Disrupted pancreatic exocrine differentiation and malabsorption in response to chronic elevated systemic glucocorticoid

Glucocorticoids are antiinflammatory therapeutics that have potent effects on cell differentiation. The aim of this study was to establish whether systemic glucocorticoid exposure significantly affects pancreatic differentiation in vivo because hepatocyte-like cells have been documented to occur in the diseased rodent pancreas. Expression of hepatic markers was examined in pancreata from mice genetically modified to secrete elevated circulating endogenous glucocorticoid [Tg(Crh)]. Tg(Crh) mice with elevated glucocorticoid appeared cushingoid and by 21 weeks of age were obese, insulin-resistant, and had extensive areas of hepatic gene expression in exocrine tissue. Acinar cells from Tg(Crh) mice costained for both amylase and cyp2e1, suggesting direct acinar-hepatic transdifferentiation. Hepatic expression increased with age in the pancreas to such an extent that malabsorption and rapid weight loss occurred in a subset of aging mice; this effect was reversed by dietary porcine pancreatic enzyme supplementation. Indeed, pancreatic expression of hepatic markers was prevented by adrenalectomy, establishing a direct role for glucocorticoid. Elevated levels of circulating glucocorticoid therefore promote a transdifferentiation of adult exocrine pancreas into hepatocyte-like cells, and chronic exposure results in pancreatic malfunction. Glucocorticoids are thus capable of modulating the differentiation of terminally differentiated adult cells.

Glucocorticoid-dependent transdifferentiation of pancreatic progenitor cells into hepatocytes is dependent on transient suppression of WNT signalling

Developmentally, the pancreas and liver are closely related and pathological conditions – including elevated glucocorticoid levels – result in the appearance of hepatocytes in the pancreas. The role of the WNT signalling pathway in this process has been examined in the model transdifferentiating pancreatic acinar AR42J-B-13 (B-13) cell. Glucocorticoid treatment resulted in a transient loss of constitutive WNT3a expression, phosphorylation and depletion of β-catenin, loss of β-catenin nuclear localisation, and significant reductions in T-cell factor/lymphoid enhancer factor (Tcf/Lef) transcriptional activity before overt changes in phenotype into hepatocyte-like (B-13/H) cells. A return to higher Tcf/Lef transcriptional activity correlated with the re-expression of WNT3a in B-13/H cells. β-catenin knock down alone substituted for and enhanced glucocorticoid-dependent transdifferentiation. Overexpression of a mutant β-catenin (pt-Xβ-cat) protein that blocked glucocorticoid-dependent suppression of Tcf/Lef activity resulted in inhibition of transdifferentiation. A small-molecule activator of Tcf/Lef transcription factors blocked glucocorticoid-dependent effects, as observed with pt-Xβ-cat expression. Quercetin – a Tcf/Lef inhibitor – did not promote transdifferentiation into B-13/H cells, but did potentiate glucocorticoid-mediated transdifferentiation. These data demonstrate that the transdifferentiation of B-13 cells into hepatocyte-like cells in response to glucocorticoid was dependent on the repression of constitutively active WNT signalling.

AR42J-B-13 cell: an expandable progenitor to generate an unlimited supply of functional hepatocytes

Hepatocytes are the preparation of choice for Toxicological research in vitro. However, despite the fact that hepatocytes proliferate in vivo during liver regeneration, they are resistant to proliferation in vitro, do not tolerate sub-culture and tend to enter a de-differentiation program that results in a loss of hepatic function. These limitations have resulted in the search for expandable rodent and human cells capable of being directed to differentiate into functional hepatocytes. Research with stem cells suggests that it may be possible to provide the research community with hepatocytes in vitro although to date, significant challenges remain, notably generating a sufficiently pure population of hepatocytes with a quantitative functionality comparable with hepatocytes. This paper reviews work with the AR42J-B-13 (B-13) cell line. The B-13 cell was cloned from the rodent AR42J pancreatic cell line, express genes associated with pancreatic acinar cells and readily proliferates in simple culture media. When exposed to glucocorticoid, 75-85% of the cells trans-differentiate into hepatocyte-like (B-13/H) cells functioning at a level quantitatively similar to freshly isolated rat hepatocytes (with the remaining cells retaining the B-13 phenotype). Trans-differentiation of pancreatic acinar cells also appears to occur in vivo in rats treated with glucocorticoid; in mice with elevated circulating glucocorticoid and in humans treated for long periods with glucocorticoid. The B-13 response to glucocorticoid therefore appears to be related to a real pathophysiological response of a pancreatic cell to glucocorticoid. An understanding of how this process occurs and if it can be generated or engineered in human cells would result in a cell line with the ability to generate an unlimited supply of functional human hepatocytes in a cost effective manner.

The PXR is a drug target for chronic inflammatory liver disease

PXR activators are used to treat pruritus in chronic inflammatory liver diseases such as primary biliary cirrhosis (PBC). The aims of this study were to determine whether PXR activators could have an additional benefit of inhibiting inflammation in the liver, and determine whether cyclosporin A - which more effectively prevents PBC recurrence in transplanted patients than FK506 - is a PXR activator. In SJL/J mice (which have constitutively high levels of hepatic portal tract inflammatory cell recruitment), feeding a PXR activator inhibited inflammation, TNFalpha and Il-1alpha mRNA expression in SJL/J-PXR(+/+), but not SJL/J-PXR(-/-). Monocytic cells - a major source of inflammatory mediators such as TNFalpha - expressed the PXR and PXR activators inhibited endotoxin-induced NF-kappaB activation and TNFalpha expression. PXR activation also inhibited endotoxin-stimulated TNFalpha secretion from liver monocytes/macrophages isolated from PXR(+/+) mice, but not from cells isolated from PXR(-/-) mice. To confirm that PXR activation inhibits NF-kappaB in vivo, 3x-kappaB-luc fibrotic mice (which express a luciferase gene regulated by NF-kappaB) were imaged after treatment with the hepatotoxin CCl(4). PXR activator inhibited the induction of hepatic NF-kappaB activity without affecting CCl(4) toxicity/hepatic damage. Using a PXR reporter gene assay, cyclosporin A - but not FK506 - was shown to be a direct PXR activator, and also to induce expression of the classic PXR-regulated CYP3A4 gene in human hepatocytes and in a cell line null for the FXR, a nuclear receptor with similar properties to the PXR.

CONCLUSION

PXR activation is anti-inflammatory in the liver and the effects of cyclosporin A in PBC disease recurrence may be mediated in part via the PXR. Since PXR activation promotes hepatocyte growth and is also anti-fibrogenic, the PXR may be an excellent drug target for the treatment of chronic inflammatory liver disease.

A role for the pregnane X receptor in flucloxacillin-induced liver injury

Drug-induced liver injury (DILI) due to flucloxacillin is a rare but serious complication of treatment. There is some evidence that flucloxacillin is a human pregnane X receptor (PXR) agonist. This study was designed to investigate the relevance of PXR to flucloxacillin toxicity and to identify genes changing in expression in response to flucloxacillin. Changes in gene expression in human hepatocytes after treatment with 500 microM flucloxacillin for 72 hours were examined by expression microarray analysis. The ability of flucloxacillin to act as a PXR agonist was investigated with reporter gene experiments. Flucloxacillin DILI cases (n = 51), drug-exposed controls without toxicity (n = 64), and community controls (n = 90) were genotyped for three common PXR polymorphisms. Luciferase reporter assays were used to assess the significance of a promoter region PXR polymorphism. Seventy-two probe sets representing 50 different genes showed significant changes in expression of 1.2-fold or higher. Most genes showing changes greater than 3-fold were known to be rifampicin-responsive, and this suggested a PXR-dependent mode of regulation. Using a luciferase-everted repeat separated by 6 base pairs element construct, we confirmed that flucloxacillin was a PXR agonist. We found a difference in the distribution of a PXR polymorphism (rs3814055; C-25385T) between flucloxacillin DILI cases and controls with the CC genotype associated with an increased risk of disease (odds ratio = 3.37, 95% confidence interval = 1.55-7.30, P = 0.0023). Reporter gene experiments showed lower promoter activity for the C allele than the T allele.

CONCLUSION

Flucloxacillin is a PXR agonist at pharmacologically relevant concentrations, and a functionally significant upstream PXR polymorphism is a risk factor for flucloxacillin-induced DILI.

The c-Rel subunit of nuclear factor-kappaB regulates murine liver inflammation, wound-healing, and hepatocyte proliferation

In this study, we determined the role of the nuclear factor-kappaB (NF-kappaB) subunit c-Rel in liver injury and regeneration. In response to toxic injury of the liver, c-Rel null (c-rel(-/-)) mice displayed a defect in the neutrophilic inflammatory response, associated with impaired induction of RANTES (Regulated upon Activation, Normal T-cell Expressed, and Secreted; also known as CCL5). The subsequent fibrogenic/wound-healing response to both chronic carbon tetrachloride and bile duct ligation induced injury was also impaired and this was associated with deficiencies in the expression of fibrogenic genes, collagen I and alpha-smooth muscle actin, by hepatic stellate cells. We additionally report that c-Rel is required for the normal proliferative regeneration of hepatocytes in response to toxic injury and partial hepatectomy. Absence of c-Rel was associated with blunted and delayed induction of forkhead box M1 (FoxM1) and its downstream targets cyclin B1 and Cdc25C. Furthermore, isolated c-rel(-/-) hepatocytes expressed reduced levels of FoxM1 and a reduced rate of basal and epidermal growth factor-induced DNA synthesis. Chromatin immunoprecipitation revealed that c-Rel binding to the FoxM1 promoter is induced in the regenerating liver.

CONCLUSION

c-Rel has multiple functions in the control of liver homeostasis and regeneration and is a transcriptional regulator of FoxM1 and compensatory hepatocyte proliferation.

Exocrine pancreas trans-differentiation to hepatocytes--a physiological response to elevated glucocorticoid in vivo

Damage or ectopic expression of some growth factors can lead to the appearance of hepatocyte-like cells within the pancreas. Since glucocorticoids promote liver hepatocyte phenotype in vitro, the effect of glucocorticoid on pancreatic differentiation in vivo was examined. Treatment of rats with glucocorticoid for 25 days at levels that significantly inhibited weight gain resulted in the appearance of acinar cells expressing cytokeratin 7 and hepatocyte markers glutamine synthetase, carbamoyl phosphate synthetase and cytochrome P450 2E (the nomenclature employed is that given at http://drnelson.utmem.edu/CytochromeP450.html). Using a plastic pancreatic acinar cell line, this response was shown to be associated with changes in the regulation of WNT signalling-related gene expression and a repression of WNT signalling activity. These data suggest that a pathological response of the pancreas in vivo to elevated glucocorticoid is a differentiation of exocrine pancreatic cells or pancreatic progenitor cells to an hepatocyte-like phenotype.

Low affinity glucocorticoid binding site ligands as potential anti-fibrogenics

BACKGROUND

Pregnane X receptor (PXR) agonists inhibit liver fibrosis. However, the rodent PXR activator pregnenolone 16alpha carbonitrile (PCN) blocks, in vitro, hepatic stellate cell-to-myofibroblast trans-differentiation and proliferation in cells from mice with a disrupted PXR gene, suggesting there is an additional anti-fibrogenic drug target for PCN. The role of the low affinity glucocorticoid binding site (LAGS) - which may be identical or associated with the progesterone receptor membrane component 1 (PGRMC1) - in mediating this anti-fibrogenic effect has been examined, since binding of dexamethasone to the LAGS in liver microsomal membranes has previously been shown to be inhibited by PCN.

RESULTS

Quiescent rat and human hepatic stellate cells (HSC) were isolated from livers and cultured to generate liver myofibroblasts. HSC and myofibroblasts expressed PGRMC1 as determined by RT-PCR and Western blotting. Quiescent rat HSC also expressed the truncated HC5 variant of rPGRMC1. Rat PGRMC1 was cloned and expression in COS-7 cells gave rise to specific binding of radiolabelled dexamethasone in cell extracts that was inhibited by PCN, suggesting that PGRMC1 may be identical to LAGS or activates LAGS binding activity. Liver microsomes were used to screen a range of structurally related compounds for their ability to inhibit radiolabelled dexamethasone binding to rat LAGS. These compounds were also screened for their ability to activate rat and human PXR and to inhibit rat HSC-to-myofibroblast trans-differentiation/proliferation. A compound (4 androstene-3-one 17beta-carboxylic acid methyl ester) was identified which bound rat LAGS with high affinity and inhibited both rat and human HSC trans-differentiation/proliferation to fibrogenic myofibroblasts without showing evidence of rat or human PXR agonism. However, despite potent anti-fibrogenic effects in vitro, this compound did not modulate liver fibrosis severity in a rat model of liver fibrosis. Immunohistochemical analysis showed that rat liver myofibroblasts in vivo did not express rPGRMC1.

CONCLUSION

LAGS ligands inhibit HSC trans-differentiation and proliferation in vitro but show little efficacy in inhibiting liver fibrosis, in vivo. The reason(s) for this disparity is/are likely associated with an altered myofibroblast phenotype, in vitro, with expression of rPGMRC1 in vitro but not in vivo. These data emphasize the limitations of in vitro-derived myofibroblasts for predicting their activity in vivo, in studies of fibrogenesis. The data also demonstrate that the anti-fibrogenic effects of PCN in vivo are likely mediated entirely via the PXR.

Antibody-targeted myofibroblast apoptosis reduces fibrosis during sustained liver injury

BACKGROUND/AIMS

Myofibroblast apoptosis promotes the resolution of liver fibrosis. However, retaining macrophages may enhance reversal. The effects of specifically stimulating myofibroblast apoptosis in vivo were assessed.

METHODS

A single chain antibody (C1-3) to an extracellular domain of a myofibroblast membrane protein was injected as a fluorescent- or gliotoxin conjugate into mice with liver fibrosis.

RESULTS

C1-3 specifically targeted alpha-smooth muscle actin positive liver myofibroblasts within scar regions of the liver in vivo and did not co-localise with liver monocytes/macrophages. Injection of free gliotoxin stimulated a 2-fold increase in non-parenchymal cell apoptosis and depleted liver myofibroblasts by 30% and monocytes/macrophages by 50% but had no effect on fibrosis severity in the sustained injury model employed. In contrast, C1-3-targeted gliotoxin stimulated a 5-fold increase in non-parenchymal cell apoptosis, depleted liver myofibroblasts by 60%, did not affect the number of monocytes/macrophages and significantly reduced fibrosis severity. Fibrosis reduction was associated with increased metalloproteinase-13 levels.

CONCLUSIONS

These data demonstrate that specific targeting of liver myofibroblast apoptosis is the most effective anti-fibrogenic therapy, supporting a role for liver monocytes and/or macrophages in the promotion of liver fibrosis reduction.

A mechanism for the anti-fibrogenic effects of the pregnane X receptor (PXR) in the liver: inhibition of NF-kappaB?

The liver is susceptible to chronic damage through exposure to a variety of toxins (e.g. alcohol) and viruses (e.g. hepatitis C). Obesity, autoimmune diseases (e.g. autoimmune hepatitis) and a variety of genetic diseases (e.g. Wilson's disease) also lead to chronic liver damage. This damage results in scarring fibrogenesis, structural disruption and functional impairment of the organ. Recent work suggests that there is cross-talk between the PXR and NF-kappaB pathways. This cross-talk may explain the observation that PXR activators inhibit liver fibrosis in in vitro and in vivo animal models of the disease. This reveiw will focus on the two transcription factors and their potential interaction.

Time of day effects on the incidence of anesthetic adverse events

BACKGROUND

We hypothesized that time of day of surgery would influence the incidence of anesthetic adverse events (AEs).

METHODS

Clinical observations reported in a quality improvement database were categorized into different AEs that reflected (1) error, (2) harm, and (3) other AEs (error or harm could not be determined) and were analyzed for effects related to start hour of care.

RESULTS

As expected, there were differences in the rate of AEs depending on start hour of care. Compared with a reference start hour of 7 am, other AEs were more frequent for cases starting during the 3 pm and 4 pm hours (p < 0.0001). Post hoc inspection of data revealed that the predicted probability increased from a low of 1.0% at 9 am to a high of 4.2% at 4 pm. The two most common event types (pain management and postoperative nausea and vomiting) may be primary determinants of these effects.

CONCLUSIONS

Our results indicate that clinical outcomes may be different for patients anesthetized at the end of the work day compared with the beginning of the day. Although this may result from patient related factors, medical care delivery factors such as case load, fatigue, and care transitions may also be influencing the rate of anesthetic AEs for cases that start in the late afternoon.

The impact of pregnane X receptor activation on liver fibrosis

The PXR (pregnane X receptor) is a nuclear receptor transcription factor that is activated by a range of endobiotics and xenobiotics. The activated PXR modulates the transcription of genes in hepatocytes (the main functional cell of the liver) associated with endobiotic and xenobiotic uptake, metabolism and excretion. However, activation of the PXR also inhibits a deleterious response of the liver to chronic damage--that of fibrosis. The antifibrogenic mode of action is mediated through changes in the expression of genes in hepatic stellate cells and liver macrophages (Kupffers). These results suggest an additional function for the PXR.

Expression of CYP2S1 in human hepatic stellate cells

Activated stellate cells are myofibroblast-like cells associated with the generation of fibrotic scaring in chronically damaged liver. Gene chip analysis was performed on cultured fibrotic stellate cells. Of the 51 human CYP genes known, 13 CYP and 5 CYP reduction-related genes were detected with 4 CYPs (CYP1A1, CYP2E1, CY2S1 and CYP4F3) consistently present in stellate cells isolated from three individuals. Quantitative RT-PCR indicated that CYP2S1 was a major expressed CYP mRNA transcript. The presence of a CYP2A-related protein and testosterone metabolism in stellate cell cultures suggest that stellate cells express specific functional isoforms of CYP of which a major form is CYP2S1.

Pregnane X receptor activators inhibit human hepatic stellate cell transdifferentiation in vitro

BACKGROUND & AIMS

The activated pregnane X receptor is antifibrogenic in rodent chronic liver injury in vivo models. The aim of this study was to determine the effects of human pregnane X receptor activators on human hepatic stellate cell transdifferentiation to a profibrogenic phenotype in vitro.

METHODS

Hepatic stellate cells were isolated from resected human liver and cultured under conditions in which they trans-differentiate into profibrogenic myofibroblasts.

RESULTS

The pregnane X receptor was expressed in primary cultures at the level of messenger RNA and protein and was activated by the ligand rifampicin as judged by increases in binding of proteins to the pregnane X receptor ER6 DNA response element and by increases in ER6-dependent reporter gene expression. Short-term treatment of hepatic stellate cells with rifampicin inhibited the expression of selected fibrosis-related genes (transforming growth factor beta1, alpha-smooth muscle actin), proliferation-related genes, and WNT signaling-associated genes. There was also an increase in interleukin-6 secretion and an inhibition in DNA synthesis. Long-term treatment with rifampicin over several weeks reduced the proliferation and transdifferentiation of hepatic stellate cells. Small interfering RNA knockdown of the pregnane X receptor in a hepatic stellate cell line reduced the binding of proteins to the ER6 DNA response element and abrogated pregnane X receptor activator-dependent changes in transforming growth factor beta1 expression, interleukin-6 secretion, and proliferation.

CONCLUSIONS

The pregnane X receptor is transcriptionally functional in human hepatic stellate cells and activators inhibit transdifferentiation and proliferation. The pregnane X receptor may therefore be an effective target for antifibrotic therapy.

Generation of a monoclonal human single chain antibody fragment to hepatic stellate cells--a potential mechanism for targeting liver anti-fibrotic therapeutics

BACKGROUND/AIMS

Hepatic stellate cells are pivotal to fibrogenesis in the liver and many potential anti-fibrotic therapeutics are required to act on targets within hepatic stellate cells. The aim of this study was to generate a human antibody fragment to hepatic stellate cells.

METHODS

Phage display was used to generate a human monoclonal antibody fragment to a peptide sequence present on an extracellular domain of synaptophysin, a protein expressed on the surface of hepatic stellate cells.

RESULTS

An antibody fragment was isolated (termed C1-3), expressed in bacteria and purified. Fluorescently-labelled C1-3 antibody associated with human hepatic stellate cells but not hepatocytes in culture. Binding of fluorescently labelled C1-3 to hepatic stellate cells was blocked by the extracellular synaptophysin peptide sequence and uptake of the antibody intracellularly was inhibited by monensin. The toxin tributyl tin-when conjugated to C1-3-retained the ability to kill hepatic stellate cells confirming that C1-3 is sequestered intracellularly.

CONCLUSIONS

This antibody fragment may be an effective means to target therapeutics to human hepatic stellate cells.

Inhibition of inhibitor of kappaB kinases stimulates hepatic stellate cell apoptosis and accelerated recovery from rat liver fibrosis

BACKGROUND & AIMS

Resolution of liver fibrosis is associated with clearance of hepatic myofibroblasts by apoptosis; development of strategies that promote this process in a selective way is therefore important. The aim of this study was to determine whether the inhibitor of kappaB kinase suppressor sulfasalazine stimulates hepatic myofibroblast apoptosis and recovery from fibrosis.

METHODS

Hepatic myofibroblasts were generated by culture activation of rat and human hepatic stellate cells. Fibrosis was established in rat livers by chronic injury with carbon tetrachloride followed by recovery with or without sulfasalazine (150 mg/kg) treatment.

RESULTS

Treatment of hepatic stellate cells with sulfasalazine (0.5-2.0 mmol/L) induced apoptosis of activated rat and human hepatic stellate cells. A single in vivo administration of sulfasalazine promoted accelerated recovery from fibrosis as assessed by improved fibrosis score, selective clearance of smooth muscle alpha-actin-positive myofibroblasts, reduced hepatic procollagen I and tissue inhibitor of metalloproteinase 1 messenger RNA expression, and increased matrix metalloproteinase 2 activity. Mechanistic studies showed that sulfasalazine selectively blocks nuclear factor-kappaB-dependent gene transcription, inhibits hepatic stellate cell expression of Gadd45beta, stimulates phosphorylation of Jun N-terminal kinase 2, and promotes apoptosis by a mechanism that is prevented by the Jun N-terminal kinase inhibitor SP600125. As further evidence for a survival role for the inhibitor of kappaB kinase/nuclear factor-kappaB pathway in activated hepatic stellate cells, a highly selective cell-permeable peptide inhibitor of kappaB kinase activation also stimulated hepatic stellate cell apoptosis via a Jun N-terminal kinase-dependent mechanism.

CONCLUSIONS

Inhibition of the inhibitor of kappaB kinase/nuclear factor-kappaB pathway is sufficient to increase the rate at which activated hepatic stellate cells undergo apoptosis both in vitro and in vivo, and drugs that selectively target inhibitor of kappaB kinase have potential as antifibrotics.

Objective measures of situation awareness in a simulated medical environment

One major limitation in the use of human patient simulators is a lack of objective, validated measures of human performance. Objective measures are necessary if simulators are to be used to evaluate the skills and training of medical practitioners and teams or to evaluate the impact of new processes or equipment design on overall system performance. Situation awareness (SA) refers to a person's perception and understanding of their dynamic environment. This awareness and comprehension is critical in making correct decisions that ultimately lead to correct actions in medical care settings. An objective measure of SA may be more sensitive and diagnostic than traditional performance measures. This paper reviews a theory of SA and discusses the methods required for developing an objective measure of SA within the context of a simulated medical environment. Analysis and interpretation of SA data for both individual and team performance in health care are also presented.

Objective measures of situation awareness in a simulated medical environment

One major limitation in the use of human patient simulators is a lack of objective, validated measures of human performance. Objective measures are necessary if simulators are to be used to evaluate the skills and training of medical practitioners and teams or to evaluate the impact of new processes or equipment design on overall system performance. Situation awareness (SA) refers to a person's perception and understanding of their dynamic environment. This awareness and comprehension is critical in making correct decisions that ultimately lead to correct actions in medical care settings. An objective measure of SA may be more sensitive and diagnostic than traditional performance measures. This paper reviews a theory of SA and discusses the methods required for developing an objective measure of SA within the context of a simulated medical environment. Analysis and interpretation of SA data for both individual and team performance in health care are also presented.