Table 2 Examples of materials to functionalize the surface of NPs proposed for drug delivery in PD

7pep-M-C6

Transferrin

Crossing of gastrointestinal barrier

Enter the cells through a specific clathrin-mediated mechanism

[114]

DA-Tf-LP

Transferrin

Crossing of BBB

BBB crossing by Tf receptor-mediated endogenous transcytosis

[117]

B-Lf-PEG-PLGA

Lactoferrin

Effective biological ligand to the striatum

The Lf receptor is overexpressed in epithelial cells, capillaries, and neurons in PD. Cellular uptake occurs via receptor-mediated transcytosis to Lf

[115]

DA-PEG-LP

Polyethylene glycol

Evasion of the immune system

PEG coating is believed to increase its biological half-life due to reduced interactions with plasma proteins or cell surface receptors

[118]

Selegiline-CS

Chitosan

Crossing of BBB and mucosal barriers

The mucoadhesive nature of QS improves mucosal retention time, improves permeability through the BBB through endocytosis by electrostatic adhesion, and through an opening of tight junctions

[119]

pDNA-NGF-GNP

Nerve growth factor

Improves neural uptake

Enhances neuronal uptake through NGF receptor-mediated endocytosis

[120]

hGDNF-Angiopep-DGL-PEG

Angiopep

Crossing of BBB

Angiopep is a ligand that specifically binds to low-density lipoprotein receptor-related protein (LRP that is overexpressed on the BBB and crosses by transcytosis

[121]

RHCl-Polysorbate 80-CS

Polysorbate 80

Crossing of BBB

Coating with polysorbate 80 helps in the adsorption of plasma proteins from blood and thus, facilitates the entry of nanoparticles to BBB by the receptor-mediated endocytosis

[122]