Long-term systemic exposure of orlistat, a lipase inhibitor, and its metabolites in obese patients

FASN deficiency induces a cytosol-to-mitochondria citrate flux to mitigate detachment-induced oxidative stress

Fatty acid synthase (FASN) maintains de novo lipogenesis (DNL) to support rapid growth in most proliferating cancer cells. Lipogenic acetyl-coenzyme A (CoA) is primarily produced from carbohydrates but can arise from glutamine-dependent reductive carboxylation. Here, we show that reductive carboxylation also occurs in the absence of DNL. In FASN-deficient cells, reductive carboxylation is mainly catalyzed by isocitrate dehydrogenase-1 (IDH1), but IDH1-generated cytosolic citrate is not utilized for supplying DNL. Metabolic flux analysis (MFA) shows that FASN deficiency induces a net cytosol-to-mitochondria citrate flux through mitochondrial citrate transport protein (CTP). Previously, a similar pathway has been shown to mitigate detachment-induced oxidative stress in anchorage-independent tumor spheroids. We further report that tumor spheroids show reduced FASN activity and that FASN-deficient cells acquire resistance to oxidative stress in a CTP- and IDH1-dependent manner. Collectively, these data indicate that by inducing a cytosol-to-mitochondria citrate flux, anchorage-independent malignant cells can gain redox capacity by trading off FASN-supported rapid growth.

FASN-deficiency induces a cytosol-to-mitochondria citrate flux to mitigate detachment-induced oxidative stress

Fatty acid synthase (FASN) maintains de novo lipogenesis (DNL) to support rapid growth in most proliferating cancer cells. Lipogenic acetyl-CoA is primarily produced from carbohydrates but can arise from glutamine-dependent reductive carboxylation under hypoxia. Here we show that reductive carboxylation also occurs in the absence of DNL in cells with defective FASN. In this state, reductive carboxylation was mainly catalyzed by isocitrate dehydrogenase-1 (IDH1) in the cytosol, but IDH1-generated citrate was not used for DNL. Metabolic flux analysis (MFA) revealed that FASN-deficiency induced a net cytosol-to-mitochondria citrate flux through citrate transport protein (CTP). A similar pathway was previously shown to mitigate detachment-induced mitochondrial reactive oxygen species (mtROS) in anchorage-independent tumor spheroids. We further demonstrate that FASN-deficient cells acquire resistance to oxidative stress in a CTP- and IDH1-dependent manner. Together with the reduced FASN activity in tumor spheroids, these data indicate that anchorage-independent malignant cells trade FASN-supported rapid growth for a cytosol-to-mitochondria citrate flux to gain redox capacity against detachment-induced oxidative stress.

Structure-activity relationship of dietary flavonoids on pancreatic lipase

Lipase is a very important digestive enzyme for triglyceride absorption in vivo. The inhibitory activities of 26 dietary flavonoids, including flavone, flavanone, isoflavone and flavanol, on lipase were determined. Flavone exhibited stronger inhibitory activity than other types of flavonoids. Among them, luteolin exhibited the strongest inhibitory activity with IC50 value of 99 ± 11 μM, followed by quercetin and baicalein. The binding affinity of these flavonoids with lipase was investigated by fluorescence titration method. The binding affinity of flavones was stronger than flavanones, and was linearly positively correlated with their inhibitory activity. The binding of flavones on lipase caused the blue-shift of fluorescence, while flavanones caused red-shift. The analysis of structure-activity relationship of flavonoids on lipase revealed that the structure of C ring is very crucial. The hydrogenation of C2=C3 bond and the absence of C=O group in C ring both caused significant decrease of inhibitory activity. Besides, the hydroxylation on ring A and B of flavones increased the activity, while glycosylation weakened the activity. Molecular docking analysis confirmed that C2=C3 bond in C ring of flavones increases the π-conjugation and contributes to maintaining the planarity of flavonoid structure, which favour its Pi-Pi interaction with lipase.

Modulation of Milk and Lipid Synthesis and Secretion in a3-Dimensional Mouse Mammary Epithelial Cell Culture Model: Effects of Palmitate and Orlistat

Human milk synthesis is impacted by maternal diet, serum composition, and substrate uptake and synthesis by mammary epithelial cells (MECs). The milk of obese/high-fat-diet women has an increased fat content, which promote excess infant weight gain and the risk of childhood/adult obesity. Yet, the knowledge of milk synthesis regulation is limited, and there are no established approaches to modulate human milk composition. We established a 3-dimensional mouse MEC primary culture that recreates the milk production pathway and tested the effects of the major saturated fatty acid in human milk (palmitate) and a lipoprotein lipase inhibitor (orlistat) on triglyceride production. Positive immunostaining confirmed the presence of milk protein and intracellular lipid including milk globules in the cytoplasm and extracellular space. The treatment with palmitate activated "milk" production by MECs (β-casein) and the lipid pathway (as evident by increased protein and mRNA expression). Consistent with these cellular changes, there was increased secretion of milk protein and triglyceride in MEC "milk". The treatment with orlistat suppressed milk triglyceride production. Palmitate increased milk and lipid synthesis, partly via lipoprotein lipase activation. These findings demonstrate the ability to examine MEC pathways of milk production via both protein and mRNA and to modulate select pathways regulating milk composition in MEC culture.

Intestinal delivery in a long-chain fatty acid formulation enables lymphatic transport and systemic exposure of orlistat

Orlistat is a pancreatic lipase (PL) inhibitor that inhibits dietary lipid absorption and is used to treat obesity. The oral bioavailability of orlistat is considered zero after administration in standard formulations. This is advantageous in the treatment of obesity. However, if orlistat absorption could be improved it has the potential to treat diseases such as acute and critical illnesses where PL transport to the systemic circulation via gut lymph promotes organ failure. Orlistat is highly lipophilic and may associate with intestinal lipid absorption pathways into lymph. Here we investigate the potential to improve orlistat lymph and systemic uptake through intestinal administration in lipid formulations (LFs). The effect of lipid type, lipid dose, orlistat dose, and infusion time on lymph and systemic availability of orlistat was investigated. After administration in all LFs, orlistat concentrations in lymph were greater than in plasma, suggesting direct transport via lymph. Lymph and plasma orlistat derivative concentrations were ~8-fold greater after administration in a long-chain fatty acid (LC-FA) compared to a lipid-free, LC triglyceride (LC-TG) or medium-chain FA (MC-FA) formulation. Overall, administration of orlistat in a LC-FA formulation promotes lymph and systemic uptake which may enable treatment of diseases associated with elevated systemic PL activity.

The Fatty Acid Lipid Metabolism Nexus in COVID-19

Enteric symptomology seen in early-stage severe acute respiratory syndrome (SARS)-2003 and COVID-19 is evidence of virus replication occurring in the intestine, liver and pancreas. Aberrant lipid metabolism in morbidly obese individuals adversely affects the COVID-19 immune response and increases disease severity. Such observations are in line with the importance of lipid metabolism in COVID-19, and point to the gut as a site for intervention as well as a therapeutic target in treating the disease. Formation of complex lipid membranes and palmitoylation of coronavirus proteins are essential during viral replication and assembly. Inhibition of fatty acid synthase (FASN) and restoration of lipid catabolism by activation of AMP-activated protein kinase (AMPK) impede replication of coronaviruses closely related to SARS-coronavirus-2 (CoV-2). In vitro findings and clinical data reveal that the FASN inhibitor, orlistat, and the AMPK activator, metformin, may inhibit coronavirus replication and reduce systemic inflammation to restore immune homeostasis. Such observations, along with the known mechanisms of action for these types of drugs, suggest that targeting fatty acid lipid metabolism could directly inhibit virus replication while positively impacting the patient's response to COVID-19.

The risk of cardiovascular complications with current obesity drugs

INTRODUCTION

Obesity is associated with an increased risk of cardiovascular morbidity and mortality. Four medications are approved by the US Food and Drug Administration (FDA) for chronic weight management when used as an adjunct to a reduced-calorie diet and increased physical activity in adults. These medications result in clinically significant weight losses, as well as improvements in some cardiometabolic risk factors.

AREAS COVERED

We briefly review the history of anti-obesity medications (AOMs) as related to cardiovascular safety, and summarize weight loss efficacy and cardiovascular data from clinical trials of orlistat, phentermine/topiramate, naltrexone/bupropion, and liraglutide.

EXPERT OPINION

Current AOMs approved for chronic weight management have generally favorable effects on some cardiometabolic parameters. However, the long-term safety of orlistat, phentermine/topiramate, and naltrexone/bupropion on cardiovascular morbidity and mortality have not been established. The cardiovascular safety of liraglutide, at a dose of 1.8 mg/d, was demonstrated in a large randomized outcomes trial in participants with type 2 diabetes.

Orlistat as a FASN inhibitor and multitargeted agent for cancer therapy

INTRODUCTION

Cancer cells have increased glycolysis and glutaminolysis. Their third feature is increased de novo lipogenesis. As such, fatty acid (FA) synthesis enzymes are over-expressed in cancer and their depletion causes antitumor effects. As fatty acid synthase (FASN) plays a pivotal role in this process, it is an attractive target for cancer therapy.

AREAS COVERED

This is a review of the lipogenic phenotype of cancer and how this phenomenon can be exploited for cancer therapy using inhibitors of FASN, with particular emphasis on orlistat as a repurposing drug.

EXPERT OPINION

Disease stabilization only has been observed with a highly selective FASN inhibitor used as a single agent in clinical trials. It is too early to say whether the absence of tumor responses other than stabilization results because even full inhibition of FASN is not enough to elicit antitumor responses. The FASN inhibitor orlistat is a 'dirty' drug with target-off actions upon at least seven targets with a proven role in tumor biology. The development of orlistat formulations suited for its intravenous administration is a step ahead to shed light on the concept that drug promiscuity can or not be a virtue.

Pharmacologic and Pharmacodynamic Equivalence of 2 Formulations of Orlistat

We sought to establish the bioequivalence of 2 weight-loss aids: orlistat 27-mg chewable tablet and orlistat 60-mg capsule, measured pharmacodynamically as percentage fecal fat excretion. Two open-label, single-center, randomized, 3-period, 3-treatment crossover studies were conducted in adults with body mass index 25-33 kg/m² . For each 9-day treatment period, subjects received orlistat 27-mg chewable tablet, 60-mg capsule, or 120-mg capsules (2 60-mg capsules) 3 times daily; a 2-day washout separated treatments. Primary bioequivalence analyses were based on 2 1-sided tests of the 90% CI of the ratio of geometric means using log-transformed data (study 1) and by the dose-scale method to calculate bias-corrected and accelerated 90% CI of relative bioavailability (f) using nontransformed data (study 2). Bioequivalence was established if 90% CIs fell within 0.80-1.25. In total, 48 and 144 subjects were randomized in study 1 and study 2, respectively. Bioequivalence between the formulations was established in both studies: study 1 ratio of geometric means of percentage fecal fat excretion was 0.96 (2 1-sided tests, 90% CI 0.87-1.06); study 2-point estimate of f was 1.09 (bias-corrected and accelerated 90% CI 0.98-1.22). Tolerability of the 27-mg tablet was consistent with the 60-mg capsule; mild gastrointestinal effects were most common.

Possible Role of Phosphatidylcholine and Sphingomyelin on Fumonisin B1-mediated Toxicity

A major corn-related mycotoxin, fumonisin B1 (FB1), continues to attract attention of researchers as well as risk-assessors due to the diverse toxicological characteristics, including distinct target tissues in different animal species and opposite susceptibility in males and females in mice and rats. More than thirty years passed since the structure identification as a sphingoid-like chemical, but the causal mechanism of the toxicity remains obscure in spites of extensive studies. Considerable amounts of knowledge have been accumulated on the biochemical/toxicological actions of FB1, but the influence on lipid dynamics and mobilization in the body has not been focused well in relation to the FB1-mediated toxicity. Considerable influences of this toxin on mobilization of sphingolipids and phospholipids and also on adaptive changes in their compositions in tissues are implicated from recent studies on FB1-interacting ceramide synthases. Accumulated patho-physiological data also suggest a possible role of hepatic phospholipid on FB1-mediated toxicity. Thus, a mechanism of FB1-mediated toxicity is discussed in relation to the mobilization of phospholipids and sphingolipids in the body in this context.

Orlistat

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Feasibility and antitumor efficacy in vivo, of simultaneously targeting glycolysis, glutaminolysis and fatty acid synthesis using lonidamine, 6-diazo-5-oxo-L-norleucine and orlistat in colon cancer

The aim of the present study was to investigate in vivo the feasibility and efficacy of the combination of lonidamine (LND), 6-diazo-5-oxo-L-norleucine (DON) and orlistat to simultaneously target glycolysis, glutaminolysis and de novo synthesis of fatty acids, respectively. The doses of LND and DON used in humans were translated to mouse doses (77.7 mg/kg and 145.5 mg/kg, respectively) and orlistat was used at 240 mg/kg. Three schedules of LND, DON and orlistat at different doses were administered by intraperitoneal injection to BALB/c mice in a 21-day cycle (schedule 1: LND, 0.5 mg/day; DON, 0.25 mg/day 1, 5 and 9; orlistat, 240 mg/kg/day; schedule 2: LND, 0.1 mg/day; DON, 0.5 mg/day 1, 5 and 9; orlistat, 240 mg/kg/day; schedule 3: LND, 0.5 mg/day; DON, 0.08 mg/day 1, 5 and 9; orlistat, 360 mg/kg/day) to assess tolerability. To determine the antitumor efficacy, a syngeneic tumor model in BALB/c mice was created using colon cancer CT26.WT cells, and a xenogeneic tumor model was created in nude mice using the human colon cancer SW480 cell line. Mice were treated with schedule 1. Animals were weighed, clinically inspected during the experiment and the tumor volume was measured at day 21. The 3 schedules assessed in the tolerability experiments were well tolerated, as mice maintained their weight and no evident clinical signs of toxicity were observed. Combination treatment with schedule 1 significantly decreased tumor growth in each mouse model. No evident signs of toxicity were observed and mice maintained their weight during treatment. The triple metabolic blockade of the malignant phenotype appears feasible and promising for cancer therapy.

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.

Assessment of Adverse Events in Protocols, Clinical Study Reports, and Published Papers of Trials of Orlistat: A Document Analysis

BACKGROUND

Little is known about how adverse events are summarised and reported in trials, as detailed information is usually considered confidential. We have acquired clinical study reports (CSRs) from the European Medicines Agency through the Freedom of Information Act. The CSRs describe the results of studies conducted as part of the application for marketing authorisation for the slimming pill orlistat. The purpose of this study was to study how adverse events were summarised and reported in study protocols, CSRs, and published papers of orlistat trials.

METHODS AND FINDINGS

We received the CSRs from seven randomised placebo controlled orlistat trials (4,225 participants) submitted by Roche. The CSRs consisted of 8,716 pages and included protocols. Two researchers independently extracted data on adverse events from protocols and CSRs. Corresponding published papers were identified on PubMed and adverse event data were extracted from this source as well. All three sources were compared. Individual adverse events from one trial were summed and compared to the totals in the summary report. None of the protocols or CSRs contained instructions for investigators on how to question participants about adverse events. In CSRs, gastrointestinal adverse events were only coded if the participant reported that they were "bothersome," a condition that was not specified in the protocol for two of the trials. Serious adverse events were assessed for relationship to the drug by the sponsor, and all adverse events were coded by the sponsor using a glossary that could be updated by the sponsor. The criteria for withdrawal due to adverse events were in one case related to efficacy (high fasting glucose led to withdrawal), which meant that one trial had more withdrawals due to adverse events in the placebo group. Finally, only between 3% and 33% of the total number of investigator-reported adverse events from the trials were reported in the publications because of post hoc filters, though six of seven papers stated that "all adverse events were recorded." For one trial, we identified an additional 1,318 adverse events that were not listed or mentioned in the CSR itself but could be identified through manually counting individual adverse events reported in an appendix. We discovered that the majority of patients had multiple episodes of the same adverse event that were only counted once, though this was not described in the CSRs. We also discovered that participants treated with orlistat experienced twice as many days with adverse events as participants treated with placebo (22.7 d versus 14.9 d, p-value < 0.0001, Student's t test). Furthermore, compared with the placebo group, adverse events in the orlistat group were more severe. None of this was stated in the CSR or in the published paper. Our analysis was restricted to one drug tested in the mid-1990s; our results might therefore not be applicable for newer drugs.

CONCLUSIONS

In the orlistat trials, we identified important disparities in the reporting of adverse events between protocols, clinical study reports, and published papers. Reports of these trials seemed to have systematically understated adverse events. Based on these findings, systematic reviews of drugs might be improved by including protocols and CSRs in addition to published articles.

Antitumor effects of a drug combination targeting glycolysis, glutaminolysis and de novo synthesis of fatty acids

There is a strong rationale for targeting the metabolic alterations of cancer cells. The most studied of these are the higher rates of glycolysis, glutaminolysis and de novo synthesis of fatty acids (FAs). Despite the availability of pharmacological inhibitors of these pathways, no preclinical studies targeting them simultaneously have been performed. In the present study it was determined whether three key enzymes for glycolysis, glutaminolysis and de novo synthesis of FAs, hexokinase-2, glutaminase and fatty acid synthase, respectively, were overexpressed as compared to primary fibroblasts. In addition, we showed that at clinically relevant concentrations lonidamine, 6-diazo-5-oxo-L-norleucine and orlistat, known inhibitors of the mentioned enzymes, exerted a cell viability inhibitory effect. Genetic downregulation of the three enzymes also reduced cell viability. The three drugs were highly synergistic when administered as a triple combination. Of note, the cytotoxicity of the triple combination was low in primary fibroblasts and was well tolerated when administered into healthy BALB/c mice. The results suggest the feasibility and potential clinical utility of the triple metabolic targeting which merits to be further studied by using either repositioned old drugs or newer, more selective inhibitors.

Lipoprotein lipase, tissue expression and effects on genes related to fatty acid synthesis in goat mammary epithelial cells

Lipoprotein lipase (LPL) serves as a central factor in hydrolysis of triacylglycerol and uptake of free fatty acids from the plasma. However, there are limited data concerning the action of LPL on the regulation of milk fat synthesis in goat mammary gland. In this investigation, we describe the cloning and sequencing of the LPL gene from Xinong Saanen dairy goat mammary gland, along with a study of its phylogenetic relationships. Sequence analysis showed that goat LPL shares similarities with other species including sheep, bovine, human and mouse. LPL mRNA expression in various tissues determined by RT-qPCR revealed the highest expression in white adipose tissue, with lower expression in heart, lung, spleen, rumen, small intestine, mammary gland, and kidney. Expression was almost undetectable in liver and muscle. The expression profiles of LPL gene in mammary gland at early, peak, mid, late lactation, and the dry period were also measured. Compared with the dry period, LPL mRNA expression was markedly greater at early lactation. However, compared with early lactation, the expression was lower at peak lactation and mid lactation. Despite those differences, LPL mRNA expression was still greater at peak, mid, and late lactation compared with the dry period. Using goat mammary epithelial cells (GMEC), the in vitro knockdown of LPL via shRNA or with Orlistat resulted in a similar degree of down-regulation of LPL (respectively). Furthermore, knockdown of LPL was associated with reduced mRNA expression of SREBF1, FASN, LIPE and PPARG but greater expression of FFAR3. There was no effect on ACACA expression. Orlistat decreased expression of LIPE, FASN, ACACA, and PPARG, and increased FFAR3 and SREBF1 expression. The pattern of LPL expression was similar to the changes in milk fat percentage in lactating goats. Taken together, results suggest that LPL may play a crucial role in fatty acid synthesis.

Reducing the risk of obesity: defining the role of weight loss drugs

The prevalence of obesity has increased dramatically in the past 20 years. As a public health concern, obesity is associated with a health care resource burden that is quickly approaching that associated with tobacco use. Although lifestyle intervention (diet and exercise) remains the mainstay of treatment of obesity, its effectiveness is limited by poor long-term adherence. Drug therapy has historically been unsuccessful in producing sustained weight loss. Many older weight loss drugs have adverse benefit-to-risk profiles. This review provides an overview of nonpharmacologic interventions for weight loss. The safety and efficacy of older weight loss drugs, as well as current data related to lorcaserin, phentermine/topiramate, and naltrexone-bupropion, are evaluated. Although associated with modest weight loss and some improvement in adverse obesity-related metabolic effects, none of these drugs has been demonstrated to reduce mortality. In addition, the long-term safety of these drugs remains largely unknown. Bariatric surgery is an option for patients with morbid obesity who have failed conventional treatment.

Carboxylesterase-2 is a highly sensitive target of the antiobesity agent orlistat with profound implications in the activation of anticancer prodrugs

Orlistat has been the most used anti-obesity drug and the mechanism of its action is to reduce lipid absorption by inhibiting gastrointestinal lipases. These enzymes, like carboxylesterases (CESs), structurally belong to the α/β hydrolase fold superfamily. Lipases and CESs are functionally related as well. Some CESs (e.g., human CES1) have been shown to hydrolyze lipids. This study was designed to test the hypothesis that orlistat inhibits CESs with higher potency toward CES1 than CES2, a carboxylesterase with little lipase activity. Liver microsomes and recombinant CESs were tested for the inhibition of the hydrolysis of standard substrates and the anticancer prodrugs pentyl carbamate of p-aminobenzyl carbamate of doxazolidine (PPD) and irinotecan. Contrary to the hypothesis, orlistat at 1 nM inhibited CES2 activity by 75% but no inhibition on CES1, placing CES2 one of the most sensitive targets of orlistat. The inhibition varied among some CES2 polymorphic variants. Pretreatment with orlistat reduced the cell killing activity of PPD. Certain mouse but not rat CESs were also highly sensitive. CES2 is responsible for the hydrolysis of many common drugs and abundantly expressed in the gastrointestinal track and liver. Inhibition of this carboxylesterase probably presents a major source for altered therapeutic activity of these medicines if co-administered with orlistat. In addition, orlistat has been linked to various types of organ toxicities, and this study provides an alternative target potentially involved in these toxicological responses.

An integrated analysis of liver safety data from orlistat clinical trials

OBJECTIVE

Orlistat is an oral gastrointestinal lipase inhibitor and is indicated for treatment of obesity in combination with a hypocaloric diet. Post-marketing reports of adverse reactions revealed hints for possible drug-induced liver injury which has prompted changes to the product information. Orlistat's development program, involving over 30,000 patients, did not indicate a hepatic safety issue.

METHODS

We analyzed liver function test data from randomized clinical trials of orlistat, using i) meta-analysis of published study safety data, ii) time-to-event analysis for individual patients, and iii) a novel and more sensitive method derived from the U.S. Food and Drug Administration's (FDA) evaluation of drug-induced serious hepatotoxicity (eDISH) technique. Over 10,000 subjects were included.

RESULTS

The combined odds ratio from a simple summary-level fixed-effects meta-analysis of treatment-emergent abnormalities in serum alanine aminotransferase (ALT) (defined as greater than the upper level of normal for 2 successive measurements) was 1.09 (95% CI 0.93-1.28), and in total bilirubin 1.24 (95% CI 1.03-1.49). Part of the small apparent effect was due to longer exposure to orlistat than to placebo, on average. A patient-level display, adjusting for regression towards the mean, and Kaplan-Meier analysis of changes in ALT and bilirubin, taking account of different exposure, showed no significant difference between orlistat and placebo. This shows that there is no signal for hepatic damage in clinical studies of orlistat.

CONCLUSION

While idiosyncratic liver injury following exposure to orlistat cannot be excluded, it is likely to be extremely rare.

Medications for weight reduction

Comparatively few drugs are available for the treatment of overweight patients, and their effectiveness is limited to palliation of the chronic disease of obesity. Nevertheless, drug development that is now underway is more rapid than in the past, and we anticipate the discovery of safe and effective pharmacologic strategies for the management of obesity and its serious complications.

Medications for weight reduction

Only two drugs are currently approved for long-term use in the treatment of obesity and four others for short-term use. Evaluating the risk-benefit profile is an essential first step. For individuals who have a low body mass index for whom the risk is small, the risk profile must make the drug acceptable for almost everyone. For higher-risk patients, such as those planning intestinal bypass or who have sleep apnea, a wider range of drugs may be considered. Obesity is a chronic disease that has many causes. Treatment is aimed at palliation-that is, producing and maintaining weight loss. Regardless of the primary site of action, the net effect must be a reduction in food intake or increase in energy expenditure.

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.

Medical therapy for obesity--current status and future hopes

In accepting any new drug for the treatment of obesity, the safety profile must make it acceptable for almost everyone. Criteria for selecting treatments involve evaluating the risks to the individual from obesity and balancing that against any possible problems with the treatment. Obesity is a chronic disease that has many causes. Cure is rare and treatment is thus aimed at palliation, that is, producing and maintaining weight loss. Wherever the primary site of action may be, however, the net effect must be a reduction in food intake or an increase in energy expenditure.

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.

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.

Drug treatment of the overweight patient

Three medications with approval for long-term use in the treatment of obesity are currently available in the United States. Sibutramine (U.S. Food and Drug Administration [FDA] approved in 1997), orlistat (FDA approved in 1999), and rimonabant (available in Europe and given FDA approvable status in 2006 and expected to be marketed in 2007) represent modern approaches to medications used adjunctively for weight management. As demonstrated in large clinical trials of 2 to 4 years' duration, these medications significantly increase weight loss compared with placebo; weight loss with these drugs reaches a nadir between 20 and 28 weeks; weight loss, averaged 8%-10%, with the placebo contributing 4%-6% of that. Weight maintenance is demonstrated as long as adherence to medication continues. All medications have side effects that need to be considered. For sibutramine, there is a rise in blood pressure and heart rate that may require discontinuation of the drug in a small percent of patients. For orlistat, steatorrhea produces the principal gastrointestinal side effects. Rimonabant appears to have a favorable safety and tolerability profile. Nausea and gastrointestinal symptoms are the chief tolerability issue, but they are usually self-limited. In addition there are several drugs and drug combinations in phase 2 or phase 2 trials that will be reported on in the coming years.

Exploring the specific features of interfacial enzymology based on lipase studies

Many enzymes are active at interfaces in the living world (such as in the signaling processes at the surface of cell membranes, digestion of dietary lipids, starch and cellulose degradation, etc.), but fundamental enzymology remains largely focused on the interactions between enzymes and soluble substrates. The biochemical and kinetic characterization of lipolytic enzymes has opened up new paths of research in the field of interfacial enzymology. Lipases are water-soluble enzymes hydrolyzing insoluble triglyceride substrates, and studies on these enzymes have led to the development of specific interfacial kinetic models. Structure-function studies on lipases have thrown light on the interfacial recognition sites present in the molecular structure of these enzymes, the conformational changes occurring in the presence of lipids and amphiphiles, and the stability of the enzymes present at interfaces. The pH-dependent activity, substrate specificity and inhibition of these enzymes can all result from both "classical" interactions between a substrate or inhibitor and the active site, as well as from the adsorption of the enzymes at the surface of aggregated substrate particles such as oil drops, lipid bilayers or monomolecular lipid films. The adsorption step can provide an alternative target for improving substrate specificity and developing specific enzyme inhibitors. Several data obtained with gastric lipase, classical pancreatic lipase, pancreatic lipase-related protein 2 and phosphatidylserine-specific phospholipase A1 were chosen here to illustrate these specific features of interfacial enzymology.

The use of orlistat in the treatment of obesity, dyslipidaemia and Type 2 diabetes

Orlistat (tetrahydrolipstatin) is an inhibitor of gastrointestinal lipases, especially pancreatic lipase. It is used as an adjunct to diet and exercise in order to achieve weight loss in obese individuals (body mass index > 30 kg/m2) or in overweight individuals (body mass index > 27 kg/m2) with other risk factors for atherosclerotic vascular disease, such as hypertension, dyslipidaemia or diabetes. Short- and long-term studies of up to 4 years duration have shown the drug to have significant benefits in weight loss, as well as in the reduction in lipids, glucose and haemoglobin A1c, and in time to onset of Type 2 diabetes compared with diet alone or placebo groups. The incremental amount of weight loss that orlistat produces is modest, but sufficient to result in improvement in obesity comorbidities such as elevated blood pressure, dyslipidaemia and hyperglycaemia compared with diet and exercise alone. Orlistat should only be prescribed for individuals who are motivated to adhere to lifestyle modifications, especially dietary fat restriction.

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.

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.

The effect of short-term (21-day) orlistat treatment on the physiologic balance of six selected macrominerals and microminerals in obese adolescents

OBJECTIVES

Orlistat is a gastrointestinal lipase inhibitor used to reduce dietary fat absorption and could be used to treat overweight and obesity in adolescents. The primary objective was to assess whether orlistat has an effect on the physiologic balance of three macrominerals (calcium, phosphorus and magnesium) and three microminerals (iron, zinc and copper).

METHODS

This was a 21-day, double-blind, randomized, parallel-group, placebo-controlled mineral balance study conducted in adolescent obese volunteers (BMI >or=85th percentile, adjusted for age and gender). Subjects were maintained on a hypocaloric diet with a normal daily mineral content in both treatment groups and received oral treatment with orlistat 120 mg (n = 16) or placebo (n = 16) three times daily for 21 days. Following a 14-day equilibration period, balances for calcium, phosphorus, magnesium, iron, copper and zinc were measured for days 15-21. Serum and urine electrolytes were also measured at baseline and at the end of treatment.

RESULTS

On average, orlistat inhibited dietary fat absorption by approximately 27%. This degree of dietary fat inhibition caused no significant changes in mineral balance between orlistat and placebo groups. In addition, serum and urine electrolytes (sodium and potassium) as well as urinary creatinine excretion were not affected by orlistat treatment. Orlistat was well tolerated; adverse events occurred mainly in the gastrointestinal tract and were of mild or moderate intensities.

CONCLUSIONS

Administration of orlistat had no significant effect on the balance of six selected minerals in adolescent obese patients.

Transfer of orlistat through oil-water interfaces

The transfer of radiolabelled orlistat ([14C]orlistat), a potent gastrointestinal lipase inhibitor, through an oil-water interface from a single oil droplet to an aqueous phase was investigated, using an oil drop tensiometer. The absolute transfer fluxes were found to be very low, even in the presence of micellar concentrations of bile salts, which increased their values from 0.2 to 2.5 and 6.5 pmol cm(-2) min(-1) in the presence of 0, 4 and 15 mM NaTDC, respectively. Adding either a lipid emulsion or pure human pancreatic lipase (HPL) or human serum albumin or beta-lactoglobulin had no effect on the flux of transfer of orlistat. The presence of colipase or a mixture of colipase and HPL was found, however, to reduce the flux of orlistat transfer, probably because it partly covered the single oil drop surface, even in the presence of bile salts. Using a finely emulsified system, we investigated the partitioning of orlistat between the aqueous and oil phases, in the absence or presence of bile salts above their CMC (4 mM NaTDC, final concentration). Under these emulsified conditions, orlistat was found to be mostly associated with the oil phase, since more than 98.8% of the total radioactivity was recovered after decantation with the oil phase. The low transfer rates of orlistat, as well as its partitioning coefficient between the oil and the aqueous phases, should help us to better understand the inhibitory effects of orlistat on lipid digestion in humans.

Pharmacotherapy of obesity

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

Effects of 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.

Combination of gemfibrozil and orlistat for treatment of combined hyperlipidemia with predominant hypertriglyceridemia

OBJECTIVE

To present a case of combined hyperlipidemia with predominant hypertriglyceridemia unresponsive to conventional diet and single-agent drug therapy but successfully treated with a combination of gemfibrozil and orlistat.

METHODS

We describe a nonobese Asian Indian man with combined hyperlipidemia. Predominant hypertriglyceridemia was unresponsive to conventional therapy. Orlistat was added to the maximal dose of gemfibrozil, and baseline lipid profiles were compared with posttreatment values after repeated challenges with each drug individually and in combination. The relevant literature was also reviewed.

RESULTS

At baseline, the patient's serum triglyceride level was 766 mg/dL and total cholesterol level was 241 mg/dL. On repeated measurements 4 months later, these values were 959 mg/dL and 309 mg/dL, respectively. With use of a reduced-fat diet and gemfibrozil (600 mg orally twice a day), serum triglyceride levels were 830 mg/dL and 909 mg/dL on two different occasions. Combination treatment with the same dosage of gemfibrozil and orlistat at 120 mg orally three times a day reduced triglyceride levels to 279 mg/dL and 244 mg/dL on two separate occasions. Rechallenges with drug monotherapy yielded triglyceride levels of up to 1,159 mg/dL with gemfibrozil alone and of up to 896 mg/dL with orlistat alone. A reduction of serum triglyceride levels to 269 mg/dL and 224 mg/dL occurred when combined treatment with both gemfibrozil and orlistat was reinstituted on two additional occasions.

CONCLUSION

The combination of gemfibrozil and orlistat was extremely effective in reducing serum triglyceride levels in this patient with combined hyperlipidemia and predominant hypertriglyceridemia, whereas either one of these agents, when used alone, was ineffective. Determining the mechanisms of this synergy will necessitate further investigation. Additional studies of the use of the gemfibrozil-orlistat combination in patients who have combined hyperlipidemia with predominant hypertriglyceridemia are needed.

Orlistat: its current status as an anti-obesity drug

Orlistat is a non-centrally acting anti-obesity agent that acts locally in the gastrointestinal tract to inhibit lipase, an enzyme that is crucial for the digestion of long-chain triglycerides. At the recommended dose of 120 mg three times daily, orlistat inhibits dietary fat absorption by about 30%. Over a 1-year period, obese patients taking orlistat in combination with a hypocaloric diet show a reduction of 2-5 kg over the weight decrease with placebo. When continued for a second year in combination with a weight maintenance diet, orlistat reduces weight regain compared to placebo-treated patients. Orlistat in combination with dietary intervention is also associated with beneficial effects on cardiovascular risk factors including total and low-density lipoprotein cholesterol, blood pressure and plasma glucose. It is not known if orlistat has any impact on clinical outcomes such as myocardial infarction, stroke and sudden death. Orlistat has not been compared with other anti-obesity agents.