Raloxifene analog (LY117018 HCL) ameliorates cyclosporin A—Induced osteopenia in oophorectomized rats

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Abstract
Cyclosporin A (CsA) administered to the oophorectomized (Ox) rat exacerbates the high turnover osteopenia associated with estrogen deficiency. 17β‐estradiol replacement therapy prevents this bone loss. The aim of this study was to see whether an estrogen‐like compound, Raloxifene analog (LY117018 HCL, Ral) could likewise ameliorate CsA‐induced osteopenia in the Ox rat. Sixty 6‐month‐old Sprague‐Dawley rats, divided into five groups, underwent oophorectomy. One group acted as a basal group and the others received either vehicle (group B), CsA 15 mg/kg/day (group C), Ral 3 mg/kg/day (group D), or CsA 15 mg/kg/day and Ral 3 mg/kg/day (group E) for 28 days by gavage. A sixth sham operated group of 12 rats received vehicle only (group A). Rats were weighed and bled on days 0, 14, and 28 for measurement of ionized calcium, glucose, osteocalcin (BGP), 17β‐estradiol, and 1,25‐dihydroxyvitamin D3 (1,25[OH]2D3). Tibiae were removed on day 28 for bone histomorphometry after double tetracycline and calcein labeling. Oophorectomy caused a significant gain in weight in groups B and C which was prevented by Ral in groups D and E. Randomized blood glucose levels and 1,25(OH)2D3 levels were elevated in both CsA‐treated groups. Blood ionized calcium levels were lower in vehicle (group B) compared with sham (group A) on day 28. Ox (group B) had significantly higher serum BGP levels compared with sham‐operated rats. Serum BGP levels were further elevated in group C compared with vehicle and were lowered in both Ral‐treated groups to vehicle levels by day 28. Bone histomorphometry revealed a high turnover osteopenia with increased parameters of bone formation and resorption and loss of cancellous bone volume postoophorectomy (group B). CsA (group C) exacerbated the effects of oophorectomy. Ral (group D) completely prevented the high turnover osteopenia caused by oophorectomy and was able to attenuate substantially the effects of CsA in the Ox rat (group E). Ral therapy ameliorated CsA‐induced osteopenia in the Ox rat and might prove a useful agent in preventing bone loss in postmenopausal women receiving CsA.
Funding Information
  • Eli Lilly
  • Co.