New Berberine Conjugates with Self-Assembly and Improved Antioxidant/Neuroprotection Properties: Effect of the Anchored Part on CMC, Shape and Size of the Nanomicelles

Berberine (Ber) as a natural isoquinoline alkaloid, with a wide range of biological activities, mainly suffers from low bioavailability, decreasing its therapeutic efficacy. In this study, two novel conjugates of Ber with self-assembly property, Ber–polyethylene glycol (B–PEG) and Ber–diethylene glycol monomethyl ether (B–DG), were synthesized to investigate the effect of the anchoring part on the CMC, morphology as well as antioxidant and neuroprotective properties of the nanomicelles. The CMC increased from 1.2 μmol in B–DG to 3.0 μmol in B–PEG, measured by pendant drop. The anchored part affected greatly the shape and CMC of the self-assembled nanomicelles. A mixture of semi-spherical and cubic nanomicelles in the average hydrodynamic size of 93 nm was achieved for B–PEG, while B–DG nanomicelles were just in semispherical morphology with the hydrodynamic size of 64 nm. The antioxidant property of the nanomicelles was studied by DPPH scavenging and ferric reducing antioxidant power assays, exhibiting improved antioxidant activity of B–PEG and B–DG conjugates compared to free Ber. The neuroprotection potency of Ber was improved significantly after conjugation compared to free Ber against H₂O₂-induced cell death and B–PEG showed activity as level as that of the standard drug, Quercetin. Owing to the self-assembly property and interesting biological activities of the introduced amphiphilic Ber–PEG conjugate, we propose application of this nanomicelle alone, or as a promising bioactive carrier of the poorly water-soluble drugs, against neurodegenerative diseases.