Prostaglandin and thromboxane synthesizing activity in isolated murine hepatocytes and nonparenchymal liver cells

Relevance between lipid metabolism-associated genes and rat liver regeneration

AIM

Lipids are important in constituting cell structure and participating in many biological processes, particularly in energy supplementation to cells. The aim of the present study is to elucidate the action of lipid metabolism-associated genes on rat liver regeneration (LR).

METHODS

Lipid metabolism-associated genes were obtained by collecting website data and retrieving related articles, and their expression changes in the regenerating rat liver were checked by the Rat Genome 230 2.0 array.

RESULTS

In total, 280 genes involved in lipid metabolism were proven to be LR-associated by comparing the gene expression discrepancy between the partial-hepatectomy and sham-operation groups. The initial and total expression numbers of these genes occurring in the initial phase, G(0)/G(1) transition, cell proliferation, cell differentiation, and structure-functional rebuilding of LR were 128, 33, 135, 6, and 267, 147, 1026, 306, respectively, illustrating that these genes were initially expressed mainly in the initiation stage and functioned in different phases. Upregulation (850 times) and downregulation (749 times), as well as 25 types of expression patterns, showed that the physiological and biochemical activities were diverse and complicated in LR.

CONCLUSION

According to the results of the chip detection, it was presumed that fatty acid synthesis at 24-66 h, leukotriene and androgen synthesis at 16-168 h, prostaglandin synthesis at 2-96 h, triglyceride synthesis at 18-24 h, glycosphingolipid synthesis at 0.5-66 h, metabolism of phosphatidyl inositol and sphingomyelin at 2-16 h, and cholesterol catabolism at 30-168 h were enhanced. Throughout almost the whole LR, the genes participating in estrogen, glucocorticoid, and progesterone synthesis, and triglyceride catabolism were upregulated, while phospholipid and glycosphingolipid catabolism were downregulated.

Minimally invasive hepatectomy: modulation of systemic reactions to operation or laparoscopic approach?

BACKGROUND

A new concept of surgical stress has been proposed that consists of both aggressiveness of operation and systemic reactions to an operation.

METHODS AND RESULTS

We have investigated a possible modulation of such systemic reactions to operation and have demonstrated the following 3 points: (1) coagulation and fibrinolytic systems are independently activated during hepatectomy and such activation can be modulated by protease inhibitors such as nafamostat mesilate and antithrombin III; (2) elevated thromboxane A2 during hepatectomy is characterized in the prostanoid system, the elevation of thromboxane A2 is inhibited by thromboxane A2 synthetase inhibitor, and postoperative liver injury is reduced; (3) cytokine response induced by hepatectomy is modulated by preoperative administration of methylprednisolone, leading to possible prevention of bacterial translocation. Therefore, modulating systemic reactions to hepatectomy may be important for successful minimally invasive hepatectomy. Another important option for minimally invasive hepatectomy is the use of operative procedures such as laparoscope or thoracoscope. We have investigated the usefulness of a laparoscopic hepatectomy from the standpoints of early and long-term outcome after hepatectomy. Laparoscopic hepatectomy, which is a difficult and dangerous procedure, can be a feasible option and can result in better short-term outcome and a similar long-term outcome after hepatectomy when compared with conventional open hepatectomy. Therefore, the laparoscopic approach is also a viable option for minimally invasive hepatectomy.

CONCLUSIONS

Modulation of systemic reactions to the operation itself and laparoscopic hepatectomy may be new strategies for performing minimally invasive hepatectomy.

The effect of indomethacin on hepatitis B virus replication in chronic healthy carriers

BACKGROUND

A chronic HBsAg carrier state, a major cause of viral spread in a community, is one of the consequences of hepatitis B virus (HBV) infection. Although successful immunization programs have been initiated to eliminate the virus, there is still a large number of people with HBV infection worldwide. This study was designed to investigate the effect of indomethacin treatment on HBV markers in humans, in comparison with a control group.

METHODS

In total, 65 chronic 'healthy' HBV carriers were involved in the study. Patients were divided randomly into two groups. Group I (n = 42) received oral indomethacin 75 mg daily for 6 months. Group II (n = 23) acted as control. Patients in both groups were followed up for 6 months, during which laboratory tests, including viral parameters, were performed periodically. Liver biopsy was done in 17 patients (11/42 of the indomethacin group and 6/23 of the control group).

RESULTS

All liver biopsies showed grade 0-2 and stage 0-1 HBV in both groups (P > 0.05). HBsAg positivity did not change in any patient in either group. Five patients who had positive HBeAg in group I became negative 4 months later, while patients in group II continued to be positive at 6 months (P < 0.001). Similarly, all patients receiving indomethacin exhibited a total anti-HBeAg immunoglobulin response at 6 months, while the control group remained the same during this period (P < 0.05). HBV DNA, as detected by polymerase chain reaction in 20/22 (91%), was negative in group I at the end of 6 months. No change was observed in group II (P = 0.007).

CONCLUSIONS

Although no biochemical analyses were performed on prostaglandins in the present study, the results suggest that the prostaglandin pathway may be involved in the pathogenesis of the immune response against HBV, and that the suppression of viral replication is achieved as indicated by the disappearance of HBeAg and HBV DNA in healthy chronic HBV carriers.

Immunohistochemical demonstration of prostaglandins in various tissues of the rat

To demonstrate the tissue localization of prostaglandin (PG) E2, PGF2 alpha and 6-keto-PGF1 alpha (a stable metabolite of PGI2) various tissues, including decalcified periodontal tissue of 7-week-old male Wistar strain rats, were immunohistochemically examined using a streptavidin-biotin complex method. Besides tissue macrophages and endothelial cells in various tissues, hepatocytes, renal tubular cells, and parietal and chief cells in the gastric mucosa showed a positive reaction for the various PGs examined. PGs were demonstrated in the cytoplasm or in association with the cell membrane. We generally observed no difference between the localization patterns of PGE2-, PGF2 alpha-, and 6-keto-PGF1 alpha-positive cells in these tissues. However, in the periodontal ligament and alveolar bone, 6-keto-PGF1 alpha was localized in the cytoplasm of osteocytes, osteoblasts, cementocytes, and cementoblasts, while no reaction for PGE2 or PGF2 alpha was revealed in these cells. We demonstrated the immunohistochemical localization of PGs in various rat tissues including decalcified periodontal tissue and discuss the important roles of PGs in the modulation of their normal functions in these tissues.

Protection by indomethacin against the lethality and hepatotoxicity of phalloidin in mice

The present study examined the possible involvement of endogenous cyclooxygenase-derived factors in the lethality and hepatic hemorrhagic necrosis induced by phalloidin. Mice were pretreated with indomethacin, aspirin or ibuprofen (all inhibitors of cyclooxygenase) and injected with phalloidin (2 mg/kg). The toxin induced 75% lethality and caused severe hemorrhagic necrosis of the liver associated with increased serum levels of AST and ALT. Indomethacin completely prevented the mortality and hepatic damage elicited by phalloidin as judged by morphologic analysis and serum AST and ALT release. The in vitro addition of indomethacin to suspensions of freshly-isolated hepatocytes decreased plasma membrane bleb formation induced by phalloidin. In contrast to indomethacin, aspirin and ibuprofen did not influence phalloidin toxicity in vivo. These results suggest that inhibition of prostanoids per se may not be the sole mechanism of protection by indomethacin.

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.

Prostaglandin E2 and rat liver regeneration

BACKGROUND

Prostaglandin (PG) is reported to be involved in hepatic regeneration. However, little is known about the detailed relation in PG-induced stimulation of the proliferation. The present study was attempted to elucidate the relation.

METHODS

The serial change of PGE2 level released from the regenerating rat liver and the effect of PGE2 on the proliferation of rat hepatocytes were studied, with special reference to PGE2 binding and cyclic AMP (cAMP).

RESULTS

The PGE2 level increased 3 hours and 10 hours after partial hepatectomy. Timings of these increases seemed to coincide with those of the first and second increase of cAMP in the liver before the initiation of DNA synthesis. DNA synthesis of hepatocytes in primary culture between 24 and 36 hours, 36 and 48 hours, and 48 and 60 hours of culture were significantly enhanced by addition of PGE2 between 4 and 24 hours of culture at concentrations of 2 nmol/L to 1 mumol/L, 2 nmol/L to 200 nmol/L, and 5 mumol/L to 10 mumol/L, and 2 nmol/L and 10 mumol/L, respectively. Enhancement of DNA synthesis with PGE2 at concentrations less than 1 mumol/L seemed to be associated with the high-affinity binding and that at high concentrations with the low-affinity binding. Intracellular cAMP level in the hepatocytes increased during culture, and its increase was enhanced by PGE2 addition.

CONCLUSIONS

It is suggested that PGE2 production in the liver increases biphasically during hepatic regeneration and that PGE2 enhances the proliferation of hepatocytes by a specific receptor-mediated process, which is largely associated with cAMP-dependent process.

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.

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.

Synthesis and degradation of eicosanoids in primary rat hepatocyte cultures

Arachidonic acid metabolites may play an important role in liver physiology, yet hepatocyte prostaglandin synthesis has not been characterized extensively. We used RIA to study production and clearance of several eicosanoids in confluent primary cultures of rat hepatocytes in serum-free, hormonally-defined medium. Under basal, unstimulated conditions 6-keto-PGF1 alpha (spontaneous breakdown product of prostacyclin) and 13,14-dihydro-15-keto-PGE (DHK-PGE, a metabolite of PGE) accumulated in the culture medium. Hepatocytes cleared 6-keto-PGF1 alpha, thromboxane B2, and DHK-PGE from the medium. Production of eicosanoids by primary cultures appeared resistant to indomethacin and several other cyclooxygenase inhibitors. This apparent resistance to indomethacin was not caused by rapid metabolism of indomethacin, by failure of the drug to enter hepatocytes, or by insensitivity of hepatocyte cyclooxygenase to the drug. Metabolism of PGE to DHK-PGE may be saturated under in vitro conditions. Hepatocytes can synthesize significant amounts of eicosanoids, although they are probably less active in this regard than are non-parenchymal cells.

Down-regulation of prostaglandin E2 receptors in regenerating rat liver and its physiological significance

The properties of prostaglandin (PG) E2 receptors in regenerating liver were studied using rat hepatocytes in primary culture. The control cells possessed stereo-specific PGE2 receptors with Bmax and Kd values, at 4 degrees C, of 526 fmol/mg protein and 6.5 nM respectively. In cells from regenerating liver after 70% hepatectomy, Bmax was reduced to 42-43% that of the controls; Kd did not change. Administration of indomethacin before surgery prevented Bmax reduction. These results indicate that PGE2, produced during the regeneration process, evoked cellular events and regulated the density of its receptors.

Arachidonic acid metabolites in carbon tetrachloride-induced liver injury

The changes in the levels of leukotrienes (LTs) and prostaglandins (PGs) in the liver tissue of rats with carbon tetrachloride (CCl4)-induced liver injury were studied. As a result, after the administration of CCl4, the levels of LTs increased at an early stage while the levels of PGs increased at a later stage. This suggests that LTs may have an adverse effect on liver injury induced by CCl4, and that PGs may not have a direct effect on liver injury. In addition, serum GOT and GPT levels improved with the administration of AA-861, a 5-lipoxygenase inhibitor, while these levels did not change with the administration of indomethacin, a cyclooxygenase inhibitor. These results suggest that arachidonic acid metabolites may play an important role in the induction of liver cell injury.

Changes of prostacyclin and thromboxane synthesis in the course of mouse liver perfusion. Stimulated thromboxane A2 synthesis of freshly prepared isolated mouse hepatocytes

The formation of prostacyclin and thromboxane A2 (measured as 6-keto PGF1 alpha and TXB2 by radioimmunoassay) was investigated during a 30 min perfusion of mouse liver in a recirculation system. After cannulation of the portal vein an immediate increase of de novo synthesis and secretion of PGI2 occurred followed by a sharp decrease. Increased PGI2 synthesis was also followed by a continuous increase of TXA2 synthesis and secretion reaching a maximum at the end of the 30 min perfusion. Elevated TXA2 synthesis was also shown in freshly isolated hepatocytes investigated in the course of a 20 min incubation period immediately after the perfusion. However, the elevated TXA2 formation was not observed when it was measured after a 120 min preincubation of the cells. Both PGI2 and TXA2 production could be provoked to a similar extent by the addition of arachidonate and A 23187 immediately after the perfusion or after a 120 min preincubation.

Prostaglandin biosynthetic capacity of hepatomas with different growth rates

1. Prostaglandin synthesis from [14C]arachidonate by microsomal fractions was measured with preparations from rat liver and from hepatomas of different growth rates. The highest rates of synthesis were observed with microsomal preparations from the rapidly growing hepatoma HTC. 2. Assay of endogenous levels of prostaglandins E2, F2 alpha and thromboxane B2 also indicated high levels in solid tumors of the HTC line. 3. With HTC cells in culture it was necessary to incubate in the absence of serum in order to detect prostaglandin synthesis. 4. The data indicated that, while prostaglandin synthesis was elevated in HTC cells, the synthesis of prostaglandins by a series of hepatomas was not closely correlated with the growth rates of the tumors.

cAMP dependent inhibition of thromboxane A2, prostacyclin and PGF2 alpha synthesis in mouse hepatocytes

The role of cAMP dependent regulation in thromboxane A2, prostacyclin and PGF2 alpha synthesis (measured by radioimmunoassay) was investigated in isolated mouse hepatocytes and in microsomal membranes prepared from these cells. In isolated hepatocytes N6,O2-dibutyryl cAMP inhibited the formation of all the three derivatives, while calcium ionophore A 23187 stimulated their synthesis. Addition of the dissociated catalytic subunit of cAMP dependent protein kinase and ATP to microsomal membranes inhibited the production of TXA2, PGI2 and PGF2 alpha by about 50% and this inhibition was counteracted by the combined addition of heat stable inhibitor protein of cAMP dependent protein kinase. It is concluded that in parenchymal liver cells cAMP dependent phosphorylation is directly involved in the inhibition of prostanoid synthesis.

Metabolic fate of arachidonic acid in hepatocytes of continuously endotoxemic rats

The present experiments were designed to characterize the kinetics of [1-14C]arachidonic acid (AA) metabolism as a function of time in hepatocytes obtained from rats infused continuously for 30 h with a nonlethal dose of Escherichia coli endotoxin (ET). Chronic endotoxemia greatly reduces the ability of hepatocytes to utilize [1-14C]AA, which is reflected from the earliest times of incubation in very low labeling of intermediates in the biosynthetic pathways of glycerolipids (phosphatidic acid and diacylglycerol) and slower removal of [1-14C]AA from the free fatty acid pool as compared with saline-infused rats. At later times of incubation, the labeling of phospholipids (especially phosphatidylethanolamine and phosphatidylinositol [PI]), but not of triacylglycerides is decreased. Analysis of fatty acid composition of individual phospholipids from cells of ET-infused rats reveals that the content of AA is significantly reduced only in PI. Hence an impairment in activation/acylation enzymatic mechanisms could affect the turnover of metabolically active phospholipid pools, i.e., PI, involved in signal transmission processes, and result in increased availability of 20:4 for eicosanoid synthesis, contributing to cellular metabolic perturbations in endotoxicosis.

Effect of prostaglandins and their analogues on hormone-stimulated glycogenolysis in primary cultures of rat hepatocytes

Hepatocytes were isolated by collagenase perfusion method from adult male rats, cultured and then prelabeled with [14C]glucose. The [14C]glycogen-labeled cells were used in experiments for effect of prostaglandins on hormone-stimulated glycogenolysis. Prostaglandin E1, prostaglandin E2 and 16,16-dimethylprostaglandin E2, but not prostaglandin D2 or prostaglandin F2 alpha, inhibited glycogenolysis stimulated by glucagon, epinephrine, isoproterenol (beta-adrenergic agonist) or epinephrine in the presence of propranolol (beta-antagonist) in primary cultured hepatocytes. The inhibitory effects on day 2 of cultures were approx. twice those on day 1. Dimethylprostaglandin E2 (10(-6)M) caused 60-70% inhibitions of the stimulations by these substances. In the case of the stimulation by glucagon, the inhibition further increased by 80-100% on day 3 of culture. Prostaglandin E1 and prostaglandin E2 caused less inhibition than dimethylprostaglandin E2 of all these stimulations. Dinorprostaglandin E1 (9 alpha,13-dihydroxy-7-ketodinorprost-11-enoic acid), which is a hepatocyte-metabolite of prostaglandin E1 and prostaglandin E2, and arachidonic acid did not have any inhibitory effects. These data indicate that the E series of prostaglandins may function as the regulation of hepatic glycogenolysis stimulated by epinephrine and glucagon, and that their rapid degradation system may contribute to the modulation of the action in liver.

Prostanoid synthesis in isolated parenchymal and nonparenchymal mouse liver cells in the presence of arachidonic acid

Prostanoid synthesis was investigated in suspensions of isolated mouse hepatocytes and nonparenchymal liver cells. A stable metabolite of thromboxane A2 (TXB2) of prostacyclin (6-keto PGF1 alpha) and one of the prostaglandins (PGF2 alpha) was detected by radio-immuno-assay (RIA). Hepatocytes synthesized mainly TXB2, while smaller amounts of 6-keto PGF1 alpha and PGF2 alpha were detected during 60 min incubation. Homogenization of hepatocytes caused a slight increase of TXB2 production and provoked the synthesis of PGF2 alpha and 6-keto PGF1 alpha. The addition of arachidonate to hepatocytes did not influence prostanoid production at concentrations below 10-5M. Higher concentrations further increased TXB2 production and also increased the synthesis of 6-keto PGF1 alpha and PGF2 alpha. Nonparenchymal cells synthesized all the three types of prostanoids and homogenization of these cells did not result in a marked change. The addition of 10(-7)-10(-5)M arachidonate increased the TXB2, 6-keto PGF1 alpha and PGF2 alpha synthesis in nonparenchymal cells. No further increase was found at higher concentrations.

Release of prostanoids into the portal and hepatic vein in patients with chronic liver disease

Arterial and hepatovenous concentrations of circulating prostaglandin E2 and prostaglandin F2 alpha, the stable metabolites of prostacyclin and thromboxane A2 were measured in patients with chronic liver disease and compared with those in control patients with coronary artery disease but without hepatic dysfunction. Specific radioimmunoassays were used after extraction on octadecyl C 18-silica gel columns and thin-layer chromatography. While low levels of all cyclooxygenase products were found in hepatic arterial blood in patients with proven cirrhosis (n = 10) and fibrosis (n = 8), significantly higher concentrations were detected in the hepatic vein. A similar concentration profile was observed in controls (n = 4). Thus, there is a marked but comparable release of prostanoids from the normal as well as the diseased liver. Hepatovenous prostaglandin E2 was 11.6-fold, prostaglandin F2 alpha was 7.5-fold, prostacyclin was 12.2.-fold and thromboxane B2 was 3.9-fold above the level in the artery in both groups of patients. The hepatovenous concentrations of all arachinodate metabolites were unrelated to changes of liver morphology, biochemical abnormalities or the presence of ascites. No correlation could be demonstrated between hepatic venous pressure gradient and the concentration of prostanoids in the hepatic vein with the exception of thromboxane B2 (r = 0.55, p less than 0.05). The occurrence of esophageal varices was not associated with a specific pattern of circulating prostanoids in the posthepatic vasculature. Moreover, the portal-venous concentrations of all prostanoids (five patients: two with fibrosis, three with cirrhosis) exceeded the level in the hepatic vein substantially.(ABSTRACT TRUNCATED AT 250 WORDS)