| BackgroundClinically, the conditions of ureteral obstruction caused by stones,narrow,or tumor result in the urine and renal pelvis calyces collection system expansion, pathologic changes occured such as renal interstitial edema, focal inflammatory cell infiltration, renal tubule fibrosis,then, kidney function is impaired, some cases are still suffering from kidney shrinks even if the upper tract obstruction lifting.Many study confirmed the cell apoptosis acted an important role in the progress of interstitial fibrosis in unilateral ureteral ligation model, in unilateral ureteral obstruction (UUO) rat model,renal tubular epithelial cells in affected side of sobstruction appears the apoptotic cells and apoptotic bodies obviously after 1 week obstructed, apoptosis mediated by oxygen free radical participated in the renal pathological changes after urinary tract obstruction. Further studies showed that the apoptosis cells were increased in both renal tubule and interstitial after ureteral obstruction,and the apoptosis regulation factors BCL-2 and Bax are mainly expressed in renal tubular epithelial cells, the former expression increased and the latter reduced, all these suggested this two factors regulated the cell apoptosis of renal tubular together. The cell apoptosis of renal tubular may be the main factors of kidney atrophy caused by obstruction.With the development of modern medicine, intravenous urography (IVU), enhanced CT and CTU is currently the main imaging examination method in the diagnosis of urinary tract obstructive diseases, and the contrast agents are required in the process, large number of clinical trails and basic researched have confirmed that contrast agent could potentially damage to the kidney, the contrast-induced acute kidney injury(CI-AKI) is one of the important cause of acute kidney injury, CI-AKI have different incidences in differet reports, ranged from 0%-58%, being poor prognosis, high incidence of complications, it has become the third largest pathogenic factors of acute renal failure in hospitalized patients. Presently, it is widely believed that CI-AKI is caused by multi-factoris, its pathogenesis may lie in the following three aspects:Renal vasoconstriction induced by contrast media, oxygen free radicals increased through oxidative stress, and direct toxicity to renal tubule.In the analysis of correlated risk factors of CI-AKI, preoperative renal abnormalities, combining type 2 diabetes mellitus, hypovolemia and over-dose of contrast agent is the important reasons for CI-AKI.Renal insufficiency is the most hazards of CI-AKI, the capacity of renal reserve drops as the conditioon of renal insufficiency, and easy to suffer CI-AKI, its incidence increases with Scr levels, and the incidence of CI-AKI is 4%～20% when the level of Scr is 106.1～256.4 umol/L, studies have shown that the incidence of CIN increased markedly in patients with thglomerular filtration rate (GFR) less than 60 ml/min 1.73 m2.As a result, contrast agent is taboo for the patients with Scr greater than 256.4 umol/L by "The Chinese guidelines of diagnosis and treatment of urology disease".To the condition of hydronephrosis caused by unilateral ureteral obstruction, the renal function was damaged in a certain degree, the glomerular filtration rate (GFR) decreased obviously in affected side. According to the present indexes, the application of the contrast agents for the cases with renal insufficiency may be increased renal tubular cell toxicity, accelerate the glomerular and renal tubule fibrosis, even may cause adverse effects for recover after the obstruction relieved. Contrast agent can stimulate the kidneys to produce oxygen free radicals, a lot of evidences suggest that the activation of oxygen free radicals are the important factor for kidney damage. I n Clinical, a lot of contrast agents are still accumulate in renal after 1-2 days of application of the contrast agents for CT,IVU or enhanced CT in patients with hydronephrosis caused by complete unilateral ureteral obstruction,For the nephrotoxicity of contrast agents, it is speculated that the accumulation of contrast agent may enhance the pathological process of renal damage caused by contrast agen to a certain extent and the pathological process is likely to influence the outcome of kidney after obstruction relieved, namely renal atrophy.To preventing this kind of damage, we should be strictly selecting indications, strictly grasp the contrast agent dose (including types of contrast agents and reduce the contrast agent dose), a large amount of researched have focused on anti-vasoconstriction, increasing blood flow of renal unit or anti oxygen free radical damage, etc.The treatments and medicines for contrast renal damage include hydration therapy, hemofiltration, preventive dialysis, sodium bicarbonate, adenosine, dopamine receptor inhibitors, diuretics, n-acetyl cysteine (NAC), calcium channel blockers, endothelin receptor inhibitor and sodium, angiotensin converting enzyme inhibitors, L-arginine, insulin-like growth factor and prostaglandin E1, etc.Because of the strong antioxidant effect, NAC has become more accepted protective drugs for renal damage caused by contrast currently.This study is based on the above clinical problems and speculation, the mechanism of renal damage caused by contrast agents in the cases with unilateral ureteral obstruction is explored through animal model, drug intervention and clinical observation. The level of NGAL in serum was detected to assess the degrees of kidney damage in this research.Section I Effects of contrast agent on kidney of rats with unilateral ureteral obstructionObjective:Clinical unilateral hydronephrosis pathophysiologic changes was simulated by recoverability completeness of unilateral ureteral obstruction animal model, injection of iohexol in tail vein simulated the application of contrast agents during imaging examination in clinical practice, The acknowledged sensitive indexes of early renal damage of neutrophils enzyme related lipid carrier protein gelatin (NGAL) in serum was choosed to to evaluate renal damage situation, and to discuss the possible mechanisms of renal damage with renal tubular cell apoptosis rate and Bax mRNA expression.Methods:42, SPF SD rats were randomly divided into sham group (14) and model group (28), model group were prepared the left completeness ureteral obstruction animal model by using the "V" tube method,sham-operation group only open, separation, and don’t clip ureter;3 weeks later, the animal model matured, then the model animals were randomly divided into contrast group (14) and the control group (14), in 22nd day, contrast group rats were injected iohexol in caudal vein (3000 mg/kg body weight), and the control group injected amount of normal saline (NS), sham group not inject drugs.1 day (i.e.,23 day) later,7 rats were randomly chose in three groups respectively, draw blood and separate the serum, detect of serum level of NGAL, and test the kidney morphology and pathological changes, renal tubular cell apoptosis rate and kidney tissues Bax mRNA expression after executed.Model group rats were operated to remove obstruction, sham is still only cut, separation, suture; All the above projects were performed 3 weeks afterobstruction removed.Statistical treatment:Using IBM SPSS Statistics 21.0 statistical analysis software, the data be shown by mean±standard deviation, the data comparison between the groups choose paired t test, P< 0.05 for the difference was statistically significant.Results:After the injection of the contrast group on one day, difference of the volume of rat kidney, renal parenchymal thickness and weight was significant, it prompted that the model replication was successful. Left kidney volume of model group rats have no significant difference to right kidney 3 weeks after relieve obstruction (P> 0.05), significantly reduced compared to before (P< 0.05), it suggested that the operation to lift the obstruction was successful;Compared to before,left kidney weight of model group rats significantly decreased 3 weeks after relieve obstruction (P< 0.05).Under the pathological change, the rat kidney on the right side were not seen obvious abnormity, the left renal cortical of rats was thinning microscopically;glomerular atrophy, reducing the number;Part of the renal tubulars expansion, flattening renal tubular epithelial cells, a small amount of protein cast, cellular cast;Part of the kidney tubules renal cavity collapse, renal tubular epithelial cells cavitation;Renal interstitial inflammatory cell infiltration;Renal interstitial fibrosis is aggravating, and there was no significant difference between the model group and contrast group in rat kidney cortex injury; left renal glomerular number of rats in model group and contrast group was significantly lower than right kidney; 1 day after injection of contrast agent or 3 weeks after remove obstruction, left renal glomerular number of rats in contrast group was the same to control group.Bax mRNA and NGAL in the contrast agent compared with control group was significantly higher (P<0.05), and the first day and the first three weeks after injection, serum NGAL and Bax mRNA of contrast agent group comparing with model group were significantly increased (P<0.05), after the first three weeks,the left renal tubular cell apoptosis in control group comparing with contrast agent group was significantly higher (P<0.05).Conclusion:The renal damage caused by contrast agent mainly displays in three aspects:firstly, change the renal hemodynamics, renal blood flow change caused by contrast media shows in dual phase reaction, briefly expansion in early stage,then renal blood flow increased, and then a continuous progressive vasoconstriction,leads to the redistribution of blood from the medulla to cortex, reduce blood flow to medulla, appeared ischemia.Second:ischemia anoxic injury occurs, the tissue hypoperfusion generates amount of active oxygen free radicals (ROS), more than the body’s antioxidant reserves, aggravate the further renal ischemic injury;Third, direct damage to the renal tubular epithelial cells, reduce renal tubular adenosine triphosphate, total adenine nucleotide and the content of potassium ion, at the same time improve the renal tubule cells of calcium ions, so that the basis of renal tubule and decoupling respiration rate decreased, damage renal tubule cells, mitochondria cytochrome release and plasma membrane destruct.All of these common result is renal medulla ischemia, pathological process of ischemic damage raised NGAL protein expression, and NGAL content in the serum of rats showed increasing;Bax mRNA expression in renal tubular epithelial cells mediated the excessive cell apoptosis, it could be one of the important mechanism of renal damage caused by contrast agents in rats with unilateral ureteral obstruction.Section Ⅱ Effect of N-acetylcysteine (NAC) on contrast media for kidney damage of rats with unilateral hydronephrosisObjective：Based on previous research, n-acetyl cysteine (NAC) which have the functionary to anti oxygen free radical was used as drug intervention for the model rats with unilateral hydronephrosis during the renal damage process caused by contrast agents, still use the sensitive index of early renal damage NGAL to evaluate renal damage, and detected the renal tubular cell apoptosis rate and the Bel-2 mRNA expression in preliminary to discuss the protection effect of NAC to the approach of renal damage caused by contrast agents.Methods:68 male SD rats were prepared refolding complete obstruction of the left ureter animal models,3 weeks later,The animal model matured, then the model animals were randomly divided into NAC group(24), NS group (24) and model control group (20), The rats in NAC group and NS group were gavaged by NAC, the same amount of NS respectively for three days,the control group was not fed. After3 days, the rats of NAC group and NS group were injected contrast medias iohexol in caudal vein (3000 mg/kg body weight), model control group rats were injected with the same amount of NS, One day after injection of the drug, taking half of the rats in each group were sacrificed to detect morphological changes in the kidney, serum NGAL, renal tubular cell apoptosisAnd expression of Bcl-2 mRNA; Surgery to remove the remaining rats ureteral obstruction, and death after the three weeks, the same as the above projects testingStatistical treatment:Using IBM SPSS Statistics 21.0 statistical analysis software, the data be shown by mean ±standard deviation, the data comparison between the same group choose variance analysis and paired t test, the comparison in multiple sets of data choose one-way analysis of variance, P< 0.05 for the difference was statistically significant.Results:Difference among Rat kidney volume, renal parenchymal thickness and weight was significant (P<0.05),NGAL of NAC treatment group and NS group with injection of contrast media after the first day,compared with model group was significantly higher (P<0.05), NAC group compared with NS group NGAL levels were significantly lower (P<0.05), there was no significant difference among three groups of the left renal tubular cell apoptosis rate expression of Bcl-2 mRNA (P >0.05); After three weeks to remove the obstruction, NGAL levels in each group were not significantly higher than before the change (P> 0.05); NAC group left renal tubule cell apoptosis rate expression of Bcl-2 mRNA in the model control group, but lower than the NS group (P<0.05).Conclusion:The previous study have preliminarily confirmed that the contrast agent can cause renal medulla ischemic changes, the condition of ischemic damage produces a large number of oxygen free radicals, the damage of oxygen free radical mediated apoptosis, cell apoptosis is a major cause which contrast agents affect the cell activity.Based on this mechanism, as an antioxidant, NAC containing sulphur (SH), can be inactivated reactive oxygen species (OFR), directly give play to the role of antioxidant, can promote the synthesis of glutathione, through which indirectly play a role of antioxidant, can also play a role of hemangiectasis through the NO and S-nitroso mercaptan, inhibit the formation of angiotensin converting enzyme and stable NO to reduce the influence of contrast media on renal function;NAC application before contrast media injection can reduce the degree of kidney damage in rats, NGAL index lower in the NS group, and 3 weeks after removing obstruction, the Bcl-2 mRNA expression in the renal tubular epithelial cells of left side in NAC group rats is higher than that of NS group, and apoptosis rate is lower than that of NS group, it prompts that NAC has certain protective effect for the renal damage caused by contrast agents in rats with unilateral hydronephrosis, the process may be realiuzed by raising the Bcl-2 mRNA expression to inhibit the cell apoptosis of renal tubular.Section Ⅲ Effects of contrast agent on NGAL in blood of patients with unilateral ureteral obstructionObjective:The renal damage index NGAL of serum used in early in basic studies was detected after accepte contrast agent injection in patients with complete unilateral ureteral obstruction, aim to observe whether the changes of serum content of NGAL of the model rats in basic research is also verified in the human body, and to explore the mechanism of renal damage caused by contrast agents in the cases with unilateral ureteral obstruction.Methods:36 patients with complete unilateral ureteral obstruction (confirmed by IVU or CTU);The control group patients include 25 patients without ureteral obstruction (also confirmed by IVU or CTU) which hospitalized in the same period; All Patients were excluded who suffer high blood pressure, diabetes, high blood uric acid, the recent history of extracorporeal lithotripsy treatment and other renal damage factors; The serum samples were collcected two hours before and after contrast agents injection, to detceced renal function index Cr and NGAL.Statistical treatment:Using IBM SPSS Statistics 21.0 statistical analysis software, the data be shown by mean ±standard deviation, the data comparison between the same group choose variance analysis and paired t test, the comparison in multiple sets of data choose one-way analysis of variance, P< 0.05 for the difference was statistically significant.Results:The levels of serum NGAL in the patients with unilateral ureteral obstruction were much higher than the control group before the injection of contrast agent (P< 0.05), and the serum content of NGAL increased after contrast agent injected 2 hours later. (P< 0.05); The serum content of NGAL in control group patients was no significant difference before and after drug (P> 0.05);Conclusion:Unilateral ureteral obstruction caused the pelvic pressure heighten, a series of pathophysiological changes resulting in kidney ischemia, the ischemic injury caused NGAL protein expression level at many points in the renal unit, NGAL protein deliver iron to the proximal renal tubule cells, the expression level of heme oxygenase-1 was up-regulated by iron, and thus play a role of protection, and the amount of NGAL protein is proportional to the duration of ischemia and ischemia, therefore, the levels of early renal damage index NGAL in patients with complete unilateral obstruction has already increased before using contrast agents, the application of conventional dose contrast agents contributed to the damage degree, this was similar to the animal experimental results.But the damage was not caused comprehensive changes in renal function, may be associated with the strong compensatory function of contralateral kidney. This kind of damage caused by contrast agents in kidney with hydronephrosis is transient or persistent? Whether it will affect the outcome of renal afeter obstruction removed?N-acetyl cysteine (NAC) as a protective drugs of renal damage in animal experiments also have a role for this process? All these problems remains to be further in-depth study. |
