Tension to passively cinch the mitral annulus through coronary sinus access: An ex vivo study in ovine model

Introduction

The transcatheter mitral valve repair (TMVR) technique utilizes a stent to cinch a segment of the mitral annulus (MA) and reduces mitral regurgitation. The cinching mechanism results in reduction of the septal–lateral distance. However, the mechanism has not been characterized completely. In this study, a method was developed to quantify the relation between cinching tension and MA area in an ex vivo ovine model.

Method

The cinching tension was measured from a suture inserted within the coronary sinus (CS) vessel with one end tied to the distal end of the vessel and the other end exited to the CS ostium where it was attached to a force transducer on a linear stage. The cinching tension, MA area, septal–lateral (S–L) and commissure–commissure (C–C) diameters and leakage was simultaneously measured in normal and dilated condition, under a hydrostatic left ventricular pressure of 90 mmHg.

Results

The MA area was increased up to 22.8% after MA dilation. A mean tension of 2.1±0.5 N reduced the MA area by 21.3±5.6% and S–L diameter by 24.2±5.3%. Thus, leakage was improved by 51.7±16.2% following restoration of normal MA geometry.

Conclusion

The cinching tension generated by the suture acts as a compensation force in MA reduction, implying the maximum tension needed to be generated by annuloplasty device to restore normal annular size. The relationship between cinching tension and the corresponding MA geometry will contribute to the development of future TMVR devices and understanding of myocardial contraction function.     

A genomic snapshot of Salmonella enterica serovar Typhi in Colombia

Little is known about the genetic diversity of Salmonella enterica serovar Typhi (S. Typhi) circulating in Latin America. It has been observed that typhoid fever is still endemic in this part of the world; however, a lack of standardized blood culture surveillance across Latin American makes estimating the true disease burden problematic. The Colombian National Health Service established a surveillance system for tracking bacterial pathogens, including S. Typhi, in 2006. Here, we characterized 77 representative Colombian S. Typhi isolates collected between 1997 and 2018 using pulse field gel electrophoresis (PFGE; the accepted genotyping method in Latin America) and whole genome sequencing (WGS). We found that the main S. Typhi clades circulating in Colombia were clades 2.5 and 3.5. Notably, the sequenced S. Typhi isolates from Colombia were closely related in a global phylogeny. Consequently, these data suggest that these are endemic clades circulating in Colombia. We found that AMR in S. Typhi in Colombia was uncommon, with a small subset of organisms exhibiting mutations associated with reduced susceptibility to fluoroquinolones. This is the first time that S. Typhi isolated from Colombia have been characterized by WGS, and after comparing these data with those generated using PFGE, we conclude that PFGE is unsuitable for tracking S. Typhi clones and mapping transmission. The genetic diversity of pathogens such as S. Typhi is limited in Latin America and should be targeted for future surveillance studies incorporating WGS.     

Immunoglobulin somatic hypermutation in a defined biochemical system recapitulates affinity maturation and permits antibody optimization

We describe a purified biochemical system to produce monoclonal antibodies (Abs) in vitro using activation-induced deoxycytidine deaminase (AID) and DNA polymerase η (Polη) to diversify immunoglobulin variable gene (IgV) libraries within a phage display format. AID and Polη function during B-cell affinity maturation by catalyzing somatic hypermutation (SHM) of immunoglobulin variable genes (IgV) to generate high-affinity Abs. The IgV mutational motif specificities observed in vivo are conserved in vitro. IgV mutations occurred in antibody complementary determining regions (CDRs) and less frequently in framework (FW) regions. A unique feature of our system is the use of AID and Polη to perform repetitive affinity maturation on libraries reconstructed from a preceding selection step. We have obtained scFv Abs against human glucagon-like peptide-1 receptor (GLP-1R), a target in the treatment of type 2 diabetes, and VHH nanobodies targeting Fatty Acid Amide Hydrolase (FAAH), involved in chronic pain, and artemin, a neurotropic factor that regulates cold pain. A round of in vitro affinity maturation typically resulted in a 2- to 4-fold enhancement in Ab-Ag binding, demonstrating the utility of the system. We tested one of the affinity matured nanobodies and found that it reduced injury-induced cold pain in a mouse model.