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At least 505 records · Page 28Linked to original sources
PubMed1993

A novel skeletal drug delivery system using self-setting bioactive glass bone cement. IV: Cephalexin release from cement containing polymer-coated bulk powder.

A novel device consisting of Eudragit-coated cephalexin as a model drug and a self-setting bioactive cement based upon CaO-SiO2-P2O5 glass was investigated. The glass cement hardened within 5 min of mixing with a phosphate buffer. After setting, in vitro drug release from homogeneous or heterogeneous drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37 degrees C continued for over 2 weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite and decreased in volume by about 5% during drug release in SBF. Consequently, 30% of the loaded drug was initially released from the homogeneous cement system, and thereafter it was released more slowly. Since the heterogeneous system consisting of the cement and a 50% polymer coated, drug-loaded pellet avoided this drug's burst, the drug was released over a longer period than that in the homogeneous system. The heterogeneous system released the polymer-coated drug very slowly, because it completely avoided the initial burst, and sustained the release over a long period.

Biocompatible Materials↗
PubMed1996

Fulminant metastatic calcinosis with cutaneous necrosis in a child with end-stage renal disease and tertiary hyperparathyroidism.

Metastatic calcinosis is a common feature of chronic renal failure. Its first manifestations are bone demineralization and non-visceral and/or visceral calcification with mostly mural deposits in arteries and arterioles. It is initially characterized by hyperphosphataemia followed by secondary or tertiary hyperparathyroidism. Cutaneous involvement is a rare complication. Histologically, the lesions show vascular calcification with ischaemic skin necrosis. Extreme cases may produce calcinosis cutis (calciphylaxis), i.e. disseminated calcification of the subcutaneous tissue and dermis in the form of hard painful cutaneous nodules and plaques with subsequent ulceration. Metastatic calcinosis is a disease affecting adults, while the dystrophic or idiopathic type can develop in children. We present the case of a 6-year-old boy with end-stage renal disease, attributed to congenital renal hypoplasia, and accompanied by secondary hyperparathyroidism. He developed fulminant tertiary hyperparathyroidism and metastatic calcinosis of the lungs, as well as cutaneous necrosis of the buttocks and legs, subsequent to calcification of arteries and arterioles. A maternal renal transplant failed to function. The serum parathormone, calcium and phosphate levels could not be controlled by maintenance dialysis, phosphate binders and calcitriol. Total parathyroidectomy without autotransplantation of parathyroid tissue rapidly returned the serum parathormone, calcium and phosphate levels to normal. In addition, topical treatment using merbromine solution and hydrocolloid dressings, healed the ulcers with significant scar formation, within 2.5 months after parathyroidectomy. A renewed increase of the calcium x phosphate product, 2 months after parathyroidectomy, was attributed to mobilization of calcium compounds from the viscera, as confirmed by a chest X-ray.

Calcinosis↗
PubMed1996

The quantification of tertiary dentine formation in response to materials commonly placed in deep cavities in general practice in the UK.

PURPOSE OF STUDY: To determine the rate of formation of tertiary dentine in dogs' teeth, in response to five commonly used lining materials. Also, to record the resulting differences in quality of the formed dentine. MATERIALS AND METHODS: Representatives of five types of materials commonly used in general practice in the UK were placed in deep standardised cavities with a remaining dentine thickness of 400-500 microns, and sealed to the cavo-surface with zinc oxide-eugenol. The daily rate of tertiary dentine formed in response to each material was measured over a period of 119 days using a tetracycline staining method. A concomitant study to show the quality of the formed dentine was undertaken using the same materials and experimental conditions. RESULTS: There was a significant difference between the rates of tertiary dentine formation for all materials except zinc oxide-eugenol and Ledermix paste. For each material there was a increased rate of tertiary dentine formation in the second period (29-49 days) compared to the first period (0-28 days). This is considered to be due, in part, to a lag period when damaged odontoblasts are differentiating from mesenchymal elements. The rate of tertiary dentine formation in response to all the test materials was always greater than that of normal physiological dentine formation in unprepared teeth. Qualitatively, there was difference in the formed tertiary dentine beneath each material. All the materials caused odontoblast destruction, altered ground substance production and alterations in the calcification process. CONCLUSION: None of the materials routinely used at present can be considered to be 'ideal' as odontoblast destruction, altered ground substance production and altered calcification occur beneath zinc oxide-eugenol preparations, calcium hydroxide preparations as well as in response to corticosteroid-containing materials such as Ledermix paste and cement.

Analysis of Variance↗
PubMed1997

Calcium supplementation.

Calcium is necessary for the prevention and treatment of diseases such as osteoporosis, hypertension, and, possibly, colon cancer. Supplementation is useful when dietary calcium intake is low, as is the current situation in North America. There are many factors to consider before recommending any one form of supplement. A consideration for calcium carbonate tablets is whether the tablet disintegrates and whether or not a lack of food or acid in the stomach will hinder utilization. Other forms of calcium, particularly the chelated calcium salts, are better absorbed in fasting achlorhydric subjects but have less calcium per gram of supplement. Interaction of calcium with other mineral nutrients and the presence of contaminating metals has focused attention on safety. Based on present evidence, chelated calcium and refined calcium carbonate tablets (including those labeled as antacids) may be safely and effectively ingested by most people at doses generally recommended for treatment or prevention of osteoporosis. One should not exceed 2,000 mg of calcium, except at the advice of their health care provider, as inadvertent mineral deficiencies may arise. Persons at risk for developing milk-alkali syndrome, such as thiazide users and persons with renal failure, should be identified and monitored for alkalosis and hypercalcemia when using calcium supplements.

Adolescent↗
PubMed1997

Bone bonding ability of bioactive bone cements.

The bone bonding ability of three types of bioactive bone cement A, B, and C consisting of glass or glass ceramic powder and bisphenol-alpha-glycidyl methacrylate resin was evaluated. Type A contained MgO-CaO-SiO2-P2O5-CaF2 glass powder; Type B, MgO-CaO-SiO2-P2O5-CaF2 glass ceramic powder; and Type C, MgO free CaO-SiO2-P2O5-CaF2 glass powder. Rectangular plates (2 x 10 x 15 mm) of Types A, B, C, and polymethylmethacrylate cements were implanted into the tibial metaphyses of male rabbits and the failure load measured by mechanical failure testing (detaching test) 10 and 25 weeks after implantation. The failure loads of Types A, B, C, and polymethylmethacrylate cements were respectively, 29.52, 41.48, 28.22, and 0.29 N at 10 weeks and 33.42, 41.27, 33.64, and 0.20 N at 25 weeks. Examination of the bone cement interface revealed that all the bioactive bone cements achieved direct bone contact with the bone. These results showed that all three types of bioactive bone cement have the ability to bond to bone, and the cement containing glass ceramic powder revealed higher bonding strength than did those containing glass powder.

Animals↗
PubMed2004

Selenium compounds modulate the calcium release channel/ryanodine receptor of rabbit skeletal muscle by oxidizing functional thiols.

Selenium compounds, such as sodium selenite and Ebselen were shown to increase high affinity ryanodine binding to the skeletal muscle type ryanodine receptor (RyR1) at nanomolar concentrations, and inhibit the receptor at low micromolar concentrations. This biphasic response was observed in both concentration and time-dependent assays. Extensive washing did not reverse either the stimulation or suppression of receptor binding, but both were prevented or reversed by addition of reduced glutathione, GSH. Selenium compounds were also shown to induce Ca(2+) release from the isolated sarcoplasmic reticulum vesicles. Sodium selenite and Ebselen stimulated the skeletal muscle ryanodine receptor by oxidizing 14 of 47 free thiols per monomer on RyR1 (as detected with the alkylating agent 7-diethylamino-3-(4'-maleimidylphenyl)-4-methylcoumarin) (CPM). Oxidation of the remaining thiols by these selenium compounds resulted in inhibition of the ryanodine receptor.

Animals↗
PubMed1990

24-homologated 1,25-dihydroxyvitamin D3 compounds: separation of calcium and cell differentiation activities.

A series of 24-homologated 1,25-dihydroxyvitamin D3 compounds have been chemically synthesized and studied with regard to their activity in inducing differentiation of human promyelocyte HL-60 cells to monocytes and in calcium mobilizing activity in vitamin D deficient rats. Homologation of 1,25-dihydroxyvitamin D3 or its delta 22 analogue by one or two carbons increases by 10-fold and three-carbon homologation reduces by half the activity in causing differentiation of HL-60. On the other hand, homologation causes a substantial decrease in in vivo calcium mobilization activity. The addition of each carbon at the 24-position decreases binding to the HL-60 receptor or rat intestinal receptor by 5-10-fold so that binding affinity of the trihomo compound for the receptors is 130 times less that of 1,25-dihydroxyvitamin D3. Thus, binding affinity for the receptor cannot account for the preferential activity of the 24-homologated compounds in inducing cell differentiation.

Animals↗
PubMed1996

Mast cell activation in human synovium explants by calcium ionophore A23187, compound 48/80, and rabbit IgG anti-human IgE, but not morphine sulfate.

To investigate human synovial mast cell physiology, we developed a model in which mast cells in human synovial explant cultures were activated by immunologic or non-immunologic mechanisms. Small (3 mm) cubes of synovial membrane were incubated with or without secretagogue for 30, 45 or 60 min, and supernatant histamine concentrations were quantified. We measured significant histamine release with compound 48/80 at concentrations > or = 1 mg/ml, and with calcium ionophore A23187 at > or = 5 micrograms/ml. Rabbit IgG anti-human IgE induced significant histamine release at all concentrations tested, maximum at 78 micrograms/ml. Morphine sulfate produced no histamine release from synovial explants, in contrast to its significant stimulation of histamine release from neonatal foreskin explants in our explant system. We confirmed synovial mast cell degranulation by electron microscopy, and showed that it corresponded with measurable histamine release. Furthermore, histamine release was not due to secretagogue-induced cytotoxicity, as assessed by supernatant lactate dehydrogenase levels and by ultrastructural analysis. Since morphine sulfate induces mast cell degranulation and histamine release in adult and neonatal human skin, our data show that although synovial and dermal mast cells have a similar granule enzyme profile and electron microscopic morphology, they differ in functional responses. These observations support recent data that among similar human mast cell subtypes there are physiologic differences. Finally, our explant model will be useful in studies of mast cell involvement in arthritis.

Antibodies, Anti-Idiotypic↗
PubMed1991

The effect of vitamin E analogues and long hydrocarbon chain compounds on calcium-induced muscle damage. A novel role for alpha-tocopherol?

Previous studies have demonstrated that supplemental alpha-tocopherol inhibited calcium-induced cytosolic enzyme efflux from normal rat skeletal muscles incubated in vitro and suggested that the protective action was mediated by the phytyl chain of alpha-tocopherol [1]. In order to investigate this further a number of hydrocarbon chain analogues of tocopherol (7,8-dimethyl tocol, 5,7-dimethyl tocol, tocol, alpha-tocotrienol, alpha-tocopherol [10], vitamin K1, vitamin K1 [10], vitamin K1 diacetate, vitamin K2 [20], phytyl ubiquinone and retinol) were tested for any ability to inhibit calcium ionophore, A23187, induced creatine kinase (CK) enzyme efflux. Some compounds were found to be very effective inhibitors and comparison of their structures and ability to inhibit TBARS production in muscle homogenates revealed that the effects did not appear related to antioxidant capacity or chromanol methyl groups, but rather the length and structure of the hydrocarbon chain was the important mediator of the effects seen.

Animals↗
PubMed1988

Apatitic calcium orthophosphates and related compounds for biomaterials preparation.

The authors show that to obtain well chemically defined apatitic bioceramics and to know the possible transformations of this material during sintering, it is necessary to prepare a good starting material. Moreover, they show that it is possible to prepare a new organic-inorganic phosphate compound. The precipitation of apatite in an aqueous medium at boiling temperature was studied using the methodology of experimental design. Independent variables were the volume of NH4OH in phosphate solution, the volume of NH4OH in calcium solution, and the time of precipitation; the response was the atomic Ca/P ratio of the obtained precipitate. A continuous variation of this ratio from 1.63 to 1.73 is observed. Implications of this result to the preparation of pure HA: Ca10(PO4)6(OH)2 is given. Moreover, when Ca/P greater than 1.67, HA reacts with Ca(OH)2 (after heating at 1000 degrees C in air for some days) to give rise to a single phase described as a modified HA (MHA), a Ca/P ratio of 1.75, an a value of 9.373 +/- 0.002 A, and a c value of 6.884 +/- 0.002 A. The reactivity (time versus temperature) of the MHA is described. If the precipitation of the calcium phosphate is realized at 37 degrees C in a water-ethanol medium in the presence of A2EP, a new apatite, chemically bonded to the organic molecule by pooling phosphate groups, is obtained.

Ammonium Hydroxide↗
PubMed1980

Interaction of some serum proteins with hydroxylapatite and other materials.

In order to investigate whether the immune system is involved in the degradation of hydroxylapatite as implant material the adsorption behavior of several serum proteins to hydroxylapatite was studied and compared with the adsorption to other calcium phosphate compounds (Ca3(PO4)2, CaHPO4), calcium carbonate, aluminium oxide, and zinc oxide. It was found that complement factors, C4 and C3, and alpha 2-HS-glycoprotein adsorbed to the calcium phosphate compounds, but not to the other materials. IgG and albumin were adsorbed to all investigated compounds. These results suggest that the complement factors are directly adsorbed on the surface of the calcium phosphate compounds. Therefore, the activation of complement, if any, proceeds by the classical pathway. The binding of complement factors to the calcium phosphate salts investigated points to a more specific involvement of the immunosystem in the degradation process of calcium phosphate implants.

Adsorption↗
PubMed1997

In vitro calcium antagonistic and antioxidant effects of Org 13061 and its enantiomers, new potential antiatherosclerotic compounds.

The calcium antagonistic and antioxidant properties of a new potential antiatherosclerotic agent, Org 13061 were compared with those of its (-) and (+) enantiomers (Org 13471 and Org 13581) In vitro and with appropriate reference drugs. Org 13061 antagonized contractions induced by potassium in rabbit aortic rings with an IC50 value of 0.50 microM and reduced the maximum rate of phase 0 depolarization (Vmax) of the 'slow' calcium-mediated transmembrane action potentials in cardiac tissue (IC25 = 0.82 microM). Similarly to reference drugs, Org 13061 was more selective in reducing vascular compared to cardiac contraction. In concentrations overlapping those exerting vasorelaxant actions, Org 13061 inhibited copper ion-induced human low density lipoprotein (LDL) peroxidation (0.1-1 microM) and inhibited lipid accumulation by rat aortic smooth muscle cells in culture (1-3 microM). Higher concentrations (3 microM) modestly inhibited proliferation of these cells. The (-) enantiomer was ten times more potent than the (+) enantiomer as a vasorelaxant but was equipotent in inhibiting lipid accumulation and LDL peroxidation (eg, lag phase of conjugated dienes formation increased by 29 and 61 min and by 22 and 56 min in response to 0.3 and 1 microM (-) and (+) enantiomers, respectively). The antioxidant probucol was approximately three times more potent than Org 13061 in inhibiting lipid accumulation but was 30 times less potent in antagonizing LDL peroxidation. The classical calcium channel blocking agents were totally ineffective on lipid accumulation (1-10 microM), whereas human LDL peroxidation was slightly reduced by nifedipine (0.1-3 microM) but unaltered by diltiazem (0.1-30 microM) and verapamil (0.1-3 microM). In conclusion, the racemic Org 13061 selectively blocks voltage-operated calcium channels (VOCs) in concentrations that also exert marked antioxidant activity. The (-) enantiomer is largely responsible for calcium channel block but as antioxidants, the enantiomers are equipotent. This mixed pharmacological profile of Org 13061, not shared by known calcium channel blocking agents, may be potentially useful in the treatment of atherosclerosis.

Animals↗
PubMed2005

Chemical and physical surface and bulk material characterization of white ProRoot MTA and two Portland cements.

OBJECTIVES: The chemical and physical properties of white ProRoot MTA were analyzed in the bulk and at the surface and compared with two common Portland cements types CEM1 and CEM2. METHODS: The main components were analyzed by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDX), and the minor constituents were identified with inductively coupled plasma optical emission spectroscopy (ICP-OES). Moreover, the setting of the different cements was studied: the chemical composition of the surface of both powder and bound cement was investigated by XPS and the morphological changes were examined by scanning electron microscopy (SEM). RESULTS: In ProRoot MTA, the amount of gypsum is approximately half of that of the Portland cements. ProRoot MTA consists of less toxic heavy metals (Cu, Mn, Sr), less chromophores (Fe3+), and less Al-species, but contains about 2 at % Bi. In contrast to Portland cements, ProRoot MTA contains about 2 at.% Bi. In all three products, the amount of sulfur at the surface in the bound cements was 3 times higher than in the powder, indicating that in terms of the kinetics of the hardening reaction, a sulfate action mechanism prolongs the setting time. The Portland cements are composed of particles with a wide range of size, whereas ProRoot MTA showed a uniform and smaller particle size. SIGNIFICANCE: With regard to chemical and physical surface and bulk properties, ProRoot MTA cannot simply be substituted by the cheaper Portland cement. Both products are similar but not equal and exhibit marked differences.

Aluminum Compounds↗
PubMed1992

[The effect of a single dose of nifedipine, intal, sodium thiosulfate and Essentiale on the blood level of calcium, hydroperoxides, thiol compounds and prostaglandins in bronchial asthma patients].

A study was made of the impact of a single intake of nifedipine, intal, sodium thiosulfate and essentiale on respiratory function, the blood content of ionized calcium, total calcium, hydroperoxides, total and non-protein thiol groups, and prostaglandins in bronchial asthma patients. All the drugs exerted an antioxidant action, which is supported by the lowering of the content of hydroperoxides after their administration and by an increase of the content of thiol groups. A rise of the level of PGE and a considerable reduction of blood serum PGF2 alpha, most remarkable after essentiale administration were also noted. In patients given nifedipine in a dose of 20 mg, an insignificant broncholytic effect was recorded in more than half the cases. An appreciable rise of blood ionized calcium was seen in all the cases. Obviously, this is a direct consequence of its limited supply to the cells via calcium channels. In contrast to patients who received other drugs, those given intal demonstrated the lowering of blood serum ionized calcium and the growth of the content of bound calcium, which may be accounted for the transformation of ionized calcium to the bound condition.

Antioxidants↗