Furan fatty acids: their role in plant systems

Furan fatty acids (F-acids) are heterocyclic fatty acids having a furan ring in their structure. Most existing studies on F-acids are related to either fish or other marine animals. Even though F-acids have been detected in many plant species, not much work has been done exclusively in plants of economic importance, especially oilseed crops. This review focuses mainly on the functions and roles of F-acids in plants. In plants, they are bound to phospholipids by substituting PUFA and function as free radical scavengers suggesting their role in defense against oxidative stress. Owing to their antioxidative property F-acids are highly unstable and their photooxidative products can contribute to the flavor of edible oils.     

Role of membrane lipid fatty acids in cold adaptation.

Psychrophilic and psychrotolerant bacteria have evolved various strategies to adapt to low temperature. One important strategy, which is crucial to the survival of the cell at low temperature, relates to the ability of the cell to modulate the fluidity of the membrane. Bacteria in general modulate membrane fluidity by altering their fatty acid composition. But, bacteria could also achieve the same by various other strategies such as by altering the lipid head group, the protein content of the membrane, the type of carotenoids synthesized, the fatty acid chain length and the proportion of cis to trans fatty acids. In addition bacteria have a two-component signal transduction pathway consisting of a membrane-bound sensor and a soluble cytoplasmic response regulator involved in the perception and transduction of low temperature signals. This review on cold adaptation highlights the various strategies by which bacteria modulate the fluidity of the membrane and the process by which it senses and transduces the low temperature signal.     

Control of gluconeogenesis: role of fatty acids in the alpha-adrenergic response

Phenylephrine increases hepatic gluconeogenesis for as long as it is present in the extracellular medium. This effect is accompanied by a parallel increase in oxygen consumption. No apparent stoichiometric relationship exists between the phenylephrine-stimulated respiration and the energy required to meet the demands of gluconeogenesis. In the absence of extracellular calcium, no sustained stimulation of respiration was observed and phenylephrine failed to enhance gluconeogenesis; however, acute and transient effects of the alpha-adrenergic agonist were still observable. The following observations indicate that fatty acids are not involved in the alpha-adrenergic response: (1) the effects of phenylephrine and octanoate on respiration and gluconeogenesis were found to be additive; (2) unlike phenylephrine, octanoate is capable of stimulating gluconeogenesis in calcium-depleted liver; (3) in the absence of calcium, phenylephrine was incapable of further stimulating respiration or gluconeogenesis in the presence of octanoate. It is concluded that the conditions of increased lipid mobilization and/or oxidation are not sufficient to explain the metabolic response to alpha-adrenergic agonists. Fatty acids and alpha-adrenergic stimulation share a common role of stimulating gluconeogenesis in a manner dependent on their ability to stimulate respiration; however, the additive nature of their effects and distinct calcium requirements indicate that they act to trigger different mechanisms.     

Uptake of fatty acids by the yeasts, Saccharomyces uvarum and Saccharomycopsis lipolytica

Yeast cells take up exogenous fatty acids with subsequent rapid incorporation into glycerolipids. beta-Oxidation does not occur in Saccharomyces uvarum and is observed in Saccharomycopsis lipolytica only 2-5 min after addition of radioactively labeled fatty acid. Rates of fatty acid uptake are linear up to 30 s with S. lipolytica and up to 2 min with S. uvarum. The uptake kinetics are consistent with a dual mode of transport, comprising a saturable component with KT values in the range 10(-5)-10(-6) M, and apparently simple diffusion that predominates at high substrate concentrations. Kinetics of fatty acid permeation are independent of metabolic energy and membrane potential. At least two fatty acid carrier systems exist in both S. lipolytica and S. uvarum, one being specific for fatty acids with 12 and 14 C atoms, respectively, the other for C16 and C18 saturated or unsaturated fatty acids. Octanoic acid and decanoic acid are not taken up by S. lipolytica. Internalization of lauric acid and oleic acid by S. lipolytica cells is preceded by a rapid (less than 5 s) initial uptake which most likely represents irreversible adsorption. This phenomenon was not observed with heat-inactivated S. lipolytica cells or with viable S. uvarum. In azide-poisoned cells of S. lipolytica an up to 20-fold accumulation of unesterified fatty acid was observed within 30 s after the addition of substrate.     

Carotenoids and fatty acids in red yeasts Sporobolomyces roseus and Rhodotorula glutinis

Rhodotorula glutinis and Sporobolomyces roseus, grown under different aeration regimes, showed differential responses in their carotenoid content. At higher aeration, the concentration of total carotenoids increased relative to biomass and total fatty acids in R. glutinis, but the composition of carotenoids (torulene > beta-carotene > gamma-carotene > torularhodin) remained unaltered. In contrast, S. roseus responded to enhanced aeration by a shift from the predominant beta-carotene to torulene and torularhodin, indicating a biosynthetic switch at the gamma-carotene branch point of carotenoid biosynthesis. The overall levels of total carotenoids in highly aerated flasks were 0.55 mol-percent and 0.50 mol-percent relative to total fatty acids in R. glutinis and S. roseus (respectively), and 206 and 412 microg g(-1) dry weight (respectively).     

Diet and kidney disease: the role of dietary fatty acids

Several general principles with respect to the role of the fatty acids in the progression of kidney disease have begun to emerge from the mass of observational detail. Interventions that increase renal exposure to prostaglandins of the E series appear to be beneficial. They include administration of prostaglandin analogues and dietary supplementation with their fatty acid precursor, linoleate. The beneficial effects may be attributed to preservation of renal blood flow and glomerular filtration, reduction in blood pressure, direct effects on the lipid composition and function of cell membranes, and immune suppression. Interventions that inhibit thromboxane and leukotriene production, such as omega-3 fatty acid supplementation of the diet or administration of enzyme or receptor inhibitors, are also protective. Prevention of vasoconstriction, inhibition of platelet activation, and regulation of cell proliferation and matrix production have all been implicated in the mediation of the observed retardation of sclerosis. Fish oil may have synergistic, suppressive effects on various parameters of immune activation. Essential fatty acid deficiency, of course, inhibits both prostaglandin E and thromboxane production, cancelling out the protective and injurious components of arachidonate oxidation. Yet, studies on its beneficial effects have revealed another aspect of eicosanoid metabolism, independent of cyclooxygenase and lipoxygenase activity, that appears to regulate monocyte migration into injured tissue. Dietary interruption of this pathway has proven protective to renal structure and function. Alterations in lipid metabolism may represent a common, mediating pathway of glomerular and interstitial susceptibility to progressive sclerosis in the kidney. The process appears to be amenable to manipulation by pharmacologic or dietary modulation of fatty acid metabolism. Eicosanoid metabolites and tissue-leukocyte signaling are two mechanisms by which lipid alterations can affect renal function. There are doubtless many others awaiting elucidation. Delineation of all the mechanisms whereby fatty acid metabolism can contribute to progressive kidney injury may provide a useful model for the examination of progressive sclerosis affecting other tissues subsequent to immune, vascular, or metabolic injury.     

Production of extracellular higher fatty acids by yeasts grown on hexadecanoic acid

Production of exocellular higher fatty acids by Candida yeasts was studied during their growth in a mineral medium with hexadecane. The qualitative and quantitative composition of exocellular higher fatty acids was investigated during cultivation of Candida lipolytica VCM Y 2378(695) under the conditions of different aeration (5 and 80% saturation of the medium with oxygen). Palmitic (C16:0), palmitooleic (C16:1), oleic (C18:1) and linoleic (C18:2) acids predominated among other higher fatty acids. The overall amount of fatty acids increased and the content of unsaturated fatty acids decreased when the yeast growth was limited with oxygen.     

The role of membrane fatty acids in mammalian hibernation

During mammalian hibernation, cellular membranes continue to function at temperatures approaching 0 C. The molecular mechanisms that confer this capacity to the membranes are unknown but may be related to the fluidity of the membrane and to the level of unsaturated fatty acids. The basic tenets of membrane fluidity and the contribution of cholesterol, polar head groups, and fatty acids toward maintaining a fluid membrane in a liquid-crystalline state are examined in this review. It is shown that although unsaturated fatty acids can enhance membrane fluidity at low temperatures, there does not appear to be a consistent trend toward increased levels of unsatruated fatty acids during hibernation in all tissues of hibernators. Consequently, there may be some other role for the alterations in the composition of membrane fatty acids found during the hibernating cycle other than increasing membrane fluidity to permit continued activity at reduced temperatures.     

The role of fatty acids in the development and progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) has emerged as a serious obesity-related disorder. NAFLD encompasses a wide spectrum of hepatic derangements ranging from a surfeit of fat in the liver (steatosis) to lipid surplus accompanied by fibrosis and cellular death (nonalcoholic steatohepatitis or NASH). The most widely accepted model to explain the progression from simple NAFLD to NASH is the "two-hit hypothesis," wherein fat over accumulation per se is not sufficient to induce the progression to statohepatitis, but renders the liver more susceptible to "second hits" that, once imposed upon the steatotic liver, cause further aberrations that culminate in the development of NASH. However, in light of recent data from our laboratory and elsewhere, we propose that an increased ratio of saturated-to-unsaturated fatty acids delivered to or stored within the liver may, in part, mediate the progression from simple steatosis to NASH. The molecular mechanisms that mediate the effect of saturated fatty acids are unclear, although proinflammatory cytokines, reactive oxygen species, and endoplasmic reticulum stress may all play a role. Collectively, these data suggest that saturated fatty acids may represent an intrinsic second hit to the liver that hastens the development of NASH.     

Postprandial activation of hemostatic factors: role of dietary fatty acids

Intake of dietary fat is an important determinant of the plasma concentration of triacylglycerol-rich lipoproteins, and the degree of alimentary lipemia is reported to have effects on hemostatic status including platelet function. Although association between the amount of dietary fat intake, lipemic response and certain cardiovascular disease (CVD) risk factors (VIIa and PAI-1) has been reported, the significance of the fatty acid composition of ingested fat for the postprandial lipid concentrations and the hemostatic factors is still unclear. Accumulating evidence suggests a relationship between dietary fatty acids and emerging hemostatic CVD risk factors, although much of this evidence is incomplete or conflicting. In order to improve our knowledge in this area, sufficient sample size in future studies are required to take into account of the genetic variation (gene polymorphisms for VII, PAI-1), sex, physical activity, stage of life factors, and sufficient duration to account for adaptation for definitive conclusions.     

On the role of catalase in the oxidation of tissue fatty acids

The role of catalase in lipid metabolism has been studied by means of a comparison of the turnover characteristics of the major lipid classes in the normal mouse with those of animals in which the catalase activity had been inhibited and blocked by aminotriazole and allylisopropylacetamide. Double isotope ratios were determined in the lipid fractions of several tissues following the injection of labeled glycerol, and a number of significant differences were identified between these treatments. Since catalase is recognized as an integral component of the peroxisomal pathway of fatty acid oxidation, these results may be taken as indicating that interruption of the process of peroxisomal beta-oxidation in this manner cause extensive perturbations of lipid metabolism in the living animal, and these perturbations extend well beyond those tissues where the predominant localization of these organelles occurs. The concept which derives from these data--that of a significant regulatory role of peroxisomes in relation to the overall balance of lipid metabolism in the animal body--is described and discussed.     

Role of fatty acids in cold adaptation of Antarctic psychrophilic Flavobacterium spp.

Cold-loving microorganisms developed numerous adaptation mechanisms allowing them to survive in extremely cold habitats, such as adaptation of the cell membrane. The focus of this study was on the membrane fatty acids of Antarctic Flavobacterium spp., and their adaptation response to cold-stress. Fatty acids and cold-response of Antarctic flavobacteria was also compared to mesophilic and thermophilic members of the genus Flavobacterium. The results showed that the psychrophiles produced more types of major fatty acids than meso- and thermophilic members of this genus, namely C_15:1 iso G, C_15:0 iso, C_15:0 anteiso, C_15:1 ω6c, C_15:0 iso 3OH, C_17:1 ω6c, C_16:0 iso 3OH and C_17:0 iso 3OH, summed features 3 (C_16:1 ω7cand/or C_16:1 ω6c) and 9 (C_16:0 10-methyl and/or C_17:1 iso ω9c). It was shown that the cell membrane of psychrophiles was composed mainly of branched and unsaturated fatty acids. The results also implied that Antarctic flavobacteria mainly used two mechanisms of membrane fluidity alteration in their cold-adaptive response. The first mechanism was based on unsaturation of fatty acids, and the second mechanism on de novo synthesis of branched fatty acids. The alteration of the cell membrane was shown to be similar for all thermotypes of members of the genus Flavobacterium.     

Temperature adaptation in Lactobacillus fermentum: interconversions of oleic, vaccenic and dihydrosterulic acids.

The interchange of octadecenoic acids and dihydrosterulic acid was a response of aerobically growing Lactobacillus fermentum to changes in growth temperature. Oleic and vaccenic acid contents decreased both at temperatures below 20 degrees C and above 26 degrees C, showing mirror image behaviour, with a concomitant increase in dihydrosterulic acid. A temperature-dependent shift from vaccenic to oleic acid synthesis, and the conversion of the latter to dihydrosterulic acid was responsible for the overall change. Consequently, the degree of fatty acid unsaturation decreased at temperatures above 26 degrees C, whereas the degree of cyclization increased. The converse occurred below 20 degrees C. The relative amount of lactobacillic acid, total cellular fatty acid content, and mean fatty acid chain length were practically temperature-independent. The occurrence of oleic acid is thought to be related to aerobic growth conditions.     

Evolution of black yeasts: possible adaptation to the human host

Ascomycetous black yeasts show adaptations to a wide array of environmental conditions. Dothideaceous black yeasts are mostly found on plant leaves, while among herpotrichiellaceous species there are numerous opportunists on humans.Factors which are of ecological significance include the presence of melanin and carotene, formation of thick cell walls and meristematic growth, presence of yeast-like phases, presence of additional forms of conidiogenesis, thermo- and osmotolerance, adhesion, hydrophobicity, production of extracellular polysaccharides, siderophores and acidic or alkaline secondary metabolites.The potential pathogenicity of a species is partly determined by its natural ecological niche. Dothideaceous black yeasts are osmotolerant rather than pathogenic. Herpotrichiellaceous black yeasts probably have low competitive ability and are found in rather special niches as secondary saprophytes, e.g., on bacterial mats, on other fungi or in poor environments. Some species possibly utilize animal vectors for dispersal.