Inhibition of dopamine and norepinephrine reuptake produces additive effects on energy balance in lean and obese mice

The effects of bupropion alone and combined with naltrexone on weight loss: a systematic review and meta-regression analysis of randomized controlled trials

BACKGROUND

The global prevalence of obesity and overweight is a significant concern in the field of public health. However, addressing and combating these conditions pose considerable challenges. Numerous interventional studies have been conducted to assess the possible impact of bupropion on weight reduction. The primary objective of this study was to conduct a comprehensive investigation into the effects of bupropiona alone and in combination with naltrexone on weight, body mass index (BMI), and waist circumferences (WC).

METHODS

A systematic search was conducted in five databases using established keywords. The purpose of this search was to uncover controlled trials that examined the impact of bupropion, either as a standalone intervention or in combination with naltrexone, on weight loss outcomes. The random-effects model analysis was used to provide pooled weighted mean difference and 95% confidence intervals.

RESULTS

Twenty five studies with 22,165 participants' were included in this article. The pooled findings showed that bupropion administration has an effect on lowering weight (WMD: -3.67 kg, 95% CI: -4.43 to -2.93) and WC (WMD: -2.98 cm, 95% CI -3.78 to -2.19) in compared with control groups. The analysis also showed that the effects of the present intervention on weight and WC during the intervention are > 26 weeks and ≤ 26 weeks compared to the other group, respectively. In addition, changes in weight loss and WC after receiving bupropion together with naltrexone were more compared to bupropion alone.

CONCLUSIONS

In conclusion, the addition of combination therapies like bupropion and naltrexone to lifestyle modifications including diet would cause significant weight loss.

Dopamine in the Regulation of Glucose Homeostasis, Pathogenesis of Type 2 Diabetes, and Chronic Conditions of Impaired Dopamine Activity/Metabolism: Implication for Pathophysiological and Therapeutic Purposes

Dopamine regulates several functions, such as voluntary movements, spatial memory, motivation, sleep, arousal, feeding, immune function, maternal behaviors, and lactation. Less clear is the role of dopamine in the pathophysiology of type 2 diabetes mellitus (T2D) and chronic complications and conditions frequently associated with it. This review summarizes recent evidence on the role of dopamine in regulating insular metabolism and activity, the pathophysiology of traditional chronic complications associated with T2D, the pathophysiological interconnection between T2D and chronic neurological and psychiatric disorders characterized by impaired dopamine activity/metabolism, and therapeutic implications. Reinforcing dopamine signaling is therapeutic in T2D, especially in patients with dopamine-related disorders, such as Parkinson's and Huntington's diseases, addictions, and attention-deficit/hyperactivity disorder. On the other hand, although specific trials are probably needed, certain medications approved for T2D (e.g., metformin, pioglitazone, incretin-based therapy, and gliflozins) may have a therapeutic role in such dopamine-related disorders due to anti-inflammatory and anti-oxidative effects, improvement in insulin signaling, neuroinflammation, mitochondrial dysfunction, autophagy, and apoptosis, restoration of striatal dopamine synthesis, and modulation of dopamine signaling associated with reward and hedonic eating. Last, targeting dopamine metabolism could have the potential for diagnostic and therapeutic purposes in chronic diabetes-related complications, such as diabetic retinopathy.

Dietary-induced binge-like eating impairs acoustic startle responses to acute nisoxetine in male mice

Sensorimotor gating disruptions have been noted in several psychiatric and neurodegenerative disorders. However, the involvement of sensorimotor gating processes in eating disorders has not been well characterized. Our objective was to examine the sensorimotor gating of the acoustic startle response following dietary-induced binge eating and high-fat diet (HFD) induced weight gain in male C57B/6J mice. Acute administration of the norepinephrine reuptake inhibitor, nisoxetine (0.5 and 5 mg/kg), and a dopamine reuptake inhibitor, GBR 12783 (1.6 and 16 mg/kg), were either given alone or in combination to assess norepinephrine and dopamine alterations, respectively. Male mice with repeated bouts of calorie restriction (Restrict) and with limited access to a sweetened fat food (Binge) demonstrated an escalation of intake over 2.5 weeks under standard chow conditions. Restrict Binge (RB) mice had a reduced startle response to the startle pulse (110 dB) compared with the Naive control group at 5 mg/kg nisoxetine. There was an overall effect of nisoxetine (0.5 and 5 mg/kg) to increase percent inhibition at pre-pulse (74 dB), %PP74. Under HFD conditions, the RB group did not demonstrate a binge-like eating phenotype. The RB group on HFD had a higher response to 74 dB with nisoxetine (5.0 mg/kg) compared with a combinational dose of nisoxetine (5.0 mg/kg) and GBR 12783 (1.6 mg/kg). These findings suggest that dietary conditions that promote binge-like eating can influence the central noradrenergic and dopaminergic controls of the acoustic startle response and potentially influence sensorimotor gating.

Levels and effects of antidepressant drugs to aquatic organisms

The use of antidepressants has been increasing globally, resulting in their presence in the aquatic environment, mainly by municipal wastewaters. This fact has aroused concern in the scientific community since these biologically active compounds can affect non-target organisms that have physiological systems regulated by these pharmaceuticals. However, the current knowledge on the toxicological effects of antidepressants on aquatic ecosystems is limited. Considering the increasing consumption pattern, quantification studies and toxicity studies, the present work aimed to review the available literature, published in the last seven years, addressing levels of antidepressants and their metabolites in rivers, surface waters, tap water, and wastewater treatment plants, as well, the effects reported in fish and invertebrates. Overall, the available laboratory studies showed that antidepressants can act at different levels of biological organisation, with detrimental effects at the individual level (e.g., survival, growth, and morphology, behaviour, and reproduction). However, the effects of prolonged exposures to environmentally relevant concentrations of these substances, a more realistic scenario, are unknown. Based on short-term studies, the long-term effects of pharmaceuticals at environmentally relevant concentrations (alone and in the presence of other environmental contaminants) should be studied.

Embryonic Exposure to Tryptophan Yields Bullying Victimization via Reprogramming the Microbiota-Gut-Brain Axis in a Chicken Model

Maternal metabolic disorder during early pregnancy may give rise to emotional and behavioral disorders in the child, vulnerable to bullying. Placental tryptophan fluctuation consequently disrupts offspring gut microbiome and brain neurogenesis with long-lasting physiological and social behavioral impacts. The aim of this study was to examine the hypothesis that the excess gestational tryptophan may affect children’s mental and physical development via modifying the microbiota-gut-brain axis, which lays the foundation of their mental status. Chicken embryo was employed due to its robust microbiota and independence of maternal influences during embryogenesis. The results indicated that embryonic tryptophan exposure reduced body weight and aggressiveness in the male offspring before and during adolescence. Additionally, the relative gut length and crypt depth were increased, while the villus/crypt ratio was decreased in tryptophan treated roosters, which was corresponding to the changes in the cecal microbiota composition. Furthermore, the catecholamine concentrations were increased in tryptophan group, which may be associated with the alterations in the gut microbiome and the gut-brain axis’s function. These changes may underlie the sociometric status of bullying; clarify how gestational tryptophan fluctuation compromises bullying and provide a strategy to prevent bullying by controlling dietary tryptophan and medication therapy during pregnancy.

Oleic acid stimulates monoamine efflux through PPAR-α: Differential effects in diet-induced obesity

Obesity continues to be a growing health concern around the world, and elevated levels of free fatty acids as a result of high-fat intake might play a role in neuroendocrine alterations leading to obesity. However, it is unclear how fatty acids affect neuroendocrine functions and energy metabolism. Since hypothalamic monoamines play a crucial role in regulating neuroendocrine functions relating to energy balance, we investigated the direct effects of oleic acid on hypothalamic monoamines and hypothesized that oleic acid would activate peroxisome proliferator-activated receptor alpha (PPAR-α), a nuclear transcription factor involved with fatty acid metabolism, to affect monoamines. We also hypothesized that this response would be subdued in diet-induced obesity (DIO). To test these hypotheses, hypothalami from Sprague Dawley and DIO rats were incubated with 0 (Control), 0.00132 mM, 0.132 mM, 1.32 mM oleic acid, 50 μM MK 886 (a selective PPAR- α antagonist), or oleic acid + MK 886 in Krebs Ringers Henseleit (KRH) solution. HPLC-EC was used to measure monoamine levels in perfusates. Oleic acid produced a significant increase in norepinephrine, dopamine, and serotonin levels in a dose-dependent manner, and incubation with MK886 blocked these effects. The effect of oleic acid on hypothalamic monoamines was attenuated in DIO rats. These findings suggest that PPARα probably plays an essential role in fatty acid sensing in the hypothalamus, by affecting monoamine efflux and DIO rats are resistant to the effects of oleic acid.

Understanding the Mechanism of Action and Clinical Implications of Anti-Obesity Drugs Recently Approved in Korea

The Korean Ministry of Food and Drug Safety has approved three anti-obesity drugs for long-term management in the past decade. In addition, since 2019, bariatric surgery has been financially supported by National Health Insurance Service in Korea. In this review, the mechanisms of action and the clinical implications of the recently approved anti-obesity drugs, lorcaserin, naltrexone/bupropion, and liraglutide are explained. Lorcaserin stimulates proopiomelanocortin (POMC)/cocaine- and amphetamine-regulated transcript (CART) neurons and inhibits neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons, which results in the activation of melanocortin 3/4 receptors. Naltrexone/bupropion stimulates POMC neurons through bupropion; this stimulation is augmented by blocking the autoinhibitory mechanism of POMC with naltrexone. The hypophagic effect of liraglutide is mediated through the direct activation of POMC/CART neurons and the indirect suppression of NPY/AgRP neurons through γ-aminobutyric acid-dependent signaling, with adjunctive suppression of the mesolimbic dopamine reward system. In addition to liraglutide, another glucagon-like peptide-1 receptor agonist, semaglutide, is expected to be added to the list of anti-obesity drugs in the near future. In patients with obesity and high cardiovascular risk, lorcaserin was considered neutral and liraglutide was considered favorable, whereas inconclusive results were obtained for naltrexone/bupropion.

Bupropion, Alone and in Combination with Naltrexone, Blunts Binge-Like Ethanol Drinking and Intake Following Chronic Intermittent Access to Ethanol in Male C57BL/6J Mice

BACKGROUND

Regular binge drinking is associated with numerous adverse consequences, yet the U.S. Food and Drug Administration (FDA) has approved only 4 medications for the treatment of alcohol use disorders, and none have been specifically targeted for treating binge drinking. Here, we assessed the effectiveness of the dopamine/norepinephrine re-uptake inhibitor, bupropion (BUP), alone and in combination with naltrexone (NAL), to reduce binge-like and chronic ethanol (EtOH) intake in mice. While BUP is an FDA-approved drug that is currently used to treat depression and nicotine dependence, there has been only limited investigation to assess the ability of BUP to reduce EtOH intake.

METHODS

Male C57BL/6J mice were tested with 20% (v/v) EtOH using "drinking in the dark" (DID) procedures to model binge-like EtOH intake and following intermittent access to EtOH (IAE). In Experiment 1, mice were given intraperitoneal (i.p.) injection of 0, 20, or 40 mg/kg BUP 30 minutes before DID testing; in Experiment 2, mice were given i.p. injection of vehicle, BUP (20 mg/kg), NAL (3 mg/kg), or BUP + NAL (20 and 3 mg/kg, respectively) 30 minutes before DID testing; and in Experiment 3, mice were given i.p. injection of 0, 20, 40, or 60 mg/kg BUP 30 minutes before EtOH access after mice had 16 weeks of IAE.

RESULTS

BUP dose dependently blunted EtOH intake with DID procedures and after 16 weeks of IAE. Administration of subthreshold doses of BUP + NAL also reduced binge-like EtOH intake. Finally, BUP failed to reduce consumption of a 3% (w/v) sucrose solution.

CONCLUSIONS

BUP, alone and in combination with NAL, may represent a novel approach to treating binge EtOH intake. We are currently assessing the efficacy of BUP to curb binge drinking in a phase II clinical trial experiment.

Gender-related issues in the pharmacology of new anti-obesity drugs

Four new medicines-liraglutide, lorcaserin, bupropion/naltrexone, and phentermine/topiramate-have been recently added to the pharmacological arsenal for obesity treatment and could represent important tools to manage this epidemic disease. To achieve satisfactory anti-obesity goals, the use of these new medicines should be optimized and tailored to specific patient subpopulations also by applying dose adjustments if needed. In the present review, we posit that gender could be among the factors influencing the activity of the new obesity drugs both because of pharmacokinetic and pharmacodynamic factors. Although evidence from premarketing clinical studies suggested that no dose adjustment by gender is necessary for any of these new medicines, these studies were not specifically designed to identify gender-related differences. This observation, together with the strong theoretical background supporting the hypothesis of a gender-dimorphic response, strongly call upon an urgent need of new real-life data on gender-related difference in the pharmacology of these new obesity drugs.

Bupropion promotes alterations in the spermatogenesis of mice and congenital malformations in the offspring

Bupropion hydrochloride (BUP) has been associated with male sexual dysfunction. The aim of this study was to evaluate the effects of BUP on the reproductive function of male mice and to evaluate offspring development. The mice were distributed into BUP group (40 mg kg−1) and control group (saline). On Day 35 of treatment the males were placed to mate with females and then killed on Day 46 for evaluation of reproductive function. On Day 18 of pregnancy, pregnant females were killed for evaluation of congenital malformations in the offspring. The BUP group showed a decrease in the Johnsen score (Control, 9.354 ± 0.092; BUP, 7.615 ± 0.147), Sertoli (Control, 5.623 ± 0.184; BUP, 4.215 ± 0.097) and Leydig (Control, 11.430 ± 0.817; BUP, 7.531 ± 0.213) cell counts, testosterone levels (Control, 783.5 ± 154.2 ng dL−1; BUP, 201.4 ± 54.8 ng dL−1) and sperm production (Control, 2.852 ± 0.211; BUP, 1.988 ± 0.116) and increased morphological alterations of the sperm head (Control, 8.134%; BUP, 10.423%) and tail (Control, 4.96%; BUP, 16.211%). The congenital malformations observed in BUP-derived offspring were: kyphosis (Control, 0.00%; BUP, 5.26%), retroverted rear legs (Control, 14.43%; BUP, 53.68%), incomplete ossification of the supraoccipital and exoccipital (Control, 21.82%; BUP, 86.00%) and sternum (Control, 25.45%; BUP, 82.00%). BUP had toxic effects on testicular function and teratogenic potential.

Metabolic and Cardiovascular Benefits and Risks of EMD386088-A 5-HT6 Receptor Partial Agonist and Dopamine Transporter Inhibitor

Since 5-HT₆ receptors play role in controlling feeding and satiety and dopamine is essential for normal feeding behavior, we evaluated the ability of EMD 386088-5-HT₆ receptor partial agonist and dopamine transporter inhibitor-to reduce body weight in obese rats, as well as its anorectic properties (calorie intake reduction) in rat model of excessive eating and the influence on metabolism (plasma glucose and glycerol levels). We also determined the effect of the studied compound on pica behavior in rats and its influence on blood pressure after single administration. EMD 386088 reduced body weight in obese rats fed high-fat diet and decreased calorie intake in both models applied (rat model of obesity and of excessive eating). In both models EMD 386088 regulated plasma glucose and increased plasma glycerol levels. The latter proves that the compound reduced body fat. We think that it might have increased lipolysis, but this requires further studies. The reduction in glucose levels is the first symptom of metabolic disorders compensation. EMD 386088 did not cause pica behavior in rats but increased blood pressure after single administration. We think that partial 5-HT₆ agonists might have potential in the treatment of obesity. Thus, EMD 386088 requires extended studies.

Bupropion-SR plus naltrexone-SR for the treatment of mild-to-moderate obesity

Naltrexone-bupropion is a recently approved drug combination for chronic weight management. In this article, we discuss the rationale for its use as a combination followed by a comprehensive review of safety and efficacy data from major preclinical, phase II and III clinical trials.

Palatability Can Drive Feeding Independent of AgRP Neurons

Feeding behavior is exquisitely regulated by homeostatic and hedonic neural substrates that integrate energy demand as well as the reinforcing and rewarding aspects of food. Understanding the net contribution of homeostatic and reward-driven feeding has become critical because of the ubiquitous source of energy-dense foods and the consequent obesity epidemic. Hypothalamic agouti-related peptide-secreting neurons (AgRP neurons) provide the primary orexigenic drive of homeostatic feeding. Using models of neuronal inhibition or ablation, we demonstrate that the feeding response to a fast ghrelin or serotonin receptor agonist relies on AgRP neurons. However, when palatable food is provided, AgRP neurons are dispensable for an appropriate feeding response. In addition, AgRP-ablated mice present exacerbated stress-induced anorexia and palatable food intake--a hallmark of comfort feeding. These results suggest that, when AgRP neuron activity is impaired, neural circuits sensitive to emotion and stress are engaged and modulated by food palatability and dopamine signaling.

Hypothalamic Obesity in Craniopharyngioma Patients: Disturbed Energy Homeostasis Related to Extent of Hypothalamic Damage and Its Implication for Obesity Intervention

Hypothalamic obesity (HO) occurs in patients with tumors and lesions in the medial hypothalamic region. Hypothalamic dysfunction can lead to hyperinsulinemia and leptin resistance. This review is focused on HO caused by craniopharyngiomas (CP), which are the most common childhood brain tumors of nonglial origin. Despite excellent overall survival rates, CP patients have substantially reduced quality of life because of significant long-term sequelae, notably severe obesity in about 50% of patients, leading to a high rate of cardiovascular mortality. Recent studies reported that both hyperphagia and decreased energy expenditure can contribute to severe obesity in HO patients. Recognized risk factors for severe obesity include large hypothalamic tumors or lesions affecting several medial and posterior hypothalamic nuclei that impact satiety signaling pathways. Structural damage in these nuclei often lead to hyperphagia, rapid weight gain, central insulin and leptin resistance, decreased sympathetic activity, low energy expenditure, and increased energy storage in adipose tissue. To date, most efforts to treat HO have shown disappointing long-term success rates. However, treatments based on the distinct pathophysiology of disturbed energy homeostasis related to CP may offer options for successful interventions in the future.

Evidence that Melanocortin Receptor Agonist Melanotan-II Synergistically Augments the Ability of Naltrexone to Blunt Binge-Like Ethanol Intake in Male C57BL/6J Mice

BACKGROUND

The nonselective opioid receptor antagonist, naltrexone (NAL), reduces alcohol (ethanol [EtOH]) consumption in animals and humans and is an approved medication for treating alcohol abuse disorders. Proopiomelanocortin (POMC)-derived melanocortin (MC) and opioid peptides are produced in the same neurons in the brain, and recent preclinical evidence shows that MC receptor (MCR) agonists reduce excessive EtOH drinking in animal models. Interestingly, there is a growing body of literature revealing interactions between the MC and the opioid systems in the modulation of pain, drug tolerance, and food intake.

METHODS

In the present report, a mouse model of binge EtOH drinking was employed to determine whether the MCR agonist, melanotan-II (MTII), would improve the effectiveness of NAL in reducing excessive binge-like EtOH drinking when these drugs were co-administered prior to EtOH access.

RESULTS

Both NAL and MTII blunt binge-like EtOH drinking and associated blood EtOH levels, and when administered together, a low dose of MTII (0.26 mg/kg) produces a 7.6-fold increase in the effectiveness of NAL in reducing binge-like EtOH drinking. Using isobolographic analysis, it is demonstrated that MTII increases the effectiveness of NAL in a synergistic manner.

CONCLUSIONS

The current observations suggest that activators of MC signaling may represent a new approach to treating alcohol abuse disorders and a way to potentially improve existing NAL-based therapies.

Naltrexone/bupropion for obesity: an investigational combination pharmacotherapy for weight loss

The mechanism of action of the combination therapy, naltrexone/bupropion (NB), for obesity has not been fully described to date. Weight loss attempts rarely result in long-term success. This is likely a result of complex interactions among multiple peripheral and CNS systems that defend against weight loss, and may explain the overwhelming lack of effective obesity treatments. NB is an investigational combination therapy for obesity that was developed based on evidence that obesity involves alterations in the hypothalamic melanocortin system as well as brain reward systems that influence food craving and mood. Naltrexone and bupropion both have actions in these brain regions that may cause them to influence food intake, food craving, and other aspects of eating behavior that affect body weight. We review the individual actions of naltrexone and bupropion in brain hypothalamic and reward systems, and describe the current in vitro, in vivo, and clinical evidence for how NB influences food intake and produces weight loss.

An evolving scientific basis for the prevention and treatment of pediatric obesity

The 2013 Pennington Biomedical Research Center's Scientific Symposium focused on the treatment and management of pediatric obesity and was designed to (i) review recent scientific advances in the prevention, clinical treatment and management of pediatric obesity, (ii) integrate the latest published and unpublished findings and (iii) explore how these advances can be integrated into clinical and public health approaches. The symposium provided an overview of important new advances in the field, which led to several recommendations for incorporating the scientific evidence into practice. The science presented covered a range of topics related to pediatric obesity, including the role of genetic differences, epigenetic events influenced by in utero development, pre-pregnancy maternal obesity status, maternal nutrition and maternal weight gain on developmental programming of adiposity in offspring. Finally, the relative merits of a range of various behavioral approaches targeted at pediatric obesity were covered, together with the specific roles of pharmacotherapy and bariatric surgery in pediatric populations. In summary, pediatric obesity is a very challenging problem that is unprecedented in evolutionary terms; one which has the capacity to negate many of the health benefits that have contributed to the increased longevity observed in the developed world.

Blocking alpha2A adrenoceptors, but not dopamine receptors, augments bupropion-induced hypophagia in rats

OBJECTIVE

Anti-obesity drugs have adverse effects which limit their use, creating a need for novel anti-obesity compounds. We studied effects of dopamine (DA) and norepinephrine (NE) reuptake inhibitor bupropion (BUP), alone and after blocking α1- or α2-adrenoceptors (AR), D1/5, D2/3, or D4 receptors, to determine which receptors act downstream of BUP.

DESIGN AND METHODS

Effects on caloric intake, meal patterning and locomotion were assessed, using an automated weighing system and telemetry in male rats with 18-h access to Western Human style diet.

RESULTS

BUP (30 mg/kg) induced hypophagia by reducing meal size and postponing meal initiation. WB4101 (α1-AR; 2 mg/kg) and imiloxan (α2B-AR; 5 mg/kg) attenuated BUP's effect on meal size, while WB4101 and BRL 44408 (α2A/D-AR; 2 mg/kg) counteracted effect on meal initiation. Atipamezole (α2-AR; 1 mg/kg) and imiloxan further postponed initiation of meals. SKF 83566 (D1/5; 0.3 mg/kg), raclopride (D2/3; 0.5 mg/kg) and to a lesser extent FAUC 213 (D4; 0.5 mg/kg), attenuated BUP-induced hypophagia. BUP stimulated locomotion, which was blocked by all antagonists, except FAUC 213 or BRL 44408.

CONCLUSIONS

Alpha1-, α2A/D- and α2B-ARs, and DA receptors underlie BUP's effects on size and initiation of meals, while blocking pre-synaptic α2-ARs enhanced BUP-induced hypophagia. An inverse agonist of (pre-synaptic) α2A-ARs could enhance BUP-induced anorexia and treat eating disorders and obesity.

Acute behavioural effects of bupropion and naltrexone, alone and in combination, in non-deprived male rats presented with palatable mash

RATIONALE

In appetite research, drugs frequently progress to clinical trials on the basis of outcome (reduced food intake/body weight gain) with insufficient attention to process (behavioural analysis). Although bupropion and naltrexone (alone and in combination) reduce food consumption in rodents and humans, their effects on behaviour during feeding tests have not been thoroughly investigated.

OBJECTIVES

This study aimed to assess the behavioural specificity of anorectic responses to bupropion, naltrexone and their combination.

METHODS

Video analysis was employed to characterise the behavioural effects of acute systemic treatment with bupropion (10.0-40.0 mg/kg), naltrexone (0.1-3.0 mg/kg) and combined bupropion (20 mg/kg) plus naltrexone (0.1-1.0 mg/kg) in non-deprived male rats exposed for 1 h to palatable mash. Particular attention was paid to the behavioural satiety sequence (BSS).

RESULTS

In experiment 1, the anorectic response to 40 mg/kg bupropion was associated with significant psychomotor stimulation and a complete disruption of the BSS. In experiment 2, the anorectic response to 3 mg/kg naltrexone was associated with an accelerated but otherwise normal BSS. In experiment 3, the co-administration of 20 mg/kg bupropion and naltrexone (0.1 and 1.0 mg/kg) not only produced an additive anorectic profile (including a reduced rate of eating), but the addition of the opioid receptor antagonist also concurrently attenuated the psychomotor stimulant response to the atypical antidepressant.

CONCLUSIONS

Low-dose co-treatment with naltrexone and bupropion produces a stronger suppression of appetite than that seen with either agent alone and has the additional advantage of reducing some of the unwanted effects of bupropion.

Naltrexone/Bupropion combination therapy in overweight or obese patients with major depressive disorder: results of a pilot study

OBJECTIVE

To evaluate the effect of 32-mg/d naltrexone sustained release and 360-mg/d bupropion sustained release (NB32) in overweight and obese patients with major depressive disorder (MDD).

METHOD

Twenty-five female patients with a DSM-IV diagnosis of MDD, an Inventory of Depressive Symptomatology-Self-Report score > 26, and a body mass index ≥ 27 and ≤ 43 kg/m(2) received up to 24 weeks of open-label treatment with NB32 with dietary and behavioral counseling (data collection: March 2008-July 2009). The primary endpoint was change from baseline in the Montgomery-Asberg Depression Rating Scale (MADRS) total score at 12 weeks; secondary endpoints included MADRS total score at week 24, change in weight, and Clinical Global Impressions-Improvement scale responder status (CGI-I score ≤ 2) at weeks 12 and 24 (modified intent-to-treat [mITT]: patients with ≥ 1 postbaseline MADRS total score on study drug; N = 23).

RESULTS

MADRS scores showed significant reductions at weeks 12 and 24 (mITT-last observation carried forward [LOCF]: -13.1 ± 7.1 and -15.3 ± 8.1, respectively, P < .001 vs baseline for all). Mean ± SD weight loss was -4.0% ± 4.6% (mITT-LOCF) and -6.1% ± 4.7% (observed cases) at week 12 and -5.3% ± 6.5% (mITT-LOCF) and -9.2% ± 6.2% (observed cases) at week 24 (P < .001 vs baseline for all). By week 24, 95% of patients (mITT-LOCF) were responders (CGI-I score ≤ 2) and 70% were in remission (CGI-I score = 1). The safety/tolerability profile of NB32 was consistent with its individual components; the most common adverse events were nausea, constipation, headache, and insomnia, with no serious adverse events attributed to NB32.

CONCLUSION

Twenty-four weeks of open-label NB32 therapy with dietary and behavioral counseling was associated with improvement in depressive symptoms and reduced body weight in overweight/obese women with MDD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT00624858.

Mechanisms underlying current and future anti-obesity drugs

Regulation of body weight is organized by distributed brain circuits that use a variety of neuropeptides and transmitters, and that are responsive to endocrine and metabolic signals. Targeting of these circuits with novel pharmaceutical drugs would be helpful additions to lifestyle interventions for the treatment of obesity. The recent FDA approval of two anti-obesity drugs holds promise in a field in which previous drugs were removed from clinical use because of unacceptable psychiatric and cardiovascular side effects. Here, the modes of action of anti-obesity drugs are reviewed.

High-fat diet-induced alterations in the feeding suppression of low-dose nisoxetine, a selective norepinephrine reuptake inhibitor

Central noradrenergic pathways are involved in feeding and cardiovascular control, physiological processes altered by obesity. The present studies determined how high-fat feeding and body weight gain alter the sensitivity to the feeding suppression and neural activation to a selective norepinephrine reuptake inhibitor, nisoxetine. Acute administration of nisoxetine (saline: 0, 3, 10, and 30 mg/kg; i.p.) resulted in a dose-dependent reduction in the 24 h refeeding response in male Sprague Dawley rats maintained on standard chow. In a similar fashion, nisoxetine resulted in reductions in blood pressure and a compensatory increase in heart rate. From these studies, the 3 mg/kg dose was subthreshold. In a separate experiment, however, 10 wk exposure to a high-fat diet (60% fat) resulted in weight gain and significant feeding suppression following administration of nisoxetine (3 mg/kg) compared with animals fed a control diet (10% fat). Nisoxetine (3 mg/kg) also resulted in greater neural activation, as measured by c-Fos immunohistochemistry, in the arcuate nucleus of the hypothalamus in animals exposed to the high-fat diet. Such data indicate acute nisoxetine doses that suppress food intake can impact cardiovascular measures. It also suggests that the feeding suppression to a low-dose nisoxetine is enhanced as a result of high-fat diet and weight gain.

Pharmacotherapy for childhood obesity: present and future prospects

Pediatric obesity is a serious medical condition associated with significant comorbidities during childhood and adulthood. Lifestyle modifications are essential for treating children with obesity, yet many have insufficient response to improve health with behavioral approaches alone. This review summarizes the relatively sparse data on pharmacotherapy for pediatric obesity and presents information on obesity medications in development. Most previously studied medications demonstrated, at best, modest effects on body weight and obesity-related conditions. It is to be hoped that the future will bring new drugs targeting specific obesity phenotypes that will allow clinicians to use etiology-specific, and therefore more effective, anti-obesity therapies.

Nicotinic regulation of energy homeostasis

INTRODUCTION

The ability of nicotine, the primary psychoactive substance in tobacco smoke, to regulate appetite and body weight is one of the factors cited by smokers that prevents them from quitting and is the primary reason for smoking initiation in teenage girls. The regulation of feeding and metabolism by nicotine is complex, and recent studies have begun to identify nicotinic acetylcholine receptor (nAChR) subtypes and circuits or cell types involved in this regulation.

DISCUSSION

We will briefly describe the primary anatomical and functional features of the input, output, and central integration structures of the neuroendocrine systems that regulate energy homeostasis. Then, we will describe the nAChR subtypes expressed in these structures in mammals to identify the possible molecular targets for nicotine. Finally, we will review the effects of nicotine and its withdrawal on feeding and energy metabolism and attribute them to potential central and peripheral cellular targets.

Unusual effects of nicotine as a psychostimulant on ambulatory activity in mice

The present study examined the effect of nicotine, alone and in combination with various drugs that act on the CNS, on ambulatory activity, a behavioral index for locomotion, in ICR (CD-1) strain mice. Nicotine at 0.25–2 mg/kg acutely reduced ambulatory activity of ICR mice. The effect of nicotine was similar to that of haloperidol and fluphenazine but distinct from that of bupropion and methylphenidate. ICR mice developed tolerance against the inhibitory effect of nicotine on ambulatory activity when nicotine was repeatedly administered. This effect was also distinct from bupropion and methylphenidate as they produced augmentation of their ambulation-stimulating effects in ICR mice. Nicotine reduced the ambulation-stimulating effects of bupropion and methylphenidate as well as haloperidol and fluphenazine. Taken together, nicotine exhibited unusual effects as a psychostimulant on ambulatory activity in ICR mice.

The effect of tesofensine on appetite sensations

Tesofensine (TE), an inhibitor of monoamine presynaptic reuptake, has produced twice the weight loss seen with currently marketed drugs. However, its long term effect on appetite in humans has not been studied. A multicentre phase II trial was divided into two parts (24 weeks each). Part 1 had a randomized, double-blind, placebo-controlled design and Part 2, an open-labeled, single-group, uncontrolled design. A drug-free period (12 ± 3 weeks) separated them. In Part 1, participants (n = 158) were assigned to 0.25, 0.5 or 1.0 mg TE, or placebo. Completers of Part 1 were invited to participate in Part 2 (n = 113), during which they all received 0.5 or 1.0 mg TE. Appetite sensations and a composite satiety score (CSS = satiety + fullness + (100 - hunger) + (100 - prospective food consumption) were assessed. In Part 1 TE induced a dose-dependent increase in CSS at week 12 that correlated with weight loss during the 24 weeks (r = 0.36, P < 0.0001). However, CSS diminished over time as weight loss progressed (e.g., for 1.0 mg; 52 ± 17 mm; 64 ± 13 mm; 55 ± 13 mm at baseline, week 12 and week 24, respectively). After drug withdrawal CSS returned to baseline values (50 ± 17 mm, in the whole sample.), despite the participants' reduced-weight state (-7.2 ± 6.7 kg, P < 0.0001). The reintroduction of TE in Part 2 increased CSS again (56 ± 17 mm at week 60), regardless of initial treatment/weight loss. We postulate that enhanced satiety is involved in early weight loss. Whether the attenuated effect on appetite seen after 24 weeks is due to a counteracting effect in the weight reduced state or whether the appetite suppressing effect of TE per se diminishes over time is, however, still unclear.

Central control of thermogenesis

In mammals and birds, conservation of body heat at around 37 °C is vital to life. Thermogenesis is the production of this heat which can be obligatory, as in basal metabolic rate, or it can be facultative such as the response to cold. A complex regulatory system has evolved which senses environmental or core temperature and integrates this information in hypothalamic regions such as the preoptic area and dorsomedial hypothalamus. These areas then send the appropriate signals to generate and conserve heat (or dissipate it). In this review, the importance of the sympathetic nervous system is discussed in relation to its role in basal metabolic rate and adaptive thermogenesis with a particular emphasis to human obesity. The efferent sympathetic pathway does not uniformly act on all tissues; different tissues can receive different levels of sympathetic drive at the same time. This is an important concept in the discussion of the pharmacotherapy of obesity. Despite decades of work the medicine chest contains only one pill for the long term treatment of obesity, orlistat, a lipase inhibitor that prevents the absorption of lipid from the gut and is itself not systemically absorbed. The central controlling system for thermogenesis has many potential intervention points. Several drugs, previously marketed, awaiting approval or in the earlier stages of development may have a thermogenic effect via activation of the sympathetic nervous system at some point in the thermoregulatory circuit and are discussed in this review. If the balance is weighted to the "wrong" side there is the burden of increased cardiovascular risk while a shift to the "right" side, if possible, will afford a thermogenic benefit that is conducive to weight loss maintenance. This article is part of a Special Issue entitled 'Central Control Food Intake'

The role of NPY in hypothalamic mediated food intake

Neuropeptide Y (NPY) is a highly conserved neuropeptide with orexigenic actions in discrete hypothalamic nuclei that plays a role in regulating energy homeostasis. NPY signals via a family of high affinity receptors that mediate the widespread actions of NPY in all hypothalamic nuclei. These actions are also subject to tight, intricate regulation by numerous peripheral and central energy balance signals. The NPY system is embedded within a densely-redundant network designed to ensure stable energy homeostasis. This redundancy may underlie compensation for the loss of NPY or its receptors in germline knockouts, explaining why conventional knockouts of NPY or its receptors rarely yield a marked phenotypic change. We discuss insights into the hypothalamic role of NPY from studies of its physiological actions, responses to genetic manipulations and interactions with other energy balance signals. We conclude that numerous approaches must be employed to effectively study different aspects of NPY action.

Tesofensine, a novel triple monoamine reuptake inhibitor, induces appetite suppression by indirect stimulation of alpha1 adrenoceptor and dopamine D1 receptor pathways in the diet-induced obese rat

Tesofensine is a novel monoamine reuptake inhibitor that inhibits both norepinephrine, 5-HT, and dopamine (DA) reuptake function. Tesofensine is currently in clinical development for the treatment of obesity, however, the pharmacological basis for its strong effect in obesity management is not clarified. Using a rat model of diet-induced obesity (DIO), we characterized the pharmacological mechanisms underlying the appetite suppressive effect of tesofensine. DIO rats treated with tesofensine (2.0 mg/kg, s.c.) for 16 days showed significantly lower body weights than vehicle-treated DIO rats, being reflected by a marked hypophagic response. Using an automatized food intake monitoring system during a 12 h nocturnal test period, tesofensine-induced hypophagia was investigated further by studying the acute interaction of a variety of monoamine receptor antagonists with tesofensine-induced hypophagia in the DIO rat. Tesofensine (0.5-3.0 mg/kg, s.c.) induced a dose-dependent and marked decline in food intake with an ED(50) of 1.3 mg/kg. The hypophagic response of tesofensine (1.5 mg/kg, s.c.) was almost completely reversed by co-administration of prazosin (1.0 mg/kg, alpha(1) adrenoceptor antagonist) and partially antagonized by co-administration of SCH23390 (0.03 mg/kg, DA D(1) receptor antagonist). In contrast, tesofensine-induced hypophagia was not affected by RX821002 (0.3 mg/kg, alpha(2) adrenoceptor antagonist), haloperidol (0.03 mg/kg, D(2) receptor antagonist), NGB2904 (0.1 mg/kg, D(3) receptor antagonist), or ritanserin (0.03 mg/kg, 5-HT(2A/C) receptor antagonist). Hence, the mechanism underlying the suppression of feeding by tesofensine in the obese rat is dependent on the drug's ability to indirectly stimulate alpha(1) adrenoceptor and DA D(1) receptor function.

MSI-1436 reduces acute food intake without affecting dopamine transporter activity

Many therapies designed to reduce food intake and body weight act, in part, by blocking the dopamine transporter (DAT) - a protein responsible for clearing extracellular dopamine (DA) after release thereby terminating its action. Here, we found that a single injection of the drug trodusquemine (MSI-1436) decreased food intake in rats. To assess the effects of MSI-1436 on DAT function, fast-scan cyclic voltammetry was used to measure DA concentration changes in the ventral striatum. DA release was evoked by electrical stimulation of the ventral tegmental area every 5 min. After 3 baseline measurements, rats were injected with MSI-1436 (10 mg/kg), the known DAT blocker bupropion (80 mg/kg) or saline and evoked DA release and reuptake were monitored for an additional hour. Neither saline nor MSI-1436 caused a significant change in the magnitude of evoked release from baseline values whereas bupropion caused a significant increase. In addition, neither saline nor MSI-1436 significantly increased DA decay rates while such an increase was observed with bupropion. Thus, over a time course when MSI-1436 suppresses food intake it does not affect DAT function. The results support MSI-1436 as an anti-obesity treatment which spares DAT.

Central and peripheral molecular targets for antiobesity pharmacotherapy

Obesity has emerged as one of the principal worldwide health concerns of the modern era, and there exists a tremendous unmet clinical need for safe and effective therapies to combat this global pandemic. The prevalence of obesity and its associated comorbidities, including cardiovascular and metabolic diseases, has focused the attention of those in drug discovery and development on generating effective modalities for the treatment and prevention of obesity. Early efforts in the field of obesity pharmacotherapy centered on the development of agents with indeterminate mechanisms of action. This led to treatment paradigms characterized by significant off-target effects. In the past two decades, new insights have been made into the physiologic regulation of energy balance and the subordinate central and peripheral circuits coordinating appetite, metabolism, and lipogenesis. These studies have revealed previously unrecognized molecular targets for controlling appetite and managing weight from which has emerged a new wave of targeted pharmacotherapies to prevent and control obesity.

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.

Psychological classification as a communication and management tool in obese patients undergoing bariatric surgery

BACKGROUND

Psychological evaluations are used to ascertain patient suitability for bariatric surgery and to challenge their ability to comply with therapy. The modern paradigm of obesity includes a neurobiologic component working in parallel with the limbic system of appetite and reward. To achieve the goals of surgery, an evaluation of the psychological fitness of the patient is often included in the clinical pathway. We present a psychological classification system with the goal of integrating the psychological factors into patient treatment.

METHODS

All patients (Roux-en-Y gastric bypass, n = 1814; laparoscopic adjustable gastric banding, n = 589) were evaluated using psychological testing/interview and assigned to groups 1-4 before surgery. The group 1 patients (n = 788; 32.8%) did not necessitate intervention, group 2 (n = 1110; 46.2%) were requested to attend the support group, groups 3A (n = 394; 16.4%) and 3B (n = 111; 4.6%) required intervention to continue to surgery, and group 4 patients were not recommended for surgery. The main outcome measures, including complication, readmission, and reoperation rates, were analyzed for differences among the psychological groups.

RESULTS

After comparing the outcome measures between each classification, no significant differences were found in the major complication rates, readmissions, reoperations, or length of stay among the groups. Groups 3A and 3B were able to achieve similar rates of success, despite their psychosocial impairment at the initial evaluation.

CONCLUSION

The assignment of a psychological classification can facilitate bariatric team recognition of the unique psychological factors that affect the success of surgery. Assessing the patient's psychological composition and addressing potential psychosocial barriers before surgery can increase the positive long-term outcomes and reduce the incidence of complications after bariatric surgery.

New central targets for the treatment of obesity

The review focuses on the central neuronal circuits involved in energy homeostasis and the opportunities these offer for pharmacological intervention to decrease feeding behaviour and reduce weight. This article is based on the presentation 'New central targets for the treatment of obesity' (Sargent, British Pharmacological society, Clinical Section Symposium, December 2008). Central neuronal substrates controlling weight offer numerous opportunities for pharmacological intervention. These opportunities range from non-specific enhancement of monoamine signalling (triple reuptake inhibitors) to targeting specific monoamine receptor subtypes (5-HT(2c) and 5-HT(6)). The data reviewed suggest that these approaches will lead to weight loss; whether this is sufficient to produce clinically meaningful effect remains to be determined. Combination therapy targeting more than one mechanism may be a means of increasing the magnitude of the response. Preclinical studies also suggest that novel approaches targeting specific neuronal pathways within the hypothalamus, e.g. MCH(1) receptor antagonism, offer an opportunity for weight reduction. However, these approaches are at an early stage and clinical studies will be needed to determine if these novel approaches lead to clinically meaningful weight loss and improvements in co-morbid conditions such as diabetes and cardiovascular disorders.

Bupropion and naltrexone: a review of their use individually and in combination for the treatment of obesity

BACKGROUND

Bupropion and naltrexone are centrally active drugs that have shown potential efficacy - alone and in combination - for the treatment of obesity.

OBJECTIVE

To explore the efficacy and safety of naltrexone and bupropion alone and in a novel combination drug that utilizes sustained-release (SR) formulations of both drugs and to evaluate their efficacy in promoting weight loss. The mechanisms of action of these centrally acting drugs are discussed. Preclinical and clinical studies of bupropion and naltrexone alone and in combination are reviewed.

RESULTS/CONCLUSIONS

Both bupropion and naltrexone have been shown individually to induce weight loss. Bupropion has greater efficacy as monotherapy. Naltrexone SR potentiates the effects of bupropion SR; thus, this synergistic combination has the potential for additional weight loss compared to monotherapy. Current Phase III trials will yield further safety and efficacy information regarding these drugs in combination.

Protein kinase A activators and the pan-PPAR agonist tetradecylthioacetic acid elicit synergistic anti-leukaemic effects in AML through CREB

Targeting of signal transduction pathways and transcriptional regulation represents an attractive approach for less toxic anti-leukaemic therapy. We combined protein kinase A (PKA) activation with a pan-peroxisome proliferator-activated receptor (PPAR) activator tetradecylthioacetic acid, resulting in synergistic decrease in viability of AML cell lines. PKA isoform II activation appeared to be involved in inhibition of proliferation but not induction of apoptosis in HL-60 cells. Inhibition of CREB function protected against this anti-leukaemic effect with higher efficiency than enforced Bcl-2 expression. Preclinical studies employing the rat AML model Brown Norwegian Myeloid Leukaemia also indicated anti-leukaemic activity of the combination therapy in vivo. In conclusion, combined PKA and pan-PPAR activation should be explored further to determine its therapeutic potential.

Knockout of the norepinephrine transporter and pharmacologically diverse antidepressants prevent behavioral and brain neurotrophin alterations in two chronic stress models of depression

Diverse factors such as changes in neurotrophins and brain plasticity have been proposed to be involved in the actions of antidepressant drugs (ADs). However, in mouse models of depression based on chronic stress, it is still unclear whether simultaneous changes in behavior and neurotrophin expression occur and whether these changes can be corrected or prevented comparably by chronic administration of ADs or genetic manipulations that produce antidepressant-like effects such as the knockout of the norepinephrine transporter (NET) gene. Here we show that chronic restraint or social defeat stress induce comparable effects on behavior and changes in the expression of neurotrophins in depression-related brain regions. Chronic stress caused down-regulation of BDNF, nerve growth factor, and neurotrophin-3 in hippocampus and cerebral cortex and up-regulation of these targets in striatal regions. In wild-type mice, these effects could be prevented by concomitant chronic administration of five pharmacologically diverse ADs. In contrast, NET knock out (NETKO) mice were resistant to stress-induced depressive-like changes in behavior and brain neurotrophin expression. Thus, the resistance of the NETKO mice to the stress-induced depression-associated behaviors and biochemical changes highlight the importance of noradrenergic pathways in the maintenance of mood. In addition, these mice represent a useful model to study depression-resistant behaviors, and they might help to provide deeper insights into the identification of downstream targets involved in the mechanisms of antidepressants.

Rational design of a combination medication for the treatment of obesity

Existing obesity therapies are limited by safety concerns and modest efficacy reflecting a weight loss plateau. Here, we explore combination therapy with bupropion (BUP), a putative stimulator of melanocortin pathways, and an opioid antagonist, naltrexone (NAL), to antagonize an inhibitory feedback loop that limits sustained weight reduction. In vitro electrophysiologic experiments were conducted to determine the extent to which BUP+NAL stimulated hypothalamic pro-opiomelanocortin (POMC) neurons in mouse brain. A subsequent study further characterized the effect of combination BUP+NAL treatment on food intake in lean and obese mice. Finally, a randomized, blinded, placebo-controlled trial in obese adult subjects was conducted. Randomization included: BUP (300 mg) + NAL (50 mg), BUP (300 mg) + placebo (P), NAL (50 mg) + P or P+P for up to 24 weeks. BUP+NAL stimulated murine POMC neurons in vitro and caused a greater reduction in acute food intake than either monotherapy, an effect consistent with synergism. Combined BUP+NAL provided sustained weight loss without evidence of an efficacy plateau through 24 weeks of treatment. BUP+NAL completers diverged from NAL+P (P < 0.01) and P+P (P < 0.001) at week 16 and from BUP+P by week 24 (P < 0.05). The combination was also well tolerated. Translational studies indicated that BUP+NAL therapy produced synergistic weight loss which exceeded either BUP or NAL alone. These results supported the hypothesis that NAL, through blockade of beta-endorphin mediated POMC autoinhibition, prevents the classic weight loss plateau observed with monotherapies such as BUP. This novel treatment approach (BUP+NAL) holds promise for the treatment of obesity.\

Interaction of cocaine-, benztropine-, and GBR12909-like compounds with wild-type and mutant human dopamine transporters: molecular features that differentially determine antagonist-binding properties

The widely abused psychostimulant cocaine is thought to elicit its reinforcing effects primarily via inhibition of the neuronal dopamine transporter (DAT). However, not all DAT inhibitors share cocaine's behavioral profile, despite similar or greater affinity for the DAT. This may be due to differential molecular interactions with the DAT. Our previous work using transporter mutants with altered conformational equilibrium (W84L and D313N) indicated that benztropine and GBR12909 interact with the DAT in a different manner than cocaine. Here, we expand upon these previous findings, studying a number of structurally different DAT inhibitors for their ability to inhibit [(3)H]CFT binding to wild-type, W84L and D313N transporters. We systematically tested structural intermediates between cocaine and benztropine, structural hybrids of benztropine and GBR12909 and a number of other structurally heterologous inhibitors. Derivatives of the stimulant desoxypipradrol (2-benzhydrylpiperidine) exhibited a cocaine-like binding profile with respect to mutation, whereas compounds possessing the diphenylmethoxy moiety of benztropine and GBR12909 were dissimilar to cocaine-like compounds. In tests with specific isomers of cocaine and tropane analogues, compounds with 3alpha stereochemistry tended to exhibit benztropine-like binding, whereas those with 3beta stereochemistry were more cocaine-like. Our results point to the importance of specific molecular features--most notably the presence of a diphenylmethoxy moiety--in determining a compound's binding profile. This study furthers the concept of using DAT mutants to differentiate cocaine-like inhibitors from atypical inhibitors in vitro. Further studies of the molecular features that define inhibitor-transporter interaction could lead to the development of DAT inhibitors with differential clinical utility.

Catecholamine reuptake inhibition causes weight loss by increasing locomotor activity and thermogenesis

Bupropion (BUP) is a dopamine (DA) and norepinephrine (NE) reuptake inhibitor that causes mild weight loss in obese adults. Subchronic (7 day) coadministration of selective DA and NE reuptake inhibitors also causes weight loss in mice. Because weight loss was not associated with decreased caloric intake, subchronic BUP might cause weight loss through increased energy expenditure. Acute studies demonstrate that BUP or DA+NE reuptake inhibitors cause transient hypophagia and increased locomotion; though the effects on temperature are inconsistent. Because subchronic DA+NE reuptake inhibition does not affect appetite, there is clearly a difference between the acute and subchronic effects of DA+NE reuptake inhibitors; however the effects of chronic (or subchronic) BUP on energy balance have never been directly studied in an animal model. Therefore, the acute and subchronic effects of BUP or selective DA and NE reuptake inhibitors on food intake, body weight, locomotor activity, and interscapular temperature were determined in mice. Generally, selective inhibition of DA reuptake (by GBR12783) increased activity while selective inhibition of NE reuptake (by nisoxetine, NIS) decreased activity and temperature. BUP increased activity and temperature but subchronic BUP did not significantly reduce body weight due to a compensatory increase in food intake. Subchronic DA+NE reuptake inhibitor coadministration mimicked the effect of BUP on activity and temperature, but caused weight loss because daily food intake was not increased. The results of this study suggest that the mild weight loss effect of BUP in humans may be due to increased locomotion or heat production. More importantly, inhibition of DA+NE reuptake (with GBR+NIS) increased energy expenditure without a compensatory increase in food intake, supporting a role for novel combination catecholamine reuptake inhibitors in pharmacotherapy for obesity.