Quercetin decreases oxidative stress, NF-kappaB activation, and iNOS overexpression in liver of streptozotocin-induced diabetic rats.

Increasing evidence in both experimental and clinical studies suggests that oxidative stress is involved in the pathogenesis and progression of diabetic tissue damage. This study investigated the protective effects of quercetin treatment on oxidative stress, nuclear factor (NF)-kappaB activation and expression of inducible nitric oxide synthase (iNOS) in streptozotocin-induced diabetic rats. Male Wistar rats were divided into 4 groups: control rats, control rats treated daily with quercetin (150 micromol/kg, i.p.), untreated diabetic rats, and diabetic rats treated with quercetin. Diabetes was induced by a single i.p. injection of streptozotocin (70 mg/kg). Eight weeks later we measured TBARS and hydroperoxide-initiated chemiluminescence (QL) in liver as markers of oxidative stress, and activities of the antioxidant enzymes catalase, superoxide dismutase (SOD), and glutathione peroxidase, NF-kappaB activation by an electrophoretic mobility shift assay and expression of IkappaB kinases (IKKalpha and IKKbeta), the inhibitor IkappaB (IkappaBalpha and IkappaBbeta), and iNOS by Western blot. The plasma glucose concentration was significantly increased in diabetic rats and was not changed by quercetin. Streptozotocin administration induced significant increases in hepatic TBARS concentration, QL, and SOD and catalase activities that were prevented by quercetin. Activation of NF-kappaB, induction of IKKalpha and iNOS protein levels, and increased degradation of IkappaBalpha were also observed in streptozotocin-treated rats. All of those effects were abolished by quercetin. These findings suggest that quercetin treatment, by abolishing the IKK/NF-kappaB signal transduction pathway, may block the production of noxious mediators involved in the development of early diabetes tissue injury and in the evolution of late complications.