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

David H Gonzalez; David A Diaz; J Puna Baumann; Andrew J Ghio; Suzanne E Paulson

doi:10.1016/j.freeradbiomed.2021.01.021

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

Free Radic Biol Med. 2021 Mar:165:79-87. doi: 10.1016/j.freeradbiomed.2021.01.021. Epub 2021 Jan 21.

Authors

David H Gonzalez¹, David A Diaz², J Puna Baumann², Andrew J Ghio³, Suzanne E Paulson⁴

Affiliations

¹ University of California at Los Angeles, Department of Atmospheric and Oceanic Sciences, 405 Hilgard Ave., Los Angeles, CA, 90405, USA.
² California State University, Northridge Department of Environmental & Occupational Health, 18111 Nordhoff St, Northridge, CA, 91330, USA.
³ US Environmental Protection Agency, Chapel Hill, NC, 27599, USA.
⁴ University of California at Los Angeles, Department of Atmospheric and Oceanic Sciences, 405 Hilgard Ave., Los Angeles, CA, 90405, USA. Electronic address: paulson@atmos.ucla.edu.

PMID: 33486087
DOI: 10.1016/j.freeradbiomed.2021.01.021

Abstract

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 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 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 O₂^.- reduction (1.9 ± 0.3) M^-1 s^-1 and (2.7 ± 0.3) M^-1s^-1 (pH = 5.5, T = 37 °C), 17-25 times the rate for free iron, which we measured to be (110 ± 20) × 10^-3 M^-1s^-1, in agreement with the literature. ^.OH generation measured from fulvic acid-Fe(II) in BALF from 8 individuals with added fulvic acid is successfully predicted rates of ^.OH generation by mixtures of Fe(II), albumin, transferrin, fulvic acid, and ascorbate in saline solution. This indicates that fulvic acid enhances ^.OH 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 O₂^.- and ultimately of ^.OH. Furthermore, we find that albumin and transferrin have significantly different impacts on Fe(II)-mediated ^.OH 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.

Keywords: Albumin; Bronchoalveolar lavage fluid; Citrate; Competitive iron binding; Fulvic acid; HULIS; Humic-like substances; Reactive oxygen species; Redox kinetics; Redox potential; Simulated lung fluid; Transferrin.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Albumins
Humans
Humic Substances* / analysis
Iron*
Lung
Oxidation-Reduction
Transferrin

Substances

Albumins
Humic Substances
Transferrin
Iron