Phosphodiesterase 4 inhibitor GPD-1116 markedly attenuates the development of cigarette smoke-induced emphysema in senescence-accelerated mice P1 strain

Abstract

Phosphodiesterase 4 (PDE4) is an intracellular enzyme specifically degrading cAMP, a second messenger exerting inhibitory effects on many inflammatory cells. To investigate whether GPD-1116 (a PDE4 inhibitor) prevents murine lungs from developing cigarette smoke-induced emphysema, the senescence-accelerated mouse (SAM) P1 strain was exposed to either fresh air or cigarette smoke for 8 wk with or without oral administration of GPD-1116. We confirmed the development of smoke-induced emphysema in SAMP1 [air vs. smoke (means ± SE); the mean linear intercepts (MLI), 52.9 ± 0.8 vs. 68.4 ± 4.2 μm, P < 0.05, and destructive index (DI), 4.5% ± 1.3% vs. 16.0% ± 0.4%, P < 0.01]. Emphysema was markedly attenuated by GPD-1116 (MLI = 57.0 ± 1.4 μm, P < 0.05; DI = 8.2% ± 0.6%, P < 0.01) compared with smoke-exposed SAMP1 without GPD-1116. Smoke-induced apoptosis of lung cells were also reduced by administration of GPD-1116. Matrix metalloproteinase (MMP)-12 activity in bronchoalveolar lavage fluid (BALF) was increased by smoke exposure (air vs. smoke, 4.1 ± 1.1 vs. 40.5 ± 16.2 area/μg protein; P < 0.05), but GPD-1116 significantly decreased MMP-12 activity in smoke-exposed mice (5.3 ± 2.1 area/μg protein). However, VEGF content in lung tissues and BALF decreased after smoke exposure, and the decrease was not markedly restored by oral administration of GPD-1116. Our study suggests that GPD-1116 attenuates smoke-induced emphysema by inhibiting the increase of smoke-induced MMP-12 activity and protecting lung cells from apoptosis, but is not likely to alleviate cigarette smoke-induced decrease of VEGF in SAMP1 lungs.