When you start thinking about things in a new way it is funny where it takes you. You end up seeing connections, where you may previously only have seen confusion. You see links where they could not, or should not, seemingly exist before. In this blog, I am going to take you from migraine to sickle cell disease, and explain how they both cause CVD – and how they both do it through exactly the same underlying mechanisms.
Before reading on, perhaps you might like to think about how this can possibly work … It is always much more satisfying to work things out for yourself. Or maybe that’s just me.
To begin. As you will have picked up from this blog, I believe that cardiovascular disease (CVD) is, essentially, a disease created by endothelial damage and/or dysfunctional blood clotting. With a bit of impaired clot repair thrown in. I spend too much of my life tracking down anything, and everything, that may cause CVD to see if this hypothesis fits – or does not.
Which is why I was interested to see a headline that appeared very recently on Doctors Net (A website for doctors in the UK). It was entitled ‘Migraine cardiovascular link examined’. Up to this point, I had not realised that migraine and CVD were related. So it was something new to me:
As the article, in the BMJ, went on to say:
Young women who suffer from regular migraine attacks appear to have an increased risk of cardiovascular disease, researchers warn today.
Women are three to four times more likely to experience regular migraines. The condition has previously been linked to an increased risk of stroke, but although the physiology of migraine has close links to the vascular system, the way in which migraine increases risk of stroke is unclear.
A team led by Professor Tobias Kurth of the Institute of Public Health in Berlin, Germany, looked at this association, and the link with cardiovascular disease in general.
They used details on 115,541 women aged 25 to 42 years at baseline, taking part in the US Nurses’ Health Study II, which began in 1989. Over the 20 years of follow-up, 15% of the women were diagnosed with migraine.
Cardiovascular disease was 50% more likely among the women with migraine. Heart attack was 39% more likely, stroke 62% more likely, and these women were 73% more likely to have a revascularization procedure.
In addition, women with migraine were 37% more likely to die from cardiovascular disease than women without migraine, and the risk was not significantly altered by age, smoking, high blood pressure, or use of hormone medications.1
So here is, yet another possible cause of CVD. There was no explanation put forward in this study, it was simply an observation. However, I find that unexplained observations are where the answers lie. These are the ghosts in the machine. Truths that occasionally emerge from the dark depths of the ocean, like oarfish, or giant squid, before slipping back into the abyss.
When I see a study like this, the first thing that I do is to look for an association with blood clotting, or endothelial damage, or both. If there is no association, then my hypothesis has suffered a serious blow. On the other hand…
So, taking a deep breath, I looked around the research done in this area. There has not been a great deal, but to my relief. [Yes, I know, a true scientist should never get too attached their own ideas. But, you know what, it’s hard not to….] To my relief I found that migraine is associated with, or causes, blood clotting abnormalities – and also damage to the endothelium.
Just to quote one short section from the Stroke Association:
‘Migraine-Related Stroke – There is evidence that patients with migraine, particularly migraine with aura, have an increased risk of stroke. The mechanism for this is unclear, although migraine is associated with abnormalities of platelet, coagulation and blood vessel inner lining function, and that may contribute to an increased risk of stroke.’ 2
Just to add further to the connections that potentially open up, I was interested to stumble across a case study where a patient’s migraines were ‘cured’ by using warfarin.
An unusual case report on the possible role of warfarin in migraine prophylaxis
Background: Migraine is a complex disease whose physiopathological mechanisms are still not completely revealed.
Findings: We describe an unusual case, not yet described in literature, of a patient who reported migraine remission, but still presented aura attacks, since starting a therapy with Warfarin.
Conclusions: This case report brings out new questions on the role of the coagulation, especially the blood coagulation pathway, in migraine with aura pathogenesis, and on the possibility to use vitamin K inhibitors, Warfarin or new generation drugs, as possible therapy to use in migraine prophylaxis.3
I must admit I never saw that one coming. Migraines can be treated with warfarin? Though, I suppose, had I thought things through, I might have worked it out. Or maybe not.
Anyway, pulling this information together, we now know that migraines increase the risk of CVD, – more often strokes than heart disease. When you look deeper, you find that migraines are also associated with endothelial dysfunction, and blood clotting abnormalities.
As should be pretty obvious, this all fits perfectly with the ‘CVD is all caused by blood clotting’ hypothesis. On the other hand, if you would like to try to explain how migraines cause CVD through any another process, please let me know. Of course, it could be that another deeper process causes both blood clotting abnormalities, and migraines, but that is for another day.
Of greater interest to me is that, whilst I was studying migraine and CVD, another condition kept popping up on the search criteria. Something that was, again, completely new to me. Which is that there is a very strong association between sickle cell disease (SCD), and CVD. I had never previously thought to link these conditions. However, a number of the migraine articles pointed me towards sickle cell disease (SCD).
Sickle cell disease is a genetic condition whereby red blood cells are malformed and have a sickle shape. This accounts for the name. It is a genetic mutation that, in milder forms, is thought to to protect against malaria, because mildly sickle shaped red blood cells are more difficult for the malaria parasite to enter. However, in its more severe forms, sickle cell disease is quite damaging. Sickle cells can burst, get stuck in smaller blood vessels, form clots in blood vessels in the eyes – leading to blindness, lung and kidney problems etc.
To cut a long story short, in sickle cell disease there are all sorts of ‘clotting’ problems. There is also the potential for significant endothelial damage due to the abnormal shape and function of the red blood cells. Given this, you might expect increased risk of CVD. Which there is, as covered in the paper ‘Atherosclerosis in sickle cell disease – a review:’
‘Ischemic (lack of oxygen) complications are the major causes of morbidity and mortality in patients with sickle cell disease (SCD). The pathogenesis (what causes these problems) of these complications is poorly understood. Ischemic events in these patients have been attributed to the effects of hemoglobin polymerization, resulting in rigid, dense and sickled cells trapped in the microcirculation. Therefore, vascular occlusion is often considered to be synonymous with occlusion of microvasculature by sickled red blood cells. Several observations suggest that other factors may also play a pathogenic role. Atherosclerosis is one of these factors and may affect many arteries all over the body.’
It is fascinating what you find, when you decide to look at things from a different perspective. You start looking at the connection between migraine, CVD, and blood clotting, and end up studying sickle cell disease. I must admit that I get a great sense of satisfaction when I come across facts like this. Somewhat like completing a jigsaw puzzle. ‘Yes, hoorah, it all fits. In fact, it all fits perfectly.’
Indeed, the article on Atherosclerosis in sickle cell disease goes on to bring in Nitric Oxide and L-arginine. I have covered both of these factors in some in detail earlier on in this series. [Sorry this section a bit jargon filled]:
‘The sickling process leads to vascular occlusion, tissue hypoxia and subsequent reperfusion injury, thus inducing inflammation and endothelial injury. This causes a blunted response to nitric oxide (NO) synthase inhibition. In recent years, investigators’ attention has been attracted by the effects of chronic hemolysis on vascular bed integrity and function in patients with congenital hemolytic anemias. Hemolysis results in the release of free hemoglobin.
On one hand, it scavenges NO by oxidizing it to nitrate and releasing red blood cell arginase. On the other hand, it hydrolyzes L-arginine, the substrate of NO synthase. Because of these effects, NO bioavailability and its action is limited. All the previous mechanisms cause impairment of NO production. NO is an important vascular relaxing factor and its deficiency would lead to large artery stiffness. In addition, NO promotes general vascular homeostasis by decreasing endothelial expression of adhesion molecules, decreasing platelet activation, and inhibiting fibroblast, smooth muscle cell and endothelial cell mitogenesis and proliferation.’
In one short section on SCD we have virtually everything I have been writing about in this series so far. There is:
- Reduced NO synthesis
- Damage to the endothelium
- Increased risk of blood clotting in general
- Increased platelet activation and adhesion
- Inhibition of endothelial cell repair and proliferation
- Increased risk of CVD and accelerated atherosclerotic plaque development
Another highly important point here is, as follows. You may recall that I said atherosclerosis almost never forms in the blood vessels in the lungs (pulmonary blood vessels). The only time it does is if you have pulmonary hypertension (high blood pressure in the blood vessels in the lungs).
Well, I just found out that if you have sickle cells disease, you are at high risk of developing atherosclerosis in the lungs:
‘The pulmonary artery is one of the common sites of atherosclerosis in sickle cell disease (SCD). Autopsy of the pulmonary artery in patients with SCD showed that approximately one-third of the patients had histological evidence of medial hypertrophy, intimal proliferation, and subintimal proliferation and fibrosis.’
Now you may not think this is particularly important, but to me it is a killer fact. Atherosclerosis in the pulmonary arteries is something so unusual that when you find it, you are looking at the mother lode. If you can cause atherosclerosis here, then you are gazing at a true underlying cause, with all other risk factors stripped out.
Here is the process (or processes) revealed. Deep joy. It is not often that I come across a fact that I had no idea existed before. Certainly not one that confirms so perfectly everything that I have been saying.
I realise that I have repeatedly stated that the primary purpose of science should be to contradict hypotheses. Here, all I have ended up doing, is providing more facts that support my own hypothesis. I would ask you to believe that I started out looking for a contradiction. I ended up with greater confirmation. Confirmation from places where I had never previously even thought to look.
1: BMJ 1 June 2016; doi: 10.1136/bmj.i2610