Silicon balance in human volunteers; a pilot study to establish the variance in silicon excretion versus intake

Silicon Resorption from Equisetum arvense Tea - A Randomized, Three-Armed Pilot Study

Equisetum arvense tea (TEA) contains high concentrations of silicon and has been used in folk medicine for the treatment of inflammatory ailments. We examined the resorption of silicon after TEA consumption. Safety and immunological effects were secondary outcomes. A monocentric, randomized, three-armed pilot study was conducted with 12 voluntary, healthy, male subjects. The study is registered in the German register for clinical trials (DRKS-ID: DRKS00016628). After a low silicon diet for 36 hours, 1000 mL TEA1 with approximately 200 000 µg silicon/L, TEA2 with approximately 750 000 µg silicon/L, or Si-low-Water (approximately 10 - 10 000 µg silicon/L as a control) were ingested on three consecutive days. Blood and urine samples were collected at baseline, day 1 examining silicon kinetics, day 3 examining silicon accumulation, and day 8 (safety, immunological parameters). Si-low-Water intake did not change silicon serum (Cmax 294 µg/L) or urine (19 000 µg/24 h) concentrations compared to baseline. Cmax was 2855 µg/L for TEA1 and 2498 µg/L for TEA2; tmax was 60 and 120 min, respectively. Silicon accumulation did not occur. Urine silica within 24 h (E24 h) was higher after TEA2 compared to TEA1 ingestion (142 000 vs. 109 000 µg/24 h). Serum silicon levels at t = 120 min differed significantly after intake of TEA2 or intake of Si-low-Water (p = 0.029). The immunological parameters did not show any significant changes indicating immunosuppressive effects in volunteers. TEA1 was well tolerated, while TEA2 caused diarrhoea in 4 subjects. Our investigations show that intake of TEA1 leads to significant rise in serum silicon concentration.

Relative absorption of silicon from different formulations of dietary supplements: a pilot randomized, double-blind, crossover post-prandial study

The purpose of the present study was to compare the relative absorption of a new powder presentation of silicon (Si) as orthosilicic acid with maltodextrin (Orgono Powder) compared to usual Si liquid presentations as orthosilicic acid with Equisetum arvense and Rosmarinus officinalis (G5 Siliplant) and orthosilicic acid with aloe vera (G7 Aloe). All dietary supplements were administered at the same Si oral dose (21.6 mg) in a randomized, double-blind, crossover post-prandial study conducted in 5 healthy men. Urine was collected at baseline and over the 6-h post-dose period in 2 separate 3-h collections for the analysis of Si concentration, which was conducted by inductively coupled plasma optical emission spectrometry as the gold standard method. No significant differences in total urinary Si excretion were found after the intake of these 3 dietary supplements; 34.6%, 32.4% and 27.2% of the ingested Si from G7 Aloe, G5 Siliplant and Orgono Powder, respectively, was excreted in urine over the 6-h follow-up period. The 3 different oral Si formulations tested, in powder and liquid presentations, provide highly bioavailable Si and present an equivalent relative absorption in healthy humans.

Effect of Silicon Supplementation in Diets with Different Calcium Levels on Balance of Calcium, Silicon and Magnesium, and Bone Status in Growing Female Rats

Silicon (Si) is important for the growth and development of bone and connective tissues. This study aimed to evaluate the effect of Si supplementation on the balance of calcium (Ca), Si, magnesium (Mg), and bone status in growing female rats fed diets with different Ca levels. Sixty 6-week-old female Wistar rats were divided into 6 groups and fed diets with different levels of Ca (0.1, 0.5, 1.5%) and Si (5, 500 ppm) for 10 weeks. Experimental groups were as follows: Low-Ca group (LCa; 0.1% Ca), Low-Ca with Si supplementation group (LCaSi), adequate-Ca group (ACa; 0.5% Ca), adequate-Ca with Si supplementation group (ACaSi), high-Ca group (HCa; 1.5% Ca), and high-Ca with Si supplementation group (HCaSi). Si retention significantly increased by Si supplementation and significantly decreased by high-Ca diet (1.5%). Mg retention significantly decreased by high-Ca diet. Serum Ca and Si contents were not significantly different among the 6 groups. Low-Ca diet significantly increased serum osteoclain and C-telopeptide cross-link of type 1 collagen (CTx) levels, and Si supplementation significantly decreased CTx levels in the low-Ca diet group. Bone mineral density was significantly increased along with Ca increase in the diet, but was decreased by Si supplementation in the high-Ca diet. Rats in the adequate-Ca diet group had a significant increase in strength of tibia after Si supplementation. These findings indicate that the effect of Si supplementation on bone metabolism may differ according to the Ca-intake level in growing females. Although further research is needed, when supplementing Si to improve bone health in growing females, Ca-intake level should be considered.

Sources, Bioavailability, and Safety of Silicon Derived from Foods and Other Sources Added for Nutritional Purposes in Food Supplements and Functional Foods

Silicon is a microelement that performs a number of important functions in the human body, being involved in the formation and maintenance of normal osteocartilaginous connective tissue, such as skin, hair, and nails, and having beneficial effects in the prevention of cardiovascular and neurodegenerative diseases. Natural sources of silicon include fruits, vegetables, cereals, and mineral water. European and North American diets are generally low in silicon, which correlates with a diet high in processed foods. Dietary silicon deficiency can be overcome by the consumption of high bioavailability silicon-rich foods and the use of silicon supplements. A good form of supplementation is orthosilicic acid (OSA), usually stabilized by the introduction of a methyl group, choline, or vanillin. OSA is naturally found in diatomaceous earth in the form of amorphous silica and extracts from silicon-rich plants, e.g., horsetail (Eguiseti herba L.) and nettles (Urtica dioica L.). This article presents the characteristics of the various sources of silicon and their bioavailability and safety of use, with particular reference to the sources used in functional foods and dietary supplements. There is a great need to produce functional foods containing dietary silicon, together with other scarce mineral components.

Determination of Total Silicon and SiO2 Particles Using an ICP-MS Based Analytical Platform for Toxicokinetic Studies of Synthetic Amorphous Silica

Synthetic amorphous silica (SAS), manufactured in pyrogenic or precipitated form, is a nanomaterial with a widespread use as food additive (E 551). Oral exposure to SAS results from its use in food and dietary supplements, pharmaceuticals and toothpaste. Recent evidence suggests that oral exposure to SAS may pose health risks and highlights the need to address the toxic potential of SAS as affected by the physicochemical characteristics of the different forms of SAS. For this aim, investigating SAS toxicokinetics is of crucial importance and an analytical strategy for such an undertaking is presented. The minimization of silicon background in tissues, control of contamination (including silicon release from equipment), high-throughput sample treatment, elimination of spectral interferences affecting inductively coupled plasma mass spectrometry (ICP-MS) silicon detection, and development of analytical quality control tools are the cornerstones of this strategy. A validated method combining sample digestion with silicon determination by reaction cell ICP-MS is presented. Silica particles are converted to soluble silicon by microwave dissolution with mixtures of HNO3, H2O2 and hydrofluoric acid (HF), whereas interference-free ICP-MS detection of total silicon is achieved by ion-molecule chemistry with limits of detection (LoDs) in the range 0.2-0.5 µg Si g-1 for most tissues. Deposition of particulate SiO2 in tissues is assessed by single particle ICP-MS.

Urinary Excretion of Silicon in Men, Non-pregnant Women, and Pregnant Women: a Cross-sectional Study

Silicon is a trace element found mainly in plant-based food and proposed to be beneficial for bone health. Urinary excretion of Si has been shown to be a surrogate measure of its uptake in the gastrointestinal tract. The objective of this study was to describe and compare the levels of urinary Si excretion, and consequently Si uptake, in Swedish men, non-pregnant women, and pregnant women. No formal assessment of dietary Si intake was carried out in this study. This cross-sectional study included 89 men, 42 non-pregnant women, and 60 pregnant women. The subjects collected urine over a 24-h period and the samples were assayed for total Si using inductively coupled plasma optical emission spectrometry. The excretion levels of creatinine were used to validate the completeness of the urine sample collections. The mean 24-h urinary excretions of Si were 7.8 mg for the cohort of young men, 7.6 mg for the cohort of non-pregnant women, and 12.4 mg for the cohort of pregnant women. Creatinine excretion was similar between pregnant and non-pregnant women (10.4 vs. 10.8 mmol/day) and significantly higher in men (15.4 mmol/day). The pregnant women excreted significantly higher levels of Si than the young men and non-pregnant women, respectively (p < 0.05). The higher urinary excretion of Si by pregnant women compared with men and non-pregnant women is a novel finding possibly caused by temporary physiological changes during pregnancy such as increased gastrointestinal uptake of Si, altered bone metabolism, and increased renal excretion of Si.

Microtubule destabilization caused by silicate via HDAC6 activation contributes to autophagic dysfunction in bone mesenchymal stem cells

BACKGROUND

Silicon-modified biomaterials have been extensively studied in bone tissue engineering. In recent years, the toxicity of silicon-doped biomaterials has gradually attracted attention but requires further elucidation. This study was designed to explore whether high-dose silicate can induce a cytotoxicity effect in bone mesenchymal stem cells (BMSCs) and the role of autophagy in its cytotoxicity and mechanism.

METHODS

Morphologic changes and cell viability of BMSCs were detected after different doses of silicate exposure. Autophagic proteins (LC3, p62), LC3 turnover assay, and RFP-GFP-LC3 assay were applied to detect the changes of autophagic flux following silicate treatment. Furthermore, to identify the potential mechanism of autophagic dysfunction, we tested the acetyl-α-tubulin protein level and histone deacetylase 6 (HDAC6) activity after high-dose silicate exposure as well as the changes in microtubule and autophagic activity after HDAC6 siRNA was applied.

RESULTS

It was found that a high dose of silicate could induce a decrease in cell viability; LC3-II and p62 simultaneously increased after high-dose silicate exposure. A high concentration of silicate could induce autophagic dysfunction and cause autophagosomes to accumulate via microtubule destabilization. Results showed that acetyl-α-tubulin decreased significantly with high-dose silicate treatment, and inhibition of HDAC6 activity can restore microtubule structure and autophagic flux.

CONCLUSIONS

Microtubule destabilization caused by a high concentration of silicate via HDAC6 activation contributed to autophagic dysfunction in BMSCs, and inhibition of HDAC6 exerted a cytoprotection effect through restoration of the microtubule structure and autophagic flux.

Relationship Between Dietary Intake and Urinary Excretion of Silicon in Free-Living Korean Adult Men and Women

Previous studies have reported that silicon (Si) has a positive effect on bone health, immune response, and cognitive health. However, basic and important studies on evaluating dietary intake and urinary excretion of Si are limited. The aim of this study was to evaluate dietary Si intake and urinary excretion according to gender and age in healthy and free-living Korean adults and to investigate the relationship between them with gender. In this cross-sectional study, anthropometric measurements, dietary assessment using a food record, and a 24-h urine collection were conducted in 80 healthy Korean adults (40 males and 40 females; groups of 8 subjects representing each decade of life [20s to 60s]) with self-selected diet. The dietary assessment and 24-h urine collection were performed twice at intervals of 3 days. Daily intake of Si was estimated using a Si database of food composition. Urinary excretion of Si was analyzed using ICP-OES. The mean dietary Si intake was 22.8 mg/day for men and 19.3 mg/day for women without significant difference according to their gender and age. Si intake was the highest from vegetables both in men and women, followed by grains, beverages, and fruits in men and by grains, fruits, and milks in women. Urinary Si excretion was significantly higher in men (9.8 mg/day) than women (9.3 mg/day), and significantly increased with age only in women. Regarding the relationship between dietary Si intake and urinary Si excretion, a significantly positive correlation was found in men, but not in women. Longitudinal and balance studies to elucidate gender differences in Si nutrition are needed.

High Concentration of Sodium Metasilicate Impairs Autophagic Flux and Induces Apoptosis in Human Umbilical Vein Endothelial Cells

Silicon-doped materials have been widely used in bone regeneration research; however, a consensus on the safety range of silicon ions has not been reached and its toxicity mechanism remains to be further elucidated. This study aims to explore whether high level of sodium metasilicate can induce toxicity effect in human umbilical vein endothelial cells (HUVEC) and the role of autophagy and apoptosis in its toxic mechanism. HUVEC was treated with different level of high silicon and then investigated with respect to morphologic change, cell viability, immunofluorescence, the level of autophagy, and apoptosis-related protein. Moreover, bafilomycin A1 (Baf A1) was applied to detect whether autophagic flux is disrupted, and 3-methyladenine (3-MA, an autophagy inhibitor) was used to determine the relationship between autophagy and apoptosis. Results demonstrated that high-level silicon induced cell viability to decrease; LC3-II, p62, and apoptosis-related proteins were up-regulated after exposure to high-dose silicon (sodium metasilicate concentration more than 1 mM). There is no significant difference in LC3-II and p62 between Baf A1 and sodium metasilicate-exposed group. Besides, 3-MA further increased the apoptotic rate by inhibiting autophagy after high silicon exposure. Collectively, high concentration of silicon can impair autophagy and induce apoptosis in human umbilical vein endothelial cells, and autophagy may play a protective role in HUVEC apoptosis. Furthermore, silicon concentration used in HUVEC should not be more than 1 mM.

Effects of Silicon Compounds on Biomineralization, Osteogenesis, and Hard Tissue Formation

Bioinspired stem cell-based hard tissue engineering includes numerous aspects: The synthesis and fabrication of appropriate scaffold materials, their analytical characterization, and guided osteogenesis using the sustained release of osteoinducing and/or osteoconducting drugs for mesenchymal stem cell differentiation, growth, and proliferation. Here, the effect of silicon- and silicate-containing materials on osteogenesis at the molecular level has been a particular focus within the last decade. This review summarizes recently published scientific results, including material developments and analysis, with a special focus on silicon hybrid bone composites. First, the sources, bioavailability, and functions of silicon on various tissues are discussed. The second focus is on the effects of calcium-silicate biomineralization and corresponding analytical methods in investigating osteogenesis and bone formation. Finally, recent developments in the manufacturing of Si-containing scaffolds are discussed, including in vitro and in vivo studies, as well as recently filed patents that focus on the influence of silicon on hard tissue formation.

Interrelationship between silicon, aluminum, and elements associated with tissue metabolism and degenerative processes in degenerated human intervertebral disc tissue

There is a growing body of evidence concerning the significant role of silicon in development and composition of both connective and bone tissue. Bio-essential silicon shows strong chemical and biological affinity to aluminum, which is toxic and biologically inessential element. The presence of silicon was confirmed in a variety of tissues; however, it has never been examined in intervertebral disc tissue, neither in healthy nor in degenerated one. In this paper, for the first time in the literature, we present the content of silicon in the degenerated intervertebral disc tissue. We also compared the results of silicon analysis with aluminum values in degenerated intervertebral disc tissue in humans. We used chemometric methods to find correlations and similarities between silicon, aluminum, and elements associated with tissue metabolism (Mg) and degenerative processes (Zn and Cu). The presence of silicon was confirmed in all 30 samples harvested from 22 patients operated on due to degenerative changes. Its concentration was within the range of 5.37-12.8 μg g-1 d.w., with the mean concentration of 7.82 μg g-1 d.w. The analysis showed significant correlation between Si and both Al and Mg and weak or negative correlation with Zn and Cu, where the latter was probably the result of degenerative processes. Although silicon is considered essential in glycosaminoglycan and collagen synthesis in connective tissue, it did not show any correlation nor similarities with elements reflecting changes associated with the degenerative process of the intervertebral disc. Silicon showed significant correlation with aluminum, similar to those observed in other human tissues.

In vitro investigation of intestinal transport mechanism of silicon, supplied as orthosilicic acid-vanillin complex

SCOPE

Silicon (Si) is one of the most abundant trace elements in the body. Although pharmacokinetics data described its absorption from the diet and its body excretion, the mechanisms involved in the uptake and transport of Si across the gut wall have not been established.

METHODS AND RESULTS

Caco-2 cells were used as a well-accepted in vitro model of the human intestinal epithelium to investigate the transport, across the intestinal barrier in both the absorption and excretion directions, of Si supplied as orthosilicic acid stabilized by vanillin complex (OSA-VC). The transport of this species was found proportional to the initial concentration and to the duration of incubation, with absorption and excretion mean rates similar to those of Lucifer yellow, a marker of paracellular diffusion, and increasing in the presence of EGTA, a chelator of divalents cations including calcium. A cellular accumulation of Si, polarized from the apical side of cells, was furthermore detected.

CONCLUSION

These results provide evidence that Si, ingested as a food supplement containing OSA-VC, crosses the intestinal mucosa by passive diffusion via the paracellular pathway through the intercellular tight junctions and accumulates intracellularly, probably by an uptake mechanism of facilitated diffusion. This study can help to further understand the kinetic of absorption of Si.

Digestive absorption of silicon, supplemented as orthosilicic acid-vanillin complex

SCOPE

Silicon (Si) is an abundant element on earth. It is found naturally in water in the form of orthosilicic acid (OSA), however this form is not stable under certain conditions such as in highly concentrated and non-neutral pH solutions, which lead to its polymerization and reduced bioavailability. This study aimed to assess the bioavailability of Si from OSA stabilized by vanillin (OSA-VC).

METHODS AND RESULTS

This was a single-center, double-blind, cross-over randomized controlled trial. Fourteen healthy subjects were recruited and consumed either OSA-VC or a placebo on two separate occasions. Blood and urine samples were collected during 6 h following ingestion and analyzed to determine Si absorption and excretion. Plasma Si area under the curve (0-6 h) was significantly higher after OSA-VC ingestion compared to placebo ingestion (p = 0.0002). Significantly higher urinary Si excretion was also reported over the 6-h period after OSA-VC ingestion compared to placebo (p<0.0001). Approximately 21% of ingested Si was excreted in urine during this period.

CONCLUSION

Although many studies have investigated the metabolism and bioavailability of Si supplemented in foods or as a food ingredient, this was the first to investigate and demonstrate the digestibility of OSA administered in a complex form with vanillin.

The decrease in silicon concentration of the connective tissues with age in rats is a marker of connective tissue turnover

Silicon may be important for bone and connective tissue health. Higher concentrations of silicon are suggested to be associated with bone and the connective tissues, compared with the non-connective soft tissues. Moreover, in connective tissues it has been suggested that silicon levels may decrease with age based upon analyses of human aorta. These claims, however, have not been tested under controlled conditions. Here connective and non-connective tissues were collected and analysed for silicon levels from female Sprague-Dawley rats of different ages (namely, 3, 5, 8, 12, 26 and 43 weeks; n=8-10 per age group), all maintained on the same feed source and drinking water, and kept in the same environment from weaning to adulthood. Tissues (696 samples) were digested in nitric acid and analysed by inductively coupled plasma optical emission spectrometry for total silicon content. Fasting serum samples were also collected, diluted and analysed for silicon. Higher concentrations of silicon (up to 50-fold) were found associated with bone and the connective tissues compared with the non-connective tissues. Although total silicon content increased with age in all tissues, the highest connective tissue silicon concentrations (up to 9.98 μg/g wet weight) were found in young weanling rats, decreasing thereafter with age (by 2-6 fold). Fasting serum silicon concentrations reflected the pattern of connective tissue silicon concentrations and, both measures, when compared to collagen data from a prior experiment in Sprague-Dawley rats, mirrored type I collagen turnover with age. Our findings confirm the link between silicon and connective tissues and would imply that young growing rats have proportionally higher requirements for dietary silicon than mature adults, for bone and connective tissue development, although this was not formally investigated here. However, estimation of total body silicon content suggested that actual Si requirements may be substantially lower than previously estimated which could explain why absolute silicon deficiency is difficult to achieve but, when it is achieved in young growing animals, it results in stunted growth and abnormal development of bone and other connective tissues.