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.