COVID-19 patient fibrinogen produces dense clots with altered polymerization kinetics, ... increased sialic acid, 2022, Moiseiwitsch et al

[SNT Gatchaman]

COVID-19 patient fibrinogen produces dense clots with altered polymerization kinetics, partially explained by increased sialic acid
Moiseiwitsch N, Zwennes N, Szlam F, Sniecinski R, Brown A

Background: Thrombogenicity is a known complication of COVID-19, resulting from SARS-Cov-2 infection, with significant effects on morbidity and mortality.

Objective: We aimed to better understand the effects of COVID-19 on fibrinogen and the resulting effects on clot structure, formation and degradation.

Methods: Fibrinogen isolated from COVID-19 patients and uninfected subjects was used to form uniformly concentrated clots (2 mg/mL), which were characterized using confocal microscopy, scanning electron microscopy, atomic force microscopy, and endogenous and exogenous fibrinolysis assays. Neuraminidase digestion and subsequent NANA assay were used to quantify sialic acid residue presence; clots made from the desialylated fibrinogen were then assayed similarly to the original fibrinogen clots.

Results: Clots made from purified fibrinogen from COVID-19 patients were shown to be significantly stiffer and denser than clots made using fibrinogen from non-infected subjects. Endogenous and exogenous fibrinolysis assays demonstrated that clot polymerization and degradation dynamics were different for purified fibrinogen from COVID-19 patients compared to fibrinogen from non-infected subjects. Quantification of sialic acid residues via the NANA assay demonstrated that SARS-Cov-2-positive fibrinogen samples contained significantly more sialic acid. Desialylation via neuraminidase digestion resolved differences in clot density. Desialylation did not normalize differences in polymerization, but did affect rate of exogenous fibrinolysis.

Discussion: These differences noted in purified SARS-Cov-2-positive clots demonstrate that structural differences in fibrinogen, and not just differences in gross fibrinogen concentration, contribute to clinical differences in thrombotic features associated with COVID-19. These structural differences are at least in part mediated by differential sialylation.

Link | PDF (J Thromb Haemost)

 

[SNT Gatchaman]

Samples of whole blood were collected from adult patients with SARS-Cov-2 viral infection confirmed by PCR testing who were admitted to the ICU at Emory University Hospital with a primary diagnosis of respiratory failure. Patients on coumadin prior to hospital admission were excluded. Control samples were obtained from SARS-Cov-2-negative patients admitted to the ICU following surgery (ICU control) or healthy volunteers (healthy control), who were screened for any pre-existing hematological abnormalities.

Atomic force microscopy was used to characterize the mechanical properties of clots made from purified fibrinogen from COVID-19 patients and control subjects. These data demonstrated that COVID-19 clots were significantly stiffer than control clots (Control, 1231±206 Pa; COVID-19, 1884±688 Pa; P= 0.0034)

The COVID-19 clots formed faster, and clots remained present for longer despite their faster instantaneous degradation rates due to their increased maximum turbidity. An enzyme-initiated polymerization assay led to similar findings

Here we characterized structural and kinetic differences between fibrinogen clots made from COVID-19 patient samples and samples from non-infected subjects. Our results indicate that COVID-19 fibrin clots are significantly stiffer, denser, and less porous than control fibrin clots. In terms of polymerization and degradation kinetics, COVID-19 clots polymerize faster and reach a greater maximum turbidity. Further, the area under the curve, a good proxy for clot burden over time, was also significantly greater for COVID-19 clots. Through the use of consistent concentrations (2 mg/mL) of fibrinogen across all clots, we were able to isolate differences in clotting to structural differences in the glycoprotein complex, rather than in the concentration of fibrinogen, or other factors in the blood.

Our findings therefore demonstrate that differences in clot structure and polymerization are not simply due to the increased concentration of fibrinogen or other clotting factors in the plasma of COVID-19 patients, but rather due to fundamental differences in the structure and functionality of their fibrinogen.

 

[Hutan]

So, not all fibrinogen is the same.

Produced by the liver, fibrinogen is subject to post-translational modification in a number of different pro-thrombotic disease states, including disseminated intravascular coagulation (DIC), liver disease, and uncontrolled diabetes mellitus.[19] One such form of post-translational modification is sialylation, wherein sialic acid residues are added to the ends of carbohydrate chains of fibrinogen. As sialic acid residues alter calcium binding to fibrinogen, they influence the polymerization and structure of fibrin clots.[20, 21] Differential sialylation is known to play a role in the pro-thrombotic associations of liver disease, and furthermore, to account for some of the structural and functional differences between adult and neonatal fibrinogen.[22, 23]

Looking for this sort of fibrinogen, with its tendency to form more resistant clots, in sufferers of post-Covid ME/CFS might be one way to approach the 'are there microclots'? question. There's still the problem of 'if this is true, why aren't isn't there more thrombosis in people with ME/CFS?'.

I've lost track of the 'micro clots in Long Covid/ME/CFS' story. Do we have any new information to suggest it's a thing?

 

[SNT Gatchaman]

There's still the problem of 'if this is true, why aren't isn't there more thrombosis in people with ME/CFS?'.

Well it could be a survivor effect. We're still looking at LC patients at most not quite 3 years in. Perhaps there are many people who were never able to "graduate" to being long-term ME patients. Perhaps the hypercoagulation could be a stage, which itself can resolve but leave the patient with metabolic compensations that are stuck or degrade further.

But more likely is that the hypercoagulation is a feature, but that it's alongside, if not mostly induced by, immunometabolic derangement, rather than being the sole cause as proposed by Pretorius et al. Perhaps this particular virus is especially damaging to vascular and thrombotic systems, hence all the cardiovascular complications and sudden deaths we're currently reading about.

I've lost track of the 'micro clots in Long Covid/ME/CFS' story. Do we have any new information to suggest it's a thing?

This week they've published a new paper which doesn't add much more I think, in terms of their overall theory. What we would need to see is replication from other teams, using different methods. I'm still very keen on amyloid fibrinogen as an important idea for a number of diseases. I guess we wait for the teased replication from the Manchester team. The new paper does provide evidence for antibodies / autoantibodies within the microclots. This is something I've been interested in as a potential explanation in the progression of autoimmune/other chronic disease, but I have limited knowledge. I do think antibodies might tend to stick to clots anyway so this might be mostly artifactual, but I will be keen to hear other expert opinion on this.

Will be interested in your and others' thoughts on that paper, if anyone gets a chance.

 

[Amw66]

Perhaps applicable relative to this thread from Twitter. If this thread has veracity it is worrying .
Clots in placentas