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PubMed2005

Preparation and characteristics of a calcium magnesium silicate (bredigite) bioactive ceramic.

In this study, new bredigite (Ca7MgSi4O16) ceramics were prepared by sintering sol-gel-derived bredigite powder compacts at 1350 degrees C for 8 h. The bending strength, fracture toughness and Young's modulus were about 156 MPa, 1.57 MPa m(1/2) and 43 GPa, respectively. The in vitro bioactivity of the bredigite ceramics was evaluated by investigating the apatite-formation ability in simulated body fluid (SBF) and the effect of ionic products from bredigite dissolution on the mouse fibroblasts cell line L929. In addition, the in vitro biocompatibility of the bredigite ceramics was evaluated by osteoblasts adhesion and proliferation assay. The results showed that bredigite ceramics could induce HAp formation in SBF. The products from bredigite dissolution significantly promoted cell growth at a certain concentration range. Furthermore, osteoblasts adhered and spread well on bredigite ceramics, and osteoblasts proliferation on bredigite ceramics was obvious.

Animals↗
PubMed2001

Constraints on nebular dynamics and chemistry based on observations of annealed magnesium silicate grains in comets and in disks surrounding Herbig Ae/Be stars.

Understanding dynamic conditions in the Solar Nebula is the key to prediction of the material to be found in comets. We suggest that a dynamic, large-scale circulation pattern brings processed dust and gas from the inner nebula back out into the region of cometesimal formation-extending possibly hundreds of astronomical units (AU) from the sun-and that the composition of comets is determined by a chemical reaction network closely coupled to the dynamic transport of dust and gas in the system. This scenario is supported by laboratory studies of Mg silicates and the astronomical data for comets and for protoplanetary disks associated with young stars, which demonstrate that annealing of nebular silicates must occur in conjunction with a large-scale circulation. Mass recycling of dust should have a significant effect on the chemical kinetics of the outer nebula by introducing reduced, gas-phase species produced in the higher temperature and pressure environment of the inner nebula, along with freshly processed grains with "clean" catalytic surfaces to the region of cometesimal formation. Because comets probably form throughout the lifetime of the Solar Nebula and processed (crystalline) grains are not immediately available for incorporation into the first generation of comets, an increasing fraction of dust incorporated into a growing comet should be crystalline olivine and this fraction can serve as a crude chronometer of the relative ages of comets. The formation and evolution of key organic and biogenic molecules in comets are potentially of great consequence to astrobiology.

Journal Article↗
PubMed1992

Interaction between polyethylene films and bromhexine HCl in solid dosage form. IV. Prevention of the sorption by addition of magnesium aluminum silicate.

The effects of magnesium aluminum silicate (MAS) addition on the sorption of bromhexine HCl to polyethylene film in tablets were studied. The addition of MAS prevented the sorption of bromhexine HCl to polyethylene film. In order to investigate the mechanism, the interaction between bromhexine HCl and MAS was studied by the powder X-ray diffraction method. It was observed that bromhexine HCl was preferentially adsorbed to the surface of MAS rather than to polyethylene film. The adsorption was accelerated at high temperature and reduced pressure conditions. The sorption of bromhexine base and bromhexine HCl to packaging material were compared using tablet dosage forms. The sorption of bromhexine base to polyethylene film was greater than that of bromhexine HCl.

Aluminum Compounds↗
PubMed1993

Role of microenvironmental deterioration of the bone marrow in the development of bone atrophy in magnesium silicate-treated rats.

The role of microenvironmental deterioration of the bone marrow in the development of bone atrophy was examined in rats with bone atrophy induced by magnesium silicate. In the tibial metaphyses, proliferation of myelocytic elements of haematopoietic tissue was prominent and caused narrowing of sinusoids, increased distance between sinusoids and trabecular bone and atrophy of trabecular bone. There was a significant correlation in volume percentage between haematopoietic cells and trabecular bone, between haematopoietic cells and sinusoids and between sinusoids and trabecular bone. These results imply that atrophy of trabecular bone is related to microenvironmental deterioration of the bone marrow, that is, a decrease in efficiency of exchange of nutrients and waste products between sinusoids and trabecular bone due to the proliferation of haematopoietic cells and a deficiency of nutrient supply to the bone marrow due to the narrowing of sinusoids.

Animals↗
PubMed1991

Insulin secretion in magnesium silicate-induced osteopenia in rats.

Local inflammation induced in rats by subcutaneous injection of magnesium silicate is followed by general metabolic, endocrine and immune reactions. Three weeks after inflammation induction, important bone loss, inflammation-mediated osteopenia (IMO) were found. The study proposes to investigate if IMO influences endogenous insulin secretion and if insulin therapy modifies the amount of bone loss, knowing its osteoprotective effect. Experiments were carried out on adult rats, three weeks after local inflammation induction. Baseline glucose and insulin levels did not change as compared to controls. After glucose stimulation, insulinogenic index decreased in the IMO group, which evidences decrease of insulin secretion. Insulin treatment initiated at the same time with IMO did not induce significant changes as regards the response to glucose tolerance test. However, bone calcium was increased as compared to the untreated IMO group, without reaching the control level.

Animals↗
PubMed2005

Molecular interaction in alginate beads reinforced with sodium starch glycolate or magnesium aluminum silicate, and their physical characteristics.

Diclofenac calcium-alginate (DCA) beads were reinforced with different amounts of sodium starch glycolate (SSG) or magnesium aluminum silicate (MAS) and were prepared using ionotropic gelation method. Complex formation of sodium alginate (SA) and SSG or MAS in calcium-alginate beads was revealed using FTIR spectroscopy. Differential scanning calorimetric study indicated that diclofenac sodium (DS) in amorphous form was dispersed in the matrix of DCA beads. The thermal behavior of SSG-DCA and MAS-DCA beads was similar to the control bead. Both additives can improve the entrapment efficiency of DCA beads. The swelling and water uptake of the beads depended on the properties of incorporated additives. The SSG-DCA beads showed a higher water uptake and swelling than MAS-DCA beads. Moreover, the swelling of the beads showed a good correlation with the square root of time. The release kinetic of the beads in pH 6.8 phosphate buffer was swelling controlled mechanism, while that in distilled water followed Higuchi's model. The slower release rate and the longer lag time in pH 6.8 phosphate buffer was obtained from the SSG-DCA and MAS-DCA beads because of complex formation between SA and SSG or MAS. However, SSG in the beads could increase the release of DS from the beads in distilled water because it acted as a channeling agent. In contrast, MAS retarded the release of DS from the beads in distilled water due to the stronger matrix formation.

Alginates↗
PubMed2005

Investigation of novel alginate-magnesium aluminum silicate microcomposite films for modified-release tablets.

Physicochemical properties of sodium alginate-magnesium aluminum silicate (SA-MAS) composite films were investigated and a potential as a film former of SA-MAS dispersion for modifying drug release from tablets was evaluated as well. Interaction between SA and MAS in the composite films was revealed using FTIR spectroscopy. Thermal behavior of the composite films was changed due to the complexation of SA and MAS. Powder X-ray diffractometry data suggested that a higher crystallinity of the composite film and a phase-separated microcomposite were formed. The composite films in the ratios of 1:0.5 and 1:1 showed the increases of tensile strength and percentage of elongation when compared with SA films. Water vapor permeability of the composite films tended to increase with increasing ratio of MAS. The decreases in water uptake and drug permeability in 0.1 M HCl were found in the composite films. A positive charge drug, propranolol HCl, provided a higher affinity on the composite films than a weakly acidic nonelectrolyte, acetaminophen, resulting in a longer lag time and a higher partition coefficient depending on the content of MAS in the composite films. This was due to the complex formation of propranolol HCl and MAS. Using SEM, the tablets coated with SA-MAS dispersion had a smooth surface, while those with SA dispersion showed a pinholing on the surface, resulting in a faster drug release. The drug release profiles of the tablets could be modified by coating with the composite film at different coating levels. This finding suggests that MAS could improve physicochemical properties of the SA films, leading to a novel coating material of the SA-MAS dispersion for modifying drug release from tablets.

Absorption↗
PubMed2005

Influence of magnesium aluminium silicate on rheological, release and permeation characteristics of diclofenac sodium aqueous gels in-vitro.

The effect of magnesium aluminium silicate (MAS) on rheological, release and permeation characteristics of diclofenac sodium (DS) aqueous gels was investigated. DS aqueous gels were prepared using various gelling agents, such as 15% w/w poloxamer 407 (PM407), 1% w/w hydroxypropylmethylcellulose (HPMC), and 1% w/w high and low viscosity grades of sodium alginate (HV-SA and LV-SA, respectively). Different amounts of MAS (0.5, 1.0 and 1.5% w/w) were incorporated into the DS gels. Incorporation of MAS into the DS gels prepared using SA or PM407 caused a statistical increase in viscosity (P<0.05) and a shift from Newtonian flow to pseudoplastic flow with thixotropic property. The DS release rates of these composite gels were significantly decreased (P<0.05) when compared with the control gels. This was due to an interaction between MAS and PM407 or SA, and adsorption of DS onto MAS particles. Moreover, a longer lag time and no change in DS permeation flux were found when MAS was added to the gels. The findings suggest that the rheological characteristics of gels prepared using PM407 or SA could be improved by incorporating MAS. However, the use of MAS could retard the DS release and extend the lag time of DS permeation.

Alginates↗
PubMed1982

Disposition, intestinal absorption and drug metabolizing enzyme activities after multiple doses of indomethacin in rat and effect of antacid and dicyclomine on the parameters.

The effect of repeated treatment with indomethacin (IND) on the disposition and intestinal absorption of the drug and microsomal drug-metabolizing enzyme activities were studied in comparison with coadministration of the drug and magnesium silicate or dicyclomine in male Wistar rats. The plasma decay curve of IND following a rapid i.v. injection (6 mg/kg) was found to be biexponential. The elimination rate constant (beta) of beta phase was 0.138 +/- 0.015 h-1. The beta after the multiple dosing of IND (6 mg/kg/d for 7 d, p.o.) was significantly decreased as compared with that after a single dosing. In the multiple dose group coadministered magnesium silicate (0.6 g/kg), the AUC0 leads to infinity was 2 times that after the multiple dosing of IND alone. The repeated administration (8 times every 16 h) with IND (4 mg/kg) alone and IND plus the antacid respectively gave the results similar to those in the multiple dosing. In the multiple treated group with IND alone, the drug-metabolizing enzyme activities were significantly decreased (32-43%) as compared with the control, however, the coadministration of magnesium silicate partly protected the decrease. The intestinal absorption rate constant of IND determined by in situ method was decreased after the multiple dosing of IND alone, but the constant was recovered to the control value after coadministration of the antacid. Following the multiple dosing of IND alone, the centrilobular necrosis in liver and a partial omission of the villi of intestinal epithelium were observed, but the concurrent dosing of magnesium silicate did not produce histopathological changes.

Animals↗
PubMed2006

Alginate-magnesium aluminum silicate films: effect of plasticizers on film properties, drug permeation and drug release from coated tablets.

The effect of hydrophilic plasticizers, namely glycerin and polyethylene glycol 400 (PEG400), on physicochemical properties of sodium alginate-magnesium aluminum silicate (SA-MAS) microcomposite films was characterized and application of the films for controlling drug release from tablets was evaluated as well. The plasticizers could possibly interact with SA or MAS by formation of hydrogen bonding, as revealed using FTIR spectroscopy. PXRD studies presented that glycerin or PEG400 could intercalate into the silicate layers of MAS and higher crystallinity of the films with PEG400 was obtained. This led to a different thermal behavior of the films. Glycerin gave more flexibility of the films than PEG400. Incorporation of plasticizers into the films did not affect water uptake in acid medium, but increasing an erosion of the films because of the leaching of the plasticizers. Water vapor permeability of the films decreased with increasing amount of plasticizers in the range of 10-30% (w/w). Diffusion coefficient (D) of acetaminophen (ACT) across the films in acid medium increased with addition of the plasticizers because the leaching of plasticizers could reduce tortuosity of aqueous pore channels of the films. The tablets coated with plasticized films had a quite smooth surface without defect as shown by SEM. The ACT release profiles from the coated tablets showed a zero-order release kinetic with drug diffusion mechanism across in situ insoluble composite films in acid medium, and coating film swelling and erosion mechanism in pH 6.8 phosphate buffer. Moreover, neither the release rate nor the release pattern of the ACT coated tablets was obviously changed. The findings show that glycerin or PEG400 could improve physicochemical properties of the SA-MAS films and the plasticized films could control the drug release from tablets in gastro-intestinal condition.

Acetaminophen↗
PubMed1997

Reduced tetracycline bioavailability caused by magnesium aluminum silicate in liquid formulations of bismuth subsalicylate.

RATIONALE: Bismuth subsalicylate, tetracycline hydrochloride, and metronidazole are widely used in combination for the treatment of Helicobacter pylori infections. As a result, there is renewed interest in the interaction between tetracycline and bismuth subsalicylate. OBJECTIVE: To determine whether the observed decrease in tetracycline bioavailability is due to the active drug bismuth subsalicylate via complexation, or to magnesium aluminum silicate (Veegum), an inactive excipient present only in the liquid formulation of bismuth subsalicylate, which might adsorb the tetracycline, rendering it unavailable for systemic absorption. METHODS: Eleven healthy volunteers participated in a randomized three-period, three-treatment complete crossover study with a 7-day washout interval between treatments. After an overnight fast, subjects received a 500-mg capsule of tetracycline hydrochloride with either tap water, 30 mL of bismuth subsalicylate (525 mg) liquid containing Veegum (Pepto-Bismol), or 30 mL of a specially formulated bismuth subsalicylate (525 mg) liquid without Veegum. Blood was collected for 24 hours after each dose of tetracycline. Serum was assayed for tetracycline concentration by HPLC. In addition, standard in vitro ultraviolet spectrophotometric methods were used to determine the capacity for complexation of bismuth with tetracycline and for adsorption of tetracycline to Veegum. RESULTS: Compared with the reference treatment of tetracycline hydrochloride with water, the liquid formulation of bismuth subsalicylate containing Veegum decreased the maximum serum concentration (Cmax) of tetracycline by 21% and the serum tetracycline AUC by 27% (p < 0.001). The bismuth subsalicylate formulation without Veegum resulted in decreases in Cmax and AUC of 11% and 13%, respectively (p > 0.05 vs. tetracycline hydrochloride with water). Multiple linear regression analysis of the spectral absorbance data demonstrated a calculated recovery of tetracycline of 100.9% and, therefore, a lack of in vitro complexation with bismuth. At pH 1.2, the amount of tetracycline adsorbed to Veegum ranged from 91.5% to 97.2% over the concentration range of 0.25 to 2 mg/mL. At pH 7.0, the values ranged from 82.9% to 83.9% over the concentration range of 0.25 to 1 mg/mL. CONCLUSIONS: In vitro and in vivo data from this study indicate that Veegum, a suspending agent, and not the active agent bismuth subsalicylate, is the primary ingredient in liquid formulations of bismuth subsalicylate responsible for a decrease in tetracycline bioavailability. In addition, the mechanism of interaction is not likely due to complexation between tetracycline and bismuth subsalicylate, as previously postulated, but rather is caused by adsorption of tetracycline to the excipient Veegum, which is present only in the liquid formulation of bismuth subsalicylate. The clinical relevance of this interaction has not been determined.

Adolescent↗
PubMed1992

An aluminum silicate binding assay for quantitation of degradation of cholecystokinin octapeptide and other short peptides.

Most available techniques for the quantitation of enzymatic degradation of peptide hormones are time-consuming and require expensive equipment and/or novel reagents. Our aim here was to develop a rapid and sensitive assay for the measurement of degradation of cholecystokinin octapeptide (CCK-8) as well as other short, hydrophobic peptides. The proposed technique is based on our novel observation that intact CCK-8, but not its degradation product(s), binds to Lloyd reagent, a form of aluminum silicate. When radiolabeled CCK-8 was exposed to rat liver cytosol containing endogenous CCK-degrading activity, there was a time-dependent decrease in the binding of radiolabel to aluminum silicate [from 86 to 8% over 60 min at 37 degrees C]. The decrease in binding closely paralleled the extent of CCK-8 degradation over time as assessed by high-performance liquid chromatography and immunoprecipitation with specific polyclonal antibodies to CCK-8. While aluminum silicate did not efficiently bind to C-terminal and N-terminal CCK tetrapeptides, magnesium silicate bound to both tetrapeptides (> 82%), but not to their radiolabeled degradation products. Both aluminum and magnesium silicate also extensively bound (> 82%) to other peptide hormones including Met-enkephalin, somatostatin, and secretin, but did not bind their degradation products. These binding assays will be useful in studies of peptidases which degrade cholecystokinin or other small, hydrophobic peptides.

Aluminum Silicates↗
PubMed1967

Isolation and identification of indole-3-ethanol (tryptophol) from cucumber seedlings.

Crude ether extracts of green shoots of Cucumis sativus L. promoted the elongation of cucumber hypocotyl segments. Purification of the extract was accomplished by DEAE cellulose, silicic acid, and magnesium silicate chromatography followed by gel filtration and preparative thin layer chromatography. Identification of the growth promoter as indole-3-ethanol was achieved by mass spectrometry, thin layer and gas chromatography, and ultraviolet and visible spectroscopy, as well as by physiological characteristics.

Journal Article↗
PubMed1983

Bioavailability of indomethacin calcium and magnesium, and effect of the salts on drug metabolizing enzyme activities in rats.

To clarify the mechanism of enhanced absorption of indomethacin (IND) when dosed with magnesium silicate, reported previously, magnesium (IND-Mg) and calcium (IND-Ca) salts of IND were prepared, and the bioavailability in rat and physical properties of these salts were studied in comparison with IND. The mean plasma levels after a single oral dosing of IND-Ca and IND-Mg were significantly higher than those after IND (6 mg/kg). The absolute bioavailability calculated was 63.7% for IND, 83.2% for IND-Mg and 96.8% for IND-Ca. The area (AUC) under the plasma concentration curve after multiple oral dosing of IND-Ca and IND-Mg was also significantly larger than that after IND multiple dosing (p less than 0.001). Thus, the increased absorption of the salts made it possible to decrease their dosage. The mean plasma levels and the AUC after multiple dosing of the salts in the decreased doses (4.16 mg/kg for IND-Ca and 4.74 mg/kg for IND-Mg) were significantly high as compared with those in IND dose (6 mg/kg) group (p less than 0.05). In IND-salt multiple dose groups, the drug-metabolizing enzyme activities were only slightly decreased as compared with the control, while activities in IND dose group were substantially decreased. There was no significant change in the plasma protein binding between the IND- and the salt-treated rats. The partition coefficient (n-octanol-water) for IND-Ca and IND-Mg was higher than that of IND. The rank order of solubility in 2% taurocholate solution was IND-Mg greater than IND greater than IND-Ca, and the solubility of IND-Mg was 3 times higher than that of IND-Ca. Therefore, the mechanism of increased absorption of these salts was probably ascribed to the enhanced lipid solubility and increased solubility in bile and intestine juice.

Animals↗
PubMed1975

Glycolipids of the fish testis.

Glycolipids were purified from the total lipid extract of the testis or milt of a kind of puffer (Fugu rubripes rubripes) by adsorption column chromatography using silicic acid and magnesium silicate and by preparative silica gel TLC. The glycolipids were identified as glucosylceramide (116 mug/g wet tissue) and galactosylceramide 26.7 mug/g). Seminolipid, a sulfagalactolipid specific to mammalian testis was not detected, but the presence of a small amount of sulfatide (15.2 mug/g) was demonstrated. The long-chain bases of both cerebrosides were mainly C18-sphingenine, but in sulfatide, C20-sphingenine was more abundant than C18-sphingenine. In both cerebrosides and sulfatide, the fatty acid compositions were similar, with nervonic acid as the predominant component. Two species of gangliosides were also obtained and were identified as N-acetylgalactosaminyl(1 leads to 4)[N-acetylneuraminyl(2 leads to 3)]galactosyl(1leads to 4)glucosylceramide (59.8 mug/g) and N-acetylneuraminyl(2 leads to 3)galactosyl(1 leads to 4)N-acetylglucosaminyl(1 leads to 3)galactosyl(1 leads to 4)glucosylceramide (45.0 mug/g). The long-chain bases of the two gangliosides consisted of C18-spingenine and C20-sphingenine, and the major fatty acids were palmitic and stearic acids.

Animals↗