At the Fred Hutchinson Cancer Research Center in Seattle Washington, researchers in the Institute’s Basic Sciences Division are making interesting use of the LI-COR LI-7000 CO₂/H₂O Gas Analyzer. A team of scientists from the laboratory of Dr. Mark Roth uses the LI-7000 to measure CO₂ exhalation as a proxy for metabolism in a variety of animals including flies, mice, and pigs in controlled conditions that induce suspended animation.
The team’s work is shedding light on the possible human medical benefits of inducing states of reduced metabolic rate. In highly controlled laboratory conditions with mice and other animals, the team discovered that reduced metabolism and associated drop in core body temperatures may lead to advancements that can one day help trauma patients or organ transplant patients, or any number of treatment situations in which tissue could be protected to extend viability for later procedures.
Some organisms can dramatically reduce metabolic activity naturally. Mammals hibernate, for example, while other animals estivate in heat and drought by reducing their respiration and heartbeat. Several species of invertebrates go dormant for years before reviving. This allows them to balance their energetic demands with the resources like food and water that are available to meet those demands.
Members of the Roth Lab design experiments using hydrogen sulfide (H₂S) and other compounds to study this biology by slowing or stopping animals’ life processes for given periods of time before reviving them without adverse effects. Observable life processes slow dramatically; the animals do not move, they breathe once per minute, and the heart rate slows to a fraction of normal. Importantly, using LI-COR’s LI-7000 to measure changes in CO₂ exhalation, the team has shown that the most rapid effect of H₂S is the immediate reduction of metabolic rate. This observation is the foundation of current research and development of drugs that could be used in human patients.
Roth’s team monitors CO₂ exhalation in real-time and recognizes the LI-7000 to be their instrument of choice for a variety of reasons. “We measure CO₂ exhalation as a proxy for metabolism in all kinds of creatures, and the LI-7000 is accurate enough to measure CO₂ given off by tiny creatures like yeast and bacteria, but it’s also able to handle the flow of CO₂ from larger animals like dogs and pigs,” Mike Morrison, a research scientist in the Roth lab says. “Another reason we use the LI-7000 is because the corrosive agents we use like H₂S don’t affect measurements or damage the instrument. It’s so robust that we don’t have to worry about any damage to it that could affect our results. And we can take it out to the desert and use it for experiments with rattlesnakes.”
The team uses chambers created from ordinary lab equipment to regulate the gaseous environment around small animals. The LI-7000 samples air flow into and out of the chambers to arrive at an accurate measurement of CO₂ output. The team uses the LI-7000’s reference estimation mode (REM) to do real-time differential calculations in order to determine rates of CO₂ exhaled by the animals. For larger animals, the team uses a mask placed over the face to regulate inhaled gases, and they use the LI-7000’s REM for real-time CO₂ measurements literally on a breath-by-breath basis.
In the team’s first experiments, when mice were exposed to 80 ppm of H₂S, oxygen consumption dropped by ~50% and their CO₂ exhalation dropped by ~60% in less than 5 minutes. If the mice were left in this environment for six hours, their CO₂ exhalation dropped to 10% of normal output under ambient room conditions. All of the mice tested were able to regain full body function and behavior when re-exposed to ambient room air concentrations of oxygen.
Results also show a relationship between the drop in metabolic rate and the corresponding drop in core body temperature. As concentrations of H₂S increase, core temperature decreases proportionately. Consequently, hypothermia accompanies reduced metabolic rate and together they contribute to the suspended animation-like state the mice experience.
Since then, research from the Roth lab has shown that H₂S is beneficial in numerous animal models of human injury and disease. For example when mice are pretreated with H₂S, they survive otherwise lethal hypoxia (lack of oxygen). This suggests that before surgery H₂S could be administered to patients to reduce tissue damage that results from temporary hypoxia. In another study, rats treated with H₂S survive otherwise lethal blood loss. This could be beneficial for many people who suffer from blood loss because of traumatic injuries. And finally, worms treated with H₂S live longer than untreated worms. Using the LI-700, the group is studying the mechanisms by which H₂S affects metabolism and the biological responses to stress.
The use of H₂S and the regulated induction of reduced metabolic rates may have great benefit for a variety of medical situations. Research from the Roth lab using the LI-7000 is leading to a better understanding of how this complex physiology works and how it can be used to improve human health.
More Information about the Roth Lab and this research
Roth Laboratory home page