M. Celadon

Age-related changes in linoleate and α-linolenate desaturation by rat liver microsomes

The first and rate limiting step in the conversion of linoleic and alpha-linolenic acid is catalyzed by the delta - 6 - desaturase (D6D) enzyme. Rat liver microsomal D6D activity decreases on linolenic acid at a rate proportional to the animal age; on alpha-linolenic acid the decrease in D6D activity begins only later than on linoleic acid. The fatty acid composition of liver microsomes determined by gas chromatographic analysis confirms the impairment of the enzymatic activity directly measured. Our data indicate a correlation between aging and D6D activity impairment. The loss of D6D activity may be a key factor in aging through altering the eicosanoid balance.

γ-Linolenic acid dietary supplementation can reverse the aging influence on rat liver microsome Δ6-desaturase activity

We have recently demonstrated that in rats the process of delta 6-desaturation of linoleic and alpha-linolenic acids slows with aging. One method of counteracting the effect of slowed desaturation of linoleic acid would be to provide the 6-desaturated metabolite, gamma-linolenic acid (18:3(n-6) GLA) directly. We have here investigated the 6-desaturation of both linoleic and alpha-linolenic acids in liver microsomes of young and old rats given GLA in the form of evening primrose oil (EPO) (B diet) in comparison to animals given soy bean oil alone (A diet), monitoring also the fatty acid composition of liver microsomes and relating this to the microviscosity of the membranes. In young rats the different experimental diets did not produce any difference in delta 6-desaturase (D6D) activity on either substrate suggesting that, when D6D activity is at or near its peak, the variations in diet tested are unable to influence it. In the old animals the rate of 6-desaturation of linoleic and particularly of alpha-linolenic acid was significantly greater in the B diet fed animals than in the A diet fed. The effects of the diets on the fatty acid composition of liver microsomes were consistent with the findings with regard to 6-desaturation. Administration of GLA partially corrected the abnormalities of n-6 essential fatty acid (EFA) metabolism by raising the concentration of 20:4(n-6) and other 6-desaturated EFAs. Furthermore, the GLA rich diet also increased the levels of dihomo-gamma-linolenic acid and of 6-desaturated n-3 EFAs in the liver microsomes. The microviscosity of microsomal membranes as indicated by DPH polarization was correlated with the unsaturation index of the same membranes. There was a very strong correlation between the two. In both young and old rats the B diet reduced the microviscosity and increased the unsaturation index. However, the effect was much greater in the old animals.

The effect of dietary polyenylphosphatidylcholine on microsomal delta-6-desaturase activity, fatty acid composition, and microviscosity in rat liver under oxidative stress

Abstract Polyenylphosphatidylcholine is a choline-glycerophospholipid containing up to 80% of total fatty acids as linoleic acid and may be an important factor in ensuring normal functioning of cell membranes. We tested the effect of a polyenylphosphatidylcholine-supplemented diet and compared it with both a trilinolein-supplemented and a laboratory chow diet on the fatty acid composition, microviscosity, and delta-6-desaturase activity of liver microsomal membranes of 12-month-old rats, in the absence or presence of oxidative stress induced by adriamycin. Polyenylphosphatidylcholine- and trilinolein-supplemented diets showed a similar increase in linoleic acid content and delta-6-desaturase activity in liver microsomes, indicating that low amounts of linoleic acid are able to partially restore the enzyme activity in old rats, independent of the source of linoleic acid. After adriamycin treatment, delta-6-desaturase activity increased in polyenylphosphatidylcholine and trilinolein groups, indicating a protective mechanism against the damage induced by polyunsaturated fatty acid peroxidation. The measurement of malondialdehyde production showed a protective effect on adriamycin-induced lipid peroxidation by polyenylphosphatidylcholine supplementation only. Microsomal membrane microviscosity did not change independent of diet and adriamycin treatment, suggesting that the response of microsomes to lipid peroxidation might be the maintenance of a given membrane order. Administration of polyenylphosphatidylcholine can prevent or minimize the liver damage induced by adriamycin treatment.

Kinetic analysis of delta-6-desaturation in liver microsomes: Influence of gamma-linoleic acid dietary supplementation to young and old rats

Previous experiments demonstrated the ability-of a gamma-linoleic acid (GLA) dietary supplementation (as evening primrose oil--EPO) to counteract the fall off in delta-6-desaturase (D6D) activity of linoleic acid and alpha-linoleic acid in aged rats. Kinetic parameters of the D6D were determined in order to test the possibility that there may be a significant influence of GLA administration to young and aged rats on the Vm and Km values for 6-desaturation of both the substrates. In young rats GLA supplementation did not affect the kinetic parameters, while in old rats it produced an increase of Vm values of 6-desaturation for both the substrates. Thus the administration of small doses of GLA to old rats might offer substantial protection against the loss of D6D affinity observed in aging, enhancing the capacity of the enzyme itself.

Influence of chronic ethanol consumption on the inositol phospholipid fatty acid composition of human peripheral blood lymphocytes

The breakdown of inositol phospholipids is an important event after the binding of antigens to the T-cell antigen receptor. In alcoholics, changes either in early or in late steps of lymphocyte activation have been documented, however no study on the role of phosphoinositide fatty acid composition in signal transduction has been reported. We have analyzed the fatty acid pattern of phosphatidylinositol, phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate from peripheral blood lymphocytes of alcoholic patients and healthy controls, in order to point out the possible compositional differences which could interfere with the signal transmission responsible for the early events in lymphocyte activation. In alcoholics, the arachidonic acid relative molar content in all the inositol phospholipid (PtdIns) fractions derived from lymphocytes was lower than in controls; all PtdIns classes appeared much more saturated than the corresponding fractions from control lymphocytes. The different fatty acid pattern of PtdIns in alcoholic patients could be responsible for an altered second messenger production, above all the production of a modified diacylglycerol which, in turn, could cause a different activation pattern of protein kinase C, with a consequent alteration in cell proliferation. The decrease in arachidonic acid molar content in the phosphoinositides and particularly in the phosphatidylinositol-4,5-bisphosphate fraction of PBL of alcoholic patients could lead to a reduced synthesis of prostanoids of the (n-6) series, and, as a consequence, to an alteration in the mitogenic response of the cells.

Phosphatidylinositol metabolism in lymphocytes of chronic alcoholic patients after anti-CD3 stimulation

The immunological alterations observed in chronic alcoholic patients may be due to alterations of signal transduction across the lymphocyte membrane. Upon binding of mitogens or antigens to specific plasma membrane receptors, the activation of phospholipase C leads to the hydrolysis of inositol phospholipids, producing inositol phosphates and diacylglycerol. One of the early events in lymphocyte activation is an increase of intracellular calcium concentration, due to both an influx from extracellular fluid and a release from intracellular stores mediated by inositol phosphates. In this study we verified whether the diminished mobilization of intracellular calcium, previously observed in alcoholics, is caused by alteration in phosphoinositide turnover. We evaluated total inositol phosphate production in peripheral blood lymphocytes after anti-CD3 stimulation, comparing control subjects and alcoholic patients. Lymphocyte activation generated inositol phosphates in both controls and alcoholics, but to a different extent, inositol phosphate production being significantly higher in controls than in alcoholics. This reduction in inositol phosphate production could be accounted either to an inhibition of PLC activity or to a modified affinity of phospholipase C for its own substrates, i.e., phosphoinositides, which fatty acid composition has been previously demonstrated to be greatly different in alcoholics in comparison to healthy subjects.

Normalization of immune response and phosphoinositide fatty acid composition of peripheral blood lymphocytes in an alcoholic patient after alcohol abstinence

After 10 months of alcohol abstinence a malnourished alcoholic patient improved his nutritional status. The analysis of peripheral blood lymphocyte response to mitogenic stimulation with the antibody anti‐CD3 and of the fatty acid composition of the (poly)‐phosphoinositide fraction derived from lymphocytes revealed: 1) a similar [3H]‐thymidine uptake as in control (non‐drinker) subjects; 2) a similar relative molar content of the main fatty acids in the (poly)‐phosphoinositides as in control subjects. Alcohol abstinence can normalize both the parameters, which are greatly altered during alcohol abuse. This suggests a link between nutritional status and lymphocyte responsiveness via phosphoinositide fatty acid composition.