Molecular Umbrella as a Nanocarrier for Antifungals.

A molecular umbrella composed of two O-sulfated cholic acid residues was applied for the construction of conjugates with cispentacin, containing a "trimethyl lock" (TML) or o-dithiobenzylcarbamoyl moiety as a cleavable linker. Three out of five conjugates demonstrated antifungal in vitro activity against C. albicans and C. glabrata but not against C. krusei, with MIC90 values in the 0.22-0.99 mM range and were not hemolytic. Antifungal activity of the most active conjugate 24c, containing the TML-pimelate linker, was comparable to that of intact cispentacin. A structural analogue of 24c, containing the Nap-NH2 fluorescent probe, was accumulated in Candida cells, and TML-containing conjugates were cleaved in cell-free extract of C. albicans cells. These results suggest that a molecular umbrella can be successfully applied as a nanocarrier for the construction of cleavable antifungal conjugates.

A Critical Role for Astrocytes in Hypercapnic Vasodilation in Brain.

Cerebral blood flow (CBF) is controlled by arterial blood pressure, arterial CO2, arterial O2, and brain activity and is largely constant in the awake state. Although small changes in arterial CO2 are particularly potent to change CBF (1 mmHg variation in arterial CO2 changes CBF by 3%-4%), the coupling mechanism is incompletely understood. We tested the hypothesis that astrocytic prostaglandin E2 (PgE2) plays a key role for cerebrovascular CO2 reactivity, and that preserved synthesis of glutathione is essential for the full development of this response. We combined two-photon imaging microscopy in brain slices with in vivo work in rats and C57BL/6J mice to examine the hemodynamic responses to CO2 and somatosensory stimulation before and after inhibition of astrocytic glutathione and PgE2 synthesis. We demonstrate that hypercapnia (increased CO2) evokes an increase in astrocyte [Ca2+]i and stimulates COX-1 activity. The enzyme downstream of COX-1 that synthesizes PgE2 (microsomal prostaglandin E synthase-1) depends critically for its vasodilator activity on the level of glutathione in the brain. We show that, when glutathione levels are reduced, astrocyte calcium-evoked release of PgE2 is decreased and vasodilation triggered by increased astrocyte [Ca2+]iin vitro and by hypercapnia in vivo is inhibited. Astrocyte synthetic pathways, dependent on glutathione, are involved in cerebrovascular reactivity to CO2 Reductions in glutathione levels in aging, stroke, or schizophrenia could lead to dysfunctional regulation of CBF and subsequent neuronal damage.SIGNIFICANCE STATEMENT Neuronal activity leads to the generation of CO2, which has previously been shown to evoke cerebral blood flow (CBF) increases via the release of the vasodilator PgE2 We demonstrate that hypercapnia (increased CO2) evokes increases in astrocyte calcium signaling, which in turn stimulates COX-1 activity and generates downstream PgE2 production. We demonstrate that astrocyte calcium-evoked production of the vasodilator PgE2 is critically dependent on brain levels of the antioxidant glutathione. These data suggest a novel role for astrocytes in the regulation of CO2-evoked CBF responses. Furthermore, these results suggest that depleted glutathione levels, which occur in aging and stroke, will give rise to dysfunctional CBF regulation and may result in subsequent neuronal damage.

Evaluation of ß-Amino Acid Replacements in Protein Loops: Effects on Conformational Stability and Structure.

ß-Amino acids have a backbone that is expanded by one carbon atom relative to α-amino acids, and ß residues have been investigated as subunits in protein-like molecules that adopt discrete and predictable conformations. Two classes of ß residue have been widely explored in the context of generating α-helix-like conformations: ß3 -amino acids, which are homologous to α-amino acids and bear a side chain on the backbone carbon adjacent to nitrogen, and residues constrained by a five-membered ring, such the one derived from trans-2-aminocyclopentanecarboxylic acid (ACPC). Substitution of α residues with their ß3  homologues within an α-helix-forming sequence generally causes a decrease in conformational stability. Use of a ring-constrained ß residue, however, can offset the destabilizing effect of αâ†’ß substitution. Here we extend the study of αâ†’ß substitutions, involving both ß3 and ACPC residues, to short loops within a small tertiary motif. We start from previously reported variants of the Pin1 WW domain that contain a two-, three-, or four-residue ß-hairpin loop, and we evaluate αâ†’ß replacements at each loop position for each variant. By referral to the ϕ,ψ angles of the native structure, one can choose a stereochemically appropriate ACPC residue. Use of such logically chosen ACPC residues enhances conformational stability in several cases. Crystal structures of three ß-containing Pin1 WW domain variants show that a native-like tertiary structure is maintained in each case.

Selective Targeting by a Mechanism-Based Inactivator against Pyridoxal 5'-Phosphate-Dependent Enzymes: Mechanisms of Inactivation and Alternative Turnover.

Potent mechanism-based inactivators can be rationally designed against pyridoxal 5'-phosphate (PLP)-dependent drug targets, such as ornithine aminotransferase (OAT) or γ-aminobutyric acid aminotransferase (GABA-AT). An important challenge, however, is the lack of selectivity toward other PLP-dependent, off-target enzymes, because of similarities in mechanisms of all PLP-dependent aminotransferase reactions. On the basis of complex crystal structures, we investigate the inactivation mechanism of OAT, a hepatocellular carcinoma target, by (1R,3S,4S)-3-amino-4-fluorocyclopentane-1-carboxylic acid (FCP), a known inactivator of GABA-AT. A crystal structure of OAT and FCP showed the formation of a ternary adduct. This adduct can be rationalized as occurring via an enamine mechanism of inactivation, similar to that reported for GABA-AT. However, the crystal structure of an off-target, PLP-dependent enzyme, aspartate aminotransferase (Asp-AT), in complex with FCP, along with the results of attempted inhibition assays, suggests that FCP is not an inactivator of Asp-AT, but rather an alternate substrate. Turnover of FCP by Asp-AT is also supported by high-resolution mass spectrometry. Amid existing difficulties in achieving selectivity of inactivation among a large number of PLP-dependent enzymes, the obtained results provide evidence that a desirable selectivity could be achieved, taking advantage of subtle structural and mechanistic differences between a drug-target enzyme and an off-target enzyme, despite their largely similar substrate binding sites and catalytic mechanisms.

Hydrophilic and Cell-Penetrable Pyrrolidinyl Peptide Nucleic Acid via Post-synthetic Modification with Hydrophilic Side Chains.

Peptide nucleic acid (PNA) is a nucleic acid mimic in which the deoxyribose-phosphate was replaced by a peptide-like backbone. The absence of negative charge in the PNA backbone leads to several unique behaviors including a stronger binding and salt independency of the PNA-DNA duplex stability. However, PNA possesses poor aqueous solubility and cannot directly penetrate cell membranes. These are major obstacles that limit in vivo applications of PNA. In previous strategies, the PNA can be conjugated to macromolecular carriers or modified with positively charged side chains such as guanidinium groups to improve the aqueous solubility and cell permeability. In general, a preformed modified PNA monomer was required. In this study, a new approach for post-synthetic modification of PNA backbone with one or more hydrophilic groups was proposed. The PNA used in this study was the conformationally constrained pyrrolidinyl PNA with prolyl-2-aminocyclopentanecarboxylic acid dipeptide backbone (acpcPNA) that shows several advantages over the conventional PNA. The aldehyde modifiers carrying different linkers (alkylene and oligo(ethylene glycol)) and end groups (-OH, -NH2, and guanidinium) were synthesized and attached to the backbone of modified acpcPNA by reductive alkylation. The hybrids between the modified acpcPNAs and DNA exhibited comparable or superior thermal stability with base-pairing specificity similar to those of unmodified acpcPNA. Moreover, the modified apcPNAs also showed the improvement of aqueous solubility (10-20 folds compared to unmodified PNA) and readily penetrate cell membranes without requiring any special delivery agents. This study not only demonstrates the practicality of the proposed post-synthetic modification approach for PNA modification, which could be readily applied to other systems, but also opens up opportunities for using pyrrolidinyl PNA in various applications such as intracellular RNA sensing, specific gene detection, and antisense and antigene therapy.

Stereo- and Regiocontrolled Syntheses of Exomethylenic Cyclohexane ß-Amino Acid Derivatives.

Cyclohexane analogues of the antifungal icofungipen [(1R,2S)-2-amino-4-methylenecyclopentanecarboxylic acid] were selectively synthesized from unsaturated bicyclic ß-lactams by transformation of the ring olefinic bond through three different regio- and stereocontrolled hydroxylation techniques, followed by hydroxy group oxidation and oxo-methylene interconversion with a phosphorane. Starting from an enantiomerically pure bicyclic ß-lactam obtained by enzymatic resolution of the racemic compound, an enantiodivergent procedure led to the preparation of both dextro- and levorotatory cyclohexane analogues of icofungipen.

In vivo stimulus-induced vasodilation occurs without IP3 receptor activation and may precede astrocytic calcium increase.

Calcium-dependent release of vasoactive gliotransmitters is widely assumed to trigger vasodilation associated with rapid increases in neuronal activity. Inconsistent with this hypothesis, intact stimulus-induced vasodilation was observed in inositol 1,4,5-triphosphate (IP3) type-2 receptor (R2) knock-out (KO) mice, in which the primary mechanism of astrocytic calcium increase-the release of calcium from intracellular stores following activation of an IP3-dependent pathway-is lacking. Further, our results in wild-type (WT) mice indicate that in vivo onset of astrocytic calcium increase in response to sensory stimulus could be considerably delayed relative to the simultaneously measured onset of arteriolar dilation. Delayed calcium increases in WT mice were observed in both astrocytic cell bodies and perivascular endfeet. Thus, astrocytes may not play a role in the initiation of blood flow response, at least not via calcium-dependent mechanisms. Moreover, an increase in astrocytic intracellular calcium was not required for normal vasodilation in the IP3R2-KO animals.

A new access route to functionalized cispentacins from norbornene ß-amino acids.

An efficient and simple new stereocontrolled access route to novel disubstituted cispentacin derivatives with multiple stereogenic centers from norbornene ß-lactam has been developed. The synthesis involves olefinic bond functionalization by dihydroxylation followed by oxidative ring cleavage and transformation of the dialdehyde intermediate through a Wittig reaction.

High-performance liquid chromatographic enantioseparation of isoxazoline-fused 2-aminocyclopentanecarboxylic acids on a chiral ligand-exchange stationary phase.

The application of a chiral ligand-exchange column for the direct high-performance liquid chromatographic enantioseparation of unusual ß-amino acids with a sodium N-((R)-2-hydroxy-1-phenylethyl)-N-undecylaminoacetate-Cu(II) complex as chiral selector is reported. The investigated amino acids were isoxazoline-fused 2-aminocyclopentanecarboxylic acid analogs. The chromatographic conditions were varied to achieve optimal separation. The effects of temperature were studied at constant mobile phase compositions in the temperature range 5-45°C, and thermodynamic parameters were calculated from plots of lnk or lnα versus 1/T. Δ(ΔH°) ranged from -2.3 to 2.2 kJ/mol, Δ(ΔS°) from -3.0 to 7.8 J mol(-1) K(-1) and -Δ(ΔG°) from 0.1 to 1.7 kJ/mol, and both enthalpy- and entropy-controlled enantioseparations were observed. The latter was advantageous with regard to the shorter retention and greater selectivity at high temperature. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes. The sequence of elution of the enantiomers was determined in all cases.

Synthesis of highly functionalized fluorinated cispentacin derivatives.

Fluorinated highly functionalized cispentacin derivatives were synthetised starting from an unsaturated bicyclic ß-lactam through C=C bond functionalization via the dipolar cycloaddition of a nitrile oxide, isoxazoline opening, and fluorination by OH/F exchange.

Quantal amplitude at the cone ribbon synapse can be adjusted by changes in cytosolic glutamate.

PURPOSE: Vision is encoded at photoreceptor synapses by the number of released vesicles and size of the post-synaptic response. We hypothesized that elevating cytosolic glutamate could enhance quantal size by increasing glutamate in vesicles. METHODS: We introduced glutamate (10-40 mM) into cone terminals through a patch pipette and recorded excitatory post-synaptic currents (EPSCs) from horizontal or OFF bipolar cells in the Ambystoma tigrinum retinal slice preparation. RESULTS: Elevating cytosolic glutamate in cone terminals enhanced EPSCs as well as quantal miniature EPSCs (mEPSCs). Enhancement was prevented by inhibiting vesicular glutamate transport with 1S,3R-1-aminocyclopentane-1,3-dicarboxylate in the patch pipette. A low affinity glutamate receptor antagonist, γD-glutamylglycine (1 mM), less effectively inhibited EPSCs evoked from cones loaded with glutamate than control cones indicating that release from cones with supplemental glutamate produced higher glutamate levels in the synaptic cleft. Raising presynaptic glutamate did not alter exocytotic capacitance responses and exocytosis was observed after inhibiting glutamate loading with the vesicular ATPase inhibitor, concanamycin A, suggesting that release capability is not restricted by low vesicular glutamate levels. Variance-mean analysis of currents evoked by flash photolysis of caged glutamate indicated that horizontal cell AMPA receptors have a single channel conductance of 10.1 pS suggesting that ~8.7 GluRs contribute to each mEPSC. CONCLUSIONS: Quantal amplitude at the cone ribbon synapse is capable of adjustment by changes in cytosolic glutamate levels. The small number of channels contributing to each mEPSC suggests that stochastic variability in channel opening could be an important source of quantal variability.

A peripheral neuroimmune link: glutamate agonists upregulate NMDA NR1 receptor mRNA and protein, vimentin, TNF-alpha, and RANTES in cultured human synoviocytes.

Human primary and clonal synovial cells were incubated with glutamate receptor agonists to assess their modulating influence on glutamate receptors N-methyl-d-aspartate (NMDA) NR1 and NR2 and inflammatory cytokines to determine potential for paracrine or autocrine (neurocrine) upregulation of glutamate receptors, as has been shown for bone and chondrocytes. Clonal SW982 synoviocytes constitutively express vimentin, smooth muscle actin (SMA), and NMDA NR1 and NR2. Coincubation (6 h) with glutamate agonists NMDA (5 microM), and the NMDA NR1 glycine site activator (+/-)1-aminocyclopentane-cis-1,3-dicarboxylic acid (5 muM), significantly increases cellular mRNA and protein levels of glutamate receptors, as well as increasing vimentin, SMA, tumor necrosis factor-alpha, and RANTES (regulated on activation, normal T-cell expressed and secreted), assessed qualitatively and quantitatively with nucleotide amplification, image analysis of immunocytochemical staining, fluorescein-activated cell sorting, Western blotting, and immunoassays. Human primary synovial cells harvested from patients with arthritic conditions also constitutively expressed NMDA NR1 with increases after agonist treatment. Glutamate receptor agonist-induced increases were blocked by the noncompetitive glutamate antagonist MK-801 (8 microg/ml) and NR1 blocking antibody. Coincubation with glutamate agonists and phorbol 12-myristate 13-acetate, a protein kinase C activator, significantly enhanced mean levels of TNF-alpha and RANTES in SW982 cell supernatants compared with incubation with either agent alone. Increases were diminished with protein kinase inhibitor and NR1 blocking antibody. The functional activation of glutamate receptors on human synoviocytes establishes a neurogenic cell signaling link between neurotransmitter glutamate released from nerve terminals and target cells in the joint capsule. The influence of glutamate on subsequent release of cellular proinflammatory mediators in non-neural tissue for activation of downstream immune events supports a peripheral neuroimmune link in arthritis.

VCD studies on cyclic peptides assembled from L-α-amino acids and a trans-2-aminocyclopentane- or trans-2-aminocyclohexane carboxylic acid.

The increasing interest in peptidomimetics of biological relevance prompted us to synthesize a series of cyclic peptides comprising trans-2-aminocyclohexane carboxylic acid (Achc) or trans-2-aminocyclopentane carboxylic acid (Acpc). NMR experiments in combination with MD calculations were performed to investigate the three-dimensional structure of the cyclic peptides. These data were compared to the conformational information obtained by electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy. Experimental VCD spectra were compared to theoretical VCD spectra computed quantum chemically at B3LYP/6-31G(d) density functional theory (DFT) level. The good agreement between the structural features derived from the VCD spectra and the NMR-based structures underlines the applicability of VCD in studying the conformation of small cyclic peptides.

Conformations of peptides containing a chiral cyclic α, α-disubstituted α-amino acid within the sequence of Aib residues.

A single chiral cyclic α,α-disubstituted amino acid, (3S,4S)-1-amino-(3,4-dimethoxy)cyclopentanecarboxylic acid [(S,S)-Ac(5)c(dOM)], was placed at the N-terminal or C-terminal positions of achiral α-aminoisobutyric acid (Aib) peptide segments. The IR and (1)H NMR spectra indicated that the dominant conformations of two peptides Cbz-[(S,S)-Ac(5)c(dOM)]-(Aib)(4)-OEt (1) and Cbz-(Aib)(4)-[(S,S)-Ac(5)c(dOM)]-OMe (2) in solution were helical structures. X-ray crystallographic analysis of 1 and 2 revealed that a left-handed (M) 3(10)-helical structure was present in 1 and that a right-handed (P) 3(10)-helical structure was present in 2 in their crystalline states.

Involvement of Group II mGluRs in mossy fiber LTD.

Mossy fiber long-term depression (LTD) has been shown to be triggered by either pharmacological or synaptic activation of Group II metabotropic glutamate receptors (mGluRs) whereas other studies indicate that synaptic activation of mGluRs is very limited. Therefore, we reexamined the role of Group II mGluRs for the induction of mossy fiber LTD. The complete depression of field potentials (fEPSPs) by 1 microM (2S,2'R,3'R)-2-(2',3'-Dicarboxycyclopropyl)glycine (DCG-IV) only partially reversed upon removal of the drug but fEPSPs were completely restored by the Group II antagonist 2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-yl)propanoic acid (LY341495) (3 microM). In contrast, fEPSPs returned back to baseline within 30 min after a brief application of 0.2 microM DCG-IV suggesting that the incomplete reversal of higher concentrations may be due to a residual receptor occupancy rather than to an induction of LTD. LY341495 itself did not increase fEPSPs and also blocked the inhibition of (2S,1'S,2'S)-2-(2-carboxycyclopropyl)glycine (L-CCG-I) (20 microM) and (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) (10 microM) and its effect was mimicked by CPPG (50 microM). Furthermore, stimulation at 1 Hz for 15 min induced an LTD of 81% +/- 3% and 80% +/- 4% in the absence and presence of LY341495, respectively (n = 7, 5). Finally, we found that synaptic activation of Group II mGluRs during 15 min of 1-Hz stimulation only produces an inhibition of release by 8% +/- 1% (30 degrees C, n = 3). Our data suggests that pharmacological activation of Group II mGluRs is fully reversible per se and does not produce a long lasting depression and that activation of Group II mGluRs is neither necessary nor sufficient for the induction of mossy fiber LTD.

Induction of an olfactory memory by the activation of a metabotropic glutamate receptor.

Female mice form an olfactory memory of male pheromones at mating; exposure to the pheromones of a strange male after that mating will block pregnancy. The formation of this memory is mediated by the accessory olfactory system, in which an increase in norepinephrine after mating reduces inhibitory transmission of gamma-aminobutyric acid from the granule cells to the mitral cells. This study shows that the activation of mGluR2, a metabotropic glutamate receptor that suppresses the gamma-aminobutyric acid inhibition of the mitral cells, permits the formation of a specific olfactory memory without the occurrence of mating by infusion of mGluR2 agonists into the female's accessory olfactory bulb. This memory faithfully reflects the memory formed at mating.

Target-specific expression of presynaptic mossy fiber plasticity.

Mossy fiber synaptic transmission at hippocampal CA3 pyramidal cells and interneurons was compared in rat brain slices to determine whether mossy terminals are functionally equivalent. Tetanic stimulation of mossy fibers induced long-term potentiation in pyramidal neurons but was either without effect or it induced depression at synapses onto interneurons. Unlike transmission onto pyramidal neurons, transmission onto interneurons was not potentiated after adenosine 3',5'-monophosphate (cAMP) activation. Furthermore, metabotropic glutamate receptor depression of transmission onto interneurons did not involve cAMP-dependent pathways. Thus, synaptic terminals arising from a common afferent pathway do not function as a single compartment but are specialized, depending on their postsynaptic target.

Gating of BDNF-induced synaptic potentiation by cAMP.

Neurotrophins have been implicated in activity-dependent synaptic plasticity, but the underlying intracellular mechanisms remain largely unknown. Synaptic potentiation induced by brain-derived neurotrophic factor (BDNF), but not neurotrophin 3, was prevented by blockers of adenosine 3',5'-monophosphate (cAMP) signaling. Activators of cAMP signaling alone were ineffective in modifying synaptic efficacy but greatly enhanced the potentiation effect of BDNF. Blocking cAMP signaling abolished the facilitation of BDNF-induced potentiation by presynaptic activity. Thus synaptic actions of BDNF are gated by cAMP. Activity and other coincident signals that modulate cAMP concentrations may specify the action of secreted neurotrophins on developing nerve terminals.

Autoradiographic imaging of phosphoinositide turnover in the brain.

With [3H]cytidine as a precursor, phosphoinositide turnover can be localized in brain slices by selective autoradiography of the product [3H]cytidine diphosphate diacylglycerol, which is membrane-bound. In the cerebellum, glutamatergic stimulation elicits an increase of phosphoinositide turnover only in Purkinje cells and the molecular layer. In the hippocampus, both glutamatergic and muscarinic cholinergic stimulation increase phosphoinositide turnover, but with distinct localizations. Cholinergic stimulation affects CA1, CA3, CA4, and subiculum, whereas glutamatergic effects are restricted to the subiculum and CA3. Imaging phosphoinositide turnover in brain slices, which are amenable to electrophysiologic studies, will permit a dynamic localized analysis of regulation of this second messenger in response to synaptic stimulation of specific neuronal pathways.

New gas chromatographic method for the enantioseparation of beta-amino acids by a rapid double derivatization technique.

A novel gas chromatographic method was developed for the enantioseparation of valuable acyclic and carbocyclic cis- and trans-beta-amino acids, including cispentacin and a number of its analogues and homologues. Excellent (in most cases baseline) separation was achieved for the racemates of these beta-amino acids on CP-Chirasil-Dex CB or CP-Chirasil L-Val columns after a simple and rapid double derivatization (esterification followed by N-acylation). The elution sequences were determined in all cases.