Bacteria in the mouth and stomach might worsen heart disease in people suffering from hardening of the arteries and other circulatory disorders, according to new research at the Royal College of Surgeons of Ireland.
Two species of bacteria, one always present in the mouth and a second, Helicobacter pylori, a known cause of stomach ulcers, can interfere with the blood-clotting process. The research showed that these bacteria cause blood cells, called platelets, to clump together to produce dangerous clots. Platelets are the blood cells which control clotting when tissue damage occurs.
The Irish research effort has become the focus of attention at this week's American Heart Association annual meeting in New Orleans. The Dublin work was one of about a dozen research projects selected from more than 8,000 studies for presentation to the media at press conferences earlier this week.
"They take presentations that they think are of interest to the public," explained the lead researcher, Dr Dermot Cox of the Royal College of Surgeons of Ireland. "They give them the full television broadcast treatment."
Despite the conference showbiz, the RCSI project has a serious side and changes our understanding of heart disease.
It demonstrates that bacterial forms common amongst the general public could contribute to heart disease, Dr Cox explained.
Dr Cox is a lecturer in the Department of Clinical Pharmacology at the RCSI. He worked with Dr Mike Byrne of Beaumont, an expert on H pylori, and Mr Steven Kerrigan, also of the RCSI who made the presentation at the New Orleans meeting. The research is funded by the Irish Heart Foundation and the Charitable Infirmary Trust.
A number of earlier studies had suggested the link between bacteria and heart disease, Dr Cox said. Research had shown an increased likelihood of H pylori in the gut in patients with heart disease. Similar studies formed a connection between mouth bacteria and damage to heart valves and other heart tissues.
The British Dental Association issued a statement last year suggesting the link between heart disease and dental decay, Dr Cox said. "The problem with them is they (the links) are only associations." The research team at the RCSI explained the biochemistry behind these associations.
The team found that both H pylori and the very common mouth bacterium Streptococcus sanguis carried proteins on their surfaces that could activate platelets.
"Platelets are very important in heart disease," Dr Cox said. They are attracted to sites of damage in hardening of the arteries, places where plaques build up.
The plaques narrow the blood vessels and the arrival of platelets makes the situation more dangerous.
The ability of mouth bacteria to get into the bloodstream through diseased and damaged gums is well established. "S sanguis is in everyone's mouth and gets into everyone's bloodstream," Dr Cox said.
No mechanism for getting H pylori into the bloodstream had yet been established, he said. The theory held that the bacteria might cause inappropriate clotting and tissue damage in the stomach lining, in turn leading to ulceration. This might give H pylori an opportunity to enter the bloodstream.
In healthy individuals the bacteria have little influence, he said. The same is not true for people with underlying heart or circulatory diseases.
Once in circulation the bacteria adhere to the surface of platelets and attract more platelets. "It has a protein on its surface that by coincidence allows it to activate the platelets."
Platelets may already have accumulated along damaged blood vessels, and the bacteria can make this situation worse.
"If you have unstable heart disease your platelets are already being activated and this may be too much of a burden," Dr Cox explained. Dangerous clots can be the result.
When tissues are damaged they release a protein called glycoprotein 1B, which attracts and then connects to platelets to stop blood flow, Dr Cox said. The bacterial surface protein mimics glycoprotein 1B, increasing the activation of platelets and the potential for unwanted blood clots.
It is difficult to control the bacteria. Antiseptic mouthwashes can wipe out S sanguis but it quickly grows back. The platelets have their own built-in "antibiotics", antimicrobial peptides, but because these bugs are so pervasive they have developed a resistance to the peptides. They also evade antibiotic treatment because they get surrounded by the clot and live safely inside where drugs can't reach them.
The best approach, Dr Cox said, was to keep the bacterial load as low as possible. Patients with heart disease in particular should see their dentists regularly and maintain good dental hygiene.
The book is not closed on the bacterial involvement in heart disease and much research work remained to be done, he said. "It adds weight to the argument, it doesn't prove anything yet." It provides compelling new information, however, and gives researchers new avenues to explore.