Role of chemokine signaling pathways in pancreatic islet rejection during allo- and xenotransplantation

Early barriers to neonatal porcine islet engraftment in a dual transplant model

Porcine islet xenografts have the potential to provide an inexhaustible source of islets for β cell replacement. Proof-of-concept has been established in nonhuman primates. However, significant barriers to xenoislet transplantation remain, including the poorly understood instant blood-mediated inflammatory reaction and a thorough understanding of early xeno-specific immune responses. A paucity of data exist comparing xeno-specific immune responses with alloislet (AI) responses in primates. We recently developed a dual islet transplant model, which enables direct histologic comparison of early engraftment immunobiology. In this study, we investigate early immune responses to neonatal porcine islet (NPI) xenografts compared with rhesus islet allografts at 1 hour, 24 hours, and 7 days. Within the first 24 hours after intraportal infusion, we identified greater apoptosis (caspase 3 activity and TUNEL [terminal deoxynucleotidyl transferase dUTP nick end labeling])-positive cells) of NPIs compared with AIs. Macrophage infiltration was significantly greater at 24 hours compared with 1 hour in both NPI (wild-type) and AIs. At 7 days, IgM and macrophages were highly specific for NPIs (α1,3-galactosyltransferase knockout) compared with AIs. These findings demonstrate an augmented macrophage and antibody response toward xenografts compared with allografts. These data may inform future immune or genetic manipulations required to improve xenoislet engraftment.

Improvement of islet graft function using liraglutide is correlated with its anti-inflammatory properties

Background and Purpose

Liraglutide improves the metabolic control of diabetic animals after islet transplantation. However, the mechanisms underlying this effect remain unknown. The objective of this study was to evaluate the anti‐inflammatory and anti‐oxidative properties of liraglutide on rat pancreatic islets in vitro and in vivo.

Experimental Approach

In vitro, rat islets were incubated with 10 μmol·L⁻¹ liraglutide for 12 and 24 h. Islet viability functionality was assessed. The anti‐inflammatory properties of liraglutide were evaluated by measuring CCL2, IL‐6 and IL‐10 secretion and macrophage chemotaxis. The anti‐oxidative effect of liraglutide was evaluated by measuring intracellular ROS and the total anti‐oxidative capacity. In vivo, 1000 islets were cultured for 24 h with or without liraglutide and then transplanted into the liver of streptozotocin‐induced diabetic Lewis rats with or without injections of liraglutide. Effects of liraglutide on metabolic control were evaluated for 1 month.

Key Results

Islet viability and function were preserved and enhanced with liraglutide treatment. Liraglutide decreased CCL2 and IL‐6 secretion and macrophage activation after 12 h of culture, while IL‐10 secretion was unchanged. However, intracellular levels of ROS were increased with liraglutide treatment at 12 h. This result was correlated with an increase of anti‐oxidative capacity. In vivo, liraglutide decreased macrophage infiltration and reduced fasting blood glucose in transplanted rats.

Conclusions and Implications

The beneficial effects of liraglutide on pancreatic islets appear to be linked to its anti‐inflammatory and anti‐oxidative properties. These findings indicated that analogues of glucagon‐like peptide‐1 could be used to improve graft survival.

Pro-inflammatory and pro-oxidant status of pancreatic islet in vitro is controlled by TLR-4 and HO-1 pathways

Since their isolation until implantation, pancreatic islets suffer a major stress leading to the activation of inflammatory reactions. The maintenance of controlled inflammation is essential to preserve survival and function of the graft. Identification and targeting of pathway(s) implicated in post-transplant detrimental inflammatory events, is mandatory to improve islet transplantation success. We sought to characterize the expression of the pro-inflammatory and pro-oxidant mediators during islet culture with a focus on Heme oxygenase (HO-1) and Toll-like receptors-4 signaling pathways. Rat pancreatic islets were isolated and pro-inflammatory and pro-oxidant status were evaluated after 0, 12, 24 and 48 hours of culture through TLR-4, HO-1 and cyclooxygenase-2 (COX-2) expression, CCL-2 and IL-6 secretion, ROS (Reactive Oxygen Species) production (Dihydroethidine staining, DHE) and macrophages migration. To identify the therapeutic target, TLR4 inhibition (CLI-095) and HO-1 activation (cobalt protoporphyrin,CoPP) was performed. Activation of NFκB signaling pathway was also investigated. After isolation and during culture, pancreatic islet exhibited a proinflammatory and prooxidant status (increase levels of TLR-4, COX-2, CCL-2, IL-6, and ROS). Activation of HO-1 or inhibition of TLR-4 decreased inflammatory status and oxidative stress of islets. Moreover, the overexpression of HO-1 induced NFκB phosphorylation while the inhibition of TLR-4 had no effect NFκB activation. Finally, inhibition of pro-inflammatory pathway induced a reduction of macrophages migration. These data demonstrated that the TLR-4 signaling pathway is implicated in early inflammatory events leading to a pro-inflammatory and pro-oxidant status of islets in vitro. Moreover, these results provide the mechanism whereby the benefits of HO-1 target in TLR-4 signaling pathway. HO-1 could be then an interesting target to protect islets before transplantation.

Role of islet culture on angiogenic and inflammatory mechanisms

Early events hampering islet engraftment may relate to instant blood-mediated inflammatory reaction (IBMIR) and to insufficient islet revascularization inducing β-cell death. We evaluated the influence of time of culture on angiogenic and inflammatory cellular mechanisms in islet loss in vitro. Rat pancreatic islets cultured for 0, 12, 24, and 48 hours were assessed for functionality using glucose stimulation tests and identification of signaling pathways using polymerase chain reaction (PCR) arrays. Islet functionality decreased significantly immediately. Index of stimulation (IS) was decreased to 2.29 ± 1.05 after 48 hours of culture versus 18.47 ± 4.84 at 0 hours (P < .001). Gene expression studies at 12 hours of culture showed significant overexpression of proinflammatory cytokines and chemokines--interleukin (IL)-6 884.22 ± 282.58 (P < .001) and Cxcl-1 448.09 ± 196.05-fold change (P < .01). Moreover, islets exhibited significant under-expression after 48 hours of genes encoding angiogenic growth factors, such as epidermal growth factor, vascular endothelial growth factor, platelet endothelial cell adhesion molecule 1, a major protein involved in angiogenesis: 0.07 ± 0.02, 0.11 ± 0.08 (P < .001), and 0.17 ± 0.15-fold change (P < .01) respectively. Moreover, tissue inhibitor of metalloproteinases 1, an inhibitor of metallopeptidase, was significantly more over-expressed, namely 54.58 ± 18.08 at 12 hours of culture versus 0.93 ± 0.15/fold change at 0 hours. This study revealed current culture conditions to be deleterious for islet engraftment, possibly due to expression of angiogenic genes and proinflamatory genes during culture.

Young porcine endocrine pancreatic islets cultured in fibrin and alginate gels show improved resistance towards human monocytes

AIM

To investigate the protective function of alginate and fibrin gels used to embed porcine endocrine pancreatic islets towards human monocytes.

METHODS

Groups of 200 islet equivalents from young pigs were embedded in either a fibrin or in an alginate gel, and as a control seeded in tissue culture polystyrene (TCPS) well plates. The islet cultures were incubated with 2×10(5) human monocytes for 24h. In addition, both islets and monocytes were separately cultured in TCPS, fibrin and alginate. Islet morphology, viability and function were investigated as well as the secretion of cytokines TNFα, IL-6, and IL-1β.

RESULTS

When freely-floating in TCPS, non-encapsulated islets were surrounded by monocytes and started to disperse after 24h. In fibrin, monocytes could be found in close proximity to embedded islets, indicating monocyte migration through the gel. In contrast, after 24h, few monocytes were found close to islets in alginate. Immunofluorescence staining and manual counting showed that integrin expression was higher in fibrin-embedded islet cultures. A TUNEL assay revealed elevated numbers of apoptotic cells for islets in TCPS wells compared to fibrin and alginate cultures. Insulin secretion was higher with islets embedded in fibrin and alginate when compared to non-encapsulated islets. TNFα, IL-6 and IL-1β were found in high concentrations in the media of co-cultures and monocyte mono-culture in fibrin.

CONCLUSION

Both alginate and fibrin provide key structural support and offer some protection for the islets towards human monocytes. Fibrin itself triggers the cytokine secretion from monocytes.

Isolation and characterization of a novel strain of mesenchymal stem cells from mouse umbilical cord: potential application in cell-based therapy

Human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) have recently been recognized as a potential source for cell-based therapy in various preclinical animal models, such as Parkinson's disease, cerebral ischemia, spinal cord injury, and liver failure; however, the precise cellular and molecular mechanisms underlying the beneficial outcomes remain under investigation. There is a growing concern regarding rejection and alteration of genetic code using this xenotransplantation approach. In this study, a novel strain of murine MSCs derived from the umbilical cord of wild-type and green fluorescent protein (GFP) transgenic mice have been successfully isolated, expanded, and characterized. After 10 passages, the mUC-MSCs developed a rather homogeneous, triangular, spindle-shaped morphology, and were sub-cultured up to 7 months (over 50 passages) without overt changes in morphology and doubling time. Cell surface markers are quite similar to MSCs isolated from other tissue origins as well as hUC-MSCs. These mUC-MSCs can differentiate into osteoblasts, adipocytes, neurons, and astrocytes in vitro, as well as hematopoietic lineage cells in vivo. mUC-MSCs also possess therapeutic potential against two disease models, focal ischemic stroke induced by middle cerebral artery occlusion (MCAo) and acute hepatic failure. Subtle differences in the expression of cytokine-related genes exist between mUC-MSCs and hUC-MSCs, which may retard and jeopardize the advance of cell therapy. Allografts of these newly established mUC-MSCs into various mouse disease models may deepen our insights into the development of more effective cell therapy regimens.

Rapamycin Augments the NMDA-Mediated TNF Suppression of MRSA-Stimulated RAW264.7 Murine Macrophages

Background. Methicillin-resistant Staphylococcus aureus (MRSA) can stimulate massive cytokine release. Ketamine suppresses tumor necrosis factor (TNF) secretion by MRSA-stimulated RAW264.7 macrophages, and the mechanism likely involves N-methyl-D-aspartic acid (NMDA) receptor antagonism. The downstream effects of NMDA-mediated TNF suppression, specifically the PI3K/Akt and mTOR modulation, have not been described. Methods. RAW264.7 cells were stimulated for 18 hrs with 10⁵ to 10⁷ CFU/mL inocula of either of two prototypical community-acquired- (CA-) MRSA isolates, USA300 strain LAC and USA400 strain MW2. Then we added the NMDA inhibitors ketamine or 2R-amino-5-phosphonopentanoate (AP5), NMDA substrate, LY294002, and rapamycin in various combinations. Results. NMDA inhibition suppressed TNF secretion by almost a third compared to the no-ketamine control. When NMDA substrate was added, the TNF secretion increased by 10%. Addition of LY294002 suppressed TNF production by macrophages by 20%. Rapamycin exhibited a concentration-dependent TNF induction-suppression response: induction at doses of 0.1 and 1 ng/mL and suppression at 10 and 100 ng/mL. Induction of TNF was abolished when LY294002 was added and the suppression became uniform. Ketamine-induced suppression of TNF secretion was intensified 10–15% when rapamycin was added, but not when LY294002 was added. Conclusion. These findings suggest that NMDA-induced TNF suppression can be augmented by concurrent mTOR inhibition.

Encapsulated porcine islet transplantation: an evolving therapy for the treatment of type I diabetes

BACKGROUND

Allogeneic tissue-based therapies for Type I diabetes have demonstrated efficacy but are limited due to tissue-sourcing constraints, as the number of patients exceeds that of tissue donors. Porcine islets derived from designated pathogen-free sources could be an alternative, particularly if delivered in a way that evades the host immune system's rejection.

METHODS

This review focuses on approaches designed to protect xenogeneic islets from immune rejection by provision of perm-selective barriers.

RESULTS

Designated pathogen-free herds could provide a supply of wild-type porcine islets that are well tolerated when administered in a suitable protective delivery vehicle. Such barrier systems have enabled amelioration of diabetes in a variety of animal models and preliminary evidence suggests that similar results could be attained in humans.

CONCLUSION

With advances in biomaterial design, source tissue selection, and the evolution of critical cell processing techniques, contemporary encapsulated porcine islet therapies offer a new level of clinical promise.

Lentivectors encoding immunosuppressive proteins genetically engineer pancreatic beta-cells to correct diabetes in allogeneic mice

The effectiveness of genetic engineering with lentivectors to protect transplanted cells from allogeneic rejection was examined using, as a model, type 1 diabetes treatment with beta-cell transplantation, whose widespread use has been limited by the requirement for sustained immunosuppressive treatment to prevent graft rejection. We examined whether lentivectors expressing select immunosuppressive proteins encoded by the adenoviral genome early region 3 (AdE3) would protect transplanted beta-cells from an alloimmune attack. The insulin-producing beta-cell line beta TC-tet (C3HeB/FeJ-derived) was transduced with lentiviruses encoding the AdE3 proteins gp19K and RID alpha/beta. The efficiency of lentiviral transduction of beta TC-tet cells exceeded 85%. Lentivector expression of gp19K decreased surface class I major histocompatibility complex expression by over 90%, whereas RID alpha/beta expression inhibited cytokine-induced Fas upregulation by over 75%. beta TC-tet cells transduced with gp19K and RID alpha/beta lentivectors, but not with a control lentivector, provided prolonged correction of hyperglycemia after transplantation into diabetic BALB/c severe combined immunodeficient mice reconstituted with allogeneic immune effector cells or into diabetic allogeneic BALB/c mice. Thus, genetic engineering of beta-cells using gp19K- and RID alpha/beta-expressing lentiviral vectors may provide an alternative that has the potential to eliminate or reduce treatment with the potent immunosuppressive agents necessary at present for prolonged engraftment with transplanted islets.

Influence of rapamycin on rat macrophage viability and chemotaxis toward allogenic pancreatic islet supernates

The aim of this work was to evaluate the effects of rapamycin on rat macrophage viability and chemotaxis toward allogereic pancreatic islet supernates. Macrophages were isolated from rats by peritoneal lavage at 3 days after intraperitoneal injection of thioglycolate. Macrophage viability was studied after 7 days of culture by Cell Titer assays in the presence of rapamycin at 0.1, 1, and 10 ng/mL (n = 6). After 48 hours of culture, pancreatic rat islet supernates were studied for there chemotactic properties toward freshly isolated macrophages in the presence of rapamycin at 0.1, 1, and 10 ng/mL. Chemotaxis was expressed as a migration index defined as the number of macrophages attracted by the test solution (islet supernate +/- rapamycin)/number of macrophages attracted by the supernate (n = 6). After 3 days of culture, macrophage viability decreased significantly by 22%, 36%, and 32% in the presence of 0.1, 1, and 10 ng/mL rapamycin, respectively (P = .008). Macrophage viability remained stable at about 70% after 7 days of culture. In the presence of islet supernates, macrophage migration increased two-fold compared with those obtained by culture medium. Rapamycin did not influence macrophage migration toward culture medium. However, the drug significantly reduced the migration of macrophages toward islet supernates from 2 +/- 0.6 to 0.9 +/- 0.4, 0.7 +/- 0.3, or 0.8 +/- 0.4 in the presence of 0.1, 1, or 10 ng/mL rapamycin, respectively (P = .04). Rapamycin decreased the survival of cultured rat macrophages and their migration toward allogenic islet supernates. These results suggested that, besides its anti-proliferative effect on T cells, rapamycin reduced macrophage attraction to the graft site.

Effects of glucose toxicity and islet purity on in vivo magnetic resonance imaging of transplanted pancreatic islets

BACKGROUND

Pancreatic islet transplantation has recently emerged as a powerful clinical modality to restore normoglycemia in diabetic patients. Despite the success of the Edmonton protocol, these patients still experience a significant islet loss immediately after transplantation. Noninvasive magnetic resonance imaging (MRI) allows for longitudinal monitoring of graft loss providing that islets are labeled with a magnetically "visible" contrast agent. To fully interpret the imaging data, it is critical to investigate factors normally present during clinical transplantation and influencing MRI of transplanted islets.

METHODS

Here, we focused on both the effect of hyperglycemia and the effect of contaminating nonendocrine tissue, which is always present in islet preparations, on MRI imaging of islet grafts. Human pancreatic islets labeled with Feridex were transplanted in diabetic and healthy animals. Separate groups of animals were transplanted with Feridex-labeled pure and nonpure (50% islets and 50% nonendocrine tissue) preparations. The fate of the graft in all groups was monitored by in vivo MRI.

RESULTS

We found that diabetic animals with transplanted islets showed a significantly higher rate of islet death than their healthy counterparts on in vivo MR images. Interestingly, transplantation of islets contaminated with nonendocrine tissue did not have any significant influence on MR images, presumably because of a low labeling rate of this tissue and a fast rate of its disappearance after transplantation.

CONCLUSIONS

We believe that this study serves as yet another step on our way to clinical use of in vivo imaging of islet transplantation.

In vitro study of using calcium phosphate cement as immunoisolative device to enclose insulinoma/agarose microspheres as bioartificial pancreas

In this study, the feasibility of using calcium phosphate cement (CPC) as immunoisolative device to enclose insulinoma/agarose microspheres as bioartificial pancreas was evaluated. We fabricated a chamber by CPC and utilized X-ray diffraction, Scanning electron microscope and Mercury intrusion porosimetry to identify the characters of the CPC chamber. The nominal molecular weight cut-off and cytotoxicity of CPC chamber were also evaluated. An insulinoma cell line (RIN-m5F) was chosen as insulin source and encapsulated in agarose microspheres and then enclosed in preformed CPC chamber. Insulin secretion was analyzed by Enzyme-linked immunosorbant assay to evaluate the function of insulinoma enclosed in CPC chamber. Results showed that the CPC chamber was non-cytotoxicity to insulinoma and can block the penetration of molecules which molecular weight larger than 12.4 kDa. Insulinoma inside the CPC chamber can secrete insulin in stable level for 30 days. This study indicated that we may use CPC as immunoisolative material to enclose insulinoma/agarose microspheres as bioartificial pancreas.