In vitro effects of reactive O2 species on the beta-receptor-adenylyl cyclase system

The patent situation concerning the treatment of diseases associated with autoantibodies directed against G-protein-coupled receptors

Agonist-like autoantibodies against receptors of the G-protein-coupled signal cascade have been identified as the pathogenic principle for a variety of diseases, especially those of the heart and vascular system. Consequently, the elimination or neutralization of such autoantibodies is an advised goal for causal therapeutic intervention. This article provides a short, noncomplete overview about remarkable developmental strategies and technical solutions for the therapy of diseases, associated with G-protein-coupled receptor autoantibodies. According to the immunoglobulin nature of the therapeutic target, several strategies are possible, such as the use of the autoantibody epitope sequences as competitors or binding molecules for specific autoantibody-elimination by apheresis. Complete immunoglobulin elimination, as is currently being tested in autoantibody-positive cardiomyopathy patients, would be a nonspecific solution as would the use of immunosuppressant agents. The use of autoantibody-binding molecules on an aptamer basis for neutralization or elimination is a newly developed specific therapeutic option.

Agonistic autoantibodies directed against G-protein-coupled receptors and their relationship to cardiovascular diseases

Agonistic autoantibodies (AABs) against G-protein-coupled receptor (GPCR) are present mainly in diseases of the cardiovascular system or in diseases associated with cardiovascular disturbances. The increasing knowledge about the role of autoantibodies against G-protein-coupled receptor (GPCR-AABs) as pathogenic drivers, the resulting development of strategies aimed at their removal or neutralization, and the evidenced patient benefit associated with such therapies have created the need for a summary of GPCR-AAB-associated diseases. Here, we summarize the present knowledge about GPCR-AABs in cardiovascular diseases. The identity of the GPCR-AABs and their prevalence in each of several specific cardiovascular diseases are documented. The structure of GPCR is also briefly discussed. Using this information, differences between classic agonists and GPCR-AABs in their GPCR binding and activation are presented and the resulting pathogenic consequences are discussed. Furthermore, treatment strategies that are currently under study, most of which are aimed at the removal and in vivo neutralization of GPCR-AABs, are indicated and their patient benefits discussed. In this context, immunoadsorption using peptides/proteins or aptamers as binders are introduced. The use of peptides or aptamers for in vivo neutralization of GPCR-AABs is also described. Particular attention is given to the GPCR-AABs directed against the adrenergic beta1-, beta2-, and α1-receptor as well as the muscarinic receptor M2, angiotensin II-angiotensin receptor type I, endothelin1 receptor type A, angiotensin (1-7) Mas-receptor, and 5-hydroxytryptamine receptor 4. Among the diseases associated with GPCR-AABs, special focus is given to idiopathic dilated cardiomyopathy, Chagas' cardiomyopathy, malignant and pulmonary hypertension, and kidney diseases. Relationships of GPCR-AABs are indicated to glaucoma, peripartum cardiomyopathy, myocarditis, pericarditis, preeclampsia, Alzheimer's disease, Sjörgren's syndrome, and metabolic syndrome after cancer chemotherapy.

Nicotinamide adenine dinucleotide phosphate oxidase and diabetes: vascular implications

Vascular disease associated with diabetes mellitus is a major cause of morbidity and mortality and is increasing in the United States. It is now recognized that oxidative stress plays a substantial role in the underlying vascular pathology of several diseases, including hypertension and diabetes. In diabetes, there is an increase in the steady state levels of reactive oxygen species. One of the primary generators of reactive oxygen species is nicotinamide adenine dinucleotide phosphate oxidase. Studies have indicated that inhibition of this system is associated with vascular benefits in diabetes. Therefore, there may be a role for therapies directed at nicotinamide adenine dinucleotide phosphate oxidase in this disease. This review will examine the structure, activation, potential role in vascular disease, and benefits of inhibition of nicotinamide adenine dinucleotide phosphate oxidase.

Modulation of adenylyl cyclase activity in young and adult rat brain cortex. Identification of suramin as a direct inhibitor of adenylyl cyclase

Adenylyl cyclase (AC) in brain cortex from young (12-day-old) rats exhibits markedly higher activity than in adult (90-day-old) animals. In order to find some possibly different regulatory features of AC in these two age groups, here we modulated AC activity by dithiothreitol (DTT), Fe(2+), ascorbic acid and suramin. We did not detect any substantial difference between the effects of all these tested agents on AC activity in cerebrocortical membranes from young and adult rats, and the enzyme activity was always about two-fold higher in the former preparations. Nevertheless, several interesting findings have come out of these investigations. Whereas forskolin- and Mn(2+)-stimulated AC activity was significantly enhanced by the addition of DTT, increased concentrations of Fe(2+) ions or ascorbic acid substantially suppressed the enzyme activity. Lipid peroxidation induced by suitable combinations of DTT/Fe(2+) or by ascorbic acid did not influence AC activity. We have also observed that PKC- or protein tyrosine kinase-mediated phosphorylation apparently does not play any significant role in different activity of AC determined in cerebrocortical preparations from young and adult rats. Our experiments analysing the presumed modulatory role of suramin revealed that this pharmacologically important drug may act as a direct inhibitor of AC. The enzyme activity was diminished to the same extent by suramin in membranes from both tested age groups. Our present data show that AC is regulated similarly in brain cortex from both young and adult rats, but its overall activity is much lower in adulthood.

On the in vitro vasoactivity of bile acids

We compared the vasorelaxant action of nine different bile acids and correlated their vasorelaxant activity with their individual indices for hydrophobicity or lipophilicity. Vasorelaxant activity correlated with the relative lipid solubility of bile acids with lipophilic bile acids exhibiting the greatest vasorelaxant activity with modest to no vasorelaxant activity exhibited by hydrophilic bile acids. We also investigated whether bile acid-induced vasorelaxation is mediated by antagonism of a prototypal contractile receptor, the alpha(1)-adrenoceptor, by stimulation of a bile acid surface membrane receptor, by the release of endothelium-derived relaxant factors, by promoting the generation of reactive oxygen species and increasing the extent of lipid peroxidation, or by modifying membrane fluidity. Lipophilic bile acids induce vasorelaxation possibly by antagonizing alpha(1)-adrenoceptors, a phenomenon that manifests itself as a lowering of the affinity of vascular alpha(1)-adrenoceptors. Bile acid-induced vasorelaxation was not dependent upon stimulation of a bile acid surface membrane receptor or the release of endothelium-derived relaxant factors. Lipophilic bile acids can also increase the extent of lipid peroxidation with a subtle reduction in the fluidity of rat vascular smooth muscle membranes not associated with loss of membrane cholesterol or phospholipid. We have concluded that lipophilic bile acids are non-selective vasorelaxants whose mechanism of action is a multifaceted process involving antagonism of contractile surface membrane receptors possibly effected by an increased extent of lipid peroxidation and/or membrane fluidity but occurs independent of the release of endothelial-derived relaxant factors or stimulation of a surface membrane bile acid binding site.

Oxygen radical system in chronic infarcted rat heart: the effect of combined beta blockade and ACE inhibition

In vitro experiments suggest that beta blockade and angiotensin-converting enzyme (ACE) inhibition may protect the failing heart by reduction of myocardial oxidative stress. To test this hypothesis in an in vivo model, the beta blocker metoprolol (350 mg) and the ACE inhibitor ramipril (1 mg) were given either alone or in combination to rats (per kilogram body weight per day) for 6 weeks after myocardial infarction. Left ventricular end-diastolic pressure (LVEDP), contractile function of papillary muscles, enzymatic antioxidative defense (indicated by the activities of the superoxide dismutase isoenzymes and glutathione peroxidase), and the extent of lipid peroxidation were studied. Placebo-treated rats showed cardiac hypertrophy, increased LVEDP, lower rates of contraction and relaxation, as well as a deficit in the myocardial antioxidative defense associated with increased lipid peroxide levels, when compared with sham-operated animals. Combined beta blockade and ACE inhibition improved the antioxidative defense, reduced hypertrophy and LVEDP, and enhanced rates of contraction. Thus prolonged beta blockade and ACE inhibition after infarction may decrease myocardial oxidative stress and thereby could be beneficial in heart failure.

Oxidative stress in the human heart is associated with changes in the antioxidative defense as shown after heart transplantation

The study was designed to demonstrate--for the first time in humans--that oxidative stress in the heart indicated by lipid peroxidation is associated with time-dependent changes in the enzymatic antioxidative defense. For this purpose, we analyzed the oxygen radical metabolism in 69 myocardial biopsies (taken between the fifth day and 6 years after transplantation) of 31 heart transplant recipients who were suspected of suffering from increased formation of oxygen radicals in the allograft. The levels of lipid peroxides (LPO), glutathione peroxidase (GSH-Px), total-, copper/zinc- and manganese superoxide dismutase (t-SOD, CuZnSOD, MnSOD) were compared in 3 post-transplantation periods (5-90 d vs. 91-365 d vs. >1 y). Significantly increased LPO levels were found (0.27+/-0.04 vs. 0. 13+/-0.02 vs. 0.27+/-0.04 nmol/mg protein) in the first and third period. Increased activities of GSH-Px (39.8+/-3.8 vs. 30.2+/-4.1 vs. 76.7+/-6.5 mU/mg protein), t-SOD (1.57+/-0.10 vs. 1.30+/-0.14 vs. 2.44+/-0.23 U/mg protein) and CuZnSOD (1.09+/-0.08 vs. 0.93+/-0.13 vs. 2.05+/-0.21 U/mg protein) occurred only in the third period. For calculation of time courses more precisely, the single data with respect to time were analyzed with a curve fitting program. Except for the first period, the allograft LPO and GSH-Px levels rose for up to 6 years after transplantation. However, the t-SOD and CuZnSOD activities switched from increase to decrease in the third period. The study provided indication for: first, the potency of the human heart to time-limited increase of the enzymatic antioxidative defense, and secondly, the inability of human heart allografts--despite this adaptation--for complete prevention of myocardial oxidative stress.

A calcium antagonist protects against doxorubicin-induced impairment of calcium handling in neonatal rat cardiac myocytes

The effects of doxorubicin (DOX) on intracellular calcium transients and the cardioprotective effects of a calcium antagonist on DOX-induced impairment of calcium handling were examined in neonatal rat cultured cardiac myocytes. Cultured cardiac myocytes isolated from neonatal Wistar-Kyoto rats were treated with DOX for 24 h. Field-stimulated calcium transients in single myocytes were measured in the presence or absence of isoproterenol using fura-2/AM. Calcium transients were also measured after the addition of DOX to myocytes pretreated with a calcium antagonist, benidipine. DOX reduced the amplitude, maximum velocity of increase and decrease of calcium transients and prolonged the time course of calcium transients and impaired the beta-adrenoceptor responsiveness of calcium transients in a concentration-dependent manner. The DOX-induced impairment of calcium transients and beta-adrenoceptor responsiveness was improved by 10(-8) mol/L of benidipine. However, these improvements decreased with increasing concentrations of benidipine. DOX impaired both the mobilization and removal of intracellular calcium ions in contraction-relaxation cycles and the response of calcium transients to beta-adrenoceptor stimulation. Appropriate concentration of benidipine ameliorated DOX-induced impairment of calcium dynamics, suggesting that benidipine, a long-acting calcium antagonist, has potential clinical usefulness on DOX-induced abnormal calcium handling.

An angiotensin-converting enzyme inhibitor protects against doxorubicin-induced impairment of calcium handling in neonatal rat cardiac myocytes

1. The effects of doxorubicin (DOX) on intracellular calcium transients were examined in neonatal rat cultured cardiac myocytes, as were the cardioprotective effects of an angiotensin-converting enzyme (ACE) inhibitor on DOX-induced impairment of calcium handling. 2. Cultured cardiac myocytes isolated from neonatal Wistar-Kyoto rats were treated with DOX for 24 h. Field-stimulated calcium transients in single myocytes were measured in the presence or in the absence of isoproterenol using fura-2/AM. Calcium transients were also measured after the addition of DOX to myocytes pretreated with M-I (an active metabolite of delapril HCL, an ACE inhibitor. 3. Doxorubicin reduced the amplitude and maximum velocity of increase and decrease of calcium transients, prolonged the time-course of calcium transients and impaired the beta-adrenoceptor responsiveness of calcium transients in a dose-dependent manner. The DOX-induced impairment of calcium transients and beta-adrenoceptor responsiveness was improved by M-I. 4. Doxorubicin impaired both the mobilization and sequestration of intracellular calcium ions in contraction-relaxation cycles and the response of calcium transients to beta-adrenoceptor stimulation. The ACE inhibitor ameliorated DOX-induced impairment of calcium dynamics, suggesting ihat M-I, an active metabolite of delapril, protects against DOX-induced abnormal calcium handling leading to cardiac dysfunction.

Alternations in beta-Adrenoceptor Mechanisms in Hearts Perfused With Xanthine Plus Xanthine Oxidase

BACKGROUND: Although beta-adrenoceptors and adenylyl cyclase are known to be affected upon exposing cardiac membranes to some oxyradical generating systems, the results are conflicting. Furthermore, functional significance of alterations in the beta-adrenoceptor-adenylyl cyclase systems in terms of changes in the inotropic responses to catecholamines is not clear. METHODS AND RESULTS: The positive inotropic effect of isoproterenol was augmented on perfusing the isolated rat hearts with xanthine (X) plus xanthine oxidase (XO) for 5 minutes but was attenuated by perfusion for 15 minutes. The isoproterenol-stimulated adenylyl cyclase activity in cardiac membranes showed an increase at 10 minutes and a decrease at 30 minutes perfusion of hearts with X plus XO. The density of beta-adrenoceptors in cardiac membraners was reduced after 10 minutes and 30 minutes of perfusion with X plus XO, whereas the affinity of beta-adrenoceptors was increased after 10 minutes and reduced after 30 minutes. Although beta-adrenoceptors was increased after 10 minutes and reduced after 30 minutes. Although beta-adrenoceptors were unaltered by 10 minutes of perfusion with X plus XO, their affinity was increased and density was decreased by 30 minutes of perfusion. The agonist competition curves using isoproterenol indicated an increase in the number of coupled receptors in the high affinity state on 10 minutes of perfusion and an increase in the low affinity state of coupled receptor due to 30 minutes of perfusion with X plus XO. The basal as well as forskolin-, NaF- and Gpp(NH)p-stimulated adenylyl cyclase activities in cardiac membranes exhibited an increase after 10 minutes and decrease after 30 minutes of perfusion with X plus XO. Although the presence of superoxide dismutase plus catalase in the perfusion medium prevented most of the alterations due to X plus XO, it did not alter the increased affinity of the beta-adrenoceptor upon perfusing hearts for 10 minutes with X plus XO. CONCLUSIONS: The results in this study suggest the biphasic nature of the oxyradical-induced alterations in both the inotropic responses to catecholamines and the beta-adrenoceptor-mediated signal transduction mechanism in the heart.

Sarcoplasmic reticulum Ca(2+)-pump dysfunction in rat cardiomyocytes briefly exposed to hydroxyl radicals

The effects of hydroxyl radical exposure of intact cardiomyocytes on sarcoplasmic reticulum (SR) function were investigated. For this purpose, isolated rat heart myocytes were exposed briefly (1 min) to the hydroxyl radical generating system (H2O2/FeCl2 or FeSO4) or 5-5'-dithiobis-nitrobenzoic acid (DTNB), a sulfhydryl oxidizing reagent, and following this a SR-enriched fraction was isolated. Marked decreases in the SR calcium uptake activities were seen in the myocytes exposed to either the hydroxyl radical-generating system or DTNB. The exposure of myocytes to the hydroxyl radical, but not DTNB, markedly increased the amount of malonyldialdehyde (MDA) in the subsequently isolated SR. Total sulfhydryl group content in SR was decreased by exposure of myocytes to DTNB. Further, there was a significant decrease in [3H]-NEM binding to SR isolated from the hydoxyl radical-treated myocytes indicating that sulfhydryl groups are affected (oxidized). Both mannitol and catalase were found to offer complete protection against the inhibitory effect of peroxide +/- iron on calcium uptake. Also the above-mentioned alterations in both MDA and sulfhydryl group content were prevented by mannitol and catalase. Exogenously added cyclic AMP-dependent protein kinase (A-PK) or calmodulin (CAM) increased SR calcium uptake activity. In the SR isolated from the treated myocytes, the stimulatory effects of A-PK and CAM were also seen, although under all assay conditions calcium uptakes were of lower magnitude. The findings are consistent with the view that the damaging effect of the hydroxyl radical and DTNB on the functioning of SR occurs rapidly in the intact cardiomyocytes. The hydroxyl radical-provoked damage involves both protein sulfhydryl and lipid oxidation.

Changes in adrenergic receptors during the development of heart failure

Moderate and severe stages of congestive heart failure due to the loss of myocardium upon coronary occlusion in rats was associated with an increase in alpha-adrenergic receptors and a decrease in beta-adrenergic receptors in the viable left ventricle. However, at early stages of heart failure the number of beta-adrenergic receptors was decreased without any changes in the number of alpha-adrenergic receptors. The affinities of these receptors to alpha receptor antagonist (3H-prazosin) and beta receptor antagonist (3H-dihydroalprenolol) were not altered in the failing hearts. On the other hand, the pattern of changes in both alpha- and beta-adrenergic receptors in heart membranes treated with oxygen free radical generating system was different from that seen in the failing hearts. In particular, the affinities for these receptors were decreased whereas the number of beta-receptors was increased and the number of alpha-receptors was decreased or unchanged. These results indicate that alterations in the adrenergic receptors in heart failure are not due to the formation of oxygen free radicals.