| With the increase of population aging,the number of patients with hypertension,diabetes mellitus and chronic renal insufficiency has increased significantly.The contrast acute kidney injury(CIN)or post-contrast acute kidney injury(PC-AKI)after iodine contrast agent injection will become a serious clinical problem.Serum creatinine(Cr)has been used as a major diagnostic criterion for contrast induced renal impairment,which typically reaches its peak at 72 h after contrast agent exposure.This suggests an intrinsic delay of therapy in patients who may have developed PC-AKI,while it prolongs the duration of hospitalization for patients without PC-AKI.Quantitative functional MRI(fMRI)has attracted considerable attention in recent years as a noninvasive approach to assess relative renal content.Moreover,functional MRI can detect abnormal renal function before the structure of the kidney is damaged.We used BOLD and IVIM technologies to monitor PC-AKI,which makes the indicators diverse,systematic and comprehensive,and can earlier diagnose the acute kidney injury caused by contrast agent than clinical indicators,thus increasing the application scope of fMRI technology in clinical practice.BOLD MRI has been shown to be competent in providing indirect measurements of real-time oxygenation status for renal damage provoked by contrast agent.In addition,intravoxel incoherent motion(IVIM)imaging could detect the diffusion of water molecules and perfusion-dependent diffusion in vivo.The underlying mechanisms leading to PC-AKI have not been fully revealed.The universally acknowledged causes of PC-AKI include hypoxic and toxicity of contrast agent and oxidative stress as well as oxidative stress leading to mitochondrial damage.Silent information regulator l(SIRT1)is a nicotinamide adenine dinucleotide-dependent protein deacetylase and the human homolog of yeast silent information regulator 2.Accumulated experimental evidence suggests that SIRT1 may inhibit inflammatory response,tubular apoptosis,and scavenge oxygen free radicals.At present,the relationship between SIRT1 and PC-AKI is the focus of research.Part 1 Evaluation of Renal Pathophysiological Processes Induced by Iodinated Contrast Agent in a Diabetic Rabbit Model using Blood Oxygenation Level-Dependent and Intravoxel Incoherent Motion 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 post-contrast acute kidney injury(PC-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).The diabetic rabbit model was established by administering a single intravenous injection of 100 mg/kg body weight of alloxan freshly dissolved in 0.9%saline.Iohexol 350 that was preheated at 37°C was intravenously injected at a dose of 2.5 g I/kg body weight.In each group,6 rabbits underwent BOLD and IVIM imaging at 1 h and 1,2,3,and 4 days after an iohexol injection while 5 rabbits were selected to undergo blood and histological examinations at these specific time points.5 diabetic rabbits were randomly selected from the remaining rabbits for blood measurements and histological studies after MRI scanning at the 5 time points(baseline,1 h,1 day,2 days,3 days).Further,the apparent transverse relaxation rate(R2~*),average pure molecular diffusion coefficient(D),perfusion-related diffusion coefficient(D~*),and perfusion fraction(f)were calculated.In each kidney,a single region of interest(ROI)corresponding to the histological sections was placed by a manual segmentation of the coronal BOLD images and IVIM images.All layers of renal tissues were segmented into three regions,including cortex(CO),outer medulla(OM),and inner medulla(IM).Results:The D and f values of the renal cortex(CO),outer medulla(OM)and inner medulla(IM)were significantly decreased compared to baseline values in the 2 groups 1day after the iohexol injection(P<0.05).A marked reduction in the D~*values for the CO,OM and IM was also observed after 1 h 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 PC-AKI aggravated in the DCA group until day 4.The HIF-1?and VEGF expression were increased at 1 hour.A marked accumulation of HIF-1?and VEGF were detectable in the renal CO and OM after day 1.The D,f,and R2~*values significantly correlated with the histological damage scores,hypoxia-inducible transcription factor-1?expression scores,and serum creatinine levels.Conclusion:A combination of BOLD and IVIM imaging may serve as a noninvasive method for detecting and monitoring PC-AKI in the early stages in the diabetic kidney.Part 2 SIRT1 Activation Contributes to the Resistance of Post-contrast Acute Kidney Injury in Rabbits with Diabetic NephropathyObjective: To examine whether the up-regulation silent information regulator l(SIRT1)could potentially ameliorate the post-contrast acute kidney injury(PC-AKI)following diabetic nephropathy(DN),and to explore its underlying mechanism in vivo and in vitro.Materials and Methods: Twenty-four DN rabbits were randomly divided into four groups: control group(Cont),resveratrol group(Res),iohexol group(PC-AKI),and resveratrol plus iohexol group(Res+PC-AKI).The animals were treated with or without resveratrol once a day,for a total of 14 days before applying iohexol.All animals underwent BOLD and IVIM examinations 24 hours after iohexol injection.Blood was used to examine the serum creatinine(Cr),urea nitrogen(BUN).Renal histology was obtained to assess silent information regulator l(SIRT1),peroxisome proliferator-activated receptor gamma coactivator-1alpha(PGC-1?),hypoxia-inducible transcription factors-1?(HIF-1?),and apoptosis-associated proteins expression in ex vivo.For the in vitro experiment,renal tubular epithelial(HK-2)cells were subjected to high glucose condition.The well-differentiated HK-2 cells were divided into five groups: Res group;Ex527 group;2-Me OE2 group;PC-AKI group;and Cont group.The cells were stimulated under high glucose or low glucose conditions for 24 hours.After Res,Ex527 or 2-Me OE2 treatment,cells were exposed to iohexol(100 mg/m L)for 16 hoursResults: The PC-AKI model with diabetic nephropathy rabbits were successful established.In the Res+PC-AKI group,the levels of serum creatinine,urea nitrogen,were all decreased when compared with PC-AKI group.No significant differences were found between Cont group and Res group in D,D*,f,R2* in the renal CO and OM(P >0.05).In the OM,the mean D(P < 0.05),f values(P < 0.05)significantly increased,the mean R2*(P < 0.05)significantly decreased at Res-PC-AKI group compared with PC-AKI group.In the CO,the mean D(P < 0.05),f values(P < 0.05)significantly increased,the mean R2*(P < 0.05)significantly decreased at Res-PC-AKI group compared with PC-AKI group.Perfusion-related parameters of D* slightly increased in the Res-PC-AKI compared with PC-AKI group;however,no significant differences were found between the renal CO(P > 0.05)and OM(P > 0.05).Histopathological examination showed no pathological alterations of the kidneys in the Cont group and in the Res group.The renal score were significantly higher in the PC-AKI group than in the Cont group,Furthermore,the co-administration of resveratrol with iohexol significantly decreased the severity score compared to the PC-AKI group.Compared to Cont group,the protein expression levels of SIRT1(P > 0.05),PGC-1?(P < 0.05)were decreased,and the expression levels of HIF-1?(P < 0.05),Cleaved caspase-3(P < 0.05)were incecreased in the PC-AKI group.Moreover,compared to PC-AKI group,the protein expression levels of SIRT1(P < 0.05),PGC-1? were increased(P < 0.05),and the expression levels of HIF-1?(P > 0.05),Cleaved caspase-3(P < 0.05)were decreased in the Res+PC-AKI group.For the in vitro experiment,compared to PC-AKI group,the protein expression levels of SIRT1(P < 0.05),PGC-1?(P < 0.05)were increased,and the expression levels of HIF-1?(P < 0.05),Bax(P < 0.05),Cleved Caspase-3(P < 0.05),Cyt-C(P < 0.05)were incecreased in the Res group,while the HIF-1? inhibitors 2-Me OE2 was able to reinforce the significant effect of resveratrol.Furthermore,the results were reversed after treating cells with the SIRTl inhibitors Ex527.Compared to Cont group,Ex527 reduced the expression of SIRTl(P = 0.201),PGC-1?(P = 0.258)and Bcl-2(P < 0.001)and increased the expression of HIF-1? protein(P = 0.008),Bax(P < 0.001),Cleaved Caspase-3(P = 0.001)and Cyt-C(P = 0.001).Conclusions: The overexpression of SIRT1 reduces the oxidative stress,mitochondrial dysfunction and renal tubular cell apoptosis by activating SIRT1-PGC-1?-HIF-1? signaling pathways in PC-AKI with DN. |
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