Smoking and adipose tissue inflammation suppress leptin expression in Japanese obese males: potential mechanism of resistance to weight loss among Japanese obese smokers

Abstract

Background: The effect of smoking on leptin regulation is controversial. Smoking may induce low-grade inflammation. Recent series of studies indicated the critical role of macrophage migration in the establishment of adipose tissue inflammation. In this study, we aimed to see the effects of smoking and inflammation on leptin regulation both at cellular and epidemiological levels.

Methods: We compared the concentration of inflammatory markers and serum leptin levels among Japanese male subjects. Additionally, leptin and intercellular adhesion molecule (ICAM) -1 gene expression was assessed in adipocytes co-cultured with or without macrophages in the presence or absence of nicotine and/or lipopolysaccharide (LPS).

Results: In subjects with BMI below 25 kg/m2, both WBC counts and soluble-ICAM-1 levels are significantly higher in smokers than in non-smokers. However, leptin concentration did not differ according to smoking status. However, in subjects with BMI over 25 kg/m2, smokers exhibited significantly lower serum leptin level as well as higher WBC counts and s-ICAM-1 concentration as compared with non-smokers. Leptin gene expression was markedly suppressed in adipocytes co-cultured with macrophages than in adipocyte culture alone. Furthermore, nicotine further suppressed leptin gene expression. ICAM-1 gene expression was markedly up-regulated in adipocytes co-cultured with macrophages when stimulated with LPS.

Conclusions: Adipose tissue inflammation appears to down-regulate leptin expression in adipose tissues. Nicotine further suppresses leptin expression. Thus, both smoking and inflammation may diminish leptin effect in obese subjects. Therefore, obese, but not normal weight, smokers might be more resistant to weight loss than non-smokers.

Figure 1

ICAM-1 gene expression in adipocytes co-cultured with macrophages with (black bar) or without (white bar) LPS stimulation. ICAM-1 gene expression was evaluated by real-time PCR, and the data are expressed as fold change of the levels at 0 h. *p < 0.05.

Figure 2

Leptin gene expression in adipocytes without co-culture (white bar), co-cultured with macrophages (gray bar), and co-cultured with macrophages in the presence of 1 ng/ml of LPS. Leptin gene expression was evaluated by real-time PCR. The data are expressed as fold changes of baseline data (expression at 0 h). *p < 0.05, **p < 0.001.

Figure 3

Leptin gene expression in adipocytes single culture without nicotine (white bar) or with nicotine (pale gray bar), and in adipocytes co-cultured with macrophages in the absence of nicotine (dark gray bar) and in the presence of nicotine (black bar). (A) One μM of nicotine was used for experiments. Co-culture with macrophages greatly suppressed leptin gene expression in adipocytes. Addition of nicotine further suppressed leptin gene expression after 12 h of stimulation. The data are expressed as fold changes of baseline data (expression at 0 h). *p < 0.05, **p < 0.001. (B) Hundred μM of nicotine was used for the experiments. In this condition, nicotine further suppressed leptin gene expression at 8 h after nicotine stimulation which was markedly suppressed when the adipocytes were co-cultured with macrophages. However, nicotine did not directly suppress leptin gene expression in adipocytes. The data are expressed as fold changes of baseline data (expression at 0 h). *p < 0.05, **p < 0.001.