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

The β-blocker propranolol affects cAMP-dependent signaling and induces the stress response in Mediterranean mussels, Mytilus galloprovincialis

Widespread occurrence of pharmaceuticals is reported in aquatic systems, posing concerns for the health of aquatic wildlife and a theoretical risk to humans. A recent concept was developed for the identification of highly active compounds amongst the environmental pharmaceuticals, based on their mode of action, the homology between human targets and possible targets in the environment, and the importance of the affected pathway for the target species. In line with this approach, this study investigated whether propranolol (PROP) affects the cAMP-dependent pathway in Mediterranean mussels, Mytilus galloprovincialis. PROP is a prototypical β-adrenoceptor antagonist, and these receptors exist in bivalves and show gross pharmacological properties similar to their mammalian counterparts. PROP also acts as a 5-HT1 receptor antagonist, which is the sole 5-HT receptor reported in bivalves to date. Importantly, β-adrenoceptor and 5HT-1 receptor subtypes are positively and negatively coupled to cAMP-mediated signaling, respectively. PROP was administered as either l-PROP or dl-PROP. A wide range of concentrations was tested including low (0.3, 3 and 30ng/L) and high (300ng/L) environmental ranges, and a concentration 5-fold above the maximum reported environmental level (30,000ng/L). After a 7-day exposure, mussel cAMP levels and PKA activities were significantly reduced in digestive gland, increased in mantle/gonads and unaffected in gills. Similar patterns were observed for the mRNA expression of the ABCB1 gene encoding the membrane transporter P-glycoprotein, hypothesised to be under PKA modulation. The effects on the digestive gland are consistent with PROP blocking β-adrenoceptors. The observed increased cAMP levels in the mantle/gonad tissue support PROP blocking 5-HT1 receptors. Catalase and glutathione-S tranferase were differently affected by PROP in the two tissues. Mussel haemocyte lysosome membrane stability, a sensitive biomarker of animal health status, was concentration-dependently reduced following PROP exposure. Our observations provide evidence for PROP affecting cell signaling in M. galloprovincialis. Moreover, the chemical interacts with specific and evolutionally conserved biochemical pathways for which it was designed. The mode of action of PROP in mussels is related with its therapeutic properties in humans, based upon these conserved human targets. It also induced a stress response, and all these effects were displayed at the lowest concentrations tested.

Treating hypertension while protecting the vulnerable islet in the cardiometabolic syndrome

Hypertension, a multifactorial-polygenic disease, interacts with multiple environmental stressors and results in functional and structural changes in numerous end organs, including the cardiovascular system. This can result in coronary heart disease, stroke, peripheral vascular disease, congestive heart failure, end-stage renal disease, insulin resistance, and damage to the pancreatic islet. Hypertension is the most important modifiable risk factor for major health problems encountered in clinical practice. Whereas hypertension was once thought to be a medical condition based on discrete blood pressure readings, a new concept has emerged defining hypertension as part of a complex and progressive metabolic and cardiovascular disease, an important part of a cardiometabolic syndrome. The central role of insulin resistance, oxidative stress, endothelial dysfunction, metabolic signaling defects within tissues, and the role of enhanced tissue renin-angiotensin-aldosterone system activity as it relates to hypertension and type 2 diabetes mellitus are emphasized. Additionally, this review focuses on the effect of hypertension on functional and structural changes associated with the vulnerable pancreatic islet. Various classes of antihypertensive drugs are reviewed, especially their roles in delaying or preventing damage to the vulnerable pancreatic islet, and thus delaying the development of type 2 diabetes mellitus.

Selective mineralocorticoid receptor blocker eplerenone reduces resistance artery stiffness in hypertensive patients

Some antihypertensive agents may improve resistance artery remodeling in hypertensive patients whereas other agents may not, for similar blood pressure reduction. We questioned whether the selective mineralocorticoid receptor blocker eplerenone improves resistance artery remodeling in hypertensive patients versus the beta-blocker atenolol. Sixteen hypertensive patients were randomly assigned to double-blind daily treatment with eplerenone or atenolol. Resistance arteries from gluteal subcutaneous tissue were assessed on a pressurized myograph. After 1 year of treatment, systolic and diastolic blood pressures were similarly well controlled in both groups. Endothelial function did not change with treatment in either group. Media/lumen ratio and cross-sectional area were unchanged in either the atenolol or the eplerenone group. In atenolol-treated patients, the arterial wall became stiffer, whereas in the eplerenone-treated patients, it became less stiff and similar to that of a normotensive control group. The media collagen/elastin ratio was reduced only after eplerenone treatment. Circulating concentrations of osteopontin, monocyte chemoattractant protein-1, basic fibroblast growth factor, interleukin-8, and interleukin-10 were significantly reduced only by eplerenone. However, plasma interleukin-1 receptor a concentration was significantly reduced by both drugs. In conclusion, in hypertensive patients, blood pressure control for 1 year with atenolol was associated with increased wall stiffness of resistance arteries, whereas eplerenone treatment was associated with reduced stiffness, decreased collagen/elastin ratio, and a reduction in circulating inflammatory mediators. These data raise the possibility that eplerenone treatment of hypertensive patients when normalizing blood pressure could potentially be associated with better vascular protection and outcomes than the beta-blocker atenolol, which remains to be demonstrated.

Assessment of Acute Respiratory and Cardiovascular Toxicity of Casiopeinas in Anaesthetized Dogs

The 99 lethal dose in an acute toxicity study of two anticancer novel molecules named casiopeinas((R)) in dogs was calculated to be 200 mg/m(2) for casiopeina III-ia and 160 mg/m(2) for casiopeina IIgly. Considering therapeutic dose ranges from 3.6 to 18 mg/m(2) for the former and 1.2 to 3 mg/m(2) for the latter, true therapeutic margin of safety varies from 4.7 to 23.6 mg/m(2) and from 20 to 50 mg/m(2), respectively. For both casiopeinas intravenous administration of the corresponding lethal dose in 100 ml of 5% dextrose solution in a time period of 30 min. induced death after an almost uneventful latency time period of 30-50 min. Then, after an apparently sudden onset, changes in blood gases indicated respiratory distress (PO(2) from 82.5% to 26.5% for casiopeina III-ia and from 88.6% to 37.5% for casiopeina IIgly; end-tidal CO(2) from 38 to 8.1 mmHg for the first and from 35.1 to 11.2 mmHg for the second, this was almost simultaneously confirmed by the onset of tachypnoea (from 16 to almost 60 breaths/min. for both casiopeinas) and by a drop in arterial blood pressure (from 117 to 51 mmHg for casiopeina III-ia and from 108 to 49 mmHg for casiopeina IIgly). Reflex tachycardia occurs at the beginning of intravenous administration followed by bradycardia a few minutes later (from 158 to 63 beats/min. for casiopeina III-ia and from 148 to 56 beats/min. for casiopeina IIgly). Finally, cardiac arrest occurred no later than 25 min. towards the end of these events lung oedema appeared as fluid dripping from the endotracheal tube. Death occurred in a mean of 15 +/- 5 min. S.D. from the beginning of the end of the latency period. For both casiopeina's data allow the speculation that lung oedema is caused by a joined toxicity to the lung capillary bed, and particularly to the heart. Carvedilol premedication for 8 days delayed the outcome of lung oedema by approximately 8 hr but could not prevent it.

Carvedilol Increases Copper-Zinc Superoxide Dismutase Activity in Patients with Acute Myocardial Infarction

Balanced and coordinated antioxidant defence enzyme activities are of utmost importance for correct physiological function and for shielding against unwelcome pathological conditions. We determined the activities of copper-zinc superoxide dismutase (CuZnSOD), catalase, glutathione peroxidase and glutathione reductase in erythrocytes isolated from patients receiving different therapy (streptokinase alone or in combination with metoprolol or with carvedilol) for up to 168 hr after starting treatment for acute myocardial infarction. We observed increased CuZnSOD activity in erythrocytes isolated from patients treated with streptokinase-carvedilol (after 6, 24 and 168 hr) and in erythrocytes isolated from patients treated with streptokinase-metoprolol (after 24 hr). In addition, positive correlation between CuZnSOD and catalase activities was found in erythrocytes isolated from patients that received streptokinase-carvedilol after 168 hr. As metoprolol does not react directly with hydrogen peroxide, it would appear that combined streptokinase-metoprolol therapy exerted its effects primarily via by beta-blockade whereas combined streptokinase-carvedilol therapy appeared to function via both beta-blockade and direct antioxidant mechanisms.

2-Styrylchromones: novel strong scavengers of reactive oxygen and nitrogen species

2-Styrylchromones are a small group of naturally occurring chromones, vinylogues of flavones (2-phenylchromones). Natural and synthetic 2-styrylchromones have been tested in different biological systems, showing activities with potential therapeutic applications. In particular, the potential and hitherto understudied antioxidant behavior of these compounds has been raised as a matter of interest. Thus the present work consisted in the study of the in vitro scavenging activities for reactive oxygen species (ROS) and reactive nitrogen species (RNS) of various 2-styrylchromone derivatives and structurally similar flavonoids. Some of the studied 2-styrylchromones proved to be extremely efficient scavengers of the different ROS and RNS, showing, in some cases, IC(50)s under 1 microM. The hydroxylation pattern of 2-styrylchromones, especially in the B-ring but also in the A ring, modulates the activity of these compounds, the catecholic derivatives being the most effective scavengers. The styryl pattern also contributes to their observed outstanding antioxidant activity. In conclusion, the scavenging activities for ROS/RNS of 2-styrylchromone derivatives, here shown for the first time, provide novel and most promising compounds to be applied as antioxidants.

iTRAQ-coupled 2D LC-MS/MS analysis on protein profile in vascular smooth muscle cells incubated with S- and R-enantiomers of propranolol: possible role of metabolic enzymes involved in cellular anabolism and antioxidant activity

Propranolol is a nonselective beta-blocker of the beta-adrenergic receptors, and the S-enantiomer is more active compared with the R-enantiomer. Clinically, it has been shown to be effective in hypermetabolic burn patients by decreasing cardiac work, protein catabolism, and lipolysis. While gene expression profiles have recently been reported in children receiving propranolol treatment, variations from one individual to another may have influenced the data analysis. Using iTRAQ-coupled 2D LC-MS/MS analysis, we report here the first study of protein profile in vascular smooth muscle cells incubated separately with the two enantiomers of propranolol. Four types of cellular proteins including metabolic enzymes, signaling molecules, cytoskeletal proteins, and those involved in DNA synthesis/protein translation displayed changes. The higher protein level of a number of enzymes involved in cellular anabolism and antioxidant activity in cells incubated with the S-enantiomer, as revealed by LC-MS/MS, was further supported by real-time PCR and Western blot analyses. Significantly, the increase in the anabolic activity associated with the higher level of metabolic enzymes was also supported by the higher intracellular concentration of the metabolic cofactor NAD+ which was a result of an increased oxidation of NADH. Our findings therefore provide molecular evidence on metabolic effect associated with propranolol treatment. The metabolic enzymes identified in our study may in turn be useful targets for future pharmaceutical interventions to reduce clinical side effects following propranolol treatment.

Agonist-stimulated reactive oxygen species formation regulates beta2-adrenergic receptor signal transduction

Generation of reactive oxygen species (ROS) can occur upon agonist stimulation of surface receptors to modulate downstream signaling processes. Here, we show that activation of the beta2 adrenergic receptor (beta2AR) by stimulation with the agonist isoproterenol leads to generation of ROS that is required for beta2AR signal transduction. Specifically, we show that inhibition of NADPH oxidase with diphenyliodonium chloride, inhibition of the small GTPase Rac1 with NSC23766, and inhibition of formed ROS with the antioxidant N-acetyl-L-cysteine decreases beta2AR-mediated cAMP formation, protein kinase A activation, and receptor phosphorylation and internalization, but does not impact ligand binding. The results also show that inhibition of ROS attenuates active beta2AR-mediated binding of GTP to alpha subunits of heterotrimeric G proteins. Based on these results, we propose that agonist-dependent ROS formation is needed for beta2AR signal transduction, perhaps through stabilization of active receptor conformers by redox-mediated modification of receptor and/or Galpha proteins cysteine residues.

Antioxidant activity of timolol on endothelial cells and its relevance for glaucoma course

PURPOSE

A growing evidence in the scientific literature suggests that oxidative damage plays a pathogenic role in primary open-angle glaucoma. Therefore, it is of interest to test whether drugs effective against glaucoma display antioxidant activity. We test the hypothesis that the classic beta-blocker therapy for glaucoma with timolol involves the activation of antioxidant protective mechanisms towards endothelial cells.

METHODS

Oxidative stress was induced in cultured human endothelial cells by iron/ascorbate with or without timolol pretreatment. Analysed parameters included cell viability (neutral red uptake and tetrazolium salt tests), lipid peroxidation (thiobarbituric reactive substances), and occurrence of molecular oxidative damage to DNA (8-hydroxy-2'-deoxyguanosine).

RESULTS

Oxidative stress decreased 1.8-fold cell viability, increased 3.0-fold lipid peroxidation and 64-fold oxidative damage to DNA. In the presence of timolol, oxidative stress did not modify cell viability, whereas lipid peroxidation was increased 1.3-fold, and DNA oxidative damage 3.6-fold only.

CONCLUSIONS

The obtained results indicate that timolol exerts a direct antioxidant activity protecting human endothelial cells from oxidative stress. These cells employ mechanisms similar to those observed in the vascular endothelium. It is hypothesized that this antioxidant activity is involved in the therapeutic effect of this drug against glaucoma.