Transport and equilibrium uptake of a peptide inhibitor of PACE4 into articular cartilage is dominated by electrostatic interactions

Arch Biochem Biophys. 2010 Jul;499(1-2):32-9. doi: 10.1016/ Epub 2010 May 4.


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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Biological Transport, Active
  • Cartilage, Articular / metabolism*
  • Cattle
  • Glycosaminoglycans / metabolism
  • In Vitro Techniques
  • Iodine Radioisotopes
  • Kinetics
  • Models, Biological
  • Oligopeptides / chemistry
  • Oligopeptides / pharmacokinetics*
  • Oligopeptides / pharmacology
  • Proprotein Convertases / antagonists & inhibitors*
  • Protease Inhibitors / chemistry
  • Protease Inhibitors / pharmacokinetics*
  • Protease Inhibitors / pharmacology
  • Radiopharmaceuticals
  • Rats
  • Recombinant Proteins / antagonists & inhibitors
  • Static Electricity


  • Glycosaminoglycans
  • Iodine Radioisotopes
  • Oligopeptides
  • Protease Inhibitors
  • Radiopharmaceuticals
  • Recombinant Proteins
  • Pcsk6 protein, rat
  • Proprotein Convertases