Metformin counters the insulin-induced suppression of fatty acid oxidation and stimulation of triacylglycerol storage in rodent skeletal muscle

The present study examined the acute effects of metformin on fatty acid (FA) metabolism in oxidative soleus (SOL) and glycolytic epitrochlearis (EPT) rodent muscle. SOL and EPT were incubated for either 30 or 180 min in the absence or presence of 2 mM metformin and with or without insulin (10 mU/ml). Metformin did not alter basal FA metabolism but countered the effects of insulin on FA oxidation and incorporation into triacylglyerol (TAG). Specifically, metformin prevented the insulin-induced suppression of FA oxidation in SOL but did not alter FA incorporation into lipid pools. In contrast, in EPT metformin blunted the incorporation of FA into TAG when insulin was present but did not alter FA oxidation. In SOL, metformin resulted in a 50% increase in AMP-activated protein kinase alpha2 activity and prevented the insulin-induced increase in malonyl-CoA content. In both fiber types, basal and insulin-stimulated glucose oxidation were not significantly altered by metformin. All effects were similar regardless of whether they were measured after 30 or 180 min. Because increased muscle lipid storage and impaired FA oxidation have been associated with insulin resistance in this tissue, the ability of metformin to reverse these abnormalities in muscle FA metabolism may be a part of the mechanism by which metformin improves glucose clearance and insulin sensitivity. The present data also suggest that increased glucose clearance is not due to its enhanced subsequent oxidation. Additional studies are warranted to determine whether chronic metformin treatment has similar effects on muscle FA metabolism.     

Ant versus bird exclusion effects on the arthropod assemblage of an organic citrus grove

1. Predation‐exclusion experiments have highlighted that top‐down control is pervasive in terrestrial communities, but most of these experiments are simplistic in that they only excluded a single group of predators and the effect of removal was evaluated on a few species from the community. The main goal of our study was to experimentally establish the relative effects of ants and birds on the same arthropod assemblage of canopy trees. 2. We conducted 1‐year long manipulative experiments in an organic citrus grove intended to quantify the independent effects of bird and ant predators on the abundance of arthropods. Birds were excluded with plastic nets whereas ants were excluded with sticky barriers on the trunks. The sticky barrier also excluded other ground dwelling insects, like the European earwig Forficula auricularia L. 3. Both the exclusion of ants and birds affected the arthropod community of the citrus canopies, but the exclusion of ants was far more important than the exclusion of birds. Indeed, almost all groups of arthropods had higher abundance in ant‐excluded than in control trees, whereas only dermapterans were more abundant in bird‐excluded than in control trees. A more detailed analysis conducted on spiders also showed that the effect of ant exclusion was limited to a few families rather than being widespread over the entire diverse spectrum of spiders. 4. Our results suggest that the relative importance of vertebrate and invertebrate predators in regulating arthropod populations largely depends on the nature of the predator–prey system.     

Imaging the cell entry of the anthrax oedema and lethal toxins with fluorescent protein chimeras

To investigate the cell entry and intracellular trafficking of anthrax oedema factor (EF) and lethal factor (LF), they were C‐terminally fused to the enhanced green fluorescent protein (EGFP) and monomeric Cherry (mCherry) fluorescent proteins. Both chimeras bound to the surface of BHK cells treated with protective antigen (PA) in a patchy mode. Binding was followed by rapid internalization, and the two anthrax factors were found to traffic along the same endocytic route and with identical kinetics, indicating that their intracellular path is essentially dictated by PA. Colocalization studies indicated that anthrax toxins enter caveolin‐1 containing compartments and then endosomes marked by phoshatidylinositol 3‐phoshate and Rab5, but not by early endosome antigen 1 and transferrin. After 40 min, both EF and LF chimeras were observed to localize within late compartments. Eventually, LF and EF appeared in the cytosol with a time‐course consistent with translocation from late endosomes. Only the EGFP derivatives reached the cytosol because they are translocated by the PA channel, while the mCherry derivatives are not. This difference is attributed to a higher resistance of mCherry to unfolding. After translocation, LF disperses in the cytosol, while EF localizes on the cytosolic face of late endosomes.     

The effect of subminimal inhibitory concentrations of antibiotics on virulence factors expressed by Staphylococcus aureus biofilms

Aims: The effect of subminimal inhibitory concentrations (sub‐MICs) of cefalexin, ciprofloxacin and roxithromycin was investigated on some virulence factors [e.g. coagulase, Toxic Shock Syndrome Toxin 1 (TSST‐1) and biofilm formation] expressed by Staphylococcus aureus biofilms. Methods and Results: Biofilms were grown with and without the presence of 1/16 MIC of antibiotics on Sorbarod filters. Eluate supernatants were collected, and coagulase and TSST‐1 production were evaluated. Coagulase production was reduced in eluates exposed to roxithromycin when compared to control, while TSST‐1 production was reduced in biofilms exposed to cefalexin and to a lesser extent, ciprofloxacin. In addition, the ability of Staph. aureus to produce biofilm in microtitre plates in the presence of sub‐MIC antibiotics indicated that cefalexin induced biofilm formation at a wide range of sub‐MICs. TSST‐1 produced from the challenged and control biofilms was purified, and its proliferative activity was studied on single cell suspension of mouse splenocytes using MTS/PMS assay. No significant difference in the activity between the treated toxin and the control has been observed. Conclusions: Antibiotics at sub‐MIC levels interfere with bacterial biofilm virulence expression depending on the type and concentration of antibiotic used. Significance and Impact of the Study: The establishment of sub‐MICs of antibiotics in clinical situations may result in altered virulence states in pathogenic bacteria.