silicon and 1-ethoxysilatrane

On repeated thawing at room temperature of frozen preparations of heavy microsomes from rat livers, HMGCoA reductase activity was solubilized due to limited proteolysis. This soluble enzyme was partially purified by fractionation with ammonium sulfate and filtration on Sephacryl S-200 column. The active enzyme was coeluted with a major 92 kDa-protein and was identified as a 58 kDa-protein after separation by SDS-PAGE and immunoblotting. Ethoxysilatrane, a hypocholesterolemic compound, which decreased the liver-microsomal activity of HMGCoA reductase on intra-peritonial treatment of animals, showed little effect on the enzyme activity with isolated microsomes or the 50 kDa-soluble enzyme when added in the assay. But it was able to inhibit the activity of the soluble 58 kDa-enzyme in a concentration-dependent, reversible manner. Cholesterol and an oxycholesterol were without effect whereas chlorophenoxyisobutyrate and ubiquinone showed small inhibition under these conditions. The extra region that links the active site domain (50 kDa protein) to the membrane, present in the 58 kDa-protein appears to be involved in mediating the inhibition by silatrane.

Topics: Animals; Anticholesteremic Agents; Blotting, Western; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Chromatography, Gel; Hydroxymethylglutaryl CoA Reductases; Hydroxymethylglutaryl-CoA Reductase Inhibitors; Male; Microsomes, Liver; Organosilicon Compounds; Rats; Rats, Inbred Strains; Silicon; Solubility

Intraperitoneal administration of the nontoxic silicon compound, 1-ethoxysilatrane, to the rat did not cause proliferation of hepatic mitochondria or of endoplasmic reticulum, nor did it affect mitochondrial oxidative phosphorylation. The activities of cholesterol 7 alpha-hydroxylase in hepatic microsomes and of cholesterol oxidase in mitochondria respectively were unaffected by silatrane treatment. The rate of release of bile, whose composition remained unchanged, also was not increased in silatrane-treated animals. The results indicated that the compound did not affect the pathway of cholesterol degradation. A progressive decrease in the activity of hepatic microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase was observed on administration of the compound over a period of three weeks. Consistent with this, cholesterol biosynthesis in liver as measured by incorporation of radioactive precursors, acetate and water but not mevalonate, was significantly decreased in silatrane-treated animals. However, enzyme-linked immunosorbent assay revealed that the concentration of HMGCoA reductase protein was not decreased by the treatment indicating that inactivated enzyme was also present in such microsomes. Addition of silatrane to microsomes in the assay system did not cause inhibition indicating that the inactivation is by an indirect mechanism. It is concluded that the hypocholesterolemic action of the compound rested entirely on the inhibition of cholesterol biosynthesis in vivo by inactivation of the rate-limiting enzyme HMGCoA reductase.

Topics: AMP-Activated Protein Kinases; Animals; Anticholesteremic Agents; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Cholesterol; Hydrolysis; Male; Microsomes, Liver; Mitochondria, Liver; Multienzyme Complexes; Organosilicon Compounds; Protein Kinases; Protein Serine-Threonine Kinases; Rats; Rats, Inbred Strains; Silicon

Topics: Animals; Anticoagulants; Arteriosclerosis; Blood Coagulation Tests; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Bridged-Ring Compounds; Cholesterol, Dietary; Organosilicon Compounds; Rabbits; Silicon

Topics: Animals; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Bridged-Ring Compounds; Cell Membrane; Lipid Bilayers; Membrane Potentials; Organosilicon Compounds; Rats; Silicon; Sodium-Potassium-Exchanging ATPase; Spectrometry, Fluorescence

Intraperitoneal administration of the organosilicon compound 1-ethoxysilatrane to the rat caused a 25% decrease in the concentration of cholesterol in serum without affecting that of triacylglycerols. The specific activity of 3-hydroxy-3-methylglutaryl CoA reductase, the rate-limiting enzyme in cholesterol biosynthesis, was depressed in hepatic microsomes of silatrane-treated animals.

Topics: Animals; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Bridged-Ring Compounds; Cholesterol; Hydroxymethylglutaryl CoA Reductases; Injections, Intraperitoneal; Male; Microsomes, Liver; Organosilicon Compounds; Rats; Rats, Inbred Strains; Silicon; Triglycerides

Topics: Abdomen; Abdominal Muscles; Animals; Biomechanical Phenomena; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Bridged-Ring Compounds; Collagen; Hemorrhage; Organosilicon Compounds; Rats; Silicon; Skin; Wound Healing

Topics: Animals; Aorta, Thoracic; Aortic Diseases; Arteriosclerosis; Bridged Bicyclo Compounds; Bridged Bicyclo Compounds, Heterocyclic; Bridged-Ring Compounds; Cholesterol, Dietary; Drug Evaluation, Preclinical; Lipid Metabolism; Organosilicon Compounds; Rabbits; Silicon; Time Factors