Antioxidant and cytoprotective activities of the calcium channel blocker mibefradil

Exploring the Impact of Prior Beta-Blocker and Calcium Channel Blocker Usage on Clinical Outcomes in Critically Ill Patients With Sepsis: An Observational Study

Background Sepsis is associated with increased Ca++ levels in many cell types that can cause cytotoxicity and cell death through multiple mechanisms. In patients with sepsis, limiting beta-adrenergic stimulation may also be beneficial. The intense adrenergic stimulation of sepsis results in cardiac and extra-cardiac effects. In the intensive care unit (ICU), the question of whether to continue calcium channel blockers (CCBs) and beta-blockers in patients with sepsis who were using these medications before ICU admission is of significant concern. Methodology In this prospective observational study, we have included 114 patients who met the inclusion criteria of being diagnosed as having sepsis, aged 18 to 65 years, and expected to stay in the ICU for more than 72 hours. These patients were divided into three groups: group 1 consisted of patients taking CCBs before admission, group 2 included those taking beta-blockers before admission, and group 3 served as the control group, comprising patients who had not taken either of these medications before admission. Disease severity in the ICU was assessed and documented by the Sequential Organ Failure Assessment (SOFA) score. Clinical outcomes among three groups were compared regarding the need for vasopressor support, serum procalcitonin (PCT), serum lactate, serum quantitative C-reactive protein (qCRP), SOFA score, and 28 days mortality. Parametric data were expressed as mean ± standard deviation. The Kruskal-Wallis test was used to analyze parametric data between the two groups and among three groups. Results Mortality was found lower in group 1 (21.05%) and group 2 (26.31%) than in group 3 (47.36%), and this association was found to be statistically significant (P = 0.033). We also found a significant difference in mortality between groups 1 and 3 (P = 0.015) and no significant difference between groups 2 and 3 (P = 0.057). Mortality was found to be significantly associated with high SOFA scores on days 1, 3, and 7. Conclusions From the aforementioned results, we concluded that the mortality rate in patients with sepsis was improved when they were pretreated with beta-blockers or CCBs before admission to the ICU and that medication should be continued if not contraindicated in the ICU course.

Atrial Cardiomyopathy: Pathophysiology and Clinical Consequences

Around the world there are 33.5 million patients suffering from atrial fibrillation (AF) with an annual increase of 5 million cases. Most AF patients have an established form of an atrial cardiomyopathy. The concept of atrial cardiomyopathy was introduced in 2016. Thus, therapy of underlying diseases and atrial tissue changes appear as a cornerstone of AF therapy. Furthermore, therapy or prevention of atrial endocardial changes has the potential to reduce atrial thrombogenesis and thereby cerebral stroke. The present manuscript will summarize the underlying pathophysiology and remodeling processes observed in the development of an atrial cardiomyopathy, thrombogenesis, and atrial fibrillation. In particular, the impact of oxidative stress, inflammation, diabetes, and obesity will be addressed.

Association Between Prior Calcium Channel Blocker Use and Mortality in Septic Patients: A Meta-Analysis of Cohort Studies

Background: The aim of this study was to comprehensively review the literature and synthesize the evidence concerning the relationship between prior calcium channel blocker (CCB) use and mortality in patients with sepsis. Methods: The Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica database (EMBASE), Cochrane CENTRAL, and Web of Science databases were searched from their inception to April 9, 2020. Cohort studies related to prior calcium channel blocker use in patients with sepsis were analyzed. Pairs of reviewers independently screened the studies, extracted the data, and assessed the risk of bias. The primary outcome of 90-days mortality or secondary outcome of short-term mortality, including 30-days, Intensive Care Unit (ICU), and in-hospital mortality, were analyzed. Heterogeneity among studies was assessed using the I 2 statistic and was considered moderate if I 2 was 50-75% and high if I 2 was ≥75%. Random-effects models were used to calculate the pooled odds ratios (ORs) and 95% confidence intervals (CIs). The quality of the studies was evaluated with the Newcastle-Ottawa Scale (NOS). Sensitivity analyses were performed to examine the robustness of the results. Results: In total, 639 potentially relevant studies were identified, and the full texts of 25 articles were reviewed. Ultimately, five cohort studies involving 280,982 patients were confirmed to have a low risk of bias and were included. Prior CCB use was associated with a significantly lower 90-days mortality in sepsis patients [OR, 0.90 (0.85-0.95); I 2 = 31.9%]. Moreover, prior CCB use was associated with a significantly reduced short-term mortality rate in septic shock patients [OR, 0.61 (0.38-0.97); I 2 = 62.4%] but not in sepsis patients [OR, 0.83 (0.66-1.04); I 2 = 95.4%]. Conclusion: This meta-analysis suggests that prior CCB use is significantly associated with improved 90-days mortality in sepsis patients and short-term mortality in septic shock patients. This study provides preliminary evidence of an association between prior CCB use and mortality in sepsis patients.

Redox control of cardiac remodeling in atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most common arrhythmia in clinical practice and is a potential cause of thromboembolic events. AF induces significant changes in the electrophysiological properties of atrial myocytes and causes alterations in the structure, metabolism, and function of the atrial tissue. The molecular basis for the development of structural atrial remodeling of fibrillating human atria is still not fully understood. However, increased production of reactive oxygen or nitrogen species (ROS/RNS) and the activation of specific redox-sensitive signaling pathways observed both in patients with and animal models of AF are supposed to contribute to development, progression and self-perpetuation of AF.

SCOPE OF REVIEW

The present review summarizes the sources and targets of ROS/RNS in the setting of AF and focuses on key redox-sensitive signaling pathways that are implicated in the pathogenesis of AF and function either to aggravate or protect from disease.

MAJOR CONCLUSIONS

NADPH oxidases and various mitochondrial monooxygenases are major sources of ROS during AF. Besides direct oxidative modification of e.g. ion channels and ion handling proteins that are crucially involved in action potential generation and duration, AF leads to the reversible activation of redox-sensitive signaling pathways mediated by activation of redox-regulated proteins including Nrf2, NF-κB, and CaMKII. Both processes are recognized to contribute to the formation of a substrate for AF and, thus, to increase AF inducibility and duration.

GENERAL SIGNIFICANCE

AF is a prevalent disease and due to the current demographic developments its socio-economic relevance will further increase. Improving our understanding of the role that ROS and redox-related (patho)-mechanisms play in the development and progression of AF may allow the development of a targeted therapy for AF that surpasses the efficacy of previous general anti-oxidative strategies. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Calcium channel blocker nilvadipine, but not diltiazem, inhibits ocular inflammation in endotoxin-induced uveitis

PURPOSE

Calcium channel blockers (CCBs), widely used for hypertensive patients, have recently been shown to inhibit atherosclerosis by their antioxidative action. The aim of the present study was to examine whether the CCBs nilvadipine and diltiazem reduce ocular inflammation in endotoxin-induced uveitis (EIU).

METHODS

EIU was induced in male C57/B6 mice with a single intraperitoneal injection of lipopolysaccharide (LPS). The animals received intraperitoneal injections of either nilvadipine, diltiazem, or vehicle for 5 days before the LPS application. Twenty-four hours after EIU induction, adherent leukocytes to the retinal vasculature were counted with a concanavalin A lectin perfusion-labeling technique. The protein concentration in the aqueous humor was measured to assess blood-ocular barrier breakdown. Retinal levels of intercellular adhesion molecule (ICAM)-1 and monocyte chemotactic protein (MCP)-1 were analyzed by enzyme-linked immunosorbent assay. LPS-stimulated generation of superoxide in murine microvascular endothelial cells was examined with a nitroblue tetrazolium assay.

RESULTS

Compared to vehicle treatment, application of nilvadipine, but not diltiazem, led to significant suppression of EIU-associated retinal leukocyte adhesion, together with anterior-chamber protein leakage, retinal expression of ICAM-1 and MCP-1, and LPS-induced superoxide generation in vitro.

CONCLUSIONS

The CCB nilvadipine exercises an inhibitory effect on the pathogenesis of ocular inflammation through the suppression of inflammation-related molecules.

T-type ca(2+) channel blockers increase smooth muscle progenitor cells and endothelial progenitor cells in bone marrow stromal cells in culture by suppression of cell death

OBJECTIVE

To examine the expression patterns and roles of voltage-dependent Ca2+ channels in bone marrow stromal cells (BMSCs).

MATERIALS AND METHODS

Ca(2+) currents of BMSCs were measured by the whole-cell patch clamp method. The number and percentage of deaths of BMSCs cultured for 14 days with or without Ca(2+) channel blockers were evaluated using a MTT assay and an LDH assay, respectively.

RESULTS

T-type Ca(2+) channel current was recorded in 0, 2, 10, and 4% of BMSCs on days 3, 10, 17, and 24 in culture, respectively. L-type Ca(2+) channel current was first recorded on day 24 in 6% of BMSCs. Addition of the T-type Ca(2+) channel blocker mibefradil but not the L-type Ca(2+) channel blocker nifedipine significantly increased the cell count. Immunocytochemical analysis revealed increases in the counts of smooth muscle progenitor cells (SMPCs) and endothelial progenitor cells (EPCs). Mibefradil but not nifedipine significantly decreased the rate of cell death.

CONCLUSION

T-type Ca(2+) channel blockers increased the numbers of SMPCs and EPCs in cultured BMSCs, partly through suppression of cell death. Thus, T-type Ca(2+) channel blockers may have the potential to provide an increased number of both BMSC-derived SMCs and ECs of potential use in cell and gene therapy.

Mitochondrial dysfunction and redox signaling in atrial tachyarrhythmia

Accumulating evidence links calcium-overload and oxidative stress to atrial remodeling during atrial fibrillation (AF). Furthermore, atrial remodeling appears to increase atrial thrombogeneity, characterized by increased expression of adhesion molecules. The aim of this study was to assess mitochondrial dysfunction and oxidative stress-activated signal transduction (nuclear factor-kappaB [NF-kappa B], lectin-like oxidized low-density lipoprotein receptor [LOX-1], intercellular adhesion molecule-1 [ICAM-1], and hemeoxgenase-1 [HO-1]) in atrial tissue during AF. Ex vivo atrial tissue from patients with and without AF and, additionally, rapid pacing of human atrial tissue slices were used to study mitochondrial structure by electron microscopy and mitochondrial respiration. Furthermore, quantitative reverse transcription polymerase chain reaction (RT-PCR), immunoblot analyses, gel-shift assays, and enzyme-linked immunosorbent assay (ELISA) were applied to measure nuclear amounts of NF-kappa B target gene expression. Using ex vivo atrial tissue samples from patients with AF we demonstrated oxidative stress and impaired mitochondrial structure and respiration, which was accompanied by nuclear accumulation of NF-kappa B and elevated expression levels of the adhesion molecule ICAM-1 and the oxidative stress-induced markers HO-1 and LOX-1. All these changes were reproduced by rapid pacing for 24 hours of human atrial tissue slices. Furthermore, the blockade of calcium inward current with verapamil effectively prevented both the mitochondrial changes and the activation of NF-kappa B signaling and target gene expression. The latter appeared also diminished by the antioxidants apocynin and resveratrol (an inhibitor of NF-kappa B), or the angiotensin II receptor type 1 antagonist, olmesartan. This study demonstrates that calcium inward current via L-type calcium channels contributes to oxidative stress and increased expression of oxidative stress markers and adhesion molecules during cardiac tachyarrhythmia.

Abnormal exhaled ethane concentrations in scleroderma

Scleroderma (systemic sclerosis) is a chronic multisystem autoimmune disease in which oxidative stress is suspected to play a role in the pathophysiology. Therefore, it was postulated that patients with scleroderma would have abnormally high breath ethane concentrations, which is a volatile product of free-radical-mediated lipid peroxidation, compared with a group of controls. There was a significant difference (p<0.05) between the mean exhaled ethane concentration of 5.27 pmol ml(-1) CO(2) (SEM=0.76) in the scleroderma patients (n=36) versus the mean exhaled concentration of 2.72 pmol ml(-1) CO(2) (SEM=0.71) in a group of healthy controls (n=21). Within the scleroderma group, those subjects taking a calcium channel blocker had lower ethane concentrations compared with patients who were not taking these drugs (p=0.05). There was a significant inverse association between lung diffusion capacity for carbon monoxide (per cent of predicted) and ethane concentration (b=-2.8, p=0.026, CI=-5.2 to -0.35). These data support the presence of increased oxidative stress among patients with scleroderma that is detected by measuring breath ethane concentrations.

Mibefradil, a T-type Ca2+ channel blocker, protects against mesenteric ischemia-reperfusion-induced oxidative injury and histologic alterations in intestinal mucosa in rats

The purpose of the present study was to investigate whether mibefradil can reduce oxidative stress and histologic damage in the rat small bowel subjected to mesenteric ischemia and reperfusion injury. Thirty Sprague-Dawley rats weighing between 210 and 220 g were divided into three groups, each containing 10 rats: group 1, sham operation; group 2, untreated ischemia-reperfusion; and group 3, ischemia-reperfusion plus mibefradil treatment group. Intestinal ischemia for 45 min and reperfusion for 60 min were applied. Ileal specimens were obtained to determine the tissue levels of MDA, CAT, SOD, and GSH-Px and histologic changes. In group 2, MDA values were significantly increased compared to those in groups 1 and 3. In addition, SOD, CAT, and GSH-Px values decreased significantly in group 2 compared to groups 1 and 3. The intestinal injury score increased significantly in group 2 and 3 rats compared to group 1 rats. However, this increase was reduced in group 3 rats compared to group 2. Histopathologically, the rats in group 1 had essentially normal testicular architecture. In group 2 rats, the lesions varied between grade 3 and grade 5. In contrast, most of the specimens in the mibefradil-treated group 3 showed grade 1 injury. Mibefradil plays a role in attenuating reperfusion injury of the small intestine by depressing free radical production and mucosal injury score and regulating postischemic intestinal perfusion while restoring intestinal microcirculatory blood flow and encountered histologic injury.

Atorvastatin inhibits angiotensin II-induced T-type Ca2+ channel expression in endothelial cells

Ca2+ channels are involved in the regulation of vascular functions. Angiotensin II is implicated in the development of atherosclerosis and vascular remodeling. In this study, we demonstrated that angiotensin II preferentially increased the expression of alpha1G, a T-type Ca2+ channel subunit, via AT1 receptors in endothelial cells. Angiotensin II-induced expression of alpha1G was inhibited by pretreatment with atorvastatin and the MEK1/2 inhibitor, PD98059. The effect of atorvastatin was reversed by mevalonate and farnesyl pyrophosphate which implicates the activation of the small GTP-binding protein, Ras. Our data indicate that angiotensin II induces alpha1G expression in endothelial cells via AT1 receptors, Ras and MEK. Angiotensin II-induced migration of endothelial cells in a wound healing model was inhibited by incubation with mibefradil, a T-type Ca2+ channel blocker. Our data indicate that angiotensin II induces T-type Ca2+ channels in endothelial cells, which may play a role in the development of vascular disorders.

Rapid pacing of embryoid bodies impairs mitochondrial ATP synthesis by a calcium-dependent mechanism--a model of in vitro differentiated cardiomyocytes to study molecular effects of tachycardia

Tachycardia may cause substantial molecular and ultrastructural alterations in cardiac tissue. The underlying pathophysiology has not been fully explored. The purpose of this study was (I) to validate a three-dimensional in vitro pacing model, (II) to examine the effect of rapid pacing on mitochondrial function in intact cells, and (III) to evaluate the involvement of L-type-channel-mediated calcium influx in alterations of mitochondria in cardiomyocytes during rapid pacing. In vitro differentiated cardiomyocytes from P19 cells that formed embryoid bodies were paced for 24 h with 0.6 and 2.0 Hz. Pacing at 2.0 Hz increased mRNA expression and phosphorylation of ERK1/2 and caused cellular hypertrophy, indicated by increased protein/DNA ratio, and oxidative stress measured as loss of cellular thiols. Rapid pacing additionally provoked structural alterations of mitochondria. All these changes are known to occur in vivo during atrial fibrillation. The structural alterations of mitochondria were accompanied by limitation of ATP production as evidenced by decreased endogenous respiration in combination with decreased ATP levels in intact cells. Inhibition of calcium inward current with verapamil protected against hypertrophic response and oxidative stress. Verapamil ameliorated morphological changes and dysfunction of mitochondria. In conclusion, rapid pacing-dependent changes in calcium inward current via L-type channels mediate both oxidative stress and mitochondrial dysfunction. The in vitro pacing model presented here reflects changes occurring during tachycardia and, thus, allows functional analyses of the signaling pathways involved.

Intermolecular differences of 3-hydroxy-3-methylglutaryl coenzyme a reductase inhibitors contribute to distinct pharmacologic and pleiotropic actions

Statin drugs inhibit 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and share the common mechanism of lowering circulating levels of low-density lipoprotein (LDL) cholesterol, a powerful indicator of risk for cardiovascular disease. Large clinical trials have documented the benefit of hypolipidemic therapy for both primary and secondary prevention of coronary artery disease and stroke. Recent clinical findings, including direct comparator studies, now indicate that certain statins may slow progression of disease at a rate and to an extent that cannot be solely attributed to LDL reduction. The proposed mechanisms for such pleiotropic actions include enhancement of endothelial-dependent nitric oxide bioavailability, anti-inflammatory activity, and inhibition of oxidative stress. To understand the biochemical basis for such differences among statins, this article reviews their physicochemical properties and pharmacology at the molecular level.

Effect of Simvastatin and Antioxidant Vitamins on Atrial Fibrillation Promotion by Atrial-Tachycardia Remodeling in Dogs

Background— There is evidence for a role of oxidant stress and inflammation in atrial fibrillation (AF). Statins have both antioxidant and antiinflammatory properties. We compared the effects of simvastatin with those of antioxidant vitamins on AF promotion by atrial tachycardia in dogs.

Methods and Results— We studied dogs subjected to atrial tachypacing (ATP) at 400 bpm in the absence and presence of treatment with simvastatin, vitamin C, and combined vitamins C and E. Serial closed-chest electrophysiological studies were performed in each dog at baseline and 2, 4, and 7 days after tachypacing onset. Atrioventricular block was performed to control ventricular rate. Mean duration of induced AF was increased from 42±18 to 1079±341 seconds at terminal open-chest study after tachypacing alone ( P <0.01), and atrial effective refractory period (ERP) at a cycle length of 300 ms was decreased from 117±5 to 76±6 ms ( P <0.01). Tachypacing-induced ERP shortening and AF promotion were unaffected by vitamin C or vitamins C and E; however, simvastatin suppressed tachypacing-induced remodeling effects significantly, with AF duration and ERP averaging 41±15 seconds and 103±4 ms, respectively, after tachypacing with simvastatin therapy. Tachypacing downregulated L-type Ca 2+ -channel α-subunit expression (Western blot), an effect that was unaltered by antioxidant vitamins but greatly attenuated by simvastatin.

Conclusions— Simvastatin attenuates AF promotion by atrial tachycardia in dogs, an effect not shared by antioxidant vitamins, and constitutes a potentially interesting new pharmacological approach to preventing the consequences of atrial tachycardia remodeling.

Antioxidant Activity of Nebivolol in the Rat Aorta

The beta-blocker nebivolol is a racemic mixture of D- and L- enantiomers that displays negative inotropic as well as direct vasorelaxant activity. In addition, it has been proposed that nebivolol exerts endothelium-protective effects caused by its antioxidant properties. In the present study we investigated the effect of D-, L-, and d/l-nebivolol on reactive oxygen species (ROS)-induced endothelial damage and compared it with carvedilol and metoprolol. Isolated rat aortic rings were exposed to ROS by electrolysis of the organ bath medium. Before and after electrolysis, endothelial function was measured by preconstricting the vessels with phenylephrine followed by the addition of methacholine. Carvedilol and nebivolol protected against ROS-induced endothelial damage, whereas metoprolol did not. The protective effect of nebivolol proved not to be stereoselective. Furthermore, we attempted to determine whether nebivolol acts a scavenger itself or whether another mechanism is involved. By means of HPLC measurements it was shown that nebivolol concentrations were decreased after exposure to electrolysis-induced ROS, thus indicating that nebivolol is degraded by its reaction with ROS. Functional experiments, in the rat aorta, demonstrated that exposure of nebivolol to ROS also affects its vasodilator activity. In conclusion, the present study demonstrates that nebivolol alleviates ROS-induced impairment of endothelium-dependent vasorelaxation. This protective effect is very likely the result of a direct ROS-scavenging action by the nebivolol molecule itself.

Pharmacological prevention of atrial tachycardia induced atrial remodeling as a potential therapeutic strategy

Atrial fibrillation (AF) is the most common cardiac arrhythmia requiring medical therapy, and present treatment modalities are inadequate. Over the past few years, we have learned a great deal about the phenomenon of electrical remodeling, by which rapid atrial activation leads to changes in atrial electrical properties that promote AF initiation and maintenance. This knowledge opens up the possibility that electrical remodeling may itself be a novel therapeutic target in AF. The present paper reviews what is known about the basic mechanisms of atrial electrical remodeling and then discusses the experimental and clinical evidence that remodeling can be prevented by drug therapy. Despite great potential value, the development of pharmacological interventions to prevent atrial electrical remodeling is still in its infancy.

Pharmacological modulators of voltage-gated calcium channels and their therapeutical application

Calcium channels (CCs) play an important role in the transduction of action potential to the cytosol. An influx of Ca(2+) is essential for muscle contraction, neurotransmitter, and hormonal release. Level of cytosolic Ca(2+) controls activities of many enzymes and regulatory proteins. Voltage-gated calcium channels (VGCCs) serve as sensors for membrane depolarization. Blood pressure reduction is due to relaxation of actomyosine filaments in vascular smooth muscles. Calcium channel blockers (CCBs) are traditionally used for treatment of cardiovascular diseases. Neurotransmitter release from presynaptic neurons is triggered by Ca(2+) influx. Blockers of neuronal CCs may be applied for pain treatment. Overload of neurons by Ca(2+) is toxic. CCBs may be applied for prevention of some neurodegenerative disorders.

Effects of the calcium channel blocker amlodipine on serum and aortic cholesterol, lipid peroxidation, antioxidant status and aortic histology in cholesterol-fed rabbits

Reactive oxygen metabolites and oxidized fatty acids are proinflammatory and are involved in the pathophysiology of atherosclerosis. Amlodipine, a unique third-generation dihydropyridine-type calcium channel blocker, seems to exert atheroprotective effects through its antioxidant properties related to its chemical structure and independent of its calcium channel-blocking effect. In this study, the interactions of amlodipine with major cellular antioxidants were investigated in order to elucidate the mechanisms underlying its atheroprotective effects. New Zealand white male rabbits were fed regular chow (group 1), chow with 1% cholesterol (group 2), regular chow plus 5 mg/kg/day amlodipine per os (group 3) and 1% cholesterol plus amlodipine (group 4) for 8 weeks. Total cholesterol, malondialdehyde (MDA) and vitamin E concentrations and catalase and superoxide dismutase (SOD) activities were determined in blood drawn before and after the experimental period. Aortic tissue was examined for atherosclerotic changes and aortic total cholesterol, MDA, catalase and SOD were determined. At the end of the 8-week treatment period, serum total cholesterol and plasma MDA were elevated in groups 2 and 4. In group 2, serum vitamin E and plasma SOD diminished (p < 0.05) and catalase increased (p < 0.05). In group 4, SOD activity increased at the end of treatment. MDA levels were lower and plasma SOD activities were higher in group 4 than in group 2. Aortic tissue investigations revealed higher total cholesterol and MDA concentrations and catalase activities in group 2 than in group 4, and the highest tissue SOD activity was recorded in group 4 (p < 0.05 for all comparisons). Morphological examination of aortic tissues exhibited endothelial disarrangement and lipid deposition in group 2. Histopathological alterations related to atherogenesis were less in group 4 than in group 2. Amlodipine seems to exert atheroprotective effects by reducing aortic cholesterol accumulation and blood and aortic lipid peroxidation, enhancing SOD activity both in blood and aortic tissue and suppressing the consumption of vitamin E. On the other hand, the suppression of catalase activity in blood and the aorta interferes with the drug's well-known antioxidant effects.

Protective effect of T-type calcium channel blocker in histamine-induced paw inflammation in rat

The aim of this paper was to investigate the protective effect of the T-type calcium channel blocker in a model of acute local inflammation (histamine-induced). The intraplantar injection of histamine elicited an inflammatory response that was characterized by a time-dependent increase in paw oedema and neutrophil infiltration in paw tissue. The maximal increase in paw volume was observed at 90 min after histamine administration (maximal paw volume: 0.97 +/- 0.07). In addition, polymorphonuclear leucocyte (PNL) number was markedly increased in the histamine-treated paw tissue (144 +/- 25.56). However, histamine-induced paw oedema was significantly reduced in a dose-dependent manner by treatment with mibefradil (given at 10, 25, 50, and 100 mg x kg(-1)) at 30, 60, 90, 120, 150, 180 min after injection of histamine. Mibefradil treatment also caused a significant reduction of the polymorphonuclear leucocyte number in the paw tissue. Our findings support the view that mibefradil exerts antiinflammatory effects.

Ascorbate attenuates atrial pacing-induced peroxynitrite formation and electrical remodeling and decreases the incidence of postoperative atrial fibrillation

Atrial fibrillation (AF), the most common chronic arrhythmia, increases the risk of stroke and is an independent predictor of mortality. Available pharmacological treatments have limited efficacy. Once initiated, AF tends to self-perpetuate, owing in part to electrophysiological remodeling in the atria; however, the fundamental mechanisms underlying this process are still unclear. We have recently demonstrated that chronic human AF is associated with increased atrial oxidative stress and peroxynitrite formation; we have now tested the hypothesis that these events participate in both pacing-induced atrial electrophysiological remodeling and in the occurrence of AF following cardiac surgery. In chronically instrumented dogs, we found that rapid (400 min(-1)) atrial pacing was associated with attenuation of the atrial effective refractory period (ERP). Treatment with ascorbate, an antioxidant and peroxynitrite decomposition catalyst, did not directly modify the ERP, but attenuated the pacing-induced atrial ERP shortening following 24 to 48 hours of pacing. Biochemical studies revealed that pacing was associated with decreased tissue ascorbate levels and increased protein nitration (a biomarker of peroxynitrite formation). Oral ascorbate supplementation attenuated both of these changes. To evaluate the clinical significance of these observations, supplemental ascorbate was given to 43 patients before, and for 5 days following, cardiac bypass graft surgery. Patients receiving ascorbate had a 16.3% incidence of postoperative AF, compared with 34.9% in control subjects. In combination, these studies suggest that oxidative stress underlies early atrial electrophysiological remodeling and offer novel insight into the etiology and potential treatment of an enigmatic and difficult to control arrhythmia. The full text of this article is available at http://www.circresaha.org.

Antioxidant activity of the monoamine oxidase B inhibitor lazabemide

Free radical-induced damage to lipid and protein constituents of neuronal membranes contributes to the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD). The development of an effective inhibitor of oxidative stress represents an important goal for the treatment of AD. In this study, the intrinsic antioxidant activity of lazabemide, a potent and reversible inhibitor of monoamine oxidase B (MAO-B), was tested in a membrane-based model of oxidative stress. Under physiologic-like conditions, lazabemide inhibited lipid peroxidation in a highly concentration-dependent manner. At low, pharmacologic levels of lazabemide (100.0 nM), there was a significant (P < 0.001) and catalytic reduction in lipid peroxide formation, as compared with control samples. The antioxidant activity of lazabemide was significantly more effective than that of either vitamin E or the MAO-B inhibitor, selegiline. The ability of lazabemide to inhibit oxidative damage is attributed to physico-chemical interactions with the membrane lipid bilayer, as determined by small angle x-ray diffraction methods. By partitioning into the membrane hydrocarbon core, lazabemide can inhibit the propagation of free radicals by electron-donating and resonance-stabilization mechanisms. These findings indicate that lazabemide is a potent and concentration-dependent inhibitor of membrane oxy-radical damage as a result of inhibiting membrane lipid peroxidation, independent of MAO-B interactions.

Inhibition of LDL oxidation and oxidized LDL-induced cytotoxicity by dihydropyridine calcium antagonists

PURPOSE

The antioxidant activity of dihydropyridine calcium channel antagonists was evaluated based on LDL oxidation kinetics, oxidative cell injury associated with reactive species generation, and increases in free intracellular calcium (Ca2+) levels. Interactions with ascorbic acid were studied under conditions representative of LDL oxidation in plasma and tissue.

METHODS

Analysis of antioxidant activity utilized measurements of one-electron oxidation potentials and scavenging of peroxy radical-mediated oxidation. LDL antioxidant potency was determined spectrophotometrically using copper-mediated oxidation kinetics in the absence and presence of 100 microM ascorbic acid. Prevention of oxidant-induced endothelial cell injury was determined from the formation of reactive oxygen species generation and increases in intracellular free calcium concentrations following addition of oxidized LDL or linoleic acid hydroperoxide.

RESULTS

Felodipine and amlodipine effectively inhibit peroxyl radical-mediated oxidation in lipoproteins and cells that is markedly enhanced in the presence of ascorbic acid. In the presence of ascorbic acid, inhibition of LDL oxidation is over four times greater than in LDL treated without antioxidants, and oxidized LDL and linoleic acid hydroperoxide-induced reactive oxygen species formation is effectively suppressed in cells. Inhibition of intracellular calcium increases was achieved using nM concentrations of felodipine or amlodipine.

CONCLUSIONS

The additive effect for ascorbic acid and the calcium channel antagonist is postulated to involve a combination of peroxide-degrading and peroxyl radical scavenging reactions, demonstrating the importance of lipid peroxides during LDL oxidation and oxidized LDL-induced cytotoxicity. Cytoprotection is associated with inhibition of oxidant-induced increases in intracellular free calcium. Both the cytoprotective and LDL antioxidant activity for these compounds is manifested at concentrations approaching the therapeutic levels found in plasma.

Inadequate ischaemia-selectivity limits the antiarrhythmic efficacy of mibefradil during regional ischaemia and reperfusion in the rat isolated perfused heart

1. Mibefradil was compared with (+/-)-verapamil for effects on ischaemia- and reperfusion-induced ventricular fibrillation (VF), and the role of ischaemia-selective L-channel block was examined. Langendorff perfused rat hearts (n=12/group) were used. 2. Neither drug at up to 100 nM reduced the incidence of VF during 30 min regional ischaemia. 300 and 600 nM (+/-)-verapamil abolished VF (P<0. 05); mibefradil was effective only at 600 nM (P<0.05). Reperfusion-induced VF incidence was reduced only by 600 nM (+/-)-verapamil (P<0.05). Both drugs at >/=100 nM increased coronary flow (P<0.05) with a similar potency and maximum effectiveness. 3. In separate hearts perfused with Krebs' solution containing 3 mM K+ (the same as that used for arrhythmia studies) neither drug at up to 600 nM affected ventricular contractility. With K+ raised to 6 mM, (+/-)-verapamil >/=30 nM reduced developed pressure (P<0.05); mibefradil did so only at 600 nM (P<0.05). With K+ raised to 10 mM the effects of (+/-)-verapamil were further increased (P<0.05) and mibefradil became active at >/=100 nM (P<0.05). Likewise both drugs impaired diastolic relaxation, with raised K+ exacerbating the effects and (+/-)-verapamil being more potent and its effects more greatly exacerbated by K+. In contrast, when K+ was normal (3 mM), coronary flow was increased by each drug at >/=30 nM (P<0.05) indicating a marked vascular : myocardial selectivity. 4. In conclusion, mibefradil differed from (+/-)-verapamil in its myocardial effects only in terms of its lower potency. As mibefradil is the more potent T-channel blocker, the T-channel is unlikely to represent the molecular target for these effects. The K+ elevations that occur in the ischaemic milieu determine the ability of both drugs to block myocardial L-channels; this is sufficient to account for the drugs' actions on VF. Neither drug possesses sufficient selectivity for ischaemic myocardium versus blood vessels to permit efficacy (VF suppression without marked vasodilatation) and so inappropriate hypotension is likely to preclude the safe use of mibefradil (or similar analogue) in VF suppression, and explains the lack of clinical effectiveness of (+/-)-verapamil.

Systemic and ocular vascular roles of the antiglaucoma agents beta-adrenergic antagonists and Ca2+ entry blockers

This review addresses whether the antiglaucoma agents beta-adrenergic antagonists and Ca2+ entry blockers cause vasoactive effects in the retinal and other ocular vasculatures, as they do in other tissues. The potent vasodilating effects of Ca2+ entry blockers on ocular vessels have recently been demonstrated in in vivo and in vitro studies, implying that the maintenance of ocular vascular tone relies almost exclusively on extracellular Ca2+. Ca2+ entry blockers may potentially play a role in relaxing the retinal, long posterior ciliary, and ophthalmociliary arteries to improve the ocular circulation in vascular diseases in which there is considerable vascular tone present. The beta-adrenergic antagonists are discussed with reference to their antihypertensive role, their effect on other vascular beds, and finally what is known of their effect in the ocular vasculature. The emerging evidence that particular selective beta-adrenergic antagonists, such as betaxolol, are also potent Ca2+ channel entry blockers in other vascular beds is presented. Betaxolol has been shown to induce vasodilatation in the retinal and other ocular vascular beds, although studies have shown that beta1-adrenergic receptors are sparse in these vascular beds. This implies that an alternative mechanism must be responsible for betaxolol-induced vasodilatation. Evidence is presented that betaxolol vasodilates via its potent Ca2+ channel entry blocking properties, and its potency and ability to vasodilate are compared with those of nimodipine and timolol, as well as with those of other Ca2+ channel entry blockers. Important areas for future research in this area are discussed.