A fluorogenic near-infrared imaging agent for quantifying plasma and local tissue renin activity in vivo and ex vivo

Abstract

. A fluorogenic near-infrared imaging agent for quantifying plasma and local tissue renin activity in vivo and ex vivo. Am J Physiol Renal Physiol 303: F593-F603, 2012. First published June 6, 2012; doi:10.1152/ajprenal.00361.2011.-The renin-angiotensin system (RAS) is well studied for its regulation of blood pressure and fluid homeostasis, as well as for increased activity associated with a variety of diseases and conditions, including cardiovascular disease, diabetes, and kidney disease. The enzyme renin cleaves angiotensinogen to form angiotensin I (ANG I), which is further cleaved by angiotensin-converting enzyme to produce ANG II. Although ANG II is the main effector molecule of the RAS, renin is the rate-limiting enzyme, thus playing a pivotal role in regulating RAS activity in hypertension and organ injury processes. Our objective was to develop a near-infrared fluorescent (NIRF) renin-imaging agent for noninvasive in vivo detection of renin activity as a measure of tissue RAS and in vitro plasma renin activity. We synthesized a reninactivatable agent, ReninSense 680 FAST (ReninSense), using a NIRF-quenched substrate derived from angiotensinogen that is cleaved specifically by purified mouse and rat renin enzymes to generate a fluorescent signal. This agent was assessed in vitro, in vivo, and ex vivo to detect and quantify increases in plasma and kidney renin activity in sodium-sensitive inbred C57BL/6 mice maintained on a low dietary sodium and diuretic regimen. Noninvasive in vivo fluorescence molecular tomographic imaging of the ReninSense signal in the kidney detected increased renin activity in the kidneys of hyperreninemic C57BL/6 mice. The agent also effectively detected renin activity in ex vivo kidneys, kidney tissue sections, and plasma samples. This approach could provide a new tool for assessing disorders linked to altered tissue and plasma renin activity and to monitor the efficacy of therapeutic treatments. optical tomography; low-salt diet; hypertension THE RENIN-ANGIOTENSIN SYSTEM (RAS) plays an important role in the regulation of blood volume, electrolyte homeostasis, and systemic vascular resistance, which together affect cardiac output and arterial pressure (11). Renin, a highly specific aspartyl protease, is primarily stored and released from juxtaglomerular (JG) cells within the afferent arterioles of the kidney glomeruli and plays an important regulatory role in RAS function. JG cells can sense a reduction in afferent arteriole pressure in the kidney leading to direct release of renin, and specialized adjacent cells (the macula densa) can also trigger JG renin release upon sensing of decreased plasma sodium chloride in renal tubules or changes in kidney sympathetic nerve signaling. Release of renin into the blood then mediates the first and rate-limiting step of the RAS cascade by cleaving angiotensinogen to generate angiotensin I (ANG I). ANG I is further cleaved by angiotensin-converting enzyme (ACE) to generate bioactive angiotensin II (ANG II), which binds to angiotensin recepto...

Identification of Bona Fide Alternative Renin Transcripts Expressed Along Cortical Tubules and Potential Roles in Promoting Insulin Resistance In Vivo Without Significant Plasma Renin Activity Elevation

“…15 Constructs of transgene (ARen2) with pCAGGS promoter are shown in Figure S4c in the online-only Data Supplement. We performed experiments to compare ARen2TG mice with wild-type littermates in terms of following phenotypes: measurement of blood pressure, 16,17 measurement of plasma renin activity, 16,18,19 the results of in vivo near-infrared imaging using the renin substrate analog ReninSense 680 FAST (Perkin Elmer, Waltham, MA), 20 the results of insulin tolerance tests, 21 fasting plasma glucose levels, the expressions of inflammatory molecules in various tissues on quantitative RT-PCR analyses, 16,18,19 and in situ histological examinations for livers of both transgenic mice and wild-type littermate using rabbit polyclonal anti-angiotensin II antibodies (NBP1-30027; Novus Biologicals, LLC, Littleton, CO). 22,23 All experiments were performed according to the protocols of manufacturer, the references, and our reports as specified above.…”

Blood Pharmacokinetics Imaging by Noninvasive Heart Fluorescence Tomography and Application to Kidney Glomerular Filtration Rate Assessment

“…Fluorescence optical imaging remains a young imaging modality but has capabilities that can support a wide range of preclinical therapeutic areas of research (Kossodo et al, 2010;Peterson et al, 2010;Ackermann et al, 2011;Zhang et al, 2012;Felix et al, 2015;Peterson, 2016;Vasquez and Peterson, 2017). Advances in photonic technology and reconstruction algorithms (Meyer et al, 2007;Lasser et al, 2008;Mohajerani et al, 2009;Mohajerani and Ntziachristos, 2016) have even taken optical imaging beyond standard twodimensional epifluorescence imaging into the realm of 3D tomographic imaging for localization and quantification of fluorescence in deep tissue.…”

Bioresponsive probes for molecular imaging: concepts and in vivo applications

“…These FAST TM self-quenched probes (~43 kDa) are significantly smaller in size compared to the macromolecular poly-L-lysine-based probes and therefore display an improved pharmacokinetic profile that enables in vivo molecular imaging at earlier time-points. These probes have successfully been used for the detection in vivo of the proteolytic activity of renin, MMPs, cathepsin B, and neutrophil elastase (52)(53)(54)(55)(56)(57)(58)(59).…”