formazans and Carcinoma--Hepatocellular

Vanillin has been reported to exhibit anti-invasive and antimetastatic activities by suppressing the enzymatic activity of matrix metalloproteinase-9 (MMP-9). However, the underlying mechanism of anti-invasive activity remains unclear so far. Herein we demonstrate that vanillin reduced 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced MMP-9 gelatinolytic activity and suppressed cell invasion through the down-regulation of MMP-9 gene transcription in HepG2 cells. Vanillin significantly reduced the 6.6-fold invasive capacity of HepG2 cells in noncytotoxic concentrations, and this anti-invasive effect was concentration-dependent in the Matrigel invasion assay. Moreover, vanillin significantly suppressed the TPA-induced enzymatic activity of MMP-9 and decreased the induced mRNA level of MMP-9. Analysis of the transcriptional regulation indicated that vanillin suppressed MMP-9 transcription by inhibiting nuclear factor-kappaB (NF-kappaB) activity. Western blot further confirmed that vanillin inhibited NF-kappaB activity through the inhibition of IkappaB-alpha phosphorylation and degradation. In conclusion, vanillin might be a potent antiinvasive agent that suppresses the MMP-9 enzymatic activity via NF-kappaB signaling pathway.

Topics: Benzaldehydes; Carcinoma, Hepatocellular; Cell Line, Tumor; Dose-Response Relationship, Drug; Down-Regulation; Formazans; Genes, Reporter; Humans; Liver Neoplasms; Luciferases; Matrix Metalloproteinase Inhibitors; Models, Biological; NF-kappa B; RNA, Messenger; Signal Transduction; Tetrazolium Salts

4-Methyl-5-(2-pyrazinyl)-1,2-dithiole-3-thione (oltipraz), a prototype drug candidate containing a 1,2-dithiole-3-thione moiety, has been widely studied as a cancer chemopreventive agent. Oltipraz and other novel 1,2-dithiole-3-thione congeners have the capability to prevent insulin resistance via AMP-activated protein kinase (AMPK) activation. Arachidonic acid (AA, a proinflammatory fatty acid) exerts a deleterious effect on mitochondria and promotes reactive oxygen species (ROS) production. This study investigated whether AA alone or in combination with iron (catalyst of autooxidation) causes ROS-mediated mitochondrial impairment, and if so, whether oltipraz and synthetic 1,2-dithiole-3-thiones protect mitochondria and cells against excess ROS produced by AA + iron. Oltipraz treatment effectively inhibited mitochondrial permeability transition promoted by AA + iron in HepG2 cells, thereby protecting cells from ROS-induced apoptosis. Oltipraz was found to attenuate apoptosis induced by rotenone (complex I inhibitor), but not that by antimycin A (complex III inhibitor), suggesting that the inhibition of AA-induced apoptosis by oltipraz might be associated with the electron transport system. AMPK activation by oltipraz contributed to cell survival, which was supported by the reversal of oltipraz's restoration of mitochondrial membrane potential by concomitant treatment of compound C. By the same token, an AMPK activator inhibited AA + iron-induced mitochondrial permeability transition with an increase in cell viability. Moreover, new 1,2-dithiole-3-thiones with the capability of AMPK activation protected cells from mitochondrial permeability transition and ROS overproduction induced by AA + iron. Our results demonstrate that oltipraz and new 1,2-dithiole-3-thiones are capable of protecting cells from AA + iron-induced ROS production and mitochondrial dysfunction, which may be associated with AMPK activation.

Topics: Apoptosis; Arachidonic Acid; Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Survival; Dose-Response Relationship, Drug; Formazans; Humans; In Situ Nick-End Labeling; Iron; Liver Neoplasms; Membrane Potential, Mitochondrial; Mitochondria; Pyrazines; Reactive Oxygen Species; Tetrazolium Salts; Thiones; Thiophenes; Time Factors

An in vitro screening model using resonance light scattering (RLS) technique with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) reagent as the reactive probe to target cancer cell was firstly developed. In this model, MTT was reduced by viable cancer cells to produce a purple formazan. Cell viability was proportional to the number of formazan induced strong light scattering signal. The inhibition rate of anticancer drug was found to vary inversely with the H(22)-MTT system RLS intensity. So it was intuitive to see the sequence of the tumor suppressive activity of six anticancer drugs without data processing by RLS/MTT screening spectra. Compared with the traditional MTT method, this method has high sensitivity, low detection limit and quite intuitive screening results which were identical to those obtained from the MTT colorimetric assay.

Topics: Animals; Antineoplastic Agents; Carcinoma, Hepatocellular; Colorimetry; Drug Screening Assays, Antitumor; Formazans; Humans; Inhibitory Concentration 50; Light; Mice; Neoplasms; Scattering, Radiation; Sensitivity and Specificity; Tetrazolium Salts; Thiazoles; Time Factors

Xenobiotics, including heavy metals, exist in nature as complex mixtures of compounds with possible interactions. Induction of DNA damage such as DNA strand breaks may exert detrimental consequences to both individuals and populations. In this study, the induction of DNA double-strand breaks was assessed using the H4IIE rat hepatoma cell line following exposure to high and environmentally relevant concentrations of chloride salts of the metals cadmium (Cd), copper (Cu), and zinc (Zn), both singly and in combination. DNA strand break analysis was performed using agarose gel electrophoresis. Median molecular lengths were calculated from fragment size distributions acquired from gel image data and were used as a quantitative measure of DNA double-strand break induction. Exposure to high concentrations of Cu and Cd in combination produced a significant increase in the occurrence of DNA strand break. However, exposing cells to high concentrations of Cu, Cd, and Zn in combination resulted in significantly lower DNA double-strand break compared to control cells. Addition of low Zn to the Cd/Cu mixture restored DNA damage level back to that of the control. Environmentally relevant concentrations of Cd, Cu, and Zn did not appear to induce DNA strand breaks in the H4IIE cell line.

Topics: Animals; Cadmium; Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Survival; Copper; DNA Breaks, Double-Stranded; DNA, Neoplasm; Dose-Response Relationship, Drug; Drug Combinations; Electrophoresis, Agar Gel; Environmental Pollutants; Formazans; Hepatocytes; Liver; Liver Neoplasms; Metals, Heavy; Rats; Tetrazolium Salts; Water Pollutants, Chemical; Zinc

Tissue engineering requires the development of three-dimensional water-stable scaffolds. In this study, silk fibroin/chitosan (SFCS) scaffold was successfully prepared by freeze-drying method. The scaffold is water-stable, only swelling to a limited extent depending on its composition. Fourier Transform Infrared (FTIR) spectra and X-Ray diffraction curves confirmed the different structure of SFCS scaffolds from both chitosan and silk fibroin. The homogeneous porous structure, together with nano-scale compatibility of the two naturally derived polymers, gives rise to the controllable mechanical properties of SFCS scaffolds. By varying the composition, both the compressive modulus and compressive strength of SFCS scaffolds can be controlled. The porosity of SFCS scaffolds is above 95% when the total concentration of silk fibroin and chitosan is below 6 wt%. The pore sizes of the SFCS scaffolds range from 100 microm to 150 microm, which can be regulated by changing the total concentration. MTT assay showed that SFCS scaffolds can promote the proliferation of HepG2 cells (human hepatoma cell line) significantly. All these results make SFCS scaffold a suitable candidate for tissue engineering.

Topics: Biocompatible Materials; Carcinoma, Hepatocellular; Cell Line, Tumor; Chitosan; Compressive Strength; Fibroins; Formazans; Humans; Liver Neoplasms; Materials Testing; Porosity; Silk; Tetrazolium Salts; Tissue Engineering; Tissue Scaffolds; X-Ray Diffraction

The effects of the alpha-diketone derivatives 2,3- and 3,4-hexanediones were investigated in three non-neuronal cell lines (MCF7, HepG(2) and CaCo-2) as well as in the neuroblastoma line, SH-SY5Y. The MTT reduction assay was employed to determine the necrotic effects of the alpha-diketones and the neurotoxin 2,5-hexanedione over 4, 24 and 48 hr exposures. Flow cytometry was also used to study the effects of the three isomers on the cell cycle of the SH-SY5Y line only. With 2,5-hexanedione, the mean MTT IC(50) decreased more than 10-fold from 4 to 48 hr. The toxicities of both alpha-diketones were similar, with a more than 18-fold increase in sensitivity of the SH-SY5Y at 24 hr compared to that of 4 hr. With flow cytometry at 48 hr, SH-SY5Y apoptosis with 2,5-hexanedione rose throughout the concentration range evaluated (0-30 mM) while 2,3- and 3,4-hexanediones showed apoptosis over the concentration range 1-1.6 mM, with 3,4-hexanedione being the more potent compared to the 2,3-isomer. At 1.6 mM nearly all the cells had entered apoptosis in the presence of the 3,4-isomer, (94.9 +/- 1.4%) but only 57.5 +/- 4.1% of the 2,3-isomer-treated cells had reached that stage. The 2,3- and 3,4-isomers in diets alone may not pose a serious threat to human health. Further studies may be necessary to evaluate the effects of other dietary components on their toxicity. These alpha-diketones also display a degree of toxic selectivity towards neuroblastoma cells, which may have therapeutic implications.

Topics: Adenocarcinoma; Apoptosis; Breast Neoplasms; Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Survival; Colonic Neoplasms; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Female; Flow Cytometry; Formazans; Hexanones; Humans; Isomerism; Neuroblastoma; Neurons; Tetrazolium Salts

In the present study, the chemoprotective effects of quercetin, rutin and ursolic acid on tert-butyl hydroperoxide (t-BHP)-induced DNA damage in a human hepatoma cell line (HepG2) were investigated by the comet assay. To determine whether protection was due to direct chemical interactions alone or to cellular-mediated responses three different types of treatments were used: simultaneous incubation of cells with individual test compounds and the toxicant; pre-treatment with test compound before addition of the toxicant followed or not by a recovery period. The expression of Hsp70 was quantified by Western blotting to test the involvement of heat shock proteins in the cellular responses to the test compounds. In addition, effects on proliferation were evaluated by the MTT assay. The results show that quercetin and ursolic acid prevented DNA damage and had antiproliferative properties in HepG2 cells suggesting an anticarcinogenic potential for these compounds. The protective effects of quercetin against t-BHP-induced DNA damage seem to be due to both direct effects on t-BHP toxicity and to cellularly mediated indirect effects which reflect the potentiation of the cellular antioxidant defenses. Ursolic acid seems to exert effects only through cellularly mediated mechanisms since it was not protective in simultaneous incubation. Quercetin and ursolic acid also showed to increase the rate of DNA repair. Rutin did not have effects at any level. These results, obtained with liver cells, emphasize and confirm the chemopreventive potential of quercetin and ursolic acid, which may help explain the lower cancer incidence in human population with high dietary intakes of fruits and vegetables. These results also demonstrate that Hsp70 is not involved in the observed effects in HepG2.

Topics: Antimutagenic Agents; Antioxidants; Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Survival; Comet Assay; DNA Damage; DNA Repair; Dose-Response Relationship, Drug; Drug Antagonism; Drug Combinations; Formazans; Hepatocytes; HSP70 Heat-Shock Proteins; Humans; Quercetin; Rutin; Tetrazolium Salts; Triterpenes; Ursolic Acid

Targeting the oxygen-sensing mechanisms of the hypoxiainducible factor (HIF) pathway provides pharmacological ways of manipulating the HIF response. Because HIF-1alpha-specific prolyl-4 hydroxylases (PHDs) prime degradation of HIF-1alpha, we have made an effort to find a small molecule capable of up-regulating the HIF pathway by inhibiting prolyl hydroxylation. Through an in vitro high-throughput screen, we have discovered a PHD2 inhibitor baicalein, which is also found to abrogate asparaginyl hydroxylation of HIF-1alpha. Such inhibitory effects are reversed by the addition of excess 2-oxoglutarate and iron(II), suggesting the involvement of baicalein's binding at the enzyme active sites, which has also been corroborated by spectroscopic binding assays between baicalein and enzyme. In addition, baicalein suppresses ubiquitination of HIF-1alpha, which works in concert with the inhibition of the HIF-specific hydroxylases to increase the HIF-1alpha content, leading to induction of HIF-1-mediated reporter gene activity and target gene transcription in tissue culture cells, whereas it induces HIF-independent activation of other genes. Furthermore, in vivo organ models based on the chick chorioallantoic membrane assay demonstrate that baicalein promotes new blood vessel formation. Together, our results indicate that baicalein possesses a proangiogenic potential and thus might have the therapeutic utility in the treatment of ischemic diseases.

Topics: 3T3-L1 Cells; Animals; Carcinoma, Hepatocellular; Cell Line, Tumor; Chick Embryo; Chorioallantoic Membrane; Dose-Response Relationship, Drug; Enzyme Induction; Enzyme Inhibitors; Flavanones; Formazans; Genes, Reporter; Humans; Hypoxia-Inducible Factor 1, alpha Subunit; Liver Neoplasms; Luciferases; Mice; Neovascularization, Physiologic; Neuroblastoma; Tetrazolium Salts; Transcription, Genetic

Hepatitis virus replication in the liver is often accompanied by inflammation resulting in the formation of reactive oxygen species (ROS) and nitric oxide (NO) and these may induce cell death. We investigated whether the expression of HBx or HCV core protein in HepG2 cells has an influence on the sensitivity of these cells for oxidative radicals. Our previous study, using the inducible HBV model of HepAD38, revealed that oxidative-stress-related genes are upregulated by virus replication. In the present study, we examined the intracellular pro-oxidant status with dichlorofluorescein (DCF) in HepG2 cell lines transfected with HBx, HbsAg and HCV core. Baseline intracellular oxidative levels were not different in the cell lines expressing viral proteins as compared to control. However, when these cells were exposed to H(2)O(2), the viral protein expressing cells, especially those expressing HBx, showed a reduced level of ROS. This suggests that HBx and HCV core transfected cells can convert H(2)O(2) to less reactive compounds at a higher rate than the control cells. When HBx or HCV core expressing cells were exposed to peroxynitrite (a highly reactive product formed under physiological conditions through interaction of superoxide (O(2)(-)) with NO) these cells were less sensitive to induction of cell death. In addition, these cell lines were less prone to cell death when exposed to H(2)O(2) directly. In conclusion, HBx and HCV core expression in HepG2 cells leads to a survival benefit under oxidative stress which in vivo can be induced during inflammation.

Topics: Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Survival; Formazans; Hepatitis C Antigens; Humans; Hydrogen Peroxide; Liver; Liver Neoplasms; Microscopy, Fluorescence; Oxidation-Reduction; Oxidative Stress; Peroxynitrous Acid; Trans-Activators; Transfection; Viral Regulatory and Accessory Proteins

The production of insulin-like growth factor-binding protein-1 (IGFBP-1) in HepG2 was increased by cadmium cation (Cd2+) at 3 microM, but not by other divalent cations. The mRNA level of IGFBP-1 was also increased by the administration of 3 microM of Cd(2+). These results suggest that Cd(2+) impacts the gene expression of IGFBP-1, which leads to production of IGFBP-1.

Topics: Cadmium; Carcinoma, Hepatocellular; Cations; Cell Line, Tumor; Cell Survival; Dose-Response Relationship, Drug; Formazans; Humans; Insulin-Like Growth Factor Binding Protein 1; Liver Neoplasms; RNA, Messenger; Tetrazolium Salts; Time Factors

A series of new pyrazole derivatives from emodin synthesized in our lab have been shown to have much stronger cytotoxicity than emodin against various tumor cell lines. This study was to examine the apoptosis-inducing activity of these new emodin derivatives in human hepatocellular carcinoma HepG2 cell culture for a better understanding of their cytotoxic effects on the cancer cells. Several major events in the induction of cell apoptosis, nuclear chromatin condensation, DNA fragmentation, caspase-3 activation and poly ADP-ribose polymerase (PARP) cleavage were detected in the cells after treatment with the compounds at various concentrations. Of the seven emodin derivatives tested at a dose of 10 microM and within a treatment period of 24 h, only compounds 1 and 3 effectively induced all these apoptotic events in the cancer cells. The apoptosis-inducing activity of the compounds showed a positive correlation to their cytotoxic activity, suggesting a close connection between the growth inhibition and apoptosis induction of the cancer cells by these pyrazole emodin derivatives.

Topics: Apoptosis; Carcinoma, Hepatocellular; Caspase 3; Cell Line, Tumor; Cell Nucleus; Cell Proliferation; Cell Survival; DNA Fragmentation; Dose-Response Relationship, Drug; Emodin; Enzyme Activation; Formazans; Humans; Liver Neoplasms; Molecular Structure; Poly(ADP-ribose) Polymerases; Tetrazolium Salts; Time Factors

Enhancer of zeste homolog 2 (EZH2) is suggested to be a potential therapeutic target and a diagnostic marker for cancer. Our previous study also showed the critical role of EZH2 in hepatocellular carcinoma (HCC) tumorigenesis. The present study is aimed at revealing the comprehensive downstream pathways of EZH2 by functional proteomic profiling. Lentivirus mediated RNA interference (RNAi) was employed to knockdown EZH2 in HCC cells. The 2-DE was employed to compare the expression profile difference between parental and EZH2-knockdown HCC cells. In total, 28 spots were differentially expressed during EZH2 inhibition. Among all, 18 proteins were identified by PMF with MALDI-TOF MS. Western blotting further validated upregulation of 60S acidic ribosomal protein P0 (L10E), and downregulation of two proteins with EZH2 inhibition: stathmin1 and probable protein disulfide isomerase (PDI) ER-60 precursor (ERp57). Moreover, L10E was downregulated with overexpression of EZH2 in hepatocytes, and L10E reversed the effect of EZH2 on cell proliferation, suggesting it a downstream target of EZH2. The comprehensive and comparative analyses of proteins associated with EZH2 could further our understanding on the downstream signal cascade of EZH2 leading to tumorigenesis.

Topics: Carcinoma, Hepatocellular; Cell Line; Cell Line, Tumor; Cell Proliferation; Databases, Protein; DNA-Binding Proteins; Enhancer of Zeste Homolog 2 Protein; Formazans; Gene Expression Profiling; Genetic Vectors; Humans; Lentivirus; Liver Neoplasms; Polycomb Repressive Complex 2; Proteomics; RNA Interference; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Tetrazolium Salts; Transcription Factors

Human fetal liver (HFL) cell culture was initiated from a pool of six normal human liver tissues. The proliferation and viability of HFL cells were evaluated using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide assay, and the cells increased by more than 100-fold by culture for 15 d. The levels of expression of albumin (ALB), hepatocyte nuclear factor 4alpha, hepatocyte growth factor, CYP3A4, CYP3A5, and CYP3A7 mRNAs in HFL cells increased with culture period, while that of alpha-fetoprotein (AFP) mRNA decreased gradually. In HepG2 cells, however, the expression levels of ALB and AFP mRNAs were not changed, and the levels of expression of CYP3A4, CYP3A5, and CYP3A7 mRNAs decreased gradually. The mRNA expression of major CYP isoforms including CYP3As, i.e., CYP1A2, CYP2A6, CYP2B6, CYP2C (2C9 and 2C19), CYP2D6, and CYP2E1, could be detected in HepG2 cells. With the exception of CYP1A2, all of the CYP mRNAs expressed in HepG2 cells were detected in HFL cells. In HFL cells, CYP3A4 and CYP3A7 mRNA expression levels were markedly up-regulated by dexamethasone (DEX), but not by rifampicin (RIF). CYP3A5 mRNA expression was increased to a level 3-fold greater than control by DEX. On the other hand, CYP3A4, CYP3A5, and CYP3A7 mRNA expression levels in HepG2 cells were increased from 2- to 3-fold by treatment with DEX and RIF. Pregnane X receptor mRNA was expressed in HepG2 cells, but not HFL cells. These results indicate that the character of HFL cells with regard to CYP expression was different from that of HepG2 cells.

Topics: Aryl Hydrocarbon Hydroxylases; Carcinoma, Hepatocellular; Cell Line, Tumor; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Dexamethasone; Enzyme Induction; Fetus; Formazans; Gene Expression Regulation, Enzymologic; Hepatocytes; Humans; Isoenzymes; Liver Neoplasms; RNA, Messenger; Tetrazolium Salts; Time Factors

The performance of alamar blue and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) cell viability assays in a high through-put format were compared. A total of 117 drugs chosen for their wide range of therapeutic areas were screened at 10 microM using both assays in human hepatoma cell line HepG2. Except for terfenadine and astemizole, which performed consistently in both assays, the alamar blue assay was slightly more sensitive than the MTT assay for most compounds. The MTT assay was less sensitive detecting an effect for daunorubicin and trifluoperazine. Seven drugs, astemizole, daunorubicin, ellipticine, fluphenazine, terfenadine, thioridazine and trifluoperazine, had percent viability results of 55% or less in the alamar blue assay at the single point screen. These were re-tested in both assays for reconfirmation of cytotoxicity and determination of the EC50 values. Except for daunorubicin, the EC50 values were comparable in both assays. Based on these results and the Z'-factor assessment of assay quality, both assays provided useful information to identify in vitro cytotoxic drugs at early stages of drug candidate selection. However, careful interpretation of data is warranted due to the possibility of false positive or negative results caused by inducers and/or inhibitors of metabolic enzymes that are responsible for transformation of cell toxicity end points, as we demonstrated using dicumarol.

Topics: Carcinoma, Hepatocellular; Cell Line, Tumor; Cell Survival; Dose-Response Relationship, Drug; Drug Evaluation, Preclinical; Formazans; Humans; Indicators and Reagents; Oxazines; Reproducibility of Results; Tetrazolium Salts; Xanthenes; Xenobiotics

To elucidate the potential role of mitochondria in Taxol-induced cytotoxicity, we studied its direct mitochondrial effects. In Percoll-gradient purified liver mitochondria, Taxol induced large amplitude swelling in a concentration-dependent manner in the microM range. Opening of the permeability pore was also confirmed by the access of mitochondrial matrix enzymes for membrane impermeable substrates in Taxol-treated mitochondria. Taxol induced the dissipation of mitochondrial membrane potential (DeltaPsi) determined by Rhodamine123 release and induced the release of cytochrome c from the intermembrane space. All these effects were inhibited by 2.5 microM cyclosporine A. Taxol significantly increased the formation of reactive oxygen species (ROS) in both the aqueous and the lipid phase as determined by dihydrorhodamine123 and resorufin derivative. Cytochrome oxidase inhibitor CN(-), azide, and NO abrogated the Taxol-induced mitochondrial ROS formation while inhibitors of the other respiratory complexes and cyclosporine A had no effect. We confirmed that the Taxol-induced collapse of DeltaPsi and the induction of ROS production occurs in BRL-3A cells. In conclusion, Taxol-induced adenine nucleotide translocase-cyclophilin complex mediated permeability transition, and cytochrome oxidase mediated ROS production. Because both cytochrome c release and mitochondrial ROS production can induce suicide pathways, the direct mitochondrial effects of Taxol may contribute to its cytotoxicity.

Topics: Animals; Antineoplastic Agents, Phytogenic; Apoptosis; Blotting, Western; Calcium; Carcinoma, Hepatocellular; Cyclosporine; Cytochrome c Group; Dose-Response Relationship, Drug; Formazans; Free Radicals; Humans; Kidney; Membrane Potentials; Microscopy, Confocal; Mitochondria, Heart; Mitochondria, Liver; Oxygen; Paclitaxel; Permeability; Rats; Rats, Wistar; Reactive Oxygen Species; Tetrazolium Salts; Tumor Cells, Cultured

Cell-mediated reduction of tetrazolium salts, including MTT, XTT, MTS, NBT, NTV, INT, in the presence or absence of intermediate electron carriers is used as a convenient test for animal or bacterial cell viability. Bioreduction of tetrazolium is considered an alternative to a clonogenic assay and a thymidine incorporation assay. However, correlation between clonogenic potential and capacity to reduce tetrazolium has not been demonstrated convincingly. Moreover, despite a wide use of tetrazolium viability assays, the mechanism and subcellular localisation of reducing systems or species in viable intact cells have not been fully elucidated. We report evidence indicating that a tetrazolium salt CTC can be reduced in the presence as well as in the absence of an electron carrier by viable HepG2 human hepatoma cells. CTC-formazan is formed within or at the outer surface of plasma membranes. We hypothesise that in the presence of an electron carrier the electron donors active in the reduction of CTC are located in the intracellular compartment, as well as in plasma membranes. However, in the absence of an electron carrier, the reduction occurs primarily via a plasma membrane-associated enzymatic system or species.

Topics: Carcinoma, Hepatocellular; Cell Membrane; Coloring Agents; Formazans; Humans; Liver Neoplasms; Oxazines; Oxidation-Reduction; Propidium; Spectrometry, Fluorescence; Spectrophotometry; Tetrazoles; Tetrazolium Salts; Tumor Cells, Cultured