Sterols, labelled

Denitration of nitro compounds with Bu- SnD provides an elegant method fci the synthesis of deiuerated compounds Recently, the synthesis of deuterium labeled plant sterols has been reported fsee Eq 11%)... 

Sea cucumbers (Holothuroidea, Echinodermata) appear to be unique in their mode of squalene oxide (37) cyclization. Tritium-labeled lanosterol (33), cycloartenol (32) and parkeol (38) were individually administered to the sea cucumber Holothuria arenicola. While the former two triterpenes were not metabolized [22], parkeol was efficiently transformed into 14x-methyl-5a-cho-lest-9(l l)-en-3/ -ol (39) (Scheme 3). Other A1 sterols present in H. arenicola were not found to be radioactive and were thus assumed to be of dietary origin. The intermediacy of parkeol was confirmed by the feeding of labeled mevalonate (23) and squalene (26) to the sea cucumber Stichopus californicus [15]. Both precursors were transformed into parkeol, but not lanosterol nor cycloartenol, aqd to 4,14a-dimethyl-5a-cholest-9(ll)-en-3/J-ol (40) and 14a-methyl-5a-cholest-9(ll)-en-3/ -ol. Thus, while all other eukaryotes produce either cycloartenol or lanosterol, parkeol is the intermediate between triterpenes and the 14-methyl sterols in sea cucumbers. 

In more recent studies the use of HPLC allowed isolation and counting of individual sterols after administration of labelled precursors. The sterols isolated from mantles and viscera of the nudibranch Doris verrucosa were identified as cholestanol, cholesterol, 24-dehydrocholesterol and 7-dehydrocholesterol [103]. After injection of dl-[2-14C]-mevalonic acid DBED salt, cholesterol (57) and 7-dehydrocholesterol (58) were isolated as the acetates by reversed phase HPLC. Both sterols were found significantly labelled specific radioactivity associated with 7-dehydrocholesterol was higher by one order of magnitude than that associated with cholesterol. This fact would indicate either that the reduction of the A1 double bond of 7-dehydrocholesterol to afford cholesterol occurs at a low rate, or that the cholesterol found in D. verrucosa comes partly from a dietary source. 

The ability of bivalve molluscs to synthesize sterols is questioned [106]. Approximately forty sterols have been identified from the oyster Crassostrea virginica and, since it appeared that many of the sterols identified must be of dietary origin, the ability of the oyster to incorporate injected radioactive acetate was studied [110]. Of the forty sterols naturally occurring in the oyster, only four were labelled by injection of labelled acetate cholesterol, desmosterol, 24-methylenecholesterol and fucosterol. However, when an oyster hearth tissue culture was grown aseptically with addition of labelled acetate, the sterols were found to be non-radioactive [111], This finding does not rule out the possibility... 

C-labelled cholesterol was used to test the recovery of 5-100 pg of faecal sterols from seawater (labelled coprostanol not being available). The radioactivity of the samples and eluates was measured by a two-channel liquid scintillation counter. Percentage recovery was calculated on the basis of the amount of labeled material recovered in the acetone eluant. The results indicate that column extraction efficiency is not adversely affected by the salinity of the water samples, i.e., in the range 95-97%. 

Genetic analysis indicates that two of the 10 sad mutants of A. strigosa that we isolated represent different mutant alleles at the Sadi locus.6 These mutants accumulate radiolabelled 2,3-oxidosqualene but not p-amyrin when the roots are fed with 14C-labelled precursor mevalonic acid, suggesting that the triterpenoid pathway is blocked between 2,3-oxidosqualene and P-amyrin.34 The roots of these mutants also lack detectable P-amyrin synthase activity, but, like the wild type and the other mutants, are unimpaired in cycloartenol synthase (CS) activity and sterol biosynthesis.34 The transcript levels for AsbASl are substantially reduced in roots of sadl mutants, while AsCSl transcript levels are unaffected,35 suggesting that the sadl mutants are either mutated in the AsbASl gene itself or in a gene involved in its regulation. 

Radioactivity distribution. The N-hexane lipido/sterolic extract (LSESr) supplemented with [ C]-labeled oleic or lauric acids or P-sitosterol was administered orally to rats. The highest level of radioactivity uptake was LSESr supplemented with [ C]-labeled oleic acid. Ratios of radioactivity in tissues compared to plasma showed an uptake of radioactivity greater in prostate as compared with other genital organs, i.e., the seminal vesicles or to other organs such as... 

The Arabidopsis mutant dwf7/ste 1 is defective in C5-desaturation of episterol (Fig. (2)) [18], thus impaired in an enzyme function involved in a very early step of brassinosteroid precursor biosynthesis. The enzymatic block of dwf7/stel was determined by feeding experiments using l3C-labelled mevalonic acid and a subsequent analysis of endogenous sterol and brassinosteroid precursors. The mutant accumulates episterol with a simultaneous decrease of downstream intermediates (24-methylenecholesterol, campesterol, castasterone, brassinolide). 

Key words Cholesterol absorption, phytosterols, cholesterol excretion, reverse cholesterol transport, ACAT, CEL, inhibitors, bile acids, fecal sterols, dual label, obesity, cardiovascular disease. 

Treatment of mice with radiolabeled sterol mix the radio-labeled sterol mix is given to the mice 1-3 h before the... 

Sterols are synthesized in nature from squalene and, therefore, ultimately from isoprene. Mevalonic acid is the immediate precursor of the isoprene unit, and the carboxylic acid group is lost as carbon dioxide when two mevalonic acid molecules combine head to tail. Thus, if the a carbon of mevalonic acid is labeled, then this carbon is always adjacent to the carbon bearing a side-chain methyl group. Examination of the way in which six isoprene units are linked in squalene (Example 6.2) shows that they are not all linked head to tail there is a point of symmetry in the structure of squalene (marked in the structure below). At this point a set of three isoprene units, linked head to tail, is joined head-to-head to a similar set of three isoprene units, to give the labeling pattern shown. 

Labeling Label as Vegetable Oil (Plant) Sterol Esters to indicate that the vegetable oil sterols and the fatty acids originate from vegetable oils. Declare the presence of any preservative, antioxidant, or other added substance. 

The sterols of starfish, which are typically A7-compounds, are thought to be derived from dietary A5-compounds, and it has been shown177 that two species of starfish can convert cholest-5-en-3/3-ol and sitosterol into their A7-analogues. However, de novo synthesis of squalene, lanosterol, and 5a-cholest-7-en-3j8-ol from [2-14C]MVA has been demonstrated178 in various starfish species, but it is of particular interest that the C26, C28, and C29 sterols were not labelled. The direct conversion of cholest-5-en-3/3-ol into 5 -cholest-7-en-3/3-ol in Calliphora eryth-rocephala has been demonstrated.179... 

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