The Experimental Study Of The Renoprotective Effects Of Soy Protein Diet On 5/6 Nephrectomized Rats

BACKGROUNDResearch into the health effects of soyfoods and soybean constituents has increased at a phenomenal pace over the past decade. It had been confirmed that soy protein had the renal protective effects, but there was no literature about their effects on nephrosclerotic rats. In this study, we used the method of 5/6 nephrectomy to induce a model of nephrosclerosis. The effects of soy protein diet on the renal were studied, and mechanisms were further discussed.METHODS1. A total of forty male Sprague-Dawley rats were randomly assigned to the followingfour groups: soy protein group(Soy), Low casin protein group(Casein), control group (Con) and sham-operated group(So). The former three groups were subjected to 5/6 nephrectomy while the last group only anesthetized.2. A 24-hour urine sample was collected just one day before the operation, so were the blood for the measurement of serum albumin, total protein, creatinine, urea, cholesterol and triglyceride. A right subcapsular nephrectomy was performed and one week later this procedure was followed by surgical resection of the upper and lower thirds of the left kidney. The renal mass reduction was performed by surgical resection.3. After surgery, the four groups were fed with different diets seperately. The low casein protein group and soy protein group were given a low casein protein diet(6%casein protein) or a soy protein diet(6% soy protein). The control group and sham-operated group were maintained on a regular laboratory diet (20% casein protein). Urine and blood sample was collected at 4, 8 and 12 week. All rats were killed when the study was finished.4. Pathologic changes within kidney were investigated by microscope. GSI was calculated to evaluate the situation of the nephrosclerosis.5. Immunohistochemistry were also employed to investigate the expression of NF- k B, MCP-1, RANTES, TGF- P 1, a -SMA, FN, ED-1 within the residual kidney.RESULT1. The body weight of all rats was increased at the end of the study. The weight of residual kidney of the operated groups was higher than sham-operated group, and that of soy protein group was the lowest in four groups.2. The serum creatinine and urea of operated rats were increased during the study. Compared with the control group and the low casein protein group, serum creatinine and urea of soy protein group were the lowest at 4,8 and 12 week.3. The rats in all operated groups gained similar serum albumin and total protein on the whole study, with no significant differences between the three groups.4. The urinary albumin excretion (UAE) was significantly increased at 4wk,extremely at 12wk. The UAE of soy protein group was markedly lower than control group and low casein group.5. In control group, the basement membrane was markedly thickened. Focal segmental glomerulosclerosis could be observed and many vitrifaction occurred. Dilated and denatured tubulars could be seen. Many vessel muscular layer were thickened even cause vascular constriction. Compared with control group, the pathological lesion of soy protein group was less serious, and GSI of soy protein group were significantly decreased.6. The deposition of NF- k B, MCP-1, RANTES, TGF- P 1, a -SMA, FN, ED-1 of the operated groups was significantly elevated compared with sham-operated group ,and that of the soy protein group was the lowest in the three operated groups.CONCLUSIONS1. 5/6 nephrectomy could induce the model of nephrosclerosis.2. Soy protein diet could partly improve the serum lipid and renal function of the 5/6 nephrectomize rats, and reduce UAE as well.3. Soy protein diet could attenuate pathological lesions of residual kidney through some mechanisms such as inhibition of the inflammation infiltration and transdifferentiation.