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Relationship: 2451


The title of the KER should clearly define the two KEs being considered and the sequential relationship between them (i.e., which is upstream and which is downstream). Consequently all KER titles take the form “upstream KE leads to downstream KE”.  More help

Oxidative Stress leads to CBF, Decreased

Upstream event
Upstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help
Downstream event
Downstream event in the Key Event Relationship. On the KER page, clicking on the Event name under Upstream Relationship will bring the user to that individual KE page. More help

Key Event Relationship Overview

The utility of AOPs for regulatory application is defined, to a large extent, by the confidence and precision with which they facilitate extrapolation of data measured at low levels of biological organisation to predicted outcomes at higher levels of organisation and the extent to which they can link biological effect measurements to their specific causes. Within the AOP framework, the predictive relationships that facilitate extrapolation are represented by the KERs. Consequently, the overall WoE for an AOP is a reflection in part, of the level of confidence in the underlying series of KERs it encompasses. Therefore, describing the KERs in an AOP involves assembling and organising the types of information and evidence that defines the scientific basis for inferring the probable change in, or state of, a downstream KE from the known or measured state of an upstream KE. More help

AOPs Referencing Relationship

This table is automatically generated upon addition of a KER to an AOP. All of the AOPs that are linked to this KER will automatically be listed in this subsection. Clicking on the name of the AOP in the table will bring you to the individual page for that AOP. More help
AOP Name Adjacency Weight of Evidence Quantitative Understanding Point of Contact Author Status OECD Status
Oxidative stress Leading to Decreased Lung Function adjacent High High Karsta Luettich (send email) Open for comment. Do not cite

Taxonomic Applicability

Select one or more structured terms that help to define the biological applicability domain of the KER. In general, this will be dictated by the more restrictive of the two KEs being linked together by the KER. Authors can indicate the relevant taxa for this KER in this subsection. The process is similar to what is described for KEs (see pages 30-31 and 37-38 of User Handbook) More help
Term Scientific Term Evidence Link
Homo sapiens Homo sapiens High NCBI
Cavia porcellus Cavia porcellus NCBI
Oryctolagus cuniculus Oryctolagus cuniculus NCBI
Bos taurus Bos taurus NCBI

Sex Applicability

Authors can indicate the relevant sex for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of the User Handbook). More help
Sex Evidence

Life Stage Applicability

Authors can indicate the relevant life stage for this KER in this subsection. The process is similar to what is described for KEs (see pages 31-32 of User Handbook). More help
Term Evidence
All life stages

Key Event Relationship Description

Provide a brief, descriptive summation of the KER. While the title itself is fairly descriptive, this section can provide details that aren’t inherent in the description of the KEs themselves (see page 39 of the User Handbook). This description section can be viewed as providing the increased specificity in the nature of upstream perturbation (KEupstream) that leads to a particular downstream perturbation (KEdownstream), while allowing the KE descriptions to remain generalised so they can be linked to different AOPs. The description is also intended to provide a concise overview for readers who may want a brief summation, without needing to read through the detailed support for the relationship (covered below). Careful attention should be taken to avoid reference to other KEs that are not part of this KER, other KERs or other AOPs. This will ensure that the KER is modular and can be used by other AOPs. More help

Because the lung interfaces with the external environment, it is frequently exposed to airborne oxidant gases and particulates, and thus prone to oxidant-mediated cellular damage (Ciencewicki et al., 2008). Oxidant stress—through the action of exogenous and endogenous free radicals, such as super oxides, hydroxyl radicals, and hydrogen peroxides—is a common factor in lung inflammation and various respiratory diseases. The presence of redox-sensitive proteins in motile cilia suggests that oxidant stresses may impact ciliary function negatively (Price and Sisson, 2019). Indeed, exposure of human or rodent ciliated airway epithelial cells to hydrogen peroxide, acetaldehyde, ozone or cigarette smoke—all of which are known to cause oxidative stress—decreases CBF in a dose- and time-dependent manner (Bayram et al., 1998; Burman and Martin, 1986; Gosepath et al., 2000; Hastie et al., 1990; Helleday et al., 1995; Kienast et al., 1994; Knorst et al., 1994a; Min et al., 1999; Simet et al., 2010).

Evidence Supporting this KER

Assembly and description of the scientific evidence supporting KERs in an AOP is an important step in the AOP development process that sets the stage for overall assessment of the AOP (see pages 49-56 of the User Handbook). To do this, biological plausibility, empirical support, and the current quantitative understanding of the KER are evaluated with regard to the predictive relationships/associations between defined pairs of KEs as a basis for considering WoE (page 55 of User Handbook). In addition, uncertainties and inconsistencies are considered. More help

Experimental studies in vitro have shown that exposure of ciliated respiratory cells directly or indirectly to sources of oxidative stress leads to decreased CBF (Burman and Martin, 1986; Wilson et al., 1987; Feldman et al., 1994; Yoshitsugu et al., 1995; Min et al., 1999), which can be reversed by treatment with antioxidants (Schmid et al., 2015). Cigarette smoke condensate, a known inducer of oxidative stress, also causes a decrease in CBF in vitro (Cohen et al., 2009), while, in human subjects exposed to different oxygen levels, oxygen stress causes a decrease in nasal CBF (Stanek et al., 1998).  

Biological Plausibility
Define, in free text, the biological rationale for a connection between KEupstream and KEdownstream. What are the structural or functional relationships between the KEs? For example, there is a functional relationship between an enzyme’s activity and the product of a reaction it catalyses. Supporting references should be included. However, it is recognised that there may be cases where the biological relationship between two KEs is very well established, to the extent that it is widely accepted and consistently supported by so much literature that it is unnecessary and impractical to cite the relevant primary literature. Citation of review articles or other secondary sources, like text books, may be reasonable in such cases. The primary intent is to provide scientifically credible support for the structural and/or functional relationship between the pair of KEs if one is known. The description of biological plausibility can also incorporate additional mechanistic details that help inform the relationship between KEs, this is useful when it is not practical/pragmatic to represent these details as separate KEs due to the difficulty or relative infrequency with which it is likely to be measured (see page 40 of the User Handbook for further information).   More help

One mode of antimicrobial defense in the airway epithelium is generation of free radicals by neutrophils and monocytes/macrophages. Some microbes have also been shown to produce oxidants in significant amounts, e.g. H2O2 production by pneumococcus. Several studies have shown that oxidants, irrespective of the source (microbial or host-derived) inhibit ciliary function. Additionally, there is a large body of experimental evidence demonstrating that exposures to environmental oxidants, including volatile aldehydes, peroxides, sulfur dioxide, nitric dioxide and Diesel exhaust particles have a detrimental impact on ciliary function. Therefore, this KER is highly plausible.

Uncertainties and Inconsistencies
In addition to outlining the evidence supporting a particular linkage, it is also important to identify inconsistencies or uncertainties in the relationship. Additionally, while there are expected patterns of concordance that support a causal linkage between the KEs in the pair, it is also helpful to identify experimental details that may explain apparent deviations from the expected patterns of concordance. Identification of uncertainties and inconsistencies contribute to evaluation of the overall WoE supporting the AOPs that contain a given KER and to the identification of research gaps that warrant investigation (seep pages 41-42 of the User Handbook).Given that AOPs are intended to support regulatory applications, AOP developers should focus on those inconsistencies or gaps that would have a direct bearing or impact on the confidence in the KER and its use as a basis for inference or extrapolation in a regulatory setting. Uncertainties that may be of academic interest but would have little impact on regulatory application don’t need to be described. In general, this section details evidence that may raise questions regarding the overall validity and predictive utility of the KER (including consideration of both biological plausibility and empirical support). It also contributes along with several other elements to the overall evaluation of the WoE for the KER (see Section 4 of the User Handbook).  More help

Several studies show that oxidants decrease CBF which can be reversed by addition of antioxidants, suggesting a direct effect. However, there is evidence suggesting that oxidant-mediated decreases in CBF cannot be prevented by addition of antioxidants. For example, a polycyanin-induced decrease in CBF in human nasal epithelium could be reversed by treatment with isobutylmethylxanthine and forskolin, both of which increase intracellular cAMP, and also by the cAMP analog dibutyryl cAMP, while antioxidants did not seem to have any effect on CBF (Kanthakumar et al., 1993). Like polycyanin, two other P. aeruginosa toxins, 1-hydroxyphenazine (1-HP) and rhamnolipid reduced CBF which was associated with a decrease in intracellular adenosine nucleotides (Kanthakumar et al., 1996). 

Inconsistent with several studies, there are studies that suggest that exposure to cigarette smoke does not inhibit CBF. A study involving 56 human subjects (27 non-smokers and 29 smokers) showed no differences in CBF between the 2 groups. However, a decrease in nasal mucociliary clearance was observed in smokers who exhaled smoke through their noses (Stanley et al., 1986). 

While several studies have shown age dependence of CBF, there is evidence that suggests otherwise  (Agius et al., 1998). 

Response-response Relationship
This subsection should be used to define sources of data that define the response-response relationships between the KEs. In particular, information regarding the general form of the relationship (e.g., linear, exponential, sigmoidal, threshold, etc.) should be captured if possible. If there are specific mathematical functions or computational models relevant to the KER in question that have been defined, those should also be cited and/or described where possible, along with information concerning the approximate range of certainty with which the state of the KEdownstream can be predicted based on the measured state of the KEupstream (i.e., can it be predicted within a factor of two, or within three orders of magnitude?). For example, a regression equation may reasonably describe the response-response relationship between the two KERs, but that relationship may have only been validated/tested in a single species under steady state exposure conditions. Those types of details would be useful to capture.  More help

Treatment of human nasal ciliated epithelial cells with 0.4 mM xanthine + 100 mU/mL xanthine oxidase—producing 159 ± 4.0 µM/h H2O2—decreased CBF by ca. 1 Hz at 1 h and ca. 2.5 Hz (37.4%) at 4 h. Catalase alone (500 U/mL), or in combination with SOD (300 U/mL ) completely protected the cells from oxidant-mediated ciliary dyskinesia (Feldman et al., 1994).

Treatment of human nasal ciliated epithelial cells with 5 mM glucose + 25 mU/mL glucose oxidase— producing 114 ± 7.7 µM/h H2O2—decreased CBF by ca. 2 Hz at 1 h and ca. 4 Hz (38%) at 4 h. The decline in CBF was even larger with 57% (approx. 6 Hz) at 4 h when 100 mU/mL glucose oxidase was used (producing 322 ± 11.5 µM/h H2O2). Catalase alone (500 U/mL) completely protected the cells from oxidant-mediated ciliary dyskinesia (Feldman et al., 1994).

Treatment of human nasal ciliated epithelial cells with H2O2 at concentrations ≥100 µM dose-dependently decreased CBF in human nasal ciliated epithelial cells, with 100 µM causing a 22.4% reduction and the maximal decrease (51.6%) seen with 500 µM H2O2 at 4 h. Adding 100 mU/mL MPO to 150 µM H2O2 enhanced the H2O2-mediated decrease in CBF (control:11.7 ±0.6 Hz; H2O2: 8.2 ± 1.1 Hz, 30% decrease; H2O2 + MPO: 5.4±0.2 Hz, 53.8% decrease). (Feldman et al., 1994).

Treatment of human nasal ciliated epithelial cells with HOCl at concentrations ≥100 µM dose-dependently decreased CBF in human nasal ciliated epithelial cells, with 100 µM causing a 26.1% reduction and 500 µM causing the maximal decrease (100%) at 4 h (Feldman et al., 1994).

Treatment of human nasal epithelial cells with 0.4 mM xanthine + 100 mU/mL xanthine oxidase decreased CBF by ca. 50% within 2 min. Addition of 300 U/mL SOD abolished this effect (Min et al., 1999).

Treatment of human nasal epithelial cells with 10 mM H2O2 decreased CBF to 36.5 ±4.4% of baseline within 5 min, with a maximal decrease in CBF of 100% seen after 10 min, whereas 1 mM H2O2 had no effect on CBF. Treatment of human nasal ciliated epithelial cells with 0.8 mM xanthine + 100 mU/mL xanthine oxidase transiently increased CBF by 12.1±1.0% from baseline. When xanthine concentration was increased to 4 and 8 mM, CBF decreased by 26.8±1.7 and 25.6±1.5%, respectively (Yoshitsugu et al., 1995).

Treatment of bovine ciliated bronchial epithelial cells with acetaldehyde, an oxidative stressor, decreased CBF in a dose-dependent manner. Significant slowing of ciliary beating by ca. 50% was observed with concentrations as low as 15-30 µM, and ciliary beating was completely abrogated at concentrations > 250 µM. Ciliary beating also decreased following treatment with 15-30 µM propionaldehyde (40-50% of control), butyraldehyde (35-65% of control), isobutyraldehyde (20-40% of control), and benzaldehyde (80-90% of control) (Sisson et al., 1991).

Exposure of rabbit tracheal explants to formaldehyde dose-dependently decreased CBF. At 66 µg formaldehyde/cm3, CBF decreased from 12.6 to 11.8 Hz; at 33 µg formaldehyde/cm3, CBF decreased from 13.0 to 10.9 Hz (Hastie et al., 1990).

Exposure of guinea pig trachea to SO2 at concentrations of 2.5-12.5 ppm for 30 min dose-dependently decreased CBF. Exposure to 2.5 ppm SO2 caused a small, non-significant decrease in mean CBF, and exposure to 5 ppm SO2 caused a 45% decrease. The greatest decrease (72 %) in mean CBF was recorded after exposure to 12.5 ppm SO2 (Knorst et al., 1994a).

Exposure of human nasal epithelial cells (cultured in Ringer’s solution) to SO2 at concentrations of 2.5-12.5 ppm for 30 min dose-dependently decreased CBF. Exposure to 2.5 ppm yielded a 42.8% decrease, whereas exposure to 12.5 ppm yielded a 96.5% decrease in CBF (Kienast et al., 1994).

A 20-min exposure to NO2, a known air pollutant, at concentrations of 1.5 or 3.5 ppm did not affect CBF in healthy human subjects at 45 min post-exposure (Helleday et al., 1995).

Exposure of human bronchial epithelial cells from healthy volunteers to 10, 50, and 100 µg/mL Diesel exhaust particles (DEP) significantly decreased CBF by 15.9%, 31.0%, and 55.5%, respectively, from baseline after 24 h (Bayram et al., 1998).

A 4-week exposure of human nasal epithelial cells to 100 µg/m3 ozone had no effect on CBF, whereas 5- and 10-times that concentration significantly decreased CBF (-11.1% at 500 µg/m3; -33.3% at 1000 µg/m3) (Gosepath et al., 2000).

Baseline CBF in tracheal rings from C57Bl/6 mice exposed to cigarette smoke (whole body exposure to mainstream and sidestream cigarette smoke via inhalation from 1R1 reference cigarettes, at 150 mg/m3 total particulate matter for 2 h/day, 5 days/week, for up to 1 year) for 1.5 to 3 months was slightly, but not significantly, increased (∼1 Hz). After 6 months of smoke exposure, however, baseline CBF significantly decreased (∼2–3 Hz) (Simet et al., 2010).  

This sub-section should be used to provide information regarding the approximate time-scale of the changes in KEdownstream relative to changes in KEupstream (i.e., do effects on KEdownstream lag those on KEupstream by seconds, minutes, hours, or days?). This can be useful information both in terms of modelling the KER, as well as for analyzing the critical or dominant paths through an AOP network (e.g., identification of an AO that could kill an organism in a matter of hours will generally be of higher priority than other potential AOs that take weeks or months to develop). Identification of time-scale can also aid the assessment of temporal concordance. For example, for a KER that operates on a time-scale of days, measurement of both KEs after just hours of exposure in a short-term experiment could lead to incorrect conclusions regarding dose-response or temporal concordance if the time-scale of the upstream to downstream transition was not considered. More help

Treatment of human nasal ciliated epithelial cells with 0.4 mM xanthine + 100 mU/mL xanthine oxidase decreased CBF over time, with a noticeable decrease by ca. 1 Hz at 1 h and a maximal decrease of 37.4% reached at 4 h (Feldman et al., 1994).

Treatment of human nasal ciliated epithelial cells with 5 mM glucose + 25 mU/mL glucose oxidase decreased CBF by ca. 2 Hz at 1 h and a maximal decrease of ca. 4 Hz (38%) at 2 h, that did not change until the end of the experiment at 4 h. When 100 mU/mL glucose oxidase was used, CBF decreased by ca. 2 Hz at 1 h, 4 Hz at 2 h, 5.5 Hz at 3 h, reaching a maximum of 57% (approx. 6 Hz) at 4 h (Feldman et al., 1994).

Treatment of human nasal epithelial cells with 0.4 mM xanthine + 100 mU/mL xanthine oxidase decreased CBF maximally by ca. 50% within 2 min, after which it began to increase again, reaching approx. 80% of the baseline value after 30 min (Min et al., 1999).

Treatment of human nasal ciliated epithelial cells with 0.8 mM xanthine + 100 mU/mL xanthine oxidase transiently increased CBF by 12.1±1.0% from baseline within 15 s, after which it rapidly returned to baseline levels (within 30 min). When xanthine concentrations were increased to 4 and 8 mM, CBF decreased by 26.8±1.7 and 25.6±1.5%, respectively (Yoshitsugu et al., 1995).

Treatment of bovine ciliated bronchial epithelial cells with acetaldehyde reduced CBF rapidly, with a significant drop in CBF occurring within 30 s and a maximal decrease by 3 min (Sisson et al., 1991).

Exposure of rabbit tracheal explants to formaldehyde time-dependently decreased CBF: At 66 µg/cm3, CBF decreased from 12.6 to 11.8 Hz immediately upon addition of HCHO to complete cessation of beating by 10 min. At 33 µg/cm3, CBF decreased from 13.0 to 10.9 Hz by 30 min (Hastie et al., 1990).

At 24 h following a 4-h exposure of healthy human subjects to 3.5 ppm NO2, there was a significant elevation in CBF from 12.4±0.9 Hz (at baseline, pre-exposure) to 13.8±0.8 Hz (Helleday et al., 1995).

Exposure of human bronchial epithelial cells to DEP significantly decreased CBF from 2 h onward after incubation with 50 to 100 µg/mL DEP and from 6 hours onward after incubation with 10 µg/mL DEP (Bayram et al., 1998).

A 4-week exposure of human nasal epithelial cells to ozone significantly reduced CBF, with effects becoming noticeable at the higher concentrations (-7.1% at 500 µg/m3;  -10.3% at 1000 µg/m3) after 2 weeks of exposure and a maximal decrease after 4 weeks (-11.1% at 500 µg/m3; -33.3% at 1000 µg/m3) (Gosepath et al., 2000).

Known modulating factors
This sub-section presents information regarding modulating factors/variables known to alter the shape of the response-response function that describes the quantitative relationship between the two KEs (for example, an iodine deficient diet causes a significant increase in the slope of the relationship; a particular genotype doubles the sensitivity of KEdownstream to changes in KEupstream). Information on these known modulating factors should be listed in this subsection, along with relevant information regarding the manner in which the modulating factor can be expected to alter the relationship (if known). Note, this section should focus on those modulating factors for which solid evidence supported by relevant data and literature is available. It should NOT list all possible/plausible modulating factors. In this regard, it is useful to bear in mind that many risk assessments conducted through conventional apical guideline testing-based approaches generally consider few if any modulating factors. More help
Known Feedforward/Feedback loops influencing this KER
This subsection should define whether there are known positive or negative feedback mechanisms involved and what is understood about their time-course and homeostatic limits? In some cases where feedback processes are measurable and causally linked to the outcome, they should be represented as KEs. However, in most cases these features are expected to predominantly influence the shape of the response-response, time-course, behaviours between selected KEs. For example, if a feedback loop acts as compensatory mechanism that aims to restore homeostasis following initial perturbation of a KE, the feedback loop will directly shape the response-response relationship between the KERs. Given interest in formally identifying these positive or negative feedback, it is recommended that a graphical annotation (page 44) indicating a positive or negative feedback loop is involved in a particular upstream to downstream KE transition (KER) be added to the graphical representation, and that details be provided in this subsection of the KER description (see pages 44-45 of the User Handbook).  More help


Domain of Applicability

As for the KEs, there is also a free-text section of the KER description that the developer can use to explain his/her rationale for the structured terms selected with regard to taxonomic, life stage, or sex applicability, or provide a more generalizable or nuanced description of the applicability domain than may be feasible using standardized terms. More help

Age-dependent decreases in CBF have been demonstrated in several species (e.g. guinea pigs, mice, and human) (Bailey et al., 2014; Grubb et al., 2016; Ho et al., 2001; Joki and Saano, 1997; Paul et al., 2013). 

Female hormones, i.e. progesterone and estrogen, have been shown to have direct effect on CBF, i.e., progesterone reduces CBF, 17β-estradiol and progesterone receptor antagonists counteract progesterone effects, but estradiol alone has also been shown to have no effect on CBF. However, the mechanism by which these hormones modulate CBF is yet to be elucidated (Jain et al., 2012; Jia et al., 2011).


List of the literature that was cited for this KER description using the appropriate format. Ideally, the list of references should conform, to the extent possible, with the OECD Style Guide (OECD, 2015). More help

Agius, A.M., Smallman, L.A., and Pahor, A.L. (1998). Age, smoking and nasal ciliary beat frequency. Clin. Otolaryngol. Allied Sci. 23, 227-230. 

Bailey, K.L., Bonasera, S.J., Wilderdyke, M., Hanisch, B.W., Pavlik, J.A., Devasure, J., et al. (2014). Aging causes a slowing in ciliary beat frequency, mediated by PKCε. Am. J. Physiol. Lung Cell. Mol. Physiol. 306, L584-L589.

Bayram, H., Devalia, J.L., Khair, O.A., Abdelaziz, M.M., Sapsford, R.J., Sagai, M., et al. (1998). Comparison of ciliary activity and inflammatory mediator release from bronchial epithelial cells of nonatopic nonasthmatic subjects and atopic asthmatic patients and the effect of diesel exhaust particles in vitro. J. Allergy Clin. Immunol. 102, 771-782.

Burman, W.J., and Martin, W.J. (1986). Oxidant-Mediated Ciliary Dysfunction: Possible Role in Airway Disease. Chest 89, 410-413. 

Ciencewicki, J., Trivedi, S., and Kleeberger, S.R. (2008). Oxidants and the pathogenesis of lung diseases. J. Allergy Clin. Immunol. 122, 456-470. 

Cohen, N.A., Zhang, S., Sharp, D.B., Tamashiro, E., Chen, B., Sorscher, E.J., et al. (2009). Cigarette smoke condensate inhibits transepithelial chloride transport and ciliary beat frequency. Laryngoscope 119, 2269-2274.

Feldman, C., Anderson, R., Kanthakumar, K., Vargas, A., Cole, P.J., and Wilson, R. (1994). Oxidant-mediated ciliary dysfunction in human respiratory epithelium. Free Radic. Biol. Med. 17, 1-10. 

Gosepath, J., Schaefer, D., Brommer, C., Klimek, L., Amedee, R.G., and Mann, W.J. (2000). Subacute effects of ozone exposure on cultivated human respiratory mucosa. Am. J. Rhinol. 14, 411-418.

Grubb, B.R., Livraghi-Butrico, A., Rogers, T.D., Yin, W., Button, B. and Ostrowski, L.E. (2016). Reduced mucociliary clearance in old mice is associated with a decrease in Muc5b mucin. Am. J. Physiol. Lung Cell. Mol. Physiol. 310, L860-L867.

Hastie, A.T., Patrick, H., and Fish, J.E. (1990). Inhibition and recovery of mammalian respiratory ciliary function after formaldehyde exposure. Toxicol. Appl. Pharmacol. 102, 282-291.

Helleday, R., Huberman, D., Blomberg, A., Stjernberg, N., and Sandstrom, T. (1995). Nitrogen dioxide exposure impairs the frequency of the mucociliary activity in healthy subjects. Eur. Respir. J. 8, 1664-1668.

Ho, J.C., Chan, K.N., Hu, W.H., Lam, W.K., Zheng, L., Tipoe, G.L., et al. (2001). The Effect of Aging on Nasal Mucociliary Clearance, Beat Frequency, and Ultrastructure of Respiratory Cilia. Am. J. Respir. Crit. Care Med. 163, 983-988.

Jain, R., Ray, J.M., Pan, J.-H. and Brody, S.L. (2012). Sex hormone-dependent regulation of cilia beat frequency in airway epithelium. Am. J. Respir. Crit. Care Med. 46, 446-453.

Jia, S., Zhang, X., He, D.Z., Segal, M., Berro, A., Gerson, T., et al., 2011. Expression and Function of a Novel Variant of Estrogen Receptor–α36 in Murine Airways. Am. J. Respir. Cell Mol. Biol. 45, 1084-1089.

Joki, S. and Saano, V. (1997). Influence of ageing on ciliary beat frequency and on ciliary response to leukotriene D4 in guinea‐pig tracheal epithelium. Clin. Exp. Pharmacol. Physiol. 24, 166-169.

Kanthakumar, K., Taylor, G., Cundell, D., Dowling, R., Johnson, M., Cole, P., et al. (1996). The effect of bacterial toxins on levels of intracellular adenosine nucleotides and human ciliary beat frequency. Pulm. Pharmacol. 9, 223-230.

Kanthakumar, K., Taylor, G., Tsang, K., Cundell, D., Rutman, A., Smith, S., et al. (1993). Mechanisms of action of Pseudomonas aeruginosa pyocyanin on human ciliary beat in vitro. Infect. Immun. 61, 2848-2853.

Kienast, K., Riechelmann, H., Knorst, M., Schlegel, J., Müller-Quernheim, J., Schellenbergt, J., et al. (1994). An experimental model for the exposure of human ciliated cells to sulfur dioxide at different concentrations. The clinical investigator 72, 215-219. 

Knorst, M.M., Kienast, K., Riechelmann, H., Müller-Quernheim, J., and Ferlinz, R. (1994). Effect of sulfur dioxide on mucociliary activity and ciliary beat frequency in guinea pig trachea. Int. Arch. Occup. Environ. Health 65, 325-328. 

Min, Y.-G., Ohyama, M., Lee, K.S., Rhee, C.-S., Oh, S.H., Sung, M.-W., et al. (1999). Effects of free radicals on ciliary movement in the human nasal epithelial cells. Auris Nasus Larynx 26, 159-163.

Paul, P., Johnson, P., Ramaswamy, P., Ramadoss, S., Geetha, B. and Subhashini, A.S. (2013). The Effect of Ageing on Nasal Mucociliary Clearance in Women: A Pilot Study. ISRN Pulmonology 2013, 5.

Price, M.E., and Sisson, J.H. (2019). Redox regulation of motile cilia in airway disease. Redox. Biol. 27, 101146-101146. 

Schmid, A., Baumlin, N., Ivonnet, P., Dennis, J.S., Campos, M., Krick, S., et al. (2015). Roflumilast partially reverses smoke-induced mucociliary dysfunction. Respir. Res. 16, 135. 

Simet, S.M., Sisson, J.H., Pavlik, J.A., DeVasure, J.M., Boyer, C., Liu, X., et al. (2010). Long-term cigarette smoke exposure in a mouse model of ciliated epithelial cell function. Am. J. Respir. Cell Mol. Biol. 43, 635-640.

Sisson, J.H., Tuma, D.J., and Rennard, S.I. (1991). Acetaldehyde-mediated cilia dysfunction in bovine bronchial epithelial cells. Am. J. Physiol. 260, L29-36. 

Stanek, A., Brambrink, A., Latorre, F., Bender, B., and Kleemann, P. (1998). Effects of normobaric oxygen on ciliary beat frequency of human respiratory epithelium. Br. J. Anaesth. 80, 660-664.

Stanley, P., Wilson, R., Greenstone, M., MacWilliam, L., and Cole, P. (1986). Effect of cigarette smoking on nasal mucociliary clearance and ciliary beat frequency. Thorax 41, 519-523.

Wilson, R., Pitt, T., Taylor, G., Watson, D., MacDermot, J., Sykes, D., et al. (1987). Pyocyanin and 1-hydroxyphenazine produced by Pseudomonas aeruginosa inhibit the beating of human respiratory cilia in vitro. J. Clin. Investig. 79, 221-229.

Yoshitsugu, M., Matsunaga, S., Hanamure, Y., Rautiainen, M., Ueno, K., Miyanohara, T., et al. (1995). Effects of oxygen radicals on ciliary motility in cultured human respiratory epithelial cells. Auris Nasus Larynx 22, 178-185.