Felix Dahm

Small‐for‐Size Syndrome After Partial Liver Transplantation: Definition, Mechanisms of Disease and Clinical Implications

Widespread application of cadaveric split or living donor liver transplantation bears considerable potential to increase the pool of available organs and thus alleviate the problem of organ shortage. Although splitting of a cadaveric liver into two grafts for adult recipients can be performed successfully, sufficient function of undersized grafts is a major concern. To minimize the risk for living donors, transplant surgeons aim at procuring the least necessary liver volume, also leading to potentially small grafts. When small partial grafts are unable to meet the functional demands, the recipients can develop a so‐called small‐for‐size syndrome (SFSS). There is currently limited data on the pathogenesis of SFSS, with clinical studies mainly focusing on portal hyperperfusion. Additional aspects include graft‐related factors such as functional and regenerative capacity, as well as recipient‐related factors, such as overall health status and severity of cirrhosis. However, there is currently no consensus on the definition of SFSS. We propose a novel definition, based on simple clinical criteria, which divides the syndrome into either nonfunction or dysfunction of a small graft after the exclusion of other causes. This definition should ease comparability of future clinical trials, and thus improve understanding of the pathogenesis of SFSS.

Characterization of time‐related changes after experimental bile duct ligation

Although bile duct ligation (BDL) in mice is used to study cholestasis, a detailed description of this animal model is lacking. The aim of this study was to define specific phases of acute and chronic injury and repair in the different cellular compartments of the liver.

Platelets and platelet-derived serotonin promote tissue repair after normothermic hepatic ischemia in mice

Hepatic ischemia and reperfusion (I/R) leads to the formation of leukocyte–platelet aggregates. Upon activation, platelets generate reactive oxygen species and release proapoptotic and proinflammatory mediators as well as growth factors. In cold hepatic ischemia, adhesion of platelets to endothelial cells mediates sinusoidal endothelial cell apoptosis. Furthermore, platelet‐derived serotonin mediates liver regeneration. We hypothesized that platelets may contribute to reperfusion injury and repair after normothermic hepatic ischemia. The aim of this study was to assess the impact of platelets in normothermic hepatic I/R injury using models of impaired platelet function and immune thrombocytopenia. Inhibition of platelet function in mice was achieved via clopidogrel feeding. Immune thrombocytopenia was induced via intraperitoneal injection of anti‐CD41 antibody. Platelet‐derived serotonin was investigated using mice lacking tryptophan hydroxylase 1. Mice were subjected to 60 minutes of partial hepatic ischemia and various time points of reperfusion. Hepatic injury was determined via AST and histological analysis of the necrotic area as well as leukocyte infiltration. Liver regeneration was determined via proliferating cell nuclear antigen and Ki67 immunohistochemistry. Neither inhibition of platelet function nor platelet depletion led to a reduction of I/R injury. Liver regeneration and repair were significantly impaired in platelet‐depleted animals. Mice lacking peripheral serotonin were deficient in hepatocyte proliferation, but otherwise displayed normal tissue remodeling. Conclusion: Platelets have no direct impact on the pathogenesis of normothermic I/R injury. However, they mediate tissue repair and liver regeneration. Furthermore, platelet‐derived serotonin is a mediator of hepatocyte proliferation in the postischemic liver, but has no impact on tissue remodeling. (HEPATOLOGY 2007;45:369–376.)

Serotonin Regulates Macrophage-Mediated Angiogenesis in a Mouse Model of Colon Cancer Allografts

Serotonin, a neurotransmitter with numerous functions in the central nervous system (CNS), is emerging as an important signaling molecule in biological processes outside of the CNS. Recent advances have implicated serotonin as a regulator of inflammation, proliferation, regeneration, and repair. The role of serotonin in tumor biology in vivo has not been elucidated. Using a genetic model of serotonin deficiency (Tph1(-/-)) in mice, we show serotonin to be crucial for the growth of s.c. colon cancer allografts in vivo. Serotonin does not enhance tumor cell proliferation but acts as a regulator of angiogenesis by reducing the expression of matrix metalloproteinase 12 (MMP-12) in tumor-infiltrating macrophages, entailing lower levels of angiostatin-an endogenous inhibitor of angiogenesis. Accordingly, serotonin deficiency causes slower growth of s.c. tumors by reducing vascularity, thus increasing hypoxia and spontaneous necrosis. The biological relevance of these effects is underscored by the reconstitution of serotonin synthesis in Tph1(-/-) mice, which restores allograft phenotype in all aspects. In conclusion, we show how serotonin regulates angiogenesis in s.c. colon cancer allografts by influencing MMP-12 expression in tumor-infiltrating macrophages, thereby affecting the production of circulating angiostatin.

Cationic long-chain ceramide LCL-30 induces cell death by mitochondrial targeting in SW403 cells

Ceramides are sphingolipid second messengers that are involved in the mediation of cell death. There is accumulating evidence that mitochondria play a central role in ceramide-derived toxicity. We designed a novel cationic long-chain ceramide [ω-pyridinium bromide d-erythro-C16-ceramide (LCL-30)] targeting negatively charged mitochondria. Our results show that LCL-30 is highly cytotoxic to SW403 cells (and other cancer cell lines) and preferentially accumulates in mitochondria, resulting in a decrease of the mitochondrial membrane potential, release of mitochondrial cytochrome c, and activation of caspase-3 and caspase-9. Ultrastructural analyses support the concept of mitochondrial selectivity. Interestingly, levels of endogenous mitochondrial C16-ceramide decreased by more than half, whereas levels of sphingosine-1-phosphate increased dramatically and selectively in mitochondria after administration of LCL-30, suggesting the presence of a mitochondrial sphingosine kinase. Of note, intracellular long-chain ceramide levels and sphingosine-1-phosphate remained unaffected in the cytosolic and extramitochondrial (nuclei/cellular membranes) cellular fractions. Furthermore, a synergistic effect of cotreatment of LCL-30 and doxorubicin was observed, which was not related to alterations in endogenous ceramide levels. Cationic long-chain pyridinium ceramides might be promising new drugs for cancer therapy through their mitochondrial preference. [Mol Cancer Ther 2006;5(6):1520–9]

Current indication of a modified Sugiura procedure in the management of variceal bleeding.

BACKGROUND The role of gastroesophageal devascularization (Sugiura-rype procedures) for the treatment of variceal bleeding remains controversial. Although Japanese series reported favorable longterm results, the technique has nor been widely accepted in the Western Hemisphere because of a high postoperative morbidity and mortality. The reasons for the different outcomes are unclear. In a multidisciplinary team approach we developed a therapeutic algorithm for patients with recurrent variceal bleeding. STUDY DESIGN The Sugiura procedure was offered only to patients with well-preserved liver function (Child A or Child B cirrhosis without chronic ascites) who were not candidates for distal splenorenal shunt, transhepatic porto-systemic shunt, or liver transplantation. RESULTS Fifteen patients with recurrent variceal bleeding underwent a modified Sugiura procedure between September 1994 and September 1997. All but one patient (operative mortality 7%) are alive after a median followup of 4 years. Recurrent variceal bleeding developed in one patient; esophageal strictures, which were successfully treated by endoscopic dilatation, developed in three patients; and one patient experienced mild encephalopathy. Major complications were noted only in patients with impaired liver function (Child B cirrhosis) or when the modified Sugiura was performed in an emergency setting. The presence of cirrhosis or the cause of portal hypertension had no significant impact on the complication rate. CONCLUSIONS This series was performed during the last decade when all modern therapeutic options for variceal bleeding were available. Our results indicate that the modified Sugiura procedure is an effective rescue therapy in patients who are not candidates for selective shunts, transhepatic porto-systemic shunt, or transplantation. Emergency settings and decreased liver function are associated with an increased morbidity.

Cholestasis protects the liver from ischaemic injury and post-ischaemic inflammation in the mouse

Background and hypothesis: Cholestasis is associated with high morbidity and mortality in patients undergoing major liver surgery, but the mechanisms responsible remain elusive. Increased ischaemic liver injury and inflammation may contribute to the poor outcome. Methods: Common bile duct ligation (biliary obstruction with hyperbilirubinaemia) or selective ligation of the left hepatic duct (biliary obstruction without hyperbilirubinaemia) was performed in C57BL/6 mice before 1 h of hepatic ischaemia and 1, 4 or 24 h of reperfusion. Infection with the intracellular hepatic pathogen Listeria monocytogenes for 12 and 48 h was used to study ischaemia-independent hepatic inflammation. Results: Cholestatic mice showed considerable protection from ischaemic liver injury as determined by transaminase release, histological liver injury and neutrophil infiltration. In cholestatic mice, reduced injury correlated with a failure to activate nuclear factor κB (NFκB) and tumour necrosis factor α (TNFα) mRNA synthesis, two key mediators of post-ischaemic liver inflammation. After selective bile duct ligation, both the ligated and the non-ligated lobes showed blocked activation of NFκB as well as reduced induction of TNFα mRNA synthesis and neutrophil infiltration. By contrast, infection with L monocytogenes showed comparable activation of NFκB and hepatic recruitment of neutrophils 12 h after infection. Conclusion: Cholestasis does not increase but rather dramatically protects the liver from ischaemic injury and inflammation. This effect is mediated by a systemic factor, but not bilirubin, and is associated with a preserved capacity to trigger an inflammatory response to other stimuli such as a bacterial pathogen.

Distribution and dynamic changes of sphingolipids in blood in response to platelet activation

Summary.  Background: Sphingolipids are signaling molecules in a range of biological processes. While sphingosine‐1‐phosphate (S1P) is thought to be abundantly stored in platelets and released upon stimulation, knowledge about the distribution and function of other sphingolipids in blood is lacking. Objectives: To analyze the sphingolipid content of blood components with special emphasis on dynamic changes in platelets. Methods: Blood components from mice and humans were prepared by gradient centrifugation and analyzed by liquid chromatography–mass spectrometry. Additionally, murine platelets were activated in vitro and in vivo. Results: Isolated non‐activated platelets of mice were devoid of S1P, but instead contained dihydrosphingosine‐1‐phosphate (dhS1P), along with a high concentration of ceramide. Activation of platelets in vitro led to a loss of dhS1P and an increase in sphingosine, accompanied by a reduction of ceramide content. Platelet activation in vivo led to an immediate and continuous rise of dhS1P in plasma, while S1P remained stable. The sphingolipid distribution of human blood was markedly different from mice. Human platelets contained dhS1P in addition to S1P. Conclusions: Mouse platelets contain dhS1P instead of S1P. Platelet activation causes loss of dhS1P and breakdown of ceramide, implying ceramidase activation. Release of dhS1P from activated platelets might be a novel signaling pathway. Finally, the sphingolipid composition of mouse and human blood shows large differences, which must be considered when studying sphingolipid biology.

Left-sided living kidney donation leads to transiently reduced adrenocortical responsiveness.

Living kidney donation is safe and established, but can lead to long‐term complications such as chronic fatigue. Since the adrenal vein is usually transected during left‐sided donor nephrectomy—which is not necessary on the right—we hypothesized that venous congestion might lead to an impairment of adrenal function, offering a possible explanation. In this prospective open label, monocentric cohort study, adrenal function was compared in left‐ and right‐sided living kidney donors. The primary endpoint was plasma cortisol response to low‐dose adrenocorticotropic hormone (ACTH) stimulation. Secondary endpoints included plasma renin and ACTH concentration as well as adrenal volume in response to donor nephrectomy. A total of 30 healthy donors—20 left‐ and 10 right‐sided donations—were included. On postoperative day 1, response to low‐dose ACTH stimulation was intact, but significantly lower after left‐sided donor nephrectomy. After 28 days, adrenal responsiveness to ACTH stimulation did not differ any longer. Magnetic resonance imaging volumetry showed no significant adrenal volume change over 4 weeks, neither after left‐ nor after right‐sided nephrectomy. In conclusion, left‐sided living kidney donation entails a transiently reduced adrenocortical responsiveness, which returns to baseline after 28 days.

Techniques of Vascular Exclusion and Caval Resection

Vascular exclusion techniques in liver surgery include continuous inflow occlusion (Fig. 1A) (first described by J.H. Pringle in 1908), intermittent inflow occlusion (Fig. 1B) (first described by M.Makuuchi in the late 1970s), and ischemic preconditioning (Fig. 1C) and (continuous) total vascular exclusion. The use of inflow occlusion varies considerably among centers - some use it routinely,while others use it only exceptionally. When using inflow occlusion, a low central venous pressure (CVP) ( 10 mm Hg) needs to be maintained. A venovenous bypass is sometimes used in this setting.