Cardioselective antiischemic ATP-sensitive potassium channel (K(ATP)) openers. 6. Effect of modifications at C6 of benzopyranyl cyanoguanidines

Cardioprotective effects of different flavonoids against myocardial ischaemia/reperfusion injury in Langendorff-perfused rat hearts

OBJECTIVE

Flavonoids are important components of 'functional foods', with beneficial effects on the cardiovascular function, mainly due to their antioxidant activity. Many flavonoids exert antihypertensive, anti-atherosclerotic and antiplatelet activity and positive effects against endothelial dysfunction. Recent evidence indicates that they exert cardioprotective effects against myocardial ischaemia/reperfusion (I/R) injury. The aim of this work was to investigate these properties for flavonoids with different structural characteristics.

METHODS

In this work, the cardioprotective effects of eight flavonoids endowed with different structural characteristics were tested on Langendorff-perfused rat hearts submitted to 30 min of global ischaemia followed by 120 min of reperfusion (I/R).

KEY FINDINGS

Only the 5-hydroxy-substituted derivatives, such as 5-hydroxy flavone, apigenin, chrysin and naringenin, conferred on the hearts an improved post-ischaemic functional recovery associated with lower extension of tissue injury. A similar pharmacological profile was exhibited by 5-methoxy flavone. In contrast, 6-hydroxy flavone, 7-hydroxy flavone and 4'-hydroxy flavanone did not confer significant protection against the injury induced by I/R.

CONCLUSIONS

Some flavonoids exhibit direct cardioprotective effects against the injury induced by drastic I/R and this pharmacological property seems to be related to their structural characteristics. Such an influence of structural requirements seems to indicate that the cardioprotective effects may be due to the interaction with specific pharmacological targets.

KR-31761, a novel K+(ATP)-channel opener, exerts cardioprotective effects by opening both mitochondrial K+(ATP) and Sarcolemmal K+(ATP) channels in rat models of ischemia/reperfusion-induced heart injury

The cardioprotective effects of KR-31761, a newly synthesized K+(ATP) opener, were evaluated in rat models of ischemia/reperfusion (I/R) heart injury. In isolated rat hearts subjected to 30-min global ischemia/30-min reperfusion, KR-31761 perfused prior to ischemia significantly increased both the left ventricular developed pressure (% of predrug LVDP: 17.8, 45.1, 54.2, and 62.6 for the control, 1 microM, 3 microM, and 10 microM, respectively) and double product (DP: heart rate x LVDP; % of predrug DP: 17.5, 44.9, 56.2, and 64.5 for the control, 1 microM, 3 microM, and 10 microM, respectively) at 30-min reperfusion while decreasing the left ventricular end-diastolic pressure (LVEDP). KR-31761 (10 microM) significantly increased the time to contracture during the ischemic period, whereas it concentration-dependently decreased the lactate dehydrogenase release during reperfusion. All these parameters were significantly reversed by 5-hydroxydecanoate (5-HD, 100 microM) and glyburide (1 microM), selective and nonselective blockers of the mitochondrial K+(ATP) (mitoK+(ATP)) channel and K+(ATP) channel, respectively. In anesthetized rats subjected to 30-min occlusion of left anterior descending coronary artery/2.5-h reperfusion, KR-31761 administered 15 min before the onset of ischemia significantly decreased the infarct size (72.2%, 55.1%, and 47.1% for the control, 0.3 mg/kg, i.v., and 1.0 mg/kg, i.v., respectively); and these effects were completely and almost completely abolished by 5-HD (10 mg/kg, i.v.) and HMR-1098, a selective blocker of sarcolemmal K+(ATP) (sarcK+(ATP)) channel (6 mg/kg, i.v.) administered 5 min prior to KR-31761 (72.3% and 67.9%, respectively). KR-31761 only slightly relaxed methoxamine-precontracted rat aorta (IC50: > 30.0 microM). These results suggest that KR-31761 exerts potent cardioprotective effects through the opening of both mitoK+(ATP) and sarcK+(ATP) channels in rat hearts with a minimal vasorelaxant effect.

Cardioprotective effects of BMS-180448, a prototype mitoK(ATP) channel opener, and the role of salvage kinases, in the rat model of global ischemia and reperfusion heart injury

To investigate the involvement of reperfusion-induced salvage kinases (RISK) as possible signaling molecules for the cardioprotective effects of BMS-180448, a prototype mitochondrial ATP-sensitive K+ (mitoK(ATP)) channel opener, we measured its cardioprotective effects in a rat model of ischemia/reperfusion (I/R) heart injury, together with western blotting analysis of five different signaling proteins. In isolated rat hearts subjected to 30-min global ischemia followed by 30-min reperfusion, BMS-180448 (1, 3 and 10 microM) significantly increased reperfusion left ventricular developed pressure (LVDP) and 30-min reperfusion double product (heart rate x LVDP) in a concentration-dependent manner, while decreasing left ventricular end-diastolic pressure (LVEDP) throughout reperfusion period in a concentration-dependent manner. SDS-PAGE/western blotting analysis of left ventricle reperfused for 30 min revealed that BMS-180448 significantly decreased phospho-GSK3beta at high concentration, whereas it tended to increase slightly phospho-eNOS and phospho-p70S6K with concentration. However, BMS-180448 had no effect on phospho-Akt and phospho-Bad. These results suggest that the cardioprotective effects of BMS-180448 against I/R heart injury may result from direct activation of mitoK(ATP) channel in cardiomyocytes, with the minimal role of RISK pathway in the activation of this channel and the cardioprotective effects of BMS-180448.

Benzopyran sulfonamides as KV1.5 potassium channel blockers

K(V)1.5 blockers have the potential to be atrium-selective agents for treatment of atrial fibrillation. The benzopyrans provide a template for the synthesis of potent and selective K(V)1.5 blockers.

N-[1-Aryl-2-(1-imidazolo)ethyl]-guanidine derivatives as potent inhibitors of the bovine mitochondrial F1F0 ATP hydrolase

A series of substituted guanidine derivatives were prepared and evaluated as potent and selective inhibitors of mitochondrial F(1)F(0) ATP hydrolase. The initial thiourethane derived lead molecules possessed intriguing in vitro pharmacological profiles, though contained moieties considered non-drug-like. Analogue synthesis efforts led to compounds with maintained potency and superior physical properties. Small molecules in this series which potently and selectivity inhibit ATP hydrolase and not ATP synthase may have utility as cardioprotective agents.

KATP channel openers: structure-activity relationships and therapeutic potential

ATP-sensitive potassium channels (K(ATP) channels) are heteromeric complexes of pore-forming inwardly rectifying potassium channel subunits and regulatory sulfonylurea receptor subunits. K(ATP) channels were identified in a variety of tissues including muscle cells, pancreatic beta-cells, and various neurons. They are regulated by the intracellular ATP/ADP ratio; ATP induces channel inhibition and MgADP induces channel opening. Functionally, K(ATP) channels provide a means of linking the electrical activity of a cell to its metabolic state. Shortening of the cardiac action potential, smooth muscle relaxation, inhibition of both insulin secretion, and neurotransmitter release are mediated via K(ATP) channels. Given their many physiological functions, K(ATP) channels represent promising drug targets. Sulfonylureas like glibenclamide block K(ATP) channels; they are used in the therapy of type 2 diabetes. Openers of K(ATP) channels (KCOs), for example, relax smooth muscle and induce hypotension. KCOs are chemically heterogeneous and include as different classes as the benzopyrans, cyanoguanidines, thioformamides, thiadiazines, and pyridyl nitrates. Examples for new chemical entities more recently developed as KCOs include cyclobutenediones, dihydropyridine related structures, and tertiary carbinols.

Molecular modeling and QSAR studies on K(ATP) channel openers of the benzopyran type

The present paper describes our molecular modeling and quantitative structure-activity relationships (QSARs) studies on K(ATP) channel openers (KCOs) of the benzopyran type. In the first part we performed molecular modeling investigations with seven benzopyrans, varied at the C3- and C4-positions, in order to understand which molecular features at these positions are essentially effecting the biological activity. The impact of C6-substitution on biological activity was studied in the second part via HANSCH analysis. For this purpose physicochemical properties (charge distributions, lowest unoccupied molecular orbital (LUMO) energies, desolvation energies, volumes and dipole moments) were calculated for a set of 50 C6-varied benzopyrans. A QSAR equation was developed showing a relationship between the vasodilator activity and the direction of the dipole vector of the ligands. The conclusion can be drawn that a direct interaction between the C6-substituents and the receptor structure is not of primary importance. However, the substitutents influence the orientation of the whole ligand approaching the binding site. An unfavorably oriented ligand cannot bind to the binding site, thus exhibiting weak activity.