The main aim of this project is to demonstrate an association between gut and oral microbiota and their metabolites to carotid atherosclerosis and risk of ischemic stroke.

The investigators aim to show that these metabolite levels are diet-dependent (mainly egg yalk and red meat) and associated with specific types of microbiota.

The investigators to assess serum microbiota metabolite levels as a predictor of stroke and plaque progression for patients with carotid atherosclerosis.

The Project will include four studies:

Study 1: (Comparative cross-sectional study) The main objective in this study is to assess if patients with carotid atherosclerosis have increased serum levels gut microbiota dependent metabolites compared to healthy controls.

This study will be done on prospectively collected information already available in our existing database. Approximately 215 patients will be included in this study where collected samples will be analyzed and levels of metabolites quantified. These metabolite levels will be compared to a control group of 70 healthy controls without carotid atherosclerosis (verified by ultrasound), cardiovascular outcome defined as stroke/TIA or vascular death, as well as traditional risk factors for ischemic stroke (diabetes, hypertension, smoking and coronary artery disease).

Study 2: (Comparative cross-sectional study) The aim of this study is to asses if microbiota and microbiota metabolite Levels are Associated With certain types of diet, in particular Rich in red meat and egg yalk.

In this study, 215 patients with ultrasound verified carotid atherosclerosis with or without symptoms of TIA/stroke will be compared to 70 controls. Dietary intake and food habits will be recorded using the SmartDiet questionnaire developed by 'Lipidklinikken Rikshospitalet'. Feces, saliva and blood will be collected analyzed for microbiota and metabolites. Antroprometrics, blood pressure and pulse will be recorded.

In patients undergoing carotid endarterectomy and immunohistochemical analysis will be done.

Study 3: (Comparative cross-sectional study) The aim of this study is to evaluate correlation between the microbiota and microbiota metabolite Levels With other inflammatory markers in blood, as well as known risk factors for stroke and inflammation on imaging modalities (ultrasound, 3-T MRI and PET/CT) .

In this study, 215 patients with ultrasound verified carotid atherosclerosis with or without symptoms of TIA/stroke will be compared to 70 controls.

Patients will undergo investigations with carotid ultrasound, carotid and cerebral MR imaging, blood tests including inflammatory biomarkers. A sub-group of patients will in addition undergo PET/CT imaging of carotid arteries.

Study 4: (Follow up study) The aim of this study is to evaluate the ability of microbiota and microbiota metabolites to predict ischemic stroke in patient With carotid stenosis.

Patients in study 2 and 3 will be followed up after 2 years with repetition of investigations. Findings with serum levels of microbiota metabolites, traditional risk factors and imaging will be correlated to clinical and radiological ischemic events and plaque progression.

Inclusion Criteria:

- patients >18 years with an symptomatic og asymptomatic atherosclerotic carotid stenosis ≥ 50% (NASCET criteria)

Exclusion Criteria:

• active infection
• current antibiotic treatment
• autoimmune or autoinflammatory disease
• malignancies

- All patients >18 years with an atherosclerotic carotid stenosis ≥ 50% admitting our department (Dep of Neurology, Rikshospitalet, OUH) as in-patient or out-patient will consecutively be considered for inclusion.

Cooperation With Dep of vascular surgery Akershus University Hospital and Dep of vascular surgery, Aker, OUH, for patients scheduled for thrombendarterectomy.

- Control Group: For study 1: Healthy volonteers For study 2 and 3: Spouses/partners where possible, otherwise matched for age and sex