Category: Pathophysiology

Concentrations of uremic bacterial metabolites in patients with post-COVID-19 syndrome

Abstract:

Post-COVID-19 syndrome (PCS) is characterized by persistent symptoms and reduced mental and physical performance following the acute phase of COVID-19. The underlying mechanisms remain unclear but may involve gut microbiota dysbiosis and immune-related changes in amino acid metabolism. This pilot study aimed to investigate whether specific bacterial uremic metabolites (BUM) are altered in patients with post-infectious syndromes and whether these alterations are associated with PCS symptoms.

We examined BUM in 25 PCS patients, 8 Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) patients, and 8 healthy controls (Ctrls). Concentrations of BUM were determined in second morning urine samples using mass spectrometry (Biovis Diagnostik, Limburg, Germany). Standardized questionnaires assesed physical, cognitive, psychological, and somatic symptoms and mental health status.

PCS and ME/CFS patients exhibited significantly higher scores for post-exertional malaise (PEM) and somatic symptom severity compared to healthy controls (p<0.001). Elevated BUM concentrations were found in 64% of PCS patients, compared to 37.5% of both healthy controls and ME/CFS patients. While overall BUM levels did not significantly differ between groups, heatmap clustering revealed distinct metabolic patterns.

Elevated tryptamine and 4-hydroxyphenylpropionic acid (HPHPA) and higher hippuric acid and trimethylamine concentrations, were exclusively analysed in patients with post-infectious syndromes. Our pilot study suggests that urine metabolomic analysis may be a useful approach for investigating the role of gut dysbiosis and BUM in patients with PCS.

Source: Brigo N, Mayr W, Taenzer M, Löffler-Ragg J, Schroll A, Engl S, Schütz B, Rappl P, Heine T, Weiss G, Kurz K. Concentrations of uremic bacterial metabolites in patients with post-COVID-19 syndrome. Front Cell Infect Microbiol. 2025 May 29;15:1582972. doi: 10.3389/fcimb.2025.1582972. PMID: 40510799; PMCID: PMC12159039. https://pmc.ncbi.nlm.nih.gov/articles/PMC12159039/ (Full text)

The Implications and Predictability of Sleep Reversal for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Machine Learning Approach

Abstract:

Background/objectives: Impaired sleep is one of the core symptoms of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), yet the mechanisms and impact of sleep-related issues are poorly understood. Sleep dysfunctions for patients with ME/CFS include frequent napping, difficulties falling asleep, waking up early, and sleep reversal patterns (e.g., sleeping throughout the day and staying awake throughout the night). The current study focuses on sleep reversal for patients with ME/CFS.

Methods: We explored the symptoms and functional impairment of those with and without sleep reversal by analyzing the responses of a large international sample (N = 2313) using the DePaul Symptom Questionnaire (DSQ) and Medical Outcomes Study 36-item Short-Form Health Survey (SF-36).

Results: We found that those in our Sleep Reversal group (N = 327) compared to those without sleep reversal (N = 1986) reported higher symptom burden for 53 out of 54 DSQ symptoms and greater impairments for all six SF-36 subscales. The most accurate predictors of sleep reversal included age (p < 0.05), body mass index (p < 0.05), eleven DSQ symptoms (p < 0.01), and two SF-36 subscales (p < 0.01).

Conclusions: These features provide clues regarding some of the possible pathophysiological underpinnings of sleep reversal among those with ME/CFS.

Source: Dietrich MP, Pravin R, Furst J, Jason LA. The Implications and Predictability of Sleep Reversal for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Machine Learning Approach. Healthcare (Basel). 2025 May 26;13(11):1255. doi: 10.3390/healthcare13111255. PMID: 40508869. https://www.mdpi.com/2227-9032/13/11/1255 (Full text)

The Relation Between Cardiac Output and Cerebral Blood Flow in ME/CFS Patients with a POTS Response During a Tilt Test

Abstract:

Background/Objectives: Orthostatic intolerance is prevalent in patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and is caused by an abnormal reduction in cerebral blood flow (CBF). In healthy controls (HCs), CBF is regulated complexly, and cardiac output (CO) is an important determinant of CBF. A review in HC showed that a 30% reduction in CO results in a 10% reduction in CBF. In contrast, we showed in ME/CFS patients with a normal HR (HR) and blood pressure response during a tilt test that CO and CBF decreased to a similar extent. The relation between CO and CBF in ME/CFS patients with postural orthostatic tachycardia syndrome (POTS) is unknown.

Therefore, the aim of this study is to assess the relation between CBF and CO, in ME/CFS patients with POTS. The methods used in this retrospective study analyze this relation in a large group of patients. We also analyzed the influence of clinical data. A total of 260 ME/CFS patients with POTS underwent tilt testing with measurements of HR, BP, CBF, CO, and end-tidal PCO2. We measured CBF using extracranial Doppler flow velocity and vessel diameters obtained with a General Electric echo system, and suprasternal aortic flow velocities were measured using the same device. We recorded end-tidal PCO2 using a Nonin Lifesense device.

Results: End-tilt HR and the HR increase were significantly higher in the patients with a %CO reduction ≥ -15% than in the other group. End-tilt CO was higher and the %CO reduction was lower in patients with %CO reduction ≥ -15% than in the other group. CBF data (supine, end-tilt and the %CBF reduction) were not different between the two patient groups. The use of HR increases and %SV reductions were not as discriminative as the %CO reduction.

Conclusions: In ME/CFS patients with POTS during tilt testing with measurements of both the CO and the CBF, two different patterns were observed: (1) appr. two-thirds of patients had an almost 1:1 relation between the %CBF reduction and the %CO reduction. (2) Appr. one-third of patients showed a limited reduction in CO together with a substantial increase in HR. In these patients, there was no relation between the CO and CBF reduction. These data suggest the presence of a hyperadrenergic response.

Source: van Campen CLMC, Visser FC. The Relation Between Cardiac Output and Cerebral Blood Flow in ME/CFS Patients with a POTS Response During a Tilt Test. J Clin Med. 2025 May 22;14(11):3648. doi: 10.3390/jcm14113648. PMID: 40507411. https://www.mdpi.com/2077-0383/14/11/3648 (Full text)

Skeletal muscle properties in long COVID and ME/CFS differ from those induced by bed rest

Abstract:

Patients with long COVID and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) suffer from a reduced exercise capacity, skeletal muscle abnormalities and post-exertional malaise (PEM), where symptoms worsen with cognitive or physical exertion. PEM often results in avoidance of physical activity, resulting in a lower aerobic fitness, which may contribute to skeletal muscle abnormalities. Here, we compared whole-body exercise responses and skeletal muscle adaptations after strict 60-day bed rest in healthy people with those in patients with long COVID and ME/CFS, and healthy age- and sex-matched controls.

Bed rest altered the respiratory and cardiovascular responses to (sub)maximal exercise, while patients exhibited respiratory alterations only at submaximal exercise. Bed rest caused muscle atrophy, and the reduced oxidative phosphorylation related to reductions in maximal oxygen uptake.

Patients with long COVID and ME/CFS did not have muscle atrophy, but had less capillaries and a more glycolytic fibers, none of which were associated with maximal oxygen uptake. While the whole-body aerobic capacity is similar following bed rest compared to patients, the skeletal muscle characteristics differed, suggesting that physical inactivity alone does not explain the lower exercise capacity in long COVID and ME/CFS.

Source: Braeden T. Charlton, Anouk Slaghekke, Brent Appelman, Moritz Eggelbusch, Jelle Y. Huijts, Wendy Noort, Paul W. Hendrickse, Frank W. Bloemers, Jelle J. Posthuma, Paul van Amstel, Richie P. Goulding, Hans Degens, Richard T. Jaspers, Michèle van Vugt, Rob C.I. Wüst. Skeletal muscle properties in long COVID and ME/CFS differ from those induced by bed rest. medRxiv 2025.05.02.25326885; doi: https://doi.org/10.1101/2025.05.02.25326885 https://www.medrxiv.org/content/10.1101/2025.05.02.25326885v1.full?_x_tr_sl=nl&_x_tr_tl=en&_x_tr_hl=en (Full text)

Extracellular vesicle proteomics uncovers energy metabolism, complement system, and endoplasmic reticulum stress response dysregulation postexercise in males with myalgic encephalomyelitis/chronic fatigue syndrome

Abstract:

Background: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a debilitating illness characterized by post-exertional malaise (PEM), a worsening of symptoms following exertion. The biological mechanisms underlying PEM remain unclear. Extracellular vesicles (EVs) play a key role in cell-cell communication and may provide insight into ME/CFS pathophysiology post-exertion. Emerging evidence suggests similarities between ME/CFS and Long COVID, including PEM and overlapping immune and metabolic dysfunctions, highlighting the need for deeper mechanistic understanding.

Methods: This study explores the EV proteome response to exercise in 10 males with ME/CFS and 12 well-matched sedentary male controls. Participants underwent a maximal cardiopulmonary exercise test, and plasma samples were collected at baseline, 15 min, and 24 h postexercise. EVs were isolated from plasma using size-exclusion chromatography and characterized with nanoparticle tracking analysis. EV protein abundance was quantified with untargeted proteomics (nanoLC-MS/MS). Comprehensive analyses included differential abundance, pathway enrichment, protein-protein interaction networks, and correlations between EV protein dynamics and clinical or exercise physiology data.

Results: ME/CFS patients exhibited many significantly altered EV proteomic responses compared with controls, including downregulation of TCA cycle-related proteins and upregulation of complement system proteins at 15 min postexercise. Changes in proteins involved in protein folding and the endoplasmic reticulum (ER) stress response during recovery were highly correlated with PEM severity, highlighting their potential as therapeutic targets. EV protein changes postexercise were also associated with disease severity and unrefreshing sleep. Correlations between EV protein levels and the exercise parameters VO₂ peak and ventilatory anaerobic threshold were observed in controls but were absent in ME/CFS patients, suggesting disrupted EV-mediated physiological processes.

Conclusions: ME/CFS patients exhibit a maladaptive EV proteomic response to exercise, characterized by metabolic impairments, immune overactivation, and ER stress response dysregulation. These findings provide insight into the molecular basis of PEM and suggest promising targets for improving recovery and energy metabolism in ME/CFS.

Source: Glass KA, Giloteaux L, Zhang S, Hanson MR. Extracellular vesicle proteomics uncovers energy metabolism, complement system, and endoplasmic reticulum stress response dysregulation postexercise in males with myalgic encephalomyelitis/chronic fatigue syndrome. Clin Transl Med. 2025 May;15(5):e70346. doi: 10.1002/ctm2.70346. PMID: 40465195; PMCID: PMC12135887. https://pmc.ncbi.nlm.nih.gov/articles/PMC12135887/ (Full text)

Truncal ataxia or disequilibrium is an unrecognised cause of orthostatic intolerance in patients with myalgic encephalomyelitis

Introduction:

Chronic fatigue syndrome (CFS) causes a marked reduction in the activities of daily living and impairs the quality of life. Recently, dysfunction of the central nervous system associated with myalgic encephalomyelitis (ME) has been postulated as the main cause of CFS.1 Most patients with ME/CFS have orthostatic intolerance (OI) which is the primary factor restricting the daily functional capacity and in turn quality of life.2-4 OI is characterised by the inability to remain upright without severe signs and symptoms, such as hypotension, tachycardia, light-headedness, pallor, fatigue, weakness, dizziness, diminished concentration, tremulousness and nausea. Most symptoms of OI have been surmised to be related to reduced cerebral blood flow with or without impaired cerebral circulatory autoregulation, and the compensatory activation of the sympathetic nervous system.5, 6 Indeed, many patients have postural orthostatic tachycardia, delayed orthostatic hypotension and neurally mediated hypotension.4, 5, 7-9 Also many patients have low cardiac output in association with a small left ventricle.10-12 With further progression of the disease, patients may have even sitting intolerance and finally become bedridden.

Although static balance is an essential element for the performance of daily activities as well as postural stability, the possible relation between disequilibrium and OI has never been investigated. The possible role of static or truncal ataxia in the genesis of both orthostatic and sitting intolerance was examined in patients with ME.

Source: Miwa K, Inoue Y. Truncal ataxia or disequilibrium is an unrecognised cause of orthostatic intolerance in patients with myalgic encephalomyelitis. Int J Clin Pract. 2017 Jun;71(6). doi: 10.1111/ijcp.12967. PMID: 28613452. https://onlinelibrary.wiley.com/doi/10.1111/ijcp.12967 (Full text)

Cerebrospinal fluid immune phenotyping reveals distinct immunotypes of myalgic encephalomyelitis/chronic fatigue syndrome

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex heterogeneous multiorgan disease that can have severe impact on individuals’ quality of life. Diagnosis of ME/CFS is based on symptom presentation, and a significant goal for the field is to establish meaningful subtypes. The heterogeneity in the literature suggests that individuals living with ME/CFS may suffer from overlapping but different underlying pathophysiological mechanisms.

We enrolled 40 participants with ME/CFS and 41 matched healthy control subjects at the Bragée Clinic in Sweden. We assessed plasma samples from both ME/CFS cases and control groups and cerebrospinal fluid (CSF) samples from individuals with ME/CFS.

We investigated dysregulated pathways and disease profiles through clinical questionnaires; multiplex analyses of cytokines, hormones, and matrix metalloproteinases; pathogen seroreactivity through peptide display bacteria libraries; and high-throughput microarray for autoantibodies. All samples used were from humans.

We show altered interaction patterns between circulating biological factors in plasma of ME/CFS participants. Our analysis of CSF from individuals with ME/CFS revealed different immunotypes of disease. We found 2 patient clusters based on matrix metalloproteinases profiles. The subgroups had similar clinical presentation but distinct pathogen exposure and CSF inflammatory profiles.

Our findings shed light on ME/CFS immune phenotypes and generate hypotheses for future research in disease pathogenesis and treatment development by exploring disease subgroups.

Source: Bastos VC, Greene KA, Tabachnikova A, Bhattacharjee B, Sjögren P, Bertilson B, Reifert J, Zhang M, Kamath K, Shon J, Gehlhausen JR, Guan L, VanElzakker M, Proal A, Bragée B, Iwasaki A. Cerebrospinal fluid immune phenotyping reveals distinct immunotypes of myalgic encephalomyelitis/chronic fatigue syndrome. J Immunol. 2025 May 15:vkaf087. doi: 10.1093/jimmun/vkaf087. Epub ahead of print. PMID: 40373264. https://academic.oup.com/jimmunol/advance-article/doi/10.1093/jimmun/vkaf087/8133211 (Full text)

Exercise Pathophysiology in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Long COVID: Commonalities Detected by Invasive Cardiopulmonary Exercise Testing

Abstract:

Rationale: There is substantial overlap of exertional symptoms in Long COVID (LC) and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) including intractable fatigue, post-exertional malaise (PEM), and orthostatic intolerance, but very little objective data liking the two. This study compares exercise pathophysiology in the two disorders and normal controls using invasive cardiopulmonary exercise testing (iCPET).

Methods: Between January 2019 and December 2024, 1,518 patients underwent a clinical iCPET at Brigham and Women’s Hospital. Exclusion criteria included morbid obesity (BMI>40 kg/m2), severe anemia ([Hb]<9.0 g/dL), elite athletes (peak VO2 (pVO2)>120% predicted), sub-maximum effort (RER<1.05), a primary pulmonary mechanical limit (VE @ AT/MVV>0.7), and comorbidities such as active/treated cancer, interstitial lung disease, or other respiratory related diseases. iCPET results from 438 ME/CFS patients, 73 LC patients, and 43 symptomatic but otherwise normal controls were analyzed. pV02, peak cardiac output (pQc), peak right atrial pressure (pRAP), peak systemic oxygen extraction (pSOE; Ca-vO2/[Hb]), and ventilatory inefficiency (VE/VCO2 slope) were compared among groups. Statistical significance was determined using Kruskal-Wallis tests for global comparisons, with post-hoc Dunn tests for pairwise group comparisons. Holm-Bonferroni adjustments were applied to control for multiple comparisons.

Results: LC and ME/CFS displayed reduced pVO2 % predicted compared to controls (LC: 78.4 ± 18%, ME/CFS: 78.1 ± 17%, Controls: 97.5 ± 10%, P≤0.0001). Reduced pQc % predicted was also observed compared to controls (LC: 91.1 ± 18%, ME/CFS: 96.3%, Controls: 101 ± 11%, P≤0.001). pRAP were significantly less compared to controls (LC: 1.1 ± 3.1 mmHg, ME/CFS: 1.3 ± 2.8 mmHg, Controls: 3.6 ± 3.4 mmHg, P≤0.001). Significant reductions in pSOE were seen for LC and ME/CFS (LC: 0.81 ± 0.1, ME/CFS: 0.81 ± 0.1, Controls, 0.91 ± 0.1, P≤0.0001). The only measure with no significant difference between disease and control was VE/VCO2 slope (LC: 31.4 ± 8.4, ME/CFS: 31.6 ± 6.9, Controls: 32.0 ± 6.7, P≥0.261). Most interestingly, no significant differences were seen between the two diseases for any of the analyzed measures (P≥0.245).

Conclusions: We report the largest cohort of ME/CFS and LC investigated with iCPET to date. ME/CFS and LC share symptomatic, reduced aerobic capacity at peak exercise, which is driven by preload insufficiency and impaired systemic O2 extraction, the latter compatible with peripheral left-to-right shunting and/or limb skeletal muscle dysfunction. These findings should drive future diagnostics and personalized medicine in both diseases. We hope these data inform the pending prospective NIH RECOVER iCPET study of LC.

Source: J. Squires, S. Palwayi, P. Li, W. Xiao, K. LeWine, S.W. Johnson, D. Felsenstein, A.B. Waxman, and D.M. Systrom. Exercise Pathophysiology in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome and Long COVID: Commonalities Detected by Invasive Cardiopulmonary Exercise Testing [abstract]. Am J Respir Crit Care Med 2025;211:A7881. https://www.atsjournals.org/doi/​10.1164/ajrccm.2025.211.Abstracts.A7881

Identifying commonalities and differences between EHR representations of PASC and ME/CFS in the RECOVER EHR cohort

Abstract:

Background: Shared symptoms and biological abnormalities between post-acute sequelae of SARS-CoV-2 infection (PASC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) could suggest common pathophysiological bases and would support coordinated treatment efforts. Empirical studies comparing these syndromes are needed to better understand their commonalities and differences.

Methods: We analyzed electronic health record data from 6.5 million adult patients from the National COVID Cohort Collaborative. PASC and ME/CFS diagnostic groups were defined based on recorded diagnoses, and other recorded conditions within the two groups were used to train separate machine learning-driven computable phenotypes (CPs). The most predictive conditions for each CP were examined and compared, and the overlap of patients labeled by each CP was examined. Condition records from the diagnostic groups were also used to statistically derive condition clusters. Rates of subphenotypes based on these clusters were compared between PASC and ME/CFS groups.

Results: Approximately half of patients labeled by one CP are also labeled by the other. Dyspnea, fatigue, and cognitive impairment are the most-predictive conditions shared by both CPs, whereas other most-predictive conditions are specific to one CP. Recorded conditions separate into cardiopulmonary, neurological, and comorbidity clusters, with the cardiopulmonary cluster showing partial specificity for the PASC groups.

Conclusions: Data-driven approaches indicate substantial overlap in the condition records associated with PASC and ME/CFS diagnoses. Nevertheless, cardiopulmonary conditions are somewhat more commonly associated with PASC diagnosis, whereas other conditions, such as pain and sleep disturbances, are more associated with ME/CFS diagnosis. These findings suggest that symptom management approaches to these illnesses could overlap.

Source: Powers JP, McIntee TJ, Bhatia A, Madlock-Brown CR, Seltzer J, Sekar A, Jain N, Hornig M, Seibert E, Leese PJ, Haendel M, Moffitt R, Pfaff ER; N3C Consortium and RECOVER-EHR. Identifying commonalities and differences between EHR representations of PASC and ME/CFS in the RECOVER EHR cohort. Commun Med (Lond). 2025 Apr 11;5(1):109. doi: 10.1038/s43856-025-00827-5. PMID: 40210986. https://www.nature.com/articles/s43856-025-00827-5 (Full text)

Advocating the role of trained immunity in the pathogenesis of ME/CFS: a mini review

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex chronic disease of which the underlying (molecular) mechanisms are mostly unknown. An estimated 0.89% of the global population is affected by ME/CFS. Most patients experience a multitude of symptoms that severely affect their lives. These symptoms include post-exertional malaise, chronic fatigue, sleep disorder, impaired cognitive functions, flu-like symptoms, and chronic immune activation. Therapy focusses on symptom management, as there are no drugs available. Approximately 60% of patients develop ME/CFS following an acute infection.

Such a preceding infection may induce a state of trained immunity; defined as acquired, nonspecific, immunological memory of innate immune cells. Trained immune cells undergo long term epigenetic reprogramming, which leads to changes in chromatin accessibility, metabolism, and results in a hyperresponsive phenotype. Initially, trained immunity has only been demonstrated in peripheral blood monocytes and macrophages. However, more recent findings indicate that hematopoietic stem cells in the bone marrow are required for long-term persistence of trained immunity. While trained immunity is beneficial to combat infections, a disproportionate response may cause disease.

We hypothesize that pronounced hyperresponsiveness of innate immune cells to stimuli could account for the aberrant activation of various immune pathways, thereby contributing to the pathophysiology of ME/CFS. In this mini review, we elaborate on the concept of trained immunity as a factor involved in the pathogenesis of ME/CFS by presenting evidence from other post-infectious diseases with symptoms that closely resemble those of ME/CFS.

Source: Humer B, Dik WA, Versnel MA. Advocating the role of trained immunity in the pathogenesis of ME/CFS: a mini review. Front Immunol. 2025 Mar 25;16:1483764. doi: 10.3389/fimmu.2025.1483764. PMID: 40201181; PMCID: PMC11975576. https://pmc.ncbi.nlm.nih.gov/articles/PMC11975576/ (Full text)