Effects of conjugated linoleic acid on oxygen diffusion‐concentration product and depletion in membranes by using electron spin resonance spin‐label oximetry

Abstract

The effect of conjugated linoleic acid (CLA) on the relation between structure and function of membranes is described in this paper. Electron spin resonance (ESR) spin-label oximetry was used in the present study to evaluate if oxygen transport and oxygen depletion were affected by incorporation of CLA instead of linoleic acid into membrane phospholipids. Specifically, 1-stearoyl-2-(9cis, 11 trans-octadecadienoyl)-phosphorylcholine (SCLAPC) was incorporated into soy plant phosphatidylcholine (soy PC) or egg yolk PC (EYPC) bilayers. The use of spin labels attached to different carbons along the fatty acid chain makes it possible to carry out structural and oximetric determinations with the same test sample. For example, the incorporation of 5 mol% SCLAPC increased the oxygen diffusion-concentration product in soy PC or EYPC liposomes at 37 degrees C, slightly decreased the ordering of the hydrocarbon chains at the C10 and C12 positions (in the region of the conjugated double bonds), and increased the rate of oxygen depletion from the aqueous medium. Similar results were not obtained by incorporating 5 mol% of 1-stearoyl-2-linoleoyl-PC (SLPC). In our model system, free-radical generation was initiated by extended incubation of the liposomes, by induction by 2,2'-azobis(2-amidinopropane)hydrochloride, or by ultraviolet irradiation of H2O2. The rate of consumption of molecular oxygen was studied by monitoring the oxygen concentration in the aqueous phases of the liposomes. The effect of 5 mol% SCLAPC in soy PC was significantly larger than 5 mol% SLPC in soy PC; the response patterns with soy PC and EYPC were similar. Furthermore, 5 mol% SCLAPC in 1-palmitoyl-2-linoleoyl-PC showed similar oxygen consumption to that observed with 5 mol% SCLAPC in EYPC. On the other hand, 5 mol% SCLAPC in synthetic PC membranes containing saturated or monounsaturated fatty acids showed low oxygen depletion rates. The perturbation of membrane structure and the increase of the relative oxygen diffusion-concentration products provided a potential mechanism by which CLA incorporated into membrane lipids could affect oxidative stress.

Differential effects of conjugated linoleic acid isomers on macrophage glycerophospholipid metabolism

“…2A ) using the abovedescribed model for CCT activation by membrane curvature stress. It is also supported by data from Yin et al showing that incorporation of c9,t11 -CLA into phospholipids substantially alters physical membrane properties and function ( 36,37 ). However, another possible explanation for the enhanced PL synthesis rates might be that c9,t11 -CLA treatment enhances PC and PE synthesis by increasing the diacylglycerol (DAG) content necessary for the last step of the Kennedy pathway (supplementary Fig.…”

Application of electron spin resonance (ESR) spectrometry in nutraceutical and food research

“…The physical principle and its application of measuring oxygen in vivo have been well reviewed by Swartz and Clarkson [38]. Recently, ESR spin-label oximetry method has been used in nutraceutical and food researches such as in vitro determination of membrane fluidity [36,37], membrane structure [5], phase transition temperature of membrane lipid bi-layer [37], and lipid peroxidation and oxygen diffusion -concentration products in liposomes and membranes [5,37,39].…”

“…This spectral change can be quantified to reflect the oxygen concentration in the closed chamber, which is the principle behind ESR spin-label oximetry measurements [36,40]. The quantification using the calibration curves relating the K parameter, which could be obtained from the ESR spectrum, to oxygen concentration has been previously described in details [5,39,40]. The results from this study demonstrated that oxygen consumption determined using the ESR spin-label oximetry method was correlated with the progress of lipid peroxidation examined by measuring TBARS.…”

“…It needs to be pointed out that CTPO is a water-soluble spin label and measures the oxygen concentration in the aqueous phase to reflect lipid peroxidation and oxygen diffusion -concentration products in the lipid bilayer of membranes. Earlier in 1999, effects of c9,t11-CLA on oxygen diffusion -concentration products and depletion in liposome suspensions containing different PCs were also investigated and compared with LA by ESR oximetry analysis using CTPO as the spin label [5]. ESR spin-label oximetry closed-chamber method may also be applied to study lipid peroxidation or oxygen diffusionconcentration product in other testing systems such as in human LDL and food systems, as well as cellular oxygen uptake [41].…”

“…The information of motion or orientation of biological molecules may also be obtained from the ESR spectra of the spin label. Moreover, ESR spin-label oximetry can be used to investigate local oxygen consumption, oxygen diffusion -concentration products, oxygen transport and depletion, and structure and dynamic properties in membranes and proteins [5,6]. It is well noted that the quantitative ESR measurement may be achieved by: (i) double integration of the ESR peaks, (ii) determining the ESR signal intensity, and (iii) measuring the line width of the peak [5,7,8].…”