Polar Lipid Synthesis Research Articles

Lipidome of the Brown Macroalga Undaria pinnatifida: Influence of Season and Endophytic Infection.

An analysis of the lipidome of the brown alga Undaria pinnatifida (Laminariales) was performed' more than 900 molecular species were identified in 12 polar lipids and 1 neutral lipid using HPLC/MS-MS. The seasonal changes of U. pinnatifida lipidome were determined. It was shown that acclimatization to winter and spring was accompanied by an increase in the unsaturation of both polar and neutral lipids. In autumn and summer, on the contrary, the contents of more saturated molecular species of all lipid classes increased. Based on the data obtained, a scheme for the polar and neutral lipid synthesis in brown algae was proposed. In addition, the influence of infection with the brown filamentous endophyte Laminariocolax aecidioides (Ectocarpales) on U. pinnatifida lipidome was studied. It was found that infection has the most noticeable effect on the molecular species composition of triacylglycerides, phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylhydroxyethylglycine of the host macrophyte. In infected samples of algae, changes in the composition of triacylglycerides were revealed both in areas with the presence of an endophyte and in adjacent intact tissues, which may indicate the occurrence of a secondary infection.

LC-MS analysis of D2O-labelled soil suggests a large fraction of membrane lipid exists within slow growing microbes

Measuring the growth of microbes is essential for understanding soil function, yet it remains challenging. Knowing the rate of synthesis of polar lipids that comprise microbial membranes would serve as an indicator of microbial growth, and also improve understanding of the biogeochemical cycling of polar lipids. The aim of this study was to develop D2O-labelling of intact polar lipids (D2O-intact lipid-SIP) as a culture- and gene-independent way of probing synthesis of membrane lipids by soil microbes. To test the feasibility of coupling D2O labelling with liquid chromatography-mass spectrometry (LC-MS) quantification, and determine appropriate incubation durations, we incubated two soils with 50 atom% D2O for durations between 3 h and 46 days. We first improved the chromatographic separation to reduce the number of co-eluting lipids and enable easier quantification of D2O enrichment. Increasing column length from 150 mm to 500 mm and the gradient separation from 45 to 300 min increased 3.4-fold the number of resolved peaks, and meant that chromatographically co-eluting lipids were generally separated in the mass dimension by a minimum of ten Da. Quantification of 2H enrichment of a broad spectrum of lipids was possible in soils incubated with 50 atom% D2O for 27 h. Enrichment and rate of lipid synthesis were determined for 34–38 membrane lipids that collectively accounted for >80% of the lipid pool. There was ten-fold variation among individual lipids in rates of synthesis and turnover, which presumably reflects differences in growth rate and abundance of soil taxa. Turnover differed among classes from 1.2 to 1.5 years in phosphatidylcholine, 0.54–0.98 years in diacylglyceryl-N,N,N-trimethylhomoserine, and 0.42–0.72 years in phosphatidylethanolamine. By quantifying the isotopologue distribution, LC-MS revealed the average turnover comprised a large population of lipid that remained unlabelled (93–95% unlabelled after 27 h and 66–75% unlabelled after 46 days), and a small population of lipid that had incorporated varying numbers of 2H. These observations are consistent with much of the microbial lipid pool residing in microbes with negligible growth, and a smaller proportion in microbes with a range of growth rates. Accordingly turnover calculated solely for the active fraction of lipid was a more rapid 20–30 days. The slow average turnover of membrane lipids likely also reflects efficient microbial recycling of lipids reducing the amount of lipid synthesis required to support growth.

Limited fatty-acid supply from the plastid and active catabolism of triacylglycerol prevent the accumulation of triacylglycerol in Coccomyxa sp. strain Obi grown under nitrogen-replete conditions

The Coccomyxa sp. strain Obi is a unicellular green alga that accumulates >40% triacylglycerol (TAG) per cell dry weight under nitrogen (N)-limiting conditions. In this study, we analyzed the de novo synthesis of TAG under N-replete and N-limiting conditions using 14C tracers and quantitative reverse transcription PCR (RT-qPCR) approaches. In cells grown under N-replete conditions, the incorporation of photosynthetically fixed 14C into TAG was <5% of that incorporated into polar lipids, whereas the incorporation of exogenous 14C-fatty acids into TAG was approximately 50% of that incorporated into polar lipids. These results demonstrated that enzyme activities that convert fatty acids to TAG are appreciably expressed under N-replete conditions; however low fatty acid supply limits the TAG synthesis in N-replete cells. In agreement with this inference, the expression of FAT1 that encodes acyl-ACP thioesterase, which releases free fatty acids from acyl-ACP, was poorly expressed under N-replete conditions but induced under N-limiting conditions. Meanwhile, pulse-chase labeling experiments demonstrated a significant turnover of TAG under N-replete conditions. Taken together, we propose that both the limited carbon flux into TAG and active catabolism of TAG prevented the accumulation of TAG under N-replete conditions, whereas the increased carbon flux into TAG and possibly decreased catabolism of TAG contributed to the enhanced accumulation of TAG under N-limiting conditions. Furthermore, pulse-chase experiments demonstrated that the rate of TAG synthesis was much slower than that of polar lipid synthesis under N-limiting conditions, partly because of the slow conversion of diacylglycerol to TAG.

Merdimonas faecis gen. nov., sp. nov., isolated from human faeces.

A strictly anaerobic Gram-stain-positive, non-motile and non-spore-forming bacterial strain, BR31T, was isolated from a faecal sample of a healthy human. Bacterial colonies were ivory-coloured on GAM agar and composed of rod-shaped cells with rounded ends approximately 1.4-2.1×0.5-0.6 µm in size. According to comparative analysis based on 16S rRNA gene sequences, strain BR31T formed a distinct phylogenetic lineage that reflects a new genus within Clostridium cluster XIVa in the family Lachnospiraceae, with highest similarity to Eubacterium contortum DSM 3982T (94.6 %). The DNA G+C content was calculated to be 47.0 mol% from whole genome sequencing. Predicted genes associated with synthesis of teichuronic acid, polyamines, polar lipids and diaminopimelic acid were detected. The peptidoglycan contained meso-diaminopimelic acid and the main polar lipid detected was phosphatidylglycerol. The major metabolic end product of glucose was acetic acid, which was in agreement with those of most members of the family. However, the profile of major cellular fatty acids (C16 : 0, C14 : 0, summed feature 4 and C13 : 0) and overall enzyme activity demonstrated phenotypic differentiation of strain BR31T from other closely related genera. Thus, based on distinct phenotypic, phylogenetic, genotypic and chemotaxonomic characteristics, strain BR31T is considered to represent a novel species of a new genus, for which the name Merdimonas faecis gen. nov., sp. nov. is proposed. The type strain of Merdimonas faecis is BR31T (=KCTC 15482T=JCM 30748T).

Influence of Growth Phase, pH, and Temperature on the Abundance and Composition of Tetraether Lipids in the Thermoacidophile Picrophilus torridus.

The abundance and composition of glycerol dibiphytanyl glycerol tetraether (GDGT) and glycerol tribiphytanyl glycerol tetraether (GTGT) lipids were determined as a function of growth phase as a proxy for nutrient availability, the pH of growth medium, and incubation temperature in cultures of the thermoacidophile Picrophilus torridus. Regardless of the cultivation condition, the abundance of GDGTs and GTGTs was greater in the polar than core fraction, with a marked decrease in core GDGTs in cultures harvested during log phase growth. These data are consistent with previous suggestions indicating that core GDGTs are re-functionalized during polar lipid synthesis. Under all conditions examined, polar lipids were enriched in a GDGT with 2 cyclopentyl rings (GDGT-2), indicating GDGT-2 is the preferred lipid in this taxon. However, lag or stationary phase grown cells or cells subjected to pH or thermal stress were enriched in GDGTs with 4, 5, or 6 rings and depleted in GDGTs with 1, 2, 3, rings relative to log phase cells grown under optimal conditions. Variation in the composition of polar GDGT lipids in cells harvested during various growth phases tended to be greater than in cells cultivated over a pH range of 0.3–1.1 and a temperature range of 53–63°C. These results suggest that the growth phase, the pH of growth medium, and incubation temperature are all important factors that shape the composition of tetraether lipids in Picrophilus. The similarity in enrichment of GDGTs with more rings in cultures undergoing nutrient, pH, and thermal stress points to GDGT cyclization as a generalized physiological response to stress in this taxon.

Identification of regulatory network hubs that control lipid metabolism in Chlamydomonas reinhardtii.

Microalgae-based biofuels are promising sources of alternative energy, but improvements throughout the production process are required to establish them as economically feasible. One of the most influential improvements would be a significant increase in lipid yields, which could be achieved by altering the regulation of lipid biosynthesis and accumulation. Chlamydomonas reinhardtii accumulates oil (triacylglycerols, TAG) in response to nitrogen (N) deprivation. Although a few important regulatory genes have been identified that are involved in controlling this process, a global understanding of the larger regulatory network has not been developed. In order to uncover this network in this species, a combined omics (transcriptomic, proteomic and metabolomic) analysis was applied to cells grown in a time course experiment after a shift from N-replete to N-depleted conditions. Changes in transcript and protein levels of 414 predicted transcription factors (TFs) and transcriptional regulators (TRs) were monitored relative to other genes. The TF and TR genes were thus classified by two separate measures: up-regulated versus down-regulated and early response versus late response relative to two phases of polar lipid synthesis (before and after TAG biosynthesis initiation). Lipidomic and primary metabolite profiling generated compound accumulation levels that were integrated with the transcript dataset and TF profiling to produce a transcriptional regulatory network. Evaluation of this proposed regulatory network led to the identification of several regulatory hubs that control many aspects of cellular metabolism, from N assimilation and metabolism, to central metabolism, photosynthesis and lipid metabolism.

Hyperglycemia Diverts Dividing Osteoblastic Precursor Cells to an Adipogenic Pathway and Induces Synthesis of a Hyaluronan Matrix That Is Adhesive for Monocytes

Isolated rat bone marrow stromal cells cultured in osteogenic medium in which the normal 5.6 mm glucose is changed to hyperglycemic 25.6 mm glucose greatly increase lipid formation between 21-31 days of culture that is associated with decreased biomineralization, up-regulate expression of cyclin D3 and two adipogenic markers (CCAAT/enhancer binding protein α and peroxisome proliferator-activated receptor γ) within 5 days of culture, increase neutral and polar lipid synthesis within 5 days of culture, and form a monocyte-adhesive hyaluronan matrix through an endoplasmic reticulum stress-induced autophagic mechanism. Evidence is also provided that, by 4 weeks after diabetes onset in the streptozotocin-induced diabetic rat model, there is a large loss of trabecular bone mineral density without apparent proportional changes in underlying collagen matrices, a large accumulation of a hyaluronan matrix within the trabecular bone marrow, and adipocytes and macrophages embedded in this hyaluronan matrix. These results support the hypothesis that hyperglycemia in bone marrow diverts dividing osteoblastic precursor cells (bone marrow stromal cells) to a metabolically stressed adipogenic pathway that induces synthesis of a hyaluronan matrix that recruits inflammatory cells and establishes a chronic inflammatory process that demineralizes trabecular cancellous bone.

Diacylglycerol Kinase Delta Promotes Lipogenesis

We have studied the relationship between diacylglycerol kinase delta (DGKδ) and lipogenesis. There is a marked increase in the expression of DGKδ during the differentiation of 3T3-L1 cells to adipocytes, as well as in the synthesis of neutral and polar lipids. When 3T3-L1 undifferentiated fibroblasts are transfected to express DGKδ, there is increased triglyceride synthesis without differentiation to adipocytes. Hence, expression of DGKδ promotes lipogenesis. Lipid synthesis is decreased in DGKδ knockout mouse embryo fibroblasts, especially for lipids with shorter acyl chains and limited unsaturation. This reduction occurs for both neutral and polar lipids. These findings suggest reduced de novo lipid synthesis. This is confirmed by measuring the incorporation of glycerol into polar and neutral lipids, which is higher in the wild type cells than in the DGKδ knockouts. In comparison, there was no change in lipid synthesis in DGKε knockout mouse embryo fibroblasts. We also demonstrate that the DGKδ knockout cells had a lower expression of acetyl-CoA carboxylase and fatty acid synthase as well as a lower degree of activation by phosphorylation of ATP citrate lyase. These three enzymes are involved in the synthesis of long chain fatty acids. Our results demonstrate that DGKδ markedly increases lipid synthesis, at least in part as a result of promoting the de novo synthesis of fatty acids.

Cell-type-specific regulation of genes involved in testicular lipid metabolism: fatty acid-binding proteins, diacylglycerol acyltransferases, and perilipin 2

Male germ cell differentiation entails the synthesis and remodeling of membrane polar lipids and the formation of triacylglycerols (TAGs). This requires fatty acid-binding proteins (FABPs) for intracellular fatty acid traffic, a diacylglycerol acyltransferase (DGAT) to catalyze the final step of TAG biosynthesis, and a TAG storage mode. We examined the expression of genes encoding five members of the FABP family and two DGAT proteins, as well as the lipid droplet protein perilipin 2 (PLIN2), during mouse testis development and in specific cells from seminiferous epithelium. Fabp5 expression was distinctive of Sertoli cells and consequently was higher in prepubertal than in adult testis. The expression of Fabp3 increased in testis during postnatal development, associated with the functional differentiation of interstitial cells, but was low in germ cells. Fabp9, together with Fabp12, was prominently expressed in the latter. Their transcripts increased from spermatocytes to spermatids and, interestingly, were highest in spermatid-derived residual bodies (RB). Both Sertoli and germ cells, which produce neutral lipids and store them in lipid droplets, expressed Plin2. Yet, while Dgat1 was detected in Sertoli cells, Dgat2 accumulated in germ cells with a similar pattern of expression as Fabp9. These results correlated with polyunsaturated fatty acid-rich TAG levels also increasing with mouse germ cell differentiation highest in RB, connecting DGAT2 with the biosynthesis of such TAGs. The age- and germ cell type-associated increases in Fabp9, Dgat2, and Plin2 levels are thus functionally related in the last stages of germ cell differentiation.

Phospholipase stimulates lipogenesis in SZ95 sebocytes

Introduction: With progressing ageing human sebocytes reduce lipid production. However, the influence of certain aging mechanisms on sebaceous lipid synthesis as well as ways to influence the latter is not fully identified. Certain lipids act as ligands of nuclear receptors such as PPAR. Phospholipase (PLA2) catalyzes the hydrolysis of the sn‐2 fatty acyl bond of phospholipids to yield free fatty acid and lysophospholipid. It has been hypothesized that PPAR may be activated by hydrolysis products of phospholipids and also by eicosanoids obtained through PLA2 activity.Materials and Methods: A method to quantify sebaceous lipid synthesis of SZ95 sebocytes in vitro was established and the cells were treated by snake venom Bothrops moojeni gel filtration fractions (Botmo GF). Botmo GF fractions were further purified by RP‐HPLC, and a fraction with PLA2 activity (Botmo GF11‐117) and a fraction without enzymatic activity (Botmo GF11‐101) were identified and additionally tested.Results: Botmo GF fractions increased lipogenesis in SZ95 sebocytes without inducing apparent toxic or apoptotic effects. Botmo GF11‐101 (1 μg/ml) enhanced neutral lipid synthesis by up to 170% and polar lipid synthesis by up to 120%. The enzymatically active PLA2 Botmo GF11‐117 (1 μg/ml) increased synthesis of neutral lipids by up to 200%, and polar lipids by up to 120% compared to untreated SZ95 sebocytes.Conclusion: PLA2 activation or suppression could be important for human sebaceous lipogenesis. PLA2 modifiers may be attractive for skin lipid research and pharmacological/cosmetic products.

Decline of hormones with increasing age regulates the biological activity of human sebocytes

Hormone deficiency occurring with age leads among other systemic disorders to deterioration of the skin quality. Systemic substitution with estradiol in females and GH in males reversed the observed alterations and retarded the skin aging process in single controlled studies. In order to evaluate the importance of sex steroids and growth factors on skin aging in vitro, human sebocytes were treated with GH, IGF‐I, 17β‐estradiol, DHEA, testosterone and progesterone in combination and as single agents in concentrations corresponding to those circulating in young (f20) and postmenopausal women (f60). Cell proliferation and lipid synthesis were measured by means of the 4‐methylumbelliferyl heptanoate fluorescence assay and nile‐red microassay/fluorescence microscopy, respectively. Cells incubated with all hormones mentioned above at f60 showed significantly lower content of sebaceous lipids (P &lt; 0.001) vs. cells at f20 relating to in vivo observations, which have documented a decline of epidermal lipids in aged skin. While progesterone and DHEA, as single agents, showed no effect on lipid synthesis, after treatment with IGF‐I for 48 h at f20 and f60 concentrations, a significant dose‐dependent increase of neutral (P &lt; 0.001) and polar lipids (P &lt; 0.001) was observed at both concentrations tested. Cell size was also increased. On the other hand, GH at f20 and f60 enhanced significantly the production of neutral (P &lt; 0.01 and P &lt; 0.05, accordingly) and polar lipids (P &lt; 0.05 and P &lt; 0.01, accordingly) in sebocytes but not in such an extent as IGF‐I. 17β‐estradiol induced only polar lipid synthesis (P &lt; 0.01) and cell size. No treatment affected the cell proliferation. In conclusion, sex steroids and growth factors and their decline with age play a key role in the regulation of the lipid synthesis in human sebocytes. Furthermore, among all hormones tested, the GH/IGF‐I axis seems to be the most potent regulator of skin lipids.

Accumulation of phospholipids and glycolipids in seed kernels of different sunflower mutants (Helianthus annuus)

AbstractPhospholipids are essential components of the oil bodies present in seeds, and they are also the main components of the commercial seed lecithins used in many food formulas. In the present study, we analyzed the characteristics of the polar lipid fraction of seeds from different sunflower FA mutants. In sunflower seeds the accumulation of polar lipids reaches a maximum 25 d after anthesis before diminishing during the final stages of maturation and desiccation. We have developed an HPLC method, using ELSD, that produces optimal separation of all polar seed lipids. This method improves the results that could be obtained with previous HPLC methods and hence, we have used it to analyze the polar lipid fraction of sunflower seeds. We show that this fraction comprises phospholipids and glycolipids, of which PC is the most abundant species. Moreover, we found that the relative polar lipid content in control and mutant seeds is similar, suggesting that the mutant traits do not affect polar lipid synthesis. The degradation of polar lipids in isolated seeds was also examined and we found that the PC and PE present in developing sunflower seed kernels were rapidly degraded owing to the activity of D‐type phospholipases.

A study of archaeal enzymes involved in polar lipid synthesis linking amino acid sequence information, genomic contexts and lipid composition

Cellular membrane lipids, of which phospholipids are the major constituents, form one of the characteristic features that distinguish Archaea from other organisms. In this study, we focused on the steps in archaeal phospholipid synthetic pathways that generate polar lipids such as archaetidylserine, archaetidylglycerol, and archaetidylinositol. Only archaetidylserine synthase (ASS), from Methanothermobacter thermautotrophicus, has been experimentally identified. Other enzymes have not been fully examined. Through database searching, we detected many archaeal hypothetical proteins that show sequence similarity to members of the CDP alcohol phosphatidyltransferase family, such as phosphatidylserine synthase (PSS), phosphatidylglycerol synthase (PGS) and phosphatidylinositol synthase (PIS) derived from Bacteria and Eukarya. The archaeal hypothetical proteins were classified into two groups, based on the sequence similarity. Members of the first group, including ASS from M. thermautotrophicus, were closely related to PSS. The rough agreement between PSS homologue distribution within Archaea and the experimentally identified distribution of archaetidylserine suggested that the hypothetical proteins are ASSs. We found that an open reading frame (ORF) tends to be adjacent to that of ASS in the genome, and that the order of the two ORFs is conserved. The sequence similarity of phosphatidylserine decarboxylase to the product of the ORF next to the ASS gene, together with the genomic context conservation, suggests that the ORF encodes archaetidylserine decarboxylase, which may transform archaetidylserine to archaetidylethanolamine. The second group of archaeal hypothetical proteins was related to PGS and PIS. The members of this group were subjected to molecular phylogenetic analysis, together with PGSs and PISs and it was found that they formed two distinct clusters in the molecular phylogenetic tree. The distribution of members of each cluster within Archaea roughly corresponded to the experimentally identified distribution of archaetidylglycerol or archaetidylinositol. The molecular phylogenetic tree patterns and the correspondence to the membrane compositions suggest that the two clusters in this group correspond to archaetidylglycerol synthases and archaetidylinositol synthases. No archaeal hypothetical protein with sequence similarity to known phosphatidylcholine synthases was detected in this study.

Lipid synthesis and metabolism in the plastid envelope

Plastid envelope membranes play a major role in the biosynthesis of glycerolipids. In addition, plastids are characterized by the occurrence of plastid‐specific membrane glycolipids (galactolipids, a sulfolipid). Plant lipid metabolism therefore has unique features, when compared to that of other eukaryotic organisms, such as animals and yeast. However, the glycerolipid biosynthetic pathway in chloroplasts is almost identical to that found in cyanobacteria, and reflects the prokaryotic origin of the chloroplast. Fatty acids generated in the plastid stroma are substrates for a whole set of enzymes involved in the synthesis of polar lipids of plastid membranes such as galactolipids, the sulfolipid, the phosphatidylglycerol. In addition, fatty acids are exported outside the plastid where they are used for extraplastidial polar lipid synthesis (phosphatidylcholine, phosphatidylethanolamine, etc.). Various desaturation steps leading to the formation of polyunsaturated fatty acids occur in various cell compartments, especially in chloroplasts, using fatty acids esterified to polar lipids as substrates. Furthermore, plant glycerolipids can be metabolized by a series of very active envelope enzymes, such as the galactolipid:galactolipid galactosyltransferase and the acyl‐galactolipid forming enzyme. The physiological significance of these enzymes is however largely unknown. One of the most active pathways involved in lipid metabolism and present in envelope membranes is the oxylipin pathway: polyunsaturated fatty acids that are released from polar lipids under various conditions (injury, pathogen attack) are converted to oxylipin. Thus, the plastid envelope membranes are also involved in the formation of signalling molecules.

Variations in the lipid composition of alfalfa roots during colonization with the arbuscular mycorrhizal fungus Glomus versiforme

Lipids and their fatty acids were characterized and quantified during the development of the arbuscular mycorrhizal fungus Glomus versiforme in roots of alfalfa (Medicago sativa). A net increase in root total lipids was observed and was proportional to the development of arbuscular mycorrhizal fungus colonization. Triacylglycerols were the main lipid class in colonized roots and appear to have been synthesized by fungi. The increase of palmitoleic acid (characteristic of triacylglycerols from arbuscular mycorrhizal fungus) in roots colonized with G. versiforme reinforced this suggestion. Phosphatidylethanolamine and to a minor extent phosphatidylcholine also increased during the endophyte growth. Variations in the lipid classes of external mycelia isolated from one-, two- and three-mo old colonized roots with G. versiforme were also analyzed. Despite the continuous increase of triacylglycerols and phosphatidylethanolamine observed, the polar lipid class predominated in the external mycelia isolated from one-mo old colonized roots and the neutral lipid class prevailed in the external mycelia obtained from three-mo old mycorrhizal roots. Biosynthesis of triacylglycerols in intra- and extramatrical mycelia as well as an induced synthesis of polar lipids in roots are suggested as the consequence of fungi colonization.

Variations in the Lipid Composition of Alfalfa Roots during Colonization with the Arbuscular Mycorrhizal Fungus Glomus versiforme

Lipids and their fatty acids were characterized and quantified during the development of the arbuscular mycorrhizal fungus Glomus versiforme in roots of alfalfa (Medicago sativa). A net increase in root total lipids was observed and was proportional to the development of arbuscular mycorrhizal fungus colonization. Triacylglycerols were the main lipid class in colonized roots and appear to have been synthesized by fungi. The increase of palmitoleic acid (characteristic of triacylglycerols from arbuscular mycorrhizal fungus) in roots colonized with G. versiforme reinforced this suggestion. Phosphatidylethanolamine and to a minor extent phosphatidylcholine also increased during the endophyte growth. Variations in the lipid classes of external mycelia isolated from one-, two- and three-mo old colonized roots with G. versiforme were also analyzed. Despite the continuous increase of triacylglycerols and phosphatidylethanolamine observed, the polar lipid class predominated in the external mycelia isolated from one-mo old colonized roots and the neutral lipid class prevailed in the external mycelia obtained from three-mo old mycorrhizal roots. Biosynthesis of triacylglycerols in intra- and extramatrical mycelia as well as an induced synthesis of polar lipids in roots are suggested as the consequence of fungi colonization.

Responses of oral epithelial cells to dental resin components.

The light-polymerized resins used in dentistry and their various constituents have been shown to produce significant levels of cytotoxicity, depending upon the material and the cell type exposed to it. These responses include altered cell growth and macromolecule synthesis. The current study examined the effects of several resin components on growth and lipid metabolism of oral epithelial cells. Resin discs were fabricated from triethyleneglycol dimethacrylate (TEGDMA) as received from the manufacturer and after removal of the stabilizer methyl ether hydroquinone (MEHQ). Some discs also contained the initiators benzoyl peroxide (BPO) and camphoroquinone (CQ), and/or an activator, dimethylaminoethyl methacrylate (DMAEMA). After polymerization, the ability of components to elute from the discs and alter cell growth and lipid synthesis were assayed by a colorimetric method and thin layer chromatography respectively. Purified TEGDMA had little effect on the cells' growth or lipid metabolism, while TEGDMA containing MEHQ did inhibit growth as well as total polar lipid synthesis. Eluates from discs containing DMAEMA inhibited cell growth as well as decreasing polar lipid formation. However, this same material produced increased synthesis of diglycerides and cholesterol esters. Eluates from BPO-containing discs, as well as those with CQ, with or without DMAEMA resulted in increased levels of diglycerides. These results demonstrate that even after polymerization, components used in dental resins may elute into the immediate environment and alter various cell metabolic processes.

Inhibition of the acidification of endosomes and lysosomes by the antibiotic concanamycin B in macrophage J774.

The antibiotic concanamycin B was found to inhibit oxidized-low-density-lipoprotein(LDL)-induced accumulation of lipid droplets in the macrophage J774 at a concentration of 5-10 nM. Concanamycin B inhibited cholesteryl-ester synthesis from [14C]oleate by 50% at 14 nM without affecting the synthesis of triacylglycerol and polar lipids. Degradation of internalized oxidized 125I-LDL was inhibited by about 80% in cells treated with 25 nM concanamycin B, while cell-surface binding of oxidized 125I-LDL at 4 degrees C, uptake of surface-bound oxidized 125I-LDL and microsomal acyl-CoA:cholesterol acyltransferase activity were not significantly affected by the antibiotic at 25 nM. When J774 cells were treated with 25 nM concanamycin B at 37 degrees C for 60 min, there was a reduction of about 50% in the activity of cell-surface receptors. This reduction appeared to be due to partial trapping of the receptors within the cells. Concanamycin B significantly inhibited ATP-dependent acidification of endosomes and lysosomes of the J774 cells at a concentration of 4 nM. Since acidic condition of these organelles is required for receptor recycling and hydrolysis of lipoproteins, the results demonstrate that concanamycin-B inhibition of oxidized-LDL-induced accumulation of lipid droplets and cholesteryl esters in macrophages J774 is associated with reduced ATP-dependent acidification of these organelles.

Inhibition of the uptake of oxidized low-density lipoprotein in macrophage J774 by the antibiotic ikarugamycin.

The antiprotozoal antibiotic ikarugamycin was found to significantly inhibit oxidized low-density lipoprotein(LDL)-induced accumulation of cholesteryl ester in macrophage J774 at a concentration over 1-4 microM. Cholesteryl ester synthesis from [14C]oleate in the macrophages was similarly inhibited by the antibiotic, while the synthesis of triacylglycerol and polar lipids was not affected. The internalization of oxidized [125I]LDL in macrophages was reduced to 50% by 2 microM ikarugamycin, while cell-surface binding of oxidized [125I]LDL, lysosomal hydrolysis of the internalized oxidized [125I]LDL and microsomal acyl-coenzyme A:cholesterol acyltransferase was not detectably inhibited by 5 microM ikarugamycin. The results demonstrated that ikarugamycin inhibited cholesteryl ester accumulation in macrophage J774 by specifically inhibiting the uptake of oxidized LDL.

Lipid metabolism of a Tertiary relic species, Kerguelen cabbage (Pringlea antiscorbutica)

The Kerguelen cabbage, Pringlea antiscorbutica R. Br., is a Tertiary relic Cruciferous species well adapted to the continuous cold conditions of this subantarctic archipelago. Each shoot exhibits all the steps of differentiation from embryonic leaves (1 mm) to mature leaves (30–40 cm). In the mature leaf, the chlorophyllous part is often reduced to a narrow peripheral strip, the chloroplasts being replaced progressively by amyloplasts toward the leaf center. This particular situation led us to compare the overall polar lipid and fatty acid composition from the green part of the mature leaves with those of the undifferentiated leaves, without chloroplasts. These lipid compositions are identical with those of all the C16:3 plants analyzed to date. The only feature characteristic of a chilling-resistant plant is the high percentage of saturated phosphatidylglycerol (16:0 + 16:1t). Polar lipid synthesis was followed by direct injection of [14C]acetate into the immature leaves. The incorporations of [14C]acetate into phosphatidylcholine and monogalactosyldiacylglycerol fatty acids closely parallel each other and there is no indication of fatty acid transfer from phosphatidylcholine to monogalactosyldiacylglycerol.