Insulin resistance, a hallmark of type 2 diabetes, is associated with oxidative stress. However, the role of reactive oxygen species or specific antioxidant enzymes in its development has not been tested under physiological conditions. The objective of our study was to investigate the impact of overexpression of glutathione peroxidase 1 (GPX1), an intracellular selenoprotein that reduces hydrogen peroxide (H 2O2) in vivo, on glucose metabolism and insulin function. The GPX1-overexpressing (OE) and WT male mice (n ‫؍‬ 80) were fed a selenium-adequate diet (0.4 mg͞kg) from 8 to 24 weeks of age. Compared with the WT, the OE mice developed (P < 0.05) hyperglycemia (117 vs. 149 mg͞dl), hyperinsulinemia (419 vs. 1,350 pg͞ml), and elevated plasma leptin (5 vs. 16 ng͞ml) at 24 weeks of age. Meanwhile, these mice were heavier (37 vs. 27 g, P < 0.001) and fatter (37% vs. 17% fat, P < 0.01) than the WT mice. At 30 -60 min after an insulin challenge, the OE mice had 25% less (P < 0.05) of a decrease in blood glucose than the WT mice. Their insulin resistance was associated with a 30 -70% reduction (P < 0.05) in the insulin-stimulated phosphorylations of insulin receptor (␤-subunit) in liver and Akt (Ser 473 and Thr 308 ) in liver and soleus muscle. Here we report the development of insulin resistance in mammals with elevated expression of an antioxidant enzyme and suggest that increased GPX1 activity may interfere with insulin function by overquenching intracellular reactive oxygen species required for insulin sensitizing.

A recent human intervention trial showed that daily supplementation with selenized yeast (Seyeast) led to a decrease in the overall cancer morbidity and mortality by nearly 50%; past research has also demonstrated that selenized garlic (Se-garlic) is very effective in mammary cancer chemoprevention in the rat model. The goal of this study was to compare certain biological activities of Se-garlic and Se-yeast and to elucidate the differences based on the chemical forms of selenium found in these two natural products. Characterization of organic selenium compounds in yeast (1922 µg/g Se) and garlic (296 µg/g Se) was carried out by high-performance liquid chromatography with inductively coupled plasma mass spectrometry or with electrospray mass spectrometry. Analytical speciation studies showed that the bulk of the selenium in Se-garlic and Se-yeast is in the form of γ-glutamyl-Se-methylselenocysteine (73%) and selenomethionine (85%), respectively. The above methodology has the sensitivity and capability to account for >90% of total selenium. In the rat feeding studies, supplementation of Se-garlic in the diet at different levels consistently caused a lower total tissue selenium accumulation when compared to Se-yeast. On the other hand, Se-garlic was significantly more effective in suppressing the development of premalignant lesions and the formation of adenocarcinomas in the mammary gland of carcinogen-treated rats. Given the present finding on the identity of selenomethionine and γ-glutamyl-Se-methylselenocysteine as the major form of selenium in Se-yeast and Se-garlic, respectively, the metabolism of these two compounds is discussed in an attempt to elucidate how their disposition in tissues might account for the differences in cancer chemopreventive activity.