title: Vascular endothelial growth factor as a survival factor for human islets: effect of immunosuppressive drugs.
abstract: OBJECTIVE
  Rapamycin, part of the immunosuppressive regimen of the Edmonton protocol, has been shown to inhibit vascular endothelial growth factor (VEGF) production and VEGF-mediated survival signalling in tumour cell lines. This study investigates the survival-promoting activities of VEGF in human islets and the effects of rapamycin on islet viability.
  
  
  METHODS
  Levels of VEGF and its receptors in isolated human islets and whole pancreas was determined by western blotting and immunostaining. Islet viability following VEGF or immunosuppressive drug treatment was determined using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Islet VEGF release was measured by ELISA. Mouse islets infected with an adenovirus expressing the gene for VEGF were transplanted syngeneically into streptozotocin-induced diabetic mice, with blood glucose levels measured three times per week.
  
  
  RESULTS
  Isolated human islets produced multiple isoforms of VEGF and VEGF receptors 1, 2 and 3 and the coreceptor neuropilin 1. Exogenous VEGF (10 ng/ml) prevented human islet death induced by serum starvation, which suggests that VEGF can act as a survival factor for human islets. Transplantation of mouse islets infected with a VEGF-expressing adenovirus in a syngeneic model, improved glycaemic control at day 1 post-transplantation (p < 0.05). Rapamycin at 10 and 100 ng/ml significantly reduced islet VEGF release (by 37 +/- 4% and 43 +/- 6%, respectively; p < 0.05) and at 100 ng/ml reduced islet viability (by 36 +/- 9%) and insulin release (by 47 +/- 7%, all vs vehicle-treated controls; p < 0.05). Tacrolimus had no effect on islet VEGF release or viability.
  
  
  CONCLUSIONS
  Our data suggest that rapamycin may have deleterious effects on islet survival post-transplantation, both through a direct effect on islet viability and indirectly through blockade of VEGF-mediated revascularisation.
authors.affiliation: Academic Renal Unit, Southmead Hospital, University of Bristol, Bristol, UK. sarah.cross@nds.ox.ac.uk
authors.forename: S E
authors.initials: SE
authors.lastname: Cross
authors.forename: S K
authors.initials: SK
authors.lastname: Richards
authors.forename: A
authors.initials: A
authors.lastname: Clark
authors.forename: A V
authors.initials: AV
authors.lastname: Benest
authors.forename: D O
authors.initials: DO
authors.lastname: Bates
authors.forename: P W
authors.initials: PW
authors.lastname: Mathieson
authors.forename: P R V
authors.initials: PR
authors.lastname: Johnson
authors.forename: S J
authors.initials: SJ
authors.lastname: Harper
authors.forename: R M
authors.initials: RM
authors.lastname: Smith
mesh_terms: D000818:Animals; D002470:Cell Survival; D002478:Cells, Cultured; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000166:cytology / Q000378:metabolism / Q000473:pathology*; D016381:Islets of Langerhans Transplantation; D051379:Mice; D008810:Mice, Inbred C57BL; D009369:Neoplasms / Q000401:mortality* / Q000473:pathology; D009389:Neovascularization, Pathologic; D040262:Receptors, Vascular Endothelial Growth Factor / Q000378:metabolism; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*
chemical_list: D007166:Immunosuppressive Agents; D042461:Vascular Endothelial Growth Factor A; D040262:Receptors, Vascular Endothelial Growth Factor; D020123:Sirolimus