Plasma as an Indicator of Bone Fluoride Levels in Rats Chronically Exposed to Fluoride

OBJECTIVE This study evaluated the use of plasma, bone surface (periosteal) and whole bone as biomarkers of chronic fluoride (F) exposure. METHODS Forty male Wistar rats were assigned to 4 groups (n=10/gr) that differed according to the F concentration they received in the drinking water. Groups 1, 2, 3 and 4 received water containing 0 (control), 5, 15, and 50 mg F/L, respectively. The rats were killed at 120 days of age. Plasma and femur were collected and analyzed for fluoride with the ion specific electrode by the direct method or after hexamethyldisiloxane-facilitated diffusion. Data were tested for statistically significant differences by ANOVA and linear regression (p<0.05). RESULTS Mean (+/- SE) plasma F concentrations ranged from 0.030 +/- 0.002 to 0.187 +/- 0.013 (mg/mL). The concentrations in surface and whole bone ranged from 610 +/- 32 to 4,693 222; and 647 +/- 22 to 3,439 +/- 134 microg/g, respectively. The surface/whole F concentration ratios were 0.941, 1.414, 1.173 and 1.377, for groups 1, 2, 3 and 4 respectively. For plasma and whole bone, the difference among all groups was statistically significant, except for group 2 compared to group 1. For bone surface, all groups differed from each other except for group 2 compared to group 3. A significant positive correlation was found between bone surface and whole bone F (r(2)=0.94), as well as between plasma and bone surface (r(2)=0.71) and plasma and whole bone (r(2)=0.74). CONCLUSIONS Data suggest that both bone surface and whole bone are suitable biomarkers of chronic F exposure in rats and plasma may be used as indicator of bone fluoride levels.