RARG and chronic obstructive pulmonary disease: But again, the attempts to stimulate lung regeneration in COPD patients with emphysema with orally administered ATRA yielded no differences in computed tomography (CT), lung function, or quality of life scores between treatment groups [13, 14], and RAR-γ selective agonist administration also showed no differences in CT scores or lung function in treated vs. nontreated COPD patients [15, 16].