Grape seed extract supplementation modulates hepatic lipid metabolism in rats. Implication of PPARß/δ.

In mammals, the liver is involved in nutrient metabolism and in the regulation of lipid and glucose homeostasis. Multiple studies have described improvements in liver disorders after regular consumption of grape seed extract (GSE). GSE prevents or ameliorates hepatic metabolic dysfunction through AMPK activation, which reduces hepatic lipogenesis while enhancing hepatic lipid oxidation. However, the involvement of ChREBPß and PPARß/δ in these effects has not been fully elucidated. We aim to demonstrate that chronic consumption of GSE at low doses (25 mg kg-1 body weight per day) produces beneficial effects on hepatic glucose and lipid metabolism in young lean Wistar rats and that part of these effects involve ChREBPß inactivation and PPARß/δ activation. In our study, increased concentrations of structurally related (-)-(epi)catechin metabolites and 5-carbon ring fission metabolites were found in the serum of GSE-supplemented rats parallel with the reduction in triglycerides and leptin levels, hepatic cholesterol content and visceral adiposity. GSE supplementation inactivates ChREBP and GSK-3ß, which has been linked to improvements in hepatic lipid and glucose metabolism. Furthermore, the consumption of GSE promotes the expression of Pparß/δ, as well as Pgc-1α and Acox-1, which control hepatic lipid oxidation. Interestingly, pharmacological inhibition of PPARß/δ slowed the induction of Pgc-1α and Acox-1, as well as the activation of AMPK triggered by GSE consumption. Our data suggest that PPARß/δ activation is involved in the metabolic reprogramming effects of chronic GSE consumption in young rats, by modulating, at least, part of the transcriptional programs that maintain hepatic and systemic fuel homeostasis.

Ageing alters the lipid sensing process in the hypothalamus of Wistar rats. Effect of food restriction.

INTRODUCTION: Lipids regulate a wide range of biological processes. The mechanisms by which fatty acids (FA) and its metabolites influence the hypothalamic regulation of energy homeostasis have been highly studied. However, the effect of ageing and food restriction (FR) on this process is unknown. METHODS: Herein, we analyzed the gene expression, protein and phosphorylation levels of hypothalamic enzymes and transcription factors related to lipid metabolism. Experiments were performed in male Wistar rats of 3-, 8- and 24-month-old Wistar rats fed ad libitum (AL), as ageing model. Besides, 5- and 21-month-old rats were subjected to a moderate FR protocol (equivalent to ≈ 80% of normal food intake) for three months before the sacrifice. RESULTS: Aged Wistar rats showed a situation of chronic lipid excess as a result of an increase in de novo FA synthesis and FA levels that reach the brain, contributing likely to the development of central leptin and insulin resistance. We observe a hypothalamic downregulation of AMP-activated protein kinase (AMPK) and stearoyl-CoA desaturase (SCD1) and an increase of carnitine palmitoyltransferase-1c (CPT1c) expression. DISCUSSION: Our results suggest an impairment in the physiological lipid sensing system of aged Wistar rats, which would alter the balance of the intracellular mobilization and trafficking of lipids between the mitochondria and the Endoplasmic Reticulum (ER) in the hypothalamus, leading probably to the development of neurolipotoxicity in aged rats. Lastly, FR can only partially restore this imbalance.Schematic representation of the fate of LCFA-CoA in the hypothalamus of young and old rats. Blood circulating LCFAs in young Wistar rats reach the hypothalamus, where they are esterified to LCFA-CoA. Into glial cells or neurons, LCFA-CoA are driven to mitochondria (CPT1a) or ER (CPT1c) where could be desaturated by SDC1 and, thereby, converted into structural and signaling unsaturated lipids as oleic acid, related with neuronal myelinization and differentiation. However, the excess of LCFA that reach to the hypothalamus in old animals, could generate an increase in LCFA-CoA, which together with an increase in CPT1c levels, could favor the capture of LCFA-CoA to the ER. The decrease in the levels of SCD1 in old rats would decrease FA unsaturation degree that could trigger lipotoxicity process and neurodegeneration, both related to the development of neurodegenerative diseases linked to age.

Leptin, Acting at Central Level, Increases FGF21 Expression in White Adipose Tissue via PPARß/δ.

The altered function of adipose tissue can result in obesity, insulin resistance, and its metabolic complications. Leptin, acting on the central nervous system, modifies the composition and function of adipose tissue. To date, the molecular changes that occur in epididymal white adipose tissue (eWAT) during chronic leptin treatment are not fully understood. Herein we aimed to address whether PPARß/δ could mediate the metabolic actions induced by leptin in eWAT. To this end, male 3-month-old Wistar rats, infused intracerebroventricularly (icv) with leptin (0.2 µg/day) for 7 days, were daily co-treated intraperitoneally (ip) without or with the specific PPARß/δ receptor antagonist GSK0660 (1 mg/kg/day). In parallel, we also administered GSK0660 to control rats fed ad libitum without leptin infusion. Leptin, acting at central level, prevented the starvation-induced increase in circulating levels of FGF21, while induced markedly the endogenous expression of FGF21 and browning markers of eWAT. Interestingly, GSK0660 abolished the anorectic effects induced by icv leptin leading to increased visceral fat mass and reduced browning capacity. In addition, the pharmacological inhibition of PPARß/δ alters the immunomodulatory actions of central leptin on eWAT. In summary, our results demonstrate that PPARß/δ is involved in the up-regulation of FGF21 expression induced by leptin in visceral adipose tissue.

Central s-resistin deficiency ameliorates hypothalamic inflammation and increases whole body insulin sensitivity.

S-resistin, a non-secretable resistin isoform, acts as an intracrine factor that regulates adipocyte maduration, inflammatory and insulin response in 3T3-L1 cells. However, its intracellular function in vivo is still unknown. In this study, we analyze the central role of s-resistin, decreasing its hypothalamic expression using an intracerebroventricular injection of lentiviral RNAi. The data present herein support an improvement in the hypothalamic leptin and insulin signaling pathway upon s-resistin downregulation. Furthermore, hypothalamic levels of pro-inflammatory markers decrease, meanwhile those of the anti-inflammatory cytokine IL-10 increases. Interestingly, peripheral NEFA decreases alike circulating leptin and resistin levels. These data demonstrate that hypothalamic s-resistin controls fuel mobilization and adipokines secretion. Importantly, central s-resistin downregulation improves systemic insulin sensitivity, as demonstrated after an IPGTT. Interestingly, our data also indicate that s-resistin downregulation could improve hypothalamic inflammation in aged Wistar rats. Altogether, our findings suggest that hypothalamic s-resistin seems to be a key regulator of the brain-fat axis which links inflammation with metabolic homeostasis.

Cloning, tissue expression and metal inducibility of an ubiquitous metallothionein from Panulirus argus.

Invertebrate metallothioneins (MT) have mainly been reported in digestive tissues, but data about the existence of a ubiquitous isoform expressed also in nervous tissue, are not available. Here we report the identification of a new metallothionein gene (MTPA) from the lobster Panulirus argus, putatively encoding a 59 residue polypeptide including 19 Cys. Tissue specific analysis indicated that MTPA is ubiquitously expressed in the hepatopancreas, intestine, nervous tissue and muscle, with the highest levels in the hepatopancreas and the lowest in muscle and nervous tissue. In addition, our data showed that MTPA is differentially regulated by metals: tissue explants exposed to Cd exhibited increased MTPA mRNA levels in all cases, except in muscle, with the highest effects in the nervous tissue, while Zn was effective only in the hepatopancreas. Interestingly, Cu showed no effects in any of the analyzed tissues. Taken together, these results suggest that MTPA in the hepatopancreas likely plays an important role in Cd detoxification and Zn homeostasis. The potent Cd-inducibility of MTPA in the nervous tissue might suggest a key function of this protein in protecting this highly sensitive tissue from cadmium-induced neurotoxicity.