Sibutramine: a novel new agent for obesity treatment

Differential regulation of metabolic parameters by energy deficit and hunger

AIMS

Hypocaloric diet decreases both energy expenditure (EE) and respiratory exchange rate (RER), affecting the efficacy of dieting inversely. Energy deficit and hunger may be modulated separately both in human and animal studies by drug treatment or food restriction. Thus it is important to separate the effects of energy deficit and hunger on EE and RER.

METHODS

Three parallel and analogous experiments were performed using three pharmacologically distinct anorectic drugs: rimonabant, sibutramine and tramadol. Metabolic parameters of vehicle- and drug-treated and pair-fed diet-induced obese mice from the three experiments underwent common statistical analysis to identify effects independent of the mechanisms of action. Diet-induced obesity (DIO) test of tramadol was also performed to examine its anti-obesity efficacy.

RESULTS

RER was decreased similarly by drug treatments and paired feeding throughout the experiment irrespective of the cause of reduced food intake. Contrarily, during the passive phase, EE was decreased more by paired feeding than by both vehicle and drug treatment irrespective of the drug used. In the active phase, EE was influenced by the pharmacological mechanisms of action. Tramadol decreased body weight in the DIO test.

CONCLUSIONS

Our results suggest that RER is mainly affected by the actual state of energy balance; conversely, EE is rather influenced by hunger. Therefore, pharmacological medications that decrease hunger may enhance the efficacy of a hypocaloric diet by maintaining metabolic rate. Furthermore, our results yield the proposal that effects of anorectic drugs on EE and RER should be determined compared to vehicle and pair-fed groups, respectively, in animal models.

Rapid screening and structural elucidation of a novel sibutramine analogue in a weight loss supplement: 11-desisobutyl-11-benzylsibutramine

A novel analogue of sibutramine, 11-desisobutyl-11-benzylsibutramine, has been discovered. During routine ion mobility spectrometry (IMS) screening of a weight loss supplement collected at an US FDA import operation facility an unknown peak was observed. Further analysis of the supplement by liquid chromatography-mass spectrometry (LC-MS) and high resolution mass spectrometry revealed an unknown peak with a relative retention time of 1.04 with respect to sibutramine and a predicted formula of C20H24NCl. In order to elucidate the analogue's structure, it was isolated from the supplement and characterized by tandem mass spectrometry and nuclear magnetic resonance (NMR), which revealed the analogue possessed a benzyl moiety at the 11 position in place of the isobutyl group associated with sibutramine.

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

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

The anorexic agents, sibutramine and fenfluramine, depress GABA(B)-induced inhibitory postsynaptic potentials in rat mesencephalic dopaminergic cells

BACKGROUND AND PURPOSE

Nutrition is the result of a complex interaction among environmental, homeostatic and reward-related processes. Accumulating evidence supports key roles for the dopaminergic neurons of the ventral midbrain in regulating feeding behaviour. For this reason, in the present study, we have investigated the electrophysiological effects of two centrally acting anorexic agents, fenfluramine and sibutramine, on these cells.

EXPERIMENTAL APPROACH

Rat midbrain slices were used to make intracellular recordings from dopaminergic neurons of the substantia nigra and the ventral tegmental area. Gamma-aminobutyric acid (GABA)-mediated synaptic transmission was assessed from the inhibitory postsynaptic potentials (IPSPs) mediated by GABA(A) and GABA(B) receptors.

KEY RESULTS

Fenfluramine and sibutramine reduced, concentration-dependently, the GABA(B) IPSPs, without affecting the GABA(A)-mediated potentials. This effect is presynaptic, as postsynaptic membrane responses induced by application of a GABA(B) receptor agonist, baclofen, were not affected by the two drugs. Furthermore, the selective 5-hydroxytriptamine 1B (5-HT(1B)) receptor antagonist, SB216641, blocked the reduction of GABA(B) IPSPs caused by fenfluramine and sibutramine, indicating that the receptor mediating this effect is 5-HT(1B).

CONCLUSIONS AND IMPLICATIONS

Two anorexic agents, fenfluramine and sibutramine, induced the activation of 5-HT(1B) receptors located on presynaptic GABAergic terminals, thus reducing the release of GABA. This action can alter the strength of synaptic afferents that modify the activity of dopaminergic neurons, inducing neuronal excitation. Our results reveal an additional mechanism of action for fenfluramine and sibutramine that might contribute to reducing food intake, by influencing the pleasurable and motor aspects of feeding behaviour.

Prevention and treatment of pediatric obesity: an endocrine society clinical practice guideline based on expert opinion

OBJECTIVE

Our objective was to formulate practice guidelines for the treatment and prevention of pediatric obesity.

CONCLUSIONS

We recommend defining overweight as body mass index (BMI) in at least the 85th percentile but < the 95th percentile and obesity as BMI in at least the 95th percentile against routine endocrine studies unless the height velocity is attenuated or inappropriate for the family background or stage of puberty; referring patients to a geneticist if there is evidence of a genetic syndrome; evaluating for obesity-associated comorbidities in children with BMI in at least the 85th percentile; and prescribing and supporting intensive lifestyle (dietary, physical activity, and behavioral) modification as the prerequisite for any treatment. We suggest that pharmacotherapy (in combination with lifestyle modification) be considered in: 1) obese children only after failure of a formal program of intensive lifestyle modification; and 2) overweight children only if severe comorbidities persist despite intensive lifestyle modification, particularly in children with a strong family history of type 2 diabetes or premature cardiovascular disease. Pharmacotherapy should be provided only by clinicians who are experienced in the use of antiobesity agents and aware of the potential for adverse reactions. We suggest bariatric surgery for adolescents with BMI above 50 kg/m(2), or BMI above 40 kg/m(2) with severe comorbidities in whom lifestyle modifications and/or pharmacotherapy have failed. Candidates for surgery and their families must be psychologically stable and capable of adhering to lifestyle modifications. Access to experienced surgeons and sophisticated multidisciplinary teams who assess the benefits and risks of surgery is obligatory. We emphasize the prevention of obesity by recommending breast-feeding of infants for at least 6 months and advocating that schools provide for 60 min of moderate to vigorous daily exercise in all grades. We suggest that clinicians educate children and parents through anticipatory guidance about healthy dietary and activity habits, and we advocate for restricting the availability of unhealthy food choices in schools, policies to ban advertising unhealthy food choices to children, and community redesign to maximize opportunities for safe walking and bike riding to school, athletic activities, and neighborhood shopping.

Effects of sibutramine on gastric emptying, intestinal motility and rectal tone in dogs

The aim of this study was to evaluate the effects of sibutramine on gastric emptying, small-bowel contractions, rectal tone and compliance, and gastrointestinal myoelectrical activity. The study was performed in 14 dogs. It was composed of three separate experiments: gastric emptying of liquids and gastrointestinal slow waves; small-bowel contractions; and rectal tone and rectal compliance. Each experiment included two sessions: a control session and a treatment session with sibutramine (5 mg/kg orally) administrated 2 h before the study. Sibutramine significantly accelerated liquid gastric emptying at 75 and 90 min after the meal but did not alter gastrointestinal slow waves. Gastric emptying at 75 and 90 min was 61.42 +/- 7.71 and 66.32 +/- 7.67% in the control session, and increased to 71.27 +/- 5.14 and 75.93 +/- 5.29% in the session with sibutramine (p < 0.05, vs. control). Sibutramine significantly inhibited postprandial small-bowel contractions. Sibutramine did not alter the rectal tone, but significantly increased rectal compliance. Sibutramine accelerates gastric emptying of liquids but inhibits small-bowel contractions. These findings suggest the peripheral mechanisms of sibutramine in reducing food intake and causing weight loss in obesity patients.

Pediatric obesity: parallels with addiction and treatment recommendations

Rates of pediatric obesity have increased dramatically over the past decade. This trend is especially alarming because obesity is associated with significant medical and psychosocial consequences. It may contribute to cardiovascular, metabolic, and hepatic complications, as well as to psychiatric difficulties. The development of obesity appears to be influenced by a complex array of genetic, metabolic, and neural frameworks, along with behavior, eating habits, and physical activity. Numerous parallels exist between obesity and addictive behaviors, including genetic predisposition, personality, environmental risk factors, and common neurobiological pathways in the brain. Typical treatments for pediatric obesity include behavioral interventions targeting diet or exercise. These treatments have yielded mixed results and typically have been examined in specialty clinic populations, limiting their generalizability. There are limited medication options for overweight children and adolescents, and no approved medical intervention in children younger than 16 years old. Bariatric surgery may be an option for some adolescents, but due to the risks of surgery, it is often seen as a last resort. The parallels between addiction and obesity aid in developing novel interventions for pediatric obesity. Motivational enhancement and cognitive-behavioral strategies used in addiction treatment may prove to be beneficial.

Impact sibutramine therapy in children with hypothalamic obesity or obesity with aggravating syndromes

OBJECTIVE

Behavioral treatment of children suffering from hypothalamic obesity or uncomplicated obesity in combination with syndromes that aggravate this condition has proven to be ineffective. The combination of comorbidities and severe obesity lower the quality of these children's lives drastically. The present goal was to determine whether treatment with sibutramine has a beneficial effect on such children.

DESIGN AND SUBJECTS

A double-blind, placebo-controlled, cross-over study (20 + 20 wk), followed by a 6-month open phase, was performed. The primary indicator of efficacy was the body mass index (BMI) sd score (SDS) value, which was analyzed using an ANOVA repeated-measures design [intention to treat (ITT)]. The 50 children (7-20 yr of age) involved included 22 with hypothalamic obesity and 28 with uncomplicated obesity plus aggravating syndromes. Forty-five patients completed the first phase, and 42 participated in the entire study.

RESULTS

The group that initially received the placebo demonstrated an insignificant decrease (-0.06) in BMI SDS during this treatment but a significant decrease (-0.68; P < 0.001) when treated with sibutramine. The other group demonstrated a reduction in their BMI SDS of -0.72 during administration of sibutramine and a rebound of +0.43 when placed on the placebo (P < 0.001 in both cases). The response of children with hypothalamic obesity was also significant but was less pronounced than that of children with nonhypothalamic obesity. During the open phase, a continuous reduction in weight was observed. The treatment was tolerated well.

CONCLUSION

The clinically and statistically significant weight reduction caused by sibutramine in this short-term study indicates that treatment of hypothalamic and syndromal obesity with this drug may be beneficial.

Therapeutic options for modifying cardiometabolic risk factors

Excessive adipose tissue is associated with increased expression or suppression of cytokines and hormones, leading to inflammation and chronic disease. In particular, abdominal adiposity, as evidenced by a high waist circumference, is a component of the metabolic syndrome, a constellation of risk factors (e.g., high waist circumference, high blood pressure, elevated triglycerides, low high-density lipoprotein cholesterol, elevated fasting glucose) that increases the risk for type 2 diabetes and cardiovascular disease. Lifestyle modification is the first-line approach to the management of obesity and the metabolic syndrome. However, for patients who cannot achieve a reduction in weight (5% to 10% of initial body weight) and cardiometabolic risk factors with lifestyle modification alone, physicians should consider adjunctive long-term pharmacotherapy. A variety of approved and investigational pharmacologic agents have been shown to reduce weight and modify metabolic syndrome components, including sibutramine, orlistat, metformin, and rimonabant. Data from four phase 3 trials suggest that rimonabant, the first cannabinoid receptor inhibitor, modulates cardiometabolic risk factors, both through its impact on body weight and through direct pathways that are not related to weight loss.

Weight management for type 2 diabetes mellitus: global cardiovascular risk reduction

Most patients with type 2 diabetes mellitus are overweight or obese, and the relation between obesity, especially of the visceral compartment, and the risk for developing diabetes is well recognized. Excessive adipose tissue is associated with insulin resistance as well as the increased expression of proinflammatory cytokines and prothrombotic factors, all of which contribute to elevating the risk for coronary artery disease (CAD). In particular, abdominal obesity, or excess visceral adiposity, has been linked to a cluster of risk factors (high blood pressure, hypertriglyceridemia, low levels of high-density lipoprotein cholesterol, and impaired fasting glucose) that constitute the metabolic syndrome, the presence of which confers an increased risk for type 2 diabetes and cardiovascular disease. In fact, a large waist circumference, a surrogate measure of abdominal adiposity, is 1 of the main criteria for diagnosing the metabolic syndrome. Lifestyle modification is the first-line approach to the management of obesity and the metabolic syndrome. However, if patients are unable to achieve a weight loss of 5%-10% of initial body weight and improve cardiometabolic risk factors with lifestyle modification alone, physicians should consider using adjunctive long-term pharmacotherapy. A variety of approved and investigational pharmacologic agents, including sibutramine, orlistat, metformin, and rimonabant, have been shown to reduce weight and ameliorate metabolic syndrome components, thereby reducing cardiovascular risk. Such global risk reduction is crucial for patients with diabetes, in whom CAD is a major cause of mortality.

Comparison of combinations of drugs for treatment of obesity: body weight and echocardiographic status

BACKGROUND

Obesity treatment with single drugs produces weight losses of about 8-10% of initial body weight. Few studies of combinations of drugs for treating obesity have been published. The combination of phentermine, an adrenergic agent, and fenfluramine, a serotonergic agent, (phen-fen) produced weight losses of about 15% of initial body weight. Fenfluramine is no longer available because it was associated with cardiac valve lesions. Phentermine-fluoxetine (phen-flu) has been proposed as an alternative for phen-fen.

OBJECTIVE

To compare the efficacy of treatment and prevalence of cardiac valve abnormalities on phen-flu vs phen-fen.

DESIGN

Retrospective chart review of all patients treated for at least 3 months with phen-flu (N=97) to a random sample of patients treated with phen-fen (N=98) in the Clinical Nutrition Clinic at the University of Wisconsin. Comparison of echocardiograms in all patients treated solely with phen-flu (N=21) to a random sample of patients treated with phen-fen (N=47), and to a group of subjects never treated with obesity drugs (N=26).

RESULTS

With last observation carried forward analysis (LOCF), at 6 months of treatment the phen-fen patients lost 12.6+/-0.6% of baseline weight and phen-flu patients lost 9.0+/-0.6% (P<0.001). With completers analysis, there were no significant differences in weight loss as a percent of baseline weight at 6 months (14.4+/-0.6 vs 13.3+/-0.9%). LOCF decreases in body mass index (BMI) at 6 months were -5.3 and -3.6 kg/m(2) for phen-fen and phen-flu, respectively (P<0.001), and 6.2+/-0.3 vs 5.4+/-0.4 kg/m(2), respectively, for the completers analysis (P - NS). Dropout rate at 6 months was higher in phen-flu subjects (44 vs 28%). In subjects without atherosclerosis of valves (presumably pre-existing), cardiac valve lesions occurred in eight of 38 phen-fen subjects and in none of 15 phen-flu subjects or 25 control subjects who had not been treated with drugs.

CONCLUSIONS

The combination of phentermine and fluoxetine was not as effective as phen-fen, but was not associated with cardiac valve lesions. Longer term, larger scale studies of phen-flu are warranted.

Chronic 5-HT6 receptor modulation by E-6837 induces hypophagia and sustained weight loss in diet-induced obese rats

E-6837 is a novel, selective and high-affinity 5-HT(6) receptor ligand (pK(i): 9.13) which in vitro demonstrates partial agonism at a presumably silent rat 5-HT(6) receptor and full agonism at a constitutively active human 5-HT(6) receptor by monitoring the cAMP signaling pathway.The effects of chronic treatment with E-6837 were determined in diet-induced obese (DIO)-rats on changes in body weight, food and water intake, plasma indices of comorbid risk factors, and weight regain on compound withdrawal. The centrally acting antiobesity drug, sibutramine, was used as the reference comparator. Sustained body weight loss and decreased cumulative food intake of DIO-rats was observed with E-6837 (30 mg kg(-1), p.o., twice a day) during the 4-week treatment period. The onset of the E-6837 effect on body weight was slower than that of sibutramine (5 mg kg(-1), p.o.), while its maximal effect was greater, that is -15.7 versus -11.0%.E-6837-induced weight loss was exclusively mediated by a decrease (31.7%) in fat mass, with a concomitant reduction (49.6%) in plasma leptin. Reduced obesity was also reflected in improved glycemic control. Although weight regain occurred after withdrawal from either compound, the body weights after E-6837 (-6.6%) remained lower than after sibutramine (-3.8%) indicating that the greater efficacy of the former did not result in profound rebound hyperphagia/weight gain. These results show that the 5-HT(6) receptor partial agonist, E-6837, is a promising new approach to the management of obesity with the potential to produce greater sustained weight loss than sibutramine.

New drug policy in childhood obesity

OBJECTIVE

To update physicians, especially paediatricians, in the rapidly developing field of pharmacotherapy of childhood and adolescent obesity.

METHODS

The paper reviews current and investigational antiobesity drugs.

RESULTS

At present, there are only few drugs approved by the Food and Drug Administration (FDA) for the treatment of adult obesity. The most important ones are sibutramine and orlistat. The FDA in the USA approved the latter drug in 2003, and it has recently been approved by the European Union for the treatment of adolescents. There are several investigational antiobesity agents but only few new and promising substances like Rimonabant (a cannabinoid receptor antagonist) and axokine (ciliary neutrotrophic factor) are already at an advanced stage of development.

CONCLUSION

In adults, it seems to be justified using drugs for long-term treatment of 'medically important' obesity. Strict guidelines concerning the treatment of obese adolescents with orlistat are needed. It is only hoped that double-blind placebo-controlled studies investigating the new and promising drugs will also include adolescents and provide sufficient scientific data to get them licensed for the treatment of obese adolescents.

Emerging drugs for eating disorder treatment

Anorexia nervosa (AN), bulimia nervosa (BN) and binge eating disorder (BED) comprise the currently recognised eating disorders. Although distinct diagnostic entities, they share certain forms of comorbid psychopathology, particularly anxiety and mood disorders. BN and BED have been studied most intensively as targets for pharmacotherapy. The list of drugs tested in eating disorders is substantial; however, the number of therapeutic classes of medications tested in these conditions is relatively modest. Antidepressant medications, including tricyclic antidepressants, selective serotonin re-uptake inhibitors, as well as some of the novel antidepressants, have shown evidence of some therapeutic value in both BN and BED. Their efficacy in AN, however, has been disappointing. The pharmacological options for AN are very limited. The number of controlled trials that have been conducted is small, and the research that has been successfully completed has generally failed to demonstrate medication efficacy. Patients with BN typically show reduced binge eating and purging frequency in medication trials, but rarely attain abstinence. In BED, patients often measure the value of their medication therapy by its ability to stimulate weight loss, which is another area on which future pharmacotherapy may improve. Novel pharmacological interventions are needed for each of these conditions. Peptide hormones are increasingly being evaluated for eating disorder treatment, including ghrelin agonists, neuropeptide Y1 and -5 antagonists, orexin receptor antagonists, corticotropin-releasing factor receptor 2 antagonists, histamine 3 antagonists, melanocortin 4 receptor antagonists, beta3-adrenoceptor agonists, 5-hydroxytryptamine-2A antagonists and growth hormone agonists. Although these compounds are in early phases of clinical testing for eating disorder treatments, data from these studies will be instructive in the quest for effective pharmacotherapy for these conditions. An overview of the current pharmacotherapy options for eating disorders is presented with a discussion of the emerging potential treatments.

Combined dietary and pharmacological weight management in obese hypopituitary patients

OBJECTIVE

The high prevalence of obesity and cardiovascular risk factors in hypopituitarism affirms the need for effective weight loss intervention. In this study, we investigated the combined effect of sibutramine, diet, and exercise in obese hypopituitary patients (HPs).

RESEARCH METHODS AND PROCEDURES

In an open-label prospective intervention trial, 14 obese well-substituted nondiabetic HPs and 14 matched simple obese controls were allocated to 11-month treatment with sibutramine (10 to 15 mg), diet (600 kcal/d deficit), and exercise. Anthropometric indices and body composition (obtained from DXA scan) were assessed monthly for the first 5 months and thereafter every second month for the next 6 months.

RESULTS

Mean (+/-SD) weight loss at 11 months was 11.3 +/- 4.8 kg in patients vs. 10.7 +/- 4.7 kg in controls. The HPs exhibited the same improvements in body composition, waist circumference, blood lipids, and fasting glucose as the simple obese. In a multivariate model, baseline weight, duration of growth hormone replacement therapy, and duration of pituitary disease explained 79% (p = 0.001) of the variation in weight loss at 4 months in the HPs. Only baseline weight and waist circumference could predict weight loss at 11 months.

DISCUSSION

HPs are not resistant to weight loss therapy. Almost all will achieve at least 5% weight loss, and 60% can lose >10% weight within 11 months. However, the long-term effect on risk factors associated with type 2 diabetes and cardiovascular disease as well as on mortality needs to be established.

Sibutramine enhances insulin sensitivity ameliorating metabolic parameters in a double-blind, randomized, placebo-controlled trial

AIM

To assess the effect of sibutramine-assisted weight reduction program on insulin sensitivity and metabolic parameters in obese normal glucose tolerant individuals over a period of 24 weeks.

RESEARCH DESIGN AND METHODS

A double-blind, placebo-controlled, parallel, prospective clinical trial was carried out at our medical centre. Forty female normal glucose tolerant patients, body mass index: 34.3 +/- 2.9 kg/m2 and age: 41.1 +/- 9.9 (range: 19-58 years), were randomized to placebo or sibutramine, 10 mg once daily.

RESULTS

Seventeen patients from sibutramine group and 14 placebo had completed the study protocol. Significant weight change was seen in sibutramine (p < 0.01) (-5.6 kg or -6.1% vs. +0.9 kg or +1.1% in placebo). Insulin sensitivity enhanced in sibutramine group (Kitt: from 4.03 +/- 1.97 to 5.09 +/- 2.48%/min; p < 0.05). Homeostasis model assessment-IR (HOMA-IR) decreased from 7.8 +/- 6.9 to 5.6 +/- 4.5 (p < 0.05). HOMA-beta also decreased from 508 +/- 381 to 374 +/- 256 (p < 0.05). No changes were observed in the placebo control group regarding insulin sensitivity or secretion. Concomitant reductions were observed in the sibutramine group in lipid parameters (triglycerides and high-density lipoprotein-cholesterol), uric acid and gamma-glutamyl transferase (p < 0.05).

CONCLUSIONS

Sibutramine has demonstrated efficacy in reducing weight in non-diabetic women along with amelioration in insulin sensitivity and additional improvement in metabolic parameters.

Preferential effects of the cannabinoid CB1 receptor antagonist, SR 141716, on food intake and body weight gain of obese (fa/fa) compared to lean Zucker rats

RATIONALE

The selective CB(1) receptor antagonist, SR 141716, has been demonstrated to reduce food consumption in a range of animal species.

OBJECTIVE

To assess the effect of chronic administration of SR 141716 on body weight and ingestive behaviour of lean and obese (fa/fa) Zucker rats.

METHODS

Lean and obese Zucker rats were orally dosed with SR 141716 (3, 10, 30 mg/kg PO), sibutramine (5 mg/kg PO) or vehicle for one week. Pair-fed controls provided insight as to whether the effect of SR 141716 on body weight was attributable to drug-induced hypophagia. Subsequently, the effect of chronic oral administration of SR 141716 (1, 3, 10 mg/kg) was assessed for 28 days. At the end of this period, all animals were given vehicle for 14 days. The incidence of wet-dog shakes, yawning, scratching, and grooming behaviours, was assessed after acute administration and at weekly intervals thereafter for 4 weeks.

RESULTS

SR 141716 dose-dependently decreased food intake and body weight gain in both lean and obese animals. The inhibition of food intake and body weight gain was greater in obese Zuckers than in lean Zucker controls. Changes in the body weights of pair-fed controls closely paralleled those of their drug-treated counterparts. Chronic 28-day treatment led to a maintained reduction of body weight gain. Withdrawal of SR 141716 on day 28 resulted in rebound hyperphagia and a significant weight gain. On acute administration, SR 141716 dose-dependently induced motor behaviours that showed tolerance upon repeated administration.

CONCLUSION

These data indicate that chronic oral treatment with SR 141716 significantly reduces the food intake and body weight gain of obese and lean Zucker rats, an effect that is greater in obese animals and reversible upon drug withdrawal.

Paradoxical effect of sibutramine on autonomic cardiovascular regulation

BACKGROUND

Sibutramine, a serotonin and norepinephrine transporter blocker, is widely used as an adjunctive obesity treatment. Norepinephrine reuptake inhibition with sibutramine conceivably could exacerbate arterial hypertension and promote cardiovascular disease.

METHODS AND RESULTS

In 11 healthy subjects (7 men, age 27+/-2 years, body mass index 23.1+/-0.7 kg/m2), we compared the effect of sibutramine or matching placebo (ingested 26, 14, and 2 hours before testing) on cardiovascular responses to autonomic reflex tests and to a graded head-up tilt test. In addition, we tested sibutramine in combination with metoprolol. Testing was conducted in a double-blind and crossover fashion. Supine systolic blood pressure was 113+/-3 mm Hg with placebo, 121+/-3 mm Hg with sibutramine (P<0.001 versus placebo), and 111+/-2 mm Hg with the combination of sibutramine and metoprolol. Similarly, sibutramine increased upright blood pressure. Sibutramine substantially increased upright heart rate. This effect was abolished with metoprolol. The blood pressure response to cold pressor and handgrip testing was attenuated with sibutramine compared with placebo. Furthermore, sibutramine decreased low-frequency oscillations of blood pressure and plasma norepinephrine concentrations in the supine position.

CONCLUSIONS

The cardiovascular effect of the antiobesity drug sibutramine results from a complex interaction of peripheral and central nervous system effects. The inhibitory clonidine-like action of sibutramine on the central nervous system attenuates the peripheral stimulatory effect. Our findings strongly suggest that current concepts regarding the action of sibutramine on the sympathetic nervous system should be reconsidered.

Leptin and the treatment of obesity: its current status

Leptin, the protein product of the ob gene, is primarily an adipocyte-secreted hormone, whose functional significance is rapidly expanding. Although early research efforts were focused on defining leptin's role in reversing obesity in rodents, there is now substantial evidence indicating that its influence extends to several hypothalamic-pituitary-endocrine axes, including gonadal, adrenal, thyroid, growth hormone, and pancreatic islets. A role for leptin in hematopoiesis, angiogenesis, immune function, osteogenesis, and wound healing has also been documented. The results of recent clinical trials with recombinant human leptin indicated that its effectiveness in restoring energy balance and correcting obesity-related endocrinopathies in genetically obese rodent models extended only partially to the management of human obesity. New efforts in drug development have focused on leptin-related synthetic peptide agonists as potential anti-obesity pharmacophores.

Surto psicótico pela possível interação medicamentosa de sibutramina com finasterida

É descrito um caso de interação medicamentosa em um paciente de 30 anos, que fazia com sucesso um tratamento antiobesidade com sibutramina. Esse medicamento é um saciogênico que inibe a recaptação da serotonina e da noradrenalina. Logo após a introdução da finasterida para tratamento da alopécia androgênica, o paciente passou a apresentar surto psicótico. Esse medicamento é um potente inibidor da 5-alfa-redutase do tipo II. A interação medicamentosa demonstra-se por meio de um rigoroso acompanhamento clínico e de uma aplicação do algoritmo de Naranjo. Também descrevem-se as condições clínicas gerais do paciente e sua evolução. Discutem-se os mecanismos prováveis que levaram à interação medicamentosa, com a conclusão de que a finasterida inibiu o metabolismo hepático da sibutramina. Esta deslocou a finasterida de seus pontos de ligações com as proteínas, aumentando sua fração livre plasmática e inibindo ainda mais o metabolismo da sibutramina. Com aumento de serotonina, noradrenalina e dopamina na fenda sináptica, desencadeia-se o surto psicótico.

Regulation of body weight and carcass composition by sibutramine in rats

OBJECTIVE

We examined the effectiveness of sibutramine to modulate food intake and body composition in rats with two levels of adiposity imposed by the duration of their maintenance on a moderate-fat diet.

RESEARCH METHODS AND PROCEDURES

Male Sprague--Dawley rats were fed a 32% fat diet from weaning until 2 or 4 months of age, at which point, body fat was either 15% or 25%, respectively, as measured by DXA. Sibutramine (0.6 or 2 mg/kg, orally) was then given daily for 2 weeks.

RESULTS

Food intake and body weight decreased acutely in a dose-related manner in both groups with sibutramine treatment. In all rats, food intake suppression was attenuated after multiple days of sibutramine. Both 15%- and 25%-fat rats had a persistent decrease in weight gain over the 2-week period in response to sibutramine. The older, 25%-fat rats were more sensitive to sibutramine than the younger, 15%-fat rats with regard to the magnitude of overall food intake inhibition, decrease in body weight gain, and caloric efficiency. Despite these differences, sibutramine produced the same relative reductions in fat mass and had no effect on lean mass in the two groups.

DISCUSSION

Thus, sibutramine produced equivalent efficacy on carcass fat loss in both groups, despite less inhibition of feeding and body weight gain in leaner rats. Whether these changes are a result of the leaner rats being younger and on a steeper growth curve compared with older, fatter rats or whether this is a direct function of their level of adiposity remains to be determined.

Treating obesity: a new target for prevention of coronary heart disease

Recognition by the American Heart Association that obesity is a major modifiable risk factor for coronary heart disease has prompted health providers to take a more active role in obesity management. Obesity has long been known to accompany a host of chronic diseases, e.g., type II diabetes, hypertension, and dyslipidemia. We now recognize that obesity is itself a chronic disease with a complex etiology; like diabetes and hypertension, it is treatable with a similar chronic disease treatment model. Relatively modest weight loss confers disproportionate health benefits, improving a roster of risk factors. Diet, exercise, and behavior modification still compose the gold standard of treatment. If these measures fail, medication and surgery should be considered for appropriate patients. With current techniques, many patients can achieve realistic weight goals that can be maintained over the long term. Published management guidelines can now assist in integrating the practical applications of obesity-related research findings into everyday clinical practice.

[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.

Focus on primary care: evaluation, management, and treatment of obesity in women

Obesity is the number one nutritional disorder in the developed world. It is now well recognized that obesity is a disease that represents a rapidly growing epidemic. It is often a lifelong problem that preferentially affects women. Modern science and medicine are just beginning to unravel the multifactorial pathophysiology of obesity. Current literature emphasizes the metabolic, hormonal, and behavioral interactions as well as genetic predisposition. This understanding has led to new recommendations for the management of the obese patient and to new pharmaceutical approaches for those at high risk. These risks include diabetes, cardiovascular disease, hypertension, gallbladder disease, and osteoarthritis. In addition, there are a number of reproductive health problems unique to obese women. Until recently, however, the evidence for benefit of weight loss was not clear. There are now numerous Category A data indicating significant benefit for weight loss as it affects multiple comorbidities It is, therefore, incumbent upon the providers of women's health care to assess patient risk and to offer resources, guidance, assistance, and reassurance to the overweight and obese patient as she embarks on a program of renewed health through weight loss.

LEARNING OBJECTIVES

After completion of this article, the reader will be able to describe the classification of overweight and obesity, explain the pathophysiology of obesity, outline the evaluation and screening of the obese patient, and list potential therapeutic interventions for weight loss.

Effects of sibutramine on body weight and serum lipids: a double-blind, randomized, placebo-controlled study in 322 overweight and obese patients with dyslipidemia

BACKGROUND

Cardiovascular risk factors associated with obesity, including dyslipidemia, can be improved by weight loss. The main dyslipidemia associated with obesity is elevated serum triglyceride and decreased serum high-density lipoprotein cholesterol (HDL-C) levels.

METHODS

A total of 322 obese patients (body mass index > or = 27) with serum triglyceride levels > or = 250 mg/dL and < or = 1000 mg/dL and serum HDL-C levels < or = 45 mg/dL (women) and < or = 40 mg/dL (men) were placed on a step I American Heart Association diet and subsequently randomized to sibutramine 20 mg (n = 162) or placebo (n = 160) once daily for 24 weeks.

RESULTS

Patients taking sibutramine had significantly greater mean weight loss than those receiving placebo (-4.9 kg vs -0.6 kg, P < or = .05). Forty-two percent of the sibutramine group lost > or = 5% of baseline weight and 12% lost > or = 10% compared with 8% and 3%, respectively, of the placebo group (P < or = .05). Mean decreases in serum triglyceride levels among 5% and 10% weight-loss responders in the sibutramine group were 33.4 mg/dL and 72.3 mg/dL, respectively, compared with an increase of 31.7 mg/dL among all patients receiving placebo (P < or = .05). Mean increases in serum HDL-C levels for 5% and 10% weight-loss responders in the sibutramine group were 4.9 mg/dL and 6.7 mg/dL, respectively, compared with an increase of 1.7 mg/dL among all patients in the placebo group (P < or = .05). Adverse events and discontinuation rates were similar in the sibutramine and placebo groups, although sibutramine-treated patients had mean increases in systolic and diastolic blood pressure of 2 to 3 mm Hg relative to placebo.

CONCLUSIONS

In overweight and obese patients with high serum triglyceride levels and low serum HDL-C levels, treatment with sibutramine was associated with significant improvements in body weight and in serum triglyceride and HDL-C levels.

The neuroendocrinology of obesity

The regulation of energy balance is enormously complex, with numerous genetic, hormonal, neural/behavioral, and societal influences. Although the current epidemic of obesity has its underpinnings in the changes in culture during the last half century, the role of the neuroendocrine system in the genesis of obesity is physiologically and therapeutically unavoidable. Increased understanding of this system has suggested organic etiologies (and therapies) for some rare and not-so-rare forms of obesity. With so many inputs, it is not implausible that dysfunction of other parts of this feedback system will be found to explain other forms of obesity in the future. Fortunately or unfortunately, diet and exercise remain the mainstays of obesity therapy. Most diet-exercise programs result in an acute 11-kg weight loss in adults; the question is whether it can be sustained without significant long-term behavior modification. In the European Sibutramine Trial of Obesity Reduction and Maintenance (STORM), 42% of treated patients dropped out; of those remaining, 77% of subjects lost more than 5% of initial body weight, but only 43% of these individuals maintained greater than 80% of this loss over 2 years. Could there be an organic component in persons who do not respond? Obesity pharmacotherapies sometimes have beneficial acute effects, but these effects are impermanent; discontinuation tends to result in a rebound weight gain, suggesting that the etiology of the obesity is still present. A useful guiding principle is that patients who do not respond to diet and exercise should undergo an initial medical evaluation, including assessments of birth weight, past medical history, weight history, family history, diet, exercise, and fasting insulin and thyroid levels. As the nosology of obesity improves, diagnostic efficiency and therapeutic success should increase, leading to a decrease in associated morbidity, mortality, and socioeconomic ramifications.

The neuroendocrinology of childhood obesity

The regulation of energy balance is enormously complex, with numerous genetic, hormonal, neural and behavioral, and societal influences. Although the current epidemic of obesity clearly has its underpinnings in the changes in culture during the past half-century (see other articles in this issue), the role of the neuroendocrine system in the genesis of obesity, as described in this article, is physiologically and therapeutically unavoidable. An understanding of this system has suggested organic causes (and therapies) for some rare and not-so-rare forms of obesity. With so many inputs, it is not far-fetched to assume that dysfunction of other parts of this feedback system will be found to explain other forms of obesity in the future. What does this mean for obese children entering the pediatrician's office? Fortunately or unfortunately, diet and exercise are the mainstays of obesity therapy for children and adults. Most diet-exercise programs result in an acute 11-kg weight loss in adults; the question is whether it can be sustained without significant long-term behavioral modification. For instance, the European Sibutramine Trial of Obesity Reduction and Maintenance trial showed that 42% of treated subjects drop out; of those remaining, 77% of subjects lost more than 5% of initial body weight, but only 43% of those maintained more than 80% of this over 2 years. Could there be an organic component in those who do not respond? Of course, obesity pharmacotherapies sometimes have beneficial acute effects, but these drugs work for only as long as they are consumed; discontinuation tends to result in a "rebound" weight gain, suggesting that the cause of the obesity is still present. Furthermore, in 2001, there are no obesity drugs approved for children. A useful guiding principle is that children deserve at the minimum an initial medical evaluation, including birth weight, medical history, family history, dietary evaluation, and exercise assessment. Perhaps the most important feature that can distinguish "organic" from "behavioral" weight gain in childhood is the age of the "adiposity rebound." The Centers for Disease Control and Prevention now supplies BMI charts for boys and girls at www.cdc.gov/growthcharts. Plotting of the BMI versus age allows pediatricians to determine the age at which the BMI starts to increase (mean, 5.5 years). The earlier the adiposity rebound, the more likely the child will be obese as an adult, and the more likely that an organic cause can be determined. In such patients, thyroid levels and fasting insulin and leptin levels should be measured. An initial attempt at diet and exercise is essential; patients who do not respond with BMI stabilization should be investigated for a more ominous cause of their obesity. As the nosology of obesity improves, pediatricians will be able to increase the diagnostic efficiency and therapeutic success of this unfortunate, debilitating, and expensive epidemic.

Influence of sibutramine on energy expenditure in African American women

OBJECTIVE

African American women have a high prevalence of obesity, which partially may be explained by their lower rates of resting energy expenditure (REE). The aim of this study was to examine the influence of acute sibutramine administration on REE and post-exercise energy expenditure in African American women.

RESEARCH METHODS AND PROCEDURES

A total of 15 premenopausal, African American women (age, 29 +/- 5 years; body fat, 38 +/- 7%) completed a randomized, double-blind cross-over design with a 30-mg ingestion of sibutramine or a placebo. Each trial was completed a month apart in the follicular phase and included a 30-minute measurement of REE 2.5 hours after sibutramine or placebo administration. This was followed by 40 minutes of cycling at approximately 70% of peak aerobic capacity and a subsequent 2-hour measurement of post-cycling energy expenditure.

RESULTS

There was no difference (p > 0.05) in REE (23.70 +/- 2.81 vs. 23.69 +/- 2.95 kcal/30 min), exercise oxygen consumption (1.22 +/- 0.15 vs. 1.25 +/- 0.15 liter/min), and post-cycling energy expenditure (104.2 +/- 12.7 vs. 104.9 +/- 11.4 kcal/120 min) between the sibutramine and placebo trials, respectively. Cycling heart rate was significantly higher (p = 0.01) during the sibutramine (158 +/- 14 beats/min) vs. placebo (150 +/- 12 beats/min) trials.

DISCUSSION

These data demonstrate that acute sibutramine ingestion does not increase REE or post-exercise energy expenditures but does increase exercising heart rate in overweight African American women. Sibutramine may, therefore, impact weight loss through energy intake and not energy expenditure mechanisms.

Sibutramine, a serotonin uptake inhibitor, increases dopamine concentrations in rat striatal and hypothalamic extracellular fluid

We measured, using microdialysis, the effects of sibutramine, given intraperitoneally, on brain dopamine and serotonin flux into striatal and hypothalamic dialysates of freely moving rats, and on the uptake of [(3)H]-DA into striatal synaptosomes. For microdialysis experiments, samples collected every 30 min were assayed by high-pressure liquid chromatography, in a single run. Administration of a low dose of sibutramine (2.0 mg/kg, i.p) had no effect on dopamine or serotonin concentrations in striatal dialysates but higher doses increased both: 5 mg/kg increased these concentrations to 196+/-24% (p<0.01) and 221+/-28% (p<0.01) of baseline, respectively; 10 mg/kg increased dopamine to 260+/-66% (p<0.01) and serotonin to 160+/-20% (p<0.05) of baseline. In hypothalamus, the 5 mg/kg sibutramine dose increased the dopamine concentration to 186+/-40% (p<0.05) and that of serotonin to 312+/-86% (p<0.01) of baseline, while the 10 mg/kg (i.p.) dose increased dopamine to 392+/-115% (p<0.01), and serotonin to 329+/-104% (p<0.01) of baseline. In vitro, sibutramine blocked [(3)H]-dopamine uptake into striatal synaptosomes, with an IC(50) value of 3.8 microM. These findings indicate that sibutramine has at least as great an effect on brain extracellular dopamine levels as on brain serotonin, and suggest that the drug's antiobesity action may result from the changes it produces in brain dopamine as well as serotonin metabolism.

Sibutramine does not decrease the number of 5-HT re-uptake sites in rat brain and, like fluoxetine, protects against the deficits produced by dexfenfluramine

The effect of sibutramine and dexfenfluramine on 5-HT re-uptake sites, labelled with [(3)H]paroxetine, have been determined in various rat brain regions. In addition, the ability of fluoxetine and sibutramine to protect against the changes in [(3)H]paroxetine binding produced by dexfenfluramine was examined. Sibutramine (9 mg/kg, p.o.) and dexfenfluramine (1, 3 and 10 mg/kg, p.o.) were administered twice daily (before 09.00 h and after 16.00 h) for four days, followed by a 14 day drug-free period. In the protection studies, fluoxetine (10 mg/kg, i.p.) and sibutramine (9 mg/kg, p.o.) were given 1 h prior to dexfenfluramine (10 mg/kg, p.o.) using the same dosing regimen as described above. Sibutramine (9 mg/kg, p.o.; three times its ED(50) to inhibit food intake at 2 h) had no significant effect on the number or affinity of 5-HT re-uptake sites the brain regions studied. In contrast, dexfenfluramine at an equivalent dose (3 mg/kg, p.o.) significantly decreased the number of 5-HT re-uptake sites in frontal cortex (by 35%), hippocampus (by 47%) and hypothalamus (by 27%). This effect was dose-dependent with marked decreases (by 58-84%) in the number of sites following 10 mg/kg, p.o. These effects were not associated with changes in binding affinity. Fluoxetine (10 mg/kg, i.p.) completely blocked the effect of dexfenfluramine (10 mg/kg, p.o.) without having any significant effect alone. Sibutramine (9 mg/kg, p.o.) also blocked the effects of dexfenfluramine, although the reversal was only partial in frontal cortex, hippocampus and hypothalamus. Thus sibutramine, unlike dexfenfluramine, does not alter brain 5-HT re-uptake sites. Furthermore, sibutramine and fluoxetine protect against the deficits in 5-HT re-uptake sites produced by dexfenfluramine. These data provide further evidence that sibutramine is a 5-HT re-uptake inhibitor and it does not have neurotoxic potential.

Weight gain from novel antipsychotic drugs: need for action

Obesity is common in schizophrenia, and people with schizophrenia appear to be at increased risk for certain obesity-related conditions, such as type 2 diabetes and cardiovascular disease. Antipsychotic drugs, used chronically to control symptoms of schizophrenia, are associated with often-substantial weight gain, a side effect that is a special concern with the latest generation of highly effective "novel" agents. That the most effective (e.g., novel) antipsychotic medications lead to substantial weight gain presents the field with a critical public health problem. Although preliminary data have been reported regarding the beneficial use of behavior therapy programs for short-term weight control in patients with schizophrenia, the available data are quite limited, and there are no data regarding the long-term beneficial effects of these programs in this population. The obesity field recently has developed programs emphasizing "lifestyle changes" (e.g., diet, exercise, and problem-solving skills) to successfully manage weight in patients without schizophrenia. Such programs can be adapted for patients with schizophrenia through the use of highly structured and operationalized modules emphasizing medication compliance, social skills development, and participation in outpatient programs. Moreover, these programs can potentially be combined with the use of adjunctive pharmacotherapy to maximize and maintain weight loss. The field must solve the paradox that some of our most effective medications for schizophrenia produce substantial weight gain and its associated troubling health risks.

Recent progress in obesity pharmacotherapy

Interest in obesity pharmacotherapy is intense, sparked by the public health threat of increases in obesity rates, as well as by increased knowledge of the biology underlying food intake and energy balance. After a hiatus of more than 20 years, three new medications approved by the US Food and Drug Administration for obesity treatment recently reached the marketplace. One of these, dexfenfluramine, has been withdrawn because of fenfluramine's and its isomer's association with valvular regurgitation. Sibutramine, a centrally acting reuptake inhibitor of monoamines, and orlistat, a pancreatic lipase inhibitor, have been approved for long-term obesity treatment. This review covers recent publications documenting clinical trial experience with these two agents and updates the evidence associating dexfenfluramine and fenfluramine with valvulopathy. As obesity rates increase throughout the world and as knowledge expands regarding the biology of obesity, an expansion of pharmacologic options for obesity treatment is certain.

Hypothalamic obesity caused by cranial insult in children: altered glucose and insulin dynamics and reversal by a somatostatin agonist

OBJECTIVE

Hypothalamic obesity is a rare sequela of cranial insult, for which pathogenesis and treatment remain obscure. In rodents ventromedial hypothalamic damage causes hyperphagia, obesity, hyperinsulinism, and insulin resistance. Reduction of insulin secretion in humans may attenuate weight gain.

METHODS

Eight children with intractable obesity after therapy for leukemia or brain tumors underwent oral glucose tolerance testing (OGTT) with simultaneous insulin levels before and after treatment with octreotide for 6 months.

RESULTS

In comparison with a 6-month pre-study observation period, patients exhibited weight loss (+6.0 +/- 0.7 kg vs -4.8 +/- 1.8 kg; P =.04) and decrease in body mass index (+2.1 +/- 0.3 kg/m(2) vs -2.0 +/- 0.7 kg/m(2); P =.0001). Recall calorie count decreased during the 6 months of treatment (P =. 015). OGTT demonstrated biochemical glucose intolerance in 5 of 8 patients initially and in 2 of 7 at study end, whereas insulin response was decreased (281 +/- 47 microU/mL vs 114 +/- 35 microU/mL; P =.04). Percent weight change correlated with changes in insulin response (r = 0.72, P =.012) and changes in plasma leptin r = 0.76, P =.0004).

CONCLUSIONS

Patients with hypothalamic obesity demonstrate excessive insulin secretion. Octreotide administration promoted weight loss, which correlated with reduction in insulin secretion on OGTT and with reduction in leptin levels. Pre-study biochemical glucose tolerance improved in several patients while they were receiving octreotide. These results suggest that normalization of insulin secretion may be an effective therapeutic strategy in this syndrome.

Obesity and diabetes

Obesity, particularly truncal obesity, is closely correlated to the prevalence of diabetes and cardiovascular disease. Plasma leptin, tumour necrosis factor-alpha and non-esterified fatty acid levels are all elevated in obesity and play a role in causing insulin resistance. Diabetic glycaemic control and insulin resistance improve with reductions in obesity, but the treatment of obesity is difficult, and sustained weight reduction rarely occurs with dietary management alone. Hypocaloric diets should be combined with education and low-impact exercise, as well as behavioural techniques used to encourage long-term changes. Weight-reducing drugs have a role in the management of obesity but only as part of such a total package. Newer anti-obesity drugs such as orlistat and sibutramine are well tolerated and have been shown to improve glycaemic control in diabetes. It is probable that drugs developed in the future will act at different sites in the pathways regulating body weight, but they may have to be used in combination.

Current concepts in the pharmacological management of obesity

The pharmacological management of obesity has gained increasing attention as new weight loss treatments are approved and a significant proportion of the public strives to lose weight. Obesity is associated with a high mortality rate, multiple chronic medical conditions, and carries an enormous financial burden. Obesity is a multifactorial condition, most often due to an imbalance in energy intake and expenditure. Despite the greater focus on management of obesity, weight loss remains a difficult goal to achieve. Obesity is a chronic medical condition that may require long term treatment, therefore the risks and benefits of all pharmacological agents must be carefully considered. Noradrenergic appetite suppressants (ie. phenyl-propanolamine, phentermine) result in weight loss but stimulatory effects limit their use. The serotonergic agents (fenfluramine, dexfenfluramine) were effective weight loss drugs, but were voluntarily withdrawn from the US market last year because of cardiovascular and pulmonary complications. The combination noradrenergic/serotonergic agent sibutramine is indicated for the management of obesity, particularly in the presence of other cardiovascular risk factors. Modest weight loss is achieved with sibutramine, although weight gain is significant after discontinuation. In addition, long term safety data are not yet available. The thermogenic combination of ephedrine plus caffeine is minimally effective, and adverse effects are usually transient. Other thermogenic agents, such as beta3-agonists, are still under investigation. Agents may alter digestion through lipase inhibition (orlistat) or fat substitution (olestra). Orlistat decreases systemic absorption of dietary fat, decreasing body weight and cholesterol. Olestra is a fat substitute that has been incorporated into snack foods. Olestra substitution for dietary fat has not been studied as a weight loss strategy, although olestra has no caloric value and may be beneficial. The use of orlistat and olestra may be limited by gastrointestinal adverse effects. Finally, the manipulation of leptin and neuropeptide Y are under investigation for the treatment of obesity. Pharmacological agents should be used as an aid to a structured diet and exercise regimen in the treatment of obesity. Weight loss agents may result in initial weight loss, but sustained weight loss is not always achieved even with continuation of treatment. The effect of weight loss obtained while using pharmacotherapeutic agents on morbidity and mortality has not been established. Therefore, diet and exercise should be the focus of any weight loss programme. There is a continued need for safe and effective pharmacotherapeutic agents for the treatment of obesity.

Thermogenic effects of sibutramine and its metabolites

1. The thermogenic activity of the serotonin and noradrenaline reuptake inhibitor sibutramine (BTS 54524; Reductil) was investigated by measuring oxygen consumption (VO2) in rats treated with sibutramine or its two pharmacologically-active metabolites. 2. Sibutramine caused a dose-dependent rise in VO2, with a dose of 10 mg kg(-1) of sibutramine or its metabolites producing increases of up to 30% that were sustained for at least 6 h, and accompanied by significant increases (0.5-1.0 degrees C) in body temperature. 3. Based on the accumulation in vivo of radiolabelled 2-deoxy-[3H]-glucose, sibutramine had little or no effect on glucose utilization in most tissues, but caused an 18 fold increase in brown adipose tissue (BAT). 4. Combined high, non-selective doses (20 mg kg(-1)) of the beta-adrenoceptor antagonists, atenolol and ICI 118551, inhibited completely the VO2 response to sibutramine, but the response was unaffected by low, beta1-adrenoceptor-selective (atenolol) or beta2-adrenoceptor-selective (ICI 118551) doses (1 mg kg(-1)). 5. The ganglionic blocking agent, chlorisondamine (15 mg kg(-1)), inhibited completely the VO2 response to the metabolites of sibutramine, but had no effect on the thermogenic response to the beta3-adrenoceptor-selective agonist BRL 35135. 6. Similar thermogenic responses were produced by simultaneous injection of nisoxetine and fluoxetine at doses (30 mg kg(-1)) that had no effect on VO2 when injected individually. 7. It is concluded that stimulation of thermogenesis by sibutramine requires central reuptake inhibition of both serotonin and noradrenaline, resulting in increased efferent sympathetic activation of BAT thermogenesis via beta3-adrenoceptor, and that this contributes to the compound's activity as an anti-obesity agent.

Insulin resistance, impaired glucose tolerance and non-insulin-dependent diabetes, pathologic mechanisms and treatment: current status and therapeutic possibilities

Impaired glucose tolerance and non-insulin-dependent diabetes (NIDDM) are the pathologic consequence of two co-incident and interacting conditions, namely insulin resistance and relative insulin deficiency. Recognised by the World Health Authority as a global health problem there are at 1995 estimates at least 110 million diagnosed diabetics world wide with at least the same number undiagnosed. Diabetes is the 4th leading cause of death in developed countries and its management exerts a vast economic and social burden. Insulin resistance is established as the characteristic pathologic feature of patients with glucose intolerance and NIDDM describing a state in which insulin stimulated glucose uptake and utilisation in liver, skeletal muscle and adipose tissue is impaired and coupled to impaired suppression of hepatic glucose output. Although the biochemical mechanisms underpinning both defects are becoming better understood, the genetic and molecular causes remain elusive; and whether insulin resistance or relative insulin deficiency represents the primary defect in patients with NIDDM is the matter of some debate. In this article we review the biochemical and molecular nature of the defects in insulin sensitivity and glucose uptake, and discuss some of the potential causative mechanisms. The genetic and environmental basis of insulin resistance is reviewed and presented, and potential therapeutic targets including thiazolidinediones are discussed.

A model for chronic care of obesity through dietary treatment

Obesity is rapidly increasing to epidemic proportions. At the same time, obesity is not well accepted as a disease among health professionals or insurance companies. The primary care physician is often forced to ignore the obesity and treat the associated risks, and the dietitian is often compelled to treat the disease for only short periods and for little reimbursement. Therefore, to treat obesity more effectively both clinically and economically, it is necessary to create a health care team. This can be done by joining the dietitian and the primary care physician, even if each health professional sees patients at a different site. Through mutual referrals and more consistent coordination of care, the team can provide cost-effective management of obesity while providing improved clinical monitoring of the patient. Both members of the team need to understand the pathophysiology of obesity and when to refer to each other. The dietitian will see the patient more regularly throughout all stages of the obesity treatment, referring to the physician when appropriate (eg, for evaluation of medications, new laboratory tests, and electrocardiography). The physician will see the patient in the acute stage (i.e., weight change stage) of the obesity treatment for any clinical changes, but will schedule less frequent visits during the chronic stage (i.e., weight maintenance). The strength of the team, therefore, lies in its members' ability to communicate with each other, monitor the clinical changes concomitant with fluctuating weight, and offer treatment and support as intensively as the disease warrants.

Sibutramine reduces food intake in non-dieting women with obesity

Sibutramine (SIB), an inhibitor of serotonin and noradrenaline reuptake, has been shown in clinical trials to be associated with a dose-related decrease in bodyweight. This double-blind, placebo-controlled, Latin square crossover study examined whether the effect on bodyweight could be due in part to a reduction in daily food intake. Twelve non-dieting, women with obesity (body mass index of 30.5 to 41.9) received three treatments (0 [matching placebo], 10, or 30 mg SIB/day) for 14 days, with 14-day washout periods in between. On days 7 and 14, participants came to the laboratory to eat breakfast, lunch, and dinner so that daily energy and macronutrient intakes and ratings of hunger and satiety could be measured. Significant reductions occurred in food intake (both grams and energy) over the 14-day study period. On day 7, SIB 30 reduced intake significantly by 1762 kJ (23% reduction from placebo), and on day 14, both SIB 10 and SIB 30 significantly reduced intake compared with placebo (SIB 10, 19% reduction [1490 kJ]; SIB 30, 26% reduction [2079 kJ]). On day 7, the percentage of energy consumed from carbohydrate increased significantly with the 30-mg dose (56.7%) compared with that of placebo (51.4%), with a reciprocal decrease in energy from fat (27.8% to 24%). The results show that SIB reduced energy intake in women with obesity who were not attempting to lose weight.

Update on the pharmacotherapy of obesity

OBJECTIVE

To review recent developments in the pharmacotherapy of obesity, including the agents currently approved for use in the management of obesity and those under development.

DATA SOURCES

A MEDLINE search from January 1990 to July 1997 was conducted to identify English literature available on the pharmacotherapy of obesity. The search was supplemented by a review of the bibliographies of identified literature.

STUDY SELECTION

All controlled and uncontrolled trials were reviewed. When available, double-blind, placebo-controlled trials were used preferentially.

DATA EXTRACTION

Agents were reviewed with regard to mechanism of action, clinical trial data regarding efficacy, adverse effects, pharmacokinetics, drug interactions, and contraindications where information was available. Study design, selected population, results, and adverse effect information were included.

DATA SYNTHESIS

The anorexiants currently available or under development for the management of obesity regulate food intake and satiety via the adrenergic and/or serotonergic pathways. Clinical trials have shown a 10-15% weight loss can typically be anticipated; however, little long-term safety and efficacy data are available. Adverse events tend to be mild and self-limiting, but serious adverse events can occur. Treatment options under development include thermogenic agents, digestive inhibitors, and analogs and antagonists of hormones that regulate food intake and satiety.

CONCLUSIONS

Several mechanisms to control weight are currently under investigation for the management of obesity. Since obesity is a chronic condition, further studies should be conducted to evaluate the long-term safety and efficacy of these agents and the role of combination therapy using different modalities.

Long-term drug treatment of obesity in a private practice setting

This study evaluated the long-term efficacy and safety of the combination of phentermine and fenfluramine for the treatment of obesity in a private practice setting. A total of 1388 consecutive, qualified patients presenting to a private general internal medicine practice in Charlotte, NC, were enrolled with eligibility criteria including: age 18 years to 60 years, 20% over "desirable" bodyweight or body mass index > 27, no serious medical or psychiatric disease, and no contraindications to drug therapy. Patients were instructed in diet, exercise, and behavior modification techniques and received phentermine (15 mg/day to 30 mg/day) and fenfluramine (20 mg/day to 60 mg/day) continuously for over 3 years. Average duration of treatment was 15.9 months, and average weight loss at the last visit was 11.6 kg, or 11.7% of initial bodyweight. For patients completing 1 year of drug treatment, mean weight loss was 16.5 kg, or 16% of initial weight. Weight loss persisted for 2 years, but partial regain was seen at 3 years. The dropout rates were 18% at 6 months, 39% at 1 year, 68% at 2 years, and 78% at 3 years. At 1 year, blood pressure of hypertensive patients fell from 151/95 mm Hg to 127/78 mm Hg, and serum cholesterol and triglycerides of hyperlipidemic patient fell by 0.750 mmol/L (29 mg/dL) and 0.937 mmol/L (83 mg/dL), respectively. Adverse events were modest. We conclude that, in a private practice setting, long-term treatment of obesity with the combination of phentermine, fenfluramine, and a weight maintenance program is generally safe and effective. More research is needed to determine efficacy and safety for longer than 3 years.

Neuroscience and appetitive behavior research: 25 years

Neuroscience techniques have made major contributions to the understanding of appetitive behavior. Highlights in six areas are summarized to illustrate progress during the 25 years of the Columbia Appetitive Behavior Seminar: (1) discovery of angiotensin and aldosterone in the control of thirst and salt appetite; (2) electrophysiological decoding of chemoreceptive information in the brain; (3) a new foundation in the hypothalamus built on peptides, such as neuropeptide Y and galanin, interacting with monoamines and steroids in the control of appetite for macronutrients; (4) discovery of numerous peptides that mediate and integrate satiety, such as cholecystokinin, insulin, leptin and enterostatin, and other systems that suppress eating during illness; (5) better understanding of appetite suppressant drugs, and (6) exploration of a circuit that translates hypothalamic signals into behavioral action through connections to brainstem reflex arcs and forebrain instrumental response systems.