Cocoa supplementation improves glucose metabolism in Zucker diabetic fatty (ZDF) rats via multiple mechanisms. Furthermore, cocoa rich-diets modify the intestinal microbiota composition both in humans and rats in healthy conditions. Accordingly, we hypothesized that cocoa could interact with the gut microbiota (GM) in ZDF rats, contributing to their antidiabetic effects. Therefore, here we investigate the effect of cocoa intake on gut health and GM in ZDF diabetic rats.Male ZDF rats were fed with standard (ZDF-C) or 10% cocoa-rich diet (ZDF-Co) during 10 weeks. Zucker Lean animals (ZL) received the standard diet. Colon tissues were obtained to determine the barrier integrity and the inflammatory status of the intestine and faeces were analysed for microbial composition, short-chain fatty acids (SCFA) and lactate levels. We found that cocoa supplementation up-regulated the levels of the tight junction protein Zonula occludens-1 (ZO-1) and the mucin glycoprotein and reduced the expression of pro-inflammatory cytokines such as tumour necrosis factorα (TNF-α), interleukin-6 (IL-6) and monocyte chemoattractant protein 1 (MCP-1) in the colon of ZDF diabetic animals. Additionally, cocoa modulated the microbial composition of the ZDF rats to values similar to those of the lean group. Importantly, cocoa treatment increased the relative abundance of acetate-producing bacteria such as Blautia and prevented the increase in the relative amount of lactateproducing bacteria (mainly Enterococcus and Lactobacillus genera) in ZDF diabetic animals. Accordingly, the total levels of SCFA (mainly acetate) increased significantly in the faeces of ZDF-Co diabetic rats. Finally, modified GM was closely associated with improved biochemical parameters related to glucose homeostasis and intestinal integrity and inflammation.These findings demonstrate for the first time that cocoa intake modifies intestinal bacteria composition towards a healthier microbial profile in diabetic animals and suggest that these changes could be associated with the improved glucose homeostasis and gut health induced by cocoa in ZDF diabetic rats.

Oxidative stress is involved in endothelial dysfunction, the key player in the development of vascular events. Flavanols, the major antioxidants in cocoa have been related to vascular protection and lower cardiovascular risk. However, the bioavailability of cocoa flavanols is very low and their bioactivity in vivo seems to be greatly mediated by the derived phenolic metabolites formed by intestinal microbiota. Hence, we investigated whether microbial-derived flavanol metabolites 3,4-dihydroxyphenylacetic acid (DHPAA), 2,3-dihydroxybenzoic acid (DHBA), 3-hydroxyphenylpropionic acid (HPPA) and a mix of them could influence endothelial function and prevent oxidative stress in human endothelial cells (Ea.hy926). Our results revealed that a mixture of flavanol colonic metabolites significantly increased phosphorylation of endothelial nitric oxide synthase (eNOS) and nitric oxide (NO) production. By using specific inhibitors, we also established the participation of the adenosine monophosphate-activated protein kinase (AMPK) and protein kinase B (AKT) in eNOS activation. Likewise, flavanol metabolite mix protected against oxidative stress-induced endothelial dysfunction and cell death by preventing increased ROS generation and activation of signaling pathways related to oxidative stress. We concluded that flavanol colonic metabolites could exert beneficial effects in endothelial cells and prevent oxidative stress-induced vascular dysfunction.

Oxidative stress may cause functional disorders of vascular endothelia which can lead to endothelial apoptosis and thus alter the function and structure of the vascular tissues. Plant antioxidants protect the endothelium against oxidative stress and then become an effective option to treat vascular diseases. Cocoa flavanols have been proved to protect against oxidative stress in cell culture and animal models. In addition, epidemiological and interventional studies strongly suggest that cocoa consumption has numerous beneficial effects on cardiovascular health.The objective of this study was to test the chemo-protective effect of realistic concentrations of a cocoa phenolic extract and its main monomeric flavanol epicatechin on cultured human endothelial cells submitted to an oxidative challenge. Both products efficiently restrained stress-induced reactive oxygen species and biomarkers of oxidative stress such as carbonyl groups and malondialdehyde, and recovered depleted glutathione, antioxidant defences and cell viability. Our results demonstrate for the first time that a polyphenolic extract from cocoa and its main flavonoid protect human endothelial cells against an oxidative insult by modulating oxygen radical generation and antioxidant enzyme and non-enzyme defences.

Oxidative stress plays a main role in the pathogenesis of the diabetic nephropathy. The present study investigated the effect of (-)-epicatechin (EC) and the colonic-derived flavonoid metabolites 2,3-dihydroxybenzoic acid, 3,4-dihydroxyphenylacetic acid (DHPAA), and 3-hydroxyphenylpropionic acid on the redox status in high-glucoseexposed renal proximal tubular NRK-52E cells. EC and DHPAA (10µM) alleviated the redox imbalance induced in high-glucose-challenged cells, as both compounds reverted to control levels reactive oxygen species (ROS) values. EC and DHPAA pre-treatment prevented the decrease of antioxidant defences and silent information regulator protein-1 (SIRT-1), and the increase of phosphorylated mitogen-activated-protein-kinases and NADPH-oxidase-4 (NOX-4) values under high-glucose-conditions. The presence of selective NOX-4 and SIRT-1 inhibitors in EC-and DHPAA-pre-treated cells showed the involvement of both proteins in EC-and DHPAA-mediated protection. These findings suggest that EC and DHPAA protected NRK-52E cells against a high-glucosechallenge by improving the cellular redox status through multiple signalling pathways, playing NOX-4/SIRT-1 a relevant role.