HMOX1 and chronic obstructive pulmonary disease: Except for lower HO-1 expression in left lung homogenate compared to Group I (p < 0.001) and higher HO-1 in blood Exos than Group I (p < 0.05), relative HO-1 expression in other tissues of Group IV mice showed no significant differences from Group I. This suggests that HO-1 content in blood, lung-derived Exos, and brain tissue of HO-1-positive COPD exacerbation mice might be twice or more that of normal non-COPD exacerbation mice.