A targeted genome association study examining transient receptor potential ion channels, acetylcholine receptors, and adrenergic receptors in Chronic Fatigue Syndrome/Myalgic Encephalomyelitis

Research progress on pathogenesis of chronic fatigue syndrome and treatment of traditional Chinese and Western medicine

Chronic Fatigue Syndrome (CFS) is a complex and perplexing medical disorder primarily characterized by persistent and debilitating fatigue, often accompanied by a constellation of symptoms, including weakness, dyspnea, arthromyalgia, sore throat, and disrupted sleep patterns. CFS is defined by its persistent or recurrent manifestation for a minimum duration of six months, marked by an enduring and unrelenting fatigue that remains refractory to rest. In recent decades, this condition has garnered significant attention within the medical community. While the precise etiology of CFS remains elusive, it is postulated to be multifactorial. CFS is potentially associated with various contributory factors such as infections, chronic stress, genetic predisposition, immune dysregulation, and psychosocial influences. The pathophysiological underpinnings of CFS encompass viral infections, immune system dysregulation, neuroendocrine aberrations, heightened oxidative stress, and perturbations in gut microbiota. Presently, clinical management predominantly relies on pharmaceutical interventions or singular therapeutic modalities, offering alleviation of specific symptoms but exhibiting inherent limitations. Traditional Chinese Medicine (TCM) interventions have emerged as a promising paradigm, demonstrating notable efficacy through their multimodal, multi-target, multi-pathway approach, and holistic regulatory mechanisms. These interventions effectively address the lacunae in contemporary medical interventions. This comprehensive review synthesizes recent advancements in the understanding of the etiological factors, pathophysiological mechanisms, and interventional strategies for CFS, drawing from a corpus of domestic and international literature. Its aim is to furnish valuable insights for clinicians actively involved in diagnosing and treating CFS, as well as for pharmaceutical researchers delving into innovative drug development pathways. Moreover, it seeks to address the intricate challenges confronted by clinical practitioners in managing this incapacitating condition.

Polyphenols as possible alternative agents in chronic fatigue: a review

Chronic fatigue syndrome (CFS) is a pathological state of extreme tiredness that lasts more than six months and may possess an impact on the social, emotional, or occupational functioning of an individual. CFS is characterized by profound disabling fatigue associated with infectious, rheumatological, and neurological symptoms. The current pharmacological treatment for CFS does not offer a complete cure for the disease, and none of the available treatments show promising results. The exact mechanism of the pathogenesis of the disease is still unknown, with current suggestions indicating the overlapping roles of the immune system, central nervous system, and neuroendocrine system. However, the pathological mechanism revolves around inflammatory and oxidative stress markers. Polyphenols are the most abundant secondary metabolites of plant origin, with potent antioxidant and anti-inflammatory effects, and can exert protective activity against a whole range of disorders. The current review is aimed at highlighting the emerging role of polyphenols in CFS from both preclinical and clinical studies. Numerous agents of this class have shown promising results in different in vitro and in vivo models of chronic fatigue/CFS, predominantly by counteracting oxidative stress and the inflammatory cascade. The clinical data in this regard is still very limited and needs expanding through randomized, placebo-controlled studies to draw final conclusions on whether polyphenols may be a class of clinically effective nutraceuticals in patients with CFS.

Graphical abstract

Impact of Misdiagnosis in Case-Control Studies of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Misdiagnosis of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) can occur when different case definitions are used by clinicians (relative misdiagnosis) or when failing the genuine diagnosis of another disease (misdiagnosis in a strict sense). This problem translates to a recurrent difficulty in reproducing research findings. To tackle this problem, we simulated data from case-control studies under misdiagnosis in a strict sense. We then estimated the power to detect a genuine association between a potential causal factor and ME/CFS. A minimum power of 80% was obtained for studies with more than 500 individuals per study group. When the simulation study was extended to the situation where the potential causal factor could not be determined perfectly (e.g., seropositive/seronegative in serological association studies), the minimum power of 80% could only be achieved in studies with more than 1000 individuals per group. In conclusion, current ME/CFS studies have suboptimal power under the assumption of misdiagnosis. This power can be improved by increasing the overall sample size using multi-centric studies, reporting the excluded illnesses and their exclusion criteria, or focusing on a homogeneous cohort of ME/CFS patients with a specific pathological mechanism where the chance of misdiagnosis is reduced.

Genetics of COVID-19 and myalgic encephalomyelitis/chronic fatigue syndrome: a systematic review

COVID‐19 and ME/CFS present with some similar symptoms, especially physical and mental fatigue. In order to understand the basis of these similarities and the possibility of underlying common genetic components, we performed a systematic review of all published genetic association and cohort studies regarding COVID‐19 and ME/CFS and extracted the genes along with the genetic variants investigated. We then performed gene ontology and pathway analysis of those genes that gave significant results in the individual studies to yield functional annotations of the studied genes using protein analysis through evolutionary relationships (PANTHER) VERSION 17.0 software. Finally, we identified the common genetic components of these two conditions. Seventy‐one studies for COVID‐19 and 26 studies for ME/CFS were included in the systematic review in which the expression of 97 genes for COVID‐19 and 429 genes for ME/CFS were significantly affected. We found that ACE, HLA‐A, HLA‐C, HLA‐DQA1, HLA‐DRB1, and TYK2 are the common genes that gave significant results. The findings of the pathway analysis highlight the contribution of inflammation mediated by chemokine and cytokine signaling pathways, and the T cell activation and Toll receptor signaling pathways. Protein class analysis revealed the contribution of defense/immunity proteins, as well as protein‐modifying enzymes. Our results suggest that the pathogenesis of both syndromes could involve some immune dysfunction.

Evaluation of Effects of Ractopamine on Cardiovascular, Respiratory, and Locomotory Physiology in Animal Model Zebrafish Larvae

Ractopamine (RAC) is a beta-adrenoceptor agonist that is used to promote lean and increased food conversion efficiency in livestock. This compound has been considered to be causing behavioral and physiological alterations in livestock like pig. Few studies have addressed the potential non-target effect of RAC in aquatic animals. In this study, we aimed to explore the potential physiological response after acute RAC exposure in zebrafish by evaluating multiple endpoints like locomotor activity, oxygen consumption, and cardiovascular performance. Zebrafish larvae were subjected to waterborne RAC exposure at 0.1, 1, 2, 4, or 8 ppm for 24 h, and the corresponding cardiovascular, respiratory, and locomotion activities were monitored and quantified. In addition, we also performed in silico molecular docking for RAC with 10 zebrafish endogenous β-adrenergic receptors to elucidate the potential acting mechanism of RAC. Results show RAC administration can significantly boost locomotor activity, cardiac performance, oxygen consumption, and blood flow rate, but without affecting the cardiac rhythm regularity in zebrafish embryos. Based on structure-based flexible molecular docking, RAC display similar binding affinity to all ten subtypes of endogenous β-adrenergic receptors, from adra1aa to adra2db, which are equivalent to the human one. This result suggests RAC might act as high potency and broad spectrum β-adrenergic receptors agonist on boosting the locomotor activity, cardiac performance, and oxygen consumption in zebrafish. To validate our results, we co-incubated a well-known β-blocker of propranolol (PROP) with RAC. PROP exposure tends to minimize the locomotor hyperactivity, high oxygen consumption, and cardiac rate in zebrafish larvae. In silico structure-based molecular simulation and binding affinity tests show PROP has an overall lower binding affinity than RAC. Taken together, our studies provide solid in vivo evidence to support that RAC plays crucial roles on modulating cardiovascular, respiratory, and locomotory physiology in zebrafish for the first time. In addition, the versatile functions of RAC as β-agonist possibly mediated via receptor competition with PROP as β-antagonist.

The SARS-CoV-2 receptor angiotensin-converting enzyme 2 (ACE2) in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: analysis of high-throughput epigenetic and gene expression studies

Patients affected by Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) show specific epigenetic and gene expression signatures of the disease. However, it is unknown whether these signatures include abnormal levels of the human angiotensin-converting enzymes, ACE and ACE2, the latter being the main receptor described for the host-cell invasion by SARS-CoV-2. To investigate that, we first re-analyzed available case-control epigenome-wide association studies based on DNA methylation data, and case-control gene expression studies based on microarray data. From these published studies, we found an association between ME/CFS and 4 potentially hypomethylated probes located in the ACE locus. We also found another disease association with one hypomethylated probe located in the transcription start site of ACE2. The same disease associations were obtained for women but not for men after performing sex-specific analyses. In contrast, a meta-analysis of gene expression levels could not provide evidence for a differentially expression of ACE and ACE2 in affected patients when compared to healthy controls. In line with this negative finding, the analysis of a new data set on the gene expression of ACE and ACE2 in peripheral blood mononuclear cells did not find any differences between a female cohort of 37 patients and 34 age-matched healthy controls. Future studies should be conducted to extend this investigation to other potential receptors used by SARS-CoV-2. These studies will help researchers and clinicians to improve the understanding of the health risk imposed by this virus when infecting patients affected by this debilitating disease.

Autoantibodies to beta-adrenergic and muscarinic cholinergic receptors in Myalgic Encephalomyelitis (ME) patients - A validation study in plasma and cerebrospinal fluid from two Swedish cohorts

Myalgic encephalomyelitis (ME) also known as ME/CFS (Chronic Fatigue Syndrome) or ME/SEID (Systemic Exertion Intolerance Disorder), is a disabling and often long-lasting disease that can drastically impair quality of life and physical/social functioning of the patients. Underlying pathological mechanisms are to a large extent unknown, but the presence of autoantibodies, cytokine pattern deviations and the presentation of cognitive and autonomic nervous system related symptoms provide evidence for ME being an immunological disorder with elements of autoimmunity. Increased levels of autoantibodies binding to adrenergic and muscarinic receptors in ME-patients have been reported. It is hypothesized that these autoantibodies have pathological significance and contribute to the ME-specific symptoms, however, these observations need to be validated. This study was designed to investigate potential differences in adrenergic and muscarinic receptor autoantibody levels in plasma and cerebrospinal fluid (CSF) samples between ME patients and gender and age-matched healthy controls, and to correlate the autoantibody levels to disease severity. We collected bodyfluids and health-related questionnaires from two Swedish ME cohorts, plasma and CSF from one of the cohorts (n ​= ​24), only plasma from the second cohort (n ​= ​24) together with plasma samples (n ​= ​24) and CSF (n ​= ​6) from healthy controls. All samples were analysed for IgG autoantibodies directed against Alpha- (α1, α2) and Beta- (β1-3) adrenergic receptors and Muscarinic (M) 1-5 acetylcholine receptors using an ELISA technique. The questionnaires were used as measures of disease severity. Significant increases in autoantibody levels in ME patients compared to controls were found for M3 and M4 -receptors in both cohorts and β1, β2, M3 and M4-receptors in one cohort. No significant correlations were found between autoantibody levels and disease severity. No significant levels of autoantibodies were detected in the CSF samples. These findings support previous findings that there exists a general pattern of increased antibody levels to adrenergic and muscarinic receptors within the ME patient group. However, the role of increased adrenergic and muscarinic receptor autoantibodies in the pathogenesis of ME is still uncertain and further research is needed to evaluate the clinical significance of these findings.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Comprehensive Review

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating chronic disease of unknown aetiology that is recognized by the World Health Organization (WHO) and the United States Center for Disease Control and Prevention (US CDC) as a disorder of the brain. The disease predominantly affects adults, with a peak age of onset of between 20 and 45 years with a female to male ratio of 3:1. Although the clinical features of the disease have been well established within diagnostic criteria, the diagnosis of ME/CFS is still of exclusion, meaning that other medical conditions must be ruled out. The pathophysiological mechanisms are unclear but the neuro-immuno-endocrinological pattern of CFS patients gleaned from various studies indicates that these three pillars may be the key point to understand the complexity of the disease. At the moment, there are no specific pharmacological therapies to treat the disease, but several studies' aims and therapeutic approaches have been described in order to benefit patients' prognosis, symptomatology relief, and the recovery of pre-existing function. This review presents a pathophysiological approach to understanding the essential concepts of ME/CFS, with an emphasis on the population, clinical, and genetic concepts associated with ME/CFS.

A novel mutation in Slc2a4 as a mouse model of fatigue

Chronic fatigue is a debilitating disorder with widespread consequences, but effective treatment strategies are lacking. Novel genetic mouse models of fatigue may prove invaluable for studying its underlying physiological mechanisms and for testing treatments and interventions. In a screen of voluntary wheel-running behavior in N-ethyl-N-nitrosourea mutagenized C57BL/6J mice, we discovered two lines with low body weights and aberrant wheel-running patterns suggestive of a fatigue phenotype. Affected progeny from these lines had lower daily activity levels and exhibited low amplitude circadian rhythm alterations. Their aberrant behavior was characterized by frequent interruptions and periods of inactivity throughout the dark phase of the light-dark cycle and increased levels of activity during the rest or light phase. Expression of the behavioral phenotypes in offspring of strategic crosses was consistent with a recessive inheritance pattern. Mapping of phenotypic abnormalities showed linkage with a single locus on chromosome 1, and whole exome sequencing identified a single point mutation in the Slc2a4 gene encoding the GLUT4 insulin-responsive glucose transporter. The single nucleotide change (A-T, which we named "twiggy") was in the distal end of exon 10 and resulted in a premature stop (Y440*). Additional metabolic phenotyping confirmed that these mice recapitulate phenotypes found in GLUT4 knockout mice. However, to the best of our knowledge, this is the first time a mutation in this gene has been shown to result in extensive changes in general behavioral patterns. These findings suggest that GLUT4 may be involved in circadian behavioral abnormalities and could provide insights into fatigue in humans.

Infection Elicited Autoimmunity and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: An Explanatory Model

Myalgic encephalomyelitis (ME) often also called chronic fatigue syndrome (ME/CFS) is a common, debilitating, disease of unknown origin. Although a subject of controversy and a considerable scientific literature, we think that a solid understanding of ME/CFS pathogenesis is emerging. In this study, we compiled recent findings and placed them in the context of the clinical picture and natural history of the disease. A pattern emerged, giving rise to an explanatory model. ME/CFS often starts after or during an infection. A logical explanation is that the infection initiates an autoreactive process, which affects several functions, including brain and energy metabolism. According to our model for ME/CFS pathogenesis, patients with a genetic predisposition and dysbiosis experience a gradual development of B cell clones prone to autoreactivity. Under normal circumstances these B cell offsprings would have led to tolerance. Subsequent exogenous microbial exposition (triggering) can lead to comorbidities such as fibromyalgia, thyroid disorder, and orthostatic hypotension. A decisive infectious trigger may then lead to immunization against autoantigens involved in aerobic energy production and/or hormone receptors and ion channel proteins, producing postexertional malaise and ME/CFS, affecting both muscle and brain. In principle, cloning and sequencing of immunoglobulin variable domains could reveal the evolution of pathogenic clones. Although evidence consistent with the model accumulated in recent years, there are several missing links in it. Hopefully, the hypothesis generates testable propositions that can augment the understanding of the pathogenesis of ME/CFS.

Open-label pilot for treatment targeting gut dysbiosis in myalgic encephalomyelitis/chronic fatigue syndrome: neuropsychological symptoms and sex comparisons

BACKGROUND

Preliminary evidence suggests that the enteric microbiota may play a role in the expression of neurological symptoms in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Overlapping symptoms with the acute presentation of D-lactic acidosis has prompted the use of antibiotic treatment to target the overgrowth of species within the Streptococcus genus found in commensal enteric microbiota as a possible treatment for neurological symptoms in ME/CFS.

METHODS

An open-label, repeated measures design was used to examine treatment efficacy and enable sex comparisons. Participants included 44 adult ME/CFS patients (27 females) from one specialist medical clinic with Streptococcus viable counts above 3.00 × 105 cfu/g (wet weight of faeces) and with a count greater than 5% of the total count of aerobic microorganisms. The 4-week treatment protocol included alternate weeks of Erythromycin (400 mg of erythromycin as ethyl succinate salt) twice daily and probiotic (D-lactate free multistrain probiotic, 5 × 1010 cfu twice daily). 2 × 2 repeated measures ANOVAs were used to assess sex-time interactions and effects across pre- and post-intervention for microbial, lactate and clinical outcomes. Ancillary non-parametric correlations were conducted to examine interactions between change in microbiota and clinical outcomes.

RESULTS

Large treatment effects were observed for the intention-to-treat sample with a reduction in Streptococcus viable count and improvement on several clinical outcomes including total symptoms, some sleep (less awakenings, greater efficiency and quality) and cognitive symptoms (attention, processing speed, cognitive flexibility, story memory and verbal fluency). Mood, fatigue and urine D:L lactate ratio remained similar across time. Ancillary results infer that shifts in microbiota were associated with more of the variance in clinical changes for males compared with females.

CONCLUSIONS

Results support the notion that specific microorganisms interact with some ME/CFS symptoms and offer promise for the therapeutic potential of targeting gut dysbiosis in this population. Streptococcus spp. are not the primary or sole producers of D-lactate. Further investigation of lactate concentrations are needed to elucidate any role of D-lactate in this population. Concurrent microbial shifts that may be associated with clinical improvement (i.e., increased Bacteroides and Bifidobacterium or decreased Clostridium in males) invite enquiry into alternative strategies for individualised treatment. Trial Registration Australian and New Zealand Clinical Trial Registry (ACTRN12614001077651) 9th October 2014. https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=366933&isReview=true.

A Molecular Neurobiological Approach to Understanding the Aetiology of Chronic Fatigue Syndrome (Myalgic Encephalomyelitis or Systemic Exertion Intolerance Disease) with Treatment Implications

Currently, a psychologically based model is widely held to be the basis for the aetiology and treatment of chronic fatigue syndrome (CFS)/myalgic encephalomyelitis (ME)/systemic exertion intolerance disease (SEID). However, an alternative, molecular neurobiological approach is possible and in this paper evidence demonstrating a biological aetiology for CFS/ME/SEID is adduced from a study of the history of the disease and a consideration of the role of the following in this disease: nitric oxide and peroxynitrite, oxidative and nitrosative stress, the blood–brain barrier and intestinal permeability, cytokines and infections, metabolism, structural and chemical brain changes, neurophysiological changes and calcium ion mobilisation. Evidence is also detailed for biologically based potential therapeutic options, including: nutritional supplementation, for example in order to downregulate the nitric oxide-peroxynitrite cycle to prevent its perpetuation; antiviral therapy; and monoclonal antibody treatment. It is concluded that there is strong evidence of a molecular neurobiological aetiology, and so it is suggested that biologically based therapeutic interventions should constitute a focus for future research into CFS/ME/SEID.