ABSTRACT
Drug-drug interactions have become a serious problem in the clinic, since plant-based medicines are extensively used. The present study investigated the effects of Ziziphus jujuba fruit (ZJ) extract on the pharmacokinetics of phenacetin, a typical substrate of a cytochrome P450 enzyme CYP 1A2, in rats. The rats were pretreated with the water extract (1.0 g · kg(-1)) or the ethanolic extract (3.6 g · kg(-1)) of ZJ for 10 days, and the pharmacokinetics of phenacetin was investigated after intravenous administration. In an in vitro assay, acetaminophen formation in the hepatic microsomes of ZJ-treated rats was investigated to assess CYP1A2 activity. Our results demonstrated that the treatment with the water and ethanolic extracts of ZJ decreased the plasma concentration of phenacetin and increased the plasma concentration of acetaminophen, resulting in a 43.2% and 15.5% reduction in the AUC0-120 of phenacetin, respectively, and a 53.2% and 64.9% increase in the AUC0-120 of acetaminophen, respectively after intravenous administration. The water or ethanolic extract of ZJ significantly increased the clearance of phenacetin and acetaminophen formation in hepatic microsomes. In conclusion, ZJ extracts displayed effects on the pharmacokinetics of phenacetin and increased the CYP1A2 activity in rats. Therefore, precaution on drug-drug interactions should be taken when ZJ is co-administered with drugs metabolized by CYP1A2, which may result in decreased concentrations of these drugs.
Subject(s)
Animals , Male , Acetaminophen , Metabolism , Area Under Curve , Cytochrome P-450 CYP1A2 , Cytochromes , Metabolism , Fruit , Herb-Drug Interactions , Liver , Microsomes, Liver , Phenacetin , Metabolism , Pharmacokinetics , Plant Extracts , Pharmacology , Rats, Sprague-Dawley , ZiziphusABSTRACT
P450 1A2 is responsible for the metabolism of clinically important drugs and the metabolic activation of environmental chemicals. Genetic variations of P450 1A2 can influence its ability to perform these functions, and thus, this study aimed to characterize the functional significance of three P450 1A2 allelic variants containing nonsynonymous single nucleotide polymorphisms (P450 1A2*8, R456H; *15, P42R; *16, R377Q). Variants containing these SNPs were constructed and the recombinant enzymes were expressed and purified in Escherichia coli. Only the P42R variant displayed the typical CO-binding spectrum indicating a P450 holoenzyme with an expression level of approximately 170 nmol per liter culture, but no P450 spectra were observed for the two other variants. Western blot analysis revealed that the level of expression for the P42R variant was lower than that of the wild type, however the expression of variants R456H and R377Q was not detected. Enzyme kinetic analyses indicated that the P42R mutation in P450 1A2 resulted in significant changes in catalytic activities. The P42R variant displayed an increased catalytic turnover numbers (k(cat)) in both of methoxyresorufin O-demethylation and phenacetin O-deethylation. In the case of phenacetin O-deethylation analysis, the overall catalytic efficiency (k(cat)/K(m)) increased up to 2.5 fold with a slight increase of its K(m) value. This study indicated that the substitution P42R in the N-terminal proline-rich region of P450 contributed to the improvement of catalytic activity albeit the reduction of P450 structural stability or the decrease of substrate affinity. Characterization of these polymorphisms should be carefully examined in terms of the metabolism of many clinical drugs and environmental chemicals.
Subject(s)
Biotransformation , Blotting, Western , Cytochrome P-450 CYP1A2 , Escherichia coli , Genetic Variation , Metabolism , Phenacetin , Polymorphism, Single NucleotideABSTRACT
OBJECTIVE: To develop a method of HPLC/MS/MS to determine phenacetin and paracetamol in rat liver microsomal incubation system. METHODS: Samples were separated on XTerra MS C18 column, different ratios of methanol- 0.1% formic acid were used as the gradient eluent, and the flow rate was 0.2mL?min-1. The electrospray ion-quadrupole mass spectrometry and multiple reaction monitor were adopted to detect the concentration of phenacetin and paracetamol. RESULTS: The calibration curves were linear in the ranges of 45～9 000ng?mL-1(r=0.999 8)and 15.2～1 520ng?mL-1(r=0.999 6) for phenacetin and paracetamol respectively; The lowest limits of assay were 9ng?mL-1 and 10ng?mL-1.The average recoveries at three concentrations of phenacetin were (96.2?2.3)%～(98.3?2.4)% and those of paracetamol were (99.6?2.1)%～(100.2?2.6)%; RSD of the intra-day and inter-day were less than 5%. CONCLUSION: The method is rapid, sensitive and suitable for determination of phenacetin and paracetamol in rat liver microsomal incubation system.
ABSTRACT
OBJECTIVE:To establish a HPLC method for the simultaneous determination of blood drug concentration of acetaminophen and phenacetin.METHODS:Diamonil C 18 was used as the chromatographic column,the mobile phase was methanol-water(45∶55),theophyllinum was used as internal standard,the detection wavelength was254nm and the column temperature was set at the room temperature.RESULTS:The minimum determination concentration of acetaminophen and phenacetin was5?g/ml,the calibration curve was linear in a range from5～25?g/ml;The recovery rate of both acetaminophen and phenacetin in this method was more than95%;both the intraday RSD and the interday RSD were less than4.0%.CONCLUSION:The method is rapid and accurate,which can satisfy the needs of the clinic blood drug concentration deter-mination of paracetamol and phenacetin.