Lipid Nanoparticles Elicit Reactogenicity and Sickness Behavior in Mice Via Toll-Like Receptor 4 and Myeloid Differentiation Protein 88 Axis

mRNA therapeutics encapsulated in lipid nanoparticles
(LNPs) offer
promising avenues for treating various diseases. While mRNA vaccines
anticipate immunogenicity, the associated reactogenicity of mRNA-loaded
LNPs poses significant challenges, especially in protein replacement
therapies requiring multiple administrations, leading to adverse effects
and suboptimal therapeutic outcomes. Historically, research has primarily
focused on the reactogenicity of mRNA cargo, leaving the role of LNPs
understudied in this context. Adjuvanticity and pro-inflammatory characteristics
of LNPs, originating at least in part from ionizable lipids, may induce
inflammation, activate toll-like receptors (TLRs), and impact mRNA
translation. Knowledge gaps remain in understanding LNP-induced TLR
activation and its impact on induction of animal sickness behavior.
We hypothesized that ionizable lipids in LNPs, structurally resembling
lipid A from lipopolysaccharide, could activate TLR4 signaling via
MyD88 and TRIF adaptors, thereby propagating LNP-associated reactogenicity.
Our comprehensive investigation utilizing gene ablation studies and
pharmacological receptor manipulation proves that TLR4 activation
by LNPs triggers distinct physiologically meaningful responses in
mice. We show that TLR4 and MyD88 are essential for reactogenic signal
initiation, pro-inflammatory gene expression, and physiological outcomes
like food intake and body weightrobust metrics of sickness
behavior in mice. The application of the TLR4 inhibitor TAK-242 effectively
reduces the reactogenicity associated with LNPs by mitigating TLR4-driven
inflammatory responses. Our findings elucidate the critical role of
the TLR4-MyD88 axis in LNP-induced reactogenicity, providing a mechanistic
framework for developing safer mRNA therapeutics and offering a strategy
to mitigate adverse effects through targeted inhibition of this pathway.