Parkinson disease (PD) is the second most common neurodegenerative disorder [1], and its incidence has increased drastically worldwide over the past few decades, placing it as one of the most rapidly expanding neurological disorders worldwide [2,3]. The rapid growth of PD is influenced by global aging, as the prevalence of PD increases with age [4]. Therefore, the development of treatment strategies for patients with PD is expected to become increasingly important.

PD is characterized by motor symptoms such as tremor, rigidity, bradykinesia, and postural instability due to altered aggregation of α-synuclein in the brain structures termed Lewy bodies, as well as by early prominent death of dopaminergic neurons in the substantia nigra [5]. However, PD is not only characterized by motor symptoms but also by nonmotor symptoms such as constipation, depression, anxiety, anosmia, pain, and sleep behavior disorder, which have been found to occur in the prodromal phase before the onset of motor symptoms, contributing to the decreased quality of life in affected patients [6]. Based on this knowledge, a study has recently suggested that PD should be approached as a systemic disease, rather than simply as a movement disorder caused by brain dysfunction [7].

Levodopa symptomatic therapy based on conventional brain pathology is the current mainstay of PD treatment [8]. However, nonmotor symptoms are known to be unresponsive to levodopa [9], and excessive and prolonged therapy is associated with a risk of adverse events, such as dopamine dysregulation syndrome [10] and levodopa-induced dyskinesia [11]. Therefore, current treatments that target the brain alone are unlikely to be effective in treating PD, indicating the need for alternative treatments.

The gut-brain axis theory posits that the gut and brain communicate bidirectionally with each other via the blood and vagus/sympathetic nerves to regulate various human physiological and pathological functions, and the gut microbiome is gaining attention as a potential modulator of the gut-brain axis [12]. As the highly complex relationship between the gut and brain in PD has been recognized, the role of gut microbiome as a modulator of PD has also been highlighted [13].

In Traditional East Asian Medicine (TEAM), both acupuncture and moxibustion have a long history of clinical use in the treatment of PD. Recently, there has been a growing demand for complementary and alternative medicine (CAM) for PD worldwide, to compensate for the limitations of conventional PD treatments, with acupuncture playing a large role [14]. In a previous review, acupuncture and moxibustion were reported to be superior to dopamine monotherapy in improving motor and nonmotor symptoms and managing long-term symptoms in PD [15]. In another study [16], the addition of acupuncture to dopamine replacement therapy was associated with significantly superior Unified Parkinson's Disease Rating Scale (UPDRS) I-IV score improvements compared with those noted with dopamine replacement therapy alone.

Recent experimental studies have shown that acupuncture modulates the gut microbial composition [17,18]. Based on this evidence, a study using an in vivo PD model reported that GB34 and ST36 acupuncture enhanced motor symptoms and dopamine neuron protection by modulating gut microbial dysbiosis and inhibiting neuroinflammation [19]. This suggests that the effects of acupuncture may also be mediated by modulating the gut-brain axis through gut microbiome regulation. However, all studies conducted in this field to date have been experimental, highlighting the need to explore the effects of acupuncture and moxibustion on gut microbiome and explore its association with clinical symptom improvement in patients with PD.

Herein, we present a protocol for a study analyzing the effects of acupuncture and moxibustion on the gut microbiome and exploring its association with symptoms in patients with PD. This study will provide new clinical evidence on the mechanisms of PD treatment with acupuncture and moxibustion, thereby increasing the level of evidence for acupuncture and moxibustion as alternative treatment methods for PD.

The study was supported by the National Research Foundation of Korea, funded by the Ministry of Science and ICT (no. 2022M3A9B6017813). Recruitment for the registry commenced on October 15, 2021, and was scheduled to end on September 13, 2023. Recruitment began on October 22, 2021, and as of February 19, 2025, participant recruitment and observation ended, and data analysis is being conducted.

The clinical efficacy of acupuncture for PD has been consistently reported. Pereira et al [40] analyzed 17 randomized controlled trials (RCTs) on acupuncture for PD published in English between January 2011 and July 2021 and found that the combination of acupuncture and conventional treatment was superior to conventional treatment alone for motor and nonmotor symptoms of PD. Similarly, Lee et al [15] analyzed 16 RCTs, investigating 15 acupuncture treatments and 1 moxibustion treatment, published between 2008 and 2013, and comparing acupuncture or moxibustion with conventional therapies such as dopamine, found that all but one showed significant improvement in the acupuncture or moxibustion treatment group. In particular, for nonmotor symptoms of PD, for which effective treatments remain lacking, Li et al [41] reported through an analysis of 27 RCTs that acupuncture treatment could improve depression, quality of life, cognition, total mentation, behavior and mood, and ADL in patients with PD. Based on these clinical study data, the Clinical Practice Guideline of Korean Medicine for Parkinson's Disease recommended combination treatment of acupuncture and anti-Parkinsonian drugs for patients with PD, while moxibustion treatment may also be considered [42].

Attempts to identify the mechanisms of action of acupuncture in PD to support clinical data are still ongoing. Previous experimental studies using PD models have shown that acupuncture exerts neuroprotective effects through activation of neuroprotective agents such as brain-derived neurotrophic factor, glial cell line-derived neurotrophic factor, and cyclophilin A [43], effective in PD symptoms by inducing neuromodulation, thus controlling inflammation and brain functional connectivity [44,45], and p53 signaling-mediated neuroprotective effect [46]. However, these opinions are insufficient to reflect the systemic nature of PD and do not fully explain the improvement in nonmotor symptoms associated with acupuncture.

The gut-brain axis mechanism of PD stemmed from the perspective that PD should be managed and treated as a systemic disease [7]. Braak et al [47] observed that unknown pathogens invade the body through the intestines, while Lewy bodies selectively move from the intestines along the central nervous system and metastasize to the brain; based on the hypothesis that the motor and nonmotor symptoms of PD appear according to this metastasis, they proposed the Braak stage, which divides this process into 6 stages. This finding has drawn attention to the role of the gut in the pathology of PD. Recently, it has also been hypothesized that PD is divided into brain-first and gut-first, based on the division of positive and negative rapid eye movement sleep behavior disorder in the prodromal phase [48]. The fact that gastrointestinal symptoms, such as constipation, appear very early in the prodromal phase [49] and that 60%-80% of patients experience gastrointestinal symptoms [50] may also support the gut-first PD hypothesis.

Imbalances in the gut-brain axis caused by gut microbial dysbiosis can lead to increased inflammatory signaling and epithelial permeability, both of which are known to play an important role in neurodegenerative diseases such as PD [19]. The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine increases α-synuclein and influences compositional changes in gut microbiome, including the phylum Proteobacteria [51]. Gut microbiome dysbiosis also induces microglial activation and neuroinflammation, which may promote α-synuclein overexpression, resulting in motor dysfunction [52,53]. Taken together, these results suggest that regulation of gut microbiome may have significant potential as a key treatment for PD, functioning through modulation of the gut-brain axis.

In the TEAM theory, the functional connection and communication between acupoints, the brain (ancient heart), and the gut is clinically important [54]. Based on the traditional theory, a previous review study [55] has reported that acupuncture has an effect on various diseases, including metabolic diseases, gastrointestinal diseases, mental disorders, and nervous system diseases, by regulating gut microbiome. Further, a large number of experimental studies on the relationship between PD and gut microbiome have been published recently, and the number is rapidly increasing [55]. In a previous experimental study including a PD model [19], we found that acupuncture treatment with GB34, which has been shown to exert neuroprotective effects on the brain, and ST36, which has been shown to enhance digestive function, improved motor function and anxiety, and increased the levels of dopaminergic fibers and neurons in the striatum and substantia nigra, increased the diversity of gut microbiome (alpha-diversity) and restored a gut microbiome to a composition more similar to that of robust controls (beta-diversity) compared with that noted in the PD group, in addition to restoring the increased levels of proteobacteria at the phylum level, suggesting that acupuncture exerts effects on improving gut microbiome imbalances. In another previous study [56], we conducted a clinical study to investigate whether acupuncture treatment for 2 weeks could effectively improve motor symptoms of PD using the UPDRS II+III in 73 patients with PD. This study showed that both the acupuncture treatment group and the control group showed improvement in motor function, with no significant intergroup difference; however, at the follow-up of 2 months after the end of treatment, the acupuncture treatment group continued to maintain these improvements in symptoms, while the control group reported a regression. Considering the results of these previous experimental studies, we hypothesized that acupuncture in this clinical study affected changes in gut microbiome to improve PD symptoms in a sustainable manner. To verify this hypothesis, we present the protocol of this study to explore changes in gut microbiome caused by acupuncture and moxibustion in patients with PD and explore its association with improvement in clinical symptoms of PD.

This protocol has limitations. First, as this study was designed as a single-group, prospective observational study with a primary focus on analyzing pre-post changes of patients with PD, a control group of healthy participants was included for baseline comparison rather than incorporating a control group within the PD cohort. This limits the internal validity of the intervention findings, as changes may be influenced by natural disease progression or placebo effects rather than the treatment itself. Second, although the sample size was determined based on feasibility rather than statistical power calculations, 60 patients with PD and 20 healthy participants may limit the reliability and generalizability of both within-group and between-group comparisons and increase the risk of type II error. Third, as no blinding was applied, the use of subjective, patient- and clinician-reported outcomes such as MDS-UPDRS, PDQ-39, and MYMOP increases the risk of detection and expectation bias, potentially compromising causal inference in this single-arm design. Fourth, adverse events are assessed by the treating Korean medicine doctors without independent adjudication or standardized grading criteria, which may limit the objectivity and consistency of safety reporting in this study. To address these limitations, future studies should adopt an RCT design with an adequately powered sample size, blinding procedures, and standardized outcome and safety assessments to enhance the internal validity, causal inference, and generalizability.

This study has limitations that must be weighed when interpreting the findings. Nutritional management is recommended for patients with PD, including dietary distribution to optimize levodopa absorption, dietary interventions for the improvement of nonmotor symptoms, and regular monitoring of food intake [57]. This leads to differences in dietary habits between PD patients and robust people, with PD patients showing higher protein and higher fiber dietary habits than robust people [58]. Fibers activate various beneficial microbiomes and suppress harmful species, and protein also has a significant impact on the gut microbiome [59]. Since this study does not investigate the nutritional intake of PD patients and healthy individuals, the influence of dietary differences should be considered when comparing the gut microbiome results between the two groups. Furthermore, levodopa dosage may affect gut microbiome composition [60]. Although this study investigates levodopa dosage in PD patients as part of clinical outcomes, it does not exclude the potential confounding effect of dosage adjustment on the gut microbiome. Therefore, any significant changes in levodopa dosage should be taken into consideration in the results.

The study will generate data on the effects of acupuncture and moxibustion on gut microbiome of patients with PD and explore its association with improvement in clinical symptoms. If the study results demonstrate that acupuncture and moxibustion change the gut microbiome in patients with PD, it will be the first clinical evidence to support a microbiome-gut-brain axis mechanism for acupuncture and moxibustion treatment of PD, ultimately contributing to the potential of acupuncture and moxibustion as an alternative treatment for PD.