Silicon excretion

Lin K, et al. Degradation and silicon excretion of the calcium silicate bioactive ceramics during bone regeneration using rabbit femur defect model. J Mater Sci Mater Med 2015 26(6) 197. 

In 1978, on the basis of a few measurements of urine calcium and phosphate excretion as well as an awareness of the previously mentioned work regarding the amounts of calcium and phosphate normally accreted in utero and postnatally, it became apparent that the demineralization, fractures and rickets we were seeing in our infants were caused by calcium deficiency. Consequently we increased the amount of calcium added to the parenteral alimentation solutions. If more than 12.5 mM of the calcium were added to a liter of hyperalimentation solution, gross precipitation would occur in the feeding solution. If 10 mM of calcium were added per liter, crystalline precipitated began to build up on the inside of our barium-impregnated silicone rubber central venous catheters. This crystalline precipitate resulted in gradual occlusion and functional loss of these lines. After several false starts and six lost catheters, chemical and crystal analysis showed that the precipitate inside these catheters was CaHPO. ... 

The apparatus was separated into two compartments(A,B) with a silicone rubber sponge sheet which had a hole in the middle to hold fish at just the back of pectoral fin. Both the head and rear parts of fish were covered with two small boxes which had many holes and were fixed to a cover plate of the apparatus. PCP-free water was supplied into the head compartment(A) at a flow rate of 1 liter/h and the overflow from (A) was reserved in an ice-cooled tank for the analysis of PCP excreted from gills. Fish urine was led by a cannula to an ice-cooled flask through... 

Chemicals vary greatly in the extent to which they are absorbed through the walls of the GI tract. At one extreme are some very inert and highly insoluble substances - sand (silicon dioxide) and certain insoluble minerals such as several of the silicates added to foods to keep them dry - that are almost entirely unabsorbed. Such substances simply wind their way down the entire length of the GI tract and end up excreted in feces. This pathway is shown in Figure 2.1 as the long arrow extending from the GI tract directly to feces. 

Trace metal disturbances may be due to the uremia per se. Indeed, as the urinary excretion route is an important pathway of elimination of many trace elements, i.e. silicon, strontium, aluminum,... impairment of the kidney will be an important determinant of their accumulation, whilst in the presence of a reabsorptive defect a number of trace elements, especially those that are reabsorbed because of their essential role, be lost resulting in a deficient state. The presence of proteinuria may reasonably result in losses of protein bound elements. It has also been shown also that residual renal funchon may importantly alter the accumulation and hence toxic effects of aluminum [2]. In uremia translocation of a particular metal from one tissue to another may also occur. As an example, under normal circumstances the kidney is an important target organ for cadmium. In chronic renal failure however, possibly as a consequence of a reduction in binding proteins (e.g. metallothionein), the concentrahon of cadmium in this tissue decreases to extremely low levels which... 

Silicic acid is readily absorbed, and plasma levels rise rapidly following intake. In normal subjects excretion is rapid, average plasma levels are 5-10 pM, and all cells and tissues contain silicon, which may be concentrated in some cells or cellular compartments, for example, in the osteoblast. Little is known of the interactions between this silicic acid and internalized aluminum. With aluminum bound strongly to transferrin and the low plasma silicic acid levels, interaction is unlikely except at sites of local concentration. Codeposited aluminum and silicon (as amorphous aluminosilicate) has, so far as is known, been reported only at the core of senile plaques. Separate groups of workers report silicon in artery walls (44) and aluminum (45) in artery walls, but no studies have been made of the association and balance of the two elements in tissue. Such studies will be required if progress is to be made. Some workers have reported an... 

Nielsen 2002). In rats, supplemental silicon (250 mg kg by DM) had no effect on skeletal development. Egg production in chicken receiving a basal diet containing from 0.6 to 143 mg Si kg DM was reduced insignificantly. Supplementation of the hens feed reduced egg production insignificantly (Vogt 1992). Normally, urinary silicon is readily excreted but, under some conditions in grazing steers and sheep, part of the urinary silicon is deposited in the kidneys, bladder, or urethra to form calculi (McDowell 1992). 

Benke and 0sborne(21) studied the rate and extent of urinary excretion of silicon in rats after oral administration of single doses of several silicates, including a 2,4 ratio sodium silicate, to rats. Two trials were conducted in the first trial, a dose of 40 mg/kg was administered, in the second trial the dose was 1000 mg/kg. At the 40 mg/kg level, 18.9% of the administered silicate was excreted in the urine, and elevated levels of Si in the urine were observed only in the first 24 hours after the oral dose. At the 1000 mg/kg level, 2.8% of the total administered silicate was excreted in the urine, and the data in Figure 4 were obtained for the rate of excretion Benke... 

Silica undergoes hydrolysis to form silicic acid, Si(OH)4. In vivo, following the degradation of silica gel granules, silicic acid was found to diffuse through the blood stream or lymph and was excreted in the urine at a rate of 1.8 mg silicon per day (Lai et al. 1998). 

With certain soil bacteria, the uptake of silicon as soluble silica in a culture medium is followed by the excretion of phosphorus. Factors that accelerated and inhibited this exchange were studied by Hdnoi (31). In the absence of glucose, silicon was lost in the presence of excess phosphate Particulate fractions isolated from the bacterial membrand were involved in the metabolism of silicon (32). Many more details were given by Heinen in 14 papers between I960 and 1967. 

The oxidative first step involves electronic carrier (hole) injection and is dependent on both electronic bandgap and doping of the semiconductor. Complete hydrolysis of the oxide phase then generates orthosihcic acid, which is the natural bioavailable form of silicon, freely diffusible in human tissues, and readily excreted via the kidneys (Jugdaohsingh et al. 2002 Refitt et al. 1999). The biocompatibility of porous sihcon is reviewed in detail elsewhere in this handbook ( Biocom-patibihty of porous sihcon ) so is not discussed here. 

Silicon Levels in Food, Common Dietary Intake, and Excretion... 

Silicon is a major constituent of diatoms, which form a large proportion of marine phytoplankton. Some other algae, fungi and the siliceous sponges also have structural parts consisting of silica. The diatoms and radiolaria can excrete silica in the form of opal (amorphous silica, Si02 WH2O). 

Herbivorous animals ingest very large amounts of silicon in their diets and excrete ten to thirty times as much in their urine as carnivorous species. A metabolism of large amounts of silicon by ruminants was also demonstrated many years ago by Forbes and Beegle. ... 

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