Chimeric mice with humanized liver

Recently, chimeric mice with humanized liver were established by transplanting human hepatocytes into an urokinase-type plasminogen activator(+/+)/severe combined immunodeficient transgenic mouse line. The replacement with human hepatocytes is more than 80-90% and is higher than any other chimeric mouse reported previously. In drug development, the liver is one of the most important organs because it is mainly involved in the pharmacokinetics of drugs and is frequently damaged by many drugs due to the accumulation of drugs and/or metabolites. The pharmacokinetics could affect the efficacy and toxicity of a drug, and thus prediction of the human pharmacokinetics is important for developing new drugs without adverse reactions and toxicity. Extrapolation from experimental animals or in vitro studies to the human in vivo pharmacokinetics is still difficult. To date, human hepatocytes and liver microsomes are recognized as better tools and are frequently used to estimate the human pharmacokinetics. We thought that chimeric mice with humanized liver could become a new tool for estimating the human toxicity and pharmacokinetics. At first, metabolism, which plays an essential role in pharmacokinetics, was investigated in the chimeric mice. In the liver of the chimeric mice, human drug metabolizing enzymes were found to be expressed and to reflect the capacities and genetic polymorphism of the donor. In an in vivo study on metabolism, human specific metabolites could be detected in the serum of the chimeric mice indicating that the chimeric mice could be used as an in vivo model to address human metabolism. These results suggested that the chimeric mice could overcome the species differences in drug metabolism and be used to evaluate drug toxicity due to genetic polymorphism. The reasons for drug interaction are often enzyme induction and inhibition. By the treatment with a typical inducer of cytochrome P450 (P450), which is the central drug-metabolizing enzyme, P450s expressed in the liver of the chimeric mice were found to possess induction potencies. After the treatment with a specific inhibitor of human P450, the area under the curve of the P450 metabolite was significantly decreased in the chimeric mice but not in the control mice. Therefore, it was indicated that the chimeric mice could be useful for assessing drug interactions in vivo. Moreover, drug excretion was determined to be humanized because cefmetazole was mainly excreted in urine both in the chimeric mice and humans but in the feces in control uPA(-/-)/SCID mice. Drug transporters expressed in the liver of the chimeric mice were also humanized. In this review, studies of the chimeric mice with humanized liver, particularly on metabolism and excretion, are summarized and the possibility of using the chimeric mice is proposed for the advanced prediction of human pharmacokinetics and toxicity.

A convenient method for local drug administration at predefined sites in the entire gastrointestinal tract: experiences from 13 phase I studies

For local administration of drugs or enzyme inhibitors in the human gut, a small-bore, smooth tube was introduced through the nose, retrieved from the pharynx, equipped with a firm radio-opaque capsule, and swallowed. Peristalsis moves the capsule to the desired location in the gut where it is anchored before administration via the tube. Drug uptake is followed by plasma sampling. One capsule type is used for solutions, another for solid formulations. With solutions, repeated administrations could be done with the capsule being anchored for 24h or longer or, alternatively, at several locations along the gut. This communication presents the method and an overview of 13 uptake and enzyme/transporter localization studies. Altogether, 268 intubations were undertaken in a total of 128 subjects. Plasma concentrations found with terbutaline and metoprolol are presented showing that terbutaline has its best uptake in the upper small intestine, whereas metoprolol shows the same bioavailability along the whole gut. Subjects could undertake most of their normal activities while carrying the equipment. No serious adverse events (AEs) occurred. Possibly intubation-related AEs were abdominal pain (n=8) and constipation (n=5). In conclusion, the method has been found to be safe, convenient and multifunctional for studies of drug uptake at predetermined gut locations in healthy subjects.

In vivo drug metabolism model for human cytochrome P450 enzyme using chimeric mice with humanized liver

We previously clarified that major human drug metabolizing enzymes were expressed in a chimeric urokinase-type plasminogen activator (uPA)+/+/severe combined immunodeficient (SCID) mouse line established recently, in which the liver could be replaced by more than 80% with human hepatocytes. In the present study, we investigated the in vivo drug metabolism of a CYP2D6 substrate, debrisoquin (DB), in chimeric mice with high (High) or low (Low) human albumin (hAlb) concentrations and in control uPA-/-/SCID mice. The hAlb in the mouse blood is one of the indices of humanized liver because the chimeric mice produce hAlb. After oral administration of DB at 2.0 mg/kg, the AUC0-8 value of a major CYP2D6 metabolite of DB, 4'-hydroxydebrisoquin (4-OH DB), in High was 3.6-fold higher than those of Low and uPA-/-/SCID mice. By pre-treatment with a typical CYP2D6 inhibitor, quinidine, the AUC0-8 value of 4-OH DB in High was decreased although such values in Low and uPA-/-/SCID mice did not change. The in vitro kinetic analyses and the Ki values of quinidine on the DB 4'-hydroxylase activity in liver microsomes also supported the humanization of the chimeric mice. In conclusion, the chimeric mice exhibited a humanized profile of drug metabolism and the inhibition of P450.

Impaired maze performance in aged rats is accompanied by increased density of NMDA, 5-HT1A, and α-adrenoceptor binding in hippocampus

Using quantitative receptor autoradiography, we assessed binding site densities and distribution patterns of glutamate, GABA(A), acetylcholine (ACh), and monoamine receptors in the hippocampus of 32-month-old Fischer 344/Brown Norway rats. Prior to autoradiography, the rats were divided into two groups according to their retention performance in a water maze reference memory task, which was assessed 1 week after 8 days of daily maze training. The animals of the inferior group showed less long-term retention of the hidden-platform task but did not differ from superior rats in their navigation performance during place training and cued trials. The decreased retention performance in the group of inferior learners was primarily accompanied by increased alpha(1)-adrenoceptors in all hippocampal subregions under inspection (CA1-CA4 and dentate gyrus), while elevated alpha(2)-adrenoceptor binding was observed in the CA1 region and DG. Furthermore, inferior learners had higher NMDA binding in the CA2 and CA4 and increased 5-HT(1A) binding sites in the CA2, CA3, and CA4 region. No significant differences between inferior and superior learners were evident with regard to AMPA, kainate, GABA(A), muscarinergic M(1), dopamine D(1), and 5-HT(2) binding densities in any hippocampal region analyzed. These results show that increased NMDA, 5-HT(1A), and alpha-adrenoceptor binding in the hippocampus is associated with a decline in spatial memory. The increased receptor binding observed in the group of old rats with inferior maze performance might be the result of neural adaptation triggered by age-related changes in synaptic connectivity and/or synaptic activity.

In vivo assessment of botanical supplementation on human cytochrome P450 phenotypes: Citrus aurantium, Echinacea purpurea, milk thistle, and saw palmetto

OBJECTIVES

Phytochemical-mediated modulation of cytochrome P450 (CYP) activity may underlie many herb-drug interactions. Single-time point phenotypic metabolic ratios were used to determine whether long-term supplementation of Citrus aurantium , Echinacea purpurea , milk thistle (Silybum marianum), or saw palmetto (Serenoa repens) extracts affected CYP1A2, CYP2D6, CYP2E1, or CYP3A4 activity.

METHODS

Twelve healthy volunteers (6 women, 6 men) were randomly assigned to receive C aurantium , E purpurea , milk thistle, or saw palmetto for 28 days. For each subject, a 30-day washout period was interposed between each supplementation phase. Probe drug cocktails of midazolam and caffeine, followed 24 hours later by chlorzoxazone and debrisoquin (INN, debrisoquine), were administered before (baseline) and at the end of supplementation. Presupplementation and postsupplementation phenotypic trait measurements were determined for CYP3A4, CYP1A2, CYP2E1, and CYP2D6 by use of 1-hydroxymidazolam/midazolam serum ratios (1-hour sample), paraxanthine/caffeine serum ratios (6-hour sample), 6-hydroxychlorzoxazone/chlorzoxazone serum ratios (2-hour sample), and debrisoquin urinary recovery ratios (8-hour collection), respectively. The content of purported "active" phytochemicals was determined for each supplement.

RESULTS

Comparisons of presupplementation and postsupplementation phenotypic ratios suggested that these particular supplements had no significant effect on CYP1A2, CYP2D6, CYP2E1, or CYP3A4 activity. Phytochemical profiles indicated that C aurantium was devoid of the CYP3A4 inhibitor 6',7'-dihydroxybergamottin. Quantities of fatty acids, flavonolignans, and cichoric acid were consistent with label claims for saw palmetto, milk thistle, and E purpurea , respectively.

CONCLUSIONS

Botanical supplements containing C aurantium , milk thistle, or saw palmetto extracts appear to pose a minimal risk for CYP-mediated herb-drug interactions in humans. Although the effects of E purpurea on CYP activity were minor, further study into the interaction potential of this botanical is merited.

Effect of chronic antidepressant treatment on beta-receptor coupled signal transduction cascade. Which effect matters most?

BACKGROUND

Beta-receptor down-regulation has been described as a common biochemical effect of chronic treatment with many but not all antidepressant drugs. Beta-receptor activation leads to elevated intracellular levels of cAMP followed by the activation of several protein kinases which in turn activate various transcription factors. One of those, CREP has received increasing interest as an relevant component within the antidepressant drug modulated signal cascade as it represents a down-stream signal not only of the beta-receptor but also of serotonin receptor activation. Chronic treatment with many antidpressant drugs has been shown to alter CREP levels in several brain regions. While beta-receptor down-regulation by chronic antidepressant treatment has been a consistent finding, alterations of CREP levels have been observed in both direction. Similarly divergent findings have been reported for BDNF a major gene targeted of CREB, where most but not all findings suggest up-regulation at least at the message level following chronic antidepressant treatment.

METHODS

Because of these rather divergent data, we investigated the possible effects of chronic treatment (9 or 19 days) with three different antidepressant drugs (reboxetine, citalopram, imipramine) on the individual parameters of the beta-receptor coupled signal transduction cascade. All animals were also tested for possible antidepressant effects using the forced swimming test.

RESULTS

While beta-receptor density was down-regulated by reboxetine and imipramine but not citalopram, CREB protein was only mildly elevated after 9 days, and not changed or slightly reduced after 19 days. BDNF protein levels were not or only slightly enhanced, but only for the 9 days treatment. Citalopram was most active. Under the conditions chosen, all three drugs were active in the forced swimming test.

CONCLUSION

Taken together, the findings reported make it difficult to identify one single component of the beta-receptor coupled signal transduction cascade as common final target of chronic antidepressant treatment.

Gender differences in drug effects: implications for anesthesiologists

BACKGROUND

The gender aspect in pharmacokinetics and pharmacodynamics of anesthetics has attracted little attention. Knowledge of previous work is required to decide if gender-based differences in clinical practice is justified, and to determine the need for research.

METHODS

Basis for this paper was obtained by Medline searches using the key words 'human' and 'gender' or 'sex,' combined with individual drug names. The reference lists of these papers were further checked for other relevant studies.

RESULTS

Females have 20-30% greater sensitivity to the muscle relaxant effects of vecuronium, pancuronium and rocuronium. When rapid onset of or short duration of action is very important, gender-modified dosing may be considered. Males are more sensitive than females to propofol. It may therefore be necessary to decrease the propofol dose by 30-40% in males compared with females in order to achieve similar recovery times. Females are more sensitive than males to opioid receptor agonists, as shown for morphine as well as for a number of kappa (OP2) receptor agonists. On this basis, males will be expected to require 30-40% higher doses of opioid analgesics than females to achieve similar pain relief. On the other hand, females may experience respiratory depression and other adverse effects more easily if they are given the same doses as males.

CONCLUSION

These examples illustrate that gender should be taken into account as a factor that may be predictive for the dosage of several anesthetic drugs. Moreover, there is an obvious need for more research in this area in order to further optimize drug treatment in anesthesia.

Tests for individual and population bioequivalence based on generalized p-values

The U.S. Food and Drug Administration (FDA) has proposed new regulations that address the 'prescribability' and 'switchability' of new formulations of already-approved drugs. These new criteria are known, respectively, as population and individual bioequivalence. Two methods have been proposed in the bioequivalence literature for assessing population and individual bioequivalence that calculate an upper 95 per cent confidence bound for the bioequivalence criterion in question, and then test bio-equivalence by comparing this bound to the limit established by the FDA. In this paper we propose applying the generalized test function (GTF) methodology of Tsui and Weerahandi (Journal of the American Statistical Association 1989; 602-607) to this problem to produce tests based on a generalized p-value (GPV). This methodology allows us to construct hypothesis tests in the presence of nuisance parameters. Using simulation we show that these tests perform well in comparison to the confidence interval methods and have superior power for assessing population bioequivalence.

Influx and efflux of amphetamine and N-acetylamphetamine in keratinocytes, pigmented melanocytes, and nonpigmented melanocytes

To establish an in vitro model of drug incorporation into hair and to elucidate the potential roles of hair cell selectivity and hair color in the incorporation of certain drugs into hair, the basic drug amphetamine and its nonbasic analog N-acetylamphetamine (N-AcAp) were analyzed for influx and efflux into and out of keratinocytes, pigmented melanocytes (PM), and nonpigmented melanocytes (NPM) as a model for incorporation and efflux of these drugs from hair cells. NPM were of the same melan-a cell line as PM, but cultured in the presence of the tyrosinase inhibitor phenylthiocarbamide. Results show that PM take up large amounts of the basic drug amphetamine (levels of uptake dependent on melanin content), whereas keratinocytes and NPM take up only small amounts of amphetamine. None of the cells take up N-AcAp above background levels. Interestingly, whereas keratinocytes and NPM quickly efflux most of the influxed drug, PM are slow to efflux and only efflux approximately 65% of influxed drug, if efflux media is not refreshed. (If efflux media is periodically refreshed, PM will eventually redistribute essentially all influxed drug back into the media.) These results demonstrate that pigmented cells take up greater amounts of the basic drug amphetamine, and efflux it more slowly than nonpigmented cells. Also, these results are consistent with previous data for in vivo incorporation of amphetamine in animal hair. In combination with previous data, an overall comparison of the amphetamine and N-AcAp incorporation data support a non-diffusion mediated model for drug incorporation into hair cells.

Cetirizine/pseudoephedrine

Cetirizine is the carboxylated metabolite of hydroxyzine, and has high specific affinity for histamine H(1) receptors. Pseudoephedrine is a sympathomimetic drug that acts directly on alpha-adrenergic receptors. black triangle Cetirizine/pseudoephedrine 5/120 mg twice daily was significantly more effective than intranasal budesonide 100 microg or placebo at improving nasal obstruction, nasal patency and reducing the volume of nasal secretion, and was significantly more effective than intranasal xylometazoline 0.1% with respect to nasal secretion, during house dust mite faeces challenge in three randomised, cross- over studies among volunteers with seasonal or perennial rhinitis. The onset of action of cetirizine/pseudoephedrine was reported to be approximately 30 minutes. black triangle The bioavailability of cetirizine and pseudoephedrine is similar after administration of cetirizine/pseudoephedrine 5/120 mg bilayer tablets or coadministration of cetirizine 5 mg tablets plus pseudoephedrine sustained-release (SR) 120 mg caplets. black triangle Cetirizine 5mg plus pseudoephedrine SR 120 mg twice daily for 2 to 3 weeks was significantly more effective than each drug given alone at reducing mean total symptom scores for seasonal or perennial allergic rhinitis in two randomised, double-blind, multicentre trials. In both studies, the mean proportion of days during which the five measured symptoms (nasal obstruction, sneezing, rhinorrhoea, nasal pruritus and ocular pruritus) were absent or mild was significantly greater in recipients of the cetirizine plus pseudoephedrine SR. black triangle In one study, cetirizine 5 mg plus pseudoephedrine SR 120 mg was significantly more effective at reducing nasal obstruction than either drug alone. black triangle Cetirizine 5mg plus pseudoephedrine SR 120 mg twice daily for 2 to 3 weeks was well tolerated in patients with seasonal or perennial allergic rhinitis. The most common adverse events were dry mouth, insomnia, headache, somnolence, asthenia and nervousness.

The CYP2D6 humanized mouse: effect of the human CYP2D6 transgene and HNF4alpha on the disposition of debrisoquine in the mouse

CYP2D6 is a highly polymorphic human gene responsible for a large variability in the disposition of more than 100 drugs to which humans may be exposed. Animal models are inadequate for preclinical pharmacological evaluation of CYP2D6 substrates because of marked species differences in CYP2D isoforms. To overcome this issue, a transgenic mouse line expressing the human CYP2D6 gene was generated. The complete wild-type CYP2D6 gene, including its regulatory sequence, was microinjected into a fertilized FVB/N mouse egg, and the resultant offspring were genotyped by both polymerase chain reaction and Southern blotting. CYP2D6-specific protein expression was detected in the liver, intestine, and kidney from only the CYP2D6 humanized mice. Pharmacokinetic analysis revealed that debrisoquine (DEB) clearance was markedly higher (94.1 +/- 22.3 l/h/kg), and its half-life significantly reduced (6.9 +/- 1.6 h), in CYP2D6 humanized mice compared with wild-type animals (15.2 +/- 0.9 l/h/kg and 16.5 +/- 4.5 h, respectively). Mutations in hepatic nuclear factor 4alpha (HNF4alpha), a hepatic transcription factor known to regulate in vitro expression of the CYP2D6 gene, could affect the disposition of CYP2D6 drug substrates. To determine whether the HNF4alpha gene modulates in vivo pharmacokinetics of CYP2D6 substrates, a mouse line carrying both the CYP2D6 gene and the HNF4alpha conditional mutation was generated and phenotyped using DEB. After deletion of HNF4alpha, DEB 4-hydroxylase activity in CYP2D6 humanized mice decreased more than 50%. The data presented in this study show that only CYP2D6 humanized mice but not wild-type mice display significant DEB 4-hydroxylase activity and that HNF4alpha regulates CYP2D6 activity in vivo. The CYP2D6 humanized mice represent an attractive model for future preclinical studies on the pharmacology, toxicology, and physiology of CYP2D6-mediated metabolism.

Complexities in the neurotoxic actions of 6-hydroxydopamine in relation to the cytoprotective properties of taurine

The neurotoxin 6-hydroxydopamine was shown to cause an imbalance between the direct and indirect pathways of the striato-nigral system as evidenced by a decreased release of gamma-aminobutyric acid and taurine in the substantia nigra but not in the globus pallidus following neostriatal stimulation with kainate (100 microM). The neurotoxicity of 6-hydroxydopamine is generally believed to result from reactive-oxygen radical formation, although it is also known to inhibit mitochondrial NADH dehydrogenase. The release of Fe(II) from the unactivated form [3Fe(III)-4S] of cytoplasmic aconitase (EC(50) < 8 microM) was shown to be followed by the slower oxidation of thiol groups in the protein. Complete loss of -SH groups, and enzyme activity, was seen after incubation of glyceraldenyde-3-phosphate dehydrogenase with 200 microM 6-hydroxydopamine for 75 min at 37 degrees C (IC(50) = 70.8 +/- 0.3 microM). Thus the cellular effects of 6-hydroxydopamine are complex, involving impairment of mitochondrial function, iron- release, sulphydryl-group oxidation, and enzyme inhibition in addition to direct generation of reactive oxygen radicals. Taurine, which is known to be neuroprotective in some other systems, only affords protection against some of these effects, thereby explaining its reported ineffectiveness against 6-hydroxydopamine toxicity.

Effect of organic cations on the renal tubular secretion of pseudoephedrine in the rat

1. Pseudoephedrine is a weak organic base that undergoes renal tubular secretion. The aim of the present study was to assess whether two other commonly used weak organic bases (cimetidine and morphine) inhibit the renal tubular secretion of pseudoephedrine in the rat isolated perfused kidney. 2. A total of 12 perfusions were performed with four perfusions in each of three treatment groups. In the control group, pseudoephedrine was administered as a bolus dose of [14C]-pseudoephedrine and unlabelled pseudoephedrine to achieve an initial perfusate concentration of 0.4 microg/mL. For the treatment groups, pseudoephedrine was administered as above and cimetidine or morphine was added to the perfusion medium in increasing concentrations of 0.5-12.5 and 0.2-5.0 microg/mL, respectively. 3. The mean (+/-SD) fraction unbound of pseudoephedrine alone in perfusate was 0.866+/-0.014 and was not different (P> 0.05) in the presence of cimetidine or morphine. 4. In control experiments, the renal excretory clearance (CLR) of pseudoephedrine was three-fold greater than glomerular filtration rate (GFR), yielding a ratio consistently greater than unity, which indicates extensive net tubular secretion of pseudoephedrine. The CLR and total clearance of pseudoephedrine were similar, suggesting an absence of renal metabolism of pseudoephedrine. 5. The CLR/GFR ratio for pseudoephedrine was not affected by morphine, but was significantly reduced (P < 0.05) in the presence of cimetidine. 6. The results indicate that cimetidine inhibits the renal tubular secretion of pseudoephedrine.

Relationship between the swelling process and the release of a water-soluble drug from a compressed swellable-soluble matrix of poly(vinyl alcohol)

An attempt was made in this study to relate the release of a highly water-soluble model drug from tablet matrices of poly(vinyl alcohol) (PVAL) with the factors that may affect the release behavior. Swelling was evaluated using a simple projection method. The swollen layer was photographed to monitor its thickness. The polymer and drug dissolution were determined simultaneously by spectrophotometric methods. The resulting change of tablet area showed that the process of swelling occurred in three different stages that were intimately related to polymer dissolution: (a) a rapid initial swelling, resulting in an increased area; (b) a period with an approximately constant area; and (c) a decrease of the tablet area. In spite of the significant dissolution of PVAL during the release process, the thickness of the gel layer gradually increased. Thus, the delivery was governed by the drug concentration gradient along the diffusional path length. The drug release appeared to be controlled by a diffusion process according to Higuchi-type kinetics. The data analysis of drug and polymer profiles confirmed the diffusional mechanism.

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.

Single-dose pharmacokinetics of modafinil and methylphenidate given alone or in combination in healthy male volunteers

Modafinil is a novel wake-promoting agent being developed for treatment of excessive daytime sleepiness associated with narcolepsy. An open, 3 x 3 Latin square, randomized, cross-over study was performed in healthy males to compare the pharmacokinetics of single-dose oral modafinil (200 mg) and methylphenidate (40 mg) administered alone or in combination. Blood samples were obtained for analysis of d- and l-threo-methylphenidate and modafinil and its acid and sulfone metabolites. Pharmacokinetic parameters were determined by noncompartmental methods, but could not be evaluated for modafinil sulfone due to plasma levels that were close to the assay quantitation limit. Although sporadic differences in plasma concentrations were observed between treatments, coadministration of modafinil and methylphenidate did not significantly alter the plasma concentrations of modafinil, modafinil acid, modafinil sulfone, or methylphenidate enantiomers compared with administration of these agents alone. Half-life (t1/2), maximum concentration (Cmax), area under the concentration-time curve (AUC0-infinity), total clearance (Cl/F), and apparent volume of distribution (Vd/F) for modafinil and t1/2, Cmax, and AUC0-infinity for modafinil acid were not affected by concomitant administration of methylphenidate. Small but statistically significant increases in time to Cmax (tmax) were observed for modafinil and modafinil acid after methylphenidate coadministration compared with modafinil alone. Modafinil coadministration did not significantly alter the pharmacokinetics of d- or l-threo-methylphenidate, except for a small decrease in Vd/F of l-threo-methylphenidate. Concomitant methylphenidate may cause a delay in the oral absorption of modafinil, but this delay might not be relevant clinically. Coadministration did not alter the extent of oral absorption and disposition of either agent. Therefore, a pharmacokinetic interaction between modafinil and methylphenidate would be unlikely.

[Transplantation of fetal dopaminergic cells simultaneously to the corpus striatum and pars reticularis of the substantia nigra in hemi-parkinsonian rats]

INTRODUCTION

Transplantation of foetal dopaminergic cells has been extensively used as restorative treatment for Parkinson's disease.

OBJECTIVE

This study was carried out to determine the survival, modifications in rotatory activity induced by D-amphetamine and total content of dopamine in the striatal and nigra regions of hemiparkinsonian rats which had had foetal mesencephalic cells simultaneously transplanted to the striatum and pars reticularis of the substancia nigra.

MATERIAL AND METHODS

The study was done using adult male Wistar rats weighing 200-250 gms. The following experimental groups were formed, depending on the site of transplant: St: transplant to striatum (n = 2); SNr: transplant to SNr (n = 20), ST + Snr; transplant to striatum and SNr simultaneously n = 20; and control (lesion with no transplant) n = 20. We studied the rotatory activity induced by D-amphetamine 1, 2, 3 and 6 months after transplantation. After this time the rats were deeply anaesthetized and randomly allocated for morphological study or biochemical determination of the total dopamine content in the St and SNr using the HPLC technique.

RESULTS

Study of conduct showed no significant differences in rotatory activity induced by D-amphetamine between the groups with intrastriatal transplants, but there was a difference between these and the SNr and control groups. Biochemical analysis showed that striatal DA content was significantly greater in the ST for the groups with intrastriatal transplants. The content of substancia nigra DA was significantly greater in the SNr of the ST + SNr group, followed by the ST group. Morphometric study showed differences, which were not significant, between ST transplanted animals and significant differences between the SNr transplanted group with a significant increase in survival of the SNr of the ST + SNr group.

CONCLUSIONS

These results suggest a positive effect due to intrastriatal transplants compared to survival following intranigral transplants.

Update on the pharmacotherapy of obesity

OBJECTIVE

To review recent developments in the pharmacotherapy of obesity, including the agents currently approved for use in the management of obesity and those under development.

DATA SOURCES

A MEDLINE search from January 1990 to July 1997 was conducted to identify English literature available on the pharmacotherapy of obesity. The search was supplemented by a review of the bibliographies of identified literature.

STUDY SELECTION

All controlled and uncontrolled trials were reviewed. When available, double-blind, placebo-controlled trials were used preferentially.

DATA EXTRACTION

Agents were reviewed with regard to mechanism of action, clinical trial data regarding efficacy, adverse effects, pharmacokinetics, drug interactions, and contraindications where information was available. Study design, selected population, results, and adverse effect information were included.

DATA SYNTHESIS

The anorexiants currently available or under development for the management of obesity regulate food intake and satiety via the adrenergic and/or serotonergic pathways. Clinical trials have shown a 10-15% weight loss can typically be anticipated; however, little long-term safety and efficacy data are available. Adverse events tend to be mild and self-limiting, but serious adverse events can occur. Treatment options under development include thermogenic agents, digestive inhibitors, and analogs and antagonists of hormones that regulate food intake and satiety.

CONCLUSIONS

Several mechanisms to control weight are currently under investigation for the management of obesity. Since obesity is a chronic condition, further studies should be conducted to evaluate the long-term safety and efficacy of these agents and the role of combination therapy using different modalities.

Disposition of fluvoxamine in humans is determined by the polymorphic CYP2D6 and also by the CYP1A2 activity

BACKGROUND

Fluvoxamine is a selective serotonin reuptake inhibitor used widely in the treatment of depression and other psychiatric diseases, but little is known about the specific isozymes involved in its metabolism. This study investigated the relationship between fluvoxamine disposition and the polymorphic CYP2D6 and the polycyclic aromatic hydrocarbon (as contained in cigarette smoke) inducible CYP1A2.

METHODS

Fluvoxamine (50 mg orally) was given to 10 extensive metabolizers and four poor metabolizers of debrisoquin, and concentrations were assessed in plasma by high performance liquid chromatography. Five of the extensive metabolizers and one of the poor metabolizers were smokers of more than 10 cigarettes per day. The CYP1A2 activity was determined by means of a urinary caffeine test.

RESULTS

Compared with nonsmoking extensive metabolizers, nonsmoking poor metabolizers had a statistically significant (p = 0.02, Mann-Whitney U test) about twofold higher maximum plasma concentration, longer half-life, and fivefold lower oral clearance of fluvoxamine. The oral clearance of fluvoxamine correlated to the CYP1A2 index in the 14 subjects (rs = 0.58; p < 0.05; Spearman rank correlation).

CONCLUSION

The disposition of fluvoxamine in humans is associated with the polymorphic CYP2D6 activity, but CYP1A2 also seems to be involved.

Bioavailability of pseudoephedrine from controlled release formulations in the presence of guaifenesin in human volunteers

A multiple-dose bioequivalence study with six healthy human volunteers was conducted. The bioavailability of an experimental controlled release tablet containing pseudoephedrine was compared with a marketed controlled release pseudoephedrine capsule in a three-way crossover study. Plasma samples, collected serially after oral drug administration, were analyzed for pseudoephedrine content using a specific HPLC method with UV detection. The bioavailability parameters, area under the concentration-time curve (AUC), maximum plasma concentration Cmax, and time to peak (Tmax) were obtained from the plasma concentration-time data. Additionally, model independent pharmacokinetic parameters were estimated. Analysis of variance of the data revealed no statistically significant differences between the test and the reference formulation. The presence of guaifenesin in the sustained release tablet did not influence pseudoephedrine bioavailability. The relative bioavailability of the tablet dosage form with respect to the capsule was found to be 100.8%. Classical and Westlake 95% confidence limits as well as the two one-sided t test, proposed by Schuirmann, and the Anderson-Hauck power analysis supported the inference that the two formulations demonstrated comparable bioavailabilty, even in the presence of guaifenesin. Using a non-linear regression program, it was found that the pharmacokinetics of pseudoephedrine followed a simple one-compartment disposition model with no lag time. Additionally, an in vitro-in vivo correlation, based on the estimation of cumulative relative fraction absorbed, was developed between the absorption of pseudoephedrine in humans and the in vitro dissolution time.

Do synthetic adrenergic agents interfere with the measurement of endogenous plasma catecholamine concentrations?

PURPOSE

It is common to administer synthetic sympathomimetic and sympatholytic agents in the intensive care unit and operating room. The present study examines whether such agents, as well as the products of catecholamine metabolism, interfere with the quantitation of endogenous catecholamines by high-performance liquid chromatography.

METHODS

Samples of drugs and metabolites were assayed before and after alumina extraction and their relative retention times were compared with dopamine, norepinephrine, and epinephrine relative retention times. Blood samples from patients receiving these drugs were also assayed for their interferences with catecholamine determination.

RESULTS

Phenylephrine interfered with the quantitation of epinephrine. Isoproterenol's peak was so delayed it appeared in the following chromatogram. Dobutamine had two small peaks in vitro, whereas in the patient samples only one peak was identified; the other was probably masked by the dopamine peak. Labetalol had one peak when the pure drug was assayed but multiple peaks in patient samples, that were probably caused by metabolites of labetalol.

CONCLUSION

Synthetic adrenergic agents and catecholamine metabolites can potentially interfere with the quantitation of the endogenous catecholamines. Thus, it is important to examine whether such interference occurs when conducting high-performance liquid chromatography assays.