High plasma levels of arginine and liver arginase in Kupffer-cell-depleted rats after partial hepatectomy

Dexamethasone restores transforming growth factor-β activated kinase 1 expression and phagocytosis activity of Kupffer cells in cholestatic liver injury

The role of transforming growth factor-β activated kinase 1 (TAK1) in modulating the function of Kupffer cells (KCs) within cholestatic livers remains unclear. This study examined the immunopharmacological action of dexamethasone (DEX) in modulating hepatic TAK1 expression and related signaling activity in a rat model of bile duct ligation-mimicked obstructive jaundice. The in vitro effects of DEX on porcine biliary extract (PBE)-modulated gene expression and phagocytosis of KCs were examined using a rat alveolar macrophage cell line (NR8383 cells). Although DEX therapy did not restore the downregulated TAK1 expression and phosphorylation, it significantly attenuated the upregulation of high-mobility group box 1 expression and caspase-3 activation in whole liver extracts of cholestatic rats, possibly via enhancing extracellular signal-regulated kinase-mediated signaling. Dual immunofluorescence staining of cholestatic livers and western detection on primary KCs isolated from cholestatic livers identified that DEX treatment indeed increased both the expression and phosphorylation levels of TAK1 in the KCs of cholestatic livers. In vitro studies using alveolar NR8383 macrophages with KC-characteristic gene expression further demonstrated that DEX not only repressed the pro-inflammatory cytokine production including with respect to interleukin (IL)-1β and IL-6, but also enhanced gene expression of TAK1 and a phagocytic marker, natural-resistance-associated macrophage protein 1, under PBE-mimicked cholestatic conditions. However, WST-1 assay showed that DEX did not protect NR8383 macrophages against the PBE-induced cytotoxicity. Immunofluorescence visualization of cellular F-actin by phalloidin suggested that DEX sustained the PBE-induced phagocytosis morphology of NR8383 macrophages. In conclusion, DEX treatment may pharmacologically restore the expression and activity of TAK1 in KCs, and sustain the phagocytic phenotype of KCs in cholestatic livers.

Intrasplenic Transplantation of Encapsulated Cells: A Novel Approach to Cell Therapy

Cell therapy is likely to succeed clinically if cells survive at the transplantation site and are protected against immune rejection. We hypothesized that this could be achieved with intrasplenic transplantation of encapsulated cells because the cells would have instant access to oxygen and nutrients while being separated from the host immune system. In order to provide proof of the concept, primary rat hepatocytes and human hepatoblastoma-derived HepG2 cells were used as model cells. Rat hepatocytes were encapsulated in 100-kDa hollow fibers and cultured for up to 28 days. Rat spleens were implanted with hollow fibers that were either empty or contained 1 × 107 rat hepatocytes. Human HepG2 cells were encapsulated using alginate/poly-l-lysine (ALP) and also transplanted into the spleen; control rats were transplanted with free HepG2 cells. Blood human albumin levels were measured using Western blotting and spleen sections were immunostained for albumin. Hepatocytes in monolayer cultures remained viable for only 6–10 days, whereas the cells cultured in hollow fibers remained viable and produced albumin throughout the study period. Allogeneic hepatocytes transplanted in hollow fibers remained viable for 4 weeks (end of study). Free HepG2 transplants lost viability and function after 7 days, whereas encapsulated HepG2 cells remained viable and secreted human albumin at all time points studied. ALP capsules, with or without xenogeneic HepG2 cells, produced no local fibrotic response. These data indicate that intrasplenic transplantation of encapsulated cells results in excellent survival and function of the transplanted cells and that the proposed technique has the potential to allow transplantation of allo- and xenogeneic cells (e.g., pancreatic islets) without immunosuppression.

The Role of IL-1 Family Members and Kupffer Cells in Liver Regeneration

Interleukin-1 (IL-1) family and Kupffer cells are linked with liver regeneration, but their precise roles remain unclear. IL-1 family members are pleiotropic factors with a range of biological roles in liver diseases, inducing hepatitis, cirrhosis, and hepatocellular carcinoma, as well as liver regeneration. Kupffer cells are the main source of IL-1 and IL-1 receptor antagonist (IL-1Ra), the key members of IL-1 family. This systemic review highlights a close association of IL-1 family members and Kupffer cells with liver regeneration, although their specific roles are inconclusive. Moreover, IL-1 members are proposed to induce effects on liver regeneration through Kupffer cells.

Ischemic preconditioning improves liver regeneration by sustaining energy metabolism after partial hepatectomy under ischemia in rats

BACKGROUND

The protective effect of ischemic preconditioning (IPC) has been reported on improvement of survival, reduction of liver necrosis and enhancement of the regenerative capacity of hepatocytes after partial hepatectomy. This study was undertaken to confirm that IPC has a significant impact on regeneration of hepatocytes after partial hepatectomy in ischemically damaged liver. In addition, we sought to examine the role of adenine nucleotides in this process.

METHODS

Wistar rats were subjected to 60 min of total hepatic ischemia, followed by 70% hepatectomy. The animals were subdivided into an IPC (10/15 min) group and a non-IPC (control) group. Liver function tests and arginase activity were analyzed. Hepatic adenosine triphosphate (ATP), adenosine diphosphate and adenosine monophosphate were measured using gradient high-performance liquid chromatography. The liver regeneration was identified using relative liver weight and proliferating cell nuclear antigen (PCNA) labeling index.

RESULTS

IPC treatment improved serum liver enzymes and tissue arginase activity (P<0.05) when compared with the control group. The preconditioned livers were associated with upregulation of ATP expression and also increased tissue energy charge. Regenerated liver weight in the IPC group was significantly higher than in the control group (P<0.05). The PCNA labeling index in the remnant livers in the IPC group was also significantly increased at 24 and 48 h after partial hepatectomy (P<0.05).

CONCLUSION

These results suggest that IPC-augmented liver regeneration after hepatectomy, probably due to the stabilization of energy metabolism in rats.

Delayed energy protection of ischemic preconditioning on hepatic ischemia/reperfusion injury in rats

BACKGROUND

Hepatic ischemia/reperfusion (IR) injuries associated with hepatic resections are unresolved problems in the clinical practice. The aim of this study is to elucidate the effect of ischemic preconditioning (IPC) on the energy charge (EC) and related mechanisms at the late phase of hepatic IR injury.

METHODS

30 Wistar rats were randomly divided into sham, IR and IPC groups. The model of partial hepatic IR was used. The rats were subjected to 60 min hepatic ischemia, pretreated by IPC (10/15 min) or not. After 24 h of reperfusion, serum alanine aminotransferase (ALT), nitrite/nitrate (NOx), malondialdehyde (MDA), hepatic tissue arginase activity, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and EC of the liver were measured.

RESULTS

Liver injury reduced by IPC is measured by liver tissue arginase activity and serum ALT. Tissue NOx levels in rats pretreated with IPC were significantly higher than levels in the IR group (p < 0.001). Tissue levels of MDA in the liver of the IPC group were found to be significantly lower than the levels in the IR group (p < 0.001). ATP and EC levels 24 h after hepatic ischemia in rats pretreated with IPC were higher than the levels in the IR (p < 0.05). All groups had similar ADP and AMP levels in the liver tissues. The IPC procedure significantly reduced the hepatic necrosis (p < 0.001).

CONCLUSION

The results of this study demonstrated that pretreatment with IPC improved tissue ATP, EC, and hepatic necrosis at late stages of ischemia reperfusion injury of the liver. Increased nitric oxide, reduced MDA and arginase activity seemed to play a regulatory role in this delayed protective effect of IPC.

Acute reduction of circulating arginine in mice does not compromise whole body NO production

The amino acid arginine is the sole precursor for nitric oxide (NO) synthesis. We have now studied the role of acutely reducing circulating arginine on whole body NO production in mice. Measurements were performed in 4 groups of mice, treated with saline (SAL) or arginase (ASE), and SAL or bacterial endotoxin (LPS). After 5 h, a 57% reduction in circulating arginine was obtained by intravenous injections of arginase (SAL/SAL: 138+/-7; ASE/SAL: 59+/-10 microM, P<0.05). Reduced circulating arginine caused a reduction in plasma arginine flux (SAL/SAL: 82+/-6; ASE/SAL: 63+/-5 nmol/(10 g b.w. min), P<0.05), but did not change whole body NO production. LPS treatment caused an increase in NO production (SAL/SAL: 1.3+/-0.3 SAL/LPS 2.3+/-0.4 nmol/(10 g b.w. min), P<0.05), presumably by NOS-2 and was unaffected by reducing circulating arginine. Also, intestinal citrulline and renal arginine production were not increased in LPS-challenged mice with reduced circulating arginine levels. The present study indicates that an acute decrease in circulating arginine does not compromise whole body NO production and provides evidence against a role for renal arginine production to counteract an acute reduction of circulating arginine.

High plasma arginine concentrations in critically ill patients suffering from hepatic failure

OBJECTIVE

In physiological conditions, the liver plays an important role in the regulation of plasma arginine concentrations by taking up large amounts of arginine from the hepatic circulation. When hepatic failure is present, arginine metabolism may be disturbed. Therefore, we hypothesized high arginine plasma concentrations in critically ill patients suffering from hepatic failure.

DESIGN

We prospectively collected blood samples from a cross-section of intensive care unit patients.

SETTING

Surgical intensive care unit of a Dutch university medical center.

SUBJECTS

A total of 52 critically ill patients with clinical evidence of dysfunction of more than two organs were recruited.

MEASUREMENTS

Plasma arginine concentrations were determined by HPLC. We identified correlations of arginine concentrations with organ failure scores and laboratory variables by univariate and multiple regression analyses.

RESULTS

High plasma arginine concentrations were found in critically ill patients developing organ failure. Patients who were in the highest quartile of plasma arginine concentrations had significantly lower fibrinogen concentrations, higher lactic acid concentrations, and longer prothrombin time. Stepwise multiple regression analysis showed that concentrations of arginine were independently associated with the presence of hepatic failure (P=0.03) and renal failure (P=0.048). In addition, lactic acid proved to be an independent determinant of plasma arginine concentration (P=0.014).

CONCLUSIONS

Critically ill patients who suffer from hepatic failure have elevated plasma arginine concentrations. Additional arginine in the treatment of these patients can be harmful, and therefore should not be used as a standard nutritional regimen until further evaluation.

Protective role of Kupffer cells in acetaminophen-induced hepatic injury in mice

Hepatic injury induced by various toxic agents, including acetaminophen (APAP), has been attributed, in part, to the production of proinflammatory cytokines and other mediators by resident Kupffer cells within the liver. However, recent evidence from our laboratory has demonstrated that hepato-protective factors, such as interleukin (IL)-10 and cyclooxygenase-derived mediators, are also upregulated in response to hepatic damage to help protect against exacerbated injury, and Kupffer cells have been suggested to be a source of these modulatory factors. In other models, Kupffer cells also serve important regulatory functions in pathophysiological states of the liver. Therefore, we reevaluated the role of Kupffer cells in a murine model of APAP-induced liver injury using liposome-entrapped clodronate (liposome/clodronate) as an effective Kupffer cell-depleting agent. We show that in contrast to pretreatment of mice with a widely used macrophage inhibitor, gadolinium chloride, which did not deplete Kupffer cells but moderately protected against APAP-induced hepatotoxicity as reported previously, the intravenous injection of liposome/clodronate caused nearly complete elimination of Kupffer cells and significantly increased susceptibility to APAP-induced liver injury as compared with mice pretreated with empty liposomes. This increased susceptibility was apparently unrelated to the metabolism of APAP since liposome/clodronate pretreatment did not alter APAP-protein adduct levels. Instead, Kupffer cell depletion by liposome/clodronate led to significant decreases in the levels of hepatic mRNA expression of several hepato-regulatory cytokines and mediators, including IL-6, IL-10, IL-18 binding protein and complement 1q, suggesting that Kupffer cells are a significant source for production of these mediators in this model. Our findings indicate that, in addition to their protoxicant activities, Kupffer cells can also have an important protective function in the liver through the production of a variety of modulatory factors which may counteract inflammatory responses and/or stimulate liver regeneration.

Induction of arginase II in livers of bile duct-ligated rats

Nitric oxide (NO) has been implicated in playing a role in liver cirrhosis, but the regulatory mechanisms are still unclear. As arginase shares a common substrate with NO synthase (NOS), the aim of this study was to investigate the expression of arginase I and II in cirrhotic liver. Liver cirrhosis was induced in rats by chronic bile duct ligation (BDL). Controls were sham-operated. Competitive polymerase chain reaction was performed to assay the expression of messenger RNA of arginase I and II. Protein expression was detected by immunohistochemistry and western-blotting. The level of arginine in plasma was lower in BDL rats, while the ornithine level in plasma was correspondingly higher (r= -0.96, P<0.0001). Arginase I messenger RNA was reduced significantly in BDL rats (3.34+/-0.32 vs. 1.32+/-0.21 x 10(4) attomole/microg of total RNA, sham vs. BDL, P<0.001), as well as arginase I protein. In contrast, arginase II mRNA was induced in the livers of BDL rats, with negligible expression in controls (0.35+/-0.11 vs. 3.64+/-0.54 attomole/microg of total RNA, sham vs. BDL, P<0.001). Arginase II protein was localized in some hepatocytes and hyperplastic bile ductular epithelial cells of cirrhotic livers but not in control livers. In conclusion, arginase II was induced in BDL livers, while the expression of arginase I was down-regulated. These data suggest that arginase I and II are regulated differently and may have different functions in the livers of BDL rats. Reduction of arginase I in BDL livers may be responsible for the lowering of arginine levels in the plasma, while induction of arginase II could be important in regulating NO synthesis as well as other important mechanisms involved in liver cirrhosis.