Study On The Stereoselective Glucuronidation Of Carvedilol By Human Liver Microsomes And Drug Interactions Of Carvedilol By HPLC With Chiral Derivatization

Carvedilol is aβ-adrenoceptor antagonist with multiple pharmacological effects, and also non-selectiveβ-blocker and selective al-blocker.Its B-blocking action and vasodilatation make cooperative antihypertensive effect,and avoid the adverse effects of peripheral vaso-constriction caused byβ-blocking and of water-sodium retention caused by common vasodilating agents.Animal experiments demonstrated that carvedilol isβ1 and al blocker at a low concentration,and is a calcium channel antagonist at a high concentration.Carvedilol has been clinically used to treat chronic heart failure as well as hypertension,angina pectoris,and cardiac arrhythmias. Compared to propranolol,its advantage is smaller dosage,better therapeutic effect,minor adverse effects.And thus carvedilol has widely application prospect on cardiovascular therapy.Carvedilol is a chiral drug and administered orally as a racemic mixture.(R)- and(S)-enantiomer exhibit different pharmacological effects, i.e.,theβ-receptor blocking activity of the(S)-carvedilol is about 200 times higher than that of(R)-carvedilol,whereas both enantiomers are equipotent a-blockers.Hence it is of necessity and importance to study the stereoselective metabolism of carvedilol.Carvedilol is a hypotensive agent,the majority of receiving administration is the middle and aged patients,the use of carvedilol might be frequently accompanied with the use of multiple drugs,which may cause undesired adverse effects by drug-drug interactions.Among the hypertension patients,only 30% patients use only one drug to control the blood pressure within normal level,while 70%patients need to co-administer with two or more drugs to keep their blood pressure controlled.Hence the investigation of the stereoselective glucuronidation of carvedilol by human liver microsomes and the risk for drug interaction is very important to instruct clinical medication.Our study focused on the stereoselective glucuronidation of carvedilol by human liver microsomes and drug-drug interactions of carvediloh and evaluate the safety and rationality of co-administration of carvedilol with other chemical medicine.1.Stereoselective glucuroniflation of carvedilol by human liver microsomesObjective:To study the stereoselectivity of carvedilol enantiomers glucuronidation in human liver microsomes.Methods:The identification of carvedilol glucuronides was confirmed by LC-MS-MS,β-glucuronidase hydrolysis and metabolism by five human recombinant UGTs.The enzyme kinetics for carvedilol enantiomers glucuronidation were determined through precolumn derivatization with GITC, followed by RP-HPLC assay using(S)-propafenone as internal standard.Results: Both data of LC-MS-MS andβ-glucuronidase hydrolysis led to the result that the two metabolite peaks observed were glucuronide conjugates.The glucuronidation of carvedilol by five human recombinant UGTs demonstrated that the two glucuronide conjugates were most likely O-linked.Through regression analysis,the values of K_m and V_maxfor(S)-carvedilol and(R)-carvedilol enantiomers were 118±44μmol·L^-1, 2500±833pmol/min/mg protein and 24±7μmol·L^-1,953±399pmol/min/mg protein, respectively.Conclusion:The kinetic results suggested that there exsited significant stereoselective glucuronidation of carvedilol enantiomers in human liver microsomes, which might partly explain the enantioselective pharmacokinetics of carvedilol.2.The metabolic interactions between carvedilol and some commonly used drugsObjective:To study the metabolic drug interactions of carvedilol with some commonly used chemicals to provide some useful information for clinicals.Methods: Carvedilol was co-incubated with several kinds of commonly used drugs,respectively. There were 16 hypotcnsive agents such as nitrcndipine etc.,4 hypoglycemic agents such as glibenclamide etc.,6 antihypcrlipidemic agents such as simvastatin etc.,8 antipyretic analgesic agents such as aspirin and kctoprofen etc.,3 antidysrhythmic drugs such as amiodarone hydrochloride etc.,2 antianxiety drugs such as oxazepam, ketoconazolc representative of antifungal drugs,as well as 6 other drugs used in the study.The interactions were evaluated by IC₅₀or K_i of the co-incubated drugs on the metabolism of carvedilol.Results:Among the 46 chosen drugs,4 dihydropyridines and 2 antihyperlipidcmic agents,i.e.,felodipine,lacidipinc,nimodipine,nitrcndipine, simvastatin and lovastatin,showed fairly strong inhibition on the glucuronidation of carvedilol in vitro,with K_i value between 0.65-63.48μmol·L^-1.The K_i values of these six drugs for carvcdilol glucuronide M1 were lower than those for carvedilol glucuronidc M2,as was evidence of stronger inhibition for M1.Among these six drugs, lacidipinc had the strongest inhibition,with the K_i value about 0.65μmol·L^-1and 6.44μmol·L^-1for M1 and M2,respectively.We also made initial study on the inhibition mechanism of nitrendipine on carvedilol glucuronidation,by fitting the kinetic data to a mixed inhibition model using nonlinear regression analysis using the SigmaPlot enzyme kinetics module.The inhibition modes for nitrendipine on M1 and M2 were found to be mixed inhibition.Conclusion:There were strong interactions between dihydropyridincs,two statins(Simvastatin,Lovastatin)and carvedilol in vitro,special attention should be paid when co-administrated.The inhibition mechanism merits further investigation.