Hajime Koganei

Antisympathetic and hemodynamic property of a dual L/N-type Ca2+ channel blocker cilnidipine in rats

The in vivo antisympathetic property of a dual L/N-type Ca(2+) channel blocker cilnidipine compared with that of typical N-type Ca(2+) channel blockers has never been clarified. We investigated the effects of the drug on a sympathetic nerve-mediated vascular response and vasodilating action in rats in comparison with those of an N-type Ca(2+) channel blocker omega-conotoxin MVIIA. In pithed rats, omega-conotoxin MVIIA preferentially suppressed the sympathetic nerve stimulation-induced pressor response, whereas cilnidipine suppressed the pressor response induced by sympathetic nerve stimulation and angiotensin II. In anesthetized rats, cilnidipine or omega-conotoxin MVIIA decreased mean blood pressure, while heart rate was decreased by omega-conotoxin MVIIA, but slightly increased by cilnidipine. These results suggest that cilnidipine can affect sympathetic N-type Ca(2+) channels in addition to vascular L-type Ca(2+) channels in antihypertensive doses in the rat in vivo. The antisympathetic activity of cilnidipine is not excessive for an antihypertensive drug in comparison with that of omega-conotoxin MVIIA.

Antithrombotic activity of AT-1015, a potent 5-HT2A receptor antagonist, in rat arterial thrombosis model and its effect on bleeding time

The antithrombotic activity of N-[2-(4-(5H-dibenzo[a,d]cyclohepten-5-ylidene)piperidino)ethyl]-1-formyl-4-piperidinecarboxamide monohydrochloride monohydrate (AT-1015; a 5-HT(2A) receptor antagonist) was studied in a photochemically induced arterial thrombosis (PIT) model in the rat femoral artery, and in the tail transection bleeding time test. Ticlopidine (an antiplatelet agent) and sarpogrelate (a selective 5-HT(2A) receptor antagonist) were studied as reference compounds. Pretreatment with AT-1015 (1 mg/kg, p.o.) significantly prolonged the time required to occlusion of the artery with thrombus, and the effect (3 mg/kg, p.o.) persisted for 24 h with significant inhibition of 5-HT-induced vascular contraction. Ticlopidine and sarpogrelate also significantly prolonged the time to occlusion at 100 mg/kg, p.o. Sarpogrelate (300 mg/kg, p.o.) showed the similar antithrombotic efficacy to AT-1015 (3 mg/kg, p.o.), while the effect disappeared within 6 h. No significant bleeding time prolongation was observed at 10 mg/kg of AT-1015, which is 10 times higher than the antithrombotic effective dose; whereas ticlopidine significantly prolonged bleeding time at the same dose as the antithrombotic effective dose. These results suggested that AT-1015 is a potent and long-acting oral antithrombotic agent in this model, which may be elucidated by its potent and long-acting inhibition of vasoconstriction through 5-HT(2A) receptor.

Different Effects of L/N-Type and L-Type Calcium Channel Blockers on the Renin-Angiotensin-Aldosterone System in SHR/Izm

Background: The L/N-type calcium channel blocker (CCB) cilnidipine has been demonstrated to suppress sympathetic nerve activity. In the present study, we investigated the effects of cilnidipine on the renin-angiotensin-aldosterone system (RAAS) in SHR/Izm rats to confirm differences from the effects of L-type CCB. Methods: Male SHR/Izm rats received vehicle, cilnidipine (0.3, 3 mg/kg) or amlodipine (0.3, 3 mg/kg) by gavage for systolic blood pressure (SBP) measurement. For biochemical analyses, the experiments were performed under anesthesia. Results: Low doses of cilnidipine or amlodipine had no effect on SBP or RAAS parameters. A high dose of either drug produced similar effects on SBP levels. Although cilnidipine had no effect on plasma renin activity or the plasma angiotensin II level, amlodipine significantly increased these parameters as compared to levels in the vehicle group. The cilnidipine group had a significantly lower plasma aldosterone level and renal cortical tissue norepinephrine level than the vehicle group. Conclusions: Cilnidipine had effects different from those of L-type CCB on the RAAS in SHR/Izm rats. Our results indicate that suppression of RAAS hyperactivity by cilnidipine can be partly explained by its sympatholytic action.

AT-1015, a novel serotonin (5-HT)2 receptor antagonist, blocks vascular and platelet 5-HT2A receptors and prevents the laurate-induced peripheral vascular lesion in rats.

The serotonin (5-HT2A) antagonistic activities and the protective effect on laurate-induced peripheral vascular lesions of AT-1015, a novel 5-HT2 receptor antagonist, were investigated. In platelet aggregation, AT-1015 selectively inhibited in vitro 5-HT2A receptor-mediated aggregation, and the activity was almost equivalent to that of ketanserin (5-HT2A/2C receptor antagonist) and 100 times more potent than sarpogrelate (5-HT2A receptor antagonist). AT-1015 also inhibited 5-HT2A receptor-mediated aggregation by oral administration in rat, and the dose required for inhibition was equivalent to ketanserin. In a 5-HT-induced vasoconstriction study in rat, AT-1015 slightly reduced maximal contraction and caused a rightward shift of the concentration-response curve (pKB value, 9.5), which was unlike competitive inhibitors such as ketanserin and sarpogrelate (pA2 value, 9.3 and 8.7, respectively). Moreover, the ex vivo inhibitory activity significantly remained after oral administration (1 mg/kg). In the rat peripheral vascular lesion model, AT-1015 (1 mg/kg, p.o.) effectively prevented progression of peripheral lesions, and it was more potent compared with ketanserin, sarpogrelate, and cilostazol. These results suggest that AT-1015 is a potent 5-HT2A receptor antagonist, and its insurmountable antagonism may be relevant to its therapeutic potential in peripheral vascular disease.

The structure–activity relationship study on 2-, 5-, and 6-position of the water soluble 1,4-dihydropyridine derivatives blocking N-type calcium channels

In order to find an injectable and selective N-type calcium channel blocker, we have performed the structure-activity relationship (SAR) study on the 2-, 5-, and 6-position of 1,4-dihydropyridine-3-carboxylate derivative APJ2708 (2), which is a derivative of Cilnidipine and has L/N-type calcium channel dual inhibitory activities. As a consequence of the optimization, 6-dimethylacetal derivative 7 was found to have an effective inhibitory activity against N-type calcium channels with more than 170-fold lower activity for L-type channel compared to that of APJ2708.

Asymmetric synthesis and biological evaluations of (+)- and (−)-6-dimethoxymethyl-1,4-dihydropyridine-3-carboxylic acid derivatives blocking N-type calcium channels

An efficient asymmetric synthesis of 1,4-dihydropyridine derivatives is described. The key step is the stereoselective Michael addition using t-butyl ester of L-valine as a chiral auxiliary to achieve good ee (>95% for all the tested experiments) and moderate yield. With this method, (+)-4-(3-chlorophenyl)-6-dimethoxymethyl-2-methyl-1,4-dihydropyridine-3,5-dicarboxylic acid cinnamyl ester was obtained and was characterized as a promising N-type calcium channel blocker with improved selectivity over L-type compared to its (-)- and racemic isomers.

Discovery and evaluation of selective N-type calcium channel blockers: 6-Unsubstituted-1,4-dihydropyridine-5-carboxylic acid derivatives

A structure-activity relationship study of 6-unsubstituted-1,4-dihydropyridine and 2,6-unsubstituted-1,4-dihydropyridine derivatives was conducted in an attempt to discover N-type calcium channel blockers that were highly selective over L-type calcium channel blockers. Among the tested compounds, (+)-4-(3,5-dichloro-4-methoxy-phenyl)-1,4-dihydro-pyridine-3,5-dicarboxylic acid 3-cinnamyl ester was found to be an effective and selective N-type calcium channel blocker with oral analgesic potential.