Triacylglycerol-mediated oxidative stress inhibits nitric oxide production in rat isolated hepatocytes

High carbohydrate high fat diet causes arterial hypertension and histological changes in the aortic wall in aged rats: The involvement of connective tissue growth factors and fibronectin

BACKGROUND

Age and diabetes are risk factors for arterial hypertension. However, the relationship between age, connective tissue growth factors, vascular aging and arterial hypertension while on a the high-carbohydrate high-fat diet (HCHFD) remains poorly understood.

PURPOSE

To estimate the relationship between humoral factors, the morphological changes of aorta and impaired blood pressure regulation under the influence of age and a HCHFD.

METHODS

A study was carried out in male Wistar rats, which were divided into the following groups: 1st (n = 15) - naive young rats; 2nd (n = 15) - young rats, exposed to HCHFD; 3rd (n = 14) - naive old rats; 4th (n = 12) - old rats exposed to HCHFD. The age of old rats was 540 days, and young rats 150 days at the end of the diet. HCHFD contained proteins 16%, fats 21%, carbohydrates 46%, including 17% fructose, 0.125% cholesterol, 90 days. Blood pressure and body weight were measured weekly, carbohydrate metabolism, histological signs of changes in the aorta, serum transforming growth factor-β (TGF-β), connective tissue growth factor (CTGF), fibronectin, and endothelin-1 levels were determined one week after the onset of diet.

RESULTS

The severity of arterial hypertension and its histological signs in the aortic wall was found to be most pronounced in elderly rats kept on a HCHFD. In young rats kept on a HCHFD, arterial hypertension was transient. An increase in systolic blood pressure has a positive correlation with the degree of obesity, serum fibronectin, and endothelin-1 content, and impaired carbohydrate metabolism. The rise in diastolic blood pressure has a positive correlation with the serum CTGF, endothelin-1, fibronectin levels and aortic wall thickness, and impaired carbohydrate metabolism. A rise in the serum concentration of fibronectin was also associated with increased endothelin-1, TGFβ and CTGF serum levels.

CONCLUSION

This study indicated that an increase in blood pressure in old rats with a high-carbohydrate high-fat diet is due to a disturbance of a structure of the vascular wall, the release of fibronectin, which can occur under the influence of carbohydrate metabolism disorders, endothelin-1, TGFβ and CTGF.

Lipid Emulsions Containing Medium Chain Triacylglycerols Blunt Bradykinin-Induced Endothelium-Dependent Relaxation in Porcine Coronary Artery Rings

Lipid emulsions for parenteral nutrition are used to provide calories and essential fatty acids for patients. They have been associated with hypertriglyceridemia, hypercholesterolemia, and metabolic stress, which may promote the development of endothelial dysfunction in patients. The aim of the present study was to determine whether five different industrial lipid emulsions may affect the endothelial function of coronary arteries. Porcine coronary artery rings were incubated with lipid emulsions 0.5, 1, or 2% (v/v) for 30 min before the determination of vascular reactivity in organ chambers and the level of oxidative stress using electron paramagnetic resonance. Incubation of coronary artery rings with either Lipidem^®, Medialipid^® containing long- and medium-chain triacylglycerols (LCT/MCT), or SMOFlipid^® containing LCT, MCT, omega-9, and -3, significantly reduced the bradykinin-induced endothelium-dependent relaxation, affecting both the nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) components, whereas, Intralipid^® containing LCT (soybean oil) and ClinOleic^® containing LCT (soybean and olive oil) did not have such an effect. The endothelial dysfunction induced by Lipidem^® was significantly improved by indomethacin, a cyclooxygenase (COX) inhibitor, inhibitors of oxidative stress (N-acetylcysteine, superoxide dismutase, catalase) and transition metal chelating agents (neocuproine, tetrathiomolybdate, deferoxamine and L-histidine). Lipidem^® significantly increased the arterial level of oxidative stress. The present findings indicate that lipid emulsions containing LCT/MCT induce endothelial dysfunction in coronary artery rings by blunting both NO- and EDH-mediated relaxations. The Lipidem^®-induced endothelial dysfunction is associated with increased vascular oxidative stress and the formation of COX-derived vasoconstrictor prostanoids.

Lipid Emulsion Attenuates Acetylcholine-Induced Relaxation in Isolated Rat Aorta

We investigated the effect of Lipofundin MCT/LCT and Intralipid on acetylcholine-induced nitric oxide- (NO-) mediated relaxation in rat aorta to determine which lipid emulsion (LE) is more potent in terms of inhibition of NO-induced relaxation. Dose-response curves of responses induced by acetylcholine, the calcium ionophore A23187, and sodium nitroprusside were generated using isolated rat aorta with or without LE. The effect of Lipofundin MCT/LCT on acetylcholine-induced endothelial nitric oxide synthase (eNOS) phosphorylation in human umbilical vein endothelial cells (HUVECs) was investigated using western blotting. Lipofundin MCT/LCT (0.1 and 0.2%) attenuated acetylcholine-induced relaxation in endothelium-intact aorta with or without tiron, whereas 0.2% Intralipid only inhibited relaxation. Lipofundin MCT/LCT inhibited relaxation induced by the calcium ionophore A23187 and sodium nitroprusside in endothelium-intact aorta, but Lipofundin MCT/LCT had no effect on sodium nitroprusside-induced relaxation in the endothelium-denuded aorta. Combined pretreatment with l-arginine plus Lipofundin MCT/LCT increased acetylcholine-induced maximal relaxation in endothelium-intact aorta compared with Lipofundin MCT/LCT alone. l-Arginine attenuated Lipofundin MCT/LCT-mediated inhibition of acetylcholine-induced eNOS phosphorylation in HUVECs. Taken together, Lipofundin MCT/LCT attenuated acetylcholine-induced NO-mediated relaxation via an inhibitory effect on the endothelium including eNOS, which is proximal to activation of guanylyl cyclase.

Effect of two lipid emulsions on reversing high-dose levobupivacaine-induced reduced vasoconstriction in the rat aortas

The goals of this study were to determine which lipid emulsion (Intralipid(®) and Lipofundin MCT/LCT(®)) is more effective in reversing high-dose levobupivacaine-induced reduced vasoconstriction in isolated rat aortas and to examine the associated cellular mechanisms with a particular focus on the endothelium. Two lipid emulsion concentration-response curves were generated using high-dose levobupivacaine-induced reduced vasoconstriction and vasodilation of isolated aortas pretreated with or without 60 mM KCl. Endothelial nitric oxide synthase (eNOS) and caveolin-1 phosphorylation were measured in rat aortic tissue treated with levobupivacaine in the presence or absence of lipid emulsion. Dichlorofluorescein oxidation, a measure of reactive oxygen species production, was measured in lipid emulsion-treated human umbilical vein endothelial cells. In levobupivacaine (0.3 mM)-induced reduced vasoconstriction of isolated aorta, the magnitude of the Intralipid(®)- and Lipofundin MCT/LCT(®)-mediated reversal was not significantly different. Lipid emulsion reversal of levobupivacaine-induced reduced vasoconstriction was greater in endothelium-intact aortas than in endothelium-denuded aortas. The two lipid emulsions similarly inhibited levobupivacaine-induced eNOS phosphorylation in aortic tissue. Pretreatment with both lipid emulsions increased dichlorofluorescein oxidation. Both Intralipid(®) and Lipofundin MCT/LCT(®) are equally effective for vascular tone recovery from high-dose levobupivacaine-induced reduced vasoconstriction. This reversal is mediated partially by decreasing nitric oxide bioavailability.

Dark chocolate reduces endothelial dysfunction after successive breath-hold dives in cool water

OBJECTIVE

The aim of this study is to observe the effects of dark chocolate on endothelial function after a series of successive apnea dives in non-thermoneutral water.

METHODS

Twenty breath-hold divers were divided into two groups: a control group (8 males and 2 females) and a chocolate group (9 males and 1 female). The control group was asked to perform a series of dives to 20 m adding up to 20 min in the quiet diving pool of Conflans-Ste-Honorine (Paris, France), water temperature was 27 °C. The chocolate group performed the dives 1 h after ingestion of 30 g of dark chocolate. Flow-mediated dilatation (FMD), digital photoplethysmography, nitric oxide (NO), and peroxynitrite ONOO−) levels were measured before and after each series of breath-hold dives.

RESULTS

A significant decrease in FMD was observed in the control group after the dives (95.28 ± 2.9 % of pre-dive values, p < 0.001) while it was increased in the chocolate group (104.1 ± 2.9 % of pre-dive values, p < 0.01). A decrease in the NO level was observed in the control group (86.76 ± 15.57 %, p < 0.05) whereas no difference was shown in the chocolate group (98.44 ± 31.86 %, p > 0.05). No differences in digital photoplethysmography and peroxynitrites were observed between before and after the dives.

CONCLUSION

Antioxidants contained in dark chocolate scavenge free radicals produced during breath-hold diving. Ingestion of 30 g of dark chocolate 1 h before the dive can thus prevent endothelial dysfunction which can be observed after a series of breath-hold dives.

Antihypertensive Effect of Quercetin in Rats Fed with a High-Fat High-Sucrose Diet

The effects of different levels of quercetin on the blood pressure were studied in 6-week-old male Sprague-Dawley rats. The rats were fed with a control diet or a high-fat high-sucrose (HFS) diet containing 0, 0.02, 0.07, 0.2, or 0.5% quercetin for 4 weeks. The systolic blood pressure and the lipid peroxides in the plasma were both higher in the rats fed with the HFS diet without quercetin than in the rats fed with the control diet. The nitric oxide synthase (NOS) activity in the vascular tissues and nitric oxide (NO) metabolites in the plasma and urine were both lower in these rats. A distinct depression of the increase in blood pressure was found in the rats fed with the HFS diets containing quercetin. Each level of quercetin examined was effective, the 0.5% level being much more effective than other levels. Dietary quercetin decreased lipid peroxidation in the plasma of the rats fed with the HFS diets. Quercetin also suppressed the decrease in NO metabolites in the plasma and urine, and the NOS activity in the vascular tissues of these rats. These results suggest that the increased NO availability caused by the elevated NOS activity, and the antioxidative activity in these rats fed with quercetin may be sources of the antihypertensive effect of quercetin.

Analysis of microRNA expression profile induced by AICAR in mouse hepatocytes

AMP-activated protein kinase (AMPK) has been proposed to act as a key energy sensor mediating the metabolism of glucose and lipids, and pharmacological activation of AMPK may provide a new strategy for the management of type 2 diabetes. MicroRNAs (miRNAs) are a group of endogenous noncoding RNA that play important roles in many biological processes including energy metabolism. Whether miRNAs mediate AMPK action in regulating metabolic process is not clear. In this study, 0.5mM 5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside (AICAR) was added to increase activation of AMPK in 8 week old C57BL/6 mice primary hepatocytes. MiRNA microarray was performed to compare the miRNA expression profiles of hepatocytes treated with or without AICAR. We discovered that 41 miRNAs were significantly altered in AICAR-treated sample (fold change: >2) compared with untreated control sample. Among them, 19 miRNAs were upregulated. MiRNA targets were predicted by TargetScan. Further bioinformatic analysis indicated that these predicted targets might be mainly involved in pathways of cellular metabolism and tumor pathogenesis. FUNDO analysis suggested that these predicted targets were enriched in cancer, diabetes mellitus, hypertension, obesity and heart failure (P<0.01). A series of miRNAs could be regulated by the activation of AMPK and might mediate the action of AMPK during metabolic processes and tumor pathogenesis. Predicted target genes discovered in this study and pathway analysis provide new insights into hepatic metabolism and tumor pathogenesis regulated by AMPK signaling and clues to the possible molecular mechanism underlying the effect of AMPK.

Modulation of spontaneous and lipopolysaccharide-induced nitric oxide production and apoptosis by d-galactosamine in rat hepatocyte culture: the significance of combinations of different methods

ABSTRACT Apoptotic markers and signals produced by xenobiotics as hepatotoxic D-galactosamine (D-GalN) and lipopolysaccharide (LPS) are extensively investigated in vivo. The contribution of various cells and factors as nitric oxide (NO) in mediating hepatocyte apoptosis in a rat model of systemic endotoxemia was reported. Therefore, the aim of the present work was to study the in vitro effect of D-GalN on nonstimulated or LPS-treated rat hepatocytes in culture and the potential involvement of NO in this process. Our results showed that the spontaneous and LPS-induced NO production was completely blocked by D-GalN during 0 to 24 hours. However, D-GalN slightly enhanced NO production during 24 to 48 hours. D-GalN was more potent to induce hepatocyte apoptosis and necrosis during 24 to 48 than 0 to 24 hours as evidenced morphologically (Annexin V/propidium iodide staining) and biochemically (caspase-3-like activity, alanine-aminotransferase leakage, MTT test). Interestingly, D-GalN treatment suppressed mitochondrial cytochrome C release throughout the study. LPS addition to D-GalN considerably aggravated apoptotic/necrotic markers only during 0 to 24 hours. Surprisingly, a share of apoptotic cells was distinctly lower after LPS + GalN treatment than after LPS alone during 0 to 24 hours, while 24- to 48-hour incubation produced massive apoptotic/necrotic hepatocytes. It may be concluded that there is a significant modulation of NO production by D-GalN. Because the role of NO is only partly decisive in the apoptotic/necrotic events, and considering the fraction of the cells completing apoptosis while others that turn toward necrosis (aponecrosis), caution should be exercised in apoptosis data interpretation and combinations of different test methods should be applied.

Fatty acids-stress attenuates gluconeogenesis induction and glucose production in primary hepatocytes

BACKGROUND

Hepatic gluconeogenesis tightly controls blood glucose levels in healthy individuals, yet disorders of fatty acids (FAs) oxidation are characterized by hypoglycemia. We studied the ability of free-FAs to directly inhibit gluconeogenesis, as a novel mechanism that elucidates the hypoglycemic effect of FAs oxidation defects.

METHODS

Primary rat hepatocytes were pre-treated with FAs prior to gluconeogenic stimuli with glucagon or dexamethasone and cAMP.

RESULTS

Pre-treatment with 1 mM FAs (mixture of 2:1 oleate:palmitate) for 1 hour prior to gluconeogenic induction, significantly decreases the induced expression of the gluconeogenic genes phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6pase) as well as the induced glucose production by the cells. The inhibitory effect of FAs upon gluconeogenesis is abolished when pre-treatment is elongated to 18 hours, allowing clearance of FAs into triglycerides by the cells. Replacement of palmitate with the non-metabolic fatty acid 2-bromopalmitate inhibits esterification of FAs into triglycerides. Accordingly, the increased exposure to unesterified-FAs allows their inhibitory effect to be extended even when pre-treatment is elongated to 18 hours. Similar changes were caused by FAs to the induction of peroxisome-proliferator-activated receptor-γ coactivator 1α (PGC1α) expression, indicating this transcriptional coactivator as the mediating link of the effect. This inhibitory effect of FAs upon gluconeogenic induction is shown to involve reduced activation of cAMP response element-binding (CREB) transcription factor.

CONCLUSIONS

The present results demonstrate that free-FAs directly inhibit the induced gluconeogenic response in hepatocytes. Hence, high levels of free-FAs may attenuate hepatic gluconeogenesis, and liver glucose output.

Endothelial nitric oxide synthase is a key mediator of hepatocyte proliferation in response to partial hepatectomy in mice

Endothelial nitric oxide synthase (eNOS) is a critical modulator of vascular tone and blood flow and plays major roles in liver physiology and pathophysiology. Nitric oxide (NO) is widely recognized as one of the key humoral factors important for the initiation of liver regeneration in response to partial hepatectomy. Liver regeneration in response to partial hepatectomy is dependent on the efficiency of growth factor-mediated cell-cycle progression. Epidermal growth factor receptor (EGFR) is a critical mediator of multiple hepatic mitogens, such as epidermal growth factor (EGF), transforming growth factor alpha, amphiregulin, and heparin-binding EGF in regenerating livers. However, the functional significance of endothelial nitric oxide synthase (eNOS) expressed in hepatocytes, and its potential role in EGFR-mediated hepatocyte proliferation, remains unexplored. We sought to determine whether eNOS is essential for hepatocyte proliferation in response to partial hepatectomy (PH). Our studies with eNOS knockout (eNOS(-/-) ) mice suggest that eNOS activation is essential for the efficient induction of early events and elicitation of a robust hepatocyte proliferative response to PH. Moreover, eNOS expression is essential for the efficient early induction of matrix metalloprotease-9, a known mediator of extracellular matrix remodeling and growth factor activation in regenerating livers. Our in vitro studies suggest that eNOS is a critical mediator of EGF-induced hepatocyte proliferation, potentially via its influence on the induction of early growth response-1 (Egr-1) and phosphorylation of c-Jun--known mediators of cell-cycle progression. EGF-induced eNOS phosphorylation at Ser 1177 is dependent on the phosphorylation and activation of EGFR/PI3 kinase/AKT signaling in hepatocytes.

CONCLUSION

Collectively, these results highlight a hitherto unrecognized role for eNOS activation in hepatocyte proliferation with implications for targeted therapies to enhance liver regenerative response in chronic disorders.

The short-term consumption of a moderately high-fat diet alters nitric oxide bioavailability in lean female Zucker rats

To determine whether short-term consumption of a moderately high-fat diet (MHFD) affects nitric oxide (NO) production, the concentration of stable NO metabolites (NOx) in urine and plasma of rats fed a MHFD (15.6 %g fat) or control diet (4.5 %g fat) was measured weekly for 4 weeks. Plasma and urine NOx levels were significantly depressed in the MHFD group by week 1 and remained so for the duration of the study. Decreased NO bioavailability may result from a decrease in NO production or the scavenging of NO by reactive oxygen species (ROS). Because endothelial NOS (eNOS) is the major contributor to NO production and circulating levels of NOx, eNOS expression was measured in several tissues. At week 1, there was a MHFD-associated decrease in eNOS expression in the liver. Subsequently, eNOS expression declined in the heart and kidney medulla of MHFD-fed rats at weeks 3 and 4, respectively. The expression of eNOS in the kidney cortex and adipose tissue did not change. These results suggest that a MHFD alters eNOS expression in a time-dependent and tissue-specific manner. In the liver, NOS activity and tissue levels of NOx and nitrotyrosine were measured. Nitrotyrosine levels were used as an indirect measure of the NO scavenged by ROS. There was a decrease in NOS activity, suggesting that the low levels of hepatic NOx were due, in part, to a decrease in NO production. In addition, there was a dramatic increase in nitrotyrosine formation, suggesting that the decline in hepatic NOx was also due to an increased interaction of NO with ROS. Tyrosine nitration commonly has detrimental effects on proteins. The decrease in NO and increase in protein nitration could potentially have adverse effects on tissue function.

Infusion of a lipid emulsion modulates AMPK and related proteins in rat liver, muscle, and adipose tissues

The primary objective of this study was to investigate the impact of lipid oversupply on the AMPK pathway in skeletal muscle, liver, and adipose tissue. Male Wistar rats were infused with lipid emulsion (LE) or phosphate-buffered saline for 5 h/day for 6 days. Muscles exposed to LE for 6 days exhibited increased AMPK and acetyl-CoA carboxylase (ACC) phosphorylation, along with a greater association between AMPK and Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK). No differences in muscle protein phosphatase 2C (PP2C) activity, LKB1 phosphorylation or AMPK and LKB1 association were observed. Muscle ACCbeta, and adiponectin receptor 1 (AdipoR1) mRNA levels and PPARgamma-co-activator 1alpha (PGC1alpha) protein levels were also increased in LE-treated rats. In contrast, AMPK and ACC phosphorylation decreased and PP2C activity increased in rat livers exposed to LE. Hepatic mRNA levels of ACCalpha, PPARalpha, AdipoR1, AdipoR2, and sterol regulatory element-binding protein-1c (SREBP1c) were also reduced after LE infusion. In adipose tissue, there was no significant alteration in AMPK or ACC phosphorylation. These results demonstrate that following lipid oversupply the AMPK pathway was enhanced in rat skeletal muscle while diminished in the liver and was unchanged in adipose tissue. CaMKK in skeletal muscle and PP2C in the liver, at least in part, appear to mediate these alterations. Alterations in AMPK pathway in the liver induced metabolic defects associated with lipid oversupply.

Nutritional lipid-induced oxidative stress leads to mitochondrial dysfunction followed by necrotic death in FaO hepatocytes

OBJECTIVE

Mitochondrial dysfunction and hepatocyte cell death have been reported in fatty liver and non-alcoholic steatohepatitis. Our aim in this study was to evaluate whether direct exposure of hepatocytes to extracellular fat could facilitate such deleterious effects.

METHODS

FaO hepatic cells treated with fat was used as an in vitro model for steatosis. FaO hepatocytes were exposed to 0.1% triacylglycerols using commercially available lipid emulsion (LE) for various periods and studied for production of reactive oxygen species (ROS), mitochondrial function, and cell death parameters. To study the type of cell death, high-mobility group box chromosomal protein 1cellular levels, DNA fragmentation, and caspase activity were evaluated.

RESULTS

Cells incubated with LE for 6 h exhibited a marked increase in the production of intracellular ROS. Using treatments with peroxisome proliferator-activated receptor activators, mitochondrial electron-transfer chain inhibitor, and different sources of LE that did or did not contain medium-chain triacylglycerols, the mitochondria were found to be the source of ROS. LE treatment resulted in phosphorylation of adenosine monophosphate-activated protein kinase, accompanied by a decrease in adenosine triphosphate levels. Changes in intracellular ROS and energy levels were followed by cell death. FaO hepatocytes showed a significant reduction in high-mobility group box chromosomal protein-1 and little DNA fragmentation. Incubation with LE for 24 h did not change caspase-3 activity, indicating that hepatocyte death was necrotic. The antioxidant N-acetylcysteine was able to attenuate the changes in intracellular energy levels and ROS levels and to prevent cell death after exposure to LE.

CONCLUSION

These results suggest that exposure of FaO cells to LE leads to an increase in mitochondrial ROS production and a decrease in cellular energy levels followed by necrotic cell death.

Lipotoxic effects of triacylglycerols in J774.2 macrophages

OBJECTIVE

Triacylglycerols (TGs) are being considered as an independent risk factor in atherosclerosis and metabolic syndrome, acting by dysregulation of the TG/high-density lipoprotein axis. Accumulation of lipids in subendothelial space attracts macrophages, leading to atherosclerotic plaque formation and increased plaque instability due to formation of foam cells and macrophage death. The aim of this study was to evaluate lipotoxic effects in macrophages caused by TG uptake.

METHODS

J774.2 macrophages were exposed to soybean or olive oil-based lipid emulsions as a source of TGs (1 mg/mL) in a presence or absence of lipase inhibitor paraoxon (20 microM) or to bovine serum albumin-complexed palmitic (150 microM), linoleic (600 microM), and oleic (600 microM) fatty acids.

RESULTS

The results demonstrated accumulation of TGs, G1/S arrest, and cell death with necrotic morphologic features after exposure to TG emulsions. These effects were prevented by treatment with an antioxidant N-acetyl-cysteine (0.5 mM). Paraoxon inhibited intracellular TG degradation but did not prevent lipotoxicity and cell death. Olive oil TG triggered macrophage death in a manner similar to soybean oil. Treatment of the macrophages with free fatty acid, mainly with palmitic acid, showed a reactive oxygen species-independent cell death pathway, which was different from that of TG and was not prevented by N-acetyl-cysteine.

CONCLUSION

This study shows a direct lipotoxic pathway for TG molecules in macrophages, which is not associated with degradation of TG molecule to free fatty acids. This study for the first time can explain at a cellular level how TGs as an independent risk factor aggravate atherosclerotic outcomes.

Thapsigargin, a selective inhibitor of sarco-endoplasmic reticulum Ca2+ -ATPases, modulates nitric oxide production and cell death of primary rat hepatocytes in culture

Increased cytosolic calcium ([Ca2+]i) and nitric oxide (NO) are suggested to be associated with apoptosis that is a main feature of many liver diseases and is characterized by biochemical and morphological features. We sought to investigate the events of increase in [Ca2+]i and endoplasmic reticulum (ER) calcium depletion by thapsigargin (TG), a selective inhibitor of sarco-ER-Ca2+ -ATPases, in relation to NO production and apoptotic and necrotic markers of cell death in primary rat hepatocyte culture. Cultured hepatocytes were treated with TG (1 and 5 micromol/L) for 0-24 or 24-48 h. NO production and inducible NO synthase (iNOS) expression were determined as nitrite levels and by iNOS-specific antibody, respectively. Hepatocyte apoptosis was estimated by caspase-3 activity, cytosolic cytochrome c content and DNA fragmentation, and morphologically using Annexin-V/propidium iodide staining. Hepatocyte viability and mitochondrial activity were evaluated by ALT leakage and MTT test. Increasing basal [Ca2+]i by TG, NO production and apoptotic/necrotic parameters were altered in different ways, depending on TG concentration and incubation time. During 0-24 h, TG dose-dependently decreased iNOS-mediated spontaneous NO production and simultaneously enhanced hepatocyte apoptosis. In addition, TG 5 micromol/L produced secondary necrosis. During 24-48 h, TG dose-dependently enhanced basal NO production and rate of necrosis. TG 5 micromol/L further promoted mitochondrial damage as demonstrated by cytochrome c release. A selective iNOS inhibitor, aminoguanidine, suppressed TG-stimulated NO production and ALT leakage from hepatocytes after 24-48 h. Our data suggest that the extent of the [Ca2+]i increase and the modulation of NO production due to TG treatment contribute to hepatocyte apoptotic and/or necrotic events.

Resveratrol exerts its antiproliferative effect on HepG2 hepatocellular carcinoma cells, by inducing cell cycle arrest, and NOS activation

The stilbene resveratrol exerts antiproliferative and proapoptotic actions on a number of different cancer cell lines, through diverse mechanisms, including antioxidant effects, enzyme, growth factor and hormone receptor binding, and nucleic acid direct or indirect interactions. Although resveratrol accumulates in the liver, its effect on hepatocellular carcinoma has not been extensively studied. We have used the human hepatocyte-derived cancer cell line HepG2 to address the possible action of resveratrol on cell growth and to examine some possible mechanisms of action. Our results indicate that the stilbene inhibits potently cell proliferation, reduces the production of reactive oxygen species and induces apoptosis, through cell cycle arrest in G1 and G2/M phases. Furthermore it modulates the NO/NOS system, by increasing iNOS and eNOS expression, NOS activity and NO production. Inhibition of NOS enzymes attenuates its antiproliferative effect. These data could be of value in possible prevention or adjuvant treatment of hepatocellular carcinoma, through an increased consumption of resveratrol-rich foods and beverages.