Advanced Development of a Mitochondrial Monitor to Detect Shock States Using Resonance Raman Spectroscopy
Abstract
The inadequate delivery of oxygen to cells represents the truest emergency in medicine, resulting in death or organ injury in a number of circumstances. In hemorrhagic shock, compromised oxygen delivery can cause the lifelong dysfunction of major organs (such as the brain and liver) or even cardiac arrest. In other instances, such as following surgery for congenital heart disease, inadequate oxygen delivery may itself cause brain injury or cause a recovering heart to pump less well or stop beating completely. Patients with primary mitochondrial disorders or tissue swelling (a common problem in critically ill patients) may not be able to process oxygen properly, with the same devastating consequences. Unfortunately, it is currently impossible to quantify whether or not a patient’s oxygen delivery is sufficient to meet their current metabolic demand. Instead, we use surrogate markers from blood tests (the most common ones being lactic acid or mixed venous oxygen saturation) or markers of organ function (such as urine output as a marker of kidney function) as guides. However, each of these endpoints represents a delayed and often confounded marker of the shock state. The accurate recognition of insufficient oxygen delivery would permit accurate triage, rapid transport, and the timely and directed treatment of patients with inadequate oxygen delivery in a number of disease states. This project proposes a device that, for the first time, quantifies the adequacy of oxygen delivery to a tissue using a continuous spectroscopic technique. Oxygen is used by a specific part of the cell known as the mitochondrion in the process of energy (specifically, a compound called ATP) production. To make ATP, the mitochondrion passes energy from the bonds in the food we eat (carried in the form of electrons) through a series of proteins within the mitochondrion called the electron transport chain (ETC). The released energy is used to pump protons across the mitochondrial membrane, creating the voltage gradient for ATP generation. Oxygen’s role is to serve as the final electron acceptor, permitting the process of proton pumping to continue uninterrupted. The higher a cell’s energy (ATP) needs, the greater the flux of electrons and the greater the requirement for oxygen. Normally, the body matches oxygen delivery to demand elegantly, but in critical illness, this can be compromised. When oxygen delivery is not sufficient to meet the flux of electrons, proteins of the ETC become progressively more reduced, meaning they have an added electron (and therefore electrons are not properly flowing and ATP is not being generated). Our technique quantifies the fraction of mitochondrial proteins in the reduced versus oxidized state using a nondestructive technique called resonance Raman spectroscopy. Using a prototype device, we have recently found that in health, the ETC is typically 20% reduced and 80% oxidized (true across species). We found that an elevation of mitochondrial redox state >40% on the myocardium was highly predictive of cardiac arrest in rodents, presumably because myocytes become unable to generate sufficient force of contraction. Currently, no tools exist that can predict cardiac arrest with this degree of accuracy. The purpose of this grant is to advance this tool to ready it for clinical use, with special emphasis on the problem of hemorrhagic shock. In Aim I, we will create a series of probes that access different sites within the body, including the tongue, cheek, stomach, and bladder (for critically ill patients), and the surface of the heart (during congenital heart surgery). We will also improve our algorithm to enable the quantification of the reduced vs. oxidized fraction of each of the four complexes individually (currently, we are measuring a composite signal). This will allow us to pinpoint how far along the oxygen deficiency spectrum a cell is, and may also open new tools for use in mitochondrial disor
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 19, 2019
- Source ID
- W81XWH1910472
Entities
People
- John N Kheir
Organizations
- Boston Children's Hospital
- United States Army