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Garth L Warnock

Publications and source records attributed to Garth L Warnock.

15 recordsLinked to original sources
PubMed2007

Effect of exenatide on beta cell function after islet transplantation in type 1 diabetes.

BACKGROUND: Islet transplantation can reduce or eliminate the need for insulin in patients with type 1 diabetes. Exenatide is a long acting analogue of Glucagon-like peptide-1 (GLP-1) that augments glucose induced insulin secretion, and may increase beta cell mass. We evaluated the effect of exenatide on insulin secretion after islet transplantation. METHODS: Eleven C-peptide positive islet cell recipients with elevated glucose levels were treated with exenatide for three months. Response was assessed by insulin requirements, meal tolerance tests, and hyperglycemic glucose clamps. RESULTS: Ten patients responded to exenatide. Two patients who had not restarted insulin achieved good glycemic control and one patient who had received 5500 IE/kg in first islet infusion was able to stop insulin. Seven other patients decreased their insulin dose by 39% on exenatide. Hyperglycemic clamp studies showed a rise in second phase insulin release (before exenatide: 246+/-88 pM; during exenatide: 644+/-294 pM, P<0.01). Meal tolerance studies before and one month after stopping exenatide did not show a difference in glucose or C-peptide values. Nausea and vomiting were the major side effects. CONCLUSIONS: Exenatide stimulates insulin secretion in islet transplant recipients. It reduces insulin dose in some patients and may delay the need to resume insulin in others. We did not find any evidence of a trophic effect on islets.

Adult↗
PubMed2006

Insulin protects islets from apoptosis via Pdx1 and specific changes in the human islet proteome.

Insulin is both a hormone regulating energy metabolism and a growth factor. We and others have shown that physiological doses of insulin initiate complex signals in primary human and mouse beta-cells, but the functional significance of insulin's effects on this cell type remains unclear. In the present study, the role of insulin in beta-cell apoptosis was examined. Exogenous insulin completely prevented apoptosis induced by serum withdrawal when given at picomolar or low nanomolar concentrations but not at higher concentrations, indicating that physiological concentrations of insulin are antiapoptotic and that insulin signaling is self-limiting in islets. Insulin treatment was associated with the nuclear localization of Pdx1 and the prosurvival effects of insulin were largely absent in islets 50% deficient in Pdx1, providing direct evidence that Pdx1 is a signaling target of insulin. Physiological levels of insulin did not increase Akt phosphorylation, and the protective effects of insulin were only partially altered in islets lacking 80% of normal Akt activity, suggesting the presence of additional insulin-regulated antiapoptotic pathways. Proteomic analysis of insulin-treated human islets revealed significant changes in multiple proteins. Bridge-1, a Pdx1-binding partner and regulator of beta-cell survival, was increased significantly at low insulin doses. Together, these data suggest that insulin can act as a master regulator of islet survival by regulating Pdx1.

Analysis of Variance↗
PubMed2006

Effect of glucagon-like peptide-1 (7-37) on beta-cell function after islet transplantation in type 1 diabetes.

Islet transplantation can improve glycemic control in patients with type 1 diabetes and reduce or eliminate the need for insulin. Glucagon-like peptide-1 (GLP-1) is an intestinal insulinotropic hormone that augments glucose induced insulin secretion, and has a trophic effect on beta-cells. We evaluated the effect of GLP-1 on insulin secretion after islet transplantation. Patients underwent hyperglycemic glucose clamp studies 1 month after their last transplant. GLP-1 was infused during the second hour of the hyperglycemic clamp. Results were compared to normal control subjects and patients with type 2 diabetes who underwent an identical hyperglycemic clamp. First phase insulin release was absent in patients, while second phase insulin was not significantly reduced (control: 118+/-29 pM; type 2 diabetes: 68+/-20 pM; transplant: 99+/-18 pM, p=ns for all). GLP-1 had a significant incretin effect on transplanted islets but the response was less than controls (control: 2108+/-344 pM; type 2 diabetes: 929+/-331 pM; transplant: 329+/-112 pM, p<0.0001 control versus transplant). Islet transplant patients had no evidence of resistance to insulin mediated glucose disposal. We conclude that transplanted islets retain the ability to respond to GLP-1.

Adult↗
PubMed2006

Glutathione depletion of stimulator cells inhibits responder T-cell immunogenicity in vitro and prolongs allograft survival in vivo.

BACKGROUND: Pretransplant donor-organ immunomodulation may attenuate allograft rejection by changing the redox state of donor cells. This study explored impact of donor-cell redox-state alteration by glutathione (GSH) depletion on graft immunogenicity. METHODS: Splenic and heart endothelial cells from Balb/c mice were treated with diethylmaleate (a GSH-depleting agent) and/or lipopolysaccharide to assess the impact of GSH depletion on alloreactivity by mixed lymphocyte reaction, endothelial cell adhesion by T-cell adhesion assay, intracellular adhesion molecule-1 expression by reverse transcriptionase-polymerase chain reaction, and nuclear factor-kappa B upregulation by electrophoretic mobility shift assay. Heterotopic heart transplants were performed as in vivo correlate. RESULTS: GSH depletion decreased endothelial cell and splenic cell alloreactivity, decreased endothelial cell intracellular adhesion molecule-1 expression through attenuation of nuclear factor-kappa B activity, decreased endothelial cell adhesion, and prolonged heterotopic heart transplant graft survival. CONCLUSIONS: GSH depletion may represent a significant immunomodulator of donor antigenicity to prevent transplant rejection.

Animals↗
PubMed2006

Suppression of human T-cell responses to beta-cells by activation of B7-H4 pathway.

B7-H4, a recently described member of the B7 family of cosignal molecules, is thought to be involved in the regulation of cellular and humoral immune responses through receptors on activated T and B cells. Human islet cells express positive B7-H4 mRNA in RT-PCR assays, but not B7-H4 protein on cell surface in flow cytometric analyses. To investigate the regulatory effects of activation of the B7-H4 pathway on the function of activated T cells of patients with type 1 diabetes (T1D), we have used our in vitro human experimental system, including human beta-cell antigen-specific T-cell clones and human beta-cell lines CM and HP62, as well as primary islet cells. B7-H4.Ig protein was purified from the culture supernatant of 293T cells transfected by a B7-H4.Ig plasmid (pMIgV, containing a human B7-H4 cDNA and a mouse IgG2a Fc cDNA). Our preliminary studies showed that immobilized fusion protein human B7-H4.Ig (coated with 5 microg/ml for 2 h at 37 degrees C), but not control Ig, clearly inhibited the proliferation of activated CD4+ and CD8+ T cells of patients induced by anti-CD3 antibody in CFSE assays. B7-H4.Ig also arrested cell cycle progression of T cells in G0/G1 phase and induced T-cell apoptosis as measured by BrdU-7-AAD flow cytometric analysis. To determine the cytoprotective effects of B7-H4, we developed transfectants of human beta-cell lines CM and HP62 and islet cells transfected with the B7-H4.Ig plasmid, using empty vector transfectants as controls. The results demonstrate that cell-associated B7-H4.Ig expressed on human beta-cells clearly inhibits the cytotoxicity of the T-cell clones to targeted human beta-cells in 51Cr release cytotoxicity assays. Activation of the B7-H4 pathway may represent a novel immunotherapeutic approach to inhibit T-cell responses for the prevention of beta-cell destruction in T1D.

Adolescent↗
PubMed2005

Improved human pancreatic islet isolation for a prospective cohort study of islet transplantation vs best medical therapy in type 1 diabetes mellitus.

HYPOTHESIS: A local multiorgan donor pancreas procurement program can provide a source for optimized isolation of purified viable islets for transplantation into patients with type 1 diabetes mellitus receiving best medical therapy. DESIGN: Prospective before-after cohort study. SETTING: Tertiary referral center. PATIENTS: Glycemic control was assessed in 10 patients with diabetes-induced renal dysfunction who were enrolled in a best medical therapy program and then crossed over to islet transplantation. INTERVENTIONS: Thirty human pancreata were retrieved from local multiorgan donors and consecutively processed with intraductal collagenase perfusion, continuous digestion, and density gradient purification (group 1, n = 9) or similarly processed but impure tissue fractions cultured in vitro and then repurified to retrieve additional islets (group 2, n = 21). Islets were implanted by percutaneous portal embolization, providing more than 10 000 islet equivalents (IE) per kilogram of body weight (infusions from 1-3 donors per patient) under cover of antithymocyte globulin, sirolimus, or mycophenolate mofetil and tacrolimus. MAIN OUTCOME MEASURES: Islet yields, purity, and cell viability (caspase 3, terminal deoxynucleotidyl transferase-mediated biotin-deoxyuridine 5-triphosphate nick-end labeling stain, and insulin secretion in vitro) were compared. In patients, monitored metabolic parameters were C-peptide secretion, insulin requirements, glycemic excursion, and hemoglobin A(1c) (HbA(1c)). RESULTS: For group 1 vs group 2, no differences were observed in pancreas age (43 vs 44 years), cold storage (5 vs 4 hours), or weight (73 vs 82 g). Group 2 yielded 453 690 IE vs 214 109 IE in group 1 (P = .002). Grafts contained 50% or more endocrine cells in both groups. No difference occurred in cell viability or insulin secretion. Islets from 90% of group 2 pancreata met release criteria for transplantation. C-peptide secretion was detected in all recipients and persisted with a median follow-up to 12 months (range, 6-21 months) after full islet transplantation. Daily insulin dependence was reversed in all patients for at least 3 months. Five patients resumed small insulin doses. Compared with the best care program, all patients had improved metabolic stability. The mean +/- SE HbA(1c) level at entry into the study was 7.8% +/- 0.5%, and this decreased to 6.9% +/- 0.2% after best care (P = .38) and further to 6.2% +/- 0.2% at 6 months after transplantation (P = .002 vs entry; P = .15 vs best care; analysis of variance). CONCLUSIONS: Local pancreas donor retrieval with islet isolation and culture conditioning enabled an offer of islets for transplantation for 90% of consecutively processed pancreata. Isolated islets secreted insulin during prolonged follow-up after implantation into patients, yielding metabolic control comparable with that achieved by best medical therapy.

Adult↗
PubMed2005

2004 MacLean-Mueller prize enteral or parenteral nutrition for severe pancreatitis: a randomized controlled trial and health technology assessment.

BACKGROUND: The optimal route of nutrition in severe pancreatitis is controversial. Parenteral nutrition (PN) is preferred, but enteral nutrition (EN) promises to attenuate inflammation and prevent sepsis. We hypothesized that EN was at least equivalent to PN in reducing inflammation, providing effective nutrition and being cost-effective. METHODS: We conducted a randomized controlled trial comparing PN to EN in pancreatitis in an academic, multi-institutional, tertiary care health system. We screened 728 consecutive patients. Twenty-eight patients with a Ranson's score greater than 2 who did not tolerate clear fluids 4 days after admission were randomized: 18 to PN and 10 to EN. Both groups were provided daily 105 kJ (25 kcal)/kg and 1.5 g/kg of protein, respectively, until they could tolerate a regular diet. RESULTS: C-reactive protein in EN patients was reduced by 50% 5 days faster than PN patients (Wilcoxon test, p = 0.09). Both groups received a similar number of kilojoules and achieved near normal prealbumin and 24-hour urinary nitrogen values. Neither regimen caused a change in cholecystokinin levels. Overall mortality was 4.9% (3 patients in the PN group). In 5 patients (4 PN, 1 EN) there were infected pancreatic collections. Nine EN patients dislodged the nasojejunal tube. EN had an average cost of dollar 1375 per patient compared with dollar 2608 for PN (p = 0.08). After sensitivity analysis, EN cost dollar 957 compared with dollar 2608 for PN (p = 0.03). CONCLUSIONS: EN or PN is safe and provides adequate nutrition in severe pancreatitis. EN shows a trend toward faster attenuation of inflammation, with fewer septic complications and is the dominant therapy in terms of cost-effectiveness. This study favours EN for nutritional support in severe pancreatitis.

Acute Disease↗