Transport and equilibrium uptake of a peptide inhibitor of PACE4 into articular cartilage is dominated by electrostatic interactions.
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.
Byun
Sangwon
S
Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Tortorella
Micky D
MD
Malfait
Anne-Marie
AM
Fok
Kam
K
Frank
Eliot H
EH
Grodzinsky
Alan J
AJ
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
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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