Effects of albumin, transferrin and humic-like substances on iron-mediated OH radical formation in human lung fluids

Inhalation of particulate matter is hypothesized to contribute to health effects by overproducing reactive oxygen species (ROS) and inducing oxidative stress. Fe(II) has been shown to contribute to ROS generation in acellular simulated lung fluids. Atmospheric humic-like substances (HULIS) have been shown to chelate Fe(II) and significantly enhance this ROS generation. Here, we investigate Fe(II)-mediated (OH)-O-center dot generation from the iron active proteins in lung fluid, albumin and transferrin, and fulvic acid, a surrogate for HULIS, in human bronchoalveolar lavage fluid (BALF). We find that albumin enhances (OH)-O-center dot generation from inorganic Fe(II) and that transferrin attenuates this enhancement. We estimate the rate constants for albumin-Fe(II) and fulvic acid-Fe(II) mediated O-2(center dot-) reduction (1.9 +/- 0.3) M-1 s(-1) and (2.7 +/- 0.3) M-1 s(-1) (pH = 5.5, T = 37 degrees C), 17-25 times the rate for free iron, which we measured to be (110 +/- 20) x 10(-3) M-1 s(-1) , in agreement with the literature. (OH)-O-center dot generation measured from fulvic acid-Fe(II) in BALF from 8 individuals with added fulvic acid is successfully predicted rates of (OH)-O-center dot generation by mixtures of Fe(II), albumin, transferrin, fulvic acid, and ascorbate in saline solution. This indicates that fulvic acid enhances (OH)-O-center dot formation in BALF, and that albumin and transferrin in BALF moderate the effect. We propose that fulvic acid, and thereby HULIS, is capable of mobilizing Fe(II) away from albumin and transferrin and this increases the formation rate of O-2(center dot-) and ultimately of (OH)-O-center dot. Furthermore, we find that albumin and transferrin have significantly different impacts on Fe(II)-mediated (OH)-O-center dot than citrate, a common component of simulated lung fluids, a factor that should be considered carefully in the interpretation of results obtained from solutions containing citrate.

Automated summary

In this study, the impact of iron active proteins in lung fluid and humic-like substances on the generation of reactive oxygen species (ROS) was investigated. It was found that albumin enhances (OH)-O-center dot generation from inorganic Fe(II), while transferrin attenuates this enhancement. The study suggests that fulvic acid, a surrogate for HULIS, is capable of mobilizing Fe(II) away from albumin and transferrin, increasing the formation rate of O-2(center dot-) and ultimately of (OH)-O-center dot.