In this randomized controlled crossover study, the investigators propose to test the hypothesis that proton pump inhibitors (PPIs) increase plasma levels of asymmetric dimethylarginine (ADMA), which is a marker of endothelial dysfunction. The authors propose to evaluate ADMA concentrations and vascular function analysis in healthy volunteers and adults with a history of cardiovascular disease given PPI vs placebo for four weeks each.

Inclusion Criteria:

• Healthy male or female volunteers aged 18 to 75 years (n=10) or male or female volunteers with a history of coronary or peripheral artery disease (n=10)
• Able to understand the nature of the study and to give written informed consent
• Able to communicate well with the investigator himself or his/her representatives
• Body Mass Index between 18 kg/m^2 and 35 kg/m^2 at the screening visit
• Creatinine <1.5, and liver enzymes <2x normal, with all laboratory tests considered normal or of no significant clinical relevance to the study by the investigator

Exclusion Criteria:

• Contra-indication to proton pump inhibitor treatment
• Current treatment with PPI or H2 antagonist, and not able to tolerate withdrawal or washout of medication.
• Current or historical evidence of clinically severe cardiovascular, neurological, hematological, hepatic, gastrointestinal, renal, pulmonary, endocrinological, metabolic or psychiatric disease.
• Any other acute or chronic disease which could influence the volunteer's health and/or the study results
• Presence or history of malabsorption or any gastrointestinal surgery except appendectomy or hernia repair
• Use of enzyme inducers or enzyme inhibitor drugs within the last three months before the first drug administration
• Participation in another ongoing clinical trial
• Past or current drug exposure amounting to drug abuse or addiction
• Past or current alcohol exposure amounting to alcohol abuse or addiction (i.e. > 28 units per week for males, where 1 unit = one measure of spirit (25 mL), one glass of wine (125 mL) or 1/2 pint beer)
• Donation of blood or any other major blood loss (>500 mL) within three months before the study
• Unwilling or unable to comply with the study protocol for any reason or in the opinion of the investigator should not participate in the study
• Positive test for hepatitis B surface antigen, hepatitis C antibody, HIV-1 or HIV-2 antibody at screening
• Known allergy or intolerance to any other compound in the study drug or any other closely related compound