β-Carotene accumulation in 3T3-L1 adipocytes inhibits the elevation of reactive oxygen species and the suppression of genes related to insulin sensitivity induced by tumor necrosis factor-α
Received 19 March 2009; accepted 3 September 2009. published online 25 January 2010. Corrected Proof
Abstract
Objective
β-Carotene is an abundant carotenoid with potent antioxidative activities and accumulates in adipose tissue. However, its physiologic functions are poorly understood. In this study, we examined whether accumulation of β-carotene for 4 d in insulin-resistant 3T3-L1 adipocytes alters the expression of genes related to insulin sensitivity.
Methods
The 3T3-L1 adipocytes were treated with/without 10 or 20μM β-carotene during differentiation for 4 d. The cells treated with 10μM β-carotene for 4 d were subsequently incubated with/without 5 ng/mL of tumor necrosis factor-α for 48h in the medium without β-carotene. The mRNA levels of genes in the cells and adiponectin protein levels in the medium were determined by real-time reverse transcription–polymerase chain reaction and enzyme-linked immunosorbent assay, respectively. Reactive oxygen species levels in the cells were assessed by oxidation of 2′,7′-dichlorodihydrofluorescein diacetate.
Result
β-Carotene treatment at a concentration of 20μM, but not 10μM, in 3T3-L1 adipocytes during differentiation for 4 d enhanced the expression of genes related to insulin sensitivity, including adiponectin, adipocyte lipid-binding protein, glucose transporter-4, peroxisome proliferator-activated receptor-γ2, and adiponectin protein in the medium. Tumor necrosis factor-α treatment repressed the expression of these genes and adiponectin protein in the medium and induced reactive oxygen species levels. In contrast, cells that accumulated β-carotene at a concentration of 10μM did not show these alterations.
Conclusion
The accumulation of the β-carotene in 3T3-L1 adipocytes restores the expression of genes related to insulin sensitivity and reactive oxygen species levels in insulin-resistant adipocytes.
aLaboratory of Nutritional Physiology, Graduate School of Nutritional and Environmental Sciences, Global COE Program, The University of Shizuoka, Shizuoka, Japan
bLaboratory of Biochemistry, Graduate School of Nutritional and Environmental Sciences, Global COE Program, The University of Shizuoka, Shizuoka, Japan
This work was supported by the Global COE Program, the Center of Excellence for Innovation in Human Health Sciences, from the Ministry of Education, Culture, Sports Science, and Technology of Japan.
ABSTRACT
μM β-carotene during differentiation for 4 d. The cells treated with 10