Effect of Linagliptin in Comparison With Glimepiride as Add on to Metformin on Postprandial Beta Cell Function, Postprandial Metabolism and Oxidative Stress in Patients With Type 2 Diabetes Mellitus

Inclusion Criteria: 1. Diabetes mellitus type 2 2. HbA1c \> 6.5% - ≤ 8.5% 3. HbA1c \> 7.0% - ≤ 8.5% for those patients with a significant cardiovascular history 4. Treatment with metformin at a maximum tolerated dose 5. Age 45 - 75 years (inclusively) 6. Patient consents that his/her family physician/diabetologist will be informed of trial participation. Exclusion Criteria: 1. Pretreatment with PPAR gamma agonists within the last three months 2. History of type 1 diabetes 3. Uncontrolled hypertension (systolic blood pressure \>160 mmHg and/or diastolic blood pressure \>90 mmHg) 4. Acute infections 5. Medical history of hypersensitivity to the study drugs or to drugs with similar chemical structures 6. History of severe or multiple allergies 7. Treatment with any other investigational drug within 3 months before trial entry. 8. Progressive fatal disease 9. History of drug or alcohol abuse in the past 2 years 10. State after kidney transplantation 11. Serum potassium \> 5.5 mmol/L 12. Pregnancy or breast feeding 13. Sexually active woman of childbearing age not practicing a highly effective method of birth control as defined as those which result in a low failure rate (i.e. less than 1% per year) when used consistently and correctly such as implants, injectables, combined oral contraceptives, hormonal IUDs, sexual abstinence or vasectomized partner. 14. Acute myocardial infarction, open heart surgery or cerebral event (stroke/TIA) within the previous 30 days 15. Any elective surgery during study participation 16. Have had more than one unexplained episode of severe hypoglycemia (defined as requiring assistance of another person due to disabling hypoglycemia) within 6 months prior to screening visit 17. History of pancreatitis 18. History of dehydration, pre-coma diabeticum or diabetic ketoacidosis 19. Acute or scheduled investigation with iodine containing radiopaque material 20. Uncontrolled unstable angina pectoris 21. History of pericarditis, myocarditis, endocarditis 22. Recent pulmonary embolism 23. Hemodynamic relevant aortic stenosis 24. Aortic aneurysm 25. Regular use of NSAID's (no acute use of NSAID within 48 hours before V2,V4,V5) 26. Lack of compliance or other similar reason that, according to investigator, precludes satisfactory participation in the study 27. History of respiratory, gastrointestinal, hepatic (ALAT and/or ASAT \> 3 times the normal reference range), renal (Creatinine \> 1.1 mg/dl in women and \> 1.5 mg/dl in men ), neurological, psychiatric and/or hematological disease as judged by the investigator 28. Lactose intolerance 29. Intake of Coumarin or coumarin derived compounds such as phenprocoumon (Marcumar) or warfarin (Coumadin, Warfant)