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Biomedical subjects

E Graf

Publications and source records attributed to E Graf.

At least 55 records · Page 3Linked to original sources
PubMed1985

Improvement of the gastric tolerance of non-steroidal anti-inflammatory drugs by polyene phosphatidylcholine (Phospholipon 100).

The effect of co-administration with polyene phosphatidylcholine (Phospholipon 100) on the oral gastrotoxicity of various non-steroidal anti-inflammatory drugs (NSAIDs) was studied in the rat. The highly unsaturated phospholipid reduced gastric mucosal lesions measured 3.5 h after oral administration of aspirin, indomethacin, phenylbutazone, diclofenac, piroxicam and sudoxicam to rats which had received a 3 day bread diet followed by 24 h fasting. The extent of reduction of gastrotoxicity varied amongst the individual NSAIDs. Phospholipon 100 also reduced gastric lesions induced by 3 day oral piroxicam and diclofenac administration. A trend towards reduction of oral diclofenac gastrotoxicity was observed following intravenous Phospholipon 100 administration. Phospholipon 100 H (100% saturated phosphatidylcholine) was less effective than Phospholipon 100 in improving acute gastric tolerance to oral phenylbutazone, diclofenac and piroxicam. Administration of the NSAID-Phospholipon 100 combination produced little change in the anti-inflammatory activities of diclofenac on carrageenan paw oedema and diclofenac and piroxicam on adjuvant arthritis in the rat. Combination with Phospholipon 100 offers a novel means for reducing the gastric side-effects of NSAID therapy.

Animals↗
PubMed1985

Dietary suppression of colonic cancer. Fiber or phytate?

The incidence of colonic cancer differs widely between various human populations. It has been suggested that dietary fiber content is of utmost importance and is inversely related to the occurrence of colonic cancer. However, high-fiber diets are not always correlated with low frequency of colonic cancer, suggesting the involvement of additional dietary constituents. Inositol hexaphosphate (phytic acid) is an abundant plant seed component present in many, but not all, fiber-rich diets. The authors have found that phytic acid is a potent inhibitor of iron-mediated generation of the hazardous oxidant, hydroxyl radical. Herein, the authors propose that inhibition of intracolonic hydroxyl radical generation, via the chelation of reactive iron by phytic acid, may help explain the suppression of colonic carcinogenesis and other inflammatory bowel diseases by diets rich in phytic acid.

Colonic Neoplasms↗
PubMed1985

Interference of enantiomers of lofexidine with alpha-adrenoceptors.

Some alpha-adrenoceptor-mediated cardiovascular activities and alpha-adrenoceptor binding affinities for (+)- and (-)-lofexidine (Dexlofexidine and Levlofexidine) have been studied in comparison with racemic lofexidine. In pithed normotensive rats, i.v. (-)-lofexidine elicited pressor effects at doses (0.1-30 micrograms/kg), which were approximately 20 times lower than those of the (+)-isomer. Both yohimbine and prazosin in selective amounts of 1.0 and 0.1 mg/kg (i.v., -15 min), respectively, attenuated the increase in diastolic pressure induced by (+/-)-, (+)- and (-)-lofexidine, showing the involvement of alpha 1- as well as alpha 2-adrenoceptors in the vasopressor responses. No differences were observed in the sensitivity of the pressor effects of the (+)- and (-)-enantiomers to blockade by either yohimbine or prazosin. Following i.v. administration to pentobarbitone-anaesthetized normotensive rats, (-)-lofexidine (0.5-5.0 micrograms/kg) was found about 20 times more effective than the dextrorotatory isomer in decreasing mean arterial pressure and heart rate. The increase in heart rate evoked by electrical stimulation in pithed rats was dose-dependently reduced by (+/-)-, (-)- and (+)-lofexidine, the (-)-isomer being about 30 times more potent than the (+)-isomer. Similarly, the electrical stimulation-induced increase in diastolic pressure was also most effectively impaired by the laevorotatory enantiomer of lofexidine. (-)-Lofexidine showed an approximately 9-fold higher affinity than (+)-lofexidine for the alpha 2-adrenoceptor-like binding sites in rat brain membranes identified by [3H]-clonidine and was 4 times more potent at displacing [3H]-prazosin from alpha 1-adrenoceptors. It is concluded that the alpha-adrenoceptor activity of lofexidine resides predominantly in the (-)-isomer. The isomeric activity ratio of the enantiomers of lofexidine (about 20-fold) is higher than normally found for other imidazolines.

Animals↗
PubMed1984

Hemoglobin. A biologic fenton reagent.

Iron and iron compounds may facilitate hydroxyl-radical generation from activated oxygen species. Earlier work on the generation of this radical has been focused on simple, low-molecular-weight iron compounds. We hypothesized that free hemoglobin, like other iron-rich substances, might also mediate hydroxyl-radical generation. We find: 1) In the presence of a superoxide anion-generating system (hypoxanthine and xanthine oxidase), hemoglobin promotes hydroxyl-radical formation in a dose-dependent fashion. 2) This generation of hydroxyl radical is greatly decreased by prior oxidation of the hemoglobin, equilibration of hemoglobin with carbon monoxide, or addition of catalase, while added superoxide dismutase has little effect. Therefore, hydroxyl radical probably arises primarily via reaction between the ferrous heme iron and H2O2. 3) In further support of this, hydroxyl radical forms as readily upon the addition of H2O2 to hemoglobin. 4) Hemoglobin also increases hypoxanthine/xanthine oxidase-driven peroxidation of poly-unsaturated fatty acids such as arachidonic acid and human red cell membrane lipids. 5) The addition of sufficient haptoglobin (the plasma hemoglobin-binding protein) suppresses both hemoglobin-driven hydroxyl radical and malondialdehyde generation. Thus, free hemoglobin may be biologically hazardous, in part because it acts as a "Fenton" reagent, having the potential to catalyze hydroxyl-radical generation in areas of inflammation. Haptoglobin, which binds hemoglobin very tightly, blocks this through a presently unknown mechanism. An important physiologic function of haptoglobin may be prevention of such hemoglobin-mediated oxidation.

Arachidonic Acid↗
PubMed1984

Iron-catalyzed hydroxyl radical formation. Stringent requirement for free iron coordination site.

The catalysis by iron of the formation of reactive oxygen species in biological systems has been well documented. In this present study, we have investigated the hypothesis that iron-catalyzed formation of hydroxyl radical (.OH) from superoxide anion radical (O-.2) and H2O2 requires the availability of at least one iron coordination site that is open or occupied by a readily dissociable ligand such as water. This hypothesis was tested by measuring the catalytic activity of 12 different iron chelates using hypoxanthine and xanthine oxidase to generate O-.2. In these same chelates, we also determined the presence or absence of coordinated water by UV-visible spectroscopy and 1H NMR relaxation measurements. Of all chelates tested, only Fe3+ coordinated to diethylenetriamine pentaacetic acid; ethylenediamine di(o-hydroxyphenylacetic acid), phytate, and Desferal lacked coordination water; and only these four complexes failed to produce hydroxyl radical. Separate determinations of the two redox half-reactions involved (i.e. Fe3+ + O-.2----Fe2+ + O2 and Fe2+ + H2O2----Fe3+ + .OH + OH-) indicate that an available coordination site is necessary for the latter (Fenton) reaction. This principle governing iron reactivity may help advance our understanding of the mechanism of oxidative damage in biological systems and may also permit the design of more effective chelators for the control of iron in biological systems.

Chelating Agents↗
PubMed1984

Effects of phytate on mineral bioavailability in mice.

Phytic acid (inositolhexaphosphoric acid) constitutes 1-3% by weight of all plant seeds and is present in numerous food commodities. Excessive dietary intake of phytate is thought to suppress the bioavailability of important polycations, such as Fe3+ and Zn2+, through the formation of insoluble metal phytate complexes. However, multiple factors may affect intestinal mineral absorption, and direct interference by phytate is still controversial. Therefore, we decided to investigate the chemical interactions between phytate and Fe3+, Zn2+ and Ca2+ in vitro and to measure the uptake of 59Fe3+ and 45Ca2+ administered to mice by intraduodenal instillation and by gavage, respectively. The results demonstrate that: 1) di- and trivalent cations studied form soluble complexes with phytate at high phytate-to-metal ratios, independent of pH and 2) phytic acid has no substantial effect on the absorption of either Ca2+ or Fe3+. These results may prompt reevaluation of the supposedly adverse effects of dietary phytate on the bioavailability of metallophytate complexes.

Animals↗
PubMed1984

Bordetella adenylate cyclase toxin: entry of bacterial adenylate cyclase into mammalian cells.

We have identified an adenylate cyclase toxin in urea extracts and culture supernatant fluids of Bordetella pertussis (2). The ability of this toxin and the lack of a strong correlation between its activity and adenylate cyclase activity found in urea extracts suggest that it is an oligomer of readily dissociable subunits. The mechanism by which Bordetella adenylate cyclase toxin interacts with target cells is unknown, but polyvalent cations are necessary. Neutrophils exposed to the toxin acquire a 39,000 Mr protein that can also be photoaffinity labeled with 32P-ATP. We anticipate that this protein will prove to be a catalytic component of Bordetella adenylate cyclase toxin. Susceptible cells exposed to Bordetella adenylate cyclase toxin are functionally aberrant. In phagocytes, decreased bactericidal capacity may be important in the pathogenesis of human whooping cough and other Bordetella infections occurring in domestic animals. The effects of the toxin on neoplastic cells may offer new insights into the factors controlling their growth and differentiation. Bordetella adenylate cyclase toxin is a unique bacterial product. Further purification and characterization of this toxin will add to our understanding of cell-protein interactions and pathogen-host relationships.

Adenylate Cyclase Toxin↗
PubMed1983

Formation of [3H, 32P]phytic acid in germinating wheat.

Doubly labeled phytic acid of high specific activity was prepared by incubating whole wheat seeds with [32P]phosphoric acid and [3H]myoinositol for 48 h and purifying by anion-exchange chromatography on AG 1- X 8 resin. Both degradation and synthesis of phytic acid were inhibited by KF to a similar extent, yet the catabolic and anabolic pathways involved distinctly different enzyme systems, as no [3H, 32P]myoinositol tetra- or pentaphosphate could be detected.

Chromatography, Ion Exchange↗
PubMed1983

Binding of (+/-)-3H-lofexidine to alpha-adrenoceptors in membranes from rat brain.

The binding of (+/-)-3H-lofexidine (spec. act. 26.8 Ci/mmol) to rat brain membranes was studied. The specific binding of (+/-)-3H-lofexidine, defined as the excess over blanks containing excess (-)-noradrenaline was a saturable process. Scatchard analysis indicated a single class of binding sites (KD = 5.5 nM). The maximal number of binding sites amounted to 280 fmol/mg protein, comparable to the number occupied by 3H-clonidine and 3H-guanfacine. Specific binding reached equilibrium by about 5 min and dissociated in a biphasic manner. A rapid and a slow component of dissociation was found. The specific binding sites identified by (+/-)-3H-lofexidine in rat brain tissue are to be classified as alpha 2-adrenoceptors. Selective agonists as well as antagonists of alpha 1-adrenoceptors were weak displacers of the binding, whereas preferential stimulants as well as blocking drugs of alpha 2-adrenoceptors displayed high affinity for the (+/-)-3H-lofexidine sites. The relative affinity of various drugs for the sites labeled by (+/-)-3H-lofexidine perfectly corresponded with that for the specific binding sites identified by 3H-clonidine and 3H-guanfacine. This study shows the usefulness of (+/-)-3H-lofexidine as an additional radioligand for a direct characterization of alpha 2-adrenoceptors in brain tissue. It is concluded that (+/-)-3H-lofexidine labels the same population of alpha 2-adrenoceptors in rat brain as accessible to 3H-clonidine and 3H-guanfacine.

Animals↗
PubMed1982

Molecular properties of calcium-pumping ATPase from human erythrocytes.

The Ca2+-pumping ATPase from human erythrocyte membranes, purified by the method previously reported [Niggli, V., Penniston, J. T., & Carafoli, E. (1979) J. Biol. Chem. 254, 9955-9958], was freed of minor impurities by extensive washing while bound to the calmodulin-Sepharose column. The pure enzyme showed a single band of Mr 138000, which contained no stainable carbohydrate. The enzyme retained calmodulin-stimulable ATPase activity; with appropriate assay conditions, an activity of 21.2 mumol/(mg x min) was obtained. Amino acid analysis showed that the ATPase had a larger proportion of polar amino acids than do other integral membrane proteins. Despite this, the ATPase showed a tendency to form dimers and higher aggregates even in the presence of sodium dodecyl sulfate and urea. The enzyme required Mg2+ but showed little activity unless a second ion was added. With regard to this second ion, the enzyme responded to alkaline earth metal ions in the order Ca2+ greater than Sr2+ much greater than Ba2+. It was highly specific for ATP and was stimulated by Na+ or K+; in all of these properties it resembled the enzyme in unfractionated membranes. Limited proteolysis using trypsin yielded, at short times, many fragments of various molecular weights; continued proteolysis resulted in two trypsin-resistant fragments of Mr 81000 and 33500. Analysis of the time course of proteolysis indicated that the ATPase existed in two or more conformations that had differing susceptibilities to proteolysis. It is suggested that these correspond to active and inactive conformers of the enzyme.

Amino Acids↗
PubMed1982

Animal experiments on the safety pharmacology of lofexidine.

These experiments were carried out to supplement the pharmacodynamic profile of 2[1-(2,6-dichlorophenoxy)-ethyl]-2-imidazoline hydrochloride (lofexidine, Lofetensin and Loxacor), a potent hypotensive imidazoline derivative with a central mode of action. Effects indicative of a central sedative action were seen in various experiments on mice and rats. However, comparative studies with clonidine, particularly those involving the interaction with hexobarbital, the effect on motor coordination on a rotating rod, the effect on body temperature and other experiments, indicated that lofexidine had a 10 to 100 fold less sedative effect than clonidine, depending on the test and the route of administration. In rats there was a dose-related, diuretic and saluretic effect. This effect was not seen in dogs. In rabbits and guinea pigs, lofexidine exhibited local anaesthetic effects and its potency and duration of action were comparable to those of the reference compounds (tetracaine or mepivacaine). Lofexidine did not modify gastric secretion in rats. On the other hand, it inhibited chemically induced (phenylbutazone) and stress-induced (swimming) gastric ulcer formation in rats. Antiinflammatory and analgesic activities in rats and mice were, at most, very weak. Lofexidine increased blood glucose levels of normoglycaemic rats; clonidine is known to have the same effect. In order to investigate the possibility of combining lofexidine with a diuretic drug for the treatment of hypertension, the interaction with hydrochlorothiazide was studied in some experiments. The results obtained from these experiments showed that there was no adverse effect and the diuretic and saluretic effects of hydrochlorothiazide were not impaired. No findings militated against the use of lofexidine as an antihypertensive drug. It is likely that lofexidine, in contrast to clonidine, has less marked central sedative effects.

Aggression↗
PubMed1982

Animal experiments on the cardiovascular effects of lofexidine.

The cardiovascular effects of 2-[1-(2,6-dichlorphenoxy)-ethyl-2-imidazoline hydrochloride (lofexidine, Lofetensin and Loxacor), a hypotensive imidazoline derivative, have been studied in anaesthetized and conscious rats and in anaesthetized cats and dogs. In all three species intravenous administration of lofexidine caused a marked and long-lasting reduction of the systolic and diastolic pressure. The experiments in conscious and anaesthetized rats showed that lofexidine is also effective by the oral route both in normotensive and in hypertensive animals (spontaneously hypertensive rats and rats with renal hypertension). Based on the effective doses (1 microgram/kg i.v. and higher), lofexidine is a potent compound comparable in this respect to clonidine. In experiments in conscious rats, following intracerebroventricular administration and in anaesthetized cats, following intravertebral administration, the substance was even more potent than by the intravenous route, so it can be assumed to have a central mechanism of action. This was confirmed by other investigations. The hypotensive effect was accompanied in all species by a more or less pronounced fall in heart rate. The reduction of myocardial contractility and cardiac output observed in cats and dogs occurred in parallel with and may have caused, the lowering of blood pressure. Following intravenous administration, there was an initial, short-lived rise in blood pressure in the three species. This was interpreted as a direct, alpha-sympathomimetic effect on the vessels. Pretreatment with atropine, diphenhydramine and amitriptyline reduced the hypotensive and bradycardiac effects of lofexidine to some extent; this is also the case with clonidine. There were no adverse interactions in tests in which lofexidine was combined with a diuretic drug (hydrochlorothiazide). There was a slight tendency for the blood pressure effect to be enhanced in anaesthetized rats and dogs. The results of these tests indicate that lofexidine has the typical pharmacodynamic profile of a centrally acting, hypotensive compound. This justifies further experimental work to develop this drug as an antihypertensive agent.

Animals↗
PubMed1981

CaATP: the substrate, at low ATP concentrations, of Ca2+ ATPase from human erythrocyte membranes.

Detailed kinetic analyses of ATP-splitting activities were obtained with purified Ca2+ ATPase from human erythrocyte membranes. At constant low total ATP levels increasing Mg2+ inhibited the activity of the enzyme, while increasing Ca2+ did not. Detailed analysis of this phenomenon with appropriate controls showed that this occurred because Ca2+ . ATP4- (CaATP) was the substrate for the enzyme: the inhibition by Mg2+ was due to the lowering of the CaATP concentration as Mg2+ replaced Ca2+ as the metal bound to ATP. Free ATP could not be the substrate, since its concentration could be lowered by increasing total Ca2+, and no inhibition of the reaction occurred. In addition to this site for CaATP, the enzyme may contain yet another metal-ATP site of much lower affinity and less specificity with respect to the metal. The data also indicate the presence of a Mg2+ site and a Ca2+ site in addition to the CaATP site. Since the enzyme also interacts with calmodulin, it effectively interacts with Ca2+ at three sites: the Ca2+ site, the CaATP site, and the Can-calmodulin site. The enzyme displays the same characteristics in the presence of calmodulin. However, the stimulation by calmodulin is always about three times higher in the presence of Mg2+ than in its absence. A model for the mechanism of this enzyme is discussed.

Adenosine Triphosphate↗