Intraluminal polyethylene glycol stabilizes tight junctions and improves intestinal preservation in the rat

Optimized partial freezing protocol enables 10-day storage of rat livers

Preserving organs at subzero temperatures with halted metabolic activity holds the potential to prolong preservation and expand the donor organ pool for transplant. Our group recently introduced partial freezing, a novel approach in high-subzero storage at -15 °C, enabling 5-day storage of rodent livers through precise control over ice nucleation and unfrozen fraction. However, increased vascular resistance and tissue edema suggested a need for improvements to extend viable preservation. Here, we describe an optimized partial freezing protocol with key optimizations, including an increased concentration of polyethylene glycol (PEG) to enhance membrane stability while minimizing shear stress during cryoprotectant unloading with an acclimation period and a maintained osmotic balance through an increase in bovine serum albumin (BSA). These approaches ensured the viability during preservation and recovery processes, promoting liver function and ensuring optimal preservation. This was evidenced by increased oxygen consumption, decreased vascular resistance, and edema. Ultimately, we show that using the optimized protocol, livers can be stored for 10 days with comparable vascular resistance and lactate levels to 5 days, outperforming the viability of time-matched static cold stored (SCS) livers as the current gold standard. This study represents a significant advancement in expanding organ availability through prolonged preservation, thereby revolutionizing transplant medicine.

Supercooled preservation of cultured primary rat hepatocyte monolayers

Supercooled preservation (SCP) is a technology that involves cooling a substance below its freezing point without initiating ice crystal formation. It is a promising alternative to prolong the preservation time of cells, tissues, engineered tissue products, and organs compared to the current practices of hypothermic storage. Two-dimensional (2D) engineered tissues are extensively used in in vitro research for drug screening and development and investigation of disease progression. Despite their widespread application, there is a lack of research on the SCP of 2D-engineered tissues. In this study, we presented the effects of SCP at -2 and -6°C on primary rat hepatocyte (PRH) monolayers for the first time and compared cell viability and functionality with cold storage (CS, + 4°C). We preserved PRH monolayers in two different commercially available solutions: Hypothermosol-FRS (HTS-FRS) and the University of Wisconsin (UW) with and without supplements (i.e., polyethylene glycol (PEG) and 3-O-Methyl-Α-D-Glucopyranose (3-OMG)). Our findings revealed that UW with and without supplements were inadequate for the short-term preservation of PRH monolayers for both SCP and CS with high viability, functionality, and monolayer integrity. The combination of supplements (PEG and 3-OMG) in the HTS-FRS solution outperformed the other groups and yielded the highest viability and functional capacity. Notably, PRH monolayers exhibited superior viability and functionality when stored at -2°C through SCP for up to 3 days compared to CS. Overall, our results demonstrated that SCP is a feasible approach to improving the short-term preservation of PRH monolayers and enables readily available 2D-engineered tissues to advance in vitro research. Furthermore, our findings provide insights into preservation outcomes across various biological levels, from cells to tissues and organs, contributing to the advancement of bioengineering and biotechnology.

Optimized Partial Freezing Protocol Enables 10-Day Storage of Rat Livers

Preserving organs at subzero temperatures with halted metabolic activity holds the potential to prolong preservation and expand the donor organ pool for transplant. Our group recently introduced partial freezing, a novel approach in high-subzero storage at -15°C, enabling 5 days storage of rodent livers through precise control over ice nucleation and unfrozen fraction. However, increased vascular resistance and tissue edema suggested a need for improvements to extend viable preservation. Here, we describe an optimized partial freezing protocol with key optimizations including increased concentration of propylene glycol to reduce ice recrystallization and maintained osmotic balance through an increase in bovine serum albumin, all while minimizing sheer stress during cryoprotectant unloading with an acclimation period. These approaches ensured the viability during preservation and recovery processes, promoting liver function and ensuring optimal preservation. This was evidenced by increased oxygen consumption, decreased vascular resistance and edema. Ultimately, we show that using the optimized protocol, livers can be stored for 10 days with comparable vascular resistance and lactate levels to 5 days, outperforming the viability of time-matched cold stored livers as the current gold standard. This study represents a significant advancement in expanding organ availability through prolonged preservation and thereby revolutionizing transplant medicine.

Intraluminal oxygen can keep small bowel mucosa intact in a segmental ischemia model

Intestinal preservation for transplantation is accompanied by hypoperfusion with long periods of ischemia with total blood cessation and absolute withdrawal of oxygen leading to structural damage. The application of intraluminal oxygen has been successfully tested in small-animal series during storage and transport of the organ but have been so far clinically unrelatable. In this study, we tested whether a simple and clinically approachable method of intraluminal oxygen application could prevent ischemic damage in a large animal model, during warm ischemia time. We utilised a local no-flow ischemia model of the small intestine in pigs. A low-flow and high-pressure intraluminal oxygen deliverance system was applied in 6 pigs and 6 pigs served as a control group. Mucosal histopathology, hypoxia and barrier markers were evaluated after two hours of no-flow conditions, in both treatment and sham groups, and in healthy tissue. Macro- and microscopically, the luminal oxygen delivered treatment group showed preserved small bowel's appearance, viability, and mucosal integrity. A gradual deterioration of histopathology and barrier markers and increase in hypoxia-inducible factor 1-α expression towards the sites most distant from the oxygen application was observed. Intraluminal low-flow, high oxygen delivery can preserve the intestinal mucosa during total ischemia of the small intestine. This finding can be incorporated in methods to overcome small bowel ischemia and improve intestinal preservation for transplantation.

Low-Molecular-Weight PEGs for Cryopreservation of Stem Cell Spheroids

Stem cell spheroids (SCSs) are a valuable tool in stem cell research and regenerative medicine. SCSs provide a platform for stem cell behavior in a more biologically relevant context with enhanced cell-cell communications. In this study, we investigated the recovery of SCSs after cryopreservation at -196 °C for 7 days. Prior to cryopreservation, the SCSs were preincubated for 0 h (no preincubation), 2 h, 4 h, and 6 h at 37 °C in the presence of low-molecular-weight poly(ethylene glycol) (PEG) with molecular weights of 200, 400, and 600 Da. The recovery rate of SCSs was markedly affected by both the PEG molecular weight and the preincubation time. Specifically, when SCSs were preincubated with a PEG200 solution for 2 to 6 h, it significantly enhanced the recovery rate of the SCSs. Internalization of PEG200 through simple diffusion into the SCSs may be the cryoprotective mechanism. The PEG200 diffuses into the SCSs, which not only suppresses osmotic pressure development inside the cell but also inhibits ice formation. The recovered SCSs demonstrated both fusibility and capabilities for proliferation and differentiation comparable to SCSs recovered after dimethyl sulfoxide 10% cryopreservation. This study indicates that PEG200 serves as an effective cryoprotectant for SCSs. A simple preincubation procedure in the presence of the polymer greatly improves the recovery rate of SCSs from cryopreservation.

Preclinical Study of DCD and Normothermic Perfusion for Visceral Transplantation

Considering recent clinical and experimental evidence, expectations for using DCD-derived intestines have increased considerably. However, more knowledge about DCD procedure and long-term results after intestinal transplantation (ITx) is needed. We aimed to describe in detail a DCD procedure for ITx using normothermic regional perfusion (NRP) in a preclinical model. Small bowel was obtained from pigs donors after 1 h of NRP and transplanted to the recipients. Graft Intestinal samples were obtained during the procedure and after transplantation. Ischemia-reperfusion injury (Park-Chiu score), graft rejection and transplanted intestines absorptive function were evaluated. Seven of 8 DCD procedures with NRP and ITx were successful (87.5%), with a good graft reperfusion and an excellent recovery of the recipient. The architecture of grafts was well conserved during NRP. After an initial damage of Park-chiu score of 4, all grafts recovered from ischemia-reperfusion, with no or very subtle alterations 2 days after ITx. Most recipients (71.5%) did not show signs of rejection. Only two cases demonstrated histologic signs of mild rejection 7 days after ITx. Interestingly intestinal grafts showed good absorptive capacity. The study's results support the viability of intestinal grafts from DCD using NRP, contributing more evidence for the use of DCD for ITx.

Intravenous Polyethylene Glycol Alleviates Intestinal Ischemia-Reperfusion Injury in a Rodent Model

Intestinal ischemia-reperfusion injury (IRI) is a common clinical entity, and its outcome is unpredictable due to the triad of inflammation, increased permeability and bacterial translocation. Polyethylene glycol (PEG) is a polyether compound that is extensively used in pharmacology as an excipient in various products. More recently, this class of products have shown to have potent anti-inflammatory, anti-apoptotic, immunosuppressive and cell-membrane-stabilizing properties. However, its effects on the outcome after intestinal IRI have not yet been investigated. We hypothesized that PEG administration would reduce the effects of intestinal IRI in rodents. In a previously described rat model of severe IRI (45 min of ischemia followed by 60 min of reperfusion), we evaluated the effect of IV PEG administration at different doses (50 and 100 mg/kg) before and after the onset of ischemia. In comparison to control animals, PEG administration stabilized the endothelial glycocalyx, leading to reduced reperfusion edema, bacterial translocation and inflammatory reaction as well as improved 7-day survival. These effects were seen both in a pretreatment and in a treatment setting. The fact that this product is readily available and safe should encourage further clinical investigations in settings of intestinal IRI, organ preservation and transplantation.

Typical and atypical properties of peripheral nerve allografts enable novel strategies to repair segmental-loss injuries

We review data showing that peripheral nerve injuries (PNIs) that involve the loss of a nerve segment are the most common type of traumatic injury to nervous systems. Segmental-loss PNIs have a poor prognosis compared to other injuries, especially when one or more mixed motor/sensory nerves are involved and are typically the major source of disability associated with extremities that have sustained other injuries. Relatively little progress has been made, since the treatment of segmental loss PNIs with cable autografts that are currently the gold standard for repair has slow and incomplete (often non-existent) functional recovery. Viable peripheral nerve allografts (PNAs) to repair segmental-loss PNIs have not been experimentally or clinically useful due to their immunological rejection, Wallerian degeneration (WD) of anucleate donor graft and distal host axons, and slow regeneration of host axons, leading to delayed re-innervation and producing atrophy or degeneration of distal target tissues. However, two significant advances have recently been made using viable PNAs to repair segmental-loss PNIs: (1) hydrogel release of Treg cells that reduce the immunological response and (2) PEG-fusion of donor PNAs that reduce the immune response, reduce and/or suppress much WD, immediately restore axonal conduction across the donor graft and re-innervate many target tissues, and restore much voluntary behavioral functions within weeks, sometimes to levels approaching that of uninjured nerves. We review the rather sparse cellular/biochemical data for rejection of conventional PNAs and their acceptance following Treg hydrogel and PEG-fusion of PNAs, as well as cellular and systemic data for their acceptance and remarkable behavioral recovery in the absence of tissue matching or immune suppression. We also review typical and atypical characteristics of PNAs compared with other types of tissue or organ allografts, problems and potential solutions for PNA use and storage, clinical implications and commercial availability of PNAs, and future possibilities for PNAs to repair segmental-loss PNIs.

Luminal polyethylene glycol solution delays the onset of preservation injury in the human intestine

The organ damage incurred during the cold storage (CS) of intestinal grafts has short and long-term consequences. Animal studies suggest that additional luminal preservation (LP) with polyethylene glycol (PEG) may alleviate this damage. This study aims to validate these findings using human intestines. Ileal segments, perfused intravascularly with IGL-1 solution, were procured from 32 multiorgan donors and divided into two parts: one containing a PEG 3350-based solution introduced luminally (LP group) and another one without luminal treatment (control). Sampling was performed after 4 h, 8 h, 14 h, and 24 h of CS. Histology was assessed using the Chiu/Park score. Tight junctions (TJ), several inflammatory markers, and transcription factors were examined by immunofluorescence, ddPCR, and western blot. Tissue water content (edema) was also measured. Apoptotic activity was assessed with caspase -2, -3, and -9 assays. LP significantly lowered mucosal injury at all time points. Redistribution of TJ proteins occurred earlier and more severely in the control group. After 24 h of CS, LP intestines showed an emerging unfolding protein response. Increased caspase-3 and -9 activity was found in the control group. The current results indicate that luminal PEG is safe and effective in reducing damage to the intestinal epithelium during CS.

Intestinal transplantation: an overview of the recent experimental studies

PURPOSE OF REVIEW

Experimental intestinal transplantation (ITx ) has generated invaluable knowledge that has ultimately benefited the clinical activity. Herein, we appraise the recent publications pertaining to experimental ITx and highlight the main current research topics.

RECENT FINDINGS

During the recent years, ischemia-reperfusion injury (IRI) and Graft-versus-host disease (GVHD) have gradually replaced acute rejection as the main research topic. New additives to established preservation solutions and relatively novel approaches such as luminal interventions during cold storage may prolong the storage time and alleviate IRI. High donor age does not seem to worsen preservation injury. The ischemic susceptibility seems to differ between species, which may impact the translatability of the experimental findings. A new experimental model of modified multivisceral transplantation including the donor spleen may offer a new tool with which to study GVHD, besides the classical Lewis-Brown Norway rat combination. Flushing the graft with fludarabine may mitigate GVHD in rats. T-cell activation inhibitor-mitochondrial was downregulated in the peripheral blood leukocytes before other signs of acute and severe chronic rejection could be observed.

SUMMARY

Experimental research in ITx has largely shifted focus from acute rejection to IRI and GVHD. Several lines of research have matured toward clinical translation, yet no breakthrough is imminent.

Polyethylene glycol-fusion repair of sciatic allografts in female rats achieves immunotolerance via attenuated innate and adaptive responses

Ablation/segmental loss peripheral nerve injuries (PNIs) exhibit poor functional recovery due to slow and inaccurate outgrowth of regenerating axons. Viable peripheral nerve allografts (PNAs) as growth-guide conduits are immunologically rejected and all anucleated donor/host axonal segments undergo Wallerian degeneration. In contrast, we report that ablation-type sciatic PNIs repaired by neurorrhaphy of viable sciatic PNAs and a polyethylene glycol (PEG)-fusion protocol using PEG immediately restored axonal continuity for many axons, reinnervated/maintained their neuromuscular junctions, and prevented much Wallerian degeneration. PEG-fused PNAs permanently restored many sciatic-mediated behaviors within 2-6 weeks. PEG-fused PNAs were not rejected even though host/donors were neither immunosuppressed nor tissue-matched in outbred female Sprague Dawley rats. Innate and adaptive immune responses to PEG-fused sciatic PNAs were analyzed using electron microscopy, immunohistochemistry, and quantitative reverse transcription polymerase chain reaction for morphological features, T cell and macrophage infiltration, major histocompatibility complex (MHC) expression, apoptosis, expression of cytokines, chemokines, and cytotoxic effectors. PEG-fused PNAs exhibited attenuated innate and adaptive immune responses by 14-21 days postoperatively, as evidenced by (a) many axons and cells remaining viable, (b) significantly reduced infiltration of cytotoxic and total T cells and macrophages, (c) significantly reduced expression of inflammatory cytokines, chemokines, and MHC proteins, (d) consistently low apoptotic response. Morphologically and/or biochemically, PEG-fused sciatic PNAs often resembled sciatic autografts or intact sciatic nerves. In brief, PEG-fused PNAs are an unstudied, perhaps unique, example of immune tolerance of viable allograft tissue in a nonimmune-privileged environment and could greatly improve the clinical outcomes for PNIs relative to current protocols.

The Impact of Age and Luminal Preservation on the Development of Intestinal Preservation Injury in Rats

BACKGROUND

Organs from older donors are believed to withstand ischemia worse than those from younger donors. The effect of age on the development of intestinal preservation injury (IPI) is unclear.

METHODS

We compared the development of IPI in intestines from young (3 mo), adult (14 mo), and old (20 mo) rat donors and assessed if luminal preservation (LP) is effective in delaying IPI. Small intestines were perfused with, and stored in, preservation solution (Custodiol) with or without LP solution (polyethylene glycol 3350). IPI was studied using histology (Chiu score, Alcian blue staining), Western blot, and electrophysiological assessment (Ussing chamber) at 4, 8, and 14 hours.

RESULTS

Intestines of old rats did not show major histological alterations, whereas their aortas and kidneys revealed typical age-related changes (arteriosclerosis and glomerulosclerosis). Intestines from old rats fared similarly to their younger counterparts at all time points regarding preservation injury and goblet cells count. Intestines undergoing LP showed fewer histological signs of damage and higher goblet cells count when compared with samples without LP, regardless of donor age. Ussing chamber experiments indicated a time-dependent deterioration of all parameters studied, which was delayed by the use of LP.

CONCLUSIONS

Older intestines did not convincingly demonstrate a faster IPI compared with intestines from adult and young donors. The small differences between the age groups were nullified by the use of LP. LP significantly delayed the IPI in all age groups and may allow for longer preservation periods without an increased risk of mucosal damage.

Deep-supercooling for extended preservation of adipose-derived stem cells

Cell preservation is an enabling technology for widespread distribution and applications of mammalian cells. Traditional cryopreservation via slow-freezing or vitrification provides long-term storage but requires cytotoxic cryoprotectants (CPA) and tedious CPA loading/unloading, cooling, and recovering procedures. Hypothermic storage around 0-4 °C is an alternative method but only works for a short period due to its high storage temperatures. Here, we report on the deep-supercooling (DSC) preservation of human adipose-derived stem cells at deep subzero temperatures without freezing for extended storage. Enabled by surface sealing with an immiscible oil phase, cell suspension can be preserved in a liquid state at -13 °C and -16 °C for 7 days with high cell viability, retention of stemness, attachment, and multilineage differentiation capacities. These results demonstrate that DSC is an improved short-term preservation approach to provide off-the-shelf cell sources for booming cell-based medicine and bioengineering.

Intestinal Preservation Injury: A Comparison Between Rat, Porcine and Human Intestines

Advanced preservation injury (PI) after intestinal transplantation has deleterious short- and long-term effects and constitutes a major research topic. Logistics and costs favor rodent studies, whereas clinical translation mandates studies in larger animals or using human material. Despite diverging reports, no direct comparison between the development of intestinal PI in rats, pigs, and humans is available. We compared the development of PI in rat, porcine, and human intestines. Intestinal procurement and cold storage (CS) using histidine-tryptophan-ketoglutarate solution was performed in rats, pigs, and humans. Tissue samples were obtained after 8, 14, and 24 h of CS), and PI was assessed morphologically and at the molecular level (cleaved caspase-3, zonula occludens, claudin-3 and 4, tricellulin, occludin, cytokeratin-8) using immunohistochemistry and Western blot. Intestinal PI developed slower in pigs compared to rats and humans. Tissue injury and apoptosis were significantly higher in rats. Tight junction proteins showed quantitative and qualitative changes differing between species. Significant interspecies differences exist between rats, pigs, and humans regarding intestinal PI progression at tissue and molecular levels. These differences should be taken into account both with regards to study design and the interpretation of findings when relating them to the clinical setting.

New Approaches to Cryopreservation of Cells, Tissues, and Organs

In this concept article, we outline a variety of new approaches that have been conceived to address some of the remaining challenges for developing improved methods of biopreservation. This recognizes a true renaissance and variety of complimentary, high-potential approaches leveraging inspiration by nature, nanotechnology, the thermodynamics of pressure, and several other key fields. Development of an organ and tissue supply chain that can meet the healthcare demands of the 21st century means overcoming twin challenges of (1) having enough of these lifesaving resources and (2) having the means to store and transport them for a variety of applications. Each has distinct but overlapping logistical limitations affecting transplantation, regenerative medicine, and drug discovery, with challenges shared among major areas of biomedicine including tissue engineering, trauma care, transfusion medicine, and biomedical research. There are several approaches to biopreservation, the optimum choice of which is dictated by the nature and complexity of the tissue and the required length of storage. Short-term hypothermic storage at temperatures a few degrees above the freezing point has provided the basis for nearly all methods of preserving tissues and solid organs that, to date, have proved refractory to cryopreservation techniques successfully developed for single-cell systems. In essence, these short-term techniques have been based on designing solutions for cellular protection against the effects of warm and cold ischemia and basically rely upon the protective effects of reduced temperatures brought about by Arrhenius kinetics of chemical reactions. However, further optimization of such preservation strategies is now seen to be restricted. Long-term preservation calls for much lower temperatures and requires the tissue to withstand the rigors of heat and mass transfer during protocols designed to optimize cooling and warming in the presence of cryoprotective agents. It is now accepted that with current methods of cryopreservation, uncontrolled ice formation in structured tissues and organs at subzero temperatures is the single most critical factor that severely restricts the extent to which tissues can survive procedures involving freezing and thawing. In recent years, this major problem has been effectively circumvented in some tissues by using ice-free cryopreservation techniques based upon vitrification. Nevertheless, despite these promising advances there remain several recognized hurdles to be overcome before deep-subzero cryopreservation, either by classic freezing and thawing or by vitrification, can provide the much-needed means for biobanking complex tissues and organs for extended periods of weeks, months, or even years. In many cases, the approaches outlined here, including new underexplored paradigms of high-subzero preservation, are novel and inspired by mechanisms of freeze tolerance, or freeze avoidance, in nature. Others apply new bioengineering techniques such as nanotechnology, isochoric pressure preservation, and non-Newtonian fluids to circumvent currently intractable problems in cryopreservation.

Effect of Ice Nucleation and Cryoprotectants during High Subzero-Preservation in Endothelialized Microchannels

Cryopreservation is of significance in areas including tissue engineering, regenerative medicine, and organ transplantation. We investigated endothelial cell attachment and membrane integrity in a microvasculature model at high subzero temperatures in the presence of extracellular ice. The results show that in the presence of heterogeneous extracellular ice formation induced by ice nucleating bacteria, endothelial cells showed improved attachment at temperature minimums of -6 °C. However, as temperatures decreased below -6 °C, endothelial cells required additional cryoprotectants. The glucose analog, 3-O-methyl-D-glucose (3-OMG), rescued cell attachment optimally at 100 mM (cells/lane was 34, as compared to 36 for controls), while 2% and 5% polyethylene glycol (PEG) were equally effective at -10 °C (88% and 86.4% intact membranes). Finally, endothelialized microchannels were stored for 72 h at -10 °C in a preservation solution consisting of the University of Wisconsin (UW) solution, Snomax, 3-OMG, PEG, glycerol, and trehalose, whereby cell attachment was not significantly different from unfrozen controls, although membrane integrity was compromised. These findings enrich our knowledge about the direct impact of extracellular ice on endothelial cells. Specifically, we show that, by controlling the ice nucleation temperature and uniformity, we can preserve cell attachment and membrane integrity. Further, we demonstrate the strength of leveraging endothelialized microchannels to fuel discoveries in cryopreservation of thick tissues and solid organs.

High Molecular Weight Polymer Promotes Bone Health and Prevents Bone Loss Under Salmonella Challenge in Broiler Chickens

As a consequence of rapid growth, broiler chickens are more susceptible to infection as well as bone fractures that result in birds being culled. Intestinal infection/inflammation has been demonstrated to promote bone loss in mice and humans. Given this link, we hypothesize that therapeutics that target the gut can benefit bone health. To test this, we infected broiler chickens (7 days old) with Salmonella and treated the birds with or without MDY, a non-absorbable mucus supplement known to benefit intestinal health, from day 1–21 or from day 14–21. Chicken femoral trabecular and cortical bone parameters were analyzed by microcomputed tomography at 21 days. Birds infected with Salmonella displayed significant trabecular bone loss and bone microarchitecture abnormalities that were specific to the femoral neck region, a common site of fracture in chickens. Histological analyses of the chicken bone indicated an increase in osteoclast surface/bone surface in this area indicating that infection-induced bone resorption likely causes the bone loss. Of great interest, treatment with MDY effectively prevented broiler chicken bone loss and architectural changes when given chronically throughout the experiment or for only a week after infection. The latter suggests that MDY may not only prevent bone loss but reverse bone loss. MDY also increased cortical bone mineral density in Salmonella-treated chickens. Taken together, our studies demonstrate that Salmonella-induced bone loss in broiler chickens is prevented by oral MDY.

A sequential assessment of the preservation injury in porcine intestines

BACKGROUND

Clinical and experimental evidence strongly suggest that ischemia-reperfusion injury after intestinal transplantation has deleterious short- and long-term effects and finding means to reduce ischemia-reperfusion injury is a major research area. The anatomical and physiological similarities between the human and porcine digestive tract favor its use as a preclinical model for translational research. Intriguingly, no systematic appraisal of the development of the intestinal preservation injury in pigs is available.

MATERIALS AND METHODS

Intestinal procurement was performed in nine pigs using histidine-tryptophan-ketoglutarate solution as preservation fluid. Ileal biopsies were obtained after 8, 14, and 24 h of static cold storage (SCS), and the preservation injury was assessed morphologically (Chiu score) as well as on the molecular level. Tight junction (zonula occludens, claudin-3 and 4, tricellulin, and occludin) and adherens junctions (E-cadherin) proteins were studied using immunofluorescence and Western blot.

RESULTS

Eight hours of SCS induced minimal mucosal changes (Chiu grade 1) that advanced to significant subepithelial edema (Chiu grade 3) after 24 h; progressive Goblet cell depletion was also noted. Apoptosis (studied by cleaved caspase-3 staining significantly increased after 24 h of SCS. Significant molecular changes with decreasing expression of zonula occludens, tricellulin, and occludin were evident already after 8 h of SCS and continuously worsened. Claudin-3 and Claudin-4 and E-cadherin expression remained relatively unaltered during SCS.

CONCLUSIONS

Important molecular alterations precede histologic changes during SCS of the porcine intestine and may be used as more sensitive injury markers than histologic changes in intestinal ischemia and transplantation.

Extracorporeal Hypothermic Perfusion Device for Intestinal Graft Preservation to Decrease Ischemic Injury During Transportation

INTRODUCTION

The small intestine is one of the most ischemia-sensitive organs used in transplantation. To better preserve the intestinal graft viability and decrease ischemia-reperfusion injury, a device for extracorporeal perfusion was developed. We present the results for the first series of perfused human intestine with an intestinal perfusion unit (IPU).

METHODS

Five human intestines were procured for the protocol. (1) An experimental segment was perfused by the IPU delivering cold preservation solution to the vascular and luminal side continually at 4 ºC for 8 h. (2) Control (jejunum and ileum) segments were preserved in static cold preservation. Tissue samples were obtained for histopathologic grading according to the Park/Chiu scoring system (0 = normal, 8 = transmural infarction).

RESULTS

Jejunal experimental segments scored 2.2 with the Park/Chiu system compared to the control segments, which averaged 3.2. Overall scoring for ileum experimental and control segments was equal with 1.6.

CONCLUSION

This data presents proof of concept that extracorporeal intestinal perfusion is feasible. The evidence shows that the IPU can preserve the viability of human intestine, and histopathologic evaluation of perfused intestine is favorable. Our early results can eventually lead to expanding the possibilities of intestinal preservation.

Intestinal preservation for transplantation: current status and alternatives for the future

PURPOSE OF REVIEW

Among transplantable abdominal organs the intestine has the shortest cold storage time, raising significant medical and logistical challenges. Herein, established and innovative, emerging concepts in intestinal preservation are summarized.

RECENT FINDINGS

The method of intestinal preservation using an in-situ vascular perfusion followed by static storage remained unchanged for almost 30 years, despite suboptimal results. Advanced preservation injury occurs within 12 h and is little influenced by the type of solution used. Recent reports indicate that several customized luminal solutions containing various amino acids and macromolecules may delay its development. In addition, gaseous interventions in the storage solutions or in the lumen seem promising and easily applicable tools that may further reduce the ischemia-reperfusion injury and safely prolong the preservation time. Rodent models are not entirely suitable for direct translation to clinical practice as the development of preservation injury is faster than in humans.

SUMMARY

The limitations of intestinal preservation originate in the methods (vascular perfusion and static storage) rather than in the solutions used. Several additional strategies promise to prolong the cold storage and reduce its impact on the intestinal graft and deserve further exploration in large animals and clinical studies.

Luminal injection of hydrogen-rich solution attenuates intestinal ischemia-reperfusion injury in rats

BACKGROUND

Luminal preservation of the intestine is an attractive method to locally mitigate preservation injury and ischemic-reperfusion injury in small bowel transplantation (SBT) because this method has a potential to maintain the intestinal graft integrity. Hydrogen is noted as an antioxidant material by reducing hydroxyl radicals. We hypothesized that hydrogen-containing solution can be an optimum material for luminal preservation method in SBT.

METHODS

Ischemic reperfusion was induced in Lewis rats by occlusion of the supramesenteric artery and vein for 90 min. Experimental protocols were divided into four groups: sham operation group, no luminal injection (control) group, luminal injection of 5% glucose saline (GS) solution group, and luminal injection of hydrogen-rich GS (HRGS) group. Two milliliters of experimental solution was locally injected into the lumen of the intestine before declamping of vessels. Oxidative stress markers, proinflammatory cytokines, apoptosis in the crypt cells, and morphologic changes of the intestine were assessed.

RESULTS

The production of malondialdehyde and 8-hydroxydeoxyguanosine, as oxidative stress markers, were markedly suppressed in HRGS group. The level of proinflammatory cytokines, such as inducible nitric oxide synthase and interleukin-6, was significantly inhibited in HRGS group. Crypt apoptosis was also significantly suppressed in HRGS group. Histopathologically, integrity of villus in intestine was maintained in HRGS group in comparison to the other groups.

CONCLUSION

Luminal injection of hydrogen-rich solution can reduce oxidative stress and consequently ameliorate ischemic-reperfusion injury. Hydrogen-containing solution can be a novel and promising luminal preservation material in SBT.

Polyethylene glycol protects primary hepatocytes during supercooling preservation

Cold storage (at 4°C) offers a compromise between the benefits and disadvantages of cooling. It allows storage of organs or cells for later use that would otherwise quickly succumb to warm ischemia, but comprises cold ischemia that, when not controlled properly, can result in severe damage as well by both similar and unique mechanisms. We hypothesized that polyethylene glycol (PEG) 35 kDa would ameliorate these injury pathways and improve cold primary hepatocyte preservation. We show that reduction of the storage temperature to below zero by means of supercooling, or subzero non-freezing, together with PEG supplementation increases the viable storage time of primary rat hepatocytes in University of Wisconsin (UW) solution from 1 day to 4 days. We find that the addition of 5% PEG 35 kDa to the storage medium prevents cold-induced lipid peroxidation and maintains hepatocyte viability and functionality during storage. These results suggest that PEG supplementation in combination with supercooling may enable a more optimized cell and organ preservation.

Polyethylene glycol protects primary hepatocytes during supercooling preservation

Cold storage (at 4°C) offers a compromise between the benefits and disadvantages of cooling. It allows storage of organs or cells for later use that would otherwise quickly succumb to warm ischemia, but comprises cold ischemia that, when not controlled properly, can result in severe damage as well by both similar and unique mechanisms. We hypothesized that polyethylene glycol (PEG) 35 kDa would ameliorate these injury pathways and improve cold primary hepatocyte preservation. We show that reduction of the storage temperature to below zero by means of supercooling, or subzero non-freezing, together with PEG supplementation increases the viable storage time of primary rat hepatocytes in University of Wisconsin (UW) solution from 1 day to 4 days. We find that the addition of 5% PEG 35 kDa to the storage medium prevents cold-induced lipid peroxidation and maintains hepatocyte viability and functionality during storage. These results suggest that PEG supplementation in combination with supercooling may enable a more optimized cell and organ preservation.

Luminal solutions protect mucosal barrier during extended preservation

BACKGROUND

Mucosal barrier injury during intestinal preservation (IP) and transplantation favors life-threatening infections. Luminal delivery of solutions containing amino acids or polyethylene glycols (PEGs) may improve preservation results and reduce this injury. We tested if solutions containing glutamine and PEG influence the mucosal injury.

MATERIALS AND METHODS

Rat intestines were perfused and stored in Viaspan-University of Wisconsin solution. Before IP, a PEG 3350 solution was introduced intraluminally alone (group 1) or supplemented with 40 mmol/L L-glutamine (group 2). Controls underwent vascular flush alone (group 3). Preservation injury was evaluated after 8, 14, and 24 h by histology and goblet cell count. Tight-junction proteins zonula occludens-1, claudin-3, claudin-4, and caveolin-1 were studied by immunofluorescence. Maltase and caspase-3 activity were also analyzed.

RESULTS

Group 1 showed mild edema at 8 h and mucosal disruption by 24 h; these features were greatly improved in group 2 where continuous mucosa was found after 24 h of IP. Intestines in group 3 did worse at all time points with subepithelial edema (Park/Chiu grade 3) and marked goblet cell depletion; caspase-3 activity was lowest in group 2. Tight-junction proteins varied continuously during IP; zonula occludens-1 expression and colocalization with claudins decreased significantly in group 3 but not in other groups. Claudin-3 was distinctly localized in the membrane, but stained diffuse, cytoplasmic at later time-points. Claudin-4 changed to a cytoplasmic granular pattern. No caveolin-1 colocalization was observed.

CONCLUSIONS

Luminal PEG and glutamine delay epithelial breakdown and preserve several important mucosal features during extended IP.

Supercooling enables long-term transplantation survival following 4 days of liver preservation

The realization of long–term human organ preservation will have groundbreaking effects on the current practice of transplantation. Herein we present a novel technique based on sub–zero non–freezing tissue preservation and extracorporeal machine perfusion that allows transplantation of rat livers preserved for up to 4 days, thereby tripling the viable preservation duration.

Organ-specific solutions and strategies for the intestinal preservation

Among the intraabdominal organs, the intestine is the most susceptible to storage injury and as a consequence its safe cold ischemic time in the clinic is restricted to below 10 hours. The current practice for the intestinal preservation (IP) consists of an in-situ vascular flush with iced University of Wisconsin or Histidine-Tryptophan-Ketoglutarate solution followed by cold storage at 4°C. Mucosal injury is initiated within 1 hour and rapidly progresses to mucosal breakdown; tissue injury worsens upon reperfusion and further impairs the mucosal barrier, favoring bacterial translocation and sepsis. In addition of releasing danger signals, an advanced ischemia-reperfusion injury (IRI) may increase graft immunogenicity and promote rejection. Several alternative approaches have been tested as alternatives to the static storage. The aim of this review is to summarize and discuss the various intraluminal interventions as additional strategies aiming to reduce the IP/reperfusion injury and highlight the underlying pathophysiological mechanisms.

Esophageal barrier function and tight junction expression in healthy subjects and patients with gastroesophageal reflux disease: functionality of esophageal mucosa exposed to bile salt and trypsin in vitro

BACKGROUND AND AIMS. Gastroesophageal reflux disease (GERD) is associated with impaired epithelial barrier function. However, the influence of acid and/or bile acids on human esophageal epithelial barrier function and the tight junction (TJ) proteins has not been fully elucidated. The aim of the study is to investigate the esophageal barrier function and TJ expression in healthy subjects and patients with GERD. The functionality of esophageal mucosa exposed to bile salt deoxycholic acid (DCA) and trypsin has been studied in vitro. MATERIAL AND METHODS. Endoscopic biopsies from healthy controls and patients with GERD-related symptom with endoscopic erosive signs, as well as esophageal mucosa taken from patients undergoing esophagectomy were evaluated in Ussing chambers and by western blot and immunohistochemistry. RESULTS. The esophageal epithelium from GERD patients had lower electrical resistance and higher epithelial currents than controls. Claudin-1 and -4 were significantly decreased in GERD patients. The bile salt DCA in the low concentration of 1.5 mM and trypsin increased the resistance and claudin-1 expression, while the higher concentration of 2.5 mM DCA and trypsin decreased the resistance and the claudin-3, -4 and E-cadherin expressions. CONCLUSION. In addition to acidic reflux, duodenal reflux components, such as bile salts and trypsin, have the potential to disrupt the esophageal barrier function, partly by modulating the TJ proteins. However, the expression of TJ is dependent on both the refluxed material as well as the concentration of the bile salt.