Lactoferrin decreases pollen antigen‐induced allergic airway inflammation in a murine model of asthma (1)
Oxidative stress occurs not only as a result of environmental exposure, but also because of inflammation, as both airway and intravascular inflammatory cells generate reactive oxygen species (ROS). Lactoferrin (LF), an iron‐binding glycoprotein present in serum and many human exocrine secretions serves as immunomodulator and a natural antioxidant. Pro‐oxidant iron is present in airway lining fluids, as well as in resident cells of airways of human and animals and it is known to have implication for oxidative stress in the lungs. Ragweed pollen extract (RWE) induced a significant increase in lipid peroxidation products, 4‐hydroxynonenal (4‐HNE) and malondialdehyde (MDA) in cells and airways of experimental animals.
A529 cells exposed LF (100µg/ml), but not LFFe (100µg/ml), significantly decreased formation of fluorescent dichlorofluorescein (DCF). When A549 cells were RWE‐treated in iron‐free medium (IFM), ROS levels were significantly lower (∼35% less) compared to the levels in cultures RWE‐treated in iron‐containing medium. Treatment of cells with Amb a 1, the most abundant allergen in RWE possessing no NAD(P)H oxidase activity, did not alter intracellular levels of ROS and LF or LFFe had no effect. DFO decreased the RWE‐induced increase in cellular ROS levels by approximately 40%. Accordingly, LF (and DFO) also significantly inhibited H2O2 accumulation.
In RWE‐sensitized mice, the BAL of mice prior to challenge contained primarily macrophages/monocytes and low number of eosinophils and neutrophils. In a full‐blown inflammation; however, 47% cells were eosinophils, 52% macrophages/monocytes and 1% neutrophils. When RWE was administered together with LF (100µg) there was a moderate accumulation of inflammatory cells in the BAL compartment, and in the subepithelium. LF significantly decreased the RWE‐induced formation of mucin‐producing cells. There was no statistically significant effect of LFFe. When DFO was added with RWE, there was only a slight decrease in inflammation. The oxidatively inactive Amb a 1 (25 µg) induced low‐grade airway inflammation. When Amb a 1 was administered together with the ROS‐generating G‐ox, eosinophil accumulation in BAL was significantly increased. G‐ox itself did not cause inflammatory cell accumulation in airways. When G‐ox plus Amb a 1 and LF were administered together, the number of inflammatory cells in BAL decreased significantly.
LF was most effective when administered concurrently with RWE. In addition, when LF was given 6, 12 or 24hr after challenge also reduced inflammatory cell accumulation.
RWE is a complete mixture of antigenic components of ragweed pollen grains and its addition to cultured cells or administration to sensitized animals mimics a natural exposure to pollens or subpollen particles. When cells were transferred into iron‐free medium RWE‐induced ROS levels were lower suggesting a significant role of iron in conversion of O2•– into highly reactive species. Most importantly LF was more effective in decreasing cellular ROS levels than in absence of iron in the culture medium or addition of the iron‐binding DFO to the cells. LF is most effective in decreasing inflammation when added together with RWE. LF can decrease the expression of pro‐inflammatory mediators, including tumour necrosis factor‐α (TNF‐α), interleukin (IL)‐1β, IL‐6 and IL‐8, major regulators of airway inflammation.