Inhibition of the Renin- Angiotensin System Affects Kidney Tissue Oxygenation Evaluated by Magnetic Resonance Imaging in Patients With Chronic Kidney Disease

Imaging of the kidney using blood oxygen level dependent (BOLD) magnetic resonance imaging (MRI) presents a major opportunity to examine differences in tissue oxygenation within the cortex and medulla applicable to human disease. The aim of this study was to evaluate BOLD signals before and after treatment with RAS inhibitors in hypertensive chronic kidney disease (CKD) patients. Ten patients with stable CKD and 5 healthy volunteers were included. Five CKD patients were subjected to BOLD MRI scan before and after chronic treatment with 300 mg/day aliskiren for at least 6 weeks. Five other CKD patients received BOLD MRI before and 1 hour after acute treatment with 50 mg captopril. A group of healthy volunteers (n=5) was scanned before and 1 hour after acute treatment with 50 mg captopril. The 10 patients had a mean age of 61 +/- 17 years; eGFR of 30 +/- 11 mL/min per 1.73 m(2). Office systolic and diastolic blood pressures when on a RAS inhibito, were 130 +/- 10 and 86 +/- 5 mmHg in CKD patients. Control subjects had normal kidney function and were not on any medication. In untreated condition, systolic and diastolic arterial blood pressure elevated, 145 +/- 6 and 95 +/- 4 mmHg, respectively. After chronic treatment with aliskiren, arterial blood pressure decreased in all patients in this group, 127 +/- 3 mmHg and 77 +/- 3 mmHg. After acute treatment with captopril arterial blood pressure reduced to 125 +/- 4 and 71 +/- 8 mmHg. Tissue intensity signal (T2*) was increased in medulla after chronic treatment from 29 +/- 6 to 34 +/- 6 and after acute treatment with captopril from 34 +/- 9 to 38 +/- 11 in CKD patients. In addition, T2* ratio between cortex and medulla decreased in CKD patients after chronic treatment and acute treatment. This ratio remained stable in healthy volunteers before and after treatment with captopril 1.62 +/- 0.1 and 1.65 +/- 0.1, respectively. This study shows for the first time that RAS inhibitors change BOLD signal in CKD patients. Importantly, in healthy volunteers, a RAS inhibitor had no such effect. Further investigation is required.