The Effect of Carbohydrate Restriction on Lipids, Lipoproteins, and Nuclear Magnetic Resonance-Based Metabolites: CALIBER, a Randomised Parallel Trial

Low-carbohydrate high-fat (LCHF) diets can be just as effective as high-carbohydrate, lower-fat (HCLF) diets for improving cardiovascular disease risk markers. Few studies have compared the effects of the UK HCLF dietary guidelines with an LCHF diet on lipids and lipoprotein metabolism using high-throughput NMR spectroscopy. This study aimed to explore the effect of an ad libitum 8-week LCHF diet compared to an HCLF diet on lipids and lipoprotein metabolism and CVD risk factors. For 8 weeks, n = 16 adults were randomly assigned to follow either an LCHF (n = 8, <50 g CHO p/day) or an HCLF diet (n = 8). Fasted blood samples at weeks 0, 4, and 8 were collected and analysed for lipids, lipoprotein subclasses, and energy-related metabolism markers via NMR spectroscopy. The LCHF diet increased (p < 0.05) very small VLDL, IDL, and large HDL cholesterol levels, whereas the HCLF diet increased (p < 0.05) IDL and large LDL cholesterol levels. Following the LCHF diet alone, triglycerides in VLDL and HDL lipoproteins significantly (p < 0.05) decreased, and HDL phospholipids significantly (p < 0.05) increased. Furthermore, the LCHF diet significantly (p < 0.05) increased the large and small HDL particle concentrations compared to the HCLF diet. In conclusion, the LCHF diet may reduce CVD risk factors by reducing triglyceride-rich lipoproteins and improving HDL functionality.

Genetically Determined Serum 25-Hydroxyvitamin D Is Associated with Total, Trunk, and Arm Fat-Free Mass: A Mendelian Randomization Study

PURPOSE

Low serum vitamin D status has been associated with reduced muscle mass in observational studies although the relationship is controversial and a causal association cannot be determined from such observations. Two-sample Mendelian randomization (MR) was applied to assess the association between serum vitamin D (25(OH)D) and total, trunk, arm and leg fat-free mass (FFM).

METHODS

MR was implemented using summary-level data from the largest genome-wide association studies (GWAS) on vitamin D (n=73,699) and total, trunk, arm and leg FFM. Inverse variance weighted method (IVW) was used to estimate the causal estimates. Weighted median (WM)-based method, and MR-Egger, leave-one-out were applied as sensitivity analysis.

RESULTS

Genetically higher serum 25(OH)D levels had a positive effect on total (IVW = Beta: 0.042, p = 0.038), trunk (IVW = Beta: 0.045, p = 0.023) and arm (right arm IVW = Beta: 0.044, p = 0.002; left arm IVW = Beta: 0.05, p = 0.005) FFM. However, the association with leg FFM was not significant (right leg IVW = Beta: 0.03, p = 0.238; left leg IVW = Beta: 0.039, p = 0.100). The likelihood of heterogeneity and pleiotropy was determined to be low (statistically non-significant), and the observed associations were not driven by single SNPs. Furthermore, MR pleiotropy residual sum and outlier test did not highlight any outliers.

CONCLUSIONS

Our results illustrate the potentially causal, positive effect of serum 25(OH)D concentration on total, trunk and upper body appendicular fat-free mass.

Novel mechanisms of TolC-independent decreased bile-salt susceptibility in Escherichia coli

Bile salts, including sodium deoxycholate (DOC), are secreted into the intestine to aid fat digestion and contribute to antimicrobial protection. Gram-negative pathogens such as Escherichia coli, however, are highly resistant to DOC, using multiple mechanisms of which the multidrug efflux pump AcrAB-TolC is the dominant one. Given that TolC-mediated efflux masks the interaction of DOC with potential targets, we sought to identify those targets by identifying genes whose mutations cause an increase in the MIC to DOC relative to the ∆tolC parental strain, that lacks TolC-associated functional efflux pumps. Using a mutant screen, we isolated twenty independent spontaneous mutants that had a higher MICDOC than the E. coli parental ∆tolC strain. Whole genome sequencing of these mutants mapped most mutations to the ptsI or cyaA gene. Analysis of knock-out mutants and complementation showed that elimination of PtsI, a component of the carbohydrate phosphotransferase system, or one of the two key proteins involved in cAMP synthesis and signaling, adenylate cyclase (CyaA) or cAMP receptor protein (Crp) causes low-level increased resistance of a ∆tolC E. coli strain to DOC.

In vitro synergy between sodium deoxycholate and furazolidone against enterobacteria

Background

Antimicrobial combinations have been proven as a promising approach in the confrontation with multi-drug resistant bacterial pathogens. In the present study, we identify and characterize a synergistic interaction of broad-spectrum nitroreductase-activated prodrugs 5-nitrofurans, with a secondary bile salt, sodium deoxycholate (DOC) in growth inhibition and killing of enterobacteria.

Results

Using checkerboard assay, we show that combination of nitrofuran furazolidone (FZ) and DOC generates a profound synergistic effect on growth inhibition in several enterobacterial species including Escherichia coli, Salmonella enterica, Citrobacter gillenii and Klebsiella pneumoniae. The Fractional Inhibitory Concentration Index (FICI) for DOC-FZ synergy ranges from 0.125 to 0.35 that remains unchanged in an ampicillin-resistant E. coli strain containing a β-lactamase-producing plasmid. Findings from the time-kill assay further highlight the synergy with respect to bacterial killing in E. coli and Salmonella.

We further characterize the mechanism of synergy in E. coli K12, showing that disruption of the tolC or acrA genes that encode components of multidrug efflux pumps causes, respectively, a complete or partial loss, of the DOC-FZ synergy. This finding indicates the key role of TolC-associated efflux pumps in the DOC-FZ synergy. Overexpression of nitric oxide-detoxifying enzyme Hmp results in a three-fold increase in FICI for DOC-FZ interaction, suggesting a role of nitric oxide in the synergy. We further demonstrate that DOC-FZ synergy is largely independent of NfsA and NfsB, the two major activation enzymes of the nitrofuran prodrugs.

Conclusions

This study is to our knowledge the first report of nitrofuran-deoxycholate synergy against Gram-negative bacteria, offering potential applications in antimicrobial therapeutics. The mechanism of DOC-FZ synergy involves FZ-mediated inhibition of TolC-associated efflux pumps that normally remove DOC from bacterial cells. One possible route contributing to that effect is via FZ-mediated nitric oxide production.

Lack of effect of cold water prawns on plasma cholesterol and lipoproteins in normo-lipidaemic men

OBJECTIVE

Dietary guidelines for the prevention of coronary heart disease (CHD) have restricted the intake of foods rich in dietary cholesterol, on the grounds that the dietary cholesterol will increase blood cholesterol. In the case of shellfish, this recommendation may limit the intake of a valuable dietary source of long chain n-3 polyunsaturated fatty acids (LC n-3 PUFA). The objective of this study was to undertake a dietary intervention to determine the effects of cold water prawns on plasma lipids and lipoproteins.

METHODS

23 healthy male subjects were randomised to receive either 225 g of cold water prawns or an equivalent weight of fish ('crab') sticks as a control for 12 weeks in a cross-over design. Blood samples were taken at the beginning and end of each intervention for the determination of plasma lipids and lipoproteins by routine enzymatic assays and iodixanol density gradient centrifugation respectively.

RESULTS

The diets were well matched for the intake of total energy and macronutrients, and body weight remained stable throughout the study. The prawn intervention increased the intake of dietary cholesterol to 750 mg/d against 200 mg/d on the control. The intake of LC n-3 PUFA from prawns was estimated to be between 0.5-0.7 g/d. The consumption of prawns produced no significant effects on the concentration of plasma total or LDL cholesterol, triacylglycerol, HDL cholesterol or apolipoproteins A-I and B relative to the control, or within each intervention group over time. There was also no significant effect on LDL density (particle size) relative to the control, or any difference between and within treatments in total plasma lipoprotein profiles by density gradient centrifugation.

CONCLUSION

These findings provide evidence to suggest that the consumption of cold water prawns, at least in healthy, male subjects, should not be restricted on the grounds of this seafood producing an adverse effect on plasma LDL cholesterol.

Oxidation of anthracene on platinum macro- and micro-electrodes: Sonoelectrochemical, cryoelectrochemical and sonocryoelectrochemical studies

The electro- and sonoelectro-chemical oxidation of anthracene in acetonitrile has been explored at room and low temperature (-40 degrees C) at a platinum micro- and macro-electrode, respectively. From both methodologies, the effective number of electrons, n(eff), in the oxidation process is evaluated at both room temperature and at the limit of the solvent-electrolyte freezing point. It is observed that n(eff) is close to 1 at low temperature while at room temperature it is higher, indicating sluggish follow up kinetics at lower temperature. The oxidative electrolysis of anthracene within an undivided cell, under various conditions is investigated with the product(s) obtained analysed and quantified by (1)H NMR. At room temperature under both 'silent' and 'sono' conditions the electrochemical oxidation produces 9,10-anthraquinone and bianthrone while at low temperature with acoustic streaming, anthracene-9,10-diol is additionally produced. Electrolyses with intentionally added water and also with oxygen saturation is investigated and its influence on the reaction pathway reported. In particular, the addition of water (1.4M) favours the formation of anthraquinone in a 3:1 ratio with bianthrone. Overall, the effect of lower temperature is to favour the formation of anthraquinone or its reduced form whilst the addition of insonation at low temperature is to substantially enhance the product yield per Coulomb of charge injected.

Glyco- and peptidomimetics from three-component Joullié-Ugi coupling show selective antiviral activity

Chlorination-elimination chemistry coupled with three-component Joullié-Ugi reaction and facile deprotection allowed efficient access to an array of polyhydroxylated pyrrolidines through parallel synthesis that may be considered to be a library of imino (aza) sugars (glycomimetics) and/or dihydroxyprolyl peptides (peptidomimetics). The utility of generating such a library was illustrated by screening against 15 different targets that revealed potent and selective inhibition of the Gaucher's disease glycosyltransferase enzyme glucosylceramide synthase and of primary pathogen model for human hepatitis C virus (HCV) and bovine diarrhoeal virus (BVDV). An observed selectivity for this HCV model over hepatitis B virus and remarkably low toxicity suggest a novel mode of action.

Fractionation of lipoprotein subclasses in self-generated gradients of iodixanol

Chapter 5 described the use of self-generated gradients of iodixanol for the fractionation of human plasma lipoproteins into the major classes: high-density, low-density, and very low density (HDL, LDL, and VLDL). During the metabolism of plasma HDL and LDL, the lipid and apoprotein composition of the lipoprotein particles changes in such a manner that a series of subclasses exists, each with a distinctive range of densities (1). Thus, in KBr gradients, the two major subclasses, HDL(2) and HDL(3), have densities of 1.063-1.125 g/mL and 1.125-1.21 g/mL, respectively (1). In some individuals a third subclass (HDL1) is recognized (1.055-1.063 g/mL). Electrophoretic (2) and immunological (3,4) techniques have identified additional subfractions. Likewise, subclasses of LDL have been identified and isolated using shallow KBr gradients (5,6). The major LDL subfractions are LDL(1), LDL(2), and LDL(3), which have densities of 1.025-1.034 g/mL, 1.034-1.044 g/mL, and 1.044-1.060 g/mL, respectively (6), and electrophoretic analysis has identified more subfractions (7). The subfractions of LDL are of particular interest, as the presence of small, dense LDL particles in the plasma appears to be associated with a predisposition to cardiovascular disease, and they are recognized as a major causative factor in atherosclerosis (8). Methods for monitoring the LDL subclass pattern in population studies and in dietary and drug intervention trials are thus of considerable interest. This chapter is concerned primarily with the subfractionation of LDL. Although HDL subfractionation systems using iodixanol self-generated gradients have not yet been validated by direct comparison with other methods (e.g., gradient gel electrophoresis or KBr gradient centrifugation), a protocol is included.

Carotenoid composition and antioxidant potential in subfractions of human low-density lipoprotein

Carotenoids and vitamin E are transported in human plasma complexed with lipoproteins. The bulk of them are associated with low-density lipoprotein (LDL), in which form they may act as antioxidants and thus delay the onset of atherosclerosis. We used a simple, rapid, ultracentrifugation technique to fractionate plasma lipoproteins in self-generating gradients of iodixanol (Optiprep), a non-ionic iodinated density gradient medium. The carotenoid content and composition of a number of LDL subfractions was determined by reversed-phase high-performance liquid chromatography. Lycopene, beta-carotene and beta-cryptoxanthin were mainly located in the larger, less-dense LDL particles whereas lutein and zeaxanthin were found preferentially in the smaller, more dense LDL particles. When the antioxidant content of these fractions was expressed per milligram of LDL protein, significantly lower concentrations of carotenoid and vitamin E were found to be associated with the smaller, protein-rich fractions of LDL. Strong positive correlations were found between total carotenoid and vitamin E plasma concentrations and the lag-time of Cu(2+)-mediated oxidation of LDL subfractions. The more dense LDL subfractions, which had lower levels of these antioxidants, were more readily oxidized, highlighting their possible role in atherosclerotic events.

Expression of an Antirrhinum dihydroflavonol reductase gene results in changes in condensed tannin structure and accumulation in root cultures of Lotus corniculatus (bird's foot trefoil)

Condensed tannins (proanthocyanidins) are an important factor in the nutritive and dietary quality of many forage crops. We report here experiments aimed at altering the levels and monomer composition of condensed tannins (CTs) in 'hairy root' cultures of Lotus corniculatus (bird's foot trefoil) using genetic manipulation. An Antirrhinum majus dihydroflavonol reductase (DFR) cDNA was expressed in sense in L. corniculatus and CT levels in transgenic root cultures were analysed. Two co-transformed lines were noted with decreased CT content relative to controls and these levels were comparable with antisense-DFR phenotypes. In ADFR10, a co-transformed line with the highest CT levels, CT structure was altered in a manner consistent with the substrate specificity of the introduced gene; that is an increase in pro-pelargonidin monomers noted after hydrolysis of CTs. RT-PCR confirmed the expression of endogenous DFR gene(s) in both putatively co-suppressed lines and also in ADFR10. Analysis of selected root culture lines indicated that the monomer composition of CTs did not change during growth and development but that levels of CTs varied in a regulated manner.