Transporter Protein Expression of Corneal Epithelium in Rabbit and Porcine: Evaluation of Models for Ocular Drug Transport Study

The transcorneal route is the main entry route for drugs
to the
intraocular parts, after topical administration. The outer surface,
the corneal epithelium (CE), forms the rate-limiting barrier for drug
permeability. Information about the role and protein expression of
drug and amino acid transporter proteins in the CE is sparse and lacking.
The aim of our study was to characterize transporter protein expression
in rabbit and porcine CE to better understand potential drug and nutrient
absorption after topical administration. Proteins, mainly Abc and
Slc transporters, were characterized with quantitative targeted absolute
proteomics and global untargeted proteomics methods. In the rabbit
CE, 24 of 48 proteins were detected in the targeted approach, and
21 of these were quantified. In the porcine CE, 26 of 58 proteins
were detected in the targeted approach, and 20 of these were quantified.
Among these, 15 proteins were quantified in both animals: 4f2hc (Slc3a2),
Aqp0, Asct1 (Slc1a4), Asct2 (Slc1a5), Glut1 (Slc2a1), Hmit (Slc2a13),
Insr, Lat1 (Slc7a5), Mct1 (Slc16a1), Mct2 (Slc16a7), Mct4 (Slc16a3),
Mrp 4 (Abcc4), Na+/K+-ATPase, Oatp3a1 (Slco3a1),
and Snat2 (Slc38a2). Overall, the global proteomics results supported
the targeted proteomics results. Organic anion transporting polypeptide
Oatp3a1 was detected and quantified for the first time in both rabbit
(1.4 ± 0.4 fmol/cm2) and porcine (11.1 ± 5.3
fmol/cm2) CE. High expression levels were observed for
L-type amino acid transporter, Lat1, which was quantified with newly
selected extracellular domain peptides in rabbit (48.9 ± 11.8
fmol/cm2) and porcine (37.6 ± 11.5 fmol/cm2) CE. The knowledge of transporter protein expression in ocular barriers
is a key factor in the successful design of new ocular drugs, pharmacokinetic
modeling, understanding ocular diseases, and the translation to human.