N-terminally modified glucagon-like peptide-1(7–36) amide exhibits resistance to enzymatic degradation while maintaining its antihyperglycaemic activity in vivo

Abstract

Glucagon-like peptide-1(7–36)amide (tGLP-1) is inactivated by dipeptidyl peptidase (DPP) IV by removal of the NH 2-terminal dipeptide His 7-Ala 8. We examined the degradation of NH 2-terminally modified His 7-glucitol tGLP-1 and its insulin-releasing and antihyperglycaemic activity in vivo. tGLP-1 was degraded by purified DPP IV after 4 h (43% intact) and after 12 h, 89% was converted to GLP-1(9–36)amide. In contrast >99% of His 7-glucitol tGLP-1 remained intact at 12 h. His 7-glucitol tGLP-1 was similarly resistant to plasma degradation in vitro. His 7-glucitol tGLP-1 showed greater resistance to degradation in vivo (92% intact) compared to tGLP-1 (27% intact) 10 min after i.p. administration to Wistar rats. Glucose homeostasis was examined following i.p. injection of both peptides (12 nmol/kg) together with glucose (18 mmol/kg). Plasma glucose concentrations were significantly reduced and insulin concentrations elevated following peptides administration compared with glucose alone. The area under the curve (AUC) for glucose for controls (AUC 691±35 mM/min) was significantly lower after administration of tGLP-1 and His 7-glucitol tGLP-1 (36 and 49% less; AUC 440±40 and 353±31 mM/min, respectively; P<0.01). This was associated with a significantly higher AUC for insulin (98–99% greater; AUC 834±46 and 838±39 ng/ml/min, respectively; P<0.01) after tGLP-1 and His 7-glucitol tGLP-1 administration compared to controls (421±30 ng/ml/min). In conclusion, His 7-glucitol tGLP-1 resists plasma DPP IV degradation while retaining potent antihyperglycaemic and insulin-releasing activities in vivo.