MORPHOLOGICAL-STUDIES OF HYDROXYAPATITE CRYSTAL EXPOSED TO DISODIUM PAMIDRONATE

''In vitro'' effects of disodium pamidronate on hydroxyapatite crystal s morphology, and some ''in vivo'' data from bone powder of tibia and vertebrae from treated young and mature rabbits are here reported. Hyd roxyapatite, synthesized following Rigoli et al method, and bone powde r from rabbits were studied with X-ray, infrared and raman emission te chniques for crystallographic analysis. Adsorption studies were also p erformed with a balanced solution of hydroxyapatite exposed to differe nt times, 48, 120 and 168 hours and concentrations 1 x 10(-5)M, 3 x 10 (-5)M, 8 x 10(-5)M y 1 x 10(-4)M of pamidronate. Infrared and raman sp ectrometry were not conclusive due to technical bias, but X-ray difrac tograms showed pure hydroxyapatite crystals in an hexagonal system. At constant time, pamidronate concentrations were varied, showing after 48 hours of exposition, a slight growth in the 002 plane, an aleatoric behavior in 213 and a marked increase in 004. After 120 hours, 002 pl ane is steady with a net growth in 004 and 213. After 168 hours, the 3 mentioned planes grow in proportion to pamidronate concentrations, te nding to enlarge the crystal shape. Plane 13 markedly grow with pamidr onate 8 x 10(-5)M a 1 x 10(-4)M, which are biologically high concentra tions. Potentiometric assessments, in the 1 x 10(-5) to 1 x 10(-4)M ra nge of concentrations show that bisphosphonate was completely adsorbed to the crystals. Additional ''in vivo'' observations showed changes i n bone powder crystals isolated from pamidronate treated young animals , involving a growing of planes 002 and 211, in samples from both epip hysis and diaphysis, regarding untreated samples. Changes were more ev ident at epiphysis. In mature rabbits, it was shown a decrease in basa l plane 002 and growing at 210, 211 and 310 with a trend to enlarge th e crystal shape in diaphysis and to shorten it in vertebrae spongiosa. The ''in vivo'' doses are equivalent to those used by Ferretti et al, in intact rats with pamidronate low dose groups, showing an improveme nt of bone material properties and stiffness. Thus, it may rather be l ower than the ''in vitro'' used concentrations. In concordance with ab ove experimental conditions it can be concluded that bisphosphonates e xert morphological changes in hydroxyapatite crystals, in a dose depen dent manner, at least when high concentrations are used. In addition, it is postulated that changes observed on ''in vivo'' samples may be t he result with other adaptative factors as for example the local mecha nical usage. The latter data were limited, and should be studied with more details if an extrapolation to the bisphosphonate treated osteopo rotic women is intended. Finally, it is suggested that any agent that changes BMU activity (all known anti-osteoporotic drugs) may potential ly modify the quality of hydroxyapatite crystals, affecting in turn th e bone resistance to fracture, independently from the quantity of bone mass gained. Thus, to help predicting the consequences on skeletal fr agility, there is a need to know the direct or indirect effect of drug s on bone crystals.