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Progress in Inflammation Research 92
Series Editors: Michael J. Parnham
Thorsten J. Maier · Emanuela Ricciotti
Bruce K. Rubin
Masaharu Shinkai Editors
Macrolides
as Immuno-
modulatory
Agents
Progress in Inflammation Research
Volume 92
Series Editors
Michael J. Parnham, Faculty of Chemistry, Biochemistry and Pharmacy, Goethe
University Frankfurt am Main, Frankfurt am Main, Germany
Thorsten J. Maier, Federal Institute for Vaccines and Biomedicines, Paul Ehrlich
Institute, Langen, Germany
Emanuela Ricciotti, Perelman School of Medicine, University of Pennsylvania,
Philadelphia, PA, USA
This book series addresses all key topical aspects of basic research, therapy and its
clinical implications in the field of inflammatory diseases. It provides a unique
reference source for academic and industrial biomedical researchers, drug develop-
ment personnel, immunologists, rheumatologists, cardiologists, allergologists and
many other relevant clinical disciplines. Each publication supplies regular scientific
updates on newest developments and allow providing access to state-of-the-art
techniques and technologies.
The series gathers knowledge from leading authorities on the multiple facets of
inflammation research, making it a valuable asset for advanced students in biomed-
ical sciences, early career investigators and for professionals in both basic and
translational research and in the clinic. Each volume comprises a carefully selected
collection of high-quality review articles on the respective field of expertise. They
also introduce new investigators to the most pertinent aspects of inflammatory
disease and allow established investigators to understand fundamental ideas, con-
cepts and data on sub-fields that they may not normally follow.
Thus chapters should not comprise extensive data reviews nor provide a means
for authors to present new data that would normally be published in peer-reviewed
journals. Instead, the chapters should provide a concise overview and guide to the
most pertinent and important literature, thus reflecting a conceptual approach rather
than a complete review of the particular field of research. Moreover, each chapter
should be intelligible for less experienced researchers or even newcomers to the
fields of pathology, mechanisms and therapy of inflammatory disease. To this end,
authors should consider introducing PhD students or postdocs who are new to the
laboratory to the major concepts and the most critical literature in their chosen field
of research.
Bruce K. Rubin • Masaharu Shinkai
Editors
Macrolides
as Immunomodulatory
Agents
Editors
Bruce K. Rubin Masaharu Shinkai
School of Medicine Clinical Trial Develop & Research Center
Virginia Commonwealth University Tokyo Shinagawa Hospital
Richmond, VA, USA Tokyo, Japan
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland
AG 2024
This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether
the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of
illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and
transmission or information storage and retrieval, electronic adaptation, computer software, or by
similar or dissimilar methodology now known or hereafter developed.
The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication
does not imply, even in the absence of a specific statement, that such names are exempt from the relevant
protective laws and regulations and therefore free for general use.
The publisher, the authors, and the editors are safe to assume that the advice and information in this
book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or
the editors give a warranty, expressed or implied, with respect to the material contained herein or for any
errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional
claims in published maps and institutional affiliations.
This Springer imprint is published by the registered company Springer Nature Switzerland AG
The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland
v
vi Preface: A Brief History of the Macrolide Antibiotics
required regular systemic corticosteroids for disease control (5). However, it was in
the early 1980s when Miazawa and Kudo in Japan first exploited these properties for
the therapy of diffuse panbronchiolitis (6) as detailed in a later chapter by Taniuchi
and Azuma.
Much has happened in the 40 years since this discovery with greater understand-
ing of the potential immunomodulatory mechanisms and effective use, in particular
for neutrophil-dominated inflammation. We bring much of this information together
in this book.
References
[1] https://www.thenewstoday.info/2005/05/03/iloilonews3.htm
[2] Morimoto S, Nagate T, Sugita K, Ono T, Numata K, Miyachi J, Misawa Y,
Yamada K, Omura S. Chemical modification of erythromycins. III. In vitro and
in vivo antibacterial activities of new semisynthetic 6-O-
methylerythromycins A, TE-031 (clarithromycin) and TE-032. J Antibiot
(Tokyo) 1990;43(3):295-305.
[3] Chantot JF, Bryskier A, Gasc JC. Antibacterial activity of roxithromycin: a
laboratory evaluation. J Antibiot (Tokyo). 1986;39(5):660-8
[4] Retsema J, Girard A, Schelkly W, Manousos M, Anderson M, Bright G,
Borovoy R, Brennan L, Mason R. Spectrum and mode of action of azithromycin
(CP-62,993), a new 15-membered-ring macrolide with improved potency
against gram-negative organisms. Antimicrob Agents Chemother 1987;31(12):
1939-47
[5] Kaplan MA and Golden M. The use of triacetyloleandomycin in chronic infec-
tious asthma. Antibiotic Annual 1958-1959. New York, Interscience Publishers.
pp 273-276
[6] Kudoh S. Applying lessons learned in the treatment of diffuse panbronchiolitis to
other chronic inflammatory diseases. Am J Med 2004; 117 (Suppl 9A):12S–19S
Contents
vii
viii Contents
C. P. Page
Sackler Institute of Pulmonary Pharmacology, King’s College London, London, UK
F. R. Gardarsson · J. A. Kricker · V. Norris
EpiEndo Pharmaceuticals, Reykjavik, Iceland
T. Gudjonsson
University of Iceland, Faculty of Medicine and Landspitali, University Hospital, Reykjavik,
Iceland
M. J. Parnham (✉)
EpiEndo Pharmaceuticals, Reykjavik, Iceland
Faculty of Chemistry, Biochemistry and Pharmacy, Goethe University Frankfurt am Main,
Frankfurt am Main, Germany
e-mail: mjp@epiendo.com
1 Introduction
Since 2000, azithromycin has become the main macrolide investigated for pharma-
cological effects beyond antibiosis. Its demonstrated efficacy now covers the treat-
ment of patients with asthma and chronic obstructive pulmonary disease (COPD) [1–
4], patients exposed to various airborne viral infections [5–7], and other diseases
associated with loss of epithelial barrier integrity.
This current review will consider the characteristics of the epithelial barrier and
the in vivo and in vitro evidence for the effects of macrolides on epithelium that may
contribute to their clinical efficacy in a range of diseases known to be associated with
epithelial dysfunction, including those in the skin, as well as data suggesting their
potential for efficacy in the gut. A novel class of modified macrolides or so-called
“Barriolides” exemplified by EP395, an azithromycin-related macrolide with
reduced antimicrobial resistance potential, that recently entered early clinical devel-
opment targeting chronic airway disease (CAD), will also be discussed [6].
All epithelial tissues share unifying structural and functional features like hexagonal
orientation and ongoing cellular renewal, as well as their undisrupted continuity,
which provides separation between the external environment and the body’s interior
tissues, acting as a contiguous surface for all organs and a lining for other tissues.
The epithelium is generally capable of remodeling itself and is often the first line
of defense against the external environment. It is widely distributed and is the key
surface lining in organs such as the airways, skin, and the gastrointestinal tract,
whereby its varying architecture reflects its different functions. Apical to basolateral
polarity, as in the upper airways and in the gastrointestinal tract, and the stratified
squamous epithelium of the skin are pivotal to the barrier function of the epithelium
and its organ-specific functions.
6 C. P. Page et al.
In the respiratory tract, the epithelium changes from being pseudostratified in the
upper airways to cuboidal in the lower bronchioles and simple squamous epithelium
in the alveoli (Fig. 2). The pseudostratified epithelium is responsible for the
mucociliary clearing of particles and infectious agents. Goblet cells produce
mucus which entraps infectious/hazardous agents and ciliated cells produce a thin
periciliary fluid, which with the help of the beating cilia, move the mucus up the
respiratory tract to be expelled through the mouth or nose. Macrolide antibiotics such
as azithromycin are well known to inhibit the secretion of mucus by the airway
epithelium [13, 14]. Basal cells are responsible for the renewal of both ciliated and
goblet cells in the trachea and large bronchi [15]. In the lower bronchi, the epithe-
lium has a simple cuboidal structure, with club cells replacing the basal cells as the
stem or progenitor cells [16]. The bronchioles open into the air-filled alveoli that are
composed of a thin layer of alveolar type 1 cells with cuboidal type 2 cells distributed
in between. Whereas the type 1 alveolar cells are responsible for the gas exchange,
type 2 cells produce surfactants to prevent the alveoli collapsing. They are also the
progenitor cells for new type 1 cells [17]. The epithelial barrier is generated by the
ability of epithelial cells to form tight contact to each other via various adhesion
proteins, most notably the tight junction complexes. Tight junctions formed by
epithelial cells regulate the paracellular flux and infiltration of leukocytes, and are
also important in generating apical-basal polarity by controlling the distribution of
phospholipids and transmembrane proteins within the semi-fluid cell membrane
[18]. The tight junctions are formed by a variety of adhesion molecules, including
transmembrane proteins, claudins, occludins, and junctional adhesion molecules
(JAM), which are linked to the actin cytoskeleton through scaffold proteins, most
notably, zonula occludens (ZO-1 to -3), cingulin, and afadin [19]. These, in turn,
are regulated by cytokines, which cause junction modifications during inflammation.
Together with numerous other proteins involved in cell signaling, they form the
intracellular tight junction plaques [20]. As discussed below in sect. 2.2,
azithromycin has been shown to modify airway epithelial tight junction molecule
expression.
Loss of epithelial integrity/barrier failure also increases during aging. Indeed,
aging results in reduced lung function which makes the elderly more vulnerable to
chronic lung diseases. Aging reduces the mucociliary clearance, thus weakening the
epithelial barrier, which makes older people more prone to infections such as
pneumonia [21]. Recently, Angelidis et al. used single cell transcriptomic and
mass-spectrometry proteomics to quantify changes in 30 lung cell types in young
and old mice. They demonstrated significant changes in gene regulation and cellular
remodeling that may affect the epithelial barrier [22]. Several respiratory diseases
affect the epithelial barrier including COPD, CF, and asthma with cigarette smoking
and other types of oxidant pollution being the main causes of COPD. Cigarette
smoking facilitates goblet cell hyperplasia and disrupts tight junctions resulting in
Macrolides and Diseases Associated with Loss of Epithelial Barrier Integrity 7
Fig. 2 The epithelial barrier in airway, skin, and gut. (a) The airway epithelium varies from the
pseudostratified layer in the bronchi to the single squamous layer in the alveoli. It extends from the
trachea and large bronchi to the smaller bronchioles and alveoli. The epithelium thus, forms a
continuous layer that protects the underlying interstitial connective tissue from pathogens and
pollutant-rich external air. In the trachea and large bronchi, the pseudostratified layers are composed
8 C. P. Page et al.
Fig. 2 (continued) of mucociliary epithelium and basal cells which represent progenitor cells. In the
bronchioles, club cells replace the basal cells as the progenitor cells. The distal part of the airway
epithelium terminates in the alveoli where gas exchange takes place. The type II alveolar cells are
responsible for surfactant production and also for the generation of new type I alveolar cells that are
responsible for gas exchange. In vitro and in vivo work indicates that azithromycin may enhance the
epithelial barrier via tight junction remodeling, enhancing epithelial cell growth, and differentiation,
reducing epithelial-derived proinflammatory cytokines, and reducing mucus (see sect. 4) (b) The
epidermis forms stratified squamous epithelium. The epidermis is composed of four layers of
epithelial cells (keratinocytes). Stratum basale sits on top of the basement membrane, which
separates the epidermis from the underlying dermis. Keratinocyte stem cells (basal cells) are located
in the stratum basale. These stem cells give rise to keratinocytes which move up to the stratum
spinosum. In the stratum spinosum, interconnections between cells are apparent, presumably
through desmosomes. Keratinocytes differentiate further and move up to the stratum granulosum.
This layer forms the water barrier. Keratinocytes are filled with lipids packed in lamellar bodies that
make this layer highly hydrophobic and which may possibly be enhanced by barrier-protective
macrolides (cf sect. 5.3). At the interface of the stratum granulosum and stratum corneum,
keratinocytes undergo keratinization which is a specific form of apoptosis, losing their nuclei and
other cellular organelles and accumulate to form the keratin- and lipid-rich stratum corneum. (c) The
colon epithelium forms a columnar single-layer barrier. The colon epithelium is mainly composed
of absorptive enterocytes, mucin-producing goblet cells, and stem cells located at the bottom of the
crypt. The stem cells give rise to new enterocytes and goblet cells. Microfold (M) cells and
enteroendocrine cells are also found within the colon epithelium (not shown in this figure), where
they contribute to the immune and hormonal systems, respectively. Potential sites of action of
barrier-protective macrolides in the gut have yet to be determined. Figures generated by BioRender.
com
Macrolides and Diseases Associated with Loss of Epithelial Barrier Integrity
9
Fig. 3 Macrolides, especially azithromycin (AZM), interfere with a number of cellular organelles and signaling pathways to elicit their effects in epithelial and
other cells. Binding to membrane phospholipids, probably by charge interactions, activates a series of signaling cascades resulting in altered gene regulation. As
a result of intracellular macrolide accumulation, particularly in lysosomes, lipid accumulation occurs with lamellar body formation and alterations in
10 C. P. Page et al.
2.1.2 Epidermis
The cellular turnover in the stratified squamous epithelium, the epidermis, is fast and
requires active stem or progenitor cells to generate new keratinocytes [27]. The
keratinocyte stem cells sit on the basement membrane in the stratum basale [28] and
give rise to keratinocytes which reach maximal differentiation in the stratum
granulosum, forming the water barrier. The water barrier between the stratum
granulosum and stratum corneum is composed of accumulated lipids (e.g., phos-
pholipids, glucosylceramide, sphingomyelin, and cholesterol) that together with
proteins form lamellar bodies (LBs) [28–31]. These stratified layers are of major
importance for the barrier function of the skin and help prevent transepidermal water
loss (TEWL).
Epidermal barrier failure and the accompanying inflammatory response are
considered a primary component of skin diseases such as atopic dermatitis (AD),
rosacea, and ichthyoses [32–35]. AD, a chronic, relapsing skin disease characterized
by dry erythematous lesions and severe itching (pruritis), has a very high prevalence,
affecting up to 3% of the worldwide population. Furthermore, the frequency of AD
and other atopic diseases has increased by two- to threefold during the past decades
in industrialized countries [36, 37]. Histological features of AD include intercellular
edema (spongiosis) of the keratinocytes within the stratum spinosum, resulting from
a lack of cell-cell binding [38]. Although the cause of AD is unknown, barrier failure
and inflammatory responses are both key features of the disease [39]. A hallmark of
AD is elevated serum concentrations of allergen-specific IgE antibodies against
various inhaled, food, and environmental allergens, probably resulting from the
epithelial barrier failure, leading to passage of allergens into the underlying connec-
tive tissues which initiate an inflammatory response triggered by cross-linking of
allergens with IgE on mast cells [40].
Loss-of-function (LOF) studies on the gene FLG, which encodes for the precur-
sor of the filament-associated protein filaggrin, have shown a strong association with
AD [41]. LOF FLG mutations are also responsible for the onset of ichthyosis
vulgaris, the most common skin disorder within ichthyoses (IC). IC are a heteroge-
neous group of skin diseases sharing the feature of barrier failure leading to water
loss and compensatory hyperproliferation of keratinocytes [42]. Common pheno-
types include dry skin (xerosis) and scaling, and IC patients are at increased risk for
AD, asthma, and other allergic disorders, probably due to the disrupted skin barrier,
subsequently allowing easier epidermal penetration of allergens and other external
inflammatory stimuli [41]. As in IC and AD, rosacea is also characterized by
increased TEWL with compromised tight junction proteins, while filaggrin remains
unchanged [43, 44]. The pathophysiology of rosacea is still not understood but
increased epithelial cell expression of cathelicidin (LL-37) and IL-33 play a key
role, together with increased expression of vascular endothelial growth factor
(VEGF) [45]. The epithelium of the skin, although multilayered compared to airway
and gut, is susceptible to breaches of the barrier resulting in imbalance and subse-
quent inflammation.
The intestine and colon epithelium are composed of multiple cell types. In the
intestine, large folding of the epithelium generates villi and crypts. Cellular
remodeling is undertaken in the crypts where stem cells deep in the crypts generate
daughter cells that differentiate either downwards to become Paneth cells (intestine)
or upwards to generate enterocytes, goblet cells and enteroendocrine cells [46]. The
epithelial barrier in the gut is of great importance for maintaining homeostasis of the
gastrointestinal tract, and barrier failure contributes to a variety of conditions such as
leaky gut [47, 48], and inflammatory bowel diseases (IBD) such as Crohn’s disease
[49], ulcerative colitis [50] and celiac disease [51]. A common denominator of
barrier failure in the gut is the aberrant regulation of tight junctions [51]. Recently,
Parikh et al. used single-cell profiling to demonstrate the intestinal and colonic
epithelial diversity in normal gut and epithelial cells derived from patients with
IBD [52]. At the top of the crypts, they found a previously unknown absorptive cell,
expressing the proton channel otopetrin 2 (OTOP2) and the satiety peptide
uroguanylin, that senses pH and is dysregulated in inflammation. In IBD, they
observed a positional remodeling of goblet cells that coincides with the
downregulation of WFDC2-an antiprotease molecule that they found to be expressed
by goblet cells and that preserves the integrity of tight junctions and prevents the
invasion of bacteria and inflammation [52]. The expression patterns of various
claudins, expressed both by gut epithelial and other mesodermal cells, have been
investigated in both humans and in murine models of IBD and shown to reflect the
interactions between the different cells involved in the disease [53].
It is apparent, therefore, that tight junctions play an important role in maintaining
gut epithelial integrity. Others have shown that increased expression of claudin
2 increases paracellular flux [54], whilst the reduced function of occludin has been
linked to increased barrier failure. IL-13 has been shown to increase claudin
2 expression resulting in increased paracellular flux, and TNF-alpha has been
shown to induce the activity of myosin light chain kinase (MLCK) that further
induces caveoli endocytosis of occludin resulting in increased leakiness of the gut
[55]. Based on the importance of the epithelial barrier for healthy organs, drugs that
maintain and/or increase the strength of the epithelial integrity may therefore be of
great importance in a range of diseases of the airways, skin, and gastrointestinal tract
and potentially open to therapy with barrier-protecting macrolides.
12 C. P. Page et al.
Advanced cell culture models are useful tools for studying epithelial biology both in
health and disease. Since many epithelial tissues are exposed to hazardous environ-
ments, cell culture models have been useful in analyzing the effects of various
toxicants and infectious agents on epithelial cells. Furthermore, these cell culture
models now provide convenient assays for analyzing the efficacy of drugs as they
can provide simple readout assays allowing for the reasonably rapid screening of
large numbers of compounds. Testing cell viability in conventional monolayer
culture is simple and fast. However, monolayer cultures have limitations, such as a
lack of an in vivo-like environment, cellular phenotype plasticity, and association
with the micro-environment [56]. For analysis of epithelial barrier integrity, cultur-
ing cells on transwell filters can provide a good option, either as liquid–liquid (LL) or
air–liquid interface (ALI) cell culture. ALI cultures are suitable for analysis of the
barrier integrity of the airway, gastrointestinal, and skin epithelium. ALI cultures are
generated by initiating cell culture in liquid-liquid conditions on coated porous filters
representing a basement membrane, and after a few days in culture, media is
removed from the apical compartment, which allows for further differentiation into
organotypic structures.
Regarding airway epithelium, culture of basal cells in ALI conditions results in
pseudostratified-like histology. This is demonstrated by formation of apical-
basolateral polarity, and formation of goblet and ciliated cells [57, 58]. Tight junc-
tions are responsible for the apical to basolateral polarity of the cells and fencing,
meaning they form the tight barrier between epithelial cells, which controls the
paracellular flux between cells. A simple readout for barrier integrity in ALI cultures
is to measure transepithelial electrical resistance (TEER) and paracellular flux
(p-flux). Thus, increased TEER and reduced p-flux are good indicators of a func-
tionally active barrier maintained by tight junctions and other adhesion molecules
[59]. Additional readout assays include RNA sequencing, proteomic, ELISA, and
metabolomic analysis. Mimicking the appropriate in vivo-like phenotype in vitro as
closely as possible is of great importance as this allows for a better understanding of
the communication between cells and histological appearance and allows investiga-
tion of the effect of external stimuli and drugs on the function of the epithelial
barrier.
Reflecting in vivo pathological conditions in cell models using challenging assays
can be a useful tool to either investigate the clinical condition in question or to study
drugs or methods to ameliorate the clinical condition. It can be said that there are
broadly three categories of challenging assays, biological, chemical, and mechani-
cal. Biological assays include challenging the cell culture model with inflammatory
cytokines and fibrosis-inducing agents such as TGFβ [60]. Chemical challenging can
be performed using, for instance, EDTA, to bind calcium and subsequently impair
cell-to-cell adhesion properties [61]. Mechanical challenging includes insults such as
stretching cell models or increasing pressure in a way that deforms the cells,
Macrolides and Diseases Associated with Loss of Epithelial Barrier Integrity 13
mimicking, for instance, what happens in ventilator-induced lung injury [62]. The
challenge, however, needs to be adapted carefully to the cell type used, as bacterial
lipopolysaccharide (LPS), for instance, does not exert the same response in different
cell lines [63].
Using ALI cultures, it has been shown how azithromycin enhances the epithelial
barrier by increasing TEER, an indicator of a strong barrier [64, 65], and in lung
epithelial cells, it was shown that this drug also induces epidermal differentiation and
the formation of lamellar bodies [66], which may be useful pharmacological prop-
erties to explain the effectiveness of macrolides in a number of diseases discussed
below.
There has been an ongoing interest in clarifying the disease modifying pharmacol-
ogy of macrolides ever since the late sixties and seventies when the dramatic
antiinflammatory and even curative effect of erythromycin on DPB was recognized
in Japan [74]. As DPB has an essentially unknown etiology and the exact patho-
physiology is still not completely understood, it has remained unclear which of the
multiple pharmacological properties of azithromycin, erythromycin, and other
macrolides are responsible for this clinical benefit of a relatively rapid remission
of inflammation and suppression of further disease progression [75–77].
However, it seems likely that the disease-modifying efficacy of macrolides on
inflammatory responses lies within the 14-membered and 15-membered analogues,
since the 16-membered compounds are not disease modifying in DPB or other
macrolide-sensitive indications [78]. The potential efficacy of solithromycin, a
14-membered fluoroketolide, was investigated against non-bacterial airway diseases,
but this drug was not well tolerated on long-term use and the trial was terminated due
to safety issues when tested in patients with COPD [71].
In this regard, it is of interest therefore, that a patient with DPB who did not
respond to erythromycin therapy did respond to clarithromycin [79], while in
contrast the 16-membered josamycin, despite having prominent 14-membered like
PMNC inhibitory effects, has been found to be clinically ineffective in treating DPB
[78]. It is worth mentioning, in this context, that clarithromycin, in addition to its
well-established antiinflammatory/immunomodulatory actions, also exerts benefi-
cial effects on epithelial cell function [67]. Thus, it seems likely that both the
14-membered and 15-membered macrolide antibiotics share features essential for
treating most cases with DPB, while those experimental antiinflammatory features
shared by them with josamycin appear less important for therapeutic benefit in DPB
[75, 78].
Macrolides and Diseases Associated with Loss of Epithelial Barrier Integrity 15
Arising from the initial studies on DPB, there has been interest in the clinical utility
of macrolides in the treatment of several respiratory diseases, including COPD,
asthma, chronic allergic rhinosinusitis, non-CF bronchiectasis, CF, and cryptogenic
organizing pneumonia (COP), previously termed bronchiolitis obliterans organizing
pneumonia (BOOP) [83]. More detailed discussions of the use of macrolides in
specific disorders are given in other chapters in this present volume. We focus here
on the key clinical studies in patients with asthma and COPD, which are clearly
associated with epithelial injury, and these are summarized below.
In asthma, small clinical trials have looked at the effects of macrolides on markers
of inflammation. For example, it has been shown that 8 weeks of treatment with
clarithromycin reduced IL-8 and neutrophilic inflammation in the sputum of patients
with refractory asthma. The effect was most marked in those with refractory
non-eosinophilic asthma [84]. In children on maintenance inhaled fluticasone pro-
pionate, 4 weeks treatment with clarithromycin reduced eosinophilic inflammation
as assessed by blood levels of eosinophils and ECP [85]. In the AMAZES trial,
48 weeks of azithromycin reduced the number of combined moderate and severe
16 C. P. Page et al.
derive benefit from ICS) or those who continue to exacerbate despite LABA/LAMA/
ICS, particularly if ex-smokers [81].
TSLP is a key epithelial cytokine released in response to multiple triggers, and
blocking TSLP with tezepelumab is effective at reducing exacerbations in asthma
[91]. The inhibition of TSLP generation from airway epithelium by azithromycin
may contribute to its therapeutic benefit in asthma [69], in addition to the other
beneficial effects of this drug on airway epithelium described previously.
Given the broad patient populations who derive clinical benefit from
azithromycin in terms of exacerbation reduction, taken together with the data from
HBEC and poly I:C stimulation, effects on the epithelium could at least in part
explain the efficacy of macrolides in reducing exacerbations in asthma and COPD.
Based on the foregoing discussion, it is likely that macrolide protective effects on the
epithelial barrier may also contribute to the therapeutic benefit observed in the
topical treatment of rosacea or atopic dermatitis with macrolide dermal formulations,
or the oral macrolide therapy of psoriasis [92–94]. While these dermal disorders are
also associated with barrier disruption, the effects of macrolides, up till now, have
been associated with inhibition of inflammatory cell and mediator reduction and
attributed exclusively to either antibacterial or antiinflammatory actions [92]. We
have also recently suggested that oral macrolides without antibacterial activity and
thus, without adverse effects on the gut microbiome, may also be of benefit in the
treatment of epithelial damage in IBD [6]. A recent article connects gut and skin
health, showing that fiber-derived short-chain fatty acids formed in the gut promote
keratinocyte metabolism and differentiation in keratinocytes from the skin [95]. In
this respect, it is worth noting that the beneficial effects of azithromycin on airway
epithelial growth and differentiation are associated both with increased expression of
a set of 51 genes also associated with epidermal differentiation and with increased
deposition of intracellular fatty acids [66], suggesting a potential common mecha-
nism in airway and skin and even intestinal epithelial protection.
In a recent review article from 2019 entitled “Azithromycin is the answer in
pediatric respiratory medicine, but what was the question?” the author, Andrew
Bush, is critical of the evolution of inappropriate over-prescription and widespread
use of macrolides in chronic inflammatory diseases both in children and adults, as
such “off-label” therapy leads to extensive resistance formation [76]. Furthermore,
he urges the medical and scientific community to focus on better understanding the
endotype of inflammatory conditions where the non-antibiotic effects of macrolides
have proven to be beneficial beyond DPB and to develop new non-antibiotic
macrolides to target strategically these identified endotypes of inflammation [76].
18 C. P. Page et al.
6 Concluding Remarks
References
1. Albert RK, Connett J, Bailey WC, Casaburi R, Cooper JA Jr, Criner GJ, et al. Azithromycin for
prevention of exacerbations of COPD. N Engl J Med. 2011;365(8):689–98.
2. Gibson PG, Yang IA, Upham JW, Reynolds PN, Hodge S, James AL, et al. Effect of
azithromycin on asthma exacerbations and quality of life in adults with persistent uncontrolled
asthma (AMAZES): a randomised, double-blind, placebo-controlled trial. Lancet. 2017;390
(10095):659–68.
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Macrolides and Inflammatory Cells,
Signaling, and Mediators
Mitsuko Kondo
1 Introduction
M. Kondo (✉)
Department of Respiratory Medicine, Tokyo Women’s Medical University School of Medicine,
Tokyo, Japan
e-mail: kondo.mitsuko@twmu.ac.jp
also suppress neutrophil activation and accumulation in the airway, which acts
indirectly on airway epithelial cells to suppress hypersecretion [5]. The characteristic
features of macrolide therapy are as follows. (1) Macrolides are effective at low-dose
and long-term administration, (2) Macrolides are effective even in Pseudomonas
aeruginosa-infected pathologies that are resistant to macrolides, (3) 14-membered
macrolides [EM, clarithromycin (CAM), roxithromycin (RXM)] and 15-membered
macrolide/azilide azithromycin (AZM) are more effective than 16-membered
macrolides [2]. Macrolide concentrations are at least tenfold higher in the epithelial
lung fluid than serum [2]. Currently, macrolides are widely used for chronic airway
inflammatory diseases with neutrophil inflammation such as chronic sinusitis, bron-
chiectasis, cystic fibrosis (CF), and COPD. In addition, the usefulness of macrolides
has been established in some cases of intractable and noneosinophilic asthma and is
being studied for the therapy of pulmonary fibrosis. In this chapter, we introduce the
effects of macrolides on airway secretion and inflammatory cells/cytokines and
describe the broad effects of macrolides on intracellular signaling mechanisms.
was reduced by half, and an increase in sputum elasticity was measured while
viscosity was unchanged [4].
2. Suppression of mucin secretion
Mucin accounts for more than 30% of the solid components of airway mucus.
Mucin is a large glycoprotein, and its core protein is composed of repeating serine
and threonine peptides decorated with sugar chains linked by O-glycosidic bonds.
There are secretory and membrane-bound mucins in the respiratory tract, the former
being gel-forming and a component of mucus. Secretory mucin-producing cells in
the airway are goblet cells, mucous cells, and serous cells in the submucosal glands.
MUC5AC and MUC5B are produced from goblet cells, and MUC5B is abundantly
produced from mucous cells of the submucosal gland [12]. When secretory stimu-
lants are administered to goblet cells, degranulation from the secretory granules
occurs rapidly. Airway mucus hypersecretion results from degranulation from secre-
tory cells and from increased mucin production. Stimulation of the autonomic
nervous system and mediators such as elastase and histamine causes degranulation.
In animal experiments, administration of CAM and EM once a day for 1 week
suppresses degranulation caused by lipopolysaccharide (LPS) stimulation, but not
with ampicillin or cefaclor [13].
3. Suppression of mucin production
The epithelial growth factor receptor (EGFR) plays an important role in mucin
production [14]. There are many EGFR ligands such as epidermal growth factor
(EGF), TGFα, HB-EGF, amphiregulin and tobaccos smoke, and when EGFR is
stimulated by these ligands, its phosphorylation occurs and the ERK1/2 pathway is
activated via Ras, Raf, and MEK [14, 15]. Transcription factors such as NFκB then
enter the nucleus to promote gene expression and mucin. Macrolides suppress
TGFα- and LPS-stimulated mucin production in NCI-H292 cells, perhaps at the
transcriptional level of NFκB [16]. EGFR can be phosphorylated when stimulated
with TNFα or H2O2 is added to NCI-H292 cells [17]. Because the antioxidant,
N-acetyl cysteine, suppresses this reaction, it is thought that this is due to reactive
oxygen species (ROS) derived from neutrophils phosphorylating EGFR [17]. The
addition of neutrophil elastase to NCI-H292 cells also causes phosphorylation of
EGFR and enhances mucin production [18]. Macrolides suppress the infiltration and
activation of neutrophils, resulting in suppression of ROS and elastase production,
suppression of EGFR activation, and reduction in mucin production. The culture
supernatant of Pseudomonas aeruginosa stimulates EGFR and enhances mucin
production [19]; therefore, macrolides can decrease mucin gene expression by
decreasing EGFR activation.
4. Regulation of inflammatory cells/cytokines
Neutrophils release chemokines including IL-8/CXCL8, leukotrienes, proteases,
and ROS. Low-dose long-term macrolide therapy decreases neutrophil numbers,
IL-8/CXCL8, and IL-1β in bronchoalveolar lavage fluid of subjects with DPB or
bronchiolitis [20]. Administration of LPS to rats enhances airway neutrophil
28 M. Kondo
IL-13 N-CLCA1
C-CLCA1
CLCA1
Mucin
Cleavage Cl-
N-CLCA1
ML
IL-4Ra IL-13Ra1 EGFR ML
ATP
TMEM16A UTP P2Y2R
TMEM16A ML Cl-
ERK1/2
ML NFkB ML Ca2+
JAK1
ML STAT6 MUC
5AC
MAPK13
CLCA1
TMEM16A MUC5AC
CLCA1
ML
Epithelial
Precursor Goblet cells
Cells
Ciliated cells
Fig. 1 The hypothesis from goblet cell metaplasia to the secretion of airway epithelial cells induced
by IL-13 and the reported points of action of macrolides Stimulation of IL-13 induces TMEM16A
via JAK1 and STAT6, after which TMEM16A migrates to the cell membrane. Similarly, CLCA1 is
also produced and secreted extracellularly by stimulation with IL-13. CLCA1 is autolyzed, and
N-CLCA1 acts on TMEM16A, contributing to the stabilization of TMEM16A on the cell mem-
brane. In addition, TMEM16A interacts with EGFR, MUC5AC is induced via activation of ERK1/
2, NFκB, and MAPK13-dependent pathway, mucin granules are formed, and goblet cell formation
is completed. IL-13 stimulation suppresses FOXA2 through activation of SPDEF and suppresses
differentiation into ciliated cells. In goblet cells, secretory stimuli such as ATP and UTP increase
intracellular Ca2+ via P2Y2 receptors and induce extracellular Ca2+ influx. As a result, TMEM16A
shows CaCC activity and causes Cl ion transport and mucin granule secretory reaction. In this
hypothesis, the blocking marks are reported as the points of action of macrolides (ML). Created
with reference to References 8, 9, 34–36
Phagocytosis
ROS
Elastase
Cl ion
Mucin
LTB4
Biofilm
Quorum sensing
Airway Barrier
epithelium -Defensin
Proinflammatory cytokine
Apoptosis Chemotaxis Efferocytosis IL-10
Fig. 2 Effect of macrolides on chronic inflammatory airways. In the chronic inflammatory airway,
barrier dysfunction of the airway epithelium, infiltration of inflammatory cells, goblet cell meta-
plasia, hypersecretion, impairment of mucociliary clearance, and recurrent airway infection are
observed. Macrolides have antiinflammatory effects such as suppression of proinflammatory
cytokine productions, adhesion molecules, chemical mediators release, reactive oxygen species
(ROS) production, and induction of apoptosis of neutrophils. For airway epithelium, macrolides
suppress secretory responses, enhance barrier function, and suppress proinflammatory cytokines
and adhesion molecules. For bacteria, macrolides suppress biofilm and quorum-sensing function.
Downward-facing arrows, inhibition by macrolides; upward-facing arrows, enhancement by
macrolides
antibacterial effect and host defense are stimulated. However, after 24 h, macrolides
decrease IL-8, proteases, and ROS and promote resolution from inflammation.
Apoptosis of neutrophils is also involved in this process such that neutrophil necrosis
decreases and the release of inflammatory mediators mitigates. Macrolides also
suppress the release of proinflammatory cytokines and inducible nitric oxide
synthase (iNOS) from monocytes and alveolar macrophages and convert M1 to
M2 macrophages after 2–3 days. M2 macrophages release the antiinflammatory
cytokine, IL-10 [42]. Macrophages enhance phagocytosis and efferocytosis of
apoptotic neutrophils in the presence of macrolides [43]. The effect of macrolides
on the resolution of inflammation lasts for weeks to months [44]. Macrolides also
reduce the expression of Toll-like receptors and the expression of IL-12 in dendritic
cells [45]. This causes macrolides to suppress differentiation into Th1 cells and, as a
result, to reduce IFNγ released from Th1 cells. Macrolides induce immune-tolerant
dendritic cells and suppress the expression of co-stimulatory molecules [45–47].
In summary, the effects of macrolides on the airway are shown in Fig. 2 and
Table 1.
Table 1 Antiinflammatory and immunomodulatory effects of macrolides on airway epithelial cells, inflammatory cells, and other cells
Airway epithelial cells Neutrophils Macrophages/Monocytes Lymphocytes Fibroblasts Endothelial cells
Inhibition of cytokine etc.
IL-8 TNFα IL-1β IL-4, IL-5, IL-13 VEGF VCAM-1
TNFα LTB4 TNFα TNFα RANTES VEGF
GM-CSF IL-1β IL-6 IL-2 Eotaxin
Eotaxin Mac1 IL-8 IL-17 IL-8
IL-6 (G)M-CSF IFNγ MMP
ICAM-1 IL-12 IL-10
IFNγ
Inhibition of function
Cl ion transport Elastase Inducible NO production T cell skewing Th1 Proliferation Angiogenesis
Mucin secretion Myeloperoxidase Phagosomal acidification Perforin Migration
MUC5AC Production ROS Co-stimularoty molecules CD69
Goblet cell metaplasia NETS TLR2,4,6,9 Granzyme B
Macrolides and Inflammatory Cells, Signaling, and Mediators
Macrolides are concentrated in tissues and cells, and their concentration is reported
to reach 10–100 times that of serum [48], suggesting a role of macrolides in
intracellular signaling. However, the target proteins and receptors are still unknown.
Intracellular signaling pathways affected by macrolides are shown in Fig. 3.
1. Intracellular calcium
Intracellular Ca2+ plays an important role in intracellular signal transduction. In
airway epithelial cells and A549 cells, EM suppresses intracellular Ca2+ level and
Ca2+ influx from the extracellular space caused by purinergic receptor stimulation
[49]. EM and AZM can decrease mucus secretion from the submucosal glands of the
airways, in part, by inhibiting calcium influx [50]. In mast cells, roxithromycin also
decreases the activation by β-defensin 2 via the Ca2+ signaling pathway [51]. In
neutrophils, EM suppresses FMLP-stimulated superoxide production and Ca2+
influx [52]. In addition, since intracellular Ca2+ is also involved in the activation
of mitogen-activated protein kinases (MAPKs) and NFκB, it is speculated that
macrolides may affect a wide range of cell functions through the regulation of
intracellular Ca2+ [2].
2. Mitogen-activated protein kinases (MAPKs)
MAPKs form a network responding to both internal and external stimuli for
signal transduction and play an important role in controlling inflammatory gene
expression, cell proliferation, cell differentiation, and apoptosis [53]. There are three
main classes of MAPKs: extracellular signal-regulated kinase (ERK), c-Jun N-ter-
minal kinase (JNK), and p38 MAPK. MAPKs induce IL-8/CXCL8 expression by
both an NFκB-dependent and independent pathway. Shinkai et al. investigated the
effect of macrolides on MAPK and IL-8/CXCL8 expression using airway epithelial
cells. CAM suppressed ERK phosphorylation in the initial 30–90 min, the level was
increased at 2 h to 3 days, and it normalized to the unstimulated level by 5 days. As a
result, IL-8/CXCL8 was maximal at 24 h, and then gradually decreased [54]. The
action of macrolides is not to suppress inflammation in one direction but to reset and
normalize it and thus is immunomodulatory with long-term therapy. Macrolides also
protect cells by moving the cell cycle to G1/G0, and they decrease the phosphoryla-
tion of ERK in airway epithelial cells [55]. Furthermore, the inhibitory effect of
CAM and AZM on MUC5AC production from airway epithelial cells and neutrophil
infiltration during Pseudomonas aeruginosa infection is also mediated by the inhi-
bition of the ERK activity [56–58]. It has been reported that EM restored steroid
sensitivity by suppressing the activation of the JNK/c-JUN pathway induced by
tobacco smoke [59].
3. Transcription factors; NFκB and AP-1
Macrolides decrease cytokine production by suppressing the transcription factors
NFκB and AP-1 in airway epithelial cells and monocytes [60–62]. NFκB is inactive
Macrolides and Inflammatory Cells, Signaling, and Mediators 33
External stimuli
(Growth factor, LPS, Pathogen, Inflammatory mediator)
GPCR
RTK TLR Ca2+ channel
PI3K PLCg G
MEKK MyD88 TRIF
PLCb
DAG DAG ER
IP3 TRAF IP3
ML Ca2+
[Ca2+] i stores
TAK1 IP3R
Akt
mTOR Caspase-1
ML I B-
Nrf2 NF B PKC
ERK Ca2+-mediated
ML CaMK
p38 cellular response
JNK ML
NLRP3
ML
inflammasome
AP1 NF B
NLRP3
ProIL-1
ProIL-18
Fig. 3 Intracellular signaling transduction pathways and the related sites of macrolide
immunomodulation. Receptor tyrosine kinases (RTKs) are receptors for many growth factors and
cytokines. For example, epithelial growth factor receptor (EGFR) activates MEKK, MEK, and
ERK1/2. Toll-like receptors (TLRs) activated by pathogens and LPS stimulate the IκB kinase (IKK)
complex and the MAPK pathway. IKK complex activates NFκB through the digestion of IκB, and
then NFκB is translocated. The MAPK pathway leads to AP-1 induction. Macrolides inhibit these
pathways and then inhibit proinflammatory gene expression. NLRP3, ProIL-1β, and ProIL-18 gene
expression form NLRP3 inflammasome, leading to IL-β and IL-18 release decomposed by
Caspase-1. G-protein-coupled receptor (GPCR) or RTK-mediated activation of phospholipase C
(PLC) produces inositol triphosphate (IP3) and diacylglycerol (DAG). IP3 increases intracellular Ca
from endoplasmic reticulum Ca stores, and DAG activates protein kinase C (PKC). RTK- or GPCR-
stimulation also induces activation of PI3K/Akt pathway. Macrolides inhibit these pathways and as
a result, modulate various cell functions. Blue arrows are major pathways influenced by macrolides.
Dashed arrows are cross-talk pathways. Red lines indicate the sites of macrolide’s inhibition.
Modified from Reference 2. Abbreviations: Akt AKT8 virus oncogene cellular homolog; AP-1
activator protein 1; CaMK calmodulin kinase; ER endoplasmic reticulum; ERK extracellular signal-
regulated kinase; GFR cytokine receptor/growth factor receptor; IKK IκB kinase; IP3R inositol
triphosphate receptor; JNK c-Jun N-terminal kinase; MEK MAPK/ERK kinase; MEKK MAPK/
ERK kinase kinase; mTOR serine/threonine kinase mammalian target of rapamycin; MyD88
myeloid differentiation factor 88; PI3K phosphoinositide 3-kinase; PKC protein kinase C; TAK1
transforming growth factor-activated protein kinase 1; TRAF TNF receptor-associated factor; TRIF
TIR-domain-containing adaptor-inducing interferon-β; TLR Toll-like receptor; Nrf2 Nuclear factor-
erythroid 2-related factor 2
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