Osteotoxicity after chronic dietary administration of 13-cis-retinoic acid, retinyl palmitate or selenium in mice exposed to tumor initiation and promotion.

In view of the clinical trials of retinoids as therapeutic agents for premalignant skin lesions, a radiographic study was undertaken to measure skeletal toxicities after chronic dietary administration of retinoids in mice exposed to tumor initiation and promotion. CD-1 mice were initiated with 0.15 moles of 7,12-dimethylbenz[a]anthracene and promoted twice daily with 8 nmoles of 12-0-tetradecanoylphorbol-13-acetate for 23 weeks. Diets were supplemented with 60 IU, 200 IU, or 700 IU of retinyl palmitate (RP) per g diet. After 5 weeks, the 700 IU of RP /g diet was lowered to 350 IU/g diet. Administration of these diets to mice during the 23 weeks of tumor promotion resulted in a 0-fold, 2-fold, or 10-fold increase in bone fractures, respectively. Osteoporotic bone lesions identified on radiographs rose 0-fold, 0-fold, and 10-fold at the respective doses, whereas metaphyseal flares increased 0-fold, 1.4-fold, and 3.6-fold. Bone deformities were augmented 0-fold, 1.8-fold and 2.9-fold at the respective doses. Addition of selenium (2 ppm in the drinking water) did not alter the bone toxicity of RP. 13-cis-retinoic acid (CRA) was less toxic at 700 IU/g diet than was RP at that dose, as evidenced by the death of 12 of 70 mice by the 6th week of dietary RP and no deaths in the 35 mice fed 700 IU CRA/g diet for 23 weeks. CRA at 700 IU/g diet resulted in 3/4 as many osteoporotic bones, 1/3 as many bone fractures, 4/5 as many metaphyseal flares, and a similar number of bone deformities as mice fed 700/350 IU/g diet. At the dose of 200 IU/g food, osteotoxicities were similar in the mice fed diets supplemented with RP and CRA. Thus, the light dose of CRA (700 IU/g diet) was less toxic than the high dose of, RP but at a lower dose (200 IU/g), CRA was as osteotoxic as was RP. Bone fractures in mice exposed to prolonged dietary administration of retinoids was a more sensitive index of retinoid toxicity than was body weight. We have detected osteotoxicity in mice at a total dose of CRA which was about twice the total dose used clinically.