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Prevention of SARS-CoV-2 entry into cells through the modulation of viral host receptors, such as ACE2, could represent a new chemoprophylactic and therapeutic approach for COVID- 19 complementing vaccination. However, the mechanisms controlling ACE2 expression remain elusive, partly due to low ACE2 levels in experimental models. To address this challenge, I use biliary epithelial cell (cholangiocyte), one of the cell types with the highest ACE2 levels, to dissect the molecular mechanisms controlling ACE2 expression. I identify the farnesoid X receptor (FXR) as a direct regulator of ACE2 transcription in multiple COVID19- affected tissues, including the gastrointestinal and respiratory systems. I use this knowledge to optimise current experimental models for SARS-CoV-2 infection and I demonstrate that reduction of FXR signalling, with the over-the-counter compound z-guggulsterone (ZGG) and the off-patent drug ursodeoxycholic acid (UDCA), downregulates ACE2 in human lung, cholangiocyte and intestinal organoids and in the corresponding tissues in mice and hamsters. I also show that UDCA-mediated ACE2 downregulation reduces susceptibility to SARS-CoV- 2 infection in vitro, in vivo and in human lungs and livers perfused ex situ. I then illustrate that UDCA reduces ACE2 expression in the nasal epithelium in humans. Finally, I present a retrospective analysis using an independent patient cohort which identify a correlation between UDCA treatment and positive clinical outcomes following SARS-CoV-2 infection, including hospitalisation, ICU admission and death using retrospective COVID-19 registry data, and confirm these findings in a second independent cohort of liver transplant recipients. In conclusion, with the work described in this dissertation I identify a novel function of FXR in controlling ACE2 expression and provide evidence that modulation of this pathway could be beneficial for reducing SARS-CoV-2 infection, thereby paving the road for future clinical trials.

The ideal composition of the perfusate for normothermic kidney perfusion is unknown, though the perfusate commonly used to perfuse human kidneys contains leukocyte-depleted packed red blood cells (RBC), as this is believed to prevent excessive inflammation. We performed a systematic search identifying 19 articles reporting on cytokine levels during normothermic pig or human kidney perfusion. Cytokine levels varied widely across the reported studies. No direct comparisons of perfusate cytokines during perfusion with RBC or whole blood were performed, and no data on how these levels are influenced by ischemia are available. Therefore, we compared perfusate IL-6, IL-1β, TNF-α, TGF-β, IL-10, IL-8, and CCL2 levels during 4 h normothermic pig kidney perfusion with a whole blood- or RBC-based perfusate. Kidneys were exposed to either 1 h of warm or 22 h of cold ischemia. We found no evidence of different perfusate cytokine or gene expression levels in whole blood or RBC perfusions. There was no clear evidence to suggest that cytokine concentrations differ between ischemically injured kidneys and controls. In conclusion, pro-inflammatory and anti-inflammatory cytokines and chemokines are detectable in the perfusate and urine of kidneys undergoing normothermic perfusion. It is unclear how cytokine levels change in different ischemic conditions and whether the use of a leukocyte filter plays a role. ispartof: Journal Of Clinical Medicine vol:11 issue:22 pages:1-11 ispartof: location:Switzerland status: Published online

With the ever-increasing disparity between the number of patients waiting for organ transplants and the number organs available, some patients are unable to receive life-saving transplantation in time. The present, widely-used form of preservation is proving to be incapable of maintaining organ quality during long periods of preservation and meeting the needs of an ever-changing legislative and transplantation landscape. This has led to the need for improved preservation techniques. One such technique that has been extensively researched is gaseous oxygen perfusion or Persufflation (PSF). This method discovered in the early 20th century has shown promise in providing both longer term preservation and organ reconditioning capabilities for multiple organs including the liver, kidneys, and pancreas. PSF utilises the organs own vascular network to provide oxygen to the organ tissue and maintain metabolism during preservation to avoid hypoxic damage. This review delves into the history of this technique, its multiple different approaches and uses, as well as in-depth discussion of work published in the past 15 years. Finally, we discuss exciting commercial developments which may help unlock the potential for this technique to be applied at scale.

Background: Organ perfusion technology is increasingly used in many countries, with a focus, however, on the Western world. This study investigates the current international trends and obstacles to the broader routine implementation of dynamic perfusion concepts in liver transplantation. Methods: A web-based anonymous survey was launched in 2021. Experts of all involved specializations from 70 centers in 34 countries were contacted, based on the published literature and experience in the field of abdominal organ perfusion. Results: Overall, 143 participants from 23 countries completed the survey. Most respondents were male (67.8%) and transplant surgeons (64.3%) working at university hospitals (67.9%). The majority had experience with organ perfusion (82%), applying mainly hypothermic machine perfusion (HMP; 38%) and other concepts. While most (94.4%) expect a higher utilization of marginal organs with machine perfusion, the majority considers HMP the best technique to reduce liver discard-rates. While most respondents (90%) believed machine perfusion should be fully commissioned, the lack of funding (34%) and knowledge (16%) as well as limited staff (19%) were the three main obstacles to a routine clinical implementation. Conclusion: Although dynamic preservation concepts are increasingly used in clinical practice, significant challenges remain. Specific financial pathways, uniform regulations, and tight collaborations among involved experts are needed to achieve wider global clinical use.

Oxygen is the key molecule for aerobic metabolism, but no animal cells can produce it, creating an extreme dependency on external supply. In contrast, microalgae are photosynthetic microorganisms, therefore, they are able to produce oxygen as plant cells do. As hypoxia is one of the main issues in organ transplantation, especially during preservation, the main goal of this work was to develop the first generation of perfusable photosynthetic solutions, exploring its feasibility for ex vivo organ preservation. Here, the microalgae Chlamydomonas reinhardtii was incorporated in a standard preservation solution, and key aspects such as alterations in cell size, oxygen production and survival were studied. Osmolarity and rheological features of the photosynthetic solution were comparable to human blood. In terms of functionality, the photosynthetic solution proved to be not harmful and to provide sufficient oxygen to support the metabolic requirement of zebrafish larvae and rat kidney slices. Thereafter, isolated porcine kidneys were perfused, and microalgae reached all renal vasculature, without inducing damage. After perfusion and flushing, no signs of tissue damage were detected, and recovered microalgae survived the process. Altogether, this work proposes the use of photosynthetic microorganisms as vascular oxygen factories to generate and deliver oxygen in isolated organs, representing a novel and promising strategy for organ preservation.

Journal of Clinical Medicine 10(13), 2816 (2021). doi:10.3390/jcm10132816 special issue: "Special Issue "Liver Transplantation: Improving Results under Worsening Conditions" / Special Issue Editor: Prof. Dr. Robert Öllinger, Guest Editor", Published by MDPI, Basel

Background Concomitant vasoactive drugs are often required to maintain adequate perfusion pressure in patients with acute myocardial infarction (AMI) and cardiogenic shock (CS) receiving hemodynamic support with an axial flow pump (Impella CP). Objective To compare the effect of equipotent dosages of epinephrine, dopamine, norepinephrine, and phenylephrine on cardiac work and end-organ perfusion in a porcine model of profound ischemic CS supported with an Impella CP. Methods CS was induced in 10 pigs by stepwise intracoronary injection of polyvinyl microspheres. Hemodynamic support with Impella CP was initiated followed by blinded crossover to vasoactive treatment with norepinephrine (0.10 μg/kg/min), epinephrine (0.10 μg/kg/min), or dopamine (10 μg/kg/min) for 30 min each. At the end of the study, phenylephrine (10 μg/kg/min) was administered for 20 min. The primary outcome was cardiac workload, a product of pressure-volume area (PVA) and heart rate (HR), measured using the conductance catheter technique. End-organ perfusion was assessed by measuring venous oxygen saturation from the pulmonary artery (SvO2), jugular bulb, and renal vein. Treatment effects were evaluated using multilevel mixed-effects linear regression. Results All catecholamines significantly increased LV stroke work and cardiac work, dopamine to the greatest extend by 341.8 × 103 (mmHg × mL)/min [95% CI (174.1, 509.5), p 2 significantly improved during all catecholamines. Phenylephrine, a vasoconstrictor, caused a significant increase in cardiac work by 437.8 × 103 (mmHg × mL)/min [95% CI (297.9, 577.6), p p = 0.001), but no significant change in LV stroke work. Also, phenylephrine tended to decrease SvO2 (p = 0.063) and increased arterial lactate levels (p = 0.002). Conclusion Catecholamines increased end-organ perfusion at the expense of increased cardiac work, most by dopamine. However, phenylephrine increased cardiac work with no increase in end-organ perfusion.

Purpose The clinical use of vasoactive drugs is not only intended to improve systemic hemodynamic variables, but ultimately to attenuate derangements in organ perfusion and oxygenation during shock. This review aims (1) to discuss basic physiology with respect to manipulating vascular tone and its effect on the microcirculation, and (2) to provide an overview of available clinical data on the relation between vasoactive drugs and organ perfusion, with specific attention paid to recent developments that have enabled direct in vivo observation of the microcirculation and concepts that have originated from it. Methods A MedLine search was conducted for clinical articles in the English language over the last 15 years pertainig to shock, sepsis, organ failure, or critically ill patients in combination with vasoactive drugs and specific variables of organ perfusion/oxygenation (e.g., tonometry, indocyanine clearance, laser Doppler, and sidestream dark field imaging). Results Eighty original papers evaluating the specific relationship between organ perfusion/oxygenation and the use of vasoactive drugs were identified and are discussed in light of physiological theory of vasomotor tone. Conclusions Solid clinical data in support of the idea that increasing blood pressure in shock improves microcirculatory perfusion/oxygenation seem to be lacking, and such a concept might not be in line with physiological theory of microcirculation as a low-pressure vascular compartment. In septic shock no beneficial effect on microcirculatory perfusion above a mean arterial pressure of 65 mmHg has been reported, but a wide range in inter-individual effect seems to exist. Whether improvement of microcirculatory perfusion is associated with better patient outcome remains to be elucidated.

Cardiac surgery in children has markedly advanced and is a mainstay for the treatment of serious congenital cardiac malformations. Because the heart, great vessels, and total blood volume are much smaller in children than in adults, the cardiopulmonary bypass procedure is challenging with respect

We describe a cost-effective, reproducible circuit in a porcine, ex vivo, continuous warm-blood, bi-ventricular, working heart model that has future possibilities for pre-transplant assessment of marginal hearts donated from brain stem dead donors and hearts donated after circulatory determination of death (DCDD). In five consecutive experiments over five days, pressure volume loops were performed. During working mode, the left ventricular end systolic pressure volume relationship (LV ESPVR) was 23.1±11.1 mmHg/ml and the LV preload recruitable stroke work (PRSW) was 67.8±7.2. (Standard PVAN analysis software) (Millar Instruments, Houston, TX, USA) All five hearts were perfused for 219±64 minutes and regained normal cardiac function on the perfusion system.They displayed a significant upward and leftward shift of the end systolic pressure volume relationship, a significant increase in preload recruitable stroke work and minimal stiffness. These hearts could potentially be considered for transplantation. The circuit was effective during reperfusion and working modes whilst proving to be successful in maintaining cardiac function in excess of four hours. Using an autologous prime of approximately 20% haematocrit (Hct), electrolytes and blood gases were easy to control within this period using standard perfusion techniques.