Maté Tea Inhibits In Vitro Pancreatic Lipase Activity and Has Hypolipidemic Effect on High‐fat Diet‐induced Obese Mice

The inhibitory effects of maté tea (MT), a beverage produced with leaves from Ilex paraguariensis, in vitro lipase activity and on obesity in obese mice models were examined. For the in vitro experiment, porcine and human pancreatic lipase (PL) activities were determined by measuring the rate of release of oleic acid from hydrolysis of olive oil emulsified with taurocholate, phospholipids, gum arabic, or polyvinyl alcohol. For the in vivo experiments, animals were fed with a standard diet (SD, n = 10) or high‐fat diet (HFD, n = 30) for 16 weeks. After the first 8 weeks on the HFD, the animals were treated with 1 and 2 g/kg of body weight of MT. The time course of the body weight and obesity‐related biochemical parameters were evaluated. The results showed that MT inhibited both porcine and human PL (half‐maximal inhibitory concentration = 1.5 mg MT/ml) and induced a strong inhibition of the porcine lipase activity in the hydrolysis of substrate emulsified with taurocholate + phosphatidylcholine (PC) (83 ± 3.8%) or PC alone (62 ± 4.3%). MT suppressed the increases in body weight (P < 0.05) and decreased the serum triglycerides and low‐density lipoprotein (LDL)‐cholesterol concentrations at both doses (from 190.3 ± 5.7 to 135.0 ± 8.9 mg/dl, from 189.1 ± 7.3 to 129.3 ± 17.6 mg/dl; P < 0.05, respectively) after they had been increased by the HFD. The liver lipid content was also decreased by the diet containing MT (from 132.6 ± 3.9 to 95.6 ± 6.1 mg/g of tissue; P < 0.05). These results suggest that MT could be a potentially therapeutic alternative in the treatment of obesity caused by a HFD.     

Diet‐induced Obese Mice Are Leptin Insufficient After Weight Reduction

Behavioral therapies aimed at reducing excess body fat result in limited fat loss after dieting. To understand the causes for maintenance of adiposity, high‐fat (HF) diet–induced obese (DIO) mice were switched to a low‐fat chow diet, and the effects of chow on histological and molecular alterations of adipose tissue and metabolic parameters were examined. DIO mice reduced and stabilized their body weights after being switched to chow (HF‐chow), but retained a greater amount of adiposity than chow‐fed mice. Reduction in adipocyte volume, not number, caused a decrease in fat mass. HF‐chow mice showed normalized circulating insulin and leptin levels, improved glucose tolerance, and reduced inflammatory status in white adipose tissue (WAT). Circulating leptin levels corrected for fat mass were lower in HF‐chow mice. Leptin administration was used to test whether reduced leptin level of HF‐chow mice inhibited further fat loss. Leptin treatment led to an additional reduction in adiposity. Finally, HF‐HF mice had lower mRNA levels of β₃ adrenergic receptor (β₃‐AR) in epididymal WAT (EWAT) compared to chow‐fed mice, and diet change led to an increase in the WAT β₃‐AR mRNA levels that were similar to the levels of chow‐fed mice, suggesting an elevation in sympathetic activation of WAT during diet switch relative to HF‐HF mice leading to the reduced leptin level and proinflammatory cytokine content. In summary, HF‐chow mice were resistant to further fat loss due to leptin insufficiency. Diet alteration from HF to low fat improved metabolic state of DIO mice, although their adiposity was defended at a higher level.     

Effects of Pravastatin on Obesity,Diabetes, and Adiponectin in Diet‐induced Obese Mice

Objective: The aim of this study was to investigate the in vivo effects of pravastatin on the development of obesity and diabetes in diet‐induced obese (DIO) mice. Methods and Procedures: We examined food intake, body‐weight changes, visceral white adipose tissue (WAT) adiponectin and resistin levels, and energy metabolism. Results: Treatment with 100 mg/kg/day pravastatin for 28 days decreased diet‐induced weight gain and visceral adiposity. In addition, the weight of the WAT, the triglyceride (TG) contents of the liver and muscles, and the levels of serum insulin improved in the pravastatin‐treated DIO mice. Furthermore, pravastatin treatment changed the WAT adiponectin and resistin mRNA expression and serum levels compared with the controls. Finally, pravastatin treatment increased oxygen consumption and decreased the respiratory quotient (RQ). Discussion: Pravastatin treatment prevents the development of obesity and diabetes in DIO mice. The prevention of obesity may be mediated by increased oxygen consumption and a decrease in the RQ. These results provide novel insights into the use of pravastatin as a therapeutic tool for metabolic syndromes.     

Sex Differences in High‐fat Diet‐induced Obesity,Metabolic Alterations and Learning,and Synaptic Plasticity Deficits in Mice

Obesity is a potential risk factor for cognitive deficits in the elder humans. Using a high‐fat diet (HFD)–induced obese mouse model, we investigated the impacts of HFD on obesity, metabolic and stress hormones, learning performance, and hippocampal synaptic plasticity. Both male and female C57BL/6J mice fed with HFD (3 weeks to 9–12 months) gained significantly more weights than the sex‐specific control groups. Compared with the obese female mice, the obese males had similar energy intake but developed more weight gains. The obese male mice developed hyperglycemia, hyperinsulinemia, hypercholesterolemia, and hyperleptinemia, but not hypertriglyceridemia. The obese females had less hyperinsulinemia and hypercholesterolemia than the obese males, and no hyperglycemia and hypertriglyceridemia. In the contextual fear conditioning and step‐down passive avoidance tasks, the obese male, but not female, mice showed poorer learning performance than their normal counterparts. These learning deficits were not due to sensorimotor impairment as verified by the open‐field and hot‐plate tests. Although, basal synaptic transmission characteristics (input–output transfer and paired‐pulse facilitation (PPF) ratio) were not significantly different between normal and HFD groups, the magnitudes of synaptic plasticity (long‐term potentiation (LTP) and long‐term depression (LTD)) were lower at the Schaffer collateral‐CA1 synapses of the hippocampal slices isolated from the obese male, but not female, mice, as compared with their sex‐specific controls. Our results suggest that male mice are more vulnerable than the females to the impacts of HFD on weight gains, metabolic alterations and deficits of learning, and hippocampal synaptic plasticity.     

Inhibition of PTP1B by Trodusquemine (MSI‐1436) Causes Fat‐specific Weight Loss in Diet‐induced Obese Mice

Trodusquemine (MSI‐1436) causes rapid and reversible weight loss in genetic models of obesity. To better predict the potential effects of trodusquemine in the clinic, we investigated the effects of trodusquemine treatment in a murine model of diet‐induced obesity (DIO). Trodusquemine suppressed appetite, reduced body weight (BW) in a fat‐specific manner, and improved plasma insulin and leptin levels in mice. Screening assays revealed that trodusquemine selectively inhibited protein‐tyrosine phosphatase 1B (PTP1B), a key enzyme regulating insulin and leptin signaling. Trodusquemine significantly enhanced insulin‐stimulated tyrosine phosphorylation of insulin receptor (IR) β and STAT3, direct targets of PTP1B, in HepG2 cells in vitro and/or hypothalamic tissue in vivo. These data establish trodusquemine as an effective central and peripheral PTP1B inhibitor with the potential to elicit noncachectic fat‐specific weight loss and improve insulin and leptin levels.     

High‐fat Diet‐induced Ultradian Leptin and Insulin Hypersecretion are Absent in Obesity‐resistant Rats*

Objective: Sprague‐Dawley rats fed a high‐fat diet (HFD) are either obesity prone (OP) or obesity resistant (OR). We tested the hypothesis that differences in the ultradian rhythmic patterns of insulin and ghrelin in OP vs. OR rats promote obesity in OP rats. Research Methods and Procedures: Rats were fed regular chow or an HFD, and ultradian fluctuations in leptin, insulin, and ghrelin were analyzed in blood samples collected at 5‐minute intervals from intrajugular cannulae of freely moving rats. Results: Regular chow feeding resulted in a slow weight gain accompanied by small increases in insulin and leptin and a decrease in ghrelin discharge, with only the pulse amplitude significantly altered. Similar changes were observed in OR rats, despite HFD consumption. In contrast, OP rats exhibited a high rate of weight gain and marked hyperinsulinemia, hyperleptinemia, and hypoghrelinemia; amplitude was altered, but frequency was stable. In a short‐term experiment, HFD elicited similar secretory patterns of smaller magnitude even in the absence of weight gain. Discussion: We showed that three hormonal signals of disparate origin involved in energy homeostasis were secreted in discrete episodes, and only the pulse amplitude component was vulnerable to age and HFD consumption. Increases in insulin and leptin and decreases in ghrelin pulse amplitude caused by HFD were exaggerated in OP rats relative to OR rats and preceded the weight increase. These findings show that a distinct genetic predisposition in the endocrine organs of OR rats confers protection against high‐fat intake‐induced ultradian hypersecretion of obesity‐promoting hormonal signals.     

Characterization of β‐Cell Mass and Insulin Resistance in Diet‐induced Obese and Diet‐resistant Rats

The selectively bred diet‐induced obese (DIO) and diet‐resistant (DR) rats represent a polygenetic animal model mimicking most clinical variables characterizing the human metabolic syndrome. When fed a high‐energy (HE) diet DIO rats develop visceral obesity, dyslipidemia, hyperinsulinemia, and insulin resistance but never frank diabetes. To improve our understanding of the underlying cause for the deteriorating glucose and insulin parameters, we have investigated possible adaptive responses in DIO and DR rats at the level of the insulin‐producing β‐cells. At the time of weaning, DR rats were found to have a higher body weight and β‐cell mass compared to DIO rats, and elevated insulin and glucose responses to an oral glucose load. However, at 2.5 months of age, and for the remaining study period, the effect of genotype became evident: the chow‐fed DIO rats steadily increased their body weight and β‐cell mass, as well as insulin and glucose levels compared to the DR rats. HE feeding affected both DIO and DR rats leading to an increased body weight and an increased β‐cell mass. Interestingly, although the β‐cell mass in DR rats and chow‐fed DIO rats appeared to constantly increase with age, the β‐cell mass in the HE‐fed DIO rats did not continue to do so. This might constitute part of an explanation for their reduced glucose tolerance. Collectively, the data support the use of HE‐fed DIO rats as a model of human obesity and insulin resistance, and accentuate its relevance for studies examining the benefit of pharmaceutical compounds targeting this disease complex.     

Roux‐en‐Y Gastric Bypass Enhances Energy Expenditure and Extends Lifespan in Diet‐induced Obese Rats

Gastrointestinal weight‐loss surgery (GIWLS) is currently the most effective treatment for severe obesity, with Roux en‐Y gastric bypass (RYGB) among the best of the available surgical options. Despite its widespread clinical use, the mechanisms by which RYGB induces its profound weight loss remain largely unknown. This procedure effects weight loss by altering the physiology of weight regulation and eating behavior rather than by simple mechanical restriction and/or malabsorption as previously thought. To study how RYGB affects the physiology of energy balance, we developed a rat model of this procedure. In this report, we demonstrate that RYGB in diet‐induced obese (DIO) rats induces a 25% weight loss, prolongs mean survival by 45%, and normalizes glucose homeostasis and lipid metabolism. RYGB induced a 19% increase in total and a 31% increase in resting energy expenditure (REE). These effects, along with a 17% decrease in food intake and a 4% decrease in nutrient absorption account for the normalization of body weight after this procedure. These effects indicate that surgery acts by altering the physiology of weight regulation and help to explain the effectiveness of RYGB in comparison to restrictive dieting and other forms of dietary and pharmacological therapies for obesity. The clinical effectiveness of RYGB and its physiological effects on body weight regulation and energy expenditure (EE) suggest that this operation provides a unique opportunity to explore the mechanisms of energy homeostasis and to identify novel therapies for obesity and related metabolic diseases.     

Diet‐Dependent Genetic and Genomic Imprinting Effects on Obesity in Mice

Although the current obesity epidemic is of environmental origin, there is substantial genetic variation in individual response to an obesogenic environment. In this study, we perform a genome‐wide scan for quantitative trait loci (QTLs) affecting obesity per se, or an obese response to a high‐fat diet in mice from the LG/J by SM/J Advanced Intercross (AI) Line (Wustl:LG, SM‐G16). A total of 1,002 animals from 78 F₁₆ full sibships were weaned at 3 weeks of age and half of each litter placed on high‐ and low‐fat diets. Animals remained on the diet until 20 weeks of age when they were necropsied and the weights of the reproductive, kidney, mesenteric, and inguinal fat depots were recorded. Effects on these phenotypes, along with total fat depot weight and carcass weight at necropsy, were mapped across the genome using 1,402 autosomal single‐nucleotide polymorphism (SNP) markers. Haplotypes were reconstructed and additive, dominance, and imprinting genotype scores were derived every 1 cM along the F₁₆ map. Analysis was performed using a mixed model with additive, dominance, and imprinting genotype scores, their interactions with sex, diet, and with sex‐by‐diet as fixed effects and with family and its interaction with sex, diet, and sex‐by‐diet as random effects. We discovered 95 trait‐specific QTLs mapping to 40 locations. Most QTLs had additive effects with dominance and imprinting effects occurring at two‐thirds of the loci. Nearly every locus interacted with sex and/or diet in important ways demonstrating that gene effects are primarily context dependent, changing depending on sex and/or diet.     

Interaction of Leptin and Amylin in the Long‐term Maintenance of Weight Loss in Diet‐induced Obese Rats

We have previously shown that combined amylin + leptin agonism elicits synergistic weight loss in diet‐induced obese (DIO) rats. Here, we assessed the comparative efficacy of amylin, leptin, or amylin + leptin in the maintenance of amylin + leptin–mediated weight loss. DIO rats pretreated with the combination of rat amylin (50 µg/kg/day) and murine leptin (125 µg/kg/day) for 4 weeks were subsequently infused with either vehicle, amylin, leptin, or amylin + leptin for an additional 4 weeks. Food intake, body weight, body composition, plasma parameters, and the expression of key metabolic genes in liver and white adipose tissue (WAT) were assessed. Amylin + leptin treatment (weeks 0–4) reduced body weight to 87.5% of baseline. Rats subsequently maintained on vehicle or leptin regained all weight (to 104.2 and 101.2% of baseline, respectively), those maintained on amylin had partial weight regain (97.0%). By contrast, weight loss was largely maintained with continued amylin + leptin treatment (91.4%), associated with a 10% decrease in adiposity. Cumulative food intake (weeks 5–8) was reduced by amylin and amylin + leptin, but not by leptin alone. Amylin + leptin, but not amylin or leptin alone, reduced plasma triglycerides (by 55%), total cholesterol (by 19%), and insulin (by 57%) compared to vehicle. Amylin + leptin also reduced hepatic stearoyl‐CoA desaturase‐1 (Scd1) mRNA, and increased WAT mRNA levels of adiponectin, fatty acid synthase (Fasn), and lipoprotein lipase (Lpl). We conclude that, in DIO rats, maintenance of amylin + leptin–mediated weight loss requires continued treatment with both agonists, and is accompanied by sustained improvements in body composition, and indices of lipid metabolism and insulin sensitivity.     

Effects of Exendin‐4 Alone and With Peptide YY3–36 on Food Intake and Body Weight in Diet‐Induced Obese Rats

Significant weight loss following Roux‐en‐Y gastric bypass surgery (RYGB) in obese humans correlates with enhanced secretion of anorexigenic gut hormones glucagon‐like peptide‐1 (GLP‐1) and peptide YY_3–36 (PYY_3–36). Our aim here was to identify a dosing strategy for intraperitoneal (IP) infusion of GLP‐1 homologue exendin‐4 alone and with PYY_3–36 that produces a sustained reduction in daily food intake and body weight in diet‐induced obese (DIO) rats. We tested 12 exendin‐4 strategies over 10 weeks. Exendin‐4 infused during the first and last 3 h of the dark period at 15–20 pmol/h (0.15 nmol/kg/day) produced a sustained 24 ± 1% reduction in daily food intake for 17 days, and decreased body weight by 7%. In a separate group of DIO rats, none of seven dosing strategies combining exendin‐4 and PYY_3–36 produced a similar reduction in daily food intake for >10 days. The subsequent decline in efficacies of exendin‐4 alone and with PYY_3–36 on food intake and body weight in each experiment suggested possible receptor downregulation and tolerance to treatments. However, when treatments were discontinued for 1 day following losses in efficacies, daily food intake significantly increased. Together, these results demonstrate that (i) intermittent IP infusion of a low dose of exendin‐4 can produce a relatively prolonged reduction in daily food intake and body weight in DIO rats, (ii) co‐infusion of exendin‐4 and PYY_3–36 does not further prolong this response, and (iii) activation of an orexigenic mechanism gradually occurs to counteract the inhibitory effects of exendin‐4 alone and with PYY_3–36 on food intake and body weight.     

Effects of BCG (Bacillus Calmette–Guérin) Vaccines on Immune Responses in Mice

The effects of killed and living BCG on antibody production against hamster erythrocytes (HRBC) and the 2, 4, 6-trinitrophenyl (TNP) group were studied in SL mice. Killed and living BCG, each in doses of 0.008 mg, 0.08 mg, 0.8 mg and 8 mg per mouse, were intravenously inoculated 7 days prior to primary immunization with HRBC. Secondary immunization was carried out 28 days later with TNP-HRBC. Anti-HRBC and anti-TNP antibodies were estimated by a hemagglutination test. The results showed that pretreatment with killed or living BCG enhanced the antibody production against both HRBC and TNP. Comparing the effects of these two BCG preparations, it was noted that killed BCG augmented the anti-HRBC antibody production more effectively than living BCG. In regard to the anti-TNP antibody production, living BCG exhibited a greater augmenting effect than killed BCG. This difference in the modes of action of killed and living BCG was remarkable when two groups given 8 mg of killed and living BCG were compared. In addition, it was shown that living BCG at a dose as high as 8 mg was able to augment the anti-TNP antibody production, even in the absence of preceding immunization with HRBC.     

β‐Aminoisobutyric Acid Prevents Diet‐induced Obesity in Mice With Partial Leptin Deficiency

β‐Aminoisobutyric acid (BAIBA), a thymine catabolite, increases fatty acid oxidation (FAO) in liver and reduces the gain of body fat mass in Swiss (lean) mice fed a standard chow. We determined whether BAIBA could prevent obesity and related metabolic disorders in different murine models. To this end, BAIBA (100 or 500 mg/kg/day) was administered for 4 months in mice totally deficient in leptin (ob/ob). BAIBA (100 mg/kg/day) was also given for 4 months in wild‐type (+/+) mice and mice partially deficient in leptin (ob/+) fed a high‐calorie (HC) diet. BAIBA did not limit obesity and hepatic steatosis in ob/ob mice, but reduced liver cytolysis and inflammation. In ob/+ mice fed the HC diet, BAIBA fully prevented, or limited, the gain of body fat, steatosis and necroinflammation, glucose intolerance, and hypertriglyceridemia. Plasma β‐hydroxybutyrate was increased, whereas expression of carnitine palmitoyltransferase‐1 was augmented in liver and white adipose tissue. Acetyl‐CoA carboxylase was more phosphorylated, and de novo lipogenesis was less induced in liver. These favorable effects of BAIBA in ob/+ mice were associated with a restoration of plasma leptin levels. The reduction of body adiposity afforded by BAIBA was less marked in +/+ mice. Finally, BAIBA significantly stimulated the secretion of leptin in isolated ob/+ adipose cells, but not in +/+ cells. Thus, BAIBA could limit triglyceride accretion in tissues through a leptin‐dependent stimulation of FAO. As partial leptin deficiency is not uncommon in the general population, supplementation with BAIBA may help to prevent diet‐induced obesity and related metabolic disorders in low leptin secretors.