Yale researchers have uncovered the molecular tricks used by bacteria to fight the effects of fluoride, which is commonly used in toothpaste and mouthwash to combat tooth decay. However, it is important to understand that this study in no way is refuting the positive use of fluoride in the prevention of tooth decay and in some case, the killing of bacteria found in gum disease.
In the Dec. 22 online issue of the journal Science Express, the researchers report that sections of RNA messages called riboswitches — which control the expression of genes — detect the build-up of fluoride and activate the defenses of bacteria, including those that contribute to tooth decay. These riboswitches are detectors made specifically to see fluoride.
Fluoride in over-the-counter and prescription toothpastes is widely credited with the large reduction in dental cavities seen since these products were made available beginning in the 1950s. This effect is largely caused by fluoride bonding to the enamel of our teeth, which hardens them against the acids produced by bacteria in our mouths. However, it has been known for many decades that fluoride at high concentrations also is toxic to bacteria, causing some researchers to propose that this antibacterial activity also may help prevent cavities.
The riboswitches work to counteract fluoride’s effect on bacteria. If fluoride builds up to toxic levels in the cell, a fluoride riboswitch grabs the fluoride and then turns on genes that can overcome its effects. Since both fluoride and some RNA sensor molecules are negatively charged, they should not be able to bind. Scientists would argue that RNA is the worst molecule to use as a sensor for fluoride, and yet there has been found more than 2000 of these strange RNAs in many organisms.
By tracking fluoride riboswitches in numerous species, the research team concluded that these RNAs are ancient — meaning many organisms have had to overcome toxic levels of fluoride throughout their history. Organisms from at least two branches of the tree of life are using fluoride riboswitches, and the proteins used to combat fluoride toxicity are present in many species from all three branches.
Cells have had to contend with fluoride toxicity for billions of years, and so they have evolved precise sensors and defense mechanisms to do battle with this ion. Now that these sensors and defense mechanisms are known, Breaker said, it may be possible to manipulate these mechanisms and make fluoride even more toxic to bacteria. Fluoride riboswitches and proteins common in bacteria are lacking in humans, and so these fluoride defense systems could be targeted by drugs. For example, the Yale team discovered protein channels that flush fluoride out of cells. Blocking these channels with another molecule would cause fluoride to accumulate in bacteria, making it more effective as a cavity fighter.
Fluoride is the 13th most common element in Earth’s crust, and it is naturally present in high concentrations throughout the United States and elsewhere. One of the highest naturally occurring concentrations in water is right her in the Bryant-Bauxite area of Arkansas! Its use in toothpaste and its addition to city water supplies across the United States sparked a controversy 60 years ago, and the dispute continues to this day. Some new studies have even looked at fluoride’s effect on the thyroid gland, prompting many people to be fearful of using fluoride at all; it is still uncertain that fluoride is having a negative effect on the thyroid gland – at least enough to warrant not using fluoride.
The new findings from Yale only reveal how microbes overcome fluoride toxicity. The means by which humans contend with high fluoride levels remains unknown. The use of fluoride has had clear benefits for dental health and that these new findings do not indicate that fluoride is unsafe as currently used.