Polyunsaturated Molecular Species Research Articles

Intramembraneous hydrogenation of mitochondrial lipids reduces the substrate availability, but not the enzyme activity of endogenous phospholipase A. The role of polyunsaturated phospholipid species

(1) Isolated rat liver mitochondria were subjected to catalytic hydrogenation using a water-soluble Pd complex and molecular H 2. This treatment resulted in a reduction of double bonds on phospholipid acyl chains as judged by gas chromatography of fatty acid methyl esters and HPLC of dinitrobenzoyldiacylglycerols. (2) After hydrogenation, mitochondria lost their ability to hydrolyze endogenous phospholipids in alkaline, Ca 2+ containing medium, while phospholipase A 2 retained full activity against exogenous substrates, regardless of whether those substrates were hydrogenated or not. (3) Inhibition by hydrogenation of endogenous phospholipid hydrolysis correlated with the loss of polyunsaturated fatty acyls, rather than with changes of the bulk membrane fluidity as measured by ESR and fluorescence studies. (4) These data suggest that the unsaturation of mitochondrial membrane lipids might be important for regulation of phospholipid breakdown by endogenous phospholipases. In particular, polyunsaturated molecular species seem to be involved in making phospholipids accessible to phospholipase A-mediated hydrolysis.

Degradation of phospholipid molecular species during experimental cerebral ischemia in rats.

Previous investigators have shown that free fatty acids that accumulate during ischemia are an indicator of evolution in ischemic brain damage. Our study describes the temporal relations between free fatty acid accumulation and degradation of phospholipid molecular species after cerebral ischemia. Using the four-vessel occlusion model of adult Wistar rats, we analyzed quantitatively the cerebral phospholipid molecular species of diacyl phosphatidylcholine and diacyl phosphatidylethanolamine and released free fatty acids during ischemia. Total diacyl phosphatidylcholine molecular species decreased gradually but did not show any significant difference even at 60 minutes. By contrast, total diacyl phosphatidylethanolamine abruptly decreased after 5 minutes and continued to decrease significantly thereafter. Polyunsaturated molecular species showed a higher ratio of degradation than saturated and monounsaturated molecular species of either phosphatidylcholine or phosphatidylethanolamine. Total free fatty acid accumulated according to the time elapsed, and statistical significance was obtained after 10 minutes. Free arachidonic and docosahexaenoic acids were attributed to these significant accumulations at 10, 15, and 30 minutes. At 60 minutes, individual free fatty acids increased nonspecifically. Free fatty acids, which are hydrolyzed from phospholipid classes, are known to be further metabolized to bioactive substances such as prostaglandins and leukotrienes. Rapid degradation of phospholipid molecular species, especially of diacyl polyunsaturated molecular species, could be an important finding to membrane perturbation. Effective prevention of these changes might enhance tolerance to ischemic brain damage.

Distribution of phospholipid molecular species containing arachidonic acid and cholesterol in V79-UF cells

V79-UF cells were isolated from Chinese hamster V79 cells as a cell line that requires exogenous unsaturated fatty acids for growth. V79-UF cells incorporated arachidonic acid into phospholipids. The molecular species of diacyl phosphatidylcholine and phosphatidylethanolamine containing arachidonic acid comprised 61.4 and 70.5% of the total phospholipid molecular species in total membranes and 58.1 and 64.7% in plasma membrane, respectively. Polyunsaturated molecular species were distributed in a higher amount in the intracellular membranes than in the plasma membrane. No significant difference was seen in the diffusion coefficient between the plasma membranes from cells supplemented with oleic and arachidonic acids in spite of a distinct difference in the degree of unsaturation between the molecular species of these plasma membranes. The amount of cholesterol in the plasma membrane was higher in the cells grown in the presence of arachidonic acid than in those grown in the presence of oleic acid.

Adaptation of biological membranes to temperature: molecular species compositions of phosphatidylcholine and phosphatidylethanolamine in mitochondrial and microsomal membranes of liver from thermally-acclimated rainbow trout

Molecular species profiles were determined for both phosphatidylcholine (PC) and phosphatidylethanolamine (PE) of mitochondrial and microsomal membrane fractions from liver tissue of thermally-acclimated rainbow trout,Salmo gairdneri. The predominant molecular species of PC were 16:0/22:6, 16:0/18:1, 16:0/20:3 and 16:0/22:5, whereas predominant molecular species of PE were 18:1/20:4, 14:0/16:0, 18:0/22:6 and 18:1/22:6. PE possessed short chain saturates (primarily 14:0/16:0) and monoenes (primarily 14:0/16:1) not present in PC and larger proportions of polyunsaturated (18:0/22:6, 18:0/22:5 and 18:1/22:6. and diunsaturated molecular species than PC. Differences between membrane fractions were most evident in warm (20°C)-acclimated trout. Mitochondria contained higher proportions of long-chain, polyunsaturated molecular species of PE, but less of the corresponding species of PC than other membrane fractions. Rankings based on unsaturation index were accordingly: mitochondria ≥heavy microsomes>light microsomes for PE, but heavy microsomes>light microsomes>-mitochondria for PC. Mitochondria were notable for high proportions of diunsaturated molecular species of both phosphatides. Growth at cold temperatures (5°C) was generally associated with a replacement of shorter chain mono- and dienoic molecular species (16:0/18:1, 16:1/18:1, 14:0/16:2 and 18:1/18:1 in the case of PC and 14:0/16:1, 14:0/16:2 and 16:1/18:1 for PE), and occasionally saturates, with long-chain, polyunsaturated molecular species (for PC, C36–38: 16:0/22:6, 16:1/22:6, 16:0/20:3 and 16:0/20:5; for PE, C38–40: 18:1/20:4, 16:1/22:6, 18:0/20:5, 18:2/20:4, 18:0/22:5 and 18:0/22:6). However, compositions of mitochondrial PE and PC from heavy microsomes were not significantly influenced by acclimation temperature. The role of phospholipase A2, in addition to other metabolic processes, in mediating these changes is discussed.

Uptake and metabolism of free fatty acids by the Morris 7777 hepatoma and host rat liver.

The relative capacity of Morris 7777 hepatomas and livers of tumor-bearing rats to take up and subsequently metabolize intravenously injected radiolabeled free fatty acids was investigated. The objective was to determine differences in lipid metabolism which may affect the lipid composition previously observed in this tumor. Both tissues demonstrated comparable selectivity in the uptake of palmitate, linoleate and arachidonate from blood, although the hepatoma took up one-tenth as much free fatty acid per g wet wt as liver. A much greater percentage of fatty acid taken up by the hepatoma was converted to aqueous soluble radioactivity, perhaps the result of oxidation. In the hepatoma, palmitate was incorporated into phospholipid molecular species in a pattern similar to that observed for diglyceride, which suggested that phospholipid synthesis occurred predominantly de novo. On the other hand, in liver, a large percentage of palmitate was incorporated into polyunsaturated phospholipid molecular species that were not present in the diglyceride pool, which suggested significant incorporation by the acylation of monoacyl phosphoglycerides. These studies indicate that the specificity for the uptake of fatty acids was not different in the two tissues; however, the subsequent metabolic processes are markedly different.