STEROL 1: Sterols Symposium
Chair(s): R. Moreau, USDA, ARS, ERRC, USA; and P. Jones, University of Manitoba, Canada
Evaluation of Bioactivities of Steryl Ferulates from Different Grain Sources. Laura Nyström, ETH Zurich, Zurich, Switzerland
Steryl ferulates are esters of ferulic acid and plant sterols, which are abundantly found in cereal grain bran layers. They decrease cholesterol levels like other plant sterol conjugates, but also provide antioxidant activity via the phenolic hydroxyl group of the ferulic acid. The capability to prevent oxidation brings about several additional health benefits including anti-inflammatory, anti-carcinogenic, anti-diabetic and neuroprotective effects. The antioxidant activity and the metabolism of steryl ferulates in the digestive system are to some extent dependent on the sterol composition of steryl ferulates, and this composition is known to depend on the grain source. We have applied an in vitro model system to evaluate the bioaccessibility of steryl ferulates from wheat, rice and corn and their products, and have demonstrated that a part of the steryl ferulates are digested in the gastrointestinal tract (1-63% depending on the source), but a negligible amount (<1.5%) is released from the grain matrix for absorption. This suggests that grain sources are not necessarily equal as sources of steryl ferulate related health benefits. This paper will evaluate the combined effects of sterol composition and steryl ferulate content in grains, and link this information to the known health benefits of different steryl ferulate compounds.
Methods for the Analysis and Removal of Steryl Glucosides from Edible Oil and from Biodiesel. R.A. Moreau, M.J. Haas, Eastern Regional Research Center, ARS, USDA, Wyndmoor, PA, USA
Steryl glucosides and acylated steryl glucosides are conjugated forms of phytosterols that are present in low levels in almost all plant cells and tissues. They are commonly associated with biological membranes in plant cells, especially the plasma membrane. However, when plant oils are extracted with solvents or via pressing, these steryl compounds can become soluble at low levels in the liquid triacylglycerol matrix. When plant oils are converted to methyl or ethyl esters to make biodiesel, most of the acylated steryl glucosides are converted to additional steryl glucosides. Steryl glucosides in biodiesel can cause problematic precipitates that foul pipes and other equipment during storage and transit and in diesel engines. This paper will review recent methods to quantitatively analyze steryl glucosides in edible plant oils and in biodiesel. It will also describe several strategies to remove problematic steryl glucosides from biodiesel.
RP-HPLC/APCI-MS Analysis of Non-Polar Oligomers Formed During Thermo-Oxidation of β-Sitosterol. E. Sosinska, R. Przybylski, Department of Chemistry and Biochemistry, University of Lethbridge, Lethbridge, AB, Canada
Sterol oligomers are formed during thermo-oxidation of phytosterols at elevated temperatures. The aim of this work was to perform analysis of non-polar oligomers formed during β-sitosterol oxidation at 180°C in the presence of oxygen. Non-polar dimer, trimer and tetramer fractions were isolated by SEC after chromatographic pre-cleaning using silica gel. Isolated factions were separated on RP-HPLC and analyzed by APCI-MS. All oligomers produced spectra with monomer ion at 397.3825 Da identified as dehydrated sitosterol. Low intensity ions with higher masses, which are characteristics for these groups of compounds, were also observed. Dimers produced mass spectra with unique pattern of ions in the mass range of 750-950 Da, representing variation of dimers. By ionization of trimers the characteristic ions at 1150-1350 Da were observed followed by monomer ions with mass range 380-430 Da. Fragments characteristics for dimers with mass range 750-950 Da were also present. This shows that under APCI conditions trimers undergo fragmentation to dimer and monomer units. Similarly, tetramers spectra contained ions in m/z range 1500-1750 Da characteristic for these compounds, followed by trimer, dimer and monomer fragments. Utilizing high resolution mass spectrometry it was possible to elucidate structures of dimers, trimers and tetramers.
Design, Synthesis and Application of Biochemical Tools for the Study of Cholesterol Trafficking. K.M. Byrd, A. Chatterjee, O. Wiest, P. Helquist, University of Notre Dame, Notre Dame, IN, USA
Cholesterol is arguably one of the most important sterols in the human body. Though we know that cholesterol participates in many processes, the mechanisms of cholesterol's cellular distribution is are poorly understood. When cholesterol trafficking is disrupted, accumulation occurs, which leads to a number of diseases. The overall goal of this project is to design, synthesize and apply cholesterol-based molecular probes that would aid in the understanding of cholesterol trafficking disorders. One such probe is a novel fluorescent cholesterol mimic that would serve as a general tool to track cholesterol movement in live cells or identify cholesterol localization in fixed cells. The other probes are cholesterol-based dual-ligand molecular probes that consist of two cholesterol units are linked from head-to-toe. Our hypothesis behind this probe design is that these dual-ligand probes can be used to identify and isolate protein pairs that participate in the transfer of cholesterol. Initially, these probes will be studied in the context of Niemann-Pick type C (NPC) disease since the proteins that are involved in the transport of cholesterol have been well studied. Once we have proven that this probe design works, we can utilize these types of probes in studies of other lipid storage diseases.
Phytosterols Decrease Cholesterol Absorption by Molecular Interactions in the Intestinal Lumen. Andrew Brown, Nutrition and Obesity Research Center, The University of Alabama at Birmingham, Birmingham, AL, USA
Phytosterols are powerful nutraceuticals capable of significantly lowering blood cholesterol and therefore decreasing cardiovascular disease risk. The decrease in blood cholesterol is most strongly attributed to phytosterols inhibiting cholesterol absorption. Several mechanisms have been identified that implicate molecular interactions in the intestinal lumen as the means by which phytosterols inhibit cholesterol uptake, including phytosterol ester interactions with cholesterol esterase, and non-esterified phytosterols competing with cholesterol for solubilizing into mixed micelles. The specificity of cholesterol esterase for phytosterol esters depends both on the phytosterol and fatty acid moieties of the ester: unsaturated fatty acid esters are more rapidly hydrolyzed than saturated esters. In turn, the ability of phytosterols to disrupt cholesterol solubility in mixed micelles is dependent on the amount of non-esterified phytosterol present, whereas phytosterol esters themselves do not affect cholesterol solubility in micelles. These trends are further observed in a hamster model of human cholesterol metabolism, in which the extent of hydrolysis of phytosterol esters determines the decrease in cholesterol absorption. Additionally, intact phytosterol esters do not appear to alter the distribution of cholesterol between the oily and aqueous phases of intestinal contents. Taken together, the mechanisms by which phytosterols lower cholesterol absorption, and thereby decrease blood cholesterol, are dependent on the amount of non-esterified phytosterol in the intestinal lumen. Therefore, the efficacies of phytosterol esters are dependent on the ability of the esters to be hydrolyzed.
Efficacy of Plant Sterols WHen Provided in Capsule and Tablet Formats. P. Jones, S. AbuMweis, S.B. Myrie, University of Manitoba, Canada