Post-lung transplant bronchiolitis obliterans syndrome (BOS) is characterized by increased exhaled nitric oxide levels and epithelial inducible nitric oxide synthase

In conditions characterized by airway inflammation, exhaled nitric oxide (e NO) levels are increased. Post-lung transplant bronchiolitis obliterans syn drome (BOS) is characterized by airway inflammation and development of prog ressive airway narrowing and fibrosis. We have previously shown that In sta ble lung transplant recipients (LTR), mean eNO levels were not elevated but were still related to the degree of airway neutrophilia within the group. The hypothesis now tested is that in BOS, eNO levels are increased in assoc iation with even greater airway neutrophilia and enhanced expression of ind ucible (iNOS) nitric oxide synthase in the bronchial epithelium. We determi ned eNO levels in 40 LTR in four groups: well and "stable": LTR (n = 20), B OS (n = 8), bacterial airway infection (Br, n = 6), and acute rejection (AR , n = 6). Following bronchoscopic sampling, we performed a quantitative ass essment of iNOS and constitutive nitric oxide synthase (cNOS) expression in endobronchial biopsies by immunohistochemistry. Mean +/- SEM eNO levels in BOS and BI were significantly higher than in stable LTR (20 +/- 1.2 parts per billion [ppb] and 24.7 +/- 1.7 ppb versus 12.5 +/- 0.9 ppb; p < 0.01. f or both). In AR, eNO levels (13.4 ppb +/- 0.5) were not different in stable LTR (p = 0.34). When compared with stable LTR, there was Increased express ion of iNOS in the bronchial epithelium and generally in the lamina propria (LP) in patients with BOS and BI. In AR, iNOS expression was increased but only in the LP in a perivascular distribution. Expression of cNOS was redu ced in BOS but not in BI and AR compared with the stable group. Using regre ssion analysis, only iNOS expression in the bronchial epithelium (r(2) = 0. 77; p < 0.0001) and %BAL neutrophils (r(2) = 0.79; p < 0.0001) were positiv ely related to eNO in stable LTR and BOS. We conclude that epithelial iNOS appears to be the major source of eNO. Exhaled NO levels also appear to ref lect the degree of airway neutrophilia in both stable LTR and BOS groups. T his suggests that serial eNO measurements may be able to predict the early development of BOS.