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

Am J Physiol Renal Physiol. 2012 Aug 15;303(4):F593-603. doi: 10.1152/ajprenal.00361.2011. Epub 2012 Jun 6.

Abstract

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 renin-activatable 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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animal Feed / analysis
  • Animals
  • Cathepsin D
  • Cathepsin G
  • Female
  • Fluorescent Dyes / pharmacology*
  • Humans
  • Mice
  • Mice, Inbred C57BL
  • Peptides / pharmacology*
  • Peptidyl-Dipeptidase A / metabolism
  • Rats
  • Renin / blood*
  • Renin / metabolism*
  • Renin-Angiotensin System / physiology
  • Sensitivity and Specificity
  • Sodium, Dietary

Substances

  • Fluorescent Dyes
  • Peptides
  • Sodium, Dietary
  • Peptidyl-Dipeptidase A
  • Cathepsin G
  • Renin
  • Cathepsin D