Effects of raloxifene against letrozole-induced bone loss in chemically-induced model of menopause in mice.
The deleterious effects of letrozole, an aromatase inhibitor, used in the adjuvant treatment of breast cancer in postmenopausal women, on bone are well-documented and represent a major drawback to its clinical use. Raloxifene, a selective estrogen receptor modulator and a clinically approved anti-osteoporotic drug, has been recently demonstrated to be efficacious in women with breast cancer. The present study evaluated the effects of preventive and curative treatment with raloxifene on letrozole-induced alterations of bone microarchitecture and turnover markers in a chemically-induced menopause model in mice.



Swiss strain albino female mice were made menopausal by inducing ovotoxicity using vinyl cyclohexene di epoxide (VCD, 160 mg/kg for 15 days followed by 30 days drug-free period) confirmed by ovarian histology and serum estradiol levels. Effects on femoral and lumbar bones were evaluated by micro CT determination of bone volume, trabecular number, separation, thickness, connective density and trabecular pattern factor and bone turnover markers including ALP, TRAP5b, hydroxyproline and RANKL. In addition to these, markers of Wnt signaling (sclerostin and dickkopf-1) were also evaluated. To rule out the involvement of pharmacokinetic interaction, plasma levels of letrozole and raloxifene were measured following drugs alone and in combination.



Though bone loss was observed in VCD treated mice (as indicated by micro CT measurements), it was further enhanced with letrozole administration (1 mg/kg) for one month particularly in epiphysis of femoral bones. Raloxifene (15 mg/kg), whether administered concurrently or post-letrozole was able to revert the structural alterations and changes in turnover markers caused by letrozole to varying degrees (p < 0.01 or p < 0.001). Further, estrogen deficiency following letrozole treatment in ovotoxic mice was associated with significant increase in sclerostin and dickkopf-1 in both lumbar and femur bones (p < 0.001) which was attenuated with preventive and curative treatment with raloxifene (p < 0.05). The plasma levels of letrozole remained unaffected by raloxifene administration and vice versa.



Our study indicates the potential of raloxifene in preventing and attenuating letrozole-induced bone loss. Further, these effects were found to be independent of a pharmacokinetic interaction between the two drugs.
Department of Pharmacology, Faculty of Pharmacy, Jamia Hamdard (Hamdard University), New Delhi 110062, India.
Abul
A
Kalam
Department of Pharmaceutics, Faculty of Pharmacy, Jamia Hamdard (Hamdard University), New Delhi 110062, India.
Sushama
S
Talegaonkar
Department of Pharmacology, Faculty of Pharmacy, Jamia Hamdard (Hamdard University), New Delhi 110062, India. Electronic address: divyavohora@hotmail.com.
Divya
D
Vohora
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D016723:Bone Remodeling / Q000187:drug effects; D001862:Bone Resorption / Q000139:chemically induced* / Q000473:pathology*; D053138:Cyclohexenes; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D006023:Glycoproteins / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D000077289:Letrozole; D008159:Lumbar Vertebrae / Q000000981:diagnostic imaging / Q000187:drug effects / Q000473:pathology / Q000503:physiopathology; D008593:Menopause / Q000187:drug effects*; D051379:Mice; D009570:Nitriles / Q000097:blood / Q000493:pharmacokinetics; D020849:Raloxifene Hydrochloride / Q000097:blood / Q000493:pharmacokinetics / Q000494:pharmacology / Q000627:therapeutic use*; D014230:Triazoles / Q000097:blood / Q000493:pharmacokinetics; D014753:Vinyl Compounds
D048868:Adaptor Proteins, Signal Transducing; D015415:Biomarkers; D053138:Cyclohexenes; C501127:Dkk1 protein, mouse; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D009570:Nitriles; C486030:Sost protein, mouse; D014230:Triazoles; D014753:Vinyl Compounds; D020849:Raloxifene Hydrochloride; C012606:4-vinyl-1-cyclohexene dioxide; D000077289:Letrozole
Bone turnover markers; Letrozole; Micro CT; Raloxifene; Sclerostin and DKK-1; VCD