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.