磁共振成像对活体兔结膜下药物注射后渗透性的评价作用

Assessment of subconjunctival delivery of ionic permeants in rabbits with Gd-DTPA and magnetic resonance imaging in vivo

目的使用磁共振成像(magnetic resonance imag-ing,MRI)评价兔结膜下药物注射后的渗透性和清除率,探讨一种能够在活体内动态观察的眼部药代动力学检测方法。方法健康新西兰白兔24只,按随机数字表法分为3组,每组8只,取右眼作为实验眼,对侧眼作为对照眼。以MRI的造影剂钆喷酸葡胺(Gadolinium-diethylene triamine pentaaceticacids,Gd-DTPA)作为示踪剂,分别于结膜下注射0.5mol/L、0.05mol/L、0.005mol/L造影剂0.1ml,对照眼注射0.9%生理盐水0.1ml。采用MRI扫描仪,于注药后1h内每间隔15min左右扫描1次,2～3h内间隔30min左右扫描1次,通过MRI观察药物的渗透性、眼内分布及结膜下的清除速度。0.5mol/L组于术前和术后24h进行角膜内皮镜检查,观察角膜内皮细胞密度、内皮细胞面积变异系数、六边形细胞百分数和中央角膜厚度。使用Excel绘制信号增强率对时间曲线,采用配对t检验分析角膜内皮细胞密度变化。结果MRI扫描可见:0.5mol/L组前房及睫状体信号明显增强,而眼后段则未探测到高信号;0.05mol/L组前房信号无明显增强,接近注射位置的睫状体信号增强;0.005mol/L组眼前、后段的药物渗透浓度均低于MRI探测阈值。睫状体部位对药物经巩膜的被动转运阻力最低,结膜下药物的体积和浓度随时间逐渐下降。结膜下Gd-DTPA用药前后,0.5mol/L组的角膜内皮细胞密度、内皮细胞面积变异系数、六边形细胞百分数和中央角膜厚度差异均无统计学意义(P>0.05)。结论MRI作为非侵袭、动态、实时的检查方法可于活体内定量分析结膜下药物注射后的渗透效率,是对传统药代动力学研究方法的有力补充。

Objective To assess the permeability and clearance rate of a model for ionic permeants after subconjunctival injection using nuclear magnetic resonance imaging （MRI）;to investigate a pharmacokinetic method for the ocular region in vivo.Methods Twenty-four rabbits were randomly divided into three groups according to a random numbers table,taking the right eye as the experimental eye and the left eye as the control eye.Experimental eyes in each group received subconjunctival injections of 0.5 mol/L,0.05 mol/L and 0.005 mol/L as a contrast agent. The control eyes received a subconjunctival injection of isotonic NaC1. All eyes were scanned once every 15 rain for the first hour and once every 30 min for the next 2-3 hours. The permeability, distribution and subconjunctival clearance rate of the drugs were observed with MRI. The corneal endothelial cell density （ECD）, coefficient of variance of the endothelial cell area （CV）, percentage of hexagonal cells （6A） and central corneal thickness （CCT） were examined before and 24 h after the subconjunctival injection of the 0.5 mol/L contrast agent using a non-contact corneal endothelial microscope. The signal enhancement rate vs. time curve was plotted with Microsoft Excel software and statistical analysis of the changes in the corneal endothelium was done using a paired t-test. Results In the 0.5 mol/L group, there was an obvious strengthening of the signal in the anterior chamber and ciliary body, however, a strong signal was not detected in the posterior segments. In the 0.05 mol/L group, there was no obvious strengthening of the signal in the an-terior chamber but the signal in the ciliary body close to the injection site strengthened. In the 0.005 mol/L group, the drugs and the osmotic concentration in the anterior and posterior segments of the eyes were below the detection threshold with MRI. The trans-scleral passive transport resistance of drugs was the lowest in the ciliary body. The subconjunctival pharmacological volume and concentration gradually decreased over time. There were no significant differences in ECD, CV, 6A and CCT before and after the experiment in the 0.5mol/L group （P〉0.05）. Conclusion Subconjunctival delivery of ionic permeants in vivo can be quantitatively analyzed by MRI. MRI is a noninvasive, dynamic and real-time complementary tech-nique to traditional pharmacokinetic methods.