Compounds of Traditional Chinese Medicine and Neuropathic Pain
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Available online at www.sciencedirect.com Chinese Journal of Natural Medicines 2020, 18(1): 28–35 doi: 10.1016/S1875-5364(20)30002-9 Compounds of traditional Chinese medicine and neuropathic pain LI Shun-Hua2Δ, LI Lin1,3Δ, YANG Ru-Nan1,3, LIANG Shang-Dong1,3, * 1 Neuropharmacology Laboratory of Physiology Department, Medical School of Nanchang University, Nanchang 330006, China; 2 Undergraduate Student of Class 155 of Nanchang University Queen Marry University of London Joint Programme, Nanchang 330006, China; 3 Jiangxi Provincial Key Laboratory of Autonomic Nervous Function and Disease, Nanchang 330006, China Available online 20 Jan., 2020 [ABSTRACT] Neuropathic pain (NP) has become a serious global health issue and a huge clinical challenge without available effect- ive treatment. P2 receptors family is involved in pain transmission and represents a promising target for pharmacological intervention. Traditional Chinese medicine (TCM) contains multiple components which are effective in targeting different pathological mechanisms involved in NP. Different from traditional analgesics, which target a single pathway, TCMs take the advantage of multiple compon- ents and multiple targets, and can significantly improve the efficacy of treatment and contribute to the prediction of the risks of NP. Compounds of TCM acting at nucleotide P2 receptors in neurons and glial cells could be considered as a potential research direction for moderating neuropathic pain. This review summarized the recently published data and highlighted several TCMs that relieved NP by acting at P2 receptors. [KEY WORDS] Traditional Chinese medicine; Diabetic neuropathic pain; HIV-gp120-associated neuropathic pain; Chronic constric- tion injury; Nucleotide receptors [CLC Number] R284, R965 [Document code] A [Article ID] 2095-6975(2020)01-0028-08 Introduction For all types of drugs, 20% to 40% of patients either experi- ence a less than 30% pain relief or have intolerable side ef- Neuropathic pain (NP) is defined as pain caused by a le- fects [5-7]. Therefore, developing novel compounds for the ef- sion or disease of the somatosensory system, belongs to fective management of NP with little influence on other nor- chronic pain. The typical symptoms of NP include spontan- mal physiological functions is necessary. eous pain, allodynia (pain response to normally innocuous Nucleotides of purinergic signaling were proposed as ex- stimuli), hyperpathia (abnormal pins-and-needles or electric- tracellular signaling molecules in 1972 [8]. Purinergic recep- shock-like sensations), and hyperalgesia (aggravated pain evoked by non-noxious stimuli) [1-3]. NP has become a seri- tors include P1 receptors and P2 receptors, which bind to ad- ous global health issue, with estimated prevalence rates ran- enosine-5′-triphosphate (ATP) and its analogues [adenosine- [9] ging from 1% to 8.9% of the total population [4]. Its long dur- 5′-diphosphate (ADP) and adenosine] respectively . Purino- ation reduces the quality of patients’ life and places a heavy ceptors are widely distributed in both the peripheral and burden on society. Although various drugs, including antide- central nervous systems (CNS), being present in neurons and [9-10] pressants, anti-epileptics, opioids, and topical anesthetics, are glia . To date, seven homomeric (P2X1, P2X2, P2X3, used for clinical treatment of NP, their side effects are marked, P2X4, P2X5, P2X6, and P2X7), and six heteromeric P2X re- and their therapeutic effects are generally limited [5-6]. Com- ceptors (P2X1/2, P2X1/4, P2X1/5, P2X2/3, P2X2/6, and [10] plete freedom from NP often cannot be achieved by drugs. P2X4/6) have been identified . P2Y receptors consist of P2Y1-12. Purinergic signaling was proposed and hypothes- ized for the initiator and modulator of pain [11]. Since then, [Received on] 27-Jul.-2019 [Research funding] This work was supported by the National Natur- many subsequent research studies have expanded this al Science Foundation of China (Nos. 81570735, 8181101216, concept. P2X and P2Y receptors are involved in the modula- 31560276, 81970749, and 81870574). tion of pain transmission. After nerve injury, ATP is released [*Corresponding author] Tel/Fax: 86-791-86360552, E-mail: liangsd @hotmail.com from the nerve endings of primary sensory neurons. Extracel- ∆These authors contributed equally to this work. lular ATP triggers the activation of different P2 receptors, These authors have no conflict of interest to declare. which induce the production and release of bioactive factors – 28 – LI Shun-Hua, et al. / Chin J Nat Med, 2020, 18(1): 28–35 including cytokines and neurotrophic factors, which in turn convulsants (e.g., gabapentin, pregabalin, and topical lido- lead to the hyperexcitability of sensory neurons and, con- caine). Opioid analgesics and tramadol are recommended as sequently, NP developed [10-11]. second-line therapies. However, they are sometimes used as Ligand-gated ion channel P2X receptor has seven sub- first-choice drugs [25]. But those therapies only offer marginal types, among which the P2X3, P2X4, and P2X7 subtypes are relief because of either a lack of efficacy or the risk of unac- most related to pain transmission [11-12]. It has been reported ceptable side effects (e.g., sedation, dizziness, edema, and that P2X antagonists were successful in relieving NP [13-14]. ataxia) [23]. Patients with NP continue to have moderately P2X3 receptor antagonists (A-317491, RO3 and RO4) have severe pain on average, despite taking prescribed medica- exhibited their potent ability to relieve NP [15-17]. An effective tions for their condition [26]. Furthermore, the development of P2X4 receptor antagonist named paroxetine has been sugges- tolerance, and the risks of addiction and abuse, significantly ted to successfully relieve NP [18]. P2X7 receptor antagonists limit the clinical application of NP pharmacotherapy. No (A-740003, KN-62 and KN-04) produced antinociceptive ef- treatment option has been shown to reverse NP. Therefore, fects in NP [19]. Among the G protein coupled P2Y receptor the discovery of novel therapeutic alternatives with superior family, only the P2Y12 receptor subtype is clearly known to effectiveness and minimal adverse effects would be beneficial. be involved in NP onset. Several genetic deletions of P2Y12 Currently, more attention has been focused on herbal for- receptors produce analgesic effect [20-22]. These observations mulations in the field of drug discovery, especially on medi- indicate that drugs selectively targeting specific P2 receptors cinal plants and herbal extracts from traditional Chinese can exert their analgesic activity at the site of receptor, thus medicine (TCM) (Fig. 1), which are increasingly used world- limiting the occurrence of unwanted side effects [9-11]. wide. TCM has unique advantages in the clinical prevention The advantage of traditional Chinese medicine in NP and treatment of NP because of its fewer complications and treatment side effects compared with synthetic drugs. Moreover, the NP, a kind of chronic pain, is the focus of many research multiple components and targets of TCM avoid the shortcom- studies due to the high incidence, complex pathogenesis, and ings of clinical drugs targeting a single pathway [27]. Several lack of efficient treatments. Trauma (surgery, amputation), studies have indicated that natural products could be a good metabolic disorders (diabetes, uremia), infection (herpes source of the new specific molecules needed for the treat- zoster, HIV), poisoning (chemotherapy), vascular disease (ar- ment of pain-related diseases through the regulation of P2 re- teritis nodosa), and malnutrition are considered to be incent- ceptors [28-29]. For example, the TCM compound Emodin acts ives for the initiation of NP [23]. NP is an area of largely un- at tumor cells to inhibit their migratory ability via P2X7 met therapeutic need due to its complex underlying patho- blockade [30]. Recently, the antagonistic effect of bioflavon- physiology and heterogeneous etiology [5, 7]. The presently oids from the methanolic extract fractions of Rheedia logifo- available treatment for NP contains non-pharmacological ap- lia on the P2X7 receptor has been found to promote analges- proaches, such as electroacupuncture [24], and drugs. On the ic action on inflammatory pain [31]. In addition, it has been re- basis of randomized clinical trials, medications are recom- ported that bioactive molecules contained in analgesic prepa- mended as first-line treatments for NP include certain antide- rations from TCM (e.g., tetramethylpyrazine, sodium ferulate, pressants [e.g., tricyclic antidepressants (TCAs), serotonin and puerarin) can inhibit P2X3-mediated pain transmission in norepinephrine reuptake inhibitors (SNRIs)] and certain anti- primary afferent neurons [28]. Thus, TCM may be an alterna- CH OH H 3 OH OH O OH OH O O H3C HO O HO O H H O OH H3C OH CH 3 OH O OH O O Emodin Resveratrol Artemisinin Quercetin O O HO O HO OH HO N O O H OO O CH3 O OH CH3 O HO O H HO Curcumin Andrographolide Osthole Sinomenine Fig. 1 Chemical structures of different TCMs – 29 – LI Shun-Hua, et al. / Chin J Nat Med, 2020, 18(1): 28–35 tive option to relieve and manage NP by acting at P2 receptors. odeficiency virus (HIV), and herpes infections, the resultant Classical drug research focuses mainly on a single active NP is often modifiable with prevention strategies. Therefore, compound. Systemic administration can reduce local drug after precise prediction of the disease risk, TCM can provide concentration