Comparison of the production of eicosanoids by human and rat peritoneal macrophages and rat Kupffer cells

Inhibition of lipoxygenase pathway in macrophages co-cultivated with tumor cells

Although there is a great deal of interest in the role played by tumor-associated macrophages in tumor progression, the knowledge of the biological mediators involved in the interplay between macrophages and tumor cells is still limited. In the present study, we investigated whether the lipoxygenase pathway in resident murine peritoneal macrophages is affected by contact with tumor cells of a different origin, e.g. murine B16 melanoma and L929 fibrosarcoma cells, and human Hs294T melanoma and HT1080 fibrosarcoma cells. Our experiments have been carried out by using macrophages co-cultivated with tumor cells at different ratios, in order to simulate the relative proportions between macrophages and tumor cells during the in vivo development of a tumor. Reverse phase HPLC analyses of the lipoxygenase products of resident peritoneal macrophages revealed a rather complex profile characterized by a high level of 12(S)-hydroxyeicosatetraenoic acid and 15(S)-hydroxyeicosatetraenoic acid followed by leukotriene B(4), 5(S)-hydroxyeicosatetraenoic acid, and lipoxins. Macrophages co-cultivated with tumor cells, both murine and human, showed a marked reduction of lipoxygenase products, mainly in the co-cultures where tumor cells prevailed over macrophages. The characteristic profile of macrophage lipoxygenase products was re-established after removal of tumor cells from the co-cultures. The inhibitory effect on lipoxygenase pathways exerted by tumor cells, was not seen when macrophages were co-cultivated with normal primary murine and human fibroblasts.

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.

Role of thromboxane A2 in early BDL-induced portal hypertension

Although the mechanisms of cirrhosis-induced portal hypertension have been studied extensively, the role of thromboxane A(2) (TXA(2)) in the development of portal hypertension has never been explicitly explored. In the present study, we sought to determine the role of TXA(2) in bile duct ligation (BDL)-induced portal hypertension in Sprague-Dawley rats. After 1 wk of BDL or sham operation, the liver was isolated and perfused with Krebs-Henseleit bicarbonate buffer at a constant flow rate. After 30 min of nonrecirculating perfusion, the buffer was recirculated in a total volume of 100 ml. The perfusate was sampled for the enzyme immunoassay of thromboxane B(2) (TXB(2)), the stable metabolite of TXA(2). Although recirculation of the buffer caused no significant change in sham-operated rats, it resulted in a marked increase in portal pressure in BDL rats. The increase in portal pressure was found concomitantly with a significant increase of TXB(2) in the perfusate (sham vs. BDL after 30 min of recirculating perfusion: 1,420 +/- 803 vs. 10,210 +/- 2,950 pg/ml; P < 0.05). Perfusion with a buffer containing indomethacin or gadolinium chloride for inhibition of cyclooxygenase (COX) or Kupffer cells, respectively, substantially blocked the recirculation-induced increases in both portal pressure and TXB(2) release in BDL group. Hepatic detection of COX gene expression by RT-PCR revealed that COX-2 but not COX-1 was upregulated following BDL, and this upregulation was confirmed at the protein level by Western blot analysis. In conclusion, these results clearly demonstrate that increased hepatic TXA(2) release into the portal circulation contributes to the increased portal resistance in BDL-induced liver injury, suggesting a role of TXA(2) in liver fibrosis-induced portal hypertension. Furthermore, the Kupffer cell is likely the source of increased TXA(2), which is associated with upregulation of the COX-2 enzyme.

DMSO induction of the leukotriene LTC4 by Lewis rat Schwann cells

Schwann cells are capable of producing many immunomodulatory molecules, which indicates that they may play an active role in autoimmune diseases of the peripheral nervous system. We have previously reported production of the prostanoids prostaglandin E2 and thromboxane A2, products of arachidonic acid metabolism, by Schwann cells. This study reports that Schwann cells are capable of producing leukotriene C4, also a product of arachidonic acid metabolism. Production of leukotriene C4 was in response to pre-incubation of the Schwann cells with the cytokines interferon-gamma and tumour necrosis factor-alpha followed by incubation with dimethylsulfoxide. The cytokines alone did not elicit a response nor did stimulation with calcium ionophore, phorbol ester or lipopolysaccharide.

Prostaglandin production by human peripheral blood monocytes changes with in vitro differentiation

To investigate the influence of in vitro culture on prostaglandin (PG) production, human monocyte enriched peripheral blood mononuclear cells were isolated and incubated on gelatin-coated plates. On days zero, five and eleven of culture, the cells were examined microscopically and the production of PGF1 alpha, PGE2, PGD2, F metabolite (PGFM) and E metabolite (PGEM) were measured by radioimmunoassay. Differences in PG output were analyzed using the Wilcoxon and Friedman tests. Freshly isolated human peripheral blood monocytes produced mainly PGE2. In vitro, however, PGE2 production decreased from 196 (48-288) fmol/10(6) cells per 3h on day zero of culture to 28 (6-51) on day eleven (p = 0.04); median (range), n = 7. Prostaglandin D2 and PGEM output decreased similarly, but these differences failed to reach significance. Prostaglandin F2 alpha and PGFM output, on the other hand, increased from 32 and 19 fmol/10(6) cells per 3h, respectively, on day zero of culture to 127 (p < 0.05) and 58 (p = 0.01) on day eleven. Changes in PG output were associated with in vitro differentiation as evidenced by changes in cellular morphology. These result suggest that differentiation of human peripheral blood monocytes in vitro is accompanied by a shift in PG output from PGE2 and PGD2, towards PGF2 alpha.

Heterogeneity of Kupffer cells and splenic, alveolar, and peritoneal macrophages for the production of TNF, IL-1, and IL-6

Kupffer cells and alveolar, splenic, and peritoneal macrophages from normal rats were incubated for various periods of time in the presence of LPS, and the culture supernatants were analyzed for IL-6, IL-1, and TNF. There was very little difference in the amounts of the cytokines produced by the macrophages when stimulated with 0.01-10 micrograms/ml of LPS. The shapes of the time course curves for the production of the cytokines by the different types of macrophages were generally similar, although only Kupffer cells continued to produce IL-6 throughout the entire incubation period and splenic macrophages showed a lag period in the production of IL-1. Kupffer cells produced more IL-6 than that produced by the other populations of macrophages, and alveolar macrophages produced more IL-1 compared to that produced by splenic cells. Kupffer cells and peritoneal macrophages produced more IL-6 in 24 h than in 6 h of culture, and splenic macrophages produced more IL-1 in 24 compared to 6 h of culture. Alveolar macrophages produced more TNF than that produced by the other populations of cells but only when integrated over the entire incubation period. These results confirm and extend the observed functional heterogeneity of macrophages obtained from different tissues of the same animal. This study and future studies will lead to a better understanding of the role of cytokines in the inflammatory response.

Interactions between cytokines and eicosanoids: a study using human peritoneal macrophages

To examine the interactions between the main pro-inflammatory cytokines and eicosanoids produced by human inflammatory cells, human peritoneal macrophages (hp-M phi) were isolated from ascitic fluid of patients with portal hypertension. Interactions between interleukin-1 beta (IL-1 beta), IL-6, tumor necrosis factor alpha (TNF-alpha), leukotriene B4 (LTB4) and prostaglandin E2 (PGE2) were studied by addition or inhibition of several cytokines and eicosanoids: human recombinant IL-1 beta (hrIL-1 beta) addition, LTB4 addition and 5-lipoxygenase inhibition (6-hydroxy-2-(4-sulfamoylbenzylamino)-4,5,7-trimethylbenzothiaz ole hydrochloride (E6080)), PGE2 addition and cyclooxygenase inhibition (indomethacin). In hp-M phi hrIL-1 beta stimulated the LTB4 production, while the PGE2 production was inhibited. HrIL-1 beta had no significant effect on IL-6 production in hp-M phi. LTB4 did not regulate IL-1 beta and IL-6 production. Increasing PGE2 down regulated the TNF-alpha production, but did not effect the IL-1 beta and IL-6 production.

Production of inflammatory mediators by human macrophages obtained from ascites

Ascites is a readily available source of human macrophages (M phi), which can be used to study M phi functions in vitro. We characterized the mediators of inflammation produced by human peritoneal M phi (hp-M phi) obtained from patients with portal hypertension and ascites. The production of the cytokines interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) was found to be lipopolysaccharide (LPS) concentration dependent (0-10 micrograms/ml) with a maximal production at 10 micrograms/ml and also dependent on the time of exposure to the stimulus (0-36 h). IL-1 beta, IL-6 and TNF-alpha production after LPS administration reached a plateau at 24 h. In vitro stimulation for 24 h with LPS does not influence the eicosanoid production from endogenous arachidonate. 13 min of exposure of the cells to the calcium ionophore A23187 gives a significant increase in eicosanoid production from both exogenous and endogenous arachidonate. The main eicosanoids produced are the 5-lipoxgenase products LTB4 and 5-hydroxyeicosatetraenoic acid (HETE). The increase in production of the other eicosanoids is not significant. The eicosanoid production depends on the stimulus concentration. The optimal A23187 concentration is 1 microM. Oxygen radical production was measured in the M phi by a flowcytometric method. The fluorescence intensity of phorbol 12-myristate 13-acetate stimulated and dihydro-rhodamine 123 loaded hp-M phi increases significantly after 15 min. We conclude that LPS stimulation of hp-M phi from liver disease results in similar production of IL-1 beta, IL-6 and TNF-alpha, but that the profile of the eicosanoid production of these M phi stimulated with LPS and A23187 differs from M phi of other origin and species.

Changes in Eicosanoid and Tumour Necrosis Factor-alpha Production by Rat Peritoneal Macrophages During Carrageenin-Induced Peritonitis

Changes and correlations in cytokine and eicosanoid production by blood monocytes, non-purified and purified peritoneal cells during a carrageenin-induced peritonitis were investigated for a period of ten days. The cells were isolated and stimulated in vitro. Cytokine and eicosanoid production of the non-purified fraction increased steadily during peritonitis. During the whole episode of peritonitis the production capacity of granulocytes was very low and hardly any effect on the production capacity of macrophages (Mϕ) was observed. Cytokine and eicosanoid production of the non-purified fraction was mainly due to the presence of Mϕ. The production capacity of the peripheral blood monocytes was not similar to that of the peritoneal Mϕ.

A comparison of hepatic, splenic, peritoneal and alveolar macrophages with respect to PGE2, TXB2, production and ADCC function

The in vitro production of PGE2 and TxA2, measured as TxB2, and the antibody-dependent cellular cytotoxicity (ADCC) as well as spontaneous cellular cytotoxicity (SCC) displayed by hepatic, peritoneal, splenic, and alveolar macrophages from 12 rats was determined and compared. Kupffer cells, the fixed macrophages of the liver, were the most active cells in the production of PGE2. Kupffer cells and peritoneal macrophages released about equal amounts of TxB2 which was much higher than that released by splenic macrophages. Kupffer cells displayed the strongest ADCC activity, and alveolar macrophages had the lowest value. These results confirm the previously reported heterogeneity among different sources of macrophages and emphasize the enhanced activity of Kupffer cells with respect to eicosanoid production and ADCC function.

Increased 5-lipoxygenase activity in massive hepatic cell necrosis in the rat correlates with neutrophil infiltration

Rats were treated with heat-killed Propionibacterium acnes and subsequent injection of a small amount of lipopolysaccharide after 7 days. After 24 hr most of the rats died of massive liver cell necrosis. Nonparenchymal liver cells were isolated from this liver injury model and incubated with arachidonic acid. Reverse-phase high-pressure liquid chromatography detected the 5-lipoxygenase metabolites (leukotriene B4 and 5-hydroxy-arachidonic acid), whereas these compounds were produced in negligible amounts when the rats were treated with P. acnes only. Immunohistochemical studies with 5-lipoxygenase antiserum revealed that the injured livers contained a large number of positively stained round cells with segmented nuclei, which were rarely found in the livers treated with P. acnes only. These positively stained cells were histologically identified as neutrophils. The results suggested that the increased 5-lipoxygenase activity in the injured rat liver is attributable to the infiltrating neutrophils rather than to nonparenchymal hepatic cells.

Different preparations of zymosan induce glycogenolysis independently in the perfused rat liver. Involvement of mannose receptors, peptide-leukotrienes and prostaglandins

Zymosan (non-boiled) induced glycogenolysis biphasically, with no lag time, in the perfused rat liver. After the zymosan was boiled, it could be separated into two fractions, both of which stimulated glycogenolysis independently. The soluble fraction of boiled zymosan (zymosan sup) showed homologous desensitization, indicating that zymosan sup-induced glycogenolysis is a receptor-mediated event. Mannan (polymannose), which is known to be a biologically active component of zymosan, induced a glycogenolytic response similar to that produced by zymosan sup, and desensitized the response to the latter. Preinfusion of platelet-activating factor (PAF, 20 nM) or isoprenaline (10 microM) did not extinguish the glycogenolytic response to zymosan sup, while the response to a secondary infusion of PAF was blocked. The glycogenolytic response to zymosan sup was completely inhibited by nordihydroguaiaretic acid (NDGA, 10 microM), a lipoxygenase inhibitor, and by ONO-1078 (100 ng/ml), a leukotriene (LT) D4 receptor antagonist. On the other hand, the glycogenolytic effect of zymosan pellet (the particulate fraction of boiled zymosan) was not affected by preinfusion of zymosan sup, and was inhibited by ibuprofen (20 microM), a cyclo-oxygenase inhibitor. Prostaglandins (PGs) detected in the perfusate were augmented with infusion of zymosan pellet. Opsonization of the zymosan pellet by serum (complement) enhanced the glycogenolytic response without a lag period, and with a concomitant enhancement of PG output. Correlations between glucose production and PGs were r = 0.832 (PGD2), r = 0.872 (PGF2 alpha), r = 0.752 (PGE2) and r = 0.349 (6-oxo-PGF1 alpha). The glycogenolytic response to non-boiled zymosan was delayed and the biphasic glycogenolytic response was not observed when mannan was infused first. NDGA mimicked the effects of the preinfusion of mannan, while ibuprofen had no effect on the non-boiled-zymosan-induced glycogenolysis. These results suggest: (1) that non-boiled zymosan stimulates glycogenolysis through a mannose receptor-dependent, but unidentified, pathway, (2) that zymosan sup induces glycogenolysis via mannose receptor activation through the production of peptide-LTs but not PAF, and (3) that zymosan pellet causes glycogenolysis through the production of prostanoids, which is enhanced in the presence of complement.

Surface contact modulation of inflammatory macrophage antibody dependent cytotoxicity and prostanoid release

Adherence to extracellular matrix proteins modulates the functional and secretory activities of mononuclear phagocytes, although the mechanisms regulating these adherence-dependent changes are poorly understood. In this study, the ability of rat inflammatory peritoneal macrophages (PM) to adhere to an endothelial cell-derived extracellular matrix or a denatured collagen/fibronectin-coated surface and perform antibody dependent cell cytotoxicity (ADCC) and secrete reactive oxygen intermediates was compared with PM adherent to tissue culture plastic. Prostaglandin E2 (PGE2) and thromboxane B2 (TxB2), two major cyclooxygenase products released by inflammatory macrophages, were also measured by PM adherent to the protein coated surfaces. Rat exudate PM were equally adherent to tissue culture plastic or wells coated with either endothelial cell derived matrix or denatured collagen (gelatin)/fibronectin. PM adherent to a denatured collagen/fibronectin-coated wells demonstrated significantly less cytolytic activity (15 +/- 2% lysis) when compared with either tissue culture plastic adherent PM (43 +/- 7% lysis) or PM adherent to extracellular matrix (59 +/- 11% lysis). PM adherent to extracellular matrix released twofold more TxB2 than plastic adherent PM, while PM adherent to denatured collagen/fibronectin released 40% more PGE2 than cells adherent to tissue culture plastic or 80% more PGE2 than PM adherent to the extracellular matrix. PM adherent to denatured collagen/fibronectin release less superoxide anion (27 +/- .9 nmoles/10(6) PM) than PM adherent to either tissue culture plastic (43 +/- 1 nmoles/10(6) PM) or the extracellular matrix (60 +/- 0.5 nmoles/10(6) PM). Furthermore, incubation of plastic adherent PM with exogenous PGE2 reduced superoxide production in a dose-dependent manner. These results demonstrate that the inhibition of ADCC and secretion of reactive oxygen intermediates by PM adherent to a denatured collagen/fibronectin surface correlated with an increased release of the immunosuppressive prostanoid PGE2. Furthermore, the addition of exogenous PGE2 to plastic adherent PM reproduced the depression in ADCC and superoxide anion production observed by PM adherent to a denatured collagen/fibronectin surface. These studies suggest that the increased production and release of PGE2 by inflammatory macrophages adherent to a denatured collagen surface may act to suppress cytotoxic mechanisms and thereby constitutes part of an autocrine feedback mechanism regulating macrophage function during wound injury.

Macrophage activation reduces mobilization of arachidonic acid by guinea-pig and rat peritoneal macrophages in vitro

We have examined species differences in the mobilization of arachidonic acid and generation of prostacyclin in non-activated and activated peritoneal macrophages in vitro. Mobilization of 3H-arachidonic acid was reduced in rat activated macrophages compared with that in non-activated macrophages, but a similar difference was not observed in guinea-pig macrophages. In guinea-pig peritoneal macrophages, exposure to formyl-Methionyl-Leucyl-Phenylalanine (fMLP), platelet-activating factor (Paf), zymosan and A23187 increased the generation of prostacyclin. In contrast, in rat peritoneal macrophages, fMLP and Paf did not stimulate the mobilization of arachidonic acid or the generation of prostacyclin, whereas both zymosan and A23187 were effective stimuli. Pretreatment of either rats or guinea-pigs by intraperitoneal injection of C. Parvum reduced prostacyclin generation by peritoneal macrophages in vitro. We conclude that there may be species differences in receptor populations between guinea-pig and rat peritoneal macrophages. However, the reduction in eicosanoid generation induced by the inflammatory stimulus, C. Parvum is not species-dependent.

Kupffer cell-hepatocyte interactions and the changes in 1-14C-arachidonate incorporation in response to endotoxin in vitro

The present experiments were undertaken to elucidate the effect of either the hepatocyte (HC) or hepatocyte supernatant on prelabeled endotoxin (LPS)-stimulated Kupffer cell (KC) arachidonic acid utilization. HC, KC, or their coculture were incubated for 18 hours with labeled 1-14C- arachidonic acid followed by a 24 hour incubation with 10 micrograms/ml LPS. LPS had no effect on the percent distribution of labeled arachidonate into the HC phospholipid or neutral lipid. KC showed a decreased percent neutral lipid labeled arachidonic acid distribution with generally no effect on the phospholipid. However, KC:HC cocultures or the addition of HC supernatant to KC exposed to LPS dramatically reversed the labeled arachidonate distribution into the KC with an increased incorporation into neutral lipid. Labeled PGE2 and PGD2 were increased in the KC following incubation with HC supernatant while only labeled PGE2 levels were elevated in the cocultures. The changes in the distribution of cell's labeled arachidonate required the addition of LPS. These results suggest that the HC can promote changes in the lipid fraction during sepsis by elaborating a substance that can modulate labeled arachidonate distribution in the KC lipids as well as stimulate prostaglandin production.

Eicosanoid synthesis in human peritoneal macrophages stimulated with S. epidermidis

Peritoneal macrophages isolated from CAPD patients phagocytosed S. epidermidis in a time dependent manner. Coincident with a maximum phagocytic uptake of 56% by 12 hours, there was secretion of a significant amount of neutral protease (1.37 +/- 0.2 mg [3H]-casein degraded/10(6) cells, P = 0.05). In contrast to these delayed effects, coincubation of PMO with S. epidermidis resulted in a significant increase in both LTB4 and LTC4 synthesis above that of controls, with 6.33 +/- 1.20 ng LTB4/10(6) cells (P less than 0.01) and 2.06 +/- 0.68 ng LTC4/10(6) cells (P = 0.014) being generated by three hours. The generation of these lipoxygenase products was both time and dose dependent, and the rapid production and release of the potently chemotactic LTB4 is consistent with the observed clinical response, where a rapid influx of PMN into the peritoneal cavity occurs during episodes of peritonitis, while the generation of LTC4 may contribute to the hyperemia and interstitial edema. In contrast, although there was a time dependent rise in cyclooxygenase product generation by unstimulated cells, a dose dependent inhibition of synthesis was clearly demonstrated when cells were incubated with bacteria, with a mean 40% reduction in generation of PGE2 and a mean 34% reduction in TXB2 generation (P = 0.01 and P less than 0.025, respectively). It was demonstrated that the inhibition was not due to lack of available substrate and that the generation of eicosanoids was unrelated to phagocytosis, bacterial/PMO contact or bacterial surface characteristics. Instead, the observed effect of S. epidermidis on the PMO was attributable to a secreted bacterial product.

Inhibition of leukotriene omega-oxidation by isonicotinic acid hydrazide (isoniazid)

Metabolism of leukotrienes via omega-oxidation represents a major degradative and inactivating pathway of these biologically active icosanoids. Isonicotinic acid hydrazide (isoniazid) inhibited this process in rats in vivo, in the isolated perfused rat liver, and in hepatic microsomes. The in vivo catabolism of leukotriene E4 via N-acetyl-leukotriene E4 to its omega-oxidized metabolites was inhibited by 50% or 71% using single intravenous isoniazid doses of 0.6 mmol or 1.0 mmol/kg body mass, respectively. Isoniazid interfered with leukotriene catabolism at the initial omega-oxidation step, resulting in an accumulation of N-acetyl-leukotriene E4. Analogous although weaker inhibition of leukotriene omega-oxidation in vivo was observed by pretreatment with isonicotinic acid 2-isopropylhydrazide and monoacetyl hydrazine. In the isolated perfused liver, isoniazid at concentrations varying over 0.2-10 mM decreased the omega-oxidation of cysteinyl leukotrienes dose-dependently by up to 94%. omega-Oxidation of both leukotriene E4 and leukotriene B4 by rat liver microsomes was inhibited by isoniazid, isonicotinic acid 2-isopropylhydrazide, and monoacetyl hydrazine with half-maximal concentrations in the range of 5-15 mM. Our measurements indicate that the impairment of leukotriene omega-oxidation by isoniazid involves both cytochrome-P450-dependent enzyme systems responsible for omega-oxidation of leukotriene E4 and leukotriene B4. In effect, under isoniazid treatment one can expect a prolongation of the proinflammatory actions of endogenously produced leukotrienes.

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.

Increased bioavailability of enzymes of eicosanoid synthesis in hepatic and extrahepatic tissues after portacaval shunting

Metabolites of arachidonic acid have been attributed to severe circulatory, metabolic and hormonal alterations in patients with chronic liver disease. In order to study changes of the tissue-specific availability of enzymes of eicosanoid synthesis, we used portacaval-shunted rats, as this model exhibits many clinical and biochemical similarities to patients suffering from cirrhosis of the liver. Microsomal mass and maximal velocity of prostaglandin H synthase, the initial enzyme of prostaglandin synthesis, were markedly and permanently increased after shunting in both hepatic and extrahepatic tissues as compared to those of sham-operated rats. Maximal velocity of thromboxane synthase and prostacyclin synthase, two more peripheral enzymes of the arachidonic acid cascade, were tissue-specifically enhanced, whereas the apparent affinities (Km) remained unchanged. Determination of 5-lipoxygenase activity in tissue preparations disclosed a preferential increase in the liver, lung and renal cortex after portacaval shunting. Furthermore, exposure to endotoxin closely mimicked the shunting-induced changes. These results suggest that after portacaval shunting and possibly in patients with advanced liver disease, profound abnormalities at the level of local enzyme expression might play a pathophysiologically important role in the control of eicosanoid synthesis.

Uptake, production and metabolism of cysteinyl leukotrienes in the isolated perfused rat liver. Inhibition of leukotriene uptake by cyclosporine

1. The isolated perfused rat liver efficiently takes up cysteinyl leukotrienes (LTs) C4, D4, E4 and N-acetyl-LTE4 from circulation. More than 70% of these cysteinyl LTs are excreted from liver into bile within 1 h of onset of a 5 min infusion, while about 5% remain in the liver. About 20% of infused N-acetyl-LTE4 escapes hepatic first-pass extraction under our conditions. 2. Metabolites of LTC4 appearing in bile within 20 min of the onset of infusion include mainly LTD4 and N-acetyl-LTE4, but also omega-hydroxy-N-acetyl-LTE4 and omega-carboxy-N-acetyl-LTE4. Metabolites generated from omega-carboxy-N-acetyl-LTE4 by beta-oxidation from the omega-end represent the major biliary LTs secreted at later times. 3. Stimulation of the isolated perfused liver by the combined infusion of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and the Ca2+ ionophore A23187 results in a transient increase of endogenous cysteinyl LT production, which is independent of extrahepatic cells. 4. The immunosuppressive drug cyclosporine causes a dose-dependent inhibition of hepatobiliary cysteinyl LT excretion, probably by interference with the sinusoidal uptake system for cysteinyl LTs.

Differential effects of malotilate on 5-, 12- and 15-lipoxygenase in human ascites cells

Macrophages isolated from fluids of patients with liver cirrhosis mainly generated the 5-lipoxygenase products leukotriene B4 and 5-monohydroxyeicosatetraenoic acid. The cyclooxygenase products 6-keto-PGF1 alpha and thromboxane B2 were the most important prostaglandin-like substances. Malotilate, an anti-fibrotic substance, selectively inhibited the 5-lipoxygenase, whereas both the 12- and the 15-lipoxygenase pathways were stimulated. The effects of malotilate on eicosanoid production differ from those of known lipoxygenase inhibitors. Such differential effects have not been reported previously.

Regulation of liver metabolism by intercellular communication

The regulation of liver metabolism by intercellular communication was assessed by studying the effect of conditioned media of Kupffer and liver endothelial cells on protein synthesis, protein phosphorylation and glycogenolysis in parenchymal cells. Kupffer and endothelial cell-conditioned media enhanced the rate of protein synthesis of parenchymal cells by a factor of 1.7-1.9. The phosphorylation state of only three specific parenchymal cell proteins was influenced by the conditioned media. One, the MW 97,000 band appeared to be phosphorylase and it was found that in parallel with an enhancement of the activity of phosphorylase the glucose output by parenchymal cells could be stimulated. The effects of the conditioned media could be mimicked by prostaglandin E1, E2 and D2, whereas the pretreatment of non-parenchymal cells with aspirin abolished the stimulatory effect of these cells on the glucose output by parenchymal cells. The data indicate that prostaglandins from Kupffer and endothelial cells, mainly PGD2, can influence glucose release from parenchymal cells. The physiological importance of cellular communication was further assessed in a liver perfusion system. The tumor promoting phorbol ester PMA stimulated glycogenolysis in the perfused liver two-fold. This stimulation was blocked by the presence of aspirin. PMA is inactive on isolated parenchymal cells. Addition of PMA to the perfused liver appears to enhance the output of PGD2 in parallel with the stimulation of the glucose output. Addition of prostaglandin D2 itself could also stimulate the glucose output in the perfused liver. Our data indicate that the stimulation of glycogenolysis in the liver by PMA is mediated by non-parenchymal cells which produce PGD2 in response to PMA, leading subsequently to activation of the phosphorylase system in the parenchymal cells. It seems possible also that the tumor-promoting activity of PMA on liver will be mediated by a primary interaction with non-parenchymal cells. It is concluded that the occurrence of intercellular communication inside the liver in response to activation of non-parenchymal cells adds a new mechanism to the complex regulation of liver metabolism which may be relevant under normal and pathological conditions.