Dietary vitamin E deficiency increases anxiety-related behavior in rats under stress of social isolation.

It has been demonstrated that vitamin E deficiency from birth increases anxiety-related behavior using knockout animals with no vitamin E transfer proteins. The current study was undertaken to elucidate the effect of dietary vitamin E deficiency on anxiety-related behavior of rats in different housing conditions. Male Wistar strain rats were divided into two groups during the weaning period and fed a control or vitamin E-deficient diet. All rats were housed in groups (three rats per cage) for 3 weeks. In the fourth week, half of the rats in each dietary treatment were kept in social housing and the other half were kept in individual housing. Before sacrifice, rota-rod and elevated plus-maze (EPM) tests were performed to measure motor coordination and anxiety, respectively. The EPM test revealed that vitamin E-deficient rats spent less time in the open arms and showed more stretch-out posture than the control rats, showing that anxiety increased with dietary vitamin E deficiency. Furthermore, vitamin E deficiency-induced anxiety behavior was observed more prominent in individual housed rats than in social housed rats. On the basis of these results, we conclude that dietary vitamin E deficiency induces anxiety in rats especially under stress of social isolation.

Effect of paraquat-induced oxidative stress on insulin regulation of insulin-like growth factor-binding protein-1 gene expression.

Oxidative stress is thought to play a role in the development of insulin resistance. In order to elucidate the molecular effect of oxidative stress on liver insulin signaling, we analyzed the effect of paraquat (1,1-dimethyl-4,4-dipyridynium; PQ)-derived oxidative stress on the expression of insulin-dependent genes and activation of liver insulin signaling pathway. Incubation of primary cultured rat hepatocytes with 2 mM PQ for 6 h impaired the suppressive effect of insulin on insulin-like growth factor-binding protein-1 (IGFBP-1) gene expression, but did not influence glucose-6-phosphatase gene expression. Insulin-dependent phosphorylation or activation of insulin receptor, insulin receptor substrate-1 and -2, phosphatidylinositol 3-kinase, Akt and forkhead in rhabdomyosarcoma were not affected by PQ pre-treatment. In contrast, PQ treatment impaired insulin-dependent phosphorylation of mammalian target of rapamycin (mTOR). These results indicate that PQ-induced oxidative stress impairs insulin-dependent mTOR activation and that this impairment probably causes inhibition of insulin-dependent repression of IGFBP-1 expression.

Effect of various radical generators on insulin-dependent regulation of hepatic gene expression.

Oxidative stress is recognized to be associated with the development of insulin resistance. Although free radicals are generated in various ways in vivo, very few radical generators have been used to investigate the effect of oxidative stress on cellular insulin signaling. In order to compare the effect of radical generators with different sites and durations of radical formation on liver insulin action, primary cultured rat hepatocytes were incubated with radical generators and insulin-dependent regulation of gene expression was examined. The hydrophobic 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN) radical and H2O2 increased plasma membrane damage, and the hydrophilic 2-2'-azobis(2-amidinopropane) dihydrochloride (AAPH) radical and buthionine sulfoxyimine (BSO) increased oxidation of intracellular substances. Paraquat (PQ) and H2O2 inhibited insulin-dependent repression of insulin-like growth factor-binding protein-1 (IGFBP-1) and phosphoenolpyruvate carboxykinase (PEPCK) gene expression. These results indicate that PQ and H2O2 impair insulin action effectively and are suitable for examining crosstalk between oxidative stress and insulin signaling in liver-cell culture systems.