Effects of preexposure to dexfenfluramine, phentermine, dexfenfluramine-phentermine, or fluoxetine on sibutramine-induced hypophagia in the adult rat

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.

Fluoxetine disrupts motivation and GABAergic signaling in adolescent female hamsters

Initial antidepressant treatment can paradoxically worsen symptoms in depressed adolescents by undetermined mechanisms. Interestingly, antidepressants modulate GABAA receptors, which mediate paradoxical effects of other therapeutic drugs, particularly in females. Although the neuroanatomic site of action for this paradox is unknown, elevated GABAA receptor signaling in the nucleus accumbens can disrupt motivation. We assessed fluoxetine's effects on motivated behaviors in pubescent female hamsters - anhedonia in the reward investigational preference (RIP) test as well as anxiety in the anxiety-related feeding/exploration conflict (AFEC) test. We also assessed accumbal signaling by RT-PCR and electrophysiology. Fluoxetine initially worsened motivated behaviors at puberty, relative to adulthood. It also failed to improve these behaviors as pubescent hamsters transitioned into adulthood. Low accumbal mRNA levels of multiple GABAA receptor subunits and GABA-synthesizing enzyme, GAD67, assessed by RT-PCR, suggested low GABAergic tone at puberty. Nonetheless, rapid fluoxetine-induced reductions of α5GABAA receptor and BDNF mRNA levels at puberty were consistent with age-related differences in GABAergic responses to fluoxetine and disruption of the motivational state. Whole-cell patch clamping of accumbal slices also suggested low GABAergic tone by the low amplitude of miniature inhibitory postsynaptic currents (mIPSCs) at puberty. It also confirmed age-related differences in GABAergic responses to fluoxetine. Specifically, fluoxetine potentiated mIPSC amplitude and frequency at puberty, but attenuated the amplitude during adulthood. These results implicate GABAergic tone and GABAA receptor plasticity in adverse motivational responses and resistance to fluoxetine during adolescence.

Investigating interactions between phentermine, dexfenfluramine, and 5-HT2C agonists, on food intake in the rat

RATIONALE

Synergistic or supra-additive interactions between the anorectics (dex)fenfluramine and phentermine have been reported previously in the rat and in the clinic. Studies with 5-HT2C antagonists and 5-HT2C knockouts have demonstrated dexfenfluramine hypophagia in the rodent to be mediated by actions at the 5-HT2C receptor. Given the recent FDA approval of the selective 5-HT2C agonist lorcaserin (BELVIQ®) for weight management, we investigated the interaction between phentermine and 5-HT2C agonists on food intake.

OBJECTIVES

This study aims to confirm dexfenfluramine-phentermine (dex-phen) synergy in a rat food intake assay, to extend these findings to other 5-HT2C agonists, and to determine whether pharmacokinetic interactions could explain synergistic findings with particular drug combinations.

METHODS

Isobolographic analyses were performed in which phentermine was paired with either dexfenfluramine, the 5-HT2C agonist AR630, or the 5-HT2C agonist lorcaserin, and inhibition of food intake measured in the rat. Subsequent studies assessed these same phentermine-drug pair combinations spanning both the full effect range and a range of fixed ratio drug combinations. Satellite groups received single doses of each drug either alone or in combination with phentermine, and free brain concentrations were measured.

RESULTS

Dex-phen synergy was confirmed in the rat and extended to the 5-HT2C agonist AR630. In contrast, although some synergistic interactions between lorcaserin and phentermine were observed, these combinations were largely additive. Synergistic interactions between phentermine and dexfenfluramine or AR630 were accompanied by combination-induced increases in brain levels of phentermine.

CONCLUSIONS

Dex-phen synergy in the rat is caused by a pharmacokinetic interaction, resulting in increased central concentrations of phentermine.

Fluoxetine treatment of rat neonates significantly reduces oxidative stress in the hippocampus and in behavioral indicators of anxiety later in postnatal life

The brain, more than any other organ in the body, is vulnerable to oxidative stress damage, owing to its requirement for high levels of oxygenation. This is needed to fulfill its metabolic needs in the face of relatively low levels of protective antioxidants. Recent studies have suggested that oxidative stress is directly involved in the etiology of both eating and anxiety behavior. The aim of this study was to evaluate the effect of fluoxetine-inhibited serotonin reuptake in nursing rat neonates on behavior and on oxidative stress in the hypothalamus and the hippocampus; brain areas responsible for behavior related to food and anxiety, respectively. The results show that increased serotonin levels during a critical period of development do not induce significant differences in food-related behavior (intake and satiety), but do result in a in a significant decrease in anxiety. Measurements of oxidative stress showed a significant reduction of lipid peroxidation in the hippocampus (57%). In the hypothalamus, antioxidant enzymes were unchanged, but in the hippocampus, the activity of catalase and glutathione-S-transferase was increased (80% and 85% respectively). This suggests that protecting neural cells from oxidative stress during brain development contributes to the anxiolytic effects of serotonin.

Understanding synergy

Analysis of the interactive effects of combinations of hormones or other manipulations with qualitatively similar individual effects is an important topic in basic and clinical endocrinology as well as other branches of basic and clinical research related to integrative physiology. Functional, as opposed to mechanistic, analyses of interactions rely on the concept of synergy, which can be defined qualitatively as a cooperative action or quantitatively as a supra-additive effect according to some metric for the addition of different dose-effect curves. Unfortunately, dose-effect curve addition is far from straightforward; rather, it requires the development of an axiomatic mathematical theory. I review the mathematical soundness, face validity, and utility of the most frequently used approaches to supra-additive synergy. These criteria highlight serious problems in the two most common synergy approaches, response additivity and Loewe additivity, which is the basis of the isobole and related response surface approaches. I conclude that there is no adequate, generally applicable, supra-additive synergy metric appropriate for endocrinology or any other field of basic and clinical integrative physiology. I recommend that these metrics be abandoned in favor of the simpler definition of synergy as a cooperative, i.e., nonantagonistic, effect. This simple definition avoids mathematical difficulties, is easily applicable, meets regulatory requirements for combination therapy development, and suffices to advance phenomenological basic research to mechanistic studies of interactions and clinical combination therapy research.

Efeitos comportamentais e imunológicos da fluoxetina em ratos submetidos ao nado forçado

No presente trabalho, os efeitos comportamentais e imunomoduladores da fluoxetina foram avaliados num modelo animal de depressão, o nado forçado. Nesse, o comportamento de flutuar é sensível a antidepressivos e é usado como índice de desespero comportamental. Foram utilizados dois grupos experimentais, sendo um grupo controle tratado com salina e outro grupo teste tratado com a fluoxetina, ambos administrados por via intra-peritoneal. Os animais foram tratados três vezes ao dia por 12 dias. Adicionalmente, a resposta imune humoral a uma imunoestimulação (hemácias de carneiro) foi avaliada. A fluoxetina provocou aumento no tempo em flutuação, queda na massa corporal e menor produção total de anticorpos. Os resultados indicam uma modulação simultânea do comportamento e do sistema imunológico pela fluoxetina.

Novel selective antagonist of the cannabinoid CB1 receptor, MJ15, with prominent anti-obesity effect in rodent models

MJ15, a novel cannabinoid CB(1) receptor selective antagonist was discovered. In receptor binding assays, MJ15 displayed a high affinity for rat cannabinoid CB(1) receptor (K(i)=27.2 pM, and IC(50)=118.9 pM), but a much lower affinity for rat cannabinoid CB(2) receptor (only 46% inhibition at 10 microM). At the cellular level, the IC(50) values against activation of cannabinoid CB(1) and CB(2) receptors induced by Win55212-2 in specially designed EGFP-CB(1)_U2OS and EGFP-CB(2)_U2OS cells were 0.11 microM and >10 microM, respectively. In addition, MJ15 dose-dependently blocked Win55212-2 mediated increase of intracellular Ca(2+) levels in hippocampal cells and reversed the inhibitory effects of cannabinoid CB(1) receptor agonist on forskolin-stimulated adenylyl cyclase activity in CHO cells expressing the human cannabinoid CB(1) receptor. In animal experiments, MJ15 demonstrated remarkable effects from 20 to 40 mg/kg, including promoted the small intestine peristalsis in ICR mice and inhibited food intake and body weight increase in diet-induced obesity (DIO) rat and mouse. 40 mg/kg MJ15 significantly reduced food intake at initial 2 weeks of treatment, prevented the increase of body weight and adipose by 46% and 28% respectively in DIO rats, and reduced body weight and adipose gain by 70% and 23% respectively in early onset obesity DIO mice after 4 weeks treatment. Meanwhile, dyslipidemia were ameliorated in both models. Taken together the in vitro and in vivo data, MJ15 is demonstrated to be a potent and selective cannabinoid CB(1) receptor antagonist and holds a prominent potency in obesity and dyslipidemia treatment.

The development of tolerance to drugs that suppress food intake

Appetite suppressants have been available as weight-reducing aids for over 50 years. The first discovered was amphetamine, which was potent, but possessed undesirable side effects (it is a stimulant and elevates blood pressure). Subsequently, a variety of appetite drugs was developed, all structurally related to amphetamine, but mostly lacking unwanted side effects. Until recently, fenfluramine (FEN) was the most widely used; presently, sibutramine is the most commonly used appetite suppressant. While these appetite suppressants are effective at reducing hunger and food intake when given as a single dose or for short periods of time, their effectiveness diminishes when administered chronically. The biological mechanisms underlying this tolerance have not been carefully studied, but many possibilities have been identified, including the down-regulation in brain of neurotransmitter receptors that might mediate the action of these drugs and adaptive responses of the appetite control circuitry in brain. To date, however, few studies have examined these possibilities in any detail. This article focuses on the question of why appetite suppressants lose efficacy, when given chronically, because this issue is important to the development of the next generation of appetite suppressants. Chronic efficacy should be an issue studied relatively early in the drug development process. This issue is of particular relevance, since obesity treatment is now recognized as a long-term, not a short-term, process. If appetite suppressants are to become a more important tool in obesity treatment, agents that do not lose efficacy when administered for extended periods of time must be identified.

Psychological underpinnings of metabolic syndrome

Metabolic syndrome (MS) is more common among socio-economically disadvantaged individuals and is associated with certain risky lifestyle practices. MS also appears to be triggered by adverse social circumstances and chronic stress. The present paper reviews accumulating evidence to imply that individuals who have certain personality and behaviour traits are particularly predisposed to develop MS, and brings together theories that relate to possible psychological mechanisms underlying MS. It considers how such factors might interact causally to encourage the development of MS. As part of the EU-funded LIPGENE Integrated Project, multi-level modelling will be undertaken to explore potential pathways to MS, taking into consideration the interplay between a range of psycho-social, demographic, cultural and lifestyle factors thought to contribute to the development of MS. Data will be gathered for this purpose from a representative sample of >50-year-olds living in Britain (n 1000) and Portugal (n 500). It is anticipated that this information will assist in the development and targetting of future intervention to prevent and treat MS in the normal population.

The effects of dexfenfluramine administration on brain serotonin immunoreactivity and lipid peroxidation in mice

Obesity continues to be an increasing health problem in worldwide and antiobesity drugs have commonly been used by obese patients. During the use of anorectic drugs, the antioxidant defense may be affected, especially by reactive oxygen species. It was decided to investigate the effects of dexfenfluramine on body weight, daily food intake, brain thiobarbituric acid-reactive substances (TBARS), glutathione (GSH) and nitric oxide (NO) levels, and 5-HT immunoreactivity. Mice were divided into two groups each containing 8 Swiss Albino adult (6 months) mice. Group 1, untreated, was used as a control; group 2 was treated with dexfenfluramine 0.4 mg/kg per day intraperitoneally for 7 days. Brain TBARS and GSH levels were assayed spectrophotometrically. The stable end-products of NO, nitrite and nitrate, were analyzed spectrophotometrically. Brain tissue 5-HT immunoreactivity was observed using an immunohistochemical method. There were significant decreases in body weight in the dexfenfluramine group (p < 0.05). Although brain GSH and NO(x) levels decreased significantly, brain TBARS levels increased in the dexfenfluramine group (p < 0.05). Brain 5-HT immunoreactivity also increased in the dexfenfluramine-treated group compared to control. In conclusion, our findings show that dexfenfluramine is effective in achieving weight loss and also increases lipid peroxidation in mouse brain.

Effects of sibutramine on the appetitive and consummatory aspects of feeding in non-human primates

This study examined how sibutramine (0.06-4.0 mg/kg, i.m.), a clinically effective weight-loss medication which increases extracellular serotonin and norepinephrine levels, affected the appetitive and consummatory aspects of feeding of non-human primates. The effects were compared to the effects of the positive control dexfenfluramine (2.0-6.0 mg/kg, p.o.), which primarily increases extracellular serotonin levels. Baboons had access to food 24 h each day, but they had to complete a two-phase operant procedure in order to eat. Responding on one lever during a 30-min appetitive phase was required before animals could start a consumption phase, where responding on another lever led to food delivery, i.e., a meal. Responding during the appetitive phase resulted in presentations of food-related stimuli only. Sibutramine increased the latency to the first meal of the session in females, and decreased consummatory behavior without affecting other appetitive behavior in males and females. In contrast, dexfenfluramine, increased the latency to the first meal of the session, and decreased both appetitive and consummatory behavior in males and females. The behavioral mechanism by which sibutramine decreases food intake is distinct from other anorectic drugs, including dexfenfluramine, that have been tested in this paradigm.

Effects of dexfenfluramine on serotonin levels of mice ileum, contractility, glutathione and malondialdehyde level

Dexfenfluramine is one of the anorectic drugs that suppresses food intake which acts via inhibition of reuptake of serotonin into brain terminal. Gastrointestinal tract is the main source of peripheral serotonin which is involved in the regulation of gastrointestinal motility. During the use of anorectic drugs, the antioxidant defence is affected especially by reactive oxygen species. The purpose of this study to search: The effect of dexfenfluramine on serotonin levels of ileum and the effect of dexfenfluramine on ileal contractility and oxidative stress.

MATERIALS AND METHODS

Twenty-two adult male Swiss-albino mice were divided two groups (1) Control, (2) Dexfenfluramine treated (i.p. twice a day 0.2 mg kg(-1) in 0.2 ml saline solution for 7 days). Animal body weights were recorded at the beginning and at the end of the experimental period. Ileum tissues contractile responses to different concentrations of KCl and acethycholine were recorded on polygraph. In the meantime ileal tissue malondialdehyde, a product of lipid peroxidation, and glutathione, endogenous antioxidant levels were assessed by spectrophotometric methods. Ileal tissue serotonin level determined by immunohistochemical method. Body weights decrease and ileal contractile response of acethycholine increased significantly by dexfenfluramine treatment. Meanwhile, ileum glutathione levels decreased and malondialdehyde levels increased in dexfenfluramine treated group. Immunohistochemical detection showed that ileal serotonin levels increased by dexfenfluramine treatments. As a conclusion, there is a relationship between increased ileal contractility and oxidant status in dexfenfluramine treated animals. These effects can be related by increased serotonin levels which is induced by dexfenfluramine in ileum.

Chemo- and stereoselective synthesis of benzocycloheptene and 1-benzoxepin derivatives as α-sympathomimetic and anorexigenic agents

The synthesis and pharmacological evaluation of cis- and trans-6-amino-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ols 4a-c and 5a-c and cis- and trans-4-amino-2,3,4,5-tetrahydro-1-benzoxepin-5-ols 4d-f and 5d-f were carried out. Chemo- and stereoselective synthesis of 5a-f was achieved by reduction of corresponding alpha-amino ketones 3a-f with LiAl(t-BuO)3H. cis-4-Amino-2,3,4,5-tetrahydro-1-benzoxepin-5-ol 4d and trans-4-amino-2,3,4,5-tetrahydro-1-benzoxepin-5-ol 5d exhibited marked anorexigenic activity in mice at a dose of LD50 800 and 500 mg/kg and ED50 75 and 55 mg/kg, respectively, while the analog cis-2,3-dihydroxy-6-amino-6,7,8,9-tetrahydro-5H-benzocyclohepten-5-ol 8 showed typical alpha-sympathomimetic activity.

Relationship between anorexia and loss of serotonin uptake sites in brain of mice and rats receiving d-norfenfluramine or d-fenfluramine

Previously, we have shown that repeated administration of d-fenfluramine (D-F) to rats is associated with development of tolerance to the initial anorexia, but that in mice no such tolerance seems to occur. In the first study, we show that chronic administration of neither d-norfenfluramine (D-NF; the principal metabolite of D-F) nor the serotonin (5-HT) 2C receptor agonist m-chlorophenyl-piperazine (mCPP) is associated with the development of anorectic tolerance tested using a dessert protocol. However, compared with mice receiving these drugs for the first time, both of these chronic treatments were associated with a significant attenuation of Fos immunoreactivity (Fos-ir) in several brain regions, including bed nucleus of the stria terminalis, paraventricular hypothalamus, and central nucleus of amygdala. This attenuation is similar to that described previously in rats. Because loss of efficacy of these agents could be related to loss of 5-HT transporter (5-HTT) sites, their presumptive primary mode of action, in the final study we determined the effect of various, low-dose regimens of D-F and D-NF on 5-HT uptake in frontal cortex of mice and rats. We show in mice that D-F causes a greater loss of 5-HT uptake than D-NF, and that at the lowest dose regimen used uptake was unaffected in rats but was reduced in mice. The data are discussed in terms of the species difference in behavioral tolerance and differences in neurochemical profile of D-F and D-NF.