Maintenance of cardiovascular risk factor changes among middle-aged women in a lifestyle intervention trial

This paper proposes and defends the small worlds hypothesis, which states that expert physicians organize diagnostic knowledge on the basis of similarities between disease categories, forming 'small worlds' consisting of small subsets of diseases and their distinguishing features. Examining existing data from several previous studies, the authors provide support for the small worlds hypothesis and for a characterization of the process of expert medical diagnostic reasoning as a succession of limited comparisons involving related diagnostic hypotheses. In one study, subjects were presented clinical endocrine cases one statement at a time and were prompted to think aloud after presentation of each statement. A combination of discourse and protocol analysis techniques were used to investigate hypothesis generation and evaluation. In another study, dialogues from doctor-patient interviews were examined. It was found that expert subjects rapidly select relatively small sets of plausible diagnostic hypotheses (small worlds) and focus on the most relevant medical findings that distinguish among the diseases in such small worlds. Results from both studies indicate that expert physicians use efficient strategies for discriminating among these alternative hypotheses in a stepwise process. In contrast, non-experts often generate large numbers of possible diagnostic hypotheses, belonging to widely differing disease categories. The results provide empirical support for the theoretical basis of small worlds. The implications of these results for the study of medical expertise and knowledge engineering are discussed, as well as considerations for the development of decision support systems.     

Structural homologies with ATP- and folate-binding enzymes in the crystal structure of folylpolyglutamate synthetase

Folylpolyglutamate synthetase, which is responsible for the addition of a polyglutamate tail to folate and folate derivatives, is an ATP-dependent enzyme isolated from eukaryotic and bacterial sources, where it plays a key role in the retention of the intracellular folate pool. Here, we report the 2.4-A resolution crystal structure of the MgATP complex of the enzyme from Lactobacillus casei. The structural analysis reveals that folylpolyglutamate synthetase is a modular protein consisting of two domains, one with a typical mononucleotide-binding fold and the other strikingly similar to the folate-binding enzyme dihydrofolate reductase. We have located the active site of the enzyme in a large interdomain cleft adjacent to an ATP-binding P-loop motif. Opposite this site, in the C domain, a cavity likely to be the folate binding site has been identified, and inspection of this cavity and the surrounding protein structure suggests that the glutamate tail of the substrate may project into the active site. A further feature of the structure is a well defined Omega loop, which contributes both to the active site and to interdomain interactions. The determination of the structure of this enzyme represents the first step toward the elucidation of the molecular mechanism of polyglutamylation of folates and antifolates.     

Endolymphatic therapy and current detoxication methods in the treatment of peritonitis

An original method of endolymphatic therapy with the stimulation of the lymph outflow was developed and used in 108 patients with peritonitis. The dynamics of intoxication parameters was studied during the endolymphatic therapy, indirect electrochemical oxidation of blood, photochemotherapy and traditional treatment. The method proposed has been found to be most efficient. The method of endolymphatic therapy with the lymph stimulation allowed lethality from peritonitis to be decreased to 7.4%.     

Membrane potential generation coupled to oxidation of external NADH in liver mitochondria

Oxidation of added NADH by rat liver mitochondria has been studied. It is found that exogenous NADH, when oxidized by rat liver mitochondria in sucrose hypotonic medium supplemented with Mg2+ and EGTA, generates a membrane potential (delta psi) even in the absence of added cytochrome c. ADP and phosphate decrease delta psi, the effect being reversed by oligomycin. Rotenone and myxothiazol do not inhibit delta psi generated by oxidation of exogenous NADH. Added cytochrome c increases the rate of the exogenous NADH oxidation and coupled delta psi formation. In sucrose isotonic medium, or in hypotonic medium without Mg2+, exogenous NADH fails to stimulate respiration and to form a membrane potential. In the presence of Mg2+, exogenous NADH appears to be effective in delta psi generation in isotonic sucrose medium if mitochondria were treated with digitonin. In isotonic KCl without Mg2+, oxidation of exogenous NADH is coupled to the delta psi formation and MgCl2 addition before mitochondria prevents this effect. In hypotonic (but not in isotonic) sucrose medium, Mg2+ makes a portion of the cytochrome c pool reducible by exogenous NADH or ascorbate. It is assumed that (i) hypotonic treatment or digitonin causes disruption of the outer mitochondrial membrane, and, as a consequence, desorption of the membrane-bound cytochrome c in a Mg2+-dependent fashion; (ii) incubation in isotonic KCI without Mg2+ results in swelling of mitochondrial matrix, disruption of the outer membrane and cytochrome c desorption whereas Mg2+ lowers the K+ permeability of the inner membrane and, hence, prevents swelling; (iii) desorbed cytochrome c is reduced by added NADH via NADH-cytochrome b5 reductase and cytochrome b5 or by ascorbate and is oxidized by cytochrome oxidase. The role of desorbed cytochrome c in oxidation of superoxide and cytoplasmic NADH as well as possible relations of these events to apoptosis are discussed.     

Integrins inhibit angiotensin II-induced contraction in rat aortic rings

Many extracellular matrix proteins contain the tripeptide sequence arginine-glycine-aspartate (RGD). This RGD motif is recognized by integrins, a family of adhesion receptors present on vascular smooth muscle cells. In the present study, we examined the ability of different RGD-containing peptides to affect the contraction of rat aortic rings in response to different agonists. We found that the peptide RGDS inhibited angiotensin-induced contraction in a dose dependent manner. In contrast, the peptides RGDW and RGES had no effect on angiotensin-induced contractility. We show that function-blocking antibodies to the integrins alphavbeta3 and alpha5beta1 also inhibit angiotensin-induced contraction. These effects were observed in the absence of an intact endothelium. In contrast, neither an antibody directed against the beta1 subunit nor the peptide RGDS had an effect on phenylephrine or 5-hydroxytryptamine-induced contraction. These data suggest that interactions of vascular smooth muscle with components of the surrounding extracellular matrix may influence the response of smooth muscle to agonists.     

Ligand-induced conformational change in transferrins: crystal structure of the open form of the N-terminal half-molecule of human transferrin

Serum transferrin binds ferric ions in the bloodstream and transports them to cells, where they are released in a process involving receptor-mediated endocytosis. Iron release is believed to be pH dependent and is coupled with a large conformational change. To help define the steps in iron release, we have determined the three-dimensional structure of the iron-free (apo) form of the recombinant N-lobe half-molecule of human serum transferrin (ApoTfN) by X-ray crystallography. Two crystal forms were obtained, form 1 with four molecules in the asymmetric unit and form 2 with two molecules in the asymmetric unit. The structures of both forms were determined by molecular replacement and were refined at 2.2 and 3.2 A resolution, respectively. Final R-factors were 0.203 (free R = 0. 292) for form 1 and 0.217 (free R = 0.312) for form 2. All six copies of the ApoTfN structure are essentially identical. Comparison with the holo form (FeTfN) shows that a large rigid-body domain movement of 63 degrees has occurred in ApoTfN, to give an open binding cleft. The extent of domain opening is the same as in the N-lobe of human lactoferrin, showing that it depends on internal constraints that are conserved in both proteins, and that it is unaffected by the presence or absence of the C-lobe. Although the conformational change is primarily a rigid-body motion, several local adjustments occur. In particular, two iron ligands, Asp 63 and His 249, change conformation to form salt bridges, with Lys 296 and Glu 83, respectively, in the binding cleft of the apo protein. Both salt bridges would have to break for iron coordination to occur. Most importantly, the structure, determined at a pH (5.3) that is close to the pH of physiological iron release, indicates that protonation of His 249 is a key step in iron release.     

Human live anthrax vaccine in the former USSR

The history of the development and use of the Soviet live spore human anthrax vaccine is described. Results of mass field trials on this vaccine following administration by scarification, by subcutaneous injection route or by aerosol exposure are presented. For the immunological assessment of these vaccinations a skin test with an original product 'Anthraxin' was used.     

Willingness to pay for community-based ivermectin distribution: a study of three onchocerciasis-endemic communities in Nigeria

OBJECTIVE: To determine the willingness to pay (WTP) for local ivermectin distribution in a community financing framework. METHOD: Contingent valuation in three communities in Nigeria, using randomly selected household heads. WTP was elicited using a bidding game, and for collecting information on the households' socio-economic status, level of knowledge, priority ranking and perception of risk of contracting the disease, structured questionnaires were used. Ordinary least squares (OLS) multiple regression analysis was used to analyse factors associated with WTP. RESULTS: Between 92.1% and 93.3 % of respondents were willing to pay amounts ranging from 5 Naira (US$ 0.06) to 100 Naira (US$ 1.25) (median: 20 Naira, US$ 0.25) in the three communities, more than three times the modelled unit direct cost of distributing ivermectin by the communities themselves. Occupation of the respondent, marital status, average monthly expenditure on health care, manifestations of onchocerciasis, the type of savings scheme embarked on by the respondent, age-group, level of education and type of property were statistically significant (P < 0.05) variables affecting WTP. CONCLUSION: This study shows that there is WTP for local ivermectin distribution in the three study communities, and that it should be assessed before instituting community-directed treatment with ivermectin.