Agonism and allosterism: the pharmacology of the free fatty acid receptors FFA2 and FFA3

The free fatty acid receptors FFA2 and FFA3 are recently de-orphanized G protein-coupled receptors that share a group of short-chain free fatty acids as endogenous ligands. The expression of FFA2 and FFA3 by immune cells, in parts of the gastro-intestinal tract and by white adipocytes has suggested their potential as therapeutic targets in conditions including inflammation and obesity. However, although FFA2 and FFA3 display distinct structure-activity relationships for stimulation by short-chain free fatty acids, the overlap between these endogenous agonists and the lack of synthetic small molecule ligands that display selectivity between these two receptors has, until recently, hindered efforts to resolve their individual functions. Recently, chloro-alpha-(1-methylethyl)-N-2-thiazolylbenzeneacetamide has been described as an FFA2 selective ago-allosteric ligand, not only being a direct agonist but also acting as a positive allosteric modulator of the function of short-chain free fatty acids at FFA2. Mutation of a pair of key arginine residues near the top of transmembrane domains V and VII of both FFA2 and FFA3 eliminates the function of short-chain free fatty acids but is without effect on the direct agonist action of chloro-alpha-(1-methylethyl)-N-2-thiazolylbenzeneacetamide at FFA2, confirming the distinct nature of the binding site of the ago-allosteric regulator from the orthosteric binding site for free fatty acids. An understanding of structure-activity relationships for ligands related to chloro-alpha-(1-methylethyl)-N-2-thiazolylbenzeneacetamide is likely to provide greater insight into the mode of action and site of binding of this ligand, but further FFA2 and FFA3 selective ligands, preferably with higher potency/affinity, will be required to fully explore the physiological function of these receptors.

The action and mode of binding of thiazolidinedione ligands at free fatty acid receptor 1

The endogenous ligands for free fatty acid receptor 1 (FFA1) are medium and longer chain free fatty acids. However, a range of selective, small molecule ligands have recently been developed as tool compounds to explore the therapeutic potential of this receptor, whereas clinically employed thiazolidinedione "glitazone" drugs are also agonists at FFA1. Each of these classes of agonist was able to promote phosphorylation of the ERK1/2 mitogen-activated protein (MAP) kinases in cells able to express human FFA1 on demand. However, although both lauric acid and the synthetic agonist GW9508X produced rapid and transient ERK1/2 MAP kinase phosphorylation, the thiazolidinedione rosiglitazone produced responses that were sustained for a substantially longer period. Despite this difference, the effects of each ligand required FFA1 and were transduced in each case predominantly via G proteins of the Galphaq/Galpha11 family. Different glitazone drugs also displayed markedly different efficacy and kinetics of sustainability of ERK1/2 MAP kinase phosphorylation. A number of orthosteric binding site mutants of FFA1 were generated, and despite variations in the changes of potency and efficacy of the three ligand classes in different functional end point assays, these were consistent with rosiglitazone also binding at the orthosteric site. Four distinct polymorphic variants of human FFA1 have been described. Despite previous indications that these display differences in function and pharmacology, they all responded in entirely equivalent ways to lauric acid, rosiglitazone, and GW9508X in measures of ERK1/2 MAP kinase phosphorylation, enhancement of binding of [35S]GTPgammaS (guanosine 5'-O-(3-[35S]thio)triphosphate) to Galphaq, and elevation of intracellular [Ca2+], suggesting that individuals expressing each variant are likely to respond equivalently to orthosteric agonists of FFA1.

International Union of Pharmacology. LXXI. Free fatty acid receptors FFA1, -2, and -3: pharmacology and pathophysiological functions

Identification of G protein-coupled receptors that are activated by free fatty acids has led to considerable interest in their pharmacology and function because of the wide range of normal physiology and disease states in which fatty acids have been implicated. Free fatty acid receptor (FFA) 1 is activated by medium- to long-chain fatty acids and is expressed in the insulin-producing beta-cells of the pancreas. Activation of FFA1 has been proposed to mediate fatty acid augmentation of glucose-stimulated insulin secretion although it is unclear whether the known long-term detrimental effects of beta-cell exposure to high levels of fatty acids are also mediated through this receptor. The related receptors FFA2 and FFA3 are both activated by short-chain fatty acids although they have key differences in the signaling pathways they activate and tissue expression pattern. The aim of this review is to provide a comprehensive overview of the current understanding of the pharmacology and physiological role of these fatty acid receptors.

Effect of Dominant-Negative Epidermal Growth Factor Receptors on Cardiomyocyte Hypertrophy

Angiotensin II (AngII) induces heart growth via cardiomyocyte hypertrophy, and central to this is the capacity of the type 1 AngII receptor (AT1R) to "transactivate" epidermal growth factor receptors (EGFRs)--a family with four main subtypes (HER1-4)--although the exact molecular mechanism remains unresolved. In this study, the pharmacological inhibition of AngII-stimulated ERK1/2 activation and cardiomyocyte hypertrophy by increasing concentrations of an EGFR inhibitor, AG1478, indicated that other EGFR subtypes, in addition to HER1, may be involved. We constructed expression vectors and adenoviruses expressing truncated mutant versions of HER1, HER2, and HER4 and determined their capacity to act as dominant-negative inhibitors when co-transfected with full-length EGFRs. It is surprising that adenoviral-mediated expression of these truncated EGFRs in cardiomyocytes led to paradoxical, ligand-independent increases in cardiomyocyte hypertrophy and unusual morphological changes. These results challenge our perception of AT1R-mediated EGFR transactivation and imply that truncated EGFRs may affect cell function through unconventional mechanisms.

The guinea-pig tracheal potential difference as an in vivo model for the study of epithelial sodium channel function in the airways

BACKGROUND AND PURPOSE

The epithelial sodium channel (ENaC) is a key regulator of airway mucosal hydration and mucus clearance. Negative regulation of airway ENaC function is predicted to be of clinical benefit in the cystic fibrosis lung. The aim of this study was to develop a small animal model to enable the direct assessment of airway ENaC function in vivo.

EXPERIMENTAL APPROACH

Tracheal potential difference (TPD) was utilized as a measure of airway epithelial ion transport in the guinea-pig. ENaC activity in the trachea was established with a dose-response assessment to a panel of well-characterized direct and indirect pharmacological modulators of ENaC function, delivered by intra-tracheal (i.t.) instillation.

KEY RESULTS

The TPD in anaesthetized guinea-pigs was attenuated by the direct ENaC blockers: amiloride, benzamil and CF552 with ED(50) values of 16, 14 and 0.2 microg kg(-1) (i.t.), respectively. 5-(N-Ethyl-N-isopropyl) amiloride, a structurally related compound but devoid of activity on ENaC, was without effect on the TPD. Intra-tracheal dosing of the Kunitz-type serine protease inhibitors aprotinin and placental bikunin, which have previously been demonstrated to inhibit proteolytic activation of ENaC, likewise potently attenuated TPD in guinea-pigs, whereas alpha(1)-antitrypsin and soya bean trypsin inhibitor were without effect.

CONCLUSIONS AND IMPLICATIONS

The pharmacological sensitivity of the TPD to amiloride analogues and also to serine protease inhibitors are both consistent with that of ENaC activity in the guinea-pig trachea. The guinea-pig TPD therefore represents a suitable in vivo model of human airway epithelial ion transport.

Prognostic significance of magnetic resonance imaging-detected extramural vascular invasion in rectal cancer

BACKGROUND

Extramural vascular invasion (EMVI) is a poor prognostic feature in colorectal cancer. The accuracy of magnetic resonance imaging (MRI) in detecting EMVI and predicting relapse-free survival (RFS) was compared retrospectively with the histological reference standard.

METHODS

Preoperative magnetic resonance images from patients diagnosed with rectal and sigmoid cancer were reviewed and an MRI-EMVI score (range 0 to 4) was assigned. Comparison was made with histology and clinical outcome.

RESULTS

Some 142 patients with a median follow-up of 3.3 (range 0.9-5.7) years were reviewed. Histological EMVI was reported in a quarter of patients. The sensitivity and specificity of MRI detection of EMVI in 94 patients undergoing primary surgery were 62 and 88 per cent respectively. On univariable analysis, RFS at 3 years was 35 per cent for patients with an MRI-EMVI score of 3-4, compared with 74 per cent for those with a score of 0-2 (P < 0.001), similar to values in patients with positive and negative histological EMVI status respectively (34 versus 73.7 per cent; P < 0.001).

CONCLUSION

High MRI-EMVI scores may help in predicting disease relapse.

Allosteric modulation of heterodimeric G-protein-coupled receptors

G-protein-coupled receptors (GPCRs) are, and will probably remain, the most tractable class of targets for the development of small-molecule therapeutic medicines. Currently, all approved GPCR-directed medicines are agonists or antagonists at orthosteric binding sites - except for the calcimimetic cinacalcet, which is a positive allosteric modulator of Ca(2+)-sensing receptors, and maraviroc, an allosteric inhibitor of CC-chemokine receptor (CCR) 5. It is now widely accepted that GPCRs exist and might function as dimers, and there is growing evidence for the physiological presence and relevance of GPCR heterodimers. Molecules that can regulate a GPCR within a heterodimer, through allosteric effects between the two protomers of the dimer or between a protomer or protomers and the associated G protein, offer the potential to function in a highly selective and tissue-specific way. Despite the conceptual attraction of such allosteric regulators of GPCR heterodimers as drugs, they cannot be identified by screening approaches that routinely use a 'one GPCR target at a time' strategy. In our opinion, this will require the development of new approaches for screening and a return to the use of physiologically relevant cell systems at an early stage in compound identification.

Preoperative computed tomography staging of nonmetastatic colon cancer predicts outcome: implications for clinical trials

Colon cancer patients routinely undergo preoperative computed tomography (CT) scanning, but local staging is thought to be inaccurate. We aimed to determine if clinical outcome could be predicted from radiological features of the primary tumour. Consecutive patients at one hospital undergoing primary resection for colon cancer during 2000-2004 were included. Patients with visible metastases were excluded. Preoperative CT scans were reviewed independently by two radiologists blinded to histological stage and outcome. Images of the primary tumour were evaluated according to conventional TNM criteria and patients were stratified into 'good' or 'poor' prognosis groups. Comparison was made between prognostic group and actual clinical outcome. Hundred and twenty-six preoperative CT scans were reviewed. T-stage and nodal status was correctly predicted in only 60 and 62%, respectively. However, inter-observer agreement for prognostic group was 79% (kappa=0.59) and 3-year relapse-free survival was 71 and 43% for the CT-predicted 'good' and 'poor' groups, respectively (P<0.0066). This compared favourably with 75 vs 43% for histology-predicted prognostic groups. Computed tomography is a robust method for stratifying patients preoperatively, with similar accuracy to histopathology for predicting outcome. Recognition of poor prognosis tumours preoperatively may permit investigation into the future use of neo-adjuvant therapy in colon cancer.

Adaptive Aerosol Delivery (AAD) technology

Jet nebulisers have, since the 1920s, been used for delivery of inhaled drugs for the treatment of asthma, chronic-obstructive pulmonary disease and pulmonary infections. During the last two decades, recognition of the shortcomings of conventional nebulisers has led to the development of new "intelligent" nebulisers such as the Adaptive Aerosol Delivery (AAD), Profile Therapeutics, a Respironics company) systems. Diseases of the airways have traditionally been logical candidates for treatment with inhaled drugs. The introduction of the "intelligent" nebulisers has, however, broadened the possibilities for inhaled treatment to include drugs targeted for systemic diseases. These nebulisers offer the possibility to deliver more precise doses of drug, maximise lung deposition, enhance adherence to treatment and compliance with the device through feedback to the patient, and last but not least, offer the possibility to reduce nebulisation times.

Tackling the EGFR in pathological tissue remodelling

Tissue remodelling is an adaptive physiological event initiated by physical and/or hormonal stimuli and characterised by extracellular matrix modifications, inflammation, cellular hypertrophy, proliferation and/or apoptosis. Although its initial effects may be beneficial for the maintenance of organ function, it is evident that sustained remodelling processes can lead to pathological outcomes, such as fibrosis in asthma, and cardiac hypertrophy in heart failure. Our research is focussed upon cardiac hypertrophy and the significant contribution of the molecular pathway, termed 'the triple membrane-passing signalling' paradigm (TMPS), to this phenomenon. Cardiac hypertrophy describes the enlargement, but not proliferation, of cardiomyocytes in response to mechanical or hormonal factors to normalise cardiac output and accompanies other features of cardiac remodelling. As a major independent risk factor for heart failure, it is imperative that the molecular mechanisms that govern this phenotype are determined to identify possible therapeutic targets. This review will focus on the importance of matrix metalloproteases and epidermal growth factor receptors in the TMPS pathway and their potential as pharmacological targets for heart failure therapy. The evidence provided may have implications for pathological tissue remodelling in other organs.

Regulation of serotonin 5-HT2C receptors by chronic ligand exposure

The effect of ligand pretreatment on human 5-hydroxytryptamine2C (5-HT2C) receptors was examined in CHO cells expressing high (CHO-1C7; 67+/-3 pmol/mg) or low (CHO-1C19; 72+/-10 fmol/mg) levels of the receptor. Seventy-two hours pretreatment of CHO-1C7 cells with various ligands did not affect receptor expression. Pretreatment with inverse agonists enhanced 5-HT-mediated inositol phosphate accumulation with no change in constitutive receptor activity. The enhanced agonist responsiveness was inversely correlated with the intrinsic activity of the pretreatment ligand. Seventy-two hours of pretreatment with the weak agonist, 5-methoxygramine, caused an elevation in constitutive activity but no alteration in 5-HT-mediated signaling. In CHO-1C19 cells, 24 but not 72 h of pretreatment with the inverse agonist mianserin enhanced 5-HT-mediated signaling, with no effect on basal signaling; pretreatment with 5-methoxygramine had no significant effect. These findings highlight differences in the pattern of chronic regulation of 5HT2C receptor signaling between high and low receptor expression levels in a common cellular background.

Hijacking epidermal growth factor receptors by angiotensin II: new possibilities for understanding and treating cardiac hypertrophy

Activation of the type 1 angiotensin II receptor (AT(1)R) is associated with the aetiology of left ventricular hypertrophy, although the exact intracellular signalling mechanism(s) remain unclear. Transactivation of the epidermal growth factor receptor (EGFR) has emerged as a central mechanism by which the G protein-coupled AT(1)R, which lacks intrinsic tyrosine kinase activity, can stimulate the mitogen-activated protein kinase signalling pathways thought to mediate cardiac hypertrophy. Current studies support a model whereby AT(1)R-dependent transactivation of EGFRs on cardiomyocytes involves stimulation of membrane-bound metalloproteases, which in turn cleave EGFR ligands such as heparin-binding EGF from a plasma membrane-associated precursor. Numerous aspects of the 'triple membrane-passing signalling' paradigm of AT(1)R-induced EGFR transactivation remain to be characterised, including the identity of the specific metalloproteases involved, the intracellular mechanism for their activation and the exact EGFR subtypes required. Here we examine how 'hijacking' of the EGFR might explain the ability of the AT(1)R to elicit the temporally and qualitatively diverse responses characteristic of the hypertrophic phenotype, and discuss the ramifications of delineating these pathways for the development of new therapeutic strategies to combat cardiac hypertrophy.

What?s new in the renin-angiotensin system?

The type 1 angiotensin receptor (AT(1)) activates an array of intracellular signalling pathways that control cell and tissue responses to the peptide hormone angiotensin II (AngII). The capacity of AT(1) receptors to initiate and maintain such signals has typically been explained on the basis of conventional heterotrimeric guanine nucleotide binding protein (G protein) activation, specifically G(q/11). Accumulating evidence from studies utilising a variety of AT(1) receptor mutants and AngII analogues indicates that some important downstream effects of AT(1) receptors are independent of classical G protein coupling. Importantly, AT(1) receptor-mediated endocytosis, tyrosine phosphorylation signalling and mitogen-activated protein kinase activation as well as transactivation of the epidermal growth factor receptor can occur in G(q/11)-uncoupled receptor mutants. These observations point to a functional partitioning of AT(1) receptor signals that permits separation of short-term AngII actions (e.g., vasoconstriction) from more extended events, such as pathological cell growth in heart and blood vessels, and may open up new avenues for selective antagonism.

Evaluation of the Digene Hybrid Capture II Assay with the Rapid Capture System for detection of Chlamydia trachomatis and Neisseria gonorrhoeae

Screening for chlamydial and gonococcal infection has been strongly recommended for all sexually active women under the age of 26. Advances in the ability to detect infection by nucleic acid detection techniques have improved access to screening methods in routine clinical practices. To meet the increasing demand for testing, a high-throughput system is desirable. We evaluated the performance of the Hybrid Capture 2 CT/GC (HC2) assay with the Digene Rapid Capture System (HC2-RCS). The results of HC2-RCS for endocervical samples from 330 women were compared to those of culture and the COBAS Amplicor PCR. For detection of chlamydial infection, HC2-RCS had a sensitivity and a specificity similar to those of PCR (P > 0.5) and an improved sensitivity compared to that of culture (P = 0.007). For identification of gonococcal infections, all assays performed similarly (P > 0.5). The performance of HC2-RCS was also compared to that of the manual HC2 format (HC2-M) with these samples and with 911 endocervical samples collected previously. The performance of HC2-RCS was equivalent to that of HC2-M; the overall concordance rates for the detection of chlamydia and gonorrhea were 99.7% (kappa = 0.97) and 99.8% (kappa = 0.97), respectively. When the HC2 assay was performed with a semiautomated system application designed for high throughput, it demonstrated high sensitivity and a high specificity for detection of both Chlamydia trachomatis and Neisseria gonorrhoeae.

Direct optical quantification of backflow in a 90 degrees twisted nematic cell

Optical guided mode observations of the transient director profile (optical tensor distribution) during the relaxation of a 90 degrees twisted nematic cell directly reveals backflow. In the first 6 ms of the relaxation process, after a voltage across the cell is removed, the midplane tilt of the director increases, reaching a maximum value of 101 degrees at 1.4 ms. This increase in midplane tilt is attributed to coupling between fluid flow (backflow) and director reorientation. A 270 degrees twisted state of the opposite handedness to the 90 degrees twisted state found at equilibrium is shown to exist during the backflow period. Good fits of theoretical models with experimentally determined time dependent director profiles yield the viscosity coefficients.

Nerve conduction studies for carpal tunnel syndrome: essential prelude to surgery or unnecessary luxury?

Although carpal tunnel syndrome is a relatively trivial condition, controversy surrounds the use of nerve conduction studies, and whether they are essential to make the diagnosis, or as a prelude to surgery. This is partly due to the lack of a generally agreed definition of the condition, and failure to recognize that the patient's first priority is rapid relief of symptoms. If nerve conduction studies do not contribute to achieving that aim it would be better not to do them. Supporters of routine preoperative nerve conduction studies ignore their shortcomings, which include lack of standardization, absence of population-based reference intervals, and lack of sensitivity and specificity. Only a controlled trial, in which patients are randomized to receive treatment either with or without nerve conduction studies, will determine whether they improve the outcome in patients with a firm clinical diagnosis of carpal tunnel syndrome.

A new statistical method for haplotype reconstruction from population data

Current routine genotyping methods typically do not provide haplotype information, which is essential for many analyses of fine-scale molecular-genetics data. Haplotypes can be obtained, at considerable cost, experimentally or (partially) through genotyping of additional family members. Alternatively, a statistical method can be used to infer phase and to reconstruct haplotypes. We present a new statistical method, applicable to genotype data at linked loci from a population sample, that improves substantially on current algorithms; often, error rates are reduced by > 50%, relative to its nearest competitor. Furthermore, our algorithm performs well in absolute terms, suggesting that reconstructing haplotypes experimentally or by genotyping additional family members may be an inefficient use of resources.

Time trends in autism and in MMR immunization coverage in California

CONTEXT

Considerable concern has been generated in the lay and medical communities by a theory that increased measles-mumps-rubella (MMR) immunization among young children may be the cause of an apparent marked increase in autism occurrence.

OBJECTIVE

To determine if a correlation exists in secular trends of MMR immunization coverage among young children and autism occurrence.

DESIGN, SETTING, AND PARTICIPANTS

Retrospective analyses of MMR immunization coverage rates among children born in 1980-1994 who were enrolled in California kindergartens (survey samples of 600-1900 children each year) and whose school immunization records were reviewed to retrospectively determine the age at which they first received MMR immunization; and of autism caseloads among children born in these years who were diagnosed with autism and were enrolled in the California Department of Developmental Services regional service center system.

MAIN OUTCOME MEASURES

Measles-mumps-rubella immunization coverage rates as of ages 17 months and 24 months and numbers of Department of Developmental Services system enrollees diagnosed with autism, grouped by year of birth.

RESULTS

Essentially no correlation was observed between the secular trend of early childhood MMR immunization rates in California and the secular trend in numbers of children with autism enrolled in California's regional service center system. For the 1980-1994 birth cohorts, a marked, sustained increase in autism case numbers was noted, from 44 cases per 100 000 live births in the 1980 cohort to 208 cases per 100 000 live births in the 1994 cohort (a 373% relative increase), but changes in early childhood MMR immunization coverage over the same time period were much smaller and of shorter duration. Immunization coverage by the age of 24 months increased from 72% to 82%, a relative increase of only 14%, over the same time period.

CONCLUSIONS

These data do not suggest an association between MMR immunization among young children and an increase in autism occurrence.

Molecular basis by which garlic suppresses atherosclerosis

The aim of this study was to determine the mechanism by which the aged garlic extract "Kyolic" has a protective effect against atherosclerosis. Plasma cholesterol of rabbits fed a 1% cholesterol-enriched diet for 6 wk was not reduced by supplementation with 800 microL Kyolic/(kg body. d). In spite of this, Kyolic reduced by 64% (P < 0.05) the surface area of the thoracic aorta covered by fatty streaks and significantly reduced aortic arch cholesterol. Kyolic also significantly inhibited by approximately 50% the development of thickened, lipid-filled lesions in preformed neointimas produced by Fogarty 2F balloon catheter injury of the right carotid artery in cholesterol-fed rabbits. In vitro studies found that Kyolic completely prevented vascular smooth muscle phenotypic change from the contractile, high volume fraction of filament (V(v)myo) state, and inhibited proliferation of smooth muscle cells in the synthetic state with a 50% effective dose (ED(50)) of 0.2%. Kyolic also slightly inhibited the accumulation of lipid in cultured macrophages but not smooth muscle, and had no effect on the expression of adhesion molecules on the surface of the endothelium or the adherence of leukocytes. It is concluded that Kyolic exerts antiatherogenic effects through inhibition of smooth muscle phenotypic change and proliferation, and by another (unclarified) effect on lipid accumulation in the artery wall.

The IBIS project: data collection in London. Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery

The primary aim of the Improved Monitoring for Brain Dysfunction during Intensive Care and Surgery (IBIS) project was to create a unique and comprehensively annotated data library (DL) of multiple physiological, including neurophysiological, signals. Data collection was undertaken in Kuopio, Finland and London, UK, and comparable protocols were used at all the sites. In London, 43 patients were recruited at the Royal Brompton Hospital, followed by nine at St. Bartholomew's Hospital, all of whom underwent cardiac or combined cardiac and carotid artery surgery. Thirty-seven patients underwent a single operation, while 15 underwent two procedures. The protocols and equipment used, problems specific to the electrically hostile environment and preliminary results are described, including those of clinical interest. The DL is being used for the development of clinically applicable neurophysiological monitoring tools.