Biochimica et Biophysica Acta (BBA) - Lipids and Lipid Metabolism最新文献

The antioxidant properties of butein, isolated from Dalbergia odorifera T. Chen, were investigated in this study. Butein inhibited iron-induced lipid peroxidation in rat brain homogenate in a concentration-dependent manner with an IC₅₀, 3.3±0.4 μM. It was as potent as α-tocopherol in reducing the stable free radical diphenyl-2-picrylhydrazyl (DPPH) with an IC_0.200, 9.2±1.8 μM. It also inhibited the activity of xanthine oxidase with an IC₅₀, 5.9±0.3 μM. Besides, butein scavenged the peroxyl radical derived from 2,2-azobis(2-amidinopropane) dihydrochloride (AAPH) in aqueous phase, but not that from 2,2-azobis(2,4-dimethylvaleronitrile) (AMVN) in hexane. Furthermore, butein inhibited copper-catalyzed oxidation of human low-density lipoprotein (LDL), as measured by conjugated dienes and thiobarbituric acid-reactive substance (TBARS) formations, and electrophoretic mobility in a concentration-dependent manner. Spectral analysis revealed that butein was a chelator of ferrous and copper ions. It is proposed that butein serves as a powerful antioxidant against lipid and LDL peroxidation by its versatile free radical scavenging actions and metal ion chelation.

Covalent modification of eucaryotic proteins, involving addition of isoprenyl groups, is a widespread phenomenon. Here we provide direct evidence for this form of covalent modification in the free-living nematode, Caenorhabditis elegans. Following incubation in the presence of [³H]mevalonolactone, specific C. elegans polypeptides became labelled in both aqueous and detergent (Triton X-114)-enriched extracts. Chemical and GC–MS analysis of modifying groups, cleaved from C. elegans polypeptides, revealed that geranylgeranylation and, to a lesser extent, farnesylation of target polypeptides occurred. Immunoblot analysis provided preliminary evidence that the ras-like let-60 polypeptide was a target for isoprenylation in C. elegans.

To study the transport of 24-hydroxycholesterol, 27-hydroxycholesterol and 3β-hydroxy-5-cholestenoic acid in the circulation, the distribution of these oxysterols was determined in plasma, very low density lipoprotein, low density lipoprotein, high density lipoprotein, and lipoprotein-free plasma. An accurate method based on isotope dilution-mass spectrometry with use of individual deuterium labeled internal standards was used. 24-Hydroxycholesterol and 27-hydroxycholesterol were found to be associated mainly with HDL and LDL, whereas 3β-hydroxy-5-cholestenoic acid was found predominantly in the lipoprotein-free fraction. While both 24-hydroxycholesterol and 27-hydroxycholesterol are present mainly in esterified form in plasma, 3β-hydroxy-5-cholestenoic acid was present as free acid only. For reasons of comparison, a number of other oxysterols were determined in plasma and in isolated lipoprotein fractions. Significant amounts of these oxysterols were formed by cholesterol autoxidation during fractionation of plasma. It was therefore not possible to calculate the distribution of these oxysterols in the different plasma fractions. The present results are consistent with our previous finding that the less polar cholesterol metabolite 27-hydroxycholesterol competes with cholesterol for transport out of cells using HDL as an acceptor molecule, whereas the transport of the more polar compound 3β-hydroxy-5-cholestenoic acid is facilitated by albumin.

Cholesteryl ester transfer protein (CETP) mRNA is more abundantly expressed in small mature adipocytes as compared to large, lipid-rich adipocytes [Radeau et al., J. Lipid Res. 36 (1995) 2552–2561]. In the present study, the stromal vascular fraction (SVF) of human adipose tissue was isolated and the presence of very small fat cells in this fraction confirmed by electron microscopy and by demonstrating the presence of mRNA for adipsin and for CCAAT enhancer binding protein α (C/EBPα), a marker of adipocyte differentiation. sn-Glycerol 3-phosphate dehydrogenase (GPDH) activity was present in the SVF but not in the preadipocyte fraction. Northern blot analysis of human adipose tissue demonstrated that CETP mRNA expression was significantly greater (+96%, P<0.03) in stromal-vascular cells (SVC) as compared to mature fat cells. By comparison, lipoprotein lipase mRNA expression was lower (−75%, P<0.03) in SVC while apolipoprotein E mRNA expression was not significantly different in SVC as compared to isolated adipocytes. By RT-PCR analysis, we demonstrated that CETP mRNA was expressed by human pre-adipocytes at levels less than those of SVC and adipocytes. The absence of monocytes/macrophages in SVC was confirmed by the absence of FcγRIII (CD16) mRNA in these fractions. These data demonstrate that CETP mRNA is most highly expressed in the immature fat cells of human adipose tissue, consistent with other experiments from this laboratory demonstrating that CETP plays an important local role in adipocyte cholesterol accumulation.

The pathogenicity of lipoprotein(a) [Lp(a)] as a risk factor for cardiovascular disease may depend upon its lysine binding sites (LBS) which impart unique functions to Lp(a) not shared with low density lipoprotein. Biologically relevant modifications of Lp(a) were tested for alterations of LBS activity using two previously described functional assays, a LBS-Lp(a) immunoassay and a lysine–Sepharose bead assay. In the LBS-Lp(a) immunoassay, minimal changes in the LBS activity of Lp(a) were observed after modification with lipoprotein lipase, sphingomyelinase, or phospholipase C. In contrast, a significant (p<0.003) increase in the LBS activity of Lp(a) occurred after phospholipase A₂ (PLA₂) treatment, and this increase was confirmed using the lysine–Sepharose bead assay. The increase depended upon the release of fatty acids from Lp(a) by PLA₂. A decrease in the LBS activity of Lp(a) occurred after oxidation of Lp(a) with 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) (44% decrease), but CuSO₄ oxidation increased LBS activity (210%). N-acetylcysteine (NAC) treatment of Lp(a) decreased (48%) LBS activity while homocysteine treatment had no (89%) effect. Thus, modification of phospholipids and protein moieties can alter the LBS-activity of Lp(a). Such enzymatic and chemical modifications may contribute to the variability in LBS function of Lp(a) seen within the population.

Catalytic amounts of Fe²⁺ or Fe³⁺ ions are widely applied to induce simulated biological lipid peroxidation reactions. Independently, whether Fe²⁺ or Fe³⁺ were used, similar products were obtained. We show in this paper that the product spectrum is indeed very different, whether one ion species, either Fe²⁺ or Fe³⁺, is present in excess; thus, decomposition of (13S,9Z,11E) 13-hydroxyperoxy-9,11-octadecadienoic acid (13S-HPODE) generates in the presence of equimolar amounts of Fe²⁺ ions mainly the corresponding alcohol (13S,9Z,11E) 13-hydroxy-9,11-octadecadienoic acid besides 12,13-epoxy-11-hydroxy-9-octadecenoic acid (12,13-epHOD) and 13-oxo-9,11-octa-decadienoic acid (13-KODE), while decomposition of 13S-HPODE with equimolar amounts of Fe³⁺ produces mainly 12,13-epHOD, hydrolysis products thereof and other oxidized products, e.g., hydroxyoxo acids. In addition, unusually large amounts of aldehydes are formed, e.g., the amount of 4-hydroxy-nonenal was found to exceed that obtained by Fe²⁺ induced air oxidation for a factor of about 100. Since these further oxidation products are suspected to cause cell damage, liberated Fe³⁺ ions seem to be responsible for generation of toxic products in inflammatory diseases, e.g., atherosclerosis.

A novel l-3-hydroxyacyl-CoA dehydrogenase from pig liver has been cloned, expressed, purified, and characterized. This enzyme is a homodimer with a molecular mass of 65.6 kDa, and is distinguished from the dehydrogenase of pig heart by its structural features and catalytic properties. Its subunit, consisting of 302 amino acid residues, has two additional residues in a key region of the active center while it lacks a sequence of seven residues in the NAD⁺-binding domain, when compared with the subunit of pig heart enzyme. In addition, there are substitutions of four single residues. The catalytic efficiency of pig liver dehydrogenase was significantly greater than that of the heart enzyme for short-chain substrate, but its catalytic rates declined with an increase in substrate chain-lengths. The distinction between pig liver and heart dehydrogenases cannot be attributed to a species difference, and thus it is concluded that there exist different isoforms of monofunctional l-3-hydroxyacyl-CoA dehydrogenases in pig. High level expression of mitochondrial l-3-hydroxyacyl-CoA dehydrogenase in Escherichia coli has provided a very convenient way to purify this important β-oxidation enzyme. There is substantial homology between pig liver dehydrogenase and various multifunctional β-oxidation enzymes in the active center of these enzymes; a consensus sequence, HX₃PX_1–3MXLXE, is proposed as the signature sequence of l-3-hydroxyacyl-CoA dehydrogenases.

The protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA) stimulates both the synthesis and phospholipase D (PLD)-mediated hydrolysis of phosphatidylcholine (PtdCho). Here, attached and suspended NIH 3T3 fibroblasts as well as variants of the MCF-7 human breast carcinoma cell line expressing PKC-α and a PtdCho-specific PLD activity at widely different levels were used to determine the possible role of PKC-α, PtdCho hydrolysis, and choline uptake in the mediation of PMA effect on PtdCho synthesis. In wild-type MCF-7 cells, which express both PKC-α and PLD activities at very low levels, PMA had little effects on the uptake or incorporation [${}^{14}\text{C}$]choline into PtdCho. In multidrug resistant MCF-7/MDR1 cells, which highly express PKC-α but lack the PtdCho-specific PLD activity, 100-nM PMA had relatively small stimulatory effects on the uptake of [${}^{14}\text{C}$]choline (∼1.5-fold) and [${}^{14}\text{C}$]PtdCho synthesis (1.5- to 2-fold). In NIH 3T3 fibroblasts and MCF-7/PKC-α cells, both expressing PKC-α and PLD activities at high levels, 10–100-nM PMA enhanced [${}^{14}\text{C}$]choline uptake only slightly (1.7- to 2.2-fold), while it had much greater (∼4–9-fold) stimulatory effects on PtdCho synthesis. PMA significantly enhanced the formation of phosphatidic acid (PtdOH) in MCF-7/PKC-α cells (2.8-fold increase), but not in MCF-7/MDR1 cells (1.4-fold increase), while in both cell lines it had only small (1.3–1.5-fold) stimulatory effects on 1,2-diacylglycerol (1,2-DAG) formation. In suspended NIH 3T3 cells, 200–300-mM ethanol blocked the stimulatory effect of PMA on PtdOH formation without affecting PtdCho synthesis indicating that neither PtdOH nor 1,2-DAG derived from it is a mediator of PMA effect on PtdCho synthesis. In attached NIH 3T3 cells, dimethylbenz[a]anthracene enhanced phosphocholine formation and, thus, choline uptake without increasing PtdCho synthesis or modifying the effect of PMA. While the results indicate that the stimulatory effect of PMA on PtdCho synthesis requires the expression of both PKC-α and a PtdCho-specific PLD, they do not support a role for 1,2-DAG, PtdOH or choline in the mediation of PMA effect.

Pulsed-field-gradient NMR spectroscopy was used to measure translational diffusion coefficients (D_s) for a peptide corresponding to a proposed lipid-binding domain of human apolipoprotein C-I, residues 7–24 (apoC-I(7–24)). Diffusion coefficients for apoC-I(7–24) were determined directly by following the decay of the resonance intensity of selected peptide protons at various concentrations of sodium dodecyl sulfate (SDS), a detergent increasingly being used to model the apolipoprotein environment. Previously, diffusion coefficients of peptides in the presence of SDS have been determined indirectly by monitoring the SDS diffusion coefficient. The direct measurement of the diffusion coefficient of the peptide enables one to distinguish whether SDS simply coats the peptide's surface to produce a uniformly charged `rod' or if the peptide associates with a micelle. Using the direct method, at SDS concentrations above 5 mM (which is below the SDS critical micelle concentration (8.1 mM)), apoC-I(7–24) exhibited diffusion coefficients consistent with the formation of a large-molecular-weight complex. Based on the ratio of the diffusion coefficients for free- and SDS-associated peptide, the molecular weight of the peptide–SDS complex was much larger than a factor of 1.4, the increase in molecular weight of the free peptide predicted if apoC-I(7–24) was uniformly surface coated with SDS.

The lipogenic enzyme fatty acid synthase (FAS) is elevated in various human primary cancers and certain human cancer cell lines. FAS overexpression in human neoplasia has clinical relevance because of its association with tumor aggression and potential chemotherapeutic intervention. Here, we surveyed FAS in cell lines established from normal murine mammary epithelium (NMuMG) and from mammary tumors induced by either rodent polyoma (Py) virus or murine mammary tumor virus (MMTV). Western blotting revealed greater content of FAS in Py-transformed A1-1 and T1 than NMuMG or MMTV-transformed Mm5MT, RIIIMT and MMT060562. These data suggest that signaling events mediated by Py transformation may increase cellular amounts of FAS. Although FAS content was elevated to similar levels in A1-1 and T1, specific activities were significantly different as enzyme activity in T1 was 3-fold higher than A1-1. Likewise, FAS activity in NMuMG was about 0.5-fold higher than the MMTV-transformed lines, even though enzyme content was similar. Immunoprecipitation studies employing anti-phosphoamino acid antibodies followed by immunoblot analysis with anti-FAS antisera (and vice versa) were used to characterize the constitutive phosphorylation state of the enzyme. Phosphoserine and phosphothreonine residues were detected in the more active FAS from T1 and NMuMG, but not in the less active FAS from Mm5MT or A1-1. Discovery of phosphorylated FAS suggests that the enzyme may have more immediate control over lipogenesis than previously thought. High-dose (10⁻⁴ M) dexamethasone induced FAS content and activity in NMuMG and MMTV-transformed lines but not Py-transformed cells. Lower concentrations (10⁻⁸, 10⁻⁶ M) of dexamethasone also activated FAS but without concomitant elevation of its protein content, which was consistent with a phosphorylated form of FAS. Finally, cell lines were treated with the FAS inhibitor cerulenin: almost all breast cancer lines were growth inhibited at significantly lower amounts of drug than normal cell lineages, suggesting that FAS plays a greater role in viability of tumor cells than normal cells. Pretreatment with palmitate (a primary end-product of FAS) prior to cerulenin rescued A1-1 cells only slightly from growth inhibition, whereas pretreatment with oleate (a monounsaturated fatty acid synthesized from palmitate) synergized cerulenin's cytotoxic effects.