Construction and characterization of a recombinant adenovirus vector carrying the human preproinsulin gene under the control of the metallothionein gene promoter

Adenovirus-mediated insulin gene transfer improves nutritional and post-hepatectomized conditions in diabetic rats

BACKGROUND

Impaired nutritional conditions in patients with diabetes are significant risk factors after major abdominal surgery. We constructed recombinant adenovirus vector carrying the human insulin gene (AxCAIns) for in vivo insulin gene transfer to improve metabolic impairments after a major operation in patients with diabetes. We tested the effects of AxCAIns on nutritional and post-hepatectomized conditions in rats with diabetes treated with streptozotocin (STZ).

METHODS

AxCAIns was injected into the spleen in diabetic rats treated with STZ. Blood levels of glucose, total protein, albumin, and C-peptide of human proinsulin were measured and the expression of transferred human insulin gene was analyzed in various organs. Diabetic rats underwent 70% partial hepatectomy with or without AxCAIns injection, and post-hepatectomized conditions were analyzed.

RESULTS

STZ-induced hyperglycemia was reduced by AxCAIns injection. Decreased serum levels of total protein and albumin in diabetic rats were significantly restored to normal levels by AxCAIns injection, and human C-peptide was detected in the sera of AxCAIns-treated rats. Human preproinsulin messenger RNA, which represented the expression of transferred insulin gene, was detected in the liver and the spleen, but not in other organs. Serum albumin levels, remnant liver weight, and ratios of postoperative body weight to preoperative body weight were significantly increased by AxCAIns in hepatectomized diabetic rats.

CONCLUSIONS

AxCAIns injection to the spleen efficiently transferred the human insulin gene mainly into the hepatocytes and produced enough human proinsulin to improve nutritional impairments and post-hepatectomized conditions in diabetic rats. Insulin gene transfer with intrasplenic injection of AxCAIns may be available to improve metabolic impairment after major abdominal surgery in patients with diabetes.

Insulin delivery with plasmid DNA

Success in controlling hyperglycemia in type I diabetics will require a restoration of basal insulin. To this end, three plasmid DNAs (pDNA) encoding preproinsulin were compared for constitutive expression and processing to insulin in nonendocrine cells in vitro. The pDNAs were designed to express rat proinsulin I (VR-3501), rat proinsulin I with the B10 aspartic acid point mutation (VR-3502), and a derivative of VR-3502 with a furin cleavage site added at the B-chain and C-peptide junction (VR-3503). Cells transfected with VR-3501 or VR-3502 were able to secrete only proinsulin, whereas transfection with VR-3503 yielded 30-70% mature insulin, which could be increased to >99% by cotransfection with a furin expression plasmid (VR-3505). The insulin produced was biologically active. The bilateral injection of 100 microg of VR-3502 plasmid into the tibialis anterior muscles of mice on two consecutive days yielded, on average, several hundred picograms of heterologous proinsulin per milliliter of serum. In BALB/c mice, serum proinsulin peaked 7-14 days postinjection and declined to preinjection levels by days 21-28. In athymic nude mice, serum proinsulin was sustained for at least 6 weeks. The therapeutic efficacy of delivering insulin via muscle injection of pDNA was evaluated in athymic nude mice made diabetic with the beta cell toxin streptozotocin (STZ). All animals given control DNA died within 1 week of receiving STZ while 40% of the mice coinjected with plasmids VR-3503 and VR-3505 lived through the duration of the 4-week experiment. Muscles of the surviving animals contained 17-100 ng of immune-reactive insulin (IRI), 86-94% of which was mature insulin. The results suggest that heterologous insulin made in muscle increased the survival rate. We propose that insulin plasmid expression in skeletal muscle may be a valid approach to basal insulin delivery. The feasibility of plasmid DNA-based delivery of basal insulin was investigated. An expression system consisting of pDNAs encoding a selectively mutated rat preproinsulin and mouse furin was developed and characterized in vitro and in vivo. When injected with preproinsulin pDNA, the mouse tibialis anterior muscle expressed and released proinsulin into serum at levels comparable to normal basal insulin in rodents. These heterologous proinsulin levels were sustained for several weeks in immune-compromised nondiabetic mice. Mouse muscle coinjected with a pDNA encoding the endopeptidase furin and a pDNA encoding a pre-proinsulin modified to contain two furin cleavage sites produced fully processed insulin. This muscle-made insulin appears to have contributed to the survival of mice treated with a highly diabetogenic dose of streptozotocin, a beta cell toxin. The results demonstrate that skeletal muscle is able to express and deliver therapeutic insulin from plasmid DNA.