Cholesterol precursor

Mice fed a diet containing the hexaisoprenoid cholesterol precursor squalene [111-02-4]... 

Vanhanen, H. X, Blomqvist, S., Ehnholm, C., et al., 1993. Sernm cholesterol, cholesterol precursors, and plant sterols in hypercholesterolemic subjects widi different apoE phenotypes during dietary sitostanol ester treatment. Journal of Lipid Research 34 1535-1544. 

This class of farnesyltransferases catalyzes the posttrans-lational modification of proteins by the cholesterol precursor, farnesylpyrophosphate. One of the substrates of this enzyme is Ras. 

Pravastatin sodium besides increasing LDL cholesterol catabolism, also inhibits LDL-cholesterol production by inhibiting hepatic synthesis of VLDL-cholesterol, the LDL-cholesterol precursor. These effects result in a reduction of total cholesterol, LDL-cholesterol, VLDL-cholesterol, apolipoprotein B and trigly-cerides, whilst increasing (HDL-cholesterol) and apolipoprotein A. It has little effect on cholesterol synthesis in other tissues. 

Synthesis of certain cholesterol precursors by hydatid protoscoleces of Echinococcus granulosus and cysticerci of Taenia hydatigena. Comparative Biochemistry and Physiology, 49B 93-8. 

Oxidation of the ketone (9) with molecular oxygen in the presence of base provides a convenient method for the degradation of the lanosterol side-chain.14 Lead tetraacetate oxidation of the resulting acid (10) followed by hydrolysis and oxidation yielded the corresponding 20-keto-derivative (11). The potential cholesterol precursors 5a-lanost-8-en-3j8,15a-diol and 5a-lanost-8-en-3j3,15/3-diol have been... 

A cholesterol precursor may be converted to 1,25-dihydroxycholecalcif-erol, the active form of vitamin D3. 

Potential research topics. Because of their steroidal structure, the brassinosteroids offer many potential avenues for research both in phytochemistry and zoochemistry. If, for example, the presence of the brassinosteroids is relatively ubiquitous in plants, is it then possible that they play a role in host parasite relationships It is of note that many plant parasitic and intestinal nematodes must obtain their cholesterol precursors from their respective hosts (18), a paradigm of the former being the plant gall inducing nematode Ditylenchus dipsaci and of the latter the somewhat large intestinal nematode Ascaris lumbricoides. Certain phytopathogenic fungi also have a sterol requirement for completion of their life cycle (19), as do certain insects (20). 

London, M., Bakht, O. London, E. Cholesterol precursors stabihze ordinary and ceramide-rich ordered hpid domains (hpid rafts) to different degrees. Imphcations for the Bloch hypothesis and sterol biosynthesis disorders. J Biol Chem 281 (2006) 21903-13. 

Fig. 4). Then, zymosterol can be metabolized sequentially by a A24-reductase, A8,A7-isomerase, and A5-desaturase to form 7-DHC, which is reduced at the A7 position to form cholesterol. Alternatively, zymosterol can be metabolized by the A8,A7-isomerase and A5-desaturase to form 7-dehydrodesmosterol. 7-Dehydrodesmosterol is metabolized by the A7-reductase to form desmosterol and then by the A24-reductase to form cholesterol. The fact that the SLOS deficiency in A7-reductase leads to a buildup of 7-DHC rather than 7-dehydrodesmosterol is interpreted to mean that the former pathway is the principal one. However, the latter pathway must also be used because desmosterol is an abundant cholesterol precursor in certain tissues. It has been suggested that the final steps in the cholesterol biosynthetic pathway are tissue specific. Perhaps, in SLOS cells, any... 

P H Jones. Cholesterol precursor to many lipid disorders. The American Journal of Managed Care 7 S289-S298, 2001. 

Congenital adrenal hyperplasia (CAH) is a family of autosomal recessive disorders caused by mutations that encode for enzyme involved in one of the various steps of adrenal steroid synthesis. These defects result in the absence or the decreased synthesis of cortisol from its cholesterol precursor. The anterior pituitary secretes excess ACTH via feedback regulation by cortisol, which results in overstimulation of the adrenals and causes hyperplasia. 

Vitamin D is unique in that it can be either obtained from the diet (as vitamin D2 or D3) or synthesized from a cholesterol precursor, a process that requires reactions in the skin, liver, and intestine. The calciferols, including several forms of vitamin D, are a family of steroids that affect calcium homeostasis (Fig. 34.26). Cholecalciferol (vitamin D3) requires ultraviolet light for its production from 7-dehydrocholesterol present in cutaneous tissues (skin) in animals and from ergosterol in plants. This irradiation cleaves the carbon-carbon bond at C9-C10 to open the B ring to form cholecalciferol, an inactive precursor of l,25-(OH)2-cholecalciferol (calcitriol). Calcitriol is the most potent biologically active form of vitamin D (see Fig. 34.26). 

Phenyl-1-propanol Sodium desoxycholate cholesterol precursor Squalene... 

Dietary and non-dietary (chemotherapeutic) methods are presently used to control hyperlipidemia. The ideal method as defined by Oliver [34] should lead to a sustained reduction of hypertriglyceridemia, as well as of hypercholesterolemia and to a reduction in the accumulation of hpid in tissues accompanied by enhanced cataboHsm of Hpids and sterols. There should be no accumulation of cholesterol precursors or metabolites, no toxic effects and only minimal side effects. The treatment should be easily administered and should not affect the normal way of living. 

T. H. Stoudt, and C. A. Fish Studies on the biosynthesis of cholesterol. VII. Formation of cholesterol precursors by yeast. Arch. Biochem. 55, 274 (1955). 

Molecules that have been synthesized using the Diels-Alder reaction (and the chemists who led the work) include morphine (above, and shown as a model), the hypnotic sedative used after many surgical procedures (M. Gates) reserpine (above), a clinically used antihypertensive agent (R. B. Woodward) cholesterol, precursor of all steroids in the body, and cortisone (also above), the antiinflammatory agent (both by R. B. Woodward) prostaglandins F2 and E2 (Section 13.11C), members of a family of hormones that mediate blood pressure, smooth... 

The existence in the brain cytoplasm of acetoacetyl-CoA synthetase and acetoacetyl-CoA thiolase makes unnecessary the existence of a transmitochondrial membrane transport of acetyl CoA for lipid synthesis. We have found a clear inhibitory effect on the activity of the thiolase by several metabolites of phenylalanine. Also the hydroxybutyrate dehydrogenase of the suckling rat brain is inhibited by these metabolites. These effects are interesting in relation to the pathophysiology of mental retardation in phenylketonuria, in which the concentration of such metabolites are considerably increased. It is worth noting that this inhibition can influence the rate of synthesis of fatty acids and cholesterol (precursors of myelin), especially during brain development. 

CHEMISTRY, METABOLISM, PROPERTIES. Akhough about 10 sterol compounds with vitamin D activity have been identified, only two of these, known as provitamins D or precursors, are of practical importance today from the standpoint of their occurrence in foods—ergocalciferol (vitamin D, calciferol, or viosterol) and cholecalciferol (vitamin D,) the name cholecalciferol of the latter is a reflection of its cholesterol precursor. Because these substances are closely related chemically, the term vitamin D is used collectively to indicate the group of substances that showthis vitamin activity. 

HMB has two fates in the body conversion to HMG-CoA and excretion in the urine.The metabolic pathway of HMB metabolism is conversion to HMG-CoA (Figure 12.1). In the cytosol, conversion of HMB to HMG-CoA occurs either through direct carboxylation or through dehydration of MCA-CoA (Figure 12.1). Subsequently, the cytosolic HMG-CoA produced can provide substrate for HMG-CoA reductase, which is the committed step in cellular cholesterol synthesis.This fact has been hypothesized as a mechanism whereby HMB can affect cellular metabolism by providing a cholesterol precursor during times of elevated need. ... 

Glucose likewise can function as a cholesterol precursor in the rabbit, since the feeding of glucose-C gives rise to labeled cholesterol. ... 

Miettinen, TA, Tilvis, RS and Kesaniemi, YA (1990) Serum plant sterols and cholesterol precursors reflect cholesterol absorption and synthesis in volunteers of arandomly selected male population. Am. J. Epidemiol., 131, 20-31. 

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