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Biomedical subjects

M Brazier

Publications and source records attributed to M Brazier.

At least 19 recordsLinked to original sources
PubMed2006

The calcium sensing receptor is directly involved in both osteoclast differentiation and apoptosis.

Intracellular transduction pathways that are dependent on activation of the CaR by Ca(o)2+ have been studied extensively in parathyroid and other cell types, and include cytosolic calcium, phospholipases C, A2, and D, protein kinase C isoforms and the cAMP/protein kinase A system. In this study, using bone marrow cells isolated from CaR-/- mice as well as DN-CaR-transfected RAW 264.7 cells, we provide evidence that expression of the CaR plays an important role in osteoclast differentiation. We also establish that activation of the CaR and resultant stimulation of PLC are involved in high Ca(o)2+-induced apoptosis of mature rabbit osteoclasts. Similar to RANKL, Ca(o)2+ (20 mM) appeared to trigger rapid and significant nuclear translocation of NF-kappaB in a CaR- and PLC-dependent manner. In summary, our data suggest that stimulation of the CaR may play a pivotal role in the control of both osteoclast differentiation and apoptosis in the systems studied here through a signaling pathway involving activation of the CaR, phospholipase C, and NF-kappaB.

Animals↗
PubMed2006

Autoantibodies, metalloproteinases and bone markers in rheumatoid arthritis patients are unable to predict their responses to infliximab.

OBJECTIVES: To identify biochemical, immunological and bone markers as predictors of rheumatoid arthritis (RA) patients' responses to infliximab. METHODS: A total of 76 patients with active RA (American College of Rheumatology criteria), refractory to disease-modifying anti-rheumatic drugs, including methotrexate, received infliximab (3 mg/kg) infusions at weeks 0, 2, 6, and then every 8 weeks in combination with methotrexate or leflunomide. At week 14, infliximab efficacy was evaluated using disease activity score (DAS)28. A serum sample, collected just before starting infliximab, was tested by ELISA (unless stated otherwise) for the following immunological markers: rheumatoid factor by agglutination and ELISA (IgA, IgG and IgM isotypes); anti-cyclic citrullinated protein; autoantibodies recognizing calpastatin domain I and its 27 C-terminal fragment, glucose-6-phosphate isomerase, alpha-enolase; anti-keratin and anti-perinuclear factor antibodies (immunofluorescence); biochemical markers: C-reactive protein (nephelometry), metalloproteinase-1 and -3, tissue inhibitors of metalloproteinases-1 and -2, antioxidants (vitamins A and E; selenium); bone resorption markers: pyridinoline, deoxypyridinoline, osteoprotegerin, soluble receptor activator of nuclear factor-kappaB ligand, cartilage oligomeric matrix protein. Each parameter's predictive value of the response to infliximab was analysed using Fisher's exact, Mann-Whitney and chi-square tests. Hierarchical clustering was performed with The Institute for Genomic Research (TIGR) multiple experiment viewer software. RESULTS: Good, moderate and non-responder rates were 6.5, 61.8 and 31.5%, respectively. No significant difference was observed between responders and non-responders, regardless of the serum parameters considered. Analysis of dichotomous or continuous variables failed to identify markers predictive of a good or poor response to infliximab. CONCLUSION: The search for soluble markers in RA patients' sera likely to predict response to infliximab because of their involvement in RA pathogenesis seems disappointing. However, because of the limited power to detect smaller differences in biomarkers, the present study is a preliminary exploratory analysis.

Adult↗
PubMed2004

Impact of inflammation and oxidative stress on vascular calcifications in chronic kidney disease.

Vascular and/or valvular calcifications in patients with chronic kidney disease (CKD) appear to indicate a poor prognosis in terms of overall survival and cardiovascular morbidity and mortality. Inflammation and oxidative stress represent new features of the arterial and/or valvular calcification process. However, only limited observational and epidemiological data are available in these areas. Therefore, the link between inflammation, oxidation and vascular and/or valvular calcifications deserves careful consideration in CKD patients, since they may become targets for the development of new therapeutic strategies.

Calcinosis↗
PubMed2004

Biological effects of drinking-water mineral composition on calcium balance and bone remodeling markers.

OBJECTIVE: To compare the effects of 2 drinking waters containing similar calcium (Ca) concentration in order to analyze the role of ions other than Ca on bone metabolism. These mineral drinking-waters differed by their mineral composition primarily concerning the concentration of bicarbonate (HCO3-), high in the HB, and sulfate, high in HS water. DESIGN: Of 60 included women, 39 completed the study. Patients were randomly assigned to an intake of 1 liter per day of mineral water HB or HS for 28 d, followed by cross-over to the alternative drinking-water for a further 28 d. At baseline and after each period of one month, Ca metabolism parameters, acid-base status, and bone remodeling markers were measured. RESULTS: Changes in Ca metabolism were significant in the HB group where the ionized Ca increased and the PTH decreased. Serum pH showed a similar increase whatever the used drinking water compared to baseline. In the HB group, significant increase in urine pH, and significant decrease in AT-HCO3- and NH4+ were observed. Bone resorption markers, urinary CTx/Cr, Pyr/Cr, and D-Pyr/Cr, significantly decreased in the HB group compared to baseline, and were not significantly modified in the HS group. CONCLUSIONS: These results showed a beneficial effect of the bicarbonaterich HB water on bone metabolism. This may account for a better bioavailability of the Ca, a greater alkalinization, and a larger decrease in PTH level secondary to a higher ionized Ca level. The higher content of silica in HB water may have also participated to the positive action on bone balance that was observed. In this short term study, these data underlined the potential role of the mineral drinking water composition on bone metabolism.

Acid-Base Equilibrium↗
PubMed2003

Regulation of bone resorption and osteoclast survival by nitric oxide: possible involvement of NMDA-receptor.

Nitric oxide has been shown to play an important role in regulation of bone resorption. However, the role of endogenous nitric oxide on osteoclast activity remains still controversial. In this work, using RT-PCR amplification, we demonstrated that rabbit mature osteoclasts express mRNA encoding for neuronal nitric oxide synthase suggesting that this enzyme could be involved in basal nitric oxide production in these cells. Then we assessed the effect of carboxy-PTIO, a nitric oxide scavenger, on in vitro bone resorption and osteoclast survival. Carboxy-PTIO (10-100 microM) inhibited osteoclastic bone resorption in a dose dependent manner and induced osteoclast apoptosis by a mechanism involving caspase 3 activation. These results suggest that basal concentration of endogenous nitric oxide may be essential for normal bone resorption by supporting osteoclast survival. Because osteoclasts express N-methyl-d-aspartate-receptor (NMDA-R), we hypothesized that in osteoclasts NMDA-R may be involved in nitric oxide production as in neuronal cells. We confirmed that blockade of NMDA-R with specific non-competitive antagonists, MK801 and DEP, strongly inhibited bone resorption. As for carboxy-PTIO, we showed that blockade of NMDA-R by both antagonists induced osteoclast apoptosis in a dose dependent manner by a mechanism dependent on caspase 3 activation. Intracellular calcium concentration in osteoclasts decreased within minutes in the presence of both antagonists. Finally, MK801-induced osteoclast apoptosis was partially reversed in the presence of small amount of SNAP (100 nM), a nitric oxide donor, suggesting that the effect of NMDA-R on osteoclast apoptotic cell death could be due to a decrease in nitric oxide production. Taken together, our results are consistent with the hypothesis that NMDA-R on osteoclasts could have a similar function as those in neuronal cells, i.e., to allow a calcium influx, which in turn activates a constitutive neuronal nitric oxide synthase. Nitric oxide generated by this pathway may be essential for osteoclast survival and hence for normal bone resorption.

Animals↗
PubMed2003

Involvement of capacitive calcium entry and calcium store refilling in osteoclastic survival and bone resorption process.

Bone resorption is closely dependent on osteoclastic survival and osteoclast apoptotic cell death could represent a key step at the end of this process. In order to precise the possible role of calcium movement in osteoclastic cell death, we investigated whether intracellular calcium store replenishment and capacitive calcium entry (CCE) are involved in osteoclastic survival and bone resorption. We demonstrate that (i). thapsigargin, a sarco-endoplasmic reticulum calcium ATPase pump (SERCA) blocker, decreases both osteoclastic survival and bone resorption process, (ii). 2-aminoethoxydiphenyl borate (2-APB) and SKF-96365, two store-operated channel (SOC) blockers, dramatically decrease osteoclastic survival and bone resorption and (iii). culture in calcium-free medium and thapsigargin exposure synergically inhibit osteoclastic survival which falls dramatically to a value close to 0% (P<0.001). Inversely, osteoclastic survival increases significantly when thapsigargin-treated cells are cultured in the presence of 20mM calcium, suggesting that increasing extracellular calcium concentration stimulates osteoclasts survival when the filling of intracellular stores is prevented. Taken together, our data strongly suggest that in osteoclasts, calcium movements between cellular compartments involved in the regulation of calcium signalling, such as calcium stores refilling and CCE, are closely associated to the regulation of osteoclast survival and bone resorption.

Animals↗
PubMed2003

Organ retention and return: problems of consent.

This paper explores difficulties around consent in the context of organ retention and return. It addresses the proposals of the Independent Review Group in Scotland on the Retention of Organs at Post Mortem to speak of authorisation rather than consent. Practical problems about whose consent determines disputes in relation to organ retention are explored. If a young child dies and his mother refuses consent but his father agrees what should ensue? Should the expressed wishes of a deceased adult override the objections of surviving relatives? The paper suggests much broader understanding of the issues embedded in organ retention is needed to provide solutions which truly meet families' and society's needs.

Adult↗
PubMed2000

Evaluation of in vitro bone resorption: high-performance liquid chromatography measurement of the pyridinolines released in osteoclast cultures.

None of the currently used methods to evaluate bone resorption by osteoclasts cultured on bone substrate measures directly the amounts of degraded bone collagen, which is a direct reflection of the osteoclast "work done." We therefore propose a reliable biochemical method to evaluate the in vitro collagenolysis process. Bone-resorbing activity was evaluated, after HPLC separation, by fluorimetric measurement of hydroxylysylpyridinoline (HP), a collagen cross-link molecule, released in culture supernatants. We first confirm previous data reporting that HP is released in the culture medium in a peptide-conjugated form. After acid hydrolysis, we show that HP is highly correlated with the lacunae area (r = 0.68, P<0.0001) and with the amounts of antigenic collagen fragments (Cross-laps for culture) released in culture medium (r = 0.77, P<0.0002). Using a cysteine protease inhibitor, we observed that lacunae areas are dramatically less inhibited (35% inhibition) than the release of bone-degraded products, including HP and antigenic collagen fragments (96 and 92% inhibition, respectively). Coupled to the resorbed area measurement, biochemical evaluations offer both quantitative and qualitative complementary measurements of the osteoclastic bone-resorbing process.

Animals↗
PubMed2000

High extracellular calcium concentrations directly stimulate osteoclast apoptosis.

Although the inhibitory effects of high extracellular calcium concentrations ([Ca](e)) on osteoclastic bone resorption have been known for several years, the exact mechanism remains poorly understood. The present study was performed to investigate the possible effect of [Ca](e) on osteoclast apoptosis. Using highly purified rabbit osteoclasts, we have shown that calcium directly promotes apoptosis in a dose-dependent manner which correlates with the dose range of calcium for the inhibition of bone resorption. A time-course experiment of apoptotic changes of osteoclasts cultured in presence of 1.8 or 20 mM calcium showed a significant difference after as early as 8 h of culture. After 72 h of culture, we observed that 80% of the cells cultured in the presence of 20 mM calcium displayed the typical features of apoptosis compared to only 20% in the medium containing 1.8 mM calcium. Calcium channel blockers and ryanodine abrogated the effects of [Ca](e) on apoptosis while neomycin, a calcium-sensing receptor agonist, did not alter cell viability. Taken together, these results suggest that calcium influx is involved in calcium-induced osteoclast apoptosis. Our results are consistent with the concept that in the presence of high [Ca](e) generated during bone demineralization, osteoclasts are subjected to negative-feedback regulation due, at least in part, to the induction of apoptosis.

Animals↗
PubMed2000

[Osteoblastic regulation of osteoclast survival: effect of calcitriol].

Throughout life, bone is remodelled in a dynamic process which results in a balance between bone formation by osteoblasts and bone resorption by osteoclasts. It is now clearly established that osteoblasts/stromal cells are crucial for differentiation of osteoclasts, through a mechanism involving cell-to-cell contact. However, the possible involvement of osteoblasts and stromal cells in the survival of osteoclasts has not yet been clearly demonstrated. In this study, we assessed the influence of cellular microenvironment, especially osteoblasts, on the osteoclast survival. Our results have shown significant differences in osteoclastic survival between unfractionated bone cells and pure osteoclasts. Furthermore, we have shown that addition of 1.25(OH)2D3 to unfractionated bone cells resulted in a dose-dependent increase in osteoclast survival. Finally, we have shown that a conditioned medium obtained from rat osteoblastic cells cultured with calcitriol was able to increase significantly survival of pure osteoclasts. Taken together, these results strongly suggest that osteoblastic cells present in the bone microenvironment might play a role in the osteoclastic survival by producing soluble factor which modulate osteoclast apoptosis.

Animals↗
PubMed2000

Effects of ultraviolet light on free and peptide-bound pyridinoline and deoxypyridinoline cross-links. Protective effect of acid pH against photolytic degradation.

Little is known about the photodegradation of pyridinoline (Pyd) and deoxypyridinoline (Dpd), which are two mature cross-links stabilizing collagen within extracellular matrix. In this study, highly purified free Pyd and Dpd cross-links have been degraded by irradiation with ultraviolet light and we have shown that photolysis varies with the pH value. Assessment of photolysis in basic (pH 9) and neutral (pH 7) solutions by high-performance liquid chromatography as well as by UV absorbance measurement indicates that both cross-links are degraded after a 24 h UV exposure, while in acidic solution (pH 3) only Dpd is photolysed, suggesting that acid pH provides major protection against Pyd photolysis. Photodegradation products have been studied by amino-acid and mass spectral analysis. Both methods confirm the lack of Pyd degradation in acid pH. Furthermore, amino-acid analysis allows us to identify hydroxylysine and lysine as a result of Pyd and Dpd photolysis, respectively, indicating that the mechanism of photodegradation involves the cleavage of the pyridinium ring on each side of the quaternary nitrogen. Finally, we have also studied the photolysis of different molecular species of type I collagen peptides, obtained by digestion with collagenase of demineralized turkey bone. Our results indicate that even when they are part of the structure of collagen peptide, Pyd and Dpd can be photolysed. However, we have shown that the larger the peptide is, the smaller are the effects of UV irradiation.

Amino Acids↗
PubMed2000

Cyclosporine bone remodeling effect prevents steroid osteopenia after kidney transplantation.

BACKGROUND: It is well established that prednisone above 7.5 mg/day may induce osteopenia in association with decreased bone formation. In contrast, the effect of cyclosporine on bone remodeling and bone mineral density (BMD) is controversial. Multiple confounding factors explain this controversy, especially after renal transplantation. METHODS: Fifty-two renal transplanted patients never exposed to aluminum while on dialysis were selected because they had no rejection and no hypercalcemia for 24 months while being treated with low dose prednisone/cyclosporine A (daily dose at 10 mg and 4.8 mg/kg, respectively, beyond 3 months). Bone remodeling markers (BRMs; plasma osteocalcin, bone and total alkaline phosphatases for formation, and urinary pyridinolines for resorption) were sequentially measured together with plasma creatinine, intact parathyroid hormone (PTH) and 25 OH vitamin D and cyclosporine from day 0 to 24 months. BMD was measured at 3, 6, 12, and 24 months by quantitative computerized tomography (QCT) at the lumbar spine and by double-energy x-ray absorptiometry (DEXA) at this site, as well as at the femoral neck, radius shaft, and ultradistal (UD) radius. RESULTS: Plasma concentrations of creatinine, PTH, and 25 OH vitamin D initially decreased and stabilized beyond three months at 137 micromol/L, 1.5 the upper limit of normal (ULN) and 11 ng/mL, respectively. All BRM increased significantly above the ULN at six months and then decreased. The BMD Z score at three months was low at all sites measured by DEXA and QCT. Follow-up measurements showed stability of absolute value and of Z score at all sites measured by DEXA. A comparison of the lumbar QCT Z score, which was available in 42 patients at 3 and 24 months, showed an increase in 28 and a decrease in 14, so that the increase for the whole group was significant (P < 0.04). Compared with patients with a decreased Z score, those with an increased Z score had significantly higher cyclosporine and lower prednisone dosages and a greater BRM increase at six months, whereas age, sex ratio, and plasma creatinine, PTH and 25 OH vitamin D were comparable and stable from months 3 through 24. The mean trough level of cyclosporine for the first six months was positively correlated to osteocalcin and total alkaline phosphatase increase at six months, and both bone formation and resorption marker increases were significantly correlated to the lumbar QCT Z score increase at 24 months. CONCLUSIONS: Combined low-dose prednisone and cyclosporine immunosuppression are associated with a stabilization of BMD measured at all sites with DEXA 3 to 24 months after renal transplantation and with a prevention of age-related loss of vertebral trabecular bone, as shown by the significant increase in lumbar spine QCT Z score. It is suggested that cyclosporine, together with the decrease of prednisone dosage but independent of renal function, PTH, and vitamin D status, contributes to a transient stimulation of bone remodeling at six months, which counterbalances the deleterious effect of prednisone on bone formation and BMD.

Absorptiometry, Photon↗
PubMed1999

Nurse prescribing: radicalism or tokenism?

The creation of The Medical Products (Prescription by Nurses, etc.) Act 1992 has been generally welcomed by the nursing profession. This article seeks to introduce a note of scepticism about the assumed motivations for its introduction through an analysis of various legal, ethical, economic and political dimensions. In reviewing the position of nursing vis-à-vis medicine it is argued that one of the ways that nursing has sought to improve its professional position is to take on work previously done by doctors, and nurse prescribing can be seen in the context of the concurrent de-regulation of medicines, allowing greater access to medicines and therefore greater consumer choice. This de-regulation stems from the liberation ideology of the previous Conservative government. Viewed in this way nurse prescribing, particularly with reference to the limited nature of the nursing formulary, can be seen to be anomalous. In the light of this analysis, the reasons generally put forward (notably in the Crown Report 1989) for the introduction of nurse prescribing could be seen to be peripheral to its real purpose. It is argued that the most convincing reasons for its introduction relate to the medical profession as a social institution. It is proposed that the three primary aims behind the introduction of nurse prescribing are: the saving of money; the transfer of routine medical work to nursing; and a challenge to the professional monolith of medicine.

Community Health Nursing↗
PubMed1999

Is low plasma 25-(OH)vitamin D a major risk factor for hyperparathyroidism and Looser's zones independent of calcitriol?

BACKGROUND: Recent reports suggest that calcitriol might not be the sole active metabolite of vitamin D and that plasma concentrations of 25-(OH)vitamin D (25OHD) are often abnormally low in hemodialysis patients. We have therefore evaluated plasma 25OHD as a risk factor for parathyroid hormone (PTH) hypersecretion and radiological bone disease. We carried out a cross-sectional study during the month of September in an Algerian dialysis center of 113 patients who were not taking supplements of alphacalcidol or calcitriol. METHODS: Plasma 25OHD, calcitriol, PTH, calcium, phosphate, bicarbonate, and aluminum were measured, and x-rays of the hands and pelvis were obtained for evaluation of subperiosteal resorption and Looser's zones. RESULTS: The median plasma 25OHD was 47.5 nmol/liter (range 2.5 to 170.0). Univariate analysis showed that plasma PTH was correlated positively with months on maintenance dialysis and negatively with plasma 25OHD, calcitriol, calcium, bicarbonate and aluminum, but not with that of phosphate. plasma 25OHD was positively correlated with calcium and calcitriol. Using multiple regression analysis, only plasma 25OHD (negative) and the duration on maintenance dialysis (positive) were independently linked to plasma PTH. The prevalence of isolated subperiosteal resorption (ISR) was 34%, and that of the combination of resorption with Looser's zones (CRLZ) was 9%; thus, only 57% of the patients had a normal x-ray appearance. These groups were comparable with regards to age, gender, and duration on dialysis. When the biochemical measurements of the patients with CRLZ were compared with those from patients without radiological lesions, plasma 25OHD was the only parameter to show a statistically significant difference, being significantly lower in the CRLZ group (26 +/- 18 vs. 57 nmol/liter, ANOVA, P < 0.004). Plasma 25OHD was also significantly lower in the ISR group (44, P < 0.05) than in the normal x-ray group, and plasma Ca (P < 0.003) and bicarbonate (P < 0.02) were lower. Logistical analysis showed that the presence of resorption was independently linked only with plasma PTH. Looser's zones and subperiosteal resorption were not seen in patients with plasma 25OHD of more than 40 (Looser's zones) and more than 100 nmol/liter (subperiosteal resorption). The optimal range for intact PTH in hemodialysis patients with mild aluminum overload is 10 to 25 pmol/liter. We found that plasma PTH was inappropriately high only when plasma 25OHD was less than 100 nmol/liter. With a plasma 25OHD of between 100 and 170 nmol/liter, hypercalcemia was present with a plasma PTH of less than 10 pmol/liter in only one case. CONCLUSIONS: This cross sectional study shows that low plasma 25OHD is a major risk factor for hyperparathyroidism and Looser's zones. In dialysis patients, we suggest that the plasma levels of 25OHD are maintained around the upper limit of the reference range of sunny countries.

Adult↗
PubMed1999

Method for the isolation and purification of pyridinoline and deoxypyridinoline crosslinks from bone by liquid chromatographic techniques.

Significant progress has been made in recent years in the development of new bone resorption markers, based principally on the urinary excretion of pyridinoline (Pyd) and deoxypyridinoline (Dpd) crosslinks. For their measurement, in spite of the recent development of immunoassays, HPLC remains the method of reference. However, the lack of an appropriate internal standard requires large amounts of pure crosslinks for external standardisation. Herein, we describe an efficient method for the isolation of both crosslinks from bone of adult turkey by isocratic semi-preparative HPLC. Demineralized bone is hydrolysed in hydrochloric acid, 9 M. A first liquid extraction step in butanol allowed to eliminate less polar compounds. The aqueous phase was concentrated and separated by gel filtration on Biogel P2 and eluted by acetic acid solution (10%). Fractions containing pyridinoline were pooled, concentrated, and purified on a CF1 cellulose column. Pyd and Dpd crosslinks were then separated isocratically by HPLC on a C18 reversed phase column (Vydac 218 TP 1010, 250x10 mm) and eluted with HFBA as the ion-pairing agent. Retention times of Pyd and DPD were 23.6 and 28.7 min, respectively. Both crosslinks prepared by HPLC were then transformed as hydrochloride to cellulose phosphate and desalted on Sephadex G-10 columns. These two further steps yielded highly purified compounds (the purity was greater than 98% evaluated by aminoacid analysis). In conclusion, the efficiency of this method allows to obtain rapidly Pyd and Dpd without interfering compounds as proven by spectral studies (NMR and mass spectroscopy).

Amino Acids↗
PubMed1999

[Role of the time of administration of calcium carbonate (before or during mealtime) in the control of hyperphosphatemia in patients on maintenance hemodialysis].

UNLABELLED: A study has claimed that at equal elemental calcium dose, CaCO3 was not less but equally efficient in controlling predialysis hyperphosphatemia as calcium acetate provided both calcium salts were given five minutes before the meals instead of during the meals because the higher acidity of a fasting gastric juice would allow a better dissociation of CaCO3. To examine the point that CaCO3 is more efficient if it is taken five minutes before compared to during the meal, we performed a two month randomised cross-over trial in twelve reliable and stable patients maintained on chronic hemodialysis while their treatment and diet remained constant. Comparison of the plasma concentrations measured during the two modes of administration showed no significant difference in creatinine, urea, bicarbonate, intact-PTH. Mean (+/- SD) plasma PO4 was significantly higher (1.93 +/- 0.50 versus 1.72 +/- 0.40 mmol/l; p = 0.02) whereas corrected plasma Ca was significantly lower (2.30 +/- 0.15 versus 2.38 +/- 0.17 mmol/l; p = 0.01) when CaCO3 was given before the meals than during the meals. CONCLUSIONS: a) administration of CaCO3 before the meal decreases its efficiency in controlling hyperphosphatemia since plasma PO4 was actually slightly higher with this timing of administration; b) administration of CaCO3 before the meal is associated with significantly lower plasma corrected calcium suggesting a smaller absorption of calcium which may be an advantage but only in hypercalcemic patients; c) there is no reason other than the prevention of its hypercalcemic effect to recommend the administration of CaCO3 just before the meals than during the meals.

Aged↗