FLUORIDE 30 (2)  1997, p. 124	International Society for Fluoride Research	Table of Contents

ALUMINUM POTENTIATES THE EFFECT OF FLUORIDE ON TYROSINE
PHOSPHORYLATION AND OSTEOBLAST REPLICATION
IN VITRO AND BONE MASS IN VIVO

J Caverzasio, T Imai, P Ammann, D Burgener and J P Bonjour
Geneva, Switzerland

Abstract from Journal of Bone & Mineral Research 11 (1) 46-55 1996

Osteosclerosis in workers exposed to fluoride (F) and aluminum (Al) (industrial fluorosis) led to the use of F as a treatment to increase bone mass in osteoporosis patients. Because the influence of traces of Al on the effects of F on bone formation is heretofore unknown, we have investigated this issue both in vitro and in vivo. We have found that minute amounts of Al (< or = 10-5 M) potentiate the effects of F in vitro such that osteoblast proliferation increased by 15 ± 2.7% at 50 microM (p < 0.001) and by 117.6 ± 5.1% at 750 microM (p < 0.001), concentrations of F with no mitogenic effect alone. F + Al time-dependently modulated a growth factor signaling pathway(s) associated with enhanced tyrosine phosphorylation (TyrP) of several proteins (p90 [2.9x], p77 [4.9x], p68 [9.6x], and mitogen activated protein kinases [3x]). TyrP was only slightly or not at all changed by F and Al alone, respectively. The effects of F + Al on TyrP and cell proliferation were markedly reduced by 100 microM tyrphostin-51, a tyrosine kinase inhibitor. Protein kinase A (PKA) and protein kinase C (PKC) pathways were not involved in this response. In vivo, F + Al administered for 8 months, at doses that had no effect when the minerals were administered individually, significantly enhanced proximal tibia bone mineral density (BMD) by 6.3 ± 1% compared with initial values and by 2-fold compared with control ovariectomized rats (p < 0.0001). These effects are consistent with a crucial role of Al in osteosclerosis observed in industrial fluorosis. The results suggest that the combination of F + Al modulates a growth factor-dependent TyrP pathway enhancing mitogen-activated protein kinase and osteoblastic proliferation and bone mass.

Key words: Aluminum, Bone, Industrial fluorosis, Osteoblasts, Tyrosine phosphorylation.
Reprints: J Caverzasio, Department of Medicine, University Hospital of Geneva, 24 Rue Micheli Crest, CH-1211 Geneva 14, Switzerland.

FLUORIDE 30 (2)  1997, p. 124	International Society for Fluoride Research
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