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.

Suppression of formalin-induced nociception by cilnidipine, a voltage-dependent calcium channel blocker.

Cilnidipine is a 1,4-dihydropyridine-derived voltage-dependent calcium channel (VDCC) blocker and suppresses N-type VDCC currents in addition to L-type VDCC currents. An earlier investigation has suggested that intrathecally injected cilnidipine produces antinociception by blocking N-type VDCCs in mice. The present study using the rat formalin model examined antinociceptive effects of intrathecally and orally administered cilnidipine to elucidate a putative site of antinociception of cilnidipine, assess the efficacy of oral cilnidipine for pain relief, and clarify the mechanism(s) responsible for the antinociceptive effect of oral cilnidipine. Cilnidipine (whether intrathecal or oral) suppressed nociception in phases 1 and 2 of the formalin model. In addition, the potency of oral cilnidipine to suppress formalin-induced nociception in phase 2 was greater than that of oral gabapentin, a clinically available drug for treatment of neuropathic pain. Cilnidipine elicited antinociceptive effects without neurological side-effects including serpentine-like tail movement, whole body shaking, and allodynia. Such side-effects can be induced by higher doses of intrathecal ziconotide, a clinically available N-type VDCC blocker. In contrast, orally administered nifedipine, an L-type VDCC blocker, had no effect on either phase of formalin-induced nociception. These results suggest that cilnidipine acts on the spinal cord to produce antinociception and is efficacious for pain relief after oral administration with better safety profile than that of ziconotide. Furthermore, the failure of orally administered nifedipine to affect formalin-induced nociception raises the possibility that oral cilnidipine produces antinociception through, at least in part, spinal N-type VDCC blockade.

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.

Discovery, structure-activity relationship study, and oral analgesic efficacy of cyproheptadine derivatives possessing N-type calcium channel inhibitory activity.

Antiallergic drug cyproheptadine (Cyp) is known to have inhibitory activities for L-type calcium channels in addition to histamine and serotonin receptors. Since we found that Cyp had an inhibitory activity against N-type calcium channel, Cyp was optimized to obtain more selective N-type calcium channel blocker with analgesic action. As a consequence of the optimization, we found 13 with potent N-type calcium channel inhibitory activity which had lower inhibitory activities against L-type calcium channel, histamine (H1), and serotonin (5-HT2A) receptors than those of Cyp. 13 showed an oral analgesic activity in rat formalin-induced pain model.

Isolation and characterization of aminopeptidase (Jc-peptidase) from Japanese cedar pollen (Cryptomeria japonica).

An aminopeptidase, Jc-peptidase, was purified from Japanese cedar pollen by seven steps, including precipitation with ammonium sulfate, ion-exchange chromatography, gel filtration, hydrophobic interaction chromatography on phenyl-agarose, and high-performance liquid chromatography. Purified Jc-peptidease has a molecular weight of 42 kDa and hydrolyzes the synthetic substrates of L-phenylalanyl-4-methylcoumaryl-7-amide (Phe-MCA) with Km = 5 x 10(-5) M, Tyr-MCA with Km = 7 x 10(-4) M, Leu-MCA with Km = 1 x 10(-3) M, and Met-MCA with Km = 1 x 10(-3) M. Other MCA analogues such as Arg-MCA or Glu-MCA failed to serve as its substrates. The activity was inhibited in the presence of phebestin, [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl-L-valyl]-L-phenylalanine, with Ki = 4.7 x 10(-5) M, or bestatin, [(2S,3R)-3-amino-2-hydroxy-4-phenylbutanoyl]-L-leucine, with Ki = 1.1 x 10(-4) M. According to amino acid sequence analysis, the N-terminal amino group seems to be blocked. The physiological function of the aminopeptidase (Jc-peptidase) has not been clarified in vivo.