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Biomedical subjects

G S Marks

Publications and source records attributed to G S Marks.

At least 127 records · Page 7Linked to original sources
PubMed1986

Requirement for reduced, unliganded hemoprotein for the hemoglobin- and myoglobin-mediated biotransformation of glyceryl trinitrate.

The biotransformation of glyceryl trinitrate (GTN) by hemoglobin (Hb) and myoglobin (Mb) was assessed using solutions of various forms of the hemoproteins, viz., the oxy-, deoxy-, carbonmonoxy- and met-forms. After incubation with these, GTN loss was observed only with the deoxy-forms of Hb and Mb. The stoichiometry and products of [14C]GTN biotransformation by deoxy-Hb and deoxy-Mb were determined by measuring the formation of [14C]glyceryl dinitrate [14C]GDN), met-Hb (or met-Mb) and inorganic nitrite anion. Biotransformation of GTN involved the oxidation of 2 mol of heme iron (II) per mol of GTN biotransformed to GDN and inorganic nitrite anion. In addition to the formation of GDN, 1 to 2.5% of the radioactivity could not be extracted from the incubation samples. The ratio of 1,2-GDN/1,3-GDN formed during incubation of deoxy-Hb with GTN was 11:1, which indicated a high degree of regioselectivity for the denitration of the nitrate ester group in position 1 or position 3 of GTN. The metabolite ratio obtained for deoxy-Mb incubation with GTN (1,2-GDN/1,3-GDN,3:1) was less than that for deoxy-Hb, which indicated less regioselectivity for the deoxy-Mb-mediated denitration reaction. This could reflect differences in the topography of the heme pocket of the two hemoproteins and steric differences in the GTN-hemoprotein interaction.

Biotransformation↗
PubMed1986

Ferrochelatase-inhibitory activity and N-alkylprotoporphyrin formation with analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) containing extended 4-alkyl groups: implications for the active site of ferrochelatase.

The ferrochelatase-inhibitory activity, porphyrin-inducing activity, and cytochrome P-450- and heme-destructive effects of a variety of analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) were studied in chick embryo liver cells. The ferrochelatase-inhibitory activity of the 4-butyl, 4-pentyl, 4-hexyl, and 4-cyclopropylmethyl analogues of DDC was considered to be due to the formation of the corresponding N-alkylporphyrins. These N-alkylporphyrins were isolated from the livers of phenobarbital-pretreated rats following administration of the corresponding DDC analogues. The 4-isobutyl analogue did not have ferrochelatase-inhibitory activity despite its ability to cause formation of an N-isobutylporphyrin in rat liver. The 4-chloromethyl analogue of DDC inhibited ferrochelatase activity. The inability to isolate an N-alkylporphyrin from rat liver with this analogue may be due to its lability. The porphyrin-inducing activity of these analogues depended on their ferrochelatase-inhibitory potency and lipophilicity. The DDC analogues caused cytochrome P-450 and heme destruction. The relative ferrochelatase-inhibitory activity of the DDC analogues has implications for a postulated model of the binding of porphyrins in the ferrochelatase active site.

Alkylation↗
PubMed1985

Exposure to toxic agents: the heme biosynthetic pathway and hemoproteins as indicator.

The heme biosynthetic pathway is closely controlled by levels of the end product of the pathway, namely, heme, and porphyrins are normally formed in only trace amounts. When control mechanisms are disturbed by xenobiotics, porphyrins accumulate and serve as a signal of the interaction between a xenobiotic and the heme biosynthetic pathway. For example, an increase in erythrocyte protoporphyrin is a useful measurement for early detection of exposure to lead and porphyrinuria was an early manifestation of a hexachlorobenzene-induced porphyria in Turkey. In recent years a variety of additional xenobiotics has been shown to interact with the heme biosynthetic pathway, namely, halogenated aromatic hydrocarbons, pesticides, sulfides, and a variety of metals. Moreover, different xenobiotics (e.g., dihydropyridines and compounds containing unsaturated carbon-carbon bonds) interact with the prosthetic heme of cytochrome P-450 forming novel N-alkylporphyrins.

Alkylation↗
PubMed1985

Role of hemoglobin in the differential biotransformation of glyceryl trinitrate and isosorbide dinitrate by human erythrocytes.

Incubation of 2 X 10(-7) M glyceryl trinitrate (GTN) at 37 degrees C with human red blood cells resuspended in saline resulted in a 73.4 +/- 3.5% (S.D.) elimination of GTN after 10 min. The elimination of GTN was accompanied by the appearance of an equimolar amount of the GTN metabolites. The biotransformation of GTN and another organic nitrate, isosorbide dinitrate (ISDN), was examined in more detail using the 25,000 X g supernatant fraction of human red blood cells (RBC-SF). Incubation of 2 X 10(-7) M GTN or ISDN at 37 degrees C with RBC-SF resulted in a 46.3 +/- 7.3% (S.D.) elimination of GTN after 40 min and a 51.8 +/- 5.9% (S.D.) elimination of ISDN after 240 min. The elimination of the parent organic nitrate was accompanied by the appearance of an equimolar amount of metabolites. The biotransformation of ISDN was inhibited completely by pretreatment of the RBC-SF with trypsin, N-ethylmaleimide or heating at 65 degrees C, whereas GTN biotransformation was only inhibited partially by these treatments. Biotransformation of GTN was inhibited partially by pretreatment of the RBC-SF with CO or potassium ferricyanide; these treatments had no effect on ISDN biotransformation. Treatment of the RBC-SF with the combination of N-ethylmaleimide plus CO or trypsin plus CO resulted in complete inhibition of GTN biotransformation. We conclude that ISDN biotransformation by erythrocytes is a sulfhydryl-dependent enzymatic process, whereas the biotransformation of GTN is due to a combination of a sulfhydryl-dependent enzymatic process and an interaction with reduced hemoglobin.

Adult↗
PubMed1985

Suicidal destruction of cytochrome P-450 and reduction of ferrochelatase activity by 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine and its analogues in chick embryo liver cells.

The ferrochelatase-reducing activity and cytochrome P-450- and heme-destructive effects of a variety of analogues of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) were studied in chick embryo liver cells. A group of DDC analogues was found in which an inability to reduce ferrochelatase activity corresponded with an inability to cause cytochrome P-450 and heme destruction. In a second group of DDC analogues, the ability to reduce ferrochelatase activity corresponded with the ability to cause cytochrome P-450 and heme destruction. These observations support the idea that the protoporphyrin IX moiety of N-alkylprotoporphyrin IX originates from the heme moiety of cytochrome P-450. A third group of DDC analogues caused cytochrome P-450 and heme destruction despite an inability to reduce ferrochelatase activity. With this third group of DDC analogues, the heme moiety of cytochrome P-450 is likely degraded to products other than N-alkylporphyrins. The inability of several lipophilic DDC analogues [4-benzyl, 4-isopropyl, 4-cyclohexyl, 4-(3-cyclohexenyl)] to reduce hepatic ferrochelatase activity may explain their low porphyrinogenicity. The pattern of porphyrin accumulation produced in response to two DDC analogues that did not inhibit ferrochelatase was investigated using high performance liquid chromatography. Coproporphyrin was the major porphyrin to accumulate in response to the 4-isopropyl analogue and uro- and heptacarboxylic acid porphyrins in response to the 4-benzyl analogue. These patterns of porphyrin accumulation are consistent with the inability of these analogues to inhibit ferrochelatase.

Animals↗
PubMed1984

Ferrochelatase and N-alkylated porphyrins.

The final step in heme synthesis is catalyzed by the mitochondrial enzyme, ferrochelatase. Characterization of this enzyme has been complicated by a number of factors including the dependence of enzyme activity on lipids. Purification of ferrochelatase from rat and bovine sources has been achieved only relatively recently using blue Sepharose CL-6B chromatography. When 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) is given to animals, it produces a hepatic porphyria resembling human variegate porphyria thus providing an experimental system in which to study this disease. DDC has been found to cause the accumulation of a green pigment, identified as N-methyl protoporphyrin IX (N-MePP), which is a potent inhibitor of ferrochelatase. The source of the N-methyl substituent of N-MePP was found to be the 4-methyl group of DDC. Considerable evidence indicates that the protoporphyrin IX moiety of N-MePP originates from the heme moiety of cytochrome P-450 and that DDC is a suicide substrate for this hemoprotein. Some studies suggest that cytochrome P-450 isozymes differ in their susceptibility to destruction by DDC and its 4-alkyl analogues. Griseofulvin has also been reported to inhibit hepatic ferrochelatase in rodents but not in the 17-day old chick embryo nor in hepatocyte culture systems. Thus, the mechanism by which griseofulvin produces an experimental porphyria in chick embryo liver cell culture is different from that for rodents.

Alkylation↗
PubMed1984

Biotransformation of glyceryl trinitrate to glyceryl dinitrate by human hemoglobin.

The elimination of glyceryl trinitrate (GTN) by man is rapid and its clearance exceeds cardiac output. It is therefore clear that a variety of tissues in addition to liver are involved in the biotransformation of GTN. Incubation of GTN with the 25 000 X g supernatant fraction of lysed human erythrocytes resulted in a 39.6% +/- 5.5 (SD) elimination of GTN after 40 min. After pretreatment of the lysate supernatant fraction with carbon monoxide, GTN elimination was only 26% +/- 4.5. These data indicated that hemoglobin might be involved in GTN elimination. When purified hemoglobin was incubated with GTN, a 77.1% +/- 6.4 elimination of GTN was observed, accompanied by glyceryl dinitrate formation. The biotransformation of GTN was inhibited by pretreatment with carbon monoxide. The results indicate that the biotransformation of GTN by human erythrocytes is due, at least in part, to interaction with hemoglobin.

Adult↗
PubMed1984

Effect of 5-isosorbide mononitrate on isosorbide dinitrate-induced relaxation of rabbit aortic rings.

The ability of isosorbide dinitrate (ISDN) and its two metabolites, 5-isosorbide mononitrate (5-ISMN) and 2-isosorbide mononitrate (2-ISMN), to relax phenylephrine-contracted rabbit aortic rings was compared. The three organic nitrates demonstrated similar efficacy. ISDN was found to be the most potent (median effective dose (ED50); 1.5 X 10(-7) +/- 1.1 X 10(-7) M), followed by 2-ISMN (ED50, 1.8 X 10(-6) +/- 9 X 10(-7) M) and 5-ISMN (ED50, 8.2 X 10(-6) +/- 3.6 X 10(-6) M). The log dose-response curve of ISDN in rabbit aortic rings was constructed in the absence and presence of three fixed concentrations of 5-ISMN (5 X 10(-6), 10(-5), and 3 X 10(-5) M). No shift in the ISDN dose-response curve at high ISDN concentrations was noted in the presence of 5-ISMN. Using the isobolographic method with fixed ISDN/5-ISMN ratio mixtures, no evidence for an antagonistic effect of 5-ISMN on ISDN-induced vasodilation was obtained. Analysis of the fixed ISDN/5-ISMN ratio mixture responses by the median-effect plot showed no antagonistic effect. It is concluded that in rabbit aortic rings 5-ISMN, the major metabolite of ISDN, is not an antagonist of ISDN at a "nitrate receptor," and no support is provided for the hypothesis that the accumulation in plasma of metabolites (e.g., 5-ISMN) with longer half-lives than the parent drug explains tolerance to organic nitrates.

Animals↗
PubMed1984

The disposition and the liver and thymus gland toxicity of 3,3',4,4'-tetrachlorobiphenyl in the female rat.

3,3',4,4'-Tetrachlorobiphenyl (TCBP) was administered orally to adult female Sprague--Dawley rats in the oral dosage regimen, 5 mg X kg-1 X day-1 for 21 days, followed by a 22-day postdosing period. Control animals received either the corn-oil vehicle (1 mL X kg-1 X day-1) or no treatment. 3,3',4,4'-TCBP distributed preferentially into the adipose tissue and liver, and apparent steady-state xenobiotic concentrations were attained in the adipose tissue (8 micrograms/g) and liver (300 ng/g) prior to the cessation of dosing. The 3,3',4,4'-TCBP concentrations in the serum, brain, kidneys, and thymus gland were lower and more variable than those in the adipose tissue and liver. During the postdosing period, 3,3',4,4'-TCBP was eliminated from the adipose tissue and liver by apparent first-order kinetics with elimination half-life values of 2.5 days and 0.8 day, respectively. The major route of excretion of unmetabolized 3,3',4,4'-TCBP was via the feces, and the amount excreted over 24 h did not exceed 8% of the dose administered on any given day. Throughout the experiment, there were no differences in the body weight or food and water intake for the 3,3',4,4'-TCBP-treated animals compared with the corn-oil-treated and nontreated rats. There was a significant increase in liver weight and a significant decrease in thymus gland weight for the 3,3',4,4'-TCBP-treated rats compared with the corn-oil-treated rats at the cessation of dosing and at 11 days thereafter, but there were no observable histological changes in these organs as assessed by light microscopy.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1983

Sex-related difference in the metabolism of isosorbide dinitrate following incubation in human blood.

Isosorbide dinitrate (ISDN) (at a concentration of 100 ng/ml) was incubated aerobically at 37 degrees in whole blood from five male and five female normal volunteers. Following incubation of the blood samples for 0, 30, 60, 120, 240 and 360 min, the samples were centrifuged and the plasma was assayed for ISDN. A linear relationship was observed between the logarithm of the concentration of ISDN remaining and incubation time, and there was a significant difference between the T1/2 of ISDN in blood from males (90.6 min) and females (161.4 min). Very little ISDN metabolism was observed when ISDN was incubated with plasma rather than whole blood. When erythrocytes, resuspended in saline, were incubated with ISDN, there was a time-dependent loss of ISDN from the saline incubation medium. Investigation of the soluble fraction obtained after hemolysis of these erythrocytes also showed a time-dependent loss of ISDN. The saline incubation medium contained sufficient concentrations of the two major ISDN metabolites (isosorbide 2- and 5-mononitrate) to account for the observed disappearance of ISDN. The results indicate that ISDN is metabolized in the cellular compartment of blood and that the metabolic rate in males is greater than that in females.

Adult↗
PubMed1983

The effect of N-methylprotoporphyrin and succinyl-acetone on the regulation of heme biosynthesis in chicken hepatocytes in culture.

The essential features of hepatic protoporphyria, namely inhibition of ferrochelatase, accumulation of protoporphyrin and stimulation of 5-aminolevulinic acid synthase (ALA-S) were all obtained by treating chicken hepatocytes in culture with small doses of N-methylprotoporphyrin. Both N-methylprotoporphyrin and succinyl-acetone, another inhibitor of heme biosynthesis, stimulated ALA-S when given on their own and also enhanced the stimulation of ALA-S caused by phenobarbital.

5-Aminolevulinate Synthetase↗
PubMed1983

Determinants of the pharmacokinetics of antithrombotic drugs.

This review describes a variety of factors which determine the pharmacokinetics of antithrombotic drugs, viz., elimination by hepatic and/or renal clearance, plasma protein binding and drug disposition in the geriatric population. An understanding of biotransformation of acetylsalicylic acid and sulfinpyrazone is critical to understanding their usefulness as antithrombotic agents. Acetylsalicylic acid is rapidly hydrolysed to salicylic acid in the body and the latter may be eliminated by five different routes. Two of the biotransformation processes involving salicylic acid are readily saturable. For this reason, salicylate concentration increases more than proportionately with an increase in dose. Acetylsalicylic acid, but not salicylic acid, acetylates cyclo-oxygenase resulting in its inactivation. It is important in pharmacokinetic studies to measure plasma levels of both acetylsalicylic acid and salicylic acid. Biotransformation of sulfinpyrazone involves oxidation to the sulfone and reduction to the sulfide. The sulfide has marked antiplatelet activity. Dipyridamole undergoes hepatic biotransformation to a monoglucuronide which is eliminated by biliary and fecal excretion. Sulfinpyrazone, dipyridamole and salicylic acid are highly bound to plasma proteins. Since binding diminishes with age, one must expect therapeutic and toxic effects at lower plasma drug concentrations in the geriatric population. Other factors to be considered in the geriatric group are altered distribution, diminished glomerular filtration rate, and diminished oxidative biotransformation.

Biotransformation↗
PubMed1983

Inhibition of uroporphyrinogen decarboxylase by 3,3',4,4'-tetrachlorobiphenyl in chick embryo liver cell culture.

An assay was developed to measure uroporphyrinogen decarboxylase activity in 17-day-old chick embryo liver cells in culture. Decarboxylation products arising from the action of uroporphyrinogen decarboxylase upon uroporphyrinogen III were quantitated using high-pressure liquid chromatography. 3,3',4,4'-Tetrachlorobiphenyl (TCBP) was added to chick embryo liver cells and 24 h later the uroporphyrinogen decarboxylase activity in the cells was measured; a significant inhibition was found. On the other hand, when TCBP was added directly to the crude uroporphyrinogen decarboxylase enzyme no inhibition was noted. The inhibition of uroporphyrinogen decarboxylase observed in this study explains the accumulation of uroporphyrin and heptacarboxylic porphyrin in chick embryo liver cell cultures treated with TCBP.

Animals↗
PubMed1983

Patterns of porphyrin accumulation in response to chemicals in chick embryo liver cells.

Four patterns of porphyrin accumulation were observed by high-pressure liquid chromatography when chemicals were added to chick embryo liver cells. These patterns provide a guide to the site of action of the chemicals. Protoporphyrin accumulated in response to 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC), a result consistent with its ability to inhibit ferrochelatase. Uroporphyrin and heptacarboxylic acid porphyrin accumulated in response to 3,3',4,4'-tetrachlorobiphenyl, 2,2',4,4',6,6'-hexachlorobiphenyl, and 3,5-diethoxycarbonyl-2,4,6-trimethylpyridine, a result suggesting inhibition of uroporphyrinogen decarboxylase. Coproporphyrin was the major porphyrin to accumulate in response to allylisopropylacetamide, aromatic amides, and steroids, a result suggesting inhibition of coproporphyrinogen oxidase. A mixture of uroporphyrin, heptacarboxylic acid porphyrin and coproporphyrin accumulated in response to aromatic di- and mono-esters, aliphatic diesters, and aliphatic amides. The pattern observed after addition of excess delta-aminolevulinic acid (ALA) the endogenous substrate of the pathway to the cells was proto- greater than copro- greater than uro-porphyrin. This pattern resembled that produced by DDC but by none of the other chemicals. It was concluded that porphyrin accumulation can not be attributed solely to the induction of ALA-synthetase. It appears that porphyrin-inducing chemicals exert an additional effect on one or other of the enzymes of the heme biosynthetic pathway.

Aminolevulinic Acid↗
PubMed1983

Investigation of the role of prostaglandins in nitroglycerin-induced relaxation of isolated rabbit blood vessels.

The effect of inhibition of prostaglandin synthesis on nitroglycerin-induced relaxation was examined in isolated rabbit mesenteric and celiac arterial rings. An indomethacin dose of 5 microM was selected as adequate to inhibit prostaglandin synthesis as this dose prevented relaxation of the arterial rings by sodium arachidonate (3.3 microM) and by bradykinin, a peptide thought to induce vasodilation via stimulation of prostaglandin synthesis. Following 20 min pretreatment with indomethacin (5 microM), indomethacin solvent, or Krebs solution (control), the arterial rings were contracted submaximally with phenylephrine (0.5-10 microM). The degree of inhibition of phenylephrine-induced tone produced after cumulative additions of nitroglycerin (10(-10) - 5 X 10(-7) M) was assessed. In control celiac and mesenteric rings the responses to nitroglycerin were as follows: mean effective dose (ED50), 5.6 X 10(-9) +/- 4.5 X 10(-9) M (SD) and 1.1 X 10(-8) +/- 5 X 10(-9) M (SD), respectively; maximum relaxation, 97 +/- 3% (SD) and 93 +/- 7% (SD), respectively. Neither indomethacin nor indomethacin solvent affected the ED50 or maximum relaxation with nitroglycerin. We conclude that nitroglycerin-induced relaxation of rabbit celiac and mesenteric arteries appears to be mediated through a mechanism other than stimulation of prostaglandin synthesis.

Animals↗
PubMed1983

Gas-liquid chromatographic determination of the distribution of 3,3',4,4'-tetrachlorobiphenyl in the adult female rat following short-term oral administration.

A gas-liquid chromatographic assay using electron-capture detection was developed for the quantitation of 3,3',4,4'-tetrachlorobiphenyl (TCBP) in the serum, urine, brain, liver, adipose tissue, and feces of the rat. The sample preparation involves extraction of 3,3',4,4'-TCBP with hexane under neutral or alkaline conditions (and washing with concentrated acid for feces only). Aqueous standards are used for calibration of the assay, except for adipose tissue. The lower limit of quantitative sensitivity of the assay for 3,3',4,4'-TCBP is 25 ng/mL for serum and urine and 125 ng/g for brain, liver, adipose tissue, and feces, which can be extended to 5 ng/mL and 25 ng/g, respectively, by analyzing a larger aliquot of the hexane extract. The overall accuracy is greater than 95% for serum, urine, brain and feces and 86% for liver, and the within-day coefficient of variation does not exceed 8.6%. 3,3',4,4'-TCBP was administered orally to adult, female, Sprague-Dawley rats in the dosage regimens: 0.2, 0.5 and 2 mg X kg-1 X day-1 for 10 days and 5 mg X kg-1 X day-1 for 4 days. 3,3',4,4'-TCBP distributed preferentially into adipose tissue and liver, where the xenobiotic concentration was greater in adipose tissue. The adipose tissue and hepatic 3,3',4,4'-TCBP concentrations were dependent on both the absolute dose and dosing schedule of the xenobiotic. Only trace concentrations, usually below the lower limit of quantitation, were detected in the serum, brain and kidney. Fecal excretion of 3,3',4,4'-TCBP was greater than urinary excretion for the 5 mg X kg-1 X day-1 X 4-day regimen.

Administration, Oral↗
PubMed1982

Inhibition of ferrochelatase by N-methylprotoporphyrin IX is not accompanied by delta-aminolevulinic acid synthetase induction in chick embryo liver cell culture.

N-Methylprotoporphyrin has been shown to markedly inhibit ferrochelatase activity in chick embryo liver cell culture without inducing delta-aminolevulinic acid (ALA) synthetase activity. This result supports the idea that the effects of 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) on ALA synthetase activity and ferrochelatase activity are dissociated and that inhibition of ferrochelatase alone is not sufficient to cause induction of ALA synthetase. We conclude that the porphyrinogenic activity of DDC can be explained only in part by the actions of N-methylprotoporphyrin.

5-Aminolevulinate Synthetase↗