Update on the pharmacotherapy of obesity

Orlistat

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Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The October 1999 Formulary monographs are on zanamivir, pioglitazone, levobupivacaine, temozolomide, and insulin glargine. The DUE is on zanamivir.

Konjac Glucomannan Dietary Supplementation Causes Significant Fat Loss in Compliant Overweight Adults

OBJECTIVES

Changes in body composition and blood chemistries between overweight adult subjects receiving a supplement containing either 3 g of konjac glucomannan/300 mg calcium carbonate or a placebo containing only 300 mg of calcium carbonate were compared as the primary objective. A secondary objective was to compare outcome differences between compliant and partially compliant subjects.

METHODS

A total of 83 overweight adults (66 women and 17 men) completed a randomized, double-blind, placebo-controlled protocol in which they received either a glucomannan or placebo supplement for 60 days. Dual-energy x-ray absorptiometry (DEXA) total body scans and a 42-measurement blood test were completed at baseline and 60 days later. Compliance was assessed by rating self-reports of (1) how many tablets were taken, (2) adherence to taking the tablets 30 minutes before eating, and (3) a sum of the ratings for (1) and (2). An anonymous poststudy questionnaire and telephone calls were also completed by 80 (96%) of the participants who were used as the study cohort.

RESULTS

No statistically significant differences were found between the groups on changes from baseline on the DEXA and blood tests. However, when subjects were classified as either compliant or partially compliant using the compliance measures, statistically significant reductions in scale weight, percentage body fat, fat mass, total cholesterol, and low-density lipoprotein (LDL) cholesterol were found in the glucomannan group compared to the placebo group.

CONCLUSIONS

This study supports the efficacy glucomannan supplementation to reduce body weight, body fat, and circulating cholesterol levels without the concomitant loss of lean mass and bone density often associated with weight loss. However, these positive outcomes were not observable until corrections for compliance were applied.

Bean amylase inhibitor and other carbohydrate absorption blockers: effects on diabesity and general health

Many believe that excessive intake of refined carbohydrates (CHO) plays a major role in the development of obesity/overweight, type 2 diabetes mellitus and insulin resistance, a collection of events commonly referred to as "diabesity," and have sought natural means to overcome these linked perturbations. As a first approach, planned diets with low portions of refined CHO have become popular. However, these diets do not satisfy everyone; and many are concerned over replacing CHO with more fats. As a second option, addition of soluble fiber to the diet can slow absorption of refined CHO, i.e., lower the glycemic index of foods and overcome or at least ameliorate many of the adverse reactions resulting from increased refined CHO ingestion. Unfortunately, the general public does not favor diets high in fiber content, and various fibers can lead to gastrointestinal problems such as gas and diarrhea. A third choice to favorably influence CHO absorption is to use natural dietary supplements that block or slow CHO absorption in the gastrointestinal tract via inhibiting enzymes necessary for CHO absorption -amylase and alpha-glucosidases. Although a number of natural supplements with anti-amylase activity have been recognized, the most studied and favored one is white kidney bean extract. Animal and human studies clearly show that this agent works in vivo and has clinical utility. This paper reviews many aspects of diabesity and the use of "carb blockers" to prevent and ameliorate the situation. In many respects, carb blockers mimic the beneficial effects of fibers.

Pharmacotherapy for the obese patient

The long-term safety of many antiobesity pharmacologic regimens has not been adequately evaluated. If recommended and prescribed, pharmacologic agents should be an adjunct to a structured diet and exercise regimen. Unfortunately, weight gain after discontinuation of antiobesity agents is common. In addition, the effect of weight loss obtained through the use of pharmacotherapeutic agents on overall morbidity and mortality has not been established.

Evidence for a role of the 5-HT2C receptor in central lipopolysaccharide-, interleukin-1 beta-, and leptin-induced anorexia

We examined the role of serotonin (5-HT) and the 5-HT(1A) and 5-HT(2C) receptors in the anorectic effects of centrally administered lipopolysaccharide (LPS), interleukin-1 beta (IL-1 beta), and leptin. Food intake was measured in rats after intracerebroventricular (ICV) injections of LPS (20 ng), IL-1 beta (10 ng), or leptin (1 microg) at lights out, followed by intraperitoneal (IP) injections of either the 5-HT(1A) autoreceptor agonist 8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT) (125 microg/kg) or the 5-HT(2C) receptor antagonist SB 242084 (0.3 mg/kg) at the onset of anorexia. SB 242084 significantly attenuated the food intake reduction caused by all compounds (all P<.01). IP 8-OH-DPAT attenuated ICV IL-1 beta-induced anorexia (P<.01). We also tested the involvement of the median raphe 5-HT(1A) receptors in peripheral LPS- and IL-1 beta-induced anorexia. Rats were injected intraperitoneally with either LPS (100 microg/kg) or IL-1 beta (2 microg/kg) at lights out, and 8-OH-DPAT (4 nmol) was administered directly into the median raphe nucleus at the onset of anorexia. Median raphe injections of 8-OH-DPAT significantly attenuated both IL-1 beta- and LPS-induced anorexia (both P<.01). These results implicate the 5-HT(2C) receptors in the mediation of central LPS-, IL-1 beta-, and leptin-induced anorexia. Our results also suggest that the midbrain raphe nuclei play a role in mediating the anorectic response to peripheral LPS and IL-1 beta.

Understanding the new and evolving profile of adverse drug effects in schizophrenia

This article has reviewed the emerging side-effect profiles of second-generation antipsychotic medications. Although these medications have favorable extrapyramidal side-effect profiles, clinicians must be aware of their propensity to cause weight gain, glucose and lipid abnormalities, and cardiac and sexual side effects. If clinicians are proactive about warning patients about these side effects and appropriately monitoring them, further morbidity and mortality may be prevented in this patient population. Initial choices of medication should be made based on the relative side-effect profiles in light of a particular patient's medical status. In the future, new treatments may be developed, with even fewer side effects.

Recent findings of green tea extract AR25 (Exolise) and its activity for the treatment of obesity

The green tea extract AR25 is an 80% ethanolic dry extract standardized at 25% catechins expressed as epigallocatechin gallate (EGCG). In vitro, green tea extract AR25 exerts a direct inhibition of gastric and pancreatic lipases and a stimulation of thermogenesis. In an open study, the effects of extract AR25 were evaluated in moderately obese patients. After 3 months, body weight was decreased by 4.6% and waist circumference by 4.48%. These results suggest the green tea extract AR25 to be a natural product for the treatment of obesity, which exerts its activity by several ways: inhibition of lipases and stimulation of thermogenesis.

Additive effects on rat brain 5HT release of combining phentermine with dexfenfluramine

OBJECTIVE AND DESIGN

This study examined the effects of the anti-obesity agents, phentermine and dexfenfluramine given alone or in combination, on in vitro and in vivo 5HT release from rat brain tissue.

RESULTS

In vitro, phentermine was without effect on basal [3H]5HT efflux from hypothalamic slices whereas dexfenfluramine (10 microM) evoked a 131% increase in [3H]5HT release. In combination, the two drugs did not alter [3H]5HT release beyond that caused by dexfenfluramine alone. At pharmacologically equivalent doses, phentermine (5.7 mg/kg, i.p.) caused a rapid, modest elevation, and dexfenfluramine (3 mg/kg, i.p.) a larger but equally rapid elevation of extracellular 5HT in the microdialysates from the rat anterior hypothalamus. In combination, the increase in extracellular 5HT evoked by these drugs was not significantly greater than the sum of their individual effects.

CONCLUSIONS

This study provides evidence that phentermine's actions are not restricted to catecholamine systems and indicates that combining phentermine with dexfenfluramine results in an additive increase in neuronal 5HT release.

Orlistat--a novel weight loss therapy

OBJECTIVE

To review the pharmacology, pharmacokinetics, clinical safety and efficacy, drug interactions, and therapeutic issues related to the use of orlistat for treatment of obesity.

DATA SOURCES

English-language articles were identified from MEDLINE (1966-July 2000), Roche Laboratories, organizational guidelines, National Institutes of Health and Food and Drug Administration Web sites, and Doctor's Guide online. Key words included obesity, orlistat, and lipase inhibitors. References were also identified from reference sections of published articles.

STUDY SELECTION AND DATA EXTRACTION

Prospective, randomized, double-blind, placebo-controlled, human trials were selected for review and discussion.

DATA SYNTHESIS

Orlistat is the first agent in the lipase inhibitor class of antiobesity drugs. Orlistat is minimally absorbed and has been shown to reduce body weight by inhibiting absorption (by approximately 30%) of ingested dietary fat. Safety and efficacy have been established in one- and two-year double-blind, placebo-controlled trials; adverse effects were primarily, and almost exclusively, gastrointestinal. Due to its ability to block fat absorption, orlistat also has the capability to inhibit absorption of fat-soluble vitamins. Therefore, a daily multiple vitamin is recommended while taking orlistat.

CONCLUSIONS

By inhibiting fat absorption, orlistat offers a new treatment modality for weight loss and maintenance. Preliminary data from clinical trials suggest that orlistat may be beneficial in patients with comorbid conditions related to obesity, such as diabetes and hyperlipidemia. However, further studies during postmarketing surveillance are needed to fully establish orlistats long-term benefits and safety. Orlistat should be considered a useful adjunctive therapy for weight loss and maintenance in obese patients (i.e., body mass index > or = 30 kg/m2 or > or = 27 kg/m2 if other risk factors are present) committed to lifestyle changes including diet, exercise, and behavioral modification.

Comparison of the effects of sibutramine and other weight-modifying drugs on extracellular dopamine in the nucleus accumbens of freely moving rats

The acute effects of systemic administration of the anti-obesity agent sibutramine on extracellular dopamine (DA) in the nucleus accumbens of freely moving rats were studied using in vivo microdialysis and compared with the actions of phentermine and d-amphetamine at doses 1x and 3x their respective 2 h ED(50) values to reduce food intake in rats. At the lower dose, sibutramine did not elevate extracellular DA concentrations; however, at the higher dose (6.0 mg kg(-1), i.p.) it caused a modest and prolonged increase in extraneuronal DA. A maximal rise was observed at 60 min post-sibutramine treatment (+231% compared to controls) with DA levels remaining elevated for up to 160 min post treatment. In contrast, phentermine and d-amphetamine significantly enhanced DA efflux at both the lower and higher doses. These elevations of DA levels were significantly greater than that seen with the corresponding dose of sibutramine over 0-80 min post treatment. Maximal rises in DA levels resulting from the higher dose of each drug were +733% (phentermine, 3.9 mg kg(-1), i.p.) and +603% (d-amphetamine, 1.5 mg kg(-1), i.p.) compared to controls 40 min post treatment. The highest doses of phentermine and d-amphetamine increased rat locomotor activity up to 100 min and 160 min post treatment, respectively, whereas the equivalent sibutramine dose had no effect. These findings therefore suggest that dopaminergic reward mechanisms are not involved in the reduction of food intake by sibutramine. Furthermore, they are consistent with the view that sibutramine lacks abuse potential.

Green tea extract (AR25®) inhibits lipolysis of triglycerides in gastric and duodenal medium in vitro

In this study, we aimed to evaluate in vitro the inhibitory activity of a green tea extract (AR25 standardized at 25% catechins) on gastric and pancreatic lipase activities. We first used tributyrin as a substrate to evaluate the capability of AR25 to induce digestive lipase inhibition. Gastric lipase was totally inhibited by 40 mg AR25/g tributyrin whereas pancreatic lipase inhibition was maximum (78.8 +/- 0.7%) with 80 mg AR25/g tributyrin. We then used triolein, a long-chain triglyceride, to check whether AR25 could alter lipase activities on a physiologic substrate. AR25 60 mg/g triolein induced a dramatic inhibition of gastric lipase (96.8 +/- 0.4%) whereas pancreatic lipase activity was partially reduced (66.50 +/- 0.92%). Finally, the concerted action of gastric and pancreatic lipases was studied with an excess of enzymes to mimic the physiologic conditions observed in vivo. Incubation of AR25 with an excess of digestive lipases resulted in a drastic decrease in gastric lipolysis but the inhibitory effect on pancreatic lipase was less marked. On the whole, as compared to the control, lipolysis of triolein under the successive action of the two digestive lipases was reduced by 37 +/- 0.6% in the presence of AR25. Because a lipid/water interface is necessary for lipolysis to occur, lipid emulsification and emulsion droplet size were measured in gastric and duodenal media in the presence of AR25. In gastric and duodenal conditions, AR25 inhibited the lipid emulsification process. From these data we conclude that (1) in vitro, fat digestion is significantly inhibited by 60 mg AR25/g triolein, and (2) gastric as well as pancreatic lipase inhibition could be related to altered lipid emulsification in gastric or duodenal media. The green tea extract AR25 exhibiting marked inhibition of digestive lipases in vitro is likely to reduce fat digestion in humans.

Leptin increases serotonin turnover by inhibition of brain nitric oxide synthesis

Leptin administration inhibits diencephalic nitric oxide synthase (NOS) activity and increases brain serotonin (5-HT) metabolism in mice. We evaluated food intake, body-weight gain, diencephalic NOS activity, and diencephalic content of tryptophan (TRP), 5-HT, hydroxyindoleacetic acid (5-HIAA), and 5-HIAA/5-HT ratio after intracerebroventricular (ICV) or intraperitoneal (IP) leptin injection in mice. Five consecutive days of ICV or IP leptin injections induced a significant reduction in neuronal NOS (nNOS) activity, and caused a dose-dependent increase of 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio. Diencephalic 5-HT metabolism showed a significant increase in 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio 3 hours after a single leptin injection. This effect was maintained for 3 hours and had disappeared by 12 hours after injection. After a single IP leptin injection, the peak for 5-HT, 5-HIAA, and the 5-HIAA/5-HT ratio was achieved at 6 hours. Single injections of ICV or IP leptin significantly increased diencephalic 5-HT content. Leptin-induced 5-HT increase was antagonized by the coadministration of L-arginine only when the latter was ICV injected, whereas D-arginine did not influence leptin effects on brain 5-HT content. Finally, in nNOS-knockout mice, the appetite-suppressant activity of leptin was strongly reduced, and the leptin-induced increase in brain 5-HT metabolism was completely abolished. Our results indicate that the L-arginine/NO pathway is involved in mediating leptin effects on feeding behavior, and demonstrate that nNOS activity is required for the effects of leptin on brain 5-HT turnover.

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.

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.