[Effect and mechanism of mulberry leaf polysaccharide on type 1 diabetic nephropathy in rats]

Objective: To observe the effects of mulberry leaf polysaccharide (MLP) on insulin-like growth factor 1 (IGF-1) and insulin-like growth factor blinding protein 3 (IGFBP-3) as well as the expression of IGF-1 and IGFBP-3 mRNA in the kidney of type 1 Diabetic Nephropathy (DN) rats, and to investigate its therapeutic effects and underlying mechanisms. Methods: Type 1 DN rat model was established by intraperitoneally injecting streptozocin (STZ). SD rats were randomly divided into the control, model, insulin and MLP groups, with eight rats in each group. Rats in MLP group were given orally with MLP 200 mg/kg daily for 8 weeks and insulin group rats were given subcutaneously injection of short acting insulin 1 U daily for 8 weeks. The changes in body weight, blood and urine parameters were recorded. Extracellular matrix (ECM) was calculated. The contents of IGF-1 and IGFBP-3 in blood serum were evaluated by enzyme-linked immunosorbent assay (ELISA). The mRNA expressions of IGF-1 and IGFBP-3 in the kidney were evaluated by fluorescence quantitative PCR. Results: Compared with rats in control group, blood glucose, triglyceride, total cholesterol, low density lipoprotein, very low density lipoprotein, 24 h urine protein, serum creatinine and urea nitrogen in the model group rats were significantly increased (all P<0.01), and these parameters of MLP group were significantly lower than the model group (all P<0.01). The contents of IGF-1 and IGFBP-3 in the blood serum of the model group were significantly higher than those in the control group (both P<0.001), while in the MLP group they were lower than the model group[IGF-1: (0.777±0.018) ng/ml vs (0.864±0.022) ng/ml, P<0.001; IGFBP-3: (0.759±0.016) ng/ml vs (0.846±0.021) ng/ml, P<0.001]. The mRNA expressions of IGF-1 and IGFBP-3 in the kidney of the model group were significantly higher than those in the control group (both P<0.001), while in the MLP group they were lower than in the model group (IGF-1: 1.450±0.032 vs 1.810±0.090, P<0.001; IGFBP-3: 1.684±0.018 vs 1.968±0.044, P<0.001). Compared with the model group rats, there were fewer pathological changes of kidney in MLP group rats. Conclusion: MLP has a certain therapeutic effect on DN, which may be achieved by decreasing the contents of IGF-1 and IGFBP-3 in the blood serum and down-regulating the over-expression of IGF-1 and IGFBP-3 mRNA in the kidney.