Review of limited systemic absorption of orlistat, a lipase inhibitor, in healthy human volunteers

Calorie restriction mimetics: can you have your cake and eat it, too?

Strong consensus exists regarding the most robust environmental intervention for attenuating aging processes and increasing healthspan and lifespan: calorie restriction (CR). Over several decades, this paradigm has been replicated in numerous nonhuman models, and has been expanded over the last decade to formal, controlled human studies of CR. Given that long-term CR can create heavy challenges to compliance in human diets, the concept of a calorie restriction mimetic (CRM) has emerged as an active research area within gerontology. In past presentations on this subject, we have proposed that a CRM is a compound that mimics metabolic, hormonal, and physiological effects of CR, activates stress response pathways observed in CR and enhances stress protection, produces CR-like effects on longevity, reduces age-related disease, and maintains more youthful function, all without significantly reducing food intake, at least initially. Over 16 years ago, we proposed that glycolytic inhibition could be an effective strategy for developing CRM. The main argument here is that inhibiting energy utilization as far upstream as possible provides the highest chance of generating a broad spectrum of CR-like effects when compared to targeting a singular molecular target downstream. As an initial candidate CRM, 2-deoxyglucose, a known anti-glycolytic, was shown to produce a remarkable phenotype of CR, but further investigation found that this compound produced cardiotoxicity in rats at the doses we had been using. There remains interest in 2DG as a CRM but at lower doses. Beyond the proposal of 2DG as a candidate CRM, the field has grown steadily with many investigators proposing other strategies, including novel anti-glycolytics. Within the realm of upstream targeting at the level of the digestive system, research has included bariatric surgery, inhibitors of fat digestion/absorption, and inhibitors of carbohydrate digestion. Research focused on downstream sites has included insulin receptors, IGF-1 receptors, sirtuin activators, inhibitors of mTOR, and polyamines. In the current review we discuss progress made involving these various strategies and comment on the status and future for each within this exciting research field.

Pharmacotherapy for obesity

Obesity is an important risk factor for metabolic disease and various cancers. Treatments of obesity include lifestyle intervention, pharmacotherapy, and bariatric surgery. If weight loss with lifestyle intervention is only modest, pharmacotherapy might be needed. Pharmacotherapy agents can be grouped by treatment period as short term or long term use agent. Several sympathomimetic drugs such as benzphetamine, diethylpropion, phendimetrazine and phentermine, are approved for short term treatment due to their safety issues. For long term treatment, orlistat, lorcaserin, and combination of phentermine/topiramate are approved by U.S. Food and Drug Administration (FDA). Orlistat partially blocks intestinal digestion of fat, therefore producing weight loss. Lorcaserin is a serotonin 2C receptor agonist. The combination of phentermine/topiramate produces a mean weight loss of 8-10 kg. Side effects of each drug are quite different. For obesity patient, side effects are important factor when choosing drugs. The goal of this article is to review currently available anti-obesity drugs.

Exploiting monitoring data in environmental exposure modelling and risk assessment of pharmaceuticals

In order to establish the environmental impact of an active pharmaceutical ingredient (API), good information on the level of exposure in surface waters is needed. Exposure concentrations are typically estimated using information on the usage of an API as well as removal rates in the patient, the wastewater system and in surface waters. These input data are often highly variable and difficult to obtain, so model estimates often do not agree with measurements made in the field. In this paper we present an approach which uses inverse modelling to estimate overall removal rates of pharmaceuticals at the catchment scale using a hydrological model as well as prescription and monitoring data for a few representative sites for a country or region. These overall removal rates are then used to model exposure across the broader landscape. Evaluation of this approach for APIs in surface waters across England and Wales showed good agreement between modelled exposure distributions and available monitoring data. The use of the approach, alongside estimates of predicted no-effect concentrations for the 12 study compounds, to assess risk of the APIs across the UK landscape, indicated that, for most of the compounds, risks to aquatic life were low. However, ibuprofen was predicted to pose an unacceptable risk in 49.5% of the river reaches studied. For diclofenac, predicted exposure concentrations were also compared to the Environmental Quality Standard previously proposed by the European Commission and 4.5% of river reaches were predicted to exceed this concentration. While the current study focused on pharmaceuticals, the approach could also be valuable in assessing the risks of other 'down the drain' chemicals and could help inform our understanding of the important dissipation processes for pharmaceuticals in the pathway from the patient to ecological receptors.

Myelopoietic efficacy of orlistat in murine hosts bearing T cell lymphoma: implication in macrophage differentiation and activation

Orlistat, an inhibitor of fatty acid synthase (FASN), acts as an antitumor agent by blocking de novo fatty acid synthesis of tumor cells. Although, myelopoiesis also depends on de novo fatty acid synthesis, the effect of orlistat on differentiation of macrophages, which play a central role in host’s antitumor defence, remains unexplored in a tumor-bearing host. Therefore, the present investigation was undertaken to examine the effect of orlistat administration on macrophage differentiation in a T cell lymphoma bearing host. Administration of orlistat (240 mg/kg/day/mice) to tumor-bearing mice resulted in a decline of tumor load accompanied by an augmentation of bone marrow cellularity and survival of bone marrow cells (BMC). The expression of apoptosis regulatory caspase-3, Bax and Bcl2 was modulated in the BMC of orlistat-administered tumor-bearing mice. Orlistat administration also resulted in an increase in serum level of IFN-γ along with decreased TGF-β and IL-10. BMC of orlistat-administered tumor-bearing mice showed augmented differentiation into macrophages accompanied by enhanced expression of macrophage colony stimulating factor (M-CSF) and its receptor (M-CSFR). The macrophages differentiated from BMC of orlistat-administered mice showed characteristic features of M₁ macrophage phenotype confirmed by expression of CD11c, TLR-2, generation of reactive oxygen species, phagocytosis, tumor cell cytotoxicity, production of IL-1,TNF-α and nitric oxide. These novel findings indicate that orlistat could be useful to support myelopoesis in a tumor-bearing host.

Bioavailability of bioactive food compounds: a challenging journey to bioefficacy

Bioavailability is a key step in ensuring bioefficacy of bioactive food compounds or oral drugs. Bioavailability is a complex process involving several different stages: liberation, absorption, distribution, metabolism and elimination phases (LADME). Bioactive food compounds, whether derived from various plant or animal sources, need to be bioavailable in order to exert any beneficial effects. Through a better understanding of the digestive fate of bioactive food compounds we can impact the promotion of health and improvement of performance. Many varying factors affect bioavailability, such as bioaccessibility, food matrix effect, transporters, molecular structures and metabolizing enzymes. Bioefficacy may be improved through enhanced bioavailability. Therefore, several technologies have been developed to improve the bioavailability of xenobiotics, including structural modifications, nanotechnology and colloidal systems. Due to the complex nature of food bioactive compounds and also to the different mechanisms of absorption of hydrophilic and lipophilic bioactive compounds, unravelling the bioavailability of food constituents is challenging. Among the food sources discussed during this review, coffee, tea, citrus fruit and fish oil were included as sources of food bioactive compounds (e.g. (poly)phenols and polyunsaturated fatty acids (PUFAs)) since they are examples of important ingredients for the food industry. Although there are many studies reporting on bioavailability and bioefficacy of these bioactive food components, understanding their interactions, metabolism and mechanism of action still requires extensive work. This review focuses on some of the major factors affecting the bioavailability of the aforementioned bioactive food compounds.

Ceramicine B, a limonoid with anti-lipid droplets accumulation activity from Chisocheton ceramicus

The Meliaceae family of plants has been shown to contain a vast number of compounds with the potential to be developed for medicinal purposes. We have previously reported the isolation of limonoids from a plant in the Meliaceae family named Chisocheton ceramicus. Ceramicine B was identified as an active compound in inhibiting lipid droplets accumulation (LDA) in the mouse preadipocyte cell line MC3T3-G2/PA6. The presence of ceramicine B was found to inhibit the expression of glucose transporter type 4, lipoprotein lipase, and 11-beta hydroxysteroid dehydrogenase mRNA, and also adipogenic master regulator, peroxisome proliferator-activated receptor-γ, and CCAAT-enhancer-binding protein-α (C/EBPα) mRNA. However, for early adipogenic regulators, such as C/EBPβ and C/EBPδ, and intermediary adipogenic regulators, Krüppel-like factors were unaffected. Western blot analysis showed that ceramicine B was found to inhibit the phosphorylation of Forkhead box O1 (Foxo1), a key process in the insulin signaling pathway. This suggested that the mechanism of anti-LDA activity of ceramicine B was partly via the inhibition of Foxo1 phosphorylation.

Inhibitors of fatty acid synthesis in prokaryotes and eukaryotes as anti-infective, anticancer and anti-obesity drugs

There is a large range of diseases, such diabetes and cancer, which are connected to abnormal fatty acid metabolism in human cells. Therefore, inhibitors of human fatty acid synthase have great potential to manage or treat these diseases. In prokaryotes, fatty acid synthesis is important for signaling, as well as providing starting materials for the synthesis of phospholipids, which are required for the formation of the cell membrane. Recently, there has been renewed interest in the development of new molecules that target bacterial fatty acid synthases for the treatment of bacterial diseases. In this review, we look at the differences and similarities between fatty acid synthesis in humans and bacteria and highlight various small molecules that have been shown to inhibit either the mammalian or bacterial fatty acid synthase or both.

In silico identification of potent pancreatic triacylglycerol lipase inhibitors from traditional Chinese medicine

Pancreatic triacylglycerol lipase (PNLIP) are primary lipases that are critical for triacylglyceride digestion in human. Since reduced metabolism of triacylglyceride might be a plausible concept for weight loss, we screened for potential PNLIP inhibitors from traditional Chinese medicine (TCM) with the aim to identify weight loss candidate compounds. TCM candidates Aurantiamide, Cnidiadin, and 2-hexadecenoic acid exhibited higher Dock Scores than the commercial drug Orlistat, and were also predicted to have inhibitory characteristics against PNLIP using constructed MLR (R² = 0.8664) and SVM (R² = 0.9030) models. Molecular dynamics indicated that the TCM-PNLIP complexes formed were stable. We identified that the PNLIP binding site has several residues that can serve as anchors, and a hydrophobic corridor that provides additional stability to the complex. Aurantiamide, Cnidiadin, and 2-hexadecenoic acid all have features that correspond to these binding site features, indicating their potential as candidates for PNLIP inhibitors. The information presented in this study may provide helpful insights to designing novel weight-control drugs.

Treatment of obesity in children and adolescents

The prevalence of childhood and adolescent obesity continues to rise in the United States (US). Immediate health consequences are being observed, and long-term risks are mounting within the pediatric population, secondary to obesity. The hallmark of prevention and treatment of obesity in children and adolescents includes lifestyle modification (i.e., dietary modification, increased physical activity, and behavioral modifications). However, when intensive lifestyle modification is insufficient to reach weight loss goals, adjunctive pharmacotherapy is recommended. Among the group of weight-loss medications, orlistat is the only US Food and Drug Administration (FDA)-approved prescription drug for the treatment of overweight and obese adolescents. Other medications, including metformin, need larger studies to establish their role in treatment. No single approach to management of pediatric obesity is the answer, given the complexity of the disorder and the many reasons for failure. Evidence of weight loss medications in addition to lifestyle modification supports short-term efficacy for treatment of obese children and adolescents, although long-term results remain unclear.

Lipases or esterases: does it really matter? Toward a new bio-physico-chemical classification

Carboxylester hydrolases, commonly named esterases, consist of a large spectrum of enzymes defined by their ability to catalyze the hydrolysis of carboxylic ester bonds and are widely distributed among animals, plants, and microorganisms. Lipases are lipolytic enzymes which constitute a special class of carboxylic esterases capable of releasing long-chain fatty acids from natural water-insoluble carboxylic esters. However, up to now, several unsuccessful attempts aimed at differentiating "lipases" from "esterases" by using various criteria. These criteria were based on the first substrate used chronologically, primary sequence comparisons, some kinetic parameters, or some structural features.Lipids are biological compounds which, by definition, are insoluble in water. Taking into account this basic physico-chemical criterion, we primarily distinguish lipolytic esterases (L, acting on lipids) from nonlipolytic esterases (NL, not acting on lipids). In view of the biochemical data accumulated up to now, we proposed a new classification of esterases based on various criteria of physico-chemical, chemical, anatomical, or cellular nature. We believe that the present attempt matters scientifically for several reasons: (1) to help newcomers in the field, performing a few key experiments to figure out if a newly isolated esterase is lipolytic or not; (2) to clarify a debate between scientists in the field; and (3) to formulate questions which are relevant to the still unsolved problem of the structure-function relationships of esterases.

Exploration of pyridine containing heteroaryl analogs of biaryl ureas as DGAT1 inhibitors

The diacylglycerol acyltransferase enzyme, DGAT1, presents itself as a potential target for obesity as this enzyme is dedicated to the final committed step in triglyceride biosynthesis. Biphenyl ureas, exemplified by compound 4, have been reported to be potent hDGAT1 inhibitors. We have synthesized and evaluated 2-pyridyl and 3-pyridyl containing biaryl ureas as hDGAT1 inhibitors. Our aim was to incorporate a heteroaryl scaffold within these molecules thereby improving the cLogP profile and making these compounds more drug-like. Compounds within this series exhibited potent hDGAT1 inhibition when evaluated using an in vitro enzymatic assay. Selected compounds were also subjected to an oral fat tolerance test in mice where the percent triglyceride reduction versus a vehicle control was evaluated. Of the studied heteroaryl analogs compound 44 exhibited an in vitro IC(50) of 17nM and a plasma triglyceride reduction of 79% along with a 12-fold improvement in solubility over the biphenyl urea compound 4.

The acyl coenzymeA:monoacylglycerol acyltransferase 3 (MGAT3) gene is a pseudogene in mice but encodes a functional enzyme in rats

Triglyceride (TAG) absorption involves its initial hydrolysis to fatty acids and monoacylglycerol (MAG), which are resynthesized back to diacylglycerol (DAG) and TAG within enterocytes. The resynthesis of DAG is facilitated by fatty acyl-CoA dependent monoacylglycerol acyltransferases (MGATs). Three MGAT enzymes have been isolated in humans and the expression of MGAT2 and MGAT3 in the intestines suggests their functional role in the TAG absorption. In this paper, we report that the Mogat3 gene appears to be a pseudogene in mice while it is a functional gene in rats. Examination of the mouse genomic Mogat3 sequence revealed multiple changes that would result in a translational stop codon or frameshifts. The rat Mogat3 gene, however, is predicted to encode a functional enzyme of 362 amino acids. Expression of rat MGAT3 in human embryonic kidney 293 (HEK293) cells led to the formation of a 36-kDa protein that displayed significant MGAT but not DGAT activity. Tissue expression analysis of rat MGAT3 by real-time PCR analysis indicated that rat MGAT3 has a high level of expression in intestines and pancreas. Our results thus provide the molecular basis to understand the relative functional role of MGAT2 and MGAT3 and also for future exploration of MGAT3 function in animal models.

Current pharmacotherapeutic concepts for the treatment of obesity in adults

Obesity is one of the greatest public health challenges of the twenty-first century. The World Health Organization (WHO) reports that in 2005 approximately 1.6 billion adults were overweight and at least 400 million adults were obese. The prevalence of obesity is still continuing to increase dramatically. Overweight and obese people carry a higher risk for a variety of cardiovascular diseases including hypertension, coronary heart disease, stroke and peripheral occlusive artery disease. Weight loss is considered to be the initial step which helps to prevent or to control the clinical consequences of obesity. In a great number of patients who are not able to reduce weight by means of non-pharmacological measures, drug therapy can assist in reaching the weight management targets. Drug treatment should only be considered as part of a systematic weight management program including dietary and lifestyle changes. This review summarizes current pharmacotherapeutic concepts for the treatment of obesity in adults focusing on efficacy and safety of anti-obesity drugs.

Tetrahydrolipstatin analogues as modulators of endocannabinoid 2-arachidonoylglycerol metabolism

A series of 21 analogues of tetrahydrolipstatin (THL, 1) were synthesized and tested as inhibitors of the formation or hydrolysis of the endocannabinoid 2-arachidonoylglycerol (2-AG). Three of the novel compounds, i.e., 11, 13, and 15, inhibited 2-AG formation via the diacylglycerol lipase alpha (DAGLalpha) with IC 50 values lower than 50 nM (IC 50 of THL = 1 microM) and were between 23- and 375-fold selective vs 2-AG hydrolysis by monoacylglycerol lipase (MAGL) as well as vs cannabinoid CB 1 and CB 2 receptors and anandamide hydrolysis by fatty acid amide hydrolase (FAAH). Three other THL analogues, i.e., 14, 16, and 18, were slightly more potent than THL against DAGLalpha and appreciably selective vs MAGL, CB receptors, and FAAH (15-26-fold). One compound, i.e., 8, was a potent inhibitor of MAGL-like activity (IC 50 = 0.41 microM), and relatively ( approximately 7-fold) selective vs the other targets tested.

Orlistat-associated adverse effects and drug interactions: a critical review

Orlistat, an anti-obesity drug, is a potent and specific inhibitor of intestinal lipases. In light of the recent US FDA approval of the over-the-counter sale of orlistat (60 mg three times daily), clinicians need to be aware that its use may be associated with less well known, but sometimes clinically relevant, adverse effects. More specifically, the use of orlistat has been associated with several mild-to-moderate gastrointestinal adverse effects, such as oily stools, diarrhoea, abdominal pain and faecal spotting. A few cases of serious hepatic adverse effects (cholelithiasis, cholostatic hepatitis and subacute liver failure) have been reported. However, the effects of orlistat on non-alcoholic fatty liver disease are beneficial. Orlistat-induced weight loss seems to have beneficial effects on blood pressure. No effect has been observed on calcium, phosphorus, magnesium, iron, copper or zinc balance or on bone biomarkers. Interestingly, the use of orlistat has been associated with rare cases of acute kidney injury, possibly due to the increased fat malabsorption resulting from the inhibition of pancreatic and gastric lipase by orlistat, leading to the formation of soaps with calcium and resulting in increased free oxalate absorption and enteric hyperoxaluria. Orlistat has a beneficial effect on carbohydrate metabolism. No significant effect on cancer risk has been reported with orlistat.Orlistat interferes with the absorption of many drugs (such as warfarin, amiodarone, ciclosporin and thyroxine as well as fat-soluble vitamins), affecting their bioavailability and effectiveness. This review considers orlistat-related adverse effects and drug interactions. The clinical relevance and pathogenesis of these effects is also discussed.

Orlistat in the prevention of diabetes in the obese patient

There has been an increase in the concern about preventing type 2 diabetes mellitus (T2DM), a disease with great and increasing prevalence. The prevalence of obesity, physical inactivity, Western processed diet, important risk factors for the development of T2DM, are also rising. Free fatty acids are increased in obesity and reduce insulin clearance and increase hepatic glucose production. Implementation of a healthy lifestyle has been show to slow the progression of impaired glucose tolerance to T2DM. Orlistat is an inhibitor of lipase activity, with proved efficacy in body weight reduction and long-term management of obesity and more favorable effects on carbohydrate metabolism and it was prospectively shown in XENDOS study that orlistat promoted long-term weight loss and prevented T2DM onset in obese individuals with normal and impaired glucose tolerance at baseline over four years. This benefit could be associated to the weight loss itself, to the limited absorption of lipids and reduction of plasma free fatty acids, to increased production of incretins or to modulation of secretion of cytokines by adipocytes, all effects secondary to orlistat treatment. A proposed strategy is to identify subjects at highest risk to receive a drug intervention, using lifestyle interventions alone at the community level.

Targeting lipid metabolism by the lipoprotein lipase inhibitor orlistat results in apoptosis of B-cell chronic lymphocytic leukemia cells

Constitutively activated pathways contribute to apoptosis resistance in chronic lymphocytic leukemia (CLL). Little is known about the metabolism of lipids and function of lipases in CLL cells. Performing gene expression profiling including B-cell receptor (BCR) stimulation of CLL cells in comparison to healthy donor CD5+ B cells, we found significant overexpression of lipases and phospholipases in CLL cells. In addition, we observed that the recently defined prognostic factor lipoprotein lipase (LPL) is induced by stimulation of BCR in CLL cells but not in CD5+ normal B cells. CLL cellular lysates exhibited significantly higher lipase activity compared to healthy donor controls. Incubation of primary CLL cells (n=26) with the lipase inhibitor orlistat resulted in induction of apoptosis, with a half-maximal dose (IC(50)) of 2.35 microM. In healthy B cells a significantly higher mean IC(50) of 148.5 microM of orlistat was observed, while no apoptosis was induced in healthy peripheral blood mononuclear cells (PBMCs; P<0.001). Orlistat-mediated cytotoxicity was decreased by BCR stimulation. Finally, the cytotoxic effects of orlistat on primary CLL cells were enhanced by the simultaneous incubation with fludarabine (P=0.003). In summary, alterations of lipid metabolism are involved in CLL pathogenesis and might represent a novel therapeutic target in CLL.

Orlistat for the management of overweight individuals and obesity: a review of potential for the 60-mg, over-the-counter dosage

Orlistat, in the 60-mg over-the-counter dose, was recently approved by the FDA. This lipase inhibitor blocks absorption of ~25% of ingested fat and has ~85% of the efficacy of the 120-mg dose for weight loss. Over 16 weeks weight loss with diet and orlistat 60 mg averages ~5% of initial body weight. The 60-mg dose is better tolerated than the 120-mg dose and the gastrointestinal side effects are minimal when individuals consume < 30% of their energy from fat. In addition to facilitating modest weight loss, orlistat use decreases serum LDL-cholesterol values by ~10%. When taken three times daily before meals, orlistat 60 mg modifies lifestyle behavior, encourages lower fat-consumption and sets the stage for other healthy lifestyle changes.

Obesity: which drug and when?

BACKGROUND

Obesity, with all its consequences, is audaciously confronting medical professionals and health service providers worldwide. Diet and exercise intervention is an essential part of any weight management strategy, but may not succeed in isolation. Effective approaches for routine practice are more likely to involve affordable, efficacious and well-tolerated drug therapy than the more expensive, case selective approach of bariatric surgery.

OBJECTIVES AND CONCLUSIONS

Advancement of pharmacotherapy is expanding the battery of available drugs; the clinician is faced with an increasingly complex therapeutic decision. Which drug to use, and when, is influenced by a range of factors, discussed here. There is a large body of high quality evidence in the literature to support the presently available drugs; however, many questions remain unanswered including duration of therapy and whether longer-term goals of improved morbidity and mortality are achievable. Clinician and patient awareness of these issues will provide a more informed therapeutic decision and ultimately improve the potential for reaching the weight management targets.

State of the Art Review: Long-term Pharmacotherapy for Overweight and Obesity: A Review of Sibutramine, Orlistat, and Rimonabant

The objective of this review is to evaluate the safety and efficacy of pharmacotherapy for long-term maintenance of weight loss in overweight and obese patients. Literature was obtained through a MEDLINE (1966 to July 2006) search and a bibliographic review of published articles. Key terms used included overweight, obesity, sibutramine, orlistat, and rimonabant. The search was further limited to clinical trials in humans and in the English language. Obesity is a chronic condition requiring long-term therapy. Two agents, sibutramine and orlistat, are currently approved by the Food and Drug Administration for the long-term treatment of obesity. Rimonabant, marketed in Europe as Accomplia, has demonstrated efficacy for long term weight loss, however an Food and Drug Administration advisory panel voted against its approval in June 2007 due to safety concerns (psychiatric effects). For clinically meaningful results, these agents must be used in conjunction with lifestyle therapy, including a hypocaloric diet, increased physical activity, and behavioral modification. This article reviews clinical trials evaluating the safety and efficacy of sibutramine, orlistat, and rimonabant in reducing weight and examines other health benefits and risks associated with these agents.

Pharmacotherapeutic options for overweight adolescents

OBJECTIVE

To evaluate the safety and efficacy of current pharmacotherapeutic options for weight loss in overweight adolescents.

DATA SOURCES

Literature was obtained through MEDLINE Ovid (1996-April 2007) and EMBASE Drugs and Pharmacology (1991-2nd quarter 2007) searches and a bibliographic review of published articles. Key words included adolescents, overweight, obesity, anti-obesity agents, drug therapy, orlistat, sibutramine, and metformin.

STUDY SELECTION AND DATA EXTRACTION

All studies published in the English language that evaluated the use of pharmacotherapy for the treatment of overweight adolescents were critically analyzed; pertinent articles were selected for this review.

DATA SYNTHESIS

Orlistat has been approved for use in adolescents between the ages of 12 and 16 years. The most frequently reported adverse effects of orlistat were gastrointestinal; reduced concentrations of fat-soluble vitamins were also observed. Of the 6 clinical trials published, 5 have shown statistically significant reductions in body mass index (BMI) from baseline, ranging from 0.55 to 4.09 kg/m2; one small trial failed to demonstrate significant weight reduction compared with placebo. Sibutramine has also been evaluated for use in overweight adolescents in 6 trials. Trials demonstrated a statistically significant reduction in BMI up to 5.6 kg/m2 (from baseline). Of concern is evidence indicating that sibutramine therapy may be associated with elevated blood pressure, increased pulse rate, depression, and suicidal ideations. Lastly, metformin has recently been evaluated for weight loss in overweight adolescents; small, short-term trials demonstrate modest reductions in weight and BMI.

CONCLUSIONS

Orlistat has been proven both safe and effective for weight reduction in overweight adolescents. Sibutramine has also been proven effective in reducing weight in this population; however, the potential for severe adverse effects requires further investigation. Metformin has demonstrated promising results in small trials; its role in the treatment of overweight adolescents will remain investigational until further research is conducted.

Visualization of 2-arachidonoylglycerol accumulation and cannabinoid CB1 receptor activity in rat brain cryosections by functional autoradiography

In neuronal signalling mediated by the endocannabinoid 2-arachidonoylglycerol, both synthetic and inactivating enzymes operate within close proximity to the G(i/o)-coupled pre-synaptic CB(1) receptors, thus allowing for rapid onset and transient duration of this lipid modulator. In rat brain, 2-arachidonoylglycerol is inactivated mainly via hydrolysis by serine hydrolase inhibitor-sensitive monoacylglycerol lipase activity. We show in this study that comprehensive pharmacological elimination of this activity in brain cryosections by methyl arachidonylfluorophosphonate or hexadecylsulphonyl fluoride results in endocannabinoid-mediated CB(1) receptor activity, which can be visualized by functional autoradiography. URB597, a specific inhibitor of anandamide hydrolysis proved ineffective. TLC indicated that the bioactivity resided in 2-arachidonoylglycerol-containing fraction and gas chromatography-mass spectroscopy detected elevated levels of monoacylglycerols, including 2-arachidonoylglycerol in this fraction. Although two diacylglycerol lipase inhibitors, tetrahydrolipstatin (THL) and RHC80267, blocked the bulk of 2-arachidonoylglycerol accumulation in methyl arachidonylfluorophosphonate-treated sections, only THL reversed the endocannabinoid-dependent CB(1) receptor activity. Further studies indicated that at the used concentrations, THL rather specifically antagonized the CB(1) receptor. These findings confirm that in brain sections there is preservation of enzymatic pathways regulating the production of endogenous receptor ligands. Furthermore, the presently described methodology may serve as an elegant and intuitive approach to identify novel membrane-derived lipid modulators operating in the CNS.

Pharmacological treatment of obesity

This review offers an overview of physiological agents, current therapeutics, as well as medications, which have been extensively used and those agents not currently available or non-classically considered anti-obesity drugs. As obesity - particularly that of central distribution - represents an important triggering factor for insulin resistance, its pharmacological treatment is relevant in the context of metabolic syndrome control. The authors present an extensive review on the criteria for anti-obesity management efficacy, on physiological mechanisms that regulate central and/or peripheral energy homeostasis (nutrients, monoamines, and peptides), on beta-phenethylamine pharmacological derivative agents (fenfluramine, dexfenfluramine, phentermine and sibutramine), tricyclic derivatives (mazindol), phenylpropanolamine derivatives (ephedrin, phenylpropanolamine), phenylpropanolamine oxytrifluorphenyl derivative (fluoxetine), a naftilamine derivative (sertraline) and a lipstatine derivative (orlistat). An analysis of all clinical trials - over ten-week long - is also presented for medications used in the management of obesity, as well as data about future medications, such as a the inverse cannabinoid agonist, rimonabant.

Pharmacotherapy for obesity

The current obesity pandemic imposes a major global disease burden. However, sustained weight loss of between 5 and 10% in the obese confers marked health benefits. Currently available pharmacotherapies, orlistat and sibutramine, can induce weight loss of between 5 and 10% over 2 years or more. However, in these trials, drug induced weight loss tends to be only 2-4 kg greater than that produced by placebo control. Despite this, in the XENDOS trial, the modest placebo-subtract weight loss produced by orlistat (2.8 kg) reduced the incidence of diabetes by over a third. Recent data on the potential anti-obesity drug rimonabant are also reviewed.

Orlistat

Orlistat (Xenical) is a reversible inhibitor of gastric and pancreatic lipases. In conjunction with a hypocaloric diet and moderate exercise, orlistat is an effective drug for use in the management of obesity in adults with or without comorbidities. Recent data have shown that orlistat is also effective as a component of weight management strategies in obese adolescents. In addition to its well established efficacy in achieving modest weight loss, orlistat has been shown to improve glycaemic parameters in obese adults with type 2 diabetes mellitus as well as some features of the metabolic syndrome. Orlistat is generally well tolerated. Thus, orlistat is an option for the treatment of obese patients with or without type 2 diabetes and also has a role in the management of obese patients with the metabolic syndrome, associated comorbidities or concomitant disorders.

The effects of orlistat on metabolic parameters and other cardiovascular risk factors

Orlistat is an antiobesity drug with a well documented efficacy in weight reduction and weight maintenance. Weight reduction with orlistat has been associated with a favourable effect on obesity-related cardiovascular risk factors. Orlistat treatment is associated with a reduction in serum insulin levels. Moreover, orlistat reduces the incidence of type 2 diabetes in patients with impaired glucose tolerance and lowers the required dose of metformin, sulfonylureas and insulin in patients with type 2 diabetes. Furthermore, orlistat can reduce total and low density lipoprotein (LDL) cholesterol levels and improve postprandial triglyceridemia, as well as the low density lipoprotein cholesterol/high density lipoprotein cholesterol ratio (LDL/HDL ratio). Moreover, orlistat appears to have a favourable effect on some inflammatory markers, such as TNF-alpha and interleukin-6 and has a time-depended effect on some haemostatic factors.

Orlistat: a review of its use in the management of patients with obesity

Orlistat is an inhibitor of gastrointestinal lipases and, therefore, prevents the absorption of dietary fat. This agent reduces weight in obese adults and adolescents with or without comorbidities (including type 2 diabetes mellitus, hypercholesterolaemia, hypertension, metabolic syndrome) who received up to 4 years of therapy in conjunction with a hypocaloric diet. In obese patients, orlistat in combination with a hypocaloric diet improved metabolic risk factors and reduced the risk of developing type 2 diabetes. Furthermore, this agent was cost effective in patients with obesity, particularly those with type 2 diabetes. Orlistat is generally well tolerated, with gastrointestinal adverse events being most commonly reported. Orlistat, in addition to lifestyle and dietary intervention, is thus an attractive option for the treatment of patients with obesity, especially those with associated comorbidities or at risk of developing type 2 diabetes.

Diabesity

Weight reduction has been shown to improve glycemic control and cardiovascular risk factors associated with insulin resistance in obese individuals with type 2 diabetes mellitus. Therapeutic options for these patients include promoting weight loss (non-pharmacologic and pharmacologic treatment) and improving glycemic control, as well as treating common associated risk factors such as arterial hypertension and dyslipidemias. This article provides an overview of anti-obesity drugs used in the treatment of obese individuals with type 2 diabetes. The most widely investigated drugs, sibutramine and orlistat, result in modest, clinically worthwhile weight loss, with demonstrable improvements in many co-morbidities, among them, type 2 diabetes. Clinical trials with these anti-obesity medications in cohorts of obese diabetic patients have been reviewed as well as cathecolaminergic agents (diethylpropion [amfepramone], fenproporex, mazindol, ephedrine-caffeine combination), serotoninergic drugs (fenfluramine, dexfenfluramine, fluoxetine), and other drugs that have some action on weight loss (the antidiabetic agent metformin, anti-epileptic agents topiramate and zonisamide, and the antidepressive bupropion [amfebutamone]). These trials show variable benefits in terms of effects on glucose profiles.

The physical properties of rectal contents have effects on anorectal continence: insights from a study into the cause of fecal spotting on orlistat

PURPOSE

The intermittent loss of oil or stool ("spotting") is an adverse effect that occurs in patients taking orlistat; the pathophysiology is unknown. This study was designed to investigate the local effects of orlistat, free fatty acids, and the effects of the physical properties of rectal contents on anorectal function and continence.

METHODS

Anorectal physiology and continence function were assessed in ten healthy patients after the application of four test enemas: 1) high-viscosity stool substitute, 2) stool substitute with free fatty acid, 3) low-viscosity oil with placebo, 4) oil with orlistat. Rectal function and capacity were assessed by barostat techniques. Anal resting pressure, squeeze pressure, and squeeze duration were assessed by manometry. A retention test was performed using the same enemas as a quantitative assessment of continence.

RESULTS

Orlistat and free fatty acid had no adverse effects on anorectal function or continence. For each enema, the maximum volume retained correlated with rectal capacity (r = 0.85; P < 0.01). Continence during rectal filling was better maintained for high-viscosity stool substitute than low-viscosity oil enemas (P < 0.03). Patients able to maintain effective squeeze pressure retained more of the low-viscosity enemas than those with short squeeze duration (P < 0.01); in contrast, the volume retained of high-viscosity enemas was unaffected by anal sphincter function.

CONCLUSIONS

The physical properties of rectal contents, rectal capacity, and voluntary anal sphincter function have effects on continence function in healthy patients. The occurrence of spotting may depend on both intrinsic anorectal function and the effects of orlistat on the volume and physical properties of stool.

Identification of acyl coenzyme A:monoacylglycerol acyltransferase 3, an intestinal specific enzyme implicated in dietary fat absorption

Acyl coenzyme A:monoacylglycerol acyltransferase (MGAT) catalyzes the synthesis of diacylglycerol using 2-monoacylglycerol and fatty acyl coenzyme A. This enzymatic reaction is believed to be an essential and rate-limiting step for the absorption of fat in the small intestine. Although the first MGAT-encoding cDNA, designated MGAT1, has been recently isolated, it is not expressed in the small intestine and hence cannot account for the high intestinal MGAT enzyme activity that is important for the physiology of fat absorption. In the current study, we report the identification of a novel MGAT, designated MGAT3, and present evidence that it fulfills the criteria to be the elusive intestinal MGAT. MGAT3 encodes a approximately 36-kDa transmembrane protein that is highly homologous to MGAT1 and -2. In humans, expression of MGAT3 is restricted to gastrointestinal tract with the highest level found in the ileum. At the cellular level, recombinant MGAT3 is localized to the endoplasmic reticulum. Recombinant MGAT3 enzyme activity produced in insect Sf9 cells selectively acylates 2-monoacylglycerol with higher efficiency than other stereoisomers. The molecular identification of MGAT3 will facilitate the evaluation of using intestinal MGAT as a potential point of intervention for antiobesity therapies.

Treatment of obesity: an update on anti-obesity medications

The information presented in this article provides an overview of physiological agents, therapeutics in current use, and medications that have been extensively used in the past but are no longer available, or are not classically considered as anti-obesity drugs. The authors present an extensive review on the criteria for anti-obesity management efficacy, on physiological mechanisms that regulate central and/or peripheral action energetic homeostasis (nutrients, monoamines and peptides), and on beta-phenethylamine pharmacological-derivative agents (fenfluramine, dexfenfluramine, phentermine, diethylpropion, fenproporex and sibutramine), tricyclic derivatives (mazindol), phenylpropanolamine derivatives (ephedrine, phenylpropanolamine), a phenylpropanolamine oxy-tri-fluor-phenyl derivative (fluoxetine), a naftilamine derivative (sertraline) and a lipstatine derivative (orlistat). An analysis of all clinical trials longer than 10 weeks in duration is also presented for medications used in the management of obesity.

Weight management and current options in pharmacotherapy: orlistat and sibutramine

BACKGROUND

Chronic obesity is associated with various cardiovascular disorders, including diabetes, dyslipidemia, and hypertension. Pharmacotherapy with antiobesity agents is an important management strategy in conjunction with lifestyle interventions.

OBJECTIVE

This article describes the pharmacologic management of obesity, concentrating on orlistat and sibutramine.

METHODS

Relevant articles were identified through a MEDLINE search (1966-February 2002) using the terms obesity, overweight, weight loss, antiobesity drugs, orlistat, and sibutramine. The search for efficacy trials was limited to randomized controlled studies of >6 months' duration. Also included in the review were relevant references cited in the bibliographies of identified articles, news reports, and the authors' own data.

RESULTS

Orlistat reduces fat absorption by inhibiting gastrointestinal lipases. In randomized, controlled trials of up to 2 years' duration, orlistat plus a hypocaloric diet produced significantly greater weight loss than placebo (P < 0.001). In the maintenance phase, patients taking orlistat had less weight regain than did placebo recipients. The weight reduction with orlistat was also associated with a significant improvement in control of cardiovascular risk factors (P < 0.05). Unlike orlistat, sibutramine works by suppressing appetite; its efficacy, however, was similar to that of orlistat in the identified clinical trials. Orlistat was associated primarily with gastrointestinal side effects. Use of orlistat was associated with minimal drug interactions, except with cyclosporine, with which it should not be taken. Sibutramine was also well tolerated, although it may cause dry mouth, anorexia, and insomnia, and should be used with caution in patients at risk for cardiovascular disease.

CONCLUSIONS

Orlistat and sibutramine demonstrated a favorable efficacy and safety profile in randomized controlled trials. Current evidence supports their use as adjuncts to lifestyle modifications in the treatment of obesity.

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.

Tratamento Farmacológico da Obesidade

A informação apresentada nesta revisão oferece uma visão da terapêutica corrente, bem como de medicamentos que já foram extensamente utilizados e que não mais estão disponíveis ou não são considerados classicamente agentes anti-obesidade. Os autores realizam uma extensa revisão sobre os critérios de avaliação de eficácia de tratamentos anti-obesidade, sobre agentes farmacológicos derivados beta-fenetilamínicos (anfepramona, fenfluramina, dexfenfluramina, fentermina e sibutramina), derivados tricíclicos (mazindol), derivados fenilpropanolamínicos (efedrina, fenilpropanolamina), derivado oxitrifluorfenil da fenilpropanolamina (fluoxetina), derivado naftilamínico (sertralina) e derivado da lipstatina (orlistat). É apresentada uma análise de todos os estudos clínicos de mais de dez semanas de duração com medicamentos usados no tratamento da obesidade.

Effects of orlistat on fat-soluble vitamins in obese adolescents

STUDY OBJECTIVES

To determine whether orlistat causes fat-soluble vitamin deficiencies in African-American and Caucasian adolescents.

DESIGN

Prospective, open-label pilot study.

SETTING

Warren Grant Magnuson Clinical Center of the National Institutes of Health.

PATIENTS

Seventeen adolescents with body mass indexes above the 95th percentile for age, race, and gender who also had at least one obesity-related comorbid condition.

INTERVENTION

Subjects received orlistat 120 mg 3 times/day and a daily multivitamin supplement containing vitamin A 5000 IU, vitamin D 400 IU, vitamin E 300 IU, and vitamin K 25 microg.

MEASUREMENTS AND MAIN RESULTS

During 3-6 months of orlistat treatment, acute absorption of retinol (vitamin A) was not significantly altered, but absorption of alpha-tocopherol (vitamin E) was significantly reduced compared with baseline levels (p<0.001). Serum levels of vitamins A and E did not change significantly; however, there was a nonsignificant decrease in vitamin K. Mean vitamin D levels were significantly reduced compared with baseline (p<0.02) after 1 month of orlistat, despite multivitamin supplementation.

CONCLUSION

It may be prudent to monitor vitamin D concentrations in adolescents who take orlistat, even when a multivitamin is prescribed.

Obesity in transplant patients: case report showing interference of orlistat with absorption of cyclosporine and review of literature

OBJECTIVE

To report a case of an obese patient who had undergone renal transplantation and who had subtherapeutic levels of serum cyclosporine after treatment with orlistat.

METHODS

The clinical and laboratory findings are presented, and the few cases reported in the literature are reviewed.

RESULTS

A 29-year-old woman had subtherapeutic plasma levels of cyclosporine after orlistat treatment (360 mg/day) was initiated. The subtherapeutic levels persisted even though orlistat was administered the recommended 2 hours before ingestion of cyclosporine and even though the dosage of orlistat was decreased to only 240 mg/day. Because an increase of body weight is common after organ transplantation, treatment with orlistat has been used. In such patients, however, six cases of reduced therapeutic plasma levels of cyclosporine have been reported. Although a drug-drug interaction has been suggested, this case suggests that the decreased plasma cyclosporine levels are due to reduced absorption of fats rather than a drug-drug interaction. Because this patient was unable to adhere to a low-fat diet, she experienced severe diarrhea, a factor that may have dramatically diminished the absorption of cyclosporine.

CONCLUSION

Adherence to a low-fat diet should be strongly recommended if orlistat is prescribed to patients taking cyclosporine. Moreover, strict surveillance of the plasma concentration of cyclosporine is important.

Inhibition of gastrointestinal lipolysis by Orlistat during digestion of test meals in healthy volunteers

The inhibition of digestive lipases by the antiobesity drug Orlistat along with lipolysis levels and fecal fat excretion were measured in healthy humans. Orlistat was found to be a powerful gastric lipase inhibitor, achieving 46.6--91.4% enzyme inhibition and thus greatly reducing gastric lipolysis of solid and liquid meals (11--33% of respective controls). Gastric lipase inhibition by Orlistat was extremely fast (half-inhibition time < 1 min). Duodenal lipolysis was reduced significantly by Orlistat given with the solid meal (32.6--37.6% of controls) but was only slightly reduced by Orlistat given with the liquid meal (74.5--100% of controls). Human pancreatic lipase (HPL) inhibition was found to be high (51.2--82.6%), however, regardless of the meal. These paradoxical results were explained when in vitro lipolysis experiments were performed. The rates of HPL inhibition by Orlistat were found to be similar with both types of meals (half-inhibition time 5--6 min), but the preemulsified triglycerides of the liquid meal were rapidly hydrolyzed by HPL before the enzyme was significantly inhibited by Orlistat. With the solid meal, the rate of hydrolysis of the meal triglycerides by HPL was slower than the rate of HPL inhibition by Orlistat. As predicted from the previous results, the effects of Orlistat on fat excretion levels were found to be much greater with the solid (40.5--57.4% of ingested fat) than with the liquid (4.2--18.8%) test meal.