For over thirty years I have been studying heart disease, or Cardiovascular Disease (CVD). I don’t think that I have Obsessive Compulsive Disorder…but maybe I have. I must admit that, at times there seemed to be no answers, at least no answers that did not have at least one Mount Everest sized contradiction.
At one point I simply decided that CVD was just a manifestation of ageing. It happened to everyone, at different rates. There was no cause – no causes. CVD was simply something humanity suffered from, get over it.
However, deep down, I knew that this could not actually be true. There were populations with almost zero rates of CVD, and others where the rates were extremely high. Just to give one example. Russia vs. Japan. In 2006 Russian men under the age of 65 suffered eighteen times the rate of CHD of men in Japan. I don’t think this ratio has changed this much.
I knew that Japanese men did not have any genetic protection. When they emigrated to other countries, their rate of CHD rose rapidly to match that of the surrounding population. Not always, but almost always. So it was obvious that something, or somethings, was causing massive differences in the rate. It wasn’t just fate, or genetics, it wasn’t just the ‘way it is.’ [By the way, the average cholesterol level in Russian men in 2006 was 5.1mmol/l, in Japanese men it was startlingly different at….. 5.1mmol/l]
Long, long ago I worked out that cholesterol, or LDL cholesterol has nothing much to do with CVD. Well, if two populations have exactly the same cholesterol levels and an eighteen-fold difference in the rate of CVD, cholesterol could only be causing 1/18th of the overall risk – absolute max. This figure assumes that the entire of the rate of CVD in Japan was caused by cholesterol, with no other factor playing any part. I don’t think I need bother telling what I think of that as a concept.
For a number of years, I pursued the alternative hypothesis that CVD was primarily caused by stress. There was a great deal of evidence to support this, and of course there still is. I still believe that stress (a concept which does need a bit of explanation) is the single most important cause of CVD. However, there were still many cases of death from heart disease and strokes where it was clear that stress had nothing (or nothing that I could see), to do with it.
For example, as mentioned before in this series of blogs. Systemic Lupus Erythematosus (SLE), where the increased (relative risk) rate of CVD in young women is up to 5,000% higher than the surrounding population. Now that is a proper increase in risk. In fact, it is the sort of increase that tells you that you are looking at a ‘true’ cause of CVD. Not some very wobbly and weak association.
I was also interested in Kawasaki’s disease. This is a vasculitis (inflammation of the blood vessels) that affects young children, who can then suffer heart attacks aged four, or five. Not exactly the same mechanism that causes heart attacks in adults, but very nearly. Again, this is highly significant. A condition that can kill children aged four from CVD is not just some anomaly that can be ignored. I knew I was looking at another true cause.
Later, my attention turned to Avastin. A cancer drug that was almost pulled from the market as it rapidly accelerated atherosclerotic plaque development, and death from CVD. No other risk factors needed to be present.
But how to link SLE, Kawasaki’s, and Avastin, through stress and other important risk factors such as smoking, or diabetes? When I discussed such things with ‘experts’ in cardiology, they would just end up saying that CVD was multifactorial. However, this has always seemed the ultimate cop out. ‘Yes of course, it is multifactorial.’ I would reply. ‘But how do this multiple factors actually fit together. Do they all create different diseases, or the same disease… through completely different process?’
In the end, if you are going to understand CVD you must be able to link all true causes of CVD into a single coherent process that fits all of the facts. If you cannot do this, you are really just stumbling about in the dark. Simply muttering ‘multifactorial’ whenever anyone asks you a question you cannot answer adds nothing to understanding.
Over the years, I found myself drawn back to the Scottish Heart Health study, for one very important reason. Which was that, in this study, fibrinogen emerged as the single most important risk factor for CVD. A fact that seemed to have popped out of nowhere. Never to be mentioned again. As a quick aside, in this same study it was found that the cholesterol was not a risk factor for heart disease. Another fact never to be mentioned again.
Was the Scottish ‘fibrinogen factor’ just an anomaly. A single observation, never to be replicated? I needed to find out. So I shifted my attention away from stress, to a focus on blood clotting factors. When I did so, I kept finding the same thing over and over again. Factors that increase blood clotting were always associated with a higher risk of CVD. Factors that reduced blood clotting always reduced the risk of CVD.
Just to give one specific example. High Density Lipoprotein (HDL cholesterol), so-called good cholesterol. Conventional thinking is that HDL sucks cholesterol out of atherosclerotic plaques and transports this back to the liver via the ‘reverse cholesterol transport’ system. A concept which has always seemed to me to look like a most desperate clutching at straws.
However…
‘The antithrombotic properties of native HDL are also related to the suppression of the coagulation cascade and stimulation of clot fibrinolysis. Furthermore, HDL stimulates the endothelial production of nitric oxide and prostacyclin, which are potent inhibitors of platelet activation. Thus, HDL’s antithrombotic actions are multiple and therefore, raising HDL may be an important therapeutic strategy to reduce the risk of arterial and venous thrombosis.’1
Yes, HDL is actually a potent anticoagulant. In addition, it protects the endothelium and increases NO synthesis in endothelial cells. So, we don’t need a reverse cholesterol transport conjecture. HDL can be looked in a completely different way. I found it fascinating that the moment you decide to look at things from another direction a very different picture emerges.
Once I had my ‘clotting’ goggles on I began to ask myself: Is CVD simply the end result of dysfunctional (and I use the word dysfunctional in the broadest sense here) blood clotting?
Of course, for this to be true, atherosclerotic plaques have to be, at their core, blood clots. Well, are they? In 1856 Karl Von Rokitansky examined atherosclerotic plaques and declared them to be blood clots – in various stages of repair – or degeneration (depending on your point of view). They contained everything you find in blood clots, platelets, red blood cells, lipoproteins, fibrin and all the rest.
Karl Von Rokitansky’s problem? He could not explain how a blood clot could form within the arterial wall itself, underneath the endothelial cells. The reason why he could not explain this is that he did not know that Endothelial Progenitor Cells (EPCs), cover over clots that form in blood vessels. This, effectively, draws them into the artery wall.
Because he had never heard of EPCs, and could not counter the central criticism of his hypothesis, Rokitansky’s ideas never took off, and the cholesterol hypothesis filled the void. The rest, as they say, is history.
A few weeks ago I was presenting on CVD and I was asked, whilst waiting in the coffee line, ‘Come on then, what does cause CVD?’ The man who asked was a doctor, a pathologist, just retired, who had spent his life doing autopsies, and examining many, many, people who had died of heart attacks. I said to him. ‘Plaques are clots, and clots are plaques. It is all due to blood clotting.’
He was not in the slightest surprised. He just nodded in affirmation. ‘I thought so.’ He said. ‘I have always thought that plaques were blood clots.’ Well, what else could they be? There is little else that they could be.
For example, if you start looking at platelets and plaques, a whole new world of information opens up. Platelets are, if you remember, small blood cells that are the key ingredient of all blood clots (thrombi). They are attracted to the site of arterial damage, they clump together and then stimulate the ‘clotting cascade’ which creates clots that are tightly bound together by fibrin.
If clots are plaques, and plaques are clots, you would expect to find that platelets are intimately involved in the entire process of plaque formation. Here, I quote a long section from a book called ‘Platelets in Thrombotic and Non-Thrombotic Disorders.’ For some, this may be a big technical, but I suggest a read, and re-read.
In this section it is pointed out that clots/thrombi form at areas of endothelial damage/stress. In addition, platelet rich thrombi are incorporated into the vessel wall at sites of injury…. Yes, the whole process is outlined here. Including the fact that platelets contain a substance that causes smooth muscles to grow and proliferate (a key finding in all plaques).
Where is cholesterol in all this…nowhere. Please read and inwardly digest:
‘von Rokitanksy and Virchow were early investigators who reported that in some instances, the development of atherosclerosis involved early vessel wall injury, thrombosis, and the incorporation of thrombi into the vessel wall. In 1887, Welch gave a clear description of arterial thrombi based on the experiments of a number of investigators, showing that they began as platelet-rich thrombi and are then transformed into masses rich in fibrin. Much later, these observations were reinforced by Duguid, Morgan, More and Haust and French.
In the 1960s, we observed that platelets were deposited on, and interacted with, the walls of arteries in regions of disturbed blood flow. These are the sites where atherosclerotic lesions develop and increased vessel permeability is demonstrable.
In 1973, Moore induced ‘thromobathererosclerosis’ in rabbits by continuous damage of the endothelium of the aorta with an indwelling catheter, and in 1976, he and his group showed that prior administration of anti-platelet serum to induce thrombocytopenia (very few platelets in the blood) prevented the development of these lesions. The finding by Ross and his colleagues in 1974 that stimulated platelets release a mitogen for smooth muscle cells (platelet derived growth factor PDGF) arose from a chance observation.
They noticed that serum prepared from platelet-free plasma did not support the proliferation of smooth muscle cells in culture, but when they prepared serum by blotting platelet rich plasma, the serum supported cell growth as effectively as serum prepared from whole blood. These results gave even more credence to the theory that platelets are involved in the development of atherosclerotic plaques because they promote the proliferation of smooth muscle cells.
The progression of atherosclerotic plaques also involved platelets since platelet rich thrombi have been shown to be incorporated into the vessel wall at sites of injury. Platelet rich thrombi that form on ruptured atherosclerotic plaque may occlude the lumen of the vessel, or may embolize (break off and travel down the artery).
When the thomboemboli impact in smaller downstream vessels, organ damage occurs. These concepts about platelets and atherosclerosis have stood the test of time. The picture developed by Ross of the development of an atherosclerotic plaque is not well known, and the signalling pathways, PGDF activated are being explored. The importance of platelet interaction with the components of ruptured atherosclerotic plaque in the thromboembolic complications of atherosclerosis is now generally accepted.2’
When I read stuff like this I think. Come on guys, you know that plaques are clots and clots are plaques. It is staring you in the face. It has been staring humanity in the face for over a hundred and sixty years. Ever since Rokitansky and Virchow started to look closely.
Next: Impaired plaque repair
References:
1: http://cardiovascres.oxfordjournals.org/content/103/3/362
2: ‘Platelets in Thrombotic and Non-Thrombotic Disorders.’ Edited by Paolo Gresele. Page 5.
