Parathyroid Hormone-related Protein Concentrations Research Articles

Dynamics of leptomycin B-sensitive nucleocytoplasmic flux of parathyroid hormone-related protein.

Parathyroid hormone-related protein is responsible for hypercalcemia induced by various tumors. The similarity of its N-terminus to that of parathyroid hormone enables parathyroid hormone-related protein to share parathyroid hormone's signaling properties, but the rest of the molecule possesses distinct functions including a role in the nucleus/nucleolus in reducing apoptosis and enhancing cell proliferation. We have previously shown that parathyroid hormone-related protein nuclear import is mediated by importin beta1. Here we use fluorescence recovery after photobleaching for the first time to show that, in living cells, parathyroid hormone-related protein is exported from the nucleus in a leptomycin B-sensitive manner, implicating CRM1 as the parathyroid hormone-related protein nuclear export receptor. Leptomycin B treatment significantly reduced the rate of nuclear export 4 -10-fold, thereby increasing parathyroid hormone-related protein concentration in the nucleus/nucleolus about 2-fold. Intriguingly, this also led to a 2-fold reduced nuclear import rate. Inhibiting the nuclear export of a protein able to shuttle between nucleus and cytoplasm through distinct receptors thus can also affect nuclear import, indicating that the subcellular localization of a protein containing distinct nuclear import and export signals is the product of an integrated system. Although there have been several recent studies examining the dynamics of intranuclear transport using fluorescence recovery after photobleaching, this represents, to our knowledge, the first use of the technique to examine the kinetics of nucleocytoplasmic flux in living cells.

The Spontaneously Hypertensive Rat Fetus, Not the Mother, is Responsible for the Reduced Amniotic Fluid PTHrP Concentrations and Growth Restriction

Intrauterine parathyroid hormone-related protein (PTHrP) concentrations are reduced in association with growth restriction in the spontaneously hypertensive rat (SHR) compared to those of its normotensive control, the Wistar Kyoto (WKY) rat, implicating PTHrP as a pivotal fetal growth factor. The aim of this study was to examine, by embryo cross-transplanation between SHR and WKY, whether the mother, fetus, or both, are responsible for the suppressed SHR amniotic fluid PTHrP. One-day-old SHR embryos were gestated in either an SHR (SHR-in-SHR) or WKY (SHR-in-WKY) surrogate, similarly one-day-old WKY embryos were gestated in either an SHR (WKY-in-SHR) or WKY (WKY-in-WKY) mother. At 20 days gestation, maternal plasma and amniotic fluid samples were collected and assayed for PTHrP concentrations. Data were analysed by two-way ANOVA (mean±sem,n =5–9 mothers/group). There were no differences in litter number or maternal plasma PTHrP concentrations. Fetal weight (P< 0.009), fetal/placental weight ratio (P< 0.004) and amniotic fluid PTHrP concentrations (P< 0.001) were lower and amniotic fluid volume (P< 0.0001) was higher with an SHR fetus compared to the WKY fetus irrespective of maternal strain. Thus, the SHR fetus is growth restricted and has suppressed amniotic fluid PTHrP, which are largely determined by the fetus or gestational tissues and are independent of maternal hypertension or maternal PTHrP. We suggest that the low SHR amniotic fluid PTHrP may play a role in the development of SHR growth restriction.

Parathyroid hormone-related protein-(1-34) inhibits intrinsic pump activity of isolated murine lymph vessels.

Parathyroid hormone-related protein (PTHrP) was originally found as a tumor-derived vasoactive factor and has also been known to produce significant relaxation of vascular smooth muscles. Thus effects of PTHrP-(1-34), a PTH receptor-binding domain, on spontaneous lymphatic pump activity was investigated in isolated pressurized lymph vessels of mice. Low concentrations (1 x 10(-10) and 3 x 10(-10) M) of PTHrP-(1-34) dilated lymph vessels and reduced the frequency of pump activity, whereas high concentrations (1 x 10(-9) to 1 x 10(-8) M) of PTHrP-(1-34) caused dilation with cessation of the lymphatic pump activity. N(omega)-nitro-L-arginine methyl ester (L-NAME; 3 x 10(-5) M) but not indomethacin (1 x 10(-5) M) significantly reduced the PTHrP-(1-34)-induced inhibitory responses of the lymphatic pump activity. In the presence of L-NAME (3 x 10(-5) M) and L-arginine (1 x 10(-3) M), the L-NAME-induced inhibition in the PTHrP-(1-34)-mediated responses was significantly reduced. Glibenclamide (1 x 10(-6) M) significantly suppressed the inhibitory responses of the lymphatic pump activity induced by PTHrP-(1-34) and S-nitroso-N-acetyl-penicillamine. The PTHrP-(1-34)-mediated inhibitory responses were significantly reduced by treatment with PTHrP-(7-34) (1 x 10(-7) M). These results suggest that PTHrP-(1-34) inhibits spontaneous pump activity of the isolated lymph vessels via PTH receptors and that production and release of endogenous nitric oxide and activation of ATP-sensitive K(+) channels in the lymph vessels contribute to the PTHrP-(1-34)-mediated inhibitory responses of the lymphatic pump activity.

Humoral Hypercalcemia of Malignancy: Severe Combined Immunodeficient/Beige Mouse Model of Adult T-Cell Lymphoma Independent of Human T-Cell Lymphotropic Virus Type-1 Tax Expression

The majority of patients with adult T-cell leukemia/lymphoma (ATL) resulting from human T-cell lymphotropic virus type-1 (HTLV-1) infection develop humoral hypercalcemia of malignancy (HHM). We used an animal model using severe combined immunodeficient (SCID)/beige mice to study the pathogenesis of HHM. SCID/beige mice were inoculated intraperitoneally with a human ATL line (RV-ATL) and were euthanized 20 to 32 days after inoculation. SCID/beige mice with engrafted RV-ATL cells developed lymphoma in the mesentery, liver, thymus, lungs, and spleen. The lymphomas stained positively for human CD45RO surface receptor and normal mouse lymphocytes stained negatively confirming the human origin of the tumors. The ATL cells were immunohistochemically positive for parathyroid hormone-related protein (PTHrP). In addition, PTHrP mRNA was highly expressed in lymphomas when compared to MT-2 cells (HTLV-1-positive cell line). Mice with lymphoma developed severe hypercalcemia. Plasma PTHrP concentrations were markedly increased in mice with hypercalcemia, and correlated with the increase in plasma calcium concentrations. Bone densitometry and histomorphometry in lymphoma-bearing mice revealed significant bone loss because of a marked increase in osteoclastic bone resorption. RV-ATL cells contained 1.5 HTLV-1 proviral copies of the tax gene as determined by quantitative real-time polymerase chain reaction (PCR). However, tax expression was not detected by Western blot or reverse transcriptase (RT)-PCR in RV-ATL cells, which suggests that factors other than Tax are modulators of PTHrP gene expression. The SCID/beige mouse model mimics HHM as it occurs in ATL patients, and will be useful to investigate the regulation of PTHrP expression by ATL cells in vivo.

Head and neck squamous cell carcinoma: Measurement of plasma parathyroid hormone-related protein and serum and urine calcium concentrations

Objectives: Parathyroid hormone-related protein (PTHrP) is expressed by squamous cell carcinomas. Our first objective was to examine the stability of PTHrP in normal human plasma. Our second objective was to determine whether plasma PTHrP could be used in patients with head and neck squamous cell carcinoma (HNSCC) as an indicator of tumor burden or relapse. Study Design and Setting: Blood and urine samples from 55 HNSCC patients undergoing tumor resection at The Ohio State University were measured for plasma PTHrP (1-86) concentration, serum ionized calcium concentration, and urine calcium/creatinine ratio. Results: Two of 55 HNSCC patients had detectable levels of plasma PTHrP. Serum ionized calcium concentrations and urinary calcium/creatinine ratios were within normal limits in all patients. Conclusions: Plasma PTHrP was not a valuable indicator of tumor presence or recurrence in our patient population. Significance: Plasma PTHrP is not a useful marker of tumor presence or recurrence in patients with stage II to IV or recurrent HNSCC. (Otolaryngol Head Neck Surg 2000;123:558-62.)

Reduced fetal, placental, and amniotic fluid PTHrP in the growth-restricted spontaneously hypertensive rat.

Evidence implicates pivotal roles for parathyroid hormone-related protein (PTHrP) in stimulating cell growth and differentiation, placental calcium transport, and placental vasodilatation. As spontaneously hypertensive rat (SHR) fetuses are growth restricted compared with those of its normotensive control, the Wistar Kyoto (WKY) rat, we examined intrauterine PTHrP and total and ionic calcium concentrations in these rats. Fetal plasma PTHrP concentrations, but not total calcium concentrations, were lower in the SHR compared with WKY (P < 0.05). SHR placental concentrations of PTHrP were lower than in WKY (P < 0.03) and failed to show the increase observed in WKY near term (P < 0.05). PTHrP concentrations in amniotic fluid from SHR were not raised near term and were lower compared with WKY (P < 0.0005). The increased ionic calcium concentrations in amniotic fluid in the WKY near term (P < 0.05) were not detected in the SHR. Thus SHR fetal plasma, placental, and amniotic fluid PTHrP concentrations were reduced and associated with fetal growth restriction. We suggest that PTHrP may play a role in the etiology of both growth restriction during pregnancy and hypertension later in life.

Parathyroid hormone-related protein as a potential target of therapy for cancer-associated morbidity.

Proinflammatory cytokines are involved in the genesis of cancer-associated cachexia. Parathyroid hormone-related protein (PTHrP) is the causative agent in humoral hypercalcemia of malignancy (HHM) and is frequently secreted from various kinds of solid tumors as well as from adult T-cell leukemia/lymphoma. PTHrP, like PTH, acts on PTH receptor type 1 (PTH1R). Activation of PTH1R may lead to stimulation of secretion of proinflammatory cytokines. It is expected, therefore, that PTHrP constitutes a key factor in the activation of the proinflammatory and cachectogenic cytokine network and consequently in the development of cachexia in patients with cancer. Two groups of cancer-bearing patients of similar clinical backgrounds were enrolled. Plasma concentrations of PTHrP and cytokines were measured with immunoradiometric assay and radioimmunoassay, respectively. Cancer tissues from patients with HHM were transplanted into nude mice or nude rats. The effects of humanized antihuman PTHrP antibody were examined. In clinical studies, Group B patients (with elevated plasma PTHrP), compared with Group A patients (with normal plasma PTHrP), tended to exhibit higher plasma levels of tumor necrosis factor (TNF)-alpha (P = 0.13), interleukin (IL)-5 (P = 0.08), and IL-8 (P = 0.08), and had significantly higher levels of IL-6 (P = < or =0.01). The levels of TNF-alpha and IL-6 correlated with those of PTHrP. In animal studies, the antibody caused a prompt and sustained decline in serum calcium. This response was accompanied by improvements in food intake, drinking, body weight gain, and general behavior. It also ameliorated the suppression of serum ADH. When those effects were compared with those induced either by bisphosphonate or calcitonin, it turned out that not all of the beneficial effects of the antibody were directly correlated with the depression of blood calcium. PTHrP is a promising molecular target for the development of a novel mode of treatment for patients with cancer-associated morbidity.

Parathyroid hormone-related protein(1-34) in gestational fluids and release from human gestational tissues.

Parathyroid hormone-related protein (PTHrP) is present in fetal and gestational tissues, in which its proposed roles include stimulation of epithelial growth and differentiation, vasodilatation of the uteroplacental vasculature, relaxation of uterine muscle and stimulation of placental calcium transport. The aim of this study was to determine whether the release of PTHrP from gestational tissue explants was tissue specific. In addition, PTHrP concentrations were measured in maternal plasma, umbilical artery and vein plasma, and amniotic fluid from term, uncomplicated pregnancies before the onset of labour. PTHrP was detected in low concentrations in the mother, fetus and placental tissue. Amniotic fluid had ten times the PTHrP concentration compared with that in the maternal or fetal circulations. Using late pregnant human gestational tissues in an in vitro explant system, we found that amnion over placenta, choriodecidua, reflected amnion, and placenta released PTHrP into culture medium in progressively greater amounts over 24 h (P<0.05). This release was not associated with a loss of cell membrane integrity, as indicated by measurement of the intracellular enzyme, lactate dehydrogenase, in the incubation media. After 24 h incubation, the fetal membranes released significantly (P<0.05) greater amounts of PTHrP than did the placenta (placenta 3. 7+/-0.5 pmol PTHrP/g protein). Amnion over placenta released significantly more PTHrP (139.3+/- 43.1 pmol PTHrP/g protein) than did reflected amnion (29.0+/-8.3 pmol PTHrP/g protein) (P<0.05). This study unequivocally demonstrated that human gestational tissues release PTHrP and it was concluded that the main contributors to PTHrP in amniotic fluid were the human fetal membranes, particularly amnion over placenta. Fetal membrane-derived and amniotic fluid PTHrP are proposed to have stimulatory effects on epithelial growth and differentiation in fetal lung, gut, skin and hair follicles and paracrine effects on placental vascular tone and calcium transport.

Technical and Clinical Validation of an Immunoradiometric Assay for Circulating Parathyroid Hormone-related Protein

Parathyroid hormone-related protein (PTHrP) plays a key role in hypercalcemia of malignancy (HM), particularly in humoral HM (HHM) (1)(2). Serum PTHrP is increased in 47–100% of HM patients (3)(4)(5)(6) and in almost all patients with HHM. In up to two-thirds of hypercalcemic patients with bone metastases, serum PTHrP is increased (5)(7). PTHrP assays may aid in the diagnosis of HHM (8). IRMAs that measure large N-terminal regions appear to be optimal for HM evaluation (9). With the first commercially available IRMA (Nichols Institute), PTHrP concentrations were found to be increased in 40 of 81 (49%) HM patients. Moreover, healthy subjects had detectable values up to 2.6 pmol/L (10), contrary to some reports (5)(8)(11). With an IRMA from Mitsubishi Petrochemical Co (12), PTHrP was increased in all 46 studied patients with hypercalcemia and solid tumors, and most healthy subjects had values <1 pmol/L. However, almost all patients had HHM, and the specificity toward normocalcemic cancer (C.NoCa) patients was not thoroughly investigated. We have evaluated a commercially available PTHrP IRMA. We particularly studied the assay specificity for HM patients compared with normocalcemic patients presenting an active cancer, with patients in complete remission from their cancer, and with patients suffering from osteopenia, osteoporosis, or chronic renal failure (CRF). The first control group included 94 patients (88 women and 6 men), median age 61 years (range, 26–80 years), referred to our bone clinic for a low bone mass or established osteoporosis. The patients were classified (13) as follows: 39 osteopenic (T score at the lumbar spine of −1.78 ± 0.09, mean ± SE); 29 osteoporotic (T score −3.16 ± 0.10); 26 established osteoporosis (low bone mass and presence of one or more fragility fractures). The second control group included …

The Role of Parathyroid Hormone-Related Protein in Intra-Tracheal Fluid.

Parathyroid hormone-related protein (PTHrP), a multi-functional protein, is produced by many tissues in fetus. PTHrP concentration in amniotic fluid is reported to be significantly higher than in either fetal or maternal plasma. Other investigators have reported that PTHrP in amniotic fluid is derived mainly from amnion. The aim of this study was to investigate the contribution of fetus to PTHrP in amniotic fluid and the role of PTHrP in human fetal lung tissue. Samples of amniotic fluid, neonatal intra-tracheal fluid, gastric fluid, and the first urine of neonates were obtained at the time of elective cesarean section (n=11), and the concentrations of PTHrP were measured. The PTHrP level in intra-tracheal fluid (41.0+/-19.6 pmol/l, mean+/-SD) was significantly higher than the levels in amniotic fluid (22.1+/-0.8), neonatal gastric fluid (13.5+/-2.5), first urine (0.95+/-0.6), umbilical cord venous and arterial plasma (1.35+/-0.2, 1.63+/-0.3) and maternal plasma (1.05+/-0.1). PTHrP and PTH/PTHrP receptor mRNA were detected in human lung tissue obtained from a fetus stillborn at 36 weeks of gestation. The effects of PTHrP on fetal lung maturation were studied in H441 cells from a human lung epithelial cell line. PTHrP (10(-7)M) significantly suppressed cell proliferation (p<0.05) to approximately 80% of the control level, while administration of PTHrP significantly increased surfactant protein A production (p<0.01). We first demonstrated the high concentration of PTHrP in intra-tracheal fluid that may suggest the positive production of this protein from the fetal lung. The results obtained by in vitro study using a human lung epithelial cell line suggest that PTHrP derived from the fetal lung might modulate its own maturation.

Transforming growth factor-beta stimulates mouse blastocyst outgrowth through a mechanism involving parathyroid hormone-related protein.

The goals of this study were 1) to compare the effects of transforming growth factor-beta (TGF-beta) and parathyroid hormone-related protein (PTHrP) on mouse blastocyst attachment and outgrowth in vitro, 2) to determine whether TGF-beta acts through a mechanism involving PTHrP, 3) to examine effects of PTHrP on preimplantation mouse embryo development, and 4) to determine the pattern of expression of PTHrP protein in the uterus of the mouse during early gestation. In the first set of experiments, hatched blastocysts were placed in fibronectin-coated wells. Cultures were treated with PTHrP or TGF-beta1 and assessed at 24, 48, and 72 h for attachment and surface area of blastocyst outgrowth. Results showed that both PTHrP and TGF-beta1 increased blastocyst outgrowth significantly. A PTHrP-neutralizing antibody blocked the stimulatory effect of both PTHrP and TGF-beta1, suggesting that TGF-beta1 acts to increase endogenous production of PTHrP by the blastocyst. Immunoassay of conditioned medium from blastocysts treated with either TGF-beta1 or PTHrP 1-34 confirmed a 3- to 4-fold increase in levels of PTHrP 1-141. In the second series of experiments, pronuclear zygotes were cultured in various concentrations of PTHrP for 96 h. Blastocysts then were subjected to differential fluorescent staining of inner cell mass and trophectoderm cells. Treatment of mouse embryos with the various concentrations of PTHrP altered neither the number developing to the blastocyst stage nor the number of inner cell mass or trophectoderm cells in the resulting blastocysts. In the third experiment, pregnant mice were killed at Days 3, 4, 5, 6, and 7 of gestation, and uterine horns were processed for immunohistochemistry. Uterine sections were stained with antibodies to PTHrP, desmin, and laminin. On Days 3, 4, and 5, uterine luminal and glandular epithelial cells stained intensely for PTHrP, while stromal cells were negative. By Days 6 and 7, decidualized stromal cells stained positively for PTHrP, desmin, and laminin. These results support the hypothesis that TGF-beta and PTHrP play an important role in the process of implantation.

Hypercalcemia in children with rhabdomyosarcoma.

Hypercalcemia complicating malignancy is a serious and frequent occurrence in adults but rare in children. The aim of this study was to determine the incidence, symptoms, outcome, and cause of hypercalcemia in children with rhabdomyosarcoma. Among 93 children with rhabdomyosarcoma, six with hypercalcemia were identified and their clinical course, pathologic findings, treatment, and outcome were evaluated. In addition, serum and intratumor parathyroid hormone-related protein (PTHrP) concentrations were measured to ascertain the potential of hypercalcemia. All six patients with hypercalcemia had bone metastasis, and four with severe hypercalcemia had multiple bone metastases. Serum PTHrP levels were moderately elevated. There were no significant trends detected based on age, gender, primary site, and pathologic type. All patients achieved transient resolution of hypercalcemia after treatment. However, none survived for a long period of time because their original tumor eventually recurred. Hypercalcemia is not an uncommon complication in patients with rhabdomyosarcoma. Bone absorption seems to be the predominant factor that induces the hypercalcemia in rhabdomyosarcoma. However, PTHrP may be a powerful stimulator of bone absorption, which contributes to the growth of bone metastasis.

Parathyroid hormone-related protein in neonatal and reproductive goats determined by a sensitive time-resolved immunofluorometric assay.

High concentrations of parathyroid hormone-related protein (PTHrP) have been found in goat milk but it is not known whether it can enter the circulation of the neonate. In this study we have developed a sensitive two-site lanthanide immunofluorometric assay (IFMA) using dissociation and enhancement time-resolved fluorometry to address this question. Affinity-purified anti-PTHrP 38-67 raised in rabbit was biotinylated and immobilized in streptavidin-coated microtitration wells as a 'capture' antibody. As a signal, affinity-purified anti-PTHrP 1-34, raised in sheep, was labeled with an europium chelate. A sensitivity of 0.3 pmol/l was achieved. PTHrP levels were determined in the plasma of eleven neonatal, seven parturient and six non-pregnant, non-lactating goats as well as in goat milk. The circulating PTHrP levels (mean +/- S.D.) were significantly increased at day 1 (6.1 +/- 1.7 pmol/l: P < 0.01) and day 3 (3.5 +/- 0.6 pmol/l: P < 0.05) after birth in the male kids (n = 8) bottle-fed with milk from the dams, compared with before (2.2 +/- 0.7 pmol/l) and 30 min after (2.0 +/- 0.6 pmol/l) the first feeding and 14 days (2.4 +/- 0.8 pmol/l) later. In the female kids (n = 3) fed with formula there was no such increase and the concentrations remained between 1.6-1.9 pmol/l. In the parturient goats the mean +/- S.D. PTHrP levels before, during and after parturition were 2.9 +/- 1.7, 4.2 +/- 2.4 and 3.7 +/- 2.2 pmol/l respectively (n = 7) which demonstrated that plasma PTHrP was higher during and after parturition in comparison with before (P < 0.05). The levels in non-pregnant, non-lactating goats were 3.3 +/- 1.5 pmol/l (n = 6). PTHrP levels in goat milk were in the nanomolar range and were highest in the colostrum. A significant increase of plasma PTHrP was observed in goat kids fed with milk from their dams and this increase was not found in kids fed with formula. Plasma PTHrP was also increased during parturition.

Evidence for a causal role of parathyroid hormone-related protein in the pathogenesis of human breast cancer-mediated osteolysis.

Breast cancer almost invariably metastasizes to bone in patients with advanced disease and causes local osteolysis. Much of the morbidity of advanced breast cancer is a consequence of this process. Despite the importance of the problem, little is known of the pathophysiology of local osteolysis in the skeleton or its prevention and treatment. Observations in patients with bone metastases suggest that breast cancer cells in bone express parathyroid hormone-related protein (PTHrP) more frequently than in soft tissue sites of metastasis or in the primary tumor. Thus, the role of PTHrP in the causation of breast cancer metastases in bone was examined using human breast cancer cell lines. Four of eight established human breast cancer cell lines expressed PTHrP and one of these cell lines, MDA-MB-231, was studied in detail using an in vivo model of osteolytic metastases. Mice inoculated with MDA-MB-231 cells developed osteolytic bone metastasis without hypercalcemia or increased plasma PTHrP concentrations. PTHrP concentrations in bone marrow plasma from femurs affected with osteolytic lesions were increased 2.5-fold over corresponding plasma PTHrP concentrations. In a separate experiment, mice were treated with either a monoclonal antibody directed against PTHrP(1-34), control IgG, or nothing before tumor inoculation with MDA-MB-231 and twice per week for 26 d. Total area of osteolytic lesions was significantly lower in mice treated with PTHrP antibodies compared with mice receiving control IgG or no treatment. Histomorphometric analysis of bone revealed decreased osteoclast number per millimeter of tumor/bone interface and increased bone area, as well as decreased tumor area, in tumor-bearing animals treated with PTHrP antibodies compared with respective controls. These results indicate that tumor-produced PTHrP can cause local bone destruction in breast cancer metastatic to bone, even in the absence of hypercalcemia or increased circulating plasma concentrations of PTHrP. Thus, PTHrP may have an important pathogenetic role in the establishment of osteolytic bone lesions in breast cancer. Neutralizing antibodies to PTHrP may reduce the development of destructive bone lesions as well as the growth of tumor cells in bone.

Effect of intrarenally infused parathyroid hormone-related protein on renal blood flow and glomerular filtration rate in the anaesthetized rat.

1. Parathyroid hormone-related protein (PTHrP) is expressed in the kidney and acts on vascular PTH/ PTHrP receptors to vasodilate the isolated kidney and to stimulate renin release. However, effects of PTHrP on renal blood flow (RBF) and glomerular filtration rate (GFR) in vivo have not been assessed in the absence of its cardiac, peripheral and central effects. We investigated the renal effects of PTH and PTHrP infused into the left renal artery of anaesthetized rats. 2. Intrarenal infusions, adjusted to generate increasing concentrations of human PTHrP(1-34) and rat PTH(1-34) in renal plasma (2 x 10(-11) to 6 x 10(-9) M) produced a comparable dose-dependent increase in RBF. The rise was 4% at the lowest and 34% at the highest concentrations of peptides. Up to a concentration of 2 x 10(-9) M, mean arterial pressure (MAP) and heart rate were not affected, but at 6 x 10(-9) M, intrarenally infused peptides reached the peripheral circulation, and caused a fall in MAP within a few minutes. While MAP returned to basal value after the last peptide infusion, RBF remained more than 10% above control for at least 30 min. 3. Two competitive PTH/PTHrP receptor antagonists, [Nle8,18, Tyr34]-bPTH(3-34)amide and [Leu11, D-Trp12]-hPTHrP(7-34)amide (2 x 10(-8) M) were devoid of agonist activity, but markedly antagonized the dose-dependent increase in RBF elicited by PTHrP. 4. GFR and urine flow were measured in left PTHrP-infused experimental kidney and right control kidney. Renal PTHrP concentration of 10(-10) M elevated left RBF by 10%, and GFR by 20% without significantly increasing filtration fraction, and increased urine flow by 57%. In the right control kidney GFR and diuresis did not change. 5. The results indicate that PTHrP has similar renal haemodynamic effects as PTH and increases RBF, GFR and diuresis in anaesthetized rats.

Circulating parathyroid hormone-related protein (109-141) in malignancy-associated hypercalcemia.

For differential diagnosis between hypercalcemia-induced bone metastasis and humoral hypercalcemia of malignancy (HHM), serum parathyroid hormone-related protein (PTHrP) concentrations were measured in normal subjects and patients with malignancy-associated hypercalcemia according to the presence or absence of bone metastasis, using a new sensitive PTHrP(109-141) radioimmunoassay system. The serum PTHrP(109-141) levels in all of 14 patients without bone metastasis were significantly higher than those in normal subjects. However, in four patients with hypercalcemia associated with bone metastasis the levels were nearly the same as those in normal subjects. The time course in two hypercalcemic patients with esophageal carcinoma revealed that serum PTHrP(109-141) levels were elevated before hypercalcemia developed and that changes in PTHrP(109-141) and corrected serum calcium levels were significantly correlated. These findings suggest that determination of serum PTHrP(109-141) may be clinically important not only for differential diagnosis of HHM but also as a useful predictive marker of hypercalcemia.

C-terminal fragment of parathyroid hormone-related protein, PTHrP-(107-111), stimulates membrane-associated protein kinase C activity and modulates the proliferation of human and murine skin keratinocytes

Low concentrations of the C-terminal parathyroid hormone-related protein (PTHrP) fragments, PTHrP-(107-111) and PTHrP-(107-139), stimulated membrane-associated protein kinase Cs (PKCs), but not adenylyl cyclase or an internal Ca2+ surge, in early passage human skin keratinocytes and BALB/MK-2 murine skin keratinocytes. The fragment maximally stimulated membrane-associated PKCs in BALB/MK-2 cells at 5 x 10(-9) to 10(-8) M. The maximally PKC-stimulating concentrations of PTHrP-(107-111) also stopped or stimulated BALB/MK-2 keratinocyte proliferation depending on whether the cells were, respectively, cycling or quiescent at the time of exposure. Thus, just one brief (30-minute) pulse of 10(-8) M PTHrP-(107-111) stopped the proliferation of BALB/MK-2 keratinocytes for at least 5 days. On the other hand, daily 30-minute pulses of 10(-8) M PTHrP-(107-111) started and then maintained the proliferation of initially quiescent BALB/MK-2 cells. Similarly PTHrP-(107-111) inhibited DNA synthesis by cycling primary adult human keratinocytes, but it stimulated DNA synthesis by quiescent human keratinocytes.

Significant decrease in parathyroid hormone-related protein concentrations in amniotic fluid with labour at term but not preterm.

It has been determined whether amniotic fluid concentrations of parathyroid hormone-related protein (PTHrP) change with labour. An evaluation of which cells from intrauterine tissues might produce PTHrP has also been conducted. Amniotic fluid was obtained by amniocentesis from women: (1) at term, not in labour; (2) in normal term labour; (3) in preterm labour, undelivered within one week; (4) in preterm labour, delivered within one week; (5) in preterm labour associated with clinical chorioamnionitis; and (6) who were gestation-matched controls for chorioamnionitis patients-women in this group were similar to those in Group 4 but were different patients. Amnion, chorion, and decidual cells were grown by standard techniques and incubated with interleukin-1 beta (IL-1 beta). PTHrP was assayed in duplicate samples of amniotic fluid or tissue culture media using an immunoradiometric assay. There was a significant reduction in amniotic fluid concentrations of PTHrP during labour at term. Preterm labour was not associated with significant changes in amniotic fluid concentrations of PTHrP although a trend for reduced concentrations was observed. Amnion and chorion produced measurable quantities of PTHrP and rates of production were increased by treatment with IL-1 beta. Decidual cells did not produce detectable amounts of PTHrP. Hence, labour at term is associated with a decrease in amniotic fluid PTHrP concentrations that may reflect reduced amnion production, which in turn may play a permissive or active role in the mechanism(s) of parturition. These data support the view that the mechanisms that control term and preterm labour may be regulated differently.

Plasma parathyroid hormone related-protein levels in patients with cancer, normocalcemic and hypercalcemic

Hypercalcemia in patients with cancer may reflect the synthesis and secretion into circulation of parathyroid hormone-related protein (PTHrP) produced by the tumor. In the present study, we have measured circulating PTHrP concentrations in healthy subjects and patients using a new immunoradiometric assay (IRMA) that is specific for the 1–86 amino acid sequence of molecule, and in plasma collected with protease inhibitors. Plasma concentrations of PTHrP(1–86) were greater than the detection limit of the assay (0.3 pmol/l) in healthy subjects. All patients with hypercalcemia-associated cancer had PTHrP(1–86) levels significantly greater (median 7.74 pmol/l, P < 0.05) than healthy subjects or patients with cancer and normal serum calcium, primary hyperparathyroidism and hyperparathyroidism secondary to chronic renal failure. Plasma PTHrP and corrected serum calcium were correlated in patients with hypercalcemia-associated cancer. In one patient, a marked decrease in PTHrP and calcium levels was observed following surgery. Our results suggest that this IRMA for PTHrP(1–86) may be useful for diagnosis and monitoring of PTHrP-producing tumors induced hypercalcemia.

Evaluation of serum concentration of parathyroid hormone-related protein and its implication in hypercalcemia in squamous cell carcinoma of the head and neck

Hypercalcemia is a common and serious complication associated with squamous cell carcinoma (SCC) and is considered to be caused by a tumor-derived factor, parathyroid hormone-related protein (PTHrP). However, the correlation between serum levels of calcium and PTHrP and the kinetics of PTHrP in SCC of the head and neck is unknown, because the behavior of the circulating form of PTHrP in patients has not been determined. In the present study, the PTHrP concentrations in serum samples from 54 patients (37 with SCC and 17 with benign tumors) were measured by a recently developed radioimmunoassay directed toward the C-terminal region of PTHrP, and the laboratory data including those calcium levels in corresponding samples were reviewed retrospectively. Results showed hypercalcemia in four patients with advanced cancer and in whom elevation of the serum PTHrP concentration was observed simultaneously. The regression analysis also revealed the linear relationship of the calcium level to the PTHrP concentration, but not to the concentration of phosphorus or creatinine, suggesting that monitoring of serum PTHrP level is useful for prediction of hypercalcemia associated with head and neck cancer.