Cytochrome P450 enzymes involved in the enhancement of propranolol N-desisopropylation after repeated administration of propranolol in rats

A Preliminary Investigation on the Effects of Atenolol for Treating Symptoms of Anxiety

INTRODUCTION

Anxiety disorders are among the most commonly diagnosed of psychiatric disorders. Many symptoms of posttraumatic stress disorder are also anxiety-related. Traditional medications used to treat these disorders, such as antidepressants and benzodiazepines, are often ineffective, not well-tolerated, and can be habit forming. An alternative agent is, therefore, needed. Beta-blockers are one class of medication with potential to treat anxiety-related disorders; however, current evidence remains limited and requires further characterization. To this end, this retrospective study aims to present a novel preliminary report on the use of the beta-blocker, atenolol, to potentially treat anxiety-related disorders.

MATERIALS AND METHODS

Ninety-two patients were identified from outpatient military mental health clinics in Okinawa, Japan, who had received atenolol for mental health-related symptoms. Primary measures collected were the rates of patient-reported (1) general beneficial/positive effect of atenolol, (2) adverse effects from atenolol, and (3) preference of atenolol to propranolol. Data were collected from patients who were given binary response options to report their perceived experiences for each primary measure. This study was approved by the Naval Medical Center San Diego Institutional Review Board.

RESULTS

The results showed 86% of patients reporting a positive effect and continuing to take atenolol, including 87% with a diagnosis of posttraumatic stress disorder, 100% with diagnosis of other specified trauma- and stressor-related disorder, and 81% diagnosed with anxiety disorders. In total, 90% of patients denied adverse effects or found the adverse effects tolerable. Additionally, 100% of patients who had previously taken propranolol for anxiety reported that they preferred atenolol.

CONCLUSIONS

The present preliminary observational data suggests that atenolol may be well-tolerated and effective among persons with anxiety disorders. These data also suggest that atenolol may be more effective and better tolerated than propranolol, which is the most commonly prescribed beta-blocker for these conditions; however, more rigorously controlled empirical studies are needed to further substantiate this claim. Despite an overwhelmingly high rate of positive reports from patients' self-evaluations of atenolol treatment for anxiety-related disorders, this early investigation was not placebo-controlled nor double-blinded, and formal outcome measures were not assessed due to a lack of availability. More detailed examinations are needed to further determine whether atenolol is a viable alternative or augmenting agent to propranolol, benzodiazepines, and antidepressants for anxiety disorders and trauma-related disorders.

Bioaccumulation and biotransformation of the beta-blocker propranolol in multigenerational exposure to Daphnia magna

Multigenerational bioaccumulation and biotransformation activity and short-term kinetics (e.g., uptake and depuration) of propranolol in Daphnia magna were investigated at environmental concentration. The body burden and the major metabolite, desisopropyl propranolol (DIP), of propranolol were quantified using LC-MS/MS at the end of each generation after exposure for 11 generations. The accumulation of propranolol in D. magna at an environmental concentration of 0.2 μg/L was not much different between the parent (F0) and the eleventh filial (F10) generation. However, at 28 μg/L, its accumulation was 1.6 times higher-up to 18.9 μg/g-in the F10 generation relative to the F0. In contrast to propranolol, DIP intensity gradually increased from F0 to F10 at 0.2 μg/L, reflecting an increase in detoxification load and biotransformation performance; no increasing trend was observed at 28 μg/L. The bioaccumulation factor (BAF) showed higher values with a lower concentration and longer period of exposure. The average values of the BAF for 21 days of long-term exposure in successive 11 generations were 440.4 ± 119.7 and 1026.5 ± 208.6 L/kg for 28 μg/L and 0.2 μg/L, respectively. These are comparable to the BAF of 192 for the short-term 72-h exposure at 28 μg/L in the parent generation. It is also recommended that future studies for pharmaceutical ingredients be conducted on drug-drug interaction and structural characteristics on the prediction of biotransformation activity and bioaccumulation rate.

Frovatriptan: a review of drug-drug interactions

OBJECTIVE

To investigate the potential for interactions involving drugs likely to be coadministered with frovatriptan.

BACKGROUND

Frovatriptan is a new 5-hydroxytryptamine (5-HT)(1B/1D) agonist. Preclinical data suggest that the pharmacokinetic and pharmacological profile of frovatriptan may differ from that of the currently available triptans.

METHODS

The potential for interactions between frovatriptan and other drugs was investigated using in vitro methods, studies in healthy volunteers, and retrospective analysis of data from phase I trials.

RESULTS

In vitro, frovatriptan was principally metabolized by cytochrome P-450 (CYP) 1A2 but was found not to be an inhibitor or inducer of this or other CYP isoenzymes. Frovatriptan was only a weak inhibitor of monoamine oxidase at very high concentrations in vitro and was not a substrate for this enzyme (unlike some other triptans). Coadministration with moclobemide, at doses known to inhibit monoamine oxidase-A, did not affect the pharmacokinetics of frovatriptan. Binding to plasma proteins was low (15%), and binding to erythrocytes was moderate (60%) and unlikely to be a source of interaction with other drugs. The pharmacokinetics of frovatriptan were not affected by moderate alcohol intake. There were slight increases in area under the curve and maximum concentration on concomitant administration with the combined oral contraceptives, propranolol, and fluvoxamine; and slight decreases in these parameters on concomitant administration with ergotamine and in tobacco smokers; these findings were considered to have no clinical significance in view of frovatriptan's large therapeutic index (well tolerated at doses ranging from 2.5 to 40 mg). These effects can be attributed primarily to modification of CYP1A2 activity but their impact is limited, probably due to frovatriptan also undergoing renal clearance and the likely role of blood cell binding in controlling the amount of unbound drug available for elimination.

CONCLUSIONS

Because it has no inhibitory or inducing effect on CYP isoenzymes and is only slightly bound to plasma proteins, it is unlikely that frovatriptan will alter the pharmacokinetics of concomitantly administered drugs. Frovatriptan, therefore, appears to have a low risk of interaction with other drugs, and adjustments of dose are unlikely to be required when it is coadministered with other agents.

Induction of Cytochrome P450 1A1 in Mice by Repeated Oral Administration of Propranolol

Pretreatment of adult male C57BL/6 mice with propranolol (PL, 100 mg/kg, p.o., once a day for five days) significantly increased PL N-deisopropylase activity and decreased PL 7-hydroxylase activity in liver microsomes, whereas PL 4- and 5-hydroxylase activities remained unchanged. In the present study, we have examined the mechanism for the elevation of the oxidation of PL side chain. Immunoblot analysis using polyclonal antibodies raised against rat liver CYP enzymes such as CYP1A1, -2B2, -2C11, -2D2, -2E1 and 3A2 showed that, compared with the vehicle-treated control, the levels of two protein bands (54 KD and 52 KD) were increased by the pretreatment. Both proteins immunochemically cross-reacted with the antibodies against rat CYP1A1, and from their molecular weights, the 54 KD and 52 KD proteins were deduced to be CYP1A1 and 1A2, respectively. Computer-assisted scanning analysis revealed that the levels of CYP1A1 and CYP1A2 proteins were increased 1.8 and 1.2 times, respectively, over those of control microsomes. PL N-deisopropylase activity correlated well with ethoxyresorufin O-deethylase (r=0.828) and phenacetin O-deethylase (r=0.851) activities in the same microsomal fractions. These results show that repeated oral administration of PL in mice induces mainly CYP1A1 and also CYP1A2 to some extent, which contrasts from our previous results in rats in which CYP1A2 only was induced with PL pretreatment [Narimatsu et al., Chemico-Biol. Interact., 101, 207-224 (1996)].

Stereoselective propranolol metabolism in two drug induced rat hepatic microsomes

AIM: To study the influence of inducers BNF and PB on the stere oselective metabolism of propranolol in rat hepatic microsomes.

METHODS: Phase I metabolism of propranolol was studied by using the microsomes induced by BNF and PB and the non-induced microsome as the control. The enzymatic kinetic parameters of propranolol enantiomers were calculated by regression analysis of Lineweaver-Burk plots. Propranolol concentrations we re assayed by HPLC.

RESULTS: A RP-HPLC method was developed to determine propranol ol concentration in rat hepatic microsomes. The linearity equations for R (+)pr opranolol and S (-)propranolol were A = 705.7C + 311.2C (R = 0.9987) and A = 697.2C+311.4C (R = 0.9970) respectively. Recoveries of each enant iomer were 98.9%, 99.5%, 101.0% at 60 μmol/L, 120 μmol/L, 240 μmol/L respectively. At the concentration level of 120 μmol/L, propranolol enantiomers were metabolized at different rates in different microsomes. The concentration ratio R (+)/S (-) of control and PB induced microsomes increased with time, whereas that of microsome induced by BNF decreased. The assayed enzyme parameters were: 1. Km. Control group: R (+)30 ± 8, S (-) 18 ± 5; BNF group: R (+) 34 ± 3, S (-)39 ± 7; PB group: R (+)38 ± 17, S (-) 36 ± 10. 2. Vmax. Control group: R (+)1.5 ± 0.2, S (-)2.9 ± 0.3; BNF group: R (+)3.8 ± 0.3, S (-)3. 3 ± 0.5 ; PB group: R (+)0.07 ± 0.03, S (-)1.94 ± 0. 07. 3. Clint. Control group: R (+)60 ± 3, S (-) 170 ± 30; BNF group: R (+)111.0 ± 1, S (-) 84 ± 5; PB group: R (+)2.0 ± 2, S (-)56.0 ± 1. The enzyme parameters compared with unpaired t tests showed that no stereoselectivity was observed in enzymatic affinity of three microsomes to enantiomers and their catalytic abilities were quite different and had stereoselectivities. Compared with the control, microsome induced by BNF enhanced enzyme activity to propranolol R (+)enantiomer, and microsome induced by PB showed less enzyme activity to propranolol S (-)-enan tiomer which remains the same stereoselectivities as that of the control.

CONCLUSION: Enzyme activity centers of the microsome were changed in composition and regioselectivity after the induction of BNF and PB, and the stereoselectivities of propranolol cytochrome P450 metabolism in rat hepatic microsomes were likely due to the stereoselectivities of the catalyzing function in enzyme. CYP-1A subfamily induced by BNF exhibited pronounced contribution to propranolol metabolism with stereoselectivity to R (+)-enantiomer. CYP-2B subfamily induced by PB exhibited moderate contribution to propranolol metabolism, but still had the stereoselectivity of S (-)-enantiomer.

Combined effect of propranolol with nifedipine or with diltiazem on rat liver monooxygenase activities

The effects of two Ca2+ antagonists nifedipine (NF) and diltiazem (DL) and of the nonselective beta-adrenergic blocking agent propranolol (PR) on the hexobarbital (HB) sleeping time and on the activity of some liver drug-metabolizing enzyme systems in male Wistar rats were studied. Two h after single oral administration PR (50 mg/kg) did not change HB sleeping time, while NF (50 mg/kg) and DL (30 mg/kg) prolonged it by 171.2 and 99.6%, respectively. Coadmistration of PR with DL or with NF significantly prolonged HB sleep by 240.7 and 129%, respectively. Only NF increased aniline 4-hidroxylase (AH) activity (by 92%) and the total P-450 content (by 24%). PR and NF increased cytochrome b5 content and this effect was also observed with the combinations PR + NF (by 109%) and PR + DL (by 102%). The NADPH cytochrome P-450 reductase activity was significantly decreased by NF and DL and after their combination with PR. The ethymorphine-N-demethylase (EMND) and amidopyrine-N-demethylase (APND) activities were not changed. The effects of PR, NF and DL administrated alone or in combination on liver oxidative metabolism are considered as possible mechanisms of drug interactions.