Nanostructured lipid carrier-mediated delivery of donepezil attenuates neuropathic pain via central cholinergic receptor modulation

OBJECTIVES: This study evaluated the analgesic efficacy of intranasally administered donepezil-loaded nanostructured lipid carriers (DPZ-NLCs) for neuropathic pain (NP), focusing on the involvement of cholinergic receptors. METHODS: Male C57BL/6 mice subjected to chronic sciatic nerve constriction were assessed for mechanical withdrawal threshold using the von Frey test. To identify receptor-specific mechanisms, selective antagonists of M2 muscarinic (M2 mAChRs) and α7 nicotinic (α7 nAChRs) receptors were administered before DPZ-NLCs. mRNA expression of these receptors, microglial markers, and cytokine levels were quantified in the spinal cord and thalamus by RT-PCR and ELISA. DPZ-NLCs effects on LPS-activated microglia were evaluated by flow cytometry. KEY FINDINGS: Pharmacological data revealed that M2 mAChRs and α7 nAChRs mediate the antinociceptive effects of DPZ-NLCs. Treatment increased α7 nAChR mRNA expression in the thalamus, and this effect was blocked by intra-thalamic α7 nAChR antagonism. DPZ-NLCs also reduced TNF-α levels in the thalamus and in LPS-stimulated microglial cultures, indicating inhibition of microglial activation. CONCLUSION: Intranasal DPZ-NLCs show promise as a therapeutic strategy for NP, likely involving central M2 mAChR- and α7 nAChR-dependent mechanisms. Limitations include the use of male mice only and the absence of pharmacokinetic assessments.