Combining Leu-enkephalin nanomedicines with enkephalinase inhibitors: a promising painkiller strategy?

Abstract

International audienceThis study investigates the potential of a novel nanomedicine approach relying on squalene nanoparticles of endogenous enkephalinase inhibitors (EEI) - opiorphin (OPN) and STR-324 - to alleviate pain by potentiating the action of enkephalins in vivo, in a model of acute inflammatory pain. A library of squalene-based EEI prodrugs was synthesized. These prodrugs were unable to self-assemble into nanoparticles, in contrast to the other squalenoylated prodrugs, probably due to their high hydrophilicity. By incorporating either squalenic acid (SQ) or enkephalin-squalene (LENK-SQ) prodrug as adjuvants with strong self-assembling properties, we successfully formulated nanoparticles of STR- or OPN-SQ (EEI-SQ NPs) and performed their physicochemical characterization. The analgesic efficacy of these formulations was evaluated in a carrageenan-induced pain model using the Hargreaves test to assess hyperalgesia. Nevertheless, the intravenous administration of EEI-SQ NPs caused systemic toxicity which was investigated through in vitro incubation assays. It was discovered that EEI-SQ bioconjugates exhibited strong interactions with divalent anions in physiological media, leading to nanoparticles aggregation, which was further confirmed in silico by molecular dynamics simulations. EEI-SQ NPs administered subcutaneously successfully enhanced the anti-hyperalgesic effect of LENK-SQ NPs. However, it was considered as not relevant enough regarding the observed local toxicity