phosphorus-radioisotopes and Weight-Loss

Bisphosphonates, potent inhibitors of bone resorption, have been used clinically to correct the continued loss of bone mass in osteoporosis and in other conditions. However, there has been some concern that long-term treatment with these compounds, as well as more recently developed drugs, may also decrease the rate of bone formation. Bisphosphonates, which are strongly bound to hydroxyapatite crystals, may alter the structure and reactivity of the crystals, interfere with new crystal nucleation and growth, as well as alter the short-range order of newly formed crystals. We have investigated the chemistry and structure of the solid calcium-phosphate mineral phase of lumbar vertebrae of ovariectomized, 6.5-month-old rats treated with bisphosphonates for 1 year after onset of osteopenia. Appropriate control groups were used for comparison. The techniques used to assess the mineral phase were chemical analyses, Fourier transform-infrared (FT-IR) and FT-Raman spectroscopy, FT-IR microspectroscopy, and phosphorus-31 magic-angle-sample spinning nuclear magnetic resonance spectroscopy ((31)P MAS NMR). The (31)P MAS NMR spectra of trabecular bone of lumbar vertebrae of control, ovariectomized, and treated animals were similar. However, there were several significant differences in the results obtained by FT-IR spectroscopy of the whole tissue samples, FT-IR microspectroscopy of sections of bone, and chemical analyses. For example, whereas chemical analyses demonstrated that the CO(3) content of the mineral phase of the ovariectomized animals was decreased compared with controls, FT-IR microspectroscopy of bone sections showed no changes in the relative CO(3) content, but some changes in the environment of the CO(3) groups. However, chemical analyses of the crystals, combined with data from all three spectroscopic methods and with data from serum analysis, did indicate small changes in the mineral phase after ovariectomy, corrected after treatment with bisphosphonates. In any event, the chemical and structural data in the present studies demonstrate that the bisphosphonate, tiludronate, does not significantly alter the mineral components of bone after 1 year of treatment during the course of which bone loss was reversed.

Topics: Animals; Apatites; Bone Diseases, Metabolic; Bone Resorption; Calcium; Cholecalciferol; Diphosphonates; Disease Models, Animal; Female; Lumbar Vertebrae; Magnetic Resonance Spectroscopy; Ovariectomy; Parathyroid Hormone; Phosphorus; Phosphorus Radioisotopes; Rats; Rats, Sprague-Dawley; Spectroscopy, Fourier Transform Infrared; Weight Loss

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] treatment in vitamin D-deficient (-D) rats results in a dose-dependent decrease in phosphorylation of a 91-kDa protein (PP-D91) in particulate fractions of the kidney. This recently reported 1,25(OH)2D3 effect was examined in detail herein. In contrast to the pattern expected of a rapid signal transduction event, time course (4 h-7 days) experiments demonstrated that PP-D91 phosphorylation was not decreased until 3-5 days 1,25(OH)2D3 treatment, resulting in a 61 +/- 3% (P < 0.01, n = 3) decrease in PP-D91 phosphorylation by 7 days. These effects paralleled increases in plasma calcium from 9.3 +/- 0.6 to 13.9 +/- 0.7 mg/dl after 0 vs 7 days 1,25(OH)2D3 treatment, respectively. Subcellular fractionation demonstrated that the renal PP-D91 was predominantly localized and 1,25(OH)2D3-regulated in crude mitochondrial and microsomal fractions. Further, PP-D91 was present and 1,25(OH)2D3-regulated in enriched preparations of both proximal and distal renal tubule segments. Tissue distribution studies demonstrated that the PP-D91 was predominantly present and 1,25(OH)2D3 regulated in the kidney, although low levels of a vitamin D-independent phosphorylated band of similar size were observed in the lung and heart. In contrast to 1,25(OH)2D3, estradiol-17B treatment (1 mg/day x 7 day) significantly (P < 0.01) increased PP-D91 phosphorylation in kidney of both -D and +D rats (increased 118.5 +/- 10.6 and 81.9 +/- 6.3%, respectively). Phosphoamino acid analysis after PP-D91 phosphorylation, isolation, and proteolysis indicated that these hormones alter 32P incorporation into phosphoserine residues. In conclusion, the 1,25(OH)2D3 effect to reduce PP-D91 phosphorylation in particulate fractions of the rat kidney is a protracted, tissue-specific effect which parallels elevated plasma calcium levels in this model. Moreover, renal PP-D91 phosphorylation is differentially regulated by 1,25(OH)2D3 vs E2 treatment and occurs on phosphoserine residues. The parallel between decreased PP-D91 phosphorylation and 1,25(OH)2D3-induced hypercalcemia may suggest a role for PP-D91 in the renal response to hypervitaminosis D.

Topics: Animals; Calcitriol; Calcium; Cell Fractionation; Electrophoresis, Polyacrylamide Gel; Estradiol; Kidney; Male; Phosphoamino Acids; Phosphoproteins; Phosphorus Radioisotopes; Phosphorylation; Phosphoserine; Progesterone; Rats; Rats, Sprague-Dawley; Testosterone; Tissue Distribution; Weight Loss