4. Discussion
Dilated cardiomyopathy is one of the most serious side effects of
doxorubicin treatment, significantly reducing its anticancer value and
causing a large societal burden. However, the mechanisms of dilated
cardiomyopathy are still unclear, and an effective therapy to prevent
the progression of existing cardiac inflammation and fibrosis induced by
DOX is urgently needed. Our study aimed to determine the potential
effect of LCZ696 and the role of TLR2 in DOX-induced cardiac
dysfunction, fibrosis and inflammation, which may help find an effective
drug to protect the heart and provide a potential signaling pathway for
the treatment of DOX-induced dilated cardiomyopathy.
In our studies, we showed that LCZ696 treatment and TLR2 deficiency
attenuated DOX-related dilated heart failure by improving the decreased
EF% and increased LVIDd. In addition, in vivo and in
vitro , our results showed that DOX stimulated the expression of matrix
proteins and inflammatory cytokines in the heart and that LCZ696
treatment and TLR2 knockdown ameliorated these alterations and
ultimately improved cardiac function. Furthermore, the underlying
mechanisms involved in DOX-induced cardiomyopathy revealed that DOX
stimulated the formation of the TLR2-MyD88 complex, which activated the
NF-κB pathway, leading to cardiac cell inflammation and fibrosis. This
TLR2-MyD88 interaction was TLR4 or MD2 independent and could be
disturbed by LZC696, which explains the strong effect of this drug in
preventing heart injury caused by DOX.
It is well established that LCZ696, as a novel angiotensin
receptor-neprilysin inhibitor, significantly reduced mortality and
hospitalization due to heart failure in HF patients with a reduced
ejection fraction (HFrEF)(Mann et al., 2020). The results of the
PARADIGM-HF trial(McMurray et al., 2014) suggest a second function of
sacubitril/valsartan: degrading peptides that regulate the
cardiovascular, nervous, inflammatory, and immune systems(D’Elia,
Iacovoni, Vaduganathan, Lorini, Perlini & Senni, 2017; Turner, Isaac &
Coates, 2001). Recent studies found that LCZ696 increased local BNP/CNP
levels, interfered with angiotensin II-mediated signaling, and then
reduced the magnitude of cardiac remodeling in animal models of
hypertension and myocardial infarction(Oatmen, Zile, Burnett & Spinale,
2018; von Lueder et al., 2015). Regarding the cardiotoxicity induced by
DOX, accumulating evidence has discovered the pathophysiological
mechanisms, but treatments to mitigate cardiac damage are still
limited(Hu et al., 2020; Yang et al., 2020). Xia Y et al found that Drp1
and its Ser-616 phosphorylation were significantly increased in dilated
cardiomyopathy (DCM) patients and demonstrated that the use of LCZ696
against DOX-induced cardiac dysfunction is associated with alleviated
Drp1-mediated mitochondrial dysfunction(Xia et al., 2017). Similar to
our results, we focused on the anti-inflammatory effect of LCZ696. Our
data indicated that LCZ696 prevented IκBα degradation, inhibited the
nuclear translation of NF-κB and reduced the expression of inflammatory
cytokines in vivo and in vitro . More impressively, we
found that pretreatment with LCZ696 inhibited the increased formation of
the TLR2/MyD88 complex induced by DOX. This finding partly explains the
mechanism of the anti-inflammatory effect of LZC696.
Similar to other TLRs, TLR2 is the most characteristic member of pattern
recognition receptors (PRRs), which play an important role in innate
immune mechanisms(Jacquet & Robinson, 2020). TLRs play different roles
in different stages of infection of atherosclerosis-related pathogens
such as Chlamydia pneumoniae(Li, Xia & Hu, 2020). Since Nozaki N et al
found that TLR2 may play a role in the regulation of inflammatory and
apoptotic mediators in the heart after DOX administration(Nozaki,
Shishido, Takeishi & Kubota, 2004) in 2004, little research has
explored the mechanism by which TLR2 mediates DOX-induced
cardiotoxicity. Our current studies indicated that DOX induced the
increased formation of the TLR2/MyD88 complex, which leads to the
activation of the NF-κB pathway and stimulates the expression of cardiac
inflammation and fibrosis. This result partially compensates for the
inflammatory mechanism of DOX-induced myocardial injury. Moreover, we
found that this interaction of TLR2 and MyD88 induced by DOX is
independent of TLR4 or MD2, but the clear role of TLR4 and MD2 in
DOX-induced cardiac side effects still needs further research.
Taken together, our results demonstrate that the mechanism by which
LCZ696 relieves DOX-induced cardiac inflammation fibrosis and heart
failure lies in reducing the formation of TLR2-MyD88
complexes. LCZ696 may be a
potential drug to treat DOX-related heart failure, and TLR2-MyD88 could
be a parallel target in the prevention and treatment of DOX-related
heart injury.