In vitro and in vivo evaluation of degradation, toxicity, biodistribution, and clearance of silica nanoparticles as a function of size, porosity, density, and composition

Silica nanoparticles (SiO₂ NPs) have potential utility in controlled release. Despite significant research in this area, there is a gap in the understanding of the correlation between SiO₂ NP physicochemical properties on the one hand and their degradation in solutions, in cells, and in vivo on the other. Here, we fabricated SiO₂ NPs with variations in size, porosity, density, and composition: 100 nm Stöber, 100 and 500 nm mesoporous, 100 nm disulfide-based mesoporous, and 100 nm disulfide-based hollow mesoporous. Degradation profiles over 28 days were investigated in simulated biological fluids and deionized water. Results show Meso 100, and 500 nanoparticles degraded faster at higher pH values. Results from macrophages indicate Meso 100 nanoparticles showed the highest degradation amount (~3.8%). Cytotoxicity evaluation of the particles in Human Aortal Endothelial Cells (HAECs) shows concentration-dependent toxicity for the particles. Results from CD-1 mice show ~53% of Meso 100 nanoparticles (25 mg kg^-1) degraded and were detected in urine after seven days. It was shown nanoparticle porosity and composition as well as pH and ionic strength of the medium play the predominant roles for degradation of SiO₂ NPs. Based on histological evaluations, at the injected doses investigated, the particles did not show toxicity.

In vivo study on the biodistribution of silica particles in the bodies of rats

BACKGROUND

Biodegradable carrier materials with nontoxic degradation products are very valuable for delivering drugs and biologically active molecules. Many organic systems (such as liposomes, micelles and polymeric nanoparticles) and inorganic systems (metal oxides and silica) have been researched for delivering active substances to organs. Silica seems to be one of the most interesting and promising materials.

OBJECTIVES

The aim of this study was to investigate the SiO2 elimination process from rats' organisms and to ascertain the distribution and prospective accumulation sites of the silica particles.

MATERIAL AND METHODS

A suspension of silica particles (Ø 150 nm) in 0.9% NaCl solution was introduced into rats' circulatory system. The degradation of these particles over time and their accumulation in the heart, lungs, kidneys and liver were observed.

RESULTS

It was found that 36% of the introduced silica particles were excreted with urine after four days. The remaining particles were accumulated in the kidneys and lungs, probably in the lung air sacs and kidney glomerulus.

CONCLUSIONS

Silica seems to be promising carrier material. Silica particles dissolve in the rat's body and are eliminated in urine.

Fluorescent silica nanoparticles with efficient urinary excretion for nanomedicine

The development of molecularly targeted probes that exhibit high biostability, biocompatibility, and efficient clearance profiles is key to optimizing biodistribution and transport across biological barriers. Further, coupling probes designed to meet these criteria with high-sensitivity, quantitative imaging strategies is mandatory for ensuring early in vivo tumor detection and timely treatment response. These challenges have often only been examined individually, impeding the clinical translation of fluorescent probes. By simultaneously optimizing these design criteria, we created a new generation of near-infrared fluorescent core-shell silica-based nanoparticles (C dots) tuned to hydrodynamic diameters of 3.3 and 6.0 nm with improved photophysical characteristics over the parent dye. A neutral organic coating prevented adsorption of serum proteins and facilitated efficient urinary excretion. Detailed particle biodistribution studies were performed using more quantitative ex vivo fluorescence detection protocols and combined optical-PET imaging. The results suggest that this new generation of C dots constitutes a promising clinically translatable materials platform which may be adapted for tumor targeting and treatment.

Silica urolithiasis in the dromedary camel in a subtropical climate

In 1998, two cases of silica urolithiasis occurred in castrated male dromedaries on an intensive camel farm in the Canary Islands. The immediate attributable cause was the ingestion of large amounts of silica in the feed, estimated as 84.44 g/day. An associated cause was the low level of salt in the diet. Daily ingestion of salt from feed and water was estimated to be 21.8 g (8.6 g of sodium). Seventy-six castrated males from the same farm were divided into four groups: group A received 30 g of salt daily; group B received 40 g; group C received 60 g; and group D received no added salt in the diet (control). The animals were maintained on these dietary regimes for 2 years. No animals from groups A, B or C suffered overt urinary retention. One animal from group D had an obstructive urinary retention 10 months after the study commenced. Thus, 52 g of salt daily appears to be sufficient to prevent urinary retention in dromedaries raised in a subtropical climate.

Silica urolithiasis without magnesium trisilicate intake

Two cases of silica stones, without previous oral intake of magnesium trisilicate, are reported. A 64-year-old Japanese woman had bilateral renal stones. Infrared spectrophotoscopy revealed that one of the fragments consisted of silicate and the others consisted of calcium oxalate. A 75-year-old woman had right renal stones. The composition of 1 stone was a mixture of silicate and unspecified matrices. Silicate urolithiasis may not necessarily be related to oral intake of silicate-containing antacids.

Minor constituents of sabulous material in equine urine

The secondary constituents accompanying calcite and vaterite (crystalline forms of calcium carbonate) in the sabulous deposits from 140 vesical samples and one renal sample of equine urine were studied by infrared spectroscopy (IR), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Apatitic calcium phosphate, present in 12 per cent of the samples, generally appeared in the form of spherulites with smooth and rough surfaces. Calcium sulphate, clearly detected by IR in 12.7 per cent of the samples, did not have a characteristic structure under SEM, although EDX detected sulphur in the samples. Amorphous silica was observed in one case and had a nodular appearance. Organic fibres were not as common as might have been expected in equine urinary deposits.

Silica stone--development due to long time oral trisilicate intake

We report a case of a 30-year-old female who had a long-term history of trisilicate-containing antacid intake for gastric discomfort. She had experienced repeated attacks of renal colic. Neither intravenous pyelography nor ureteroscopy could define the presence of calculi. The metabolic evaluations were normal. However, X-ray diffraction revealed a silicate stone. We suggest that the attack of renal colic in those patients with long-term history of trisilicate intake should arouse the possibility of silica urolithiasis.

Diet calcium carbonate, phosphorus and acidifying and alkalizing salts as factors influencing silica urolithiasis in rats fed tetraethylorthosilicate

Three experiments were conducted to determine the effects of excess dietary calcium carbonate, phosphorus and urine acidifying and alkalizing salts on silica urolith formation in a model using rats fed dextrose-based diets containing 2% tetraethylorthosilicate (TES). Diets containing 2% TES lowered weight gains to 91-95% of gains made by rats fed non-TES diets. Urine silica concentrations of rats fed TES were generally in the range of 50-60 mg/dl. In experiment 1, rats fed TES with no additional dietary calcium carbonate had a silica urolith incidence of 35%. With additions of 1 and 2% calcium carbonate to the basal-TES diet, respective urolith incidences were 45 and 60% (r = 0.99, P less than 0.02). In experiment 2, monobasic sodium phosphate (MP) providing 0.2% additional phosphorus resulted in a mean urine pH of 6.42 and no uroliths. Dibasic sodium phosphate (DP) without and with 0.5% sodium bicarbonate (SB) resulted in respective urine pH values of 6.78 and 7.14 and urolith incidences of 15 and 20% (MP less than DP and DP + SB, P less than 0.05). However, the uroliths were small averaging less than 1 mg. In experiment 3, substitution of autoclaved egg albumin for casein, the protein source in experiments 1 and 2, resulted in urine pH of 7.45 and a silica urolith incidence of 46%. An equal-molar mixture of MP and DP providing an added 0.2% phosphorus resulted in a urine pH of 7.07 and reduced the urolith incidence to 4%, and 0.75% of dietary ammonium chloride either with or without the added 0.2% phosphorus gave urine acidification and complete protection from uroliths.(ABSTRACT TRUNCATED AT 250 WORDS)

Canine uroliths. Analysis of data derived from 813 specimens

This article contains an analysis of data compiled from 813 specimens of canine uroliths submitted to the Urinary Stone Analysis Laboratory at University of California School of Veterinary Medicine.

Etiopathogenesis, clinical manifestations, and management of canine silica urolithiasis

Silica uroliths were first recognized in dogs in the mid 1970s. Currently available data suggest that dietary factors may play a role in their pathogenesis. Diagnosis is facilitated by their typical jackstone appearance but must be verified by quantitative analysis. Surgery is the only feasible method of treatment.

Silica stones in humans

Twenty cases of silica stones (including a personal one, the first case ever observed--April 1952) are reviewed. Almost all of the patients had been taking magnesium trisilicate for several years, one up to 40 years. The average age of the patients was 54 years. There were 9 males and 1 female. The patients came from the following locations, given in chronological order: Beirut, Lebanon (1952); Stockholm, Sweden (1953, 1962); Houston, Tex., USA (1958, 1961); New York, N.Y., USA (1960); Johannesburg, South Africa (1964); London, UK (1973, 1982); Osaka, Japan (1978); Madrid, Spain (1978, 1981); and Torrance, Calif., USA (1984). 14 patients passed out the stones spontaneously. In 3 patients, the stone was formed in the left kidney. Bilateral renal stones were found in 2 patients. In 2 patients, they were removed from the left ureter and in 2 patients they were found in the bladder. The size of the stones varied between 2 mm and 3 cm, the weight from 8 mg to 3.6 g. The silica stone is of a relatively low radio density. Our case is the only one in whom the level of urinary silica was determined; it was of the order of 0.006% i.e. 1 mmol/l.

[Are silicates only gravel stones?]

The presence of silicon dioxide in urinary calculi usually indicates the presence of artefacts. However in isolated cases infra-red and X-ray spectroscopy and electron-ray microanalysis have clearly demonstrated the presence of silicate in crystalline urinary sediment and as a phase of urinary calculi, probably as a result of overdoses of silicon preparations. A local silicon enrichment of up to 2% is certain in phosphate phases and makes an isomorphic incorporation of SiO4 ions probable.

The structure of a new sialic acid-containing decasaccharide from the urine of a patient with mucolipidosis

A new sialic acid-containing oligosaccharide has been isolated from urine of a patient with a type of mucolipidosis newly recognized by Orii et al. (1972). This compound was found to be composed of galactose (2 moles), mannose (3 moles), N-acetylglucosamine (3 moles) and sialic acid (2 moles). On the basis of the results of sequential glycosidase digestion, of methylation analysis, and of the Smith degradation, the structure of this oligosaccharide was elucidated as follows: NeuAcalpha2-6Galbeta1-4GlcNAcbeta1-2Manalpha1-3[NeuAcalpha2-6Galbeta1-4GlcNAcbeta1-2Manalpha1-6]Manbeta1-4GlcNAc. The increased excretion of this oligosaccharide may be caused by the impaired metabolism of glycoproteins having N-glycosidic linkage.

Ingested mineral fibers: elimination in human urine

Sediment in human urine examined by transmission electron microscopy contains amphibole fibers which originate from the ingestion of drinking water contaminated with these mineral fibers. The ingestion of filtered water results in the eventual disappearance of amphibole fibers from urine. These observations provide the first direct evidence for the passage of mineral fibers through the human gastro-intestinal mucosa under normal conditions of the alimentary canal.