Background. The flavonoid 2′, 4′-dihydroxy-5′-(1′′′, 1′′′-dimethylallyl)-8-prenylpinocembrin (8PP) obtained from Dalea elegans roots inhibits cell growth and cdr pumps, in addition to reversing fluconazole (FCZ) resistance in Candida albicans.

Aims. To study the effects of 8PP and FCZ on cdr-associated ATPase and cell energy generation in azole-resistant C. albicans planktonic cultures.

Materials and methods. ATPase activity was measured as oligomycin-sensitive release of inorganic phosphate in fractions containing plasmatic membranes. Cell oxidoreductase activity was evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) reduction in C. albicans cells.

Results. FCZ, 8PP and their combination at a concentration of 125 µM of each compound inhibit ATPase activity by 61; 58 and 70, respectively. Inhibitory concentration 50 % (IC₅₀) of 8PP was 78.59 ± 1.45 and 104.70 ± 1.25 µM for FCZ. In combination with 125 µM 8PP, FCZ IC₅₀ was reduced by 3 times. K_m was 0.96 ± 0.35 mM and V_max 43.58 ± 5.49 picomoles/mg protein.min. At 125 µM, 8PP shifts the ATP saturation plot to right. A Dixon study using 2 and 5 mM ATP suggests a competitive interaction of 8PP and ATP for the hydrolysis enzymatic site. FCZ, 8PP or their combination at 125 µM does not produce cytotoxicity dependent on oxidoreductase activity. At higher concentrations, toxic effects are observed with both drugs at the MTT assay. IC₅₀ (µM) was 355 ± 6 and 789 ± 11, for 8PP and FCZ, respectively.

Conclusions. The flavonoid 8PP inhibits competitively oligomycin-sensitive ATPase activity associated to cdr transporters and decreases oxidoreductase-dependent cell viability in azole-resistant Candida albicans.