| Background and objective:Minimal changed nephrotic syndrome (MCNS) is the most common pathological type in children with primary nephrotic syndrome(PNS). Hyperlipidemia is one of the most important pathological physiology changes in PNS, with increased total cholesterol and low density lipoprotein (LDL). A lot of research have showed that the hyperlipidemia and lipid deposition in kidney is an important risk factor of glomerular sclerosis. However, the mechanism of renal lipid deposition and the production of renal foam cells in the development of renal damage in PNS is not fully clear.CXCL16is one of chemokine and membrane binding protein, which was discovered in the macrophages of atherosclerosis in2000. The transmembrane combination type CXCL16can combine oxidative low density lipoprotein (ox-LDL) and mediate lipid endocytosis. It may participate in the formation of macrophage-derived foam cell. The secretory type CXCL16has a function of chemokine and plays an important role in modulating the immune system. ADAM10is the key factor in the transformation of these two forms. According to the previous studies, the level of urinary CXCL16in patients with lupus nephritis and acute tubular necrosis was increased, thus CXCL16might be a marker of these kidney disease. However the relationship of CXCL16and minimal change nephrotic syndrome has not been reported.An important function of transmembrane combination type CXCL16is the scavenger receptor of ox-LDL. Gutwein P et al have confirmed in vitro studies that ox-LDL uptake were increased when podocytes were stimulated with IFN-y, in the conditions with or without metal protease inhibitors. And the absorption of ox LDL by podocytes was reduced significantly when using specific block antibody of CXCL16. These results suggested that CXCL16was an important scavenger receptor for ox-LDL in podocytes. CXCR6is the only receptor of CXCL16. There are rare reports about relationship of CXCL16and lipid deposition in nephrotic syndrome. How CXCL16mediate the kidney damage as a scavenger receptor of ox-LDL is still unknown.Statins, namely3-hydroxy-3-methyl glutaric acyl coenzyme A (HMG CoA) reductase inhibitor, can inhibit the activity of endogenous cholesterol synthesis limiting velocity enzyme HMG CoA reductase competitively and block the pathway of A hydroxyl pentanoic acid metabolic in cells so that they can reduce the cholesterol synthesis and plasma cholesterol levels. Simvastatin is one of the most effective and wide-used statins. Statins have the renal-protective roles not only by lowering cholesterol, but also by inhibiting cell proliferation and inflammation, as well as modulating immune system. However, whether statins play a role of renal protection by influencing CXCL16expression in kidney tissues and interfering with the ox-LDL uptake has not been reported.Minimal lesions and focal segmental glomerular sclerosis in adriamycin-induced nephropathy mouse model is extremely similar with renal pathology of PNS in clinic. In our study, we established an adriamycin-induced nephropathy model and used simvastatin as an interventional method to observe the variation of CXCL16and ox-LDL in the serum and kidney and renal pathological damage degree, in order to discover the relationships between CXCL16/ox-LDL and the development of renal damage, and possible mechanisms of renal protection of simvastatin in adriamycin-induced nephropathy.Methods: Seventy-five healthy male Balb/c mice were separated into modeling group (n=50) and control group (n=25). Mice in modeling group were intravenously injected with a single dose of Adriamycin (10.5mg/kg). The mice with heave Proteinuria (determined24h urinary≥50mg/kg) and hypoalbuminemia(ALB<25g/L) after one week were regarded as models with adriamycin-induced nephropathy. Forty-eight mice were successfully established and divided into model group and simvastatin treatment group randomly. Treatment group were fed with simvastatin (20mg/kg) every day. Mice were sacrificed at0,1st,3rd,5th,7th week.24h urinary were observed. Serum cholesterol were determined by automatic biochemical analyzer. Serum CXCL16, ox-LDL, IFN-γ and urinary CXCL16were determined by ELISA. The protein expression of CXCL16, CXCR6, ADAM10and ox-LDL in kidney tissue were analyzed by semiquantitative immunohistochemistry. Renal pathology were observed by light and electron microscopy.Results:1. The changes of biochemical index in serum and urineIn model group and simvastatin-treatment group, serum albumin was decreased (P<0.05), cholesterol levels were raised (P<0.05) and24h urine protein content was increased (P<0.01), compared with those in control group. The changes about the above results in treatment group were improved, compared with model group (P<0.05). All the index variation mentioned above continued until the end of the study.2. The levels of serum and urinary CXCL16and serum ox-LDLCompared with those in control group, the levels of serum and urinary CXCL16and serum ox-LDL and IFN-γ were increased (P<0.01), and kept increasing trend with the longer course in the model and treatment groups. In comparison with model group, the changes about the above results in treatment group were lighter (P (0.01)3. Renal pathology under the light microscopeCompared with the control group at the same time, mice in the model and treatment groups showed glomerular mesangial proliferation, stromal hyperplasia, capsular synechia, focal segmental sclerosis, renal tubule epitheliums swelling can be found under Light microscope and their glomerular chronic index (CI) increased as time progresses (P<0.01). Kidney tissue in the treatment group mice showed lighter changes, and CI was smaller compared with the model group mice.4. Renal pathology under the electron microscopeThere was no change in the process of the whole experiment in the control group. Fused foot process, increased messegium and thicken basilar membrane were observed in model group. Lesions in the treatment group mice were improved obviously.5. The expression of CXCL16, CXCR6, ADAM10and ox-LDL in renal tissueImmunohistochemistry semiquantitative analysis revealed that the protein expression of CXCL16, CXCR6, ADAM10and ox-LDL in the glomeruli in model group were strengthened remarkably, compared with those in control group(P<0.01). Meanwhile the changes kept increasing trend with the longer course. The changes about the above results in treatment group were improved (P<0.01), compared with model group at the same time.6. The correlation between the indexesCorrelation analysis showed that CXCL16expression in kidney had positive correlation with CXCL16levels in serum and urine, ox-LDL levels in serum and renal tissues, CXCR6protein expression in the renal tissues, and the renal CI in the model group (P<0.01). The renal CI was correlated positively with CXCL16levels in serum and urine, ox-LDL level in serum and renal tissues(P<0.01). Serum CXCL16levels had positive correlation with serum IFN-γ levels and renal ADAM10proetin expression (P<0.01).Conclusion:1. Compared with those of control group, the levels of ox-LDL in serum and renal tissue in model group mice increased obviously, and kept an increasing trend over time. Correlation analysis showed the serum and kidney ox-LDL expressions had positive correlation with renal chronic index, which suggested that ox-LDL might take part in the occurrence and development of Adriamycin nephrosis, and it relates to the severity of renal pathological damage.2. In comparison with those in control group, the levels of CXCL16in serum, urine and renal tissue in model group mice were increased obviously, and increased gradually over time. Correlation analysis showed that the serum, urinary and kidney CXCL16levels were correlated positively with renal chronic index, which showed that CXCL16may participate in the occurrence and development of Adriamycin nephrosis, and relate to the severity of renal pathological damage.3. Correlation analysis showed that the serum and urinary CXCL16levels had positive correlation with kidney CXCL16expression, which suggested that CXCL16levels in serum and urine might be used as an uninvasive index to evaluate the severity of the renal pathological damage.4. Correlation analysis showed that kidney CXCL16expression had positive correlation with kidney ox-LDL expression, which suggested that kidney CXCL16expression may associate with ox-LDL deposition in the kidney tissue as one of transmembrane proteins in development of Adriamycin nephropathy.5. After simvastatin treatment, kidney pathological damage were alleviated, chronic index was decreased, CXCL16levels in serum, urine and kidney as well as serum and kidney ox-LDL expressions were dropped, which suggested that simvastatin might play a role of renal protection by decreasing CXCL16expression in kidney tissues and interfering with the intracellular ox-LDL uptaken. |
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