Structure-activity relationship of a novel K+ channel opener, KRN4884, and related compounds in porcine coronary artery

Characterization and bioactivity of novel calcium antagonists - N-methoxy-benzyl haloperidol quaternary ammonium salt

BACKGROUND AND PURPOSE

Calcium antagonists play an important role in clinical practice. However, most of them have serious side effects. We have synthesized a series of novel calcium antagonists, quaternary ammonium salt derivatives of haloperidol with N-p-methoxybenzyl (X1), N-m-methoxybenzyl (X2) and N-o-methoxybenzyl (X3) groups. The objective of this study was to investigate the bioactivity of these novel calcium antagonists, especially the vasodilation activity and cardiac side-effects. The possible working mechanisms of these haloperidol derivatives were also explored.

EXPERIMENTAL APPROACH

Novel calcium antagonists were synthesized by amination. Compounds were screened for their activity of vasodilation on isolated thoracic aortic ring of rats. Their cardiac side effects were explored. The patch-clamp, confocal laser microscopy and the computer-fitting molecular docking experiments were employed to investigate the possible working mechanisms of these calcium antagonists.

RESULTS

The novel calcium antagonists, X1, X2 and X3 showed stronger vasodilation effect and less cardiac side effect than that of classical calcium antagonists. They blocked L-type calcium channels with an potent effect order of X1 > X2 > X3. Consistently, X1, X2 and X3 interacted with different regions of Ca2+-CaM-CaV1.2 with an affinity order of X1 > X2 > X3.

CONCLUSIONS

The new halopedidol derivatives X1, X2 and X3 are novel calcium antagonists with stronger vasodilation effect and less cardiac side effect. They could have wide clinical application.

Design, synthesis, and pharmacological evaluation of haloperidol derivatives as novel potent calcium channel blockers with vasodilator activity

Several haloperidol derivatives with a piperidine scaffold that was decorated at the nitrogen atom with different alkyl, benzyl, or substituted benzyl moieties were synthesized at our laboratory to establish a library of compounds with vasodilator activity. Compounds were screened for vasodilatory activity on isolated thoracic aorta rings from rats, and their quantitative structure-activity relationships (QSAR) were examined. Based on the result of QSAR, N-4-tert-butyl benzyl haloperidol chloride (16c) was synthesized and showed the most potent vasodilatory activity of all designed compounds. 16c dose-dependently inhibited the contraction caused by the influx of extracellular Ca(2+) in isolated thoracic aorta rings from rats. It concentration-dependently attenuated the calcium channel current and extracellular Ca(2+) influx, without affecting the intracellular Ca(2+) mobilization, in vascular smooth muscle cells from rats. 16c, possessing the N-4-tert-butyl benzyl piperidine structure, as a novel calcium antagonist, may be effective as a calcium channel blocker in cardiovascular disease.

Effects of N-n-butyl haloperidol iodide on L-type calcium channels and intracellular free calcium in rat ventricular myocytes

The ability of N-n-butyl haloperidol iodide (F2) to cause vasodilation, and thereby produce a cardioprotective effect, has been well documented. The aim of this study was to investigate whether F2 might act as a Ca2+ antagonist. Myocytes were obtained from rat heart, and the whole-cell patch-clamp technique was used to record Ca2+ current. Laser scanning confocal microscopy was used to measure intracellular free calcium ([Ca2+]i). The results obtained from this study demonstrate that F2 reduced calcium current (ICa) in a concentration-dependent manner with an IC50 of 1.19 micromol/L, upshifted the current-voltage curve of ICa, shifted the inactivation kinetics of ICa leftward, and slowed down the recovery of ICa from inactivation. F2 decreased the fluorescent intensity of [Ca2+]i elevation induced by KCl with an IC50 of 1.61 micromol/L, and had no effects on the intracellular calcium release induced by caffeine and inositol-1,4,5-trisphosphate. These findings indicate that F2 may act as a calcium antagonist, which could account for its cardiovascular benefits.

Relaxation of human placental arteries and veins by ATP-sensitive potassium channel openers

BACKGROUND

Adenosine triphosphate (ATP)-sensitive potassium channels (K(ATP)) are important modulators of vascular tone. Preliminary data from our laboratory suggests that K(ATP) channels are expressed in the fetoplacental vasculature where addition of pinacidil, a specific K(ATP) opener, promotes relaxation. We aimed to assess the effects of KRN2391 and KRN4884 on the fetoplacental vasculature, which are putative K(ATP) channel openers.

MATERIALS AND METHODS

Functional activity of K(ATP) channels was assessed in chorionic plate arteries and veins using wire myography. Cromakalim-, KRN2391- and KRN4884-induced relaxations were assessed in the presence and absence of agonist-induced pretone. Cromakalim, an established K(ATP) channel opener, acted as control.

RESULTS

KRN2391 evoked significantly greater relaxation of chorionic plate arteries and veins than either KRN4884 or cromakalim. KRN2391-induced relaxation of precontracted arteries and veins was reduced in the presence of inhibitors of the nitric oxide pathway (L-NNA or LY83583). With KRN4884, there was no contribution of nitric oxide to the induced relaxation.

CONCLUSIONS

We conclude that K(ATP) channels play an important role in controlling placental vascular tone. KRN2391 induces relaxation of human placental blood vessels by activation of K(ATP) channels and via activation of nitric oxide-dependent pathways.

Effects of KRN4884, a Novel K+ Channel Opener, on Ionic Currents in Rabbit Femoral Arterial Myocytes

Effects of KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine), a novel K(+) channel opener, on ionic currents were examined in rabbit femoral arterial myocytes (RFAMs). Under whole-cell clamp conditions where cells were superfused with 5.9 mM K(+) bathing solution, KRN4884 elicited an outward current at -30 mV. KRN4884-induced current had a reversal potential of -78 mV and was abolished by application of glibenclamide (glib). KRN4884 was approximately 43 times more potent than levcromakalim in activating an ATP-sensitive K(+) current (I(K-ATP)). On the other hand, KRN4884 affected neither voltage-dependent Ca(2+) nor delayed rectifier K(+) channel currents. In the inside-out patch clamp configuration where cells were superfused with the symmetrical 140 mM K(+) solution, KRN4884 activated 47 pS K(+) channels in the presence of adenosine diphosphate. Similar 47 pS K(+) channels, which were reversibly inhibited by glib, were recorded under outside-out patch conditions. Using RT-PCR analysis, we found that inward rectifier K channel 6.1 (Kir6.1) and sulfonylurea 2B (SUR2B) transcripts were predominantly expressed in rabbit femoral artery. These results indicate that KRN4884 potently activates I(K-ATP) in RFAMs. The KRN4884-sensitive 47 pS K(+) channel activity underlying I(K-ATP) is a vascular type K(ATP) channel consisting of Kir6.1 and SUR2B and has similar characteristics to those of ATP-sensitive K(+) channels activated by K(+) channel openers in other types of smooth muscles.

ATP-sensitive potassium channel openers may mimic the effects of hypoxic preconditioning on the coronary artery

BACKGROUND

This study was designed to investigate the effects of the potassium channel opener KRN4884 in mimicking hypoxic preconditioning on coronary arteries and to explore the possible mechanisms.

METHODS

In the organ chamber, porcine coronary artery rings (n = 96) were studied in 6 groups (n = 16 in each group): I.

CONTROL

normoxia (pO2 > 200 mmHg); II. Hypoxia-reoxygenation: 60-minute hypoxia (pO2 < 15 mmHg) followed by 30-minute reoxygenation; III. Preconditioning: 5-minute hypoxia followed by 10-minute reoxygenation prior to hypoxia-reoxygenation; IV. KRN4884-pretreatment: KRN4884 (30 microM) was added into the chamber 20 minutes before hypoxia-reoxygenation; V. 5-HD-pretreatment: sodium 5-hydroxydecanoate (5-HD, 10 microM) was given 20 minutes prior to KRN4884-pretreatment; and VI. GBC-pretreatment: glibenclamide (GBC, 3 microM) was added 20 minutes prior to KRN4884-pretreatment. Concentration-contraction curves for U46619 (n = 8 in each group) were constructed. Concentration-relaxation curves for bradykinin (n = 8 in each group) related to endothelium-derived hyperpolarizing factor (EDHF) were established in the rings precontracted with U46619 (30 microM) in the presence of Nomega-nitro-L-arginine (L-NNA, 300 microM) and indomethacin (7 microM).

RESULTS

The maximal relaxation induced by bradykinin was reduced in hypoxia-reoxygenation (54.6 +/- 4.3% versus 85.2 +/- 5.7% in control, p = 0.001). This reduced relaxation was recovered in KRN4884-pretreatment (78.9 +/- 3.7%, p = 0.014) or preconditioning (79.9 +/- 3.7%, p = 0.009). 5-HD- but not GBC-pretreatment abolished the effect of KRN4884-pretreatment (78.9 +/- 3.7% versus 53.5 +/- 4.7%, p = 0.009).

CONCLUSIONS

Hypoxia-reoxygenation reduces the relaxation mediated by EDHF in the coronary artery. This function can be restored by either hypoxic preconditioning or the potassium channel opener KRN4884. The mechanism of such effect is mainly related to the mitochondrial ATP-sensitive K+ channels.

Effects of potassium channel opener KRN4884 on human conduit arteries used as coronary bypass grafts

AIMS

The effects of a new potassium channel opener KRN4884 on human arteries have not been studied. This study was designed to investigate the effects of KRN4884 on the human internal mammary artery (IMA) in order to provide information on possible clinical applications of KRN4884 for preventing and relieving vasospasm of arterial grafts in coronary artery bypass grafting.

METHODS

IMA segments (n = 140) taken from patients undergoing coronary surgery were studied in the organ chamber. Concentration-relaxation curves for KRN4884 were established in the IMA precontracted with noradrenaline (NA), 5-hydroxytryptamine (5-HT), angiotensin II (ANG II), and endothelin-1 (ET-1). The effect of glibenclamide (GBC) on the KRN4884-induced relaxation was also examined in NA or 5-HT-precontracted IMA. Concentration-contraction curves for the four vasoconstrictors were constructed without/with pretreatment of KNR4884 (1 or 30 microM) for 15 min.

RESULTS

KRN4884 induced less relaxation (P < 0.05) in the precontraction induced by ET-1 (72.9 +/- 5.5%) than by ANG II (94.2 +/- 3.2%) or NA (93.7 +/- 4.1%) with lower EC50 (P < 0.05) for ANG II (-8.54 +/- 0.54 log M) than that for NA (-6.14 +/- 0.15 log M) or ET-1 (-6.69 +/- 0.34 log M). The relaxation in the IMA pretreated with GBC was less than that in control (P < 0.05). KRN4884-pretreatment significantly reduced the contraction (P < 0.05) induced by NA (151.3 +/- 18.4% vs 82.7 +/- 8. 7%), 5-HT (82.7 +/- 12.2% vs 30.1 +/- 7.3%), and ANG II (24.3 +/- 6. 3% vs 5.4 +/- 1.6%), but did not significantly reduce the contraction induced by ET-1 (P > 0.05).

CONCLUSION

KRN4884 has marked vasorelaxant effects on the human IMA contracted by a variety of vasoconstrictors and the effect is vasoconstrictor-selective.

Effects of the K+ channel opener KRN4884 on the cardiovascular metabolic syndrome model in rats

We examined the effects of the potassium channel opener KRN4884 (5-amino-N-[2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine ) on cardiovascular metabolic syndrome (i.e., syndrome X), in rats. High-fructose diet rats developed hypertension, hypertriglyceridemia, increased total cholesterol/HDL (high-density lipoprotein)-cholesterol ratio, and hyperinsulinemia, KRN4884 (0.3-3.0 mg/kg, twice a day for 14 days, p.o.) alleviated the risk factors in fructose-fed rats. Furthermore, fructose-fed rats exhibited impairment of glucose tolerance and excess insulin secretion when loaded with glucose orally. Treatment with KRN4884 (1.0 mg/kg, twice a day for 14 days, p.o.) improved the glucose intolerance and inhibited hypersecretion of insulin in the glucose-loaded, fructose-fed rats. In contrast, KRN4884 (0.3-1.0 mg/kg, twice a day for 10 days, p.o.) did not affect serum triglyceride, cholesterol, glucose, or insulin concentrations in normal rats. LPL (lipoprotein lipase) activities in skeletal muscle and adipose tissue, and HTGL (hepatic triglyceride lipase) activity in liver were measured after administration of KRN4884 or vehicle twice a day for 14 days in fructose-fed rats. KRN4884 caused a significant increase in LPL activity in muscle and tended to increase LPL activity in adipose tissue in fructose-fed rats. HTGL was decreased in fructose-fed rats as compared with normal controls and was unaffected by KRN4884. These findings suggested that KRN4884 enhances insulin sensitivity and LPL activity, which are related to glucose and lipid metabolism and may be useful for the treatment of syndrome X.

Effects of KRN4884 (a novel K+ channel opener), levcromakalim, nilvadipine and propranolol on endothelin-1-induced heart disorders in anesthetized rats

The effects of KRN4884 (5-amino-N-[2-(2-chrolophenyl)ethyl]-N'-cyano-3-pyridinecarboxa midine), a novel K+ channel opener, on the electrocardiogram changes caused by the intracoronary administration of endothelin-1 (ET-1) were studied in anesthetized rats and compared with the effects of levcromakalim, a K+ channel opener; nilvadipine, a Ca2+ antagonist; and propranolol, a beta-adrenoceptor antagonist. KRN4884 (50 microg/kg, i.v.) and levcromakalim (300 microg/kg, i.v.) inhibited the ST segment elevation and the development of arrhythmias induced by ET-1 (5 microg, i.c.) and decreased the incidence of death. Nilvadipine (300 microg/kg, i.v.) and propranolol (1000 and 3000 microg/kg, i.v.) each prevented the ST segment elevation, but the suppressions of the occurrence of arrhythmias produced by nilvadipine and propranolol were less than that shown by KRN4884. KRN4884 (30 and 50 microg/kg, i.v.), levcromakalim (100 and 300 microg/kg, i.v.) and nilvadipine (100 and 300 microg/kg, i.v.) significantly decreased the mean blood pressure in a dose-dependent manner, but propranolol did not. The heart rate was decreased by nilvadipine (100 and 300 microg/kg, i.v.) and propranolol (1000 and 3000 microg/kg, i.v.), but was not affected by KRN4884 (30 and 50 microg/kg, i.v.) or levcromakalim (100 and 300 microg/kg, i.v.). These results suggest that pretreatments with KRN4884 and levcromakalim are more effective on ET-1-induced electrocardiogram changes than those with nilvadipine and propranolol.

Protective effect of the K+ channel opener KRN4884 on peripheral occlusive arterial disease in rats

1. The effect of the potassium channel opener KRN4884 on the peripheral arterial occlusion model induced by laurate was examined and compared with that of beraprost sodium and nilvadipine. 2. KRN4884 or beraprost sodium prevented macroscopic changes in the paw after the injection of laurate. In contrast, nilvadipine did not improve the lesions. 3. KRN4884 produced a dose-dependent increase in gastrocnemius blood flow in the chronic femoral artery-ligated rats. The effect of KRN4884 on the blood flow was stronger in the hypoxic muscle than in the normal muscle. 4. KRN4884 did not have a direct antiplatelet aggregation activity. 5. These findings suggest that KRN4884 is useful for the therapy of peripheral arterial occlusive disease and that the effect of KRN4884 is associated with an increase in blood flow in ischemic skeletal muscle.

Effects of the potassium channel openers KRN4884 and levcromakalim on the contraction of rat aorta induced by A23187, compared with nifedipine

We examined the different vasodilatory effects of the K+ channel openers levcromakalim and 5-amino-N- [2-(2-chlorophenyl)ethyl]-N'-cyano-3-pyridinecarboxamidine (KRN4884), and the Ca2+ channel blocker nifedipine in the rat aorta. KRN 4884 (10(-10)-10(-5) M) and nifedipine (10(-10)-10(-5) M) produced concentration-dependent relaxation in the rat aorta precontracted by 25 mM KCl. The K+ channel blocker glibenclamide (1 microM) inhibited the relaxation induced by KRN4884 but did not influence nifedipine-induced relaxation. KRN4884 had almost no effect on contraction induced by 80 mM KCl, whereas nifedipine completely relaxed the muscle precontracted by 80 mM KCl, whereas nifedipine completely relaxed the muscle precontracted by 80 mM KCl. These results indicate that KRN4884 is a K+ channel opener. We investigated the relaxant effects of KRN4884 (10(-10)-10(-5) M), levcromakalim (10(-9)-10(-5) M) and nifedipine (10(-9)-10(-5) M) on A23187 (1 microM)-induced contraction. KRN4884 and levcromakalim had a potent relaxant effect but nifedipine only a weak effect on the smooth muscle contracted by A23187. Glibenclamide (1 microM) inhibited the relaxation induced by KRN4884 and levcromakalim, but did not influence the nifedipine-induced relaxation. KRN4884 (1 microM) produced a larger relaxation of A23187-induced contraction but had little effect on the increase in intracellular [Ca2+] induced by A23187. These results suggest that KRN4884 is a specific K+ channel opener and its vasodilating mechanisms involve not only deactivation of Ca2+ channels but also a decrease in the Ca2+ sensitivity of contractile elements.