Induction of cytochrome P450 1A1 in rat liver slices by 7-ethoxycoumarin and 4-methyl-7-ethoxycoumarin

Effect of chronic administration of ostruthin on depression-like behavior in chronically stressed mice

We have previously shown that a single dose of a TREK-1 channel activator, ostruthin, exhibited antidepressant and anxiolytic effects in acute behavioral test models in mice. To assess the potential clinical application, it is essential to evaluate the effects of long-term administration of ostruthin in a chronically stressed mouse model, which is considered to be similar to the clinical condition of major depression in humans. Here, we tested the effects of a single and a 7-day administration of ostruthin on mice that were subjected to chronic unpredictable mild stress (CUMS). A single administration of ostruthin showed antidepressive effects in the tail suspension and forced swim tests of CUMS-treated mice. Unexpectedly, the 7-day administration exhibited only insignificant antidepressive and anxiolytic effects. The 7-day regimen did not affect food intake or body-weight gain, suggesting the absence of apparent cytotoxicity. The mice receiving the 7-day administration had significantly lower blood concentrations of ostruthin compared to those receiving a single dose, suggesting an upregulation of drug-metabolizing activities. These findings suggest that there is a need for stable TREK-1 channel activators that are not affected by drug metabolism.

Hydrogel embedding of precision-cut liver slices in a microfluidic device improves drug metabolic activity

A microfluidic-based biochip made of poly-(dimethylsiloxane) was recently reported for the first time by us for the incubation of precision-cut liver slices (PCLS). In this system, PCLS are continuously exposed to flow, to keep the incubation environment stable over time. Slice behavior in the biochip was compared with that of slices incubated in well plates, and verified for 24 h. The goal of the present study was to extend this incubation time. The viability and metabolic activity of precision-cut rat liver slices cultured in our novel microflow system was examined for 72 h. Slices were incubated for 1, 24, 48, and 72 h, and tested for viability (enzyme leakage (lactate dehydrogenase)) and metabolic activity (7-hydroxycoumarin (phase II) and 7-ethoxycoumarin (phase I and II)). Results show that liver slices retained a higher viability in the biochip when embedded in a hydrogel (Matrigel) over 72 h. This embedding prevented the slices from attaching to the upper polycarbonate surface in the microchamber, which occurred during prolonged (>24 h) incubation in the absence of hydrogel. Phase II metabolism was completely retained in hydrogel-embedded slices when medium supplemented with dexamethasone, insulin, and calf serum was used. However, phase I metabolism was significantly decreased with respect to the initial values in gel-embedded slices with medium supplements. Slices were still able to produce phase I metabolites after 72 h, but at only about ∼10% of the initial value. The same decrease in metabolic rate was observed in slices incubated in well plates, indicating that this decrease is due to the slices and medium rather than the incubation system. In conclusion, the biochip model was significantly improved by embedding slices in Matrigel and using proper medium supplements. This is important for in vitro testing of drug metabolism, drug-drug interactions, and (chronic) toxicity.

An in vivo and in vitro comparison of CYP induction in rat liver and intestine using slices and quantitative RT-PCR

Xenobiotics, including drugs, can influence cytochrome P450 (CYP) activity by upregulating the transcription of CYP genes. To minimize potential drug interactions, it is important to ascertain whether a compound will be an inducer of CYP enzymes early in the development of new therapeutic agents. In vivo and in vitro studies are reported that demonstrate the use of liver and intestinal slices as an in vitro model to predict potential CYP induction in vivo. Rat liver slices and intestinal slices were incubated, for 24 h and 6 h, respectively, with beta-naphthoflavone (betaNF), phenobarbital (PB) or dexamethasone (DEX). In an in vivo study, rats were treated with the same compounds for 3 days. In vivo and in vitro CYP mRNA levels were measured by using real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). In addition, CYP enzyme activities were determined in rat liver slices after 48 h incubation. In both rat liver and intestinal slices, betaNF significantly induced CYP1A1, CYP1A2 and CYP2B1 mRNA levels. PB significantly induced CYP2B1. In liver slices a minor induction of CYP1A1 and CYP3A1 by PB was observed, whereas DEX significantly induced CYP3A1, CYP2B1 and CYP1A2 mRNA levels. The induction profiles (qualitative and quantitative) observed in vivo and in vitro are quite similar. All together, these data demonstrate that liver and intestinal slices are a useful and predictive tool to study CYP induction.

Precision-cut tissue slices from transgenic mice as an in vitro toxicology system

In these experiments precision-cut tissue slices from two existing transgenic mouse strains, with transgenes that couple promoting or binding elements to a reporter protein, were used for determination of reporter induction. This approach combines the power of transgenic animals with the practicality of in vitro systems to investigate the biological impact of xenobiotics. Additionally, the normal cellular architecture and heterogeneity is retained in precision-cut tissue slices. Two transgenic mouse strains, one of which couples the promoting region of CYP 1A1 to beta-galactosidase, and another which couples two forward and two backward 12-O-tetradecanoyl phorbol-13-acetate (TPA) repeat elements (TRE) to luciferase (termed AP-1/luciferase), were used to determine the feasibility of this approach. Precision-cut kidney and liver slices from both transgenic strains remain viable as determined by slice K(+) ion content and LDH enzyme release. Liver slices harvested from the CYP 1A1/beta-galactosidase transgenic mice exhibit a 14-fold increase in beta-galactosidase activity when incubated with beta-napthoflavone for 24 h. Kidney and liver slices obtained from the AP-1/luciferase transgenic mice demonstrate induction of luciferase (up to 2.5-fold) when incubated with phorbol myristate acetate (PMA or TPA) up to 4 h. These data indicate that precision-cut tissue slices from transgenic mice offer a novel in vitro method for toxicity evaluation while maintaining normal cell heterogeneity.

Oxidations of 17β-estradiol and estrone and their interconversions catalyzed by liver, mammary gland and mammary tumor after acute and chronic treatment of rats with indole-3-carbinol or β-naphthoflavone

Altered cytochrome P450-catalyzed metabolism of 17β-estradiol (E2) and estrone (E1) in the liver and (or) extrahepatic tissues may affect estrogen-sensitive tumorigenesis. We examined the effects of oral treatments of (i) indole-3-carbinol (I3C) at 250 or 500 mg/kg or β-naphthoflavone (β-NF) at 40 mg/kg of body weight (bw)/day from 51 to 54 days of age (acute regimen), and (ii) I3C at 250 mg/kg or β-NF at 20 mg/kg bw given 3x/week from 10 to 22 weeks of age (chronic regimen) in female Sprague-Dawley rats. We determined the effects of these treatments on the P450 content and P450 (CYP)-specific activities in the liver, P450-dependent metabolism of E2 and E1 by the liver and mammary gland, and interconversion of E1 and E2 catalyzed by 17β-hydroxysteroid dehydrogenase (17β-HSD) in these tissues and malignant mammary tumors. I3C at the two levels of acute regimen elicited similar responses. Acute and chronic treatments with I3C, but not β-NF, increased P450 content ~2-fold. I3C, and to a lesser extent β-NF, increased CYP1A1 and CYP1A2 probe activities in liver up to 117- and 27- fold, respectively, and after acute regimens, that of CYP3A by ~1.8-fold. I3C also increased activity of CYP2B up to 100-fold. Overall hepatic metabolism of E2 and E1, which was ~2-fold greater at 55 than 155 days of age, was increased (~2.8-fold) by I3C with 2-, 4-, 16α-, 6α-, 6β-, and 15α-hydroxy (OH) comprising [Formula: see text]54, 3, 2, ~2, ~5, 7, and 2%, respectively, of E1 and E2 metabolites. Acute regimens of β-NF increased 2- and 15α-OH-E2 (62 and 5% of total) from E2 and 2-, 4-, and 6α-OH-E1 + 6β-OH-E1 (32, 13, and 4% of total) from E1. Mammary gland metabolized E2 to E1 and small amounts of 15α-, 4-, 16α-, 6β-, and 6α-OH-E2. After the acute IC3 regimen, E2 was also converted to 2-OH-E2. 17β-HSD-catalyzed oxidation of E2 was favored in the liver and reduction of E1 was favored in mammary gland and tumor (= 1% of hepatic activity). An increased (~2-fold) ratio of reductive to oxidative activities in malignant mammary tumors by chronic I3C regimen may stimulate tumor growth. This is the first report showing that after chronic oral regimens, the I3C-, but not β-NF-, induced changes in CYP complement led to elevated E2 and E1 metabolism. The persistent effects of increased putative carcinogenic and estrogenic 4- and 16α-OH as well as 6α- and 6β-OH-E2 and 6β-OH-E1 might counteract those of the less estrogenic 2-OH metabolites, thus accounting for the lack of suppression of mammary tumorigenesis by I3C in our previous study.Key words: estrogen metabolism, P450, 17β-hydroxysteroid dehydrogenase, indole-3-carbinol, β-naphthoflavone.

Morphology and cytochrome P450 isoforms expression in precision-cut rat liver slices

Precision-cut liver slices are a widely accepted in vitro system for the examination of drug metabolism, enzyme induction, or hepatotoxic effects of xenobiotics. The maintenance of the distinct lobular expression and induction pattern of phase I biotransformation enzymes, however, has not been examined systematically so far. Thus, in the present study, both longitudinal and transversal sections of male rat liver slices were investigated morphologically, as well as immunohistochemically for the expression of different cytochrome P450 (CYP) isoforms after prolonged incubation or after exposure to typical inducers. Histopathological examinations revealed an increasing vacuolization of the periportal hepatocytes mainly in the middle of the slices from 6 h of incubation on, paralleled by a loss of glycogen in the respective cells. After 24 h, mainly in the center of the slices, necroses of cells occurred. After 48 h of incubation, typically a central band of coagulative necrosis flanked by superficial layers of viable cells was observed. Freshly prepared slices displayed a CYP subtypes expression as normal liver specimen, a very low centrilobular CYP 1A1 immunostaining, but a strong CYP 2B1 and 3A2 expression predominantly in the central and intermediate lobular zones. From 2 h on, the immunostaining for CYP 2B1 and 3A2 was to some extent reduced. After 24 h of incubation with beta-naphthoflavone, the CYP 1A1 and 2B1 expression was induced mainly in the viable cells around central veins, around some portal fields with bigger vessels and in the cell layers close to the slice surface. At the same sites, phenobarbital led to an increased CYP 2B1 and 3A2 expression and dexamethasone to an elevated CYP 3A2 immunostaining. These results show, that an in vitro induction of phase I enzymes in precision-cut liver slices can be demonstrated also immunohistochemically.

Para-nitrophenol glucuronidation and sulfation in rat and human liver slices

Para-nitrophenol (PNP) is a well-known substrate for both phase I (hydroxylation at cytochrome P450) and phase II reactions (glucuronidation and sulfation). HPLC separation of PNP conjugates has already been described, but not for respective studies with liver slices, which nowadays have proven to be a suitable model for metabolic studies. Therefore we adapted an HPLC method for the simultaneous measurement of PNP glucuronidation (PNP-G) and sulfation (PNP-S) in this in vitro system. Both activities are substantially maintained over an incubation period of 24 h. PNP-G activity, however, seems to be better preserved, as indicated by stable values for PNP-G but reduced PNP-S values after 48 h liver slice preincubation. 24 h exposure of the slices to beta-naphthoflavone or phenobarbital does not change PNP-G or PNP-S activities.