Extra-adipocyte leptin release in human obesity and its relation to sympathoadrenal function

The link between the human sympathoadrenalmedullary system and the adipocyte hormone leptin is controversial. We measured total and regional norepinephrine spillover, epinephrine secretion rate, and extra-adipocyte leptin release in 22 lean [body mass index (BMI) < 26] and 20 obese (BMI > 28) normotensive men who underwent arterial and central venous catheterization. Because plasma clearance of leptin is primarily by renal removal, for men at steady state we could estimate whole body leptin release to plasma from renal plasma leptin extraction. Whole body leptin release was 1,950 +/- 643 (means +/- SE) ng/min in obese men and 382 +/- 124 ng/min in lean men (P < 0.05). Total and renal norepinephrine spillover rates correlated directly with whole body leptin secretion rate. Leptin is released from multiple nonadipocyte sites, which we tested by use of simultaneous arteriovenous blood sampling. We found a surprisingly large contribution of brain leptin release to the plasma leptin pool, 529 +/- 175 ng/min (> 40% whole body leptin release), with greater leptin release in obese than in lean men, 935 +/- 321 vs. 160 +/- 59 ng/min (P = 0.045). In parallel with leptin measurements, we also quantified brain serotonin turnover and jugular overflow of neuropeptide Y (NPY). Brain serotonin turnover was higher in obese than in lean men, 227 +/- 112 vs. 21 +/- 14 ng/min (P = 0.019), as was overflow of NPY from the brain, 12.9 +/- 1.4 vs. 5.3 +/- 2.2 ng/min (P = 0.042). These results suggest that leptin is released within the brain and at an increased rate in obese humans, in whom activation of brain serotonergic and NPY mechanisms also exists.     

A biomimetic motility assay provides insight into the mechanism of actin-based motility

Abiomimetic motility assay is used to analyze the mechanism of force production by site-directed polymerization of actin. Polystyrene microspheres, functionalized in a controlled fashion by the N-WASP protein, the ubiquitous activator of Arp2/3 complex, undergo actin-based propulsion in a medium that consists of five pure proteins. We have analyzed the dependence of velocity on N-WASP surface density, on the concentration of capping protein, and on external force. Movement was not slowed down by increasing the diameter of the beads (0.2 to 3 microm) nor by increasing the viscosity of the medium by 10(5)-fold. This important result shows that forces due to actin polymerization are balanced by internal forces due to transient attachment of filament ends at the surface. These forces are greater than the viscous drag. Using Alexa488-labeled Arp2/3, we show that Arp2/3 is incorporated in the actin tail like G-actin by barbed end branching of filaments at the bead surface, not by side branching, and that filaments are more densely branched upon increasing gelsolin concentration. These data support models in which the rates of filament branching and capping control velocity, and autocatalytic branching of filament ends, rather than filament nucleation, occurs at the particle surface.     

Natural transformation of Campylobacter jejuni requires components of a type II secretion system

The human pathogen Campylobacter jejuni is one of more than 40 naturally competent bacterial species able to import macromolecular DNA from the environment and incorporate it into their genomes. However, in C. jejuni little is known about the genes involved in this process. We used random transposon mutagenesis to identify genes that are required for the transformation of this organism. We isolated mutants with insertions in 11 different genes; most of the mutants are affected in the DNA uptake stage of transformation, whereas two mutants are affected in steps subsequent to DNA uptake, such as recombination into the chromosome or in DNA transport across the inner membrane. Several of these genes encode proteins homologous to those involved in type II secretion systems, biogenesis of type IV pili, and competence for natural transformation in gram-positive and gram-negative species. Other genes identified in our screen encode proteins unique to C. jejuni or are homologous to proteins that have not been shown to play a role in the transformation in other bacteria.     

Actin-based motility: from molecules to movement

Extensive progress has been made recently in understanding the mechanism by which cells move and extend protrusions using site-directed polymerization of actin in response to signalling. Insights into the molecular mechanism of production of force and movement by actin polymerization have been provided by a crosstalk between several disciplines, including biochemistry, biomimetic approaches and computational studies. This review focuses on the biochemical properties of the proteins involved in actin-based motility and shows how these properties are used to generate models of force production, how the predictions of different theoretical models are tested using a biochemically controlled reconstituted motility assay and how the changes in motility resulting from changes to the concentrations of components of the assay can help understand diverse aspects of the motile behavior of living cells.     

Structure-activity relationships of novel anti-malarial agents: part 5. N-(4-acylamino-3-benzoylphenyl)-[5-(4-nitrophenyl)-2-furyl]acrylic acid amides

We have developed the [5-(4-nitrophenyl)-2-furyl]acrylic acid substituted benzophenone 4g as a novel lead for anti-malarial agents. Here, we demonstrated that the acyl residue at the 2-amino group of the benzophenone core structure has to be a phenylacetic acid substructure substituted in its para-position with methyl or other substituents of similar size. The trifluoromethyl substituted derivative displayed an IC(50) of 47 nM against the multi-drug resistant Plasmodium falciparum strain Dd2.     

Pharmacokinetics of Isoniazid,Pyrazinamide, and Ethambutol in Newly Diagnosed Pulmonary TB Patients in Tanzania

Exposure to lower-than-therapeutic levels of anti-tuberculosis drugs is likely to cause selection of resistant strains of Mycobacterium tuberculosis and treatment failure. The first-line anti-tuberculosis (TB) regimen consists of rifampicin, isoniazid, pyrazinamide, and ethambutol, and correct management reduces risk of TB relapse and development of drug resistance. In this study we aimed to investigate the effect of standard of care plus nutritional supplementation versus standard care on the pharmacokinetics of isoniazid, pyrazinamide and ethambutol among sputum smear positive TB patients with and without HIV. In a clinical trial in 100 Tanzanian TB patients, with or without HIV infection, drug concentrations were determined at 1 week and 2 months post initiation of anti-TB medication. Data was analysed using population pharmacokinetic modelling. The effect of body size was described using allometric scaling, and the effects of nutritional supplementation, HIV, age, sex, CD4+ count, weight-adjusted dose, NAT2 genotype, and time on TB treatment were investigated. The kinetics of all drugs was well characterised using first-order elimination and transit compartment absorption, with isoniazid and ethambutol described by two-compartment disposition models, and pyrazinamide by a one-compartment model. Patients with a slow NAT2 genotype had higher isoniazid exposure and a lower estimate of oral clearance (15.5 L/h) than rapid/intermediate NAT2 genotype (26.1 L/h). Pyrazinamide clearance had an estimated typical value of 3.32 L/h, and it was found to increase with time on treatment, with a 16.3% increase after the first 2 months of anti-TB treatment. The typical clearance of ethambutol was estimated to be 40.7 L/h, and was found to decrease with age, at a rate of 1.41% per year. Neither HIV status nor nutritional supplementations were found to affect the pharmacokinetics of these drugs in our cohort of patients.