Explore the vast range of titles available.

Although the pharmacological activity of capsaicin has been explained by its specific binding to transient receptor potential vanilloid type 1, the amphiphilic structure of capsaicin may enable it to act on lipid bilayers. From a mechanistic point of view, we investigated whether capsaicin and its antagonist capsazepine interact with biomimetic membranes, and how capsazepine influences the membrane effect of capsaicin. Liposomal phospholipid membranes and neuro-mimetic membranes were prepared with 1,2-dipalmitoylphosphatidylcholine and with 1-palmitoyl-2-oleoylphosphatidylcholine and sphingomyelin plus cholesterol, respectively. These membrane preparations were subjected to reactions with capsaicin and capsazepine at 0.5–250 μM, followed by measuring fluorescence polarization to determine the membrane interactivity to modify the fluidity of membranes. Both compounds acted on 1,2-dipalmitoylphosphatidylcholine bilayers and changed membrane fluidity. Capsaicin concentration-dependently interacted with neuro-mimetic membranes to increase their fluidity at low micromolar concentrations, whereas capsazepine inversely decreased the membrane fluidity. When used in combination, capsazepine inhibited the effect of capsaicin on neuro-mimetic membranes. In addition to the direct action on transmembrane ion channels, capsaicin and capsazepine share membrane interactivity, but capsazepine is likely to competitively antagonize capsaicin’s interaction with neuro-mimetic membranes at pharmacokinetically-relevant concentrations. The structure-specific membrane interactivity may be partly responsible for the analgesic effect of capsaicin.

The B1 receptor for kinins, stimulated by kinin metabolites without the C‐terminal Arg residue (e.g., des‐Arg9‐bradykinin (BK) and Lys‐des‐Arg9‐BK), is an increasingly recognized molecular target for the development of analgesic and anti‐inflammatory drugs. Recently developed antagonists of this receptor were compared to a conventional antagonist, Ac‐Lys‐[Leu8]‐des‐Arg9‐BK, in pharmacological assays based on the rabbit B1 receptor. B‐9858 (Lys‐Lys‐[Hyp3, Igl5, D‐Igl7, Oic8]des‐Arg9‐BK) and three other analogues possessing the α‐2‐indanylglycine5 (Igl5) residue (order of potency B‐9858 ∼ B‐10146>B‐10148>B‐10050) were partially insurmountable antagonists of des‐Arg9‐BK in the contractility assay based on rabbit aortic rings. B‐9858‐induced depression of the maximal effect was more pronounced in tissues treated with the protein synthesis inhibitor cycloheximide to block the spontaneous increase of response attributed to the post‐isolation formation of B1 receptors, and only partly reversible on washing. By comparison, Ac‐Lys‐[Leu8]des‐Arg9‐BK was a surmountable antagonist (pA2 7.5), even in cycloheximide‐treated tissues. B‐9958 (Lys‐[Hyp3, CpG5, D‐Tic7, CpG8]des‐Arg9‐BK) was also surmountable (pA2 8.5). The binding of [3H]‐Lys‐des‐Arg9‐BK to recombinant rabbit B1 receptors expressed in COS‐1 cells was influenced by two of the antagonists: while Ac‐Lys‐[Leu8]des‐Arg9‐BK competed for the radioligand binding without affecting the Bmax, B‐9858 decreased the Bmax in a time‐dependent and washout‐resistant manner. B‐9858 and analogues possessing Igl5 are the first reported non‐competitive, non‐equilibrium antagonists of the kinin B1 receptor. British Journal of Pharmacology (2000) 131, 885–892; doi:10.1038/sj.bjp.0703656

Macrocyclic imine phycotoxins are an emerging class of chemical compounds associated with harmful algal blooms and shellfish toxicity. Earlier binding and electrophysiology experiments on nAChR subtypes and their soluble AChBP surrogates evidenced common trends for substantial antagonism, binding affinities, and receptor-subtype selectivity. Earlier, complementary crystal structures of AChBP complexes showed that common determinants within the binding nest at each subunit interface confer high-affinity toxin binding, while distinctive determinants from the flexible loop C, and either capping the nest or extending toward peripheral subsites, dictate broad versus narrow receptor subtype selectivity. From these data, small spiroimine enantiomers mimicking the functional core motif of phycotoxins were chemically synthesized and characterized. Voltage-clamp analyses involving three nAChR subtypes revealed preserved antagonism for both enantiomers, despite lower subtype specificity and binding affinities associated with faster reversibility compared with their macrocyclic relatives. Binding and structural analyses involving two AChBPs pointed to modest affinities and positional variability of the spiroimines, along with a range of AChBP loop-C conformations denoting a prevalence of antagonistic properties. These data highlight the major contribution of the spiroimine core to binding within the nAChR nest and confirm the need for an extended interaction network as established by the macrocyclic toxins to define high affinities and marked subtype specificity. This study identifies a minimal set of functional pharmacophores and binding determinants as templates for designing new antagonists targeting disease-associated nAChR subtypes.

To characterize binding sites for nonpeptide angiotensin antagonists on the human angiotensin II receptor type 1 (AT1receptor) we have systematically exchanged segments of the human receptor with corresponding segments from a homologous Xenopus laevis receptor, which does not bind the nonpeptide compounds. Substitution of transmembrane segment VII of the human AT1receptor dramatically reduced the binding affinity of all of the 11 nonpeptide antagonists tested (55- to >2000-fold) with no effect on the binding of angiotensin. The affinity for the nonpeptide compounds decreased additionally one order of magnitude when transmembrane segment VI and the connecting extracellular loop 3 from the Xenopus receptor were also introduced into the human AT1receptor. Exchanges of smaller segments and single residues in transmembrane segments VI and VII and extracellular loop 3 revealed that the binding of nonpeptide antagonists was dependent on nonconserved residues located deep within the transmembrane segments VI and VII, in particular Asn295in transmembrane segment VII. Surprisingly, all exchanges in transmembrane segment VII, including the Asn295to Ser substitution, had a more pronounced effect on the binding of the competitive antagonists relative to the insurmountable antagonists. It is concluded that the binding mode for peptide and nonpeptide ligands on the AT1receptor is rather different and that competitive and insurmountable antagonists presumably bind to overlapping but distinct sites located in transmembrane segments VI and VII.

The aim of the present study was to investigate whether endothelin-1 (ET-1) in cerebral arteries is inhibited by the new, non-peptidergic ET^sub A^ receptor antagonist Ro 61-1790 and, if it is, whether that inhibition reduces the lesion volume induced by cold injury in the parietal cortex. In vitro experiments were performed by measuring the isometric contractions of the rat middle cerebral and basilar arteries. A cold lesion was induced in vivo by the application of a pre-cooled (-78°C) copper cylinder (diameter 3 mm) to the intact dura of rats for 6 s. After 24 h, lesion volume was determined by the triphenyltetrazolium method. In vitro, ET-1 (10^sup -12^-3×10^sup -7^ M) caused a dose-dependent contraction under resting conditions in the middle cerebral and basilar arteries of control rats. Ro 61-1790 (3×10^sup -9^ M, 10^sup -7^ M) shifted the concentration-effect curves for ET-1 in a parallel fashion (E^sub max^ unaltered). Post-treatment with Ro 61-1790 (10^sup -7^-10^sup -5^ M) also inhibited the prior contraction elicited by ET-1 (3×10^sup -9^ M) significantly. In vitro ET-1 application 3 h after the intracerebroventricular in vivo administration of Ro 61-1790 showed that the antagonist had reached the arteries and was bound to their ET^sub A^ receptors. Intracerebroventricular pre-treatment of Ro 61-1790 reduced significantly the lesion volume by 23% after the injury. We conclude that ET-1 is involved in the development of secondary brain damage and that intracerebroventricular treatment with Ro 61-1790 reduces the size of the brain lesion caused by cold injury.[PUBLICATION ABSTRACT]

The effect of the oxystilbene derivative F3 was tested on nAChRs of whole‐cell patch‐clamped rat chromaffin cells in vitro and of rat adrenal gland membranes using 125I‐epibatidine. F3 (30 nM) rapidly and reversibly blocked inward currents generated by pulse applications of nicotine, shifting the dose‐response curve to the right in a parallel fashion without changing the maximum response. The action of F3 was voltage insensitive and not due to altered current reversal potential. The R isomer of F3 was more potent (IC50=350±30 nM) than its S‐enantiomer (IC50=1.5±0.3 μM). Nicotine‐evoked currents were insensitive to 10 μM α‐bungarotoxin. Equi‐amplitude currents evoked by nicotine or epibatidine were similarly antagonized by R‐F3 in a reversible fashion. Epibatidine‐evoked currents readily produced receptor desensitization. Adrenal membranes specifically bound 125I‐epibatidine with a single population of binding sites endowed with high affinity (KD=159 pM) and Bmax of 6.5±1.3 fmol mg−1 of protein. 125I‐epibatidine binding was specifically displaced by cytisine (Ki=68 nM) or ACh (Ki=348 nM). F3 specifically displaced 125I‐epibatidine binding although with lower affinity (Ki=29.6 μM) than in electrophysiological experiments. 125I‐epibatidine binding to rat adrenal tissue was insensitive to α‐bungarotoxin which readily antagonized 125I‐epibatidine binding to bovine adrenal tissue. The present results suggest that F3 is a relatively potent and apparently competitive antagonist of nAChRs on rat chromaffin cells. Since previous studies have indicated that F3 targets different subtypes on chick neuronal tissue, it appears that nAChRs display interspecies differences to be considered for drug development studies. British Journal of Pharmacology (2000) 129, 1771–1779; doi:10.1038/sj.bjp.0703264

Adhesion ability to the host is a classical selection criterion for potential probiotic bacteria that could result in a transient colonisation that would help to promote immunomodulatory effects, as well as stimulate gut barrier and metabolic functions. In addition, probiotic bacteria have a potential protective role against enteropathogens through different mechanisms including production of antimicrobial compounds, reduction of pathogenic bacterial adhesion and competition for host cell binding sites. The competitive exclusion by probiotic bacteria has a beneficial effect not only on the gut but also in the urogenital tract and oral cavity. On the other hand, prebiotics may also act as barriers to pathogens and toxins by preventing their adhesion to epithelial receptors. In vitro studies with different intestinal cell lines have been widely used along the last decades to assess the adherence ability of probiotic bacteria and pathogen antagonism. However, extrapolation of these results to in vivo conditions still remains unclear, leading to the need of optimisation of more complex in vitro approaches that include interaction with the resident microbiota to address the current limitations. The aim of this mini review is to provide a comprehensive overview on the potential effect of the adhesive properties of probiotics and prebiotics on the host by focusing on the most recent findings related with adhesion and immunomodulatory and antipathogenic effect on human health.

Bacterial contact-dependent killing in spatially structured systems is shaped by physical constraints and biological interactions. In this study, we demonstrate the importance of fungal hyphae in facilitating bacterial dispersal and promoting contact-dependent killing during surface-associated growth. Using Vibrio cholerae as the killing bacterium and Pseudomonas stutzeri as the target bacterium, we show that fungal hyphae act as dispersal agents that facilitate bacterial spatial intermixing and promote contact-dependent killing. Specifically, we show that dispersal along fungal hyphae increases the number of contacts between V. cholerae and P. stutzeri cells, which in turn increases the extent of killing via the type VI secretion system encoded by V. cholerae. This enables V. cholerae to achieve growth dominance despite initial population disadvantages. We further show that the effect of fungal hyphae on the killing efficacy of V. cholerae depends on flagellar motility. Our study underscores the multifaceted effects of fungal hyphae in enhancing bacterial dispersal and intensifying interspecies interactions, highlighting the ecological significance of fungal–bacterial interactions in spatially structured systems.