Silicon facilitation of copper utilization in the rat

Silicic Acid and Beer Consumption Reverses the Metal Imbalance and the Prooxidant Status Induced by Aluminum Nitrate in Mouse Brain

BACKGROUND

Emerging evidence suggests that by affecting mineral balance, aluminum (Al) may enhance some events associated with neurodegenerative diseases.

AIM

To examine the effect of Al(NO3)3 exposure on brain Al, cooper (Cu), iron (Fe), magnesium (Mg), manganese (Mn), silicon (Si), and zinc (Zn) levels, and the metal-change implication in brain oxidant and inflammatory status.

METHODS

Four groups of six-week-old male NMRI mice were treated for three months: i) controls, administrated with deionized water; ii) Al, which received Al(NO3)3; iii) Al+silicic acid, which were given Al(NO3)3 plus silicic acid; and iv) Al+beer, which received Al(NO3)3 plus beer.

RESULTS

Brain Al and TBARS levels and TNFα and GPx expressions increased, while Cu, Mn, and Zn levels, and catalase and CuZn-SOD expression decreased (at least, p < 0.05) in Al versus control animals. Al, Si, and TBARS levels and TNFα expression decreased (p < 0.05) in Al+silicic acid and Al+beer specimens while Cu, Mn, and Zn levels and antioxidant expression increased versus the Al group. Brain Al levels correlated negatively with those of Cu, Fe, Mn, and Zn, and catalase, CuZn-SOD, and GPx enzyme expressions but positively with Si and TBARS levels and TNFα expression. Two components of the principal component analysis (PCA) explained 71.2% of total data variance (p < 0.001). PCA connected the pro-oxidant markers with brain Al content, while brain Zn and Cu levels were closer to antioxidant enzyme expression.

CONCLUSION

Administration of Al(NO3)3 induced metal imbalance, inflammation, and antioxidant status impairment in the brain. Those effects were blocked to a significant extent by silicic acid and beer administration.

Silicon as Versatile Player in Plant and Human Biology: Overlooked and Poorly Understood

Silicon (Si) serves as bioactive beneficial element. Si is highly abundant in soil, and occurs ubiquitously in all organisms including plants and humans. During the last three decades, nutritional significance of Si for plant and human health has received increasing attention. Plant Si plays a pivotal role in growth and development, and this beneficial effect depends usually on accumulation in plant tissues, which are then protected from various forms of biotic and abiotic stresses. Likewise, human exposure to Si imparts health benefits and essentially occurs through plant-derived food products. Si bioavailability in human diet, e.g., strengthens bones and improves immune response, as well as neuronal and connective tissue health. Despite this empiric knowledge, the essentiality of Si still remains enigmatic. Thus the link between Si availability for plant development and its profound implication for human welfare should receive attention. This review aims to provide a broad perspective on Si as important element for plant and human nutrition and to define research fields for interdisciplinary research.

Positive association between serum silicon levels and bone mineral density in female rats following oral silicon supplementation with monomethylsilanetriol

Observational (epidemiological) studies suggest the positive association between dietary silicon intake and bone mineral density may be mediated by circulating estradiol level. Here, we report the results of a silicon supplementation study in rats that strongly support these observations and suggest an interaction between silicon and estradiol.

INTRODUCTION

Epidemiological studies report strong positive associations between dietary silicon (Si) intake and bone mineral density (BMD) in premenopausal women and indicate that the association may be mediated by estradiol. We have tested this possibility in a mixed-gender rodent intervention study.

METHODS

Tissue samples were obtained from three groups of 20-week-old Sprague Dawley rats (five males and five females per group) that had been supplemented ad libitum for 90 days in their drinking water with (i) <0.1 mg Si/L (vehicle control), (ii) 115 mg Si/L (moderate dose) or (iii) 575 mg Si/L (high dose). All rats received conventional laboratory feed, whilst supplemental Si was in the form of monomethylsilanetriol, increasing dietary Si intakes by 18 and 99 %, for the moderate- and high-dose groups, respectively.

RESULTS

Fasting serum and tissue Si concentrations were increased with Si supplementation (p < 0.05), regardless of gender. However, only for female rats was there (i) a trend for a dose-responsive increase in serum osteocalcin concentration with Si intervention and (ii) strong significant associations between serum Si concentrations and measures of bone quality (p < 0.01). Correlations were weaker or insignificant for tibia Si levels and absent for other serum or tibia elemental concentrations and bone quality measures.

CONCLUSIONS

Our findings support the epidemiological observations that dietary Si positively impacts BMD in younger females, and this may be due to a Si-estradiol interaction. Moreover, these data suggest that the Si effect is mediated systemically, rather than through its incorporation into bone.

Update on the possible nutritional importance of silicon

Convincing evidence that silicon is a bioactive beneficial trace element continues to accumulate. The evidence, which has come from human, animal, and in vitro studies performed by several laboratories, indicate that silicon in nutritional and supra nutritional amounts promotes bone and connective tissue health, may have a modulating effect on the immune or inflammatory response, and has been associated with mental health. A plausible mechanism of action for the beneficial effects of silicon is the binding of hydroxyl groups of polyols such that it influences the formation and/or utilization of glycosaminoglycans, mucopolysaccharides, and collagen in connective tissue and bone. In addition, silicon may affect the absorption, retention or action of other mineral elements (e.g., aluminum, copper, magnesium). Based on findings from both animal and human experiments, an intake of silicon of near 25mg/d would be a reasonable suggestion for an adequate intake that would assure its nutritional benefits. Increased intakes of silicon through consuming unrefined grains, certain vegetables, and beverages and cereals made from grains should be recognized as a reasonable dietary recommendation.

Effects of high levels of dietary silicon on bone development of growing rats and turkeys fed semi-purified diets

Two experiments were conducted using a completely randomized design to study the effects of high levels of silicon (Si) supplementation on bone development, structure, and strength in growing rats and turkeys. Rats were supplemented at two dietary Si levels: 0 and 500 ppm; and the turkeys were supplemented at four dietary Si levels: 0, 135, 270, and 540 ppm in semi-purified diets of dextrose-albumin for rats and dextrose-casein for turkeys. The experiments lasted 8 and 4 weeks for the rats and turkeys, respectively. Physical, mechanical, and chemical parameters of bones were measured. All the physical and mechanical measures of bone size and strength were not different (P > 0.05) between treatments in rats and turkeys except the moment of inertia, which was lower (P < 0.01) in rats on the 500 ppm Si level of supplementation. There were small but consistent reductions in structural and strength parameters with Si supplementation which were not wholly due to differences in bodyweights of the rats and turkeys. Although bone mineral composition was not affected (P > 0.05) by Si supplementation, plasma magnesium (P = 0.08) in rats and plasma calcium (P < 0.05) in turkeys were reduced by high levels of Si supplementation. The antagonistic relations of high Si levels with calcium and magnesium were deemed to be the mechanisms through which high Si imposes its deleterious effects on bone size and strength.

Copper-silicon interaction studies in young, rapidly growing turkeys fed semipurified starter diets

A 3x3 factorial experiment was conducted to study the interactions between Cu and Si in growing turkeys fed a basal dextrose-casein semipurified diet supplemented at 0, 270, and 540 ppm Si, and 2, 8, and 75 ppm Cu levels of inclusion. There were no significant (p>0.05) Cu, Si, or Cu-Si interaction effects on turkey growth. However, there were significant (p<0.05) Si effects on hemoglobin concentrations, and Cu-Si interaction effects on hematocrit and plasma Mg levels (p<0.01). Plasma Ca, P, Zn, Cu, total cholesterol, and serum alkaline phosphatase activity were not affected (p>0.05) by Cu, Si, or Cu-Si interaction. Heart and liver weights were affected (p<0.05) by the Cu-Si interaction. In general, a 8-ppm Cu supplemental level prevented cardiac hypertrophy only in the presence of 270 or 540 ppm Si inclusion in the diets. There were significant (p<0.05) Cu effects on liver Cu and Mn and heart Zn concentrations, Si effects on liver Mn levels, and Cu-Si interaction on liver Zn concentrations. Within the 0- and 270-ppm Si groups, Cu-deficient turkeys (2 ppm Cu) had higher liver Zn levels but not within the 540-ppm Si group. The Cu-Si interaction did not affect (p>0.05) concentrations of Cu in the heart and liver tissues. It is postulated that the Cu-Si interactions demonstrated in this study could have profound implications on the cardiovascular and skeletal health of birds.

Biochemical interactions among silicon, iron and ascorbic acid in the rat

A 2 x 2 x 2 factorial experiment was conducted using two dietary levels each (mg/kg of diet) of silicon, 0 and 500; iron, 35 and 187; and ascorbic acid, 0 and 900, to identify biochemical interactions occurring among these nutrients. Supplemental silicon, in conjunction with the higher dietary-iron level, prevented the plasma-iron decreasing effect observed for the higher level of iron in the absence of silicon. In the absence of ascorbic acid, silicon also increased iron concentration in the liver. Lower growth of the silicon and iron-supplemented rats is believed to be a response to a subsequent iron-imposed aberration of copper or zinc metabolism. This is supported by decreased intestinal metallothionein, increased weights (g/100 g body weight) of liver, heart, and testes, and decreased packed-cell volume and hemoglobin concentration. The lower plasma-iron level associated with the higher level of dietary iron appeared to be an expression of the iron-imposed reduction of liver copper stores. Ascorbic acid decreased plasma-iron concentration and prevented the silicon-related increase in liver iron.