Cyclosporin A metabolism in human liver, kidney, and intestine slices. Comparison to rat and dog slices and human cell lines.
Drug Safety Assessment, Sandoz Pharma Ltd., Basel, Switzerland.
This study assesses the contribution of cyclosporin A (CsA) metabolism at sites of CsA-induced toxicity: kidney and liver, and a site of absorption, the intestine. With organ slice cultures (8 mm phi), it has been possible to demonstrate that the extrahepatic metabolism of CsA is significant. Both human kidney and colonic mucosal tissue metabolize CsA (1 microM, 24 hr) as analyzed by HPLC. The major metabolite M17 was formed in the kidney at an initial rate of 3 pmol/hr/mg slice protein, which was comparable to M17 formation in the liver slices (5 pmol/hr/mg slice protein). The rate of total CsA metabolism by human kidney slices represents about 42% the rate in liver slices. The metabolism of CsA to M17 was the same in the human kidney cell line 293; however, CsA metabolism was not detectable using human kidney microsomes, nor was metabolism clearly evident in either rat or dog kidney slice cultures. The metabolism of CsA by human colonic mucosal slices to at least three metabolites and the metabolism of CsA by the human intestinal cell line FHs74 Int indicates that the intestinal metabolism of CsA contributes to the first-pass effect of the drug. The liver proved to be the major site of CsA biotransformation in terms of the complexity of metabolites produced, whereas the human liver HepG2 cell line proved not to be a suitable model for CsA metabolism. A time course revealed that the first metabolites formed in the liver slice cultures were the monohydroxylated, M1 and M17, and N-demethylated, M21, followed by the secondary metabolites (including M8, M13, and M18).(ABSTRACT TRUNCATED AT 250 WORDS)
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, AB T6G 2N8, Canada.
Valspodar is a P-glycoprotein inhibitor widely used in preclinical and clinical studies for overcoming multidrug resistance. Despite this, the pharmacokinetics of valspodar in rat, a commonly used animal model, have not been reported. Here, we report on the pharmacokinetics of valspodar in Sprague-Dawley rats following intravenous and oral administration of its Cremophor EL formulation, which has been used for humans in clinical trials. After intravenous doses, valspodar displayed properties of slow clearance and a large volume of distribution. Its plasma unbound fraction was around 15% in the Cremophor EL formulation used in the study. After 10 mg kg(-1) orally it was rapidly absorbed with an average maximal plasma concentration of 1.48 mg l(-1) within approximately 2 h. The mean bioavailability of valspodar was 42.8%. In rat, valspodar showed properties of low hepatic extraction and wide distribution, similar to that of its structural analogue cyclosporine A.
University of Groningen, Department of Pharmacokinetics and Drug Delivery, Research Institute for Pharmacy, A. Deusinglaan 1, 9713 AV Groningen, The Netherlands. I.A.M.de.Graaf@rug.nl
Precision-cut tissue slices have been applied by many researchers because they represent an organ mini-model that closely resembles the organ from which it is prepared, with all cell types present in their original tissue-matrix configuration. Preparation and incubation methods of precision-cut tissue slices from various tissues are discussed and recommendations are given for optimal handling and culturing to retain optimal viability and functional integrity. The potential of precision-cut tissue slices from several organs to predict metabolite profiles and metabolic clearance of novel drugs, the involvement of transporters and the induction and inhibition of drug metabolism is discussed. To allow regular use of tissue slices in drug discovery and development, improvement of cryopreservation methods for precision-cut tissue slices is of great importance. It is concluded that the use of tissue slices in the pharmaceutical industry and in academic research can contribute significantly to obtain relevant information about metabolism and drug-drug interactions in various organs and pharmacokinetics of novel chemical entities in man, and thereby to the development of safe drugs.
Department of Pharmacokinetics and Drug Delivery, Groningen University Institute for Drug Exploration, Groningen, The Netherlands.
Although the liver has long been thought to play the major role in drug metabolism, also the metabolic capacity of the intestine is more and more recognized. In vivo studies eventually pointed out not only the significance of first-pass metabolism by the intestinal wall for the bioavailability of several compounds, but also the relevance of transporters in this process. Only a few methods are available to study drug metabolism in vivo or in situ and with most of these methods it remains difficult to discriminate between the contribution of liver and extrahepatic tissues. To study intestinal drug metabolism in vitro, apart from subcellular fractions, several intact cell systems are nowadays available. This review discusses the available intestinal in vitro methods to study drug metabolism. The advantages and limitations of intact cell systems (isolated intestinal perfusion, everted sac, Ussing chamber preparations, biopsies, precision-cut slices, primary cells), subcellular fractions (S9 fractions, microsomes) and intestinal cell lines (caco-2, LS180 cells amongst others) are discussed. Their applicability to different species and to study phase I and II metabolism/transport and drug-drug interactions are summarized. Furthermore, causes of variation within and between methods are discussed and metabolic rates obtained with different methods are compared. Whereas subcellular fractions and cell lines are efficient methods to study mechanistic aspects of drug metabolism at the enzyme level, the isolated intestinal perfusion, everted sac and Ussing chamber appear particularly useful for studying drug metabolism of rapidly metabolised drugs and interactions with transporters. Biopsies, precision-cut slices and primary cells seem all appropriate to study induction and metabolism of slowly metabolised drugs.
Correlations between Calcineurin Phosphatase Inhibition and Cyclosporine Metabolites Concentrations in Kidney Transplant Recipients: Implications for Immunoassays.
Nikolaos Karamperis, Pernille Bundgaard Koefoed-Nielsen, Pia Brahe, Carsten Højskov, Martin Egfjord, Jørgen Hjelm Poulsen, Kaj Anker Jørgensen
Research Laboratory C, Department of Renal Medicine C, Skejby, Aarhus University Hospital, Aarhus, Denmark.
Cyclosporine exhibits a wide spectrum of metabolites that vary considerably in the extent to which they interfere with the various parent drug monitoring immunoassays. There is no consensus regarding the clinical significance of metabolites. Cyclosporine exerts its immunosuppressive action by inhibiting the enzyme calcineurin phosphatase. Determination of the enzyme's activity is one of the most promising pharmacodynamic markers. It is unknown how calcineurin phosphatase inhibition correlates with various cyclosporine monitoring assays and what is the potential impact of metabolites in this perspective? The aim of the present study was to determine the concentration of cyclosporine (by means of three different assay methods) and the four most significant metabolites (AM1, AM4N, AM9, and AM1C) in relation to calcineurin phosphatase inhibition. Twelve randomly selected cyclosporine-treated renal transplant patients were included in the study. Blood samples were drawn before, 1, 2, 3, 4, 6, 8, and 12 hr after oral intake of cyclosporine. Parent drug and metabolites were determined by liquid chromatography/tandem mass spectrometry (LC/MSMS). Additionally, cyclosporine concentration was determined by the enzyme multiplied immunoassay technique (EMIT) and by the polyclonal fluorescence polarization immunoassay (pFPIA). Calcineurin phosphatase activity was measured by its ability to dephosphorylate a previously phosphorylated 19-amino acid peptide. We found that calcineurin phosphatase inhibition correlates strongly with parent cyclosporine metabolites concentrations determined by all three assay methods. Determination methods that took metabolites into consideration exhibit stronger correlations with calcineurin phosphatase inhibition (sum of cyclosporin plus metabolites r=-0.93, LC/MSMS; pFPIA r=-0.94, P</=0.001), compared with methods that measure exclusively the parent drug (EMIT:-0.84; LC/MS-MS:-0.81, P</=0.05). Our results indicate that the immunosuppressive role of cyclosporines metabolites should not be considered valueless per se. Further research is required in order to verify the potential clinical importance of our observations.
Evaluation of microsomal incubation conditions on CYP3A4-mediated metabolism of cyclosporine A by a statistical experimental design.
Department of Pharmaceutical Biosciences, School of Pharmacy, University of Oslo, Norway. firstname.lastname@example.org
The effect of changes in microsomal incubation conditions (NADPH, Mg(2+), Cl(-), NADPH-regenerating system and pH) on the formation of the CYP3A4 metabolites AM1 and AM9 from CsA were studied by application of a fractional factorial design. Metabolism was studied in microsomes of transfected human liver epithelial (THLE) cells specifically expressing CYP3A4. Within the conditions tested, a 3-4-fold difference in formation of CsA metabolites was observed. Formation of both AM1 and AM9 was favoured by a low Mg(2+) concentration (0.5 mM) and no addition of Cl(-) to the incubation matrix. However, while a high NADPH concentration (1.75 mM) was the single most important factor for the formation of AM1, changes in NADPH concentration between 0.25 and 1.75 mM had no influence on AM9 formation. Formation of the two metabolites also differed in their influence by pH changes, as a change in pH from 7.2 to 7.5 significantly increased the formation of AM9, while formation of AM1 was unaffected by this change. The present study showed that relatively small changes in the incubation matrix had a significant influence on the microsomal CYP3A4-mediated metabolism of CsA. Systematic studies on microsomal incubation conditions could be a key to improve metabolic in vitro-in vivo extrapolations in drug development.
Comparative in vitro metabolism of methoxychlor in male and female rats: metabolism of demethylated methoxychlor metabolites by precision-cut rat liver slices.
Institute of Environmental Toxicology, Ibaraki, Japan. email@example.com
The in vitro metabolism of demethylated methoxychlor (MXC) metabolites, mono-OH-MXC (including (R)- and (S)-isomers) and bis-OH-MXC (mono- and bis-demethylated MXC, respectively), was conducted using precision-cut liver slices to understand the sex-dependent metabolism of MXC in rats. In the study with bis-OH-MXC, the substrate underwent extensive conjugation producing its glucuronide and glucuronide/sulphate diconjugate, and no significant sex differences were found. On the contrary, the metabolism of mono-OH-MXC appeared to exhibit the sex differences in the metabolic profiles. The bis-OH-MXC glucuronide and glucuronide/sulphate diconjugate were major metabolites in male rat, whereas the mono- and bis-OH-MXC glucuronides predominated in the female. The per cent distribution of the demethylated products (sum of bis-OH-MXC derivatives) was approximately 90% for the male (for both isomers) and 81 (R-) to 56%(S-) for the female. The metabolic profiles in (S)-mono-OH-MXC, which is the predominant enantiomer preferentially produced in MXC metabolism in rats, showed a similar pattern to that of MXC compared with the (R)-isomer. The results indicate that the sex differences in oxidative demethylation of the intermediate,(S)-mono-OH-MXC, could be one of the probable reasons for the sex-dependent metabolism of MXC in rats, and the stereo-structural preference of the contributing demethylase enzymes appear to be involved.
Oxidative metabolism by P450 and function coupling to efflux systems: modulation of mycotoxin toxicity.
Service de Pharmacologie et d'Immunologie, DRM, France.
Man is permanently exposed to exogenous substances, either natural ones (e.g. mycotoxins, plant extracts) or man-made compounds such as pesticides or drugs. In some cases, such foreign compounds can exert either therapeutic (drugs) or toxic effects, or both. In particular, fungi are the source of a number of different secondary metabolites having such therapeutic or toxic effects. The efficiency or toxicity of foreign compounds depends on their ability to cross the cytoplasmic membrane. The exogenous molecules subsequently bind to their specific receptor in the cytoplasm or nucleus of the cell, but they are also attacked by the detoxification proteins, which in mammals are mainly composed of two types of membrane enzyme systems: cytochrome P450s, which functionalize hydrophobic xenobiotics, and an active P-glycoprotein (P-gp) transport system involved in the efflux of xenobiotics. These processes are illustrated through the use of two fungal cyclopeptides, cyclosporin A (CsA) and roquefortine C. The former, CsA, is known to be an immunosuppressor, while the latter, roquefortine C, is a potentially neurotoxic compound. CsA inhibits P-gp in a different way from its metabolites, whereas roquefortine C activates P-gp and also inhibits P450-3A and other haemoproteins. The current observations show that the two detoxification systems complement each other, resulting in a given toxicity level. The two mammal enzyme systems might therefore prove useful in the development of toxicity screening procedures.
An in vivo and in vitro comparison of CYP induction in rat liver and intestine using slices and quantitative RT-PCR.
Preclinical Development, Nerviano Medical Science, Viale Pasteur 10, 20014 Nerviano (MI), Italy. firstname.lastname@example.org
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.
A new technique for preparing precision-cut slices from small intestine and colon for drug biotransformation studies.
Ruben de Kanter, Annemarie Tuin, Esther van de Kerkhof, Marcella Martignoni, Annelies L Draaisma, Marina H de Jager, Inge A M de Graaf, Dirk K F Meijer, Geny M M Groothuis
Nerviano Medical Science Srl., Viale Pasteur 10, 20014 Nerviano (MI), Italy. email@example.com
INTRODUCTION A new technique was developed to prepare precision-cut slices from small intestine and colon with the object of studying the biotransformation of drugs in these organs. METHODS Rat intestinal slices were prepared in two different ways. In the first method, slices were punched out of the small intestine. In the second method, precision-cut slices were made from agarose-filled and -embedded intestines, using the Krumdieck tissue slicer. This method was also applied to colon tissue. Viability of the slices was determined by analysis of intracellular ATP and RNA levels and morphology. Drug metabolizing activity was studied using lidocaine, testosterone, and 7-ethoxycoumarin (7-EC) as phase I substrates, and 7-hydroxycoumarin (7-HC) as a phase II substrate. RESULTS Precision-cut slices made from agarose-filled and -embedded intestine better preserved ATP levels than tissue that was punched out of the intestinal wall. After 24 h of incubation, morphology in precision cut-slices showed was quite well preserved while punched out tissue was almost completely autolytic after incubation. In addition, total RNA amount and quality was much better maintained in precision-cut slices, when compared to punched out tissue. Both intestinal slices and punched-out tissue showed high, and comparable, phase I and phase II biotransformation activities. DISCUSSION It is concluded that preparing precision-cut 0.25 mm slices out of agarose-filled and -embedded intestine provides an improvement, compared with punched-out tissue, and that both intestinal and colon slices are useful preparations for in vitro biotransformation studies.
Yang Dai, Kazunori Iwanaga, Yvonne S Lin, Mary F Hebert, Connie L Davis, Weili Huang, Evan D Kharasch, Kenneth E Thummel
Department of Pharmaceutics, University of Washington, Seattle, WA 98195, USA.
The objectives of this study were to characterize and compare the metabolic profile of cyclosporine A (CsA) catalyzed by CYP3A4, CYP3A5 and human kidney and liver microsomes, and to evaluate the impact of the CYP3A5 polymorphism on product formation from parent drug and its primary metabolites. Three primary CsA metabolites (AM1, AM9 and AM4N) were produced by heterologously expressed CYP3A4. In contrast, only AM9 was formed by CYP3A5. Substrate inhibition was observed for the formation of AM1 and AM9 by CYP3A4, and for the formation of AM9 by CYP3A5. Microsomes isolated from human kidney produced only AM9 and the rate of product formation (2 and 20 microM CsA) was positively associated with the detection of CYP3A5 protein and presence of the CYP3A5*1 allele in 4 of the 20 kidneys tested. A kinetic experiment with the most active CYP3A5*1-positive renal microsomal preparation yielded an apparent Km (15.5 microM) similar to that of CYP3A5 (11.3 microM). Ketoconazole (200 nM) inhibited renal AM9 formation by 22-55% over a CsA concentration range of 2-45 microM. Using liver microsomes paired with similar CYP3A4 content and different CYP3A5 genotypes, the formation of AM9 was two-fold higher in CYP3A5*1/*3 livers, compared to CYP3A5*3/*3 livers. AM19 and AM1c9, two of the major secondary metabolites of CsA, were produced by CsA, AM1 and AM1c when incubated with CYP3A4, CYP3A5, kidney microsomes from CYP3A5*1/*3 donors and all liver microsomes. Also, the formation of AM19 and AM1c9 was higher from incubations with liver and kidney microsomes with a CYP3A5*1/*3 genotype, compared to those with a CYP3A5*3/*3 genotype. Together, the data demonstrate that CYP3A5 may contribute to the formation of primary and secondary metabolites of CsA, particularly in kidneys carrying the wild-type CYP3A5*1 allele.
Other papers by authors:
Biotransformation of the antiemetic 5-HT3 antagonist tropisetron in liver and kidney slices of human, rat and dog with a comparison to in vivo.
Sandoz Pharma Ltd, Basel, Switzerland.
Species differences in the biotransformation of the antiemetic tropisetron, a potent 5-hydroxytryptamine type 3 (5-HT3) receptor antagonist, were evident in liver slice incubates of human, rat and dog, and reflected the species differences observed in vivo with respect to the relative importance of individual pathways. The dominant biotransformation pathway of tropisetron (10 microM) in human liver slices was formation of 6-hydroxy-tropisetron, whereas in rat liver slices it was 5-hydroxy-tropisetron, and in dog liver slices N-oxide formation. Initial rates of tropisetron metabolite formation in the liver slices (8 mm in diameter, 200 +/- 25 microns thickness) of human (83 +/- 61 pmol/h/mg slice protein), rat (413 +/- 98 pmol/h/mg slice protein) and dog (426 +/- 38 pmol/h/mg slice protein) would predict less of a first-pass effect in humans compared to the rat or the dog. For human and rat, the prediction matched well with the species ranking of tropisetron bioavailability; however, for dog the in vitro data overestimated the apparent first-pass effect. The jejunum is not expected to contribute to the first-pass effect in humans, since human jejunum microsomes did not metabolize tropisetron. The major organ of excretion for tropisetron and its metabolites is the kidney, but the contribution of the kidney to the overall metabolism of tropisetron would be small. Species independent N-oxide formation (2-12 pmol/h/mg slice protein) was the major pathway in human, rat and dog kidney slices, and was comparable to N-oxide formation in the rat and human liver slices but was 1/10 the rate in dog liver slices. This study has demonstrated that the liver is the primary site of tropisetron biotransformation, and the usefulness of organ slices to characterize cross species differences in the dominant biotransformation pathways.
Sites of biotransformation for the cyclosporin derivative SDZ IMM 125 using human liver and kidney slices and intestine. Comparison with rat liver slices and cyclosporin A metabolism.
Sandoz Pharma Ltd., Basel, Switzerland.
SDZ IMM 125 (IMM), the hydroxyethyl derivative of cyclosporin A (CSA), is metabolized by human liver slices to analogous primary metabolites, hydroxylated IMM1 and IMM9 and N-demethylated IMM4N, as for CSA (M17/AM1, M1/AM9, and M21/AM4N), but the rate and extent of IMM biotransformation is less than for CSA. Initial rates of IMM metabolite formation in the human liver slice cultures are 6.6 +/- 2.8 nmol/hr/g liver at 1 microM IMM and 24.3 +/- 22.9 nmol/hr/g liver at 10 microM IMM, whereas the rate of CSA metabolite formation is 1.8-fold faster at both concentrations. The percentage of unchanged IMM is 73% at 1 microM and 80% at 10 microM after 24 hr, reflecting the lower extent of IMM metabolism, about one-third (1 microM) and one-half (10 microM) that of CSA. In rat liver slices, IMM is metabolized to the same primary metabolites as in human liver slices, but more slowly and remains 90% unchanged at 24 hr. Human jejunum formed the same primary metabolites of IMM and CSA as in liver. Upscaling the slice rate of biotransformation revealed that human jejunum would contribute considerably to the first-pass of IMM and CSA, being approximately 2 to 3-fold slower than the rate in liver. The inhibition of both IMM and CSA biotransformation by triacetyloleandomycin implicates the involvement of cytochrome P4503A proteins. Human kidney cortex slices metabolized IMM to IMM1 and IMM9, accounting for approximately 75% of the total metabolites. Total metabolite formation represented approximately 64% of liver metabolite formation.(ABSTRACT TRUNCATED AT 250 WORDS)
Human and rat lung biotransformation of cyclosporin A and its derivatives using slices and bronchial epithelial cells.
Preclinical Safety, Novartis Pharma Ltd., East Hanover, NJ 07936, USA.
Lung biotransformation of the immunosuppressants, cyclosporin A (CSA), the hydroxyethyl derivative SDZ IMM 125 (IMM), and the methylcarbonate derivative SDZ SCP 764 (SCP), was demonstrated in slices from human and rat. The major biotransformation pathway for CSA and IMM (0.1-10 microM) was hydroxylation at amino acid 1 to form AM1 or IMM1, while for SCP it was an esterase cleavage of the methylcarbonate group to form AM1 in both species. The initial rate (0-1 hr) of human total metabolite formation increased proportionally with substrate concentration. AM1 formation was five times greater from SCP, an esterase pathway, than CSA, an oxidative pathway which was inhibited (50%) by ketoconazole. At 24 hr human lung CSA metabolite formation was greater than IMM (3-fold) or SCP (2-fold), whereas rat lung and liver and human bronchial epithelial cell SCP metabolite formation generally exceeded CSA or IMM metabolism. CSA biotransformation is expected to occur throughout the human lung as demonstrated by the similar metabolite profile and extent of metabolism by slices derived from five different regions. The scaling of slice total metabolism to organ metabolism revealed that initially lung CSA metabolite formation would be equal to liver but with time liver metabolism would exceed lung for human and rat. This study has demonstrated that human and rat lung are metabolically active, exhibiting oxidative and esterase pathways toward cyclosporin derivatives. The lung will play an important role in this metabolism, particularly when administered via inhalation; however, the liver will also be a major organ involved in the total clearance of these compounds.
The biotransformation of the ergot derivative CQA 206-291 in human, dog, and rat liver slice cultures and prediction of in vivo plasma clearance.
Drug Safety Assessment, Sandoz Pharma Ltd, Basel, Switzerland.
Liver slice cultures from humans, dogs, and rats were used to investigate the biotransformation of the dopaminergic ergot agonist CQA 206-291 and to predict pharmacokinetic values for hepatic intrinsic clearance and plasma clearance. CQA 206-291 was extensively metabolized in the liver slice cultures and in vivo. The HPLC metabolite patterns from the liver slice cultures were similar for all three species, indicating the occurrence of the same metabolic pathways for CQA 206-291 biotransformation. The rate of formation of CQ 32-084, a pharmacologically active N-deethylated metabolite, exceeded that of metabolite d, a primary metabolite, by 1.4 fold in human liver slices, and by 1.7 fold in rat liver slices. In dog liver slice cultures, metabolite d formation exceeded CQ 32-084 formation by 1.3 fold and was formed at a statistically significantly greater rate (3 fold) than in either human or rat liver slices. The metabolism of ergots like CQA 206-291 by human fetal liver was also demonstrated in this study. However, the prominent metabolite from fetal and adult human liver microsomes was metabolite d with minor amounts of CQ 32-089 being formed. A major route of excretion for the metabolites of CQA 206-291 is the kidney, yet the kidney does not contribute to the metabolism of CQA 206-291. Kidney slices derived from humans, rats, and dogs did not metabolize CQA 206-291 within 24 hr. CQA 206-291 intrinsic clearance was derived from the half-life of parent drug disappearance in the liver slice and hepatocyte cultures, and from the ratio of Vmax/Km of human and rat liver microsomes.(ABSTRACT TRUNCATED AT 250 WORDS)
The polymorphic cytochrome P-4502D6 is involved in the metabolism of both 5-hydroxytryptamine antagonists, tropisetron and ondansetron.
Sandoz Pharma Ltd., Basel, Switzerland.
Tropisetron and ondansetron, which are potent and selective 5-hydroxytryptamine (5-HT3) receptor antagonists, were both metabolized by human liver microsomes to several metabolites. These metabolites include the major metabolites found in humans, which are the 5-, 6-, and 7-hydroxy tropisetron and the 7- and 8-hydroxy ondansetron. The cytochrome P-450 (CYP) 2D6 inhibitor quinidine (1 microM) reduced the hydroxylation of tropisetron (67%) and ondansetron (18%). Confirmation of CYP2D6 involvement in the hydroxylation of tropisetron and ondansetron was obtained by the formation of these metabolites in recombinant V79 cells expressing human CYP2D6. The CYP3A substrate/inhibitor, cyclosporine A (CsA) had little effect on tropisetron hydroxylation (< 10%), whereas CsA and triacetyloleandomycin reduced ondansetron 7- and 8-hydroxylation up to 27%. Substrates for CYP1A (phenacetin and acetanilide), CYP2C (mephenytoin), and CYP2E (chlorzoxazone) had negligible inhibitory effects on the hydroxylation of either tropisetron or ondansetron. For the CYP2D6-dependent O-demethylation of dextromethorphan, tropisetron and ondansetron were competitive inhibitors with Ki values of 14 and 29 microM, respectively. The CYP3A specific metabolism of CsA was also competitively inhibited by tropisetron (Ki = 2.1 mM) and ondansetron (Ki = 31 microM). Other metabolites, which are only minor in vivo were also inhibited by CsA, 47-60% for tropisetron metabolism and 43% for ondansetron metabolism. To summarize, this study has identified the involvement of CYP2D6 in the formation of the hydroxylated metabolites of tropisetron and ondansetron and in addition of CYP3A in ondansetron hydroxylation. Because these are the major pathways in vivo, coadministration of drugs competing for CYP2D6 and possibly CYP3A4 could influence the human kinetics of tropisetron and ondansetron.
J M Catania, A R Parrish, D S Kirkpatrick, M Chitkara, G T Bowden, C J Henderson, C R Wolf, A J Clark, K Brendel, R L Fisher, A J Gandolfi
Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, 1703 E. Mabel St., Tucson, AZ 85721-0207, USA.
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.
Vitro, Inc., Tucson, Arizona 85747, USA. firstname.lastname@example.org
Donated human liver in the form of precision-cut tissue slices or isolated hepatocytes, is increasingly being used to predict metabolism and toxicity of xenobiotics in man. These tissue slices or hepatocytes can also be cold-preserved and cryopreserved to prolong their use for biological experiments. The viability of human liver could substantially affect the outcome of such experimentation. The goal of this investigation was to assess the viability of donated human livers, in the form of tissue slices, as they were received and to determine how varying degrees of liver quality affect experimental outcomes. Over one hundred human livers were categorized according to initial viability, as assessed by ATP content, K+ retention, protein synthesis, and LDH leakage. Each liver was placed in a low-, a medium-, or a high-quality group. The results showed that 76% of transplant-grade tissue (procured for transplantation) fell into the high-viability classification while the majority of research-grade tissue (not procured for transplantation) fell into the lowest viability classification. It was also found that only tissue slices prepared from highly viable human liver could be cold-preserved and cryopreserved. Dichlorobenzene metabolism was also greater in slices from highly viable human livers as compared to less viable livers. This study showed that human liver tissue acquired for medical research substantially varies in its viability and that these differences will affect the experimental data obtained.
Preclinical Safety, Novartis Institute for Biomedical Research, East Hanover, New Jersey 07936, USA.
Tegaserod is a selective 5-HT(4) receptor partial agonist with promotile activity in the gastrointestinal tract. This study was designed to describe the metabolic pathways of tegaserod in the human liver and small intestine in vitro, to identify the enzymes involved in tegaserod metabolism, and to investigate the effect of tegaserod on CYP-catalyzed reactions involving other compounds. Tegaserod was metabolized in human liver microsomes to O-desmethyl tegaserod at a low rate. This metabolite was also formed by cDNA expressed CYP2D6, and the reaction in human liver microsomes was inhibited by quinidine. In human liver slices, direct N-glucuronidation of tegaserod at the guanidine nitrogens (M43.2, M43.8, and M45.3) was found, with M43.8 being the major metabolite. Human small intestine slices also metabolized tegaserod to the N-glucuronides, suggesting a contribution of the small intestine to the presystemic metabolism. 5-Methoxyindole-3-carboxylic acid (M29.0), the main metabolite in human plasma, was generated in vitro by a sequence of reactions starting with nonenzymatic acid-catalyzed hydrolysis, followed by enzymatic oxidation and conjugation with glucuronic acid. Tegaserod inhibited CYP2C8, CYP2C9, CYP2C19, CYP2E1, and CYP3A only to a small extent with IC(50) values >30 microM. Tegaserod more effectively inhibited CYP1A2 and CYP2D6 with K(i) values of 0.84 and 0.85 microM, respectively. However, these K(i) values are approximately 140-fold greater than the maximal tegaserod plasma concentrations following the clinically relevant 6-mg oral dose given to healthy volunteers. M29.0, the main circulating metabolite, did not demonstrate any inhibitory potential toward cytochrome P450 enzymes in vitro. Therefore, clinically relevant metabolic drug interactions with tegaserod seem unlikely.
Multiple cytochrome P-450s involved in the metabolism of terbinafine suggest a limited potential for drug-drug interactions.
Drug Metabolism and Pharmacokinetics, Novartis Institute for Biomedical Research, East Hanover, New Jersey 07936, USA.
Biotransformation pathways and the potential for drug-drug interactions of the orally active antifungal terbinafine were characterized using human liver microsomes and recombinant human cytochrome P-450s (CYPs). The terbinafine metabolites represented four major pathways: 1) N-demethylation, 2) deamination, 3) alkyl side chain oxidation, and 4) dihydrodiol formation. Michaelis-Menten kinetics for the pathways revealed mean K(m) values ranging from 4.4 to 27.8 microM, and V(max) values of 9.8 to 82 nmol/h/mg protein. At least seven CYP enzymes are involved in terbinafine metabolism. Recombinant human CYPs predict that CYP2C9, CYP1A2, and CYP3A4 are the most important for total metabolism. N-demethylation is primarily mediated by CYP2C9, CYP2C8, and CYP1A2; dihydrodiol formation by CYP2C9 and CYP1A2; deamination by CYP3A4; and side chain oxidation equally by CYP1A2, CYP2C8, CYP2C9, and CYP2C19. Additionally, characteristic CYP substrates inhibited pathways of terbinafine metabolite formation, confirming the involvement of multiple enzymes. The deamination pathway was mainly inhibited by CYP3A inhibitors, including troleandomycin and azole antifungals. Dihydrodiol formation was inhibited by the CYP1A2 inhibitor furafylline. Terbinafine had little or no effect on the metabolism of many characteristic CYP substrates. Terbinafine, however, is a competitive inhibitor of the CYP2D6 reaction, dextromethorphan O-demethylation (K(i)= 0.03 microM). In summary, terbinafine is metabolized by at least seven CYPs. The potential for terbinafine interaction with other drugs is predicted to be insignificant with the exception that it may inhibit the metabolism of CYP2D6 substrates. Clinical trials are needed to assess the relevance of these findings.
The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor fluvastatin: effect on human cytochrome P-450 and implications for metabolic drug interactions.
Drug Metabolism and Pharmacokinetics, Novartis Institute for Biomedical Research, East Hanover, New Jersey 07936, USA. email@example.com
Fluvastatin, a 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, was metabolized by human liver microsomes to 5-hydroxy-, 6-hydroxy-, and N-deisopropyl-fluvastatin. Total metabolite formation was biphasic with apparent Km values of 0.2 to 0.7 and 7.9 to 50 microM and intrinsic metabolic clearance rates of 1.4 to 4 and 0.3 to 1.5 ml/h/mg microsomal protein for the high and low Km components, respectively. Several enzymes, but mainly CYP2C9, catalyzed fluvastatin metabolism. Only CYP2C9 inhibitors such as sulfaphenazole inhibited the formation of both 6-hydroxy- and N-deisopropyl-fluvastatin. 5-Hydroxy-fluvastatin formation was reduced by compounds that are inhibitors of CYP2C9, CYP3A, or CYP2C8. Fluvastatin in turn inhibited CYP2C9-catalyzed tolbutamide and diclofenac hydroxylation with Ki values of 0.3 and 0.5 microM, respectively. For CYP2C8-catalyzed 6alpha-hydroxy-paclitaxel formation the IC50 was 20 microM and for CYP1A2, CYP2C19, and CYP3A catalyzed reactions, no IC50 could be determined up to 100 microM fluvastatin. All three fluvastatin metabolites were also formed by recombinant CYP2C9, whereas CYP1A1, CYP2C8, CYP2D6, and CYP3A4 produced only 5-hydroxy-fluvastatin. Km values were approximately 1, 2.8, and 7.1 microM for CYP2C9, CYP2C8, and CYP3A, respectively. No difference in fluvastatin metabolism was found between the CYP2C9R144 and CYP2C9C144 alleles, suggesting the absence of polymorphic fluvastatin metabolism by these alleles. CYP1A2, CYP2A6, CYP2B6, CYP2C19, CYP2E1, and CYP3A5 did not produce detectable amounts of any metabolite. This data indicates that several human cytochrome P-450 enzymes metabolize fluvastatin with CYP2C9 contributing 50-80%. Any coadministered drug would therefore only partially reduce the metabolic clearance of fluvastatin; therefore, the likelihood for serious metabolic drug interactions is expected to be minimal.
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Department of Biology and Environmental Protection, Poznan University of Medical Sciences, Poznań, Poland. Electronic address: firstname.lastname@example.org.
Cylindrospermopsin (CYN) is a secondary metabolite produced by several cyanobacteria species. Its potential effect on human health includes liver, kidneys, lungs, spleen and intestine injuries. CYN can be cyto- and genotoxic to a variety of cell types. Occurrence and expansion of species able to synthesize CYN in European water bodies has been recently reported and raised awareness of potential harm to human health. Therefore, surface water of different human use should be monitored for the presence of toxic species of blue-green algae. This paper aims to describe the distribution of CYN producers in Europe and the potential effects of the toxin on human health according to the current state of knowledge.
Quantitative proteomic analysis of cyclosporine-induced toxicity in a human kidney cell line and comparison with tacrolimus.
INSERM, UMR-S850, Limoges, France. email@example.com
The calcineurin-inhibitors (CNIs) cyclosporine (CsA) and tacrolimus (TAC) remain the pillars of modern immunosuppression regimens used in solid organ transplantation. Nephrotoxicity is an adverse effect that limits their successful use. The precise molecular mechanisms underlying this nephrotoxicity remain unclear. Using SILAC together with LC-MALDI-TOF/TOF, we investigated the CNIs-induced proteomic perturbations in renal cells. Among the 495 proteins quantifiable in both forward and reverse SILAC, 69 displayed CsA-induced perturbations: proteins involved in ER-stress/protein folding, apoptosis, metabolism/transport or cytoskeleton pathways were up-regulated, while cyclophilin B as well as nuclear and RNA-processing proteins were down-regulated. Co-administration of CsA with the antioxidant N-acetylcysteine significantly decreased lipid peroxidation and also partially corrected the CsA-induced unfolded protein response. TAC toxicity profile was apparently different from that of CsA, especially without perturbation of cyclophilins A and B, up-regulation of ER-chaperones nor down-regulation of a number of nuclear proteins. These results provide a new insight and are consistent with recent data regarding the molecular mechanisms of CNIs-induced nephrotoxicity. Our findings offer new directions for future research aiming to identify specific biomarkers of CsA nephrotoxicity.
Ciprofloxacin decreases survival in HT-29 cells via the induction of TGF-beta1 secretion and enhances the anti-proliferative effect of 5-fluorouracil.
Leonidas A Bourikas, George Kolios, Vassilis Valatas, George Notas, Ioannis Drygiannakis, Iordanis Pelagiadis, Pinelopi Manousou, Stefanos Klironomos, Ioannis A Mouzas, Elias Kouroumalis
Department of Gastroenterology, University of Crete, Heraklion, Greece.
BACKGROUND AND PURPOSE Fluoroquinolones are potent anti-microbial agents with multiple effects on host cells and tissues. Previous studies have highlighted their pro-apoptotic effect on human cancer cells and an immunoregulatory role in animal models of inflammatory bowel disease. We examined the effect of ciprofloxacin on proliferation, cell cycle and apoptosis of HT-29 cells, a human colonic epithelial cell line sensitive to transforming growth factor (TGF)-beta1-mediated growth inhibition and its role in TGF-beta1 production. We also examined the effect of ciprofloxacin on proliferation of HT-29 cells in combination with 5-fluorouracil (5-FU), a well-established pro-apoptotic agent. EXPERIMENTAL APPROACH Using subconfluent cultures of HT-29 and Caco-2 cells, we studied the effect of ciprofloxacin, TGF-beta1 and 5-FU on proliferation, apoptosis, necrosis and cell cycle. The effect of ciprofloxacin on TGF-beta1 mRNA expression and production was studied in RNA extracts and cell culture supernatants respectively, using confluent cultures. KEY RESULTS Ciprofloxacin decreased proliferation of HT-29 cells in a concentration- and time-dependent manner. This was mediated by accumulation of HT-29 cells into the S-phase but without any effect on apoptosis or necrosis. Additionally, ciprofloxacin enhanced the antiproliferative effect of 5-FU. Interestingly, ciprofloxacin was found to up-regulate TGF-beta1 production by HT-29 cells and its anti-proliferative effect was abolished when TGF-beta1 was blocked. Confirming this mechanism further, ciprofloxacin had no effect on Caco-2, a human colonic epithelial cell line that lacks functional TGF-beta1 receptors. CONCLUSIONS AND IMPLICATIONS We demonstrate a novel anti-proliferative and immunoregulatory effect of ciprofloxacin on human intestinal epithelial cells mediated via TGF-beta1.
Monolayer and spheroid culture of human liver hepatocellular carcinoma cell line cells demonstrate distinct global gene expression patterns and functional phenotypes.
Department of Surgery, University of California, San Francisco, San Francisco, California 94121, USA. firstname.lastname@example.org
Understanding cell biology of three-dimensional (3D) biological structures is important for more complete appreciation of in vivo tissue function and advancing ex vivo organ engineering efforts. To elucidate how 3D structure may affect hepatocyte cellular responses, we compared global gene expression of human liver hepatocellular carcinoma cell line (HepG2) cells cultured as monolayers on tissue culture dishes (TCDs) or as spheroids within rotating wall vessel (RWV) bioreactors. HepG2 cells grown in RWVs form spheroids up to 100 mum in diameter within 72 h and up to 1 mm with long-term culture. The actin cytoskeleton in monolayer cells show stress fiber formation while spheroids have cortical actin organization. Global gene expression analysis demonstrates upregulation of structural genes such as extracellular matrix, cytoskeletal, and adhesion molecules in monolayers, whereas RWV spheroids show upregulation of metabolic and synthetic genes, suggesting functional differences. Indeed, liver-specific functions of cytochrome P450 activity and albumin production are higher in the spheroids. Enhanced liver functions require maintenance of 3D structure and environment, because transfer of spheroids to a TCD results in spheroid disintegration and subsequent loss of function. These findings illustrate the importance of physical environment on cellular organization and its effects on hepatocyte processes.
Department of Cell Technology and Applied Stem Cell Biology, Biomedical and Biotechnology Centre (BBZ), University of Leipzig, Leipzig, Germany.
The purpose of this study was to investigate the species-specific cyclosporin biotransformation in primary rat, human, and porcine liver cell cultures, and to investigate the suitability of a modified sandwich culture technique with non-purified liver cell co-cultures for drug metabolism studies. A sandwich culture was found to enhance hepatocellular metabolic activity and improve cellular morphology and ultrastructure. The cyclosporin metabolites AM9 and AM1 were formed in porcine and human liver cell sandwich co-cultures at levels corresponding to the respective in vivo situations. In contrast, metabolite profiles in rat hepatocytes were at variance with the in vivo situation. However, for all cell types, the overall metabolic activity was positively influenced by sandwich co-culture. The initial levels of albumin synthesis were higher in sandwich cultures than in those without matrix overlay. It is hypothesized that the sandwich culture system provides an improved microenvironment and is, therefore, an advantageous tool for in vitro studies of drug metabolism.
Cytotoxicity of bioactive polymeric fractions from grape cell culture on human hepatocellular carcinoma, murine leukemia and non-cancerous PK15 kidney cells.
Department of Natural Resources and Environmental Sciences, 1021 Plant Sciences Laboratory MC 634, University of Illinois at Urbana-Champaign, 1201 S. Dorner Drive, 61801, USA.
Previously, we isolated two fractions (TP-4 and TP-6) from grape cell culture that were potent catalytic inhibitors in a human DNA topoisomerase II assay for cancer chemoprevention. The objectives of this study were to further assess cytotoxicity of these fractions on cancerous and non-cancerous cells, and to subfractionate and characterize the composition of TP-6, a fraction that was selectively cytotoxic to carcinoma cell lines. Both TP-4 and TP-6 provided significant cytotoxicity to L1210 mouse leukemia cells. Only TP-6, a procyanidin-rich fraction, significantly reduced viability in HepG2 human liver cancer cells, yet unlike resveratrol, caused no cytotoxicity to non-cancerous PK15 pig kidney cells. After further subfractionation of TP-6 (maximal toxicity = 67.2%; ED(50)= 50.5 microM), the cytotoxicity of subfractions on HepG2 cells was TP-6-5 (maximal toxicity=71.8%; ED(50)= 14.1 microM), TP-6-6 (maximal toxicity=64.3%; ED(50)= 67.0 microM), and TP-6-4 (maximal toxicity = 27.6%; ED(50)= 118.0 microM) in descending order. LC-ESI/MS data suggested that cytotoxicity of these procyanidin mixtures to HepG2 cells was proportional to the degree of polymerization. Because TP-6 and its subfractions were selectively cytotoxic to cancerous cell lines tested, they warrant further investigation as potential natural anticancer agents.
Glucuronidation of 2-(4-chlorophenyl)-5-(2-furyl)-4-oxazoleacetic acid (TA-1801A) in humans: species differences in liver and intestinal microsomes.
Exploratory Toxicology & DMPK Research Laboratories, Tanabe Seiyaku Co., LTD., Saitama, Japan. email@example.com
The metabolism of ethyl 2-(4-chlorophenyl)-5-(2-furyl)-4-oxazoleacetate (TA-1801), a potent hypolipidemic agent, was studied in humans after oral administration and compared with that found in rats, rabbits, and dogs previously. Hydrolysis of the ethyl ester to produce metabolite M1 (TA-1801 active form; TA-1801A) is the first metabolic step and the subsequent biotransformation includes the glucuronidation to form the metabolite M4 and the oxidation to form the metabolites M2 and M3. The metabolism of TA-1801 in humans was qualitatively similar to that in the experimental animals studied, although species differences were seen in the amount of metabolites. M4, the glucuronide of TA-1801A was the most abundant metabolite in human urine (24.3% of the dose). In vitro studies using human liver and jejunum microsomes indicated that the TA-1801A glucuronosyltransferase activity in human jejunum microsomes was 2-fold higher than that in liver microsomes. With regard to the interspecies differences in the TA-1801A glucuronosyltransferase activities, the intrinsic clearance for the TA-1801A glucuronidation in liver microsomes was in the following order: rabbit>monkey>human=rat=dog. In jejunum microsomes, the intrinsic clearance for the TA-1801A glucuronidation was in the following order: human>monkey>rabbit>rat=dog. These results suggest that the species differences in the intestinal TA-1801A glucuronidation contribute to the species differences in the excretion rate of TA-1801A glucuronide into the urine.
Identification of 14 quercetin phase II mono- and mixed conjugates and their formation by rat and human phase II in vitro model systems.
Division of Toxicology, Wageningen University, Tuinlaan 5, 6703 HE Wageningen, The Netherlands. firstname.lastname@example.org
In this study, the HPLC, UV-vis, LC-MS, and 1H NMR characteristics of 14 different phase II mono- and mixed conjugates of quercetin were determined, providing a useful tool in the identification of quercetin phase II metabolite patterns in various biological systems. Using these data, the phase II metabolism of quercetin by different rat and human liver and intestine in vitro models, including cell lines, S9 samples, and hepatocytes, was investigated. A comparison of quercetin phase II metabolism between rat and human liver and intestinal cell lines, S9, and hepatocytes showed considerable variation in the nature and ratios of quercetin conjugate formation. It could be established that the intestine contributes significantly to the phase II metabolism of quercetin, especially to its sulfation, that organ-dependent phase II metabolism in rat and man differ significantly, and that human interindividual variation is higher for quercetin sulfation than for glucuronidation or methylation. Furthermore, quercetin conjugation by different in vitro models from corresponding origins may differ significantly. The identification of the various mono- and mixed quercetin phase II conjugates revealed significant differences in phase II conjugation by a variety of in vitro models and led to the conclusion that none of the in vitro models converted quercetin to a phase II metabolite mixture similar to the in vivo plasma metabolite pattern of quercetin. Altogether, the identification of a wide range of phase II metabolites of quercetin as presented in this study allows the determination of quercetin phase II biotransformation patterns and opens the way for a better-funded assessment of the biological activity of quercetin in a variety of biological systems.
Garlic inhibits microsomal triglyceride transfer protein gene expression in human liver and intestinal cell lines and in rat intestine.
Institute of Molecular Biology, Open Laboratory of Chemical Biology, Institute of Molecular Technology for Drug Discovery and Synthesis, The University of Hong Kong, Hong Kong, China. email@example.com
Epidemiologic studies have suggested that fresh garlic has lipid-lowering activity. Because the microsomal triglyceride transfer protein (MTP) plays a pivotal role in the assembly and secretion of apolipoprotein B (apoB)-containing lipoproteins, we evaluated the effect of garlic on the expression of the MTP gene in vitro in cell lines and in vivo in rats. Fresh garlic extract (FGE) reduced MTP mRNA levels in both the human hepatoma HepG2 and intestinal carcinoma Caco-2 cells in dose-dependent fashion; significant reductions were detected with 3 g/L FGE. Maximal 72 and 59% reductions, respectively, were observed with 6 g/L FGE. To evaluate the in vivo effect of garlic on MTP gene expression, rats were given a single oral dose of fresh garlic homogenate (FGH), with hepatic and intestinal MTP mRNA measured 3 h after dosing. Rats fed FGH had significantly (46% of the control) lower intestinal MTP mRNA levels compared with the control rats, whereas hepatic MTP mRNA levels were not affected. These results suggest a new mechanism for the hypolipidemic effect of fresh garlic. Long-term dietary supplementation of fresh garlic may exert a lipid-lowering effect partly through reducing intestinal MTP gene expression, thus suppressing the assembly and secretion of chylomicrons from intestine to the blood circulation.
Localization of mRNAs encoding peroxisomal proteins in cell culture by non-radioactive in situ hybridization. Comparison of rat and human hepatoma cells and their responses to two divergent hypolipidemic drugs.
Institute of Medical Chemistry, University of Vienna, Währingerstrasse 10, 1090 Vienna, Austria.
A non-radioactive in situ hybridization (ISH) protocol for localization of mRNAs encoding peroxisomal proteins in hepatoma cell lines from humans (HepG2) and rats (MH1C1) is presented. In comparison to a similar procedure reported for tissue sections, the cell culture preparations require only brief fixation in 4% paraformaldehyde and their permeabilization is achieved by a very low concentration (1 microg/ml) of proteinase K. The exclusive localization of transcripts in the cytoplasm of hepatoma cells with the absence of nuclear staining and the completely negative sense controls confirm the specificity of the method. The marked differences in signal intensity between the results of albumin and beta-actin mRNAs which are of high abundance in contrast to moderate to low abundance of peroxisomal mRNAs show the high sensitivity and the wide range of applicability of our protocol. This is also confirmed by divergent results of treatment of hepatoma cell lines with clofibrate and cetaben on mRNA levels of catalase and acyl-CoA oxidase. The ISH results of drug treatment of cell lines are confirmed also by slot blot analysis of total RNA extracts using 32P-labeled probes. Thus the protocol presented here provides a sensitive tool for ISH localization of mRNAs encoding peroxisomal proteins. In combination with immunocytochemistry it may be useful to monitor intercellular differences in expression levels of specific mRNAs in correlation with the abundance of structurally divergent forms of peroxisomes (tubular versus spherical) and their importance in the biogenesis of peroxisomes.