1. Introduction
Doxorubicin (DOX), a member of the family of anthracyclines and an
antitumor antibiotic, has been widely used to treat breast cancer,
bladder cancer and so on(Tacar, Sriamornsak & Dass, 2013). However, it
has been well documented that the most dangerous side effect of
doxorubicin is dilated cardiomyopathy, which leads to congestive heart
failure, and this side effect is positively correlated with the
cumulative dose of DOX(Chatterjee, Zhang, Honbo & Karliner, 2010).
Previous studies have suggested that doxorubicin causes cardiomyopathy
related to oxidative stress, downregulation of contractile protein genes
and p53-mediated apoptosis(Vejpongsa & Yeh, 2014). Recent studies have
found that doxorubicin has a strong inflammatory effect, which mainly
manifests as doxorubicin further promoting the expression of the
following cardiac inflammatory factors: 1) DOX indirectly induces
interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) through
autocrine and paracrine processes; 2) DOX promotes cardiac fibroblast
proliferation and extracellular matrix protein synthesis; and 3)
Toll-like receptor-4, PI3Kγ and other inflammatory mediators are
activated, which leads to a vicious cycle of inflammatory reactions in
cardiac cells(Li et al., 2018; Riad et al., 2008). Increasing attention
should be paid to the inflammatory response to cardiomyopathy caused by
doxorubicin.
LCZ696, also known as sacubitril/valsartan, consists of the neprilysin
inhibitor sacubitril and the angiotensin receptor blocker valsartan, is
a combination drug for use in patients with heart failure and a reduced
ejection fraction(Hubers & Brown, 2016; Lillyblad, 2015; Yancy et al.,
2016). Recently, many studies have explored the anti-inflammatory effect
of LCZ696 in basic research, with evidence that this drug can attenuate
cardiac dysfunction after myocardial infarction(von Lueder et al.,
2015), inhibit oxidative stress, inflammation, and fibrosis, improve
renal function in CKD(Jing et al., 2017) and ameliorate NLRP3 after
relieving the pressure overload in mice(Li et al., 2020). In addition,
Yan et al found that LCZ696 protects cardiac function from
doxorubicin-induced dilated cardiomyopathy by alleviating Drp1-mediated
mitochondrial dysfunction(Xia et al., 2017). However,
the potential effect of LCZ696 on
DOX-induced cardiac inflammation and cardiac dysfunction, especially the
underlying mechanisms of its anti-inflammatory effects, remains to be
elucidated.
TLR2 is part of the family of Toll-like receptors (TLRs),
which mainly mediate
pathogen-induced inflammation in innate immunity(Elshabrawy, Essani,
Szekanecz, Fox & Shahrara, 2017; Henrick, Yao, Taha, German &
Rosenthal, 2016). Although there is no involvement of endotoxins such as
viruses and bacteria, recent studies have demonstrated that TLR2 may
play a potential role in this inflammatory response to the process of
cardiac remodeling caused by DOX. Naoki Nozaki et al found that TLR2
knockout mice exhibited preserved cardiac function and an increased
survival rate compared to DOX-challenged mice through mediating cardiac
inflammatory and apoptosis(Nozaki, Shishido, Takeishi & Kubota, 2004),
and Liang et al found that the levels of TLR2 were upregulated in
doxorubicin-treated patients who developed heart dysfunction(Liang,
Xinyong, Hongmin, Jing, Lang & Ping, 2018). Similarly, after analyzing
a large amount of clinical data, Pop-Moldovan AL et al found that the
expression of TLR4 and TLR2 was higher in patients with diastolic
dysfunction treated with doxorubicin(Pop-Moldovan et al., 2017). These
findings indicated that TLR2 may play a role in the mediation of
DOX-induced cardiomyopathy. However, how DOX activates TLR2-related
inflammation and whether LCZ696 can attenuate DOX-induced cardiac
failure in a TLR2-dependent manner remain unaddressed.
In this study, utilizing LCZ696 and TLR2 knockout mice, we investigated
the effect of LCZ696 and TLR2 deficiency on DOX-induced mouse
cardiomyopathy. Our results found that LCZ696 treatment and TLR2
deficiency reversed DOX-induced diastolic heart failure, cardiac
fibrosis and inflammation. More interestingly, we found that LCZ696 may
directly inhibit the formation of the TLR2/MyD88 complex activated by
DOX, which results in the attenuation of DOX-induced dilated
cardiomyopathy.