Membrane stabilizing, anti-oxidative interactions of propranolol and dexpropranolol with neutrophils

The role of beta-adrenoreceptors in postoperative ileus in rats

The aim of the research was to evaluate the influence of antagonists of specific beta-adrenergic receptor subtypes on bowel motility following abdominal surgery in rat model of postoperative ileus. Bowel motility was measured by the intestinal transit of Evans blue introduced via orogastric tube after surgical procedures of skin incision, laparotomy and laparotomy with gut manipulation. Male rats were given individual adrenergic receptor subtypes antagonists intraperitoneally, and the influence of administered agents on intestinal transit of Evans blue was then evaluated. No statistically significant differences in the length of intestine in tested rats were observed. Propranolol administered prior to surgical procedure has shown protective effect on Evans blue migration in rats undergoing laparotomy and gut manipulation. Intestinal dye transit for propranolol doses of 10, 30 and 45 mg/kg was 18.00 ± 1.88c m, 23.75 ± 1.71 cm and 22.5 ± 2.43 cm, respectively, and for last two doses, statistically significant increase of dye passage was noted, compared to Evans blue transit of 11.00 ± 2.43 cm in the control group. No acceleration of dye migration was seen following administration of beta1-, beta2- and beta3-selective adrenergic receptor antagonist metoprolol, ICI 118.551 and SR58894A, respectively. Our research confirmed that propranolol at high doses, as seen by other researchers, improved bowel motility in early phase of postoperative ileus. That slight acceleration of intestinal dye transit after surgery with gut manipulation is rather connected with membrane-stabilizing action, than the receptor blocking effect, as this effect was not observed after the application of selective antagonists of respective subtypes of beta-adrenergic receptor.

The Activation of Endothelial Cells Relies on a Ferroptosis-Like Mechanism: Novel Perspectives in Management of Angiogenesis and Cancer Therapy

The activation of endothelial cells (ECs) is a crucial step on the road map of tumor angiogenesis and expanding evidence indicates that a pro-oxidant tumor microenvironment, conditioned by cancer metabolic rewiring, is a relevant controller of this process. Herein, we investigated the contribution of oxidative stress-induced ferroptosis to ECs activation. Moreover, we also addressed the anti-angiogenic effect of Propranolol. We observed that a ferroptosis-like mechanism, induced by xCT inhibition with Erastin, at a non-lethal level, promoted features of ECs activation, such as proliferation, migration and vessel-like structures formation, concomitantly with the depletion of reduced glutathione (GSH) and increased levels of oxidative stress and lipid peroxides. Additionally, this ferroptosis-like mechanism promoted vascular endothelial cadherin (VE-cadherin) junctional gaps and potentiated cancer cell adhesion to ECs and transendothelial migration. Propranolol was able to revert Erastin-dependent activation of ECs and increased levels of hydrogen sulfide (H₂S) underlie the mechanism of action of Propranolol. Furthermore, we tested a dual-effect therapy by promoting ECs stability with Propranolol and boosting oxidative stress to induce cancer cell death with a nanoformulation comprising selenium-containing chrysin (SeChry) encapsulated in a fourth generation polyurea dendrimer (SeChry@PURE_G4). Our data showed that novel developments in cancer treatment may rely on multi-targeting strategies focusing on nanoformulations for a safer induction of cancer cell death, taking advantage of tumor vasculature stabilization.

Propranolol Is an Effective Topical and Systemic Treatment Option for Experimental Epidermolysis Bullosa Acquisita

Propranolol is an ADRB2 blocker that regulates heart muscle contractions, smooth muscle relaxation, and glycogenolysis. In addition, an increasing number of applications in dermatology have been described, most prominently, the use as a first-line treatment for infantile hemangiomas. We here show that propranolol enhances IL-8-induced neutrophil chemotaxis and reduces the release of ROS after immune complex stimulation. To obtain further molecular insights into the modulatory effects of propranolol in activated neutrophils, we performed RNA sequencing of immune complex-stimulated neutrophils in the absence and presence of the drug. We identified the transcriptomic signature of propranolol and demonstrated an ADR2-independent immunomodulatory effect. To determine if the anti-inflammatory transcriptomic signature of propranolol also translates into clinical effects, we next evaluated the impact of propranolol in a prototypical neutrophil-dependent skin disease, specifically, antibody transfer-induced epidermolysis bullosa acquisita in mice. To validate the identified propranolol gene signature obtained in human neutrophils, we analyzed a selection of genes by RT-PCR in mouse epidermolysis bullosa acquisita skin and confirmed TNF, among others, to be differentially regulated by propranolol treatment. Our data clearly indicate that, based on its molecular impact on immune complex-activated neutrophils, propranolol is a potential treatment option for neutrophil-mediated inflammatory skin diseases.

Effect of β-Adrenergic Antagonists on In-Hospital Mortality after Ischemic Stroke

BACKGROUND

Ischemic stroke accounts for 85%-90% of all strokes and currently has very limited therapeutic options. Recent studies of β-adrenergic antagonists suggest they may have neuroprotective effects that lead to improved functional outcomes in rodent models of ischemic stroke; however, there are limited data in patients. We aimed to determine whether there was an improvement in mortality rates among patients who were taking β-blockers during the acute phase of their ischemic stroke.

METHODS

A retrospective analysis of a prospectively collected database of ischemic stroke patients was performed. Patients who were on β-adrenergic antagonists both at home and during the first 3 days of hospitalization were compared with patients who were not on β-adrenergic antagonists to determine the association with patient mortality rates.

RESULTS

The study included a patient population of 2804 patients. In univariate analysis, use of β-adrenergic antagonists was associated with older age, atrial fibrillation, hypertension, and more-severe initial stroke presentation. Despite this, multivariable analysis revealed a reduction in in-hospital mortality among patients who were treated with β-adrenergic antagonists (odds ratio, .657; 95% confidence interval, .655-.658).

CONCLUSIONS

The continuation of home β-adrenergic antagonist medication during the first 3 days of hospitalization after an ischemic stroke is associated with a decrease in patient mortality. This supports the work done in rodent models suggesting neuroprotective effects of β-blockers after ischemic stroke.

Beta-blockers in septic shock: a review

In septic shock, high adrenergic stress is associated with cardiovascular and systemic adverse effects, which can negatively affect the results. Beta-adrenergic receptor block has been shown to be effective in controlling the disproportionate increase in heart rate, maintaining a favorable hemodynamic profile and apparently improving the efficiency of the cardiovascular system in order to maintain tissue perfusion. They have also been shown to modulate favorably catecholamine-induced immunosuppression and to decrease insulin resistance, protein catabolism, and proinflammatory cytokine expression associated with cardiovascular dysfunction. Selective beta-1 blockers appear to provide better results than non-selective blockers, even suggesting a positive impact on mortality. Future clinical trials are still needed to confirm these findings and define the scope of their benefits.

Pre-stroke use of beta-blockers does not affect ischaemic stroke severity and outcome

BACKGROUND AND PURPOSE

It is unclear whether pre-stroke beta-blockers use may influence stroke outcome. This study evaluates the independent effect of pre-stroke use of beta-blockers on ischaemic stroke severity and 3 months functional outcome.

METHODS

Pre-stroke use of beta-blockers was investigated in 1375 ischaemic stroke patients who had been included in two placebo-controlled trials with lubeluzole. Stroke severity was assessed by either the National Institute of Health Stroke Scale (NIHSS) or the European Stroke Scale (ESS). A modified Rankin scale (mRS) score of >3 at 3 months was used as measure for the poor functional outcome.

RESULTS

Two hundred and sixty four patients were on beta-blockers prior to stroke onset, and 105 patients continued treatment after their stroke. Pretreatment with beta-blockers did not influence baseline stroke severity. There was no difference in stroke severity between nonusers and those on either a selective beta(1)-blocker or a non-selective beta-blocker. The likelihood of a poor outcome at 3 months was not influenced by pre-stroke beta-blocker use or beta-blocker use before and continued after stroke onset.

CONCLUSIONS

  Pre-stroke use of beta-blockers does not appear to influence stroke severity and functional outcome at 3 months.

Pharmacology of benzydamine

Benzydamine is a topical anti-inflammatory drug which is widely available and used topically for the treatment of the mouth. It is also used as a gel for application to inflamed joints. It has physicochemical properties and pharmacological activities which differ markedly from those of the aspirin-line non-steroidal anti-inflammatory drugs. Benzydamine is a weak base unlike the aspirin-like drugs which are acids or metabolized to acids. A major contrast with the aspirin-like drugs is that benzydamine is a weak inhibitor of the synthesis of prostaglandins but it has several properties which may contribute to its anti-inflammatory activity. These properties include inhibition of the synthesis of the inflammatory cytokine, tumour necrosis factor-alpha (EC(50), 25 micromol/L). Inhibition of the oxidative burst of neutrophils occurs under some conditions at concentrations of 30 to 100 micromol/L, concentrations which may be produced within oral tissues after local application. A further activity of benzydamine is a general activity known as membrane stabilization which is demonstrated by several actions including inhibition of granule release from neutrophils at concentrations ranging from 3 to 30 micromol/L and stabilization of lysosomes. Lack of knowledge of the tissue concentrations of benzydamine limit the correlation between pharmacological activities in vitro and in vivo. The concentration of benzydamine in the mouthwash is 4 mmol/L but the concentrations in oral tissues have not been studied adequately. Limited data in the rat indicates that concentrations of benzydamine in oral tissues are approximately 100 micromol/L.

Inflammatory factors that contribute to upregulation of ERG and cardiac arrhythmias are suppressed by CPU86017, a class III antiarrhythmic agent

The aim of this study was to verify whether exaggerated arrhythmogenesis is attributed to inflammatory factors actively involving an excess of reactive oxygen species (ROS), transforming growth factor (TGF)-beta and endothelin (ET). We hypothesized that CPU86017, derived from berberine, which possesses multi-channel blocking activity, could suppress inflammatory factors, resulting in inhibition of over-expression of ether-a-go-go (ERG) and an augmented incidence of ventricular fibrillation (VF) in ischaemia/reperfusion (I/R). Rats with cardiomyopathy (CMP) induced by thyroxine (0.2 mg(-1)kg(-1) s.c. daily for 10 days) were treated with propranolol (10 mgkg(-1) p.o.) or CPU86017 (80 mgkg(-1) p.o.) on days 6-10. On the 11th day, arrhythmogenesis of the CMP was evaluated by I/R. In the CMP control group, an increase in VF incidence was found with the I/R episode, accompanied by increased ROS, which manifested as an increased level of malondialdehyde and decreased activities of SOD, glutathione peroxidase and catalase in the myocardium. Levels of inducible nitric oxide synthase and TGF-beta mRNA were increased in association with upregulation of preproET-1 and ET-converting enzyme. We found increased levels of ERG, which correlated well with arrhythmogenesis. Treatment with CPU86017 or propranolol reversed these changes. These experiments verified our hypothesis that the inflammatory factors ROS, iNOS, TGF-beta and ET-1 are actively involved in upregulation of ERG and arrhythmogenesis. CPU86017 and propranolol reduced VF by suppressing these inflammatory factors in the myocardium.

Nebivolol: pharmacologic profile of an ultraselective, vasodilatory beta1-blocker

Beta-blockers are well-established therapeutic agents in the treatment of hypertension and cardiovascular disease. However, these agents are highly heterogeneous. Beta-blockers differ in their ancillary pharmacologic properties, which are clinically important. Nebivolol is a highly selective beta(1)-adrenergic receptor blocker that induces vasodilation through stimulation of the endothelial nitric oxide/L-arginine pathway. As a racemic mixture of d- and l-enantiomers, nebivolol is highly lipophilic and rapidly absorbed. Nebivolol undergoes extensive hepatic metabolism through the cytochrome P450 2D6 (CYP2D6) system. As a result of genetic polymorphisms, CYP2D6 has variable activity, manifested by extensive and poor metabolizers of nebivolol. Time to maximum concentration is 0.5 to 2 hours, and half-life is 11 hours in extensive metabolizers; these values are about 3 times longer in poor metabolizers. Urinary and fecal excretion of unchanged nebivolol is less than 0.5% of the dose. Nebivolol has a unique hemodynamic profile of reduced systemic vascular resistance and increased left ventricular function. These properties are attributed to its vasodilating action and contrast with the hemodynamic effects of conventional beta-blockers. Nebivolol is thus a novel beta-blocker with several important pharmacologic properties that distinguish it from traditional beta-blockers. These unique properties may confer clinical benefits beyond simple blood pressure lowering.

Screening of drug metabolism by CE

The use of CE for rapid assessment of metabolic stability of drugs with cytochrome P450 (CYP) enzymes, based on relative rates of reduced nicotinamide adenine dinucleotide phosphate (NADPH) consumption and nicotinamide adenine dinucleotide phosphate (NADP) production, was investigated. The separation conditions were as follows: capillary, 80.5 cm (75 microm id, 72 cm effective length for UV detection, 58 cm effective length for fluorescence detection); 25 mM sodium phosphate buffer (pH 8.8); 28 kV (80 microA) applied voltage; UV, 260 nm; fluorescence detection, excitation wavelength, 310 nm, emission wavelength, 418 nm; capillary temperature, 25 degrees C. For UV detection, the incubation conditions were as follows: CYP3A4: 20 pmol/mL; NADPH: 1 mM; EDTA: 1 mM; concentration of the substrate: 5-10 times its reported literature K(m) value; temperature: 37 degrees C; incubation time: 15 min. For fluorescence detection, the concentrations were reduced to CYP3A4: 4 pmol/mL, NADPH: 20 microM, EDTA: 20 microM and substrate: 10 microM. Blank incubations were performed in the absence of substrate. Compared with the blank, significant differences were found for the consumption of NADPH and the production of NADP. The development of this assay system allows rapid assessment of metabolic stability relative to standard compounds, as well as potential identification of the major CYP involved in the metabolism. It would reduce the backlog of compounds that require LC/MS analysis, and thereby expedite the process of metabolic stability screening.

Antioxidant activity of β-blockers: An effect mediated by scavenging reactive oxygen and nitrogen species?

The therapeutic effects of beta-blockers are normally explained by their capacity to block the beta-adrenoceptors, however, some of the beneficial cardiovascular effects shown by this group of compounds have already been associated with the antioxidant properties that some of them seem to possess. The beta-blockers atenolol, labetalol, metoprolol, pindolol, propranolol, sotalol, timolol, and carvedilol were tested for their putative scavenging activity for ROS (O(2)(-), H(2)O(2), HO(.), HOCl, and ROO(.)) and RNS ((.)NO and ONOO(-)). Some of the studied compounds are effective ROS and/or RNS scavengers, these effects being possibly useful in preventing oxidative damage verified in hypertension as well as in other cardiovascular diseases that frequently emerge in association with oxidative stress.

Potent Antioxidant Properties of 4-Hydroxyl-propranolol

The antioxidant properties of 4-HO-propranolol (4HOP), a major metabolite of propranolol, were studied and compared with that of propranolol and vitamin E (Trolox). When isolated hepatic microsomal membranes were peroxidized by an iron-catalyzed.OH-generating system [dihydroxyfumarate +Fe (III)], 4HOP potently and concentration-dependently inhibited lipid peroxidation; the IC50 value was 1.1 microM, whereas those for Trolox and propranolol were 4.3 and 168 microM, respectively. When isolated human low-density lipoprotein (LDL) was oxidized by 7.5 microM Cu(II) for 9 h, 4HOP at 3 microM delayed the lag phase significantly by 108 min, which was comparable with that of probucol (98-min delay) but was far greater than that provided by propranolol (6 min) or Trolox (47 min). At 1 microM 4HOP, the delay was 45 min. When confluent cultured bovine aortic endothelial cells were exposed to the Fe-catalyzed oxy-radical system, acute loss of glutathione occurred (55% decrease in 50 min). Pretreatment of the cells with 0.067 to 6.7 microM 4HOP for 30 min provided increasing degrees of protection against the glutathione loss; the EC50 value was 1.2 microM, whereas those for Trolox and propranolol were 7.9 and 49 microM, respectively. The loss of cell survival due to the radical stress was also effectively preserved by 4HOP. In separate experiments, when the endothelial glutathione was oxidatively depleted by a peroxynitrite-generating system (3-morpholinosydnonimine), 4HOP also provided potent protective activities. In conclusion, 4HOP is 4- to 8-fold more potent than vitamin E and >100-fold more active than propranolol as a "chain-breaking" antiperoxidatant against membrane and LDL oxidation and can provide superior endothelial cytoprotective efficacy against oxygen- or nitrogen-derived oxidant-mediated cell injury. Being a major metabolite in human and with its plasma level approaching that of propranolol, 4-HO-propranolol may contribute, in part, to the cardiovascular therapeutic benefits of propranolol.

Protective effects of quinaprilat and trandolaprilat, active metabolites of quinapril and trandolapril, on hemolysis induced by lysophosphatidylcholine in human erythrocytes

We examined the effects of the angiotensin converting enzyme (ACE) inhibitors captopril, enalaprilat, quinapril, and trandolapril, and their active metabolites quinaprilat and trandolaprilat, on hemolysis induced by lysophosphatidylcholine (LPC) in human erythrocytes. LPC induced hemolysis at the concentrations above the critical micelle concentration (4 microM). Propranolol, used as a reference drug, attenuated the 50% hemolysis induced by 6 microM LPC at concentrations ranging from 100 nM to 100 microM. Similarly, quinaprilat (10 microM) and trandolaprilat (10, 100 microM) significantly attenuated the LPC-induced hemolysis, but other ACE inhibitors did not. Since propranolol possesses a membrane stabilizing action correlated with high lipophilicity, it appears that the high lipophilicity of quinaprilat or trandolaprilat is responsible for the protection from the damage induced by LPC. However, quinapril and trandolapril were not effective, although both drugs have higher lipophilicity than quinaprilat and trandolaprilat. Hence, it is suggested that the high lipophilicity alone may not contribute to the protective effects of ACE inhibitors against LPC-induced hemolysis. None of ACE inhibitors attenuated the hypotonic hemolysis (60 mM NaCl), although propranolol did. Furthermore, neither propranolol (100 microM) nor quinaprilat (50 microM) and trandolaprilat (50 microM) affected LPC micelle formation, suggesting that these drugs do not directly bind to LPC. We therefore believe that the protective effects of quinaprilat and trandolaprilat on the LPC-induced hemolysis may be related physicochemically to their highly lipophilic and ACE inhibitory structures, which probably maintain erythrocyte membrane integrity by a mechanism other than ACE inhibition, prevention of LPC micelle formation or protection against osmotic imbalance.

Neuroprotection is associated with beta-adrenergic receptor antagonists during cardiac surgery: evidence from 2,575 patients

OBJECTIVE

To determine the impact of perioperative beta-adrenergic receptor (betaAR) antagonist administration on neurologic complications.

DESIGN

Observational database analysis.

SETTING

A clinical investigation at a single tertiary academic medical center.

PARTICIPANTS

Elective coronary artery bypass graft surgical patients operated on in the period 1994-1996.

INTERVENTIONS

Patients were divided into 2 groups: (1) patients given betaAR antagonist-blocking drugs in the perioperative period, including during operation, and (2) patients not given betaAR antagonists.

MEASUREMENTS AND MAIN RESULTS

betaAR antagonist use in 2,575 consecutive patients undergoing coronary artery bypass graft surgery (1994-1996) was determined using the Cardiovascular Database and Anesthesia Information System Database. Outcome variables were postoperative stroke, coma, and transient ischemic attack. Of patients, 113 (4.4%) had postoperative neurologic complications, including stroke (n = 44), coma (n = 12), and transient ischemic attack (n = 3). Of patients, 2,296 (89%) received perioperative betaAR antagonist therapy, and 279 (11%) did not. Adverse neurologic events occurred in 3.9% (n = 90) of patients who received perioperative betaAR antagonists and 8.2% (n = 23) of patients who did not receive betaAR antagonists (odds ratio, 0.45; 95% confidence interval, 0.28 to 0.73; p = 0.003, unadjusted.) Severe neurologic outcomes (stroke and coma) occurred in 1.9% (n = 44) of patients who received betaAR antagonists and 4.3% (n = 12) of patients who did not receive betaAR antagonists (odds ratio, 0.43; 95% confidence interval, 0.23 to 0.83; p = 0.016).

CONCLUSION

Use of beta-adrenergic antagonists was associated with a substantial reduction in the incidence of postoperative neurologic complications. A prospective randomized trial is needed to verify this potentially important neuroprotective strategy in cardiac surgery.

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.

A comparison of atenolol, labetalol, esmolol, and landiolol for altering human neutrophil functions

IMPLICATIONS

Neutrophils play a pivotal role in the antibacterial host defense system. Atenolol, labetalol, esmolol, and landiolol at clinically relevant concentrations failed to change neutrophil functions. Our findings indicate that we may be able to use these beta-antagonists without great caution in clinical settings.

Modulation by propranolol of the uptake of ethidium bromide by rat submandibular acinar cells exposed to a P2X(7) agonist or to maitotoxin

We have compared the formation of pores in rat submandibular acinar cells in response to 2',3'-O-(4-benzoylbenzoyl) adenosine 5'-triphosphate (Bz-ATP) and maitotoxin. Bz-ATP (100 microM) permeabilized the cells to ethidium bromide. The uptake of ethidium increased to 29+/-1% of maximal uptake in 10 min. DL-Propranolol (300 microM) inhibited the Bz-ATP-induced uptake of ethidium bromide by 40% without affecting the P2X(7)-gated cation channel. The inhibitory effect of DL-propranolol on the formation of pores by Bz-ATP was reproduced by D-propranolol, an optical isomer with very poor beta-blocking activity. Tenidap, an antiinflammatory drug, enhanced the permeabilization in response to Bz-ATP. Propanolol inhibited the response to tenidap plus Bz-ATP. The effect of propranolol was reproduced by labetolol, a beta-adrenergic antagonist with membrane-stabilizing properties, but not by atenolol, which blocks beta-adrenergic receptors but has no effect on the stability of the membrane. In the presence of extracellular calcium, maitotoxin also increased the uptake of ethidium bromide. Tenidap had no effect on this response, which was delayed by propranolol. In conclusion, we have shown that propranolol, in a range of 10-300 microM, inhibits the pore-forming activity of the P2X(7) receptor without affecting the opening of the cation channel coupled to this receptor. This inhibition is not related to its beta-adrenergic blocking activity but rather to its membrane-stabilizing properties. Propranolol also delays the uptake of ethidium bromide in response to maitotoxin. This is in agreement with the current view that P2X(7) agonists and maitotoxin share a common pore.

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.

The ketolide antimicrobial agent HMR-3004 inhibits neutrophil superoxide production by a membrane-stabilizing mechanism

We have investigated the membrane-stabilizing potential of the prototype ketolide antimicrobial agent, HMR-3004 (3.75-125 microM), as well as the effects of this agent on the production of superoxide by human neutrophils activated with FMLP, the calcium ionophore A23187, phorbol 12-myristate 13-acetate (PMA) or opsonized zymosan (OZ), each of which uses different transductional mechanisms to activate NADPH-oxidase. Membrane-stabilizing activity was investigated using a hemolytic procedure, while superoxide production was assayed by lucigenin-enhanced chemiluminescence. At concentrations of 3.75 microM and greater, HMR-3004 caused dose-related inhibition of superoxide production by neutrophils activated by all four stimuli of membrane-associated oxidative metabolism, which was not associated with cytotoxicity or superoxide-scavenging activity. At the same concentrations, HMR-3004 antagonized the hemolytic actions of the membrane-disruptive bioactive phospholipids, lysophosphatidylcholine (LPC), platelet-activating factor (PAF) and lyso-PAF. A mechanistic relationship between the membrane-stabilizing and the anti-oxidative properties of HMR-3004 was suggested by the observation that treatment of neutrophils with non-cytolytic concentrations of LPC antagonized the inhibitory effects of the ketolide on superoxide production by these cells. These membrane-stabilizing, anti-oxidative activities of HMR-3004 suggest that in addition to its antimicrobial properties, this agent possesses anti-inflammatory properties which are superior to those of the presently available macrolide and azalide agents.

Extrinsic inputs to intrinsic neurons in the porcine heart in vitro

Convergence of inputs from extrinsic cardiac nerves [vagus and cardiopulmonary (CPN)] on intrinsic cardiac neurons was investigated in the pig (Sus scrofa). A segment of the right atrial wall containing epicardial neurons along with attached stumps of the right vagus nerve and CPN was maintained in vitro; intracellular recordings were made from 57 neurons. Three types of neuron were identified by their responses to long intracellular depolarizing current pulses: phasic [discharged 1 action potential (AP); 40%]; accommodating (discharged multiple APs decrementing in frequency during pulse; 33%); and tonic (discharged multiple APs at a high frequency; 27%). Sixty-six percent of the neurons responded with excitatory postsynaptic potentials (EPSP) to vagal nerve stimulation; two-thirds of these cells fired APs when EPSP amplitude exceeded threshold level. Postsynaptic responses to vagal nerve stimulation were mediated by nicotinic ion channels; responses were eliminated by hexamethonium. CPN stimulation produced EPSPs but no APs in 17% of the neurons. All neurons responding with postsynaptic depolarizations to CPN stimulation also received vagal inputs. Combined stimulation of the vagus nerve and CPN produced APs in all but one of these neurons. Timolol eliminated postsynaptic responses from CPN stimulation, indicating that these responses involved beta-adrenergic receptors and likely resulted from activation of sympathetic postganglionic terminals. These results show that some intrinsic cardiac neurons receive convergent inputs from the CPN and vagus nerve. It is suggested that such neurons represent intraganglionic sites for sympathetic-parasympathetic interactions in neural control of the heart.

Alpha1A-adrenergic receptors mediate vasoconstriction of the isolated spiral modiolar artery in vitro

Several lines of evidence suggest that cochlear blood flow is under the control of the sympathetic nervous system and that this control is mediated via alpha-adrenergic receptors. The goal of the present study was to determine whether alpha-adrenergic receptors mediate vasoconstriction of the spiral modiolar artery and, if so, to determine which subtype dominates this response. Vascular diameter was measured with video microscopy in the isolated superfused spiral modiolar artery in vitro. The diameter of the spiral modiolar artery under control conditions was 61 +/- 2 microm (n = 60). Spontaneous vasomotion was observed in most specimens. Addition of norepinephrine to the superfusate caused a phasic vasoconstriction and an increase in the amplitude of vasomotion. These effects were limited to the vicinity of arteriolar branch points of the spiral modiolar artery. Norepinephrine-induced vasoconstriction occurred with EC50 of (1.9 +/- 0.4) x 10(-5) M (n = 44) and the vascular diameter was maximally reduced by a factor of 0.87 +/- 0.01 (n = 29). Neither the phasic nature nor the EC50 of the norepinephrine-induced vasoconstrictions was altered in the presence of the beta2-adrenergic receptor antagonist 10(-5) M ICI118551 or the nitric oxide synthase inhibitor 10(-4) M NOARG. In contrast, the alpha2-adrenergic receptor antagonist 10(-7) M yohimbine and the alpha1-adrenergic receptor antagonist 10(-9) and 10(-8) M prazosin caused a significant shift in the dose-response curve. The affinity constants (K(DB)) for yohimbine and prazosin were (5+/-2) x 10(-8) M (n=4) and (2.0+/-0.7) x 10(-10) M (n=18), respectively. The alpha1A-adrenergic receptor antagonist 10(-8) M 5-methyl urapidil and the alpha1D-adrenergic receptors antagonist 5 x 10(-6) M BMY7378 caused a significant shift in the dose-response curve. The K(DB) values for 5-methyl urapidil and for BMY7378 were (2.7 +/- 0.7) x 10(-10) M (n = 8) and (4.4 +/- 2.7) x 10(-7) M (n = 8), respectively. Further, total RNA was isolated from microdissected spiral modiolar arteries and the presence of transcripts for alpha1-adrenergic receptor subtypes was determined by reverse transcription polymerase chain reaction (RT-PCR). Primers specific for gerbil alpha1-adrenergic receptor subtypes were developed using RNA from rat and gerbil brain. Analysis of RNA extracted from the spiral modiolar artery revealed RT-PCR products of the appropriate size for the alpha1A-adrenergic receptor, however, no evidence for the alpha1B- and alpha1D-adrenergic receptor was found. Further, analysis of RNA extracted from blood, which was a contaminant of the microdissected spiral modiolar arteries, revealed no RT-PCR products. Sequence analysis of the RT-PCR product of the alpha1A-adrenergic receptor from the spiral modiolar artery confirmed its identity. Identity between the 175 nt gerbil sequence fragment and the known rat, mouse and human alpha1A-adrenergic receptor sequences was 90.9, 92.0 and 85.2%, respectively. These observations demonstrate that the spiral modiolar artery contains alpha1A-adrenergic receptors which mediate vasoconstriction at branch points.

Protective effects of dilazep and its derivative K-7259 on the haemolysis induced by amphiphiles in rat erythrocytes

The effects of dilazep and K-7259, a dilazep derivative, on the haemolysis (as evidenced by release of haemoglobin) induced by palmitoyl-L-carnitine (PAL-CAR) or palmitoyl 1-alpha-lysophosphatidylcholine (PAL-LPC) have been determined in rat erythrocytes. At concentrations above the critical micelle concentration both PAL-CAR and PAL-LPC induced haemolysis; the concentrations of PAL-CAR and PAL-LPC producing 50% haemolysis were approximately 13 and 14 microM, respectively. The 50% haemolysis induced by PAL-CAR or PAL-LPC was attenuated by dilazep (1, 10 or 100 microM) but not at the highest concentration used (1 mM). K-7259 attenuated the 50% haemolysis induced by PAL-CAR or PAL-LPC at concentrations ranging from 1 microM to 1 mM. Similarly, dilazep (1 to 100 microM) and K-7259 (1 microM to 1 mM) significantly or insignificantly attenuated the 25% and 75% haemolysis induced by PAL-CAR or PAL-LPC. Neither dilazep nor K-7259 affected micelle formation by PAL-CAR or PAL-LPC, nor, at concentrations of 1 and 10 microM, did they attenuate the haemolysis induced by osmotic imbalance (hypotonic haemolysis). These results suggest that both dilazep and K-7259 protect the erythrocyte membrane from the damage induced by PAL-CAR or PAL-LPC. The protective effects of dilazep and K-7259 are mediated by some mechanism other than prevention of micelle formation or protection of the erythrocyte membrane against osmotic imbalance.