Regulated hepatic insulin gene therapy of STZ-diabetic rats

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Abstract
Effective and safe insulin gene therapy will require regulation of transgenic insulin secretion. We have created a liver-targeted insulin transgene by engineering glucose responsive elements into a hepatic promoter containing an inhibitory insulin response sequence. In this work, we demonstrate application of this transgene for the treatment of diabetes mellitus in vivo, by administering a recombinant adenovirus vector, Ad/(GIRE)3BP-1 2xfur, to rats made diabetic with streptozotocin. We verified hepatic expression of transgenic insulin by RT-PCR, and confirmed glucose responsive stimulation of transgenic insulin secretion in vivo by serum RIA. Following a portal system injection of either Ad/(GIRE)3BP-1 2xfur, or an empty adenoviral vector, animals made diabetic with either low (120 mg/kg), or high (290 mg/kg) dose streptozotocin (STZ) were monitored for changes in body weight, and blood glucose. Without subcutaneous insulin injections, blood glucose values of sham-treated animals (n = 8) remained elevated, and animals failed to gain weight (n = 4), or died (n = 4). In contrast, body weight of Ad/(GIRE)3BP-1 2xfur-treated animals (n = 13) increased, and blood glucose remained at near normal levels from one to 12 weeks. Glucose values <50 mg/dl were infrequently observed, and no Ad/(GIRE)3BP-1 2xfur-treated animal succumbed to hypoglycemia. Treatment with the insulin transgene enabled diabetic animals to reduce blood sugars following a glucose load, and to maintain blood sugar levels during a 10-h fast. Hepatic production of human insulin produced near normal glycemia, and weight gain, without exogenous insulin, and without lethal hypoglycemia. In conclusion, we have demonstrated the feasibility of utilizing transcription to control transgenic insulin production in a rodent model of diabetes mellitus.