Role of 8-oxoG in pollen-induced allergic airway inflammation

Introduction: Pollen-induced allergic airway inflammation is believed to be orchestrated by reactive oxygen species (ROS) generated by intrinsic NAD(P)H oxidases of pollen grains. The pollen-derived reactive radicals enhance the allergen-induced mucin production, as well as perivascular and peribronchial accumulation of inflammatory cells. It has previously been demonstrated that pollen-generated ROS cause damage to macromolecules, including DNA in the lungs. The primary target of ROS in DNA is guanine, because it has the lowest redox potential among the four nucleobases and 7,8-dihydro-8-oxoguanine (8-oxoG) is the most frequent oxidation product. In mammalian cells, repair of 8-oxoG is initiated by the 8-oxoguanine DNA glycosylase 1 (OGG1). In a recent study, it has been found that OGG1-mediated repair of 8-oxoG augments antigen-driven allergic immune responses.
Aim: The present study aimed to test whether pollen NAD(P)H oxidase activity can be replaced with free 8-oxoG base in ragweed pollen extract (RWE) to induce allergic airway inflammation.
Methods: BALB/c mice were sensitized intraperitoneally with RWE on days 0 and 4. On day 11 mice were intranasally challenged with RWE, RWEH (heat-inactivated RWE, which lacks NAD(P)H oxidase activity), Amb a 1 (the major ragweed allergen), RWEH + 8-oxoG or Amb a 1 + 8-oxoG. On day 14, mice were euthanized and bronchoalveolar lavage fluid (BALF) samples were collected. Total cell counts and differential cell counts were determined on cytocentrifuge preparations. Mucin (MUC5AC) levels in BALF samples were assessed by ELISA.
Results: We found that parallel intranasal administration of free 8-oxoG with either Amb a 1 or RWEH significantly increased their potential to recruit eosinophils into the airways of RWE-sensitized mice. Combined challenges with 8-oxoG also enhanced the capacity of Amb a 1 and RWEH to augment MUC5A/C levels in BALF.
Conclusion: Our findings confirm that effects of pollen-derived ROS on the airway epithelium are mediated at least partially by OGG1-dependent mechanisms and a transient modulation of OGG1 expression/activity in airway epithelial cells could have clinical benefits.