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

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?

 

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.

 

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.

 

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).