Synthetic cathinones continue to emerge in recreational drug markets worldwide. 1-(1,3-Benzodioxol-5-yl)-2-(methylamino)butan-1-one (butylone) and 1-(1,3-benzodioxol-5-yl)-2-(methylamino)pentan-1-one (pentylone) are derivatives of the cathinone compound, 1-(1,3-benzodioxol-5-yl)-2-(methylamino)propan-1-one (methylone), that are being detected in drug products and human casework.

3,4-Methylenedioxypyrovalerone (MDPV) is a psychoactive component of so-called bath salts products that has caused serious medical consequences in humans. In this chapter, we review the neuropharmacology of MDPV and related analogs, and supplement the discussion with new results from our preclinical experiments. MDPV acts as a potent uptake inhibitor at plasma membrane transporters for dopamine (DAT) and norepinephrine (NET) in nervous tissue. The MDPV formulation in bath salts is a racemic mixture, and the S isomer is much more potent than the R isomer at blocking DAT and producing abuse-related effects. Elevations in brain extracellular dopamine produced by MDPV are likely to underlie its locomotor stimulant and addictive properties. MDPV displays rapid pharmacokinetics when injected into rats (0.5-2.0 mg/kg), with peak plasma concentrations achieved by 10-20 min and declining quickly thereafter. MDPV is metabolized to 3,4-dihydroxypyrovalerone (3,4-catechol-PV) and 4-hydroxy-3-methoxypyrovalerone (4-OH-3-MeO-PV) in vivo, but motor activation produced by the drug is positively correlated with plasma concentrations of parent drug and not its metabolites. 3,4-Catechol-PV is a potent uptake blocker at DAT in vitro but has little activity after administration in vivo. 4-OH-3-MeO-PV is the main MDPV metabolite but is weak at DAT and NET. MDPV analogs, such as alpha-pyrrolidinovalerophenone (alpha-PVP), display similar ability to inhibit DAT and increase extracellular dopamine concentrations. Taken together, these findings demonstrate that MDPV and its analogs represent a unique class of transporter inhibitors with a high propensity for abuse and addiction.

The abuse of synthetic cathinone compounds, often sold as “bath salts” or “research chemicals”, is an emerging public health concern. 3,4‐Methylenedioxymethcathinone (methylone) is a popular synthetic cathinone that is now illegal, but new analogs are being marketed as replacements. The purpose of the present investigation was to examine the interaction of new methylone analogs with transporters for dopamine (DAT) and 5‐HT (SERT). β‐Keto‐N‐methylbenzodioxolylbutanamine (butylone) and β‐keto‐N‐methylbenzodioxolylpentanamine (pentylone) were the analogs studied. In vitro assays were carried out in rat brain synaptosomes to assess drug‐induced effects on transporter‐mediated uptake and release. In vivo microdialysis was carried out in the nucleus accumbens of conscious rats to assess drug‐induced changes in extracellular dopamine and 5‐HT. Methylone, butylone and pentylone were fully efficacious uptake blockers at DAT and SERT, but pentylone was more DAT‐selective than the other drugs. Methylone was a substrate‐type releaser at both transporters, while butylone evoked release at SERT but not at DAT. Pentylone failed to evoke release at either transporter. Administration of butylone (1–3 mg/kg, i.v.) increased extracellular concentrations of 5‐HT more than dopamine, while pentylone (1–3 mg/kg. i.v.) increased both neurotransmitters to the same extent. All drugs produced significant locomotor activation, but the effects of butylone were blunted compared to pentylone. Our data show that each of the compounds examined displays a unique profile of in vitro transporter activity. Butylone has “hybrid” transporter effects, acting as a substrate at SERT but a blocker at DAT. Pentylone is a DAT‐preferring uptake blocker which lacks substrate activity. Overall, the data show that increasing the α‐carbon chain length of methylone creates compounds with reduced releasing activity, converting them to DAT blockers. All of the compounds elevate extracellular dopamine and stimulate motor activity to some degree, suggesting the drugs possess a significant risk for abuse.Support or Funding InformationThis research was generously supported by the Intramural Research Program of NIDA, NIH, DHHS.

The cadherin 13 (CDH13) gene encodes a cell adhesion molecule likely to influence development and connections of brain circuits that modulate addiction, locomotion and cognition, including those that involve midbrain dopamine neurons. Human CDH13 mRNA expression differs by more than 80% in postmortem cerebral cortical samples from individuals with different CDH13 genotypes, supporting examination of mice with altered Cdh13 expression as models for common human variation at this locus. Constitutive cdh13 knockout mice display evidence for changed cocaine reward: shifted dose response relationship in tests of cocaine-conditioned place preference using doses that do not alter cocaine conditioned taste aversion. Reduced adult Cdh13 expression in conditional knockouts also alters cocaine reward in ways that correlate with individual differences in cortical Cdh13 mRNA levels. In control and comparison behavioral assessments, knockout mice display modestly-quicker acquisition of rotarod and water maze tasks, with a trend toward faster acquisition of 5 choice serial reaction time tasks that otherwise displayed no genotype-related differences. They display significant differences in locomotion in some settings, with larger effects in males. In assessments of brain changes that might contribute to these behavioral differences, there are selective alterations of dopamine levels, dopamine/metabolite ratios, dopaminergic fiber densities and mRNA encoding the activity dependent transcription factor npas4 in cerebral cortex of knockout mice. These novel data and previously reported human associations of CDH13 variants with addiction, individual differences in responses to stimulant administration and attention deficit hyperactivity disorder (ADHD) phenotypes suggest that levels of CDH13 expression, through mechanisms likely to include effects on mesocortical dopamine, influence stimulant reward and may contribute modestly to cognitive and locomotor phenotypes relevant to ADHD.

Despite the prominence of human laboratory and clinical trial research in the development of interventions for substance use disorders, this research presents numerous ethical challenges. Ethical principles outlined in the Belmont Report, including respect for persons, beneficence, and justice, have traditionally guided research conduct. Few empirical studies exist examining substance abuse research ethics. The present study examined perceptions of beneficence and respect for persons in substance use research, including relative risk and desired monetary compensation, using an online sample of cocaine users.The study was conducted on Amazon.com's Mechanical Turk (mTurk), a crowdsourcing website used for survey-based research. Of 1764 individuals screened, 138 reported past year cocaine use. These respondents completed a battery of standardized and experimenter-designed questionnaires used to characterize each respondent's self-reported attitudes, beliefs, and behaviors about drug use and the relative risks and desired monetary compensation associated with research participation.Ratings of relative risk revealed that most respondents found common research practices as less than or equal to the relative risk of everyday life. Receiving experimental medication outside the hospital was rated as the most risky research activity, but on average was not rated as presenting more risk than everyday life. Desired compensation for research participation was associated with the perceived risk of research activities. Increases in desired compensation for participation were only observed for research perceived as much more risky than everyday activities.These findings indicate that cocaine users assess risk in a way that is consistent with standard research practice.

Cell cycle checkpoints provide surveillance mechanisms to activate the DNA damage response, thus preserving genomic integrity. The heterotrimeric Rad9–Rad1–Hus1 (9–1–1) clamp is a DNA damage response sensor and can be loaded onto DNA. 9–1–1 is involved in base excision repair (BER) by interacting with nearly every enzyme in BER. Here, we show that individual 9–1–1 components play distinct roles in BER directed by MYH DNA glycosylase. Analyses of Hus1 deletion mutants revealed that the interdomain connecting loop (residues 134–155) is a key determinant of MYH binding. Both the N-(residues 1–146) and C-terminal (residues 147–280) halves of Hus1, which share structural similarity, can interact with and stimulate MYH. The Hus1K136A mutant retains physical interaction with MYH but cannot stimulate MYH glycosylase activity. The N-terminal domain, but not the C-terminal half of Hus1 can also bind DNA with moderate affinity. Intact Rad9 expressed in bacteria binds to and stimulates MYH weakly. However, Rad91−266 (C-terminal truncated Rad9) can stimulate MYH activity and bind DNA with high affinity, close to that displayed by heterotrimeric 91−266–1–1 complexes. Conversely, Rad1 has minimal roles in stimulating MYH activity or binding to DNA. Finally, we show that preferential recruitment of 91−266–1–1 to 5′-recessed DNA substrates is an intrinsic property of this complex and is dependent on complex formation. Together, our findings provide a mechanistic rationale for unique contributions by individual 9–1–1 subunits to MYH-directed BER based on subunit asymmetry in protein–protein interactions and DNA binding events.

3,4-Methylenedioxypyrovalerone (MDPV) is a commonly abused synthetic cathinone in the United States and is associated with dangerous side effects. MDPV is a dopamine transporter blocker that is 10-fold more potent than cocaine as a locomotor stimulant in rats. Previous in vitro and in vivo metabolism studies identified 3,4-dihydroxypyrovalerone (3,4-catechol-PV) and 4-hydroxy-3-methoxypyrovalerone (4-OH-3-MeO-PV) as the two primary MDPV metabolites. This study examined MDPV pharmacokinetics and metabolism, along with associated pharmacodynamic effects in rats receiving 0.5, 1.0 and 2.0 mg/kg subcutaneous (s.c.) MDPV. Blood was collected by an indwelling jugular catheter before dosing and at 10, 20, 30, 60, 120, 240 and 480 minutes thereafter. Plasma specimens were analyzed by liquid chromatography coupled to high-resolution tandem mass spectrometry. Maximum concentrations (Cmax ) and area-under-the-curve (AUC) for MDPV and two metabolites increased proportionally with administered dose, showing linear pharmacokinetics. MDPV exhibited the highest Cmax at all doses (74.2-271.3 μg/l) and 4-OH-3-MeOH-PV the highest AUC (11 366-47 724 minutes per μg/l), being the predominant metabolite. MDPV time to Cmax (Tmax ) was 12.9-18.6 minutes, while 3,4-catechol-PV and 4-OH-3-MeO-PV peaked later with Tmax 188.6-240 minutes after s.c. dosing. Horizontal locomotor activity (HLA) and stereotypy correlated positively with plasma MDPV concentrations, while HLA correlated negatively with MDPV metabolites. These results suggest that the parent compound mediates motor stimulation after systemic MDPV administration, but additionally, metabolites may be inhibitory, may not be active or may not pass the blood brain barrier.