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

The effect of conjugated linoleic acid (CLA) on the relation between struct ure and function of membranes is described in this paper. Electron spin res onance (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-s tearoyl-2-(9cis,11trans-octadecadienoyl)-phosphorylcholine (SCLAPC) was inc orporated into soy plant phosphatidylcholine (soy PC) or egg yolk PC (EYPC) bilayers. The use of spin labels attached to different carbons along the f atty acid chain makes it possible to carry out structural and oximetric det erminations 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 h ydrocarbon chains at the C10 and C12 positions (in the region of the conjug ated double bonds), and increased the rate of oxygen depletion from the aqu eous medium. Similar results were not obtained by incorporating 5 mol% of 1 -stearoyl-2-linoleoyl-PC (SLPC). In our model system, free-radical generati on 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 effec t of 5 mol% SCLAPC in soy PC was significantly larger than 5 mol% SLPC in s oy PC; the response patterns with soy PC and EYPC were similar. Furthermore , 5 mol% SCLAPC in 1-palmitoyl-2-linoleoyl-PC showed similar oxygen consump tion to that observed with 5 mol% SCLAPC in EYPC. On the other hand, 5 mol% SCLAPC in synthetic PC membranes containing saturated or monounsaturated f atty acids showed low oxygen depletion rates. The perturbation of membrane structure and the increase of the relative oxy; gen diffusion-concentration products provided a potential mechanism by which CLA incorporated into mem brane lipids could affect oxidative stress.