Phytosterols, phytostanols, and their conjugates in foods: structural diversity, quantitative analysis, and health-promoting uses

Nonalcoholic steatohepatitis (NASH) is considered the progressive form of nonalcoholic fatty liver disease (NAFLD) and is characterized by liver steatosis, inflammation, hepatocellular injury and different degrees of fibrosis. A central issue in this field relates to the identification of those factors that trigger inflammation, thus fuelling the transition from nonalcoholic fatty liver to NASH. These triggers of liver inflammation might have their origins outside the liver (such as in adipose tissue or the gut) as well as inside the organ (for instance, lipotoxicity, innate immune responses, cell death pathways, mitochondrial dysfunction and endoplasmic reticulum stress), both of which contribute to NASH development. In this Review, we summarize the currently available information on the key upstream triggers of inflammation in NASH. We further delineate the mechanisms by which liver inflammation is resolved and the implications of a defective pro-resolution process. A better knowledge of these mechanisms should help to design targeted therapies able to halt or reverse disease progression.

Triggering and resolution of inflammation in NASH.

In recent years, the impressive development of molecular genetics tools, the sequencing of the Arabidopsis thaliana genome, the availability of DNA or transposon tagged mutants, and the multiple possibilities offered by stable transformation with DNA in sense and antisense orientation have enabled the application of a strategy of gain or loss of function to study the sterol biosynthesis pathway. Here we describe the results obtained with these techniques. The results essentially confirm data obtained previously with sterol biosynthesis inhibitors (SBIs) and enable the precise dissection of biosynthetic pathways. We discuss the advantages and disadvantages of molecular genetics techniques as applied to sterol metabolism. The greater selectivity of these techniques constitutes an invaluable advantage and has led to the discovery of a role for sterols in plant development.

Biosynthesis and accumulation of sterols

Sterol glucosides from Prunella vulgaris

Chromatographic analysis of plant sterols in foods and vegetable oils

Sterols of the Cucurbitaceae

The major sterols of the seeds ofBenincasa cerifera, Cucumis sativus, Cucurbita maxima, C. pepo andTrichosanthes japonica and of the mature plant tissues (leaves and stems) ofCitrullus battich, Cucumis sativus andGynostemma pentaphyllum of the family Cucurbitaceae were 24-ethyl-Δ(7)-sterols which were accompanied by small amounts of saturated and Δ(5)-and Δ(8)-sterols. The 24-ethyl-Δ(7,22),Δ(7,25(27)) and Δ(7,22,25(27))-sterols constituted the predominant sterols for the seed materials, whereas the 24-ethyl-Δ(7) and Δ(7,22)-sterols were the major ones for the mature plant tissues. The configurations of C-24 of the alkylsterols were examined by high resolution(1)H NMR and(13)C NMR spectroscopy. Most of the 24-methyl- and 24-ethylsterols examined which lack a Δ(25(27))-bond (i.e., 24-methyl-, 24-methyl-Δ(22)-, 24-ethyl- and 24-ethyl-Δ(22) sterols) were shown to occur as the C-24 epimeric mixtures in which the 24α-epimers predominated in most cases. The 24-ethylsterols which possess a Δ(25(27)) (i.e., 24-ethyl-Δ(25(27))-and 24-ethyl-Δ(7,22,25(27))-sterols) were, on the other hand, composed of only 24β-epimers. The Δ(8)-sterols identified and characterized were four 24-ethyl-sterols: 24α-and 24β-ethyl-5α-cholesta-8,22-dien-3β-ol, 24β-ethyl-5α-cholesta-8,25(27)-dien-3β-ol and 24β-ethyl-5α-cholesta-8,22,25(27)-trien-3β-ol. This seems to be the first case of the detection of Δ(8)-sterols lacking a 4-methyl group in higher plants, and among the four Δ(8)-sterols the latter two are considered to be new sterols. The probable biogenetic role of the Δ(8)-sterols and the possible biosynthetic pathways leading to the 24α- and 24β-alkylsterols in Cucurbitaceae are discussed.

Sterols of cucurbitaceae: The configurations at C-24 of 24-Alkyl-Δ5-,Δ7- and Δ8-sterols

Forty weanling male Sprague rats were randomly assigned to two dietary treatments, copper-deficient (9.0 mumol/kg diet) and copper-adequate (102.2 mumol/kg diet). After 7 wk of treatment, reductions in body weight and hematocrit, and an increase in relative heart weight, were observed in the copper-deficient rats. Plasma VLDL, LDL and HDL were isolated by ultracentrifugation and Sepharose column chromatography. In copper-deficient rats, the percent composition of protein was reduced by one-half, and triglyceride was increased by 1.6- and 2.7-fold in LDL and VLDL fractions, respectively. In VLDL, the marked increase in triglyceride was compensated by at least a 75% decrease in percent composition of cholesterol and phospholipids as a result of copper deficiency. No treatment difference in percent composition of HDL components was detected. When the data were expressed as the amount present in the vascular pool corrected for body weight, the plasma pool size of protein, triglyceride, phospholipid and cholesterol of LDL and HDL were increased twofold or more by copper deficiency. In VLDL, a sixfold increase in triglyceride, a 36% reduction in cholesterol, and no change in phospholipid and protein pool size were observed in copper-deficient rats. These data suggest that copper deficiency may enlarge the particle size but not particle number of VLDL, increase both particle size and number of LDL, and elevate particle number but not size of HDL.

Copper deficiency alters plasma pool size, percent composition and concentration of lipoprotein components in rats.

This study examined the influence of dietary copper status on the in vivo hepatic fatty acid synthesis and the incorporation of nascent fatty acids into various hepatic lipid classes. Fifty weanling male Sprague-Dawley rats were assigned to two dietary treatments, copper deficient (5.4 nmol/g of diet) and copper adequate (102 nmol/g of diet). After 7 weeks of treatment, rats were injected with 0.111 MBq of [1-14C] acetate (1.85 GBq/mM)/100 g body wt through the femoral vein. Five rats from each treatment were sacrificed at 3, 6, 9, 12, and 24 min after injection. Radioactivities of nascent fatty acid samples were used to determine relative rates of fatty acid synthesis and their assembly into triacylglycerols and phospholipids. Linear increases were observed up to 12 min after injection for total hepatic fatty acid synthesis and their assembly into triacylglycerols and phospholipids for both treatments. In addition, 46% and 30% of total fatty acid synthesized were assembled into triacylglycerols and phospholipids, respectively, for both groups. Furthermore, hepatic fatty acid synthesis and assembly into triacylglycerols and phospholipids were enhanced more than 2-fold by copper deficiency when the data were expressed as per liver per 100 g body weight.

Copper deficiency increases in vivo hepatic synthesis of fatty acids, triacylglycerols, and phospholipids in rats.

Compositions of the triterpene alcohol fractions of the unsaponifiable lipids obtained from 28 seed and mature plant [aerial parts (leaves and stems), pericarp of the fruits, and roots] of 13 genera of the family Cucurbitaceae were determined by gas liquid chromatography (GLC) on an OV-17 glass capillary column. Among the 14 tetracyclic and pentacyclic triterpene alcohols identified, isomultiflorenol was found to be the major component for most of the seed materials. The abundance of this triterpene suggests that it may be a taxonomical marker of the seeds of Cucurbitaceae since only a few higher plants are known to contain isomultiflorenol. The mature plant materials of the Cucurbitaceae, on the other hand, were shown to contain either one or some of the common triterpene alcohols such asα- andβ-amyrins, cycloartenol and 24-methylenecycloartanol as the major triterpene constituents.

Fumiko U. Rosenstein

Papers

Sterols of the Cucurbitaceae

Sterols of cucurbitaceae: The configurations at C-24 of 24-Alkyl-Δ5-,Δ7- and Δ8-sterols

Copper deficiency alters plasma pool size, percent composition and concentration of lipoprotein components in rats.

Copper deficiency increases in vivo hepatic synthesis of fatty acids, triacylglycerols, and phospholipids in rats.

Compositions of triterpene alcohols of seeds and mature plants of family cucurbitaceae