Multiple cytokines are required to induce hepatocyte nitric oxide production and inhibit total protein synthesis

Hepatocellular oxidative DNA injury induced by macrophage-derived nitric oxide

Previous studies have indicated that splenic macrophages migrate into the liver and play a role in endotoxin-induced hepatic damage. The present study was designed to elucidate the mechanisms of hepatocyte injury induced by activated splenic macrophages, focusing especially on endogenously released NO and oxidative DNA alterations in hepatocytes. Splenic macrophages isolated from Wistar rats were incubated with either lipopolysaccharide (LPS) or interferon-gamma (IFN-gamma) and cocultured with hepatocytes. Nitrite and nitrate levels in the culture medium were measured, and inducible-type NO synthase (iNOS) and nitrotyrosine were determined by immunofluorescence staining. The ratio of 8-hydroxy-deoxyguanosine (8-OH-dG) to deoxyguanosine (dG) was measured by high-performance liquid chromatography, and single-stranded DNA in hepatocytes was detected with acridine orange. NO release and nitrotyrosine expression in hepatocytes increased after 8 h of coculture with activated macrophages, and this coculture also induced increases in the 8-OH-dG/dG ratio and single-stranded DNA in the hepatocytes. These alterations were attenuated by superoxide dismutase (SOD) and NO synthesis inhibitors. A similar pattern of alterations was observed in hepatocytes incubated with SIN-1, and these changes were also prevented by SOD. These results suggest that activated macrophage-derived NO and its oxidative metabolite, peroxynitrite, play key roles in hepatocyte injury during inflammation, and cause subsequent DNA damage in surviving hepatocytes.

Prooxidant and antioxidant functions of nitric oxide in liver toxicity

In response to tissue damage and inflammation induced by a variety of xenobiotics including acetaminophen, carbon tetrachloride, ethanol, galactosamine, and endotoxin, as well as disease states such as viral hepatitis, and postischemic and regenerative injury, the liver produces large quantities of nitric oxide. Indeed, nearly all cell types in the liver including hepatocytes, Kupffer cells, stellate cells, and endothelial cells have the capacity to generate nitric oxide. Thus, these cells, as well as infiltrating leukocytes, may indirectly augment tissue injury. In many models of liver damage, nitric oxide and its oxidation products such as peroxynitrite contribute to the injury process by directly damaging the tissue or by initiating additional immunologic reactions that result in damage. In some models, nitric oxide donors or peroxynitrite can mimic the cytotoxic actions of liver toxins. Moreover, agents that prevent the generation of nitric oxide or antioxidants that bind reactive nitrogen intermediates, or knockout mice with reduced capacity to produce nitric oxide, are protected from xenobiotic-induced tissue injury. In contrast, there have been reports that blocking nitric oxide production enhances xenobiotic-induced tissue injury. This has led to the concept that nitric oxide either inactivates proteins critical for xenobiotic-induced tissue injury or acts as an antioxidant, reducing cellular levels of cytotoxic reactive oxygen intermediates. Whether or not nitric oxide or secondary oxidants generated from nitric oxide act as mediators of tissue injury or protect against toxicity is likely to depend on the precise targets of these reactive nitrogen intermediates, as well as levels of superoxide anion present and the extent to which tissue injury is mediated by reactive oxygen intermediates. In addition, as toxicity is a complex process involving a variety of cell types and many soluble mediators, the contribution of each of these factors must be taken into account when considering the role of nitric oxide as a determinant of tissue injury.

Inducible nitric oxide synthase is critical for immune-mediated liver injury in mice

Concanavalin A (Con A) causes severe TNF-alpha-mediated and IFN-gamma-mediated liver injury in mice. In addition to their other functions, TNF-alpha and IFN-gamma both induce the inducible nitric oxide (NO) synthase (iNOS). Using different models of liver injury, NO was found to either mediate or prevent liver damage. To further elucidate the relevance of NO for liver damage we investigated the role of iNOS-derived NO in the Con A model. We report that iNOS mRNA was induced in livers of Con A-treated mice within 2 hours, with iNOS protein becoming detectable in hepatocytes as well as in Kupffer cells within 4 hours. iNOS-/- mice were protected from liver damage after Con A treatment, as well as in another TNF-alpha-mediated model that is inducible by LPS in D-galactosamine-sensitized (GalN-sensitized) mice. iNOS-deficient mice were not protected after direct administration of recombinant TNF-alpha to GalN-treated mice. Accordingly, pretreatment of wild-type mice with a potent and specific inhibitor of iNOS significantly reduced transaminase release after Con A or GalN/LPS, but not after GalN/TNF-alpha treatment. Furthermore, the amount of plasma TNF-alpha and of intrahepatic TNF-alpha mRNA and protein was significantly reduced in iNOS-/- mice. Our results demonstrate that iNOS-derived NO regulates proinflammatory genes in vivo, thereby contributing to inflammatory liver injury in mice by stimulation of TNF-alpha production.

Animal models of hepadnavirus-associated hepatocellular carcinoma

Animal models of hepatitis B virus infection have been valuable for determining the mechanisms of hepadnavirus replication, for studies of pathogenesis, and for investigations of viral hepatocarcinogenesis. The woodchuck model also seems to be useful in the discovery and development of antiviral drugs to treat HBV infection and for testing new forms of immunotherapy. In particular, the woodchuck seems to be ideal for studying the effect of antiviral treatment and immunotherapy on the outcome of hepadnavirus infection and on survival. The median life expectancy of experimentally infected, chronic WHV carriers is approximately 29 months, and almost all develop HCC. New types of prophylaxis or therapy can be evaluated under controlled experimental conditions, in a relevant animal model, and within a reasonable time frame.

iNOS expression by activated neutrophils from patients with sepsis

BACKGROUND

Enhanced production of nitric oxide (NO) is associated with various inflammatory diseases such as sepsis. Although activated neutrophils are presumably involved in septic organ injury, the expression of inducible nitric oxide synthase (iNOS) by these cells has not been elucidated. The authors investigated whether activated neutrophils in sepsis could induce mRNA for iNOS and produce NO.

METHODS

Peripheral blood neutrophils were obtained from healthy volunteers, and septic patients underwent a surgical operation. The neutrophils of the healthy volunteers were stimulated with lipopolysaccharide (LPS) and/or tumour necrosis factor-alpha (TNF-alpha). The iNOS expression and NO production were examined by the reverse transcription-polymerase chain reaction and Griess method, respectively.

RESULTS

Circulating neutrophils obtained from patients with sepsis expressed higher levels of iNOS mRNA than those from patients with systemic inflammatory response syndrome (SIRS). Resting neutrophils from normal controls did not express iNOS mRNA and thus did not produce NO. After in vitro stimulation with LPS and TNF-alpha, the neutrophils did express iNOS mRNA and thus produce NO.

CONCLUSION

Activated neutrophils may be one source of NO production in sepsis.

Inhibition of the nitrosothiol production of cultured osteoarthritic chondrocytes by rhein, cortisol and diclofenac

OBJECTIVE

Nitric oxide (NO degrees ) is a free molecule produced by NO synthases which acts as a mediator in inflammatory processes. NO degrees can react with thiol groups of proteins to produce nitrosothiols. Increased concentrations of these bioactive compounds have been found in sera and synovial fluids from patients with osteoarthritis (OA). The aim of this study was to assess the ability of human osteoarthritic chondrocytes to synthesize nitrosothiols and to compare the in vitro effects of rhein, cortisol and diclofenac on nitrosothiol and nitrite production.

METHODS

Osteoarthritic chondrocytes were incubated for 24 h with 1 ng/ml of recombinant human interleukin-1beta (IL-1beta) in the presence or absence of rhein (1.3x10(-5) M, 6.5x10(-6) M, or 1.3x10(-6) M), cortisol (10(-5) M) or diclofenac (10(-5) M or 10(-6) M). Nitrite levels were measured in cell supernatants by the Griess method; nitrosothiol levels were determined in supernatants and cellular lysates by fluorimetry.

RESULTS

At the basal level, nitrosothiols represented 80% of the total of nitrite and nitrosothiol production. After IL-1beta stimulation, NO degrees production was highly increased in the supernatants (45-fold increase in nitrite, 60-fold increase in nitrosothiols) as well as in cell lysates (35-fold increase in nitrosothiols). Rhein caused a dose-dependent decrease in nitrosothiol and nitrite production. In comparison, diclofenac (10(-5) M) moderately decreased nitrite and nitrosothiol levels in the supernatants but had no effect on lysate nitrosothiol. Cortisol had no significant effect on NO degrees production.

CONCLUSIONS

The IL-1beta stimulation increased nitrosothiol production by osteoarthritic chondrocytes. These results demonstrate the need to measure nitrosothiol as well as nitrite production. Rhein inhibited the IL-1beta induced NO degrees production, and may be a suitable treatment for osteoarthritis.

Cytopathic hypoxia. Mitochondrial dysfunction as mechanism contributing to organ dysfunction in sepsis

Several lines of evidence support the notion that cellular energetics are deranged in sepsis, not on the basis of inadequate tissue perfusion, but rather on the basis of impaired mitochondrial respiration and/or coupling; that is, organ dysfunction in sepsis may occur on the basis of cytopathic hypoxia. If this concept is correct, then the therapeutic implications are enormous. Efforts to improve outcome in patients with sepsis by monitoring and manipulating cardiac output, systemic Do2, and regional blood flow are doomed to failure. Instead, the focus should be on developing pharmacologic strategies to restore normal mitochondrial function and cellular energetics.

Nitric oxide-dependent ribosomal RNA cleavage is associated with inhibition of ribosomal peptidyl transferase activity in ANA-1 murine macrophages

NO can regulate specific cellular functions by altering transcriptional programs and protein reactivity. With respect to global cellular processes, NO has also been demonstrated to inhibit total protein synthesis and cell proliferation. The underlying mechanisms are unknown. In a system of ANA-1 murine macrophages, iNOS expression and NO production were induced by exposure to endotoxin (LPS). In selected instances, cells were exposed to an exogenous NO donor, S-nitroso-N-acetylpenicillamine or a substrate inhibitor of NO synthesis. Cellular exposure to NO, from both endogenous and exogenous sources, was associated with a significant time-dependent decrease in total protein synthesis and cell proliferation. Gene transcription was unaltered. In parallel with decreased protein synthesis, cells exhibited a distinctive cleavage pattern of 28S and 18S rRNA that were the result of two distinct cuts in both 28S and 18S rRNA. Total levels of intact 28S rRNA, 18S rRNA, and the composite 60S ribosome were significantly decreased in the setting of cell exposure to NO. Finally, 60S ribosome-associated peptidyl transferase activity, a key enzyme for peptide chain elongation, was also significantly decreased. Our data suggest that NO-mediated cleavage of 28S and 18S rRNA results in decreased 60S ribosome associated peptidyl transferase activity and inhibition of total protein synthesis.

Nitric oxide synthesis enhances human immunodeficiency virus replication in primary human macrophages

Macrophages are suspected to play a major role in human immunodeficiency virus (HIV) infection pathogenesis, not only by their contribution to virus dissemination and persistence in the host but also through the dysregulation of immune functions. The production of NO, a highly reactive free radical, is thought to act as an important component of the host immune response in several viral infections. The aim of this study was to evaluate the effects of HIV type 1 (HIV-1) Ba-L replication on inducible nitric oxide synthase (iNOS) mRNA expression in primary cultures of human monocyte-derived macrophages (MDM) and then examine the effects of NO production on the level of HIV-1 replication. Significant induction of the iNOS gene was observed in cultured MDM concomitantly with the peak of virus replication. However, this induction was not accompanied by a measurable production of NO, suggesting a weak synthesis of NO. Surprisingly, exposure to low concentrations of a NO-generating compound (sodium nitroprusside) and L-arginine, the natural substrate of iNOS, results in a significant increase in HIV replication. Accordingly, reduction of L-arginine bioavailability after addition of arginase to the medium significantly reduced HIV replication. The specific involvement of NO was further demonstrated by a dose-dependent inhibition of viral replication that was observed in infected macrophages exposed to N(G)-monomethyl L-arginine and N(G)-nitro-L-arginine methyl ester (L-NAME), two inhibitors of the iNOS. Moreover, an excess of L-arginine reversed the addition of L-NAME, confirming that an arginine-dependent mechanism is involved. Finally, inhibitory effects of hemoglobin which can trap free NO in culture supernatants and in biological fluids in vivo confirmed that endogenously produced NO could interfere with HIV replication in human macrophages.

GTP cyclohydrolase I is coinduced in hepatocytes stimulated to produce nitric oxide

GTP cyclohydrolase I is the rate-controlling enzyme in the production of tetrahydrobiopterin (BH(4)), an essential cofactor for nitric oxide (NO) synthase. Here we show that GTP cyclohydrolase I mRNA was present in unstimulated hepatocytes and was up-regulated 2- to 3-fold concurrently with iNOS induction induced in vivo by LPS injection and in vitro by stimulation with LPS and inflammatory cytokines tumor necrosis factor alpha, interleukin-1 beta, and interferon-gamma. Hepatocyte GTP cyclohydrolase I enzyme activity increased 2-fold in vivo after LPS. This coinduction of GTP cyclohydrolase I resulted in increased total intracellular biopterin which supported induced NO synthesis. The addition of a GTP cyclohydrolase I inhibitor to the stimulated hepatocytes decreased intracellular biopterin levels and resulted in a decrease in NO production. The results show that GTP cyclohydrolase I is up-regulated by certain acute inflammatory conditions. Further, the results indicate that biopterin is essential as a cofactor for induced NO synthase activity in hepatocytes.

Lipopolysaccharide tolerance and ethanol modulate hepatic nitric oxide production in a gender-dependent manner

This study was directed at the role of tolerance to endotoxin (lipopolysaccharide, LPS) and ethanol (EtOH) intoxication in modulating hepatic nitric oxide (NO) production, and the demonstration of gender differences. Previous studies demonstrated that tolerance to either LPS or EtOH was associated with reduced hepatic production of superoxide anions. We now tested the hypothesis that the reduced hepatic production of superoxide anions during tolerance to LPS and the altered response to EtOH are accompanied by increased sensitivity of hepatic NO release to stimulation. Age-matched male and female Sprague-Dawley rats were made tolerant to LPS by an i.v. injection of LPS (0.5 or 0.45 mg/kg) 2 days prior to an in vivo EtOH infusion for 3 h (LPS-EtOH group). Control groups were saline-pretreated, saline-infused; saline-pretreated, EtOH-infused; and LPS-pretreated, saline-infused. At the end of the infusion, isolated hepatocytes, Kupffer, and sinusoidal endothelial cells were cultured for 20 h for subsequent measurement of basal (spontaneous) and in vitro-stimulated nitrite release. LPS-tolerance resulted in significantly enhanced stimulated NO production by hepatocytes and Kupffer cells in both male and female rats. EtOH abolished this priming effect in hepatocytes from male, but not from female rats. The priming effect was markedly diminished by EtOH in Kupffer cells of female rats only. LPS-tolerance increased NO production by stimulated endothelial cells of males, and decreased NO production by cells of females. EtOH infusion did not influence NO production by endothelial cells from male rats and it reversed the LPS-tolerance-induced inhibition in females. These data demonstrate that modulation by LPS-tolerance of hepatic NO release in EtOH-treated rats leads to enhanced stimulated NO production, while hepatic superoxide anion release was previously shown to be reduced within the same time frame. Since NO is able to scavenge superoxide, the LPS-tolerance-induced alterations in the EtOH effects on NO production may have a potential significance in modulating - in a time-dependent manner - oxidative injury associated with LPS and acute EtOH intake.

Regulation of nitric oxide synthesis in the liver

Nitric oxide signalling during the past two decades has been one of the most rapidly growing areas in biology. This simple free radical gas can regulate an ever-growing list of biological processes. Here the regulation of NO synthesis in the liver is reviewed. The biogenesis of nitric oxide (NO) is catalysed by nitric oxide synthases (NOS). These enzymes catalyse the oxidation of one of the guanidino nitrogens of l-arginine by molecular oxygen to form NO and citrulline. Three NOS have been identified: two constitutive (cNOS: type 1 or neuronal and type 3 or endothelial) and one inducible (iNOS: type 2). As to the liver, cNOS activity is normally detectable in Kupffer cells, whereas no cNOS is ever encoded in hepatocytes. However, hepatocytes, Kupffer and stellate cells (the three main types of liver cells) are prompted to express an intense iNOS activity once exposed to effective stimuli such as bacterial lipopolysaccharide and cytokines. This review is focused mainly on two aspects: regulation of NOS activity and expression by endogenous and exogenous compounds. Because NO production has beneficial and detrimental effects, understanding the molecular mechanisms that govern NOS is critical to developing strategies to manipulate NO production in liver diseases.

Hypoxic signal transduction in critical illness

Derangements in tissue perfusion occur during critical illness, and the resulting deficit in oxygen delivery may play an important role in the pathogenesis of hemorrhagic and septic shock. Cells and organisms have developed a variety of adaptive strategies to maintain adequate energy production to maintain normal cellular function under hypoxic conditions. Recent studies from our laboratory suggest that certain proinflammatory cytokines, which are likely to be elaborated during or after shock, can interfere with the ability of cells to adapt to hypoxia, and thereby contribute to the development of organ system dysfunction.

Nitric oxide production and hepatic dysfunction in patients with postoperative sepsis

1. Although hepatic function is well known to deteriorate following bacterial infection, the underlying mechanisms remain poorly understood. We have previously reported that nitric oxide (NO) radical leads to a decrease in the ketone body ratio (KBR) and in ATP content due to the inhibition of mitochondrial electron transport in primary cultured rat hepatocytes. 2. To evaluate the effects of NO radical on the liver in patients with postoperative sepsis, we analysed both the stable end-product of nitric oxide radical (NOx) as well as the arterial KBR (AKBR), which reflects liver tissue NAD+/NADH. 3. Twenty patients who had undergone general abdominal surgery and who developed postoperative sepsis were divided into two groups: (i) surviving; and (ii) non-surviving. Blood samples were collected before the development of postoperative sepsis and every 3 days until the patient either died or was discharged from hospital. 4. Plasma NOx levels in seven patients who subsequently died became progressively higher than those in the 13 surviving patients over the clinical course of postoperative sepsis. 5. In the non-surviving group, the AKBR was significantly lower than in surviving patients, indicating impaired hepatic function. In contrast, plasma NOx levels in non-surviving patients were significantly higher than in surviving patients. 6. Decreases in AKBR to levels below 0.7 in non-surviving patients followed high NOx levels. Moreover, plasma NOx levels were closely correlated with the AKBR, indicating that NO radical is associated with mitochondrial dysfunction in the liver. 7. It is likely that the overproduction of NO radical plays an important role in causing fatal metabolic disorders in patients with postoperative sepsis.

Ionizing radiation potentiates the induction of nitric oxide synthase by interferon-gamma (Ifn-gamma) or Ifn-gamma and lipopolysaccharide in bnl cl.2 murine embryonic liver cells: role of hydrogen peroxide

The effects of ionizing irradiation on the nitric oxide (NO) production in murine embryonic liver cell line, BNL CL.2 cells, were investigated. Various doses (5-40 Gy) of radiation made BNL CL.2 cells responsive to interferon-gamma alone for the production of NO in a dose-dependent manner. Small amounts of lipopolysaccharide (LPS) or tumor necrosis factor-alpha (TNF-alpha) synergized with IFN-gamma in the production of NO from irradiated BNL CL.2 cells, even though LPS or TNF-alpha alone did not induce NO production from the same cells. Immunoblots showed parallel induction of inducible nitric oxide synthase (iNOS). NO production in irradiated BNL CL.2 cells by IFN-gamma or IFN-gamma plus LPS was decreased by the addition of catalase, suggesting that H(2)O(2) produced by ionizing irradiation primed the cells to trigger NO production in response to IFN-gamma or IFN-gamma plus LPS. Furthermore, the treatment of nongamma-irradiated BNL CL.2 cells with H(2)O(2) made the cells responsive to IFN-gamma or IFN-gamma plus LPS for the production of NO. This study shows that ionizing irradiation has the ability to induce iNOS gene expression in responsive to IFN-gamma via the formation of H(2)O(2) in BNL CL.2 murine embryonic liver cells.

Role of nitric oxide in haemodialysis hypotension

To investigate the possible involvement of nitric oxide (NO) in haemodialysis hypotension, we measured plasma concentrations of nitrate anion (NO3-), a metabolite of NO, in 114 patients undergoing maintenance haemodialysis. Mean plasma NO3- concentrations before dialysis were greater in subjects with lower blood pressure (155 +/- 16 micromol L-1) than in those with middle (117 +/- 8 micromol L-1) or higher blood pressure (105 +/- 12 micromol L-1) before dialysis. Further, mean plasma NO3- concentrations before dialysis were greater in subjects with lower blood pressure (186 +/- 13 micromol L-1) than in those with middle (112 +/- 7 micromol L-1) or higher blood pressure (64 +/- 11 micromol L-1) after dialysis. Plasma NO3- concentrations before dialysis were inversely correlated with mean blood pressure before dialysis (r=0.318, P=0.0006), and showed a strong inverse correlation with mean blood pressure after dialysis (r=0.608, P=0.0001). In the selected participants who had equal range of mean blood pressure before dialysis, mean plasma NO3- concentrations were greater in subjects with severe hypotension during dialysis (180 +/- 14 micromol L-1) than in those with mild hypotension (99 +/- 11 micromol L-1) or without hypotension (53 +/- 12 micromol L-1); plasma NO3- concentrations before dialysis were inversely correlated with changes in mean blood pressure during dialysis and mean blood pressure after dialysis. Results indicate that enhanced NO production may be involved in acute hypotension during dialysis, and suggest the possible involvement of NO in the pathogenesis of chronic hypotension associated with maintenance haemodialysis.

Nitric oxide inhibits neonatal hepatocyte oxidative metabolism

BACKGROUND/PURPOSE

Liver function is frequently impaired in neonates with sepsis. Nitric oxide (NO) is thought to be a mediator of organ dysfunction and liver oxidative metabolism during sepsis. The authors developed an in vitro model to investigate the effect of NO and the combined effect of NO plus H2O2 on neonatal hepatocyte oxidative metabolism.

METHODS

Hepatocytes were isolated from neonatal rats. Oxygen consumption was measured polarographically. In Study A, cells were exposed to S-Nitroso-N-acetylpenicillamine (SNAP), an NO donor, at various concentrations. In study B, myxothiazol and oligomycin, inhibitors of mitochondrial respiration, were added to investigate the site of action of NO. In study C, hepatocytes were incubated in the presence of both SNAP (300 micromol/L) and H2O2 (1.5 mmol/L). In study D, morphological alterations induced by NO and NO plus H2O2 were investigated by hepatocyte electron microscopy.

RESULTS

In study A, SNAP caused a dose-dependent decrease in oxygen consumption. A significant inhibition was reached at 300 micromol/L SNAP. In study B, the lack of further inhibition when SNAP was given together with myxothiazol indicates that NO acts intramitochondrially. Similarly, no further inhibition occurred when the NO donor was given together with oligomycin, suggesting that the effect of NO is mainly at the level of ATP synthase. In study C, concomitant addition of 300 micromol/L SNAP and 1.5 mmol/L H2O2 to hepatocytes caused further inhibition of oxygen consumption compared with either SNAP or H2O2 alone. In study D, mild alterations in hepatocyte morphology were noted in the presence of SNAP or SNAP plus H2O2.

CONCLUSIONS

In neonatal hepatocytes, NO significantly inhibits mitochondrial oxygen consumption, possibly at the level of ATP synthase. The effect of NO is additive to that of H2O2. Morphological findings were consistent with these biochemical effects and suggest that NO and H2O2 are important mediators of liver damage during sepsis.

Study on the correlation of plasma NO, ET-1 and ALT in the patients with chronic hepatitis and cirrhosis

The levels of plasma nitric oxide (NO), endothelin-1 (ET-1) and ALT in the patients with chronic hepatitis B and active cirrhosis and the correlation among them were observed and analyzed. NO3- was restored by using cadmium column assay and NO2- measured by heavy nitrogen assay. The primitive NO3- and total restored NO2- (NO3-/NO2-) in plasma of the patients with chronic hepatitis and cirrhosis. Plasma ET-1 and ALT levels were determined by using radioimmunological assay and Lai's assay, respectively. Compared with normal control group, the plasma levels of NO2-/NO2- and ET-1 in the patients with chronic active hepatitis and active cirrhosis were significantly increased (P < 0.05-0.01). There was a positive correlation between NO and ALT, and ET-1 and ALT in the patients with chronic active hepatitis and active cirrhosis respectively. It was suggested that elevation of both NO and ET-1 levels were closely related with injury severity of liver function.

Gram-negative bacterial sepsis and the sepsis syndrome

Gram-negative sepsis syndrome is an increasingly common complication in medical and surgical patients. The molecular and cellular mechanisms underlying this dreaded complication are yielding to investigation. These studies have led to a multiplicity of targets for novel therapies. Despite highly promising results in many animal studies, clinical studies have been disappointing.

21-aminosteroids prevent the down-regulation of hepatic cytochrome P450 induced by hypoxia and inflammation in conscious rabbits

1 This study was conducted to assess whether a 21-aminosteroid, U74389G, could prevent the down-regulation of hepatic cytochrome P450 (P450) induced by acute moderate hypoxia or an inflammatory reaction. 2 The rabbits of two groups (n = 6 per group) were subjected to acute moderate hypoxia (PaO2 approximately 35 mmHg), one pre-treated with U74389G (3 mg kg-1 i.v. every 6 h, for 48 h). The rabbits of two other groups received 5 ml of turpentine s.c., one of them being pre-treated with U74389G (3 mg kg-1 i.v. every 6 h, for 72 h). The kinetics of theophylline (2.5 mg kg-1) were assessed to evaluate the activity of the P450. Once the rabbits were sacrificed, the P450 content and the amount of thiobarbituric acid reactive substances (TBARS), a marker of lipid peroxidation, were estimated in the liver. 3 Compared with control rabbits, hypoxia and inflammation increased theophylline plasma concentrations, as a result of a decrease in theophylline systemic clearance (P<0.05). Both experimental conditions reduced hepatic content of P450 by 40-50% (P<0.05) and increased the amount of hepatic TBARS by around 50% (P<0.05). Pre-treatment with U74389G prevented the hypoxia- and inflammation-induced decrease in theophylline systemic clearance, the down-regulation of hepatic P450, and the increase in liver TBARS. 4 It is concluded that in the rabbit, U74389G prevents hepatic P450 depression produced by acute moderate hypoxia and a turpentine-induced inflammatory reaction, possibly by eliciting a radical quenching antioxidant activity.

Effects of parenteral arginine supplementation on the intestinal adaptive response after massive small bowel resection in the rat

BACKGROUND

Arginine (ARG) and its metabolic products (polyamines and nitric oxide) are known to affect gut function and protein synthesis in various tissues. The aim was to study the effect of parenteral ARG supplementation on intestinal adaptation and intestinal function in rats after massive small bowel resection (SBR).

METHODS

Fasted rats (275 g) were studied 24 h after 80% SBR. At t = 6 h, t = 12 h, and t = 18 h after SBR, a 300 mM ARG solution (ARG, n = 9), 5 ml/100 g body weight, was given subcutaneously. Controls received iso-osmolaric amounts of NaCl (NaCl, n = 9) or alanine (ALA, n = 8). Twenty-four hours after operation substrate fluxes across the gut were determined together with intestinal protein synthesis, polyamine concentrations in gut tissue, and gut function by testing intestinal permeability using the urinary recovery of lactulose and rhamnose.

RESULTS

Intestinal fluxes did not differ among groups, except for an increased production of ornithine and a decreased uptake of glutamine after ARG supplementation. Also, intracellular arginine and ornithine concentrations were higher in the jejunum, accompanied by lower concentrations of other amino acids. Intracellular putrescine and gamma-aminobutyric acid, a breakdown product of putrescine, were higher. However, spermidine and spermine were not. Protein synthesis was lower in the ARG group, while intestinal permeability decreased.

CONCLUSIONS

Parenteral arginine supplementation in rats with massive SBR leads to a slowing of intestinal adaptation, indicated by reduced glutamine uptake and protein synthesis. The exact mechanism of this inhibitory effect remains to be elucidated. Intestinal permeability, however, benefits from arginine supplementation, possibly related to better enterocyte differentiation.

Impact of experimental peritonitis on bone marrow cell function

BACKGROUND

The effects of abdominal sepsis on the regulation of cell turnover in bone marrow and on the function of hematopoietic stem cells were investigated.

METHODS

In a new mouse model of abdominal sepsis (colon ascendens stent peritonitis [CASP]) the proliferation, apoptosis, and colony-forming capacity of bone marrow cells were determined.

RESULTS

Both experimental peritonitis and sham surgery increased proliferation of bone marrow cells significantly (P < .01). Incubation with granulocyte-macrophage colony-stimulating factor but not granulocyte colony-stimulating factor further augmented proliferation of bone marrow cells from septic mice. In contrast to cell proliferation, bone marrow cell apoptosis was significantly (P < .001) increased in response to CASP but not to sham surgery. CASP surgery and treatment of normal bone marrow cells with lipopolysaccharide, tumor necrosis factor-alpha, interleukin 1 beta, and interferon gamma increased the number of apoptotic cells to a similar extent. Stem cell assays revealed that during the late phase of peritonitis the colony formation by granulocytic-monocytic precursors was increased, whereas mature erythroid colony-forming cells were suppressed. Incubation of normal bone marrow cells with lipopolysaccharide and cytokines showed similar effects.

CONCLUSIONS

These results reveal differential effects of experimental peritonitis on various hematopoietic lineages and suggest a potential role of inflammatory mediators for the dysregulation of bone marrow cell function during abdominal sepsis.

Nitric oxide in septic shock

Septic shock is a major cause of death following trauma and is a persistent problem in surgical patients throughout the world. It is characterised by hypotension and vascular collapse, with a failure of the major organs within the body. The role of excessive nitric oxide (NO) production, following the cytokine-dependent induction of the inducible nitric oxide synthase (iNOS), in the development of septic shock is discussed. Emphasis is placed upon the signal-transduction process by which iNOS is induced and the role of NO in cellular energy dysfunction and the abnormal function of the cardiovascular system and liver during septic shock.

The effect of lymphatic blockage on the amount of endotoxin in portal circulation, nitric oxide synthesis, and the liver in dogs with peritonitis

This study was performed to investigate the effect of lymphatic blockage on the amount of endotoxin in portal venous blood, nitric oxide synthesis, the release of aspartate aminotransferase (AST) from the liver, hepatic damage, and survival in an experimental model of dogs with peritonitis. The dogs were divided into a control group (group 1), an unligated thoracic duct peritonitis group (group 2), and a ligated thoracic duct peritonitis group (group 3). Peritoneal fluid and blood from the portal vein and femoral artery were taken for peritoneal culture, endotoxin, and AST assay, respectively, and liver biopsies were performed to assess for hepatic damage and for nitric oxide assay. There was a higher bacteria count in the peritoneal fluid from group 3 than in that from group 2 (P < 0.0001). Bacteria grew in all of the blood cultures from the group 2 animals, but growth was seen only in blood cultures from four of the group 3 animals. The levels of endotoxin, nitrite, and AST levels in group 3 were significantly increased in comparison with those in group 2 (P < 0.0001). Extensive hepatocellular necrosis with hemorrhage was observed in the livers of the group 3 animals, and all of them died within 48 h. The results of this study suggest that the blockage of lymph flow has a negative effect on liver and survival in dogs with peritonitis, and that hepatic damage is directly related to the amount of endotoxin to which the liver is exposed.

Nitric oxide mediates hepatocyte injury

The degree of acute hepatic failure after severe trauma and sepsis is related to the extent of hepatocyte (HC) damage and cell death resulting from either necrosis or apoptosis. We have previously demonstrated that tumor necrosis factor-alpha (TNF-alpha) and lipopolysaccharide (LPS) can directly lead to HC necrosis, but not apoptosis. To date, the reactive oxygen intermediates (ROI) and nitric oxide (NO) have been shown to play a potential role in the induction of cell apoptosis. However, it is unknown whether ROI and NO are involved in HC cell death. Therefore, in this study we tested the hypothesis that NO and ROI exert different effects on HC cell death. TNF-alpha and LPS alone failed to induce HC apoptosis but when combined with antioxidants resulted in HC apoptosis and DNA fragmentation, which is correlated with an increase in NO production. This effect was attenuated by the NO synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). Moreover, the NO donor sodium nitroprusside resulted in HC apoptosis and cell damage as represented by hepatocellular enzyme release. Antioxidants inhibited TNF-alpha- and LPS-mediated ROI generation and peroxynitrite formation in HC. TNF-alpha- and LPS-induced HC damage could be further reduced by the combination of antioxidants and L-NMMA. These results indicate that NO is involved in HC injury, primarily through the induction of HC apoptosis.

Depression of the hepatic cytochrome P450 by an acute inflammatory reaction: characterization of the nature of mediators in human and rabbit serum, and in the liver

There is increasing evidence suggesting that several mediators are involved in the cascade of events leading to the depression of the cytochrome P450 (P450) by an inflammatory reaction. The present study aimed to confirm the presence of mediators in the serum (RS(INFLA)) and hepatocytes (H(INFLA)) of rabbits with an acute inflammatory reaction, and in the serum of humans with an acute upper respiratory tract viral infection (HS(URTVI)). The inflammatory reaction was induced by the s.c. injection of 5 ml of turpentine. Incubation of RS(INFLA) or HS(URTVI) with H(INFLA) depressed the P450, diminished the formation of theophylline metabolites (3-methylxanthine, 1-methyluric acid, and 1,3-dimethyluric acid), and increased lipid peroxidation. The addition of preheated RS(INFLA) or HS(URTVI) to H(INFLA) did not diminish the amount of P450 or theophylline metabolites, and prevented the increase in lipid peroxidation. Incubating the filtrate of RS(INFLA) or HS(URTVI) dialyzed through membranes with cut-off of 10, 30, 50 and 100 kd, with H(INFLA) showed that rabbit and human mediators have molecular weights ranging from 10 to 30 kd. Incubation of H(INFLA) with hepatocytes from control rabbits (H(CONT)) did not decrease further the P450. However, when RS(INFLA) was added to co-cultured H(CONT) + H(INFLA), the depression of P450 was 37% greater (p<0.05), and the amount of theophylline metabolites generated was around 30% (p<0.05) smaller than that observed when H(CONT) or H(INFLA) were incubated with RS(INFLA). Based on the present results we may speculate that human and rabbit serum mediators are proteins of molecular weights ranging from 10 to 30 kd, and in addition, primed hepatocytes once exposed to the serum mediators release mediators able to depress the P450 in H(CONT).

Nitric oxide inactivates rat hepatic methionine adenosyltransferase In vivo by S-nitrosylation

We investigated the mechanism of nitric oxide (NO) action on hepatic methionine adenosyltransferase (MAT) activity using S-nitrosoglutathione (GSNO) as NO donor. Hepatic MAT plays an essential role in the metabolism of methionine, converting this amino acid into S-adenosylmethionine. Hepatic MAT exists in two oligomeric states: as a tetramer (MAT I) and as a dimer (MAT III) of the same subunit. This subunit contains 10 cysteine residues. In MAT I, S-nitrosylation of 1 thiol residue per subunit was associated with a marked inactivation of the enzyme (about 70%) that was reversed by glutathione (GSH). In MAT III, S-nitrosylation of 3 thiol residues per subunit led to a similar inactivation of the enzyme, which was also reversed by GSH. Incubation of isolated rat hepatocytes with S-nitrosoglutathione monoethyl ester (EGSNO), a NO donor permeable through the cellular membrane, induced a dose-dependent inactivation of MAT that was reversed by removing the NO donor from the cell suspension. MAT, purified from isolated rat hepatocytes, contained S-nitrosothiol groups and the addition of increasing concentrations of EGSNO to the hepatocyte suspension led to a progressive S-nitrosylation of the enzyme. Removal of the NO donor from the incubation media resulted in loss of most NO groups associated to the enzyme. Finally, induction in rats of the production of NO, by the administration of bacterial lipopolysaccharide (LPS), induced a fivefold increase in the S-nitrosylation of hepatic MAT, which led to a marked inactivation of the enzyme. Thus, the activity of liver MAT appears to be regulated in vivo by S-nitrosylation.

Nitric oxide as an inflammatory mediator in autoimmune MRL-lpr/lpr mice

Nitric oxide (.NO) may exhibit proinflammatory features. .NO synthase type 2 (NOS2) is overexpressed and .NO overproduced in rodent models of induced inflammation. Blockage of .NO production by administration of NOS inhibitors prevents or reduces various types of induced inflammation in mice and rats. We have shown that autoimmune MRL-lpr/lpr mice overexpress NOS2 and overproduce .NO in an age-dependent fashion that parallels expression of arthritis, glomerulonephritis, and vasculitis. Blocking .NO production by oral administration of the NOS inhibitor NG-monomethyl-L-arginine reduced the arthritis, glomerulonephritis, and vasculitis, but it did not modify serum anti-DNA antibody levels or glomerular deposition of immune complexes. When mice with genetically disrupted NOS2 were backcrossed to MRL-lpr/lpr mice, the resultant (-/-) mice expressed no NOS2 and produced no .NO, the wild-type (+/+) mice overexpressed NOS2 and overproduced .NO (in comparison to normal, control mice), and the heterozygous (+/-) mice expressed and produced intermediate levels. Nephritis and arthritis in the (-/-) mice were comparable to that in MRL-lpr/lpr mice, but vasculitis was markedly decreased. Levels of anti-DNA antibodies were comparable in all mice, but IgG rheumatoid factor production was markedly reduced in the (-/-) mice. These results of studies in MRL-lpr/lpr mice with genetically disrupted NOS2 highlight the heterogeneity and complexity of the role of NOS2 and .NO in inflammation.

Beneficial effects of FK409, a novel nitric oxide donor, on reperfusion injury of rat liver

BACKGROUND

Nitric oxide (NO) seems to play an important role in modulating tissue injury during reperfusion of the liver. In this study, we have evaluated and compared the effects of FK409 (FK), a potent spontaneous NO releaser, and L-arginine in ischemia-reperfusion injury of the rat liver.

METHODS

Male Sprague-Dawley rats underwent 90 min of hepatic ischemia followed by reperfusion. FK or L-arginine was used (intravenously) in two different doses for each drug (group I, 3.2 mg/kg FK; group II, 1.6 mg/kg FK; group IV, 100 mg/kg L-arginine; and group V, 300 mg/kg L-arginine). Saline was used in control animals (group III). Hepatic enzyme status, microcirculation, serum nitrite (NO2-) and nitrate (NO3-) and tissue injury score were evaluated at predetermined times.

RESULTS

Serum NO2-/NO3- was elevated immediately by FK treatment dose-dependently but not by L-arginine. However, L-arginine caused late (6-24 hr) elevation of the NO metabolites dose-dependently. The elevation of serum aspartate aminotransferase and alanine aminotransferase was suppressed and hepatic microcirculation was improved in the FK-treated groups dose-dependently. L-Arginine also improved the microcirculation, but hepatic enzymes at 24 hr of reperfusion were significantly higher in group V than in the control group. These findings were well reflected by the extent of tissue injury in respective groups.

CONCLUSION

FK treatment in the immediate reperfusion period improves hepatic microcirculation and confers a significant protective effect on hepatic ischemia-reperfusion injury in the rat.

Hepatocyte nitric oxide production is induced by Kupffer cells

To investigate the cellular communication in the liver, nitric oxide (NO) production by sinusoidal cells and hepatocytes by stimulation with cytokines and Kupffer cell-conditioned medium was quantitatively analyzed. NO production by the cells was measured by the Griess reaction, and nitric oxide synthase (iNOS) transcription level by a competitive RT-PCR assay using mutant iNOS mRNA as a standard. NO production and iNOS mRNA transcriptional levels in Kupffer cells were markedly increased by stimulation with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma), and moderately by interleukin-1beta (IL-1beta). NO production by hepatocytes was not significantly enhanced by LPS, but was markedly enhanced by IL-1beta or the combination of tumor-necrosis factor-alpha (TNF-alpha) and IFN-gamma. Hepatocyte NO production and iNOS mRNA levels were markedly enhanced by the LPS-activated Kupffer cell conditioned medium, but these effects were reduced by heat treatment or anti-TNF antibody. Although NG-monomethyl-L-arginine acetate and dexamethasone reduced NO production by the cells, the iNOS mRNA level was reduced by dexamethasone only. Gel-shift assay showed NF-kappaB activation in hepatocytes during this activation. These data reinforce the importance of cellular communication between sinusoidal cells and hepatocytes.

Down-regulation of cytochrome P450 mRNAs and proteins in mice lacking a functional NOS2 gene

Endotoxemia results in both the down-regulation of multiple cytochrome P450 genes and the induction of inducible nitric oxide synthase (NOS2). The nitric oxide (NO) released during inflammation has been implicated as the mediator of the decreased catalytic activity and expression of several cytochrome P450 isozymes. We examined the role of NO in the decreases in both gene expression and activity of three P450s in endotoxemic parental and NOS2 knockout mice. Twenty-four hours of endotoxin (LPS) treatment significantly suppressed CYP2C29 and CYP3A11 mRNA expression in both the parental and NOS2 knockout strains. Microsomal CYP2E1, CYP2C-like, and CYP3A-like protein levels were also decreased in both strains of mouse. Similar results were obtained in parental strain endotoxemic mice co-administered the NOS inhibitor aminoguanidine. Six hours after LPS treatment, there was an NO-dependent decrease in testosterone 6beta-hydroxylase activity, because no decreases in activity were observed in the NOS2 knockout mice or in mice co-administered aminoguanidine. LPS also evoked decreases in testosterone 15alpha- and 16beta-hydroxylase activity after 24 hr that were observed in the parental strain and not in NOS2 knockout mice. Our results demonstrate that the down-regulation of CYP2C-like, CYP3A-like and CYP2E1 proteins and mRNAs, in the endotoxemic mouse can occur independently of NO production. We do, however, show that the NO released during endotoxemia is capable of causing decreases in some cytochrome P450 catalytic activities.

Chylomicrons alter the hepatic distribution and cellular response to endotoxin in rats

Chylomicrons (CM) can bind endotoxin (lipopolysaccharide [LPS]), forming CM-LPS complexes, and protect against endotoxic shock and death in rodent models of gram-negative sepsis. The liver appears to play a central role in this process, as demonstrated by the increased uptake of LPS by this organ. We examined the effect of CM on the uptake and cellular response to injected 125I-LPS by hepatocytes and hepatic nonparenchymal cells. Whereas CM increased the uptake of LPS by both hepatocytes and Kupffer cells, the increase was proportionately greater in hepatocytes than Kupffer cells. Importantly, CM-LPS complexes inhibited inducible nitric oxide synthase (iNOS) mRNA expression and NO production in Kupffer cells and endothelial cells, reducing mRNA levels by 45% to 50% as compared with LPS alone. CM-bound LPS also reduced NO production by hepatocytes in response to cytokine stimulation. Lastly, CM-LPS complexes yielded a concentration-dependent inhibition of LPS-induced tumor necrosis factor alpha (TNF-alpha) production by Kupffer cells in vitro. These data indicate that the mechanism by which CM protect against endotoxicity may involve an increased uptake of LPS by hepatocytes. Moreover, uptake of CM-bound LPS by liver cells attenuates the capacity of these cells to respond to proinflammatory stimulation. These results highlight important anti-inflammatory properties of CM.

The role of nitric oxide in hepatic metabolism

Nitric oxide (NO) may regulate hepatic metabolism directly by causing alterations in hepatocellular (hepatocyte and Kupffer cell) metabolism and function or indirectly as a result of its vasodilator properties. Its release from the endothelium can be elicited by numerous autacoids such as histamine, vasoactive intestinal peptide, adenosine, ATP, 5-HT, substance P, bradykinin, and calcitonin gene-related peptide. In addition, NO may be released from the hepatic vascular endothelium, platelets, nerve endings, mast cells, and Kupffer cells as a response to various stimuli such as endotoxemia, ischemia-reperfusion injury, and circulatory shock. It is synthesized by nitric oxide synthase (NOS), which has three distinguishable isoforms: NOS-1 (ncNOS), a constitutive isoform originally isolated from neuronal sources; NOS-2 (iNOS), an inducible isoform that may generate large quantities of NO and may be induced in a variety of cell types throughout the body by the action of inflammatory stimuli such as tumor necrosis factor and interleukin (IL)-1 and -6; and NOS-3 (ecNOS), a constitutive isoform originally located in endothelial cells. Another basis for differentiation between the constitutive and inducible enzymes is the requirement for calcium binding to calmodulin in the former. NO is vulnerable to a plethora of biologic reactions, the most important being those involving higher nitrogen oxides (NO2-), nitrosothiol, and nitrosyl iron-cysteine complexes, the products of which (for example, peroxynitrite), are believed to be highly cytotoxic. The ability of NO to react with iron complexes renders the cytochrome P450 series of microsomal enzymes natural targets for inhibition by NO. It is believed that this mechanism provides negative feedback control of NO synthesis. In addition, NO may regulate prostaglandin synthesis because the cyclooxygenases are other hem-containing enzymes. It may also be possible that NO-induced release of IL-1 inhibits cytochrome P450 production, which ultimately renders the liver less resistant to trauma. It is believed that Kupffer cells are the main source of NO during endotoxemic shock and that selective inhibition of this stimulation may have future beneficial therapeutic implications. NO release in small quantities may be beneficial because it has been shown to decrease tumor cell growth and levels of prostaglandin E2 and F2 alpha (proinflammatory products) and to increase protein synthesis and DNA-repair enzymes in isolated hepatocytes. NO may possess both cytoprotective and cytotoxic properties depending on the amount and the isoform of NOS by which it is produced. The mechanisms by which these properties are regulated are important in the maintenance of whole body homeostasis and remain to be elucidated.

Interleukin 1beta-stimulated production of nitric oxide in rat hepatocytes is mediated through endogenous synthesis of interferon gamma

The multiple interlocking regulatory mechanisms that underlie induction of hepatocyte inducible nitric oxide synthase (iNOS) expression are largely unknown. Although previous work has indicated the requirement for multiple proinflammatory cytokines to induce hepatocyte NO production, investigators have recently shown that interleukin-1beta (IL-1beta) alone can initiate iNOS expression. In contrast, interferon gamma (IFN-gamma) serves as the sole initiating factor in other cell systems. On the basis of the known ability of IL-1beta to induce transcription and translation of the IFN family of genes, we hypothesized that IL-1beta-mediated hepatocyte expression of iNOS is dependent on endogenous IFN-gamma synthesis. In a system of rat hepatocytes in primary culture, IL-1beta induced production of both NO and IFN-gamma. Using in situ hybridization and immunoblot analysis, IFN-gamma messenger RNA (mRNA) and protein were detected in hepatocytes exposed to IL-1beta. Inhibition of NO synthesis using the competitive substrate inhibitor N-monomethyl-L-arginine (100 micromol/L) did not alter the extent of IL-1beta-mediated IFN-gamma synthesis. In contrast, anti-IFN-gamma antibody or inhibition of IFN-gamma mRNA translation by addition of antisense IFN-gamma oligodeoxynucleotide probes resulted in undetectable levels of NO metabolites and iNOS protein. Repletion of IFN-gamma to the system restored NO production to levels noted in the presence of IL-1beta alone. Transient transfection analysis using a rat hepatocyte iNOS promoter-reporter gene plasmid construct showed that IL-1beta-induced promoter activation was abolished in the presence of anti-IFN-gamma or antisense IFN-gamma. Again, addition of IFN-gamma to the system restored activity of the iNOS promoter. Parallel experiments examining IL-1beta-mediated endogenous hepatocyte IL-1beta and TNF-alpha synthesis indicated no role for these cytokines in the induction of iNOS expression by IL-1beta. It is concluded that IL-1beta-mediated hepatocyte synthesis of NO is dependent on the simultaneous endogenous synthesis of IFN-gamma.

Interferon-beta-1-b (IFN-B) decreases induced nitric oxide (NO) production by a human astrocytoma cell line

Inducible nitric oxide synthase (iNOS) is expressed by astrocytes in demyelinating regions of multiple sclerosis (MS) brain plaques, suggesting that NO contributes to MS pathology. Since the immunosuppressive cytokine IFN-B ameliorates MS disease activity, it is of interest to assess the modulatory role of IFN-B on NO production. We studied the effects of IFN-B, as well as dexamethasone, IL-10, and transforming growth factor-beta (TGF-B), on cytokine-induced NO production by the human astrocytoma cell line, A172. L-NMMA and aminoguanidine, competitive inhibitors of iNOS suppressed NO production as measured by the NO byproduct, nitrite, as did IFN-B. Dexamethasone enhanced NO production, and IFN-B decreased the amount of the enhancement. Neither IL-10 nor TGF-B inhibited nitrite production. The therapeutic effect of IFN-B in MS may be partly due to suppression of pathogenic NO production.

Expression of nitric-oxide synthase in rat Kupffer cells is regulated by cAMP

Treatment of cultured rat Kupffer cells with lipopolysaccharide (LPS) resulted in a time-dependent increase in the expression of the inducible isoform of nitric-oxide synthase (iNOS). Agents that elevated intracellular cAMP levels (e.g. forskolin, dibutyryl cAMP, cholera toxin, and isoproterenol) markedly decreased nitrite production and iNOS protein formation by LPS-stimulated Kupffer cells. Furthermore, inhibition of LPS-induced nitrite formation and iNOS protein levels by these agents was enhanced in the presence of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine. Forskolin, the most potent inhibitor of LPS-induced nitrite formation by Kupffer cells, decreased iNOS mRNA levels in a time-dependent manner. Time course studies indicated that forskolin was most effective at inhibiting LPS-induced nitrite formation and iNOS mRNA levels by Kupffer cells when added before LPS. Message stability studies established that forskolin did not enhance the rate of decay of LPS-induced iNOS mRNA. Nuclear run-on assays revealed that forskolin decreased LPS-induced transcription of the iNOS gene. Treatment of Kupffer cells with LPS induced the translocation of the p65 subunit of nuclear factor kappaB (NF-kappaB) into the nucleus, and this process was abolished by forskolin. In addition, the LPS-dependent degradation of IkappaBalpha was not observed in forskolin-treated cells; the levels of the p65 subunit of NF-kappaB were minimal in the nucleus at the same time. Also, we observed that forskolin induced transcription of the IkappaBalpha gene in a time-dependent manner and in addition up-regulated LPS-induced IkappaBalpha mRNA levels. Taken together, this study indicates that the attenuation of LPS-induced iNOS formation in Kupffer cells by elevated intracellular cAMP levels occurs by preventing the degradation of IkappaBalpha which suppresses the activation of NF-kappaB and inhibits the onset of transcription of the iNOS gene.

Autonomic nervous system activity during infusion of L-arginine in patients with liver cirrhosis

Patients with liver cirrhosis exhibit a hyperdynamic circulatory state as evidenced by tachycardia and an increase in cardiac output accompanied by an elevation of sympathetic tone. This condition is due to the excessive release of nitric oxide (NO), an endogenous vasodilator, which is in turn related to the abnormal induction of NO synthase. The present study investigated whether the intravenous infusion of L-arginine, the precursor of NO, may cause a similar hyperdynamic circulatory state. A new method, the analysis of power spectrum heart rate variability, was used to evaluate autonomic nervous activity. Twenty patients with liver cirrhosis underwent continuous Holter monitoring of the ECG during the intravenous administration of L-arginine (10 g) (Fisher's solution) infused over 60 min. Power spectral analysis was computed from 512 beats of the Holter ECG data. Low frequency (LF; 0.04-0.15 Hz) and high frequency (HF; 0.15-0.40 Hz) spectral powers and the ratio of LF to HF (LF/HF) were calculated every 10 min before and after the infusion of L-arginine. The LF power, which reflects sympathetic tone modified by vagal tone, and the LF/HF, an indicator of sympathetic tone, were both significantly increased during the infusion (p<0.05). HF power, an indicator of parasympathetic tone, showed no significant change in the early stage of the infusion but was significantly increased in the late stage (p<0.05). The administration of L-arginine thus led to an elevation of sympathetic tone. Fisher's solution, which is administered to patients with hepatic insufficiency, contains L-arginine, and may also produce a hyperdynamic circulatory state as an adverse effect related to an elevation of the plasma level of NO by L-arginine. The monitoring of such patients is thus indicated.

Effects of L-arginine on the systemic, mesenteric, and hepatic circulation in patients with cirrhosis

Nitric oxide (NO) is known to play an important role in modulating both the hepatic and mesenteric circulation under physiological and pathological conditions. We investigated how L-arginine, a precursor of NO, modifies the hepatic and mesenteric circulation in patients with cirrhosis. The study design was a single-blind controlled study. We measured the systemic and portal hemodynamics before and following intravenous L-arginine and saline infusion using pulsed Doppler ultrasonography in 20 patients with cirrhosis, and then the effects were compared with those found in 20 healthy subjects. In these patients, the effects of L-arginine on hepatic circulation were investigated using hepatic catheterization. L-Arginine infusion induced systemic vasodilation in both the healthy controls and the cirrhotic patients in a similar hemodynamic manner. In these patients, the L-arginine-induced increase in the portal flow was significantly higher than that of cardiac output (CO); however, the relation was the inverse in healthy subjects. Moreover, the L-arginine-induced increase in the portal flow was greater in the cirrhotic patients than that seen in healthy subjects. As a result, L-arginine infusion was thus found to selectively augment the hepatopetal portal blood flow in the cirrhotic liver. In patients, L-arginine infusion induced marked hepatic vasodilation as demonstrated by the reduced hepatic sinusoidal resistance (HSR) and increased estimated hepatic blood flow (EHBF) associated with the ameliorated intrinsic clearance of indocyanine green. Despite the fall in HSR, the hepatic venous pressure gradient (HVPG) increased following L-arginine infusion. The mesenteric and hepatic vascular areas of cirrhosis exhibited an increased susceptibility to the dilator action of L-arginine. These findings suggest that the enhanced NO production in the splanchnic vascular area has an important role in the hepatic circulation in patients with cirrhosis.

The importance of nitric oxide in the cytokine-induced inhibition of glucose formation by cultured hepatocytes incubated with insulin, dexamethasone, and glucagon

Culturing hepatocytes with a combination of tumor necrosis factor alpha, interferon gamma, and interleukin 1 beta plus lipopolysaccharide resulted in an induction of nitric oxide synthase and concomitant inhibition of both hepatic gluconeogenesis and glycogenolysis. The inhibition of gluconeogenesis was evident both under basal conditions and in cells stimulated acutely with glucagon. The stimulation of glycogen mobilization by glucagon was largely prevented by the presence of the cytokines. Chronic 24-h treatment of the cells with glucagon attenuated the cytokine response on both glucose output and NO formation in the dexamethasone-treated cells. This effect was antagonized by insulin. Inclusion of 1 mM NG-nitro-L-arginine methyl ester or 0.5 mM NG-monomethyl-L-arginine in the incubation abolished the increase in NO2- plus NO3- induced by the cytokine mixture and partially reversed the inhibitory effects on glucose mobilization in the presence of either insulin or glucagon, confirming the involvement of NO. In contrast the NO synthase inhibitors had little effect on either gluconeogenesis or glycogenolysis in the presence of dexamethasone alone, indicating that NO is only partially responsible for the inhibitory action of the cytokines, and the extent of its involvement depends upon the influence of other hormonal factors on the pathways. The antioxidant trolox also suppressed the inhibition of glucose release by the cytokines under conditions where nitric oxide synthase inhibitors were ineffective, suggesting that both reactive oxygen intermediates and NO may act as mediators, the relative importance of each depending upon the metabolic status of the cell.

Regulation of cytochromes P450 during inflammation and infection

Hepatic P450 activities are profoundly affected by various infectious and inflammatory stimuli, and this has clinical and toxicological consequences. Whereas the expression of most P450s in the liver is suppressed, some are induced. Many of the effects observed in vivo can be mimicked by pro-inflammatory cytokines and IFNs, and P450s are differentially regulated by these agents. Therefore, different cytokine profiles and concentrations in the vicinity of the hepatocyte in different models of inflammation may result in qualitatively and quantitatively different effects on populations of P450s. In addition to cytokines, glucocorticoids may have an important role in P450 regulation in stress conditions, including that caused by inflammatory stimuli. Although in many cases the decreases in activity are due primarily to a down-regulation of P450 gene transcription, it is likely that modulation of RNA and protein turnover, as well as enzyme inhibition, contributes to some of the observed effects. The mechanisms whereby these effects are produced may also vary with both the P450 under study and the time course of the effect. The complexity of the P450 response to inflammation and infection means that all of the above factors must be considered when trying to predict the effect of a given infectious or inflammatory condition on the clinical or toxic response of humans or animals to an administered drug or toxin. The question of whether the down-regulation of the hepatic P450 system to inflammation or infection is a homeostatic or pathological response cannot be answered at present. It is difficult to discern the physiological benefit of reducing hepatic P450 activities, unless it is to prevent the generation of reactive oxygen species generated by uncoupled catalytic turnover of the enzymes. On the other hand, as we proposed some years ago [64], the suppression of P450 may be due to the liver's need to utilize its transcriptional machinery and energy for the synthesis of APPs involved in the inflammatory response. In that case, one could ask why the organism has gone to the trouble of employing differential mechanisms for suppression of P450. One answer could be that the response evolved after the divergence of many of the P450 genes, necessitating the evolution of multiple redundant mechanisms for P450 suppression. In contrast to the down-regulation of P450s in the liver, the induction of several forms in this and other tissues suggests a more specific homeostatic role of these effects, e.g., in generation or catabolism of bioactive metabolites.

Origin of endotoxemia influences the metabolic response to endotoxin in dogs

Different routes of endotoxin administration have been used to mimic inflammatory and metabolic responses observed during sepsis. Because the origin of endotoxemia may affect the reactions to endotoxin, we compared the induction of tumor necrosis factor (TNF), interleukin-6 (IL-6), hormones, and glucose production after endotoxin (1.0 microg/kg Escherichia coli 0111:B4) administration into a peripheral (n = 8) versus the portal (n = 8) vein in anesthetized dogs. Prior to endotoxin, a laparotomy was performed for cannulation of hepatic vessels. To evaluate the effects of surgery and anesthesia, we also studied the effects of peripheral endotoxin administration in six awake dogs. The rate of appearance of glucose was measured by primed continuous infusion of [6,6-2H2]glucose. In anesthetized dogs, arterial concentrations of TNF and IL-6 increased after endotoxin administration (P < 0.01 vs basal; NS between groups). Net hepatic TNF production was increased after endotoxin administration (peripheral vs portal endotoxin administration: 533 +/- 177 vs 2135 +/- 1127 ng/min, both P < 0.05 vs basal; NS between groups). Net hepatic IL-6 production was stimulated only after portal endotoxin delivery (from 86 +/- 129 to 4740 +/- 1899 ng/min, P < 0.05; NS between groups). Although there were no differences in neuroendocrine activation, portal endotoxin administration resulted in decreased glucose production compared with peripheral administration (13.6 +/- 0.9 vs 16.8 +/- 1.2 micromol/kg.min, P < 0. 05). In contrast to anesthetized dogs, endotoxin increased glucose production considerably in awake dogs from 13.8 +/- 1.2 to 24.2 +/- 3.2 micromol/kg.min (P < 0.05; P < 0.05 vs anesthetized dogs). The contribution of anesthesia and surgery increased the endotoxin-induced IL-6 response by approximately 350% compared with the effect of endotoxin in awake dogs (P < 0.01). In conclusion, there are no major differences in the responses to endotoxin between peripherally treated and portally treated dogs, except for differences in glucose production. Portal delivery compared with systemic delivery of endotoxin alters hepatic metabolism through nonendocrine mechanisms, reflected in decreased glucose production. The inflammatory, endocrine, and metabolic effects of endotoxin are altered by the combination of surgery and anesthesia.

Nitric oxide-independent suppression of P450 2C11 expression by interleukin-1beta and endotoxin in primary rat hepatocytes

Hepatic expression of multiple cytochrome P450 genes is suppressed in the livers of rats undergoing an inflammatory response. Nitric oxide (NO) released during inflammation has been implicated in the decreased activities and expression of several cytochrome P450 isozymes. We examined the role of cytokine-mediated NO release on cytochrome P450 2C11 expression in rat hepatocytes cultured on Matrigel. Lipopolysaccharide (LPS), interleukin-1beta (IL-1beta), IL-6, and tumor necrosis factor-alpha (TNF-alpha), but not interferon-gamma (IFN-gamma), suppressed the expression of P450 2C11 mRNA. Neither IL-6 nor IFN-gamma caused NO release into the medium or induction of inducible nitric oxide synthase (iNOS) mRNA. IL-1beta and LPS were the most effective in causing NO release and iNOS induction, and in down-regulating P450 2C11 mRNA expression. Combinations of the cytokines, IFN-gamma, and LPS produced an additive release of NO but did not synergize to further suppress P450 2C11 mRNA. To investigate the role of NO in the IL-1beta- or LPS-mediated suppression of P450 2C11, N-monomethyl-L-arginine (NMA) was administered at concentrations ranging from 30 to 300 microM. Three hundred micromolar NMA returned NO release back to control levels, but did not affect the IL-1beta- or LPS-mediated down-regulation of P450 2C11 mRNA or protein expression. Our results suggest that NO is not required for IL-1beta- or LPS-mediated down-regulation of P450 2C11 expression in cultured hepatocytes.

Inhibition of cytokine-induced inducible nitric oxide synthase expression by glucagon and cAMP in cultured hepatocytes

Addition of lipopolysaccharide plus interferon gamma, tumour necrosis factor alpha and interleukin 1 beta to cultured hepatocytes resulted in the induction of inducible nitric oxide synthase (iNOS) activity as measured by NO3(-)+NO2- formation, the conversion of L-[U-14C]arginine into citrulline and Western blotting of the iNOS protein. The inclusion of 1 microM glucagon during the induction period significantly decreased the effect of the cytokines on iNOS activity, the major effect being at the level of the total amount of protein, rather than alterations in substrate supply or covalent modification of the existing protein. In contrast, 1 microM insulin was without effect. The effect of glucagon was mediated via cAMP and could be mimicked by the presence of either dibutyryl cAMP or forskolin to activate adenylate cyclase directly. It was rapid in onset and long-lived, a 30 min pretreatment period protecting the cells from the induction of NO synthesis over the next 21 h in the presence of cytokines. Addition of glucagon at any time point up to 9 h after treatment of the cells with lipopolysaccharide plus the cytokines resulted in a significant inhibition of iNOS activity, glucagon being most potent when added during the first 3 h.

Role of nitric oxide in Sjögren's syndrome

OBJECTIVE

To measure levels of salivary nitrite (NO2-) and to localize nitric oxide synthases (NOS) in the labial salivary glands (LSGs) of patients with Sjögren's syndrome (SS).

METHODS

NO2- was measured by the Griess reaction. LSGs were analyzed using NADPH-diaphorase histochemical and immunohistochemical studies to determine the constitutive NOS (neuronal [ncNOS] and endothelial [ecNOS]) and inducible NOS (iNOS) isoforms.

RESULTS

The NO2- concentration (mean +/- SEM 307 +/- 51 microM versus 97 +/- 16 microM; P < 0.05) and output (166 +/- 46 nmoles/minute versus 37 +/- 7 nmoles/minute) were increased in SS patients compared with healthy control subjects. NADPH-diaphorase was found in some nerve fibers and endothelial cells, and, in SS, was found in myoepithelial, acinar, and ductal epithelial cells, but in only a few inflammatory cells. In SS, ncNOS-immunoreactive nerve fibers were sparse and ecNOS was found in a minority of the CD31-positive vascular endothelial cells and acinar cells, whereas iNOS was localized in myoepithelial, acinar, and ductal epithelial cells, often together with tumor necrosis factor alpha.

CONCLUSION

Nitrite was found in normal human saliva. NO produced by ncNOS probably acts as a nonadrenergic, noncholinergic neurotransmitter, whereas that produced by ecNOS exerts a vasodilatory effect. SS patients had increased NO2- concentrations, with most of the superfluous salivary NO being produced not by the immigrant inflammatory cells, but rather, by the resident salivary gland cells. NO may contribute to inflammatory damage and acinar cell atrophy in SS.