8.D.2.  The Lipid Nanoparticle (LNP) Family 

Liposomes can be used as biocompatible carriers of drugs, peptides, proteins, plasmic DNA, antisense oligonucleotides or ribozymes for pharmaceutical and biochemical purposes. The enormous versatility in particle size and in the physical parameters of the lipids affords an attractive potential for constructing tailor-made vehicles for a wide range of applications. Different properties (size, colloidal behavior, phase transitions, and polymorphism) of diverse lipid formulations (liposomes, lipoplexes, cubic phases, emulsions, and solid lipid nanoparticles) for distinct applications (parenteral, transdermal, pulmonary, and oral administration) have been reviewed (Ulrich 2002). This author considers specific targeting of cargo, and how to trigger drug release and membrane fusion. LNPs can carry any of a number of dyes and other ligands for a variety of purposes (Becker-Ritt et al. 2017). They have even been used for modified mRNA-mediated theraputics (Granot and Peer 2017). Lipoprotein complexes are naturally occurring protein-lipid nanoparticles that transport lipids in the circulation of animals (Gursky 2015).

Solid lipid particulate systems such as solid lipid nanoparticles (S-LNPs), lipid microparticles (LMPs) and lipospheres have been used as alternative carriers for therapeutic peptides, proteins and antigens. Under optimized conditions, they can be produced to incorporate hydrophobic or hydrophilic proteins and seem to fulfil the requirements for a particulate carrier system. Proteins and antigens intended for therapeutic purposes may be incorporated or adsorbed onto S-LNPs (Almeida and Souto 2007). Formulation of S-LNPs confers improved protein stability, avoids proteolytic degradation, and allows sustained release of the incorporated molecules. Important peptides such as cyclosporine A, insulin, calcitonin and somatostatin have been incorporated into solid lipid particles. They have been used for delivery of antiretroviral drugs to the brain (Wong et al. 2010) as well as antioxidant, anti-inflammatory, anti-carcinogenic and anti-aging compounds (Neves et al. 2012). Bicontinuous lipid cubic phases may consist of a single lipid bilayer that forms a continuous periodic membrane lattice structure with pores formed by two interwoven water channels (Barriga et al. 2019). Lipid nanoparticle technologies for the study of G protein-coupled receptors in various lipid environments have been considered (Lavington and Watts 2020).

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