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World J Pharmacol. Mar 9, 2013; 2(1): 1-17
Published online Mar 9, 2013. doi: 10.5497/wjp.v2.i1.1
Utility of transporter/receptor(s) in drug delivery to the eye
Sai HS Boddu, Jerry Nesamony
Sai HS Boddu, Jerry Nesamony, Department of Pharmacy Practice, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, Toledo, OH 43614, United States
Author contributions: Both the authors have contributed equally to each of the three activities: (1) substantial contributions to conception and design; (2) drafting the article or revising it critically for important intellectual content; and (3) final approval of the version to be published.
Supported by The Research Start-Up Funds from the University of Toledo
Correspondence to: Sai HS Boddu, PhD, Assistant Professor of Pharmaceutics, Department of Pharmacy Practice, College of Pharmacy and Pharmaceutical Sciences, University of Toledo, 3000 Arlington Ave. (MS1013), Toledo, OH 43614, United States.
Telephone: +1-419-3831959 Fax: +1-419-3831950
Received: February 4, 2012
Revised: June 20, 2012
Accepted: December 1, 2012
Published online: March 9, 2013

The eye is a highly protected organ, and designing an effective therapy is often considered a challenging task. The anatomical and physiological barriers result in low ocular bioavailability of drugs. Due to these constraints, less than 5% of the administered dose is absorbed from the conventional ophthalmic dosage forms. Further, physicochemical properties such as lipophilicity, molecular weight and charge modulate the permeability of drug molecules. Vision-threatening diseases such as glaucoma, diabetic macular edema, cataract, wet and dry age-related macular degeneration, proliferative vitreoretinopathy, uveitis, and cytomegalovirus retinitis alter the pathophysiological and molecular mechanisms. Understanding these mechanisms may result in the development of novel treatment modalities. Recently, transporter/receptor targeted prodrug approach has generated significant interest in ocular drug delivery. These transporters and receptors are involved in the transport of essential nutrients, vitamins, and xenobiotics across biological membranes. Several influx transporters (peptides, amino acids, glucose, lactate and nucleosides/nucleobases) and receptors (folate and biotin) have been identified on conjunctiva, cornea, and retina. Structural and functional delineation of these transporters will enable more drugs targeting the posterior segment to be successfully delivered topically. Prodrug derivatization targeting transporters and receptors expressed on ocular tissues has been the subject of intense research. Several prodrugs have been designed to target these transporters and enhance the absorption of poorly permeating parent drug. Moreover, this approach might be used in gene delivery to modify cellular function and membrane receptors. This review provides comprehensive information on ocular drug delivery, with special emphasis on the use of transporters and receptors to improve drug bioavailability.

Keywords: Anterior segment, Posterior segment, Transporter, Receptor, Eye, Ocular diseases