Effect of n-6 polyunsaturated fatty acids on growth and lipid composition of neoplastic and non-neoplastic canine prostate epithelial cell cultures

Investigating lipid headgroup composition within epithelial membranes: a systematic review

Membrane lipid composition is often quoted within the literature, but with very little insight into how or why these compositions vary when compared to other biological membranes. One prominent area that lacks understanding in terms of rationale for lipid variability is the human gastro-intestinal tract (GIT). We have carried out a comprehensive systematic literature search to ascertain the key lipid components of epithelial membranes, with a particular focus on addressing the human GIT and to use compositional data to understand structural aspects of biological membranes. Both bacterial outer membranes and the human erythrocyte membrane were used as a comparison for the mammalian [epithelial] membranes and to understand variations in lipid presence. We show that phosphatidylcholine (PC) lipid types tend to dominate (33%) with phosphatidylethanolamines (PE) and cholesterol having very similar abundances (25 and 23% respectively). This systematic review presents a detailed insight into lipid headgroup composition and roles in various membrane types, with a summary of the distinction between the major lipid bilayer forming lipids and how peripheral lipids regulate charge and fluidity. The variety of lipids present in biological membranes is discussed and rationalised in terms function as well as cellular position.

Profiling of advanced glycation end products uncovers abiotic stress-specific target proteins in Arabidopsis

Non-enzymatic post-translational modifications of proteins can occur when the nucleophilic amino acid side chains of lysine and arginine encounter a reactive metabolite to form advanced glycation end products (AGEs). Glycation arises predominantly from the degradation of reducing sugars, and glycation has been observed during metabolic stress from glucose metabolism in both animals and plants. The implications of glycating proteins on plant proteins and biology has received little attention, and here we describe a robust assessment of global glycation profiles. We identified 112 glycated proteins that were common under a range of growth conditions and abiotic stress treatments, but also showed rosette age, diurnal, and drought stress-specific targets. Among 18 drought stress-specific glycation targets included several thioredoxin and thioredoxin-like proteins. In vitro glycation of two carbohydrate metabolism enzymes led either to a reduction or to a complete inhibition of activity, demonstrating the impact of glycation on protein function. Taken together, our results suggest that stress-specific glycation patterns of a small number of regulatory proteins may have a much broader impact on downstream target proteins that are, for example, associated with primary metabolism.

Estimation of Lipid Hydroperoxide Levels in Tropical Marine Macroalgae

The incipient levels of lipid hydroperoxides (LHPOs) were determined in selected green, brown, and red macroalgae by the FOX assay using hydroperoxy HPLC mix. The LHPOs contents varied between the investigated species and showed relatively low values in this study. Among the greens, it varied from 12 ± 6.2 μg · g(-1) (Codium sursum) to 31.5 ± 2.8 μg · g(-1) (Ulva lactuca), whereas in reds, from 5.7 ± 1.6 μg · g(-1) (Gracilaria corticata) to 46.2 ± 6 μg · g(-1) (Sarconema filiforme), and in browns, from 4.6 ± 4.4 μg · g(-1) (Dictyota bartayresiana) to 79 ± 5.0 μg · g(-1) (Sargassum tenerrimum), on fresh weight basis. These hydroperoxides represented a minor fraction of total lipids and ranged from 0.04% (S. swartzii) to 1.1% (S. tenerrimum) despite being a rich source of highly unsaturated fatty acids. The susceptibility of peroxidation was assessed by specific lipid peroxidazibility (SLP) values for macroalgal tissues. The LHPO values were found to be independent of both the PUFAs contents and their degree of unsaturation (DBI), as evident from the PCA analysis. SLP values were positively correlated with the LHPOs and negatively with DBI. The FOX assay gave ≥20-fold higher values for LHPOs as compared to the TBARS method for all the samples investigated in this study. Furthermore, U. lactuca cultured in artificial seawater (ASW) enriched with nutrients (N, P, and NP) showed a sharp decline in LHPOs contents relative to those cultured in ASW alone P ≤ 0.05. It is inferred from this study that the FOX assay is an efficient, rapid, sensitive, and inexpensive technique for detecting the incipient lipid peroxidation in macroalgal tissues.

Tear analysis and lens-tear interactions: part II. Ocular lipids-nature and fate of meibomian gland phospholipids

PURPOSE

Published data indicate that the polar lipid content of human meibomian gland secretions (MGS) could be anything between 0.5% and 13% of the total lipid. The tear film phospholipid composition has not been studied in great detail and it has been understood that the relative proportions of lipids in MGS would be maintained in the tear film. The purpose of this work was to determine the concentration of phospholipids in the human tear film.

METHODS

Liquid chromatography mass spectrometry (LCMS) and thin layer chromatography (TLC) were used to determine the concentration of phospholipid in the tear film. Additionally, an Amplex Red phosphatidylcholine-specific phospholipase C (PLC) assay kit was used for determination of the activity of PLC in the tear film.

RESULTS

Phospholipids were not detected in any of the tested human tear samples with the low limit of detection being 1.3 μg/mL for TLC and 4 μg/mL for liquid chromatography mass spectrometry. TLC indicated that diacylglycerol (DAG) may be present in the tear film. PLC was in the tear film with an activity determined at approximately 15 mU/mL, equivalent to the removal of head groups from phosphatidylcholine at a rate of approximately 15 μM/min.

CONCLUSIONS

This work shows that phospholipid was not detected in any of the tested human tear samples (above the lower limits of detection as described) and suggests the presence of DAG in the tear film. DAG is known to be at low concentrations in MGS. These observations indicate that PLC may play a role in modulating the tear film phospholipid concentration.

Influence of sporophore development, damage, storage, and tissue specificity on the enzymic formation of volatiles in mushrooms (Agaricus bisporus)

The enzymic oxidation of the polyunsaturated fatty acid-linoleic acid leads, in fungi, to the formation of a unique class of nonconjugated hydroperoxides, which are cleaved to form eight-carbon volatiles characteristic of mushroom and fungal flavor. However, the enzymes involved in this biosynthetic pathway, the bioavailability of the fatty acid substrate, and the occurrence of the reaction products (hydroperoxides and eight-carbon volatiles) are not fully understood. This study investigated the lipids, fatty acids, and hydroperoxide levels, as well as eight-carbon volatile variations in the fungal model Agaricus bisporus, according to four parameters: sporophore development, postharvest storage, tissue type, and damage. Eight-carbon volatiles were measured using solid phase microextraction and gas chromatography-mass spectrometry. Tissue disruption had a major impact on the volatile profile, both qualitatively and quantitatively; 3-octanone was identified as the main eight-carbon volatile in whole and sliced sporophore, an observation overlooked in previous studies due to the use of tissue disruption and solvent extraction for analysis. Fatty acid oxidation and eight-carbon volatile emissions decreased with sporophore development and storage, and differed according to tissue type. The release of 1-octen-3-ol and 3-octanone by incubation of sporophore tissue homogenate with free linoleic acid was inhibited by acetylsalicylic acid, providing evidence for the involvement of a heme-dioxygenase in eight-carbon volatile production.

15-lipoxygenase metabolites of gamma-linolenic acid/eicosapentaenoic acid suppress growth and arachidonic acid metabolism in human prostatic adenocarcinoma cells: possible implications of dietary fatty acids

Although gammalinolenic acid (GLA) and eicosapentaenoic acid (EPA) have independently been reported to suppress growth of cancer cells, their relative potencies are unknown. To determine the possible attenuating efficacies of dietary GLA or EPA on prostate carcinogenesis, we hereby report the in vitro effects of GLA, EPA and their 15-lipoxygenase (15-LOX) metabolites: 15(S)-HETrE and 15(S)-HEPE, respectively, on growth and arachidonic acid (AA) metabolism in human androgen-dependent (LNCaP) and androgen-independent (PC-3) prostatic cancer cells in culture. Specifically, both cells were preincubated respectively with the above PUFAs. Growth was determined by [3H]thymidine uptake and AA metabolism by HPLC analysis of the extracted metabolites. Our data revealed increased biosynthesis of prostaglandin E2 (PGE2) and 5-hydroxyeicosatetraenoic acid (5(S)-HETE) by both cells. Preincubation of the cells with 15(S)-HETrE or 15(S)-HEPE more markedly inhibited cellular growth and AA metabolism when compared to precursor PUFAs. Notably, 15(S)-HETrE exerted the greatest inhibitory effects. These findings therefore imply that dietary GLA rather than EPA should better attenuate prostate carcinogenesis via its in vivo generation of 15(S)-HETrE, thus warranting exploration.

In vitro studies on the relationship between polyunsaturated fatty acids and cancer: tumour or tissue specific effects?

In vitro cell culture experiments have lead to the consensus in the literature that certain PUFAs have a selective cytotoxic or anti-proliferative effect on tumour cells and a minimal, or no effect on normal cells. Re-examination of key publications showed that when normal cells were used for comparison, they were generally not from the same cell, tissue, or species type as the tumour cells. Recently, investigations have included more appropriate normal control cells, and though tumour specific cytotoxic/anti-proliferative PUFA effects are found in some cell types, in others the normal cells are more sensitive. Cell type differences were found in the relative ability of individual PUFAs to act. However, within a cell type differences in susceptibility were influenced by grade and stage of tumour, immortalisation and tumourigenic status, cell culture media and cell plating density. Together these results suggest that the consensus is not valid, and that susceptibility to PUFA is cell type specific, and alters during neoplastic progression. Furthermore, the cytotoxic/anti-proliferative effect induced by both n-3 and n-6 PUFAs on a wide variety of cell types, associated with an increase in lipid peroxidation in vitro, cannot account for the in vivo data on the relationship between dietary fat and certain cancers. However, the effects of PUFAs and their metabolites on cell signalling pathways may explain the in vivo data.

Molecular and biochemical characterization of postharvest senescence in broccoli

Postharvest senescence in broccoli (Brassica oleracea L. var Italica) florets results in phenotypic changes similar to those seen in developmental leaf senescence. To compare these two processes in more detail, we investigated molecular and biochemical changes in broccoli florets stored at two different temperatures after harvest. We found that storage at cooler temperatures delayed the symptoms of senescence at both the biochemical and gene expression levels. Changes in key biochemical components (lipids, protein, and chlorophyll) and in gene expression patterns occurred in the harvested tissue well before any visible signs of senescence were detected. Using previously identified senescence-enhanced genes and also newly isolated, differentially expressed genes, we found that the majority of these showed a similar enhancement of expression in postharvest broccoli as in developmental leaf senescence. At the biochemical level, a rapid loss of membrane fatty acids was detected after harvest, when stored at room temperature. However, there was no corresponding increase in levels of lipid peroxidation products. This, together with an increased expression of protective antioxidant genes, indicated that, in the initial stages of postharvest senescence, an orderly dismantling of the cellular constituents occurs, using the available lipid as an energy source. Postharvest changes in broccoli florets, therefore, show many similarities to the processes of developmental leaf senescence.

Antisense-mediated depletion of potato leaf omega3 fatty acid desaturase lowers linolenic acid content and reduces gene activation in response to wounding

Fatty acid omega3 desaturases act on membrane lipids to catalyse the formation of trienoic fatty acids, the most abundant in plant tissues being alpha-linolenic acid. This fatty acid is a precursor of jasmonic acid, a plant growth regulator involved in the control of wound-induced gene activation in plants and in the induction of tuberization in potato. We isolated a potato omega3 desaturase cDNA, possibly encoding a plastidial isoform, and used it to investigate its expression pattern throughout plant development and in response to wounding. Plastidial omega3 desaturase gene transcripts accumulate rapidly upon wounding, preceding the jasmonate-dependent induction of the wound-responsive proteinase inhibitor II gene. We generated transgenic potato plants constitutively expressing an antisense RNA to this plastidial omega3 desaturase. Selected transgenic lines in which the cognate omega3 desaturase mRNA is largely depleted show a marked reduction, of up to 60%, in trienoic acids in leaves and tubers. In these lines, a corresponding reduction in jasmonate content and proteinase inhibitor II expression is observed upon wounding. Our results indicate that a reduction in omega3 desaturase mRNA levels compromises the wound-induced activation of proteinase inhibitor II, suggesting that wound-induced synthesis of linolenic acid is required for jasmonic acid production. The antisense-mediated depletion of fatty acid omega3 desaturases is a viable alternative for reducing trienoic fatty acid content in plant species in which a mutant screening approach is not applicable.

Differentiating agents and nontoxic therapies

The discovery of the oncogene and the mechanism by which these genetic changes create malignant transformation has provided new opportunities for drug development. Suramin is the first drug shown to exert its anticancer activity by blocking autocrine loops involved in malignant transformation. Phenylacetate and related aromatic fatty acids are potent inducers of differentiation in normal and malignant cells. Arachidonate, a fatty acid, plays a role in prostate cancer survival, growth, invasiveness, and immunosuppression. The actions of arachidonic acid can be moderated by diet or blocked by pharmacologic agents. Other agents that promise low toxicity include vitamin D and its analogs, genistein and related isoflavones, green tea polyphonols, and retinoic acid analogs.

Comparative anti-mitotic effects of lithium gamma-linolenate, gamma-linolenic acid and arachidonic acid, on transformed and embryonic cells

The effects of gamma-linolenic acid (GLA), the lithium salt of gamma-linolenic acid (LiGLA) and arachidonic acid (AA) were compared at doses of 50 microg/ml for periods of 6 and 24 h on cell cycle progression and apoptosis induction in transformed and in normal cells. In WHCO3 (oesophageal cancer) cells and on primary embryonic equine lung cells, we found LiGLA to be the most effective in apoptosis induction. After 24 h, 94% of the WHCO3 cancer cells and 44% of the primary embryonic equine lung cells exposed to LiGLA were apoptotic. The WHCO3 cancer cells were also very susceptible to the apoptosis-inducing effects of AA (56%) and GLA (44%), whereas the embryonic equine lung cells were much less affected by these two fatty acids. After 6 h exposure to all three compounds, most of the cycling WHCO3 cancer cells were blocked in S-phase. After 24 h treatment, some of the S-phase cells exposed to AA and GLA were apparently able to move into the G2/M phase, the LiGLA exposed cells were mostly apoptotic and no cycling cells were present. The primary embryonic equine lung cells were fairly resistant to the cytotoxic effects of GLA and AA. From our studies we conclude that, although LiGLA was the most toxic to the cancer cells, it is apparently less selective, compared to AA and GLA, in the killing of cancer and normal cells. It would also appear that the lithium might have added to the cytotoxic effects of LiGLA. The mechanism needs to be clarified.

Biosynthesis of triacylglycerol in the filamentous fungus Mucor circinelloides

Lipid metabolism was studied in 2-d-old liquid cultures of Mucor circinelloides grown at 25 degrees C. Under these conditions, oil accumulated to 0.5 g l-1 with a gamma-linolenic acid content (gamma 18:3) of 60 mg l-1. The major labelled lipids in cultures incubated with [14C]acetate were triacylglycerol (TAG), phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The proportion of label declined in the phospholipids and increased in TAG with time. [14C]18:1 and [14C]18:2 rapidly appeared in PC and PE and later accumulated in [14C]gamma 18:3. TAG-synthesizing capacity was greatest in the microsomal membrane fraction, which accumulated high levels of phosphatidic acid in the presence of glycerol 3-phosphate and acyl-CoA substrates at pH 7.0. Further metabolism of phosphatidic acid to diacylglycerol and TAG was achieved by increasing the pH to 8.0. Lysophosphatidic acid: acyl-CoA acyltransferase (LPAAT) activity was particularly high and may have accounted for the rapid accumulation of phosphatidic acid in the membranes. The glycerol-3-phosphate: acyl-CoA acyltransferase (GPAAT) and LPAAT were non-specific for a range of saturated and unsaturated species of acyl-CoA although the GPAAT showed a marked selectivity for palmitoyl-CoA and the LPAAT for oleoyl- and linoleoyl-CoA. gamma-Linolenic acid was detected at all three positions of sn-TAG and was particularly enriched at the sn-3 position. The preparation of active in vitro systems (microsomal membranes) capable of the complete biosynthetic pathway for TAG assembly may be valuable in understanding the assembly of oils in future transgenic applications.