Interaction between lung surfactant and nitric oxide production by alveolar macrophages stimulated by group B streptococci.

The major etiologic agent in neonatal pneumonia and meningitis is group B streptococci (GBS). Nitric oxide (NO) production by alveolar macrophages (AM) in response to Gram-positive bacteria such as GBS and the effect of surfactant on this production have received little attention. We studied production of NO by GBS-stimulated AM using the Griess reaction, the effect of lung surfactant on this NO production, and the possible lipid peroxidation (LPO) of surfactant caused by NO. The LPO test was used to measure surfactant peroxidation. Heat-killed and live GBS were found to stimulate NO production by rat alveolar macrophages, and the presence of interferon gamma (IFN-gamma) increased this stimulation in a synergistic manner. Curosurf(R), the natural surfactant used in our study, significantly reduced NO production in various sets of experiments. Lipid peroxidation of surfactant was noted when NO was produced by stimulated AM, a phenomenon that could be suppressed by NG-monomethyl L-arginine (L-NMMA), the inhibitor of NO synthase. In the lung of GBS-infected neonates, nitric oxide produced by AM might contribute to the destruction of surfactant caused by inflammatory cells. Pediatr Pulmonol. 2000; 30:106- 113.

Phagocyte-induced lipid peroxidation of lung surfactant.

Surfactant therapy is given routinely to premature newborns with respiratory failure. However, alterations in surfactants have been shown to be a significant factor in some forms of respiratory failure in newborns in animal models of lung injury. To investigate whether antioxidant supplementation might help to protect exogenous surfactant from damage by oxygen free radicals, we examined the influence of vitamin E in combination with surfactant on superoxide production as estimated by the nitroblue tetrazolium reduction test, and measured surfactant peroxidation with a new colorimetric method with or without addition of superoxide dismutase (SOD) or vitamin E. Our results showed that surfactant interacts with free radicals; surfactant reduced superoxide production by neutrophils and was peroxidized when incubated with resting and with stimulated cells. Vitamin E supplementation decreased superoxide radical production and in a dose-dependent manner decreased surfactant peroxidation. The decrease in lipid peroxidation by SOD was not significant. These findings suggest that phagocytes induce lipid peroxidation of lung surfactant, a reaction that might be prevented by antioxidants.

Lipid peroxidation of lung surfactant by bacteria.

The epithelium of the lung is lined with extracellular pulmonary surfactant. This is the surface that invading bacteria first come into contact with when they enter the alveoli. As bacteria become established and interact with this layer, various characteristics of surfactant may become altered. We studied free radical production by three bacterial species, group B streptococci, Escherichia coli, and Pseudomonas aeruginosa, as well as the effect of two concentrations of lung surfactant (Curosurf at 0.04 and 0.4 mg/ml) on this production estimated by the nitro blue tetrazolium reduction test. We also measured the lipid peroxidation of surfactant at various incubation times (0-20 h), using a LPO-586 test kit. In addition, the effect of vitamin E as an antioxidant in a concentration of 0.5 microM was determined by the lipid peroxidation test. We found that the nitro blue tetrazolium reduction by the three bacterial species and lipid peroxidation of lung surfactant increased with time. Vitamin E reduced the lipid peroxidation of this surfactant. By measuring bacterial growth at various incubation times we showed that lung surfactant was bactericidal to group B streptococcal and E. coli strains and that P. aeruginosa strains were resistant to surfactant. We conclude that bacteria, probably by their production of reactive oxygen species, cause lipid peroxidation of lung surfactant.

Lipid peroxidation of lung surfactant in experimental neonatal group B streptococcal pneumonia.

Group B streptococcal (GBS) pneumonia, with neutrophilic granulocytes immigrating into the lungs, may occur in neonates. The incidence is particularly high among preterm infants, who often are treated with exogenous surfactant. We have previously demonstrated in vitro that neutrophils stimulated by GBS cause lipid peroxidation (LPO) and functional impairment of lung surfactant. The present study aimed at evaluating LPO of exogenous lung surfactant (Curosurf) and the protective effect of the natural antioxidant, vitamin E in immature ventilated newborn rabbits with experimental neonatal GBS pneumonia. There was a prominent proliferation of GBS in the lungs of animals treated with surfactant and ventilated for 5 h. GBS-infected rabbits had a higher LPO of lung lavage fluid than non-infected ones. The LPO could be diminished using vitamin E, which, however, did not affect bacterial proliferation. During the 5-h incubation period, mean lung-thorax compliance values were significantly lower in GBS-infected than in noninfected animals. We speculate that addition of vitamin E to exogenous surfactant preparations may improve their resistance to LPO and make them more suitable for treatment of neonates with pneumonia.

Direct and phagocyte-mediated lipid peroxidation of lung surfactant by group B streptococci.

In newborn infants, group B streptococci (GBS) often cause pneumonia, with polymorphonuclear leukocytes (PMN) migrating into the lungs. Because surfactant therapy may be needed in such patients, we evaluated the interaction between GBS or GBS-stimulated PMN and a surfactant preparation (Curosurf) in vitro. The superoxide production of GBS strains or GBS-activated PMN was measured, using the nitroblue tetrazolium (NBT) test and the subsequent lipid peroxidation (LPO) as the content of malondialdehyde (MDA) and 4-hydroxyalkenals (4-HNE). The growth of GBS in surfactant was determined and related to the LPO. Finally, the effect of LPO on surfactant activity, caused by GBS-stimulated PMN, was assessed by measuring dynamic surface tension in a pulsating bubble surfactometer. Curosurf diminished the NBT reduction by both live GBS and GBS-stimulated PMN. Surfactant was peroxidized by reactive oxygen species (ROS) from both GBS and GBS-stimulated PMN in a time-dependent manner. Vitamin E significantly reduced the peroxidation level of surfactant in both cases. Surfactant peroxidation was associated with a reduction in the number of live bacteria. The biophysical activity of Curosurf was impaired by GBS-stimulated PMN, as reflected by increased minimum surface tension during cyclic compression. These findings indicate that Curosurf undergoes LPO by ROS produced by GBS and/or PMN. We speculate that exogenous surfactant preparations should be supplemented with vitamin E or another antioxidant, when given to infants with GBS pneumonia.

Lipid peroxidation caused by oxygen radicals from Fusobacterium-stimulated neutrophils as a possible model for the emergence of periodontitis.

OBJECTIVE: The possible contribution of bacteria and polymorphonuclear neutrophils (PMN) to the disease process of periodontitis was evaluated. DESIGN: Fusobacterium nucleatum has been associated with chronic adult periodontitis. Intracellular production and extracellular release of reactive oxygen species (ROS) by PMN stimulated by fusobacteria were evaluated. To estimate the potential extracellular damage that might be caused by the ROS, the lipid peroxidation (LPO) of an exogenous phospholipid, Intralipid, was assayed. METHODS: The ROS production of PMN was studied by the nitroblue tetrazolium and chemiluminescence tests. The levels of malonaldehyde (MDA) and 4-hydroxyalkenals were used to indicate LPO. RESULTS: Fusobacterium nucleatum strains stimulated neutrophils to produce a large amount of ROS, independently of plasma complement factors. The two strains tested induced considerable intracellular, but no extracellular chemiluminescence responses during the first hour, indicating that ROS were released into phagosomes. However an incubation period of 4 h, in the presence of the extracellular lipid resulted in a high degree of LPO, presumably caused by ROS release from the Fusobacterium-stimulated PMN. ROS production and lipid peroxidation could be counteracted by vitamin E. CONCLUSION: In periodontitis local bacteria might stimulate PMN to release ROS, which cause inflammation and destruction.