The oral microbiota as a biomarker for metabolic syndrome
The definition of metabolic syndrome does not always meet with general agreement, but its association with low-grade inflammation, its cardiovascular consequences and the risk of type 2 diabetes mellitus are real. Korean researchers have tried to determine whether the oral microbiota might contain bacterial biomarkers that would help identify a metabolic syndrome and predict its complications.
Metabolic syndrome (MetS) is characterized by obesity, dyslipidemia, hyperglycemia and high blood pressure. A number of studies have dealt with the role of the intestinal microbiota in the disease. Although easier to access, the oral microbiota has been very little studied. The oral pathogenic bacteria are known to have a pro-inflammatory action at both local and systemic level. The researchers therefore monitored two cohorts of families (with and without MetS) and ran comparative analyses on the oral and intestinal microbiotas (subgingival plaque / stools) according to subject status. Twins were enrolled in order to identify any potential genetic factors.
Metabolic abnormality of the host
Opposite results were obtained depending on the sample location: in MetS individuals, bacterial diversity is decreased in the intestines, but increased in the oral region. Reduced intestinal microbial diversity had already previously been observed in patients presenting with metabolic syndrome. It is thought to be explained by both metabolic and functional abnormalities. In the oral region, more extensive investigations have demonstrated increased microbial diversity and abundance in patients with hyperglycemia and hypertriglyceridemia. Conversely, low diversity of the oral microbiota is an indicator of good orodental health.
Association with Granulicatella adiacens
In comparing the oral microbiota of MetS patients and that of controls, it emerges that Granulicatella (known to cause infective endocarditis) and Neisseria (associated with low HDL cholesterol levels and cardiovascular diseases such as endocarditis and acute cardiac failure) are the most abundant species in MetS subjects. In contrast, Peptococcus is more abundant in healthy subjects. The statistical analysis adjusted for age and gender shows a significant association between G. adiacens and metabolic syndrome, particularly high blood pressure. This bacterium is both more abundant in MetS subjects and present in lower amounts in healthy subjects.
No genetic factor
Finally, analysis of the oral microbiota of twins (monozygotic and dizygotic) demonstrated that the host’s genetic factors did not influence oral microbial composition, as had already been shown by previous studies. The authors suspect that environmental factors (tobacco, diet, hygiene…) have a greater influence on the structure of the oral microbial population. They consider that the oral microbiota could be a source of biomarkers which would help identify subjects at risk of developing cardiovascular diseases or type 2 diabetes mellitus from metabolic syndrome. They conclude that their study opens the way to non-invasive diagnostic techniques.
J. Si, C. Lee, et G. Ko. Oral Microbiota: Microbial Biomarkers of Metabolic Syndrome Independent of Host Genetic Factors. Front. Cell. Infect. Microbiol., vol. 7, 2017.