Role of fatty acid structure in the reversible activation of phosphatidylcholine synthesis in lymphocytes

The dietary form of choline during lactation affects maternal immune function in rats

PURPOSE

The present study was designed to determine the effects of both choline form and availability on maternal immune function during lactation.

METHODS

Sprague-Dawley rats were randomized to one of the three diets 24-48 h before parturition and fed ad libitum until 21 days postnatal: 1 g/kg choline as free choline (C, n = 11), the current form, and amount of choline in commercial diets; 1 g/kg choline as phosphatidylcholine (PC1, n = 11); or 2.5 g/kg choline as PC (PC2.5, n = 8). Choline metabolites in offspring stomach contents were quantified. At 21 days, lymphocytes from mothers' mesenteric lymph nodes and spleens were isolated and phenotypes and ex vivo cytokine production after mitogen exposure were determined.

RESULTS

There was a higher proportion of choline and a lower proportion of lyso-PC in stomach contents (representing dam's milk) of C pups compared to PC1. In the mesenteric lymph nodes, feeding PC1 compared to C led to a higher IL-2 production after Concanavalin A (ConA) stimulation and a higher proportion of T cells (CD3+) and a lower proportion of B cells [immunoglobulin (Ig)κ, CD45RA+, and IgM+; P < 0.05]. Splenocytes from the PC1 group produced more IL-6 and TNF-α after lipopolysaccharides stimulation compared to C (P < 0.05). Splenocytes from the PC2.5 group produced more IL-2 and IL-6 after ConA stimulation compared to PC1 (P < 0.05).

CONCLUSIONS

Feeding choline as PC in the maternal diet improved the ability of immune cells to respond ex vivo to mitogens and increasing the amount of PC in the diet further improved T cell proliferation.

Apoptotic death in adenocarcinoma cell lines induced by butyrate and other histone deacetylase inhibitors

n-Butyrate inhibits the growth of colon cancer cell lines. In the HCT 116 cell line, butyrate-induced growth inhibition is almost fully reversible, whereas in the VACO 5 cell line, a subpopulation undergoes apoptosis within 30 hr of treatment with butyrate. Concurrent treatment of VACO 5 cells with butyrate and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) accelerates and increases the incidence of cell death to nearly 100% of the population, whereas HCT 116 cells largely remain alive during treatment with this combination. The action of butyrate as an inhibitor of histone deacetylase was assessed in these cell lines by examining extracted core histones for their electrophoretic mobility in Triton/acid/urea gels. The concentrations of butyrate that were effective for inducing apoptosis were similar to the concentrations that caused hyperacetylation of core histones in the VACO 5 cell line. Furthermore, an examination of other carboxylic acids for induction of apoptosis revealed a rank order that corresponded to the order of potency in causing hyperacetylation of core histones. Specifically, the active acids were 3-5 carbons in length and lacked substitution at the 2-position. Isovaleric and propionic acids, in particular, proved to be effective inducers of both hyperacetylation and apoptosis at 5 mM concentrations, a finding of potential relevance to the unusual pancytopenia occurring after acidotic episodes in isovaleric and propionic acidemias. The duration of butyrate treatment required for chromatin fragmentation (10-20 hr) corresponded to the time required for histone H4 to become predominantly tetraacetylated. Furthermore, trichostatin A, a structurally dissimilar inhibitor of histone deacetylase, mimicked butyrate-induced apoptosis of VACO 5 cells and growth inhibition of HCT 116 cells. The dramatic enhancement of VACO 5 cell death by TPA, and the high level resistance of HCT 116 cells to butyrate were not evident from histone acetylation determinations. Thus, applications of butyrate for cytoreduction therapy will benefit from pharmacodynamic assessment of histone acetylation, but will require additional work to predict susceptibility to butyrate-induced death.

Phospholipid metabolism of lymphocytes with inhibited glutathione synthesis using L-buthionine-S,R-sulfoximine

The potential role of phospholipid metabolism in restricting lymphocyte proliferation under conditions of oxidative stress was investigated using [1-14C]-arachidonic acid (14C-AA) and 32P-orthophosphoric acid. Human peripheral blood lymphocytes (PBL) and PBL depleted of glutathione with L-buthionine-S,R-sulfoximine (BSO-PBL) were compared. The relative uniformity of glutathione depletion in the PBL population was assessed by flow cytometry. BSO-PBL were 40 to 90% depleted of glutathione 1 to 3 days after activation, respectively, and the BSO-PBL had unimpaired early activation events based on 32P-phosphatidylinositol levels. However, unlike stimulated PBL, which showed a progressive decrease in radioactivity incorporated into phosphatidylcholine and a corresponding increase into phosphatidylethanolamine, no significant differences occurred with BSO-PBL. Prelabeled BSO-PBL showed considerably more 14C radioactivity in the supernatant following 72-120 h stimulation with anti-CD3 than control PBL, which was mostly in the form of unmetabolized 14C-AA. Higher levels of leukotriene B4, 5-hydroxyeicosatetraenoate and 12-hydroxy-5,8,10-heptadecatrienoate also were observed with L-buthionine-S,R-sulfoximine treatment, which could explain the impaired proliferation obtained with a depletion of cellular glutathione. Both lysophosphatidylcholine and liberated free 14C-AA increased with L-buthionine-S,R-sulfoximine treatment following 72 h stimulation, suggesting functional impairment in the reacylating enzymes. The increased release of 14C-AA by BSO-PBL also may contribute to the imparied proliferation that occurs with loss of glutathione.

Differential effects of unsaturated fatty acids on phospholipid synthesis in human leukemia monocytic U937 cells

The biosynthesis of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in monocyte-like leukemia U937 cells was monitored by adding [3H]choline, [14C]ethanolamine or [14C]glycerol to the culture media; incorporation into phospholipid (PL) increased with time. The effect of unsaturated fatty acids (UFA) on PC and PE synthesis was investigated by pretreating U937 cells for 72h with 10 microM 18:1 (n - 9), 18:2 (n - 6), 18:3 (n - 3), 20:4 (n - 6) and 20:5 (n - 3). The UFA caused no alteration in cell growth, as evidenced by light microscopy and the incorporation of [3H]thymidine and [3H]leucine. Total cellular uptake of radioactive precursors remained unaffected by all the treatments. Pretreatment with 20:5 resulted in approximately 25 per cent reduction in the incorporation of [3H]choline into PL, while no significant effect was detected with the other UFAs. 18:3, 20:4 and 20:5 depressed the incorporation of [14C]ethanolamine into PL by 34 per cent, 28 per cent and 49 per cent respectively. However, there was no redistribution of label with any of the treatments. 18:3, 20:4 and 20:5 also antagonized the stimulatory effect of endotoxin (LPS) on PC and PE synthesis. In addition, the incorporation from [14C]glycerol into PC and PE was reduced by 18:3, 20:4 and 20:5. Although the PL composition of the cells remained essentially unaffected, our study shows that chronic treatment of U937 cells with n - 3 PUFA (20:5) depressed PC and PE synthesis, and 18:3 and 20:4 also caused inhibition of PE synthesis.

Fatty acids stimulate phosphatidylcholine synthesis and CTP:choline-phosphate cytidylyltransferase in type II pneumocytes isolated from adult rat lung

The regulation by cyclic AMP and fatty acids of phosphatidylcholine (PC) synthesis in rat alveolar type II cells was studied. In contrast with results with hepatocytes, cyclic AMP and its potent chlorophenylthio analogue had no inhibitory effect on [Me-14C]choline incorporation into PC in pulse-chase studies with alveolar type II cells. The inclusion of the fatty acids palmitate, oleate or linoleate in the chase incubation medium stimulated the incorporation of [Me-14C]choline into PC by type II cells. The effect of palmitate, which was more pronounced than that of the other fatty acids, appeared to be concentration-dependent. Increased [Me-14C]choline incorporation into PC was paralleled by an accelerated disappearance of the radiolabel from choline phosphate, which is consistent with an activation of CTP:choline-phosphate cytidylyltransferase. This enzyme is considered to be rate-limiting in the synthesis of PC de novo by type II cells. As fatty acids are also substrate for PC synthesis, their effect could also be due to compensation for a fatty acid deficiency. To test this possibility, fatty acid synthesis in the type II cells was stimulated by addition of lactate. Even then, an additional stimulation of PC synthesis by palmitate was observed, which supports the regulatory influence of exogenous fatty acids. Incubation of type II cells in the presence of 0.2 mM-palmitate resulted in a 45% increase in the membrane-bound CTP:choline-phosphate cytidylyltransferase activity, whereas the soluble activity remained unchanged. Choline kinase activity in the soluble fraction increased by 48%. However, the increase in choline kinase is unlikely to be responsible for the increased metabolic flux through the choline phosphate pathway, because there is a relatively large pool of choline phosphate in type II cells. Therefore it is suggested that the microsomal CTP:choline-phosphate cytidylyltransferase is the form of this enzyme which is active in surfactant PC synthesis, and possibly has a regulatory role in this pathway.

Concurrent changes in Dunaliella salina ultrastructure and membrane phospholipid metabolism after hyperosmotic shock

Hyperosmotic shock, induced by raising the NaCl concentration of Dunaliella salina medium from 1.71 to 3.42 M, elicited a rapid decrease of nearly one-third in whole cell volume and in the volume of intracellular organelles. The decrease in cell volume was accompanied by plasmalemma infolding without overall loss of surface area. This contrasts with the dramatic increase in plasmalemma surface area after hypoosmotic shock (Maeda, M., and G. A. Thompson. 1986. J. Cell Biol. 102:289-297). Although plasmalemma surface area remained constant after hyperosmotic shock, the nucleus, chloroplast, and mitochondria lost membrane surface area, apparently through membrane fusion with the endoplasmic reticulum. Thus the endoplasmic reticulum serves as a reservoir for excess membrane during hyperosmotic stress, reversing its role as membrane donor to the same organelles during hypoosmotically induced cell expansion. Hyperosmotic shock also induced rapid changes in phospholipid metabolism. The mass of phosphatidic acid dropped to 56% of control and that of phosphatidylinositol 4,5-bisphosphate rose to 130% of control within 4 min. Further analysis demonstrated that within 10 min after hyperosmotic shock, there was 2.5-fold increase in phosphatidylcholine turnover, a twofold increase in lysophosphatidylcholine mass, a four-fold increase in lysophosphatidate mass, and an elevation in free fatty acids to 124% of control, all observations suggesting activation of phospholipase A. The observed biophysical and biochemical phenomena are likely to be causally interrelated in providing mechanisms for successful accommodation to such severe osmotic extremes.

Role of arachidonic acid release in the G2 delay induced by tumor promoter TPA in HeLa cells

The tumor promoter TPA2 (12-O-tetradecanoylphorbol-13-acetate) has been shown to exhibit a radiomimetic activity on the cell cycle of HeLa cells (V. Kinzel, J. Richards, and M. Stöhr (1980) Science 210, 429). The response includes a delay of cells in G2 phase. The relation between TPA-induced release of arachidonic acid (AA) and the inhibition in G2 phase was studied. Exogenous AA (greater than 10(-4) M; in presence of 10% serum) is shown to delay HeLa cells in G2 and to enhance the effectiveness of TPA in this respect. The inhibition of the TPA-induced AA liberation by fluocinolone acetonide, however, does not influence the TPA-effected G2 delay. The diacylglycerols 1,2-dioctanoyl-glycerol and 1-oleoyl-2-acetylglycerol delay HeLa cells in G2 but without major stimulation of AA liberation. On the basis of the data it is concluded that AA released from HeLa cells due to the action of TPA is not involved in the TPA-induced delay of cells in G2 phase.

Translocation of CTP: phosphocholine cytidylyltransferase from cytosol to membranes in HeLa cells: stimulation by fatty acid, fatty alcohol, mono- and diacylglycerol

Addition of oleate, oleyl alcohol, or palmitate to HeLa cell medium resulted in a rapid stimulation of PC synthesis and activation of CTP: phosphocholine cytidylyltransferase. Stimulation was optimal with 0.35 mM oleate, 0.3 mM oleyl alcohol and 5 mM palmitate, or 1 mM palmitate if EGTA were added to the medium. The cytidylyltransferase was activated by translocation of the inactive cytosolic form to membranes. In untreated cells approx. 30% of the total cytidylyltransferase was membrane bound, while in treated cells, 80-90% was membrane associated. Addition of bovine serum albumin (10 mg/ml) to cells previously treated with oleate (0.35 mM) rapidly removed cellular fatty acid, and the membrane-bound cytidylyltransferase activity returned to approx. 30%. Similar results were obtained by extraction of membranes with albumin in vitro. Although 95% of the free fatty acid was extracted, 30-40% of the membrane cytidylyltransferase remained bound. Translocation of cytidylyltransferase between isolated cytosol and microsomal fractions was promoted by addition of oleate, palmitate, oleyl alcohol, and monoolein. Addition of diacylglycerol, lysophosphatidylcholine, lysophosphatidylethanolamine, calcium palmitate, and detergents such as Triton X-100, cholate or Zwittergent did not stimulate translocation of the enzyme. Addition of oleoyl-CoA promoited translocation, however, 40% of it was hydrolyzed releasing free oleic acid. Cytosolic cytidylyltransferase bound to microsomes pre-treated with phospholipase C, which had 7-fold elevated diacylglycerol content. Fatty acid-promoted translocation was blocked by Triton X-100, but not by 1 M KCl. These results suggest that a variety of compounds with differing head group size and charge, and number of hydrocarbon chains can function as translocators, and that hydrophobic rather than ionic interactions mediate the binding of cytidylyltransferase to membranes.

Early changes in the arachidonic acid metabolism of HeLa cells in response to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and related compounds

In order to search for possible mediators involved in the transient radiomimetic effectiveness of TPA and related compounds early changes in the AA metabolism of HeLa cells prelabeled with 1-14C-AA have been analyzed. Maximum release of AA with different concentrations of TPA (3 X 10(-9) to 3 X 10(-5) M) was observed after 2-3 h treatment in the presence of 10% calf serum. Released AA was reincorporated by the cells after that period, a phenomenon which was largely abolished or delayed by cycloheximide. Reincorporation of released AA was observed in the presence of 10% fresh serum as well as with 0.5% BSA, and appears to be due to an induction of responsible enzyme(s) by the phorbol ester. The earliest metabolites of AA produced via the cyclooxygenase such as PGE2 and PGF2 alpha and via lipoxygenases such as 12-, and 15-hydroxyeicosatetraenoic acids appear in small amounts and after later time points. AA release exhibited a pluriphasic dose response to TPA with maxima at 3 X 10(-8) M and greater than or equal to 10(-5) M. Comparative dose response measurements with respect to AA release were established using various promoting skin mitogens which exhibited the following order of potency: TPA greater than teleocidin approximately equal to RPA greater than mezerein much greater than EPA greater than 4-O-Me-TPA. For reasons discussed it appears unlikely that AA, Prostaglandins, or hydroxyeicosatetraenoic acid products play a significant role as mediators of the radiomimetic effects of TPA in G2 of the cell cycle.

Analysis of the effects of fatty acids and related compounds on the synthesis of phosphatidylcholine in lymphocytes

Phosphatidylcholine synthesis in cultured bovine lymphocytes is stimulated by cis-unsaturated fatty acids. This stimulation is correlated with an activation of the enzyme cytidyltransferase (EC 2.7.7.15) and its apparent translocation from the cytosol to the membrane/particulate of cells. In addition, these agents increase the levels of cytidine diphosphocholine - a product of the cytidyltransferase reaction and a precursor to phosphatidylcholine. Retinoic acid and 5,8,11,14-eicosatetraynoic acid both activate cytidyltransferase activity and raise cytidine diphosphocholine levels, yet they are ineffective as stimulators of overall phosphatidylcholine synthesis. The effects of all of these lipids are reversed by the delayed addition of bovine serum albumin. The data point to the view that cytidyltransferase activation is required but is not sufficient for stimulation of phosphatidylcholine synthesis: regulation at another step is suggested.