Expression Of COX-2 And Prostaglandins In Kidney Of Diabetic Rats And Effects Of Benazepril

Objectives:Diabetic nephropathy is one of the most common blood capillary complication of diabetes mellitus, and the incidence of end-stage renal disease caused by diabetic nephropathy increases year by year. So, it is very important to clarify the pathogenesis, seeking methods to prevent and treat diabetic nephropathy.Diabetic nephropathy is pathologically characterized by glomerular hypertransfusion, hyperfiltration , glomerula hypertrophy,mesangial region over-accumulation of extracellular matrix proteins,renal interstitial fibrosis,which lead to glomerular sclerosis in the end.The diabetic nephropathy patients may have glomerular hyperfiltration in their early onset,which is the foundation of the renal function and morphous change. Prostaglandin system and renin-angiotensin system are two important vasomotion systems,which participate in renal hemodynamic change. Prostaglandins metabolic abnormality is one of the factors on glomerular hyperfiltration.Cyclooxygenase(COX) is the rate limiting enzyme for prostaglandins synthesis and has two forms:constitutive enzyme COX-1 and inducible enzyme COX-2, COX-1expresses stably and mediates physiological prostaglandins synthesis.COX-2 takes part in adjusting renal blood supply and rennin release.It is low express in physiological condition, but can be induced by a variety of stimuli.Lately research indicate that oxidative stress(OS) in diabetic rats can up-regulate COX-2 expression,while ROS scavenger can inhibited COX-2 over-expression .In addition,many researches have shown that ACEI can lighten OS in diabetic rats. Herein, this study want to discover two things:(1) the relationship among COX-2,Angâ…¡and OS;(2) whether ACEI can down-regulate COX-2 expression via blocking back OS and Angâ…¡path. It may be a new strategy for the treatment of diabetic nephropathy. In this study,the expression of COX-2 and SOD was observed and the interrelationship between these factors and development of renal alterations was analysed.The urinary TXB₂ and 6-keto-PGF_1α were determined by radioimmunoassay.The possible mechanism for benazepril to protect renal function was also investigated in order to provide theoretical basis for the prevention and treatment of diabetic nephropathy.Methods:Sixty healthy male Wistar rats (weigh 180-200g) were randomly divided to 3 groups:normal control group(A),diabetic group(B),and benazepril-treated diabetic group(C).The rats of group B and C received a single intraperitoneal injection of STZ(dissolved in 0.1 mol/l citrate buffer pH4.5) at a dose of 60mg/kg and the rats of group A only received an injection of the same volume of sodium citrate.The diabetic model was considered to be successful when the blood glucose was 16.7mmol/l and urinary glucose(+++)-(++++) after 72hours of STZ injection.The rats of group C were treated with benapril(10mg/kg/d) and the the rats of group A and B were treated with the same volume of normal sodium.All rats were allowed free access to food and water during the experiment,whereas insulin and other hypoglycrmic drugs were not supplied.At 4 and 8 weeks after the onset of diabetes,blood glucose(BG),urinary creatinine(Ucr),24-hours protein ,kidney mass/body mass ratio were measured,then ten rats were sacrificed for each group respectively.The renal tissues were obtained and used for HE and PAS light microscopy.The expression values of COX-2 and SOD protein, COX-2 mRNA in renal were measured with immunohistochemical method and hybridization in situ.Results:At week 4 and week 8,kidney mass/body mass ratio,Ccr and 24-hours urinary protein were higher in group B than in group A(P<0.01) and these parameters were significantly decreased in group C.Urinary TXB₂,6-keto-PGF_1αconcentration were higher in group B than in group A,and these parameters were significantly decreased in group C.Immunohistochemical and hybridization in situ showed the COX-2 protein and mRNA,SOD protein in renal were obviously increased in group B than in group A and these parameters were significantly decreased in group C.Conclusions:1.The expression of COX-2,SOD were up-regulated in renal of diabetic rats and urinary TXB₂, 6-keto-PGF_1α excretion are increased.It indicate that COX-2 and PGs participate in the occurrence and development of diabetic nephropathy.2.The expression of COX-2 mRNA and protein,SOD protein were decreased in benazepril group than diabetic group,which indicates that ACEI may down-regulate COX-2 expression via inhibit oxidative stress and Angâ…¡, then decreased pathological TXB₂, 6-keto-PGF_1α synthesize,lessen glomerular hypertransfusion, hyperfiltration in diabetic rats,decrease 24-hours urinary protein,prevent the development of DN.