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Review 1: "Multi-omics provide evidence for an anti-inflammatory immune signature and metabolic alterations in patients with Long COVID Syndrome – an exploratory study"

Published onOct 06, 2022
Review 1: "Multi-omics provide evidence for an anti-inflammatory immune signature and metabolic alterations in patients with Long COVID Syndrome – an exploratory study"
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key-enterThis Pub is a Review of
Multi-omics provide evidence for an anti-inflammatory immune signature and metabolic alterations in patients with Long COVID Syndrome – an exploratory study

AbstractDespite the increasing prevalence of patients with Long Covid Syndrome (LCS), to date the pathophysiology of the disease is still unclear, and therefore diagnosis and therapy are a complex effort without any standardization. To address these issues, we performed a broad exploratory screening study applying state-of-the-art post-genomic profiling methods to blood plasma derived from three groups: 1) healthy individuals vaccinated against SARS-CoV-2 without exposure to the full virus, 2) asymptomatic fully recovered patients at least three months after SARS-CoV-2 infection, 3) symptomatic patients at least 3 months after a SARS-CoV-2 infection, here designated as Long Covid Syndrome (LCS) patients. Multiplex cytokine profiling indicated slightly elevated cytokine levels in recovered individuals in contrast to LCS patients, who displayed lowest levels of cytokines. Label-free proteome profiling corroborated an anti-inflammatory status in LCS characterized by low acute phase protein levels and a uniform down-regulation of macrophage-derived secreted proteins, a pattern also characteristic for chronic fatigue syndrome (CFS). Along those lines, eicosanoid and docosanoid analysis revealed high levels of omega-3 fatty acids and a prevalence of anti-inflammatory oxylipins in LCS patients compared to the other study groups. Targeted metabolic profiling indicated low amino acid and triglyceride levels and deregulated acylcarnithines, characteristic for CFS and indicating mitochondrial stress in LCS patients. The anti-inflammatory osmolytes taurine and hypaphorine were significantly up-regulated in LCS patients. In summary, here we present evidence for a specific anti-inflammatory and highly characteristic metabolic signature in LCS which could serve for future diagnostic purposes and help to establish rational therapeutic interventions in these patients.One sentence SummaryMulti-omics plasma analyses demonstrate anti-inflammatory and hypo-metabolic signatures in patients with Long COVID Syndrome.

RR:C19 Evidence Scale rating by reviewer:

  • Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.



The multi-omic approach used by Kovarik and collaborators to examine two small groups of patients with Recovered (R) vs Long COVID Syndrome (LCS) with respect to Healthy (H) (N=13/group) has successfully been used as a strategy to search for potential biomarkers and for the identification of subjacent pathomechanisms, as the authors point out in the Introduction (citations 11-13).  

Given the small study group, the paper’s title correctly announces this study is “exploratory”. The data shown should therefore be valued as potentially informative and only relevant if the detected anti-inflammatory profile in LCS becomes validated in extended cohorts. The weakest point is the comparison of the proteome and eicosanoid/docosanoid analysis obtained from the LCS group and that from U937 in vitro M1 and M2 differentiated macrophages (quite indirect evidence to claim a pathomechanism for LCS).  

Although the grammar and orthography of this preprint seem proper, the Results section has many interpretations and citations that are perhaps more adequate for the Discussion, and the Discussion holds excessive repetition of Results. So, the writing of these two sections could be improved.  

The study complies with ethical standards. However, it seems quite difficult to ensure no exposure to the SARS-CoV-2 for the initial H group or to track exposure that did not happen in the extra 10 subjects receiving nutritional supplements. Results for anti-N (-)/anti-S (+) status are mentioned in the Results section with no indication of Figures to allocate the data. Confirmation for anti-N (-)/anti-S (+) status before/after nutritional treatment of this last group of 10 participants. An additional aspect to be considered is how long these antibodies last.  

Also, detailed inclusion/exclusion criteria for the selected participants are not clear. Table 1 shows one participant in the H group is diagnosed with psoriasis and three participants in the R group are diagnosed with inflammatory diseases such as asthma, dermatitis, etc. The selection of participants is key for unbiased study outcomes. For example, a question that comes up after reviewing participants’ profiles in Table 1 is whether the participant with very high levels of IL-18, MCP-1, etc in the R group (Fig. 1A) presents one of these additional health conditions mentioned in Table 1. 

In summary, the study provides extensive descriptive data of the proteome and metabolome of a small cohort of LCS patients pointing at the anti-inflammatory status that contrasts with previous reports and with a specific metabolic signature with some overlaps with ME/CFS, aspects that should be carefully interpreted due to the small size group analyzed.

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