AUTHOR=Wang Xin , Ma Qiang , Niu Xiaohao , Liu Zhu , Kang Xinyun , Mao Yanni , Li Na , Wang Guiqin 

TITLE=Inhibitory Effect of Andrographis paniculata Lactone on Staphylococcus aureus α-Hemolysin

JOURNAL=Frontiers in Pharmacology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/pharmacology/articles/10.3389/fphar.2022.891943

DOI=10.3389/fphar.2022.891943

ISSN=1663-9812

ABSTRACT=<p>We investigated the effect of andrographolide (AP) on the hemolytic capacity of <italic>Staphylococcus aureus</italic> (<italic>S. aureus</italic>) isolated from our region. AP is a labdane diterpenoid isolated from the stem and leaves of <italic>Andrographis paniculata</italic>. The <italic>hla</italic> gene from 234 <italic>S. aureus</italic> strains and the quality control standard strain ATCC29213 in dairy cows in some areas of Ningxia was analyzed. Evolutionary analysis, homology modeling, and functional enrichment annotation of α-hemolysin Hla detected from our region were performed through bioinformatics. The hemolytic ability of <italic>S. aureus</italic> isolates from the region was examined using the hemolysis test, and the effect of AP on <italic>S. aureus</italic> was quantified. Moreover, the effect of AP on the transcript levels of <italic>hla</italic> and genes highly related to <italic>hla</italic> (i.e., <italic>clfA</italic> and <italic>fnbA</italic>) was examined through fluorescence quantitative PCR. The mode of action of AP on the detected Hla was analyzed through molecular docking and dynamic simulation. The results showed that <italic>S. aureus</italic> in our region has a high rate of <italic>hla</italic> carriage. The hemolytic activity of strains NM98 and XF10 was significant, and ATCC29213 also exhibited some hemolytic activity. AP could inhibit the expression of Hla and its related proteins by downregulating <italic>hla</italic>, <italic>clfA</italic>, and <italic>fnbA</italic> transcript levels, which in turn attenuated the <italic>S. aureus</italic> hemolytic activity. Meanwhile, the AP molecule can form three hydrogen bonds with residues ASN105, SER106, and THR155 of Hla protein; bind with PRO103 through alkyl intermolecular forces; and form carbon hydrogen bonds with LYS154, reflecting that the AP molecule has a comparatively ideal theoretical binding activity with Hla protein. Among them, PRO103 and LYS154 are highly conserved in Hla protein molecules and play pivotal roles in the biological functions of Hla, and their binding may affect these functions. Their binding may also prevent the conformational transition of Hla from a monomer to an oligomer, thus inhibiting Hla hemolytic activity. This study offers a molecular basis for use of AP as an antivirulence drug and new ideas for developing novel drugs against <italic>S. aureus</italic> infection.</p>