Hepatocellular carcinoma progression during bridging before liver transplantation.

BACKGROUND: Recipient selection for liver transplantation in hepatocellular carcinoma (HCC) is based primarily on criteria affecting the chance of long-term success. Here, the relationship between pretransplant bridging therapy and long-term survival was investigated in a subgroup analysis of the SiLVER Study. METHODS: Response to bridging, as defined by comparison of imaging at the time of listing and post-transplant pathology report, was categorized into controlled versus progressive disease (more than 20 per cent tumour growth or development of new lesions). RESULTS: Of 525 patients with HCC who had liver transplantation, 350 recipients underwent pretransplant bridging therapy. Tumour progression despite bridging was an independent risk factor affecting overall survival (hazard ratio 1.80; P = 0.005). For patients within the Milan criteria (MC) at listing, mean overall survival was longer for those with controlled versus progressive disease (6.8 versus 5.8 years; P < 0.001). Importantly, patients with HCCs outside the MC that were downsized to within the MC before liver transplantation had poor outcomes compared with patients who never exceeded the MC (mean overall survival 6.2 versus 6.6 years respectively; P = 0.030). CONCLUSION: Patients with HCCs within the MC that did not show tumour progression under locoregional therapy had the best outcomes after liver transplantation. Downstaging into the limits of the MC did not improve the probability of survival.Prognostic factors determining the long-term success of liver transplantation in patients with hepatocellular carcinoma are still under discussion. A subgroup analysis of the SiLVER trial showed that disease control under bridging therapy is strongly associated with improved prognosis in terms of overall survival. However, in tumours exceeding the limits of the Milan criteria, downstaging did not restore the probability of survival compared with that of patients within the Milan criteria.

Cyclosporine A Inhibits the T-bet-Dependent Antitumor Response of CD8(+) T Cells.

Transplant recipients face an increased risk of cancer compared with the healthy population. Although several studies have examined the direct effects of immunosuppressive drugs on cancer cells, little is known about the interactions between pharmacological immunosuppression and cancer immunosurveillance. We investigated the different effects of rapamycin (Rapa) versus cyclosporine A (CsA) on tumor-reactive CD8(+) T cells. After adoptive transfer of CD8(+) T cell receptor-transgenic OTI T cells, recipient mice received either skin grafts expressing ovalbumin (OVA) or OVA-expressing B16F10 melanoma cells. Animals were treated daily with Rapa or CsA. Skin graft rejection and tumor growth as well as molecular and cellular analyses of skin- and tumor-infiltrating lymphocytes were performed. Both Rapa and CsA were equally efficient in prolonging skin graft survival when applied at clinically relevant doses. In contrast to Rapa-treated animals, CsA led to accelerated tumor growth in the presence of adoptively transferred tumor-reactive CD8(+) OTI T cells. Further analyses showed that T-bet was downregulated by CsA (but not Rapa) in CD8(+) T cells and that cancer cytotoxicity was profoundly inhibited in the absence of T-bet. CsA reduces T-bet-dependent cancer immunosurveillance by CD8(+) T cells. This may contribute to the increased cancer risk in transplant recipients receiving calcineurin inhibitors.

Extracellular Citrate in Health and Disease.

Citrate is one of the major substrates for intracellular metabolism. The extracellular level of citrate is stable in blood but varies locally, with slightly increased levels in brain and high levels in prostate. Recent metabolomics research suggests that citrate level is a potential harbinger of different pathophysiological states; its decrease has been correlated with male infertility, brain diseases and metastatic cancer. In this review we discuss the role of citrate as an energy substrate for sperm. We also review the function of citrate released by astrocytes in the normal operation of neurons, and consequently we suggest a potential role of neuronal plasma membrane citrate transporters in mental disorders. Finally, we review recent relevant publications studying blood, urine and tissue citrate levels in cancer patients and hypothesize that extracellular citrate supports cancer cell metabolism critical for metastasis. Despite the importance of extracellular citrate in physiological and pathophysiological processes, surprisingly little is known about citrate synthesis in specialized cells, or about citrate transporters controlling citrate movement across various membranes. Determination of the molecular origin of citrate transporters in astrocytes, sperm and cancer cells could offer novel therapeutic targets and the possibility to pharmacologically regulate citrate release and uptake for preventing male infertility, treating mental diseases and targeting cancer.

mTOR inhibition improves fibroblast growth factor receptor targeting in hepatocellular carcinoma.

BACKGROUND: Systemic therapy has proven only marginal effects in hepatocellular carcinoma (HCC) so far. The aim of this study was to evaluate the effect of targeting fibroblast growth factor receptor (FGFR) on tumour and stromal cells in HCC models. METHODS: Human and murine HCC cells, endothelial cells (ECs), vascular smooth muscle cells (VSMCs), hepatic stellate cells (HSCs), human HCC samples, FGFR inhibitor BGJ398 and mammalian target of rapamycin (mTOR) inhibitor rapamycin were used. Effects on growth, motility, signalling and angiogenic markers were determined. In vivo subcutaneous and syngeneic orthotopic tumour models were used. RESULTS: In tumour cells and ECs, targeting FGFR showed significant inhibitory effects on signalling and motility. Minor effects of FGFR inhibition were observed on VSMCs and HSCs, which were significantly enhanced by combining FGFR and mTOR blockade. In vivo daily (5 mg kg(-1)) treatment with BGJ398 led to a significant growth inhibition in subcutaneous tumour models, but only a combination of FGFR and mTOR blockade impaired tumour growth in the orthotopic model. This was paralleled by reduced tumour cell proliferation, vascularisation, pericytes and increased apoptosis. CONCLUSIONS: Targeting FGFR with BGJ398 affects tumour cells and ECs, whereas only a combination with mTOR inhibition impairs recruitment of VSMCs and HSCs. Therefore, this study provides evidence for combined FGFR/mTOR inhibition in HCC.

Rapamycin impairs UV induction of mutant-p53 overexpressing cell clusters without affecting tumor onset.

Because of its antitumor effect, the immunosuppressant rapamycin holds great promise for organ transplant recipients in that it may lower their cancer risk. In a mouse model, we showed previously that rapamycin inhibits the outgrowth of primary skin carcinomas induced by UV radiation. However, the tumors that did grow out showed an altered p53 mutation spectrum. Here, we investigated whether this shift in p53 mutations already occurred in the smallest tumors, which were not affected in onset. We found that rapamycin did not alter the mutational spectrum in small tumors and in preceding microscopic clusters of cells expressing mutant-p53. However, rapamycin did reduce the number of these cell clusters. As this reduction did not affect tumor onset, we subsequently investigated whether rapamycin merely suppressed expression of mutated p53. This was not the case, as we could demonstrate that switching from a diet with rapamycin to one without, or vice versa, did not affect the number of existing mutant-p53 expressing cell clusters. Hence, rapamycin actually reduced the formation of mutant-p53 cell clusters. In wild-type and p53-mutant mice, we could not measure a significant enhancement of UV-induced apoptosis, but we did observe clear enhancement in human skin equivalents. This was associated with a clear suppression of HIF1α accumulation. Thus, we conclude that rapamycin reduces the formation of mutant-p53-expressing cell clusters without affecting tumor onset, suggesting that tumors grow out of a minor subset of cell clusters, the formation of which is not affected by rapamycin.

Mesenchymal stem cells together with mycophenolate mofetil inhibit antigen presenting cell and T cell infiltration into allogeneic heart grafts.

Donor-derived mesenchymal stem cells (MSC) can induce long-term acceptance in a rat heart transplantation model when injected prior to transplantation in combination with mycophenolate mofetil (MMF). In contrast, MSC alone cause accelerated graft rejection. To better understand these conflicting data we studied the effects of MSC and MMF on lymphocyte populations in heart allografts and secondary lymphatic organs. Allogeneic MSC injected prior to transplantation are immunogenic in this model because activated CD4+ and CD8+ cells emerged earlier in secondary lymphatic organs of MSC- and MSC/MMF-treated animals, compared to animals not treated with MSC. Consequently T cells infiltrated the grafts of MSC-only treated animals promptly causing accelerated graft rejection. However, few T cells or antigen-presenting cells (APC) infiltrated the grafts of animals treated with MSC and MMF. Consistent with this finding, intercellular adhesion molecule 1 (ICAM-1) and E-selectin was down-regulated exclusively in MSC/MMF-treated grafts, indicating that MSC together with MMF interfere with endothelial activation. Additionally, the presence of interferon-gamma (IFN-γ) enhanced MSC capabilities to suppress T cell proliferation in vitro. Interestingly, MMF did not influence serum IFN-γ levels in vivo. Together, our data indicate that MSC pre-activate T cells, but co-treatment with MMF eliminates these T cells, decreases intragraft APC and T cell trafficking by inhibiting endothelial activation, and allows IFN-γ stimulation of suppressive MSC.

Can immunosuppressive strategies be used to reduce cancer risk in renal transplant patients?

The risk of renal transplant recipients developing a malignancy is increasingly recognized as a major issue impacting long-term overall survival. As immunosuppression is thought to contribute to the development of cancer but is therapeutically required to protect against kidney rejection, reducing cancer in this setting is a challenging objective. An important question is whether there is a selective difference between pharmacological immunosuppressants regarding effects on malignancy. Both experimental and clinical studies thus far suggest that calcineurin inhibitors tend to promote tumor development; mycophenolic acid prodrugs such as mycophenolate mofetil have exhibited some capacity to inhibit tumors, but the concentrations needed for this effect are well above levels sustainable in transplant recipients. In contrast to these immunosuppressive substances, despite its potent immunosuppressive effects, rapamycin has demonstrated an impressive ability to inhibit de novo tumor development, as well as reduce tumor growth once cancer is already established. The antitumor effects of rapamycin are being studied extensively and appear to stem from the central role that the mammalian target of rapamycin molecule plays in basic cellular processes such as cell growth and proliferation, which are also essential for neoplasm development. Pilot trials and retrospective analyses of clinical data, especially using sirolimus, are highly suggestive that rapamycin can inhibit tumors in the clinical transplant setting. Prospective clinical trials are currently underway that will bring definitive answers as to whether rapamycin treatment can act simultaneously as an immunosuppressive and anticancer agent, with the aim of reducing the long-term problem of posttransplant malignancy.

VEGF: a surrogate marker for peripheral vascular disease.

This study aims to evaluate the value of VEGF as a surrogate marker for peripheral vascular disease (PVD). Prior to treatment, serum VEGF levels were evaluated by enzyme-linked immunosorbent assay (ELISA) in 293 PVD patients. Risk factors and clinical parameters of PVD were documented. Twenty-six age-matched healthy volunteers served as controls. Serum VEGF values strongly correlated with Fontaine stages (p<0.006, stage IV vs. controls). High VEGF values prior to treatment were associated with poor outcome. Serum VEGF appears to indicate the severity of PVD and might serve as a surrogate indicator of disease severity.

Early and late effects of the immunosuppressants rapamycin and mycophenolate mofetil on UV carcinogenesis.

Increased skin cancer risk in organ transplant recipients has been experimentally emulated with enhanced UV carcinogenesis from administering conventional immunosuppressants. However, newer generation immunosuppressive drugs, rapamycin (Rapa) and mycophenolate mofetil (MMF), have been shown to impair angiogenesis and outgrowth of tumor implants. To ascertain the overall effect on UV carcinogenesis, Rapa and MMF were admixed into the food pellets of hairless SKH1 mice receiving daily sub-sunburn UV dosages. With immunosuppressive blood levels neither of the drugs affected onset of tumors (<2 mm), but in contrast to MMF, Rapa significantly increased latency of large tumors (>or=4 mm, medians of 190 vs 125 days) and reduced their multiplicity (1.6 vs 4.5 tumors per mouse at 200 days). Interestingly, tumors (>2 mm) from the Rapa-fed group showed a reduction in UV-signature p53 mutations (39% vs 90%) in favor of mutations from putative base oxidation. This shift in mutation spectrum was not essentially linked to the reduction in large tumors because it was absent in large tumors similarly reduced in number when feeding Rapa in combination with MMF, possibly owing to an antioxidant effect of MMF. Significantly fewer tumor cells were Vegf-positive in the Rapa-fed groups, but a correspondingly reduced expression of Hif1alpha target genes (Vegf, Ldha, Glut1, Pdk1) that would indicate altered glucose metabolism with increased oxidative stress was not found. Remarkably, we observed no effect of the immunosuppressants on UV-induced tumor onset, and with impaired tumor outgrowth Rapa could therefore strongly reduce skin carcinoma morbidity and mortality rates in organ transplant recipients.

Rapamycin inhibits oncogenic intestinal ion channels and neoplasia in APC(Min/+) mice.

The adenomatous polyposis coli (APC) gene is mutated in familial adenomatous polyposis. Mice with a heterozygous APC(Min) mutation develop multiple intestinal neoplasia (Min) leading to premature death. Early in colorectal carcinogenesis, APC(Min/+) mice show enhanced Akt-mammalian target of rapamycin (mTOR) signaling, which is paralleled by upregulation of oncogenic K(+) channels. In this study, we tested the effect of mTOR inhibition with rapamycin on tumor formation in APC(Min/+) mice and evaluated ion channel regulation. We found that continuous long-term rapamycin treatment of APC(Min/+) mice dramatically inhibits intestinal neoplasia. Moreover, although untreated APC(Min/+) mice lose weight, experience intestinal bleeding and succumb to multiple neoplasia by 22.3+/-1.4 weeks of age, mice treated with rapamycin maintain stable weight and survive long term (39.6+/-3.4 weeks), with more than 30% surviving >1 year. Impressively, abnormalities in colonic electrolyte transport typical for APC(Min/+) mice are abolished, along with the suppression of epithelial Na(+) channel (ENaC) and oncogenic K(+) ion channels BK, Elk1 and Erg1, both functionally and at mRNA levels. These results show that continuous prophylaxis by rapamycin markedly inhibits the development of APC mutation-related polyposis, and suggest a novel contributing mechanism of action through the blockade of intestinal oncogenic ion channels.

Mesenchymal stem cells require a sufficient, ongoing immune response to exert their immunosuppressive function.

Mesenchymal stem cells (MSC) have emerged to be one of the most promising candidates for cellular immunotherapy in solid organ transplantation because the reduction of conventional immunosuppression is highly desirable. However, little is known about the details of MSC-mediated immunomodulation and their clinical relevance. To address conflicting studies about the ability of MSC to suppress or augment T-cell proliferation, we introduce a transplantation-related rat model that allows studying the influence of MSC on alloproliferation. Hearts transplanted in a fully allogeneic transplantation model (LEW to ACI) were rejected earlier when recipients were pretreated with donor MSC, indicating activation of T cells in vivo. In additional co-culture experiments, T cells were differently affected by allogeneic MSC depending on the extent of previous activation: When conditions were rendered proinflammatory by adding high concanavalin A (ConA) concentrations or proinflammatory cytokines (interferon-gamma, interleukin-2, or tumor necrosis factor-alpha), MSC inhibited proliferation. Application of low doses of ConA or anti-inflammatory cytokines like IL-10 abrogated the suppressive effect of MSC. For application of MSC in solid organ transplantation, it will be important to further describe this switch effect of MSC function.

Fighting malignancy in organ transplant recipients.

The development of malignancy in immunosuppressed organ transplant recipients has recently gained increasing attention. Increased awareness of this problem has come from recent data indicating that vascular disease and cancer are the leading causes of death in transplant recipients. Despite the realization of this fact, few efforts have been made to thwart deaths due to cancer in transplant recipients. However, now that many transplant recipients maintain their organ allografts for decades, the risk for cancer is increasing even more, exposing a need for possible solutions. Fundamentally, transplant recipients are at a high risk for cancer because the immunosuppressive drugs used in their treatment regimen suppress immune reactivity against arising cancer cells. Some of these drugs directly impede DNA repair, induce cancer cell aggressiveness, and promote tumor angiogenesis. In situations where cancer has developed in transplant recipients, one potential action is to reduce their daily immunosuppression. In some cases immunosuppression minimization can reduce tumor growth or even result in tumor regression, but the threat of rejection increases substantially. Another possible solution is to move toward mammalian target of rapamycin (mTOR)-based immunosuppression, use of which has been experimentally demonstrated to have both immunosuppressive and potent anticancer effects. Clinical studies are presently underway to test this idea, which could help to alleviate the problem of cancer in transplant recipients. In this overview, the topic of cancer in transplant recipients will be addressed, as well as new approaches to reduce this increasingly recognized problem in transplantation.

Immunosuppression for liver transplantation.

In the last few decades liver transplantation (LTx) has become a reliable life-saving procedure for patients with chronic end-stage liver diseases. LTx has an outstanding success rate in the first few years after allografting, especially considering that many patients are on the brink of survival at the time of transplantation. The success of LTx is owed to the pioneers who developed the surgical procedures and to researchers who discovered the medications to help prevent immunological rejection of allografts. However, several problems continue to impose serious limits on LTx today, including a shortage of donor livers, recurrence of disease (eg, hepatitis, hepatocellular cancer), preservation of long-term allograft function and the side effects of anti-rejection drugs. While the dilemma of organ shortage is not a focus of this review, we will address the latter issues as they relate to the "oldest" and "newest" approaches to immunosuppression, and discuss the prospect that recipients could potentially be made immunologically tolerant to liver transplants. Due to the critical shortage of organs, new strategies to preserve transplanted liver allografts for the longest possible time are of paramount importance.

Cytokines mediating the induction of chronic colitis and colitis-associated fibrosis.

To investigate the immunopathogenesis of inflammation-associated fibrosis we analyzed the chronic colitis and late-developing fibrosis occurring in BALB/c mice administered weekly doses of intrarectal trinitrobenzene sulfonic acid (TNBS). We showed first in this model that an initial T helper type 1 response involving interleukin (IL)-12p70 and interferon-gamma subsides after 3 weeks to be supplanted by an IL-23/IL-25 response beginning after 4-5 weeks. This evolution is followed by gradually increasing production of IL-17 and cytokines ordinarily seen in a T helper type 2 response, particularly IL-13, which reaches a plateau at 8-9 weeks. We then show that IL-13 production results in the induction of an IL-13 receptor formerly thought to function only as a decoy receptor, IL-13Ralpha(2), and this receptor is critical to the production of tumor growth factor (TGF)-beta(1) and the onset of fibrosis. Thus, if IL-13 signaling through this receptor is blocked by administration of soluble IL-13Ralpha(2)-Fc, or by administration of IL-13Ralpha(2)-specific siRNA, TGF-beta(1) is not produced and fibrosis does not occur. These studies show that in chronic TNBS colitis, fibrosis is dependent on the development of an IL-13 response that acts through a novel cell-surface-expressed IL-13 receptor to induce TGF-beta(1).

The impact of mTOR inhibitors on the development of malignancy.

Although continuous improvements have been made in fighting rejection with immunosuppressive drugs in transplant recipients, this success story has been tempered by an associated high incidence of cancer. The latest projections are that cancer might exceed cardiovascular disease as the leading cause of death among transplant recipients. Indeed, immunosuppression reduces our natural ability to destroy cancer cells and to inhibit viral infections potentially linked to cancer development. Therefore, a strategy to counter the problem of cancer in transplantation is needed. Recently, mammalian target of rapamycin (mTOR) inhibitors have demonstrated potential as both immunosuppressive and anticancer agents. Although mTOR inhibitors prevent organ transplant rejection, this class of drugs has potential anticancer properties that may be useful in the "balance of effects" toward cancer-free survival in transplant recipients. Mechanisms of mTOR inhibitors' anticancer effects are multiple, affecting processes including angiogenesis, cell proliferation, cell survival, and molecular oncogenic signaling. Importantly, experimental work supports the view that tumor inhibition can be accomplished with mTOR inhibitors while protecting allografts against rejection. Most recently, prospective randomized clinical studies have been initiated to test the concept that mTOR inhibitors reduce cancer while simultaneously inhibiting allograft rejection. One such study, the SiLVER trial, examines hepatocellular carcinoma recurrence in mTOR inhibitor-treated liver transplant patients. More robust evidence as to whether cancer risk can be reduced in transplant recipients with mTOR inhibitors may come from such clinical trials.

Mesenchymal stem cells can induce long-term acceptance of solid organ allografts in synergy with low-dose mycophenolate.

The induction of tolerance towards allogeneic solid organ grafts is one of the major goals in transplantation medicine. Mesenchymal stem cells (MSC) inhibit the immune response in vitro, and thus are promising candidate cells to promote acceptance of transplanted organs in vivo. Such novel approaches of tolerance induction are needed since, to date, graft acceptance can only be maintained through life-long treatment with unspecific immunosuppressants that are associated with toxic injury, opportunistic infections and malignancies. We demonstrate that donor-derived MSC induce long-term allograft acceptance in a rat heart transplantation model, when concurrently applied with a short course of low-dose mycophenolate. This tolerogenic effect of MSC is at least partially mediated by the expression of indoleamine 2,3-dioxygenase (IDO), demonstrated by the fact that blocking of IDO with 1-methyl tryptophan (1-MT) abrogates graft acceptance. Moreover we hypothesize that MSC interact with dendritic cells (DC) in vivo, because allogeneic MSC are rejected in the long-term but DC acquire a tolerogenic phenotype after applying MSC. In summary, we demonstrate that MSC constitute a promising tool for induction of non-responsiveness in solid organ transplantation that warrants further investigation in clinical trials.

Prolongation of heart allograft survival after long-term expression of soluble MHC class I antigens and vIL-10 in the liver by AAV-plasmid-mediated gene transfer.

INTRODUCTION: The essential prerequisite for successful gene therapy in vivo is an effective and long-lasting transfer of the desired gene into the respective cell type or tissue. Over the last decades, many different methods have been developed for this purpose. The use of plasmid DNA seems to be a good alternative to the commonly used viral vectors because its large-scale production is simple, and side effects are low. Unfortunately, most reports describe only short-term expression in vivo, probably due to the lack of genomic integration in the target cell. This problem can possibly be addressed by the use of adeno-associated virus plasmids (AAV plasmids), where the coding sequences are cloned between the AAV-specific inverted terminal repeats. Here, we report our results after allogeneic heart transplantation, which followed AAV-plasmid-mediated gene transfer of the rat soluble major histocompatibility complex class I antigen RT1.A(a) and viral interleukin (vIL)-10 in the "high"-responder Dark Agouti to Lewis rat strain combination. RESULTS: A high and stable long-term expression was achieved by in vivo transfection of the liver using AAV plasmids. Serum levels over 1,000 ng/ml of soluble RT1.A(a) and over 300 pg of vIL-10, respectively, were achieved. Expression levels remained high for up to several months. A mean prolongation of heart allograft survival of 1 to 2 days was demonstrated after transfection of either RT1.A(a) or vIL-10.

Preferential migration of CD62L cells into the appendix in mice with experimental chronic colitis.

BACKGROUND: Clinical and experimental studies suggest that appendectomy can protect against development of ulcerative colitis and Crohn's disease. However, how T cells in the appendix affect the development of colitis has not been clarified. AIM: To investigate the in vivo migration and activation of colitis-inducing CD62L+ cells during development of chronic colitis. METHODS: CD62L+CD4+ cells were fluorescently labeled and transferred to severe combined immunodeficient (SCID) mice to induce colitis. In vivo migration of T cells into the mucosa of the appendix and colon was quantified by in vivo microscopy after 7 weeks. In a second experiment, unlabeled CD62L+CD4+ cells were transferred, reisolated after 7 weeks, and adhesion molecule (integrin alpha4beta7) and costimulatory molecule (CD154) expression was analyzed. RESULTS: Six to eight weeks after CD62L+CD4+ cell transfer, SCID mice developed chronic colitis. In vivo microscopic analysis demonstrated a preferential migration of fluorescence-labeled CD62L+CD4+ cells into the mucosa of the appendix versus the colon. Re-isolation of lamina propria cells from mice with colitis confirmed that CD62L+CD4+ cell migration was significantly enhanced in the appendix, compared to the colon (3.5-fold). Furthermore, a higher proportion of CD62L+CD4+ cells re-isolated from the appendix expressed integrin alpha4beta7 and CD154 than from the colon. CONCLUSION: This study demonstrates the preferential migration of CD62L+CD4+ cells into the appendix as compared to the colon. This migration pattern correlated with upregulation of integrin alpha4beta7 and CD154 (CD40 ligand) on T cells. Our results suggest an important role of the appendix in the pathogenesis of colitis.

Conditioning of liver grafts with prostaglandins improves bile acid transport.

INTRODUCTION: Conditioning of liver grafts by bolus pretreatment with prostaglandins has been previously demonstrated to improve hepatic bile flow. However, the underlying mechanisms have not been investigated. To elucidate whether improved bile flow after prolonged ischemia is due to maintained bile acid secretion or due to increased paracellular permeability, we performed a study using increasing doses of the marker acid taurocholate in the isolated perfused rat liver system. METHODS: Livers were harvested from adult Lewis rats and stored for 24 hours in UW solution. Pretreatment of livers was performed 1 minute before preservation. One group received prostaglandin I2, the second group received prostaglandin E1, and the control group was treated with saline. After 24 hours of cold storage the grafts were investigated in the isolated perfused rat liver system by perfusion with an oxygenated Krebs-Ringer-Henseleit buffer. Increasing doses of the radiolabeled marker bile acid taurocholate were infused to investigate bile acid transport. RESULTS: Bile flow and bile acid output were increased by pretreatment of the livers with prostaglandin I2 and prostaglandin E1, as compared to the control group. More specifically, the maximum transport rate was tripled by prostaglandin I2 and by prostaglandin E1 preconditioning of liver grafts, in comparison to the control group (P < .01 vs prostaglanin I2 and E1). CONCLUSION: The results clearly demonstrate that increased bile flow after conditioning of liver grafts with prostaglandins is not due to increased paracellular permeability but is based on markedly improved bile acid output.