Further insight into mechanism of action of clodronate: inhibition of mitochondrial ADP/ATP translocase by a nonhydrolyzable, adenine-containing metabolite.
Bisphosphonates are currently the most important class of antiresorptive drugs used for the treatment of diseases with excess bone resorption. Recent studies have shown that bisphosphonates can be divided into two groups with distinct molecular mechanisms of action depending on the nature of the R(2) side chain. Alendronate, like other nitrogen-containing bisphosphonates, inhibits bone resorption and causes apoptosis of osteoclasts and other cells in vitro by preventing post-translational modification of GTP-binding proteins with isoprenoid lipids. Clodronate, a bisphosphonate that lacks a nitrogen, does not inhibit protein isoprenylation but can be metabolized intracellularly to a beta-gamma-methylene (AppCp-type) analog of ATP, which is cytotoxic to macrophages in vitro. The detailed molecular basis for the cytotoxic effects of adenosine-5'-[beta,gamma-dichloromethylene]triphosphate (AppCCl(2)p) has not been determined yet. We addressed this question by studying the effects of alendronate, clodronate, and the clodronate metabolite AppCCl(2)p on isolated mitochondria, mitochondrial fractions, and mitochondrial membrane potential in isolated human osteoclasts. We found that AppCCl(2)p inhibits mitochondrial oxygen consumption by a mechanism that involves competitive inhibition of the ADP/ATP translocase. Alendronate or the native form of clodronate did not have any immediate effect on mitochondria. However, longer treatment with liposome-encapsulated clodronate caused collapse of the mitochondrial membrane potential, although prominent apoptosis was a late event. Hence, inhibition of the ADP/ATP translocase by the metabolite AppCCl(2)p is a likely route by which clodronate causes osteoclast apoptosis and inhibits bone resorption.
Lehenkari
Petri P
PP
Department of Surgery, University of Oulu, Oulu, Finland.
Kellinsalmi
Maarit
M
Näpänkangas
Juha P
JP
Ylitalo
Kari V
KV
Mönkkönen
Jukka
J
Rogers
Michael J
MJ
Azhayev
Alex
A
Väänänen
H Kalervo
HK
Hassinen
Ilmo E
IE
D000225:Adenine / Q000378:metabolism; D000227:Adenine Nucleotides / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology*; D017209:Apoptosis; D001692:Biological Transport; D048429:Cell Size / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004002:Clodronic Acid / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects* / Q000201:enzymology / Q000502:physiology; D000226:Mitochondrial ADP, ATP Translocases / Q000037:antagonists & inhibitors*; D010010:Osteoclasts / Q000187:drug effects / Q000473:pathology / Q000502:physiology; D010101:Oxygen Consumption; D051381:Rats; D017207:Rats, Sprague-Dawley
D000227:Adenine Nucleotides; D000963:Antimetabolites; D004791:Enzyme Inhibitors; D004002:Clodronic Acid; C056864:adenosine-5'-O-(beta,gamma-dichloromethane)triphosphate; D000255:Adenosine Triphosphate; D000226:Mitochondrial ADP, ATP Translocases; D000225:Adenine