Stimulation of the nitric oxide synthase pathway in human hepatocytes by cytokines and endotoxin.

Nitric oxide (NO) is a short-lived biologic mediator that is shown to be induced in various cell types and to cause many metabolic changes in target cells. Inhibition of tumor cell growth and antimicrobial activity has been attributed to the stimulation of the inducible type of the NO synthase (NOS). However, there is limited evidence for the existence of such inducible NOS in a human cell type. We show here the induction of NO biosynthesis in freshly isolated human hepatocytes (HC) after stimulation with interleukin 1, tumor necrosis factor (TNF), IFN-gamma, and endotoxin. Increased levels of nitrite (NO2-) and nitrate (NO3-) in culture supernatants were associated with NADPH-dependent NOS activity in the cell lysates. The production of NO2- and NO3- was inhibited by NG-monomethyl L-arginine and was associated with an increase in cyclic guanylate monophosphate release. The data presented here provide evidence for the existence of typical inducible NO biosynthesis in a human cell type.

Endogenous nitric oxide inhibits the synthesis of cyclooxygenase products and interleukin-6 by rat Kupffer cells.

Macrophage production of nitric oxide (.N = O) leads to considerable alterations of vital metabolic pathways in various target cells. The present study tested whether .N = O synthesis by Kupffer cells (KCs), the resident macrophages of the liver, interferes with the secretory function of these cells. As in other macrophage-type cells, the combination of lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) was a potent stimulus of .N = O synthesis by KC. Treatment with LPS and IFN-gamma also induced significant production of prostaglandin E2 (PGE2), thromboxane B2 (TBX2), tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1), and IL-6. Inhibition of .N = O synthesis by KC. Treatment with LPS and IFN-gamma also induced significant production of prostaglandin E2 (PGE2), thromboxane B2 (TBX2), tumor necrosis factor alpha (TNF-alpha), interleukin-1 (IL-1), and IL-6. Inhibition of .N = O synthesis by the L-arginine analogue of NG-monomethyl-L-arginine (NMA) resulted in a further increase of PGE2, TXB2, and IL-6 but not IL-1 and TNF-alpha production, indicating specific inhibitory effects of endogenous .N = O synthesis on the secretory activity of KCs. PGE2 production was most sensitive to the suppressive effect of .N = O and increased 24 h after stimulation with LPS and IFN-gamma from 16.3 +/- 4.9 ng/10(6) KCs without NMA to 94.3 +/- 17.9 ng/10(6) KCs with NMA. This effect of NMA was reversed by a 10-fold increase of the L-arginine concentration. No recovery of PGE2 production was seen when .N = O synthesis was blocked after 24 h. NMA treatment increased cyclooxygenase activity more than threefold, suggesting that .N = O inhibits PGE2 and TXB2 production through diminished PGH2 availability. .N = O synthesis did not significantly affect total protein synthesis or viability of the KCs. These results show that .N = O influences the production of specific inflammatory mediators by KCs.

Cytokine induction of interferon regulatory factor-1 in hepatocytes.

BACKGROUND: Interferon regulatory factor-1 (IRF-1) is a transcriptional factor originally cloned from fibroblasts that activates interferons and certain interferon-responsive genes. Because IRF-1 is an "early-immediate" nuclear protein, it can function acutely after trauma or septic stimuli. We have identified IRF-1 expression in hepatocytes in vivo in sepsis. The purpose of this study was to characterize the cytokine signals that up-regulate IRF-1 messenger RNA (mRNA) in cultured hepatocytes. METHODS: Rat hepatocytes were isolated by in situ collagenase perfusion and stimulated in vitro with cytokines. IRF-1 mRNA levels were determined by Northern blot hybridization with a DNA probe for hepatocyte IRF-1 generated with reverse transcription polymerase chain reaction with custom-designed oligonucleotide primers based on the known sequence for T-cell IRF-1. RESULTS: Northern blot of hepatocyte RNA showed a single IRF-1 mRNA band at approximately 2.4 Kb. The mRNA levels were markedly up-regulated (vs control hepatocytes) 2 hours after in vitro stimulation with the cytokines interferon-gamma (17-fold), tumor necrosis factor-alpha (3-fold), and interleukin-1 beta (2-fold). Lipopolysaccharide had no direct effect. CONCLUSIONS: The results showed that IRF-1 is up-regulated in hepatocytes primarily in response to interferon-gamma and to a lesser extent after tumor necrosis factor-alpha or interleukin-1 beta stimulation. This suggests that IRF-1 plays a role in regulating liver gene expression in sepsis; however, the specific genes controlled by IRF-1 remain to be determined.

Induction of hepatocyte lipopolysaccharide binding protein in models of sepsis and the acute-phase response.

Lipopolysaccharide binding protein (LBP) is a serum glycoprotein that complexes with lipopolysaccharide (LPS) to facilitate macrophage response to endotoxin. To determine the conditions that stimulate LBP production in vivo, we measured the induction of LBP in models of inflammation produced by LPS, Corynebacterium parvum, and turpentine injection. Plasma aspartate aminotransferase and alanine aminotransferase concentrations and hepatocyte fibrinogen synthesis were elevated in all models. Northern blot analysis revealed 17-, 14-, and 20-fold upregulation of hepatocyte LBP mRNA following treatment with LPS, C parvum, and turpentine, respectively. Peritoneal macrophage interleukin 6 and tumor necrosis factor production following endotoxin stimulation was augmented by cultured hepatocyte supernatants, suggesting increased LBP synthesis in these groups. The results show that LBP mRNA is induced during hepatic inflammation and suggest that LBP is an acute-phase protein important in regulating the in vivo response to endotoxin.

Differential induction of nitric oxide synthase in hepatocytes during endotoxemia and the acute-phase response.

OBJECTIVE: Nitric oxide (NO) is a potent biologic mediator produced by hepatocytes following exposure to cytokines and lipopolysaccharide (LPS). These cytokines are also known to regulate induction of the hepatic acute-phase response. The objective of this study was to determine whether inducible nitric oxide synthase (iNOS), the enzyme that produces NO, is expressed as part of the hepatic acute-phase response. DESIGN: The gene expression for inducible NOS (iNOS) as well as alpha 1-acid glycoprotein (AGP), an established acute-phase reactant, was measured by Northern blot analysis in rat hepatocytes in vivo during endotoxemia (LPS injection) and during the acute-phase response produced by hindlimb turpentine injection. Hepatocyte iNOS messenger RNA (mRNA) levels were correlated with iNOS activity and circulating plasma nitrite and nitrate levels. In vitro, iNOS and AGP mRNA levels were determined in cultured hepatocytes stimulated with interleukin 6 (IL-6), interleukin 1 beta (IL-1 beta), tumor necrosis factor alpha (TNF-alpha), or dexamethasone. RESULTS: The AGP mRNA levels were increased in vivo following both LPS and turpentine injection, while iNOS expression was induced only by LPS injection. Hepatocyte iNOS activity and plasma nitrite and nitrate levels also increased after LPS treatment. In vitro, the cytokine combination IL-6, IL-1 beta, and TNF-alpha induced hepatocyte iNOS expression but had minimal effects on AGP in the absence of dexamethasone. Addition of dexamethasone alone markedly increased AGP mRNA levels, with further increases seen with TNF-alpha or IL-1 beta addition. In contrast, dexamethasone decreased iNOS expression. CONCLUSION: The results show that hepatocyte iNOS expression is not part of the acute-phase response induced by remote inflammation and indicates that iNOS is differentially regulated from the acute-phase reactant, AGP.

Nitric oxide and transforming growth factor-beta levels during experimental uveitis in the rabbit.

OBJECTIVE: To determine changes in the levels of nitric oxide metabolites and transforming growth factor-beta (TGF-beta) in the rabbit aqueous humour during ocular inflammation. DESIGN: Active experimental uveitis was induced by injection of porcine lens protein (PLP) in three rabbits and of human serum albumin (HSA) in three rabbits; three control rabbits received an injection of saline. OUTCOME MEASURES: Degree of inflammation, antibody titres (determined with the enzyme-linked immunosorbent assay), and aqueous humour levels of nitric oxide metabolites and TGF-beta. A modified Griess assay for nitrites and nitrates (NO2- and NO3-) was used as a measure of nitric oxide generation, and a modification of the CCL-64 mink lung epithelial cell bioassay was used to quantify TGF-beta levels. RESULTS: Following the primary immunologic challenge both experimental groups initially showed a two- to fourfold increment in aqueous levels of nitric oxide metabolites and TGF-beta compared with baseline values. At the peak of the clinically observed inflammation there was a significant increase in the mean nitric oxide metabolite level compared with the control value (p < or = 0.005) (432 nmol/mL for the PLP group and 112 nmol/mL for the HSA group) and a significant decrease (p < or = 0.03) in the mean TGF-beta level (3.1 ng/mL and 0.3 ng/mL respectively). CONCLUSIONS: Nitric oxide may be used as a marker for intraocular inflammation. The increased production of nitric oxide may reflect the loss of immunologic privilege of the ocular microenvironment that occurs during inflammation.

Comparison of Three 7-Day Pantoprazole-Based Helicobacter pylori Eradication Regimens in a Mexican Population with High Metronidazole Resistance.

OBJECTIVE: To compare the efficacy and tolerability of three 7-day pantoprazole-based regimens to eradicate Helicobacter pylori in Mexican patients with peptic ulcer (PU) or non-ulcer dyspepsia (NUD). BACKGROUND: Short-term therapeutic regimens based on a proton pump inhibitor (PPI) and two antibiotics have been recommended for the eradication of H. pylori. Resistance of H. pylori to metronidazole may adversely affect the efficacy of such regimens. PATIENTS AND METHODS: This was a single-centre, randomised, open-label, parallel-group study in which three groups of H. pylori-positive patients with PU or NUD were compared (n = 159; intention-to-treat population). Patients were randomised to receive a 7-day pantoprazole-based triple therapy for eradication of H. pylori. Patients received pantoprazole (P) 40mg twice daily in combination with either i) amoxicillin (A) 1000mg twice daily and clarithromycin (C) 500mg three times daily (PAC regimen, n = 51 patients), or ii) clarithromycin 500mg three times daily and metronidazole (M) 500mg three times daily (PCM regimen, n = 55 patients), or iii) amoxicillin 1000mg twice daily and metronidazole 500mg three times daily (PAM regimen, n = 53 patients). After completing eradication therapy, all PU patients were further treated with once-daily pantoprazole 40mg, either for another 3 weeks (patients with duodenal ulcer) or for another 7 weeks (patients with gastric ulcer), to ensure complete ulcer healing. At baseline examination, all patients underwent the (14)C-urea breath test and endoscopy; biopsy specimens were taken for histology, CLO-test, H. pylori culture and antibiotic susceptibility testing (agar dilution E-test). Eradication of H. pylori was assessed after all treatment with pantoprazole had been discontinued for at least 4 weeks, using the (14)C-urea breath test. RESULTS: In the per-protocol population (n = 153), eradication was achieved in 81.3% (39/48) of patients receiving PAC, 66.0% (35/53) of PCM recipients, and 48.1 % (25/52) of those receiving PAM (p = 0.13 for PAC vs PCM and 0.001 for PAC vs PAM). In the intention-to-treat population, respective eradication rates were 76.5 (39/51), 63.6 (35/55) and 47.2% (25/53) [p = 0.22 for PAC vs PCM and 0.004 for PAC vs PAM]. Patient compliance was very good in all treatment groups. The main adverse event affecting 40% of all patients was a metallic taste, assessed as likely related to the antibiotics. Susceptibility to the three study antibiotics was determined for H. pylori isolates using the pretreatment biopsies from 103 patients. Resistance to metronidazole was present in 68.2% of patients and to clarithromycin in 24.3%. In 16.8% of patients, H. pylori isolates were resistant to both metronidazole and clarithromycin. In patient populations with H. pylori strains resistant to one or both of the antibiotics used in the respective treatment regimen, eradication rates were consistently lower than in those with susceptible H. pylori strains. However, these differences were not statistically significant, probably due to the small sample size. CONCLUSIONS: The 7-day H. pylori eradication regimen with PAC was superior to PCM and PAM. This is probably due to the high resistance rate to metronidazole in the Mexican population. Thus, H. pylori eradication regimens that involve metronidazole cannot be recommended for Mexican patients. RESULTS from this study highlight the regional differences in efficacy of some well established H. pylori eradication regimens, and suggest that culture and susceptibility testing to define H. pylori resistance patterns in specific geographical areas may be indicated before recommending any particular eradication schedule.

[Clinical superiority of pantoprazole over ranitidine in the treatment of reflux esophagitis grade II and III. A prospective, double-blind, double-placebo study. Mexican clinical experience. Mexican Pantoprazole Study Group]. / Superioridad clínica del pantoprazol sobre la ranitidina en la curación de la esofagitis por reflujo grado II y III. Estudio prospectivo, doble ciego, doble placebo. Experiencia clínica mexicana Grupo Mexicano de Estudio del Pantoprazol.

OBJECTIVE: To compare and contrast the efficacy and tolerability of a proton pump inhibitor, pantoprazole, to that of an H2 antagonist, ranitidine, in the treatment of patients with mild to severe reflux esophagitis. BACKGROUND: Reflux esophagitis is a common illness affecting 5-10% of the world's population. Acid reflux plays a major role in the disease's genesis, as do esophageal and gastric motility disturbances. METHODS: 315 patients (intent to treat) with endoscopically confirmed reflux esophagitis (Savary-Miller (SM) stages II and III) were recruited to the study by 46 mexican investigators in nine centers. Patients received either pantoprazole 40 mg once daily or ranitidine 150 mg twice daily in this double blind, randomized, parallel group study. Patients not achieving complete endoscopic healing after four weeks of therapy received an additional four weeks of treatment. Drug tolerability was assessed by adverse event reporting during the study. RESULTS: After four weeks pantoprazole therapy, 81% of patients with SM II and 67% of the patients with SM III were healed; in contrast ranitidine healed only 67 and 30% of the patients respectively, all results expressed on an per-protocol basis. After eight weeks therapy the healing rates for pantoprazole group increased to 94% and the ranitidine group to 74% (p = 0.001). The incidence of adverse events was less than 2% in both treatment groups, thus both therapies were found to be well tolerated. CONCLUSIONS: Pantoprazole is superior to ranitidine in the treatment of mild to severe reflux esophagitis and is equally well tolerated.

[Comparison of 2 schedules based on pantoprazole for eradication of Helicobacter pylori in patients with active duodenal ulcer]. / Comparación de dos esquemas basados en pantoprazol para erradicación de Helicobacter pylori en pacientes con úlcera duodenal activa.

OBJECTIVE: To compare the efficacy and tolerability of a triple vs dual pantoprazole based therapy to eradicate Helicobacter pylori (H. pylori) in mexican patients with florid duodenal ulcer. BACKGROUND: The treatment of peptic ulcer disease was revolutionized by the fact that H. pylori generally induces chronic gastritis and peptic ulcer disease and that the cure of the infection prevents ulcer relapses. MATERIAL AND METHODS: 74 H. pylori positive patients with florid duodenal ulcer were randomized to receive either pantoprazole 40 mg bid in combination with clarithromycin 500 mg tid and amoxicillin 1 g bid (triple regimen PAC) or pantoprazole in combination with clarithromycin and placebo (dual regimen PC) during 14 days. To ensure complete ulcer healing all patients received an additional 2 weeks treatment with pantoprazole 40 mg od. 14C Urea Breath test (UBT) was the main criteria used to determine eradication rate with < 150 disintegrations per minute (DPM) to consider a patient eradicated. In all patients culture, antibiotic susceptibility (E-test) and histology were performed. RESULTS: In the per protocol analysis (n = 66) the eradication rate was: PAC 93.5% vs PC 54.3% (p < 0.001). 76% of H. pylori strains were resistant to metronidazole. Tolerance and compliance were excellent in both groups. CONCLUSIONS: Triple therapy (PAC) was shown to be superior to dual therapy (PC) for H. pylori eradication in mexican patients with florid duodenal ulcer.

[Breath tests as a noninvasive diagnostic method in Helicobacter pylori infection]. / La prueba de aliento como método diagnóstico no invasivo en la infección por Helicobacter pylori.

There are several diagnostic methods for Helicobacter pylori infection, some of them need an endoscopic procedure and biopsy to be performed (invasive) like the rapid urease test, culture and histology. Recently non invasive, specific, sensible, easy to perform and patient's well accepted methods had been developed known as breath test, based on the hydrolysis of labelled urea by Helicobacter pylori urease enzyme, to release ammonia and bicarbonate. Labelled CO2 reaches the bloodstream and the lungs, from where can be collected into the breath for quantification. Labelled urea has to options: 13C stable, non-radioactive and 14C unstable, radioactive. Breath test with 13C is based on the atomic mass difference between 12C and 13C and it is necessary a mass spectrometer and 40 minutes to perform it. Breath test with 14C has 1 uCi (one micro-curie) of radioactivity (1/300 of total radiation received in one year from the environment); the test takes 10 minutes and the samples are read in a beta counter. Both non-invasive tests had demonstrated sensitivity and specificity comparable to established "gold standards" for Helicobacter pylori infection diagnosis.

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.

Polytetrafluoroethylene microprosthesis in the arterial system of the rat.

The experimental behavior of a 1-mm internal diameter (i.d.) polytetrafluoroethylene (PTFE) microprosthesis, as a substitute for an abdominal aortic segment in the rat, was reviewed. Fifty Wistar rats were divided into four groups: Group I--12 rats with autotransplant of an abdominal aortic segment (AAS); Group II--12 rats with allotransplant of an AAS obtained from Long-Evans rats; Group III--12 rats with xenotransplant of an AAS taken from rabbit femoral arteries; and Group IV--14 rats with substitution of an AAS by a 1-mm i.d. PTFE microprosthesis. The rats were sacrificed at different time intervals ranging from five to 360 days, with previous aortography. In Group I, there was a 100 percent patency at a mean of 152.41 days; in Group II, a 91.6 percent patency at a mean of 100.08 days; in Group III, an 83.3 percent patency with a 75 percent aneurysmal dilation at a mean of 107.58 days; in Group IV, a 71.42 percent patency with two anastomotic aneurysms at a mean of 105 days (P less than 0.05, chi square) between Groups I and IV, autotransplant vs. PTFE). The 1-mm PTFE microprosthesis placed in the arterial system of the rat proved to be a reliable alternative for microvascular substitution.

Glutathione regulates nitric oxide synthase in cultured hepatocytes.

OBJECTIVE: The authors determine the relationship between glutathione and nitric oxide (NO) synthesis in cultured hepatocytes. SUMMARY BACKGROUND DATA: Glutathione is a cofactor for a number of enzymes, and its presence is essential for maximal enzyme activity by the inducible macrophage nitric oxide synthase (iNOS), which produces the reactive nitric oxide radical. Hepatocytes contain substantial quantities of glutathione, and this important tripeptide is decreased in hepatocytes stressed by ischemia/reperfusion or endotoxemia. Endotoxemia also induces the synthesis of inflammatory cytokines that result in the production of nitric oxide from hepatocytes by iNOS, suggesting that hepatocytes may be attempting to synthesize nitric oxide at times when intracellular glutathione is reduced. METHODS: Hepatocytes were cultured with buthionine sulfoximine and 1,3-bis(chloroethyl)-1-nitrosourea (BCNU) to inhibit glutathione. After exposure to cytokines, NO synthesis was assessed by supernatant nitrite levels, cytosolic iNOS enzyme activity, and iNOS mRNA levels. RESULTS: Inhibition of glutathione synthesis with buthionine sulfoximine or inhibition of glutathione reductase activity with BCNU inhibited nitrite synthesis. Both buthionine sulfoximine and BCNU inhibited the induction of iNOS mRNA, as detected by Northern blot analysis. Exogenous glutathione increased cytokine-stimulated iNOS induction, overcame the inhibitory effects of BCNU, and increased nitrite production by intact hepatocytes, induced hepatocyte cytosol, and partially purified hepatocyte iNOS. CONCLUSIONS: In cultured hepatocytes, adequate glutathione levels are required for optimal nitric oxide synthesis. This finding is predominantly due to an effect on iNOS mRNA levels, although glutathione also participates in the regulation of iNOS enzyme activity.

Tumor necrosis factor-alpha regulates in vivo nitric oxide synthesis and induces liver injury during endotoxemia.

Tumor necrosis factor-alpha is a principal mediator of the pathophysiological effects of endotoxemia and endotoxin shock. Tumor necrosis factor-alpha also contributes to the stimulation of nitric oxide synthesis by the induction of the enzyme nitric oxide synthase in a variety of tissues. Although the importance of tumor necrosis factor-alpha in the induction of nitric oxide synthase activity in vitro is well known, its role in in vivo nitric oxide synthesis has not been convincingly established. We were interested in determining whether tumor necrosis factor-alpha plays a significant role in the in vivo induction of nitric oxide synthesis. In Corynebacterium parvum-primed mice, lipopolysaccharide injection resulted in elevated serum tumor necrosis factor-alpha levels early and increased hepatic enzyme release (641 +/- 80 IU AST/L; 22.7 +/- 1.9 IU ornithine carbamoyltransferase per liter) and plasma nitrite and nitrate (804 +/- 84 mumol/L) 5 hr after lipopolysaccharide injection. Polyclonal rabbit anti-mouse anti-tumor necrosis factor-alpha reduced in vivo tumor necrosis factor-alpha levels (1 hr, 7,332 +/- 1,492 U tumor necrosis factor-alpha per milliliter) and reduced nitric oxide synthesis as measured by plasma nitrite and nitrate (352 +/- 69 mumol/L). Polyclonal rabbit anti-mouse anti-tumor necrosis factor-alpha also reduced lipopolysaccharide-induced hepatic enzyme release (428 +/- 33 IU AST/L; 16.0 +/- 2.5 IU ornithine carbamoyltransferase per liter). NG-monomethyl-L-arginine, a competitive inhibitor of nitric oxide synthesis, also decreased plasma nitrite and nitrate (104 +/- 9 mumol/L) but increased the lipopolysaccharide-induced hepatic injury (797 +/- 66 IU AST/L; 33.1 +/- 2.1 IU ornithine carbamoyltransferase per liter).(ABSTRACT TRUNCATED AT 250 WORDS)

Human hepatocytes are more resistant than rat hepatocytes to anoxia-reoxygenation injury.

We performed this study to determine whether perfused isolated human and rat hepatocytes have different sensitivities to anoxia-reoxygenation injury. Oxygen free radicals were detected by lucigenin-enhanced chemiluminescence. Lipid peroxidation was assessed by measuring malondialdehyde release. Cell injury was evaluated by measuring lactate dehydrogenase release and trypan blue uptake. During the control period, lucigenin-enhanced chemiluminescence, malondialdehyde and lactate dehydrogenase release and trypan blue uptake were similar in rat and human hepatocytes. During 3.5 hr of anoxia, lucigenin-enhanced chemiluminescence decreased to background levels and malondialdehyde release remained constant in both groups. In contrast, lactate dehydrogenase release increased eightfold in rat hepatocytes but only threefold in human hepatocytes. With reoxygenation after 2.5 hr of anoxia, in rat hepatocytes lucigenin-enhanced chemiluminescence increased 13-fold within 15 min and then declined toward control levels. Malondialdehyde release doubled after 1 hr of reoxygenation. The rate of lactate dehydrogenase release increased to a level almost twice that observed in cells kept continuously anoxic. In contrast, with human hepatocytes lucigenin-enhanced chemiluminescence increased only fourfold, whereas malondialdehyde and lactate dehydrogenase releases did not differ significantly from those levels measured in cells perfused continuously under anoxic conditions. At the end of the experiment, the increase in trypan blue uptake was significantly greater with rat hepatocytes than with human hepatocytes. These results demonstrate that (a) during reoxygenation following 2.5 hr of anoxia, isolated human hepatocytes generate fewer oxygen free radical, and lipoperoxides than do rat hepatocytes, and (b) human hepatocytes are more resistant to cell injury during anoxia-reoxygenation than are rat hepatocytes.

Nitric oxide-induced S-nitrosylation of glyceraldehyde-3-phosphate dehydrogenase inhibits enzymatic activity and increases endogenous ADP-ribosylation.

Using conditions that produced chronic inflammation in rat liver, we were able to find a correlation between induction of nitric oxide production and inhibition of glyceraldehyde-3-phosphate dehydrogenase (GAPDH; EC 1.2.1.12). This enzyme is a tetramer composed of identical M(r) 37,000 subunits. The tetramer contains 16 thiol groups, four of which are essential for enzymatic activity. Our information indicates that four thiol groups are S-nitrosylated by exposure to authentic nitric oxide (NO) gas. Furthermore, NO decreased GAPDH activity while increasing its auto-ADP-ribosylation. Reduced nicotinamide adenine dinucleotide and dithiothreitol are required for the S-nitrosylation of GAPDH caused by the NO-generating compound sodium nitroprusside. Our results suggests that a new and important action of nitric oxide on cells is the S-nitrosylation and inactivation of GAPDH. S-Nitrosylation of GAPDH may be a key covalent modification of multiple regulatory consequences in chronic liver inflammation.

Tumor necrosis factor alpha inhibits hepatocyte mitochondrial respiration.

Although direct cytotoxicity is a well-established phenomenon of tumor necrosis factor alpha (TNF alpha)-induced tissue damage, the intracellular events leading to cell death are still poorly understood. To study the cytotoxic effects of TNF alpha on normal parenchymal cells, rat hepatocytes were purified and incubated with various concentrations of TNF alpha. Mitochondrial respiration, total protein synthesis, and enzyme release were measured to assess metabolic performance and cell integrity. Treatment with TNF alpha suppressed mitochondrial respiration in a concentration-dependent fashion, resulting in a reduction of the activity of complex I of the respiratory chain to 67.0 +/- 3.5% of that of untreated hepatocytes by 2000 U/mL TNF alpha. Under these conditions protein synthesis and the release of intracellular enzymes were significantly increased. Both hepatocellular enzyme release and inhibition of mitochondrial respiration appear to be associated with the generation of reactive oxygen intermediates by the hepatocyte itself, because oxygen radical scavengers prevented these adverse effects of TNF alpha. Inhibition of protein synthesis by cycloheximide as well as addition of cyclic adenosine monophosphate synergistically enhanced the suppression of mitochondrial respiration by TNF alpha, resulting in complex I activity of 6.9 +/- 1.6% and 24.9 +/- 2.9% of that of untreated cells. These data indicate that inhibition of mitochondrial respiration is one of the mechanisms by which TNF alpha induces tissue injury.