Effect of very low calorie diet on body composition and exercise response in sedentary women.

The effect of very low calorie diet (VLCD) on fat-free mass (FFM) and physiological response to exercise is a topic of current interest. Ten moderately obese women (aged 23-57 years) received VLCD (1695 kJ.day-1) for 6 weeks. FFM, estimated by four conventional techniques, and heart rate (fc), blood lactate (la(b)), mean arterial pressure (MAP), respiratory exchange ratio (R) and rating of perceived exertion (RPE) were measured during a submaximal cycle ergometry test 1 week before, in the 2nd and 6th week, and 1 week after VLCD treatment. Strength and muscular endurance of the quadriceps and hamstrings were tested by isokinetic dynamometry. The 11.5-kg reduction in body mass was approximately 63% fat and 37% FFM. The latter was attributed largely to the loss of water associated with glycogen. Whilst exercise fc increased by 9-14 beats.min-1 (P < 0.01), there were substantial decreases (P < 0.01) in submaximal MAP (1.07-1.73 kPa), la(b) (0.75-1.00 mmol.l-1 and R (0.07-0.09) during VLCD. R and fc returned to normal levels after VLCD. Gross strength decreased (P < 0.01) by 9 and 13% at 1.05 rad.s-1 and 3.14 rad.s-1, respectively. Strength expressed relative to body mass (Nm.kg-1) increased (P < 0.01) at the lower contraction velocity, but there was no change at the faster velocity. Muscular endurance also decreased (P < 0.01) by 62 and 82% for the hamstrings and quadriceps, respectively. We concluded that the strength decrease was a natural adaptation to the reduction in body mass as the ratio of strength to FFM was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)     

Establishment of an in vitro sciarid fly larvae assay to study plant resistance

Mechanisms underlying natural plant resistance to herbivorous invertebrates are still poorly understood in comparison with bacterial or fungal interactions. One reason is the difficulty in reliably and reproducibly assessing the effects under controlled conditions. This article describes a newly developed in vitro biological assay system that enables the interactions between sciarid larvae and plants, whose roots they feed on, to be studied under highly controlled conditions. The bioassay eliminates the problems created by the often variable environmental factors by providing an aseptic arena where experimental plants can be germinated and grown on agar within a Petri dish. Sciarid fly eggs are then collected, sterilised and added to the Petri dish. The system allows the eggs to hatch and the larvae to feed on the plant roots. A range of developmental parameters can then be recorded over time which can then be correlated with the experimental plant type. This assay system also allows a simultaneous comparison or 'choice chamber' between two (or more) different genotypes. The assay should greatly help to facilitate the identification of new components involved in insect resistance mediated pathway via the characterisation of mutant plants.     

Assembly and transport properties of invariant chain trimers and HLA-DR-invariant chain complexes.

The MHC class II-associated invariant chain behaves as a resident endoplasmic reticulum protein in the absence of class II molecules. In humans, two predominant forms exist; one, p35, differs from the other, p33, by an N-terminal cytoplasmic extension of 16 amino acids that contains a strong endoplasmic reticulum-retention signal. Here we show that one mechanism for retention of p33 is its association with p35 in mixed invariant chain trimers. However, even for p33 homotrimers transport from the endoplasmic reticulum is inefficient. In an MHC class II-positive B cell line, the formation of invariant chain trimers is rapid and is the first intermediate in the assembly of a nine-chain alpha beta-invariant chain complex. With time, three higher molecular weight complexes are progressively formed. These correspond to an invariant chain trimer with one alpha beta dimer, two alpha beta dimers, and three alpha beta dimers, respectively. No free alpha beta dimers are detectable early in biosynthesis. However, beginning at 2 h of chase, alpha beta dimers begin to appear concomitant with the disappearance of the completely assembled alpha beta-invariant chain complex. This conversion is virtually complete by 4 h, and presumably reflects the proteolytic degradation of the invariant chain component of the alpha beta-invariant chain complex and the generation of endosomal alpha beta dimers capable of binding antigenic peptides.     

The specific 18-kilodalton antigen of Mycobacterium leprae is present in Mycobacterium habana and functions as a heat-shock protein

A mAb previously thought to be specific for Mycobacterium leprae has been found to cross-react with a cultivable mycobacterium, Mycobacterium habana TMC5135. The epitope is present on a protein of identical molecular mass (18 kDa) in both species. When M. habana is subjected to heat shock, expression of the protein is significantly increased, whereas other forms of environmental stress do not increase its expression. Since immunization of mice with M. habana results in protection against infection with M. leprae, the possibility of using a molecular genetic approach to investigate the role of this protein in protective immunity is raised.     

Pseudomonas aeruginosa–induced nociceptor activation increases susceptibility to infection

We report a rapid reduction in blink reflexes during in vivo ocular Pseudomonas aeruginosa infection, which is commonly attributed and indicative of functional neuronal damage. Sensory neurons derived in vitro from trigeminal ganglia (TG) were able to directly respond to P. aeruginosa but reacted significantly less to strains of P. aeruginosa that lacked virulence factors such as pili, flagella, or a type III secretion system. These observations led us to explore the impact of neurons on the host’s susceptibility to P. aeruginosa keratitis. Mice were treated with Resiniferatoxin (RTX), a potent activator of Transient Receptor Potential Vanilloid 1 (TRPV1) channels, which significantly ablated corneal sensory neurons, exhibited delayed disease progression that was exemplified with decreased bacterial corneal burdens and altered neutrophil trafficking. Sensitization to disease was due to the increased frequencies of CGRP-induced ICAM-1⁺ neutrophils in the infected corneas and reduced neutrophil bactericidal activities. These data showed that sensory neurons regulate corneal neutrophil responses in a tissue-specific matter affecting disease progression during P. aeruginosa keratitis. Hence, therapeutic modalities that control nociception could beneficially impact anti-infective therapy.     

Mutagenicity tests with metrifonate in Drosophila melanogaster

The organophosphorus insecticide metrifonate (O,O-dimethyl(1-hydroxy-2,2,2-trichloroethyl)phosphonate), also known as trichlorfon or Dipterex ®, was tested for its ability to induce sex-linked and autosomal recessive lethal mutations in Drosophila melanogaster. There was no evidence of an increase in the frequency of lethal mutations after feeding adult males with metrifonate, but the high toxicity of the compound meant that only low concentrations could be used in this test system.