Automated docking of glucosyl disaccharides in the glucoamylase active site

To better understand the molecular basis of glucomylase selectivity, low-energy conformers of glucosyl disaccharides obtained from relaxed-residue conformational mapping were flexibly docked into the glucoamylase active site using AutoDock 2.2. This procedure ensures that significant conformational space is searched and can produce bound structures comparable to those obtained by protein crystallography. alpha-Linked glucosyl disaccharides except alpha,alpha-trehalose dock easily into the active site while exclusively beta-linked disaccharides do not, explaining why only the former are glucoamylase substrates. The optimized docking modes are similar at the nonreducing end of the different substrates. Individual atomic energies of intermolecular interaction allow the definite identification of key hydroxyl groups for each substrate. This approach confirmed the versatility of the second subsite of the glucoamylase active site in binding different substrates.     

The interaction of the general anesthetic etomidate with the gamma-aminobutyric acid type A receptor is influenced by a single amino acid

The gamma-aminobutyric acid type A (GABAA) receptor is a transmitter-gated ion channel mediating the majority of fast inhibitory synaptic transmission within the brain. The receptor is a pentameric assembly of subunits drawn from multiple classes (alpha1-6, beta1-3, gamma1-3, delta1, and epsilon1). Positive allosteric modulation of GABAA receptor activity by general anesthetics represents one logical mechanism for central nervous system depression. The ability of the intravenous general anesthetic etomidate to modulate and activate GABAA receptors is uniquely dependent upon the beta subunit subtype present within the receptor. Receptors containing beta2- or beta3-, but not beta1 subunits, are highly sensitive to the agent. Here, chimeric beta1/beta2 subunits coexpressed in Xenopus laevis oocytes with human alpha6 and gamma2 subunits identified a region distal to the extracellular N-terminal domain as a determinant of the selectivity of etomidate. The mutation of an amino acid (Asn-289) present within the channel domain of the beta3 subunit to Ser (the homologous residue in beta1), strongly suppressed the GABA-modulatory and GABA-mimetic effects of etomidate. The replacement of the beta1 subunit Ser-290 by Asn produced the converse effect. When applied intracellularly to mouse L(tk-) cells stably expressing the alpha6beta3gamma2 subunit combination, etomidate was inert. Hence, the effects of a clinically utilized general anesthetic upon a physiologically relevant target protein are dramatically influenced by a single amino acid. Together with the lack of effect of intracellular etomidate, the data argue against a unitary, lipid-based theory of anesthesia.     

Neuropsychological asymmetry in Alzheimer's disease: verbal versus visuoconstructional deficits across stages of dementia

The incidence of clinically apparent asymmetric profiles of neuropsychological deficits in Alzheimer's disease (AD) patients similar to those reported in the PET literature is currently unclear. This study investigated lateral neuropsychological asymmetry using principal component factor analysis in a sample of 153 patients diagnosed with probable AD. Using factor scores, patients were classified into groups exhibiting asymmetric or symmetric profiles of neuropsychological deficits. In the analysis of lateral asymmetry, 27.5% of patients were classified as asymmetric (10% verbally and 17% visuospatially). Consistent with reports of continued asymmetry beyond the mild dementia stage, asymmetry was exhibited in the mild, moderate, and severely demented groups. These findings of neuropsychological asymmetry across stages of dementia are consistent with the picture of significant neuropsychological heterogeneity in AD that has been emerging in the decade.     

Intensified treatment of acute childhood lymphoblastic leukaemia has improved prognosis, especially in non-high-risk patients: the Nordic experience of 2648 patients diagnosed between 1981 and 1996. Nordic Society of Paediatric Haematology and Oncology (NOPHO)

In a multinational, population-based study from the five Nordic countries (Denmark, Finland, Iceland, Norway and Sweden), 2648 children below 15 y of age were diagnosed with acute lymphoblastic leukaemia (ALL) in the years 1981-1996. The annual incidence was 3.9/100000 children and was stable throughout the study period. The development from regional or national protocols to common Nordic treatment protocols for all risk groups was completed in 1992 through a successive intensification of therapy, based on multidrug chemotherapy including pulses of methotrexate in high doses and avoidance of cranial irradiation in most children. For children with non-B-cell ALL (n=2602), the event-free survival (p-EFS) increased from 0.53+/-0.02 (diagnosed 7/81-6/86) to 0.67+/-0.02 (7/86-12/91) to 0.78+/-0.02 (1/92-12/96). The corresponding p-EFS values at 5 y were 0.57, 0.70 and 0.78, respectively. The main improvements were seen in the group of children with non-high risk leukaemia, with 5-y p-EFS values increasing from 0.60 to 0.76 and 0.85 for the three periods. In high-risk patients, progress has been moderate, especially in children with high white blood cell values at diagnosis. During the last 5-y period, only 10% of the patients received cranial irradiation in first remission while 90% of the patients received high doses of cytostatic infusions (methotrexate isolated or combined with cytarabinoside) and multiple intrathecal injections of methotrexate as CNS-adjusted treatment without any indication of an increased CNS relapse rate.     

Cystic fibrosis: present and future

Cystic fibrosis (CF) is an inherited disorder of epithelial chloride transport affecting primarily pancreas, lungs, gut, liver and exocrine glands. The defect is caused by defects of the cystic fibrosis transmembrane regulation gene on chromosome 7. Genotyping has proved useful in identifying gene carriers, a definitive diagnosis, and in antenetal diagnosis. Genotype/phenotype relationships have shown that the commonest cause of pancreatic insufficiency is the D F508 mutation. Clinical trials are exploring the use of somatic gene therapy but this is not yet a viable treatment option. Liver, lung and intestinal disease result in malnutrition which causes further dysfunction of these organs. Aggressive nutritional and pancreatic enzyme therapy results in improved disease, normal growth and increased survival. However, high-dose enzyme therapy may in some individuals cause a fibrosing colonopathy. For those with end-stage liver and lung disease, transplantation holds out some hope.     

Swallow recovery in an oral cancer patient following surgery, radiotherapy, and hyperthermia

BACKGROUND: No study has examined the nature and extent of swallowing impairment in oral cancer patients following treatment with combined hyperthermia and interstitial radiotherapy. Few studies have examined the effects of voluntary swallow maneuvers (supersupraglottic and Mendelsohn) on pharyngeal phase swallowing in the oral cancer patient treated with surgery or radiotherapy. This study examined the effects of combined radiotherapeutic salvage treatments of hyperthermia and interstitial implantation and swallow recovery using swallow maneuvers in a surgically treated and irradiated oral cancer patient. METHODS: The patient under study, a 51-year-old man, underwent radiotherapy, according to Radiation Therapy Oncology Group (RTOG) protocol #8419, consisting of a combination of interstitial irradiation and hyperthermia to the base of tongue, for a recurrent squamous cell cancer. He underwent videofluorographic (VFG) examination of his swallowing, a modified barium swallow at three time points: 2 days following radiotherapy treatment (VFG1), 4 weeks later (VFG2), and 8 months later (VFG3). Temporal and biomechanical analyses of swallows were performed at each time point. RESULTS: Swallow maneuvers and time resulted in improved laryngeal elevation and laryngeal vestibule closure during the swallows on VFG2. Maximum upper esophageal sphincter (UES) opening width and duration were more normal. Fewer swallows were required for bolus clearance through the pharynx. Base of tongue tissue necrosis occurred as a complication of radiotherapy between VFG2 and VFG3, with resultant severe reduction in posterior movement of the tongue base, incomplete tongue base contact to the posterior pharyngeal wall, reduced laryngeal elevation, and incomplete laryngeal vestibule closure during swallowing at VFG3. UES opening became less normal and a greater number of swallows were required for bolus clearance through the pharynx. CONCLUSIONS: Combined interstitial irradiation and hyperthermia can cause oropharyngeal swallowing problems. Time and swallow therapy can improve these swallow disorders. Tongue base tissue necrosis can cause further swallow impairment, emphasizing the importance of the tongue base in normal deglutition. Further studies are needed to examine the impact of combined hyperthermia and interstitial implantation for treatment of tongue base tumors on swallow functioning in a larger group of patients.