[Effects of valsartan, mycophenolate mofetil and their combined application on TRAIL and nuclear factor-kappaB expression in the kidneys of diabetic rats].

OBJECTIVE

To evaluate the expression of TNF-related apoptosis inducing ligand (TRAIL) and nuclear factor (NF)-kappaB in the kidney tissues of diabetic rats and the effects of valsartan, mycophenolate mofetil (MMF), and their combined application on the renal TRAIL and NF-kappaB expression.

METHODS

Eighty uninephrectomized male Wistar rats were randomly divided into 2 groups: normal control (NC) group (n = 28), undergoing intraperitoneal injection of citric acid buffer, and diabetes mellitus (DM) group, undergoing intraperitoneal injection of streptozotocin (STZ) to establish DM models. The 52 DM rats were randomly divided into 7 equal subgroups: DM without treatment for 4 weeks (DM4), DM without treatment for 8 weeks (DM8) DM without treatment for 12 weeks (DM12) , and DM without treatment for 16 weeks (DM16), valsartan treatment (DM + V), MMF treatment (DM + M), and combined treatment (DM + V + M). The treatment subgroups were treated for 8 weeks immediately after the diabetic models ere established. Twenty-four hour urine was collected to measure the amount of protein 4, 8, 12, and 16 weeks after the induction of DM respectively. The rats were sacrificed. Blood samples were collected from the abdominal aorta to detect the blood urea nitrogen (BUN), serum creatinine (sCr), albumin, and glucose. The kidneys were taken out. Hypertrophy index (left kidney weight/body weight) was determined. Quantitative real time RT-PCR was performed to detect the expression of TRAIL and NF-kappaB mRNA. Immunohistochemistry was used to detect the protein expression of TRAIL and NF-kappaB.

RESULTS

1. The 24 h urine protein levels and hypertrophy indexes of all DM subgroups were significantly higher than those of the NC groups (all P <0.05). 24 h urine protein and hypertrophy index increased gradually and peaked in the l2th week; blood albumin gradually decreased since the 8th week(P <0.01), and BUN and sCr began to decrease only since the 16th week (both P <0.01). Compared with the DM 8 subgroup, the hypertrophy index and 24 h urine protein of the different treatment subgroups, especially the DM + V + M subgroup, were significantly lower (all P <0.05). 2) Quantitative real time RT-PCR showed that compared with the NC group, the TRAIL expression levels of the DM subgroups were significantly lower before the 12th week after induction of DM model (all P < 0.01), and then significantly higher in the 16th week (all P < 0.01). The TRAIL expression of the treatment groups, especially that of the DM + M subgroup, were significantly higher than that of the DM8 group (all P <0.05). Compared with the NC group, the NF-kappaB expression levels of the DM subgroups were significantly higher time-dependently (all P <0.01). Compared with the DM8 group, the NF-kappaB expression levels of the treatment subgroups, especially that of the DM + V + M subgroup were significantly lower (all P <0.05). 3) The expression of TRAIL was mainly located in the convoluted tubule of kidney, and no TRAIL protein expression was detected in the glomeruli or renal vasculature. The levels of NF-kappaB protein expression, shown in glomeruli and convoluted tubules, of all DM subgroups were all higher than that of the NC group. The NF-kappaB protein expression level of the DM + V + M subgroup was significantly lower. The number of NF-kappaB positive cells was significantly related to the mononuclear macrophage infiltration , kidney function, and structural lesion.

CONCLUSION

An important monitoring factor in the autoimmune system, TRAIL closely participates in the pathogenesis of diabetic nephropathy, possibly controlled by NF-kappaB. In the early stage combination of valsartan and MMF may upregulate the expression of TRAIL, thus protecting the kidney function.