Search PubMed⌕ Search

Biomedical subjects

A Rubinacci

Publications and source records attributed to A Rubinacci.

At least 19 recordsLinked to original sources
PubMed2006

CGRP inhibits osteoprotegerin production in human osteoblast-like cells via cAMP/PKA-dependent pathway.

The osteoprotegerin (OPG)/receptor activator of nuclear factor-kappaB ligand (RANKL)/receptor activator of nuclear factor-kappaB (RANK) system was evaluated as a potential target of CGRP anabolic activity on bone. Primary cultures of human osteoblast-like cells (hOB) express calcitonin receptor-like receptor (CLR) and receptor activity modifying protein 1, and, because CGRP stimulates cAMP (one of the modulators of OPG production in osteoblasts), it was investigated whether it affects OPG secretion and expression in hOB. CGRP treatment of hOB (10(-11) M-10(-7) M) dose-dependently inhibited OPG secretion with an EC(50) of 1.08 x 10(-10) M, and also decreased its expression. This action was blocked by the antagonist CGRP(8-37). Forskolin, a stimulator of cAMP production, and dibutyryl cAMP also reduced the production of OPG. CGRP (10(-8) M) enhanced protein kinase A (PKA) activity in hOB, and hOB exposure to the PKA inhibitor, H89 (2 x 10(-6) M), abolished the inhibitory effect of CGRP on OPG secretion. Conditioned media from CGRP-treated hOB increased the number of multinucleated tartrate-resistant acid phosphatase-positive cells and the secretion of cathepsin K in human peripheral blood mononuclear cells compared with the conditioned media of untreated hOB. These results show that the cAMP/PKA pathway is involved in the CGRP inhibition of OPG mRNA and protein secretion in hOB and that this effect favors osteoclastogenesis. CGRP could thus modulate the balance between osteoblast and osteoclast activity, participating in the fine tuning of all of the bone remodeling phases necessary for the subsequent anabolic effect.

Acid Phosphatase↗
PubMed2006

Different skeletal regional response to continuous brain infusion of leptin in the rat.

This study was designed to evaluate whether or not continuous intracerebroventricular infusion of leptin (1.5 microg/rat/24 h, for 28 days) produced different regional response on the skeleton of growing rats. Leptin reduce the accretion of total femoral bone mineral content (BMC) and density (BMD). This effect was related to a reduction of metaphyseal femur as no changes were detected in the diaphysis. Despite the reduced accretion in the volumetric of both femur and tibia compared to controls, leptin had no significant effects on the lumbar vertebrae. Urine deoxypyrydinoline and serum osteocalcin remained more elevated in the leptin-treated group as compared to controls. The results demonstrate that long-term central infusion of leptin activates bone remodeling with a negative balance. Leptin induces distinct responses in the different structure of bone and in the axial and appendicular skeleton.

Animals↗
PubMed2005

Bone as an ion exchange organ: evidence for instantaneous cell-dependent calcium efflux from bone not due to resorption.

The current study tests the hypothesis that basal level and minute-by-minute correction of plasma Ca2+ by outward and inward Ca2+ fluxes from and into an exchangeable ionic pool in bone is controlled by an active partition system without contributions from the bone remodeling system. Direct real-time measurements of Ca2+ fluxes were made using the scanning ion-selective electrode technique (SIET) on living bones maintained ex vivo in physiological conditions. SIET three-dimensional measurements of the local Ca2+ concentration gradient (10 microm spatial resolution) were performed on metatarsal bones of weanling mice after drilling a 100-mum hole through the cortex to expose the internal bone extracellular fluid (BECF) to the bathing solution, whose composition mimicked the extracellular fluid (ECF). Influxes of Ca2+ towards the center of the cortical hole (15.1+/-4.2 pmol cm-2 s-1) were found in the ECF and were reversed to effluxes (7.4+/-2.9 pmol cm-2 s-1) when calcium was depleted from the ECF, mimicking a plasma demand. The reversal from influx to efflux and vice versa was immediate and fluxes in both directions were steady throughout the experimental time (>or=2 h, n=14). Only the efflux was nullified within 10 min by the addition of 10 mM/L Na-Cyanide (n=7), demonstrating its cell dependence. The timeframes of the exchanges and the stability of the Ca2+ fluxes over time suggest the existence of an exchangeable calcium pool in bone. The calcium efflux dependency on viable cells suggests that an active partition system might play a central role in the short-term error correction of plasma calcium without the contribution of bone remodeling.

Animals↗
PubMed2005

Osteoprotegerin and bone turnover markers in heavily pretreated HIV-infected patients.

OBJECTIVES: To characterize osteoprotegerin (OPG) levels, bone remodelling and bone mineral density (BMD) in heavily pretreated HIV-infected patients on antiretroviral therapy, and to evaluate the clinical factors associated with bone density decline. METHODS: Heavily pretreated (> 5 years) HIV-positive patients were enrolled in this cross-sectional, observational study, which was based on a total body bone densitometry examination and a comprehensive evaluation of bone and mineral parameters. RESULTS: Sixty-eight patients (55 male and 13 female) with a median age of 41 years (range 25-60 years) were included in the study. Their antiretroviral treatment lasted for 82 months. On the basis of the World Health Organization criteria, nine patients (13.2%) were osteoporotic [T-score < -2.5 standard deviation (SD)] and 19 patients (27.9%) were osteopenic (T-score between -1 and -2.5). The principal outcomes associated with the presence of a low BMD were high OPG and lysylpyridinoline/creatinine ratio (Dpd) values. Most of the patients (39 of 48; 81.25%) showed vitamin D insufficiency [Vitamin D (25(OH)D) < 18 ng/mL] with secondary hyperparathyroidism (13 of 50 patients: 26%), which proved to be correlated to osteocalcin (BGP) levels [parathyroid hormone (PTH) vs. BGP: r = 0.34; P < 0.01]. There was an inverse correlation between T-scores and serum osteocalcin and alkaline phosphatase (AP) levels, on one hand, and Dpd, on the other. High AP and Dpd values were associated with relative risks of 4.1 [95% confidence interval (CI) = 1.01-17.6] and 7.2 (95% CI = 1.67-31.03), respectively, of a pathological T-score. Multivariate analysis revealed that the factors associated with the presence of osteopenia or osteoporosis were older age and lower body mass index. CONCLUSIONS: About 40% of our heavily pretreated subjects with advanced HIV infection had a low BMD, and 56% (24 of 44 patients) showed a high bone turnover rate with marked osteoclast activation. High OPG levels may protect against bone resorption.

Adult↗
PubMed2004

In vivo leptin expression in cartilage and bone cells of growing rats and adult humans.

The present investigation was carried out to analyse, immunohistochemically, in vivo leptin expression in cartilage and bone cells, the latter restricted to the elements of the osteogenic system (stromal cells, osteoblasts, osteocytes, bone lining cells). Observations were performed on the first lumbar vertebra, tibia and femur of four rats and on the humerus, femur and acromion of four patients. Histological sections of paraffin-embedded bone samples were immunostained using antibody to leptin. The results showed that, in growing rat bone, leptin is expressed in chondrocytes and stromal cells, but not in osteoblasts; bone lining cells were not found in the microscopic fields examined. In adult human bone, leptin is expressed in chondrocytes, stromal cells and bone lining cells; osteoblasts were not found in the microscopic fields examined. Osteocytes were found to be leptin positive only occasionally and focally in both rat and human bone. The in vivo findings reported show, for the first time, that leptin appears to be expressed only in the cells of the osteogenic lineage (stromal cells, bone lining cells, osteocytes) that, with respect to osteoblasts, are permanent and inactive, i.e. in those cells that according to our terminology constitute the bone basic cellular system (BBCS). Because the BBCS seems to be primarily involved in sensing and integrating mechanical strains and biochemical factors and then in triggering and driving bone formation and/or bone resorption, it appears that leptin seems to be mainly involved in modulating the initial phases of bone modelling and remodelling processes.

Acromion↗
PubMed2002

Human osteoblast-like cell proliferation induced by calcitonin-related peptides involves PKC activity.

The calcitonin peptides [calcitonin (CT), calcitonin gene-related peptide (CGRP), amylin] share many biological actions, including activity on bone cells. In the present study, CT (10(-11) to 10(-9) M) stimulated [(3)H]thymidine incorporation in primary cultures of human osteoblasts (hOB), as already demonstrated for CGRP and amylin. RT-PCR analysis showed that the calcitonin receptor and the calcitonin receptor-like receptor are both expressed in hOB. In these cells, CT (10(-10) M) and amylin (10(-9) M), in contrast to CGRP (10(-8) M), did not increase cAMP production. All three peptides stimulated protein kinase C (PKC) activity. To evaluate PKC involvement in hOB proliferation, cells were incubated with phorbol 12,13-dibutyrate, a stimulator of PKC activity; cell proliferation was increased in a dose-dependent manner (EC(50) = 3.4 x 10(-8) M). Staurosporine (10(-9) M), a PKC inhibitor, blocked phorbol 12,13-dibutyrate-induced PKC activity and cell proliferation. Inhibition of PKC by staurosporine also counteracted the stimulatory effect of CT, CGRP, and amylin on hOB proliferation. From these data, it is deduced that the activation of PKC is important for hOB proliferation and that it is involved in the anabolic effect of CT peptides on bone.

Amyloid↗
PubMed2002

Bone as an ion exchange system: evidence for a link between mechanotransduction and metabolic needs.

To detect whether the mutual interaction occurring between the osteocytes-bone lining cells system (OBLCS) and the bone extracellular fluid (BECF) is affected by load through a modification of the BECF-extracellular fluid (ECF; systemic extracellular fluid) gradient, mice metatarsal bones immersed in ECF were subjected ex vivo to a 2-min cyclic axial load of different amplitudes and frequencies. The electric (ionic) currents at the bone surface were measured by a vibrating probe after having exposed BECF to ECF through a transcortical hole. The application of different loads and different frequencies increased the ionic current in a dose-dependent manner. The postload current density subsequently decayed following an exponential pattern. Postload increment's amplitude and decay were dependent on bone viability. Dummy and static loads did not induce current density modifications. Because BECF is perturbed by loading, it is conceivable that OBLCS tends to restore BECF preload conditions by controlling ion fluxes at the bone-plasma interface to fulfill metabolic needs. Because the electric current reflects the integrated activity of OBLCS, its evaluation in transgenic mice engineered to possess genetic lesions in channels or matrix constituents could be helpful in the characterization of the mechanical and metabolic functions of bone.

Animals↗
PubMed2002

Bone effects of hexarelin, a GH-releasing peptide, in female rats: influence of estrogen milieu.

OBJECTIVE: The present study was performed to evaluate the potential influence of the estrogen milieu in modulating the effects of GH/IGF stimulation by a GH-releasing peptide, hexarelin (HEXA), on bone metabolism and mineral density in middle-aged female rats. METHODS: HEXA was administered for 60 days (50 microg/kg s.c. twice a day) to intact and ovariectomized (OVX) 11-month-old female rats and changes in bone parameters were evaluated with respect to those of the same rats under baseline conditions and with those of control rats (intact and OVX) administered isovolumetric amounts of physiological saline. Serum total alkaline phosphatase (ALP) and urinary deoxypyridinoline (Dpd) were measured before and at various times during HEXA treatment. Bone mineral content (BMC) and density of lumbar vertebrae and femoral mid-diaphyses were measured by dual energy X-ray absorptiometry before and after treatment. In all groups, serum IGF-I levels were determined before and during treatment and the GH secretory response to HEXA was assessed at the end of the experiment. RESULTS: In intact rats, HEXA did not modify Dpd urinary excretion, induced a trend toward an increase of serum ALP activity and significantly increased BMC (+6.5%) and bone area (+4.1%) only at lumbar vertebrae. In OVX rats, HEXA did not modify the OVX-induced increase in bone turnover markers (Dpd and ALP) and did not affect the OVX-induced vertebral bone loss, but significantly increased BMC (+7.2%) and bone area (+5.3%) at femoral mid-diaphyses. HEXA significantly increased serum IGF-I levels at day 14, but not at day 60, in both intact and OVX rats, whereas the GH secretory response to HEXA was higher in the former than in the latter. CONCLUSIONS: Overall, the present data demonstrate that chronic HEXA treatment increases BMC and bone area at lumbar vertebrae in intact rats and at femoral diaphyses in OVX rats. The different sensitivity to HEXA of the skeletal districts examined is related to the estrogen milieu and may reflect a complex interplay between estrogens and GH/IGF function.

Animals↗
PubMed2000

Effects of calcitonin gene-related peptide and amylin on human osteoblast-like cells proliferation.

Expression of mRNA for calcitonin gene-related peptide (CGRP) and CGRP receptor has been detected in osteoblasts indicating that CGRP could play a role in bone metabolism. In the present study, we evaluated the effect of CGRP on primary culture of human osteoblast-like cells proliferation. The peptide was able to stimulate [3H]thymidine incorporation in human osteoblast-like cells with a maximal effect at 10(-8) M. The proliferating activity of CGRP was not inhibited by the two antagonists, CGRP-(8-37) or amylin-(8-37), whereas amylin fragment antagonized the proliferating activity of amylin. In human osteoblast-like cells CGRP, but not amylin, was able to stimulate adenylyl cyclase activity and this effect was completely antagonized only by CGRP-(8-37) and not by amylin-(8-37). These data suggest that the CGRP induced stimulation of cAMP is not involved in the peptide proliferating effect in human osteoblast-like cells and that in this cell population there are receptor subtypes for CGRP, distinct from that of amylin.

Aged↗
PubMed2000

Bone as an ion exchange system: evidence for a pump-leak mechanism devoted to the maintenance of high bone K(+).

To provide evidence of active accumulation of K(+) in bone extracellular fluid (BECF), electric currents driven by damaged living metatarsal bones of weanling mice, immersed in physiological media at different [K(+)], in the presence of blockers of the K(+) channels or of the Na(+)-K(+-)ATPase inhibitor, were measured by means of a voltage-sensitive two-dimensional vibrating probe. At 4 mM extracellular K(+) concentration ([K(+)](o)), an inward steady current density (7.85-38.53 microA/cm(2)) was recorded at the damage site, which was significantly dependent on [K(+)](o). At [K(+)](o) equal to that of BECF (25 mM), current density was reduced by 76%. At [K(+)](o) of 0 mM, the current density showed an increase, which was hindered by tetraethylammonium (TEA). Basal current density was reduced significantly after exposure to TEA or BaCl(2) and was unchanged after long- term exposure to ouabain. By changing control medium with a chloride-free medium, current density was reversed. The results support the view that K(+) excess in bone is maintained by a biologically active cellular system. Because the osteocyte-bone lining cell syncytium was at the origin of the current in bone, it is likely that this system controls the ionic composition of BECF.

Animals↗
PubMed1999

Hexarelin, a growth hormone - releasing peptide, counteracts bone loss in gonadectomized male rats.

The age-related decline in growth hormone (GH) secretion has been implicated in the pathogenesis of involutional bone loss. Whether restoration of GH secretion might be helpful in maintaining and/or improving bone mass during aging is still unsettled. The aim of the present study was to examine the effects of 30-day treatment with hexarelin (HEXA, 50 microg/kg subcutaneously b.i.d.), a highly effective GH-releasing compound, on bone metabolism and bone mineral density (BMD) in intact and osteopenic gonadectomized (GDX) mature male rats. Serum total alkaline phosphatase (ALP, bone formation marker) and bone resorption markers (lysylpyridinoline, LP and hydroxylysylpyridinoline, HP) were measured before and 7, 14 and 30 days after treatment. BMD was measured by dual-energy X-ray absorptiometry at lumbar vertebrae, femoral metaphysis and diaphysis before and at the end of the experiment. In intact rats, HEXA significantly (P<0.05) decreased LP (-36.3%) and HP (-22.8%) excretion at day 7, whereas it did not change serum ALP activity and BMDs. In GDX rats, HEXA completely prevented the significant (P<0. 01) increase in urinary excretion of both LP (+143.8%) and HP (+119. 4%), the early decrease in ALP activity (-26.5%) and the significant (P<0.05) decrease in BMDs in the femoral metaphysis (-7.9%) and lumbar vertebrae (-6.8%) caused by androgen deficiency. The bone-protective effects of HEXA could be attributed, at least in part, to its GH-releasing activity since chronic-treated rats maintained the GH response to an acute challenge with HEXA. The evidence that HEXA, unlike GH, inhibits bone resorption indicates that other mechanisms contribute to the bone sparing effect of HEXA.

Alkaline Phosphatase↗
PubMed1999

Total and free deoxypyridinoline after acute osteoclast activity inhibition.

BACKGROUND: Deoxypyridinoline (Dpd) is one of the two pyridinium cross-links that provide structural rigidity to type I collagen in bone. During osteoclastic resorption, Dpd is released into circulation and is excreted in the urine in free and peptide-bound forms. Free and total Dpd are highly correlated, but whether the free-to-total cross-link ratio is constant in both normal and high bone turnover states remains controversial. To compare free and total Dpd performance in a physiological condition, urinary free and total Dpd were measured after a short-term inhibition of osteoclast activity such as that induced by an oral calcium load. METHODS: Total and free Dpd were measured by HPLC and by immunosorbent assay, respectively, in two groups of subjects, one (calcium-treated; n = 16) taking calcium and the other not (control; n = 9). RESULTS: The urinary excretion of total Dpd at 2 and 4 h after oral calcium loading was decreased compared with controls. By contrast, changes in free Dpd were similar in the calcium-treated and control groups, reflecting only circadian rhythm. CONCLUSIONS: Total and free Dpd do not show comparable sensitivity in detecting short-term inhibition of osteoclast activity. The degradation process of peptide-bound to free Dpd could render free Dpd insensitive to acute changes of osteoclast activity.

Adult↗
PubMed1999

Study of calcium metabolism in idiopathic hypercalciuria by strontium oral load test.

Calcium excretion and absorption were evaluated in hypercalciuric calcium stone formers by the study of Sr2+ excretion and absorption after an oral load. Ca2+ stone formers (n = 140) were studied, and the results were compared in the 83 of them who had idiopathic hypercalciuria and in the 57 who had Ca2+ excretion within reference values. Hypercalciuric patients showed increased renal Sr2+ clearance (CRE; 5.26 +/- 0.358 vs 3.29 +/- 0.277 mL/min; P <0.001), whereas Sr2+ absorption [assessed as the area under the serum concentration-time curve (AUC)] was increased at 30 and 60 min (1.53 +/- 0.087 vs 1.21 +/- 0.071 mmol. L-1. min; P <0.05), but not at 240 min after the load. In hypercalciuric patients, the AUCs were positively correlated with urinary Sr2+ fractional excretion (P <0. 001). Conversely, in normocalciuric patients plasma parathyroid hormone (PTH) was negatively correlated with the AUCs (P <0.01) and CRE (P <0.05), whereas 1,25-dihydroxyvitamin D plasma concentrations normalized to PTH were positively correlated with the AUCs (P <0.05). The results of Sr2+ load tests suggest that in the hypercalciuric population, Ca2+ absorption is altered predominantly in the duodenum and that the normal regulation exerted by calciotropic hormones on tubular and enteral Ca2+ handling is lost.

Administration, Oral↗
PubMed1998

Osteocyte-bone lining cell system at the origin of steady ionic current in damaged amphibian bone.

A wound-generated steady electric current was measured by a two-dimensional vibrating probe system in the metatarsal bones of 22 adult frogs (Xenopus laevis) placed in amphibian Ringer. Inward currents were recorded entering a micrometric hole drilled through the cortex at middiaphyseal level. These steady state currents (mean +/- SD 8.50 +/- 2.77 microA/cm2) last approximately 2 hours, were dependent on the presence of sodium in the incubation medium, were no more detectable after fixation, and were reduced to background level when the cell membranes were solubilized. These results agree with previous recordings of metatarsal bones of weanling mice, under identical conditions. Both results suggest that the measured ionic currents have a cellular origin. Metatarsal bones of adult amphibian were purposely selected for this study because, unlike mammalian bones, their shafts are avascular and only contain an osteocyte-bone lining cell system, as documented by scanning and transmission electron observations. Thus, unlike the data from previous investigations on mammals, the results succeeded in giving the first convincing evidence that the osteocyte-bone lining cell system is the origin of damage-generated ionic currents. As damage exposes bone ionic compartment to plasma, damage-generated ionic currents are representative of ion fluxes at bone plasma interface, and cells at the origin of the current generate the driving force of such fluxes. By demonstrating that osteocytes and bone lining cells are at the origin of the current, this study suggests that the osteocyte-bone lining cell system, though operating as a cellular membrane partition, regulates ionic flow between bone and plasma. Since strain-related adaptive remodeling could also depend on ionic characteristics and flow of the bone fluid through the osteocyte lacuno-canalicular network, the results reported here support the view that osteocyte and bone lining cells may constitute a functional syncytium involved in mineral homeostasis as well as in bone adaptation to mechanical loading.

Animals↗
PubMed1998

Responsiveness of urinary markers of bone resorption to orchiectomy and clodronate treatment in mature rats: a comparative study.

OBJECTIVE: The aim of this study was to assess the responsiveness of two classes of bone resorption markers to the enhancement of osteoclastic activity induced by orchiectomy and to its inhibition by clodronate treatment in mature rats. DESIGN: Bone mineral density (BMD) at femural metaphysis, femural diaphysis, lumbar vertebrae, and the urinary excretion of pyridinoline (Pyr), deoxypyridinoline (D-Pyr), galactosylhydroxylysine (GHyl) and glucosylgalactosylhydroxylysine (GGHyl) were monitored at regular intervals for 30 days prior to and for 60 days following orchiectomy in eleven rats, divided into two groups: five rats untreated and the other six treated with clodronate. RESULTS: Prior to orchiectomy, a significant (P < 0.01) decrease in BMD was observed only at the distal femural metaphysis. This decrease appeared to be associated with a time-dependent increase in the urinary excretion of all markers. Following orchiectomy, the BMD of the untreated group decreased significantly (P < 0.01) at all bone sites. The bone loss was accompanied by a significant (P < 0.01) increase in Pyr and D-Pyr concentrations in urine, whereas urinary GHyl and GGHyl did not change significantly. In the clodronate-treated group, the BMD of the three skeletal sites did not change significantly, while the urinary excretion of all urinary biochemical markers decreased significantly (P < 0.001). CONCLUSION: This study showed that pyridinolines are able to monitor the bone response to orchiectomy and to clodronate treatment response in androgen-deficient mature male rat. whereas glycosides appear prone to confounding factors.

Aging↗
PubMed1998

Strontium absorption and excretion in normocalciuric subjects: relation to calcium metabolism.

The relationships of Sr intestinal absorption and renal excretion with biohumoral factors regulating Ca metabolism were studied in 47 normocalciuric subjects with Ca kidney stones. Sr concentrations were measured in serum and urine after an oral load of stable Sr (30.2 mumol/kg body wt). Enteral absorption of the ion (9.77 +/- 0.438 mmol.L-1.min, 240 min after Sr administration), expressed as the area under the plasma concentration-time curve (AUC), and renal clearance (CRE) in these subjects during the test (2.80 +/- 0.336 mL/min) were not different from values for 27 controls. CRE was not correlated with AUCs. Plasma concentrations of parathyroid hormone (PTH) negatively correlated with AUCs (P < 0.01) and correlated with CRE after one outlier was excluded (P < 0.05). Plasma concentrations of 1,25-dihydroxyvitamin D correlated positively with AUCs (P < 0.01) when normalized to the plasma concentration of PTH. Multiple stepwise regression showed that PTH and phosphatemia were significantly related to AUC values at 240 min (P < 0.01). These findings suggest that Sr absorption and excretion reflect the regulation of Ca metabolism, but some differences in renal handling of the two ions may exist.

Administration, Oral↗
PubMed1997

A comparative study on biochemical markers of bone collagen breakdown in post-menopausal women.

The aim of this study was to compare urinary galactosylhydroxylysine (GHyl) and deoxypyridinoline (d-Pyr) as biochemical markers of bone resorption in post-menopausal women treated and untreated with estrogen and cyclic etidronate. Fasting urinary GHyl, D-Pyr, pyridinoline, serum osteocalcin and total alkaline phosphatase were measured in three subgroups, i.e. post-menopausal women undergoing hormone replacement therapy, untreated post-menopausal women and post-menopausal women with low BMD treated with disodium etidronate. The results indicated that GHyl did not significantly discriminate between untreated post-menopausal women and estrogen replated ones unless an osteoporotic untreated group was selected. d-Pyr and GHyl showed similar performances when their values after bisphosphonate treatment were compared to those found in untreated post-menopausal women, thus suggesting that both markers were equal in their ability to detect the bone response to cyclic etidronate administration. This observation further proves the statement that GHyl is prone to confounding factors under estrogen therapy but it is adequate as is d-Pyr in monitoring the bone response to bisphosphonate treatment.

Aged↗