Donepezil Nanoemulsion\nInduces a Torpor-like State\nwith Reduced Toxicity in Nonhibernating Xenopus laevis Tadpoles

Achieving a reversible decrease of metabolism and other\nphysiological\nprocesses in the whole organism, as occurs in animals that experience\ntorpor or hibernation, could contribute to increased survival after\nserious injury. Using a Bayesian network tool with transcriptomic\ndata and chemical structure similarity assessments, we predicted that\nthe Alzheimer’s disease drug donepezil (DNP) could be a promising\ncandidate for a small molecule drug that might induce a torpor-like\nstate. This was confirmed in a screening study with Xenopus laevis tadpoles, a nonhibernator whole animal\nmodel. To improve the therapeutic performance of the drug and minimize\nits toxicity, we encapsulated DNP in a nanoemulsion formulated with\nlow-toxicity materials. This formulation is composed of emulsified\ndroplets <200 nm in diameter that contain 1.250 mM DNP, representing\n≥95% encapsulation efficiency. The DNP nanoemulsion induced\ncomparable torpor-like effects to those produced by the free drug\nin tadpoles, as indicated by reduced swimming motion, cardiac beating\nfrequency, and oxygen consumption, but with an improved biodistribution.\nUse of the nanoemulsion resulted in a more controlled increase of\nDNP concentration in the whole organism compared to free DNP, and\nto a higher concentration in the brain, which reduced DNP toxicity\nand enabled induction of a longer torpor-like state that was fully\nreversible. These studies also demonstrate the potential use of <i>Xenopus</i> tadpoles as a high-throughput in vivo screen to\nassess the efficacy, biodistribution, and toxicity of drug-loaded\nnanocarriers.