Propranolol as xanthine oxidase inhibitor: implications for antioxidant activity

Novel Properties of Old Propranolol-Assessment of Antiglycation Activity through In Vitro and In Silico Approaches

Hypertension has earned the "silent killer" nickname since it may lead to a number of comorbidities, including diabetes and cardiovascular diseases. Oxidative stress and protein glycation play vital roles in the pathogenesis of hypertension. Several studies have shown that they profoundly account for vascular dysfunction, endothelial damage, and disruption of blood pressure regulatory mechanisms. Of particular note are advanced glycation end products (AGEs). AGEs alter vascular tissues' functional and mechanical properties by binding to receptors for advanced glycation end products (RAGE), stimulating inflammation and free radical-mediated pathways. Propranolol, a nonselective beta-adrenergic receptor antagonist, is one of the most commonly used drugs to treat hypertension and cardiovascular diseases. Our study is the first to analyze propranolol's effects on protein glycoxidation through in vitro and in silico approaches. Bovine serum albumin (BSA) was utilized to evaluate glycoxidation inhibition by propranolol. Propranolol (1 mM) and BSA (0.09 mM) were incubated with different glycating (0.5 M glucose, fructose, and galactose for 6 days and 2.5 mM glyoxal and methylglyoxal for 12 h) or oxidizing agents (chloramine T for 1 h). Biomarkers of protein glycation (Amadori products (APs), β-amyloid (βA), and advanced glycation end products (AGEs)), protein glycoxidation (dityrosine (DT), kynurenine (KYN), and N-formylkynurenine (NFK)), protein oxidation (protein carbonyls (PCs), and advanced oxidation protein products (AOPPs)) were measured by means of colorimetric and fluorimetric methods. The scavenging of reactive oxygen species (hydrogen peroxide, hydroxyl radical, and nitric oxide) and the antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl radical and ferrous ion chelating (FIC) assays)) of propranolol were also evaluated. Additionally, in silico docking was performed to showcase propranolol's interaction with BSA, glycosides, and AGE/RAGE pathway proteins. The products of protein glycation (↓APs, ↓βA, ↓AGEs), glycoxidation (↓DT, ↓KYN, ↓NFK), and oxidation (↓PCs, ↓AOPPs) prominently decreased in the BSA samples with both glycating/oxidizing factors and propranolol. The antiglycoxidant properties of propranolol were similar to those of aminoguanidine, a known protein oxidation inhibitor, and captopril, which is an established antioxidant. Propranolol showed a potent antioxidant activity in the FIC and H2O2 scavenging assays, comparable to aminoguanidine and captopril. In silico analysis indicated propranolol's antiglycative properties during its interaction with BSA, glycosidases, and AGE/RAGE pathway proteins. Our results confirm that propranolol may decrease protein oxidation and glycoxidation in vitro. Additional studies on human and animal models are vital for in vivo verification of propranolol's antiglycation activity, as this discovery might hold the key to the prevention of diabetic complications among cardiology-burdened patients.

Effects of Atenolol, Labetalol and Methyldopa on Endogenous Antioxidants In-vitro

The aim of this study was to investigate whether atenolol, labetalol and methyldopa, which are commonly used for the treatment of hypertension in pregnancy, can induce antioxidant activity.

Reactive oxygen species scavengers (plasma thiol, red cell lysate thiol, red cell superoxide dismutase, red cell membrane thiol and plasma glutathione) were measured after incubation of peripheral blood with atenolol and methyldopa, respectively.

The results showed that atenolol and labetalol could significantly raise the levels of plasma thiol and membrane thiol but had no effects on lysate thiol, superoxide dismutase and glutathione. The effects on membrane thiol occurred after 60 min incubation and on plasma thiol after 120 min incubation.

The data also suggest that atenolol and labetalol at lower concentrations tend to have additive effects on reactive oxygen species scavengers but at higher concentrations do not.

Methyldopa had no significant effect on any of the parameters measured.

These findings suggest that atenolol and labetalol are able to induce higher levels of antioxidant activity.

Effect of beta-blockers on endothelial function during biological aging: a nanotechnological approach

Biological aging is an independent risk factor for many cardiovascular diseases; some are treated with beta-blockers that may protect dysfunctional endothelium during aging by increasing NO, decreasing ONOO, and restoring NO/ONOO balance. A nanotechnological approach was used to simultaneously monitor NO and ONOO produced by a single aortic endothelial cell from Wistar-Kyoto rats of different ages. beta-blockers (metoprolol and atenolol) were administered 2 weeks before the animals were sacrificed. Nanosensors were placed near the endothelium, and calcium ionophore- stimulated NO and ONOO release was measured. Endothelial nitric oxide synthase (eNOS) undergoes uncoupling with aging, manifested by a decrease in NO (from 503 +/- 12 to 163 +/- 5 nmol/L) and a 3-fold increase in ONOO for 16-week-old and 110- week- old rats, respectively. Metoprolol reversed eNOS uncoupling, increased the production rate and concentration of NO, and increased an overall ratio of NO]/ONOO]. This effect was not observed with atenolol, but L-arginine, sepiapterin, and superoxide dismutase were beneficial.

Vascular effects of long-term propranolol administration after chronic nitric oxide blockade

Long-term propranolol treatment reduces arterial blood pressure in hypertensive individuals mainly by reducing peripheral vascular resistance, but mechanisms underlying their vasodilatory effect remain poorly investigated. This study aimed to investigate whether long-term propranolol administration ameliorates the impairment of relaxing responses of aorta and mesenteric artery from rats made hypertensive by chronic nitric oxide (NO) deficiency, and underlying mechanisms mediating this phenomenon. Male Wistar rats were treated with N(omega)-Nitro-L-arginine methyl ester (L-NAME; 20 mg/rat/day) for four weeks. DL-Propranolol (30 mg/rat/day) was given concomitantly to L-NAME in the drinking water. Treatment with L-NAME markedly increased blood pressure, an effect largely attenuated by DL-propranolol. In phenylephrine-precontracted aortic rings, the reduction of relaxing responses for acetylcholine (0.001-10 microM) in L-NAME group was not modified by DL-propranolol, whereas in mesenteric rings the impairment of acetylcholine-induced relaxation by L-NAME was significantly attenuated by DL-propranolol. In mesenteric rings precontracted with KCl (80 mM), DL-propranolol failed to attenuate the impairment of acetylcholine-induced relaxation by L-NAME. The contractile responses to extracellular CaCl2 (1-10 mM) were increased in L-NAME group, and co-treatment with DL-propranolol reduced this response in both preparations in most Ca2+ concentrations used. The NO2/NO3 plasma levels and superoxide dismutase (SOD) activity were reduced in L-NAME-treated rats, both of which were significantly prevented by DL-propranolol. In conclusion, propranolol-induced amplification of the relaxation to acetylcholine in mesenteric arteries from L-NAME-treated rats is sensitive to depolarization. Additional mechanisms involving blockade of Ca2+ entry in the vascular smooth muscle and increase in NO bioavailability contributes to beneficial effects of long-term propranolol treatment.

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 role of nebivolol in hydroxyl radical induced injury

Increased oxidative stress has been postulated as one of the main mechanisms underlying stunned myocardium, and may play an important role in and during development of heart failure. Pharmacological interventions may attenuate or prevent detrimental effects of oxygen free radicals on the myocardium. Nebivolol has been shown to attenuate contractile dysfunction in hydroxyl radical mediated injury, but the mechanism(s) remain unknown. It was investigated whether nebivolol could partly attenuate the contractile dysfunction through a direct effect on the myofilaments. In demembranized muscles from explanted human hearts, nebivolol induced a slight desensitization of the myofilaments to calcium. Therefore, during the calcium overload that occurs during reperfusion after an ischemic event, the contractile dysfunction is less severe in the presence of nebivolol. We conclude that the protection of nebivolol in hydroxyl radical induced contractile dysfunction is mediated in part through a direct effect on the myofilaments, in addition to the previously shown preservation of sarcoplasmic reticulum function.

Inhibition of lipid peroxidation by pindolol

Among beta-blockers, including atenolol, metaproterenol, pindolol and propranolol, only pindolol strongly inhibited lipid peroxidation induced by xanthine oxidase-hypoxanthine in the presence of adenosine-5'-phosphate-Fe3+. In the reaction system, superoxide predominantly reduced iron because superoxide dismutase strongly prevented the iron reduction. However, pindolol had no effect on the superoxide-dependent iron reduction. Adding superoxide dismutase immediately stopped the lipid peroxidation, indicating that superoxide is closely connected with forming the initiator of xanthine oxidase-hypoxanthine-induced lipid peroxidation. On the other hand, pindolol also inhibited lipid peroxidation, whereas it did not react with superoxide, indicating that it inhibited xanthine oxidase-hypoxanthine-induced lipid peroxidation by an independent mechanism of superoxide. Pindolol sharply scavenged 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonate) radical cations, but the ability of pindolol to scavenge peroxyl radicals of 2,2'-azobis(2-amidinopropane)-dihydrochloride and 2,2'-diphenyl-p-picrylhydrazyl radicals was low. In addition, pindolol did not scavenge hydroxyl radicals at physiologically significant concentrations. These results suggest that the ability of pindolol to inhibit lipid peroxidation was due to scavenging carbon-centered radicals rather than peroxyl radicals.

Effect of beta-Adrenoceptor Antagonists on Phospholipid N-Methylation Activities of Cardiac Sarcolemma

BACKGROUND: Some beta-adrenoceptor antagonists exert a negative inotropic action by affecting Ca(2+) fluxes in the myocardial cell as a consequence of their interaction with sarcolemmal and sarcoplasmic reticular membranes. This action may be caused by their effects on the chemicophysical properties of membranes phospholipids. Because phosphatidylethanolamine (PE) N-methylation can influence the chemicophysical properties of membranes, these agents may affect PE N-methylation. This study was undertaken to examine the effects of propranolol, acebutolol, and atenolol on PE-N-methylation in rat heart sarcolemma (SL). METHODS AND RESULTS: Sarcolemmal membrane was isolated from rat hearts by the hypotonic shock LiBr method. Incorporation of radiolabeled methyl groups from S-adenosyl-l-methionine was assayed at three catalytic sites involved in the PE N-methylation reaction in the presence and absence of these drugs. A biphasic effect of propranolol at site I was noted; low concentrations (10(-8) M) were inhibitor. Acebutolol (10(-9)-10(-3) M) depressed methyl group incorporation in SL at site II in a dose-dependent manner, whereas atenolol showed no effect. Propranolol also exerted a biphasic effect on sarcoplasmic reticular (SR) methylation at site I, whereas acebutolol depressed the SR enzyme activity at site II and atenolol had no effect. The mitochondrial methyltransferase activities at sites I, II, and III were unaltered by any of these drugs. CONCLUSIONS: It is suggested that propranolol and acebutolol alter SL and SR PE N-methyltransferase activity at site I and site II, respectively, either by affecting the enzyme directly or by changing the physiochemical properties of the membrane.

Are the reactive oxygen-derived species (ROS) interactive properties of the many therapeutic drugs from various categories pertinent to their beneficial effects?

Many pathologic states are known to involve the generation of reactive oxygen species, (ROS). It is not known at present to what extent these phenomena are due to ROS formation, or if their formation is a result of the disease. Many therapeutic drugs either scavenge ROS or inhibit their formation. The purpose of this review is to match the drugs used for certain diseases with their anti-ROS actions. This attempted correlation is made to try to give an answer to the title question.

Inhibition of xanthine oxidase-xanthine-iron mediated lipid peroxidation by eugenol in liposomes

The effect of eugenol on xanthine oxidase (XO) xanthine(X)-Fe+3-ADP mediated lipid peroxidation was studied in liver microsomal lipid liposomes. Eugenol inhibited the lipid peroxidation in a dose dependent manner as assessed by formation of thiobarbituric acid reactive substances. When tested for its effect on XO activity per se, (by measuring uric acid formation) eugenol inhibited the enzyme to an extent of 85% at 10 microm concentration and hence formation of O2.- also. However, the concentration of eugenol required for XO inhibition was more in presence of metal chelators such as EDTA, EGTA and DETAPAC, but not in presence of deferoxamine, ADP and citrate. The antiperoxidative effect of eugenol was about 35 times more and inhibition of XO was about 5 times higher as compared to the effect of allopurinol. Eugenol did not scavenge O2.- generated by phenazine methosulfate and NAD but inhibited propagation of peroxidation catalyzed by Fe2+ EDTA and lipid hydroperoxide containing liposomes. Eugenol inhibits XO-X-Fe+3 ADP mediated peroxidation by inhibiting the XO activity per se in addition to quenching various radical species.

Characterization of drugs as antioxidant prophylactics

There is growing interest in the evaluation of drugs (prescription only medicines and over-the-counter medicines) as antioxidant prophylactics. Although free radical mechanism in human degenerative diseases is now generally recognised, the mechanisms of tissue injury in humans are very complex and it may not be possible to clearly identify the role played by free radicals in the process. This review examines the current evidence to support the notion that drugs for a particular therapeutic category might possess useful antioxidant capacity hence minimising tissue injury due to free radicals.

A re-evaluation of the tissue distribution and physiology of xanthine oxidoreductase

Xanthine oxidoreductase is an enzyme which has the unusual property that it can exist in a dehydrogenase form which uses NAD+ and an oxidase form which uses oxygen as electron acceptor. Both forms have a high affinity for hypoxanthine and xanthine as substrates. In addition, conversion of one form to the other may occur under different conditions. The exact function of the enzyme is still unknown but it seems to play a role in purine catabolism, detoxification of xenobiotics and antioxidant capacity by producing urate. The oxidase form produces reactive oxygen species and, therefore, the enzyme is thought to be involved in various pathological processes such as tissue injury due to ischaemia followed by reperfusion, but its role is still a matter of debate. The present review summarizes information that has become available about the enzyme. Interpretations of contradictory findings are presented in order to reduce confusion that still exists with respect to the role of this enzyme in physiology and pathology.

Low density lipoprotein composition and oxidizability in coronary disease — apparent favourable effect of beta blockers

The oxidative modification of LDL in vivo may have an important role in atherogenesis. To determine whether LDL fatty acid, anti-oxidant composition and sensitivity to oxidation in vitro is different in subjects with established atherosclerosis we compared 20 men with angiogram proven coronary disease with 25 controls without clinical evidence of arterial disease. LDL-cholesterol, total triglycerides and LDL fatty acid composition did not differ significantly between the groups. LDL oxidation lag time and oxidation rate in coronary patients (132 min, 0.02 absorbance units/min) and controls (140, 0.017) were not significantly different. However coronary disease subjects taking beta-blockers had evidence for reduced LDL oxidizability (lag time 148 +/- 7 min; oxidation rate 0.017 +/- 0.002 abs units/min) compared with those not on beta-blockers (lag time 114 +/- 7 min, rate 0.025 +/- 0.003, P < 0.005). LDL beta-carotene was significantly lower in coronary patients (0.92 mumol/mmol LDL cholesterol; controls 1.58; P = 0.001). LDL alpha-tocopherol appeared lower in coronary patients (2.8 mumol/mmol LDL cholesterol; controls 3.3; P = 0.056) and was significantly lower in smokers (2.56; non-smokers 3.24; P = 0.04). LDL oxidation rate was negatively correlated with LDL alpha-tocopherol (r = -0.51, P = 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Carvedilol, a new beta-adrenoceptor antagonist and vasodilator antihypertensive drug, inhibits superoxide release from human neutrophils

Carvedilol produced a dose-dependent inhibition of superoxide (O2-) release from human neutrophils (PMNs) (IC50 = 28 microM) and scavenged O2- generated during dihydroxyfumaric acid (DHF) autooxidation (IC50 = 41 microM). Other beta-blockers, such as celiprolol, labetalol and atenolol, or the antioxidant, 'lazaroid', U74500A had no effect on O2- either released from PMNs or generated during DHF autooxidation. Propranolol, at 0.3 mM, inhibited O2- release from PMNs (73%) but failed to scavenge O2- generated from DHF. The novel free radical-scavenging effect of carvedilol may contribute to the cardioprotective activity of the compound.

Picroliv, picroside-I and kutkoside from Picrorhiza kurrooa are scavengers of superoxide anions

Picroliv, the active principle of Picrorhiza kurrooa, and its main components which are a mixture of the iridoid glycosides, picroside-I and kutkoside, were studied in vitro as potential scavengers of oxygen free radicals. The superoxide (O2-) anions generated in a xanthine-xanthine oxidase system, as measured in terms of uric acid formed and the reduction of nitroblue tetrazolium were shown to be suppressed by picroliv, picroside-I and kutkoside. Picroliv as well as both glycosides inhibited the non-enzymic generation of O2- anions in a phenazine methosulphate NADH system. Malonaldehyde (MDA) generation in rat liver microsomes as stimulated by both the ascorbate-Fe2+ and NADPH-ADP-Fe2+ systems was shown to be inhibited by the Picroliv glycosides. Known antioxidants tocopherol (vitamin E) and butylated hydroxyanisole (BHA) were also compared with regard to their antioxidant actions in the above system. It was found that BHA afforded protection against ascorbate-Fe(2+)-induced MDA formation in microsomes but did not interfere with enzymic or non-enzymic O2- anion generation; and tocopherol inhibited lipid peroxidation in microsomes by both prooxidant systems and the generation of O2- anions in the non-enzymic system but did not interfere with xanthine oxidase activity. The present study shows that picroliv, picroside-I and kutkoside possess the properties of antioxidants which appear to be mediated through activity like that of superoxide dismutase, metal ion chelators and xanthine oxidase inhibitors.

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.

The effect of selected antiarrhythmic drugs on neutrophil free oxygen radicals production measured by chemiluminescence

The evidence that free oxygen radicals produced by polymorphonuclear neutrophils (PMN) participate in generation of reperfusion arrhythmias is well documented. The in vitro effect of selected antiarrhythmic drugs on PMN free radicals production was evaluated by luminol- (LuCL) and lucigenin- (LgCL) amplified chemiluminescence stimulated with opsonized zymosan (o.z.) and phorbol myristate acetate (PMA). Fast sodium channel inhibitors varied in the influence on PMN chemiluminescence: from an inhibition in all models studied by procainamide, to lack of an effect by mexiletine. Propafenone, similarly to ajmaline and verapamil, inhibited LuCL stimulated with PMA, as well as LgCL after stimulation with both PMA and o.z. Bretylium tosylate decreased LuCL stimulated with both inducers, with no effect on LgCL. Amiodarone in high concentrations inhibited both LuCL and LgCL. beta-blockers propranolol and practolol impaired LuCL stimulated with o.z., as well as LgCL induced with PMA, whereas alpha-blocker phentolamine inhibited LuCL and LgCL stimulated with both inducers. The drugs' effect on PMN free oxygen radicals production may constitute an additional mechanism of their activity.

High density lipoprotein is a scavenger of superoxide anions

Present work describes a new property of HDL to act as a scavenger of O2- free radicals in vitro. This lipoprotein prevents both enzymic and non-enzymic generation of O2- anions as evidenced by inhibition of xanthine oxidase, peroxidase, peroxidation of pyrogallol and phenazine methosulphate-NADH reaction. Ascorbate stimulated MDA formation in microsomes has been shown to be suppressed by HDL and these effects are comparable with that of BHA.

Free radical generation, lipid peroxidation and essential fatty acids in uncontrolled essential hypertension

Vascular endothelium produces prostacyclin (PG12) and endothelium-derived vascular relaxing factor (EDRF), which are potent vasodilators and hence, may have a role in the regulation of blood pressure. Both PG12 and EDRF are readily degraded by free radicals, especially superoxide anion. Hence, we studied free radical generation and lipid peroxidation in patients with uncontrolled essential hypertension. It was observed that superoxide anion and hydrogen peroxide production by polymorphonuclear leukocytes (PMN) and the levels of lipid peroxides (measured by thiobarbituric acid assay) were higher in uncontrolled hypertensives compared to controls. Both free radical generation and the levels of lipid peroxides reverted to normal values when assayed after the control of hypertension. The calcium antagonist, verapamil, and beta-1 blocker, metoprolol, at the doses used inhibited free radical generation by phorbolmyristate acetate-stimulated PMNs. On the other hand, angiotensin II augmented free radical generation in normal PMN. In addition, it was also observed that both linoleic acid and arachidonic acid levels are low in the plasma of patients with hypertension compared to controls. These results suggest that increase in free radical generation by PMN and alterations in the plasma concentrations of essential fatty acids are closely associated with uncontrolled hypertension.