Maintained imbalance of triglycerides, apolipoproteins, energy metabolites and cytokines in long-term COVID-19 syndrome (LTCS) patients

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Abstract

Deep metabolomic, proteomic and immunologic phenotyping of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) patients have matched a wide diversity of clinical symptoms with potential biomarkers for coronavirus disease 2019 (COVID-19). Within here, several studies described the role of metabolites, lipoproteins and inflammation markers during infection and in recovered patients. In fact, after SARS-CoV-2 viral infection almost 20-30% of patients experience persistent symptoms even after 12 weeks of recovery which has been defined as long-term COVID-19 syndrome (LTCS). Emerging evidence revealed that a dysregulated immune system and persisting inflammation could be one of the key drivers of LTCS. However, how these small biomolecules such as metabolites, lipoprotein, cytokines and chemokines altogether govern pathophysiology is largely underexplored. Thus, a clear understanding how these parameters into an integrated fashion could predict the disease course may help to stratify LTCS patients from acute COVID-19 or recovered specimen and would help to elucidate a potential mechanistic role of these biomolecules during the disease course. Here, we report an integrated analysis of blood serum and plasma by in vitro diagnostics research NMR spectroscopy and flow cytometry-based cytokine quantification in a total of 125 individuals (healthy controls (HC; n=73), recovered (n=12), acute (n=7) and LTCS (n=33)). We identified that in LTCS patients lactate and pyruvate were significantly different from either healthy controls or acute COVID-19 patients. Further correlational analysis of cytokines and metabolites indicated that creatine, glutamine, and high-density lipoprotein (HDL) phospholipids were distributed differentially amongst patients or individuals. Of note, triglycerides and several lipoproteins (apolipoproteins Apo-A1 and A2) in LTCS patients demonstrate COVID-19-like alterations compared to HC. Interestingly, LTCS and acute COVID-19 samples were distinguished mostly by their creatinine, phenylalanine, succinate, 3-hydroxybutyrate (3-HB) and glucose concentrations, illustrating an imbalanced energy metabolism. Most of the cytokines and chemokines were present at low levels in LTCS patients compared with HC except IL-18 chemokine, which tended to be higher in LTCS patients and correlated positively with several amino acids (creatine, histidine, leucine, and valine), metabolites (lactate and 3-HB) and lipoproteins. The identification of these persisting plasma metabolites, lipoprotein and inflammation alterations will help to better stratify LTCS patients from other diseases and could help to predict ongoing severity of LTCS patients.

Layman summary & significance of the research

Almost 20-30% of individuals infected with the SARS-CoV-2 virus regardless of hospitalization status experience long-term COVID-19 syndrome (LTCS). It is devasting for millions of individuals worldwide and hardly anything is known about why some people experience these symptoms even after 3 to 12 months after the acute phase. In this, we attempted to understand whether dysregulated metabolism and inflammation could be contributing factors to the ongoing symptoms in LTCS patients. Total blood triglycerides and the Cory cycle metabolites (lactate and pyruvate) were significantly higher, lipoproteins (Apo-A1 and A2) were drastically lower in LTCS patients compared to healthy controls. Correlation analysis revealed that either age or gender are positively correlated with several metabolites (citrate, glutamate, 3-hydroxybutyrate, glucose) and lipoproteins (Apo-A1, HDL Apo-A1, LDL triglycerides) in LTCS patients. Several cytokines and chemokines were also positively correlated with metabolites and lipoproteins thus, dysregulation in metabolism and inflammation could be a potential contributory factor for LTCS symptoms.

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  1. Peer review report

    Title: Maintained imbalance of triglycerides, apolipoproteins, energy metabolites and cytokines in long-term COVID-19 syndrome (LTCS) patients

    version: 1

    Referee: Christopher Gerner

    Institution: University of Vienna

    email: Christopher.gerner@univie.ac.at

    ORCID iD: 0000-0003-4964-0642


    General assessment

    The manuscript of Berezhnoy et al. is a well written report regarding metabolomics and cytokines in long term COVID-19 syndrome patients. The applied methodology is of some interest and I cannot detect methodological errors. However, I have some concerns which need to be addressed before the manuscript should sent for journal publication.

    Most importantly, the manuscript did not adhere to good scientific practice regarding literature research. There are papers about LTCS patients published more than a year ago following highly similar research strategies with quite similar results. It is not sufficient to cite them in subordinate clauses in the Discussion, they need to be cited in the Introduction accordingly, as well when discussing the results. Indeed, relevant similarities in the results would deserve some discussion, such as the dysregulation of cytokines in LTCS.

    Another weakness is the structure of data interpretation. It is mentioned in the Introduction that several cell types were reported to show altered metabolism after a COVID-19 infection. I cannot see how plasma analysis should allow to verify such observations as it represents a mixture of all cell types in the body. This obvious challenge regarding data interpretation should be addressed.

    This is in line with another weak aspect. The numerous findings a reported without a clear structure regarding potential pathomechanisms. As such, the manuscript is sometimes not easy to read.

    To sum up, the manuscript reports interesting analysis results largely corroborating previous results, which deserved publication after some essential improvements.


    Essential revisions that are required to verify the manuscript

    An improved appreciation of existing literature is essential, as well as an improved data interpretation.


    Other suggestions to improve the manuscript

    A discussion of the pros and cons of NMR-based metabolomics in contrast to other techniques would be helpful.


    Decision

    Verified with reservations: The content is academically sound but has shortcomings that could be improved by further studies and/or minor revisions.

  2. Peer review report

    Title: Maintained imbalance of triglycerides, apolipoproteins, energy metabolites and cytokines in long-term COVID-19 syndrome (LTCS) patients

    version: 1

    Referee: Paola Turano

    Institution: University of Florence

    email: turano@cerm.unifi.it

    ORCID iD: 0000-0002-7683-8614


    General assessment

    This is an integrated study reporting NMR-based metabolomics data and flow cytometry-based cytokine in the blood of 125 individuals (healthy controls (HC; n=73), COVID-19-recovered (n=12), COVID-19 acute (n=7) and LTCS (n=33)).

    The main goal appears to be that of demonstrating alterations in the metabolome and immune markers of patients with long COVID. This condition is defined as the continuation or development of new symptoms 3 months after the initial SARS-CoV-2 infection, with these symptoms lasting for at least 2 months with no other explanation.

    As admitted by the authors, the 4 groups are very unbalanced in terms of numbers of enrolled subjects; moreover, all numbers are low but those in the recovered groups and even more in the acute phase are extremely low. Therefore, the only reliable comparison appears to be that between HC and LTCS. And this is a pity because the most important comparison to define the signature associated with long-COVID symptoms would have been the one between recovered and LTCS subjects.

    Another problem is that there is no information on the status of the LTCS before infection nor during the acute phase. This, combined with the low number of individuals, does not allow to draw a real trajectory of the alterations during the observed time line. It is therefore difficult to be 100% sure that alterations in certain metabolites of lipoproteins are a consequence of LTCS or instead intrinsic characteristics of a group of individual that make them more prone to develop LTCS.

    These critical aspects have nothing to do with the experimental approach, which is powerful and carefully performed. Unfortunately, the available cohort is not the best to achieve the goal of a molecular characterization of LTCS.

    In any case the present manuscript provides useful hints to be further investigated in future studies and therefore might deserve publication.


    Essential revisions that are required to verify the manuscript

    If it were possible to enlarge the cohort of patients, confirming the observed trends, this would lead to a significant improvement in the impact of the work. But I understand the practical difficulties in achieving this goal.


    Decision

    Verified with reservations: The content is academically sound but has shortcomings that could be improved by further studies and/or minor revisions.