Determination of testosterone metabolites in human hepatocytes. I. Development of an on-line sample preparation liquid chromatography technique and mass spectroscopic detection of 6beta-hydroxytestosterone

Metabolic Stability and Metabolite Identification of CYP450 Probe Substrates in Ferret Hepatocytes

BACKGROUND

Ferrets exhibit similar lung physiology to humans and display similar clinical signs following influenza infection, making them a valuable model for studying high susceptibility and infection patterns. However, the metabolic fate of several common human CYP450 probe substrates in ferrets is still unknown and has not been studied.

OBJECTIVE

The purpose of this study was to investigate the metabolism of nine human CYP450 probe substrates in ferret hepatocytes and explore their metabolic rate differences between ferrets and other species.

METHOD

Nine substrates were individually incubated in ferret hepatocytes for up to 120 min. At each time point, 30 μL mixtures were extracted for stability analysis using LC-MS/MS methods. After a 120-minute incubation period, 400 μL of the mixtures were extracted for metabolite identification using UHPLC-QExactive Plus.

RESULTS

The metabolic clearance was determined as follows: testosterone > phenacetin > bupropion > omeprazole > midazolam > dextromethorphan > chlorzoxazone > taxol > diclofenac. Seven metabolites were identified from phenacetin. Deethylation was found to be the major pathway, and the major metabolite was matched with acetaminophen as probed with the CYP1A2 enzyme. Six metabolites were identified from diclofenac. Glucuronidation was the primary pathway, and a metabolite was found to match 4-OH-diclofenac as probed with the CYP2C9 enzyme. Twenty-two metabolites were identified from omeprazole. The major metabolic pathways included mono-oxygenation and sulfoxide to thioether conversion. No metabolite was found to match with 5-OH-omeprazole as probed with the CYP2C19 enzyme. Twenty-two metabolites were identified from dextromethorphan. Demethylation was found to be the major metabolic pathway, and one demethylation metabolite was matched with dextrorphan as probed with the CYP2D6 enzyme. Fourteen metabolites were identified from midazolam. Mono-oxygenation was found to be the primary metabolic pathway, and one of the mono-oxygenation metabolites was matched with 1-OH-midazolam as probed with the CYP3A4 enzyme. Eight metabolites were identified from testosterone. Mono-oxygenation and glucuronidation were identified as the major metabolic pathways. One mono-oxygenation was matched with 6-.-testosterone as probed with the CYP3A4 enzyme. Six metabolites were identified from taxol. Hydrolysis and mono-oxygenation were the top two metabolic pathways. No metabolite was matched with 6-.-OH-taxol as probed with the CYP2C8 enzyme. Ten metabolites were identified from bupropion. Mono-oxygenation and hydrogenation were identified as the top two metabolic pathways. No mono-oxygenation metabolite was matched with hydroxy-bupropion as probed with the CYP2B6 enzyme. Nine metabolites were identified from chlorzoxazone. Monooxygenation and sulfation were the top two metabolic pathways. One mono-oxygenation metabolite was matched with 6-OH-chlorzoxazone as probed with the CYP2E1 enzyme.

CONCLUSION

Nine human CYP probe substrates were clearly metabolized in ferret hepatocytes, demonstrating substrate-dependent metabolic rates in ferret hepatocytes and species-dependent metabolic rates in mouse, rat, dog, monkey, and human hepatocytes. Except for 6-a-5-OH-omeprazole, 6-.-OH-taxol, and hydroxy-bupropion, specific metabolites of other six probe substrates in ferret hepatocytes were detected and identified as probed with six human CYP enzymes, respectively.

In vitro inhibition and induction of human liver cytochrome P450 enzymes by a novel anti-fibrotic drug fluorofenidone

Fluorofenidone (AKF-PD) is an analog of pirfenidone and shows stronger antifibrotic effect and lower toxicity compared to pirfenidone in preclinical studies. However, the inhibitory and inducible effects of AKF-PD on human CYP450s are unclear. The aim of this study was to evaluate the ability of AKF-PD to inhibit and induce CYP450s in vitro.In inhibition study, the inhibitory effects of CYP1A2, CYP3A4, CYP2C9, CYP2E1, CYP2C19 and CYP2D6 by AKF-PD were evaluated with the metabolic rate of probe drug of each enzyme in pooled human liver microsomes. The enzyme inducible potential of AKF-PD was evaluated by the mRNA expression and enzyme activity of CYP1A2, CYP2B6 and CYP3A4 in human hepatocytes. The results suggested that AKF-PD produced weak inhibition on CYP1A2 and CYP2C19, while no inhibitory effects were found on the other enzymes. Since the plasma concentration of AKF-PD is much lower than the IC₅₀ values of both CYP1A2 and CYP2C19, the inhibitory effects can be reasonably ignored.On the other hand, AKF-PD showed no inducible effects on CYP1A2 while showed potential inducible ability on CYP2B6 and CYP3A4 in some test groups. Further study of this novel anti-fibrotic drug should take into account in clinical therapies.

The enhancement of cardiotoxicity that results from inhibiton of CYP 3A4 activity and hERG channel by berberine in combination with statins

Metabolism of most endogenous and exogenous compounds is usually produced by the oxidation of cytochrome P450. Due to drug-drug interactions caused by the inhibition or induction of cytochrome P450 enzymes, changes in drug metabolism are the major causes of drug toxicity, CYP3A4 is one of the key isozymes, and involved in the metabolism of over 60% of clinical drugs. Human ether-a-go-go related genes (hERG) potassium channel is the most important target of many drugs and plays an important role in cardiac repolarization. Blockade of this channel may lead to long QT syndrome (LQTS), leading to sudden cardiac death. Therefore, it is necessary to evaluate the inhibitory properties of drugs on cytochrome P450 enzymes and hERG channel. We primarily evaluate the safety of berberine in combination with statins. Based on these findings, berberine in combination with statins has a greater inhibitory effect on CYP3A4 activity and CYP3A4 protein and mRNA expression than berberine alone. Simvastatin and atorvastatin reduce hERG current by accelerating channel inactivation. At the same time, the inhibitory effect of berberine and statin combination increased on hERG current by reducing the time constant of inactivation than the single drug alone. These results indicate that berberine in combination with statins can increase cardiotoxicity by inhibiting CYP3A4 and hERG channel.

The enhancement of cardiac toxicity by concomitant administration of Berberine and macrolides

As is well-known, hERG plays an essential role in phase III repolarization of cardiac action potentials. Blocking of hERG channels can lead to LQTS. Inhibition of the metabolism of CYPs activities may elevate plasma levels, to further increase accumulation of drug on cardiac. The elevated serum levels may however elicit unexpected toxicities. Therefore, the inhibition tests of hERG and CYP are central to the preclinical studies because they may lead to severe cardiac toxicity. Berberine is widely used as an antibacterial agent and often combined with macrolides to treat gastropathy. Our objective was to assess cardiac toxicity during the combined use of Berberine with macrolides. (1) Azithromycin reduced hERG currents by accelerated channel inactivation. (2) The combination of Berberine with Azithromycin reduced hERG currents, producing an inhibitive effect stronger than use of a single drug alone, due to the high binding affinity for the onset of inactivation. (3) When cells were perfused concomitantly with Berberine and Clarithromycin, they showed a stronger inhibitive effect on hERG currents by decreasing the time constant for the onset of inactivation. (4) The combined administration of Berberine with Clarithromycin had a powerful inhibitive effect on CYP3A activities than use of a single drug alone. Collectively, these results demonstrated that concomitant use of Berberine with macrolides may require close monitoring because of potential drug toxicities, especially cardiac toxicity.

Pinelliae rhizoma, a toxic chinese herb, can significantly inhibit CYP3A activity in rats

Raw Pinelliae Rhizoma (RPR) is a representative toxic herb that is widely used for eliminating phlegm or treating cough and vomiting. Given its irritant toxicity, its processed products, including Pinelliae Rhizoma Praeparatum (PRP) and Pinelliae Rhizoma Praeparatum cum Zingibere et Alumine (PRPZA), are more commonly applied and administered concomitantly with other chemical drugs, such as cough medications. This study aimed to investigate the effects of RPR, PRP, and PRPZA on CYP3A activity. Testosterone (Tes) and buspirone (BP) were used as specific probe substrates ex vivo and in vivo, respectively. CYP3A activity was determined by the metabolite formation ratios from the substrates. Ex vivo results show that the metabolite formation ratios from Tes significantly decreased, indicating that RPR, PRP, and PRPZA could inhibit CYP3A activity in rats. CYP3A protein and mRNA levels were determined to explore the underlying mechanism. These levels showed marked and consistent down-regulation with CYP3A activity. A significant decrease in metabolite formation ratios from BP was also found in PRPZA group in vivo, implying that PRPZA could inhibit CYP3A activity. Conclusively, co-administration of PR with other CYP3A-metabolizing drugs may cause drug–drug interactions. Clinical use of PR-related formulae should be monitored carefully to avoid adverse interactions.

Coadministration of Pinellia ternata Can Significantly Reduce Aconitum carmichaelii to Inhibit CYP3A Activity in Rats

Chuanwu (CW), the mother root of Aconitum carmichaelii Debx., is a traditional Chinese medicine (TCM) for treating traumatic injuries, rheumatoid arthritis, and tumors. CW coadministered with banxia (BX), the root of Pinellia ternata, is also widely prescribed in clinical practice. However, the mechanism of this combination is yet deciphered. Current study aimed to investigate the effects of CW, including raw chuanwu (RCW) and processed chuanwu (PCW) alone, as well as CW coadministered with BX on CYP3A activity. Buspirone (BP) and testosterone (Tes) were used as specific probe substrates in vivo and ex vivo, respectively. CYP3A activity was determined by the metabolites formation ratios from the substrates. Compared with those in the control group, the metabolites formation ratios significantly decreased in the RCW and PCW alone groups, accompanied by a marked decrease in CYP3A protein and mRNA levels. However, there was a significant increase in those ratios in the RCW-BX and PCW-BX groups compared to the RCW and PCW alone groups. The results indicated that both RCW and PCW can inhibit CYP3A activity in rats because of downregulation of CYP3A protein and mRNA levels. Decreases in CYP3A activity can be reversed by coadministration with BX.

Herb-drug interaction of 50 Chinese herbal medicines on CYP3A4 activity in vitro and in vivo

The purpose of this study is to evaluate the effects of Chinese herbal medicines on the enzymatic activity of CYP3A4 and the possible metabolism-based herb-drug interactions in human liver microsomes and in rats. Fifty single-herbal preparations were screened for the activity of CYP3A4 using human liver microsomes for an in vitro probe reaction study. The enzymatic activity of CYP3A4 was estimated by determing the 6β-hydroxytestosterone metabolized from testosterone performed on a liquid chromatography-tandem mass spectrometry (LC-MS/MS). Huang Qin (Scutellaria baicalensis Geprgi), Mu Dan Pi (Paeonia suffruticosa Andr.), Ji Shiee Terng (Spatholobus suberectus Dunn.) and Huang Qi (Astragalus membranaceus [Fisch] Bge) have been demonstrated to have remarkable inhibiting effects on the metabolism of CYP3A4, whereas Xi Yi Hua (Magnolia biondii Pamp.) exhibited a moderate inhibition. These five single herbs were further investigated in an animal study using midazolam. Mu Dan Pi, Ji Shiee Terng and Huang Qi were observed to have greatly increased in the C(max) and AUC of midazolam. This study provides evidence of possible herb-drug interactions involved with certain single herbs.

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.

Restricted-access media supports for direct high-throughput analysis of biological fluid samples: review of recent applications

This review presents an update on the use of restricted-access materials (RAMs) for direct injection of biological samples. The fundamental improvements in the preparation of tailored RAMs and the diversity of applications with these phases are presented. Insights into diminishing the matrix effect by the use of RAM supports in methods by LC–MS and into the low number of methods for enantiomeric separations by direct injections of biological samples are addressed. The diversity of systems that incorporate RAMs for selective sample clean-up or fractionation in proteome and peptidome analysis is also covered.

Rapid quantitation of testosterone hydroxyl metabolites by ultra-performance liquid chromatography and mass spectrometry

A rapid and sensitive ultra-performance liquid chromatography and mass spectrometry (UPLC/MS) method was developed to simultaneously quantify seven monohydroxyl testosterone metabolites (16alpha-, 2alpha-, 7alpha-, 6alpha-, 2beta-, 6beta-, and 16beta-hydroxyl testosterones) in rat liver microsomes. The UPLC system used a short 1.7-microm particle size column coupled to a Sciex 4000 Q trap in multiple reaction monitor (MRM) mode. All hydroxyl testosterones were resolved within 2.5 min. A 4-day validation was performed to determine the linearity, repeatability, reproducibility and accuracy of the method in rat liver microsomes. This method is applicable to the measurement of the testosterone hydroxylase activity in biological matrices such as the liver microsome incubates.

Enzyme induction in cryopreserved human hepatocyte cultures

Freshly isolated human hepatocytes are considered as the gold standard for in vitro testing of drug candidates. Meanwhile also cryopreserved human hepatocyte suspensions are available. However, a drawback of these cells is the incalculability of attachment to the culture dish. Therefore, we established a technique freezing hepatocytes cultured on a collagen gel. After thawing damaged cells were removed to a certain extent by gentle washing with culture medium prior to adding an upper gel layer. The morphology of the resulting hepatocyte cultures could not be distinguished from that of non-frozen cells. However, basal activities of cytochrome P450 isoforms decreased in cryopreserved compared to non-frozen hepatocytes, as evidenced by analysis of testosterone hydroxylation (OHT) in positions 6beta, 16alpha, 2beta and 6alpha. Nevertheless, enzyme induction factors caused by 24 h incubation with 50 microM rifampicin were similar in cryopreserved and non-frozen hepatocytes. In cryopreserved hepatocytes rifampicin caused an increase in mean values of 6beta-OHT formation from 57.2 to 157.7 pmol/well/min (2.8-fold), compared to an increase from 115.8 to 269.1 pmol/well/min (2.3-fold) in non-frozen cells. Similarly, 16alpha- and 2beta-OHT showed induction factors of 2.4- and 2.3-fold in cryopreserved compared to 1.6- and 2.4-fold in non-frozen hepatocytes, respectively. In conclusion, human hepatocytes cryopreserved on collagen gels show a clear induction of CYP3A4 by rifampicin, although the basal activities are reduced compared to non-frozen cells.

Development and validation of a microsomal online cytochrome P450 bioreactor coupled to solid-phase extraction and reversed-phase liquid chromatography

The development and validation of an online cytochrome P450 (CYP)-based bioreactor coupled to automated solid-phase extraction (SPE) and gradient HPLC separation is described. The analytical method was checked on intra- and inter-day repeatability of the ethoxyresorufin-O-demethylation (EROD) reaction with CYP 1Al/1A2 containing beta-NF induced rat liver microsomes as an enzyme source. These experiments showed that CYP activity was linearly decreased with 16% over an 11 h period. Inter-day measurements had a CV of 9.1%. Furthermore, Km and Vmax values of the EROD reaction, measured with the bioreactor, were 2.72 +/- 0.46 microM and 7.9 +/- 0.5 nmol/min/mg protein, respectively. These were in good correspondence with Km and Vmax values, measured with standard batch assay, which amounted 0.66 +/- 0.08 microM and 6.4 +/- 0.2 nmol/min/mg protein respectively. In conclusion the newly developed analytical method can be used effectively and at a microliter scale for online generation, extraction and separation of metabolites.

Liquid chromatographic–mass spectrometric method to assess cytochrome P450-mediated metabolism of testosterone by rat everted gut sacs

A rapid, sensitive and specific method was developed for the simultaneous assay of testosterone, androstenedione and 6beta-hydroxytestosterone (6beta-OHT) in the TC199 tissue culture medium used in intestinal drug metabolism studies with the rat everted gut sac model. An electrospray LC-MS method was validated in the concentration range of 0.025-9.5 microM (7.2 ng-2.7 microg/mL) for testosterone and androstenedione and 0.01-4 microM (3 ng-1.2 microg/mL) for 6beta-hydroxytestosterone. The limits of quantification (LOQ) with an injection volume of 10 microL were 0.0005 microM (4.9 fmol, 1.4 pg injected), 0.004 microM (0.04 pmol, 11.4 pg injected) and 0.03 microM (0.3 pmol, 91 pg injected), respectively. The method also detected the other testosterone metabolites, the 16alpha-, 16beta-, 2beta- and 2alpha-hydroxytestosterones and was then used to study the metabolism of testosterone during its absorption by rat intestine in vitro, using everted gut sacs.

Analysis of anabolic steroids by partial filling micellar electrokinetic capillary chromatography and electrospray mass spectrometry

A partial filling micellar electrokinetic capillary chromatography (PF-MEKC) separation of six anabolic androgenic steroids (androstenedione, metandienone, fluoxymesterone, methyltestosterone, 17-epimetandienone and testosterone) is introduced. The method utilises a mixed micellar solution consisting of sodium dodecyl sulphate (SDS) and sodium taurocholate. The analytes are detected with a photodiode array detector at 247 nm wavelength. Methyltestosterone is used as internal standard. The detection limits were 39 microg/L for androstenedione, 40 microg/L for testosterone, 45 microg/L for fluoxymesterone, 45-90 microg/L for 17-epimetandienone, 59 microg/L for methyltestosterone and 90 microg/L for metandienone. Linear correlation between concentration (0.1-5.0 mg/L) and detector response was obtained with r2 of 0.994 for fluoxymesterone, 0.998 for 17-epimetandienone and 0.999 for androstenedione, metandienone and testosterone. In addition, ionisation of the investigated compounds in electrospray mass spectrometry (ESI-MS) was studied in positive ion mode. The most intense signal (100%) was the protonated molecular ion [M + H]+, except for 17-epimetandienone, which gave its strongest signal at m/z corresponding to [M - H2O + H]+. Finally, separation and identification of fluoxymesterone, androstenedione and testosterone by PF-MEKC-ESI-MS is described. This is the first use of PF-MEKC and PF-MEKC-ESI-MS assays for anabolic androgenic steroids.

Restricted access materials and large particle supports for on-line sample preparation: an attractive approach for biological fluids analysis

An analytical process generally involves four main steps: (1) sample preparation; (2) analytical separation; (3) detection; and (4) data handling. In the bioanalytical field, sample preparation is often considered as the time-limiting step. Indeed, the extraction techniques commonly used for biological matrices such as liquid-liquid extraction (LLE) and solid-phase extraction (SPE) are achieved in the off-line mode. In order to perform a high throughput analysis, efforts have been engaged in developing a faster sample purification process. Among different strategies, the introduction of special extraction sorbents, such as the restricted access media (RAM) and large particle supports (LPS), allowing the direct and repetitive injection of complex biological matrices, represents a very attractive approach. Integrated in a liquid chromatography (LC) system, these extraction supports lead to the automation, simplification and speeding up of the sample preparation process. In this paper, RAM and LPS are reviewed and particular attention is given to commercially available supports. Applications of these extraction supports, are presented in single column and column-switching configurations, for the direct analysis of compounds in various biological fluids.