The effect of free fatty acids on spectrin organization in lymphocytes

Global Trends in Research of Lipid Metabolism in T lymphocytes From 1985 to 2022: A Bibliometric Analysis

Lipids are involved in both energy metabolism and signaling transduction. Abnormal lipid metabolism in T cells is associated with the differentiation, longevity and activity of T cells, which has received increasing concern since its firstly reported in 1985. To evaluate the trends of lipid metabolism in T cells and map knowledge structure, we employed bibliometric analysis. A total of 286 related publications obtained from the Web of Science Core Collection published between 1985 and 2022 were analyzed using indicators of publication and citation metrics, countries, institutes, authors, cited references and key words. The present research status, the global trends and the future development directions in lipid metabolism and T cells were visualized and discussed. In summary, this study provides a comprehensive display on the field of lipid metabolism in T cells, which will help researchers explore lipid metabolism in T cells more effectively and intuitively.

Cis-unsaturated free fatty acids block VIP-mediated GH and PRL secretion by perturbing the cAMP/protein kinase A pathway

Cis-unsaturated free fatty acids (FFA) like oleic acid are strong blockers of both basal and stimulated GH secretion in vivo by acting directly on the somatotroph cell. Several lines of evidence suggest that this inhibitory action is the result of a perturbation of the function of several plasma membrane integral proteins. It has been reported recently that cis-FFA are able to block several steps in the inositolphosphates/phospholipase C/Ca2+ (InsPs/PLC/Ca2+) signal transduction pathway triggered by the activation of the TRH receptor. In this paper we present evidence showing that the inhibition of growth hormone (GH) and prolactin (PRL) secretion by cis-FFA in vitro is also exerted at several different levels on the cAMP-protein kinase A (cAMP/PKA) pathway triggered by the stimulation of the vasoactive intestinal peptide (VIP) receptor in pituitary clonal cells. By means of a sequential analysis of signal transduction events, we observed that cis-unsaturated FFA; (1) reduce the activity of adenylate cyclase; (2) perturb the activity of protein kinase A; (3) suppress the VIP-triggered Ca2+ influx, and (4) do not perturb VIP binding or the homologous desensitization of the VIP receptor.

Interaction of free fatty acids with phospholipid bilayers

The partition of free fatty acids (FFA) to egg-phosphatidylcholine (egg-PC) and egg-phosphatidylethanolamine (egg-PE) vesicles was studied. Upon the addition of FFA to the suspension of vesicles, the pH of the aqueous phase changed depending on the length and saturation of the FFA hydrocarbon chain, as well as on the vesicle composition. The medium pH decreased faster if FFA was added to egg-PE as compared to egg-PC vesicles. The fluorescent free fatty acid indicator (ADIFAB) was used to measure the amount of FFA remaining in the aqueous phase. Most of the FFA added to the suspension of egg-PE vesicles remained in the aqueous phase, whereas in the presence of egg-PC vesicles the FFA partitioned preferentially into the lipid phase. The amount of FFA incorporated into the lipid bilayers was estimated by measuring the changes of pH at the lipid bilayer surface, using fluorescein-PE. At high surface concentrations of FFA, decreasing pH at the bilayer surface caused the protonation of FFA, and raised the pK of FFA at the bilayer surface from 5 to about 7. The partition of FFA in egg-PE vesicles was an order of magnitude lower than that in egg-PC vesicles. The incorporation amount was determined more by the molecular packing than by the nature of lipid headgroups, because steroylcaprioyl-PE, which preferred the bilayer structure, behaved more like egg-PC than egg-PE. Understanding FFA partition characteristics would help to interpret the hydrolysis measurements of phospholipids, and to explain many biological activities of FFA.

Cytokine production and DNA synthesis by human peripheral lymphocytes in response to palmitic, stearic, oleic, and linoleic acid

Effects of palmitic, stearic, oleic, and linoleic acid on mitogen-induced DNA synthesis, on production of IL-1 beta, IL-2, IFN-gamma, and TNF-alpha, and on IL-2R expression were determined in human peripheral lymphocytes. Free fatty acids (FFA) were added over a wide range of concentrations to cells cultured under serum free conditions with fatty acid free albumin. DNA synthesis was stimulated by low and inhibited by high FFA concentrations. Physiological concentrations were stimulatory, except for linoleic acid. Cytokine production became affected by all FFA tested. Palmitic acid enhanced the release of IFN-gamma at concentrations that diminished TNF-alpha production. Saturated fatty acids were significantly more potent than unsaturated fatty acids in affecting cytokine production. IFN-gamma secretion was significantly more stimulated or inhibited by the various FFA compared with the other cytokines. IL-2R expression correlated with the production of IL-2. When tested in combination, stimulatory as well as inhibitory effects of the individual FFA became attenuated. It is suggested that palmitic, stearic, oleic, and linoleic acid are physiological regulators of DNA synthesis and cytokine release in human peripheral lymphocytes. Modulation of FFA ratios may be an effective means for the fine tuning of the immune system. As secretory mechanisms of cytokines appear to exhibit substrate specificity for FFA, the release of individual cytokines may be selectively influenced by FFA.

Membrane partition of fatty acids and inhibition of T cell function

Short-term exposure to elevated levels of free fatty acids (FFA) perturbs a variety of cellular functions. It is frequently observed that cis-unsaturated fatty acids (FA) mediate these perturbations while trans-unsaturated or saturated FA are relatively inert. This dichotomy has generally been ascribed to the differential effects of these FA on membrane structure, specifically, that cis but not saturated FA alter lipid acyl chain order. Direct support for this view, however, is lacking because membrane partition of FA has not been determined for the relevant FA and for the conditions of the functional studies. Previous measurements of membrane partition of natural long-chain FA have relied on the determination of the amount bound to the membrane rather than the aqueous-phase concentration of FA. Because [FFA] is low, however, the partition coefficient (Kp) is relatively insensitive to the membrane-bound concentration and, therefore, accurate determinations of Kp require direct [FFA] measurements. In this study FA partition between the aqueous phase and either lipid bilayer vesicles or cytotoxic T lymphocytes (CTL) was measured using a recently developed fluorescent indicator of FFA. This indicator is composed of recombinant intestinal fatty acid binding protein derivatized with acrylodan and is termed ADIFAB. Using ADIFAB, partition coefficients were determined for seven saturated and cis-unsaturated FA under conditions that parallel those in which cis FA have been shown to inhibit CTL signaling. In general, Kp values were approximately an order of magnitude greater than previous determinations and were found to be greater for the noninhibitory saturated FA than the inhibitory cis FA.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between membrane lipid mobility and spectrin distribution in lymphocytes

We have previously established that T and B lymphocytes in situ are remarkably heterogeneous with respect to the cytoskeletal protein spectrin. Since in erythrocytes spectrin is known to play an important role in the regulation of membrane fluidity, lipid organization and lateral mobility of membrane proteins, we have sought to determine if the heterogeneous patterns of spectrin distribution that we have observed are related to possible differences in membrane lipid organization in these various subsets. To this end, we have utilized a fluorescent pyrene-labelled phospholipid as a probe of the lipid lateral mobility and have examined two related T cell systems maintained in vitro, DO.11.10 cells and a spontaneously arising variant, DO.11.10V. In these (and other cloned in vitro systems) we have previously observed that the cells homogeneously express one of the kinds of spectrin distribution patterns observed in situ. Thus the uniformity of staining of these systems permits us to address whether the various patterns of spectrin distribution may be predictive of differences in membrane lipid properties. Here we show that in cells in which there is little or nor spectrin at the plasma membrane (DO.11.10) that the lipids in the plasma membrane are considerably less mobile than in its related variant in which spectrin is diffusely distributed within the cell and at the plasma membrane. From this and previous results, we conclude that differences in the distribution of the cytoskeletal protein spectrin among lymphocytes may be a useful parameter in helping to predict the status of membrane lipid organization.