Pseudotargeted metabolomics for exploring the changes of neurotransmitters profile in aging rat brain and the potential neuroprotective effect of alkaloids from Uncaria rhynchophylla

Background: Aging is an essential risk factor for most neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. However, changes in the levels of neurotransmitters that are associated with aging are not well understood. Methods: Methods such as liquid-liquid extraction, protein precipitation, and solid-phase extraction, using 20 different extraction solvents, were evaluated to optimize the extraction of neurotransmitters. A pseudotargeted metabolomics approach was developed to detect neurotransmitters in brain tissues using ultra-high-performance liquid chromatography coupled with tandem triple quadrupole mass spectrometry. Alkaloids that crossed into the brain were used to evaluate the effect of glutamic acid-induced excitatory neurotoxicity in SH-SYSY cells. Results: The overall extraction efficiency using protein precipitation was high. The changes in neurotransmitters' levels in the brain exhibited changes during the different growth cycles. The levels of seven neurotransmitters (aspartic acid, tyrosine, isoleucine, leucine, tryptophan, valine, and gamma-aminobutyric acid) were significantly different. Meanwhile, alkaloids could reduce the excitatory neurotoxicity of glutamic acid-induced SH-SY5Y cells via suppression of oxidative stress. Conclusion: Significant differences were observed in neurotransmitter profiling between 1-and 8-month-old rats, and the discrepant neurotransmitters were associated with aging. Seven indole alkaloids from Uncaria rhynchophylla, which could cross the blood-brain barrier, were screened and used to explore their protective effects against aging. Uncaria rhynchophylla alkaloids exhibited a neuroprotective effect by inhibiting oxidative stress, indicating that the alkaloid could be a potential therapeutic candidate for neurological disorders caused by glutamic acid toxicity.