Cycloadditions in mixed aqueous solvents: the role of the water concentration

We examined the kinetics of a series of cycloaddition reactions in mixtures of water with methanol, acetonitrile and poly(ethylene glycol) (MW 1000). The reactions include the Diels–Alder (DA) reaction between cyclopentadiene and N-n-butylmaleimide or acridizinium bromide, the retro-Diels-Alder (RDA) reaction of 1,4,4a,9a-tetrahydro-4a-methyl-(1α,4α,4aα,9aα)-1,4-methaneanthracene-9,10-dione and the 1,3-dipolar cycloaddition of benzonitrile oxide with N-n-butylmaleimide. Plots of logk vs the molar concentration or volume fraction of water are approximately linear, but with a characteristic break around 40 M water. This break, absent for the RDA reaction, is ascribed to hydrophobic effects. Comparison with aqueous mixtures of the more hydrophobic 1-propanol shows that these mixtures induce qualitatively similar effects on the rate, but that preferential solvation effects cause the mixtures of 1-propanol to exhibit a more complex behavior of logk on composition. The results are analyzed using the Abraham–Kamlett–Taft model. The solvent effects in aqueous mixtures are not satisfactorily described by this model. For some cycloadditions, small maxima in rate are observed in highly aqueous mixtures of alcohols. The origin of these maxima and the aforementioned breaks is most likely the same.

Ex Situ Machine Perfusion of Human Donor Livers via the Surgically Reopened Umbilical Vein:A Proof of Concept

Background. Machine perfusion of donor livers is typically performed via the portal vein main stem. Instead, cannulation of a reopened umbilical vein could allow machine perfusion during organ procurement and subsequent implantation in the recipient without interruption of the portal venous circulation. We aimed to assess the feasibility of portal venous machine perfusion via the umbilical vein. Methods. During back table inspection of 5 human livers declined for transplantation, the umbilical vein was surgically reopened, dilated, and cannulated. Hypothermic and normothermic oxygenated machine perfusion (NMP) were performed using the umbilical vein for portal inflow. Three livers were perfused with hypothermic machine perfusion, 1 full liver graft underwent NMP for 4 hours, and 1 left lateral split procedure was performed under continuous NMP with portal perfusion via the umbilical vein. Results. In all livers, access to the portal venous system via the umbilical vein was successfully achieved with good portal flows and macroscopically homogeneous perfusion. The full liver graft that underwent NMP via the umbilical vein for 4 hours showed good lactate clearance, normalized pH, and achieved good bile production with pH >7.55. During the split procedure under continuous NMP via the umbilical vein, the left lateral segment and extended right lobe remained equally perfused, as demonstrated by Doppler ultrasound. Conclusions. Machine perfusion with portal perfusion via the umbilical vein is feasible. Portal venous flows were similar to those obtained after cannulation of the portal vein main stem. This technique enables continuous oxygenated perfusion of liver grafts during procurement, splitting, and implantation

The first case of ischemia-free organ transplantation in humans:A proof of concept

With great interest we have read the article by Xiaoshun He and colleagues regarding their first patient who underwent successful ischemia-free organ transplantation (IFOT).1 This group transplanted a liver donated after brain death to a 51-year-old patient with decompensated cirrhosis and hepatocellular carcinoma without any ischemic episode or interruption of the blood circulation. The graft was procured, ex-situ preserved and implanted under continuous normothermic machine perfusion using the Liver Assist device (Organ Assist, Groningen, The Netherlands). The donor liver had 85-95% macrovesicular steatosis, however there was no post-reperfusion syndrome observed after revascularization of the graft and the recipient had an uneventful recovery. This article is protected by copyright. All rights reserved

Oxygenated versus non-oxygenated flush out and storage of donor livers:An experimental study

Background: During donor organ procurement and subsequent static cold storage (SCS), hepatic adenosine triphosphate (ATP) levels are progressively depleted, which contributes to ischemia-reperfusion injury (IRI). We sought to investigate a simple approach to prevent ATP depletion and IRI using a porcine donation after circulatory death (DCD) liver reperfusion model. Methods: After 30 min warm ischemia, porcine livers were flushed via the portal vein with cold (4 degrees C) non-oxygenated University of Wisconsin (UW) preservation solution (n = 6, control group) or with oxygenated UW (n = 6, OxyFlush group). Livers were then subjected to 4 h SCS in non-oxygenated (control) or oxygenated (OxyFlush) UW, followed by 4 h normothermic reperfusion using whole blood. Hepatic ATP levels were compared, and hepatobiliary function and injury were assessed. Results: At the end of SCS, ATP was higher in the OxyFlush group compared to controls (delta ATP of +0.26 vs. -0.68 mu mol/g protein, p = 0.04). All livers produced bile and metabolized lactate, and there were no differences between the groups. Grafts in the OxyFlush group had lower blood glucose levels after reperfusion (p = 0.04). Biliary pH, glucose and bicarbonate were not different between the groups. Injury markers including liver transaminases, lactate dehydrogenase, malondialdehyde, cell-free DNA and flavin mononucleotide in the SCS solution and during reperfusion were also similar. Histological assessment of the parenchyma and bile ducts did not reveal differences between the groups. Conclusion: Oxygenated flush out and storage of DCD porcine livers prevents ATP depletion during ischemia, but this does not seem sufficient to mitigate early signs of IRI

Extended hypothermic oxygenated machine perfusion enables ex situ preservation of porcine livers for up to 24 hours

Background & Aims: End-ischemic hypothermic oxygenated machine perfusion (HOPE) of the donor liver for 1-2 h mitigates ischemia-reperfusion injury during subsequent liver transplantation. Extended preservation time may be preferred to facilitate difficult recipient hepatectomy or to optimize logistics. We therefore investigated whether end-ischemic dual HOPE (DHOPE) could extend preservation time for up to 24 h using a porcine liver reperfusion model. Methods: Following 30 min warm ischemia, porcine livers were subjected to 2 h static cold storage (SCS), followed by 2 h, 6 h, or 24 h DHOPE (n = 6 per group). Subsequent normothermic reperfusion was performed for 4 h using autologous blood. Two livers preserved by 24 h SCS served as additional controls. A proof of principle confirmation was carried out in 2 discarded human livers subjected to extended DHOPE. Hepatocellular and cholangiocyte injury and function were assessed. Oxidative stress levels and histology were compared between groups. Results: Perfusion flows remained stable during DHOPE, regardless of duration. After normothermic reperfusion, livers perfused for 24 h by DHOPE had similar lactate clearance, blood pH, glucose, and alanine aminotransferase levels, and biliary pH, bicarbonate, and LDH levels, as livers perfused for 2 h and 6 h. Levels of malondialdehyde and high-mobility group box 1 in serum and liver parenchyma were similar for all groups. Histological analysis of bile ducts and liver parenchyma revealed no differences between the groups. Extended DHOPE in discarded human livers preserved hepatocellular and cholangiocyte function and histology after reperfusion. In contrast, livers preserved by 24 h SCS were non-functioning. Conclusion: Extended end-ischemic DHOPE enabled successful preservation of porcine and discarded human donor livers for up to 24 h. Extended DHOPE enables safe extension of preservation time, which may facilitate allocation and transplantation from a logistical perspective, and further expand the donor pool. Lay summary: It has been suggested that preserving liver grafts with a technique called (dual) hypothermic oxygenated machine perfusion ([D]HOPE) leads to better outcomes after transplantation than if livers are stored on ice, especially if an organ is of lesser quality. In this study, we showed that DHOPE could be used to preserve liver grafts for up to 24 h. This extended procedure could be used globally to facilitate transplantation and expand the donor pool

Kinetic solvent effects on 1,3-dipolar cycloadditions of benzonitrile oxide

The kinetics of 1,3-dipolar cycloadditions of benzonitrile oxide with a series of N-substituted maleimides and with cyclopentene are reported for water, a wide range of organic solvents and binary solvent mixtures. The results indicate the importance of both solvent polarity and specific hydrogen-bond interactions in governing the rates of the reactions. The aforementioned reactions are examples for which these factors often counteract, leading to a complex dependence of rate constants on the nature of the solvent. For the reactions of N-ethylmaleimide and N-n-butylmaleimide with benzonitrile oxide, isobaric activation parameters have been determined in several organic solvents, water, and water–1-propanol mixtures. Interestingly, the activation parameters reveal significant differences in solvation in different solvents that are not clearly reflected in the rate constants. In highly aqueous mixtures, enforced hydrophobic interactions lead to an increase in rate constant, relative to organic solvents. However, the overall rate enhancement in water is modest, if present at all, because the solvent polarity diminishes the rate constant. This pattern contrasts with common Diels–Alder reactions, where polarity, hydrogen-bond donor capacity and enforced hydrophobic interactions work together, which can result in impressive rate accelerations in water.

Restoration of Bile Duct Injury of Donor Livers During Ex Situ Normothermic Machine Perfusion

BACKGROUND: End-ischemic ex situ normothermic machine perfusion (NMP) enables assessment of donor livers prior to transplantation. The objective of this study was to provide support for bile composition as a marker of biliary viability and to investigate whether bile ducts of high-risk human donor livers already undergo repair during NMP.METHODS: Forty-two livers that were initially declined for transplantation were included in our NMP clinical trial. After NMP, livers were either secondary declined (n = 17) or accepted for transplantation (n = 25) based on the chemical composition of bile and perfusate samples. Bile duct biopsies were taken before and after NMP and assessed using an established histological injury severity scoring system and a comprehensive immunohistochemical assessment focusing on peribiliary glands (PBGs), vascular damage, and regeneration.RESULTS: Bile ducts of livers that were transplanted after viability testing during NMP showed better preservation of PBGs, (micro)vasculature, and increased cholangiocyte proliferation, compared with declined livers. Biliary bicarbonate, glucose, and pH were confirmed as accurate biomarkers of bile duct vitality. In addition, we found evidence of PBG-based progenitor cell differentiation toward mature cholangiocytes during NMP.CONCLUSIONS: Favorable bile chemistry during NMP correlates well with better-preserved biliary microvasculature and PBGs, with a preserved capacity for biliary regeneration. During NMP, biliary tree progenitor cells start to differentiate toward mature cholangiocytes, facilitating restoration of the ischemically damaged surface epithelium.</p

Dual Versus Single Oxygenated Hypothermic Machine Perfusion of Porcine Livers:Impact on Hepatobiliary and Endothelial Cell Injury

Background: Hypothermic oxygenated machine perfusion (HOPE) reduces ischemia-reperfusion injury of donor livers and is increasingly used in clinical transplantation. However, it remains unclear whether perfusion via the portal vein alone (HOPE) or via both the portal vein and hepatic artery (dual HOPE or DHOPE) is superior. Methods: Twelve porcine livers donated after circulatory death were randomized for 2 h of HOPE (n = 6) or DHOPE (n = 6), followed by 4 h of warm reperfusion with whole blood, to mimic transplantation. Hepatobiliary and endothelial cell function and injury markers were determined in perfusate and bile samples. Biopsies of bile ducts, hepatic arteries, and liver parenchyma were collected to assess histological damage and the expression of endothelial protective genes (KLF-2, eNOS, ET-1, CD31, VWF, VEGF-A). Results: There were no differences in hepatobiliary function and injury after warm reperfusion between the groups, apart from a 2-fold lower concentration of alanine aminotransferase in the perfusate (P = 0.045) and a lower peak lactate dehydrogenase in bile (P = 0.04) of livers preserved by DHOPE. Endothelial cell function and injury, as assessed by perfusate nitric oxide and von Willebrand factor antigen levels, as well as endothelial protective gene expressions, were similar between the groups. The hepatic arteries of both groups showed no microscopic evidence of injury. Conclusions: This study did not reveal major differences in hepatobiliary or endothelial function and injury after preservation by single or dual HOPE of porcine livers donated after circulatory death