Enhancement of energy expenditure following a single oral dose of flavan-3-ols associated with an increase in catecholamine secretion

Abstract

Numerous clinical studies have reported that ingestion of chocolate reduces the risk of metabolic syndrome. However, the mechanisms by which this occurs remain unclear. In this murine study, the metabolic-enhancing activity of a 10 mg/kg mixture of flavan-3-ol fraction derived from cocoa (FL) was compared with the same single dose of (-)-epicatechin (EC). Resting energy expenditure (REE) was significantly increased in mice treated with the FL versus the group administered the distilled water vehicle (Cont) during periods of ad libitum feeding and fasting. Mice were euthanized under the effect of anesthesia 2, 5, and 20 hr after treatment with FL or Cont while subsequently fasting. The mRNA levels of the uncoupling protein-1 (UCP-1) and peroxisome proliferator-activated receptor gamma coactivator-1 alpha (PGC-1α) in brown adipose tissue (BAT) were significantly increased 2 hr after administration of FL. UCP-3 and PGC-1α in the gastrocnemius were significantly increased 2 and 5 hr after administration of the FL. The concentrations of phosphorylated AMP-activated protein kinase (AMPK) 1α were found to be significant in the gastrocnemius of mice 2 and 5 hr after ingesting FL. However, these changes were not observed following treatment with EC. Plasma was collected for measurement of catecholamine levels in other animals euthanized by decapitation 2 and 4 hr after their respective group treatment. Plasma adrenaline level was significantly elevated 2 hr after treatment with FL; however, this change was not observed following the administration of EC alone. The present results indicated that FL significantly enhanced systemic energy expenditure, as evidenced by an accompanying increase in the type of gene expression responsible for thermogenesis and lipolysis, whereas EC exhibited this less robustly or effectively. It was suggested the possible interaction between thermogenic and lipolytic effects and the increase in plasma catecholamine concentrations after administration of a single oral dose of FL.

Figure 1. Respiratory energy expenditure (REE) 20 hr after administration of flavan-3-ols during ad libitum feeding (a) and the fasting period (c).

Respiratory exchange ratio (RER) was calculated via oxygen consumption (VO₂) and carbon dioxide excretion (VCO₂) using the Weir equation. Total REE and light cycle (from 12:00 to 18:00 and from 6:00 to 8:00) or dark (from 18:00 to 6:00) REE was shown in (b; feeding period) and (d; fasting period). The animals were administrated vehicle (Cont, n = 13 during ad libitum feeding, n = 8 during fasting), 10 mg/kg FL (n = 13 during ad libitum feeding, n = 8 during fasting), or 10 mg/kg EC (n = 8 during fasting only). Values represent the mean ± standard deviation. Statistical analyses were performed by Dunnett's post-test. Significantly different from vehicle, *p<0.05.

Figure 2. mRNA expression of UCPs and PGC1-αin BAT (a, b) or gastrocnemius (c, d) after administration of FL or EC.

The animals were euthanized 2, 5, and 20 hr after administration of the vehicle (Cont, n = 8), 10 mg/kg FL (n = 8), or 10 mg/kg EC (n = 8). Values represent the mean ± standard deviation. Statistical analyses were performed by Dunnett's post-test. Significantly different from vehicle, *p<0.05, **p<0.01.

Figure 3. Phosphorylation of AMPK1αin BAT (a) or gastrocnemius (b) after administration of mixed flavan-3-ols or (−)-epicatechin.

The animals was euthanized 2, 5, and 20 hr after administration of the vehicle (Cont, n = 8), 10 mg/kgFL (n = 8), or 10 mg/kg EC (n = 8). Values represent the mean ± standard deviation. Statistical analyses were performed by Dunnett's post-test. Significantly different from vehicle, *p<0.05, **p<0.01.

Figure 4. Blood noradrenaline (a) and adrenaline (b) concentrations after administration of mixed FL or EC.

The animals were euthanized 2, 5, and 20 hr after administration of the vehicle (Cont, n = 8), 10 mg/kg of FL (n = 8) or 10 mg/kg of EC (n = 8). Values represent the mean ± standard deviation. Statistical analyses were performed by Dunnett's post-test. Significantly different from vehicle, *p<0.05.