The safety and efficacy of lorcaserin in the management of obesity

Experimental strategies to discover and develop the next generation of psychedelics and entactogens as medicines

Research on classical psychedelics (psilocybin, LSD and DMT) and entactogen, MDMA, has produced a renaissance in the search for more effective drugs to treat psychiatric, neurological and various peripheral disorders. Psychedelics and entactogens act though interaction with 5-HT_2A and other serotonergic receptors and/or monoamine reuptake transporters. 5-HT, which serves as a neurotransmitter and hormone, is ubiquitously distributed in the brain and peripheral organs, tissues and cells where it has vasoconstrictor, pro-inflammatory and pro-nociceptive actions. Serotonergic psychedelics and entactogens have known safety and toxicity risks. For these drugs, the risks been extensively researched and empirically assessed through human experience. However, novel drug-candidates require thorough non-clinical testing not only to predict clinical efficacy, but also to address the risks they pose during clinical development and later after approval as prescription medicines. We have defined the challenges researchers will encounter when developing novel serotonergic psychedelics and entactogens. We describe screening techniques to predict clinical efficacy and address the safety/toxicity risks emerging from our knowledge of the existing drugs: 1) An early-stage, non-clinical screening cascade to pharmacologically characterise novel drug-candidates. 2) Models to detect hallucinogenic activity. 3) Models to differentiate hallucinogens from entactogens. 4) Non-clinical preclinical lead optimisation technology (PLOT) screening to select drug-candidates. 5) Modified animal models to evaluate the abuse and dependence risks of novel psychedelics in Safety Pharmacology testing. Our intention has been to design non-clinical screening strategies that will reset the balance between benefits and harms to deliver more effective and safer novel psychedelics for clinical use. This article is part of the Special Issue on 'National Institutes of Health Psilocybin Research Speaker Series'.

Gastric Serotonin Biosynthesis and Its Functional Role in L-Arginine-Induced Gastric Proton Secretion

Among mammals, serotonin is predominantly found in the gastrointestinal tract, where it has been shown to participate in pathway-regulating satiation. For the stomach, vascular serotonin release induced by gastric distension is thought to chiefly contribute to satiation after food intake. However, little information is available on the capability of gastric cells to synthesize, release and respond to serotonin by functional changes of mechanisms regulating gastric acid secretion. We investigated whether human gastric cells are capable of serotonin synthesis and release. First, HGT-1 cells, derived from a human adenocarcinoma of the stomach, and human stomach specimens were immunostained positive for serotonin. In HGT-1 cells, incubation with the tryptophan hydroxylase inhibitor p-chlorophenylalanine reduced the mean serotonin-induced fluorescence signal intensity by 27%. Serotonin release of 147 ± 18%, compared to control HGT-1 cells (set to 100%) was demonstrated after treatment with 30 mM of the satiating amino acid L-Arg. Granisetron, a 5-HT3 receptor antagonist, reduced this L-Arg-induced serotonin release, as well as L-Arg-induced proton secretion. Similarly to the in vitro experiment, human antrum samples released serotonin upon incubation with 10 mM L-Arg. Overall, our data suggest that human parietal cells in culture, as well as from the gastric antrum, synthesize serotonin and release it after treatment with L-Arg via an HTR3-related mechanism. Moreover, we suggest not only gastric distension but also gastric acid secretion to result in peripheral serotonin release.

Obesity Therapy: How and Why?

Background:

Obesity represents the second preventable mortality cause worldwide, and is very often associated with type 2 Diabetes Mellitus (T2DM). The first line treatment is lifestyle modification to weight-loss, but for those who fail to achieve the goal or have difficulty in maintaining achieved results, pharmacological treatment is needed. Few drugs are available today, because of their side effects.

Objective:

We aim to review actual pharmacological management of obese patients, highlighting differences between Food and Drug Administration - and European Medicine Agency-approved molecules, and pointing out self-medications readily obtainable and widely distributed.

Methods:

Papers on obesity, weight loss, pharmacotherapy, self- medication and diet-aid products were selected using Medline. Research articles, systematic reviews, clinical trials and meta-analyses were screened.

Results:

Anti-obesity drugs with central mechanisms, such as phentermine and lorcaserin, are available in USA, but not in Europe. Phentermine/topiramate and naltrexone/bupropion combinations are now available, even though the former is still under investigation from EMA. Orlistat, with peripheral mechanisms, represents the only drug approved for weight reduction in adolescents. Liraglutide has been approved at higher dose for obesity. Anti-obesity drugs, readily obtainable from the internet, include crude-drug products and supplements for which there is often a lack of compliance to national regulatory standards.

Conclusion:

Mechanisms of weight loss drugs include the reduction of energy intake or the increase in energy expenditure and sense of satiety as well as the decrease of hunger or the reduction in calories absorption. Few drugs are approved, and differences exist between USA and Europe. Moreover, herbal medicines and supplements often sold on the internet and widely used by obese patients, present a risk of adverse effects.

Effects of long-term high-fat food or methamphetamine intake and serotonin 2C receptors on reversal learning in female rhesus macaques

Perseverative behavior has been highly implicated in addiction. Activation of serotonin 2C receptors (5-HT_2CRs) attenuates cocaine and high caloric food intake, but whether a 5-HT_2CR agonist can reduce high caloric diet (HCD) or methamphetamine (METH) intake and response perseveration remains unknown. Clarifying the role of 5-HT_2CRs in these behaviors will improve knowledge of neurochemical processes that regulate flexible decision-making and whether improvements in decision-making are accompanied by decreases in HCD or METH intake. This study evaluated the effects of long-term HCD and METH intake on reversal learning in female rhesus monkeys. The effects of the 5-HT_2CR agonist WAY163909 on reversal learning before and after extended HCD or METH intake, and on food intake, was also tested. Moreover, we examined whether the 5-HT_2CR is necessary for the effects of WAY163909. WAY163909 was given prior to reversal learning at baseline and after extended HCD or METH intake, and prior to measures of food intake. Extended intake of METH or the HCD increased perseverative errors during reversal. WAY163909 increased correct responses and decreased perseverative errors, both before and after extended HCD or METH intake. Similarly, WAY163909 decreased consumption of a HCD, but not a low caloric diet. The effects of WAY163909 on all these measures were blocked by co-administration with a 5-HT_2CR antagonist. These data indicate that long-term HCD or METH intake disrupts flexible decision-making. Further, the results suggest that reductions in food intake produced by WAY163909 are associated with parallel improvements in decision-making strategies, underscoring the role of the 5-HT_2CR for these behavioral effects.

Evolution of pharmacological obesity treatments: focus on adverse side-effect profiles

Pharmacotherapy directed toward reducing body weight may provide benefits for both curbing obesity and lowering the risk of obesity-associated comorbidities; however, many weight loss medications have been withdrawn from the market because of serious adverse effects. Examples include pulmonary hypertension (aminorex), cardiovascular toxicity, e.g. flenfluramine-induced valvopathy, stroke [phenylpropanolamine (PPA)], excess non-fatal cardiovascular events (sibutramine), and neuro-psychiatric issues (rimonabant; approved in Europe, but not in the USA). This negative experience has helped mould the current drug development and approval process for new anti-obesity drugs. Differences between the US Food and Drug Administration (FDA) and the European Medicines Agency, however, in perceptions of risk-benefit considerations for individual drugs have resulted in discrepancies in approval and/or withdrawal of weight-reducing medications. Thus, two drugs recently approved by the FDA, i.e. lorcaserin and phentermine + topiramate extended release, are not available in Europe. In contrast, naltrexone sustained release (SR)/bupropion SR received FDA approval, and liraglutide 3.0 mg was recently approved in both the USA and Europe. Regulatory strategies adopted by the FDA to manage the potential for uncommon but potentially serious post-marketing toxicity include: (i) risk evaluation and mitigation strategy programmes; (ii) stipulating post-marketing safety trials; (iii) considering responder rates and limiting cumulative exposure by discontinuation if weight loss is not attained within a reasonable timeframe; and (iv) requiring large cardiovascular outcome trials before or after approval. We chronicle the adverse effects of anti-obesity pharmacotherapy and consider how the history of high-profile toxicity issues has shaped the current regulatory landscape for new and future weight-reducing drugs.

Regulation of food intake and the development of anti-obesity drugs

As the most significant cause of death worldwide, obesity has become one of the world's most important public health problems, but approved anti-obesity drugs are extremely limited. This article summarizes the feeding control circuits and regulators involved in obesity development, highlight the hypothalamus, melanocortin system and brain-gut peptide actions in this process, and the five US FDA approved anti-obesity medications in long term use, namely phentermine/topiramate, lorcaserin, naltrexone/bupropion, liraglutide and orlistat.

Structure and function of serotonin G protein-coupled receptors

Serotonin receptors are prevalent throughout the nervous system and the periphery, and remain one of the most lucrative and promising drug discovery targets for disorders ranging from migraine headaches to neuropsychiatric disorders such as schizophrenia and depression. There are 14 distinct serotonin receptors, of which 13 are G protein-coupled receptors (GPCRs), which are targets for approximately 40% of the approved medicines. Recent crystallographic and biochemical evidence has provided a converging understanding of the basic structure and functional mechanics of GPCR activation. Currently, two GPCR crystal structures exist for the serotonin family, the 5-HT1B and 5-HT2B receptor, with the antimigraine and valvulopathic drug ergotamine bound. The first serotonin crystal structures not only provide the first evidence of serotonin receptor topography but also provide mechanistic explanations into functional selectivity or biased agonism. This review will detail the findings of these crystal structures from a molecular and mutagenesis perspective for driving rational drug design for novel therapeutics incorporating biased signaling.