Skeletal Fluorosis - Mechanism of Action

Mechanism of Action

The best way to view the mechanism of action by which fluorine breaks down bones and causes skeletal fluorosis is in a step-wise fashion.

1. Fluorine enters the body by two paths: Ingestion or respiration. Both paths lead to corrosion of exposed tissue in high concentrations. Since the most likely form of fluorine to enter the body is hydrogen fluoride (HF) gas, this is what starts the process. Exposed tissues will be utilized by HF in neutralization reactions.
2. This will leave F− free to pass further into the body.
3. It reacts with the concentrated HCl in the stomach to form the weak acid, HF.
4. This compound is then absorbed by the gastro-intestinal tract and passes into the liver via the portal vein. Since F is the strongest oxidizer known currently, it is immune to phase 1 metabolic reactions, which are generally oxidation reactions, in the liver. These reactions are the body’s first line of defense to biotransform harmful compounds into something more hydrophilic and more easily excreted.
5. The HF is now free to pass into the blood stream and be distributed to all tissues including bones.
6. Bones are largely composed of Ca compounds, particularly carbonated hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂); the reaction of Ca and HF forms an insoluble salt, CaF₂.
7. This salt must be cleared by the body and as a result washes away some of the calcium that would be part of the bone matrix.
8. This process results in increased density, but decreased strength in bones.