Demarcation of Sepsis-Induced Peripheral and Central Acidosis with pH (Low) Insertion Cycle Peptide
Kelly E. Henry, Aisling M. Chaney, Veronica L. Nagle, Haley C. Cropper, Saghar Mozaffari, Gregory Slaybaugh, Keykavous Parang, Oleg A. Andreev, Yana K. Reshetnyak, Michelle L. James, Jason S. Lewis
Abstract
Acidosis is a key driver for many diseases, including cancer, sepsis, and stroke. The spatiotemporal dynamics of dysregulated pH across disease remain elusive, and current diagnostic strategies do not provide localization of pH alterations. We sought to explore if PET imaging using hydrophobic cyclic peptides that partition into the cellular membrane at low extracellular pH (denoted as pH [low] insertion cycles, or pHLIC) can permit accurate in vivo visualization of acidosis. Methods: Acid-sensitive cyclic peptide c[E 4 W 5 C] pHLIC was conjugated to bifunctional maleimide-NO2A and radiolabeled with 64 Cu (half-life, 12.7 h). C57BL/6J mice were administered lipopolysaccharide (15 mg/kg) or saline (vehicle) and serially imaged with [ 64 Cu]Cu-c[E 4 W 5 C] over 24 h. Ex vivo autoradiography was performed on resected brain slices and subsequently stained with cresyl violet to enable high-resolution spatial analysis of tracer accumulation. A non-pH-sensitive cell-penetrating control peptide (c[R 4 W 5 C]) was used to confirm specificity of [ 64 Cu]Cu-c[E 4 W 5 C]. CD11b (macrophage/microglia) and TMEM119 (microglia) immunostaining was performed to correlate extent of neuroinflammation with [ 64 Cu]Cu-c[E 4 W 5 C] PET signal. Results: [ 64 Cu]Cu-c[E 4 W 5 C