Flavonoid-rich Chardonnay grape seed flour supplementation ameliorates diet-induced visceral adiposity, insulin resistance, and glucose intolerance via altered adipose tissue gene expression

Highlights

• Chardonnay grape seed decreased expression of genes related to oxidative stress, inflammatory, and innate immune signals.

• Expression of PGC-1α, insulin receptor, and genes involved in fatty acid oxidation were increased.

• Altered adipose gene profiles are associated with amelioration of obesity, insulin resistance, and glucose intolerance.

Abstract

The effect of flavonoid-rich wine grape seed flour, a byproduct of winemaking, on global adipose tissue gene expression and obesity-induced insulin resistance was assessed in high fat (HF) diet-induced obese (DIO) mice. DIO mice were fed HF diet supplemented with either partially defatted Chardonnay grape seed flour (ChrSd) or microcrystalline cellulose (MCC, control) for 5 weeks. ChrSd diet suppressed the HF diet-induced increase in total body, liver, and adipose tissue weights with a significant decrease in feed efficiency. ChrSd intake significantly lowered the 2-h insulin and glucose areas under the curve suggesting that ChrSd improves insulin sensitivity and glucose metabolism. Gene expression profiling analysis of adipose tissue from mice fed a ChrSd diet, by exon microarray and RT-PCR, revealed a down-regulation of genes related to oxidative stress, inflammation, immune response, protein carbonylation, and fatty acid synthesis. Conversely, genes related to the scavenging of free radicals, antioxidants, insulin sensitivity, and fatty acid oxidation, were up-regulated. Pathway analysis of microarray data identified genes related to innate immune response, inflammatory response, and infectious disease as being differentially regulated by the ChrSd diet. Thus, ChrSd ameliorates HF-induced obesity, insulin resistance, and glucose intolerance in DIO mice by modulating expression of genes in adipose tissue.

Introduction

Chronic oxidative stress and low-grade inflammation are linked to the onset of obesity-related insulin resistance (IR) (Hummasti & Hotamisligil, 2010). Systemic low-grade inflammation and disturbance of metabolic immune pathways without an increase in energy expenditure (referred to as metaflammation) in white adipose tissue eventually initiate the production of inflammatory cytokines and inhibit insulin signalling in target organs, leading to insulin resistance.

Consumption of diets incorporating high amounts of flavonoid-rich grapes and their products, such as grape juice, wine, grape extracts, and purified compounds, may be a beneficial dietary strategy for suppression of oxidative stress and inflammation in adipose tissues of obese subjects. A number of putative mechanisms could play a role in the prevention of obesity-related oxidative stress and inflammation by grape flavonoids, including: (1) up-regulation of antioxidant processes (promotion of free radical scavenging and metal chelating activities, stimulation of antioxidant enzyme activity, and increased gene expression); (2) inhibition of endoplasmic reticulum (ER) stress signalling; and (3) inhibition of the production of pro-inflammatory cytokines or endotoxin-mediated kinases (Balu et al, 2005, Charradi et al, 2013, Chis et al, 2009, Rho, Kim, 2006, Soobrattee et al, 2005).

Health benefits of flavonoids present in grape seeds, a byproduct of winemaking process, have recently attracted attention due to the high concentrations of flavonoids present. Two-thirds of the total extractable flavonoids present in grape are found in the seeds, including the highest concentrations of flavan-3-ols, the most common flavonoids. Approximately 20% of the total product volume in the winemaking process consists of pomace (seed and skin) byproduct. Flavan-3-ols (flavanols) are the most abundant class of flavonoids and include catechin, epicatechin, their 3-O-gallates, and (epi)catechin dimers, oligomers, and polymers. Following ingestion, monomeric (epi)catechin is readily absorbed from the small intestine, but oligomers and polymers need to be further metabolized by the intestinal bacteria in the colon into phenolic acids before they can be absorbed (Manach, Scalbert, Morand, Remesy, & Jimenez, 2004). Dietary supplementation with grape products (Chardonnay grape seed procyanidin extract, grape polyphenol extract, and grape pomace extract) has been shown to elicit antioxidant activity and anti-inflammatory effects, reducing markers of oxidative stress and insulin resistance in in-vitro and in-vivo studies (Balu et al, 2005, Charradi et al, 2013, Chis et al, 2009, De Groote et al, 2012, Decorde et al, 2009, Gonzalez-Gallego et al, 2010, Hogan et al, 2010, Hokayem et al, 2013, Kar et al, 2009, Rho, Kim, 2006, Savini et al, 2013, Xia et al, 2010, Yilmaz, Toledo, 2004).

Our previous work showed hypolipidaemic and anti-obesity effects of partially defatted whole grape seed flour, a byproduct derived from winemaking process in hamsters. Hamsters fed a HF and hypercholesterolaemic diet supplemented with white wine (Chardonnay) grape seed flour (ChrSd) significantly lowered plasma concentrations of low-density lipoprotein (LDL)-, very low-density lipoprotein (VLDL)-, and total-cholesterol, abdominal adipose tissue weight, and total body weight gain, as compared to animals fed a control diet. These alterations were mediated by the regulation of expression of genes related to cholesterol, bile acid, and lipid metabolism in the liver and adipose tissue. The anti-obesity effect of ChrSd supplementation was associated with an alteration in the expression of a limited number of selected genes related to adipogenesis and inflammation since whole genome of the hamster has not been completely sequenced. The beneficial effect of ChrSd on health was paralleled by the flavonoids content in the grape seed flour. However, most studies performed thus far utilized aqueous or alcoholic polyphenolic grape seed extracts. This study aimed to gain novel biological insights into the action of ChrSd supplementation and determine whether ChrSd supplementation modulates free radical scavenging and reduces oxidative stress and inflammation in adipose tissue during the progression of HF diet-induced insulin resistance. We evaluated insulin tolerance and analysed global gene expression using exon microarrays in adipose tissue obtained from HF diet-induced obese (DIO) mice fed a diet supplemented with grape seed flour obtained from the byproducts of white wine production.