Quercetin, a functional compound of onion peel, remodels white adipocytes to brown-like adipocytes

Abstract

Adipocyte browning is a promising strategy for obesity prevention. Using onion-peel-derived extracts and their bioactive compounds, we demonstrate that onion peel, a by-product of onion, can change the characteristics of white adipocytes to those of brown-like adipocytes in the white adipose tissue of mice and 3T3-L1 cells. The expression of the following brown adipose tissue-specific genes was increased in the retroperitoneal and subcutaneous adipose tissues of 0.5% onion-peel-extract-fed mice: PR domain-containing 16, peroxisome proliferator-activated receptor gamma coactivator 1α, uncoupling protein 1, fibroblast growth factor 21 and cell death-inducing DFFA-like effector. In 3T3-L1 adipocytes, onion peel extract induced the expression of brown adipose tissue-specific genes and increased the expression of carnitine palmitoyltransferase 1α. This effect was supported by decreased lipid levels and multiple small-sized lipid droplets. The ethyl acetate fraction of the onion peel extract that contained the highest proportion of hydrophobic molecules showed the same browning effect in 3T3-L1 adipocytes. A high-performance liquid chromatography analysis further identified quercetin as a functional compound in the browning effect of onion peel. The quercetin-associated browning effect was mediated in part by the activation of AMP-activated protein kinase. In summary, our study provides the first demonstration of the browning effects of onion peel and quercetin using both animal and cell models. This result indicates that onion peel has the potential to remodel the characteristics of white adipocytes to those of brown-like adipocytes.

Anti-Inflammatory and Antioxidant Effects of Anthocyanins of Trifolium pratense (Red Clover) in Lipopolysaccharide-Stimulated RAW-267.4 Macrophages

“…Petals of the red clover were cleaned and dried at room temperature. Dried petals (50 g) were extracted with 1 L of 80% aqueous methanol (v/v) by homogenization and sonication [18]. Red clover extract (RC) yield was 13.2%.…”

“…For the gene expression, cells were treated with 1 µg/mL LPS for 3 h. On the completion of the incubation, total RNA and protein were extracted. Cytotoxicity of RC, RCA, and LPS was determined as previously described [18].…”

“…Total RNA was extracted using a Trizol and then cDNA was synthesized using XLAScript cDNA MasterMix (Exella GmbH, Feucht, Germany) according to manufacturers' instructions. The expression of genes that are involved in the regulation of inflammation and antioxidant was examined using the Fast Start Essential DNA Green Light Master kit (Roche, Indianapolis, IN, USA) in a LightCycler 96 (Roche) [18]. Primer sequences were designed using Primer3 (http://bioinfo.ut.ee/primer3-0.4.0/) and confirmed using a Primer-Blast (NCBI database).…”

“…Total protein extraction and a Western blot analysis were performed as previously described [18]. To examine the inhibitory effects of RCA on translocation of NF-κB between nuclear and cytoplasm, cells had the same pretreatments with RCA described above and then were treated with RCA and 0.5 µg/mL LPS for 1 h [19].…”

A pivotal role of AMPK signaling in medicarpin‐mediated formation of brown and beige

“…WAT browning by means of phytochemicals involves increased expression of thermogenic genes and transcription factors or activation of related regulatory signaling pathways . The activation of whole‐body energy sensor and regulator, AMPK, was reported in all of the above‐mentioned studies on phytochemicals and browning of WAT except for the rutin . Some reports revealed that overexpression of UCP‐1 in skeletal muscle leads to an increase in the AMP/ATP ratio with subsequent activation of AMPK .…”