Nitric oxide protects cultured rat hepatocytes from tumor necrosis factor-alpha-induced apoptosis by inducing heat shock protein 70 expression

Molecular mechanisms underlying the role of nitric oxide in the cardiovascular system

In the cardiovascular system, nitric oxide (NO) is involved in the short and long-term regulation of haemodynamics, and in a number of their pathological alterations. Investigation into the biochemistry of NO-synthase isoforms has confirmed that they also all produce superoxide anion (O(*)). The free radical NO can interact with many targets on which novel information has been recently obtained. The major results of these interactions are not only the well known activation of guanylyl cyclase, but also the formation of potentially cytotoxic peroxynitrite (ONOO(-)), and the formation of S-nitrosothiols and non-haem iron-dinitrosyl dithiolate complexes. Tissue O(2), O(*), low molecular weight thiols and transition metals (especially FeII) play a pivotal role in directing NO towards targets responsible for biological effects, or storage or release from these stores. In addition, circulating forms of NO have been proposed with S-nitrosation of blood proteins. All these mechanisms provide potential pharmacological targets for future therapeutic strategies.

[Main determinants of liver microcirculation during systemic inflammation]

More than 50% of all patients on intensive care units acquire a systemic inflammation such as systemic inflammatory response syndrome (SIRS) or sepsis. The development of hepatic microcirculatory failure with consecutive organ damage might occur during the course of the systemic inflammation. The liver microcirculation is regulated by a complex network of cellular components and specific mediators. The perfusion in liver sinusoids is regulated by the tonus of the contractile Ito cells. Nitric oxide (NO) and carbon monoxide (CO) influence each other and cause the Ito cells to dilate while endothelin results in a contraction of the Ito cells. On-going studies are investigating the role of angiotensin II, catecholamines and prostaglandins for the regulation of the hepatic microcirculatory system during systemic inflammation. Some investigations aim to determine the impact of sedatives and analgesics on the hepatic microcirculation in sepsis and SIRS. Therefore, a decisive recommendation about the choice and dosage of sedatives and analgesics for these patients is not possible. Nevertheless, ketamine, midazolam and fentanyl with their potential anti-inflammatory properties seem to be suitable for patients with systemic inflammation.

Nitric Oxide Inhibition of Homocysteine-induced Human Endothelial Cell Apoptosis by Down-regulation of p53-dependent Noxa Expression through the Formation of S-Nitrosohomocysteine

Hyperhomocysteinemia is believed to induce endothelial dysfunction and promote atherosclerosis; however, the pathogenic mechanism has not been clearly elucidated. In this study, we examined the molecular mechanism by which homocysteine (HCy) causes endothelial cell apoptosis and by which nitric oxide (NO) affects HCy-induced apoptosis. Our data demonstrated that HCy caused caspase-dependent apoptosis in cultured human umbilical vein endothelial cells, as determined by cell viability, nuclear condensation, and caspase-3 activation and activity. These apoptotic characteristics were correlated with reactive oxygen species (ROS) production, lipid peroxidation, p53 and Noxa expression, and mitochondrial cytochrome c release following HCy treatment. HCy also induced p53 and Noxa expression and apoptosis in endothelial cells from wild type mice but not in the p53-deficient cells. The NO donor S-nitroso-N-acetylpenicillamine, adenoviral transfer of inducible NO synthase gene, and antioxidants (alpha-tocopherol and superoxide dismutase plus catalase) but not oxidized SNAP, 8-Br-cGMP, nitrite, and nitrate, suppressed ROS production, p53-dependent Noxa expression, and apoptosis induced by HCy. The cytotoxic effect of HCy was decreased by small interfering RNA-mediated suppression of Noxa expression, indicating that Noxa up-regulation plays an important role in HCy-induced endothelial cell apoptosis. Overexpression of inducible NO synthase increased the formation of S-nitroso-HCy, which was inhibited by the NO synthase inhibitor N-monomethyl-l-arginine. Moreover, S-nitroso-HCy did not increase ROS generation, p53-dependent Noxa expression, and apoptosis. These results suggest that up-regulation of p53-dependent Noxa expression may play an important role in the pathogenesis of atherosclerosis induced by HCy and that an increase in vascular NO production may prevent HCy-induced endothelial dysfunction by S-nitrosylation.

Induction of molecular chaperones in carbon tetrachloride-treated rat liver: implications in protection against liver damage

Carbon tetrachloride (CCl4) induces liver damage, apparently through the formation of free-radical metabolites. Molecular chaperones such as heat shock protein (Hsp) of 70 kDa have been found to protect cells from various stresses. We previously found that cytosolic chaperone pairs of the Hsp70 family and their DnaJ homolog cochaperones prevent nitric oxide-mediated apoptosis and heat-induced cell death. Expression of cytosolic chaperones, including Hsp70; heat shock cognate (Hsc) 70; and DnaJ homologs dj1 (DjB1/Hsp40/hdj-1), dj2 (DjA1/HSDJ/hdj-2), dj3 (DjA2), and dj4 (DjA4), in the liver of CCl4-treated rats was analyzed. Messenger ribonucleic acids for all these chaperones were markedly induced 3-12 hours after CCl4 treatment with a maximum at 6 hours. Hsp70 and dj1 proteins were markedly induced at 6-24 hours with a maximum at 12 hours, whereas dj2 and dj4 were moderately induced at around 12 hours. Hsc70 was weakly induced after treatment, and dj3 was little induced. To better understand the significance of the induction of chaperones, the effect of preinduction of chaperones on CCl4-induced liver damage was analyzed. When chaperones were preinduced in the liver by heat treatment, increase in serum alanine aminotransferase activity after CCl4 treatment was significantly attenuated. Hsp90, another major cytosolic chaperone, also was induced by heat treatment. On the other hand, Mn- and Cu/Zn-superoxide dismutase were not induced by heat treatment or by CCl4 treatment. These results suggest that cytosolic chaperones of Hsp70 and DnaJ families or Hsp90 (or both) are induced in CCl4-treated rat liver to protect the hepatocytes from the damage being inflicted.

Heme oxygenase modulates hepatic leukocyte sequestration via changes in sinusoidal tone in systemic inflammation in mice

Heme oxygenase (HO) modulates the accumulation of leukocytes within the liver during the early stages of a systemic inflammatory response syndrome (SIRS), but the anti-inflammatory mechanism(s) remain to be tested. The influence of HO on the adhesion molecule expression within the liver and on circulating leukocytes was assessed. In addition, the effect of HO and nitric oxide synthase (NOS) on the liver microcirculation was tested. Mice were subjected to 1 h bilateral hindlimb ischemia followed by 3 h of reperfusion, at which time blood samples and the liver were harvested and adhesion molecule expression determined (ICAM-1, CD49d and CD11b). Direct measures of sinusoidal diameter and estimates of volumetric blood flow were obtained using intravital microscopy. HO was specifically induced and inhibited by hemin and chromium mesoporphyrin (CrMP), respectively, whereas NOS was inhibited by N-nitro-L-arginine methyl ester (L-NAME). ICAM-1 expression was increased following hindlimb ischemia-reperfusion. Hemin caused only a modest, but significant decrease in ICAM-1 expression, whereas inhibition of HO had no effect. However, HO inhibition significantly reduced sinusoidal diameters and volumetric flow and such vessels were correlated with significantly increased numbers of stationary leukocytes. Inhibition of NOS had no effect on sinusoidal diameter or volumetric flow. In conclusion, the anti-inflammatory benefits afforded by HO activity within the liver appear to involve the control of sinusoidal diameter and volumetric blood flow rather than altered adhesion molecule expression during the early stages of SIRS.

"The stress of dying": the role of heat shock proteins in the regulation of apoptosis

Heat shock proteins (Hsps) are a family of highly homologous chaperone proteins that are induced in response to environmental, physical and chemical stresses and that limit the consequences of damage and facilitate cellular recovery. The underlying ability of Hsps to maintain cell survival correlates with an inhibition of caspase activation and apoptosis that can, but does not always, depend upon their chaperoning activities. Several mechanisms proposed to account for these observations impact on both the "intrinsic", mitochondria-dependent and the "extrinsic", death-receptor-mediated pathways to apoptosis. Hsps can inhibit the activity of pro-apoptotic Bcl-2 proteins to prevent permeabilization of the outer mitochondrial membrane and release of apoptogenic factors. The disruption of apoptosome formation represents another mechanism by which Hsps can prevent caspase activation and induction of apoptosis. Several signaling cascades involved in the regulation of key elements within the apoptotic cascade are also subject to modulation by Hsps, including those involving JNK, NF-kappaB and AKT. The coordinated activities of the Hsps thus modulate multiple events within apoptotic pathways to help sustain cell survival following damaging stimuli.

PGE1 abolishes the mitochondrial-independent cell death pathway induced by D-galactosamine in primary culture of rat hepatocytes

BACKGROUND AND AIM

PGE1 reduces in vivo and in vitro D-galactosamine (D-GalN)-induced cell death in hepatocytes. The present study was undertaken to elucidate the intracellular pathway by which D-GalN induces cell death in cultured hepatocytes. In addition, we evaluated if PGE1 was able to modulate different parameters related to D-GalN-induced apoptosis in cultured rat hepatocytes.

METHODS

Hepatocytes were isolated from male Wistar rats (225-275 g) by the classical collagenase procedure. PGE1 (1 microM) was administered 2 h before D-GalN (5 mM) in primary culture of rat hepatocytes. Apoptosis was determined by DNA fragmentation and caspase-3, -6, -8 and -9 activation in hepatocytes. Caspase activation was evaluated by the detection of the related cleaved product and its associated activity. Cell necrosis was determined by the measurement of lactate dehydrogenase (LDH) activity in culture medium. To elucidate the role of mitochondria, we measured neutral (nSMase) and acid (aSMase) sphingomyelinase, as well as the expression of cytochrome c in mitochondria and cytoplasm fractions from D-GalN treated hepatocytes.

RESULTS

D-GalN induced caspase-3 activation and DNA fragmentation in hepatocytes. This apoptotic response was not associated with the activation of caspase-6, -8 or -9. The use of specific inhibitors confirmed that only caspase-3 was involved in D-GalN-induced apoptosis. D-GalN did not modify nSMase and aSMase activities, nor mitochondrial cytochrome c release in hepatocytes.

CONCLUSIONS

D-GalN induced apoptosis through caspase-3 activation but without modification of the activity of caspase-6, -8, -9, SMases or cytochrome c release. PGE1 appears to prevent D-GalN-induced apoptosis by a mitochondria-independent mechanism.

Apoptosis and porcine reproductive and respiratory syndrome virus

Despite numerous studies examining the possible induction of apoptosis in porcine reproductive and respiratory syndrome virus (PRRSV)-infected cells, it remains unclear if PRRSV infection results in direct apoptotic induction. There is clear evidence that apoptotic cells are present in tissues from PRRSV-infected pigs. However, many of these studies have failed to show that the apoptotic cells are infected with PRRSV. This has led some investigators to propose that "bystander" cells, not infected cells, become apoptotic during PRRSV infection by a yet undetermined mechanism. Studies examining the induction of the apoptotic gene expression response to PRRSV infection are needed to determine if PRRSV replication triggers an apoptotic response. We have utilized microarray and semi-quantitative reverse-transcription polymerase chain reaction (sqRT-PCR) to evaluate apoptotic gene expression in PRRSV-infected MARC-145 cells. Twenty-six apoptosis-related genes were examined during the first 24 h of infection and found to be unaltered, indicating that apoptotic induction was not occurring in PRRSV-infected cells. Additionally, using detection of free nucleosomal complexes, we examined cells for both apoptotic and necrotic death resulting from PRRSV infection at varying multiplicities of infection. This study indicates that PRRSV-infected MARC-145 cells undergo necrosis at a much higher level than apoptosis, and increases with virus levels used to infect the cells.

L-gamma-Glutamyl-L-cysteinyl-glycine (glutathione; GSH) and GSH-related enzymes in the regulation of pro- and anti-inflammatory cytokines: a signaling transcriptional scenario for redox(y) immunologic sensor(s)?

Of the antioxidant/prooxidant mechanisms mediating the regulation of inflammatory mediators, particularly cytokines, oxidative stress-related pathways remain a cornerstone. It is conspicuous that there is a strong association between free radical accumulation (ROS/RNS; oxidative stress) and the evolution of inflammation and inflammatory-related responses. The scenario that upholds a consensus on the aforementioned is still evolving to unravel, from an immunologic perspective, the molecular mechanisms associated with ROS/RNS-dependent inflammation. Cytokines are keynote players when it comes to defining an intimate relationship among reduction-oxidation (redox) signals, oxidative stress and inflammation. How close we are to identifying the molecular basis of this intricate association should be weighed against the involvement of specific signaling molecules and, potentially, transcription factors. L-gamma-Glutamyl-L-cysteinyl-glycine, or glutathione (GSH), an antioxidant thiol, has shaped, and still is refining, the face of oxidative signaling in terms of regulating the milieu of inflammatory mediators, ostensibly via the modulation (expression/repression) of oxygen- and redox-responsive transcription factors, hence termed redox(y)-sensitive cofactors. When it comes to the arena of oxygen sensing, oxidative stress and inflammation, nuclear factor-kappaB (NF-kappaB) and hypoxia-inducible factor-1alpha (HIF-1alpha) are key players that determine antioxidant/prooxidant responses with oxidative challenge. It is the theme therein to underlie current understanding of the molecular association hanging between oxidative stress and the evolution of inflammation, walked through an elaborate discussion on the role of transcription factors and cofactors. Would that classify glutathione and other redox signaling cofactors as potential anti-inflammatory molecules emphatically remains of particular interest, especially in the light of identifying upstream and downstream molecular pathways for conceiving therapeutic, alleviating strategy for oxidant-mediated, inflammatory-related disease conditions.

Intracellular signaling mechanisms in photodynamic therapy

In photodynamic therapy (PDT) a sensitizer, light and oxygen are used to induce death of tumor cells and in the treatment of certain noncancerous conditions. Cell death in PDT may occur by apoptosis or by necrosis, depending on the sensitizer, on the PDT dose and on the cell genotype. Some sensitizers that have been used in PDT are accumulated in the mitochondria, and this may explain their efficiency in inducing apoptotic cell death, both in vitro and in vivo. In this review we will focus on the events that characterize apoptotic death in PDT and on the intracellular signaling events that are set in motion in photosensitized cells. Activation of phospholipases, changes in ceramide metabolism, a rise in the cytosolic free Ca2+ concentration, stimulation of nitric oxide synthase (NOS), changes in protein phosphorylation and alterations in the activity of transcription factors and on gene expression have all been observed in PDT-treated cells. Although many of these metabolic reactions contribute to the demise process, some of them may antagonize cell death. Understanding the signaling mechanisms in PDT may provide means to modulate the PDT effects at the molecular level and potentiate its antitumor effectiveness.

Ergothioneine pretreatment protects the liver from ischemia-reperfusion injury caused by increasing hepatic heat shock protein 70

BACKGROUND

Reperfusion of the liver after ischemia induces the expression of the heat shock genes and the synthesis of the heat shock proteins (HSP). We studied the effects of the natural antioxidant ergothioneine (EGT) treatment on the expression of HSP70 in ischemic-reperfused (IR) liver.

METHODS

Adult male Wistar rats were randomly divided into three groups: Sham group given standard laboratory chow and water for 3 weeks followed by sham operation; Control group given standard laboratory chow and water for 3 weeks followed by liver IR injury; EGT group given standard laboratory chow supplementation l-ergothioneine (1.2 mg/kg/d body weight) administered by gavage and water for 3 weeks followed by liver IR injury. Ten rats from each group were killed to determine serum aspartate aminotransferase (AST), alanine aminotransferase (ALT), lactic dehydrogenase (LDH), tissue malondialdehyde (MDA), HSP70 levels, and histologic changes at 30, 60, and 120 min of reperfusion, respectively. Survival was followed for 1 week.

RESULTS

IR caused significant increase in serum AST, ALT, LDH, and tissue MDA levels. As compared with the control group, animals treated with EGT experienced a significant decrease in serum AST, ALT, and LDH levels in all reperfusion periods. Tissue MDA levels in animals receiving EGT were significantly reduced as compared with control group at 30 min and 60 min after reperfusion. After ischemia, reperfusion caused a remarkable production of HSP70 in the control group. When the rats were pretreated with EGT, the levels of HSP70 increased significantly in their livers after reperfusion compared with the control group. Liver injury in the EGT-treated animals was lower to that in the control group. The 7-day survival rate was significantly improved (from 50% to 80%) by EGT pretreatment.

CONCLUSION

HSP70 has been shown to induce tolerance against warm IR injury in rat livers. EGT pretreatment protects the liver from IR injury by over-expression of HSP and the subsequent suppression of lipid peroxidation.

Role of nitric oxide in the regulation of neuronal proliferation, survival and differentiation

Nitric oxide (NO), an important cellular messenger, has been linked to both neurodegenerative and neuroprotective actions. In the present review, we focus on recent data establishing a survival and differentiation role for NO in several neural in vitro and in vivo models. Nitric oxide has been found to be essential for survival of neuronal cell lines and primary neurons in culture under various death challenges. Furthermore, its lack may aggravate some neuropathological conditions in experimental animals. Several cellular pathways and signaling systems subserving this neuroprotective role of NO are considered in the review. Survey of recent data related to the developmental role of NO mainly focus on its action as a negative regulator of neuronal precursor cells proliferation and on its role of promotion of neuronal differentiation. Discussion on discrepancies arising from the literature is focused on the Janus-faced properties of the molecule and it is proposed that most controversial results are related to the intrinsic property of NO to compensate among functionally opposed effects. As an example, the increased proliferation of neural cell precursors under conditions of NO shortage may be, later on in the development, compensated by increased elimination through programmed cell death as a consequence of the lack of the survival-promoting action of the molecule. To elucidate these complex, and possibly contrasting, effects of NO is indicated as an important task for future researches.

Concentration-dependent effects of endogenous S-nitrosoglutathione on gene regulation by specificity proteins Sp3 and Sp1

The activities of certain nuclear regulatory proteins are modified by high concentrations of S-nitrosothiols associated with nitrosative stress. In the present study, we have studied the effect of physiological (low microM) concentrations of the endogenous S-nitrosothiol, GSNO (S-nitrosoglutathione), on the activities of nuclear regulatory proteins Sp3 and Sp1 (specificity proteins 3 and 1). Low concentrations of GSNO increased Sp3 binding, as well as Sp3-dependent transcription of the cystic fibrosis transmembrane conductance regulatory gene, cftr. However, higher GSNO levels prevented Sp3 binding, augmented Sp1 binding and prevented both cftr transcription and CFTR (cystic fibrosis transmembrane conductance regulator) expression. We conclude that low concentrations of GSNO favour Sp3 binding to 'housekeeping' genes such as cftr, whereas nitrosative stress-associated GSNO concentrations shut off Sp3-dependent transcription, possibly to redirect cellular resources. Since low micromolar concentrations of GSNO also increase the maturation and activity of a clinically common CFTR mutant, whereas higher concentrations have the opposite effect, these observations may have implications for dosing of S-nitrosylating agents used in cystic fibrosis clinical trials.

Combined action of extracellular signal-regulated kinase and p38 kinase rescues Molt4 T cells from nitric oxide-induced apoptotic and necrotic cell death

The mechanisms that regulate nitric oxide (NO)-induced apoptosis, especially in T cell apoptosis, are largely uncharacterized. Here, we report that protection from NO-induced cell death by phorbol 12-myristate 13-acetate (PMA) is dependent on both p38 and extracellular signal-regulated kinase (ERK) activation. Exposure of Molt4 cells to NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) induced both apoptotic and necrotic modes of cell death along with a sustained increase in p38 kinase phosphorylation. However, the p38 inhibitor SB202190 only slightly protected Molt4 cells from NO toxicity. In contrast, PMA rapidly phosphorylated both p38 kinase and ERK, and the phosphorylation statuses were not altered in the presence of SNAP. Interestingly, although each mitogen-activated protein kinase (MAPK) inhibitor by itself had only a modest effect, the combination of inhibitors for both MAPKs almost completely abolished the protective effect of PMA. Furthermore, dominant negative or catalytically inactive variants that modulate p38 and ERK mimicked the effects of MAPK inhibitors. We located the action of p38 and ERK upstream of the p53/mitochondrial membrane potential loss and caspases cascade. Together, these findings suggest that the PMA-induced activations of ERK and p38 kinase are parallel events that are both required for inhibition of NO-induced death of Molt4 cells.

Serum bioactive lysophospholipids prevent TRAIL-induced apoptosis via PI3K/Akt-dependent cFLIP expression and Bad phosphorylation

Serum contains a variety of biomolecules, which play an important role in cell proliferation and survival. We sought to identify the serum factor responsible for mitigating tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis and to investigate its molecular mechanism. TRAIL induced effective apoptosis without serum, whereas bovine serum decreased apoptosis by suppressing cytochrome c release and caspase activation. Indeed, albumin-bound lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) inhibited TRAIL-induced apoptosis by suppressing caspase activation and cytochrome c release. LPA increased phosphatidylinositol 3-kinase (PI3K)-dependent Akt activation, cellular FLICE-inhibitory protein (cFLIP) expression, and Bad phosphorylation, resulting in inhibition of caspase-8 activation and Bad translocation to mitochondria. The antiapoptotic effect of LPA was abrogated by PI3K inhibitor, transfection with dominant-negative Akt, and specific downregulation of cFLIP expression using siRNA and further increased by siRNA-mediated suppression of Bad expression. Moreover, sera from ovarian cancer patients showed more protective effect against TRAIL-induced apoptosis than those from healthy donors, and this protection was suppressed by PI3K inhibitor. Our results indicate that albumin-bound LPA and S1P prevent TRAIL-induced apoptosis by upregulation of cFLIP expression and in part by Bad phosphorylation, through the activation of PI3K/Akt pathway.

Effects of heat shock protein 70 activation by metabolic inhibition preconditioning or kappa-opioid receptor stimulation on Ca2+ homeostasis in rat ventricular myocytes subjected to ischemic insults

Heat shock protein 70 (HSP70) mediates delayed cardioprotection of preconditioning. Cytosolic calcium ([Ca(2+)])(i) overload precipitates injury, whereas attenuation of [Ca(2+)](i) overload is believed to be responsible for cardioprotection. There is evidence suggesting a link between HSP70 and [Ca(2+)](i) homeostasis. We hypothesize that activation of HSP70 by preconditioning may restore [Ca(2+)](i) homeostasis altered by ischemic insults. To test the hypothesis, we determined the effects of preconditioning with metabolic inhibition or pretreating with U50,488H [trans-(+)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide (a kappa-opioid receptor agonist)] on viability and injury, HSP70 expression, and [Ca(2+)](i) in ventricular myocytes subjected to metabolic inhibition and anoxia (MI/A), with blockade of HSP70 synthesis. In myocytes with vehicle pretreatment, the percentage of dead cells determined by trypan blue exclusion, the injury reflected by release of lactate dehydrogenase, and the resting [Ca(2+)](i) measured by spectrofluorometry significantly increased, whereas the amplitude of electrically induced [Ca(2+)](i) transient decreased, after 10 min with 10 mM 2-deoxy-d-glucose and 10 mM sodium dithionite, known to cause MI/A. However, when myocytes were subjected for 30 min to either 20 mM lactate and 10 mM 2-deoxy-d-glucose (MIP) or 30 microM U50,488H (UP) 20 h before MI/A, the changes in viability and injury, and [Ca(2+)](i) responses were significantly attenuated. These were accompanied by a significantly increased HSP70 expression. Furthermore, blockade of HSP70 synthesis with selective antisense oligonucleotides abolished the beneficial effects of MIP or UP. This study provides first evidence that activation of HSP70 induced by preconditioning, which conferred delayed cardioprotection, restored partially the [Ca(2+)](i) homeostasis altered by ischemic insults.

Nitric oxide induces BNIP3 expression that causes cell death in macrophages

Nitric oxide (NO) is involved in many physiological processes and also causes pathological effects by inducing apoptosis. It can enhance or suppress apoptosis depending on its concentration and the cell type involved. In this report, we used cDNA microarray analysis to show that SNAP, an NO donor, strongly induces Bcl-2/adenovirus E1B 19kDa-interacting protein 3 (BNIP3) in macrophages. BNIP3 is a mitochondrial pro-apoptotic protein that contains a Bcl-2 homology 3 domain and a COOH-terminal transmembrane (TM) domain. Macrophages activated by LPS/IFN-gamma produce nitric oxide synthase 2 (NOS2) and release endogenous NO. Expression of BNIP3 was also induced in macrophages by LPS/IFN-gamma, and the induction was blocked by a NOS2 inhibitor, S-methyl-isothiourea. Peritoneal macrophages from NOS2-null mice failed to produce BNIP3 in response to LPS/IFN-gamma. We conclude that BNIP3 expression in macrophages is controlled by the intracellular level of nitric oxide. Overexpression of BNIP3 but not of BNIP3 deltaTM, a BNIP3 mutant without the TM domain and C-terminal tail, led to apoptosis of the cells. Promoter analysis showed that the region between -281 and -1 of the 5'-upstream enhancer region of murine BNIP3 was sufficient for NO-dependent expression of BNIP3.

Nitric Oxide Inhibits Glucocorticoid-induced Apoptosis of Thymocytes by Repressing the SRG3 Expression

Nitric oxide (NO) plays many roles in the immune system. It has been known that NO rescues thymocytes from glucocorticoid (GC)-induced apoptosis. However, the downstream target of NO in the protection from GC-induced thymocyte apoptosis has yet to be identified. We previously reported that GC sensitivity of developing thymocytes is dependent on the expression level of SRG3. In the present report, we found that NO repressed the SRG3 expression in both primary thymocytes and 16610D9 thymoma cells. Specifically, NO down-regulated the transcription of SRG3 via the inactivation of the transcription factor Sp1 DNA-binding activity to the SRG3 promoter. In addition, overexpression of SRG3 by a heterologous promoter reduced NO-mediated rescue of thymocytes from GC-induced apoptosis. These observations strongly suggest that NO may be involved in protecting immature thymocytes from GC-induced apoptosis by repressing the SRG3 expression in thymus.

Protective effect of heat shock protein 70 against oxidative stresses in human corneal fibroblasts

We evaluated DNA protection effect of heat shock protein (HSP) against cytotoxic effects of exogenous nitric oxide (NO) and reactive oxygen intermediate (ROI). Cultured human corneal fibroblasts were divided into 4 groups. Control (Group I) was not exposed to a sub-lethal heat treatment. Other 3 groups were exposed to 43 degrees C for 1 hr, then incubated at 37 degrees C during different duration (1, 6, 24 hr, Group II, III, IV, respectively). Expression pattern of HSP 70 was analyzed by Western blot. Cell viability was measured by MTT assay and the relationship between HSP 70 expression and DNA damage was examined by terminal deoxyribonucleotidyl transferase mediated dUTP-digoxigenin nick and labeling (TUNEL) stain and single cell gel electrophoresis. Expression pattern of HSP 70 was dependent on recovery times. Cell viability following heat treatment was significantly increased and the TUNEL positive cell number was decreased at 6 hr. In single cell gel electrophoresis, tail moments were increased in a dose-dependent manner by SNAP and X/XO. Following heat treatment, tail moments showed decreased significantly at 6 hr. These results suggest that induction of HSP 70 by sub-lethal heat treatment is closely related with cytoprotective effects against oxidative stresses in human corneal fibroblasts.

Inhibition of Farnesyltransferase Prevents Collagen-Induced Arthritis by Down-Regulation of Inflammatory Gene Expression through Suppression of p21ras-Dependent NF-κB Activation

Farnesylation of p21(ras) is an important step in the intracellular signaling pathway of growth factors, hormones, and immune stimulants. We synthesized a potent and selective farnesyltransferase inhibitor (LB42708) with IC(50) values of 0.8 nM in vitro and 8 nM in cultured cells against p21(ras) farnesylation and examined the effects of this inhibitor in the settings of inflammation and arthritis. LB42708 suppressed NF-kappaB activation and iNOS promoter activity by suppressing the I-kappaB kinase activity and I-kappaBalpha degradation. The inhibitor suppressed the expression of inducible NO synthase, cyclooxygenase-2, TNF-alpha, and IL-1beta and the production of NO and PGE(2) in immune-activated macrophages and osteoblasts as well as LPS-administrated mice. Furthermore, in vivo administration of LB42708 significantly decreased the incidence and severity of arthritis as well as mRNA expression of inducible NO synthase, cyclooxygenase-2, TNF-alpha, and IL-1beta in the paws of collagen-induced arthritic mice compared with controls. These observations indicate that the anti-inflammatory and antiarthritic effects of the farnesyltransferase inhibitor may be ascribed to the inhibition of I-kappaB kinase activity and subsequent suppression of NF-kappaB-dependent inflammatory gene expression through the suppression of p21(ras) farnesylation. Together, these findings reveal that the inhibitory effect of LB42708 on p21(ras)-dependent NF-kappaB activation may have potential therapeutic value for arthritis and other inflammatory diseases.

Nitric oxide-induced apoptosis is mediated by Bax/Bcl-2 gene expression, transition of cytochrome c, and activation of caspase-3 in rat vascular smooth muscle cells

BACKGROUND

In contrast to the anti-apoptotic action of nitric oxide (NO) on endothelial cells, NO exerts a pro-apoptotic effect on vascular smooth muscle cells (VSMCs). This study was designed to elucidate the mechanism underlying NO-induced apoptosis in rat VSMCs.

METHODS AND RESULTS

(1) Using the terminal deoxynucleotidyl transferase-mediated digoxigenin-11-dUTP nick end labeling (TUNEL) assay and fluorescence activated cell sorter (FACS) analyses, apoptosis of rat VSMCs were confirmed after exposure to sodium nitroprusside (SNP) (0.5 to 4 mmol/l), an exogenous NO donor. The effects of SNP were blocked by hemoglobin. (2) A universal caspase inhibitor, z-VAD-fmk, dose-dependently inhibited NO-induced apoptosis. VSMCs degraded Ac-DEVD-pNA rather than Ac-WHED-pNA after exposure to SNP, which suggested that the activation of caspase 3 rather than caspase 1 was involved in the process. Immunoblot analysis confirmed the activation of caspase-3. (3) Exposure to SNP induced the release of cytochrome c from the mitochondria to the cytosol, which was detected by immunoblot analysis of mitochondrial and cytosol fractions. (4) SNP exposure increased the ratio of Bax/Bcl-2 protein expression twofold by immunoblot analysis.

CONCLUSIONS

The mechanism of NO-induced apoptosis in rat VSMCs involves an increase in the ratio of Bax/Bcl-2 gene expression, which leads to the release of cytochrome c from the mitochondria to the cytosol, finally activating caspase-3 and resultant apoptosis.

eNOS protects prostate cancer cells from TRAIL-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a potent anti-cancer agent because it induces apoptosis of most tumor cells with little or no effect on normal cells. In this study, we investigated the effect of TRAIL on human prostate normal and cancer cell lines, and found that the prostate cancer cell lines PC-3, ALVA-31, DU 145 and TSU-Pr1 were sensitive to TRAIL-induced apoptosis, while normal PrEC cells and cancer cell line LNCaP were resistant. No correlation was found between the sensitivity of cells to TRAIL and the expression of TRAIL receptors DR4 and DR5, and pro-apoptotic proteins Bax and Bak. However, LNCaP cells displayed a high Akt activity. Furthermore, we found that endothelial nitric oxide synthase (eNOS), one of the Akt substrates, was highly expressed in LNCaP but not in other cells. Inhibition of eNOS activity by NOS inhibitor sensitized LNCaP cells to TRAIL. Moreover, PC-3 cell clones stably expressing eNOS were resistant to TRAIL-induced apoptosis. Taken together, these results indicate that eNOS can regulate the sensitivity of prostate cancer cells to TRAIL, and down-regulation of eNOS activity may sensitize prostate cancer cells to TRAIL-based therapy.

Inhaled nitric oxide attenuates apoptosis in ischemia-reperfusion injury of the rabbit lung

BACKGROUND

Lung ischemia-reperfusion injury occurs after lung transplantation and various clinical procedures. Recently, apoptosis was reported to be induced after ischemia-reperfusion. We investigated the effects of inhaled nitric oxide (NO) on lung ischemia-reperfusion and apoptosis after ischemia-reperfusion.

METHODS

As a control group, the left pulmonary hilum of Japanese white rabbits (n = 10) was occluded for 120 minutes and reperfused for 120 minutes. In the inhaled NO group (n = 10), 20 parts per million nitric oxide was inhaled during reperfusion. The sham-operated group was ligated at the right hilum and perfused by the left lung only for 120 minutes. The mean pulmonary arterial pressures and Pao2 were measured during reperfusion. The wet-to-dry weight ratio of the left lower lobe of the lung was calculated. The number of apoptotic cells was estimated using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) technique. The TUNEL staining for a time course study was done using 15 control animals that were killed by exsanguination at 15, 30, and 60 minutes after reperfusion.

RESULTS

After 120 minutes of reperfusion, the mean pulmonary arterial pressures in the control group and in the inhaled NO group were 23.0 +/- 3.2 mm Hg and 13.6 +/- 2.4 mm Hg, respectively (p < 0.01). At the same time point, the Pao2 in the control group and in the inhaled NO group were 46.1 +/- 15.9 mm Hg and 88.1 +/- 14.7 mm Hg, respectively (p < 0.01). The wet-to-dry weight ratios in the control group and in the inhaled NO group were 0.856 +/- 0.024 and 0.808 +/- 0.006, respectively (p < 0.01). Apoptotic cells appeared in the early phase of reperfusion (after 15 minutes' reperfusion). The number of apoptotic cells was significantly lower in the inhaled group than in the control group after 120 minutes' reperfusion (1.76% versus 2.87%, p < 0.01).

CONCLUSIONS

Our results suggest that the inhaled NO prevents lung ischemia-reperfusion injury and attenuates apoptosis after reperfusion in the rabbit lung.

Effect of thermal preconditioning before excimer laser photoablation

The purposes of this study were to assess the expression patterns of heat shock proteins (Hsps), after eyeball heating or cooling, and to elucidate their relationships with corneal wound healing and intraocular complications after excimer laser treatment. Experimental mice were grouped into three according to local pretreatment type: heating, cooling, and control groups. The preconditioning was to apply saline eyedrops onto the cornea prior to photoablation. Following photoablation, we evaluated corneal wound healing, corneal opacity and lens opacity. Hsp expression patterns were elucidated with Western blot and immunohistochemical staining. The heating and cooling groups recovered more rapidly, and showed less corneal and lens opacity than the control group. In the heating and cooling groups, there were more expressions of Hsps in the cornea and lens than in the control group. These results were confirmed in the Hsp 70.1 knockout mouse model. Our study showed that Hsps were induced by the heating or cooling preconditioning, and appeared to be a major factor in protecting the cornea against serious thermal damage. Induced Hsps also seemed to play an important role in rapid wound healing, and decreased corneal and lens opacity after excimer laser ablation.

Regulation of the apoptosis-necrosis switch

Execution of the apoptotic program involves a relatively limited number of pathways. According to a general view, these would converge to activate the caspase family of proteases. However, there is increasing evidence that apoptotic-like features can also be found when caspases are inhibited. Moreover, under pathological conditions, apoptosis and nonapoptotic death paradigms are often interwined, which suggest that, in vivo, cells may use diverging execution pathways. Molecular switches between apoptosis and necrosis include adenosine triphosphate-dependent steps in the activation of caspases or steps sensitive to reactive oxygen/nitrogen species. In turn, caspase activation can cause necrosis by promoting ion overload.

Comparison of chondrocyte apoptosis in vivo and in vitro following acute osteochondral injury

The objective of the present study was to directly compare levels of chondrocyte apoptosis produced by osteochondral injury in vivo and in vitro. Adult New Zealand White rabbits underwent 2 mm osteochondral drilling of the medial and lateral femoral condyles of a single hind limb. Animals were euthanized, and specimens were harvested at 0, 2, 4, 7, 10, and 14 days following injury. At the time of euthanasia, identical injuries were created in the femoral condyles of the contralateral hind limb. These condyles were maintained in vitro under standard tissue culture conditions until harvesting at time points corresponding to the in vivo specimens (i.e. after 0, 2, 4, 7, 10 and 14 days in culture). The extent of apoptosis in the in vivo and in vitro specimens was quantified by TUNEL analysis. The amount and distribution of TUNEL positive cells followed similar patterns in both in vivo and in vitro specimens with a maximal percentage of apoptotic chondrocytes observed on post-injury day 4. On post-injury day 4, in vivo specimens displayed a statistically significant increased overall level of apoptosis compared to in vitro specimens [in vivo=32.5+/-8.6%; in vitro=22.2+/-4.8%; (p=0.03)]. These experiments suggest that the majority of programmed cell death observed after osteochondral injury can be attributed to processes intrinsic to the cartilage itself; however, additional factors present within the acutely traumatized joint also appear to potentiate chondrocyte apoptosis following injury.

Study of the effects of interferon a on several human hepatoma cell lines: analysis of the signalling pathway of the cytokine and of its effects on apoptosis and cell proliferation

BACKGROUND

Interferon alpha (IFNalpha), currently used for the treatment of chronic viral hepatitis, is also known to prevent the development of hepatocellular carcinoma (HCC), the mechanism of this action being still debatable.

AIMS

To study thoroughly in human hepatoma cell lines (HHL)--Hep3B, HepG2, HuH7, SKHep1, and Chang-Liver--submitted to rhIFNalpha, the signalling pathway of IFNalpha, the binding activity of the cytokine on specific gamma-activated sequence (GAS) and interferon-stimulated regulatory element (ISRE) nuclear sequences, and its effects on apoptosis and cell proliferation.

METHODS

The behaviour of signal transducer and activator of transcription (STAT)1, STAT2, p48(IRF9) and the binding of nuclear proteins were investigated by immunoblot and electro-mobility shift assay. Expression of some IFNalpha-dependent proteins--p21/(WAF1), inducible nitric oxide synthase, IRF1 and 2--were studied by immunoblot. Apoptosis and the cell cycle were studied by morphological and biochemical methods.

RESULTS

Transduction of INFalpha was unaltered, although there were some variations in the different HHL. Nuclear protein binding to GAS or ISRE showed that ISRE was mainly involved. Apoptosis did not occur. The cell cycle was slightly modified in HuH7. Three GAS- and/or ISRE-dependent proteins increased, suggesting that IFNalpha may have some biological effects on HHL.

CONCLUSIONS

The IFNalpha signalling pathway is functional in several HHL, but the cytokine has no apoptotic effect and a moderate anti-proliferative effect. This suggests that the preventive role of IFNalpha on HCC cannot be explained by an apoptotic and/or an anti-proliferative effect, but possibly by its action on several specific nuclear sequences that protect liver cells from transformation.

Carbon monoxide protection against endotoxic shock involves reciprocal effects on iNOS in the lung and liver

Carbon monoxide (CO) has recently emerged as having potent cytoprotective properties; the mechanisms underlying these effects, however, are just beginning to be elucidated. In a rat model of lipopolysaccharide (LPS)-induced multiorgan failure, we demonstrate that exposure to a low concentration of CO for only 1 h imparts a potent defense against lethal endotoxemia and effectively abrogates the inflammatory response. Exposure to CO leads to long-term survival of >80% of animals vs. 20% in controls. In the lung, CO suppressed LPS-induced lung alveolitis and associated edema formation, while in the liver, it reduced expression of serum alanine aminotransferase, a marker of liver injury. This protection appears to be based in part on different mechanisms in the lung and liver in that CO had reciprocal effects on LPS-induced expression of iNOS and NO production, important mediators in the response to LPS. CO prevented the up-regulation of iNOS and NO in the lung while augmenting expression of iNOS and NO in the liver. Studies of primary lung macrophages and hepatocytes in vitro revealed a similar effect; CO inhibited LPS-induced cytokine production in lung macrophages while reducing LPS-induced iNOS expression and nitrite accumulation and protected hepatocytes from apoptosis while augmenting iNOS expression. Although it is unclear to which extent these changes in iNOS contribute to the cytoprotection conferred by CO, it is fascinating that in each organ CO influences iNOS in a manner known to be protective in that organ: NO is therapeutic in the liver while it is damaging in the lung.

CD95-tyrosine Nitration Inhibits Hyperosmotic and CD95 Ligand-induced CD95 Activation in Rat Hepatocytes

Epidermal growth factor receptor-dependent CD95-tyrosine phosphorylation was recently identified as an early step in apoptosis induction via the CD95 system (Reinehr, R., Schliess, F., and Häussinger, D. (2003) FASEB J. 17, 731-733). The effect of peroxynitrite (ONOO(-)) on modulation of the hyperosmotic and CD95 ligand (CD95L)-induced CD95 activation process was studied. Pretreatment of hepatocytes with ONOO(-) inhibited CD95L- and hyperosmolarity-induced CD95 membrane trafficking and formation of the death-inducing signaling complex, but not epidermal growth factor receptor activation and its association with CD95. Under these conditions, however, no tyrosine phosphorylation of CD95 occurred; instead, CD95 was tyrosine-nitrated. When ONOO(-) was added after induction of CD95-tyrosine phosphorylation by CD95L or hyperosmolarity, tyrosine nitration of CD95 was largely prevented and death-inducing signaling complex formation occurred. CD95-tyrosine nitration abolished the hyperosmotic sensitization of hepatocytes toward CD95L-induced apoptosis. Additionally, in CD95-yellow fluorescent protein-transfected Huh7-hepatoma cells, ONOO(-) induced CD95 Tyr nitration and prevented CD95L-induced Tyr phosphorylation and apoptosis. Tyrosine-nitrated CD95 was also found in rat livers derived from an in vivo model of endotoxinemia. The data suggest that CD95-tyrosine nitration prevents CD95 activation by inhibiting CD95-tyrosine phosphorylation. Apparently, CD95-tyrosine phosphorylation and nitration are mutually exclusive. The data identify critical tyrosine residues of CD95 as another target of the anti-apoptotic action of NO.

Protection of the liver by ischemic preconditioning: a review of mechanisms and clinical applications

Ischemic preconditioning refers to the endogenous mechanism of protection against a sustained ischemic insult following an initial, brief ischemic stimulus. Ischemia-reperfusion injury of the liver is a major cause of morbidity and mortality in liver surgery and transplantation and ischemic preconditioning is a promising strategy for improving the outcome of liver surgery. The preconditioning phenomenon was first described in a canine model of myocardial ischemia-reperfusion injury in 1986 and since then has been shown to exist in other organs including skeletal muscle, brain, kidneys, retina and liver. In the liver, the preconditioning effect has been demonstrated in rodents and a recent study has demonstrated human clinical benefits of preconditioning during hemihepatectomies. Ischemic preconditioning has been described as an adaptive response and although the precise mechanism of hepatoprotection from preconditioning is unknown it is likely to be a receptor-mediated process. Several hypotheses have been proposed and this review assesses possible mechanisms of ischemic preconditioning and its role in hepatic surgery and liver transplantation. The future lies in defining the mechanisms of the ischemic preconditioning effect to allow drug targeting to induce the preconditioning response.

Lack of detrimental effects of nitric oxide inhibition in bile duct-ligated rats with hepatic encephalopathy

BACKGROUND

The pathogenetic mechanisms of hepatic encephalopathy (HE) are not fully understood. Vasodilatation induced by nitric oxide (NO) may be involved in the development of HE. There is no comprehensive data concerning the effects of NO inhibition on HE in chronic liver disease.

METHODS

Male Sprague-Dawley rats weighing 240-270 g at the time of surgery were selected for experiments. Secondary biliary cirrhosis was induced by bile duct ligation (BDL). Counts of movements were compared between BDL rats and rats receiving a sham operation. In another series of experiments, BDL rats received either Nomega-nitro-L-arginine methyl ester (L-NAME, 25 mg kg-1 day-1 in tap water) or tap water (control) from the 36th to 42nd days after BDL. Besides motor activities, plasma levels of tumour necrosis factor (TNF)-alpha and nitrate/nitrite, liver biochemistry tests and haemodynamics were determined after treatment.

RESULTS

Compared with the sham-operated rats, the total, ambulatory and vertical movements were significantly decreased in the BDL rats (P </= 0.001). The L-NAME group had a significantly higher mean arterial pressure than that of the control group (119.0 +/- 2.5 mmHg vs. 97.3 +/- 2.8 mmHg, P = 0.002). However, the counts of motor activities, plasma levels of TNF-alpha and nitrate/nitrite, and serum biochemistry tests were not significantly different between the L-NAME and control groups.

CONCLUSIONS

Bile duct ligation may induce HE evidenced by a decrease in motor activities. However, chronic L-NAME administration did not have significantly detrimental or therapeutic effects on the severity of encephalopathy in BDL rats.

Nitric oxide and pro-inflammatory cytokines in acute hepatitis B

Background: Experimental studies demonstrate that hepatitis B virus may induce nitric oxide (NO) production in infected hepatocytes. Its presence in acute hepatitis B patients has not been studied. Methods: Serum levels of nitric oxide and its regulatory pro-inflammatory cytokines were detected in 15 patients with uncomplicated acute hepatitis B, 19 blood donors and 15 chronic hepatitis B patients. Cytokines were determined with an immunoassay. Nitric oxide was measured as the serum metabolic products of nitrates and nitrites using a modification of the Griess reaction. Results: All detected cytokines were increased in acute hepatitis B patients compared to healthy controls (p<0.001 for TNF-alpha, p<0.05 for IL-6, p<0.001 for IL1-beta and p<0.001 for IFN-gamma). High serum levels of nitric oxide were found in acute hepatitis B patients (156.96+/-9.76 micromol/l) compared to healthy controls (51+/-6.2 micromol/l, p<0.001) and chronic hepatitis B patients (63.97+/-3.78 micromol/l, p<0.001). No significant correlations were found between NO, cytokine levels and transaminases. Conclusions: High levels of nitric oxide and its regulatory cytokines were found in a group of patients with uncomplicated acute hepatitis B. The exact role of NO in the disease pathogenesis and outcome needs to be studied further.

Heparin-binding epidermal growth factor-like growth factor and intestinal ischemia-reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury affects patients of different ages, especially premature babies and the elderly. The outcome after intestinal I/R is often dismal, which may be attributed to loss of the barrier and immune functions of the intestines, as well as development of secondary injury in remote organs. The available treatment for advanced gut ischemia mandates extensive resection, which may cause growth retardation in infants and nutritional problems in the elderly. Throughout the past decade we have been investigating the potential therapeutic role of heparin-binding epidermal growth factor-like factor (HB-EGF) in intestinal I/R. The mitogenic and chemoattractant functions of HB-EGF formed the initial rationale for our investigations. In addition, HB-EGF is a potent antiapoptotic protein that enables cells and tissues exposed to different apoptotic stimuli to survive hypoxic, oxidative, and nutritional stresses. HB-EGF is known to have a vital role in wound healing and postischemic regeneration in different organs. In the current review, we summarize the results of our findings of the beneficial effects of HB-EGF in intestinal I/R, supported by additional evidence from the literature and an explanation of different possible mechanisms of its actions. Collectively, the data strongly suggest a potential therapeutic role for the use of HB-EGF to treat intestinal ischemic diseases such as I/R and necrotizing enterocolitis.

Carbon monoxide protects against liver failure through nitric oxide-induced heme oxygenase 1

Carbon monoxide (CO) and nitric oxide (NO) each have mechanistically unique roles in various inflammatory disorders. Although it is known that CO can induce production of NO and that NO can induce expression of the cytoprotective enzyme heme oxygenase 1 (HO-1), there is no information whether the protective effect of CO ever requires NO production or whether either gas must induce expression of HO-1 to exert its functional effects. Using in vitro and in vivo models of tumor necrosis factor α–induced hepatocyte cell death in mice, we find that activation of nuclear factor κB and increased expression of inducible NO are required for the protective effects of CO, whereas the protective effects of NO require up-regulation of HO-1 expression. When protection from cell death is initiated by CO, NO production and HO-1 activity are each required for the protective effect showing for the first time an essential synergy between these two molecules in tandem providing potent cytoprotection.

Til cell death do us part: nitric oxide and mechanisms of hepatotoxicity

Like many juggernauts in biology, the elusive nature of nitric oxide (NO) sprints through the fields, sometimes the savior, at other times the scimitar. In the liver, which is the metabolic center of the organism, hepatocytes and immune cells trade blows using the reactive diatomic molecule NO to induce cellular damage under toxic conditions. In response, hepatocytes can utilize several mechanisms of NO to their protective advantage by prohibiting the activation of programmed cell death, a.k.a. apoptosis. The balance of these effects in this reactive milieu set the stage for the homeostatic response to cellular injury that determines whether hepatocytes will live, die, or regenerate. Insights that we and others have gained from the liver under pathologic conditions of stress can be applied to the understanding of cellular death mechanisms in other organs and tissues.

The liver-selective nitric oxide donor O2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO) protects HepG2 cells against cytochrome P450 2E1-dependent toxicity

HepG2 cells expressing CYP2E1 (E47 cells) are more susceptible to toxicity by arachidonic acid (AA) or after glutathione depletion with an inhibitor of glutamate-cysteine ligase, l-buthionine-(S,R)-sulfoximine (BSO), compared with control HepG2 cells (C34 cells). The ability of nitric oxide (NO) to protect against CYP2E1-dependent toxicity has not been evaluated. We therefore studied the ability of O2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO), a liver-selective NO donor, to protect against CYP2E1-dependent toxicity and compared this with protection by chemical NO donors. E47 cells incubated with V-PYRRO/NO produced NO, whereas C34 cells did not. Incubation of E47 cells with 50 microM AA or 100 microM BSO for 2 days resulted in a 50% loss of cell viability. VPYRRO/NO (1 mM) blocked this toxicity of AA and BSO by a mechanism involving NO release via CYP2E1 metabolism of VPYRRO/NO. NO scavengers hemoglobin and 2-(4-carboxophenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide blocked the protective effects of V-PYRRO/NO. V-PYRRO/NO inhibited CYP2E1 activity and production of reactive oxygen species, whereas hemoglobin prevented these events. AA and BSO induced lipid peroxidation and decreased mitochondrial membrane potential; both of these effects were blocked by V-PYRRO/NO. Unlike V-PYRRO/NO, the chemical donors spermine/NO and (S)-nitroso-N-acetylpenicillamine release NO directly when added to the medium; however, they could partially protect against the CYP2E1-dependent toxicity. These results suggest that VPYRRO/NO protects HepG2 cells against CYP2E1-dependent toxicity through inhibition of CYP2E1-derived reactive oxygen species production and lipid peroxidation by the generated NO and that this compound may be valuable in protecting against CYP2E1-dependent toxicity via liver P450-specific generation of NO.

Anti-inflammatory actions of St. John's wort: inhibition of human inducible nitric-oxide synthase expression by down-regulating signal transducer and activator of transcription-1alpha (STAT-1alpha) activation

St. John's wort (SJW) has been described to show anti-inflammatory properties due to its inhibitory effects on the expression of pro-inflammatory genes like cyclooxygenase-2, interleukin-6, and inducible nitric-oxide synthase (iNOS). Since iNOS plays a critical role in chronic inflammatory diseases, we have focused our attention on the regulation of iNOS expression by SJW in two different human epithelial cell lines, alveolar A549/8 and colon DLD-1 cells. SJW extract concentration dependently inhibited human iNOS expression evaluated by measuring the amounts of iNOS mRNA, iNOS protein, and NO production in both cell lines. This inhibitory effect resulted from transcriptional inhibition as shown in reporter gene experiments. With electrophoretic mobility shift experiments, we found a SJW-mediated down-regulation of the DNA binding activity of the transcription factor signal transducer and activator of transcription-1alpha (STAT-1alpha), but not of nuclear factor-kappaB. This down-regulation of the STAT-1alpha DNA binding was shown to result from reduced tyrosine phosphorylation of the STAT-1alpha protein. The diminished STAT-1alpha tyrosine phosphorylation resulted from SJW-mediated reduction of Janus kinase 2 activity. These data suggest that extracts from SJW may be a promising anti-inflammatory principle in chronic inflammatory diseases.

Ischemic preconditioning decreases C-X-C chemokine expression and neutrophil accumulation early after liver transplantation in rats

AIM: Polymorphonuclear neutrophil (PMN) plays a major role in liver ischemia/reperfusion injury. Protective effect of ischemic preconditioning (IP) has been confirmed in liver ischemia/reperfusion injury. The purpose of this study was to investigate the effect of IP on C-X-C chemokine expression and PMNs recruitment early after liver transplantation.

METHODS: Male Sprague-Dawley rats were used as donors and recipients of orthotopic liver transplantation (OLT). The donor liver was stored 24 h in University of Wisconsin (UW) solution at 4 °C pre-implantation. IP was done by clamp of the portal vein and hepatic artery of the donor liver for 10 minutes followed by reperfusion for 10 minutes before harvesting. The neutrophilic infiltration in liver was quantified using a myeloperoxidase (MPO) assay. Intragraft expression of macrophage inflammatory protein-2 (MIP-2) mRNA was investigated with in situ hybridization. The serum levels of MIP-2 and tumor necrosis factor (TNF)-α were also monitored.

RESULTS: After liver transplantation without IP, the hepatic MPO increased significantly compared with sham operated group. In IP group, PMN in liver indicated by MPO was reduced significantly. In situ hybridization showed no MIP-2 mRNA in sham group but dramatic expression in hepatocytes in non-IP group. In IP group, MIP-2 mRNA was significantly down-regulated. Similarly, serum MIP-2 and TNF-α levels were significantly elevated in non-IP group and both were reduced in IP group.

CONCLUSION: IP might protect graft liver from preservation-reperfusion injury after OLT through down-regulating C-X-C chemokine expression of hepatocytes, and alleviating PMNs recruitment after reperfusion.

Nitric oxide prevents UV-induced phosphorylation of the p53 tumor-suppressor protein at serine 46: a possible role in inhibition of apoptosis

Ser-46 of p53 is phosphorylated in response to DNA-damage in vivo, and it plays a pivotal role for apoptotic signaling by p53 through regulating the transcriptional activation of genes involved in apoptosis. We found that the presence of the nitric oxide (NO) donor S-nitroso-N-acetyl-D,L-penicillamine (200-800 microM) during UV-irradiation of MCF-7 cells resulted in a significant reduction in the Ser-46 phosphorylation, compared to the UV-irradiated cells without NO. This reduction occurred independently of cyclic GMP generation and without affecting activities of p53 kinases such as the PI3K family, p38 MAPK, and HIPK2. The presence of NO was found to protect HCT116 human colon tumor cells containing wild-type p53 from UV-induced apoptosis, whereas no apparent inhibitory effect of NO on UV-induced apoptosis was observed in those deficient in p53. Our results suggest that NO-mediated protection of apoptosis is p53-dependent, occurring at least partly through NO-inhibition of phosphorylation of p53 on Ser-46.

L-carnitine alleviates alcohol-induced liver damage in rats: role of tumour necrosis factor-alpha

AIMS

Excessive alcohol intake induces hepatic fatty infiltration, which has been suggested to sensitize the liver to further damage. To test this hypothesis, L-carnitine, a constitutional lipotropic compound, was administered to rats chronically treated with ethanol by liquid diet feeding for 10 weeks.

RESULTS

Ethanol administration caused marked steatosis, mild inflammation and elevated plasma alanine aminotransferase and tumour necrosis factor alpha (TNF-alpha) concentrations. Dietary supplementation with L-carnitine significantly reduced all these parameters as well as the hepatic concentration of thiobarbituric acid reactive substances, an indicator of lipid peroxidation products. Pretreatment with L-carnitine also significantly blunted ethanol-induced stimulation of TNF-alpha release by isolated Kupffer cells.

CONCLUSIONS

This study provides direct support for the notion that steatosis sensitizes the liver to further damage and suggests an involvement of TNF-alpha in this process.

Flow-dependent regulation of endothelial nitric oxide synthase: role of protein kinases

Vascular endothelial cells are directly and continuously exposed to fluid shear stress generated by blood flow. Shear stress regulates endothelial structure and function by controlling expression of mechanosensitive genes and production of vasoactive factors such as nitric oxide (NO). Though it is well known that shear stress stimulates NO production from endothelial nitric oxide synthase (eNOS), the underlying molecular mechanisms remain unclear and controversial. Shear-induced production of NO involves Ca2+/calmodulin-independent mechanisms, including phosphorylation of eNOS at several sites and its interaction with other proteins, including caveolin and heat shock protein-90. There have been conflicting results as to which protein kinases-protein kinase A, protein kinase B (Akt), other Ser/Thr protein kinases, or tyrosine kinases-are responsible for shear-dependent eNOS regulation. The functional significance of each phosphorylation site is still unclear. We have attempted to summarize the current status of understanding in shear-dependent eNOS regulation.

Protective effect of prolactin and placental lactogen on NO-induced Nb2 lymphoma cell apoptosis

Nitric oxide (NO) is an important modulator involved in immune regulation. Here, we describe conditions under which NO-donors induce apoptosis on Nb2 lymphoma cells, as evidenced by decreased cell viability and increased hypodiploid DNA content determined by flow cytometry. In addition, DNA fragmentation typical of apoptosis was shown by agarose gel electrophoresis. This apoptosis was accompanied by a significant increase of caspase-3-like enzymatic activity. Both ovine prolactin (oPRL) and ovine placental lactogen (oPL) exerted a protective effect on the NO-donor-induced apoptosis. Furthermore, dexamethasone (Dex)-induced cell death was also associated with caspase-3-like activity and oPL had the same potency as oPRL in its protective effect on Dex-induced apoptosis of Nb2 cells.

Hepatic ischemia reperfusion injury: pathogenic mechanisms and basis for hepatoprotection

This review highlights recent advances in our understanding of mechanisms underlying reperfusion injury to the liver after warm hepatic ischemia. Sinusoidal endothelial cells and hepatocytes are targets of injury in the early 'cytotoxic' phase, although participation of apoptosis in the cell-death process remains contentious. Kupffer cells may play an important role as the initial cytotoxic cell type and are likely a source of reactive oxygen species and proinflammatory mediators, particularly tumor necrosis factor (TNF)-alpha. The latter are involved with subsequent neutrophil activation and recruitment. Microcirculatory disruption results from an imbalance between the actions of vasoconstrictors and vasodilators, such as nitric oxide, and also has a major impact on reperfusion injury. There is growing evidence that a brief prior ischemia-reperfusion period, termed 'ischemic preconditioning', is hepatoprotective. This can be mimicked by drugs that produce oxidative stress, and by interleukin-6 and TNF-alpha; both these cytokines are involved with priming hepatocytes to enter the cell cycle. Several mechanisms have been implicated including mobilization of adenosine and activation of adenosine type 2 receptors, nitric oxide, abrogation of TNF synthesis, preservation of energy metabolism, protection of the microcirculation and accelerated cell-cycle entry. A better understanding of preconditioning mechanisms will lead to novel approaches to improve outcomes of liver surgery.

Rho protein-mediated changes in the structure of the actin cytoskeleton regulate human inducible NO synthase gene expression

Rho proteins (Rho, Rac, Cdc 42) are known to control the organization of the actin cytoskeleton as well as gene expression. Inhibition of Rho proteins by Clostridium difficile toxin B disrupted the F-actin cytoskeleton and enhanced cytokine-induced inducible nitric oxide synthase (iNOS) expression in human epithelial cells. Also specific inhibition by Y-27632 of p160ROCK, which mediates Rho effects on actin fibers, caused a disruption of the actin cytoskeleton and a superinduction of cytokine-induced iNOS expression. Accordingly, direct disruption of the actin cytoskeleton by cytochalasin D, latrunculin B, or jasplakinolide enhanced cytokine-induced iNOS expression. The transcription factor serum response factor (SRF) has been described as mediating actin cytoskeleton-dependent regulation of gene expression. Direct targets of SRF are activating protein 1 (AP1)-dependent genes. All compounds used inhibited SRF- and AP1-dependent reporter gene expression in DLD-1 cells. However, the enhancing effect of the actin cytoskeleton-disrupting compounds on human iNOS promoter activity was much less pronounced than the effect on iNOS mRNA expression. Therefore, besides transcriptional mechanisms, posttranscriptional effects seem to be involved in the regulation of iNOS expression by the above compounds. In conclusion, our data suggest that Rho protein-mediated changes of the actin cytoskeleton negatively modulate the expression of human iNOS.

Nitric oxide prevents 6-hydroxydopamine-induced apoptosis in PC12 cells through cGMP-dependent PI3 kinase/Akt activation

Nitric oxide (NO) functions not only as an important signaling molecule in the brain by producing cGMP, but also regulates neuronal cell apoptosis. The mechanism by which NO regulates apoptosis is unclear. In this study, we demonstrated that NO, produced either from the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) or by transfection of neuronal NO synthase, suppressed 6-hydroxydopamine (6-OHDA)-induced apoptosis in PC12 cells by inhibiting mitochondrial cytochrome c release, caspase-3 and -9 activation, and DNA fragmentation. This protection was significantly reversed by the soluble guanylyl cyclase inhibitor 1H-(1,2,4)-oxadiazole[4,3-a]quinoxalon-1-one, indicating that cGMP is a key mediator in NO-mediated anti-apoptosis. Moreover, the membrane-permeable cGMP analog 8-Br-cGMP inhibited 6-OHDA-induced apoptosis. These anti-apoptotic effects of SNAP and 8-Br-cGMP were suppressed by cGMP-dependent protein kinase G (PKG) inhibitor KT5823, indicating that PKG is a downstream signal mediator in the suppression of apoptosis by NO and cGMP. Both SNAP and 8-Br-cGMP induced endogenous Akt activation and Bad phosphorylation, resulting in the inhibition of Bad translocation to mitochondria; these effects were inhibited by KT5823 and the phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 and Wortmannin. Our data suggest that the NO/cGMP pathway suppresses 6-OHDA-induced PC12 cell apoptosis by suppressing the mitochondrial apoptosis signal via PKG/PI3K/Akt-dependent Bad phosphorylation.

Nitric oxide at a low concentration protects murine macrophage RAW264 cells against nitric oxide-induced death via cGMP signaling pathway

1. We investigated the cytoprotective effect of low-dose nitric oxide (NO) on NO-induced cell death in mouse macrophage-like cell line RAW264. 2. Sodium nitroprusside (SNP), an NO donor, at a high concentration (4 mM) released cytochrome c from mitochondria and induced death in RAW264 cells. Acetyl-L-aspartyl-L-glutamyl-L-valyl-L-aspart-1-al (Ac-DEVD-CHO, 100-200 microM), a caspase-3 inhibitor, attenuated the SNP-induced cell death in a concentration-dependent manner. 3. Pretreatment with 100 microM SNP for 24 h, which had no effect on cell viability, attenuated the cell death and reduced cytochrome c release from mitochondria to the cytosol induced by 4 mM SNP. 4. LY83583 (1-3 microM) and 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ, 30-100 microM), soluble guanylate cyclase inhibitors, negated the protective effect of the 100 microM SNP pretreatment. 5. Pretreatment with 1 mM dibutylyl guanosine-3',5'-cyclic monophosphate (DBcGMP), a cell-permeable guanosine-3',5'-cyclic monophosphate (cGMP) analogue, for 24 h inhibited both cytochrome c release and cell death induced by SNP. 6. Protein kinase G inhibitor KT5823 (10 microM) significantly reduced the cytoprotective effects of low-dose SNP and DBcGMP. 7. These results indicate that low-dose NO protects RAW264 cells from NO-induced apoptosis through cGMP production and activation of protein kinase G.