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Ascorbic acid and alpha-tocopherol down-regulate apolipoprotein A-I gene expression in HepG2 and Caco-2 cell lines
Arshag D Mooradian1, Michael J Haas, Khuram Wadud
1Division of Endocrinology, Diabetes and Metabolism, Department of Internal Medicine, Saint Louis University School of Medicine, St. Louis, MO 63104, USA. mooradad@slu.edu
Metabolism: Clinical and Experimental
|January 21, 2006
Summary
Certain antioxidants like alpha-tocopherol and ascorbate significantly reduce apolipoprotein A-I (apoA-I) gene expression and protein levels at high concentrations. Dimethyl sulfoxide (DMSO) conversely increases apoA-I expression, independent of the antioxidant response element (ARE).
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- Apolipoprotein A-I (apoA-I) is crucial for cholesterol transport.
- Antioxidants modulate cellular pathways, but their specific effects on apoA-I are not fully understood.
- Understanding apoA-I gene regulation is vital for metabolic research.
Purpose of the Study:
- To investigate the molecular mechanisms by which antioxidants affect apoA-I expression.
- To determine if changes in apoA-I expression occur at the transcriptional level.
- To elucidate the role of the antioxidant response element (ARE) in mediating these effects.
Main Methods:
- Treatment of HepG2 and Caco-2 cells with alpha-tocopherol, ascorbate, dimethyl sulfoxide (DMSO), and hydrogen peroxide.
- Measurement of apoA-I mRNA and protein levels.
- Reporter gene assays using chloramphenicol acetyltransferase (CAT) with the apoA-I promoter and its deletion constructs.
- Electrophoretic mobility shift assays (EMSA) to assess nuclear factor binding.
Main Results:
- Alpha-tocopherol and ascorbate significantly reduced apoA-I mRNA and protein in a dose-dependent manner.
- DMSO treatment significantly increased apoA-I mRNA and protein levels.
- High concentrations of alpha-tocopherol and ascorbate decreased apoA-I promoter activity, while DMSO increased it.
- The effects of alpha-tocopherol and ascorbate were independent of the ARE, unlike DMSO's effect.
Conclusions:
- High concentrations of certain antioxidants (alpha-tocopherol, ascorbate) can suppress apoA-I gene expression.
- DMSO enhances apoA-I expression through a mechanism potentially independent of its antioxidant properties.
- The regulation of apoA-I by these compounds involves pathways distinct from the canonical ARE, possibly involving indirect effects or post-translational modifications.