Evaluation Of Early Renal Impairment In Diabetic Rats Using Blood Oxygen Level-Dependent MRI

[Background and Aims]Diabetic nephropathy (DN) is one of the major microvascular complications of diabetes and the most common cause of end stage of renal diseases(ESRD). There is increasing evidence suggestingan association between chronic renal hypoxia and the development and progression of diabetic nephropathy. At the onset of diabetes mellitus, the intrarenal hemodynamic abnormalities manifest in the form of glomerular hyperfiltration and high oxygen consumption and may be the factors that are responsible for the onset and progression of DN. In order to slow down or even stop the progress of diabetic nephropathy, it is important to be able to monitoring early changes in renal oxygenation noninvasively.Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) is a promising technique that has the potential to noninvasively measure intrarenal oxygenation by using deoxyhemoglobin as an endogenous contrast agent. The purpose of this study was to investigate the oxygen saturation of diabetic kidney detecting early renal impairment in diabetic rats by BOLD MRI.[Objects and Methods]Forty SD rats were randomly divided to2groups:normal control group(group NC), diabetic mellitus group (group DM). Rats of group DM were given streptozocin(STZ) by intraperitoneal injection to establish animal model of diabetes,rats of group NC were given citrate-trisodium citrate buffer by intraperitoneal injection. Kidney BOLD MRI studies were performed respectively at3,7,14,21,28,35,42,49,56,63and70days after induction of diabetes and before modeling, scanning sequence includes axial T2WI, T1WI and coronal BOLD MRI, BOLD MRI was obtained by an8echoes fast spoiled gradient echo sequence. All data were transferred to GE ADW4.4workstations, regions of interest were placed in both cortex and outer medulla to measure R2*values using the renal hilum slice, comparative analysis will be made between two groups. Urine samples were obtained to measure urinary albumin one day before the MRI scanning, determination of urinary albumin excretion by rate nephelometry.[Results]1. The rats of group DM show signs of increased urine output, sparse and fragile fur, blood glucose increased significantly and sustained at high level. The body weight of group DM showed increase slowly or decrease in the mean value after the induction of diabetes, the difference compared with group NC were significantly different (P<0.001).2. Urinary albumin excretion of group DM was markedly increased since the second week, difference compared with group NC were significantly (P<0.01or P<0.001).3. R2*values in cortex and outer medulla of group DM show significant difference compared to NC groups(P<0.01or P<0.001)after DM model rats were established; R2*value in cortex and outer medulla of the DM group was gradually increased in initial weeks, especially in the outer medulla. R2*values decreased starting from the forty-second day, but still higher than NC group.4. Transmission electron microscopy revealed podocyte structural integrity in group NC, foot process neat and clear; compared with group NC, group DM foot process partial fusion, glomerular basal membrane was homogeneous shape, mesangial matrix increase.[Conclusion]1. The renal impairment occurred in diabetic rat mode at hyperglycemia state were accordance with pathological changes in renal tissue damage of DN.2. R2*values in cortex and outer medulla of group DM were higher than group NC, which indicate the oxygen concentration in cortex and outer medulla of group DM is lower than group NC.3. BOLD MRI proved to be a noninvasive method for the early detection and dynamic monitoring of renal oxygenation changes in diabetic kidney. So BOLD MRI could provide more complementary information for treatment and prognostic assessment.4. The technique of BOLD MRI can detect renal impairment in diabetes earlier than the urinary albumin excretion examination.