Body Iron Stores and Oxidative Damage in Humans Increased during and after a 10- to 12-Day Undersea Dive1–3

Abstract

The National Aeronautics and Space Administration Extreme Environment Mission Operations (NEEMO) underwater habitat is a useful analogue for spaceflight. However, the increased air pressure in the habitat exposes crewmembers to higher oxygen pressures, which increases their risk for oxidative damage to DNA, proteins, and lipids. Studies from a previous NEEMO mission suggested that DNA oxidation occurs at an increased level, similar to that in smokers and astronauts returning from space. Astronauts in space and NEEMO crewmembers also have similar changes in iron metabolism. Newly formed RBC are destroyed and body iron stores are elevated. Because excess iron can act as an oxidant and cause tissue damage, we investigated aspects of oxidative damage and tested whether toxic forms of iron were present when iron stores increased during NEEMO missions. Subjects (n = 12) participated in 10- to 12-d saturation dives, and blood and 24-h urine samples were collected twice before, twice during, and twice after the dive. During the dive, ferritin was higher (P < 0.001), transferrin was lower (P < 0.001), and transferrin receptors were lower (P < 0.01). Serum iron was higher during and immediately after the dive (P < 0.001). Total homocysteine (P < 0.001) and superoxide dismutase (SOD) (P < 0.05) activity were affected by time; homocysteine increased during the dive and SOD decreased during and after the dive. Labile plasma iron was measurable only during the dive. These data indicate that the NEEMO environment increases body iron stores and labile forms of iron, which may contribute to oxidative damage.