Search PubMed⌕ Search

Biomedical subjects

S H Vincent

Publications and source records attributed to S H Vincent.

At least 37 records · Page 2Linked to original sources
PubMed1989

Oxidative effects of heme and porphyrins on proteins and lipids.

Heme and porphyrins catalyze the formation of various reactive oxygen species under widely different conditions. Porphyrins are potent photosensitizers capable of transferring the energy of their excited state to oxygen, forming 1O2. Heme, by virtue of its iron content, is not a photosensitizer, but it can react with H2O2 forming reactive oxygen intermediates whose nature depends on the oxidation state of the iron. Ferric heme gives rise to a porphyrin cation radical, while ferrous heme catalyzes the formation of OH.. The reactive species formed by heme and porphyrins oxidize susceptible functional groups on protein and lipid components of membranes as well as serum and cytosolic proteins. Oxidation of membrane-bound proteins occurs independently of lipid peroxidation and it is characterized by extensive cross-linking, which takes place subsequent to amino acid oxidation. Serum and cytosolic proteins that bind and may transport heme and porphyrins are of special interest since they can modulate their toxicity by affecting their availability and reactivity. In addition, these proteins are particularly susceptible to oxidation, especially by heme, due to their proximity to the oxidizing species that are formed.

Animals↗
PubMed1988

Decreased cytosolic levels of the heme binding Z protein in rat hepatocyte nodules and hepatocellular carcinomas.

Hepatocyte nodules and hepatocellular carcinomas were induced in male Fischer rats using the resistant hepatocyte model. The immunoreactive cytosolic levels of the heme-binding Z protein (HBP) were reduced by 56% (P less than 0.001; 2-tailed t-test) in early hepatocyte nodules (25 weeks) and hepatocellular carcinomas (10-12 months). This finding is in accordance with the previously reported reduced heme content of hepatocyte nodules and is consistent with the postulated role for HBP in intracellular heme transport and distribution. The immunoreactive levels of the glutathione S-transferase isozymes (GST) which like HBP bind heme, were elevated 2-fold (P less than 0.01) in early and late hepatocyte nodules and were unchanged in hepatocellular carcinomas.

Animals↗
PubMed1988

The influence of heme-binding proteins in heme-catalyzed oxidations.

We show here that heme-binding proteins may enhance, decrease, or completely inhibit heme-catalyzed oxidations and that in doing so the proteins themselves may be oxidized depending upon their relative affinities for heme and the nature of their interactions with this metalloporphyrin. That release of iron from heme was not responsible for the catalytic effect is indicated by the observation that heme induced more peroxidation of rat liver microsomal lipid in the presence of H2O2 than iron and that iron release is very low under the conditions employed. Hemopexin, which binds heme with high affinity, completely inhibited heme-catalyzed lipid peroxidation at concentrations slightly higher than that of heme, suggesting a unique role for this acute phase protein in antioxidant defense mechanisms. The protein itself was not oxidized, presumably because the putative bis-histidyl heme-hemopexin complex cannot interact with H2O2. Rat and human albumin and rat glutathione S-transferases (GST), proteins with moderate affinities for heme, decreased heme-catalyzed lipid peroxidation in a dose-dependent manner but were subject to oxidation. The GST were crosslinked forming a nondisulfide covalently linked subunit dimer as well as products of higher molecular weight whereas the oxidation products of the albumins had molecular weights only slightly higher than those of the native proteins. The changes in the electrophoretic patterns of GST and albumin were accompanied by a decrease in their tryptophan fluorescence and the formation of bityrosine-like products. Proteins with lower affinities for heme, such as bovine albumin and rat liver fatty acid-binding protein (L-FABP), enhanced lipid peroxidation at all concentrations tested. While bovine albumin was modified, L-FABP was not crosslinked nor were its tyrosine residues oxidized. Thus, the susceptibility of a protein to heme-mediated oxidative damage would appear to be determined by factors such as its affinity for heme, the nature of the amino acids in the vicinity of the bound catalyst and the availability of a free coordination site on the iron.

Animals↗
PubMed1987

Effects of porphyrins on proteins of cytosol and plasma. In vitro photo-oxidation and cross-linking of proteins by naturally occurring and synthetic porphyrins.

We examined the photodynamic effects of porphyrins, known photosensitizers, on proteins of cytosol and plasma that bind them and are implicated in their transport. Their susceptibility to photodecomposition by porphyrins was found to be higher than that of proteins with low or no affinity for tetrapyrroles. Inhibition of porphyrin binding by the addition of equimolar amounts of heme had no effect, indicating that protein photodecomposition may be induced, in part, by free or nonspecifically bound porphyrins. HBP, a heme-binding Z protein of liver cytosol, exhibited the highest susceptibility of all proteins tested, including glutathione S-transferases, albumin, hemopexin, and apotransferrin. HBP was extensively photo-oxidized, as evidenced by a decrease in its antigenicity and electrophoretic mobility, and it was cross-linked by naturally occurring porphyrins as well as by the synthetic tin-protoporphyrin and hematoporphyrin derivative. The water-soluble singlet oxygen scavengers L-histidine (50 mmol/L) and sodium azide (100 mmol/L) completely prevented the photodynamic effects of uroporphyrin (100 mumol/L) on HBP. Hydroxyl radical scavengers such as manitol and benzoate were partially effective, whereas water-insoluble singlet oxygen scavengers such as beta-carotene were totally ineffective. Preferential inhibition of cross-linking over other photodynamic effects of uroporphyrin was consistent with previous reports that cross-linking occurs subsequently to amino acid oxidation.

Animals↗
PubMed1986

Porphyrin-induced photodynamic cross-linking of hepatic heme-binding proteins.

Three types of hepatic proteins, a heme-binding Z protein, a mixture of the glutathione S-transferases and a cytochrome P450 isozyme, were shown to be susceptible to photodynamic cross-linking and loss in antigenicity by naturally occurring porphyrins. At 50 microM, uroporphyrin caused the most and protoporphyrin the least photodecomposition. Hemopexin, a specific serum heme carrier, was photodecomposed but no cross-linking was detected. Heme and scavengers of singlet oxygen partially prevented protein photodecomposition.

Animals↗
PubMed1985

A protein of the Z class of liver cytosolic proteins in the rat that preferentially binds heme.

A low molecular weight protein purified from rat liver cytosol was observed to bind heme with an affinity higher than that for other organic anions. Purification was achieved by two procedures, one employing affinity chromatography on oleic acid-agarose, and the other using sequential ion-exchange and gel filtration chromatography after initial removal of aprotinin-sensitive proteases. Removal rather than inhibition of proteases improved the yield four times. Both procedures produced a stable protein. The purified protein binds heme with a higher affinity (Kd 0.15 microM) than any other organic anion tested including other (metallo)porphyrins, bilirubin, and oleic acid. Based on its molecular weight, amino acid composition, immunological properties, and the increase of its tissue levels in response to the administration of hypolipidemic agents, the protein was identified as being related to proteins of the Z class, whose members include fatty acid binding protein and sterol carrier protein. Like other Z proteins, our protein exhibits several forms on electrofocusing, but differs from fatty acid-binding protein and sterol carrier protein in that its major form exhibits a pI of 7.4. In view of its distinct isoelectric focusing pattern, its higher affinity for heme than for oleic acid, and its apparent inability to bind cholesterol and steroids, we cannot identify this protein as any of the above-mentioned proteins of the Z class. Consequently we have provisionally designated it heme-binding protein.

Amino Acids↗
PubMed1985

Purification and characterization of protein Z from rabbit liver cytosol.

Protein Z was purified from rabbit liver cytosol by affinity chromatography on oleic acid-agarose and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After removal of sodium dodecyl sulfate, the renatured protein was found to bind heme and bilirubin with a Kd of approximately 1 microM which produced large red shifts in their absorption spectra. On isoelectric focusing, rabbit protein Z exhibited two main bands with pI around 6.0.

Animals↗
PubMed1985

Cardiovascular responses in healthy subjects to a novel oral dopamine agonist, fenoldopam.

Two double-blind randomized crossover studies were carried out in healthy male subjects to determine the cardiovascular effects of fenoldopam and to assess whether they could be modified by metoclopramide. Blood pressure (BP) and heart rate (HR) were measured supine and upright, before and for up to 4 h after dosing. Single oral doses of fenoldopam 50, 100 or 150 mg or placebo were administered in one study. In the other study, subjects received 20 mg metoclopramide or placebo intravenously, 20 min before an oral dose of 100 mg fenoldopam or placebo. Fenoldopam produced decreases in diastolic BP and increases in HR indicative of an orally active systemic arteriolar vasodilator. Mean peak responses occurred 30-60 min after dosing and values had returned to pretreatment levels within 3-4 h. The decrease in diastolic BP was partially attenuated by pretreatment with metoclopramide. Thus, at least in part, the fall in BP following fenoldopam could be due to an interaction with dopamine receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1982

Carbonic anhydrase activity in mitochondria from rat liver.

An 18O exchange method has been used to determine the location of carbonic anhydrase in mitochondria from rat liver and to examine the role of this enzyme in the kinetics of CO2 in resting and respiring mitochondria. Using digitonin subfractionation, we have determined that a substantial fraction, 40 to 60%, of the carbonic anhydrase activity in the mitochondrion from rat liver is located in the space between the inner and outer membranes; the remaining activity was found in the matrix with no detectable activity in the sedimented membranes. The total catalytic CO2 hydration activity measured in intact mitochondria from rat liver was about 1% of that found in an equal volume of rat erythrocytes. The apparent permeability constant representing the barrier for the diffusion of HCO3(-) from external solution to intramitochondrial carbonic anhydrase, 9 X 10(-5) cm s-1, is near in magnitude to the permeability constant for the diffusion of HCO3(-) across the rat erythrocyte membrane, 4 X 10(-4) cm s-2. Calcium-induced respiratory jumps were shown to cause changes in the rate of 18O exchange between CO2 and H2O that were consistent with a net uptake of CO2 by the mitochondria.

Animals↗
PubMed1981

Tissue distribution studies of [18F]haloperidol, [18F]-beta-(4-fluorobenzoyl)propionic acid, and [82Br]bromperidol by external scintigraphy.

Tissue distribution studies of [18F]haloperidol and [82Br]bromperidol, two potent neuroleptic drugs, were performed in rats by serial sacrifice. The usefulness of external scintigraphy in obtaining tissue distribution data in large animals is demonstrated by the tissue distribution of [18F]haloperidol in rhesus monkeys. Both serial sacrifice and external scintigraphic studies demonstrated that uptake of the two drugs after intravenous administration into their target organ, the brain, was very fast and that the ratio of brain to blood levels was high throughout the 2-hr observation. Bromperidol appeared to reach peak brain levels faster than its chloro analog, haloperidol. Both bromperidol and haloperidol concentrated overwhelmingly in the rat lung. Haloperidol also showed a high affinity for the monkey lung. The disposition pattern in rats of [18F]-beta-(4-fluorobenzoyl)propionic acid, an apparent intermediate in butyrophenone metabolism, was entirely different from that of the parent drugs. This metabolite did not concentrate in the rat brain.

Animals↗
PubMed1980

Synthesis of [82Br]bromperidol and preliminary tissue distribution studies in the rat.

A procedure is described for the preparation of [82Br]bromperidol with specific activity 440 muCi/mg. The incorporation of bromine-82 into the molecule was accomplished through Brackman and Smit's modification of the Sandmeyer reaction, during the last step of the synthetic route. This involved the formation of a complex between Cu82Br2 and nitric oxide gas in acetonitrile, which was then allowed to react with 4-[4-(aminophenyl)-4-hydroxy-piperidinyl]-1-(4-fluorophenyl)-1-butanone (aminoperidol, 10) to give [82Br]bromperidol in about 1.5 h. Cupric 82Br]bromide was prepared in situ from K82Br and CuSO4.5H2O. The radiochemical and chemical yields for the preparation of [82Br]bromperidol from K82Br were 10.4 and 12%, respectively. Preliminary tissue distribution studies with the labeled bromperidol in the rat showed that the uptake of radioactivity by the liver, brain, kidneys, and the lungs was very fast and was in the declining phase in the latter organs 15 min after iv administration.

Animals↗
PubMed1980

Histamine H2 receptors and intrinsic factor secretion.

Intrinsic factor (IF) secretion in healthy male subjects was studied in response to pentagastrin stimulation with and without cimetidine, and to impromidine, a histamine H2 receptor agonist. Peak and total IF output were reduced by cimetidine, but the concentration was unchanged and the response was unaffected by administration of the compound for 1 week. The IF secretory response to impromidine was similar to that to pentagastrin. It is suggested that the acid and IF components of the parietal cell secretory response are mediated via different intracellular pathways, that histamine H2 receptors do not fulfill and obligatory role in the secretion of IF and that synthesis of IF is probably not altered by cimetidine.

Cimetidine↗
PubMed1979

Controlled comparison of cimetidine and carbenoxolone sodium in gastric ulcer.

Fifty-four outpatients with endoscopically diagnosed benign gastric ulcer were allocated at random to treatment with either cimetidine 800 mg daily for six weeks or carbenoxolone sodium 300 mg daily for one week then 150 mg daily for five weeks. Ulcers were reassessed by endoscopy at the end of the trial. The endoscopist was unaware of the treatment and did not take part in the clinical care of the patients. Twenty-one of the 27 patients (78%) given cimetidine and 14 of the 27 (52%) given carbenoxolone had healed ulcers. Symptomatic response occurred earlier with cimetidine but was not significantly better. Unwanted effects were more common in the carbenoxolone group: 12 patients developed hypokalaemia, four of whom needed oral potassium supplements. The results suggest that histamine H2-receptor blockade is at least as effective as carbenoxolone sodium for benign gastric ulcer and produces fewer side effects.

Administration, Oral↗