Effects of dietary fucoxanthin on cholesterol metabolism in diabetic/obese KK-Ay mice

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Abstract

Background

Fucoxanthin is a xanthophyll present in brown seaweeds and has several beneficial effects, including anti-obesity and anti-diabetic effects. However, we and another group previously observed that fucoxanthin increases serum cholesterol levels in rodents. Cholesterol is an important component of cell membranes and biosynthesis of bile acids. Serum cholesterol levels are also closely associated with atherosclerosis. Therefore, we sought to identify the mechanism underlying the increase in serum cholesterol levels by fucoxanthin.

Methods

Diabetic/obese KK- A ^y mice were fed a diet containing 0.2% fucoxanthin for 4 weeks. The mice were sacrificed, and total blood samples were collected for the measurement of serum total cholesterol, HDL-cholesterol and non-HDL-cholesterol levels. Cholesterol content in tissues was also analyzed. Real-time PCR and Western blotting were performed to determine hepatic mRNA and protein expression of genes involved in cholesterol metabolism, respectively.

Results

Dietary fucoxanthin significantly increased serum HDL and non-HDL cholesterol levels, and reduced hepatic cholesterol content. In liver, the expression of SREBP1, SREBP2 and their target genes involved in cholesterol biosynthesis significantly increased and tended to increase in the fucoxanthin-fed mice, respectively. In contrast, hepatic levels of LDLR and SR-B1 proteins which is important factors for LDL-cholesterol and HDL-cholesterol uptake in the liver from serum, decreased to 60% and 80% in the fucoxanthin-fed mice, respectively, compared with the control mice. Further, we found that dietary fucoxanthin significantly increased the mRNA expression of proprotein convertase subtilisin/kexin type 9 (PCSK9), which enhances intracellular degradation of LDLR in lysosomes.

Conclusions

Fucoxanthin increased HDL-cholesterol and non-HDL-cholesterol levels in KK- A ^y mice by inducing SREBP expression and reduced cholesterol uptake in the liver via down-regulation of LDLR and SR-B1, resulted in increased serum cholesterol in the mice.

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Most cited references 26

Record: found
Abstract: found
Article: not found

Combined analysis of oligonucleotide microarray data from transgenic and knockout mice identifies direct SREBP target genes.

Jay Horton, Nila A Shah, Janet A Warrington … (2003)

The synthesis of fatty acids and cholesterol, the building blocks of membranes, is regulated by three membrane-bound transcription factors: sterol regulatory element-binding proteins (SREBP)-1a, -1c, and -2. Their function in liver has been characterized in transgenic mice that overexpress each SREBP isoform and in mice that lack all three nuclear SREBPs as a result of gene knockout of SREBP cleavage-activating protein (SCAP), a protein required for nuclear localization of SREBPs. Here, we use oligonucleotide arrays hybridized with RNA from livers of three lines of mice (transgenic for SREBP-1a, transgenic for SREBP-2, and knockout for SCAP) to identify genes that are likely to be direct targets of SREBPs in liver. A total of 1,003 genes showed statistically significant increased expression in livers of transgenic SREBP-1a mice, 505 increased in livers of transgenic SREBP-2 mice, and 343 showed decreased expression in Scap-/- livers. A subset of 33 genes met the stringent combinatorial criteria of induction in both SREBP transgenics and decreased expression in SCAP-deficient mice. Of these 33 genes, 13 were previously identified as direct targets of SREBP action. Of the remaining 20 genes, 13 encode enzymes or carrier proteins involved in cholesterol metabolism, 3 participate in fatty acid metabolism, and 4 have no known connection to lipid metabolism. Through application of stringent combinatorial criteria, the transgenic/knockout approach allows identification of genes whose activities are likely to be controlled directly by one family of transcription factors, in this case the SREBPs.

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Record: found
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A receptor-mediated pathway for cholesterol homeostasis.

M. Brown, J Goldstein (1986)

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Record: found
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Article: not found

Binding of proprotein convertase subtilisin/kexin type 9 to epidermal growth factor-like repeat A of low density lipoprotein receptor decreases receptor recycling and increases degradation.

Da-Wei Zhang, Thomas Lagace, Rita Garuti … (2007)

Proprotein convertase subtilisin/kexin type 9 (PCSK9) promotes degradation of hepatic low density lipoprotein receptors (LDLR), the major route of clearance of circulating cholesterol. Gain-of-function mutations in PCSK9 cause hypercholesterolemia and premature atherosclerosis, whereas loss-of-function mutations result in hypocholesterolemia and protection from heart disease. Recombinant human PCSK9 binds the LDLR on the surface of cultured hepatocytes and promotes degradation of the receptor after internalization. Here we localized the site of binding of PCSK9 within the extracellular domain of the LDLR and determined the fate of the receptor after PCSK9 binding. Recombinant human PCSK9 interacted in a sequence-specific manner with the first epidermal growth factor-like repeat (EGF-A) in the EGF homology domain of the human LDLR. Similar binding specificity was observed between PCSK9 and purified EGF-A. Binding to EGF-A was calcium-dependent and increased dramatically with reduction in pH from 7 to 5.2. The addition of PCSK9, but not heat-inactivated PCSK9, to the medium of cultured hepatocytes resulted in redistribution of the receptor from the plasma membrane to lysosomes. These data are consistent with a model in which PCSK9 binding to EGF-A interferes with an acid-dependent conformational change required for receptor recycling. As a consequence, the LDLR is rerouted from the endosome to the lysosome where it is degraded.

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Author and article information

Journal

Journal ID (nlm-ta): Lipids Health Dis

Journal ID (iso-abbrev): Lipids Health Dis

Title: Lipids in Health and Disease

Publisher: BioMed Central

ISSN (Electronic): 1476-511X

Publication date Collection: 2012

Publication date (Electronic): 10 September 2012

Volume: 11

Page: 112

Affiliations

[1 ]Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato Hakodate, Hokkaido, 041-8611, Japan

[2 ]Laboratory for Redox Regulation, Tohoku University Graduate School of Dentistry, 4-1 Seiryo-cho, Aoba-ku, Sendai, 980-8575, Japan

Article

Publisher ID: 1476-511X-11-112

DOI: 10.1186/1476-511X-11-112

PMC ID: 3477094

PubMed ID: 22962999

SO-VID: 7e931eff-49c7-4285-aa18-85c8986bb5fc

License:

This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.