Type 2 diabetes is associated with chronic sterile low-grade inflammation, usually caused by hyperglycemia and associated biochemical abnormalities, as well as by overweight/obesity. The co-existence of chronic renal failure further exacerbates inflammation in diabetic patients, and this contributes to the exceedingly high morbidity and mortality of this category of patients. One key element of this type of inflammation is the pro- versus anti-inflammatory polarization of circulating monocytes and tissue macrophages. Diabetes indeed causes an imbalance of this polarization, in favour of the pro-inflammatory (M1) monocytes at the expenses of anti-inflammatory (M2) monocytes. Cells belonging to the monocyte/macrophage lineage are of great importance in diabetes pathophysiology, as they are involved in atherosclerosis and adipose tissue biology, both of which determine diabetes outcomes. It is recognized that M1/M2 polarization relies on the expression of chemokines/cytokines and their respective receptors. Interestingly, among non-incretin substrates of DPP-4 are several chemokines (e.g. MCP-1 and -2, RANTES and SDF-1a), which may regulate M1/M2 polarization. Linagliptin (terminal half-life \>100 hours, and effective half-life for accumulation approximately 12 hours) can be safely used in type 2 diabetic patients with renal impairment without dose adjusting, because the drug is excreted \>90% with feces and has a minor renal excretion. The possibility to modulate the M1/M2 inflammatory pathway with the DPP-4 inhibitor linagliptin entails a hitherto unappreciated opportunity for protecting diabetic patients with renal disease from the detrimental consequences of chronic inflammation on vascular and adipose tissue biology. We have set up a protocol to assess M1/M2 polarization of circulating monocyte/macrophage cells by flow cytometry. Our preliminary data indicate that diabetes is associated with an imbalance in M1/M2 polarization versus non diabetic controls, in favour of M1 cells in diabetic patients. Hyperglycemia per se may affect M1/M2 polarization and it is expected that any effect of linagliptin on monocytes can be detected as soon as DPP-4 inhibition reaches steady-state. Therefore, in order to provide a proof-of-concept for the effect of linagliptin on M1/M2 polarization and to avoid the confounding of improved glucose control, the time point of the study will be very short (4 days). Our preliminary data in cell cultures indicate that a few days of treatment with a stimulus is sufficient to modulate monocyte/macrophage polarization. This will provide valuable information on the direct effects of the drug on this inflammatory pathway.

Endothelial progenitor cells (EPCs) are vasculoprotective cells released from the bone marrow (BM) in response to ischemia, hypoxia and tissue injury. Once in the bloodstream, EPCs home to damaged tissues and help restoring a healthy and functional vasculature, by means of endothelial repair and angiogenesis. In steady-state conditions, CD34+KDR+ EPCs circulate in peripheral blood (PB) at very low levels and their release from the BM is coordinated by the sympathetic nervous system. It has been demonstrated that levels of EPC and generic CD34+ PC are predictors of future cardiovascular events, cardiovascular death and all-cause mortality. We have previously shown that Sitagliptin raised EPCs levels in 4 weeks. Herein, we aim to confirm those findings using Linagliptin, with a shorter time point.