Baicalin Alleviates Pam3CSK4-mediated Inflammatory Response And Protects Mice From MRSA Infection

[Objective] Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection.One of the most common pathogens is Staphylococcus aureus(S.aureus),especially methicillin-resistant S.aureus(MRSA),which leads to significant morbidity and mortality.Therefore,innovative and effective approaches to combat the problems are urgently needed.Recently,host-directed therapy(HDT)is becoming viable adjuncts to the treatment of infectious diseases especially those caused by antibiotic-resistant bacteria.HDT aims to promote host defense,inhibit exaggerated inflammation and alleviate tissue damage.Baicalin(BAI)is a predominant flavonoid and bioactive compound isolated from the roots of traditional Chinese medicine Scutellaria baicalensis.It has been reported that BAI exhibited multiple biological properties such as anti-oxidant,anti-tumor and anti-inflammatory role.In this study,we intended to investigate the beneficial effects of BAI on sepsis triggered by systemic infection of MRSA,and the molecular mechanisms underlying its anti-inflammatory effects in bacteremia.[Methods](1)Mouse macrophages were stimulated with Pam3CSK4,peptidoglycan(PGN)or heat-killed MRSA(HK-MRSA)for a certain period with or without BAI,and the expression of inflammatory cytokines was detected by q RT-PCR and ELISA.(2)The effects of BAI on the activation of Pam3CSK4-triggered signaling pathways(such as MAPK,PI3K/Akt and NF-kB pathways)in Raw264.7 were examined by Western blot.(3)The acute infectious model was established by intraperitoneal injection of MRSA to mimic sepsis,and then was treated by BAI and other drugs.The release of inflammatory mediators in sera was examined with CBA method by FACS.Liver and kidney tissues were homogenized and diluted for the detection of colony-forming units(CFU).(4)The septic shock model was carried out by injecting mice with a lethal dose of MRSA.Mice were treated with BAI and the survival status was recorded.[Results] BAI inhibited the expression of inflammatory cytokines(IL-6,TNF-a,IL-1b,etc.)in Pam3CSK4 or PGN-induced mouse macrophage.BAI also reduced the production of IL-6 and TNF-a induced by heat-killed MRSA in mouse primary peritoneal macrophages and immortalized bone marrow-derived macrophages(i BMDMs).The extensively inhibitory effects of BAI on the signaling pathways downstream of TLR2(ERK,JNK,IKKa/b,etc.)might largely account for the reduction of inflammatory cytokines.In vivo,BAI in combination with vancomycin(VAN)inhibited the release of inflammatory cytokines,reduced the bacterial load and alleviated tissues damage.Furthermore,BAI in combination with dexamethasone DXM had protective effects in MRSA-challenged mice.[Conclusions] BAI helps to maintain immune equilibrium and inhibits overwhelming inflammatory response induced by Pam3CSK4,PGN or heat-killed MRSA.Furthermore,the protective roles of BAI on sepsis triggered by MRSA infection was observed.Therefore,BAI may be a promising immunomodulatory and/or anti-inflammatory agent of HDT which can treat infectious diseases as an adjuvant.It provides an insight into the potential therapeutic role of BAI in sepsis,especially those caused by drug-resistant bacteria.