Selective Enhancement of Swine Myocardium with a Novel Ultrasound Enhancing Agent During Transthoracic Echocardiography

Ultrasound enhancing agents are approved to delineate the endocardial border and opacify the left ventricle cavity (LVC). We present a nested phase change agent (NPCA) designed to enable selective myocardial enhancement without enhancing the LVC by employing a dual-activation mechanism dependent on sufficient ultrasound intensity and the microenvironment of the myocardium. Swine received bolus injections of NPCA while echocardiograms were collected and processed to determine background-subtracted acoustic intensities (AI) in the LVC and septal myocardium. At mechanical index (MI) ≥ 0.8, the NPCA enhanced the myocardium selectively (p < 0.001) while the LVC remained at baseline AI. A 5-mL bolus of NPCA enhanced swine myocardium and enhancement persisted for > 5 min at 1.4 MI, while hemodynamics and EKG remained normal. Our findings demonstrate that the NPCA enhances swine myocardium selectively without enhancing the LVC. The NPCA could have utility for functional and structural echocardiographic studies with clinical ultrasound using standard settings.

A Voltage-Sensitive Ultrasound Enhancing Agent for Myocardial Perfusion Imaging in a Rat Model

Echocardiographers with specialized expertise sometimes perform myocardial perfusion imaging using U.S. Food and Drug Administration-approved microbubbles in an off-label capacity, correlating microbubble replenishment in the near field with blood flow through the myocardium. This study reports the in vivo clinical feasibility of a voltage-sensitive ultrasound enhancing agent (UEA) for myocardial perfusion imaging. Four UEAs were injected into Sprague-Dawley rats while ultrasound images were collected to quantify brightness in the left ventricular (LV) cavity, septal wall, and posterior wall in systole and diastole. Formulation IV, a phase change agent nested within a negatively charged phospholipid bilayer, increased the tissue-to-cavity ratio in both systole and diastole in the septal wall, 6 dB, and in the posterior wall, 5 dB, while leaving the LV cavity at baseline. This outcome improves the signal of the myocardium relative to the LV cavity and shows promise as a myocardial perfusion UEA.

An Ultrasound Enhancing Agent with Nonlinear Acoustic Activity that Depends on the Presence of an Electric Field

The nonlinear acoustic properties of microbubble ultrasound enhancing agents have allowed for the development of subharmonic, second harmonic, and contrast-pulse sequence ultrasound imaging modes, which enhance the quality, reduce the noise, and improve the diagnostic capabilities of clinical ultrasound. This study details acoustic scattering responses of perfluorobutane (PFB) microbubbles, an un-nested perfluoropentane (PFP) nanoemulsion, and two nested PFP nanoemulsions-one comprising a negatively charged phospholipid bilayer and another comprising a zwitterionic phospholipid bilayer-when excited at 1 or 2.25 MHz over a peak negative pressure range of 200 kPa to 4 MPa in the absence and presence of a 1-Hz, 1-V/cm electric field. The only sample that exhibited an increase in nonlinear activity in the presence of an electric field at both excitation frequencies was the negatively charged nested PFP nanoemulsion; the most pronounced effect was observed at an excitation of 2.25 MHz. Interestingly, the application of an electric field not only increased the nonlinear acoustic activity of the negatively charged nested PFP nanoemulsion but increased it beyond that seen when the nanoemulsion is un-nested and on the same scale as PFB microbubbles.

Nitrile bonds as infrared probes of electrostatics in ribonuclease S

Three different nitrile-containing amino acids, p-cyanophenylalanine, m-cyanophenylalanine, and S-cyanohomocysteine, have been introduced near the active site of the semisynthetic enzyme ribonuclease S (RNase S) to serve as probes of electrostatic fields. Vibrational Stark spectra, measured directly on the probe-modified proteins, confirm the predominance of the linear Stark tuning rate in describing the sensitivity of the nitrile stretch to external electric fields, a necessary property for interpreting observed frequency shifts as a quantitative measure of local electric fields that can be compared with simulations. The X-ray structures of these nitrile-modified RNase variants and enzymatic assays demonstrate minimal perturbation to the structure and function, respectively, by the probes and provide a context for understanding the influence of the environment on the nitrile stretching frequency. We examine the ability of simulation techniques to recapitulate the spectroscopic properties of these nitriles as a means to directly test a computational electrostatic model for proteins, specifically that in the ubiquitous Amber-99 force field. Although qualitative agreement between theory and experiment is observed for the largest shifts, substantial discrepancies are observed in some cases, highlighting the ongoing need for experimental metrics to inform the development of theoretical models of electrostatic fields in proteins.

Click to fit: versatile polyvalent display on a peptidomimetic scaffold

We describe an efficient protocol to effect multisite conjugation reactions to oligomers on solid-phase support. Sequence-specific N-substituted glycine "oligopeptoids" were utilized as substrates for azide-alkyne cycloaddition reactions. Diverse groups, including nucleobases and fluorophores, were conjugated at up to six positions on peptoid side chains with yields ranging from 88 to 96%. This strategy will be broadly applicable for generating polyvalent displays on peptides and other scaffolds, allowing precise control of spacing between the displayed groups.