COMPOUND FROM TRIPTERYGIUM WILFORDII PROTECTS ISOLATED GLOMERULI FROM INCREASED ALBUMIN PERMEABILITY CAUSED BY FSGS SERUM

Abstract

276 Extracts from the plant Tripterygium wilfordii have been used extensively by physicians in China to treat proteinuric renal disease. We have previously shown that sera from patients with focal segmental glomerulosclerosis (FSGS) increase albumin permeability of isolated rat glomeruli in a unique in vitro bioassay, and that crude extract from T. wilfordii prevents the increase in albumin permeability caused by FSGS serum (Nephrol Dial Transplant 12:2064-2068, 1997). The active compound(s) responsible for this protective effect have yet to be identified. In the present studies, we tested four compounds purified from T. wilfordii to determine which may confer protection against the FSGS factor. All compounds were similar in chemical structure with minor differences and included celastrol, tingenone, salaspermic acid and oleanolic acid. Glomeruli were isolated from normal male Sprague-Dawley rats in medium containing 5% bovine serum albumin (BSA). Glomeruli were preincubated with test compound (100 μg/ml) for 10 minutes at 37°C, then washed with fresh isolation medium. Glomeruli were then incubated with FSGS serum for 10 minutes at 37°C. An oncotic gradient was generated by changing the bathing medium to 1% BSA, and volumetric change of glomeruli recorded using videomicroscopy. This change in glomerular volume due to the oncotic gradient was used to calculate convectional albumin permeability (Palbumin). FSGS serum alone and pooled normal serum were used as positive and negative controls, respectively. Palbumin of <0.5 indicated protection from the effect of FSGS serum on glomeruli. Our results show that preincubation with celastrol protected glomeruli from the increase in Palbumin caused by FSGS serum: 0.05 ± 0.12 (celastrol, n=10 glomeruli) vs 0.02 ± 0.02 (normal serum, n=10) vs 0.90 ± 0.13 (FSGS serum, n=15). The other compounds tested did not protect glomeruli from FSGS serum, with Palbumin values significantly higher than normal serum: 0.54 ± 0.13 (tingenone, n=5), 0.63 ± 0.22 (salaspermic acid, n=5), 0.68 ± 0.18 (oleanolic acid, n=5). We conclude that celastrol, a compound purified from extract of T. wilfordii, protects the protein permeability barrier of isolated glomeruli from the effect of FSGS serum. Whether this is the only protective compound from T. wilfordii remains to be determined by further testing.