Spatial Charge-Hydrophobicity Configuration Modulates Cationic Peptide Transport in Cartilage.

Abstract

Charge-based delivery systems offer a promising approach for targeting dense, negatively charged tissues such as cartilage, which presents a significant transport barrier due to its high fixed charge density (FCD) from aggrecan glycosaminoglycans (GAGs). Cationic nano-carriers, including peptide-based systems, can overcome these barriers by leveraging electrostatic interactions to enhance intra-tissue penetration. However, the effectiveness of these carriers depends not only on their net positive charge, which drives Donnan partitioning, but also on the precise spatial arrangement of cationic and hydrophobic residues, which influences transport, binding, and retention. In this study, we investigated the impact of spatial charge distribution and hydrophobicity on the intra-cartilage transport and retention of arginine-rich cationic peptide carriers (CPCs) with a net charge of +14, optimized for effective cartilage targeting. Using both experimental methods and molecular modeling, we examined the transport properties of CPCs with varied charge and hydrophobic cluster arrangements in healthy and degenerated cartilage with different FCDs. Our findings reveal that peptides with a higher degree of clustered cationic or hydrophobic residues exhibit greater intra-cartilage diffusivity due to weaker binding interactions with aggrecan GAGs and a more flexible structural conformation that incurs an entropic penalty. However, while hydrophobic residues can enhance intra-tissue retention, particularly in degenerated tissues, they also promote competitive binding within synovial fluid (SF), emphasizing the need for hydrophilic designs. Overall, our results indicate that evenly distributed cationic residues and minimal hydrophobicity yield the most effective carriers for deep, long-term tissue penetration, providing a framework for the rational design of tissue-targeting cationic peptide carriers. The design principles established in this work can be broadly applied to the rational development of cationic carriers for targeted drug delivery in a wide range of negatively charged tissues.