Mouth Bacteria May Trigger RA
Studies highlight the role of microbes in rheumatoid arthritis and other inflammatory diseases.
By Linda Rath
A century ago, people believed that gum infections were the source of many inflammatory diseases, including appendicitis and rheumatoid arthritis (RA). The treatment for so-called oral sepsis was total tooth extraction — which rarely improved symptoms and was unpopular with patients — and by the 1930s, the oral sepsis theory had largely been discredited.
Today, thinking has come full circle. In the last few years, a great deal of research, aided by DNA sequencing techniques, has shown germs that cause gum disease may contribute to many health problems, including RA and other inflammatory disorders. Gum disease also has been associated with other inflammatory forms of arthritis and rheumatic conditions, including psoriatic arthritis and lupus.
Collectively called the microbiota or microbiome, the trillions of bacteria that live on and in the human body are mostly beneficial and protective — aiding digestion and guarding against pathogens and inflammation. But altering the makeup of complex microbial communities — as happens in periodontal disease — can trigger an immune response that targets the body’s own tissues.
A 2010 epidemiological study in the Journal of Periodontology found that RA patients were twice as likely to have gum disease compared to those without RA and their periodontal disease was more severe. Ten years later, Spanish researchers reported similar findings. They found that people with severe periodontal disease also had severe rheumatoid arthritis. Patients with the most plaque, bleeding and gum tissue breakdown had worse RA by all measures, including disease activity and inflammatory markers. Other studies have found that even with treatment, RA patients with periodontitis continue to have worse arthritis symptoms and are 50% less likely to be in remission.
The relationship between gum disease and arthritis isn’t seen only in adults. Kids with juvenile idiopathic arthritis (JIA) have inflammatory mouth bacteria not found in their healthy peers. Different types of bacteria seem to correspond to specific aspects of JIA. Some are associated with higher disease activity and others with a greater number of affected joints. Some are also linked to cavities that don’t respond to fluoride treatment.
How Mouth Bacteria Harm Joints
Ideas about how and where RA starts have changed radically in recent decades. Evidence now points to RA beginning not in the joints, but instead resulting from autoantibodies produced in other parts of the body, including the digestive tract and even the lungs. Microbes in the mouth are particularly good at creating autoantibodies. That’s because P. gingivalis — an oral microbe linked to arthritis — contains a unique enzyme that alters proteins so the body perceives them as a threat. This process, known as citrullination, can lead to the production of antibodies against the proteins in the joint lining.
Scientists used to think periodontal disease had wide-ranging effects on health due to systemic inflammation. This would account for its association with diverse disorders such as heart disease, kidney problems, pancreatic cancer and poor pregnancy outcomes, as well as RA. But researchers have since found oral bacteria in the synovial fluid (the viscous fluid between joints) of patients with RA as well as those with osteoarthritis. It now seems likely the bacteria escape from the mouth through damaged gum tissue, enter the bloodstream and travel to sites throughout the body.
Future RA Prevention and Treatment
Evidence about the role of bacteria in diseases like RA has sparked intense speculation about future treatments. Stephen Paget, physician-in-chief emeritus of rheumatology at Hospital for Special Surgery in New York City and an expert on autoimmune disease, has suggested that therapies may need to focus on enhancing immunity rather than suppressing it. Other experts argue for restoring healthy gut communities with probiotics or fecal therapy. And still others think treating gum infections might cure a variety of systemic diseases. All say more research is needed.
Reviewed April 14, 2021
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