Effects of 14-Alpha-Lipoyl Andrographolide on Quorum Sensing in Pseudomonas aeruginosa

Abstract

<jats:title>ABSTRACT</jats:title><jats:p>In<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">Pseudomonas aeruginosa</jats:named-content>, the quorum-sensing (QS) system is closely related to biofilm formation. We previously demonstrated that 14-alpha-lipoyl andrographolide (AL-1) has synergistic effects on antibiofilm and antivirulence factors (pyocyanin and exopolysaccharide) of<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">P. aeruginosa</jats:named-content>when combined with conventional antibiotics, while it has little inhibitory effect on its growth. However, its molecular mechanism remains elusive. Here we investigated the effect of AL-1 on QS systems, especially the Las and Rhl systems. This investigation showed that AL-1 can inhibit LasR–3-oxo-C<jats:sub>12</jats:sub>-homoserine lactone (HSL) interactions and repress the transcriptional level of QS-regulated genes. Reverse transcription (RT)-PCR data showed that AL-1 significantly reduced the expression levels of<jats:italic>lasR</jats:italic>,<jats:italic>lasI</jats:italic>,<jats:italic>rhlR</jats:italic>, and<jats:italic>rhlI</jats:italic>in a dose-dependent manner. AL-1 not only decreased the expression level of Psl, which is positively regulated by the Las system, but also increased the level of secretion of ExoS, which is negatively regulated by the Rhl system, indicating that AL-1 has multiple effects on both the Las and Rhl systems. It is no wonder that AL-1 showed synergistic effects with other antimicrobial agents in the treatment of<jats:named-content xmlns:xlink="http://www.w3.org/1999/xlink" content-type="genus-species" xlink:type="simple">P. aeruginosa</jats:named-content>infections.</jats:p>

Mechanistic analysis of a synthetic inhibitor of the Pseudomonas aeruginosa LasI quorum-sensing signal synthase

“…This biofilm is known to be dependent on the Psl exopolysaccharide polymers which attach the biofilm to the surface 21 . The Psl production is controlled by the QS las system 43 so we examined surface biofilm formation to determine the effects of inhibiting QS with TZD. In recent studies, the most obvious choice of QS inhibitors has been signal molecule analogues, such as those involved in LasR activation 39 , or other natural compounds with QS inhibition effects, such as trans-cinnamaldehyde 42 or cinnamaldehyde 44 , for which in silico study approaches have been explored.…”

Control of Biofilm Formation: Antibiotics and Beyond

“…Antimicrobial peptides Cationic AMPs interact with anionic biofilm surface (37) Relative selectivity, broad-spectrum activity, cationic and amphipathic properties, disruption of bacterial cell membrane with low frequency, and slow emergence of bacterial tolerance (28,29) Development of resistance to AMPs via modification of bacterial lipopolysaccharides or using efflux pumps (43) AMPs inactivate the twitching motility of P. aeruginosa and inhibit biofilm formation (37) Bactericidal activity against slow-growing bacteria within biofilm (30) Susceptibility of some AMPs to proteolytic enzymes as well as their high cost of purification and sequences (140) Disrupt expression of biofilm formation essential genes, downregulate expression of type IV pili, rhamnolipid, quorum-sensing, and flagellar assembly genes (38) Antimicrobial activity improved and cytotoxicity reduced by modifying and hybridization the sequences of primary amino acids (31,32) Insufficient selectivity of STAMPs (140) Bind to eDNA and accelerate detachment of the biofilm (41) Possible hemolytic effect and potential cytotoxic effect (140) Biofilm-degrading enzymes Degradation of extracellular matrix components (polysaccharides, protein, and eDNA) (63) Efficient inhibition of biofilm formation, disruption of EPS production, dispersing preformed biofilm (64, 66) High quantities of EPS and proteolytic exoenzymes by mature biofilm counteract the enzymatic activity (64) Reduces no. of biofilm-viable cells (70) Quorum-sensing inhibitors Inhibition of cell-to-cell or cell-to-surface attachment QSIs possess high species specificity and effectively act against certain pathogens (138) Reported toxicity of and resistance to QSI (136) Essential oils Attack cellular ATP and ATPase, acting on cytoplasmic enzyme and membrane proteins/fatty acids leading to the leakage of metabolites and ions (94) Have a broad-spectrum activity against a wide range of pathogenic microbes (93) Some EOs produce oxidative stress and possess toxic properties, inducing killing activity against eukaryotes (141) Anti-quorum-sensing activity by downregulation of QS genes leading to reduced virulence factor production and biofilm formation (94) Have been used as ethnomedicine against bacterial infection and cancer for a long time (95,96) Increased albumin level and skin irritation (see review by Patel et al …”

In vitro anti-biofilm activity of 14-deoxy-11,12-didehydroandrographolide from Andrographis paniculata against Pseudomonas aeruginosa

“…In figure, black line represents control group without any drug treatment; red line represents bacteria treated with only AZI (6 μg/mL); light blue represents treated with only GEN (4 μg/mL); purple line represents only DDAG-treated group; green and dark blue lines represent DDAG with AZI or GEN, respectively. Each value represents as mean ± SD of three independent experiments Andrographolide (AG) was identified as an inhibitor of QS system of P. aeruginosa [11], and its derivative 14-alpha-lipoyl andrographolide inhibits biofilm formation in a better way [49,50]. Another report highlighted that andrographolide and its three derivatives such as 14-dehydroxy-11,12-didehydroandrographolide-3,19-bis ( s u c c i n i c a c i d ) p o t a s s i u m s o d i u m s a l t , 1 4dehydroxyandrographolide-12-sulfonic acid sodium salt, and 14-dehydroxy-11,12-didehydroandrographolide-3,19bis (succinic acid) potassium salt have been used clinically to get relief from inflammation, fever, and pain due to bacterial and viral infections for the last 40 years in China [7].…”

“…In the present study, two major diterpenoids isolated from A. paniculata, 14-dehydroxy-11,12-didehydroandrographolide and andrographolide, were evaluated for their effects on inhibition of biofilm formation. For this purpose, AG or DDAG individually or along with either of any antibiotics AZI or GEN was used in vitro using P. aeruginosa model, which is completely established representation by the researchers for QS signaling pathway as well as biofilm study [7,49,50]. Here, we have selected 0.1 mM of DDAG with standard antibiotics (AZI or GEN) at sub-MIC dose as optimum concentration to stop more than 90% biofilm formation along with production of extracellular polymeric substances of biofilm, expression of virulence factor such as protease activity, LasB activity, and pyocyanin production.…”