Low levels of salivary metals, oral microbiome composition and dental decay

Abstract

Salivary microbiome composition can change following exposure to environmental toxicants, e.g., heavy metals. We hypothesized that levels of salivary nutrients and metals would correlate with salivary microbiome composition and be associated with dental decay. Here we assess the salivary concentrations of 5 essential minerals (cobalt, copper, manganese, molybdenum, and zinc), 4 metals with some evidence of normal physiological function (chromium, nickel, tungsten, and vanadium), and 12 with known toxicity (antimony, arsenic, barium, beryllium, cadmium, cesium, lead, mercury, platinum, thallium, tin, and uranium), and their associations with salivary microbiome composition and dental decay in 61 children and adults. 16 metals were detected in 54% of participants; 8 were found in all. Marked differences in salivary bacterial taxa were associated with levels of antimony, arsenic, and mercury, after adjusting for multiple testing. further, antimony levels were associated with the presence of decayed teeth. thus, salivary metal levels, even at low concentrations, may impact oral health. The salivary microbiome provides a window into the overall health of the body and likely changes in response to environmental exposures, such as metals. Like humans, bacteria require certain metals to carry out metabolic processes, and often compete with host cells to take up these metals through transporters and other acquisition systems 1,2. However, toxicity is a concern for bacteria, as some metals-such as cadmium and copper-are bactericidal at certain concentrations 3. Further, even essential metals can be toxic, depending on the dose (Supplemental Tables S1-S3). Therefore, we hypothesized that there will be changes in the salivary microbiome composition in response to salivary metal levels which may directly affect oral health. Dental caries is the most common chronic disease in children aged 6-19 4 and periodontal disease is the most common cause of adult tooth loss 5. The oral microbiome is an important determinant of both dental caries and periodontal disease. As it is now clear that the microbiome at all body sites responds to environmental stressors such as pathogens and environmental chemicals, it is critical to understand the implications of metal exposures on the structure, composition, and function of the oral microbiome, taking into account whether the metal is exclusively toxic, an essential mineral, or has some physiological functions. When certain toxic metals, e.g., lead or cadmium, are measured in blood or urine the resulting levels can be compared to guidelines for concentrations of concern 6 ; however, no guidelines exist for salivary metal levels. Saliva biomarker exposure assessment could be particularly useful in studies where the oral cavity is the primary target region of toxicity (e.g., studies of the oral microbiome or dental health). Some studies have assessed salivary metals, but the number of publications and the scope of metals assessed are limited. Lead 7,8 and mercury 9 have been of particular intere...

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