Effects of FK506 on experimental membranous glomerulonephritis induced by cationized bovine serum albumin in rats

Background. There have been no reports on the effect of FK5 06, a new immunosuppressive agent, on experimental membranous glomerulonephritis (MN) induced by an exogenous antigen. Therefore we investigated the effects of FK506 on MN induced by cationized bovine serum albumin (C-BSA) in rats. Methods. Two weeks after the rats were immunized with 1 mg of C-BSA and Freund's complete adjuvant, they received intravenous injections of 3 mg/kg of C-BSA 3 times weekly for 4 weeks. Rats were divided into four groups: group A (n=5) received intramuscular injections of 3 mg/kg of FK506 daily for 5 days beginning 2 days before the first immunization; group B (n=4) received 1 mg/kg of FK506 daily for 2 weeks beginning 2 weeks after the first immunization; and group C (n=4) received 1 mg/kg of FK506 daily for 2 weeks beginning 4 weeks after the first immunization. Group D (n=5) received no FK506 and served as the control group. Rats were sacrificed 8 weeks after the first immunization. Results. Administration of FK506 in the preimmunization stage almost completely suppressed the development of MN in group A. Histological findings in groups B and C were similar to those in group D, the control group. However, urinary protein excretion was significantly lower in group B (24 +/- 46 mg/day) and C (220 +/- 44 mg/day) than in group D (330 +/- 61 mg/day). Expression of intracellular adhesion molecule-1 in glomeruli and the number of leukocyte functioning-associated molecules-1 were significantly decreased in groups A, B, and C compared with the control group. Administration of FK506 was not associated with any significant side-effects or histological abnormalities. The whole-blood trough levels of FK506 in groups B and C were 9.1 ng/ml and 9.2 ng/ml respectively. Conclusions. 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 may be useful in patients with intractable nephrotic syndrome such as MN.