Oxygen radical-mediated injury of myocytes-protection by propranolol

Calcium channel blocker, azelnidipine, reduces lipid hydroperoxides in patients with type 2 diabetes independent of blood pressure

Anti-hypertensive agents with antioxidative effects are potentially useful for diabetic patients with hypertension to prevent the onset and progression of their complication. While dihydropyridine-type calcium antagonists are among the frequently used anti-hypertensive drugs, azelnidipine, a novel calcium antagonist, has been reported to have a unique anti-oxidative effect in vitro and in animals. In this study, we measured lipid hydroperoxides in human sample using diphenyl-1-pyrenylphosphine for the first time, and used the value of lipid hydroperoxides as an index of oxidative stress. Then, we compared the antioxidative properties of azelnidipine and amlodipine, a frequently used calcium antagonist in hypertensive diabetic patients. Administration of vitamin C and E for 8 weeks significantly reduced lipid hydroperoxides in erythrocyte membrane in normal subjects. In hypertensive diabetic patients, azelnidipine treatment for 12 weeks induced a more significant fall in erythrocyte lipid hydroperoxide level than amlodipine, though blood pressure during each treatment was comparable. Our data confirm the usefulness of lipid hydroperoxides in erythrocyte membrane as a marker of oxidative stress in vivo, and indicate that azelnidipine has a unique antioxidative property in human.

Antioxidant and lysosomotropic properties of acute D-propranolol underlies its cardioprotection of postischemic hearts from moderate iron-overloaded rats

The benefits of acute D-propranolol (D-Pro, non-beta-adrenergic receptor blocker) pretreatment against enhanced ischemia/reperfusion (I/R) injury of hearts from moderate iron-overloaded rats were examined. Perfused hearts from iron-dextran-treated rats (450 mg/kg/week for 3 weeks, intraperitoneal administration) exhibited normal control function, despite iron treatment that elevated plasma iron and conjugated diene levels by 8.1-and 2.5-fold, respectively. However, these hearts were more susceptible to 25 mins of global I/R stress compared with non-loaded hearts; the coronary flow rate, aortic output, cardiac work, left ventricular systolic pressure, positive differential left ventricular pressure (dP/dt), and left ventricular developed pressure displayed 38%, 60%, 55%, 13%, 41%, and 15% lower recoveries, respectively, and a 6.5-fold increase in left ventricular end-diastolic pressure. Postischemic hearts from iron-loaded rats also exhibited 5.6-, 3.48-, 2.43-, and 3.45-fold increases in total effluent iron content, conjugated diene levels, lactate dehydrogenase (LDH) activity, and lysosomal N-acetyl-beta-glucosaminidase (NAGA) activity, respectively, compared with similarly stressed non-loaded hearts. A comparison of detection time profiles during reperfusion suggests that most of the oxidative injury (conjugated diene) in hearts from iron-loaded rats occurred at later times of reperfusion (8.5-15 mins), and this corresponded with heightened tissue iron and NAGA release. D-Pro (2 microM infused for 30 mins) pretreatment before ischemia protected all parameters compared with the untreated iron-loaded group; pressure indices improved 1.2- to 1.6-fold, flow parameters improved 1.70- to 2.96-fold, cardiac work improved 2.87-fold, and end-diastolic pressure was reduced 56%. D-Pro lowered total release of tissue iron, conjugated diene content, LDH activity, and NAGA activity 4.59-, 2.55-, 3.04-, and 4.14-fold, respectively, in the effluent of I/R hearts from the iron-loaded group. These findings suggest that the enhanced postischemic dysfunction and tissue injury of hearts from iron-loaded rats was caused by excessive iron-catalyzed free radical stress, and that the membrane antioxidant properties of D-Pro and its stabilization of sequestered lysosomal iron by D-Pro may contribute to the cardioprotective actions of D-Pro.

D-propranolol attenuates lysosomal iron accumulation and oxidative injury in endothelial cells

The influence of selected beta-receptor blockers on iron overload and oxidative stress in endothelial cells (ECs) was assessed. Confluent bovine ECs were loaded with iron dextran (15 muM) for 24 h and then exposed to dihydroxyfumarate (DHF), a source of reactive oxygen species, for up to 2 h. Intracellular oxidant formation, monitored by fluorescence of 2',7'-dichlorofluorescin (DCF; 30 microM), increased and peaked at 30 min; total glutathione decreased by 52 +/- 5% (p < 0.01) at 60 min. When the ECs were pretreated 30 min before iron loading with 1.25 to 10 microM d-propranolol, glutathione losses were attenuated 15 to 80%, with EC(50) = 3.1 microM. d-Propranolol partially inhibited the DCF intensity increase, but atenolol up to 10 microM was ineffective. At 2 h, caspase 3 activity was elevated 3.2 +/- 0.3-fold (p < 0.01) in the iron-loaded and DHF-treated ECs, and cell survival, determined 24 h later, decreased 47 +/- 6% (p < 0.01). Ten micromoles of d-propranolol suppressed the caspase 3 activation by 63% (p < 0.05) and preserved cell survival back to 88% of control (p < 0.01). In separate experiments, 24-h iron loading resulted in a 3.6 +/- 0.8-fold increase in total EC iron determined by atomic absorption spectroscopy; d-propranolol at 5 microM reduced this increase to 1.5 +/- 0.4-fold (p < 0.01) of controls. Microscopic observation by Perls' staining revealed that the excessive iron accumulated in vesicular endosomal/lysosomal structures, which were substantially diminished by d-propranolol. We previously showed that propranolol could readily concentrate into the lysosomes and raise the intralysosomal pH; it is suggested that the lysosomotropic properties of d-propranolol retarded the EC iron accumulation and thereby conferred the protective effects against iron load-mediated cytotoxicity.

Inhibition of neutrophil migration and oxygen free radical release by metipranolol and timolol

Propanolol and metoprolol exert adrenoceptor-independent effects including scavenging of free radicals and inhibition of protein kinase C leading to inhibition of leukocyte migration and radical release as a consequence. Whether topically used metipranolol and timolol exert such effects is unknown. Neutrophil chemotaxis was tested using modified Boyden microchemotaxis chambers. Respiratory burst activity of neutrophils was detected fluorometrically. Radical scavenging properties were tested using 2',7'-dichlorofluorescein diacetate. Metipranolol and timolol inhibited neutrophil chemotaxis at doses in the micromolar range, oxygen free radical production triggered with formyl-Met-Leu-Phe was inhibited at higher concentration. Protein kinase C involvement, suggested to trigger free radical production with phorbol myristate acetate, was antagonized. A direct radical scavenging effect of the beta-blockers was also seen. Inhibition of neutrophil chemotaxis and free radical production is a novel mode of action of metipranolol and timolol that may be relevant for beneficial effects in the topical treatment of eye disease.

Adrenaline (via α1B-adrenoceptors) and ethanol stimulate OH radical production in isolated rat hepatocytes

Adrenaline is able to increase the oxidative damage caused by some xenobiotic agents in the liver. Ethanol produces oxidative changes in hepatic tissue, while an acute intoxication with alcohol increases adrenaline blood levels. The aim of this study was to determine whether adrenaline increases ethanol-induced hydroxyl free radical production in isolated hepatocytes. Adrenaline augmented hydroxyl radicals in a concentration-dependent manner and was blocked by chloroethylclonidine, an alpha(1B)-adrenoceptor antagonist, while adrenaline plus ethanol added their individual effects. It is suggested that adrenaline increases hydroxyl radicals by an alpha(1B)-adrenoceptor-mediated mechanism, while ethanol does so by a receptor-independent mechanism.

Antioxidant and lysosomotropic properties of acridine-propranolol: protection against oxidative endothelial cell injury

The antioxidant and lysosomotropic properties of a fluorescent analogue of propranolol, 9-amino-acridine-propranolol (9-AAP) were compared to those of propranolol. Using isolated microsomal membranes exposed to a superoxide and hydroxyl radical generating system, 9-AAP was found to be at least 10-fold more potent than propranolol (and about 50% as potent as vitamin E) in inhibiting lipid peroxidation. In cultured endothelial cells, 9-AAP afforded moderate protective effect against acute loss of glutathione but potent cytoprotective activity against free radical-mediated loss of viability/survival. Intracellular localization of 9-AAP was examined by fluorescent microscopy and compared with two known fluorescent lysosomal markers: acridine orange and Lysosensor. All three agents appeared to localize to similar peri-nuclear vesicles, presumably lysosomes or pre-lysosomes. Lysosensor fluorescence was not observable in the presence of 9-AAP, foreclosing the possibility of a direct dual labeling experiment. We employed the pH sensitivity of acridine orange to determine if it labels the same vesicles as 9-AAP. When the endothelial cells were preloaded with acridine orange, washed and resuspended in buffer containing 9-AAP, the dark orange-labeled vesicles observed with acridine orange alone became increasingly lighter with time. Since the fluorescence of acridine orange is altered by pH change, this spectral shift in fluorescence emission is consistent with the indication that added propranolol (or the analog) leads to lysosomal alkalization. In conclusion, 9-AAP is both a strong antioxidant and a lysosomotropic agent that is remarkably insensitive to photobleaching. These properties may contribute to the enhanced endothelial cytoprotective effects against free radical-induced injury.

Ca(2+)-dependent production of reactive oxygen metabolites by human neutrophils in response to fluorinated propranolol analogues

Fluorinated analogues of propranolol, namely trifluoroethyl propranolol (F3), pentafluoropropyl propranolol (F5), and heptafluorobutyl propranolol (F7), were found to induce reactive oxygen metabolite (ROM) production in human neutrophils in a dose-dependent manner. Preincubation of neutrophils with the calcium chelator BAPTA-AM or the tyrosine kinase inhibitor genistein inhibited this ROM production. Direct measurements of intracellular calcium revealed that these analogues caused a transient increase in intracellular calcium. In addition, these fluorinated analogues of propranolol caused a transient increase in actin polymerization. The effects of these compounds were found to be dependent upon the degree of fluorination of the parent compound. Propranolol, on the other hand, had no direct effect on ROM, calcium, or actin polymerization when added alone to neutrophils, although it did modify responses of cells to various stimuli. Whereas ROM production induced by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine was enhanced in a dose-dependent manner, the response to the particulate stimulus, latex beads, was abolished.

Modulation of neutrophil migration and superoxide anion release by metoprolol

In addition to having anti-sympathotonic effects, beta-blockers are thought to have some adrenoceptor-independent properties. Such ancillary effects are described for carvedilol acting as oxygen radical scavenger and for propranolol which blocks protein kinase C and phosphatidate phosphohydrolase. The goal of our in vitro experiments was to identify ancillary effects of the widely used beta-blockers metoprolol and atenolol in neutrophils. Neutrophil chemotaxis was tested using the leading front assay in a modified Boyden microchemotaxis chamber. Respiratory burst activity was detected fluorometrically. Inhibition of protein kinase C activity was tested with purified alpha-, beta- and gamma-isoenzyme preparation. Metoprolol dose-dependently inhibited formyl peptide-stimulated neutrophil chemotaxis and formylpeptide- and phorbol myristate acetate-triggered oxygen free radical production. These actions were not affected by the competitive presence of the beta-receptor agonist, orciprenaline. Effects of metoprolol, as well as of propranolol, and the signaling enzyme blockers were strongly time dependent. Propranolol mimicked effects of staurosporine on respiratory burst, whereas the effects of metoprolol were similar to bisindolylmaleimide, a specific protein kinase C blocker. Atenolol, a hydrophilic beta-blocker, neither affected neutrophil chemotaxis nor respiratory burst. In a cell-free system, metoprolol did not interfere with the activity of the purified protein kinase C alpha-, beta- and gamma-isoenzymes. Adrenoceptor-independent inhibition of neutrophil chemotaxis and free radical production is a novel mode of action of metoprolol that may be relevant for beneficial effects ot the beta-blocker in heart failure and endothelial preconditioning.

Loss of red blood cell glutathione during Mg deficiency: prevention by vitamin E, D-propranolol, and chloroquine

Mg deficiency results in loss of red blood cell glutathione and was thought to be due to decreased Mg-dependent synthesis. The effects of vitamin E, D-propranolol, and chloroquine on red blood cell glutathione levels in Mg-deficient rats were examined. Feeding the rats a Mg-deficient diet for 3 wk resulted in an approximately 80% decrease in serum Mg and a 55% loss of red blood cell glutathione; concomitantly, plasma thiobarbituric acid reactive (TBAR) materials rose 240%. All three drug treatments had no effect on the plasma Mg levels but significantly inhibited the rise in TBAR content and attenuated (60-80% effective) the loss of glutathione. Red blood cell ghost membranes from the Mg-deficient rats also exhibited 2.3-fold higher TBAR content, which was attenuated by vitamin E treatment. With isolated red blood cells from Mg-sufficient rats, loss of glutathione could be induced by a chemical oxyradical system. Direct protective effects were afforded by alpha-tocopherol and D-propranolol but not by chloroquine. The data suggest that 1) the loss of glutathione during Mg deficiency was due to increased oxidative degradation, 2) both vitamin E and D-propranolol protected by a membrane antiperoxidative action, and 3) chloroquine probably protected by diminishing prooxidant activity secondary to its inhibition of cytokine induction during Mg deficiency.

Blockade of cardiac inflammation in Mg2+ deficiency by substance P receptor inhibition

In previous work we reported the elevation of circulating inflammatory cytokines in rodents maintained on a Mg(2+)-deficient diet. Within the first week of Mg2+ deficiency, significant elevation of the neuropeptides substance P (SP) and calcitonin gene-related peptide (CGRP) occurs. The present study was designed to assess the effects of SP receptor blockade by CP-96,945 and its inactive enantiomer CP-96,344 on tissue cytokine levels and in vivo oxidative indexes. CP-96,345 had no significant effect on circulating levels of SP or CGRP; however, at the tissue level, a significant decrease (P < .01) in myocardial accumulation of SP occurred; the inactive enantiomer was only slightly effective. In addition, CP-96,345 significantly reduced (by 53%) the accumulation of tumor necrosis factor-alpha (TNF-alpha) (but not interleukin-1 and interleukin-6) within the lesions; the effect of the enantiomer was insignificant. We conclude that treatment with CP-96,345 inhibits SP and TNF-alpha tissue levels in cardiac lesions, indicating a linkage between this neuropeptide and TNF-alpha. Both SP and TNF-alpha can trigger free radical production; plasma thiobarbituric acid-reactive materials were elevated 2.5-fold and red blood cell reduced glutathione was reduced 55% during Mg2+ deficiency. In the presence of CP-96,345, both indexes of in vivo oxidation were significantly attenuated; the enantiomer was ineffective. These latter observations point to a neuropeptide/TNF-alpha/free radical-triggered mechanism that may be the major pathway of systemic oxidative injury inducing the cardiomyopathic lesions seen during Mg2+ deficiency.

Neurogenic peptides and the cardiomyopathy of magnesium-deficiency: effects of substance P-receptor inhibition

Dietary deficiency of magnesium (Mg) in rodents results in cardiomyopathic lesion formation. In our rat model, these lesions develop after 3 weeks on the Mg-deficient diet; significant elevation of several cytokines, IL-1, IL-6 and TNF alpha also occurs. In probing the mechanisms of lesion formation, we obtained data supporting the participation of free radicals (Freedman AM et al.: Bioch Biophys Res Commun 1990; 170: 1102). Recently, we identified an early elevation of circulating substance P and proposed a role of neurogenic peptides during Mg-deficiency (Weglicki WB, Phillips TM: AM J Phys 1992;262:R734). The present study was designed to evaluate the contribution of neurogenic peptides to the pathogenesis of Mg-deficiency. In the blood, substance-P and calcitonin gene related peptide (CGRP) are elevated during the first week on the diet. During the second week, circulating histamine, PGE2 and TBAR-materials were elevated and red cell glutathione was reduced, all prior to the elevation of the inflammatory cytokines during the third week. When the rats were treated with the substance P-receptor blocker [CP-96,345], the levels of substance P and CGRP remained elevated; however, increases in histamine, PGE2, TBAR-materials, and the decrease in red cell glutathione were inhibited; also, the development of cardiac lesions was inhibited significantly. These data support a central role for neurogenic peptides, especially substance P, in the development of cardiomyopathic lesions during Mg-deficiency.

Antioxidant drug mechanisms: transition metal-binding and vasodilation

In our work evaluating the antioxidant properties of a number of cardiovascular drugs, we have emphasized the importance of lipophilicity as a property contributing to antioxidant potency. Thus, the dihydropyridine calcium channel blockers and propranolol, one of the most lipophilic beta-blockers, were found to exhibit the greatest potency in membrane and cellular models. Both beta-blockers and calcium channel blockers are classified as antihypertensive agents. We found that the specific chemical moieties of various drugs may participate in the antioxidant mechanism of action. While reviewing relevant work from the past literature, it became apparent that some of the chemical moieties of antihypertensive and vasodilator drugs may bind transition metals. Thus, this present review focuses on common properties of transition metal-interaction that are shared, to a greater or lesser degree, by a number of vasoactive drugs and chemical agents. Although this observation has been pursued by other investigators in the past, we submit that the potential relevance to the newer pharmacological agents needs to be explored further. In addition, new information regarding the role of transition metals and free radicals involving vascular cells focuses greater importance on transition metal-interaction as a potential mechanism in vasodilation. This review does not intend to be inclusive of all chemical structures capable of binding transition metals; only those that are clinically relevant will be considered in some detail. Potential mechanisms of metal-chelating actions leading to vasodilation are also discussed.

Magnesium deficiency in vitro enhances free radical-induced intracellular oxidation and cytotoxicity in endothelial cells

The effect of magnesium (Mg)-deficient culture on endothelial cell susceptibility to oxidative stress was examined. Bovine endothelial cells were cultured in either control sufficient (0.8 mM) or deficient (0.4 mM) levels of MgCl2. Oxygen radicals were produced extracellularly by the addition of dihydroxyfumarate and Fe(3+)-ADP. Isolated Mg-deficient endothelial cells produced 2- to 3-fold higher levels of thiobarbituric acid (TBA)-reactive materials when incubated with this free radical system. Additional studies were performed using digitized video microscopy and 2',7'-dichlorofluorescein diacetate (DCFDA) as an intracellular indicator for oxidative events at the single cell level. In response to the exogenous oxidative stress, endothelial cells exhibited a time-dependent increase in fluorescence, suggestive of intracellular lipid peroxidation. The increase in cellular fluorescence began within 1 min of free radical addition; the Mg-deficient cells exhibited a more rapid increase in fluorescence than that of Mg-sufficient cells. In separate experiments, cellular viability was assessed using the Trypan blue exclusion assay. Mg deficiency increased cytotoxicity of the added oxyradicals, but the loss of cellular viability began to occur only after 15 min of free radical exposure, lagging behind the detection of intracellular oxidation products. These results suggest that increased oxidative endothelial cell injury may contribute to vascular injury during Mg deficiency.

Oxygen free radicals and cardiac reperfusion abnormalities

Oxygen free radicals are highly reactive compounds causing peroxidation of lipids and proteins and are thought to play an important role in the pathogenesis of reperfusion abnormalities including myocardial stunning, irreversible injury, and reperfusion arrhythmias. Free radical accumulation has been measured in ischemic and reperfused myocardium directly using techniques such as electron paramagnetic resonance spectroscopy and tissue chemiluminescence and indirectly using biochemical assays of lipid peroxidation products. Potential sources of free radicals during ischemia and reperfusion have been identified in myocytes, vascular endothelium, and leukocytes. In several different experimental models exogenous free radical-generating systems have been shown to produce alterations in cardiac function that resemble the various reperfusion abnormalities described above. Injury to processes involved in regulation of the intracellular Ca2+ concentration may be a common mechanism underlying both free radical-induced and reperfusion abnormalities. Direct effects of free radicals on each of the known Ca(2+)-regulating mechanisms of the cell as well as the contractile proteins and various ionic membrane currents have been described. Free radicals also inhibit critical enzymes in anaerobic and aerobic metabolic pathways, which may limit the metabolic reserve of reperfused myocardium and contribute to intracellular Ca2+ overload. Inhibiting free radical accumulation during myocardial ischemia/reperfusion with free radical scavengers and inhibitors has been demonstrated to reduce the severity of myocardial stunning, irreversible injury, and reperfusion arrhythmias in many, but not all, studies. This evidence strongly implicates free radical accumulation during myocardial ischemia/reperfusion as an important pathophysiological mechanism of reperfusion abnormalities, although many issues remain unresolved.

Erythrocytes from magnesium-deficient hamsters display an enhanced susceptibility to oxidative stress

Previous studies in our laboratory have indicated a role for free radical participation in magnesium deficiency cardiomyopathy. We have demonstrated the ability of various antioxidant drugs and nutrients to protect against magnesium deficiency-induced myocardial injury. In this study, we have examined erythrocytes from normal and magnesium-deficient animals and compared their susceptibility to an in vitro oxidative stress. Syrian male hamsters were placed on either magnesium-deficient or magnesium-supplemented diets. Animals from each group also received vitamin E in doses of 10 and 25 mg as subcutaneous implants. Erythrocytes obtained after 14 days on the diet were exposed to an exogenous hydroxyl (.OH) radical generating system (dihydroxyfumarate not equal to Fe3+ ADP) at 37 degrees C for 20 min. Erythrocyte crenation was observed and quantified by scanning electron microscopy. Lipid peroxidation, hemolysis (%), and intracellular glutathione levels were determined. In addition, serum lipid changes and membrane phospholipids were characterized. Our data demonstrate that erythrocytes from magnesium-deficient animals are more susceptible to free radical injury, supporting our hypothesis that magnesium deficiency reduces the threshold antioxidant capacity.

Antioxidant effects of calcium channel blockers against free radical injury in endothelial cells. Correlation of protection with preservation of glutathione levels

The effects of four calcium channel blockers (nicardipine, nifedipine, verapamil, and diltiazem) on free radical injury in cultured endothelial cells were studied and compared with those of butylated hydroxytoluene. When the cultured cells were exposed to a superoxide and hydroxyl radical generating system for up to 60 minutes, lipid peroxidation occurred, and cellular viability decreased by 60% at 30 minutes. Concomitantly, total cellular glutathione decreased by 40%, whereas total protein thiols changed minimally. Preincubation of the cells with each of the calcium blockers (5 and 20 microM) before free radical addition resulted in various degrees of significant protection against cell death, and losses of glutathione correlated significantly (r = 0.89, p less than 0.001). The order of efficacy was nicardipine greater than nifedipine greater than verapamil greater than diltiazem; butylated hydroxytoluene was about fourfold more potent than nicardipine. Because none of the agents affected the level of hydroxyl radicals generated in the aqueous phase, the data suggest that the protective mechanisms were mediated by their lipid antiperoxidative activities, which also prevented the glutathione decrease caused by inhibition of peroxide generation.

Mechanisms in acute septic cardiomyopathy: evidence from isolated myocytes

Although often not considered, the heart is one of the targets of multiple organ failure in sepsis and septic shock, with myocardial depression being a prominent component of this "acute septic cardiomyopathy". Hypotheses concerning the etiology of this depression are increasingly elucidated on a cellular level, including dysfunction of the beta-adrenoceptor/G protein/adenylate cyclase system, calcium channel blockade by cardiodepressant factor, contractile impairment by activated leucocytes, as well as inhibition of protein synthesis by Pseudomonas exotoxin A. In the search for "mechanisms of myocardial depression in sepsis", isolated cardiomyocytes may play a role as research tools with respect to: a) discrimination between direct and indirect cardiodepressant effects; b) identifying not only the acute, but also chronic toxin- and mediator-induced cardiodepression; c) clarification of the mechanism of action of cardiodepressant bacterial toxins and sepsis mediators; d) establishment of in vitro models of leucocyte-mediated cardiodepression in sepsis.

Free radical scavenging and inhibition of lipid peroxidation by beta-blockers and by agents that interfere with calcium metabolism. A physiologically-significant process?

It has been proposed that beta-blockers and agents affecting Ca2+ metabolism might exert cardioprotective actions because of their ability to act as antioxidants in vivo. The feasibility of this proposal was tested by examining the reaction of a series of such compounds with various oxygen-derived species. None of the compounds tested was sufficiently reactive with superoxide radical, hydrogen peroxide or hypochlorous acid for scavenging of these species to be feasible in vivo at the drug concentrations present in patients given the usual therapeutic doses. All the drugs tested were powerful scavengers of hydroxyl radical except for flunarizine, which stimulated iron ion-dependent hydroxyl radical generation from hydrogen peroxide. However, none of the drugs significantly inhibited production of hydroxyl radicals in this system. Propranolol, verapamil and flunarizine had significant inhibitory effects on the peroxidation of rat liver microsomes in the presence of iron ions and ascorbic acid. All three compounds exerted weaker inhibitory effects on peroxidation of arachidonic acid caused by a mixture of myoglobin and H2O2: pindolol stimulated peroxidation in this system. It is concluded that the ability of beta-blockers and "Ca(2+)-blockers" to inhibit lipid peroxidation varies with the lipid substrate used and the mechanism by which peroxidation is induced. We conclude that suggestions that beta-blockers and "Ca(2+)-blockers" exert antioxidant effects in vivo are not well founded, although there is a possibility that verapamil and propranolol might have some inhibitory effects against peroxidation if they accumulate in membranes to a sufficiently-high concentration in vivo. We could not confirm the reported ability of propranolol to inhibit the enzyme xanthine oxidase.

Propranolol preserves ultrastructure in adult cardiocytes exposed to anoxia/reoxygenation: a morphometric analysis

The protective effect of d,l-propranolol was studied using freshly isolated canine ventricular cardiocytes (1.5 x 10(6)/mL) exposed to 30 min anoxia (95% N2/5% CO2) and 0, 3, 20, and 45 min of reoxygenation (95% O2/5% CO2). In addition to preventing lipid peroxide formation, propranolol maintained cellular viability, and minimized ultrastructural alterations. In the absence of propranolol, the outer mitochondria become swollen and rounded up within the first few minutes of reoxygenation. The perinuclear mitochondrial area increased only slightly. We observed that the cellular injury process proceeded differentially from the exterior to the interior, with a mitochondrial area increase and outer membrane rupture. Sarcolemmal damage was also observed with prevalent blebbing and membrane loss. The Z-lines became wider and more diffuse with reoxygenation. Injury to the nuclear double membrane was observed. Incubation with propranolol showed significant protection during postanoxia reoxygenation. In contrast, the more water soluble beta-blocker atenolol only exhibited slight protection. In addition, d-propranolol (the non beta-blocking isomer) and the antioxidant enzymes, SOD and catalase, showed significant protection. These data support previous findings concerning the antioxidant properties of propranolol which appear to be independent of beta-receptor blockade.