Membrane Fatty Acid Metabolism Research Articles

Mechanisms of low susceptibility to the disinfectant benzalkonium chloride in a multidrug-resistant environmental isolate of Aeromonas hydrophila.

Excessive discharge of quaternary ammonium disinfectants such as benzalkonium chloride (BAC) into aquatic systems can trigger several physiological responses in environmental microorganisms. In this study, we isolated a less-susceptible strain of Aeromonas hydrophila to BAC, designated as INISA09, from a wastewater treatment plant in Costa Rica. We characterized its phenotypic response upon exposure to three different concentrations of BAC and characterized mechanisms related to its resistance using genomic and proteomic approaches. The genome of the strain, mapped against 52 different sequenced A. hydrophila strains, consists of approximately 4.6 Mb with 4,273 genes. We found a massive genome rearrangement and thousands of missense mutations compared to the reference strain A. hydrophila ATCC 7966. We identified 15,762 missense mutations mainly associated with transport, antimicrobial resistance, and outer membrane proteins. In addition, a quantitative proteomic analysis revealed a significant upregulation of several efflux pumps and the downregulation of porins when the strain was exposed to three BAC concentrations. Other genes related to membrane fatty acid metabolism and redox metabolic reactions also showed an altered expression. Our findings indicate that the response of A. hydrophila INISA09 to BAC primarily occurs at the envelop level, which is the primary target of BAC. Our study elucidates the mechanisms of antimicrobial susceptibility in aquatic environments against a widely used disinfectant and will help better understand how bacteria can adapt to biocide pollution. To our knowledge, this is the first study addressing the resistance to BAC in an environmental A. hydrophila isolate. We propose that this bacterial species could also serve as a new model to study antimicrobial pollution in aquatic environments.

2,4-epibrassinolide enhance chilling tolerance of loquat fruit by regulating cell wall and membrane fatty acid metabolism

2,4-epibrassinolide (EBR) treatment has the effect of reducing chilling injury (CI) on many kinds of fruits. However, the effect on loquat fruit is unknown. The impacts of 15 μM EBR in response to CI of loquat fruit by regulating cell wall and fatty acid metabolism have been investigated in this study. Our results indicated that EBR treatment notably attenuated the symptom of CI, particularly, inhibited the accumulation of lignin, positively correlated with firmness. In contrast to control fruit, higher levels of water-soluble pectin and chelate-soluble pectin, as well as lower levels of sodium carbonate-soluble pectin, hemicellulose and cellulose were observed in EBR preconditioned fruit. The activities of polygalacturonase (PG), cellulase (Cel) and β-galactosidase (β-gal) were higher in EBR treated-loquat fruit than those in control. The reduction of oleic acid, linoleic acid and linolenic acid were retarded by EBR treatment, which was the consequence of the lower lipoxygenase (LOX) and phospholipase D (PLD) activities. Hence, this work demonstrated that EBR enhanced chilling tolerance in loquat fruit attribute to maintaining the high level of soluble cell wall polysaccharides and unsaturated fatty acids by regulating related-enzymes activities.

Biochemical and molecular effects of glycine betaine treatment on membrane fatty acid metabolism in cold stored peaches

The effect of glycine betaine (GB) treatment on chilling injury (CI), cell membrane integrity and membrane fatty acid metabolism in peach fruit during storage were investigated using biochemical and transcriptomic analysis in this study. The results showed that GB treatment alleviated the CI by suppressing lipoxygenase (LOX), phospholipase D (PLD) and lipase gene expression and enzyme activities, resulting in higher levels of unsaturated fatty acids and degree of unsaturation. In addition, this study suggested that GB treatment could inhibit the release of cytochrome C and caspase-3 activity, thus suppressing cell breakdown and contributing to membrane function. Moreover, transcriptome analysis revealed that genes related to fatty acid biosynthesis and desaturation were enhanced, while genes related to fatty acid degradation and activation of caspases were suppressed by GB treatment. Therefore, GB treatment could maintain normal cell membrane structure and function through upregulating membrane fatty acid biosynthesis and desaturation metabolism and downregulating caspase activation to alleviate CI in peaches.

Glycine betaine treatment alleviates chilling injury in zucchini fruit (Cucurbita pepo L.) by modulating antioxidant enzymes and membrane fatty acid metabolism

The effect of glycine betaine (GB) treatment on chilling injury (CI) and its relation with the physiological response of zucchini fruit to chilling tolerance have been investigated. GB treatment significantly reduced postharvest CI of zucchini fruit at the concentration of 10 mmol L–1 during a fifteen-days period of storage at 1 ℃ followed by an additional three days at 20 ℃. CI index, the activities of lipoxygenase (LOX) and plant phospholipase D (PLD), proline content and fatty acid composition were assessed. The activities of various antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) were essayed along with their regulatory gene transcript levels. Results suggested that amelioration of CI in zucchini fruit by GB treatment was associated with the accumulation of proline and the reduction in lipid peroxidation. Meanwhile, GB-treated fruit also showed lower levels of palmitic acid and stearic acid, and lower LOX and PLD activities, but higher activity levels of enzymes related to proline metabolism such as △1-pyrroline-5-carboxylate synthetase (P5CS) and ornithine d-aminotransferase (OAT). Both gene expressions and antioxidant enzyme activities of SOD, CAT and APX in GB-treated fruit were significantly higher than that of control fruit. Thus, exogenous GB treatment could alleviate CI in cold-stored zucchini fruit through improved antioxidant enzymatic mechanisms. Principal component analysis (PCA) indicated that GB treatment possessed a better performance to delay chilling injury of zucchini fruit based on antioxidant levels and fatty acid metabolism than control fruits during 9 d of storage.

Cognitive training increases platelet PLA 2 activity in healthy elderly subjects

Phospholipases A 2 (PLA 2) are ubiquitous enzymes involved in membrane fatty acid metabolism and intracellular signalling. Recent studies have shown that PLA 2 subtypes are implicated in the modulation of pathways related to memory acquisition and retrieval. We investigated the effects of cognitive training on platelet PLA 2 activity in healthy elderly individuals. Twenty-three cognitively unimpaired older adults were randomly assigned to receive memory training or standard outpatient care only. Both groups were cognitively assessed by the same protocol, and the experimental group (EG) underwent a four-session memory training intervention. Pre- and post-test measures included prose and list recall, WAIS-III digit symbol, strategy use measures and platelet PLA 2 group activity. After cognitive training, patients in the EG group had significant increase in cytosolic, calcium-dependent PLA 2 (cPLA 2), extracellular (or secreted), calcium-dependent PLA 2 (sPLA 2), total platelet PLA 2 activity, and significant decrease in platelet calcium-independent PLA 2 (iPLA 2) activity. Our results suggest that memory training may have a modulating effect in PLA 2-mediated biological systems associated with cognitive functions and neurodegenerative diseases.

Impaired phospholipid-related signal transduction in advanced Huntington's disease.

The aim of this study was to test the hypothesis that Huntington's disease is associated with impaired phospholipid-related signal transduction using the niacin skin flush test. This is the first reported use of this test in this patient group. The response to topical aqueous methyl nicotinate solution was recorded at 5 min intervals over 20 min in six in-patients with advanced (stage III) Huntington's disease and in 14 age- and sex-matched normal individuals with no history of this or any other major neurological disorder. The volumetric niacin response (VNR) (mean +/- S.E.M.) in the patients with Huntington's disease, 16.3 +/- 2.6 mol x s x l(-1), was significantly lower than the mean VNR of 28.3 +/- 2.1 mol x s x l(-1) in the control group (P = 0.004). These results are consistent with the conclusion that Huntington's disease may be associated with an abnormality of neuronal membrane fatty acid metabolism, possibly as a consequence of an as yet unidentified action of huntingtin.

Effects of hexadecylphosphocholine on fatty acid metabolism: relation to cytotoxicity.

The cytotoxicity of the antineoplastic drug hexadecylphosphocholine (HePC) was determined in a human monocytic tumor cell line, THP1, and in primary cultures of rat mesangial cells. Both cell types were susceptible to HePC toxicity, the concentrations producing 50% inhibition of cell viability (LD50 values) being 7 micrograms/ml for THP1 cells and 19 micrograms/ml for mesangial cells. The degree of toxicity was dependent on the culture conditions. In the absence of serum, HePC was highly toxic independent of cell proliferation. As a potential molecular mechanism, the effect of HePC on long-chain fatty acyl metabolism was investigated. HePC had no effect on fatty acid incorporation into cellular lipids or on release of fatty acids from lipid stores. The distribution of labeled fatty acids, however, was shifted from the phospholipid fraction to the triacylglycerol fraction. This effect was in accordance with an inhibition of the activity of the reacylating enzyme lysophosphatide acyltransferase. There was, however, no correlation between the interference with fatty acid distribution and HePC cytotoxicity in vitro. The data argue against interference with membrane fatty acid metabolism as a necessary prerequisite of HePC toxicity, the mechanism of which remains to be elucidated.

Effects of an acetyl-coenzyme A carboxylase inhibitor and a sodium-sparing diuretic on aldosterone-stimulated sodium transport, lipid synthesis, and phospholipid fatty acid composition in the toad urinary bladder

A correlation study of the effects of two agents, 2-methyl-2-[p-(1,2,3,4-tetrahydro-1-naphthyl)phenoxy]propionic acid (TPIA) and amiloride, on aldosterone-induced alterations in Na+ transport, lipid synthesis, and phospholipid fatty acid composition has been carried out in the toad urinary bladder. TPIA, an inhibitor of acetyl-CoA carboxylase, inhibits aldosterone-stimulated Na+ transport as well as hormone-induced lipid synthesis and the increase in weight percentage of phospholipid long-chain polyunsaturated fatty acids. Amiloride, a diuretic which blocks sodium entry into the transporting epithelium, does not alter aldosterone's effects on lipid and fatty acid metabolism but prevents the hormone-induced increase in Na+ transport. These results support the conclusion that aldosterone increases Na+ transport in the toad urinary bladder by altering membrane fatty acid metabolism and that the lipid biosynthetic events following aldosterone treatment are a primary response to the hormone and not secondary to increased Na+ transport.