We are delighted to speak with Anna Pearson (MS student) and her mentor Dr. Michael Tift, Assistant Professor at the University of North Carolina – Wilmington. Anna presented her research “First report of red blood cell lifespan in a marine mammal: An insight into endogenous carbon monoxide (CO) production” at the 2021 Experimental Biology conference last month.
What made you interested in studying red blood cells in dolphins?
Dr. Tift became interested in determining the red blood cell lifespan in marine mammals after discovering elevated levels of carbon monoxide (CO) in northern elephant seals. In humans, low levels of carbon monoxide are naturally produced in the body as a byproduct of the degradation of hemoglobin, the oxygen carrying protein found inside red blood cells. Elephant seals have the highest mass-specific blood volume of any animal on earth, which could explain the source of the high CO in their blood. There is a wide diversity of blood volumes amongst marine mammal species, and therefore, the next logical step was to study the red blood cell lifespan in a marine mammal to see how carbon monoxide and red blood cell lifespan are related. Surprisingly, red blood cell lifespans have never been published for any marine mammal species.
It is interesting to learn that some marine mammals have high levels of carbon monoxide in their blood. How do they develop such high levels?
There are a couple of different reasons why marine mammals would have elevated levels of carbon monoxide in their blood. In humans, we know that the majority of carbon monoxide is produced as a byproduct of hemoglobin degradation, which normally happens when red blood cells reach the end of their lifespan (~120 days in humans). Therefore, the natural turnover of red blood cells is a primary source of CO production in the body. Other sources of carbon monoxide production in the body include hemolytic diseases where red blood cells die faster than they would in a healthy individual. It is possible that certain marine mammals, such as elephant seals, have elevated levels of carbon monoxide in their blood as a result of a short red blood cell lifespan. On the other hand, many deep-diving marine mammals, such as elephant seals, have large blood volumes which might be slowly turned over and result in the constant production of large amounts of CO. To address this, we have focused on two species of cetaceans, bottlenose dolphins and beluga whales. The dolphins have blood volumes similar to humans, while the belugas have much larger blood volumes. Upon completion of our study, we will know if the amount of CO in the animals is more closely related to their red blood cell lifespan, or the total volume of blood in the animals.
Are there complications or benefits from having such high levels?
Exposure to high levels of carbon monoxide can certainly be dangerous, as the gas competitively competes for oxygen binding sites on proteins which store and transport oxygen. Meaning, that high levels of CO in the body can interfere or inhibit oxygen delivery in the body. However, exposure to low or moderate doses of carbon monoxide can actually be beneficial in specific circumstances, as the gas has shown to have protective properties at these levels (e.g., anti-inflammation). In surgeries and organ transplants where blood flow is cut off to certain tissues, carbon monoxide can prevent inflammatory injuries which often occur when blood flow is reestablished to the tissues. Ironically, marine mammals will restrict blood flow to peripheral tissues when they are diving in order to conserve oxygen for organs that are extremely sensitive to low oxygen (e.g., brain and heart). Once an animal returns to the surface, the blood returns to the peripheral tissues. Despite their tissues constantly undergoing similar conditions to that seen from patients undergoing organ transplantations, we do not see injuries in these animals. Therefore, it has been hypothesized that the elevated levels of carbon monoxide in marine mammals may serve a protective role that prevents these animals from experiencing the injuries associated with fluctuations in blood flow to their tissues.
Do you think the high CO levels are related to red blood cell longevity in dolphins?
Our preliminary results suggest that red blood cells have a maximum lifespan longer than humans. However, there seems to be more non-age dependent removal than we see in healthy humans. Meaning, that they get rid of more red blood cells than humans when the cells are younger. In healthy humans, the red blood cells will circulate in the body for about 120 days and then they will be removed from circulation. In the bottlenose dolphins, we observed red blood cell removal occurring right after the cells are produced. The red blood cell lifespan curve we observed in the first two bottlenose dolphins is therefore similar to curves seen in humans with blood pathologies that result in shortened red blood cell lifespans. It is possible elevated levels of carbon monoxide could come from this continual non-age dependent removal.
What are you studying right now?
The non-age dependent removal observed in bottlenose dolphins has spurred several projects to investigate the mechanisms behind aging and removal of red blood cells in marine mammals. This includes investigating the protein composition between terrestrial and marine mammal red blood cells as well as the molecular markers that occur as red blood cells age in mammals.
The Tift Lab is also measuring carbon monoxide in several different marine and terrestrial animals. Our goal is to understand the diversity of carbon monoxide in wild species, and to determine if there is any unique patterns of species or conditions in nature which have resulted in high production of carbon monoxide. We’re studying the production of CO from the level of the whole organism down to the function of specific cells, and even the genetic components that regulate the production of the gas. We’re in the early stages of most studies, so be sure to stay tuned as we will have several new findings coming out soon!