The modulation of protein kinase C activity by membrane lipid bilayer structure.

Docosahexaenoic acid (DHA), a long-chain polyunsaturated omega 3 fatty acid, is tested to determine its mode of action as an anti-cancer agent. We demonstrate that DHA can increase the permeability of phospholipid vesicles, as monitored by vesicle swelling in isosmolar erythritol and leakage of sequestered carboxyfluorescein, and T27A tumor cells, as monitored by swelling in isosmolar erythritol and release of sequestered 51Cr. DHA was incorporated into lipid vesicles as either the free fatty acid or as 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine. DHA was incorporated into the tumor cells by fusion with vesicles made from the mixed-chain phosphatidylcholines. DHA is demonstrated here to be much more effective in increasing permeability than is oleic acid, the major unsaturated fatty acid normally found in tumor plasma membranes. It is proposed that incorporation of DHA makes tumor plasma membranes substantially more permeable, which may explain, in part, its anti-tumor properties.

Docosahexaenoic acid increases permeability of lipid vesicles and tumor cells.

A comparison of the effects of linolenic (18:3Ω3) and docosahexaenoic (22:6Ω3) acids on phospholipid bilayers

Home cage behavior of rhesus monkeys with long-term deficiency of omega-3 fatty acids

Long-chain polyunsaturated (n-3) fatty acids have been proposed to be involved in a wide variety of biological activities. In this study, mitochondrial docosahexaenoic acid (DHA) levels were increased by either dietary manipulation or by fusing the mitochondria with phospholipid vesicles made from 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (18:0/22:6 PC). The fused mitochondria exhibited a DHA-induced decrease in respiratory control index (RCI) and membrane potential and an increase in proton movement. The modified mitochondria also demonstrated an increase in fluidity (as detected by 1,6-diphenyl-1,3,5-hexatriene anisotropy) and changes in membrane structure detected by the fluorescence probes MC540 and pyrene decanoate. Proton movement in lipid vesicles made from mitochondrial lipid extracts was shown to be enhanced by incorporated 18:0/22:6 PC. Mitochondria were isolated from young (5-mon) and old (24-mon) mice which were maintained on either a diet rich in saturated fats (hydrogenated coconut oil) or rich in n−3 polyunsaturated fats (menhaden oil). Mitochondrial bioenergetic function was followed by RCI, state 3 respiration, ATP level, and phosphate uptake. In addition, lipid composition, phospholipid area/molecule, and extent of lipid peroxidation were also determined. Decreases in RCI for the menhaden oil diet-modified mitochondria paralleled those in which DHA levels were enhanced by fusion with phospholipid vesicles. RCI reductions are attributed to DHA-induced increases in H+ movement, producing diminished mitochondrial membrane potentials. One purpose of this project was to determine if the deleterious effects of aging on mitochondrial bioenergetic function could be reversed by addition of n−3 fatty acids. The experiments reported here indicate that incorporation of long-chain polyunsaturated n−3 fatty acids into mitochondrial membranes does not appear likely to reverse the effects of age on mitochondrial function.

C.L. Pryor

Papers

The effects of dietary (n-3) fatty acid supplementation on lipid dynamics and composition in rat lymphocytes and liver microsomes.