Regulatory Cycles of Orexin and Glucagon-Like Peptide-1 in Post-Viral Syndromes

Abstract:

Post-viral syndromes are heterogeneous multisystem diseases without a uniform etiology that occur as a result of acute viral infections. During the COVID-19 pandemic, the number of patients increased dramatically due to infections with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This is known as post-acute sequelae of COVID-19 (PASC), with many cases also meeting the criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), the most severe form of a post-viral disease, characterized by severe fatigue, post-exertional malaise (PEM), unrefreshing sleep, neurocognitive impairment, and autonomic and immune dysregulation.

Orexin (OX) neuropeptides, which regulate arousal, metabolism, and neuroendocrine functions, may serve as a central link between stress, immune activation, and metabolic changes in these syndromes. Notable phenotypic similarities between OX system dysfunction and core features of PASC and ME/CFS, including fatigue, sleep issues, impaired glucose metabolism, and neuropsychiatric symptoms, support a mechanistic model in which impaired OX signaling contributes to post-viral endocrine and metabolic dysfunction.

This review examines the role of OX in regulating glucose metabolism, HPA axis activity, and systemic homeostasis, with a specific focus on sexually dimorphic expression and function in relation to post-viral syndromes. We also highlight the effect of glucagon-like peptide-1 (GLP-1), another key player in metabolism, which also has neuroprotective, anti-inflammatory, vasoprotective, and immunomodulatory effects. We further emphasize emerging therapeutic strategies, such as GLP-1 receptor agonists (GLP-1RAs) and drugs targeting the OX system.

Together, these insights provide an integrated framework for understanding and targeting the neuroendocrine-metabolic underpinnings of PASC, ME/CFS, and other post-viral syndromes.

Source: Ruhrländer J, Schieffer E, Schieffer B. Regulatory Cycles of Orexin and Glucagon-Like Peptide-1 in Post-Viral Syndromes. Endocr Rev. 2026 Apr 27:bnag009. doi: 10.1210/endrev/bnag009. Epub ahead of print. PMID: 42037238. https://pubmed.ncbi.nlm.nih.gov/42037238/

A hypothesis connecting dysgeusia due to defects in ATP-P2X3 signaling and fatigue in myalgic encephalomyelitis/chronic fatigue syndrome: lessons learned from long-COVID

Abstract:

Myalgic encephalomyelitis (ME)/chronic fatigue syndrome (CFS) is a neuroimmune disease characterized by debilitating post-exertional malaise (PEM), brain-fog/cognitive problems, and dysregulation of the autonomic nervous system. Currently, there are no objective biomarkers for ME/CFS despite decades of research.

Here, we compile evidence from literature that supports taste dysfunction, particularly alterations of taste perception mediated by Type II taste receptor cells, may be a critical underrecognized feature of ME/CFS. The impetus is drawn from the emerging evidence of clinicopathological similarities between long-COVID and ME/CFS. We discuss in parallel the mechanisms of cellular metabolism, inflammation, vascular dysfunction, and autonomic dysregulation in ME/CFS and long-COVID pathophysiology.

We postulate that mechanistically, dysregulation of ATP signaling through P2X2/P2X3 purinergic receptors underlies both gustatory impairment and core ME/CFS symptoms. Adopting information from the NIH-RECOVER shared resources, we present evidence that suggests chemosensory dysfunction as a potential indicator of progression/severity of PEM. We discuss standardized taste testing as a non-invasive screening tool complementary to molecular biomarkers for ME/CFS.

Notwithstanding, we acknowledge the limitations, confounding and contributing factors such as medications and deficiencies that may exacerbate or independently cause taste-related symptoms in ME/CFS.

In conclusion, we present a compelling case for the multi-factorial role of taste dysfunction in ME/CFS and suggest specific research priorities for investigating the relationship between chemosensory function and post-viral chronic illness.

Source: Srinivasan M, Joseph PV. A hypothesis connecting dysgeusia due to defects in ATP-P2X3 signaling and fatigue in myalgic encephalomyelitis/chronic fatigue syndrome: lessons learned from long-COVID. Front Med (Lausanne). 2026 Apr 8;13:1808646. doi: 10.3389/fmed.2026.1808646. PMID: 42040552; PMCID: PMC13107777. https://pmc.ncbi.nlm.nih.gov/articles/PMC13107777/ (Full text)

Cardiopulmonary Exercise Testing Reveals Functional Limitations and Work Disability in Severe Post-COVID-19 and ME/CFS Patients

Abstract:

Background: Patients severely affected by post-COVID-19 condition (PCC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often experience long-term work incapacity, contributing to a growing economic burden. Organ-centered clinical diagnostics frequently fail to explain their work disability.

Objectives: We aimed to objectively assess physical work ability using cardiopulmonary exercise testing (CPET) in a cohort of long-standing and severely affected PCC patients. We hypothesized: (1) patients with ME/CFS exhibit lower peak oxygen uptake (VO₂peak [mL/min/kg]) and peak power output (PPO [W/kg]) than those without; (2) most patients demonstrate objective work disability, closely aligned with subjective perception of disability; (3) oxygen pulse (O2 pulse [mL/bpm]) is reduced in ME/CFS, independent of comorbidity.

Methods: The study was conducted in the Department of Sports Medicine, Prevention and Rehabilitation at Johannes Gutenberg-University Mainz (Mainz, Germany). Between July 31, 2023, and March 31, 2025, a total of 92 PCC patients with suspected occupational disease underwent symptom-limited CPET and completed the Canadian Consensus Criteria, Bell Disability Scale (Bell-Score), and DePaul Symptom Questionnaire (Post-Exertional Malaise) Short Form (DSQ-PEM).

Results: Nearly half of the patients (49%) met ME/CFS criteria and 79% screened positive on the DSQ-PEM. ME/CFS patients showed significantly lower VO₂peak (13.0 ± 3.1 vs. 15.4 ± 4.9, p = 0.012), PPO (0.9 ± 0.3 vs. 1.1 ± 0.5, p = 0.014), and O₂ pulse (7.7 ± 2.0 vs. 8.5 ± 1.9, p = 0.047) compared to those without ME/CFS. Overall, 66% of patients met objective thresholds for work disability (VO₂peak < 15 mL/min/kg or PPO < 1 W/kg). Forty-five patients (51%) had a Bell-Score ≤ 30 and 82% from those had VO₂peak < 15 and/or PPO < 1. VO₂peak and PPO significantly correlated with Bell-Score (r = 0.3, p = 0.005 and r = 0.3, p = 0.003) and were the lowest among patients on medical sick leave (13.3 ± 3.3 and 0.9 ± 0.3), compared to those in occupational reintegration (16.0 ± 3.9, p = 0.04 and 1.2 ± 0.5, p = 0.024) or currently working (18.0 ± 7.1, p = 0.036 and 1.2 ± 0.5, p = 0.015).

Conclusions: Severely affected PCC patients exhibit objective work disability, particularly those with ME/CFS. VO₂peak and PPO are associated with subjective disability and occupational status. Therefore, early integration of CPET into clinical and occupational evaluations can inform individualized therapy planning and return-to-work decisions.

Trial registration DRKS, DRKS00032394. Registered 28 July 2023, https://drks.de/search/de/trial/DRKS00032394.

Source: Tomaskovic A, Weber V, Ochmann DT, Hillen B, Neuberger EWI, Brahmer A, Lachtermann E, Lieb K, Simon P. Cardiopulmonary Exercise Testing Reveals Functional Limitations and Work Disability in Severe Post-COVID-19 and ME/CFS Patients. Sports Med Open. 2026 Apr 27;12(1):50. doi: 10.1186/s40798-026-00995-1. PMID: 42043742. https://link.springer.com/article/10.1186/s40798-026-00995-1 (Full text)

Health, labour market, and social service outcomes for people with Myalgic Encephalomyelitis / Chronic Fatigue Syndrome on a health or disability related benefit: an Aotearoa | New Zealand nationwide cross-sectional study using the integrated data infrastructure

Abstract:

Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a debilitating chronic condition characterised by persistent fatigue and multisystem symptoms, often leading to long-term disability and socioeconomic disadvantage. In Aotearoa New Zealand (NZ), little is known about the health, labour market, and social service outcomes of people with ME/CFS.

Methods: We conducted a nationwide cross-sectional study using the Integrated Data Infrastructure (IDI) to identify a cohort of working-age individuals (16–64 years) receiving a health or disability-related benefit with a recorded ME/CFS diagnosis. Outcomes were compared to propensity score-matched cohorts: (1) benefit recipients without ME/CFS, and (2) a general population not receiving any benefit. We examined sociodemographic characteristics, co-occurring conditions, health service utilisation, disability support use, employment and income, and benefit reliance.

Results: The study population included 1,902 individuals with ME/CFS. Compared to the general population, the ME/CFS cohort had significantly higher rates of emergency department visits (18.8% vs. 12.8%) and pharmaceutical use (32.8% vs. 14.2% for > 10 medications), and lower current employment (18.3% vs. 83.8%). Compared to other benefit recipients, those with ME/CFS had lower hospitalisation (11.2% vs. 20.9%) and disability support service use (1.6% vs. 7.2%), but higher rates of Supported Living Payment (64.7% vs. 49.0%) and long-term benefit receipt. The ME/CFS cohort was disproportionately female and European, with notable underrepresentation of Māori, Pacific, and Asian ethnic groups.

Conclusions: People with ME/CFS on a benefit in NZ, while only representative of a small fraction of those affected by ME/CFS, still face substantial health burdens, economic vulnerability, and limited access to appropriate supports. The findings highlight systemic policy exclusions that disadvantage individuals with chronic, fluctuating conditions. Improved diagnostic coding, inclusive eligibility criteria, and integrated, person-centred care models are urgently needed to address inequities and support this underserved population.

Source: Bowden N, McLeod K, Anns F, Catchpole L, Charlton F, Taylor B, Vallings R, Vu H, Tate W. Health, labour market, and social service outcomes for people with Myalgic Encephalomyelitis / Chronic Fatigue Syndrome on a health or disability related benefit: an Aotearoa | New Zealand nationwide cross-sectional study using the integrated data infrastructure. BMC Public Health. 2026 Apr 24. doi: 10.1186/s12889-026-27499-7. Epub ahead of print. PMID: 42032509. https://link.springer.com/article/10.1186/s12889-026-27499-7 (Full text available as PDF file)

Neuroendocrine signature of ME/CFS: Meta-analytic evidence for bioactive cortisol deficit and exaggerated feedback sensitivity

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a major clinical challenge as a complex multisystemic disorder with no well-established pathophysiological mechanism, characterized by persistent fatigue and post-exertional malaise, along with unrefreshing sleep, cognitive impairment, and impaired stress recovery. Despite decades of investigation into the hypothalamic-pituitary-adrenal (HPA) axis, a definitive neuroendocrine hallmark has remained elusive due to inconsistent findings across various cortisol matrices. Therefore, this systematic review and meta-analysis aimed to provide an integrated understanding of HPA-axis regulation in ME/CFS.

We identified 46 case-control studies (comprising 46 independent datasets, including 12 pharmacological challenge studies), involving 1388 ME/CFS patients (71.9% female; mean age 37.3 ± 6.2 years) and 1349 matched healthy controls. Meta-analyses showed lower salivary cortisol at awakening and in the morning. Reductions were also observed in 24-h urinary cortisol and hair cortisol. In pharmacological challenge tests, patients exhibited impaired cortisol release in response to adrenocorticotropic hormone (ACTH) stimulation and exaggerated suppression following glucocorticoid administration.

Collectively, these alterations indicate reduced free cortisol availability and enhanced HPA-axis negative feedback sensitivity, consistent with a hyporeactive endocrine state in ME/CFS. This neuroendocrine hypo-reactivity may underlie hallmark clinical features such as unrefreshing sleep, post-exertional malaise, and severe fatigue, as well as cognitive slowing, emotional blunting, and diminished stress resilience frequently observed in ME/CFS and related functional disorders. Integrating neuroendocrine and psychological perspectives may help clarify mechanisms of chronic stress maladaptation and inform psychobiological interventions for fatigue syndromes.

Source: Woo TW, Choi YJ, Kim JY, Lee JS, Son CG. Neuroendocrine signature of ME/CFS: Meta-analytic evidence for bioactive cortisol deficit and exaggerated feedback sensitivity. Mol Psychiatry. 2026 Apr 23. doi: 10.1038/s41380-026-03608-1. Epub ahead of print. PMID: 42026257. https://pubmed.ncbi.nlm.nih.gov/42026257/

Investigating the ME/CFS experience through qualitative analysis of memorial entries

Abstract:

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is an impairing chronic condition characterized by exhaustion and worsening symptoms following exertion, often accompanied by pain, sleep issues, and cognitive issues. Historically, ME/CFS was not considered to be linked to mortality, however, more recent studies have questioned this assumption.

National Chronic Fatigue and Immune Dysfunction Syndrome (CFIDS) Foundation maintains a memorial list consisting of deceased individuals who had ME/CFS. This secondary qualitative thematic analysis analyzed 505 entries on the National CFIDS Foundation memorial list, inductively developing a codebook from the publicly available memorial records. Two coders independently coded each entry before meeting to develop themes that incorporated the understanding of each coder.

Themes emerged within four societal levels: systemic neglect and institutional failure; clinical neglect and failures; social disconnection and advocacy; and personal burden and quality of life. Describing systemic neglect and institutional failure, entries recounted a lack of acknowledgement by health, insurance, and disability authorities, as well as a lack of investment in research and treatment of ME/CFS at the federal level. Negative healthcare experiences included misdiagnosis and misattribution of symptoms, dismissal, inadequate knowledge and experience with treating ME/CFS, and the recommendation of unhelpful treatments. The disbelief and misattribution by acquaintances described in the entries contributed to feelings of social isolation, leading some to turn to advocacy work and support groups.

Entries also described the individual impact of the condition, including functional impairments, the impact of symptoms, management strategies, financial stress, and mental health symptoms. Some deaths were directly and indirectly attributed to ME/CFS by individuals with ME/CFS and their acquaintances. This analysis provides a glimpse of the lived experience as well as death of individuals with ME/CFS through the lens of acquaintances of the deceased, emphasizing the substantial impact of the condition.

Source: Sirotiak Z, Amro HJ (2026) Investigating the ME/CFS experience through qualitative analysis of memorial entries. PLoS One 21(4): e0343374. https://doi.org/10.1371/journal.pone.0343374 https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0343374 (Full text)

Facility-Measured Sleep Electroencephalographic Microstructures in Long COVID

Abstract:

Study objectives: Sleep electroencephalographic (EEG) microstructures are related to brain functions, providing a window into the unrefreshing, non-restorative sleep and daytime fatigue symptoms in long COVID (LC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). We aim to characterize sleep EEG microstructural differences in individuals with LC and age-sex-matched healthy controls (HC), and also ME/CFS, using overnight in-lab facility-measured polysomnography (PSG).

Methods: 28 LC and 28 HC participants came from a single-center research study. 19 ME/CFS participants came from a single clinical center. Sleep EEG was processed to extract spectral band powers, spindles, slow oscillations (SO, 0.5-1 Hz), spindle-SO coupling, brain age index (BAI), alpha-delta patterns, and infraslow oscillation relative band power (ISO, 0.005-0.03 Hz).

Results: Compared to HC, LC had higher SO power during wake before sleep and REM sleep. In N2 and N3, LC showed a faster within-spindle frequency drop (chirp) and shorter SO peak duration in the frontal region. LC showed widespread, early spindle-SO coupling phase at SO trough for both fast and slow spindles, with early fast spindle-SO coupling associated with worse sleep quality. ME/CFS shared some differences with LC but had higher SO-uncoupled slow spindle densities in frontal and central regions, more alpha-delta patterns in the first half of the night, and widespread elevated ISO power in the slow sigma band (11-13 Hz).

Conclusions: These findings suggest that LC and ME/CFS are associated with plausibly pathological sleep EEG microstructure changes, illuminating the pathobiology of post-infectious processes on brain activity.

CLINICAL TRIAL INFORMATION

Trial 1: Sleep and Inflammatory Resolution Pathway, https://clinicaltrials.gov/study/NCT03377543, NCT03377543.

Trial 2: Pain in Long COVID-19: the Role of Sleep, https://clinicaltrials.gov/study/NCT05606211, NCT05606211.

Source: Sun H, Dang R, Li P, Xiao W, Scott-Sutherland J, Sassower KC, Westover MB, Felsenstein D, Thomas RJ, Haack M, Mullington JM. Facility-Measured Sleep Electroencephalographic Microstructures in Long COVID. Sleep. 2026 Apr 22:zsag090. doi: 10.1093/sleep/zsag090. Epub ahead of print. PMID: 42017829. https://pubmed.ncbi.nlm.nih.gov/42017829/

PTPRN2 hypomethylation and PHB2-associated miR-153-3p maturation define dual epigenetic features linked to symptom variability in Myalgic encephalomyelitis

Abstract:

Background: Myalgic encephalomyelitis (ME) is a chronic, debilitating condition increasingly linked to epigenetic changes. With its unclear pathophysiology and no validated diagnostic biomarkers, DNA methylation becomes of interest. Specifically, DNA methylation patterns in saliva, to study ME-related epigenetic changes.

Methods: Saliva samples from 54 ME patients and 21 sedentary healthy controls were analyzed by DNA methylation array. Symptom assessment was conducted using validated questionnaires (SF-36, MFI-20, and DSQ).

Results: A significant DNA hypomethylation at the CpG site cg19803194 (Bonferroni-corrected and adjusted for saliva composition, p = 2.14 × 10− 7) within the PTPRN2 gene body was identified. This hypomethylation was associated with cognitive impairments in both sexes, such as difficulties expressing thoughts and comprehension, commonly known as “brain fog,” and respiratory symptoms in male patients. The hypomethylation also corresponded with reduced circulating levels of miR-153-3p, an intronic microRNA of PTPRN2, which was associated with impaired memory recall in both sexes. Interestingly, the mitochondrial protein Prohibitin 2 (PHB2) was associated with reduced miR-153-3p activity. This association was consistent with a predominant cytoplasmic localization of PHB2 and selective reduction of mature miR-153-3p without changes in its immature forms, suggesting involvement at a post-transcriptional stage that may be attenuated in female patients due to increased extracellular export of PHB2.

Conclusions: These findings suggest a potential epigenetic relationship in ME involving PTPRN2 body hypomethylation and PHB2-associated variation in miR-153-3p levels. While the directionality between gene-body methylation and expression remains a biological hypothesis, these results shed light on potential molecular pathways associated with symptom variability and sex differences in ME severity.

Source: Chalder L, Elremaly W, Li D, Fang Y, Caraus I, Leveau C, Elbakry M, Franco A, Godbout C, Di Tomasso G, Nepotchatykh E, Rostami-Afshari B, Gimenez M, Legault P, Moreau A. PTPRN2 hypomethylation and PHB2-associated miR-153-3p maturation define dual epigenetic features linked to symptom variability in Myalgic encephalomyelitis. J Transl Med. 2026 Apr 20. doi: 10.1186/s12967-026-08162-6. Epub ahead of print. PMID: 42010606. https://link.springer.com/article/10.1186/s12967-026-08162-6 (Full text available as PDF file)

Comparing ME/CFS following mononucleosis with Long COVID

Abstract:

Objectives: Long COVID following SARS-CoV-2 and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) following infectious mononucleosis (IM) are examples of post-infectious chronic illnesses. Behavioral and pathophysiological underpinnings of both ME/CFS following IM and Long COVID are not well understood.

Methods: We studied ME/CFS development following IM in a diverse group of college students who were enrolled before the onset of IM. We categorized those meeting either moderate or severe ME/CFS criteria. We subsequently recruited a matched sample of those infected with SARS-CoV-2, some of whom recovered and others of whom developed Long COVID. We compared and contrasted ME/CFS and Long COVID following IM and SARS-CoV-2 infection in terms of somatic symptoms, coping strategies, depression and anxiety symptoms, and functional status.

Results: In general, the Long COVID group’s symptom burden was less than that of the Severe ME/CFS group but more than that of the Moderate ME/CFS group.

Discussion: These findings may allow investigators a better understanding of these post-viral illness pathophysiologies.

Source: Jason LA, Furst J, Katz BZ. Comparing ME/CFS following mononucleosis with Long COVID. Chronic Illn. 2026 Apr 15:17423953251347108. doi: 10.1177/17423953251347108. Epub ahead of print. PMID: 41984971. https://pubmed.ncbi.nlm.nih.gov/41984971/

Testing a Personalised Dysautonomia Management Protocol in Patients with Orthostatic Intolerance and a Diagnosis of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome or Long COVID

Abstract:

Background/Objectives: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) and Long COVID (LC) are complex multisystem conditions with significant functional disability. Many patients experience symptoms of orthostatic intolerance, which can be captured in some cases as Orthostatic Hypotension (OH) or Postural orthostatic Tachycardia Syndrome (PoTS) on objective testing. Conservative treatments are recommended for first-line symptom management, but there is a lack of efficacy evidence. This study aims to assess the feasibility of an 8-week clinically supervised, personalised Dysautonomia Management Protocol (DMP) in a cohort of ME/CFS and LC patients with subjective and objective evidence of orthostatic intolerance (dysautonomia).

Methods: ME/CFS and LC patients with objective dysautonomia on the 10 min active Lean Test (LT) were recruited to an 8-week DMP, with interventions introduced cumulatively every two weeks. Interventions included increasing daily fluid intake to 3 litres and salt intake to 10 g, pacing to avoid crashes and calf activation. Baseline and weekly data collection included the LT, Composite Autonomic Symptom Score questionnaire (COMPASS-31) and Yorkshire Rehabilitation Scale (YRS).

Results: Sixteen participants completed the 8-week program, five discontinued during the program, and one was withdrawn following a severe crash. The COMPASS-31 improved by 7.7 points from week 1 to week 8 (p = 0.045), with a medium Cohen’s d effect size of 0.55. For the same period, there was a non-significant (p = 0.16) improvement in the YRS symptom severity score by 2 points. Comparing the final two weeks of the program with the first two weeks, mean heart rate during the LT decreased by 4.8 beats per minute (p = 0.032), with a medium Cohen’s d effect size of 0.44. Adherence to the interventions was highly variable, with none of the patients able to fully employ all four recommendations.

Conclusions: The results suggest that targeted conservative interventions could influence autonomic function and symptom reduction. However, the magnitude of change was limited, and statistical significance might not necessarily relate to a clinically significant improvement in symptoms.

Source: Barr J, Marsden L, Dassanayake T, Almutairi N, McKeever V, Gaber T, Tarrant R, Godfrey B, Witton S, Sivan M. Testing a Personalised Dysautonomia Management Protocol in Patients with Orthostatic Intolerance and a Diagnosis of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome or Long COVID. J Clin Med. 2026 Mar 25;15(7):2510. doi: 10.3390/jcm15072510. PMID: 41976810. https://www.mdpi.com/2077-0383/15/7/2510 (Full text)