DAMP production by human islets under low oxygen and nutrients in the presence or absence of an immunoisolating-capsule and necrostatin-1

Abstract

In between the period of transplantation and revascularization, pancreatic islets are exposed to low-oxygen and low-nutrient conditions. In the present study we mimicked those conditions in vitro to study the involvement of different cell death processes, release of danger-associated molecular patterns (DAMP), and associated in vitro immune activation. Under low-oxygen and low-nutrient conditions, apoptosis, autophagy and necroptosis occur in human islets. Necroptosis is responsible for DAMP-release such as dsDNA, uric acid, and HMGB1. The sensors of the innate immune system able to recognize these DAMPs are mainly TLR, NOD receptors, and C-type lectins. By using cell-lines with a non-functional adaptor molecule MyD88, we were able to show that the islet-derived DAMPs signal mainly via TLR. Immunoisolation in immunoprotective membranes reduced DAMP release and immune activation via retention of the relative large DAMPs in the capsules. Another effective strategy was suppressing necroptosis using the inhibitor nec-1. Although the effect on cell-survival was minor, nec-1 was able to reduce the release of HMGB1 and its associated immune activation. Our data demonstrate that in the immediate post-transplant period islets release DAMPs that in vitro enhance responses of innate immune cells. DAMP release can be reduced in vitro by immunoisolation or intervention with nec-1.Islet transplantation has the potential to supply patients with type 1 diabetes with an endogenous insulin source that regulates the glucose levels on a minute-to-minute level. A major breakthrough was reported in 2000 when insulin independence in a series of seven patients for a period of a year was reported 1 . Despite this breakthrough, the approach has not yet reached the stage of large-scale clinical application. The reasons for this is the shortage of organ donors and the relative short duration of graft survival with inevitable lost in functionality. Two years after transplantation, less than 50% of the patients is still insulin-independent 2 and five years following transplantation this percentage is not more than 10% 3 . Although during recent years some groups have been more successful 4 , the overall conclusion has to be that many factors remain to be improved in the islet-transplantation procedures before large-scale clinical application is a realistic option.During recent years many groups have focused on the identification of factors determining success or failure of islet grafts. Factors that have been implicated in the low success rates are the instant blood

Survival of encapsulated islets: More than a membrane story

“…Microcapsules retain part of the DAMPs, however significant amounts are still released. Adding NEC1, an inhibitor of necroptosis reduced DAMP release and activation of immune cells and rescued larger part of the islet cells [212] . Combined, these data highlight that the adequacy of the intracapsular microenvironment should be taken into consideration.…”

The Role of HMGB1 in the Pathogenesis of Type 2 Diabetes

“…However, there was no further study of HMGB1 involvement in islet inflammation later. Instead, there were studies focusing on the role of HMGB1 in islet transplantation [128–133]. HMGB1 inhibition by anti-IL-6R antibody, HMGB1 A-box, NF- κ B inhibitor, or the Na(+)/Ca(2+) exchanger inhibitor was able to ameliorate inflammatory responses and islet survival after islet transplantation by reducing the amount of innate immune cells and cytokines like TNF- α and interferon- (IFN-) γ [129–132].…”

Recent progress in the use and tracking of transplanted islets as a personalized treatment for type 1 diabetes

“…Another pitfall in microencapsulated islet cell transplantation can be cell death, due to the lack of oxygen or nutrients [37, 38, 59]. Certain molecules, known as danger-associated molecular patterns (DAMPs), e.g., dsDNA, RNA, HMGB1, and uric acid [59], can be present in the intracellular space.…”

“…Certain molecules, known as danger-associated molecular patterns (DAMPs), e.g., dsDNA, RNA, HMGB1, and uric acid [59], can be present in the intracellular space. After damage occurs, DAMPs are released into the extracellular space, and diffuse out of the capsule where they can be recognized by TLRs of the host cells, inducing an immediate immune reaction [53, 57, 60, 61, 62].…”

“…The presence of PAMPs and DAMPs should be avoided to obtain a maximum therapeutic efficacy of islet cell microencapsulation. One solution we have proposed to reduce the amount of DAMPs from necroptotic cells is to co-encapsulate necrostatin-1 as an alginate additive [59], a potent inhibitor of necrosis [63]. …”