Author Correction: Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Interrogating surface versus intracellular transmembrane receptor populations using cell-impermeable SNAP-tag substrates

Employing self-labelling protein tags for the attachment of fluorescent dyes has become a routine and powerful technique in optical microscopy to visualize and track fused proteins. However, membrane permeability of the dyes and the associated background signals can interfere with the analysis of extracellular labelling sites. Here we describe a novel approach to improve extracellular labelling by functionalizing the SNAP-tag substrate benzyl guanine ("BG") with a charged sulfonate ("SBG"). This chemical manipulation can be applied to any SNAP-tag substrate, improves solubility, reduces non-specific staining and renders the bioconjugation handle impermeable while leaving its cargo untouched. We report SBG-conjugated fluorophores across the visible spectrum, which cleanly label SNAP-fused proteins in the plasma membrane of living cells. We demonstrate the utility of SBG-conjugated fluorophores to interrogate class A, B and C G protein-coupled receptors (GPCRs) using a range of imaging approaches including nanoscopic superresolution imaging, analysis of GPCR trafficking from intra- and extracellular pools, in vivo labelling in mouse brain and analysis of receptor stoichiometry using single molecule pull down.

Social class and type of schizophrenia

Objective

Current and past research strongly indicates a high prevalence of schizophrenia in the lower class in the USA and other stratified societies. To date, no study has tested for a connection between type of schizophrenia and socioeconomic status (SES). We tested for an interrelationship between schizophrenic subtype, SES and race.

Methods

Positive and negative symptom scales were used to evaluate 436 schizophrenic patients at a state hospital in the USA. All patients were also diagnosed by DSM standards. Social class of origin was assessed by the Occupational Classification Distributions of the U.S. Bureau of the Census. Multivariate analysis was conducted with the likelihood ratio chi-square.

Results

We uncovered a distinct propensity for deficit schizophrenia to be elevated among the poor. The finding presents as a pure SES effect since the likelihood of deficit schizophrenia does not vary by race when social class is held constant.

Conclusion

The finding is potentially an important new insight into the epidemiology of schizophrenia. It offers a better understanding for poor outcome among lower class patients in stratified societies such as the United States. It is also consistent with longitudinal research by European investigators.

Super-resolution microscopy compatible fluorescent probes reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics

The glucagon-like peptide-1 receptor (GLP1R) is a class B G protein-coupled receptor (GPCR) involved in metabolism. Presently, its visualization is limited to genetic manipulation, antibody detection or the use of probes that stimulate receptor activation. Herein, we present LUXendin645, a far-red fluorescent GLP1R antagonistic peptide label. LUXendin645 produces intense and specific membrane labeling throughout live and fixed tissue. GLP1R signaling can additionally be evoked when the receptor is allosterically modulated in the presence of LUXendin645. Using LUXendin645 and LUXendin651, we describe islet, brain and hESC-derived β-like cell GLP1R expression patterns, reveal higher-order GLP1R organization including membrane nanodomains, and track single receptor subpopulations. We furthermore show that the LUXendin backbone can be optimized for intravital two-photon imaging by installing a red fluorophore. Thus, our super-resolution compatible labeling probes allow visualization of endogenous GLP1R, and provide insight into class B GPCR distribution and dynamics both in vitro and in vivo.

Glucagon-like peptide-1 receptor is an important regulator of appetite and glucose homeostasis. Here the authors describe super-resolution microscopy and in vivo imaging compatible fluorescent probes, which reveal endogenous glucagon-like peptide-1 receptor distribution and dynamics in islets and brain.

Conditional and Reversible Activation of Class A and B G Protein-Coupled Receptors Using Tethered Pharmacology

Understanding the activation and internalization of G protein-coupled receptors (GPCRs) using conditional approaches is paramount to developing new therapeutic strategies. Here, we describe the design, synthesis, and testing of ExONatide, a benzylguanine-linked peptide agonist of the glucagon-like peptide-1 receptor (GLP-1R), a class B GPCR required for maintenance of glucose levels in humans. ExONatide covalently binds to SNAP-tagged GLP-1R-expressing cells, leading to prolonged cAMP generation, Ca²⁺ rises, and intracellular retention of the receptor. These effects were readily switched OFF following cleavage of the introduced disulfide bridge using the cell-permeable reducing agent beta-mercaptoethanol (BME). A similar approach could be extended to a class A GPCR using GhrelON, a benzylguanine-linked peptide agonist of the growth hormone secretagogue receptor 1a (GHS-R1a), which is involved in food intake and growth. Thus, ExONatide and GhrelON allow SNAP-tag-directed activation of class A and B GPCRs involved in gut hormone signaling in a reversible manner. This tactic, termed reductively cleavable agONist (RECON), may be useful for understanding GLP-1R and GHS-R1a function both in vitro and in vivo, with applicability across GPCRs.

Potent Prearranged Positive Allosteric Modulators of the Glucagon-like Peptide-1 Receptor

Drugs that allosterically modulate G protein-coupled receptor (GPCR) activity display higher specificity and may improve disease treatment. However, the rational design of compounds that target the allosteric site is difficult, as conformations required for receptor activation are poorly understood. Guided by photopharmacology, a set of prearranged positive allosteric modulators (PAMs) with restricted degrees of freedom was designed and tested against the glucagon-like peptide-1 receptor (GLP-1R), a GPCR involved in glucose homeostasis. Compounds incorporating a trans-stilbene comprehensively outperformed those with a cis-stilbene, as well as the benchmark BETP, as GLP-1R PAMs. We also identified major effects of ligand conformation on GLP-1R binding kinetics and signal bias. Thus, we describe a photopharmacology-directed approach for rational drug design, and introduce a new class of stilbene-containing PAM for the specific regulation of GPCR activity.

RAMP2 Influences Glucagon Receptor Pharmacology via Trafficking and Signaling

Endogenous satiety hormones provide an attractive target for obesity drugs. Glucagon causes weight loss by reducing food intake and increasing energy expenditure. To further understand the cellular mechanisms by which glucagon and related ligands activate the glucagon receptor (GCGR), we investigated the interaction of the GCGR with receptor activity modifying protein (RAMP)2, a member of the family of receptor activity modifying proteins. We used a combination of competition binding experiments, cell surface enzyme-linked immunosorbent assay, functional assays assessing the Gαs and Gαq pathways and β-arrestin recruitment, and small interfering RNA knockdown to examine the effect of RAMP2 on the GCGR. Ligands tested were glucagon; glucagonlike peptide-1 (GLP-1); oxyntomodulin; and analog G(X), a GLP-1/glucagon coagonist developed in-house. Confocal microscopy was used to assess whether RAMP2 affects the subcellular distribution of GCGR. Here we demonstrate that coexpression of RAMP2 and the GCGR results in reduced cell surface expression of the GCGR. This was confirmed by confocal microscopy, which demonstrated that RAMP2 colocalizes with the GCGR and causes significant GCGR cellular redistribution. Furthermore, the presence of RAMP2 influences signaling through the Gαs and Gαq pathways, as well as recruitment of β-arrestin. This work suggests that RAMP2 may modify the agonist activity and trafficking of the GCGR, with potential relevance to production of new peptide analogs with selective agonist activities.

The preanalytical stability of glucagon as measured by liquid chromatography tandem mass spectrometry and two commercially available immunoassays

Background One of the main challenges in the measurement of glucagon is the premise that it is unstable in human plasma. Traditionally, protease inhibitors have been used to prevent its degradation; however, their use is controversial. Here, we investigated the optimal method of sample collection for glucagon, with measurement by liquid chromatography tandem mass spectrometry (LC-MS/MS) and two commercially available immunoassays. Methods Blood from healthy fasting volunteers (n = 10) was processed under a variety of preanalytical conditions including collection in EDTA vs. lithium heparin tubes and the addition of aprotinin and/or a dipeptidyl-peptidase IV (DPPIV) inhibitor. Additionally, the effect of freeze thaw was assessed. Plasma glucagon concentrations were measured by LC-MS/MS and two commercially available immunoassays (HTRF® sandwich immunoassay, Cisbio and Milliplex MAP Human Metabolic Hormone Panel, Merck Millipore). Results A systematic bias of Milliplex > LC-MS/MS > HTRF was noted and plasma glucagon concentrations were significantly different between methods (Milliplex vs. LC-MS/MS P < 0.01; Milliplex vs. HTRF P < 0.0001; LC-MS/MS vs. HTRF P < 0.001). The addition of aprotinin, DPPIV inhibitor or a combination of aprotinin and DPPIV inhibitor had no effect on plasma glucagon concentrations when compared to 'non-stabilized' samples or each other. Whether samples were taken in EDTA tubes or lithium heparin tubes made no difference to plasma glucagon concentrations. These findings were consistent for all three methods. Plasma glucagon concentrations were not significantly different after two freeze-thaw cycles (performed on samples in EDTA tubes containing aprotinin and DPPIV inhibitor). Conclusions This study demonstrates that glucagon is stable in both EDTA and lithium heparin tubes when stored at -80℃. Furthermore, the addition of aprotinin and DPPIV inhibitors is unnecessary.

Allosteric Optical Control of a Class B G-Protein-Coupled Receptor

Allosteric regulation promises to open up new therapeutic avenues by increasing drug specificity at G-protein-coupled receptors (GPCRs). However, drug discovery efforts are at present hampered by an inability to precisely control the allosteric site. Herein, we describe the design, synthesis, and testing of PhotoETP, a light-activated positive allosteric modulator of the glucagon-like peptide-1 receptor (GLP-1R), a class B GPCR involved in the maintenance of glucose homeostasis in humans. PhotoETP potentiates Ca(2+) , cAMP, and insulin responses to glucagon-like peptide-1 and its metabolites following illumination of cells with blue light. PhotoETP thus provides a blueprint for the production of small-molecule class B GPCR allosteric photoswitches, and may represent a useful tool for understanding positive cooperativity at the GLP-1R.

Optical Control of Insulin Secretion Using an Incretin Switch

Incretin mimetics are set to become a mainstay of type 2 diabetes treatment. By acting on the pancreas and brain, they potentiate insulin secretion and induce weight loss to preserve normoglycemia. Despite this, incretin therapy has been associated with off-target effects, including nausea and gastrointestinal disturbance. A novel photoswitchable incretin mimetic based upon the specific glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide was designed, synthesized, and tested. This peptidic compound, termed LirAzo, possesses an azobenzene photoresponsive element, affording isomer-biased GLP-1R signaling as a result of differential activation of second messenger pathways in response to light. While the trans isomer primarily engages calcium influx, the cis isomer favors cAMP generation. LirAzo thus allows optical control of insulin secretion and cell survival.

Biofilm formation is a risk factor for mortality in patients with Candida albicans bloodstream infection-Scotland, 2012-2013

Bloodstream infections caused by Candida species remain a significant cause of morbidity and mortality in hospitalized patients. Biofilm formation by Candida species is an important virulence factor for disease pathogenesis. A prospective analysis of patients with Candida bloodstream infection (n = 217) in Scotland (2012–2013) was performed to assess the risk factors associated with patient mortality, in particular the impact of biofilm formation. Candida bloodstream isolates (n = 280) and clinical records for 157 patients were collected through 11 different health boards across Scotland. Biofilm formation by clinical isolates was assessed in vitro with standard biomass assays. The role of biofilm phenotype on treatment efficacy was also evaluated in vitro by treating preformed biofilms with fixed concentrations of different classes of antifungal. Available mortality data for 134 patients showed that the 30-day candidaemia case mortality rate was 41%, with predisposing factors including patient age and catheter removal. Multivariate Cox regression survival analysis for 42 patients showed a significantly higher mortality rate for Candida albicans infection than for Candida glabrata infection. Biofilm-forming ability was significantly associated with C. albicans mortality (34 patients). Finally, in vitro antifungal sensitivity testing showed that low biofilm formers and high biofilm formers were differentially affected by azoles and echinocandins, but not by polyenes. This study provides further evidence that the biofilm phenotype represents a significant clinical entity, and that isolates with this phenotype differentially respond to antifungal therapy in vitro. Collectively, these findings show that greater clinical understanding is required with respect to Candida biofilm infections, and the implications of isolate heterogeneity.

Minireview: Glucagon in stress and energy homeostasis

Glucagon is traditionally thought of as an antihypoglycemic hormone, for example in response to starvation. However, it actually increases energy expenditure and has other actions not in line with protection from hypoglycemia. Furthermore, it is often found to be elevated when glucose is also raised, for example in circumstances of psychological and metabolic stress. These findings seem more in keeping with glucagon having some role as a hormone enhancing the response to stress.

First reported deliveries in Ireland using surgically retrieved sperm for non-obstructive azoospermia

Couples presenting with male factor infertility comprise an important proportion of clinical reproductive endocrinology consultations. Indeed, a problem with the male is the only cause, or a contributing cause, of infertility in ~40% of infertility evaluations. Here we present the first published deliveries obtained from IVF utilising surgically retrieved sperm in Ireland; pregnancy and delivery are also described following transfer of cryopreserved/thawed embryos derived from such sperm. Finding no sperm from a semen analysis in a man without a vasectomy can be a devastating event, and substantially influences the scope of the reproductive endocrinology consultation. Successful treatment of non-obstructive azoospermia is possible without reliance on anonymous donor sperm.

Appropriateness of the National Academy of Clinical Biochemistry recommendation of repeating HbA1c analysis for extreme results in clinical practice

Background

The National Academy of Clinical Biochemistry (NACB) recommends that the presence of a variant or modified haemoglobin be considered when any HbA1c result is below the lower limit of the reference interval or ≥15%. In those instances where a variant haemoglobin is suspected, repeat measurement using an alternative method is the usual course of action. In the present study, we undertook to determine the impact of this guideline on our identification of variant and modified haemoglobins.

Methods

All requests for HbA1c estimation received over a 32-month period, and which gave a result of <4% or >15% were re-analysed by a different method and the results compared.

Results

Over the 32-month period, 94 samples with a HbA1c result of <4% or ≥15% were identified. Of these, 80 were re-analysed using a different method. No chromatographic abnormalities were seen and there were no significant differences between the results obtained using the two methods.

Conclusions

No variant or modified haemoglobins were identified in this study and this observation is likely to be representative of the ethnic makeup of our patient population. On the basis of this finding, we recommend that laboratories consider local factors when deciding whether to comply with the NACB guidelines.

Requesting patterns for serum calcium concentration in patients on long-term lithium therapy

AIM

Long-term lithium therapy is associated with hypercalcaemia in 10-60% of patients, but unlike creatinine and thyroid stimulating hormone (TSH), monitoring by general practitioners of serum calcium for patients on lithium is not a requirement of the Qualities and Outcomes Framework (QOF) of 2004. We aimed to assess requesting patterns for serum calcium in patients on long-term lithium therapy and subsequent diagnosis of hypercalcaemia.

METHODS

We identified 100 patients on long-term lithium therapy, as indicated by regular monitoring of lithium levels in our laboratory for at least 1 year. We determined how many of these patients had had serum calcium analysed, noting the assay date, concentration, source of request and clinical details stated.

RESULTS

Forty-three out of hundred patients had serum calcium analysed during the course of their treatment including 28 in the previous 15 months. Twenty-one patients had serum calcium analysed by their GP, including 12 in the previous 15 months. Hypercalcaemia was diagnosed in five patients (11.6%).

CONCLUSION

A significant proportion of patients in whom calcium was checked developed hypercalcaemia on lithium therapy. However, only 12% of the patients had serum calcium requested by their GP in the previous 15 months, which compares unfavourably with TSH and creatinine, for which monitoring approaches 100%. We recommend that serum calcium be checked every 15 months along with creatinine and TSH. This might be achieved by incorporating appropriate targets into the QOF, or by reflective or reflex adding-on of calcium to lithium specimens from patients who have not had calcium analysed in the previous 15 months.

Immunosuppression by mesenchymal stromal cells: from culture to clinic

Extensive in vitro studies have shown that multipotent mesenchymal stromal cells (MSC) can exert profound immunosuppressive effects via modulation of both cellular and innate immune pathways. Their ability to be readily isolated from a number of tissues and expanded ex vivo makes them attractive candidates for systemic immunosuppressive therapy. In this article, we will review recent experimental data on the mechanisms by which MSC inhibit the alloproliferative response and the clinical relevance for their potential use in hematopoietic stem cell transplantation, solid organ transplantation, and treatment of autoimmune diseases. While in vitro data consistently demonstrate the immunosuppressive capability of MSC, current studies in animals and humans suggest that MSC are less effective in producing systemic immunosuppression. Further mechanistic studies and randomized controlled trials using standardized cell populations are needed to define the optimal conditions for the use of MSC as immunotherapy.

Limitations and drawbacks of 'fine bore' nasogastric feeding tubes

The clinical use of unweighted nasogastric feeding tubes (n = 491) was compared with that of weighted nasogastric feeding tubes. No advantage was found in the use of the weighted tubes.

The roles of lactose and Clostridium difficile in the pathogenesis of enteral feeding associated diarrhoea

This study investigated the influence of the disaccharide lactose on the incidence of clinically significant enteral feeding associated diarrhoea. In this double blind study both groups each of 25 patients were randomised to receive either a lactose containing diet Clinifeed 400 in 25 patients or a lactose free diet Ensure in 25 patients. Diarrhoea occurred with equal frequency in both treatment groups, even in those patients with symptomatic and biochemical evidence of impaired lactose handling. Although the onset of diarrhoea was significantly associated with antibiotic administration (p<0.01), Cl. difficile was not isolated from the stools of any patient with diarrhoea.

Radiotherapy treatment delays and their influence on tumour control achieved by various fractionation schedules

There is often a considerable delay from initial tumour diagnosis to the start of radiotherapy treatment. This paper extends the calculations of a previous paper on the effects of delays before the initiation of radiotherapy treatment to include results from a variety of practical fractionation regimes for three different types of tumour: squamous cell carcinoma (head and neck), breast and prostate. The linear quadratic model of radiation effect, logarithmic tumour growth (coupled with delay times where relevant) and the Poisson model for tumour control probability (TCP) are used to calculate the change in TCP for delays between diagnosis and treatment. Within the limitations of radiobiological modelling, these data can be used to tentatively assess the interactions between delays, dose fractionation and TCP. The results show that delays in the start of radiotherapy treatment do have an adverse effect on tumour control for fast-growing tumours. For example, calculations predict a reduction in local tumour control of up to 1.5% per week's delay for head and neck cancers treated following surgery. In addition, there may be a variety of fractionation regimes that will yield very similar clinical results for each tumour type. It is shown theoretically that, for the tumour types considered here, it is possible to increase the dose per fraction and decrease the number of fractions while maintaining or increasing TCP relative to standard 2 Gy fractionation regimes, although there may be some advantage to using hyperfractionated regimes for head and neck cancers in order to reduce normal tissue effects.

Immunosuppression by placental indoleamine 2,3-dioxygenase: a role for mesenchymal stem cells

BACKGROUND/OBJECTIVES

Mesenchymal stem cells (MSC) can be isolated from human placenta and have the potential to contribute to the immunosuppressive properties of placental tissue. The objectives of this study were to investigate the phenotype and differentiation characteristics of MSC derived from human placenta and evaluate the role of the tryptophan degrading enzyme, indoleamine 2,3 dioxygenase (IDO), in mediating their immunosuppressive affect.

METHODS

MSC obtained from placental tissue (pMSC) were characterised using flow cytometry and tested for multipotency by determining differentiation into all mesenchymal lineages. The immunosuppressive properties of pMSC were tested in allogeneic mixed lymphocyte reactions and IDO expression and activity were measured by semi-quantitative real-time PCR and HPLC respectively.

RESULTS

Multipotent stem cells were isolated from placenta and displayed chondrogenic, osteogenic and limited adipogenic differentiation. Cell surface antigen expression of pMSC was similar to bone marrow MSC (bMSC) with lack of the haematopoietic and common leukocyte markers (CD34, CD45), and expression of adhesion (CD29, CD166, CD44) and stem cell (CD 90, CD105, CD73) markers. Placental MSC were suppressive of allogeneic T-cell proliferation, an effect which was intensified following IDO induction by IFN-gamma. Replenishment of tryptophan or treatment with the IDO-blocker, 1-methyl-tryptophan (1-MT), attenuated the immunosuppressive action of pMSC.

CONCLUSIONS

These results suggest that placental tissue contains MSC, which are phenotypically and functionally similar to bMSC, and that IDO is a key mediator of their immunosuppressive effect. Further investigation is needed to determine if pMSC function effects pregnancy outcome.

Postnatal epithelial growth of the small intestine in the rat occurs by both crypt fission and crypt hyperplasia

Studies of growth of the small intestine have largely concentrated on crypt hyperplasia rather than crypt fission. The aim of this study was to investigate quantitatively both crypt fission and crypt hyperplasia. DAxPVG/c rats were killed at 7, 11, 14, 17, 19, 21, 25, 55, and 72-73 days of life. Samples of jejunum at one third of the intestinal length were taken for morphometry (villous area, crypt area, percentage of bifid crypts, and crypt mitotic count) by microdissection. Growth factors and their receptors were assessed by oligonucleotide microarray. Crypt fission was 10.5%, 5.2%, and 1.5% at days 11, 25, and 72-73 of life, respectively. Crypt hyperplasia increased from day 21. No conventional growth factor was identified during crypt fission. We conclude that crypt fission contributes to growth of the small intestine prior to weaning and crypt hyperplasia to growth after weaning.

Differences in the preparation and practice of male and female physicians from combined baccalaureate--MD degree programs

OBJECTIVE

To account for age and premedical education in determining whether or not men and women medical school graduates differ significantly in opinions of their medical school preparation, in professional activities, and in personal qualities and values.

METHODS

727 graduates (1983-1987) of seven combined baccalaureate-MD degree programs were surveyed. Men's and women's responses were compared.

RESULTS

Women graduates were more likely than men to work less than full time and to report less preparation in the basic sciences, less scholarly activity, and more concern about psychosocial issues.

CONCLUSION

Differences between men and women graduates have persisted despite women's increased access to medical school. Even a special curriculum does not moderate these differences. We call on academic medicine to value humanism in health care, not just economics.

Prenatal illness and subtypes of schizophrenia: the winter pregnancy phenomenon

Seasonality of birth patterns is examined among a sample of 801 patients with schizophrenia separated into Type I and Type II schizophrenia. Findings indicate that both groups of patients were in utero during the winter but during different trimesters. Patients with Type I schizophrenia were more likely to be in utero during the third trimester. Patients with Type II schizophrenia were more likely to have been in the womb during the first trimester. Implications for fetal brain development are discussed.

SB-224289--a novel selective (human) 5-HT1B receptor antagonist with negative intrinsic activity

1. Human 5-HT1B (h5-HT1B) and human 5-HT1D (h5-HT1D) receptors show remarkably similar pharmacology with few compounds discriminating the receptors. We report here on a novel compound, SB-224289 (1'-Methyl-5-[[2'-methyl-4'-(5-methyl- 1,2,4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydro spiro [furo [2,3-f]indole-3,4'-piperidine] oxalate), which has high affinity for h5-HT1B receptors (pK1=8.16+/-0.06) and displays over 75 fold selectivity for the h5-HT1B receptor over all other 5-HT receptors including the h5-HT1D receptor and all other receptors tested thus far. 2. Functional activity of SB-224289 was measured in a [15S]GTPgammaS binding assay on recombinant h5-HT1B and h5-HT1D receptors expressed in Chinese Hamster Ovary (CHO) cells. SB-224289 displayed negative intrinsic activity at both receptors with higher potency at h5-HT1B receptors. SB-224289 caused a rightward shift of agonist concentration response curves consistent with competitive antagonism and generated affinities comparable with those obtained from competition radioligand receptor binding studies. 3. SB-224289 potentiated [3H]5-HT release from electrically stimulated guinea-pig cerebral cortical slices to the same extent as as the non-selective 5-HT1 antagonist methiothepin. SB-224289 also fully reversed the inhibitory effect of exogenously superfused 5-HT on electrically stimulated release. 4. Using SB-224289 as a tool compound, we confirm that in guinea-pig cerebral cortex the terminal 5-HT autoreceptor is of the 5-HT1B subtype.

Uptake of gallium-67 in transfected cells and tumors absent or enriched in the transferrin receptor

Gallium-67 has been a controversial tumor-imaging agent in nuclear medicine for decades. This controversy centers on why tumors are variable in gallium-avidity, whether 67Ga uptake is a transferrin-independent or dependent process, and whether tumors and normal tissues differ in mechanism of uptake. If the factors that control uptake of 67Ga were understood better, then efforts to improve oncologic imaging with 67Ga by increasing the tumor activity, or by decreasing the background, may be warranted.

METHODS

Conventional systems for evaluating the mechanism and control of 67Ga uptake have significant limitations. We have endeavored to circumvent these by developing a pair of transfected cell lines. One cell line has no transferrin receptor. In the other, the human transferrin receptor has been restored by transfection and is over-expressed constitutively, without the necessity to manipulate factors such as cell growth or iron content. The uptake of 67Ga, both as a citrate salt and as a gallium-transferrin complex, was examined in these pairs of cells in vitro. The effect of calcium and of soluble (ionic) iron concentration on 67Ga uptake also was determined. Tumors were grown as explants of these cells in nude mice and comparisons of uptake of 67Ga by these tumors in vivo were made.

RESULTS

The in vivo uptake of 67Ga is significantly increased in tumors in which the transferrin receptor is overexpressed, compared to those without a functional transferrin receptor. However, a notable amount of accumulation of 67Ga also occurs, both in vitro and in vivo, by a transferrin-independent route. In vitro experiments demonstrate that the uptake of 67Ga by the transferrin-independent route can be enhanced further to levels that equal or exceed those achieved by the transferrin-dependent route by increasing the content of calcium or iron salts in the incubation medium.

CONCLUSION

Significant transferrin-independent uptake of 67Ga occurs both in vitro and in vivo. This uptake can be stimulated further in vitro, suggesting that in vivo enhancement might also be possible to enhance the utility of the radiometal for tumor imaging.

The selective 5-HT1B receptor inverse agonist 1'-methyl-5-[[2'-methyl-4'-(5-methyl-1,2, 4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6,7-tetrahydro- spiro[furo[2,3-f]indole-3,4'-piperidine] (SB-224289) potently blocks terminal 5-HT autoreceptor function both in vitro and in vivo

5-HT1 receptors are members of the G-protein-coupled receptor superfamily and are negatively linked to adenylyl cyclase activity. The human 5-HT1B and 5-HT1D receptors (previously known as 5-HT1Dbeta and 5-HT1Dalpha, respectively), although encoded by two distinct genes, are structurally very similar. Pharmacologically, these two receptors have been differentiated using nonselective chemical tools such as ketanserin and ritanserin, but the absence of truly selective agents has meant that the precise function of the 5-HT1B and 5-HT1D receptors has not been defined. In this paper we describe how, using computational chemistry models as a guide, the nonselective 5-HT1B/5-HT1D receptor antagonist 4 was structurally modified to produce the selective 5-HT1B receptor inverse agonist 5, 1'-methyl-5-[[2'-methyl-4'-(5-methyl-1,2, 4-oxadiazol-3-yl)biphenyl-4-yl]carbonyl]-2,3,6, 7-tetrahydrospiro[furo[2,3-f]indole-3,4'-piperidine] (SB-224289). This compound is a potent antagonist of terminal 5-HT autoreceptor function both in vitro and in vivo.

Ovarian nitric oxide synthase (NOS) gene expression during peripubertal development

Nitric oxide (NO) is generated from L-arginine by different isoforms of the enzyme nitric oxide synthase (NOS) and is known to be involved in mediating several biological functions, some of which are associated with reproduction. In this study, we examined the ability of the prepubertal ovary to express the inducible (i), as well as the neuronal-type constitutive (c) form of NOS and also, investigated whether either isoform undergoes changes in the ovary during peripubertal development. Results indicate that both forms of NOS were expressed in the ovary and that the iNOS mRNA transcripts were expressed without being exogenously induced. When compared with juvenile levels, iNOS, but not cNOS, mRNA increased (p<0.01) during the early proestrous phase of development. By the late proestrous phase, the levels of iNOS mRNA declined markedly (p<0.001) and remained low throughout both the first estrous and diestrous phases. Western blot analysis revealed both iNOS and cNOS protein expression in each phase of puberty with only iNOS showing a significant change during the peripubertal period. Specifically, there was an initial increase in the expression of iNOS protein during the late proestrous phase (p<0.05) which was accompanied by preovulatory increases in serum estradiol (p<0.01) and LH (p<0.001). The iNOS protein levels then dramatically increased to peak on the morning of first estrus (p<0.001), an event associated with declining (p<0.05) serum levels of estradiol. These data demonstrate developmental changes in the expression of ovarian iNOS mRNA and protein both before and after first ovulation; hence, suggesting a role for NO in the ovary during pubertal maturation and furthermore, providing compelling evidence at the gene level supporting the hypothesis that the NO/NOS system plays a physiological role in ovarian function.

SB-216641 and BRL-15572--compounds to pharmacologically discriminate h5-HT1B and h5-HT1D receptors

Despite only modest homology between h5-HT1B and h5-HT1D receptor amino acid sequences, these receptors display a remarkably similar pharmacology. To date there are few compounds which discriminate between these receptor subtypes and those with some degree of selectivity, such as ketanserin, have greater affinity for other 5-HT receptor subtypes. We now report on two compounds, SB-216641 (N-[3-(2-dimethylamino) ethoxy-4-methoxyphenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl)-(1,1'-biphenyl)-4-carboxamide) and BRL-15572 3-[4-(3-chlorophenyl) piperazin-1-yl]-1,1-diphenyl-2-propanol), which display high affinity and selectivity for h5-HT1B and h5-HT1D receptors, respectively. In receptor binding studies on human receptors expressed in CHO cells, SB-216641 has high affinity (pKi = 9.0) for h5-HT1B receptors and has 25-fold lower affinity at h5-HT1D receptors. In contrast, BRL-15572 has 60-fold higher affinity for h5-HT1D (pKi = 7.9) than 5-HT1B receptors. Similar affinities for these compounds were determined on native tissue 5-HT1B receptors in guinea-pig striatum. Functional activities of SB-216641 and BRL-15572 were measured in a [35S]GTPgammaS binding assay and in a cAMP accumulation assay on recombinant h5-HT1B and h5-HT1D receptors. Both compounds were partial agonists in these high receptor expression systems, with potencies and selectivities which correlated with their receptor binding affinities. In the cAMP accumulation assay, results from pK(B) measurements on the compounds again correlated with receptor binding affinities (SB-216641, pK(B) = 9.3 and 7.3; BRL-15572, pK(B) = <6 and 7.1, for h5-HT1B and h5-HT1D receptors respectively). These compounds will be useful pharmacological agents to characterise 5-HT1B and 5-HT1D receptor mediated responses.

(+)-WAY 100135, a partial agonist, at native and recombinant 5-HT1B/1D receptors

1. We have studied the effects of the purportedly selective 5-HT1A receptor antagonist (+)-WAY 100135 on electrically stimulated 5-hydroxytryptamine (5-HT) efflux in the ventrolateral geniculate nucleus (vLGN), and its affinity at human 5-HT1B and 5-HT1D receptors stably expressed in Chinese hamster ovary (CHO) cells. 2. On short 'pseudo single pulse' stimulations (20 pulses at 100 Hz, 190 ms train duration), (+)-WAY 100135 (1.0 microM) decreased 5-HT efflux in the vLGN to 68 +/- 8% of pre-drug values (P < 0.01). This decrease could be blocked by the 5-HT1D/1B receptor antagonist GR 127935 (50 nM). Conversely, when long stimulations (20 pulses at 20 Hz, 950 ms train) were used, (+)-WAY 100135 had no effect on 5-HT efflux (84 +/- 8% of pre-drug values) although both methiothepin (200 nM) and GR 127935 (50 nM) caused significant increases (to 175 +/- 18 and 130 +/- 10% of pre-drug values, respectively). 3. Paroxetine (100 nM), the selective 5-HT reuptake inhibitor, increased stimulated 5-HT efflux and reuptake half-life (to 145 +/- 18% and 649 +/- 121%, respectively) on pseudo single pulse stimulations. When (+)-WAY 100135 was added in combination with the uptake blocker, the effect of paroxetine on stimulated 5-HT efflux was potentiated to 282 +/- 48% (P < 0.01) without further effect on the 5-HT reuptake half-life. 4. The affinity and intrinsic activity of (+)-WAY 100135 were determined at recombinant human 5-HT1B and 5-HT1D receptors expressed in CHO cells, by use of radioligand binding and [35S]-GTP gamma S binding (+)-WAY 100135 was a partial agonist at human 5-HT1B and 5-HT1D receptors with moderately high affinity for 5-HT1D receptors (pEC50 = 7.61). 5. In conclusion, (+)-WAY 100135 was found to be not a selective 5-HT1A autoreceptor antagonist but may act as a partial agonist at the 5-HT1B/1D receptor, displaying agonist or antagonist properties depending on the stimulation protocol used and the resultant 5-HT 'tone' at the receptor.

The role of 5-HT(1B/1D) receptors in the modulation of 5-hydroxytryptamine levels in the frontal cortex of the conscious guinea pig

The role of 5-HT(1B/1D) receptors in modulating extracellular 5-hydroxytryptamine (5-HT) levels in the guinea pig was investigated with the non-selective 5-HT(1B/1D) receptor inverse agonist, methiothepin, and the selective 5-HT(1B/1D) receptor partial agonists, GR 127935 (n-[4-methoxy-3-(4-methyl-1-piperizinyl)phenyl]-2'-methyl-4'-(5-me thyl-1,2,4-oxadiazole-3-yl)[1,1'-biphenyl]-4-carboxamide) and GR 125743 (n-[4-methoxy-3-(4-methyl-1-piperizinyl)phenyl]-3-methyl-4-(4-pyri dinyl)benzamide). Extracellular 5-HT levels were measured using the technique of brain microdialysis, in the frontal cortex of the freely moving guinea-pig. Extracellular 5-HT was tetrodotoxin sensitive and calcium dependent, and increased when perfused with a high concentration of K+. In addition, extracellular 5-HT levels were lowered by the 5-HT(1B/1D) receptor agonist, sumatriptan, and the 5-HT1A receptor agonist, 8-hydroxy-2-(di-n-propylamino)tetralin, while perfusion of the selective serotonin re-uptake inhibitor, paroxetine, increased 5-HT in a concentration-dependent manner. Perfusion of methiothepin, GR 127935 and GR 125743 into the frontal cortex caused significant but transient increases of extracellular 5-HT. However, systemic administration of methiothepin, GR 127935 and GR 125743, at 0.3 mg/kg i.p., produced significant decreases in extracellular 5-HT, to minima of 27 +/- 3%, 31 +/- 12% and 27 +/- 13% of basal, respectively. The increase of extracellular 5-HT, following 5-HT(1B/1D) receptor inverse and partial agonist perfusion into the frontal cortex, was probably a consequence of attenuation of an endogenous 5-HT tone at terminal 5-HT autoreceptors. The unexpected decrease in 5-HT levels following systemic administration may be a result of additional attenuation of endogenous 5-HT tone at cell body autoreceptors in the raphe. Such an increase in local 5-HT levels could then stimulate 5-HT1A receptors to inhibit cell firing and hence decrease 5-HT levels in the terminal regions. This was confirmed when co-administration of the 5-HT1A receptor antagonist, WAY 100635, significantly attenuated the GR 127935 decrease in 5-HT.

Ceramide induces hepatocyte cell death through disruption of mitochondrial function in the rat

Although ceramide signaling pathways have been implicated in cell death, neither their role in hepatocellular death nor the cellular mechanisms mediating ceramide-induced cell death are known. The mitochondrial membrane permeability transition (MMPT) has been proposed as a common final pathway in cell death. Thus the aims of our study were to determine if ceramides cause hepatocellular death by necrosis and not apoptosis as confirmed by morphology and the absence of internucleosomal DNA cleavage. Ceramide-mediated hepatocyte necrosis was acyl chain-length, concentration, and time-dependent. Ceramides induced cell necrosis was associated with adenosine triphosphate (ATP) depletion and mitochondrial depolarization suggesting that ceramides caused mitochondrial dysfunction. In isolated mitochondria, ceramides induced the cyclosporine A-sensitive MMPT in an acyl chain-length and concentration dependent manner. Ceramide toxicity was specific as the less potent dihydro form did not induce cell necrosis, significant ATP depletion, mitochondrial depolarization nor the MMPT. In conclusion, ceramide induced cell death is acyl-chain length dependent and mediated by the MMPT. These data show for the first time that ceramide acts as a mediator of hepatocyte necrosis by causing mitochondrial failure.