Effects of the fatty acid composition of phosphatidylserine and diacylglycerol on the in vitro activity of protein kinase C from rat spleen: influences of (n-3) and (n-6) polyunsaturated fatty acids

Immunoinflammatory effects of dietary bioactive compounds

Inflammation is a key mechanism of the immune system that can be elicited by several factors, among them several chemical, physical and biological agents. Once stimulated, the inflammatory response activates a series of signaling pathways and a number of immune cells which promote, in a very coordinated manner, the neutralization of the infectious agent. However, if uncontrolled, the inflammatory status may become chronic leading, potentially, to tissue damage and disease onset. Several risk factors are associated with the development of chronic inflammation and, among these factors, diet plays an essential role. In this chapter the effects of some dietary bioactive compounds, including micronutrients, omega-3 fatty acids, nucleotides and polyphenols, on the immunoinflammatory responses in different cellular, animal and human studies have been summarized.

Implication of acyl chain of diacylglycerols in activation of different isoforms of protein kinase C

We synthesized diacylglycerols (DAGs) containing omega-6 or omega-3 polyunsaturated fatty acids [i.e., 1-stearoyl-2-arachidonoyl-sn-glycerol (SAG), 1-stearoyl-2-docosahexaenoyl-sn-glycerol (SDG), and 1-stearoyl-2-eicosapentaenoyl-sn-glycerol (SEG)] and assessed their efficiency on activation of conventional (alpha, beta I, gamma) and novel (epsilon, delta) protein kinase C (PKC). SAG exerted significantly higher stimulatory effects than SDG and SEG on activation of PKC alpha and PKC delta. Activation of PKC beta I by SEG and SDG was higher than that by SAG. Activation of PKC gamma did not differ significantly among DAG molecular species. Addition of SAG to assays containing SEG and SDG exerted additive effects on activation of alpha and epsilon, but not on beta I and gamma, isoforms of PKC. SDG- and SEG-induced activation of PKC delta was significantly curtailed by the addition of SAG. Three DAG species significantly curtailed the PMA-induced activation of beta Iota, gamma, and delta, but not of alpha and epsilon, isoforms of PKC. Our study demonstrates for the first time that in vitro activation of different PKC isoenzymes vary in response to different DAG species, and one can envisage that this differential regulation may be responsible for their in vivo effects on target organs.

Modulatory effects of dietary lipids on immune system functions

Dietary lipid manipulation may affect a great number of immune parameters, such as lymphocyte proliferation, cytokine synthesis, natural killer (NK) cell activity, phagocytosis and so on. The immunomodulation induced by dietary fatty acids may be applied in the amelioration of inflammatory disorders, such as autoimmune diseases. However, the mechanisms that participate in these processes are still poorly understood. It is probable that modulation of immune system by fatty acids of the diet may occur by alteration of membrane fluidity, lipid peroxide formation, eicosanoid production or regulation of gene expression. However, recent studies have reported the effects of several free fatty acids on apoptosis induction of in vitro cultures. In fact, a possible explanation of the effects that fatty acids promote on the immune system cells could be associated with an apoptotic process performed in an irreversible way. In vivo studies have demonstrated the ability of fatty acids to alter the survival of animals fed diets containing oils and infected with a pathogenic bacterium. Experimental infection in animals fed dietary lipids produces a modification of resistance to micro-organisms. The present review analyses all of these parameters that dietary fatty acids are capable of altering in order to modify the immune response. Further studies will be needed to establish the mechanisms involved in immune system regulation, reduction of symptoms derived from autoimmune pathologies and so on.

Polyunsaturation in cell membranes and lipid bilayers and its effects on membrane proteins

The effect of variation of the degree of cis-unsaturation on cell membrane protein functioning was investigated using a model lipid bilayer system and protein kinase C (PKC). This protein is a key element of signal transduction. Furthermore it is representative of a class of extrinsic membrane proteins that show lipid dependent interactions with cell membranes. To test for dependence of activity on the phospholipid unsaturation, experiments were devised using a vesicle assay system consisting of phosphatidylcholine (PC) and phosphatidylserine (PS) in which the unsaturation was systematically varied. Highly purified PKC alpha and epsilon were obtained using the baculovirus-insect cell expression system. It was shown that increased PC unsaturation elevated the activity of PKC alpha. By contrast, increasing the unsaturation of PS decreased the activity of PKC alpha, and to a lesser extent PKC epsilon. This result immediately rules out any single lipid bilayer physical parameter, such as lipid order, underlying the effect. It is proposed that while PC unsaturation effects are explainable on the basis of a contribution to membrane surface curvature stress, the effects of PS unsaturation may be due to specific protein-lipid interactions. Overall, the results indicate that altered phospholipid unsaturation in cell membranes that occurs in certain disease states such as chronic alcoholism, or by dietary manipulations, are likely to have profound effects on signal transduction pathways involving PKC and similar proteins.

Fatty acids, inflammation and immune responses

Evidence obtained from experiments in vitro and in vivo suggests that certain unsaturated fatty acids (FA) may be safe and effective antiinflammatory and immunomodulatory agents. Generation of a unique eicosanoid profile with different biological effects by administration of FA precursors other than arachidonic acid is one approach under investigation. In addition to their role as eicosanoid precursors, FA are of major importance in maintaining cell membrane structure, are key determinants of membrane bound enzyme activity and receptor expression. FA can exert these functions directly and therefore may themselves be important regulators of immune responses. For example, certain FA influence cytokine production and proliferation of human T lymphocytes in a manner that is direct and not due to their conversion to eicosanoids. The observations indicate that FA can modulate immune responses by acting directly on T-cells and suggest that alteration of cellular FA may be a worthwhile approach to control of inflammation.

Differential effects of omega-3 fish oils on protein kinase activities in vitro

We studied the in vitro effects of omega-3 fish oils and other fatty acids on the activity of crude protein kinase C from S49 lymphoma cells, on partially purified enzyme from rat cerebrum, on homogeneous protein kinase C from bovine brain, and, for comparison, on type I adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. In the absence of exogenous phospholipid, the fish oils cis-5,8,11,14,17-eicosapentaenoic acid (EPA) and acid (DCHA) enhance the catalytic cis-4,7,10,13,16,19-docosahexaenoic activity of protein kinase C and support the binding of [3H]phorbol 12,13-dibutyrate, both to approximately 50% of the level supported by phosphatidylserine. In the presence of phosphatidylserine, the omega-3 fatty acids reduce catalytic activity and [3H]phorbol 12,13-dibutyrate binding by about one-half. The effects of the omega-3 fatty acids on enzyme activity suggest that fish oils act as partial agonists competitively with phosphatidylserine. EPA, DCHA, and arachidonate (but not a variety of saturated fatty acids) inhibit the cAMP-dependent protein kinase. Thus dietary fish oils and cellular fatty acids mobilized by the action of phospholipase A2 may differentially modulate the activities of protein kinase C and cAMP-dependent protein kinase. These data suggest means by which unsaturated fatty acids mobilized within cells may act as second messengers.

Positive ion fast atom bombardment mass spectrometric analysis of the molecular species of glycerophosphatidylserine

The structure of 1,2-dipalmitoyl-sn-glycero-3-phosphoserine was analyzed by positive ion fast atom bombardment mass spectrometry and collisional activation mass-analyzed ion kinetic energy spectroscopy. The molecular weight, the polar-head group, and the fatty acid composition of this species were identified by the appearance of protonated and solvated protonated species ions, diglyceride and monoglyceride fragment ions. After purification of glycerophosphatidylserine from bovine brain and rat kidney by normal phase high-performance liquid chromatography, molecular species were identified by either positive or negative ion fast atom bombardment mass spectrometry. The study suggests that negative ion fast atom bombardment ionization is a more powerful tool for the identification of the molecular species of glycerophosphatidylserine from biological samples. Positive ion fast atom bombardment represents a useful alternative for analysis of major molecular species in natural glycerophosphatidylserine.