Objective: Chitosan-based nanoparticles (NPs) were prepared to promote intracellular sustained delivery of the synthetic delta opioid D-Ala(2)-D-Leu(5)-enkephalin ( DADLE), prolonging peptide activity and inducing a safe and reversible hypometabolic state. Materials and methods: NPs were prepared by combining ionotropic gelation and ultrasonication treatment. NP uptake studies and the effects of encapsulated DADLE on HeLa cells proliferation were tested by transmission electron microscopy (TEM) analysis, by immuno-fluorescence and immuno-cytochemistry. Results: DADLE-loaded NPs are produced with suitable characteristics, a satisfactory process yield (55.4%% +/-+/- 2.4%%) and encapsulation efficiency (64.6%% +/-+/- 2.1%%). NPs are effective in inducing a hypometabolic stasis at a 10

Keywords:chitosan nanoparticles;DADLE;reversible hypometabolism;non-hibernating cells;transcription