Possible induction of fatty acid cyclo-oxygenase in lipopolysaccharide-stimulated rat Kupffer cells

Glycine: The Smallest Anti-Inflammatory Micronutrient

Glycine is a non-essential amino acid with many functions and effects. Glycine can bind to specific receptors and transporters that are expressed in many types of cells throughout an organism to exert its effects. There have been many studies focused on the anti-inflammatory effects of glycine, including its abilities to decrease pro-inflammatory cytokines and the concentration of free fatty acids, to improve the insulin response, and to mediate other changes. However, the mechanism through which glycine acts is not clear. In this review, we emphasize that glycine exerts its anti-inflammatory effects throughout the modulation of the expression of nuclear factor kappa B (NF-κB) in many cells. Although glycine is a non-essential amino acid, we highlight how dietary glycine supplementation is important in avoiding the development of chronic inflammation.

Receptors, mediators, and mechanisms involved in bacterial sepsis and septic shock

Bacterial sepsis and septic shock result from the overproduction of inflammatory mediators as a consequence of the interaction of the immune system with bacteria and bacterial wall constituents in the body. Bacterial cell wall constituents such as lipopolysaccharide, peptidoglycans, and lipoteichoic acid are particularly responsible for the deleterious effects of bacteria. These constituents interact in the body with a large number of proteins and receptors, and this interaction determines the eventual inflammatory effect of the compounds. Within the circulation bacterial constituents interact with proteins such as plasma lipoproteins and lipopolysaccharide binding protein. The interaction of the bacterial constituents with receptors on the surface of mononuclear cells is mainly responsible for the induction of proinflammatory mediators by the bacterial constituents. The role of individual receptors such as the toll-like receptors and CD14 in the induction of proinflammatory cytokines and adhesion molecules is discussed in detail. In addition, the roles of a number of other receptors that bind bacterial compounds such as scavenger receptors and their modulating role in inflammation are described. Finally, the therapies for the treatment of bacterial sepsis and septic shock are discussed in relation to the action of the aforementioned receptors and proteins.

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.

Involvement of cyclooxygenase-2 in the potentiation of allyl alcohol-induced liver injury by bacterial lipopolysaccharide

Bacterial endotoxin (lipopolysaccharide; LPS) augments the hepatotoxicity of a number of xenobiotics including allyl alcohol. The mechanism for this effect is known to involve the inflammatory response elicited by LPS. Upregulation of cyclooxygenase-2 (COX-2) and production of eicosanoids are important aspects of inflammation, therefore studies were undertaken to investigate the role of COX-2 in LPS-induced enhancement of liver injury from allyl alcohol. Rats were pretreated (iv) with a noninjurious dose of LPS or sterile saline vehicle and 2 h later were treated (ip) with a noninjurious dose of allyl alcohol or saline vehicle. COX-2 mRNA was determined by semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), and liver injury was assessed from activities in serum of alanine and aspartate aminotransferases (ALT and AST, respectively) and from histology. Liver injury was observed only in rats cotreated with LPS and allyl alcohol. Serum ALT activity was increased by 4 h after administration of LPS and continued to increase through 8 h. COX-2 mRNA was detectable at low levels in livers from rats receiving only the vehicles at any time up to 8 h. Expression of COX-2 mRNA was increased by 30 min after administration of LPS and remained elevated through 6 h. Allyl alcohol treatment alone caused an increase in COX-2 mRNA at 4 h (2 h after allyl alcohol) that lasted less than 2 h. In livers from rats cotreated with LPS and allyl alcohol, levels of COX-2 mRNA were greater than levels seen with either LPS or allyl alcohol alone. The increased expression of COX-2 mRNA was accompanied by an increase in the concentration of prostaglandin (PG) D(2) in plasma. Plasma PGD(2) concentration was increased to a greater extent in rats treated with LPS plus allyl alcohol compared to allyl alcohol or LPS alone. Pretreatment with the COX-2 selective inhibitor, NS-398, abolished the increase in plasma PGD(2) and reduced the increase in ALT and AST activities observed in rats cotreated with LPS and allyl alcohol. NS-398 did not affect liver injury from allyl alcohol alone administered at a larger, hepatotoxic dose. In addition, ibuprofen, a nonselective inhibitor of cyclooxygenases, did not protect against liver injury from LPS plus allyl alcohol. In isolated hepatocytes PGD(2), but not PGE(2), reduced the concentration of allyl alcohol required to cause half-maximal cytotoxicity. These results suggest that products of COX-2 play a role in the augmentation of allyl alcohol-induced liver injury by LPS.

Activation of Kupffer cells and caspase-3 involved in rat hepatocyte apoptosis induced by endotoxin

BACKGROUND/AIMS

Sepsis and lipopolysaccharides (LPS) cause mild to severe hepatic dysfunction. In this study, Kupffer cell activation, involvement of TNFalpha and caspases downstream of the TNFalpha receptor were examined in hepatocyte apoptosis induced by LPS.

METHODS

In in vivo experiments, male Sprague-Dawley rats were injected intravenously with LPS, and small amounts of the blood and liver were sampled to evaluate apoptosis. Kupffer cells were inactivated by pretreatment with gadolinium chloride for 2 days. In in vitro experiments, hepatocytes and Kupffer cells were separately isolated from rat livers using collagenase perfusion.

RESULTS

LPS induced time-dependent and dose-dependent increases in the number of TUNEL-positive cells, which coincided with the apoptotic features of hepatocytes demonstrated by electron microscopy and DNA ladder. Activation of caspase-3-like proteases was observed with an increase in the number of apoptotic hepatocytes. Immunostaining with activated caspase-3-specific antibody showed that caspase-3 was activated only in the cytoplasm of TUNEL-positive hepatocytes. Inactivation of Kupffer cells by gadolinium chloride was concomitantly accompanied by the prevention of caspase-3 activation, hepatocyte apoptosis and liver injury induced by LPS. The co-culture system of hepatocytes and Kupffer cells, but neither cell culture system, individually, showed LPS-induced hepatocyte apoptosis. Kupffer cell-conditioned medium induced hepatocyte apoptosis, whereas addition of anti-TNFalpha antibody to Kupffer cell-conditioned medium did not. Additions of acetyl-DEVD-CHO, acetyl-YVAD-CHO, and acetyl-IETD-CHO to Kupffer cell-conditioned medium decreased the number of apoptotic hepatocytes.

CONCLUSIONS

These results suggest that the activation of Kupffer cells, TNFalpha and caspases downstream of TNFR1 were involved in hepatocyte apoptosis induced by LPS.

Kupffer cell-mediated down regulation of rat hepatic CMOAT/MRP2 gene expression

Lipopolysaccharides (LPS) induces intrahepatic cholestasis and canalicular multispecific organic anion transporter (CMOAT/MRP2) plays a central role in hepatic bilirubin transport. This study examined the role of Kupffer cell in LPS-induced cholestasis. Rats were injected intravenously with LPS. Kupffer cells were inactivated with gadolinium chloride (Gd). CMOAT/MRP2 mRNA expression was time- and dose-dependently decreased by LPS injection with a decrease in bile flow and an increase in serum bilirubin level. Gd pretreatment inhibited decrease in CMOAT/MRP2 mRNA and bile flow, and increase in serum bilirubin. Kupffer cell-conditioned medium decreased CMOAT/MRP2 expression. Addition of anti-IL-1 or anti-TNFalpha antibody restored CMOAT/MRP2 expression, whereas IL-1 and TNFalpha decreased the expression. MAP kinases were activated by addition of the conditioned medium, and addition of PD98059 or SB203580 restored CMOAT/MRP2 expression. These results suggest that LPS activates Kupffer cells to secrete IL-1 and TNFalpha, which in turn activate MAP kinases and decrease CMOAT/MRP2 expression.

Pathophysiology of dogs after 84% hepatectomy with emphasis on prostaglandin metabolites and the effect of a thromboxane A2 synthesis inhibitor and a prostaglandin I2 analog

The pathophysiological conditions following 84% hepatectomy were examined in terms of the changes in thromboxane A2 (TxA2) and prostaglandin I2 (PGI2) in a canine model. OKY-046, a TxA2 inhibitor, and OP-2507, a PGI2 analog, were administered to evaluate the possibility of extending hepatic resection. The 2-week survival rate following 84% hepatectomy significantly improved after the administration of OKY-046 and OP-2507, from 12.5% to 58.3% and 75.0%, respectively. Furthermore, OP-2507 significantly improved impaired hepatocyte and sinusoidal endothelial cell function after 84% hepatectomy, resulting in a satisfactory recovery to the preoperative levels. Within 24 h after 84% hepatectomy, the plasma levels of thromboxane B2 (TxB2) increased significantly, and the 6-keto-prostaglandin F1 alpha (6-KF) levels became slightly elevated. OKY-046 and OP-2507 decreased TxB2 and increased 6-KF in the plasma, resulting in the maintenance of sufficient blood flow in the portal vein and hepatic tissue and the mitigation of microcirculatory disorders. Moreover, the cytoprotective effects of the two drugs inhibited functional impairment of the residual liver. In conclusion, abnormal prostaglandin metabolites were produced after 84% hepatectomy, being involved in residual liver disorders. However, the administration of either an inhibitor of TxA2 synthesis or a PGI2 analog ameliorated the functional impairment of the residual liver, which suggests their potential value for extending the resectability of the liver from what is presently feasible.

Studies on the induction of cyclooxygenase isozymes by various prostaglandins in mouse osteoblastic cell line with reference to signal transduction pathways

A mouse osteoblastic cell line MC3T3-E1 has a cyclooxygenase enzyme, and produces prostaglandin E2. When the cells were cultured in the presence of iloprost (a stable analogue of prostacyclin) or prostaglandin E1 or F2 alpha, the activity of cyclooxygenase increased in a dose- and time-dependent manner. The increase of the enzyme activity was attributed mostly to the cyclooxygenase isoform-2 because immunoprecipitation using an anti-cyclooxygenase-2 antibody removed the majority of the cyclooxygenase activity from the solubilized enzyme fraction, and the corresponding activity was detected in the immunoprecipitant. In addition, there was a marked increase in the cyclooxygenase-2 protein which was demonstrated by Western blotting. As analyzed by Northern blotting, the cyclooxygenase-2 mRNA increased and reached a maximum 1 and 3 h after the addition of iloprost and prostaglandin F2 alpha (about 15- and 60-fold increase), respectively, whereas the cyclooxygenase-1 mRNA increased slowly and only by about 3-fold. Iloprost and prostaglandin E1 stimulated the production of cAMP by 60-fold over the basal level, whereas the cAMP level was almost unchanged by prostaglandin F2 alpha. In contrast, prostaglandin F2 alpha stimulated IP3 production more efficiently than iloprost and prostaglandin E1. These results suggest that the stimulated syntheses prominently of cyclooxygenase-2 and to a lesser extent of cyclooxygenase-1 are mediated by at least two distinct signal transduction pathways involving the cAMP-synthesis stimulated by iloprost and prostaglandin E1 and the phosphoinositide turnover stimulated by prostaglandin F2 alpha.

Upregulation of mouse CD14 expression in Kupffer cells by lipopolysaccharide

Western blot analysis showed that a monoclonal antibody against recombinant mouse CD14 (mCD14), designated rmC5-3, specifically reacted with mouse macrophage cell line J774, but not myeloma cell line NS1. Fluorographic and immunocytochemical analysis demonstrated specific binding of rmC5-3 with mouse resident macrophages, inflammatory monocytes and neutrophils, and macrophage cell lines. Immunohistochemical staining using rmC5-3 showed that CD14-positive Kupffer cells (KC) were small in number in the liver in nonstimulated mice. The number of stained KC, which were rich in the midzonal and periportal regions, gradually increased with time after intraperitoneal injection of lipopolysaccharide (LPS), peaked 6 h after injection, and returned to normal by 20 h after injection. Staining intensity over time was proportional to the number of KC. A slight increase in mCD14 expression was observed in peritoneal macrophages 2 h after LPS administration in vivo using flow cytometric analysis. mCD14 mRNA became detectable at 1 h after the intraperitoneal injection of LPS (20 micrograms/mice), and the level dramatically increased with time, peaking at 3 h, and sharply dropped at 6 h. The resident peritoneal macrophages demonstrated a constitutively high mCD14 mRNA expression, which slightly increased 2 h after LPS (100 ng/ml) stimulation in vitro. The level of mCD14 expression in macrophages did not increase after intraperitoneal injection of LPS (20 micrograms/mice).