Application of isolated hepatocytes to studies of drug metabolism in large food animals

Short Culture of Bovine Hepatocytes Biopsied from Dairy Cows as a Model for Toxicological Studies-CYP 1A1 Activity Response to Zearalenone Treatment

This study presents a simple and cost-effective method for isolating hepatocytes from liver biopsies obtained from healthy and ketotic dairy cows, which can be utilized for studying cellular metabolism, drug toxicity, and hepatocyte-specific gene function and regulation. The expression of hepatocyte marker genes (G6PC, ALB, CYP1A2) was measured and found to be highest at 6 h post-isolation, with a subsequent decrease over time. Cells isolated from ketotic livers exhibited lower expression levels than those from healthy livers. Furthermore, for the functional characterization of ketotic hepatocytes, the cells were exposed to varying doses of zearalenone (ZEA). While doses of 10-50 µM did not affect cell viability, the highest dose of ZEA (100 µM) significantly decreased cell viability, as measured using XTT assay. Additionally, the potential induction of cytochrome P450 A1 (CYP1A1) by ZEA was found. Despite limitations such as a short-term culture, this model provides a useful tool for conducting toxicological research.

Measurement of Xenobiotic Metabolising Enzyme Activities in Primary Monolayer Cultures of Immature Rainbow Trout Hepatocytes at Two Acclimatisation Temperatures

Rainbow trout hepatocytes with a high viability were isolated by two-step collagenase perfusion through the portal vein. The yield was 1-2.5 x 106cells/g body weight. Culture conditions were defined for providing enhanced attachment and long-term cell survival at 7 ± 0.5°C and 15 ± 0.5°C, respectively. The hepatocytes, attached to Primaria™ plastic and cultured in Leibowitz L-15 medium with 9% fetal calf serum, were maintained as monolayers for 6–7 days. The activities in hepatocytes from immature trout of the biotransformation enzymes ethoxyresorufin-O-deethylase (EROD), aldrine epoxidase (AEPOX), NADPH-cytochrome c reductase (NCR), glutathione-S-transferase (GST) and UDP-glucuronosyltransferase (UDPGT), were all stable during the culture period. Differences in enzyme stability and activity (particularly the activity of EROD) between hepatocytes from different fish were observed at both temperatures. The temperature did not influence the activities of EROD or NCR, whereas AEPOX showed metabolic compensation. Both GST and UDPGT exhibited inverse temperature compensation. Hepatocyte monolayers, cultured from immature trout, may provide a useful system in pharmacological and toxicological research for investigating drug metabolism.

Evaluation of the hepatocyte-derived cell line BFH12 as an in vitro model for bovine biotransformation

The knowledge of drug metabolising enzymes (DMEs) in cattle is rather limited. The capability of the bovine foetal hepatocyte-derived cell line BFH12 to serve as model for biotransformation was evaluated. Gene expression analysis of DMEs was performed by reverse transcription PCR (RT-PCR). The presence of efflux transporters was visualised by immunocytochemistry, and functional induction of cytochrome P450 (CYP) 1A was assessed by the ethoxyresorufin-O-deethylase (EROD) assay. The production of bile acids was measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). RT-PCR revealed the expression of cytochromes 1A1, 1A2, 3A4 and phase II enzymes UGT1A1, UGT1A6 and GSTM1. Immunofluorescence demonstrated efflux transporters ABCG2 and ABCC1. The EROD assay revealed a dose-dependent CYP1A induction after treatment with benzo[a]pyrene (BP). LC-MS/MS analysis of cell culture supernatants showed the production of bile acids including taurocholic acid, tauro-chenodeoxycholic acid, taurodeoxycholic acid and taurolithocholic acid. The results strongly suggest the applicability of the cell line BFH12 for subsequent experiments in the emerging field of bovine biotransformation.

In vitro culture of functionally active buffalo hepatocytes isolated by using a simplified manual perfusion method

Background

In farm animals, there is no suitable cell line available to understand liver-specific functions. This has limited our understanding of liver function and metabolism in farm animals. Culturing and maintenance of functionally active hepatocytes is difficult, since they survive no more than few days. Establishing primary culture of hepatocytes can help in studying cellular metabolism, drug toxicity, hepatocyte specific gene function and regulation. Here we provide a simple in vitro method for isolation and short-term culture of functionally active buffalo hepatocytes.

Results

Buffalo hepatocytes were isolated from caudate lobes by using manual enzymatic perfusion and mechanical disruption of liver tissue. Hepatocyte yield was (5.3±0.66)×10⁷ cells per gram of liver tissue with a viability of 82.3±3.5%. Freshly isolated hepatocytes were spherical with well contrasted border. After 24 hours of seeding onto fibroblast feeder layer and different extracellular matrices like dry collagen, matrigel and sandwich collagen coated plates, hepatocytes formed confluent monolayer with frequent clusters. Cultured hepatocytes exhibited typical cuboidal and polygonal shape with restored cellular polarity. Cells expressed hepatocyte-specific marker genes or proteins like albumin, hepatocyte nuclear factor 4α, glucose-6-phosphatase, tyrosine aminotransferase, cytochromes, cytokeratin and α1-antitrypsin. Hepatocytes could be immunostained with anti-cytokeratins, anti-albumin and anti α1-antitrypsin antibodies. Abundant lipid droplets were detected in the cytosol of hepatocytes using oil red stain. In vitro cultured hepatocytes could be grown for five days and maintained for up to nine days on buffalo skin fibroblast feeder layer. Cultured hepatocytes were viable for functional studies.

Conclusion

We developed a convenient and cost effective technique for hepatocytes isolation for short-term culture that exhibited morphological and functional characteristics of active hepatocytes for studying gene expression, regulation, hepatic genomics and proteomics in farm animals.

Influence of verapamil on the efflux and metabolism of 14C moxidectin in cultured rat hepatocytes

Moxidectin (MOX) is an antiparasitic drug widely used in cattle, sheep and companion animals. As a result of the implication of cytochrome P450 3 A in the metabolism of MOX and the role of competitor substrates of P-glycoprotein (Pgp) in modification of the bioavailability of endectocides, we studied the influence of verapamil (a multidrug-resistance reversing agent) on the metabolism of 14C moxidectin in cultured rat hepatocytes over 72 h. The metabolism of MOX remained low: 10.79 +/- 1.99% of the total 14C moxidectin for the main detected metabolite in verapamil-treated cells and 7.17 +/- 0.74% for the control cells after 24 h. The main detected metabolite in rat hepatocytes was the same as that detected in rat hepatic microsomes (the C29 monohydroxymethyl metabolite). Verapamil increased the quantity of MOX in the cells after 24, 48 and 72 h. Examination of the Area Under the concentration time Curve (AUC) of the main detected metabolite revealed a significant increase in the exposure of cells to MOX after verapamil treatment throughout the experiment. It is hypothesized that verapamil interfered with MOX as a substrate for Pgp during the initial incubation period. After this initial interaction, verapamil metabolites were able to interfere with Pgp. This experiment demonstrated the implication of Pgp in the transport of MOX and allowed prediction of the drug-drug interactions which might modify the bioavailability of endectocides.

Comparative Metabolism of Thiabendazole in Cultured Hepatocytes from Rats, Rabbits, Calves, Pigs, and Sheep, Including the Formation of Protein-Bound Residues

Cultured hepatocytes from rat, rabbit, calf, pig, and sheep were used to study metabolism and formation of protein-bound residues of thiabendazole ([(14)C]TBZ), a benzimidazole anthelmintic and fungicide. In all investigated species, major pathways corresponded to 5-hydroxylation of TBZ and its further conjugation. However, marked interspecies differences in rates of TBZ disappearance and 5-hydroxy metabolite formation were demonstrated. Rabbit hepatocytes presented the fastest TBZ biotransformation and were the most extensive hydroxylators. By contrast, the lowest capacity of oxidation was observed for the rat. Two unidentified minor metabolites, designated M1 and M2, were particularly produced by sheep hepatocytes. Moreover, the protein-bound residues in these cells, which could be related to cytochrome P450-dependent oxidation, were formed in 4 times greater amounts than in the other animal cells. These findings substantiate hepatocytes as an in vitro model for prediction of hepatic metabolism in vivo.

The use of cultured hepatocytes from goats and cattle to investigate xenobiotic oxidative metabolism

The oxidative metabolism of aldicarb (ALD), a carbamate pesticide, and fenbendazole (FBZ), an anthelmintic, was studied using cultured hepatocytes obtained from 4 goats and a bullock and incubated with ALD (50 mumol/L) and FBZ (10 mumol/L). The parent compounds and the metabolites were measured by HPLC. Both compounds are metabolized at the sulphur atom via two sequential oxidations, first to the sulphoxide (aldicarb sulphoxide and oxfendazole, respectively) and then to the sulphone. Oxfendazole and fenbendazole sulphone from FBZ, and aldicarb sulphoxide from ALD were found in both species. Aldicarb sulphone was not produced by the hepatocyte preparations from the bullock. The good correlation obtained comparing the in vitro results of FBZ metabolism with published in vivo data obtained on FBZ kinetics in the same species confirmed the usefulness of in vitro models for predictive analysis of in vivo xenobiotic biotransformations.

Functional activity of isolated pig hepatocytes attached to different extracellular matrix substrates. Implication for application of pig hepatocytes in a bioartificial liver

For the manufacture of a bioartificial liver for human application, large amounts of viable and active hepatocytes are needed. Pig hepatocytes are considered to be the best alternative to scarce human hepatocytes. In vitro hepatocyte functions have so far been tested under different circumstances, mainly with rat hepatocytes. Pig hepatocytes were isolated with a single two-step isolation procedure, resulting in a high yield of viable hepatocytes. The hepatocytes were tested for their ability to synthesise urea, to metabolise 7-ethoxycoumarin (cytochrome P450 activity), and to synthesise and secrete proteins. These activities of hepatocytes while attached to tissue culture plastic were compared to the activity of the cells attached to several extracellular matrix constituents: collagen I and IV, laminin, fibronectin, Engelbreth-Holm-Swarm Natrix and in the presence of Matrigel. With the exception of Matrigel, neither of the extracellular matrix substrates enhanced pig hepatocyte function compared to tissue culture plastic. However, relatively large amounts of murine proteins leak out of the Matrigel. The advisability of using Matrigel or other extracellular matrix proteins in a bioartificial liver loaded with pig hepatocytes is discussed.

Applicability of cultured hepatocytes derived from goat, sheep and cattle in comparative drug metabolism studies

1. Using trimethoprim (TMP), scoparone (SCOP), ethylmorphine (EtM), 1-naphthol (1-N) and phenol red (PhR) as test substrates, biotransformation activities were investigated in cultured hepatocytes from male and female rat, male and female goat, and female sheep and cattle. 2. As compared with rat hepatocytes, the total culture cytochrome P450 content was relatively well maintained in ruminant hepatocytes. In 72 h, it decreased to approximately half the initial content, whereas in rat hepatocytes only 30% was maintained. In ruminant hepatocytes, sulphation of 1-N remained fairly stable, glucuronidation of PhR decreased gradually, and glucuronidation of 1-N increased during the 72-h culture period. 3. Oxidative metabolism of TMP was rapid in goat and sheep hepatocytes, as compared with rat hepatocytes, reflecting species differences in TMP pharmacokinetics in vivo. In contrast with rat hepatocytes, 6-O-demethylation was by far the major pathway of scoparone metabolism in ruminant hepatocytes. The glucuronidation and sulphation activities were similar among the species. 4. In goat liver cells, sex differences in some oxidative biotransformations were observed, females being more active than males. In rat hepatocytes, a reverse sex difference was observed. 5. In conclusion, cultured hepatocytes from agricultural target species appear a useful in vitro model to study comparative metabolism of veterinary drugs and other xenobiotics. Comparing rat and ruminant, sex and species differences and similarities in drug metabolism can be observed that reflect the in vivo situation.

Sulfadimidine metabolism in vitro: II. Comparative studies in cultured rat, goat, sheep and cattle hepatocytes

Hydroxylation and acetylation of sulphadimidine (SDD) and the deacetylation of N4-acetyl SDD was investigated in cultured hepatocytes from male and female rats, from male and female goats and from female sheep and cattle. Significant sex differences were observed for hydroxylation of SDD in hepatocytes from rat and goat. In goat, sheep and cow hepatocytes, the hydroxylation pathway is relatively important, whereas in rat hepatocytes, acetylation is predominant. Hepatocytes of all four species deacetylated N4-acetyl SDD. In ruminant hepatocytes, deacetylating activity was of considerable importance, whereas in rat hepatocytes, it appeared a minor pathway of metabolism. Similar to the in vivo situation, formation of N4-acetyl SDD in cultured hepatocytes results from an equilibrium of acetylation and deacetylation. A good correlation was found between results in isolated hepatocytes and previous findings in vivo, both in levels of species-related activities and in acetylation-hydroxylation ratios. In conclusion, cultured hepatocytes appear a useful in vitro model to study comparative sulfonamide metabolism.

Effects of various medium formulations and attachment substrata on the performance of cultured ruminant hepatocytes in biotransformation studies

1. A procedure for the isolation and primary culture of hepatocytes from goat and cattle is described. Hepatocyte culture performance was monitored for 51 h by measuring viability, cytochrome P-450 maintenance, dealkylation of scoparone and ethylmorphine, and glucuronidation of phenol red. 2. Culture medium composition is discussed in relation to differences between splanchnic blood composition of ruminant and monogastric animal species. Main differences are in glucose and volatile fatty acid concentrations. Modified Williams' E culture medium did not yield higher culture performance than non-modified Williams' E. 3. Coating of culture dishes with either collagen or fibronectin did not improve culture performance. 4. Williams' E, although developed for rodent cells, proves to be a suitable basal medium for ruminant hepatocytes. In this medium, culture quality is high for at least several days. 5. In cultured goat hepatocytes, biotransformation rate for scoparone amounted to 20 nmol/mg protein per h, for ethylmorphine 96 nmol/mg protein per h and for phenol red 2 nmol/mg protein per h. Biotransformation activity in cow hepatocytes is approximately half that in goat hepatocytes.

The use of porcine hepatocytes for biotransformation studies of veterinary drugs

1. Cultures of porcine hepatocytes with high viability were isolated from a liver sample by a simple procedure. In ageing monolayer cultures the cytochrome P-450 content and 7-ethoxycoumarin-O-deethylase activity decreased gradually while glutathione levels increased. 2. The nitrofuran, furazolidone, was rapidly metabolized, partly resulting in the formation of 3-(4-cyano-2-oxobutylidene amino)-2-oxazolidone. 3. Acetylating and deacetylating activities towards sulphadimidine and its N4-acetyl metabolite were present in porcine hepatocytes. Relative and absolute levels of these activities varied in different batches of hepatocytes. 4. No differences were seen in a number of enzyme activities measured in cytosolic and microsomal fractions isolated from different lobes of one liver. Differences between livers from different animals were marked.

Biotransformation of beta-nortestosterone by cultured porcine hepatocytes

The metabolism of beta-nortestosterone by porcine hepatocytes was investigated. Initially beta-nortestosterone was rapidly oxidized to norandrostenedione, which was further transformed into a number of more hydrophilic compounds. It is assumed that most of these compounds were glucuronides, considering the effect of beta-glucuronidase treatment. The main product of enzymatic cleavage was investigated by gas chromatography-mass spectrometry but could not be identified until now.