Plant sterols structure

The practical development of plant sterol drugs as cholesterol-lowering agents will depend both on structural features of the sterols themselves and on the form of the administered agent. For example, the unsaturated sterol sitosterol is poorly absorbed in the human intestine, whereas sitostanol, the saturated analog, is almost totally unabsorbable. In addition, there is evidence that plant sterols administered in a soluble, micellar form (see page 261 for a description of micelles) are more effective in blocking cholesterol absorption than plant sterols administered in a solid, crystalline form. 

The structurally simplest steroids, the aromatic A ring estrogens, have ironically proven most difficultly accessible because this aromatic ring is not found in any of the plant sterols available in commercial quantities. The main task of partial synthesis from naturally occurring material thus becomes... 

Herbal products used for the relief of menopausal symptoms are purported to act by a number of different mechanisms. Phytoestrogens are plant sterols that are structurally similar to human and animal estrogen. Soy protein is a common source of phytoestrogens and can be found in products such as tofu, soy milk, soy flour, and tempeh. Various studies have demonstrated conflicting results as to the efficacy of... 

The fourth isolated and identified compound from Palmer amaranth is chondri 11 asterol (5a-stigmasta-7,22-dien-30-ol), a sterol closely related structurally to the major plant sterols, stigmasterol and sitosterol. This compound, isolated as the free sterol, is not soluble in water or 0.1% DMS0, and germination bioassays required pretreatment of the test seed with a 0.1 mM solution of the sterol in DCM. 

Some of the more interesting examples of nutrient - nonnutrient interactions include some of the compounds that are analogs of nutrients. Mattson et al (16) found that cholesterol absorption decreased when various plant sterols were added to the diets of rats. A number of plant amino acids are not ordinarily required by herbivores and are usually not incorporated into proteins. For example, the structure of 3,4-dihydroxyphenyl-alanlne (L-dopa) is similar to that of tyrosine. L-Dopa may play a role in favism (17), as well as having a number of other deleterious effects (18, 19, 20). Essential amino acids themselves can be deleterious if they are ingested in excessive quantities or if they are not in balance with other amino acids... 

Plant Sterols. Sterols have been identified in almost all types of living organisms and can be isolated, in varying quantities, from many different plants. Similar to cholesterol, plant sterols have a structural and functional role in biological systems and serve as intermediates in the biosynthesis of an assortment of biologically active steroids. 

For cholesterol absorption, one can take advantage of the fact that plant sterols (phytosterols) are poorly absorbed by mice and humans despite close structural similarity to cholesterol. Beta sitosterol, for example, differs from cholesterol only by the addition of an ethyl group to carbon 24 of the sterol side chain (see Fig. 10.1). This reduces absorption to 6% (34, 35) as compared to 60-80% for cholesterol. Sitostanol, which has a saturated C5-C6 bond in addition to the ethyl group, is only absorbed at 3% (34, 35) and is widely used as a non-absorbed sterol marker (Fig. 10.1). 

Figure 10.2 Chemical structures of common plant sterols and cholesterol.

Just as all animal tissues and foods contain cholesterol, which is needed for life itself, all plants have phytosterols, plant sterols. The molecular structures of cholesterol and phytosterols are virtually identical (see the illustration). Because they are so similar, the human body cannot tell the difference. 

The chemical structure of phytosterols is similar to that of cholesterol so that these compounds may be involved in oxidative reactions. Przybylski and Eskin (42) found some oxidation products formed from plant sterols during storage of fried food products. Similar oxidation products were found in soybean oil and wheat flour (43). In light of health concerns associated with cholesterol oxidation products, potential health risks of phytosterol oxidation products are now receiving serious attention. 

While many diets call for reduced intake levels of cholesterol, the plant sterols such as stigmasterol, which are very similar in structure to cholesterol, are not restricted. One of the reasons for the lack of strictures on plant sterols is ... 

Sitosterol. Sitosterol is a plant sterol, who.se structure is identical with that of cholesterol, except for the sub.stitutcd ethyl group on C-24 nf its side chain. Although the mechanism of its hypolipidemic effect is not clearly understood, it is suspected that the drug inhibits the absorption of dietary cholesterol from the gastrointestinal iraci. Sitosterols are absorbed poorly from the mucosal lining and appear to compete with cholesterol fnr absorption sites in the intestine. 

Phytosterols are a group of plant chemicals called steroid alcohols (sterols), indicating that they have chemical structures like steroids that dissolve in lipid layers as easily as alcohol does. In the plant, sterols serve as a vehicle for communication between cells and for supporting anatomical structure. 

These plant sterols have similar chemical structures to cholesterol (Figure 6.6) and the capacity to lower plasma cholesterol and LDL cholesterol. The higher the dietary intake of plant sterols from the diet, the lower the serum cholesterol level. 

Practically all plant steroid molecules are sterols. The function of plant sterols is still relatively unclear. They undoubtedly play an important role in membrane structure and function. Certain sterol derivatives, such as the cardiac glycosides, are known to protect plants that produce them from predators. Most plant sterols... 

Kraft-mill effluent) contain various plant sterols, primarily P-sitosterol (e.85%) and stigmasterol (c.3%) (see Fig. 2.22 for structures), which have oestrogenic activity (they are known to cause masculinization in fish),... 

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