M2 Muscarinic Receptor Activation Impairs Mitotic Progression and Bipolar Mitotic Spindle Formation in Human Glioblastoma Cell Lines

Background: Glioblastoma multiforme (GBM) is characterized by several genetic abnormalities, leading to cell cycle deregulation and abnormal mitosis caused by a defective checkpoint. We previously demonstrated that arecaidine propargyl ester (APE), an orthosteric agonist of M2 muscarinic acetylcholine receptors (mAChRs), arrests the cell cycle of glioblastoma (GB) cells, reducing their survival. The aim of this work was to better characterize the molecular mechanisms responsible for this cell cycle arrest. Methods: The arrest of cell proliferation was evaluated by flow cytometry analysis. Using immunocytochemistry and time-lapse analysis, the percentage of abnormal mitosis and aberrant mitotic spindles were assessed in both cell lines. Western blot analysis was used to evaluate the modulation of Sirtuin2 and acetylated tubulin—factors involved in the control of cell cycle progression. Results: APE treatment caused arrest in the M phase, as indicated by the increase in p-HH3 (ser10)-positive cells. By immunocytochemistry, we found a significant increase in abnormal mitoses and multipolar mitotic spindle formation after APE treatment. Time-lapse analysis confirmed that the APE-treated GB cells were unable to correctly complete the mitosis. The modulated expression of SIRT2 and acetylated tubulin in APE-treated cells provides new insights into the mechanisms of altered mitotic progression in both GB cell lines. Conclusions: Our data show that the M2 agonist increases aberrant mitosis in GB cell lines. These results strengthen the idea of considering M2 acetylcholine receptors a novel promising therapeutic target for the glioblastoma treatment.

The Combination of the M2 Muscarinic Receptor Agonist and Chemotherapy Affects Drug Resistance in Neuroblastoma Cells

One of the major limits of chemotherapy is depending on the ability of the cancer cells to elude and adapt to different drugs. Recently, we demonstrated how the activation of the M2 muscarinic receptor could impair neuroblastoma cell proliferation. In the present paper, we investigate the possible effects mediated by the preferential M2 receptor agonist arecaidine propargyl ester (APE) on drug resistance in two neuroblastoma cell lines, SK-N-BE and SK-N-BE(2C), a sub-clone presenting drug resistance. In both cell lines, we compare the expression of the M2 receptor and the effects mediated by the M2 agonist APE on cell cycle, demonstrating a decreased percentage of cells in S phase and an accumulation of SK-N-BE cells in G1 phase, while the APE treatment of SK-N-BE(2C) cells induced a block in G2/M phase. The withdrawal of the M2 agonist from the medium shows that only the SK-N-BE(2C) cells are able to rescue cell proliferation. Further, we demonstrate that the co-treatment of low doses of APE with doxorubicin or cisplatin significantly counteracts cell proliferation when compared with the single treatment. Analysis of the expression of ATP-binding cassette (ABC) efflux pumps demonstrates the ability of the M2 agonist to downregulate their expression and that this negative modulation may be dependent on N-MYC decreased expression induced by the M2 agonist. Our data demonstrate that the combined effect of low doses of conventional drugs and the M2 agonist may represent a new promising therapeutic approach in neuroblastoma treatment, in light of its significant impact on drug resistance and the possible reduction in the side effects caused by high doses of chemotherapy drugs.

The metronomic combination of paclitaxel with cholinergic agonists inhibits triple negative breast tumor progression. Participation of M2 receptor subtype

Triple negative tumors are more aggressive than other breast cancer subtypes and there is a lack of specific therapeutic targets on them. Since muscarinic receptors have been linked to tumor progression, we investigated the effect of metronomic therapy employing a traditional anti-cancer drug, paclitaxel plus muscarinic agonists at low doses on this type of tumor. We observed that MDA-MB231 tumor cells express muscarinic receptors, while they are absent in the non-tumorigenic MCF-10A cell line, which was used as control. The addition of carbachol or arecaidine propargyl ester, a non-selective or a selective subtype 2 muscarinic receptor agonist respectively, plus paclitaxel reduces cell viability involving a down-regulation in the expression of ATP “binding cassette” G2 drug transporter and epidermal growth factor receptor. We also detected an inhibition of tumor cell migration and anti-angiogenic effects produced by those drug combinations in vitro and in vivo (in NUDE mice) respectively. Our findings provide substantial evidence about subtype 2 muscarinic receptors as therapeutic targets for the treatment of triple negative tumors.

Tissue-specific and maturity-dependent distribution of pyridine alkaloids in Areca triandra

Areca nuts (seeds of Areca catechu L.) are a traditional and popular masticatory in India, Bangladesh, Malaysia, certain parts of China, and some other countries. Four related pyridine alkaloids (arecoline, arecaidine, guvacoline, and guvacine) are considered being the main functional ingredients in areca nut. Until now, A. catechu is the only known species producing these alkaloids in the Arecaceae family. In the present study, we investigated alkaloid contents in 12 Arecaceae species and found that only Areca triandra Roxb. contained these pyridine alkaloids. We further analyzed in more detail tissue-specific and development-related distribution of these alkaloids in leaves, male and female flowers and fruits in different stages of maturity in A. triandra by ultra-performance liquid chromatography-quadrupole/time-of-flight mass spectrometry. Results revealed that the alkaloids were most abundant in young leaves, the pericarp of ripe fruits and the endosperm of unripe fruits in developmental stage 2. Abundance of the 4 different alkaloids in A. triandra fruits varied during maturation. Pericarps of ripe fruits had the highest arecaidine concentration (4.45 mg g^-1) and the lowest guvacoline concentration (0.0175 mg g^-1), whereas the endosperm of unripe fruits of developmental stage 2 contained the highest guvacoline concentration (3.39 mg g^-1) and the lowest guvacine concentration (0.245 mg g^-1). We conclude that A. triandra is useful in future as a further valuable source of Areca alkaloids.

CYP450-mediated mitochondrial ROS production involved in arecoline N-oxide-induced oxidative damage in liver cell lines

BACKGROUND

IARC has classified the betel nut as a human environmental carcinogen. Previous studies have found that arecoline (AR) is the major alkaloid present in the saliva of betel quid chewers. Saliva contains a large content of AR which has been further shown to cause mutation of oral mucosa cells, resulting in oral cancer. Whereas, to date, there are only few studies reported the hepatotoxicity associated with arecoline and betel nut chewing. Therefore, the main purpose of this study was to determine the toxic effects of AR and its oxidative metabolite, arecoline N-oxide (ARNO), in normal liver cell lines.

METHODS

The cytotoxic, genotoxic, and mutagenic effects were detected by crystal violet staining, alkaline comet assay, and Salmonella mutagenicity test, respectively. Measurement of intracellular reactive oxygen species (ROS) generation was determined using the H2-DCFDA assay.

RESULTS

Our results demonstrated that ARNO exerted higher cytotoxicity, DNA damage, and mutagenicity than its parent compound arecoline in liver cells. Antioxidants, such as N-acetylcysteine, Trolox, and penicillamine, strongly protected liver cells from ARNO-induced DNA damage and ROS production. Furthermore, co-treatment with Mito-TEMPO also effectively blocked ARNO-induced ROS production in liver cells. Besides antioxidants, co-treatment with 1-aminobenzotriazole and methimazole nearly completely suppressed ARNO-induced ROS production in liver cells.

CONCLUSIONS

Our data suggest that arecoline ingested from the habit of chewing betel quid can be primarily oxidized to ARNO, thereby enhancing its toxicity through increased ROS production. Considering the excellent protective effects of both mitochondria-targeted antioxidant and CYP450 inhibitor on ARNO-induced ROS production in liver cells, mitochondria CYP450-mediated metabolism of ARNO may be a key mechanism. Collectively, our results provide novel cellular evidence for the positive connection between habitual betel quid chewing and the risk for liver damage.

Arecoline N-Oxide Upregulates Caspase-8 Expression in Oral Hyperplastic Lesions of Mice

Areca nut is strongly associated with oral squamous cell carcinoma (OSCC) occurrence. Arecoline N-oxide (ANO), a metabolite of the areca alkaloid arecoline, exhibits an oral fibrotic effect in NOD/SCID mice. Caspase-8, a cysteine protease encoded by the CASP8 gene, is a central mediator in the extrinsic apoptotic pathway via death receptors. Deregulation of caspase-8 in OSCC has been reported. This study investigates the regulation of caspase-8 in ANO-induced oral squamous epithelial hyperplasia that represents the initial highly proliferative stage of oral carcinogenesis. CASP8 somatic mutations were identified from whole-exome sequencing of OSCC samples. Immunohistochemical staining showed upregulation of caspase-8 in ANO-induced hyperplasia of both NOD-SCID and C57BL/6 mice. Levels of expression of CASP8, APAF-1, BAX, and BAD increased in ANO-treated DOK cells. Co-localization of increased caspase-8 and PCNA levels was detected in ANO-induced hyperplastic lesions, whereas no co-localization among γ-H2A.X, caspase-3, and upregulated caspase-8 was observed. The findings indicate that upregulation of caspase-8 is involved in cell proliferation rather than apoptosis during the initial stage of ANO-mediated oral tumorigenesis.

Determination of contents of four alkaloids in Pericarpium arecae by quantitative analysis of multi-components by single-marker

By using a typical component in traditional Chinese medicine Pericarpium Arecae (PA), quantitative analysis of multi-components by single-marker (QAMS) was performed to determine the contents of four alkaloids. With a column packed with strong cation exchange bonded silica particles, the alkaloids were well separated, showing linear relationships within certain ranges. The limit of detection, limit of quantitation, precision, stability, repeatability and recovery all met requirements. By employing arecoline as internal standard, relative correction factors for arecaidine, guvacine and guvacoline at five concentrations were detected with three HPLC systems and three HPLC columns. The peaks of arecaidine, guvacine and guvacoline were positioned, during which the columns with the same packing materials from different manufacturers significantly affected relative retention values and retention time differences of the alkaloids. However, the columns, from different batches, managed to give relative retention values satisfying the requirements of HPLC peak positioning. The Thermo Fisher Scientific column packed with strong cation exchange bonded silica particles was finally selected by considering resolution and peak time. Compared with the external standard method, QAMS detected the alkaloid contents in 12 PA samples more accurately and reliably. The results provide valuable evidence for content determination and quality control of alkaloids in PA.

Fibrotic Effects of Arecoline N-Oxide in Oral Potentially Malignant Disorders

The metabolites of environmental chemicals play key roles in carcinogenesis. Areca nut is strongly associated with the development of oral potentially malignant disorders (OPMD) or cancer. The main alkaloid in the areca nut is arecoline, which is highly cytotoxic and genotoxic. Arecoline N-oxide, a metabolite of areca nut alkaloids, which has been identified in animal urine, has been shown to induce mutagenicity in bacteria. In this study, it was found that its protein adduct could be detected in oral keratinocytes treated with areca nut extract. Increased collagen expression and severity of squamous hyperplasia were observed in arecoline N-oxide treated mice. In cultured oral fibroblasts, arecoline N-oxide showed stronger effects on the increase of fibrotic related genes including TGF-beta1, S100A4, MMP-9, IL-6, and fibronectin and a decrease of E-cadherin as compared with arecoline. Finally, arecoline N-oxide stimulation effectively increased the DNA damage marker, gamma-H2A.X, both in vitro and in vivo. Taken together, these results indicate that arecoline N-oxide shows a high potential for the induction of OPMD.

[Optimization of Preparation of Cutting-processed Arecae Pericarpium with Multi-index Orthogonal Method]

OBJECTIVE

10 optimize the preparation of cutting-processed Arecae Pericarpium by the orthogonal method.

METHODS

With four alkaloids such as arecoline, arecaidine, guvacoline, guvacine and yield of water-soluble decoction as indexes, a L9 (3(4)) orthogonal test was adopted to compare the effect of different factors on cutting-processed Arecae Pericarpium.

RESULTS

According to the finalized optimal process, Arecae Pericarpium was washed quickly, moisturized, chopped lengthwise in 1 cm segment and then dried for 2.5 h at 50 °C.

CONCLUSION

The optimal process method is reasonable and reliable, it can provide basis for the preparation of cutting-processed Arecae Pericarnium.

Characterization of protein adducts formed by toxic alkaloids by nano-scale liquid chromatography with mass spectrometry

Betel quid chewing is associated with cytotoxicity, genotoxicity and carcinogenicity in diseases such as oral cancer, liver cirrhosis, hepatocellular carcinoma and diabetes mellitus. Arecoline and arecaidine, which are the main alkaloids in the areca nut, are potential exposure biomarkers in habitual betel quid users. This study developed a method of detecting arecoline- and arecaidine-protein adducts by mass spectrometry (MS). First, bovine serum albumin was used to predict and confirm the binding sites of proteins modified by arecoline or arecaidine. Cells were then treated with arecoline to identify new protein adducts after cellular metabolic processing. Finally, human plasma was used to model long-term exposure to arecoline and arecaidine. Following isolation proteins were tryspin digested. The peptides afforded were separated and analyzed by nano-scale liquid chromatography with MS using an LTQ Orbitrap mass spectrometer. The experimental findings showed that cysteine is the predominant amino acid in protein adduct formation. The goal of this study was to establish a screening platform for identifying novel protein adducts that form covalent bonds with arecoline or arecaidine. Use of this strategy to survey new protein-toxic adducts may help to identify novel biomarkers of betel nut exposure.

Arecoline N-oxide: its mutagenicity and possible role as ultimate carcinogen in areca oral carcinogenesis

The areca nut is the most widely consumed psychoactive substance in Taiwan, India, and Southeast Asia. It is considered to be an environmental risk factor for the development of oral submucous fibrosis and cancer. Arecoline, the major alkaloid of areca nut, has been known to cause cytotoxicity and genotoxicity in various systems. However, the active compound accounting for arecoline-induced damage in normal human oral cells is still uncharacterized. The present study was undertaken to identify the active metabolite of arecoline that might induce damage in human oral tissues and cause mutagenicity in Salmonella typhimurium tester strains TA 100 and TA 98. It is interesting to find that the major metabolite of arecoline, arecoline N-oxide, is moderately mutagenic to these Salmonella tester strains. This mutagenicity was potently inhibited by sulfhydryl compounds, namely, glutathione, N-acetylcysteine, and cysteine, whereas methionine is inactive in this inhibition. The mutagenicity of arecoline N-oxide was strongly inhibited by the N-oxide reducing agent titanium trichloride. The possible role of arecoline N-oxide in the induction of oral carcinogenesis by areca nut chewing is discussed.

High-throughput simultaneous analysis of five urinary metabolites of areca nut and tobacco alkaloids by isotope-dilution liquid chromatography-tandem mass spectrometry with on-line solid-phase extraction

BACKGROUND

Areca nut and tobacco are commonly used drugs worldwide and have been frequently used in combination. We describe the use of on-line solid-phase extraction and isotope-dilution liquid chromatography-tandem mass spectrometry for the simultaneous measurement of five major urinary metabolites of both areca nut and tobacco alkaloids, namely, arecoline, arecaidine, N-methylnipecotic acid, nicotine, and cotinine.

METHODS

Automated purification of urine was accomplished with a column-switching device. After the addition of deuterium-labeled internal standards, urine samples were directly analyzed within 13 minutes. This method was applied to measure urinary metabolites in 90 healthy subjects to assess areca nut/tobacco exposure. Urinary time course of arecoline, arecaidine, and N-methylnipecotic acid was investigated in five healthy nonchewers after oral administration of areca nut water extracts.

RESULTS

The limits of detection were 0.016 to 0.553 ng/mL. Interday and intraday imprecision were <10%. Mean recoveries of five metabolites in urine were 97% to 114%. Mean urinary concentrations of arecoline, arecaidine, N-methylnipecotic acid, nicotine, and cotinine in regular areca nut chewers also smokers were 23.9, 5,816, 1,298, 2,635, and 1,406 ng/mg creatinine, respectively. Time course study revealed that after administration of areca nuts extracts, the major urinary metabolite was arecaidine with a half-life of 4.3 hours, followed by N-methylnipecotic acid with a half-life of 7.9 hours, and very low levels of arecoline with a half-life of 0.97 hour.

CONCLUSIONS

This on-line solid-phase extraction liquid chromatography-tandem mass spectrometry method firstly provides high-throughput direct analysis of five urinary metabolites of areca nut/tobacco alkaloids.

IMPACT

This method may facilitate the research into the oncogenic effects of areca nut/tobacco exposure.

Effect of novel arecoline thiazolidinones as muscarinic receptor 1 agonist in Alzheimer's dementia models

The discovery of cholinergic deficit in Alzheimer's disease (AD) patient's brain has triggered research efforts, using cholinomimetic approaches for their efficacy in AD therapy. Various therapies may be of potential clinical use in AD. Among these are cholinergic agents, which include muscarinic agonists, acetylcholinesterase inhibitors, and acetylcholine releasing agents. One of the muscarinic agonists tested in AD is arecoline and its bioisosters, which are widely explored as muscarinic receptor 1 agonist (M1 receptor agonist) in AD research. In this regard, five-membered heterocyclic ring system attached arecoline basic nucleus (N-methyl tetrahydropyridines) at third position has been extensively researched on. The present research involved synthesis of arecoline thiazolidinones 5(a-j) by using dipolar addition of 3-aminopyridine and alkyl/aryl carboxaldehydes in presence of gamma ferrite as catalyst. The resulting products were methylated and reduced to get desired products. Subsequently the synthesized arecoline thiazolidinones were subjected to in vitro muscarinic receptor binding studies using male Wistar rat brain (cerebral cortex) membrane homogenate and extended this in vitro study to in vivo pharmacological evaluation of memory and learning in male Wistar rats. Four derivatives (5a-5c and 5e) showed considerable M1 receptor binding affinity (in vitro) and elicited beneficial effects in vivo memory and learning models (Rodent memory evaluation, plus and Y maze studies).

Cholinergic activation of phasic activity in the isolated bladder: possible evidence for M3- and M2-dependent components of a motor/sensory system

OBJECTIVES

To analyse pressure changes induced by muscarinic agonists on the isolated bladder in order to examine whether there are different responses representing different components of a motor/sensory system within the bladder wall.

MATERIALS AND METHODS

Whole isolated bladders from 19 female guinea-pigs (280-400 g) were used. A cannula was inserted into the urethra to monitor intravesical pressure and the bladder was suspended in a heated chamber containing carboxygenated physiological solution at 33-36 degrees C. Initially, the responses to the cholinergic agonists, arecaidine but-2-ynyl ester tosylate and carbachol were assessed. Then, in an attempt to identify the muscarinic receptor subtypes involved, the effects of selective muscarinic antagonists on the arecaidine-induced bladder responses were assessed. The antagonists used were the relatively M(3)-selective 4-diphenylacetoxy-N-methylpiperidine methobromide (4-DAMP) and darifenicin, and relatively M(2)-selective AFDX-116. All drugs were added to the solution bathing the ablumenal surface of the bladder.

RESULTS

The whole bladders exposed to cholinergic agonists respond with complex changes in intravesical pressure. Immediately after application of the agonist there was a burst of high frequency transient contractions. During continued application of agonist the frequency of the transients decreased and their amplitude increased. Thus, there appear to be two components to the response: an initial fast phase and a later slow component. The maximum frequency of the initial burst increased with increasing concentrations of agonist. By contrast, the frequency of the transients in the steady state showed little dependence on agonist concentration. There were quantitative differences between the responses to arecaidine and carbachol. Arecaidine was less effective in generating the initial burst of high-frequency activity and the transients were significantly larger. At low dose, arecaidine was more effective in producing the large transients in the steady state. Pre-exposure of the bladder to 4-DAMP (0.1-10 nM) or darifenicin (0.1-10 nM) significantly reduced the frequency of the initial burst of activity; 0.3 nM 4-DAMP reduced the frequency by half. In this concentration range, 4-DAMP reduced the amplitude of the initial transients but did not affect the frequency of the transients in the steady state. There were similar results with darifenicin. However, darifenicin was less effective in reducing the amplitude of the initial transients. By contrast, ADFX-116 had little effect on the frequency of the initial transients but did reduce amplitude; 300 nM AFDX-116 was needed to reduce the frequency of the initial burst by half.

CONCLUSIONS

This analysis suggests that there are different but interrelated mechanisms in the isolated bladder contributing to complex contractile activity. Three components can be identified: a mechanism operating during voiding to produce a global contraction of the whole bladder and two mechanisms, pacemaker and conductive, involved in generating and propagating local contractions in the bladder wall. The pacemaker component is more sensitive to darifenicin and 4-DAMP than to AFDX-116 suggesting that the underlying processes rely predominantly on M(3) receptors and less so on M(2) (M(3) > M(2)). The phasic activity in the later stages is less affected by M(3) antagonists and might therefore involve predominantly M(2) receptors (M(2) > M(3)). The potential importance of these results in terms of the general physiology and pharmacology of the bladder is discussed.

A metabolomic approach to the metabolism of the areca nut alkaloids arecoline and arecaidine in the mouse

The areca alkaloids comprise arecoline, arecaidine, guvacoline, and guvacine. Approximately 600 million users of areca nut products, for example, betel quid chewers, are exposed to these alkaloids, principally arecoline and arecaidine. Metabolism of arecoline (20 mg/kg p.o. and i.p.) and arecaidine (20 mg/kg p.o. and i.p.) was investigated in the mouse using a metabolomic approach employing ultra-performance liquid chromatography-time-of-flight mass spectrometric analysis of urines. Eleven metabolites of arecoline were identified, including arecaidine, arecoline N-oxide, arecaidine N-oxide, N-methylnipecotic acid, N-methylnipecotylglycine, arecaidinylglycine, arecaidinylglycerol, arecaidine mercapturic acid, arecoline mercapturic acid, and arecoline N-oxide mercapturic acid, together with nine unidentified metabolites. Arecaidine shared six of these metabolites with arecoline. Unchanged arecoline comprised 0.3-0.4%, arecaidine 7.1-13.1%, arecoline N-oxide 7.4-19.0%, and N-methylnipecotic acid 13.5-30.3% of the dose excreted in 0-12 h urine after arecoline administration. Unchanged arecaidine comprised 15.1-23.0%, and N-methylnipecotic acid 14.8%-37.7% of the dose excreted in 0-12 h urine after arecaidine administration. The major metabolite of both arecoline and arecaidine, N-methylnipecotic acid, is a novel metabolite arising from carbon-carbon double-bond reduction. Another unusual metabolite found was the monoacylglyceride of arecaidine. What role, if any, that is played by these uncommon metabolites in the toxicology of arecoline and arecaidine is not known. However, the enhanced understanding of the metabolic transformation of arecoline and arecaidine should contribute to further research into the clinical toxicology of the areca alkaloids.

The metabolomics of (+/-)-arecoline 1-oxide in the mouse and its formation by human flavin-containing monooxygenases

The alkaloid arecoline is a main constituent of areca nuts that are chewed by approximately 600 million persons worldwide. A principal metabolite of arecoline is arecoline 1-oxide whose metabolism has been poorly studied. To redress this, synthetic (+/-)-arecoline 1-oxide was administered to mice (20mg/kg p.o.) and a metabolomic study performed on 0-12h urine using ultra-performance liquid chromatography-coupled time-of-flight mass spectrometry (UPLC-TOFMS) with multivariate data analysis. A total of 16 mass/retention time pairs yielded 13 metabolites of (+/-)-arecoline 1-oxide, most of them novel. Identity of metabolites was confirmed by tandem mass spectrometry. The principal pathways of metabolism of (+/-)-arecoline 1-oxide were mercapturic acid formation, with catabolism to mercaptan and methylmercaptan metabolites, apparent CC double-bond reduction, carboxylic acid reduction to the aldehyde (a novel pathway in mammals), N-oxide reduction, and de-esterification. Relative percentages of metabolites were determined directly from the metabolomic data. Approximately, 50% of the urinary metabolites corresponded to unchanged (+/-)-arecoline 1-oxide, 25% to other N-oxide metabolites, while approximately, 30% corresponded to mercapturic acids or their metabolites. Many metabolites, principally mercapturic acids and their derivatives, were excreted as diastereomers that could be resolved by UPLC-TOFMS. Arecoline was converted to arecoline 1-oxide in vitro by human flavin-containing monooxygenases FMO1 (K(M): 13.6+/-4.9muM; V(MAX): 0.114+/-0.01nmolmin(-1)microg(-1) protein) and FMO3 (K(M): 44.5+/-8.0microM; V(MAX): 0.014+/-0.001nmolmin(-1)microg(-1) protein), but not by FMO5 or any of 11 human cytochromes P450. This report underscores the power of metabolomics in drug metabolite mining.

Effects of isoarecolone, a nicotinic receptor agonist in rodent models of nicotine dependence

RATIONALE

The nicotinic receptor agonist, isoarecolone, has 'nicotine-like' subjective properties as detected by rats in a discrimination paradigm. However, isoarecolone lacks the intra-accumbens dopamine-releasing effects, a feature akin to most abused substances. In the five-choice serial reaction time task, isoarecolone can enhance attention and thus may be developed as a cognitive enhancer.

OBJECTIVE

The present experiments assess the dependence profile of isoarecolone in rodent models of nicotine dependence.

METHOD AND RESULTS

Tests for cross-substitution in which isoarecolone is substituted for nicotine [0.3 mg/kg/infusion (inf)] self-administration suggest isoarecolone to have nominal reinforcing properties (0.3 or 1.0 mg/kg/inf); intake of isoarecolone declined over three test sessions in which responding was no different from saline extinction, and behaviour was reinstated by re-presenting nicotine. In a model of nicotine-seeking behaviour, rats having been extinguished by removal of nicotine (0.03 mg/kg/inf) and associated cues, the presentation of priming doses of nicotine (0.1-0.4 mg/kg s.c.) with the cues robustly reinstated responding of nicotine-seeking behaviour. Tests with priming doses of isoarecolone (1-20 mg/kg s.c.) shown previously to generalise to nicotine in discrimination tests produced significant levels of reinstatement but the responses were significantly less compared to nicotine-induced reinstatement.

CONCLUSION

Overall, these results suggest that isoarecolone with its unique profile of behavioural activity should be further examined for treating chronic diseases that are characterised by attentional dysfunction.

Genetic damage in cultured human keratinocytes stressed by long-term exposure to areca nut extracts

Chewing betel quid (BQ) is a popular habit worldwide. A causal association between BQ chewing and oral cancer has been well documented. Emerging evidence indicates that sustained exposure to stress induces epigenetic reprogramming of some mammalian cells and increases the mutation rate to accelerate adaptation to stressful environments. In this study, we first confirmed that 24-h treatment with areca nut extracts (ANE; a major component of BQ) at doses over 40 microg/ml induced mutations at the hypoxanthine phosphoribisyltransferase (HPRT) locus in human keratinocytes (HaCaT cells). We then investigated whether the stress of long-term exposure to sublethal doses of ANE (0, 5 and 20 microg/ml for 35 passages) could enhance genetic damage to HaCaT cells. Compared to cells exposed to 0 or 5 microg/ml ANE, cells exposed to 20 microg/ml ANE were slightly but significantly more resistant to a 72-h treatment with ANE and its major ingredients, arecoline and arecaidine, but did not develop cross-resistance to other BQ ingredients or alcohol. The cells that received 20 microg/ml ANE for 35 passages also had a significantly increased mutation frequency at the HPRT locus and an increased frequency in the appearance of micronuclei compared to lower doses. Moreover, increased intracellular levels of reactive oxygen species and 8-hydroxyguanosine in cells exposed to 20 microg/ml ANE suggested that long-term ANE exposure results in the accumulation of oxidative damage. However, cells subjected to long-term treatment of 20 microg/ml ANE contained higher levels of glutathione than unexposed cells. Therefore, after long-term exposure to sublethal doses of ANE, intracellular antioxidative activity may also be enhanced in response to increased oxidative stress. These results suggest that stress caused by long-term ANE exposure enhances oxidative stress and genetic damage in human keratinocytes.

Muscarinic stimulation of the rat isolated whole bladder: pathophysiological models of detrusor overactivity

1 Hypotheses as to the pathophysiological basis of bladder detrusor muscle overactivity (DO) have identified both central nervous and peripheral mechanisms as likely contributory factors. In this paper, we describe peripheral autonomous bladder activity in two animal models of DO and discuss how the differences observed between the two models support the likelihood that clinical DO has a multifactorial basis. 2 A total of 12 adult female Sprague-Dawley rats underwent obstruction or sham operation for 1 or 4 weeks. Six adult female spontaneously hypertensive rats (SHR) were compared with normal Wistar controls. Bladders were microsurgically removed and mounted in whole organ tissue baths. Recordings of intravesical pressure in response to the muscarinic receptor agonist arecaidine were performed under standardized conditions. 3 In the partially obstructed rat bladder, the amplitude of pressure fluctuations elicited by the muscarinic agonist arecaidine was significantly increased compared with sham-operated animals. The tonic component of the response was no different for the two groups. No difference from controls was apparent in the SHR. 4 We conclude that alterations in autonomous bladder activity in the obstructed rat model suggest that peripheral functional changes contribute to the pathophysiological abnormality. In contrast, the fundamental abnormality in the SHR appears to be at a more central level. The observations support the supposition that lesions at widely separate sites can give rise to apparently similar abnormalities of lower urinary tract function.

Muscarinic stimulation of the mouse isolated whole bladder: physiological responses in young and ageing mice

1 Peripheral autonomous bladder activity is an incompletely understood property that may be important both in normal bladder function and in functional problems of the lower urinary tract. We describe how a muscarinic agonist, arecaidine, influences intravesical pressure and intramural bladder contractions in the isolated mouse and how response varies in ageing mice. 2 A group of 12 mice aged 3-4 months was compared with an 'ageing' group of 12 mice age 28-34 months. Bladders were microsurgically removed and mounted in whole organ tissue baths. The effects of the muscarinic agonist arecaidine on intravesical pressure and intramural contractions were performed at different bladder volumes. 3 In normal mice, arecaidine elicited tonic and phasic contractions, the latter showing a more substantial increase in amplitude with bladder distension. Localized 'micromotion' contractions were seen in the bladder wall, with regional differences arising after exposure to arecaidine. A background release of acetylcholine was inferred from the pressure increase induced by the cholinesterase inhibitor physostigmine. 4 Both micromotion activity and the phasic component of the arecaidine response were substantially reduced in ageing mice; the tonic component was preserved in the same specimens. 5 We conclude that the enhanced pressure fluctuations seen at high bladder volumes may act as a peripheral determinant of bladder capacity, and that changes in such activity may contribute to altered functional capacity and lower urinary tract symptoms in ageing individuals.

Bladder Volume Alters Cholinergic Responses of the Isolated Whole Mouse Bladder

PURPOSE

The isolated bladder expresses autonomous activity, which may contribute to the generation of lower urinary tract sensation or pathophysiology. We evaluated how the effect of a cholinergic agonist on autonomous activity alters with increasing volume and in the presence of substances known to modulate functional bladder capacity.

MATERIALS AND METHODS

The bladder of 22 adult female C57 black mice were mounted in whole organ tissue baths. Recordings of intravesical pressure were performed under standardized conditions at different bladder volumes.

RESULTS

At low volume the muscarinic agonist arecaidine elicited an initial peak response, which subsided to a sustained steady state pressure. At high volume phasic pressure fluctuations were also apparent. An M2-receptor antagonist caused a significantly greater decrease in peak and steady state responses than in pressure fluctuations. An M3-receptor antagonist decreased all 3 components. Alpha, beta-methylene adenosine triphosphate markedly decreased fluctuations, in contrast to norepinephrine, which eliminated the steady state response while preserving fluctuations.

CONCLUSIONS

The response to cholinergic stimulation of the isolated bladder has 3 components. The initial tonic peak response increases with bladder distention and it is inhibited by M2 and M3 muscarinic receptor antagonists. The tonic steady state response does not vary with bladder volume and it is inhibited by M2 and M3-receptor antagonists, and by beta3-adrenergic receptor agonists. Phasic fluctuations are minimal at low bladder volume, and with alpha, beta-methylene adenosine triphosphate or an M3-receptor antagonist. Thus, the response to cholinergic stimulation varies with bladder volume. It can be differentially modulated by muscarinic antagonists and also by agents acting through nonmuscarinic receptors.

[Synthesis and vascular relaxing activity of arecoline derivatives coupled with nitric oxide donors]

AIM

To search for potential anti-atherosclerosis drugs with vascular relaxation activity, a series of agonists of endothelial targets were designed and synthesized.

METHODS

Coupling N-methyl-1,2, 3,6-tetrahydrapyridine ring system with 3,4-dibenzenesulfonyl-1,2,5-oxadiazole-2-oxide through esterification or amidation, a series of arecoline derivatives containing NO donors were designed and synthesised.

RESULTS

A novel series of compounds structurally related to arecoline have been prepared, the proposed structures of eighteen new compounds were established by IR, 1H NMR, MS spectroscopy and elemental analysis. The effects of the target compounds on the vasodilation activity were tested in the isolated preparation of mice thoratic aorta.

CONCLUSION

This preliminary pharmacological tests showed that the candidates have good vasodilation activities and were worthy to be intensively studied.

Comparison study of autonomous activity in bladders from normal and paraplegic rats

AIM

To identify differences in the pattern of pressure generated by isolated bladders from normal and paraplegic rats.

MATERIALS AND METHODS

Nine female Wister rats were made paraplegic by spinal cord transsection at the vertebral level T8-T9 and sacrificed between D21 and D28. A further group (n = 9) was used as a control group. Each bladder was excised and placed in an organ bath where intravesical pressures were measured. Pressure changes were divided in two well-defined groups: macro-transients and spikes. The effects of intravesical volume load and muscarinic (M) agonists were studied.

RESULTS

We demonstrated a higher frequency, a longer duration, and a higher variance of duration in macro-transients in the neurogenic group. Intravesical volume load influenced the amplitude and frequency of macro-transients in both groups similarly. The effects of the muscarinic (M(2))-selective agonist arecaïdine were different in neurogenic bladder; the effects of the non-selective muscarinic (M)-agonist carbachol were similar in both groups.

CONCLUSION

We showed that the pattern of autonomous activity was significantly different between normal and neurogenic rat bladders. We also found evidence for alterations in the muscarinic response of isolated neurogenic rat bladders. This model offers an exciting new research tool to evaluate the detrusor activity in neurogenic and normal conditions.

Activation of muscarinic K+ channels by arecaidine propargyl ester in isolated guinea-pig atrial myocytes

Arecaidine propargyl ester (APE) was developed as a potential candidate compound for the treatment of Alzheimer's disease. APE has been shown to have cardiovascular effects. APE produces negative chronotropic and inotropic effects in isolated atria. However, the ionic mechanisms underlying the cardiovascular effects of APE in guinea-pig atria are unclear. The aims of this study were: (1) to examine the shortening effect of APE on action potential duration (APD) and to compare the difference in potency between APE and muscarine in isolated single guinea-pig atrial myocytes by using the current clamp method, (2) to examine by using patch clamp techniques the ionic mechanisms underlying the cardiac effects of APE, and (3) to determine whether the cardiac effects caused by APE affect the usefulness of APE as a potential candidate for the treatment of Alzheimer's disease. The APE significantly reduced the APD in guinea-pig atria and produced no direct effect on ventricular myocytes. APE is approximately 20 times as potent as muscarine in shortening the APD. Attenuation of the APD was consistently accompanied by a hyperpolarization of the resting membrane potential in a concentration-dependent manner. The APE activated muscarinic K+ channels and increased potassium conductance in guinea-pig atrial myocytes. In the cell-attached configuration, the APE contained in the pipette increased the channel-opening probability and decreased the closed-state time interval. The proposal that APE can be used as a potential remedy for the treatment of Alzheimer's disease should be taken into consideration the undesirable cardiovascular side effects that APE causes at lower concentrations.

Volume-induced effects on the isolated bladder: a possible local reflex

OBJECTIVES

To: (i) determine the effects of changing intravesical volume on autonomous activity in the isolated whole bladder of the guinea pig; (ii) identify the mechanisms which might contribute to induced changes; and (iii) explore the idea that changes in bladder volume which affect phasic activity are part of a local reflex operating within the bladder wall.

MATERIALS AND METHODS

Bladders were isolated from female guinea pigs, cannulated via the urethra and maintained in vitro in Tyrode's solution. The intravesical pressure (IVP) was monitored and drugs added to the bathing solution.

RESULTS

The isolated unstimulated bladder containing 500-600 microL of fluid generates small (1-2 cm H2O) phasic rises in IVP, i.e. autonomous activity. When the bladder volume was increased, autonomous activity increased. In the presence of muscarinic agonists (100 nmol/L arecaidine and carbachol 100 nmol/L) autonomous activity is augmented, giving rise to large (>10 cm H2O) phasic rises in IVP. When the volume was increased, both the amplitude and frequency of the transients increased. When the bladder volume was reduced there was a period of marked inhibition of phasic activity. To explore the mechanisms underlying these changes the possible involvement of local neural reflexes was explored. The neurotoxin tetrodotoxin had no effect on the volume-induced changes. Sensory nerves are insensitive to tetrodotoxin and thus to assess their possible contribution bladders were exposed to capsaicin (10 micromol/L) to stimulate and eliminate sensory fibres; capsaicin caused complex changes in phasic activity, i.e. an initial increase, a secondary slowing and decrease, followed by a period of recovering amplitude and increased frequency. These changes suggest actions of the sensory nerves on the phasic mechanism indicative of a local axonal reflex. Once the phasic activity had returned to levels before capsaicin, changes in bladder volume still produced increases in activity and inhibition after the volume decrease. Interstitial cells (cells capable of increasing cGMP) are found in the bladder wall; to assess their possible role in the volume-induced changes, bladders were treated with 30 micromol/L ODQ, an inhibitor of guanyl cyclase, for 30-60 min. The volume-induced rise in frequency was little affected but the inhibition seen on volume reduction was reduced.

CONCLUSIONS

These results show that there are components in the bladder wall which respond to distension by affecting phasic activity. This stimulus/response may reflect a volume 'reflex' within the bladder wall, consisting of excitatory and inhibitory components. This local reflex does not appear to involve directly motor or sensory nerves, although the latter can affect phasic activity, and their actions may represent a further reflex mechanism in the bladder wall. The possible involvement of guanyl cyclase in the volume-induced inhibition may indicate a role for interstitial cells. The physiological role of these mechanisms as a component of a motor/sensor system in the bladder wall is discussed.

Proteasome inhibitors; synthesis and activity of arecoline oxide tripeptide derivatives

We describe the synthesis and biological activities of a series of methyl 3,4-epoxypiperidine-3-carboxylate tripeptide derivatives that inhibit the chymotryptic and tryptic active sites of the 20S proteasome. Of the series, compound 2 which contains 3-hydroxy-2-methylbenzoyl group at its N-terminal position, displayed the greatest inhibitory potency (IC(50) <1 microM). All derivatives showed favourable pharmacokinetic properties.

Cholinergic regulation of the evoked quantal release at frog neuromuscular junction

The effects of cholinergic drugs on the quantal contents of the nerve-evoked endplate currents (EPCs) and the parameters of the time course of quantal release (minimal synaptic latency, main modal value of latency histogram and variability of synaptic latencies) were studied at proximal, central and distal regions of the frog neuromuscular synapse. Acetylcholine (ACh, 5 x 10(-4) M), carbachol (CCh, 1 x 10(-5) M) or nicotine (5 x 10(-6) M) increased the numbers of EPCs with long release latencies mainly in the distal region of the endplate (90-120 microm from the last node of Ranvier), where the synchronization of transmitter release was the most pronounced. The parameters of focally recorded motor nerve action potentials were not changed by either ACh or CCh. The effects of CCh and nicotine on quantal dispersion were reduced substantially by 5 x 10(-7) M (+)tubocurarine (TC). The muscarinic agonists, oxotremorine and the propargyl ester of arecaidine, as well as antagonists such as pirenzepine, AF-DX 116 and methoctramine, alone or in combination, did not affect the dispersion of the release. Muscarinic antagonists did not block the dispersion action of CCh. Cholinergic drugs either decreased the quantal content m(o) (muscarinic agonist, oxotremorine M, and nicotinic antagonist, TC), or decreased m(o) and dispersed the release (ACh, CCh and nicotine). The effects on m(o) were not related either to the endplate region or to the initial level of release dispersion. It follows that the mechanisms regulating the amount and the time course of transmitter release are different and that, among other factors, they are altered by presynaptic nicotinic receptors.

Activation of muscarinic acetylcholine receptors elicits pigment granule dispersion in retinal pigment epithelium isolated from bluegill

BACKGROUND

In fish, melanin pigment granules in the retinal pigment epithelium disperse into apical projections as part of the suite of responses the eye makes to bright light conditions. This pigment granule dispersion serves to reduce photobleaching and occurs in response to neurochemicals secreted by the retina. Previous work has shown that acetylcholine may be involved in inducing light-adaptive pigment dispersion. Acetylcholine receptors are of two main types, nicotinic and muscarinic. Muscarinic receptors are in the G-protein coupled receptor superfamily, and five different muscarinic receptors have been molecularly cloned in human. These receptors are coupled to adenylyl cyclase, calcium mobilization and ion channel activation. To determine the receptor pathway involved in eliciting pigment granule migration, we isolated retinal pigment epithelium from bluegill and subjected it to a battery of cholinergic agents.

RESULTS

The general cholinergic agonist carbachol induces pigment granule dispersion in isolated retinal pigment epithelium. Carbachol-induced pigment granule dispersion is blocked by the muscarinic antagonist atropine, by the M1 antagonist pirenzepine, and by the M3 antagonist 4-DAMP. Pigment granule dispersion was also induced by the M1 agonist 4-[N-(4-chlorophenyl) carbamoyloxy]-4-pent-2-ammonium iodide. In contrast the M2 antagonist AF-DX 116 and the M4 antagonist tropicamide failed to block carbachol-induced dispersion, and the M2 agonist arecaidine but-2-ynyl ester tosylate failed to elicit dispersion.

CONCLUSIONS

Our results suggest that carbachol-mediated pigment granule dispersion occurs through the activation of Modd muscarinic receptors, which in other systems couple to phosphoinositide hydrolysis and elevation of intracellular calcium. This conclusion must be corroborated by molecular studies, but suggests Ca2+-dependent pathways may be involved in light-adaptive pigment dispersion.

Cholinergic modulation of nociceptive responses in vivo and neuropeptide release in vitro at the level of the primary sensory neuron

Muscarinic acetylcholine receptors (mAChRs) have been widely reported as pharmacological targets for the treatment of pain. However, most of these efforts have focused on CNS mAChRs and their role in modulating nociception at the level of the spinal cord. The present study examines the contribution of peripheral mAChRs in trigeminal nociceptive pathways using a combination of in vivo and in vitro approaches. In the formalin model of orofacial nociception in rats, a peri-oral co-injection of the M2 agonist arecaidine dose-dependently inhibited phase 2 nocifensive behavior up to approximately 50% at 5 nmol. This effect was blocked by co-treatment with the mAChR antagonist atropine and was not seen when arecaidine was administered under the skin of the back, a site distant from that of the formalin injection. In vitro superfusion of isolated rat buccal mucosa with the non-selective mAChR agonist muscarine or arecaidine led to a concentration-dependent inhibition of capsaicin-evoked CGRP release to 39% (EC50=255 nM) and 28% (EC50=847 nM) of control values, respectively. Both responses were blocked by the non-selective mAChR antagonist atropine or the M2 antagonist gallamine. Further, the endogenous ligand ACh produced a bi-phasic response, potentiating evoked CGRP release to 195% of control (EC50= 918nM) and inhibiting evoked CGRP release to 45% of control (EC50=255 microM), effects that were shown to be mediated by nAChRs and mAChRs, respectively. Finally, combined in situ hybridization/immunofluorescence demonstrated that m2 mRNA was present in 20% of trigeminal ganglion neurons between 30 and 60 microm in diameter and that 5-9% of these also expressed CGRP or VR1 immunoreactivity. These results show that activation of peripheral M2 receptors produces antinociception in vivo and the inhibition of nociceptor activity in vitro. While histological analyses at the level of the trigeminal neuronal cell bodies leave open the question of whether the effects of M2 agonists are direct or indirect, these data indicate that primary sensory neuronal M2 receptors may represent a viable peripheral target for the treatment of pain and inflammation.

Arecoline Tripeptide Inhibitors of Proteasome

The 26S proteasome is a multicatalytic protease complex that plays an essential role in intracellular protein degradation. We have synthesized and tested a series of arecoline peptide derivatives where the peptide portion derives from a screening of tripeptide sequences, and the arecoline moiety has been considered as a potential substrate for catalytic threonine. Derivatives 17-19 are the best compounds of the series, showing chymotryptic-like (beta5) inhibition (IC(50) congruent with 1 microM) and favorable pharmacokinetic properties.

Comparative in vitro permeability of human vaginal, small intestinal and colonic mucosa

Our previous experience with a continuous flow-through perfusion system has demonstrated its usefulness for studying diffusion kinetics of drugs across small intestinal mucosa for bioavailability/bioequivalence (BA/BE) studies. During the last decade, delivery of drugs to the colon for systemic absorption as well as for local delivery in certain colonic diseases, has been extensively investigated. For this reason, we sought to assess the in vitro comparative permeability of human vaginal, small intestinal and colonic mucosa using a flow-through perfusion method. It was clear from our studies that human colonic epithelium was statistically significantly (P<0.05) more permeable to water, 17beta-estradiol, arecoline and arecaidine than intestinal mucosa. However, both these mucosae were statistically significantly less permeable to the above four permeants than human vaginal mucosa. As previously shown for small intestinal mucosa, the low in vitro permeability of colonic mucosa to drugs with molecular weight >300Da may necessitate using other epithelial membranes, e.g. vaginal mucosa, as alternative barriers for in vitro BA/BE studies. We also concluded that the flow-through mucosal perfusion system used in our laboratory is therefore also potentially useful for determining the permeability of a therapeutic agent from the colon for registration purposes.

Attentional effects of nicotinic agonists in rats

Nicotine can increase stimulus detection, response rate and speed in the five-choice serial reaction time task, a rodent test of attention. In the present experiments, four other nicotinic agonists with different pharmacological profiles were compared in the same procedure. The response profile of epibatidine resembled that previously obtained with nicotine in that response accuracy was enhanced and omission errors and correct response latency decreased. ABT-418 transiently increased accuracy in the first 10 min of test sessions and reduced response latency. Isoarecolone caused a dose-related increase in accuracy, but had no effect on omissions or response latency. This absence of effects on response rate- or speed-related measures may be related to its previously reported reduced ability to release dopamine as compared with nicotine. The alpha7-agonist AR-R17779 was without effect on any measure, indicating that this receptor subtype may not mediate nicotinic effects on attention. Affinity constants of compounds, determined in competition binding assays targeting the alpha4beta2, alpha7, alpha3beta4 and alpha3beta2* nAChR subtypes, could not explain the differential behavioural effects observed. Differences in their functional efficacy at nAChR subtypes may instead be responsible. The finding that attentional performance and response rate and speed can be selectively modulated by nicotinic agonists is encouraging for the development of drugs with therapeutic properties similar to those of nicotine but with reduced unwanted effects.

Agonist- and nerve-induced phasic activity in the isolated whole bladder of the guinea pig: evidence for two types of bladder activity

Spontaneous localised propagating waves of contraction and localised stretches have been reported to occur in the isolated whole bladder of the guinea pig. The physiological role and the cellular processes underlying these events are unknown. In order to gain insight into the mechanisms generating this complex activity, experiments were performed to examine and compare the responses of the whole bladder preparation to (i) the muscarinic agonists carbachol and arecaidine, (ii) the nicotinic ligand lobeline and (iii) nerve stimulation. High concentrations of the muscarinic agonists (>3 micro M) induced a slow rise in intra-vesical pressure upon which were superimposed pressure transients, while low concentrations (< 300 nM) induced only phasic rises in pressure. One interpretation of these data is that there are two separate mechanisms activated by muscarinic agonists: one generating contracture and the other phasic activity. Immunocytochemical staining revealed M(3) muscarinic receptors on smooth muscle cells within trabeculae and a second population of positive cells in the sub-urothelial layer. This observation raises the possibility that the actions of muscarinic agonists are a consequence of activating different cell types. Lobeline (1-60 micro M) activated phasic contractions but did not cause a rise in basal pressure. Atropine did not inhibit the lobeline-induced responses but abolished the muscarinic responses. Also, hexamethonium or tetrodotoxin did not affect the lobeline-induced responses. These observations suggest that the mechanism generating phasic activity is activated by a nicotinic stimulus that does not involve ganglia, nerves or the neuromuscular junction. Stimulation of the bladder nerve at frequencies between 20 and 30 Hz for 5 s resulted in a rapid rise in intra-vesical pressure. Prolonged nerve stimulation (10-200 s) at frequencies between 1 and 10 Hz activated phasic rises in pressure. Low frequency nerve stimulation increased the frequency of agonist-induced phasic activity. Thus, nerve stimulation can also produce two forms of activity and low frequency stimulation can augment the processes generating phasic activity. These observations suggest that there are two distinct types of bladder activity: global contractions involving most of the bladder wall and phasic contractions comprising propagating waves of contraction. The mechanisms generating these contractile events appear to be different and they may involve cells located in different regions of the bladder. The nature of these mechanisms and their possible physiological significance is discussed.

Autonomous activity in the isolated guinea pig bladder

Phasic changes in pressure have been reported to occur in the bladder which are not associated with micturition. Spontaneous intravesical pressure changes can be recorded from bladders in vitro or bladders in vivo isolated from the central nervous system suggesting that the bladder itself is capable of autonomous activity. Experiments using isolated cells and muscle strips indicate that the smooth muscle can generate spontaneous activity. Whether this is the origin of phasic changes in the intact organ remains unknown. The present study set out to establish the presence and characteristics of autonomous activity in the isolated guinea pig bladder. Multiple-point motion analysis and concurrent intravesical pressure recording were used to identify and quantify spontaneous and evoked activity. Highly complex autonomous activity was observed in unstimulated bladders. This activity comprised localised micro-contractions in single or multiple discrete regions, waves of activity and micro-stretches. Low-amplitude phasic 'micro-transients' were seen in the intravesical pressure trace in association with micro-contractions. Incremental increases in the intravesical volume recruited additional areas of activity. Atropine and tetrodotoxin had no effect on the micro-transients or micro-contractions. Exposure to the muscarinic agonist arecaidine (10-300 nM) initially increased the incidence of micro-contractions which subsequently became co-ordinated into phasic pressure rises and contraction waves, interspersed with periods of total quiescence. The findings describe the generation and co-ordination of autonomous activity in the bladder wall and also demonstrate complex phasic activity. This approach has shown the importance of assessing the integrative properties of the entire organ in studies of the physiology and patho-physiology of the bladder.

[Pharmacological parameters of muscarinic cholinoreceptors in skeletal muscles]

It has been shown that bath application of muscarine delayed the early post-denervation depolarization in the muscle fibers incubated for 3 h in culture medium. The greatest reduction of the post-devervation depolarization was observed with 50 nmol/l muscarine. Atropine, a muscarinic antagonist, clozapine, a specific inhibitor of M1/M5-cholinergic receptors, and nitrocaramiphen, a M1-antagonist, completely removed the hyperpolarizing effect of muscarine. 4-DAMP, a specific inhibitor of M3-cholinergic receptors, himbacine, an antagonist of M2-cholinergic receptors, and tropicamide, a specific inhibitor of M2/M4-cholinergic receptors, failed to prevent the effect of muscarine. A M1/M2 muscarine agonists propargyl and but-2-ynyl esters of arecaidine had apparent muscarine-like effect. Nitrocaramiphen, and not himbacine, prevented the hyperpolarizing effect of these cholinomimetics. It is concluded that muscarine and esters of arecaidine delay the development of early postdenervation depolarization in M1-cholinergic receptors of skeletal muscle.

Areca nut extract lowers the permeability of vaginal mucosa to reduced arecoline and arecaidine

Areca nut chewing has been implicated in the development of oral cancer and oral submucous fibrosis. Arecoline and arecaidine, which are alkaloids present in the areca nut, are thought to play a major role in the development of adverse effects resulting from this chewing habit. Because these alkaloids appear to be associated with the development of the above diseases, we determined their diffusion kinetics through human vaginal mucosa in the presence and absence of a 1% areca nut extract. Seven clinically healthy vaginal mucosa specimens (mean patient age+/-standard deviation, 52+/-13 years; age range, 38-74 years) were obtained during surgery. In vitro flux values of reduced arecoline and arecaidine (r-arecoline and r-arecaidine) were determined through use of a flow-through diffusion apparatus. Analysis of variance, a Duncan multiple range test, and an unpaired t-test were used to determine steady state kinetics and flux differences over time intervals. The flux values across vaginal mucosa of r-arecoline and r-arecaidine were decreased in the presence of 1% areca nut extract. For r-arecoline, these flux values were significantly lower statistically when compared to those obtained in the absence of areca nut extract. These findings concur with results previously obtained for water, where the astringent action of the tannins present in the areca nut extract was thought to alter the barrier properties of the epithelium, resulting in decreased permeability.

Muscarinic M2 receptors inhibit heat-induced CGRP release from isolated rat skin

The action of cholinergic agonists on modulating basal and heat-induced CGRP release was investigated in isolated rat skin. Nicotine (10(-6), 10(-5) and 10(-4) M) induced a bimodal increase of CGRP release, that was significant for the two larger concentrations (by 113 and 36%, respectively). On the contrary, muscarine (10(-4) M) and arecaidine (10(-5) M) significantly decreased the basal CGRP release (by 16 and 23%, respectively). The substantial increase of CGRP release evoked by noxious heat (47 degrees C) remained unaltered upon co-application of nicotine, but was diminished by 35% upon muscarine. Arecaidine was more effective in this respect causing significant dose-dependent depressions by 30% (at 10(-6) M) and by 60% (at 10(-5) M). These data support a role of muscarinic M2 receptors in nociceptor desensitization.

Diffusion of reduced arecoline and arecaidine through human vaginal and buccal mucosa

Because alkaloids from areca nut, arecoline and arecaidine, have been implicated in the development of oral submucous fibrosis, we determined their diffusion kinetics through human buccal and vaginal mucosa. Four clinically healthy vaginal mucosa specimens (mean patient age +/- standard deviation: 47 +/- 15 years; age range: 31-60 years) and 4 buccal mucosa specimens from 2 male patients and 2 female patients (mean patient age +/- standard deviation: 31 +/- 9 years; age range: 17-53 years) were obtained during surgery. In vitro flux rates of reduced arecoline and arecaidine (r-arecoline and r-arecaidine) were determined by use of a flow-through diffusion apparatus. Analysis of variance, a Duncan multiple range test, and an unpaired t-test were used to determine steady state kinetics and flux differences over time intervals. Although statistically significant differences were observed between flux values for both alkaloids and tissues at certain time points, these were not considered to be of biological (clinical) significance. However, the flux rates across both mucosa of r-arecoline were significantly higher statistically than those of rarecaidine. The findings demonstrated the differences in the diffusion kinetics between r-arecoline and r-arecaidine across human buccal and vaginal mucosa, an observation that could be explained in terms of their ionisation characteristics. Additionally, the results obtained further support the hypothesis that human vaginal mucosa can be used as a model for buccal mucosa in studies of permeability to various chemical compounds.

Cancer induction in the DMBA hamster cheek pouch: a modified technique using a promoter

OBJECTIVE

To evaluate a modified method of carcinogenesis induction using the 9,10-dimethyl-1,2-benzanthracene (DMBA) sustained-release suture technique followed by arecaidine promotion in the hamster cheek pouch model.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Number 3-0 cotton sutures were impregnated with DMBA and coated with silicone elastomer. These sutures were placed in the cheek pouch of Syrian hamsters in the submucosal space to a length of approximately 1.5 cm. The suture placement was confirmed every 2 weeks and replaced if lost. After 12 weeks, the DMBA-coated sutures were removed. The cheek pouches were everted and painted with a solution of arecaidine three times weekly for up to an additional 4 weeks or until the tumor reached a size of 100 mm2.

RESULTS

We placed sutures in 165 Syrian hamster cheek pouches. Of these, 133 hamsters (80.6%) produced squamous cell carcinomas that reached a size of 100 mm2 and then were randomly selected for treatment in a new drug trial. Twenty-six hamsters (15.8%) were found dead and 6 (3.6%) were killed because of severe inflammation.

CONCLUSIONS

The DMBA hamster cheek pouch model is a reliable and efficient animal model for inducing squamous cell carcinoma and can be used to study upper aerodigestive tract tumors.

Carbachol and acetylcholine delay the early postdenervation depolarization of muscle fibres through M1-cholinergic receptors

The resting membrane potential (RMP) of denervated muscle fibres of rat diaphragm muscle is depolarized by approximately 8-10 mV during the first 3 h after nerve section and this early postdenervation depolarization is reduced substantially by the presence of 5x10(-8) M acetylcholine (ACh) or carbachol (CB). The muscarinic antagonist atropine (Atr; 5x10(-9) to 5x10(-6) M) reduced the effect of CB in a dose-dependent manner (K(i)=7x10(-8) M) and increased the rate of the early postdenervation depolarization. In lower doses (5x10(-7) M), Atr acted only in the presence of an allosteric stabilizator hexamethylene-bis-[dimethyl-(3-phtalimidopropyl)ammonium] (W-84). Also pirenzepine, a specific inhibitor of the M1 subtype of muscarinic receptor, blocked the action of CB in a dose-dependent manner with an apparent inhibition constant K(i)=1x10(-7) microM. DAMP, a specific M3 antagonist, was without effect on the muscle hyperpolarization induced by CB. CB also hyperpolarized the membrane potentials of muscles which were denervated for 1-3 days. It is concluded that ACh and CB protect the muscle fibres from early depolarization through M1-cholinergic receptors on the muscle membrane. These particular receptors can apparently mediate the 'trophic', non-impulse regulation of RMP in skeletal muscles when they are activated by acetylcholine released non-quantally.

Characteristics of the ligand-binding site interaction for a series of arecoline-derived muscarinic agonists: a quantum chemical study

This work focuses on electronic and conformational structure of bicyclic analogues of arecoline and sulfoarecoline--muscarinic receptor agonists structurally related to 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) and its S-methylsulfonium derivative (DHTO). Conformational freedom of six-member rings containing sulphur and nitrogen has been investigated by means of semiempirical AM1 method. Interaction between 'cationic heads' of two representative compounds and HCO2- ion serving as a model of carboxyl group of Asp in the muscarinic receptor has been modelled using DFT method in local approximation (LDA with VWN exchange correlation functional). Electrostatic potential (ESP) around studied complexes and ligands with added electron (simulation of complex formation) are presented and analysed. Position and depth of ESP minima in a series of studied ligands correlate well with their activity as muscarinic agonists. On the basis of our results the mechanism of ligand-binding site interaction may be elucidated. The calculations allow also for the comparison of bicyclic analogues of arecoline with already existing model for muscarinic pharmacophore and for rationalization of model parameters.

Interaction of a semirigid agonist with Torpedo acetylcholine receptor

The binding of the semirigid agonist [(3)H]arecolone methiodide to the Torpedo nicotinic acetylcholine receptor has been correlated with its functional properties measured both in flux studies with Torpedo membrane vesicles and by single-channel analysis after reconstitution in giant liposomes. Under both equilibrium and preequilibrium conditions, the binding of arecolone methiodide is similar to that of other agonists such as acetylcholine. At equilibrium, it binds to two sites per receptor with high affinity (K(d) = 99 +/- 12 nM), and studies of its dissociation kinetics suggest that each of these sites is made up of two subsites that are mutually exclusive at equilibrium. The kinetics of arecolone methiodide binding were monitored by the changes in the receptor intrinsic fluorescence, and the data are consistent with a model in which the initial binding event is followed by sequential conformational transitions of the receptor-ligand complex. In flux studies, arecolone methiodide was approximately 3-fold more potent (EC(50) = 31 +/- 5 microM) than acetylcholine but its maximum flux rate was 4-10-fold lower. This phenomenon has been studied further by single-channel analysis of Torpedo receptors reconstituted in giant liposomes. Whereas the flexible agonist carbamylcholine (5 microM) was shown to induce channels with conductances of 56 and 34 pS with approximately equal frequency, arecolone methiodide (2 microM) preferentially induced the channel of lower conductance. These results are interpreted in terms of a simple model in which the rigidity of arecolone methiodide restrains the conformation that the receptor-ligand complex can adopt, thus favoring the lower conductance state.

Muscarinic properties of compounds related to arecaidine propargyl ester

A series of new analogues of the arecaidine propargyl ester (CAS 35516-99-5), APE, 1a) with alcohols consisting of 4 or 5 carbon atoms were investigated at muscarinic receptor subtypes. The muscarinic activity of the quaternary and tertiary salts of the APE-related compounds were assayed on the isolated guinea-pig ileum (M3 receptor subtype) and guinea-pig left atria (M2 receptor subtype) as well as on rabbit isolated vas deferens (M1 receptor subtype). The structural variations made in the APE molecule, replacing the triple bond in the ester side chain with structures such as double bond, an allene moiety, a single bond, a cyclopropyl group or two triple bonds should alter the selectivity and potency in favour of the M2 subtype. Enhanced, though modest, selectivity for M2 receptors was achieved with the 2-butynyl ester 2a. The other structural variations resulted in a loss of potency, but not necessarily of efficacy.

Synthesis and muscarinic receptor pharmacology of a series of 4,5,6,7-tetrahydroisothiazolo[4,5-c]pyridine bioisosteres of arecoline

A series of O- and ring-alkylated derivatives of 4,5,6,7-tetrahydroisothiazolo[4,5-c]pyridin-3-ol was synthesized via treatment of appropriately substituted 4-benzylamino-1,2,5,6-tetrahydropyridine-3-carboxamides with hydrogen sulfide and subsequent ring closure by oxidation with bromine. The muscarinic receptor affinity as well as estimated relative efficacy and subtype selectivity of this series of bicyclic arecoline bioisosteres were determined using rat brain membranes and a number of tritiated muscarinic receptor ligands. The effects at the five cloned human muscarinic receptor subtypes of a selected series of chiral analogues, with established absolute stereochemistry, were studied using receptor selection and amplification technology (R-SAT). The potency, relative efficacy, and receptor subtype selectivity of these compounds were related to the structure of the O-substituents and the position and stereochemical orientation of the piperidine ring methyl substituents.

Neuronal soma-dendritic and prejunctional M1-M4 receptors in gastrointestinal and genitourinary smooth muscle

A variety of neurons in gastrointestinal and genitourinary smooth muscle express muscarinic auto- as well as heteroreceptors. These receptors are found on the soma and dendrites of many cholinergic, sympathetic and NANC neurons and on axon terminals. A given neuron may contain both excitatory and inhibitory presynaptic muscarinic receptors. The subtypes involved are species- and tissue-dependent, and neuronal M1 to M4 receptors have been shown to be expressed in smooth muscle tissues. In this study, the ability of several selective muscarinic receptor antagonists to inhibit the effect of arecaidine propargyl ester (APE) on prejunctional muscarinic receptors on sympathetic nerve endings in the rabbit anococcygeus muscle (RAM) was investigated to characterise the receptor subtype involved. Electrical field stimulation (EFS) resulted in a release of noradrenaline (NA) eliciting monophasic contractions due to stimulation of postjunctional alpha1-adrenoceptors. The selective muscarinic agonist APE did not reduce contractions to exogenous NA, but caused a concentration-related and N-methylatropine-sensitive inhibition of neurogenic responses. All muscarinic antagonists investigated failed to affect the EFS-induced contractions, but shifted the concentration-response curve of APE to the right in a parallel and surmountable fashion. Schild analysis yielded regression lines of unit slope, indicating competitive antagonism. The following rank order of antagonist potencies (pA2 values) was found: tripitramine (9.10) > AQ-RA 741 (8.26) > or = himbacine (8.04) > or = (S)-dimethindene (7.69) > pirenzepine (6.46) > or = p-F-HHSiD (6.27). A comparison of the pA2 values determined in the present study with literature binding and functional affinities obtained at native or recombinant M1 to M5 receptors strongly suggests that NA release from sympathetic nerve endings in RAM is inhibited by activation of prejunctional muscarinic M2 receptors.

Deficiency in collagen and fibronectin phagocytosis by human buccal mucosa fibroblasts in vitro as a possible mechanism for oral submucous fibrosis

Oral submucous fibrosis (OSF), a chronic oral mucosal condition commonly found in south Asians, is a disorder characterized by a quantitative as well as a qualitative alteration of collagen deposition within the subepithelial layer of the oral mucosa. Since degradation of collagen by fibroblast phagocytosis is an important pathway for physiological remodelling of soft connective tissues, we have investigated phagocytosis of collagen- and fibronectin-coated latex beads by fibroblast cultures with an in vitro model system. Coated fluorescent latex beads were incubated with human oral mucosa fibroblasts and the fluorescence associated with internalized beads was measured by flow cytometry. Cells from normal tissues that had been incubated with beads for 16 h contained a mean of 75% collagen phagocytic cells and 70% fibronectin phagocytic cells; however, about 15% and 10% of phagocytic cells individually contained more than twice the mean number of beads per cell. In contrast, cells from OSF tissues exhibited a 40% reduction of the proportions of collagen phagocytic cells (mean=35%) and a 48% decrease of the proportions of fibronectin phagocytic cells (mean=22%), none of the cells having a high number of beads as compared to normal fibroblasts. OSF lesions appear to contain fibroblasts with marked deficiencies in collagen and fibronectin phagocytosis. To investigate if inhibition of phagocytosis could be demonstrated in vitro, normal fibroblast cultures were incubated with areca nut alkaloids (arecoline, arecaidine). The cultures had a dose-dependent reduction in the proportions of phagocytic cells. On the other hand, corticosteroid used in the treatment of OSF exhibited a dose-dependent enhancement in the proportion of phagocytic cells. Therefore, our hypothesis for OSF, although oversimplified, is that betel nut alkaloids (arecoline, arecaidine) inhibit fibroblast phagocytosis and this provides a mechanism for the development of OSF. The benefit of a local intralesional injection of corticosteroid is also possibly, at least in part, through an enhancement of fibroblast collagen phagocytosis.

Inhibition of brain choline uptake by isoarecolone and lobeline derivatives: implications for potential vector-mediated brain drug delivery

Delivery of certain compounds to brain is restricted by the nature of the blood-brain barrier (BBB). Many valuable pharmaceuticals are excluded from the CNS due to hydrophilicity or charge. These limitations have been overcome by numerous methods. One method we use is to take advantage of saturable nutrient transporters located at the barrier. These systems transport hydrophilic and charged nutrients into brain such as choline, a quaternized neurotransmitter precursor. Using knowledge of their substrate specificity, it is possible to deliver agents into brain using these nutrient carriers. In this report, derivatives of lobeline and isoarecolone were evaluated to determine if they may gain access to brain by the blood-brain barrier basic amine transporter using the in situ brain perfusion technique. These compounds do bind the blood-brain barrier basic amine transporter and may enter brain by this transport system.

Quantitative colorimetric and gas chromatographic determination of arecaidine propargyl ester

Arecaidine propargyl ester (APE) is a potent muscarinic agonist often used in pharmacological studies. To date, no sensitive quantitative analytical method for APE has been published. In this study, two methods for the quantitative determination of APE are compared: a colorimetric assay, based on the formation of the corresponding ferric(III)-hydroxamic acid complex, and a direct gas chromatographic method, using arecoline as the internal standard. The latter method was found to be more precise. The utility of the gas chromatographic assay was further demonstrated in a stability study of the drug in the biological fluid aqueous humor of rabbits.

The mutagenicities of alkaloids and N-nitrosoguvacoline from betel quid

In Taiwan, betel quid is a natural masticatory, which is composed of fresh green areca fruit, Piper betle and slaked lime paste. Areca fruit contains some alkaloids, of which arecoline is the major one. N-Nitrosoguvacoline (NG), one of the N-nitrosation products of arecoline, is the only one N-nitrosamine found in Taiwanese betel quid chewing saliva. The mutagenic studies in Ames Salmonella microsome test showed that crude alkaloid extracts of areca fruit and arecoline were active in Salmonella typhimurium TA100, and NG was weakly active in TA98 and TA100. The activities in both arecoline and NG decreased further in the presence of rat liver S9 mix. Nitrite was significantly consumed during the N-nitrosation of arecoline and sodium nitrite at acidic condition (pH 3), whereas the formation of NG was favored at neutral condition (pH 7). Crude phenolic extracts of leaf and inflorescence of Piper betle inhibited the formation of NG by blocking the nitrite. However, a high amount of crude phenolic extracts of areca fruit enhanced the formation of NG.

Minimal arecaidine concentrations showing a promotion effect during DMBA-induced hamster cheek pouch carcinogenesis

The purpose of the present study was to determine the minimal arecaidine concentrations showing a synergistic effect on DMBA-induced hamster cheek pouch carcinogenesis. One hundred and twelve male adult Syrian golden hamsters were divided into 16 groups, each containing seven animals. After eight weeks of DMBA initiation and then four weeks of arecaidine promotion, 100% tumor incidence was found with arecaidine concentrations of 400 micrograms/ml and 500 micrograms/ml; average tumor numbers were 1.86 +/- 0.63 and 1.86 +/- 0.93 respectively (P < 0.05). After four weeks of DMBA and a subsequent eight weeks of arecaidine painting, all hamsters developed visible tumors with arecaidine concentrations of 900 micrograms/ml and 1000 micrograms/ml; average tumor numbers were 1.86 +/- 0.82 and 2.14 +/- 1.09 respectively (P < 0.05). The tumor dimensions varied little and differences were not statistically significant. Without DMBA pretreatment, regardless of the high arecaidine concentrations (1000 micrograms/ml, 2000 micrograms/ml and 3000 micrograms/ml) applied, no visible tumor growth was observed; only hyperkeratosis and inflammation could be discerned histologically. Thus, the minimal concentrations of arecaidine displaying a synergistic effect in the DMBA-induced hamster cheek pouch of carcinogenesis were found to be 400 micrograms/ ml applied for four weeks after eight weeks of DMBA application, and 900 micrograms/ml applied for eight weeks after four weeks of DMBA painting. These findings may be useful for other studies concerning the tumorgenicity of arecaidine.