Our findings, along with previous research suggest that MDPV is rapidly absorbed, readily crosses the blood-brain barrier and is excreted primarily as metabolites. MDPV acts as a typical stimulant with modest hyperthermic and psychomimetic properties, consistent with a primarily dopaminergic mechanism of action.
Since no specific signs of acute toxicity were observed, even at the highest doses used, clinical care and harm-reduction guidance should be in line with that available for other stimulants and cathinones. Despite their common origin, cathinone derivatives have heterogeneous effects and mechanisms of action and it remains difficult to reliably predict the behavioural and physiological effects of NPSs based on their structural similarities [ 11 ].
Since controlled studies are not usually possible in humans, animal studies provide useful indicators of effects in vivo [ 12 ]. Studying effects on an NPS-by-NPS basis in animal models and in vitro continues to be a central approach oriented to obtaining knowledge with translational relevance to humans e. Here, we present data pertinent to further understanding of the acute pharmacokinetic, metabolic, behavioural, and thermoregulatory effects of the high-potency pyrovalerone cathinone 3,4-methylenedioxypyrovalerone MDPV.
Pyrrolidinophenones' stimulant effects reflect their inhibition of monoamine transporter sites where they are highly selective for the dopamine and norepinephrine transporter DAT and NET , with particularly powerful effects on DAT, and only a negligible effect on the serotonin transporter SERT [ 4 , 14 — 20 ], but see [ 21 ].
Recreational users report that the desirable subjective effects of MDPV include euphoria, sensory and physical stimulation [ 25 , 26 ], similar to amphetamine to which MDPV is chemically related; [ 1 , 27 , 7 ].
Recreational users typically ingest MDPV orally or by insufflation [ 4 , 25 ]. Typical low-moderate active dosages for human recreational use range between 3 and 10 mg [ 25 ] with reported onset of subjective effects within 30 min and a duration of — min, with after-effects up to 8 h, [ 25 , 28 ]. In vivo studies in rats that examined the concentrations of MDPV in plasma after subcutaneous sc.
In vitro studies of human liver microsomes have shown that MDPV is metabolised first to 3,4-dihydroxypyrovalerone demethylenyl-MDPV via O -demethylenation of its 3,4-methylenedioxy ring, and then to 4-hydroxymethoxypyrovalerone demethylenyl-methyl-MDPV by O -methylation; these phase II metabolites are excreted in urine in conjugated form ] 31 , but see 32 ].
Demethylenyl-methyl-MDPV is the most abundant urinary metabolite in both species, humans and rats [ 32 ]. However, since MDPV has been implicated more frequently in cases of serious intoxication [ 7 , 34 , 35 ] and confirmed in a number of fatalities [ 7 , 36 — 39 ] than other cathinones, it may have higher risk of acute toxicity. Psychiatric symptoms such as paranoia, delirium and hallucinations may be present, and serotonin syndrome, deterioration of muscle tissue and kidney failure have also been reported [ 26 , 28 , 37 , 40 — 42 ].
Prominent in cathinone-related toxidrome in humans is hyperthermia; however, prior research on the effects of MDPV specifically on thermoregulation in rodents has been inconsistent.
MDPV can elevate body temperature under conditions of higher ambient temperatures or social interaction, [ 21 , 43 , 44 ], however effects can be negligible, even under such conditions [ 45 ]. MDPV is a highly reinforcing psychostimulant with notable addictive potential [ 20 , 22 , 46 — 51 ].
Increased extracellular dopamine DA , particularly in the nucleus accumbens NAcc , is an indicator of the reinforcement potential of drugs, and the accompanying locomotor response itself can be used as a marker of this. MDPV's stimulatory effects are most likely mediated by striatal extracellular DA [ 29 , 30 ], see [ 4 ]. MDPV has been shown to increase both locomotion in rodents [ 14 , 45 , 52 — 55 ], see also [ 50 ], for a recent review as well as increased NAcc DA [ 4 , 14 , 29 ].
Moreover, locomotor stimulation positively correlates with MDPV concentrations in the striatum [ 30 ], in plasma, and with extracellular DA concentrations [ 56 ] in the NAcc [ 4 , 29 ]. Although effects of MDPV have been characterised in a number of other locomotor tests activity cage, running wheel and rotorod , there is only one study of its effects in the open field using Sprague-Dawley rats, which showed 0. Prepulse inhibition PPI of the acoustic startle response ASR is a behavioural operationalisation of sensorimotor gating that reflects pre-attentional filtering of redundant information [ 59 ].
PPI is useful in assessing the psychomimetic properties of drugs and is a behavioural endophenotype of psychosis [ 60 ]. Stimulants and cathinones can disrupt PPI, but usually only at higher doses [ 61 — 68 ], but see [ 69 ]. As already described, MDPV use in humans can, like other cathinones, result in psychotic symptoms such as hallucinations, however to date, MDPV has not been tested in PPI, nor have any other pyrrolidinophenones.
The aim of the present manuscript is to provide a detailed characterisation of the effects of subcutaneous sc. The study was performed as a part of an experimental series performed in our laboratory enabling direct comparisons with other NPSs belonging to cathinones, phenethylamines as well as aminoindanes e.
Based on these findings and methods as well as more recent ones presented by others [ 22 , 31 , 72 ], we expected MDPV to peak within first hour after administration in serum and brain, and due to its lipophilicity to accumulate into lung tissue. Additionally, levels of major metabolites were evaluated in tissues, sera as well as in urine. In order to simulate the typical environmental situations in which human MDPV use occurs, we measured body temperature under isolated and aggregated conditions with the prediction that aggregation will lead to more pronounced hyperthermic effects.
In order to evaluate the characteristic inverted U locomotor dose-response curve we recorded open field activity at three MDPV doses at two testing-onsets following drug administration. Rats were acclimatised for 7—10 days prior to testing, during which they were weighed twice and handled four times. Across all experiments, rats were used. For the biotransformation study the total number of rats was three.
As previously described, data from vehicle VEH control animals for PPI, open field and temperature studies were collected twice per annum as part of a series of standardised NPS studies undertaken in our laboratory e.
MDPV has been shown to be behaviourally active in locomotor tests in rodents at between 0. The dose rage tested was similar to that used by Novellas et al. Sample preparation, LC and MS conditions, method of validation and calibration were based on Meyer et al. For a full description of pharmacokinetic methods, please refer to Horsley et al.
Rats were housed singly vs. Thereafter, observations were at 0. For a fuller description, see e. Ethovision Colour-Pro version 3.
The procedures used were the same as those used previously, e. Finally, six pulse alone trials were delivered. A fuller description can be found in our previously published work e.
Planned pairwise comparisons to follow up significant main effects and interactions involving MDPV used independent t -tests. In order to limit inflation of type 1 error the number of comparisons was restricted to those necessary to test the primary hypotheses MDPV vs. VEH, no between dose comparisons were made , and in the thermoregulation study, comparisons were focused on early time points with observable mean differences.
Where Levene's test for equality of variance was significant, corrected statistics are presented. Corrected degrees of freedom are rounded to the nearest whole number for presentational purposes. The same applied to tissues where influx was not detectably delayed compared to serum since maximal concentrations were also observed at 30 min: Figure 1.
For graphical purposes, at 6 h a mean of 4 and a standard deviation of 1 is used. MDPV itself was present in urine but was extracted primarily as metabolites.
We adopted the nomenclature of Meyer et al. All other metabolites were in a minority. Table 1. Figure 2. In serum demethylenyl-oxo-MDPV was present at low levels maximum value Figure 3 shows that the groups had equivalent body temperatures at the 8. VEH rats' temperatures remained steady at about Figure 3. At both testing-onsets, rats showed a normal pattern of locomotor habituation progressively diminishing activity over the session which was not disturbed by any dose MDPV. Figure 4.
VEH white. Shown alongside 5 min bins on the x axis are minutes elapsed since drug administration. Example trajectory patterns are shown in C. Figure 5. Mean T centre A and mean thigmotaxis B over 30 min tested 15 or 60 min after drug administration: sc.
Figure 6. Our biotransformation study detected a number of metabolites in sera and tissues, however at very low levels. As previous studies have shown we found a small increase in temperature in individually-housed rats, which was exacerbated by crowded cage conditions. The highest concentrations of MDPV in serum, brain, and lung tissue were recorded at 30 min followed by a rapid decline, suggesting that in all cases, the actual peaks were prior to our first measurement.
Previous pharmacokinetic data in rats which were not published at the time of our data collection showed peak plasma concentrations of MDPV at 10—20 min post-administration [ 29 , 30 ]. Novellas et al. From 30 min and the following 2 h, the brain concentration was approximately twice that in the sera. Evidence suggests a kinetic profile of fast onset and relatively short duration, consistent with our short-lasting peak behavioural effects, and with estimates of the onset and duration of subjective effects in humans [ 25 , 28 ].
MDPV's short duration may have a causal role in re-dosing and escalating use shown in human and rodent studies , and together with fast penetration of the brain [ 30 ] these characteristics are indicative of MDPV's addictive potential [ 36 ]. We observed levels of MDPV that were approximately four times higher in lungs than in sera.
Rapid transition of substances such as drugs from blood to lungs is characteristic of parenterally administered cationic compounds with a lipophilic profile [ 75 ]. The rapidity and magnitude of accumulation is partly a consequence of the relatively large volume of blood flowing to the lungs in compared to other organs, such as the brain, where molecules become trapped by lysosomes and mitochondria and accumulate in lung tissue as gradually eluting pools [ 75 ].
In consequence, accumulation in, and elimination from lung tissue is usually rapid, which was supported by our data, where lung concentrations of MDPV declined more quickly than in the brain.
The relevance if any of drug accumulation in the lungs for MDPV toxicity is unclear; pyrrolidinophenone toxicity primarily involve CNS and cardiovascular related problems [ 13 , 56 ].
In support of this notion, Scholze et al demonstrated that the serotonin uptake blocker imipramine evokes low-efficacy efflux of [ 3 H]serotonin from HEK cells expressing human SERT.
Thus, monensin clearly differentiates the mechanism of efflux produced by amphetamine from that produced by MDPV.
The present results also highlight the utility of monensin as a reliable tool to discriminate transporter substrates from blockers in cells stably expressing transporter proteins. Our in vitro data reveal a clear mechanistic dichotomy among the most common bath salts constituents: namely, ring-substituted analogs of methcathinone like mephedrone and methylone act as transporter substrates, whereas pyrrolidinophenones like MDPV act as transporter blockers. There are notable differences in transporter selectivity across this group of compounds as well.
Mephedrone and methylone are non-selective transporter substrates that produce neurochemical effects akin to those produced by MDMA Baumann et al, ; Kehr et al, By contrast, MDPV is a catecholamine-selective uptake blocker. Such findings suggest that ring-substituted analogs of methcathinone will produce MDMA-like behavioral effects, while pyrrolidinophenones will be more stimulant-like in their profile of actions.
In agreement with this proposal, recent findings in rats have shown that wheel-running behavior produced by mephedrone is MDMA-like, while that produced by MDPV is more methamphetamine-like Huang et al, Additional investigations are warranted to compare the effects of ring-substituted cathinones and pyrrolidinophenones in animal models and in human subjects under controlled laboratory conditions. Using fast-scan cyclic voltammetry, we found that MDPV exhibits powerful dose-related effects on dopamine clearance.
As is typically observed in cyclic voltammetry experiments, uptake inhibition results in a large increase in the magnitude of evoked dopamine signal and a profound broadening of the dopamine decay curve Schmitz et al, The mechanistic explanation for the heightened efficacy of MDPV in the slice preparation is not known, but we hypothesize that the potency of MDPV might be a critical factor.
Owing to its high potency at DAT, MDPV may display a slow dissociation from the site ie, persistent binding , thereby augmenting and extending its pharmacological effects.
In fact, previous voltammetric studies have shown that high-affinity dopamine uptake blockers like nomifensine and GBR produce marked inhibition of dopamine clearance that mirrors the effects of MDPV shown here Bull et al, ; Schmitz et al, It also remains possible that MDPV interacts with non-transporter sites of action, which further enhance its effects on dopamine clearance, and this proposal warrants examination.
In vivo microdialysis methods were used to compare the effects of MDPV and cocaine on extracellular dopamine in the nucleus accumbens, a brain region implicated in addictive properties of drugs Bonci et al, ; Willuhn et al, As predicted from the in vitro findings, both drugs elicit dose-related increases in dialysate dopamine, but MDPV is at least 10 times more potent than cocaine in this regard Figure 4a and b.
Furthermore, the rise in extracellular dopamine associated with MDPV is sustained when compared with the short-lived effects of cocaine. It is well established that drug-induced elevations in extracellular dopamine in the nucleus accumbens are involved with locomotor-activating properties of stimulant drugs Ikemoto, ; Pennartz et al, Our previous experiments examining stimulant drug effects in rats have shown strong positive correlations between dialysate dopamine responses and the extent of hyperactivity Baumann et al, ; Zolkowska et al, The present data show that MDPV produces robust dose-related forward locomotion and stereotypy.
Consistent with the voltammetric findings, locomotor effects of MDPV are much greater in magnitude than the comparable effects of cocaine see Figure 4c and d. Collectively, the potent and efficacious actions of MDPV on extracellular dopamine and motor activity suggest a high potential for abuse. A recent study by Watterson et al demonstrates that MDPV is readily self-administered by rats, and the range of self-injected doses 0.
Two of the most serious side-effects of bath salts ingestion in human users are acute tachycardia and hypertension Ross et al, ; Spiller et al, Here we compared the effects of MDPV and cocaine on cardiovascular parameters in conscious rats. Similar to its effects on other in vivo endpoints, MDPV is more potent than cocaine in its ability to increase heart rate and blood pressure.
Our preclinical findings may have important implications for people who take bath salts products for recreational purposes. The potent blockade of dopamine uptake caused by MDPV predicts that the drug has a high risk for abuse, whereas the potent blockade of norepinephrine uptake portends dangerous cardiovascular stimulation. Patients admitted to emergency departments for bath salts overdose, who have toxicological verification of MDPV consumption, display symptoms, including agitation, psychosis, violent behavior, hyperthermia, and tachycardia Borek and Holstege, ; Kyle et al, ; Murray et al, ; Spiller et al, The constellation of adverse effects produced by high-dose MDPV resembles the life-threatening excited delirium syndrome associated with acute cocaine toxicity Mash et al, ; Ruttenber et al, Accordingly, the preclinical findings in the present study, demonstrating powerful cocaine-like actions of MDPV, suggest that efforts to remediate symptoms of bath salts overdose should aim to manage excessive dopaminergic and noradrenergic stimulation.
It is noteworthy that new legal cathinone-related compounds are being marketed to replace Schedule I drugs like MDPV, mephedrone, and methylone Shanks et al, The designer methcathinone analogs, mephedrone and methylone, are substrates for monoamine transporters in brain tissue. Neuropsychopharmacology 37 : — In vivo effects of amphetamine analogs reveal evidence for serotonergic inhibition of mesolimbic dopamine transmission in the rat.
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Cocaine works in a similar way, but in a lab test, MDPV was a much more potent inhibitor than cocaine. Other norepinephrine-dopamine reuptake inhibitors NDRIs include pharmaceuticals such as methylphenidate known as ritalin and used to treat ADHD and buproprion an antidepressant. Pyrovalerone — a hybrid of mephedrone and MDPV — is an approved appetite suppressant used medically for weight loss.
Studies in laboratory animals highlight the stimulating effects of MDPV, and also its potential for dependence. In fatal cases involving a single synthetic cathinone, death has been attributed to complications arising from extremely high body temperatures or damage to the vessels of the heart. Fortunately, specialised drug testing can detect MDPV and its derivatives. Although simple colour-based reagent tests may identify MDPV, these tests may also cross-react with similar cathinones, some of which are less dangerous, and some of which are more so.
For reliable identification, more sophisticated technology such as mass spectrometry or infrared spectroscopy, of the type drug experts are campaigning to take place at festivals, is required.
In this regard, small, portable, and relatively cheap infrared analysers may be useful for on-site testing services.
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