Free
iron in lung can cause the generation of
reactive oxygen species, an important factor in
chronic obstructive pulmonary disease (
COPD) pathogenesis.
Iron accumulation has been implicated in oxidative stress in other diseases, such as Alzheimer's and Parkinson's diseases, but little is known about
iron accumulation in
COPD. We sought to determine if
iron content and the expression of
iron transport and/or storage genes in lung differ between controls and
COPD subjects, and whether changes in these correlate with
airway obstruction. Explanted lung tissue was obtained from transplant donors,
GOLD 2-3
COPD subjects, and
GOLD 4 lung transplant recipients, and bronchoalveolar lavage (BAL) cells were obtained from non-smokers, healthy smokers, and
GOLD 1-3
COPD subjects.
Iron-positive cells were quantified histologically, and the expression of
iron uptake (
transferrin and
transferrin receptor), storage (
ferritin) and export (
ferroportin) genes was examined by real-time RT-PCR assay. Percentage of
iron-positive cells and expression levels of
iron metabolism genes were examined for correlations with airflow limitation indices (forced expiratory volume in the first second (FEV1) and the ratio between FEV1 and forced vital capacity (FEV1/FVC)). The alveolar macrophage was identified as the predominant
iron-positive cell type in lung tissues. Furthermore, the quantity of
iron deposit and the percentage of
iron positive macrophages were increased with
COPD and
emphysema severity. The
mRNA expression of
iron uptake and storage genes
transferrin and
ferritin were significantly increased in
GOLD 4
COPD lungs compared to donors (6.9 and 3.22 fold increase, respectively). In BAL cells, the
mRNA expression of
transferrin,
transferrin receptor and
ferritin correlated with
airway obstruction. These results support activation of an
iron sequestration mechanism by alveolar macrophages in
COPD, which we postulate is a protective mechanism against
iron induced oxidative stress.