In vitro characterization of ephedrine-related stereoisomers at biogenic amine transporters and the receptorome reveals selective actions as norepinephrine transporter substrates

Determination of the metabolites of the new designer drugs bk-MBDB and bk-MDEA in human urine

This is the first report on identifying the specific metabolites of the new designer drugs 2-methylamino-1-(3,4-methylenedioxyphenyl)butan-1-one (bk-MBDB) and 2-ethylamino-1-(3,4-methylenedioxyphenyl)propan-1-one (bk-MDEA) in human urine using synthesized standards. Based on GC/MS and LC/MS, we identified N-dealkylation, demethylenation followed by O-methylation, and beta-ketone reduction as their major metabolic pathways. The quantitative analyses by LC/MS revealed that both demethylenation followed by O-methylation and beta-ketone reduction were superior to N-dealkylation and that both bk-MBDB and bk-MDEA were mainly metabolized into their corresponding 4-hydroxy-3-methoxy metabolites (4-OH-3MeO metabolites). After hydrolysis, the concentrations of 4-OH-3MeO metabolites and 3-hydroxy-4-methoxy metabolites of both bk-MBDB and bk-MDEA dramatically increased, suggesting that the metabolites mainly exist as their conjugates.

Studies of the biogenic amine transporters. 13. Identification of "agonist" and "antagonist" allosteric modulators of amphetamine-induced dopamine release

Recent studies identified novel allosteric modulators of the dopamine (DA) transporter (DAT). N-(Diphenylmethyl)-2-phenyl-4-quinazolinamine (SoRI-9804), N-(2,2-diphenylethyl)-2-phenyl-4-quinazolinamine (SoRI-20040), and N-(3,3-diphenylpropyl)-2-phenyl-4-quinazolinamine (SoRI-20041) partially inhibited [(125)I]3beta-(4'-iodophenyl)tropan-2beta-carboxylic acid methyl ester (RTI-55) binding, slowed the dissociation rate of [(125)I]RTI-55 from the DAT, and partially inhibited [(3)H]dopamine uptake. In the present study, we report that SoRI-9804 and SoRI-20040, at doses that do not alter release, partially inhibited d-amphetamine-induced DAT-mediated release of [(3)H]1-methyl-4-phenylpyridinium (MPP(+))or[(3)H]dopamine from striatal synaptosomes ("DAT-mediated DA release") in a dose-dependent manner. SoRI-20041, which does not alter DAT-mediated DA release measured with [(3)H]DA, reversed the effect of SoRI-20040. SoRI-20040 and SoRI-9804 also partially inhibited DAT-mediated DA release induced by DA or (+/-)-3,4-methylenedioxyamphetamine, demonstrating that the observed partial inhibition is not specific for a particular DAT substrate. SoRI-9804 and SoRI-20040 did not attenuate D-amphetamine-induced release of [(3)H]5-hydroxytryptamine from serotonergic, or [(3)H]MPP(+) from noradrenergic, nerve terminals. Kinetic experiments demonstrated that SoRI-9804, in contrast to cocaine, slowed D-amphetamine-induced release of [(3)H]MPP(+) from dopaminergic nerve terminals without altering the apparent rate constants. The two major findings of this study are 1) the identification of both "agonist" (SoRI-9804 and SoRI-20040) and "antagonist" (SoRI-20041) allosteric modulators of D-amphetamine-induced DAT-mediated DA release and 2) [(3)H]DA uptake and d-amphetamine-induced DAT-mediated efflux can be separately modulated. Such agents may have therapeutic potential for the treatment of stimulant addiction, Parkinson's disease, and other psychiatric disorders.

Evidence for the involvement of dopamine transporters in behavioral stimulant effects of modafinil

Modafinil is prescribed for numerous medical conditions, but the drug's mechanism of action is unclear. Here, we examined the interaction of modafinil with receptors and transporters in vitro and compared pharmacological effects of the drug with those produced by indirect dopamine (DA) agonists 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR12909) and (+)-methamphetamine (METH). Modafinil was screened at various receptors and transporters using binding assays. Transporter-mediated uptake and release were examined in rat brain synaptosomes. Effects of modafinil on motor activity and neurochemistry were determined in rats undergoing in vivo microdialysis in nucleus accumbens. Of the receptors and transporters assayed, modafinil displayed measurable potency only at DA transporters (DAT), inhibiting [(3)H]DA uptake, with an IC(50) value of 4.0 microM. Accordingly, modafinil pretreatment (10 microM) antagonized METH-induced release of the DAT substrate [(3)H]1-methyl-4-phenylpyridinium. Intravenous modafinil (20 and 60 mg/kg) produced dose-dependent increases in motor activity and extracellular DA, without affecting serotonin (5-HT). Analogous results were observed for GBR12909 (1 and 3 mg/kg), whereas METH (0.3 and 1 mg/kg) increased DA and 5-HT. Locomotor effects of all drugs were positively correlated with dialysate DA (P < 0.001). Interestingly, modafinil pretreatment reduced METH-induced ambulation and DA release. Our data show that modafinil interacts with DAT sites in rat brain, a property shared with agonist medications under investigation for treating cocaine dependence. Nondopaminergic mechanisms may also contribute to the pharmacology of modafinil. Finally, the results suggest that modafinil should be tested as an adjunct for treating METH addiction.

Protracted 'anti-addictive' effects of adolescent phenylpropanolamine exposure in C57BL/6J mice

Exposure to the once highly prevalent over-the-counter (OTC) sympathomimetic phenylpropanolamine (PPA; +/--norephedrine) during pre-adolescence alters the developmental trajectory of catecholamine and amino acid neurotransmitter systems in the nucleus accumbens (NAC) that culminate in a 'pro-addictive' phenotype in adulthood. Thus, the present study sought to extend these earlier data by examining the long-term consequences of repeated PPA treatment during adolescence upon the behavioral and neurochemical responses to cocaine. For this, C57BL/6J mice were pre-treated with PPA (0-40 mg/kg) during postnatal days 35-44, and the capacity of cocaine (4 x 15 mg/kg) to elicit a conditioned place-preference, as well as behavioral and neurochemical sensitization within the NAC, were then assessed in adulthood. While adolescent PPA exposure did not influence spontaneous locomotor activity or the motor responses to either acute or repeated cocaine (4 x 15 mg/kg), PPA pre-exposure dose-dependently reduced the expression of a conditioned place-preference. As observed previously for juvenile PPA treatment, adolescent PPA administration blunted the dopamine and norepinephrine response to acute cocaine, prevented the development of catecholamine sensitization but did not influence cocaine-induced elevations in serotonin. However, unlike juvenile PPA treatment, adolescent PPA also prevented the development of glutamate sensitization within the NAC. These data provide evidence that adolescent exposure to a formerly prevalent OTC sympathomimetic produces protracted effects upon cocaine-induced changes in NAC glutamate transmission that may reduce vulnerability to cocaine addiction in later life and further the hypothesis that early exposure to sympathomimetic drugs may be an environmental factor contributing to the etiology of addiction.

The rush to adrenaline: drugs in sport acting on the beta-adrenergic system

Athletes attempt to improve performance with drugs that act on the beta-adrenergic system directly or indirectly. Of three beta-adrenoceptor (AR) subtypes, the beta(2)-AR is the main target in sport; they have bronchodilator and anabolic actions and enhance anti-inflammatory actions of corticosteroids. Although demonstrable in animal experiments and humans, there is little evidence that these properties can significantly improve performance in trained athletes. Their actions may also be compromised by receptor desensitization and by common, naturally occurring receptor mutations (polymorphisms) that can influence receptor signalling and desensitization properties in individuals. Indirectly acting agents affect release and reuptake of noradrenaline and adrenaline, thereby influencing all AR subtypes including the three beta-ARs. These agents can have potent psychostimulant effects that provide an illusion of better performance that does not usually translate into improvement in practice. Amphetamines and cocaine also have considerable potential for cardiac damage. beta-AR antagonists (beta-blockers) are used in sports that require steadiness and accuracy, such as archery and shooting, where their ability to reduce heart rate and muscle tremor may improve performance. They have a deleterious effect in endurance sports because they reduce physical performance and maximum exercise load. Recent studies have identified that many beta-AR antagonists not only block the actions of agonists but also activate other (mitogen-activated PK) signalling pathways influencing cell growth and fate. The concept that many compounds previously regarded as 'blockers' may express their own spectrum of pharmacological properties has potentially far-reaching consequences for the use of drugs both therapeutically and illicitly.

A review of the neuropharmacological properties of khat

BACKGROUND

The psychostimulant khat (Catha edulis Forsk), is a herbal drug cultivated and chewed as a recreational and socializing drug in East Africa and the Arabian Peninsula for centuries. Due to increasing air transportation and the loosening of customs restrictions, it is now readily available in the Western Countries mainly used by immigrants from khat growing areas causing a concern to policy-makers.

OBJECTIVE

We conducted this review to further gain an insight to the neuropharmacological effects of khat.

METHODOLOGY

PubMed search engine with key terms 'khat' or 'qat' or 'mirra' or'qaad/jaad' or 'cathinone' was used to obtain articles relevant to khat chewing. In total 284 English written articles published from 1959 to 2007 were screened.

RESULTS

Most of the studies focused on cathinone, the postulated active psychostimulant alkaloid in khat. There were few studies which investigated the entire plant extract in either in vitro or animal studies. In the majority of the studies it was reported that both cathinone and cathine, another psychoactive constituent, have actions that are similar to those of amphetamine.

CONCLUSIONS

It seems that the well investigated khat alkaloids have many features similar to amphetamines; however there is a need for a more thorough examination of khat itself in well designed in vitro, animal and human studies with a range of comparator drugs before confirming the claim that khat is a "natural amphetamine".

Studies of the biogenic amine transporters. 12. Identification of novel partial inhibitors of amphetamine-induced dopamine release

Previous studies identified partial inhibitors and allosteric modulators of 5-hydroxytryptamine ([5-amino-3-(3,4-dichlorophenyl)-1,2-dihydropyrido[3,4-b]pyrazin-7-yl]carbamic acid ethyl ester [SoRI-6238], 4-(2-[bis(4-fluorophenyl)methoxy]ethyl)-1-(2-trifluoromethyl-benzyl)-piperidine [TB-1-099]) and dopamine transporters N-(diphenylmethyl)-2-phenyl-4-quinazolinamine, [SoRI-9804]). We report here the identification of three novel allosteric modulators of the dopamine transporter [N-(2,2-diphenylethyl)-2-phenyl-4-quinazolinamine [SoRI-20040], N-(3,3-diphenylpropyl)-2-phenyl-4-quinazolinamine [SoRI-20041], and [4-amino-6-[(diphenylmethyl)amino]-5-nitro-2-pyridinyl]carbamic acid ethyl ester [SoRI-2827]]. Membranes were prepared from human embryonic kidney cells expressing the cloned human dopamine transporter (hDAT). [(125)I]3beta-(4'-Iodophenyl)tropan-2beta-carboxylic acid methyl ester ([(125)I]RTI-55) binding and other assays followed published procedures. SoRI-20040, SoRI-20041, and SoRI-2827 partially inhibited [(125)I]RTI-55 binding, with EC(50) values ranging from approximately 1.4 to 3 microM and E(max) values decreasing as the [(125)I]RTI-55 concentrations increased. All three compounds decreased the [(125)I]RTI-55 B(max) value and increased the apparent K(d) value in a manner well described by a sigmoid dose-response curve. In dissociation rate experiments, SoRI-20040 (10 microM) and SoRI-20041 (10 microM), but not SoRI-2827 (10 microM), slowed the dissociation of [(125)I]RTI-55 from hDAT by approximately 30%. Using rat brain synaptosomes, all three agents partially inhibited [(3)H]dopamine uptake, with EC(50) values ranging from 1.8 to 3.1 microM and decreased the V(max) value in a dose-dependent manner. SoRI-9804 and SoRI-20040 partially inhibited amphetamine-induced dopamine transporter-mediated release of [(3)H]1-methyl-4-phenylpyridinium ion from rat caudate synaptosomes in a dose-dependent manner. Viewed collectively, we report several compounds that allosterically modulate hDAT binding and function, and we identify novel partial inhibitors of amphetamine-induced dopamine release.

Khat chewing from the pharmacological point of view: an update

Khat chewing is deeply rooted in the every day life of people living in the Horn of Africa and in South Arabia, where Catha edulis is endemic. Considered little more than an exotic habit producing just mild pharmacological effects, systematic investigations on its active principles have instead lead to the isolation and chemical characterization of cathinone, a compound structurally related to amphetamine. Three decades of intense experimental and clinical research on khat have depicted a consistently clear picture of its pharmacological and toxicological effects.

In vitro study of the effects of khat (Catha edulis Forsk) extract on isolated mouse interstitial cells

Isolated mouse interstitial cells were incubated with different concentrations of khat (Catha edulis) extract (0.06 mg/ml, 0.6 mg/ml, 6 mg/ml, 30 mg/ml and 60 mg/ml) and cell viability as well as testosterone concentration measured at 30 min intervals over a 3h incubation period. High concentrations of khat extract (30 mg/ml and 60 mg/ml) significantly inhibited testosterone production while low concentrations (0.06 mg/ml, 0.6 mg/ml and 6 mg/ml) significantly stimulated (P<0.05) testosterone production by mouse interstitial cells. Similarly, at concentrations of 30 mg/ml and 60 mg/ml, there was a significant decrease in interstitial cell viability, whereas at 0.06 mg/ml, 0.6 mg/ml and 6 mg/ml there was no significant decrease. There was only a weak correlation (r=0.39) between testosterone production and viable interstitial cells. We postulate that khat extract at high concentrations may cause reproductive function impairment in the user but at low concentrations, may enhance testosterone production with accompanying effects on reproductive functions in male mice.

Pharmacological effects of ephedrine alkaloids on human alpha(1)- and alpha(2)-adrenergic receptor subtypes

Ephedra species of plants have both beneficial and adverse effects primarily associated with the presence of ephedrine alkaloids. Few reports have appeared that examine the direct actions of ephedrine alkaloids on human subtypes of adrenergic receptors (ARs). In the present study, ephedrine alkaloids were evaluated for their binding affinities on human alpha(1A)-, alpha(1B)-, alpha(1D)-, alpha(2A)-, alpha(2B)-, and alpha(2C)-AR subtypes expressed in HEK and Chinese hamster ovary cells. Cell-based reporter gene assays were used to establish functional activity of ephedrine alkaloids at alpha(1A)-, alpha(2A)-, and alpha(2C)-ARs. The data showed that ephedrine alkaloids did not activate alpha(1)- and alpha(2)-ARs and that they antagonized the agonist-mediated effects of phenylephrine and medetomidine on alpha(1)- and alpha(2)-ARs, respectively. As in the binding studies, 1R,2R- and 1R,2S-ephedrine showed greater functional antagonist activity than the 1S,2R- and 1S,2S-isomers. The rank order of affinity for the isomers was 1R,2R > 1R,2S > 1S,2R > 1S,2S. The rank order of potencies of alkaloids containing a 1R,2S-configuration was norephedrine > or = ephedrine >> N-methylephedrine. These studies have demonstrated that orientation of the beta-hydroxyl group on the ethylamino side chain and the state of N-methyl substitution are important for alpha-AR binding and functional activity of the ephedrine alkaloids. In conclusion, the ephedrine isomers and analogs studied did not exhibit any direct agonist activity and were found to possess moderate antagonist activities on cloned human alpha-ARs. The blockade of presynaptic alpha(2A)- and alpha(2C)-ARs may have a pharmacological role in the direct actions of Ephedra alkaloids.

Catha edulis extract and its active principle cathinone induce ipsilateral rotation in unilaterally lesioned rats

Catha edulis extract, a natural psychostimulant, and its active component, S-(-)-cathinone, were evaluated for their rotational effects in unilaterally lesioned rats. In our earlier study, we demonstrated that commercially available S-(-)-cathinone, the active principle of C. edulis extract, reverses haloperidol-induced catalepsy. In the current study, we evaluated the effect of C. edulis extract or its active principle, cathinone, in 6-hydroxydopamine unilaterally lesioned rats. Evaluation of the rotational behaviour induced by this natural psychostimulant was made upon acute and repeated oral administration. The data show that C. edulis extract or S-(-)-cathinone induced ipsilateral rotation in 6-hydroxydopamine unilaterally lesioned rats. The ipsilateral rotation produced by commercially available S-(-)-cathinone was more marked than the response produced by oral administration of lyophilized C. edulis extract at the dose and periods specified. In addition, upon repeated administration, the effect was more pronounced (i.e. there was sensitization). In conclusion, the results demonstrate that the plant induces ipsilateral rotation, like its close relative amphetamine.

Use of knockout technology to resolve pharmacological problems

Knock-out (KO) mouse technology has given pharmacologists a powerful tool to study function in the absence of selective antagonists or inhibitors. Such KO technology can confirm predicted function, serendipitously reveal unrecognized function, or help define the mode of action of a drug. In this issue, Liles et al. demonstrate, employing mice unable to synthesize noradrenaline due to the KO of the dopamine-beta-hydroxylase gene, that the sympathomimetic actions of ephedrine are directly, rather than indirectly, mediated. This may end 50 years of debate about the actions of ephedrine.

Pressor responses to ephedrine are not impaired in dopamine beta-hydroxylase knockout mice

BACKGROUND AND PURPOSE

Ephedrine and amphetamine can cause substantial increases in systemic arterial pressure. However, the role of endogenous noradrenaline release in mediating the pressor response to ephedrine is controversial. Studies using pharmacologic agents to decrease the synthesis, storage, and release of catecholamines have supported both a direct and an indirect mechanism of action for ephedrine. The purpose of the present study was to determine if endogenous noradrenaline release is required for cardiovascular responses to ephedrine and amphetamine using a genetic mouse model.

EXPERIMENTAL APPROACH

Increases in systemic arterial pressure and heart rate in response to ephedrine and amphetamine were investigated and compared in dopamine beta-hydroxylase knockout (Dbh -/-) mice that cannot synthesize noradrenaline. Dbh +/- littermates have normal noradrenaline and adrenaline tissue levels, and served as controls in all experiments.

KEY RESULTS

In Dbh -/- mice the increases in systemic arterial pressure and heart rate in response to i.v. injections of ephedrine were not impaired whereas responses to amphetamine were markedly reduced, when compared with responses in Dbh +/- mice. The pressor response to tyramine was abolished whereas pressor responses to noradrenaline, phenylephrine, dopamine, and angiotensin II were similar in Dbh -/- and Dbh +/- mice.

CONCLUSIONS AND IMPLICATIONS

The present results in Dbh -/- mice provide support for the hypothesis that pressor responses to ephedrine are directly mediated whereas responses to amphetamine are dependent on the release of noradrenaline and suggest that Dbh +/- and Dbh -/- mice are useful for the study of direct and indirect mechanisms.

Convergent Synthesis of Complex Diketopiperazines Derived from Pipecolic Acid Scaffolds and Parallel Screening against GPCR Targets

A convergent approach to highly functionalized diketopiperazines (DKPs) using enantioenriched pipecolic acids is described. Scandium triflate-catalyzed [4 + 2] aza-annulation was employed to produce stereochemically well-defined building blocks. A resin "catch and release" strategy was devised to convert annulation products to pipecolic acid monomers. Complex diketopiperazines were efficiently assembled utilizing one-pot cyclodimerization of pipecolic acids. Massively parallel screening of the complex DKPs against a panel of molecular targets identified novel ligands for a number of G-protein-coupled receptors (GPCRs).

The potential impact of novel investigational compounds on human fertility

There is considerable concern that the incidence of infertility in humans may be increasing, in some instances due to the action of bioactive xenobiotic compounds found in our environment; for example, high concentrations of xenobiotics with estrogenic activity can interfere with normal testicular function and fertility. However, recent studies have shown that very low concentrations of several estrogenic xenobiotics can have subtle, unexpected effects on sperm function. When tested in vitro, these compounds stimulate spermatozoa to become fertile very quickly, but continued stimulation causes them to burn out and lose fertilising ability; similar responses occurring in vivo could reduce fertility. In contrast, several other compounds, structurally related to amfetamine, have been shown to act on spermatozoa in vitro in a positive manner, stimulating cells to 'switch on' quickly and then preventing burnout so that they maintain fertilising potential; similar responses occurring in vivo could enhance fertility. These results could have implications for either reducing or enhancing natural fertility.

Screening the receptorome: an efficient approach for drug discovery and target validation

The receptorome, comprising at least 5% of the human genome, encodes receptors that mediate the physiological, pathological and therapeutic responses to a vast number of exogenous and endogenous ligands. Not surprisingly, the majority of approved medications target members of the receptorome. Several in silico and physical screening approaches have been devised to mine the receptorome efficiently for the discovery and validation of molecular targets for therapeutic drug discovery. Receptorome screening has also been used to discover, and thereby avoid, the molecular targets responsible for serious and unforeseen drug side effects.

The potential adverse effects of habitual use of Catha edulis (khat)

The habit of Catha edulis Forsk (khat) chewing has prevailed for centuries among populations in the horn of Africa and the Arabian peninsula. Fresh leaves of Catha edulis are customarily chewed to attain a state of stimulation. The fact that cathinone has a closer structural similarity with amphetamine, and both share common pharmacodynamic features, led to the conclusion that cathinone is the most important active ingredient of Catha edulis, which causes the major pharmacological effects. Problems associated with repeated consumption of Catha edulis leaves are becoming evident. Literature surveys and clinical diagnostic studies revealed an association with prevalence of psychiatric morbidity. Repeated intermittent oral administration of Catha edulis to laboratory animals lead to development and expression of locomotor sensitisation. Catha edulis also leads to several peripheral effects that include increases in blood pressure and has been associated with the increased incidence of acute coronary vasospasm and myocardial infarction. Catha edulis also accounts for a number of gastrointestinal tract problems, oesophagitis, gastritis and delay intestinal absorption, as well as the development of oral keratotic white lesions at the site of chewing. Administration of Catha edulis extracts showed a deranged systemic capacity to handle oxidative radicals and induces cytotoxic effects in cells of liver and kidney, as well as induction of cell death in various human leukaemia cell lines and in peripheral human blood leukocytes.

Identification of functional alpha2- and beta-adrenergic receptors in mammalian spermatozoa

BACKGROUND

A recent study of several compounds, structurally related to amphetamine, provided evidence that mammalian spermatozoa might have adrenergic receptors able to regulate cAMP production. The present study investigated this possibility using physiological and immunochemical analyses of mouse and human spermatozoa.

METHODS

Antibodies specific for different receptor subtypes were used for Western blotting of mouse and human sperm lysates and for immunocytochemical evaluation of whole mouse and human spermatozoa. Uncapacitated and capacitated mouse spermatozoa were incubated with specific agonists and antagonists for alpha2-, beta1-, beta2- and beta3-adrenergic receptors for approximately 35 min and then assessed using chlortetracycline (CTC) fluorescence.

RESULTS

Western blotting revealed proteins of the correct size for all these receptors; immunolocalization indicated their presence on the head, especially acrosomal and neck regions, and flagellum of both mouse and human spermatozoa. CTC results indicated significant responses to agonists for all of the beta-receptors in uncapacitated cells, with agonist effectiveness being beta1 > beta2 > beta3; relevant antagonists blocked responses. In contrast, an agonist and antagonist for alpha2-receptors acted only on capacitated spermatozoa.

CONCLUSION

These experiments provide the first good evidence that mammalian spermatozoa have both beta-adrenergic receptors, known to stimulate cAMP production by membrane-associated adenylyl cyclases (mACs), and alpha2-adrenergic receptors, known to inhibit cAMP production by mACs. Responses are capacitation state dependent and provide a mechanism for inhibiting spontaneous acrosome reactions and helping to maintain fertilizing ability. These results suggest that the use of amphetamine-related compounds, either for medical or for social reasons, might have an unexpected positive impact on fertility.

Receptor systems: will mining the receptorome yield novel targets for pharmacotherapy?

We have recently defined the receptorome as 'that part of the proteome encoding receptors'. In this article, I provide a general overview of the members of the receptorome as well as methods used to screen the receptorome-both in silico and physically. Case histories of receptorome-based discovery efforts are then highlighted and the relevance of this approach to the discovery and validation of molecular targets for drug abuse treatment is emphasized.

Dopamine-mediated actions of ephedrine in the rat substantia nigra

Although ephedrine is a centrally active stimulant, its effect on midbrain dopamine neurons is not known. To study the effect of ephedrine on dopamine-containing cells, current-clamp microelectrode recordings were made from substantia nigra pars compacta (SNC) neurons in horizontal brain slice preparations. Ephedrine (100-1000 microM) slowed spontaneous firing and produced a modest concentration-dependent hyperpolarization of membrane potential (EC50 279 microM), with a concomitant net decrease in membrane resistance. These effects were blocked by the D2-like dopamine antagonist sulpiride (1 microM). Electrically evoked inhibitory synaptic potentials mediated by GABAB receptors were reduced 28% by ephedrine. However, ephedrine did not reduce fast synaptic potentials mediated by GABAA or ionotropic glutamate receptors. Inhibition of the GABAB response appeared to be mediated by a postsynaptic mechanism because ephedrine also reduced baclofen-induced hyperpolarization by 28%. Both ephedrine-induced hyperpolarization and inhibition of baclofen-induced hyperpolarization were abolished when slices were superfused with the tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (AMPT). Despite perfusion with AMPT, the ability of ephedrine to cause hyperpolarization was restored after perfusing the slice with dopamine (30 microM). Taken together, these results suggest that ephedrine causes hyperpolarization and suppresses GABAB receptor-mediated effects by releasing endogenous dopamine. However, the high concentrations required to observe these effects in vitro suggest that biologically relevant central effects of ephedrine are more likely to be mediated either by non-dopamine systems, such as those involving noradrenaline, or by dopamine systems outside the SNC.

Targeted screening for biogenic amine transporters: Potential applications for natural products

The biogenic amine transporters (BATs) are integral membrane proteins that terminate the actions of dopamine (DA), serotonin (5-HT) and norepinephrine (NE) by pumping these substrates from the extracellular space back into the nerve terminal. Numerous drugs and medications target BATs, acting as inhibitors or substrates. This paper will review some of the methods used to measure the activity of test drugs at the BATs. These methods include traditional uptake inhibition assays and transporter binding assays, as well as methods developed in our lab to determine if a test agent is a BAT substrate or inhibitor. Newer methods, developed in our lab, are used to determine the potency of test drugs as BAT substrates in a relatively high throughput manner. The potential application of these methods to characterizing natural products will be discussed in reference to results obtained with "purified" natural products, such as ephedrine stereoisomers.

Pharmacologic analysis of non-synonymous coding h5-HT2A SNPs reveals alterations in atypical antipsychotic and agonist efficacies

The 5-HT(2A)-serotonin receptor is a major molecular target for most atypical antipsychotic drugs as well as most hallucinogens, which can exacerbate psychotic symptoms. In this study, we examined whether random sequence variations in the gene (single nucleotide polymorphisms, SNPs) encoding the 5-HT(2A)-serotonin receptor could explain inter-individual variability in atypical antipsychotic and agonist drug response. We examined the in vitro pharmacology of four non-synonymous SNPs, which give rise to T25N, I197V, A447V, and H452Y variant 5-HT(2A)-serotonin receptors. Our data indicate that these non-synonymous SNPs exert statistically significant, although modest, effects on the affinity and functional effects of several currently approved atypical antipsychotics (aripiprazole, clozapine, olanzapine, quetiapine, risperidone, and ziprasidone). Also, the 5-HT(2A) receptor SNPs slightly altered the potency and relative efficacy of a small number of selected agonists (2,5-dimethoxy-4-iodoamphetamine, tryptamine, 5-hydroxytryptamine, m-chlorophenylpiperazine, and 5-methoxy-N, N-dimethyltryptamine). In all, our results show that the in vitro pharmacological effects of the SNPs are drug specific.

Screening the receptorome for plant-based psychoactive compounds

Throughout time, humans have used psychoactive plants and plant-derived products for spiritual, therapeutic and recreational purposes. Furthermore, the investigation of psychoactive plants such as Cannabis sativa (marijuana), Nicotiana tabacum (tobacco) and analogues of psychoactive plant derivatives such as lysergic acid diethylamide (LSD) have provided insight into our understanding of neurochemical processes and diseases of the CNS. Currently, many of these compounds are being used to treat a variety of diseases, such as depression and anxiety in the case of Piper methysticum Kava Kava (Martin et al., 2002; Singh and Singh, 2002). G-protein coupled receptors (GPCRs) are the most common molecular target for both psychoactive drugs and pharmaceuticals. The "receptorome" (that portion of the genome encoding ligand reception) encompasses more than 8% of the human genome (Roth et al., 2004) and as such provides a large number of possible targets for psychoactive drug interactions. A systematic, comprehensive study is necessary to identify novel active psychoactive plant-based compounds and the molecular targets of known compounds. Herein we describe the development of a high throughput system (HTS) to screen psychoactive compounds against the receptorome and present two examples (Salvia divinorum, the "magic mint" hallucinogen and Banisteriopsis caapi, the main component of Ayahuasca, a psychoactive beverage) where HTS enabled the identification of the molecular target of each compound.

Screening the receptorome reveals molecular targets responsible for drug-induced side effects: focus on ‘fen–phen’

The in vitro pharmacological profiling of drugs using a large panel of cloned receptors (e.g., G protein-coupled receptors, ligand-gated ion channels, Na(+)-dependent monoamine transporters), an approach that has come to be known as 'receptorome screening', has unveiled novel molecular mechanisms responsible for the actions and/or side effects of certain drugs. For instance, receptorome screening has been employed to uncover novel molecular targets involved in the actions of antipsychotic medications and the hallucinogenic mint extract salvinorin A. This review highlights the recent application of receptorome screening to discover why the anorexigen fenfluramine causes serious cardiopulmonary side effects. Receptorome screening has implicated N-deethylation of fenfluramine and serotonin 5-hydroxy-t-ryptamine 2B receptors in the adverse effects of the drug; subsequent studies corroborated this finding. The results discussed highlight the utility of determining the potential activity of drugs -- and, importantly, of their in vivo metabolites -- at as many molecular targets as possible in order to reliably predict side effect profiles. Receptorome screening represents one of the most effective methods for identifying potentially serious drug-related side effects at the preclinical stage, thereby avoiding significant economic and human health consequences.

Psychiatric symptoms associated with ephedra use

The objective of this review is to describe psychiatric adverse events occurring after ingestion of dietary supplements containing herbal ephedra and to assess the possible relationship between supplement use and the events. The authors reviewed all adverse event reports related to dietary supplements containing herbal ephedra from US FDA MedWatch files as of 30 September, 2001. Psychosis, mania or severe agitation, severe depression, hallucinations, delusions, suicide attempts, paranoia and violent behaviour were classified as serious psychiatric events. Events were categorised based on the amount of information supporting a causal relationship. Out of almost 1800 total adverse events, 57 were classified as both psychiatric in nature and serious. Two-thirds of these psychiatric cases involved patients with pre-existing psychological/psychiatric conditions and/or use of other mood-altering medications or illicit substances. The majority of case reports were insufficiently documented to make an informed judgment about a relationship between the use of ephedra and the adverse event in question. The case reports evaluated do not prove a definitive causal link between ephedra and psychiatric complications. However, they do raise concern that such a relationship may exist.

Repeated Catha edulis oral administration enhances the baseline aggressive behavior in isolated rats

The effects of repeated oral administration of the psychostimulant plant, Catha edulis and its active principle, cathinone on rats were studied using isolation induced aggression paradigm. The behavioral responses were videotaped and scored later by offline data analyses. Rats were decapitated at the end of the behavioral experiment and in the relevant brain regions, monoamines were assessed. The results demonstrate that isolation of male rats produces a baseline aggression. Treatments with the psychostimulant plant, Catha edulis or commercial S-(--)-cathinone enhanced significantly: The locomotor activities and the baseline aggression behaviors compared with vehicle treated rats. Neurochemical correlates revealed a significant depletion of serotonin (5-HT) and its corresponding metabolites (5-HIAA) in both the anterior and posterior striatum. There was also a reduction in the level of homovanillic acid (HVA) in the hippocampus. Additionally, elevation of dopamine level was observed in the nucleus accumbens, especially, in those rats treated with Catha edulis extract. Cathinone, on the other hand, increased the level of HVA in the posterior striatum and decreased HVA in the nucleus accumbens. In conclusion, the present data demonstrate that repeated administration of Catha edulis or S-(--)-cathinone enhances aggression in rats, presumably by decreasing the level of serotonin and its corresponding metabolites. Besides, the data obtained do not rule out the involvement of dopamine in aggression behavior.

Pressor Responses to Ephedrine Are Mediated by a Direct Mechanism in the Rat

The mechanism of the pressor response to ephedrine is controversial. In the present study. i.v. injections of ephedrine increased systemic and pulmonary arterial pressure, and i.a. injections decreased hindlimb blood flow in a dose-related manner. Responses to ephedrine were inhibited by alpha-receptor blocking agents and were not attenuated by blockade of the norepinephrine reuptake transporter (NET) or by catecholamine depletion using reserpine or a combination of reserpine and alpha-methyl-p-tyrosine, whereas responses to tyramine and amphetamine were inhibited by these treatments. The magnitude of the pressor response to ephedrine was similar in anesthetized and conscious rats. Tachyphylaxis developed to pressor responses to ephedrine and amphetamine with sequential injections; however, ephedrine tachyphylaxis differed in that subsequent responses to alpha-receptor agonists were attenuated. These results suggest that the systemic and pulmonary pressor and hindlimb vasoconstrictor responses to ephedrine are mediated by direct action on alpha-adrenergic receptors and that the release of norepinephrine from adrenergic terminals plays no significant role. These results provide support for the hypothesis that responses to ephedrine are directly mediated in the intact rat, whereas responses to amphetamine are mediated in a large part by the release of norepinephrine from adrenergic terminals.

Clozapine attenuates the locomotor sensitisation and the prepulse inhibition deficit induced by a repeated oral administration of Catha edulis extract and cathinone in rats

Locomotor sensitisation and deficits in prepulse inhibition (PPI) induced by psychostimulants are two paradigms that have been widely studied as animal behavioural models of psychosis. Clozapine is one of the atypical antipsychotic agents which has been widely employed to reverse the aforementioned behavioural changes in these usual models. In this particular study, locomotor sensitisation and prepulse inhibition deficit were induced under the same context by intermittent oral administration of S-(-)-cathinone or Catha edulis extract in rats. The rats were then challenged by administration of the atypical antipsychotic drug, clozapine and were finally challenged with psychostimulants after 2-week of withdrawal. Locomotor activity and PPI were assessed and later analyses of the neurotransmitter levels were made. The results of this experiment show that repeated oral administration of cathinone or C. edulis extract enhanced locomotor and exploratory activity and lead to a gradual deficit in prepulse inhibition. This locomotor sensitisation and PPI deficit could be reversed by administration of clozapine. A challenge with psychostimulant on day 40 (i.e., after 2-week of withdrawal) resulted in a response similar to the initial exposure (day 1). Neurotransmitter level analyses showed a significant increase in the level of dopamine in the prefrontal cortex (p < 0.05). There was also a significant decrease in the level of 5-hydroxytryptamine (5-HT) in the nucleus accumbens (p < 0.05) and its metabolite, 5-hydroxyindole acetic acid (5-HIAA) in the prefrontal cortex (p < 0.01). In the remaining regions (anterior and posterior striatum), there were no significant changes. In conclusion, this is the first study to demonstrate that repeated administration of C. edulis extract, or commercial cathinone, induces prepulse inhibition deficit and clozapine reverses both C. edulis or cathinone-induced sensitised locomotion and prepulse inhibition deficit.

The highly efficacious actions of N-desmethylclozapine at muscarinic receptors are unique and not a common property of either typical or atypical antipsychotic drugs: is M1 agonism a pre-requisite for mimicking clozapine's actions?

RATIONALE

Recent studies have suggested that the salutary actions of clozapine in schizophrenia may be due to selective activation of M(1) muscarinic receptors by clozapine and/or its major active metabolite N-desmethylclozapine.

OBJECTIVE

We systematically tested this hypothesis by screening a large number of psychoactive compounds, including many atypical antipsychotic drugs, for agonist activity at cloned, human M(1), M(3) and M(5) muscarinic receptors.

RESULTS

Only three of the 14 atypical antipsychotic drugs we tested were found to possess partial agonist actions at M(1) muscarinic receptors (fluperlapine, JL13, clozapine). A few additional miscellaneous compounds had a modest degree of M(1) agonist actions. Only carbachol and N-desmethylclozapine had appreciable M(3) muscarinic agonism at M(3) muscarinic receptors, although several were M(5) partial agonists including MK-212, N-desmethylclozapine and xanomeline.

CONCLUSION

Although M(1) muscarinic receptor-selective partial agonists have shown promise in some preclinical antipsychotic drug models, these studies indicate that it is unlikely that the salutary actions of clozapine and similar atypical antipsychotic drugs are mediated solely by M(1) muscarinic receptor activation. It is possible, however, that the M(1) agonism of N-desmethylclozapine contributes to the uniquely beneficial actions of clozapine. Thus, these results are consistent with the notion that a balanced degree of activity at multiple biogenic amine receptors, including M(1) muscarinic agonism, is responsible for the uniquely beneficial actions of clozapine.

Relationship between the serotonergic activity and reinforcing effects of a series of amphetamine analogs

It has been reported that among drugs with mixed actions on central nervous system monoamine systems, increased serotonergic activity is associated with decreased potency as a reinforcer. The present experiment was designed to examine this relationship for amphetamine analogs that varied in serotonin releasing potency and to evaluate whether serotonergic actions can affect reinforcing efficacy. Compounds PAL 313 and 314 are para- and meta-methylamphetamine, respectively. PAL 303 and 353 are para- and meta-fluoroamphetamine, respectively. All compounds had similar potencies as in vitro releasers of dopamine (DA) and norepinephrine (NE) but differed in potency for 5-hydroxytryptamine (serotonin) (5-HT) release [EC(50) (nanomolar) PAL 313 = 53.4; PAL 314 = 218; PAL 303 = 939; PAL 353 = 1937]. When made available to rhesus monkeys (Macaca mulatta)(n = 4) for self-administration under a fixed-ratio 25 schedule, all were positive reinforcers with biphasic dose-response functions (0.003-1.0 mg/kg) and were equipotent. PAL 313 was self-administered at a lower rate than the other compounds, which were indistinguishable. Under a progressive-ratio schedule (n = 5), all drugs were positive reinforcers. Dose-response functions increased to a maximum or were biphasic (0.01-1.0 mg/kg), and drugs were equipotent. At maximum, PAL 313 maintained less responding than other PAL drugs, which maintained similar maxima. Thus, all compounds were positive reinforcers under both schedules, consistent with their potent DA actions. Responding was lower when 5-HT potency was higher and comparable with DA and NE potency. The results suggest that the mechanism for this effect involves a decrease in reinforcing potency and efficacy among monoamine releasing agents when 5-HT releasing potency is increased relative to DA.

Screening the receptorome to discover the molecular targets for plant-derived psychoactive compounds: a novel approach for CNS drug discovery

Because psychoactive plants exert profound effects on human perception, emotion, and cognition, discovering the molecular mechanisms responsible for psychoactive plant actions will likely yield insights into the molecular underpinnings of human consciousness. Additionally, it is likely that elucidation of the molecular targets responsible for psychoactive drug actions will yield validated targets for CNS drug discovery. This review article focuses on an unbiased, discovery-based approach aimed at uncovering the molecular targets responsible for psychoactive drug actions wherein the main active ingredients of psychoactive plants are screened at the "receptorome" (that portion of the proteome encoding receptors). An overview of the receptorome is given and various in silico, public-domain resources are described. Newly developed tools for the in silico mining of data derived from the National Institute of Mental Health Psychoactive Drug Screening Program's (NIMH-PDSP) K(i) Database (K(i) DB) are described in detail. Additionally, three case studies aimed at discovering the molecular targets responsible for Hypericum perforatum, Salvia divinorum, and Ephedra sinica actions are presented. Finally, recommendations are made for future studies.

Khat (Catha edulis)-induced apoptosis is inhibited by antagonists of caspase-1 and -8 in human leukaemia cells

Khat chewing is a widespread habit that has a deep-rooted sociocultural tradition in Africa and the Middle East. The biological effects of khat are inadequately investigated and controversial. For the first time, we show that an organic extract of khat induces a selective type of cell death having all morphological and biochemical features of apoptotic cell death. Khat extract was shown to contain the major alkaloid compounds cathinone and cathine. The compounds alone and in combination also induced apoptosis. Khat-induced apoptosis occurred synchronously in various human cell lines (HL-60, NB4, Jurkat) within 8 h of exposure. It was partially reversed after removal of khat and the effect was dependent on de novo protein synthesis, as demonstrated by cotreatment with cycloheximide. The cell death was blocked by the pan-caspase inhibitor Z-VAD-fmk, and also by submicromolar concentrations of Z-YVAD-fmk and Z-IETD-fmk, inhibitors of caspase-1 and -8, respectively. The 50% inhibition constant (IC(50)) for khat (200 microg ml(-1))-induced apoptosis by Z-VAD-fmk, Z-YVAD-fmk and Z-IETD-fmk was 8 x 10(-7) M as compared to 2 x 10(-8) M and 8 x 10(-8) M, respectively. Western blot analysis showed a specific cleavage of procaspase-3 in apoptotic cells, which was inhibited by Z-VAD-fmk. The cell death by khat was more sensitively induced in leukaemia cell lines than in human peripheral blood leukocytes. It is concluded that khat induces a rather swift and sensitive cell death by apoptosis through mechanisms involving activation of caspase-1, -3 and -8.

Cathine and norephedrine, both phenylpropanolamines, accelerate capacitation and then inhibit spontaneous acrosome loss

BACKGROUND

Cathinone, released when Catha edulis leaves (khat) are chewed, has euphoric, stimulatory properties. It is metabolized to the phenylpropanolamines (PPAs) cathine and norephedrine. This study investigated whether PPAs affect mammalian sperm function, using primarily mouse, but also human, spermatozoa.

METHODS

Uncapacitated sperm suspensions were treated with cathine, norephedrine, adrenaline and noradrenaline, then assessed using chlortetracycline (CTC) fluorescence. Cathine and adrenaline were also evaluated using in vitro fertilization. Capacitated suspensions were treated with PPAs+/-progesterone and+/-pertussis toxin. Finally, cAMP production was evaluated in uncapacitated and capacitated suspensions.

RESULTS

In uncapacitated mouse spermatozoa, cathine, norephedrine, adrenaline and noradrenaline all significantly accelerated capacitation; uncapacitated human spermatozoa responded similarly to cathine. Consistent with these results, cathine- and adrenaline-treated suspensions were significantly more fertile than controls. In capacitated spermatozoa, both PPAs inhibited spontaneous acrosome reactions (ARs) but progesterone could over-ride this inhibition. Pertussis toxin abolished cathine's inhibition of ARs, suggesting G protein involvement. Finally, cathine and adrenaline significantly stimulated cAMP production in uncapacitated suspensions, but significantly inhibited it in capacitated suspensions.

CONCLUSIONS

This is the first demonstration that PPAs can directly affect mammalian sperm function, accelerating capacitation and inhibiting spontaneous ARs. These responses correlated with initial stimulation and subsequent inhibition of cAMP production. Adrenaline/noradrenaline elicited similar responses, suggesting the presence of adrenergic receptors. Therefore, regulation of adenylyl cyclase/cAMP in a G protein-mediated fashion by PPAs may possibly involve adrenergic receptors. These results suggest that PPAs, at appropriate doses, might provide a novel approach to enhance natural fertility.

Caveolin-1 Interacts with 5-HT2A Serotonin Receptors and Profoundly Modulates the Signaling of Selected Gαq-coupled Protein Receptors

5-Hydroxytryptamine 2A (5-HT(2A)) serotonin receptors are important for a variety of functions including vascular smooth muscle contraction, platelet aggregation, and the modulation of perception, cognition, and emotion. In a search for 5-HT(2A) receptor-interacting proteins, we discovered that caveolin-1 (Cav-1), a scaffolding protein enriched in caveolae, complexes with 5-HT(2A) receptors in a number of cell types including C6 glioma cells, transfected HEK-293 cells, and rat brain synaptic membrane preparations. To address the functional significance of this interaction, we performed RNA interference-mediated knockdown of Cav-1 in C6 glioma cells, a cell type that endogenously expresses both 5-HT(2A) receptors and Cav-1. We discovered that the in vitro knockdown of Cav-1 in C6 glioma cells nearly abolished 5-HT(2A) receptor-mediated signal transduction as measured by calcium flux assays. RNA interference-mediated knockdown of Cav-1 also greatly attenuated endogenous Galpha(q)-coupled P2Y purinergic receptor-mediated signaling without altering the signaling of PAR-1 thrombin receptors. Cav-1 appeared to modulate 5-HT(2A) signaling by facilitating the interaction of 5-HT(2A) receptors with Galpha(q). These studies provide compelling evidence for a prominent role of Cav-1 in regulating the functional activity of not only 5-HT(2A) serotonin receptors but also selected Galpha(q)-coupled receptors.

Salvinorin A, an active component of the hallucinogenic sage salvia divinorum is a highly efficacious kappa-opioid receptor agonist: structural and functional considerations

The diterpene salvinorin A from Salvia divinorum has recently been reported to be a high-affinity and selective kappa-opioid receptor agonist (Roth et al., 2002). Salvinorin A and selected derivatives were found to be potent and efficacious agonists in several measures of agonist activity using cloned human kappa-opioid receptors expressed in human embryonic kidney-293 cells. Thus, salvinorin A, salvinorinyl-2-propionate, and salvinorinyl-2-heptanoate were found to be either full (salvinorin A) or partial (2-propionate, 2-heptanoate) agonists for inhibition of forskolin-stimulated cAMP production. Additional studies of agonist potency and efficacy of salvinorin A, performed by cotransfecting either the chimeric G proteins Gaq-i5 or the universal G protein Ga16 and quantification of agonist-evoked intracellular calcium mobilization, affirmed that salvinorin A was a potent and effective kappa-opioid agonist. Results from structure-function studies suggested that the nature of the substituent at the 2-position of salvinorin A was critical for kappa-opioid receptor binding and activation. Because issues of receptor reserve complicate estimates of agonist efficacy and potency, we also examined the agonist actions of salvinorin A by measuring potassium conductance through G protein-gated K(+) channels coexpressed in Xenopus oocytes, a system in which receptor reserve is minimal. Salvinorin A was found to be a full agonist, being significantly more efficacious than (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane-sulfonate hydrate (U50488) or (trans)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane-sulfonate hydrate (U69593) (two standard kappa-opioid agonists) and similar in efficacy to dynorphin A (the naturally occurring peptide ligand for kappa-opioid receptors). Salvinorin A thus represents the first known naturally occurring non-nitrogenous full agonist at kappa-opioid receptors.