目的：在大鼠2型糖尿病(T2DM)造模的基础上继续制备糖尿病视网膜病变(DR)模型，观察二甲双胍对T2DM大鼠DR的预防及保护作用和对血清胱抑素C(Cys C)的影响，并对其机制进行探讨。

方法：筛选120只雄性SD大鼠，随机取30只分为空白对照组A(10只)，T2DM组(10只)和二甲双胍干预组A(10只)； 其余90只随机分为三组，分别为空白对照组B(30只)，DR组(30只)和二甲双胍干预组B(30只)。除空白对照组A、B外，其余所有组大鼠均构建T2DM模型，成模后二甲双胍干预组A大鼠给予二甲双胍灌胃，空白对照组A和T2DM组大鼠均给予生理盐水灌胃，干预3mo后分别测量三组大鼠的空腹血糖(FBG)和空腹血清胰岛素(FINS)指标，计算并分析胰岛素抵抗指数(HOMA-IR)； 测各组大鼠血清Cys C、肿瘤坏死因子-α(TNF-α)、白细胞介素-8(IL-8)、血管内皮生长因子(VEGF)和活性氧(ROS)水平，并行FFA、HE染色及透射电镜观察大鼠视网膜组织及血管形态； 在T2DM病程3mo后，二甲双胍干预组B大鼠开始给予二甲双胍灌胃，其余大鼠均给予生理盐水灌胃，按干预时长不同，分别于第4、5、6mo各组取10只大鼠进行观察，测各组大鼠血清Cys C、TNF-α、IL-8、VEGF和ROS水平，并行FFA、HE染色及透射电镜观察大鼠视网膜组织及血管形态。

结果：空白对照组A、T2DM组和二甲双胍干预组A三组间大鼠血清FBG、FINS、HOMA-IR、Cys C、TNF-α、IL-8、VEGF和ROS的表达均有差异(P<0.05)，且均为T2DM组最高，二甲双胍干预组A低于T2DM组； 空白对照组B、DR组和二甲双胍干预组B分别在4、5、6mo各同龄组中，三组间大鼠血清Cys C、TNF-α、IL-8、VEGF和ROS的表达均有差异(P<0.05)，且均为DR组最高，二甲双胍干预组B的表达低于DR组，随着DR病程的延长，Cys C、TNF-α、IL-8、VEGF和ROS的表达也进一步增加； FFA结果显示：与对应的空白对照组相比，各模型组大鼠视网膜血管走行迂曲，并且随着病程的延长可见微动脉瘤及荧光渗漏； HE染色结果显示：与对应的空白对照组相比，各模型组大鼠视网膜细胞排列紊乱，并随着病程的延长可见异常扩张的血管； 透射电镜结果显示：与对应的空白对照组相比，各模型组大鼠视网膜毛细血管损伤严重； 但与对应模型组比较，各二甲双胍干预组大鼠FFA、HE和透射电镜结果均有不同程度的改善。

结论：二甲双胍可通过下调血清Cys C介导的炎症和氧化应激水平，改善视网膜组织病变，从而对T2DM大鼠视网膜病变起预防和治疗作用。

METHODS: A total of 120 male SD rats were selected and 30 rats were randomly divided into blank control group A(10 rats), T2DM group(10 rats)and metformin intervention group A(10 rats). The remaining 90 rats were randomly divided into three groups: blank control group B(30 rats), DR group(30 rats)and metformin intervention group B(30 rats). Except for blank control groups A and B, T2DM models were constructed in all other groups. After modeling, rats in metformin intervention group A were given metformin by gavage, and rats in blank control group A and T2DM group were given normal saline by gavage. After 3mo of intervention, fasting blood glucose(FBG)and fasting serum insulin(FINS)indexes of the three groups were measured respectively, and the homeostasis model assessment of insulin resistance(HOMA-IR)was calculated and analyzed; The serum Cys C, tumor necrosis factor-α(TNF-α), the levels of Interleukin-8(IL-8), vascular endothelial growth factor(VEGF)and reactive oxygen species(ROS)were measured, and we observed the retinal tissue and vascular morphology of rats by FFA, HE staining and transmission electron microscopy; rats in metformin intervention group B began to give metformin by gavage 3mo after the course of T2DM, and other rats were given normal saline. According to the length of intervention, 10 rats were taken from each group and observed at 4, 5 and 6mo respectively. Serum levels of Cys C, TNF-α, IL-8, VEGF and ROS were measured in each group. We observed the retinal tissue and vascular morphology of rats by FFA, HE staining and transmission electron microscopy.

RESULTS: The expressions of serum FBG, FINS, HOMA-IR, Cys C, TNF-α, IL-8, VEGF and ROS were statistically significant among the blank control group A, T2DM group and metformin intervention group A(P<0.05), which were the highest in T2DM group, and the metformin intervention group A were lower than T2DM group; The expression of Cys C, TNF-α, IL-8, VEGF and ROS of rat serum were statistically significant among the blank control group B, DR group and metformin intervention group B within the same age groups at 4, 5 and 6mo respectively(P<0.05), and were all the highest in DR group. The expressions of metformin intervention group B were lower than those of the DR group. With the prolongation of DR course, the expression of Cys C, TNF-α, IL-8, VEGF and ROS also increased further; FFA results showed that compared with the corresponding blank control group, the retinal blood vessels of each model group were tortuous, and microaneurysms and fluorescence leakage were visible with the prolongation of the disease course; HE staining results showed that compared with the corresponding blank control group, the retinal cells of each model group were arranged disorderly, and abnormal dilated blood vessels were visible with the prolongation of the disease course; Transmission electron microscopy results showed that compared with the corresponding blank control group, the retinal capillaries in each model group were seriously damaged; However, compared with the corresponding model group, the results of FFA, HE and transmission electron microscopy of rats in each metformin intervention group had different degrees of improvement.

CONCLUSIONS: Metformin can improve retinal tissue lesions by down-regulating serum Cys C-mediated levels of inflammation and oxidative stress, thus playing a preventive and therapeutic role in the retinopathy in T2DM rats.