Interaction of chlorisondamine with the neuronal nicotinic acetylcholine receptor

Nicotine versus 6-hydroxy-l-nicotine against chlorisondamine induced memory impairment and oxidative stress in the rat hippocampus

6-Hydroxy-l-nicotine (6HLN), a nicotine derivative from nicotine degradation by Arthrobacter nicotinovorans pAO1 strain was found to improve behavioral deficits and to reverse oxidative stress in the rat hippocampus. Rats were given CHL (10mg/kg, i.p.) were used as an Alzheimer's disease-like model. The nicotine (0.3mg/kg) and 6HLN (0.3mg/kg) were administered alone or in combination in the CHL-treated rats. Memory-related behaviors were evaluated using Y-maze and radial arm-maze tests. The antioxidant enzymes activity and the levels of the biomarkers of oxidative stress were measured in the hippocampus. Statistical analyses were performed using two-way ANOVA and Tukey's post hoc test. F values for which p<0.05 were regarded as statistically significant. CHL-caused memory deficits and oxidative stress enhancing were observed. Both nicotine and 6HLN administration attenuated the cognitive deficits and recovered the antioxidant capacity in the rat hippocampus of the CHL rat model. Our results suggest that 6HLN versus nicotine confers anti-amnesic properties in the CHL-induced a rat model of memory impairment via reversing cholinergic function and decreasing brain oxidative stress, suggesting the use of this compound as an alternative agent in AD treatment.

Cellular membrane phospholipids act as a depository for quaternary amine containing drugs thus competing with the acetylcholine/nicotinic receptor

We previously demonstrated that ammonium- or guanidinium-phosphate interactions are key to forming noncovalent complexes (NCXs) through salt bridge formation with G-protein coupled receptors (GPCR), which are immersed in the cell membrane's lipids. The present work highlights MALDI ion mobility coupled to orthogonal time-of-flight mass spectrometry (MALDI IM oTOF MS) as a method to determine qualitative and relative quantitative affinity of drugs to form NCXs with targeted GPCRs' epitopes in a model system using, bis-quaternary amine based drugs, α- and β- subunit epitopes of the nicotinic acetylcholine receptor' (nAChR) and phospholipids. Bis-quaternary amines proved to have a strong affinity for all nAChR epitopes and negatively charged phospholipids, even in the presence of the physiological neurotransmitter acetylcholine. Ion mobility baseline separated isobaric phosphatidyl ethanolamine and a matrix cluster, providing an accurate estimate for phospholipid counts. Overall this technique is a powerful method for screening drugs' interactions with targeted lipids and protein respectively containing quaternary amines and guanidinium moieties.

Competition between covalent and noncovalent bond cleavages in dissociation of phosphopeptide-amine complexes

Interactions between quaternary amino or guanidino groups with anions are ubiquitous in nature and have been extensively studied phenomenologically. However, little is known about the binding energies in non-covalent complexes containing these functional groups. Here, we present a first study focused on quantifying such interactions using complexes of phosphorylated A(3)pXA(3)-NH(2) (X = S, T, Y) peptides with decamethonium (DCM) or diaguanidinodecane (DGD) ligands as model systems. Time- and collision energy-resolved surface-induced dissociation (SID) of the singly charged complexes was examined using a specially configured Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS). Dissociation thresholds and activation energies were obtained from RRKM modeling of the experimental data that has been described and carefully characterized in our previous studies. For systems examined in this study, covalent bond cleavages resulting in phosphate abstraction by the cationic ligand are characterized by low dissociation thresholds and relatively tight transition states. In contrast, high dissociation barriers and large positive activation entropies were obtained for cleavages of non-covalent bonds. Dissociation parameters obtained from the modeling of the experimental data are in excellent agreement with the results of density functional theory (DFT) calculations. Comparison between the experimental data and theoretical calculations indicate that phosphate abstraction by the ligand is rather localized and mainly affected by the identity of the phosphorylated side chain. The hydrogen bonding in the peptide and ligand properties play a minor role in determining the energetics and dynamics of the phosphate abstraction channel.

Hetero-dimerization of serotonin 5-HT(2A) and dopamine D(2) receptors

In the present study, detailed information is presented on the hetero-dimerization of the serotonin 5-HT(2A) receptor and the dopamine D(2) receptor. Biophysical approaches (fluorescence spectroscopy as well as fluorescence lifetime microscopy) were used to determine the degree of fluorescence resonance energy transfer (FRET) between cyan and yellow fluorescent protein labeled receptor variants co-expressed in human embryonic kidney 293 cells (HEK293). Recorded data demonstrate the existence of energy transfer between the wild-type forms of 5-HT(2A)R and D(2)R, pointing toward the formation of hetero-5-HT(2A)R/D(2)R dimers and homo-5-HT(2A)R/5-HT(2A)R dimers. Moreover, the present study investigates the role of specific motifs (one containing adjacent arginine residues (217RRRRKR222) in the third intracellular loop (ic3) of D(2)R, and the other consisting of acidic glutamate residues (454EE455) in the C-tail of (5-HT(2A)R) in the formation of noncovalent complexes between these receptors. Our results suggest that these regions of 5-HT(2A)R and D(2)R may be involved in the interaction between these two proteins. On the other hand, the above-mentioned motifs do not play an important role in the homo-dimerization of these receptors. Furthermore, we estimated the influence of specific receptor ligands on the dimerization processes. Agonists (DOI and quinpirole) and antagonists (ketanserin and butaclamol) cause different effects on FRET efficiency depending on whether homo- or hetero-complexes are present. These data may have therapeutic implications, since (using the immunofluorescence double labeling protocols) the co-localization of these two receptors was demonstrated in the medial prefrontal cortex and pars reticulate of the substantia nigra of the rat brain.

Investigation of double-stranded DNA/drug interaction by ESI/FT ICR: orientation of dissociations relates to stabilizing salt bridges

Noncovalent complexes of DNA and Hoechst 33258 were investigated by ESI-FT/ICR MS in various activation modes (collision-induced dissociation (CID), sustained off-resonance irradiation collision-induced dissociation (SORI-CID), infrared multiphoton dissociation (IRMPD) and electron detachment dissociation (EDD)). The binding selectivity of Hoechst 33258 was confirmed by the comparative study of its noncovalent association with different DNA sequences. The CID spectra of [ds + HO - 5H](5-) obtained with a linear hexapole ion trap resulted in unzipping of the strands. This outcome is a clue to the drug-binding mode, shading light on the localization of the binding sites of Hoechst 33258 to the DNA sequence. The IRMPD and SORI-CID experiments mainly gave DNA backbone cleavages and internal fragment ions. From this result, information on the localization of the binding sites of Hoechst 33258 in the DNA sequence was obtained. No sodium cationization was observed on the DNA sequence ions although they were present on fragmentation of the duplex, indicating that the backbone cleavages were generated from the single strand associated with the Hoechst 33258 where the number of alkali cation is restricted. Under electron detachment (ED) conditions, multiple EDs were achieved for the [ds + HO - 5H](5-) ion without any significant dissociation. The presence of drug appears to enhance the stability of the multiply charged system. It was proposed that the studied noncovalent complex involved the formation of zwitterions and consequently strong salt-bridge interactions between DNA and drug.

How calmodulin interacts with the adenosine A(2A) and the dopamine D(2) receptors

Receptor heteromerization is a mechanism used by G protein-coupled receptors to diversify their properties and function. We previously demonstrated that these interactions occur through salt bridge formation between epitopes of the involved receptors. Recent studies claim that calmodulin (CaM) binds to an Arg-rich epitope located in the amino-terminus of the dopamine D(2) receptor third intracellular loop. This is the same epitope involved in adenosine A(2A)-D(2) receptor heteromerization, through Coulombic interaction between the Arg residues and a phosphorylated serine (pS) located in the medial segment of the C-terminus of the A(2A) receptor. Mass spectrometric analysis indicates that an electrostatic interaction involving the D(2) receptor Arg-rich epitope and several CaM acidic epitopes are mainly responsible for the D(2) receptor-CaM binding. CaM could also form multiple noncovalent complexes by means of electrostatic interactions with an epitope localized in the proximal segment of the C-terminus of the A(2A) receptor. Ca(2+) disrupted the binding of CaM to the D(2) but not to the A(2A) receptor epitope, and CaM disrupted the electrostatic interactions between the D(2) receptor epitope and the more distal A(2A) receptor epitope. A model is introduced with the possible functional implications of A(2A)-D(2)-CaM interactions. These in vitro findings imply a possible regulatory role for CaM in receptor heteromers formation.

Amazing stability of phosphate-quaternary amine interactions

We have previously used MALDI mass spectrometry to highlight ammonium- or guanidinium-aromatic interactions via cation-pi bonding and ammonium- or guanidinium-phosphate interactions through salt bridge formation. In the present work, the gas-phase stability and dissociation pathways of the interaction between phosphorylated peptides and compounds containing quaternary amines are demonstrated using electrospray ionization mass spectrometry. The presence of one quaternary amine in a compound is enough to form a noncovalent complex with a phosphorylated residue. However, if two quaternary amines are present in one molecule, the electrostatic interactions of the quaternary amines with the phosphate results in a "covalent-like" stability, and these bonds can withstand fragmentation by collision-induced dissociation at energies similar to those that fragment covalent bonds. Such interactions are important in accounting for physiological, pathophysiological, and pharmacological effects of many therapeutic compounds and small molecules containing quaternary amines or phosphates.

Brain tissue lipidomics: direct probing using matrix-assisted laser desorption/ionization mass spectrometry

Lipidomics is the new frontier in biomolecular structural studies. Not only are lipids the main components in membranes that define the contours of the cell and its organelles, but they are also used for storage. Lipids form stable noncovalent complexes with proteins as well as with many drugs. Lipids are a storage depot for drugs and certain types of organic molecules. To study lipid composition and distribution, complex and time-consuming techniques are used. However, recent advances in mass spectrometry, mainly matrix-assisted laser desorption/ionization (MALDI) have made it possible to directly probe tissues to study structural components, as well as for the localization of drugs. Direct tissue imaging is a powerful tool as it gives a more complete and accurate structural picture and can trace and follow where drugs localize in tissue with minimal anatomical disruption and a minimum of manipulations. Hence, we believe that in addition to its accuracy and efficiency, this new approach will lead to a better understanding of physiological processes as well as the pathophysiology of disease.

Brain tissue lipidomics: direct probing using matrix-assisted laser desorption/ionization mass spectrometry

Lipidomics is the new frontier in biomolecular structural studies. Not only are lipids the main components in membranes that define the contours of the cell and its organelles, but they are also used for storage. Lipids form stable noncovalent complexes with proteins as well as with many drugs. Lipids are a storage depot for drugs and certain types of organic molecules. To study lipid composition and distribution, complex and time-consuming techniques are used. However, recent advances in mass spectrometry, mainly matrix-assisted laser desorption/ionization (MALDI) have made it possible to directly probe tissues to study structural components, as well as for the localization of drugs. Direct tissue imaging is a powerful tool as it gives a more complete and accurate structural picture and can trace and follow where drugs localize in tissue with minimal anatomical disruption and a minimum of manipulations. Hence, we believe that in addition to its accuracy and efficiency, this new approach will lead to a better understanding of physiological processes as well as the pathophysiology of disease.

Study of the Interaction of Chlorisondamine and Chlorisondamine Analogues with an Epitope of the α-2 Neuronal Acetylcholine Nicotinic Receptor Subunit

Chlorisondamine (CHL), a neuronal nicotinic ganglionic blocker, when injected in the cerebral ventricle of rats chronically blocks the increase in locomotion and rearing by subcutaneous nicotine injection. The blocking of the ion channel(s) prevents nicotine from exerting its rewarding effects on the CNS. When administered intraperitoneally, a dose 400-500 times the intracerebroventricular one is needed to cross the blood-brain barrier and to generate the same level of nicotine antagonism, resulting in severe side-effects, thus making it unlikely to be used as a therapeutical compound. Three CHL analogues, 2-(indolin-1-yl)-N,N,N-trimethylethanaminium iodide, 2-(1,3-dioxoisoindolin-2-yl)- N,N,N-trimethylethanaminium iodide, and 2-(1H-indole-3-carboxamido)- N,N,N-trimethylethanaminium iodide, were synthesized in the hope of circumventing the parent compound's shortcomings. They all share a modified indole ring, lack the four chlorines CHL carries, and have one tertiary amine and one quaternary amine. The CHL analogues form noncovalent complexes with an epitope of the alpha-2 nicotinic receptor subunit, GEREE(p)TEEEEEEEDEN, previously proposed as the possible site of CHL interaction. Complexes were analyzed using matrix-assisted laser desorption/ionization mass spectrometry for comparison with CHL. Overall, all three analogues showed better affinity than CHL for complex formation with both the nonphosphorylated and phosphorylated epitopes.

Lipid/peptide/nucleotide separation with MALDI-ion mobility-TOF MS

Matrix-assisted laser desorption/ionization when combined with ion mobility-orthogonal time-of-flight mass spectrometry is a viable technique for fast separation and analysis of biomolecules in complex mixtures. Isobaric lipid, peptide, and oligonucleotide ions are preseparated before mass analysis by differences of up to 30% in mobility drift time. Ions of similar chemical type fall along well-defined "trend lines" (with deviations of approximately 3%) when plotted in two-dimensional representations of ion mobility as a function of m/z. Discussion of fundamental and technical limitations of the technique point to its potential for being most useful when applied to systems such as bodily fluids and intact tissue, where an alternative chemical or chromatographic preseparation step prior to mass analysis is either impractical or undesirable.

Direct tissue analysis of phospholipids in rat brain using MALDI-TOFMS and MALDI-ion mobility-TOFMS

After water, lipids are the most common biomolecules found in the brain (12%). A brief perusal of the physiology, anatomy, and pathophysiology of the brain illustrates the importance of lipids. Recent advances in mass spectrometry have allowed the direct probing of tissues. However, most studies have focused on proteins. In the present work, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) and MALDI-ion mobility (IM)-TOFMS were employed for direct analysis of phospholipids in rat brain tissue. Molecular ions (MH+) corresponding to phosphatidylcholines, phosphatidylethanolamines, and sphingomyelin, were recorded. When studying pharmacology, we learn that many therapeutic compounds are stored in the body's adipose tissue. MALDI-TOFMS and MALDI- IM-TOFMS were thus used to analyze rat brain tissue with chlorisondamine added directly onto the tissue slice. With both techniques, noncovalent complexes between the tissue phospholipids and chlorisondamine were detected. In addition, MALDI-IM-TOFMS of noncovalent complexes between phospholipids and chlorisondamine displayed a mobility between that of an isobaric lipid and peptide.

Combining mass spectrometry and pull-down techniques for the study of receptor heteromerization. Direct epitope-epitope electrostatic interactions between adenosine A2A and dopamine D2 receptors

Previous results from FRET and BRET experiments and computational analysis (docking simulations) have suggested that a portion of the third intracellular loop (I3) of the human dopamine D2 receptor (D2R) and the C-tail from the human adenosine A2A receptor (A2AR) are involved in A2AR-D2R heteromerization. The results of the present studies, using pull-down and mass spectrometry experiments, suggest that A2AR-D2R heteromerization depends on an electrostatic interaction between an Arg-rich epitope from the I3 of the D2R (217RRRRKR222) and two adjacent Asp residues (DD401-402) or a phosphorylated Ser (S374) residue in the C-tail of the A2AR. A GST-fusion protein containing the C-terminal domain of the A2AR (GST-A2ACT) was able to pull down the whole D2R solubilized from D2R-tranfected HEK-293 cells. Second, a peptide corresponding to the Arg-rich I3 region of the D2R (215VLRRRRKRVN224) and bound to Sepharose was able to pull down both GST-A2ACT and the whole A2AR solubilized from A2AR-tranfected HEK-293 cells. Finally, mass spectometry and pull-down data showed that the Arg-rich D2R epitope binds to two different epitopes from the C-terminal part of the A2AR, containing the two adjacent Asp residues or the phosphorylated Ser residue (388HELKGVCPEPPGLDDPLAQDGAVGS412 and 370SAQEpSQGNT378). The present results are the first example of epitope-epitope electrostatic interaction underlying receptor heteromerization, a new, expanding area of protein-protein interactions.

Adenosine A2A-dopamine D2 receptor–receptor heteromers. Targets for neuro-psychiatric disorders

Emerging evidence shows that G protein-coupled receptors can form homo- and heteromers. These include adenosine A(2A) receptor-dopamine D(2) receptor heteromers, which are most probably localized in the dendritic spines of the striatopallidal GABAergic neurons, where they are in a position to modulate glutamatergic neurotransmission. The discovery of A(2A) receptor-dopamine D(2) receptor heteromers gives a frame for the well-known antagonistic interaction between both receptors, which is the bases for a new therapeutic approach for neuro-psychiatric disorders, such as Parkinson's disease and schizoprenia. The present review deals mainly with the biochemical and molecular aspects of A(2A) receptor-dopamine D(2) receptor interactions. Recent results at the molecular level show that A(2A) receptor-dopamine D(2) receptor heteromers represent the first example of epitope-epitope electrostatic interaction underlying receptor heteromerization. Most probably A(2A) receptor-D(2) receptor heteromerization is not static, but subject to a dynamic regulation, related to the phosphorylation dependence of the A(2A) receptor epitope and to the ability of the D(2) receptor epitope to bind different partners. Finding out the mechanisms involved in this dynamic regulation can have important implications for the treatment of basal ganglia disorders, schizophrenia and drug addiction.

The Mighty Arginine, the Stable Quaternary Amines, the Powerful Aromatics, and the Aggressive Phosphate: Their Role in the Noncovalent Minuet

In the age of proteomics, the role of certain amino acid residues and some post-translational modifications in noncovalent complex formation are gaining in importance, as the understanding of interactions between biological molecules, is at the heart of the structure function relationship puzzle. In this work, mass spectrometry is used to highlight ammonium- or guanidinium-aromatic interactions through Cation-pi bonds and ammonium- or guanidinium-phosphate interactions through salt bridge formation. Such interactions are crucial factors in certain ligand-receptor interactions and receptor-receptor interactions. In addition, the ability of phosphorylated residues and phosphorylated lipids to form noncovalent complexes with guanidinium and quaternary ammonium (mostly through Coulombic interactions) is demonstrated, and could explain the stability of certain membrane embedded protein, or a possible role for phosphorylation in protein-protein interactions. Dougherty's work demonstrates cation-pi interactions in intra-protein interactions and folding, the present work explores inter-peptide interactions, i.e., the formation of noncovalent complexes between peptides' epitopes containing adjacent aromatic residues and ones containing adjacent Arg as a model to better understand the role of cation-pi complexes in protein-protein interaction. Complexes of peptides containing aromatic residues with quaternary amines as well as the interaction of aromatic compounds, with the guanidinium group of Arg are also investigated. Considering that an inordinate number of therapeutic compounds contain aromatic rings and quaternary amines, the above-described interactions could possibly be of great importance in better understanding their mechanism of action.

Investigation of sample preparation and instrumental parameters in the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of noncovalent peptide/peptide complexes

The application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) to the direct detection and investigation of noncovalent solution-phase complexes is far from being routine and some principal problems and questions still exist. Therefore, this study systematically investigates several main problems, namely, the effect of sample preparation and some instrument-related parameters on the stability of the noncovalent complexes as well as the formation of nonspecific cluster ions in the case of the MALDI-MS analysis of specific peptide/peptide complexes. The complexes formed between biologically active fragments of human gastrin I, which contain the sequence motif EEEEE, and different peptides, which contain the interacting sequence motifs RR and RKR, were chosen as examples. A broad variety of MALDI matrices and sample preparation protocols were screened systematically and evaluated. The two 'less acidic' matrices 2,4,6-trihydroxyacetophenone and 6-aza-2-thiothymine, in combination with carefully selected solvents and additives, turned out to allow the reproducible detection of the solution-phase peptide/peptide complexes with good intensity, whereas the classical MALDI matrices could not be applied with the same success. Because both matrices also tend to induce the formation of nonspecific cluster ions, control experiments using nonbinding peptides were performed to definitely prove the specificity of the detected complexes. In contrast to the sensitivity of the peptide/peptide complexes to solution-phase conditions, the gas-phase stability during desorption/ionization was found to be extraordinary high. Neither the application of high laser fluence nor switching from continuous to delayed extraction mode as well as variation of the delay time up to 520 ns had considerable effect on the relative intensities of the specific peptide/peptide complexes.