Thermo-responsive hydrogel loading hypericin induces pro-inflammatory response against Trichinella spiralis infection via toll-like receptor 3 activation

Background: Trichinella spiralis can cause animal and human trichinellosis, which is fatal for human beings. Study demonstrated that toll-like receptor 3 (TLR3) agonist was effective in reducing trichinella infections. Hypericin (Hyp) has great potential in activating TLR3 and may be a favorable choice for immunotherapy of trichinellosis. However, its applications are hampered by poor water solubility and dose-dependent phototoxicity.

Purpose: This study aimed to overcome the disadvantage of Hyp by using thermo-responsive hydrogel, better exert its immunotherapeutic efficacy against T. spiralis by activating TLR3.

Study design and methods: We used P(NIPAM-co-AM) hydrogel prepared by acrylamide (AM) and N-isopropylacrylamide (NIPAM) to load Hyp, and named P(NIPAM-co-AM)/Hyp. Subsequently, its lower critical solution temperature (LCST) characterization, biocompatibility, immunomodulatory activity via TLR3 signaling pathway, and therapeutic efficacy against T. spiralis were evaluated.

Results: The study showed that the controllable drug release rate of P(NIPAM-co-AM)/Hyp owed to its remarkable temperature sensitivity. P(NIPAM-co-AM)/Hyp exhibited exceptional efficacy in activating the TLR3 signaling pathway and significantly promoting DC cells maturation. P(NIPAM-co-AM)/Hyp effectively elicited a robust pro-inflammatory immune response with up-regulation of tumor necrosis factor-α (TNF-α), interferon-γ (IFN-γ), interleukin-2 (IL-2), interleukin-12 (IL-12) in T. spiralis-infected mice. Compared to Hyp and albendazole (ABZ), P(NIPAM-co-AM)/Hyp exhibited a significant decrease in the encysted muscle larvae number and histopathological destruction. The muscle larvae burden was dropped from 58,733 to 32,833 per mice at a dose of 10 mg/kg, with a reduction rate of 42.8 %. Moreover, the reduction rate increased to 64.30 % at a dose of 20 mg/kg.

Conclusions: This study confirms the therapeutic efficacy of P(NIPAM-co-AM)/Hyp as a TLR3 agonist and provides a new study direction for immunotherapy strategy and vaccine development by targeting parasites.