枸杞多糖对糖尿病大鼠视网膜病理改变及其VEGF表达的影响

Effects of lycium barbarum polysaccharides on retinal pathological change and expression of VEGF in retina of diabetic rats

糖尿病视网膜病变（DR）的主要病理基础是缺氧和炎症引起的新生血管形成,导致血-视网膜屏障（BRB）的破坏,而血管内皮生长因子（VEGF）是主要的血管生成因子.研究证实,枸杞多糖（LBP）具有保护细胞抗氧化损伤的作用,但其在眼科疾病的应用研究较少. 目的 观察LBP对不同时期糖尿病大鼠视网膜的病理改变及VEGF表达的影响. 方法 取SPF级健康雄性SD大鼠117只,以随机数字表法将动物随机分为正常对照组、糖尿病组和LBP组.糖尿病组和LBP组大鼠一次性腹腔内注射55 mg/kg链脲佐菌素（STZ）柠檬酸缓冲液诱导1型糖尿病大鼠模型,正常对照组注射等体积的柠檬酸钠-柠檬酸缓冲液.造模成功后LBP组大鼠每日以250 mg/kg LBP定时定量灌胃,分别于成模后4、10、16周取各组大鼠行伊文思蓝（EB）染色视网膜铺片,动态观察视网膜血管的形态改变;以45 mg/kg EB由大鼠右颈静脉缓慢注入,循环2h后将质量分数1％多聚甲醛由左心室灌注,循环3 min后摘除眼球并分离视网膜,用标准曲线法检测视网膜中EB质量分数.采用免疫组织化学法和实时荧光定量PCR（real-time PCR）法分别检测视网膜中VEGF蛋白及其mRNA的表达. 结果 EB视网膜铺片显示,造模后4、10、16周,LBP组大鼠视网膜血管的走行、管径及渗漏等形态学改变均明显轻于糖尿病组大鼠.造模后4、10、16周,LBP组大鼠视网膜中EB的质量分数分别为（12.17±1.55）、（16.46±1.60）和（19.55± 1.49） mg/g,均明显低于同时期糖尿病组大鼠的（15.76±1.90）、（21.61±2.05）和（26.30±2.28） mg/g,差异均有统计学意义（P＜0.05）.免疫组织化学染色结果显示,造模后4、10、16周,大鼠视网膜中VEGF蛋白的表达以视网膜神经节细胞（RGCs）层为主,LBP组大鼠各时间点VEGF蛋白的染色明显弱于糖尿病组.免疫组织化学法检测表明,造模后4、10、16周LBP组大鼠VEGF蛋白在视网膜中的表达量分别为0.234±0.011、0.331±0.023和0.536±0.031,均明显低于同期糖尿病组大鼠的0.281±0.018、0.533±0.055和0.765±0.075,差异均有统计学意义（P＜0.05）.Real-time PCR显示,造模后4、10、16周LBP组VEGF mRNA的相对表达量分别为0.157±0.013、0.505±0.114和1.577±0.074,均低于同期糖尿病组的0.235±0.209、1.043±0.084和2.446±0.061,差异均有统计学意义（P＜0.05）. 结论 LBP可以减轻糖尿病造成的视网膜血管形态改变,减少血管壁的渗漏,从而保护BRB功能.

Background The primary pathological basis of diabetic retinopathy （DR） is new blood formation due to anoxia and inflammation,which results in breakdown of blood-retinal barrier （BRB）.Vascular endothelial growth factor （VEGF） is a key factor promoting neovascularization.Researches determined that lycium barbarum polysaccharides （LBP） can protect cells against oxidative damage.However,the study of LBP in ophthalmology is lack.Objective This study was to investigate the effects of LBP on the dynamic pathological change of retinal vessels and expression of VEGF in retina of diabetic rats.Methods One hundred and seventeen SPF male SD rats were randomly divided into the normal control group,the diabetic mellitus （DM） group and the LBP group according to random number table.Type 1 DM models were induced by intraperitoneal injection of streptozotocin （STZ,55 mg/kg） in the rats of the DM group and the LBP group,and then 250 mg/kg LBP was intragastically administered in the rats of the LBP group.The morphological change of retinal vessels was dynamically observed by retinal stretched preparation with Evans blue （EB） in 4,10 and 16 weeks after modeling.E B （45 mg/kg） was slowly injection via jugular vein,and 1% polyoxymethylene was infused into the left ventricule.The eyeballs were extracted and retina were isolated.EB content in the retinas （mg/g） was calculated using retinal stretched preparation method at the time points mentioned above.Expressions of VEGF protein and mRNA in the retinas were detected by immunohistochemistry and real-time quantitative PCR at various time points,respectively.Results Retinal stretched preparation with EB exhibited that the abnormal degree in the shape,diameter of vessels and leakage of the retinal blood vessels were significantly slighter in the LBP group than those of the DM group in 4,10,16 weeks after modeling.At 4,10,16 weeks,EB content in the retinas was （12.17±1.55）,（16.46±1.60） and （19.55±1.49） mg/g,which was significantly lower than （15.76± 1.90）,（21.61 ±2.05） and （26.30±2.28） mg/g of the DM group （P〈0.05）.Immunochemistry showed that the expression of VEGF protein primarily located at retinal ganglion cells （RGCs） layer.The staining intensity for VEGF protein was weaker in the LBP group than that of the DM group.The expression levels of VEGF protein （A value） in the LBP group were 0.234±0.011,0.331±0.023 and 0.536±0.031at various time points,with significant decline in comparison with 0.281±0.018,0.533±0.055 and 0.765±0.075 of the DM group （all at P〈0.05）.Real-time quantitative PCR revealed that the expression levels of VEGF mRNA were 0.157±0.013,0.505 ±0.114 and 1.577±0.074 in the LBP group at various time points,which were significantly lower than 0.235±0.209,1.043±0.084 and 2.446±0.061 of the DM group （all at P〈0.05）.Conclusions LBP can alleviate the DM-induced retinal vasculopathy,lessen the leakage of vessels well,and further protect the BRB.