| [Background and Objective]Renal interstitial fibrosis(RIF) is a morphologic hallmark of chronic progressive renal disease. RIF is also thought to be the final common mechanism leading to the end stage renal failure. Unilateral ureteral obstruction (UUO) has emerged as an important model for the study of the mechanisms underlying renal fibrogenesis and also for the evaluation of the impact of potential therapeutic approaches to ameliorate renal disease because that the major characteristic of the UUO kidney is RIF. The studies on the level of molecules and cells indict that the disorders of interstitial cell proliferation and cellular interstitium metabolism are demonstrated, which are effected by the localized or circular cytokines, to be the central cause of RIF. Mast cell (MC) infiltration was observed in several types of renal diseases, which was revealed in the recent years. MC may produce lots of mediators and cytokines. MC is also one of the main inflammatory cells, which indicted that MC had important significance in the chronic interstitial injury and play a key role in the development of organ fibrosis. Mast cells extrude from their secretory granules a plethora of preformed and formed inflammatory substances, including lipid mediators, cytokines, matrix metalloproteinases and matrix proteins. Therefore MC may exert multiple effects on the renal interstitial inflammation and fibrosis and contribute to the progression of RIF through multiple mechanisms. So it is reasonable for us to propose the following hypothesis: Tranilast, as a MC stabilizer, can reduce the release of inflammatory mediators, so ameliorate theprogress of RIF. By making the model of UUO, the study is mainly to investigate the effects of Tranilast on tryptase release rate, connective tissue growth factor (CTGF), collagen Ⅲ (Col Ⅲ) and the severity of RIF in rat kidney, and to discuss the mechanism of protective role of Tranilast in RIF, and try to look for a new approach of treatment for RIF.[methods] Female Sprague-Dawley rats were randomly assigned to four groups: sham-operated group(C group, n=6), sham-operated + Tranilast group( C + Tranilast group, n=6), operation group (UUO group, n=6), Tranilast(150mg·kg-1·d-1) treatment group after UUO ( UUO + Tranilast group, n=6). Obstructed kidneys were harvested 14 days after operation. The samples of blood and the urine of 24 hours were collected to detect the concentration of serum creatinine, the quantity of urinary protein and creatinine , Tryptase release rate was measured by chemical colourimetry method. HE, toluidine blue and Masson staining were performed ,as well as CTGF and Col III were immunostained by ABC Kit in the kidneys of all rats. All of the enumeration data was recordedas X ± s. After tested by the test for homogeneity of variance, the data was analyzed by one-way analysis of variance. The significance of mean between two groups was tested by the least significant difference. The relationship between two groups was tested by linear correlation. The standard of significant difference was defined as α =0.05. The SPSS 10.0 software packet was applied to the statistic analysis. [Results] By 14 days after operation, the results appeared as:(1) The quantity of urinary protein of 24 hours and the clearance of creatinine rate: There were no significant difference in the quantity of urinary protein of 24 hours (0.259 ±0.034vs. 0.258±0.026 vs. 0.273 ± 0.025 vs. 0.265 ± 0.017, P >0.05) ,and neither in the clearance of creatinine rate(0.353 ± 0.019vs. 0.355± 0.024vs. 0.326±0.019 vs. 0.340±0.016, P>0.05).(2) Tryptase Release Rate(TRR): There was no significance between C group and C + Tranilast group(8.348±2.629 vs. 9.135±2.314, P>0.05). the TRR ofUUO group and UUO + Tranilast group increased significantly compared with what in C group(19.285±5.477 vs. 8.348 + 2.629, 9.206 + 0.964 vs. 8.348± 2.629, P<0.01), TRR in UUO group increased significantly compared with what in UUO group(19.285 + 5.477vs.9.206 +0.964, P<0.01).(3) The numbers of interstitial infiltrating MC: The amounts of mast cell between C group and C + Tranilast group had no significantly difference(1.21 + 0.17vs.l.22 + 0.12, P>0.05). The numbers of MC of UUO group and UUO + Tranilast group increased significantly compared with what in C group(30.15 + 2.47vs. 1.21 + 0.17, 15.98+ 2.06vs.l.21 +0.17, P<0.01), the amount of MC in UUO + Tranilast group decreased significantly compared what in UUO group(15.98 + 2.06vs. 30.15 + 2.47, P<0.01).(4) The severity of RIF: The severity of RIF of C group had no significant difference with what in C + Tranilast group(0.587±0.078vs.0.593±0.048, P> 0.05), the severity of RIF in UUO group and UUO + Tranilast group increased significantly compared with what in C group(2.570±0.316vs.0.587±0.078, 1.424±0.347vs.0.587±0.078, P<0.01), so did in UUO group compared with what in UUO + Tranilast group(2.570±0.316vs.l.424±0.347, P<0.01).(5) The expression of CTGF: The immunostaining of CTGF in interstitium of C group and C + Tranilast group had no significant difference(0.120 + 0.034vs.0.129±0.009, P>0.05), the immunostaining of CTGF in UUO group and UUO + Tranilast group increased significantly compared with what in C group(2.231 + 0.119vs.0.120 +0.034, 1.683 + 0.113vs.0.120 + 0.034, P<0.01), the immunostaining of CTGF in UUO group increased significantly compared with what in UUO + Tranilast group(2.231±0.119vs.l.683 +0.113, P<0.01).(6) The expression of ColIII: The immunostaining of ColIII in interstitium of C group and C + Tranilast group had no significant difference(0.371 + 0.050vs.0.372 +0.045, P>0.05), the immunostaining of ColIII in UUO group and UUO + Tranilast group increased significantly compared with what in Cgroup(2.272±0.115vs.0.371 ±0.050, 1.560±0.099vs.0.371 ±0.050, P<0.01), the immunostaining of ColHI in UUO group increased significantly compared with what in UUO + Tranilast group(2.272+0.115vs.l.560+0.099, P<0.01).(7) The relationships among the amount of MC, tryptase release rate, the expression of CTGF and Col III, and the severity of RIF: The amount of infiltrating MC had significantly positive correlations with the expression of CTGF, the expression of ColHIand the severity of RIF(r =0.916 , r = 0.975 , r =0.883, P<0.01). So did the tryptase release rate with the expression of CTGF, the expression of ColIHand the severity of RIF(r =0.708 , r = 0.699 , r =0.750, P[ Conclusions ] (1) Renal interstitial infiltration of mast cell was tightly associated with the severity of renal interstitial fibrosis.(2)The release of tryptase was positively correlated to the expression of CTGF and Coim.(3) Tranilast can prevent mast cell from releasing inflammatory mediators such as tryptase by degranulation, reducing the expression of CTGF and the deposition of ColUJ. Therefore Tranilast can ameliorate the development of renal interstitial fibrosis.
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