Diabetes mellitus is characterized by changes in endothelial cells that alter monocyte recruitment, increase classic (M1-type) tissue macrophage infiltration and lead to self-sustained inflammation. Our and other groups recently showed that chronic inhibition of phosphodiesterase-5 (PDE5i) affects circulating cytokine levels in patients with diabetes; whether PDE5i also affects circulating monocytes and tissue inflammatory cell infiltration remains to be established. Using murine streptozotocin (STZ)-induced diabetes and in human vitro cell-cell adhesion models we show that chronic hyperglycemia induces changes in myeloid and endothelial cells that alter monocyte recruitment and lead to self-sustained inflammation. Continuous PDE5i with sildenafil (SILD) expanded tissue anti-inflammatory TIE2-expressing monocytes (TEMs), which are known to limit inflammation and promote tissue repair. Specifically, SILD: 1) normalizes the frequency of circulating pro-inflammatory monocytes triggered by hyperglycemia (53.7 ± 7.9% of CD11b+Gr-1+ cells in STZ vs. 30.4 ± 8.3% in STZ+SILD and 27.1 ± 1.6% in CTRL, P<0.01); 2) prevents STZ-induced tissue inflammatory infiltration (4-fold increase in F4/80+ macrophages in diabetic vs. control mice) by increasing renal and heart anti-inflammatory TEMs (30.9 ± 3.6% in STZ+SILD vs. 6.9 ± 2.7% in STZ, P <0.01, and 11.6 ± 2.9% in CTRL mice); 3) reduces vascular inflammatory proteins (iNOS, COX2, VCAM-1) promoting tissue protection; 4) lowers monocyte adhesion to human endothelial cells in vitro through the TIE2 receptor. All these changes occurred independently from changes of glycemic status. In summary, we demonstrate that circulating renal and cardiac TEMs are defective in chronic hyperglycemia and that SILD normalizes their levels by facilitating the shift from classic (M1-like) to alternative (M2-like)/TEM macrophage polarization. Restoration of tissue TEMs with PDE5i could represent an additional pharmacological tool to prevent end-organ diabetic complications.

Diabetic Nephropathy (DN) is the leading cause of end-stage renal disease. Preclinical and experimental studies show that PDE5 inhibitors (PDE5is) exert protective effects in DN improving perivascular inflammation. Using a mouse model of diabetic kidney injury we investigated the protective proprieties of PDE5is on renal hemodynamics and the molecular mechanisms involved. PDE5i treatment prevented the development of DN-related hypertension (P < 0.001), the increase of urine albumin creatinine ratio (P < 0.01), the fall in glomerular filtration rate (P < 0.001), and improved renal resistive index (P < 0.001) and kidney microcirculation. Moreover PDE5i attenuated the rise of nephropathy biomarkers, soluble urokinase-type plasminogen activator receptor, suPAR and neutrophil gelatinase-associated lipocalin, NGAL. In treated animals, blood vessel perfusion was improved and vascular leakage reduced, suggesting preserved renal endothelium integrity, as confirmed by higher capillary density, number of CD31+ cells and pericyte coverage. Analysis of the mechanisms involved revealed the induction of bone morphogenetic protein-7 (BMP7) expression, a critical regulator of angiogenesis and kidney homeostasis, through a PDE5i-dependent downregulation of miR-22. In conclusion PDE5i slows the progression of DN in mice, improving hemodynamic parameters and vessel integrity. Regulation of miR-22/BMP7, an unknown mechanism of PDE5is in nephrovascular protection, might represent a novel therapeutic option for treatment of diabetic complications.

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