Quercetin Sensitizes Fluconazole-Resistant Candida albicans To Induce Apoptotic Cell Death by Modulating Quorum Sensing

Abstract

dQuorum sensing (QS) regulates group behaviors of Candida albicans such as biofilm, hyphal growth, and virulence factors. The sesquiterpene alcohol farnesol, a QS molecule produced by C. albicans, is known to regulate the expression of virulence weapons of this fungus. Fluconazole (FCZ) is a broad-spectrum antifungal drug that is used for the treatment of C. albicans infections. While FCZ can be cytotoxic at high concentrations, our results show that at much lower concentrations, quercetin (QC), a dietary flavonoid isolated from an edible lichen (Usnea longissima), can be implemented as a sensitizing agent for FCZresistant C. albicans NBC099, enhancing the efficacy of FCZ. QC enhanced FCZ-mediated cell killing of NBC099 and also induced cell death. These experiments indicated that the combined application of both drugs was FCZ dose dependent rather than QC dose dependent. In addition, we found that QC strongly suppressed the production of virulence weapons-biofilm formation, hyphal development, phospholipase, proteinase, esterase, and hemolytic activity. Treatment with QC also increased FCZmediated cell death in NBC099 biofilms. Interestingly, we also found that QC enhances the anticandidal activity of FCZ by inducing apoptotic cell death. We have also established that this sensitization is reliant on the farnesol response generated by QC. Molecular docking studies also support this conclusion and suggest that QC can form hydrogen bonds with Gln969, Thr1105, Ser1108, Arg1109, Asn1110, and Gly1061 in the ATP binding pocket of adenylate cyclase. Thus, this QS-mediated combined sensitizer (QC)-anticandidal agent (FCZ) strategy may be a novel way to enhance the efficacy of FCZ-based therapy of C. albicans infections. Candidiasis is a prevalent fungal infection caused by species of the yeast genus Candida. There are more than Candida 20 species, the most common of which is Candida albicans. Candidiasis is the fourth most common cause of health care-associated bloodstream infections in India and the United States (1). This yeast normally lives on the skin and mucous membranes without causing infection. However, overgrowth of these microbes can cause superficial mycoses, invasive mucosal infections, and disseminated systemic disease, particularly in AIDS patients, transplant recipients, and other immunocompromised people (2, 3). It is well documented that the emergence of drug-resistant C. albicans is increasing at an alarming pace (4-6). Therefore, the need for effective anticandidal therapy is increasing, as the available drugs are still very restricted.Currently available therapies for candidiasis are based on antifungal drugs including azoles, echinocandins, and inhibitors of calcineurin, Hos2 deacetylase, and Hsp90 (7-10). Fluconazole (FCZ) is most widely used to treat candidiasis infections because of its high bioavailability and low toxicity (11-13). However, excessive and indiscriminate clinical use of FCZ has led to the emergence of multiple-drug-resistant (MDR) strains of C. albicans (5,14,15). Importantly, t...

Quercetin Assists Fluconazole to Inhibit Biofilm Formations of Fluconazole-Resistant Candida Albicans in In Vitro and In Vivo Antifungal Managements of Vulvovaginal Candidiasis

“…6A) and the thickness of biofilm matrix (Fig. 6B) in a VVC isolate consistent with the previous results [18]. Notably, it was reported that ALS1 and HWP1 were also hypha-specific genes as the expression of former mRNA was correlated well with hyphal growth and the protein product encoded by the latter was only expressed on hyphae [51][52][53].…”

“…Intriguingly, the synergism of QCT and FCZ was independent of strain phenotype of resistance/susceptibility. As a matter of fact, most of the flavonoids were good at inhibiting the growth of FCZ-susceptible free-living cells and bad at dealing with FCZ-resistant clinical isolates and biofilms in C. albicans, but they usually performed satisfactorily in combination with FCZ in biofilm removal [18,28,35,36].…”

Scaffold of Selenium Nanovectors and Honey Phytochemicals for Inhibition of Pseudomonas aeruginosa Quorum Sensing and Biofilm Formation

“…Hence, binding of HP to the LasR signal receptor could cause a decrease in RhlR production that could result in a decrease in the rhlAB operon and rhlI production while eliminating transcriptional repression of mvfR . Related to earlier investigations, cationic Se (Dutta and Willcox, 2014), quercetin (Singh B. N. et al, 2015), kaempferol (Vikram et al, 2010), apigenin (Nazzaro et al, 2013), and caffeic acid (Borges et al, 2014) exhibited significant anti-QS effects. They can significantly reduce the secretion of virulence factors and biofilm formation in human pathogenic bacteria.…”

“…In particular, it is lethal to cystic fibrosis patients (common genetic disorder in Caucasians) by developing mucoid in lung tissue leading to pneumonia. Opportunely, numerous plant-derived QS inhibitors have been developed and the infection rate has decreased in the past few years (Hentzer et al, 2002; Hentzer and Givskov, 2003; Singh et al, 2009b; Singh B. N. et al, 2015). However, the current anti-QS therapies often are not straightforward owing to their lower bioavailability and inadequate penetration of bacterial biofilm and thus results in significant casualties (Defoirdt et al, 2013).…”

Inhibition of growth of U87MG human glioblastoma cells by Usnea longissima Ach.

“…Antioxidative (Halici et al 2005), insecticidal (Yildirim et al 2012a) and antifungal (goel et al 2011 properties of U. longissima extracts were reported. Likewise, insecticidal (emsen et al 2012, Yildirim et al 2012b), antioxidant (Atalay et al 2011, Choudhary 2011), antifungal (goel et al 2011), acaricidal (Shang et al 2014) and anticancer (Odabasoglu et al 2012, Karagoz et al 2014, Singh et al 2015 activities by some isolated U. longissima compounds were shown. Nevertheless, there is blank of knowledge in literature about studies exploring antiproliferative, oxidative and genotoxic effects of U. longissima water extract (Ule) on primary mixed glial-neuronal (PMGN) non-cancerous and human GBM U87MG cells.…”