Faster pulmonary oxygen uptake kinetics in children vs adults due to enhancements in oxygen delivery and extraction.

This study aimed to examine if the faster pulmonary oxygen uptake (VO2p) phase 2 in children could be explained by increased O2 availability or extraction at the muscle level. For that purpose, O2 availability and extraction were assessed using deoxyhemoglobin (HHb) estimated by near-infrared spectroscopy during moderate-intensity constant load cycling exercise in children and young adults. Eleven prepubertal boys and 12 men volunteered to participate in the study. They performed one maximal graded exercise to determine the power associated with the gas exchange threshold (GET) and four constant load exercises at 90% of GET. VO2p and HHb were continuously monitored. VO2p , HHb, and estimated capillary blood flow (Qcap) kinetics were modelled after a time delay and characterized by the time to achieve 63% of the amplitude (τ) and by mean response time (MRT: time delay + τ), respectively. Mean values of τ for VO2p (P < 0.001), of MRT for HHb (P < 0.01) and of MRT for Qcap (P < 0.001) were significantly shorter in children. Faster VO2p kinetics have been shown in children; these appear due to both faster O2 extraction and delivery kinetics as indicated by faster HHb and Qcap kinetics, respectively.

[Liver malignancy in a patient with Wilson's disease]. / Maladie de Wilson et tumeur hépatique maligne.

Hepatocellular carcinoma and other tumours of the liver are extremely rare in Wilson's disease. We report a patient who presented with a cholangiocarcinoma associated with Wilson's disease. The literature review underlines that patients with Wilson's disease should be considered at risk of hepatocellular carcinoma, cholangiocarcinoma and undifferentiated carcinoma in the liver. Risk factors seem to be long disease duration and probably a poor observance to therapy. A liver imaging should be included in the follow-up of patients with Wilson's disease.

Two months of endurance training does not alter diastolic function evaluated by TDI in 9-11-year-old boys and girls.

OBJECTIVE: Superior global cardiac performance (ie stroke volume) is classically reported after training in children. Current knowledge of the impact of exercise training on myocardial relaxation, a major component of left ventricular (LV) filling and subsequently stroke volume, is, however, limited in the paediatric population. This study aimed to investigate the effect of aerobic training on LV wall motion velocities by tissue Doppler imaging (TDI) in healthy children. METHODS: 25 children (11 girls, 14 boys) were enrolled in a 2 month high-intensity aerobic training programme and 25 (12 girls and 13 boys) served as controls. The children (9-11 years old) performed a graded maximal exercise test on a treadmill to evaluate maximal oxygen uptake. Standard Doppler echocardiography and TDI measurements were performed at baseline and end of the study. Tissue Doppler systolic, early and late myocardial velocities were obtained at the mitral annulus in the septal, lateral, inferior and posterior walls. RESULTS: Maximal oxygen uptake increased by 6.5% (before: 51.6 (SD 4.2), after: 55.0 (4.5) ml/min/kg p<0.001) after training. A modest but significant increase in left ventricular end-diastolic diameter was also noticed (before: 46.1 (3.4), after: 48.3 (4.3) mm.BSA(-1/2), p<0.001), whereas left ventricular wall thickness and mass were unchanged. Neither transmitral inflow velocities nor early and late wall motion (Em: before = 18.4 (2.7), after = 18.0 (2.3) cm/s, Am: before = 6.8 (1.2), after = 6.7 (1.3) cm/s) were affected by training. Shortening fraction and regional systolic function (Sm: before = 10.1 (1.6), after = 10.2 (1.4) cm/s) by TDI were also unchanged. CONCLUSION: High-intensity aerobic sessions repeated over a 2 month period failed to improve regional diastolic function assessed by TDI in healthy young children.

Degradation of carboxy-terminal-tagged cytoplasmic proteins by the Escherichia coli protease HflB (FtsH).

Proteins with short nonpolar carboxyl termini are unstable in Escherichia coli. This proteolytic pathway is used to dispose of polypeptides synthesized from truncated mRNA molecules. Such proteins are tagged with an 11-amino-acid nonpolar destabilizing tail via a mechanism involving the 10Sa (SsrA) stable RNA and then degraded. We show here that the ATP-dependent zinc protease HflB (FtsH) is involved in the degradation of four unstable derivatives of the amino-terminal domain of the lambdacI repressor: three with nonpolar pentapeptide tails (cI104, cI105, cI108) and one with the SsrA tag (cI-SsrA). cI105 and cI-SsrA are also degraded by the ClpP-dependent proteases. Loss of ClpP can be compensated for by overproducing HflB. In an in vitro system, cI108 and cI-SsrA are degraded by HflB in an energy-dependent reaction, indicating that HflB itself recognizes the carboxyl terminus. These results establish a tail-specific pathway for removing abnormal cytoplasmic proteins via the HflB and Clp proteases.

The HflB protease of Escherichia coli degrades its inhibitor lambda cIII.

The cIII protein of bacteriophage lambda is known to protect two regulatory proteins from degradation by the essential Escherichia coli protease HflB (also known as FtsH), viz., the lambda cII protein and the host heat shock sigma factor sigma32. lambda cIII, itself an unstable protein, is partially stabilized when the HflB concentration is decreased, and its half-life is decreased when HflB is overproduced, strongly suggesting that it is degraded by HflB in vivo. The in vivo degradation of lambda cIII (unlike that of sigma32) does not require the molecular chaperone DnaK. Furthermore, the half-life of lambda cIII is not affected by depletion of the endogenous ATP pool, suggesting that lambda cIII degradation is ATP independent (unlike that of lambda cII and sigma32). The lambda cIII protein, which is predicted to contain a 22-amino-acid amphipathic helix, is associated with the membrane, and nonlethal overproduction of lambda cIII makes cells hypersensitive to the detergent sodium dodecyl sulfate. This could reflect a direct lambda cIII-membrane interaction or an indirect association via the membrane-bound HflB protein, which is known to be involved in the assembly of certain periplasmic and outer membrane proteins.

The SIGNAL experiment in BIORACK: Escherichia coli in microgravity.

Microgravity affects certain physical properties of fluids, such as convection movement and surface tension. As a consequence, cells and living organisms may exhibit different behaviour in space, which may result from differences in the immediate environment of the cell or changes in the structure of the membrane in microgravity. Two experiments to examine the effects of microgravity on cell microenvironment and signal transduction through membranes were performed using a well-characterized system with different strains of the non-pathogenic Gram-negative bacterium Escherichia coli. Our results indicate that (i) microgravity appears to reduce the lag period of a non-motile culture of E. coli, and (ii) the ompC gene, regulated by the two-component system EnvZ-OmpR, is induced as well or better in microgravity than in ground controls.

Degradation of sigma 32, the heat shock regulator in Escherichia coli, is governed by HflB.

The heat shock response in Escherichia coli is governed by the concentration of the highly unstable sigma factor sigma 32. The essential protein HflB (FtsH), known to control proteolysis of the phage lambda cII protein, also governs sigma 32 degradation: an HflB-depleted strain accumulated sigma 32 and induced the heat shock response, and the half-life of sigma 32 increased by a factor up to 12 in mutants with reduced HflB function and decreased by a factor of 1.8 in a strain overexpressing HflB. The hflB gene is in the ftsJ-hflB operon, one promoter of which is positively regulated by heat shock and sigma 32. The lambda cIII protein, which stabilizes sigma 32 and lambda cII, appears to inhibit the HflB-governed protease. The E. coli HflB protein controls the stability of two master regulators, lambda cII and sigma 32, responsible for the lysis-lysogeny decision of phage lambda and the heat shock response of the host.

ppGpp concentration, growth without PBP2 activity, and growth-rate control in Escherichia coli.

Escherichia coli strains partially induced for the stringent response are resistant to mecillinam, a beta-lactam antibiotic which specifically inactivates penicillin-binding protein 2, the key enzyme determining cell shape. We present evidence that mecillinam resistance occurs whenever the intracellular concentration of the nucleotide ppGpp (guanosine 3'-diphosphate 5'-diphosphate), the effector of the stringent response, exceeds a threshold level. First, the ppGpp concentration was higher in a mecillinam-resistant mutant than in closely related sensitive strains. Second, the ppGpp pool was controlled by means of a plasmid carrying a ptac-relA' gene coding for a hyperactive (p)ppGpp synthetase, RelA'; increasing the ppGpp pool by varying the concentration of lac operon inducer IPTG resulted in a sharp threshold ppGpp concentration, above which cells were mecillinam resistant. Third, the ppGpp pool was increased by using poor media; again, at the lowest growth rate studied, the cells were mecillinam resistant. In all experiments, cells with a ppGpp concentration above 140 pmoles/A600 were mecillinam resistant whereas those with lower concentrations were sensitive. We discuss a possible role for ppGpp as transcriptional activator of cell division genes whose products seem to become limiting in the presence of mecillinam, when cells form large spheres. We confirmed the well-known inverse correlation between growth rate and ppGpp concentration but, surprisingly, for a given growth rate, the ppGpp concentration was lower in poor medium than in richer medium in which RelA' is induced. We conclude that, for E. coli growing in poor media, the concentration of the nucleotide ppGpp is not the major growth rate determinant.

Penicillin-binding protein 2 inactivation in Escherichia coli results in cell division inhibition, which is relieved by FtsZ overexpression.

Aminoacyl-tRNA synthetase mutants of Escherichia coli are resistant to amdinocillin (mecillinam), a beta-lactam antibiotic which specifically binds penicillin-binding protein 2 (PBP2) and prevents cell wall elongation with concomitant cell death. The leuS(Ts) strain, in which leucyl-tRNA synthetase is temperature sensitive, was resistant to amdinocillin at 37 degrees C because of an increased guanosine 5'-diphosphate 3'-diphosphate (ppGpp) pool resulting from partial induction of the stringent response, but it was sensitive to amdinocillin at 25 degrees C. We constructed a leuS(Ts) delta (rodA-pbpA)::Kmr strain, in which the PBP2 structural gene is deleted. This strain grew as spherical cells at 37 degrees C but was not viable at 25 degrees C. After a shift from 37 to 25 degrees C, the ppGpp pool decreased and cell division was inhibited; the cells slowly carried out a single division, increased considerably in volume, and gradually lost viability. The cell division inhibition was reversible when the ppGpp pool increased at high temperature, but reversion required de novo protein synthesis, possibly of septation proteins. The multicopy plasmid pZAQ, overproducing the septation proteins FtsZ, FtsA, and FtsQ, conferred amdinocillin resistance on a wild-type strain and suppressed the cell division inhibition in the leuS(Ts) delta (rodA-pbpA)::Kmr strain at 25 degrees C. The plasmid pAQ, in which the ftsZ gene is inactivated, did not confer amdinocillin resistance. These results lead us to hypothesize that the nucleotide ppGpp activates ftsZ expression and thus couples cell division to protein synthesis.

Disseminated intravascular coagulation in Fusobacterium necrophorum septicemia.

A previously healthy 42-year-old man developed, after a neglected tonsillitis, a severe Fusobacterium necrophorum septicemia with disseminated intravascular coagulation. Peripheral, painful, cyanotic and gangrenous lesions appeared on toes, external ears and nose tip. The patient survived. Consumption coagulopathy associated with tonsillitis should suggest F. necrophorum infection. Growth of these bacteria in blood cultures is slow and confirmation of the infection may thus be delayed.

[Necrotizing fasciitis of the face. Clinical and therapeutic aspects]. / Les fasciites nécrosantes de la face. Aspects cliniques et thérapeutiques.

Necrotizing fasciitis is a synergic infection, the chief causal agents of which are beta-hemolytic group A streptococci. The authors insistingly review the different aspects of this rare affection and stress the importance of emergent medical and surgical management, as the evolution of the disease is still often lethal.