50% and it increased the number of mitotic malsegregants from 311% to 607% over the control value. Tallysomycin at concentrations between 2 and 16 micrograms/ml (which inhibited the germination of conidia from 30 to 90%) also increased the number of methionine suppressor revertants from 59 to 368 per 10(6) conidia. With regard to the mechanism for induced mitotic segregation it was shown that this may involve non-disjunction of chromosomes which through the intermediate formation of unstable aneuploids resulted in formation of stable haploid and diploid segregants.

Aneuploidy↗
PubMed1986

Control of heme metabolism with synthetic metalloporphyrins.

Studies with synthetic metal-porphyrin complexes in which the central iron atom of heme is replaced by other elements indicate that those heme analogues that cannot be enzymatically degraded to bile pigments possess novel biological properties that may have considerable clinical as well as experimental value. Such studies have revealed the important role that the central metal atom plays in determining the physiological and pharmacological properties of metal-porphyrin complexes; and they have demonstrated that the form in which animals and humans are exposed to trace metals, i.e., inorganic, organified, porphyrin-chelated, etc., can be of great importance in determining the biological responses that such elements elicit, especially with respect to actions on heme synthesis and degradation and cytochrome P-450 formation and function. Study of the biological properties of synthetic metalloporphyrins represents a potentially fruitful area of research and the results may have significant value for basic as well as clinical disciplines.

5-Aminolevulinate Synthetase↗
PubMed1986

Sn-protoporphyrin inhibition of fetal and neonatal brain heme oxygenase. Transplacental passage of the metalloporphyrin and prenatal suppression of hyperbilirubinemia in the newborn animal.

Sn(tin)-protoporphyrin, a potent competitive inhibitor of heme oxygenase, can suppress hyperbilirubinemia in animal neonates and significantly reduce plasma bilirubin levels in animals and man. To further explore the biological actions and metabolic disposition of Sn-protoporphyrin, we have examined its effect in the suckling neonate when administered to the mother either 24-48 h before or immediately after birth. Sn-protoporphyrin, when administered before birth, crossed the placental membranes, inhibited fetal heme oxygenase, and suppressed the transient hyperbilirubinemia that occurs in the neonate after birth in a dose-dependent manner. Tissue heme oxygenase activity in the neonate was also lowered in a dose-dependent manner. The blood-brain barrier of the neonate was permeable to Sn-protoporphyrin for a period of between 20-28 d of postnatal life. Sn-protoporphyrin, however, was not retained in brain, but left the brain space with a t1/2 of 1.7 d. In addition, Sn-protoporphyrin administered once at birth to neonates inhibited brain heme oxygenase in a dose-dependent manner. The results of this study demonstrate that Sn-protoporphyrin can cross the placental membranes, inhibit tissue heme oxygenase activity in the fetus, and can also, following such prenatal treatment, suppress the hyperbilirubinemia of the newborn animal.

Animals↗