Alternative bisphosphonate targets and mechanisms of action

Bisphosphonates and atherosclerosis: why?

The increasing knowledge on bone calcification processes has revealed some similarities with vascular tissue, where calcifications of arteries and cardiac valves contribute to several cardiovascular problems, such as heart failure, systolic hypertension, and myocardial and peripheral ischemic disease. Bisphosphonates have been used extensively for over two decades for the treatment of diseases associated with excessive bone resorption, i.e., osteoporosis, osteolytic bone metastasis, hypercalcemia and Paget's disease, by blocking osteoclastic function. Etidronate, pamidronate and clodronate has been shown to inhibit the development of experimental atherosclerosis, and proposed mechanisms for this action include inhibition of arterial calcification and lipid accumulation, degradation of atherogenic LDL-cholesterol and reduced foam cell formation. Bisphosphonates inhibit various enzymes involved in cholesterol biosynthesis and suppress macrophages in atheromatous lesions. The possibility of pharmacological agents that effectively treat both osteoporosis and atherosclerosis is attractive, however, current evidence is not conclusive and further research is necessary to confirm these actions in the clinical setting.

Endodontic Implications of Bisphosphonate-Associated Osteonecrosis of the Jaws: A Report of Three Cases

Bisphosphonates are commonly used in medicine to maintain bone density in patients with certain nonneoplastic diseases or cancers. A serious adverse effect of bisphosphonates that has substantial dental significance is osteonecrosis that appears to uniquely affect the mandible and maxilla without occurring in other bones of the skeleton. Patients with bisphosphonate associated osteonecrosis of the jaws may present with pain and exposed necrotic bone. This has substantial clinical implications because surgical procedures (including extractions or endodontic surgical procedures) are contraindicated in the jaws of these patients and the presenting pain may mimic pain of odontogenic origin. This report describes three patients with bisphosphonate associated osteonecrosis and emphasizes the endodontic implications of managing these patients.

Bisphosphonates induce inflammation and rupture of atherosclerotic plaques in apolipoprotein-E null mice

The apolipoprotein E knockout (Apo-E-/-) mouse is a well-known model of atherosclerosis. Bisphosphonates, through their affinity to hydroxyapatite, are known to reduce arterial calcification in several animal models. Thus, we examined the effect of two therapeutically used oral bisphosphonates, alendronate and risedronate, on plaque formation in the Apo-E-/- mouse. The drugs were administered by gavage to 16-week-old Apo-E-/- mice for 8 weeks. At 8 weeks, there was no difference in bone mineral density (BMD) of the alendronate- and risedronate-treated mice at any site. A time-dependent increase in BMD was demonstrated in Apo-E-/- mice with risedronate (p<0.01). Histological evaluation revealed that both bisphosphonates caused atherosclerotic plaque rupture. Five of 17 mice had severe inflammation with or without plaque rupture, while seven mice showed inflammation, but without plaque rupture. Neither caspase 3 nor metalloproteinases 2 and 9 were increased in ruptured plaques on immunocytochemistry. Quantitative measurements of arterial caliber remained unaffected. Our finding of plaque inflammation and rupture in bisphosphonate-treated Apo-E-/- mice may provide the first animal model for studies aimed at characterizing mechanisms of plaque rupture in animal models.