Sara Di Marino

Omega-3 fatty acids regulate the interaction of the Alzheimer's aβ(25-35) peptide with lipid membranes.

Polyunsaturated omega-3 fatty acids are increasingly proposed as dietary supplements able to reduce the risk of development or progression of the Alzheimers disease (AD). To date, the molecular mechanism through which these lipids act has not been yet univocally identified. In this work, we investigate whether omega-3 fatty acids could interfere with the fate of the Alzheimer-related amyloid peptide by tuning the microstructural and dynamical properties of the neuronal membrane. To this aim, the influence of the omega-3 lipid, 1,2-didocosahexaenoyl-sn-glycero-3-phosphocholine [22:6(cis)PC] on the biophysical properties of lipid bilayers, and on their interaction with the amyloid peptide fragment Aβ(25-35) has been investigated by Electron Spin Resonance (ESR), using spin-labeled phospholipids. The results show that the peptide selectively interacts with bilayers enriched in cholesterol (Chol) and sphingomyelin (SM). [22:6(cis)PC] enhances the Aβ(25-35)/membrane interaction, favoring a deeper internalization of the peptide among the lipid acyl chains and, consequently, hindering its pathogenic self-aggregation.

Effect of flavonoids on the Aβ(25-35)-phospholipid bilayers interaction.

Amyloid-beta peptide (Abeta) is the major component of amyloid deposits found in the brain tissue of Alzheimer patients. The tendency of amyloid peptide to form amyloid plaques is known to be related to the features of the plasma membrane. Flavonoids, a group of naturally occurring molecules, exert beneficial properties to human health thanks to their antioxidant property; this property depends on their capacity to interact and permeate the cell membrane lipid bilayer. In the present research we report an Electron Paramagnetic Resonance (EPR) investigation of 2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membranes interacting with the beta-amyloid fragment Abeta(25-35), in the presence of flavonoids rutin, quercetin, naringin and naringenin. Our results, evidencing a flavonoid-dependent rigidifying effect of the bilayer, may provide the molecular basis to explain the known neuroprotective effect of flavonoid compounds.

Synthesis of new antifungal peptides selective against Cryptococcus neoformans

Many drugs are available for the treatment of systemic or superficial mycoses, but only a limited number of them are effective antifungal drugs, devoid of toxic and undesirable side effects. Furthermore, resistance development and fungistatic rather than fungicidal activities represent limitations of current antifungal therapy. Therefore there remains an urgent need for a new generation of antifungal agents. According to a polypharmacological approach, the present work concerns the synthesis and antifungal activity of a set of peptides designed to simultaneously target the fungal cell surface and lanosterol demethylase, a key enzyme involved in ergosterol synthesis. Our peptides include amino acid sequences characteristic of membrane-active antimicrobial peptides (AMP), and due to the presence of His residues, they carry the imidazole ring characteristic of azole compounds. The peptides synthesized by us, were tested against different yeast species, and displayed general antifungal activity, with a therapeutically promising antifungal specificity against Cryptococcus neoformans.

Binding of the hemopressin peptide to the cannabinoid CB1 receptor: structural insights.

Hemopressin, a bioactive nonapeptide derived from the α1 chain of hemoglobin, was recently shown to possess selective antagonist activity at the cannabinoid CB(1) receptor [Heimann, A. S., et al. (2007) Proc. Natl. Acad. Sci. U.S.A. 104, 20588-20593]. CB(1) receptor antagonists have been extensively studied for their possible therapeutic use in the treatment of obesity, drug abuse, and heroin addiction. In particular, many compounds acting as CB(1) receptor antagonists have been synthesized and subjected to experiments as possible anti-obesity drugs, but their therapeutic application is still complicated by important side effects. Using circular dichroism and nuclear magnetic resonance spectroscopy, this work reports the conformational analysis of hemopressin and its truncated, biologically active fragment hemopressin(1-6). The binding modes of both hemopressin and hemopressin(1-6) are investigated by molecular docking calculations. Our conformational data indicate that regular turn structures in the central portion of hemopressin and hemopressin(1-6) are critical for an effective interaction with the receptor. The results of molecular docking calculations, indicating similarities and differences in comparison to the most accepted CB(1) pharmacophore model, suggest the possibility of new chemical scaffolds for the design of new CB(1) antagonist lead compounds.

β-Amyloid-acetylcholine molecular interaction: new role of cholinergic mediators in anti-Alzheimer therapy?

BACKGROUND For long time Alzheimers disease has been attributed to a cholinergic deficit. More recently, it has been considered dependent on the accumulation of the amyloid beta peptide (Aβ), which promotes neuronal loss and impairs neuronal function. Results/methodology: In the present study, using biophysical and biochemical experiments we tested the hypothesis that in addition to its role as a neurotransmitter, acetylcholine may exert its action as an anti-Alzheimer agent through a direct interaction with Aβ. CONCLUSION Our data provide evidence that acetylcholine favors the soluble peptide conformation and exerts a neuroprotective effect against the neuroinflammatory and toxic effects of Aβ. The present paper paves the way toward the development of new polyfunctional anti-Alzheimer therapeutics capable of intervening on both the cholinergic transmission and the Aβ aggregation.

Structural Evidence of N6-Isopentenyladenosine As a New Ligand of Farnesyl Pyrophosphate Synthase

N6-isopentenyladenosine (i6A), a modified nucleoside belonging to the cytokinin family, has shown in humans many biological actions, including antitumoral effects through the modulation of the farnesyl pyrophosphate synthase (FPPS) activity. To investigate the relationship between i6A and FPPS, we undertook an inverse virtual screening computational target searching, testing i6A on a large panel of 3D protein structures involved in cancer processes. Experimentally, we performed an NMR investigation of i6A in the presence of FPPS protein. Both inverse virtual screening and saturation transfer difference (STD) NMR outcomes provided evidence of the structural interaction between i6A and FPPS, pointing to i6A as a valuable lead compound in the search of new ligands endowed with antitumoral potential and targeting FPPS protein.

Antifungal peptides at membrane interaction.

Many drugs are available for the treatment of systemic or superficial mycoses, but only a limited number of them are effective antifungal drugs, devoid of toxic and undesirable side effects. Furthermore, resistance development and fungistatic rather than fungicidal activities represent limitations of current antifungal therapy. Therefore an urgent need for a new generation of antifungal agents remains. We recently synthesised a set of linear and cyclic peptides characterized by sequences typical of membrane-active antimicrobial peptides (AMP). AMT2, cyclo-AMT2, AMT3 and cyclo-AMT3 (Scheme 1) were tested against different yeast species and exhibited general antifungal activity, with a specificity against Cryptococcus neoformans. To evaluate the role of the membrane cell in the mechanism of antifungal activity, we investigated the conformational behaviour of AMT2, cyclo-AMT2, AMT3 and cyclo-AMT3 in different bio-membrane mimicking systems using a combined approach based on spectroscopy and microscopy techniques. Our data highlight the behaviour of the peptides to interact with the bilayer surface, excluding their ability to destabilize or permeabilize the fungal cell wall. Microbial membrane, indeed, may be an important platform for specific interactions of peptides with specific targets involved in the cell wall synthesis.

Solvent independent conformational propensities of [1,2,3]triazolyl‐bridged parathyroid hormone‐related peptide‐derived cyclo‐nonapeptide analogues

The recently introduced Cu(I)‐catalyzed azide–alkyne 1,3‐dipolar Huisgen cycloaddition as a prototypic “click chemistry reaction” presented an opportunity for introducing the 1,4‐disubstituted‐[1,2,3]triazolyl moiety as a new isostere for peptide bonds in the backbone. Previous study in our lab focused on the synthesis of a model i‐to‐i+4 side chain‐to‐side chain 1,4‐ and 4,1‐disubstituted‐[1,2,3]triazolyl‐bridged cyclo‐nonapeptide I (Scheme 1 ) as analogues of its structurally related helical i‐to‐i+4 lactam‐bridged cyclo‐nonapeptide [Lys13(& 1),Asp17(& 2)]parathyroid hormone related peptide (PTHrP)(11–19)NH21 a truncated version of the α‐helical and potent parathyroid hormone receptor 1 agonist [Lys13(& 1),Asp17(& 2)]PTHrP(1‐34)NH2,2,3 Nα‐Ac‐Lys‐Gly‐Lys(& 1)‐Ser‐Ile‐Gln‐Asp(& 2)‐Leu‐Arg‐NH2]. Systematic [1,2,3]triazolyl‐containing bridge structure–conformation relationship studies in hexafluoroacetone/water mixture included incorporation of bridges varied in size and position and orientation of the triazolyl ring within the bridge. These studies revealed that the size of methylene bridge flanking triazolyl moiety is critical to reproduce in the heterodetic cyclo‐nonapeptides. The conformational features of the analogues cyclo‐nonapeptide in which Lys13 and Asp17 are bridged by the isosteric lactam. Here, we extend our conformational analysis to dimethyl sulfoxide/water mixture in an effort to characterize inherent conformational properties of the heterodetic cyclopeptides that are solvent independent. Our present study shows that the physicochemical properties of the structure‐supporting solvent cannot override the effect of the size of methylene bridge to form helical mimetic structures. Moreover, we prove that [1,2,3]triazolyl ring is not a simple bioisostere of lactam bond, but it affects the secondary structure of the peptide, in relation to its positioning orientation.

Beta-amyloid-acetylcholine structural interaction: evidence for neuroprotective effects of acetylcholine in neural cells

Alzheimer’s disease (AD) is regarded as a multifactorial disease characterized by a complex pathogenesis including a cholinergic deficit - due to degeneration of cholinergic projections from the basal forebrain - and the extracellular accumulation of amyloid beta (Aβ) peptide. Aβ containing 39 to 42 amino acids is the predominant component of the senile plaques that, together with neurofibrillary tangles, are regarded as the neuropathological hallmarks of AD (Sorrentino et al. 2014). Aβ may assume different conformations changing from random coil or α-helical monomers to β-sheet structures forming toxic oligomers and/or β-sheet mature fibrils. In this framework, we studied the effect of acetylcholine (ACh) on the conformation of Aβ by circular dichroism analysis. Moreover we investigated the ability of ACh to protect neuronal cells from the toxic action of amyloid peptide and to modulate the neuroinflammatory response occurring via the phospholipase A2 (PLA2). Results show that the amount of Aβ(25-35) β-strand raised linearly in absence of ACh, whereas it remained almost constant in presence of ACh. In addition, in a micelle solution mimicking the membrane environment ACh was found effective in increasing and stabilizing the soluble and not toxic helical content of Aβ(25-35) suggesting that ACh is capable to preserve the soluble form of Aβ(25-35), reducing the incipit of Aβ aggregation. In order to assess the neuro-protective ability of ACh against toxic Aβ(25-35) accumulation, we used neural cell (NCC) cultures containing both astrocytes and glial cells prepared from brains embryos from timed pregnant Wistar rats and infused ACh for 48h. By immunostaining, we observed that ACh reduced Aβ(25-35)-induced cell death. Then, we tested the protective effect of ACh on inflammation induced by Aβ administration. NCC were challenged with Aβ(25-35) in the presence and absence of ACh and immunostained for astroglial and neuronal markers: results showed a reduction of the morphological features of astrogliosys in ACh treated cells. PLA2 expression analysis corroborated these data also underlying that ACh can negatively regulate inflammation pathways in glial cells.