The plasma metabolome of long COVID-19 patients two years after infection

Background: One of the major challenges currently faced by global health systems is the prolonged COVID-19 syndrome (also known as long COVID) which has emerged as a consequence of the SARS-CoV-2 epidemic. The World Health Organization (WHO) recognized long COVID as a distinct clinical entity in 2021. It is estimated that at least 30% of patients who have had COVID-19 will develop long COVID. This has put a tremendous strain on still-overstretched healthcare systems around the world. Methods: In this study, our goal was to assess the plasma metabolome in a total of 108 samples collected from healthy controls, COVID-19 patients, and long COVID patients recruited in Mexico between 2020 and 2022. A targeted metabolomics approach using a combination of LC-MS/MS and FIA MS/MS was performed to quantify 108 metabolites. IL-17 and leptin concentrations were measured in long COVID patients by immunoenzymatic assay. Results: The comparison of paired COVID-19/post-COVID-19 samples revealed 53 metabolites that were statistically different (FDR < 0.05). Compared to controls, 29 metabolites remained dysregulated even after two years. Notably, glucose, kynurenine, and certain acylcarnitines continued to exhibit altered concentrations similar to the COVID-19 phase, while sphingomyelins and long saturated and monounsaturated LysoPCs, phenylalanine, butyric acid, and propionic acid levels normalized. Post-COVID-19 patients displayed a heterogeneous metabolic profile, with some showing no symptoms while others exhibiting a variable number of symptoms. Lactic acid, lactate/pyruvate ratio, ornithine/citrulline ratio, sarcosine, and arginine were identified as the most relevant metabolites for distinguishing patients with more complicated long COVID evolution. Additionally, IL-17 levels were significantly increased in these patients. Conclusions: Mitochondrial dysfunction, redox state imbalance, impaired energy metabolism, and chronic immune dysregulation are likely to be the main hallmarks of long COVID even two years after acute COVID-19 infection. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement CONACyT grant number 311880 CONACyT grant number 319503 Christus Muguerza del Parque Hospital, Chihuahua, Mexico. Instituto Mexicano de Seguridad Social. Genome Alberta (a division of Genome Canada) grant number TMIC MC4, the Canadian Institutes of Health Research (CIHR) grant number FS 148461, the Canada Foundation for Innovation (CFI) grant number MSIF 35456. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was revised and approved by the Research and Ethics Committees of the Instituto Mexicano de Seguridad Social, with the registration number R-2022-3301-038, and Christus Muguerza del Parque Hospital (HCMP-CEI-15042020-3, and HCMP-CEI-28022022-A01). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The datasets generated and analyzed during the current study are available in the Mendeley repository (https://data.mendeley.com) (doi: 10.17632/8zfdjsypd8.1).