Hydroxyhydroquinone, a by-product of coffee bean roasting, increases intracellular Ca2+ concentration in rat thymic lymphocytes

Hydroxyhydroquinone (HHQ) is generated during coffee bean roasting. A cup of coffee contains 0.1-1.7 mg of HHQ. The actions of HHQ on mammalian DNA were examined because HHQ is a metabolite of benzene, which causes leukemia. Currently, information on the cellular actions of HHQ is limited. We examined the effects of sublethal levels of HHQ on the concentration of intracellular Ca²⁺ in rat thymic lymphocytes by using a flow cytometric technique with fluorescent probes. HHQ at 10 μM or more significantly elevated intracellular Ca²⁺ levels by increasing the membrane permeability of divalent cations, resulting in hyperpolarization via the activation of Ca²⁺-dependent K⁺ channels. HHQ-induced changes in the intracellular Ca²⁺ concentration and membrane potential may affect the cell functions of lymphocytes. HHQ-reduced coffee may be preferable in order to avoid the possible adverse effects of HHQ.