Identification of ubiquinone-50 as the major methylated nonpolar lipid in human monocytes. Regulation of its biosynthesis via methionine-dependent pathways and relationship to superoxide production

Ubiquinone-10 content in lymphocytes of phenylketonuric patients

OBJECTIVES

To investigate the ubiquinone-10 content in lymphocytes from phenylketonuric patients.

DESIGN AND METHODS

We compared 23 patients with 25 age-matched controls. Ubiquinone-10 was analyzed by HPLC with electrochemical detection.

RESULTS

Ubiquinone-10 concentrations were significantly lower in patients (77-270 nmol/g of protein) compared with controls (190-550) (p < 0.001). Significantly negative correlation was observed between ubiquinone-10 and phenylalanine (r = -0.441; p < 0.05).

CONCLUSIONS

Ubiquinone-10 concentrations are decreased in lymphocytes from phenylketonuric patients. This deficiency is associated with high plasma phenylalanine concentrations.

Differential changes in lipid metabolism of myeloid and lymphoid cell lines induced by treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA)

Treatment of the myeloid cell lines, U-937 or HL-60, with 10 nM of the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), for 24 h increased the rate of incorporation of [3H]glycerol into total chloroform extracts. A proportionally greater labeling of the non-polar lipid (NL) fraction compared to the polar, phospholipid (PL), fraction was observed. Chromatographic analysis showed a 6-fold increase in the labeling of triacylglycerols (TAG), a 2-fold increase in diacylglycerols, and no changes in monoacylglycerols. PL labeling showed a 3-fold increase in phosphatidylcholine (PC). The effect of TPA on TAG labeling was selectively observed in myeloid cell lines. No such a change was found in the lymphoid cell line. MOLT-3, which did respond to TPA with increased PC labeling. Incorporation of [3H]arachidonic acid (AA) into TAG by U-937 cells was selectively increased (2.5-fold) after treatment with TPA for 24 h. Treatment of U-937 cells with TPA in serum-free medium resulted in no increased labeling of TAG. These studies suggest that changes in TAG metabolism may be characteristic of myeloid differentiation and depend on the presence of serum factor(s).

Alteration in the membrane fatty acid composition of human lymphocytes and cultured transformed cells induced by interferon

The effects of interferon (IFN) treatment on the lipid composition of human peripheral blood lymphocytes or transformed cell line cells were investigated. The major phospholipid classes of lymphocytes as analyzed by 2-dimensional TLC and quantified by phosphorous content were phosphatidylcholine (PC, 43%) and phosphatidylethanolamine (PE, 28%), along with phosphatidylserine (9%) and phosphatidylinositol (8%). The membrane-impermeant reagent, trinitrobenzenesulfonate was used to covalently label cell surface PE. Fatty acid (FA) composition, determined by gas-liquid chromatography, showed a distinct pattern in each lipid class, with a predominance of 16 and 18 carbon fatty acids (FA) in PC and PE respectively. Arachidonic acid (20:4) and, to a lesser extent, docosahexanoic acid (22:6) were predominant in PE. The degree of unsaturation in each class, expressed as the ratio between unsaturated and saturated FA (U/S), was higher in PE (1.72) than in derivatized trinitrophenyl cell surface PE (TNP-PE, 0.57) or PC (0.64). Treatment with IFN resulted in an increased U/S ratio in cell surface PE (1.10) but not in other PE species (1.46). A small increase in unsaturation (0.88) was also observed in PC. Most of the increase in TNP-PE U/S was accounted for by an increase in 20:4 and a concomitant decrease in 18:0. These alterations were observed in the absence of quantitative change in the principal phospholipid classes or in the FA composition of the total lipid extract. In K562, a transformed cell line with characteristics of the erythromyeloid lineage, PE was found to be the most saturated lipid class with a predominance of 18:0. In PC, 16:0 was most abundant. Among unsaturated FA, 18:1 predominated in all lipid classes studied. Treatment with natural IFN alpha for 30 hr generally resulted in a decrease in saturated FA and an increase in unsaturated FA, which was most marked in PE. The U/S ratio in PE was highest in K562 cells during the time of maximal cell proliferation as assessed by tritiated thymidine incorporation. TNP-PE simultaneously decreased. Daudi cells, a B-lymphoblastoid cell line, demonstrated changes in FA composition of lipids with decreased saturated and monoenoic FA after IFN treatment, whereas DIF3 (a clone selected for lack of sensitivity to IFN) showed no change. These studies document changes in membrane FA composition of lymphocytes treated with IFN and correlate IFN-induced changes in transformed cell line FA with effects on proliferation. They further show the existence of a transverse molecular species asymmetry of PE in the plasma membrane of these cells which is altered after IFN treatment.