We have shown that lipid droplets (LDs) are rapidly upregulated by the host early following viral infection. This upregulation drives enhanced antiviral cytokine production (IFN-β & IFN-λ) and restricts viral replication (ZIKV, DENV & HSV-1). Recently, we have demonstrated that LDs can also be secreted and taken up by neighbouring cells, conferring protection on target cells during infection. Harnessing this process presents an exciting opportunity to develop LD-based antiviral therapies, and therefore, this study aimed to optimise an artificial LD (aLD) system for in vivo use.
We first characterised the lipidome of virally induced LDs to identify lipid changes associated with enhanced immunity in cells and determine key lipids to include in an aLD system. Antiviral LDs showed a significant shift in their lipidomic composition, including (1) a global increase in long and very-long polyunsaturated fatty acids such as docosahexaenoic acid and arachidonic acid, and (2) a modest but significant enrichment of phosphatidylinositol and phosphatidylethanolamine in the LD membrane. Recapitulating this, we developed an aLD incorporating a complex phospholipid membrane and triglyceride core. These aLDs demonstrated uptake across 12 cell types in vitro, with the highest uptake observed in brain cell types, specifically astrocytes and neurons. aLDs demonstrated a broad biodistribution in vivo following intravenous injection in mice and cardinal vein injection in zebrafish, where they localised to the lungs, heart, liver, and, most excitingly, to the brain and facial region within 6 hours and persisted for over 48 hours. aLDs demonstrated a strong antiviral capacity, which was enhanced via the addition of select long-chain fatty acids.
As a small lipid particle system, aLDs with complex membranes demonstrate superior organ delivery compared to extracellular vesicles and lipid nanoparticles. This flexible system allows us to change lipids and cargo, offering a promising platform for antiviral cargo delivery to the brain.