Cheruvu Narayan P S, Kompella Uday B
Department of Pharmaceutical Sciences, University of Nebraska Medical Center, Omaha, NE 68198-5840, USA.
Invest Ophthalmol Vis Sci. 2006 Oct;47(10):4513-22. doi: 10.1167/iovs.06-0404.
To determine the influence of the choroid-Bruch's layer and solute lipophilicity on in vitro transscleral drug permeability in bovine and porcine eyes.
The in vitro permeability of two VEGF inhibitory drugs, budesonide and celecoxib, which are lipophilic and neutral at physiologic pH, and of three marker solutes, 3H-mannitol (hydrophilic, neutral), sodium fluorescein (hydrophilic, anionic), and rhodamine 6G (lipophilic, cationic), were determined across freshly excised scleras, with or without the underlying choroid-Bruch's layer. Select studies were performed using porcine sclera with and without choroid-Bruch's layer. Neural retina was removed by exposure of the eyecup to isotonic buffer and wherever required, the retinal pigment epithelial (RPE) layer of the preparation was disrupted and removed by exposure to hypertonic buffer. Because of the poor solubility of celecoxib and budesonide, permeability studies were conducted with 5% wt/vol of hydroxypropyl-beta-cyclodextrin (HPbetaCD). For other solutes, permeability studies were conducted, with and without HPbetaCD. Partitioning of the solutes into bovine sclera and choroid-Bruch's layer was also determined.
The calculated log (distribution coefficient) values were -2.89, -0.68, 2.18, 3.12, and 4.02 for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G, respectively. Removal of RPE was confirmed by transmission electron microscopy and differences in the transport of mannitol. The order of the permeability coefficients (Papp) across sclera and sclera-choroid-Bruch's layers in bovine and porcine models was 3H-mannitol > fluorescein > budesonide > celecoxib > rhodamine 6G, with HPbetaCD, and 3H-mannitol > fluorescein > rhodamine 6G, without HPbetaCD. The presence of choroid-Bruch's layer reduced the bovine scleral permeability by 2-, 8-, 16-, 36-, and 50-fold and porcine tissue permeability by 2-, 7-, 15-, 33-, and 40-fold, respectively, for mannitol, sodium fluorescein, budesonide, celecoxib, and rhodamine 6G. The partition coefficients measured in bovine tissues correlated positively with the log (distribution coefficient) and exhibited a trend opposite that of transport. The partition coefficient ratio of bovine choroid-Bruch's layer to sclera was approximately 1, 1.5, 1.7, 2, and 3.5, respectively, for the solutes, as listed earlier.
The choroid-Bruch's layer is a more significant barrier to drug transport than is sclera. It hinders the transport of lipophilic solutes, especially a cationic solute, more than hydrophilic solutes and in a more dramatic way than does sclera. The reduction in transport across this layer directly correlates with solute binding to the tissue. Understanding the permeability properties of sclera and underlying layers would be beneficial in designing better drugs for transscleral delivery.
确定脉络膜-布鲁赫膜以及溶质亲脂性对牛眼和猪眼体外经巩膜药物渗透性的影响。
测定两种在生理pH值下呈亲脂性且为中性的VEGF抑制药物布地奈德和塞来昔布，以及三种标记溶质[³H-甘露醇（亲水性、中性）、荧光素钠（亲水性、阴离子型）和罗丹明6G（亲脂性、阳离子型）]在有无脉络膜-布鲁赫膜的新鲜离体巩膜上的体外渗透性。部分研究使用了有无脉络膜-布鲁赫膜的猪巩膜。通过将眼杯暴露于等渗缓冲液去除神经视网膜，必要时，通过将制剂暴露于高渗缓冲液破坏并去除视网膜色素上皮（RPE）层。由于塞来昔布和布地奈德的溶解度较差，渗透性研究使用5%（重量/体积）的羟丙基-β-环糊精（HPβCD）进行。对于其他溶质，在有和没有HPβCD的情况下进行渗透性研究。还测定了溶质在牛巩膜和脉络膜-布鲁赫膜中的分配情况。
甘露醇、荧光素钠、布地奈德、塞来昔布和罗丹明6G的计算log（分配系数）值分别为-2.89、-0.68、2.18、3.12和4.02。通过透射电子显微镜和甘露醇转运差异证实了RPE的去除。在牛和猪模型中，经巩膜和巩膜-脉络膜-布鲁赫膜的渗透系数（Papp）顺序为：使用HPβCD时，³H-甘露醇＞荧光素＞布地奈德＞塞来昔布＞罗丹明6G；不使用HPβCD时，³H-甘露醇＞荧光素＞罗丹明6G。脉络膜-布鲁赫膜的存在使牛巩膜对甘露醇、荧光素钠、布地奈德、塞来昔布和罗丹明6G的渗透性分别降低2倍、8倍、16倍、36倍和50倍，使猪组织的渗透性分别降低2倍、7倍、15倍、33倍和40倍。在牛组织中测得的分配系数与log（分配系数）呈正相关，且呈现出与转运相反的趋势。如前所述，溶质的牛脉络膜-布鲁赫膜与巩膜的分配系数比分别约为1、1.5、1.7、2和3.5。
脉络膜-布鲁赫膜对药物转运的阻碍比巩膜更大。它对亲脂性溶质尤其是阳离子溶质转运的阻碍比对亲水性溶质更大，且比巩膜的阻碍作用更显著。跨该层转运的降低与溶质与组织的结合直接相关。了解巩膜及其下层的渗透特性将有助于设计更好的经巩膜给药药物。
