The influence of vascular anatomy on carotid artery stenting: A parametric study for damage assessment

Carotid artery stenting is emerging as an alternative technique to surgery for the treatment of symptomatic severe carotid stenosis. Clinical and experimental evidence demonstrates that both plaque morphology and biomechanical changes due to the device implantation can be possible causes of an unsuccessful treatment. In order to gain further insights of the endovascular intervention, a virtual environment based on structural finite element simulations was built to emulate the stenting procedure on generalized atherosclerotic carotid geometries which included a damage model to quantify the injury of the vessel. Five possible lesion scenarios were simulated by changing both material properties and vascular geometrical features to cover both presumed vulnerable and stable plaques. The results were analyzed with respect to lumen gain and wall stresses which are potentially related to the failure of the procedure according to previous studies. Our findings show that an elliptic lumen shape and a thinner fibrous cap with an underlying lipid pool result in higher stenosis reduction, while large calcifications and fibrotic tissue are more prone to recoil. The shielding effect of a thicker fibrous cap helps to reduce local compressive stresses in the soft plaque. The presence of a soft plaque reduces the damage in the healthy vascular structures. Contrarily, the presence of hard plaque promotes less damage volume in the fibrous cap and reduces stress peaks in this region, but they seem to increase stresses in the media-intima layer. Finally the reliability of the achieved results was put into clinical perspective.     

Does human genome editing reinforce or violate human dignity?

Germline genome editing is often disapproved of at the international policy level because of its possible threats to human dignity. However, from a critical perspective the relationship between this emerging technology and human dignity is relatively understudied. We explore the main principles that are referred to when ‘human dignity' is invoked in this context; namely, the link with eugenics, the idea of a common genetic heritage, the principle of equal birth and broader equality and justice concerns. Yet the concept is also used in favour of germline genome editing as it might improve the overall well-being of future generations. We conclude that dignity concerns do not justify a complete ban on safe heritable genome editing but should inform the implementation of side constraints to ensure that the value judgements about human traits that are inherent in this practice do not result in a diminished basic respect for those people affected by them.     

Limitations of Doppler echocardiography for the post-operative evaluation of aortic coarctation.

Doppler blood flow measurements and derived pressure differences, through the Bernoulli equation, are used in the diagnosis of aortic coarctation, a congenital stenosis distal to the left subclavian artery. Doppler velocities remain elevated at the coarctation site after successful repair of coarctation, leading to high Doppler derived pressure differences without significant arm-leg pressure differences. We studied this apparent contradiction of two diagnostic methods, in vivo using patient and control data, and in vitro using a hydraulic model. Clinical and echocardiographic data from 31 patients, aged 13.0 +/- 4.0, 10.5 +/- 4.7 yr after coarctectomy by end-to-end anastomosis, and 18 age-matched healthy subjects were reviewed. Doppler peak velocities at the aortic isthmus were elevated in patients (2.2 +/- 0.4 vs. 1.2 +/- 0.2m/s, P < 0.001), corresponding to significant Doppler differences (20 +/- 7 mmHg), however, without significant arm-leg pressure differences. In all patients, a mild anatomic stenosis could still be observed. Local stiffness was increased. The hypothesis that the less distensible surgical scar in post-coarctectomy patients leads to a significant dynamic obstruction in systole was validated in a latex model of the aorta. Rigid rings (0.5-1.5 cm), matching the unloaded aortic diameter, were mounted around the aorta. Under loading conditions, Doppler peak velocities increased by 40 +/-7%, yielding Doppler differences of 21 +/- 3 mmHg, without a significant pressure drop. An alternative expression to calculate pressure differences, using both velocity and geometric information, was validated in the model. In conclusion, post-operatively, Doppler velocities remain elevated due to a mild anatomical and significant dynamic narrowing, but the specific geometry, resembling a tubular hypoplasia rather than an abrupt stenosis, permits an almost complete pressure recovery explaining the occurrence of Doppler differences in disagreement with the negligible arm-leg pressure difference.     

Modelling the left ventricle using rapid prototyping techniques

Biomechanical research of left ventricular function involves the assessment and understanding of both ventricular wall mechanics and deformation and intraventricular flow patterns, as well as how they interact. Experimental research using hydraulic bench models should therefore aim for an as realistic as possible simulation of both. In previous experimental investigations, wall deformation was studied by means of thin-walled passive experimental models, consisting of a silicone membrane in a closed box, which is squeezed passively by an externally connected piston pump. Although the pump function of these models has already been well established, the membrane deformation remains unpredictable and the effect of muscle contraction – and hence natural wall deformation – cannot be simulated. In this study, we propose a new design of an experimental hydraulic left ventricular model in which left ventricular wall deformation can be controlled. We built this model by a combination of rapid prototyping techniques and tested it to demonstrate its wall deformation and pump function. Our experiments show that circumferential and longitudinal contraction can be attained and that this model can generate fairly normal values of pressure and flow.     

Inhibition of Thrombin Formation by Active Site Mutated (S360A) Activated Protein C

Activated protein C (APC) down-regulates thrombin formation through proteolytic inactivation of factor Va (FVa) by cleavage at Arg⁵⁰⁶ and Arg³⁰⁶ and of factor VIIIa (FVIIIa) by cleavage at Arg³³⁶ and Arg⁵⁶². To study substrate recognition by APC, active site-mutated APC (APC(S360A)) was used, which lacks proteolytic activity but exhibits anticoagulant activity. Experiments in model systems and in plasma show that APC(S360A), and not its zymogen protein C(S360A), expresses anticoagulant activities by competing with activated coagulation factors X and IX for binding to FVa and FVIIIa, respectively. APC(S360A) bound to FVa with a K_D of 0.11 ± 0.05 nm and competed with active site-labeled Oregon Green activated coagulation factor X for binding to FVa. The binding of APC(S360A) to FVa was not affected by protein S but was inhibited by prothrombin. APC(S360A) binding to FVa was critically dependent upon the presence of Arg⁵⁰⁶ and not Arg³⁰⁶ and additionally required an active site accessible to substrates. Inhibition of FVIIIa activity by APC(S360A) was >100-fold less efficient than inhibition of FVa. Our results show that despite exosite interactions near the Arg⁵⁰⁶ cleavage site, binding of APC(S360A) to FVa is almost completely dependent on Arg⁵⁰⁶ interacting with APC(S360A) to form a nonproductive Michaelis complex. Because docking of APC to FVa and FVIIIa constitutes the first step in the inactivation of the cofactors, we hypothesize that the observed anticoagulant activity may be important for in vivo regulation of thrombin formation.     

Diversity and endemism in Rotifera: a review,and <Emphasis Type="Italic">Keratella</Emphasis> Bory de St Vincent

We confront patterns in the chorology and diversity of freshwater and limnoterrestrial Rotifera with predictions following from the recently revived ubiquity theorem on the distribution of microscopic organisms. Notwithstanding a strong taxonomic impediment and lack of data, both bdelloid and monogonont rotifers appear to conform to the hypothesis’ predictions that local diversity is relatively high compared to global diversity and that cosmopolitism is important. To the contrary, however, a latitudinal diversity gradient is obvious, and endemicity is present, and exhibits diverse patterns. This is illustrated by the case of Keratella rotifers, in which we identify purported relict endemicity hotspots in the east Palaearctic (China) and in temperate and cold regions of the southern hemisphere, and a recent radiation in North America. The apparent paradox may result from an antagonism between rotifer’s high population sizes and presence of potentially highly efficient propagules, versus pre-emption of habitats and local adaptation by resident populations, specific dispersal ability, and ecological and geographical factors. We conclude that distribution patterns of microscopic organisms, as represented by rotifers, most likely span the whole range of alternatives, from full cosmopolitanism to local endemism, and suggest that studying this diversity is more productive to come to an understanding of their chorology and diversity. Special Issue: Protist diversity and geographic distribution. Guest editor: W. Foissner.     

The Freshwater Animal Diversity Assessment: an overview of the results

The geographic genetic structure of two common encrusting sponges, Hymeniacidon sinapium and Hymeniacidon flavia (family Halichondriidae), was investigated using two DNA markers, Internal Transcribed Spacers (ITS) of nuclear ribosomal DNA and NADH dehydrogenase subunit 5 (nad5) of mitochondrial DNA. In the ITS analyses, multiple sequence types were identified within each species. Geographic distribution patterns of sequence types showed higher diversity in the western than eastern areas in both species. However, intraspecific genetic diversity of the two species in Japan differed markedly. Hymeniacidon flavia had far more diverse sequence types, and several genetic differentiations between localities were detected. In contrast, H. sinapium had only four sequence types in Japan, and two Atlantic Hymeniacidon species had sequence types similar to this species. In comparison to ITS, nad5 showed very low genetic diversity in both species, with two haplotypes identified in each species. In H. flavia, frequency of haplotype changed gradually from north to south. In H. sinapium, one haplotype was predominant in most regions, and another haplotype was minor and distributed only in the Korean and Tsushima populations. Based on the unique distribution patterns of sequence types around Shikoku and Kyushu, geographical history and ocean currents were assumed to affect the generation of genetic structure. The geographic genetic structure of H. flavia suggests low dispersal ability of pelagic larvae, whereas higher larval dispersal ability and a far broader distribution range are suggested in H. sinapium. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: C. Sturmbauer     

An introduction to the Freshwater Animal Diversity Assessment (FADA) project

The Freshwater Animal Diversity Assessment (FADA) project aims at compiling an overview of genus- and species-level diversity of animals in the continental, aquatic ecosystems of the world. It is a collective effort of 163 experts, and presents 59 articles treating the diversity and endemism of different animal taxa, ranging from microscopic worms to mammals, at global and regional scales. Given their structural importance, an article on macrophytes is also added. Here, we give an overview of the project’s history, and outline the common framework of the various articles, as well as the conventions the experts agreed to adhere to in their treatises. Furthermore, we briefly introduce future prospects.

Light microscopical detection of leukocyte cell surface antigens with a one-nanometer gold probe.

The potential of ultrasmall gold particles for the light microscopical detection of leukocyte cell surface differentiation antigens was investigated. Suspensions and cytocentrifuge preparations of peripheral blood leukocytes were first incubated with monoclonal antibodies and then with goat antimouse antibodies coupled to colloidal gold particles of 1-nanometer diameter. Cytocentrifuge preparations were made from the cell suspensions. Silver enhancement was performed on all preparations. Then they were counterstained with May-Grünwald Giemsa and examined in light microscopy. The immunostaining appeared as fine dark granules on the surface membrane of the cells. Labeling conditions were determined which gave a dense specific immunostaining and a low background. High dilutions of the ultrasmall gold probe could be used to detect all antigen expressing cells in the samples. The labeling efficiency of the IGSS method with the 1 nanometer probe was comparable to that described earlier for 5 nanometer gold particles. Lymphocyte subsets enumerated with this method in normal peripheral blood were similar to those found with immunofluorescence microscopy. We concluded that one nanometer probes do not offer a major advantage in comparison with 5 nanometer probes for the study of cell surface antigens.     

Towards a better understanding of Lactobacillus rhamnosus GG - host interactions

Background

An industrial approach to protein production demands maximization of cloned gene expression, balanced with the recombinant host’s viability. Expression of toxic genes from thermophiles poses particular difficulties due to high GC content, mRNA secondary structures, rare codon usage and impairing the host’s coding plasmid replication. TaqII belongs to a family of bifunctional enzymes, which are a fusion of the restriction endonuclease (REase) and methyltransferase (MTase) activities in a single polypeptide. The family contains thermostable REases with distinct specificities: TspGWI, TaqII, Tth111II/TthHB27I, TspDTI and TsoI and a few enzymes found in mesophiles. While not being isoschizomers, the enzymes exhibit amino acid (aa) sequence homologies, having molecular sizes of ~120 kDa share common modular architecture, resemble Type-I enzymes, cleave DNA 11/9 nt from the recognition sites, their activity is affected by S-adenosylmethionine (SAM).

Results

We describe the taqIIRM gene design, cloning and expression of the prototype TaqII. The enzyme amount in natural hosts is extremely low. To improve expression of the taqIIRM gene in Escherichia coli (E. coli), we designed and cloned a fully synthetic, low GC content, low mRNA secondary structure taqIIRM, codon-optimized gene under a bacteriophage lambda (λ) P _R promoter. Codon usage based on a modified ‘one amino acid–one codon’ strategy, weighted towards low GC content codons, resulted in approximately 10-fold higher expression of the synthetic gene. 718 codons of total 1105 were changed, comprising 65% of the taqIIRM gene. The reason for we choose a less effective strategy rather than a resulting in high expression yields ‘codon randomization’ strategy, was intentional, sub-optimal TaqII in vivo production, in order to decrease the high ‘toxicity’ of the REase-MTase protein.

Conclusions

Recombinant wt and synthetic taqIIRM gene were cloned and expressed in E. coli. The modified ‘one amino acid–one codon’ method tuned for thermophile-coded genes was applied to obtain overexpression of the ‘toxic’ taqIIRM gene. The method appears suited for industrial production of thermostable ‘toxic’ enzymes in E. coli. This novel variant of the method biased toward increasing a gene’s AT content may provide economic benefits for industrial applications.