COPD is a leading cause of morbidity and mortality, the main causative agent being cigarette smoke. Cessation of smoking is currently the only way to slow disease progression (Culpitt et al, 2000). We have previously shown that cigarette smoke extract (CSE) is capable of initiating release of IL-8 from THP-1 monocytes and that it synergises with IL-1β in chemokine release (Walters et al, 2003). In asthma, corticosteroids are the gold standard therapy to treat airway inflammation. However, in COPD, steroids are ineffective. In order to understand this phenomenon, we have compared the effects of a range of steroids on IL-8 release by THP-1 monocytes stimulated with CSE and and/or IL-1β.

Briefly CSE was made by bubbling mainstream cigarette smoke from 4 Marlboro cigarettes into 100ml RPMI 1640. This was then filter sterilised and diluted with non-smoked medium to the desired concentration (Walters and Mitchell, 2003). THP-1 monocytes were plated in 96-well plates and incubated in RPMI 1640 containing FCS (2%). Cells were treated with the following steroids for 2 hours hydrocortisone, budesonide, prednisolone, dexamethasone or hydrocortisone. Cells were then stimulated by the addition of CSE (10%, see Walters and Mitchell, 2002), IL-1β (1ng/ml) or the combination of CSE plus IL-1β for 24 hours. IL-8 was then measured using ELISA.

Figure 1                                                                  Figure2

Figure 3

Effect of dexamethasone (Dex, □), prednisolone (Pred, ■), budesonide (Bud, ○) or hydrocortisone (Hydro, ●) on smoke (CSE; 10%; Figure 1), IL-1β (Figure 2) or CSE plus IL-1β (1ng/ml), (Figure 3). Results are the mean ± S.E.M. for n=8-16 wells from 4-8 experimental days. *p<0.05; one sample t-test for normalised data.

Release of IL-8 by THP-1 cells in medium alone low (30±3.3 pg/ml). CSE (10%), IL-1β (1ng/ml) or the combination of IL-1β plus CSE increased IL-8 release to 130±22 pg/ml, 230±36 pg/ml and 582±44 pg/ml respectively. Each steroid tested induced concentration related inhibitions of IL-8 release stimulated by CSE. By contrast, steroids were unable to effectively inhibit IL-8 release induced by IL-1β pr IL-1β plus CSE.

CSE induced IL-8 release is exquisitely sensitive to inhibition by a range of steroids. However, when CSE is present together with IL-1β, a situation likely to occur in the lungs of smokers, IL-8 release is steroid insensitive. The molecular mechanisms responsible for steroid resistance in this system remain the subject of investigation.

Culpitt S., et al (2000) Expert Opin Pharmacother, 1(5), 1007-20
Walters M.J, et al (2003) Brit. J. Pharmcol ,138, 44P