title: Subconjunctivally Implanted Hydrogels for Sustained Insulin Release to Reduce Retinal Cell Apoptosis in Diabetic Rats.
abstract: OBJECTIVE
  Diabetic retinopathy (DR) is a leading cause of blindness in diabetic patients that involves early-onset retinal cell loss. Here, we report our recent work using subconjunctivally implantable hydrogels for sustained insulin release to the retina to prevent retinal degeneration.
  
  
  METHODS
  The hydrogels are synthesized by UV photopolymerization of N-isopropylacrylamide and a dextran macromer containing oligolactate-(2-hydroxyetheyl methacrylate) units. Insulin was loaded into the hydrogels during the synthesis. The ex vivo bioactivity of insulin released from the hydrogels was tested on fresh rat retinas using immunoprecipitation and immunoblotting to measure insulin receptor tyrosine and Akt phosphorylation. The biosafety and the effect on the blood glucose of the hydrogels were evaluated in rats 2 months after subconjunctival implantation. The release of insulin from the hydrogels was studied both in vitro in PBS (pH 7.4), and in vivo using confocal microscopy and RIA kit. The in vivo bioactivity of the released insulin was investigated in diabetic rats using DNA fragmentation method.
  
  
  RESULTS
  The hydrogels could load insulin with approximately 98% encapsulation efficiency and continuously release FITC-insulin in PBS (pH = 7.4) at 37°C for at least 5 months depending on their composition. Insulin lispro released from the hydrogels was biologically active by increasing insulin receptor tyrosine and Akt serine phosphorylation of ex vivo retinas. In vivo studies showed normal retinal histology 2 months post subconjunctival implantation. Insulin released from subconjunctivally implanted hydrogels could be detected in the retina by using confocal microscopy and RIA kit for 1 week. The implanted hydrogels with insulin lispro did not change the blood glucose level of normal and diabetic rats, but significantly reduced the DNA fragmentation of diabetic retinas for 1 week.
  
  
  CONCLUSIONS
  The developed hydrogels have great potential to sustain release of insulin to the retina via subconjunctival implantation to minimize DR without the risk of hypoglycemia.
authors.affiliation: Department of Ophthalmology, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Hisanori
authors.initials: H
authors.lastname: Imai
authors.affiliation: Department of Surgery, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States.
authors.forename: Gauri P
authors.initials: GP
authors.lastname: Misra
authors.affiliation: Department of Surgery, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States 3Department of Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Linfeng
authors.initials: L
authors.lastname: Wu
authors.affiliation: Department of Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Dileep R
authors.initials: DR
authors.lastname: Janagam
authors.affiliation: Department of Ophthalmology, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States 4Department of Ophthalmology and Visual Sciences, University of Michigan, Ann Arbor, Michigan, United States.
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Gardner
authors.affiliation: Department of Surgery, Pennsylvania State University, College of Medicine, Hershey, Pennsylvania, United States 3Department of Pharmaceutical Sciences, University of Tennessee Health Science Center, Memphis, Tennessee, United States.
authors.forename: Tao L
authors.initials: TL
authors.lastname: Lowe
mesh_terms: D000818:Animals; D017209:Apoptosis; D002454:Cell Differentiation; D003228:Conjunctiva; D003692:Delayed-Action Preparations / Q000008:administration & dosage; D003921:Diabetes Mellitus, Experimental / Q000188:drug therapy* / Q000473:pathology; D003930:Diabetic Retinopathy / Q000188:drug therapy* / Q000473:pathology; D004343:Drug Implants; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate / Q000008:administration & dosage*; D007004:Hypoglycemic Agents / Q000008:administration & dosage; D007328:Insulin / Q000008:administration & dosage*; D008297:Male; D018613:Microscopy, Confocal; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000187:drug effects / Q000473:pathology*
chemical_list: D003692:Delayed-Action Preparations; D004343:Drug Implants; D007004:Hypoglycemic Agents; D007328:Insulin; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate