Objective Bevacizumab ( BM ) is an angiogenesis inhibitor widely used in cancer therapy, but its off-target effect of proteinuria may lead to discontinuation of treatment.This study was to explore the mechanisms of BM inducing proteinuria in mice. Methods Twenty-four healthy mice were randomly divided into four groups, saline control, low-dose BM, medium-dose BM, and high-dose BM, treated by injection of normal saline and BM at 10, 35, and 60 mg per kg of the body weight, respectively, though the tail vein.At 4 weeks after injection, 24-hour urine was collected to determine the total urine protein and blood obtained from the eyeballs for biochemical analysis.Then all the mice were sacrificed and the kidneys harvested for observation of pathologic changes in the glomeruli as well as for immunohistochemistry, Western blotting, and real-time PCR analysis. Results Compared with normal saline,BM obviously elevated the level of 24-hour urine protein, with statistically significant differences between the control and the medium-and high-dose BM groups (0.23 ±0.02 vs 1.14 ±0.13 and 1.43 ±0.10, P<0.01), but not between the control and the low-dose BM (0.23 ±0.02 vs 0.29 ±0.07, P>0.05).No significant differences were observed among the four groups in the levels of Cr, BUN, AST and ALT (P>0.05).Under the optical microscope, the kidneys showed normal structures in the control group, no signifi-cant pathologic changes in the low-dose BM, and vacuolus-like alteration with atrophic glomerular endothelial cells in the medium-and high-dose BM groups.Immunohistochemical analysis demonstrated the expressions of VEGF and podocin were moderately or strongly positive in the control and low-dose BM groups, by weakly positive or negative in the medium-and high-dose BM groups.Compared with the control group, the expression of the VEGF protein in the renal tissue was significantly decreased in the high-dose BM group (0.76 ±0.09 vs 0.39 ±0.05, P<0.01) but had no remarkable difference from that in the low-dose (0.81 ±0.10) or medium-dose BM (0.64 ±0.08) group (P>0.05), and the expression of the podocin protein was significantly reduced in the medium-dose BM (0.67 ±0.07 vs 0.43 ±0.10, P<0.05) and high-dose BM (0.67 ±0.07 vs 0.19 ±0.04, P<0.01), but not in the low-dose BM group (0.67 ±0.03) (P>0.05).The mRNA expressions of VEGF and podocin were not significantly changed in the low-dose BM group as compared with the control (1.07 ±0.61 and 1.12 ±0.09 vs 1.23 ±0.25 and 1.17 ±0.19, P>0.05) but remarkably de-creased in the medium-dose (0.82 ±0.38 and 0.71 ±0.18) and high-dose BM groups and (0.47 ±0.64 and 0.42 ±0.09) groups (P<0.01). Conclusion Bevacizumab damages glomerular filtration membrane and induce proteinuria partially by down-regulating the protein and mRNA expressions of VEGF and podocin.%目的：贝伐珠单抗在肿瘤靶向治疗中已广泛应用，蛋白尿作为其不良反应之一在一定程度上影响了临床疗效。文中探索抗血管生成剂贝伐珠单抗诱导小鼠蛋白尿形成的机制。方法24只健康清洁级小鼠随机数字表法分为对照组、贝伐珠单抗低、中、高剂量组[贝伐珠单抗用量分别为10、35、60 mg／（ kg· w）]。贝伐珠单抗组小鼠静脉注射不同剂量贝伐珠单抗，对照组静脉注射相同体积的等渗盐水。4周末收集24 h尿液，测尿蛋白总量，随后眼球取血，检测生化值，最后处死小鼠，留取肾组织，观察肾小球病理变化，并行免疫组化、Western blot及Real time-PCR方法检测。结果与对照组24 h尿蛋白量（0．23±0．02）比较，贝伐珠单抗低剂量组蛋白表达（0．29±0．07）升高，但差异无统计学意义（ P＞0．05）；贝伐珠单抗中、高剂量组小鼠24 h尿蛋白量表达升高[1．14±0．13、1．43±0．10]，差异有统计学意义（P＜0．05）；贝伐珠单抗低、中、高剂量组两两比较的差异有统计学意义（P＜0．05）。4组血肌酐（Scr）、尿素氮（BUN）、谷丙转氨酶（ALT）、谷草转氨酶（AST）差异无统计学意义（P＞0．05）。光镜下观察对照组小鼠肾组织结构正常，贝伐珠单抗低剂量组未见明显病理改变，贝伐珠单抗中、高剂量组小鼠肾小球内皮细胞萎缩，呈空泡状改变。免疫组化显示对照组及贝伐珠单抗低剂量组血管内皮生长因子（ vascular endothelial growth factor， VEGF）、podocin表达中或强阳性，贝伐珠单抗中、高剂量组呈弱阳性或阴性。同时Western blot法测定肾组织中VEGF、podocin蛋白的表达量：与对照组VEGF表达（0．76±0．09）比较，贝伐珠单抗低剂量组和贝伐珠单抗中剂量组VEGF表达（0．81±0．10、0．64±0．08）无明显差异（P＞0．05），而贝伐珠单抗高剂量组（0．39±0．05）明显降低（P＜0．01）。与对照组podocin蛋白表达量（0．67±0．07）比较，贝伐珠单抗中剂量组、贝伐珠单抗高剂量组（0．43±0．10、0．19±0．04）明显下降（P＜0．05），贝伐珠单抗低剂量组（0．67±0．03）差异无统计学意义（P＞0．05）。与对照组VEGF、podocin mRNA表达（1．23±0．25、1．17±0．19）相比，贝伐珠单抗低剂量组VEGF、podocin mRNA（1．07±0．61、1．12±0．09）表达无明显变化（ P＞0，05），贝伐珠单抗中、高剂量组VEGF、podocin mRNA表达（0．82±0．38、0．71±0．18；0．47±0．64、0．42±0．09）均明显降低，差异有统计学意义（P＜0．01）。结论贝伐珠单抗可损伤肾小球滤过膜，导致蛋白尿形成，其部分机制可能与下调VEGF、podocin蛋白及其mRNA表达有关。
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