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The liver is the major detoxifying organ, clearing the blood from drugs and other xenobiotics. The extent of hepatic clearance (CL) determines drug exposure and hence, the efficacy and toxicity associated with exposure. Drug-drug interactions (DDIs) that alter the hepatic CL may cause more or less severe outcomes, such as adverse drug reactions. Accurate predictions of drug CL and DDI risk from in vitro data are therefore crucial in drug development. Liver CL depends on several factors including the activities of transporters involved in the hepatic uptake and efflux. The work in this thesis aimed at developing new in vitro and in silico methods to predict hepatic transporter-mediated CL and DDIs in vivo. Particular emphasis was placed on interactions involving the hepatic uptake transporters OATP1B1, OATP1B3, and OATP2B1. These transporters regulate the plasma concentration-time profiles of many drugs including statins. Inhibition of OATP-mediated transport by 225 structurally diverse drugs was investigated in vitro. Several novel inhibitors were identified. The data was used to develop in silico models that could predict OATP inhibitors from molecular structure. Models were developed for static and dynamic predictions of in vivo transporter-mediated drug CL and DDIs. These models rely on a combination of in vitro studies of transport function and mass spectrometry-based quantification of protein expression in the in vitro models and liver tissue. By providing estimations of transporter contributions to the overall hepatic uptake/efflux, the method is expected to improve predictions of transporter-mediated DDIs. Furthermore, proteins of importance for hepatic CL were quantified in liver tissue and isolated hepatocytes. The isolation of hepatocytes from liver tissue was found to be associated with oxidative stress and degradation of transporters and other proteins expressed in the plasma membrane. This has implications for the use of primary hepatocytes as an in vitro model of the liver. Nevertheless, by taking the altered transporter abundance into account using the method developed herein, transport function in hepatocyte experiments can be scaled to the in vivo situation. The concept of protein expression-dependent in vitro-in vivo extrapolations was illustrated using atorvastatin and pitavastatin as model drugs.

Le virus de l’hépatite C (HCV) est l’agent responsable de l’hépatite C, maladie qui touche environ 3% de lapopulation mondiale. Une des caractéristiques de cette infection est son évolution dans 60 à 90% des casvers des formes chroniques avec des complications sévères telles que la cirrhose et le carcinomehépatocellulaire. Un des handicaps majeurs de la recherche sur le HCV est l’absence de systèmes decultures in vitro efficaces et de modèles animaux adaptés car le HCV n’infecte que l’homme et le chimpanzé.l’anticorps D32.10. Pour cela, nous avons développé un test de cellbindinget nous avons montré quel’interaction des particules virales sériques (HCVsp) radiomarquées à l’Iode 125 avec les celluleshépatocytaires (Huh‐7 et HepaRG) est spécifique et saturable impliquant des sites de haute et faible affinité.De plus, l’anticorps D32.10 est capable d’inhiber spécifiquement et efficacement les interactions de hauteaffinité entre les HCVsp et les cellules HepaRG avec une IC50 ≤ 0,5 μg/ml. Nous avons mis en évidence quel’inhibition est plus efficace lorsque nous utilisons sélectivement une population de particules HCVenveloppées exprimant fortement E1E2. Récemment, nous avons développé un système d’infection originaldes cellules HepaRG qui sont des cellules progénitrices du foie par les HCVsp et avons montré quel’infection, la réplication et la propagation dépendent de l’état de prolifération/différenciation de cescellules. Nous avons aussi démontré que les particules virales produites dans ce système contiennent del’ARN viral, expriment les protéines d’enveloppe E1E2 et sont infectieuses. Des études préliminairesmontrent que l’anticorps D32.10 inhibe fortement l’infection (95% à 80% aux jours 14 et 21 aprèsinfection) vraisemblablement au niveau des étapes précoces du cycle viral.Dans un second temps, nous avons recherché la prévalence des anticorps de même spécificité que le D32.10(anti‐E1E2A,B) dans différents groupes de patients HCV positifs afin de déterminer leur significationbiologique. Par un test ELISA utilisant les peptides biotinylés E1, E2A et E2B dans la phase de capture, nousavons démontré que la réponse anticorps anti‐E1E2A,B était présente dans 90% des cas chez les patientsqui guérissent spontanément avec des titres élevées (≥ 1/1000). Cette réponse humorale est absente ourare (< 10%) chez les patients porteurs chroniques non traités ou non répondeurs aux traitementsantiviraux. Une étude longitudinale a été réalisée chez des patients non répondeurs ou répondeursdéveloppant une réponse virologique soutenue à une bithérapie standard, interféron pégylé plus ribavirine.L’analyse statistique des résultats a montré que les anticorps anti‐E1E2A,B pouvaient être prédictifs de laréponse au traitement avec une spécificité et une valeur prédictive positive de 100%.La convergence des résultats in vitro et in vivo supporte un rôle neutralisant de l’anticorps monoclonalD32.10, permettant d’envisager son utilisation en immunothérapie. / Hepatitis C Virus (HCV) is the major etiological agent of liver disease in the world with approximately180 million people who are seropositive. The majority (60‐90%) of infected individuals progressesto chronic hepatitis that increases their risk for developing cirrhosis and hepatocellular carcinoma.One of the major limitations of HCV research is the lack of efficient in vitro culture systems andappropriateanimal models. vitro direct cell‐binding assay and an infection system of the human HepaRG cell line were developedby using HCVsp. The HepaRG cells possess potent ability to acquire a mature hepatocyte phenotype.The E1E2‐specific mAb D32.10 was shown to inhibit efficiently and specifically high affinityinteractionsthrough glycosaminoglycans and the CD81 tetraspanin between HCVsp and HepaRGcells with an IC50 = 0.5 μg/ml. This inhibition was more efficient when E1E2‐positive envelopedHCVsp were used selectively for binding studies (IC50 < 0.5 μg/ml). Establishment of infection,replication and propagation of HCVsp were shown to depend on the proliferation/differentiationstage of HepaRG cells. Persistent HCV infection in HepaRG cells could be obtained with production ofE1E2/RNA(+) infectious HCV particles. Preliminary data showed a complete early inhibitory effect ofthe D32.10 mAb on virion RNA production in HepaRG culture supernatants (95% at D14 and 80% atD21 post‐infection).Furthermore, the detection of the anti‐E1E2/D32.10‐binding peptide antibodies during natural HCVinfection demonstrated significant prevalence (90%) of these antibodies: (1) in patients whorecovered spontaneously from HCV infection with high titers compared to patients with chronichepatitis C, and (2) in patients who are complete responders compared to non responders toantivirals. Kinetic analyses revealed that the anti‐E1E2/D32.10‐like humoral response appeared veryearly with high titers (≥ 1/1000) and was associated with complete virus eradication. The positiveand negative predictive values (ROC curve analysis) for achieving or not a sustained viral response toantiviral therapy are 100% and 86%, respectively, reflecting diagnostic accuracy. The anti‐E1E2/D32.10‐binding peptide antibodies may thus predict the outcome of HCV infection andrepresent a new relevant pronostic marker in serum for the HCV diagnosis.Convergence of in vitro and in vivo data strongly support the neutralizing activity of the D32.10 mAb,and thus immunotherapeutic potential of this unique anti‐E1E2 D32.10 mAb.

Overweight has become a major health care problem in Western societies and is accompanied by an increasing incidence and prevalence of non-alcoholic fatty liver disease (NAFLD). The progression from NAFLD to non-alcoholic steatohepatitis (NASH) marks a crucial tipping point in the progression of severe and irreversible liver diseases. This study aims to gain further insight into the molecular processes leading to the evolution from steatosis to steatohepatitis. Steatosis was induced in cultures of primary human hepatocytes by continuous five-day exposure to free fatty acids (FFAs). The kinetics of lipid accumulation, lipotoxicity, and oxidative stress were measured. Additionally, ER stress was evaluated by analyzing the protein expression profiles of its key players: PERK, IRE1a, and ATF6a. Our data revealed that hepatocytes are capable of storing enormous amounts of lipids without showing signs of lipotoxicity. Prolonged lipid accumulation did not create an imbalance in hepatocyte redox homeostasis or a reduction in antioxidative capacity. However, we observed an FFA-dependent increase in ER stress, revealing thresholds for triggering the activation of pathways associated with lipid stress, inhibition of protein translation, and apoptosis. Our study clearly showed that even severe lipid accumulation can be attenuated by cellular defenses, but regenerative capacities may be reduced.

Non-alcoholic fatty liver disease (NAFLD), characterized by lipid accumulation in the liver, is the most common cause of liver diseases in Western countries. NAFLD is a major risk factor for developing hepatocellular carcinoma (HCC); however, in vitro evaluation of hepatic cancerogenesis fails due to a lack of liver models displaying a proliferation of hepatocytes. Originally designed to overcome primary human hepatocyte (PHH) shortages, upcyte hepatocytes were engineered to obtain continuous proliferation and, therefore, could be a suitable tool for HCC research. We generated upcyte hepatocytes, termed HepaFH3 cells, and compared their metabolic characteristics to HepG2 hepatoma cells and PHHs isolated from resected livers. For displaying NAFLD-related HCCs, we induced steatosis in all liver models. Lipid accumulation, lipotoxicity and energy metabolism were characterized using biochemical assays and Western blot analysis. We showed that proliferating HepaFH3 cells resemble HepG2, both showing a higher glucose uptake rate, lactate levels and metabolic rate compared to PHHs. Confluent HepaFH3 cells displayed some similarities to PHHs, including higher levels of the transaminases AST and ALT compared to proliferating HepaFH3 cells. We recommend proliferating HepaFH3 cells as a pre-malignant cellular model for HCC research, while confluent HepaFH3 cells could serve as PHH surrogates for energy metabolism studies.

Nonalcoholic fatty liver disease (NAFLD) is among the leading causes of end-stage liver disease. The impaired hepatic lipid metabolism in NAFLD is exhibited by dysregulated PPARα and SREBP-1c signaling pathways, which are central transcription factors associated with lipid degradation and de novo lipogenesis. Despite the growing prevalence of this disease, current pharmacological treatment options are unsatisfactory. Genistein, a soy isoflavone, has beneficial effects on lipid metabolism and may be a candidate for NAFLD treatment. In an in vitro model of hepatic steatosis, primary human hepatocytes (PHHs) were incubated with free fatty acids (FFAs) and different doses of genistein. Lipid accumulation and the cytotoxic effects of FFAs and genistein treatment were evaluated by colorimetric and enzymatic assays. Changes in lipid homeostasis were examined by RT-qPCR and Western blot analyses. PPARα protein expression was induced in steatotic PHHs, accompanied by an increase in CPT1L and ACSL1 mRNA. Genistein treatment increased PPARα protein expression only in control PHHs, while CPTL1 and ACSL1 were unchanged and PPARα mRNA was reduced. In steatotic PHHs, genistein reversed the increase in activated SREBP-1c protein. The model realistically reflected the molecular changes in hepatic steatosis. Genistein suppressed the activation of SREBP-1c in steatotic hepatocytes, but the genistein-mediated effects on PPARα were abolished by high hepatic lipid levels.

Overweight has become a major health care problem in Western societies and is accompanied by an increasing incidence and prevalence of non-alcoholic fatty liver disease (NAFLD). The progression from NAFLD to non-alcoholic steatohepatitis (NASH) marks a crucial tipping point in the progression of severe and irreversible liver diseases. This study aims to gain further insight into the molecular processes leading to the evolution from steatosis to steatohepatitis. Steatosis was induced in cultures of primary human hepatocytes by continuous five-day exposure to free fatty acids (FFAs). The kinetics of lipid accumulation, lipotoxicity, and oxidative stress were measured. Additionally, ER stress was evaluated by analyzing the protein expression profiles of its key players: PERK, IRE1a, and ATF6a. Our data revealed that hepatocytes are capable of storing enormous amounts of lipids without showing signs of lipotoxicity. Prolonged lipid accumulation did not create an imbalance in hepatocyte redox homeostasis or a reduction in antioxidative capacity. However, we observed an FFA-dependent increase in ER stress, revealing thresholds for triggering the activation of pathways associated with lipid stress, inhibition of protein translation, and apoptosis. Our study clearly showed that even severe lipid accumulation can be attenuated by cellular defenses, but regenerative capacities may be reduced.

Although human liver tumor cells have reduced metabolic functions as compared to primary human hepatocytes (PHH) they are widely used for pre-screening tests of drug metabolism and toxicity. The aim of the present study was to modify liver cancer cell lines in order to improve their drug-metabolizing activities towards PHH. It is well-known that epigenetics is strongly modified in tumor cells and that epigenetic regulators influence the expression and function of Cytochrome P450 (CYP) enzymes through altering crucial transcription factors responsible for drug-metabolizing enzymes. Therefore, we screened the epigenetic status of four different liver cancer cell lines (Huh7, HLE, HepG2 and AKN-1) which were reported to have metabolizing drug activities. Our results showed that HepG2 cells demonstrated the highest similarity compared to PHH. Thus, we modified the epigenetic status of HepG2 cells towards ‘normal’ liver cells by 5-Azacytidine (5-AZA) and Vitamin C exposure. Then, mRNA expression of Epithelial-mesenchymal transition (EMT) marker SNAIL and CYP enzymes were measured by PCR and determinate specific drug metabolites, associated with CYP enzymes by LC/MS. Our results demonstrated an epigenetic shift in HepG2 cells towards PHH after exposure to 5-AZA and Vitamin C which resulted in a higher expression and activity of specific drug metabolizing CYP enzymes. Finally, we observed that 5-AZA and Vitamin C led to an increased expression of Hepatocyte nuclear factor 4α (HNF4α) and E-Cadherin and a significant down regulation of Snail1 (SNAIL), the key transcriptional repressor of E-Cadherin. Our study shows, that certain phase I genes and their enzyme activities are increased by epigenetic modification in HepG2 cells with a concomitant reduction of EMT marker gene SNAIL. The enhancing of liver specific functions in hepatoma cells using epigenetic modifiers opens new opportunities for the usage of cell lines as a potential liver in vitro model for drug testing and development.

Os corantes sintéticos são amplamente empregados em indústrias têxteis, de cosméticos, alimentícia, farmacêutica, dentre diversas outras. Entretanto, vários destes compostos apresentam elevada toxicidade intrínseca, e são precursores de intermediários tóxicos e/ou mutagênicos gerados durante a metabolização. Portanto, o emprego de corantes naturais destaca-se como uma alternativa aos sintéticos, na busca por compostos seguros para a saúde humana e ambiental. Neste contexto, no presente trabalho nós investigamos o potencial toxicológico e ecotoxicológico do corante natural eritrostominona (Ery), uma naftoquinona extraída de micro-organismo, utilizando modelos alternativos à experimentação animal. Adicionalmente, foi avaliada a ecotoxicidade do Basic Red 51 (BR51), um corante sintético azo utilizado em indústrias têxteis e de cosméticos, e do Ery degradado (EryD) após a exposição à luz, visando uma alternativa simples para o tratamento de efluentes industriais contendo o corante. As avaliações ecotoxicológicas foram realizadas em diferentes níveis tróficos: nos microcrustáceos Daphnia magna e nos estágios iniciais de desenvolvimento de zebrafish (Danio rerio). As avaliações toxicológicas do Ery foram realizadas em linhagem hepatocelular humana (HepG2) como órgão-alvo de metabolização de xenobióticos, e em epiderme humana equivalente (EHE), um modelo 3D construído com queratinócitos humanos imortalizados (HaCaT), visto que é esperado o contato dérmico devido ao potencial uso como corante de cosmético. Nossos resultados mostraram que o Ery e o BR51 são tóxicos para D. magna e zebrafish. O BR51 induziu alterações na imobilidade, na reprodução, no consumo de oxigênio e no comportamento de D. magna em concentrações até 200 vezes superiores às do Ery capazes de alterar a imobilidade, reprodução e comportamento. Todavia, para embriões e larvas de zebrafish ambos os corantes apresentaram efeitos tóxicos em concentrações próximas, com alterações do desenvolvimento embrionário e do comportamento, indução de efeitos pró-oxidantes e alterações no balanço energético dos organismos. O EryD interessantemente não apresentou nenhum efeito tóxico para os organismos aquáticos, demonstrando que a luz foi capaz de reduzir e/ou inativar a toxicidade da estrutura inicial. Para as linhagens celulares humanas, o Ery foi citotóxico para HepG2, tendo a apoptose como a principal causa de morte celular. O Ery também causou um atraso no ciclo celular de HepG2, em particular na fase da mitose (G2/M), diminuindo a proliferação das células. Por outro lado, o Ery não apresentou potencial genotóxico e mutagênico para HepG2 e não induziu citotoxicidade e genotoxicidade após exposições por períodos curtos em EHE. Em conclusão, o Ery e o BR51 são classificados como tóxicos e muito tóxicos para o ambiente aquático, respectivamente. O Ery também induz efeitos pró-apoptóticos, o qual pode estar ligado à estrutura química das quinonas. No entanto, o Ery apresenta potencial aplicabilidade industrial como um corante eco-friendly, com destaque para a simples e rápida fotodegradação, e como um corante não genotóxico e mutagênico para células humanas. Avaliações adicionais sobre os mecanismos de apoptose devem ser realizadas para assegurar a segurança à saúde humana / Synthetic dyes are widely used by textiles, cosmetic, food and pharmaceutical industries. However, several compounds have high inherent toxicity, and many are precursors of mutagenic and/or carcinogenic intermediates produced during metabolism. Thereby, the use of natural dyes became an alternative to the synthetic ones, in search of safe compounds for human and environmentl health. In this context, we aimed to investigate the toxicological and ecotoxicological potential of the natural dye erythrostominone (Ery), a naphthoquinone compound extracted from microorganism, using alternative methods to animal experimentation. Additionally, it was assessed the ecotoxicity of the Basic Red 51 (BR51), an azo synthetic dye used bu cosmetic and textile industries, and the Ery degraded (EryD) after exposure to light, aiming an easy alternative to industrial effluent treatments containing the dye. Ecotoxicological assessment was performed at different trophic levels: in the microcrutaceans Daphnia magna and in zebrafish (Danio rerio) early life stages. Toxicological assessment of Ery was also performed in human hepatocellular line (HepG2) as target organ of xenobiotic metabolism, and in equivalent human epidermis (EHE), a 3D model constructed with immortalized human keratinocytes (HaCaT), since dermal contact is expected due to potential use as cosmetic dye. Our results showed that Ery and BR51 are toxic for D. magna and zebrafish. BR51 induced alterations in immobility, reproduction, oxygen uptake and behavior of D. magna at concentrations up to 200-fold higher than those of Ery able to impair immobility, reproduction and behavior. However, for zebrafish embryos and larvae, both dyes showed toxic effects at close concentrations, with changes in embryo development and behavior, induction of pro-oxidant effects and changes in the energy balance of organisms. Interestingly, EryD showed no toxic effect on aquatic organisms, demonstrating that light was able to reduce and/or inactivate the toxicity of the initial chemical structure. For human cell lines, Ery showed to be cytotoxic to HepG2, with apoptosis being the main source of cell death. Ery also induced a delay in HepG2 cell cycle, particularly in the mitosis phase (G2/M), decreasing cell proliferation. On the other hand, Ery presented no genotoxic and mutagenic potential for HepG2 and did not induce cytotoxicity and genotoxicity after short-term exposure to EHE. In conclusion, Ery and BR51 are classified as toxic and very toxic to the aquatic environment, respectively. Ery also induces pro-apoptotic effects, which may be linked to the chemical structure of quinones. Therefore, Ery presents potential industrial applicability as an eco-friendly dye, highlighting the easy and rapid photodegradation, and the non-genotoxic and mutagenic effects for human cells. Further assessment of apoptosis mechanisms should be performed to ensure safety to human health

Der nach Leberoperation und -transplantation auftretende Ischämie-/ Reperfusionsschaden (I/R) und die konsekutive Inflammation des Lebergewebes stellen ein bedeutendes klinisches Problem dar. In der vorliegenden Arbeit wurden Einflüsse der warmen und kalten Ischämie (100% N2 bei 37°C bzw. 4°C) sowie der Exposition inflammatorischer Zytokine und Endotoxin (IL-1beta, 10 U/ml; IFN-gamma, 100 U/ml; TNF-alpha, 500 U/ml; LPS, 5 µg/ml) auf die Expression der Hämoxygenase-1 (HO- 1) mRNA und seines Proteins, einem Vertreter der Hitze-Schock-Proteine mit potentiell antioxidativer Wirkung, in humanen Hepatozytenprimärkulturen untersucht. Warme und kalte Ischämie stimulierten die HO-1 mRNA Expression in humanen Hepatozyten nach 0,5 bis 1h. Das HO-1 Protein wurde über 0,5-6h maximal exprimiert. Der Zellschaden, gemessen an der AST und LDH Freisetzung unter ischämischen Bedingungen wurde insbesondere nach 24 h beobachtet. Nach Zytokinexposition wurde die höchste Expressionsrate der mRNA durch IFN-gamma hervorgerufen, gefolgt von TNF-alpha, LPS und IL-1beta. Jedes einzelne Zytokin stimulierte die HO-1 mRNA Expression nach 0,5 h, erreichte ein Maximum nach 3 h und fiel nach 6 h ab. Nach Stimulation mit einem Zytokinmix (CM; IFN-gamma, TNF-alpha, IL-1beta, LPS) trat ein Maximum der HO-1 mRNA Expression erst nach 6 h ein, wobei ein signifikanter Zellschaden nach 12 h beobachtet wurde. Die HO-1 mRNA und Proteinexpression war nach Exposition von 6 h des Sauerstoffperoxides (H2O2, 200- 1000 µM) erhöht. Die HO-1 mRNA und Proteinexpression war nach S- nitrosoacetylpenicillamin (0.5 mM) Exposition, einem NO Donator, für 3-12 h verstärkt. Nach Cobalt-protoporphyrin (CoPP, 1µM) Exposition, einem potenten HO-1 Induktor, wurde eine erhöhte mRNA- und Proteinexpression beobachtet. Dass CoPP die HO-1 mRNA- und Proteinneusynthese induziert, konnte durch die selektive Blockade mit Actinomycin D und Cycloheximide bewiesen werden. Die Neusynthese konnte ebenfalls unter warmer und kalter Ischämie gezeigt werden. Hemin (10 µM), ein weiterer Induktor der HO-1, induzierte die HO-1 mRNA nach 3 h und das Protein nach 6 h. Die HO-1 Enzymaktivität wurde mittels Bilirubinbildung und Messung des Fe2+ Gehalts der Zellen bestimmt. Bei der Bilirubinbildung wurde die höchste Aktivität nach warmer Ischämie gemessen, gefolgt von kalter Ischämie, CM und der Kontrollgruppe. Die intrazelluläre Fe2+ Messung ergab ebenfalls die höchste Enzymaktivität nach warmer Ischämie. Die Vorbehandlung humaner Hepatozyten mit CoPP (1-50 µM) für 8 h, schützte die Zellen teilweise vor einer warmen und kalten Ischämie. Zusammenfassend zeigt diese Arbeit, dass die pharmakologische Induktion der HO-1 somit bei großen allgemeinchirurgischen Eingriffen, wie der Leberteilresektion oder der Transplantation, einen protektiven Effekt entfalten könnte. / Hepatic injury induced by ischemia/ reperfusion (I/R) and inflammation following surgeries or transplantations creates important clinical problems. In this study, the effect of inflammatory conditions such as cytokine/ endotoxin exposure (IL-1beta, IFN-gamma, TNF-alpha, LPS), warm and cold ischemia on HO-1 mRNA and protein, a member of heat shock proteins, was investigated. It was observed that IFN-gamma caused the highest HO-1 mRNA expression, followed by TNF-alpha, LPS and IL- 1beta. Each stimuli increased HO-1 mRNA expression after 0.5 h, peaked at 3 h and decreased after 6 h. Highest HO-1 protein expression was observed after 0.5 to 1 h of stimulation with IFN-gamma, which was followed by LPS, TNF-alpha and IL-1beta. The peak of HO-1 expression using all four stimuli (CM) was after 6 h. CM caused a significant increase in LDH and AST after 12 h. Warm and cold ischemia stimulated HO-1 mRNA expression in human hepatocytes at 0.5-1 h. HO-1 protein expression had its maximum between 0.5-6 h. Cellular damage measured as the release of LDH and AST was significant after 24 h. Mimicking oxydative stress, hepatocytes were exposed to 200-1000 µM H2O2 for 6 h which also showed an increased HO-1 mRNA and protein expression. HO-1 mRNA and protein expression revealed an increase after SNAP exposure at 3-12 h. Results with CoPP (10 µM), a potent inducer of HO- 1, displayed an increase in HO-1 mRNA and protein expression. It was proved, that CoPP induced new synthesis of mRNA and protein by its blocking agents such as actinomycin D and cycloheximide, respectively. Hemin (10 µM), another inducer of HO-1, triggered HO-1 mRNA expression after 3 h and protein expression after 6 h. The HO-1 enzyme activity was measured by bilirubin production after exposure to CM, as well as warm and cold ischemia. The highest enzyme activity was found after warm ischemia, followed by cold ischemia, CM and then by the control group. Fe2+ content of the cells, used as another method to judge HO-1 activity, confirmed our findings. Pre-treatment of human hepatocytes with different concentrations of CoPP (1-50 µM) protect cells against warm or cold ischemia. Therefore, we conclude that pharmacological induction of HO-1 may have therapeutic potential under inflammatory conditions such as seen during liver resection or liver transplantation.