Got Plaque?

Got Biofilms?

 

As long time readers of this blog know, I consider metabolic syndrome (insulin resistance, hypertension, cardiovascular disease, etc.) as fundamentally caused by translocating gut bacteria to the liver and systemic circulation. This explains what initiates what I’ve termed “The Inflammatory-Cortisol Ballet” and the metabolic consequences that flow from that.

When it comes to heart disease and stroke, I’ve written that they can’t be explained simply by referring to what happens to changes in concentrations of lipoproteins, be they LDL or HDL. While there is clearly an association between dyslipidemia and arterial disease, focusing solely on these markers is not likely to get you very far in unraveling the processes underlying plaque formation and rupture.

Today I want to cover a scientific paper that confirmed the presence of bacterial pathogens in arterial plaque. (1) While this isn’t the first study to find evidence of bacteria in plaque, it is the first to find these pathogens living in biofilms.

A biofilm is any grouping of bacteria adhering to a surface and protected by formation of what is called an extracellular polymeric substance. This substance is also popularly referred to as slime.

Pathogens living in biofilms are much harder to kill because of this slimy protective cover, much like politicians are harder to kick out of office for the same reason. Not only is it more difficult for antibiotics to kill bacteria within these communities, it’s also more difficult for our immune system to eradicate them. Many pathogens that would normally succumb to immune cells like neutrophils and macrophages are better able to evade these defenses when part of a biofilm. (2) (3) (4)

In this study, samples of diseased carotid arteries were obtained from fifteen patients, all of whom exhibited advanced arteriosclerosis. The samples were subjected to bacterial analysis using gene sequencing.

All samples were found to contain genetic material from a number of bacterial species. Five out of the fifteen samples were subjected to further genetic analysis to determine the unique bacterial composition contained within their plaque.

Each of these five samples was found to contain anywhere from 10 to 18 different bacterial pathogens living in the biofilm equivalent of The Jersey Shore hot tub. Eight bacterial species were common to all five arterial samples, while the rest were unique to each patient.

In a previous paper, this research group identified one particular pathogen—Pseudomonas aeruginosa (P. aeruginosa)—as a common colonizing bacteria in many diseased arterial samples. To see if this was the case here, all samples were analyzed for the presence of this gram-negative pathogen. Five of the fifteen carotid samples tested positive for this particular bad boy, and one tested positive for another strain of Pseudomonas.

Further analysis of five sub-samples confirmed that these bacteria were grouped together in biofilms located in various locations of the arterial wall:

 

Courtesy: Bacteria Present in Carotid Arterial Plaques Are Found as Biofilm Deposits Which May Contribute to Enhanced Risk of Plaque Rupture

Courtesy: Bacteria Present in Carotid Arterial Plaques Are Found as Biofilm Deposits Which May Contribute to Enhanced Risk of Plaque Rupture

 

In the lower left-hand corner, we see a cross-section illustration of an artery displaying an atheromatous plaque held in place by a fibrous cap. Contrary to the popular belief that fat and cholesterol somehow plaster themselves to the internal arterial wall or tunica interna, we clearly see that plaque accumulates from below the arterial wall.

The background area in green is a flourescence scan of patient number one’s carotid artery. The first biofilm, labeled L1, was found next to the internal elastic lamina, and the second, labeled L2, was located within the tunica externa.

Patient number two’s sample showed a single biofilm located next to the internal elastic lamina just below the fibrous cap. Patient three also had one bacterial biofilm, but theirs was located in the tunica interna and showed signs of previous rupture.

Patient four showed an extensive bacterial colony within the tunica interna. And patient five had a biofilm residing next to the internal elastic lamina. Of all the bacterial biofilms detected, 76.5% were located either near the internal elastic lamina or the tunica interna and fibrous cap.

Now before I continue, this discovery of biofilms in arterial plaque dovetails nicely with what we know of cardiovascular disease as an inherently inflammatory process. As most of you know from my heart disease series, cholesterol and the lipoproteins that transport it, have a role in innate immunity. As I wrote then:

“All lipoproteins—chylomicrons, VLDL, IDL, LDL and HDL—bind to and i-n-a-c-t-i-v-a-t-e lipopolysaccharides. They also protect against gram-positive bacterial pathogens, viruses and parasites.

And yes, that includes “bad” LDL cholesterol, the lipoprotein that has been vilified within an inch of its life. Do you honestly believe that nature designed our livers to produce a substance that is out to kill us? Really?

Take two sets of mice and give each of them a lethal dose of gram-negative E.coli. Give one set of mice an infusion of human-derived chylomicrons and VLDL and the survival rate of these mice is 100%. In other words, they don’t die from an otherwise deadly dose. Infuse them with human LDL and HDL and you get the same result.

Want another example? OK, how about using some LDL receptor deficient mice. Because they have been genetically bred to lack the LDL receptor, they have unusually high levels of LDL coursing through their little arteries and veins. The blood work from these rodents would cause the typical physician to suffer a conniption fit.

Now pair these LDL-engorged mice against normal wild-type mice. Once again, give both sets of mice an infusion of gram-negative E. coli. The mice with very high levels of LDL cholesterol will have a significantly increased survival rate. These LDL mice don’t begin dying off until their endotoxin levels are eight times higher than their American Heart Association-approved litter mates. Their levels of circulating inflammatory cytokines are also far lower.

Now, with the same set of mice, infect them with Klebsiella pneumoniae, another gram-negative pathogen that is commonly found in arterial plaque. Again, the LDL mice show increased survival rates. After acute infection, only 42% of the mice with higher LDL levels die as opposed to 67% of the controls.”

So what this study suggests is that cholesterol’s involvement with cardiovascular disease is the same as the immune cells also found residing in plaque, namely as an innate immune response to bacterial infiltration of the arterial wall. Whatever oxidation of LDL cholesterol is found in plaque is likely the normal outcome of being subjected to the reactive oxygen and nitrogen species generated by immune cells in an attempt to destroy these bacterial colonies.

But where are these bacteria coming from? The most likely answer is a digestive tract incapable of keeping them confined to the oral and/or intestinal cavity. That would explain why periodontal and inflammatory bowel diseases are highly associated with increased risk of cardiovascular disease. (5) (6) (7) (8) (9) (10) (11)

For what I consider one of the best explanations of how pathogens cause development of arterial plaque, I refer you to this paper by doctors Uffe Ravnskov and Kilmer S. McCully. Their hypothesis is certainly a credible elucidation of how immune responses to these pathogens initiate this process.

Returning to the research paper under review, these scientists did not just stop at cataloging the number and location of arterial biofilms. They sought to test another hypothesis about how acute stress may weaken and rupture the fibrous cap that contains this mixture of bacteria, oxidized cholesterol, lipids and immune cells.

This part of the paper is admittedly the most speculative in that the following experiments were done in vitro or in the laboratory. What’s true for a test tube experiment doesn’t necessarily translate to real-world biological processes, but their findings are certainly intriguing and worthy of further investigation.

In order to suffer a stroke or heart attack, more is needed than the buildup of arterial plaque. While plaque does narrow arterial passageways, a blockage of that artery requires that a plaque formation rupture and form a clot or thrombus. It is this clot that prevents the flow of blood and oxygen needed by the brain or heart causing damage and possibly death should the blockage not be cleared in a timely manner.

It has long been known that stress is often a precipitating factor for cardiovascular events. So too sudden physical exertion and emotional upset. The question, however, is how are these states connected to the rupture of plaque, and what role, if any, bacteria may play in this chain of events.

To answer this question, these researchers subjected biofilms of P. aeruginosa to two substances to determine if this would cause a dispersal of bacteria that could conceivably undermine the integrity of a plaque formation containing them.

The first of these substances was free iron. Iron, in its free or unbound state, can be utilized by a number of bacteria to grow.

In this experiment, they found that the addition of free iron to the culture medium did indeed cause the release of bacteria from biofilms after about 20 minutes. However, there was no evidence that bacterial populations grew in this time period leading to speculation that the slime containing these pathogens was somehow undermined. Nonetheless, free iron is not how this element is typically stored or transported through our bodies so its real-world relevance is doubtful, which explains the rationale for the next experiment.

In this second experiment, biofilms were now subjected to norepinephrine and the bound form of iron, transferrin. Norepinephrine as I explained in my “Inflammatory-Cortisol Ballet” series, is one of the catecholamines released during the stress response, along with cortisol. It shares this category with epinephrine (aka adrenaline) and dopamine.

Epinephrine and norepinephrine are part of the fight-or-flight response, and like cortisol release from the adrenals, are regulated by the hypothalamic-pituitary-adrenal (HPA) axis. This is the same axis activated by bacterial translocation through the gut wall during acute episodes of leaky gut.

Addition of norepinephrine in concentrations typically seen during a stress response caused an increase in free iron concentrations that in turn caused a significant release of bacteria from their biofilm. Now, whenever bacteria escape from within a biofilm, they must produce degradative enzymes to break down the extracellular polymeric substance or slime that otherwise encases them, and it appears that free iron contributes to this chain of events.

These researchers hypothesize that these enzymes are not only capable of degrading biofilm slime, they may also be capable of destabilizing the fibrous cap. As they point out:

“Biofilm dispersion by this microorganism was also shown here to be inducible by the addition of norepinephrine to transferrin-containing culture medium. Thus, under laboratory conditions, an in vitro spike in hormone concentration was shown to induce biofilm dispersion. It is unclear at this time whether a biofilm dispersion response is inducible in vivo. For instance, sequestration of biofilm deposits within atheromas may have a mitigating effect on the ability of norepinephrine to induce iron release in the vicinity of the infecting bacteria. Furthermore, the association of degradative enzyme release during the biofilm dispersion response with collateral tissue damage is speculative on our part. We have no direct evidence that this occurs in vivo; however, we believe that the potential for additional damage to surrounding tissues due to bacterial enzyme release may be an additional significant factor contributing to thrombogenesis [clot formation].”

Moreover, they point to other non-bacterial factors that may contribute to disruption of the fibrous cap, such as inflammatory cytokines and C-reactive protein. Another factor is composition of the lipids that are contained in plaque. Of these, polyunsaturated omega-6 fatty acids (omega 6 PUFAs) have been associated with plaque rupture given their propensity to readily oxidize and form pro-inflammatory lipid peroxidation byproducts. (12) (13) (14) Nevertheless, this hypothesis may offer another clue to the puzzle as to how acute stress precipitates a cardiovascular event separate and apart from transitory increases in blood pressure and constriction of arteries.

If, as I believe, the source of these pathogens is the digestive tract, then it becomes imperative to prevent their translocation, which cannot be accomplished without the active assistance of beneficial oral and gut flora that line the digestive cavity. As beneficial gut flora is also necessary for maintaining a healthy immune response, their reduction or absence makes it more likely that these pathogens will escape immune destruction prior to forming arterial biofilms. And once biofilms do form, clearing these pathogens becomes much more difficult.

Controlling blood sugar levels is also important as chronically elevated blood glucose is associated with immune suppression and increased risk of infection. This likely explains the higher incidence of heart disease in diabetics.

However, as I’ve noted elsewhere, pre- and type 2 diabetes is itself a reaction to translocating gut bacteria that in turn causes inflammation in the liver and increases cortisol generation in that organ. It is this increase in intracellular hepatic cortisol generation via up-regulation of the enzyme 11β-hydroxysteroid dehydrogenase type 1 that likely causes a liver to become deaf to the insulin secreted by an overworked pancreas. (15)  Once this occurs, runaway hepatic glucose production is the result. (16)

This increase in intracellular cortisol concentrations has an anti-inflammatory effect. But as all of you know by now, anti-inflammatory is another way of saying immune suppressing. This chronic activation of the cortisol-cortisone shunt by a leaky gut always results in suppressing the very system that could eradicate these pathogens from systemic circulation and arterial plaque.

This study adds to a growing body of evidence that cardiovascular diseases are primarily driven by the interaction between pathogens, the immune response to these agents, genetic predisposition and the regulatory systems (HPA-axis and cortisol-cortisone shunt) that drive catecholamine responses and determine extracellular and intracellular cortisol concentrations.

It neatly explains why practices like binge drinking are highly associated with heart attack and stroke risk. As I wrote in this post, this mode of imbibing alcohol increases oral dysbiosis, compromises gastric-barrier function, promotes disturbances to gut flora populations, increases intestinal permeability, contributes to liver damage, activates the cortisol-cortisone shunt, acutely stimulates the HPA-axis and causes immune suppression. In other words, this drug on its own is more than capable of rapidly promoting arterial disease when abused.

However, alcohol is far from the only drug that would be expected to increase dysbiosis and elevate the risk of cardiovascular disease. Acid-suppressing drugs, antibiotics, non-steroidal anti-inflammatories (NSAIDs), glucocorticoids and opioid-based analgesics can all contribute to development of dysbiosis if used for extended periods of time. Acid suppressors because they compromise gastric-barrier function, antibiotics by the collateral damage done to beneficial bacteria, NSAIDs by causing increased intestinal permeability, glucocorticoids by suppressing immune function and opioids by depressing intestinal peristalsis and thereby contributing to the onset of small intestinal fungal and bacterial overgrowth.

And any dietary recommendations offered to lessen cardiovascular disease risk must also be evaluated for their effects on oral and gut flora populations, intestinal permeability, immune function, the liver and cortisol and catecholamine responses. Otherwise, the advice given—most often as a result of blindly following the associative and confounded results of nutritional epidemiology, which is inherently incapable of proving causation or effect on any of the aforementioned bodily processes—is just as likely to produce ill rather than good health.

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