No evidence of drug-induced pancreatitis in rats treated with exenatide for 13 weeks

Abstract

Aims: The potential association of glucagon-like peptide receptor agonists (GLP-1RAs) with the development of pancreatitis or pancreatic malignancies in patients with diabetes has been suggested. This study evaluated the long-term effects of the GLP-1RA exenatide on pancreatic exocrine structure and function in the Zucker diabetic fatty (ZDF) rat model of type 2 diabetes.

Methods: Rats received subcutaneous twice-daily injections of 0 (control), 6, 40 and 250 µg/kg/day exenatide for 3 months. Clinical signs, body and pancreas weight, food consumption, HbA1c, fasting serum amylase, lipase, glucose and insulin concentrations were evaluated during treatment and after a 28-day off-drug period to assess the reversibility of any observed effects. Morphometric analysis of pancreatic ductal cell proliferation and apoptosis were performed.

Results: Plasma exenatide concentrations were several-fold higher than therapeutic levels observed in humans. No exenatide-related effects were observed on clinical signs, lipase concentration, pancreatic weight, pancreatic histology, ductal cell proliferation or apoptosis. Exenatide improved animal survival, physical condition, glucose concentrations and HbA1c, decreased food intake, and increased serum insulin concentration. Total amylase concentrations, although within normal ranges, were slightly higher in exenatide-treated rats; following the off-drug period, total amylase concentrations were comparable in treated and untreated rats. Exenatide-related minimal-to-moderate islet hypertrophy was observed at doses ≥6 µg/kg/day, with dose-related increases in incidence and degree. These changes were still present after the off-drug period.

Conclusions: Chronic administration of exenatide in ZDF rats resulted in the expected metabolic benefits and improved animal survival, with no adverse effects noted on pancreatic exocrine structure and function.

Figure 1

Time course of (A) body weight and (B) food intake changes in ZDF rats dosed subcutaneously with twice daily exenatide (6, 40 and 250 µg/kg/day) or vehicle injections for 3 months followed by a 1-month recovery period without treatment. *p < 0.05 exenatide at 40 and 250 µg/kg/day, **p < 0.05 all exenatide groups, respectively, versus vehicle control. (C) Terminal pancreatic weight normalized to body weight, *p < 0.05 all exenatide groups versus vehicle control.

Figure 2

Time course of (A) HbA1c and (B) serum fasting glucose in ZDF rats dosed subcutaneously with twice daily exenatide (6, 40 and 250 µg/kg/day) or vehicle injections for 3 months followed by a 1-month recovery period without treatment. *p < 0.05 all exenatide groups, **p < 0.05 exenatide at 6 and 40 µg/kg/day, respectively, versus vehicle control. (C) Time course of serum fasting insulin in diabetic ZDF rats dosed subcutaneously with twice daily exenatide (6, 40 and 250 µg/kg/day) or vehicle injections for 3 months followed by a 1-month recovery period without treatment. *p < 0.05 all exenatide groups. (D) Exenatide improved survival of ZDF rats dosed subcutaneously twice daily at 6, 40 and 250 µg/kg/day for 3 months in comparison to control untreated group, *p < 0.001.

Figure 3

Effects of exenatide on (A) serum fasting amylase and (B) lipase in ZDF rats dosed subcutaneously twice daily at 6, 40 and 250 µg/kg/day or with vehicle for 3 months followed by a 1-month recovery period without treatment. *p < 0.05 all exenatide groups, **p < 0.05 exenatide at 250 µg/kg/day, #p < 0.05 exenatide at 40 and 250, respectively, versus vehicle control.

Figure 4

Plasma exenatide exposure in ZDF rats dosed subcutaneously twice daily at 6, 40 and 250 µg/kg/day or with vehicle for 3 months. (A) Peak plasma exenatide concentrations (C_max) and (B) calculated AUC_[0–∞]. Dotted horizontal lines represent mean values observed in patients with type 2 diabetes mellitus treated with the standard exenatide regimen: C_max = 0.211 ng/ml and AUC_[0–∞] = 1.036 ng/h/ml.

Figure 5

Ki-67 expression in the pancreatic ductal cells was examined after vehicle (A) or exenatide 6 µg/kg/day (B), 40 µg/kg/day (C) or 250 µg/kg/day (D) treatments. Ki-67-positively stained nuclei (black arrow head) were rarely seen in the pancreatic ductal cells, identified via immunocytochemical staining with CK-20 (purple) or other regions of the pancreas (blue arrow heads). Scale bar, 50 µm. Exenatide did not have any effect on the proliferation of pancreatic ductal cells in diabetic ZDF rats.