Gum disease bug linked to rheumatoid arthritis
"Want to avoid arthritis? Then brush your teeth … bugs that cause gum infections also trigger the crippling joint pain," the Mail Online reports.
Rheumatoid arthritis is an autoimmune disease where the immune system attacks the cells that line joints by mistake. Exactly what causes this response is still unclear.
This latest study aimed to examine whether rheumatoid arthritis could have a possible bacterial cause, and whether these bacteria could come from the mouth.
Researchers examined gum fluid of people with gum disease (periodontitis) and found it contained high levels of what are known as citrullinated proteins. These are a type of protein known to trigger an immune response in people with rheumatoid arthritis.
Researchers also found evidence that a strain of bacteria called Aggregatibacter actinomycetemcomitans (Aα) seemed to be causing these high levels of citrullinated proteins.
However, this doesn't provide the whole answer to the rheumatoid arthritis puzzle. Not everyone with rheumatoid arthritis has an immune response to the citrullinated proteins. And conversely not everyone with this immune response had symptoms of rheumatoid arthritis.
Similarly, not everyone with gum disease develops rheumatoid arthritis, and vice versa.
Still, despite all of these uncertainties, regularly brushing your teeth is always a good idea. Gum disease may be linked with many other health complications, including stroke, diabetes and heart disease. Read more about the health risks of gum disease.
Where did the story come from?
The study was carried out by researchers from Johns Hopkins University School of Medicine and various other institutions in the US, and Aarhus University in Denmark. Individual researchers report several sources of financial support, including the Jerome L. Greene Foundation, the Donald B. and Dorothy L. Stabler Foundation, and the National Institute of Arthritis and Musculoskeletal and Skin Diseases.
The study was published in the peer-reviewed journal Science Translational Medicine.
The Mail Online's take on the research is arguably overly simplistic. The research does not prove that if you brush your teeth you will stop yourself getting "arthritis", or that people with arthritis have had poor dental hygiene. The findings are very unlikely to provide the whole answer to the causes of rheumatoid arthritis – and rheumatoid arthritis is only one type of arthritis.
What kind of research was this?
This was a laboratory study which aimed to look into a possible bacterial cause of rheumatoid arthritis.
Rheumatoid arthritis is an autoimmune condition where the body's immune cells attack the joints (often starting with the small joints of the hands and feet) causing inflammation, swelling, pain and stiffness. Although there are some known risk factors for rheumatoid arthritis, such as smoking, the causes aren't established.
Researchers say that some recent studies have suggested mucosal surfaces in the body, like those in the gums, digestive system or lungs, could be the origin of the disease process. In particular they say that periodontitis – a bacterial inflammatory disease of the gums – has often been observed in people with rheumatoid arthritis and could be the start of the autoimmune, inflammatory process.
The study aimed to look into this question further.
What did the researchers do?
The researchers collected blood samples from 109 people with periodontitis and 100 healthy controls. They obtained samples of fluid from the space between the gums and teeth (gingival crevicular fluid) from nine of the people with periodontitis and eight controls.
They also identified another sample of 196 people who met standard disease criteria for rheumatoid arthritis, from whom they obtained blood and joint fluid samples.
The researchers analysed the gum fluid in the laboratory to look at its composition and see how it differed between controls and people with gum disease. They also looked at what similarities there were to the blood and joint fluid samples of people with rheumatoid arthritis.
What did they find?
The researchers found that the gum fluid of people with periodontitis reflected the inflammatory environment of the rheumatoid arthritis joint. There were extensive citrullinated proteins in the fluid, and people with rheumatoid arthritis are often found to produce antibodies against these proteins. The antibodies are known as anti-cyclic citrullinated peptides (anti-CCP).
By comparison, healthy people had minimal citrullinated proteins in their gum fluid.
When researchers conducted analysis to see what could be causing these high citrullinated proteins, they found several potential groups of bacteria, but one single bacterial species called Aggregatibacter actinomycetemcomitans (Aα) emerged as the most likely candidate.
Aα causes high production of citrullinated proteins within a particular type of white blood cell (neutrophil). It does this by producing a toxin called leukotoxin A (LtxA). This toxin splits open neutrophil cells which releases citrullinated proteins.
The researchers found that the citrullinated proteins in the gum fluid showed marked overlap with those found in the joint fluid of people with rheumatoid arthritis, with 44 of 86 proteins in common.
They also found that in people with rheumatoid arthritis, antibodies specifically targeting LtxA were found to be associated with the presence of anti-CCP antibodies.
What did the researchers conclude?
The researchers conclude: "These studies identify the periodontal pathogen Aα as a candidate bacterial trigger of autoimmunity in rheumatoid arthritis".
Conclusions
This research aimed to investigate a possible bacterial origin of rheumatoid arthritis and found one potential candidate – Aggregatibacter actinomycetemcomitans (Aα). It seems these bacteria could cause the high levels of citrullinated proteins which are known to trigger an immune reaction in people with rheumatoid arthritis.
However, it's important to put these findings into the right context.
Though antibodies against citrullinated proteins, anti-cyclic citrullinated peptide (anti-CCP), are one of the possible diagnostic findings in people with rheumatoid arthritis – not everyone with rheumatoid arthritis has these antibodies, and not everyone with these antibodies has rheumatoid arthritis. These are not an exclusive, defining hallmark of the disease. Therefore this will not provide the whole answer to the disease process.
Even if high citrullinated proteins were the single defining hallmark of rheumatoid arthritis, we still don't know that the Aα bacteria provide the whole answer to what causes this. There may be other infective and inflammatory processes contributing to the raised levels of these cellular proteins.
Care must also be taken when linking "arthritis" with dental care, as the media has done.
Not everyone with gum disease develops rheumatoid arthritis, and not everyone with rheumatoid arthritis has had previous gum disease or poor dental hygiene. There is nothing to say that the mouth is the one source of any potential causative infective process.
Overall, the findings are of interest and give further understanding of the potential causes of autoimmune disease processes like rheumatoid arthritis, which currently have no established cause. However, there are no immediate preventative or treatment implications.
Regularly brushing your teeth can help prevent a whole range of unpleasant conditions, such as tooth decay, toothache and gum diseases. But it cannot be said with confidence at this time that brushing can also prevent rheumatoid arthritis.
