Implanted islet mass influences the effects of dipeptidyl peptidase-IV inhibitor LAF237 on transplantation outcomes in diabetic mice

Abstract Background Previous studies showed inconsistent Results of the effects of dipeptidyl peptidase (DPP)-IV inhibitors on syngeneic mouse islet transplantation. We hypothesized that the implanted islet numbers are critical for the effects of DPP-IV inhibitors on the outcomes of transplantation. Methods One hundred and fifty or three hundred islets were syngeneically transplanted under the renal capsule of each streptozocin-diabetic C57/B6 mouse and recipients were then treated without or with LAF237 (10 mg/kg/day, po) for 6 weeks. After transplantation, recipients’ blood glucose, body weight and intraperitoneal glucose tolerance test (IPGTT) were followed-up periodically. The graft was removed for the measurement of β-cell mass at 6 weeks. Results In recipients with 150 islets, it was not significantly different between the LAF237- treated group (n=14) and control group (n=14) in terms of the blood glucose, body weight, glucose tolerance at 2, 4 and 6 weeks or the graft β-cell mass at 6 weeks. In contrast, in recipients with 300 islets, the LAF237-treated group (n=24) did have a lower area under the curve of the IPGTT at 4 weeks (p = 0.0237) and 6 weeks (p = 0.0113) as well as more graft β-cell mass at 6 weeks (0.655 ± 0.008 mg vs. 0.435 ± 0.006 mg, p=0.0463) than controls (n=24). Conclusions Our findings revealed 6-week treatment of LAF237 improves glucose tolerance and increases graft β-cell mass in diabetic mice transplanted with a sufficient number but not marginal number of islets. These indicate that the effects of DPP-IV inhibitors are influenced by the implanted islet mass.