Model for the drug–drug interaction responsible for CYP3A enzyme inhibition. II: establishment and evaluation of dexamethasone-pretreated female rats

In vitro demonstration of antedrug mechanism of a pharmacokinetic booster to improve CYP3A4 substrates by CYP3A4-mediated metabolism inhibition

We previously reported novel benzyl-ether derivatives with an imidazole ring and a hydroxyl group (A-01) or carboxyl group (B-01) and esters (2 esters of A-01, and 7 esters of B-01) as pharmacokinetics (PK) boosters. This study demonstrates how these ester compounds embody the concept of a safe pharmacokinetic booster, with potent and transient inhibition of CYP3A4-mediated drug metabolism. As a model CYP3A4 substrate and CYP3A4 enzyme, midazolam (MDZ) and rat liver microsomes were used. A-01 inhibited MDZ metabolism significantly, while B-01 induced only slight inhibition. Although rat liver microsomes hydrolyzed the ester compounds over time, several ester compounds strongly inhibited MDZ metabolism. Due to the significant activity of A-01, A-01 esters affected MDZ metabolism, irrespective of hydrolysis state. Time-dependent inhibition evaluation indicated that the B-01 ester inhibition is not mechanism-based, as hydrolysis eliminated MDZ metabolism inhibition. We report that the B-01 esters significantly inhibit CYP3A4-mediated drug metabolism, and upon hydrolysis this property is eliminated. In conclusion, B-01 ester compounds may be safe PK boosters with antedrug characteristics.

Integrated Metabolomics and Network Pharmacology to Decipher the Latent Mechanisms of Protopanaxatriol against Acetic Acid-Induced Gastric Ulcer

Gastric ulcer (GU) is a peptic disease with high morbidity and mortality rates affecting approximately 4% of the population throughout the world. Current therapies for GU are limited by the high relapse incidence and side effects. Therefore, novel effective antiulcer drugs are urgently needed. Ginsenosides have shown good anti-GU effects, and the major intestinal bacterial metabolite of ginsenosides, protopanaxatriol (PPT), is believed to be the active component. In this study, we evaluated the anti-GU effect of PPT in rats in an acetic acid-induced GU model. High (H-PPT) and medium (M-PPT) doses of PPT (20.0 and 10.0 mg/mg/day) significantly reduced the ulcer area and the ET-1, IL-6, EGF, SOD, MDA and TNF-α levels in serum were regulated by PPT in a dose-dependent manner. We also investigated the mechanisms of anti-GU activity of PPT based on metabolomics coupled with network pharmacology strategy. The result was that 16 biomarkers, 3 targets and 3 metabolomic pathways were identified as playing a vital role in the treatment of GU with PPT and were further validated by molecular docking. In this study, we have demonstrated that the integrated analysis of metabolomics and network pharmacology is an effective strategy for deciphering the complicated mechanisms of natural compounds.

Induction of CYP3A by morroniside in rats

Morroniside is one of the most important iridoid glycosides in the herbal drug Cornus officinalis Sieb. et Zucc. The current study was designed to investigate the ex vivo and in vivo effects of morroniside on CYP3A activity in rats after treatment with morroniside for 7 days (at 10, 30, 90 mg/kg, i.g.). Morroniside was found to induce CYP3A. According to the ex vivo experiment, the activity of CYP3A was measured by the quantification of 1-hydroxymidazolam, which was the metabolite from CYP3A probe substrate, midazolam. The concentration of 1-hydroxymidazolam was determined by using a validated liquid chromatography coupled with tandem mass spectrometry detection (LC-MS/MS) method. The levels of messenger RNA (mRNA) and protein of CYP3A were determined by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting analysis, respectively. The pharmacokinetics of midazolam in rats after treatment with morroniside for 7 days (at 10, 30, 90 mg/kg, i.g.) were investigated in vivo. After treatment with morroniside, the activity, mRNA and protein expression of CYP3A were significantly induced and the absorbance and bioavailability of midazolam in rats were reduced. The results indicated that morroniside could induce the activity of CYP3A.

Gastroprotective efficacy and safety evaluation of scoparone derivatives on experimentally induced gastric lesions in rodents

This study investigated the gastroprotective efficacy of synthesized scoparone derivatives on experimentally induced gastritis and their toxicological safety. Six scoparone derivatives were synthesized and screened for gastroprotective activities against HCl/ethanol- and indomethacin-induced gastric ulcers in rats. Among these compounds, 5,6,7-trimethoxycoumarin and 6,7,8-trimethoxycoumarin were found to have gastroprotective activity greater than the standard drug rebamipide; 6-methoxy-7,8-methylenedioxycoumarin, 6-methoxy-7,8-(1-methoxy)-methylenedioxycoumarin, 6,7-methylenedioxycoumarin, and 6,7-(1-methoxy)-methylenedioxycoumarin were found to be equipotent or less potent that of rebamipide. Pharmacological studies suggest that the presence of a methoxy group at position C-5 or C-8 of the scoparone's phenyl ring significantly improves gastroprotective activity, whereas the presence of a dioxolane ring at C-6, C-7, or C-8 was found to have decreased activity. In order to assess toxicological safety, two of the potent gastroprotective scoparone derivatives-5,6,7-trimethoxycoumarin and 6,7,8-trimethoxycoumarin-were examined for their acute toxicity in mice as well as their effect on cytochrome P450 (CYP) enzyme activity. These two compounds showed low acute oral toxicity in adult male and female mice, and caused minimal changes to CYP3A4 and CYP2C9 enzyme activity. These results indicate that compared to other scoparone derivatives, 5,6,7-trimethoxycoumarin and 6,7,8-trimethoxycoumarin can improve gastroprotective effects, and they have low toxicity and minimal effects on drug-metabolizing enzymes.

Impact of nonlinear midazolam pharmacokinetics on the magnitude of the midazolam-ketoconazole interaction in rats

Numerous groups have described the rat as an in vivo model for the assessment and prediction of drug-drug interactions (DDIs) in humans involving the inhibition of cytochrome P450 3A forms. Even for a well-established substrate-inhibitor pair like midazolam-ketoconazole, however, the magnitude of the DDI in rats (e.g. 1.5- to 5-fold) does not relate to what is observed clinically (e.g. 5- to 16-fold). Because nonlinear substrate pharmacokinetics (PK) may result in a weaker interaction, it was hypothesized that the lower magnitude of interaction observed in rats was due to the saturation of metabolic pathway(s) of midazolam at the doses used (10-20 mg/kg). Therefore, the inhibitory effects of ketoconazole were reevaluated at lower oral (1 and 5 mg/kg) and intravenous (IV) (1 mg/kg) doses of midazolam. In support of the hypothesis, oral exposure at 5 mg/kg dose of midazolam was 18-fold higher compared to that at 1 mg/kg. Furthermore, when the interaction was investigated at the lower midazolam dose (1 mg/kg), ketoconazole increased the IV and oral exposure of midazolam by 7-fold and 11-fold, respectively. A weaker DDI (1.5- to 1.8-fold) was observed at the higher oral midazolam dose. Collectively, these results suggest that the lower reported interaction in rats is likely due to saturation of midazolam clearance at the doses used. Therefore, when the rat is used as a DDI model to screen and differentiate compounds, or predict CYP3A inhibition in humans, it is important to use low doses of midazolam and ensure linear PK.

Effects of Radix Astragali and Radix Rehmanniae, the components of an anti-diabetic foot ulcer herbal formula, on metabolism of model CYP1A2, CYP2C9, CYP2D6, CYP2E1 and CYP3A4 probe substrates in pooled human liver microsomes and specific CYP isoforms

The present study investigated the effects of Radix Astragali (RA) and Radix Rehmanniae (RR), the major components of an anti-diabetic foot ulcer herbal formula (NF3), on the metabolism of model probe substrates of human CYP isoforms, CYP1A2, CYP2C9, CYP2D6, CYP2E1 and CYP3A4, which are important in the metabolism of a variety of xenobiotics. The effects of RA or RR on human CYP1A2 (phenacetin O-deethylase), CYP2C9 (tolbutamide 4-hydroxylase), CYP2D6 (dextromethorphan O-demethylase), CYP2E1 (chlorzoxazone 6-hydroxylase) and CYP3A4 (testosterone 6β-hydroxylase) activities were investigated using pooled human liver microsomes. NF3 competitively inhibited activities of CYP2C9 (IC(50)=0.98mg/ml) and CYP3A4 (IC(50)=0.76mg/ml), with K(i) of 0.67 and 1.0mg/ml, respectively. With specific human CYP2C9 and CYP3A4 isoforms, NF3 competitively inhibited activities of CYP2C9 (IC(50)=0.86mg/ml) and CYP3A4 (IC(50)=0.88mg/ml), with K(i) of 0.57 and 1.6mg/ml, respectively. Studies on RA or RR individually showed that RR was more important in the metabolic interaction with the model CYP probe substrates. RR dose-dependently inhibited the testosterone 6β-hydroxylation (K(i)=0.33mg/ml) while RA showed only minimal metabolic interaction potential with the model CYP probe substrates studied. This study showed that RR and the NF3 formula are metabolized mainly by CYP2C9 and/or CYP3A4, but weakly by CYP1A2, CYP2D6 and CYP2E1. The relatively high K(i) values of NF3 (for CYP2C9 and CYP3A4 metabolism) and RR (for CYP3A4 metabolism) would suggest a low potential for NF3 to cause herb-drug interaction involving these CYP isoforms.

Polysaccharide peptides from Coriolus versicolor competitively inhibit model cytochrome P450 enzyme probe substrates metabolism in human liver microsomes

Polysaccharide peptide (PSP), isolated from COV-1 strain of Coriolus versicolor, is commonly used as an adjunct in cancer chemotherapy or health supplement in China. Previous studies have shown that PSP decreased antipyrine clearance and inhibited rat CYP2C11-mediated tolbutamide 4-hydroxylation and in human CYP2C9. In this study, the effects of the water extractable fraction of PSP on the metabolism of model CYP1A2, CYP2D6, CYP2E1 and CYP3A4 probe substrates were investigated in pooled human liver microsomes. PSP (1.25-20μM) dose-dependently decreased CYP1A2-mediated metabolism of phenacetin to paracetamol (IC(50) 19.7μM) and CYP3A4-mediated metabolism of testosterone to 6β-hydroxytestosterone (IC(20) 7.06μM). Enzyme kinetics studies showed the inhibition of CYP1A2 activity was competitive and concentration-dependent (K(i)=18.4μM). Inhibition of testosterone to 6β-hydroxytestosterone was also competitive and concentration-dependent (K(i)=31.8μM). Metabolism of dextromethorphan to dextrorphan (CYP2D6-mediated) and chlorzoxazone to 6-hydroxychlorzoxazone (CYP2E1-mediated) was only minimally inhibited by PSP, with IC(20) values at 15.6μM and 11.9μM, respectively. This study demonstrated that PSP competitively inhibited the CYP1A2- and CYP3A4-mediated metabolism of model probe substrates in human liver microsomes in vitro. The relatively high K(i) values for CYP1A2 and CYP3A4 would suggest a low potential for PSP to cause herb-drug interaction related to these CYP isoforms.

Investigation of cytochrome P450 1A2 and 3A inhibitory properties of Danshen tincture

Danshen (Salvia miltiorrhiza Bunge) as a famous Traditional Chinese medicine is widely used in the treatment of cardiovascular and cerebrovascular diseases in the world. Danshen tincture (DT), extracted from Danshen root with a mixture of water and alcohol, is a commonly used preparation method for human consumption. The aim of this study was to investigate the effects of DT on the cytochrome P450 (CYP) 1A2 and 3A activities by human and rat liver microsomes. Effects of DT were assessed with use of Danshen ethanolic extract (DEE) and selective substrates, markers of CYP activities. DEE (0.5-10 μg/ml) competitively inhibited human and rat liver microsomal CYP1A2 activity with inhibition constant (K(i)) values at 3.40 and 5.16 μg/ml, respectively. At the same time, DEE (2.5-20 μg/ml) not only noncompetitively inhibited human liver microsomal CYP3A4/5 activity with a K(i) of 11.9 μg/ml, but also competitively inhibited rat liver microsomal CYP3A1/2 activity with a K(i) of 52.1 μg/ml. The data indicate that DEE inhibited the metabolism of CYP1A2 and 3A substrates in human and rat liver in vitro with different mode of inhibition. This study may be helpful for clinical application of Danshen tincture.

Major tanshinones of Danshen (Salvia miltiorrhiza) exhibit different modes of inhibition on human CYP1A2, CYP2C9, CYP2E1 and CYP3A4 activities in vitro

This study investigated the effects of tanshinones on human CYP1A2 (phenacetin O-deethylase), CYP2C9 (tolbutamide 4-hydroxylase), CYP2E1 (chlorzoxazone 6-hydroxylase) and CYP3A4 (testosterone 6beta-hydroxylase) activities in vitro using pooled human liver microsomes and specific human CYP isoforms. Tanshinone I, tanshinone IIA, and cryptotanshinone were potent competitive CYP1A2 inhibitors (K(i)=1.5-2.5 microM); medium competitive inhibitors of CYP2C9 (K(i)=22-62 microM); medium competitive inhibitors of CYP2E1 (K(i)=3.67 microM) for tanshinone I and 10.8 microM for crytotanshinone; but weak competitive inhibitors of CYP3A4 (K(i)=86-220 microM). Dihydrotanshinone was a competitive inhibitor of human CYP1A2 (K(i)=0.53 microM) and CYP2C9 (K(i)=1.92 microM), a noncompetitive inhibitor of CYP3A4 (K(i)=2.11 microM) but an uncompetitive CYP2E1 inhibitor. In conclusion, these results showed that tanshinones inhibited the metabolism of various CYP probe substrates in human liver microsomes and specific human CYP isoforms in vitro. Given that CYP1A2, 2C9, 2E1 and 3A4 are responsible for the metabolism and disposition of a large number of drugs currently used, the potential herb-drug interactions of Danshen preparations containing the major tanshinones with drugs which are substrates of these CYPs may be important.

In vitro evaluation of reversible and irreversible cytochrome P450 inhibition: current status on methodologies and their utility for predicting drug-drug interactions

It is widely accepted that today's practice of polypharmacy inevitably increases the incidence of drug-drug interactions (DDIs). Serious DDI is a major liability for any new chemical entity (NCE) entering the pharmaceutical market. As such, pharmaceutical companies employ various strategies to avoid problematic compounds for clinical development. A key cause for DDIs is the inhibition of cytochrome P450 enzymes (CYPs) that are responsible for metabolic clearance of many drugs. Screening for inhibition potency of CYPs by NCEs has therefore become a routine practice during the drug discovery stage. However, in order to make proper use of DDI data, an understanding of the strengths and weaknesses of the various experimental systems in current use is required. An illustrated review of experimental practices is presented with discussion of likely future developments. The combination of high quality in vitro data generation and the application of in vivo CYP inhibition modelling approaches should allow more informed decisions to be made in the search for drug molecules with acceptable DDI characteristics.

Generation of specific antibodies and their use to characterize sex differences in four rat P450 3A enzymes following vehicle and pregnenolone 16alpha-carbonitrile treatment

The purpose of this study was to identify isozyme-specific antibodies and use them to determine the expression levels of four P450 3A enzymes in the livers of vehicle- and pregnenolone 16alpha-carbonitrile (PCN)-treated rats of both sexes, since previous work on mRNA levels has shown considerable sexual dimorphism. Using Western blot analysis with four isozyme-specific antibodies, we show that P450 3A1, 3A2, and 3A9 were expressed in vehicle-treated adult female rats at very low levels whereas P450 3A18 was not detected. PCN treatment of females strongly induced the expression of P450 3A1 in the livers with protein product increases of 214-, 3-, and 5-fold for P450 3A1, 3A2, and 3A9, respectively, and P450 3A18 was induced to 3.7 pmol/mg protein. In contrast, all four P450 3As were detected in livers of vehicle-treated males, in the order of 3A2 >> 3A18 > 3A9 approximately = 3A1. The protein product increases induced by PCN treatment of male rats were 92-, 3-, 6-, and 16-fold for P450 3A1, 3A2, 3A9, and 3A18, respectively.