Structure-activity relationships among the halogenated amphetamines

Phencyclidine-Like Abuse Liability and Psychosis-Like Neurocognitive Effects of Novel Arylcyclohexylamine Drugs of Abuse in Rodents

Abuse of novel arylcyclohexylamines (ACX) poses risks for toxicities, including adverse neurocognitive effects. In vivo effects of ring-substituted analogs of phencyclidine (PCP), eticyclidine (PCE), and ketamine are understudied. Adult male National Institutes of Health Swiss mice were used to assess locomotor effects of PCP and its 3-OH, 3-MeO, 3-Cl, and 4-MeO analogs, PCE and its 3-OH and 3-MeO analogs, and ketamine and its deschloro and 2F-deschloro analogs, in comparison with those of methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA), and two benzofuran analogs of MDMA. PCP-like interoceptive effects for all of these ACXs were determined using a food-reinforced drug discrimination procedure in adult male Sprague Dawley rats. A novel operant assay of rule-governed behavior incorporating aspects of attentional set-shifting was used to profile psychosis-like neurocognitive effects of PCP and 3-Cl-PCP in rats, in comparison with cocaine and morphine. PCP-like ACXs were more effective locomotor stimulants than the amphetamines, PCE-like ACXs were as effective as the amphetamines, and ketamine-like ACXs were less effective than the amphetamines. Addition of -Cl, -OH, or -OMe at the 3-position on the aromatic ring did not impact locomotor effectiveness, but addition of -OMe at the 4-position reduced locomotor effectiveness. Lethal effects were induced by drugs with -OH at the 3-position or -OMe at the 3- or 4-position. All novel ACXs substituted at least partially for PCP, and PCP and 3-Cl-PCP elicited dose-dependent psychosis-like neurocognitive deficits in the rule-governed behavior task not observed with cocaine or morphine. Novel ACXs exhibit substantial abuse liability and toxicities not necessarily observed with their parent drugs. SIGNIFICANCE STATEMENT: Novel arylcyclohexylamine analogs of PCP, PCE, and ketamine are appearing on the illicit market, and abuse of these drugs poses risks for toxicities, including adverse neurocognitive effects. These studies demonstrate that the novel ACXs exhibit PCP-like abuse liability in the drug discrimination assay, elicit varied locomotor stimulant and lethal effects in mice, and induce psychosis-like neurocognitive effects in rats.

Serotonin discovery and stepwise disclosure of 5-HT receptor complexity over four decades. Part I. General background and discovery of serotonin as a basis for 5-HT receptor identification

This review contains background information on the serotonin system, furthermore the suggestion to introduce the term Contemporary Witness Report (CWR) for a novel type of review and, as the main part, an overview over the history of serotonin discovery as a basis for the identification of its receptor heterogeneity and the increase in complexity by genetic and allosteric variation. The present article conforms to CWRs in historical and autobiographical elements, in more emphasis on the author's work than in conventional reviews and in aspects neglected in previous reviews, but not in the main feature namely the work of a scientist with comprehensive expertise in a field in which, over long time, he/she continuously performed research and published. A scientist complying with these requirements is a contemporary witness in that field. His report on the scientific achievements in that period, a CWR, comprises confirmation and putative re-interpretation of data from a superior viewpoint. Identification of serotonin's vascular properties (publication year: 1912) as an "adrenaline mimicking substance" (without attempt to isolate it) by O'Connor preceded the discovery of serotonin in the gastrointestinal tract by Erspamer [1937] and in blood by Rapport [1948, 1949], who identified its structure as 5-hydroxytryptamine [1949]. Detection as a neurotransmitter in invertebrates suggested its occurrence in vertebrate CNS as well. This was verified by finding it in dog, rat and rabbit brain [1953]. The Falck-Hillarp technique [1962] visualized serotonin neurones as fluorescent structures. The neurotoxin 5,7-dihydroxytryptamine [1972] indirectly proved the involvement of 5-HT in multiple CNS functions.

Prilocaine- and lidocaine-induced methemoglobinemia is caused by human carboxylesterase-, CYP2E1-, and CYP3A4-mediated metabolic activation

Prilocaine and lidocaine are classified as amide-type local anesthetics for which serious adverse effects include methemoglobinemia. Although the hydrolyzed metabolites of prilocaine (o-toluidine) and lidocaine (2,6-xylidine) have been suspected to induce methemoglobinemia, the metabolic enzymes that are involved remain uncharacterized. In the present study, we aimed to identify the human enzymes that are responsible for prilocaine- and lidocaine-induced methemoglobinemia. Our experiments revealed that prilocaine was hydrolyzed by recombinant human carboxylesterase (CES) 1A and CES2, whereas lidocaine was hydrolyzed by only human CES1A. When the parent compounds (prilocaine and lidocaine) were incubated with human liver microsomes (HLM), methemoglobin (Met-Hb) formation was lower than when the hydrolyzed metabolites were incubated with HLM. In addition, Met-Hb formation when prilocaine and o-toluidine were incubated with HLM was higher than that when lidocaine and 2,6-xylidine were incubated with HLM. Incubation with diisopropyl fluorophosphate and bis-(4-nitrophenyl) phosphate, which are general inhibitors of CES, significantly decreased Met-Hb formation when prilocaine and lidocaine were incubated with HLM. An anti-CYP3A4 antibody further decreased the residual formation of Met-Hb. Met-Hb formation after the incubation of o-toluidine and 2,6-xylidine with HLM was only markedly decreased by incubation with an anti-CYP2E1 antibody. o-Toluidine and 2,6-xylidine were further metabolized by CYP2E1 to 4- and 6-hydroxy-o-toluidine and 4-hydroxy-2,6-xylidine, respectively, and these metabolites were shown to more efficiently induce Met-Hb formation than the parent compounds. Collectively, we found that the metabolites produced by human CES-, CYP2E1-, and CYP3A4-mediated metabolism were involved in prilocaine- and lidocaine-induced methemoglobinemia.

Psychosis from a bath salt product containing flephedrone and MDPV with serum, urine, and product quantification

INTRODUCTION

The use of designer drugs commonly marketed as bath salts or plant food has risen dramatically in recent years. Several different synthetic cathinones have been indentified in these products, including mephedrone, 3,4-methylenedioxypyrovalerone (MDPV), and 4-fluoromethcathinone (flephedrone). We report a case of bath salt intoxication with quantitative MDPV and flephedrone levels in a patient's serum and urine, and from the bath salt product.

CASE REPORT

A 23-year-old male with a prior psychiatric history arrived via EMS for bizarre behavior, suicidality, and hallucinations after reportedly insufflating a bath salt. He was found to have MDPV levels of 186 and 136 ng/mL in his serum and urine, respectively, and flephedrone levels of 346 and 257 ng/mL in the serum and urine, respectively. The white powder in question was found to contain 143 μg MDPV and 142 μg flephedrone per milligram powder. His psychosis and agitation resolved with lorazepam, droperidol, and observation in the emergency department.

DISCUSSION

Agitation, psychosis, movement disorders, tachycardia, and hypertension have all been attributed to the use of MDPV; there are no prior reports detailing clinical experience with flephedrone. Considering that our patient's serum flephedrone levels were twofold higher than his MDPV level, it is likely flephedrone contributed to his clinical toxicity. This case suggests the possibility that fluorinated cathinones, such as flephedrone, may have altered metabolism and/or elimination which may affect their course of clinical toxicity. This case highlights the evolving composition of synthetic cathinones found in bath salt products.

Therapeutic and adverse actions of serotonin transporter substrates

A variety of drugs release serotonin (5-HT, 5-hydroxytryptamine) from neurons by acting as substrates for 5-HT transporter (SERT) proteins. This review summarizes the neurochemical, therapeutic, and adverse actions of substrate-type 5-HT-releasing agents. The appetite suppressant (+/-)-fenfluramine is composed of (+) and (-) isomers, which are N-de-ethylated in the liver to yield the metabolites (+)- and (-)-norfenfluramine. Fenfluramines and norfenfluramines are potent 5-HT releasers. (+/-)-3,4-Methylenedioxymethamphetamine ((+/-)-MDMA, "ecstasy") and m-chlorophenylpiperazine (mCPP) are substrate-type 5-HT releasers. Fenfluramines, (+/-)-MDMA, and mCPP release neuronal 5-HT by a common non-exocytotic diffusion-exchange mechanism involving SERTs. (+)-Norfenfluramine is a potent 5-HT(2B) and 5-HT(2C) receptor agonist. The former activity may increase the risk of valvular heart disease, whereas the latter activity is implicated in the anorexic effect of systemic fenfluramine. Appetite suppressants that increase the risk for developing primary pulmonary hypertension (PPH) are all SERT substrates, but these drugs vary considerably in their propensity to increase this risk. For example, fenfluramine and aminorex are clearly linked to the occurrence of PPH, whereas other anorectics are not. Similarly, some SERT substrates deplete brain tissue 5-HT in animals (e.g., fenfluramine), while others do not (e.g., mCPP). In addition to the established indication of obesity, 5-HT releasers may help treat psychiatric disorders, such as drug and alcohol dependence, depression, and premenstrual syndrome. Viewed collectively, we believe new medications can be developed that selectively release 5-HT without increasing the risk for adverse effects of valvular heart disease, PPH, and neurotoxicity. Such agents may be useful for treating a variety of psychiatric disorders.

Psychostimulant-like effects of p-fluoroamphetamine in the rat

The present study was undertaken to compare the pharmacological properties of p-fluoroamphetamine with those of amphetamine and of other halogenated amphetamines, using several in vivo and in vitro tests. These included substitution testing in (+)-amphetamine (1 mg/kg, 5.4 mu mol/kg, i.p.)-, (+)-N-methyl-1-(1,3-benzodioxol-5-yl)-2-butanamine [(+)-MBDB] (1.75 mg/kg, 7.8 mu mol/kg, i.p.)-, and 5-methoxy-6-methyl-2-aminoindan (MMAI) (1.71 mg/kg, 8 mu mol/kg, i.p.)-trained rats, [3H]5-HT and [3H]dopamine uptake inhibition in whole brain synaptosomes, and changes in striatal extracellular levels of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) as measured by in vivo microdialysis in freely moving rats. In drug discrimination substitution tests, p-fluoroamphetamine fully mimicked (+)-amphetamine (ED50 0.43 mg/kg, 2.11 mu mol/kg), whereas 'no substitution' was observed in rats trained to discriminate the serotonin (5-hydroxytryptamine, 5-HT)-releasing agents (+)-MBDB or MMAI from saline. p-Chloroamphetamine did not substitute for amphetamine but fully substituted for the (+)-MBDB and MMAI cues (ED50 0.17 mg/kg, 0.82 mu mol/kg, and 0.14 mg/kg, 0.69 mu mol/kg, respectively). p-Fluoroamphetamine, in comparison with p-chloroamphetamine and p-iodoamphetamine, showed much stronger inhibition of [3H]dopamine than [3H]5-HT uptake into rat brain synaptosomes but was less selective than amphetamine. p-Fluoroamphetamine (7.0 mg/kg, i.p.), 1 h after administration, strongly elevated (849% of baseline) extracellular dopamine in rat striatum measured using in vivo microdialysis. Amphetamine (2 mg/kg, i.p.) increased extracellular dopamine in rat striatum with a maximum at the same time as did p-fluoroamphetamine, but the latter gave a smaller increase. The data presented suggest that p-fluoroamphetamine resembles amphetamie more than it does the 5-HT-releasing type amphetamines.

The substituted amphetamines 3,4-methylenedioxymethamphetamine, methamphetamine, p-chloroamphetamine and fenfluramine induce 5-hydroxytryptamine release via a common mechanism blocked by fluoxetine and cocaine

The abilities of the substituted amphetamines 3,4-methylenedioxymethamphetamine (MDMA), methamphetamine, p-chloroamphetamine (PCA) and fenfluramine to induce synaptosomal [3H]serotonin (5-HT) release were compared using a novel microassay system. The rank order of release potencies was found to be (+/-)PCA congruent to (+)-fenfluramine greater than (+)-MDMA much greater than (+)-methamphetamine. Combination of two drugs at their EC50 did not cause more release than either drug alone at an equivalent concentration. In addition, the 5-HT uptake blockers fluoxetine and cocaine inhibited the release induced by MDMA, methamphetamine, PCA and fenfluramine to the same percentage. However, threshold concentrations of the substituted amphetamines known to inhibit uptake did not attenuate the release caused by higher concentrations of these compounds. These results suggests that MDMA, methamphetamine, PCA and fenfluramine cause 5-HT release via a common mechanism. Furthermore, these results indicate that the 5-HT uptake blockade induced by these substituted amphetamines in vitro is different from that induced by either fluoxetine or cocaine.

The neurotoxic effects of p-chloroamphetamine in rat brain are blocked by prior depletion of serotonin

Systemic administration of p-chloroamphetamine (PCA) causes degeneration of serotonergic (5-HT) axons, but recent data indicate that this drug itself is not neurotoxic when applied directly to 5-HT axons. The present study was designed to test whether the toxic effects of PCA in the brain are dependent on release of endogenous 5-HT and to identify which stores of 5-HT are involved. The long-term effects of PCA on brain levels of 5-HT and on central 5-HT axons were determined in rats that had been initially depleted of 5-HT by administration of p-chlorophenylalanine and reserpine. The results show that transient depletion of 5-HT provides substantial protection against subsequent PCA-induced degeneration of 5-HT axon terminals; the neurotoxicity induced by PCA thus appears to be dependent on the presence of endogenous stores of 5-HT. In addition, the protective effect of 5-HT depletion is found only after pretreatment regimens that deplete peripheral as well as central stores of 5-HT. We interpret this finding as evidence that release of 5-HT from peripheral storage sites may be necessary for the expression of PCA-induced toxicity. Based on these results, we propose that central neurotoxicity is not induced by a direct action of PCA alone but may require or be augmented by a toxic metabolite of 5-HT.

Lack of neurochemical evidence for neurotoxic effects of repeated cocaine administration in rats on brain monoamine neurons

Rats were injected with cocaine (20 mg/kg, s.c. or i.p. twice daily for 8 days) or saline and killed at 1, 8, 15 or 48 days after the last injection. The concentrations of norepinephrine (NE), dopamine (DA), serotonin (5-HT) and their metabolites, assayed by HPLC-EC, in frontal cortex, hippocampus, striatum, hypothalamus, midbrain, pons-medulla and spinal cord were not significantly different from those in the saline-injected controls at any of the time points examined. These data suggest that the repeated cocaine administration in rats does not produce any long-term depletion in brain catecholamine and 5-HT content suggesting no neurotoxic effects of the drug.

Unlike systemic administration of p-chloroamphetamine, direct intracerebral injection does not produce degeneration of 5-HT axons

Systemic administration of the amphetamine derivative p-chloroamphetamine (PCA) causes degeneration of 5-HT axon terminals in rat brain. The present study was designed to determine whether PCA induces neurotoxic effects by a direct action on 5-HT axon terminals. PCA was administered by microinjection directly into the cerebral cortex of rats. Continuous intracerebral infusions were made over extended time periods (10 min-48 h) to explore whether the induction of neurotoxicity requires a prolonged exposure of axon terminals to the drug. Two weeks after drug administration, brain sections that passed through the injection site were processed for 5-HT immunohistochemistry. The 5-HT innervation of cerebral cortex in PCA-injected animals was compared with that after intracortical injection of saline or of 5,7-dihydroxytryptamine. The results demonstrate that, in the concentrations used, direct application of PCA into the neocortex does not elicit axonal degeneration, even after a continuous infusion for 2 days. This finding suggests that PCA itself is not directly toxic to 5-HT axons.

Depletion of serotonin using p-chlorophenylalanine (PCPA) and reserpine protects against the neurotoxic effects of p-chloroamphetamine (PCA) in the brain

The present study attempts to determine whether the neurotoxicity of p-chloroamphetamine (PCA) is dependent on a releasable pool of serotonin (5-HT). Rats treated with PCA alone or with reserpine and PCA exhibit a profound loss of 5-HT innervation in cerebral cortex after a 2-week survival period. However, depletion of 5-HT by combined treatment with p-chlorophenylalanine (PCPA) and reserpine provides substantial protection against the neurotoxic effects of PCA. These results indicate that release of 5-HT is a necessary step in the neurotoxicity of PCA and that a peripheral source of 5-HT is involved. We suggest that 5-HT release from platelets into the peripheral circulation may result in the formation of a neurotoxic 5-HT metabolite.

p-Chloroamphetamine formation responsible for long-term depletion of brain serotonin after N-cyclopropyl-p-chloroamphetamine injection in rats

After the injection of N-cyclopropyl-p-chloroamphetamine (N-cyclopropyl-PCA) into rats, p-chloroamphetamine (PCA) was identified in brain by high performance liquid chromatography with UV detection and was quantitated by that method and by spectrofluorometric analysis involving reaction with fluorescamine. The identity of PCA in brains of rats treated with N-cyclopropyl-PCA was confirmed by mass spectrometry. The peak concentrations of PCA in brain occurred 4 hrs after N-cyclopropyl-PCA injection. Brain concentrations of PCA and of N-cyclopropyl-PCA were measured at 1 or 4 hrs, respectively, after the injection of various doses of PCA or of N-cyclopropyl-PCA into rats. The depletion of brain serotonin and 5-hydroxyindoleacetic acid (5-HIAA) was measured 1 week after injection of those same doses of PCA or N-cyclopropyl-PCA. Comparing peak concentrations of PCA with the degree of depletion of brain serotonin supported the interpretation that PCA formed metabolically accounted for the long-term depletion of brain 5-hydroxyindoles after injection of N-cyclopropyl-PCA in rats.

Comparison of the effects of amphetamine and a fluorinated analogue on locomotion and exploratory activity in the mouse

(+)-Amphetamine (AM) and its fluorinated analogue (+)-2-amino-3-fluoro-1-phenylpropane (fluoroamphetamine, FAM) were compared with regard to their effects on locomotor and exploratory activity in mice. Both drugs caused a reduction in spontaneous exploration, but this effect was more marked with FAM than with AM at 1 h after injection. Both compounds increased locomotor activity 10 min after injection, but FAM had sedative effects after 1 h, while AM continued to be stimulatory.

Environmental determinants of parachloroamphetamine toxicity in rats

The present investigation assessed PCA toxicity at 0.0, 5.0, and 10.0 mg/kg, in both social (4 rats per cage) and non-social (acrylic tube-restraint or tube restraint-plus-tail shock) circumstances with 16 rats per drug-environment condition. The results indicated that no dose of PCA alone yielded mortality under individual housing, and similarly no environmental circumstance by itself yielded mortality in the absence of PCA. However, various drug-environment interactions produced a dose-related enhancement of PCA toxicity. For both 5.0 mg/kg and 10 mg/kg parachloroamphetamine dose levels, restraint-plus-shock generated the highest percent mortality, followed by restraint-only, with conspecific aggregation producing a mortality incidence lower still. Further, the mortality displayed under each of these environmental conditions was greater for the 10.0 mg/kg PCA treatment than for the 5.0 mg/kg treatment. The results are discussed in terms of the relative aversiveness of the environmental setting and it is suggested that stress-related drug toxicity may be further analyzed in non-social settings. It is proposed that toxic environment-PCA interactions may result from altered cardiovascular and/or thermoregulatory processes, mediated by enhanced catecholaminergic activity.

Analysis of a monofluorinated analogue of amphetamine in brain tissue using gas chromatography with electron-capture detection

1. Difficulties encountered in the analysis of the monofluorinated amphetamine, 2-amino-3-fluoro-1-phenylpropane (AFP), are discussed. 2. A novel assay procedure and its application to the analysis of AFP in the rat brain are described. The procedure involves pentafluorobenzoylation of AFP under aqueous conditions and quantitation by a gas chromatography equipped with a capillary column and an electron-capture detector.

Long-lasting depletion of striatal dopamine by a single injection of amphetamine in iprindole-treated rats

A single injection of amphetamine given to rats treated concurrently with iprindole so that they could not metabolize the amphetamine by para-hydroxylation resulted in a decrease in the concentration of striatal dopamine 1 week later. The decrease was antagonized by amfonelic acid, an inhibitor of uptake into dopamine neurons. The long-lasting depletion of cerebral dopamine by amphetamine may be analogous to the depletion of cerebral serotonin by halogenated derivatives of amphetamine.