血糖波动对2型糖尿病大鼠认知功能的影响

Effect and mechanism of blood glucose fluctuation on cognitive function in type 2 diabetic rats

目的探讨血糖波动对2型糖尿病大鼠认知功能的影响及其与海马组织氧化应激指标的相关性。方法通过高糖高脂饮食联合腹腔注射链脲菌素(streptozotocin,STZ)建立2型糖尿病(type 2 diabetes mellitus,T2DM)模型,采用简单随机化法分为血糖正常对照组(control group,C group)(n=10)和2型糖尿病组(n=26)。24只造模成功的2型糖尿病大鼠采用简单随机化法随机分为持续高糖组(sustained hyperglycemia group,SHG group)(n=12)和血糖波动组(intermittent hyperglycemia group,IG group)(n=12),其中IG组通过改变大鼠的饮食习惯和生活节律来建立血糖波动模型。6周后每周随机测定各组大鼠一日内9个时间点的血糖浓度,从而得到血糖日平均水平(mean blood glucose,MBG)、日平均血糖的标准差(standard deviation of daily average blood glucose,SDBG)、最大血糖波动幅度(largest amplitude of glycemic excursions,LAGE)和平均血糖波动幅度(mean amplitude of glycemic excursion,MAGE)的改变情况。第10周Morris水迷宫检测各组大鼠空间学习记忆能力。第11周检测大鼠海马组织内氧化应激指标丙二醛(malondialdehyde,MDA)、超氧化物歧化酶(superoxide dismutase,SOD)、谷胱甘肽过氧化物酶(glutathione peroxidase,GSH-Px),比较各组氧化应激指标及其与认知功能的相关性。结果1)血糖波动6周后,IG组和SHG组MBG、SDBG、LAGE、MAGE均明显高于C组(P<0.05);IG组的SDBG、LAGE、MAGE高于SHG组,MBG低于SHG组(P<0.05)。2)大鼠学习记忆能力比较,糖尿病大鼠(IG组和SHG组)第4天的逃避潜伏期比C组延长(P<0.05),且第5天穿越平台的次数、经过目标象限(定位航行实验中平台所在象限)的活动路程比与活动时间比均较C组减少(P<0.05)。IG组与SHG组比较,第5天穿越平台次数、经过目标象限的活动路程比与活动时间比均较少(P<0.05)。3)氧化应激指标检测:IG组、SHG组与C组比较,MDA含量升高,SOD及GSH-Px含量降低(P<0.05)。IG组与SHG组比较,MDA升高、SOD及GSH-Px降低。4)氧化应激指标与学习记忆能力相关性分析显示:MDA与活动路程比、活动时间比及穿越平台次数呈负相关(P<0.01)。GSH-Px、SOD与活动路程比、活动时间比及穿越平台次数呈正相关(P<0.01)。结论1)通过高糖高脂饮食联合腹腔注射小剂量的STZ(30 mg/kg),并通过改变饮食习惯及生物节律可以成功建立T2DM血糖波动模型。2)血糖波动比持续高血糖更易影响T2DM大鼠的认知功能。3)血糖波动会加剧海马区氧化应激损伤。

Objective To investigate the effect of blood glucose fluctuation on cognitive function in type 2 diabetic rats and its correlation with oxidative stress in hippocampus.Methods Type 2 diabetes mellitus(T2DM)was established by high sugar and high fat diet combined with intraperitoneal injection of streptozotocin(STZ).The rats were randomly divided into sustained hyperglycemia group(SHG group)(n=12)and intermittent hyperglycemia group(IG group)(n=12).In the IG group,the blood glucose fluctuation model was established by changing the diet habit and life rhythm of rats.The normal blood glucose control group(C group)(n=10)was established.After 6 weeks,the blood glucose levels in each group were measured at 9 points in time within a day,and the mean blood glucose(MBG),standard deviation of daily average blood glucose(SDBG),the largest amplitude of glycemic excursions(LAGE)and mean amplitude of glycemic excursions(MAGE)were obtained.Morris water maze was used to detect the spatial learning and memory ability of the rats in each group at the 10th week.The contents of malondialdehyde(MDA),superoxide dismutase(SOD)and glutathione peroxidase(GSH-Px)in the hippocampus were measured at the 11th week.The correlation between oxidative stress and cognitive function was analyzed.Results 1)After 6 weeks of blood glucose fluctuation,MBG,SDBG,LAGE and MAGE in the IG group and SHG group were significantly higher than those in the C group(P<0.05).SDBG,LAGE and MAGE in the IG group were higher than those in the SHG group,while MBG was lower than that of SHG group(P<0.05).2)With regard to the learning and memory ability of rats,the escape latency of diabetic rats(IG group and SHG group)on the 4th day was longer than that in the C group(P<0.05).The number of crossing platform on the 5th day,the activity distance ratio and time ratio of passing through the target quadrant(the quadrant where the platform is in the positioning navigation experiment)were lower than that in the C group(P<0.05).Compared with the SHG group,the times of crossing platform,the activity distance ratio and time ratio of passing through the target quadrant in the IG group on the 5th day were shorter(P<0.05).3)Detection of oxidative stress index:compared with the C group,the content of MDA in the IG group and SHG group increased,while the content of SOD and GSH-Px decreased(P<0.05).Compared with the SHG group,the content of MDA in the IG group increased,while the content of SOD and GSH-Px decreased(P<0.05).4)The analysis correlation between oxidative stress index and learning and memory ability showed that MDA was negatively correlated with activity distance ratio,activity time ratio and times of crossing platform(P<0.01),while GSH-Px and SOD were positively correlated with activity distance ratio,activity time ratio and times of crossing platform(P<0.01).Conclusion 1)High glucose and high-fat diet combined with low-dose STZ(30 mg/kg)could successfully establish the model of T2DM,and the blood glucose fluctuation model of T2DM could be successfully established by changing diet habits and biological rhythm.2)Blood glucose fluctuation is more likely to affect the cognitive function of T2DM rats than continuous hyperglycemia.3)The fluctuation of blood glucose may aggravate the oxidative stress injury in hippocampus.