Estimating age at maturation and energy-based life-history traits from individual growth trajectories with nonlinear mixed-effects models

A new method is presented to estimate individuals’ (1) age at maturation, (2) energy acquisition rate, (3) energy expenditure for body maintenance, and (4) reproductive investment, and the multivariate distribution of these traits in a population. The method relies on adjusting a conceptual energy allocation model to individual growth curves using nonlinear mixed-effects modelling. The method’s performance was tested using simulated growth curves for a range of life-history types. Individual age at maturation, energy acquisition rate and the sum of maintenance and reproductive investment rates, and their multivariate distribution, were accurately estimated. For the estimation of maintenance and reproductive investment rates separately, biases were observed for life-histories with a large imbalance between these traits. For low reproductive investment rates and high maintenance rates, reproductive investment rate estimates were strongly biased whereas maintenance rate estimates were not, the reverse holding in the opposite situation. The method was applied to individual growth curves back-calculated from otoliths of North Sea plaice (Pleuronectes platessa) and from scales of Norwegian spring spawning herring (Clupea harengus). For plaice, maturity ogives derived from our individual estimates of age at maturation were almost identical to the maturity ogives based on gonad observation in catch samples. For herring, we observed 51.5 % of agreement between our individual estimates and those directly obtained from scale reading, with a difference lower than 1 year in 97 % of cases. We conclude that the method is a powerful tool to estimate the distribution of correlated life-history traits for any species for which individual growth curves are available.     

A Non-classical Assembly Pathway of Escherichia coli Pore-forming Toxin Cytolysin A

Cytolysin A (ClyA) is an α-pore forming toxin from pathogenic Escherichia coli (E. coli) and Salmonella enterica. Here, we report that E. coli ClyA assembles into an oligomeric structure in solution in the absence of either bilayer membranes or detergents at physiological temperature. These oligomers can rearrange to create transmembrane pores when in contact with detergents or biological membranes. Intrinsic fluorescence measurements revealed that oligomers adopted an intermediate state found during the transition between monomer and transmembrane pore. These results indicate that the water-soluble oligomer represents a prepore intermediate state. Furthermore, we show that ClyA does not form transmembrane pores on E. coli lipid membranes. Because ClyA is delivered to the target host cell in an oligomeric conformation within outer membrane vesicles (OMVs), our findings suggest ClyA forms a prepore oligomeric structure independently of the lipid membrane within the OMV. The proposed model for ClyA represents a non-classical pathway to attack eukaryotic host cells.     

Biophysical and structural investigation of bacterially expressed and engineered CCR5, a G protein-coupled receptor

The chemokine receptor CCR5 belongs to the class of G protein-coupled receptors. Besides its role in leukocyte trafficking, it is also the major HIV-1 coreceptor and hence a target for HIV-1 entry inhibitors. Here, we report Escherichia coli expression and a broad range of biophysical studies on E. coli-produced CCR5. After systematic screening and optimization, we obtained 10 mg of purified, detergent-solubilized, folded CCR5 from 1L culture in a triply isotope-labeled (²H/¹⁵N/¹³C) minimal medium. Thus the material is suitable for NMR spectroscopic studies. The expected α-helical secondary structure content is confirmed by circular dichroism spectroscopy. The solubilized CCR5 is monodisperse and homogeneous as judged by transmission electron microscopy. Interactions of CCR5 with its ligands, RANTES and MIP-1β were assessed by surface plasmon resonance yielding K_D values in the nanomolar range. Using size exclusion chromatography, stable monomeric CCR5 could be isolated. We show that cysteine residues affect both the yield and oligomer distribution of CCR5. HSQC spectra suggest that the transmembrane domains of CCR5 are in equilibrium between several conformations. In addition we present a model of CCR5 based on the crystal structure of CXCR4 as a starting point for protein engineering.     

Household Transmission of Rotavirus in a Community with Rotavirus Vaccination in Quininde,Ecuador

Background

We studied the transmission of rotavirus infection in households in peri-urban Ecuador in the vaccination era.

Methods

Stool samples were collected from household contacts of child rotavirus cases, diarrhea controls and healthy controls following presentation of the index child to health facilities. Rotavirus infection status of contacts was determined by RT-qPCR. We examined factors associated with transmissibility (index-case characteristics) and susceptibility (household-contact characteristics).

Results

Amongst cases, diarrhea controls and healthy control household contacts, infection attack rates (iAR) were 55%, 8% and 2%, (n = 137, 130, 137) respectively. iARs were higher from index cases with vomiting, and amongst siblings. Disease ARs were higher when the index child was <18 months and had vomiting, with household contact <10 years and those sharing a room with the index case being more susceptible. We found no evidence of asymptomatic infections leading to disease transmission.

Conclusion

Transmission rates of rotavirus are high in households with an infected child, while background infections are rare. We have identified factors associated with transmission (vomiting/young age of index case) and susceptibility (young age/sharing a room/being a sibling of the index case). Vaccination may lead to indirect benefits by averting episodes or reducing symptoms in vaccinees.     

Knowledge and Perceptions about Clinical Trials and the Use of Biomedical Samples: Findings from a Qualitative Study in Rural Northern Ghana

IntroductionClinical trials conducted in sub-Saharan Africa have helped to address the prevalent health challenges. The knowledge about how communities perceive clinical trials is however only now evolving. This study was conducted among parents whose children participated in past clinical trials in northern Ghana to assess their knowledge and perceptions of clinical trials and the use of biomedical samples.MethodThis was a qualitative study based on eighty in-depth interviews with parents. The participants were randomly selected from among parents whose children were enrolled in a clinical trial conducted in the Kassena-Nankana districts between 2000 and 2003. The interviews were transcribed and coded into emergent themes using Nvivo 9 software. The thematic analysis framework was used to analyze the data.ResultsStudy participants reported that clinical trials were carried out to determine the efficacy of drugs and to make sure that these drugs were suitable for human beings to use. The conduct of clinical trials was perceived to have helped to reduce the occurrence of diseases such as malaria, cerebrospinal meningitis and diarrhea. Quality of care was reported to be better in clinical trials than in the routine care. Parents indicated that participation in clinical trials positively influenced their health-seeking behavior. Apprehensions about blood draw and the use to which samples were put were expressed, with suspicion by a few participants that researchers sold blood samples. The issue of blood draw was most contentious.ConclusionParents perception about the conduct of clinical trials in the study districts is generally positive. However, misconceptions made about the use of blood samples in this study must be taken seriously and strategies found to improve transparency and greater community acceptability.     

All-Cause and Cause-Specific Mortality among Users of Basal Insulins NPH,Detemir, and Glargine

Background

Insulin therapy in type 2 diabetes may increase mortality and cancer incidence, but the impact of different types of basal insulins on these endpoints is unclear. Compared to the traditional NPH insulin, the newer, longer-acting insulin analogues detemir and glargine have shown benefits in randomized controlled trials. Whether these advantages translate into lower mortality among users in real life is unknown.

Objective

To estimate the differences in all-cause and cause-specific mortality rates between new users of basal insulins in a population-based study in Finland.

Methods

23 751 individuals aged ≥40 with type 2 diabetes, who initiated basal insulin therapy in 2006–2009 were identified from national registers, with comprehensive data for mortality, causes of death, and background variables. Propensity score matching was performed on characteristics. Follow-up time was up to 4 years (median 1.7 years).

Results

2078 deaths incurred. With NPH as reference, the adjusted HRs for all-cause mortality were 0.39 (95% CI, 0.30–0.50) for detemir, and 0.55 (95% CI, 0.44–0.69) for glargine. As compared to glargine, the HR was 0.71 (95% CI, 0.54–0.93) among detemir users. Compared to NPH, the mortality risk for both cardiovascular causes as well as cancer were also significantly lower for glargine, and especially for detemir in adjusted analysis. Furthermore, the results were robust in various sensitivity analyses.

Conclusion

In real clinical practice, mortality was substantially higher among users of NPH insulin as compared to insulins detemir or glargine. Considering the large number of patients who require insulin therapy, this difference in risk may have major clinical and public health implications. Due to limitations of the observational study design, further investigation using an interventional study design is warranted.