Hepatocyte inducible nitric oxide synthesis is influenced in vitro by cell density

Effect of matrine on primary human hepatocytes in vitro

Matrine is a bioactive component of the traditional Chinese medical herb Sophora flavescens that has been used in China to treat various kinds of diseases including virus hepatitis. However, the molecular mechanisms underlying its hepatoprotective effects remains elusive. In the present study, primary human hepatocytes were employed to elucidate the protective effects and molecular mechanisms of matrine. We observed that low concentrations of matrine had no significant impact on albumin secretion, but high concentrations (>140 mg/L) of matrine decreased the albumin secretion in hepatocytes. Western blot data indicated that matrine at 140 mg/L at 72 h induced protein expression of CYP2A6, CYP2B6 and CYP3A4. Furthermore, high concentrations of matrine reduced LDH and AST levels and were cytotoxic to hepatocytes, leading to a decreased cell viability and total protein amount. Moreover, low concentrations of matrine, enhanced the ECOD activity and decreased the level of NO2 (-) induced by cytokines in human hepatocytes. Taken together, the present study sheds novel light on the molecular mechanisms of matrine and potential application of matrine in hepatic diseases.

The protective role of HO-1 and its generated products (CO, bilirubin, and Fe) in ethanol-induced human hepatocyte damage

It has been reported that naturally occurring quercetin exerts hepatoprotective effects through heme oxygenase-1 (HO-1) induction. However, the precise mechanism of how ethanol-associated liver damage is counteracted by quercetin-enhanced HO-1 metabolism still remains unclear. To further decipher the protective role of quercetin on ethanol-induced liver damage, we treated human hepatocytes with quercetin and various (end) products of the HO-1 pathway. Our data clearly showed that quercetin treatment attenuated ethanol-induced damage, whereas hemoglobin and zinc protoporphyrin 9 (ZnPP) abolished such effects. Iron-II aggravated ethanol toxicity and was only partially reduced by quercetin. In contrast, carbon monoxide (CO) dose dependently inhibited ethanol-induced cytochrome P450 2E1 (CYP 2E1) activity and hepatotoxicity but had no influence on CYP 2E1 protein expression. Similarly, hemoglobin dramatically stimulated CYP 2E1 activity but not the protein expression in quercetin- and ethanol-cotreated hepatocytes. ZnPP significantly promoted CYP 2E1 protein expression in the presence and absence of CO treatment but inhibited ethanol-induced CYP 2E1 activation following CO incubation in quercetin- and ethanol-cotreated hepatocytes. These results suggested that quercetin virtually attenuated ethanol-derived oxidative damage via HO-1 induction. Heme degradation and CO release may mediate the protective effects through inhibiting ethanol-induced CYP 2E1 synthesis and enzymatic activity, respectively.

Quercetin protects human hepatocytes from ethanol-derived oxidative stress by inducing heme oxygenase-1 via the MAPK/Nrf2 pathways

BACKGROUND/AIMS

Flavonoids, including quercetin, have been reported to have potent hepatoprotective effects, which may be associated with HO-1 induction. However, since the effect and signaling pathway of quercetin involved in HO-1 induction against alcoholic liver damage are still not fully understood, this is the target of the present study.

METHODS

Human hepatocytes were incubated with ethanol (100 mM) and quercetin (10-200 microM), and cellular damage and HO-1 activity were measured. Nrf2 expression in cytosolic and nuclear fractions was studied following the incubation with MAPK inhibitor(s).

RESULTS

Ethanol exposure resulted in a sustained glutathione depletion, malondialdehyde elevation, and evident release of cellular LDH and AST. Quercetin exerted a dose-dependent protective effect against alcoholic oxidative stress, and increased the EC50 of ethanol by approx. 40%, which is parallel to HO-1 induction with quercetin. Zinc protoporphyrin-9 abrogated the protective effect and dramatically enhanced ethanol cytotoxicity. SB203580 (p38 inhibitor) and especially PD98059 (ERK inhibitor) blocked quercetin-derived HO-1 induction and Nrf2 translocation, and subsequently inhibited the quercetin-related protection.

CONCLUSIONS

HO-1 up-regulation by quercetin protected human hepatocytes from ethanol-induced oxidative stress. Among MAPK signaling pathways, p38 and ERK mediated quercetin-derived Nrf2 translocation into nuclei and subsequent induction of HO-1 activity, and the latter showed a stronger mediating effect.

Human hepatocytes are protected from ethanol-induced cytotoxicity by DADS via CYP2E1 inhibition

We investigated the protective effects of diallyl disulfide (DADS), a potent inhibitor of cytochrome P450 2E1 (CYP2E1), on ethanol-induced toxicity in human hepatocytes. We found a clear dose-dependent response between ethanol and CYP2E1 activity. The ethanol-dependent CYP2E1 enzyme activity and protein expression, lactate dehydrogenase and aspartate transaminase release, malondialdehyde formation and caspase-3 activity decreased dramatically in the presence of DADS. Furthermore, DADS increased the hepatocellular glutathione (GSH) content and prevented the ethanol-dependent cellular GSH depletion. Our data show that DADS reduces ethanol-induced toxicity in human hepatocytes by reducing CYP2E1 activity and/or stabilizing the cellular GSH content, which might be of therapeutic interest.

Modulation of macrophage nitric oxide production by prostaglandin D2

BACKGROUND

Nitric oxide and prostaglandins readily become activated in response to inflammatory events. The overproduction of nitric oxide is detrimental to the host. The present study was conducted to examine whether prostaglandin D(2) (PGD(2)) modulates nitric oxide production in macrophages in response to an inflammatory stimulus.

METHODS

Cultures of RAW 264.7 murine macrophages were exposed to Escherichia coli lipopolysaccharide (LPS, 0.01 and 1.0 microg/ml) before and after exposure to PGD(2) (0.01 to 10 nmol). After 24-h incubation, supernatants were collected and nitrite was quantitated by Greiss reaction as a measure of nitric oxide synthesis. Inducible nitric oxide synthase (iNOS) protein was measured by Western blot analysis.

RESULTS

Macrophages exposed to 0.01 and 1.0 microg/ml LPS produced 8.3 +/- 0.2 and 15.0 +/- 1.4 nmol/1.1 x 10(6) cells/24 h of nitrite, respectively. The simultaneous addition of PGD(2) with LPS inhibited nitrite production in a dose-dependent fashion and suppressed iNOS protein expression. A strong time effect was also exhibited when macrophages were incubated with PGD(2) 1 hour before as compared to 7 hours after the addition of LPS (0.01 or 1.0 microg/ml), indicating that the earlier the time PGD(2) was added to the culture media, the greater the inhibition. Prostaglandin D(2) had the capacity to block nitrite synthesis even when added as much as 7 hours after an LPS challenge. Blocking endogenous prostaglandins, using indomethacin (10 microM), suppressed nitrite production.

CONCLUSION

Exogenous PGD(2) caused dose- and time-dependent decreases in LPS-stimulated nitrite production by RAW 264.7 macrophages by hindering iNOS protein expression. Conversely, the endogenous prostaglandins released by these same cells in response to an LPS challenge stimulated nitrite production, which may consequently dampen the inhibitory actions of exogenous PGD(2).

CYP2E1-dependent hepatotoxicity and oxidative damage after ethanol administration in human primary hepatocytes

AIM: To observe the relationship between ethanol-induced oxidative damage in human primary cultured hepatocytes and cytochrome P450 2E1 (CYP2E1) activity, in order to address if inhibition of CYP2E1 could attenuate ethanol-induced cellular damage.

METHODS: The dose-dependent (25-100 mmol/L) and time-dependent (0-24 h) exposures of primary human cultured hepatocytes to ethanol were carried out. CYP2E1 activity and protein expression were detected by spectrophotometer and Western blot analysis respectively. Hepatotoxicity was investigated by determination of lactate dehydrogenase (LDH) and aspartate transaminase (AST) level in hepatocyte culture supernatants, as well as the intracellular formation of malondialdehyde (MDA).

RESULTS: A dose-and time-dependent response between ethanol exposure and CYP2E1 activity in human hepatocytes was demonstrated. Moreover, there was a time-dependent increase of CYP2E1 protein after 100 mmol/L ethanol exposure. Meanwhile, ethanol exposure of hepatocytes caused a time-dependent increase of cellular MDA level, LDH, and AST activities in supernatants. Furthermore, the inhibitor of CYP2E1, diallyl sulfide (DAS) could partly attenuate the increases of MDA, LDH, and AST in human hepatocytes.

CONCLUSION: A positive relationship between ethanol-induced oxidative damage in human primary cultured hepatocytes and CYP2E1 activity was exhibited, and the inhibition of CYP2E1 could partly attenuate ethanol-induced oxidative damage.

Human monocyte-derived neohepatocytes: a promising alternative to primary human hepatocytes for autologous cell therapy

BACKGROUND

There is growing interest in new therapeutic options for the treatment of end-stage liver diseases. In addition to mechanical devices supporting liver function, such as bioreactors, the transplantation of hepatocyte-like cells derived from (adult) stem cells offer great perspectives. We have generated hepatocyte-like (NeoHep) cells from terminally differentiated peripheral blood monocytes and, in this study, have evaluated these cells as a possible tool for autologous cell therapy.

METHODS

Peripheral blood monocytes were cultured under conditions that promote hepatocyte-like differentiation and were characterized for hepatocyte marker expression by reverse-transcriptase polymerase chain reaction, immunohistochemistry, and immunoblotting and for specific secretory and metabolic functions with the appropriate biochemical assays.

RESULTS

NeoHep cells resembled primary human hepatocytes with respect to morphology, expression of hepatocyte markers (albumin, cytochrome P450 isoenzymes, asialoglycoprotein receptor, coagulation factor VII), various secretory and metabolic functions (albumin secretion, urea production, lactate formation, and lactate dehydrogenase and aspartate transaminase release), and drug detoxification activities (phase I metabolization of ethoxycoumarin into 7OH-coumarin after stimulation with 3-methylcholanthren, induction of CYP3A4 activity, and phase II metabolization through UDP-glucuronidation of 4-methyl-umbelliferone).

CONCLUSIONS

These data convincingly show that NeoHep cells display a phenotype and specific in vitro metabolic functions that are quantitatively and qualitatively comparable in part with those of primary human hepatocytes. These cells could thus be clinically applied in an autologous setting for the treatment of end-stage liver diseases or for improving liver function in patients who have undergone critical liver-mass resection.

Effects of phenobarbital on metabolism and toxicity of diclofenac sodium in rat hepatocytes in vitro

Diclofenac sodium (DF-Na) was a nonsteroidal anti-inflammatory drug used in various aspects of inflammatory disease. The purpose of this study was to examine the effects of phenobarbital (PB) on metabolism and toxicity of DF-Na in vitro and explore the potential mechanism of DF-Na induced hepatotoxicity. Rat hepatocytes were isolated by a modification of the two-step in situ collagenase perfusion technique and the harvested rat hepatocytes were cultured with sandwich method. Control or PB (2 mM) pre-treated hepatocytes were incubated with DF-Na (0.1, 0.05 or 0.01 mM) in vitro and cytosolic enzyme leakage levels, cytochrome P450 (CYP) 3A activity, and metabolite content of DF-Na in cell culture medium were measured. The results showed that without any treatment hepatocyte CYP 3A activity gradually decreased with culture time. On day four, CYP 3A activity was 53% of the initial value. The decline of CYP 3A was partially reversed by CYP inducer PB, and the maximum induction of CYP 3A was 2.2-fold over control after continuous exposure of hepatocytes to 2 mM PB for 48 h. Lactic dehydrogenase (LDH), aspartate transaminase (AST), and alanine transamine (ALT) activity and the contents of the DF-Na metabolites 4'-hydroxydiclofenac (4'-OH-DF) and 5-hydroxydiclofenac (5-OH-DF) in media appeared to increase with increasing DF-Na concentrations, though there were no significant differences between DF-Na exposed and control hepatocytes. However, if the hepatocytes first were pre-treated with 2 mM PB for 2 days and then exposed to DF-Na, the concentrations of DF-Na metabolites and the activity of LDH in the media were significantly higher than that of control group. These findings suggest that the hepatotoxicity and metabolism of DF-Na in rat hepatocytes are increased when hepatic CYP 3A activity is increased.

Steroid administration before partial hepatectomy with temporary inflow occlusion does not influence cyclin D1 and Ki-67 related liver regeneration

BACKGROUND AND AIMS

If temporary inflow occlusion is required during liver resection, the postoperative course might be complicated by ischaemia-reperfusion injury. Steroids protect against ischaemia-reperfusion injury; however, due to its anti-proliferative character concerns exist on its use on liver regeneration after resection. We investigated the effects of methylprednisolone on hepatocyte proliferation after partial hepatectomy with temporary inflow occlusion.

PATIENTS AND METHODS

Prior to surgery, one group of Wistar rats received methylprednisolone, while a second group served as non-treated controls. Ischaemia-reperfusion injury was indicated by AST, ALT, and GLDH at 6 h after surgery. Immunohistochemistry tools were used to determine the mitotic index and Ki-67 expression, while cyclin D1 expression characterized the proliferative activity on days 1, 4, 7, and 10.

RESULTS

The post-ischaemic liver enzyme release had significantly decreased in the methylprednisolone group, while expression of cyclin D1, percentage of Ki-67-positive cells, and mitotic cell index were comparable in both groups. Similar results were found for bilirubin and albumin and for weight of proliferating liver.

CONCLUSION

Although steroid administration significantly reduced ischaemia-reperfusion-associated tissue injury, it has no apparent effects on hepatic regeneration. Thus, steroids could be recommended if a temporary liver ischaemia is required during surgery, in order to reduce complications caused by severe ischaemia-related organ dysfunction.

Ischemic preconditioning and methylprednisolone both equally reduce hepatic ischemia/reperfusion injury

BACKGROUND

Ischemic preconditioning (I/P) and methylprednisolone (MP) have been suggested to protect against ischemia-reperfusion (IR) injury, which results in an increased tolerance against organ hypoxia.

METHODS

Before 45 minutes of hepatic ischemia, male Wistar rats were pretreated with either I/P (5/30 minutes) or MP (30 mg/kg BW). The degree of IR injury and the postischemic inflammatory (leukocyte infiltration, myeloperoxidase, intercellular adhesion molecule-1) and apoptotic (TUNEL, caspase 3, cytochrome C) activity was measured in both groups and compared with non-pretreated (ischemic) animals.

RESULTS

Histology and enzyme release revealed that I/P and MP treatment provided significant protection as compared with ischemic controls. TUNEL-positive cells, as well as caspase 3 and cytochrome C expression, were clearly reduced in hepatic tissue of MP-treated animals and partially reduced in I/P-treated animals when compared with ischemic animals. The inflammatory response was considerably reduced in MP- and I/P-treated animals, especially in the early period after ischemia. NF-kappaB/Rel-binding activity was increased after I/P and decreased in MP-treated animals, whereas ischemic controls showed a constant binding activity.

CONCLUSIONS

MP (probably by downregulation of NF-kappaB-binding activity) and I/P attenuated the postischemic apoptotic and inflammatory response. Both treatments equally reduced IR-related hepatocellular damage, and, thus, may also be applied equally in surgery involving warm organ hypoxia.

Induction of Apoptosis Following Blunt Chest Trauma

The cause for the high morbidity of blunt chest trauma is not fully understood. It is still unclear if and to what extent a second insult, e.g., apoptotic tissue damage initiated by the primary insult itself, may contribute to the development of serious complications. This study was done to elucidate whether a pulmonary contusion may induce programmed cell death. Sixty-four Wistar rats were evenly randomized to eight experimental groups: four sets were subjected to a standardized blast wave injury and sacrificed 6, 24, 48, and 72 h after the trauma; four groups served as controls for the same time points. Lung and liver samples were stained (H & E; TUNEL), and PMN infiltration was determined by myeloperoxidase (MPO) activity. Caspase 8 was analyzed by Western blot, and TNF-alpha plasma levels by ELISA. Postmortem examination revealed bilateral pulmonary contusion in trauma animals with higher (P < 0.05) numbers of apoptotic cells in lung but not in liver tissue as early as 6 h after the injury. This amount gradually increased and reached a maximum after 48 h: 6.8 +/- 1.1 apoptotic cells/hpf vs. 0.6 +/- 0.06 in controls. Chest trauma caused an increased expression of active caspase 8 in lung but not in liver tissue at 48 and 72 h. TNF-alpha plasma levels were not different. MPO activity in lung tissue of trauma animals increased (P < 0.05) after 6 h and peaked at 72 h. This study has provided the first evidence that apoptotic cell death in lung tissue is initiated following (experimental) pulmonary contusion. The exact mechanism remains, however, unclear and has to be elucidated further.

Cell density-enhanced expression of inducible nitric oxide synthase in murine macrophages mediated by interferon-beta

Nitric oxide (NO) has an important cytotoxic role in host defense processes against invading microorganisms and neoplastic cells. Here we demonstrate the effect of culture density on the expression of NO synthase and NO production by lipopolysaccharide (LPS)-activated RAW 264.7 macrophages. At high cell densities, the LPS-induced expression of iNOS message, protein, and activity is markedly enhanced. We demonstrate the effects to be mediated by a diffusible macrophage product. Increasing cell density correlates with activation of IFN-dependent signaling pathways. We observe enhanced phosphorylation of STAT-1 on tyrosine 701 and serine 727, and an increase in STAT-1 DNA binding. Expression of the IFN-stimulated transcription factor IRF-1 is also enhanced. The data are consistent with the reported involvement of IFN-beta as an autocrine co-activator of iNOS expression. Considering the importance of NO as a cytotoxic mediator of host immunity, the data suggest that macrophage density is important in regulating the magnitude of NO production, and thus, the host response to infection.

Effects of hepatocellular iron imbalance on nitric oxide and reactive oxygen intermediates production in a model of sepsis

BACKGROUND/AIMS

In mammals iron homeostasis is most important, as imbalance of iron such as iron overload may lead to severe diseases. Recently, it has been shown that the iron regulatory protein-1 is partially controlled by nitric oxide and reactive oxygen intermediates, molecules frequently seen in inflammatory events. The aim of the present study was to investigate the effects of impaired iron homeostasis on the interaction of nitric oxide, and reactive oxygen intermediate formation in hepatocytes in a model of acute inflammation.

METHODS

Hepatocytes isolated from Corynebacterium parvum (C parvum)-injected rats were used to examine the formation of nitrogen and oxygen intermediates by iron deprivation and iron overload in the presence of lipopolysaccharide. In addition, we investigated the RNA binding and aconitase activity of iron regulatory protein-1.

RESULTS

In the present study we show that iron overload in lipopolysaccharide-treated C. parvum-primed hepatocytes downregulated the RNA binding of iron regulatory protein-1 and aconitase activity. Subsequently, we observed a reduced formation of nitrite/nitrate and S-nitrosothiols but an increased production of reactive oxygen species, and hepatocellular damage. Moreover, the addition of iron to cell cultures caused a further increase in cellular damage, a drop in the cellular glutathione pool, and an increase in peroxynitrite and hydroxyl-like radicals. In contrast, addition of deferoxamine (an iron chelator) to lipopolysaccharide-treated C. parvum-primed hepatocytes protected cells by stabilizing the GSH content, maintaining the nitric oxide formation, and by reducing Fenton oxidants.

CONCLUSIONS

Our results show that the antioxidative effects of iron chelators prevent the formation of toxic Fenton oxidants in severe inflammatory events, which should be considered in the treatment of disorders characterized by an iron imbalance.

Oxygen regulation of rat hepatocyte iNOS gene expression

BACKGROUND/AIMS

The human iNOS promoter contains a consensus sequence for binding the hypoxia inducible factor. The aim of this study was to see whether iNOS gene expression is triggered by oxygen tension in rat hepatocytes exposed in vivo to high (periportal) and low (perivenous) oxygen tension.

METHODS

Hepatocytes transfected or not with a plasmid containing rat iNOS promoter linked to chloramphenicol acetyltransferase were cultured at 21% and 5% oxygen tension. In normal hepatocytes, iNOS protein, mRNA and activity were detected. In transfected cells, chloramphenicol acetyltransferase activity was measured.

RESULTS

In cells cultured in a hypoxic environment, both iNOS protein and mRNA increased, whereas the nitrite level in the medium decreased. However, electron paramagnetic resonance analysis and in vitro iNOS activity indicated that iNOS was active. Transfection experiments showed that the expression of chloramphenicol acetyltransferase driven by iNOS promoter was increased in cells maintained at low oxygen tension.

CONCLUSIONS

Our experiments show that in rat hepatocytes: 1) iNOS is induced by low oxygen tension; 2) the modification occurs at the transcriptional level; 3) the enzyme at 5% oxygen is able to catalyze the synthesis of NO, although no nitrites are accumulated in the medium. These findings could have physiopathological relevance, e.g. in determining the resistance of perivenous hepatocytes to ischemia injury.

A non-nucleotide-bridged DNA decoy inhibits renal epithelial nitric oxide synthase expression

A non-nucleotide-bridged DNA decoy inhibits renal epithelial nitric oxide synthase expression.

BACKGROUND

The expression of inducible nitric oxide synthase (iNOS) is subject to strict tissue-specific transcriptional control. In mouse renal epithelium, an interferon-gamma (IFN-gamma)-induced signaling protein, IFN-gamma regulatory factor 1 (IRF-1), appears to mediate the induction of iNOS expression by cytokines and bacterial lipopolysaccharide (LPS).

METHODS

We used a novel technique, namely, blockade of cytosolic IRF-1 activity with a triethyleneglycol-bridged decoy DNA oligonucleotide (ODN) containing the IRF-1 consensus binding sequences present in the iNOS promoter to inhibit iNOS gene expression. Cultured mouse renal epithelial cells were treated with a combination of LPS (1 microg/mL) and IFN (100 U/mL) in the absence or presence of IRF-1 decoy ODN followed by determinations of NO production and iNOS protein and mRNA expression.

RESULTS

Treatment with IRF-1 decoy ODN resulted in concentration-dependent inhibition of NO production and a marked reduction in iNOS protein and mRNA levels. A scrambled ODN failed to affect LPS/IFN-stimulated NO production or iNOS protein and mRNA levels. Transcriptional assays showed that the IRF-1 decoy ODN inhibited transcriptional activity of an iNOS promoter-CAT gene construct.

CONCLUSIONS

Decoy ODN-based techniques effectively inhibit iNOS expression in renal epithelium and represent a potentially useful approach for selective blockade of this enzyme in pathologic conditions associated with excessive NO production.

Isolation and characterization of a human hepatic epithelial-like cell line (AKN-1) from a normal liver

The isolation and characterization of human liver cell lines are rather difficult due to limited material and poor growth in cell culture. In this report, we present the isolation, culture and characterization of a new epithelial-like liver cell line (AKN-1) with a heterogeneous cell population and many characteristics of the biliary epithelium. The AKN-1 cell line stained positively with antibodies to epithelial cytokeratin polypetides CK 8, 18, and 19. In addition, the cell line expressed the anti-human epithelial-related antigen (MOC-31), the human epithelial antigen (HEA), and the gamma-glutamyl transpeptidase, the hematopoietic growth factor, stem cell factor, and also its receptor, c-kit. The cell line failed to express albumin and factor 8 by immunohistochemistry. It did show, however, a twofold increase in 7-ethoxyresorufin-O-deethylase activity. Cytogenetic characterization revealed rare breakpoints in chromosome 2, which to our knowledge, have not yet been reported in liver cells.

pH-dependent changes of nitric oxide, peroxynitrite, and reactive oxygen species in hepatocellular damage

Low arterial blood pH and sustained nitric oxide (NO) production are critical parameters in inflammatory events such as sepsis, and appropriate treatment is still under debate. Because the stability of nitrogen and oxygen intermediates is dependent on the surrounding pH, we investigated whether the relationship among NO, peroxynitrite (ONOO-), and reactive oxygen species production also depends on the pH value, particularly with respect to their effects on hepatocellular damage. Our studies demonstrate that the extracellular pH influences NO and hydroxyl radical (OH) production in hepatocytes. Acidification (pH 7.0) of the medium revealed a significant increase (P < 0.05) of OH-like radicals, enhanced hepatocellular damage, and a sharp drop in cellular glutathione (GSH) content compared with levels measured at physiological or alkaline pH conditions. Furthermore, inhibition of NO synthesis at all pH conditions resulted in decreased NO production and cellular GSH levels but a simultaneous increase of OH-like radicals and hepatocellular damage with a maximum seen at pH 7.0. Our results suggest that hepatocellular damage is in part regulated by the surrounding pH and that inhibition of NO synthesis at acidic conditions (e.g., in sepsis) leads to increased reactive oxygen-mediated cell injury.

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

Nitric oxide (NO) and tumor necrosis factor-alpha (TNFalpha) play important roles in the pathogenesis of liver disease during acute inflammation. The present study was designed to elucidate the effect of NO pre-exposure on TNFalpha-induced hepatotoxicity. Pretreatment of primary cultures of rat hepatocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced the expression of heat shock protein 70 (HSP70) mRNA and protein, which was associated with thermotolerance and cytoprotection from TNFalpha+actinomycin D-induced hepatotoxicity and apoptosis. SNAP transiently changed the intracellular redox state by inducing glutathione (GSH) oxidation associated with the formation of S-nitrosoglutathione (GSNO). HSP70 mRNA was also induced by the GSH-oxidizing agent diamide and the GSH-conjugating agent N-ethylmaleimide, suggesting that NO induces HSP70 expression through GSH oxidation. The protective effect of SNAP pretreatment on TNFalpha-induced apoptosis correlated with the level of HSP70 expression. SNAP pretreatment inhibited reactive oxygen intermediate generation and lipid peroxidation effects that were reversed by blocking HSP70 expression using an antisense oligonucleotide to HSP70. Finally, endogenous NO formation, induced in hepatocytes stimulated with interferon-gamma and interleukin-1beta, led to the formation of GSNO and GSSG, induced HSP70, and attenuated TNFalpha-mediated cytotoxicity. These findings demonstrated that NO can induce resistance to TNFalpha-induced hepatotoxicity, possibly through the stimulation of HSP70 expression.

Metallothionein and HSP-72 are induced in the liver by hemorrhagic shock and resuscitation but not by shock alone

BACKGROUND

Previous reports have indicated that HSP-72 and metallothionein mRNA undergo induction in the liver after resuscitated hemorrhagic shock. In this study we investigated whether unresuscitated shock triggers induction and whether protein induction also occurs.

METHODS

Rats were subjected to resuscitated and unresuscitated shock protocols of varying severity; livers were isolated and processed for Northern, Western, and immunohistochemical analysis. Cadmium binding assay was used to measure metallothionein protein.

RESULTS

Unresuscitated shock led to no induction of HSP-72 or metallothionein. Severe resuscitated shock led to prompt induction of HSP-72 mRNA and protein in hepatocytes, up to 20-fold over sham group; metallothionein mRNA induction appeared later than HSP-72 and did not lead to elevated protein levels. Mild resuscitated shock had little effect.

CONCLUSIONS

These findings indicate resuscitated severe shock, not shock alone, leads to induction of HSP-72 and metallothionein in the liver. Metallothionein expression lags behind HSP-72 expression.

Effect of multiple cytokines plus bacterial endotoxin on glucose and nitric oxide production by cultured hepatocytes

Treatment of cultured hepatocytes with a combination of cytokines, including tumour necrosis factor-alpha, interferon-gamma and interleukin-1 beta, plus lipopolysaccharide resulted in a time-dependent induction of nitric oxide (NO) synthase (as measured by NO2- (+) NO3- production) and inhibition of hepatic gluconeogenesis and glycogen breakdown. The inhibition of glucose release was comparable with the observed following treatment of rats with lipopolysaccharide or treatment of isolated hepatocytes with artificial NO donors. In addition, this effect was also evident with all substrates tested that enter the gluconeogenic pathway below the level of phosphoenolpyruvate carboxykinase, suggesting that this combination of cytokines may underlie the inhibition of gluconeogenesis observed in endotoxic shock. The maximal inhibition of glucose output required the presence of all the cytokines plus lipopolysaccharide, whereas the induction of NO synthase was independent of the lipopolysaccharide when the cytokines were employed. Inclusion of interferon-gamma was essential to obtain a maximal response for either parameter. Inclusion of 1 mM N(G)-monomethyl-L-arginine in the incubation abolished the increase in NO2- (+) NO3- observed with the complete cytokine mixture and various combinations; however, it failed to prevent the inhibition in glucose output, indicating that mechanisms other than NO underlie the cytokine-induced inhibition of glucose release.

Inducible nitric oxide synthase expression in cerebrovascular smooth muscle and neutrophils after traumatic brain injury in immature rats

The inflammatory response after traumatic brain injury (TBI) includes cytokine production, leukocyte infiltration, and microglial activation. Production of nitric oxide by inducible nitric oxide synthase (iNOS) occurs during acute inflammation outside of the CNS and in models of cerebral ischemia, and therefore may contribute to the inflammatory response after TBI. The purpose of this study was to localize and define the time course of iNOS expression after TBI in the immature rat. Immature Wistar rats (age 3.5-4.5 wk) were anesthetized and subjected to percussive trauma to the right parietal cortex. Nontraumatized rats were used as controls (n = 7). At 2, 24, 48, or 168 h (n = 3/group) posttrauma rats were killed by perfusion fixation. Brains were removed, frozen, sectioned, immunostained with antibodies against iNOS and glial fibrillary acidic protein (GFAP, a marker specific for astrocytes), and imaged using fluorescent detection systems. There was no detectable expression of iNOS in control brains. At 2h, minimal cerebrovascular iNOS expression was seen in the peritrauma area. At 24 and 48 h, there was marked peritrauma cerebrovascular iNOS expression that appeared to be restricted to vascular smooth muscle cells and infiltrated leukocytes. Further dual-immunolabeling showed that the leukocytes expressing iNOS were predominantly neutrophils. At 168 h, iNOS expression was no longer detectable. iNOS was not detectable in GFAP-positive cells. The prominent expression of iNOS protein after TBI in cerebrovascular smooth muscle cells and infiltrated neutrophils suggests that iNOS may play a role in cerebrovascular disturbances and secondary brain injury after trauma.

NF-kappa B and transcriptional control of renal epithelial-inducible nitric oxide synthase

Expression of the inducible isoform of nitric oxide synthase (iNOS) is subject to strict tissue specific transcriptional control. Recently, the NF-kappa B/Rel family of transcription factors, and particularly c-rel, was shown to mediate bacterial lipopolysaccharide (LPS) induction of iNOS in macrophages. Since LPS is only a weak inducer of iNOS in most nonimmune cells, we investigated the role of NF-kappa B in the regulation of iNOS expression in mouse renal epithelial cells. We report that LPS activates NF-kappa B in renal epithelium, but that this is not sufficient for induction of iNOS activity. The NF-kappa B complexes activated by LPS in renal epithelium differ from those in macrophages in that they lack c-rel, which may explain the absence of iNOS induction in renal epithelium. Conversely, LPS and interferon-gamma (IFN) synergize to induce renal epithelial iNOS. Functional iNOS promoter analysis indicate that this synergistic induction requires NF-kappa B. We conclude that NF-kappa B is necessary but not sufficient for the induction of renal epithelial iNOS expression, and that in contrast to macrophages, c-rel does not appear to play a major role in the regulation of renal epithelial iNOS.

Nitric oxide in the liver: physiopathological roles

Many of the known roles of arginine (e.g. in immune function, wound healing, and protection against ammonia intoxication) are mediated by a metabolic pathway synthesising nitric oxide (NO) in the liver. Contrary to some of the current views, liver-produced NO may be basically beneficial, as it exerts both protective actions against tissue injury and cytotoxic effects on invading microorganisms, parasites, or tumor cells. An ongoing equilibrium between NO and other NO-reactive compounds (e.g. O2 and non-heme iron-sulphur-containing moieties) appears to be important in this respect, even under critical conditions. Thus, NO may prevent liver tissue harm from oxidant stress. Only when this putative counterbalance is upset by an uncontrolled, prolonged and/or massive production of NO, liver tissue damage may occur leading to hepatic inflammation or even tumor development. Moreover, the currently available data support the working hypothesis that hepatocytes partake not only to immunoregulatory processes, but even to immune defence mechanisms. Thus, the liver constitutes an excellent model for investigations into the crosstalks regulating the production of NO which take place among not only the various networks operating inside a single hepatic cell, but even the individual types of liver cells.