In vitro characterisation of the muscarinic receptor partial agonist, sabcomeline, in rat cortical and heart membranes

We have investigated the pharmacology of the functionally selective muscarinic M1 receptor partial agonist, sabcomeline [SB-202026 (R-(Z)-(+)-alpha-(methoxyamino)-1-azabicyclo[2.2.2] octane-3-acetonitrile)], in rat cortex and heart using radioligand binding and functional studies. The Quinuclidinyl benzilate/Oxotremorine-M acetate ratio from radioligand binding studies suggested that sabcomeline and xanomeline [3(3-hexyloxy-1,25-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-met hylpyridine] are muscarinic receptor partial agonists in cortical and heart membranes. In [35S]GTPgammaS binding studies in rat cortex, carbachol stimulated binding via muscarinic M2/M4 receptors which could be blocked by sabcomeline with a pA2 of 7.2. In rat heart membranes, carbachol also stimulated [35S]GTPgammaS binding studies through muscarinic M2 receptors. Sabcomeline caused a small stimulation of basal [35S]GTPgammaS binding in both rat and heart tissues. Sabcomeline did not stimulate phosphoinositide hydrolysis in rat cortical slices, but did block the muscarinic M1 receptor-mediated response caused by carbachol with apparent pKb of 6.9. Xanomeline and milameline also had no effect on phosphoinositide hydrolysis up to 100 microM. In adenylyl cyclase studies in rat atria, sabcomeline inhibited forskolin-stimulated adenylyl cyclase activity to a similar extent to that of carbachol, xanomeline and milameline. The present study, using the techniques of radioligand binding, supports previous publications which have claimed that sabcomeline is a muscarinic receptor partial agonist. As expected, this study shows that the functional actions of this compound at muscarinic receptor subtypes and in different tissues will depend on receptor reserve.

Tumorigenesis in Mlh1 and Mlh1/Apc1638N mutant mice

An3 1 KAL I MutL homologue 1 (MLH1) is a member of the family of proteins required for DNA mismatch repair. Germ-line mutations in MLH1 lead to the cancer susceptibility syndrome hereditary nonpolyposis colorectal cancer (HNPCC). We generated mice carrying a null mutation in the Mlh1 gene. We showed that mice heterozygous and homozygous for the Mlh1 gene are predisposed to developing tumors of the gastrointestinal (GI) tract, lymphomas, and a number of other tumor types. We also examined the role of adenomatous polyposis coli gene (Apc) gene mutations in the GI tumors of Mlh1 mutant mice by different methods and showed that the GI tumors in Mlh1 mice express little or no adenomatous polyposis coli protein. When an Apc gene mutation was bred into the Mlh1 mutant mice, the GI tumor incidence increased 40-100-fold. The wild-type Apc allele in these tumors was found to contain mutations. Together, these results show that we have developed two mouse models for human HNPCC and that the mechanisms of tumor development in the GI tract of these mice involve loss of Apc gene function in a manner very similar to that seen in the GI tumors of HNPCC.

Simple O-acylated derivatives of lysergol and dihydrolysergol-I: synthesis and interaction with 5-HT2A, 5-HT2C and 5-HT1B receptors, and alpha1 adrenergic receptors

A series of simple O-acylated derivatives of the naturally occurring clavine alkaloids lysergol and dihydrolysergol-I were synthesized and tested in-vitro for their ability to interact with 5-HT2A receptors in rat tail artery, 5-HT2C receptors in piglet choroid plexus, 5-HT1B receptors in guinea-pig iliac artery and alpha1-adrenergic receptors in rat aorta. In contrast to the classical ergoline 5-HT2A receptor antagonists methysergide and LY53857, the compounds produced competitive antagonism of the 5-HT response in rat tail artery. Affinities of ergolines 3-14 were higher (pA2 values of 7.33-8.40) than those of the parent alcohols lysergol (1) and dihydrolysergol-I (2), respectively. The introduction of an isopropyl substituent at the N(1) position of the compounds failed to enhance 5-HT2A receptor affinity. Compounds 3-14 exhibited lower affinities for alpha1-adrenergic receptors than for 5-HT2A receptors. In particular, those lysergol derivatives that had an isopropyl substituent at the N(1) position were highly specific 5-HT2A receptor antagonists (ratio 5-HT2A/alpha1 = 302-3548). Selected derivatives of lysergol (3-5, 9-11) which were assayed for radioligand binding at 5-HT2C receptors in piglet choroid plexus had affinities that were similar to those found in rat tail artery. Additionally, lysergol and its N(1)-unsubstituted derivatives were found to be partial agonists (alpha of 0.2-0.4) for 5-HT2C receptor-mediated inositol phosphate accumulation in piglet choroid plexus. On the other hand, analogues with an isopropyl substituent at N(1) showed no measurable agonist activity. The observation that N(1)-unsubstituted derivatives of lysergol possessed agonist properties at 5-HT2C receptors whereas their agonist activity at 5-HT2A receptors was marginal (alpha of 0.05 for compound 3 at 1 microM) or not measurable, suggests that these compounds have different abilities to cause conformational change at the two receptor types. Selected derivatives of lysergol (3-5, 9-11) which were examined as ligands for 5-HT1B receptors in guinea-pig iliac artery caused insurmountable blockade of the contractile effect of 5-HT. N(1)-isopropyl derivatives had 30-50-fold lower affinities for 5-HT1B receptors of this tissue than their N(1)-unsubstituted analogues. It is concluded that O-acylated derivatives of the clavine alkaloids lysergol and dihydrolysergol-I mimic therapeutically relevant ergolines due to the complexity of their pharmacological profile as partial agonists and antagonists at 5-HT2A, 5-HT2C and 5-HT1B receptors, and at alpha1-adrenergic receptors.

A methodology for simulating biological systems using Microsoft Excel

The objective of this present study was to develop a simple, easily understood methodology for solving biologically based models using a Microsoft Excel spreadsheet. The method involves the use of in-cell formulas in which Rows and Columns of new data are generated from data typed into the spreadsheet, but does not require any programming skills or use of the macro language. The approach involves entering the key parameter values into the spreadsheet and conducting the simulation by solving a set of equations based on these parameter values. The examples used in this paper are firstly, a simple voltage clamp simulation in which initial parameter values are used to calculate a system in steady state. The second example is a current clamp simulation where steady state is not reached and the solution of the equations for each time increment is used as the input for the next time increment in the simulation. The calculations are based on the Hodgkin Huxley mathematical equations that describe the voltage dependence of ion channel behavior. The problems and flexibility of the method are briefly discussed. The methodology developed in this present study should help novice modelers to create simple simulations without the need to learn a programming language or purchase expensive software.

Glucose phosphorylation is essential for the turnover of neutral lipid and the second stage assembly of triacylglycerol-rich ApoB-containing lipoproteins in primary hepatocyte cultures

Primary hepatocytes cultured in a medium supplemented with amino acids and lipogenic substrates responded to increased extracellular glucose by increasing the secretion of VLDL apoB. This effect was accompanied by an increased secretion of VLDL triacylglycerol (TAG) derived from endogenous stores. Glucose also stimulated intracellular TAG mobilization via the TAG lipolysis/esterification cycle. All these effects were abolished in the presence of mannoheptulose (MH), an inhibitor of glucose phosphorylation. Glucose also gave rise to a modest (50% to 60%) increase in the incorporation of 35S methionine into newly synthesized apoB (P<0.05) and to a doubling of newly-synthesized apoB secretion as VLDL (P<0. 05). The magnitude of these effects was similar for apoB-48 and for apoB-100. MH inhibited apoB-48 and apoB-100 synthesis and VLDL secretion at all glucose concentrations. The effects of glucose and MH on the secretion of newly-synthesized apoB-48 or apoB-100 as small dense particles were less pronounced. Glucose had no effects on the posttranslational degradation of newly-synthesized apoB-100 or apoB-48. However, this process was significantly enhanced by MH. The results suggest that glucose stimulates TAG synthesis, turnover, and output as VLDL. These effects are associated with an increased VLDL output of apoB mediated mainly by an increase in the net synthesis of both apoB-48 and apoB-100. All these changes are prevented by interference with glucose phosphorylation. Output of small, dense, apoB-containing particles is relatively unaffected by the glucose and MH-induced changes in TAG synthesis and lipolysis, an observation which suggests that only the bulk lipid addition step of VLDL assembly is affected by changes in glucose metabolism.

Administration of n-3 fatty acids in the diets of rats or directly to hepatocyte cultures results in different effects on hepatocellular ApoB metabolism and secretion

Hepatocytes derived either from rats fed a diet enriched in n-3 fatty acids or from rats fed a low-fat diet and cultured with an n-3 fatty acid (eicosapentaenoic acid, EPA) in vitro were used to distinguish between the dietary effects and the direct effects of n-3 fatty acids on hepatocellular apolipoprotein (apo) B metabolism and secretion. ApoB-48 and apoB-100 synthesis, degradation, and secretion as large (d<1.006) and small (d>1.006) particles were determined after a pulse label with [35S]methionine. These effects were compared with changes in triacylglycerol (TAG) synthesis and secretion and with changes in de novo fatty acid synthesis (using 3H2O incorporation) under identical conditions. When n-3 fatty acid was given via the dietary route, apoB-48 very low density lipoprotein (VLDL) secretion was inhibited, but there was no effect on the secretion of apoB-100 VLDL. There was no effect on the secretion of either apoB-48 or apoB-100 as small, dense particles (d>1.006). Cellular TAG synthesis was significantly inhibited under these conditions, and fatty acid synthesis de novo was inhibited by 80%. By contrast, after direct addition of EPA to hepatocytes from normal rats, the secretion of both apoB-48 and apoB-100 VLDL was suppressed. The secretion of apoB-48, but not of apoB-100, as dense particles was also inhibited. However, there was little or no effect on TAG synthesis nor on fatty acid synthesis de novo. In addition, whereas dietary administration of n-3 fatty acid gave rise to decreased net synthesis and degradation of apoB-48, direct administration in vitro resulted in increased degradation with no effect on net synthesis. We conclude that the effects of n-3 fatty acids on hepatic lipid and apoB metabolism differ according to whether they are administered in vivo, via the dietary route, or in vitro, via direct addition to hepatocyte cultures.

Modulation by DLST of the genetic risk of Alzheimer's disease in a very elderly population

The mitochondrial alpha-ketoglutarate dehydrogenase complex (KGDHC) is deficient in Alzheimer's disease (AD). The DLST gene encodes the core, dihydrolipoyl succinyltransferase (DLST) component of KGDHC, and recent reports indicate an association between polymorphisms of DLST and AD in both white and Japanese patients. We therefore examined the relationship between AD and the DLST and apolipoprotein E (APOE) genes in elderly (89 +/- 7 years) AD patients, in whom the epsilon4 allele of APOE (APOE4) is a weak risk factor for AD. Polymorphisms of DLST (A19,117G and T19,183C), shown to be of interest in previous studies, were analyzed by restriction fragment length polymorphism analysis after polymerase chain reaction amplification. In a series of 429 white subjects from two Jewish nursing homes, an association of APOE4 with AD was found only in patients homozygous for the G,C allele of DLST. Similar relationships occurred in the "very elderly" (> or =85 years, n = 302) subgroup of this series, and also in an autopsy series (n = 225) that included white subjects from the Jewish nursing homes as well as other white subjects. These findings suggest a relationship between APOE4 and a DLST locus in the pathogenesis of AD in very elderly subjects.

Functional effects of the muscarinic receptor agonist, xanomeline, at 5-HT1 and 5-HT2 receptors

Xanomeline [3(3-hexyloxy-1,2,5-thiadiazol-4-yl)-1,2,5,6-tetrahydro-1-me thylpyridine] has been reported to act as a functionally selective muscarinic partial agonist with potential use in the treatment of Alzheimer's disease. This study examined the functional activity of xanomeline at 5-HT1 and 5-HT2 receptors in native tissue and/or human cloned receptors. Xanomeline had affinity for muscarinic receptors in rat cortical membranes where the ratio of the displacement affinity of [3H]-Quinuclidinyl benzilate vs that of [3H]-Oxotremorine-M was 16, indicative of partial agonist activity. Radioligand binding studies on human cloned receptors confirmed that xanomeline had substantial affinity for M1, M2, M3, M4, M5 receptors and also for 5-HT1 and 5-HT2 receptor subtypes. Carbachol and xanomeline stimulated basal [35S]-GTPgammaS binding in rat cortical membranes with micromolar affinity. The response to carbachol was attenuated by himbacine and pirenzepine with pA2 of 8.2, 6.9 respectively consistent with the response being mediated, predominantly, via M2 and M4 receptors. Xanomeline-induced stimulation of [35S]-GTPgammaS binding was inhibited by himbacine with an apparent pKb of 6.3, was not attenuated by pirenzepine up to 3 microM and was inhibited by the selective 5-HT1A antagonist WAY100635 with an apparent pKb of 9.4. These data suggest the agonist effect of xanomeline in this tissue is, in part, via 5-HT1A receptors. Similar studies on human cloned receptors confirmed that xanomeline is an agonist at human cloned 5-HT1A and 5-HT1B receptors. In studies using the fluorescent cytoplasmic Ca2+ indicator FLUO-3AM, xanomeline induced an increase in cytoplasmic Ca2+ concentration in SH-SY5Y cells expressing recombinant human 5-HT2C receptors. Atropine antagonized this response, consistent with mediation via endogenously-expressed muscarinic receptors. In the presence of atropine, xanomeline antagonized 5-HT-induced cytoplasmic changes in Ca2+ concentration in cells expressing h5-HT2A, h5-HT2B and h5-HT2c receptors with potencies similar to its affinity at these receptors. These studies indicate that xanomeline is a potent agonist at 5-HT1A and 5-HT1B receptors and an antagonist at 5-HT2 receptor subtypes.

Wnt signaling stabilizes the dual-function protein beta-catenin in diverse cell types

The Wnt proteins constitute a large family of secreted signaling factors that performed a wide variety of inductive and regulatory functions in embryonic and postnatal development. In mammals, these include crucial roles in morphogenesis of the central nervous system, kidneys, limbs, and mammary glands. In recent years, much progress has been made in identifying components of the intracellular Wnt-1 signal transduction pathway through studies in Drosophila, C. elegans, Xenopus, and mammalian systems. Several features of this pathway are remarkably well conserved in evolution. A key component of the Wnt pathway is the cytoplasmic protein beta-catenin, whose stability is increased as a result of Wnt signaling. Although morphological effects of Wnt-1 in cell culture are seen in only a limited number of cell lines, we show here that responsiveness to Wnt-1 at the biochemical level is a common property of both epithelial and mesenchymal cells. The increased abundance of beta-catenin may have at least two functional consequences, depending on the subcellular localization of the protein. In some cell lines that respond to Wnt-1, there is a significant increase in the beta-catenin fraction associated with the plasma membrane, where the protein acts as a component of cell-cell adhesive junctions. In other cell types, the major effect of Wnt signaling is an increase in the cytosolic pool of beta-catenin. Increased abundance of this pool has recently been correlated with entry of beta-catenin into the nucleus, where the protein forms complexes with Tcf transcription factors and is thought to modulate the expression of specific genes. The dual consequences of Wnt signaling on cell adhesion and/or gene expression provide at least two potential mechanisms by which this key pathway can function in the regulation of morphogenesis.

Separable effects of human Kvbeta1.2 N- and C-termini on inactivation and expression of human Kv1.4

1. The Kvbeta subunits of voltage-gated K+ channels alter the functional expression and gating of non- or slowly inactivating Kvalpha1 subunits via two separate domains. To determine how Kvbeta subunits modulate a rapidly inactivating Kvalpha1 subunit, we did two-microelectrode voltage clamp experiments on human Kv1.4 voltage-gated K+ channels expressed heterologously in Xenopus oocytes. In addition we tested a slowly inactivating mutant of Kv1.4 lacking amino acids 2-146 of the N-terminal alpha-ball domain (Kv1. 4DeltaN2-146). Kv1.4 or Kv1.4DeltaN2-146 were co-expressed with either rat Kvbeta2 or human Kvbeta1.2. To separate domain effects, we also used a mutant of Kvbeta1.2 lacking the unique 79 amino acid N-terminal beta-ball domain (Kvbeta1-C). 2. For the mutant Kv1.4DeltaN2-146 we found that Kvbeta1-C or Kvbeta2 increased current amplitude without altering activation or inactivation. By contrast Kvbeta1.2 produced rapid inactivation and slowed deactivation due to block produced by the beta-ball. The beta-ball also increased the rate of C-type inactivation in 5 mM, but not 50 mM, external K+ consistent with an effect of blockade on K+ efflux. 3. For Kv1.4, Kvbeta1-C produced a voltage-independent increase in the rate of inactivation and shifted the inactivation curve to more hyperpolarized potentials, but had no effect on deactivation. Kvbeta1-C, Kvbeta2 and Kvbeta1.2 slowed recovery from inactivation similarly, thereby excluding involvement of the beta-ball. Kvbeta1.2 produced an additional more rapid, voltage-dependent component of inactivation, significantly reduced peak outward current and shifted steady-state inactivation towards hyperpolarized potentials. 4. Yeast two-hybrid studies showed that alpha-beta interaction was restricted to the N-terminus of Kv1.4 and the C-terminus of Kvbeta1. 2 or Kvbeta2. Direct interaction with the alpha-ball did not occur. Our interpretation is that Kvbeta1-C and Kvbeta2 enhanced N-type inactivation produced by the Kv1.4 alpha-ball allosterically. 5. We propose that Kvbeta1.2 has three effects on Kv1.4, the first two of which it shares with Kvbeta2. First, Kvbeta1-C and Kvbeta2 have a current-enhancing effect. Second, Kvbeta1-C and Kvbeta2 increase block by the alpha-ball allosterically. Third, the beta-ball of Kbeta1.2 directly blocks both Kv1.4 and Kv1.4DeltaN2-146. When both alpha- and beta-balls are present, competition for their respective binding sites slows the block produced by either ball.

Effects of mutations in the human uncoupling protein 3 gene on the respiratory quotient and fat oxidation in severe obesity and type 2 diabetes

Human uncoupling protein 3 (UCP3) is a mitochondrial transmembrane carrier that uncouples oxidative ATP phosphorylation. With the capacity to participate in thermogenesis and energy balance, UCP3 is an important obesity candidate gene. A missense polymorphism in exon 3 (V102I) was identified in an obese and diabetic proband. A mutation introducing a stop codon in exon 4 (R143X) and a terminal polymorphism in the splice donor junction of exon 6 were also identified in a compound heterozygote that was morbidly obese and diabetic. Allele frequencies of the exon 3 and exon 6 splice junction polymorphisms were determined and found to be similar in Gullah-speaking African Americans and the Mende tribe of Sierra Leone, but absent in Caucasians. Moreover, in exon 6-splice donor heterozygotes, basal fat oxidation rates were reduced by 50%, and the respiratory quotient was markedly increased compared with wild-type individuals, implicating a role for UCP3 in metabolic fuel partitioning.

Progesterone stimulates the activity of the promoters of peripheral myelin protein-22 and protein zero genes in Schwann cells

To understand better the mechanisms by which progesterone (PROG) promotes myelination in the PNS, cultured rat Schwann cells were transiently transfected with reporter constructs in which luciferase expression was controlled by the promoter region of either the peripheral myelin protein-22 (PMP22) or the protein zero (P0) genes. PROG stimulated the P0 promoter and promoter 1, but not promoter 2, of PMP22. The effect of PROG was specific, as estradiol and testosterone only weakly activated promoters. Dose-response curves for stimulation of both promoter constructs by PROG were biphasic. RU486, a PROG antagonist, did not abolish the effect of PROG, but stimulated promoter activities by itself. In the human carcinoma cell line T47D expressing high levels of PROG receptor, PROG did not stimulate the P0 and PMP22 promoters, whereas the promoter region of the mouse mammary tumor virus was fully activated. Thus, the activation by PROG of promoter activity of two peripheral myelin protein genes is Schwann-cell specific.

Use of cytosolic triacylglycerol hydrolysis products and of exogenous fatty acid for the synthesis of triacylglycerol secreted by cultured rat hepatocytes

The fatty acyl moieties incorporated into triacylglycerol (TAG) secreted by rat hepatocytes are derived from diacylglycerol (DAG) that is synthesized de novo through the phosphatidate pathway or derived from endogenous, cytosolic TAG after hydrolysis to DAG and re-esterification. We have used a dual-labeling technique (overnight labeling of cell TAG with [3H]oleate, followed by 3 h incubation with [14C]oleate) to quantify the contributions of the two sources towards TAG secretion by cultured rat hepatocytes. A wide range of TAG secretion rates was achieved by short-term incubation of the cells under a variety of conditions. There was no correlation between the overall amount of exogenous 14C-labeled fatty acid metabolized and the rate of either [14C]- or [3H]TAG secretion. By contrast, there was a strong positive correlation between the fraction of newly synthesized [14C]TAG that was secreted (the fractional secretion rate, FSR) and the absolute rate of TAG secretion. This suggests that the partitioning of DAG between (re)synthesis of cytosolic TAG and synthesis of secreted TAG is an important locus for the control of the rate of TAG secretion. Comparison of the ratio: oxidation/TAG secretion for 3H- and 14C-labeled acyl moieties indicated that, for all conditions studied, approximately half the acyl moieties already esterified to the glyceroyl backbone within cytosolic TAG remain unavailable for oxidation when this pool of TAG is mobilized for the synthesis of secreted TAG. The data provide evidence that hydrolysis of cytosolic triacylglycerol (TAG) does not proceed fully to the constituent fatty acids and glycerol, but only to the level of diacylglycerol, followed by re-modelling of approximately half of its acyl chains, before re-esterification to form secretory TAG.

Visual field extent in children 3.5-30 months of age tested with a double-arc LED perimeter

Visual field extent along the four diagonal meridia was measured cross-sectionally in 180 normal children (infants and toddlers), and 22 adults. Infants were tested monocularly at 3.5, 7, or 9 months, and toddlers were tested binocularly at 11, 17, or 30 months. Adult control data were obtained under monocular viewing. Three testing methods were investigated: static and hybrid static-kinetic perimetry, using LED arrays under computer control, and kinetic perimetry, using white styrofoam spheres manipulated by hand. Data analysis included corrections for false positives in the method of constant stimuli and for errors of anticipation in the ascending method of limits. Across all data sets from children, kinetic perimetry yielded larger, more adult-like fields, which approached adult levels around 17 months, whereas static and hybrid static-kinetic perimetry yielded smaller visual fields, approaching adult levels only at 30 months.

Identification and cloning of a developmentally regulated Cryptosporidium parvum gene by differential mRNA display PCR

To identify Cryptosporidium parvum genes expressed during intracellular development, differential mRNA display was used to detect differences in gene expression between mock-infected and C. parvum-infected human epithelial cells. A reproducible band present only in C. parvum-infected cells, ddHC-23, was isolated and cloned. Southern blot analysis demonstrated that ddHC-23 represented a C. parvum gene. RT-PCR revealed that HC-23 mRNA levels decreased from 6 to 12h post-infection (pi), were maximally expressed at 24h pi, and returned to low levels at 48 and 72h pi. Northern blot analysis determined that the approx. 3.6kb transcript is expressed by sporozoites prior to invasion of epithelial cells. Screening of a C. parvum genomic library with ddHC-23 isolated a genomic subclone which contained a 2790bp ORF, uninterrupted by introns. Sequence analysis indicated that the encoded protein, which displayed no similarity to any sequences in the public databases, contained a high proportion of polar amino acids, with the most abundant being Asp (17.3%), Ser (15.8%) and Gly (8.1%). Numerous potential sites for posttranslational modification were present including: casein kinase II and protein kinase C phosphorylation sites, N-myristolation sites and N-glycosylation sites. These findings demonstrate the usefulness of differential mRNA display for identifying developmentally regulated C. parvum genes within the background of genes expressed by the host cell. 1998 Elsevier Science B.V.

5-HT1B receptor-mediated contractions in human temporal artery: evidence from selective antagonists and 5-HT receptor mRNA expression

1. In the human temporal artery both 5-HT1-like and 5-HT2A receptors mediate the contractile effects of 5-hydroxytryptamine (5-HT) and we have suggested that the 5-HT1-like receptors resemble more closely recombinant 5-HT1B than 5-HT1D receptors. To investigate further which subtype is involved, we investigated the blockade of 5-HT-induced contractions by the 5-HT1B-selective antagonist SB-224289 (2,3,6,7-tetrahydro-1'-methyl-5-[2-methyl-4'[(5-methyl-1,2,4-oxadiazole- 3-yl) biphenyl-4-yl] carbonyl] furo[2,3-f]indole-3-spiro-4'-piperidine oxalate) and the 5-HT1D-selective antagonist BRL-15572 (1-phenyl-3[4-3-chlorophenyl piperazin-1-yl] phenylpropan-2-ol). We also used RT-PCR to search for the mRNA of 5-HT1B, 5-HT1D and other 5-HT receptors. 2. The contractile effects of 5-HT in temporal artery rings were partially antagonized by SB-224289 (20, 200 nM) (apparent KB = 1 nM) and ketanserin (1 microM) but not by BRL-15572 (500 nM). 3. Sumatriptan evoked contractions (EC50, 170 nM) that were resistant to blockade by BRL-15572 (500 nM) but antagonized by SB-224289 (20, 200 nM). 4. The potency of 5-HT (EC50) was estimated to be 94 nM for the ketanserin-sensitive receptor and 34 nM for the SB-224289-sensitive receptor. The fraction of maximal 5-HT response mediated through SB-224289-sensitive receptors was 0.20-0.67, the remainder being mediated through ketanserin-sensitive receptors. 5. We detected arterial receptor mRNA for the following receptors (incidence): 5-HT1B (8/8), 5-HT1D (2/8), 5-HT1F (0/4), 5-HT2A (0/8) 5-HT2B (0/8), 5-HT2C (0/8), 5-HT4 (4/8) and 5-HT7 (4/8). 6. We conclude that the ketanserin-resistant fraction of the 5-HT effects and the effects of sumatriptan are mediated by 5-HT1B receptors. The lack of antagonism by BRL-15572 rules out 5-HT1D receptors as mediators of the contractile effects of 5-HT and sumatriptan.

Expression of cadherins and catenins in oral epithelial dysplasia and squamous cell carcinoma

The immunocytochemical expression of cadherins and catenins was examined during the process of oral carcinogenesis by comparing their expression in normal and dysplastic epithelium with primary and metastatic carcinomas. While control epithelium showed normal distribution for P and E cadherin and the catenins, in severe dysplasia P-cadherin was upregulated. In other cases and in carcinoma-in-situ adjacent to infiltrating carcinomas, membranous expression of the cadherins and catenins was reduced or lost. The changes in expression of E-cadherin and the catenins suggest that disruption of the E-cadherin/catenin complex is a late event associated with invasion. In primary carcinomas reduced membranous and cytoplasmic staining were observed for both cadherins and catenins. Abnormal localisation of E-cadherin occurred in the more superficial parts of the better differentiated carcinomas, suggesting abnormality to the E-cadherin complex(es). In contrast, membranous expression of cadherins and catenins was reduced or lost in the deep invasive margin of primary carcinomas and in most poorly differentiated carcinomas. For E-cadherin at least, this reduction appears associated with differentiation, invasion and possibly prognosis. Possible mechanisms involved for changes in expression of the cadherins and associated catenins and areas for further study are discussed.

Blockade of HERG and Kv1.5 by ketoconazole

Ketoconazole, a widely used fungicide in patients, has been associated with Q-T prolongation and torsade de pointes when co-administered with terfenadine (Seldane). Both compounds use the same cytochrome-P450 metabolic pathway, resulting in an increase in plasma concentration of terfenadine. We previously showed that terfenadine blocked HERG (Human Ether-a-Gogo Related Gene), an important component of the repolarizing cardiac delayed rectifier IK with concentration needed to obtain 50% of the block (IC50) in the therapeutic range (300 nM). Another target is Kv1.5 (delayed outward rectifier potassium current), an important component of human atrial ultrarapid delayed rectifier current. Whether Kv1.5 and HERG proteins are direct targets for ketoconazole has yet to be addressed. We heterologously expressed HERG and Kv1.5 in Xenopus oocytes and compared their sensitivities to ketoconazole. HERG and Kv1.5 currents were reduced comparably with apparent IC50 values of 49 microM and 107 microM, respectively, when measured using the two-microelectrode recording technique. The differences in the IC50 may help explain the preferential ventricular origin of the ketoconazole-associated arrhythmias during overdose. The mechanism of block was different between Kv1.5 and HERG. Cumulative application of terfenadine and ketoconazole at their respective IC50 concentrations resulted in current reductions that suggest an additive rather than a competitive type of block by the two drugs. We conclude that ketoconazole may potentiate the effects of terfenadine first by an indirect pharmacokinetic action to elevate plasma levels and second by a direct pharmacodynamic action on HERG currents. These potential dual actions on HERG currents suggest that precautions should be taken in long-term ketoconazole treatment, particularly for patients who have decreased liver function or are on a drug regimen requiring simultaneous medications that use cytochrome-P450 for breakdown, such as terfenadine or erythromycin, or Class III antiarrhythmic drugs.

The use of SIMS, XPS and in situ AFM to probe the acid catalysed hydrolysis of poly(orthoesters)

Due to poly(orthoesters) being susceptible to acid catalysed hydrolysis, these polymers have attracted considerable interest for the controlled delivery of therapeutic agents within biodegradable matrices. The pH-sensitivity of the poly (orthoesters) has lead to several drug delivery systems being developed, whose rate of drug release is predominantly controlled by the rate of polymer hydrolysis. This study reports on the use of X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and atomic force microscopy (AFM) in a multitechnique approach to probe the effect of acid catalysed hydrolysis at the interface of poly(orthoesters). The molecular specificity of SIMS was successfully employed, suggesting that the preferred mechanism for hydrolysis was via the cleavage of an exocyclic alkoxy bond in the 3,9,-diethylidene-2,4,8,10-tetraoxaspiro [5,5] undecane(DETOSU) unit. The resulting change in the surface chemical structure of the partially hydrolysed poly(orthoester) is such that it was not detectable by XPS analysis. Images acquired from an in situ AFM study of the hydrolysis ofa poly(orthoester), showed changes in the surface morphology, seen as the formation of pits, and an overall thinning of the polymer film. The use of SIMS, XPS and AFM has enabled changes in surface chemistry to be compared with changes in surface morphology. These complementary data, on the behaviour of the polymer during degradation have important implications for the further design of novel biodegradable materials.

Functional characterisation of the human cloned 5-HT7 receptor (long form); antagonist profile of SB-258719

1. The functional profile of the long form of the human cloned 5-HT7 receptor (designated h5-HT7(a)) was investigated using a number of 5-HT receptor agonists and antagonists and compared with its binding profile. Receptor function was measured using adenylyl cyclase activity in washed membranes from HEK293 cells stably expressing the recombinant h5-HT7(a) receptor. 2. The receptor binding profile, determined by competition with [3H]-5-CT, was consistent with that previously reported for the h5-HT7(a) receptor. The selective 5-HT7 receptor antagonist SB-258719 ((R)-3,N-Dimethyl-N-[1-methyl-3-(4-methylpiperidin-1-yl)propyl]ben zene sulfonamide) displayed high affinity (pKi 7.5) for the receptor. 3. In the adenylyl cyclase functional assay, 5-CT and 8-OH-DPAT were both full agonists compared to 5-HT and the rank order of potency for agonists (5-CT > 5-HT > 8-OH-DPAT) was the same in functional and binding studies. 4. Risperidone, methiothepin, mesulergine, clozapine, olanzapine, ketanserin and SB-258719 antagonised surmountably 5-CT-stimulated adenylyl cyclase activity. Schild analysis of the antagonism by SB-258719 gave a pA2 of 7.2+/-0.2 and slope not significantly different from 1, consistent with competitive antagonism. 5. The same antagonists also inhibited basal adenylyl cyclase activity with a rank order of potency in agreement with those for antagonist potency and binding affinity. Both SB-258719 and mesulergine displayed apparent partial inverse agonist profiles compared to the other antagonists tested. These inhibitory effects of antagonists appear to be 5-HT7 receptor-mediated and to reflect inverse agonism. 6. It is concluded that in this expression system, the h5-HT7(a) receptor shows the expected binding and functional profile and displays constitutive activity, revealing inverse agonist activity for a range of antagonists.

Influence of concomitant disease on patterns of hospitalization in patients with heart failure discharged from Scottish hospitals in 1995

AIMS

To determine the prevalence of common, serious, concomitant conditions complicating admissions with heart failure and how such conditions influence the length of hospital stay.

METHODS AND RESULTS

Data from Scottish morbidity records (SMR1) were used to determine the rate of deaths and discharges for heart failure (ICD-9 428.0, 428.9), concomitant discharge diagnoses and length of stay in 1995. 27,477 SMR1 records listing heart failure as a diagnosis were identified with heart failure in the first position in 11,560 (42%) records. 63.3% of deaths or discharges results from emergency admission. 13.2% of admissions were associated with acute myocardial infarction, 7.3% with angina or chest pain, 11.8% with chronic airways obstruction, 8.3% with chronic or acute renal failure and 5.3% had had a stroke. Length of stay including those patients who died was 7.6 days when acute myocardial infarction was the principal diagnosis but 26.3 days when stroke was the principal diagnosis.

CONCLUSION

A large proportion of deaths and discharges for heart failure are associated with conditions other than heart failure that may precipitate, contribute to or complicate admission. Treatment for heart failure that does not also seek to reduce the risk associated with common concomitant diseases may miss opportunities to reduce the overall risk of hospitalization.

A recessive variant of the Romano-Ward long-QT syndrome?

BACKGROUND

The congenital long-QT syndrome (LQTS) is a genetically heterogeneous disease characterized by prolonged ventricular repolarization and life-threatening arrhythmias. Mutations of the KVLQT1 gene, a cardiac potassium channel, generate two allelic diseases: the Romano-Ward syndrome, inherited as a dominant trait, and the Jervell and Lange-Nielsen syndrome, inherited as an autosomal recessive trait.

METHODS AND RESULTS

A consanguineous family with the clinical phenotype of LQTS was screened for mutations in the KVLQT1 gene. Complementary RNAs for injection into Xenopus oocytes were prepared, and currents were recorded with the double microelectrode technique. A homozygous missense mutation, leading to an alanine-to-threonine substitution at the beginning of the pore domain of the KVLQT1 channel, was found in the proband, a 9-year-old boy with normal hearing, a prolonged QT interval, and syncopal episodes during physical exercise. The parents of the proband were heterozygous for the mutation and had a normal QT interval. The functional evaluation of the mutant channel activity showed reduction in total current, a hyperpolarizing shift in activation, and a faster activation rate consistent with a mild mutation likely to require homozygosity to manifest the phenotype.

CONCLUSIONS

These findings provide the first evidence for a recessive form of the Romano-Ward long-QT syndrome and indicate that homozygous mutations on KVLQT1 do not invariably produce the Jervell and Lange-Nielsen syndrome. The implications of this observation prompt a reconsideration of the penetrance of different mutations responsible for LQTS and suggest that mild mutations in LQTS genes may be present among the general population and may predispose to drug-induced ventricular arrhythmias.