Comparative antidopaminergic properties of thioridazine, mesoridazine and sulforidazine on the corpus striatum

The functional antidopaminergic potencies of the atypical antipsychotic drug thioridazine (THD), as well as its active metabolites mesoridazine (MES) and sulforidazine (SUL), were assessed by testing their blockade of the inhibitory effects of endogenous dopamine (DA) or apomorphine on the electrically evoked release of radiolabeled DA and acetylcholine (ACh) from perfused rabbit striatal slices. These functional comparisons (reflecting presynaptic and postsynaptic DA receptors, respectively) were correlated with potency estimations of these drugs in competing for D2 DA receptors (i.e., [3H]spiperone binding sites) in rabbit striatal homogenates. Similar orders of potency (SUL greater than MES much greater than THD) were found for blockade of pre- and postsynaptic DA receptors modulating DA and ACh release, respectively, as well as in competing for [3H]spiperone binding sites in the striatum. MES, SUL and haloperidol were 2 to 3 times more potent at DA release modulatory receptors than postsynaptic DA receptors. In contrast, THD was 8 times more potent at antagonizing the apomorphine-induced inhibition of DA release than against apomorphine's effect on ACh release. THD was virtually inactive in antagonizing the inhibition of ACh release induced when nomifensine was used to increase endogenous synaptic DA, despite significantly antagonizing these effects on DA release in the same slices. Together, these data indicate that: 1) MES and SUL are responsible for a significant part of the antidopaminergic effects attributed to THD; 2) THD should produce less cholinergic activation than other neuroleptics; and 3) that nonreceptor-mediated effects at high THD concentrations may mask effects due to receptor blockade.     

Effects of BMY 14802, a potential antipsychotic drug, on rat brain dopaminergic function

The potential neuroleptic alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine-butanol HCl (BMY 14802-1) was tested for its effects on mesotelencephalic dopamine (DA) neurons in albino rats. BMY 14802-1 increased DA turnover in DA terminal regions, increased nigral DA neuronal impulse flow and blocked the behavioral stimulation and inhibition of DA neuronal impulse flow caused by DA agonists. BMY 14802-1 also increased tyrosine hydroxylase activity in vivo but did not directly affect tyrosine hydroxylase activity in vitro. In contrast to these findings, BMY 14802-1 did not cause catalepsy at any dose and reversed catalepsy produced by haloperidol. BMY 14802-1 did not block DA autoreceptors on either DA neuron soma/dendrites or on striatal nerve terminals, as assessed by inhibition of DA neuronal impulse flow by microiontophoresed DA and by inhibition of tyrosine hydroxylase activity by apomorphine, respectively. BMY 14802-1 had very low affinity for striatal D-2 receptors (IC50 greater than 10(-5) M) as determined by displacement of [3H]spiperone binding in vitro. Finally, BMY 14802-1 increased impulse flow of nigral DA neurons after pretreatment with haloperidol but had no effect on impulse flow when microiontophoresed directly onto DA neurons. It is concluded that BMY 14802-1 blocked DA-mediated effects in the mesostriatal and mesocortical/limbic systems through a non-DA receptor mechanism. BMY 14802-1 has potential as a neuroleptic with little indication of extrapyramidal motor effects.     

Peripheral airways as a determinant of ventilatory function in the human lung.

We have investigated the morphological differences responsible for the variability in two tests of pulmonary function, maximal expiratory flow rates (MEF) and the frequency dependence of dynamic compliance (CDYN ratio). Functional measurements were obtained from 53 normal and minimally diseased postmortem human lungs. Morphological measurements performed on these same lungs included airway diameter at three levels in the bronchial tree, the amount of bronchial gland mass, and the alveolar surface to volume ratio. Multiple regression analysis suggests that the diameter of the peripheral conduction airways (membranous bronchioles) is the major morphological determinant for both MEF and the CDYN ratio in lungs at any particular age. Age-dependent changes in both functional tests were associated primarily with differences in the alveolar surface to volume ratio. Minimal emphysema and a lesion associated with cigarette smoking, respiratory bronchiolitis, have no demonstrable effect on either MEF or the CDYN ratio. These studies provide further evidence that the peripheral conducting airways are a major determinant of ventilatory function in the normal human lung.     

Effects of dose, age, inhibition of metabolism and elimination on the toxicokinetics of 2-butoxyethanol and its metabolites

Acute exposure to 2-butoxyethanol (BE) causes dose- and age-dependent hemolytic anemia in rats. Recently, we have shown that butoxyacetic acid (BAA) is the proximate hemolytic agent and that inhibition of alcohol or aldehyde dehydrogenases protected rats against BE-induced hemolytic anemia. In the present investigations, the kinetics of 14C-BE metabolism and clearance were studied in control adult (3-4 months old) and old (12-13 months old) male F344 rats and in adult male F344 rats treated with pyrazole, cyanamide or probenecid. Our results showed that the area under the curve (AUC), maximum plasma concentration (Cmax) and systemic clearance (Cls) of BE were dose-dependent. In contrast, there was no effect of dose on half-life (T1/2) or volume of distribution (Vd) of BE. These results also showed that there was no age effect on T1/2, Vd or Cls of BE. However, Cmax and AUC of BE increased as a function of age. Also, analysis of variance indicated no significant interactions (P less than or equal to .05) between dose and age in relation to BE kinetics. As expected, inhibition of BE metabolism by pretreatment of rats with pyrazole or cyanamide resulted in a significant increase in the T1/2 and AUC of BE, whereas it caused a significant decrease in the Cls. Furthermore, pyrazole had no effect, whereas cyanamide had decreased Vd of BE. Analysis of the toxicokinetic parameters of BAA revealed that T1/2, AUC and Cmax of BAA were directly related to the age of the rats and the dose of BE administered.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of phenylalanine and its metabolites on the metabolism of leucocytes and lymphocytes.

1. The pathogenesis of the mental retardation in phenylketonuria remains obscure. Leucocytes have proved of value in the study of other inborn errors of metabolism. The lymphocyte is a suitable model cell for the study of mammalian metabolism, because of its ability to divide in vitro in response to various stimuli. 2. We have examined the effects of phenylalanine, phenylpyruvate, phenyl-lactate and phenylacetate on the human leucocyte and the resting and phytohaemagglutinin-stimulated rabbit lymphocyte. 3. Phenylpyruvate and phenyl-lactate reduced acetate incorporation into leucocyte lipid by 38% and 48% respectively. Only phenyl-lactate reduced acetate incorporation into the resting and stimulated lymphocyte, by 20% and 34% respectively. 4. Glucose incorporation into leucocyte lipid was unaffected by phenylalanine, phenylpyruvate and phenyl-lactate. Only phenyl-lactate inhibited (46%) the production of CO2 from glucose. 5. Phenylalanine and leucine incorporation into trichloroacetic acid-insoluble material of resting and stimulated lymphocytes was inhibited by phenyl-lactate (10-42%), phenylpyruvate (27-57%) and phenylacetate (19-39%). 6. Uridine incorporation into resting and stimulated cells was inhibited by phenyl-lactate (22-26%), phenylpyruvate (42-52%) and phenylacetate (20%). 7. Thymidine incorporation into resting lymphocytes was reduced by phenyl-lactate, phenylpyruvate, phenylacetate and phenylalanine by 12-26%. Incorporation into the stimulated cell was inhibited by phenylpyruvate and phenyl-lactate (90%) and phenylacetate (66%). 8. Phenylalanine inhibited lymphocyte pyruvate kinase and phenylpyruvate inhibited citrate synthetase. 9. These results are compared with published data relating to experimental hyperphenylalaninaemia and the effects of these metabolites on nervous tissue in vitro.     

Effects of cimetidine and ranitidine on hepatic drug metabolism

Cimetidine has been shown to impair elimination of a number of drugs metabolized by the hepatic mixed-function oxidase enzymes. It is uncertain whether this is related to its histamine H2-receptor antagonism or to its intrinsic structure. Ranitidine is a more potent H2-receptor antagonist and has a completely different structure. Cimetidine (1 gm/day for 7 days) induced a 23% and 35% fall in mean systemic clearance of antipyrine and theophylline, whereas ranitidine (300 mg/day 7 days) had no significant effect on the clearance of either drug. Our data suggest that the inhibition of drug metabolism by cimetidine is not related to histamine H2-receptor antagonism.     

Effects of renal failure on drug transport and metabolism

Renal failure not only alters the renal elimination, but also the non-renal disposition of drugs that are extensively metabolized by the liver. Although reduced metabolic enzyme activity in some cases can be responsible for the reduced drug clearance, alterations in the transporter systems may also be involved in the process. With the development of renal failure, the renal secretion of organic ions mediated by organic anion transporters (OATs) and organic cation transporters (OCTs) is decreased. 3-Carboxy-4-methyl-5-propyl-2-furanpropanoic acid (CMPF) and other organic anionic uremic toxins may directly inhibit the renal excretion of various drugs and endogenous organic acids by competitively inhibiting OATs. In addition, the expression of OAT1 and OCT2 was reduced in chronic renal failure (CRF) rats. Renal failure also impairs the liver uptake of drugs and organic anions, such as bromosulphophthalein (BSP), indocyanine green (ICG), and thyroxine, where organic anion transport polypeptides (OATPs) are the major transporters. Most previous studies have been done in animals or cell culture, very often in rat models, but these are presumed to reflect the presentation of advanced renal disease in humans as well. Recent studies demonstrate that the uremic toxins CMPF and indoxyl sulfate (IS) can directly inhibit rOatp2 and hOATP-C in hepatocytes. The protein content of the liver uptake transporters Oatp1, 2, and 4 were significantly decreased in CRF rats. Decreased activity of the intestinal efflux transporter, P-glycoprotein (P-gp), was also observed in CRF rats, with no significant change of protein content, suggesting that uremic toxins may suppress P-gp function. However, increased protein levels of multidrug resistance-associated protein (MRP) 2 in the kidney and MRP3 in the liver were found in CRF rats, suggesting an adaptive response that may serve as a protective mechanism. Increases in drug areas under the curve (AUCs) in subjects with advanced renal disease for drugs that are not renally excreted are consistent with uremic toxin effects on either intestinal or hepatic cell transporters, metabolizing enzymes, or both. In conclusion, alterations of drug transporters, as well as metabolic enzymes, in patients with renal failure can be responsible for reduced drug clearance.     

Discriminative stimulus effects of intravenous heroin and its metabolites in rhesus monkeys: opioid and dopaminergic mechanisms

Heroin has characteristic subjective effects that contribute importantly to its widespread abuse. Drug discrimination procedures in animals have proven to be useful models for investigating pharmacological mechanisms underlying the subjective effects of drugs in humans. However, surprisingly little information exists concerning the mechanisms underlying the discriminative stimulus (DS) effects of heroin. This study characterized the DS effects of heroin in rhesus monkeys trained to discriminate i.v. heroin from saline. In drug substitution experiments, heroin, its metabolites 6-monoacetylmorphine, morphine, morphine-6-glucuronide, and morphine-3-glucuronide, and the mu-agonists fentanyl and methadone engendered dose-dependent increases in heroin-lever responding, reaching average maximums of >80% (full substitution) at doses that did not appreciably suppress response rate. In contrast, the delta-agonist SNC 80, the kappa-agonist spiradoline, and the dopamine uptake blockers/releasers cocaine, methamphetamine, and GBR 12909 did not engender heroin-like DS effects regardless of dose. In antagonism studies, in vivo apparent pA2 and pK(B) values for naltrexone combined with heroin, morphine, and 6-monoacetylmorphine (8.0-8.7) were comparable with those reported previously for naltrexone antagonism of prototypical mu-agonists. The results show that the DS effects of heroin are pharmacologically specific and mediated primarily at mu-opioid receptors. Moreover, the acetylated and glucuronated metabolites of heroin appear to play significant roles in these effects. Despite previous speculation that morphine-3-glucuronide lacks significant opioid activity, it substituted fully for heroin in our study, suggesting that it can exhibit prominent mu-agonist effects in vivo.     

Plasma levels of thioridazine and metabolites are influenced by the debrisoquin hydroxylation phenotype

The pharmacokinetics of thioridazine and its metabolites were studied in 19 healthy male subjects: 6 slow and 13 rapid hydroxylators of debrisoquin. The subjects received a single 25 mg oral dose of thioridazine, and blood samples were collected during 48 hours. Concentrations of thioridazine and metabolites in serum were measured by HPLC. Slow hydroxylators of debrisoquin obtained higher serum levels of thioridazine with a 2.4-fold higher Cmax and a 4.5-fold larger AUC(0-infinity) associated with a twofold longer half-life compared with that of rapid hydroxylators. The side-chain sulphoxide (mesoridazine) and sulphone (sulphoridazine), which are active metabolites, appeared more slowly in serum and had lower Cmax values, but comparable AUC. The thioridazine ring-sulphoxide attained higher Cmax and 3.3-fold higher AUC in slow hydroxylators than in rapid hydroxylators of debrisoquin. Thus the formation of mesoridazine from thioridazine and the 4-hydroxylation of debrisoquin seem to be catalyzed by the same enzyme, whereas the formation of thioridazine ring-sulphoxide is probably formed mainly by another enzyme.     

Acute and subchronic effects of MJ-13859, a potential antipsychotic drug, on rat brain dopaminergic function

The potential antipsychotic drug, MJ-13859, was tested for its acute and subchronic effects on rat brain dopaminergic neurotransmission and function. This drug exhibited an IC50 for displacement of [3H]spiperone binding of 6.35 nM which was similar to trifluoperazine, a potent classical antipsychotic drug. In female rats, MJ-13859 was slightly less potent than trifluoperazine for induction of catalepsy, inhibition of stimulant-induced hyperactivity and for increasing striatal, frontal cortical and olfactory tubercule dopamine metabolism. Both drugs also blocked dopamine autoreceptors on striatal dopamine nerve endings. When administered i.p., rather than s.c., the effect of MJ-13859 on dopamine metabolism was reduced significantly. When administered to male rats, the response of dopamine metabolism to drug was reduced, but a similar inhibition of stimulated activity occurred as in female rats. These results suggest a rapid first pass metabolism of MJ-13859 in the rat and that the antistimulant effect may be partly independent of the antidopaminergic effects. Osmotic minipumps were implanted s.c. for 2 week continuous infusion of MJ-13859 at doses of 1.0 or 3.0 mg/kg/day. Unlike classical antipsychotic drugs, MJ-13859 did not cause a subsensitivity to the ability of acute haloperidol challenge (0.1 mg/kg s.c.) to increase dopamine metabolism. After allowing a 4-day drug washout period before [3H]spiperone binding assay for D2 receptors, neither the maximum binding nor Kd were altered in rats treated for 2 weeks with 3.0 mg/kg/day of MJ-13859. Haloperidol at 1.0 mg/kg/day for 2 weeks caused a 57% increase in D2 receptor maximum binding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of tricyclic antidepressants on drug metabolism.

The effects of chronic treatment with amitriptyline and nortriptyline on the elimination from plasma of warfarin, dicumarol, phenytoin, and tolbutamide were examined in man. No alteration of plasma half-life of warfarin, phenytoin, or tolbutamide was observed following dosage with the tricyclic antidepressants used. There was no consistent effect on the metabolism of dicumarol following treatment with amitriptyline or nortriptyline although the bioavailability of dicumarol appeared to be increased. In some subjects, this increased bioavailability was associated with significant prolongation of the plasma half-life of dicumarol due to its dose-dependent kinetics.     

Modulation of 4E-BP1 function as a critical determinant of enzastaurin-induced apoptosis

Enzastaurin (LY317615.HCl) is currently in a phase III registration trial for diffuse large B-Cell lymphoma and numerous phase II clinical trials. Enzastaurin suppresses angiogenesis and induces apoptosis in multiple human tumor cell lines by inhibiting protein kinase C (PKC) and phosphoinositide 3-kinase (PI3K)/AKT pathway signaling. PI3K/AKT pathway signaling liberates eukaryotic translation initiation factor 4E (eIF4E) through the hierarchical phosphorylation of eIF4E binding proteins (4E-BP). When hypophosphorylated, 4E-BPs associate with eIF4E, preventing eIF4E from binding eIF4G, blocking the formation of the eIF4F translation initiation complex. Herein, we show that enzastaurin treatment impacts signaling throughout the AKT/mTOR pathway leading to hypophosphorylation of 4E-BP1 in cancer cells of diverse lineages (glioblastoma, colon carcinoma, and B-cell lymphoma). Accordingly, enzastaurin treatment increases the amount of eIF4E bound to 4E-BP1 and decreases association of eIF4E with eIF4G, thereby reducing eIF4F translation initiation complex levels. We therefore chose to evaluate whether this effect on 4E-BP1 was involved in enzastaurin-induced apoptosis. Remarkably, enzastaurin-induced apoptosis was blocked in cancer cells depleted of 4E-BP1 by siRNAs, or in 4EBP1/2 knockout murine embryonic fibroblasts cells. Furthermore, eIF4E expression was increased and 4E-BP1 expression was decreased in cancer cells selected for reduced sensitivity to enzastaurin-induced apoptosis. These data highlight the importance of modulating 4E-BP1 function, and eIF4F complex levels, in the direct antitumor effect of enzastaurin and suggest that 4E-BP1 function may serve as a promising determinant of enzastaurin activity.     

Effects of cocaine and its major metabolites on the HERG-encoded potassium channel

Cocaine abuse has been reported to result in QT prolongation in humans; however, the mechanisms underlying this effect are still poorly understood. In this study we compared the direct effects of cocaine and its major metabolites in human embryonic kidney 293 cells stably transfected with human ether-a-go-go-related gene (HERG). Cocaine blocked HERG-encoded potassium channels with an IC50 of 4.4 +/- 1.1 microM (22 degrees C). Cocaethylene (a metabolite formed in the presence of ethanol) had a significantly lower IC50 of 1.2 +/- 1.1 microM (P < 0.0001), and cocaine's primary pyrolysis metabolite methylecgonidine blocked HERG with a higher IC50 of 171.7 +/- 1.2 microM. In contrast, 1 mM ecgonine methylester or benzoylecgonine produced only a minimal block (21 +/- 4 and 15 +/- 8%, respectively). Blockade of HERG by cocaine, cocaethylene, and methylecgonidine increased significantly over the voltage range where HERG activates, but became constant at voltages where HERG activation was maximal, indicating that all three drugs block open channels, but by a mechanism that is not highly sensitive to voltage per se. Cocaine and cocaethylene also significantly slowed the time course of deactivation at -60 mV, an effect consistent with open channel block. We conclude that cocaethylene is slightly more potent than cocaine as a blocker of HERG, whereas methylecgonidine has much lower potency, and both benzoylecgonine and ecgonine methyl ester are essentially inactive at clinically relevant concentrations.     

Effects of the anti-migraine drug sumatriptan on muscle energy metabolism: relationship to side-effects

Sumatriptan succinate (Imitrex) is a 5-HT (5-hydroxytryptamine) agonist used for relief of migraine symptoms. Some individuals experience short-lived side-effects, including heaviness of the limbs, chest heaviness and muscle aches and pains. The effects of this drug on skeletal muscle energy metabolism were studied during short submaximal isometric exercises. We studied ATP flux from anaerobic glycolysis (An Gly), the creatine kinase reaction (CK) and oxidative phosphorylation (Ox Phos) using 31P nuclear magnetic resonance spectroscopy (31P MRS) kinetic data collected during exercise. It was found that side-effects induced acutely by injection of 6 mg sumatriptan succinate s.c. were associated with reduced oxygen storage in peripheral skeletal muscle 5-20 min after injection as demonstrated by a transient reduction in mitochondrial function at end-exercise. These results suggest that mild vasoconstriction in peripheral skeletal muscle is associated with the action of sumatriptan and is likely to be the source of the side-effects experienced by some users. Migraine with aura patients were more susceptible to this effect than migraine without aura patients.