Age-dependent modulation of central ghrelin effects on food intake and lipid metabolism in rats

Physiological Effect of Ghrelin on Body Systems

Ghrelin is a relatively novel multifaceted hormone that has been found to exert a plethora of physiological effects. In this review, we found/confirmed that ghrelin has effect on all body systems. It induces appetite; promotes the use of carbohydrates as a source of fuel while sparing fat; inhibits lipid oxidation and promotes lipogenesis; stimulates the gastric acid secretion and motility; improves cardiac performance; decreases blood pressure; and protects the kidneys, heart, and brain. Ghrelin is important for learning, memory, cognition, reward, sleep, taste sensation, olfaction, and sniffing. It has sympatholytic, analgesic, antimicrobial, antifibrotic, and osteogenic effects. Moreover, ghrelin makes the skeletal muscle more excitable and stimulates its regeneration following injury; delays puberty; promotes fetal lung development; decreases thyroid hormone and testosterone; stimulates release of growth hormone, prolactin, glucagon, adrenocorticotropic hormone, cortisol, vasopressin, and oxytocin; inhibits insulin release; and promotes wound healing. Ghrelin protects the body by different mechanisms including inhibition of unwanted inflammation and induction of autophagy. Having a clear understanding of the ghrelin effect in each system has therapeutic implications. Future studies are necessary to elucidate the molecular mechanisms of ghrelin actions as well as its application as a GHSR agonist to treat most common diseases in each system without any paradoxical outcomes on the other systems.

Lipoprotein Profile in Aged Rats Fed Chia Oil- or Hydroxytyrosol-Enriched Pork in High Cholesterol/High Saturated Fat Diets

Restructuring pork (RP) by adding new functional ingredients, like Chia oil (one of the richest natural source of α-linolenic acid) or hydroxytyrosol (HxT) (potent antioxidant), both with hypolipidemic activities, is one of the strategies that may help to reduce the potential negative effects of high meat products consumption. The aim of this study was to evaluate the Chia oil- or HxT-enriched-RP effect on the lipoprotein profile of aged rats fed high-fat, high-energy, and cholesterol-enriched diets. RP samples were prepared by mixing lean pork and lard with or without Chia oil (152.2 g/kg fresh matter) or HxT (3.6 g/kg fresh matter). Diets were prepared by mixing a semisynthetic diet with freeze-dried RP. Groups of 1-year male Wistar rats were fed the following experimental diets for 8 weeks: C, control-RP diet; HC, cholesterol-enriched-RP diet; and Chia oil-RP (CHIA) and HxT, Chia oil- or hydroxytyrosol-RP, cholesterol-enriched diet. Plasma lipid, lipoprotein profile, SREBP-1c protein, and low-density lipoproteins (LDL) receptor gene (Ldlr) expressions were evaluated. Compared to C diet, the HC diet increased plasma cholesterol, triglycerides, free fatty acids, total lipids, and SREBP-1c expression, but reduced Ldlr expression and significantly modified the lipoprotein profile, giving rise to the presence of high levels of atherogenic cholesterol-enriched very low-density lipoproteins (VLDL) particles. Compared to the HC diet, the HxT diet did not produce significant changes in feed intake but it reduced the body weight. Chia oil and HxT partially arrested the negative effects of the high-fat, high-energy, and cholesterol-enriched meat-based diets on lipemia and lipoproteinemia, mostly by reducing the amount of cholesterol content in VLDL (60% and 74% less in CHIA and HxT vs. HC, respectively) and the VLDL total mass (59% and 63% less in CHIA and HxT vs. HC, respectively). Free fatty acids (FFA) significantly correlated with adipose tissue weight and VLDL total mass (both p < 0.05), and plasma triglycerides, phospholipids, total lipids, and SREBP-1c (all p < 0.001), suggesting the important role of FFA in lipoprotein metabolism. Results support the recommendation to include these ingredients in pork products addressed to reduce the presence of increased atherogenic particles in aged people at CVD risk consuming large amounts of pork.

Ghrelin, a gastrointestinal hormone, regulates energy balance and lipid metabolism

Ghrelin, an acylated peptide hormone of 28 amino acids, is an endogenous ligand of the released growth hormone secretagogue receptor (GHSR). Ghrelin has been isolated from human and rat stomach and is also detected in the hypothalamic arcuate nucleus. Ghrelin receptor is primarily located in the neuropeptide Y and agouti-related protein neurons. Many previous studies have shown that ghrelin and GHSR are involved in the regulation of energy homeostasis, and its administration can increase food intake and body weight gain. AMP-activated protein kinase is activated by ghrelin in the hypothalamus, which contributes to lower intracellular long-chain fatty acid level. Ghrelin appears to modulate the response to food cues via a neural network involved in the regulation of feeding and in the appetitive response to food cues. It also increases the response of brain areas involved in visual processing, attention, and memory to food pictures. Ghrelin is also an important factor linking the central nervous system with peripheral tissues that regulate lipid metabolism. It promotes adiposity by the activation of hypothalamic orexigenic neurons and stimulates the expression of fat storage-related proteins in adipocytes. Meanwhile, ghrelin exerts direct peripheral effects on lipid metabolism, including increase in white adipose tissue mass, stimulation of lipogenesis in the liver, and taste sensitivity modulation.

Taste preference changes throughout different life stages in male rats

Taste preference, a key component of food choice, changes with aging. However, it remains unclear how this occurs. To determine differences in taste preference between rats in different life stages, we examined the consumption of taste solutions and water using a two-bottle test. Male Sprague-Dawley rats of different ages were used: juvenile (3-6 weeks), young adult (8-11 weeks), adult (17-20 weeks), middle-aged (34-37 weeks), and old-aged (69-72 weeks). The intakes of the high and low concentration solutions presented simultaneously were measured. We observed that the old-aged group had lower preference ratios for 0.3 M sucrose and 0.1 M MSG in comparison with other groups. The preference ratio for 0.03 mM QHCl was higher in the middle-aged group than in the three younger groups and higher in the old-aged group than the juvenile group. The taste preferences for HCl and NaCl did not significantly differ among the age groups. The old-aged group tended to prefer high concentrations of sucrose, QHCl, NaCl, and MSG to low concentrations, indicating age-related decline in taste sensitivity. We also aimed to investigate differences between life stages in the electrophysiological responses of the chorda tympani nerve, one of the peripheral gustatory nerves, to taste stimuli. The electrophysiological recordings showed that aging did not alter the function of the chorda tympani nerve. This study showed that aging induced alterations in taste preference. It is likely that these alterations are a result of functional changes in other peripheral taste nerves, the gastrointestinal system, or the central nervous system.

Neuronal systems and circuits involved in the control of food intake and adaptive thermogenesis

With the still-growing prevalence of obesity worldwide, major efforts are made to understand the various behavioral, environmental, and genetic factors that promote excess fat gain. Obesity results from an imbalance between energy intake and energy expenditure, which emphasizes the importance of deciphering the mechanisms behind energy balance regulation to understand its physiopathology. The control of energy balance is assured by brain systems/circuits capable of generating adequate ingestive and thermogenic responses to maintain the stability of energy reserves, which implies a proper integration of the homeostatic signals that inform about the status of the energy stores. In this article, we overview the organization and functionality of key neuronal circuits or pathways involved in the control of food intake and energy expenditure. We review the role of the corticolimbic (executive and reward) and autonomic systems that integrate their activities to regulate energy balance. We also describe the mechanisms and pathways whereby homeostatic sensing is achieved in response to variations of homeostatic hormones, such as leptin, insulin, and ghrelin, while putting some emphasis on the prominent importance of the mechanistic target of the rapamycin signaling pathway in coordinating the homeostatic sensing process.

Effects of Silicon vs. Hydroxytyrosol-Enriched Restructured Pork on Liver Oxidation Status of Aged Rats Fed High-Saturated/High-Cholesterol Diets

Background

Pork is an essential component of the diet that has been linked with major degenerative diseases and development of non-alcoholic steatohepatitis (NASH). Previous studies have. Previous studies have demonstrated the in vitro antioxidant activity of silicon (Si). Furthermore, when Si is added to restructured pork (RP) strongly counterbalances the negative effect of high-cholesterol-ingestion, acting as an active hypocholesterolemic and hypolipemic dietary ingredient in aged rats.

Objective

This study was designed to evaluate the effects of Si vs hydroxytyrosol (HxT) RP on liver antioxidant defense in aged rats fed cholesterol-enriched high saturated/high cholesterol diets as a NASH model.

Methods

Four diets were prepared: Control RP diet (C) with non-added cholesterol; Cholesterol-enriched high-saturated/high-cholesterol control RP diet (CHOL-C) with added cholesterol and cholic acid; Si- or HxT-RP cholesterol-enriched high-saturated/high-cholesterol diets (CHOL-Si and CHOL-HxT). Groups of six male Wistar rats (1-yr old) were fed these modified diets for eight weeks. Total cholesterol, hepatosomatic index, liver Nrf2 and antioxidant (CAT, SOD, GSH, GSSG, GR, GPx) markers were determined.

Results

Both CHOL-Si and CHOL-HxT diets enhanced the liver antioxidant status, reduced hepatosomatic index and increased SOD actvity. Hydrogen peroxide removal seemed to be involved, explaining that the value of redox index was even lower than C without changing the CAT activity. CHOL-Si results were quite better than CHOL-HxT in most measured parameters.

Conclusions

Our study suggests that Si incorporated into RP matrix was able to counterbalance, more efficiently than HxT, the deleterious effect of consuming a high-saturated/high-cholesterol diet, by improving the liver antioxidant defenses in the context of NASH.

Silicon-Enriched Restructured Pork Affects the Lipoprotein Profile, VLDL Oxidation, and LDL Receptor Gene Expression in Aged Rats Fed an Atherogenic Diet

BACKGROUND

Research has shown that silicon can play an important role in protecting against degenerative diseases. Restructuring pork by partially disassembling meat permits the incorporation of active components with potential functional effects. However, there has been no research to date on the impact that silicon, as a functional ingredient in restructured pork (RP), has on lipoprotein composition, metabolism, and oxidation.

OBJECTIVE

This study was designed to evaluate the effect of silicon-enriched RP on lipemia, lipoprotein profile, and oxidation markers of aged rats fed high-fat, high-energy, cholesterol-enriched diets.

METHODS

RP samples similar to commercial sausages (16% protein and 22% fat, wt:wt) were prepared by mixing lean pork and lard alone or with silicon (1.3 g Si/kg fresh matter) under controlled conditions and then freeze-dried. Saturated fat-rich diets were designed by mixing 78.3% purified diet with 21.7% freeze-dried RP. Three groups composed of 8 aged male Wistar rats (1 y old) were fed for 8 wk a control RP (C) diet, a cholesterol-enriched RP (Chol-C) diet [C diet enriched with 1.26% cholesterol plus 0.25% cholic acid, or a cholesterol and silicon-enriched RP (Chol-Si) diet (same as the Chol-C diet but containing silicon)]. Plasma lipid concentrations, lipoprotein profile, the degree of VLDL oxidation, and LDL receptor gene (Ldlr) expression were tested.

RESULTS

Compared with the C diet, the Chol-C diet did not modify food intake or body weight but significantly increased (P < 0.05) plasma cholesterol (32%) and total lipids (19%), VLDL and intermediate density lipoprotein + LDL cholesterol (both >600%), total lipids and proteins (both >300%), and the degree of VLDL oxidation [conjugated dienes >250%; thiobarbituric acid-reactive substance (TBARS), 900%] and reduced Ldlr expression (64%) and liver arylesterase activity (54%). The Chol-Si diet partially normalized changes induced by the Chol-C diet. Compared with the Chol-C group, Chol-Si rats had lower VLDL compound concentrations (P < 0.001; e.g., 75% less VLDL cholesterol) and VLDL oxidation (65% less conjugated dienes and 85% less TBARS) but greater Ldlr expression (200%).

CONCLUSIONS

Silicon added to RP strongly counterbalanced the negative effect of high-cholesterol-ingestion, functioning as an active hypocholesterolemic, hypolipemic, and antioxidative dietary ingredient in aged rats.

The Role of Ghrelin in Senescence: A Mini-Review

Ghrelin, a 28-amino acid hormone produced mainly by the X/A-like endocrine cells in gastric mucosa, has a widespread tissue distribution and diverse physiological functions such as hormonal, orexigenic, metabolic, cardiovascular, neurological, and immunological activities. Considerable evidence has suggested that ghrelin plays an important role in organism senescence or aging. The present review provides a comprehensive picture of this new development. We first reviewed the aging (senescence)-dependent reduction of ghrelin signaling, and then highlighted its relationship with the aging-associated alteration in food intake, energy metabolism, cardiovascular function, neurological activity, and adaptive immunity. Our literature review suggests that ghrelin is an innovative and promising agent in the treatment of these pathophysiological conditions associated with senescence.

The role of ghrelin in metabolic regulation

PURPOSE OF REVIEW

To discuss recent research on the role of ghrelin in the regulation of carbohydrate and lipid metabolism in the context of its wider role in regulating energy balance.

RECENT FINDINGS

Ghrelin possesses a range of centrally and peripherally mediated metabolic actions influencing insulin glucose homeostasis and fatty acid metabolism and appetite. Although acyl ghrelin was previously thought to be the active hormone, recent evidence suggests that des-acyl ghrelin also possesses activity, and the enzyme ghrelin-O-acyl transferase regulates their interconversion. In partnership with insulin and leptin, ghrelin defends against energy deficit by enhancing hunger, conserving carbohydrate and promoting fat oxidation. In the postprandial state, it contributes to satiety, energy storage and favours glucose oxidation. New research suggests a range of new roles including addictive behaviours, cardiovascular protection, neuroprotection and regeneration and perhaps the ageing process.

SUMMARY

Ghrelin functions primarily as a short-term metabolic switch at the onset of fasting, gearing the fuel economy away from glucose uptake, conserving glucose for vital functions, favouring fatty acid oxidation and triggering food-seeking behaviour. The ghrelin system is a potential target for a range of pharmacological interventions, but its pleiotropic nature makes selective treatments challenging.