Effect of weight loss,independent of change in diet composition,on apolipoprotein AI kinetic in men with metabolic syndrome

We investigated the effect of weight loss, independent of change in diet composition, on HDL and apoAI metabolism in men with metabolic syndrome (MetS). Subjects (19 men with MetS [NCEP-ATPIII]) were fed an isoenergetic Mediterranean-style diet for 5 weeks (all foods provided). Participants then underwent a 20-week free-living period during which they were counseled to restrict energy intake, after which they were again fed an isoenergetic Mediterranean-style diet for 5 weeks. At the end of the two controlled diets, participants received a single bolus of [5,5,5-²H₃] _L-leucine, and fasting blood samples were collected over a 96 h period. ApoAI kinetic was assessed using multicompartmental modeling of the tracer enrichment data. Participants achieved a 9.1 ± 2.8% reduction in body weight (P < 0.001). Weight loss resulted in an increase in plasma HDL-cholesterol (HDL-C) concentrations of 6.0% (P = 0.059) and HDL₃-C of 7.9% (P = 0.045), attributable to a reduction in apoAI fractional catabolic rate (−7.8%; P = 0.046) with no change in apoAI production rate (2.2%; P = 0.58). These data indicate that weight loss, independent of variation in diet composition, increases plasma HDL primarily by delaying the catabolism of apoAI.     

Significance of the hydrophobic residues 225–230 of apoA-I for the biogenesis of HDL

We studied the significance of four hydrophobic residues within the 225–230 region of apoA-I on its structure and functions and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of an apoA-I[F225A/V227A/F229A/L230A] mutant in apoA-I^−/− mice decreased plasma cholesterol, HDL cholesterol, and apoA-I levels. When expressed in apoA-I^−/− × apoE^−/− mice, approximately 40% of the mutant apoA-I as well as mouse apoA-IV and apoB-48 appeared in the VLDL/IDL/LDL. In both mouse models, the apoA-I mutant generated small spherical particles of pre-β- and α4-HDL mobility. Coexpression of the apoA-I mutant and LCAT increased and shifted the-HDL cholesterol peak toward lower densities, created normal αHDL subpopulations, and generated spherical-HDL particles. Biophysical analyses suggested that the apoA-I[225–230] mutations led to a more compact folding that may limit the conformational flexibility of the protein. The mutations also reduced the ability of apoA-I to promote ABCA1-mediated cholesterol efflux and to activate LCAT to 31% and 66%, respectively, of the WT control. Overall, the apoA-I[225–230] mutations inhibited the biogenesis of-HDL and led to the accumulation of immature pre-β- and α4-HDL particles, a phenotype that could be corrected by administration of LCAT.     

Serum albumin acts as a shuttle to enhance cholesterol efflux from cells

An important mechanism contributing to cell cholesterol efflux is aqueous transfer in which cholesterol diffuses from cells into the aqueous phase and becomes incorporated into an acceptor particle. Some compounds can enhance diffusion by acting as shuttles transferring cholesterol to cholesterol acceptors, which act as cholesterol sinks. We have examined whether particles in serum can enhance cholesterol efflux by acting as shuttles. This task was accomplished by incubating radiolabeled J774 cells with increasing concentrations of lipoprotein-depleted sera (LPDS) or components present in serum as shuttles and a constant amount of LDL, small unilamellar vesicles, or red blood cells (RBC) as sinks. Synergistic efflux was measured as the difference in fractional efflux in excess of that predicted by the addition of the individual efflux values of sink and shuttle alone. Synergistic efflux was obtained when LPDS was incubated with cells and LDL. When different components of LPDS were used as shuttles, albumin produced synergistic efflux, while apoA-I did not. A synergistic effect was also obtained when RBC was used as the sink and albumin as shuttle. The previously observed negative association of albumin with coronary artery disease might be linked to reduced cholesterol shuttling that would occur when serum albumin levels are low.     

Thematic Review Series: New Lipid and Lipoprotein Targets for the Treatment of Cardiometabolic Diseases: Niacin,an old drug with a new twist

Niacin (nicotinic acid) has been used for decades as a lipid-lowering drug. The clinical use of niacin to treat dyslipidemic conditions is limited by its side effects. Niacin, along with fibrates, are the only approved drugs which elevate high density lipoprotein cholesterol (HDLc) along with its effects on low density lipoprotein cholesterol (LDLc) and triglycerides. Whether niacin has a beneficial role in lowering cardiovascular risk on the background of well-controlled LDLc has not been established. In fact, it remains unclear whether niacin, either in the setting of well-controlled LDLc or in combination with other lipid-lowering agents, confers any therapeutic benefit and if so, by which mechanism. The results of recent trials reject the hypothesis that simply raising HDLc is cardioprotective. However, in the case of the clinical trials, structural limitations of trial design complicate their interpretation. This is also true of the most recent Heart Protection Study 2-Treatment of HDLc to Reduce the Incidence of Vascular Events (HPS2-THRIVE) trial in which niacin is combined with an antagonist of the D prostanoid (DP) receptor. Human genetic studies have also questioned the relationship between cardiovascular benefit and HDLc. It remains to be determined whether niacin may have clinical utility in particular subgroups, such as statin intolerant patients with hypercholesterolemia or those who cannot achieve a sufficient reduction in LDLc. It also is unclear whether a potentially beneficial effect of niacin is confounded by DP antagonism in HPS2-THRIVE.     

A metabonomic investigation of the effects of 60 days exposure of rats to two types of pyrethroid insecticides

Type I and II pyrethroid insecticides display different neurotoxicity. To investigate the long-term (60 days exposure) metabolic effect of the two types of pyrethroid insecticides deltamethrin and permethrin, ¹H nuclear magnetic resonance (NMR) spectroscopy-based metabonomics was used to analyze the biochemical composition of urine and serum samples from rats administrated daily with deltamethrin or permethrin for 60 consecutive days, and principal component analysis used to visualize similarities and differences in the resultant biochemical profiles. Rats treated with either deltamethrin or permethrin displayed increased levels of urinary acetate, dimethylamine, dimethylglycine, trimethylamine and serum free amino acids, and decreased urinary 2-oxoglutarate, all of which are indicative of kidney lesions and nephrotoxicity. The reduced excretion of tricarboxylic acid cycle intermediates, together with increased 3-D-hydroxybutyrate, acetate, and lactate in treated rats could suggest disturbance of the energy metabolism, including an increased rate of anaerobic glycolysis, enhanced fatty acid β-oxidation and ketogenesis. These results show that these two types of insecticides have similarities in the urine and serum spectra, indicating that similar metabolic pathways are perturbed by the insecticides, which induced hepatotoxicity and nephrotoxicity. This approach may lead to the discovery of novel biomarkers of pyrethroids toxicity and thereby provide new insights into the toxicological mechanisms of pesticides pyrethroids.     

Ascorbyl palmitate interaction with phospholipid monolayers: Electrostatic and rheological preponderancy

Ascorbyl palmitate (ASC₁₆) is an anionic amphiphilic molecule of pharmacological interest due to its antioxidant properties. We found that ASC₁₆ strongly interacted with model membranes. ASC₁₆ penetrated phospholipid monolayers, with a cutoff near the theoretical surface pressure limit. The presence of a lipid film at the interface favored ASC₁₆ insertion compared with a bare air/water surface. The adsorption and penetration time curves showed a biphasic behavior: the first rapid peak evidenced a fast adsorption of charged ASC₁₆ molecules to the interface that promoted a lowering of surface pH, thus partially neutralizing and compacting the film. The second rise represented an approach to the equilibrium between the ASC₁₆ molecules in the subphase and the surface monolayer, whose kinetics depended on the ionization state of the film. Based on the Langmuir dimiristoylphosphatidylcholine + ASC₁₆ monolayer data, we estimated an ASC₁₆ partition coefficient to dimiristoylphosphatidylcholine monolayers of 1.5 × 10⁵ and a ΔG_p = − 6.7 kcal·mol^− 1. The rheological properties of the host membrane were determinant for ASC₁₆ penetration kinetics: a fluid membrane, as provided by cholesterol, disrupted the liquid-condensed ASC₁₆-enriched domains and favored ASC₁₆ penetration. Subphase pH conditions affected ASC₁₆ aggregation in bulk: the smaller structures at acidic pHs showed a faster equilibrium with the surface film than large lamellar ones. Our results revealed that the ASC₁₆ interaction with model membranes has a highly complex regulation. The polymorphism in the ASC₁₆ bulk aggregation added complexity to the equilibrium between the surface and subphase form of ASC₁₆, whose understanding may shed light on the pharmacological function of this drug.     

Design of a novel LOX-1 receptor antagonist mimicking the natural substrate

The lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1), the major receptor for oxidized low-density lipoprotein (ox-LDL) in endothelial cells, is overexpressed in atherosclerotic lesions. LOX-1 specific inhibitors, urgently necessary to reduce the rate of atherosclerotic and inflammation processes, are not yet available. We have designed and synthesized a new modified oxidized phospholipid, named PLAzPC, which plays to small scale the ligand-receptor recognition scheme. Molecular docking simulations confirm that PLAzPC disables the hydrophobic component of the ox-LDL recognition domain and allows the interaction of the l-lysine backbone charged groups with the solvent and with the charged/polar residues located around the edges of the LOX-1 hydrophobic tunnel. Binding assays, in a cell model system expressing human LOX-1 receptors, confirm that PLAzPC markedly inhibits ox-LDL binding to LOX-1 with higher efficacy compared to previously identified inhibitors.     

Discovery of XEN445: A potent and selective endothelial lipase inhibitor raises plasma HDL-cholesterol concentration in mice

Endothelial lipase (EL) activity has been implicated in HDL metabolism and in atherosclerotic plaque development; inhibitors are proposed to be efficacious in the treatment of dyslipidemia related cardiovascular disease. We describe here the discovery of a novel class of anthranilic acids EL inhibitors. XEN445 (compound 13) was identified as a potent and selective EL inhibitor, that showed good ADME and PK properties, and demonstrated in vivo efficacy in raising plasma HDLc concentrations in mice.