Toward a More Accurate Description of “Low-Oxygen” Cell Culture Work

It’s funny how things can get labeled with certain words that don’t completely make sense. Misnomers are all over the place. Jellyfish aren’t fish. Rhode Island isn’t an island. Koala bears are marsupials. The West Indies are nowhere near India. Chinese checkers didn’t originate in China. The last two examples were named based on the current knowledge that was later found to be incorrect.

This is happening in the field of science formerly known as hypoxia. Hypoxia literally means “less oxygen.” “Less” is a relative term, and therefore, a comparison between at least two situations must exist. It has become standard to compare “hypoxic” environments to our primary surroundings; i.e., anything less than atmospheric oxygen (21% O₂) has been referred to as “hypoxia.” When working with plants or whole animals, this seems appropriate. They normally breathe 21% atmospheric oxygen, so anything less would be considered hypoxic. But what about cells? Organs? Tissues? Are they normally exposed to 21% oxygen? The answer is no.

Researchers everywhere have shown that each tissue and organ within the body has a naturally occurring range of oxygen that promotes the ideal health of that tissue (see Figure 1). Once you discover and provide the ideal O₂ concentration for your tissue type, the phenotypes of your cell culture drastically improve. So, if the naturally occurring concentration of oxygen in the brain is 2%, why does that get labeled as hypoxic? That is the tissue’s physiological oxygen concentration. For brain tissue, only an O2 concentration that is lower than 2% could be accurately described as hypoxic, while O2 as low as 3% would be hyperoxic. Atmospheric oxygen (21% O2) would be hyperoxic too, not normoxic.

Therefore, we at Baker and Baker Ruskinn are proponents of the movement to change the physiological oxygen terminology. “Normoxia” shall no longer be used. It is not specific enough. “Atmospheric oxygen” will be used to describe 21% O₂. “Physiological oxygen” will be used to describe the normal oxygen concentration at each specific tissue. “Hypoxia” will be used primarily to describe relative oxygen concentration in reference to physiological oxygen. Perhaps some fun abbreviations can be used too. PhOx, PhysOx, or AtmOx anyone?

Let’s keep our terminology as specific and up-to-date as possible. There is no use for outdated misnomers. Get on board!