Characterization of Intra-Cartilage Transport Properties of Cationic Peptide Carriers

Armin Vedadghavami; Shikhar Mehta; Ambika G. Bajpayee

doi:10.3791/61340

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Method Article

Characterization of Intra-Cartilage Transport Properties of Cationic Peptide Carriers

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DOI:

10.3791/61340

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August 10th, 2020

Armin Vedadghavami¹ , Shikhar Mehta¹ , Ambika G. Bajpayee¹^,²

¹Department of Bioengineering, Northeastern University, ²Department of Mechanical & Industrial Engineering, Northeastern University

Summary

This protocol determines equilibrium uptake, depth of penetration and non-equilibrium diffusion rate for cationic peptide carriers in cartilage. Characterization of transport properties is critical for ensuring an effective biological response. These methods can be applied for designing an optimally charged drug carriers for targeting negatively charged tissues.

Abstract

Several negatively charged tissues in the body, like cartilage, present a barrier to the targeted drug delivery due to their high density of negatively charged aggrecans and, therefore, require improved targeting methods to increase their therapeutic response. Because cartilage has a high negative fixed charge density, drugs can be modified with positively charged drug carriers to take advantage of electrostatic interactions, allowing for enhanced intra-cartilage drug transport. Studying the transport of drug carriers is, therefore, crucial towards predicting the efficacy of drugs in inducing a biological response. We show the design of three experiments which can quantify the equilibrium uptake, depth of penetration and non-equilibrium diffusion rate of cationic peptide carriers in cartilage explants. Equilibrium uptake experiments provide a measure of the solute concentration within the cartilage compared to its surrounding bath, which is useful for predicting the potential of a drug carrier in enhancing therapeutic concentration of drugs in cartilage. Depth of penetration studies using confocal microscopy allow for the visual representation of 1D solute diffusion from the superficial to deep zone of cartilage, which is important for assessing whether solutes reach their matrix and cellular target sites. Non-equilibrium diffusion rate studies using a custom-designed transport chamber enables the measurement of the strength of binding interactions with the tissue matrix by characterizing the diffusion rates of fluorescently labeled solutes across the tissue; this is beneficial for designing carriers of optimal binding strength with cartilage. Together, the results obtained from the three transport experiments provide a guideline for designing optimally charged drug carriers which take advantage of weak and reversible charge interactions for drug delivery applications. These experimental methods can also be applied to evaluate the transport of drugs and drug-drug carrier conjugates. Further, these methods can be adapted for the use in targeting other negatively charged tissues such as meniscus, cornea and the vitreous humor.

Introduction

Drug-delivery to negatively charged tissues in the body remains a challenge due to the inability of drugs to penetrate deep into the tissue to reach cell and matrix target sites¹. Several of these tissues comprise of densely-packed, negatively-charged aggrecans which create a high negative fixed charge density (FCD)² within the tissue and act as a barrier for the delivery of most macromolecules³^,⁴. However, with the assistance of positively charged drug carriers, this negatively charged tissue barrier can actually be converted into a drug depot via electrostatic ....