title: Transport and equilibrium uptake of a peptide inhibitor of PACE4 into articular cartilage is dominated by electrostatic interactions.
abstract: The availability of therapeutic molecules to targets within cartilage depends on transport through the avascular matrix. We studied equilibrium partitioning and non-equilibrium transport into cartilage of Pf-pep, a 760 Da positively charged peptide inhibitor of the proprotein convertase PACE4. Competitive binding measurements revealed negligible binding of Pf-pep to sites within cartilage. Uptake of Pf-pep depended on glycosaminoglycan charge density, and was consistent with predictions of Donnan equilibrium given the known charge of Pf-pep. In separate transport experiments, the diffusivity of Pf-pep in cartilage was measured to be approximately 1 x 10(-6) cm(2)/s, close to other similarly-sized non-binding solutes. These results suggest that small positively charged therapeutics will have a higher concentration within cartilage than in the surrounding synovial fluid, a desired property for local delivery; however, such therapeutics may rapidly diffuse out of cartilage unless there is additional specific binding to intra-tissue substrates that can maintain enhanced intra-tissue concentration for local delivery.
authors.affiliation: Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
authors.forename: Sangwon
authors.initials: S
authors.lastname: Byun
authors.forename: Micky D
authors.initials: MD
authors.lastname: Tortorella
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Malfait
authors.forename: Kam
authors.initials: K
authors.lastname: Fok
authors.forename: Eliot H
authors.initials: EH
authors.lastname: Frank
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Grodzinsky
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001693:Biological Transport, Active; D002358:Cartilage, Articular / Q000378:metabolism*; D002417:Cattle; D006025:Glycosaminoglycans / Q000378:metabolism; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D007700:Kinetics; D008954:Models, Biological; D009842:Oligopeptides / Q000737:chemistry / Q000493:pharmacokinetics* / Q000494:pharmacology; D043484:Proprotein Convertases / Q000037:antagonists & inhibitors*; D011480:Protease Inhibitors / Q000737:chemistry / Q000493:pharmacokinetics* / Q000494:pharmacology; D019275:Radiopharmaceuticals; D051381:Rats; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors; D055672:Static Electricity
chemical_list: D006025:Glycosaminoglycans; D007457:Iodine Radioisotopes; D009842:Oligopeptides; D011480:Protease Inhibitors; D019275:Radiopharmaceuticals; D011994:Recombinant Proteins; C513087:Pcsk6 protein, rat; D043484:Proprotein Convertases
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