Effect of iodinated contrast medium in diabetic rat kidneys as evaluated by blood-oxygenation-level-dependent magnetic resonance imaging and urinary neutrophil gelatinase-associated lipocalin

Evaluation of contrast-induced acute kidney injury using IVIM and DKI MRI in a rat model of diabetic nephropathy

Objective

To assess the potential of intravoxel incoherent motion (IVIM) and diffusion kurtosis imaging (DKI) in monitoring renal changes in a diabetic nephropathy (DN) rat model with acute kidney injury (CI-AKI) induced by iso-osmotic contrast media (IOCM) and low-osmotic contrast media (LOCM).

Methods

A diabetic nephropathy rat model was established, and the animals were randomly split into the LOCM group and IOCM group (n = 13 per group), with iopamidol and iodixanol injection, respectively (4 g iodine/kg). MRI including IVIM and DKI was performed 24 h before contrast medium injections (baseline) and 1, 24, 48, and 72 h after injections. Changes in pure molecular diffusion (D), pseudo-diffusion coefficient (D*), perfusion fraction (f), mean diffusion (MD), mean kurtosis (MK), serum creatinine (SCr) and urea nitrogen (BUN), histopathology alterations, and α-smooth muscle actin (α-SMA) expression were assessed. Inter-observer agreement was evaluated using the intraclass correlation coefficient (ICC).

Results

Compared against baseline levels, significant decreases in D, D*, and f were observed in all anatomical kidney compartments after contrast injection (p < 0.05). MD in the cortex (CO) and outer medullary (OM) gradually decreased, and MK in OM gradually increased 24–72 h after injection. D, D*, f, and MD were negatively correlated with the histopathologic findings and α-smooth muscle actin (α-SMA) expression in all anatomical kidney compartments. Inter-observer reproducibility was generally good (ICCs ranging from 0.776 to 0.979).

Conclusions

IVIM and DKI provided noninvasive imaging parameters, which might offer effective detection of CI-AKI in DN.

Magnetic resonance diffusion tensor imaging applied to rat model of contrast-induced acute kidney injury

Objectives

In this preclinical investigation, the feasibility of using diffusion tensor imaging (DTI) to study contrast-induced acute kidney injury (CIAKI) is explored, comparing radiographic outcomes with histopathologic and immunohistochemical findings after repeated animal exposures to iodinated contrast agent.

Materials and Methods

Forty-five male wistar rats were allocated to three groups (n = 15 each), each receiving two separate injections 1 day apart: group 1 (iodixanol then saline); group 2 (iodixanol twice); and control group (saline twice). Five rats were then randomly selected from each group at three separate time points (1 h, 24 h, and 120 h) for magnetic resonance imaging (MRI). Upon MRI completion, the animals were sacrificed, examining renal tissue and serum creatinine level. DTI data served to calculate fractional anisotropy (FA) and apparent diffusion coefficient (ADC).

Results

FA values were significantly lower in group 2 than in the others. Compared with controls, FA assessments at 1 h, 24 h, and 120 h after injections commenced were significantly lower in group 2; and ADC was significantly more pronounced at 24 h. Serum creatinine levels at 24 h were markedly elevated in both groups 1 and 2. Pearson correlation analysis revealed significant negative correlations between FA (r = −0.730; p < 0.05) or ADC (r = −0.827; p < 0.05) and tubular injury and between FA (r = −0.563; p < 0.05) or ADC (r = −0.805; p < 0.05) and hypoxia-inducible factor-1α.

Conclusions

Analytic approaches to DTI with better reproducibility should aid in monitoring the early pathophysiologic derangements of CIAKI, thus facilitating timely reversal of the detrimental effects.

Contrast Media-Different Types of Contrast Media, Their History, Chemical Properties, and Relative Nephrotoxicity

History of contrast dates back to the 1890s, with the invention of the radiograph. Nephrotoxicity has been a main limitation in ideal contrast media (CM). High-osmolar contrast media no longer are in clinical use due to overwhelming evidence supporting greater nephrotoxicity with these CM compared with current CM. Contrast-induced nephropathy (CIN) remains a common cause of in-hospital acute kidney injury. The choice contrast agent is determined mainly by cost and institution practice. This review focuses on the history, chemical properties, and experimental and clinical studies on the various groups of CM and their role in CIN.

Pathophysiology of Contrast-Induced Acute Kidney Injury (CIAKI)

Contrast-induced acute kidney injury (CIAKI) is a severe complication associated with the use of iodinated contrast media (CM); a sudden but potentially reversible fall in glomerular filtration rate (GFR) typically occurring 48-72 hours after CM administration. Principal risk factors related with the presentation of CIAKI are preexisting chronic kidney disease and diabetes mellitus. Studies on CIAKI present considerable complexity because of differences in CM type and dose, controversies in definition and baseline comorbidities. Despite that, it should be noted that CIAKI poses a serious health problem because it is a very common cause of hospitalacquired AKI, linked to increased morbidity and mortality and utilizing growing healthcare resources. The pathogenesis of CIAKI is heterogeneous and, thus, is incompletely understood. Three basic mechanisms appear to simultaneously occur for CIAKI development: Renal vasoconstriction and medullary hypoxia, tubular cell toxicity and reactive oxygen species formation. The relative contribution of each one of these mechanisms is unknown but they ultimately lead to epithelial and endothelial cell apoptosis and GFR reduction. Further research is needed in order to better clarify CIAKI pathophysiology and accordingly introduce effective preventive and therapeutic strategies.

Evaluation of Renal Pathophysiological Processes Induced by an Iodinated Contrast Agent in a Diabetic Rabbit Model Using Intravoxel Incoherent Motion and Blood Oxygenation Level-Dependent Magnetic Resonance Imaging

OBJECTIVE

To examine the potential of intravoxel incoherent motion (IVIM) and blood oxygen level-dependent (BOLD) magnetic resonance imaging for detecting renal changes after iodinated contrast-induced acute kidney injury (CI-AKI) development in a diabetic rabbit model.

MATERIALS AND METHODS

Sixty-two rabbits were randomized into 2 groups: diabetic rabbits with the contrast agent (DCA) and healthy rabbits with the contrast agent (NCA). In each group, 6 rabbits underwent IVIM and BOLD imaging at 1 hour, 1 day, 2 days, 3 days, and 4 days after an iohexol injection while 5 rabbits were selected to undergo blood and histological examinations at these specific time points. Iohexol was administrated at a dose of 2.5 g I/kg of body weight. Further, the apparent transverse relaxation rate (R2*), average pure molecular diffusion coefficient (D), pseudo-diffusion coefficient (D*), and perfusion fraction (f) were calculated.

RESULTS

The D and f values of the renal cortex (CO) and outer medulla (OM) were significantly decreased compared to baseline values in the 2 groups 1 day after the iohexol injection (p < 0.05). A marked reduction in the D* values for both the CO and OM was also observed after 1 hour in each group (p < 0.05). In the OM, a persistent elevation of the R2* was detected for 4 days in the DCA group (p < 0.05). Histopathological changes were prominent, and the pathological features of CI-AKI aggravated in the DCA group until day 4. The D, f, and R2* values significantly correlated with the histological damage scores, hypoxia-inducible transcription factor-1α expression scores, and serum creatinine levels.

CONCLUSION

A combination of IVIM and BOLD imaging may serve as a noninvasive method for detecting and monitoring CI-AKI in the early stages in the diabetic kidney.

Resveratrol Protects Against Post-Contrast Acute Kidney Injury in Rabbits With Diabetic Nephropathy

Resveratrol (Res) is a multi-functional polyphenol compound that has protective functions in acute kidney diseases. Here, we examined whether the resveratrol could ameliorate post-contrast acute kidney injury (PC-AKI) following diabetic nephropathy (DN), and explored any underlying mechanism(s) in vivo and in vitro. Twenty-four rabbits with DN were randomly divided into four groups: control (Cont), resveratrol (Res), iohexol (PC-AKI), and resveratrol plus iohexol (Res+PC-AKI) groups. Functional magnetic resonance imaging, renal histology, blood and urinary biomarkers, silent information regulator l (SIRT1), peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α), hypoxia-inducible transcription factor-1α (HIF-1α), and apoptosis-associated protein expression were assessed ex vivo. For in vitro experiments, renal tubular epithelial (HK-2) cells subjected to high glucose conditions were treated with resveratrol, Ex527, an SIRT1 inhibitor, or 2-methoxyestradiol (2-MeOE2), HIF-1α inhibitor, before treatment with iohexol. With regard to the rabbit model of acute renal injury in DN, compared to the PC-AKI group, the Res+PC-AKI group showed decreased levels of cystatin C and urinary neutrophil gelatinase-associated lipocalin, increased pure molecular diffusion (D) and the fraction of water flowing in capillaries (f), a decreased apparent relaxation rate (R2*), renal injury score and apoptosis rate, increased protein expression levels of SIRT1 and PGC-1α, and decreased levels of HIF-1α and apoptosis-associated protein. In addition, iohexol decreased HK-2 cell survival and increased the cell apoptosis rate; results were reversed after treating cells with resveratrol. Resveratrol reduced renal hypoxia, mitochondrial dysfunction and renal tubular cell apoptosis by activating SIRT1-PGC-1α-HIF-1α signaling pathways in PC-AKI with DN.

Effect of Repeated Injection of Iodixanol on Renal Function in Healthy Wistar Rats Using Functional MRI

Purpose

To determine the optimal time interval of repeated intravenous injections of iodixanol in rat model and to identify the injury location and causes of renal damage in vivo.

Materials and Methods

Rats were randomly divided into Control group, Group 1 with one iodixanol injection, and Group 2 with two iodixanol injections. Group 2 was subdivided into 3 cohorts according to the interval between the first and second iodixanol injections as 1, 3, and 5 days, respectively. Blood oxygen level-dependent (BOLD) imaging and diffusion weighted imaging (DWI) were performed at 1 hour, 1 day, 3 days, 5 days, and 10 days after the application of solutions.

Results

Compared with Group 1 (7.2%), Group 2 produced a remarkable R2^⁎ increment at the inner stripe of the renal outer medulla by 15.37% (P = 0.012), 14.83% (P = 0.046), and 13.53% (P > 0.05), respectively, at 1 hour after repeated injection of iodixanol. The severity of BOLD MRI to detect renal hypoxia was consistent with the expression of HIF-1α and R2^⁎ was well correlated with HIF-1α expression (r = 0.704). The acute tubular injury was associated with urinary NGAL and increased significantly at 1 day.

Conclusions

Repetitive injection of iodixanol within a short time window can induce acute kidney injury, the impact of which on renal damage in rats disappears gradually 3–5 days after the injections.

Glucose and magnetic-responsive approach toward in situ nitric oxide bubbles controlled generation for hyperglycemia theranostics

Stimuli-responsive devices that deliver drugs or imaging contrast agents in spatial-, temporal- and dosage-controlled fashions have emerged as the most promising and valuable platform for targeted and controlled drug delivery. However, implementing high performance of these functions in one single delivery carrier remains extremely challenging. Herein, we have developed a sequential strategy for developing glucose and magnetic-responsive microvesicle delivery system, which regulates the glucose levels and spatiotemporally controls the generation of nitric oxide gas free bubbles. It is observed that such injectable microvesicles loaded with enzyme and magnetic nanoparticles can firstly regulate hyperglycemic level based on the enzymatic reactions between glucose oxidase and glucose. In a sequential manner, concomitant magnetic field stimuli enhance the shell permeability while prompts the reaction between H2O2 and l-arginine to generate the gasotransmitters nitric oxide, which can be imaged by ultrasound and further delivered for diabetic nephropathy therapy. Therefore, magnetic microvesicles with glucose oxidase may be designed as a novel theranostic approach for restoring glucose homeostasis and spatiotemporally control NO release for maintaining good overall diabetic health.