Over time, individuals with type 2 diabetes (T2D) face a gradual decline in β-cell function, often leading to poor glycemic control and increased dependence on medications. The GRADE study offers a unique opportunity to evaluate how different glucose-lowering drugs impact β-cell health over a five-year period.

      This subanalysis of the GRADE trial applied mathematical modeling to OGTT (oral glucose tolerance test) data to explore how four treatments—insulin glargine, glimepiride, liraglutide, and sitagliptin (each added to metformin)—differentially affect components of β-cell function. Parameters included insulin secretion rate (ISR), glucose sensitivity, rate sensitivity, potentiation, and more. These were also assessed for their ability to predict glycemic deterioration.

      Key Findings:

• Liraglutide (a GLP-1 receptor agonist) led to the greatest initial improvements in ISR, glucose sensitivity, and potentiation at year 1. However, these benefits declined by year 3 but remained above baseline through year 5.
• Sitagliptin (a DPP-4 inhibitor) showed modest improvements in glucose sensitivity but notably enhanced rate sensitivity, indicating better early-phase insulin secretion.
• Glimepiride (a sulfonylurea) increased ISR and rate sensitivity in year 1, but glycemic control worsened more rapidly afterward.
• Insulin glargine improved rate sensitivity early on, likely through its glucose-lowering effects, but had minimal impact on other β-cell function parameters.

      Despite treatment-induced improvements in β-cell parameters in year 1, all therapies showed a decline over time. Notably, glucose sensitivity emerged as the strongest predictor of glycemic failure. Individuals with lower glucose sensitivity, ISR, or potentiation were more likely to lose glycemic control.

      Interestingly, while liraglutide led to slower progression to glycemic failure, the statistical models showed that it was the β-cell functional parameters themselves, not the treatment label, that predicted glycemic outcomes—highlighting the central role of β-cell dysfunction in T2D progression.

      This is the first large-scale trial to compare model-based β-cell function measures across commonly used T2D medications. These insights underline the importance of preserving β-cell function—not just lowering A1C—for long-term diabetes management. Liraglutide's robust effect on glucose sensitivity may inform its preferential use in patients at higher risk of glycemic decline, while sitagliptin may still offer early-phase benefits in select populations.