Posts Tagged ‘endothelium’
covid 19: health in Kazakhstan, megakaryocytes, the endothelial hypothesis
two megakaryocytes in the bone marrow, arrowed
Jacinta: So just to point out, from our last post, that Dr Seheult described long-term inhaled corticosteroid as sometimes having serious side-effects, such as cataracts, osteoporosis and pneumonia. He also presented contradictory rat studies on using NAC as a supplement, highlighting the need for more systematic RCTs in humans.
Canto: And what do we make of the Chinese embassy in Kazakhstan warning of a pneumonia outbreak there, which they claim is deadlier than covid19? Can we trust this?
Jacinta: Well, the Kazakhstan government has denied that the pneumonia problem was new and unknown, but it is clearly a problem, and sadly I can’t find any news about it that’s less than a month old, at about the time the news broke internationally. Some Chinese health officials are claiming that the pneumonia outbreak is related to covid19, but there’s no clear evidence about that, and this pneumonia problem in Kazakhstan is well over a year old, though it has become more of a problem with the advent of covid19. More research and information required.
Canto: Update 95 is dated July 14, and starts with conditions in Dr Seheult’s own county in California, where as we know the cases numbers have risen almost catastrophically. Some parts of the county’s hospitals have been newly transformed into ICUs. He presents a graph showing the recent increase in covid19 patients, but also a diminution in the number of suspected cases, indicating an improvement in diagnosis. And then he looks at a paper about ‘megakaryocytes and platelet fibrin thrombi [which] characterise multi-organ thrombosis at autopsy in covid19’..
Jacinta: Yes it looks at some autopsies and finds these megakaryocytes, which are precursors to platelets – they’re large as the name suggests, and they’re produced in the bone marrow, and are normally relatively rare, constituting 1 in 10,000 bone marrow cells, but can rapidly increase in response to some infections – they found these cells throughout the body. So how did they get to these multiple organs? Thrombosis was a feature of multiple organs regardless of anticoagulation treatment, suggesting that this thrombosis process started early in the infection cycle. The paper presents some fairly graphic images of large-scale thrombosis in the pulmonary artery and thickening of alveolar walls, with diffuse alveolar damage (DAD) preventing effective oxygenation, and also megakaryocytes in the kidneys. Other sites, such as the heart epicardium, feature large numbers of white blood cells and megakaryocytes. We also see ECGs apparently during myocardial infarction (heart attack) but I don’t know how to read those. The conclusion of the paper finds that the many thrombi found throughout the microvasculature of principal organs occurred in situ and before death. This was confirmed by ‘lines of Zahn’, visible layering which reveals clot formation while the blood is flowing, pumped by a beating heart. Now, this is very complex but important stuff, so I’m going to quote from the paper and try to make sense of it:
The extensive nature of platelet-fibrin thrombi in the alveolar capillaries in our patients may explain the observation that oxygenation is disrupted in an exaggerated fashion early in the disease course of patients with covid19, as this suggests evidence of ventilation-perfusion mismatch unrelated to hyaline membrane formation. Our patients’ lungs all had histopathologic findings of DAD, which has been the most frequently reported finding in covid19 autopsies thus far.
So firstly, what are hyaline membranes? They’re a composite of fibrin (an insoluble protein used in blood clotting), cellular debris, including various blood cells or parts thereof, and other eosinophilic stuff – stuff that boosts inflammation and curbs infection, or tries to. So what’s being said here is that the ‘ventilation-perfusion mismatch’, the problems with oxygenation, may be more related to the platelet-fibrin thrombi than the hyaline membrane formation, found mostly in the lungs. So now I’m going to quote something even more technical – it’s all a learning process:
Thrombi were located in veins and in the pulmonary arteries and arterioles and in microvessels, but not in systemic arteries. Despite elevated fibrin degradation products, in only one case of a patient with cirrhosis did we observe glomerular thrombotic microangiopathy, arguing against disseminated intravascular coagulation, haemolytic-uremic syndrome, or thrombotic thrombocytopenic purpura as a predominant pathophysiological pathway. Schistocytes may suggest endothelial damage, but we found them only rarely. We found no endothelial abnormalities on microscopic review, in alignment with previous studies, but we cannot rule out increased exposure of tissue factor, erosion of the endothelial glycocalyx, or other mechanisms of endothelial dysfunction that could be pro-coagulant without showing histopathological evidence of activation or erosion.
Canto: Scheisse! I can’t unpack too much of that, but I do note they ‘found no endothelial abnormalities… in alignment with previous studies’. I thought we were establishing that this is an endothelial disease, über alles? Are we being led up zie garden path?
Jacinta: Well let’s look more closely. The systemic arteries are those that carry oxygenated blood away from the heart to the other organs, and return deoxygenated blood to the heart. The pulmonary arteries, on the other hand, carry deoxygenated blood to the lungs. What this means in terms of thrombi I’m not sure. Fibrin degradation products (FDPs) (one sub-type of which are D-dimers, types of protein fragments) are produced by clot degeneration. Clotting creates a net of fibrin as part of the healing process, and after this process the net is broken down by an enzyme called plasmin, releasing protein fragments – FDPs. Now, they say that they observed ‘globular thrombotic microangiopathy’ in only one case of a patient with cirrhosis. Cirrhosis is essentially scar tissue of the liver, and it’s generally permanent – you can’t really unscar it, though you can of course prevent more damage being done. The scarring is a kind of self-repair of damage from a variety of sources – hepatitis, alcohol abuse and other liver diseases. As to glomerular thrombotic angiopathy, a glomerulus is a network of capillaries at the end of each nephron in the kidneys. Thrombotic microangiopathy is a rare but serious disease of those capillaries or microvessels, mostly in the kidney and the brain, obviously involving thrombosis.So the general lack of globular thrombotic microangiopathy – and remember they were only looking at at a handful of autopsy subjects – argued against these other pathologies as a pathway in the aetiology of covid19. But let’s look at them – disseminated intravascular coagulation (DIC) is as it sounds, blood clots forming throughout the body, often blocking small blood vessels…
Canto: But I thought that was just what was happening with covid19? That it was proving to be a a vascular, endothelial disease.
Jacinta: Yes I’m a bit confused too. I just tell myself I’m only the messenger.. So haemolytic-uremic syndrome (HUS) is a group of blood disorders in which the red blood count goes down, platelets are also very low and the kidneys are failing. Very nasty symptoms.
Canto: Right – that hasn’t been associated with covid19 before.
Jacinta: Not that I know of, FWIW. Finally, thrombotic thrombocytopenic purpura (TTP) is another blood disorder with clots forming in small blood vessels throughout the body, and a drop in red blood cells and platelets. Its weird, but perhaps what is written next about schistocytes is key here. They didn’t find many schistocytes in these bodies. These are fragments of red blood cells, broken down, jagged pieces of cells that are characteristic by-products, I think, of the the above-mentioned diseases. So that’s something that marks off covid19. So they found no evidence of endothelial dysfunction, though they couldn’t rule out such things as ‘erosion of the endothelial glycocalyx’. This glycocalyx is a mesh of bound glycoproteins and such covering the lumen side of the endothelium. Anyway, all in all this seems a blow, though maybe only a minor one, to the endothelial hypothesis.
Canto : Well, that was all very technical. Time for a rest….
References
Coronavirus Pandemic Update 94: Inhaled Steroids COVID-19 Treatment; New Pneumonia in Kazakhstan?
Coronavirus Pandemic Update 95: Widespread Clotting on Autopsy; New COVID-19 Prognostic Data
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1915585/
https://en.wikipedia.org/wiki/Schistocyte
https://en.wikipedia.org/wiki/Thrombotic_thrombocytopenic_purpura
more Covid-19 gleanings from MedCram updates 67-69
I’m continuing my self-education re everything Covid-19 thanks to Dr Seheult’s updates and other useful sites. Update 67 carries on from where we left off, summarising again how SARS-CoV2 induces endothelial dysfunction, before focusing on thrombosis. So we repeat again that a key molecule in normal endothelial function and in the working of AT-1,7 is nitric oxide (NO). Endothelial function (and, to be clear, the endothelium lines the vasculature, which means the body’s blood vessels) is also dependent on the various other enzymes mentioned in the last post, e.g. superoxide dismutase (SOD), and glutathione peroxidase (GPx).
So how does Covid-19 bring about oxidative stress and how does this effect thrombosis? Seheult discusses an article from April this year which addresses this. It describes a previously healthy elderly male admitted to hospital with fever and respiratory symptoms. After rapid deterioration he was sent to ICU, having developed ARDS, acute renal insufficiency and other health problems. Among various measures noted was a ‘massive elevation of von Willebrand factor (VWF), as well as ‘factor VIII of the coagulation cascade’. To quote from the article:
The increased VWF points toward massive endothelial stimulation and damage with release of VWF from Weibel-Palade bodies. Interestingly, endothelial cells express ACE-2, the receptor for SARS-CoV2, thus possibly mediating endothelial activation.
To explain some of these terms: Weibel-Palade bodies are found only in epithelial cells, and they contain VWF, which are released when required for haemostasis and coagulation. VWF is a stringy material of amino acid proteins which combine with platelets (aka thrombocytes) to coagulate the blood. When endothelial cells suffer serious damage, Weibel-Palade bodies inject large amounts of VWF into the bloodstream. Dr Seheult presents the abstract from a 2017 article on the topic:
The main function of VWF is to initiate platelet adhesion upon vascular injury. The hallmark of acute and chronic inflammation is the widespread activation of endothelial cells which provokes excessive VWF secretion from the endothelial cell storage pool. The level of VWF in blood not only reflects the state of endothelial activation early on in the pathogenesis, but also predicts disease outcome. Elevation in the blood level of VWF occurs either by pathologic increase in the rate of basal VWF secretion or by increased evoked VWF release from dysfunctional/activated endothelial cells. The increase in plasma VWF is predictive of prothrombotic complications and multi-organ system failure associated with reduced survival in the context of severe inflammatory response syndrome, type 2 diabetes mellitus, stroke and other inflammatory cardiovascular disease states.
The article points out that an over-production of VWF in highly elongated form is an indication of pathology. This is apparently being seen in serious Covid-19 patients. On the molecular level, the VWF is able to remodel itself from its usual globular conformation when it senses shear forces – note this definition from Science Direct: Shear stress is defined as the frictional force generated by blood flow in the endothelium, that is, the force that the blood flow exerts on the vessel wall, expressed in force-area unit (typically dynes/cm2). The VWF, under this stress, ‘turns into an extended chain format that forms ultra-large strings to which platelets bind to initiate clot formation at sites of vascular damage’. When the shear stress reaches a certain level, factor VIII is released. All of this can be essential for haemostasis, but too much of the multimeric, elongated form of VWF will lead to thrombosis, as appeared to be occurring in the patient described above.
So, as Seheult summarises, SARS-CoV2 binds to ACE-2 receptors and reduces ACE-2 production. This reduction has the effect of increasing AT-2 production and reducing AT-1,7. This results in an increase in superoxide production, oxidative stress and endothelial dysfunction. This in turns leads to an increase in VWF activity in the bloodstream, and local thrombosis. There is evidence from autopsies that thrombosis is a feature of Covid-19 mortality.
In his update 68 Dr Seheult looks at the predisposition of some ethnic groups (in the USA) to the more severe symptoms associated with Covid-19. He discussed a May CDC MMWR (morbidity and mortality weekly report) on 580 hospitalised Covid-19 patients which found that 45% were white, as far as they could ascertain, compared to 55% in that region’s community. 33% were black, compared to 18% in the community, and 8% were Hispanic compared to 14% in the community. A smallish sample, but suggestive. The CDC also reported on New York figures showing that Covid-19 death rates among black/African Americans and Hispanic/Latino persons were substantially higher than in the white population. Many possible reasons – work and living conditions, lower access to care – all generally related to relative poverty. There may also be other, purely physiological grounds for the disparity. A 16-year-old research article published in Circulation describes the results of placing nanosensors in isolated human umbilical vein endothelial cells (HUVECS) from blacks and whites (pardon the over-simplification, I’m only the messenger), as an attempt to measure endothelial oxidative stress. I can’t follow the details of the research, but what they found was that blacks expressed much more NADPH oxidase than whites (that’s bad). Nitric oxide, a reducer of oxidative stress, was produced in greater quantities in whites than in blacks, and the bad superoxides were produced in greater quantities in blacks. I won’t go further into the complex biochemistry, but I must say I find these apparent racial differences very surprising.
Update 68 also looks at increasing hospitalisations (at least in May) of young children due to Kawasaki disease, or something similar. The disease is characterised by inflammation of blood vessels. Symptoms include fever, high heart rate and possibly sepsis. There are a number of similarities to Covid-19, including ‘systemic vascular lesions’. Kawasaki disease is normally rare, and believed to be viral, or a response to a virus. A ten-year-old research paper on the disease hypothesises that the infection enters through the respiratory or gastro-intestinal systems, and so unsurprisingly there are similarities to the reaction to SARS-CoV2. Whether there’s a connection between Covid-19 and an uptick in Kawasaki disease has yet to be confirmed (but I’m behind the times on the research on this).
I’m moving now to update 69, and I’m going to follow Dr Seheult through the whole oxidative stress process again. It’s about reduction of oxygen – the adding of electrons. Adding an electron to oxygen, mediated by NADPH oxidase, produces superoxide. Add another electron and you get hydrogen peroxide. Another electron produces hydroxyl, and yet another produces water, moving from most oxidised to most reduced, and adding electrons also brings on protons. So at both ends of this chain you have neutral or positive molecules, but in between you have, I think ROS, reactive oxygen species, which are a problem. The body’s defence against these include the enzyme superoxide dismutase (SOD), which converts superoxide into hydrogen peroxide and also back into oxygen, and catalase which converts hydrogen peroxide into water and oxygen. Another important enzyme which protects against oxidative damage is glutathione peroxidase (GPx). It takes reduced glutathione (2GS-H, called a sulph-hydryl group) and uses it to reduce hydrogen peroxide into water, in the process oxidising the glutathione into a form of disulphide G-S-S-G. This oxidised form is in turn ‘regenerated back’ by taking the reduced form of NADP+ (NADPH) and converting it via glutathione reductase to NADP+.
So the point is that the accumulation of superoxide in people with diabetes, hypertension, coronory disease etc will be exacerbated by Covid-19. And going through that once more, Covid-19 blocks the ACE-2 receptor, causing an accumulation of AT-2 which stimulates superoxide production, and also a deficiency of AT-1,7, which, mediated by nitric oxide, inhibits superoxide production. The SARS-CoV2 virus also attracts PMNs (polymorphonuclear leukocytes – immune cells including neutrophils), which boost superoxide production, with attendant endothelial damage.
I’ll be continuing this series, and no doubt getting further behind, over the next few weeks.
References
Coronavirus pandemic update 67, presented by Dr Roger Seheult, as with all other updates
Coronavirus pandemic update 68
Coronavirus pandemic update 69 (first 5 minutes or so)
https://www.verywellhealth.com/polymorphonuclear-leukocyte-2252099