Dexfenfluramine. An updated review of its therapeutic use in the management of obesity

5-HT2C Receptor Stimulation in Obesity Treatment: Orthosteric Agonists vs. Allosteric Modulators

Obesity is a substantial health and economic issue, and serotonin (5-hydroxytryptamine, 5-HT) is an important neurotransmitter system involved in the regulation of body weight. The 5-HT2C receptors (5-HT2CRs), one of 16 of the 5-HT receptor (5-HTRs) subtypes, play a significant role in food intake and body weight control. In this review, we focused on the 5-HTR agonists, such as fenfluramines, sibutramine, and lorcaserin, which act directly or indirectly at 5-HT2CRs and have been introduced into the clinic as antiobesity medications. Due to their unwanted effects, they were withdrawn from the market. The 5-HT2CR positive allosteric modulators (PAMs) can be potentially safer active drugs than 5-HT2CR agonists. However, more in vivo validation of PAMs is required to fully determine if these drugs will be effective in obesity prevention and antiobesity pharmacology treatment. Methodology strategy: This review focuses on the role of 5-HT2CR agonism in obesity treatment, such as food intake regulation and weight gain. The literature was reviewed according to the review topic. We searched the PubMed and Scopus databases and Multidisciplinary Digital Publishing Institute open-access scientific journals using the following keyword search strategy depending on the chapter phrases: (1) “5-HT2C receptor” AND “food intake”, and (2) “5-HT2C receptor” AND “obesity” AND “respective agonists”, and (3) “5-HT2C receptor” AND “PAM”. We included preclinical studies (only present the weight loss effects) and double-blind, placebo-controlled, randomized clinical trials published since the 1975s (mostly related to antiobesity treatment), and excluded the pay-walled articles. After the search process, the authors selected, carefully screened, and reviewed appropriate papers. In total, 136 articles were included in this review.

The effect of ciprofloxacin on doxorubicin cytotoxic activity in the acquired resistance to doxorubicin in DU145 prostate carcinoma cells

The present study aimed to assess the influence of ciprofloxacin (CIP) against the doxorubicin (DOX)-resistant androgen-independent prostate cancer DU145 cells. The DOX-resistant DU145 (DU145/DOX20) cells were established by exposing DU145 cells to the increasing concentrations of DOX. The antiproliferative effect of CIP was examined through employing MTT, colony formation, and 3D culture assays. DU145/DOX20 cells exhibited a twofold higher IC₅₀ value for DOX, an increased ABCB1 transporter activity, and some morphological changes accompanied by a decrease in spheroid size, adhesive and migration potential compared to DU145 cells. CIP (5 and 25 µg mL^-1) resulted in a higher reduction in the viability of DU145/DOX20 cells than in DU145 cells. DU145/DOX20 cells were more resistant to CIP in 3D culture compared to the 2D one. No spheroid formation was observed for DU145/DOX20 cells treated with DOX and CIP combination. CIP and DOX, alone or in combination, significantly reduced the growth of DU145 spheroids. CIP in combination with 20 nM DOX prevented the colony formation of DU145 cells. The clonogenicity of DU145/DOX20 cells could not be estimated due to their low adhesive potential. CIP alone caused a significant reduction in the migration of DU145 cells and resulted in a more severe decrease in the wound closure ability of DOX-exposed ones. We identified that CIP enhanced DOX sensitivity in DU145 and DU145/DOX20 cells. This study suggested the co-delivery of low concentrations of CIP and DOX may be a promising strategy in treating the DOX-resistant and -sensitive hormone-refractory prostate cancer.

Social Experience Interacts with Serotonin to Affect Functional Connectivity in the Social Behavior Network following Playback of Social Vocalizations in Mice

Past social experience affects the circuitry responsible for producing and interpreting current behaviors. The social behavior network (SBN) is a candidate neural ensemble to investigate the consequences of early-life social isolation. The SBN interprets and produces social behaviors, such as vocalizations, through coordinated patterns of activity (functional connectivity) between its multiple nuclei. However, the SBN is relatively unexplored with respect to murine vocal processing. The serotonergic system is sensitive to past experience and innervates many nodes of the SBN; therefore, we tested whether serotonin signaling interacts with social experience to affect patterns of immediate early gene (IEG; cFos) induction in the male SBN following playback of social vocalizations. Male mice were separated into either social housing of three mice per cage or into isolated housing at 18-24 d postnatal. After 28-30 d in housing treatment, mice were parsed into one of three drug treatment groups: control, fenfluramine (FEN; increases available serotonin), or pCPA (depletes available serotonin) and exposed to a 60-min playback of female broadband vocalizations (BBVs). FEN generally increased the number of cFos-immunoreactive (-ir) neurons within the SBN, but effects were more pronounced in socially isolated mice. Despite a generalized increase in cFos immunoreactivity, isolated mice had reduced functional connectivity, clustering, and modularity compared with socially reared mice. These results are analogous to observations of functional dysconnectivity in persons with psychopathologies and suggests that early-life social isolation modulates serotonergic regulation of social networks.

Molecular bases of anorexia nervosa, bulimia nervosa and binge eating disorder: shedding light on the darkness

Eating-disorders (EDs) consequences to human health are devastating, involving social, mental, emotional, physical and life-threatening aspects, concluding on impairment and death in cases of extreme anorexia nervosa. It also implies that people suffering an ED need to find psychiatric and psychological help as soon as possible to achieve a fully physical and emotional recovery. Unfortunately, to date, there is a crucial lack of efficient clinical treatment to these disorders. In this review, we present an overview concerning the actual pharmacological and psychological treatments, the knowledge of cells, circuits, neuropeptides, neuromodulators and hormones in the human brain- and other organs- underlying these disorders, the studies in animal models and, finally, the genetic approaches devoted to face this challenge. We will also discuss the need for new perspectives, avenues and strategies to be developed in order to pave the way to novel and more efficient therapeutics.

A Guide to Medications Inducing Salivary Gland Dysfunction, Xerostomia, and Subjective Sialorrhea: A Systematic Review Sponsored by the World Workshop on Oral Medicine VI

BACKGROUND

Medication-induced salivary gland dysfunction (MISGD), xerostomia (sensation of oral dryness), and subjective sialorrhea cause significant morbidity and impair quality of life. However, no evidence-based lists of the medications that cause these disorders exist.

OBJECTIVE

Our objective was to compile a list of medications affecting salivary gland function and inducing xerostomia or subjective sialorrhea.

DATA SOURCES

Electronic databases were searched for relevant articles published until June 2013. Of 3867 screened records, 269 had an acceptable degree of relevance, quality of methodology, and strength of evidence. We found 56 chemical substances with a higher level of evidence and 50 with a moderate level of evidence of causing the above-mentioned disorders. At the first level of the Anatomical Therapeutic Chemical (ATC) classification system, 9 of 14 anatomical groups were represented, mainly the alimentary, cardiovascular, genitourinary, nervous, and respiratory systems. Management strategies include substitution or discontinuation of medications whenever possible, oral or systemic therapy with sialogogues, administration of saliva substitutes, and use of electro-stimulating devices.

LIMITATIONS

While xerostomia was a commonly reported outcome, objectively measured salivary flow rate was rarely reported. Moreover, xerostomia was mostly assessed as an adverse effect rather than the primary outcome of medication use. This study may not include some medications that could cause xerostomia when administered in conjunction with others or for which xerostomia as an adverse reaction has not been reported in the literature or was not detected in our search.

CONCLUSIONS

We compiled a comprehensive list of medications with documented effects on salivary gland function or symptoms that may assist practitioners in assessing patients who complain of dry mouth while taking medications. The list may also prove useful in helping practitioners anticipate adverse effects and consider alternative medications.

Adverse Drug Reactions in the Orofacial Region

A wide spectrum of drugs can sometimes give rise to numerous adverse orofacial manifestations, particularly dry mouth, taste disturbances, oral mucosal ulceration, and/or gingival swelling. There are few relevant randomized double-blind controlled studies in this field, and therefore this paper reviews the data from case reports, small series, and non-peer-reviewed reports of adverse drug reactions affecting the orofacial region (available from a MEDLINE search to April, 2003). The more common and significant adverse orofacial consequences of drug therapy are discussed.

Weight Loss After RYGB Is Independent of and Complementary to Serotonin 2C Receptor Signaling in Male Mice

Roux-en-Y gastric bypass (RYGB) typically leads to substantial, long-term weight loss (WL) and diabetes remission, although there is a wide variation in response to RYGB among individual patients. Defining the pathways through which RYGB works should aid in the development of less invasive anti-obesity treatments, whereas identifying weight-regulatory pathways unengaged by RYGB could facilitate the development of therapies that complement the beneficial effects of surgery. Activation of serotonin 2C receptors (5-HT2CR) by serotonergic drugs causes WL in humans and animal models. 5-HT2CR are located on neurons that activate the melanocortin-4 receptors, which are essential for WL after RYGB. We therefore sought to determine whether 5-HT2CR signaling is also essential for metabolic effects of RYGB or whether it is a potentially complementary pathway, the activation of which could extend the benefits of RYGB. Diet-induced obese male mice deficient for the 5-HT2CR and their wild-type littermates underwent RYGB or sham operation. Both groups lost similar amounts of weight after RYGB, demonstrating that the improved metabolic phenotype after RYGB is 5-HT2CR independent. Consistent with this hypothesis, wild-type RYGB-treated mice lost additional weight after the administration of the serotonergic drugs fenfluramine and meta-chlorophenylpiperazine but not the nonserotonergic agent topiramate. The fact that RYGB does not depend on 5-HT2CR signaling suggests that there are important WL mechanisms not fully engaged by surgery that could potentially be harnessed for medical treatment. These results suggest a rational basis for designing medical-surgical combination therapies to optimize clinical outcomes by exploiting complementary physiological mechanisms of action.

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.

Effect of fenfluramine on reinstatement of food seeking in female and male rats: implications for the predictive validity of the reinstatement model

RATIONALE AND OBJECTIVES

Relapse to old unhealthy eating habits while dieting is often provoked by stress or acute exposure to palatable foods. We adapted a rat reinstatement model, which is used to study drug relapse, to study mechanisms of relapse to palatable food seeking induced by food-pellet priming (non-contingent exposure to a small amount of food pellets) or injections of yohimbine (an alpha-2 adrenoceptor antagonist that causes stress-like responses in humans and non-humans). Here, we assessed the predictive validity of the food reinstatement model by studying the effects of fenfluramine, a serotonin releaser with known anorectic effects, on reinstatement of food seeking.

METHODS

We trained food-restricted female and male rats to lever-press for 45-mg food pellets (3-h sessions) and first assessed the effect of fenfluramine (0.75, 1.5, and 3.0 mg/kg, i.p.) on food-reinforced responding. Subsequently, we extinguished the food-reinforced responding and tested the effect of fenfluramine (1.5 and 3.0 mg/kg) on reinstatement of food seeking induced by yohimbine injections (2 mg/kg, i.p.) or pellet priming (four non-contingent pellets).

RESULTS

Fenfluramine decreased yohimbine- and pellet-priming-induced reinstatement. As expected, fenfluramine also decreased food-reinforced responding, but a control condition in which we assessed fenfluramine's effect on high-rate operant responding indicated that the drug's effect on reinstatement was not due to performance deficits.

CONCLUSIONS

The present data support the predictive validity of the food reinstatement model and suggest that this model could be used to identify medications for prevention of relapse induced by stress or acute exposure to palatable food during dietary treatments.

Pharmacogenetics and schizophrenia

The wide interindividual variability in clinical response and tolerability of antipsychotic medications has led investigators to postulate that these variabilities may be under genetic control. Although not always consistent, there are promising indications from emergent pharmacogenetic studies that efficacy of antipsychotic medications for the various symptom domains of psychopathology in schizophrenia may be genetically regulated. This is an encouraging approach. Moreover, there are also suggestive findings that the side-effect profiles of second-generation antipsychotic medications and their propensity to cause weight gain and glucose and lipid abnormalities as well as tardive dyskinesia may be related to pharmacogenetic factors in this patient population. Ultimately, such approaches could drive choices of antipsychotic medication based on the likelihood of clinical response and development of side effects in light of a particular patient's genetic profile. In the future, this targeted approach (personalized medicine) may become informative for clinicians choosing an antipsychotic medication for an individual patient with schizophrenia.

Opposing alterations in anxiety and species-typical behaviours in serotonin transporter overexpressor and knockout mice

Human gene association studies have produced conflicting findings regarding the relationship between the 5-HT transporter (5-HTT) and anxiety. In the present study genetically modified mice were utilised to examine the effects of changes in 5-HTT expression on anxiety. In addition, the influence of 5-HTT expression on two innate "species-typical" behaviours (burrowing and marble burying) and body weight was explored. Across a range of models, 5-HTT overexpressing mice displayed reduced anxiety-like behaviour whilst 5-HTT knockout mice showed increased anxiety-like behaviour, compared to wildtype controls. In tests of species-typical behaviour 5-HTT overexpressing mice showed some facilitation whilst 5-HTT knockout mice were impaired. Reciprocal effects were also seen on body weight, as 5-HTT overexpressors were lighter and 5-HTT knockouts were heavier than wildtype controls. These findings show that variation in 5-HTT gene expression produces robust changes in anxiety and species-typical behaviour. Furthermore, the data add further support to findings that variation of 5-HTT expression in the human population is linked to changes in anxiety-related personality traits.

Pharmacogenetics of antipsychotic-induced side effects

Currently available antipsychotic drugs (APDs) carry significant, though highly variable, liability to neurologic and metabolic side effects. Pharmacogenetics approaches offer the possibility of identifying patient-specific biomarkers for predicting risk of these side effects. To date, a few single nucleotide polymorphisms (SNPs) in a handful of genes have received convergent support across multiple studies. The primary focus has been on SNPs in dopamine and serotonin receptor genes: persuasive meta-analytic evidence exists for an effect of the dopamine D2 and D3 receptor genes (DRD2 and DRD3) in risk for tardr inesia (TD) and for an effect of variation at the receptor gene (HTR2C) for liability to APD-inducec gain. However, effect sizes appear to be modest, and pharmacoeconomic considerations have not been sufficiently studied, thereby limiting clinical applicability at this time. Effects of these genes and others on risk for TD, extrapyramidal side effects, hyperprolactinemia, and weight gain are revieved in this article.

Glucagon-like peptide 1 (7-36) amide (GLP-1) and exendin-4 stimulate serotonin release in rat hypothalamus

Glucagon-like peptide 1 (7-36) amide (GLP-1) and exendin-4 are gastrointestinal hormones as well as neuropeptides involved in glucose homeostasis and feeding regulation, both peripherally and at the central nervous system (CNS), acting through the same GLP-1 receptor. Aminergic neurotransmitters play a role in the modulation of feeding in the hypothalamus and we have previously found that peripheral hormones and neuropeptides, which are known to modulate feeding in the central nervous system, are able to modify catecholamine and serotonin release in the hypothalamus. In the present paper we have evaluated the effects of GLP-1 and exendin-4 on dopamine, norepinephrine, and serotonin release from rat hypothalamic synaptosomes, in vitro. We found that glucagon-like peptide 1 (7-36) amide and exendin-4 did not modify either basal or depolarization-induced dopamine and norepinephrine release; on the other hand glucagon-like peptide 1 (7-36) amide and exendin-4 stimulated serotonin release, in a dose dependent manner. We can conclude that the central anorectic effects of GLP-1 agonists could be partially mediated by increased serotonin release in the hypothalamus, leaving the catecholamine release unaffected.

Synergistic impairment of glucose homeostasis in ob/ob mice lacking functional serotonin 2C receptors

To investigate how serotonin and leptin interact in the regulation of energy balance and glucose homeostasis, we generated a genetic mouse model, the OB2C mouse, which lacks functional serotonin 2C receptors and the adipocyte hormone leptin. The OB2C mice exhibited a dramatic diabetes phenotype, evidenced by a synergistic increase in serum glucose levels and water intake. The severity of the animals' diabetes phenotype would not have been predicted from the phenotypic characterization of mice bearing mutations of either the leptin (OB mutant mice) or the serotonin 2C receptor gene (2C mutant mice). The synergistic impairment in glucose homeostasis developed at an age when OB2C mice did not differ in body weight from OB mice, suggesting that this impairment was not an indirect consequence of increased adiposity. We also demonstrated that the improvement in glucose tolerance in wild-type mice treated with the serotonin releaser and reuptake inhibitor fenfluramine was blunted in 2C mutant mice. These pharmacological and genetic findings provide evidence that the serotonin 2C receptor has direct effects on glucose homeostasis.

The synthesis and biological activity of pentafluorosulfanyl analogs of fluoxetine, fenfluramine, and norfenfluramine

The trifluoromethyl group of fluoxetine 1 and fenfluramine and norfenfluramine, 2 and 3, was substituted by the pentafluorosulfanyl group. On examination of the efficacy of the pentafluorosulfanyl containing compounds as inhibitors of 5-hydroxytryptamine receptors, it was found that substitution could lead to enhanced selectivity and in the case of the pentafluorosulfanyl analog of fenfluramine, 18, it significantly enhanced potency against the 5-HT(2b), 5-HT(2c), and 5-HT(6) receptors.

Pharmacogenetics and schizophrenia

Emergent pharmacogenetic studies indicate that the efficacy of antipsychotic medications in schizophrenia may be predicted through genetic analysis. There also is evidence that the side-effect profiles of second-generation antipsychotic medications and their propensity to cause weight gain, glucose and lipid abnormalities, and tardive dyskinesia may be predicted by pharmacogenetic analysis in this patient population. In the future, this targeted approach with the choice of antipsychotic medication based on the likelihood of clinical response and development of side effects in light of a particular patient's genetic status may gain hold as new treatments are developed with even fewer side effects.

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.

Safety of drug therapies used for weight loss and treatment of obesity

Some of the medications used for weight loss in the management of obesity have been associated with unacceptable morbidity and mortality. Safety concerns have led to the withdrawal of aminorex, followed by the fenfluramines in 1997, and phenylpropanolamine (norephedrine) in 2000. Aminorex was associated with an increased prevalence of primary pulmonary hypertension (PPH), fenfluramines with an increased prevalence of PPH and valvulopathy, and phenylpropanolamine with an increased risk of haemorrhagic stroke. Several studies have investigated the safety of the fenfluramines, yet the benefit-risk profile has not been conclusively quantified. This is due to several deficiencies in the published studies, including a lack of data on the baseline prevalences of comorbid conditions in obese subjects, and potential confounders and biases in the study designs. Although several studies and systematic reviews support an increased risk of PPH and valvulopathy in patients who have taken fenfluramines, without knowledge of the background prevalence it is not possible to determine if the exposure preceded the outcome. The population at higher risk of these adverse effects includes those taking higher doses or with a longer duration of exposure to fenfluramines and those with pre-existing cardiac disease or a genetic predisposition. Patients exposed to fenfluramines continue to be monitored, with some follow-up studies indicating no overall worsening in valvulopathy over time. There are limited efficacy and safety data for amfepramone (diethylpropion) and phentermine and their approval for the management of obesity is limited to short-term use. Orlistat and sibutramine are the only currently approved medications for long-term management of obesity. Although the benefit-risk profiles of sibutramine and orlistat appear positive, sibutramine continues to be monitored because of long-term safety concerns. The safety and efficacy of currently approved drug therapies have not been evaluated in children and elderly patient populations and there is limited information in adolescents, whilst the long-term safety of current and potential new drug therapies in adults will require several years of postmarketing surveillance to fully elucidate their adverse effect profiles.

Pharmacotherapy for obesity

Pharmacotherapy for the management of obesity is primarily aimed at weight loss, weight loss maintenance and risk reduction, and has included thyroid hormone, amphetamines, phentermine, amfepramone (diethylpropion), phenylpropanolamine, mazindol, fenfluramines and, more recently, sibutramine and orlistat. These agents decrease appetite, reduce absorption of fat or increase energy expenditure. Primary endpoints used to evaluate anti-obesity drugs most frequently include mean weight loss, percentage weight loss and proportion of patients losing >or=5% and >or=10% of initial bodyweight. Secondary endpoints may include reduction in body fat, risk factors for cardiovascular disease and the incidences of diseases such as diabetes mellitus. Most pharmacotherapies have demonstrated significantly greater weight loss in patients on active treatment than those receiving placebo in short-term (<or=1 year) randomised controlled trials of pharmacological treatment in conjunction with a calorie-controlled diet or lifestyle intervention. The evidence of long-term efficacy is limited to sibutramine (2 years) and orlistat (4 years). These are the only drugs currently approved for the long-term management of obesity in adults. Sibutramine recipients randomised following 6 months' treatment to either sibutramine or placebo demonstrated significantly better weight maintenance at 2 years than those taking placebo (p<0.001), with >or=10% loss of initial bodyweight in 46% of patients. For patients taking orlistat, weight loss was 2.2 kg greater than those on placebo at 4 years (p<0.001), with significantly more patients achieving >or=10% loss of initial bodyweight (26.2% and 15.6%, respectively; p<0.001). Other drugs that have been evaluated for weight loss include ephedrine, the antidepressants fluoxetine and bupropion, and the antiepileptics topiramate and zonisamide. Two clinical trials with fluoxetine both reported no significant difference in weight loss compared with placebo at 52 weeks. Clinical trials evaluating ephedrine, bupropion, topiramate and zonisamide have demonstrated significantly greater weight loss than placebo but have been limited to 16-26 weeks' treatment. A major obstacle to the evaluation of the clinical trials is the potential bias resulting from low study completion rates. Completion rates varied from 52.8% of phentermine recipients in a 9-month study, to 40% of fenfluramine recipients in a 24-week comparative study with phentermine and 18% of amfepramone recipients in a 24-week study. One-year completion rates range from 51% to 73% for sibutramine and from 66% to 85% for orlistat. Other potential sources of bias include run-in periods and subsequent patient selection based on compliance or initial weight loss. Several potential new therapies targeting weight loss and obesity through the CNS pathways or peripheral adiposity signals are in early phase clinical trials. Over the next decade the drug treatment of obesity is likely to change significantly because of the availability of new pharmacotherapies to regulate eating behaviours, nutrient partitioning and/or energy expenditure.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Endocannabinoid Receptor Antagonists

Obesity has been described as a global epidemic. Its increasing prevalence is matched by growing costs, not only to the health of the individual, but also to the medical services required to treat a range of obesity-related diseases. In most instances, obesity is a product of progressively less energetic lifestyles and the over-consumption of readily available, palatable, and highly caloric foods. Past decades have seen massive investment in the search for effective anti-obesity therapies, so far with limited success. An important part of the process of developing new pharmacologic treatments for obesity lies in improving our understanding of the psychologic and physiologic processes that govern appetite and bodyweight regulation. Recent discoveries concerning the endogenous cannabinoids are beginning to give greater insight into these processes. Current research indicates that endocannabinoids may be key to the appetitive and consummatory aspects of eating motivation, possibly mediating the craving for and enjoyment of the most desired, most fattening foods. Additionally, endocannabinoids appear to modulate central and peripheral processes associated with fat and glucose metabolism. Selective cannabinoid receptor antagonists have been shown to suppress the motivation to eat, and preferentially reduce the consumption of palatable, energy-dense foods. Additionally, these agents act to reduce adiposity through metabolic mechanisms that are independent of changes in food intake. Given the current state of evidence, we conclude that the endocannabinoids represent an exciting target for new anti-obesity therapies.

Body weight and abdominal fat gene expression profile in response to a novel hydroxycitric acid-based dietary supplement

Obesity is a global public health problem, with about 315 million people worldwide estimated to fall into the WHO-defined obesity categories. Traditional herbal medicines may have some potential in managing obesity. Botanical dietary supplements often contain complex mixtures of phytochemicals that have additive or synergistic interactions. The dried fruit rind of Garcinia cambogia, also known as Malabar tamarind, is a unique source of (-)-hydroxycitric acid (HCA), which exhibits a distinct sour taste and has been safely used for centuries in Southeastern Asia to make meals more filling. Recently it has been demonstrated that HCA-SX or Super Citrimax, a novel derivative of HCA, is safe when taken orally and that HCA-SX is bioavailable in the human plasma as studied by GC-MS. Although HCA-SX has been observed to be conditionally effective in weight management in experimental animals as well as in humans, its mechanism of action remains to be understood. We sought to determine the effects of low-dose oral HCA-SX on the body weight and abdominal fat gene expression profile of Sprague-Dawley rats. We observed that at doses relevant for human consumption dietary HCA-SX significantly contained body weight growth. This response was associated with lowered abdominal fat leptin expression while plasma leptin levels remained unaffected. Repeated high-density microarray analysis of 9960 genes and ESTs present in the fat tissue identified a small set (approximately 1% of all genes screened) of specific genes sensitive to dietary HCA-SX. Other genes, including vital genes transcribing for mitochondrial/nuclear proteins and which are necessary for fundamental support of the tissue, were not affected by HCA-SX. Under the current experimental conditions, HCA-SX proved to be effective in restricting body weight gain in adult rats. Functional characterization of HCA-SX-sensitive genes revealed that upregulation of genes encoding serotonin receptors represent a distinct effect of dietary HCA-SX supplementation.

The effect of the anorectic agent, d-fenfluramine, and its primary metabolite, d-norfenfluramine, on intact human platelet serotonin uptake and efflux

Dexfenfluramine, a drug formerly prescribed for treatment of obesity, caused heart valve damage and pulmonary hypertension in some people. The cause of the toxicity has not been defined, but 5-HT has been implicated. The objective of this study was to evaluate the effect of the anorectic agent, d-fenfluramine, and its major metabolite, d-norfenfluramine, on intact human platelet serotonin (5-HT) transport in vitro. The effects of d-fenfluramine and d-norfenfluramine on platelet uptake and efflux of 3H-5-HT were measured in buffer at pH 6.7, to optimize serotonin transporter (SERT) function, and at pH 7.4. Uptake of 3H-5-HT at pH 6.7 and 7.4 was inhibited by both agents at micro m concentrations (IC50, d-fenfluramine approximately 3 microM; d-norfenfluramine approximately 10 microM). However, no efflux of 3H-5-HT from labeled platelets at either pH 6.7 or 7.4 occurred at similar concentrations of d-fenfluramine or d-norfenfluramine. With inhibition of platelet dense granule 3H-5-HT uptake by reserpine, efflux of 3H-5-HT was observed at pH 6, but not at pH 7.4. Fluoxetine, a SERT inhibitor, was a more potent inhibitor of uptake (IC50 0.05 microM) than d-fenfluramine, but the anorectic agent, phentermine, had no effect. Therefore, d-fenfluramine and d-norfenfluramine inhibit human platelet uptake of 5-HT in vitro at tissue concentrations attainable in vivo, but they do not stimulate 5-HT efflux due to dense granule sequestration. Inhibition of platelet 5-HT uptake may play a role in the cardiopulmonary toxicity of d-fenfluramine, but other factors probably contribute, since similar toxicity has not been observed with fluoxetine.

Herbal preparations for obesity: are they useful?

The opportunities for additional research in this area are plentiful. Unfortunately, there has been relatively limited funding for research on herbal supplements compared with the amount of funding that is available for research on pharmaceuticals. Botanical dietary supplements often contain complex mixtures of phytochemicals that have additive or synergistic interactions. For example, the tea catechins include a group of related compounds with effects that are demonstrable beyond those that are seen with epigallocatechin gallate, the most potent catechin. The metabolism of families of related compounds may be different than the metabolism of purified crystallized compounds. In some cases, herbal medicines may simply be less purified forms of single active ingredients, but in other cases they represent unique formulations of multiple, related compounds that may have superior safety and efficacy compared with single ingredients. Obesity is a global epidemic, and traditional herbal medicines may have more acceptance than prescription drugs in many cultures with emerging epidemics of obesity. Several ethnobotanical studies found herbal treatments for diabetes, and similar surveys, termed bioprospecting, for obesity treatments may be productive. Beyond increasing thermogenesis, there are other biological rationales for the actions of several different alternative medical and herbal approaches to weight loss. For example, several supplements and herbs claim to result in nutrient partitioning so that ingested calories will be directed to muscle, rather than fat. These include an herb (Garcinia cambogia), and a lipid which is the product of bacterial metabolism (conjugated linoleic acid). Moreover, a series of approaches attempt to physically affect gastric satiety by filling the stomach. Fiber swells after ingestion and has was found to result in increased satiety. A binding resin (Chitosan) has the ability to precipitate fat in the laboratory and is touted for its ability to bind fat in the intestines so that it is not absorbed. In double-blind studies, however, this approach was found to be ineffective. There are two key attractions of alternative treatments to obese patients. First, they are viewed as being natural and are assumed by patients to be safer than prescription drugs. Second, there is no perceived need for professional assistance with these approaches. For obese individuals who cannot afford to see a physician, these approaches often represent a more accessible solution. Finally, for many others, these approaches represent alternatives to failed attempts at weight loss with the use of more conventional approaches. These consumers are often discouraged by previous failures, and are likely to combine approaches or use these supplements at doses higher than are recommended. It is vital that the primary care physician is aware of the herbal preparations that are being used by patients so that any potential interaction with prescription drugs or underlying medical conditions can be anticipated. Unfortunately, there have been several instances where unscrupulous profiteers have plundered the resources of the obese public. Although Americans spend $30 billion per year on weight loss aids, our regulatory and monitoring capability as a society are woefully inadequate. Without adequate resources, the FDA resorted to "guilt by association" adverse events reporting, which often results in the loss of potentially helpful therapies without adequate investigation of the real causes of the adverse events that are reported. Scientific investigations of herbal and alternative therapies represent a potentially important source for new discoveries in obesity treatment and prevention. Cooperative interactions in research between the Office of Dietary Supplements, the National Center for Complementary and Alternative Medicine, and the FDA could lead to major advances in research on the efficacy and safety of the most promising of these alternative approaches.

Drug effects on salivary glands: dry mouth

OBJECTIVE

To identify drugs associated with the complaint of dry mouth.

MATERIALS AND METHODS

MEDLINE was searched for papers 1980-2002 using keywords, oral, mouth, salivary, drugs, dry mouth and xerostomia, and relevant secondary references were hand-searched.

RESULTS

Evidence was forthcoming for a number of xerogenic drugs, especially antimuscarinic agents, some sympathomimetic agents, and agents affecting serotonin and noradrenaline uptake, as well as a miscellany of other drugs such as appetite suppressants, protease inhibitors and cytokines.

CONCLUSION

Dry mouth has a variety of possible causes but drugs--especially those with anticholinergic activity against the M3 muscarinic receptor--are the most common cause of reduced salivation.

Effect of repeated administration of dexfenfluramine on feeding and brain Fos in mice

The present study examines whether repeated administration of dexfenfluramine (DFEN) to mice is associated with progressive attenuation of its anorectic action and induction of Fos-immunoreactivity (Fos-ir) in some brain regions, both known effects in rats. ICR:Cd-1 mice were adapted to receiving for 30 min daily a sweetened milk gelatin dessert in addition to ad libitum access to chow. Mice were then injected with either DFEN (5-10 mg/kg) or saline vehicle every other day. These doses of DFEN acutely suppressed intake by approximately 50% and this action was sustained for at least eight injections. The anorectic effect of DFEN was no different between drug-naïve and DFEN-pretreated mice under conditions that produce complete tolerance in rats. In addition, unlike in rats, the acute anorectic effect of m-chlorophenylpiperazine (mCPP) was unaffected by prior DFEN treatment. Mice were perfused after the intake test on the final experimental day and their brain processed for Fos-ir. DFEN induced Fos-ir in brain regions analogous to those reported in rats and, also, as in rats, DFEN pretreatments reduced substantially the Fos-ir induced by acute DFEN in regions including central nucleus of amygdala, bed nucleus of stria terminalis, and the paraventricular hypothalamus (magno- and parvocellular divisions; PVN). Thus, while DFEN pretreatments reduce the effects of DFEN in many brain regions in both rats and mice, mice are unlike rats insofar as there is no tolerance to the anorectic action, at least in the nondeprivation protocol used here.

Pharmacotherapy of obesity

The growing recognition of the health risks of obesity coupled with the difficulties in treating it successfully by lifestyle modification predicates a need for effective drug treatment. The history of drug treatment in the second half of the 20th century is, however, one of disappointment and concern over drug toxicity. However, the advances in our understanding of the mechanism of weight control, together with improved ways of evaluating anti-obesity drugs, has resulted in two effective compounds, sibutramine and orlistat, becoming available for clinical use. Sibutramine has actions on both energy intake and expenditure and had been shown to enhance weight loss and weight maintenance achieved by diet, in simple obesity as well as when accompanied by complications of diabetes or hypertension. About 50-80% of patients can achieve a >5% loss, significantly more than if patients receive the same lifestyle intervention with placebo. Orlistat, which acts peripherally to block the absorption of dietary fat, has had similar results in clinical trials; a recent study (XENDOS) has just reported results which show that the enhanced, albeit modest, weight loss achieved with orlistat delays the development of diabetes over a 4-year period. A number of other compounds are expected to complete or enter clinical trials over the next decade. There is considerable optimism that we will soon have the pharmacological tools needed to make the treatment of obesity feasible.

Effects of ghrelin and amylin on dopamine, norepinephrine and serotonin release in the hypothalamus

Ghrelin and amylin are gut-derived hormones that stimulate and inhibit food intake, respectively. Feeding is modulated by aminergic neurotransmitters in the hypothalamus. We have evaluated the effects of ghrelin and amylin on dopamine, norepinephrine and serotonin release from rat hypothalamic synaptosomes. We found that ghrelin did not modify dopamine or norepinephrine release, but inhibited serotonin release. On the other hand, amylin inhibited dopamine release, without affecting norepinephrine or serotonin. We conclude that the appetite-stimulating activity of ghrelin could be mediated by inhibited serotonin release, while the anorectic effects of amylin could involve inhibited release of dopamine in the hypothalamus.

Therapeutic and adverse actions of serotonin transporter substrates

A variety of drugs release serotonin (5-HT, 5-hydroxytryptamine) from neurons by acting as substrates for 5-HT transporter (SERT) proteins. This review summarizes the neurochemical, therapeutic, and adverse actions of substrate-type 5-HT-releasing agents. The appetite suppressant (+/-)-fenfluramine is composed of (+) and (-) isomers, which are N-de-ethylated in the liver to yield the metabolites (+)- and (-)-norfenfluramine. Fenfluramines and norfenfluramines are potent 5-HT releasers. (+/-)-3,4-Methylenedioxymethamphetamine ((+/-)-MDMA, "ecstasy") and m-chlorophenylpiperazine (mCPP) are substrate-type 5-HT releasers. Fenfluramines, (+/-)-MDMA, and mCPP release neuronal 5-HT by a common non-exocytotic diffusion-exchange mechanism involving SERTs. (+)-Norfenfluramine is a potent 5-HT(2B) and 5-HT(2C) receptor agonist. The former activity may increase the risk of valvular heart disease, whereas the latter activity is implicated in the anorexic effect of systemic fenfluramine. Appetite suppressants that increase the risk for developing primary pulmonary hypertension (PPH) are all SERT substrates, but these drugs vary considerably in their propensity to increase this risk. For example, fenfluramine and aminorex are clearly linked to the occurrence of PPH, whereas other anorectics are not. Similarly, some SERT substrates deplete brain tissue 5-HT in animals (e.g., fenfluramine), while others do not (e.g., mCPP). In addition to the established indication of obesity, 5-HT releasers may help treat psychiatric disorders, such as drug and alcohol dependence, depression, and premenstrual syndrome. Viewed collectively, we believe new medications can be developed that selectively release 5-HT without increasing the risk for adverse effects of valvular heart disease, PPH, and neurotoxicity. Such agents may be useful for treating a variety of psychiatric disorders.

Pharmacological approaches for the treatment of obesity

The high incidence of obesity, its multifactorial nature, the complexity and lack of knowledge of the bodyweight control system, and the scarcity of adequate therapeutics have fuelled anti-obesity drug development during a considerable number of years. Irrespective of the efforts invested by researchers and companies, few products have reached a minimum level of effectiveness, and even fewer are available in medical practice. As a consequence of anti-obesity research, our knowledge of the bodyweight control system increased but, despite this, the pharmacological approaches to the treatment of obesity have not resulted yet in effective drugs. This review provides a panoramic of the multiple different approaches developed to obtain workable drugs. These approaches, however, rely in only four main lines of action: control of energy intake, mainly through modification of appetite;control of energy expenditure, essentially through the increase of thermogenesis;control of the availability of substrates to cells and tissues through hormonal and other metabolic factors controlling the fate of the available energy substrates; andcontrol of fat reserves through modulation of lipogenesis and lipolysis in white adipose tissue. A large proportion of current research is centred on neuropeptidic control of appetite, followed by the development of drugs controlling thermogenic mechanisms and analysis of the factors controlling adipocyte growth and fat storage. The adipocyte is also a fundamental source of metabolic signals, signals that can be intercepted, modulated and used to force the brain to adjust the mass of fat with the physiological means available. The large variety of different approaches used in the search for effective anti-obesity drugs show both the deep involvement of researchers on this field and the large amount of resources devoted to this problem by pharmaceutical companies. Future trends in anti-obesity drug research follow closely the approaches outlined; however, the increasing mass of information on the molecular basis of bodyweight control and obesity will in the end prevail in our search for effective and harmless anti-obesity drugs.

The discovery and status of sibutramine as an anti-obesity drug

Sibutramine is a serotonin-norepinephrine reuptake inhibitor indicated for the management of obesity in conjunction with a reduced calorie diet. Though sibutramine was originally evaluated for possible use as an antidepressant, its research development was eventually redirected to evaluate it as an anorexiant. The pharmacological mechanisms by which sibutramine exerts its weight loss effect are likely due to a combination of reduced appetite, feelings of satiety, and possibly the induction of thermogenesis. Its efficacy for inducing an initial weight-loss and the subsequent maintenance of the weight-loss is well proven in short- and long-term clinical trials of up to 2 years duration. In general, sibutramine has been well tolerated. Increases in blood pressure and heart rate are possible adverse effects that require regular monitoring. Sibutramine is one of the few established and well-proven agents for obesity available for use today and should be considered effective in the management of patients requiring pharmacotherapy as part of the multi-modal approach to weight-loss.

Serotonin releasing agents. Neurochemical, therapeutic and adverse effects

This review summarizes the neurochemical, therapeutic and adverse effects of serotonin (5-HT) releasing agents. The 5-HT releaser (plus minus)-fenfluramine is composed of two stereoisomers, (+)-fenfluramine and (minus sign)-fenfluramine, which are N-de-ethylated to yield the metabolites, (+)-norfenfluramine and (minus sign)-norfenfluramine. Fenfluramines and norfenfluramines are 5-HT transporter substrates and potent 5-HT releasers. Other 5-HT releasing agents include m-chlorophenylpiperazine (mCPP), a major metabolite of the antidepressant drug trazodone. Findings from in vitro and in vivo studies support the hypothesis that fenfluramines and mCPP release neuronal 5-HT via a non-exocytotic carrier-mediated exchange mechanism involving 5-HT transporters. (+)-Norfenfluramine is a potent 5-HT(2B) and 5-HT(2C) receptor agonist. The former activity may increase the risk of developing valvular heart disease (VHD), whereas the latter activity is implicated in the anorectic effect of systemic fenfluramine. Anorectic agents that increase the risk of developing primary pulmonary hypertension (PPH) share the common property of being 5-HT transporter substrates. However, these drugs vary considerably in their propensity to increase the risk of PPH. In this regard, neither trazodone nor mCPP is associated with PPH. Similarly, although some 5-HT substrates can deplete brain 5-HT (fenfluramine), others do not (mCPP). In addition to the established indication of obesity, 5-HT releasers may be helpful in treating psychiatric problems such as drug and alcohol dependence, depression and premenstrual syndrome. Viewed collectively, it seems possible to develop new medications that selectively release 5-HT without the adverse effects of PPH, VHD or neurotoxicity. Such agents may have utility in treating a variety of psychiatric disorders.

Intermittent, chronic fenfluramine administration to rats repeatedly suppresses food intake despite substantial brain serotonin reductions

The mechanisms by which fenfluramine suppresses food intake and body weight have been linked to its ability to enhance transmission across serotonin synapses in brain. This drug initially lowers body weight and suppresses food intake, yet after repeated administration food intake soon returns to normal and body weight no longer decreases. Fenfluramine also causes rapid and prolonged reductions in brain serotonin concentrations, which might account for its loss of appetite suppression. This possibility has been evaluated in rats by assessing if intermittent, chronic fenfluramine administration could suppress food intake during each treatment period, and if so, whether such an effect occurs in the presence of reduced brain serotonin levels. Rats were injected once daily with 10 mg/kg D,L-fenfluramine for 5 days, and then received no injections for the next 5 days. Control rats received only vehicle injections. This 10-day sequence was repeated five more times. During each period of fenfluramine administration, daily food intake dropped markedly the first 1-2 days of treatment, but returned to pretreatment values by day 5. Daily food intake was normal or slightly above normal during non-injection periods. Body weight dropped modestly during each period of fenfluramine administration, and rose during each subsequent period when injections had ceased. Serotonin concentrations and synthesis rates in several brain regions were markedly reduced at early, middle, and late periods of the experiment. Despite the long-term reduction in brain serotonin pools produced by fenfluramine, the drug continues to reduce food intake and body weight. Several possible interpretations of these findings are considered, based on the multiple mechanisms through which this drug has been proposed to modify synaptic serotonin transmission.

Studies on modulation of feeding behavior by atypical antipsychotics in female mice

The aim of this study was to examine the effects of different doses of typical antipsychotics, chlorpromazine (0.25-1 mg/kg) and haloperidol (0.25-1 mg/kg), and atypical antipsychotics, clozapine (0.5-2 mg/kg), olanzapine (0.25-1 mg/kg), risperidone (0.5-2 mg/kg), sulpiride (10-40 mg/kg) and dopamine D1 antagonist, SCH 23390 (0.25-1 mg/kg) on feeding behavior at different time intervals after acute administration. The study further investigated the central dopamine and serotonergic receptor involvement in clozapine-induced hyperphagia using SKF 38393, quinpirole and quipazine. Then, the authors also examined the effect of subchronic treatment for 21 days with fluoxetine on clozapine-induced hyperphagia and modulation of body weight and fat pad weights. The feeding behavior was assessed in nondeprived mice by presenting the palatable chow to different groups of mice in glass petri dishes and recording the food consumed at different time intervals. After acute administration, significant (P<.05) increase in food intake was observed at different time intervals with different doses of both typical and atypical antipsychotics. Further, clozapine-induced hyperphagia was significantly (P<.05) reversed after treatment with SKF 38393 (dopamine D1 agonist), quinpirole (dopamine D2 agonist) and quipazine (5-HT1B, 5-HT2 and 5-HT3 agonist). In subchronic study, treatment with fluoxetine (10 mg/kg) significantly (P<.05) antagonized the increase in body weight and food intake induced by clozapine (2 mg/kg). The current investigations underscore the reported increases in food intake and body weight gain observed with antipsychotics. The study further confirms the involvement of dopamine D1, D2 and serotonergic receptor involvement in clozapine-mediated hyperphagia. Further, the serotonergic agents may prove useful to counteract antipsychotic-induced obesity.

Effect of nonnicotine pharmacotherapy on smoking behavior

Smoking-related disease is the single biggest preventable cause of morbidity and mortality in the United States, yet approximately 25% of Americans continue to smoke. Various dosage forms of nicotine replacement therapy increase smoking quit rates relative to placebo, but they generally do not result in 1-year quit rates of over 20%. To increase these rates, a number of nonnicotine agents have been investigated. Drugs that modulate noradrenergic neurotransmission (bupropion, nortriptyline, moclobemide) are more effective than those affecting serotonin (selective serotonin reuptake inhibitors, buspirone, ondansetron) or other neurotransmitters.

Effects of cocaine- and amphetamine-regulated transcript peptide, leptin and orexins on hypothalamic serotonin release

We have studied the effects of cocaine- and amphetamine-regulated transcript (CART) peptide-(55-102), leptin, orexin-A and orexin-B on basal and depolarization (K(+) 15 mM)-induced serotonin (5-hydroxytryptamine, 5-HT) release from rat hypothalamic neuronal endings (synaptosomes) in vitro. We have found that leptin and CART peptide-(55-102) have no effect on 5-HT release, while orexin-A and orexin-B inhibit depolarization-stimulated serotonin release. We can conclude that leptin and CART peptide-(55-102), which play a physiological role as feeding inhibitors, do not acutely affect 5-HT release from hypothalamic synaptosomes; on the other hand, feeding induced by orexin-A and orexin-B could be partially explained by decreased 5-HT release.

[Monoaminergic anorectic agents]

Catecholamine, dopamine, serotonine (5HT) and neuronal histamine are anorectic monoamines and act as anorectic neurotransmitters. The anorectic agents as modulators of these monoamines inhibit appetite by activating release together with suppressing reuptake of those monoamines. The anorectic agents were classified in clinical use into either alpha 1, beta-adrenergic receptor agonists or 5HT-receptor agonist. Dexfenfluramine, a 5HT-receptor agonist, was inhibited in clinical use because of its cardiac complications including pulmonary hypertension and valvelar disease. Mazindol is an adrenergic agonist and the solitary anti-obesity drug used clinically in Japan. Sibutramine shows the effects of both beta-adrenergic and serotonergic receptor agonists. Sibutramine induces not only appetite suppression but also acceleration of peripheral energy expenditure. No histaminergic anorectics have been employed in the clinical situation to date. L-Histizine, precursor amino acid of endogenous neuronal histamine, is useful for suppression of food intake, lipolytic acceleration of peripheral adipose tissues and enhanced energy expenditure in both animals and humans. L-Histizine thus inspires development of more effective and safer anorectics that can be used without suffering from the rebound phenomenon of body weight.

Study of the brain serotonergic system with labeled alpha-methyl-L-tryptophan

alpha-Methyl-L-tryptophan (alpha-MTrp) is an artificial amino acid and an analog of tryptophan (Trp), the precursor of the neurotransmitter serotonin (5-HT). In this article we have summarized available data, which suggest that the measurement of the unidirectional uptake of alpha-MTrp and its conversion to 5-HT synthesis rates is a valid approach for the determination of brain 5-HT synthesis rates. The main feature on which the model is based is the trapping of labeled alpha-MTrp in brain tissue. An overview of opposing opinions, which suggest that there is a need for a metabolic conversion of tracer, is also presented and discussed critically. As with all biological modeling there is likely to be room for improvements of the proposed biological model. In addition, there are a limited number of clearly defined circumstances in which the method is confounded by the metabolism of labeled alpha-MTrp via the kynurenine pathway. Nonetheless, a significant body of evidence suggests that labeled alpha-MTrp is a useful tracer to study brain 5-HT synthesis in most circumstances. Calculation of 5-HT synthesis rates depends on the plasma-free tryptophan concentration, which, according to the balance of arguments in the literature, is a more appropriate parameter than the total-plasma tryptophan. The method, as proposed by us, can be used in conjunction with autoradiographic measurements in laboratory animals, and with positron emission tomography in large animals and humans. We review studies in animals looking at the normal control of 5-HT synthesis and the way in which it is altered by drugs, as well as initial studies investigating healthy humans and patients with neuropsychiatric disorders.

The safety and efficacy of pharmaceutical and herbal caffeine and ephedrine use as a weight loss agent

Since passage of the Dietary Supplement Health and Education Act of 1994, the sale of herbal dietary supplements containing caffeine and ephedrine for weight loss has become widespread in the United States. Reports of adverse events associated with the use of these non-prescription supplements have raised concerns in the United States regulatory community. Restricting the use of these products is now being considered. Such restriction should be based upon controlled clinical trials. This review of the literature in Medline relative to the use of caffeine and ephedrine in the treatment of obesity concludes that caffeine and ephedrine are effective in causing weight loss. Caffeine and ephedrine give equivalent weight loss to Diethylpropion and superior weight loss compared to dexfenfluramine. Caffeine and ephedrine have a long history of safe, non-prescription use. The adverse events accompanying acute dosing are mild and transient. Adverse events with caffeine and ephedrine reach and remain at placebo levels after 4-12 weeks of continuous treatment, but data from randomized trials up to 6 months only are available. Obesity is chronic, requires chronic treatment, its incidence is increasing and it has few effective treatments. The benefits of caffeine and ephedrine in treating obesity appear to outweigh the small associated risks. Restriction of dietary herbal supplements containing caffeine and ephedrine, often with other ingredients, should be based on controlled clinical trials of these products.

Lack of effect of HPA axis hyperactivity on hormonal responses to d-fenfluramine in major depressed patients: implications for pathogenesis of suicidal behaviour

There is evidence for inhibitory effects of adrenocorticosteroids on serotonergic (5-HT) activity. However, in depression the relationship between altered cortisol levels and brain 5-HT function remains to be clarified. The aim of this study was to investigate whether hypothalamic-pituitary-adrenal (HPA) axis hyperactivity is associated with 5-HT dysfunction in depressed patients, especially in those with suicidal behaviour. Cortisol levels following the dexamethasone suppression test (DST, 1 mg PO) and prolactin, corticotropin and cortisol responses to the d-fenfluramine test (d-FEN, 45 mg PO) - a specific 5-HT releaser/uptake inhibitor - were measured in 71 drug-free DSM-IV major depressed inpatients (40 with a history of suicide attempt, 31 without) and 34 hospitalized healthy control subjects. Depressed patients showed higher post-DST cortisol levels but similar responses to d-FEN compared with control subjects. Hormonal responses to d-FEN were not correlated with cortisol levels (basal or post-DST). Among the depressed patients, DST suppressors and DST nonsuppressors exhibited no significant difference in endocrine responses to d-FEN. However, patients with a history of suicide attempt, when compared with patients without such a history, showed lower hormonal responses to d-FEN but comparable basal and post-DST cortisol levels. Taken together these results suggest that, in depression, HPA axis hyperactivity is not responsible for the reduced 5-HT activity found in patients with a history of suicidal behavior.

Rapid clot formation and abnormal fibrin structure in a symptomatic patient taking fenfluramine--a case report

A 35-year-old woman experienced symptomatic calf pain while taking a combination of fenfluramine and phentermine. All symptoms resolved when the medications were stopped, but pain returned when fenfluramine was restarted. Laboratory evaluation revealed mild elevations of aspartate aminotransferase and lactate dehydrogenase and a remarkably shortened prothrombin time (6.3 seconds). Additional studies revealed that the clots were composed of very thin fibrin fibers. All laboratory abnormalities, including the abnormal fibrin structure, completely resolved when fenfluramin was stopped. Direct addition of fenfluramine or phentermine to normal plasma did not alter either coagulation kinetics or fibrin structure, supporting the concept that the induced changes may have originated at the hepatic level. Clots composed of thin fibers are much more resistant to fibrinolysis, and could potentially put such patients at risk for thrombotic complications. This is the first report of clotting abnormalities associated with fenfluramine use. Subsequent to its use in this patient, fenfluramine was removed from clinical use due to reports of acquired valvular heart disease.

Serotonergic and noradrenergic function in depression: clinical correlates

The present study was conducted in order to investigate the relationships between central noradrenergic (NA) and serotonergic (5-HT) function and clinical characteristics of a major depressive episode according to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. We measured growth hormone response (ΔGH) to clonidine (CLO) (an α2 NA agonist), as an index of central NA function, and prolactin response (APRL) to d-fenfluramine (d-FEN) (a specific 5-HT releaser/uptake inhibitor), as an index of central 5-HT function, in 53 medication-free depressed inpatients. On the basis of their CLO and d-FEN test responses, patients were classified into 4 groups. Group 1 (blunted ΔPRL_d-FEN alone [11 %]) was characterized by a recent violent suicide attempt, a high degree of medical damage, and mild anxiety. Group 2 (blunted ΔGH_CLO alone [32%]) was characterized by an absence of a history of suicide attempt and by severe anxiety. Group 3 (combination of blunted ΔGH_CLO and APRL_d-FEN [18%]) was characterized by a history of suicide attempts, total duration of the illness of over W years, age over 40 years, and more than 3 previous hospitalizations. Group 4 (no abnormality [39%]) had no specific clinical profile. These results suggest that, in depression, specific psychopathological features may be linked to 5-HT and/or NA dysfunction. However, our results also suggest that NA and/or 5-HT dysfunction are less likely to be the primary cause of mood disorders but are more indicative of failure of compensatory mechanisms involved in affective homeostatic processes.

Dexfenfluramine-induced contraction of human and rat isolated pulmonary arteries

Mechanisms of dexfenfluramine-induced vasoconstriction were studied in isolated pulmonary arteries suspended in organ baths for isometric tension recording. Dexfenfluramine (10(-7)-10(-4) M) caused concentration-dependent contractions in rat and human pulmonary arteries with and without endothelium. In pulmonary arteries of the rat, the response to dexfenfluramine was nearly abolished by treatment with the alpha-adrenoceptor antagonists, phentolamine (10(-6) M) or prazosin (10(-7) M). In human pulmonary arteries, the concentration-response curve to dexfenfluramine was unaltered by the presence of phentolamine (10(-6) M), prazosin (10(-7) M), ketanserin (10(-6) M), or indomethacin (3x10(-6) M). The results suggest that dexfenfluramine causes contraction of pulmonary vascular smooth muscle by multiple mechanisms, one of which involves activation of alpha-adrenoceptors within the blood vessel wall. The mechanisms by which dexfenfluramine causes pulmonary vasoconstriction may differ between rat and human pulmonary arteries.

Antiobesity pharmacotherapy in the management of type 2 diabetes

Obesity is a well-known risk factor for the development of Type 2 diabetes mellitus. The management of the obese diabetic patient remains a challenge for the clinician but, in any case, weight reduction should be considered as a key objective. In this respect, several antiobesity drugs have demonstrated potential. However, while fenfluramine and dexfenfluramine have been shown to promote weight loss and to directly improve insulin sensitivity, being two mechanisms contributing to better blood glucose control in obese Type 2 diabetic patients, they were recently withdrawn due to safety problems. Sibutramine, a new selective norepinephrine and serotonin reuptake inhibitor, promotes weight loss by decreasing food intake, an effect which leads to a mild improvement (significant in patients losing > or =5% of initial body weight) of blood glucose control in obese diabetic patients. Similarly, orlistat, a selective gastrointestinal lipase inhibitor which increases faecal fat losses, enhances diet-induced weight reduction and improves both blood glucose control and vascular risk profile, especially dyslipidaemia, in obese Type 2 diabetic patients. Further studies are required to better identify good responders to pharmacotherapy and specify the role of antiobesity agents in the overall long-term management of obese subjects with Type 2 diabetes. Other novel pharmacological approaches deserve further consideration, for instance beta-3 agonists aiming to increase energy expenditure, drugs interfering with tumor necrosis factor-alpha (TNF-alpha) or free fatty acid release by the adipose tissue or agents that slow gastric emptying. However, until now, results regarding efficacy and/or safety have been disappointing or preliminary in humans.