Effects of 7,8‐dihydro‐8‐oxo‐deoxyguanosine on antigen challenge in ovalbumin‐sensitized mice may be mediated by suppression of Rac

Background and purpose:  Earlier we reported that 7,8‐dihydro‐8‐oxo‐deoxyguanosine (8‐oxo‐dG), an oxidatively modified guanine nucleoside, exerted anti‐inflammatory activity through inactivation of the GTP binding protein, Rac. In the present study, the effects of 8‐oxo‐dG were investigated on responses to antigen challenge in sensitized mice, as Rac is also involved at several steps of the immune process including antigen‐induced release of mediators from mast cells. Experimental approach:  Mice were sensitized and challenged with ovalbumin without or with oral administration of 8‐oxo‐dG during the challenge. Effects of 8‐oxo‐dG were assessed by measuring lung function, cells and cytokines in broncho‐alveolar lavage fluid (BALF) and serum levels of antigen‐specific IgE. Rac activity in BALF cells was also measured. Key results:  8‐oxo‐dG inhibited the increased airway resistance and decreased lung compliance of sensitized and challenged mice to the levels of non‐sensitized control mice and lowered the increased leukocytes particularly, eosinophils, in BALF. Furthermore, 8‐oxo‐dG suppressed allergy‐associated immune responses, such as raised anti‐ ovalbumin IgE antibody in serum, increased expression of CD40 and CD40 ligand in lung, increased interleukin‐4, ‐5, ‐13, interferon‐γ and tumour necrosis factor‐α in BALF and mRNA levels of these cytokines in BALF cells, dose‐dependently. The corresponding purine, 8‐oxo‐guanine, showed no effects in the same experiments. Finally, 8‐oxo‐dG, but not 8‐oxo‐guanine, inhibited the increased Rac activity in sensitized and challenged mice. Conclusion and implications:  8‐Oxo‐dG had anti‐allergic actions that might be mediated by Rac inactivation. This compound merits further evaluation of its therapeutic potential in allergic asthma.