Recognition of osteopontin and related peptides by an alpha v beta 3 integrin stimulates immediate cell signals in osteoclasts

We have investigated the nature of immediate cell signals produced by occupancy of the chicken osteoclast alpha v beta 3 integrin. Synthetic osteopontin and peptides from the osteopontin and bone sialoprotein sequences containing Arg-Gly-Asp stimulated immediate reductions in osteoclast cytosolic Ca2+. The changes in cytosolic Ca2+ required the Arg-Gly-Asp sequence and were blocked by a monoclonal antibody to the alpha v beta 3 integrin, LM609. Osteoclast stimulation by the proteins through the integrin did not require immobilization since soluble peptides produced changes in cytosolic Ca2+ and inhibited osteoclast binding to bone particles and bone resorption. The decrease in cytosolic Ca2+ stimulated by osteopontin and related peptides appeared to be due to activation of a plasma membrane Ca(2+)-ATPase by calmodulin. Thus, the data suggest that ligand binding to the osteoclast alpha v beta 3 integrin results in calmodulin-dependent reduction in cytosolic Ca2+ which participates in regulation of osteoclast function.

Generation of avian cells resembling osteoclasts from mononuclear phagocytes

Several lines of indirect evidence suggest that a monocyte family precursor gives rise to the osteoclast, although this hypothesis is controversial. Starting with a uniform population of nonspecific esterase positive, tartrate-sensitive, acid phosphatase-producing, mannose receptor-bearing mononuclear cells, prepared from dispersed marrow of calcium-deprived laying hens by cell density separation and selective cellular adherence, we generated multinucleated cells in vitro. When cultured with devitalized bone, these cells show, by electron microscopy, the characteristic osteoclast morphology in that they are mitochondria-rich, multinucleated, and, most importantly, develop characteristic ruffled membranes at the matrix attachment site. Moreover, as documented by scanning electron microscopy, these cells pit bone slices in a manner identical to freshly isolated osteoclasts. In addition, isoenzymes of acid phosphatase from generated osteoclasts, separated by 7.5% polyacrylamide gel electrophoresis at pH 4, are identical to those of mature osteoclasts in migration pattern and tartrate resistance, although the precursor cells from which the osteoclasts are generated produce an entirely different isoenzyme, which is tartrate-sensitive and migrates less rapidly at pH 4. The fused cells also exhibit a cAMP response to prostaglandin E2. Therefore, osteoclast-like cells can be derived by in vitro culture of a marrow-derived monocyte cell population.

Immunohistochemical localization of calbindins (28K and 9K) in the tissues of the baboon Papio ursinus

An indirect immunoperoxidase procedure was used to detect the presence of calbindin-D28K and calbindin-D9K in the cerebellum, kidney, and duodenum of the baboon Papio ursinus. Antibodies to chick calbinding-D28K and to both rat and mouse calbindin-D9K were used. The cerebellum and kidney were shown to contain calbindin-D28K; the doudenum contained calbindin-D9K. In the cerebellum, positive staining was found in the Purkinje cells only; in the kidney, positive staining was found in the distal convoluted tubules, connecting tubules, and collecting tubules, extending deep into the medullary regions of the kidney. Staining in the duodenum was confined to the enterocytes of the villi, with no stain present in the crypt regions or goblet cells. Thus the baboon, a primate, contains the larger of the calbindins in both the cerebellum and kidney as does the human and monkey, but its distribution in the kidney is more generalized than that found in humans. The molecular weight of calbindin-D9K was found to be similar to that found in other animals. However, the calbindin-D28K from the baboon tissues appears to be slightly smaller than the protein found in other animals and may therefore be of similar size to the human calbindin-D28K (Mr 26,000).

Appearance during chick embryogenesis of vitamin D-dependent calcium-binding protein (calbindin-D28K)

The appearance of the vitamin D-dependent calcium-binding protein (calbindin-D28K) in embryonic chick tissues was determined using a sensitive immunohistochemical assay to elucidate the possible role of calbindin-D28K during embryogenesis. This protein first occurs in renal, cerebellar and intestinal cells during the final stages of maturation and/or differentiation. It is during this period of their development that these tissues become functional. On the basis of our observations, we suggest that the onset of cell function may be coupled with the appearance of calbindin-D28K.

Endemic skeletal fluorosis in children: hypocalcemia and the presence of renal resistance to parathyroid hormone

Although endemic skeletal fluorosis has been reported in children, hypocalcemia has not been previously noted. In a prevalence study of 260 schoolchildren living in an endemic fluorosis area in South Africa (water fluoride content 8-12 ppm), hypocalcemia was documented in 23%. Furthermore in a separate study of nine children with skeletal symptoms due to endemic fluorosis, hypocalcemia was found in six. 1,25-Dihydroxyvitamin D levels were elevated in the seven children in whom it was measured. Parathyroid hormone (PTH) stimulation tests on admission revealed evidence of impaired phosphaturic responses, typical of acquired pseudohypoparathyroidism type II, and a direct correlation between serum calcium values and the degree of phosphaturia was noted. Repeat tests performed in two of the children after correction of the hypocalcemia by dietary means, revealed a return of normal renal responsiveness. Serum calcium values also correlated inversely with the degree of osteomalacia on iliac crest bone histomorphometry. It is suggested that low dietary calcium intakes might exacerbate the severity of the bone lesions in children living in areas of endemic fluorosis.

Bone mineralization and mineral homeostasis in very low-birth-weight infants fed either human milk or fortified human milk

Abnormalities in bone mineral metabolism are frequently found in very low-birth-weight infants, especially if fed breast milk. To assess the efficacy of a breast-milk fortifier in the feeding of these very small infants, very low-birth-weight babies (between 1,000 g-1,500 g at birth) were randomly assigned to one of two groups on day 4 of life. The fortified group received the fortifier mixed in equal proportions with their own mother's milk, while the breast-milk group received only their own mother's milk. All infants received an oral vitamin D supplement of 750 IU/day. The study was continued until the infants weighed 1,800 g, at which stage breast feeding was encouraged. Thirty infants in the breast-milk group and 29 in the fortified group completed the study. Infants in the fortified group had significantly lower alkaline phosphatase values, a greater bone mineral content (BMC) and BMC/bone width ratio, and lower urinary calcium excretion than the breast-milk group at a weight of 1,800 g. At follow-up study 3 months after delivery, when most of the infants in both groups had been breast fed for at least 6 weeks, the breast-milk group's biochemical and BMC abnormalities were almost totally corrected and were now similar to those of the fortified group. Thus, the addition of the fortifier to breast milk during the first 4-6 weeks of life decreased the biochemical evidence of abnormal bone mineral homeostasis and increased BMC in very low-birth-weight infants. By 3 months of age, however, the breast-milk group had almost totally corrected its abnormalities.

Selective culture of primate marrow-derived macrophages in medium devoid of protein additives

Viable cultures of bone marrow-derived macrophages (BMM phi) from a primate source, the baboon, were maintained for up to 4 weeks in culture in the absence of any exogenous protein in the medium. Baboon peripheral blood monocytes, spleen, lung, and liver M phi s or human BMM phi failed to survive for greater than 4 days. The protein-free BMM phi cultures were morphologically distinctive by virtue of the extremely dendritic appearance of the M phi s. In contrast baboon marrow cultured in the presence of fetal calf serum led to the overgrowth of fibroblastoid cells and in the presence of horse serum produced numbers of giant cells or polykaryocytes in addition to M phi s. The BMM phi were capable of nonimmune phagocytosis of yeast particles, expressed Ia antigen on their surfaces (59%), and were positive cytochemically for nonspecific (alpha-naphthyl acetate) esterase, oil red O, and tartrate resistant acid phosphatase. The addition of sera to established protein-free BMM phi cultures induced a rapid change of shape, viz., retraction of the dendritic processes and rounding up of the M phi s apparent within 10 min. This shape change was not induced by the addition of hemopoietic growth factors granulocyte-macrophage colony-stimulating factor (GM-CSF), granulocyte CSF (G-CSF), macrophage CSF (M-CSF), or interleukin 3 (IL-3), nor could it be inhibited by the calcium channel blocking agent Nifedipine. Low levels of M-CSF activity, assayed by the murine bone marrow proliferation assay, were detected in the supernatant.

25-Hydroxyvitamin D3 metabolism in a human leukemia cell line

1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is a potent inducer of monocytic differentiation of the human promyelocytic leukemia cell line, HL-60. We have noted that 25-hydroxyvitamin D3 (25(OH)D3) in high doses is also capable of promoting monocytic differentiation of this cell line. To test the possibility that the latter activity is due to conversion of 25OHD3 to 1,25(OH)2D3 by HL-60, we exposed HL-60 cells to 25OHD3 and analyzed the products by HPLC and radioreceptor assay. When chromatographed in the traditional solvent system (isopropanol-hexane), a new peak appears which migrates with authentic 1,25(OH)2D3. However, in a solvent system containing dichloromethane, 90% of the peak migrates with another metabolite, 19-Nor-10-Keto-25OHD3 (19-Nor-25OHD3). Production of this metabolite is enhanced by living cells and is synthesized by both virgin HL-60 and those which have undergone differentiation. We next determined if authentic 19-Nor-25OHD3 also promotes differentiation of this cell. As assessed by appearance of the monocyte-specific surface antigen (63D3) and macrophage-specific esterase activity, we find that this metabolite does, in fact, induce monocytic differentiation of HL-60 with a potency of approximately 1/200 that of 1,25(OH)2D3 and similar to that of 25OHD3. In agreement with the effect upon cell maturation, 19-Nor-25OHD3 displaces 3H-1,25(OH)2D3 from its HL-60 receptor with an efficiency comparable to 25OHD3. Hence, HL-60 cells convert 25OHD3 to 19-Nor-25OHD3, and 19-Nor-25OHD3 induces monocytic differentiation of HL-60 with comparable efficiency to its precursor, 25OHD3.

Acquired hypophosphataemic vitamin D resistant rickets in black children

The case histories of five black children aged between 4 1/2 and 9 years, with acquired hypophosphataemic vitamin D resistant rickets are presented. Muscle weakness was a striking feature clinically, while radiographically all had marked osteopenia in association with classical florid rickets. Biochemically, they were normocalcaemic and hypophosphataemic, with normal parathyroid hormone concentrations. In three of the children 1,25-dihydroxyvitamin D concentrations were low. One child responded to no specific therapy, while three required continuous 1 alpha-hydroxyvitamin D and oral phosphate supplementation, and the fifth 1 alpha-hydroxyvitamin D therapy alone before the clinical, biochemical and radiographic picture responded. The features in three of the children resemble oncogenous rickets, but the features of the other two do not fit any known aetiology. Although the group as a whole may be heterogeneous, until the pathogenetic mechanisms are determined, the authors believe they should be grouped together as acquired hypophosphataemic vitamin D resistant rickets.

Specific binding of 24R,25-dihydroxyvitamin D3 to chick intestinal mucosa: 24R,25-dihydroxyvitamin D3 is an allosteric effector of 1,25-dihydroxyvitamin D3 binding

We have previously described a significant decrease in the positive cooperativity level and affinity of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] binding to its chick intestinal chromatin receptor induced in vitro by a physiological 10-fold molar excess of (24R)-25-dihydroxyvitamin D3 [24R,25(OH)2D3] [F. Wilhelm and A. W. Norman (1985) Biochem. Biophys. Res. Commun. 126, 496-501]. In this report, we have initiated a comparative study of the binding of 24R,25(OH)2[3H]D3 and 1,25(OH)2[3H]D3 to the the intestinal chromatin fraction obtained from vitamin D-replete birds. 24R,25(OH)2[3H]D3 specific binding to this chromatin fraction was characterized by a dissociation constant (Kd) of 34.0 +/- 6.4 nM, a positive cooperativity level (nH) of 1.40 +/- 0.13, and a capacity (Bmax) of 47 +/- 8 fmol/mg protein. The very low relative competitive index (RCI) of 24R,25(OH)2D3 (0.11 +/- 0.03%) for the 1,25(OH)2D3 binding site/receptor, as well as the inability of 1,25(OH)2D3 to displace 24R,25(OH)2D3 from its binding site at a physiological molar ratio of 1:10, strongly suggest the independence of 24R,25(OH)2D3 and 1,25(OH)2D3 binding sites. Stereospecificity of the 24R,25(OH)2D3 binding sites was attested by the displacement of only 45 +/- 6% of 24R,25(OH)2D3 specific binding by equimolar concentrations of 24S,25(OH)2D3. Collectively these results suggest the existence of a binding domain/receptor for 24,25(OH)2D3 in the chick intestine which is independent of the 1,25(OH)2D3 receptor.

Mineral homeostasis in very low birth weight infants fed either own mother's milk or pooled pasteurized preterm milk

As part of a randomised controlled study to assess the effect of pasteurization of breast milk on the growth of very-low-birth-weight infants, the longitudinal changes in serum calcium, phosphorus, alkaline phosphatase, 25-hydroxyvitamin D, and bone-gla-protein concentrations were investigated. Infants fed untreated own mother's milk grew more rapidly than those fed pasteurized pooled preterm milk and had higher serum alkaline phosphatase and lower phosphorus values. Serum calcium and 25-hydroxyvitamin D (25-OHD) concentrations were similar in the two groups. Despite the provision of 750 IU vitamin D daily from the 2nd week of life, serum 25-OHD values remained low in a number of infants in both groups, suggesting that either malabsorption of vitamin D or hepatic immaturity might be responsible for the persistently low values. Bone-gla-protein rose significantly after birth and was correlated with alkaline phosphatase values, but not with 25-OHD or phosphorus values. The study supports previous work that indicates that the low phosphorus content of breast milk is probably responsible for biochemical evidence of inadequate bone mineralization and that despite vitamin D supplementation, 25-OHD values do not rise adequately. Thirty-six infants were reexamined between 4 and 11 months after birth. The 25-OHD values had risen significantly in all infants except one who had vitamin D deficiency rickets.

Activity of ornithine decarboxylase and creatine kinase in soft and hard tissue of vitamin D-deficient chicks following parenteral application of 1,25-dihydroxyvitamin D3 or 24R,25-dihydroxyvitamin D3

We investigated the stimulation of creatine kinase (CK) and ornithine decarboxylase (ODC) by 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3] in doses ranging from 1.625 to 6500 pmol in 4-week-old vitamin D-deficient chicks. Enzyme activities were monitored for 72 h. 1,25(OH)2D3 but not 24R,25(OH)2D3 enhanced the activity of ODC in duodenum and bone. The time course of ODC activity in bone was biphasic, with an increase after 1 h and a higher peak after 24 h. Diaphyses and epiphyses responded equally well after a dose of 6500 pmol. The kidney, liver, and lung showed 1.5-3.8-fold increase in CK activity following 1,25(OH)2D3, reaching a maximum between 3-5 h. However, sustained stimulation of CK activity could still be demonstrated after 72 h, and the 48-h levels in the lung even exceeded the 5-h values. No change of activity of either enzyme was noted in heart and brain after application of 1,25(OH)2D3. There was no coincidence of stimulation of ODC and CK by 1,25(OH)2D3 in the same tissue, and the dose-responsiveness of both enzymes differed considerably. Near maximum activities of ODC were achieved with 19.5 pmol 1,25(OH)2D3 in duodenum and pancreas, while maximum responses of CK occurred in the liver at 195 pmol and in lung and kidney at 6500 pmol. 24R,25(OH)2D3 failed to produce any consistent effects of either enzyme in all tissues examined. These results, particularly the lack of response to 24R,25(OH)2D3, are different from those reported in rats.

Baboon erythrocyte ghosts contain beta-adrenergic receptors

We have used the beta-adrenergic antagonist [3H]dihydroalprenolol [( 3H]DHA) to identify binding sites on the erythrocyte membrane of the primate Papio ursinus. Analysis of the saturation isotherm revealed binding to be saturable with a maximal number of binding sites of 499 fmol/mg protein. [3H]DHA binds specifically to the erythrocyte ghosts with an apparent dissociation constant (Kd) of 0.57 +/- 0.06 nM. A similar value for Kd (0.46 +/- 0.07 nM) was evaluated from the rate constants of association (0.013 +/- 0.003 X nM-1 X min-1) and dissociation (0.006 +/- 0.001 X min-1). beta-adrenergic agonists compete for the binding sites with an order of potency (dl-isoproterenol greater than l-epinephrine greater than l-norepinephrine) typical of a beta 2-adrenergic receptor. Binding was shown to be stereospecific with l-stereoisomers being more potent than their corresponding d-stereoisomers in causing half-maximal inhibition. Isoproterenol stimulated the production of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) in a concentration-dependent manner, maximal levels (1.130 +/- 0.358 pmol cAMP/10(8) cells) being four times the basal levels. The results demonstrate the existence of a large number of beta-adrenergic receptors on baboon erythrocyte ghosts.

Is craniotabes a pathognomonic sign of rickets in 3-month-old infants?

Fifty-eight well Black infants between the ages of 10 and 15 weeks were examined for the presence of craniotabes and investigated for the presence of vitamin D deficiency and rickets. Thirty-five infants were found to have craniotabes and 5 of these had radiological evidence of rickets. No difference in dietary history, birth weight, weight gain, length or skull circumference was found between those with and those without craniotabes. Significantly more females than males had craniotabes. The majority of infants with craniotabes had normal biochemical values. Craniotabes is a common finding in 3-month-old infants and is of no help in diagnosing rickets in this age group.

Maternal-infant vitamin D relationships during breast-feeding

To evaluate the effect of maternal dietary vitamin D intake on infant vitamin D status in a country with a temperate climate, but where the commercial milk supply is not vitamin D fortified, this randomized, double-blind study was conducted on term mother-infant pairs during the winter months. Well-nourished, white nursing mothers were given a placebo, 500 IU vitamin D/day or 1,000 IU vitamin D/day; their infants were not given supplemental vitamin D. After six weeks, mothers receiving supplemental vitamin D had higher levels of 25-hydroxyvitamin D than had mothers receiving placebo. A direct relationship was observed between maternal and infant levels of 25-hydroxyvitamin D at six weeks, implying that maternal vitamin D intake directly affects the vitamin D concentration in breast milk. A control group of infants who had received 400 IU vitamin D/day had even higher concentrations of 25-hydroxyvitamin D, suggesting that infant supplementation with vitamin D is more efficacious than maternal supplementation. Despite the favorable climate in South Africa, during winter breast-fed infants have low serum vitamin D values if maternal dietary vitamin D intake is low.

Histological osteomalacia due to dietary calcium deficiency in children

We performed a histomorphometric study of trabecular-bone formation and resorption in undecalcified sections of iliac crest from three children presenting with clinical, radiologic, and biochemical evidence of rickets associated with dietary calcium deficiency. All three children had severe osteomalacia documented by hyperosteoidosis and reduced static and dynamic indicators of bone mineralization. There was a reduction of the calcified bone volume associated with a decreased bone formation rate and features of increased bone resorption. Correction of dietary calcium intake in two of the patients led to normal serum and urinary calcium levels and reduced alkaline phosphatase levels. After calcium therapy, the calcified bone volume was normal and indicators of bone mineralization returned to normal. We conclude that low calcium intake in children may be associated with a histologic picture of severe osteomalacia. Our finding that adequate amounts of calcium rapidly improved bone mineralization demonstrates that calcium deficiency can cause osteomalacia in children.

On the pyrogenic action of intravenous lipid A in rabbits

1. Previous evidence purporting to show that lipid A is the pyrogenic moiety of endotoxin is demonstrably inconclusive. 2. We have extracted lipid A from endotoxin of Salmonella typhosa and tested the pyrogenic action of the lipid A, the residual polysaccharide and the parent endotoxin, by intravenous injection in conscious rabbits. 3. Lipid A dissolved in an aqueous solution of rabbit serum albumin induced a significant pyrexia of short latency, while neither rabbit serum albumin alone, nor the polysaccharide from S. typhosa, affected body temperature. The physical presence in the injectate of the polysaccharide from S. typhosa did not enhance the pyrogenicity of the lipid. 4. Dose-response curves for lipid A and the parent endotoxin, over the dose range 10 ng-20 micrograms, showed that lipid A incorporated in endotoxin was much more pyrogenic than pure lipid A in solution. When separated from the polysaccharide component of endotoxin, lipid A lost more than 99.9% of its pyrogenic activity, at threshold doses.

Recent advances in the understanding of the metabolism and functions of vitamin D

Many advances have been made in the past several years in our understanding of the metabolism and mechanism of action of vitamin D. Recognition of the clinical implications of this knowledge continues to grow. Despite these gains, however, many questions remain unanswered. These include the role of 24,25(OH)2D3 in physiologic processes, the nature of the contribution of vitamin D metabolism to bone growth and development, the responses of other possible target tissues such as the pancreas and parathyroid gland, and the further elucidation of interactions between vitamin D metabolites and parathyroid hormone in the maintenance of calcium and phosphorus homeostasis. The next decade of research is bound to bring insight into these and other questions.

Biochemical properties of the 1 alpha, 25-dihydroxyvitamin D3 cytosol receptors from human and chicken intestinal mucosa

Specific cytoplasmic receptors for 1 alpha,25-dihydroxyvitamin D3 are shown to be present in human intestinal cytosol which are very similar to the analogous 1 alpha,25-dihydroxyvitamin D3 receptors present in chick intestinal cytosol. Both receptors are 3.5S proteins which aggregate under low ionic strength conditions. They have molecular weights of approximately 60,000 and Stokes' molecular radii of 33 A. The equilibrium dissociation constants for the receptors were both 2 X 10(-10) M at 4 C. The association rate constant for the human receptor was found to be 2.5 X 10(7) M-1 min-1 at 0 C, while a value of 0.5 X 10(7) M-1 min-1 was obtained for the chick receptor. The dissociation rate constants at 4 C were 6.4 X 10(-4) min-1 (human) and 3.6 X 10(-5) min-1 (chick). In addition, it was found that both receptors possessed reduced cysteine residues near the 1 alpha,25-dihydroxyvitamin D3-binding site which were critical for receptor-binding activity. The similarities between the human and the chick receptors suggests that homologous mechanisms for 1 alpha,25-dihydroxyvitamin D3 interactions may be at work in both mammalian and avian intestinal systems.

Characterization of the 1 alpha,25-dihydroxyvitamin D3 receptor from rat intestinal cytosol

The 1 alpha,25-dihydroxyvitamin D3 receptor from rat intestinal cytosol has been partially characterized. Sucrose density gradient sedimentation and analytical gel filtration analyses of this receptor yielded values of 3.1 S, 80,000, and 36 A for the sedimentation coefficient, molecular weight (Mr), and Stokes molecular radius (Rs), respectively. The receptor was found to be a protein by its susceptibility to protease but not nuclease digestion, and studies with N-ethylmaleimide and iodoacetamide revealed the presence of a reduced cysteine residue near the ligand binding site of the receptor. Kinetic and equilibrium binding studies showed an equilibrium dissociation constant of 7.4 x 10(-10) M (4 degrees C), an association rate constant of 1.7 x 10(7) M-1 min-1 (0 degrees C) and a dissociation rate constant of 7.2 x 10(-4) min-1 (4 degrees C, t1/2 = 16 h).