Submitted to: Analytical Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/6/2005
Publication Date: 9/15/2005
Citation: Chan, J.W., Motton, D., Rutledge, J.C., Keim, N.L., Huser, T. Raman spectroscopic analysis of biochemical changes in individual triglyceride-rich lipoproteins in the pre- and postprandial state.. Analytical Chemistry 77:5870-5876, 2005. Interpretive Summary: Lipoproteins circulating in the blood are responsible for the transport of triglycerides, fatty acids, and cholesterol to various tissues and organs throughout the body, and they may also play a role in the development of cardiovascular disease. Traditional methods of isolating and characterizing lipoproteins are of limited value because of extremely large naturally-occurring variations in lipoprotein size and chemical composition. Both size and composition are important factors in lipoprotein metabolism by the body, and new methods are needed to measure these characteristics simultaneously and also determine how these qualities change dynamically over time in response to eating and fasting. We developed a new method that allows the trapping of individual lipoproteins, followed by analysis of the trapped particle yielding information on its chemical structure. This new technique will enable future clinical studies that more accurately describe the characteristics of circulating lipoproteins and examine how these characteristics affect the transport and delivery of lipids throughout the body.
Technical Abstract: Individual triglyceride-rich lipoprotein (TGRL) particles derived from human volunteers are analyzed in a clinical study by confocal laser tweezers Raman micro-spectroscopy. This noninvasive, laser-based optical technique provides quantitative chemical information about the composition of individual nanometer-sized lipoproteins and their relative distribution in blood. The combination of Raman spectroscopy with optical trapping (“laser tweezers”) allows single TGRL to be immobilized and probed for extended periods of time while they are suspended in their native environment. We show that the Raman signature of optically trapped TGRL exhibits distinct peaks associated with molecular vibrations of fatty acids, protein, and lipids. A comparison of the spectra of pre- and postprandial TGRL reveals an increase in the degree of saturation of fatty acids and triacylglycerols in particles following consumption of mixed meals containing 30% total fat with polyunsaturated to saturated fat (P:S) ratios less than 0.20. In addition, a particle distribution analysis based on the degree of saturation allows us to extract additional information that bulk spectroscopy techniques cannot provide. Our analysis reveals that 3 hour postprandial particles exhibit lower saturation after consumption of a low glycemic load test meal compared to a high glycemic load test meal. We attribute this variation to the different P:S content found in each individual meal. The results of this study indicate that laser tweezers Raman spectroscopy is a powerful new technique that enables single, nanometer-size particle analysis even in a clinical environment.