ABSTRACT
Tetrahydropalmatine (THP), with one chiral center, is an active alkaloid ingredient in Rhizoma Corydalis. The aim of the present paper is to study whether THP enantiomers are metabolized stereoselectively in rat, mouse, dog, and monkey liver microsomes, and then, to elucidate which Cytochrome P450 (CYP) isoforms are predominately responsible for the stereoselective metabolism of THP enantiomers in rat liver microsomes (RLM). The results demonstrated that (+)-THP was preferentially metabolized by liver microsomes from rats, mice, dogs, and monkeys, and the intrinsic clearance (Cl(int)) ratios of (+)-THP to (-)-THP were 2.66, 2.85, 4.24, and 1.67, respectively. Compared with the metabolism in untreated RLM, the metabolism of (-)-THP and (+)-THP was significantly increased in dexamethasone (Dex)-induced and ß-naphthoflavone (ß-NF)-induced RLM; meanwhile, the Cl(int) ratios of (+)-THP to (-)-THP in Dex-induced and ß-NF-induced RLM were 5.74 and 0.81, respectively. Ketoconazole had stronger inhibitory effect on (+)-THP than (-)-THP, whereas fluvoxamine had stronger effect on (-)-THP in untreated and Dex-induced or ß-NF-induced RLM. The results suggested that THP enantiomers were predominately metabolized by CYP3A1/2 and CYP1A2 in RLM, and CYP3A1/2 preferred to metabolize (+)-THP, whereas CYP1A2 preferred (-)-THP.
Subject(s)
Berberine Alkaloids/chemistry , Berberine Alkaloids/metabolism , Microsomes, Liver/metabolism , Animals , Berberine Alkaloids/pharmacokinetics , Cytochrome P-450 CYP1A2 , Cytochrome P-450 CYP3A/metabolism , Cytochrome P-450 CYP3A Inhibitors , Cytochrome P-450 Enzyme Inhibitors , Cytochrome P-450 Enzyme System/metabolism , Cytochromes/antagonists & inhibitors , Cytochromes/metabolism , Dexamethasone/pharmacology , Dogs , Fluvoxamine/pharmacology , Haplorhini , Ketoconazole/pharmacology , Male , Membrane Proteins/antagonists & inhibitors , Membrane Proteins/metabolism , Metabolic Clearance Rate , Mice , Mice, Inbred ICR , Microsomes, Liver/drug effects , Rats , Rats, Sprague-Dawley , Stereoisomerism , Substrate Specificity , beta-Naphthoflavone/pharmacologyABSTRACT
Tetrahydropalmatine (THP) is one of the active alkaloid ingredients of Rhizoma Corydalis. THP has a chiral center, and the stereoselective pharmacokinetics and tissue distribution have been reported. The aim of the present article is to study the stereoselective protein binding of THP using equilibrium dialysis followed by HPLC-UV analysis. The results showed that THP stereoselectively binds to human serum albumin (HSA), alpha(1)-acid glycoprotein (AGP), and proteins in human plasma. The fraction binding of (+)-THP was significantly higher than that of (-)-THP, whereas such stereoselectivity was not found in rat plasma. The affinity of HSA and AGP to (+)-THP, expressed as nK(A), were 9.0 x 10(3) M(-1) and 2.34 x 10(5) M(-1), respectively, which were notablely higher than to (-)-THP, with the nK(A) of 3.4 x 10(3) M(-1) and 1.44 x 10(5) M(-1), respectively. The binding site of HSA for (-)-THP was Site I, whereas for (+)-THP was both Site I and Site II. The F1/S variants of AGP were proved to be the key variants (-)- and (+)-THP binding to both. Finally, the AGP binding drugs, such as mifepristone, were demonstrated to reduce the fraction binding of (-)- and (+)-THP with pure AGP (1 mg/ml) but did not affect the fraction binding of both (-)- and (+)-THP with proteins in human plasma. It can be concluded that protein binding of THP is species dependent and stereoselective, both HSA and AGP contribute to the stereoselective binding to THP enatiomers, and AGP binding drugs may not cause the drug-drug interaction on THP in healthy human plasma.
Subject(s)
Berberine Alkaloids/chemistry , Berberine Alkaloids/metabolism , Orosomucoid/metabolism , Plasma/metabolism , Serum Albumin/metabolism , Animals , Berberine Alkaloids/blood , Binding, Competitive , Drug Interactions , Humans , Ibuprofen/pharmacology , Imipramine/pharmacology , Male , Mifepristone/pharmacology , Plasma/chemistry , Protein Binding/drug effects , Rats , Rats, Sprague-Dawley , Stereoisomerism , Substrate Specificity , Warfarin/pharmacologyABSTRACT
To investigate the difference in absorptive of tetrahydropalmatine (THP) and l-tetrahydropalmatine (l-THP) in rat intestine as well as the mechanism of the absorption of THP, in situ single pass perfusion model was used and the concentration of THP in perfusate was determined by HPLC. The absorption rate constant (k(a)) and effective permeability values (P(eff)) of THP had no significant difference (P > 0.05) at concentration of 8, 16 and 32 microg x mL(-1) in perfusion or in four different regions of intestine of rat (duodenum, jejunum, ileum, colon). The absorption of l-THP and THP in jejunum had significant difference (P < 0.05). The k(a) and P(eff) of THP increased obviously when verapamil was co-perfused with THP, while those of l-THP were not influenced by verapamil. The absorption of THP in intestine showed the passive diffusion process, and without a special absorption region. The stereoselective absorption difference may result from stereoselective combination of P-glycoprotein with d-THP.
