title: Drug Distribution to Retinal Pigment Epithelium: Studies on Melanin Binding, Cellular Kinetics, and Single Photon Emission Computed Tomography/Computed Tomography Imaging.
abstract: Melanin binding is known to affect the distribution and elimination of ocular drugs. The purpose of this study was to evaluate if the extent of drug uptake to primary retinal pigment epithelial (RPE) cells could be estimated based on in vitro binding studies with isolated melanin and evaluate the suitability of single photon emission computed tomography/computed tomography (SPECT/CT) in studying pigment binding in vivo with pigmented and albino rats. Binding of five compounds, basic molecules timolol, chloroquine, and nadolol and acidic molecules methotrexate and 5(6)-carboxy-2',7'-dichlorofluorescein (CDCF), was studied using isolated melanin from porcine choroid-RPE at pH 5.0 and 7.4. The uptake to primary porcine RPE cells was studied with timolol, chloroquine, methotrexate, and CDCF. The cell study setting was modeled using parameters from the in vitro binding study. In vivo kinetics of 3-[I-123]-iodochloroquine was studied by the SPECT/CT method in albino and pigmented rats. All basic compounds bound to melanin at both pH values, whereas the acidic compounds bound more at pH 5.0 than at pH 7.4. The basic compounds (chloroquine, timolol) showed significant cellular uptake, unlike the acidic compounds (methotrexate, CDCF). On the basis of the modeling, melanin binding was a major factor governing the overall drug distribution to the RPE cells. Likewise, melanin binding explained distribution of 3-[I-123]-iodochloroquine in the pigmented RPE, whereas drug accumulation was not seen in the albino rat. This study demonstrates the suitability of noninvasive SPECT/CT imaging in monitoring ocular melanin binding in vivo. These studies are a useful step toward understanding the pharmacokinetic impact of melanin binding.
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.
authors.forename: Anna-Kaisa
authors.initials: AK
authors.lastname: Rimpelä
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.
authors.forename: Mechthild
authors.initials: M
authors.lastname: Schmitt
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.
authors.forename: Satu
authors.initials: S
authors.lastname: Latonen
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.
authors.forename: Marja
authors.initials: M
authors.lastname: Hagström
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.
authors.forename: Maxim
authors.initials: M
authors.lastname: Antopolsky
authors.affiliation: Department of Thermodynamics, Faculty of Physics, University of Valencia , E-46100 Burjassot, Spain.
authors.forename: José A
authors.initials: JA
authors.lastname: Manzanares
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.
authors.forename: Heidi
authors.initials: H
authors.lastname: Kidron
authors.affiliation: Centre for Drug Research, Division of Pharmaceutical Biosciences, Faculty of Pharmacy, University of Helsinki , P.O. Box 56, FI-00014 Helsinki, Finland.|School of Pharmacy, University of Eastern Finland , P.O. Box 1627, FI-70211 Kuopio, Finland.
authors.forename: Arto
authors.initials: A
authors.lastname: Urtti
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002738:Chloroquine / Q000378:metabolism; D005123:Eye / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007457:Iodine Radioisotopes; D007700:Kinetics; D008543:Melanins / Q000378:metabolism*; D008727:Methotrexate / Q000378:metabolism; D009248:Nadolol / Q000378:metabolism; D011485:Protein Binding; D051381:Rats; D055213:Retinal Pigment Epithelium / Q000378:metabolism*; D000072098:Single Photon Emission Computed Tomography Computed Tomography / Q000379:methods*; D013552:Swine; D013999:Timolol / Q000378:metabolism
chemical_list: D007457:Iodine Radioisotopes; D008543:Melanins; D009248:Nadolol; D013999:Timolol; D002738:Chloroquine; D008727:Methotrexate
keywords: SPECT/CT; binding parameters; melanin binding; ocular pharmacokinetics; retinal pigment epithelium