Differential inhibition of prostaglandin and superoxide production by dexamethasone in primary cultures of rat Kupffer cells

Liver parenchyma heterogeneity in the response to extracellular NAD+

The perfused rat liver responds intensely to NAD+ infusion (20-100 microM). Increases in portal perfusion pressure and glycogenolysis and transient inhibition of oxygen consumption are some of the effects that were observed. The aim of the present work was to investigate the distribution of the response to extracellular NAD+ along the hepatic acinus. The bivascularly perfused rat liver was used. Various combinations of perfusion directions (antegrade and retrograde) and infusion routes (portal vein, hepatic vein and hepatic artery) were used in order to supply NAD+ to different regions of the liver parenchyma, also taking advantage of the fact that its extracellular transformation generates steep concentration gradients. Oxygen uptake was stimulated by NAD+ in retrograde perfusion (irrespective of the infusion route) and transiently inhibited in antegrade perfusion. This indicates that the signal causing oxygen uptake inhibition is generated in the periportal area. The signal responsible for oxygen uptake stimulation is homogenously distributed. Stimulation of glucose release was more intense when NAD+ was infused into the portal vein or into the hepatic artery, indicating that stimulation of glycogenolysis predominates in the periportal area. The increases in perfusion pressure were more pronounced when the periportal area was supplied with NAD+ suggesting that the vasoconstrictive elements responding to NAD+ predominate in this region. The response to extracellular NAD+ is thus unequally distributed in the liver. As a paracrine agent, NAD+ is likely to be released locally. It can be concluded that its effects will be different depending on the area where it is released.

COX-1 and COX-2 contribute differentially to the LPS-induced release of PGE2 and TxA2 in liver macrophages

LPS induces an immediate release of thromboxane TxA2 and a delayed release of PGE2. Dexamethasone suppresses the LPS-induced release of TxA2 and PGE2. In the first 8 h after LPS addition, the specific COX-2 inhibitor SC236 inhibits the PGE2 and TxA2 release by about 80% and 20%, whereas the release of PGE2 and TxA2 between 8 and 24 h is inhibited by about 40% and 35%, respectively. Resident liver macrophages express substantial amounts of COX-1, TxAS, cPGES and mPGES-2, small amounts of COX-2 but almost no detectable amounts of mPGES-1. LPS induces an increase of COX-2 and mPGES-1, but does not change COX-1, cPGES, mPGES-2 and TxAS at protein level. Dexamethasone suppresses almost completely the LPS-induced effects on COX-2 and mPGES-1. It is concluded that (1) COX-1 and COX-2 are involved in the LPS-induced synthesis of TxA2 and PGE2; (2) TxA2 release is catalyzed at early time-points by the combined action of COX-1 and TxAs, whereas at later time points the newly expressed COX-2 couples to TxAS and contributes to the TxA2 release; (3) PGE2 release within the first 8 h is predominantly catalyzed by COX-2, whereas at later time-points COX-1 couples to the newly expressed mPGES-1 and contributes to the PGE2 release.

Ischaemic preconditioning modulates the activity of Kupffer cells during in vivo reperfusion injury of rat liver

This work was performed to elucidate further the main cellular events underlying the protective effect of ischaemic preconditioning in an in vivo rat liver model of 90 min ischaemia followed by 30 min reperfusion. A significant attenuation of the various aspects of post-ischaemic injury, namely necrosis and the levels of hydrogen peroxide and 5- and 15-hydroperoxyeicosatetraenoic acids, was afforded by the prior application of a short cycle of ischaemia/reperfusion (10 + 10 min) or when rats were previously treated with gadolinium chloride. However, when preconditioning was applied on Kupffer cell-depleted livers, no additional level of ischaemic tolerance was obtained. In terms of cellular pathology, this result could be suggestive of Kupffer cells as the target of the preconditioning phenomenon during the warm ischaemia/reperfusion injury. Accordingly, modulation of Kupffer cell activity was associated with a well-preserved hepatocyte integrity, together with low levels of pro-oxidant generation during reperfusion. As activated Kupffer cells can generate and release potentially toxic substances, their modulation by ischaemic preconditioning could help to provide new surgical and/or pharmacological strategies to protect the liver against reperfusion damage.

Kupffer cells are a major source of increased platelet activating factor in the CCl4-induced cirrhotic rat liver

BACKGROUND/AIMS

Endothelin-1 (ET-1) stimulates the synthesis of platelet-activating factor (PAF) by Kupffer cells in vitro. Hepatic concentrations of both ET-1 (a potent vasoconstrictor) and PAF (a mediator of hepatic vasoconstriction and the cirrhotic hyperdynamic state) increase in cirrhosis. The aim of this study was to determine if the responsiveness of Kupffer cells to produce PAF upon ET-1 challenge is modified by cirrhosis.

METHODS

Kupffer cells, isolated from the livers of control and CCl(4)-induced cirrhotic rats, were placed in serum-free medium after overnight culture. PAF and ET-1 receptors, ET-1-induced PAF synthesis, and PAF- and ET-1-induced prostaglandin E(2) (PGE(2)) synthesis were determined 24 h later.

RESULTS

Both basal and ET-1-stimulated PAF synthesis was increased in cirrhotic Kupffer cells as indicated by increased cell-associated and released PAF. Cirrhotic Kupffer cells also had elevated densities of functional receptors for both PAF and ET-1 (exclusively ET(B)), as measured by ligand binding, mRNA expression of the respective receptors, and ligand-stimulated PGE(2) synthesis.

CONCLUSIONS

Cirrhosis sensitizes Kupffer cells to both ET-1 and PAF by elevating their respective receptor levels. Since both mediators individually cause portal hypertension, an increase in ET-1-stimulated PAF synthesis in Kupffer cells will exacerbate the hepatic and extrahepatic complications of cirrhosis.

Caspase 9-dependent killing of hepatic stellate cells by activated Kupffer cells

BACKGROUND & AIMS

Hepatic stellate cells play an important role in liver fibrogenesis, and hepatic stellate cell death may be involved in the termination of this response.

METHODS

Molecular mechanisms of hepatic stellate cell killing were studied in hepatic stellate cell/Kupffer cell cocultures.

RESULTS

Lipopolysaccharide stimulation of hepatic stellate cell/Kupffer cell cocultures, but not of hepatic stellate cell monocultures, induced profound alterations of hepatic stellate cell morphology and hepatic stellate cell death. Kupffer cell-induced hepatic stellate cell killing required hepatic stellate cell/Kupffer cell contacts and was prevented by dexamethasone, prostaglandin E(2), tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor 2 antagonists, and down-regulation of receptor-interacting protein, but not by antioxidants, tumor necrosis factor receptor, or CD95 antagonists. Hepatic stellate cell death was characterized by activation of caspases 3, 8, and 9, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling negativity, lack of gross calcium overload, and TRAIL trafficking to the plasma membrane. Inhibition of caspase 9, but not of caspases 3, 8, or 10, prevented hepatic stellate cell death. Lipopolysaccharide induced a dexamethasone- and prostaglandin E(2)-sensitive expression of TRAIL in Kupffer cells. TRAIL receptors 1 and 2, FLIP (caspase 8-inhibitory protein), and receptor-interacting protein were up-regulated during hepatic stellate cell transformation; however, TRAIL addition did not induce hepatic stellate cell death. Hepatic stellate cell susceptibility toward Kupffer cell-induced death paralleled receptor-interacting protein and TRAIL-receptor expression levels.

CONCLUSIONS

Activated Kupffer cell can effectively kill hepatic stellate cell by a caspase 9- and receptor-interacting protein-dependent mechanism, possibly involving TRAIL. The data may suggest a novel form of hepatic stellate cell death.

NADPH oxidase-derived free radicals are key oxidants in alcohol-induced liver disease

In North America, liver disease due to alcohol consumption is an important cause of death in adults, although its pathogenesis remains obscure. Despite the fact that resident hepatic macrophages are known to contribute to early alcohol-induced liver injury via oxidative stress, the exact source of free radicals has remained a mystery. To test the hypothesis that NADPH oxidase is the major source of oxidants due to ethanol, we used p47(phox) knockout mice, which lack a critical subunit of this major source of reactive oxygen species in activated phagocytes. Mice were treated with ethanol chronically, using a Tsukamoto-French protocol, for 4 weeks. In wild-type mice, ethanol caused severe liver injury via a mechanism involving gut-derived endotoxin, CD14 receptor, production of electron spin resonance-detectable free radicals, activation of the transcription factor NF-kappaB, and release of cytotoxic TNF-alpha from activated Kupffer cells. In NADPH oxidase-deficient mice, neither an increase in free radical production, activation of NF-kappaB, an increase in TNF-alpha mRNA, nor liver pathology was observed. These data strongly support the hypothesis that free radicals from NADPH oxidase in hepatic Kupffer cells play a predominant role in the pathogenesis of early alcohol-induced hepatitis by activating NF-kappaB, which activates production of cytotoxic TNF-alpha.

Peroxisome proliferator-activated receptor alpha is restricted to hepatic parenchymal cells, not Kupffer cells: implications for the mechanism of action of peroxisome proliferators in hepatocarcinogenesis

Peroxisome proliferators increase hepatocyte proliferation and cause liver tumors in rodents, yet the mechanism of action is not understood. Based on studies with null mice it is known that peroxisome proliferator-activated receptor-alpha (PPARalpha) is involved. There is also evidence that Kupffer cells play a central role in peroxisome proliferator-induced carcinogenesis, most likely via mechanisms involving increases in superoxide, activation of nuclear factor kappaB and production of tumor necrosis factor-alpha (TNFalpha). However, it is not known whether PPARalpha is constitutively expressed in Kupffer cells. Therefore, the expression of PPAR isoforms in rat Kupffer and parenchymal cells was examined. Kupffer cells and hepatocytes of >99% purity were isolated from rats fed either a control diet or one containing 0.1% WY-14,643 for 1 week. Protein and RNA were obtained and PPAR expression was analyzed using northern and western blots. PPARalpha, PPARbeta and PPARgamma mRNA was detected in purified hepatocytes. In Kupffer cells, mRNA encoding PPARgamma was present while transcripts for PPARalpha and PPARbeta were not detected. Immunoblots were consistent with the results found by northern analysis. Moreover, when Kupffer cells from wild-type or PPARalpha-null mice were treated with WY-14,643 in vitro, superoxide production was similar. Combined, these results show that PPARalpha is expressed in rat parenchymal cells but not in Kupffer cells. These data are consistent with the hypothesis that parenchymal cells respond to Kupffer cell-derived TNFalpha via mechanisms dependent on PPARalpha within the parenchymal cells.

Involvement of CD95 (Apo-1/Fas) ligand expressed by rat Kupffer cells in hepatic immunoregulation

BACKGROUND & AIMS

CD95 (Apo-1/Fas) ligand suppresses inflammatory responses in immune-privileged organs. In this study, modulation of the hepatic CD95 receptor/ligand system by interferon gamma and cyclosporin A was investigated.

METHODS

CD95 receptor and ligand expression were measured at the messenger RNA level by using quantitative reverse-transcription polymerase chain reaction and immunocytochemistry in primary cultures of rat Kupffer cells, hepatocytes, and T lymphocytes. Soluble CD95 in culture supernatants was detected by enzyme-linked immunosorbent assay and apoptosis by the TUNEL method.

RESULTS

Interferon gamma treatment led to an increase in CD95 ligand messenger RNA levels in Kupffer cells followed by an overexpression of the soluble CD95 receptor. Supernatants derived from 24-hour but not from 48-hour interferon gamma-treated Kupffer cells killed lymphocytes by a CD95-dependent mechanism. Cyclosporin A inhibited CD95 ligand expression in Kupffer cells and lymphocyte killing. In liver parenchymal cells, interferon gamma increased messenger RNA levels of the transmembrane CD95 isoform and sensitivity of these cells toward CD95-mediated apoptosis.

CONCLUSIONS

The expression pattern of CD95 receptor and ligand in response to interferon gamma points to a coordinated interplay between Kupffer cells, hepatocytes, and T lymphocytes in which Kupffer cells may regulate programmed cell death of T lymphocytes and hepatocytes.

Kupffer cell oxidant production is central to the mechanism of peroxisome proliferators

Increased cell proliferation most likely plays a key role in peroxisome proliferator-induced liver cancer. Recently, Kupffer cells were shown to be responsible for Wy-14,643-induced cell proliferation. However, the mechanism by which peroxisome proliferators activate Kupffer cells is unknown. Since gut-derived endotoxin is a known activator of Kupffer cells, the hypothesis that it is involved was evaluated. Increased cell proliferation and peroxisome induction were unaffected by gut sterilization. Moreover, endotoxin was not detectable in portal blood following treatment with Wy-14,643. Therefore, it is concluded that gut-derived endotoxin is not responsible for Kupffer cell activation. To test the hypothesis that Kupffer cells are activated by Wy-14,643 directly, Kupffer cell superoxide production was measured following treatment in vitro. Wy-14,643 increased superoxide production in a dose-dependent manner (0.1 and 50 microM) with half-maximal stimulation at 2.5 microM. Diethylhexylphthalate (DEHP) and ethylhexanol did not increase superoxide production even at doses 50 times higher than Wy-14,643; however, monoethylhexylphthalate (MEHP) activated superoxide production as effectively as Wy-14,643 with half-maximal stimulation at 5 microM. Treatment with Wy-14,643 for 21 days caused a 2-fold increase in Kupffer cell superoxide production while DEHP did not. Pretreatment of Kupffer cells with staurosporine (0.01-10 pM) completely blocked generation of superoxide demonstrating that protein kinase C is required. Moreover, Wy-14,643 increased Kupffer cell protein kinase C activity 3-fold. Pretreatment of Kupffer cells with the amino acid glycine (0.01-3 mM), which blunts calcium signaling, inhibited Wy-14,643-stimulated superoxide production and increased protein kinase C activity completely. These data are consistent with the hypothesis that potent peroxisome proliferators (Wy-14,643 and MEHP) directly activate Kupffer cell production of oxidants via mechanisms involving protein kinase C. Further, peroxisome proliferator treatments that sustain elevated rates of cell proliferation (e.g. Wy-14,643) activate Kupffer cell superoxide production following long-term dietary treatment supporting the hypothesis that Kupffer cell-derived oxidants are involved in peroxisome proliferator-induced neoplasia.

Compatible organic osmolytes in rat liver sinusoidal endothelial cells

Compatible organic osmolytes, such as betaine and taurine are involved in the regulation of Kupffer cell (KC) function, but nothing is known about osmolytes in liver endothelial cells. This was investigated here by studying the effect of aniso-osmotic exposure of rat liver sinusoidal endothelial cells (SEC) on osmolyte transport and the messenger RNA (mRNA) levels for the transport systems for betaine (BGT1), taurine (TAUT), and myo-inositol (SMIT). Compared with normo-osmotic exposure (305 mosmol/L), hyperosmotic exposure (405 mosmol/L) of SEC led to an increase in the mRNA levels for these transport systems and simultaneously to a stimulation of betaine, taurine, and myo-inositol uptake, which led to an increase of cell volume. Conversely, hypo-osmotic exposure decreased osmolyte uptake. When hyperosmotically pre-exposed SEC were loaded with betaine, taurine, or myoinositol, hypo-osmotic stress stimulated the efflux of these osmolytes from the cells. Studies on osmolyte tissue levels revealed that taurine was an important compatible organic osmolyte under normo-osmotic conditions and predominantly released following hypo-osmotic stress. Conversely, following hyperosmotic exposure, the increase in cellular betaine and myo-inositol exceeded that of taurine. In lipopolysaccharide (LPS)-treated SEC, hyperosmotic exposure markedly raised the mRNA levels for cyclo-oxygenase-2 (COX-2), but not for inducible nitric oxide synthase (iNOS). The increase of COX-2 mRNA levels was counteracted by betaine and taurine and, to a lesser extent, by myo-inositol. The findings indicate that SEC use taurine, betaine, and myo-inositol as compatible organic osmolytes.

Regulation of CD95 (APO-1/Fas) receptor and ligand expression by lipopolysaccharide and dexamethasone in parenchymal and nonparenchymal rat liver cells

The effect of lipopolysaccharide (LPS) on the expression of CD95 (APO-1/Fas) receptor and ligand (CD95L) was studied in primary cultures of rat liver Kupffer cells (KCs), sinusoidal endothelial cells (SECs), and parenchymal cells (PCs) at the messenger RNA (mRNA) level and by means of immunocytochemistry. LPS treatment of KCs and SECs led to a three- to five-fold increase in CD95L mRNA levels within 6 hours, which declined thereafter. Within 24 hours, the number of KCs and SECs staining positive for CD95L strongly increased. After a lag phase of 12 hours after LPS addition, in both cell types the mRNA levels for the soluble CD95 isoform increased approximately 10-fold; however, the number of KCs and SECs staining positive for transmembrane CD95 remained low and did not significantly increase. Compared with nonparenchymal cells, CD95L mRNA levels in primary hepatocyte cultures were low in the absence and presence of LPS. On the other hand, functionally active CD95 expression markedly increased in response to LPS in these cells. Dexamethasone diminished the LPS-induced stimulation of CD95L expression in nonparenchymal cells but markedly stimulated CD95L expression in PCs. Apoptosis of PCs and thymic lymphocytes was stimulated by the addition of supernatants derived from LPS-treated KC or SEC cultures and was apparently mediated by CD95L as assessed by its sensitivity to inhibitors of the CD95-dependent apoptotic pathway in PCs. The data suggest a complex and timely coordinated interplay between the various liver cell populations with respect to LPS-induced activation of the apoptotic machinery with potential relevance for immunoregulation.

myo-Inositol is an osmolyte in rat liver macrophages (Kupffer cells) but not in RAW 264.7 mouse macrophages

The role of myo-inositol as an osmolyte was studied in cultured rat liver macrophages (Kupffer cells). Hyperosmotic exposure of Kupffer cells stimulated myo-inositol uptake and led to an increase in the mRNA levels for the sodium/myo-inositol cotransporter (SMIT). Conversely, hypo-osmotic (205 m-osM) exposure diminished myo-inositol uptake when compared with normo-osmotic (305 m-osM) control incubations. The hyperosmolarity-induced SMIT mRNA increase was counteracted by added myo-inositol or betaine. In contrast with Kupffer cells, there was only a slight hyperosmotic stimulation of myo-inositol uptake in RAW 264.7 mouse macrophages, and the myo-inositol transporter (SMIT) mRNA was not detectable. Further, a slight stimulation of taurine uptake and an increase in taurine transporter (TAUT) mRNA level by hyperosmolarity was observed in RAW 264.7 cells, whereas hypo-osmolarity led to a decrease in taurine uptake and TAUT mRNA level. When Kupffer cells were preloaded with myo-inositol, hypo-osmotic exposure led to a rapid efflux of myo-inositol from the cells. Myo-inositol efflux was also stimulated by phagocytosis of latex particles; however, latex was without effect on the hyperosmolarity-induced increase of SMIT mRNA levels. The results suggest a role of myo-inositol as an osmolyte in rat Kupffer cells but not in RAW 264.7 mouse macrophages. The functional relevance of this osmolyte strategy might lie in the maintenance of cell volume homeostasis during phagocytosis in Kupffer cells; however, the interplay with the other osmolytes betaine and taurine remains to be established.

Taurine is an osmolyte in rat liver macrophages (Kupffer cells)

BACKGROUND/AIMS

The availability of betaine as an osmolyte was recently shown to interfere strongly with important cell functions of liver macrophages (Kupffer cells), such as eicosanoid and tumor necrosis factor-alpha production or phagocytosis. We therefore investigated whether taurine is also used as an osmolyte by Kupffer cells and whether it is involved in the control of Kupffer cell functions.

METHODS/RESULTS

Hyperosmotic (hypoosmotic) exposure of cultured rat liver macrophages (Kupffer cells) for 6-12 h led to an increase (decrease) in the mRNA levels of the taurine transporter (TAUT) and an increase (decrease) in taurine transport into the cells. The hyperosmolarity-induced increase in TAUT-mRNA levels was diminished by 37+/-10% upon addition of taurine, but not upon addition of betaine. When Kupffer cells were preloaded with taurine, hypoosmotic exposure led to a rapid efflux of taurine from the cells, which was significantly delayed in the presence of the anion exchanger inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS). Taurine efflux was also stimulated during phagocytosis of Latex particles; however, Latex was without effect on the hyperosmolarity-induced increase of TAUT mRNA levels. Lipopolysaccharide (LPS) led to an induction of cyclooxygenase-2, which was markedly enhanced during hyperosmotic conditions. Taurine diminished the induction of cyclooxygenase-2 and inhibited the LPS/hyperosmolarity-induced stimulation of prostaglandin E2 formation.

CONCLUSIONS

The data suggest that, in addition to betaine, taurine also acts as an osmolyte in Kupffer cells, and that taurine availability may be an important modulater of Kupffer cell functions such as eicosanoid synthesis.

Somatostatin modulates the function of Kupffer cells

Recent studies have shown that somatostatin modulates lymphocyte and peritoneal macrophage function, but the effects of somatostatin on hepatic macrophages (Kupffer cells) are not clearly defined. In the present study, hepatic macrophages obtained from male rats were treated in vitro with somatostatin or octreotide and their effects on the release of nitrite, tumor necrosis factor (TNF), and hydrogen peroxide (H2O2) determined. At concentrations of 10(-14) M to 10(-12) M, or greater than 10(-10) M, somatostatin suppressed nitrite release by Kupffer cells. At concentrations of less than 10(-9) M or greater than 10(-9) M, octreotide inhibited nitrite release by Kupffer cells. Kupffer cells treated with 10(-10) M to 10(-14) M or greater than 10(-8) M of somatostatin released significantly less amounts of TNF than did the untreated controls. TNF release by Kupffer cells treated with 10(-15) M to 10(-5) M of octreotide was significantly inhibited as compared to that of untreated controls. Kupffer cells treated with 10(-14) M to 10(-11) M and 10(-9) M to 10(-8) M of somatostatin released more H2O2 than did the untreated controls. The amount of H2O2 released by noncirrhotic Kupffer cells treated with 10(-6) M or 10(-5) M of somatostatin was less than that of controls. These findings demonstrate that somatostatin and octreotide modulate the release of nitric oxide, TNF, H2O be Kupffer cells depending on the concentration of hormones used.

Modulation of phagocytosis by anisoosmolarity and betaine in rat liver macrophages (Kupffer cells) and RAW 264.7 mouse macrophages

Hypoosmotic exposure (205 mosmol/l) of rat liver macrophages (Kupffer cells) for 12 h stimulated phagocytosis of latex particles by about 20%, whereas hyperosmotic exposure (405 mosmol/l) resulted in 30-40% inhibition. Inhibition of phagocytosis by hyperosmolarity was fully prevented in the presence of betaine, which acts as an osmolyte in liver macrophages. When hyperosmotically exposed Kupffer cells were preloaded with betaine, induction of phagocytosis by addition of latex particles led to the stimulation of betaine efflux from the cells. Stimulation of phagocytosis also inhibited the hyperosmolarity-induced cumulative uptake of betaine into Kupffer cells, but did not prevent the hyperosmolarity-induced increase in BGT1-mRNA levels. Whereas these findings suggest an involvement of cell volume and betaine in the regulation of phagocytosis in Kupffer cells, betaine transport was not affected upon induction of phagocytosis in RAW 264.7 mouse macrophages. The findings are compatible with a role of betaine in maintaining cell volume homeostasis during phagocytosis in Kupffer cells, but not in RAW 264.7 mouse macrophages. This may be relevant for the maintenance of liver hemodynamics, since volume changes of liver macrophages following ingestion of phagocytozable material might otherwise impair sinusoidal perfusion.

The preventive effects of OK432 on endotoxin-induced liver injury: liver protection by the modulation of hepatic macrophage function

The present study was conducted to clarify whether endotoxin-induced liver injury could be improved by modulating the function of hepatic macrophages using OK432, an immunostimulant derived from Streptococcus. OK432 elevated the capacity of hepatic macrophages to produce superoxide and tumor necrosis factor (TNF), and enhanced the mRNA expression of interleukin-1-alpha, -beta, and TNF-alpha in liver nonparenchymal cells (NPC). However, intravenous (iv) preadministration of OK432 reduced the mRNA expression of TNF-alpha in liver NPC enhanced by the endotoxin injection, decreased the serum level of GOT and lactic dehydrogenase (LDH), and improved the survival rate of endotoxin-injected rats. Histological examination revealed a significant reduction in cell vacuolization and focal necrosis in the livers of the endotoxin-injected rats pretreated with OK432. These results indicate that hepatic macrophages play a crucial role in endotoxin-induced liver injury, and that TNF-alpha is one of the factors most likely to be implicated in the development of endotoxin-induced liver injury. Thus, it is suggested that the administration of OK432 provides liver protection by modulating the responsiveness of hepatic macrophages against endotoxin.

Role of cytosolic phospholipase A2 in arachidonic acid release of rat-liver macrophages: regulation by Ca2+ and phosphorylation

In this study we have verified the existence of a cytosolic phospholipase A2 (cPLA2) in rat-liver macrophages. Stimulation of these cells with phorbol 12-myristate 13-acetate (PMA), zymosan and lipopolysaccharide (LPS), but not with the Ca(2+)-ionophore A23187, leads to phosphorylation of cPLA2 and activation of mitogen-activated protein (MAP) kinase, supporting the hypothesis that MAP kinase is involved in cPLA2 phosphorylation. We show furthermore, that the tyrosine kinase inhibitor genistein prevents the LPS- but not the PMA- or zymosan-induced phosphorylation of cPLA2 and activation of MAP kinase, indicating that tyrosine kinases participate in LPS- but not in PMA- and zymosan-induced cPLA2 phosphorylation and MAP kinase activation. Phosphorylation of cPLA2 does not strongly correlate with stimulation of the arachidonic acid (AA) cascade: (1) A23187, a potent stimulator of AA release, fails to induce cPLA2 phosphorylation; (2) withdrawal of extracellular Ca2+, which inhibits PMA-stimulated AA release (Dieter, Schulze-Specking and Decker (1988) Eur. J. Biochem. 177, 61-67), has no effect on PMA-induced phosphorylation of cPLA2; (3) LPS induces cPLA2 phosphorylation within minutes, whereas increased AA release upon treatment with LPS is detectable for the first time after 4 h; and (4) genistein, which prevents LPS-induced cPLA2 phosphorylation, does not inhibit AA release in response to LPS. From these data we suggest that a rise in intracellular Ca2+, but not phosphorylation of cPLA2, is essential for activation of the AA cascade in rat-liver macrophages.

Differential regulation of phospholipase D and phospholipase C by protein kinase C-beta and -delta in liver macrophages

We have studied activation of phospholipase (PL) C and PLD in liver macrophages labelled with [3H]arachidonic acid. Zymosan, phorbol 12-myristate 13-acetate (PMA), A23187 and fluoride but not arachidonic acid or lipopolysaccharide (LPS) induce an activation of PLD ([3H]phosphatidylethanol (PEt) accumulation). An activation of PLC ([3H]diacylglycerol (DAG) accumulation) is measured with zymosan, PMA and fluoride but not with A23187, LPS or arachidonic acid whereas inositol phosphates are formed with zymosan, only. Removal of extracellular calcium reduces the formation of [3H]PEt and [3H]DAG while pretreatment of the cells with dexamethasone reduces [3H]PEt formation, only. PMA- and zymosan-induced activation of PLD and PMA-induced activation of PLC both seem to be mediated by protein kinase (PK) C-beta whereas zymosan-induced activation of PLC is negatively controlled by PKC-delta. We could furthermore present evidence that the release of [3H]arachidonic acid in these cells occurs independent of an activation of PLD.

Differential activation of transcription factors NF-kappa B and AP-1 in rat liver macrophages

Liver macrophages (Kupffer cells) respond to many stimulations with the production of bioactive substances including cytokines, eicosanoids, and inorganic radicals. In this study the activation of transcription factors by substances inducing cytokine gene expression or superoxide formation in rat Kupffer cells was examined. Using primary cultures of rat Kupffer cells the role of NF-kappa B and activator protein 1 (AP-1) in the expression of the tumor necrosis factor-alpha (TNF-alpha) gene by lipopolysaccharide (LPS) was investigated. Both transcription factors were strongly activated but with different kinetics. Maximal DNA-binding activity was induced with 50 ng of LPS/mL of medium and persisted for at least 24 hours. At that time, NF-kappa B- as well as AP-1-DNA complexes decreased their mobilities in native gels. Among the cytokines tested only TNF-alpha and macrophage colony-stimulating factor (M-CSF) were able to activate NF-kappa B in Kupffer cells. Phorbol ester and zymosan activated AP-1 but not NF-kappa B; the treatment of zymosan yielding a modified form of AP-1. Of all substances found to interfere with TNF-alpha production by Kupffer cells (pyrrolidine dithiocarbamate, dexamethasone, prostaglandin E2, interleukin [IL]-4, IL-10, and transforming growth factor-beta [TGF-beta]) only pyrrolidine dithiocarbamate was able to completely inhibit the activation of NF-kappa B by LPS. Although not abrogating the LPS activation of NF-kappa B, dexamethasone inhibited that of AP-1. The results indicate a direct participation of NF-kappa B in the regulation of TNF-alpha synthesis and a differential effect of LPS on NF-kappa B and AP-1, respectively.

Reactive oxygen inducing vasoconstriction in the isolated perfused rat liver

The effect of reactive oxygen generation on intact livers was studied. Production of reactive oxygen species in perfused livers isolated from normal and endotoxin-treated rats was measured using chemically enhanced chemiluminescence. The resting state chemiluminescence of the livers increased on endotoxin administration and was maximal about 6 h after treatment. Chemiluminescence from the livers was further stimulated severalfold by inclusion of phorbol myristate acetate in the perfusion medium, reaching maximum intensity 3 h after endotoxin treatment. Oxygen consumption by the endotoxin-treated liver showed a transient increase followed by a significant decrease on phorbol myristate acetate stimulation, which was inhibited by dexamethasone. These results are consistent with the occurrence of a respiratory burst followed by oxygen-radical-species-induced vasoconstriction in the intact perfused liver. The evaluation of reactive oxygen species by resident and accumulated macrophages in the intact liver is made possible by these studies, and related effects on the liver could be conveniently and quantitatively followed using this model.

The role of prostaglandins in hepatic resection

The role of prostaglandins (PGs) and the efficacy of PGE1 were investigated in hepatic resection. Patients who underwent hepatic resection were randomly assigned to two groups consisting of a control (n = 5) and a PGE1 treatment group (n = 6). Then the amount of 6-keto PF1 alpha, thromboxane B2 and (TXB2) and PGE2 were serially measured both before and after hepatic resection. Regarding changes in the PGs, a remarkable increase in TXB2 during hepatectomy was demonstrated in both groups. In the control group, both 6-keto PF1 alpha and PGE2 showed only a slight increase both during and after the operation. Regarding the efficacy of PGE1 on liver damage, no significant difference in postoperative liver function was found, however the lipoperoxide level at postoperative day 3 in the PGE1 treatment group (1.9 +/- 0.4 nmol/ml) was significantly lower than that in the control (2.6 +/- 0.5 nmol/ml: P < 0.05). Judging from the remarkable increase of TXB2, a stable metabolite of TXA2 during hepatectomy, it may be suggested that TXA2 plays an important role in the development of liver damage during hepatic resection.

The first application of a chemiluminescence probe, 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (MCLA), for detecting O2- production, in vitro, from Kupffer cells stimulated by phorbol myristate acetate

The purpose of this study was to investigate the generation of superoxide anion radical, O2-, by Kupffer cells in vivo in rat liver. Phorbol myristate acetate (PMA) was infused into perfused rat liver which had been continuously infused with 2-methyl-6-[p-methoxyphenyl]-3,7-dihydroimidazo- [1,2-a]pyrazin-3-one (MCLA, a highly sensitive luminescence reagent for O2-) and the MCLA luminescence from the liver surface was detected with a sensitive photon counter. Under identical conditions, but without MCLA infusion, PMA and nitro blue tetrazolium were infused to verify generation of O2- by formation of formazan deposition. Based on MCLA luminescence and formazan deposition, both dependent on the O2- reaction, we have concluded that liver Kupffer cells generate O2- in vivo in response to stimuli such as PMA. Further, the generation of O2- by Kupffer cells may be by the same mechanism as displayed by macrophages.

Formation of diacylglycerol, inositol phosphates, arachidonic acid and its metabolites in macrophages

Treatment of macrophages with zymosan, 4 beta-phorbol 12-myristate 13-acetate (PMA) and fluoride but not with A 23187 or arachidonic acid (delta Ach) leads to a generation of diacylglycerol (acyl2Gro). Formation of inositol phosphates is achieved with zymosan, only. An elevation of intracellular calcium is obtained with zymosan and A 23187 but not with PMA, fluoride or delta Ach. Prior treatment of the cells with phorbol ester for 3 h which has been shown recently to result in a down-regulation of protein kinase (PK) C-beta but not PKC-delta [Duyster, J., Schwende, H., Fitzke, E., Hidaka H. & Dieter P. (1993) Biochem. J. 292, 203-207] has no effect on the zymosan-induced formation of acyl2Gro or inositol phosphates but inhibits the PMA-induced generation of acyl2Gro. Down-regulation of PKC-delta by prior phorbol ester treatment for 24 h augments the zymosan-induced generation of acyl2Gro and inositol phosphates. The acyl2Gro lipase inhibitor RG 80267 inhibits the PMA-induced and fluoride-induced generation of prostaglandin (PG) E2, reduces the zymosan-induced release of PGE2 by 50% but has no effect on PGE2 formation of unstimulated, A 23187-treated or delta Ach-treated cells. Furthermore, RG 80267 enhances accumulation of delta Ach-labeled acyl2Gro in response to zymosan, PMA and fluoride. These data indicate that zymosan activates a phosphatidylinositol 4,5-bisphosphate-specific phospholipase (PL) C, that generation of acyl2Gro by PMA and fluoride occurs via hydrolysis of other phospholipids, that PKC-beta is involved in the PMA-induced generation of acyl2Gro and PKC-delta negatively modulates the zymosan-induced activation of PLC and PMA and fluoride induce a liberation of delta Ach from acyl2Gro, A 23187 activates the PLA2 pathway and zymosan stimulates both, the acyl2Gro- and PLA2-pathway.

Glycogenolytic and haemodynamic responses to bovine serum albumin in isolated perfused livers from sensitized rats

Infusion of BSA into isolated perfused livers of rats sensitized by intraperitoneal injection of BSA led to rapid increases in portal-vein pressure, glucose output and the lactate/pyruvate ratio in the effluent perfusate, with concomitant decreases in oxygen consumption and lactate+pyruvate efflux. The responses were attenuated at low (approximately 7 microM) perfusate Ca2+, but were restored on re-addition of normal Ca2+ concentration. Co-infusion of the cyclo-oxygenase inhibitor ibuprofen (50 microM) or of the platelet-activating factor receptor antagonist WEB 2170 (1.2 microM) inhibited haemodynamic responses to BSA (5 micrograms/ml) by 48% and 59% respectively. Responses to BSA were also attenuated by prior infusion of the beta-adrenergic agonist isoprenaline. Glycogen phosphorylase a activity was increased by 26% in livers freeze-clamped 2 min after onset of BSA infusion; tissue prostaglandin E2 content was increased at 2 min, but returned to control levels at 5 min. Homologous desensitization of hepatic responses to BSA was observed, but heterologous desensitization with heat-aggregated IgG did not take place. It is concluded that livers from rats sensitized to antigen respond directly to subsequent antigen administration by vasoconstriction and glycogenolysis, and that autacoid mediators are involved in these responses.

Different roles of protein kinase C-beta and -delta in arachidonic acid cascade, superoxide formation and phosphoinositide hydrolysis

In contrast with protein kinase C (PKC)-beta, PKC-delta is exclusively detectable in the membrane fraction of liver macrophages. After long-term treatment with phorbol 12-myristate 13-acetate (PMA) PKC-beta is depleted faster (within 3 h) than PKC-delta (> 7h). Simultaneously, pretreatment with PMA for 3 h inhibits the PMA- and zymosan-induced generation of superoxide and the PMA-induced formation of prostaglandin (PG) E2, whereas a preincubation of more than 7 h is required to affect the zymosan-induced release of PGE2 and inositol phosphates. These results support an involvement of PKC-beta in the PMA-induced activation of the arachidonic acid cascade and in superoxide formation and imply an involvement of PKC-delta in zymosan-induced phosphoinositide hydrolysis and PGE2 formation. Two phorbol ester derivates, sapintoxin A (SAPA) and 12-deoxyphorbol 13-phenylacetate 20-acetate (DOPPA), which have been previously reported to activate preferentially PLC-beta but not PKC-delta in vitro [Ryves, Evans, Olivier, Parker and Evans (1992) FEBS Lett. 288, 5-9], induce the formation of PGE2 and superoxide, down-regulate PKC-delta and potentiate inositol phosphate formation in parallel SAPA, but not DOPPA, down-regulates PKC-beta and inhibits the PMA-induced formation of eicosanoids and superoxide.

Transient activation of hepatic glycogenolysis by thrombin in perfused rat livers

Thrombin, a peptide with native protease activity, caused a rapid (less than 1 min) increase in glycogenolysis of about 30%, assessed from rates of production of glucose+lactate+pyruvate, and in oxygen uptake in perfused rat liver. These increases were followed by a rapid return to basal values within 5 min. The effect of thrombin on glycogenolysis was dose-dependent and was maximal at perfusate concentrations around 1 U/ml. Interestingly, the effect of thrombin on glycogenolysis could be elicited only once in any given liver. The activation of glycogenolysis by thrombin was diminished nearly 50% by prior infusion of the protease inhibitor, diisopropyl fluorophosphate (10 microM), and over 90% when thrombin was treated with diisopropyl fluorophosphate prior to infusion. The stimulation of glycogenolysis by thrombin could be detected in isolated hepatocytes or in livers stored for 24 h in cold Euro-Collins solution, a treatment which destroys endothelial cells. Further, thrombin stimulated production of prostaglandin D2 from arachidonic acid in cultured hepatic endothelial but not Kupffer cells. The effect of thrombin on carbohydrate output was also blocked by a phospholipase A2 inhibitor (quinacrine, 50 microM) and by an inhibitor of the cyclooxygenase (indomethacin, 20 microM), suggesting the involvement of cyclooxygenase in the mechanism of action of thrombin. In support of this idea, the transient kinetics of stimulation of glycogenolysis by thrombin and arachidonic acid was nearly identical to release of thromboxane B2 (80-420 pg/ml) and prostaglandin D2 (300-900 pg/ml) from the perfused liver. Further, a second addition of thrombin failed to increase thromboxane and prostaglandin D2 release as well as carbohydrate production, supporting a causal link between these phenomena. Taken together, these data support the hypothesis that thrombin interacts with receptors in the liver, possibly on endothelial cells, leading to activation of phospholipase A2 and subsequent transient production of prostaglandins and thromboxanes. These mediators subsequently interact with receptors on parenchymal cells, leading to a transient stimulation of glycogenolysis.

Platelet-activating factor-mediated synthesis of prostaglandins in rat Kupffer cells

Synthesis of prostaglandins was stimulated in rat Kupffer cells upon challenge with platelet-activating factor (PAF). PAF-mediated synthesis of prostaglandins was inhibited by the Ca2+ ion chelator (EGTA), the Ca2+ channel antagonist (nifedipine) and U66985, a structural analogue and antagonist of the biological effects of PAF in other cellular systems. Inhibitors of protein kinase C, staurosporine and polymixin B, did not affect PAF-induced prostaglandin synthesis. Phorbol 12-myristate 13-acetate (PMA), an activator of protein kinase C, stimulated synthesis of prostaglandins in Kupffer cells; PAF and PMA exerted additive actions on this process. Both PAF- and PMA-stimulated prostaglandin production was inhibited by TMB-8. PAF-stimulated synthesis of prostaglandins also was inhibited upon treatment of Kupffer cells with pertussis toxin. Cholera toxin, in contrast, stimulated the production of prostaglandins in a concentration-dependent manner; cholera toxin and PAF together had an additive effect. These results suggest that PAF-induced synthesis of prostaglandins is stimulated via a specific receptor coupled to a pertussis toxin-sensitive G-protein, is dependent upon extracellular Ca2+ and is not influenced by protein Kinase C activation. Since PAF and prostaglandins are produced in the liver under conditions such as endotoxemia, PAF-mediated synthesis of these lipid autacoids may be of importance in the regulation of hepatic function during pathophysiological episodes.

Enhancement of prostaglandin E2 production by liver macrophages (Kupffer cells) after stimulation with biological response modifiers

PGE2 production by liver macrophages (Kupffer cells) activated by biological response modifiers was examined. Kupffer cells obtained from a normal rat liver possessed cyclooxygenase activity and produced TXB2, PGD2, and PGE2 from (1-14C)arachidonic acid. The major product was PGD2. When Kupffer cells were incubated in the presence of lipo-polysaccharide (LPS), OK-432, or heat-killed Propionibacterium acnes for 24 h, the amount of arachidonate cyclooxygenase products increased and the major product changed from PGD2 to PGE2. When liver macrophages including Kupffer cells were prepared from rats after an injection of LPS, OK-432, or heat-killed P. acnes, it was noticed that the number of cells obtained and PGE2 production increased compared with those of normal rat. These results suggested that PGE2 production by rat liver was induced when they were treated with biological response modifiers.

Proteinkinase C beta-isoform triggers the formation of prostanoids and superoxide in liver macrophages

The zymosan- and phorbolester-induced formation of prostanoids in cultured rat liver macrophages has been shown recently to be controlled by proteinkinase C (1). Using specific antibodies raised against the alpha-, beta-, gamma- and epsilon-isoforms of proteinkinase C, we show that proteinkinase-beta is the predominant isoform in rat liver macrophages. Northern blot analysis with a beta-isoform-specific c-DNA probe revealed the expression of m-RNA for proteinkinase-beta. In resting cells the beta-isoform of proteinkinase C is nearly equally distributed between the cytosolic and membrane fractions. Zymosan and phorbolester led to a translocation of proteinkinase-beta from the cytosol to the membranes, whereas exogenously added arachidonic acid and the calcium ionophore A23187 had no effect. These data indicate that the beta-isoform of proteinkinase C takes part in the prostaglandin and superoxide formation following PMA and zymosan treatment of rat liver macrophages.

Protein kinase C involved in zymosan-induced release of arachidonic acid and superoxide but not in calcium ionophore-elicited arachidonic acid release or formation of prostaglandin E2 from added arachidonate

Zymosan and phorbol ester induced in liver macrophages the release of arachidonic acid, prostaglandin E2, and superoxide; the calcium ionophore A 23187 elicited a release of arachidonic acid and prostaglandin E2 but not of superoxide, and exogenously added arachidonic acid led to the formation of prostaglandin E2 only. The zymosan- and phorbol-ester-induced release of arachidonic acid, prostaglandin E2, and superoxide was dose-dependently inhibited by staurosporine and K252a, two inhibitors of protein kinase C, and by pretreatment of the cells with phorbol ester which desensitized protein kinase C. The release of arachidonic acid or prostaglandin E2 following the addition of A 23187 or arachidonic acid was not affected by these treatments. Zymosan and phorbol ester but not A 23187 or arachidonic acid induced a translocation of protein kinase C from the cytosol to membranes in intact cells. These results demonstrate an involvement of protein kinase C in the zymosan- and phorbol-ester-induced release of arachidonic acid, prostaglandin E2, and superoxide; the release of arachidonic acid and prostaglandin E2 elicited by A 23187 and the formation of prostaglandin E2 from exogenously added arachidonic acid, however, is independent of an activation of protein kinase C.

A comparative study of endothelin- and platelet-activating-factor-mediated signal transduction and prostaglandin synthesis in rat Kupffer cells

Endothelin-3 (ET-3) stimulated phosphoinositide metabolism and synthesis of prostaglandins in cultured rat Kupffer cells. ET-3-induced hydrolysis of phosphoinositides was characterized by the production of various inositol phosphates and of glycerophosphoinositol. The mechanism of ET-3-stimulated metabolism of phosphoinositides and synthesis of prostaglandins appeared to be distinct from the effect of platelet-activating factor (PAF) on these processes described previously [Gandhi, Hanahan & Olson (1990) J. Biol. Chem. 265, 18234-18241]. On a molar basis ET-3 was significantly more potent than PAF in stimulating phosphoinositide metabolism, e.g. ET-3-induced hydrolysis of phosphoinositides occurred at 1 pM, whereas PAF was ineffective at concentrations less than 1 nM. Upon challenging Kupffer cells with both ET-3 and PAF, an additive stimulation of phosphoinositide metabolism was observed, suggesting that the actions of these factors may be exerted on separate phosphoinositide pools. Treatment of Kupffer cells with pertussis toxin resulted in an inhibition of ET-3-induced phospholipase C activation; in contrast, cholera toxin treatment caused potentiation of ET-3-stimulated phospholipase C activity. Both toxins, however, inhibited PAF-stimulated phospholipase C activity. The present results suggest that the stimulatory effects of ET-3 and PAF on the phosphodiesteric metabolism of phosphoinositides in Kupffer cells require different guanine-nucleotide-binding proteins. Furthermore, the effects of bacterial toxins on ET-3- and PAF-induced phosphoinositide metabolism were not mediated by cyclic AMP. ET-3-induced metabolism of phosphoinositides was inhibited completely in Kupffer cells pretreated with ET-3, suggesting homologous ligand-induced desensitization of the ET-3 receptors. In contrast, similar experiments using PAF showed only a partial desensitization of subsequent PAF-induced phosphoinositide metabolism. In contrast to the increased production of prostaglandins E2 and D2 observed upon stimulation of Kupffer cells with PAF, ET-3 stimulated the biosynthesis of prostaglandin E2 only. Consistent with their additive effects on phosphoinositide metabolism, PAF and ET-3 exhibited an additive stimulation of the synthesis of prostaglandin E2.

Enhancement of rat hepatic macrophages by treatment with interleukin-2 and streptococcal preparation OK432, with reference to antitumor activity, soluble factor production and Ia expression

The effect of biological response modifiers, such as interleukin-2 (IL-2) and streptococcal preparation OK432, on the functions of hepatic macrophages was investigated. The macrophages, even with no exogenous stimulation, produced superoxide anion (O2-) and tumor necrosis factor (TNF), displayed cytotoxicity against K562 cells and cytostasis against P815 cells and expressed immune-region-associated antigen (Ia). IL-2 administered in vitro or in vivo enhanced O2- production by hepatic macrophages and the intravenous injection of OK432 also enhanced O2 production. Furthermore, IL-2 added to the culture medium of hepatic macrophages isolated from OK432-injected rats augmented O2- production even more. The TNF production and Ia expression of the macrophages were also increased by the intravenous injection of OK432. As with O2- production, the cytotoxicity of the cells was enhanced by OK432 injection or by IL-2 added to the culture medium and the combination of OK432 and IL-2 augmented their cytotoxicity even more. Thus, the present study suggested that IL-2 and OK432 induce the augmentation of the antitumor activity of hepatic macrophages, partly as a result of the increase in production of O2- and TNF and Ia expression.

Enhancement and hepatocyte-modulating effect of chemical mediators and monokines produced by hepatic macrophages in rats with induced sepsis

We investigated the production of chemical mediators by hepatic macrophages from rats with sepsis and the modulation of hepatocyte function by these hepatic macrophages. The chemical mediators we measured were superoxide (O2-), TNF, IL-1, and PGE2. Production of these mediators by hepatic macrophages from rats with sepsis was significantly increased. Furthermore, protein synthesis by cultured hepatocytes was inhibited in a co-culture system of hepatocytes and hepatic macrophages from rats with sepsis, and it was even inhibited by the supernatant of cultured hepatic macrophages from septic rats. These results demonstrate that hepatic macrophages are activated in sepsis and may play a role in inducing hepatic dysfunction in sepsis.

RO 31-8220 and RO 31-7549 show improved selectivity for protein kinase C over staurosporine in macrophages

Two new potent protein kinase C inhibitors, RO 31-8220 and RO 31-7549, and staurosporine were found to inhibit dose-dependently the phorbol ester-induced formation of prostaglandin E2 and superoxide in cultured liver macrophages. Prostaglandin E2 formation from exogenously added arachidonate was not affected by these compounds. The zymosan-induced formation of inositol phosphates was decreased by simultaneous addition of phorbol ester and was enhanced by prior desensitization of protein kinase C indicating that protein kinase C negatively modulates phospholipase C activation in these cells. While staurosporine suppressed almost totally the zymosan-induced formation of inositol RO 31-8220 and RO 31-7549 inhibited the protein kinase C-mediated effect on inositol phosphate formation, only. Phagocytosis of zymosan was not affected by RO 31-8220 and RO 31-7549 but was decreased by staurosporine. These results demonstrate that two new potent protein kinase C inhibitors, RO 31-8220 and RO 31-7549, are more selective in their actions as staurosporine and are useful tools to determine an involvement of protein kinase C in cellular systems.

Glucocorticoids inhibit formation of inositol phosphates in macrophages

Glucocorticoids inhibited the zymosan-induced formation of inositol phosphates in macrophages. No inhibition was observed with progesterone. Inhibitors of protein (cycloheximide) and RNA (actinomycin D) synthesis exhibited similar inhibitory effects. The activity of phospholipase C in subcellular fractions was not altered by hormone treatment of the cells. However, the incorporation of inositol into membrane lipids was reduced by dexamethasone. These data indicate that glucocorticoids are able to inhibit the formation of inositol phosphates; the effect of the hormone is rather due to an inhibition of the incorporation of inositol in membrane lipids than to an inhibition of phospholipase C. The anti-inflammatory action of glucocorticoids may, therefore, also be attributed to their effect on the polyphosphoinositide cycle and inositol phosphate-mediated processes.

Interferon gamma modulates production of interleukin 1 and tumor necrosis factor by murine Kupffer cells

When mononuclear phagocytes, including Kupffer cells, are activated by various agents, they synthesize and release cytokines such as interleukin 1 (IL-1) and tumor necrosis factor (TNF). In this study, we examined the effect of in vitro Kupffer cell activation by recombinant murine interferon gamma (IFN gamma) on IL-1 and TNF secretion. IFN gamma enhanced TNF production in the presence or absence of lipopolysaccharide (LPS), but suppressed IL-1 production by Kupffer cells. Because IFN gamma also stimulated prostaglandin E2 (PGE2) production, the effect of indomethacin, which is an inhibitor of cyclooxygenase and which inhibits PGE2 biosynthesis, on IL-1 and TNF production by Kupffer cells was examined. As a result, indomethacin enhanced TNF production by Kupffer cells, but had no effect on IL-1 synthesis. These results suggested that IFN gamma modulates the production of IL-1 and TNF by Kupffer cells through different mechanisms.

Activation of phospholipase C is not correlated to the formation of prostaglandins and superoxide in cultured rat liver macrophages

This study evaluates the role of inositol phosphates as possible mediators of the activation of phospholipase A2 and NADPH oxidase in cultured rat liver macrophages. Inositol phosphate formation was achieved by zymosan, immune complexes, latex particles and calcium ionophore while the release of arachidonic acid and the formation of prostaglandin E2 was also elicited by phorbol ester and NaF, but not by latex particles; generation of superoxide was obtained by zymosan and phorbol ester only. The kinetics of the formation of inositol phosphates revealed that within the first few minutes after zymosan addition inositol trisphosphate was formed, followed by inositol bisphosphate and inositol monophosphate. Pre-treatment of the cells with dexamethasone or removal of extracellular calcium led to an inhibition of the zymosan-induced formation of inositol phosphates and prostaglandin E2 but had no effect on the generation of superoxide; inhibition of the Na+/H+ exchanger by removal of extracellular sodium ions led to a decrease of the zymosan-induced synthesis of prostaglandin E2, but did not affect the formation of inositol phosphates and superoxide. Pre-treatment of the cells with phorbol ester decreased the zymosan-induced synthesis of prostaglandin E2 and superoxide, but even enhanced the zymosan-induced formation of inositol phosphates. These data indicate that in cultured rat liver macrophages the formation of prostaglandins and superoxide cannot be correlated to an activation of phospholipase C.

Enhancement of hepatic macrophages in septic rats and their inhibitory effect on hepatocyte function

In the present study, the function of hepatic macrophages and the modulation of hepatocytes by sepsis-elicited hepatic macrophages were investigated in rats with induced sepsis. The functional state of hepatic macrophages was determined by the following indicators: phagocytic index, protein-synthesizing capacity, and superoxide (O2-) producing capacity. These indices of changes in hepatic macrophages were much higher in rats with sepsis than in healthy controls. Moreover, the activated hepatic macrophages had some biological properties which were different from those of the resident Kupffer cells. It was found that protein synthesis by cultured hepatocytes was inhibited in the co-culture system of hepatocytes and sepsis-elicited hepatic macrophages, and that the supernatant of hepatic macrophages from rats with sepsis also reduced the protein-synthesizing capacity of cultured hepatocytes. Thus, activated hepatic macrophages may play a role in inducing hepatic dysfunction in sepsis.

Effect of prostaglandin E2 on urea synthesis and hepatic hemodynamics in rat livers. An in vivo/in vitro study

The study was carried out on 30 rats. PGE2 was found to inhibit both the ammonium uptake and urea formation by hepatocytes, i.e. PGE2 inhibited the ornithine cycle in a non-recirculating perfusion of the liver. Simultaneously PGE2 inhibited liver oxygen uptake and raised portal pressure. Inhibition of urea synthesis in the liver and decrease of hepatic hemodynamics by PGE2 were also found in experiments in vivo. The PGE2 inhibiting effect on urea synthesis may be achieved mainly through decreasing hepatic blood flow and perhaps, by hypoxia.

Interdependence of tumor necrosis factor, prostaglandin E2, and protein synthesis in lipopolysaccharide-exposed rat Kupffer cells

Kupffer cells are the main producers of tumor necrosis factor-alpha (TNF; cachectin) and eicosanoids in the liver exposed to lipopolysaccharide (endotoxin; LPS). A very rapid but transient release of TNF is followed by a slow, steady synthesis of prostaglandin E2 (PGE2). TNF itself is able to provoke eicosanoid synthesis in Kupffer cells; the rate and pattern of prostaglandin production are similar to those observed after treatment with LPS. Anti-TNF antibodies completely neutralize TNF action on Kupffer cells, thus ruling out any participation of contaminating LPS. LPS stimulation of PGE2 production in Kupffer cells is reduced by the antiserum to 50%, indicating an involvement of TNF in the stimulatory action of LPS. On the other hand, PGE2, a potent inhibitor of LPS-elicited TNF release, is able to suppress LPS- but not TNF-stimulated eicosanoid synthesis in rat Kupffer cells. In addition to this autocrine circuit, extrahepatic factors participate in the regulation of Kupffer cell activation: glucocorticoids not only inhibit TNF or prostaglandin production, they also reverse the LPS-specific changes in the prostaglandin pattern of Kupffer cells. LPS, TNF or cycloheximide when given alone in the concentration range applied in this study do not affect the viability of rat Kupffer cells. However, the combinations of cycloheximide and either LPS or TNF cause rapid death of the cultured cells. The cytolytic potential of either combination cannot be alleviated by treatment with glucocorticoids.

Interferon gamma stimulates prostaglandin E2 production by mouse Kupffer cells

When mononuclear phagocytes, including Kupffer cells, are activated by various agents, they synthesize and release arachidonic acid metabolites, prostaglandins (PGs) and leukotrienes (LTs). In this study, we examined the effect of in vitro Kupffer cell activation with recombinant murine IFN gamma on PGE2 and LTB4 secretion. IFN gamma enhanced PGE2 secretion, and this effect of IFN gamma was stronger than that of IL-1 or TNF. Moreover, IFN gamma promoted LTB4 release especially in the absence of PGs. On the other hand, dexamethasone and indomethacin inhibited and, EGTA and TMB-8, which reduce intracellular Ca++ Levels, blocked IFN gamma induced PGE2 production, which suggested that the activation of phospholipase A2 and cyclooxygenase in Kupffer cells requires the elevation of intracellular Ca++ levels.

Hepatic circulation: potential for therapeutic intervention

In recent years, knowledge of the physiology and pharmacology of hepatic circulation has grown rapidly. Liver microcirculation has a unique design that allows very efficient exchange processes between plasma and liver cells, even when severe constraints are imposed upon the system, i.e. in stressful situations. Furthermore, it has been recognized recently that sinusoids and their associated cells can no longer be considered only as passive structures ensuring the dispersion of molecules in the liver, but represent a very sophisticated network that protects and regulates parenchymal cells through a variety of mediators. Finally, vascular abnormalities are a prominent feature of a number of liver pathological processes, including cirrhosis and liver cell necrosis whether induced by alcohol, ischemia, endotoxins, virus or chemicals. Although it is not clear whether vascular lesions can be the primary events that lead to hepatocyte injury, the main interest of these findings is that liver microcirculation could represent a potential target for drug action in these conditions.