Neutrophils from asthmatics exhibit diminished responsiveness to 2-chloroadenosine which is reversed by theophylline. Evidence for a cyclic-AMP-independent pathway on human neutrophils

Theophylline's effect on neutrophil function and the late asthmatic response

BACKGROUND

The decrement in lung function associated with the late asthmatic response after allergen challenge is believed to be mediated by an inflammatory response in the airways. Theophylline has been shown to inhibit the late asthmatic response, but the mechanisms are not clear.

OBJECTIVE

The study was designed to determine whether theophylline would inhibit the late asthmatic response by reducing neutrophil activation and subsequent superoxide production.

METHODS

Twelve subjects with asthma underwent treatment in this double-blind, randomized, crossover study. Each subject received theophylline and placebo in random order in two treatment periods of 3 weeks each. Each treatment period was followed by an allergen challenge and blood neutrophil function analysis.

RESULTS

At therapeutic levels theophylline increased FEV1 at baseline and during the allergen challenge and increased the percentage suppression of neutrophil superoxide production by adenosine.

CONCLUSION

Theophylline improved pulmonary function at baseline and during an allergen challenge, in part perhaps, by increasing the neutrophil's response to feedback inhibition by adenosine. However, theophylline did not decrease the severity and duration of the late asthmatic response.

Anti-inflammatory effects of theophylline: modulation of cytokine production

BACKGROUND

The basis for the efficacy of theophylline in the treatment of asthma remains enigmatic. Although commonly classified as a bronchodilator, its ability to dilate smooth muscle is considered fairly poor and clinical responses are often independent of bronchodilation. Recent studies have suggested that immunomodulatory activities may contribute to the therapeutic benefit mediated by theophylline.

OBJECTIVE

We performed these preliminary studies to determine whether theophylline modulates cytokine production by peripheral blood mononuclear cells.

METHODS

Peripheral blood mononuclear cells were obtained from 24 asthmatic subjects and were left in a resting state or stimulated with either mitogens (phytohemagglutinin, lipopolysaccharide) or antigen (tetanus, cat) with or without the additional presence of theophylline (15 micrograms/dL). Supernatants were collected and evaluated for cytokine concentration by ELISA.

RESULTS

Theophylline neither inhibited production of allergenic cytokines such as IL-4 nor modulated the repertoire of cytokines produced by TH cells. A statistically significant inhibition of spontaneous interferon-gamma synthesis was observed (24.5 +/- 8.6 to 13.4 +/- 4.2; P < .05). Theophylline did have anti-inflammatory effects on cytokines primarily produced by mononuclear phagocytic cells. Theophylline mediated a slight inhibition of TNF-alpha production (0.26 +/- 0.08 to 0.21 +/- 0.06; P < .05). Theophylline was also associated with a 2.8-fold increase in spontaneous production of the anti-inflammatory cytokine IL-10 (0.35 +/- 0.08 to 0.98 +/- 0.16 ng; P < .01).

CONCLUSIONS

A relative absence of IL-10 characterizes the asthmatic airways and may contribute to the development and severity of allergic inflammation. Induction of IL-10 production by theophylline may therefore mitigate inflammation and contribute to the clinical efficacy of this class of medications.

Activities of superoxide dismutases and NADPH oxidase in neutrophils obtained from asthmatic and normal donors

PMN obtained from asthmatic subjects demonstrate a heightened respiratory burst with increased superoxide generation compared to normals. This enhanced superoxide anion generation could be secondary to increased activity of the respiratory burst NADPH oxidase or diminished metabolism of superoxide via superoxide dismutase (SOD). The two forms of SOD expressed in PMN, CuZnSOD expressed constitutively in the cytosol and inducible mitochondrial MnSOD, were investigated in asthmatics. Resting PMN from asthmatics (N = 9) contained significantly less MnSOD activity compared to controls (0.46 +/- 0.16 vs. 0.79 +/- 0.17 units/10(7) PMN, respectively; P = 0.0002). As several cytokines including interleukins (IL) -1, -4, and -6 as well as granulocyte macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF) enhance the PMN respiratory burst and are synthesized in the asthmatic lung, their effects on PMN MnSOD activity were assayed. In contrast to its effects on lymphocytes, both IL-1 and IL-6 significantly inhibited in a dose-dependent fashion the induction of MnSOD in PMN from normals (0.42 +/- 0.12 and 0.45 +/- 0.05 units/10(7) PMN, respectively, at 10 units/ml of each cytokine; P = 0.02 compared to resting cells) but failed to further modulate MnSOD production in asthmatic PMN. IL-4 and GM-CSF had no effect on MnSOD production, and TNF effects could not be studied because of its effects on cell viability. There were no differences in the activity of CuZnSOD (N = 9) or NADPH oxidase (N = 4) in the two groups. Inhibition of MnSOD activity in PMN secondary to cytokine exposure in the asthmatic lung could explain, at least in part, the increased generation of superoxide from PMN obtained from asthmatics. This would promote the presence and severity of inflammation in the asthmatic lung. These data further support a role for IL-1 and IL-6 in allergic inflammation.