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.
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 20 μM β-carotene during differentiation for 4 d. The cells treated with 10 μM β-carotene for 4 d were subsequently incubated with/without 5 ng/mL of tumor necrosis factor-α for 48 h 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.


RESULTS
β-Carotene treatment at a concentration of 20 μM, but not 10 μM, 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 10 μM did not show these alterations.


CONCLUSIONS
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.
Kameji
Hiroyuki
H
Graduate School of Nutritional and Environmental Sciences, Global COE Program, The University of Shizuoka, Shizuoka, Japan.
Mochizuki
Kazuki
K
Miyoshi
Noriyuki
N
Goda
Toshinao
T
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000378:metabolism*; D050156:Adipogenesis; D052242:Adiponectin / Q000235:genetics / Q000378:metabolism; D000818:Animals; D050556:Fatty Acid-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D051275:Glucose Transporter Type 4 / Q000235:genetics / Q000378:metabolism; D007333:Insulin Resistance; D051379:Mice; D009994:Osmolar Concentration; D018384:Oxidative Stress; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*; D015854:Up-Regulation; D019207:beta Carotene / Q000378:metabolism*
D052242:Adiponectin; C499919:Adipoq protein, mouse; C493411:Fabp4 protein, mouse; D050556:Fatty Acid-Binding Proteins; D051275:Glucose Transporter Type 4; D047495:PPAR gamma; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; C495693:Slc2a4 protein, mouse; D014409:Tumor Necrosis Factor-alpha; D019207:beta Carotene