Effects of Linagliptin on Pancreatic α Cells of Type 1 Diabetic Mice.

The dipeptidyl peptidase-4 inhibitor linagliptin promotes ß-cell survival and insulin secretion by prolonging endogenous glucagon-like peptide 1 (GLP-1) action and therefore helps to maintain normoglycemia in diabetic patients. The effect of linagliptin on glucagon-producing α cells, however, was not clear. In this study, we investigated whether linagliptin had any effects on α cells with regard to their proliferation and hormonal production using type 1 diabetes mouse models, including streptozotocin-induced and nonobese diabetes mice. After diabetes development, the mice were either untreated or treated with linagliptin or insulin for up to 6 weeks. Our results showed that linagliptin significantly increased circulating GLP-1 levels in both type 1 diabetes models, but therapeutic benefit was detected in nonobese diabetes mice only. Circulating C-peptide and glucagon levels (nonfasting) were not significantly altered by linagliptin treatment in either model. In addition, we found that linagliptin did not increase α-cell proliferation compared with the untreated or insulin-treated controls as assessed by in vivo 5-bromo-2'-deoxyuridine labeling assay. Finally, we examined whether linagliptin treatment altered GLP-1 vs glucagon expression in pancreatic α cells. Immunohistochemistry assays showed that linagliptin treatment resulted in detection of GLP-1 in more α cells than in control groups, suggesting linagliptin was able to increase intraislet GLP-1 presence, presumably by inhibiting GLP-1 degradation. In summary, this study indicates that linagliptin would not confer adverse effect on α cells, such as causing α cell hyperplasia, and instead may facilitate a blood glucose-lowering effect by increasing GLP-1 presence in α cells.

Differential Effects of Linagliptin on the Function of Human Islets Isolated from Non-diabetic and Diabetic Donors.

Linagliptin is a dipeptidyl Peptidase-4 (DPP-4) inhibitor that inhibits the degradation of glucagon-like peptide 1 (GLP-1), and has been approved for the treatment of type 2 diabetes (T2D) in clinic. Previous studies have shown linagliptin improves ß cell function using animal models and isolated islets from normal subjects. Since ß cell dysfunction occurs during diabetes development, it was not clear how human islets of T2D patients would respond to linagliptin treatment. Therefore, in this study we employed human islets isolated from donors with and without T2D and evaluated how they responded to linagliptin treatment. Our data showed that linagliptin significantly improved glucose-stimulated insulin secretion for both non-diabetic and diabetic human islets, but its effectiveness on T2D islets was lower than on normal islets. The differential effects were attributed to reduced GLP-1 receptor expression in diabetic islets. In addition, linagliptin treatment increased the relative GLP-1 vs glucagon production in both non-diabetic and diabetic islets, suggesting a positive role of linagliptin in modulating α cell function to restore normoglycemia. Our study indicated that, from the standpoint of islet cell function, linagliptin would be more effective in treating early-stage diabetic patients before they develop severe ß cell dysfunction.

What Are We Learning from the FDA-Mandated Cardiovascular Outcome Studies for New Pharmacological Antidiabetic Agents?

Cardiovascular disease (CVD) is common in patients with diabetes. For these patients, clinicians should seek diabetes treatment that is beneficial rather than harmful in relation to CVD. Until recently, there have been many treatments for hyperglycemia, whose impact on CVD has been controversial. The aims of this review are to evaluate the effectiveness of antihyperglycemic medications on risk factors for CVD and to examine the impact of these drugs on CVD in cardiovascular (CV) outcome trials. In this article, we summarize current knowledge about the impacts of these drugs on various risk factors as well as CV outcomes. We identify the recent emergence of trials with antihyperglycemic agents showing newly discovered CV benefits as well as past trials with antihyperglycemic agents not showing much benefit on CV events. Rather than focusing on treatment strategies, we review the effects of individual drug classes on CV outcomes. We also briefly review goal-driven glycemia reduction and its impact on CVD. We conclude that antihyperglycemic agents are associated with improvement in CV risk factors in patients with diabetes and insulin resistance; in fact, a few drugs reduced CV events in randomized CV outcome trials. Therefore, the use of these drugs is appropriate for reducing glucose and decreasing CV event risk in a select subpopulation.