The Effect Of TLR4/NF-κB Signaling Pathway On Astragaloside Ⅳ Inhibits Myocardial Hypertrophy Induced By Isoproterenol

ObjectiveTo observe the expression of Toll-like receptor4(TLR4)/nuclearfactor-kappaB (NF-κB) signaling pathway on myocardial hypertrophy inducedby isoproterenol and test the hypothesis that Astragaloside IV can amelioratethe myocardial hypertrophy and inflammatory effect induced by β-adrenergichyperactivity, we carried out in vivo and in vitro experiments.MethodsIn in vivo study, the isoproterenol (Iso)(5mgï¹'kg-1ï¹'d-1) was used as a modelof myocardial hypertrophy by intraperitoneal injection. SD rats were randomlyassigned to following six groups: the control group, Iso group, Iso plus As IV20,40,80mgï¹'kg-1ï¹'d-1groups and Iso plus Pro40mgï¹'kg-1ï¹'d-1group. In in vitrostudy, cultured neonatal rat cardiomyocytes were pretreated with As IV (3,10,30μmolï¹'L-1), Propranolol (2μmolï¹'L-1) and BAY11-7082(5μmolï¹'L-1) for30min, and then incubated with Iso (10μmolï¹'L-1) for48h.For the rats in each group, the heart mass index (HMI) and the left ventricularmass index (LVMI) were measured. To measure the transverse diameter of leftventricular myocardial cells (TDM), the hematoxylin-eosin staining method wasapplied. In addition, the volume and the total protein content of cardiomyocyteswere measured, the mRNA expression of ANP and TLR4were quantified by RT-PCR, the protein expression of TLR4, IκBα and p65were quantified byWestern blot, and the level of TNF-α and IL-6were measured by ELISA.ResultsIn vivo: Comparing the Iso group with the control, the differences were in thefollowings: the HMI, LVMI, TDM were significantly increased; the expression ofANP, TLR4mRNA, and TNF-α, IL-6in serum were significantly increased; theprotein expression of TLR4and p65were increased, while the IκBα weredecreased (P<0.01). Comparing the other3groups (Iso plus As IV) with the Isogroup, the differences were in the followings: the HMI, LVMI, TDM weresignificantly decreased; the protein expression of TLR4and p65weredecreased, while the IκBα were increasedï¼›the expression of TLR4and ANPmRNA were decreased, TNF-α, IL-6in serum were significantly decreased,and the differences were positively related to dose of three groups.In vitro: Compared with the control group, the cell size, total protein content,ANP and TLR4mRNA, TLR4, p65, TNF-α and IL-6were increased, andexpression of IκBα protein was decreased in Iso group (P<0.01). As IV,BAY11-7082and Propranolol could remarkably down-regulate theover-expression of the cell size, total protein content, ANP and TLR4mRNA,TLR4, p65, TNF-α and IL-6, and increased the expression of IκBα (P<0.05).ConclusionAstragaloside IV has good protective effect on myocardial hypertrophyinduced by isoproterenol. More specifically, the cardioprotection is related toinhibiting the TLR4/NF-кB signaling pathway and the attenuating inflammatoryeffect.