N-oxygenation of amphetamine and methamphetamine by the human flavin-containing monooxygenase (form 3): role in bioactivation and detoxication.
(+)- And (-)-amphetamine and methamphetamine were N-oxygenated by the cDNA expressed adult human flavin-containing monooxygenase form 3 (FMO3), their corresponding hydroxylamines. Two major polymorphic forms of human FMO3 were studied, and the results suggested preferential N-oxygenation by only one of the two enzymes. Chemically synthesized (+/-)-amphetamine hydroxylamine was also a substrate for the human FMO3 and it was converted to phenylpropanone oxime with a stereoselectivity ratio of trans/cis of 5:1. Human FMO3 also N-oxygenated methamphetamine to produce methamphetamine hydroxylamine. Methamphetamine hydroxylamine was also N-oxygenated by human FMO3, and the ultimate product observed was phenylpropanone. For amphetamine hydroxylamine, studies of the biochemical mechanism of product formation were consistent with the production of an N, N-dioxygenated intermediate that lead to phenylpropanone oxime. This was supported by the observation that alpha-deutero (+/-)-amphetamine hydroxylamine gave an inverse kinetic isotope effect on product formation in the presence of human FMO3. For methamphetamine, the data were consistent with a mechanism of human FMO3-mediated N,N-dioxygenation but the immediate product, a nitrone, rapidly hydrolyzed to phenylpropanone. The pharmacological activity of amphetamine hydroxylamine, phenylpropanone oxime, and methamphetamine hydroxylamine were examined for effects at the human dopamine, serotonin, and norepinephrine transporters. Amphetamine hydroxylamine and methamphetamine hydroxylamine were apparent substrates for the human biogenic amine transporters but phenylpropanone oxime was not. Presumably, phenylpropanone oxime or nitrone formation from amphetamine and methamphetamine, respectively, represents a detoxication process. Because of the potential toxic nature of amphetamine hydroxylamine and methamphetamine hydroxylamine metabolites and the polymorphic nature of N-oxygenation, human FMO3-mediated metabolism of amphetamine or methamphetamine may have clinical consequences. (+info)
Electrophysiological examination of the effects of sustained flibanserin administration on serotonin receptors in rat brain.
5-HT1A receptor agonists have proven to be effective antidepressant medications, however they suffer from a significant therapeutic lag before depressive symptoms abate. Flibanserin is a 5-HT1A receptor agonist and 5-HT2A receptor antagonist developed to possibly induce a more rapid onset of antidepressant action through its preferential postsynaptic 5-HT1A receptor agonism. Flibanserin antagonized the effect of microiontophoretically-applied DOI in the medial prefrontal cortex (mPFC) following 2 days of administration, indicating antagonism of postsynaptic 5-HT2A receptors. This reduction in the effect of locally-applied DOI was no longer present following 7-day flibanserin administration. Two-day flibanserin administration only marginally reduced the firing activity of dorsal raphe (DRN) 5-HT neurons. Following 7 days of administration, 5-HT neuronal firing activity had returned to normal and the somatodendritic 5-HT1A autoreceptors were desensitized. The responsiveness of postsynaptic 5-HT1A receptors located on CA3 hippocampus pyramidal neurons and mPFC neurons, examined using microiontophoretically-applied 5-HT and gepirone, was unchanged following a 7-day flibanserin treatment. As demonstrated by the ability of the 5-HT1A receptor antagonist WAY 100635 to selectively increase the firing of hippocampal neurons in 2- and 7-day treated rats, flibanserin enhanced the tonic activation of postsynaptic 5-HT1A receptors in this brain region. The results suggest that flibanserin could be a therapeutically useful compound putatively endowed with a more rapid onset of antidepressant action. (+info)
Dose linearity study of selegiline pharmacokinetics after oral administration: evidence for strong drug interaction with female sex steroids.
AIMS: The purpose of this study was to characterize the dose relationship of selegline and desmethylselegiline pharmacokinetics within the selegiline dose range from 5 to 40 mg. METHODS: Eight female subjects, of whom four were using oral contraceptives, ingested a single dose of 5 mg, 10 mg, 20 mg or 40 mg of selegiline HCl in an open four-period randomized study. Concentrations of selegiline and desmethlylselegiline in serum were measured by gas chromatography for 5 h. As it became evident that the use of oral steroids had a drastic effect on selegiline concentrations, the pharmacokinetic analyses were performed separately for oral contraceptive users and those not receiving any concomitant medication. RESULTS: The total AUC and Cmax of selegiline were 10-to 20-fold higher in those subjects taking oral steroids compared with subjects with no concomitant medication; this finding was consistent and statistically significant at all the four dose levels. The dose linearity of selegiline pharmacokinetics failed to be demonstrated in both groups. The AUC and Cmax of desmethylselegiline were only moderately higher (about 1.5-fold; P=NS at each dose level) in the subjects taking oral steroids than in those not receiving concomitant medication. The AUC values of desmethylselegiline increased in a dose linear manner in subjects with no concomitant medication, but not in the oral steroid group. The metabolic ratio (AUC(desmethylselegiline)/AUC(selegiline)) was several-fold lower in the group receiving oral steroids compared with the no-concomitant-medication group (P<0.005 at all the four dose levels). CONCLUSIONS: Concomitant use of oral contraceptives caused a drastic (20-fold) increase in the oral bioavailability of selegiline. The highly significant difference in the metabolic ratio between the groups provides evidence that the mechanism of the interaction between selegiline and female sex steroids involves reduced T-demethylation of selegiline. The present results suggest that concomitant use of selegiline with exogenous female sex steroids should be avoided or the dosage of selegiline should be reduced in order to minimize the risks of selegiline related adverse drug reactions. (+info)
Amphetamines induce apoptosis and regulation of bcl-x splice variants in neocortical neurons.
Amphetamineanalogs have emerged as popular recreational drugs of abuse. The number of reports of these substances producing severe acute toxicity and death is increasing. In 'Ecstasy' -associated deaths, focal necrosis in the liver and individual myocytic necrosis has been reported. Furthermore, serotonergic and dopaminergic neuronal cell damage has been observed in experimental amphetamine intoxication in laboratory animals. Here we demonstrate that subchronic exposure to D-amphetamine, methamphetamine, methylenedioxyamphetamine, and methylenedioxymethamphetamine ('Ecstasy') results in significant neurotoxicity in rat neocortical neurons in vitro. This neuronal cell death is accompanied by endonucleosomal DNA cleavage and differential expression of anti- and proapoptotic bcl-xL/S splice variants. In addition, we observed pronounced induction of cell stress-associated transcription factor c-jun and translation initiation inhibitor p97 after amphetamine treatment. These data support that the neurotoxic effects of different amphetamines are extended to rat neocortical neurons and that apoptotic pathways are involved in amphetamine-induced neurotoxicity. (+info)
Amphetamine and fenproporex levels following multidose administration of fenproporex.
Drugs that are metabolized to amphetamine or methamphetamine are potentially of significant concern in the interpretation of positive drug-testing results for amphetamines. A number of different drugs have been reported to produce amphetamine in the urine of users. One of these compounds, fenproporex, has been shown to be metabolized to amphetamine, and previous reports indicated the parent compound could be detected at low levels for up to 48 h. Administration of fenproporex for seven days (one 10-mg dose per day) to five healthy volunteers resulted in amphetamine being detected in the urine of all subjects. Peak concentrations of amphetamine ranged from approximately 2850 to 4150 ng/mL. Amphetamine could be detected (> or = 5 ng/mL) in the urine for up to nearly 170 h after the last dose. Analysis of the metabolically produced amphetamine showed the presence of both enantiomers, which can be helpful in the differentiation of some illicit amphetamine use from the use of this precursor drug. In addition, evaluation of the enantiomeric composition of the metabolite (amphetamine) can be a valuable tool in the interpretation of time since last dose. More significantly, all samples that contained amphetamine at a concentration of > or = 500 ng/mL were shown to also contain detectable amounts of the parent compound. (+info)
The evolution of cerebral blood flow in the developing brain: evaluation with iodine-123 iodoamphetamine SPECT and correlation with MR imaging.
BACKGROUND AND PURPOSE: Although it is well established that brain maturation correlates temporally with the functions the newborn or infant performs at various stages of development, the precise relationship between function and anatomic brain maturation remains unclear. The purpose of this study was to investigate the developmental changes of regional cerebral blood flow (rCBF) in infants and children using iodine-123 iodoamphetamine (123I-IMP) and single-photon emission computed tomography (SPECT). These findings were correlated with the MR imaging appearance of the brain and with known developmental changes. METHODS: Twenty-one 123I-IMP SPECT examinations of 17 patients, ranging in age from neonates to 2 years, were reviewed retrospectively. All children had had transient neurologic events in the neonatal period that did not significantly affect subsequent neuropsychological development. MR studies were performed in 12 of these patients and the MR findings were correlated with the SPECT results. RESULTS: SPECT studies showed a consistent pattern of evolving changes in 123I-IMP uptake, most likely reflecting evolution of rCBF. From the 34th postconceptional week until the end of the second month after term delivery, there was predominant uptake in the thalami, brain stem, and paleocerebellum, with relatively less cortical activity. Radionuclide uptake in both the perirolandic and occipital cortices was well seen around the 40th postconceptional week and increased rapidly thereafter, with a predominance of parietal activity. By 3 months, radionuclide uptake in the cerebellar hemispheres and parietofrontal cortices increased. Frontal and temporal activity increased by age 6 to 8 months. Uptake in the basal ganglia increased by 8 months. By the beginning of the second year, rCBF showed a similar topographic pattern to that in adults. CONCLUSION: The time course of the changes in 123I-IMP uptake in the developing brain as detected by SPECT is similar to that of myelination and most likely reflects an overall topologic maturational pattern of the brain. (+info)
Direct agonists for serotonin receptors enhance locomotor function in rats that received neural transplants after neonatal spinal transection.
We analyzed whether acute treatment with serotonergic agonists would improve motor function in rats with transected spinal cords (spinal rats) and in rats that received transplants of fetal spinal cord into the transection site (transplant rats). Neonates received midthoracic spinal transections within 48 hr of birth; transplant rats received fetal (embryonic day 14) spinal cord grafts at the time of transection. At 3 weeks, rats began 1-2 months of training in treadmill locomotion. Rats in the transplant group developed better weight-supported stepping than spinal rats. Systemic administration of two directly acting agonists for serotonergic 5-HT(2) receptor subtypes, quipazine and (+/-)-1-[2, 5]-dimethoxy-4-iodophenyl-2-aminopropane), further increased weight-supported stepping in transplant rats. The improvement was dose-dependent and greatest in rats with poor to moderate baseline weight support. In contrast, indirectly acting serotonergic agonists, which block reuptake of 5-HT (sertraline) or release 5-HT and block its reuptake (D-fenfluramine), failed to enhance motor function. Neither direct nor indirect agonists significantly improved locomotion in spinal rats as a group, despite equivalent upregulation of 5-HT(2) receptors in the lumbar ventral horn of lesioned rats with and without transplants. The distribution of immunoreactive serotonergic fibers within and caudal to the transplant did not appear to correspond to restoration of motor function. Our results confirm our previous demonstration that transplants improve motor performance in spinal rats. Additional stimulation with agonists at subtypes of 5-HT receptors produces a beneficial interaction with transplants that further improves motor competence. (+info)
Evidence for a role for central 5-HT2B as well as 5-HT2A receptors in cardiovascular regulation in anaesthetized rats.
1. The effects of injections i.c.v. of quipazine, (2 micromol kg-1) and 1-(2,5-di-methoxy-4-iodophenyl)-2-aminopropane (DOI; 2 micromol kg-1) on renal sympathetic and phrenic nerve activity, mean arterial blood pressure (MAP) and heart rate were investigated in alpha-chloralose anaesthetized rats pretreated with a peripherally acting 5-HT2 receptor antagonist. 2. Quipazine or DOI caused a rise in MAP which was associated with a tachycardia and renal sympathoinhibition in rats pretreated (i.c.v.) with the antagonist vehicle 10% PEG. These effects of quipazine were completely blocked by pretreatment with cinanserin (a 5-HT2 receptor antagonist) and attenuated by spiperone (a 5-HT2A receptor antagonist). However, pretreatment with SB200646A (a 5-HT2B/2C receptor antagonist) only blocked the sympathoinhibition, while pretreatment with SB204741 (a 5-HT2B receptor antagonist) reversed the sympathoinhibition to excitation as it also did for DOI. Quipazine also caused renal sympathoexcitation in the presence (i.v.) of a vasopressin V1 receptor antagonist. 3. Injection (i.v.) of the V1 receptor antagonist at the peak pressor response evoked by quipazine alone and in the presence of SB204741 caused an immediate fall in MAP. For quipazine alone the renal sympathoinhibition was slowly reversed to an excitation, while the renal sympathoexcitation observed in the presence of SB204741 was potentiated. In both, the quipazine-evoked tachycardia was unaffected. 4. The data indicate that cardiovascular responses caused by i.c.v. quipazine and DOI are primarily due to activation of central 5-HT2A receptors, which causes the release of vasopressin and a tachycardia. This released vasopressin appears to suppress a 5-HT2A receptor-evoked central increase in sympathetic outflow, which involves the activation of central 5-HT2B receptors indirectly by the released vasopressin. (+info)