Untargeted analysis in post-COVID-19 patients reveals dysregulated lipid pathways two years after recovery 2023 López-Hernández et al

[Andy]

Introduction: Similar to what it has been reported with preceding viral epidemics (such as MERS, SARS, or influenza), SARS-CoV-2 infection is also affecting the human immunometabolism with long-term consequences. Even with underreporting, an accumulated of almost 650 million people have been infected and 620 million recovered since the start of the pandemic; therefore, the impact of these long-term consequences in the world population could be significant. Recently, the World Health Organization recognized the post-COVID syndrome as a new entity, and guidelines are being established to manage and treat this new condition. However, there is still uncertainty about the molecular mechanisms behind the large number of symptoms reported worldwide.

Aims and Methods: In this study we aimed to evaluate the clinical and lipidomic profiles (using non-targeted lipidomics) of recovered patients who had a mild and severe COVID-19 infection (acute phase, first epidemic wave); the assessment was made two years after the initial infection.

Results: Fatigue (59%) and musculoskeletal (50%) symptoms as the most relevant and persistent. Functional analyses revealed that sterols, bile acids, isoprenoids, and fatty esters were the predicted metabolic pathways affected in both COVID-19 and post-COVID-19 patients. Principal Component Analysis showed differences between study groups. Several species of phosphatidylcholines and sphingomyelins were identified and expressed in higher levels in post-COVID-19 patients compared to controls. The paired analysis (comparing patients with an active infection and 2 years after recovery) show 170 dysregulated features. The relationship of such metabolic dysregulations with the clinical symptoms, point to the importance of developing diagnostic and therapeuthic markers based on cell signaling pathways.

Open access, https://www.frontiersin.org/articles/10.3389/fmolb.2023.1100486/full

 

[SNT Gatchaman]

Sphingomyelins cropping up again.

Lipid classes belonging to sterols, steroids, and fatty esters were dysregulated in both COVID-19 groups studied. Very recently, Guntur et al. (2022) found higher levels of poly and highly unsaturated fatty acids in patients with post-COVID- 19 syndrome (more than 28 days after infection: recruitment phase done in a time-interval of two years). This finding was consistent with a reduced fatty acid oxidation at mitochondrial level. The accumulation of such molecules has been associated with erythrocyte dysfunction and impairment of oxygen transportation that could persist for months, thereby explaining symptoms such as fatigue and exercise intolerance.

Remarkably, fatigue was the predominant alteration reported (59%), as well as musculoskeletal symptoms such as arthralgias and myalgias. Therefore, measuring the plasma lipid profile was relevant, as lipids plays an essential role in energy metabolism.

When the lipid profile was analyzed, multivariate analysis showed that after two years of recovery, post-COVID-19 patients cannot be grouped with negative controls neither clustered with COVID-19 patients, even though most basic laboratory parameters are normalized; yet, the presence of a wide spectrum of symptoms reflects that metabolic mediators are not reestablished at all.

Sphingolipids (SLs) also represent an important group of bioactive molecules involved in crucial processes such as inflammation, cellular differentiation, regeneration, aging, among others, particularly important in musculoskeletal cells (Meacci et al., 2022). The results of this study showed a dysregulation in sphingolipid metabolism, that could be associated with the reported symptoms: fatigue and muscular pain.

[Meacci et al is Skeletal Muscle and COVID-19: The Potential Involvement of Bioactive Sphingolipids (2022, Biomedicines) which I haven't read.]

Ceramides and Hexocylceramides, which are derivatives of sphingomyelins, have been found increased in female patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and among those with chronic hepatitis C infection and autoimmune disease.

Regarding ME/CFS, a general agreement is that metabolic features are consistent with a hypometabolic state, characterized by a decrease in sphingolipids, glycosphingolipids, phospholipids, purines, microbiome aromatic amino acid, and branch chain amino acid. In this study, an increase in sphingolipids and phosphocholines was observed, so an underlying mechanism like ME/CFS unlikely explains the fatigue and muscular alterations seen.

That might vary over time.

From Multi-‘omics of gut microbiome-host interactions in short- and long-term myalgic encephalomyelitis/chronic fatigue syndrome patients (2023) who found sphingomyelins were lower in short term ME and increased in long term ME —

Interestingly, most metabolic species either decreased across experimental groups (control > short term > long term; e.g., xanthine), or increased (control < short term < long term; e.g., sphingomyelins, diacylglycerol, phosphatidylcholine, and ceramides, p < 0.01

From the preprint Immunometabolic rewiring in long COVID patients with chronic headache (2023) —

Remarkably, numerous lipid metabolites, including sphingomyelins, plasmalogen, phospholipids, sphingolipids, and cholesterol, were elevated exclusively in the plasmas of long COVID patients throughout the progression of chronic headache. This phenomenon not only recapitulated the lipotoxicity observed in metabolic disorders such as obesity, but also highlighted the implication of a dysregulated lipid metabolism underpinning meta-inflammation-like conditions in long COVID-headache patients.

Discussing the very severe ME patient in Phenotypic characteristics of peripheral immune cells of Myalgic encephalomyelitis/ chronic fatigue syndrome via transmission electron microscopy: A pilot study (2022) —

Integrating TEM analyses with whole exome sequencing data suggested a missense mutation in SMPD1 (sphingomyelin phosphodiesterase 1, acid lysosomal) variant might play a role in the increased lipid droplet-like vacuoles in this extremely severe ME/CFS patient.
[...]
We also identified a rare damaging homozygous SMPD1 variant in the extremely severely ill ME/CFS patient, targeting the metallophosphatase (MPP) domain of the gene. SMPD1 is responsible for the conversion of the sphingomyelin to ceramide as well as immune system regulation, apoptosis, and death-inducing signaling pathways.

In A map of metabolic phenotypes in patients with myalgic encephalomyelitis/chronic fatigue syndrome (2021) there were three different metabolic subgroups, yet (CER = ceramide, SM = sphingomyelin) —

Only 3 single lipid species were uniformly elevated — the sphingolipids, CER(18:1), SM(18:0), and SM(18:1)

 

[SNT Gatchaman]

Also sphingomyelin relates to thrombosis, involving platelets, tissue factor and lipid rafts.

See —
Alterations to Sphingomyelin Metabolism Affect Hemostasis and Thrombosis (2022, Arteriosclerosis, Thrombosis, and Vascular Biology)
Function of Platelet Glycosphingolipid Microdomains/Lipid Rafts (2021, Int J Metabolic Sciences)

Global alterations in sphingomyelin metabolism may, in addition to affecting TF activity in monocytes and other cell types, also affect platelet function, the function of other membrane-dependent procoagulant complexes, and the formation of neutrophil extracellular traps.

Fibrin is translocated to sphingomyelin-rich rafts and platelet sphingomyelin-rich rafts act as platforms where extracellular fibrin and intracellular actomyosin join to promote clot retraction. On the other hand, the collagen receptor glycoprotein VI is known to be translocated to cholesterol-rich rafts during platelet adhesion to collagen. Furthermore, the functional roles of platelet glycosphingolipids and platelet raft-binding proteins including G protein-coupled receptors, stomatin, prohibitin, flotillin, and HflK/C-domain protein family, tetraspanin family, and calcium channels are discussed.

 

[Hutan]

Mexican study - the authors are in no doubt that Long Covid exists and is important.

It's not super clear from the abstract, but they have plasma samples from acute Covid-19 (28 people; mild, severe, critically ill) and negative Covid (15 people). The "post-Covid-19" group consists of 22 patients (mixed gender), two years after hospital discharge. It isn't clear if this last group all had ongoing symptoms. These are all small samples.

The plasma from the acute Covid and negative Covid group was stored for longer than the post-Covid group.

In the post-Covid-19 group, only about 50% had fatigue two years later, about the same percentage as those with persistent anxiety. They didn't assess post-exertional malaise. So, it's very questionable as to whether these people are a homogeneous group, and whether they have an ME/CFS-like illness. Given there's only 22 of them to start with, I'm not sure there is a lot of chance of finding real differences. This is disappointing. I think lipidomics is very interesting, but it's a waste of time if the sample isn't well characterised and big enough.

Also, there are no comparisons of people who had a Covid infection and don't have persistent symptoms with people who had a Covid infection and do have persistent symptoms. Maybe this isn't a huge problem, as we might expect lipids to have returned to pre-illness levels 2 years after an illness, although perhaps not after a critical illness?

 

[Midnattsol]

Haven't read the study, but lipids can be changed by lipids in the diet. Things like increasing intake of pre-made foods after becoming ill could contribute to differences between patients and controls as sources of fat in these foods could be different than what is used when cooking onesself.

I'd also like to add that lipid rafts would in theory be able to influence more functions than those already mentioned, they are important in cell signaling after all.

 

[Hutan]

Paired analysis
They had 13 patients with blood samples from their acute illness phase (3 mild; 8 severely ill; 2 critically ill with intubation) and then two years later, when they had persistent symptoms. They found 170 differences, but I think the differences are impossible to interpret in terms of Long Covid pathology. It's not surprising that there are differences in the lipids of someone in the middle of an acute disease, especially one that has them hospitalised, and then two years later, even if it's just, as @Midnattsol says, because they are eating different foods.

 

[Midnattsol]

When I had timeseries metabolome data there were large variation from measurement to measurement on a lot of the compounds (in total we had 1700+), not difficult to find a difference between two groups by chance. Data was then measured every two, four or ten weeks. We even had near perfect separation between groups on a handful of compounds at the beginning of the study even if group allocation had been randomised (group size 25 and 26 participants).