Functional Characterization of Amino Acid Transport System for Transport of Phenylalanine on Mammalian Cornea for Better Ocular Drug Delivery

In last few years transporter targeted drug delivery has drawn attention of research to identify and explore various nutrient transport systems including amino acid transporters for better drug delivery. The aim of the present study was to investigate and characterize the transport of L-phenylalanine across goat cornea. Transport of Lphenylalanine (0.5 % w/v aqueous solution) through excised goat cornea using modified Franz diffusion cell was investigated to characterize the effect of concentration, pH, presence of sodium ions, presence of metabolic inhibitors like sodium azide, presence of sodium potassium ATPase pump inhibitor like ouabain and presence of other amino acids. Effect of presence of aspartame (a dipeptide) and tripeptide (glutathione) was also investigated. To characterize the effect of stereo specificity, corneal transport of DL-phenylalanine and D-phenylalanine was studied. The results of studies revealed that transport of L-phenylalanine is concentration dependent, pH independent, sodium independent and inhibited by cationic and neutral amino acids along with the dipeptide aspartame. Cationic and neutral amino acids seem to share the same transporter for corneal transport. The transporter identifies and prefers the transport of L form of amino acid as compared to DL and D form. All the result are consistent with the previous reports on transport of L-phenylalanine through mammalian epithelial membrane and suggests functional presence of L-type of amino acid transport system on goat cornea.