Effects of triptolide on the podocyte protein expression of Nephrin and Podocin and its mechanism in type 2 diabetic rats

Objective To observe the effect of triptolide on podocyte protein expression of Nephrin and Podocin and investigate its mechanism in kidney of type 2 diabetic rats. Methods 50 eight-week SPF male Wistar rats weighted (200±20) g were randomly divided into two groups : normal control group (n=10) and model group (n=40). Rats were fed a high fat high sugar diet for 8 weeks and given a low dose of streptozotocin (30 mg/kg) developed type 2 diabetic model rats. Rats were fed with regular chow. The successfully induced rats (n=28) were randomly divided into two groups: type 2 diabetic mellitus without treatment group (n=14) and type 2 diabetic mellitus group treated with triptolide (n=14, 200 μg·kg-1·d-1). After administration of triptolide for 8 weeks, serum biochemistry, kidney weight/body weight and urinary albumin (UAL) were detected. The rats were sacrificed for the observation of renal histomorphology through optic microscope and transmission electron microscope. The mRNA and protein expressions of Nephrin, Podocin, osteopontin, transforming growth factor-β1 (TGF-β1) and monocyte\macrophage surface specific antigen (ED-1) in renal tissue were determined by quantitative real-time PCR, semi-quantitative immunohistochemical assays and western blot technique. Results Compared with NC, UAL level was significantly increased in type 2 diabetic rats (F=181.51, P<0.01). The protein expressions of Nephrin (F=36.82, P<0.05) and Podocin (F=32.57, P<0.05) in the kidney were significantly decreased and mRNA expressions of Nephrin(F=88.45, P<0.01)and Podocin (F=55.43, P<0.01)were also significantly decreased in diabetic rats, compared with NC group. After administration of triptolide for 8 weeks, the protein expressions of Nephrin ((1.82±0.06) and (1.63±0.06), P<0.05) and Podocin ((1.80±0.06) and (1.60±0.06), P<0.05) were up-regulated, and the mRNA expressions of Nephrin ((0.73±0.12) and (0.19±0.08), P<0.01) and Podocin ((0.60±0.12) and (0.26±0.07), P<0.01) were also up-regulated in diabetic rats. The protein expressions of osteopontin (F=40.06, P<0.05), TGF-β1 (F=28.84, P<0.05)and mRNA expressions of osteopontin (F=177.46, P<0.01), TGF-β1 (F=161.27, P<0.01) were all significantly up-regulated than those in NC group (P<0.01). Triptolide inhibited the protein expressions of osteopontin ((1.27±0.03) and (1.39±0.05), P<0.05), TGF-β1 ((1.23±0.03) and (1.44±0.02), P<0.05) and mRNA expressions of osteopontin ((2.05±0.16) and (3.26±0.26), P<0.01), TGF-β1((4.0±0.70) and (6.5±0.71), P<0.01). Conclusion These results showed that triptolide ameliorated podocyte injury in type 2 diabetic rats. Renoprotection of triptolide on podocyte may be mediated through, at least partly, suppressing the renal inflammatory stress and infiltration of macrophage. Key words: Triptolide; Diabetic nephropathy; Nephrin; Podocin; Osteopontin