| Objective: To investigate the effect of FK506, a new immunosuppressive agent,on experimental membranous nephropathy(MN) induced by cationized bovine serum albumin(C-BSA) in rat.Methods:Membranous nephropathy rat animal model were induced by C-BSA. 24 male Wistar rats weighing 200~230g were divided into four groups,(in every group n=6):group N(normal rats),M(MN rats),ME(earlier period of MN +FK506) and MF(MN+FK506).The rats in group M,ME and MF were immunized with 5mg C-BSA and Freund's incomplete adjuvant. One week later,rats were injected intravenously with 3mg of C-BSA 3 times weekly for 4 weeks.Group ME received intragastric administration of 2mg/kg FK506 daily for 30 days from the 3rd week after the first immunization;Group MF received intragastric administration of 2mg/kg FK506 daily for 30 days from the 5th week after the first immunization;Group M served as the disease control group and received no FK506.Group N were normal group with no immunization and drugs. Urine samples were collected every 2 weeks,and urinary protein excretion was measured using the colorimetric method.Rats were sacrificed 8 weeks after the first immunization.At sacifice,rats were anaesthetized and blood was obtained via cardiac puncture.Then they were immediately killed and the kidney were removed.The blood sample was conserved for measuring serum level of BUN,creatinine and albumin. Kidney specimens were routinely processed for light,electron microscopy.For linght microscopy,sections were stained with haematoxylin-eosin(HE),periodic acid-Schiff(PAS),periodicacid-Schiff methenamine silver(PAM),and Masson's trichrome(Masson). Immunohistochemistry method was performed to observe the express of TGF-β1 and NF-κB.Result: (1) Urinary protein excretion in group M was significantly higher than in group N (128.21±32.48 vs 9.24±1.82 mg/24h ,P<0.01).The serum level of albumin in group M was lower than in group N(30.97±3.21 vs 40.13±2.24 g/l ,P<0.05).There was no significant difference in serum creatinine and urea nitrogen level between group M and group N ( 86.40±15.82 vs 78.35±16.85μmol/L, 4.62±0.84 vs 5.09±0.76mmol/L, P>0.05).Transmission electron microscopy showed the structure of glomerular capillary walls was normal in group N. A patchy and diffuse distribution of subepithelial electron-dense deposits(EDDs) and diffuse fusion of the foot processes was observed in group M. Meanwhile,up-regulation of TGF-β1 and NF-κB expression was observed in immunohistochemical findings.(2) Compared with M group, in two treatment groups, urinary protein excretion was significantly decreased(17.01±3.99,32.67±8.00 vs 148.42±49.45 mg/24h, P<0.01). Urinary protein excretion in group ME was lower than in group MF at 6th and 8th week. The serum level of albumin in two treatment groups was significantly increased(39.64±4.05,38.00±2.49 vs 30.97±3.21 g/l,P<0.01). There was no significant difference in the serum creatinine level and light microscopic findings among groups. Scattered EDDs were observed in subepithelial sites in groups ME and MF,but the foot processes were preserved. Pathological changes were linghter in group ME than in group MF. The TGF-β1 and NF-κB scores were significantlylower in the treatment groups than in group M.Conclusions: TGF-β1 and NF-κB play important role in the development of MN. Tacrolimus could ameliorate the progression of rat MN, its renoprotective mechanism may be, at least in part,related with inhibition TGF-β1 overexpression and NF-κB activation in renal tissue of nephritic rats.Moreover, the efficacy of FK506 was significantly increased when the drug was administered in the early phase of immunization in this model. The present study suggests that FK506 is effective in patients with MN.
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