Crosstalk between Acupuncture and NF-κB in Inflammatory Diseases

Acupuncture has been used in China for thousands of years and concerned as a typical alternative medicine in inflammatory diseases nowadays. The nuclear factor-κB (NF-κB) transcription factor is an important regulator of inflammation. In this article, we discuss the role of acupuncture in NF-κB pathways and also present the acupoints selection, acupuncture administration, and related inflammation diseases and models from previous studies to bring readers close to a more complete understanding of the mechanisms between acupuncture and NF-κB in inflammatory diseases.


Introduction
Acupuncture is an oldest part of traditional Chinese medicine (TCM) with a history of more than three thousand years [1]. In recent decades, the evidence supported acupuncture which could be used as an efficient alternative therapy [2]. In the TCM theory, the combination of specific acupoints can relieve inflammatory symptoms, and it is widely studied in pain [3], obesity [4], and digestive system [5] diseases.
In mammals, the nuclear factor-κB (NF-κB) represents a family of inducible transcription factors [6]. Most of the inflammatory responses caused by infection, inflammatory cytokines, and engagement of antigen receptors are associated with the activation of NF-κB [7]. e canonical pathway of NF-κB activation consists of a series of steps [6]. First, TGFβ-activated kinase 1 could be activated in the intracellular signaling cascade and further activates a trimeric IκB kinase (IKK), which is composed of IKKα, β, and c. In turn, the IKK complex will degrade IκB family members with ubiquitination and phosphorylation, resulting in NF-κB release and nuclear translocation. In general, the degradation of IκB, a key inhibition of NF-κB, is crucial for NF-κB activation and acts as a potential antiinflammatory target [8].
MicroRNAs (miRNAs) are a kind of small endogenous RNAs, which could silence genes posttranscriptionally [9]. e communication of miRNAs and NF-κB was identified during inflammation [10]. In ulcerative colitis (UC), the contribution of miRNA in lowering IKKα expression levels could result in the activation of the NF-κB pathway [11].
Other classes of molecules could also act as a regulator of NF-κB. In inflammation and metabolic disorders, SIRT1 shows an antagonistic role of NF-κB [12]. P38, usually activated in proliferating cells, could act as an upstream agent of the NF-κB pathway in inflammatory response [13].
Not only in inflammation, but NF-κB could also contribute in many other cellular processes, including proliferation, apoptosis, and immune response [14], that may be a core of cellular homeostasis [15]. e TCM theory believes that harmony is the most important goal of health. Hence, we reviewed current literatures, trying to clarify the detail role of acupuncture and NF-κB in inflammatory diseases.

Methods
e research questions were combined into three key focus areas. (1) e mechanisms on how acupuncture could modulate NF-κB. (2) e detail of acupuncture regulating NF-κB in inflammation response. (3) e evidences that acupuncture could cure inflammatory diseases through NF-κB pathways.
Systematic searches were performed in the PubMed database with key words related to "acupuncture," "electroacupuncture," "NF-κB," "IκB," and "P65". Papers published before 13 April 2020, present in English, containing clear intervention by acupuncture and providing objective outcome using randomized controlled trials were selected.

Results
is review contains 8 articles which reveal the mechanisms on how acupuncture could regulate NF-κB, 9 articles which introduce the detail of acupuncture regulating NF-κB in inflammation response, and 22 articles which show evidence that acupuncture could ameliorate inflammatory diseases through NF-κB pathways. All of them are animal studies.

Mechanisms of Acupuncture
Regulating NF-κB. All articles in this review promote that acupuncture could inhibit the activation of NF-κB, but only a few of them investigated the detailed mechanisms. Based on current studies, acupuncture may modulate NF-κB through different ways ( Figure 1).
In the upstream of NF-κB, α7nAChR [16], Sirt1 [17], and P38 [18] were identified as targets of acupuncture in NF-κB pathways. Meanwhile, miRNAs also play a great role in this process. e regulation of acupuncture on miRNAs may be different depending on their function. Studies observed that acupuncture decreases miR-155 and miR-21 and increase miR-146a, which leads to inhibition of NF-κB [19], and the decrease of miR-155 by acupuncture is also observed [20].
When it comes to the canonical pathway of NF-κB activation, acupuncture shows great potential in inhibiting the degradation of IκB [21]. Wei et al. observed that acupuncture enhances the expression of IKKα against the activation of NF-κB [22].

Further Intervention of Acupuncture on Inflammation
Responses after Regulating NF-κB. In most studies, NF-κB has been used as a marker to measure the efficacy of acupuncture in inflammation. Meanwhile, some research studies suggest that the regulation of NF-κB by acupuncture could induce the further intervention of inflammatory cells or inflammatory cytokines to relieve inflammatory response ( Figure 2).
Wei et al. investigated that acupuncture could modulate the activity of 17 and Treg cells and the number of CD4 + IL-17A + cells and CD4 + Foxp3 + cells in asthma rats [22]. Wang et al. identified that the anti-inflammation effect of acupuncture on allergic diseases is targeting inflammatory cytokines including IL-6, TNF-α, IL-13, and MCP-1 in mast cells [20]. In a study performed by Wu et al., acupuncture attenuates IL-1β, IL-6, TNF-α, and MMP-3 on knee osteoarthritis [23]. In research studies about obesity, acupuncture could regulate inflammatory cytokines, such as TNF-α, IL-6, and IL-1β [24] and inflammatory cells, such as macrophages [17]. Similar phenomenon was observed in acupuncture treating pruritus [25]. Liu et al. [26] and Xue et al. [27] also found that acupuncture could act against the release of proinflammatory cytokines by the regulation of NF-κB.

Inflammatory Diseases Could Be Ameliorated by Acupuncture through NF-κB Pathways.
e current evidence supports that acupuncture could be administrated as an obvious NF-κB inhibitor to treat extensive inflammatory diseases (Table 1). e strategy of acupoints selection in different diseases was basically according to the TCM theory. But, some specific acupoints with high frequency were used. For example, due to its enhanced immune function in the TCM theory, ST36 was widely applied in different studies with the same effect on inhibiting NF-κB and relieving inflammation.
In acupuncture delivery, manual acupuncture (MA) or electroacupuncture (EA) was adopted in different studies. e overall data indicate that both MA and EA could decrease NF-κB and suppress inflammation.
ere is not enough evidence to show a significant difference in regulating NF-κB between MA and EA, including different waveform, frequency, and current.
Analyzing all the results as a whole, acupuncture has an optimistic effect on the inflammatory response in various organs, tissues, and cells. Whether it is a 'long-term or shortterm treatment, all subjects are benefited from acupuncture treatment. Since all the studies were conducted on animals, the side effects of acupuncture are unclear.

Discussion
Nowadays, the curative effect of acupuncture is recognized all around the world. ere are plenty of clinical trials, which demonstrate acupuncture as a useful alternative medical therapy in inflammatory diseases [39] or inflammatory responses in diseases [40]. Evidence-Based Complementary and Alternative Medicine NF-κB has been studied in inflammation for a long time, and it is found closely associated with multiple signaling pathways [8]. NF-κB could regulate a variety of cellular mechanisms, making it a key factor in inflammation, immunity, and even tumors [41].
In this article, we discussed current studies about acupuncture, which regulate NF-κB pathways in inflammatory diseases. e evidence supplies that acupuncture effectively inhibits the activation of NF-κB. However, compared with the complexity of NF-κB pathways, the mechanism of acupuncture in inhibiting NF-κB in current studies is still superficial.
e regulation of acupuncture on NF-κB was only identified on miRNAs, sirtuins, and other upstream agents and IκB in the canonical pathway. is information may explain how acupuncture could modulate NF-κB pathways. But considering future research, there are much more unknown mechanisms, such as the noncanonical pathway, subunit target of NF-κB, and other combined signal pathways. In addition, the subsequent modification on inflammatory cytokines and inflammatory cells may be crucial to explain the detail of acupuncture and NF-κB on inflammation. Some cell experiments, which investigated the complex mechanisms of acupuncture regulating NF-κB pathways, provide us a deeper understanding [42]. But there was no acupuncture intervention in their protocol, making them unsuitable to this review. e intervention of acupuncture on NF-κB pathways is effective on treating various inflammatory diseases in animal models. We also searched clinical trials with this topic. Although present trials did not involve the NF-κB pathway, the efficacy of acupuncture in some inflammatory diseases, including asthma [43], chronic atrophic gastritis [44], cognitive impairment [45], chronic obstructive pulmonary disease [46], and brain damage [47], was recognized.
One of the objectives of this article is to better apply acupuncture in the clinical practice of inflammatory

NF-κB IκB
Degradation P38 * MAPK α7nAChR * Figure 1: Mechanisms of acupuncture regulating NF-κB. * Acupuncture could inhibit NF-κB through sirtuins, P38, α7nAChR, miRNAs, and IκB in this review. Infection, inflammatory cytokines, and engagement of antigen receptors can activate NF-κB leading to inflammation responses. IκB is a key to inhibit this progress. Current evidence showed that acupuncture could modulate IKKα and sirtuins to decrease the activation of NF-κB. e role of miRNAs in inflammation is multiple, and acupuncture could dual-regulate the level of different miRNAs based on their function. As a result, acupuncture could be concerned as an efficient NF-κB antagonist, and there may be other complex mechanisms which are still unclear. diseases. e selection of acupoints is crucial for the acupuncture therapy in TCM. ere may be some broadspectrum anti-inflammation acupoints such as ST-36, which could be used in various inflammatory diseases. To our knowledge, different waveform, frequency, and current of EA may have different therapeutic effects. We have detailed the setting of EA delivery, but it is hard to recommend an optimal option of EA for treating inflammation based on the current findings.
ere are some limitations that need to be considered. First, in order to ensure the authenticity and reliability of the conclusions, only a small number of studies were identified based on our searching criteria. Although the inhibitory effect of acupuncture on NF-κB was significant, there were insufficient duplication experiments to explain the detail of this process. Many unknown mechanisms need to be investigated. Second, publication bias may also exist. Last, all studies in this review were based on animals. When it comes to human, higher levels of evidence and treatment protocols are necessary. And because of the diversity and particularity of inflammatory diseases, all possible adverse reactions in acupuncture treatment should be noticed.

Conclusion
is article provided an overview of the crosstalk between acupuncture and NF-κB in inflammatory diseases. A variety of studies with different diseases and models support acupuncture as an efficient NF-κB antagonist and modulate inflammatory cytokines and inflammatory cells to relieve inflammation. It may help us in understanding the role of acupuncture and NF-κB in inflammatory diseases better. Acupuncture has a bidirectional regulatory effect on the TLR2/4-NF-κB signaling pathway-related genes TLR2, TLR4, and NF-κB in the TBI rat cortex, promoting their expression in the early stage and inhibiting it in the later stage [37] VD CMi rat model ST36 Verum acupuncture Acupuncture could protect cognitive function against oxidative stress induced by CMi, which is partially associated with suppression of NF-κB-p53 activation [38] MA: manual acupuncture; EA: electroacupuncture; OVA: ovalbumin; DNCB: 1-chloro-2,4-dini-trobenzene; DNFB: 2,4-dinitrofluorobenzene; CAG: chronic atrophic gastritis; MNNG: N-methyl-N′-nitro-N-nitrosoguanidine; I/R: ischemia/reperfusion; COPD: chronic obstructive pulmonary disease; HIBD: hypoxic-ischemic brain damage; PTX: paclitaxel; OA: osteoarthritis; RA: rheumatoid arthritis; MACo: middle cerebral artery occlusion; SAP: severe acute pancreatitis; TBI: traumatic brain injury; VD: vascular dementia; CMi: cerebral multi-infarction.
More studies are still needed in the future to provide highlevel evidence.

Conflicts of Interest
e authors declare that they have no conflicts of interest.