Lipid patterns in human leukocytes maintained in long-term culture

Mechanisms of sphingosine and sphingosine 1-phosphate generation in human platelets

The bioactive molecule sphingosine 1-phosphate (S1P) is abundantly stored in platelets and can be released extracellularly. However, although they have high sphingosine (Sph) kinase activity, platelets lack the de novo sphingolipid biosynthesis necessary to provide the substrates. Here, we reveal a generation pathway for Sph, the precursor of S1P, in human platelets. Platelets incorporated extracellular 3H-labeled Sph much faster than human megakaryoblastic cells and rapidly converted it to S1P. Furthermore, Sph formed from plasma sphingomyelin (SM) by bacterial sphingomyelinase (SMase) and neutral ceramidase (CDase) was rapidly incorporated into platelets and converted to S1P, suggesting that platelets use extracellular Sph as a source of S1P. Platelets abundantly express SM, possibly supplied from plasma lipoproteins, at the cell surface. Treating platelets with bacterial SMase resulted in Sph generation at the cell surface, conceivably by the action of membrane-bound neutral CDase. Simultaneously, a time-dependent increase in S1P levels was observed. Finally, we demonstrated that secretory acid SMase also induces S1P increases in platelets. In conclusion, our results suggest that in platelets, Sph is supplied from at least two sources: generation in the plasma followed by incorporation, and generation at the outer leaflet of the plasma membrane, initiated by cell surface SM degradation.

Changes in the balance between mitogenic and antimitogenic lipid second messengers during proliferation, cell arrest, and apoptosis in T-lymphocytes

Control of lymphocyte cell survival and proliferation is critical for both the immune response and for the prevention of autoimmune and infectious diseases. The actions of interleukin-2, the major T-cell regulatory cytokine, are mediated by the complex network of divergent signalling pathways controlled by its high-affinity receptor. Various studies have indicated that the generation of certain lipid second messengers is an important mechanism in the control of proliferation and cell death. We have examined the relationship between diacylglycerol and ceramide and the levels of the lipids phosphatidylcholine and sphingomyelin, their potential precursors, in the human T-cell line Kit 225 cultured in three distinct conditions to favor apoptosis, cell arrest, and proliferation. Our data show that, in proliferating cells, the ratios of diacylglycerol/ceramide and phosphatidylcholine/sphingomyelin are higher than those found in arrested cells and increase with time in culture. These ratios are rapidly reversed in apoptotic cells. Further experiments reveal that de novo synthesis of both diacylglycerol and phosphatidylcholine is greatest in proliferating cells, whereas sphingomyelin synthase activity is increased in cells undergoing apoptosis. In summary, our results demonstrate for the first time that the ratio of mitogenic/antimitogenic lipids changes dramatically during T-cell proliferation and cell death. These results indicate that lipid second messengers and the enzymes that are responsible for their generation may provide targets for novel therapeutic interventions in the clinical management of immunosuppression and autoimmune disease.

Long chain fatty acid utilization of T-cells from autoimmune MRL-lpr/lpr mice

To test the hypothesis that T-cells which exhibit abnormal immunological behavior manifest derangements in the de novo synthesis of phospholipids, the utilization of [3H]palmitic acid in B220+ T-cells from autoimmune MRL-lpr/lpr mice was investigated. The rate of incorporation of [3H]palmitic acid into membrane phospholipids was markedly increased in intact B220+ T-cells compared to that in T-cells from immunologically normal mice. The activities of two key enzymes involved in the de novo synthesis of palmitoyl-phospholipids, acyl-coenzyme (CoA) ligase and acyl-CoA; sn-glycerol-3-phosphate acyl transferase, were significantly higher in homogenates from B220+ T-cell membranes compared with those in controls. Despite these findings, the molar concentration of individual palmitoyl glycerolipids was equivalent in the membranes of B220+ T-cells and control lymph node T-cells. The results indicate that T-cells from lupus mice exhibit complex defects in the biosynthesis and turnover of membrane phospholipids and suggest the possibility that these aberrations contribute to T-cell dysfunction in autoimmune diseases.

Metabolism of pyrenedecanoic acid in Epstein-Barr virus-transformed lymphoid cell lines from normal subjects and from a patient with multisystemic lipid storage myopathy

A lymphoid cell line has been established from a patient with multisystemic lipid storage myopathy and showed a major triacylglycerol storage, whereas the content of other neutral lipids and phospholipids was in the normal range. The metabolism of the triacylglycerols has been investigated in this lymphoid cell line from multisystemic lipid storage myopathy as well as in control cells through pulse-chase experiments using 10-(1-pyrene)decanoic acid (P10), a fluorescent fatty acid derivative, as precursor. After 1 h incubation, the uptake of P10 was not significantly different in multisystemic lipid storage myopathy and control lymphoid cells. The amount of fluorescent lipids synthesized by the lymphoid cells was proportional to the concentration of P10 in the culture medium. After 24 h incubation, at any extracellular concentration of P10, the content of P10-labelled triacylglycerols was much higher in multisystemic lipid storage myopathy cells than in controls. Chase experiments showed an impairment in the rate of degradation of biosynthesized triacylglycerols in multisystemic lipid storage myopathy lymphoblasts compared to controls with time of chase (the ratio P10-triacylglycerols/P10-phospholipids increased in mutant cells while it decreased in normal cells). Elsewhere, no enzyme deficiency of the neutral triacylglycerol lipase activity, has been found in multisystemic lipid storage myopathy lymphoid cells.

Hypocholesterolemia, an unfavorable feature of prognostic value in chronic myeloid leukemia

In chronic myeloid leukemia (CML) low serum cholesterol is not uncommon and has been linked to the activity of the disease. Despite these observations, most studies concerned with prognostic signs in CML have not included cholesterol. In our study, cholesterol correlated positively with survival (p = 0.0012) and with the duration of chronic phase (p = 0.0059) in a univariate analysis. The multivariate Cox regression model selected cholesterol as a parameter of additive prognostic value in addition to marrow myeloblasts plus promyelocytes, sex, eosinophilia and lactate dehydrogenase.

Human growth hormone-stimulated mitogenesis of Nb2 node lymphoma cells is not mediated by an immediate acceleration of phosphoinositide metabolism

Lactogenic hormones stimulate the mitogenesis of Nb2-11C rat lymphoma cells and this stimulation is enhanced by 12-O-tetradecanoyl phorbol ester (TPA). The effect of human growth hormone (hGH) and TPA on phosphoinositide metabolism in Nb2-11C cells was tested by measuring the incorporation of [3H]myo-inositol or 32P or measuring the breakdown of polyphosphoinositides in cells prelabeled with [3H]myo-inositol, 32P or [3H]arachidonic acid. We found that none of these processes is immediately stimulated by either hGH and/or TPA. Our results indicate that the overall phosphoinositide turnover is slow or confined to small fractions only. On the other hand, the phosphorylation-dephosphorylation cycle of polyphosphoinositides is quite fast and remarkably exceeds the rate of incorporation of [3H]myo-inositol. Our present results indicate, therefore, that the mitogenic effect of hGH and its enhancement by TPA is not mediated by an immediate increase in phosphoinositide metabolism.

Lymphoid cell lines as a model system for the study of Wolman's disease: enzymatic, metabolic and ultrastructural investigations

Epstein-Barr virus (EBV) transformed lymphoid cell lines (LCL) were established from blood lymphocytes of a patient affected with Wolman's disease (WD) and from her parents. These LCL showed a severe deficiency in acid lipase activity using every substrate in comparison to LCL from normal subjects, in which acid lipase activity was similar to that in blood lymphocytes. In the LCL from Wolman's disease a major accumulation of neutral lipids was observed, mainly cholesteryl esters, CE (amount around 7 times higher than in normal cells and ratio of esterified/free cholesterol increased by 10 times) and to a lesser extent triglycerides, TG (amount increased by 1.5 times). Electron microscopy showed the storage vacuoles of neutral lipids quite characteristic of this lysosomal disease. The reported data demonstrated the validity of transformed LCL as a cellular model system in culture for experimental studies of Wolman's disease and for investigating the lysosomal metabolism of neutral lipids.

Fluorescence polarization as a parameter of plasma lipids in patients with hematologic malignancies

Abnormal diphenylhexatriene fluorescence polarization measurements (FP values) of plasma have previously been reported in patients with hematologic malignancies. However, the biological significance of this measurement is unclear. We have prospectively studied plasma from 39 patients with leukemia and lymphoma as well as normal donors for total cholesterol, total triglyceride, and lipoprotein-cholesterol fractions, and correlated these values with measured FP values. Total triglyceride, very low density lipoproteins (VLDL), high density lipoprotein (HDL) levels, and FP values were all strongly correlated with clinical and biochemical measures of tumor burden and varied directly with the presence of malignancy. Although the presence of abnormal FP values was confirmed in patients with leukemia and lymphoma, it was not a particularly sensitive measure for minimal tumor and it appeared to correlate directly with other measures of lipids and cholesterol, particularly triglyceride. It is suggested that further studies of conventional plasma lipids and lipoproteins be pursued in order to elucidate the apparently pervasive alterations in lipid metabolism present in these patients.

Composition and metabolism of phospholipids of human leukocytes

Human mononuclear (MN) and polymorphonuclear (PMN) leukocytes were analyzed for their phospholipid, triglyceride, cholesterol and fatty acid content. The phospholipid/cholesterol ratio was 1.24 for both cells. MN cells contain more phosphatidylcholine (PC), but less phosphatidylserine (PS), Phosphatidylethanolamine (PE) and sphingomyelin (SPH) than PMN cells when expressed as percent of total phospholipid. When expressed on the basis of lipid content per cell, MN cells contain less PS, PE and SPH but more triglyceride than PMN cells. PMN cells incorporate palmitic, stearic, linoleic and linolenic acids into their phospholipids, triglycerides or cholesterol esters. The incorporation into triglycerides was highest for all fatty acids. Of the phospholipids, the incorporation was highest into PC. Labeled fatty acids also were found in proteins which had been delipidized by exhaustive extraction with organic solvents. These represent tightly or covalently bound fatty acids. The incorporation [3H] palmitic acid into this protein fraction is stimulated by insulin.

Plasma lipid alterations in leukemia and lymphoma

Plasma lipids and lipoproteins were studied at presentations in 25 patients with acute leukemia and non-Hodgkin's lymphoma. All patients demonstrated an abnormally in at least one plasma lipid fraction, and most exhibited a predictable pattern of lipid alterations that consisted of extremely low levels of high-density lipoprotein cholesterol (median [Xm] = 23), elevated triglyceride (Xm = 165) and elevated very-low-density lipoprotein (Xm = 26). Patients restudied during remission demonstrated a return to normal values. The degree of lipid abnormality was directly related to the underlying tumor burden and particularly to the presence of bone marrow involvement. However, even patients with minimal tumor bulk demonstrated plasma lipid abnormalities. The results suggest that an abnormality in systemic lipid metabolism, possibly in triglyceride clearance, is present in these patients and that its incidence in this population is high.

Characterization of hypocholesterolemia in myeloproliferative disease. Relation to disease manifestations and activity

Characterization of the hypocholesterolemia observed in polycythemia vera and agnogenic myeloid metaplasia revealed significant reductions in plasma total cholesterol, low-density lipoprotein (LDL) cholesterol and high-density lipoprotein (HDL) cholesterol in an age- and sex-matched comparison with the Framingham population. Men with myeloproliferative disease also had significantly lower total and LDL cholesterol levels than did those with relative or secondary polycythemia. LDL and HDL cholesterol were significantly correlated, suggesting a generalized disturbance of cholesterol metabolism, unexplained by nutritional status. Evaluation of the relationship among hematic cell proliferation, degree of myeloid metaplasia and hypocholesterolemia by multiple regression analysis revealed that spleen size was the variable of most significance in explaining the variation in plasma total, LDL and HDL cholesterol levels. Uncontrolled disease activity was accompanied by a decline in LDL cholesterol levels. Splenectomy or control of proliferation with chemotherapy or splenic irradiation reversed this abnormality. Levels of plasma total and lipoprotein cholesterol provide information that may be of value in diagnosis and assessment of myeloproliferative disease activity.

Cellular fractionation and isolation of the plasma membrane of Burkitt's lymphoma cells

A procedure for cellular fractionation and preparation of plasma membrane from a Burkitt's lymphoma cell line is described. This procedure involves homogenization with a Polytron in buffered isotonic sucrose, and separation of cellular fractions by differential and isopycnic centrifugation in sucrose. The isolated plasma membrane fraction contains 44% of the cellular cholesterol, 50% of the ouabain-sensitive (Na+ + K+)-ATPase activity, 43% of the gamma-glutamyltranspeptidase activities and 16% of the phospholipid. This fraction contains only 3% of cellular protein and is contaminated with less than 4% of the total cellular activities of microsomal, lysosomal, mitochondrial, Golgi and soluble marker enzymes. The cholesterol : phospholipid molar ratio of the crude plasma membrane is 0.56. The membranes in this fraction are in the form of vesicles. Further purification of plasma membrane is achieved by sucrose density gradient centrifugation and results in a 25- to 30-fold enrichment of plasma membrane markers. Plasma membrane markers band in these gradients between 1.10 and 1.15 g/cm3. The distribution patterns in the cell fractions of 18 cellular constituents are quantitatively determined. Most constituents are found to distribute in a fashion consistent with the results obtained in other systems. Thymidine-5'-phosphodiesterase (phosphodiesterase I), esterase, nucleoside diphophatase and glucose-6-phosphatase, however, are shown to be poor markers of membrane fractions in this system. Lactoperoxidase-catalyzed iodination was used to identify several plasma membrane proteins which are exposed at the surface. After separation of labeled polypeptides by sodium dodecyl sulfate gel electrophoresis, the predominant labeled protein was identified as the heavy chain of IgM. Several lesser labeled proteins were observed.

Fatty acid differences amongst leukemia cell types, with special reference to hairy cell leukemia: a preliminary report

Fatty acid analyses of malignant cells from hairy cell leukemia patients revealed a profile which was rich in arachidonate and relatively low in linoleate and oleate. This profile was distinct from that of mononuclear cells derived from patients with other lymphoproliferative diseases or myeloproliferative disorders, and may reflect the unique membrane morphology of the hairy cell.

The significance of lymphocyte lipid changes after smoking hashish

The increase of lymphocyte total lipids and phospholipids after smoking hashish, indicates either a lipid transfer from their site of production after smoking the drug or a mobilization of their biosynthetic mechanism in the lymphocyte. A fluctuation of individual phospholipid concentrations after "smoking" is related to the influence of certain hashish compounds on the various biosynthetic pathways of phospholipids in lymphocytes. Changes in phosphatidylcholine, phosphatidylinositol and phosphatidylserine are related to a possible fluctuation of the overall immune ability of the lymphocyte, by affecting the lymphocyte membrane enzyme mechanisms.

Studies on the glycolipids of sheep thymus and of normal and concanavalin A-stimulated sheep peripheral lymphocytes

The neutral glycolipids and gangliosides of sheep thymus and of sheep peripheral lymphocytes were compared. The patterns of both of these major classes of glycolipids were more complex in thymus than in the lymphocytes. The incorporation of radioactivity from D-[1-14C]galactose into the individual glycolipids of control and concanavalin A-stimulated sheep peripheral lymphocytes was also studied. A marked enhancement of incorporation into trihexosylceramide and an alteration of the pattern of incorporation into gangliosides were noted in the mitogen-treated cells. The results suggest that significant alterations of glycolipid composition and metabolism may occur during at least certain stages of lymphocyte differentiation.