Magnesium attenuates the neutrophil respiratory burst in adult asthmatic patients

Introduction: IV magnesium (Mg²⁺) has been proposed as an emergent treatment for acute asthma exacerbations. Recent studies have focused on the effects of Mg²⁺ on bronchial smooth muscle, yet asthma is primarily an inflammatory disease. Objective: To assess the effects of Mg²⁺ on the neutrophil respiratory burst of adult patients with asthma. Methods: A prospective, blind study of volunteer adult asthmatic patients was performed. The patients' polymorphonuclear neutrophils (PMNs) were isolated, purified, and placed into phosphate-buffered saline with the following test conditions: concentrations of magnesium chloride (MgCl₂) added: 0 mmol MgCl₂, 1 mmol MgCl₂ (low), and 10 mmol MgCl₂ (high) both with and without the calcium (Ca²⁺) ionophore A23187 (0.1 mmol). PMNs were activated using N-formyl- methionyl-leucyl-phenylalanine (fMLP) (10 μmol), and the production of superoxide (O₂/^-) was measured by the spectrophotometric reduction of cytochrome c. Results: Mg²⁺ reduced activated PMN O₂/^- production compared with that for no Mg²⁺ (1.0 ± 0.1 nmol O₂/^-/5 x 10⁵ PMN/min) in both low (-0.52* ± 0.3 nmol O₂/^-/5 x 10⁵ PMN/min) and high (-0.76* ± 0.3 nmol O₂/^-/5 x 10⁵ PMN/min; *p < 0.05) concentrations. The addition of A23187 increased O₂/^- production in both the high (0.53* ± 0.02 nmol O₂/^-/5 x 10⁵ PMN/min) and the low (1.5* ± 0.6 nmol O₂/^-/5 x 10⁵ PMN/min) Mg²⁺ groups, with no change in the control group (1.2 ± 0.2 nmol O₂/^-/10⁵ PMN/min). Conclusions: In clinically relevant concentrations, Mg²⁺ attenuates the neutrophil respiratory burst in adult asthmatic patients. Mg²⁺ appears to affect PMNs by interfering with extracellular Ca²⁺ influx. Mg²⁺ may have a beneficial anti-inflammatory effect in asthmatic individuals.