A score test for determining sample size in matched case-control studies with categorical exposure

The paper considers the problem of determining the number of matched sets in 1 : M matched case-control studies with a categorical exposure having k + 1 categories, k > or = 1. The basic interest lies in constructing a test statistic to test whether the exposure is associated with the disease. Estimates of the k odds ratios for 1 : M matched case-control studies with dichotomous exposure and for 1 : 1 matched case-control studies with exposure at several levels are presented in Breslow and Day (1980), but results holding in full generality were not available so far. We propose a score test for testing the hypothesis of no association between disease and the polychotomous exposure. We exploit the power function of this test statistic to calculate the required number of matched sets to detect specific departures from the null hypothesis of no association. We also consider the situation when there is a natural ordering among the levels of the exposure variable. For ordinal exposure variables, we propose a test for detecting trend in disease risk with increasing levels of the exposure variable. Our methods are illustrated with two datasets, one is a real dataset on colorectal cancer in rats and the other a simulated dataset for studying disease-gene association.     

Transient permeability induced by alkyl derivatives of amphotericin B in lipid membranes

Individual ionic channels were shown to be formed in the brain cholesterol containing phospholipid membranes by two-sided addition of the amphotericin B alkyl derivatives. At concentrations between 10⁻⁸ and 10⁻⁷ M, the resulting conductance appeared to be transient. Existence of different antibiotic assemblies was justified by the kinetic analysis of the membrane conductance decline following the antibiotic washing out. In order to account for the transient characteristics of the induced conductance, it was proposed that the antibiotic oligomers incorporate into the membrane from the aqueous phase, form channels aggregating with cholesterol, and then dissociate in the bilayer into non-active degraded oligomeric or monomeric forms.     

西双版纳地区附生与非附生植物叶片对雾水的吸收

采用蒸馏水喷雾(模拟雾)法,测定了西双版纳地区干季中10种附生植物和非附生植物叶片水势(Φ)、相对含水量(RWC)和吸水量的变化,探讨了不同类型植物叶片的吸收雾水的能力.结果表明,随喷雾时间的延长,植物叶片Φ、RWC和吸水量均升高,说明附生植物和非附生植物叶片都能吸收雾水,但附生植物叶片吸水后Φ升高明显快于非附生植物.附生植物附着实蕨和爬树龙叶片吸水快、RWC变化大,表明其叶片吸收雾水的能力强;贝母兰和掌唇兰叶片吸水能力低于非附生植物中的穿鞘花和野靛稞,但高于其它4种非附生植物.傍晚雾生之前附生植物叶片Φ显著低于清晨,表明夜间附生植物叶片吸收了雾水;而非附生植物傍晚叶片Φ与清晨水势差异不显著,夜间几乎不吸收雾水.除贝母兰外,附生植物叶生物量分数高于非附生植物,利于其吸收雾水.由于西双版纳地区干季多雾,该区植物叶片最低水势均在-0.8 MPa以上,水分胁迫不严重.     

Occurrence and dominance of six Pacific Northwest conifer species

Questions: Can probability of occurrence and dominance be accurately estimated for six important conifer species with varying range sizes? Does range size impact the accuracy of species probability of occurrence models? Is species predicted probability of occurrence significantly related to observed dominance? Location: Pacific Northwest region, North America (60°–40°N, 140°–110°W). Methods: This study develops near range‐wide predictive distribution maps for six important conifer species (Pseudotsuga menziesii, Tsuga heterophylla, Pinus contorta, Thuja plicata, Larix occidentalis, and Picea glauca) using forest inventory data collected across the United States and Canada. Species model accuracies are compared with range size using a rank scoring system. A suite of climate and topographic predictor variables are used to investigate environmental constraints that limit species range and quantify relationships between species predicted probability of occurrence and dominance at both plot and landscape scales. Results: Evaluation statistics revealed significant and accurate probability of occurrence models were developed for all six species. Based on ranked evaluation statistics, Tsuga heterophylla had highest overall model accuracy (statistic rank score=5) and Pinus contorta the lowest (statistic rank score=17). Across species, ranked evaluation statistics also revealed a pattern of decreasing model accuracy with increasing range size. At plot level, correlations between dominance and probability of occurrence were weakly positive for all species with only half of the species having statistically significant correlations. Pseudotsuga menziesii had the highest correlation (r=0.36, P<0.001) and Thuja plicata lowest (r=0.038, P=0.799). At the 50‐km scale, correlations between dominance and probability of occurrence improved for all species except Pinus contorta. Pseudotsuga menziesii displayed the highest correlation (r=0.68, P<0.001) and Thuja plicata the lowest (r=0.07, P>0.709). Conclusions: Species probability of occurrence model accuracy decreased with increasing range size. The strength and significance of correlations between probability of occurrence and dominance varied considerably by species and across spatial scales. Apart from Pseudotsuga menziesii and L. occidentalis, the results suggest that probability of occurrence is not a consistently reliable surrogate for species dominance in Pacific Northwest forests. We demonstrate how the degree of correlation between species occurrence and dominance can be used as an indicator of how well predictions of occurrence characterize the optimal niche of a species.     

One-year clinical follow-up of a registry evaluating a percutaneous revascularisation strategy combining a pre-specified simple selection process with the use of a new thin-strut bare cobalt-chromium stent

Objectives. To evaluate clinical events in a specifically selected cohort of patients with obstructive coronary artery disease (CAD), using a new generation thin-strut bare cobalt-chromium coronary stent. Methods. Patients with single- or multi-vessel, stable or unstable CAD eligible for percutaneous implantation of at least one bare cobalt-chromium stent were evaluated in a single-centre registry. Prospective pre-specified criteria for bare cobalt-chromium stent implantation in our centre were: any acute ST-elevation myocardial infarction (MI), otherwise 1) de novo coronary lesion, and 2) lesion length <20 mm, and 3) reference vessel diameter >2.6 mm, and 4) no diabetes, unless reference vessel diameter >3.5 mm. Endpoints, retrospectively collected, were death, MI and clinically driven target-lesion revascularisation (TLR) and target-vessel revascularisation (TVR) after 12 months. Results. Between September 2005 and June 2007, 712 patients (48.7% one-vessel, 29.9% two-vessel, 20% three-vessel and 1.4% left main disease; 7.9% diabetics) were treated with 800 bare cobalt-chromium stents, for stable angina (40.9%), unstable angina (20.9%) or acute ST-elevation MI (38.2%). The procedural success rate was 99.3%. Peri-procedural MI rate was 2.2% in the semi-elective group. At 12 months there were 17 deaths (2.4%), of which nine non-cardiac, 20 (2.8%) MI, 19 (2.7%) TLR and 29 (4.1%) TVR. Early and late definite stent thrombosis occurred in four (0.6%) and three (0.4%) patients, respectively. Conclusion. A strategy aimed at minimising drug-eluting stent use and combining a pre-specified simple selection process with the use of a new thin-strut bare cobalt-chromium stent is safe and effective at one-year clinical follow-up. (Neth Heart J 2010;18:486-92.)     

Depletion of abundant proteins from non-human primate serum for biomarker studies

Non-human primates are an important biomedical research model organism and offer great promise for serum biomarker proteomic studies. However, potential obstacles to these studies include affinity serum depletion methods based on human antigens, depletion methods altering quantitation, and incomplete non-human primate genome sequences for protein identification. In the present study, high-abundance protein removal from monkey serum using a human multiple affinity removal system (MARS) was shown to be specific and did not alter quantitation. Depleted serum also demonstrated greater sensitivity for previously masked, lower-abundance proteins.     

Non-covalent interaction of 2', 4', 5', 7'-tetrabromo-4, 5, 6, 7-tetrachlorofluorescein with proteins and its application

The interactions of 2', 4', 5', 7'-tetrabromo-4, 5, 6, 7-tetrachlorofluorescein (TBTCF) with BSA, ovalbumin (OVA) and poly-L-lysine (PLYS) at pH 3.70 have been investigated by combination of the spectral correction technique and the Langmuir isothermal adsorption. The active connection actions such as ion pairs, van der Waals' force, hydrogen bond, hydrophobic bond were proposed to explain the non-covalent interaction between TBTCF and BSA, OVA and PLYS. Effects of the electrolyte and high temperature indicated that union of the active connections between TBTCF and BSA and OVA was too firm to be destroyed. The relationship between the binding number of TBTCF and variety fraction of the amino acid residues was analyzed. The binding number of TBTCF depended on the number of positively charged amino acid residues. The other amino acid residues surrounded and seized TBTCF by hydrogen bonds and hydrophobic bonds when the electrostatic attraction pulled TBTCF to link protein. In addition, a novel method named the absorbance ratio difference was established for determination of protein in trace level and was applied with much higher sensitivity than the ordinary method.     

The mlo resistance alleles to powdery mildew infection in barley trigger a developmentally controlled defence mimic phenotype

Recessive mlo resistance alleles of the Mlo locus in barley control a non race-specific resistance response to infection by the obligate biotrophic fungus Erysiphe graminis f.sp. hordei. All the mlo alleles analysed stop fungal growth at the same developmental stage within a subcellularly restricted, highly localized cell wall apposition directly beneath the site of abortive fungal penetration. We report that near-isogenic lines carrying the alleles mlo ₁, mlo ₃ or mlo ₅ undergo dramatic spontaneous formation of cell wall appositions, not only in the absence of the fungal pathogen but also in sterile grown plants. A comparative study of spontaneous and infection-triggered cell wall appositions reveals a high degree of similarity with respect to structure, chemical composition and distinct localization within plant tissue. We show that the rate of spontaneous apposition formation is dependent on the genetic background of the plant and that its onset is under developmental control. Furthermore, spontaneous formation of wall appositions is specifically triggered by mlo alleles, since it is unaffected in the presence of the race-specific resistance allele Mlg. We propose a model for the function of the Mlo locus that suggests that both Mlo and mlo alleles control qualitatively the same apposition-based resistance mechanism, which, in the presence of the wild-type Mlo allele, is merely less efficient to provide protection against the currently common races of E. graminis f.sp. hordei.