Levcromakalim

Preclinical Pharmacokinetic Profile of Topical Ophthalmic and Intravenous Delivery of QLS-101, a Novel ATP-Sensitive Potassium Channel Opening Ocular Hypotensive Agent

Purpose: To evaluate the pharmacokinetic profiles of the ocular hypotensive agent QLS-101, a novel ATP-sensitive potassium channel opening prodrug, and its active moiety levcromakalim, following topical ophthalmic and intravenous dosing of normotensive rabbits and dogs. Methods: Dutch belted rabbits (n = 85) and beagle dogs (n = 32) were dosed with QLS-101 (0.16-3.2 mg/eye/dose) or formulation buffer for 28 days. Pharmacokinetic profiles of QLS-101 and levcromakalim were evaluated in ocular tissues and blood by LC-MS/MS. Tolerability was assessed by clinical and ophthalmic examinations. Maximum systemic tolerated dose was evaluated in beagle dogs (n = 2) following intravenous bolus administrations of QLS-101 (0.05 to 5 mg/kg). Results: Plasma analysis following topical dosing of QLS-101 (0.8-3.2 mg/eye/dose) for 28 days indicated an elimination half-life (T1/2) of 5.50-8.82 h and a corresponding time (Tmax) range of 2-12 h in rabbits, and a T1/2 of 3.32-6.18 h with a Tmax range of 1-2 h in dogs. Maximum tissue concentration (Cmax) values ranged from 54.8-540 (day 1) to 50.5-777 ng/mL (day 28) in rabbits, and 36.5-166 (day 1) to 47.0-147 ng/mL (day 28) in dogs. Levcromakalim plasma T1/2 and Tmax were similar to QLS-101, while Cmax was consistently lower. Topical ophthalmic delivery of QLS-101 was well tolerated in both species, with sporadic mild ocular hyperemia noted in the group treated with the highest concentration (3.2 mg/eye/dose). Following topical ophthalmic dosing, QLS-101 and levcromakalim were found primarily in the cornea, sclera, and conjunctiva. Maximum tolerated dose was determined to be 3 mg/kg. Conclusions: QLS-101 was converted to its active moiety levcromakalim and showed characteristic absorption, distribution, and safety profiles of a well-tolerated prodrug.

Pharmacological Profile and Ocular Hypotensive Effects of Cromakalim Prodrug 1, a Novel ATP-Sensitive Potassium Channel Opener, in Normotensive Dogs and Nonhuman Primates

Purpose: To evaluate pharmacokinetic parameters and ocular hypotensive effects of cromakalim prodrug 1 (CKLP1) in normotensive large animal models. Methods: Optimal CKLP1 concentration was determined by dose response and utilized in short- (5-8 days) and long-term (60 days) evaluation in hound dogs (n = 5) and African Green Monkeys (n = 5). Blood pressure was recorded 3-5 times per week with a tail cuff. Concentrations of CKLP1 and the parent compound levcromakalim were assessed in hound dog plasma and select tissues by LC-MS/MS after bilateral ocular treatment with CKLP1 for 8 days. Pharmacokinetic parameters were calculated from days 1, 4, and 8 data. After necropsy, histology was assessed in 43 tissue samples from each animal. Results: In hound dogs and African Green monkeys, 10 mM CKLP1 (optimal concentration) significantly lowered intraocular pressure (IOP) by 18.9% ± 1.1% and 16.7% ± 6.7%, respectively, compared with control eyes (P < 0.05). During treatment, no significant change in systolic or diastolic blood pressure was observed in either species (P > 0.1). Average values for half-life of CKLP1 was 295.3 ± 140.4 min, Cmax, 10.5 ± 1.6 ng/mL, and area under the concentration vs. time curve (AUClast) 5261.4 ± 918.9 ng·min/mL. For levcromakalim, average values of half-life were 96.2 ± 27 min, Cmax 1.2 ± 0.2 ng/mL, and AUClast 281.2 ± 110.8 ng·min/mL. No significant pathology was identified. Conclusions: CKLP1 lowered IOP in hound dogs and African green monkeys with no effect on systemic blood pressure. Ocular topical treatment of CKLP1 showed excellent tolerability even after extended treatment periods.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Evaluation of the potassium channel activator levcromakalim (BRL38227) on the lipid profile, electrolytes and blood glucose levels of streptozotocin-diabetic rats

BACKGROUND

Levcromakalim is a vasorelaxant used in the management of hypertension in diabetes mellitus. Thus, the effects of levcromakalim were investigated in streptozotocin (STZ)-diabetic rats.

METHODS

Diabetes was induced in Wistar albino rats with a single injection of STZ (60 mg/kg, i.p.) following chronic (4 weeks) treatment with levcromakalim (75 μg/kg per day). Rats were then divided into the following groups (n = 5 in each group): (i) a normal saline (2 mL/kg)-treated group; (ii) a 5 mg/kg glibenclamide-treated group; (iii) 350 mg/kg metformin-treated group; and (iv) 5, 10, 20 and 40 IU/kg insulin-treated groups. Rats were transferred to metabolic cages and the lipid profile, plasma and urine electrolytes and blood glucose levels were determined 24 h after drug administration.

RESULTS

Levcromakalim treatment significantly reduced total cholesterol, low-density lipoprotein (LDL), and triglyceride levels in diabetic rats (all P < 0.05 compared with untreated diabetic rats). In addition, levcromakalim reduced plasma sodium, bicarbonate, and chloride levels, but increased urinary bicarbonate and chloride levels, in diabetic rats (all P < 0.05 compared with untreated diabetic rats). Levcromakalim significantly inhibited the effects of glibenclamide, metformin, and low-dose (20 IU/kg) insulin treatment in diabetic rats (all P < 0.05). Only 40 IU/kg insulin produced significant reductions in hyperglycemia in levcromakalim-treated diabetic rats.

CONCLUSION

Levcromakalim induced resistance to glibenclamide, metformin, and low-dose insulin treatment in diabetic rats, leading to persistent hyperglycemia. However, reductions in LDL, total cholesterol and triglyceride levels following chronic levcromokalim treatment may decrease the risk of cardiovascular disease in diabetic rats.

Synthesis and vasorelaxant activity of new 1,4-benzoxazine derivatives potassium channel openers

As part of a search for new potassium channel openers, the synthesis and vasorelaxant activity of new 1,4-benzoxazine derivatives derived from transformation of the benzopyran skeleton of cromakalim were described. Several new 1,4-benzoxazine derivatives were provided with significant vasorelaxant activity with an overall pharmacological behavior similar to CRK (1f, 1i, 2d, 2e, 2f and 2i).

Novel potassium channel openers. Part 4: transformation of the 1,4-benzoxazine skeleton into 1,4-benzothiazine, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroquinoxaline, indoline, and 1,5-benzoxazepine

As part of a search for a new potassium channel opener, the 1,4-benzoxazine skeleton derived from the benzopyran skeleton of cromakalim, was transformed into other fused rings such as 1,4-benzothiazine, 1,2,3,4-tetrahydroquinoline, 1,2,3,4-tetrahydroquinoxaline, indoline, and 1,5-benzoxazepine. The 1,4-benzothiazine derivative displayed approximately 20 times more potent vasorelaxant activity than cromakalim.

Neuroregulation of mucus secretion by opioid receptors and K(ATP) and BK(Ca) channels in ferret trachea in vitro

1. Opioid agonists inhibit neurogenic mucus secretion in the airways. The mechanism of the inhibition is unknown but may be via opening of potassium (K+) channels. We studied the effect on neurogenic secretion in ferret trachea in vitro of the OP1 receptor (formerly known as delta opioid receptor) agonist [D-Pen2,5]enkephalin (DPDPE), the OP2 receptor (formely kappa) agonist U-50,488H, the OP3 receptor (formerly micro) agonist [D-Ala2, N-Me-Phe, Gly-ol5]enkephalin (DAMGO), the ATP-sensitive K+ (K(ATP)) channel inhibitor glibenclamide, the large conductance calcium activated K+ (BK(Ca)) channel blocker iberiotoxin, the small conductance K(Ca) (SK(Ca)) channel blocker apamin, the K(ATP) channel opener levcromakalim, a putative K(ATP) channel opener RS 91309, and the BK(Ca) channel opener NS 1619. Secretion was quantified by use of 35SO4 as a mucus marker. 2. Electrical stimulation increased tracheal secretion by up to 40 fold above sham-stimulated levels. DAMGO or DPDPE (10 microm each) significantly inhibited neurogenic secretion by 85% and 77%, respectively, effects which were reversed by naloxone. U-50,488H had no significant inhibitory effect on neurogenic secretion, and none of the opioids had any effect on ACh-induced or [Sar9]substance P-induced secretion. 3. Inhibition of neurogenic secretion by DAMGO or DPDPE was reversed by iberiotoxin (3 microM) but not by either glibenclamide or apamin (0.1 microM each). Iberiotoxin alone did not affect the neurogenic secretory response. 4. Levcromakalim, RS 91309 or NS 1619 (3 nM-3 microM) inhibited neurogenic secretion with maximal inhibitions at 3 microM of 68%, 72% and 96%, respectively. Neither levcromakalim nor RS 91309 at any concentration tested significantly inhibited acetylcholine (ACh)-induced secretion, whereas inhibition (60%) was achieved at the highest concentration of NS 1619, a response which was blocked by iberiotoxin. 5. Inhibition of neurogenic secretion by levcromakalim (3 microM) or RS 91309 (30 nM) was inhibited by glibenclamide but not by iberiotoxin. In contrast, inhibition by NS 1619 (30 nM and 3 microM) was blocked by iberiotoxin but not by glibenclamide. 6. We conclude that, in ferret trachea in vitro, OP1 or OP3 opioid receptors inhibit neurogenic mucus secretion at a prejunctional site and that the mechanism of the inhibition is via opening of BK(Ca) channels. Direct opening of BK(Ca) channels or K(ATP) channels also inhibits neurogenic mucus secretion. In addition, opening of BK(Ca) channels inhibits ACh-evoked secretion of mucus. Drugs which open BK(Ca) channels may have therapeutic anti-secretory activity in bronchial diseases in which neurogenic mechanisms and mucus hypersecretion are implicated in pathophysiology, for example asthma and chronic bronchitis.

Kinetics of bupivacaine after levcromakalim treatment in mice

Previous workers have reported that 0.01 mg kg-1 of levcromakalim injected intraperitoneally did not modify bupivacaine-induced neurotoxicity but increased the duration of action of bupivacaine. This study was designed to document possible changes in the pharmacokinetic behaviour of bupivacaine and its main metabolite, N-desbutylbupivacaine in mice after a single 0.01 mg kg-1 intraperitoneal injection of levcromakalim. The kinetic parameters of bupivacaine were determined after a single 20 mg kg-1 intraperitoneal injection of bupivacaine in controls and in levcromakalim-treated mice. It was found that levcromakalim did not change any kinetic parameters of bupivacaine or of its main metabolite, N-desbutylbupivacaine. The previously reported findings of the influence of the low dose (0.01 mg kg-1) of levcromakalim on bupivacaine-induced toxicity agree well with the lack of influence of 0.01 mg kg-1 of levcromakalim on bupivacaine and N-desbutylbupivacaine pharmacokinetics, although the reported increase in the duration of action of bupivacaine after levcromakalim treatment can hardly be explained by the pharmacokinetics of bupivacaine when associated with levcromakalim. We suggest that levcromakalim might interfere directly with ion-channel block caused by bupivacaine by altering conduction properties or indirectly by enhancing bupivacaine-induced voltage and time-dependent sodium-channel block.

Potassium channel agonists modify the local anaesthetic activity of bupivacaine in mice

PURPOSE

The mechanisms of action of local anaesthetics and potassium channel agonists (PCAs) may interfere by acting in a direct or indirect manner on the same ion channels. In a previously reported study, the bupivacaine-induced mortality was shown to be modified in different ways by four PCAs tested (diazoxide (D), levcromakalim (L), nicorandil (N) and pinacidil (P)) since bupivacaine-induced mortality was increased by high doses of P and L, decreased by N and stayed unchanged by D. The present study was designed to document the changes in bupivacaine (B) local anaesthetic activity in mice after a single injection of one of the four PCAs (D, L, N and P).

METHODS

Each PCA was tested at three different dosages. Controls received saline. The local anaesthetic activity was evaluated using sciatic nerve blockade. After injection of bupivacaine in the region of the sciatic nerve, the local anaesthetic activity was estimated as the loss of motor control of the injected limb.

RESULTS

PCA treatment increased (P = 0.0001) the time needed for recovery from bupivacaine-induced local anaesthesia. The area under the effect vs time curve, assessing the total anaesthetic effect, was greater for N (P = 0.0016) and P (P = 0.038) but not for L (P = 0.11). Compared with controls, the maximal effect (Emax) was less for D (P = 0.009) and N (P = 0.038) but not for L (P = 0.185) or P (P = 0.45) treated groups. The injection of the PCA in the region of the sciatic nerve of the right hindlimb did not induce any alteration of the motor activity of the injected limb.

CONCLUSION

The four PCAs decreased the maximal local anaesthetic effect and increased the duration of action of bupivacaine.

Effects of glibenclamide on the regional haemodynamic actions of alpha-trinositol and its influence on responses to vasodilators in conscious rats

1. In conscious rats, alpha-trinositol (D-myo-inositol-1, 2, 6 triphosphate; 5-80 mg kg-1 h-1 infusion) caused dose-dependent hypotension, tachycardia and hyperaemic dilatation in renal, mesenteric and hindquarters vascular beds. These effects were accompanied by inhibition of the renal vasodilator effects of acetylcholine (ACh), and of the mesenteric vasodilator effects of sodium nitroprusside (SNP) and, particularly, of levcromakalim (LCK). 2. In the light of the latter finding, in a second experiment, we assessed the influence of the KATP channel inhibitor, glibenclamide (20 mg kg-1), on resting haemodynamics, on responses to ACh, bradykinin (BK), SNP and LCK, on the haemodynamic action of alpha-trinositol, and on the effects of the latter on responses to the vasodilators, over a period of 3 days. 3. In the presence of saline, glibenclamide caused a reproducible pressor effect, accompanied by renal, mesenteric, and hindquarters vasoconstrictions on all 3 experimental days; these effects were unrelated to changes in blood glucose. In the presence of glibenclamide, only the hindquarters vasodilator response to BK, and all the cardiovascular actions of LCK were inhibited. 4. On the first experimental day, the hindquarters vasodilator effect of alpha-trinositol was substantially inhibited by glibenclamide, the renal vasodilatation less so, and the mesenteric vasodilatation not at all. However, over the subsequent two days, the mesenteric vasodilator effect of alpha-trinositol became increasingly sensitive to glibenclamide. 5. In the presence of alpha-trinositol and glibenclamide, on the first experimental day, the inhibition of the renal vasodilator effect of ACh was no greater than with alpha-trinositol alone in the first experiment. Moreover, on the third experimental day, both before and after glibenclamide, the inhibition by alpha-trinositol of the renal vasodilator response to ACh was less than on the first experimental day. Similarly, the alpha-trinositol-induced inhibition of the mesenteric vasodilator effect of SNP, and of the hindquarters vasodilator action of BK, waned over the 3 experimental days. The inhibition of the cardiovascular effects of LCK were similar on all 3 experimental days, but no greater in the presence of alpha-trinositol and glibenclamide than with glibenclamide alone. 6. These results indicate that KATP channels are involved in the maintenance of resting vasodilator tone in renal, mesenteric and hindquarters vascular beds. However, although additional activation of KATP channels is responsible for all the haemodynamic effects of LCK, it contributes only to the hindquarters vasodilator action of BK and is not involved in any of the responses to ACh or SNP. The hindquarters, renal and mesenteric vasodilator effects of alpha-trinositol may involve (in the same rank order) activation of KATP channels, probably through an indirect mechanism. However, it is unlikely that direct or indirect interaction of alpha-trinositol with KATP channels explains the ability of the drug to inhibit the renal vasodilator action of ACh, or the mesenteric vasodilator effects of SNP or LCK.

Effects of BRL55834 in rat portal vein and bovine trachea: evidence for the induction of a glibenclamide-resistant, ATP-sensitive potassium current

1. The effects of the benzopyran K-channel opener, BRL55834, on mechanical activity in bovine trachealis and rat portal vein were studied together with membrane currents in freshly-isolated single cells derived from these tissues. 2. BRL55834 (3 nM-1 microM) produced a concentration-dependent relaxation of bovine trachealis precontracted with 100 microM histamine and reduced the spontaneous mechanical activity of rat portal veins, effects which were antagonized by glibenclamide (1-10 microM) but were not reversible on washing. In contrast, charybdotoxin (250 nM) did not modify the spasmolytic effect of BRL55834 in bovine trachealis. 3. BRL55834 (10 nM-10 microM) did not relax segments of bovine trachealis precontracted with 80 mM KCl. 4. In some freshly-isolated single cells from bovine trachealis held at -10 mV, BRL55834 (3 microM) induced a time-independent outward K-current which was partially resistant to inhibition by glibenclamide (10 microM). In other cells, a very noisy, outwardly-rectifying and charybdotoxin-sensitive current developed in the presence of BRL55834 (3 microM) and in time-matched control cells. 5. In freshly-isolated single cells from rat portal vein held at -10 mV, BRL55834 (3 microM) induced a time- and calcium-independent outward K-current which was partially resistant (approximately 25% inhibition at +40 mV) to subsequent inhibition by glibenclamide (10 microM). In contrast, levcromakalim induced a time-independent outward K-current which was completely inhibited by glibenclamide 10 microM. 6. With the non-hydrolysable ATP analogue, AMP-PCP (5 mM), in the pipette, the ability of BRL55834 to induce a time-independent K-current in portal vein cells was markedly reduced (approximately 80% inhibition at +40 mV) whereas the effects of 10 microM levcromakalim were totally inhibited. 7. The glibenclamide-resistant current component induced by BRL55834 was totally inhibited by phentolamine (100 microM), a concentration that had no effect on the peak current (IBK(Ca)) induced by NS1619 (33 microM). 8. Stationary fluctuation analysis of the noise associated with the glibenclamide-insensitive K-current induced by BRL55834 in rat portal vein cells indicated that the unitary current flowing through the underlying channels was 0.26 pA at -10 mV, a value inconsistent with the involvement of BKCa. 9. It is concluded that the relaxations of both bovine trachea and rat portal vein produced by BRL55834 are associated with the opening of K-channels. These are probably identical to the ATP-sensitive K-channel opened by levcromakalim, although the involvement of an additional K-channel cannot be excluded. The reduced sensitivity of the BRL55834-induced changes to glibenclamide and toAMP-PCP may result from avid binding of BRL55834 to its site of action.

The effect of levcromakalim (BRL 38227) on bladder function in patients with high spinal cord lesions

The effects of the potassium channel opener levcromakalim (BRL 38227) 7.5 micrograms kg-1 were examined on urodynamic variables and blood pressure during inflow and voiding cystometry in six high spinal cord lesion patients. Levcromakalim administration significantly increased the duration of bladder contraction (197 +/- 128 s to 267 +/- 167 s, P < 0.05) and also reduced blood pressure (126 +/- 13/67 +/- 9 mm Hg to 104 +/- 25/52 +/- 12 mm Hg) but was without effect on other urodynamic parameters. Because of concerns about hypotensive responses, further studies involving higher doses of levcromakalim should be considered only if the drug was administered intravesically.