Vascular effects of PTHrP (1-34) and PTH (1-34) in the human fetal-placental circulation

PTH-rP and PTH-R1 Expression in Placentas from Pregnancies Complicated by Gestational Diabetes: New Insights into the Pathophysiology of Hyperglycemia in Pregnancy

Background: this study investigated the expression of parathyroid hormone-related protein (PTH-rP) and PTH/PTH-rP receptor PTH-R1 in placentas from women with gestational DM (GDM), and the relationship between PTH-R1 and PTH-rP expression and pregnancy characteristics. Methods: we prospectively enrolled 78 pregnant women with GDM, and immunochemistry for PTH-rP and PTH-R1 was performed on placentas. Patients were grouped according to the positivity of PTH-R1 or PTH-rP expression, and pregnancy characteristics were compared between the two groups. Results: PTH-rP and PTH-R1 expression were highest in the extravillous cytotrophoblast and in the decidua. In extravillous cytotrophoblast, PTH-rP expression was higher in women with abnormal at fasting glycemia compared to women with abnormal 60′ or 120′ glycemia (25/25, 50% vs. 6/28, 21.4%, χ2 = 6.12, p = 0.01), and PTH-R1 expression was higher in women with abnormal oral glucose tolerance test (OGTT) at fasting glycemia compared to women with abnormal 60′ or 120′ glycemia (37/50, 74% vs. 15/28, 53.6%, χ2 = 3.37, p = 0.06). In syncytiotrophoblast, PTH-rP-positive placentas were characterized by higher incidence of 1 min Apgar score < 7 (2/9, 22.2% vs. 2/69, 2.9%, χ2 = 6.11, p = 0.01) and maternal obesity (4/9, 44.4% vs. 11/69, 16.7%, χ2 = 3.81, p = 0.05). Conclusion: placental PTH-rP and PTH-R1 expression is dependent on the type of maternal hyperglycemia, and it is associated with adverse pregnancy outcomes.

Cardiovascular Safety of Abaloparatide in Postmenopausal Women With Osteoporosis: Analysis From the ACTIVE Phase 3 Trial

CONTEXT

Abaloparatide is a US Food and Drug Administration-approved parathyroid hormone-related peptide analog for treatment of osteoporosis in postmenopausal women at high risk of fracture.

OBJECTIVES

We assessed the cardiovascular safety profile of abaloparatide.

DESIGN

Review of heart rate (HR), blood pressure (BP), and cardiovascular-related adverse events (AEs), including major adverse cardiovascular events (MACEs) and heart failure (HF) from: (a) ACTIVE (NCT01343004), a phase 3 trial that randomized 2463 postmenopausal women with osteoporosis to abaloparatide, teriparatide, or placebo for 18 months; (b) ACTIVExtend (NCT01657162), where participants from the abaloparatide and placebo arms received alendronate for 2 years; and (c) a pharmacology study in 55 healthy adults.

RESULTS

Abaloparatide and teriparatide transiently increased HR relative to placebo. Following first dose, mean (standard deviation [SD]) HR change from pretreatment to 1 hour posttreatment was 7.9 (8.5) beats per minute (bpm) for abaloparatide, 5.3 (7.5) for teriparatide, and 1.2 (7.1) for placebo. A similar pattern was observed over subsequent visits. In healthy volunteers, HR increase resolved within 4 hours. The corresponding change in mean supine systolic and diastolic BP 1 hour posttreatment was -2.7/-3.6 mmHg (abaloparatide), -2.0/-3.6 (teriparatide), and -1.5/-2.3 (placebo). The percentage of participants with serious cardiac AEs was similar among groups (0.9%-1.0%). In a post hoc analysis, time to first incidence of MACE + HF was longer with abaloparatide (P = 0.02 vs placebo) and teriparatide (P = 0.04 vs placebo).

CONCLUSIONS

Abaloparatide was associated with transient increases in HR and small decreases in BP in postmenopausal women with osteoporosis, with no increase in risk of serious cardiac AEs, MACE, or HF.

Parathyroid Hormone-Related Protein-induced Relaxation of Rat Uterine Arteries: Influence of the Endothelium During Gestation

OBJECTIVE

Parathyroid hormone-related protein (PTHrP) has been reported to relax different vessels. We investigated the influence of both endothelium and gestation on the relaxation of uterine arteries (UA), which supply blood to myometrium and placenta.

METHODS

Small uterine and mesenteric arteries (MA) with (E+) and without endothelium (E-) from day 20 pregnant (P) and nonpregnant (NP) rats were mounted in a myograph, precontracted with phenylephrine (PE) in a physiologic salt solution. Relaxations to PTHrP, acetylcholine, and forskolin were performed and expressed as a percentage of the PE-induced contraction. Blockade of nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF) was also studied with Nomega-nitro-L-arginine methyl ester (L-NAME) and with charybdotoxin + apamin, respectively.

RESULTS

Gestation significantly increases maximal vasodilating effect of acetylcholine in UA (68% vs 52%, P < .05) and sensitivity to acetylcholine in small mesenteric vessels (P < .05). PTHrP relaxes uterine (maximal relaxation P: 32%, NP: 46%), as well as small MA (P: 68%, NP: 89%), but the maximal relaxation is significantly greater in NP than in P rats (P: 32%, NP: 46%, P < .01) in both vascular beds. In addition, in the UA of P rats, PTHrP only produces relaxation if functional endothelium is present; nevertheless in the absence of endothelium, forskolin still elicits relaxation (65%, P < .01). L-NAME significantly impairs relaxation of E+ UA (P < .05), and so does the association of charybdotoxin + apamin (P < .05). Thus, NO and EDHF contribute largely to this vasorelaxant effect.

CONCLUSION

PTHrP induces a relaxation on UA that is strongly endothelium-dependent during gestation, in contrast to what happens simultaneously in MA.

Physiological skeletal gains and losses in rat mothers during pregnancy and lactation are not observed following uteroplacental insufficiency

Fluctuations in maternal bone mass during pregnancy and lactation facilitate calcium transfer to offspring. Uteroplacental insufficiency causes fetal growth restriction and programs poor adult bone health. We aimed to characterise maternal skeletal phenotype during normal pregnancy and pregnancy complicated by uteroplacental insufficiency. Uteroplacental restriction (Restricted) or sham surgery (Control) was performed on gestational Day 18 (term=22 days) in pregnant Wistar-Kyoto rats. Maternal right femurs were collected on embryonic Day 20, postnatal Day 1 and Weeks 5, 7 and 9 postnatal. Dual-energy X-ray absorptiometry was used to quantify global bone mineral content, density and body composition. Peripheral quantitative computed tomography was utilised to determine trabecular and cortical content, density, circumferences and strength. Control rats exhibited expected reductions in trabecular and cortical content, density and bone strength from embryonic Day 20 to postnatal Day 1 (P<0.05). These skeletal alterations were absent in Restricted rats. By postnatal Day 7, bone parameters in Control and Restricted rats were not different from non-pregnant rats, indicating restoration of maternal bone. The lack of bone loss in mothers suffering uteroplacental insufficiency suggests that calcium transfer to pups would be impaired. This reduction in calcium availability is a likely contributor to the programming of poor adult bone health in growth-restricted offspring.

Uteroplacental restriction in the rat impairs fetal growth in association with alterations in placental growth factors including PTHrP

During pregnancy, parathyroid hormone-related protein (PTHrP) is one of many growth factors that play important roles to promote fetal growth and development, including stimulation of placental calcium transport. Angiotensin II, acting through the AT1a receptor, is also known to promote placental growth. We examined the effects of bilateral uterine artery and vein ligation (restriction), which mimics placental insufficiency in humans, on growth, intrauterine PTHrP, placental AT1a, and pup calcium. Growth restriction was surgically induced on day 18 of pregnancy in Wistar-Kyoto female rats by uterine vessel ligation. Uteroplacental insufficiency reduced fetal body weight by 15% and litter size ( P < 0.001) compared with the control rats with no effect on placental weight or amniotic fluid volume. Uteroplacental insufficiency reduced placental PTHrP content by 46%, with increases in PTHrP (by 2.6-fold), parathyroid hormone (PTH)/PTHrP receptor (by 11.6-fold), and AT1a (by 1.7-fold) relative mRNA in placenta following restriction compared with results in control ( P < 0.05). There were no alterations in uterine PTHrP and PTH/PTHrP receptor mRNA expression. Maternal and fetal plasma PTHrP and calcium concentrations were unchanged. Although fetal total body calcium was not altered, placental restriction altered perinatal calcium homeostasis, as evidenced by lower pup total body calcium after birth ( P < 0.05). The increased uterine and amniotic fluid PTHrP ( P < 0.05) may be an attempt to compensate for the induced impaired placental function. The present study demonstrates that uteroplacental insufficiency alters intrauterine PTHrP, placental AT1a expression, and perinatal calcium in association with a reduction in fetal growth. Uteroplacental insufficiency may provide an important model for exploring the early origins of adult diseases.

PTH/PTHrP Receptor and Mid-molecule PTHrP Regulation of Intrauterine PTHrP: PTH/PTHrP Receptor Antagonism Increases SHR Fetal Weight

Parathyroid hormone-related protein (PTHrP) has important roles in fetal growth and development through stimulation of placental calcium transport, vasodilatation of the uteroplacental vasculature and regulation of cellular growth and differentiation. The growth restricted spontaneously hypertensive rat (SHR) has reduced fetal plasma, placental and amniotic fluid PTHrP concentrations compared to its progenitor, the Wistar Kyoto (WKY) rat. The aim of this study was to determine whether intrauterine PTHrP infusions can restore PTHrP levels and promote SHR fetal growth. PTHrP(1-34), midmolecule PTHrP(67-94), the PTH/PTHrP receptor antagonist [Asn(10), Leu(11)]-PTHrP(7-34) or vehicle were infused via a mini-osmotic pump between 10 and 20 days of gestation into the uterine lumen of SHR and WKY rats. Uterine, placental, amniotic fluid and plasma (fetal and maternal) PTHrP were measured via N-terminal radioimmunoassay. PTH/PTHrP receptor antagonism and mid-molecule PTHrP(67-94) induced endogenous intrauterine PTHrP production with receptor antagonism eliciting a greater and more wide spread effect. The PTH/PTHrP receptor antagonist [Asn(10), Leu(11)]-PTHrP(7-34) acting through a receptor other than the PTH/PTHrP receptor increased SHR fetal and placental weights above vehicle (P<0.05) to that of the WKY and restored SHR amniotic fluid volume (P<0.05). This was associated with a highly significant up regulation of placental, uterine and plasma (fetal and maternal) PTHrP (P<0.05). Modest increases in placental and uterine PTHrP (P<0.05) following intrauterine infusions of PTHrP(1-34) and PTHrP(67-94) had no effect on WKY and SHR fetal weight. Effective growth promoting actions of increased endogenous PTHrP were observed following PTH/PTHrP receptor antagonism rather than exogenous PTHrP administration. A novel finding was that mid-molecule PTHrP also up regulates endogenous intrauterine N-terminal PTHrP production supporting the existence of a mid-molecule receptor. This study highlights that an increase in endogenous uterine, placental and fetal plasma PTHrP following PTH/PTHrP receptor antagonism was associated with increased SHR fetal growth presumably by improving placental growth and function.

Parathyroid hormone-related protein and its receptors: nuclear functions and roles in the renal and cardiovascular systems, the placental trophoblasts and the pancreatic islets

The cloning of the so-called 'parathyroid hormone-related protein' (PTHrP) in 1987 was the result of a long quest for the factor which, by mimicking the actions of PTH in bone and kidney, is responsible for the hypercalcemic paraneoplastic syndrome, humoral calcemia of malignancy. PTHrP is distinct from PTH in a number of ways. First, PTHrP is the product of a separate gene. Second, with the exception of a short N-terminal region, the structure of PTHrP is not closely related to that of PTH. Third, in contrast to PTH, PTHrP is a paracrine factor expressed throughout the body. Finally, most of the functions of PTHrP have nothing in common with those of PTH. PTHrP is a poly-hormone which comprises a family of distinct peptide hormones arising from post-translational endoproteolytic cleavage of the initial PTHrP translation products. Mature N-terminal, mid-region and C-terminal secretory forms of PTHrP are thus generated, each of them having their own physiologic functions and probably their own receptors. The type 1 PTHrP receptor, binding both PTH(1-34) and PTHrP(1-36), is the only cloned receptor so far. PTHrP is a PTH-like calciotropic hormone, a myorelaxant, a growth factor and a developmental regulatory molecule. The present review reports recent aspects of PTHrP pharmacology and physiology, including: (a) the identification of new peptides and receptors of the PTH/PTHrP system; (b) the recently discovered nuclear functions of PTHrP and the role of PTHrP as an intracrine regulator of cell growth and cell death; (c) the physiological and developmental actions of PTHrP in the cardiovascular and the renal glomerulo-vascular systems; (d) the role of PTHrP as a regulator of pancreatic beta cell growth and functions, and, (e) the interactions of PTHrP and calcium-sensing receptors for the control of the growth of placental trophoblasts. These new advances have contributed to a better understanding of the pathophysiological role of PTHrP, and will help to identify its therapeutic potential in a number of diseases.

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.

Preterm fetal growth restriction is associated with increased parathyroid hormone-related protein expression in the fetal membranes

OBJECTIVE

Parathyroid hormone-related protein has roles in normal fetal growth, placental calcium transport, and vascular tone regulation; these factors are compromised in growth-restricted fetuses. Our objective was to determine whether intrauterine parathyroid hormone-related protein expression was increased in association with fetal growth restriction.

STUDY DESIGN

The expression of parathyroid hormone-related protein was examined in intrauterine tissues from women with idiopathic fetal growth restriction with preterm (n = 8-10) and term (n = 8-10) gestations and from gestation-matched control subjects. The abundance and immunoreactive content of parathyroid hormone-related protein messenger ribonucleic acid were determined by Northern blot and radioimmunoassay, respectively, in the placenta, amnion, and chorion-decidua.

RESULTS

The expression of parathyroid hormone-related protein messenger ribonucleic acid was increased in the amnion (placental and reflected) in association with preterm fetal growth restriction (P <.05). Both parathyroid hormone-related protein messenger ribonucleic acid and protein expression were increased in chorion-decidua in association with preterm fetal growth restriction (P <.05). In term gestations both parathyroid hormone-related protein messenger ribonucleic acid and protein expression were greater in amnion over placenta than in reflected amnion (P <.05); these in turn were greater than those in chorion-decidua (P <.05). No significant changes were detected in parathyroid hormone-related protein messenger ribonucleic acid or in protein expression in association with term fetal growth restriction.

CONCLUSION

Either parathyroid hormone-related protein messenger ribonucleic acid or protein expression, or both, was increased in the fetal membranes in association with fetal growth restriction in preterm but not term gestations, suggesting that parathyroid hormone-related protein may be involved in the pathogenesis of preterm fetal growth restriction.

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.

Intrauterine expression of parathyroid hormone-related protein in normal and pre-eclamptic pregnancies

Maternal hypertension, vasoconstriction and placental insufficiency are features of pre-eclampsia. Alterations in calcium homeostasis and in the production of calciotropic hormones and vasoactive agents have also been described in association with pre-eclampsia. Parathyroid hormone-related protein (PTHrP) is abundantly expressed in intrauterine tissues during normal pregnancy and has roles in fetal growth and calcium homeostasis, placental calcium transport and vascular tone regulation. Intrauterine PTHrP mRNA expression and tissue PTHrP content were determined by Northern blot analysis and radio-immunoassay, respectively, in preterm and term pre-eclamptic women. PTHrP mRNA expression and PTHrP content in placenta, amnion over placenta, reflected amnion and choriodecidua from preterm pre-eclamptic women (n=8-10) were not different from preterm controls (n= 10-12). PTHrP mRNA expression and content in amnion over placenta and reflected amnion were significantly greater in term compared to preterm pre-eclamptics (P<0.05). PTHrP mRNA expression was significantly lower in choriodecidua from term pre-eclamptic women (n=8) compared to term controls (n=28, P<0.05), but was not different in placenta or amnion. PTHrP content was not altered in term pre-eclamptic women (n=8) compared to controls (n=25) for any tissue. In summary, PTHrP expression in placenta and amnion was not increased in pre-eclamptic women in association with maternal hypertension, placental insufficiency and vasoconstriction. PTHrP mRNA expression was decreased in choriodecidua in association with term but not preterm pre-eclampsia, however, levels of the protein were not decreased. The data suggest that PTHrP is not involved in the placental pathophysiology of pre-eclampsia in late gestation.

Expression and specific immunolocalization of the human parathyroid hormone/parathyroid hormone-related protein receptor in the uteroplacental unit

OBJECTIVE

Our purpose in these studies was to determine the expression and cellular localization of the parathyroid hormone/parathyroid hormone-related protein receptor in the human uteroplacental unit.

STUDY DESIGN

Human uteroplacental tissues were obtained and ribonucleic acid was extracted. Reverse transcriptase-polymerase chain reaction was performed with use of primers for both the parathyroid hormone/parathyroid hormone-related protein receptor and human phosphoglyceraldehyde dehydrogenase. Ethidium bromide-stained gels and Southern blots were evaluated, and polymerase chain reaction fragments were sequenced. For immunohistochemistry, slides were incubated with a newly developed antibody (3D1.1) specific for the parathyroid hormone/parathyroid hormone-related protein receptor, and bound monoclonal antibody was detected by use of the avidin-biotin technique.

RESULTS

Reverse transcriptase polymerase chain reaction gels and blots showed that receptor messenger ribonucleic acid was present in choriodecidua, placenta, and myometrium. Sequence analysis revealed complete identity of the receptor product and the known nucleotide sequence in the receptor. There was intense receptor staining of the myometrial smooth muscle as well as staining of the endothelium and smooth muscle of the associated vasculature. In umbilical cord immunoreactive receptor was found in the vascular endothelium and vascular smooth muscle cells and in stromal cells. In choriodecidua receptor was found in chorionic trophoblasts and decidualized endometrial stromal cells. In all tissues immunostaining was specific, as evidenced by the blocking of staining after addition of receptor peptide to the antibody (absorbed controls).

CONCLUSION

The parathyroid hormone/parathyroid hormone-related protein receptor is widely expressed in the human uteroplacental unit. The cellular localizations of the receptor in smooth muscle reflect the ability of parathyroid hormone-related protein to relax both uterine and vascular smooth muscle. The presence of novel autocrine and paracrine systems in the human uteroplacental unit is suggested by the finding that the same cells or adjacent cells produce both parathyroid hormone-related protein and its receptor.