Human Small Intestine Transplantation: Segmental Susceptibility to Ischemia Using Different Preservation Solutions and Conditions

Nitric oxide protects intestinal mucosal barrier function and prevents acute graft rejection after intestinal transplantation: A mini-review

Intestinal transplantation is a complex technical procedure that provides patients suffering from end-stage intestinal failure an opportunity to enjoy improved quality of life, nutrition and survival. Compared to other types of organ transplants, it is a relatively new advancement in the field of organ transplantation. Nevertheless, great advances have been made over the past few decades to the present era, including the use of ischemic preconditioning, gene therapy, and addition of pharmacological supplements to preservation solutions. However, despite these strides, intestinal transplantation is still a challenging endeavor due to several factors. Notable among them is ischemia-reperfusion injury (IRI), which results in loss of cellular integrity and mucosal barrier function. In addition, IRI causes graft failure, delayed graft function, and decreased graft and recipient survival. This has necessitated the search for novel therapeutic avenues and improved transplantation protocols to prevent or attenuate intestinal IRI. Among the many candidate agents that are being investigated to combat IRI and its associated complications, nitric oxide (NO). NO is an endogenously produced gaseous signaling molecule with several therapeutic properties. The purpose of this mini-review is to discuss IRI and its related complications in intestinal transplantation, and NO as an emerging pharmacological tool against this challenging pathological condition. i.

Progress in preservation of intestinal grafts by oxygenated hypothermic machine perfusion

Intestine transplantation (IT) is a critical treatment strategy for irreversible intestinal failure. Among all abdominal solid organ transplants, the intestine was the most vulnerable to ischemia and reperfusion injury (IRI). The static cold storage (SCS) technique is currently the most commonly used graft preservation method, but its hypoxia condition causes metabolic disorders, resulting in the occurrence of IRI, limiting its application in marginal organs. It is especially important to improve preservation techniques in order to minimize damage to marginal donor organs, which draws more attention to machine perfusion (MP). There has been much debate about whether it is necessary to increase oxygen in these conditions to support low levels of metabolism since the use of machine perfusion to preserve organs. There is evidence that oxygenation helps to restore intracellular ATP levels in the intestine after thermal or cold ischemia damage. The goal of this review is to provide an overview of the role of oxygen in maintaining environmental stability in the gut under hypoxic conditions, as well as to investigate the possibilities and mechanisms of oxygen delivery during preservation in intestine transplantation studies and clinical models.

When less is more: Experimental Bishop-Koop technique for reduction in the use of laboratory animals for intestinal pathophysiological studies

The use of animals to gain knowledge and understanding of diseases needs to be reduced and refined. In the field of intestinal research, because of the complexity of the gut immune system, living models testing is mandatory. Based on the 3Rs (replacement, reduction and refinement) principles, we aimed to developed and apply the derived-intestinal surgical procedure described by Bishop and Koop (BK) in rats to refine experimental gastrointestinal procedures and reduce the number of animals used for research employing two models of intestinal inflammation: intestinal ischemia-reperfusion injury and chemical-induced colitis. Our results show the feasibility of the application of the BK technique in rodents, with good success after surgical procedure in both small and large intestine (100% survival, clinical recovery and weight regain). A considerable reduction in the use of the number of rats in both intestinal inflammation models (80% in case of intestinal ischemia-reperfusion damage and 66.6% in chemical-induced colitis in our experimental design) was achieved. Compared with conventional experimental models described by various research groups, we report excellent reproducibility of intestinal damage and functionality, survival rate and clinical status of the animals when BK is applied.

The efficacy of bone marrow mesenchymal stem cells on rat intestinal immune-function injured by ischemia/reperfusion

Background

Transplantation of bone marrow mesenchymal stem cells (BMSCs) has a promising therapeutic efficiency for varieties of disorders caused by ischemia or reperfusion impairment. It has been shown that BMSCs can mitigate intestinal ischemia/reperfusion (I/R) injuries, but the underlying mechanism is still unclear. This study aimed at investigating the efficacy of BMSCs on the immune function of intestinal mucosal microenvironment after I/R injuries.

Methods

Twenty adult Sprague-Dawley rats were randomly assigned to a treatment or a control group. All the rats underwent superior mesenteric artery clamping and unclamping. In the treatment group, BMSCs were implanted into the intestine of ten rats by direct submucosal injection whereas the other ten rats in the control group were injected with the same volume of saline. On the fourth and seventh day after BMSCs transplantation, intestinal samples were examined for the CD4 (CD4-positive T-lymphocytes)/CD8 (CD8-positive T-lymphocytes) ratio of the bowel mucosa via flow cytometry, and for the level of Interleukin-2 (IL-2), Interleukin-4 (IL-4) and Interleukin-6 (IL-6) via ELISA. Paneth cell counts and Secretory Immunoglobulin A (SIgA) level were examined via immunohistochemical (IHC) analysis. Real time PCR (RT-PCR) was used to detect the expression levels of tumor necrosis factor-α (TNF-α) and trypsinogen (Serine 2) (PRSS2) genes. White blood cell (WBC) count was measured by manual counting under the microscope.

Results

The CD4/CD8 ratio in the treatment group was significantly lower compared with that in the control group. The concentration of IL-2 and IL-6 was lower in the treatment group compared with the control group, while the level of IL-4 is the reverse between the two groups. The number of Paneth cells in intestinal mucosa increased significantly, while the level of SIgA in intestinal mucosa decreased significantly, after BMSCs transplantation. The gene expression levels of TNF-α and PRSS2 in intestinal mucosa of treatment group were significantly lower than those of control group. The WBC count in the treatment group was significantly lower than that in the control group.

Conclusion

We identified immune-relevant molecular changes that may explain the mechanism of BMSCs transplantation efficacy in alleviating rat intestinal immune-barrier after I/R.

Hypothermic machine perfusion alleviates ischemia-reperfusion injury of intestinal transplantation in pigs

Background

Intestinal transplantation (IT) has become an important procedure for the treatment of irreversible intestinal failure. However, IT is extremely vulnerable to ischemia-reperfusion injury (IRI). Due to the limitations of static cold storage (SCS), hypothermic machine perfusion (HMP) is rapidly gaining popularity. In this study, the intestinal HMP system is established and HMP is compared with SCS.

Methods

An intestinal HMP system was built. Ten miniature pigs were randomly divided into the HMP and SCS groups, and their intestines were perfused using the HMP device and SCS, respectively, followed by orthotopic auto-transplantation. Analysis was done on the grafts between the two groups.

Results

Operation success rates of the surgery were 100% in both groups. The 7-day survival rate was 100% in the HMP group, which was significantly higher than that of the SCS group (20%, P< 0.05). The pathological results showed that fewer injuries of grafts were in the HMP group. Endotoxin (ET), IL-1, IL-6, IFN-γ and TNF-α levels in the HMP group were significantly lower than in the SCS group (P<0.05), whereas IL-10 levels were significantly higher (P<0.05).The intestinal expression levels of ZO-1 and Occludin were higher in the HMP group compared to the SCS group, whereas Toll-like receptor 4 (TLR4), nuclear factor kappa B (NFκB), and caspase-3 were lower.

Conclusions

In this study, we established a stable intestinal HMP system and demonstrated that HMP could significantly alleviate intestinal IRI and improve the outcome after IT.

The Effects of Rapamycin on the Intestinal Graft in a Rat Model of Cold Ischemia Perfusion and Preservation

Attenuating the rheological and structural consequences of intestinal ischemia-reperfusion-injury (IRI) is important in transplant proceedings. Preconditioning is an often-proposed remedy. This technique uses physical or pharmacological methods to manipulate key ischemia pathways, such as oxidation, inflammation, and autophagy, prior to ischemia. This study determined the time-dependent effects of Rapamycin preconditioning on small-bowel grafts undergoing cold ischemia perfusion and preservation. Our main parameters were mucosa and cell injury and autophagy. A total of 30 male Wistar rats were divided into 5 groups: sham, preservation-control, and 3 treated groups (Rapamycin administered either 0, 30, or 60 min prior to perfusion). After perfusion, the intestines were placed in chilled IGL-1 solution for 12 h. Thereafter, they were reperfused. Histology and bioanalysis (LDH and lactate) were used to ascertain intestinal injury while immunohistochemistry was used for measuring changes in autophagy markers (Beclin-1, LC3B, and p62 proteins). The results show no significant difference amongst the groups after vascular perfusion. However, intestinal injury findings and autophagy changes demonstrate that administering Rapamycin 30 min or 60 min prior was protective against adverse cold ischemia and reperfusion of the intestinal graft. These findings show that Rapamycin is protective against cold ischemia of the small intestine, especially when administered 30 min before the onset.

Potential options to expand the intestinal donor pool: a comprehensive review

PURPOSE OF REVIEW

Intestinal donation is currently restricted to 'perfect' donors, as the intestine is extremely vulnerable to ischemia. With generally deteriorating donor quality and increasing indications for intestinal transplantation (ITx), the potential to safely increase the donor pool should be evaluated.

RECENT FINDINGS

Increasing awareness on intestinal donation (often forgotten) and cautiously broadening the strict donor criteria (increasing age, resuscitation time and ICU stay) could expand the potential donor pool. Donors after circulatory death (DCD) have so far not been considered for ITx, due to the particularly detrimental effect of warm ischemia on the intestine. However, normothermic regional perfusion might be a well tolerated strategy to render the use of DCD intestinal grafts feasible. Furthermore, machine perfusion is under continuous development and might improve preservation of the intestine and potentially offer a platform to modulate the intestinal graft. Lastly, living donation currently represents only a minority of all ITxs performed worldwide. Various studies and registry analysis show that it can be performed safely for the donor and successfully in the recipient.

SUMMARY

Several potential strategies are available to expand the current intestinal donor pool. Most of them require further investigation or technical developments before they can be implemented in the clinical routine.

Histone deacetylase inhibitor attenuates intestinal mucosal injury in fatally scalded rats

Background

Severe burns, trauma and shock can cause intestinal epithelial barrier dysfunction, which can lead to intestinal endotoxemia and even sepsis and multi-organ dysfunction. Many studies have shown that histone deacetylase inhibitors (HDACIs) can improve cell tolerance to hypoxia and inflammation, thus protecting the functions of important organs in the body, and at the same time, inhibiting the degradation of tight junction (TJ) proteins, protecting the intercellular barrier, and reducing tissue edema and organ damage. However, the mechanism is unclear.

Methods

Eighty male Sprague-Dawley rats (weighing 280-300 g) with a 50% total body surface area full-thickness dermal burn were randomly assigned to 4 groups (20 rats/group): sham control (SC group), scald + normal saline (SN group), scald + 2-methyl-2pentenoic acid (2M2P group), and scald + valproic acid (VPA group). After scalding, we measured the following parameters at various time intervals postburn injury: intestinal mucosal injury score, diamine oxidase (DAO) activity, intestinal protein expression of acetyl histone H3 at K9 (Ac-H3K9), hypoxia inducible factor 1α (HIF-1α), erythropoietin (EPO), zonula occludens-1 (ZO-1), endothelial nitric oxide synthase (eNOS) content, nitric oxide (NO) content, and intestinal mucosal blood flow (IMBF).

Results

Intestinal mucosa showed significant morphologic injury at 4 and 8 hours after scalding that was attenuated by VPA. DAO activity in the VPA group was significantly decreased compared with the other scald groups. At 4 and 8 hours after scalding, VPA enhanced Ac-H3K9 and ZO-1 expression and decreased HIF-1α and EPO expression in the intestine compared with the other scald groups. At 4 and 8 hours after scalding, eNOS and NO protein content and IMBF in the VPA group were markedly increased compared with the other scald groups.

Conclusions

HDACIs attenuated intestinal mucosal injury in fatally scalded rats. This may have involved VPA enhancing Ac-H3K9 and ZO-1 expression, inhibiting HIF-1α and EPO expression and inducing eNOS and NO increments.

Emerging role of carbon monoxide in intestinal transplantation

Intestinal transplantation has become an established therapeutic option that provides improved quality of life to patients with end-stage intestinal failure when total parenteral nutrition fails. Whereas this challenging life-saving intervention has shown exceptional growth over the past decade, illustrating the evolution of this complex and technical procedure from its preclinical origin in the mid-20th century to become a routine clinical practice today with several recent innovations, its success is hampered by multiple hurdles including technical challenges such as surgical manipulation during intestinal graft procurement, graft preservation and reperfusion damage, resulting in poor graft quality, graft rejection, post-operative infectious complications, and ultimately negatively impacting long-term recipient survival. Therefore, strategies to improve current intestinal transplantation protocol may have a significant impact on post-transplant outcomes. Carbon monoxide (CO), previously considered solely as a toxic gas, has recently been shown to be a physiological signaling molecule at low physiological concentrations with therapeutic potentials that could overcome some of the challenges in intestinal transplantation. This review discusses recent knowledge about CO in intestinal transplantation, the underlying molecular mechanisms of protection during intestinal graft procurement, preservation, transplantation and post-transplant periods. A section of the review also discusses clinical translation of CO and its challenges in the field of solid organ transplantation.

H2S donor molecules against cold ischemia-reperfusion injury in preclinical models of solid organ transplantation

Cold ischemia-reperfusion injury (IRI) is an inevitable and unresolved problem that poses a great challenge in solid organ transplantation (SOT). It represents a major factor that increases acute tubular necrosis, decreases graft survival, and delays graft function. This complicates graft quality, post-transplant patient care and organ transplantation outcomes, and therefore undermines the success of SOT. Herein, we review recent advances in research regarding novel pharmacological strategies involving the use of different donor molecules of hydrogen sulfide (H₂S), the third established member of the gasotransmitter family, against cold IRI in different experimental models of SOT (kidney, heart, lung, liver, pancreas and intestine). Additionally, we discuss the molecular mechanisms underlying the effects of these H₂S donor molecules in SOT, and suggestions for clinical translation. Our reviewed findings showed that storage of donor organs in H₂S-supplemented preservation solution or administration of H₂S to organ donor prior to organ procurement and to recipient at the start and during reperfusion is a novel, simple and cost-effective pharmacological approach to minimize cold IRI, limit post-transplant complications and improve transplantation outcomes. In conclusion, experimental evidence demonstrate that H₂S donors can significantly mitigate cold IRI during SOT through inhibition of a complex cascade of interconnected cellular and molecular events involving microcirculatory disturbance and microvascular dysfunction, mitochondrial injury, inflammatory responses, cell damage and cell death, and other damaging molecular pathways while promoting protective pathways. Translating these promising findings from bench to bedside will lay the foundation for the use of H₂S donor molecules in clinical SOT in the future.

Characterizing Autophagy in the Cold Ischemic Injury of Small Bowel Grafts: Evidence from Rat Jejunum

Cold ischemic injury to the intestine during preservation remains an unresolved issue in transplantation medicine. Autophagy, a cytoplasmic protein degradation pathway, is essential for metabolic adaptation to starvation, hypoxia, and ischemia. It has been implicated in the cold ischemia (CI) of other transplantable organs. This study determines the changes in intestinal autophagy evoked by cold storage and explores the effects of autophagy on ischemic grafts. Cold preservation was simulated by placing the small intestines of Wistar rats in an IGL-1 (Institute George Lopez) solution at 4 °C for varying periods (3, 6, 9, and 12 h). The extent of graft preservation injury (mucosal and cellular injury) and changes in autophagy were measured after each CI time. Subsequently, we determined the differences in apoptosis and preservation injury after activating autophagy with rapamycin or inhibiting it with 3-methyladenine. The results revealed that ischemic injury and autophagy were induced by cold storage. Autophagy peaked at 3 h and subsequently declined. After 12 h of storage, autophagic expression was reduced significantly. Additionally, enhanced intestinal autophagy by rapamycin was associated with less tissue, cellular, and apoptotic damage during and after the 12-h long preservation. After reperfusion, grafts with enhanced autophagy still presented with less injury. Inhibiting autophagy exhibited the opposite trend. These findings demonstrate intestinal autophagy changes in cold preservation. Furthermore, enhanced autophagy was protective against cold ischemia-reperfusion damage of the small bowels.