Analgesic effect of bisphosphonates in mice

Bisphosphonates are analogues of inorganic pyrophosphate and are inhibitors of bone resorption. Many derivatives have been developed for the treatment of enhanced bone resorption; several reports reveal that treatment with bisphosphonates is able to reduce the pain associated with different painful diseases. This study tested the antinociceptive action of four bisphosphonates, clodronate, alendronate, pamidronate and etidronate, in comparison with that of morphine and acetylsalicylic acid using two algesimetric tests in mice, tail-flick and writhing tests. In the tail-flick test, after intravenous (i.v.) injection, a dose-dependent antinociception was present after pamidronate, clodronate and acetylsalicylic acid whereas etidronate and alendronate produced an analgesic effect only with the highest dose tested. We also studied the central effect of clodronate and pamidronate and, after intracerebroventricular injection, both bisphosphonates showed a dose-dependent antinociceptive effect. In the writhing test clodronate and pamidronate showed a statistically significant antinociceptive action after i.v. and intramuscular administration. To verify if clodronate and pamidronate could modulate the peripheral opioid receptors we evaluated the gastrointestinal transit time in mice, but we did not find any effect on the gastrointestinal motility. These data indicate that clodronate and pamidronate present a central and peripheral antinociceptive effect; however, the main mechanism cannot be determined from the present data. We discuss the possible pharmacological hypothesis to interpret the present results. The findings suggest a pharmacological role of the bisphosphonates in the modulation of antinociception even in acute conditions not related to accelerated osteolytic and inflammatory response, with a possible clinical application to control pain.