Biomimetic ZIF-8 Nanoparticles: A Novel Approach for Biomimetic Drug Delivery Systems.

Metal-organic frameworks (MOFs) are porous materials resulting from the coordination of metal clusters or ions with organic ligands, merging macromolecular and coordination chemistry features. Among these, zeolitic imidazolate framework-8 (ZIF-8) stands out as a widely utilized MOF known for its robust stability in aqueous environments owing to the robust interaction between its constituent zinc ions (Zn2+) and 2-methylimidazole (2-MIM). ZIF-8 readily decomposes under acidic conditions, serving as a promising candidate for pH-responsive drug delivery systems. Moreover, biomimetic materials typically possess good biocompatibility, reducing immune reactions. By mimicking natural structures or surface features within the body, they enhance the targeting of nanoparticles, prolong their circulation time, and increase their bioavailability in vivo. This review explores the latest advancements in biomimetic ZIF-8 nanoparticles for drug delivery, elucidating the primary obstacles and future prospects in utilizing ZIF-8 for drug delivery applications.

Insight into chitosan/zeolite-A nanocomposite as an advanced carrier for levofloxacin and its anti-inflammatory properties; loading, release, and anti-inflammatory studies.

Chitosan/zeolite-A nanocomposite (CH/ZA) was synthesized as a potential carrier for levofloxacin (LVOX) of enhanced technical properties. The CH/ZA composite displayed enhanced loading capacity (425 mg/g) as compared to chitosan (188.8 mg/g) and zeolite-A (234.6 mg/g). The loading behavior follows Pseudo-Second-order and Langmuir as kinetic and isotherm models. The equilibrium studies, Gaussian energy (8.15 KJ/mol), and thermodynamic parameters demonstrate homogenous and monolayer loading by complex chemical and physical reactions that are of spontaneous and exothermic nature. The CH/ZA composite is of slow and continuous release profile (200h) with 94.3% as the maximum release percentage. The release reactions are of non-Fickian behavior involving both diffusion and erosion mechanisms. The loading of LVOX into CH/ZA induced its anti-inflammatory effect against the cytokine production (IL-6 and IL-8) within the human bronchial epithelia cells (NL20). The cytotoxicity studies on the normal cells demonstrated a high safety value for the composite.

In vitro and in vivo comparative performance studies of gadolinium-loaded zeolites and Gd-DOTA as contrast agents for MRI applications.

Gadolinium-based contrast agents (CAs) were synthesized using faujasite zeolite (NaX) and zeolite beta (BEA) and their performances in vitro and in vivo were compared to the widely used commercial CA, gadoteric acid (Gd-DOTA). Magnetic resonance imaging (MRI) relaxometry studies (considering longitudinal [T1 ] and transverse [T2 ] relaxation times) were performed using Gd-DOTA and the zeolitic materials loaded with Gd3+ . The Gd-loaded NaX, which presented large pores and cavities (7.35 and 11.24 Å, respectively), exhibited relaxivity values of around 52 mM-1 s-1 , while BEA, which presented smaller pore and cavity diameters (5.95 and 6.68 Å, respectively) showed lower relaxivity values of ~4.8 mM-1 s-1 . The effect of the Gd-loaded NaX as MRI CA was tested in vivo in Sprague-Dawley rats, employing a 7 T scanner, with comparison to Gd-DOTA MRI angiography. The relaxivity measurements showed that the Gd-loaded NaX (50 mM-1 s-1 ) provided better image contrast than Gd-DOTA (5.1 mM-1 s-1 ). Clearance studies of the CAs using urine and blood showed that both Gd-loaded NaX and Gd-DOTA were eliminated from the body after 2 days, demonstrating the potential of Gd-loaded NaX for use as an MRI CA.

Zeolite Clinoptilolite: Therapeutic Virtues of an Ancient Mineral.

Zeolites are porous minerals with high absorbency and ion-exchange capacity. Their molecular structure is a dense network of AlO4 and SiO4 that generates cavities where water and other polar molecules or ions are inserted/exchanged. Even though there are several synthetic or natural occurring species of zeolites, the most widespread and studied is the naturally occurring zeolite clinoptilolite (ZC). ZC is an excellent detoxifying, antioxidant and anti-inflammatory agent. As a result, it is been used in many industrial applications ranging from environmental remediation to oral applications/supplementation in vivo in humans as food supplements or medical devices. Moreover, the modification as micronization of ZC (M-ZC) or tribomechanically activated zeolite clinoptilolite (TMAZ) or furthermore as double tribomechanically activated zeolite clinoptilolite (PMA-ZC) allows improving its benefits in preclinical and clinical models. Despite its extensive use, many underlying action mechanisms of ZC in its natural or modified forms are still unclear, especially in humans. The main aim of this review is to shed light on the geochemical aspects and therapeutic potentials of ZC with a vision of endorsing further preclinical and clinical research on zeolites, in specific on the ZC and its modified forms as a potential agent for promoting human brain health and overall well-being.

Chromium-Doped Zinc Gallogermanate@Zeolitic Imidazolate Framework-8: A Multifunctional Nanoplatform for Rechargeable In Vivo Persistent Luminescence Imaging and pH-Responsive Drug Release.

Multifunctional theranostic nanoplatforms greatly improve the accuracy and effectiveness in tumor treatments. Much effort has been made in developing advanced optical imaging-based tumor theranostic nanoplatforms. However, autofluorescence and irradiation damage of the conventional fluorescence imaging technologies as well as unsatisfied curative effects of the nanoplatforms remain great challenges against their wide applications. Herein, we constructed a novel core-shell multifunctional nanoplatform, that is, chromium-doped zinc gallogermanate (ZGGO) near-infrared (NIR) persistent luminescent nanoparticles (PLNPs) as a core and zeolitic imidazolate framework-8 (ZIF-8) as a shell (namely ZGGO@ZIF-8). The ZGGO@ZIF-8 nanoplatform possessed dual functionalities of the autofluorescence-free NIR PersL imaging as well as the pH-responsive drug delivery, thus it has high potential in tumor theranostics. Notably, the loading content of doxorubicin (DOX) in ZGGO@ZIF-8 (LC = 93.2%) was quite high, and the drug release of DOX-loaded ZGGO@ZIF-8 was accelerated in an acidic microenvironment such as tumor cells. The ZGGO@ZIF-8 opens up a new material system in the combination of PLNPs with metal-organic frameworks and may offer new opportunities for the development of advanced multifunctional nanoplatforms for tumor theranostics, chemical sensing, and optical information storage.

Size-Controlled Synthesis of Drug-Loaded Zeolitic Imidazolate Framework in Aqueous Solution and Size Effect on Their Cancer Theranostics in Vivo.

Recently, metal-organic frameworks (MOFs) or coordination polymers have shown great potential for drug delivery, yet little has been done to study how particle size affects their tumor targeting and other in vivo features. This plight is probably due to two challenges: (1) the lack of a biocompatible method to precisely control the size of drug-loaded MOFs and (2) the lack of a robust and facile radiolabeling technique to trace particles in vivo. Here, we report a one-pot, rapid, and completely aqueous approach that can precisely tune the size of drug-loaded MOF at room temperature. A chelator-free 64Cu-labeled method was developed by taking the advantage of this rapid and aqueous synthesis. Cancer cells were found to take drug-loaded MOFs in a size-dependent manner. The in vivo biodistribution of drug-loaded MOF was analyzed with positron emission tomography imaging, which, as far as we know, was used for the first time to quantitatively evaluate MOF in living animals, unveiling that 60 nm MOF showed longer blood circulation and over 50% higher tumor accumulation than 130 nm MOF. Altogether, this size-controlled method helps to find the optimal size of MOF as a drug carrier and opens new possibilities to construct multifunctional delivery systems for cancer theranostics.

Natural zeolite for adsorbing and release of functional materials.

Using multiphoton microscopy (MPM), we demonstrated that effective inducing of two-photon excited luminescence and second-harmonic generation signals in nano/microparticles of clinoptilolite type of zeolite (CZ) by femtosecond near-infrared laser excitation can be successfully utilized in multiphoton imaging of the drug adsorption processes. Adsorption of photodynamic active dyes (hypericin, chlorin e6, methylene blue, and fluorescein) and their release from CZ pores in the presence of biomolecules, such as collagen from bovine Achilles tendon, albumin, and hemoglobin, were investigated by absorption and fluorescence spectrometry. To quantify the experimental results on hypericin release, here we use a kinetic curves fitting approach and calculate hypericin release rates in different environments. This approach allows to compare various mathematical models and uses more parameters to better characterize drug release profiles. In addition, magnetic CZ particles were fabricated and proposed as a promising material for drug delivery and controlled release in biological systems. Optical spectrometry and MPM are effective approaches that may reveal potential of natural zeolites in controlled drug delivery and biomedical imaging.

Zeolite-loaded alginate-chitosan hydrogel beads as a topical hemostat.

Hemorrhage is the leading cause of preventable death after a traumatic injury, and the largest contributor to loss of productive years of life. Hemostatic agents accelerate hemostasis and help control hemorrhage by concentrating coagulation factors, acting as procoagulants and/or interacting with erythrocytes and platelets. Hydrogel composites offer a platform for targeting both mechanical and biological hemostatic mechanisms. The goal of this work was to develop hydrogel particles composed of chitosan, alginate, and zeolite, and to assess their potential to promote blood coagulation via multiple mechanisms: erythrocyte adhesion, factor concentration, and the ability to serve as a mechanical barrier to blood loss. Several particle compositions were synthesized and characterized. Hydrogel bead composition was optimized to achieve the highest swelling capacity, greatest erythrocyte adhesion, and minimal in vitro cytotoxicity. These results suggest a polymer hydrogel-aluminosilicate composite material may serve as a platform for an effective hemostatic agent that incorporates multiple mechanisms of action. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1662-1671, 2018.

Antimicrobial Activity of Glass lonomer Cement Incorporated with Chlorhexidine-Loaded Zeolite Nanoparticles.

A functional dental restorative system with antimicrobial properties was developed using zeolite (ZE) nanoparticles (NPs) as a drug delivery carrier. ZE NPs loaded with chlorhexidine (CHX) were prepared using the ionic immobilization method. The resulting CHX-loaded ZE NPs were then incorporated into commercial dental glass ionomer cement (GIC). The average size of the CHX-loaded ZE NPs was about 100 to 200 nm, and the NPs were dispersed homogeneously in the GIC. The in vitro release profile of encapsulated GIC containing CHX showed an early release burst of approximately 30% of the total CHX by day 7, whereas GIC containing CHX-loaded ZE NPs showed a sustained release of CHX without the early release burst in a 4-week immersion study. The agar diffusion test results showed that the GIC incorporated with CHX-loaded ZE NPs showed a larger growth inhibition zone of Streptococcus mutans than GIC alone, indicating that this innovative delivery platform potently imparted antimicrobial activity to the GIC. Moreover, these findings suggest that a range of antimicrobial drugs that inhibit the growth of oral bacteria can be incorporated efficiently into dental GIC using CHX-loaded ZE NPs.

Synthetic Zeolites as Controlled-Release Delivery Systems for Anti-Inflammatory Drugs.

Scientists have always been trying to use artificial zeolites to make modified-release drug delivery systems in the gastrointestinal tract. An ideal carrier should have the capability to release the drug in the intestine, which is the main area of absorption. Zeolites are mineral aluminosilicate compounds with regular structure and huge porosity, which are available in natural and artificial forms. In this study, soaking, filtration and solvent evaporation methods were used to load the drugs after activation of the zeolites. Weight measurement, spectroscopy FTIR, thermogravimetry and scanning electronic microscope were used to determine drug loading on the systems. Finally, consideration of drug release was made in a simulated gastric fluid and a simulated intestinal fluid for all matrixes (zeolites containing drugs) and drugs without zeolites. Diclofenac sodium (D) and piroxicam (P) were used as the drug models, and zeolites X and Y as the carriers. Drug loading percentage showed that over 90% of drugs were loaded on zeolites. Dissolution tests in stomach pH environment showed that the control samples (drug without zeolite) released considerable amount of drugs (about 90%) within first 15 min when it was about 10-20% for the matrixes. These results are favorable as NSAIDs irritate the stomach wall and it is ideal not to release much drugs in the stomach. Furthermore, release rate of drugs from matrixes has shown slower rate in comparison with control samples in intestine pH environment.

Assessment of asbestos body formation by high resolution FEG-SEM after exposure of Sprague-Dawley rats to chrysotile, crocidolite, or erionite.

This work presents a comparative FEG-SEM study of the morphological and chemical characteristics of both asbestos bodies and fibres found in the tissues of Sprague-Dawley rats subjected to intraperitoneal or intrapleural injection of UICC chrysotile, UICC crocidolite and erionite from Jersey, Nevada (USA), with monitoring up to 3 years after exposure. Due to unequal dosing based on number of fibres per mass for chrysotile with respect to crocidolite and erionite, excessive fibre burden and fibre aggregation during injection that especially for chrysotile would likely not represent what humans would be exposed to, caution must be taken in extrapolating our results based on instillation in experimental animals to human inhalation. Notwithstanding, the results of this study may help to better understand the mechanism of formation of asbestos bodies. For chrysotile and crocidolite, asbestos bodies are systematically formed on long asbestos fibres. The number of coated fibres is only 3.3% in chrysotile inoculated tissues. In UICC crocidolite, Mg, Si, and Fe are associated with the fibres whereas Fe, P and Ca are associated with the coating. Even for crocidolite, most of the observed fibres are uncoated as coated fibres are about 5.7%. Asbestos bodies do not form on erionite fibres. The crystal habit, crystallinity and chemistry of all fibre species do not change with contact time, with the exception of chrysotile which shows signs of leaching of Mg. A model for the formation of asbestos bodies from mineral fibres is postulated. Because the three fibre species show limited signs of dissolution in the tissue, they cannot act as source of elements (primarily Fe, P and Ca) promoting nucleation and growth of asbestos bodies. Hence, the limited number of coated fibres should be due to the lack of nutrients or organic nature.

Encapsulating (111)In in nanocontainers for scintigraphic imaging: synthesis, characterization, and in vivo biodistribution.

A new strategy for the radiolabeling of porous nanocontainers has been developed, and the first experiments in vivo are reported. Our approach consists of the use of nanometer-sized zeolites whose channels have been filled with the positively charged gamma-emitter (111)In(3+) via simple ion exchange. To avoid leaching of the isotope under physiological conditions, the entrances of the channels have been closed using a specifically designed molecular stopcock. This stopcock has a positively charged group that enters the channels and entraps the loaded radionuclides via electrostatic and steric repulsion. The other side of the stopcock is a bulky triethoxysilane group that can covalently bind to the walls of the zeolite entrances, thereby irreversibly closing the channels. The surface of the zeolites has been functionalized with different chemical groups in order to investigate the different biodistributions depending of the nature of the functionalizations. Preliminary in vivo experiments with Wistar rats have been performed and showed the potential of the approach. This strategy leads to a nanoimaging probe with a very high density of radioisotopes in a confined space, which is highly stable in physiological solution and could allow a large variety of functionalities on its external surface.

The safety of synthetic zeolites used in detergents.

Synthetic zeolites are replacing phosphates as builders in laundry detergents; workers and consumers may, therefore, increasingly be exposed to these materials and it is important to assess their safety. This article puts mechanistic, toxicological and exposure data into context for a safety assessment. Zeolites are hygroscopic compounds with ion-exchanging properties. They may partially decompose under acidic conditions such as in the stomach releasing sodium ions, silicic acid and aluminum salts. The intact molecule is not bioavailable after oral intake or exposure through the dermal and inhalational routes. Under current conditions of manufacture and use, no systemic toxicity is to be expected from neither the intact molecule nor the degradation products; a significant effect on the bioavailability of other compounds is not likely. Zeolites may cause local irritation. It is, therefore, important to minimise occupational exposure. The co-operation of detergent manufacturers with the manufacturers of washing machines is necessary to find the right balance between environmental aspects such as energy and water savings and the occurrence of detergent residues on textiles due to insufficient rinsing.

Selective adsorption of bacterial cells onto zeolites.

Zeolites adsorb microbial cells on their surfaces and selective adsorption for specific microorganisms was seen with certain zeolites. Tests for the adsorption ability of zeolites were conducted using various established microbial cell lines. Specific cell lines were shown to selectively absorb to certain zeolites, species to species. In order to understand the selectivity of adsorption, we tested adsorption under various pH conditions and determined the zeta-potentials of zeolites and cells. The adsorption of some cell lines depended on the pH, and some microorganisms were preferentially adsorbed at acidic pH. The values of zeta-potentials were used for calculating the electric double layer interaction energy between zeolites and microbial cells. There was a correlation between the experimental adsorption results and the interaction energy. Moreover, we evaluated the surface hydrophobicity of bacterial cells by using the microbial adherence to hydrocarbon (MATH) assay. In addition, we also applied this method for zeolites to quantify relative surface hydrophobicity. As a result, we found a correlation between the adsorption results and the hydrophobicity of bacterial cells and zeolites. These results suggested that adsorption could be explained mainly by electric double layer interactions and hydrophobic interactions. Finally, by using the zeolites Na-BEA and H-Y, we succeeded in clearly separating three representative microbes from a mixture of Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Zeolites could adsorb each of the bacterial cell species with high selectivity even from a mixed suspension. Zeolites can therefore be used as effective carrier materials to provide an easy, rapid and accurate method for cell separation.

[Natural zeolites with medical applications--preliminary preparation and characterization]. / Zeoliti naturali cu aplicatii medicale. Preparare si caracterizare preliminara.

The aim of this research is to carry out a preliminary study of the chemical behavior of natural zeolites under thermal and chemical activation. Taking into account the biological properties reported for the NZ, the authors study the influence of different activations on the structural behavior of the raw material, aiming at the future preparation of slow release systems. The raw material used in this study was the purified natural zeolites from Bârsana, Piatra Verde and Slanic Moldova deposits. The samples were characterized following specific techniques: XRD, SEM, EDAX, IR, pH measurements and determinations of the specific surface. The results indicate that the natural zeolites could used like as carriers in medical applications because they increase their specific surface after activation. Studies of the release of pharmaceuticals from the zeolitic host systems are in progress.

Comparison of synthetic zeolite catalysts and alumina binders administered intratracheally to rats.

An intratracheal (IT) screening assay was performed in rats on a series of aluminosilicate catalysts (synthetic zeolites) and alumina binders to compare their relative ability to cause pulmonary fibrosis and related changes. Before initiation of IT screens, both the uniformity of deposition and residence time of a prototype catalyst in the lung were determined. Subsequently, the test materials were instilled and animals were evaluated 6 mo later for lung volumes, pulmonary pressure-volume curves, pulmonary hydroxyproline (OHPro) content, lung weights, and histopathology. Negative controls were saline and glass beads; the positive control was quartz. The test materials were organic-free ZSM-5 crystals, organic form of ZSM-5 crystals, alumina-bound ZSM-5, nickel/ZSM-5/ Al2O3 binder, used nickel/ZSM-5/Al2O3 binder, nickel-tungsten/ZSM-5/Al2O3 binder, and Bayer pseudoboehmite. For each, groups of 12 male rats were dosed once with either 25 or 50 mg of ground particles (> or =95% less than 2.4 microm). Second to quartz, the sample of alumina caused the most pronounced pulmonary reactions at 6 mo after dosing. Therefore, the effects of four aluminas were subsequently compared (Bayer pseudoboehmite, Bayer gammaAl2O3, Ziegler pseudoboehmite, and Ziegler gammaAl2O3). The results support the idea of a lack of long-term effects from exposure to normal concentrations of these materials in the workplace. Also, the IT assay proved to be a very useful tool for ranking the relative effects of this series of zeolites and aluminas.

Wheat response to differences in water and nutritional status between zeoponic and hydroponic growth systems.

Hydroponic culture has traditionally been used for controlled environment life support systems (CELSS) because the optimal environment for roots supports high growth rates. Recent developments in zeoponic substrate and microporous tube irrigation (ZPT) also offer high control of the root environment. This study compared the effect of differences in water and nutrient status of ZPT or hydroponic culture on growth and yield of wheat (Triticum aestivum L. cv. USU-Apogee). In a side-by-side test in a controlled environment, wheat was grown in ZPT and recirculating hydroponics to maturity. Water use by plants grown in both culture systems peaked at 15 to 20 L m-2 d-1 up to Day 40, after which it declined more rapidly for plants grown in ZPT culture due to earlier senescence of leaves. No consistent differences in water status were noted between plants grown in the two culture systems. Although yield was similar, harvest index was 28% lower for plants grown in ZPT than in hydroponic culture. Sterile green tillers made up 12 and 0% of the biomass of plants grown in ZPT and hydroponic culture, respectively. Differences in biomass partitioning were attributed primarily to NH4-N nutrition of plants grown in ZPT compared with NO3-N in hydroponic nutrient solution. It is probable that NH4-N-induced Ca deficiency produced excess tillering and lower harvest index for plants grown in ZPT culture. These results suggest that further refinements in zeoponic substrate would make ZPT culture a viable alternative for achieving high productivity in a CELSS.

Effects of inorganic adsorbents and cyclopiazonic acid in broiler chickens.

Previous studies with cyclopiazonic acid (CPA) have indicated that this mycotoxin strongly adsorbs onto the surface of a naturally acidic phyllosilicate clay (AC). The objective of this study was to determine whether AC (and similar adsorbents) could protect against the toxicity of CPA in vivo. Acidic phyllosilicate clay, neutral phyllosilicate clay (NC, or hydrated sodium calcium aluminosilicate), and a common zeolite (CZ, or clinoptilolite) were evaluated. One-day-old broiler chicks consumed diets containing 0 or 45 mg/kg CPA alone or in combination with 1% AC, NC, or CZ ad libitum from Day 1 to 21. Body weight, feed consumption, feed:gain, hematology, serum biochemical values, and enzyme activities were evaluated. Compared to controls, CPA alone reduced body weight at Day 21 by a total of 26% and resulted in a significantly higher feed:gain ratio. Toxicity of CPA was also expressed through increased relative weights of kidney, proventriculus, and gizzard. Also, there were some alterations in hematology, serum biochemical values, and enzyme activities. Treatment with inorganic adsorbents did not effectively diminish the growth-inhibitory effects of CPA or the increased weights of organs, although there was some protection from hematological, serum biochemical, and enzymatic changes produced by CPA. The results of this study suggest that in vitro binding of CPA to clay does not accurately forecast its efficacy in vivo; the reasons for this discrepancy are not clear, but they may be related to differences in clay binding capacity and ligand selectivity for CPA in vitro vs in vivo. Predictions about the ability of inorganic adsorbents to protect chickens from the adverse effects of mycotoxins should be approached with caution and should be confirmed in vivo, paying particular attention to the potential for nutrient interactions.

Gadolinium zeolite as an oral contrast agent for magnetic resonance imaging.

The purpose of this study was to evaluate efficacy and safety of a gadolinium (Gd) zeolite suspension as an oral MRI contrast agent. Serial dilutions of GADO-LITE Oral Suspension 1,2-300 micrograms of Gd(III)/mL) were prepared. MRI (T1 and T2 weighted) of standards and dogs (precontrast and postcontrast) were performed. Toxicity and Gd absorption were also assessed. Subsequently, 30 normal male adult volunteers were divided into six groups of five subjects each. Gd zeolite po suspension was administered before and after MRI in volumes and concentrations ranging from 250 to 1500 mL; 6 to 60 micrograms of Gd+3/mL. The images were rated (efficacy score) by a blinded reader. Vital signs, blood chemistries and urinalysis were recorded. Gadolite Oral Suspension produced excellent enhancement of the dog gastrointestinal (GI) tract. No toxicity or absorption of Gd was observed in dogs receiving doses up to 4 times the anticipated human dose daily for 14 consecutive days. In clinical trials, Gd zeolite significantly improved the efficacy scores for all groups and all pulsing sequences (all P values < .05). Efficacy scores and signal intensities generally increased with concentration and volume. No Gd was detected in blood or urine specimens. No significant adverse events were reported. Gd zeolite is a promising contrast medium for enhancement of the GI tract in MRI.

Pharmacokinetic study of zeolite A, sodium aluminosilicate, magnesium silicate, and aluminum hydroxide in dogs.

Zeolite A is a synthetic zeolite which may have therapeutic utility in osteoporotic individuals because of its ability to stimulate bone formation. A study of Zeolite A (30 mg/kg), sodium aluminosilicate (16 mg/kg), magnesium trisilicate (20 mg/kg), and aluminum hydroxide (675 mg) was designed in beagle dogs. The purpose of this study was to compare the oral bioavailability of silicon and aluminum from Zeolite A, sodium aluminosilicate, magnesium trisilicate, and aluminum hydroxide in dogs. Twelve female dogs received each compound as a single dose separated by one week in a randomized, 4-way, crossover design. Plasma samples were drawn at time 0 and for 24 hours after dosing. The concentrations of silicon and aluminum were determined by graphite furnace atomic absorption. The mean plasma silicon AUC values (+/- S.D.) were 9.5 +/- 4.5, 7.7 +/- 1.6, 8.8 +/- 3.0, 6.1 +/- 1.9 mg.hr/L and the mean plasma silicon Cmax values (+/- S.D.) were 1.07 +/- 1.06, 0.67 +/- 0.27, 0.75 +/- 0.31, 0.44 +/- 0.17 mg/L for Zeolite A, sodium aluminosilicate, magnesium trisilicate, and aluminum hydroxide respectively. Although mean silicon AUC and Cmax values were elevated when compared to baseline after administration of the silicon containing compounds, only the AUC from Zeolite A reached statistical significance (p = 0.041). The mean plasma silicon Tmax values (+/- S.D.) were 7.9 +/- 6.4, 5.8 +/- 4.6, 6.9 +/- 6.3 and 8.5 +/- 3.4 hrs for Zeolite A, sodium aluminosilicate, magnesium trisilicate and aluminum Hydroxide respectively.(ABSTRACT TRUNCATED AT 250 WORDS)