Archive for the ‘endothelium’ Category
stuff on the immune system and that recent pandemic: 1 – how to get lost in a single cell
got that?
Canto: So, looking way back to the Covid-19 year or two, which we survived (and I’m wondering if the virus has too), have we retained what we’ve learned from all those Medcram videos we watched, and from the various ‘vaccine hesitant’ characters we encountered…
Jacinta: One of whom was a nurse as I recall, but I must say, mind like a sieve, I don’t feel I’ve retained much, so we’re reading Nobel Prize-winning immunologist Peter Doherty’s An insider’s plague year, to help us set down some info and promote our lifelong learning.
Canto: So what’s the difference between a drug and a vaccine, Doherty asks, noting that even experienced journalists confuse the two. Drug of course is a broad term, for anything chemical used to treat people, by pill, injection, bottle, patch or suppository. At the beginning of his ‘plague journal’ Doherty mentions two drugs I recall from our Medcram viewings, hydroxychloraquine, an anti-malarial, and remdesivir, ‘an experimental anti-Ebola drug’.
Jacinta: Yes, hydroxychloraquine was touted early on in the year (2020) as being of some use. A USA site, Drugbank online, said this:
Chloroquine and hydroxychloroquine are both being investigated for the treatment of SARS-CoV-2
followed by this:
The FDA emergency use authorization for hydroxychloroquine and chloroquine in the treatment of COVID-19 was revoked on 15 June 2020.
Remdesivir seems to have been somewhat more effective in reducing symptoms, as was seen earlier in treating MERS-CoV sufferers. It received the FDA’s authorisation just a few weeks before the other drug’s authorisation was revoked.
Canto: The word drug features in the USA’s FDA (Food and Drug Administration), while in Australia we have the TGA (Therapeutic Goods Administration), and therapeutic is simply medicalese for drug. The first of these tended to be natural remedies such as quinine, a useful anti-malarial extracted from Cinchona tree bark. Tonic water has quinine in it, hence the name. Another natural anti-malarial is artemisinin, from sweet wormwood. These ingredients, extracted and purified, have been extremely important in combatting the biggest killer disease in the global south.
Jacinta: In treating SARS-CoV2, remdesivir was the only effective antiviral in the first 12 months, apart from – monoclonal antibodies. I’ve heard of them, now I’m going to try and explain them. I’ll start with this quote from the Mayo Clinic:
Monoclonal antibodies are laboratory-produced molecules engineered to serve as substitute antibodies that can restore, enhance, modify or mimic the immune system’s attack on cells that aren’t wanted, such as cancer cells.
Antibodies (aka immunoglobulin, of which there are 5 types) are Y-shaped proteins that can bind to specific antigens (the foreign nasties) via a lock-and-key mechanism. Monoclonal antibodies, as mentioned above, have been particularly effective in some cancer treatments.
Canto: Well, only this month our TGA has posted an update on the decreased effectiveness of monoclonal antibodies against emerging SARS-CoV2 variants:
emerging data show that anti-spike protein monoclonal antibodies demonstrate a significant decrease in their in-vitro neutralising activities against many newer circulating SARS-CoV-2 variants, particularly Omicron and its subvariants.
Jacinta: Mmm. So let’s go on with our very basic training in immunology. So it’s the organs of the lymphatic system – the lymph nodes, the thymus, the spleen and the bone marrow – that produce or harbour and further develop our immune cells. Now, these immune cells come in different types with different names, such as phagocytes, which are a type of white blood cell (WBC)…
Canto: Yes, this immune system stuff might require dozens or hundreds of posts. Phagocytes can be ‘professional’ or non-professional’ depending on effectiveness. The professionals include neutrophils, macrophages, mast cells, dendritic cells and monocytes – all WBCs. They’re all more or less good at detecting antigens. And I believe these WBCs form what’s called the innate, rather than adaptive, immune system.
Jacinta: So getting back to the SARS-CoV2 Betacoronavirus – we’ll be jumping around a lot in these posts, methinks – it has this thing called a spike protein on its outer coat, and this protein has a receptor-binding domain (RBD) with binds to the angiotensin-converting enzyme (ACE) receptor, or ACE2 receptor. ACE2 receptors exist throughout the body but the principal pathway for this virus involves the epithelial cells at the base of the lungs and in the blood vessels. So I’m reading a Nature article, referenced below, entitled ‘Mechanisms of SARS-CoV-2 entry into cells’, and I want to frame this stuff in my own words to understand it. Apparently ACE2 is the receptor for other Betacoronaviruses and Alphacoronaviruses, so immunologists and virologists are pretty familiar with it.
Canto: Yes, and there’s all this terminology – for example a virion is the whole viral particle – not just the DNA or RNA core and its proteins but the external envelope – everything that allows it to exist extra-cellularly. So a coronavirus virion is made up of nucleocapsid and other proteins, including the spike proteins that facilitate entry into potential host cells via the ACE2 receptors.
Jacinta: So let’s focus for now on the nucleocapsid (N) protein. Another Nature article, with multiple authors, has this title: ‘The SARS-CoV-2 nucleocapsid protein is dynamic, disordered, and phase separates with RNA’, which sounds ominous. And the article starts with a problem:
The SARS-CoV-2 nucleocapsid (N) protein is an abundant RNA-binding protein critical for viral genome packaging, yet the molecular details that underlie this process are poorly understood.
Yes, especially by me. I get that these N proteins bind and ‘package’ the RNA, but I don’t get ‘phase separation’…
Canto: Phase separation is a key biological concept, it seems, but complex, and probably something that requires lab work to fully comprehend. Here’s a quote from ScienceDirect that might help:
Many biological macromolecules, such as proteins and nucleic acids, exert their biological functions by forming phase-separated condensates, and phase separation is closely related to various human diseases. Gene transcriptional regulation is an indispensable part of gene expression and normal function in cells. Its abnormal regulation often causes the occurrence of different diseases. In recent years, the occurrence of phase separation during transcriptional regulation has become an area of intense research.
It sounds like problems with phase separation may lead to irregular transcription, or vice versa, resulting in variants, mutations and such, but I’m guessing.
Jacinta: So reading further into the ScienceDirect article, you’re right, it’s near impossible to understand this stuff just through reading – you surely need to see it happening in cells. And cells, such as our own, are effing complex. Here’s another (long) quote to prove it:
In cells, which are the basic unit of the structure and function of organisms, the need for various components to perform their corresponding functions at the correct time and space is a problem that cells continuously need to solve. To this end, cells have evolved a set of organelles, including membrane-encapsulated organelles (such as mitochondria, nuclei, lysosomes, the Golgi apparatus, and endoplasmic reticulum) and membrane-less organelles (such as nucleoli, Cajal bodies, stress granules, P bodies, U bodies, and signaling bodies) …. Membrane-encapsulated organelles enclose specific proteins, nucleic acids and other substances to perform their functions within a particular space. Still, how other types of membrane-less organelles form and exert their biological functions has eluded investigators for many years. In recent years, it has been discovered that different intracellular biological macromolecules assemble and separate from each other to form liquid-like structures called “biomolecular condensates”….
and it goes on. It’s dauntingly complex, but I must say I wish I was 40 years younger and working in this fascinating field. To work out more precisely the processes involved and then to be able to manipulate them…
Canto: Homo deus indeed.
Jacinta: Femo deus if you don’t mind, and that’s not even a recognised term. I just can’t wait for the 31st century.
Canto: Well let’s just stay in the shallows and say a few words about these membraned and unmembraned intracellular organelles. Mitochondria we know a bit about, the ATP-yielding (making?) organelles that existed separately eons ago as prokaryotes…
Jacinta: Thank the indefatigable iconoclast Lynn Margulis for presenting this argument, and endosymbiosis in general, against vociferous mostly male opposition…
Canto: Lysosomes are the ‘digestive system’ of the cell, containing enzymes that break down the polymeric structures of proteins, lipids, nucleic acids and carbohydrates. They vary greatly in size depending on the digestive tasks they work on. The Golgi apparatus or complex is, unsurprisingly, a complex organelle that packages proteins to be sent out into the intracellular or intercellular world – nuff said. The endoplasmic reticulum has two sub-units, rough and smooth. They’re kind of attached to the nuclear membrane of the cell, the smooth further out than the rough. It’s involved in transportation and protein folding, let’s say no more.
Jacinta: So now to the membrane-less organelles – but it looks like phase transition as a subject for analysis is about how these organelles transition from dormant to active states or how they transition from one task to another. Anyway, just a few words to introduce these organelles. Nucleoli are defined briefly as ‘small dense spherical structures in the nucleus of a cell during interphase’. They also appear to segregate in unexpected ways as cells divide – again something about phase transition. Cajal bodies are often associated with nucleoli and are involved in the processing of some RNA molecules. They appear to have other roles that aren’t yet fully understood. Stress granules are these changeable, dynamic, liquid-solid entities made from RNP (ribonucleoprotein). P bodies are somewhat similar, as are U bodies, named for being ‘uridine-rich’, whatever that may mean. In any case P and U bodies appear to act co-operatively. Signalling bodies, according to Khan Academy:
A signaling molecule is released by one cell, then travels through the bloodstream to bind to receptors on a distant target cell elsewhere in the body.
Canto: Okay, that’s enough terminology, and we won’t do all the references as nobody reads this stuff anyway.
Jacinta: Fine, we’re having fun, though it may take till doomsday to get our heads around this stuff. Wish I could afford a lab, and all its equipment….
References
Peter Doherty, An insider’s plague year, 2021
https://go.drugbank.com/drugs/DB01611
https://www.nejm.org/doi/full/10.1056/nejmoa2007764
https://www.tga.gov.au/news/news/update-effectiveness-monoclonal-antibodies-against-covid-variants
covid19: corticosteroids, male susceptibility, evaluating health, remdesivir, coagulation factors
from The Lancet, ‘the four horsemen of a viral apocalpse’
Canto: So short-course use of some steroids was being advocated in the medcram update 88, though without thorough RCT evidence.
Jacinta: Well, data was presented from the Oxford RCT on those on oxygen or on ventilators showing a statistically significant reduction of mortality from short-course (up to 10 days) low dosage of dexamethasone, a freely-available steroid medication. The study involved some 2000 patients, but only those severely afflicted were helped by the medication.
Canto: An interesting aside to the data is that in the study males outnumbered females by almost 2 to 1, and that accords with the overall ratio of male to female covid19 patients Dr Seheult is finding, which rather shocked me. Why would more males be coming down with the disease? Presumably that’s not the infection rate, but the rate at which they need to be hospitalised.
Jacinta: Yes, you’re right, according to this Australian site (unfortunately undated):
Reports continue to emerge that men are significantly more vulnerable to COVID-19 than women. The commonly held perception that more men smoke and this makes them more susceptible along with other lifestyle factors does not tell the whole picture. White House COVID-19 Task Force director Dr Deborah Birx highlighted a “concerning trend” that men in all age brackets were becoming seriously ill from the virus at a higher rate than women, including younger males.
They’re suggesting more research needs to be done on this gender difference, for health issues in general. Some are claiming that estrogen makes a difference. In any case I think cardiovascular problems are more common in males – but maybe not so much in younger males.
Canto: So update 89 is fairly short, and deals with US data about cases and deaths, most of it out of date now, and more on corticosteroids and the dangers of unsupervised use. Update 90 introduces us to a tool I’ve never heard of called ‘Discern’. Very useful for we autodidacts in helping us, for example, to enlighten our doctors as to our condition. Discern is a tool for evaluating internet health info, such as medcram’s updates on youtube, or anything else on youtube. The instrument asks you to evaluate the material according to 16 different criteria. Interestingly, this tool has been tested on covid19 material by a study out of Poland done in March. The results weren’t so good, especially for news channels.
Jacinta: Yes, physicians’ information did best – but of course we don’t go to news channels for health information, and we’d advise against anyone else doing so. The study evaluated the Discern tool itself and found it excellent, then used the tool to evaluate health information, specifically on youtube. Of course know that there’s ‘viral misinformation’ from various news outlets that gets posted on youtube. And good to see that the medcram updates were some of the most highly rated using the Discern tool.
Canto: So we’re now into reporting from early July with update 91. It starts by looking at a ‘covid risk calculator’ in which you can type in your age, gender, BMI, underlying conditions, waist circumference, and other data which you might need a full medical checkup to find out about (and that’s overdue for me), including, for example, %FMD, a measure I’ve never heard of, but which has to do with endothelial function.
Jacinta: FMD stands for fibromuscular dysplasia. The Johns Hopkins medicine site describes it as a rare blood vessel disease in which the cells of some arteries become more stiff and fibrous and less flexible. This leads to weakness and damage. Not sure how it relates to covid19 but surely any pre-existing blood vessel damage is a danger for those contracting the virus.
Canto: Right, so it’s unlikely anyone will know offhand their percentage of FMD. I don’t even know my HDL and LDL levels, never mind my HbA1c or lipids. I’d love to be able to take measures of all these myself, without visiting a doctor.
Jacinta: Typical male control freak. So all of this is to measure your risk of covid19 hospitalisation, ICU admission or mortality. Fun times. So next the update looks at Gilead, the makers of the antiviral remdesivir, who donated all their supplies of the drug to the USA in early May. But of course they kept manufacturing the drug and have to recoup the money they spent researching, developing and trialling it etc. The Wall Street Journal reports that a typical course of the drug will cost over $3000 per patient. Interestingly the Trump administration is wanting the drug to stay in the USA as much as possible, rather than be available overseas, and is spending money to that effect.
Canto: Hmm. Is that protectionism?
Jacinta: Yes I suppose. It’s not surprising that a country wants to look after its own first, especially via a product produced within its own borders. But I suspect this government would’t be interested in helping any other country – unless there was a quid pro quo. And there’s another antiviral, favipiravir, currently being trialled in Japan and the USA (I mean as of early July), and a vaccine, developed in China, is being used on the Chinese military in what seems a rather rushed and somewhat secretive fashion – we don’t know if they got the soldiers’ permission on this seemingly untried vaccine. At least at the phase 3 level.
Canto: Very CCP.
Jacinta: So onto update 92, and we revisit the electron transport chain, with four successive electron transfers converting molecular oxygen into water. Problems within this chain can produce reactive oxygen species (ROS) such as superoxide, hydrogen peroxide and hydroxy radicals, which are destructive in excess. We also look, yet again, at covid19’s impact on angiotensin and particularly the production of superoxide, which in turn causes endothelial dysfunction, increased von Willebrand factor activity, which leads to thrombosis. People were presenting as ‘happy hypoxics’, looking and feeling fine but with very low oxygen levels, and autopsies revealed ‘microthrombi in the interalveolar septa’ of victims’ lungs. All this leading to a paper published in The Lancet which looked at factors in this process of coagulation and thrombosis:
We assessed markers of endothelial cell and platelet activation, including VWF antigen, soluble thrombomodulin [a marker of endothelial cell activation], soluble P-selectin [a marker of endothelial cell and platelet activation], and soluble CD40 ligand [a marker of platelet and T-cell activation], as well as coagulation factors, endogenous anticoagulants, and fibrinolytic enzymes.
So this was about getting to the bottom of the increased clotting. And the results were hardly surprising, but the final discussion section is worth quoting at length, as it seems to capture much that we know about covid19’s effects (at least short-term effects) at the moment:
We therefore propose that COVID-19-associated coagulopathy is an endotheliopathy that results in augmented VWF release, platelet activation, and hypercoagulability, leading to the clinical prothrombotic manifestations of COVID-19-associated coagulopathy, which can include venous, arterial, and microvascular thrombosis. The factors responsible for this endotheliopathy and platelet activation are uncertain but could include direct viral infection of endothelial cells, collateral damage to the tissue as a result of immune infiltration and activation, complement activation, or any number of inflammatory cytokines believed to play a role in COVID-19 disease.
They suggest anti-platelet therapy and endothelial cell modification treatments as well as anticoagulation treatments, and they suggest some agents ‘which might have therapeutic potential’.
Canto: Potential? You’d think they’d be onto all this by now.
Jacinta: Well there’s also potential for untried medications – at least untried in this context – to go terribly wrong. And it’s also likely that some hospitals are already onto using the safer forms of treatment. Dr Seheult speaks of the antioxidant N-acetylcysteine (NAC) in this context, as it has been shown to be a thrombolytic when used intravenously. There are studies pending on the effects of NAC in treating covid19 patients.
Canto: Now, I’ve just been watching something on monoclonal antibodies as perhaps the most promising treatment yet, short of a vaccine. Can you explain….
Jacinta: Yes I’ll try, maybe next time.
References
Coronavirus Pandemic Update 88: Dexamethasone History & Mortality Benefit Data Released From UK
Coronavirus Pandemic Update 89: COVID 19 Infections Rising in Many States; Dexamethasone Cautions
Coronavirus Pandemic Update 90: Assess The Quality of COVID-19 Info With A Validated Research Tool
Coronavirus Pandemic Update 91: Remdesivir Pricing & Disparities in Drug Availability
Coronavirus Pandemic Update 92: Blood Clots & COVID-19 – New Research & Potential Role of NAC
amhf.org.au/covid_19
https://www.thelancet.com/journals/lanhae/article/PIIS2352-3026(20)30216-7/fulltext
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
SARS-Cov2 and oxidative stress
So I feel it’s time for me to get back to the epidemiology and immunology stuff that I know so little about, especially as it pertains to SARS-Cov2. Watching Dr Seheult’s Medcram updates again after a long hiatus, and catching up with them from the end of April, I note that he’s arguing – and I presume this is a mainstream view, as he clearly keeps an eye on the latest research – that the virus mostly does its damage in attacking the body’s endothelium, and that this in turn causes oxidative stress. The endothelium is a thin layer of cells, or a layer of thin cells, that form the inner lining of the blood and lymph vessels (one day I’ll find out what lymph actually is and does).
Oxidative stress is associated with an imbalance in the level of oxidants such as super-oxide anion and hydrogen peroxide, reduced forms of oxygen (with extra electrons). I don’t really understand this, so I’ll start from scratch. But just preliminary to that, the effects of oxidative stress are manifold. Here’s a summary from news-medical.net:
Oxidative stress leads to many pathophysiological conditions in the body. Some of these include neurodegenerative diseases such as Parkinson’s disease and Alzheimer’s disease, gene mutations and cancers, chronic fatigue syndrome, fragile X syndrome, heart and blood vessel disorders, atherosclerosis, heart failure, heart attack and inflammatory diseases.
It’s known that SARS-Cov2 enters via the lungs, and does damage there, but it’s now thought that most of the damage is done in the endothelium. To understand this, Dr Seheult is going to teach me some ‘basic’ stuff about metabolism, oxidation, energy production and such. So, we start with mitochondria, the energy-producing organelles inside our cells, which have their own DNA passed down the female line. Looking into a mitochondrion, we have the matrix inside, and around it, between the inner and outer membranes, is the inter-membrane space (IMS). Our food, broken down into its essential components, carbs, fats and proteins, is absorbed into the matrix, and somehow turned into ‘two-carbon units’ called acetyl coenzyme A. This is metabolism, apparently. These molecules go through a famous process called the Krebs cycle, of which I know nothing except that it’s about more metabolism… Although now I know that it produces electrons, tied up in two important molecules, NADH and FADH2. These electrons ‘love to be given up’, a way of saying they ‘want’ to be reduced. The molecule that gives up electrons is said to be oxidised, the receiving molecule is reduced. So think of a molecule being reduced as the opposite of losing, rather counter-intuitively. The oxidised molecule is the one that loses electrons. All this is about energy production within the matrix, and the aim is to end up with a molecule I’ve heard and forgotten much about, adenosine triphosphate (ATP). This molecule is the energy molecule, apparently, and the energy is produced by ‘knocking off’ one of the phosphates, according to Dr Seheult, leaving, apparently, adenosine diphosphate (ADP) plus ‘energy’ (clearly, this part needs a little more detail). So going from the diphosphate form to the triphosphate requires energy, going the other way releases energy – none of which really explains why ATP is the body’s energy source. Anyway…
Returning to the carbs, fats and proteins, they go through these mitochondrial processes to produce electrons which want to reduce stuff. So NADH goes to the membrane which separates the IMS from the matrix of the mitochondrion, where proteins can be found that are willing to accept electrons, i.e. to be reduced. The electrons are brought in ‘at the very top of the scale’ (?) and lose some of their reducing ability, so they go down to a lower state of reduction, and protons are pumped into the IMS. (I’m sure this is all true but making sense of it is another matter. It certainly makes me think of proton pump inhibitors, drugs that reduce gastric reflux, but that would be the subject of another set of posts). Then ‘it goes to another species’ by which I think Seheult means another protein, judging from the video, but what he means by ‘it’ I’ve no idea. The NADH? The wave/body of electrons? Anyway, things keep going down to a lower level, becoming more oxidised, and more and more protons are pumped out. So there comes to be a very high concentration of protons (H+) in the IMS, creating a very low PH (high acidity). Meanwhile, the electron transport chain has gone down so many levels that it can only reduce oxygen itself, which by accepting electrons turns finally into water. It’s apparently essential to have sufficient oxygen to keep this cycle going, and to keep the protons pumping, because the protons in the IMS want to move to a place of lower concentration, in the matrix. In doing this, they pass through a channel, which involves, somehow, a coupling of ADP to ATP. Without enough oxygen, this process is stymied, ATP can’t be supplied, leading to insufficient energy and cell death.
So, I think I understand this, as far as it goes. Now, if you over-eat, with lots of high-calorie fats and carbs entering the cells, you’ll likely end up with a surplus of electrons, tied up in NADH and FADH2, which can cause problems. This is where super-oxides come in.
Oxygen is the final electron acceptor in the electron transport chain, and when you add an electron to this final acceptor you get a super-oxide, an oxygen molecule with an additional electron, aka a radical. These are very reactive and dangerous. They can cause DNA damage and serious inflammation, and the body uses them to kill bacteria. If you add another electron, you get H2O2, hydrogen peroxide, and another one again produces a hydroxy radical, OH. Another electron gives water, so it’s these intermediate molecules that are called ‘dangerous species’. Cells such as neutrophils (a type of white blood cell) make these, via an enzyme called NADPH oxidase, as part of their defence against antigens, but an accumulation of these radicals is problematic and needs to be dealt with.
One enzyme the body uses to bring down these accumulating radicals is super-oxide dismutase (SOD), which takes two super-oxides and converts them into O2 and H2O2. SOD comes in three types, related to where they reside – in the mitochondria, the cytosol and the extracellular matrix. These enzymes are powered by zinc, copper and, in the mitochondria, manganese. So what happens to the extra hydrogen peroxide created? An enzyme called glutathione peroxidase (GPx) reduces H2O2 to water by giving it two electrons. Where do these electrons come from? According to Seheult, and this is presumably ‘basic’ microbiology, the antioxidant glutathione has two forms, oxidised and reduced. The reduced form is 2GS-H, with a hydrogen bonded to the sulphur group. The oxidised form is G-S-S-G, a disulphide bond replacing the hydrogen. With the reduced form, GPx donates its extra two electrons to H2O2, reducing it to water. The glutathione system is recharged by reducing it back with NADPH, which has two electrons which are converted to NADP+ (?) Glutathione reductase is the key enzyme in that process. It might take me a few lifetimes to get my head around just this much.
Meanwhile there’s another system… Catalase, an iron-boosted enzyme, can convert two molecules of H2O2 into O2 and H2O. This occurs in organelles called peroxisomes. The major point to remember in all this is that super-oxides are harmful species that can cause oxidative stress, and the major solutions come in the form of SOD and GPx. In fact the general name for these harmful molecules – super-oxides, hydrogen peroxide, and hydroxy radicals – is reactive oxygen species (ROS).
So we have to relate all this to the effects of SARS-Cov2, which enters the body through the ACE-2 (angiotensin-converting enzyme-2) receptor. According to a 2008 research paper, ACE-2, the receptor for which is blocked by SARS-Cov2, ‘confers endothelial protection and attenuates atherosclerosis’. Quoting from the paper, we find a section called ‘ACE-2 modulates ANG II(angiotensin 2)-induced ROS production in endothelial cells’. The researchers’ essential finding was that ‘ACE-2 functions to improve endothelial homeostasis’, and it seems this function is being disrupted by SARS-Cov2. As Dr Seheult puts it, SARS-Cov2 inhibits the inhibitor, that is it inhibits ACE-2, which normally acts to regulate angiotensin 1,7 (not explained in this particular video), thus allowing NADPH oxidase to keep producing super-oxides, with the resultant oxidative stress. As Seheult concludes here, subjects with compromised systems caused by diabetes, cardiovascular disease or obesity, affecting the production or effectiveness of SOD and GPx, might be relying on ACE-2 and angiotensin 1,7 to maintain some semblance of health. Are these the subjects that are succumbing most to the virus? That’s to be explored in future videos, and future posts here.
Reference
Coronavirus Pandemic Update 63: Is COVID-19 a Disease of the Endothelium (Blood Vessels and Clots)? (video by Dr Roger Seheult – clearly a hero in this time)