Study On The Interaction Of Baicalein With UDP-glucuronosyltransferase (UGT) In

Baicalein (5,6,7-trihydroxyflavone, Ba), a bioactive flavonoid and the major constitutein of Chinese herbal Huangqin (Scutellaria baicalensis Georgi), is the major constitutes ofmany widely used traditional herbal prescriptions and modern herbal medications, includingHuang-Qin-Tang, Huang-Qin tablets, Shuang-Huang-Lian granules and Yin-Huang oralsolution. Baicalein has drawn much attention for its various desirable pharmacologicalfunctions, including anti-inflammatory, anti-allergic, anti-viral, antioxidant activity,anxiolytic-like effect, and the protective effect against amnesia. Nowadays, increasinglyevidence show that baicalein has good inhibition on solid tumor cells.First pass elimination is a common point of flavonoid absorption which is a main reasonfor low bioavailability. Ba could be well absorbed after oral administration, and thenconverted to the corresponding conjugates (mainly7-O-and6-O-glucuronides) by UGTs ofmucous membrane of small intestine. Within the metabolites excretion, bioavailability offlavonoids decreases. With the development of UGTs, more and more herb medicine wasexcretion by this path and many of them could have inhibition or induction on UGT whichonce combination with other drugs, the exposure may have a significant change, includingrendered less useful through low exposure and even poisoning through high exposure.Compared with western medicines, herbs can be directly used for phase II metabolismwithout phase I metabolism enzyme functional modification and glucuronidation is the mostimportant path way of mono-Hydroxyl or multi-Hydroxyl flavonoids. It cannot only improvethe rational use of drugs, but also to improve the efficacy and safety of traditional Chinesemedicine through in-depth study the effect of traditional medicine on metabolism enzymeUGTs. Recently, flavonoids, with its excellent pharmacological activity, their metabolicprocesses have received widespread concern. Therefore, learn from the successful experienceof new drug research and development in the western, the ADME/Tevaluation, especially the scientific evaluation of early assessment of metabolic propertiesand toxicity of traditional Chinese medicine, will accelerate the modernization of traditionalChinese medicine modernization.To further clarify the pharmacokinetics of Ba, this subject, combined withthe clinical practical, tightly focused on drug metabolism upon the most important drugmetabolizing enzymes-UDP-glucuronosyltransferase (UGT); in the meanwhile, constructivelyresearch the methods of pharmacokinetics of traditional Chinese medicine. Within themethods and technologies of metabolism in vitro, we conducted the species differences,gender differences, metabolism stability and drug-drug interaction research, as well asanalysis the specific results the above mentioned.1. Establish the methods of HPLC for baicalein and its metabolites.This article established the method of Ba and its metabolites in the liver microsomes by high performance liquid detection at first. The method has good specificity, which precision,accuracy and stability of them are in line with methodology requirements, and the method canwell meet the quantitative requirements for the following study. Based on the method, thepaper focuses on the studies on the in vitro metabolism of baicalein glucuronidation, clarifythe pathway of metabolism and difference in species and gender, in addition to drug-druginteraction.2. The study of baicalein glucuronidation species differences.Species difference of Ba glucuronidation was investigated in this study which showedthat metabolic profiling existed not significant difference-Ba can metabolized into B-7G andB-6G in the human, SD, monkey, dog and pig liver microsomes. However, the kinetics ofthem had significant differences, which showed the reaction velocity increased with theconcentration of Ba. The metabolism rate of Ba in the pig liver microsomes is the fastest, andthen in turns of human, monkey, SD rat and dog. As to the clearance, pig liver microsome isalso the fastest, then clearance order of Ba was as follows: for B-6G formation was PLM>RLM> HLM> MLM> DLM, but for B-7G formation, the order was PLM> RLM> MLM>DLM> HLM. The clearance between human and monkey is similar due to high Vmaxandlow Kmin monkey. Therefore, monkey maybe is the most suitable model for Baglucuronidation. Baicalein glucuronidations in liver microsomes exhibited species-dependentdifferences, no animal models can represent human in terms of these biotransformationprocesses.3. The study of baicalein glucuronidation gender differences.On the foundation of species differences, gender differences of systemic verificationwere investigated. The results showed that there is apparent gender diversity of Baglucuronidation in SD rat. The metabolic rate in male is much higher than in female, and theclearance is10times in male as much as in the female. It is likely associated with metabolicenzyme which probably resulted by estrogen unbalanced level in male and female.Nevertheless, the difference in monkey and dog was not as significant as SD rat showed, forthe UGTs diversity and it’s maybe related to expression of UGT1A1. Thus, we can inferUGT1A1has something to do with Ba glucuronidation.4. Baicalein glucuronidation metabolic stability in vitro.Based on the previous study, we find the relationship between UGT1A1and Baglucuronidation. So, we extremely investigated the pathway of it in UGTs. The twomono-glucuronidations were metabolized by different Phenotypes. B-7G was mainlymetabolized by UGT1A1, UGT1A8, UGT1A9and UGT2B15, in the meanwhile, UGT1A1,UGT1A8and UGT1A9mediated B-6G in common. What’s more, selective inhibitor in the human, SD rat, monkey, dog and pig liver microsomes were used to prove whether UGT1A1is the most important drug metabolic enzyme. Finally, it’s confirmed that UGT1A1issignificantly contributed to Ba glucuronidation. We should pay attention, combined with otherdrugs which are UGT1A1inhibitors, to avoid the accumulation of drug in the body, or causepoisoning adverse events.5. Evaluation of drug-drug interactionDrug-drug interaction is a part of the evaluation of drug safety and efficacy. Theevaluation of induction of CYP450and inhibition of UGTs of candidate has become anessential portion in new drug research and development. The methods of fresh orcryopreserved human hepatocytes and recombinant UGT enzyme were used for evaluationof interaction between drug-metabolic enzyme and baicalin. After compared withthe positive drug, there is no significant induction of Ba on CYP1A2, CYP3A4and CYP2B6which required by FDA as well as the UGTs. Though deeply studied the mechanism ofdrugs on the induction of CYP and inhibition of UGTs can promote the rational use of drugs,improve the effectiveness and safety of drug use.This study is helpful to evaluate the “medicine” of the mono-constitute of traditionalmedicine in the process of drug development. Studied the properties of baicalein, we can havea prediction on toxicity and adverse effect on the compound and give guidance for reasonableusing these drugs to avoid poison and other adverse effect with UGT1A1inhibitors. Theinteraction among traditional Chinese medicine could cause unbelievable adverse event, andit’s a most common phenomenon in drug-drug interaction. On the other hand, it’s key pointthat avoids the interaction of medicine-medicine and medicine-drug.