Serum depletion, multidrug resistance and fluorescent probes: methodological implications in free radicals evaluation

Intracellular probes used for oxidative burst evaluation could be a substrate of the multidrug resistance proteins (MDR), which may cause misinterpretation of experimental data. We aimed to study the effect of the culture condition and of the MDR-interfering antioxidant quercetin on free radical measurement in serum depleted HCT-8 cells and chick embryo hepatocytes. Serum depletion and/or quercetin affected the traffic of 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF) and calcein. The comparative results obtained with 2',7'-dichlorofluorescein (DCF) and with the plasma-membrane probe C11-BODIPY 581/591 [4,4-difluoro-5-(4-phenyl-1,3-butadienyl)-4-bora-3a,4a-diaza-s-indacene-3-undecanoic acid], suggest caution in the use of intracellular probes to evaluate oxidative stress in vitro.