The Caenorhabditis elegans DEG-3/DES-2 Channel Is a Betaine-Gated Receptor Insensitive to Monepantel

Natural plant compounds, such as betaine, are described to have nematocidal properties. Betaine also acts as a neurotransmitter in the free-living model nematode Caenorhabditis elegans, where it is required for normal motility. Worm motility is mediated by nicotinic acetylcholine receptors (nAChRs), including subunits from the nematode-specific DEG-3 group. Not all types of nAChRs in this group are associated with motility, and one of these is the DEG-3/DES-2 channel from C. elegans, which is involved in nociception and possibly chemotaxis. Interestingly, the activity of DEG-3/DES-2 channel from the parasitic nematode of ruminants, Haemonchus contortus, is modulated by monepantel and its sulfone metabolite, which belong to the amino-acetonitrile derivative anthelmintic drug class. Here, our aim was to advance the pharmacological knowledge of the DEG-3/DES-2 channel from C. elegans by functionally expressing the DEG-3/DES-2 channel in Xenopus laevis oocytes and using two-electrode voltage-clamp electrophysiology. We found that the DEG-3/DES-2 channel was more sensitive to betaine than ACh and choline, but insensitive to monepantel and monepantel sulfone when used as direct agonists and as allosteric modulators in co-application with betaine. These findings provide important insight into the pharmacology of DEG-3/DES-2 from C. elegans and highlight the pharmacological differences between non-parasitic and parasitic nematode species.

Genotypic characterisation of monepantel resistance in historical and newly derived field strains of Teladorsagia circumcincta

Recent reports of monepantel (MPTL) resistance in UK field isolates of Teladorsagia circumcincta has highlighted the need for a better understanding of the mechanism of MPTL-resistance in order to preserve its anthelmintic efficacy in this economically important species. Nine discrete populations of T. circumcincta were genotypically characterised; three MPTL-susceptible isolates, three experimentally selected MPTL-resistant strains and three field derived populations. Full-length Tci-mptl-1 gene sequences were generated and comparisons between the MPTL-susceptible isolates, MPTL-resistant strains and one field isolate, showed that different putative MPTL-resistance conferring mutations were present in different resistant isolates. Truncated forms of the Tci-mptl-1 gene were also observed. The genetic variability of individual larvae, within and between populations, was examined using microsatellite analyses at 10 'neutral' loci (presumed to be unaffected by MPTL). Results confirmed that there was little background genetic variation between the populations, global FST <0.038. Polymorphisms present in exons 7 and 8 of Tci-mptl-1 enabled genotyping of individual larvae. A reduction in the number of genotypes was observed in all MPTL-resistant strains compared to the MPTL-susceptible strains that they were derived from, suggesting there was purifying selection at Tci-mptl-1 as a result of MPTL-treatment. The potential link between benzimidazole (BZ)-resistance and MPTL-resistance was examined by screening individual larvae for the presence of three SNPs associated with BZ-resistance in the β-tubulin isotype-1 gene. The majority of larvae were BZ-susceptible homozygotes at positions 167 and 198. Increased heterozygosity at position 200 was observed in the MPTL-resistant strains compared to their respective MPTL-susceptible population. There was no decrease in the occurrence of BZ-resistant genotypes in larvae from each population. These differences, in light of the purifying selection at this locus in all MPTL-resistant isolates, suggests that Tci-mptl-1 confers MPTL-resistance in T. circumcincta, as in Haemonchus contortus, but that different mutations in Tci-mptl-1 can confer resistance in different populations.

Monepantel is a non-competitive antagonist of nicotinic acetylcholine receptors from Ascaris suum and Oesophagostomum dentatum

Zolvix^® is a recently introduced anthelmintic drench containing monepantel as the active ingredient. Monepantel is a positive allosteric modulator of DEG-3/DES-2 type nicotinic acetylcholine receptors (nAChRs) in several nematode species. The drug has been reported to produce hypercontraction of Caenorhabditis elegans and Haemonchus contortus somatic muscle. We investigated the effects of monepantel on nAChRs from Ascaris suum and Oesophagostomum dentatum heterologously expressed in Xenopus laevis oocytes. Using two-electrode voltage-clamp electrophysiology, we studied the effects of monepantel on a nicotine preferring homomeric nAChR subtype from A. suum comprising of ACR-16; a pyrantel/tribendimidine preferring heteromeric subtype from O. dentatum comprising UNC-29, UNC-38 and UNC-63 subunits; and a levamisole preferring subtype (O. dentatum) comprising UNC-29, UNC-38, UNC-63 and ACR-8 subunits. For each subtype tested, monepantel applied in isolation produced no measurable currents thereby ruling out an agonist action. When monepantel was continuously applied, it reduced the amplitude of acetylcholine induced currents in a concentration-dependent manner. In all three subtypes, monepantel acted as a non-competitive antagonist on the expressed receptors. ACR-16 from A. suum was particularly sensitive to monepantel inhibition (IC₅₀ values: 1.6 ± 3.1 nM and 0.2 ± 2.3 μM). We also investigated the effects of monepantel on muscle flaps isolated from adult A. suum. The drug did not significantly increase baseline tension when applied on its own. As with acetylcholine induced currents in the heterologously expressed receptors, contractions induced by acetylcholine were antagonized by monepantel. Further investigation revealed that the inhibition was a mixture of competitive and non-competitive antagonism. Our findings suggest that monepantel is active on multiple nAChR subtypes.

Inhibition of endopeptidase and exopeptidase activity of cathepsin B impairs extracellular matrix degradation and tumour invasion

Cathepsin B is a lysosomal cysteine protease that is implicated in a number of physiological processes, including protein turnover in lysosomes. Changes in its expression are associated with a variety of pathological processes, including cancer. Due to the structural feature, termed the occluding loop, cathepsin B differs from other cysteine proteases in possessing both, endopeptidase and exopeptidase activity. Here we investigated the impact of both cathepsin B activities on intracellular and extracellular collagen IV degradation and tumour cell invasion using new selective synthetic inhibitors, 2-{[(8-hydroxy-5-nitroquinoline-7-yl)methyl]amino}-acetonitrile (1), 8-(4-methylpiperidin-1-yl)-5-nitroquinoline (2) and 7-[(4-methylpiperidin-1yl)methyl]-5-nitroquinolin-8-ol (3). All three compounds (5 μM) reduced extracellular degradation of collagen IV by MCF-10A neoT cells by 45-70% as determined by spectrofluorimetry and they (50 μM) attenuated intracellular collagen IV degradation by 40-60% as measured with flow cytometry. Furthermore, all three compounds (5 μM) impaired MCF-10A neoT cell invasion by 40-80% as assessed by measuring electrical impedance in real time. Compounds 1 and 3 (5 μM), but not compound 2, significantly reduced the growth of MMTV-PyMT multicellular tumour spheroids. Collectively, these data suggest that the efficient strategy to impair harmful cathepsin B activity in tumour progression may include simultaneous and potent inhibition of cathepsin B endopeptidase and exopeptidase activities.

[ANTHELMINTIC SUBSTANCES: MAIN CLASSES, PROBLEMS, TRENDS IN DEVELOPMENT AND PROSPECTS]

The review chronologically considers the main classes of the currently available anthelminthic substances: early anthelmintic compounds, benzimidazoles, imidazolthiazoles, tetrahydropyrimidines, avermectins and milbemycins, and salicylanilides. Great attention is paid to novel substances (emodepside, monepantel, derquantel, tribendimidine) and promising developments. Some aspects of the molecular mechanisms of action of anthelmintics, their resistance, and alternative dehelmintization methods are discussed.

Alcohol alters the activation of ERK1/2, a functional regulator of binge alcohol drinking in adult C57BL/6J mice

BACKGROUND

Binge alcohol drinking is a particularly risky pattern of alcohol consumption that often precedes alcohol dependence and addiction. The transition from binge alcohol drinking to alcohol addiction likely involves mechanisms of synaptic plasticity and learning in the brain. The mitogen-activated protein kinase (MAPK) signaling cascades have been shown to be involved in learning and memory, as well as the response to drugs of abuse, but their role in binge alcohol drinking remains unclear. The present experiments were designed to determine the effects of acute alcohol on extracellular signaling-related kinases (ERK1/2) expression and activity and to determine whether ERK1/2 activity functionally regulates binge-like alcohol drinking.

METHODS

Adult male C57BL/6J mice were injected with ethanol (EtOH) (3.0 mg/kg, intraperitoneally) 10, 30, or 90 minutes prior to brain tissue collection. Next, mice that were brought to freely consume unsweetened EtOH in a binge-like access procedure were pretreated with the MEK1/2 inhibitor SL327 or the p38 MAPK inhibitor SB239063.

RESULTS

Acute EtOH increased pERK1/2 immunoreactivity relative to vehicle in brain regions known to be involved in drug reward and addiction, including the central amygdala and prefrontal cortex. However, EtOH decreased pERK1/2 immunoreactivity relative to vehicle in the nucleus accumbens core. SB239063 pretreatment significantly decreased EtOH consumption only at doses that also produced nonspecific locomotor effects. SL327 pretreatment significantly increased EtOH, but not sucrose, consumption without inducing generalized locomotor effects.

CONCLUSIONS

These findings indicate that ERK1/2 MAPK signaling regulates binge-like alcohol drinking. As alcohol increased pERK1/2 immunoreactivity relative to vehicle in brain regions known to regulate drug self-administration, SL327 may have blocked this direct pharmacological effect of alcohol and thereby inhibited the termination of binge-like drinking.

A causative link between inner ear defects and long-term striatal dysfunction

There is a high prevalence of behavioral disorders that feature hyperactivity in individuals with severe inner ear dysfunction. What remains unknown is whether inner ear dysfunction can alter the brain to promote pathological behavior. Using molecular and behavioral assessments of mice that carry null or tissue-specific mutations of Slc12a2, we found that inner ear dysfunction causes motor hyperactivity by increasing in the nucleus accumbens the levels of phosphorylated adenosine 3',5'-monophosphate response element-binding protein (pCREB) and phosphorylated extracellular signal-regulated kinase (pERK), key mediators of neurotransmitter signaling and plasticity. Hyperactivity was remedied by local administration of the pERK inhibitor SL327. These findings reveal that a sensory impairment, such as inner ear dysfunction, can induce specific molecular changes in the brain that cause maladaptive behaviors, such as hyperactivity, that have been traditionally considered exclusively of cerebral origin.

acr-23 Encodes a monepantel-sensitive channel in Caenorhabditis elegans

Monepantel is a member of the recently identified class of anthelmintics known as the amino-acetonitrile derivatives (AADs). Monepantel controls all major gastro-intestinal nematodes in sheep including those that are resistant to the classical anthelmintics. Previous studies have shown that the Caenorhabditis elegans acr-23 and the Haemonchus contortus Hco-mptl-1 genes may be prominent targets of monepantel. With this discovery it became possible to investigate the mode of action of monepantel in nematodes at the molecular level. In the present study, we show that a C. elegans mutant acr-23 strain is fully rescued by expressing the wild-type acr-23 gene. Moreover, we present a new mutant allele, and characterize acr-23 alleles genetically. We also show that acr-23 is expressed in body wall muscle cells, and provide therefore a possible explanation for the paralysis caused by monepantel. Furthermore, genetic evidence suggests that the chaperone RIC-3 is required for expression of full monepantel resistance. Finally, we present reconstitution of the C. elegans ACR-23 receptor in Xenopus laevis oocytes and provide direct evidence of its modulation by monepantel. Conversely, co-injection of the chaperone RIC-3 had no impact for channel reconstitution in X. laevis oocytes. These results reinforce the involvement of the ACR-23 family in the mode of action of monepantel and advance our understanding of this new class of anthelmintics.

Worldwide, sheep and cattle farming are endangered by anthelmintic-resistant gastro-intestinal nematodes. Monepantel, a member of the recently identified class of anthelmintics known as the amino-acetonitrile derivatives (AADs) exhibits excellent efficacy against various species of livestock-pathogenic nematodes and, more importantly, overcomes existing resistances to the currently available anthelmintics. Previous studies conducted with the non-parasitic model nematode Caenorhabditis elegans have found that acr-23 mutants are fully resistant to monepantel. In this study, we confirm the role of acr-23 as a primary target of monepantel by 1) restoring monepantel sensitivity in the presence of extrachromosomal copies of wild-type acr-23, 2) finding that ACR-23 is mainly expressed in muscle cells, and 3) showing that acr-23 forms a monepantel-sensitive channel in Xenopus oocytes.

Mitogen-activated protein kinase in the amygdala plays a critical role in lithium chloride-induced taste aversion learning

The intracellular mitogen-activated protein kinase (MAPK) pathway in the brain is necessary for the formation of a variety of memories including conditioned taste aversion (CTA) learning. However, the functional role of MAPK activation in the amygdala during lithium chloride (LiCl)-induced CTA learning has not been established. In the present study, we investigated if local microinjection of SL327, a MAPK kinase inhibitor, into the rat amygdala could alleviate LiCl-induced CTA learning. Our results revealed that acute administration of a high dose of LiCl (0.15M, 12 ml/kg, i.p.) rapidly increased the level of phosphorylated MAPK (pMAPK)-positive cells in the central nucleus of the amygdala (CeA) and nucleus of the solitary tract (NTS) of rats as measured by immunohistochemistry. Local microinjection of SL327 (1 μg/0.5 μl/hemisphere) into the CeA 10 min before LiCl administration decreased both the strength of LiCl-induced CTA paired with 0.125% saccharin and the level of LiCl-induced pMAPK-positive cells in the CeA, but not in the NTS. Our data suggest that the intracellular signaling cascade of the MAPK pathway in the CeA plays a critical role in the processing of visceral information induced by LiCl for CTA learning.

In vitro and in vivo efficacy of Monepantel (AAD 1566) against laboratory models of human intestinal nematode infections

Background

Few effective drugs are available for soil-transmitted helminthiases and drug resistance is of concern. In the present work, we tested the efficacy of the veterinary drug monepantel, a potential drug development candidate compared to standard drugs in vitro and in parasite-rodent models of relevance to human soil-transmitted helminthiases.

Methodology

A motility assay was used to assess the efficacy of monepantel, albendazole, levamisole, and pyrantel pamoate in vitro on third-stage larvae (L3) and adult worms of Ancylostoma ceylanicum, Necator americanus and Trichuris muris. Ancylostoma ceylanicum- or N. americanus-infected hamsters, T. muris- or Ascaris suum-infected mice, and Strongyloides ratti-infected rats were treated with single oral doses of monepantel or with one of the reference drugs.

Principal Findings

Monepantel showed excellent activity on A. ceylanicum adults (IC₅₀ = 1.7 µg/ml), a moderate effect on T. muris L3 (IC₅₀ = 78.7 µg/ml), whereas no effect was observed on A. ceylanicum L3, T. muris adults, and both stages of N. americanus. Of the standard drugs, levamisole showed the highest potency in vitro (IC₅₀ = 1.6 and 33.1 µg/ml on A. ceylanicum and T. muris L3, respectively). Complete elimination of worms was observed with monepantel (10 mg/kg) and albendazole (2.5 mg/kg) in A. ceylanicum-infected hamsters. In the N. americanus hamster model single 10 mg/kg oral doses of monepantel and albendazole resulted in worm burden reductions of 58.3% and 100%, respectively. Trichuris muris, S. ratti and A. suum were not affected by treatment with monepantel in vivo (following doses of 600 mg/kg, 32 mg/kg and 600 mg/kg, respectively). In contrast, worm burden reductions of 95.9% and 76.6% were observed following treatment of T. muris- and A. suum infected mice with levamisole (200 mg/kg) and albendazole (600 mg/kg), respectively.

Conclusions/Significance

Monepantel reveals low or no activities against N. americanus, T. muris, S. ratti and A. suum in vivo, hence does not qualify as drug development candidate for human soil-transmitted helminthiases.

Soil-transmitted helminthiases affect more than one billion people among the most vulnerable populations in developing countries. Currently, control of these infections primarily relies on chemotherapy. Only five drugs are available, all of which have been in use for decades. None of the drugs are efficacious using single doses against all soil-transmitted helminths (STH) species and show low efficacy observed against Trichuris trichiura. In addition, the limited availability of current drug treatments poses a precarious situation should drug resistance occur. Therefore, there is great interest to develop novel drugs against infections with STH. Monepantel, which belongs to a new class of veterinary anthelmintics, the amino-acetonitrile derivatives, might be a potential drug candidate in humans. It has been extensively tested against livestock nematodes, and was found highly efficacious and safe for animals. Here we describe the in vitro and in vivo effect of monepantel, on Ancylostoma ceylanicum, Necator americanus, Trichuris muris, Strongyloides ratti, and Ascaris suum, five parasite-rodent models of relevance to human STH. Since we observed that monepantel showed only high activity on one of the hookworm species and lacked activity on the other parasites tested we cannot recommend the drug as a development candidate for human soil-transmitted helminthiases.

The MEK inhibitor SL327 blocks acquisition but not expression of lithium-induced conditioned place aversion: a behavioral and immunohistochemical study

RATIONALE

Recent evidence involves extracellular signal-regulated kinase (ERK) in positive motivational properties of drugs as determined by conditioned place preference but, to date, its role in conditioned place aversion (CPA) still awaits to be fully characterized.

OBJECTIVES

The aim of this study was to assess whether activated ERK (pERK) plays a role in the acquisition and/or expression of lithium-induced CPA.

METHODS

C57BL/6J mice were subjected to lithium (150 mg/kg)-induced CPA. The role of pERK was determined by administering the mitogen-activating extracellular kinase inhibitor, SL327, (a) 25 and 50 mg/kg, before each exposure to the lithium-associated compartment (acquisition), and (b) 25, 50, and 100 mg/kg, before post-conditioning test (expression). To assess whether ERK is activated by acute lithium and, in distinct experiments, during CPA expression, mice were sacrificed, 30 min after lithium, and immediately after post-conditioning test, respectively, for pERK immunohistochemistry.

RESULTS

Lithium increased pERK-positive neurons in bed nucleus of stria termialis, in central and basolateral amygdala and elicited significant CPA. SL327 (50 mg/kg) significantly prevented its acquisition. In addition, the post-conditioning test of lithium-conditioned mice determined a significant increase of pERK-positive neurons in the dorsal striatum and SL327 (50 mg/kg), administered before post-conditioning test, while failing at the doses of 25, 50, and 100 mg/kg, to affect lithium-induced CPA expression, completely prevented it.

CONCLUSIONS

These results indicate that pERK is critical for acquisition, but not expression, of lithium-induced CPA and that its activation in the dorsal striatum, during expression, is not critical for retrieval of the aversive memory.

Phylogenomics of ligand-gated ion channels predicts monepantel effect

The recently launched veterinary anthelmintic drench for sheep (Novartis Animal Health Inc., Switzerland) containing the nematocide monepantel represents a new class of anthelmintics: the amino-acetonitrile derivatives (AADs), much needed in view of widespread resistance to the classical drugs. Recently, it was shown that the ACR-23 protein in Caenorhabditis elegans and a homologous protein, MPTL-1 in Haemonchus contortus, are potential targets for AAD action. Both proteins belong to the DEG-3 subfamily of acetylcholine receptors, which are thought to be nematode-specific, and different from those targeted by the imidazothiazoles (e.g. levamisole). Here we provide further evidence that Cel-ACR-23 and Hco-MPTL-1-like subunits are involved in the monepantel-sensitive phenotype. We performed comparative genomics of ligand-gated ion channel genes from several nematodes and subsequently assessed their sensitivity to anthelmintics. The nematode species in the Caenorhabditis genus, equipped with ACR-23/MPTL-1-like receptor subunits, are sensitive to monepantel (EC₅₀<1.25 µM), whereas the related nematodes Pristionchus pacificus and Strongyloides ratti, which lack an ACR-23/MPTL-1 homolog, are insensitive (EC₅₀>43 µM). Genome sequence information has long been used to identify putative targets for therapeutic intervention. We show how comparative genomics can be applied to predict drug sensitivity when molecular targets of a compound are known or suspected.

Increased use of anthelmintics has contributed to the emergence of drug-resistant nematodes, causing serious problems for more than one billion sheep worldwide. The last class of compounds indicated for livestock was introduced 28 years ago. Recently, however, Novartis AH developed a new anthelmintic active against drug-resistant nematodes of sheep, the amino-acetonitrile derivative (AAD) monepantel. We have previously indirectly shown that the AADs have a novel mode of action involving acetylcholine receptor subunits: the ACR-23 protein in Caenorhabditis elegans and a homologous protein, MPTL-1 in Haemonchus contortus. To better understand the mode of action of the AADs, we performed comparative genomics of all ligand-gated ion channel genes from a range of organisms, including members from all nematode clades. We confirmed that MPTL-1 belongs to a unique, nematode-specific sub-family of receptor subunits. We also found that some nematode species lack ACR-23/MPTL-1 and predicted them to be monepantel insensitive. We challenged this hypothesis in a panel of drug tests: several species of Caenorhabditis nematodes equipped with ACR-23/MPTL-1-like receptor subunits were found susceptible to monepantel, whereas Pristionchus pacificus, closely related to these worms but lacking an ACR-23/MPTL-1 homolog, was tolerant. The parasitic nematode Strongyloides ratti, which has only a remote homolog of DES-2 and ACR-23/MPTL-1, was also tolerant to monepantel. This confirms our prediction and highlights how comparative genomic data can be used to predict a drug effect.

Increased operant responding for ethanol in male C57BL/6J mice: specific regulation by the ERK1/2, but not JNK, MAP kinase pathway

RATIONALE

Extracellular signal-regulated protein kinase (ERK(1/2)) is a member of the mitogen-activated protein kinase (MAPK) signaling pathway and a key molecular target for ethanol (EtOH) and other drugs of abuse.

OBJECTIVE

The aim of the study was to assess the role of two MAPK pathways, ERK(1/2) and c-Jun N-terminal kinase (JNK), on the modulation of EtOH and sucrose self-administration.

MATERIALS AND METHODS

C57BL/6J mice were trained to lever press on a fixed-ratio 4 schedule with 9% EtOH/2% sucrose, or 2% sucrose, as the reinforcer. In experiments 1 and 2, mice were injected with the MEK(1/2) inhibitor SL 327 (0-100 mg/kg) and the JNK inhibitor AS 6012452 (0-56 mg/kg) prior to self-administration. In experiment 3, SL 327 (0-100 mg/kg) was administered prior to performance on a progressive ratio (PR) schedule of EtOH reinforcement. In experiment 4, SL 327 and AS 601245 were injected 2 h before a locomotor test.

RESULTS

SL 327 (30 mg/kg) significantly increased EtOH self-administration without affecting locomotion. Higher doses of SL 327 and AS 601245 reduced EtOH-reinforced responding and locomotor activity. Reductions of both ligands on sucrose self-administration were due to decreases in motor activity. SL 327 pretreatment had no effect on PR responding.

CONCLUSIONS

ERK(1/2) activity is more directly involved in modulating the reinforcing properties of EtOH than JNK activity due to its selective potentiation of EtOH-reinforced responding. The specificity of this effect to EtOH self-administration, rather than sucrose self-administration, suggests that the mechanism by which ERK(1/2) increases EtOH-reinforced responding does not generalize to all reinforcing solutions and is not due to increased motivation to consume EtOH.

Haemonchus contortus acetylcholine receptors of the DEG-3 subfamily and their role in sensitivity to monepantel

Gastro-intestinal nematodes in ruminants, especially Haemonchus contortus, are a global threat to sheep and cattle farming. The emergence of drug resistance, and even multi-drug resistance to the currently available classes of broad spectrum anthelmintics, further stresses the need for new drugs active against gastro-intestinal nematodes. A novel chemical class of synthetic anthelmintics, the Amino-Acetonitrile Derivatives (AADs), was recently discovered and the drug candidate AAD-1566 (monepantel) was chosen for further development. Studies with Caenorhabditis elegans suggested that the AADs act via nicotinic acetylcholine receptors (nAChR) of the nematode-specific DEG-3 subfamily. Here we identify nAChR genes of the DEG-3 subfamily from H. contortus and investigate their role in AAD sensitivity. Using a novel in vitro selection procedure, mutant H. contortus populations of reduced sensitivity to AAD-1566 were obtained. Sequencing of full-length nAChR coding sequences from AAD-susceptible H. contortus and their AAD-1566-mutant progeny revealed 2 genes to be affected. In the gene monepantel-1 (Hco-mptl-1, formerly named Hc-acr-23H), a panel of mutations was observed exclusively in the AAD-mutant nematodes, including deletions at intron-exon boundaries that result in mis-spliced transcripts and premature stop codons. In the gene Hco-des-2H, the same 135 bp insertion in the 5′ UTR created additional, out of frame start codons in 2 independent H. contortus AAD-mutants. Furthermore, the AAD mutants exhibited altered expression levels of the DEG-3 subfamily nAChR genes Hco-mptl-1, Hco-des-2H and Hco-deg-3H as quantified by real-time PCR. These results indicate that Hco-MPTL-1 and other nAChR subunits of the DEG-3 subfamily constitute a target for AAD action against H. contortus and that loss-of-function mutations in the corresponding genes may reduce the sensitivity to AADs.

Worldwide, sheep and cattle farming are threatened by anthelmintic-resistant gastro-intestinal nematodes. A novel chemical class of synthetic anthelmintics was recently discovered, the Amino-Acetonitrile Derivatives (AADs), which exhibit excellent efficacy against various species of livestock-pathogenic nematodes and, more importantly, overcome existing resistances to the currently available anthelmintics. Haemonchus contortus, the largest nematode found in the abomasum of sheep and cattle, is a blood-feeding parasite that causes severe anemia that can lead to the sudden death of the infected animal; H. contortus is highly susceptible to AADs. In order to elucidate the mode of action of the AADs, we have developed 2 independent H. contortus mutants with reduced sensitivity to monepantel (AAD-1566). Both mutants were affected in their acetylcholine receptor (ACR) genes of the DEG-3 subfamily. In particular, we discovered a panel of mutations in the gene monepantel-1 (Hco-mptl-1) including deletions leading to mis-splicing, insertions and point mutations leading to premature termination of translation of the protein. These findings support the notion that Hco-MPTL-1 and other nAChR subunits of the DEG-3 subfamily are targets of the AADs. The fact that the DEG-3 subfamily of acetylcholine receptors is nematode-specific may explain the good therapeutic index of AADs in mammals.

Effects of the MEK inhibitor, SL-327, on rewarding, motor- and cellular-activating effects of D-amphetamine and SKF-82958, and their augmentation by food restriction in rat

RATIONALE

Food restriction (FR) enhances learned and unlearned behavioral responses to drugs of abuse and increases D-1 dopamine (DA) receptor-mediated activation of extracellular signal-regulated kinases (ERK) 1/2 MAP kinase in nucleus accumbens (NAc). While a role has been established for ERK signaling in drug-mediated associative learning, it is not clear whether ERK regulates unconditioned behavioral effects of abused drugs.

OBJECTIVES

The purpose of this study was to determine whether blockade of ERK signaling, using the brain-penetrant MEK inhibitor, SL-327, decreases behavioral or NAc cellular responses to acute drug treatment and their augmentation by FR.

MATERIALS AND METHODS

Separate experiments assessed the effects of SL-327 (50 mg/kg, intraperitoneally) on (1) the reward-potentiating effect of D-amphetamine in an intracranial self-stimulation protocol, (2) the locomotor-activating effect of the D-1 agonist, SKF-82958, and (3) Fos-immunostaining induced in the NAc by SKF-82958.

RESULTS

FR rats displayed enhanced responses to drug treatment on all measures. SL-327 had no effect on sensitivity to rewarding brain stimulation or the reward-potentiating effect of D-amphetamine. The MEK inhibitor, U0126, microinjected into the NAc was also without effect. The locomotor-activating effect of SKF-82958 was unaffected by SL-327. In contrast, SL-327 decreased NAc Fos-immunostaining and abolished the difference between feeding groups.

CONCLUSIONS

These results support the conclusion that ERK signaling does not mediate unlearned behavioral responses to drug treatment. However, the upregulation of ERK and downstream transcriptional responses to acute drug treatment may underlie the reported enhancement of reward-related learning in FR subjects.

Extracellular signal-regulated kinase 1/2 involvement in the enhancement of contextual fear conditioning by nicotine

Contextual fear conditioning is enhanced by nicotine, but the cellular mechanisms underlying this effect are unknown. Extracellular signal regulated kinase 1/2 (ERK 1/2) has been shown to play an integral role in the formation of contextual fear memories. As such, it is possible that ERK 1/2 is involved in the enhancement of contextual fear conditioning by nicotine. To determine whether ERK 1/2 plays a role in this enhancement, a dose of SL327 (a selective, systemic ERK 1/2 inhibitor) that is subthreshold for inhibiting contextual fear conditioning was coadministered with nicotine prior to training, testing, or both training and testing of contextual fear conditioning in C57BL/6 mice. When administered prior to training, this subthreshold dose of SL327 attenuated the enhancement of contextual fear conditioning by nicotine to levels similar to those of vehicle-treated animals. When administered prior to testing, the subthreshold dose of SL327 did not significantly alter conditioning. These results suggest that activation of ERK 1/2 by nicotine during acquisition leads to an enhancement of contextual fear conditioning.

Broad-spectrum efficacy across cognitive domains by alpha7 nicotinic acetylcholine receptor agonism correlates with activation of ERK1/2 and CREB phosphorylation pathways

The alpha7 nicotinic acetylcholine receptor (nAChR) plays an important role in cognitive processes and may represent a drug target for treating cognitive deficits in neurodegenerative and psychiatric disorders. In the present study, we used a novel alpha7 nAChR-selective agonist, 2-methyl-5-(6-phenyl-pyridazin-3-yl)-octahydro-pyrrolo[3,4-c]pyrrole (A-582941) to interrogate cognitive efficacy, as well as examine potential cellular mechanisms of cognition. Exhibiting high affinity to native rat (Ki = 10.8 nM) and human (Ki = 16.7 nM) alpha7 nAChRs, A-582941 enhanced cognitive performance in behavioral assays including the monkey delayed matching-to-sample, rat social recognition, and mouse inhibitory avoidance models that capture domains of working memory, short-term recognition memory, and long-term memory consolidation, respectively. In addition, A-582941 normalized sensory gating deficits induced by the alpha7 nAChR antagonist methyllycaconitine in rats, and in DBA/2 mice that exhibit a natural sensory gating deficit. Examination of signaling pathways known to be involved in cognitive function revealed that alpha7 nAChR agonism increased extracellular-signal regulated kinase 1/2 (ERK1/2) phosphorylation in PC12 cells. Furthermore, increases in ERK1/2 and cAMP response element-binding protein (CREB) phosphorylation were observed in mouse cingulate cortex and/or hippocampus after acute A-582941 administration producing plasma concentrations in the range of alpha7 binding affinities and behavioral efficacious doses. The MEK inhibitor SL327 completely blocked alpha7 agonist-evoked ERK1/2 phosphorylation. Our results demonstrate that alpha7 nAChR agonism can lead to broad-spectrum efficacy in animal models at doses that enhance ERK1/2 and CREB phosphorylation/activation and may represent a mechanism that offers potential to improve cognitive deficits associated with neurodegenerative and psychiatric diseases, such as Alzheimer's disease and schizophrenia.

Cellular mechanisms underlying the anxiolytic effect of low doses of peripheral Delta9-tetrahydrocannabinol in rats

We investigated the effect of low doses of intraperitoneal Delta(9)-tetrahydrocannabinol (THC) on anxiety behavior in rats using the elevated plus maze (EPM). An anxiolytic effect was obtained in a range of doses between 0.075 and 1.5 mg/kg, the 0.75 dose being the most effective. Pretreatment with the CB1 receptor antagonist AM251 fully reversed THC's effect, suggesting CB1 receptors were involved. In order to elucidate the neuroanatomical substrates underlying the effect of the maximal effective dose of THC, we investigated cFos expression in anxiety-related brain regions (prefrontal cortex, nucleus accumbens, amygdala, and hippocampus) of rats exposed to the EPM. THC significantly lowered the amount of cFos in prefrontal cortex and amygdala without affecting the other cerebral areas. As there is increasing evidence that CREB function regulates anxiety-like behavior in rats, the second biochemical parameter we measured was phosphorylated CREB in the same brain areas. Rats treated with THC showed a significant increase in CREB activation in the prefrontal cortex and hippocampus. In the prefrontal cortex this increased activation was linked to an increase in ERK activation, whereas in the hippocampus there was a drop in the activity of CAMKII, a kinase with inhibitory effect on CREB activation. All these effects were reversed by AM251 pretreatment, suggesting that stimulation of CB1 receptors is fundamental for triggering the biochemical events. Our results suggest that the stimulation of these receptors in the prefrontal cortex, amygdala, and hippocampus with the subsequent activation of different signaling pathways is the first event underlying the effects of cannabinoids on anxious states.

The striatal-enriched protein tyrosine phosphatase gates long-term potentiation and fear memory in the lateral amygdala

BACKGROUND

Formation of long-term memories is critically dependent on extracellular-regulated kinase (ERK) signaling. Activation of the ERK pathway by the sequential recruitment of mitogen-activated protein kinases is well understood. In contrast, the proteins that inactivate this pathway are not as well characterized.

METHODS

Here we tested the hypothesis that the brain-specific striatal-enriched protein tyrosine phosphatase (STEP) plays a key role in neuroplasticity and fear memory formation by its ability to regulate ERK1/2 activation.

RESULTS

STEP co-localizes with the ERKs within neurons of the lateral amygdala. A substrate-trapping STEP protein binds to the ERKs and prevents their nuclear translocation after glutamate stimulation in primary cell cultures. Administration of TAT-STEP into the lateral amygdala (LA) disrupts long-term potentiation (LTP) and selectively disrupts fear memory consolidation. Fear conditioning induces a biphasic activation of ERK1/2 in the LA with an initial activation within 5 minutes of training, a return to baseline levels by 15 minutes, and an increase again at 1 hour. In addition, fear conditioning results in the de novo translation of STEP. Inhibitors of ERK1/2 activation or of protein translation block the synthesis of STEP within the LA after fear conditioning.

CONCLUSIONS

Together, these data imply a role for STEP in experience-dependent plasticity and suggest that STEP modulates the activation of ERK1/2 during amygdala-dependent memory formation. The regulation of emotional memory by modulating STEP activity may represent a target for the treatment of psychiatric disorders such as posttraumatic stress disorder (PTSD), panic, and anxiety disorders.

A novel, conformation-specific allosteric inhibitor of the tachykinin NK2 receptor (NK2R) with functionally selective properties

The orthosteric agonist neurokinin A (NKA) interacts with the tachykinin NK2 receptors (NK2Rs) via an apparent sequential binding process, which stabilizes the receptor in at least two different active conformations (A1L and A2L). The A1L conformation exhibits fast NKA dissociation kinetics and triggers intracellular calcium elevation; the A2L conformation exhibits slow NKA dissociation kinetics and triggers cAMP production. The new compound LPI805 is a partial and noncompetitive inhibitor of NKA binding to NK2Rs. Analysis of NKA dissociation in the presence of LPI805 suggests that LPI805 decreases the number of NKA-NK2R complexes in A2L conformation while increasing those in the A1L conformation. Analysis of signaling pathways of NK2Rs shows that LPI805 dramatically inhibits the NKA-induced cAMP response while slightly enhancing the NKA-induced calcium response. Analysis of NKA association kinetics reveals that LPI805 promotes strong and specific destabilization of the NKA-NK2R complexes in the A2L conformation whereas access of NKA to the A1L conformations is unchanged. Thus, to our knowledge, LPI805 is the first example of a conformation-specific allosteric antagonist of a G-protein-coupled receptor. This work establishes the use of allosteric modulators in order to promote functional selectivity on certain agonist-receptor interactions.

Dopamine D4 receptor signaling in the rat paraventricular hypothalamic nucleus: Evidence of natural coupling involving immediate early gene induction and mitogen activated protein kinase phosphorylation

The dopamine D4 receptor has been investigated for its potential role in several CNS disorders, notably schizophrenia and more recently, erectile dysfunction. Whereas studies have investigated dopamine D4 receptor-mediated signaling in vitro, there have been few, if any, attempts to identify dopamine D4 receptor signal transduction pathways in vivo. In the present studies, the selective dopamine D4 agonist PD168077 induces c-Fos expression and extracellular signal regulated kinase (ERK) phosphorylation in the hypothalamic paraventricular nucleus (PVN), a site known to regulate proerectile activity. The selective dopamine D4 receptor antagonist A-381393 blocked both c-Fos expression and ERK1/2 phosphorylation produced by PD168077. In addition, PD168077-induced ERK1/2 phosphorylation was prevented by SL327, an inhibitor of ERK1/2 phosphorylation. Interestingly, treatment with A-381393 alone significantly reduced the amount of Fos immunoreactivity as compared to basal expression observed in vehicle-treated controls. Dopamine D4 receptor and c-Fos coexpression in the PVN was observed using double immunohistochemical labeling, suggesting that PD168077-induced signaling may result from direct dopamine D4 receptor activation. Our results demonstrate functional dopamine D4 receptor expression and natural coupling in the PVN linked to signal transduction pathways that include immediate early gene and MAP kinase activation. Further, the ability of the selective dopamine D4 antagonist A-381393 alone to reduce c-Fos expression below control levels may imply the presence of a tonic dopamine D4 receptor activation under basal conditions in vivo. These findings provide additional evidence that the PVN may be a site of dopamine D4 receptor-mediated proerectile activity.

Role of the ERK pathway in psychostimulant-induced locomotor sensitization

BACKGROUND

Repeated exposure to psychostimulants results in a progressive and long-lasting facilitation of the locomotor response that is thought to have implications for addiction. Psychostimulants and other drugs of abuse activate in specific brain areas extracellular signal-regulated kinase (ERK), an essential component of a signaling pathway involved in synaptic plasticity and long-term effects of drugs of abuse. Here we have investigated the role of ERK activation in the behavioral sensitization induced by repeated administration of psychostimulants in mice, using SL327, a brain-penetrating selective inhibitor of MAP-kinase/ERK kinase (MEK), the enzyme that selectively activates ERK.

RESULTS

A dose of SL327 (30 mg/kg) that reduced the number of activated ERK-positive neurons by 62 to 89% in various brain areas, had virtually no effect on the spontaneous locomotor activity or the acute hyperlocomotion induced by cocaine or D-amphetamine. Pre-treatment with SL327 (30 mg/kg) prior to each drug administration prevented the locomotor sensitization induced by repeated injections of D-amphetamine or cocaine. The SL327 pre-treatment abolished also conditioned locomotor response of mice placed in the context previously paired with cocaine or D-amphetamine. In contrast, SL327 did not alter the expression of sensitized response to D-amphetamine or cocaine.

CONCLUSION

Altogether these results show that ERK has a minor contribution to the acute locomotor effects of psychostimulants or to the expression of sensitized responses, whereas it is crucial for the acquisition of locomotor sensitization and psychostimulant-conditioned locomotor response. This study supports the important role of the ERK pathway in long-lasting behavioral alterations induced by drugs of abuse.

Odorant-induced activation of extracellular signal-regulated kinase/mitogen-activated protein kinase in the olfactory bulb promotes survival of newly formed granule cells

Extracellular signal-regulated kinase 1/2 (Erk1/2)/mitogen-activated protein (MAP) kinase (MAPK) plays a significant role in neuronal survival, including odorant-induced, activity-dependent survival of olfactory sensory neurons in the main olfactory epithelium. Here, we examined the role of MAPK for the survival of neurons in the olfactory bulb. To study odorant-induced activation of MAPK in the olfactory bulb, mice were exposed to odorants in vivo, and MAPK was assayed. Exposure of mice to some odorants in vivo activated MAPK in granule cells 10 min after exposure. Activation of MAPK was particularly evident in the nucleus and dendrites of granule cells. Because MAPK activation can augment neuronal survival, odorant enhancement of granule cell survival was monitored by bromodeoxyuridine (BrdU) incorporation. Long-term exposure to odorants increased the survival of newly formed granule cells as well as the number of granule cells that were both BrdU+ and phospho-Erk+. Inhibition of MAPK by administration of SL327 in vivo blocked the odorant-induced increase in newly formed granule cells, suggesting that activation of MAPK promotes the survival of granule cells in the olfactory bulb. Studies using cultured granule cells confirmed that activation of MAPK in granule cells protects them against strong apoptotic signals. These data suggest that stimulation of MAPK in olfactory bulb granule cells by some odorants may contribute to the survival of newly formed granule cells caused by odorant exposure.

Inhibition of ERK pathway or protein synthesis during reexposure to drugs of abuse erases previously learned place preference

Repeated association of drugs of abuse with context leads to long-lasting behavioral responses that reflect reward-controlled learning and participate in the establishment of addiction. Reactivation of consolidated memories is known to produce a reconsolidation process during which memories undergo a labile state. We investigated whether reexposure to drugs had similar effects. Cocaine administration activates extracellular signal-regulated kinase (ERK) in the striatum, and ERK activation is required for the acquisition of cocaine-induced conditioned place preference (CPP). When mice previously conditioned for cocaine-place preference were reexposed to cocaine in the drug-paired compartment after systemic administration of SL327, an inhibitor of ERK activation, CPP response was abolished 24 h later. This procedure also abolished the phosphorylation of ERK and glutamate receptor-1 observed in the ventral and dorsal striatum, 24 h later, during CPP test. Erasure of CPP by SL327 required the combination of cocaine administration and drug-paired context and did not result from enhanced extinction. Similarly, reexposure to morphine in the presence of SL327 long-lastingly abolished response of previously learned morphine-CPP. The effects of SL327 on cocaine- or morphine-CPP were reproduced by protein synthesis inhibition. In contrast, protein synthesis inhibition did not alter previously acquired locomotor sensitization to cocaine. Our findings show that an established CPP can be disrupted when reactivation associates both the conditioned context and drug administration. This process involves ERK, and systemic treatment preventing ERK activation during reexposure erases the previously learned behavioral response. These results suggest potential therapeutic strategies to explore in the context of addiction.

Extracellular signal-regulated mitogen-activated protein kinase inhibitors decrease amphetamine-induced behavior and neuropeptide gene expression in the striatum

The aim of this study was to determine whether inhibition of the extracellular-regulated kinase signaling pathway decreases acute amphetamine-induced behavioral activity and neuropeptide gene expression in the rat striatum. Western blotting revealed that extracellular-regulated kinase1/2 phosphorylation was highly induced in the rat striatum 15 min after an acute amphetamine (2.5 mg/kg, i.p.) injection without altering the total amount of extracellular-regulated kinase protein. In a separate experiment, the systemic injection of SL327, a selective inhibitor of extracellular regulated kinase kinase that crosses the blood-brain barrier, 1 h prior to amphetamine administration decreased amphetamine-induced vertical and horizontal activity. Quantitative in situ hybridization histochemistry showed that SL327 abolished the high levels of preproenkephalin and preprodynorphin mRNA induced by amphetamine in the striatum with no alteration of their basal levels. In another set of experiments, the hyperlocomotor activity induced by amphetamine was reduced by pretreatment with intra-striatal infusion of U0126. U0126 also blocked the amphetamine-induced increases in phospho-extracellular-regulated kinase and preproenkephalin and preprodynorphin gene expression in the striatum. These data indicate that activation of the extracellular-regulated kinase cascade contributes to the behavioral effects and changes in striatal neuropeptide gene expression induced by acute amphetamine.

β-Substituted Cyclohexanecarboxamide: A Nonpeptidic Framework for the Design of Potent Inhibitors of Cathepsin K

A new series of nonpeptidic cathepsin K inhibitors that are based on a beta-substituted cyclohexanecarboxamide motif has been developed. Lead optimization yielded compounds with sub-nanomolar potency and exceptional selectivity profiles against cathepsins B, L, and S. Use of fluorine atoms to block metabolism on the cyclohexyl ring led to compounds with excellent pharmacokinetic properties. Considering the well-established role of cathepsin K in osteoclast-mediated bone turnover, compounds such as (-)-34a (hrab Cat K IC(50) 0.28 nM; >800-fold selectivity vs Cat B, L, and S; PK data in dogs: F 55%, t(1/2) = 15 h) exhibit great potential for development as an orally bioavailable therapeutic for treatment of diseases that involve bone loss.

Regulation of cocaine-induced activator protein 1 transcription factors by the extracellular signal-regulated kinase pathway

Extracellular signal-regulated kinases and activator protein 1 transcription factor have been functionally linked to addiction. It has also been shown that extracellular signal-regulated kinase activation can regulate cocaine-induced expression of c-Fos and FosB, two possible components of activator protein 1. A direct link between extracellular signal-regulated kinases and activator protein 1 activation has, however, remained unexplored. In this study, we investigated the role of extracellular signal-regulated kinases in the regulation of DNA-binding activity and composition of activator protein 1 induced in the mouse caudate putamen by cocaine treatment. We have found that pre-treatment with SL327, a selective inhibitor the extracellular signal-regulated kinase pathway, has no influence on cocaine-induced DNA-binding activity of activator protein 1, when examined one hour after an acute cocaine treatment. This phenomenon results from simultaneous decrease of c-Fos protein level and increases in JunB and deltaFosB protein levels. SL327 pre-treatment, however, reduces the DNA-binding activity of the activator protein 1 complex induced six hours after an acute cocaine treatment as well as one hour after the last of the chronic cocaine injections, a phenomenon that results from the concomitant reduction of all cocaine-induced proteins (c-Fos, FosB, deltaFosB, JunB). In conclusion, we have found that extracellular signal-regulated kinase inhibition may not only interfere with cocaine-induced gene expression and activator protein 1 complex activation, but may also disturb the time-course of gene expression and composition of activator protein 1 complex. Our results support the notion that inhibitors of the extracellular signal-regulated kinase pathway could be valuable tools to obliterate cocaine-induced molecular changes and the development of addiction.

Mitochondrial oxidative burst involved in apoptotic response in oats

Apoptotic cell response in oats is induced by victorin, a host-selective toxin secreted by Cochliobolus victoriae and thought to exert toxicity by inhibiting mitochondrial glycine decarboxylase (GDC) in Pc-2/Vb oats. We examined the role of mitochondria, especially the organelle-derived production of reactive oxygen species (ROS), in the induction of apoptotic cell death. Cytofluorimetric analysis showed that victorin caused mitochondrial deltaPsim breakdown and mitochondrial oxidative burst. Ultrastructural analysis using a cytochemical assay based on the reaction of H2O2 with CeCl3 detected H2O2 eruption at permeability transition pore-like sites on the mitochondrial membrane in oat cells treated with victorin. ROS generation preceded the apoptotic cell responses seen in chromatin condensation and DNA laddering. Both aminoacetonitrile (a specific GDC inhibitor) and antimycin A (a mitochondrial complex III inhibitor) also induced mitochondrial H2O2 eruption, and led to the apoptotic response in oat cells. ROS scavengers such as N-acetyl-l-cysteine and catalase suppressed the mitochondrial oxidative burst and delayed chromatin condensation and DNA laddering in the victorin- or antimycin A-treated leaves. These findings indicate possible involvement of mitochondria, especially mitochondrial-derived ROS generation, as an important regulator in controlling apoptotic cell death in oats.

Transglutaminase activity in aging articular chondrocytes and articular cartilage vesicles

OBJECTIVE

Transglutaminases (TGases) (E.C. 2.3.2.13) catalyze a posttranslational modification of proteins and are associated with biomineralization in growth plate cartilage. Type II TGase participates in the activation of latent transforming growth factor beta (TGFbeta), a crucial factor for both normal cartilage mineralization and the pathologic mineralization that results in calcium pyrophosphate dihydrate (CPPD) crystal formation in aging articular cartilage. To explore a possible association between TGase levels and CPPD crystal formation in mature articular cartilage, TGase activity in articular chondrocytes from old and young pigs and in the articular cartilage vesicle (ACV) fraction of porcine articular cartilage was examined. In addition, the effects of TGase inhibitors on the production of inorganic pyrophosphate (PPi), a process necessary for CPPD crystallogenesis, were determined.

METHODS

TGase activity was measured with a radiometric assay in cultured articular chondrocytes from the knee joints of old (3-5 years old) and young (2-6 weeks old) pigs and in the ACVs. PPi levels were measured in chondrocyte-conditioned media in the presence of TGase inhibitors or control compounds.

RESULTS

Levels of TGase activity in the cytosolic fraction of old chondrocytes were 7-fold higher than those in identically cultured young chondrocytes. The mean +/- SD activity level in the membrane fraction of lysed chondrocytes was 6.0 +/- 0.6 units/mg protein in old articular chondrocytes and was undetectable in young chondrocytes. In ACVs, the mean +/- SD TGase activity level was 1.23 +/- 0.1 units/mg protein. Type II TGase protein was present in chondrocyte cytosol and in ACVs. TGase activity was increased by TGFbeta to 120% of control values (P < 0.01), and decreased by insulin-like growth factor 1 to 80% of control values (P < 0.01). TGase inhibitors blocked media accumulation of PPi, an essential precursor of CPPD crystal formation, and a sensitive marker of TGFbeta effect.

CONCLUSION

These data suggest a potential link between TGase activity and processes of pathologic biomineralization that result in CPPD crystal formation in aging articular cartilage.

Involvement of CYP2E in 8-hydroxylation of theophylline in mouse hepatic microsomes-difference from its N-demethylations

We examined which cytochrome P-450 (P-450) species other than CYP1A participates in the oxidative metabolism of theophylline (TP) in mouse hepatic microsomes. Among the three metabolic pathways of TP, only 8-hydroxylation was selectively enhanced by acetone, a potent inducer of CYP2E. We assumed that two P-450 populations with different metabolic ability were involved in this metabolic process, and kinetic analyses revealed that the enhancement was due to the induction of a high-capacity P-450 population. The 8-hydroxylation at a substrate concentration, where most of the total activity was attributed to the catalysis of the high-capacity phase, was markedly impaired by CYP2E inhibitors such as 4-methylpyrazole and aminoacetonitrile, whereas the N-demethylations were little affected by these agents. The activity of TP 8-hydroxylation was significantly correlated with that of p-nitrophenol hydroxylation, a probe for CYP2E, in untreated microsomes. The activities of these oxidative reactions were modified to a similar degree by known enzyme inhibitors with a range of inhibitory potencies and affinity for P-450 isoforms. On the other hand, a relationship between TP N-demethylations and p-nitrophenol hydroxylation was not apparent, but there was a behavioral similarity between the two types of N-demethylations. The results indicated that TP 8-hydroxylation, which accounts for a large portion of TP oxidations, involves CYP2E, and that its N-demethylations are mediated by a common or closely similar P-450 species distinct from CYP2E.

Collagen responsible for tooth eruption? A study of the eruption of rat incisors

The rate of turnover of collagen in periodontal ligament (PDL) is closely associated with the process of tooth eruption and tissue adaptation allowing good anchorage of the tooth within the socket. Collagen may even be associated with orthodontic relapse. As the collagen protein seems to play a key role in tooth eruption, the investigation concentrated on the presence and maturation of collagen and its possible function in the process of tooth eruption.

Strength and viscoelastic properties of anisotropic rat skin after treatment with desmotropic drugs

Male Sprague-Dawley rats were treated 10 times either with 2 or 10 mg/kg s.c. prednisolone acetate or with 300 or 1,000 mg/kg p.o. D-penicillamine or with 100 or 300 mg/kg p.o. aminoacetonitrile bisulfate. Samples of dorsal skin were tested either longitudinally or perpendicularly to the body axis. Relaxation and hysteresis experiments were performed at different degrees of elongation. Finally, ultimate values were measured. In all groups, ultimate strain was much higher perpendicularly than longitudinally to the body axis. A dose-dependent increase of all parameters indicating strength or elasticity was found after prednisolone acetate treatment, whereas the indicators of viscosity showed a decrease. D-Penicillamine treatment decreased all parameters of strength and elasticity and increased viscosity and plasticity. Aminoacetonitrile bisulfate induced biphasic changes: after high-dose treatments strength and elasticity were increased and viscosity decreased. The results are discussed in view of changes of biochemical composition and cross-linking of collagen.

Morphological abnormalities in vitamin B6 deficient tarsometatarsal chick cartilage

The aim of this study was to test the hypothesis that deficiency of vitamin B6 would produce morphological characteristics of osteochondral lathyrism. To accomplish this goal, morphological characteristics of chick cartilage in which lathyrism was produced by two separate dietary regimens was compared to morphological changes encountered in vitamin B6 deficiency. Vitamin B6 deficiency should reduce activity of lysyloxidase needed for producing intermolecular cross-links. The question to be addressed was: would this latter deficiency impair collagen morphological features and secondarily other structures indirectly by reducing collagen molecular assembly? Failure of cross-linking of collagen in the positive controls was related to a lack of functional aldehyde cross-link intermediates which are blocked by homocysteine and aminoacetonitrile. Day-old-male Lohmann chicks were fed adequate (6 mg/kg) or vitamin B6-deficient diets. Cross-link defects were induced by homocysteine-rich diets (0.6% w/w) or a diet containing aminoacetonitrile (0.1% w/w). Animals were sacrificed at 6 weeks of age and Ossa tarsalia articular cartilage specimens, as well as the proximal end of tarsometatarsus were dissected from the tibial metatarsal joint, a major weight-bearing site. Light microscopic observations revealed reduction of subarticular trabecular bone formation, concurrent with overexpansion of the hypertrophic cell zone. Ultrastructural electron microscopy observation of articular fibro-cartilage indicated significant thickening of collagen fibers in vitamin B6 deficient birds, as well as the positive controls in comparison to that of cage-matched control birds. It was concluded that vitamin B6 deficient cross-linking may be responsible for the observed delay in bone development and aforementioned cartilage histological alterations.

The role of metabolism in carbon tetrachloride-mediated immunosuppression: in vivo studies

The role of metabolic bioactivation for carbon tetrachloride-mediated suppression of humoral responses was investigated in B6C3F1 mice. Subchronic studies with CCl4 demonstrated that this chlorinated hydrocarbon markedly suppressed T-dependent antibody responses following 7 consecutive days of administration at doses between 500 and 5000 mg/kg. No significant difference in the magnitude of suppression was observed between the ip and oral routes of exposure. Thirty-day ip administration of CCl4 at doses as low as 25 mg/kg also resulted in a significant inhibition of T-dependent antibody responses. The results from both the 7-day and the 30-day studies indicate that a greater than 50% suppression of antibody responses could not be achieved even at doses of CCl4 as high as 5000 mg/kg. In vivo studies utilized the cytochrome P450 competitive inhibitor, aminoacetonitrile (AAN), in an effort to block the effects of exposure to CCl4. Both the hepatotoxicity, as measured by serum glutamic pyruvic transaminase levels, and the suppression of the T-dependent antibody response to sRBC were reversed by treatment with AAN. Conversely, induction of cytochrome P450, by pretreatment of mice with ethanol prior to treatment with CCl4, resulted in the potentiation of the immunosuppressive effects of CCl4. AAN and ethanol administered alone had no effect on antibody responses. In order to assess the effect of CCl4 treatment on cytochrome P450 activity at doses which cause immunosuppression, measurements of total microsomal protein and specific substrate activities were determined. Significant decreases were observed in both total hepatic microsomal protein as well as in aminopyrine N-demethylase activity, aniline hydroxylase activity, and aryl hydrocarbon hydroxylase activity following treatment with CCl4 for 7 days at doses ranging from 5 to 1000 mg/kg. All of the cytochrome P450 parameters that were measured, following CCl4 treatment, demonstrated very flat dose-response curves which appeared to parallel the effects of CCl4 on antibody responses.

Effects of lathyrogens on the mechanical strength of the periodontal ligament in the rat mandibular first molar

Effects of lathyrogens such as aminoacetonitrile (AAN), beta-aminopropionitrile (BAPN) and cysteamine--known inhibitors of cross-linking of collagen--on the mechanical strength of the periodontal ligament of the rat mandibular first molar were examined by measuring the ultimate load required to extract the tooth from its socket in the dissected jaw. Single injections of AAN (40 approximately 100 mg/100 g body weight) or of BAPN (100 mg/100 g body weight) caused significant decreases of the mechanical strength 24 h after administration of the drugs but that of cysteamine (30 mg/100 g body weight) did not. Significant correlations between the dose of AAN or of BAPN and the mechanical strength were found following daily administrations of the drugs for 5 days. The relative potency of AAN to BAPN was estimated to be 4.5 by a slope ratio assay. The rapid appearance and disappearance of the effect of lathyrogens on the mechanical strength of the periodontal ligament of the rat mandibular first molar provide further evidence that the turnover of the collagen in the tissue is fast. The half-time of collagen synthesis was estimated to be approximately 3 d.

Differential effects of coadministration of aminoacetonitrile on immunosuppression and hepatotoxicity produced by dimethylnitrosamine

Aminoacetonitrile (AAN) has been reported to be a dimethylnitrosamine (DMN) demethylase inhibitor which prevents the metabolic activation of DMN to a hepatotoxin. The purpose of this investigation was to determine if AAN pretreatment, which ameliorates hepatotoxicity, would also prevent the immunotoxicity associated with DMN exposure. Female B6C3F1 mice were exposed to either 3 or 6 mg/kg of DMN (in saline) or saline i.p. for 7 consecutive days. The animals were also treated (i.p.) twice daily, 1 hr before and 6 hr after DMN exposure, with either, 10, 30 or 100 mg/kg of AAN (in saline) or saline. Mice were sensitized with sheep red blood cells i.v. on day 8. On day 12, body and organ weights were determined, serum chemistry and histopathology were evaluated and day 4 immunoglobulin M antibody response was measured. Hepatotoxicity caused by DMN, as reflected by an increase in body weight attributed to the production of ascites, a 485.7% increase in the serum glutamic pyruvic transaminase levels and histopathology was reversed by doses of AAN as low as 10 mg/kg. Conversely, doses of AAN as high as 100 mg/kg were unable to reverse the suppression of the antibody forming cells response to sheep red blood cells produced by DMN. The results of this investigation indicate that DMN-induced immunosuppression and hepatotoxicity can be separated and that an immunosuppressive metabolite of DMN is produced by an AAN-insensitive pathway.

Role of the transfer of metabolites from hepatocytes to splenocytes in the suppression of in vitro antibody response by dimethylnitrosamine

The metabolism and subsequent immunosuppressive effects of dimethylnitrosamine (DMN) were investigated in mixed cultures of mouse hepatocytes and mouse splenocytes. Hepatocytes were shown to activate DMN to an immunosuppressive form that caused the suppression of the in vitro antibody response to the T-dependent antigen, sheep erythrocytes (SRBC). A significant increase in the binding of DMN metabolites to trichloroacetic acid (TCA) precipitable material in splenocytes was induced when 94 microM [14C-methyl]DMN was added to the co-culture medium, indicating that reactive intermediates of DMN were transferred from hepatocytes to splenocytes and resulted in alkylation of macromolecules in splenocytes. The amount of [14C]DMN bound to TCA precipitable material in splenocytes increased in a time-dependent manner up to 4 hr of incubation. Aminoacetonitrile (AAN), a high-affinity DMN demethylase inhibitor, reversed the suppression by low concentrations of DMN (0.5 to 5 mM), but not by high concentrations of DMN (greater than 5 mM). AAN also inhibited the binding of [14C]DMN to both hepatocytes and splenocytes. These results suggest that reactive metabolites of DMN are released from hepatocytes and that the suppression of the antibody response by DMN is mediated via these reactive intermediates.

67Ga uptake and heparan sulfate content of Ehrlich solid tumor in mice

The relationship between 67Ga uptake and heparan sulfate (HS) content in Ehrlich solid tumor (EST) of mice was investigated, and the effect of cyanomethylamine, papain, streptozotocin, or bleomycin pretreatment on 67Ga uptake in EST was studied. 67Ga uptakes in EST and kidney were much higher than other tissues, and these tissues also contained large amounts of HS. 67Ga uptakes and HS synthesis in the EST were inhibited by pretreatment with cyanomethylamine or papain (inhibitors of fibrosis). Parallel reductions of 67Ga uptake and HS synthesis in EST were observed in EST transplanted into streptozotocin-induced diabetic mice. The weight of EST in the bleomycin-injected group was decreased to less than half of the control, but no effect was observed on 67Ga uptake per gram of EST. These results suggest that 67Ga uptake in the tumor and inflammatory lesions are related to the quantity of HS in these tissues, and the correlation between the uptake of 67Ga and the rate of cellular proliferation is secondary.

The effect of mixed-function oxidase and amine oxidase inhibitors on the activation of dialkylnitrosamines and 1,2-dimethylhydrazine to bacterial mutagens in mice

The effect of the mixed-function oxidase inhibitor phenylimidazole (PI) and the amine oxidase inhibitors iproniazid (IPRO) and aminoacetonitrile (AAN) on the mutagenic activity of various carcinogens was determined in intrasanguineous host-mediated assays, using mice as hosts and E. coli 343/113 as an indicator of mutagenic activity. The carcinogenic compounds dimethyl-, diethyl-, methylethyl-, and diethanolnitrosamine (DMNA, DENA, MENA, and DELNA respectively) and 1,2-dimethylhydrazine (SDMH) were administered i.p. to mice pretreated or not with one of the inhibitors. After 4 h exposure to each of the carcinogens, E. coli cells recovered from the liver of non-pretreated mice showed considerable induction of VALr mutations; after pretreatment of the hosts with the three inhibitors, significant reduction of the amounts of induced mutants in vivo was observed. Particularly, PI proved a very efficient inhibitor of DENA, MENA, DELNA, and SDMH mutagenicity (93%-97% reduction), suggesting that these carcinogens are mainly activated by cytochrome P-450-dependent enzymes. However, since PI might also inhibit the NAD-mediated activation of DELNA by alcohol dehydrogenase (ADH), the present experiments do not rule out an additional role of ADH in the in vivo mutagenic activation of DELNA. AAN and IPRO were less and much less effective, respectively, in reducing the mutagenic activity of all compounds. Surprisingly, PI showed less inhibition of the mutagenic activity of DMNA (60% reduction), as compared to the other carcinogens; this indicates that metabolic routes other than the cytochrome P-450-dependent enzyme system may be important for the activation of DMNA.

Lathyrogens and the role of collagen in the eruption of rat incisors

Collagen fibres in the periodontal ligament may have two functions: to resist displacing forces and to cause the tooth to erupt. Their function was examined in the continuously-erupting incisor of the rat using various concentrations and types of lathyrogens. Lathyrogens retarded tooth eruption and increased the quantity of salt-soluble collagen in the ligament, indicating inhibition of the maturation of salt-soluble (young) collagen into salt-insoluble (old) collagen, which would lead to reduction in the tensile strength of the fibres and decrease resistance to occlusal forces. The easy extractability of the teeth is explained by the greater susceptibility to lathyrogens of the fibres in the alveolar-related part of the periodontal ligament, compared with those in the other parts.

Nature of N-nitrosodimethylamine demethylase in hepatic microsomes of rats

The nature of enzymes involved in demethylation of N-nitrosodimethylamine (NDMA) was investigated in hepatic microsomes of rats. Compared to the other cytochrome P-450-dependent enzymes. NDMA demethylase had anomalous properties as reported in the literature. However, kinetic analysis suggested a qualitative change in NDMA demethylase induced by phenobarbital (PB) and 3-methylcholanthrene (MC) pretreatment. The inhibition of demethylase by alpha-naphthoflavone in MC-treated microsomes also suggested that cytochrome P-450 species induced by MC are active in demethylating NDMA. The enhancement of NDMA demethylase activity by metyrapone in PB-treated microsomes was greater than in non-treated ones, and was not observed in MC-treated ones. The result is almost the same as in acetanilide hydroxylation, depending on cytochrome P-450. Pyrazole, tranylcypromine, and aminoacetonitrile, which are selective inhibitors of NDMA demethylation, interacted with cytochrome P-450 species to produce type-II spectra, and typical type-II compounds (aniline, imidazole, and nicotinamide) were inhibitors of the NDMA demethylation. Tranylcypromine irreversibly inhibited microsomal monoamine oxidase [EC 1.4.3.4], but not NDMA demethylase. Semicarbazide (a copper- and pyridoxal-containing amine oxidase [EC 1.4.3.6] inhibitor) had no effect on demethylation. From these results it is concluded that NDMA demethylation depends only on cytochrome P-450-dependent monooxygenases.

Contribution of fibrin stabilization to clot strength. Supplementation of factor XIII-deficient plasma with the purified zymogen

The contribution of fibrin stabilization to clot strength, measured as the static elastic modulus, was evaluated in human plasma by two independent procedures. In the first approach, amine inhibitors of fibrin stabilization were examined for their effects on the rigidity of normal plasma clots. It is a unique property of these inhibitors that they do not interfere with the reversible aggregation of fibrin molecules, i.e., do not delay clotting time, but selectively prevent only the formation of gamma-glutamyl-epsilon-lysine protein-to-protein linkages. Though the compounds tested were of different chemical structures and potencies, a fivefold reduction in clot strength was obtained in each instance. This value of 20% of normal seems to correspond to the rigidity of the Factor XIII-deficient plasma clot because, as demonstrated by the second approach, when a plasma specimen that genetically lacked the fibrin stabilizing factor was supplemented by the addition of measured amounts of the purified zymogen, a fivefold increase in clot strength could be achieved. The described procedure of evaluating Factor XIII in terms of correcting the elastic modulus of a deficient plasma clot is considered an important assay for the functional competence of purified preparations of the zymogen for the purpose of therapeutic application.

Inhibition by aminoacetonitrile and propargylamine of glycine cleavage system from rat brain and liver mitochondria

Glycine degradation in the CNS is catalyzed by the glycine cleavage system (GCS). We have tested several compounds with a structural analogy to glycine for their inhibition of the GCS. Compounds having an inhibitory activity, such as aminoacetonitrile and propargylamine, are characterized by having a primary amine group and a pi-electron system present in the group substituting for the carboxylic function. The inhibition by these compounds of glycine degradation may be of pharmacological interest given the neurotransmitter role of glycine.

[3H]Fucose incorporation by healing skin wounds and the effect of transglutaminase inhibitors

Punch wounds (3 mm) were made in the skin of rats and the animals were killed after 1 or 3 days. Plugs (4 mm) of wounded and unwounded skin were incubated in vitro with [3H]fucose. The labelled plugs were homogenized and subjected to sequential extraction with buffered salt solutions, ethanol-ether, and 8 M urea - 50 mM dithiothreitol (DTT). Nondialysable counts in the extracts and insoluble residue were determined and the incorporation of label by wounded and unwounded skin plugs was compared. Wound plugs showed a greater total incorporation of [3H]fucose. In addition, a greater proportion of [3H]fucose was found in the urea-DTT extracts. The highest specific activity (disintegrations per minute [3H]fucose per milligram dry weight) was found in a finely dispersed precipitate, sedimenting at 10000 x g but not at 1000 x g. The transglutaminase inhibitors aminoacetonitrile and dansyl cadaverine were found to increase the extractability of a portion of the material which incorporated [3H]fucose without affecting the total incorporation. These results show that healing wounds have an increased biosynthetic capacity for an insoluble fucosylated glycoprotein fraction and they suggest that transglutaminase is necessary to make this fraction fully insoluble.

Prevention of thioacetamide-induced liver necrosis by prior aminoacetonitrile or imidazole administration

Prior administration of aminoacetonitrile (AAN) or imidazole but not isoxazole to rats, was able partially to prevent thioacetamide (TAC)-induced liver necrosis at 24 h. AAN and isoxazole did not prolong the pentobarbital sleeping time of the rats, while imidazole did. These and previous observations suggest a possible participation of non-cytochrome P-450 (P-450)-dependent aminoxidases in TAC activation to a necrogenic metabolite.

Effects of glyceryl trinitrate and SIN-1A on musculature and vasculature of the dog trachea in situ

In dog trachea in situ, perfused arterially with blood, isoprenaline, glyceryl trinitrate and N-nitroso-N-morpholinoamino-acetonitrile (SIN-1A) given intra-arterially, decreased tracheal tone which had been elevated by neostigmine and increased tracheal blood flow. Glyceryl trinitrate and SIN-1A were more effective on the tracheal musculature than on the tracheal vasculature whereas isoprenaline was equally effective on both.

Comparative effects of indole and aminoacetonitrile derivatives on dimethylnitrosamine-demethylase and aryl hydrocarbon hydroxylase activities

The effect of in vivo administration of indole and five 3-indolyl derivatives including L-tryptophan, as well as of aminoacetonitrile and 3 of its derivatives, were studied on the carcinogen-metabolizing hepatic mixed-function oxidases dimethylnitrosamine (DMN)-demethylase I and II and aryl hydrocarbon hydroxylase (AHH). Indole, 3-indolylmethanol, 3-indolyl-acetonitrile, 3-indolylacetone and L-tryptophan induce AHH activity from 3- to 6-fold of the control level, whereas beta-3-indolylethanol has no effect; the latter compound produces a 21% decrease of the endoplasmic reticulum content in the tissue. Only L-tryptophan induces DMN-demethylase I and only L-tryptophan and 3-indolylmethanol induce DMN-demethylase II, representing a doubling of enzyme activity in all 3 instances. Aminoacetonitrile is a potent repressor of DMN-demethylase I. Substitutions on the amino group bring about strong decrease or abolishment of mixed-function oxidase repressor activity; thus, iminodiacetonitrile has only about 1/5th the repressor activity of the parent compound, whereas nitrilotriacetonitrile and dimethylaminoacetonitrile appear to be inactive. Aminoacetonitrile and its derivatives studied have no effect on DMN-demethylase II and AHH activities. The mixed-function oxidase-modifying effects of the indole compounds and of aminoacetonitrile and its derivatives illustrate the potential complexity of effects of dietary constituents on the carcinogenic responses.

Denitrosation of N-nitrosomorpholine by liver microsomes; possible role of cytochrome P-450

Liver microsomes from male mice and rats were incubated with N-nitrosomorpholine (MoNA) and an NADPH-regenerating system. The formation of nitrite was measured after induction or inhibition of the microsomal monooxygenase system. Pretreatment of the animals with phenobarbital (PB) enhanced nitrite formation by about 200%, while 3-methylcholanthrene (3-MC)-induction showed no exceptional effects. Various specific inhibitors of the monooxygenase function including carbon monoxide decreased nitrite formation. In conjunction with results obtained by spectra studies it is suggested that N-nitrosomorpholine is denitrosated by a reduction process in which cytochrome (cyt.) P-450 seems to be involved. Nitricoxide formed is partly converted to nitrite under these conditions.