Gene expression profile of CD14+ blood monocytes following lifestyle-induced weight loss in individuals with metabolic syndrome.

Lifestyle-induced weight loss is regarded as an efficient therapy to reverse metabolic syndrome (MetS) and to prevent disease progression. The objective of this study was to investigate whether lifestyle-induced weight loss modulates gene expression in circulating monocytes. We analyzed and compared gene expression in monocytes (CD14+ cells) and subcutaneous adipose tissue biopsies by unbiased mRNA profiling. Samples were obtained before and after diet-induced weight loss in well-defined male individuals in a prospective controlled clinical trial (ICTRP Trial Number: U1111-1158-3672). The BMI declined significantly (- 12.6%) in the treatment arm (N = 39) during the 6-month weight loss intervention. This was associated with a significant reduction in hsCRP (- 45.84%) and circulating CD14+ cells (- 21.0%). Four genes were differentially expressed (DEG's) in CD14+ cells following weight loss (ZRANB1, RNF25, RB1CC1 and KMT2C). Comparative analyses of paired CD14+ monocytes and subcutaneous adipose tissue samples before and after weight loss did not identify common genes differentially regulated in both sample types. Lifestyle-induced weight loss is associated with specific changes in gene expression in circulating CD14+ monocytes, which may affect ubiquitination, histone methylation and autophagy.

Increased Circulating VAP-1 Levels Are Associated with Liver Fibrosis in Chronic Hepatitis C Infection.

Vascular adhesion protein-1 (VAP-1) is a multifunction protein. While membrane-bound VAP-1 is an adhesion protein, soluble VAP-1 catalyzes the deamination of primary amines through its semicarbazide-sensitive amino oxidase (SSAO) activity. VAP-1 supports the transmigration of leukocytes and increases oxidative stress. In chronic liver diseases, it plays a role in leukocyte infiltration and fibrogenesis. Here, we measured VAP-1 plasma concentration and its SSAO activity in 322 patients with chronic hepatitis C infection and evaluated the association of VAP-1 with fibrosis stages. VAP-1 concentration strongly correlated with liver stiffness and was the second strongest influencing variable after gamma-glutamytransferase (GGT) for liver stiffness in regression analysis. The VAP-1 concentration increased with advancing fibrosis stages and the highest concentrations were found in patients with cirrhosis. According to the receiver operating characteristic (ROC) analysis, a VAP-1 cut-off value of 541 ng/mL predicted histologically confirmed cirrhosis (sensitivity 74%; specificity 72%). SSAO activity correlated only moderately with liver stiffness, showing a relatively small increase in advanced fibrosis. To our knowledge, this is the first study on VAP-1 in chronic hepatitis C infection showing its association with progressive fibrosis. In conclusion, VAP-1 plasma concentration, rather than its SSAO activity, may represent a non-invasive biomarker for monitoring fibrogenesis in patients with chronic hepatitis C infection.

The Gut Microbiota and Hematopoietic Stem Cell Transplantation: Challenges and Potentials.

The human gut microbiota gained tremendous importance in the last decade as next-generation technologies of sequencing and multiomics analyses linked the role of the microbial communities to host physiology and pathophysiology. A growing number of human pathologies and diseases are linked to the gut microbiota. One of the main mechanisms by which the microbiota influences the host is through its interactions with the host immune system. These interactions with both innate and adaptive host intestinal and extraintestinal immunity, although usually commensalistic even mutualistic with the host, in some cases lead to serious health effects. In the case of allogenic hematopoietic stem cell transplantation (allo-HSCT), the disruption of the intestinal microbiota diversity is associated with acute graft-versus-host disease (GvHD). Causing inflammation of the liver, skin, lungs, and the intestine, GvHD occurs in 40-50% of patients undergoing allo-HSCT and results in significant posttransplantation mortality. In this review, we highlight the impact of the gut microbiota on the host immunity in GvHD and the potential of microbiota in alleviation or even prevention of GvHD.

Hepatocytes of Wistar and Sprague Dawley rats differ significantly in their central metabolism.

Wistar and Sprague-Dawley (SD) rats are most commonly used experimental rats. They have similar genetic background and are therefore, not discriminated in practical research. In this study, we compared metabolic profiles of Wistar and SD rat hepatocytes from middle (6 months) and old (23 months) age groups. Principle component analysis (PCA) on the specific uptake and production rates of amino acids, glucose, lactate and urea indicated clear differences between Wistar and SD rat hepatocytes. SD rat hepatocytes showed higher uptake rates of various essential and non-essential amino acids, particularly in early culture phases (0-12 h) compared to later phases (12-24 h). SD hepatocytes seem to be more sensitive to isolation procedure and in vitro culture requiring more amino acids for cellular maintenance and repair. Major differences between Wistar and SD rat hepatocytes were observed for glucose and branched chain amino acid metabolism. We conclude that the observed differences in the central carbon metabolism of isolated hepatocytes from these two rats should be considered when using one or the other rat type in studies on metabolic effects or diseases such as diabetes or obesity.

Proteomic Characterization of Primary Mouse Hepatocytes in Collagen Monolayer and Sandwich Culture.

Dedifferentiation of primary hepatocytes in vitro makes their application in long-term studies difficult. Embedding hepatocytes in a sandwich of extracellular matrix is reported to delay the dedifferentiation process to some extent. In this study, we compared the intracellular proteome of primary mouse hepatocytes (PMH) in conventional monolayer cultures (ML) to collagen sandwich culture (SW) after 1 day and 5 days of cultivation. Quantitative proteome analysis of PMH showed no differences between collagen SW and ML cultures after 1 day. Glycolysis and gluconeogenesis were strongly affected by long-term cultivation in both ML and SW cultures. Interestingly, culture conditions had no effect on cellular lipid metabolism. After 5 days, PMH in collagen SW and ML cultures exhibit characteristic indications of oxidative stress. However, in the SW culture the defense system against oxidative stress is significantly up-regulated to deal with this, whereas in the ML culture a down-regulation of these important enzymes takes place. Regarding the multiple effects of ROS and oxidative stress in cells, we conclude that the down-regulation of these enzymes seem to play a role in the loss of hepatic function observed in the ML cultivation. In addition, enzymes of the urea cycle were clearly down-regulated in ML culture. Proteomics confirms lack in oxidative stress defense mechanisms as the major characteristic of hepatocytes in monolayer cultures compared to sandwich cultures. J. Cell. Biochem. 119: 447-454, 2018. © 2017 Wiley Periodicals, Inc.

Towards a 21st-century roadmap for biomedical research and drug discovery: consensus report and recommendations.

Decades of costly failures in translating drug candidates from preclinical disease models to human therapeutic use warrant reconsideration of the priority placed on animal models in biomedical research. Following an international workshop attended by experts from academia, government institutions, research funding bodies, and the corporate and non-governmental organisation (NGO) sectors, in this consensus report, we analyse, as case studies, five disease areas with major unmet needs for new treatments. In view of the scientifically driven transition towards a human pathways-based paradigm in toxicology, a similar paradigm shift appears to be justified in biomedical research. There is a pressing need for an approach that strategically implements advanced, human biology-based models and tools to understand disease pathways at multiple biological scales. We present recommendations to help achieve this.

Accessing 3D microtissue metabolism: Lactate and oxygen monitoring in hepatocyte spheroids.

3D hepatic microtissues, unlike 2D cell cultures, retain many of the in-vivo-like functionalities even after long-term cultivation. Such 3D cultures are increasingly applied to investigate liver damage due to drug exposure in toxicology. However, there is a need for thorough metabolic characterization of these microtissues for mechanistic understanding of effects on culture behaviour. We measured metabolic parameters from single human HepaRG hepatocyte spheroids online and continuously with electrochemical microsensors. A microsensor platform for lactate and oxygen was integrated in a standard 96-well plate. Electrochemical microsensors for lactate and oxygen allow fast, precise and continuous long-term measurement of metabolic parameters directly in the microwell. The demonstrated capability to precisely detect small concentration changes by single spheroids is the key to access their metabolism. Lactate levels in the culture medium starting from 50µM with production rates of 5µMh-1 were monitored and precisely quantified over three days. Parallel long-term oxygen measurements showed no oxygen depletion or hypoxic conditions in the microwell. Increased lactate production by spheroids upon suppression of the aerobic metabolism was observed. The dose-dependent decrease in lactate production caused by the addition of the hepatotoxic drug Bosentan was determined. We showed that in a toxicological application, metabolic monitoring yields quantitative, online information on cell viability, which complements and supports other methods such as microscopy. The demonstrated continuous access to 3D cell culture metabolism within a standard setup improves in vitro toxicology models in replacement strategies of animal experiments. Controlling the microenvironment of such organotypic cultures has impact in tissue engineering, cancer therapy and personalized medicine.

Metabolic fate of desomorphine elucidated using rat urine, pooled human liver preparations, and human hepatocyte cultures as well as its detectability using standard urine screening approaches.

Desomorphine is an opioid misused as "crocodile", a cheaper alternative to heroin. It is a crude synthesis product homemade from codeine with toxic byproducts. The aim of the present work was to investigate the metabolic fate of desomorphine in vivo using rat urine and in vitro using pooled human liver microsomes and cytosol as well as human liver cell lines (HepG2 and HepaRG) by Orbitrap-based liquid chromatography-high resolution-tandem mass spectrometry or hydrophilic interaction liquid chromatography. According to the identified metabolites, the following metabolic steps could be proposed: N-demethylation, hydroxylation at various positions, N-oxidation, glucuronidation, and sulfation. The cytochrome P450 (CYP) initial activity screening revealed CYP3A4 to be the only CYP involved in all phase I steps. UDP-glucuronyltransferase (UGT) initial activity screening showed that UGT1A1, UGT1A8, UGT1A9, UGT1A10, UGT2B4, UGT2B7, UGT2B15, and UGT2B17 formed desomorphine glucuronide. Among the tested in vitro models, HepaRG cells were identified to be the most suitable tool for prediction of human hepatic phase I and II metabolism of drugs of abuse. Finally, desomorphine (crocodile) consumption should be detectable by all standard urine screening approaches mainly via the parent compound and/or its glucuronide assuming similar kinetics in rats and humans.

Novel human hepatic organoid model enables testing of drug-induced liver fibrosis in vitro.

Current models for in vitro fibrosis consist of simple mono-layer cultures of rodent hepatic stellate cells (HSC), ignoring the role of hepatocyte injury. We aimed to develop a method allowing the detection of hepatocyte-mediated and drug-induced liver fibrosis. We used HepaRG (Hep) and primary human HSCs cultured as 3D spheroids in 96-well plates. These resulting scaffold-free organoids were characterized for CYP induction, albumin secretion, and hepatocyte and HSC-specific gene expression by qPCR. The metabolic competence of the organoid over 21 days allows activation of HSCs in the organoid in a drug- and hepatocyte-dependent manner. After a single dose or repeated exposure for 14 days to the pro-fibrotic compounds Allyl alcohol and Methotrexate, hepatic organoids display fibrotic features such as HSC activation, collagen secretion and deposition. Acetaminophen was identified by these organoids as an inducer of hepatotoxic-mediated HSC activation which was confirmed in vivo in mice. This novel hepatic organoid culture model is the first that can detect hepatocyte-dependent and compound-induced HSC activation, thereby representing an important step forward towards in vitro compound testing for drug-induced liver fibrosis.

In Silico Modeling for the Prediction of Dose and Pathway-Related Adverse Effects in Humans From In Vitro Repeated-Dose Studies.

Long-term repeated-dose toxicity is mainly assessed in animals despite poor concordance of animal data with human toxicity. Nowadays advanced human in vitro systems, eg, metabolically competent HepaRG cells, are used for toxicity screening. Extrapolation of in vitro toxicity to in vivo effects is possible by reverse dosimetry using pharmacokinetic modeling. We assessed long-term repeated-dose toxicity of bosentan and valproic acid (VPA) in HepaRG cells under serum-free conditions. Upon 28-day exposure, the EC50 values for bosentan and VPA decreased by 21- and 33-fold, respectively. Using EC(10) as lowest threshold of toxicity in vitro, we estimated the oral equivalent doses for both test compounds using a simplified pharmacokinetic model for the extrapolation of in vitro toxicity to in vivo effect. The model predicts that bosentan is safe at the considered dose under the assumed conditions upon 4 weeks exposure. For VPA, hepatotoxicity is predicted for 4% and 47% of the virtual population at the maximum recommended daily dose after 3 and 4 weeks of exposure, respectively. We also investigated the changes in the central carbon metabolism of HepaRG cells exposed to orally bioavailable concentrations of both drugs. These concentrations are below the 28-day EC(10) and induce significant changes especially in glucose metabolism and urea production. These metabolic changes may have a pronounced impact in susceptible patients such as those with compromised liver function and urea cycle deficiency leading to idiosyncratic toxicity. We show that the combination of modeling based on in vitro repeated-dose data and metabolic changes allows the prediction of human relevant in vivo toxicity with mechanistic insights.

A shift in paradigm towards human biology-based systems for cholestatic-liver diseases.

Cholestatic-liver diseases (CLDs) arise from diverse causes ranging from genetic factors to drug-induced cholestasis. The so-called diseases of civilization (obesity, diabetes, metabolic disorders, non-alcoholic liver disease, cardiovascular diseases, etc.) are intricately implicated in liver and gall bladder diseases. Although CLDs have been extensively studied, there seem to be important gaps in the understanding of human disease. Despite the fact that many animal models exist and substantial clinical data are available, translation of this knowledge towards therapy has been disappointingly limited. Recent advances in liver cell culture such as in vivo-like 3D cultivation of human primary hepatic cells, human induced pluripotent stem cell-derived hepatocytes; and cutting-edge analytical techniques such as 'omics' technologies and high-content screenings could play a decisive role in deeper mechanistic understanding of CLDs. This Topical Review proposes a roadmap to human biology-based research using omics technologies providing quantitative information on mechanisms in an adverse outcome/disease pathway framework. With modern sensitive tools, a shift in paradigm in human disease research seems timely and even inevitable to overcome species barriers in translation.

State-of-the-art of 3D cultures (organs-on-a-chip) in safety testing and pathophysiology.

Integrated approaches using different in vitro methods in combination with bioinformatics can (i) increase the success rate and speed of drug development; (ii) improve the accuracy of toxicological risk assessment; and (iii) increase our understanding of disease. Three-dimensional (3D) cell culture models are important building blocks of this strategy which has emerged during the last years. The majority of these models are organotypic, i.e., they aim to reproduce major functions of an organ or organ system. This implies in many cases that more than one cell type forms the 3D structure, and often matrix elements play an important role. This review summarizes the state of the art concerning commonalities of the different models. For instance, the theory of mass transport/metabolite exchange in 3D systems and the special analytical requirements for test endpoints in organotypic cultures are discussed in detail. In the next part, 3D model systems for selected organs--liver, lung, skin, brain--are presented and characterized in dedicated chapters. Also, 3D approaches to the modeling of tumors are presented and discussed. All chapters give a historical background, illustrate the large variety of approaches, and highlight up- and downsides as well as specific requirements. Moreover, they refer to the application in disease modeling, drug discovery and safety assessment. Finally, consensus recommendations indicate a roadmap for the successful implementation of 3D models in routine screening. It is expected that the use of such models will accelerate progress by reducing error rates and wrong predictions from compound testing.

Long-term maintenance of HepaRG cells in serum-free conditions and application in a repeated dose study.

Chronic repeated-dose toxicity studies are still carried out on animals and often do not correlate with the effects in human beings mainly due to species-specific differences in biotransformation. The human hepatoma cell line HepaRG has been used for human relevant toxicity assessment. However, HepaRG cells are commonly maintained in serum containing medium which limits their use in 'omics'-based toxicology. In this study, we compared the maintenance of HepaRG cells in standard serum-supplemented and serum-free conditions. Viability and Cytochrome P450 (CYP) activity during long-term cultivation were assessed. Liver-specific albumin and urea production was measured. The extracellular metabolome (amino acids, glucose, lactate and pyruvate) was measured to compare different cultivation conditions using metabolic flux analysis. Although metabolic flux analysis reveals differences in certain parts of the metabolism, e.g. production of urea, the overall metabolism of serum-free and serum-supplemented cultured HepaRG cells is similar. We conclude that HepaRG cells can be maintained in optimized serum-free conditions for 30 days without viability change and with high CYP activity. We also tested the acute (24 h) and long-term repeated-dose (7 doses, every second day) toxicity of valproic acid. We calculated an EC50 value of 1.4 mM after repeated exposure which is close to the cmax value for valproic acid. Maintenance of HepaRG cells in serum-free conditions opens up the opportunity for the use of these cells in human long-term repeated-dose hepatotoxicity studies and for application in systems toxicology.

3D organotypic HepaRG cultures as in vitro model for acute and repeated dose toxicity studies.

Predictive in vitro models alternative to in vivo animal will have a significant impact in toxicology. Conventional 2D models do not reflect the complexity of a 3D organ resulting in discrepancies between experimental in vitro and in vivo data. Using 3D HepaRG organotypic cultures we tested four drugs (aflatoxin B1, amiodarone, valproic acid and chlorpromazine) for toxic effects and compared the results with 2D HepaRG and HepG2 cultures. We show that 3D HepaRG cultures are more sensitive than the other tested cultures to aflatoxin B1 which is only toxic upon metabolic activation in the liver. We observed that CYP3A4 activity is higher in the 3D HepaRG cultures compared to the 2D HepaRG cultures. Furthermore, we investigated repeated dose toxicity of chlorpromazine and assessed its effects on glucose and lactate metabolism. Sub-toxic concentrations of chlorpromazine induced significant metabolic changes in both 2D and 3D HepaRG cultures upon acute and repeated dose (3 doses) exposure. In summary, our data support the hypothesis that 3D cell culture models better mimic the in vivo tissue and improve cellular functionality. The 3D HepaRG organotypic cultures represent a high throughput system for drug toxicity screening. This system is therefore a promising tool in preclinical testing of human relevance which can allow reducing and/or replacing animal testing for drug adverse effects.

Metabolomics in toxicology and preclinical research.

Metabolomics, the comprehensive analysis of metabolites in a biological system, provides detailed information about the biochemical/physiological status of a biological system, and about the changes caused by chemicals. Metabolomics analysis is used in many fields, ranging from the analysis of the physiological status of genetically modified organisms in safety science to the evaluation of human health conditions. In toxicology, metabolomics is the -omics discipline that is most closely related to classical knowledge of disturbed biochemical pathways. It allows rapid identification of the potential targets of a hazardous compound. It can give information on target organs and often can help to improve our understanding regarding the mode-of-action of a given compound. Such insights aid the discovery of biomarkers that either indicate pathophysiological conditions or help the monitoring of the efficacy of drug therapies. The first toxicological applications of metabolomics were for mechanistic research, but different ways to use the technology in a regulatory context are being explored. Ideally, further progress in that direction will position the metabolomics approach to address the challenges of toxicology of the 21st century. To address these issues, scientists from academia, industry, and regulatory bodies came together in a workshop to discuss the current status of applied metabolomics and its potential in the safety assessment of compounds. We report here on the conclusions of three working groups addressing questions regarding 1) metabolomics for in vitro studies 2) the appropriate use of metabolomics in systems toxicology, and 3) use of metabolomics in a regulatory context.

3D organotypic cultures of human HepaRG cells: a tool for in vitro toxicity studies.

Drug-induced human hepatotoxicity is difficult to predict using the current in vitro systems. In this study, long-term 3D organotypic cultures of the human hepatoma HepaRG cell line were prepared using a high-throughput hanging drop method. The organotypic cultures were maintained for 3 weeks and assessed for (1) liver specific functions, including phase I enzyme and transporter activities, (2) expression of liver-specific proteins, and (3) responses to three drugs (acetaminophen, troglitazone, and rosiglitazone). Our results show that the organotypic cultures maintain high liver-specific functionality during 3 weeks of culture. The immunohistochemistry analyses illustrate that the organotypic cultures express liver-specific markers such as albumin, CYP3A4, CYP2E1, and MRP-2 throughout the cultivation period. Accordingly, the production rates of albumin and glucose, as well as CYP2E1 activity, were significantly higher in the 3D versus the 2D cultures. Toxicity studies show that the organotypic cultures are more sensitive to acetaminophen- and rosiglitazone-induced toxicity but less sensitive to troglitazone-induced toxicity than the 2D cultures. Furthermore, the EC50 value (2.7mM) for acetaminophen on the 3D cultures was similar to in vivo toxicity. In summary, the results from our study suggest that the 3D organotypic HepaRG culture is a promising in vitro tool for more accurate assessment of acute and also possibly for chronic drug-induced hepatotoxicity.

Real-time in situ viability assessment in a 3D bioreactor with liver cells using resazurin assay.

Three-dimensional cultivation of human cells is promising especially for long-term maintenance of specific functions and mimicking the in vivo tissue environment. However, direct viability assessment is very difficult in such systems. Commonly applied indirect methods such as glucose consumption, albumin or urea production are greatly affected by culture conditions, stress and time of cultivation and do not reflect the real time viability of the cells. In this study we established a real-time in situ viability assay namely; resazurin assay, in a 3D hollow-fiber bioreactor using human liver cells. Resazurin assay is based on the conversion of resazurin to a fluorescent dye by cytoplasmatic and mitochondrial enzymes. We show that the resazurin reagent in concentrations used in this study is non-toxic and could be rapidly removed out of the system. Moreover, we observed that dead cells do not affect the results of the assay. We optimized the assay on HepG2 cells and tested it with primary human hepatocytes. Moreover, we maintained primary human hepatocytes in the 3D bioreactor system in serum-free conditions and also assessed viability before and after the exposure to amiodarone using the resazurin assay. We show that this approach is applicable during long-term cultivation of cells in bioreactors under different conditions and can moreover be applied to pharmacological studies, e.g. investigation of chronic drug effects in such 3D bioreactors.

Biotransformation of diclofenac and effects on the metabolome of primary human hepatocytes upon repeated dose exposure.

In vitro repeated dose testing for the assessment of chronic drug-induced effects is a huge challenge in preclinical pharmaceutical drug development. Chronic toxicity results in discontinuation of therapy or post-marketing withdrawal of drugs despite in vivo preclinical screening. In case of hepatotoxicity, due to limited long term viability and functionality of primary hepatocytes, chronic hepatic effects are difficult to detect. In this study, we maintained primary human hepatocytes in a serum-free cultivation medium for more than 3 weeks and analyzed physiology, viability and drug metabolizing capacities of the hepatocytes. Moreover, we assessed acute (24 h) diclofenac toxicity in a range of (10-1000 µM) concentrations. The chronic (9 repeated doses) toxicity at one clinically relevant and another higher concentration (6.4 and 100 µM) was also tested. We investigated phase I and II metabolism of diclofenac upon repeated dose exposure and analyzed effects on the cellular exometabolome. Acute 24 h assessment revealed toxicity only for the highest tested concentration (1 mM). Upon repeated dose exposure, toxic effects were observed even at a low, clinically relevant concentration (6.4 µM). Biotransformation pathways were active for 3 weeks and diclofenac-acylglucuronide was detected as the predominant metabolite. Dose dependent diclofenac-induced effects on exometabolome, such as on the production of lactate and 3-hydroxybutyric acid as well as glucose and galactose metabolism, were observed upon nine repeated doses. Summarizing, we show that repeated dose testing on long-term functional cultures of primary human hepatocytes may be included for the assessment of long term toxic effects in preclinical screening and can potentially help replace/reduce in vivo animal testing.

Doxorubicin increases oxidative metabolism in HL-1 cardiomyocytes as shown by 13C metabolic flux analysis.

Doxorubicin (DXR), an anticancer drug, is limited in its use due to severe cardiotoxic effects. These effects are partly caused by disturbed myocardial energy metabolism. We analyzed the effects of therapeutically relevant but nontoxic DXR concentrations for their effects on metabolic fluxes, cell respiration, and intracellular ATP. (13)C isotope labeling studies using [U-(13)C(6)]glucose, [1,2-(13)C(2)]glucose, and [U-(13)C(5)]glutamine were carried out on HL-1 cardiomyocytes exposed to 0.01 and 0.02 µM DXR and compared with the untreated control. Metabolic fluxes were calculated by integrating production and uptake rates of extracellular metabolites (glucose, lactate, pyruvate, and amino acids) as well as (13)C-labeling in secreted lactate derived from the respective (13)C-labeled substrates into a metabolic network model. The investigated DXR concentrations (0.01 and 0.02 µM) had no effect on cell viability and beating of the HL-1 cardiomyocytes. Glycolytic fluxes were significantly reduced in treated cells at tested DXR concentrations. Oxidative metabolism was significantly increased (higher glucose oxidation, oxidative decarboxylation, TCA cycle rates, and respiration) suggesting a more efficient use of glucose carbon. These changes were accompanied by decrease of intracellular ATP. We conclude that DXR in nanomolar range significantly changes central carbon metabolism in HL-1 cardiomyocytes, which results in a higher coupling of glycolysis and TCA cycle. The myocytes probably try to compensate for decreased intracellular ATP, which in turn may be the result of a loss of NADH electrons via either formation of reactive oxygen species or electron shunting.

Metabolic flux analysis gives an insight on verapamil induced changes in central metabolism of HL-1 cells.

Verapamil has been shown to inhibit glucose transport in several cell types. However, the consequences of this inhibition on central metabolism are not well known. In this study we focused on verapamil induced changes in metabolic fluxes in a murine atrial cell line (HL-1 cells). These cells were adapted to serum free conditions and incubated with 4 µM verapamil and [U-¹³C5] glutamine. Specific extracellular metabolite uptake/production rates together with mass isotopomer fractions in alanine and glutamate were implemented into a metabolic network model to calculate metabolic flux distributions in the central metabolism. Verapamil decreased specific glucose consumption rate and glycolytic activity by 60%. Although the HL-1 cells show Warburg effect with high lactate production, verapamil treated cells completely stopped lactate production after 24 h while maintaining growth comparable to the untreated cells. Calculated fluxes in TCA cycle reactions as well as NADH/FADH2 production rates were similar in both treated and untreated cells. This was confirmed by measurement of cell respiration. Reduction of lactate production seems to be the consequence of decreased glucose uptake due to verapamil. In case of tumors, this may have two fold effects; firstly depriving cancer cells of substrate for anaerobic glycolysis on which their growth is dependent; secondly changing pH of the tumor environment, as lactate secretion keeps the pH acidic and facilitates tumor growth. The results shown in this study may partly explain recent observations in which verapamil has been proposed to be a potential anticancer agent. Moreover, in biotechnological production using cell lines, verapamil may be used to reduce glucose uptake and lactate secretion thereby increasing protein production without introduction of genetic modifications and application of more complicated fed-batch processes.