Biomedical subjects

A Bast

Publications and source records attributed to A Bast.

At least 217 records · Page 12Linked to original sources

PubMed1986

Influence of lipid peroxidation on beta-adrenoceptors.

The peroxidation of lipids in biological membranes is a destructive phenomenon that can be elicited in various ways. Surface receptor molecules that allow cells to respond to hormones are possibly inactivated during lipid peroxidation. Effects of lipid peroxidation on receptors have not been extensively examined thus far. This investigation shows that there is a decrease in beta-adrenoceptor density (measured as specific (-)-[125I]iodocyanopindolol binding) during lipid peroxidation, in both lungs and erythrocytes of the rat. To this end, lung membranes (containing both beta 1- and beta 2-adrenoceptors) and intact erythrocytes (containing a homogeneous beta 2-adrenoceptor population) were pretreated with cumene hydroperoxide (lung membranes with 0.1 mM and erythrocytes with 1 mM) and Fe2+ (1 X 10(-5) M) for 60 min which resulted in extensive lipid peroxidation measured as malondialdehyde formation. The ration beta 1-:beta 2-adrenoceptor density in lung membranes after treatment with cumene hydroperoxide did not change and remained at 30%:70%. A single injection (i.p.) with the herbicide paraquat (50 mg/kg, 24 h), which is known to cause lung damage via lipid peroxidation, resulted in similar alterations in receptor density to those caused by cumene hydroperoxide in the in vitro experiments.

Animals↗

PubMed1986

Red blood cell anti-oxidant parameters in silicosis.

The anti-oxidant phenotype was determined in red blood cells and plasma of a group of male control subjects (n = 48) and a number of silicosis patients (n = 19). Haemoglobin, reduced and oxidized glutathione, glutathione peroxidase and superoxide dismutase were determined in red blood cells after haemolysis. In plasma, water soluble fluorescent substances were determined as a measure of in vivo lipid peroxidation. A significant increase in red blood cell glutathione was observed in silicosis patients. Moreover, some factors of the anti-oxidant system are strongly correlated in the diseased, but not in the healthy subjects. We hypothesize that individual susceptibility differences towards the development of silicosis after prolonged inhalation of silica is associated with a genetically controlled anti-oxidant phenotype.

Aged↗

PubMed1986

The effects of 4-hydroxy-2,3-trans-nonenal on beta-adrenoceptors of rat lung membranes.

Lung membranes are susceptible to oxygen radicals, formed during inflammation, redox cycling of toxic agents, exposition to ozon etc. Oxygen radicals may modify the beta-adrenergic response. However, at the same time beta-adrenoceptors of the lung are frequently addressed in therapy. We embarked upon this problem by studying the effects of the aldehyde 4-hydroxy-2,3-transnonenal (HNE), one of the major products of lipid peroxidation, on the density of beta-adrenoceptors of rat lung membranes. It is shown, that the physiological important sulfhydryl blocking agent HNE inactivates the beta-adrenoceptors in a time- and concentration dependent (0.5-2.5 mM) way, indicated by a decrease in (-)-[3H]dihydroalprenolol (DHA) binding to lung membranes. Moreover, it is shown that combined treatment of HNE with (-)-isoproterenol (0.5 microM) or 1-alprenolol (0.5-10 nM) does not influence the extent of inactivation of beta-adrenoceptors by HNE. This is in contrast with previous studies, conducted with other, synthetic, sulfhydryl blocking agents, such as N-ethylmaleimide (NEM), suggesting that an other mechanism of inactivation is involved upon HNE treatment.

Aldehydes↗

PubMed1986

The role of lipid peroxidation in acute doxorubicin-induced cardiotoxicity as studied in rat isolated heart.

Doxorubicin induces an acute cardiotoxicity that becomes manifest in isolated hearts as a deterioration in mechanical function. The oxidative component in this myocardial damage has been investigated. The effects of doxorubicin on the activity of superoxide dismutase and the capacity of the glutathione system, factors of the cellular protective mechanism against free radicals, were examined in rat isolated heart. Doxorubicin was found to reduce the capacity of the protective mechanisms. Whether oxidative membrane damage due to excessive free radical formation plays a role in the pathogenesis of the acute cardiotoxic action of doxorubicin was also examined. Its acute effect on myocardial contraction amplitude, frequency of beating, coronary flow and on the above mentioned biochemical parameters was compared in rat hearts sufficient or deficient in vitamin E. Peroxidation of lipids was measured as the formation of malondialdehyde, one of the final products of this process. Vitamin E deficiency neither aggravated the decrease in the capacity of the cellular protective factors nor worsened the reduction in myocardial function. Nor did induction of lipid peroxidation by doxorubicin occur in vitamin E-deficient hearts. It was concluded that lipid peroxidative damage most probably is not decisive in the development of the acute cardiomyopathy in rats.

Animals↗

PubMed1986

Non-enzymic lipid peroxidation in microsomes and microsomal phospholipids induced by anthracyclines.

The stimulation of non-enzymic lipid peroxidation by doxorubicin, daunorubicin and 7 derivatives was investigated in extracted microsomal phospholipids and in intact microsomes. Evidence was obtained for the necessity of a free amino-sugar moiety for a stimulative effect on lipid peroxidation. Binding of anthracyclines to RNA (which is present in microsomes) was inhibitory towards stimulation. Drugs that stimulated lipid peroxidation in a non-enzymic system with extracted phospholipids also were stimulative in an enzymic, NADPH-dependent, microsomal system. They were not always effective in intact microsomes without the enzymic system. The role of the enzymic system in the stimulation of anthracycline induced lipid peroxidation is thought to be the reduction of iron ions rather than the stimulation of oxygen radical production via the anthracyclines.

Animals↗

PubMed1986

The effect of vitamin E-deficiency in isolated rat heart on the cellular defence system against free radicals during normal reperfusion after hypoxic, ischemic and Ca(2+)-free perfusion.

We investigated whether vitamin E plays a role in the protection against potential free radical formation and related biochemical changes in hypoxic, ischemic and Ca(2+)-depleted rat heart upon normal reperfusion. In the heart of normally fed rats a decrease in the activity of superoxide dismutase and the capacity of the glutathione system, factors of the cellular protective mechanisms against free radicals, occurred upon exposure to the above mentioned treatments. This decrease was not further enhanced if vitamin E-deficient rat hearts were treated. Vitamin E-deficiency, however, led to detectable peroxidation of lipids if Ca(2+)-depleted or hypoxic hearts were reperfused. Lipid peroxidation was measured as the formation of thiobarbituric acid reactive material, which is readily formed during this process. Reflow after ischemia did not induce lipid peroxidation either in normal or in vitamin E-deficient rat heart. Since changes in Ca(2+)-homeostasis are thought to be primarily responsible for the Ca(2+)-reperfusion injury, a role for Ca(2+)-ions in lipid peroxidative processes, either directly or indirectly, seems indicated. Furthermore the results imply that even a sharp and extensive decrease of reduced glutathione, as seen upon Ca(2+)-repletion after a period of Ca(2+)-depletion, does not necessarily induce peroxidation of lipids in heart tissue. Obviously, vitamin E is very important in the protection of cardiac membranes. Replenishment of the water-soluble protective factors in the heart seems, however, more important during above mentioned treatments, especially since repair of the vitamin E-free radical is dependent on water-soluble factors.

Animals↗

PubMed1985

Effect of vitamin E on the balance between pro- and antioxidant activity of ascorbic acid in microsomes from rat heart, kidney and liver.

The effect of the vitamin E status of membranes on the balance between pro- and antioxidant activity of ascorbic acid was studied in microsomes from rat heart, kidney and liver. Lipid peroxidation was initiated by 5 microM ferrous ions, in combination with amounts of ascorbic acid ranging from 0-4 mM. Lipid peroxidation was assessed after 1 h of incubation as production of thiobarbituric acid reactive material. It was found that the vitamin E status of the microsomal membranes had little effect on the balance between pro- and antioxidant activity of vitamin C. The sensitivity of the membranes to ferrous ions/ascorbic acid-induced lipid peroxidation, however, was highly dependent on the vitamin E content of the membranes. Vitamin E depletion, in combination with different ascorbic acid concentrations, showed that vitamin E deficiency is not an incontestable model system for enhanced sensitivity to lipid peroxidation in all organs.

Animals↗

PubMed1985

Anthracycline-induced oxygen consumption and oxidative damage in rat liver microsomes are not necessarily coupled. A study with 8 structurally related anthracyclines.

The stimulative effect of 8 anthracyclines (the parent compounds daunorubicin and doxorubicin and 6 structurally closely related anthracyclines) on the production of thiobarbituric acid (TBA)-reactive material was investigated in liver microsomes. Except for daunorubicinone and doxorubicinone, all derivatives stimulated NADPH-dependent production of TBA-reactive material. Doxorubicinone had no effect, daunorubicinone inhibited TBA-reactivity at concentrations up to 50 microM. However, the latter two compounds stimulated oxygen consumption in the presence of EDTA to a degree comparable to that induced by the parent compounds. Since the oxygen uptake under these circumstances represents redox cycling of the drugs, apparently redox cycling and production of TBA-reactive material were not coupled for these compounds. Spectral measurements showed no decisive role for interaction with free iron (Fe3+) ions in the non-coupling of redox cycling and production of TBA reactive material. Evidence for a role of bound iron ions was not obtained. It is discussed that for the aglycones oxygen consumption and production of TBA reactive material might be non-coupled through their different interaction with microsomal RNA.

Animals↗

PubMed1985

The involvement of an oxidative mechanism in the adriamycin induced toxicity in neonatal rat heart cell cultures.

In order to investigate the oxidative component of adriamycin-induced cardiotoxicity in the rat, we used neonatal cardiac myocytes in culture. All incubations, with or without adriamycin (ADM), were performed under normoxic circumstances and additionally under circumstances which make cells more vulnerable towards oxidative challenges: hyperoxia or treatment with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). ADM (100 microM) produced a decrease in the beating rate and enzyme release of the cultures. These effects were potentiated by hyperoxia and by BCNU treatment. Cellular GSH was depleted due to ADM. However, no significant increase in GSSG could be detected, even if the O2-concentration was increased. Lipid peroxidation, measured as thiobarbituric acid reactive material, could be detected only in case ADM plus additional stress were given to the cells. It is concluded that redox-cycling of ADM occurs in rat cardiac myocytes. Formation of ADM-glutathione conjugates or mixed disulfides is strongly indicated. From this it can be inferred that ADM-toxicity in cardiac cells may involve an oxidative mechanism. An important role for the glutathione system is indicated in the detoxification of reactive intermediates. In addition the results implicate that neonatal rat heart cell cultures provide a good screening system for the evaluation of oxidative challenges in the cardiotoxic action of anthracycline analogs.

Animals↗

PubMed1984

Decreased defence against free radicals in rat heart during normal reperfusion after hypoxic, ischemic and calcium-free perfusion.

Excessive formation of free radicals possibly plays an important role in the origin of irreversible damage of the heart after hypoxic, ischemic or Ca2+-free treatment. The effect of these treatments on the activity of superoxide dismutase and the glutathione system was studied on isolated rat heart. These activities reflect the protective capacity of the heart against reactive substances. In addition the peroxidation of lipids is determined in the treated hearts using malondialdehyde formation as an indicator. All experiments were performed using a Langendorff-apparatus with recirculating perfusion. The observed changes in the components of the glutathione system and superoxide dismutase activity both after hypoxic, ischemic and Ca2+-free perfusion, as measured upon reperfusion, indicate a decrease in cellular defense mechanisms in the heart against free radicals. The effect was most pronounced upon Ca2+-repletion after a period of Ca2+-free perfusion. No malondialdehyde could however be detected either in the tissue of the treated hearts or in the perfusate. Our data give reason to expect beneficial effects of an adequate pharmacological treatment, which replenishes the cellular defence systems.

Animals↗

PubMed1984

Relationship between molecular structure and cytochrome P450-metabolic intermediate complex formation, studied with orphenadrine analogues.

Complexation of ferrous cytochrome P450 by metabolic intermediates formed during NADPH-catalyzed metabolism of compounds structurally related to orphenadrine was studied. This so-called metabolic intermediate complexation was determined in rat liver microsomes, obtained from phenobarbital-pretreated rats, at 455 nm using 33 microM of the orphenadrine derivatives. Using secondary amine derivatives with various N-alkyl substituents, a parabolic relationship between the logarithm of percentage of cytochrome P450 complexation and hydrophobic fragmental constant was observed. The derivative with a bulky tertiary butyl group, however, was devoid of metabolic intermediate-complexing activity. This indicates that steric factors besides lipid solubility may govern the complexing activity; also substitution at the phenyl group affects metabolic intermediate complex formation.

Animals↗

PubMed1984

Sex differences in the cellular defence system against free radicals from oxygen or drug metabolites in rat.

In this study, it was investigated whether sex-related differences in the protective mechanisms against oxygen radicals and free radical metabolites from drugs were present in rat liver, heart, and kidney. To that end, superoxide dismutase, catalase, the factors of the glutathione system and vitamin E were measured. In addition, NADPH-dependent cytochrome c-reductase activity was established, as this enzyme is involved in the formation of free radicals in the presence of many xenobiotics. The total capacity of the cellular systems that detoxify reactive oxygen species or free radical-drug metabolites seems to be higher in female liver as compared to male. No differences were found for heart and kidney tissue. It is hypothesized that female rats probably are less vulnerable for those drugs whose hepatotoxic action is induced by excessive formation of free radical species.

Animals↗

PubMed1984

Evidence for lipid peroxidation during the calcium paradox in vitamin E-deficient rat heart.

Vitamin E is known to play an important role in the protective capacity of tissues as a free radical scavenger. Rats were made deficient in vitamin E, in order to demonstrate more clearly the formation of free radicals after exposing the rat heart to sudden changes in calcium homeostasis. The formation of malondialdehyde was taken as measure for lipid peroxidation. Malondialdehyde was detected in appreciable amounts both in heart tissue and coronary perfusate of vitamin E-deficient rat hearts after exposing them to the sudden changes in calcium concentration as seen during the calcium paradox. These findings emphasize a the hearts of normally fed rats no malondialdehyde could be detected in tissue or coronary perfusate after the calcium paradox. Therefore an essential role for vitamin E against oxidative stress in heart tissue is also indicated.

Animals↗

PubMed1984

Adriamycin stimulates NADPH-dependent lipid peroxidation in liver microsomes not only by enhancing the production of O2 and H2O2, but also by potentiating the catalytic activity of ferrous ions.

The antitumor drug, adriamycin, enhances NADPH-dependent lipid peroxidation in liver microsomes via the formation of superoxide anion radicals (O2) and hydrogen peroxide (H2O2). In the presence of metal ions additional reactive species are generated, causing stimulation of lipid peroxidation. However, in this study it was found that the stimulation of NADPH-dependent lipid peroxidation by adriamycin was not only affected by the production of O2 and H2O2. Adriamycin also enhances the catalysis by metal ions of the formation of those reactive oxygen species which initiate peroxidation. This was inferred from the fact that adriamycin stimulated malondialdehyde production at low ferrous ion concentrations, whereas at high ferrous ion concentrations no stimulation was found. Additional evidence was found in experiments in which the enzymic redox cycle of adriamycin in microsomes was abolished by heat-inactivation of the microsomes, and O2 and H2O2 were only produced with xanthine and xanthine oxidase. In this case in the presence of ferrous ions, adriamycin stimulated lipid peroxidation.

Animals↗

PubMed1984

Inhibition of mono-oxygenase and oxidase activity of rat-hepatic cytochrome P-450 by H2-receptor blockers.

Of four H2 blockers, cimetidine, tiotidine, oxmetidine and ranitidine, all except ranitidine showed ligand (type II) interactions with oxidized cytochrome P-450. High- and low-affinity binding sites were observed in hepatic microsomes of control, phenobarbital (PB)-treated and 3-methylcholanthrene (3-MC)-treated rats. All H2 blockers except for ranitidine (up to 400 microM) produced a concentration-dependent inhibitory effect of the metabolic intermediate (MI)-cytochrome P-450 complex formation which is displayed during metabolism of tofenacine in PB hepatic microsomes in vitro. At 400 microM, of all H2 blockers only oxmetidine was able to dissociate in vitro the isosafrole metabolite-cytochrome P-450 complex formed in vivo. Endogenous NADPH-dependent microsomal H2O2 production is inhibited in control, PB and 3-MC microsomes by the H2 blockers to various extents. In liver microsomes of phenobarbital-pretreated rats, substrate-dependent inhibition of H2O2 production correlates with inhibition of MI-cytochrome P-450 complex formation of tofenacine. Moreover, the magnitude of ligand (type II) binding of the H2 blockers correlates with inhibition of H2O2 formation. This indicates that prevention of oxygen activation by ligand binding decreases endogenous H2O2 production. Inhibition of both mono-oxygenase as well as oxidase activity of cytochrome P-450 may lead to adverse drug interactions. On the other hand formation of reactive or deleterious intermediates formed as a consequence of cytochrome P-450 activities can be prevented.

Animals↗

PubMed1983

Protection against lipid peroxidation by a microsomal glutathione-dependent labile factor.

Glutathione (GSH) protects rat liver microsomes against ascorbic acid (0.2 mM)/ferrous iron (10 microM)-induced lipid peroxidation for some time. The inhibitory effect of GSH is concentration-dependent (0.1-1.0 mM). Our data suggest that GSH acts by preventing initial radical formation rather than via radical scavenging or GSH--peroxidase activity. A labile GSH-dependent factor is involved in the inhibition of microsomal lipid peroxidation by GSH, inasmuch as heating the microsomes abolishes the GSH effect. We found that besides heating, lipid peroxidation also destroys the GSH-dependent factor. Consequently, continuous radical stress will produce lipid peroxidation, despite the presence of GSH. Moreover, a detrimental effect of in vivo-induced lipid peroxidation (CCl4-treatment) on the GSH-dependent factor was observed. The implications of the present data for the genesis of and the protection against peroxidative damage are discussed.

Animals↗

PubMed1983

Cytochrome P450 oxidase activity and its role in NADPH dependent lipid peroxidation.

A comparison is made between microsomal NADPH-dependent H2O2 production and malondialdehyde (MDA) formation in rat liver microsomes, obtained from phenobarbital pretreated rats. An increase in H2O2 formation was observed during NADPH-dependent disposition (10 min) of 100 microM diazepam (33%) and 2 mM hexobarbital (69%). In contrast orphenadrine (100 microM) and its mono-N-demethylated metabolite tofenacine (100 microM) decreased the H2O2 formation (35% and 55%, respectively). However, all these substrates were found to inhibit NADPH-dependent lipid peroxidation (60 min), estimated by measuring MDA formation, to various extents. These data strongly suggest that the oxidase activity of cytochrome P450 (H2O2 production) is not involved in a rate-limiting step in NADPH-dependent lipid peroxidation.

Animals↗

PubMed1983

Effect of multiple administration of orphenadrine or mono-N-desmethylorphenadrine on cytochrome P-450 catalyzed reactions in the rat.

Multiple administration (i.p.) of orphenadrine or its mono-N-demethylated metabolite, tofenacine (day 1, 20 mg/kg; day 2-5, 30 mg/kg) results in a considerable induction (50%) of the total cytochrome P-450 content. In addition, approximately 6% of the total amount of cytochrome P-450 was found to be blocked by a metabolic intermediate, formed from orphenadrine or tofenacine. Induction is apparent in enhancing the in vitro N-demethylation of aminopyrine and ethylmorphine and the p-hydroxylation of aniline. Pretreatment induced orphenadrine metabolism in vitro. The metabolism of tofenacine, however, was reduced. Probably this is due to a specific inhibition caused by the irreversible interaction of the metabolic intermediate with cytochrome P-450. In vivo, no induction of the aminopyrine metabolism (30 mg/kg, i.v.) is apparent, i.e., no change in the clearance was observed after pretreatment. This is probably due to the presence of relatively high, inhibitory concentrations of tofenacine (in the vicinity of cytochrome P-450). These results show that during chronic administration of orphenadrine or tofenacine, the in vivo disposition of concomitantly ingested compounds is determined by the influence of induction, high substrate and/or metabolite levels and complexation of cytochrome P-450. Moreover, based on these results an hypothesis is put forward in order to explain the phenomenon of product inhibition, which has been suggested to occur in man under chronic orphenadrine dosing conditions.

Aminopyrine↗