Investigation of aquaporins and apparent diffusion coefficient from ultra-high b-values in a rat model of diabetic nephropathy

BACKGROUND: To assess kidney damage in a rat model of type-2 diabetic nephropathy based on apparent diffusion coefficient (ADC) data obtained from ultra-high b-values and discuss its relationship to the expression of aquaporins (AQPs). METHODS: This study was approved by the institutional Animal Care and Use Committee. Thirty male Sprague-Dawley rats were randomised into two groups: (1) untreated controls and (2) diabetes mellitus (DM). All rats underwent diffusion-weighted imaging (DWI) with 18 b-values (0–4500 s/mm(2)). Maps of low ADC (ADC(low)), standard ADC (ADC(st)) and ultra-high ADC (ADC(uh)) were calculated from low b-values (0–200 s/mm(2)), standard b-values (300–1500 s/mm(2)) and ultra-high b-values (1700–4500 s/mm(2)), respectively. The expression of AQPs in the kidneys was studied using immunohistochemistry. Laboratory parameters of diabetic and kidney functions, ADC(low), ADC(st), ADC(uh), and the optical density (OD) of AQP expression in the two groups were compared using an independent t test. Correlations between ADCs and the OD of AQP expression were evaluated by Pearson’s correlation analysis. RESULTS: ADC(uh) were significantly higher in the cortex (CO), outer stripe of the outer medulla (OS) and inner stripe of the outer medulla (IS), and the OD values of AQ-2 were significantly higher in the OS, IS and inner medulla (IM) in DM animals compared with control animals. ADC(uh) and OD values of AQP-2 expression were positively correlated in the OS, IS and IM of the kidney. CONCLUSIONS: ADC(uh) may work as useful metrics for early detection of kidney damage in diabetic nephropathy and may be associated with AQP-2 expression.