Mammalian Pharmacology Research Articles

Environmental pharmacology-Dosing the environment: IUPHAR review 36.

Pesticide action is predominantly measured as a toxicological outcome, with pharmacological impact of sublethal doses on bystander species left largely undocumented. Likewise, chronic exposure, which often results in responses different from acute administration, has also been understudied. In this article, we propose the application of standard pharmacological principles, already used to establish safe clinical dosing regimens in humans, to the 'dosing of the environment'. These principles include relating the steady state dose of an agent to its beneficial effects (e.g. pest control), while minimising harmful impacts (e.g. off-target bioactivity in beneficial insects). We propose the term 'environmental therapeutic window', analogous to that used in mammalian pharmacology, to guide risk assessment. To make pharmacological terms practically useful to environmental protection, quantitative data on pesticide action need to be made available in a freely accessible database, which should include toxicological and pharmacological impacts on both target and off-target species.

Pharmacological classes that extend lifespan of Caenorhabditis elegans.

Recent progress in the field of aging has resulted in ever increasing numbers of compounds that extend lifespan in Caenorhabditis elegans. Lifespan extending compounds include metabolites and synthetic compounds, as well as natural products. For many of these compounds, mammalian pharmacology is known, and for some the actual targets have been experimentally identified. In this review, we explore the data available in C. elegans to provide an overview of which pharmacological classes have potential for identification of further compounds that extend lifespan.

An integrated approach for prioritizing pharmaceuticals found in the environment for risk assessment, monitoring and advanced research

Numerous active pharmaceutical ingredients (APIs), approved prior to enactment of detailed environmental risk assessment (ERA) guidance in the EU in 2006, have been detected in surface waters as a result of advancements in analytical technologies. Without adequate knowledge of the potential hazards these APIs may pose, assessing their environmental risk is challenging. As it would be impractical to commence hazard characterization and ERA en masse, several approaches to prioritizing substances for further attention have been published. Here, through the combination of three presentations given at a recent conference, “Pharmaceuticals in the Environment, Is there a problem?” (Nîmes, France, June 2013) we review several of these approaches, identify salient components, and present available techniques and tools that could facilitate a pragmatic, scientifically sound approach to prioritizing APIs for advanced study or ERA and, where warranted, fill critical data gaps through targeted, intelligent testing. We further present a modest proposal to facilitate future prioritization efforts and advanced research studies that incorporates mammalian pharmacology data (e.g., adverse outcomes pathways and the fish plasma model) and modeled exposure data based on pharmaceutical use.

From Complex Behavior to New Drugs: Chemoinformatics Shows the Way

​IfIf you are a medicinal chemist casting your net for new drugs, you have a choice: you can take a bottom-up approach, in which you begin with a molecule that hits a known molecular target and hope it translates eventually into a physiological effect; or you can take a top-down approach, in which you begin with a molecule that causes the desired physiological effect and then find the molecular target in order to better understand the effect and optimize your drug's interaction with it. A computational approach to target identification is applied to elucidate the pharmacological targets underlying the regulation of feeding behavior in the nematode C. elegans. This top-down approach, called a phenotypic screen, seems to be the most practical route when you want to alter a complex behavior, such as feeding, which involves multiple tissues and unknown molecular pathways. But after finding the right molecule, discovering the target it hits and the pathway it affects can be challenging. Additionally, these discovery steps are by necessity performed in a lab model, and the targets and pathways in the model must still be shown to be relevant to human physiology. In a new study in this issue of PLOS Biology, George Lemieux, Bryan Roth, Brian Shoichet, Kaveh Ashrafi, and colleagues analyze a set of compounds emerging from a phenotypic screen of fat content in worms. By combining chemoinformatics, in vitro testing, and in vivo assays, they identify previously unknown pathways that affect feeding behavior in worms and that are likely to have important effects in mammals. The authors began with a set of 84 compounds they had found altered fat metabolism in the worm. For all but one of these compounds, no biological targets were known. To find likely targets, they interrogated a database of almost 2,500 targets and more than 8 million ligand interactions with mostly mammalian targets, comparing the structure of their compounds with ligand sets in the database. They found possible targets for 79 of the 84 compounds, and chose 16 compounds for in vitro testing against the predicted mammalian targets, many of which were enzymes or membrane receptors. Next, they returned to worms. In the original screen, fat accumulation (assayed by fluorescence microscopy) stood in for feeding. Here, they measured the rate of contraction of the pharynx—swallowing, essentially—for a more direct indication of the related physiology of feeding behavior. Four compounds stood out for their ability to increase feeding in larvae and adults. But did these four do so through interacting with worm counterparts of mammalian targets that were identified? To find out, the authors knocked down the predicted target using RNA interference. They reasoned that if the compound interacted with the predicted target, its effect was almost certainly inhibitory (virtually all drugs inhibit, rather than facilitate, action of the biomolecules they interact with). Therefore, knocking down the predicted target should have the same effect as the compound, and furthermore, adding the compound shouldn't increase the effect, since the target would already be out of commission. According to database predictions and in vitro testing, the compound D20 inhibited a human receptor tyrosine kinase (RTK) called Flt-3. Worms have no exact match, but they do have many similar RTKs. Testing each of them without and then with D20, they found that one, called ver-3, increased feeding when knocked down but was insensitive to additional D20, indicating that D20 acted on ver-3. Using the same strategy, the authors also showed that another compound, called F15, acted on a receptor similar to human oxytocin receptor, which is known to influence feeding behavior in mammals. Further analysis identified two other pathways, for a total of four, all previously undescribed with respect to feeding regulation in the worm and all with relevance to vertebrate feeding regulation. It is not yet clear whether the pathways affect feeding behavior in humans. The strategy exploited in this study has wide applicability for discovering drugs for other behaviors, as long as a phenotypic correlate can be found and measured in an animal model. Not every compound identified will have a relevant human target, but if the success rate in future trials approximates that from this study, this method may prove to be a rich source of new compounds, targets, and pathways that can aid the design of the next generation of drugs for human use. Lemieux GA, Keiser MJ, Sassano MF, Laggner C, Mayer F, et al. (2013) In silico Molecular Comparisons of C. elegans and Mammalian Pharmacology Identify Distinct Targets that Regulate Feeding. doi:10.1371/journal.pbio.1001712

In Silico Molecular Comparisons of C. elegans and Mammalian Pharmacology Identify Distinct Targets That Regulate Feeding

Author SummaryMany beneficial pharmacological interventions were first discovered by observing the effects of perturbation of intact biological systems by small organic molecules without a priori knowledge of their targets. This forward pharmacological approach has the advantage of directly identifying new pharmacological agents that are active on complex biological processes. However, because of experimental feasibility, systematic application of this approach is generally limited to small animals such as the roundworm C. elegans and zebrafish, raising the question of whether use of these animals could identify compounds that act on ortholgous mammalian targets. A significant challenge in addressing this question is the determination of the molecular identities of the compounds' targets responsible for the desired phenotypic outcomes. Here we describe a computational approach for target identification based on structural similarities of newly identified compounds to known ligand interactions with mostly mammalian targets. For several of the compounds emerging from a C. elegans phenotypic screen, we predict and confirm mammalian targets using in vitro binding assays. Using genetic and pharmacological assays, we then demonstrate that a subset of these compounds alter C. elegans feeding rates through the C. elegans counterparts of the predicted mammalian targets.

A pharmacological network for lifespan extension in Caenorhabditis elegans

One goal of aging research is to find drugs that delay the onset of age-associated disease. Studies in invertebrates, particularly Caenorhabditis elegans, have uncovered numerous genes involved in aging, many conserved in mammals. However, which of these encode proteins suitable for drug targeting is unknown. To investigate this question, we screened a library of compounds with known mammalian pharmacology for compounds that increase C. elegans lifespan. We identified 60 compounds that increase longevity in C. elegans, 33 of which also increased resistance to oxidative stress. Many of these compounds are drugs approved for human use. Enhanced resistance to oxidative stress was associated primarily with compounds that target receptors for biogenic amines, such as dopamine or serotonin. A pharmacological network constructed with these data reveal that lifespan extension and increased stress resistance cluster together in a few pharmacological classes, most involved in intercellular signaling. These studies identify compounds that can now be explored for beneficial effects on aging in mammals, as well as tools that can be used to further investigate the mechanisms underlying aging in C. elegans.

In Silico Molecular Comparisons of C. elegans and Mammalian Pharmacology Identify Distinct Targets That Regulate Feeding

In Silico Molecular Comparisons of C. elegans and Mammalian Pharmacology Identify Distinct Targets That Regulate Feeding

Potential insight for drug discovery from high-fidelity receptor-mediated transduction mechanisms in insects

Introduction: There is a pervasive and growing concern about the small number of new pharmaceutical agents. There are many proposed explanations for this trend that do not involve the drug-discovery process per se, but the discovery process itself has also come under scrutiny. If the current paradigms are indeed not working, where are novel ideas to come from? Perhaps it is time to look to novel sources.Areas covered: The receptor-signaling and second-messenger transduction processes present in insects are quite similar to those in mammals (involving G proteins, ion channels, etc.). However, a review of these systems reveals an unprecedented degree of high potency and receptor selectivity to an extent greater than that modeled in most current drug-discovery approaches.Expert opinion: A better understanding of insect receptor pharmacology could stimulate novel theoretical and practical ideas in mammalian pharmacology (drug discovery) and, conversely, the application of pharmacology and medicinal chemistry principles could stimulate novel advances in entomology (safer and more targeted control of pest species).

Effects of the antihistamine diphenhydramine on selected aquatic organisms

In recent years pharmaceuticals have been detected in aquatic systems receiving discharges of municipal and industrial effluents. Although diphenhydramine (DPH) has been reported in water, sediment, and fish tissue, an understanding of its impacts on aquatic organisms is lacking. Diphenhydramine has multiple modes of action (MOA) targeting the histamine H1, acetylcholine (ACh), and 5-HT reuptake transporter receptors, and as such is used in hundreds of pharmaceutical formulations. The primary objective of this study was to develop a baseline aquatic toxicological understanding of DPH using standard acute and subchronic methodologies with common aquatic plant, invertebrate, and fish models. A secondary objective was to test the utility of leveraging mammalian pharmacology information to predict aquatic toxicity thresholds. The plant model, Lemna gibba, was not adversely affected at exposures as high as 10 mg/L. In the fish model, Pimephales promelas, pH affected acute toxicity thresholds and feeding behavior was more sensitive (no-observed-effect concentration = 2.8 µg/L) than standardized survival or growth endpoints. This response threshold was slightly underpredicted using a novel plasma partitioning approach and a mammalian pharmacological potency model. Interestingly, results from both acute mortality and subchronic reproduction studies indicated that the model aquatic invertebrate, Daphnia magna, was more sensitive to DPH than the fish model. These responses suggest that DPH may exert toxicity in Daphnia through ACh and histamine MOAs. The D. magna reproduction no-observed-effect concentration of 0.8 µg/L is environmentally relevant and suggests that additional studies of more potent antihistamines and antihistamine mixtures are warranted.

Chronic effects assessment and plasma concentrations of the β-blocker propranolol in fathead minnows ( Pimephales promelas)

The presence of many human pharmaceuticals in the aquatic environment is now a worldwide concern, yet little is known of the chronic effects that these bioactive substances may be having on aquatic organisms. Propranolol, a non-specific beta adrenoreceptor blocker (β-blocker), is used to treat high blood pressure and heart disease in humans. Propranolol has been found in surface waters worldwide at concentrations ranging from 12 to 590 ng/L. To test the potential for ecologically relevant effects in fish in receiving waters, short-term (21 days) adult reproduction studies were conducted, in which fathead minnows were exposed to nominal concentrations of propranolol hydrochloride [CAS number 318-98-9] ranging from 0.001 to 10 mg/L (measured concentrations typically from 78 to 130%). Exposure of fish to 3.4 mg/L (measured) over 3 days caused 100% mortality or severe toxicity requiring euthanasia. The most sensitive endpoints from the studies were a decrease in hatchability (with regard to the number of days to hatch) and a concentration-related increase in female gonadal somatic index (GSI), giving LOEC hatchability and LOEC female GSI values of 0.1 mg/L. Concentration-related decreases in weights of male fish were also observed, with LOEC male wet weight value of 1.0 mg/L, and the LOEC reproduction value was 1.0 mg/L. Collectively, these data do not suggest that propranolol was acting as a reproductive toxin. Plasma concentrations of propranolol in male fish exposed to nominal concentrations of 0.1 and 1.0 mg/L were 0.34 and 15.00 mg/L, respectively, which constitutes 436 and 1546% of measured water concentrations. These compare with predicted concentrations of 0.07 and 0.84 mg/L, and thus to a degree support the use of partition coefficient models for predicting concentrations in plasma in fish. In addition, propranolol plasma concentrations in fish exposed to water concentrations of 0.1 and 1.0 mg/L were greater than the human therapeutic plasma concentration and hence these data very strongly support the fish plasma model proposed by Huggett et al. [Huggett, D.B., Cook, J.C., Ericson, J.F., Williams, R.T., 2003a. A theoretical model for utilizing mammalian pharmacology and safety data to prioritize potential impacts of human pharmaceuticals to fish. Hum. Ecol. Risk Assess. 9, 1789–1799].

Uptake of propranolol, a cardiovascular pharmaceutical, from water into fish plasma and its effects on growth and organ biometry

Pharmaceuticals in the environment (PIE) are of importance since these compounds are designed to affect biological receptors/enzymes that are often conserved across vertebrate families. Across-species extrapolation of these therapeutic targets suggests potential for impacting amphibia and fish in the aquatic environment. Due to the scarcity of relevant ecotoxicological data, the long-tem impact of PIE remains a research question. Efficient use of mammalian data has been proposed to better understand and predict the potential for a given pharmaceutical to impact the environment. Using a model cardiovascular pharmaceutical (propranolol, a non-specific β 1/β 2-adrenergic antagonist), the hypothesis that mammalian data can be used to predict toxicity in fish was tested. Rainbow trout ( Oncorhynchus mykiss (Walbaum)) have β-adrenergic signalling mechanisms analogous to human cardiovascular receptors that respond to pharmacological doses of agonists and antagonists. Trout absorbed propranolol from water such that after 40 days of exposure, the linear relationship was [plasma] = 0.59[water] ( n = 31, r = 0.96). Growth rate was affected only at very high aqueous concentrations (10-day growthNOEC = 1.0 and growthLOEC = 10 mg/l). Growth recovered with time (40-day growthNOEC = 10 mg/l), suggesting possible adaptation to the pharmaceutical, although the internal plasma concentration in trout exposed to 10 mg propranolol/l of water was higher than the mammalian therapeutic plasma concentration. Additional endpoints suggested subtle changes of liver and heart size at much lower concentrations may have occurred, although these were not concentration-related. There was, however, a dose-dependent effect upon overall body condition. The trout plasma concentrations at these effective aqueous concentrations fell within the range of mammalian effective plasma concentrations, supporting the potential for developing ‘read-across’ from mammalian pharmacology safety data to fish ecotoxicology. Despite these effects at relatively high concentrations, propranolol is not expected to pose a risk to fish at the concentrations considered to be present in the aquatic environment.

A Theoretical Model for Utilizing Mammalian Pharmacology and Safety Data to Prioritize Potential Impacts of Human Pharmaceuticals to Fish

Due to the potential for long-term, low-level exposure of environmental species to pharmaceuticals in the environment, concerns over chronic ecotoxicity have been raised. Pharmaceuticals typically have specific enzyme and receptor-based modes of action, which are extensively studied in mammals during drug development. A survey of the literature demonstrated that there is conservation of many enzyme/receptor systems between mammalian and teleost systems. Based on this conservation of enzyme/receptor systems across teleost species, a model has been developed to utilize the information from mammalian pharmacology and toxicology studies to evaluate the potential for chronic receptor mediated responses in fish. In this model, a measured human therapeutic plasma concentration (HTPC) is compared to a predicted steady state plasma concentration (FSSPC) in fish, and an effect ratio (ER = HTPC/FSSPC) is computed. The lower the ER, the greater the potential for a pharmacological response in fish. Data collection and model validation will strengthen the applicability of this approach as a viable tool for prioritizing research initiatives that examine the potential impact of pharmaceuticals on fish.

The pharmacology of the cholinoceptor in muscle preparations of Ascaris lumbricoides var. suum.

1. The preparation of a muscle strip of Ascaris lumbricoides for the study of the effect of drugs in vitro is described.2. Stimulant drugs which are classified as nicotine-like in mammalian pharmacology increased the isometric tension of this preparation. These drugs were, in descending order of potency: dimethylphenylpiperazinium, nicotine, acetylcholine, carbachol, decamethonium and pyridine-2-aldoxime methiodide.3. Muscarine-like drugs (oxotremorine, methacholine, pilocarpine) had no activity.4. Potassium and barium ions stimulated the tissue, while the anti-cholinesterases, dichlorvos and eserine, increased the resting tension of the preparation and potentiated the responses to acetylcholine.5. Adrenaline neither stimulated the tissue nor affected the responses to nicotine-like drugs.6. The relative potency of several blocking agents which antagonize the responses to nicotine-like drugs was assayed. These blocking agents were, in descending order of potency: mecamylamine, (+)-tubocurarine, hexamethonium, atropine and piperazine. Acetylcholine, dimethylphenylpiperazinium and pyridine-2-aldoxime methiodide apparently act on a common receptor, for each blocking agent had a similar molar inhibitory concentration against these stimulants.7. It is concluded that the cholinoceptor in muscle preparations of Ascaris lumbricoides is pharmacologically similar to that of the mammalian autonomic ganglion.

Pharmacological properties of betabeta-di-methyl-acryloylcholine and some other beta-substituted acryloylcholines.

The mammalian pharmacology of a new naturally occurring ester of choline, betabeta-dimethylacryloylcholine (DMAC), has been studied, mainly in the cat, together with that of two synthetic beta-substituted acryloylcholines, crotonoylcholine and pent-2-enoylcholine. Comparisons have been made with the reduced form of DMAC, isovalerylcholine, with another naturally ocurring beta-substituted acryloylcholine, murexine (urocanoylcholine), and with suxamethonium. DMAC has been shown to be a ganglion stimulating and neuromuscular blocking agent generally similar, in potency and properties, to murexine. It is also a powerful respiratory stimulant. The other unsaturated esters behaved similarly but were less potent.