It has been indicated that HDAC expression and activity are reduced in the lungs of patients with COPD, and that chronic treatment with a specific HDAC inhibitor, trichostatin A, causes pulmonary emphysema in rats38, while HDAC1 levels were decreased in the lungs of the triple n/i/eNOSs−/− mice. This evidence concerns the gene HDAC9 and chronic obstructive pulmonary disease.