John A Allen - US grants

Acute; Binding; Binding (Molecular Function); Biological Function; Biological Process; Blood; Blood Vessels; Blood leukocyte; Body Tissues; Bone structure of radius; CRISP; Cardiovascular Diseases; Cause of Death; Cells; Computer Retrieval of Information on Scientific Projects Database; Condition; Contracting Opportunities; Contracts; Contrast Agent; Contrast Drugs; Contrast Media; Detection; Development; Diagnosis, Ultrasound; Diagnostic Imaging; Dysfunction; Echography; Echotomography; Encapsulated; Equilibrium; Fostering; Foundations; Frequencies (time pattern); Frequency; Functional disorder; Funding; Grant; Hawaii; Image; Individual; Institution; Investigators; Leukocytes; Ligands; Marrow leukocyte; Medical Imaging, Ultrasound; Methods; Methods and Techniques; Methods, Other; Molecular; Molecular Interaction; NIH; National Institutes of Health; National Institutes of Health (U.S.); Physiologic; Physiological; Physiopathology; Radial Bone; Radiopaque Media; Radius; Radius Bone; Relative; Relative (related person); Research; Research Personnel; Research Resources; Researchers; Resources; Reticuloendothelial System, Blood; Reticuloendothelial System, Leukocytes; Site; Source; Staging; Techniques; Tissues; Translations; Ultrasonic Imaging; Ultrasonogram; Ultrasonography; Ultrasound Test; Ultrasound, Medical; United States; United States National Institutes of Health; White Blood Cells; White Cell; balance; balance function; cardiovascular disorder; cost; diagnostic ultrasound; imaging; improved; molecular imaging; novel; pathophysiology; portability; radius bone structure; sonogram; sonography; sound measurement; ultrasound; ultrasound imaging; ultrasound scanning; vascular; white blood cell; white blood corpuscle

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Cardiovascular disease is a leading cause of illness and death in the United States and in Hawaii. Upon closer examination of the mortality rate from cardiovascular disease in Hawaii, it is clear that Filipinos and Native Hawaiians have a disproportionally higher mortality rate than the general population. Moreover, cardiovascular disease is a responsible for a significant portion of the state health care costs from hospitalizations. Sudden cardiac death and acute heart often occur without warning and these complications are typically associated with a plaque rupture corresponding to advanced stages of coronary atherosclerotic disease. Recommendations in terms in diet and exercise have been developed to prevent the onset of atherosclerotic disease but less effort has been made to aid patients who may be at risk for vulnerable plaque rupture. Coronary angiography has limitations as it does not allow for inspection of the vessel wall and can only determine narrowing of the luminal. Intravascular ultrasound (IVUS) provides a two dimensional cross sections view of the arterial wall and offers some ability to determine lumen and vessels areas. However, severe limitations exist in the classifications of plaques. The high frequency signal may be confused with acoustic shadowing aspects. The mechanisms of plaque rupture are not well understood and currently no imaging modality currently exists which can robustly detect vulnerable plaques. Vulnerable plaques are characterized by a large lipid core with a thin and inflamed fibrous cap. Low endothelial shear stress from the surrounding blood flow can serve as stimulus for the progression and differentiation of an early fibroatheroma to a high risk plaque. It has been hypothesized that vasa vasorum which supplies nutrients to the adventia may serve as a means for which white blood cells migrate into the lining of the wall. Subsequently, expansive vascular remodeling can occur within these plaques. The addition of molecular imaging capabilities to IVUS probes would provide an improvement in detecting biomarkers for plaque rupture such as neovascularization and inflammation. Targeted ultrasound contrast agents are encapsulated microbubbles with attached ligands which allow them to bind to specific diseased sites. The center frequency of IVUS probes (35-50 MHz) is much higher than conventional diagnostic ultrasound systems. We investigate the targeting efficacy in physiological flow conditions for large vessels and the optimal acoustical response of targeted agents at high frequency.

Inadequate dopamine (DA) neurotransmission in brain neural pathways is a pathophysiological underpinning of many disabling neurologic and psychiatric illnesses including substance use disorders, attention deficit hyperactivity disorder and cognitive impairments in schizophrenia. The DA D1 receptor (D1R) is a G protein- coupled receptor (GPCR) identified as playing a central role in motor control, reward, attention and working memory. While activation of the D1R could provide a valuable therapeutic strategy for treating diverse brain disorders, undesirable properties of established catechol ligands have prevented therapeutic development for over 40 years. Our research group recently solved this catechol problem and reported the first non-catechol D1R selective agonists that have unprecedented drug-like properties. Many GPCRs, including the D1R, can signal not only through G proteins, but also via G protein-independent interactions with other signaling proteins including, most prominently, ?-arrestins. Unexpectedly, several of the novel non-catechol D1R agonists show biased signaling activity via G proteins, without engagement of ?-arrestins. This G protein biased signaling by novel D1R agonists may result in superior activation and/or reduced side effect profiles relative to unbiased D1R agonists, providing the innovative opportunity to fine tune D1R activity for neurotherapeutics. Historically, GPCR ligands have been optimized based on their potency, efficacy and specificity; however, another crucial parameter that impacts receptor signaling is the duration of ligand binding to the receptor (i.e., binding kinetics). We hypothesize that the duration of ligand binding is a key mechanism that determines signaling bias of selective D1R agonists towards G proteins versus ?-arrestin signaling. The goal of this research project is to validate and quantify the biased agonist activity of these novel D1R agonists and evaluate if faster ligand-receptor binding kinetics is a mechanism driving biased signaling. Aim 1 will use a combination of approaches including functional D1R signaling assays, competition and kinetic binding assays to define a scale of signaling bias for D1R agonists and the kinetic binding parameters (Koff, Kon) for unbiased and biased agonists. We will then correlate these kinetic binding parameters of agonists to ?-arrestin-mediated signaling outcomes of desensitization and internalization. Aim 2 will determine if faster binding kinetics drive non-catechol D1R agonist efficacy in vivo. We will assess kinetic binding parameters (Koff, Kon) for unbiased and biased non-catechol D1R agonists from mouse striatal membranes and compare the functional efficacy of D1R agonists on cocaine-induced locomotor behavior using wildtype and ?-arrestin2 knockout mice. This research project will expand our highly limited appreciation of ligand properties and mechanisms governing D1R biased signaling. If we discover that the duration of agonist binding is a mechanism underlying biased D1R signaling, we will provide a defining and measurable ligand property to aid in the design of biased agonists. This project will also validate the relevance and potential usefulness of G protein biased agonism for D1R function.