Inflammation Aggravating Lipids Mediated Renal Injury And Renoprotective Effect Of Simvastatin On Adriamycin Induced Nephropathy Rats

PART ONE: ADRIAMYCIN INDUCED NEPHROPATHY IN YOUNG RATSObjective To replicate the model of adriamycin (ADR) induced nephropathy in young rats.Methods Male Sprague-Dawley rats (4 to 5 wk old) were randomly divided into control and ADR nephropathy groups. ADR nephropathy was induced by a single tail intravenous injection of ADR (6.5mg/kg weight). The rats were sacrificed at 2, 4, 8, and 12 wk after ADR injection, then biochemical study and renal histopathology were evaluated.Results The ADR nephropathy rats developed marked proteinuria, hypoalbuminemia, and hyperlipoidemia at 2 wk after ADR injection, and renal histopathology was similar to human minimal change nephrotic syndrome in earlier phase of disease. Progressively focal segmental glomerulosclerosis accompanied with renal function loss was observed since 8 wk. Conclusion This successful replication ADR induced nephropathy model in young rats provided useful tool for the subsequent research of nephropathy.PART TWO: THE ROLE OF SREBP AND LDL RECEPTOR PATHWAY IN LIPIDS MEDIATED RENAL INJURY IN ADRIAMYCIN INDUCED NEPHROPATHY RATSObjective To explore the role of sterol regulatory element binding protein-2 (SREBP-2) and low density lipoprotein receptor (LDLr) pathway in lipids mediated renal injury in adriamycin induced nephropathy rats.Methods Total cholesterol, free cholesterol and cholesterol ester in kidney were measured by enzymic assay. Oil Red O staining was used to examine kidney morphology. LDLr and SREBP-2 mRNA expression were measured by reverse transcription-polymerase chain reaction. LDLr and SREBP-2 protein expression were detected by Western-blotting assay.Results The expression of LDLr and SREBP-2 mRNA and protein in kidney were increased as a time-dependent manner from 8th to 12th week, accompanied with increased cholesterol accumulation in nephropathy rats kidney, and there was a significant positive correlation ship between the intrarenal cholesterol levels and glomerulosclerosis.Conclusion The disrupted LDLr feedback regulation in adriamycin induced nephropathy rats may lead to upregulating expression of the pathway of SREBP-2 and LDLr, which may be the cause of the increasing cholesterol accumulating in kidney.PART THREE: THE ROLE OF INFLAMMATION IN LIPIDS MEDIATED RENAL INJURY IN ADRIAMYCIN INDUCED NEPHROPATHY RATSObjective To explore the role of inflammation in lipids mediated renal injury in adriamycin induced nephropathy rats.Methods Local expression of Interleukin-1β(IL-1β) and transforming growth factor-β1 (TGF-β1) in kidney were detected by immunohistochemistry method, IL-1βmRNA and protein expression were measured by reverse transcription-polymerase chain reaction and enzyme linked immunosorbent assay, respectively. Transcription factor-nuclear factor-κB (NF-κB) p65 protein expression was evaluated by Western-blotting assay. Results Expression of NF-κB p65 protein was increased as a time-dependent manner from 8th to 12th week, accompanied with upregulation expression of IL-1βmRNA and protein, and TGF-β1 protein.Conclusion The overexpression of inflammation in renal region may contribute to development of glomerulosclerosis in ADR-induced nephropathy rats. NF-κB activity upregulation and increasing expression of IL-1βwere the main characteristics of this kind of inflammation.PART FOUR: MECHANISM OF SIMVASTATIN RENOPROTECTIVE EFFECTS ON ADRIAMYCIN INDUCED NEPHROPATHY RATSObjective To investigate simvastatin renoprotective effects on adriamycin (ADR) induced nephropathy rats and the mechanism.Methods The model of ADR induced nephropathy in young rats (model group) was replicated, meanwhile, the ADR induced nephropathy simvastatin treatment group (treated group) was designed. 6 days after adriamycin injection, simvastatin at 3mg/kg body weight was administered once a day by gavage for 11 weeks, while 0.9% saline 5ml/kg once a day by gavage in control group and model group. The rats were sacrificed at 2, 4, 8, and 12 wk after ADR injection, then biochemical study, renal histopathology, lipids accumulation and the expression of inflammation factors in kidney were evaluated.Results At each experimental period, there was no significant difference in serum lipids between treated group and model group. The 24 h urinary protein excretion in treated group at 4 and 8 week, the serum creatinine level in treated group at 12 week and the glomerulosclerosis index in treated group at 8 and 12 week were lower than model group (P<0.05 or P<0.01), respectively. The activity of NF-κB p65 protein, and the expression of IL-1β, TGF-β1, LDLr and SREBP-2, and the intrarenal cholesterol contents in treated group at 8 and 12 week were lower than model group (P<0.05 or P<0.01), respectively.Conclusion Simvastatin had renoprotective effects on ADR induced nephropathy rats, independent of serum lipids lowering effects. Simvastatin decreased renal region inflammation, and may downregulate the expression of SREBP-2 and LDLr by reversing the disruption of SREBP-2 and LDLr feedback regulation, which was induced by inflammation. Through the way, simvastatin decreased cholesterol accumulation in kidney, and played a role in renal protection.