Activation of M4 muscarinic receptors in the striatum reduces tic-like behaviours in two distinct murine models of Tourette syndrome

BACKGROUND AND PURPOSE

Current pharmacotherapies for Tourette syndrome (TS) are often unsatisfactory and poorly tolerated, underscoring the need for novel treatments. Insufficient striatal acetylcholine has been suggested to contribute to tic ontogeny. Thus, we tested whether activating M1 and/or M4 receptors-the two most abundant muscarinic receptors in the striatum-reduced tic-related behaviours in mouse models of TS.

EXPERIMENTAL APPROACH

Studies were conducted using CIN-d and D1CT-7 mice, two TS models characterized by early-life depletion of striatal cholinergic interneurons and cortical neuropotentiation, respectively. First, we tested the effects of systemic and intrastriatal xanomeline, a selective M1/M4 receptor agonist, on tic-like and other TS-related responses. Then, we examined whether xanomeline effects were reduced by either M1 or M4 antagonists or mimicked by the M1/M3 agonist cevimeline or the M4 positive allosteric modulator (PAM) VU0467154. Finally, we measured striatal levels of M1 and M4 receptors and assessed the impact of VU0461754 on the striatal expression of the neural marker activity c-Fos.

KEY RESULTS

Systemic and intrastriatal xanomeline reduced TS-related behaviours in CIN-d and D1CT-7 mice. Most effects were blocked by M4, but not M1, receptor antagonists. VU0467154, but not cevimeline, elicited xanomeline-like ameliorative effects in both models. M4, but not M1, receptors were down-regulated in the striatum of CIN-d mice. Additionally, VU0467154 reduced striatal c-Fos levels in these animals.

CONCLUSION AND IMPLICATIONS

Activation of striatal M4, but not M1, receptors reduced tic-like manifestations in mouse models, pointing to xanomeline and M4 PAMs as novel putative therapeutic strategies for TS.

Systemic administration of ivabradine, a hyperpolarization-activated cyclic nucleotide-gated channel inhibitor, blocks spontaneous absence seizures

OBJECTIVE

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are known to be involved in the generation of absence seizures (ASs), and there is evidence that cortical and thalamic HCN channel dysfunctions may have a proabsence role. Many HCN channel blockers are available, but their role in ASs has been investigated only by localized brain injection or in in vitro model systems due to their limited brain availability. Here, we investigated the effect on ASs of orally administered ivabradine (an HCN channel blocker approved for the treatment of heart failure in humans) following injection of the P-glycoprotein inhibitor elacridar, which is known to increase penetration into the brain of drug substrates for this efflux transporter. The action of ivabradine was also tested following in vivo microinjection into the cortical initiation network (CIN) of the somatosensory cortex and in the thalamic ventrobasal nucleus (VB) as well as on cortical and thalamocortical neurons in brain slices.

METHODS

We used electroencephalographic recordings in freely moving Genetic Absence Epilepsy Rats From Strasbourg (GAERSs) to assess the action of oral administration of ivabradine, with and without elacridar, on ASs. Ivabradine was also microinjected into the CIN and VB of GAERSs in vivo and applied to Wistar CIN and GAERS VB slices while recording patch-clamped cortical Layer 5/6 and thalamocortical neurons, respectively.

RESULTS

Oral administration of ivabradine markedly and dose-dependently reduced ASs. Ivabradine injection into CIN abolished ASs and elicited small-amplitude 4-7-Hz waves (without spikes), whereas in the VB it was less potent. Moreover, ivabradine applied to GAERS VB and Wistar CIN slices selectively decreased HCN channel-dependent properties of cortical Layer 5/6 pyramidal and thalamocortical neurons, respectively.

SIGNIFICANCE

These results provide the first demonstration of the antiabsence action of a systemically administered HCN channel blocker, indicating the potential of this class of drugs as a novel therapeutic avenue for ASs.

Dose constraints for whole breast radiation therapy based on the quality assessment of treatment plans in the randomised Danish breast cancer group (DBCG) HYPO trial

Purpose

Quality assessment of the treatment plans in the Danish Breast Cancer Group (DBCG) HYPO trial was carried out based on prospectively reported dosimetric parameters and evidence-based dose constraints for whole breast radiation therapy were derived.

Materials and methods

From 2009 to 2014, 1882 patients (pts) were randomised between 50 Gy/25fractions (fr) versus 40 Gy/15fr. Doses to CTVp_breast (V_95%, V_107%-V_110%, D_max, and in addition for 40 Gy plans V_105%-V_107%), ipsilateral lung (V_20Gy/V_17Gy), heart (V_20Gy/V_17Gy, V_40Gy/V_35Gy), and left anterior descending coronary artery (LADCA) (D_max) and use of respiratory gated technique were prospectively reported to the DBCG database. After end of accrual, these dosimetric parameters from all plans in the trial were compared to the pre-specified treatment constraints.

Results

In total, 1854 pts from eight radiation therapy (RT) centres in three countries were treated. No statistically significant differences were found between the results for 40 Gy and 50 Gy plans, except for CTVp_breast hot-spot volume (V_107%-V_110%). Of the 40 Gy pts, 90% with CTVp_breast > 600 mL and 95% with CTVp_breast ≤ 600 mL had a CTVp_breast hot-spot volume (V_105%-V_107%) <2%. In 95% of the 50 Gy plans, the CTVp_breast absolute hot-spot volume (V_107%-V_110%) was <0.5 mL and 1.7 mL for CTVp_breast ≤ 600 mL and > 600 mL, respectively. Compliance was >99% for both heart and lung constraints. Largest deviation from protocol constraints was found for the volume of CTVp_breast covered with 95% of the prescription dose or more (V_95%). The CTV dose coverage (V_95%) was >94.3% in 95% of the right-sided pts, whereas the figures for 95% of the left-sided pts treated with and without respiratory gating were 93.2% and 88.8%, respectively.

Conclusion

A high degree of compliance with protocol dose constraints was found for treatment plans in the DBCG HYPO trial. New constraints for dose to organs at risk and high-dose volumes in the breast are suggested for breast-only RT planning.

Probing the putative α7 nAChR/NMDAR complex in human and murine cortex and hippocampus: Different degrees of complex formation in healthy and Alzheimer brain tissue

α7 nicotinic acetylcholine receptors (nAChRs) and N-methyl-D-aspartate receptors (NMDARs) are key mediators of central cholinergic and glutamatergic neurotransmission, respectively. In addition to numerous well-established functional interactions between α7 nAChRs and NMDARs, the two receptors have been proposed to form a multimeric complex, and in the present study we have investigated this putative α7 nAChR/NMDAR assembly in human and murine brain tissues. By α-bungarotoxin (BGT) affinity purification, α7 and NMDAR subunits were co-purified from human and murine cortical and hippocampal homogenates, substantiating the notion that the receptors are parts of a multimeric complex in the human and rodent brain. Interestingly, the ratios between GluN1 and α7 levels in BGT pull-downs from cortical homogenates from Alzheimer’s disease (AD) brains were significantly lower than those in pull-downs from non-AD controls, indicating a reduced degree of α7 nAChR/NMDAR complex formation in the diseased tissue. A similar difference in GluN1/α7 ratios was observed between pull-downs from cortical homogenates from adult 3xTg-AD and age-matched wild type (WT) mice, whereas the GluN1/α7 ratios determined in pull-downs from young 3xTg-AD and age-matched WT mice did not differ significantly. The observation that pretreatment with oligomeric amyloid-β_1–42 reduced GluN1/α7 ratios in BGT pull-downs from human cortical homogenate in a concentration-dependent manner provided a plausible molecular mechanism for this observed reduction. In conclusion, while it will be important to further challenge the existence of the putative α7 nAChR/NMDAR complex in future studies applying other methodologies than biochemical assays and to investigate the functional implications of this complex for cholinergic and glutamatergic neurotransmission, this work supports the formation of the complex and presents new insights into its regulation in healthy and diseased brain tissue.

Nicotinic Acetylcholine Receptors in the Pathophysiology of Al zheimer's Disease: The Role of Protein-Protein Interactions in Current and Future Treatment

Nicotinic acetylcholine receptors (nAChRs) have been pursued for decades as potential molecular targets to treat cognitive dysfunction in Alzheimer's disease (AD) due to their positioning within regions of the brain critical in learning and memory, such as the prefrontal cortex and hippocampus, and their demonstrated role in processes underlying cognition such as synaptic facilitation, and theta and gamma wave activity. Historically, activity at these receptors is facilitated in AD by use of drugs that increase the levels of their endogenous agonist acetylcholine, and more recently nAChR selective ligands have undergone clinical trials. Here we discuss recent findings suggesting that the expression and function of nAChRs in AD may be regulated by direct interactions with specific proteins, including Lynx proteins, NMDA-receptors and the Wnt/β-catenin pathway, as well as β-amyloid. The ability of protein interactions to modify nAChR function adds a new level of complexity to cholinergic signaling in the brain that may be specifically altered in AD. It is currently not known to what degree current nAChR ligands affect these interactions, and it is possible that the difference in the clinical effect of nAChR ligands in AD is related to differences in their ability to modulate nAChR protein interactions, rather than their effects on ion flow through the receptors. Drugs designed to target these interactions may thus provide a new avenue for drug development to ameliorate cognitive symptoms in AD. Notably, the development of experimental drugs that specifically modulate these interactions may provide the opportunity to selectively affect those aspects of nAChR function that are affected in AD.

Accessing targeted nanoparticles to the brain: the vascular route

The blood-brain barrier (BBB), formed by brain capillary endothelial cells, prevents the entry of several drug molecules to the brain, especially molecules hydrophilic in nature. Advanced drug carriers like nanoparticles share the potential to allow entry of therapeutic proteins and genetic molecules into the central nervous system (CNS). Taking a targeting approach by conjugating molecules acting as ligands or monoclonal antibodies with affinity for proteins expressed on the luminal side of brain capillary endothelial cells, the nanoparticles can be designed to enable transport into the brain endothelium, or perhaps even through the endothelium leading to blood to brain transport. Currently, the iron-binding protein transferrin or antibodies raised against the transferrin receptor denote the most feasible molecule for targeting purposes at the BBB. This manuscript reviews the targetability of nanoparticles to the brain capillary endothelial cells, how nanocarriers may enter and transfer through the brain endothelium, and how likely restraints denoted by the threedimensional mesh of the extracellular proteins forming the brain capillary basement membrane challenge the possibilities for enabling transport of large molecules through the BBB encapsulated in nanoparticles.

α7 and β2 Nicotinic Acetylcholine Receptor Subunits Form Heteromeric Receptor Complexes that Are Expressed in the Human Cortex and Display Distinct Pharmacological Properties

The existence of α7β2 nicotinic acetylcholine receptors (nAChRs) has recently been demonstrated in both the rodent and human brain. Since α7-containing nAChRs are promising drug targets for schizophrenia and Alzheimer’s disease, it is critical to determine whether α7β2 nAChRs are present in the human brain, in which brain areas, and whether they differ functionally from α7 nAChR homomers. We used α-bungarotoxin to affinity purify α7-containing nAChRs from surgically excised human temporal cortex, and found that α7 subunits co-purify with β2 subunits, indicating the presence of α7β2 nAChRs in the human brain. We validated these results by demonstrating co-purification of β2 from wild-type, but not α7 or β2 knock-out mice. The pharmacology and kinetics of human α7β2 nAChRs differed significantly from that of α7 homomers in response to nAChR agonists when expressed in Xenopus oocytes and HEK293 cells. Notably, α7β2 heteromers expressed in HEK293 cells display markedly slower rise and decay phases. These results demonstrate that α7 subunits in the human brain form heteromeric complexes with β2 subunits, and that human α7β2 nAChR heteromers respond to nAChR agonists with a unique pharmacology and kinetic profile. α7β2 nAChRs thus represent an alternative mechanism for the reported clinical efficacy of α7 nAChR ligands.

The relative influence of local to regional drivers of variation in reef fishes

In this study, fishes and habitat attributes were quantified, four times over 1 year, on three reefs within four regions encompassing a c. 6° latitudinal gradient across south-western Australia. The variability observed was partitioned at these spatio-temporal scales in relation to reef fish variables and the influence of environmental drivers quantified at local scales, i.e. at the scale of reefs (the number of small and large topographic elements, the cover of kelp, fucalean and red algae, depth and wave exposure) and at the scale of regions (mean and maximum nutrient concentrations and mean seawater temperature) with regard to the total abundance, species density, species diversity and the multivariate structure of reef fishes. Variation in reef fish species density and diversity was significant at the regional scale, whereas variation in the total abundance and assemblage structure of fishes was also significant at local scales. Spatial variation was greater than temporal variation in all cases. A systematic and gradual species turnover in assemblage structure was observed between adjacent regions across the latitudinal gradient. The cover of red algae within larger patches of brown macroalgae (a biological attribute of the reef) and the number of large topographic elements (a structural attribute of the reef) were correlated with variation observed at local scales, while seawater temperature correlated with variation at the scale of regions. In conclusion, conservation efforts on reef fishes need to incorporate processes operating at regional scales with processes that shape local reef fish communities at local scales.

Pharmacokinetics of repaglinide in healthy caucasian and Japanese subjects

The objective of this study was to investigate the pharmacokinetics of three different single doses (0.5, 1.0, and 2.0 mg) of repaglinide in healthy Caucasian and Japanese subjects. In this single-center, open-label, randomized, three-period crossover study, 27 healthy male subjects (15 Caucasian and 12 Japanese) each received three different single doses of repaglinide (0.5, 1.0, and 2.0 mg) at consecutive 24-hour intervals. Pharmacokinetic profiles, including area under the curve (AUC0-t), maximum serum concentration (Cmax), time to Cmax (tmax), and half-life (t1/2), were determined for each dose of repaglinide. The relative change in blood glucose level (RC1h) and area under the blood glucose curve (AUGC0-1) at 1 hour after dose were also measured. After oral dosing, both Cmax and AUC0-t increased linearly with dose within the 0.5- to 2.0-mg dose range, regardless of ethnic group. Both Cmax and AUC0-t were significantly higher in Japanese subjects than in Caucasian subjects. At each dose of repaglinide, Cmax and AUC were statistically significantly higher in Japanese than in Caucasian subjects (p = 0.0038 and 0.023, respectively). Discrepancies in body weight and body mass index (BMI) between Caucasian and Japanese subjects could not explain the between-group differences in Cmax or AUC0-t. Statistically significant differences in pharmacodynamic parameters (RC1h and AUGC0-1) were found between ethnic groups (p < 0.0001), the difference being more pronounced for RC1h than AUGC0-1. At a dose of 2.0 mg, the mean decrease in RC1h was 41% for Japanese subjects and 24% for Caucasian subjects. Hypoglycemic reactions were more common at the highest dose (2.0 mg), where they were observed more frequently in Japanese (7 cases) than in Caucasian subjects (4 cases). It was concluded that higher serum levels of repaglinide and greater reductions in blood glucose levels are found in Japanese than in Caucasian subjects following a single oral dose of repaglinide within the 0.5- to 2.0-mg dose range. Repaglinide is well tolerated in both ethnic groups. The results indicate that glycemic control targets may be achieved at lower doses within the recommended range (0.5-4.0 mg/meal) when repaglinide is used to treat Japanese patients in comparison to Caucasian patients.

Pharmacokinetics and safety of FFR-rFVIIa after single doses in healthy subjects

FFR-rFVIIa is an antithrombotic agent, which has also proven to have antirestenotic properties in animal models. FFR-rFVIIa is a modified recombinant FVIIa in which the catalytic site is irreversibly inactivated by a synthetic tripeptide covalently bound with the FVIIa molecule. The modified rFVIIa retains its tissue factor (TF) binding capacity but is otherwise enzymatically inactive. A double-blind, placebo-controlled, randomized dose escalation trial was conducted to investigate eight single i.v. doses of FFR-rFVIIa (0.01, 0.02, 0.05, 0.08, 0.12, 0.18, 0.27, or 0.40 mg/kg body weight) in healthy male volunteers (n = 62). Safety, pharmacokinetics, and pharmacodynamics of FFR-rFVIIa were assessed. Mean (SD)AUC0-infinity ranged from 0.35 (0.11) to 28.8 (3.5)microg.h/ml, and mean Cmax ranged from 0.078 (0.019) to 4.8 (0.7) microg/ml. The mean elimination half-life ranged from 3.8 to 5.8 hours. Mean AUC0-infinity increased with increasing dose levels. Cmax appeared to be proportional to the dose level, with the exception of the lowest dose level. A dose-dependent prolongation of the prothrombin time was found, demonstrating that FFR-rFVIIa inhibited coagulation via the TF-dependent pathway FFR-rFVIIa was generally well tolerated at all dose levels studied.

The pharmacokinetics, pharmacodynamics, safety and tolerability following 7 days daily oral treatment with NN703 in healthy male subjects

The aim of the present study was to assess the safety, pharmacokinetics and pharmacodynamics (including specificity) of NN703 (tabimorelin), a growth hormone (GH) secretagogue, in healthy male subjects following treatment for 7 days once-daily. This was a randomized, double-blind and placebo-controlled study with four active dose levels: 1.71, 3.0, 4.5 and 6.86 mg/kg body weight. There was a dose-related increase for GH area under the curve (AUC) (0-12 h) and GH C(max)(0--12 h); these were significantly higher on both days 1 and 7 as compared with placebo treatment (P = 0.04 to P< 0.0001); however, an overall significant decrease in GH release was found from day 1 to day 7 (P< 0.001). Insulin-like growth factor-I (IGF-I) and IGF binding protein 3 (IGFBP-3) increased at all dose levels (including placebo); however, a significantly higher increase as compared with placebo treatment was observed at the three highest dose levels for IGF-I (P = 0.04--0.0006) and at the highest dose level for IGFBP-3 (P = 0.03). There was no statistically significant increase in AUC (0-5 h) for follicle-stimulating hormone, luteinizing hormone and cortisol between active and placebo treatment for day 1 or 7. On day 1 only, a statistically significant increase in AUC (0--5 h) was found for prolactin at 1.71 and 6.86 mg/kg (P< 0.05), for thyroid-stimulating hormone (TSH) at 3.0 mg/kg (P< 0.01) and for adrenocorticotrophic hormone (ACTH) at 4.5 mg/kg (P< 0.05); however, no dose--response relationship was observed for TSH or ACTH. In addition, a statistically significant decrease in AUC (0--5 h) for ACTH (3.0 and 6.86 mg/kg) and cortisol (1.71 mg/kg) was observed on day 7 (P< 0.05). Thus, NN703 is a promising candidate for treatment of absolute or relative GH deficiency.

The pharmacokinetics, pharmacodynamics, safety and tolerability of a single dose of NN703, a novel orally active growth hormone secretagogue in healthy male volunteers

The aim of the present study was to investigate the pharmacodynamics, pharmacokinetics, safety and tolerability of a single dose of NN703 (tabimorelin), a growth hormone secretagogue in healthy male subjects. The study design was double blind, randomized and placebo-controlled, with eight escalating dose levels (0.05-12 mg/kg bodyweight (BW)). NN703 was well tolerated by the subjects. The GH area under the curve (AUC) (0-24 h) was significantly higher when compared to placebo for the three highest dose levels (3.0 mg/kg: P = 0.027, 6.0 mg/kg: P = 0.0023, 12 mg/kg: P< 0.0001), and for GH maximal concentration C(max)the four highest dose levels were also significantly higher when compared to placebo (1.5 mg/kg: P = 0.04, 3.0 mg/kg: P = 0.0143, 6.0 mg/kg: P = 0.0053, 12 mg/kg: P = 0.0007). Furthermore, there was a significant increase in IGF-1 levels when compared to placebo for the 6.0 and 12.0 mg/kg BW dose levels (P< 0. 0001). Statistical analysis comparing the AUC (0-24 h) of the NN703 (four highest dose levels) and placebo-treated groups showed no significant increases following NN703 for ACTH, LH, FSH, TSH, prolactin, and cortisol, however, subtle individual changes were noted in ACTH, cortisol and prolactin at doses above 3.0 mg/kg. In conclusion, NN703 is a promising potential candidate for treatment of GH deficiency/insufficiency.

Cardiac effects of co-artemether (artemether/lumefantrine) and mefloquine given alone or in combination to healthy volunteers

Co-artemether is an oral tablet of artemether (20 mg) and lumefantrine (120 mg) for the treatment of falciparum malaria. Administration in the presence of mefloquine is likely, as co-artemether may be used following failure of antimalarial prophylaxis or treatment with mefloquine.

OBJECTIVE

The effects on the QTc interval were compared among treatment with three doses of mefloquine (500, 250, 250 mg over 12 h) followed by six doses of co-artemether (6 x 4 tablets over 60 h) and either treatment alone. The study was performed in a randomised, double-blind, parallel group design in 14 healthy male subjects per dose group.

METHODS

Electrocardiograms (ECGs) were recorded before dosing and repeatedly thereafter. The Bazett formula was used to calculate the QTc interval. The maximum and average QTc intervals for the first, third and sixth dosing intervals of co-artemether treatment were compared among treatments. Drug plasma concentrations were determined at identical times with the ECG recordings for exploratory pharmacokinetic/pharmacodynamic evaluation.

RESULTS

No clinically relevant differences in the QTc interval were observed after sequential administration of mefloquine and co-artemether relative to either treatment given alone, and there were no clinically relevant study drug-related effects on the QTc interval after either treatment. Plasma drug measurements revealed adequate systemic exposure to artemether, dihydroartemisinin, lumefantrine and mefloquine, well in line with the clinical setting. No correlation between the length of the QTc interval and plasma drug concentrations was found for any of the compounds.

CONCLUSIONS

Untoward effects on the QTc interval are unlikely to occur when co-artemether is administered following prophylaxis or treatment with mefloquine.

Pharmacokinetic interaction trial between co-artemether and mefloquine

Forty-two healthy subjects were randomized in a parallel three-group design trial to investigate potential electrocardiographic and pharmacokinetic interactions between the new antimalarial co-artemether, a combination of artemether and lumefantrine (both of which are predominantly metabolized through CYP3A4), and mefloquine, another antimalarial described as a substrate (and possible inhibitor) of CYP3A4. Subjects were assigned to one of the three possible treatment groups (i.e., co-artemether alone or mefloquine alone or the combination of both). The dosage was 1000 mg mefloquine (divided into three doses over 12 h) followed 12 h later by six applications of co-artemether (40 mg artemether+480 mg lumefantrine each) over 60 h. The study medications were generally well tolerated after all treatments. Concomitant administration with mefloquine caused statistically significant lower (around 30-40%) plasma concentrations of lumefantrine than when co-artemether was administered alone. Even if important, this decrease in lumefantrine exposure was considered unlikely to impact clinical efficacy given the wide therapeutic index of co-artemether and the usual high variability in lumefantrine plasma levels, mostly and more importantly influenced by food intake. However, patients should be encouraged to eat at dosing times to compensate for this decreased bioavailability. The pharmacokinetics of artemether, DHA or mefloquine were not affected. Artemether concentrations significantly decreased over doses, independently of mefloquine co-administration, while DHA concentrations slightly (not significantly) increased. Therefore, no clinically relevant risks due to pharmacokinetic drug-drug interaction are expected at the enzymatic level following co-administration of co-artemether with CYP3A4 substrates with similar affinity to that of mefloquine.

Drug interaction studies with repaglinide: repaglinide on digoxin or theophylline pharmacokinetics and cimetidine on repaglinide pharmacokinetics

Drug interaction studies were carried out to ensure that hypoglycemia due to inhibition of repaglinide elimination or chronic hyperglycemia due to inhibition of repaglinide absorption was avoided. Conversely, the effects of repaglinide on the pharmacokinetics of drugs with only a narrow margin between effective and toxic concentrations, such as digoxin or theophylline, were determined. The studies reported here compared monotherapy with combined therapies in healthy volunteers. There were no significant differences between the pharmacokinetic parameters of repaglinide when given as monotherapy and when administered concurrently with cimetidine. Similarly, the coadministration of repaglinide and digoxin did not influence the pharmacokinetics of digoxin administered alone. When repaglinide was coadministered with theophylline, the only pharmacokinetic change was that the peak plasma theophylline concentration was slightly reduced. No direct drug-drug interactions were found in these studies, suggesting that repaglinide may be coprescribed with cimetidine, digoxin, or theophylline at the dosage used for monotherapy.

Lack of pharmacokinetic interaction between tiagabine and erythromycin

This study was conducted to investigate the effects on the pharmacokinetics of tiagabine at steady state when coadministered with therapeutic doses of erythromycin. Tiagabine doses of 4 mg twice daily and erythromycin doses of 500 mg twice daily were administered for 4 days in an open-label, crossover, two-period interaction trial in 13 healthy volunteers. No statistically significant differences in maximum plasma concentration (Cmax), area under the concentration-time curve (AUC tau), or half-life (t1/2) of tiagabine were observed when tiagabine was administered alone or in combination with erythromycin. A statistically significant treatment effect was observed for time to maximum concentration (tmax; 0.72 after tiagabine alone versus 0.56 hours after administration with erythromycin). No statistically significant differences were seen between men and women except in tmax and t1/2; these differences were thought to be of no clinical significance. The decrease in tmax seen in women in this study is interpreted as a differential effect of erythromycin on gastric emptying of females and not as an interaction between tiagabine and erythromycin. No changes in laboratory parameters or vital signs were attributable to trial medication. The most common treatment-emergent adverse events that were possibly related to trial medication were central nervous system effects (e.g., headache, dizziness); all adverse events were transient, the majority were rated mild in severity, and did not require additional action. Coadministration of erythromycin in healthy subjects does not significantly affect the pharmacokinetics of tiagabine at the doses tested.

Benzene-induced genotoxicity in mice in vivo detected by the alkaline comet assay: reduction by CYP2E1 inhibition

The myelotoxic and genotoxic effects of benzene have been related to oxidative DNA damage after metabolism by CYP2E1. Single cell gel electrophoresis (alkaline comet assay) detects DNA damage and may thus be a convenient method for the study of benzene genotoxicity. Benzene exposure to NMRI mice as a single oral gavage at 40, 200 or 450 mg/kg resulted in dose-related DNA damage indicated by an increased comet tail length of peripheral blood lymphocytes and bone marrow nucleated cells sampled 6 h after exposure. After a dose of 40 mg/kg, there was a 1.6-fold increase of 'tail length' in bone marrow nucleated cells in comparison with the control (p < 0.01). There was no significant increase in DNA damage in peripheral blood lymphocytes in the same animals. At 200 mg/kg, the tail length was 4.8-fold and 4.0-fold increased in the two cell types, respectively (p < 0.01). At 450 mg/kg, the tail length was further increased to 5.4-fold and 6.6-fold of the control values, respectively (p < 0.01). Pretreatment with propylene glycol (5 microliters/g b.wt., twice with a 60-min interval), a selective CYP2E1 inhibitor, reduced the increase in the tail length by about half at all doses in both cell types (p < 0.01). By comparing our data with those from genotoxicity studies on benzene using other methods, we conclude that the 'alkaline comet assay' is a sensitive method to detect DNA damage induced by benzene. We also infer that CYP2E1 contributes, at least partly, to the formation of the 'comet'-inducing metabolites in the chosen cell types.

Cytochrome P4502E1 inhibition by propylene glycol prevents acetaminophen (paracetamol) hepatotoxicity in mice without cytochrome P4501A2 inhibition

Acetaminophen hepatotoxicity is associated with its biotransformation to the reactive metabolite N-acetyl-p-benzoquinone imine that binds to protein. Two forms of cytochrome P450, CYP2E1 and CYP1A2, have been implicated as primarily responsible for the bioactivation. To determine the relative contributions of these P450's, overnight fasted male NMRI mice were pretreated with 10 ml of 50% v/w propylene glycol/kg or fluvoxamine (10 mg/kg) at -80 and -20 min. relative to acetaminophen dosing to inhibit CYP2E1 and CYP1A2, respectively. Mice were sacrificed at 0.5 or 4 hr after a hepatotoxic dose of acetaminophen (300 mg/kg). Propylene glycol or propylene glycol plus fluvoxamine, but not fluvoxamine alone protected against acetaminophen hepatotoxicity as indicated by abolished increase in serum alanine aminotransferase activity, less depletion of hepatic glutathione and lower liver:body weight ratios. Propylene glycol inhibited the activity of CYP2E1 as indicated by 84% reduction in the clearance of 3 mg/kg dose of chlorzoxazone, whereas fluvoxamine inhibited the activity of CYP1A2 as indicated by 40% reduction in the clearance of a 10 mg/kg dose of caffeine. For this animal model, the data are consistent with the notion that hepatoxicity is associated with bioactivation of acetaminophen by CYP2E1 but not by CYP1A2.

Heteroteansplantation of a human mammary carcinoma to the mouse mutant nude

A human mammary carcinoma was heterotransplanted to athymic nude mice. Viable tumour tissue was maintained throughout the observation periods which, because of the limited life span of nude mice, were relatively short; in one animal surviving for a longer period, actual tumour growth was observed. It is concluded that human mammary carcinoma is capable of growing in nude mice but, because of the frequently low growth rate of these tumours, prolonged periods of observation are required in order to reveal such growth.