Dietary modulation of circulating leptin levels: site-specific changes in fat deposition and ob mRNA expression.

In order to study the effects of diet on fat distribution, circulating leptin levels and ob mRNA expression, diets of different macronutrient composition were fed to lean mice and gold thioglucose-obese mice. A high-fat diet and 2 high-carbohydrate diets, one containing mostly high-glycaemic-index starch and the other containing low-glycaemic-index starch were fed ad libitum for 10 weeks and were compared to standard laboratory chow. Weight gain was attenuated by feeding low-glycaemic-index starch in all mice and by feeding a high-fat diet in lean mice. Reduced adiposity was seen in lean mice fed low-glycaemic-index starch, whereas increased adiposity was seen in both lean and obese mice fed on the high-fat diet. Circulating leptin levels, when corrected for adiposity, were decreased in all mice fed either the high-fat diet or the low-GI diet. In epididymal fat pads, decreased ob mRNA expression was seen after both high-fat and high-glycaemic-index starch feeding. These results show that diet macronutrient composition contributes to the variability of circulating leptin levels by the combined effects of diet on fat distribution and on site-specific changes in ob mRNA expression.     

Regulation of advanced glycation end product (AGE) receptors and apoptosis by AGEs in osteoblast-like cells

It has been reported that apelin functions as an adipokine, which has been associated to obesity and insulin resistance. The objective of this study was to analyze the apelin mRNA expression in white adipose tissue (WAT) from high-fat (Cafeteria) fed rats, in order to examine potential relationships with obesity markers and other related risk factors. Animals fed on the high-fat diet during 56 days increased their body weight, total body fat and WAT depots weights when compared to controls. Apelin subcutaneous mRNA expression was higher in the Cafeteria than in the Control fed group and this increase was partially reversed by dietary vitamin C supplementation. Statistically significant associations between subcutaneous apelin gene expression and almost all the studied variables were identified, being of special interest the correlations found with serum leptin (r = 0.517), liver malondialdehyde (MDA) levels (r = 0.477), and leptin, IRS-3 and IL-1ra retroperitoneal mRNA expression (r = 0.701; r = 0.692 and r = 0.561, respectively). These associations evidence a possible role for apelin in the excessive weight gain induced by high-fat feeding and increased adiposity, insulin-resistance, liver oxidative stress and inflammation.     

Carya cathayensis leaf extract attenuates ectopic fat deposition in liver,abdomen and aortic arch in ovariectomized rats fed a high-fat diet

BackgroundCarya cathayensis¹is a commercially cultivated plant in the Zhejiang Province, China. Its nuts exhibit properties of tonifying kidneys and relieving asthma. There have been a few pharmacological studies addressing the function of the leaves of this plant. Our previous studies on C. cathayensis leaf extract (CCE) showed a significant inhibitory effect on weight gain in mice fed a high-fat diet, particularly in female mice.Hypothesis/purposeTo investigate the biological and molecular mechanisms underlying the regulation of ectopic adipose tissue deposition by CCE in ovariectomized rats fed a high-fat diet.Study designFemale Sprague–Dawley rats were ovariectomized and treated with CCE (50, 100, and 200 mg/kg body weight, oral) or estradiol (1 mg/kg body weight, oral) for 8 weeks.MethodsCCE was subjected to high-performance liquid chromatography to quantify major components. Body weight gain, abdominal fat coefficient, and aortic arch fat coefficient were determined; serum was collected for biochemical analysis; tissues were collected for histopathological examination, quantitative polymerase chain reaction (Q-PCR), and western blotting.ResultsThe total flavonoid content was determined to be 57.30% in the CCE and comprised chrysin, cardamomin, pinostrobin chalcone, and pinocembrin. Compared with the model group (OVX), CCE treatment reduced body weight gain, abdominal and aortic arch fat coefficients, serum and hepatic lipid profiles, including total cholesterol (TC), total triglycerides (TG), and free fatty acids (FFA) levels; decreased lipid droplets in liver cells; decreased fat accumulation in the aortic arch blood vessel wall and increased its smoothness; decreased the diameter of abdominal fat cells; and reduced serum leptin and adiponectin levels significantly. Serum adiponectin levels significantly correlated with serum TG and hepatic TC levels. Leptin levels positively correlated with serum TG levels and negatively correlated with hepatic TG. Leptin mRNA, peroxisome proliferator-activated receptor (PPARγ) mRNA, and protein expression levels in abdominal adipose tissue were significantly down-regulated. Adiponectin mRNA levels were slightly reduced but not significantly.ConclusionCCE attenuated ectopic fat deposition induced by deficient estrogen and a high-fat diet in rats; this may be associated with activated leptin sensitivity, improved leptin resistance, and regulated adiponectin levels. CCE may improve adipose function to regulate adipocyte differentiation by down-regulating PPARγ. Overall, these results suggest that CCE is a potential phytoestrogen.     

Downregulation of STRA6 in Adipocytes and Adipose Stromovascular Fraction in Obesity and Effects of Adipocyte-Specific STRA6 Knockdown In Vivo

To investigate the mechanisms by which elevated retinol-binding protein 4 (RBP4) causes insulin resistance, we studied the role of the high-affinity receptor for RBP4, STRA6 (stimulated by retinoic acid), in insulin resistance and obesity. In high-fat-diet-fed and ob/ob mice, STRA6 expression was decreased 70 to 95% in perigonadal adipocytes and both perigonadal and subcutaneous adipose stromovascular cells. To determine whether downregulation of STRA6 in adipocytes contributes to insulin resistance, we generated adipose-Stra6^−/− mice. Adipose-Stra6^−/− mice fed chow had decreased body weight, fat mass, leptin levels, insulin levels, and adipocyte number and increased expression of brown fat-selective markers in white adipose tissue. When fed a high-fat diet, these mice had a mild improvement in insulin sensitivity at an age when adiposity was unchanged. STRA6 has been implicated in retinol uptake, but retinol uptake and the expression of retinoid homeostatic genes (encoding retinoic acid receptor β [RARβ], CYP26A1, and lecithin retinol acyltransferase) were not altered in adipocytes from adipose-Stra6^−/− mice, indicating that retinoid homeostasis was maintained with STRA6 knockdown. Thus, STRA6 reduction in adipocytes in adipose-Stra6^−/− mice fed chow resulted in leanness, which may contribute to their increased insulin sensitivity. However, in wild-type mice with high-fat-diet-induced obesity and in ob/ob mice, the marked downregulation of STRA6 in adipocytes and adipose stromovascular cells does not compensate for obesity-associated insulin resistance.     

Effect of peripheral administration of leptin on the renal sympathetic nerve activity in high-fat diet-related hypertensive rats

A previous study of ours demonstrated that a high-fat diet (FAT) causes body fat accumulation, as well as elevation of plasma leptin level, renal sympathetic nerve activity (RSNA), and blood pressure (BP). In the study reported here, we analyzed the role of leptin in these elevations of the RSNA and BP due to FAT feeding by assessing sympathetic and cardiovascular responses to intravenous (IV) administration of leptin in rats fed either a FAT or a high-carbohydrate diet (CHO). The results showed that baseline body fat, plasma leptin level, RSNA and BP were significantly higher in the FAT group than in the CHO group, and that IV administration of leptin elevated RSNA and plasma leptin levels but lowered BP in the CHO group. However, these effects of leptin were eliminated in the FAT group. These findings suggest that FAT-fed rats which expose basal elevation of plasma leptin levels, RSNA and BP might be hyposensitive to endogenous leptin. Therefore, leptin resistance appeared obviously in FAT-induced hypertension might indicate that leptin is implicated in generating the elevation of RSNA and BP induced by long-term FAT feeding.     

Acute changes in the response to peripheral leptin with alteration in the diet composition

Dietary induced obesity in rodents is associated with a resistance to leptin. We have investigated the hypothesis that dietary fat per se alters the feeding response to peripheral leptin in rats that were fed either their habitual high- or low-fat diet or were naively exposed to the alternative diet. Osborne-Mendel rats were adapted to either high- or low-fat diet. Food-deprived rats were given either leptin (0.5 mg/kg body wt ip) or saline, after which they were provided with either their familiar diet or the alternative diet. Food intake of rats adapted and tested with the low-fat diet was reduced 4 h after leptin injection, whereas rats adapted and tested with a high-fat diet did not respond to leptin. Leptin was injected again 1 and 5 days after the high-fat diet-adapted rats were switched to the low-fat diet. Leptin reduced the food intake on both days. In contrast, when low-fat diet-adapted rats were switched to a high-fat diet, the leptin inhibitory response was present on day 1 but not observed on day 5. Peripheral injection of leptin increased serum corticosterone level and decreased hypothalamic neuropeptide Y mRNA expression in rats fed the low-fat but not the high-fat diet for 20 days. The data suggest that dietary fat itself, rather than obesity, may induce leptin resistance within a short time of exposure to a high-fat diet.     

Cloning and tissue distribution of Leptin mRNA in the pig∗

Abstract

The sequence of the pig ob cDNA, which codes for the protein leptin, has been determined by screening a pig adipose cDNA library with an RT‐PCR amplified cDNA fragment of this gene. The 501 bp ob cDNA has 89% identity to the human ob cDNA, 92% identity to the bovine ob cDNA, 84% identity to the mouse ob cDNA and 84% identity to the rat ob cDNA. At the amino acid level, pig leptin which codes for a protein with a predicted molecular weight of 18,661‐dalton, has 86% identity to human leptin, 93% identity to bovine leptin, 84% identity to rat leptin and 84% identity to mouse leptin. RT‐PCR screening of RNA isolated from pig adipose, skeletal muscle, cardiac muscle, pancreas, stomach, kidney, spleen and jejunum detected ob mRNA only in adipose tissue; Northern blots with an ob cDNA probe identified a 4.0 kb species in adipose tissue. The conservation of sequence and expression pattern of leptin in the pig reported here indicates that as in other species, this protein likely plays an important role in controlling food intake and fat deposition in the pig.     

Dietary diacylglycerol suppresses high fat and high sucrose diet-induced body fat accumulation in C57BL/6J mice

Diacylglycerol (DG) comprises up to approximately 10% of various edible oils. In the present study, we examined the effects of dietary DG consisting mainly of 1,3-species on body weight, body fat accumulation, and mRNA levels of various genes involved in energy homeostasis in obesity-prone C57BL/6J mice. Five-month feeding with the high triacylglycerol (TG) diet (30% TG + 13% sucrose) resulted in significant increases in body weight, visceral fat accumulation, and circulating insulin and leptin levels compared with mice fed the control diet (5% TG). Compared with mice fed the high TG diet, body weight gain and visceral fat weight were reduced by 70% and 79%, respectively, in those fed the high DG diet (30% DG + 13% sucrose). In addition, circulating leptin and insulin levels were reduced to the respective control levels. Compared with high TG feeding, high DG feeding suppressed the elevation of leptin mRNA expression in adipose tissue, and up-regulated acyl-coenzyme (Co)A oxidase and acyl-CoA synthase mRNA expression in the liver. These results indicate that dietary DG is beneficial for suppression of high fat diet-induced body fat accumulation. Furthermore, it is suggested that structural differences in DG and TG, but not the composition of fatty acid, markedly affect nutritional behavior of lipids. -- Murase, T., T. Mizuno, T. Omachi, K. Onizawa, Y. Komine, H. Kondo, T. Hase, and I. Tokimitsu. Dietary diacylglycerol suppresses high fat and high sucrose diet-induced body fat accumulation in C57BL/6J mice. J. Lipid Res. 2001. 42: 372--378.     

Effects of Exogenous Gonadal Steroids on Leptin Homeostasis in Rats

WU-PENG, SHARON, MICHAEL ROSENBAUM, MARGERY NICOLSON, STREAMSON C. CHUA, AND RUDOLPH L. LEIBEL. Effects of exogenous gonadal steroids on leptin homeostasis in rats. Obes Res. Background: In humans, circulating concentrations of the hormone leptin, normalized to body fat mass, are significantly higher in females compared to males. This experiment was designed to determine whether the administration of exogenous androgen or estrogen would significantly alter the relationship between plasma leptin and fat mass in rats. Methods: In the first experiment, plasma leptin and retro-peritoneal and parametrial (female)/epididymal (male) adipose tissue expression of leptin mRNA were measured in five male and five female 9. 5-week-old Sprague-Dawley rats. In a second experiment, gonadectomized 10. 5-week-old female Sprague-Dawley rats received 1 or 2 weeks of daily intraperitoneal injections (in oil) of 750 mg testosterone propionate, 2. 5 μg of estradiol benzoate or vehicle. At 0, 1, and 2 weeks, plasma concentrations of leptin, fat pad weight of parametrial and retroperitoneal fat pads, and leptin mRNA expression by Northern blot in retroperitoneal fat pads were determined. Daily weight and food intake of animals were monitored throughout the study. Results: Circulating leptin concentrations per unit of fat pad mass and leptin mRNA expression normalized to actin mRNA were higher in gonadally intact female compared to male rats. Compared to placebo, estrogen administration decreased food intake and body weight, but had no significant effect on leptin mRNA expression or on circulating leptin concentration. Testosterone administration increased body weight and decreased expression of leptin mRNA (only after 2 weeks), but did not change food intake or circulating leptin concentration. Conclusions: Administration of estrogen did not affect either leptin expression or the circulating concentration of leptin. Administration of androgen decreased expression of leptin mRNA. However, even after 2 weeks of testosterone administration to gonadectomized females, plasma leptin concentration, corrected for fat pad weight, was higher in gonadectomized females than in intact males, Thus, sex steroid-associated changes in plasma leptin concentration and leptin mRNA expression are not sufficient to explain the observed sexual dimorphism in plasma leptin concentrations in rats.     

Leptin responses to glucose infusions in obesity-prone rats

The secretion of leptin is dually regulated. In fasting animals, plasma leptin concentrations reflect body fat stores, whereas the incremental leptin response to fasting or refeeding most likely reflects insulin-mediated energy flux and metabolism within adipocytes. Impaired secretion of leptin in either pathway could result in obesity. We therefore measured plasma leptin concentrations in fasted animals and plasma leptin concentrations after an intravenous glucose infusion in a rat model of obesity. Young Sprague-Dawley (S-D) and Fischer 344 (F344) rats had similar percent body fat and fasting glucose and fasting leptin concentrations. However, F344 animals had higher insulin concentrations and leptin responses to intravenous glucose than did the S-D animals. The animals were then fed a control or high-fat diet for 6 wk. High-fat fed animals gained more weight and body fat than did the control fed animals. Control and high-fat fed F344 animals gained approximately 40% (P < 0.0001) more weight and >100% (P < 0.01) more body fat than did the S-D animals. Fasting leptin concentrations and leptin concentrations after intravenous glucose infusions and feeding were more than double (P < 0.05) in F344 animals compared with S-D animals. Whether an animal is fed a control or high-fat diet had little effect on the leptin response to intravenous glucose. In conclusion, young, lean F344 animals, before the onset of obesity, demonstrated a greater acute leptin response to intravenous glucose than similarly lean S-D animals. After a 6-wk diet, F344 animals had a greater percent increase in body weight and insulin resistance and exhibited higher fasting leptin concentrations and a greater absolute leptin response to intravenous glucose compared with the S-D animals. The chronic diet (control or high fat) had little impact on the acute leptin response to intravenous glucose. F344 animals exhibit leptin resistance in young, lean animals and after aging and fat accumulation.     

Altered mRNA expression of hepatic lipogenic enzyme and PPARalpha in rats fed dietary levan from Zymomonas mobilis

Levan or high molecular beta-2,6-linked fructose polymer is produced extracellularly from sucrose-based substrates by bacterial levansucrase. In the present study, to investigate the effect of levan feeding on serum leptin, hepatic lipogenic enzyme and peroxisome proliferation-activated receptor (PPAR) alpha expression in high-fat diet-induced obese rats, 4-week-old Sprague-Dawley male rats were fed high-fat diet (beef tallow, 40% of calories as fat), and, 6 weeks later, the rats were fed 0%, 1%, 5% or 10% levan-supplemented diets for 4 weeks. Serum leptin and insulin level were dose dependently reduced in levan-supplemented diet-fed rats. The mRNA expressions of hepatic fatty acid synthase and acetyl CoA carboxylase, which are the key enzymes in fatty acid synthesis, were down-regulated by dietary levan. However, dietary levan did not affect the gene expression of hepatic malic enzyme, phosphatidate phosphohydrolase and HMG CoA reductase. Also, the lipogenic enzyme gene expression in the white adipose tissue (WAT) was not affected by the diet treatments. However, hepatic PPARalpha mRNA expression was dose dependently up-regulated by dietary levan, whereas PPARgamma in the WAT was not changed. The results suggest that the in vivo hypolipidemic effect of dietary levan, including anti-obesity and lipid-lowering, may result from the inhibition of lipogenesis and stimulation of lipolysis, accompanied with regulation of hepatic lipogenic enzyme and PPARalpha gene expression.     

The effect of high-fat diet on plasma ghrelin and leptin levels in rats

Ghrelin and leptin regulate appetite and energy homeostasis in humans and rodents. The effects of different nutritional factors on ghrelin and leptin secretion are not well documented in rats. Therefore, the aim of our study was to investigate the effect of a high-fat diet on plasma ghrelin and leptin levels and on adiposity. Twenty male Wistar rats, body weight220–260 g, were used in the study. Rats were randomized either on a standard chow diet (n=10) or on a high-fat diet (a mixture of nuts) forad libitum 11-week period. Body weight was measured once per week. At the end of the nutritional period, rats were sacrificed. Blood was collected for determination of lipids and glucose, as well as plasma ghrelin and leptin levels by ELISA method. The weight of different organs was determined. Rats fed on a high-fat diet showed significant increase in total body weight compared to control group. The long-term intake of high-fat diet caused hyperleptinemia and hypoghrelinemia. There was a significant positive correlation between plasma leptin levels and epididymal fat mass, liver and heart. In contrast, ghrelin levels showed inverse correlation with epididymal fat mass and liver weight. In conclusion, long-term intake of high-fat diet induced changes in plasma ghrelin and leptin in male rats, as well as in epididymal fat mass, liver and heart weights.     

Beneficial effects of hydro-alcoholic extract of Caralluma fimbriata against high-fat diet-induced insulin resistance and oxidative stress in Wistar male rats

The main aim of this study was to investigate the beneficial effects of hydro-alcoholic extract of Caralluma fimbriata (CFE) on the effects of high-fat diet feeding on insulin resistance and oxidative stress in Wistar rats. High-fat diet (60 % of fat) and CFE (200 mg/kg body weight/day) were given concurrently to the rats for a period of 90 days. Feeding with high-fat diet resulted in the development of hyperglycemia, hyperinsulinemia, hyperleptinemia, and hypertriglyceridemia and impaired insulin sensitivity (P?<?0.05). Administration of CFE to high-fat diet-fed rats for 90 days resulted in a significant improvement in plasma glucose, insulin, leptin, and triglycerides. Regarding liver antioxidant status, high-fat fed rats showed higher levels of lipid peroxidation, protein oxidation and lower GSH levels and lower activities of enzymatic antioxidants, while CFE treatment prevented all these observed abnormalities. In conclusion, intake of CFE may be beneficial for the suppression of high-fat diet-induced insulin resistance and oxidative stress.     

Ghrelin, macronutrient intake and dietary preferences in long-evans rats

Ghrelin is a recently discovered peptide that is primarily produced by the stomach. As a ligand of the growth hormone (GH) secretagogue (GHS) receptor, it stimulates GH secretion but it also stimulates feeding and has adipogenic effects in rodents. Although its circulating levels are modulated by fasting and refeeding, its relationship with diet composition is not known. In the present paper, we measured plasma ghrelin as well as two important hormones (leptin and insulin) in Long-Evans rats placed in two different feeding situations, e.g., either with imposed diets or with food choice. In the first case, the rats were fed unbalanced diets (either high-carbohydrate (HC) or high-fat (HF) diets) for 14 weeks, whereas in the second situation, they had the choice between these 2 diets for 2 weeks and were selected for their fat or carbohydrate preference. The intake of the HF diet for 14 weeks was associated with lower levels of ghrelin (-30% vs control diet; P < 0.01). These levels increased when the percentage of carbohydrate in the diet increased (+26 to +42% vs control diet; P < 0.01 or less). Ghrelin was inversely correlated with plasma leptin (r = -0.55; P < 0.003) and blood glucose (r = -0.58; P < 0.001) as well as with body weight (r = -0.63; P < 0.0001) and body fat content estimated by the sampling of specific fat pads (r = -0.62; P < 0.0001). In the food choice experiment, fat-preferring rats had plasma ghrelin levels lower than the carbohydrate-preferring rats (-33%; P < 0.0002). Ghrelin secretion was therefore very sensitive to the diet composition. Its down-regulation by fat ingestion might serve as a counterregulatory mechanism to limit the development of dietary-induced adiposity. Ghrelin may signal when a high calorie diet is ingested.