Modulatory effects of natural curcuminoids on P-glycoprotein ATPase of insecticide-resistant pest Helicoverpa armigera (Lepidopetera: Noctüidae).

Three major curcuminoids (I, II and III) were purified from turmeric and tested for their ability to modulate the function of P-glycoprotein ATPase of the insecticide-resistant pest Helicoverpa armigera (Ha-Pgp). The curcumin mixture inhibited the activity of Ha-Pgp ATPase by 80-90% at 100 μM concentration. Along with curcuminoids I, II and III, it inhibited the verapamil- and ethylparaoxon-stimulated Ha-Pgp ATPase activity. Curcuminoid binding was quantitated by quenching the intrinsic Trp fluorescence of purified Ha-Pgp ATPase. Transport was monitored in proteoliposomes containing Ha-Pgp ATPase using the high-affinity fluorescent substrate tetramethylrosamine (TMR) in real time. Addition of the curcuminoid mixture collapsed the TMR concentration gradient generated by Ha-Pgp ATPase. Inhibition studies on Ha-Pgp ATPase activity are important to develop strategies to overcome insecticide resistance in this pest.