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Acupuncture has been historically practiced to treat medical disorders by mechanically stimulating specific acupoints. Despite its well-documented efficacy, its biological basis largely remains elusive. Recent studies suggested that cell apoptosis and autophagy might play key roles in acupuncture therapy. Therefore, we searched PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI), aiming to find the potential relationship between acupuncture and cell apoptosis and autophagy. To provide readers with objective evidence, some problems regarding the design method, acupoints selection, acupuncture intervention measure, and related diseases existing in 40 related researches were shown in this review. These findings demonstrated that acupuncture has a potential role in modulating cell apoptosis and autophagy in animal models, suggesting it as a candidate mechanism in acupuncture therapy to maintain physiologic homeostasis.
Acupuncture is a key component of traditional Chinese medicine (TCM) and a main form of alternative medicine . The therapy functions by means of stimulating certain acupoints in the human body to activate meridians and collaterals and regulate the function of Zang-Fu organs and Qi and blood . Acupuncture, with many categories such as manual acupuncture (MA), electroacupuncture (EA), laser acupuncture, and acupoint injection, has turned out to be relatively safe with few adverse effects .
Apoptosis and autophagy are two important cellular processes which control cell survival or death  and are also considered as a balanced response to pathogens and other immune stimuli that play an important role in maintaining physiologic homeostasis . Apoptosis- and autophagy-related mechanisms have been increasingly valued in neurological diseases , diabetes mellitus , and cancer . However, there are few effective and safe ways to regulate cell apoptosis and autophagy in clinical practice right now.
The treatment of acupuncture in diseases like nerve injury has been extensively studied for a long time . Acupuncture could regulate multiple molecules and signaling pathways that lead to excitoxicity, oxidative stress, inflammation, and neurons death and survival and also promote neurogenesis, angiogenesis, and neuroplasticity after ischemic damage .
Based on recent studies, the mechanism of acupuncture to treat medical disorders has a high degree of overlap with cell apoptosis and autophagy, which may provide a new direction for the clinical application and basic research. Up to now, there has been no review to clarify the potential relationship between acupuncture and cell apoptosis and autophagy. Herein, we performed a review, in particular focused on the therapy of acupuncture, including design method, acupoints selection, acupuncture intervention measure, and related diseases, trying to find out the detailed mechanism and objective evidence for modulation of acupuncture on cell apoptosis and autophagy.
Relevant studies were identified from the online electronic databases PubMed, Embase, Web of Science, and China National Knowledge Infrastructure (CNKI). Search terms consisted of three groups: apoptosis and autophagy (an important mechanism for the treatment of diseases or maintaining homeostasis), intervention (acupuncture and other related terms), and study type (randomized controlled trial and other related terms). Methodological quality of individual studies was assessed by (1) risk of bias, (2) inconsistency, (3) indirectness, (4) imprecision, and (5) publication bias. Finally, 40 articles were identified in this review, which were published in English only and provided full text until May 2017.
All 40 articles were randomized controlled trials for animal studies. There was a huge change regarding the literature published from 2003 to 2017. During the first decade, only a few reports were published each year, with a substantial increase in the last four years (Figure 1).
Acupoints selection was performed according to both clinical reports and traditional Chinese medicine theory. Most articles were related to neurological diseases like ischemia-reperfusion (I/R) that caused some certain acupoints to be used more frequently than others such as GV20 (Baihui) and ST36 (Zusanli).
All results indicated that acupuncture has the effect of suppressing cell death (TUNEL assay or other tests, p < 0.05 or 0.01), inhibiting inflammation, or removing pathologic products though regulating cell apoptosis and autophagy (p < 0.05 or 0.01). The mechanism of acupuncture in modulation of cell apoptosis and autophagy, which was associated with regulating the expression of Bcl-2/Bax, caspase family, Fas/FasL, c-Fos, TNF-α, or NFκB, has been extensively and intensively studied from biological and immunological perspectives. Detailed information of all researches is shown in Table 1.
To our knowledge, this is the first review to explore the efficacy of acupuncture for modulating cell apoptosis and autophagy. Based on the biological and immunological results in 40 studies, it is indicated that acupuncture could regulate the expression of Bcl-2/Bax, caspase family, Fas/FasL, c-Fos, TNF-α, and NFκB, which modulated cell apoptosis and autophagy to reduce cell death (TUNEL assay or other tests, p < 0.05 or 0.01) in different pathological states especially ischemic stroke. Most studies suggested that acupuncture suppresses cell apoptosis. However, it is interesting that acupuncture plays a dual role in regulating autophagy. Acupuncture could not only promote autophagy to remove pathology products, but also inhibit autophagy against cell death in different periods of diseases. All the results suggested that acupuncture on cell apoptosis and autophagy does not have specificity and involves numerous pathways.
Acupuncture has been known as an effective therapy in neurobiology  and immunology , but the mechanism is still unclear. It is recognized that cell apoptosis and autophagy are associated with more and more diseases. Apoptosis, a key regulator of tissue homeostasis, is tightly regulated with the interaction of activating and inhibitory pathways. Aberrant induction of cell apoptosis may result in neurodegenerative, chronic, inflammatory, and autoimmune diseases, among others . Autophagy, an intracellular process in which cytoplasmic materials are transported by double-membraned autophagosomes to lysosomes for degradation , is a highly conservative biological degradation pathway that plays essential roles in cell homeostasis, development, and survival . So, we hypothesize that cell apoptosis and autophagy might play key roles in acupuncture treatment of diseases.
The latest researches reported that epigenetic modification plays a great role in cell apoptosis and autophagy [15, 16]. SIRT1 (silent mating type information regulation 2 homolog 1) is an NAD-dependent deacetylase which has a deacetylation activity in the modulation of cell stress signals via epigenetics , and the deacetylation of histone via SIRT1 was considered as an important intervention for apoptosis and autophagy . Our previous study confirmed that acupuncture induces the activation of SIRT1 , so it is expected that acupuncture-SIRT1-epigenetic modification to modulate cell apoptosis and autophagy will be investigated in the near future.
There are some limitations to this review. Firstly, our search only included English articles and excluded those articles published in other languages. Although we have performed comprehensive literature search, the total number of studies and the total sample size were too small to be reliable. Secondly, articles which reported negative results may not be popular to publish so that the effectiveness of published articles would be better than those unpublished, which may cause publication bias. Thirdly, due to the lack of repeat test under the same conditions, the conviction of the conclusion is still insufficient. Based on the above limitations, detailed results of each study were shown in this review to provide objective evidence on acupuncture modulation of apoptosis and autophagy.
In conclusion, studies suggested that acupuncture has a potential role in modulating cell apoptosis and autophagy in animal models, suggesting it as a candidate mechanism in acupuncture therapy to maintain physiologic homeostasis. However, detailed mechanisms were still not very legible and the publication bias may reduce persuasiveness of positive results. Hence, more high-quality randomized controlled trials to clarify the role of the relevant mechanisms are needed in the future.
This review was supported by the National Natural Science Foundation of China (no. 81574065).
The authors declare no conflicts of interest.