[Morphological studies of hydroxyapatite crystals exposed to disodium pamidronate]

"In vitro" effects of disodium pamidronate on hydroxyapatite crystals morphology, and some "in vivo" data from bone powder of tibia and vertebrae from treated young and mature rabbits are here reported. Hydroxyapatite, synthesized following Rigoli et al method, and bone powder from rabbits were studied with X-ray, infrared and raman emission techniques for crystallographic analysis. Adsorption studies were also performed with a balanced solution of hydroxyapatite exposed to different 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 spectrometry were not conclusive due to technical bias, but X-ray difractograms 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 plane is steady with a net growth in 004 and 213. After 168 hours, the 3 mentioned planes grow in proportion to pamidronate concentrations, tending to enlarge the crystal shape. Plane 13 markedly grow with pamidronate 8 x 10(-5) M a 1 x 10(-4) M, which are biologically high concentrations. Potentiometric assessments, in the 1 x 10(-5) to 1 x 10(-4) M range of concentrations show that bisphosphonate was completely adsorbed to the crystals. Additional "in vivo" observations showed changes in bone powder crystals isolated from pamidronate treated young animals, involving a growing of planes 002 and 211, in samples from both epiphysis and diaphysis, regarding untreated samples. Changes were more evident at epiphysis. In mature rabbits, it was shown a decrease in basal plane 002 and growing at 210, 211 and 310 with a trend to enlarge the crystal shape in diaphysis and to shorten it in vertebrate spongiosa. The "in vivo" doses are equivalent to those used by Ferretti et al. in intact rats with pamidronate low dose groups, showing an improvement of bone material properties and stiffness. Thus, it may rather be lower than the "in vitro" used concentrations. In concordance with above experimental conditions it can be concluded that bisphosphonates exert morphological changes in hydroxyapatite crystals, in a dose dependent manner, at least when high concentrations are used. In addition, it is postulated that changes observed on "in vivo" samples may be the result with other adaptative factors as for example the local mechanical usage. The latter data were limited, and should be studied with more details if an extrapolation to the bisphosphonate treated osteoporotic women is intended. Finally, it is suggested that any agent that changes BMU activity (all known anti-osteoporotic drugs) may potentially modify the quality of hydroxyapatite crystals, affecting in turn the bone resistance to fracture, independently from the quantity of bone mass gained. Thus, to help predicting the consequences on skeletal fragility, there is a need to know the direct or indirect effect of drugs on bone crystals.