One year of sitagliptin treatment protects against islet amyloid-associated β-cell loss and does not induce pancreatitis or pancreatic neoplasia in mice

Abstract

The dipeptidyl peptidase-4 (DPP-4) inhibitor sitagliptin is an attractive therapy for diabetes, as it increases insulin release and may preserve β-cell mass. However, sitagliptin also increases β-cell release of human islet amyloid polypeptide (hIAPP), the peptide component of islet amyloid, which is cosecreted with insulin. Thus, sitagliptin treatment may promote islet amyloid formation and its associated β-cell toxicity. Conversely, metformin treatment decreases islet amyloid formation by decreasing β-cell secretory demand and could therefore offset sitagliptin's potential proamyloidogenic effects. Sitagliptin treatment has also been reported to be detrimental to the exocrine pancreas. We investigated whether long-term sitagliptin treatment, alone or with metformin, increased islet amyloid deposition and β-cell toxicity and induced pancreatic ductal proliferation, pancreatitis, and/or pancreatic metaplasia/neoplasia. hIAPP transgenic and nontransgenic littermates were followed for 1 yr on no treatment, sitagliptin, metformin, or the combination. Islet amyloid deposition, β-cell mass, insulin release, and measures of exocrine pancreas pathology were determined. Relative to untreated mice, sitagliptin treatment did not increase amyloid deposition, despite increasing hIAPP release, and prevented amyloid-induced β-cell loss. Metformin treatment alone or with sitagliptin decreased islet amyloid deposition to a similar extent vs untreated mice. Ductal proliferation was not altered among treatment groups, and no evidence of pancreatitis, ductal metaplasia, or neoplasia were observed. Therefore, long-term sitagliptin treatment stimulates β-cell secretion without increasing amyloid formation and protects against amyloid-induced β-cell loss. This suggests a novel effect of sitagliptin to protect the β-cell in type 2 diabetes that appears to occur without adverse effects on the exocrine pancreas.

Keywords: DPP-4 inhibitor; IAPP; amyloid; exocrine pancreas pathology; β-cell mass.

Fig. 1.

Body weight (A; n = 18–24) throughout the study in human islet amyloid polypeptide (hIAPP) transgenic (T; filled symbols) and nontransgenic (NT; open symbols) mice following 1 yr of no treatment (No R_x; squares) or treatment with sitagliptin (SIT; circles), metformin (MET; triangles), or sitagliptin + metformin (S+M; crosses), ANOVA P < 0.001. Food intake at 0, 3, 6, 9, and 12 mo of treatment (B; n = 4–13 cages, 8–35 mice, ANOVA P < 0.001), ambulatory activity (C; n = 4–7, ANOVA P < 0.01), and oxygen consumption (D; n = 4–7, ANOVA P < 0.001) after 17 wk of treatment. B–D: No R_x, filled bars; SIT, open bars; MET, light gray bars; S+M, dark gray bars. *P < 0.05 vs. No R_x. In A, for all treatment groups, all points between parentheses are significantly different from the corresponding time point for No R_x.

Fig. 2.

Inverse incremental AUC glucose during an ip insulin tolerance test (ANOVA P < 0.01) in hIAPP transgenic (filled bars) and nontransgenic mice (open bars). Mice were No R_x or treated with SIT, MET, or S+M for 1 yr; n = 4–7. *P < 0.05 vs. No R_x.

Fig. 3.

Plasma glucose levels (A), rate of glucose disappearance (K_g; inset in A, ANOVA P < 0.001), plasma insulin levels (B), and the acute insulin response to glucose (AIRg, inset in B, ANOVA P < 0.001) during an iv glucose tolerance test in hIAPP transgenic (T; filled symbols) and nontransgenic mice (NT; open symbols). Mice were No R_x (squares) or treated with SIT (circles), MET (triangles), or S+M (crosses) for 1 yr; n = 10–18. *P < 0.05 vs. No R_x; †P < 0.05 vs. NT.

Fig. 4.

A: representative photomicrographs of pancreas sections showing amyloid deposits (green) and insulin immunostaining (red). B: amyloid deposition in hIAPP transgenic mice (ANOVA P = 0.01). Nontransgenic mice did not develop any islet amyloid, as expected; thus, amyloid data are not shown for those groups. C: β-cell mass (ANOVA P < 0.001) in hIAPP transgenic (filled bars) and nontransgenic mice (open bars). Pancreata were analyzed following 1 yr of No R_x or treatment with SIT, MET, or S+M; n = 10–21. Scale bar, 100 μm. *P < 0.05 vs. No R_x; †P < 0.05 vs. NT.

Fig. 5.

Ductal proliferation in hIAPP transgenic (filled symbols) and nontransgenic mice (open symbols). Mice were No R_x or treated with SIT, MET, or S+M for 1 yr; n = 10–15, ANOVA P = 0.18. Individual points (circles) represent data for each mouse, with mean ± interquartile range for each group also depicted (lines).

Fig. 6.

Percentage of mice with exocrine pancreas pathology, assessed as ductal abnormalities (A), hemorrhage (B), fibrosis (C, P = 0.4), inflammatory cell infiltration (D, P = 0.3), and necrosis (E, P = 0.4) in hIAPP transgenic and nontransgenic mice. Mice were No R_x or treated with SIT, MET, or S+M for 1 yr; n = 10–21. Absence of abnormalities is denoted by open bars, with mild abnormalities shown in gray hatched bars and moderate abnormalities shown in filled bars. Note: no mice exhibited any severe abnormalities.