Silk fibroin preserves beta cell function under inflammatory stress while stimulating islet cell surface GLUT2 expression.

Silk fibroin is a novel biomaterial for enhancing transplanted islet cell function and survival. This study investigated whether silk fibroin may have unique properties that improve islet function in the face of inflammatory-mediated stress during transplantation. Murine islet function was tested in vitro with either silk fibroin or alginate and challenged with inflammatory cytokines. The glucose-stimulated insulin secretion index for all conditions decreased with inflammatory cytokines, but was better preserved for islets exposed to silk compared to those exposed to alginate or medium. GLUT2 transporter expression on the cell surface of islets exposed to silk was increased compared to alginate or medium alone. Upon cytokine stress, a greater percentage of islet cells exposed to silk expressed GLUT2 on their surface. We conclude that preconditioning islets with silk fibroin stimulates islet cell surface GLUT2 expression, an increase, which persists under inflammatory stress, and may improve islet engraftment and function after transplantation.

TSG-6 protein expression in the pancreatic islets of NOD mice.

The histologic hallmark of the development of type 1 diabetes (T1D) is insulitis, characterized by leukocytic infiltration of the pancreatic islets. The molecules controlling the early influx of leukocytes into the islets are poorly understood. Tumor necrosis factor alpha (TNFalpha)-stimulated gene 6 (TSG-6) is involved in inflammation, extracellular matrix formation, cell migration, and development. In the present study, we examined the expression and cellular localization of TSG-6 protein in islets of female non-obese diabetic (NOD) mice using frozen section immunofluorescence staining. Pancreata from nondiabetic (8 and 25 weeks old), prediabetic (230-280 mg/dl blood glucose) and diabetic (>300 mg/dl blood glucose) NOD mice were stained for TSG-6, insulin, CD3, CD11c, Mac3 and CD31. TSG-6 protein was detected in 67% of islets of prediabetic mice, 27% of islets of 25-week old nondiabetic mice, and less than 7% of islets of diabetic mice and 8-week old nondiabetic mice. Lastly, islet-derived TSG-6 protein was localized to the infiltrating CD3 and CD11c positive leukocytes.

Islet cell survival during isolation improved through protein kinase C epsilon activation.

Strategies inhibiting cell death signaling pathways may enhance the availability of islet transplantation for patients with type 1 diabetes mellitus. The epsilon isoform of protein kinase C (PKC epsilon) has been shown to have an anti-apoptotic effect in many cell types. The present study investigated whether activation of PKC epsilon may improve the yield of functional islet cells for transplantation. Islet cells were isolated from wild-type BALB/c mice preconditioned with either a PKC epsilon activator (psi epsilon RACK) or a TAT carrier control peptide and further treated with the same agents during isolation and in vitro for either 0, 1, 16, or 40 hours. Islet cells were assessed at each time point for viability, apoptosis, and function. psi epsilon RACK-treated islets showed significantly decreased islet cell death up to 40 hours after isolation compared with TAT-treated control islets. Beta-cell function in response to high glucose challenge remained unchanged.

Comparison of rejection rate and functional outcome of small bowel transplantation alone or in conjunction with the ileocecal valve versus combined small and large bowel transplantation.

Preservation of the ileocecal valve improves absorptive function and decreases the amount of small bowel needed for survival in patients with short gut syndrome. We compared the results of small and large bowel transplant (SLBTx), small bowel transplant only (SBTx), and SBTx with the ileocecal valve (ICVTx) in a porcine model. Total enterectomy was performed on 18 Yorkshire-Landrace pigs followed by orthotopic SBLTx (n = 6), SBTx (n = 6), and ICVTx (n = 6). A jejunostomy and an ileostomy were constructed for biopsies. Overall mean survival was 17 d with no statistically significant difference between groups. Rejection was seen in 6/6 SLBTx, 4/6 SBTx, and 4/6 ICVTx recipients. Acute rejection was seen in 84.3% of SLBTx, 52.3% of SBTx, and 42.5% of the ICVTx mucosal biopsy samples. Two cases of intra-abdominal infection were in the ICVTx group only. Weight loss was 147 g/d in the SLBTx group, 643 g/d in the SBTx group, and 393 g/d in the ICVTx group. While the functional outcome after SLBTx and ICVTx was noticeably better than the SBTx group, the increased rejection and intra-abdominal infection rates make transplanting the large bowel or the ileocecal valve a less attractive clinical option.

Comparison of jejunal and ileal surveillance biopsies in a porcine model of intestinal transplantation.

BACKGROUND: The optimal biopsy site of bowel allografts for rejection surveillance remains controversial. We compared the results of jejunal (JBx) and ileal (IBx) biopsies after bowel transplantation in a porcine model. METHODS: Eighteen Yorkshire-Landrace pigs served as donors. Eighteen recipient pigs underwent total enterectomy followed by orthotopic small bowel transplantation with or without the colon. A jejunostomy and a Bishop-Koop ileostomy were constructed for biopsies. Immunosuppression consisted of FK506 (target level 10-15 ng/ml by enzyme immunoparticle assay) and prednisone administered via the jejunostomy. Simultaneous JBx and IBx were performed twice weekly. Acute rejection was graded as mild, moderate, or severe based on previously published criteria. RESULTS: Mean overall survival after the transplant was 17.4 days. A total of 162 specimens were collected and evaluated for rejection (JBx, 81; IBx, 81). Acute rejection was detected in 41 JBx cases (50.7%) and 40 IBx cases (49.4%). The presence or absence of rejection was concordant between JBx and IBx in 70 of 81 case pairs (86.4%). Of the 11 discordant case pairs, 6 were JBx positive/IBx negative, whereas 5 were JBx negative/IBx positive. A total of 35 case pairs were synchronously positive, 24 (68.8%) of which demonstrated the same degree of rejection. CONCLUSIONS: The correlation between JBx and IBx of bowel allografts in diagnosing the presence of acute rejection is quite good. However, performing IBx alone would have missed about 7.5% of the rejection episodes. Because the early treatment of rejection in bowel transplantation is of paramount importance, in selected cases, biopsies from both the ileum and jejunum should be considered if technically feasible.