| OBJECTIVE 1. To study the histologic changes of lipid-induced renal injury in rabbits and the protective effect of tea polyphenols on it. 2. To study the inhibitive effect of tea polyphenols on lipoprotein intake in cultured rats' mesangial cells.METHODS In the vivo study, 19 rabbits were divided randomly into 3 groups, 6 rabbits on normal diets (normal control, NC), 6 rabbits who were induced renal injury with high fat and cholesterol diets but without any treatment (lipid-induced renal injury, LRI), 7 rabbits on high fat and cholesterol diets who were treated with oral tea polyphenols 200mg/kg per day (TP). Serum lipid levels and activity of lipoprotein lipase (LPL) and hepatic lipase (HL) in blood plasma, urinary albumin, renal cortex's malondialdehyde (MDA) content, and lipase activity of renal tissue were measured. Pathological and ultrastrctural examinations of renal tissue were also held finally.-4-In the vitro study, rats' mesangial cells were cultured in hyperlipoprotein conditions built respectively by very low density lipoprotein (VLDL), low density lipoprotein (LDL), and oxidized low density lipoprotein (OX-LDL). Mesangial cells in each condition were further treated respectively with tea polyphenols at different concentrations. Total cholesterol (TC) of the mesangial cells and proportion of mesangial cells containing lipid droplets was measured, and ultrastructure observation was performed under electron microscope.RESULTS Vivo: Serum TC, triglyceride(TG), high density lipoprotein cholesterol (HDL-c) and low density lipoprotein cholesterol (LDL-c) increased significantly in LRI during the study. LRI's renal cortex's MDA content and urinary albumin excretion were both obviously higher than the other two groups (P<0.05). It's renal tissue's lipase activity was lower than NC's (P<0.05). Atherosclerosis, irregularly shaped glomeruli, straitness and closure of glomerular capillary lumina, and shrink of glomerular basement membrane were observed by light microscope examination in renal cortex of rabbits in LRI. In electron microscope observation, we found many lipid droplets in capillary endothelia's and mesangial cells' plasma, proliferation of capillary endothelia, mesangial cells and podocytes, and dropsy of cytoplasm and mitochondria in-5-endothelia and podocytes. Such morphological abnormalities were alleviated obviously in TP, and urinary albumin was less excreted in TP than in LRI (P<0.05). IP's serum lipid levels increased less than LRI's (PO.05) during the study. It's final serum TC and LDL-c levels were significantly higher than NC's (P<0.05) and also higher than their own at the beginning of the study (P<0.05), while there was no statistical difference in the renal cortex's MDA content between LRI's and NC's (P>0.05). IP's renal tissue's lipase activity was significantly lower than NC's (PO.05), and showed insignificant difference with LRI's. There was no remarkable difference in blood plasma LPL and HL activity among the 3 groups (P>0.05) during the study.Vitro: Foam cells were observed in hyperlipoprotein-conditioned mesangial cells, and both the TC level and the proportion of mesangial cells containing lipid droplets in these cells were higher than those in the cells cultured in lipid free conditions. Gradual declinations of TC levels and lipid-droplet-containing cells' proportions were observed in 0.004ng/100μl~40ng/100μl tea polyphenols treated lipoprotein-conditoned mesangial cells, which presented dosage-depended relationships. Number of lipid droplets in these cells were also decreased. These changes were not furthered in LDL-conditoned and VLDL-conditioned mesangial cells treated-6-with 4000ng/100μl tea polyphenols.CONCLUSION Histological changes, such as atherosclerosis, ischemia injuries and lipid deposition and cells' proliferation in glomeruli, take place in renal cortex of rabbits fed with high fat and cholesterol diets, accompanied with proteinuria in these rabbits. Tea polyphenols alleviate lipid-induced renal injury mainly by antiperoxidiz...
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