Effect of Vildagliptin vs. Glibenclamide on Circulating Endothelial Progenitor Cell Number Type 2 Diabetes

Inclusion Criteria: * Age equal or above 35 years; * Diagnosis of type 2 diabetes mellitus as defined by the American Diabetes Association , with at least one year of disease duration at the time of the screening visit; * Blood glucose lowering treatment with Metformin alone (monotherapy) at a stable dose of at least 1.5 g/day (or maximum tolerated dose) in the 3 months prior to the screening visit; * Insufficient metabolic control as defined by recent (last six months) HbA1c ≥ 7% in any peripheral laboratory and confirmed at the time of the screening; * Absence of a recent clinically-relevant progression of micro- and macro-vascular complications (see exclusion criteria); * Written informed consent to participate to the study. Exclusion criteria: * Age below 35 years * Type 1 diabetes or other causes of diabetes (pancreatectomy, gestational diabetes, etc.) * HbA1c \< 7% or ≥ 9% at the screening visit * Treatment with any blood glucose lowering treatment other than Metformin in the six months before screening visit * BMI \< 20 or ≥ 40 kg/m2, or current/ past history of clinically-relevant eating disorders (including -but no limited to- nervous anorexia, bulimia, binge-eating disorders, etc.) * Significant progression of diabetic macro-angiopathy or cardiovascular disease in the six months prior to study visit * Significant progression of diabetic micro-angiopathy in the six months prior to study visit * Organ failure or other severe diseases limiting life expectancy; * Beginning, in the three months before screening visit, of any kind of drug which can modify glycemic levels (beta-blockers, diuretics…), or acute disease (acute infection, urinary tract infection…) in three months before screening visit * History of inflammatory/infective/autoimmune chronic disease * History of unexplained pancreatitis, chronic pancreatitis, pancreatectomy, gastric surgery, inflammatory bowel disease; * Any clinically significant abnormality identified on physical examination, laboratory tests, ECG or vital signs at screening that in the judgment of the investigator would preclude safe completion of the study; * Uncontrolled or inadequately controlled hypertension at screening (Systolic Blood Pressure (SBP)\>190 or Diastolic Blood Pressure (DBP) \>100 mmHg) * Ongoing pregnancy or absence of effective contraception in women with childbearing potential * Contraindications to the maintenance of the background therapy (Metformin), including -but not limited to- chronic kidney failure or plasma creatinine concentrations \> 1.5 mg/dL, severe respiratory failure, etc.; * Contraindications to the use of a Sulfonylurea; * Contraindications to the use of a DPP-IV Inhibitor; * Laboratory findings, or other disease conditions, at the screening visit that might interfere with study measurements: 1. Hemoglobinopathy known to affect HbA1c assays; 2. Known chronic liver diseases, including HBV (hepatitis B virus) and HCV (hepatitis C virus) infection; 3. Liver makers (aspartate transaminase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), Gamma-glutamyltransferase (GGT) , bilirubin) above 2 times the upper normal limit; 4. Amylase and/or lipase above 2 times the upper normal limit; * Chronic use of systemic and/or inhaled corticosteroids (only topical corticosteroids are allowed); * History of low compliance, clinically-relevant psychiatric disorders or any current/ historical finding suggesting the patient as inappropriate to follow the study procedures.