Impaired Nitric Oxide Synthetase Activity in Primary Ciliary Dyskinesia-Data-Driven Hypothesis

Abstract

Low nasal nitric oxide (nNO) is a typical feature of Primary Ciliary Dyskinesia (PCD). nNO is part of the PCD diagnostic algorithm due to its discriminative power against other lung diseases, such as cystic fibrosis (CF). However, the underlying pathomechanisms are elusive. To better understand NO dysregulation in PCD, the L-arginine/NO (Arg/NO) pathway in patients with PCD (pwPCD) and CF (pwCF) and in healthy control (HC) subjects was investigated. In a prospective, controlled study, we measured in 24 pwPCD, 25 age-matched pwCF, and 14 HC the concentrations of the NO precursors Arg and homoarginine (hArg), the arginase metabolite ornithine (Orn), the NO inhibitor asymmetric dimethylarginine (ADMA), and the major NO metabolites (nitrate, nitrite) in sputum, plasma, and urine using validated methods. In comparison to HC, the sputum contents (in µmol/mg) of L-Arg (PCD 18.43 vs. CF 329.46 vs. HC 9.86, p < 0.001) and of ADMA (PCD 0.055 vs. CF 0.015 vs. HC 0.010, p < 0.001) were higher. In contrast, the sputum contents (in µmol/mg) of nitrate and nitrite were lower in PCD compared to HC (nitrite 4.54 vs. 9.26, p = 0.023; nitrate 12.86 vs. 40.33, p = 0.008), but higher in CF (nitrite 16.28, p < 0.001; nitrate 56.83, p = 0.002). The metabolite concentrations in urine and plasma were similar in all groups. The results of our study indicate that PCD, unlike CF, is associated with impaired NO synthesis in the lung, presumably due to mechano-chemical uncoupling.

Keywords: L-arginine; cystic fibrosis; nitric oxide; nitric oxide synthetase; primary ciliary dyskinesia.

Figure 1

Flow chart of the recruitment process of the study. *¹Age of one patient below 10 (9.7 years) due to false age information at the time of recruitment. *³ One patient mistakenly gave consent twice. Patient data were collected and included only once.

Figure 2

Concentrations of (A) nasal nitric oxide (nNO, nL/min) and of its metabolites nitrite (B) and nitrate (C) in sputum (µmol/mg sputum) of patients with PCD (light grey) or CF (dark grey) and of healthy controls (HC, white). * = Significance PCD vs. CF, # = Significance PCD vs. HC, + = Significance CF vs. HC.

Figure 3

Simplified schematic showing differences in L-Arg/NO pathway in the sputum in PCD (light grey) or CF (dark grey) in comparison to a healthy state. Modified according to Grasemann et al. [30]. Arrows indicate higher or lower. * = Significance PCD vs. CF, # = Significance PCD vs. HC, + = Significance CF vs. HC. Abbreviations. ADMA, asymmetric dimethylarginine; ADC, arginine decarboxylase; AGMAT, agmatinase; BH₄, tetrahydrobiopterin; DDAH, dimethylarginine dimethylaminohydrolase; NO, nitric oxide; NOS, nitric oxide synthetase; OAT, ornithine aminotransferase; ODC1, ornithine decarboxylase; PRMTs, protein arginine N-methyltransferases; RARS, arginyl-tRNA-synthetase.