Trigonelline recovers memory function in Alzheimer's disease model mice: evidence of brain penetration and target molecule.

Trigonelline (TGN; 1-methylpyridin-1-ium-3-carboxylate) is a widely distributed alkaloid derived from plants. Since we previously found a neurite outgrowth effect of TGN, we hypothesised that TGN might help to improve memory deficits. Here, the efficacy of TGN in restoring amyloid β (Aβ)-induced axonal degeneration and in improving memory function was investigated in Alzheimer's disease 5XFAD model mice that overexpress mutated APP and PS1 genes. Exposure of Aβ25-35 for 3 days induced atrophy of axons and dendrites. Post treatment of TGN recovered the lengths of axons and dendrites. Following oral administration of TGN in mice, TGN itself was detected in the plasma and cerebral cortex. Oral administration of TGN to 5XFAD mice for 14 days showed significant improvement in object recognition memory (P < 0.001) and object location memory (P < 0.01). TGN administration also normalised neurofilament light levels in the cerebral cortex (P < 0.05), which is an axonal damage-associated biomarker. Analysis of target proteins of TGN in neurons by a drug affinity responsive target stability (DARTS) method identified that creatine kinase B-type (CKB) is a direct binding protein of TGN. Treatment with a CKB inhibitor cancelled the TGN-induced axonal and dendritic growth. In conclusion, we found for the first time that TGN penetrates the brain and may activate CKB, leading to axonal formation. This study shows the potential of TGN as a new drug candidate, and a new target molecule, CKB, in memory recovery signalling.