Neutral Sterols

The first step in CTO distillation is depitching. A relatively small distillation column is used as a pitch stripper. The vapor from the pitch stripper is fed directiy into the rosin column, where rosin and fatty acids are separated. Rosin is taken from the bottoms of the column and fatty acids as a sidestream near the top. Palmitic acid and light neutrals are removed in the rosin column as heads. The operation is designed to minimize holdup and product decomposition. Care is taken to prevent carryover of some of the heavier neutrals, such as the sterols, from the depitcher to the rosin column (24). 

The major components of candelilla wax are hydrocarbons, esters of long-chain alcohols and acids, long-chain alcohols, sterols, and neutral resins, and long-chain acids. Typically, candelilla wax has a melting point of 70°C, a penetration of 3 drum at 25°C, an acid number of 14, and a saponification number of 55. Principal markets for candelilla include cosmetics, foods, and pharmaceuticals. The FDA affirmed Candelilla as GRAS for certain food apphcations in 21 CFR 184.1976. 

Various mechanisms have been proposed to explain the hypocholesterolemic effect of GA (Annison et al., 1995 Tiss et al., 2001). Some studies have suggested that the viscosity of fermentable dietary fiber contributes substantially to the reduction of lipids in animals and humans (Gallaher et al., 1993 Moundras et al., 1994). However, other studies suggested that this property is not related to plasma lipids (Evans et al., 1992). The mechanism involved is clearly linked to increased bile acid excretion and fecal neutral sterol or a modification of digestion and absorption of lipids (Moundras et al., 1994). 

Although not very commonly used in the separation of nentral hpids, two-dimensional systems have been nsed to separate hydrocarbons, steryl esters, methyl esters, and mixed glycerides that move close to each other in one-dimensional systems. Complex neutral lipids of Biomphalaria glabrata have been first developed in hexane diethyl ether (80 20), dried, and the plates have been turned 90°, followed by the second development in hexane diethyl ether methanol (70 20 10) for complete separation of sterol and wax esters, triglycerides, free fatty acids, sterols, and monoglycerides [54]. 

Nystatin and amphotericin B, in the presence of sterols, form temporary channels across lipid bilayers. Neutral molecules under the size of glucose can traverse the... 

The overall metabolism of vitamin A in the body is regulated by esterases. Dietary retinyl esters are hydrolyzed enzymatically in the intestinal lumen, and free retinol enters the enterocyte, where it is re-esterified. The resulting esters are then packed into chylomicrons delivered via the lymphatic system to the liver, where they are again hydrolyzed and re-esterified for storage. Prior to mobilization from the liver, the retinyl esters are hydrolyzed, and free retinol is complexed with the retinol-binding protein for secretion from the liver [101]. Different esterases are involved in this sequence. Hydrolysis of dietary retinyl esters in the lumen is catalyzed by pancreatic sterol esterase (steryl-ester acylhydrolase, cholesterol esterase, EC 3.1.1.13) [102], A bile salt independent retinyl-palmitate esterase (EC 3.1.1.21) located in the liver cell plasma hydrolyzes retinyl esters delivered to the liver by chylomicrons. Another neutral retinyl ester hydrolase has been found in the nuclear and cytosolic fractions of liver homogenates. This enzyme is stimulated by bile salts and has properties nearly identical to those observed for... 

B. S. Reddy and E. L. Wynder, Metabolic epidemiology of colon cancer. Fecal bile acids and neutral sterols in colon cancer patients and patients with adenomatous polyps. Cancer, 1977, 39(6), 2533. 

Czubayko F, Beumers B, Lammsfuss S, Lutjohann D, von Bergmann (1991) A simplified micro-method for quantification of fecal excretion of neutral and acidic sterols for outpatient studies in humans. J Lipid Res 32 1861-1867... 

The ring structure of cholesterol cannot be metabolized to C02 and HfeO in humans. Rather, the intact sterol nucleus is eliminated from the body by conversion to bile acids and bile salts, which are excreted in the feces, and by secretion of cholesterol into the bile, which transports it to the intestine for elimination. Some of the cholesterol in the intestine is modified by bacteria before excretion. The primary compounds made are the isomers coprostanol and cholestanol, which are reduced derivatives of cholesterol. Together with cholesterol, these compounds make up the bulk of (neutral fecal sterols. 

Degradation of choles terol Mechanisms of choles terol disposal DEGRADATION OF CHOLESTEROL (p. 222) The ring structure of cholesterol can not be metabolized in humans. Cholesterol can be elim inated from the body either by conversion to bile salts or by secretion into the bile. Intestinal bacteria can reduce cholesterol to coprostanol and cholestanol, which together with cholesterol make up the bulk of neutral fecal sterols. 

Figure D1.6.6 latroscan TLC-FID chromatograms of (A) a lipid fraction enriched with neutral lipids isolated from cod flesh and stored in ice (B) neutral lipids spiked with authentic 1 -0-palmityl-glyceryl ether dipalmitate (GE), coinciding in position with authentic highly unsaturated acids such as 22 6n-3 (C) hydrogenated neutral lipids spiked with GE. The solvent system was 97 3 1 (v/v/v) hexane/diethyl ether/formic acid for 40 min. Abbreviations O, origin SF, solvent front FFA, free fatty acid PL, phospholipids SE, steryl ester ST, free sterol TG, triglyceride. Reproduced from Ohshima et al. (1987) with permission from AOCS Press.

The lipids of the external tear film namely, neutral oils, phospholipids, sterol esters, various waxes, and other lipids are requisite for regulation of evaporation. These lipids are produced by the Meibomiam and other glands. The ability of the glandular structures situated in the conjunctiva and the lid propia to produce the tear film may be impaired due to exposure to pollutants and irritants or as a result of age-related dysfunction. 

Jenkins, K.J. and Atwal, A.S. 1994. Effects of dietary saponins on fecal bile acids and neutral sterols, and availability of vitamins A and E in the chick. J. Nutr. Biochem. 5, 134-137. 

Gas chromatograph (GC) with correct column and configuration to detect neutral sterols... 

The mass of bile acids per 0.5 g feces = mass in 1 ml methanol x dpm 14C-taurocholate added/dpm recovered in 1 ml methanol. As for neutral sterols, the total excreted per 3 days is calculated from the total fecal mass collected and data are reported as mass (or moles) excreted per day per gram body weight. 

Total neutral sterol excretion by mice (male, C57BL/6) fed a chow diet is typically 80 15 nmol per day per gram body weight and bile acid excretion is 50 10 nmol per day per g body weight. On semi-purified diets, which are low in fiber and reduce gut motility, neutral sterol excretion is reduced as much as 50% and bile acid excretion can be reduced as much as 5-fold or more (unpublished results). Thus, the diet used in a given study must be chosen carefully. Since human diets have a tendency to be low in fiber, a chow diet may partially mask potential treatment benefits because sterol excretion is already quite high. 

GC data should be evaluated carefully. The main sterols of interest are cholesterol and lathosterol, the latter being a late-stage intermediate in cholesterol synthesis. Coprostanol is formed by the action of colonic bacteria on cholesterol and may vary considerably between mice. Peaks for coprostanol and other minor animal-derived sterols appear very close to, and may overlap with, that of cholesterol. Lathosterol is usually resolved between the cholesterol and the first phytosterol peak. Neutral sterol excretion should be reported as the sum of cholesterol, its precursors, and its derivatives. Evaluation excluding precursors is also appropriate. 

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