In addition to the overall degree and pattern of protein oxidation, surfactant protein A (SP-A) was investigated as an example of a lung-specific protein. We demonstrated that SP-A was readily oxidized, as it was found heavily labeled even in CF patients with a very low degree of oxidation (n = 3; mean overall BALF carbonyls, 18 pmol/mL) [Fig 5]. In all samples with higher degrees of oxidation (n = 5; mean overall BALF carbonyls, 9,050 pmol/mL), SP-A was undetectable or present only at extremely low amounts.
CF patients had significantly higher level of oxidative stress than control subjects, as assessed by protein oxidation from the content of protein carbonyls in their BALF. The highest levels were found in patients with pathologic pulmonary function or with highly elevated neutrophil counts. Compared to control subjects without lung disease, CF patients with normal lung function, defined as FEV1 > 80% of predicted, also had significantly higher protein carbonyl levels.
These data show direct a strong association between increased oxidative stress in the lungs and lung function of these patients with CF. The data support the hypothesis that an abundance of ROS may be a major contributor to the progressive pulmonary damage observed in CF patients. Our findings are consistent with the excessive PMN infiltration in the lungs of CF patients. The relevance of the PMN infiltration for the oxidative damage to proteins is suggested by our observations that the level of protein carbonyls strongly correlated with the number of PMNs in BALF, and that the oxidative damage was higher in the groups with a higher neutrophil counts. review
Several lines of evidence suggest that CF patients have inadequate antioxidant defenses to cope with the elevated oxidative stress that they regularly experience. Patients with CF have an impaired absorption of antioxidant nutrients, resulting in lower levels of antioxidants together with increased oxidative stress caused by chronic pulmonary infections. Specifically in the lungs decreased levels of reduced glutathione in the epithelial lining fluid have been linked to an impaired export of glutathione by the epithelial cells due to lack of CF conductance regulator.
Figure 5. Oxidation of SP-A in CF. Western blot of BAL sample from a CF patient with low BALF neutrophil count (1.5%). SP-A was substantially modified by oxidation identified by anti-DNPH immunostaining (right panel) and anti-SP-A immunostaining (left panel) after stripping of the blot (no signal was detected before the second staining). MW = molecular weight.