Flavonoids are naturally occurring polyphenols, which are widely taken in diets, supplements and herbal medicines. Epidemiological studies have shown a flavonoid-rich diet is associated with the decrease in incidence of a range of diseases. Pharmacological evidences also reveal flavonoids display anti-oxidant, anti-allergic, anti-cancer, anti-inflammatory, anti-microbial and anti-diarrheal activities. Therefore, it is critical to study the biotransformation and disposition of flavonoids in human. This review summarizes the major metabolism pathways of flavonoids in human. First, lactase-phlorizin hydrolase (LPH) and human intestinal microflora mediate the hydrolysis of flavonoid glycosides, which is recognized as the first and determinant step in the absorption of flavonoids. Second, phase II metabolic enzymes (UGTs, SULTs and COMT) dominate the metabolism of flavonoids in vivo. UGTs are the most major contributors, followed by SULTs and COMT. By contrast, phase I metabolism pathway mediated by CYPs only plays a minor role. Third, the coupling of transporters (such as BCRP and MRPs) and phase II enzymes (UGTs and SULTs) plays an important role in the disposition of flavonoids, especially in the enteroenteric and enterohepatic circulations. Thus, all the above factors should be taken into consideration when studying pharmacokinetics of flavonoids. Here we describe a comprehensive metabolism profile of flavonoids, which will enhance our understanding of the mechanisms underlying the disposition and pharmacological effects of flavonoids in vivo.

Chrysanthemum morifolium extract (CME) has the protective effect on cardiovascular diseases. Luteolin and apigenin are two major bioactive components in vivo when CME is orally administrated to experimental animal. The present paper shows the study of the absorption and excretion of luteolin and apigenin in rats after a single oral dose of CME (200 mg/kg). The levels of luteolin and apigenin in plasma, urine, feces, and bile were measured by HPLC after deconjugation with hydrochloric acid or beta-glucuronidase/sulfatase. The results showed that the plasma concentrations of luteolin and apigenin reached the highest peak level at 1.1 and 3.9 h after dosing, respectively. The area under the concentration-time curves (AUC) for luteolin and apigenin were 23.03 and 237.6 microg h mL-1, respectively. The total recovery of the dose was 37.9% (6.6% in urine; 31.3% in feces) for luteolin and 45.2% (16.6% in urine; 28.6% in feces) for apigenin. The cumulative luteolin and apigenin excreted in the bile was 2.05% and 6.34% of the dose, respectively. All of the results suggest apigenin may be absorbed more efficiently than luteolin in CME in rats, and both luteolin and apigenin have a slow elimination phase, with a quick absorption, so a possible accumulation of the two flavonoids in the body can be hypothesized.

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Renal cell carcinoma (RCC) is known for its multidrug resistance. Using data obtained from the cancer transcriptome database Oncomine and the proteome database The Human Protein Atlas, we identified the repression of organic cation transporter OCT2 as a potential factor contributing to oxaliplatin resistance in RCC. By analyzing OCT2 expression in collected patient tissues and commercial tissue microarray specimens, we demonstrated OCT2 repression in RCC at both transcription and protein levels. Epigenetic analysis revealed that the repressed OCT2 promoter in RCC is characterized by hypermethylated CpG islands and the absence of H3K4 methylation. Further mechanistic studies showed that DNA hypermethylation blocked MYC activation of OCT2 by disrupting its interaction with the E-Box motif, which prevented MYC from recruiting MLL1 to catalyze H3K4me3 at the OCT2 promoter and resulted in repressed OCT2 transcription. Targeting this mechanism, we designed a sequential combination therapy and demonstrated that epigenetic activation of OCT2 by decitabine sensitizes RCC cells to oxaliplatin both in vitro and in xenografts. Our study highlights the potential of translating "omics" data into the development of targeted therapies.

Chiral drugs show distinct biochemical and pharmacological behaviors in the human body. The binding of chiral drugs to plasma proteins usually exhibits stereoselectivity, which has a far-reaching influence on their pharmacological activities and pharmacokinetic profiles. In this review, the stereoselective binding of chiral drugs to human serum albumin (HSA), α1-acid glycoprotein (AGP) and lipoprotein, three most important proteins in human plasma, are detailed. Furthermore, the application of AGP variants and recombinant fragments of HSA for studying enantiomer binding properties is also discussed. Apart from the stereoselectivity of enantiomer-protein binding, enantiomer-enantiomer interactions that may induce allosteric effects are also described. Additionally, the techniques and methods used to determine drug-protein binding parameters are briefly reviewed.

Luteoin is one of the main flavones and the crucial effective component of peanut hull extract (PHE). The present paper aims to elucidate the absorption mechanism of luteolin and clarify whether its absorption occurs primarily at a specific site of the intestine by an in situ single-pass intestinal perfusion (SPIP) model. Moreover, the paper investigates the difference in absorption of luteolin when it is administered in PHE form and as pure luteolin by the SPIP model and in vivo pharmacokinetics studies. Results showed that the effective permeability ( P eff) and absorption rate constant ( k a) of pure luteolin(5.0 microg/mL) in duodenum and jejunum were not significantly different, but markedly higher than that in the colon and ileum. The P eff and k a of luteolin in jejunum were concentration-independent, and the ATP inhibitor (DNP) did not influence P eff and k a of pure luteolin. However, the P eff and k a of luteolin in PHE were significantly greater than that of pure luteolin. The pharmacokinetics study showed that following oral administration of a single dose of pure luteolin (14.3 mg/kg) or PHE (= 14.3 mg/kg of luteolin) in rats, the peak concentration of luteolin in plasma ( C max) and the area under the concentration curve (AUC) for pure luteolin were 1.97 +/- 0.15 microg/mL and 10.7 +/- 2.2 microg/mL.h, respectively. These parameters were significantly lower than those of the PHE group ( P < 0.05), C max = 8.34 +/- 0.98 microg/mL and AUC = 20.3 +/- 1.3 microg/mL.h, respectively. It can be concluded that luteolin is absorbed passively in the intestine of rats and that its absorption is more efficient in the jejunum and duodenum than in the colon and ileum. The bioavailability of luteolin in PHE form is significantly greater than that of pure luteolin.

ABSTRACT:Luteolin is mainly metabolized by phase II enzymes in animals and humans with glucuronidation and sulfation as the two known metabolic pathways. Although methylation of luteolin was reported previously, the structure of the methylated metabolites and the enzymes involved in the process have not been clarified. In our study, two methylated metabolites, M1 (chrysoeriol) and M2 (diosmetin), were identified in the urine after intravenous administration of luteolin to rats, and the data suggested that the methylation was mediated by catechol-O-methyltransferase (COMT). When luteolin was coadministered with a specific COMT inhibitor, entacapone, the formation of M1 and M2 was significantly reduced, whereas the plasma concentration of luteolin increased. Methylation of luteolin was also studied in vitro using rat tissue homogenates. The apparent kinetic parameters associated with the formation of M1 and M2 in vitro were estimated, and regioselectivity of methylation of luteolin was observed. In the in vitro experiment, there was a preference for the formation of M2 over M1. In contrast, accumulation of M1 was preferred in vivo in both rat plasma and urine after an intravenous dose of luteolin. In conclusion, COMT played a crucial role in the disposition of luteolin in rats. Our results indicated that the methylation pathway in rats was significantly reduced when luteolin was coadministered with a specific COMT inhibitor. Therefore, COMT-associated drug-drug interactions need be considered in the future in luteolin clinical trials because the plasma concentrations and related therapeutic effects may be altered in vivo in the presence of a COMT inhibitor.

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