Plant sterols: biosynthesis, biological function and their importance to human nutrition

Abstract

Plant sterols are an essential component of the membranes of all eukaryotic organisms. They are either synthesised de novo or taken up from the environment. Their function appears to be to control membrane¯uidity and permeability, although some plant sterols have a speci®c function in signal transduction. The phytosterols are products of the isoprenoid pathway. The dedicated pathway to sterol synthesis in photosynthetic plants occurs at the squalene stage through the activity of squalene synthetase. Although the activity of 3-hydroxymethyl-3-glutaryl coenzyme A (HGMR) is rate-limiting in the synthesis of cholesterol, this does not appear to be the case with the plant sterols. Up-regulation of HGMR appears to increase the biosynthesis of cycloartenol but not the D 5-sterols. A decline in sterol synthesis is associated with a suppression of squalene synthetase activity, which is probably a critical point in controlling carbon¯ow and end-product formation. The major post-squalene biosynthetic pathway is regulated by critical rate-limiting steps such as the methylation of cycloartenol into cycloeucalenol. Little is known about the factors controlling the biosynthesis of the end-point sterol esters or stanols. The commonly consumed plant sterols are sitosterol, stigmasterol and campesterol which are predominantly supplied by vegetable oils. The oils are a rich source of the steryl esters. Less important sources of sterols are cereals, nuts and vegetables. The nutritional interest derives from the fact that the sterols have a similar structure to cholesterol, and have the capacity to lower plasma cholesterol and LDL cholesterol. Since the morbidity and mortality from cardiovascular disease have been dramatically reduced using cholesterol-lowering drugs (statins), the interest in plant sterols lies in their potential to act as a natural preventive dietary product. Stanols (saturated at C-5) occur in low amounts in the diet and are equally effective in lowering plasma cholesterol and do not cause an increase in plasma levels, unlike the sterols which can be detected in plasma.

Dynamic viscosity mapping of the oxidation of squalene aerosol particles

“…Squalene is a 30-carbon naturally occurring triterpene ( Figure S1, ESI) which herein we use as a model organic aerosol. It has a vital role in the synthesis of sterols in animals and plants 23,24 and is also produced by human skin 25,26 and found as an ingredient in many household oils, used for cooking and frying 27 . Due to skin shedding (desquamation), squalene containing skin flakes are likely a major constituent of indoor dust and hence aerosol.…”

Influence of production system, age an sex on carcass parameters and some biochemical meat quality characteristics of reindeer (Rangifer tarandus tarandus L.)

“…It is known that minor components of the diet, such as plant sterols or phenolic compounds, can affect consumer health (Parr & Bolwell, 2000;Piironen et al, 2000;Ostlund et al, 2002), and thus we also aimed to identify an unknown substance found in the neutral lipid (NL) fraction of reindeer meat during fatty acid analyses (Sampels, 2005).…”

Effects of elderberry juice on fasting and postprandial serum lipids and low-density lipoprotein oxidation in healthy volunteers: a randomized, double-blind, placebo-controlled study

“…Such a risk estimation might be further influenced by the presence of postprandial hyperlipidemia (Ebenbichler et al, 1995). Dietary products with a lipid-lowering and/or antioxidative capacity may be important in the reduction of risk of coronary heart disease (Hollman et al, 1996;Piironen et al, 2000). Flavonoids, which have been shown to exert antioxidant actions, have been extensively studied.…”