The development of tolerance to drugs that suppress food intake

The anorexic effect of DL-fenfluramine is dependent on animals' habituation to different food types

Background

As rates of obesity and diabetes have increased dramatically over the past few decades, the use of anti-obesity drugs has now become a routine therapeutic measure. However, the pharmacological effects of chronic use of these drugs in humans frequently lead to reduced efficacy in reducing appetite and body weight through as-yet-unidentified mechanisms. An example of this can be found in animal studies where the appetite suppressant DL-fenfluramine (FEN) is chronically administered and its tolerance develops in animals and humans. The appetite effects of FEN are typically measured in several animal studies by the feeding changes in a balanced standard diet. To determine whether FEN differentially altered appetite suppression in animals with long-term expression with different macronutrient diet compositions, its anorexic effects were measured specifically in male rats that had previously been chronically maintained on normal chow (NC) or a high-fat and high-carbohydrate western diet (WD).

Methods

Three experiments were conducted by feeding the animals either NC or WD for 1 month to habituate them with their diet. Animals maintained on either NC or WD were subsequently offered both diet options ad libitum for a 2- or 7-day adaptation period while receiving daily systemic FEN treatment.

Results

The results suggested that long-term habituated food affected the food preference of animals and their appetite even after chronic systemic FEN administration. Therefore, the effectiveness and success or failure of repeated use of chronic anti-obesity drugs may depend on habituated food type.

Conclusion

The appetite suppressant effect was found to be determined by the palatability of a specific macronutrient and the habituated food rather than by a change in the concentration of the administered FEN. This results in a critical analysis of the rationale for taking medication considering the patient's past dietary habits to achieve successful weight loss.

Associations between MDMA/ecstasy use and physical health in a U.S. population-based survey sample

INTRODUCTION

3,4-Methylenedioxymethamphetamine (MDMA/"ecstasy") is an empathogen that can give rise to increased pleasure and empathy and may effectively treat post-traumatic stress disorder. Although prior research has demonstrated associations between ecstasy use and favorable mental health outcomes, the associations between ecstasy and physical health have largely been unexplored. Thus, the goal of this study was to examine the associations between ecstasy use and physical health in a population-based survey sample.

METHOD

This study utilized data from the National Survey on Drug Use and Health (2005-2018), a yearly survey that collects information on substance use and health outcomes in a nationally representative sample of U.S. adults. We used multinomial, ordered, and logistic regression models to test the associations between lifetime ecstasy use and various markers of physical health (self-reported body mass index, overall health, past year heart condition and/or cancer, past year heart disease, past year hypertension, and past year diabetes), controlling for a range of potential confounders.

RESULTS

Lifetime ecstasy use was associated with significantly lower risk of self-reported overweightness and obesity (adjusted relative risk ratio range: 0.55-0.88) and lower odds of self-reported past year heart condition and/or cancer (adjusted odds ratio (aOR): 0.67), hypertension (aOR: 0.85), and diabetes (aOR: 0.58). Ecstasy use was also associated with significantly higher odds of better self-reported overall health (aOR: 1.18).

CONCLUSION

Ecstasy shares protective associations with various physical health markers. Future longitudinal studies and clinical trials are needed to more rigorously test these associations.

Combined First Month Body Weight Loss and Development of Tolerance as Predictors of 6-Month Efficacy of Mazindol in Mild and Moderate Obese Subjects

The weight loss response to anti-obesity drugs is highly variable and poorly understood, which does not allow us to know, in advance, in which subjects the drug will be effective and in which it will not. The objective of this study was to explore the body weight reduction in kilograms in the first month (1mo-BWRkg) and the development of tolerance as predictors of 6-month efficacy for treatment with 1 mg mazindol twice a day. One hundred ninety-six obese subjects were individually or jointly analyzed. Approximately 60% of subjects developed tolerance to mazindol and achieved increasing proportional levels of 6-month efficacy according to 1mo-BWRkg intervals (<1 kg, 1 to <2 kg, 2 to <4 kg and ≥4 kg). Both moT and 1mo-BWRkg were significantly correlated with the mean percentage body weight reduction (BWR%) after 6-months of treatment. The qualitative analysis of both predictors on the progressive efficacy of mazindol was used to classify patients according to expected efficacy (inefficient, slightly effective, partially effective, or fully effective), based on the mean percentage efficacy and the number of subjects reaching a BWR% of <5%, 5 to <10%, 10 to <15% or ≥15%. In conclusion, combined 1mo-BWRkg and moT were early predictors for the progressive efficacy of 6-month mazindol anti-obesity therapy. This finding represents progress in predictive, preventive, and personalized medicine which could serve for estimating the expectations of individual efficacy with the use of the drug. and highlights the basic principle of personalized medicine, “one size does not fit all”.

Weight Loss at First Month and Development of Tolerance as Possible Predictors of 30 mg Phentermine Efficacy at 6 Months

The efficacy of anti-obesity drugs usually does not consider the high degree of interindividual variability in responses to the drug which could affect the decision to withdraw the drug early due to ineffectiveness or to continue therapy according to specific expectations of success. The aim of this study was to analyze body weight loss in kilograms during the first month (1 mo-BWL_kg) of treatment with 30 mg phentermine and development of tolerance to phentermine, on its 6-month efficacy. One hundred sixty-six subjects with obesity were individually or jointly analyzed in the study. Subjects with 1 mo-BWL_kg of <1 kg, 1–3 kg, 3–5 kg, and ≥5 kg reached 6-month mean percentage body weight reductions (BWR%) of approximately 3%, 5%, 10%, and 15%, respectively. Development of late tolerance (4–6 months) to phentermine had a lower impact than early tolerance (2–3 months). Subjects with 1 mo-BWL_kg < 3 kg who developed early tolerance did not achieve relevant BWR% (≥5%) at month 6, while the rest of the subgroups achieved increasing and progressive BWR%, according to their 1 mo-BWL_kg range and time of onset of tolerance. The 1 mo-BWL_kg and development of tolerance to phentermine could be useful to predict the expected 6-month efficacy trends in obese patients treated with 30 mg phentermine.

Modeling energy intake and body weight effects of a long-acting amylin analogue

The inhibitory effect of anti-obesity drugs on energy intake (EI) is counter-acted by feedback regulation of the appetite control circuit leading to drug tolerance. This complicates the design and interpretation of EI studies in rodents that are used for anti-obesity drug development. Here, we investigated a synthetic long-acting analogue of the appetite-suppressing peptide hormone amylin (LAMY) in lean and diet-induced obese (DIO) rats. EI and body weight (BW) were measured daily and LAMY concentrations in plasma were assessed using defined time points following subcutaneous administration of the LAMY at different dosing regimens. Overall, 6 pharmacodynamic (PD) studies including a total of 173 rats were considered in this evaluation. Treatment caused a dose-dependent reduction in EI and BW, although multiple dosing indicated the development of tolerance over time. This behavior could be adequately described by a population model including homeostatic feedback of EI and a turnover model describing the relationship between EI and BW. The model was evaluated by testing its ability to predict BW loss in a toxicology study and was utilized to improve the understanding of dosing regimens for obesity therapy. As such, the model proved to be a valuable tool for the design and interpretation of rodent studies used in anti-obesity drug development.

Further delineation between typical and atypical dopamine uptake inhibitors: effects on food-maintained behavior and food consumption

The present studies compared the acute effects of benztropine analogs (4-Cl-BZT, JHW 007, AHN 1-055), which are atypical dopamine uptake inhibitors, with those of the standard dopamine uptake inhibitors GBR 12909 and cocaine, on the reinforcing efficacy of food and food intake in male Sprague-Dawley rats. Repeated drug effects of JHW 007 on food intake were also determined. The number of ratios completed under a progressive-ratio schedule of food delivery was used as an index of reinforcing efficacy. Food intake was determined by measuring powdered laboratory-chow consumption during daily 40 min food-availability time periods. Under the progressive-ratio schedule, cocaine and GBR 12909 dose-dependently increased the number of ratios completed. JHW 007 decreased ratios completed, whereas neither 4-Cl-BZT nor AHN 1-055 increased ratios completed with a magnitude that approximated any of the increases produced by cocaine or GBR 12909. Acute administration of each drug dose-dependently decreased food intake; however, the benztropine analogs were more potent than cocaine and GBR 12909. A reduction in food intake emerged after repeated administration of a low dose of JHW 007. Future studies that compare JHW 007 with standard anorectic drugs (e.g. phentermine) and continue investigation of the repeated drug effects under similar experimental procedures are clearly warranted.

Pituitary Adenylate-Cyclase Activating Polypeptide Regulates Hunger- and Palatability-Induced Binge Eating

While pituitary adenylate cyclase activating polypeptide (PACAP) signaling in the hypothalamic ventromedial nuclei (VMN) has been shown to regulate feeding, a challenge in unmasking a role for this peptide in obesity is that excess feeding can involve numerous mechanisms including homeostatic (hunger) and hedonic-related (palatability) drives. In these studies, we first isolated distinct feeding drives by developing a novel model of binge behavior in which homeostatic-driven feeding was temporally separated from feeding driven by food palatability. We found that stimulation of the VMN, achieved by local microinjections of AMPA, decreased standard chow consumption in food-restricted rats (e.g., homeostatic feeding); surprisingly, this manipulation failed to alter palatable food consumption in satiated rats (e.g., hedonic feeding). In contrast, inhibition of the nucleus accumbens (NAc), through local microinjections of GABA receptor agonists baclofen and muscimol, decreased hedonic feeding without altering homeostatic feeding. PACAP microinjections produced the site-specific changes in synaptic transmission needed to decrease feeding via VMN or NAc circuitry. PACAP into the NAc mimicked the actions of GABA agonists by reducing hedonic feeding without altering homeostatic feeding. In contrast, PACAP into the VMN mimicked the actions of AMPA by decreasing homeostatic feeding without affecting hedonic feeding. Slice electrophysiology recordings verified PACAP excitation of VMN neurons and inhibition of NAc neurons. These data suggest that the VMN and NAc regulate distinct circuits giving rise to unique feeding drives, but that both can be regulated by the neuropeptide PACAP to potentially curb excessive eating stemming from either drive.

Mitochondria-targeted dodecyltriphenylphosphonium (C12TPP) combats high-fat-diet-induced obesity in mice

Background:

A membrane-penetrating cation, dodecyltriphenylphosphonium (C₁₂TPP), facilitates the recycling of fatty acids in the artificial lipid membrane and mitochondria. C₁₂TPP can dissipate mitochondrial membrane potential and may affect total energy expenditure and body weight in animals and humans.

Methods:

We investigated the metabolic effects of C₁₂TPP in isolated brown-fat mitochondria, brown adipocyte cultures and mice in vivo. Experimental approaches included the measurement of oxygen consumption, carbon dioxide production, western blotting, magnetic resonance imaging and bomb calorimetry.

Results:

In mice, C₁₂TPP (50 μmol per (day•kg body weight)) in the drinking water significantly reduced body weight (12%, P<0.001) and body fat mass (24%, P<0.001) during the first 7 days of treatment. C₁₂TPP did not affect water palatability and intake or the energy and lipid content in feces. The addition of C₁₂TPP to isolated brown-fat mitochondria resulted in increased oxygen consumption. Three hours of pretreatment with C₁₂TPP also increased oligomycin-insensitive oxygen consumption in brown adipocyte cultures (P<0.01). The effects of C₁₂TPP on mitochondria, cells and mice were independent of uncoupling protein 1 (UCP1). However, C₁₂TPP treatment increased the mitochondrial protein levels in the brown adipose tissue of both wild-type and UCP1-knockout mice. Pair-feeding revealed that one-third of the body weight loss in C₁₂TPP-treated mice was due to reduced food intake. C₁₂TPP treatment elevated the resting metabolic rate (RMR) by up to 18% (P<0.05) compared with pair-fed animals. C₁₂TPP reduced the respiratory exchange ratio, indicating enhanced fatty acid oxidation in mice.

Conclusions:

C₁₂TPP combats diet-induced obesity by reducing food intake, increasing the RMR and enhancing fatty acid oxidation.

Exploratory Literature Meta-Analysis to Characterize the Relationship Between Early and Longer Term Body Weight Loss for Antiobesity Compounds

The presented analysis was performed to characterize the relationship between treatment-related early (week 4) and longer term (3-6 months) weight loss to understand the potential utility of 4-week proof-of-mechanism studies in the early decision-making process during clinical development of new antiobesity compounds. A regression-based meta-analysis was performed leveraging publically available clinical outcomes data to (1) characterize the within-trial relationship between treatment-related early and longer term body weight loss and (2) identify and quantify key covariate effects on this relationship. Data from 89 randomized clinical trials with 209 treatment arms, representing observations from 54 461 patients and 9 treatments, were available for the meta-analysis. Results indicated that (1) there is a correlation between treatment-related early and longer term body weight loss (r > 0.9), (2) baseline body weight influences the relationship between early and longer term weight loss, whereas comorbidity such as type 2 diabetes mellitus, class of drugs including GLP-1 analogues and the antiobesity compounds lorcaserin or phentermine/topiramate showed no significant effects on this relationship. The model was externally evaluated with data from the investigational compound beloranib, for which longer term weight loss could be successfully predicted based on early response data. Based on these results, the identified strong relationship between treatment-related early and longer term weight loss appears to be independent of mechanism of action. Thus, findings from this analysis can optimize design of clinical studies and facilitate development of new anti-obesity compounds.

Requirements for multi-level systems pharmacology models to reach end-usage: the case of type 2 diabetes

We are currently in the middle of a major shift in biomedical research: unprecedented and rapidly growing amounts of data may be obtained today, from in vitro, in vivo and clinical studies, at molecular, physiological and clinical levels. To make use of these large-scale, multi-level datasets, corresponding multi-level mathematical models are needed, i.e. models that simultaneously capture multiple layers of the biological, physiological and disease-level organization (also referred to as quantitative systems pharmacology-QSP-models). However, today's multi-level models are not yet embedded in end-usage applications, neither in drug research and development nor in the clinic. Given the expectations and claims made historically, this seemingly slow adoption may seem surprising. Therefore, we herein consider a specific example-type 2 diabetes-and critically review the current status and identify key remaining steps for these models to become mainstream in the future. This overview reveals how, today, we may use models to ask scientific questions concerning, e.g., the cellular origin of insulin resistance, and how this translates to the whole-body level and short-term meal responses. However, before these multi-level models can become truly useful, they need to be linked with the capabilities of other important existing models, in order to make them 'personalized' (e.g. specific to certain patient phenotypes) and capable of describing long-term disease progression. To be useful in drug development, it is also critical that the developed models and their underlying data and assumptions are easily accessible. For clinical end-usage, in addition, model links to decision-support systems combined with the engagement of other disciplines are needed to create user-friendly and cost-efficient software packages.

Neural Regulatory Pathways of Feeding and Fat in Caenorhabditis elegans

The compact nervous system of Caenorhabditis elegans and its genetic tractability are features that make this organism highly suitable for investigating energy balance in an animal system. Here, we focus on molecular components and organizational principles emerging from the investigation of pathways that largely originate in the nervous system and regulate feeding behavior but also peripheral fat regulation through neuroendocrine signaling. We provide an overview of studies aimed at understanding how C. elegans integrate internal and external cues in feeding behavior. We highlight some of the similarities and differences in energy balance between C. elegans and mammals. We also provide our perspective on unresolved issues, both conceptual and technical, that we believe have hampered critical evaluation of findings relevant to fat regulation in C. elegans.

5-hydroxytryptamine medications for the treatment of obesity

The central 5-hydroxytryptamine (5-HT; serotonin) system represents a fundamental component of the brain's control of energy homeostasis. Medications targeting the 5-HT pathway have been at the forefront of obesity treatment for the past 15 years. Pharmacological agents targeting 5-HT receptors (5-HTR), in combination with genetic models of 5-HTR manipulation, have uncovered a role for specific 5-HTRs in energy balance and reveal the 5-HT2 C R as the principal 5-HTR mediating this homeostatic process. Capitalising on this neurophysiological machinery, 5-HT2 C R agonists improve obesity and glycaemic control in patient populations. The underlying therapeutic mechanism has been probed using model systems and appears to be achieved primarily through 5-HT2 C R modulation of the brain melanocortin circuit via activation of pro-opiomelanocortin neurones signalling at melanocortin4 receptors. Thus, 5-HT2 C R agonists offer a means to improve obesity and type 2 diabetes, which are conditions that now represent global challenges to human health.

D1 and D2 antagonists reverse the effects of appetite suppressants on weight loss, food intake, locomotion, and rebalance spiking inhibition in the rat NAc shell

Obesity is a worldwide health problem that has reached epidemic proportions. To ameliorate this problem, one approach is the use of appetite suppressants. These compounds are frequently amphetamine congeners such as diethylpropion (DEP), phentermine (PHEN), and bupropion (BUP), whose effects are mediated through serotonin, norepinephrine, and dopaminergic pathways. The nucleus accumbens (NAc) shell receives dopaminergic inputs and is involved in feeding and motor activity. However, little is known about how appetite suppressants modulate its activity. Therefore, we characterized behavioral and neuronal NAc shell responses to short-term treatments of DEP, PHEN, and BUP. These compounds caused a transient decrease in weight and food intake while increasing locomotion, stereotypy, and insomnia. They evoked a large inhibitory imbalance in NAc shell spiking activity that correlated with the onset of locomotion and stereotypy. Analysis of the local field potentials (LFPs) showed that all three drugs modulated beta, theta, and delta oscillations. These oscillations do not reflect an aversive-malaise brain state, as ascertained from taste aversion experiments, but tracked both the initial decrease in weight and food intake and the subsequent tolerance to these drugs. Importantly, the appetite suppressant-induced weight loss and locomotion were markedly reduced by intragastric (and intra-NAc shell) infusions of dopamine antagonists SCH-23390 (D1 receptor) or raclopride (D2 receptor). Furthermore, both antagonists attenuated appetite suppressant-induced LFP oscillations and partially restored the imbalance in NAc shell activity. These data reveal that appetite suppressant-induced behavioral and neuronal activity recorded in the NAc shell depend, to various extents, on dopaminergic activation and thus point to an important role for D1/D2-like receptors (in the NAc shell) in the mechanism of action for these anorexic compounds.

Modeling energy intake by adding homeostatic feedback and drug intervention

Energy intake (EI) is a pivotal biomarker used in quantification approaches to metabolic disease processes such as obesity, diabetes, and growth disorders. Eating behavior is however under both short-term and long-term control. This control system manifests itself as tolerance and rebound phenomena in EI, when challenged by drug treatment or diet restriction. The paper describes a model with the capability to capture physiological counter-regulatory feedback actions triggered by energy imbalances. This feedback is general as it handles tolerance to both increases and decreases in EI, and works in both acute and chronic settings. A drug mechanism function inhibits (or stimulates) EI. The deviation of EI relative to a reference level (set-point) serves as input to a non-linear appetite control signal which in turn impacts EI in parallel to the drug intervention. Three examples demonstrate the potential usefulness of the model in both acute and chronic dosing situations. The model shifts the predicted concentration-response relationship rightwardly at lower concentrations, in contrast to models that do not handle functional adaptation. A fourth example further shows that the model may qualitatively explain differences in rate and extent of adaptation in observed EI and its concomitants in both rodents and humans.

Adolescent MDMA exposure diminishes the physiological and neurotoxic consequences of an MDMA binge in female rats

Intermittent MDMA pretreatment blocked the reductions in serotonin transporter (SERT) binding induced by an MDMA binge in a prior study in adolescent male rats. The objective of this investigation was to determine if the physiological, behavioral, and neurochemical responses to MDMA are sexually dimorphic. Female Sprague-Dawley rats received MDMA (10 mg/kg × 2) or Saline on every fifth day from postnatal day (PD) 35-60 and an MDMA binge (5 mg/kg × 4) on PD 67. The MDMA binge induced a pronounced temperature dysregulation in MDMA-naïve, but not MDMA-pretreated, groups. Similarly, MDMA-pretreated animals were resistant to the binge-induced SERT reductions, especially in the hippocampus. Motor activity at PD 68 was not reduced by the binge, unlike the responses found in males. These results show that female rats differ from males in their responses to an MDMA binge but are similar with respect to preconditioning from prior MDMA exposure.

Course and moderators of emotional eating in anorectic and bulimic patients: a follow-up study

Emotion dysregulation has been found to be associated with specific eating attitudes and behavior in Eating Disorder (ED) patients. The present study evaluated whether emotional eating profile of ED patients changes over time and the possible effects of a psychotherapeutic intervention on the emotional eating dimension. One hundred and two ED patients (28 with Anorexia Nervosa restricting type [AN-R], 35 with Anorexia Nervosa binge/purging subtype [AN-B/P] and 39 with Bulimia Nervosa [BN]) were evaluated at baseline, at the end of a Cognitive Behavioral Therapy, at 3 and 6 year follow-up. The Structured Clinical Interview for DSM IV Axis I Disorders, the Emotional Eating Scale (EES) and several self-reported questionnaires for eating specific and general psychopathology were applied. A control group of 86 healthy subjects was also studied, in order to compare psychopathological variables at baseline. A significant EES total score reduction was observed among AN-B/P and BN patients, whereas no significant change was found in the AN-R group. Mixed Models analyses showed that a significant effect on EES total score variation was found for cocaine or amphetamine abuse (b = .25; p < .01). Patients who assumed these substances reported no significant EES reduction across time, unlike other patients. The present results suggest that ED patients with a history of cocaine or amphetamine abuse represent a sub-population of patients with lasting dysfunctional mood modulatory mechanisms.

Citrange fruit extracts alleviate obesity-associated metabolic disorder in high-fat diet-induced obese C57BL/6 mouse

Obesity is becoming one of the global epidemics of the 21st century. In this study, the effects of citrange (Citrus sinensis × Poncirus trifoliata) fruit extracts in high-fat (HF) diet-induced obesity mice were studied. Female C57BL/6 mice were fed respectively a chow diet (control), an HF diet, HF diet supplemented with 1% w/w citrange peel extract (CPE) or 1% w/w citrange flesh and seed extract (CFSE) for 8 weeks. Our results showed that both CPE and CFSE regulated the glucose metabolic disorders of obese mice. In CPE and CFSE-treated groups, the body weight gain, blood glucose, serum total cholesterol (TC) and low density lipoprotein cholesterol (LDL-c) levels were significantly (p < 0.05) reduced relative to those in the HF group. To explore the mechanisms of action of CPE and CFSE on the metabolism of glucose and lipid, related genes’ expressions in liver were assayed. In liver tissue, the expression level of peroxisome proliferator-activated receptor γ (PPARγ) and its target genes were down-regulated by CPE and CFSE supplementation as revealed by qPCR tests. In addition, both CPE and CFSE decreased the expression level of liver X receptor (LXR) α and β, which are involved in lipid and glucose metabolism. Taken together, these results suggest that CPE and CFSE administration could ameliorate obesity and related metabolic disorders in HF diet-induced obesity mice probably through the inhibition of PPARγ and LXRs gene expressions.

Scientific evidence for traditional claim of anti-obesity activity of Tecomella undulata bark

ETHNOPHARMACOLOGICAL RELEVANCE

The bark of Tecomella undulata is traditionally claimed in the treatment of various disease ailments including obesity and cancer. Till now there are no studies about anti-obesity activity of Tecomella undulata bark.

AIM OF THE STUDY

The present study was aimed to establish a scientific evidence for anti-obesity efficiency of ethyl acetate extract of Tecomella undulata bark (EATUB). Further to standardize the active fractions of EATUB using different biomarkers.

MATERIALS AND METHODS

We investigated activity of EATUB fractions (F1-F7) using 3T3-L1 fibroblasts. Further, F1-mediated effects were characterized by determining mRNA and protein levels of SIRT1, one of the key targets for the treatment of obesity, using semi-quantitative RT-PCR (sqRT-PCR) and western blot analysis. The consequences of modulation of SIRT1 on mRNA and protein levels of various adipogenesis mediators like PPARγ, C/EBPα, E2F1, leptin, adiponectin and LPL were also studied. In vivo studies were performed using High Fat Diet (HFD) obese mice.

RESULTS

Our data showed that compared to controls, preadipocytes and adipocytes incubated with F1 exhibited a significant decrease in adipogenesis and lipogenesis. In addition, sqRT-PCR and western blot analysis showed significant increase in SIRT1 and adiponectin levels and decrease in PPARγ, C/EBPα, E2F1, leptin and LPL levels in preadipocytes and adipocytes. In vivo studies of F1 in HFD induced obese mice showed significant improvement in lipid profile and glucose levels. The bioactive fraction (F1) was determined to possess 4.95% of ferulic acid.

CONCLUSION

Thus, our findings signified the beneficial effects of Tecomella undulata bark in pharmacologic interventions related to obesity and metabolic disorders. Ferulic acid and rutin are being reported and quantified for the first time from the bark of Tecomella undulata.

Citrus ichangensis Peel Extract Exhibits Anti-Metabolic Disorder Effects by the Inhibition of PPARγ and LXR Signaling in High-Fat Diet-Induced C57BL/6 Mouse

Obesity is a common nutritional disorder associated with type 2 diabetes, cardiovascular diseases, dyslipidemia, and certain cancers. In this study, we investigated the effects of Citrus ichangensis peel extract (CIE) in high-fat (HF) diet-induced obesity mice. Female C57BL/6 mice were fed a chow diet or an HF diet alone or supplemented with 1% w/w CIE for 8 weeks. We found that CIE treatment could lower blood glucose level and improve glucose tolerance. In the HF+CIE group, body weight gain, serum total cholesterol (TC) and low-density lipoprotein cholesterol (LDL-c) levels, and liver triglyceride (TG) and TC concentrations were significantly (P < 0.05) decreased relative to those in the HF group. To elucidate the mechanism of CIE on the metabolism of glucose and lipid, related genes expression in liver were examined. In liver tissue, CIE significantly decreased the mRNA expression levels of peroxisome proliferator-activated receptor γ (PPARγ) and its target genes, such as fatty acid synthase (FAS) and acyl-CoA oxidase (ACO). Moreover, CIE also decreased the expression of liver X receptor (LXR) α and β which are involved in lipid and glucose metabolism. These results suggest that CIE administration could alleviate obesity and related metabolic disorders in HF diet-induced obesity mice through the inhibition of PPARγ and LXR signaling.

Sibutramine effects on central mechanisms regulating energy homeostasis

During the last 50 years the global pandemic of obesity and associated life-threatening co-morbidities strongly promoted the development of anti-obesity pharmacotherapy. Sibutramine is an anti-obesity drug that in conjunction with lifestyle modifications reduces food intake and body weight. This may result from several effects: inhibition of presynaptic reuptake of monoaminergic neurotransmitters in the central nervous system, thereby suppressing appetite, induction of an increase in anorexigenic and a decrease in orexigenic neuropeptide secretion, induction of an increase in energy expenditure, and induction of peripheral sympathomimetic effects. The effects of sibutramine on anabolic and catabolic signals that regulate energy homeostasis in the hypothalamus are not completely understood. So, the aim of this review is to summarize the central mechanisms of action of sibutramine, responsible for its weight and food intake reducing potential. Despite being a useful drug in obesity treatment, awareness about the loss of long-term effectiveness and detrimental side effects of sibutramine has recently emerged. As a consequence, new drugs that produce safer and more persistent weight loss are currently undergoing clinical trials.

Conjugated linoleic acids mediate insulin release through islet G protein-coupled receptor FFA1/GPR40

Among dietary components, conjugated linoleic acids (CLAs) have attracted considerable attention as weight loss supplements in the Western world because they reduce fat stores and increase muscle mass. However, a number of adverse effects are also ascribed to the intake of CLAs such as aggravation of insulin resistance and the risk of developing diabetes. However, the mechanisms accounting for the effects of CLAs on glucose homeostasis are incompletely understood. Herein we provide evidence that CLAs specifically activate the cell surface receptor FFA1, an emerging therapeutic target to treat type 2 diabetes. Using different recombinant cellular systems engineered to stably express FFA1 and a set of diverse functional assays including the novel, label-free non-invasive dynamic mass redistribution technology (Corning® Epic® biosensor), both CLA isomers cis-9, trans-11-CLA and trans-10, cis-12-CLA were found to activate FFA1 in vitro at concentrations sufficient to also account for FFA1 activation in vivo. Each CLA isomer markedly increased glucose-stimulated insulin secretion in insulin-producing INS-1E cells that endogenously express FFA1 and in primary pancreatic β-cells of wild type but not FFA1-/- knock-out mice. Our findings establish a clear mechanistic link between CLAs and insulin production and identify the cell surface receptor FFA1 as a molecular target for CLAs, explaining their acute stimulatory effects on insulin secretion in vivo. CLAs are also revealed as insulinotropic components in widely used nutraceuticals, a finding with significant implication for development of FFA1 modulators to treat type 2 diabetes.

The effects of dose and repeated administration on the longer-term hypophagia produced by amphetamine in rats

Rats are hypophagic approximately 1-3 and 13-27h after receiving amphetamine (2.0mg/kg). This study examined how these short- and longer-term phases of hypophagia were affected by repeated administration of different amphetamine doses. Throughout eight five-day tests, the rats could lever press for food pellets for 1-hour periods beginning every three hours. On test day 1, the rats were treated with saline, and on test day 3, they were treated with a dose of amphetamine. Across tests, for one group, treatment on day 3 alternated between 0.0 (saline) and 0.5mg/kg amphetamine; for a second, group treatment on day 3 alternated between 1.0 and 2.0mg/kg amphetamine; and for a third group, treatment on day 3 was always 1.0mg/kg amphetamine. The patterns of food intake following day 1 saline and day 3 treatment were compared. Short-term food intake was abolished by 0.5, 1.0, and 2.0mg/kg amphetamine, and no tolerance was observed to this effect. Longer-term hypophagia was produced by 1.0 and 2.0 but not by 0.5mg/kg. Tolerance to longer-term hypophagia was seen when 1.0mg/kg alone was used as the day 3 treatment, but not when 1.0 and 2.0mg/kg were alternated across tests as the day 3 treatment. Short- and longer-term hypophagia were dissociated by threshold doses for elicitation and by differential tolerance. Occasional receipt of a higher amphetamine dose may sometimes increase the longer-term hypophagia produced by a lower dose.

The novel triple monoamine reuptake inhibitor tesofensine induces sustained weight loss and improves glycemic control in the diet-induced obese rat: comparison to sibutramine and rimonabant

Tesofensine, a novel triple monoamine reuptake inhibitor, produces a significant weight loss in humans. The present study aimed at characterizing the weight-reducing effects of tesofensine in a rat model of diet-induced obesity. Sibutramine and rimonabant were used as reference comparators. Compared to baseline, long-term treatment with tesofensine (28 days, 1.0 or 2.5mg/kg, p.o.) resulted in a significant, dose-dependent and sustained weight loss of 5.7 and 9.9%, respectively. Sibutramine (7.5mg/kg, p.o.) treatment caused a sustained weight loss of 7.6%, whereas the employed dose of rimonabant (10mg/kg, p.o.) only produced a transient weight reduction. While all compounds exhibited a significant inhibitory effect on food intake which gradually wore off, the hypophagic effect of tesofensine was longer lasting than sibutramine and rimonabant. In contrast to tesofensine, the body weight of pair-fed rats returned to baseline at the end of the study, which may indicate that tesofensine stimulated energy expenditure. The differential efficacy on weight reduction was also reflected in lowered body fat depots, as tesofensine and sibutramine most efficiently reduced abdominal and subcutaneous fat mass which was paralleled by reduced plasma lipid levels. In an oral glucose tolerance test, only tesofensine significantly suppressed the plasma insulin response below the level that could be obtained by paired feeding, indicating that tesofensine further improved glycemic control. In conclusion, the robust weight loss with long-term tesofensine treatment is likely due to a combined synergistic effect of appetite suppression and increased energy expenditure.

Prieurianin Causes Weight Loss in Diet-Induced Obese Mice and Inhibits Adipogenesis in Cultured Preadipocytes

The global increase in the incidence of obesity has emerged as one of the most serious public health risks in recent years. Despite the enormity of the obesity pandemic, there are currently only two FDA-approved therapies for its treatment and these drugs exhibit modest efficacy and have limiting side effects. Prieurianin is a plant limonoid product that deters feeding in insect larvae. We investigated in this study the effects of prieurianin on weight loss and adipogenesis. Our results showed that prieurianin causes weight loss by reducing energy intake in obese mice on high-calorie diet. We also found that prieurianin is anti-adipogenic in cultured preadipocytes and adipocytes by inhibiting proliferation and differentiation of preadipocytes into adipocytes, and induces either dedifferentiation or delipidation of mature adipocytes. Whether prieurianin can potentially be used for obesity treatment in human warrants further investigation.

Pharmacological targeting of the serotonergic system for the treatment of obesity

The attenuation of food intake as induced by an increase in serotonergic (5-hydroxytryptamine, 5-HT) efficacy has been a target of antiobesity pharmacotherapies. However, the induction of tolerance and/or side-effects limited the clinical utility of the earliest serotonin-related medications. With the global prevalence of obesity rising, there has been renewed interest in the manipulation of the serotonergic system as a point of pharmacological intervention. The serotonin(2C) receptor (5-HT(2C)R), serotonin(1B) (rodent)/serotonin(1Dbeta) (human) receptor (5-HT(1B/1Dbeta)R) and serotonin(6) receptor (5-HT(6)R) represent the most promising serotonin receptor therapeutic targets. Canonical serotonin receptor compounds have given way to a myriad of novel receptor-selective ligands, many of which have observable anorectic effects. Here we review serotonergic compounds reducing ingestive behaviour and discuss their clinical potential for the treatment of obesity.

Serotonin regulates C. elegans fat and feeding through independent molecular mechanisms

We investigated serotonin signaling in C. elegans as a paradigm for neural regulation of energy balance and found that serotonergic regulation of fat is molecularly distinct from feeding regulation. Serotonergic feeding regulation is mediated by receptors whose functions are not required for fat regulation. Serotonergic fat regulation is dependent on a neurally expressed channel and a G protein-coupled receptor that initiate signaling cascades that ultimately promote lipid breakdown at peripheral sites of fat storage. In turn, intermediates of lipid metabolism generated in the periphery modulate feeding behavior. These findings suggest that, as in mammals, C. elegans feeding behavior is regulated by extrinsic and intrinsic cues. Moreover, obesity and thinness are not solely determined by feeding behavior. Rather, feeding behavior and fat metabolism are coordinated but independent responses of the nervous system to the perception of nutrient availability.