Functional and genomic comparative study of the bitter taste receptor family TAS2R: Insight into the role of human TAS2R5

Bitterness is perceived in humans by 25 subtypes of bitter taste receptors (hTAS2R) that range from broadly tuned to more narrowly tuned receptors. hTAS2R5 is one of the most narrowly tuned bitter taste receptors in humans. In this study, we review the literature on this receptor and show there is no consensus about its role. We then compare the possible role of hTAS2R5 with that of the proteins of the TAS2R family in rat, mouse, and pig. A phylogenetic tree of all mammalian TAS2R domain-containing proteins showed that human hTAS2R5 has no ortholog in pig, mouse, or rat genomes. By comparing the agonists that are common to hTAS2R5 and other members of the family, we observed that hTAS2R39 is the receptor that shares most agonists with hTAS2R5. In mouse, some of these agonists activate mTas2r105 and mTas2r144, which are distant paralogs of hTAS2R5. mTas2r144 seems to be the receptor that is most similar to hTAS2R5 because they are both activated by the same agonists and have affinities in the same range of values. Then, we can conclude that hTAS2R5 has a unique functional specificity in humans as it is activated by selective agonists and that its closest functional homolog in mouse is the phylogenetically distant mTas2r144.

Grape-Seed Proanthocyanidin Extract Reverts Obesity-Related Metabolic Derangements in Aged Female Rats

Obesity and ageing are current issues of global concern. Adaptive homeostasis is compromised in the elderly, who are more likely to suffer age-related health issues, such as obesity, metabolic syndrome, and cardiovascular disease. The current worldwide prevalence of obesity and higher life expectancy call for new strategies for treating metabolic disorders. Grape-seed proanthocyanidin extract (GSPE) is reported to be effective in ameliorating these pathologies, especially in young animal models. In this study, we aimed to test the effectiveness of GSPE in modulating obesity-related pathologies in aged rats fed an obesogenic diet. To do so, 21-month-old rats were fed a high-fat/high-sucrose diet (cafeteria diet) for 11 weeks. Two time points for GSPE administration (500 mg/kg body weight), i.e., a 10-day preventive GSPE treatment prior to cafeteria diet intervention and a simultaneous GSPE treatment with the cafeteria diet, were assayed. Body weight, metabolic parameters, liver steatosis, and systemic inflammation were analysed. GSPE administered simultaneously with the cafeteria diet was effective in reducing body weight, total adiposity, and liver steatosis. However, the preventive treatment was effective in reducing only mesenteric adiposity in these obese, aged rats. Our results confirm that the simultaneous administration of GSPE improves metabolic disruptions caused by the cafeteria diet also in aged rats.

Glucagon Shows Higher Sensitivity than Insulin to Grapeseed Proanthocyanidin Extract (GSPE) Treatment in Cafeteria-Fed Rats

The endocrine pancreas plays a key role in metabolism. Procyanidins (GSPE) targets β-cells and glucagon-like peptide-1 (GLP-1)-producing cells; however, there is no information on the effects of GSPE on glucagon. We performed GSPE preventive treatments administered to Wistar rats before or at the same time as they were fed a cafeteria diet during 12 or 17 weeks. We then measured the pancreatic function and GLP-1 production. We found that glucagonemia remains modified by GSPE pre-treatment several weeks after the treatment has finished. The animals showed a higher GLP-1 response to glucose stimulation, together with a trend towards a higher GLP-1 receptor expression in the pancreas. When the GSPE treatment was administered every second week, the endocrine pancreas behaved differently. We show here that glucagon is a more sensitive parameter than insulin to GSPE treatments, with a secretion that is highly linked to GLP-1 ileal functionality and dependent on the type of treatment.

A Ten-Day Grape Seed Procyanidin Treatment Prevents Certain Ageing Processes in Female Rats over the Long Term

Adaptive homeostasis declines with age and this leads to, among other things, the appearance of chronic age-related pathologies such as cancer, neurodegeneration, osteoporosis, sarcopenia, cardiovascular disease and diabetes. Grape seed-derived procyanidins (GSPE) have been shown to be effective against several of these pathologies, mainly in young animal models. Here we test their effectiveness in aged animals: 21-month-old female rats were treated with 500 mg GSPE/kg of body weight for ten days. Afterwards they were kept on a chow diet for eleven weeks. Food intake, body weight, metabolic plasma parameters and tumor incidence were measured. The GSPE administered to aged rats had an effect on food intake during the treatment and after eleven weeks continued to have an effect on visceral adiposity. It prevented pancreas dysfunction induced by ageing and maintained a higher glucagon/insulin ratio together with a lower decrease in ketonemia. It was very effective in preventing age-related tumor development. All in all, this study supports the positive effect of GSPE on preventing some age-related pathologies.

Effects of Flavanols on Enteroendocrine Secretion

Some beneficial effects of grape seed proanthocyanidin extract (GSPE) can be explained by the modulation of enterohormone secretion. As GSPE comprises a combination of different molecules, the pure compounds that cause these effects need to be elucidated. The enterohormones and chemoreceptors present in the gastrointestinal tract differ between species, so if humans are to gain beneficial effects, species closer to humans-and humans themselves-must be used. We demonstrate that 100 mg/L of GSPE stimulates peptide YY (PYY) release, but not glucagon-like peptide 1 (GLP-1) release in the human colon. We used a pig ex vivo system that differentiates between apical and basolateral intestinal sides to analyse how apical stimulation with GSPE and its pure compounds affects the gastrointestinal tract. In pigs, apical GSPE treatment stimulates the basolateral release of PYY in the duodenum and colon and that of GLP-1 in the ascending, but not the descending colon. In the duodenum, luminal stimulation with procyanidin dimer B2 increased PYY secretion, but not CCK secretion, while catechin monomers (catechin/epicatechin) significantly increased CCK release, but not PYY release. The differential effects of GSPE and its pure compounds on enterohormone release at the same intestinal segment suggest that they act through chemosensors located apically and unevenly distributed along the gastrointestinal tract.

Protective properties of grape-seed proanthocyanidins in human ex vivo acute colonic dysfunction induced by dextran sodium sulfate

PURPOSE

Anti-inflammatory and barrier-protective properties have been attributed to proanthocyanidins in the context of intestinal dysfunction, however little information is available about the impact of these phytochemicals on intestinal barrier integrity and immune response in the human. Here we assessed the putative protective properties of a grape-seed proanthocyanidin extract (GSPE) against dextran sodium sulfate (DSS)-induced acute dysfunction of the human colon in an Ussing chamber system.

METHODS

Human proximal and distal colon tissues from colectomized patients were submitted ex vivo for a 30-min preventive GSPE treatment (50 or 200 µg mL^-1) followed by 1-h incubation with DSS (12% w v^-1). Transepithelial electrical resistance (TEER), permeation of a fluorescently-labeled dextran (FD4) and proinflammatory cytokine release [tumor necrosis factor (TNF)-α and interleukin (IL)-1β] of colonic tissues were determined.

RESULTS

DSS reduced TEER (45-52%) in both the proximal and distal colon; however, significant increments in FD4 permeation (fourfold) and TNF-α release (61%) were observed only in the proximal colon. The preventive GSPE treatment decreased DSS-induced TEER loss (20-32%), FD4 permeation (66-73%) and TNF-α release (22-33%) of the proximal colon dose-dependently. The distal colon was not responsive to the preventive treatment but showed a reduction in IL-1β release below basal levels with the highest GSPE concentration.

CONCLUSIONS

Our results demonstrate potential preventive effects of GSPE on human colon dysfunction. Further studies are required to test whether administering GSPE could be a complementary therapeutic approach in colonic dysfunction associated with metabolic disorders and inflammatory bowel disease.

Epoxygenase inactivation exacerbates diet and aging-associated metabolic dysfunction resulting from impaired adipogenesis

OBJECTIVE

When molecular drivers of healthy adipogenesis are perturbed, this can cause hepatic steatosis. The role of arachidonic acid (AA) and its downstream enzymatic cascades, such as cyclooxygenase, in adipogenesis is well established. The exact contribution of the P450 epoxygenase pathway, however, remains to be established. Enzymes belonging to this pathway are mainly encoded by the CYP2J locus which shows extensive allelic expansion in mice. Here we aimed to establish the role of endogenous epoxygenase during adipogenesis under homeostatic and metabolic stress conditions.

METHODS

We took advantage of the simpler genetic architecture of the Cyp2j locus in the rat and used a Cyp2j4 (orthologue of human CYP2J2) knockout rat in two models of metabolic dysfunction: physiological aging and cafeteria diet (CAF). The phenotyping of Cyp2j4-/- rats under CAF was integrated with proteomics (LC-MS/MS) and lipidomics (LC-MS) analyses in the liver and the adipose tissue.

RESULTS

We report that Cyp2j4 deletion causes adipocyte dysfunction under metabolic challenges. This is characterized by (i) down-regulation of white adipose tissue (WAT) PPARγ and C/EBPα, (ii) adipocyte hypertrophy, (iii) extracellular matrix remodeling, and (iv) alternative usage of AA pathway. Specifically, in Cyp2j4-/- rats treated with a cafeteria diet, the dysfunctional adipogenesis is accompanied by exacerbated weight gain, hepatic lipid accumulation, and dysregulated gluconeogenesis.

CONCLUSION

These results suggest that AA epoxygenases are essential regulators of healthy adipogenesis. Our results uncover their synergistic role in fine-tuning AA pathway in obesity-mediated hepatic steatosis.