Spectroscopic studies on the interaction of carteolol hydrochloride and urea-induced bovine serum albumin.

The interaction of carteolol hydrochloride, to 0.2 mol L(-1) urea-induced bovine serum albumin in aqueous solution has been first investigated by fluorescence spectra and ultraviolet-visible (UV-vis) spectra at pH 7.40. The quenching mechanism, binding parameter and sites (n), the binding mode (ΔG, ΔH, and ΔS) as well as the binding distance (r) have been obtained according to the experimental results. We also use the synchronous fluorescence method to study the effect of CTL on the conformation change of urea-induced BSA.

Assessment of systemic adverse reactions induced by ophthalmic beta-adrenergic receptor antagonists.

To assess quantitatively the risks of ophthalmic beta-blocking agents for cardiovascular and respiratory adverse reactions, we analyzed the binding kinetics of beta-blocking agents to the beta-1 and beta-2 adrenoceptors. The relationship between the occupancies for beta-1 and beta-2 adrenoceptors and the effects on the exercise pulse rate or the forced expiratory volume in one second (FEV1) after topical administration of carteolol, befunolol, timolol and betaxolol was analyzed using a ternary complex model. The beta-1 and beta-2 receptor occupancies after ophthalmic administration were calculated to be quite high as well as those after oral administration. The maximum occupancies for beta-1 and beta-2 receptors after ordinary ophthalmic administration were 52% and 88% for carteolol, 52% and 61% for befunolol, 62% and 82% for timolol, and 44% and 3% for betaxolol, respectively. Concave relationships were obtained between a decrease in exercise pulse rate and the beta-1 receptor occupancy and between a decrease in FEV1 and beta-2 receptor occupancy, respectively. Nasolacrimal occlusion was estimated to decrease the exercise pulse rate and FEV1 by 65% and 50%, respectively. The beta-1 and beta-2 adrenoceptor occupancies were proved to be the most appropriate indicators for cardiac and pulmonary adverse reactions evoked by ophthalmic beta-blocking agents.

Involvement of human cytochrome P450 3A4 in reduced haloperidol oxidation.

OBJECTIVE: The present study was conducted to identify in vitro the cytochrome P450(CYP) isoform involved in the metabolic conversion of reduced haloperidol to haloperidol using microsomes derived from human AHH-1 TK +/- cells expressing human cytochrome P450s. The inhibitory and/or stimulatory effects of reduced haloperidol or haloperidol on CYP2D6-catalyzed carteolol 8-hydroxylase activity were also investigated. RESULTS: The CYP isoform involved in the oxidation of reduced haloperidol to haloperidol was CYP3A4. CYP1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, and 2E1 were not involved in the oxidation. The kM value for the CYP3A4 expressed in the cells was 69.7 micromol x l(-1), and the Vmax was 4.87 pmol x min(-1) x pmol(-1) P450. Troleandomycin, a relatively selective probe for CYP3A enzymes, inhibited the CYP3A4-mediated oxidation of reduced haloperidol in a dose-dependent manner. Quinidine and sparteine competitively inhibited the oxidative reaction with a k(i) value of 24.9 and 1390 micromol x l(-1), respectively. Carteolol 8-hydroxylase activity, which is a selective reaction probe for CYP2D6 activity, was inhibited by reduced haloperidol with a k(i) value of 4.3 micromol x l(-1). Haloperidol stimulated the CYP2D6-mediated carteolol 8-hydroxylase activity with an optimum concentration of 1 micromol x l(-1), whereas higher concentrations of the compound (> 10 micromol x l(-1)) inhibited the hydroxylase activity. CONCLUSION: It was concluded that CYP3A4, not CYP2D6, is the principal isoform of cytochrome P450 involved in the metabolic conversion of reduced haloperidol to haloperidol. It was further found that reduced haloperidol is a substrate of CYP3A4 and an inhibitor of CYP2D6, and that haloperidol has both stimulatory and inhibitory effects on CYP2D6 activity.

Involvement of CYP2D1 in the metabolism of carteolol by male rat liver microsomes.

1. The metabolism of carteolol, a beta-adrenoceptor blocking drug, was investigated in male Sprague-Dawley rat liver microsomes. 2. The formation of 8-hydroxycarteolol was the principal metabolic pathway of carteolol in vitro and followed Michaelis-Menten kinetics with a K(m) = 11.0 +/- 5.4 microM and a Vmax = 1.58 +/- 0.64 nmol/min/nmol P450 respectively (mean +/- SD, n = 5). Eadie-Hofstee plot analysis of carteolol 8-hydroxylase activity confirmed single-enzyme Michaelis-Menten kinetics. 3. The cytochrome P450 isoforms involved in 8-hydroxylation of carteolol were investigated using selective chemical inhibitors and polyclonal anti-P450 antibodies. Quinine (Ki = 0.06 microM) and quinidine (Ki = 2.0 microM), selective inhibitors of CYP2D1, competitively inhibited 8-hydroxycarteolol formation. Furthermore, only anti-human CYP2D6 antibody inhibited this reaction. 4. These results suggest that carteolol is metabolized to 8-hydroxycarteolol by CYP2D1. The K(m) of carteolol for CYP2D1 in male rat liver microsomes was much greater than those of propranolol or bunitrolol, indicating that carteolol has a lower affinity for CYP2D1 compared with these other beta-adrenoceptor blocking drugs.

Metabolism of carteolol by cDNA-expressed human cytochrome P450.

OBJECTIVES: To determine human cytochrome P450 isoform(s) (CYPs) involved in the metabolism of carteolol, the biotransformation of the compound was investigated in vitro using ten isoforms of human cytochrome P450 expressed in human AHH-1 TK +/- cell lines. In addition, the inhibitory effects of carteolol on the activities of important CYP isoforms, namely, CYP1A2, 2C9, 2C19, 2E1, and 3A4, were examined. RESULTS: Carteolol was metabolised to 8-hydroxycarteolol by CYP 2D6 with KM and Vmax values of 183 mumoles.l-1 and 26.09 pmol.min-1.pmol-1 P450, respectively. CYP1A1, 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2E1 and 3A4 were not involved in the metabolism of the compound. CYPD6-mediated carteolol 8-hydroxylase activity was inhibited by quinidine, propranolol, nortriptyline, dextromethorphan, sparteine, bufuralol, and biperiden. Biperiden competitively inhibited the catalytic reaction with a Ki value of 0.45 mumoles.l-1. Carteolol did not affect the following catalytic reactions: CYP1A2-mediated (R)-warfarin 6-hydroxylation, CYP2C9-mediated tolbutamide methylhydroxylation, CYP2C19-mediated (S)-mephenytoin 4-hydroxylation, CYP2E1-mediated chlorzoxazone 6-hydroxylation, and CYP3A4-mediated testosterone 6 beta-hydroxylation. CONCLUSION: 8-Hydroxylation is the only cytochrome P450-catalyzed metabolic reaction of carteolol by its expressed microsomes, and CYP2D6 is the principal isoform of the enzyme involved in the catalytic reaction. Carteolol has neither stimulative nor inhibitory effects on CYP1A2, 2C9, 2C19, 2E1, and 3A4 activities.

Differentiation of binding sites of CGP12177, a beta 3-adrenoceptor partial agonist, and carteolol, a beta 1/beta 2-adrenoceptor partial agonist, to the beta-adrenoceptors in guinea-pig taenia caecum.

Differentiation of binding sites of CGP12177 and carteolol to the beta-adrenoceptors in the guinea-pig taenia caecum was investigated. Carteolol and CGP12177 competitively antagonized the relaxation responses to isoprenaline, and the pA2 values were 9.87 and 9.33, respectively. Butoxamine, a beta 2-selective antagonist, caused competitive antagonism of the relaxant responses to carteolol, and the pA2 value for butoxamine was 6.22. However, butoxamine (10(-4) M) did not significantly affect the relaxant responses to CGP12177. CGP12177 caused competitive antagonism of the relaxant responses to carteolol, and the pA2 value for CGP12177 was 9.32. However, carteolol (10(-6) M) did not significantly affect the relaxant responses to CGP12177. The competitive inhibition curve for specific binding of 50 nM [3H]befunolol by carteolol showed a biphasic shape, although the curve by CGP12177 was monophasic. Moreover, the competitive inhibition curve for specific binding of 100 nM [3H]CGP12177 by CGP12177 showed a biphasic shape, although the curve by carteolol indicated partial inhibition. These results suggest that the low affinity site of beta-adrenoceptor and beta 3-adrenoceptors are different from each other.

Comparison of interactions of R(+)- and S(-)-isomers of beta-adrenergic partial agonists, befunolol and carteolol, with high affinity site of beta-adrenoceptors in the microsomal fractions from guinea-pig ciliary body, right atria and trachea.

1. The stereoselectivities of beta-adrenergic partial agonists for the high affinity binding site of beta-adrenoceptors in the guinea-pig ciliary body, right atria and trachea were studied. 2. The inhibition curves by the S(-)-isomers of befunolol and carteolol were not significantly different from that by the R(+)-isomers in the guinea-pig ciliary body. 3. The inhibition curves by the S(-)-isomers of befunolol and carteolol were about 10 times as potent as the R(+)-isomers in the guinea-pig atria and trachea. 4. The pKi values of the S(-)-isomers of befunolol and carteolol were significantly larger than those of R(+)-isomers in the guinea-pig atria and trachea but not larger than those of the R(+)-isomers in the guinea-pig ciliary body. 5. These results suggest that the high affinity binding site of beta-adrenoceptors in ciliary body cannot discriminate stereoselectively between the R(+)- and S(-)-isomers, while in other tissues there is stereoselectivity between the two enantiomers.

[Effect of topical 8-hydroxy carteolol on intraocular pressure and melanin granules].

It was reported that 8-Hydroxycarteolol (8-OH CA), the major metabolite of carteolol hydroxychloride (CA), has a slightly different pharmacological effect from CA. We studied the reduction of intraocular pressure (IOP) on a single eyedrop application of 8-OH CA in albino and pigmented rabbit eyes. To determine the characteristic of 8-OH CA and CA, we investigated the binding ability of these drugs to synthetic melanin. In the present study, topically applied 2% CA did not significantly decrease IOP in albino and pigmented rabbit eyes. Topically applied 0.01, 0.05, 0.1 and 1.0% 8-OH CA significantly decreased the IOP of albino rabbit as did 0.1 and 1.0% 8-OH to pigmented rabbit eyes. The maximum reduction of IOP was 3.5 +/- 0.33 mmHg (mean +/- SEM) in albino rabbit and 3.0 +/- 0.45 mmHg (mean +/- SEM) in pigmented rabbit. Maximum IOP reduction was obtained after 30 min. from topical application in albino rabbit, but in pigmented rabbit after 1 hour or later. Our binding studies to melanin show that the melanin binding ability is less for 8-OH CA than for CA at any concentrations. These results may indicate that lower concentrations of topically applied 8-OH CA profoundly reduce IOP compared to CA, and 8-OH CA has less effect on melanin than CA.

Thermodynamic analysis of beta-adrenergic partial agonists (befunolol and carteolol) interaction with low and high affinity binding sites of beta-adrenoceptors in guinea-pig taenia caecum.

1. Effects of temperatures (0, 10 and 32 degrees C) on the bindings of beta-adrenergic partial agonists, befunolol and carteolol, with beta-adrenoceptors were studied using the microsomal fractions from the guinea-pig taenia caecum. 2. The affinities of befunolol and carteolol to the low affinity binding site were higher at low temperatures, whereas those to the high affinity binding site were not influenced by change in temperature. 3. The interactions of the low affinity binding site with befunolol and carteolol decreased both enthalpy and entropy. The interactions of both the drugs with the high affinity binding site increased only entropy. 4. These results support our view that beta-adrenoceptors contain two different affinity binding sites and that the interactions of beta-adrenergic partial agonists with the low affinity binding site induce the beta-adrenomimetic action, whereas the competitive antagonism by the beta-partial agonists and beta-adrenoceptor blockers is due to their ability to compete with beta-stimulant for the high affinity binding site.

Interactions of carteolol and other beta-adrenoceptor blocking agents with serotonin receptor subtypes.

The importance of the anti-serotonergic activity of carteolol and other beta-adrenoceptor blockers in their efficacy as anti-migraine agents has been examined in the membrane fraction of rat brain frontal cortex and pig choroid plexus, using radioligand binding methods. Carteolol and l-propranolol, which are suggested to have anti-migraine activity in man, were found to be active inhibitors of the binding of [125I]ICYP to 5-HT1B recognition sites and of [3H]-8-OH-DPAT to 5-HT1A recognition sites. Carteolol is devoid of activity at 5-HT1C and 5-HT2 recognition sites, whereas l-propranolol shows substantial affinity for these receptor subtypes. Atenolol, another beta-adrenoceptor blocker with anti-migraine activity, is devoid of activity at any of the 5-HT receptor subtypes examined. The possibility that carteolol and other beta-adrenoceptor antagonists exert their pharmacological effects through central 5-HT receptor subtypes is discussed in relation to the potential mechanism of the anti-migraine activity of carteolol.

Pharmacokinetics of carteolol in relation to renal function.

The plasma levels and urinary excretion of carteolol and its main metabolites 8-hydroxycarteolol and carteolol glucuronide were investigated in 6 healthy subjects and 9 patients with varying degrees of renal impairment following a single oral dose of 30 mg carteolol hydrochloride. In healthy subjects the half-life of carteolol was 7.1 h. 63% of the administered dose was recovered unchanged in urine, and in all 84% was excreted by the kidneys. The renal clearance of carteolol was 255 ml/min. In chronic renal failure (CRF) the terminal half-life was increased to a maximum of 41 h. Both the elimination rate constant and renal clearance were closely related to the creatinine clearance. In CRF the recovery of carteolol and its metabolites from urine was considerably reduced, suggesting that another pathway of drug elimination becomes relevant in renal disease. To avoid an increase in side-effects due to drug accumulation, the dosage of carteolol should be adjusted in relation to the reduction in creatinine clearance. The maintenance dose should be reduced to a half in patients with a creatinine clearance below 40 ml/min and above 10 ml/min. In those with a creatinine clearance of 10 ml/min or less, the dose should be reduced to 1/4.

[Animal experimental studies on the pharmacokinetics of carteolol]. / Tierexperimentelle Untersuchungen zur Pharmakokinetik von Carteolol.

From investigations in rats and dogs it is known that the proportion of 5-(3-tert-butylamino-2-hydroxy-propoxy)-3, 4-dihydro-2(1H)-quinolinone hydrochloride (carteolol hydrochloride, Endak, Endak mite) absorbed after oral administration is 60-80%. In dogs (as in human beings) most of it is excreted via the kidneys, but in rats biliary elimination predominates. In addition to 8-hydroxycarteolol--which also possesses pharmacological activity--the main metabolites found in dogs and rats are glucuronides of carteolol and 8-hydroxycarteolol. The elimination half-lives in dogs, rats and rabbits are between 1.2 and 3.0 h. Distribution studies point to the existence of a blood-brain barrier (rats and dogs) and a placental barrier (mice). The apparent volume of distribution measured after i.v. injection was from 2.5 to 8.5 l/kg depending on species. Passage into the milk was demonstrated in rats. Plasma protein binding is minimal. In a long-term study in dogs there was no evidence of cumulation except at the very high dosage of 200 mg/kg.

Pharmacokinetics and absolute bioavailability of carteolol, a new beta-adrenergic receptor blocking agent.

The pharmacokinetics and absolute bioavailability of a new nonselective beta-adrenoreceptor blocking agent, carteolol, were investigated after administration of single intravenous and oral doses to eight normal volunteers. Plasma and urine drug concentrations were measured by an HPLC method. The pharmacokinetic parameters after intravenous dosing were obtained by a two-compartment analysis: elimination or beta-phase t1/2 4.7 +/- 0.3 h; Vc, 0.74 +/- 0.101/kg; Vd, 4.05 +/- 0.48 l/kg; Cl, 10.13 +/- 0.94 ml/min/kg; ClR, 6.56 +/- 0.58 ml/min/kg; and ClNR, 3.57 +/- 0.40 ml/min/kg. The absolute bioavailability obtained from plasma data was 83.7 +/- 8.0%, which was consistent with that derived from analysis of urine of 82.7 +/- 4.2%. The amounts excreted unchanged in urine up to 48 h after the intravenous and oral doses were 65.0 +/- 1.5% and 53.8 +/- 3.2% of the administered doses, respectively. The t1/2 for removal of the drug derived from plasma and urine findings after intravenous and oral dosing were similar, which indicates that the main route of elimination of carteolol is via the kidneys. As the ClR of carteolol exceeded the Cl of creatinine there may be renal tubular secretion of the drug.

[Pharmacodynamics of carteolol]. / Zur Pharmakodynamik von Carteolol.

The compound known as 5-(3-tert-butylamino-2-hydroxy-propoxy)-3,4-dihydro-2 (1H)-quinolinone hydrochloride (carteolol hydrochloride, Endak, Endak mite) has been tested in extensive experimental pharmacological investigations both in vivo in various animal species and in appropriate in vitro systems. From the results it is clear that carteolol is a beta-adrenolytic agent with the following characteristics: 1. Carteolol exerts potent and long lasting blockade of adrenergic receptors, by oral or intravenous administration alike. 2. The effect comprises beta 1- and beta 2-receptors to an equal extent, and for this reason the drug produces haemodynamic changes and metabolic shifts in addition to cardiac effects. Carteolol can therefore be classified as a nonspecific beta-adrenergic blocker. 3. The drug displays a striking feeble local anaesthetic or nonspecific membrane-stabilizing action, probably owing to its pronounced hydrophilia. 4. There is evidence that carteolol has a relatively strong intrinsic sympathomimetic activity (ISA). This has been shown by appropriately planned investigations, and is also apparent after exceeding the doses or concentrations required for adrenolysis. 5. Carteolol causes dose-dependent changes in the electrophysiological parameters of cardiac function. In low doses or concentrations it slows heart rate and in higher doses it sometimes accelerates it. 6. Carteolol is converted - with species-specific differences - almost exclusively and to a relatively small extent into 8-hydroxycarteolol. This metabolite closely resembles the original substance and exceeds it only in ISA.

High-pressure liquid chromatographic determination of 8-hydroxycarteolol in plasma and urine using electrochemical detection.

Assay of 8-hydroxycarteolol (a metabolite of carteolol) was achieved using high-pressure liquid chromatography with electrochemical detection. Plasma or urine samples alkalinized by addition of a sodium carbonate solution were extracted with ethyl acetate or chloroform. The residues from evaporation of the organic extracts were redissolved in pH 2.1 phosphate buffer, and the solutions were chromatographed on a Partisil 10 SCX chromatographic column. The detection of 8-hydroxycarteolol was accomplished using an electrochemical detector. The procedure is rapid, specific, and highly sensitive. Reproducible results can be obtained, with relative standard deviations from analysis of replicate samples within +/- 8%. With 1-ml samples, the lower quantifiable concentrations of 8-hydroxycarteolol in plasma and urine are approximately 5 and 25 ng/ml, respectively.