Dietary n-3 PUFAs affect the blood pressure rise and cardiac impairments in a hyperinsulinemia rat model in vivo

The cardiovascular consequences of eicosapentaenoic acid (EPA)- and docosahexaenoic acid (DHA)-specific intake were evaluated in vivo in a hyperinsulinemia (HI) model induced by dietary fructose intake. Wistar rats were fed a diet containing (or not for control) either EPA or DHA. The rise in blood pressure (BP), heart rate, and ECG were continuously monitored using an intra-abdominal telemetry system. The myocardial phospholipid fatty acid profile was significantly affected by DHA intake but less by EPA intake. The data indicated a reduced rise in BP in both DHA and EPA HI groups compared with controls. This result was confirmed by tail-cuff measurement after 5 wk [133.3 +/- 1.67 and 142.5 +/- 1.12 mmHg in n-3 polyunsaturated fatty acid (PUFA) and control groups, respectively], whereas n-3 PUFA did not affect BP in non-HI rats (116.3 +/- 3.33 mmHg). The heart rate was lower in the HI DHA group than in the other two dietary HI groups. Moreover, DHA induced a significantly shorter QT interval. It is concluded that the cardioactive component of fish oils is DHA through a mechanism that may involve the cardiac adrenergic system.     

Putative type IV secretion genes in Bacillus anthracis

Although the physiology of Bacillus anthracis, the causative agent of anthrax, has been studied extensively, we still do not know how toxins are dispatched from the bacterial cell. Here, by means of distant homology and genome context analyses, we identify genes encoding putative type IV secretion system-related elements on the B. anthracis plasmids pXO1 and pXO2 and in the chromosome. We argue that this type IV secretion system-like system could be responsible for anthrax toxin secretion, although we also discuss the possibilities of its involvement in the processes of sporulation, germination or conjugation.     

The effect of n-3 PUFA on eNOS activity and expression in Ea hy 926 cells

The aim of this study was to evaluate the effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on NO synthase (eNOS) activation in Ea hy 926 endothelial cells. EPA or DHA (0-80 microM), added to the culture medium during 24h, were dose-dependently incorporated into the cells. In control medium, eNOS activity (evaluated by the citrulline assay) and eNOS phosphorylation on Ser 1177 were correlated. They were increased by 10 microM histamine and prevented by 20 microM lysophosphatidylcholine (LPC). By contrast, EPA or DHA increased basal phosphorylation without affecting eNOS activity in non-stimulated cells, but dose-dependently decreased this activity in histamine-stimulated cells without modifying the phosphorylation level. Furthermore, EPA and DHA did not prevent the deleterious effects of LPC on histamine stimulation. In conclusion, incorporation of EPA and DHA could be deleterious for endothelial cells by deregulating the activation of eNOS and preventing NO liberation.     

Deleterious impact of elaidic fatty acid on ABCA1-mediated cholesterol efflux from mouse and human macrophages

Consumption of trans fatty acids (TFA) increase cardiovascular risk more than do saturated FA, but the mechanisms explaining their atherogenicity are still unclear. We investigated the impact of membrane incorporation of TFA on cholesterol efflux by exposing J774 mouse macrophages or human monocyte-derived macrophages (HMDM) to media enriched or not (standard medium) with industrially produced elaidic (trans-9 18:1) acid, naturally produced vaccenic (trans-11 18:1) acid (34 h, 70 μM) or palmitic acid. In J774 macrophages, elaidic and palmitic acid, but not vaccenic acid, reduced ABCA1-mediated efflux by ~23% without affecting aqueous diffusion, SR-BI or ABCG1-mediated pathways, and this effect was maintained in cholesterol-loaded cells. The impact of elaidic acid on the ABCA1 pathway was weaker in cholesterol-normal HMDM, but elaidic acid induced a strong reduction of ABCA1-mediated efflux in cholesterol-loaded cells (-36%). In J774 cells, the FA supplies had no impact on cellular free cholesterol or cholesteryl ester masses, the abundance of ABCA1 mRNA or the total and plasma membrane ABCA1 protein content. Conversely, TFA or palmitic acid incorporation induced strong modifications of the membrane FA composition with a decrease in the ratio of (cis-monounsaturated FA+polyunsaturated FA):(saturated FA+TFA), with elaidic and vaccenic acids representing each 20% and 13% of the total FA composition, respectively. Moreover, we demonstrated that cellular ATP was required for the effect of elaidic acid, suggesting that it contributes to atherogenesis by impairing ABCA1-mediated cholesterol efflux in macrophages, likely by decreasing the membrane fluidity, which could thereby reduce ATPase activity and the function of the transporter.     

Influence of phospholipid long chain polyunsaturated fatty acid composition on neonatal rat cardiomyocyte function in physiological conditions and during glucose-free hypoxia-reoxygenation

There is evidence that dietary polyunsaturated fatty acids (PUFA) may protect against cardiovascular diseases, but the involvement of the cardiac muscle cell in this beneficial action remain largely unknown. The present study compared the respective influence of n-3 and n-6 PUFA on the function of cultured neonatal rat cardiomyocytes (CM). Cells were grown for 4 days in media enriched either n-3 (eicosapentaenoic acid, EPA and docosahexaenoic acid, DHA) or n-6 (arachidonic acid, AA) PUFA. The PUFA n-6/n-3 ratio in the phospholipids was close to 1 and 20 in the n-3 and n-6 cells, respectively. The transmembrane potentials were recorded using microelectrodes and the contractions were monitored with a photoelectric device. In physiological conditions, the increase of n-6 PUFA level in the phospholipids resulted in a significant decrease in the maximal rate of initial depolarization (–16%). In opposition, the action potential amplitude and duration were not altered, and the cell contractio n outline was not affected. Ischemia was simulated in vitro using a substrate-free, hypoxia-reoxygenation procedure in a specially designed gas-flow chamber. The progressive loss of electrical activity induced by the substrate-free, hypoxic treatment was affected by the n-6/n-3 ratio, since the n-6 rich CM displayed a slower depression of the AP amplitude and duration parameters. Conversely, the recovery of the resting potential (MDP) during reoxygenation was faster in n-3 CM, whereas the recovery of the contraction parameters was unaffected by the fatty acid composition of the cells. These results suggested that, in physiological conditions, the modification of long chain PUFA balance in the phospholipids of cardiac muscle cells may modulate the initial AP upstroke, which is governed by sodium channels. Moreover, the presence of n-3 PUFA appeared to accelerate the electrical depression during substrate-free hypoxia but in turn to allow a faster recovery upon reoxygenation. (Mol Cell Biochem 175: 253–262, 1997)     

In vitro study of docosahexaenoic acid incorporation into phosphatidylcholine by enzymes of rat heart

Several studies have shown that in animals fed fish oils, docosahexaenoic acid (DHA) is incorporated into cardiac phosphatidylcholines (PC) mainly at the expense of arachidonic acid. In this study we were interested in examining if the enzymatic system involved in the remodeling of membrane PC presented any selectivity for DHA in rat heart. The enzymes that were studied from sequential incubations carried out in parallel, were acyl-CoA synthetase (EC 6.2.1.3) and acyl-CoA:lysophosphatidylcholine acyltransferase (EC 2.3.1.23) (ACLAT). The heart preparations examined were homogenates of whole heart and of purified cultured rat ventricular myocytes.Results showed that ACLAT tended to preferentially incorporate into PC the polyunsaturated fatty acids of the n-6 series (+30%) rather than those of the n-3 series. DHA, however, inhibited the incorporation of arachidonic acid (AA) into PC by 50% at a molar ratio (DHA/AA) of 1.5. This phenomenon seems to be related to the competitive inhibition exerted by DHA on the thio-esterification of AA, a reaction catalyzed by acyl-CoA synthetase. This inhibitory effect appears to be dependent on the kinetic properties of the acyl-CoA synthetase toward DHA which, among the fatty acids examined, exhibited the lowest apparent Km and Vmax.It is suggested that the intracellular pool of DHA-CoA is the determinant species in altering the DHA composition of cardiac PC in animals given fish oils.     

Eicosapentaenoic and docosahexaenoic acids in cultured rat ventricular myocytes and hypoxia-induced alterations of phospholipase—A activity

Hypoxia was reported to induce a decrease in phosphatidylcholine-hydrolyzing phospholipase activity (PC-PLA) in cultured rat cardiomyocytes. This work was intended to compare the influence of the presence of either eicosapentae noic acid (EPA) or docosahexaenoic acid (DHA) in the phospholipids on the PC-PLA activity in normoxic and hypoxic conditions. The enrichment of the medium with EPA or DHA resulted in cell phospholipids containing about 2% or 22% DHA, respectively. These cells were then submitted for 3.5 h to either normoxia or hypoxia and the PC-PLA activities were assayed using [1-¹⁴C] dioleoyl-PC (pH 8.4 for PC-PLA2 and 4.9 for PC-PLAT). The results show that both enzymic activities are significantly higher in DHA-rich cardiomyocytes. Hypoxia induced a significant decrease in PC-PLA2 (about 25%) which was not statistically different between the two groups of cells. The hypoxia-induced decrease in PC-PLA1 was not found significant. In conclusion, the nature of the long chain n-3 polyunsaturated fatty acids in the phospholipids appears to contribute to the regulation of PC-PLA activity but not to influence its decrease during hypoxia. (Mol Cell Biochem116: 75–78, 1992)     

Recurrent horizontal transfer of bacterial toxin genes to eukaryotes

In this work, we report likely recurrent horizontal (lateral) gene transfer events of genes encoding pore-forming toxins of the aerolysin family between species belonging to different kingdoms of life. Clustering based on pairwise similarity and phylogenetic analysis revealed several distinct aerolysin sequence groups, each containing proteins from multiple kingdoms of life. These results strongly support at least six independent transfer events between distantly related phyla in the evolutionary history of one protein family and discount selective retention of ancestral genes as a plausible explanation for this patchy phylogenetic distribution. We discuss the possible roles of these proteins and show evidence for a convergent new function in two extant species. We hypothesize that certain gene families are more likely to be maintained following horizontal gene transfer from commensal or pathogenic organism to its host if they 1) can function alone; and 2) are immediately beneficial for the ecology of the organism, as in the case of pore-forming toxins which can be utilized in multicellular organisms for defense and predation.     

Sensor domains encoded in Bacillus anthracis virulence plasmids prevent sporulation by hijacking a sporulation sensor histidine kinase

Anthrax toxin and capsule, determinants for successful infection by Bacillus anthracis, are encoded on the virulence plasmids pXO1 and pXO2, respectively. Each of these plasmids also encodes proteins that are highly homologous to the signal sensor domain of a chromosomally encoded major sporulation sensor histidine kinase (BA2291) in this organism. B. anthracis Sterne overexpressing the plasmid pXO2-61-encoded signal sensor domain exhibited a significant decrease in sporulation that was suppressed by the deletion of the BA2291 gene. Expression of the sensor domains from the pXO1-118 and pXO2-61 genes in Bacillus subtilis strains carrying the B. anthracis sporulation sensor kinase BA2291 gene resulted in BA2291-dependent inhibition of sporulation. These results indicate that sporulation sensor kinase BA2291 is converted from an activator to an inhibitor of sporulation in its native host by the virulence plasmid-encoded signal sensor domains. We speculate that activation of these signal sensor domains contributes to the initiation of B. anthracis sporulation in the bloodstream of its infected host, a salient characteristic in the virulence of this organism, and provides an additional role for the virulence plasmids in anthrax pathogenesis.     

Functional and physical interactions of Faf1p, a Saccharomyces cerevisiae nucleolar protein

We report the discovery and characterisation of a novel nucleolar protein of Saccharomyces cerevisiae. We identified this protein encoded by ORF YIL019w, designated in SGD base as Faf1p, in a two hybrid interaction screen using the known nucleolar protein Krr1 as bait. The presented data indicate that depletion of the Faf1 protein has an impact on the 40S ribosomal subunit biogenesis resulting from a decrease in the production of 18S rRNA. The primary defect is apparently due to inefficient processing of 35S rRNA at the A(0), A(1), and A(2) cleavage sites.