Pulmonary function tests, sputum induction, and bronchial provocation tests: diagnostic tools in the challenge of distinguishing asthma and COPD phenotypes in clinical practice

BACKGROUND

despite a number of important differences in the pathogenesis, course, and prognosis, asthma and chronic obstructive pulmonary disease (COPD) have many features in common. Furthermore, smoking induces considerable overlap in pathogenesis and clinical features between these conditions. This study aimed to reveal what inflammatory patterns prevail in clinically established diagnosis groups, including overlap phenotypes of asthma and COPD, and to evaluate the correlation with airway reversibility and hyperreactivity in these overlapping conditions.

METHODS

a total of 110 patients (17 healthy subjects; 16 "healthy" smokers; 46 asthma patients: 24 smokers and 22 non-smokers; and 31 COPD patients: 10 COPD patients with reversibility and 21 without) participated in the study. Induced sputum, reversibility testing, methacholine and adenosine 5'monophosphate (AMP) provocation challenges, and skin prick testing were performed. Airways inflammation was assessed by differential cell counts, and cytokines (interleukin-8 [IL-8] and tumor necrosis factor-alpha [TNF-α]) were measured in induced sputum by enzyme-linked immunosorbent assay (ELISA).

RESULTS

COPD patients with reversibility had increased sputum neutrophils, IL-8, and TNF-α levels compared to smoking asthmatics. No difference was found in inflammatory cells and cytokines between COPD subgroups. Sputum neutrophilia was inversely correlated with the change in forced expiratory volume in one second (ΔFEV(1)) in smoking asthmatic patients (r = -0.563, P = 0.036). No correlation was found between airway hyperresponsiveness (AHR), either with methacholine or AMP, and inflammation in asthmatic patients, regardless of smoking. Reversibility was not correlated with inflammation in COPD patients. However, the response to AMP challenge was correlated with sputum neutrophils (r = 0.844, P = 0.001).

CONCLUSION

although overlaps exist in the disease characteristics of asthma and COPD, the combination of lung function testing, sputum induction, and AHR reveals information that facilitates the distinction between these diseases, allowing clinicians to better tailor their therapy.

IL-18 in induced sputum and airway hyperresponsiveness in mild asthmatics: effect of smoking

Interleukin 18 (IL-18) is a pro-inflammatory cytokine, which has been shown to be implicated in the induction of airway hyperresponsiveness (AHR) in murine asthma models. The association of IL-18 with AHR in human bronchial asthma is not clear as yet. As cigarette smoking modifies airway inflammation we aimed to assess the relationship of IL-18 with airway hyperresponsiveness (AHR) in non-smoking versus smoking asthmatics. IL-18 was measured in sputum supernatants obtained from asthmatic (24 smokers and 22 non-smokers) and healthy subjects (16 smokers and 17 non-smokers). All subjects were assessed by spirometry, skin-prick tests to common aeroallergens and bronchial provocation to methacholine (Mch). There was no significant difference in IL-18 levels between healthy and asthmatic smokers and between healthy and asthmatic non-smokers. IL-18 levels in sputum were significantly lower in healthy smokers compared to non-smokers (p=0.048); similarly, in asthmatic smokers as compared to non-smokers (p=0.037). An inverse correlation was found between IL-18 levels, FEV(1) (% pred) (r=-0.495, p=0.043), and PD(20)Mc(h) in non-smoking asthmatics (r=-0.621, p=0.024). A positive correlation was found in smoking asthmatics between IL-18 levels in sputum and FEV(1) (% pred) (r=0.627, p=0.002), FVC (% pred) (r=0.460, p=0.031), and PD(20)Mc(h) (r=0.809, p=0.005). Cigarette smoking reduced IL-18 levels in induced sputum in healthy and asthmatic smokers. IL-18 levels were correlated with airway obstruction and AHR in an inverse way in smoking and non-smoking asthmatics. These results suggest the implication of IL-18 in airway hyperresponsiveness characterizing bronchial asthma, which is modified by smoking.

Regulation of the expression of soluble guanylyl cyclase by reactive oxygen species

BACKGROUND AND PURPOSE

Superoxide anions produced during vascular disease scavenge nitric oxide (NO), thereby reducing its biological activity. The aim of the present study was to investigate whether reactive oxygen species (ROS) have a direct effect on soluble guanylyl cyclase (sGC) subunit levels and function and to ascertain the mechanism(s) involved.

EXPERIMENTAL APPROACH

Rat aortic smooth muscle cells (RASM) or freshly isolated vessels were exposed to reactive oxygen species (ROS)-generating agents and sGC subunit expression was determined at the mRNA and/or protein level. cGMP accumulation was also determined in RASM exposed to ROS.

KEY RESULTS

Incubation of smooth muscle cells with H(2)O(2), xanthine/xanthine oxidase (X/XO) or menadione sodium bisulphite (MSB) significantly decreased protein levels of alpha1 and beta1 subunits of sGC and reduced SNP-induced cGMP formation. Similarly, sGC expression was reduced in freshly isolated vessels exposed to ROS-generating agents. The ROS-triggered inhibition of alpha1 and beta1 levels was not blocked by proteasome inhibitors, suggesting that decreased sGC protein was not due to protein degradation through this pathway. Real time RT-PCR analysis demonstrated a 68% reduction in steady state mRNA levels for the alpha1 subunit following exposure to H(2)O(2). In addition, alpha1 promoter-driven luciferase activity in RASM decreased by 60% after H(2)O(2) treatment.

CONCLUSION AND IMPLICATIONS

We conclude that oxidative stress triggers a decrease in sGC expression and activity that results from reduced sGC steady state mRNA levels. Altered sGC expression is expected to contribute to the changes in vascular tone and remodeling observed in diseases associated with ROS overproduction.

Interaction between the 90-kDa heat shock protein and soluble guanylyl cyclase: physiological significance and mapping of the domains mediating binding

The 90-kDa heat shock protein (hsp90) regulates the stability and function of many client proteins, including members of the NO-cGMP signaling pathway. Soluble guanylyl cyclase (sGC), an NO receptor, was recently reported to be an hsp90-interacting partner. In the present study, we show that hsp90 binds to both subunits of the most common sGC form (alpha(1)beta(1)) when these are expressed individually but only interacts with beta(1) in the heterodimeric form of the enzyme. Characterization of the region of hsp90 required to bind each subunit in immunoprecipitation experiments revealed that residues 310 to 456 of hsp90 interact with the sGC subunits. The region of beta(1) responsible for binding to hsp90beta was mapped using in vitro binding assays and immunoprecipitation experiments and was found to lie in the regulatory domain. The physiological importance of the hsp90/sGC interaction was investigated by treating rat smooth muscle cells with the hsp90 inhibitors radicicol and geldanamycin (GA) and determining both sGC activity and protein levels. Long-term (24 or 48 h) inhibition of hsp90 resulted in a strong decrease of both alpha(1) and beta(1) protein levels and sGC activity. Moreover, incubation of smooth muscle cells with the proteasome inhibitor N-benzoyloxycarbonyl (Z)-Leu-Leu-leucinal (MG132) blocked the GA-induced down-regulation of sGC. We conclude that the N-terminal region of the beta(1) subunit mediates binding of the heterodimeric form of sGC to hsp90 and that this interaction involves the M domain of hsp90. Hsp90 binding to sGC regulates the pool of active enzymes by affecting the protein levels of the two subunits.

On the structural and functional importance of the highly conserved Glu56 of Thermus thermophilus L4 ribosomal protein

The structural and functional importance of the highly conserved amino acid residue glutamic acid 56 (Glu56) of the ribosomal protein L4 from Thermus thermophilus (TthL4) has been investigated by replacing this residue by alanine or glutamine, and by incorporating the resulted mutants into Escherichia coli ribosomes. The catalytic properties of peptidyltransferase estimated for the mutants as well as for the wild-type TthL4 by the puromycin reaction, were quite different. The binding of tRNA to the P and A-site was affected. In addition, replacement of the native L4 protein by wild-type TthL4 or by TthL4-Ala56 mutant resulted in reduced capability of 50S subunits for association with 30S subunits. In contrast, neither the assembly of the 50S subunits nor the fixation of the tRNA 3'-end at the P or A-site was affected. These results are used to discuss critically the hypothesis that the delta-carboxyl group of the highly conserved Glu56 is essential for stabilizing a flexible loop of L4, which extended into the ribosome interior region, influences the mechanism of peptide bond formation. Mutations concerning the semi-conserved glycine 55 (Gly55) were investigated. Replacement of Gly55 by serine did not affect the measured functions. In contrast, replacement of Gly55 by alanine resulted in enhanced peptidyltransferase activity and increased tRNA affinity for the P and A-sites, indicating a possible implication of this amino acid in the local loop conformation of TthL4.