OBJECTIVETo optimize the experimental model of nitric oxide (NO) production in mouse peritoneal macrophages in response to lipopolysaccharides (LPS) stimulation.

METHODSMouse resident peritoneal macrophages were collected by lavaging the peritoneal cavity of mice with Hank's solution and stimulated with Pseudomonas aeruginosa LPS for NO production. NO concentration in the culture supernatants was measured with Griess Reagent. The influences of cell density, LPS concentration, LPS stimulation duration and culture medium volume on NO production were investigated. Finally, the feasibility of the model was confirmed with specific anti-inflammatory drugs.

RESULTSThe density of macrophages produced the most significant effect on NO production (P<0.001), and optimal results were obtained at the macrophage density of 6×10(6) cells/ml with a volume of 100 µl in each well in 96-well plate. At a LPS concentration below 1 µg/ml, NO production increased proportionally with the increment of LPS concentration (P<0.001), but the increment of NO production declined obviously at LPS concentrations beyond 1 µg/ml, and the peak NO production occurred at a LPS concentration of 10 µg/ml. NO production also increased significantly with the prolongation of LPS stimulation (P<0.05), and the increments were greater within 24-48 h than those in 48-72 h. NO content in the culture supernatant was associated with the medium volume, and the highest level occurred in a system volume of 100 µl. Aspirin (1 mmol/L), dexamethasone (10 µmol/L), and cyclosporin A (10 µmol/L) all significantly inhibited LPS-stimulated production of NO in mouse resident peritoneal macrophages (P<0.001).

CONCLUSIONSMacrophage density, LPS concentration, and the duration of LPS stimulation are the main factors affecting LPS-stimulated NO production in mouse resident peritoneal macrophages. The optimal results can be obtained with a macrophage density of 5×10(6) cells/ml (100 µl per well), LPS concentration of 10 µg/ml, LPS stimulation duration of 24 h or 48 h, and a culture medium volume of 100 to 200 µl.