Associations and dissociations between serum bone Gla protein and alkaline phosphatase in skeletal metabolism

Serum bone Gla protein (BGP) and alkaline phosphatase (AP) activity were compared for the assessment of skeletal status in 11 normal pregnant women, 12 normal women on days 3 and 13 of the menstrual cycle, five postmenopausal women before and after 1 month of treatment with ethinyl estradiol (20 micrograms/day), five patients with cancer and hypercalcemia during treatment with calcitonin, and one patient with Paget disease during treatment with Plicamycin. BGP and AP correlated with each other only in the pregnant women. In all other circumstances, there was no correlation between these two serum osteoblast products. Furthermore, there were conditions in which the two measurements became discordant. These studies demonstrate that BGP and AP commonly are dissociated when used as measurements of skeletal status. Although both are osteoblast products, BGP and AP probably reflect different aspects of osteoblast differentiation and function.

Parathyroid hormone-like protein is a secretory product of atrial myocytes

Parathyroid hormone-like protein (PLP) was originally identified from tumors associated with hypercalcemia. Recently, it has been found to be expressed in a stretch-responsive manner in several types of smooth muscle. We studied adult rat heart muscle for the presence of the PLP. Using immunohistology and the PCR, we demonstrated the presence of PLP and its mRNA in all heart chambers. Immunoelectron microscopy demonstrated PLP in secretory vesicles of atrial mycocytes. Using immunoassay, we demonstrated that atria contained a higher concentration of PLP than ventricles. Furthermore, primary cultures of both chambers released PLP into conditioned medium, with atria secreting more than ventricles. Considered with studies of the role of PLP in other tissues, our observations suggest that the production and secretion of PLP by cardiac myocytes represents a calcium-related regulatory function for this stretch-responsive polypeptide in the cardiovascular system. PLP in the heart may be the calcium counterpart for the atrial natriuretic-sodium regulatory axis of the cardiovascular system.

Immunohistochemical localization of parathyroid hormone-related protein in human prostate cancer

Parathyroid hormone-related protein (PTHrP) is produced by a variety of malignant tumors and has been implicated as a major cause of humoral hypercalcemia of malignancy. Expression of PTHrP in prostate cancer tissue was studied immunohistochemically using 33 radical prostatectomy specimens from patients with clinically localized carcinoma of the prostate. None of these patients demonstrated hypercalcemia prior to the surgery. Acetone-methyl benzoate-xylene-processed, paraffin-embedded tissues were stained with a validated mouse monoclonal antibody to an amino acid fragment, PTHrP(109-141), using the streptavidin-peroxidase enzyme conjugate method. All cases (33 of 33; 100%) studied demonstrated some degree of immunoreactivity throughout the cytoplasm of the tumor cells, but immunostaining was absent from inflammatory and stromal cells. The intensity of the staining appeared to directly correlate with increasing tumor grade. The widespread immunohistochemical localization of PTHrP in carcinoma of the prostate suggests that PTHrP may play some local role in the growth of transformed cells in the prostate. Furthermore, overexpression of PTHrP may be a possible marker to evaluate the malignant potential of carcinoma of the prostate.

Synthesis and release of calcitonin-like immunoreactivity by anterior pituitary cells: evidence for a role in paracrine regulation of prolactin secretion

Calcitonin (CT) is a potent and specific inhibitor of basal and TRH-induced PRL release and PRL mRNA levels in rat anterior pituitary (AP) cells, an action mediated through specific inhibition of the Ca(2+)-inositol phosphate messenger system. Because CT and CT-like peptides have been reported to be present in the AP, the present studies investigated 1) whether 35S-labeled CT-like substances can be precipitated from rat AP cell lysates, 2) whether immunoreactive CT is secreted from rat AP cells, as assessed from a cell blot assay and from RIA of spent medium from cultured AP cells, and 3) whether the release of PRL from cultured rat AP cells can be influenced by immunoneutralization of endogenous CT. Dispersed rat AP cells were labeled with [35S]cysteine, CT-like substances were immunoprecipitated from the lysate with antihuman CT (anti-hCT) and antisalmon CT (anti-sCT) immunoglobulin G conjugated to protein-A-Sepharose beads, and the immunoprecipitates were fractionated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis and identified by fluorography. The results revealed that both anti-sCT and anti-hCT sera precipitated three major bands of 35S-labeled material from AP cell lysates, with approximate molecular masses of 23, 6.5, and 3.5 kilodaltons. Synthetic sCT completely displaced anti-sCT-precipitable bands and partially displaced anti-hCT precipitates. The cell blot assay revealed the presence of CT-immunopositive AP cells, and secretion of this substance was indicated by zones of secretion surrounding these cells. Immunoreactive CT was also detected in spent medium from cultured rat AP cells, and the average rate of release over 4 days of culture was approximately 1 ng sCT eq/3 million AP cells.24 h. Both anti-sCT and anti-hCT sera significantly stimulated PRL release from rat AP cells, and the stimulatory effect of anti-sCT serum was dose dependent up to a concentration of 1:50. The present findings demonstrate that CT-like peptide(s) is synthesized and released from cultured AP cells and suggest that this peptide may participate in the regulation of PRL secretion via paracrine or autocrine actions.

Vitamin D3 compounds regulate human immunodeficiency virus type 1 replication in U937 monoblastoid cells and in monocyte-derived macrophages

We studied the effects of vitamin D3 compounds on the replication of human immunodeficiency virus type 1 (HIV-1) in the monoblastoid cell line U937 and in primary monocyte-derived macrophage cultures to understand how modulators of monocyte/macrophage effector function might affect the pathogenesis of HIV-1 infection. U937 cell cultures exposed to 1, alpha 25-dihydroxyvitamin D3 prior to HIV-1 infection showed enhanced virus replication that was apparently due to increased cellular resistance to viral cytopathic effects; a marked inhibition of virus replication was noted in cells exposed to 1 alpha,25-dihydroxyvitamin D3 subsequent to infection. Exposure of blood-derived monocyte/macrophages to vitamin D3 compounds prior to infection also affected virus growth; in most cases, substantial inhibition of HIV-1 replication was noted in vitamin D3-treated macrophage cultures. Our results demonstrate that vitamin D3 compounds with recognized abilities to induce cellular differentiation can modulate HIV-1 infection of human macrophages.

Management of primary hyperparathyroidism

Primary hyperparathyroidism is a common disease that can be accurately diagnosed and effectively treated in most patients. The diagnosis is established by a persistent elevation of serum calcium and parathyroid hormone and by clinical evaluation. Surgery is the appropriate treatment, and preoperative localization procedures are seldom indicated. Selected patients with mild disease may be followed by procedures devised to identify deterioration of skeletal, neurological, and renal function. The accurate diagnosis and effective treatment of primary hyperparathyroidism are rewarding clinical experiences for the endocrinologist and surgeon.

The parathyroid hormone-related protein (PTHrP) gene preferentially utilizes a GC-rich promoter and the PTHrP 1-139 coding pathway in normal human amnion

Parathyroid hormone-related protein (PTHrP) is an oncofetal protein that is widely expressed in mammalian tissues. The PTHrP gene is a complex with three transcriptional start-sites, two TATA boxes and a GC-rich region, and three predicted polypeptide products, PTHrP 1-141, PTHrP 1-139, and PTHrP 1-173. The originally discovered form of PTHrP, PTHrP 1-141, and the classical TATA box promoters are generally assumed to be the major pathways of PTHrP gene expression. We have used the polymerase chain reaction (PCR) to study PTHrP gene expression in the human amnion. Our studies demonstrate that the GC-rich promoter is preferentially used and that PTHrP 1-139 is the major PTHrP mRNA expressed in human amnion. PTHrP 1-139 lacks the carboxy-terminal arginine and histidine residues of PTHrP 1-141; these two basic amino acids could have significant effects on the biological activity of PTHrP. These preferential pathways for PTHrP gene expression are shared by malignant and normal human tissues.

Two-Site Immunoradiometric Assay of Intact Salmon Calcitonin

We developed a two-site immunoradiometric assay (IRMA) of salmon calcitonin (SCT) that detects intact SCT(1-32) and not peptide fragments of the hormone. This was accomplished by using monoclonal antibodies prepared against the peptide fragments SCT(1-11) and SCT(11-32). Two antibodies with specificity for each of the peptides were purified from their respective ascites and evaluated in a two-site format wherein one of the antibodies was adsorbed to polystyrene beads and the other was radioiodinated. In this assay format, the antibody pair detected intact SCT(1-32) but did not react with either SCT(1-11) or SCT(11-32). The sensitivity of the assay could be increased by exchanging the antibodies with respect to bead adsorption and radioiodination. Furthermore, by increasing the incubation time and volume of incubation of sample with the polystyrene-bead-adsorbed antibody, the effective detection limit of the assay could be improved. This assay system can be used to detect intact SCT when the presence of fragments of the hormone might otherwise complicate interpretation of assay data.

Two-site assays of bone gla protein (osteocalcin) demonstrate immunochemical heterogeneity of the intact molecule

We developed a panel of monoclonal antibodies to human bone gla protein (BGP; osteocalcin) peptides that span the linear sequence of the molecule, specifically BGP 1-12 (N-terminal), BGP 15-30 (midregion), and BGP 38-49 (C-terminal). These antibodies were evaluated in various combinations of two-site formats in studies of serum BGP concentrations. For clinical studies, we selected from a panel of antibodies the two most sensitive antibody pairs for the intact molecule (N-C); we also used a polyclonal RIA based on BGP-C. For the two-site format, we used two N-terminal antibodies, 029 and 052, adsorbed to polystyrene beads, and radioiodinated a C-terminal antibody, 663. The standard for each of the assays was purified human BGP. The following BGP serum concentrations (microgram/L, mean +/- SE) were measured with the various assays: by the 029-663 assay, results for normal subjects were 7 +/- 3, for patients with renal failure 25 +/- 8, and for patients with Paget disease 12 +/-4; by the 052-663 assay, the respective results were 22 +/- 4, 44 +/- 12, and 31 +/- 7; by the polyclonal assay, the results were 3 +/- 0.2, 13 +/- 2, and 5 +/- 1. The two intact (N-C) assays were significantly (P < 0.01) correlated (r = 0.94), but their serum values differed by more than twofold in terms of the same BGP standard. The polyclonal assay significantly correlated with each of the intact assays (r = 0.83, 0.77), but it, too, gave different serum values for BGP. These studies demonstrate the immunochemical heterogeneity of circulating BGP, heterogeneity that is manifest even in immunoassays specific for the same region of the molecule.

Two-site immunoradiometric assay of intact salmon calcitonin

We developed a two-site immunoradiometric assay (IRMA) of salmon calcitonin (SCT) that detects intact SCT(1-32) and not peptide fragments of the hormone. This was accomplished by using monoclonal antibodies prepared against the peptide fragments SCT(1-11) and SCT(11-32). Two antibodies with specificity for each of the peptides were purified from their respective ascites and evaluated in a two-site format wherein one of the antibodies was adsorbed to polystyrene beads and the other was radioiodinated. In this assay format, the antibody pair detected intact SCT(1-32) but did not react with either SCT(1-11) or SCT(11-32). The sensitivity of the assay could be increased by exchanging the antibodies with respect to bead adsorption and radioiodination. Furthermore, by increasing the incubation time and volume of incubation of sample with the polystyrene-bead-adsorbed antibody, the effective detection limit of the assay could be improved. This assay system can be used to detect intact SCT when the presence of fragments of the hormone might otherwise complicate interpretation of assay data.

Two-Site Assays of Bone Gla Protein (Osteocalcin) Demonstrate Immunochemical Heterogeneity of the Intact Molecule

We developed a panel of monoclonal antibodies to human bone gla protein (BGP; osteocalcin) peptides that span the linear sequence of the molecule, specifically BGP 1-12 (N-terminal), BGP 15-30 (midregion), and BGP 38-49 (C-terminal). These antibodies were evaluated in various combinations of two-site formats in studies of serum BGP concentrations. For clinical studies, we selected from a panel of antibodies the two most sensitive antibody pairs for the intact molecule (N-C); we also used a polyclonal RIA based on BGP-C. For the two-site format, we used two N-terminal antibodies, 029 and 052, adsorbed to polystyrene beads, and radioiodinated a C-terminal antibody, 663. The standard for each of the assays was purified human BGP. The following BGP serum concentrations (microgram/L, mean +/- SE) were measured with the various assays: by the 029-663 assay, results for normal subjects were 7 +/- 3, for patients with renal failure 25 +/- 8, and for patients with Paget disease 12 +/-4; by the 052-663 assay, the respective results were 22 +/- 4, 44 +/- 12, and 31 +/- 7; by the polyclonal assay, the results were 3 +/- 0.2, 13 +/- 2, and 5 +/- 1. The two intact (N-C) assays were significantly (P &lt; 0.01) correlated (r = 0.94), but their serum values differed by more than twofold in terms of the same BGP standard. The polyclonal assay significantly correlated with each of the intact assays (r = 0.83, 0.77), but it, too, gave different serum values for BGP. These studies demonstrate the immunochemical heterogeneity of circulating BGP, heterogeneity that is manifest even in immunoassays specific for the same region of the molecule.

Multiple hamartoma syndrome (Cowden's disease) associated with renal cell carcinoma and primary neuroendocrine carcinoma of the skin (Merkel cell carcinoma)

A case of multiple hamartoma syndrome (Cowden's disease) associated with renal cell adenocarcinoma and primary neuroendocrine carcinoma of the skin is described. Neither of these neoplasms has been documented previously in association with this genodermatosis. A search for epidermal growth factor receptor (c-erb-B protooncogene) gene abnormalities in the kidney, liver, and thyroid, as well as in tissue of the primary neuroendocrine carcinoma, was negative. Serum obtained from the patient before his death contained elevated levels of both chromogranin A (2641 ng/mL; normal level, less than 20 ng/mL) and calcitonin (517 pg/mL; normal level, less than 200 pg/mL), suggesting that the patient's principal tumor was neuroendocrine in origin.

Presence of calcitonin-like immunoreactivity (iCT) in human prostate gland: evidence for iCT secretion by cultured prostate cells

Immunoreactive calcitonin (iCT) has been detected in human prostate tissue extracts as well as seminal plasma. The present studies were undertaken to examine whether iSCT (immunoreactive salmon CT-like human peptide) co-exists with iHCT (thyroid CT-like substance) in human prostate tissue extracts, and whether these substances are secreted by primary prostate cells in culture. Since the local secretion of these substances seems to increase in some neoplasms, a second objective of the study was to examine whether basal secretion of iCTs from primary prostate cells is increased in carcinoma. The present results have shown that both iHCT and iSCT were present in prostate tissue extracts. The mean iHCT levels in extracts of benign hyperplastic prostates (BPH) were 0.59 ng/g prostate, and these were significantly lower than iHCT concentrations in prostatic carcinoma (PC) (2.53 ng/g). No significant differences in their iSCT contents were observed. However, the results from culture of over 90 individual prostate tissue specimens from BPH or PC indicate that primary prostate cells secreted detectable quantities of iSCT and the basal release of this material from PC prostate cultures was almost four-fold higher than that from BPH prostate cultures. These results suggest that a CT-like immunoreactive material is secreted by primary prostate cells in culture, and the basal secretion of this material is significantly higher in PC cells as compared to BPH cells. Endogenous secretion of prostatic CT, and the elevation of its expression in PC suggest that it may serve as a regulatory factor in the pathophysiology of the prostate gland.

Bone alkaline phosphatase in Paget's disease

The measurement of bone proteins and peptides and their derived products has been very useful in the diagnosis and management of patients with skeletal disease. This group of assays includes alkaline phosphatase (AP) and bone Gla protein (BGP). We here describe the comparison of a new immunoassay that is specific for bone alkaline phosphatase (BAP) to measurements of total alkaline phosphatase (TAP) and BGP in Paget's disease. In our studies, we demonstrated that BAP was increased in the serum of patients with Paget's disease. Comparisons with the other measurements revealed that BAP correlated better with total AP (r = 0.92) than with BGP (r = 0.51); the lowest correlation occurred between BGP and total AP (r = 0.26). In patients with liver disease, the BAP was indistinguishable from normal whereas the TAP was elevated. These studies indicate that BAP assesses different aspects of bone cell function than BGP in Paget's disease. This discordancy also exists between BGP and total serum AP activity. BAP measurements by immunoassay offer a novel method of assessing skeletal status. Thus, the information that measurement of different bone-specific proteins provides should be separately useful in assessing the skeleton for a variety of metabolic bone diseases.

All major lung cancer cell types produce parathyroid hormone-like protein: heterogeneity assessed by high performance liquid chromatography

We examined the production of parathyroid hormone-like protein (PLP) by all major lung cancer cell types, including epidermoid, small cell, and adenocarcinoma. We demonstrated that cell lines derived from each cell type released PLP into culture medium. To determine the predominant species of PLP produced by the cell lines, guanidine hydrochloride extracts were prepared and analyzed for PLP by high performance size exclusion chromatography under denaturing conditions. Cell lines from each of the major lung tumors produced multiple and different forms of PLP. The estimated molecular sizes of the PLP species ranged from 3.5-11.7 kilodaltons. Our results demonstrate that PLP is produced by all major lung cancer cell types and extend these observations to adenocarcinoma and large cell carcinomas of the lung. Furthermore, we observed PLP heterogeneity among these different cell types, which may represent tissue-specific PLP processing among different human lung tumors.

Parathyroid hormone-related protein, chromogranin A, and calcitonin gene products in the neuroendocrine skin carcinoma cell lines MKL1 and MKL2

We studied the production of parathyroid-hormone-related protein, chromogranin A, calcitonin and calcitonin-gene-related peptide in the neuroendocrine skin cell line, MKL1, and a subsequently derived cell line designated MKL2. Both cell lines had cytological, histological and electron-microscopic features typical of neuroendocrine differentiation. Immunohistology and radioimmunoassay studies demonstrated the presence of parathyroid-hormone-related protein, chromogranin A, calcitonin-gene-related peptide, and calcitonin in the MKL2 cell line and the last three substances in both cell lines. The secretion of each of the first three substances was regulated by phorbol in the MKL2 cells. Additional immunohistochemical studies demonstrated the variable expression of bombesin, substance P, and vasoactive intestinal polypeptide in MKL2 cells, and the expression of synaptophysin in both MKL1 and MKL2 cells. These studies demonstrate the neuroendocrine characteristics of the MKL cell lines and provide a novel model for studies of the production and interactions of several neuroendocrine proteins and peptides by human skin cells.

Bone protein and peptide assays in the diagnosis and management of skeletal disease

The measurement in blood of bone proteins is an important adjunct to imaging procedures for clinical assessment of the skeleton. The discovery of new bone proteins and their structural characterization has led to immunochemical procedures of improved sensitivity and specificity for their quantification. An appreciation of the advantages and disadvantages of these evolving methodologies will assist in their clinical application.

Calcium-stimulated parathyroid hormone-like protein secretion: potentiation through a protein kinase-C pathway

The effect of altering intracellular calcium levels on PTH-like protein (PLP) secretion was assessed in the NCI-H727 cell line. Ionomycin stimulated PLP secretion in a dose- and time-dependent manner, with a maximum rate of secretion occurring within minutes. Phorbol esters (phorbol 12-myristate 13-acetate and phorbol 12,13-didecanoate) stimulated PLP secretion at 10(-7)-10(-5) M, whereas forskolin treatment had no effect. When cells were treated initially with phorbol esters, ionomycin-stimulated PLP secretion was potentiated. The kinetics of this effect were rapid (t1/2, less than 1 min), and pretreatment with cycloheximide or actinomycin-D before phorbol ester and ionomycin treatment did not alter PLP secretion. Pretreatment for 24 h with phorbol 12-myristate 13-acetate to desensitize the cells or use of inactive phorbol ester isomer 4 alpha-phorbol 12,13-didecanoate did not potentiate the ionomycin-stimulated PLP secretion. Treatment with exogenously added phospholipase-C caused a dose-dependent increase in PLP secretion. These data indicate that PLP secretion can be stimulated through a phospholipase-C-mediated mechanism.

Chromogranin A: its role in endocrine function and as an endocrine and neuroendocrine tumor marker

CgA is a 49 kilodalton protein that is present in the secretory granules of most endocrine and many neuroendocrine cells. Detection of CgA in cells by immunocytochemistry and measurement of CgA in serum by immunoassay can serve as tissue and serum markers for CgA-producing tumors. CgA is of diagnostic value in classical endocrine tumors, in hormone-negative tumors, and in endocrine tumors in which other diagnostic procedures have their limitations. Although the biological function of CgA is yet unknown, it may serve as a precursor molecule, like POMC, for a family of biologically active peptides. CgA is an important new tool for the endocrinologist in the diagnosis and management of patients with endocrine and neuroendocrine tumors.

Liposome-entrapped calcitonin and parathyroid hormone are orally effective in rats

We have demonstrated that liposomally entrapped calcitonin (CT) and parathyroid hormone (PTH) can be orally effective in regulating blood calcium. Liposomal CT produced hypocalcemia and liposomal PTH produced hypercalcemia upon oral administration to rats. Specific liposomal formulations were necessary to affect the appropriate decrease and increase in blood calcium concentration. Future extension of these studies may lead to clinically valuable forms of liposomal-peptide preparations.

Plasma chromogranin A as a marker of sympathochromaffin activity in humans

The extent to which the sympathochromaffin system compared with other endocrine/neuroendocrine tissues contributes to the plasma chromogranin A pool has not been defined. To test the hypothesis that the sympathochromaffin system is the major source of circulating chromogranin A only when that system is activated markedly, we measured chromogranin A concentrations in 200 human plasma samples known to have a broad range of norepinephrine and epinephrine concentrations, reflecting therefore a broad range of sympathochromaffin activity at the time of sampling. Plasma chromogranin A and norepinephrine concentrations were highly correlated when the sympathochromaffin system was activated markedly (cardiac arrest samples, n = 13, r = 0.8392, P less than 0.0005) and when there was release of large amounts of norepinephrine from tumors (pheochromocytoma samples, n = 17, r = 0.8132, P less than 0.001). However, when the sympathochromaffin system was activated less markedly, resulting in plasma catecholamine concentrations that spanned the physiological and lower pathophysiological range (nonpheochromocytoma noncardiac arrest samples, n = 170), correlations between plasma chromogranin A and norepinephrine (r = 0.2877, P less than 0.0001) and epinephrine (r = 0.3814, P less than 0.0001) levels were relatively weak, although still statistically significant. Thus, at basal through moderate stress levels, norepinephrine and epinephrine concentrations accounted for only approximately 10-15% of the variance in plasma chromogranin A levels. We conclude that, although plasma chromogranin A concentrations are a valid marker of sympathochromaffin activity in humans, they are not a sensitive marker under physiological conditions.

Intraperitoneal free fatty acids induce severe hypocalcemia in rats: a model for the hypocalcemia of pancreatitis

Indirect evidence suggests a causative role for intraperitoneal free fatty acids (FFA) in hypocalcemia associated with pancreatitis. We examined the effects of intraperitoneal injection of four naturally occurring FFAs on serum calcium in rats. Two saturated FFAs, stearate and palmitate, induced little or no hypocalcemia. Two unsaturated FFAs, oleate and linoleate, caused dramatic hypocalcemia in treated versus control rats (6.3 +/- 1.4 and 5.3 +/- 0.7 mg/dl, respectively, versus 10.1 +/- 0.6). Dose-response studies demonstrated that minute quantities of oleate (100 microliters per 250 g rat) caused marked hypocalcemia (7.2 +/- 0.3 mg/dl). Treated versus control rats also revealed a decrease in ionized calcium (3.15 +/- 0.2 versus 5.6 +/- 0.05 mg/dl) and magnesium (1.4 +/- 0.15 versus 2.0 +/- 0.10), an appropriate increase in PTH levels (1670 +/- 451 versus 396 +/- 235 pg/ml), and a fall in calcitonin levels (70.4 +/- 21.3 versus 47.5 +/- 16.4 pg/ml) but no change in albumin or phosphate levels. In vitro, the Ksp of calcium dioleate was shown to be 5.3 x 10(-8) m3/liter3; thus under physiologic conditions 100 microliters oleate binds 7.2 mg calcium, or approximately twice the total ECF ionized calcium in the rat. The amounts of intraperitoneal FFA that can easily be achieved in pancreatitis complex pathophysiologically significant amounts of calcium and may lead to severe hypocalcemia.

Factors influencing the enhanced hypocalcemic action of liposome-entrapped calcitonin

The mechanism whereby liposomal entrapment enhances the hypocalcemic effect of calcitonin (CT) was evaluated in the rat. Phosphatidylcholine (PC) and PC plus cholesterol (PCC) preparations of large multilammelar vesicles (MLV) and small unilammelar vesicles (SUV) were used to entrap human calcitonin (hCT). The effect of each of these preparations was assessed by measuring plasma calcium after their parenteral administration. Changes in calcium were compared with plasma concentrations of liposomal hCT (L-hCT) and free hCT (F-CT). The plasma form of hCT was also evaluated by gel filtration chromatography. Most of the liposomal preparations had a greater hypocalcemic effect than unencapsulated hCT. Following I.V. administration, the MLV-hCT preparations had the greatest hypocalcemic effect. Thus, to enhance the hypocalcemic effect of hCT, large vesicular size is important for I.V. administration and the absence of cholesterol in the liposome is important for I.M. administration. In general, the greatest hypocalcemic effect was achieved by those liposomal preparations that resulted in the most sustained increase of L-hCT and F-hCT in plasma. Thus, liposomal entrapment enhances the hypocalcemic effect of hCT by prolonging the presence of the peptide in the peripheral circulation.

A chromogranin A-derived peptide differentially regulates the secretion of calcitonin gene products

We studied the regulation of the secretion of CT and CGRP by chromogranin A (CgA)-derived peptides in a human lung tumor cell line. The amino-terminal peptide of CgA, CgA1-40, stimulated the secretion of CGRP and inhibited the secretion of CT; both effects occurred in a dose-dependent manner. These studies demonstrate a differential effect of a CgA-derived peptide on two products of the CT gene, CT itself and CGRP. CgA may be processed at its multiple dibasic sites to peptides that specifically regulate the secretion of its coresident hormones, in this case two calcitonin gene products that are present in the same secretory vesicle. This novel mechanism represents a new pathway for the control of calcium regulating hormones.

Serum markers of bone formation in parenteral nutrition patients

Bone gamma-carboxyglutamic acid containing protein (BGP) has been utilized effectively as a serum marker of bone turnover in healthy normals and in individuals with a variety of metabolic bone disorders including postmenopausal osteoporosis and Paget's disease. The utility of this serum marker in other bone disorders, including that associated with the maintenance of patients on long-term parenteral nutrition, still requires definition. Because of our interest in this clinical syndrome and the availability of serum and of bone formation rates (BFR) measured directly from double tetracycline labeling in 11 long-term parenteral nutrition patients, we measured BGP levels in these patients and attempted to correlate this measure with BFR. Serum vitamin D metabolites, immunoreactive parathyroid hormone (PTH), and alkaline phosphatase (alk phos) were also measured. Serum BGP was only weakly and not significantly correlated (r = 0.24, p = NS) with bone formation rate for the group as a whole. However, in a subgroup of 10 patients without hyperparathyroidism, there was strong and significant correlation (r = 0.81, P less than 0.01) between BGP and BFR. There was also a strong correlation between bone formation rate and serum 1,25 dihydroxyvitamin D [1,25(OH)2D] levels (r = 0.89, P less than 0.01, n = 11). The mechanism of this association could not be established. A correlation of borderline significance was observed between bone formation rate and serum alk phos (r = 0.60, P = 0.05, n = 11). The current data suggest that additional studies may help to more fully define the utility of serum measurements in quantifying bone dynamics in parenteral nutrition patients, and that measures of vitamin D metabolites, BGP, and alk phos may prove useful.