[Effects of alfacalcidol on osteoporosis in ovariectomized rats]

OBJECTIVE

To investigate the effects of alfacalcidol on osteoporosis in rats induced by ovariectomy (OVX).

METHODS

Fifty-three virgin female Wistar rats of six months old were divided into 6 groups: (1) rats in baseline group (base) were sacrificed what 6 months before OVX, and those in the other 5 groups were either bilaterally OVX or sham-operated (sham) as follows: (2) Sham; (3) OVX baseline (OVXb); (4) OVX end (OVXe); (5) OVX + 17beta-estradiol 20 microgram/kg.(-1) SC. (O + E); and (6) OVX + alfacalcidol 0.1 microgram/kg.(-1) oral (O + VD). Rats in OVXb group were sacrificed 6 weeks after OVX and the others were sacrificed 14 weeks after surgery. Alfacalcidol (TEVA, Israel) was fed orally at 6 weeks after OVX and lasted for 8 weeks. Urine and serum samples were collected before sacrifice to determine the bone turnover markers. The right tibia was processed undecalcified for histomorphometric analysis, and the right femur was prepared for pQCT scanning and bone biomechanical measurement with indentation test.

RESULTS

Treatment of OVX rats with alfacalcidol (O + VD) increased tibial cancellous bone volume in histomorphometric analysis (12.0% +/- 1.1% vs 5.8% +/- 1.3%, P < 0.01). pQCT scanning showed that trabecular BMC and BMD were sharply elevated in O + VD group compared with OVXe group, increased 109.2% and 133.1% respectively (P < 0.01). In consistency with these changes in mechanical competency of cancellous bone in distal femur, maximal load was enhanced in O + VD group compared with OVXe group (21.3% +/- 4.0% N vs 7.9% +/- 1.9% N, P < 0.05). All these changes in O + VD group were similar to those in 17beta-estradiol treatment group (O + E). Serum calcium concentration increased in O + VD group. Histomorphometric and biochemical indices of bone resorption reduced in O + VD group.

CONCLUSION

Alfacalcidol effectively prevent bone loss in OVX rats and restore partly the trabecula, with evidenced increasing density, contents as well as maximal loads of cancellous bone, and reduce bone resorption.

Synthesis and biological activities of the two C(23) epimers of 1alpha,23,25-trihydroxy-24-oxo-19-nor-vitamin D(3): novel analogs of 1alpha,23(S),25-trihydroxy-24-oxo-vitamin D(3), a natural metabolite of 1alpha,25-dihydroxyvitamin D(3)

In a previous report, we indicated that 1alpha,23(S), 25-trihydroxy-24-oxovitamin D(3) [1alpha,23(S), 25(OH)(3)-24-oxo-D(3)], a natural metabolite of 1alpha, 25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is almost equipotent to 1alpha,25(OH)(2)D(3) in suppressing parathyroid hormone (PTH) secretion (Lee et al., 1997. Biochemistry 36, 9429-9437). Also, 1alpha,23(S),25(OH)(3)-24-oxo-D(3) has been shown to possess only weak in vivo calcemic actions. Thus, vitamin D(3) analogs structurally related to 1alpha,23(S),25(OH)(3)-24-oxo-D(3) may have therapeutic value. Furthermore, biologic activity studies of various synthetic analogs of 1alpha,25(OH)(2)D(3) showed that the removal of carbon-19 (C-19) reduces the calcemic activity of 1alpha, 25(OH)(2)D(3.) Therefore, in an attempt to produce vitamin D(3) analogs with a better therapeutic index, we synthesized C(23) epimers of 1alpha,23,25(OH)(3)-24-oxo-19-nor-vitamin D(3) [1alpha,23, 25(OH)(3)-24-oxo-19-nor-D(3)]. The two epimers were compared to 1alpha,25(OH)(2)-19-nor-D(3) and 1alpha,25(OH)(2)D(3) in their ability to generate biologic activities in several in vitro assay systems. In the assay measuring the suppression of parathyroid hormone (PTH) secretion in bovine parathyroid cells, 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3) was as potent as 1alpha, 25(OH)(2)-19-nor-D(3) but was less potent than 1alpha,25(OH)(2)D(3). In the same assay 1alpha,23(R),25(OH)(3)-24-oxo-19-nor-D(3) exhibited greater potency than 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3). In the assays measuring the ability of vitamin D compounds to inhibit clonal growth and to induce differentiation of human promyelocytic leukemia (HL-60) cells, 1alpha,23(S),25(OH)(3)-24-oxo-19-nor-D(3) was less potent than 1alpha,25(OH)(2)-19-nor-D(3) but was equipotent to 1alpha, 25(OH)(2)D(3). More importantly, in the same assays, 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3) was more potent than 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3) and was equipotent to 1alpha, 25(OH)(2)-19-nor-D(3). Also, the vitamin D receptor-mediated transcriptional activity of 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3) was almost equal to that of 1alpha, 25(OH)(2)-19-nor-D(3), but higher than that of 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3). This finding explains in part the greater in vitro biologic activities of 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3). In summary, our results indicate that 1alpha,23(R),25(OH)(3)-24-oxo-19-nor-D(3) and to a lesser extent 1alpha,23(S),25(OH)(3)-24-oxo-19-nor-D(3) are potent 19-nor vitamin D(3) analogs, which suppress PTH secretion in bovine parathyroid cells and strongly inhibit clonal growth and induce differentiation of HL-60 cells in vitro.

Alfacalcidol inhibits bone resorption and stimulates formation in an ovariectomized rat model of osteoporosis: distinct actions from estrogen

Although alfacalcidol has been widely used for the treatment of osteoporosis in certain countries, its mechanism of action in bone, especially in the vitamin D-replete state, remains unclear. Here we provide histomorphometric as well as biochemical evidence that alfacalcidol suppresses osteoclastic bone resorption in an ovariectomized rat model of osteoporosis. Furthermore, when compared with 17beta-estradiol, a representative antiresorptive drug, it is evident that alfacalcidol causes a dose-dependent suppression of bone resorption, and yet maintains or even stimulates bone formation, as reflected in increases in serum osteocalcin levels and bone formation rate at both trabecular and cortical sites. 17beta-Estradiol, which suppresses bone resorption to the same extent as alfacalcidol, causes a parallel reduction in the biochemical and histomorphometric markers of bone formation. As a final outcome, treatment with alfacalcidol increases bone mineral density and improves mechanical strength more effectively than 17beta-estradiol, with a more pronounced difference in cortical bone. We conclude that estrogens depress bone turnover primarily by suppressing bone resorption and, as a consequence, bone formation as well, whereas alfacalcidol "supercouples" these processes, in that it suppresses bone resorption while maintaining or stimulating bone formation.

Induction of differentiation by 1alpha-hydroxyvitamin D(5) in T47D human breast cancer cells and its interaction with vitamin D receptors

The role of the active metabolite of vitamin D, 1,25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), in cell differentiation is well established. However, its use as a differentiating agent in a clinical setting is precluded due to its hypercalcaemic activity. Recently, we synthesised a relatively non-calcaemic analogue of vitamin D(5), 1alpha-hydroxyvitamin D(5) (1alpha(OH)D(5)), which inhibited the development of carcinogen-induced mammary lesions in culture and suppressed the incidence of chemically induced mammary carcinogmas in rats. In the present study, we determined the differentiating effects of 1alpha-(OH)D(5) in T47D human breast cancer cells and compared its effects with 1,25(OH)(2)D(3). Cells incubated with either 10 or 100 nM of the analogues inhibited cell proliferation in a dose-dependent manner, as measured by the dimethylthiazolyl-2,5-diphenyltetrazolium bromide (MTT) assay. Similar growth-inhibitory effects were also observed for MCF10(neo) cells. Both vitamin D analogues induced cell differentiation, as determined by induction of casein expression and lipid production. However, MCF10(neo) cells failed to respond to either vitamin D analogue and did not undergo cell differentiation. Since the cell differentiating effect of vitamin D is considered to be mediated via the vitamin D receptor (VDR), we examined the induction of VDR using reverse transcriptase-polymerase chain reaction (RT-PCR) in both cells. The results showed that, in T47D cells, both 1,25(OH)(2)D(3) and 1alpha(OH)D(5) induced VDR in a dose-dependent manner. Moreover, both analogues of vitamin D upregulated the expression of vitamin D response element-chloramphenicol acetyl transferase (VDRE-CAT). These results collectively indicate that 1alpha-(OH)D(5) may mediate its cell-differentiating action via VDR in a manner similar to that of 1,25(OH)(2)D(3).

Association of transforming growth factor beta1 genotype with therapeutic response to active vitamin D for postmenopausal osteoporosis

Transforming growth factor beta (TGF-beta) is an important regulator of bone metabolism, its effects being intertwined with those of estrogen and vitamin D. A T-->C polymorphism in exon 1 of the TGF-beta1 gene, which results in the substitution of proline for leucine, is associated with bone mineral density (BMD). However, it is not known whether this polymorphism affects the response to treatment with active vitamin D or to hormone replacement therapy (HRT) in individuals with osteoporosis. Changes in BMD at the lumbar spine (L2-L4 BMD) were compared among TGF-beta1 genotypes in 363 postmenopausal Japanese women who were divided into three groups: an untreated, control group (n = 130), an active vitamin D treatment group (n = 117), and an HRT group (n = 116). TGF-beta1 genotype was determined with an allele-specific polymerase chain reaction assay. In the control group, the rate of bone loss decreased according to the rank order of genotypes TT (homozygous for the T allele) > TC (heterozygous) > CC (homozygous for the C allele), with a significant difference detected between the CC and TT genotypes. The positive response of L2-L4 BMD to HRT increased according to the rank order of genotypes TT < TC < CC, although the differences among genotypes were not statistically significant. Individuals with the CC genotype responded to active vitamin D treatment with an annual increase in L2-L4 BMD of 1.6%, whereas those with the TT or TC genotypes similarly treated lost bone to a similar extent as did untreated subjects of the corresponding genotype. These results suggest that TGF-beta1 genotype is associated with both the rate of bone loss and the response to active vitamin D treatment.

Effect of low-calcium hemodialysate on bone metabolism

In the present study, we investigated the kinetics of bone metabolism by determining serum bone metabolic markers and quantifying bone mineral density by dual-energy X-ray absorptiometry to clarify the effect of long-term use of low-calcium hemodialysate on bone metabolism. After changing the calcium concentration in the dialysate from 3.0 mEq/l to 2.5 mEq/l, serum intact parathyroid hormone level, serum highly sensitive parathyroid hormone level, and serum bone metabolic markers were determined in ten patients with chronic nondiabetic renal insufficiency during 1 year. The doses of an oral phosphate binder and activated vitamin D were carefully regulated to control serum ionized calcium levels and serum inorganic phosphorus levels. Bone mineral density was determined at the distal 1/3 and 1/6 of the radius on the nonshunt side. As a result, the required amount of oral phosphate binder was increased; however, there was no need to significantly increase the amount of activated vitamin D. Intact parathyroid hormone showed no significant variation, but the highly sensitive parathyroid hormone was significantly increased. There were no significant changes in any bone metabolic markers or in bone mineral density. From these study results, it was found that it was difficult to increase the dose of activated vitamin D even if low-calcium hemodialysate was used, and that during use of the low-calcium hemodialysate the serum level of parathyroid hormone tended to increase but led to neither acceleration of bone turnover nor a decrease in bone mineral density.

Differentiation of human breast carcinoma cells by a novel vitamin D analog: 1alpha-hydroxyvitamin D5

The active metabolite of vitamin D, 1alpha,25-dihydroxyvitamin D3, can induce differentiation in breast cancer cells; however, it is hypercalcemic in vivo. Therefore, development of non-calcemic analogs of vitamin D has received considerable attention. Recently, we synthesized an analog of vitamin D [1alpha(OH)D5] that exhibits much less calcemic activity than 1alpha,25-dihydroxyvitamin D3. In this study, we evaluated the cell-differentiating action of 1alpha(OH)D5 in breast cancer cells. Following 10 days treatment with 1alpha(OH)D5 [(10-7 M) in UISO-BCA-4], we observed induction of intracytoplasmic casein, intracytoplasmic lipid droplets, ICAM-1, nm23, and specific biomarkers associated with breast cell differentiation. 1alpha(OH)D5 treatment also showed induction of vitamin D receptor and TGFbeta1 proteins. UISO-BCA-4 cells pretreated for 10 days in vitro with 1 microM 1alpha(OH)D5 failed to form tumors when transplanted into athymic mice. Similarly, 4 and 8 ng 1alpha(OH)D5 treatment three times weekly inhibited the growth of UISO-BCA-4 cells injected into athymic mice. These results suggest that this new vitamin D analog may be of significant therapeutic value for breast cancer.

1Alpha-hydroxyvitamin D3 prevents the decrease of bone mineral density in lactating beagles

We assessed the change of bone mineral density (BMD) in lactating beagles with dual energy X-ray absorptiometry (DXA) and the preventive effect of 1alpha-hydroxyvitamin D3 (1alpha(OH)D3) on the BMD. Beagles, two to five years old, were used for detecting the time course change of BMD. Since the coefficient of variation (CV(%)) on detecting lumber vertebral (L2-L4) and tibial BMD by DXA was about 0.5%, DXA was useful to detect the change of BMD in beagles. There was a marked decrease in vertebral BMD during lactational period in the control group. The BMD levels after weaning were found to reverse to the initial level at mating. The same tendency was observed in tibial BMD as vertebral BMD, though the BMD changes were not marked. Beagles were administered at a dose of 0.1 microg/kg of 1alpha(OH)D3 three times in a week, and it was found to suppress the decrease in vertebral BMD during the breast feeding period. Also, the administration of 1alpha(OH)D3 promoted the prevention of decreased BMD during lactation both in vertebrae and tibiae. Significant effects of 1alpha(OH)D3 administration on tibial BMD were not observed. No adverse effects, such as hypercalcemia and hypercalciuria, were observed during the experimental period. Therefore, DXA was useful for detecting the changes of BMD in lactating beagles and the change of BMD was marked in lumber vertebrae, which are rich in trabecular bone. The preventive effect of 1alpha(OH)D3 on the decrease of BMD during the lactation period was observed in beagles.

The effect of vitamin K and D supplementation on ovariectomy-induced bone loss

This study was designed to assess the effect of vitamin K and D supplementation on ovariectomy-induced bone loss. Female Sprague-Dawley rats aged 8-9 months were ovariectomized (OVX) or sham operated and divided into five experimental groups: (1) ovariectomy (OVX), (2) OVX plus vitamin K supplementation, (3) OVX plus vitamin D supplementation, (4) OVX plus vitamin K and vitamin D supplementation, and (5) sham operation. The trabecular bone area was estimated by bone histomorphometry by microradiography and histological examination. Bone loss in OVX plus vitamin K and vitamin D group was significantly reduced at both 7 and 14 weeks compared with the OVX group. No significant bone loss in OVX plus vitamin K or OVX plus vitamin D groups was found. A similar effect of vitamin K and D supplementation on ovariectomy-induced bone loss was recognized in histological examination. Our findings indicate that vitamins K and D may have a synergistic effect on reducing bone loss. This is valuable information for the treatment of bone loss in postmenopausal women with osteoporosis.

Alfacalcidol and calcitriol in the prevention of bone loss after organ transplantation

There is increasing evidence that D-hormones (active vitamin D metabolites) are effective agents in preventing posttransplantation bone loss of various organs. This effect may relate to several mechanisms including reversal of secondary hyperparathyroidism from cyclosporine, reversal of corticosteroid effects on bone, or immunomodulatory effects with corticosteroid sparing. Further clinical trials are necessary to establish their comparative efficacy to other agents, but D-hormones should be considered as prophylactic therapy in patients undergoing organ transplantation.

The advantage of alfacalcidol over vitamin D in the treatment of osteoporosis

Although alfacalcidol is widely used in the treatment of osteoporosis, its mechanism of action in bone is not fully understood. Alfacalcidol stimulates intestinal calcium (Ca) absorption, increases urinary Ca excretion and serum Ca levels, and suppresses parathyroid hormone (PTH) secretion. It remains to be clarified, especially under vitamin D-replete conditions, whether alfacalcidol exerts skeletal effects solely via these Ca-related effects, whether the resultant suppression of PTH is a prerequisite for the skeletal actions of alfacalcidol, and, by inference, whether alfacalcidol has an advantage over vitamin D in the treatment of osteoporosis. To address these issues, we (1) compared the effects of alfacalcidol p.o. (0.025-0.1 microg/kg BW) vis-à-vis vitamin D(3) (50-400 microg/kg BW) on bone loss in 8-month-old, ovariectomized (OVX) rats as a function of their Ca-related effects, and (2) examined whether the skeletal effects of alfacalcidol occur independently of suppression of PTH, using parathyroidectomized (PTX) rats continuously infused with hPTH(1-34). The results indicate that (1) in OVX rats, alfacalcidol increases BMD and bone strength more effectively than vitamin D(3) at given urinary and serum Ca levels: larger doses of vitamin D(3) are required to produce a similar BMD-increasing effect, in the face of hypercalcemia and compromised bone quality; (2) at doses that maintain serum Ca below 10 mg/dl, alfacalcidol suppresses urinary deoxypyridinoline excretion more effectively than vitamin D(3); and (3) alfacalcidol is capable of increasing bone mass in PTX rats with continuous infusion of PTH, and therefore acts independently of PTH levels. It is suggested that alfacalcidol exerts bone-protective effects independently of its Ca-related effects, and is in this respect superior to vitamin D(3), and that the skeletal actions of alfacalcidol take place, at least in part, independently of suppression of PTH. Together, these results provide a rationale for the clinical utility of alfacalcidol and its advantage over vitamin D(3) in the treatment of osteoporosis.

Prevention of osteopenia induced with a gonadotropin-releasing hormone agonist in rats

We investigated the effects of conjugated estrogens as an add-back replacement drug, incadronate sodium as a bisphosphonate, and alfacalcidol as a vitamin D(3) analog on femoral bone mineral density (BMD) and bone mineral content (BMC) in female rats chronically treated with the gonadotropin-releasing hormone (GnRH) agonist leuprorelin acetate. The chemical castration of the rats by the administration of GnRH agonist for 16 weeks reduced the BMD values to 92.3%, 91.3%, and 93.3% of those of the normal control animals in the whole femur, metaphysis, and diaphysis of the femur, respectively. The BMC value was decreased to 91.0% of that of the normal control animals by the chronic GnRH agonist treatment. However, a simultaneous 8-week administration of conjugated estrogens, bisphosphonate, and vitamin D(3) analog markedly augmented the BMC values to 110.3%, 110.1%, and 114.4%, respectively, of those in the rats treated with the GnRH agonist alone. These findings indicate that antiosteoporotic agents could be useful for preventing induced osteopenia under the careful monitoring of biochemical markers of osteoblastic activity or bone resorption and BMD or BMC in patients undergoing GnRH treatment.

Urinary pyridinoline and deoxypyridinoline as bone metabolic markers in predicting therapeutic effects of estrogen and alfacalcidol in women with osteoporosis

The purpose of the present study was to evaluate the clinical usefulness of urinary pyridinoline (Pyr) and deoxypyridinoline (Dpyr) in predicting therapeutic effects of estrogen and alfacalcidol (1alpha-D3) in patients with postmenopausal osteoporosis. We measured urinary excretion of Pyr and Dpyr, and determined bone mineral density (BMD) using a dual-energy x-ray absorptiometry in 48 women with osteoporosis (average age, 55.9+/-8.4 years). Patients were treated with estrogen (HRT, n = 13), 1alpha-D3 (n = 20), or calcium alone (n = 15). Baseline mean levels of urinary Pyr and Dpyr were significantly higher in the 48 patients compared to those in the age-matched postmenopausal women. The levels of urinary Pyr and Dpyr were inversely correlated with BMD. After treatment with estrogen or 1alpha-D3, a significant decrease of urinary Pyr and Dpyr was observed, and elevated urinary Pyr and Dpyr were reduced to the level in premenopausal women. A significant inverse correlation was found in Pyr and Dpyr at 6 months and in lumbar BMD after 24 months of treatment (r = -0.43 to -0.52; P < 0.01). We concluded that urinary Pyr and Dpyr have clinical utility for predicting response to estrogen and 1alpha-D3 therapy of osteoporosis patients.

Effect of intravenous alfacalcidol on lymphocyte phenotyping in hemodialysis patients

Chronic renal failure is associated with decreased production of active vitamin D and also results in altered lymphocyte population. We studied the effect of alfacalcidol on lymphocyte phenotype. There were 15 patients (10 males, 5 females) with a mean age of 54.3+/-14.4 years who had been on chronic maintenance haemodialysis for a mean period of 3.2+/-1.5 years. Intravenous alfacalcidol was given three times weekly during dialysis for a duration of 6 months. Our results show a significant increase in NK cells from 0.20+/-0.12 to 0.27+/-0.28 (P=0.001), without a significant change in CD2, CD19, CD4, CD8 population, and CD4/CD8 ratio.

Long-term effects of intermittent oral alphacalcidol, calcium carbonate and low-calcium dialysis (1.25 mmol L-1) on secondary hyperparathyroidism in patients on continuous ambulatory peritoneal dialysis

OBJECTIVES

(i) To examine the effect of alphacalcidol [1 alpha(OH)D3] given as an oral dose twice weekly in combination with CaCO3 and low-calcium dialysis (1.25 mmol L-1) on the secondary hyperparathyroidism in continuous ambulatory peritoneal dialysis (CAPD). (ii) To examine the changes in peritoneal mass transfer for calcium, phosphorus, magnesium, lactate, creatinine, urea, glucose, pH and albumin after shift to low-calcium dialysis solution.

DESIGN

An open study in patients on CAPD.

SETTING

Renal division, Rigshospitalet, Copenhagen.

SUBJECTS

Thirty-nine patients were included and completed 12 weeks of treatment. Thirty of the patients completed 52 weeks of treatment. A peritoneal equilibrium test (PET) was performed in seven patients.

INTERVENTIONS

Following two sets of blood samples obtained as basal values the calcium concentration was reduced in the dialysis fluid from 1.75 mmol L-1 to 1.25 mmol L-1. Increasing doses of oral 1 alpha(OH)D3 were then administered under careful control of p-ionized calcium (p-Ca2+) and p-inorganic phosphate (p-P1). Blood samples were obtained every 2-4 weeks for 52 weeks. PET was performed using standard dialysis fluid and 1 week later using low-calcium dialysis fluid after a preceding overnight dwell. Two litres of glucose 22.7 mg mL-1 were used.

MAIN OUTCOME MEASURES

Intact parathyroid hormone (PTH), p-Ca2+, p-P1, doses of CaCO3, doses of 1 alpha(OH)D3, peritoneal mass transfer for calcium, inorganic phosphate, magnesium, lactate, creatinine, urea, glucose and albumin.

RESULTS

Thirty nine patients with initial PTH values 144 +/- 26 pg mL-1 were followed for 12 weeks and 30 patients for 52 weeks. A negative calcium balance was induced after shifting to low-calcium dialysis fluid. After 2 weeks of treatment a significant increase of PTH by approximately 60% and a small but significant decrease of p-Ca2+ was observed. After 12 weeks of treatment with increasing doses of 1 alpha(OH)D3 and CaCO3, PTH was again reduced to levels not significantly different from the initial values. After 52 weeks of treatment no deterioration of the secondary hyperparathyroidism was seen.

CONCLUSIONS

A calcium concentration of 1.25 mmol L-1 in the CAPD dialysate made it possible to reduce the amount of aluminium-containing phosphate binder, to increase the doses of CaCO3 and to use pulse oral 1 alpha(OH)D3 without causing severe hyper-calcaemia in the patients. After a short elevation of PTH, the PTH levels remained at normal or near normal levels and the long-term results clearly demonstrated that an aggravation of the secondary hyperparathyroidism could be inhibited.

Inhibitory effect of 1alpha-hydroxyvitamin D3 on N-methyl-N'-nitro-N-nitrosoguanidine-induced gastrointestinal carcinogenesis in Wistar rats

The effect of 1alpha-hydroxyvitamin D3 (1alpha(OH)D3) on gastrointestinal carcinogenesis induced by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) was investigated in male Wistar rats. After oral treatment with 0.01% MNNG for 24 weeks, rats were given 0.04 microg of 1alpha(OH)D3 or its vehicle by gastric intubation three times a week for 24 weeks. The incidence of gastrointestinal tumors was 16/30 (53%) in rats treated with MNNG alone, 16/30 (53%) in those treated with MNNG plus vehicle and 8/30 (27%, P < 0.05) in those treated with MNNG plus 1alpha(OH)D3. The number of tumors per rat in the group treated with MNNG plus 1alpha(OH)D3 was half those in the control groups (P < 0.05). Results indicated that a non-hypercalcemic dose of 1alpha(OH)D3 had an inhibitory effect on MNNG-induced duodeno-intestinal carcinogenesis.

A highly sensitive method for large-scale measurements of 1,25-dihydroxyvitamin D

A quantitative method for measuring 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) was developed utilizing a luciferase reporter gene under the control of the highly inducible 25-hydroxyvitamin D3 24-hydroxylase promoter in a stably transfected cell line. Transient transfections with constructs containing the 24-hydroxylase gene promoter 5' to a luciferase reporter were first performed in cell lines with high levels of vitamin D receptor, i.e., the rat osteosarcoma (ROS 17/2.8) and human breast cancer (T-47D) cell lines. ROS 17/2.8 cells, stably transfected with the plasmid, gave a 60-fold stimulation with 10(-10) M 1,25-(OH)2D3. A standard curve was constructed showing a large range of response to 1,25-(OH)2D3 (1 pg to 1 ng). The assay was adapted to microtiter plates, which permits a large number of samples to be assayed simultaneously. Other metabolites of vitamin D and analogs such as 25-hydroxyvitamin D3, 24,25-dihydroxyvitamin D3, and 1 alpha-hydroxyvitamin D3 have negligible effects on the detection of 1,25-(OH)2D3, thus eliminating the need for purification of sample. The sensitivity of the method permitted the use of 100 microliters of serum with excellent results. Comparison of this method with a commercially available assay demonstrates that it gives higher sensitivity, simpler manipulations, and comparable results.

Utilization of phytate and nonphytate phosphorus in chicks as affected by source and amount of vitamin D3

Commercial and laboratory-strain crossbred chicks responded (P < .01) markedly to 1alpha-hydroxycholecalciferol (1alpha-OH D3) during the 2nd and 3rd wk of life. Bone-ash responses exceeded 50% when this compound was added at 20 microg/kg to phosphorus (P)-deficient corn-soybean meal diets containing surfeit levels (25 microg/kg) of cholecalciferol (D3). Phosphorus excretion was decreased (P < .01) and, thus, retention was increased (P < .01) when 1alpha-OH D3 was supplemented. A P-deficient (.10% P) casein-amino acid purified diet, devoid of D3, was used to determine whether 15 microg/kg of D3 was sufficient to facilitate optimal absorption of the nonphytate P contained in this diet. Bone ash responded to .075% P addition (KH2PO4), and chicks fed diets with .175% nonphytate P exhibited further bone-ash responses to 15 microg/kg of D3 or 10 microg/kg 1alpha-OH D3. Higher levels of either of these D3 compounds did not produce additional responses. This suggested that 15 to 25 microg/kg of D3 in a P-deficient corn-soybean meal diet (.28% phytate P and .14% nonphytate P) is more than adequate to facilitate optimal absorption of the nonphytate P present in the diet. A P-deficient casein-dextrose diet (.13% nonphytate P and 15 microg/kg D3) was fed in the final chick assay, and chicks fed this diet did not show bone ash responses to 1alpha-OH D3 or to microbial-derived phytase (1,470 units/kg). Thus, with P-deficient corn-soybean meal diets containing at least 15 microg D3/kg, 1alpha-OH D3 supplementation markedly increased weight gain and bone ash because it increased the utilization of phytate P.

Iron bioavailability in soybean meal as affected by supplemental phytase and 1 alpha-hydroxycholecalciferol

An Fe depletion-repletion chick bioassay was conducted to determine whether supplemental microbial phytase or 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) would improve the bioavailability of Fe in soybean meal (SBM). Weight gain, hemoglobin, and hematocrit were markedly improved when increasing levels (0, 10, 20, and 80 mg/kg) of Fe from analytical grade ferrous sulfate (FeSO4.7H2O) were added to the Fe-deficient casein-dextrose basal diet containing 20 mg Fe/kg. Addition of 19 mg Fe/kg from SBM to the basal diet improved (P < 0.05) hemoglobin and hematocrit, but the response was less than that obtained from 10 mg Fe/kg from FeSO4.7H2O. Phytase (1,430 units/kg), 1 alpha-OHD3 (10 micrograms/kg), or the combination, added to the SBM-fortified basal diet did not further improve hematocrit or hemoglobin, indicating that Fe bioavailability of SBM was not increased by either of these feed additives. Based on standard-curve methodology, and using hemoglobin as a criterion, the relative bioavailability of Fe was 38.5% for SBM, 21.0% for SBM+phytase, 23.2% for SBM+1 alpha-OHD3, and 29.2% for SBM+phytase+ 1 alpha-OHD3.

1alpha-hydroxycholecalciferol does not increase the specific activity of intestinal phytase but does improve phosphorus utilization in both cecectomized and sham-operated chicks fed cholecalciferol-adequate diets

Two chick assays were conducted in an attempt to understand how 1alpha-hydroxylated cholecalciferol compounds [1,25-(OH)2 D3 and 1alpha-OH D3] function in chicks to improve utilization of phytate-bound phosphorus (P) and trace minerals. Mucosal tissue from chicks fed a P-deficient corn-soybean meal diet, with or without supplemental 1alpha-OH D3, was incubated with sodium phytate. Inorganic P (Pi) release from sodium phytate, a measure of mucosal phytase activity, was not influenced by 1alpha-OH D3 presence in the diet. Increasing doses of mucosal protein in tubes containing sodium phytate resulted in marked increases (P < 0.01) in Pi release, but 1alpha-OH D3 in the diet from which the duodenal mucosal tissue was obtained had no effect on Pi release. Similarly, addition of either 1alpha-OH D3 or 1,25-(OH)2 D3 directly to the incubation tubes had no effect on Pi production. Efficacy of supplemental 1alpha-OH D3 and phytase was also tested in cecectomized vs. sham-operated chicks that were fed P-deficient and cholecalciferol-adequate corn-soybean meal diets. Removal of the twin ceca was done in an attempt to remove much of the intestinal microbial activity, and in turn, much of the gut microbial phytase activity. Marked increases (P < 0.01) in bone ash occurred in response to phytase or 1alpha-OH D3 supplementation, and cecectomized birds responded to either addition in the same manner as sham-operated controls. The data suggest that the marked phytate-P releasing capacity of dietary 1alpha-OH D3 or 1, 25-(OH)2 D3 is not caused by an increased specific activity of intestinal phytase.

[Effects of long-term administration of alfacalcidol on bone mass and bone metabolism in patients with primary osteoporosis--comparison with calcium preparations]

Long-term administration of active vitamin D3 can reduce the loss of bone mass and the incidence of fractures in Japanese whose intake of calcium (Ca) is low. In a crossover study, we examined the safety and efficacy of 1 alpha (OH)D3 and combination therapy with a Ca preparation. We measured bone mass, the incidence of fractures and bone metabolism in 33 elderly patients with a high risk of fracture (mean age: 77.5 %/- 7.8 (SD) years). Subjects were randomly assigned to receive calcium lactate alone for 12 months after 12 months of combination therapy with 1 alpha (OH)D3 (1 microgram/day) (A-C group, 17 patients) or to take calcium lactate alone for 12 months and then undergo 12 months of combination therapy with 1 alpha(OH)D3 (C-A group, 16 patients). These subjects were followed for 24 months. In the A-C group, the bone mineral density (BMD) of the lumbar spine (L2-4 BMD) measured 6 months after the start of 1 alpha (OH)D3 administration was 3% higher than the baseline value. In the C-A group, L2-4 BMD measured 6 months after the start of calcium lactate administration had decreased by approximately 2%. The rate of decrease was the same 12 months after the start of administration. The differences in L2-4 BMD between the two groups 6 and 12 months after the start of administration were significant (p = 0.023 and p = 0.005, respectively). In the A-C group, the mean BMD of the distal one-third radius measured 6 months after the start of administration had increased by 5%, but the increase was 1% when measured 12 months after the start of administration. In the C-A group, there were no such changes. The incidence of vertebral fracture during combination therapy with 1 alpha(OH) D3 and Ca preparations in the A-C group was significantly lower than that in the C-A group (chi square test, p < 0.05). The serum Ca level in the C-A group gradually increased, as measured 6 and 12 months after the start of combination therapy with 1 alpha(OH) D3 and Ca preparations, although these changes were within the reference range. There was no hypercalciuria. Serum intact parathyroid hormone levels had decreased from 26.5 +/- 11.3 pg/ml and 30.7 +/- 10.3 pg/ml to 19.8 +/- 9.7 pg/ml and 25.5 +/- 9.6 pg/ml in the A-C group and the C-A group, respectively, by 6 months after the start of administration. The rate of decrease was significantly higher in the A-C group (p = 0.004). These findings suggest that long-term administration of 1 alpha(OH)D3 is safe even when combined with administration of Ca preparations, and that this agent inhibits parathyroid function, and thus prevents loss of bone mass and reduces the incidence of vertebral fracture.

1alpha-hydroxyvitamin D2 partially dissociates between preservation of cancellous bone mass and effects on calcium homeostasis in ovariectomized rats

Vitamin D metabolites can prevent estrogen depletion-induced bone loss in ovariectomized (OVX) rats. Our aim was to compare the bone-protective effects of 1alpha,25-dihydroxyvitamin D3 (1, 25(OH)2D3), 1alpha,25-dihydroxyvitamin D2 (1,25(OH)2D2), 1alpha-hydroxyvitamin D3 (1alpha(OH)D3), and 1alpha-hydroxyvitamin D2 (1alpha(OH)D2) in OVX rats. 1alpha(OH)D3 and 1alpha(OH)D2 are thought to be activated in the liver to form 1,25(OH)2D3 and 1, 25(OH)2D2, respectively. Forty-four 12-week-old female Fischer-344 rats were either OVX or sham-operated (SHAM). Groups of OVX rats (n = 7 each) received vehicle alone, 1,25(OH)2D3, 1,25(OH)2D2, 1alpha(OH)D3, or 1alpha(OH)D2, starting 2 weeks after surgery. All vitamin D metabolites were administered orally at a dose of 15 ng/day/rat. Urine and blood samples were collected 6, 9, 12, and 16 weeks after surgery. Serum samples were analyzed for total calcium and phosphate. Calcium, phosphate, creatinine, and free collagen cross-links (ELISA) were determined in urine. After tetracycline double labeling, the rats were sacrificed 16 weeks postsurgery, and the proximal tibiae and the first lumbar vertebrae were processed undecalcified for static and dynamic bone histomorphometry. 1,25(OH)2D3 and, to a slightly lesser extent, 1,25(OH)2D2 elevated vertebral cancellous bone mass in OVX rats to a level beyond that observed in SHAM animals, and both compounds increased serum calcium and urinary calcium excretion to similar extents. 1alpha(OH)D3 and 1alpha(OH)D2 resulted in a 64% and 84%, respectively, inhibition of ovariectomy-induced vertebral cancellous bone loss. In the proximal tibial metaphysis, all vitamin D metabolites tested could only partially prevent post-OVX trabecular bone loss, with a tendency for 1alpha(OH)D3 to be the least active compound. The effects of 1alpha(OH)D3 and 1alpha(OH)D2 on calcium homeostasis differed markedly, however. The mean increase in urinary calcium excretion over the whole experiment was fivefold for 1alpha(OH)D3, whereas the corresponding increase for 1alpha(OH)D2 was only twofold. We conclude that, compared with 1alpha(OH)D3, 1alpha(OH)D2 combined at least equal or higher bone-protective activity in OVX rats with distinctly less pronounced effects on calcium homeostasis. This effect was not due to a differential action of the corresponding main activation products, 1,25(OH)2D3 and 1,25(OH)2D2.

Prophylactic effects of 1,24,25-trihydroxyvitamin D3 on ovariectomy-induced cancellous bone loss in the rat

Vitamin D metabolites can prevent estrogen depletion-induced bone loss in ovariectomized (OVX) rats. In this study, we investigated the bone-sparing effects of oral 1alpha,24R,25-trihydroxyvitamin D3 (1,24,25(OH)3D3) in a wide dose range in aged OVX rats. Fifty-three female Fischer-344 rats (6 months old, 170 g BW) were either ovariectomized or sham-operated (SHAM). Eight rats served as baseline controls. Groups of OVX rats (n = 7-8 each) received vehicle alone or graded oral doses of 1,24,25(OH)3D3 (0.05, 0.1, 0.2, and 0.3 microg/kg BW/day), starting five days after surgery. Urine and blood samples were collected one, two, three, and four months after surgery. Serum samples were analyzed for total calcium and alkaline phosphatase. Calcium, hydroxyproline, and collagen crosslinks (HPLC) were determined in urine. After fluorochrome double labeling, the rats were sacrificed four months postsurgery and the first lumbar vertebrae and the proximal tibiae were processed undecalcified for bone histomorphometry. Ovariectomy induced a 28% and a 69% reduction in vertebral and tibial cancellous bone area, respectively. Osteopenia in OVX rats was associated with increased histomorphometric and biochemical indices of bone turnover. The administration of 1,24,25(OH)3D3 to OVX rats dose-dependently increased vertebral and tibial cancellous bone mass, serum calcium, and urinary calcium excretion, and reduced histomorphometric and biochemical indices of bone resorption. 1,24,25(OH)3D3 at doses of 0. 2 and 0.3 microg/kg/day produced strong anabolic effects, especially on vertebral cancellous bone in OVX rats, and increased mineral apposition rate and wall width of completed remodeling units relative to vehicle-treated OVX rats. Even at high doses, 1,24, 25(OH)3D3 did not impair bone mineralization. We conclude that oral administration of 1,24,25(OH)3D3 can effectively prevent estrogen depletion-induced cancellous bone osteopenia in the aged OVX rat model. The therapeutic window for 1,24,25(OH)3D3 in OVX rats, however, is also narrow, comparable to that for calcitriol.

Effect of 1 alpha-hydroxyvitamin D3 on loss of bone mineral density immediately after artificial menopause

To evaluate the effects of 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3), a series of clinical trials, preventive and therapeutic, were performed in an open label manner in women immediately after oophorectomy. The series included a total of 121 oophorectomized subjects, whose lumbar bone mineral density (L2-4BMD) was followed by the use of dual energy X-ray absorptiometry. (1) Preventive trial: 61 women who had undergone premenopausal bilateral oophorectomy, were divided into 3 groups (Group C: control; Group L: 0.25 micrograms 1 alpha (OH)D3/day; Group H: 0.50-0.75 micrograms 1 alpha (OH)D3/day). The changes in BMD and chemical indices were followed up for one year. (2) Therapeutic trial: the trial included 60 premenopausally oophorectomized subjects having L2-4BMD lower than the normal control level minus 1SD which has been reported in age-matched normal Japanese women. These subjects were divided into 3 groups and treated in the same way as in the preventive trial. In the preventive trial, L2-4BMD decreased by 8.2%, 6.5% and 4.5% in groups C, L and H, respectively, at 12 months of treatment, whereas in the therapeutic trial, L2-4BMD decreased by 3.6%, 3.2% and 0.8% in the groups C, L and H, respectively, at 12 months of treatment. In conclusion, 1 alpha(OH)D3 was found to be effective both to prevent the bone loss subsequent to bilateral oophorectomy and improve low bone mass after oophorectomy.

Prevention of preneoplastic mammary lesion development by a novel vitamin D analogue, 1alpha-hydroxyvitamin D5

BACKGROUND

The form of vitamin D (vitamin D3) in fortified milk and the provitamin D produced by the body undergo metabolic activation to a biologically active form, 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. This compound can induce cell differentiation and can prevent proliferation of cancer cells. However, because 1alpha,25(OH)2D3 is hypercalcemic (effective in increasing serum calcium level), it is not suitable for use in cancer prevention or cancer therapy trials.

PURPOSE

We synthesized a vitamin D5 series analogue, 1alpha-hydroxy, 24-ethyl-cholecalciferol, or 1alpha-hydroxyvitamin D5 [1alpha(OH)D5], and evaluated its chemopreventive activity in carcinogen-treated mammary glands in organ culture experiments.

METHODS

The analogue 1alpha(OH)D5 was synthesized from sitosterol acetate and was characterized by nuclear magnetic resonance. Its purity was evaluated by high-pressure liquid chromatography. The calcemic activities of vitamin D3 and D5 analogues were determined in vitamin D-deficient Sprague-Dawley rats. Mammary glands of BALB/c mice were placed in organ culture and treated with the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA) to induce preneoplastic lesions. Vitamin D analogues were added to the culture medium at four different concentrations, and formation of mammary lesions was evaluated. The effects of 1alpha(OH)D5 and 1alpha,25(OH)2D3 on the expression of vitamin D receptors (VDRs) and transforming growth factor-beta1 (TGF-beta1) were studied by immunohistochemistry. Statistical significance was determined by the chi-squared test. All reported P values were two-sided.

RESULTS

1alpha,25(OH)2D3 was fourfold more calcemic than 1alpha(OH)D5 at a dose of 0.042 microg/kg per day in rats. Both 1alpha,25(OH)2D3 and 1alpha(OH)D5 inhibited the development of DMBA-induced preneoplastic lesions in mouse mammary glands compared with untreated glands. The effect of the vitamin D3 analogue was observed at a much lower concentration (0.01 microM). Treatment with 1alpha(OH)D5 resulted in a dose-related (0.01-10.0 microM) inhibition without any toxicity, whereas the vitamin D3 analogue was highly potent but toxic at concentrations of 1.0 microM or higher. Normal mouse mammary glands poorly express VDR and TGF-beta1; incubation with 1alpha(OH)D5 or 1alpha,25(OH)2D3 dramatically induced their expression.

CONCLUSIONS

This is the first report showing the possibility of chemoprevention by a vitamin D5 series compound. We conclude that 1alpha(OH)D5 is less calcemic than 1alpha,25(OH)2D3. It is nontoxic at a wide range of concentrations, but it is potent in inhibiting the development of preneoplastic lesions in mammary glands in organ culture. In addition, we show for the first time the induction of TGF-beta1 in normal mammary tissues by a chemopreventive agent.

IMPLICATIONS

1alpha(OH)D5 is a good candidate for in vivo chemoprevention studies. It may mediate its action by inducing expression of VDR and of TGF-beta1, as is seen in other systems.

Efficacy of supplemental 1 alpha-hydroxycholecalciferol and microbial phytase for young pigs fed phosphorus- or amino acid-deficient corn-soybean meal diets

Young pigs (5 wk of age and 8 kg) were used to test the efficacy of 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) and microbial phytase for improving the utilization of phytate phosphorus (P) and amino acids present in corn-soybean meal (SBM) diets. Phytase supplementation (1,200 units/kg) to a vitamin D3-adequate, P-deficient corn-SBM diet elicited a marked response (P < .05) in weight gain and ash content of fibula, scapula, and metatarsal bones, but dietary addition of 1 alpha-OH D3 (20 micrograms/kg) was without effect. A P- and vitamin D3-adequate, amino acid-deficient corn-SBM diet (15.5% CP) also was supplemented with 1,200 units/kg of phytase to evaluate the efficacy of phytase in improving amino acid utilization. Pigs gained faster (P < .05) and more efficiently (P < .05) when this diet was supplemented with limiting amino acids, and phytase addition also increased (P < .05) weight gain, regardless of whether the diet was deficient or adequate in amino acids. Feed efficiency was improved (P < .05) by phytase addition to the amino acid-deficient diet but not to the amino acid-adequate diet. Pigs fed the low-CP, amino acid-fortified diet gained as fast and as efficiently as those fed a 19.5% CP (1.19% lysine) positive-control diet.

In vivo implantation of human osteosarcoma cells in nude mice induces bones with human-derived osteoblasts and mouse-derived osteocytes

Two human osteosarcoma cell lines, Hu09 and OST, were suspended in Matrigel (Becton Dickinson Labware, Bedford, Massachusetts) and implanted subcutaneously in the backs of nude mice. To study phenotypic changes of tumor cells and host cells, expression of mRNA for osteopontin (OPN), osteocalcin (OC), and osteonectin (ON) was analyzed by in situ hybridization. Bone tissue was formed in the tumors derived from Hu09 cells. OPN mRNA was transcribed predominantly in osteocyte-like cells within the bone, whereas OC mRNA was transcribed in osteoblast-like cells that surrounded the bone. ON mRNA was detected in both types of cells. The similarity of the expression pattern of OPN, OC, and ON during osteogenesis of Hu09 cells to that of normal skeletal development suggests that the bone formed in Hu09-implanted mice is the same as normal bone tissue. By DNA-DNA in situ hybridization using a human-specific Alu probe and a mouse-specific m-L1 probe, osteoblast-like cells in Hu09 tumorous bone were, however, of human origin, whereas osteocyte-like cells were of mouse origin. In the tumors derived from OST cells, no osteogenesis was observed during the experimental period, and the expression of OPN, OC, and ON was not detected in tumor cells. An endochondral bone formation was not evident when these cells were simply implanted into muscle tissue. An endochondral bone was, however, reactively induced in the host mUscle tissue either when 1 alpha-hydroxyvitamin D3 and all-transretinoic acid were administered to OST-implanted mice or when Hu09 cells were pretreated with dexamethasone before implantation. Hu09 implantation seems to be a useful tool not only for the study of the differentiation of osteosarcoma cells but also for the investigation of the mechanism of bone formation. This system, using Hu09 and OST, may provide us with a new tool for the isolation of the unidentified factors that induce or inhibit osteogenesis in vivo.

1 alpha-Hydroxylated cholecalciferol compounds act additively with microbial phytase to improve phosphorus, zinc and manganese utilization in chicks fed soy-based diets

Seven experiments were conducted to determine the efficacy of 1,25-dihydroxycholecalciferol [1,25-(OH)2D3] and microbial phytase in improving P, Zn and Mn utilization of chicks fed P, Zn- and Mn-deficient soy protein diets containing surfeit levels of cholecalciferol. Efficacy of 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) was also studied. A dose titration study indicated that supplemental phytase at 1200 units/kg diet would increase bone ash by at least 65% when added to a corn-soybean meal diet containing 0.43 g P/100 g (0.1 g nonphytate P/100 g). These responses were similar to those obtained from supplemental P (0.1 g/100 g) as KH2PO4 or from added 1,25-(OH)2D3 (10 micrograms/kg). Dietary addition of both 1200 units phytase and 10 micrograms/kg 1,25-(OH)2D3 elicited bone ash responses that were near 100%. When chicks were fed a Zn-deficient soy-concentrate diet (13 mg Zn/kg), diet supplementation with 1,25-(OH)2D3 or phytase increased growth rate by 40% and tibia Zn content by > 100%; adding 1,25-(OH)2D3 together with phytase increased tibia Zn content by 160%. Utilization of both Zn and Mn contained in the corn-soybean meal diet also was markedly enhanced by supplemental phytase, 1,25-(OH)2D3, or the combination. The cholecalciferol analog 1 alpha-OH D3 was found to improve dietary P utilization maximally (70% bone ash response) at a dose of 20 micrograms/kg diet, and effects were additive when 1 alpha-OH D3 was fed in the presence of phytase.(ABSTRACT TRUNCATED AT 250 WORDS)

Elevated superoxide generation in mononuclear phagocytes by treatment with 1 alpha hydroxyvitamin D3: changes in kinetics and in oxidase cytosolic factor p47

The effect of 1 alpha-hydroxyvitamin D3 (1 alpha OHD3) treatment on the superoxide production of phagocytic cells in patients undergoing continuous ambulatory peritoneal dialysis (CAPD) was studied. A 3-day treatment of CAPD patients with 3 micrograms per day of 1 alpha OHD3 (high-dose treatment) significantly increased NADPH oxidase and killing activities in peritoneal macrophages and peripheral blood monocytes (P < 0.001) as compared with low-dose (0.25 microgram/day of 1 alpha OHD3) treatment or nontreatment. The high oxidase activity observed in macrophages and monocytes after the treatment with 1 alpha OHD3, correlated significantly to the increase in the amount of the cytosolic factor p47 of the NADPH oxidase as detected by western blotting analysis. Superoxide production by the peripheral blood neutrophils of these patients only slightly increased with 1 alpha OHD3 treatment, and the amount of p47 was not affected by 1 alpha OHD3 administration. In order to evaluate the significance of the oxidase cytosolic factor in dictating oxidase activity, a reconstitution of NADPH oxidase was conducted by mixing macrophage cytosols and membranes in a cell-free system. The addition of macrophage cytosol from patients on high-dose treatment to macrophage membranes from patients in all of the categories of treatment resulted in significantly higher (P < 0.001) superoxide production as opposed to the macrophage cytosol from nontreated patients. These results suggest that 1,25(OH)2D3 causes an increase in NADPH oxidase activity in the peritoneal macrophages and monocytes of CAPD patients by inducing synthesis and elevating the amount of the cytosolic factor p47.(ABSTRACT TRUNCATED AT 250 WORDS)

Osteopenia in genetically diabetic DB/DB mice and effects of 1alpha-hydroxyvitamin D3 on the osteopenia. Basic Research Group

To explore the pathogenesis of non-insulin-dependent diabetes mellitus associated osteopenia, we examined age-related changes of the femur metaphyseal bone mineral density in genetically diabetic (db/db) mice and non-diabetic (+/+) mice of the same strain using single photon absorptiometry and characterized the osteopenia pharmacologically and biochemically. Bone mineral density increased with age in the +/+ mice from 5 to 16 weeks of age, but reached a plateau in the db/db mice at 8 weeks of age, and significant differences between the two groups were observed after 12 weeks of age. Ash weight (A) and dry weight (D) of the femur and A/D ratio were significant lower in the db/db mice than in the +/+ mice after 8 weeks of age. Significant elevations of serum calcium and parathyroid hormone (PTH) were observed after 8 weeks and 12 weeks of age, respectively. Serum 1alpha,25-dihydroxyvitamin D levels were significantly decreased in the db/db mice compared to the +/+ mice. Daily oral treatment with 1alpha-hydroxyvitamin D3 (1alpha-(OH)D3) for 4 weeks starting from 8 weeks of age significantly attenuated the bone loss in the db/db mice. These results suggest that an impaired bone mineralization probably by insufficient vitamin D activity and high PTH levels are involved in the osteopenia in the db/db mice. 1alpha-(OH)D3 exerted beneficial effects on the bone loss.

Effects of 24R,25-dihydroxyvitamin D3 in combination with 1 alpha-hydroxyvitamin D3 in predialysis renal insufficiency: biochemistry and histomorphometry of cancellous bone

The effect of combined administration of 24R,25-dihydroxyvitamin D3 (24,25-(OH)2D3) and 1 alpha-hydroxyvitamin D3 (1 alpha-(OH)D3) was studied in 24 non-dialyzed patients with chronic renal insufficiency (CRI), matched pairwise as to age, sex, and creatinine clearance (Cr.cl). Low Ca intake had been supplemented beforehand. Then, 1 alpha-(OH)D3 (mean dose 0.55 micrograms daily) was given orally to all patients for 3 months (T0 to T3). Subsequently, patients were assigned randomly to 6 months further treatment either with 1 alpha-(OH)D3 alone (Group A) or with 1 alpha-(OH)D3 plus a high dosage of 24,25-(OH)2D3 (50 micrograms orally, twice weekly) (Group B). Histomorphometry was performed at T0, T3, and T9. In both groups iPTH was equally suppressed, into the lower normal range. Whereas in Group A, serum Ca rose steadily and Cr.cl declined, in Group B both parameters levelled off between T6 and T9. At T9, in Group A the elevated resorption and osteoid indices had normalized markedly, but osteoblasts (Ob.Pm) and mineralizing boundaries (M.Bd) were depressed considerably between T3 and T9. In contrast, in Group B, preservation of Ob.Pm and improved mineralizing activity were observed (M.Bd at T9 > T3 > T0). Resorption indices hardly changed. In the patients with high Ob.Pm at T0, cancellous bone area increased significantly. This was not observed in Group A. Thus, in Group B, osteoblast recruitment appeared maintained and M.Bd appeared normalized. Decline of remodeling toward an adynamic state with an increased risk of hypercalcemia appeared prevented.

[Immune modulation by vitamin D analogs in the prevention of autoimmune diseases]

Vitamin D has been discovered at the beginning of this century. 7-Dehydrocholesterol is converted to vitamin D3 in the skin and after several hydroxylations it is further converted to the active hormonal form, 1 alpha,25-(OH)2D3. Vitamin D stimulates the absorption of calcium and phosphate and is an essential link in bone resorption and formation and calcium metabolism. 1 alpha,25-(OH)2D3 acts through a vitamin D receptor. These receptors are not only present in clinical target organs (kidney, gut, liver) but can also be found in a wide variety of "non-classical" tissues (keratinocytes, cells belonging to the immune system). Moreover, numerous cells (keratinocytes, macrophages) can locally synthetize or can be induced to synthetize 1 alpha,25-(OH)2D3 and these cells are responsive to its action. When these data are combined, a possible paracrine function of 1 alpha,25-(OH)2D3 can be suspected. Via this paracrine function 1 alpha,25-(OH)2D3 can suppress the cellular and humoral immunity. Based on the discovery of these effects on immune cells in vitro it became clear that 1 alpha,25-(OH)2D3 might be an interesting molecule to prevent autoimmune diseases and organ transplantation. This has already been shown in several animal models (Heymann nephritis, diabetes mellitus, experimental allergic-encephalomyelitis, lupus). 1 alpha,25-(OH)2D3 demonstrates however some side-effects (hypercalciuria, hypercalcemia, bone resorption) and for this reason 1 alpha,25-(OH)2D3-analogs are developed with dissociated effects i.e. an activity profile that allows a specific action on non-classical tissues without calcemic effects. Some chemical modifications of the side chain, A and/or CD-ring results in "superanalogs" with 10 to 100-fold more activity on cell differentiation and the immune system then 1 alpha,25-(OH)2D3 but with less calcemic activity in vivo. These biological effects can be explained by differences in pharmacokinetics (low affinity for the plasma vitamin D-binding protein and short extracellular half-life) and increased intracellular activation and gen transactivation. Preclinical research must still be done to select the most potent superanalogs and to find the exact protocols for the prevention and treatment of autoimmune diseases and rejection of transplanted organs.

Bone-resorbing activities of 24-epi-1 alpha-hydroxyvitamin D2 and 24-epi-1 alpha,25-dihydroxyvitamin D2

Bone-resorbing activities of 24-epi-1 alpha-hydroxyvitamin D2 [24-epi-1 alpha(OH)D2], 24-epi-1 alpha,25-dihydroxyvitamin D2 [24-epi-1,25(OH)2D2], and 1 alpha,24S,25-trihydroxyvitamin D2 [1,24S,25(OH)3D2], which might be a metabolite of 24-epi-1,25(OH)2D2, were investigated. In an in vitro bone resorption test, the activity of 24-epi-1 alpha(OH)D2 was similar to that of 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] at 10(-9) M-10(-6) M. The activity of 24-epi-1,25(OH)2D2 was weaker than that of 1 alpha,25-dihydroxyvitamin D3 [1,25(OH)2D3] at 10(-11) M-10(-8) M. On the other hand, the activity of 1,24S,25(OH)3D2 was similar to that of 24-epi-1,25(OH)2D2 at 10(-11) M-10(-9) M. In the formation assay of osteoclast-like cells, the activity of 24-epi-1 alpha(OH)D2 was weaker than that of 1 alpha(OH)D3 at 10(-7) M. The activity of 24-epi-1,25(OH)2D2 was almost similar to that of 1,25(OH)2D3 at 10(-11) M-10(-7) M. The activity of 1,24S,25(OH)3D2 was significantly weaker than that of 24-epi-1,25(OH)2D2 at 10(-11) M-10(-9) M. In the two experiments, the potencies of 24-epi-1,25(OH)2D2 were about 100 times higher than those of 24-epi-1 alpha(OH)D2. In an in vivo/in vitro bone resorption test, the activity of 24-epi-1 alpha(OH)D2 was almost similar to those of 1 alpha(OH)D3 and 1,25(OH)2D3 and higher than those of 24-epi-1,25(OH)2D2 and 1,24S,25(OH)3D2. 24-epi-1 alpha-(OH)D2 and 1 alpha(OH)D3 were longer lasting than 24-epi-1,25(OH)2D2 and 1,25(OH)2D3 in this experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of 1 alpha-hydroxyvitamin D3 on lumbar bone mineral density and vertebral fractures in patients with postmenopausal osteoporosis

The effects of 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] on bone mineral density, fracture incidence, and bone metabolism were evaluated by a double-blind, placebo-controlled study. Eighty postmenopausal osteoporotic Japanese women (71.9 +/- 7.3 years, mean +/- SD) were randomly assigned to 1 microgram of 1 alpha(OH)D3 daily or inactive placebo for 1 year. All patients were given supplemental calcium (300 mg of elemental calcium daily). Lumbar (L2-L4) bone mineral density (BMD) determined by dual energy X-ray absorptiometry increased 0.65% with 1 alpha(OH)D3 treatment and decreased 1.14% with placebo (P = 0.037). BMD in both the femoral neck and Ward's triangle did not yield any significant differences between the two groups, whereas trochanter BMD in the 1 alpha(OH)D3-treated group increased 4.20% and decreased 2.37% with placebo (P = 0.055). X-ray analysis demonstrated that new vertebral fractures occurred in two patients with 1 alpha(OH)D3 and in seven patients with placebo. The vertebral fracture rate in the treated group was significantly less (75/1000 patient years) than in the control group (277/1000 patient years; P = 0.029). Hypercalcemia (12.1 mg/100 ml) occurred in one patient receiving 1 alpha(OH)D3; however, the serum calcium level in this patient promptly decreased to the reference range after cessation of the treatment. There were no significant changes in serum creatinine level in either group. A significant increase in urinary excretion of calcium was found but there was no significant change in urinary excretion of hydroxyproline in the treated group. The serum level of bone-derived alkaline phosphatase activity significantly decreased by -26 +/- 26 (mU/ml) after the treatment (P = 0.003).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of intravenous 1 alpha-hydroxycholecalciferol on parathyroid hormone, osteocalcin and calcitriol in man

The acute effects of a single intravenous injection of 2 micrograms of 1 alpha-hydroxycholecalciferol (alfacalcidol) were studied for a 24-h period in six normal males (mean age 33 years), six women with primary hyperparathyroidism (mean age 72 years) and six women with established osteoporosis (mean age 63 years). In all three groups, serum calcitriol levels rose to a peak 2-3 h after administration of alfacalcidol. Basal levels were highest in the primary hyperparathyroidism group at (mean +/- SEM) 81 +/- 2 vs 62 +/- 12 (normal males) (p < 0.05) and 56 +/- 5 pmol/l (osteoporosis) (p < 0.01). Highest peak levels were found also in the primary hyperparathyroidism group at 150 +/- 15 vs 114 +/- 15 (normal males) (p < 0.05) and 127 +/- 15 pmol/l (osteoporosis) (p < 0.01). The rise in calcitriol was higher in the primary hyperparathyroidism group than either the normal males or osteoporotic patients (p < 0.05). No significant differences were evident in basal serum calcidiol concentrations among the three treatment groups. As might be expected, highest basal concentrations of parathyroid hormone (PTH), serum calcium and serum osteocalcin were noted in the primary hyperparathyroid group (PTH: 17.1 +/- 7.7 vs 1.9 +/- 0.5 (normal males) (p < 0.01) and 2.1 +/- 0.3 pmol/l (osteoporosis) (p < 0.01); calcium: 3.06 +/- 0.08 vs 2.50 +/- 0.02 (normal males) (p < 0.01) and 2.43 +/- 0.02 mmol/l (osteoporosis) (p < 0.01); osteocalcin: 1.10 +/- 0.08 vs 0.56 +/- 0.16 (normal males) (p < 0.05) and 0.53 +/- 0.21 nmol/l (osteoporosis) (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effect of oral, intraperitoneal, and intravenous 1 alpha-hydroxycholecalciferol on markers of bone metabolism

OBJECTIVE

To study the acute effect of 1 alpha-hydroxycholecalciferol (1 alpha-OHD3) on serum levels of alkaline phosphatase, Ca2+, osteocalcin, parathyroid hormone (PTH), phosphate and type I and III procollagens (PICP and PIIINP respectively) in patients undergoing peritoneal dialysis. Also, 1,25-(OH)2D3 was measured.

DESIGN

Single doses of 1 alpha-OHD3 (80 ng/kg body wt) were given in randomized cross-over fashion, orally, intraperitoneally (i.p.) and intravenously (i.v.) on three occasions. Blood was sampled at 0, 1, 6, 12, and 24 h after administration of 1 alpha-OHD3.

MAIN RESULTS

Following oral administration of 1 alpha-OHD3, a decrease in serum alkaline phosphatase was seen when levels at 1 and 6 h were compared to baseline (P < 0.05). Oral and i.v. drug administrations resulted in an increasing trend in serum Ca2+ throughout the study (P < 0.05). Moreover, a difference in serum Ca2+ was found when 24-h levels after oral 1 alpha-OHD3 dose was compared to baseline (P < 0.05). Serum osteocalcin at 12 and 24 h after oral 1 alpha-OHD3 compared to baseline were increased (P < 0.05). Intact PTH followed a circadian rhythm after all three routes of drug delivery. After 24 h, significant decreases of intact PTH were observed in the oral and i.v. group. No changes in serum phosphate and serum PICP levels were observed over time after oral, i.p., and i.v. delivery of 1 alpha-OHD3. However, serum PIIINP following oral and i.p. administration of 1 alpha-OHD3 decreased at 1 and 6 h (P < 0.05).

CONCLUSION

Oral and i.v. administration of 1 alpha-OHD3 does influence serum levels of osteocalcin, PTH, and PIIINP: Noticeable is the significant increase in serum osteocalcin after oral administration of 1 alpha-OHD3, the remarkable increase (22.6%) in osteocalcin 24 h after i.v. 1 alpha-OHD3, though not statistically significant, the increase in serum PTH levels 12 h following oral and i.v. doses of 1 alpha-OHD3 and the moderate effect on serum Ca2+ levels.

Effect of 1,25,28-trihydroxyvitamin D2 and 1,24,25-trihydroxyvitamin D3 on intestinal calbindin-D9K mRNA and protein: is there a correlation with intestinal calcium transport?

Although analogs and metabolites of vitamin D have been tested for their calciotropic activity, very little information has been available concerning the effects of these compounds on gene expression. In this study one analog of vitamin D, 1,25,28-trihydroxyvitamin D2 [1,25,28-(OH)3D2], and one metabolite, 1,24,25-trihydroxyvitamin D3 [1,24,25-(OH)3D3], were tested for their effect on intestinal calbindin-D9K mRNA and protein as well as for their effect on intestinal calcium absorption and bone calcium mobilization. These compounds were also evaluated for their ability to compete for rat intestinal 1,25-(OH)2D3 receptor sites and to induce differentiation of human leukemia (HL-60) cells as indicated by reduction of nitro blue tetrazolium. In vivo studies involved intrajugular injection of 12.5 ng 1,25-(OH)2D3 or test compound to vitamin D-deficient rats and sacrifice after 18 h. 1,25,28-Trihydroxyvitamin D2 had no effect on intestinal calcium absorption, bone calcium mobilization, or intestinal calbindin-D9K protein and mRNA. Competitive binding to 1,25-(OH)2D3 receptors was 0.8% of that observed using 1,25-(OH)2D3. However, 20- and 40-fold higher doses of 1,25,28-(OH)3D2 (250 and 500 ng) resulted in significant inductions in calbindin-D9K protein and mRNA (3.5 to 7.4-fold), although doses as high as 800 ng were found to have no effect on intestinal calcium absorption or bone calcium mobilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of heparin-induced osteopenia in rats

Heparin has been known to induce osteopenia, but its precise mechanism of action is unknown. In the present study, we examined the effect of heparin on the rat femur using single photon absorptiometry and characterized the osteopenia biochemically and pharmacologically. Daily heparin injection dose dependently induced osteopenia in rats. Significant bone loss was observed from 2 weeks after starting heparin treatment (2000 U/kg.day) and peaked at 4 weeks. Serum PTH levels were significantly elevated from 1 week onward after starting heparin treatment, whereas no significant changes were seen in serum total calcium or ionized calcium levels. A bone resorption inhibitor, FR78844 (a bisphosphonate compound), significantly attenuated the heparin-induced osteopenia, as did 1 alpha-hydroxyvitamin D3; with the latter, the effective dose was 10 times lower than that needed for a similar effect against immobilization and ovariectomy-induced osteopenia, suggesting an up-regulation of 1 alpha, 25-dihydroxyvitamin D3 receptors in the heparin-treated rats. This speculation was supported by the finding that serum 1 alpha, 25-dihydroxyvitamin D levels were significantly decreased by 54% in the heparin-treated rats compared to those in normal rats. These results suggest that the enhanced bone resorption by high PTH blood levels and the reduction of 1 alpha, 25-dihydroxyvitamin D are involved in the pathogenesis of heparin-induced osteopenia.

Oscillations in inositol 1,4,5-trisphosphate and diacyglycerol induced by vitamin D3 metabolites in confluent mouse osteoblasts

For the last 5 years, attention has focused on the nongenomic effects of 1,25-(OH)2D3, but considerably less is known about the mechanisms of the nonnuclear actions of 24,25-(OH)2D3. The present study examines and compares the rapid (5-90 s) effects of 100 pM to 10 nM 24,25-(OH)2D3, 10 pM to 1 nM 1,25-(OH)2D3, and 1-100 nM 25-OHD3 on the formation of inositol phosphates and lipids in confluent mouse osteoblasts. 24,25-(OH)2D3 and 25-OHD3 effects were dose dependent; those of 1,25-(OH)2D3 were dose dependent in a bell-shaped manner. The two dihydroxylated metabolites induced a multiphasic response in inositol 1,4,5-trisphosphate (IP3) formation with three stimulation peaks; the IP3 response to 25-OHD3 was monophasic. The amplitude of the IP3 response to 24,25-(OH)2D3 was greater and its oscillation period was slower than that induced by 1,25-(OH)2D3. The diacylglycerol (DAG) responses to secosteroids showed two stimulation peaks that appeared at different times depending on the secosteroid used. Pretreatment with neomycin totally inhibited the first DAG response; neomycin had no effect on the second peak of DAG induced by 25-OHD3, whereas it partially blocked the second response of DAG to 24,25-(OH)2D3 and 1,25-(OH)2D3. These data show for the first time that 24,25-(OH)2D3 can modulate phospholipid metabolism in confluent mouse osteoblasts as early as 5-10 s. The first pathway used by all three secosteroids is that of the hydrolysis of phosphatidylinositol 4,5-bisphosphate via phospholipase C activation, leading to the formation of the two second messengers, IP3 and DAG, since neomycin totally blocked the response. Thus, the action of these secosteroids on the osteoblast membrane may also implicate several steps of the phosphatidylcholine cycle, according to the metabolite tested. Finally, these data point to a direct interaction of vitamin D metabolites with specific membrane recognition moieties.

Selective biological response by target organs (intestine, kidney, and bone) to 1,25-dihydroxyvitamin D3 and two analogues

The hormonally active form of vitamin D, 1 alpha,25-dihydroxyvitamin D3 [1 alpha,25(OH)2D3] stimulates biological responses related to calcium homeostasis, cell differentiation, and immunomodulation in many target cells, including leukemic cells. Most of these responses are dependent upon 1 alpha,25(OH)2D3 interaction with a nuclear receptor protein. Structural analogues of 1 alpha,25(OH)2D3 might allow for separation of biological function, avoiding adverse calcemic effects. This report quantitates intestinal calcium absorption, bone calcium resorption, induction of intestinal and renal calcium-binding protein (CaBP), and occupancy of the intestinal and renal nuclear 1 alpha,25(OH)2D3 receptor in vitamin D-deficient chicks after a single dose of 1 alpha,25(OH)2D3, 1 alpha,25-dihydroxyvitamin-16-ene-23-yne-D3 (analogue V), or 22-[m-(dimethylhydroxymethyl)phenyl]-23,24,25,26,27- pentanor-1 alpha-hydroxy-vitamin D3 (analogue EV). The interaction of these compounds with chick intestinal nuclear 1 alpha,25(OH)2D3 receptor and chick plasma vitamin D-binding protein was determined in vitro; analogues V and EV bound 68% and 62% [1 alpha,25(OH)2D3 receptor] and 8% and 13% (vitamin D-binding protein), respectively, as well as 1 alpha,25(OH)2D3 (100%). 1 alpha,25(OH)2D3 doses (0.075-1.2 nmol) generated responses in intestinal calcium absorption, bone calcium resorption, intestinal CaBP, and renal CaBP. When analogue V (1.2-300 nmol) was administered, increases in bone calcium resorption and renal CaBP were noted. However, a significant response in intestinal calcium absorption and intestinal CaBP appeared only after a 300-nmol dose. Unoccupied nuclear 1 alpha,25(OH)2D3 receptor in the intestine and kidney was determined in vivo after doses of 1 alpha,25(OH)2D3, analogue V, or analogue EV. Doses (0.25-6.0 nmol) of 1 alpha,25(OH)2D3 and analogue EV reduced unoccupied receptor to 24% and 59% (intestine) and to 13% and 41% (kidney), respectively. Analogue V (6.0-600 nmol) decreased unoccupied receptor in the kidney. In the intestine analogue V (300-600 nmol) reduced unoccupied receptor only to 75%. These results confirm that some vitamin D analogues can generate selective biological responses and different levels of target organ receptor occupancy.

[Effect of 1 alpha-OH-D3 on the bone metabolism after high tibial osteotomy]

The effect of 1-hydroxycholecalciferol (1 alpha-OH-D3) on bone metabolism during osteotomized bone healing was investigated. The study based on 19 female patients with gonarthrosis who underwent the high tibial osteotomy. In 10 selected randomly from these patients 1 alpha-OH-D3 (1.0 micrograms/day) was administered before and after the surgery. After operation the changes in bone density (by MD-method) and biochemical parameters were followed. In the non-treated group the serum level of [Ca] x [P] product temporarily decreased at 3 days after surgery. Average bone density at two months after the surgery was 8.8% lower than the preoperative value. In contrast, 1 alpha-OH-D3 treated group showed significantly less decrease of serum [Ca] x [P] product at the third day than the control group and no significant decrease of bone density at two months after the operation. From these results, it was concluded that the 1 alpha-OH-D3 suppresses the decrease of serum Ca and P level and systemic osteopenia after osteotomy and may have an beneficial effect on fracture healing.

Malignant osteopetrosis treated with high doses of 1 alpha-hydroxyvitamin D3 and interferon gamma

A male infant with malignant osteopetrosis was treated with high doses of 1 alpha-hydroxyvitamin D3 and interferon gamma. Therapy with 1 alpha-hydroxyvitamin D3 increased the serum calcium level despite the markedly elevated serum level of 1 alpha, 25-dihydroxyvitamin D before treatment. Recombinant human interferon gamma increased neither the bone mineral nor matrix turnover, and was not tolerated because of bone marrow suppression.

[Does the administration of derivatives of vitamin D to dairy cows in late pregnancy for the prevention of parturient paresis affect the maternal-fetal mineral metabolism?]

Intramuscular injection of 1 alpha-hydroxyvitamin D3 (with or without 25-hydroxyvitamin D3) to highly pregnant dairy cows caused a significant increase of ionized calcium in blood and of total calcium and inorganic phosphate with a concomitant decrease of magnesium in blood plasma 3,5 +/- 1,9 days later (resp. 12-48 h a.p.). This brought about a higher Ca level at parturition preventing parturient paresis. The changes of maternal mineral and vitamin D status had no effect on the mineral concentrations of blood in newborn calves. However, the increase in calcium and phosphate concentrations in maternal blood after injection was accompanied by an increase of the minerals in the amniotic fluid reflecting their strong reciprocal exchange. On the other hand, the composition of allantoic fluid showed no significant changes. Therefore, analysis of both fetal fluids does not refer to disorders of fetal mineral metabolism. As a consequence, there seems to be no potential risk of intoxication after a prepartal injection of the substances to the mother for their offspring.

Calcitriol attenuates the thyrotropin-releasing hormone-stimulated inositol phosphate production in clonal rat pituitary (GH4C1) cells

Three days pretreatment of the prolactin (PRL) secreting GH4C1 cells with 10 nM calcitriol attenuated both the basal and thyrotropin-releasing hormone (TRH)-stimulated (1 microM, 5 s) inositol trisphosphate (IP3) production by 30 and 26%, respectively. The effect was detectable at 10 nM (basal) and 1 pM (TRH-stimulated), and maximal at 1 microM (basal) and 10 nM (TRH), respectively. Calcitriol was at least 100 times more potent than calcidiol and 24-hydroxycalcidiol, and the effect was reversible upon cessation of pretreatment. Calcitriol pretreatment (1 microM, 5 days) also decreased the levels of phosphatidyl-inositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate by 23, 55 and 32%, respectively. GTP gamma S-stimulated (100 microM, 30 s) IP3 production was decreased by 45% after calcitriol pretreatment (10 nM, 5 days). Pertussis toxin (1 nM, 4 h) attenuated both the basal and TRH-stimulated IP3 production, but this effect was omitted by calcitriol pretreatment. Thus, calcitriol specifically attenuates both the basal and TRH-stimulated inositol phosphate production in GH4C1 cells. The mechanism, at least partly, involves decreased availability of phosphoinositides for phospholipase C. Calcitriol regulation of a pertussis toxin-sensitive G-protein might also play some role.

[The effect of parenteral administration of 25-hydroxycholecalciferol and 1 alpha-hydroxycholecalciferol on the mineral concentrations in the blood of cows in late pregnancy]

The effect of 1 - 3 intramuscular injections of the vitamin D3 metabolite 25-OHD3, synthetic 1 alpha-OHD3, and a combination of both on the plasma concentrations of calcium (Ca), inorganic phosphate (P(i)) and magnesium (Mg) was tested in 67 older dry dairy cows. Administering 4,0 mg 25-OHD3 reduced Ca and P(i) for some time while Mg blood levels remained constant. Injecting 210 micrograms 1 alpha-OHD3 plus 2.0 mg 25-OHD3 only brought a marked increase in P(i) concentrations, whereas 420 micrograms 1 alpha-OHD3 plus 4.0 mg 25-OHD3, and 350 micrograms 1 alpha-OHD3 alone significantly raised Ca and P(i) levels beginning on the 2nd day after injection and lasting for at least 6 days. These higher levels can be maintained by repeated injections. Another effect of injecting 1 alpha-OHD3 was to depress Mg blood levels, and a negative effect on the Ca and vitamin D3 metabolism is suggested which may cause hypocalcaemia when the effect of 1 alpha-OHD3 subsides. Metastatic calcifications of soft tissues were observed in some 1 alpha-OHD3-treated cows.

Effects of insulin and 1 alpha-hydroxy vitamin D3 on streptozotocin-induced diabetic rats fed a low zinc diet

Streptozotocin-induced diabetic rats (LZ-DM rats) developed nephrocalcinosis after being fed a low zinc diet for 4 weeks. However, administration of 1 alpha-hydroxy vitamin D3 (1-OHD3) or insulin inhibited the formation of nephrocalcinosis. The urinary calcium level increased when 1-OHD3 was administered to these rats, but decreased in the group receiving insulin. It was also observed that the femur recovered its hardness when insulin was administered, although the hardness in the LZ-DM rats remained lower than that of the control rats. Rat femur hardness, however, did not completely recover with 1-OHD3 treatment. These results indicate that the effects of insulin and 1-OHD3 differ, even though nephrocalcinosis was reduced by administration of either insulin or 1-OHD3. It appears that insulin assists bone formation, and the 1-OHD3 hastens calcium excretion.

Evidence for estrogen receptor-linked calcium transport in the intestine

Intestinal calcium malabsorption in postmenopausal osteoporotic women is often linked indirectly to decreased serum 1,25(OH)2 vitamin D or to intestinal resistance to its action, rather than directly to the low circulating estrogen that results following menopause. The studies presented indicate that the intestinal mucosal cells of rats contain estrogen receptor immunoreactivity, express the mRNA for estrogen receptors, and respond directly to 17 beta-estradiol with enhanced calcium transport that is suppressed by gene transcription and protein synthesis inhibitors. These findings suggest that estrogen has a physiological role in the regulation of intestinal calcium absorption and that its deficiency in postmenopausal osteoporosis, and following therapeutic oophorectomy, may result directly in calcium malabsorption that is believed to be an important factor in the bone loss that occurs in these conditions.