Effect of the Biphenyl Neolignan Honokiol on Aβ42-Induced Toxicity in Caenorhabditis elegans, Aβ42 Fibrillation, Cholinesterase Activity, DPPH Radicals, and Iron(II) Chelation

The biphenyl neolignan honokiol is a neuroprotectant which has been proposed as a treatment for central nervous system disorders such as Alzheimer's disease (AD). The death of cholinergic neurons in AD is attributed to multiple factors, including accumulation and fibrillation of amyloid beta peptide (A beta) within the brain; metal ion toxicity; and oxidative stress. In this study, we used a transgenic Caenorhabditis elegans model expressing full length A beta(42) as a convenient in vivo system for examining the effect of honokiol against A beta-induced toxicity. Furthermore, honokiol was evaluated for its ability to inhibit A beta(42) oligomerization and fibrillation; inhibit acetylcholinesterase and butyrylcholinesterase; scavenge 2,2diphenyl-1-picrylhydrazyl (DPPH) radicals; and chelate iron(II). Honokiol displayed activity similar to that of resveratrol and (-) epigallocatechin gallate (EGCG) in delaying A beta(42)-induced paralysis in C. elegans, and it exhibited moderate-to-weak ability to inhibit A beta(42) on-pathway aggregation, inhibit cholinesterases, scavenge DPPH radicals, and chelate iron(II). Moreover, honokiol was found to be chemically stable relative to EGCG, which was highly unstable. Together with its good drug-likeness and brain availability, these results suggest that honokiol may be amenable to drug development and that the synthesis of honokiol analogues to optimize these properties should be considered.