Hyperbaric oxygen and hypoxia alter production of nitric oxide by J774 murine macrophages

Abstract

Improvements in rates of healing of wounds and bacterial clearance in infected tissue during intermittent exposure to hyperbaric oxygen (HBO) have been documented. Increased bacterial clearance may partly stem from changes in production of nitric oxide (NO) by resident macrophages (M(D) in wounds while exposed to increased oxygen tensions that occur during HBO treatments. This theory was tested using the murine M[] cell line J774, stimulated with gamma-interferon (y-INF) and lipopolysaccharide (LPS). Production of nitric oxide was assayed spectrophotometrically by determining concentrations of nitrite in cellular supernatant. Results were expressed as [LM nitrite concentration and as the percent change of nitrite concentration from control (no HBO), within each experiment. Control cells, incubated in P02 20mmHg or 40mmHg, produced significantly (P < 0.0001) less NO, ([] respectively), than did cells exposed to 95% room air (RA), 5% C02-Cells incubated in P02 = 20mmHg or 40mmHg, and intermittently exposed to HBO (12 PSIg), significantly (P < 0.0001) increased production of NO when compared to their untreated control cells, ([], respectively). Cells incubated in 957o RA and treated with HBO showed little increase in production of NO, (1 1.4 ︢11.47o), when compared to control cells. There was no significant difference in production of NO when comparing HBO-treated cells that were incubated with different oxygen tensions; however, cells that were incubated with P02 = 20mmHg and treated with HBO produced slightly more NO, 13.5 ︢9.2%, than did HBO-treated cells that were incubated with 95% RA. These data show that, 1) J774 murine M[] exposed to relatively low oxygen tensions, produce less NO than do those which are incubated in 95% room air, and that, 2) production of NO is augmented when these cells are intermittently exposed to HBO. Further research will determine if hypoxia serves concomitantly with other factors to increase production of NO in this model. Intermittent HBO therapy may alter production of NO by M[] in wounds.