Secondary osteoporosis and its treatment--diabetes mellitus

Japanese epidemiological study showed higher frequency of osteopenia/osteoporosis in diabetic patients as compared with sex- and age-matched control. The mechanism by which bone loss occurs in diabetic patients could be explained by a reduction of insulin/insulin-like growth factor-I action, sustained hyperglycemic state, a generation of advanced glycosylation end-products, and diabetic complication such as neuropathy, nephropathy and myopathy. Osteoblast deficit is hypothesized to play a major role in the occurrence of diabetic osteopenia. Besides the deficiency of insulin and insulin-like growth factor-I, we demonstrated that sustained hyperglycemia alone causes suppression of osteoblast proliferation and its response to parathyroid hormone and 1 alpha, 25-dihydroxyvitamin D, Hyporesponse of osteoblast to 1 alpha, 25-dihydroxyvitamin D, was also confirmed in diabetic patients as reflected by a reduction in an incremental response of serum osteocalcin during 1 alpha, 25-dihydroxyvitamin D administration. The regimens having stimulatory effect on bone turnover, such as intermittent PTH therapy and vitamin D, are recommended to treat diabetic osteopenia, besides improvement of diabetic control state.     

Bronchogenic cyst: an unusual cause of lump in the neck

This article describes a patient in whom disseminated infection with coccidioidomycosis was associated with hypercalcemia. The patient had a low level of 1,25-dihydroxyvitamin D and a suppressed parathyroid hormone value, an indication that the hypercalcemia was not mediated by vitamin D or parathyroid hormone. The episode resolved readily with administration of pamidronate, an outcome suggesting that this is effective treatment of hypercalcemia of this origin. On follow-up of the patient while he was receiving antifungal therapy for Coccidioides immitis, calcium values remained normal.     

Parathyroid hormone-related protein: a regulated calcium-mobilizing product of the mammary gland

Parathyroid hormone-related protein shares similarities in sequence and function with the endocrine hormone, parathyroid hormone. However, unlike parathyroid hormone, a product of the parathyroid glands, parathyroid hormone-related protein has a wide distribution in tissues, including the mammary gland. Although during pregnancy the expression of parathyroid hormone-related protein in the mammary gland is low, following birth, protein levels rise sharply in the gland in response to elevations in serum prolactin. Large amounts of parathyroid hormone-related protein are secreted into milk, suggesting a possible role in the neonate. Transient phosphaturia and elevations of parathyroid hormone-related protein in mammary vein plasma support a possible endocrine function for parathyroid hormone-related protein during lactation. Recent evidence suggests a local function for parathyroid hormone-related protein in the lactating mammary gland, and evidence exists that parathyroid hormone-related protein stimulates calcium secretion by the goat mammary gland. Parathyroid hormone-related protein, a putative vasodilator, is produced by the external nutrient vasculature of the mammary gland, and levels within this tissue are regulated during lactation. Infusion of parathyroid hormone-related protein into the ovine mammary artery increases gland blood flow, suggesting a role for the protein in modulation of mammary gland hemodynamics. Regulation of parathyroid hormone-related protein synthesis by the lactating gland, together with the protein's actions on regional blood flow and calcium secretion, support an important function in the mammary gland during lactogenesis.     

In vivo parathyroid hormone stimulates in vitro bone resorption by bovine monocytes

Cells of the monocyte-macrophage lineage have been thought to play a role in bone resorption. We examined the effects of in vivo administration of parathyroid hormone and 1,25-dihydroxyvitamin D3 on the ability of monocytes to degrade bone in vitro. Administration of parathyroid hormone for 4 d resulted in sustained hypercalcemia and a transient 1-d increase in plasma 1,25-dihydroxyvitamin D3. Parathyroid hormone significantly stimulated bone degradation by monocytes 2.6 times more than that of pretreatment controls. Parathyroid hormone treatment significantly enhanced (threefold) release of superoxide anion by monocytes stimulated with phorbol 12-myristate 13-acetate and increased migration of monocytes to bone particles in vitro. Continuous 7-d infusion of 1,25-dihydroxyvitamin D3 (50 micrograms/d) elevated plasma 1,25-dihydroxyvitamin D3 until infusions were discontinued. Increased 1,25-dihydroxyvitamin D3 was associated with hypercalcemia, which continued for several days postinfusion. In vivo administration of 1,25-dihydroxyvitamin D3 did not affect in vitro ability of monocytes to degrade bone. We concluded that in vivo administration of parathyroid hormone enhanced in vitro responsiveness of isolated monocytes in a manner consistent with a role for monocytes in bone remodeling. Furthermore, these data suggested that circulating monocytes could be a useful experimental model for further studies on parathyroid hormone responsiveness and bone resorption for the cow with milk fever.     

Vitamin D receptor expression, 24-hydroxylase activity, and inhibition of growth by 1alpha,25-dihydroxyvitamin D3 in seven human prostatic carcinoma cell lines

Although prostatic cancer is often viewed as an androgen-dependent malignancy, a number of other hormones including 1alpha, 25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] are now recognized to modulate its growth and differentiated phenotype. Seven different continuous human prostatic carcinoma cell lines were examined for the presence of biologically active receptors for 1alpha,25(OH)2D3. All seven lines were found to contain mRNA for the vitamin D receptor using an RNase protection assay. Six of the seven cell lines were found to have high-affinity saturable binding sites for 1alpha,25(OH)2D3. The seventh line was found to contain vitamin D receptors by sucrose gradient analysis. All seven lines were found to express 24-hydroxylase activity by a HPLC assay that measures the conversion of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3. 24-Hydroxylase activity was up-regulated in all seven cell lines by preincubation with 1alpha,25(OH)2D3. In the presence of fetal bovine serum, the growth of four of the seven cell lines was inhibited. In the majority of cell lines growth inhibition was related not only to the number of receptors per cell, but also in inverse proportion to the 24-hydroxylase activity of each cell line. The ubiquitous presence of vitamin D receptor and 24-hydroxylase activity in human prostatic carcinoma cells suggests new alternatives for the pharmacological treatment of advanced prostatic cancer and implies that chemoprevention strategies could also make use of this endocrine axis.     

Aspects of 1,25-dihydroxyvitamin D3 binding sites in fish: an autoradiographic study

The distribution of specific binding sites for vitamin D3 in adult female and male Xiphophorus helleri is studies after injection of tritiated 1,25-dihydroxyvitamin D3 (vitamin D) by thaw-mount autoradiography. Five hours after injection of labeled vitamin D specific nuclear binding is present in brain, pituitary, skin, gills, cartilage, gut, liver, pancreas, spleen, kidney, muscle, ovary, and testis. Cytoplasmic binding exists strongest in gills, gut, and kidney while it is comparatively weak in hepatocytes. In reproductive organs cytoplasmic retention of radioactivity is also present in oocytes. Weak nuclear labeling exists in interstitial cells in ovary. Conspicuous nuclear labeling exists in active lobules of testis, while inactive lobules show occasionally a few labeled cells. The results demonstrate specific binding and retention of vitamin D in many target organs of teleost fish, suggesting an extensive and multifunctional regulatory role of this steroid hormone of sunlight.     

Cloning of human 25-hydroxyvitamin D-1 alpha-hydroxylase and mutations causing vitamin D-dependent rickets type 1

The secosteroid hormone, 1,25-dihydroxyvitamin D [1,25(OH)2D], plays a crucial role in normal bone growth, calcium metabolism, and tissue differentiation. The key step in the biosynthesis of 1,25(OH)2D is its 1 alpha-hydroxylation from 25-hydroxyvitamin D (25-OHD) in the kidney. Because its expression in the kidney is very low, we cloned and sequenced cDNA for 25-OHD-1 alpha-hydroxylase (P450c1 alpha) from human keratinocytes, in which 1 alpha-hydroxylase activity and mRNA expression can be induced to be much greater. P450c1 alpha mRNA was expressed at much lower levels in human kidney, brain, and testis. Mammalian cells transfected with the cloned P450c1 alpha cDNA exhibit robust 1 alpha-hydroxylase activity. The identity of the 1,25(OH)2D3 product synthesized in transfected cells was confirmed by HPLC and gas chromatography-mass spectrometry. The gene encoding P450c1 alpha was localized to chromosome 12, where the 1 alpha-hydroxylase deficiency syndrome, vitamin D-dependent rickets type 1 (VDDR-1), has been localized. Primary cultures of human adult and neonatal keratinocytes exhibit abundant 1 alpha-hydroxylase activity, whereas those from a patient with VDDR-1 lacked detectable activity. Keratinocyte P450c1 alpha cDNA from the patient with VDDR-1 contained deletion/frameshift mutations either at codon 211 or at codon 231, indicating that the patient was a compound heterozygote for two null mutations. These findings establish the molecular genetic basis of VDDR-1, establish a novel means for its study in keratinocytes, and provide the sequence of the key enzyme in the biological activation of vitamin D.     

A definition of catheter-related infection

A 5 year old boy with normal phenotype and normal renal function presented tetany. Hypocalcemia and hyperphosphatemia, with increased serum levels of parathyroid hormone (PTH) were detected in serial measurements. Pseudohypoparathyroidism was diagnosed. This disease presents the biochemical abnormalities of hypoparathyroidism (hypocalcemia, hyperphosphatemia) with peripheral resistance to PTH activity. The patient was treated effectively with calcium and vitamin D supplements. The causes of hypocalcemia related to parathyroid gland activity are reviewed and the physiopathology of pseudohypoparathyroidism is described.     

Targeted ablation of the vitamin D receptor: an animal model of vitamin D-dependent rickets type II with alopecia

Vitamin D, the major steroid hormone that controls mineral ion homeostasis, exerts its actions through the vitamin D receptor (VDR). The VDR is expressed in many tissues, including several tissues not thought to play a role in mineral metabolism. Studies in kindreds with VDR mutations (vitamin D-dependent rickets type II, VDDR II) have demonstrated hypocalcemia, hyperparathyroidism, rickets, and osteomalacia. Alopecia, which is not a feature of vitamin D deficiency, is seen in some kindreds. We have generated a mouse model of VDDR II by targeted ablation of the second zinc finger of the VDR DNA-binding domain. Despite known expression of the VDR in fetal life, homozygous mice are phenotypically normal at birth and demonstrate normal survival at least until 6 months. They become hypocalcemic at 21 days of age, at which time their parathyroid hormone (PTH) levels begin to rise. Hyperparathyroidism is accompanied by an increase in the size of the parathyroid gland as well as an increase in PTH mRNA levels. Rickets and osteomalacia are seen by day 35; however, as early as day 15, there is an expansion in the zone of hypertrophic chondrocytes in the growth plate. In contrast to animals made vitamin D deficient by dietary means, and like some patients with VDDR II, these mice develop progressive alopecia from the age of 4 weeks.     

Observations on pain and suffering

The researches on the mode of action of vitamin D have shown that vitamin D3 in animals is not utilized as such but after Hydrosylation of carbon 25 in the liver and of carbon 1 in the kidney. 1alpha,25-dihdroxycholecalciferol (1alpha,25-(OH)2D3) is the active on two target organis the intestin and bones, acting as a steroid hormone. In the intestin it controls the syntesis of a specific calcium binding protein (CaPB) responsable for calcium absorption. At the bone level it act on the deposition of calcium salts, and whenever necessary on its mobilization. Therefore 1alpha,25(OH)2D3 is active part of the calcium homeostatic system in the organism together with specific hormones such as parathyroid hormone and calcitonin.     

The histostructure of the adrenal gland in the Campbell hamster after extirpation of a specific midventral gland]

The receptors for retinoic acid (RA) and for 1 alpha,25-dihydroxyvitamin D3 (VD), RAR, RXR, and VDR are ligand-inducible members of the nuclear receptor superfamily. These receptors mediate their regulatory effects by binding as dimeric complexes to response elements located in regulatory regions of hormone target genes. Sequence scanning of the tumor necrosis factor-alpha type 1 receptor (TNF alpha RI) gene identified a 3' enhancer region composed of two directly repeated hexameric core motifs spaced by 2 nucleotides (DR2). On this novel DR2-type sequence, but not on a DR5-type RA response element, VD was shown to act through its receptor, the vitamin D receptor (VDR), as a repressor of retinoid signalling. The repression appears to be mediated by competitive protein-protein interactions between VDR, RAR, RXR, and possibly their cofactors. This VDR-mediated transrepression of retinoid signaling suggests a novel mechanism for the complex regulatory interaction between retinoids and VD.     

Parathyroidectomy reduces 25-hydroxyvitamin D3-1 alpha-hydroxylase activity in the hypocalcemic vitamin D-deficient chick

To test the hypothesis that in the vitamin D-deficient state the activity of 25-hydroxyvitamin D3-1 alpha-hydroxylase (25-OHD3-1 alpha-hydroxylase) is modulated by parathyroid hormone and the plasma concentration of phosphate only in the presence of small amounts of 1,25-dihydroxyvitamin D3 (or some other metabolite of vitamin D), we measured the activity of this enzyme 24 h after parathyroidectomy (PTX) in frankly hypocalcemic, vitamin D-deficient chicks that were not supplemented with vitamin D or one of its metabolites. The otherwise predictable complications of PTX in this metabolic setting (hypocalcemia of increasing severity, tetany, moribundity, and death) were prevented by continuous intravenous administration of calcium (as a solution of calcium chloride/calcium gluconate 1:1) through a catheter in the external jugular vein placed at the time of PTX. The findings were as follows: (a) The activity of 25-OHD3-1 alpha-hydroxylase was significantly less in the parathyroidectomized group than in the sham-operated control chicks (P less than 0.001). (b) The reductive effect of PTX on the activity of this enzyme was significantly attenuated when hypophosphatemia was increased in severity by administration of glucose. (c) In the post-PTX state the activity of 25-OHD3-1 alpha-hydroxylase and plasma concentration of phosphate were significantly, inversely related (P less than 0.001). (d) In the sham-operated control group the activity of this enzyme and the plasma concentration of phosphate were not significantly correlated. These findings indicate that in the vitamin D-deficient state, both circulating parathyroid hormone and the plasma concentration of phosphate can significantly modulate the activity of 25-OHD3-1 alpha-hydroxylase in the absence of vitamin D or its metabolites. The findings also suggest that in the vitamin D-deficient state the plasma concentration of phosphate modulates the activity of this enzyme only when the concentration of circulating parathyroid hormone is not increased.     

Calcium and vitamin D status of pregnant teenagers in Maiduguri, Nigeria

This study investigates parameters related to calcium and bone metabolism by determining the concentrations of total calcium, 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, parathyroid hormone, and phosphorous in young pregnant women. The patient population was 30 pregnant Nigerian teenage women grouped by trimester (10 per group), 10 women immediately following delivery, and 21 healthy age-matched controls. On the basis of serum prealbumin levels, the general nutrition of the pregnant women was found to be significantly below that of the more privileged and better-educated nonpregnant controls. The mean total calcium concentration in sera of the third-trimester women was 8.83 mg/dL, which was significantly below that of the controls (9.77 mg/dL) and the first-trimester group (9.30 mg/dL). Despite the 10% to 15% decline in the serum level of total calcium during pregnancy, the parathyroid hormone level decreased markedly from 0.60 to 0.61 ng/mL in the first and second trimesters to 0.41 ng/mL in the third trimester. Serum vitamin D and 1,25-dihydroxyvitamin D levels in the second and third trimesters were within the normal range. These data indicate that toward the end of gestation, pregnant teenagers in northern Nigeria appear to become calcium deficient and do not exhibit the expected increase in serum parathyroid hormone levels normally seen in pregnant women.     

Association of nucleoside diphosphate kinase nm23-H2 with human telomeres

In this study, the effect of dietary calcium and vitamin D on serum parathyroid hormone and vitamin D metabolites was measured in 376 free-living women aged 65-77 y. Mean calcium intake in both groups was close to the recommended dietary allowance of 800 mg/d. Mean vitamin D intake in the 245 women not taking vitamin D supplements was 3.53 microg/d (141 IU/d), which is below the recommended dietary allowance of 5 microg/d (200 IU/d). To test the hypothesis that vitamin D is more important than calcium in reducing serum parathyroid hormone, the source of dietary calcium intake was subdivided into milk, which is fortified with vitamin D, and nonmilk sources. The serum parathyroid hormone concentration was inversely correlated with calcium intake derived from milk (r = -0.20, P < 0.01) but not from nonmilk sources (r = -0.06). Furthermore, serum calcidiol correlated with milk calcium intake (r = 0.35, P < 0.001) but not with nonmilk calcium intake (r = 0.10). Multivariate analysis showed a significant effect of season on serum calcidiol but not on serum parathyroid hormone. Serum parathyroid hormone was inversely correlated with serum calcidiol (r = -0.33, P < 0.001) and the regression predicted that mean serum parathyroid hormone would be reduced in the elderly to concentrations considered normal in the young when serum calcidiol is 122 nmol/L (49 ng/mL); this would require a much higher recommended dietary allowance for vitamin D than 5 microg/d (200 IU/d).     

Calcitropic peptides: neural perspectives

In mammals and higher vertebrates, calcitropic peptides are produced by peripheral endocrine glands: the parathyroid gland (PTH), thyroid or ultimobranchial gland (calcitonin) and the anterior pituitary gland (growth hormone and prolactin). These hormones are, however, also found in the neural tissues of lower vertebrates and invertebrates that lack these endocrine organs, suggesting that neural tissue may be an ancestral site of calcitropic peptide synthesis. Indeed, the demonstration of CNS receptors for these calcitropic peptides and their induction of neurological actions suggest that these hormones arose as neuropeptides. Neural and neuroendocrine roles of some of these calcitropic hormones (calcitonin and parathyroid hormone) and related peptides (calcitonin gene related peptide, stanniocalcin and parathyroid hormone related peptide) are thus the focus of this review.     

A memorial. Professor Sylvester E. Berki, 1930-1996

1 alpha,25-Dihydroxyvitamin D3[1 alpha,25(OH)2D3], an active form of vitamin D, has roles in many biological phenomena such as calcium homeostasis and bone formation, which are thought to be mediated by the 1 alpha,25(OH)2D3 receptor (VDR), a member of the nuclear hormone receptor superfamily. However, the molecular basis for the actions of 1 alpha,25(OH)2D3 in bone formation, its role during development and VDR genetic polymorphisms for predicting bone mineral density are uncertain. To investigate the functional role of VDR, we generated mice deficient in VDR by gene targeting. We report here that in VDR null mutant mice, no defects in development and growth were observed before weaning, irrespective of reduced expression of vitamin D target genes. After weaning, however, mutants failed to thrive, with appearance of alopoecia, hypocalcaemia and infertility, and bone formation was severely impaired as a typical feature of vitamin D-dependent rickets type II (refs 8, 9). Unlike humans with this disease, most of the null mutant mice died within 15 weeks after birth, and uterine hypoplasia with impaired folliculogenesis was found in female reproductive organs. These defects, such as alopoecia and uterine hypoplasia, were not observed in vitamin D-deficient animals. The findings establish a critical role for VDR in growth, bone formation and female reproduction in the post-weaning stage.     

Effects of dietary vitamin D intake on plasma levels of parathyroid hormone and vitamin D metabolites in healthy Japanese

To clarify the nutritional status of vitamin D in Japanese, effects of dietary intake of vitamin D on plasma levels of intact and highly sensitive parathyroid hormone (I-PTH and HS-PTH), 25-hydroxyvitamin D (25-OH-D), 1,25-dihydroxyvitamin D (1,25(OH)2D), calcium (Ca) and phosphorus (P(i)) in 79 healthy Japanese were investigated. The plasma levels of 25-OH-D in men were significantly higher than those in women, whereas those of HS-PTH in men were significantly lower than those in women. The levels of 25-OH-D in men were generally higher than those in women. Significant correlations were observed between the dietary vitamin D intake and the plasma 25-OH-D or HS-PTH levels. Correlations between the plasma 25-OH-D levels and the plasma HS-PTH levels were also significant. These results suggest that dietary intake of sufficient amounts of vitamin D is effective for improving the vitamin D nutritional status through normalizing PTH levels.     

Electrolyte quintet: Calcium

Abnormalities in serum calcium concentration may have profound effects on neurological, gastrointestinal, and renal function. Maintenance of the normal serum calcium is a result of tightly regulated ion transport by the kidney, intestinal tract, and bone, mediated by calcaemic hormones especially parathyroid hormone and 1,25-dihydroxyvitamin D3. Abnormalities in calcium transport that result in uncompensated influx into, or efflux from, the extracellular fluid, will result in hypercalcaemia or hypocalcaemia, respectively. When possible the biologically important ionised calcium concentration should be measured. A variety of common disorders are responsible for abnormalities in the serum calcium. Treatment of both hypercalcaemia and hypocalcaemia is dependent on the underlying disorder, the magnitude of the deviation of the serum calcium, and the severity of symptoms. Fortunately, in the case of hypercalcaemia, there is a broad selection of effective medications, especially the bisphosphonates. Treatment of hypocalcaemia relies on the provision of calcium and often vitamin D. In this article we review the mechanisms responsible for abnormalities in calcium homoeostasis, the differential diagnosis of hypercalcaemia and hypocalcaemia, and appropriate therapy.     

Synthesis, stereochemistry, and biological activity of 1alpha,23,25-trihydroxy-24-oxovitamin D3, a major natural metabolite of 1alpha,25-dihydroxyvitamin D3

The C(23) epimers of 1alpha,23,25(OH)3-24-oxovitamin D3, a major natural metabolite of the secosteroid hormone, 1alpha,25(OH)2D3, were chemically synthesized for the first time. The metabolite was synthesized by palladium coupling of the appropriate CD ring analog with an A ring enyne. Various approaches from quinic acid to the A ring precursors were explored, and a new route to the A ring enyne from quinic acid was developed. The C(23) stereochemistry of the natural 1alpha,23,25(OH)3-24-oxovitamin D3 produced in neonatal human keratinocytes was determined to be S on the basis of the 1H NMR and the HPLC data. The biological activity of 1alpha,23(S), 25(OH)3-24-oxovitamin D3 in primary cultures of bovine parathyroid cells was determined by comparing the potency of this metabolite to that of 1alpha,25(OH)2D3 in suppression of parathyroid hormone (PTH) secretion. The results indicate that 1alpha,23(S), 25(OH)3-24-oxovitamin D3 potently suppressed PTH secretion even at concentrations as low as 10(-)12 M and is equipotent with 1alpha, 25(OH)2D3. The high activity of 1alpha,23(S),25(OH)3-24-oxovitamin D3 cannot be explained on the basis of its affinity for the vitamin D receptor as this metabolite was found to be 10 times less effective than radioinert 1alpha,25(OH)2D3 in blocking the uptake and receptor binding of [3H]-1alpha,25(OH)2D3 in intact parathyroid cells. Further studies are required to explain the molecular basis for the activity of 1alpha,23(S),25(OH)3-24-oxovitamin D3 in its ability to suppress PTH secretion. In summary, our present study indicates that the C(23) stereochemistry of the natural 1alpha,23, 25(OH)3-24-oxovitamin D3 is S and this metabolite is equipotent to 1alpha,25(OH)2D3 in suppressing PTH secretion.     

Molecular cloning and hormonal regulation of PiT-1, a sodium-dependent phosphate cotransporter from rat parathyroid glands

The extracellular concentration of inorganic phosphate (Pi) is an important determinant of parathyroid cell function. The effects of Pi may be mediated through specific molecules in the parathyroid cell membrane, one candidate molecule for which would be a Na+-dependent Pi cotransporter. A complementary DNA encoding a Na+-Pi cotransporter, termed rat PiT-1, has now been isolated from rat parathyroid. The 2890-bp complementary DNA encodes a protein of 681 amino acids that shows sequence identities of 97% and 93% with the type III Na+-Pi cotransporters mouse PiT-1 and human PiT-1, respectively. Expression of rat PiT-1 in Xenopus oocytes revealed that it possesses Na+-dependent Pi cotransport activity. PiT-1 messenger RNA (mRNA) is widely distributed in rat tissues and is most abundant in brain, bone, and small intestine. The amount of PiT-1 mRNA in the parathyroid of vitamin D-deficient rats was reduced compared with that in normal animals and increased markedly after administration of 1,25-dihydroxyvitamin D3. Furthermore, the abundance of PiT-1 mRNA in the parathyroid was much greater in rats fed a low-Pi diet than in those fed a high-Pi diet. Thus, rat PiT-1 may contribute to the effects of Pi and vitamin D on parathyroid function.