BACKGROUNDSmoking and body mass index (BMI) are the key risk factors for chronic obstructive pulmonary disease (COPD). Adiponectin with both anti-inflammatory and pro-inflammatory properties is a vital modulator of inflammatory processes, which is expressed in epithelial cells in the airway in COPD-emphysema. The aim of this study was to examine the effects of adiponectin on tobacco smoke-induced emphysema in rats, which were fed different diets.

METHODSSeventy-six adult (6-8 weeks old) male Sprague-Dawley rats (average weight 220 ± 20 g) were exposed to smoke or smoke-free room atmosphere and fed different diets (regular, high-fat, or low-fat diets) for 6 months. The rats were randomly divided into six groups. They are nonsmoke-exposed regular diet (n = 10), nonsmoke-exposed high-fat diet (n = 14), nonsmoke-exposed low-fat diet (n = 14), smoke-exposed regular diet (n = 10), smoke-exposed high-fat diet (n = 14), and smoke-exposed low-fat diet groups (n = 14). A full 2 3 factorial design was used to evaluate the effect of independent variables on smoke exposure and different rearing methods. Serum adiponectin and inflammatory cytokines were measured by the enzyme-linked immunosorbent assay (ELISA).

RESULTSSerum adiponectin levels in rats fed low-fat and regular diets exposed to smoke exposure were remarkably higher than that of rats exposed to room air while serum adiponectin levels of fat-rich diet rats exposed to tobacco smoke were lower than that of rats exposed to room air. Compared with regular diet or low-fat diet group, serum adiponectin levels in high-fat diet rats exposed to tobacco smoke were lower (t = 6.932, 11.026; all P < 0.001). BMI was inversely correlated with serum adiponectin levels (r = -0.751, P = 0.012). Serum interleukin 6 (IL-6), tumor necrosis factor-α (TNF-α), and 4-hydroxy 2-nonenal (HNE) levels in rats exposed to low-fat or fat-rich diets were remarkably higher than that of rats exposed to normal diets (IL-6, t = 4.196, 3.480; P < 0.01, P = 0.001; TNF-α, t = 4.286, 3.521; P < 0.01, P = 0.001; 4-HNE, t = 4.298, 4.316; all P < 0.001). In nonhigh-fat diet rats exposed to tobacco smoke, serum adiponectin levels correlated positively with serum IL-6, TNF-α, and 4-HNE, bronchoalveolar lavage cell count, and mean linear intercept. In contrast, in high-fat diet rats, serum adiponectin levels correlated inversely with these parameters.

CONCLUSIONSIn smoke-induced emphysema and fat-rich diet rat model, serum adiponectin level was decreased, and the anti-inflammatory effect was attenuated. By contrast, nonhigh-fat diet elevated serum adiponectin and enhanced the role of pro-inflammatory.