Pyrroloquinoxaline hydrazones as fluorescent probes for amyloid fibrils.

Here we describe the identification and preliminary characterization of a new class of pyrrolo(imidazo)quinoxaline hydrazones as florescent probes for Aß(1-42) fibrils. All the newly developed compounds were able to bind amyloid fibrils formed in vitro and some of them displayed an increase of their fluorescence upon binding. When tested on brain tissue preparations presenting Aß deposits, the described hydrazones selectively stained amyloid structures and did not display aspecific binding. The hydrazones did not show antifibrillogenic activity and electron microscopy analysis revealed that they do not interfere with fibrils structure. The described pyrrolo(imidazo)quinoxalines could be useful for studying amyloid structures in vitro. Moreover, their experimentally proven ability to cross the blood-brain barrier in mouse opens the possibility of developing these compounds as potential amyloid imaging agents for in vivo applications.

The SIRT1 activator resveratrol protects SK-N-BE cells from oxidative stress and against toxicity caused by alpha-synuclein or amyloid-beta (1-42) peptide.

Human sirtuins are a family of seven conserved proteins (SIRT1-7). The most investigated is the silent mating type information regulation-2 homolog (SIRT1, NM_012238), which was associated with neuroprotection in models of polyglutamine toxicity or Alzheimer's disease (AD) and whose activation by the phytocompound resveratrol (RES) has been described. We have examined the neuroprotective role of RES in a cellular model of oxidative stress, a common feature of neurodegeneration. RES prevented toxicity triggered by hydrogen peroxide or 6-hydroxydopamine (6-OHDA). This action was likely mediated by SIRT1 activation, as the protection was lost in the presence of the SIRT1 inhibitor sirtinol and when SIRT1 expression was down-regulated by siRNA approach. RES was also able to protect SK-N-BE from the toxicity arising from two aggregation-prone proteins, the AD-involved amyloid-beta (1-42) peptide (Abeta42) and the familiar Parkinson's disease linked alpha-synuclein(A30P) [alpha-syn(A30P)]. Alpha-syn(A30P) toxicity was restored by sirtinol addition, while a partial RES protective effect against Abeta42 was found even in presence of sirtinol, thus suggesting a direct RES effect on Abeta42 fibrils. We conclude that SIRT1 activation by RES can prevent in our neuroblastoma model the deleterious effects triggered by oxidative stress or alpha-syn(A30P) aggregation, while RES displayed a SIRT1-independent protective action against Abeta42.

Enhancement of cortical extracellular 5-HT by 5-HT1A and 5-HT2C receptor blockade restores the antidepressant-like effect of citalopram in non-responder mice.

We recently found that the response of DBA/2 mice to SSRIs in the forced swim test (FST) was impaired and they also had a smaller basal and citalopram-stimulated increase in brain extracellular serotonin (5-HT) than 'responder' strains. We employed intracerebral microdialysis, FST and selective antagonists of 5-HT1A and 5-HT2C receptors to investigate whether enhancing the increase in extracellular 5-HT reinstated the anti-immobility effect of citalopram in the FST. WAY 100635 (0.3 mg/kg s.c.) or SB 242084 (1 mg/kg s.c.), respectively a selective 5-HT1A and 5-HT2C receptor antagonist, raised the effect of citalopram (5 mg/kg) on extracellular 5-HT in the medial prefrontal cortex of DBA/2N mice (citalopram alone 5.2+/-0.3 fmol/20 microl, WAY 100635+citalopram 9.9+/-2.1 fmol/20 microl, SB 242084+ citalopram 7.6+/-1.0 fmol/20 microl) to the level reached in 'responder' mice given citalopram alone. The 5-HT receptor antagonists had no effect on the citalopram-induced increase in extracellular 5-HT in the dorsal hippocampus. The combination of citalopram with WAY 100635 or SB 242084 significantly reduced immobility time in DBA/2N mice that otherwise did not respond to either drug singly. Brain levels of citalopram in mice given citalopram alone or with 5-HT antagonists did not significantly differ. The results confirm that impaired 5-HT transmission accounts for the lack of effect of citalopram in the FST and suggest that enhancing the effect of SSRIs on extracellular 5-HT, through selective blockade of 5-HT1A and 5-HT2C receptors, could be a useful strategy to restore the response in treatment-resistant depression.

Strain differences in paroxetine-induced reduction of immobility time in the forced swimming test in mice: role of serotonin.

We studied the antidepressant-like effect of paroxetine in strains of mice carrying different isoforms of tryptophan hydroxylase-2 (TPH-2), the enzyme responsible for the synthesis of brain serotonin (5-HT). The effect of paroxetine alone and in combination with pharmacological treatments enhancing or lowering 5-HT synthesis or melatonin was assessed in the forced swimming test in mice carrying allelic variants of TPH-2 (1473C in C57BL/6 and 1473G in DBA/2 and BALB/c). Changes in brain 5-hydroxytryptophan (5-HTP) accumulation and melatonin levels were measured by high-performance liquid chromatography. Paroxetine (2.5 and 5 mg/kg) reduced immobility time in C57BL/6J and C57BL/6N mice but had no such effect in DBA/2J, DBA/2N and BALB/c mice, even at 10 mg/kg. Enhancing 5-HT synthesis with tryptophan reinstated the antidepressant-like effect of paroxetine in DBA/2J, DBA/2N and BALB/c mice whereas inhibition of 5-HT synthesis prevented the effect of paroxetine in C57BL/6N mice. The response to paroxetine was not associated with changes in locomotor activity, brain melatonin or brain levels of the drug measured at the end of the behavioral test. These results support the importance of 5-HT synthesis in the response to SSRIs and suggest that melatonin does not contribute to the ability of tryptophan to rescue the antidepressant-like effect of paroxetine.

Liquid chromatography-tandem mass spectrometry of I3,II8-biapigenin, the major biflavone in Hypericum perforatum extracts.

High-performance liquid chromatography method coupled with tandem mass spectrometry was developed for the quantitative determination of I3,II8-biapigenin. The procedure includes solid-phase extraction and separation on an XTerra MS C18. The assay was linear over a wide range; precision and accuracy were acceptable. Biapigenin was present in mouse and rat plasma after a standardized Hypericum perforatum extract. It was not detected in brain (<5ngg(-1)), suggesting poor brain-to-blood permeability. Biapigenin concentrations were measurable in mice after intraperitoneal biapigenin (10mgkg(-1)) but these amounted to about 2% of the equivalent systemic exposure, after correction for the contribution from residual blood.

N-dealkylation of arylpiperazine derivatives: disposition and metabolism of the 1-aryl-piperazines formed.

In recent years several arylpiperazine derivatives have reached the stage of clinical application, mainly for the treatment of depression, psychosis or anxiety. Examples are the pyrimidinylpiperazine buspirone, the chlorophenylpiperazine derivatives nefazodone and trazodone, the dichlorophenylpiperazine aripiprazole and the benzisothiazolyl derivatives perospirone and ziprasidone. Most of them undergo extensive pre-systemic and systemic metabolism including CYP3A4-dependent N-dealkylation to 1-aryl-piperazines. These metabolites are best known for the variety of serotonin receptor-related effects they cause in man and animals, although some have affinity for other neurotransmitter receptors; others, however, are still largely unexplored despite uncontrolled use as amphetamine-like designer drugs. Once formed they distribute extensively in tissues, including brain which is the target site of most arylpiperazine derivatives, and are then primarily biotransformed by CYP2D6-dependent oxidation to hydroxylates which are excreted as conjugates; only 1-(2-benzisothiazolyl)-piperazine is more susceptible to sulfur oxidation than to aromatic hydroxylation. In studies analysing animal brain and human blood, 1-aryl-piperazine concentrations were either higher or lower than the parent compound(s), although information is available only for some derivatives. At steady state, the metabolite-to-parent drug ratios varied widely among individuals taking the same dosage of the same arylpiperazine derivative. This is consistent with the known individual variability in the expression and activity of CYP3A4 and CYP2D6. This review also surveys current published information on physiological and pathological factors affecting the 1-aryl-piperazine-to-parent drug ratios and examines the potential role of 1-aryl-piperazine formation in the pharmacological actions of the arylpiperazine derivatives that are already or will shortly be available in major markets.

Genotype-dependent activity of tryptophan hydroxylase-2 determines the response to citalopram in a mouse model of depression.

Polymorphism of tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of brain serotonin (5-HT), is associated with less synthesis of brain 5-HT in DBA/2J and BALB/c than in C57BL/6J and 129/Sv mice. We selected the forced swimming test, a mouse model used to assess the antidepressant potential of drugs, and neurochemical techniques to study strain differences in the response to citalopram, a selective 5-HT reuptake inhibitor. Citalopram reduced immobility time in C57BL/6J and 129/Sv mice but had no such effect in DBA/2J and BALB/c mice. The drug reduced accumulation of 5-hydroxytryptophan (5-HTP), an indicator of 5-HT synthesis, in C57BL/6J and 129/Sv mice but much less in DBA/2J and BALB/c mice. Pretreatment with tryptophan raised 5-HTP accumulation and reinstated the antidepressant-like effect of citalopram in DBA/2J and BALB/c mice, whereas pharmacological inhibition of 5-HT synthesis prevented the effect of citalopram in C57BL/6J and 129/Sv mice. Because there were no strain differences in catecholamine synthesis, locomotor activity, and brain levels of citalopram at the end of the behavioral test, the results suggest that the failure of citalopram to reduce immobility time in DBA/2J and BALB/c mice is attributable to genotype-dependent impairment of 5-HT synthesis. Interstrain comparisons could probably be a useful strategy for understanding the mechanisms underlying the response to selective serotonin reuptake inhibitors.

In vitro responsiveness of human-drug-resistant tissue to antiepileptic drugs: insights into the mechanisms of pharmacoresistance.

Pharmacoresistance in epileptic patients may be ascribed to at least two, not mutually exclusive, mechanisms: a pharmacokinetic mechanism and a decreased sensitivity or availability of targets to antiepileptic drugs (AEDs; i.e., carbamazepine and phenytoin (CBZ, PHT)). Brain:plasma drug concentration ratios were determined intraoperatively during lobectomies performed to alleviate drug-resistant seizures. The brain:plasma ratio of CBZ was 1.48 when therapeutic serum levels (15-34 microM) were achieved. When concentrations of CBZ found in multiple-drug-resistant brain were directly applied to human cortical slices from drug-resistant patients made hyperexcitable and hypersynchronous by Mg(2+)-free media, bursting frequency was not significantly affected and overall excitability was reduced by 40%. Similar results were obtained for PHT. At higher AED concentrations (60-200 microM), a dose-dependent decrease of bursting frequency and amplitude was observed. Slices from drug-resistant epileptic patients made hypersynchronous/hyperexcitable by elevated potassium or inhibition of GABA-A receptors behaved similarly. Of note is the response of slices from human multiple-drug-resistant brain, which was greater than in rodent cortex from naive animals. Taken together, our results support the hypothesis that multiple drug resistance to AEDs involves cerebrovascular changes that impede the achievement of appropriate drug levels in the central nervous system.

Limbic seizures induce P-glycoprotein in rodent brain: functional implications for pharmacoresistance.

The causes and mechanisms underlying multidrug resistance (MDR) in epilepsy are still elusive and may depend on inadequate drug concentration in crucial brain areas. We studied whether limbic seizures or anticonvulsant drug treatments in rodents enhance the brain expression of the MDR gene (mdr) encoding a permeability glycoprotein (P-gp) involved in MDR to various cancer chemotherapeutic agents. We also investigated whether changes in P-gp levels affect anticonvulsant drug concentrations in the brain. Mdr mRNA measured by RT-PCR increased by 85% on average in the mouse hippocampus 3-24 hr after kainic acid-induced limbic seizures, returning to control levels by 72 hr. Treatment with therapeutic doses of phenytoin or carbamazepine for 7 d did not change mdr mRNA expression in the mouse hippocampus 1-72 hr after the last drug administration. Six hours after seizures, the brain/plasma ratio of phenytoin was reduced by 30% and its extracellular concentration estimated by microdialysis was increased by twofold compared with control mice. Knock-out mice (mdr1a/b -/-) lacking P-gp protein showed a 46% increase in phenytoin concentrations in the hippocampus 1 and 4 hr after injection compared with wild-type mice. A significant 23% increase was found in the cerebellum at 1 hr and in the cortex at 4 hr. Carbamazepine concentrations were measurable in the hippocampus at 3 hr in mdr1a/b -/- mice, whereas they were undetectable at the same time interval in wild-type mice. In rats having spontaneous seizures 3 months after electrically induced status epilepticus, mdr1 mRNA levels were enhanced by 1.8-fold and fivefold on average in the hippocampus and entorhinal cortex, respectively. Thus, changes in P-gp mRNA levels occur in limbic areas after both acute and chronic epileptic activity. P-gp alterations significantly affect antiepileptic drugs concentrations in the brain, suggesting that seizure-induced mdr mRNA expression contributes to MDR in epilepsy.

Antidepressant-like components of Hypericum perforatum extracts: an overview of their pharmacokinetics and metabolism.

Extracts of Hypericum perforatum are becoming increasingly popular for the treatment of mild to moderate depression, despite the lack of consensus on their efficacy. Although the mechanism(s) of this action are still debated, several components, including the naphthodianthrones hypericin and pseudohypericin, the acylphloroglucinol hyperforin and some flavonols, are believed to play major roles in the antidepressant-like effects. Some of these also increase the expression of the P-glycoprotein transporter and others the expression of cytochrome P450 enzymes, possibly contributing to the interactions involving the extracts and conventional drugs. However, few pharmacokinetic studies of naphthodianthrones and hyperforin have appeared and none has yet evaluated the exposure to unchanged quercetin and its glycosides after intake of extracts. There are no formal pharmacokinetic studies in special populations. Bioavailability appears low, giving variable steady-state plasma concentrations, whose prediction may be complicated by non-linearity for hypericin and hyperforin. Data on tissue distribution are scarce, and it appears that hypericin and hyperforin do not reach the central nervous system in appreciable concentrations in animals. Clearance is low-intermediate, with little or no unchanged compounds excreted with urine. Although some potentially active conjugated metabolites have been identified for quercetin and its glycosides after intake of authentic compounds or flavonol-rich foods, these too have been characterised little with regard to their pharmacokinetics and central activities. Thus, further pharmacokinetic and pharmacodynamic studies of the main components and their metabolites are urgently needed to clarify the role of each constituent and provide more rational and safe regimens for people preferring "natural" drugs.

Potential antidepressant properties of IDN 5491 (hyperforin-trimethoxybenzoate), a semisynthetic ester of hyperforin.

Hyperforin is one of the possible active principles mediating the antidepressant activity of Hypericum perforatum L. extracts. The ester derivative IDN 5491 (hyperforin-trimethoxybenzoate) showed antidepressant-like properties in the forced swimming test (FST) in rats, with no effect on open-field activity, when given as three intraperitoneal injections in 24 h at 3.125 and 6.25 mg/kg. The plasma concentrations of IDN 5491 were 30-50 microM, and those of hyperforin much lower but still close to those after effective doses of hyperforin-dicyclohexylammonium and Hypericum extract. This suggests that hyperforin plays a role in the antidepressant-like effect of the ester and of Hypericum extract. In vitro binding and uptake data showed that IDN 5491 is inactive on a wide panel of CNS targets at a concentration (14 microM) much higher than that measured in the brain of treated rats (0.3 microM). Like the extract, the antidepressant-like effect of IDN 5491 was blocked by (-)-sulpiride, a selective D2 receptor antagonist and by BD-1047, a selective sigma1 antagonist. Ex-vivo binding studies showed that brain sigma1 receptors are occupied after in vivo treatment with IDN 5491, possibly by an unknown metabolite or by endogenous ligand induced by hyperforin.

Selective antagonist at D3 receptors, but not non-selective partial agonists, influences the expression of cocaine-induced conditioned place preference in free-feeding rats.

The non-selective dopamine (DA) D(3) partial agonist BP 897 influenced rats' seeking behavior induced by cocaine-associated cues but there are contradictions about its ability to modulate cocaine-induced conditioned place preference (CPP), and mechanisms involved. We therefore re-evaluated its activity on both acquisition and expression of these behaviors, taking into consideration the actual brain concentrations of unchanged drug and its potential active metabolite 1-(2-methoxyphenyl)-piperazine (oOCH(3)PP), as well as its negative motivational properties. BP 897 induced conditioned place aversion (CPA) at 3 mg/kg, but not at 0.3 and 1 mg/kg. However, in this range of amply spaced doses BP 897 did not affect the acquisition and expression of cocaine (10 mg/kg i.p.) CPP in rats, although its brain concentrations were well above those affecting in vitro D(3) receptors. Concentrations of oOCH(3)PP were below the limits of quantification of the analytical procedure. As concerns the expression behavior, its structurally and pharmacologically related derivative N-[4-[4-(2-methoxyphenyl)piperazin-1-yl]butyl]benzo[b]furan-2-carboxamide (1 and 3 mg/kg, i.p.) also had no such effect. By contrast, the selective D(3) receptor antagonist SB-277011-A (3 mg/kg, i.p.) antagonized the expression of cocaine-induced CPP, supporting the suggestion that "full" antagonist activity at D(3) receptors is necessary to prevent 10 mg/kg cocaine-induced place conditioning in free-feeding rats.

5-HT2A and 5-HT2C/2B receptor subtypes modulate dopamine release induced in vivo by amphetamine and morphine in both the rat nucleus accumbens and striatum.

In vivo microdialysis and single-cell extracellular recordings were used to assess the involvement of serotonin(2A) (5-HT(2A)) and serotonin(2C/2B) (5-HT(2C/2B)) receptors in the effects induced by amphetamine and morphine on dopaminergic (DA) activity within the mesoaccumbal and nigrostriatal pathways. The increase in DA release induced by amphetamine (2 mg/kg i.p.) in the nucleus accumbens and striatum was significantly reduced by the selective 5-HT(2A) antagonist SR 46349B (0.5 mg/kg s.c.), but not affected by the 5-HT(2C/2B) antagonist SB 206553 (5 mg/kg i.p.). In contrast, the enhancement of accumbal and striatal DA output induced by morphine (2.5 mg/kg s.c.), while insensitive to SR 46349B, was significantly increased by SB 206553. Furthermore, morphine (0.1-10 mg/kg i.v.)-induced increase in DA neuron firing rate in both the ventral tegmental area and the substantia nigra pars compacta was unaffected by SR 46349B (0.1 mg/kg i.v.) but significantly potentiated by SB 206553 (0.1 mg/kg i.v.). These results show that 5-HT(2A) and 5-HT(2C) receptors regulate specifically the activation of midbrain DA neurons induced by amphetamine and morphine, respectively. This differential contribution may be related to the specific mechanism of action of the drug considered and to the neuronal circuitry involved in their effect on DA neurons. Furthermore, these results suggest that 5-HT(2C) receptors selectively modulate the impulse flow-dependent release of DA.

New antipsychotic agents for schizophrenia: pharmacokinetics and metabolism update.

The so-called atypical antipsychotics undergo extensive metabolism, except for amisulpride, which is substantially excreted unchanged. Risperidone is oxidized by CYP2D6/CYP3A4 and iloperidone is reduced by cytosolic enzymes, although CYP1A2, CYP2E1 and CYP3A4 are involved as well. Olanzapine is both conjugated and oxidized (mainly by CYP1A2), while quetiapine and zotepine primarily undergo CYP3A4-mediated oxidation. Ziprasidone pathways include aldehyde oxidase-mediated reduction and CYP3A4-mediated oxidation. The main metabolites of risperidone, zotepine and possibly perospirone and ziprasidone contribute to the parent drug's effect. Information is limited, however, on some promising antipsychotics in the pipeline.

Role of hyperforin in the antidepressant-like activity of Hypericum perforatum extracts.

RATIONALE: Hyperforin has been identified as an active constituent of Hypericum perforatum but its importance in the antidepressant effect of this plant's extracts is not really known. OBJECTIVE: To evaluate the antidepressant-like activity of two extracts in relation to the content of hyperforin and its plasma and whole brain concentrations, compared with a stable salt of hyperforin (dicyclohexylammonium; DCHA). METHODS: The effects of the extracts and hyperforin were evaluated in the rat forced swimming test. The specificity of the effects was demonstrated evaluating the rats' locomotor activity. Plasma and brain concentrations of hyperforin were determined by high performance liquid chromatography. RESULTS: The 4.5% extract (but not the 0.5% extract) given as three IP injections in 24 h (3.12-6.25 mg/kg) reduced the total immobility of rats, yielding dose-related plasma concentrations of hyperforin. These concentrations were of a similar magnitude to those after hyperforin DCHA which also significantly reduced immobility when given on the basis of the hyperforin content of the 4.5% extract (0.14 and 0.28 mg/kg). However, hyperforin was undetectable in rat brain, possibly because of poor passage of the blood-brain barrier. CONCLUSION: These results support the view that hyperforin plays a key role in the antidepressant-like activity of Hypericum p. However, brain concentrations after effective doses are probably far from those active in vitro on the neurotransmitter mechanisms so far investigated.

Hyperforin contributes to the hepatic CYP3A-inducing effect of Hypericum perforatum extract in the mouse.

This study in mice investigated whether hyperforin accounts for the inductive effects on cytochrome P4503A enzymes of St. John's wort extracts (SJW; Hypericum perforatum), one of the most popular herbal preparations because of its alleged activity in mild to moderate depression. A hydroalcoholic extract containing 4.5% hyperforin was given at a dose of 300 mg/kg, bis in die (b.i.d.), for 4 and 12 days. Hyperforin, its main phloroglucinol component, was given as dicyclohexylammonium (DCHA) salt (18.1 mg/kg, b.i.d.) on the basis of its content in the extract, to ensure comparable exposure to hyperforin. The extract increased hepatic erythromycin-N-demethylase (ERND) activity, which is cytochrome P450 enzyme (CYP) 3A-dependent, about 2.2-fold after 4 days of dosing, with only slightly greater effect after 12 days (2.8 times controls). Hyperforin too increased ERND activity within 4 days, much to the same extent as the extract (1.8 times the activity of controls), suggesting that it behaves qualitatively and quantitatively like the extract as regards induction of CYP3A activity. This effect was confirmed by Western blot analysis of hepatic CYP3A expression. Exposure to hyperforin at the end of the 4-day treatment was still similar to that with SJW extract, although it was variable and lower than after the first dose in both cases, further suggesting that hyperforin plays a key role in CYP3A induction by the SJW extract in the mouse. Standardization of the extracts based on the hyperforin content can be proposed for further evaluation of their potential action on first-pass metabolism and clearance of coadministered CYP3A substrates.

Targeting thalamic nuclei is not sufficient for the full anti-absence action of ethosuximide in a rat model of absence epilepsy.

Absence epilepsy is characterised by recurrent periods of physical and mental inactivity coupled to bilateral, synchronous spike and wave discharges (SWDs) on the electroencephalogram. The mechanism of action of ethosuximide (ETX), a drug specific for absence seizures, is believed to involve a reduction in the low threshold T-type Ca(2+) current in thalamocortical and nucleus reticularis thalami (NRT) neurones, although other electrophysiological data have questioned this. Here, we employed a genetic rat model of absence seizures to investigate the effects of directly administering ETX to the thalamus.SWDs were immediately and substantially reduced (approximately 90%) by systemic administration of ETX (177-709 micromol/kg), or by bilateral microinfusion into the thalamus of the GABA(B) antagonist, CGP 36742 (5-27 nmol per side). However, infusion of ETX (1-200 nmol per side) into the ventrobasal complex or the NRT resulted in a reduction of SWDs that was delayed (30-60 min) and less marked (approximately 50%). Administration of ETX (0.2 mM to 1M) to a greater volume of thalamus by reverse microdialysis also produced significant but delayed reduction of SWDs at concentrations >1mM. Only at 5mM were seizures significantly reduced (approximately 70%) within 30 min of administration. These results suggest that targeting of the thalamus alone may be insufficient for an immediate and full anti-absence action for ETX. Concomitant or exclusive actions in the cortex remain a possibility.

Pharmacokinetics and Safety of a Potential Antidementia Compound, CL 275,838, after Multiple Oral Doses in Patients with Dementia of Alzheimer Type or Vascular Dementia.

The multiple-dose pharmacokinetics and safety of a new potential antidementia compound, CL 275,838, were examined in two randomized, double-blind, parallel-group, placebo-controlled studies. The Alzheimer Disease Assessment Scale (ADAS) was employed to preliminarily assess the patients' cognitive and the behavioral profiles. In the first study, nine patients with Alzheimer type or vascular dementia were treated for 2 weeks with daily doses of 50 mg. In the second study, nine other patients, selected with the same inclusion/exclusion criteria and treated following the same experimental design, were given 100 mg day(minus sign1) CL 275,838. At the lower dose, no side effects were detected; in the 100-mg day(minus sign1) study, mild drowsiness (one patient) and moderate agitation (two patients) were observed. Laboratory tests showed no changes in either study, apart from a slight, transient increase in serum bilirubin in one patient given 100 mg. At the dose of 50 mg, no patients showed any modification on the ADAS, whereas three patients given 100 mg showed some improvement. During the 2 weeks of oral dosing, predose plasma concentrations of the parent compounds and its metabolites II and IV increased but not in proportion to the dose, although at both doses, accumulation was essentially complete within 10 days. At 50 mg, the mean steady-state C(max) and C(ss) of the parent compound were similar to those reached in young males after a comparable regimen. Mean steady-state metabolite-to-parent drug ratios were higher in patients than in healthy individuals, although there was wide variation in our patient group. Mean washout t(1/2) of the parent compound (34 h) and its metabolites II (37 h) and IV (41 h) were longer than in young men and were similar in all cases to those observed after single doses in healthy elderly subjects. After 100 mg, mean C(max) and C(ss) of the unchanged compound rose more than proportionally and the apparent t(1/2) tended to rise, compared with the lower dose. Mean steady-state oral clearance decreased, changing the metabolite-to-parent drug ratios, suggesting nonlinear kinetics after several relatively high oral doses. This might explain why the higher dose was less well tolerated.

Liquid chromatographic determination of minocycline in brain-to-plasma distribution studies in the rat.

An isocratic reversed-phase high-performance liquid chromatographic procedure was developed for the determination of minocycline in rat plasma and brain and applied to brain-to-blood (plasma) distribution studies. The procedure is based on isolation of the compound and the internal standard (either demeclocycline or tetracycline may be used) from plasma and brain constituents using the Oasis HLB cartridge, with satisfactory recovery and specificity, and separation on a Symmetry Shield RP8 (15 cm x 4.6 mm, 3.5 microm) column coupled with a UV detector set at 350 nm. The assay was linear over a wide range, with a lower limit of quantification of 50 ng ml(-1) or g(-1), using 0.2 ml of plasma and about 200 mg of brain tissue. Precision and accuracy were acceptable. In the rat minocycline crossed the blood-brain barrier slowly, achieving mean brain concentrations between 30 and 40% of the equivalent systemic exposure, regardless of the dose and route of administration.

Liquid chromatographic assay for riluzole in mouse plasma and central nervous system tissues.

An isocratic, reversed-phase high-performance liquid chromatographic procedure (HPLC) was developed for determination of the neuroprotective agent riluzole in mice plasma, brain and spinal cord. The procedure is based on isolation of the compound and the internal standard from plasma and central nervous system tissues using a Bakerbond spe C8 cartridge, with satisfactory recovery and specificity. Separation was on a C18 column, coupled with an UV detector at 263 nm. The assay was linear over a wide range, with a lower limit of quantification of 100 ng ml(-1) or g(-1) using 0.1 ml of plasma and about 100mg of brain tissue. The precision and accuracy were within the acceptable limits for an HPLC assay. The method is currently used to support pharmacological studies of the activity of riluzole when given in combination with other potential neuroprotective agents in an animal model of familiar amyotrophic lateral sclerosis (SOD1-G93A transgenic mice).