Quantitative in vivo mapping of myocardial mitochondrial membrane potential

PLOS ONE, Nov 2019

Background Mitochondrial membrane potential (ΔΨm) arises from normal function of the electron transport chain. Maintenance of ΔΨm within a narrow range is essential for mitochondrial function. Methods for in vivo measurement of ΔΨm do not exist. We use 18F-labeled tetraphenylphosphonium (18F-TPP+) to measure and map the total membrane potential, ΔΨT, as the sum of ΔΨm and cellular (ΔΨc) electrical potentials. Methods Eight pigs, five controls and three with a scar-like injury, were studied. Pigs were studied with a dynamic PET scanning protocol to measure 18F-TPP+ volume of distribution, VT. Fractional extracellular space (fECS) was measured in 3 pigs. We derived equations expressing ΔΨT as a function of VT and the volume-fractions of mitochondria and fECS. Seventeen segment polar maps and parametric images of ΔΨT were calculated in millivolts (mV). Results In controls, mean segmental ΔΨT = -129.4±1.4 mV (SEM). In pigs with segmental tissue injury, ΔΨT was clearly separated from control segments but variable, in the range -100 to 0 mV. The quality of ΔΨT maps was excellent, with low noise and good resolution. Measurements of ΔΨT in the left ventricle of pigs agree with previous in in-vitro measurements. Conclusions We have analyzed the factors affecting the uptake of voltage sensing tracers and developed a minimally invasive method for mapping ΔΨT in left ventricular myocardium of pigs. ΔΨT is computed in absolute units, allowing for visual and statistical comparison of individual values with normative data. These studies demonstrate the first in vivo application of quantitative mapping of total tissue membrane potential, ΔΨT.

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0190968&type=printable

Quantitative in vivo mapping of myocardial mitochondrial membrane potential

January Quantitative in vivo mapping of myocardial mitochondrial membrane potential Nathaniel M. Alpert 0 1 Nicolas Guehl 0 1 Leon Ptaszek 1 Matthieu Pelletier-Galarneau 0 1 Jeremy Ruskin 1 Moussa C. Mansour 1 Dustin Wooten 0 1 Chao Ma 0 1 Kazue Takahashi 0 1 Yun Zhou 1 Timothy M. Shoup 0 1 Marc D. Normandin 0 1 Georges El Fakhri 0 1 0 Gordon Center for Medical Imaging, Massachusetts General Hospital, Harvard Medical School , Boston , Massachusetts, United States of America, 2 Cardiac Arrhythmia Service, Massachusetts General Hospital, Harvard Medical School , Boston , Massachusetts, United States of America, 3 The Russell H. Morgan Department of Radiology and Radiological Science, School of Medicine Johns Hopkins University , Baltimore, Maryland , United States of America 1 Editor: Cecilia Zazueta, Instituto Nacional de Cardiologia Ignacio Chavez , MEXICO Mitochondrial membrane potential (ΔΨm) arises from normal function of the electron transport chain. Maintenance of ΔΨm within a narrow range is essential for mitochondrial function. Methods for in vivo measurement of ΔΨm do not exist. We use 18F-labeled tetraphenylphosphonium (18F-TPP+) to measure and map the total membrane potential, ΔΨT, as the sum of ΔΨm and cellular (ΔΨc) electrical potentials. - Funding: This work was funded by two grants from the United States National Institutes of Health: R01HL110241 (GEF) and R01HL137230 (GEF), https://www.nhlbi.nih.gov. These grants were awarded as part of the standard peer review process for new grants. The study design and analysis are solely the work of the study authors, meaning that the funders had no role in study Background Methods (mV). Results Eight pigs, five controls and three with a scar-like injury, were studied. Pigs were studied with a dynamic PET scanning protocol to measure 18F-TPP+ volume of distribution, VT. Fractional extracellular space (fECS) was measured in 3 pigs. We derived equations expressing ΔΨT as a function of VT and the volume-fractions of mitochondria and fECS. Seventeen segment polar maps and parametric images of ΔΨT were calculated in millivolts In controls, mean segmental ΔΨT = -129.4±1.4 mV (SEM). In pigs with segmental tissue injury, ΔΨT was clearly separated from control segments but variable, in the range -100 to 0 mV. The quality of ΔΨT maps was excellent, with low noise and good resolution. Measurements of ΔΨT in the left ventricle of pigs agree with previous in in-vitro measurements. Conclusions We have analyzed the factors affecting the uptake of voltage sensing tracers and developed a minimally invasive method for mapping ΔΨT in left ventricular myocardium of pigs. ΔΨT is computed in absolute units, allowing for visual and statistical comparison of individual values design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. with normative data. These studies demonstrate the first in vivo application of quantitative mapping of total tissue membrane potential, ΔΨT. Introduction Mitochondria produce approximately 90% of cellular adenosine triphosphate (ATP) through oxidative phosphorylation [ 1 ]. The electron transport chain (ETC) of the mitochondrion is ultimately responsible for converting the foods we eat into electrical and chemical energy gradients by pumping protons across the inner membrane in the mitochondrial intermembrane space. The energy stored in the electric field, referred to as mitochondrial membrane potential (ΔCm), is then used to power the conversion of ADP to ATP. In a typical cell, the ΔCm remains constant with time and is about -140 mV [ 2 ]. Table 1 lists ΔCm for mitochondria of different cell types. If ΔCm remains within the physiological range, a small amount of reactive oxygen species (ROS) is produced. However, in mitochondrial dysfunction, ΔCm falls outside the normal range, with concomitant increase in ROS release, and impairment of ATP production [ 10 ]. And because mitochondria are the most important source of energy and ROS in the cell, mitochondrial dysfunction is at the core of many diseases, including myopathies [ 11 ], diabetes [ 12 ], degenerative diseases [ 13 ], inflammation [ 14 ], cancer [ 15 ], and cardiac arrhythmias [ 16, 17 ]. Despite continuing scientific interest in voltage sensitive probes, a noninvasive method for measuring ΔCm in living animals does not currently exist. The basic physiological studies conducted several decades ago are highly relevant but not always mentioned: Historically, fluorescent dyes [ 18 ] and lipophilic cationic tracers have been developed for quantitative assay of ΔCm in isolated mitochondria [ 4 ], cells [ 19 ], and isolated heart preparations [ 6 ]. Electrodes sensitive to tetraphenylphosphonium (TPP) have also been developed and used to evaluate ΔCm in isolated mitochondrial fractions [ 9, 20 ]. [14C or 3H]-labeled lipophilic catio (...truncated)


This is a preview of a remote PDF: https://journals.plos.org/plosone/article/file?id=10.1371/journal.pone.0190968&type=printable

Nathaniel M. Alpert, Nicolas Guehl, Leon Ptaszek, Matthieu Pelletier-Galarneau, Jeremy Ruskin, Moussa C. Mansour, Dustin Wooten, Chao Ma, Kazue Takahashi, Yun Zhou, Timothy M. Shoup, Marc D. Normandin, Georges El Fakhri. Quantitative in vivo mapping of myocardial mitochondrial membrane potential, PLOS ONE, 2018, Volume 13, Issue 1, DOI: 10.1371/journal.pone.0190968