Established HPLC fraction analysis to predict furanocoumarin-based herb-drug metabolic interactions.

An attempt was made in this study to predict the potential for metabolic interactions of herbal extracts of drugs from their chromatographic profiles in reverse-phase high-performance liquid chromatography (RP-HPLC). Twenty-nine structurally related furanocoumarin compounds with known inhibitory interactions with cytochrome P450 3A (CYP3A), which is important for phase-I drug metabolism, were selected as a model system. A sigmoidal relationship was established between the CYP3A inhibitory potency (y) and the RP-HPLC total peak response unit (R(u), x) as y = 85.36 x (14.86 + x)⁻¹ with a correlation coefficient of 0.63. The sigmoidal curve could be divided into three ranges designated low, medium and high risk that were used to indicate the relative inhibitory potency of the metabolic interactions of herbs or traditional Chinese herb medicines with CYP3A. These predictive classifications provide information or might be useful for 'risk category' decisions concerning herb-drug interactions.

Development of a reversed-phase high-performance liquid chromatographic method for analyzing furanocoumarin components in citrus fruit juices and Chinese herbal medicines.

A rapid and sensitive reversed-phase high performance liquid chromatographic method for the quantitation of five furanocoumarins (bergaptol, psoralen, bergapten, 6',7'-dihydroxybergamottin, and bergamottin) is developed and validated. HPLC analysis of these five furanocoumarins is performed on a reversed-phase Inertsil ODS-2 column with a particle size of 5 microm. Using only water and acetonitrile as solvents, good separation, good precision, and high accuracy are obtained for the analysis of furanocoumarin components. This method is validated and applied to analyze the composition of five furanocoumarins in four citrus fruit juices (grapefruit, pomelo I, pomelo II, and shaddock) and ten Chinese herbal medicines (Bai-Zhi, Qiang-Huo, Du-Huo, Fang-Feng, Dang-Gui, Huang-Qin, Gan-Cao, Chen-Pi, Ge-Gen, and Yin-Chen-Hao) prepared by water decoction or an alcohol infusion. Results show that four of the five furanocoumarins (but not bergapten) are detected in grapefruit, pomelo I, and pomelo II, and the highest amount of these components is found in grapefruit juice. In the ten Chinese herbal medicines, the five furanocoumarins are not detected in Ge-Gen or Yin-Chen-Hao. The remaining herbs contain various compositions and amounts of furanocoumarins. In general, Chinese herbal medicines prepared by the 40% ethanol infusion contain larger amounts of furanocoumarins than those prepared by hot water decoction.

Biotransformation of sildenafil in the male rat: evaluation of drug interactions with testosterone and carbamazepine.

The biotransformation of sildenafil to its major circulating metabolite, UK-103,320, was studied in male rat liver microsomes. The conversion of sildenafil to UK-103,320 by rat microsomes followed Michaelis-Menten kinetics, for which the parameters were V(max) = 1.96 microM/minand K(m) = 27.31 microM. Using substrates of CYP3A4 of testosterone and carbamazepine, the active sites on CYP3A4 responsible for metabolizing sildenafil were also evaluated. Sildenafil biotransformation was inhibited in the individual presence of testosterone and carbamazepine. The results showed drug interaction was observed in the sildenafil-testosterone and sildenafil-carbamazepine. Although testosterone and carbamazepine can inhibit sildenafil demethylation in concentration- and incubation time-dependent manners, sildenafil did not inhibit testosterone hydroxylation or carbamazepine epoxidation. These results may be explained by a model in which multiple substrates or ligands can concurrently bind to the active site of a single CYP3A4 molecule. However, the contribution of separate allosteric sites and conformational heterogeneity to the atypical kinetics of CYP3A4 cannot be ruled out in this study.