Abstract
Radix Polygalae (also known as Yuanzhi in China) is the dried rhizome of Polygala tenuifolia Willd. or Polygala sibirica L., which is a famous Chinese herb and has been widely used for centuries in traditional medicines including expectorants, tonics, tranquilizers, antipsychotic, and so on. This article reviews the neuroprotective effects of Radix Polygalae in preclinical models of central nervous system (CNS) disorders, especially anxiety, depression, declining cognition, Alzheimer's disease (AD), and Parkinson's disease (PD). The chemical composition of Radix Polygalae as well as the underlying mechanisms of action were also reviewed. We found that Radix Polygalae possesses a broad range of beneficial effects on the abovementioned conditions. The multifold mechanisms of action include several properties such as antioxidant and associated apoptotic effects; anti-inflammatory and associated apoptotic effects; neurogenesis, regeneration, differentiation, and neuronal plasticity improvement; hypothalamic–pituitary–adrenal axis (HPA) regulation; neurotransmitter release; and receptor activation (A2AR, NMDA-R, and GluR). Nevertheless, the detailed mechanisms underlying this array of pharmacological effects observed in vitro and in vivo still need further investigation to attain a coherent neuroprotective profile.
Highlights
The central nervous system (CNS) is the most important regulatory system in the human body, playing a leading role in various life systems
Reports proved that the crude extract of P. tenuifolia (100 and 200 mg/kg) significantly improved impaired spatial memory in aging mice in the Morris water maze (MWM) and step-down tests, an effect that was related to the disruption of superoxide dismutase (SOD) and catalase (CAT) activities, the inhibition of MAO and acetylcholinesterase (AChE) activities, and the decrease in the levels of MDA in the brain tissue [35]
Senegenin, an active component of extracts from P. tenuifolia root, significantly inhibited the mRNA and protein expression of several key pro-inflammatory cytokines by downregulating the inflammation signaling pathways dependent on TLR4/MyD88/NF-κB and TLR4/TRIF/NF-κB and by reducing tumor necrosis factor-α (TNF-α), IL-1β, IL-6, and IL-8 levels in hippocampal tissues in the postoperative cognitive dysfunction model of elderly rats having undergone splenectomy [41]. These results suggest that Radix Polygalae (RP) might exert a significant neuroprotective effect by improving learning and memory, driven in part by the modulation of cholinergic activity and neuroinflammation
Summary
The central nervous system (CNS) is the most important regulatory system in the human body, playing a leading role in various life systems. A saponin-rich fraction obtained by the purification of P. tenuifolia crude extract significantly improved learning and memory in normally aged mice in the Morris water maze (MWM), the step-down passive avoidance tests [35], and the eight-arm radial maze task in rats [37] and in 5xFAD transgenic mice [36] All of these effects may be involved in the regulation of the TLR4/MyD88/NF-κB and TLR4/TRIF/NF-κB signaling pathways. Reports proved that the crude extract of P. tenuifolia (100 and 200 mg/kg) significantly improved impaired spatial memory in aging mice in the MWM and step-down tests, an effect that was related to the disruption of superoxide dismutase (SOD) and catalase (CAT) activities, the inhibition of MAO and acetylcholinesterase (AChE) activities, and the decrease in the levels of MDA in the brain tissue [35] (see Table 2).
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