High bone turnover persisting after vitamin D repletion: beware of calcium deficiency.

Treatment of vitamin D deficiency with vitamin D is a common procedure when taking care of elderly patients, calcium supplementation being added only when calcium dietary intake is insufficient. Here, we report the case of a 58-year-old female who was referred to our unit because of suspicion of Paget's disease of the skull, based on elevated serum alkaline phosphatase and high skull methylene diphosphonate-technetium uptake. She had been prescribed cholecalciferol (100,000 IU/month) and calcium salts for the past 7 months after discovery of severe vitamin D deficiency by her primary care physician. No specific skull bone lesions were observed on both X-ray and computerized tomography. Serum calcium, phosphate and 25(OH) vitamin D levels were normal, while serum C-terminal cross-linked telopeptide, bone alkaline phosphatase and calcitriol were high and daily urinary calcium excretion was low. We found that she had not been compliant with the calcium prescription while vitamin D had been thoroughly taken. We suspected osteomalacia due to calcium deficiency. Both skull uptake and biological abnormalities normalised in few months after adding calcium supplementation to the vitamin D treatment, and spine bone mineral density increased by 9.5 % after 14 months of full treatment. The present case illustrates the necessity for adequate calcium intake during vitamin D repletion to normalise bone mineralisation and turnover and maintain the skeletal integrity.

Space flight is associated with rapid decreases of undercarboxylated osteocalcin and increases of markers of bone resorption without changes in their circadian variation: observations in two cosmonauts.

BACKGROUND: Microgravity induces bone loss by mechanism(s) that remain largely unknown. METHODS: We measured biochemical markers related to bone remodeling in two cosmonauts before, during, and after 21- and 180-day space flights, respectively. RESULTS: During both flights, type I procollagen propeptide and bone alkaline phosphatase decreased as early as 8 days after launch. Undercarboxylated osteocalcin percentage increased early and remained high during both flights. Vitamin K supplementation restored carboxylation of osteocalcin during the long-term flight. Urinary and serum C-telopeptide of type I collagen (CTX) increased as early as day 8 of the flights; the increase was greater in serum than in urine. Pyridinoline, free deoxypyridinoline, and N-telopeptide increased less than CTX during the short-term space flight. The circadian rhythm of bone resorption assessed by urine CTX and free deoxypyridinoline was not altered by microgravity. CONCLUSION: Vitamin K metabolism or action and bone remodeling may be altered in cosmonauts.

Mineralization and alkaline phosphatase activity in collagen lattices populated by human osteoblasts.

Adult human osteoblastic cells were grown in a native type I collagen gel. Proliferation and viability analyses showed that cells rapidly stopped dividing and became blocked in the G0G1 phase (91% on day 13). Carboxyfluorescein diacetate cell staining and flow cytometry showed that osteoblasts were viable for the first 16 days and then viability decreased (58% viable cells on day 22). Osteoblasts were able to retract the matrix. Betaglycerophosphate (betaGP) stimulated the deposition of mineral particles in the collagen network, and electron probe microanalysis showed that they were principally calcium and phosphorus, with a Ca/P ratio of about 1.7. Various times of betaGP supply were tested. We compared 10 mM betaGP added only once at day 0, or continuously from day 0, day 8, or day 21. Mineralization was observed in conditions where betaGP was added at day 0. Furthermore, 10 mM betaGP added once during gel preparation was sufficient to induce mineralization with mineral accumulation up to day 15 whereas the speed of the gel contraction decreased. In every condition, cultures expressed high alkaline phosphatase (ALP) levels as early as day 3, which decreased afterwards. These kinetics might explain why the other conditions did not prove favorable to the mineralization process. The model was used to study the influence of blocking gel retraction. Blocking retraction delayed the ALP activity decrease, but had no effect on mineralization. In conclusion, human adult osteoblasts cultured in native collagen gel stopped proliferation and underwent mineralization very early. This model should be used to investigate the influence of effectors on the early stages of culture.

Bisphosphonate effects in rat unloaded hindlimb bone loss model: three-dimensional microcomputed tomographic, histomorphometric, and densitometric analyses.

The effects of antiresorptive drugs on bone loss remain unclear. Using three-dimensional microtomography, dual X-ray/densitometry, and histomorphometry, we evaluated tiludronate effects in the bone loss model of immobilization in tail-suspended rats after 7, 13, and 23 days. Seventy-eight 12-week-old Wistar male rats were assigned to 13 groups: 1 baseline group, and for each time point, 1 control group treated with vehicle and three tail-suspended groups treated with either tiludronate (0.5 or 5 mg/kg) or vehicle, administered s. c. every other day, during the last week before sacrifice. In primary spongiosa (ISP), immobilization-induced bone loss plateaued after day 7 and was prevented by tiludronate. In secondary spongiosa (IISP), bone loss appeared at day 13 with a decrease in trabecular thickness and trabecular number (Tb.N) as assessed by three-dimensional microtomography. Osteoclastic parameters did not differ in tail-suspended rats versus control rats, whereas bone formation showed a biphasic pattern: after a marked decrease at day 7, osteoblastic activity and recruitment normalized at days 13 and 23, respectively. At day 23, the 80% decrease in bone mass was fully prevented by high-dose tiludronate with an increase in Tb.N without preventing trabecular thinning. In summary, at day 7, tiludronate prevented bone loss in ISP. After day 13, tiludronate prevented bone loss in ISP and IISP despite a further decrease in bone formation. Thus, the preventive effects of tiludronate in this model may be related to the alteration in bone modeling with an increase in Tb.N in ISP and subsequently in IISP.

Recurrence of vertebral fracture with cyclical etidronate therapy in osteoporosis: histomorphometry and X-Ray microanalysis evaluation.

In an open prospective study, we evaluated differences between patients with (wRVF group) and without recurrence of vertebral fracture (woRVF group) during cyclical etidronate therapy for osteoporosis. Thirty-two patients (age 64 +/- 1.8 years) characterized by at least one osteoporotic VF were treated during 1 year. At baseline, body mass index was significantly lower (23.3 +/- 0.6 vs. 26.9 +/- 1.0 kg/m2, p< 0.05), the number of previous VFs was higher (4.0 +/- 0. 4 vs. 2.4 +/- 0.4, NS), and patients were older in the wRVF group as compared with the woRVF group (67.8 +/- 3 vs. 62.6+/- 2.2 year, NS). Trabecular bone volume (11.6 +/- 1.2 vs. 15 +/- 0.9%, p< 0.05) and trabecular number (1.06 +/- 0.08 vs. 1.27 +/- 0.05, p < 0.05) were significantly lower in the wRVF group. None of the baseline resorptive variables differed, whereas the bone formation rate (BFR) was 2-fold lower in the wRVF group (p< 0. 05). After 1 year of treatment, osteoclast number, active eroded surfaces, and resorption depth dramatically decreased in both groups (p< 0. 01). To a lesser extent, the mineral apposition rate and serum alkaline phosphatase level were significantly reduced (p< 0.05). No impaired mineralization was observed. Using X-ray microanalysis, we found no abnormality in bone mineral but a significant increase of the calcium/phosphorus ratio during treatment in the wRVF group. Our results demonstrate that recurrence of VFs within the first year of cyclical etidronate therapy was related neither to a lack of histologic response to the treatment nor induction of an abnormality of mineralization. VFs were more likely in the presence of a decreased BFR and lower trabecular connectivity, providing support for treating osteoporotic patients with etidronate early in the course of the disease.

Space-related bone mineral redistribution and lack of bone mass recovery after reambulation in young rats.

This study reports the effects of a 14-day spaceflight followed by a 14-day reambulation period on bones of 56-day-old male rats compared with synchronous (S) and vivarium (V) control animals. Femur, tibia, and humerus bone mineral densities (BMD); bone calcium and phosphorus concentrations ([Ca2+] and [P]), measured by X-ray microanalysis (XRM), on tibia, vertebra, and calvaria; and histomorphometric data on proximal primary and secondary spongiosae (I and II SP, respectively) of the tibia and humerus were measured. After the flight in flown rats (compared with S), BMD was lower in the distal femur and remained similar to S in humerus and tibia, [Ca2+] and [P] were lower in tibia II SP and higher in calvaria, tibia I SP width and II SP bone volume were lower, resorption was markedly higher in tibia II SP, and no difference in formation parameters was observed. After reambulation, BMD was lower in long bones of both flight and S groups compared with V. Bone loss appeared in humeral II SP and worsened in tibial II SP in flown rats. Tibial formation parameters were higher in flown rats compared with V and S, indicating the onset of an active recovery. Tibial XRM [Ca2+] and [P] in flown rats remained below control levels.

Effect of physical training on bone adaptation in three zones of the rat tibia.

This study as been conducted to examine the effects of physical exercise on the bone trabecular network and the cellular adaptations in three different areas of a single bone, the tibia. Male Wistar rats (9 weeks old) were treadmill-trained for 0, 3, 4, or 5 weeks at 60% of their measured maximal O2 consumption (VO2max). Histomorphometric analysis of the proximal tibia of running and age-matched control groups was performed in the epiphyseal trabecular bone, in the primary spongiosa and in the secondary spongiosa. Dynamic and static bone cell activities and serum calcium and phosphorus levels were measured. VO2max increased significantly by 18.4% after 5 weeks of training. In the epiphysis, a 9% increase in bone volume, associated with more numerous trabeculae (8%) was detected the third week of training. In primary spongiosa a significant increase (6.7%) in newly formed trabeculae was found. In secondary spongiosa bone volume increased significantly by 26.2% the fifth week of exercise and was associated with thicker trabeculae. The number of osteoclast profiles was significantly depressed. Osteoid surfaces and bone formation rate increased significantly in weeks 3 to 5. Serum calcium levels were found to be significantly decreased in weeks 3 and 4. There was no change in osteoid thickness or mineral apposition rate. These results suggest 1) a rapid increase in osteoblastic recruitment without change of the cell activity in response to moderate exercise; 2) a decreased bone resorption associated with a marked increased in bone formation from the third week of training; 3) adaptation of the trabecular network to exercise that seems to be bone-site-dependent, suggesting a cell sensitivity to training-engendered strain distribution within the bone or to strain-related local factors.

[Effects of weightlessness on phospho-calcium metabolism and its hormonal regulation in man during the 51 G Franco-American space flight]. / Effects de l'apesanteur sur le métabolisme phospho-calcique et sa régulation hormonale chez l'homme au cours du vol spatial Franco-Américain 51 G.

During the 51 G franco-american mission in weightlessness, calcium metabolism and hormonal regulation were analyzed in two astronauts (a male, a female) before (30,7 and 4 days) and after (0,2 and 5 days) the 7-day spaceflight. Calcium, phosphate, alkaline phosphatase, GLA protein, 25 hydro-vitamin D, 1-25 dihydroxyvitamin D, parathyroid hormone, 24 h urinary calcium, total, dialysable and nondialysable hydroxyproline and glycosaminoglycans (GAG) were measured in blood and urine. Only urinary parameters are increased after space flight. Blood parameters, in particular hormone measurements, are unchanged. The data indicate stimulation of resorptive activity which could result in bone matrix atrophy and demineralisation. On the contrary, no bone formation impairment is noted since alkaline phosphatase and GLA protein are unchanged. These changes are not dependent on hormonal variations. They could only reflect the mechanical bone adaptation to weightlessness.

[Effects of weightlessness on phosphorus and calcium metabolism and bone remodeling]. / Effets de l'apesanteur sur le métabolisme phospho-calcique et le remodelage osseux.

Weightlessness results in negative calcium balance which can only reflect a redistribution of calcium in the body: the loss of calcium in the faeces and/or urine is constant, but an increase in urinary hydroxyproline indicating bone collagen destruction is not always detectable; moreover, a slowing down of collagen maturation may be suspected. Bone analysis by histomorphometry in animals and by indirect, non-invasive methods in man shows a decrease in bone mass. However, this bone tissue atrophy might only reflect excessive ageing of the bone during weightlessness, as suggested by slow bone formation and lack of variation in bone resorption. Since the experimental results obtained in men and animals during simulated weightlessness on earth are not strictly identical with those observed in space- flights, their validity may be questioned. Additional studies (notably histomorphometric studies) are therefore required for a better knowledge, as well as prevention, of the problems raised by human life in space.