Les "Small Integrin Binding Ligand N-Linked Glycoproteins" constituent un groupe de protéines matricellulaires fortement impliquées dans la formation et la minéralisation osseuse, et qui inclut la Sialoprotéine Osseuse (BSP) et l’Ostéopontine (OPN). Le phénotype des souris BSP-/- montre qu’elles sont dès la naissance plus petite, avec des os longs plus courts à l’âge adulte. L’analyse de leur développement s’est trouvée compliquée par un trouble comportemental des femelles BSP-/- qui ne forment pas de nid. Les croisements entre les souris-/-, +/+ et +/- ont établi que le phénotype osseux de ces souris est d’origine purement génétique. Le taux circulant d’OPN plus élevé chez ces souris suggère une compensation de l’absence de la BSP par l’OPN. Dans un modèle d’injection de PTH sur la moitié droite de l’os pariétal que nous avons développé, la PTH induit localement une augmentation des paramètres histologiques, microtomographiques et moléculaires de formation osseuse dans les deux génotypes. L’injection in vivo de siARN bloquant l’expression d’OPN ne change pas l’effet anabolique de la PTH chez les souris BSP+/+, mais bloque cet effet chez les souris BSP-/-. Ces résultats suggèrent que l’OPN pourrait remplacer la BSP dans certaines de ses fonctions. Le modèle d’ablation médullaire permet d’analyser sur un temps court la revascularisation du conduit osseux. Trois jours après l’ablation l’os des souris BSP-/- présentait une densité vasculaire plus élevée que les BSP+/+, associée à une expression élevée d’OPN et de VEGF, suggérant l’intervention de l’un ou de ces deux facteurs dans la stimulation de l’angiogenèse. En conclusion, l’absence de BSP affecte l’interaction entre l’ostéogenèse, l’angiogenèse / The Small Integrin Binding Ligand N-Linked Glycoproteins family is involved in bone formation and angiogenesis, and it includes bone sialoprotein (BSP) and osteopontin (OPN). Our laboratory has characterized the phenotype of BSP-/- mice, which have a hypomineralised skeleton and are smaller presenting shorter long bone in adulthood. The analysis of their development has been complicated by a behavioral disorder of female BSP-/-, which do not form a nest after parturition. We performed a series of crossfoster breedings, which established that the bone phenotype of BSP-/- is of purely genetic origin. After birth, BSP-/- pups showed higher circulating level of OPN, which suggests a compensation of the lack of BSP by OPN. We developed a model of intermittent injection of PTH over the periosteum of the right mouse hemicalvaria to test the latter hypothesis. PTH induced a local increase of histological microtomographic and molecular bone formation parameters in both genotypes. The Inhibition of this protein by injection of siRNA did not change the anabolic effect of PTH in wild mice, in contrast, this anabolic effect was blocked in BSP-/- mice. These results suggest that OPN could replace BSP in some of its functions. Knowing that OPN is overexpressed in the absence of BSP and is highly angiogenic, we used a model of bone marrow ablation to analyze the revascularization of bone shaft. Three days after ablation BSP-/- femurs showed higher vessel density with higher expression of OPN and VEGF suggesting the involvement of one or both of these factors in the stimulation of angiogenesis. In conclusion, the absence of BSP affects the interplay between osteogenesis, angiogenesis

Circadian rhythm of parathyroid hormone (PTH) is well documented, but its physiological role is not fully understood. In healthy individuals, biochemical markers of bone remodeling follow a similar circadian rhythm to PTH with a nocturnal rise in bone resorption and formation. The loss of PTH diurnal variation was observed not only in primary hyperparathyroidism, but also in patients with postmenopausal osteoporosis. Continuously elevated concentrations of PTH lead to excessive stimulation of bone resorption, whereas intermittent PTH administration has a strong osteoanabolic effect in patients with osteoporosis. It has not been examined whether the skeletal sensitivity to PTH action depends also on the time of its application. The aim of our study was to verify the hypothesis that the application of teriparatide (TPTD, recombinant human PTH [1-34]) at different times of the day in the context of its diurnal variability affects the physiological circadian rhythm of bone remodeling and also the bone mineral density (BMD) after the long-term TPTD treatment. Fourteen women with postmenopausal osteoporosis treated with 20 micrograms of TPTD daily, applied subcutaneously either in the morning or evening, were included in the first study. The concentration of serum C-terminal telopeptide of type I collagen...

Elevation in serum parathyroid hormone (PTH) often accompanies vitamin D deficiency and renal impairment. PTH elevation in renal failure is viewed as an unfavorable development. Evidence is increasing that PTH elevation may be associated with increased morbidity and mortality. In many instances these PTH effects appear to be independent of vitamin D status. PTH mediates its effects through the ubiquitous type 1 PTH/PTH-related peptide receptor, which is notably present in the cardiovascular system. Increased PTH may promote cardiovascular disease through diminished cardiac contractility, enhanced coronary risk, and cardiac valvular and vascular calcification. High PTH levels appear to be linked to the metabolic syndrome and are aligned with hyperlipidemia, decreased insulin sensitivity, and, perhaps, decreased insulin secretion. Increased PTH also is associated with neuroendocrine activation, increased sympathetic activity, and endothelial stress. The relation between PTH and vitamin D is complex and may show significant threshold variations, especially when calcium intake, age, and race are considered. Moreover, evidence is increasing that fragments of PTH may not only be hormonally active but also may have opposing effects to PTH. Despite these caveats, PTH values provide useful clinical diagnostic and prognostic information in monitoring many chronic ailments such as heart and renal failure and multiple sclerosis.

We here report a novel strategy to control the bioavailability of the fibrillizing parathyroid hormone (PTH)-derived peptides, where the concentration of the bioactive form is controlled by an reversible, photoswitchable peptide. PTH1–84, a human hormone secreted by the parathyroid glands, is important for the maintenance of extracellular fluid calcium and phosphorus homeostasis. Controlling fibrillization of PTH1–84 represents an important approach for in vivo applications, in view of the pharmaceutical applications for this protein. We embed the azobenzene derivate 3-{[(4- aminomethyl)phenyl]diazenyl}benzoic acid (3,40-AMPB) into the PTH-derived peptide PTH25–37 to generate the artificial peptide AzoPTH25–37 via solid-phase synthesis. AzoPTH25–37 shows excellent photostability (more than 20 h in the dark) and can be reversibly photoswitched between its cis/trans forms. As investigated by ThT-monitored fibrillization assays, the trans-form of AzoPTH25–37 fibrillizes similar to PTH25–37, while the cis-form of AzoPTH25–37 generates only amorphous aggregates. Additionally, cis-AzoPTH25–37 catalytically inhibits the fibrillization of PTH25–37 in ratios of up to one-fifth. The approach reported here is designed to control the concentration of PTH-peptides, where the bioactive form can be catalytically controlled by an added photoswitchable peptide.

No description available.

No description available.

No description available.

The initiation of lactation involves an increased flow of Ca into mammary secretions, which leads to responses of serum concentrations of Ca and parathyroid hormone (PTH) that may be influenced by dietary Ca. Eight light mares from Farm A and eight Thoroughbred mares from Farm B were bled and milked 10 d pre-foaling, and eight mares (four from each farm) were bled and milked 5 d post-foaling. Milk Ca was measured by two commercial tests, one for [Ca + Mg] and the other [Ca]. Serum PTH and total Ca were measured in 16 mares, and ionized Ca in four mares. Parturition was induced in all mares with fenoprostalene on Farm A, and in four mares with oxytocin on Farm B; no significant difference was found between induction methods or between induced and spontaneous foaling mares. Dietary Ca was 34% DM on Farm A and .79% on Farm B. Mean serum total Ca concentrations decreased from 12.5 mg/dl to a nadir of 11 mg/dl on d 2 post-partum, and mean PTH increased from 46 pg/ml to a peak of 186 pg/ml on d 2 post-partum. Mean serum PTH concentrations were lower (P = .03) and total Ca concentrations were higher (P = -01) on Farm B in comparison to Farm A, probably reflecting the difference in Ca intake. The nadir in mean ionized Ca and total Ca concentrations was reached on d 2 post-partum, 1 day later than has been observed previously in the dairy cow. Milk Ca concentrations increased from 50 ppm 7 d pre-foaling to 350 ppm on the day of foaling, with no difference between farms. The [Ca + Mg] test reached a critical level of 200 ppm 4.5 d pre-foaling, the [Ca] test 2 d pre-foaling. The [Ca + Mg] and [Ca] tests reached 250 ppm 2.5 and 1 d pre-partum, respectively. In short, serum Ca and PTH concentrations showed periparturient changes which reflected dietary Ca pre-partum. Foaling date was more closely associated with milk [Ca] than with [Ca + Mg] and by a critical level of 250 ppm than by 200 ppm. / Master of Science

Calcium (Ca) homeostasis is the maintenance of a stable plasma Ca concentration in the human body in the presence of Ca variability in the physiological environment (e.g. by ingestion and/or excretion). For normal physiological function, the total plasma Ca concentration must be maintained within a very narrow range (2.2-2.4mM). Meeting such stringent requirements is the task of a regulatory system that employs parathyroid hormone (PTH) and calcitriol (CTL) to regulate Ca flux between the plasma and the kidneys, intestines and bones. On the other hand, plasma phosphate control is less tightly, but simultaneously, regulated via the same hormonal actions. Chronic imbalances in plasma Ca levels are associated with disorders of the regulatory organs, which cause abnormal hormonal secretion and activity. These changes in hormonal activity may lead to long-term problems, such as, osteoporosis (increased loss of bone mineral density), which arises from primary hyperparathyroidism (PHPT) – hyper secretion of PTH. Existing in silico models of Ca homeostasis in humans are often cast in the form of a single monolithic system of differential equations and are not easily amenable to the sort of tractable quantitative analysis from which one can acquire useful fundamental insight. In this research, the regulatory systems of plasma Ca and plasma phosphate are represented as an engineering control system where the physiological sub-processes are mapped onto corresponding block components (sensor, controller, actuator and process) and underlying mechanisms are represented by differential equations. Following validation of the overall model, Ca-related pathologies are successfully simulated through induced defects in the control system components. A systematic approach is used to differentiate PHPT from other diseases with similar pathophysiologies based on the unique hormone/ion responses to short-term Ca disturbance in each pathology model. Additionally, based on the changes in intrinsic parameters associated with PTG behavior, the extent of PHPT progression can be predicted and the enlarged gland size estimated a priori. Finally, process systems engineering methods are used to explore therapeutic intervention in two Ca-related pathologies: Primary (PHPT) and Secondary (SHPT) Hyperparathyroidism. Through parametric sensitivity analysis and parameter space exploration, the calcium-sensing receptor (sensor) is identified as a target site in both diseases and the extent of potential improvement is determined across the spectrum of severity of PHPT. The findings are validated against existing drug therapy, leading to a method of predicting drug dosage for a given stage of PHPT. Model Predictive Control is used in drug therapy in SHPT to customize the drug dosage for individual patients given the desired PTH outcome, and drug administration constraints. / Ph. D.

As doenças renais crônicas (DRC) evoluem com distúrbios na homeostase do cálcio e do fósforo, diminuição na produção de vitamina D e aumento na secreção de PTH. Osteodistrofia renal (OR) é o termo usado para definir as alterações ósseas dos pacientes com DRC e classifica-se em doença de alta remodelação representada pela osteíte fibrosa (OF) e doença mista (DM); e de baixa remodelação representada pela osteomalácia (OM) e pela doença adinâmica (DOA). Pacientes com DRC apresentam elevada incidência de fraturas e recentemente demonstrou-se que a hiperfosfatemia leva a diminuição do volume ósseo. Estudamos o efeito isolado do fósforo no tecido ósseo de animais com insuficiência renal mantidos com infusão fixa de PTH variando o conteúdo de fósforo na dieta. Cinqüenta e cinco ratos Wistar foram submetidos à paratireoidectomia (PTX) e nefrectomia (Nx) com reposição de PTH em diferentes concentrações ou foram sham operados e recebiam infusão de veículo. Todos os animais receberam a mesma dieta variando apenas a concentração de P (pobre em P (pP): 0,2% e rico em P (rP):1,2%). Dividimos os grupos em: Sham (N=8); Sham-pP (N=8); Sham-rP (N=7); NxPTHn-pP (N=8); NxPTHn-rP (N=8); NxPTHe-pP (N=9); NxPTHe-rP (N=7). Após 2 meses, realizamos análises bioquímicas e histomorfometria do fêmur proximal. Os animais que ingeriram dieta rica em fósforo apresentaram hiperfosfatemia assim como menor valor de cálcio sérico. A reposição de PTH foi efetiva e proporcional às concentrações infundidas. A histomorfometria óssea mostrou que os ratos que ingeriram dieta rica em fósforo independente da uremia tinham diminuição do volume ósseo (BV/TV), e que este efeito foi amenizado pela reposição do PTH em concentrações elevadas. Nossos resultados demonstram que o fósforo é deletério para o tecido ósseo e que na uremia são necessários níveis mais elevados de PTH para manter a integridade óssea. / Chronic kidney disease (CKD) involves disturbances in calcium and phosphorus metabolism, reduced vitamin D production and increased parathormone (PTH) secretion. Renal osteodistrophy (RO) is a term used to define bone disease complications of patients with CKD, and is classified in high turnover disease represented by osteitis fibrosa (OF) and mixed bone disease; and low turnover disease represented by osteomalacia (OM) and adynamic bone disease (ABD). It is already known that patients with CKD have high incidence of bone fractures, and it has been demonstrated that hyperphosphatemia results in to decreased trabecular bone volume (BV/TV). We evaluated the effect of phosphorus (P) in rats? bone tissue submitted to experimental uremia that received continuous infusion of 1-34 rat PTH in physiologic or five times the normal values. Fifty five Wistar rats were submitted to parathyroidectomy (PTX), nephrectomy (Nx) and received PTH in different concentrations or some were PTX and NX controls (Sham) that received only vehicle. Rats received identical diets, excepted for the P content which was different according to the group [Low P (LP): 0,2% and high P (HP): 1,2%]. Groups were divided as follow: Sham (N=8), Sham LP (N=8), Sham-HP (N=7), NxPTHn-LP (N=8), NxPTHn-HP (N=8), NxPTHh-LP (N=9), NxPTHh-HP (N=7). After two months, animals were sacrificed and biochemical and bone histomorphometry were performed. Rats who received high P diet developed hyperphosphatemia and hypocalcemia. PTH replacement was effective and in accordance with infusion concentration. Bone histomorphometric analysis showed that HP rats presented low trabecular bone volume (BV/TV) independently of the uremia. BV/TV decreased slightly in the group where PTH continuous infusion was five times the physiologic values. Our results demonstrated that P has a deleterious action on bone tissue and in uremia it is necessary high levels of PTH to maintain bone integrity.