Effects of Quercetin Metabolites on Glucose-Dependent Lipid Accumulation in 3T3-L1 Adipocytes

Abstract

The aim of the study was to assess the effects of quercetin metabolites (QMs) on lipid accumulation in adipocytes under high-glucose and physiological-glucose concentrations and to elucidate the mechanisms involved. 3T3-L1 mature adipocytes were exposed to a physiological glucose concentration, as a model of caloric restriction (CR), or high glucose (control), with and without QMs (quercetin-3-glucuronide [Q3G] and isorhamnetin [ISOR]). Cells were treated with Q3G (0.3 and 0.6 µmol/L) and ISOR (0.2 and 0.4 µmol/L) for 48 h. Lipid accumulation (Oil Red O staining) and Δ glucose level (HPLC) were assessed. Under high glucose, Q3G and ISOR reduced lipid accumulation (-10.8% and -10.4%; p < 0.01) and Δ glucose level (-13.6% and -14.2%; p < 0.05). Under CR, QMs increased Δ glucose level (+21.6% for Q3G and +21% for ISOR; p < 0.05). ISOR increased pAMPK levels under high glucose (+1.4-fold; p < 0.05). Under CR, Q3G and ISOR increased pAMPK (+1.4- and +1.5-fold; p < 0.05), while ISOR upregulated SIRT1 and PGC-1α (+2.3- and +1.5-fold; p < 0.05). Findings support, for the first time, the potential contribution of QMs, especially ISOR, in the regulation of lipid metabolism in vitro, possibly via AMPK activation. Further studies, including in vivo, are encouraged to strengthen evidence of the mechanisms observed.

Keywords: (poly)phenols; AMPK; adipocytes; caloric restriction; quercetin.

FIGURE 1

Effect on adipocytes’ lipid accumulation determined by Oil Red O staining assay. (a) Effects on adipocytes’ lipid accumulation after 48 h incubation under two different concentrations of glucose (control, 4.5 g/L vs. caloric restriction [CR, 1 g/L]). (b) Effects on adipocytes’ lipid accumulation after 48 h incubation with quercetin metabolites under high‐glucose condition. (c) Effects on adipocytes’ lipid accumulation after 48 h incubation with quercetin metabolites under low‐glucose condition. Data are presented as mean ± standard error of the mean (SEM) of three independent experiments, with each condition performed in duplicate. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.

FIGURE 2

Effect on adipocytes’ lipolytic activity for 48 h, determined by glycerol quantification in cell culture medium. (a) Effects on adipocytes’ lipolytic activity after 48 h incubation under two different concentrations of glucose (control, 4.5 g/L vs. caloric restriction [CR, 1 g/L]). (b) Effects on adipocytes’ lipolytic activity after incubation with quercetin metabolites under high‐glucose condition. (c) Effects on adipocytes’ lipolytic activity after incubation with quercetin metabolites under low‐glucose condition. Data are reported as mean ± standard error of the mean (SEM) of three independent experiments, with each condition performed in duplicate. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.

FIGURE 3

Effect on changes in glucose concentration (Δ glucose level) in cell supernatants after 48 h, determined by HPLC. The Δ glucose level was measured by determining the difference in glucose concentration before and after the experiments. (a) Effects on Δ glucose level after 48 h incubation of adipocytes under two different concentrations of glucose (control, 4.5 g/L vs. caloric restriction [CR, 1 g/L]). (b) Effects on Δ glucose level after 48 h incubation of adipocytes with quercetin metabolites under high‐glucose condition. (c) Effects on Δ glucose level after 48 h incubation of adipocytes with quercetin metabolites under low‐glucose condition. Data are presented as mean ± standard error of the mean (SEM) of three independent experiments, with each condition performed in duplicate. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.

FIGURE 4

Effect on adipocytes’ markers related to lipogenesis and thermogenesis. (a) Effects on phosphorylated‐ 5' AMP‐activated protein kinase (pAMPK) protein levels after incubation with quercetin metabolites under high‐glucose and low‐glucose conditions. (b) Effects on peroxisome proliferator‐activated receptor‐gamma coactivator‐1alpha (PGC‐1α) protein levels after incubation with quercetin metabolites under high‐glucose and low‐glucose conditions. (c) Effects on sirtuin‐1 (SIRT‐1) protein levels after incubation with quercetin metabolites under high‐glucose and low‐glucose conditions. (d) Effects on adiponectin (ADP) protein levels after incubation with quercetin metabolites under high‐glucose and low‐glucose conditions. (e) Effects on peroxisome proliferator‐activated receptor‐gamma (PPAR‐γ) protein levels after incubation with quercetin metabolites under high‐glucose and low‐glucose conditions. (f) Effects on uncoupling protein‐1 (UCP‐1) protein levels after incubation with quercetin metabolites under high‐glucose and low‐glucose conditions. Data are presented as mean ± standard error of the mean (SEM) of three independent experiments, with each condition performed in duplicate. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.