The neuroprotective effect of traditional Chinese medicinal plants-A critical review

Abstract

Neurodegenerative and neuropsychiatric diseases are increasingly affecting individuals' quality of life, thus increasing their cost to social and health systems. These diseases have overlapping mechanisms, such as oxidative stress, protein aggregation, neuroinflammation, neurotransmission impairment, mitochondrial dysfunction, and excitotoxicity. Currently, there is no cure for neurodegenerative diseases, and the available therapies have adverse effects and low efficacy. For neuropsychiatric disorders, such as depression, the current therapies are not adequate to one-third of the patients, the so-called treatment-resistant patients. So, searching for new treatments is fundamental. Medicinal plants appear as a strong alternative and complement towards new treatment protocols, as they have been used for health purposes for thousands of years. Thus, the main goal of this review is to revisit the neuroprotective potential of some of the most predominant medicinal plants (and one fungus) used in traditional Chinese medicine (TCM), focusing on their proven mechanisms of action and their chemical compositions, to give clues on how they can be useful against neurodegeneration progression.

Keywords: Alzheimer's disease; Clinical trials; Depression; Medicinal plants; Neurodegeneration; Oxidative stress; Parkinson's disease; Toxicology.

Graphical abstract

Figure 1

Neurodegeneration mechanisms of the reviewed Chinese medicinal plants: oxidative stress-induced neuroinflammation and apoptosis, protein aggregation toxicity and neurotransmitter system imbalance. ROS, reactive oxygen species; RNS, reactive nitrogen species; ONOO^‒, peroxynitrite; O₂•^‒, superoxide anion radical; •NO, nitric oxide; •OH, hydroxyl radical; H₂O₂, hydrogen peroxide; IL, interleukin; Aβ, amyloid beta; AChE, acetylcholinesterase; BuChE, butyrylcholinesterase; MAO, monoamine oxidase; SERT, serotonin transporter; NAT, noradrenaline transporter; DAT, dopamine transporter; GAT1, GABA transporter; EAAT1, glutamate transporter; mAChR, metabotropic acetylcholine receptor; mGluR, metabotropic glutamate receptor; GABA_AR, metabotropic GABA receptors; 5-HT₁ and 5-HT₂, metabotropic serotonin receptors; CB1 and CB2, cannabinoid receptors; α1, α2 and β, metabotropic adrenergic receptors; nAChR, ionotropic acetylcholine receptor; NMDAR, N-methyl-d-aspartate receptor; AMPAR, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor; KAR, kainate receptors; 5-HT₃, ionotropic serotonin receptors; species 1–22, 21 medicinal plants and one fungus discussed in Section 2.

Figure 2

PRISMA flow diagram representing the original papers included in Section 2 “Chinese medicinal plants”.

Figure 3

Neuroprotective compounds present in the 20 Chinese medicinal plants and one fungus reviewed in Section 2.