Modulation of Drug Resistance by Furanochromones in NorA Overexpressing Staphylococcus Aureus

Abstract

Khellin and visnagin are natural furanochromones that photoreact with DNA. Khellin has been used in the treatment of vitiligo and psoriasis, as well as in the treatment of angina pectoris and asthma due to its potent action as a coronary vasodilator and antispasmodic agent. The present study aimed to investigate whether the compounds khellin and visnagin act as inhibitors of NorA protein, an efflux pump overproduced by the strain of Staphylococcus aureus SA-1199B that confers resistance to the fluoroquinolones, such as norfloxacin and ciprofloxacin. These substances alone did not show antibacterial activity against the strain tested. On the other hand, when these compounds were added to the culture medium at subinhibitory concentration, they were able to reduce the minimum inhibitory concentration (MIC) of norfloxacin, ethidium bromide, as well as berberine, suggesting that these compounds are modulating agents of norfloxacin resistance, possibly due to NorA inhibition. Molecular docking analysis showed that both khellin and visnagin form hydrogen bonds with Arg310, an important residue in the interaction between NorA and its substrates, supporting the hypothesis that these compounds are NorA inhibitors. These results suggest a possible application of khellin and visnagin as adjuvants to norfloxacin in the treatment of infections caused by strains of S. aureus that overproduce NorA.

Synthesis, Herbicidal Activity, and Structure–Activity Relationships of O-Alkyl Analogues of Khellin and Visnagin

“…33 However, visnagin has also been reported to bind human cyclooxygenase-2 (COX-2), an enzyme not found in plants, 34 and in silico binding studies have also reported that khellin and visnagin bind still other human and bacterial proteins. 35,36 Our earlier work of the physiological effects of khellin and visnagin on plants led us to conclude that these compounds may have a complex mode of action, involving more than one molecular target. 8 Considering the number of mammalian proteins with which these compounds interact, this seems highly possible, making the use of binding studies with only one target protein less useful in optimizing the effect of these compounds as a herbicide.…”

3-Substituted Coumarins Inhibit NorA and MepA Efflux Pumps of Staphylococcus aureus

“…With the NorA efflux pump, osthol potentiated the antibiotic activity against S. aureus 1199B and had in silico affinity with the protein, highlighting the hydrophobic interactions and hydrogen bonds, for example, with Arg98, as occurred with coumarin C2 [38]. Furanochromones are compounds structurally similar to coumarins, and the study by Rodrigues et al [39] showed that khellin, like C1, interacts with the NorA model through hydrophobic interactions with Phe16 and Ile136. The amino acids Arg310, Asn340, Gln51, Met109, Ser333, and Ser337 also appear in both studies but are involved in different types of interactions.…”

“…π-sulfur interaction (CPZ), carbon-hydrogen bonds (including with serine), and van der Waals interactions were also identified. Other amino acids, such as Ala48, Arg310, and Asn340, for example, are targets of EPIs and coumarins, but with different interactions [39,40].…”

The Major Facilitator Superfamily and Antimicrobial Resistance Efflux Pumps of the ESKAPEE Pathogen Staphylococcus aureus

“…The docking study revealed that the molecule interacted with the NorA efflux pump's Ser-218, Ile-135, Thr-335, and Asn-339 residues [131]. Thiophene, a curcuminoid, showed competitive inhibition against norfloxacin, and formed an H bond with the Arg-310 residue of NorA [132]. The furanochromones khellin and visnagin showed EPI activity by interacting with the Arg-310 residue of the NorA efflux pump, resulting in a two-fold reduction in the MIC of norfloxacin [132].…”