Urinary excretion of amphetamine and 4'-hydroxyamphetamine by Sprague Dawley and dark Agouti rats

Increased effects of 3,4-methylenedioxymethamphetamine (ecstasy) in a rat model of depression

3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is associated with increases in core body temperature (T(C)) and depressive mood states in users. Flinders Sensitive Line (FSL) rats represent a rat model of depression originally bred from Sprague-Dawley (SD) rats. They are more sensitive to both muscarinic and serotonergic agonists and have altered thermoregulatory responses to various drugs. To examine the link between MDMA and depression, eight FSL and eight SD rats were administered saline and 5 and 7.5 mg/kg MDMA. Immediately following administration, rats were confined to an area with an ambient temperature (T(A)) of 30 ± 1°C for 30 minutes before being allowed access to a thermal gradient for four hours. The brains were removed one week after final dose of MDMA and concentrations of serotonin and dopamine were measured. Treatment with MDMA at both doses led to a higher T(C) in the FSL rats than the SD rats at high T(A) (P < 0.01). Fatalities due to hyperthermia occurred in the FSL rats after both doses, whereas all but one of the SD rats recovered well. Heart rate was also much higher after MDMA in the FSL rats throughout the experiments. The FSL rats showed significant decreases in all transmitters measured (P < 0.05). These differences between strains were not accounted for by altered blood or brain concentrations of MDMA. The results indicate that the FSL rats may be more susceptible to developing MDMA-induced hyperthermia and possible damage to the brain. These findings may be of importance to human users of MDMA who also have depression.

Nicotine and amphetamine acutely cross-potentiate their behavioral and neurochemical responses in female Holtzman rats

RATIONALE

Psychostimulants are often used in close temporal proximity to nicotine and have been reported to enhance acutely nicotine's desirability in humans.

OBJECTIVE

To investigate the acute associations between amphetamine and nicotine, we examined the potentiative interactions between clinically relevant, low doses of these drugs on locomotor activity, and dopamine overflow in the rat.

MATERIALS AND METHODS

Locomotor activity was measured by telemetry in the home cage environment, and dopamine overflow was evaluated in striatal slice preparations from female Holtzman rats.

RESULTS

When administered simultaneously, nicotine and amphetamine produced a predominantly additive effect on locomotor behavior. However amphetamine, when given 2-4 h before nicotine, strongly potentiated nicotine-induced locomotor activity. Correspondingly, nicotine given 1-4 h before amphetamine robustly enhanced amphetamine-stimulated locomotor activity even when the effects of the nicotine pretreatment dissipated. Acute nicotine pretreatment similarly potentiated the effects of dopamine transporter ligands, cocaine, nomifensine, and methamphetamine but not a direct dopamine receptor agonist. Consistent with the behavioral studies, in vivo nicotine pretreatment exaggerated amphetamine-induced dopamine efflux from rat striatal slices. Likewise, in vivo pretreatment of rats with amphetamine potentiated nicotine-induced dopamine efflux from striatal slices. Direct pretreatment of striatal tissue by nicotine also potentiated subsequent amphetamine-stimulated dopamine overflow, further suggesting that the nicotine-amphetamine interaction occurs at the level of the dopamine terminal.

CONCLUSION

Overall, the present data demonstrate that acute interactions of nicotine and other psychomotor stimulants produce potentiative effects and that these transient interactions may play a role in the frequent co-use and abuse of nicotine and other stimulants.

Differences in cytochrome P450 and nuclear receptor mRNA levels in liver and small intestines between SD and DA rats

This study aimed to clarify the differences in mRNA levels of cytochrome P450 (CYP) isoforms and nuclear receptors between Dark Agouti (DA) and Sprague-Dawley (SD) rats which are animal models for poor metabolizers and extensive metabolizers for CYP2D6, respectively. Using liver and small intestine tissues of both rat strains, we investigated the mRNA levels of CYP1A, 2A, 2B, 2C, 2D, 2E, and 3A subfamilies and nuclear receptors which regulate the transcription of CYP isoforms. In the liver, male DA rats showed a low CYP2D2 mRNA level but high mRNA levels of CYP3A1, 3A2, and 1A1 compared to SD rats. No significant difference was noted in other CYP isoforms. The mRNA levels of CAR were higher in DA rats than those in SD rats. In small intestine, the mRNA levels of CYP isoforms and nuclear receptors exhibited no significant strain differences. In addition, the activity of CYP3A in small intestinal microsome did not differ between SD and DA rats. Female DA rats exhibited higher mRNA levels of CYP3A1, 3A2, and 2B1 in the liver than female SD rats. In conclusion, the mRNA levels of CYP3A1 and 3A2 isoforms and CAR in the liver but not in the small intestines were different between DA and SD rats in both sexes.

Pharmacological and behavioral determinants of cocaine, methamphetamine, 3,4-methylenedioxymethamphetamine, and para-methoxyamphetamine-induced hyperthermia

RATIONALE

Cocaine, methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA, ecstasy), and para-methoxyamphetamine (PMA) disrupt normal thermoregulation in humans, with PMA being associated with more severe cases of hyperthermia. Harm minimization advice on how to prevent overheating depends on appropriate thermoregulatory behavior by drug users.

OBJECTIVES

The purpose of the current study was to establish dose-response relationships for the effects of a number of commonly used illicit stimulants and investigate the behavioral response to increased core temperature.

MATERIALS AND METHODS

Sprague-Dawley rats with telemetry implants were administered either saline or 4, 12, 26, 40 or 80 micromol/kg of cocaine, methamphetamine, MDMA, or PMA and confined to an ambient temperature of 30 degrees C for 30 min, before being able to choose their preferred temperature on a thermally graded runway (11-41 degrees C).

RESULTS

The increased core temperature caused by administration of cocaine, methamphetamine, and MDMA treatment led to the animals seeking the cool end of the runway to correct their core temperature, although this did not occur in PMA-treated rats. The order of potency for increasing core temperature was methamphetamine >PMA = MDMA>cocaine. This differed to the slopes of the dose-response curves where MDMA and PMA showed the steepest slope for the doses used followed by methamphetamine then cocaine.

CONCLUSIONS

These results suggest that behavioral aspects of thermoregulation are important in assessing the potential of individual drugs to cause harmful increases in core temperature.

Pharmacokinetics and metabolism of metoprolol and propranolol in the female DA and female Wistar rat: the female DA rat is not always an animal model for poor metabolizers of CYP2D6

The purpose of this study was to clarify the pharmacokinetics of CYP2D6 substrates in female DA and Wistar rats, which are regarded as animal models of poor metabolizers and extensive metabolizers, respectively. In vivo pharmacokinetic and in vitro metabolic studies were conducted using metoprolol and propranolol, which show substantial and marginal polymorphisms in humans, respectively. After oral administration, the areas under the plasma concentration curves (AUC) for metoprolol and propranolol in DA rats were ca. 5- and 35-fold higher, respectively, than those in Wistar rats. There were no strain differences for serum protein binding or metabolism inhibition by quinine between the two compounds. Using a substrate depletion assay, the intrinsic clearances estimated for the two strains differed by 7.2-fold for metoprolol and 4.5-fold for propranolol. The discrepancy between the in vitro and in vivo profiles observed for propranolol, but not metoprolol, would be due to nonlinearity between the normalized AUC and the oral doses in DA rats, being associated with lower K(m) values. The larger strain difference in the AUCs of propranolol was proved by the in vitro kinetic parameters, implying that DA rats do not always reflect the polymorphic profiles in humans.

Effects of acute citalopram treatment on the methamphetamine-induced locomotor activity

1. Previously the authors have shown that acute citalopram treatment increased the dopamine D2 receptor expression in rat brain striatum (Kameda et al., 2000). In the present study, the authors attempted to determine whether these effects of citalopram influence the methamphetamine-induced locomotor activity. 2. The pretreatment with a single administration of citalopram (10 mg/kg, i.p.) resulted in the significant enhancement of the locomoter activity induced by methamphetamine treatment (1 mg/kg, i.p.). The enhancement was observed 30 min, 12 hours, 24 hours, but not 7 days after withdrawal of citalopram administration. 3. Then the authors determined the methamphetamine concentration in rat brain striatum by gas chromatography-mass spectrometry (GC-MS) The results showed that the concentration of methamphetamine wars significantly higher in the rats 24 hours, and also 7 days after withdrawal of citalopram administration, compared to the control rats. 4. These results emphasized the involvement of the high methamphetamine concentration, caused by the pretreatment with citalopram, in the enhancement of the methamphetamine-induced locomotor activity. However high methamphetamine concentration alone could not account for this enhancement, since the high concentration of methamphetamine observed 7 days after withdrawal of citalopram administration did not appear to enhance the methamphetamine-induced locomotor activity. Another mechanism through which the pretreatment with citalopram enhanced the methamphetamine-induced locomotor activity, such as the increased expression of the dopamine D2 receptors, could not be excluded.

Determination of amphetamine and its metabolite p-hydroxyamphetamine in rat urine by reversed-phase high-performance liquid chromatography after dabsyl derivatization

The consumption of amphetamine is illicit and controlled due to both the elicited behavioural deviations and the toxicity effects reported in abusers. Thus, amphetamine levels in biological samples must be monitored in several clinical and forensic circumstances. In spite of the interspecies differences in the preferred route of biotransformation, benzylmethylketone, benzoic acid and 4-hydroxyamphetamine are the principal metabolites of amphetamine. However, the clinical and forensic studies are focused in the parent compound and in 4-hydroxyamphetamine since benzylmethylketone is a minor metabolite in human and benzoic acid is also an endogenous compound. In the present study amphetamine and its metabolite, 4-hydroxyamphetamine, are quantified in urine by HPLC after derivatization with 4-dimethylaminoazobenzene-4'-sulfonyl chloride (dabsyl chloride). This derivatization procedure transforms amphetamine and its hydroxylated metabolite in compounds with similar lipofilicity, enabling their quantitative and simultaneous extraction with an organic solvent. The precision of the HPLC technique was 7.3 and 10.0% for amphetamine and 4-hydroxyamphetamine derivatives, respectively. For the overall procedure, including enzymatic hydrolysis, derivatization and extraction of the derivatives, the obtained values were 9.3 and 6.2%. Recoveries obtained from spiked urines for amphetamine and 4-hydroxyamphetamine were better than 97% and 94% (mean value), respectively. The detection limits of the method was 10 ng for both compounds. The principal advantages of the present proposed method are the stability of the dabsyl derivatives at room temperature and the detection carried out in the visible region, reducing the interferences detected.

Urinary excretion of 4-hydroxyamphetamine and amphetamine in male and female Sprague-Dawley and Dark Agouti rats following multiple doses of amphetamine

Previous studies have demonstrated that the cytochrome P450 2D subfamily is involved in the 4-hydroxylation of amphetamine in the rat. These studies followed urinary levels of 4-hydroxyamphetamine and amphetamine after a single dose of amphetamine given with the P450 2D inhibitor quinidine or in P450 2D-deficient Dark Agouti (DA) rats. Multiple doses of amphetamine are used by humans and in experimental neurotoxicity studies of amphetamine. We hypothesized that the elimination of amphetamine (as opposed to 4-hydroxyamphetamine) will remain elevated in the DA rat after multiple doses, implying that no alternative pathway is induced to compensate for reduced 4-hydroxylation. Male and female Sprague-Dawley (SD) and DA rats were given daily i.p. injections of 5 mg/kg amphetamine for 5 days. Urine was collected at 12-h intervals and analyzed by HPLC for the presence of amphetamine and 4-hydroxyamphetamine. The amount of amphetamine detected in the urine remained elevated with a corresponding reduction of 4-hydroxyamphetamine in the DA rats when compared to SD rats over the entire time course. This reduction in 4-hydroxyamphetamine was greater in female than male DA rats; no difference was found between male and female SD rats. At the dose used, amphetamine did not increase with time and total amphetamine and 4-hydroxyamphetamine excreted by all rats was not different, implying no accumulation of amphetamine. These results suggest that no alternative pathway is induced following multiple doses of amphetamine in normal SD or P450 2D deficient DA rats.

Subchronic fluoxetine treatment induces a transient potentiation of amphetamine-induced hyperlocomotion: possible pharmacokinetic interaction

The results of the present study show that 5 days of systemic treatment with fluoxetine (5 mg/kg) resulted in an augmented locomotor response to amphetamine (0.5 mg/kg). This augmented response to amphetamine was observed 24 and 48 h, but not 5 days, after the cessation of fluoxetine treatment. Subchronic fluoxetine treatment also produced an increase in the brain concentration of amphetamine when rats were challenged with amphetamine 48 h, but not 5 days, after the cessation of fluoxetine treatment. Thus, the effect of subchronic fluoxetine in augmenting amphetamine-induced hyperactivity was consistent with the effect of subchronic fluoxetine in augmenting the amphetamine concentration in the brain. This pattern of results indicates that subchronic fluoxetine potentiates the response to amphetamine within a limited time-window, and that this potentiating effect is likely to be due to the reduced metabolism of amphetamine via the inhibition of cytochrome P450 by fluoxetine and/or its metabolite norfluoxetine.

Metabolism of drugs of abuse by cytochromes P450

Studies of most drugs of abuse utilize in vivo animal experimentation so that the responses measured reflect the pharmacokinetics of the administered drug as well as its pharmacodynamics. These drugs are generally lipid soluble chemicals and their elimination is dependent on metabolism, so an understanding of this process is critical to the interpretation of responses. This review summarizes the interaction between drugs of abuse and cytochromes P450, the oxidative enzymes that catalyze the first step of the metabolic process. Although they process their substrates by a common chemical mechanism, these enzymes differ markedly in their regulation, i.e. induction and inhibition, their substrate selectivities, the metabolites they generate and their relative concentration in different species. The activity of an enzyme catalyzing a specific metabolic reaction can be altered by prior xenobiotic exposure, by its genetics and by a co-administered drug, so that the pharmacokinetics of the drug under study can vary with the history of the individual subject. These issues are obviously important in human studies so, when possible, the relevant human enzymes involved in the processes described have been identified.

The corticosteroid synthesis inhibitor metyrapone markedly enhances the behavioural effects of d-amphetamine

The clinically utilized corticosteroid synthesis inhibitor metyrapone attenuates the behavioural effects of cocaine in the rat. Given the potential therapeutic implications of this interaction, we felt it important to determine if metyrapone's action would generalize to another widely abused psychostimulant, namely d-amphetamine. However, rather than producing attenuation, metyrapone preadministration (3 x 100 mg/kg) markedly enhanced both the locomotor activating and stereotypy-inducing actions of d-amphetamine (dose equivalent to 2.5 mg/kg free base). The fact that the corticosteroid synthesis inhibitor trilostane did not affect the behavioural action of d-amphetamine suggests that inhibition of corticoid synthesis does not underlie the action of metyrapone. Instead, it is argued that inhibition of debrisoquine hydroxylase (cytochrome p450 2D1), an enzyme involved in the metabolism of d-amphetamine, represents the critical mechanism of action.

CYP2D6 polymorphism is not crucial for the disposition of selegiline

OBJECTIVE

To determine the possible impact of CYP2D6 polymorphism on the pharmacokinetics and pharmacodynamics of selegiline.

METHODS

Five poor metabolizers and 8 extensive metabolizers of debrisoquin (INN, debrisoquine) were given 10 mg selegiline hydrochloride. The concentrations of selegiline and its main metabolites in serum were determined for 4 days. The pharmacodynamics were quantitated by measuring platelet monoamine oxidase type B activity for 3 weeks. In addition, the effect of selegiline and its main metabolites on the CYP2D6-catalyzed dextromethorphan O-demethylase activity and the effect of quinidine on the metabolism of selegiline were studied in human liver microsomes.

RESULTS

Peak serum concentrations of selegiline were reached rapidly and ranged from 1 to 32 nmol/L. The metabolite concentrations were considerably higher and remained so for a longer period. There were no significant differences in the pharmacokinetic parameters of selegiline, desmethylselegiline, and l-amphetamine between poor metabolizers and extensive metabolizers. However, the area under the serum concentration-time curve (AUC) values of l-methamphetamine were, on average, 46% higher (P = .01) in poor metabolizers than in extensive metabolizers. No significant correlations were found between debrisoquin metabolic ratio and AUC values of selegiline or its metabolites, except for l-methamphetamine (rs = 0.90; P < .001). The maximum monoamine oxidase type B inhibition was 97% in both groups. The inhibitory potency of selegiline, desmethylselegiline, and l-methamphetamine toward dextromethorphan O-demethylase was very low (50% inhibitory concentration values from 160 to 580 mumol/L). Quinidine (< or = 100 mumol/L) did not inhibit the formation of desmethylselegiline or l-methamphetamine from selegiline.

CONCLUSIONS

CYP2D6 is not important in the primary elimination of selegiline, and the biological effect of selegiline seems to be similar in poor metabolizers and extensive metabolizers of debrisoquin. The inhibitory effect of selegiline and its main metabolites on CYP2D6 activity seems to be negligible.

Determination of amphetamine, methamphetamine and amphetamine-derived designer drugs or medicaments in blood and urine

This paper reviews procedures for the determination of amphetamine, methamphetamine and amphetamine-derived designer drugs or medicaments in blood and urine. Papers published from 1991 to early 1997 were taken into consideration. Gas chromatographic and liquid chromatographic procedures with different detectors (e.g., mass spectrometer or diode array) were considered as well as the seldom used thin-layer chromatography and capillary electrophoresis. Enantioselective procedures are also discussed. A chapter deals with amphetamine-derived medicaments, e.g. anoretics, antiparkinsonians or vasodilators, which are metabolized to amphetamine or methamphetamine. Differentiation of an intake of such medicaments from amphetamine or methamphetamine intake is discussed. Basic information about the biosample assayed, internal standard, work-up, GC column or LC column and mobile phase, detection mode, reference data and validation data of each procedure is summarized in Tables. Examples of typical applications are presented.

Major role of the CYP2C isozymes in deamination of amphetamine and benzphetamine: evidence for the quinidine-specific inhibition of the reactions catalysed by rabbit enzyme

1. The cytochrome P450 isozymes involved in the deamination of amphetamine (AP) and benzphetamine (BZP) have been studied in liver microsomes from rabbit and rat using isozyme-specific inhibitors. 2. Metabolism of BZP in rat yielding phenylacetone and formaldehyde was moderately inhibited by testosterone and chloramphenicol. N-Debenzylation was thought to be P450-dependent, but all inhibitors except for a non-specific inhibitor, SKF-525A, failed to inhibit this reaction. 3. In rabbit, quinidine and testosterone were potent inhibitors of both BZP deamination and dealkylation. Deamination of AP in rabbit was extensively inhibited only with quinidine. 4. AP deamination with purified rabbit CYP2C3, which was previously identified as the major isozyme responsible for this metabolism, was extensively inhibited with quinidine, previously thought to be a specific inhibitor of CYP2D. 5. These results strongly support the notion that the CYP2C isozymes play a major role in the deamination of both AP and BZP, but not for N-debenzylation of BZP in rat. However, on the basis of different sensitivities toward inhibitors, multiple isozymes seem to be involved in BZP deaminations in both species.