Therapeutic Approaches to Preserve Islet Mass in Type 2 Diabetes

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Abstract
Type 2 diabetes is characterized by hyperglycemia resulting from insulin resistance in the setting of inadequate β-cell compensation. Currently available therapeutic agents lower blood glucose through multiple mechanisms but do not directly reverse the decline in β-cell mass. Glucagon-like peptide-1 (GLP-1) receptor agonists, exemplified by Exenatide (exendin-4), not only acutely lower blood glucose but also engage signaling pathways in the islet β-cell that lead to stimulation of β-cell replication and inhibition of β-cell apoptosis. Similarly, glucose-dependent insulinotropic polypeptide (GIP) receptor activation stimulates insulin secretion, enhances β-cell proliferation, and reduces apoptosis. Moreover, potentiation of the endogenous postprandial levels of GLP-1 and GIP via inhibition of dipeptidyl peptidase-IV (DPP-IV) also expands β-cell mass via related mechanisms. The thiazolidinediones (TZDs) enhance insulin sensitivity, reduce blood glucose levels, and also preserve β-cell mass, although it remains unclear whether TZDs affect β-cell mass via direct mechanisms. Complementary approaches to regeneration of β-cell mass involve combinations of factors, exemplified by epidermal growth factor and gastrin, which promote islet neogenesis and ameliorate diabetes in rodent studies. Considerable preclinical data support the concept that one or more of these therapeutic approaches, alone or in combination, may potentially reverse the decline in β-cell mass that is characteristic of the natural history of type 2 diabetes.