Unravelling the nature of postexertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome: the role of elastase, complement C4a and interleukin-1beta

Proteomic Analysis to Identify Prospective Biomarkers of Treatment Outcome After Microvascular Decompression for Trigeminal Neuralgia: A Preliminary Study

Trigeminal neuralgia (TN) is a severe neuropathic facial pain disorder, often caused by vascular or neuronal compression of the trigeminal nerve. In such cases, microvascular decompression (MVD) surgery can be used to treat TN, but pain relief is not guaranteed. The molecular mechanisms that affect treatment response to MVD are not well understood. In this exploratory study, we performed label-free quantitative proteomic profiling of plasma and cerebrospinal fluid samples from patients undergoing MVD for TN, then compared the proteomic profiles of patients graded as responders (n = 7) versus non-responders (n = 9). We quantified 1,090 proteins in plasma and 1,087 proteins in the cerebrospinal fluid, of which 12 were differentially regulated in the same direction in both sample types. Functional analyses of differentially regulated proteins in protein-protein interaction networks suggested pathways of the immune system, axon guidance, and cellular stress response to be associated with response to MVD. These findings suggest potential biomarkers of response to MVD, as well as possible mechanisms of variable treatment success in TN patients. PERSPECTIVE: This exploratory study evaluates proteomic profiles in plasma and cerebrospinal fluid of patients undergoing microvascular decompression surgery for trigeminal neuralgia. Differential expression of proteins between surgery responders versus non-responders may serve as biomarkers to predict surgical success and provide insight into surgical mechanisms of pain relief in trigeminal neuralgia.

Immunological Patient Stratification in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex disease characterized by profound fatigue, post-exertional malaise (PEM), and neurocognitive dysfunction. Immune dysregulation and gastrointestinal symptoms are commonly observed in ME/CFS patients. Despite affecting approximately 0.89% of the general population, the underlying pathophysiological mechanisms remain poorly understood. This study aimed to elucidate the relationship between immunological characteristics and intestinal barrier function in ME/CFS patients. ME/CFS patients were stratified into two groups based on their immune competence. After documentation of detailed medical records, serum and plasma samples were collected for the assessment of inflammatory immune mediators and biomarkers for intestinal barrier integrity by ELISA. We found reduced complement protein C4a levels in immunodeficient ME/CFS patients suggesting a subgroup-specific innate immune dysregulation. ME/CFS patients without immunodeficiencies exhibit a mucosal barrier leakage, as indicated by elevated levels of Lipopolysaccharide-binding protein (LBP). Stratifying ME/CFS patients based on immune competence enabled the distinction of two subgroups with different pathophysiological patterns. The study highlights the importance of emphasizing precise patient stratification in ME/CFS, particularly in the context of defining suitable treatment strategies. Given the substantial health and socioeconomic burden associated with ME/CFS, urgent attention and research efforts are needed to define causative treatment approaches.

Biomarkers for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS): a systematic review

BACKGROUND

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a multifaceted condition that affects most body systems. There is currently no known diagnostic biomarker; instead, diagnosis is dependent on application of symptom-based case criteria following exclusion of any other potential medical conditions. While there are some studies that report potential biomarkers for ME/CFS, their efficacy has not been validated. The aim of this systematic review is to collate and appraise literature pertaining to a potential biomarker(s) which may effectively differentiate ME/CFS patients from healthy controls.

METHODS

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and Cochrane review guidelines. PubMed, Embase and Scopus were systematically searched for articles containing "biomarker" and "ME/CFS" keywords in the abstract or title and if they included the following criteria: (1) were observational studies published between December 1994 and April 2022; (2) involved adult human participants; (3) full text is available in English (4) original research; (5) diagnosis of ME/CFS patients made according to the Fukuda criteria (1994), Canadian Consensus Criteria (2003), International Consensus Criteria (2011) or Institute of Medicine Criteria (2015); (6) study investigated potential biomarkers of ME/CFS compared to healthy controls. Quality and Bias were assessed using the Joanna Briggs Institute Critical Appraisal Checklist for Case Control Studies.

RESULTS

A total of 101 publications were included in this systematic review. Potential biomarkers ranged from genetic/epigenetic (19.8%), immunological (29.7%), metabolomics/mitochondrial/microbiome (14.85%), endovascular/circulatory (17.82%), neurological (7.92%), ion channel (8.91%) and physical dysfunction biomarkers (8.91%). Most of the potential biomarkers reported were blood-based (79.2%). Use of lymphocytes as a model to investigate ME/CFS pathology was prominent among immune-based biomarkers. Most biomarkers had secondary (43.56%) or tertiary (54.47%) selectivity, which is the ability for the biomarker to identify a disease-causing agent, and a moderate (59.40%) to complex (39.60%) ease-of-detection, including the requirement of specialised equipment.

CONCLUSIONS

All potential ME/CFS biomarkers differed in efficiency, quality, and translatability as a diagnostic marker. Reproducibility of findings between the included publications were limited, however, several studies validated the involvement of immune dysfunction in the pathology of ME/CFS and the use of lymphocytes as a model to investigate the pathomechanism of illness. The heterogeneity shown across many of the included studies highlights the need for multidisciplinary research and uniform protocols in ME/CFS biomarker research.

A 2-day cardiopulmonary exercise test in chronic fatigue syndrome patients who were exposed to humidifier disinfectants

Some survivors of humidifier disinfectants (HDs) complain of chronic, inexplicable fatigue, and post-exertional malaise (PEM). Two-day cardiopulmonary exercise tests (CPETs) performed 24 hours apart (2-day CPET protocol) are increasingly employed to evaluate PEM and related disabilities among individuals with chronic fatigue syndrome (CFS). The purpose of this study was to assess the reproducibility of CPET variables in individuals who had been exposed to HD and to show that 2-day CPET is an objective means of differentiating between fatigue conditions in people with CFS symptoms who have been exposed to HDs. Twenty-nine HD survivors with CFS symptoms were enrolled in this study. To document and assess PEM in CFS, a 2-day CPET was conducted to measure baseline functional capacity (CPET1) and provoke PEM. Twenty-four hours later, a second CPET assessed changes in related variables, focusing on PEM effects on functional capacity. This CPET also measured changes in energy production and physiological function, objectively documenting PEM effects. In the 2-day CPET, the peak oxygen consumption (VO2peak), VO2 at ventilatory threshold (VO2@VT), time to reach VO2peak, and time to reach VO2@VT were significantly decreased (p<0.001). The peak O2 pulse and O2 pulse at VT also decreased significantly (p<0.001). A 6-minute walk test revealed significantly decreased distance (p<0.01). This is the first study to conduct a 2-day consecutive CPET in previously exposed HD participants with CFS symptoms. Our results confirm previous work that demonstrated abnormal responses to PEM in CFS patients. Therefore, a 2-day CPET is an objective measure to differentiate fatigue conditions in people with CFS symptoms who have been exposed to HDs.

Exosome-associated mitochondrial DNA from patients with myalgic encephalomyelitis/chronic fatigue syndrome stimulates human microglia to release IL-1β

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating disease that presents with fatigue, sleep disturbances, malaise, and cognitive problems. The pathogenesis of ME/CFS is presently unknown, and serum levels of potential biomarkers have been inconsistent. Here, we show that mitochondrial DNA (mtDNA) associated with serum exosomes, is increased in ME/CFS patients only after exercise. Moreover, exosomes isolated from patients with ME/CFS stimulate significant release of IL-1β from cultured human microglia. These results provide evidence that activation of microglia by serum-derived exosomes may serve as a potential novel pathogenetic factor and target for treatment of ME/CFS.

Toward the unity of pathological and exertional fatigue: A predictive processing model

Fatigue is a common experience in both health and disease. Yet, pathological (i.e., prolonged or chronic) and transient (i.e., exertional) fatigue symptoms are traditionally considered distinct, compounding a separation between interested research fields within the study of fatigue. Within the clinical neurosciences, nascent frameworks position pathological fatigue as a product of inference derived through hierarchical predictive processing. The metacognitive theory of dyshomeostasis (Stephan et al., 2016) states that pathological fatigue emerges from the metacognitive mechanism in which the detection of persistent mismatches between prior interoceptive predictions and ascending sensory evidence (i.e., prediction error) signals low evidence for internal generative models, which undermine an agent’s feeling of mastery over the body and is thus experienced phenomenologically as fatigue. Although acute, transient subjective symptoms of exertional fatigue have also been associated with increasing interoceptive prediction error, the dynamic computations that underlie its development have not been clearly defined. Here, drawing on the metacognitive theory of dyshomeostasis, we extend this account to offer an explicit description of the development of fatigue during extended periods of (physical) exertion. Accordingly, it is proposed that a loss of certainty or confidence in control predictions in response to persistent detection of prediction error features as a common foundation for the conscious experience of both pathological and nonpathological fatigue.

Reduced Parasympathetic Reactivation during Recovery from Exercise in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Although autonomic nervous system (ANS) dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) has been proposed, conflicting evidence makes it difficult to draw firm conclusions regarding ANS activity at rest in ME/CFS patients. Although severe exercise intolerance is one of the core features of ME/CFS, little attempts have been made to study ANS responses to physical exercise. Therefore, impairments in ANS activation at rest and following exercise were examined using a case-control study in 20 ME/CFS patients and 20 healthy people. Different autonomous variables, including cardiac, respiratory, and electrodermal responses were assessed at rest and following an acute exercise bout. At rest, parameters in the time-domain represented normal autonomic function in ME/CFS, while frequency-domain parameters indicated the possible presence of diminished (para)sympathetic activation. Reduced parasympathetic reactivation during recovery from exercise was observed in ME/CFS. This is the first study showing reduced parasympathetic reactivation during recovery from physical exercise in ME/CFS. Delayed HR recovery and/or a reduced HRV as seen in ME/CFS have been associated with poor disease prognosis, high risk for adverse cardiac events, and morbidity in other pathologies, implying that future studies should examine whether this is also the case in ME/CFS and how to safely improve HR recovery in this population.

Numeric Rating Scales Show Prolonged Post-exertional Symptoms After Orthostatic Testing of Adults With Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Introduction: Muscle pain, fatigue, and concentration problems are common among individuals with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). These symptoms are commonly increased as part of the phenomenon of postexertional malaise (PEM). An increase in the severity of these symptoms is described following physical or mental exercise in ME/CFS patients. Another important symptom of ME/CFS is orthostatic intolerance, which can be detected by head-up tilt testing (HUT). The effect of HUT on PEM has not been studied extensively. For this purpose, we assessed numeric rating scales (NRS) for pain, fatigue, and concentration pre- and post-HUT. As pain is a core symptom in fibromyalgia (FM), we subgrouped ME/CFS patients by the presence or absence of FM. Methods and Results: In eligible ME/CFS patients who underwent HUT, NRS of pain, fatigue, and concentration were obtained pre-HUT, immediately after HUT, at 24 and 48 h, and at 7 days posttest. We studied 174 ME/CFS patients with FM, 104 without FM, and 30 healthy controls (HC). Values for all symptoms were unchanged for HC pre- and post-HUT. Compared with pre-HUT, the three NRS post-HUT were significantly elevated in both ME/CFS patient groups even after 7 days. NRS pain was significantly higher at all time points measured in the ME/CFS patients with FM compared with those without FM. In ME/CFS patients, the maximum fatigue and concentration scores occurred directly post-HUT, whereas pain perception reached the maximum 24 h post-HUT. Conclusion: NRS scores of pain, fatigue, and concentration were significantly increased even at 7 days post-HUT compared with pre-HUT in ME/CFS patients with and without FM, suggesting that orthostatic stress is an important determinant of PEM.

Exercise-induce hyperalgesia, complement system and elastase activation in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome - a secondary analysis of experimental comparative studies

Background and aims The interaction between the immune system and pain has been thoroughly explored in the recent decades. The release of inflammatory mediators from immune cells has the capability of activating neurons and glial cells, in turn sensitizing the nervous system. Both immune system alterations and pain modulation dysfunctions have been shown in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) following exercise. However, no studies tried to explore whether these two phenomena are linked and can explain exercise-induced symptoms worsening in people with ME/CFS. We hypothesized that exercise-induced changes in descending pain modulation is associated to changes in immune system functions. We used complement system product C4a and elastase activity as indicators of immune system activity. Methods The study design was a secondary analysis of controlled experimental studies. Twenty-two patients with ME/CFS and 22 healthy sedentary controls were enrolled. In experiment 1, subjects performed an aerobic submaximal exercise test; in experiment 2 they underwent a self-paced exercise test. One week of rest period were set between the two exercise tests. Before and after each experiment, subjects underwent clinical assessment, pain thresholds (PPTs) measurement, and blood sampling. Immune system function was assessed measuring complement system C4a products and elastase activity. Results Changes in elastase activity were not associated to changes in PPTs. Associations were observed in the ME/CFS group between changes in PPTs and C4a products, following both types of exercise. After submaximal exercise, the change in C4a products was associated with the change in PPT at the thumb in patients (r=0.669, p=0.001). Similarly, after self-paced exercise the change in C4a products was associated witht the change in PPT at the calf in patients (r=0.429, p=0.047). No such correlations were found in healthy controls. Regression analysis showed that C4a changes after the submaximal exercise significantly predicted the change in PPTs (R2=0.236; p=0.02). Conclusions Moderate associations between exercise-induced changes in PPTs and immune system activity were found only in ME/CFS. The change in the complement system following submaximal exercise might be able to explain part of the change in patient's pain thresholds, providing evidence for a potential link between immune system alteration and dysfunctional endogenous pain modulation. These results have to be taken with caution, as only one out of three measures of PPTs was found associated with C4a changes. We cannot reject the hypothesis that C4a might therefore be a confounding factor, and changes during exercise might be mediated by other mechanism. Implications Immune system changes following exercise might contribute to exercise-induced symptoms worsening in patients with ME/CFS. However, the role of the complement system is questionable.

Exercise-Induced Hypoalgesia in Pain-Free and Chronic Pain Populations: State of the Art and Future Directions

Exercise is considered an important component of effective chronic pain management and it is well-established that long-term exercise training provides pain relief. In healthy, pain-free populations, a single bout of aerobic or resistance exercise typically leads to exercise-induced hypoalgesia (EIH), a generalized reduction in pain and pain sensitivity that occurs during exercise and for some time afterward. In contrast, EIH is more variable in chronic pain populations and is more frequently impaired; with pain and pain sensitivity decreasing, remaining unchanged or, in some cases, even increasing in response to exercise. Pain exacerbation with exercise may be a major barrier to adherence, precipitating a cycle of physical inactivity that can lead to long-term worsening of both pain and disability. To optimize the therapeutic benefits of exercise, it is important to understand how EIH works, why it may be impaired in some people with chronic pain, and how this should be addressed in clinical practice. In this article, we provide an overview of EIH across different chronic pain conditions. We discuss possible biological mechanisms of EIH and the potential influence of sex and psychosocial factors, both in pain-free adults and, where possible, in individuals with chronic pain. The clinical implications of impaired EIH are discussed and recommendations are made for future research, including further exploration of individual differences in EIH, the relationship between exercise dose and EIH, the efficacy of combined treatments and the use of alternative measures to quantify EIH. PERSPECTIVE: This article provides a contemporary review of the acute effects of exercise on pain and pain sensitivity, including in people with chronic pain conditions. Existing findings are critically reviewed, clinical implications are discussed, and recommendations are offered for future research.

Relationship Between Exercise-induced Oxidative Stress Changes and Parasympathetic Activity in Chronic Fatigue Syndrome: An Observational Study in Patients and Healthy Subjects

PURPOSE

Oxidative stress has been proposed as a contributor to pain in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). During incremental exercise in patients with ME/CFS, oxidative stress enhances sooner and antioxidant response is delayed. We explored whether oxidative stress is associated with pain symptoms or pain changes following exercise, and the possible relationships between oxidative stress and parasympathetic vagal nerve activity in patients with ME/CFS versus healthy, inactive controls.

METHODS

The present study reports secondary outcomes from a previous work. Data from 36 participants were studied (women with ME/CFS and healthy controls). Subjects performed a submaximal exercise test with continuous cardiorespiratory monitoring. Levels of thiobarbituric acid-reactive substances (TBARSs) were used as a measure of oxidative stress, and heart rate variability was used to assess vagal activity. Before and after the exercise, subjects were asked to rate their pain using a visual analogic scale.

FINDINGS

Significant between-group differences in pain at both baseline and following exercise were found (both, P < 0.007). In healthy controls, pain was significantly improved following exercise (P = 0.002). No change in oxidative stress level after exercise was found. Significant correlation between TBARS levels and pain was found at baseline (r = 0.540; P = 0.021) and after exercise (r = 0.524; P = 0.024) in patients only. No significant correlation between TBARS and heart rate variability at baseline or following exercise was found in either group. However, a significant correlation was found between exercise-induced changes in HRV and TBARS in healthy controls (r = -0.720; P = 0.001).

IMPLICATIONS

Oxidative stress showed an association with pain symptoms in people with ME/CFS, but no exercise-induced changes in oxidative stress were found. In addition, the change in parasympathetic activity following exercise partially accounted for the change in oxidative stress in healthy controls. More research is required to further explore this link.

Neuroinflammation and Cytokines in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS): A Critical Review of Research Methods

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is the label given to a syndrome that can include long-term flu-like symptoms, profound fatigue, trouble concentrating, and autonomic problems, all of which worsen after exertion. It is unclear how many individuals with this diagnosis are suffering from the same condition or have the same underlying pathophysiology, and the discovery of biomarkers would be clarifying. The name "myalgic encephalomyelitis" essentially means "muscle pain related to central nervous system inflammation" and many efforts to find diagnostic biomarkers have focused on one or more aspects of neuroinflammation, from periphery to brain. As the field uncovers the relationship between the symptoms of this condition and neuroinflammation, attention must be paid to the biological mechanisms of neuroinflammation and issues with its potential measurement. The current review focuses on three methods used to study putative neuroinflammation in ME/CFS: (1) positron emission tomography (PET) neuroimaging using translocator protein (TSPO) binding radioligand (2) magnetic resonance spectroscopy (MRS) neuroimaging and (3) assays of cytokines circulating in blood and cerebrospinal fluid. PET scanning using TSPO-binding radioligand is a promising option for studies of neuroinflammation. However, methodological difficulties that exist both in this particular technique and across the ME/CFS neuroimaging literature must be addressed for any results to be interpretable. We argue that the vast majority of ME/CFS neuroimaging has failed to use optimal techniques for studying brainstem, despite its probable centrality to any neuroinflammatory causes or autonomic effects. MRS is discussed as a less informative but more widely available, less invasive, and less expensive option for imaging neuroinflammation, and existing studies using MRS neuroimaging are reviewed. Studies seeking to find a peripheral circulating cytokine "profile" for ME/CFS are reviewed, with attention paid to the biological and methodological reasons for lack of replication among these studies. We argue that both the biological mechanisms of cytokines and the innumerable sources of potential variance in their measurement make it unlikely that a consistent and replicable diagnostic cytokine profile will ever be discovered.

Deconstructing post-exertional malaise in myalgic encephalomyelitis/ chronic fatigue syndrome: A patient-centered, cross-sectional survey

BACKGROUND

Post-exertional malaise (PEM) is considered to be the hallmark characteristic of myalgic encephalomyelitis/ chronic fatigue syndrome (ME/CFS). Yet, patients have rarely been asked in formal studies to describe their experience of PEM.

OBJECTIVES

To describe symptoms associated with and the time course of PEM.

METHODS

One hundred and fifty subjects, diagnosed via the 1994 Fukuda CFS criteria, completed a survey concerning 11 symptoms they could experience after exposure to two different types of triggers. We also inquired about onset and duration of PEM and included space for subjects to write in any additional symptoms. Results were summarized with descriptive statistics; McNemar's, paired t-, Fisher's exact and chi-square goodness-of-fit tests were used to assess for statistical significance.

RESULTS

One hundred and twenty-nine subjects (90%) experienced PEM with both physical and cognitive exertion and emotional distress. Almost all were affected by exertion but 14 (10%) reported no effect with emotion. Fatigue was the most commonly exacerbated symptom but cognitive difficulties, sleep disturbances, headaches, muscle pain, and flu-like feelings were cited by over 30% of subjects. Sixty percent of subjects experienced at least one inflammatory/ immune-related symptom. Subjects also cited gastrointestinal, orthostatic, mood-related, neurologic and other symptoms. Exertion precipitated significantly more symptoms than emotional distress (7±2.8 vs. 5±3.3 symptoms (median, standard deviation), p<0.001). Onset and duration of PEM varied for most subjects. However, 11% reported a consistent post-trigger delay of at least 24 hours before onset and 84% endure PEM for 24 hours or more.

CONCLUSIONS

This study provides exact symptom and time patterns for PEM that is generated in the course of patients' lives. PEM involves exacerbation of multiple, atypical symptoms, is occasionally delayed, and persists for extended periods. Highlighting these characteristics may improve diagnosis of ME/CFS. Incorporating them into the design of future research will accelerate our understanding of ME/CFS.

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.

Muscle fatigue: general understanding and treatment

Muscle fatigue is a common complaint in clinical practice. In humans, muscle fatigue can be defined as exercise-induced decrease in the ability to produce force. Here, to provide a general understanding and describe potential therapies for muscle fatigue, we summarize studies on muscle fatigue, including topics such as the sequence of events observed during force production, in vivo fatigue-site evaluation techniques, diagnostic markers and non-specific but effective treatments.

Interleukin-1 as a mediator of fatigue in disease: a narrative review

Fatigue is commonly reported in a variety of illnesses, and it has major impact on quality of life. Previously, it was thought that fatigue originates in the skeletal muscles, leading to cessation of activity. However, more recently, it has become clear that the brain is the central regulator of fatigue perception. It has been suggested that pro-inflammatory cytokines, especially interleukin-1 alpha (IL-1α) and interleukin-1 beta (IL-1β), play a prominent role in the development of central fatigue, and several studies have been performed to elucidate the connection between inflammation and these central processes.In this narrative review, mechanisms of action of IL-1 are described, with special attention to its effect on the central nervous system. In addition, we present a summary of studies that (i) investigated the relationship between circulating IL-1α and IL-1β and fatigue severity and/or (ii) evaluated the effect of inhibiting IL-1 on fatigue. We aim to improve the understanding of fatigue in both inflammatory and non-inflammatory illnesses, which could help develop strategies to treat fatigue more effectively.Reviewing the studies that have been performed, it appears that there is a limited value of measuring circulating IL-1. However, inhibiting IL-1 has a positive effect on severe fatigue in most studies that have been conducted.

Optimized Treatment of Heparinized Blood Fractions to Make Them Suitable for Analysis

BACKGROUND

It has been known for decades that many cytokines, such as IL-2, IL-6, and IL-12, bind to heparin. Even though some enzyme-linked immunosorbent assays (ELISA) use antibody-recognizing epitopes not affected by this binding, ELISA manufacturers often warn that heparinized plasma or serum fractions containing more than 3 IU (international units)/mL of heparin should not be used in assays so as to prevent heparin interference in the reaction. In addition, enzyme-based nucleic acid amplifications from heparinized samples have been shown defective by several research groups. The aim of this study was to determine optimal degradation and/or removal of heparin from heparinized blood samples to best turn them into fractions for appropriate ELISA and RT-PCR analysis.

METHODS AND RESULTS

A colorimetric reporter assay based on the metachromatic effect of the binding of heparin to toluidine blue was shown to be a low-cost effective method to discriminate assay compatible blood fractions with heparin levels below 3 IU/mL. Heparin removal from human blood fractions was best achieved by treatment with either Bacteroides Heparinase II or the less expensive Heparinase I at a final concentration of 0.1 U/μL and incubations at 30°C for a period between 30 min and 4 h, or by adsorption to Ecteola slurries at a concentration of 20 mg/mL for 20 min at room temperature (RT). The fact that both enzymatic and resin-based optimized treatments allowed for replication of the readings obtained with heparin-free equivalent fractions in both ELISA and RT-PCR assays indicates they should be appropriate for quantitative studies such as expression profiling at both the protein and nucleic acid level.

CONCLUSIONS

The cost-effective protocols developed in this study could make heparinized, otherwise unusable, blood-derived collections suitable for analysis by ELISA and RT-PCR amplifications, among other analyses, enhancing the possibilities for studying valuable bio-banked heparinized human samples.

Chronic fatigue syndrome and circulating cytokines: A systematic review

There has been much interest in the role of the immune system in the pathophysiology of chronic fatigue syndrome (CFS), as CFS may develop following an infection and cytokines are known to induce acute sickness behaviour, with similar symptoms to CFS. Using the PRISMA (Preferred Reporting Items for Systematic reviews and Meta-analyses) guidelines, a search was conducted on PubMed, Web of Science, Embase and PsycINFO, for CFS related-terms in combination with cytokine-related terms. Cases had to meet established criteria for CFS and be compared with healthy controls. Papers retrieved were assessed for both inclusionary criteria and quality. 38 papers met the inclusionary criteria. The quality of the studies varied. 77 serum or plasma cytokines were measured without immune stimulation. Cases of CFS had significantly elevated concentrations of transforming growth factor-beta (TGF-β) in five out of eight (63%) studies. No other cytokines were present in abnormal concentrations in the majority of studies, although insufficient data were available for some cytokines. Following physical exercise there were no differences in circulating cytokine levels between cases and controls and exercise made no difference to already elevated TGF-β concentrations. The finding of elevated TGF-β concentration, at biologically relevant levels, needs further exploration, but circulating cytokines do not seem to explain the core characteristic of post-exertional fatigue.

Myalgic Encephalomyelitis: Symptoms and Biomarkers

Myalgic Encephalomyelitis (ME) continues to cause significant morbidity worldwide with an estimated one million cases in the United States. Hurdles to establishing consensus to achieve accurate evaluation of patients with ME continue, fueled by poor agreement about case definitions, slow progress in development of standardized diagnostic approaches, and issues surrounding research priorities. Because there are other medical problems, such as early MS and Parkinson's Disease, which have some similar clinical presentations, it is critical to accurately diagnose ME to make a differential diagnosis. In this article, we explore and summarize advances in the physiological and neurological approaches to understanding, diagnosing, and treating ME. We identify key areas and approaches to elucidate the core and secondary symptom clusters in ME so as to provide some practical suggestions in evaluation of ME for clinicians and researchers. This review, therefore, represents a synthesis of key discussions in the literature, and has important implications for a better understanding of ME, its biological markers, and diagnostic criteria. There is a clear need for more longitudinal studies in this area with larger data sets, which correct for multiple testing.

Discriminative validity of metabolic and workload measurements for identifying people with chronic fatigue syndrome

BACKGROUND

Reduced functional capacity and postexertion fatigue after physical activity are hallmark symptoms of chronic fatigue syndrome (CFS) and may even qualify for biomarker status. That these symptoms are often delayed may explain the equivocal results for clinical cardiopulmonary exercise testing in people with CFS. Test reproducibility in people who are healthy is well documented. Test reproducibility may not be achievable in people with CFS because of delayed symptoms.

OBJECTIVE

The objective of this study was to determine the discriminative validity of objective measurements obtained during cardiopulmonary exercise testing to distinguish participants with CFS from participants who did not have a disability but were sedentary.

DESIGN

A prospective cohort study was conducted.

METHODS

Gas exchange data, workloads, and related physiological parameters were compared in 51 participants with CFS and 10 control participants, all women, for 2 maximal exercise tests separated by 24 hours.

RESULTS

Multivariate analysis showed no significant differences between control participants and participants with CFS for test 1. However, for test 2, participants with CFS achieved significantly lower values for oxygen consumption and workload at peak exercise and at the ventilatory or anaerobic threshold. Follow-up classification analysis differentiated between groups with an overall accuracy of 95.1%.

LIMITATIONS

Only individuals with CFS who were able to undergo exercise testing were included in this study. Individuals who were unable to meet the criteria for maximal effort during both tests, were unable to complete the 2-day protocol, or displayed overt cardiovascular abnormalities were excluded from the analysis.

CONCLUSIONS

The lack of any significant differences between groups for the first exercise test would appear to support a deconditioning hypothesis for CFS symptoms. However, the results from the second test indicated the presence of CFS-related postexertion fatigue. It might be concluded that a single exercise test is insufficient to reliably demonstrate functional impairment in people with CFS. A second test might be necessary to document the atypical recovery response and protracted fatigue possibly unique to CFS, which can severely limit productivity in the home and workplace.

International Union of Basic and Clinical Pharmacology. [corrected]. LXXXVII. Complement peptide C5a, C4a, and C3a receptors

The activation of the complement cascade, a cornerstone of the innate immune response, produces a number of small (74-77 amino acid) fragments, originally termed anaphylatoxins, that are potent chemoattractants and secretagogues that act on a wide variety of cell types. These fragments, C5a, C4a, and C3a, participate at all levels of the immune response and are also involved in other processes such as neural development and organ regeneration. Their primary function, however, is in inflammation, so they are important targets for the development of antiinflammatory therapies. Only three receptors for complement peptides have been found, but there are no satisfactory antagonists as yet, despite intensive investigation. In humans, there is a single receptor for C3a (C3a receptor), no known receptor for C4a, and two receptors for C5a (C5a₁ receptor and C5a₂ receptor). The most recently characterized receptor, the C5a₂ receptor (previously known as C5L2 or GPR77), has been regarded as a passive binding protein, but signaling activities are now ascribed to it, so we propose that it be formally identified as a receptor and be given a name to reflect this. Here, we describe the complex biology of the complement peptides, introduce a new suggested nomenclature, and review our current knowledge of receptor pharmacology.

Biomarkers of peripheral muscle fatigue during exercise

BACKGROUND

Biomarkers of peripheral muscle fatigue (BPMFs) are used to offer insights into mechanisms of exhaustion during exercise in order to detect abnormal fatigue or to detect defective metabolic pathways. This review aims at describing recent advances and future perspectives concerning the most important biomarkers of muscle fatigue during exercise.

RESULTS

BPMFs are classified according to the mechanism of fatigue related to adenosine-triphosphate-metabolism, acidosis, or oxidative-metabolism. Muscle fatigue is also related to an immunological response. impaired calcium handling, disturbances in bioenergetic pathways, and genetic responses. The immunological and genetic response may make the muscle susceptible to fatigue but may not directly cause muscle fatigue. Production of BPMFs is predominantly dependent on the type of exercise. BPMFs need to change as a function of the process being monitored, be stable without appreciable diurnal variations, correlate well with exercise intensity, and be present in detectable amounts in easily accessible biological fluids. The most well-known BPMFs are serum lactate and interleukin-6. The most widely applied clinical application is screening for defective oxidative metabolism in mitochondrial disorders by means of the lactate stress test. The clinical relevance of most other BPMFs, however, is under debate, since they often depend on age, gender, physical fitness, the energy supply during exercise, the type of exercise needed to produce the BPMF, and whether healthy or diseased subjects are investigated.

CONCLUSIONS

Though the role of BPMFs during fatigue is poorly understood, measuring BPMFs under specific, standardised conditions appears to be helpful for assessing biological states or processes during exercise and fatigue.

Kinesiophobia, catastrophizing and anticipated symptoms before stair climbing in chronic fatigue syndrome: an experimental study

PURPOSE

Kinesiophobia and catastrophizing are frequent among people with chronic fatigue syndrome (CFS). This study was aimed at examining (1) whether kinesiophobia, anticipated symptoms and fatigue catastrophizing are related to stair climbing performance in people with CFS; and (2) whether kinesiophobia and fatigue catastrophizing are related to daily physical activity in CFS.

METHOD

Patients with CFS filled in a set of questionnaires, performed a physical demanding task (two floors stair of climbing and descending) with pre-test and post-test heart rate monitoring and immediate post-stair climbing symptom assessment. Real-time activity monitoring was used between the baseline and second assessment day (7 days later).

RESULTS

Kinesiophobia and fatigue catastrophizing were strongly related (ρ = 0.62 and 0.67, respectively) to poorer stair climbing performance (i.e. more time required to complete the threatening activity). Kinesiophobia and fatigue catastrophizing were unrelated to the amount of physical activity on the first day following stair climbing or during the seven subsequent days.

CONCLUSION

These findings underscore the importance of kinesiophobia and fatigue catastrophizing for performing physical demanding tasks in everyday life of people with CFS, but refute a cardinal role for kinesiophobia and fatigue catastrophizing in determining daily physical activity level in these patients.

Loss of capacity to recover from acidosis on repeat exercise in chronic fatigue syndrome: a case-control study

BACKGROUND

Chronic fatigue syndrome (CFS) patients frequently describe difficulties with repeat exercise. Here, we explore muscle bioenergetic function in response to three bouts of exercise.

METHODS

A total of 18 CFS (CDC 1994) patients and 12 sedentary controls underwent assessment of maximal voluntary contraction (MVC), repeat exercise with magnetic resonance spectroscopy and cardio-respiratory fitness test to determine anaerobic threshold.

RESULT

Chronic fatigue syndrome patients undertaking MVC fell into two distinct groups: 8 (45%) showed normal PCr depletion in response to exercise at 35% of MVC (PCr depletion >33%; lower 95% CI for controls); 10 CFS patients had low PCr depletion (generating abnormally low MVC values). The CFS whole group exhibited significantly reduced anaerobic threshold, heart rate, VO(2) , VO(2) peak and peak work compared to controls. Resting muscle pH was similar in controls and both CFS patient groups. However, the CFS group achieving normal PCr depletion values showed increased intramuscular acidosis compared to controls after similar work after each of the three exercise periods with no apparent reduction in acidosis with repeat exercise of the type reported in normal subjects. This CFS group also exhibited significant prolongation (almost 4-fold) of the time taken for pH to recover to baseline.

CONCLUSION

When exercising to comparable levels to normal controls, CFS patients exhibit profound abnormality in bioenergetic function and response to it. Although exercise intervention is the logical treatment for patients showing acidosis, any trial must exclude subjects who do not initiate exercise as they will not benefit. This potentially explains previous mixed results in CFS exercise trials.

Differences in metabolite-detecting, adrenergic, and immune gene expression after moderate exercise in patients with chronic fatigue syndrome, patients with multiple sclerosis, and healthy controls

OBJECTIVE

Chronic fatigue syndrome (CFS) and multiple sclerosis (MS) are characterized by debilitating fatigue, yet evaluation of this symptom is subjective. We examined metabolite-detecting, adrenergic, and immune gene expression (messenger ribonucleic acid [mRNA]) in patients with CFS (n = 22) versus patients with MS (n = 20) versus healthy controls (n = 23) and determined their relationship to fatigue and pain before and after exercise.

METHODS

Blood samples and fatigue and pain ratings were obtained at baseline and 0.5, 8, 24, and 48 hours after sustained moderate exercise. Leukocyte mRNA of four metabolite-detecting receptors (acid-sensing ion channel 3, purinergic type 2X4 and 2X5 receptors, and transient receptor potential vanilloid type 1) and four adrenergic (α-2a, β-1, and β-2 receptors and catechol-O-methyltransferase) and five immune markers (CD14, toll-like receptor 4 [TLR4], interleukin [IL] 6, IL-10, and lymphotoxin α) was examined using quantitative polymerase chain reaction.

RESULTS

Patients with CFS had greater postexercise increases in fatigue and pain (10-29 points above baseline, p < .001) and greater mRNA increases in purinergic type 2X4 receptor, transient receptor potential vanilloid type 1, CD14, and all adrenergic receptors than controls (mean ± standard error = 1.3 ± 0.14- to 3.4 ± 0.90-fold increase above baseline, p = .04-.005). Patients with CFS with comorbid fibromyalgia (n = 18) also showed greater increases in acid-sensing ion channel 3 and purinergic type 2X5 receptors (p < .05). Patients with MS had greater postexercise increases than controls in β-1 and β-2 adrenergic receptor expressions (1.4 ± 0.27- and 1.3 ± 0.06-fold increases, respectively, p = .02 and p < .001) and greater decreases in TLR4 (p = .02). In MS, IL-10 and TLR4 decreases correlated with higher fatigue scores.

CONCLUSIONS

Postexercise mRNA increases in metabolite-detecting receptors were unique to patients with CFS, whereas both patients with MS and patients with CFS showed abnormal increases in adrenergic receptors. Among patients with MS, greater fatigue was correlated with blunted immune marker expression.

Chronic fatigue syndrome, the immune system and viral infection

The chronic fatigue syndrome (CFS), as defined by recent criteria, is a heterogeneous disorder with a common set of symptoms that often either follows a viral infection or a period of stress. Despite many years of intense investigation there is little consensus on the presence, nature and degree of immune dysfunction in this condition. However, slightly increased parameters of inflammation and pro-inflammatory cytokines such as interleukin (IL) 1, IL6 and tumour necrosis factor (TNF) α are likely present. Additionally, impaired natural killer cell function appears evident. Alterations in T cell numbers have been described by some and not others. While the prevalence of positive serology for the common herpes viruses appears no different from healthy controls, there is some evidence of viral persistence and inadequate containment of viral replication. The ability of certain herpes viruses to impair the development of T cell memory may explain this viral persistence and the continuation of symptoms. New therapies based on this understanding are more likely to produce benefit than current methods.

Pacing as a strategy to improve energy management in myalgic encephalomyelitis/chronic fatigue syndrome: a consensus document

PURPOSE

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating condition characterized by a number of symptoms which typically worsen following minimal exertion. Various strategies to manage the limited energy levels have been proposed. Of these, pacing has been consistently rated as one of the most helpful in surveys conducted by patient groups. This review is a response to the paucity of the information on pacing in the scientific literature.

METHOD

We describe the principle of pacing and how this can be adapted to meet individual abilities and preferences. A critical evaluation of the research was conducted to ascertain the benefits and limitations of this strategy.

RESULTS

Based on various studies, it is proposed that pacing can help to stabilize the condition and avoid post-exertional malaise.

CONCLUSION

Pacing offers practitioners an additional therapeutic option which is acceptable to the majority of patients and can reduce the severity of the exertion-related symptoms of ME/CFS.

Patients with chronic fatigue syndrome performed worse than controls in a controlled repeated exercise study despite a normal oxidative phosphorylation capacity

Background

The aim of this study was to investigate the possibility that a decreased mitochondrial ATP synthesis causes muscular and mental fatigue and plays a role in the pathophysiology of the chronic fatigue syndrome (CFS/ME).

Methods

Female patients (n = 15) and controls (n = 15) performed a cardiopulmonary exercise test (CPET) by cycling at a continuously increased work rate till maximal exertion. The CPET was repeated 24 h later. Before the tests, blood was taken for the isolation of peripheral blood mononuclear cells (PBMC), which were processed in a special way to preserve their oxidative phosphorylation, which was tested later in the presence of ADP and phosphate in permeabilized cells with glutamate, malate and malonate plus or minus the complex I inhibitor rotenone, and succinate with rotenone plus or minus the complex II inhibitor malonate in order to measure the ATP production via Complex I and II, respectively. Plasma CK was determined as a surrogate measure of a decreased oxidative phosphorylation in muscle, since the previous finding that in a group of patients with external ophthalmoplegia the oxygen consumption by isolated muscle mitochondria correlated negatively with plasma creatine kinase, 24 h after exercise.

Results

At both exercise tests the patients reached the anaerobic threshold and the maximal exercise at a much lower oxygen consumption than the controls and this worsened in the second test. This implies an increase of lactate, the product of anaerobic glycolysis, and a decrease of the mitochondrial ATP production in the patients. In the past this was also found in patients with defects in the mitochondrial oxidative phosphorylation. However the oxidative phosphorylation in PBMC was similar in CFS/ME patients and controls. The plasma creatine kinase levels before and 24 h after exercise were low in patients and controls, suggesting normality of the muscular mitochondrial oxidative phosphorylation.

Conclusion

The decrease in mitochondrial ATP synthesis in the CFS/ME patients is not caused by a defect in the enzyme complexes catalyzing oxidative phosphorylation, but in another factor.

Trial registration

Clinical trials registration number: NL16031.040.07