Molecular-level characterization of the interaction between monolayer-protected Au nanoparticles and model lipid membranes and proteins

In this thesis we study the interactions of monolayer-protected gold nanoparticles with proteins and model lipid membranes. Gold nanoparticles are a paradigm in biological applications of nanomaterials, thanks to their peculiar physico-chemical properties; among these, the possibility to bind different kinds of molecules (ligands) to gold atoms in clusters via thiol bonds is particularly important for biomedical use of nanoparticles. In fact, the ligand shell is what nanoparticles expose to the biological environment in which they are used. In in vivo applications, nanoparticles come in contact with many biological molecules before being delivered to cells, which are the target of most of biological applications of nanoparticles. Among them, proteins are particularly relevant since they can irreversibly bind to nanoparticles, thus changing the surface they expose to the biological environment. In this thesis we use molecular dynamics simulations to study how different ligands can influence the interaction of nanoparticles with the most abundant protein in blood, human serum albumin. We test two zwitterionic ligands with different hydrophobic content and we find that ligand conformation, which is affected by hydrophobicity, promotes different adhesion strengths between nanoparticles and albumin. We then study the interaction of nanoparticles with a model cell membrane, the first barrier they encounter in cell-targeted applications. We use molecular dynamics simulations to study the mechanism of interaction between a negatively charged nanoparticle and a neutral lipid membrane. We find that the process develops in three stages which involves the adsorption on the membrane surface and the progressive penetration in the membrane core of the nanoparticle. Finally, we study the influence of the sign of the charge on nanoparticles on their interaction with a model membrane. We use experiments of fluorescent dye-leakage from neutral liposomes to probe the effect of positively and negatively charged nanoparticles on the model membrane of the lipid vesicles. In particular, we find that both anionic and cationic nanoparticles behave similarly in the interaction with a zwitterionic lipid membrane. We use molecular dynamics simulations to support the experimental findings and observe that anionic and cationic nanoparticles share similar interaction processes and energetics

Local Enhancement of Lipid Membrane Permeability Induced by Irradiated Gold Nanoparticles

Photothermal therapies are based on the optical excitation of plasmonic nanoparticles in the biological environment. The effects of the irradiation on the biological medium depend critically on the heat transfer process at the nanoparticle interface, on the temperature reached by the tissues, as well as on the spatial extent of temperature gradients. Unfortunately, both the temperature and its biological effects are difficult to be probed experimentally at the molecular scale. Here, we approach this problem using nonequilibrium molecular dynamics simulations. We focus on photoporation, a photothermal application based on the irradiation of gold nanoparticles by single, short-duration laser pulses. The nanoparticles, stably bound to cell membranes, convert the radiation into heat, inducing transient changes of membrane permeability. We make a quantitative prediction of the temperature gradient around the nanoparticle upon irradiation by typical experimental laser fluences. Water permeability is locally enhanced around the nanoparticle, in an annular region that extends only a few nanometers from the nanoparticle interface. We correlate the local enhancement of permeability at the nanoparticle-lipid interface to the temperature inhomogeneities of the membrane and to the consequent availability of free volume pockets within the membrane core

Medication overuse headache, addiction and personality pathology: a controlled study by SWAP-200

Background: Medication Overuse Headache (MOH) is a type of chronic headache, whose mechanisms are still unknown. Some empirical investigations examining the addiction-like behaviors and processes, as well as personality characteristics underlying MOH development, reached contrasting findings. This study aimed at detecting personality and its disorders (PDs) in MOH patients, with a specific attention to the features of addiction. Methods: Eighty-eight MOH patients have been compared with two clinical populations including 99 patients with Substance Use Disorder (SUD) and 91 with PDs using the Shedler-Westen Assessment Procedure-200 (SWAP-200). MANCOVAs were performed to evaluate personality differences among MOH, SUD and PD groups, controlling for age and gender. Results: MOH patients showed lower traits of the SWAP-200’s clusters A and B disorders than SUD and PD patients, whom presented more severe levels of personality impairment. No differences in the SWAP-200’s cluster C have been found, indicating common personality features in these populations. At levels of specific PDs, MOH patients presented higher obsessive and dysphoric traits, as well as better overall psychological functioning than SUD and PD patients. Conclusions: The study supported the presence of a specific pattern of personality in MOH patients including obsessive (perfectionist) and dysphoric characteristics, as well as good enough psychological resources. No similarities with drug addicted and personality-disordered patients were found. Practitioners’ careful understanding of the personality of MOH patients may be useful to provide more effective treatment strategies and patient-tailored intervention programs

Au Nanoparticles in Lipid Bilayers: a Comparison between Atomistic and Coarse Grained Models

The computational study of the interaction between charged, ligand-protected metal nanoparticles and model lipid membranes has been recently addressed both at atomistic and coarse grained level. Here we compare the performance of three versions of the coarse grained Martini force field at describing the nanoparticle-membrane interaction. The three coarse-grained models differ in terms of treatment of long-range electrostatic interactions and water polarizability. The NP-membrane interaction consists in the transition from a metastable NP- membrane complex, in which the NP is only partially embedded in the membrane, to a configuration in which the NP is anchored to both membrane leaflets. All the three coarse grained models provide a description of the metastable NP-membrane complex that is consistent with that obtained using an atomistic force field. As for the anchoring transition, the polarizable- water Martini correctly describes the molecular mechanisms and the energetics of the transition. The standard version of the Martini model, instead, underestimates the free energy barriers for anchoring and does not completely capture the membrane deformations involved in the transition process

Drug addicted mothers and their empathic reactivity to painful cues.

Introduction: Mother-infant relationship is crucial for offspring\u2019s development. Substance-abuse has been shown to affect adults\u2019 ability to care for their children, in particular in the affective- relational aspects of parenting, such as the attachment bond and the ability to provide protection. Surprisingly, no previous study has explored neural responses associated with empathy towards children\u2019s pain in mothers with such history. Empathy is a more general construct than parenting and deficits in neural empathic responses may better explain failures in caring of addicted mothers. Aims of the study: This study was aimed at investigating the empathic response to pain inflicted by a dangerous tool to hands of kids when compared to neutral situations in a sample of mothers with history of drug-abuse. We used Event-Related Potentials (ERPs) technique to explore the time-course of neural empathic responses to pain by virtue of its excellent time resolution. In particular, we asked whether empathic responses to pain of children would differ in drug-addicted mothers compared to control group, during a relatively automatic early stage of processing or during a more controlled delayed one involving mentalizing. Material and methods: Event-related potentials (ERPs) have been recorded from drug-addicted mothers (i.e., clinical) and control groups to track neural activity in a pain decision task. Stimuli were pictures showing one infant hand in painful (harmful object applied to the hand) and neutral situations (harmful object located close to the hand). Results: Neural empathic responses towards children in pain differed between the two groups such that ERPs diverged between the painful and neutral stimulation at delayed stages of processing only for the clinical group. Conclusions: We interpreted these results as indicating that the control group implicitly judged also the neutral situations involving children as potentially painful supporting a lack of mentalizing abilities in the clinical group when compared with controls

An overview of molecular mechanisms in fabry disease

Fabry disease (FD) (OMIM #301500) is a rare genetic lysosomal storage disorder (LSD). LSDs are characterized by inappropriate lipid accumulation in lysosomes due to specific enzyme deficiencies. In FD, the defective enzyme is alpha-galactosidase A (alpha-Gal A), which is due to a mutation in the GLA gene on the X chromosome. The enzyme deficiency leads to a continuous deposition of neutral glycosphingolipids (globotriaosylceramide) in the lysosomes of numerous tissues and organs, including endothelial cells, smooth muscle cells, corneal epithelial cells, renal glomeruli and tubules, cardiac muscle and ganglion cells of the nervous system. This condition leads to progressive organ failure and premature death. The increasing understanding of FD, and LSD in general, has led in recent years to the introduction of enzyme replacement therapy (ERT), which aims to slow, if not halt, the progression of the metabolic disorder. In this review, we provide an overview of the main features of FD, focusing on its molecular mechanism and the role of biomarkers

Cyclotron production of 43Sc for PET imaging

Recently, significant interest in 44Sc as a tracer for positron emission tomography (PET) imaging has been observed. Unfortunately, the co-emission by 44Sc of high-energy γ rays (Eγ = 1157, 1499 keV) causes a dangerous increase of the radiation dose to the patients and clinical staff. However, it is possible to produce another radionuclide of scandium—43Sc—having properties similar to 44Sc but is characterized by much lower energy of the concurrent gamma emissions. This work presents the production route of 43Sc by α irradiation of natural calcium, its separation and purification processes, and the labeling of [DOTA,Tyr3] octreotate (DOTATATE) bioconjugate. Methods: Natural CaCO3 and enriched [40Ca]CaCO3 were irradiated with alpha particles for 1 h in an energy range of 14.8–30 MeV at a beam current of 0.5 or 0.25 μA. In order to find the optimum method for the separation of 43Sc from irradiated calcium targets, three processes previously developed for 44Sc were tested. Radiolabeling experiments were performed with DOTATATE radiobioconjugate, and the stability of the obtained 43Sc-DOTATATE was tested in human serum. Results: Studies of natCaCO3 target irradiation by alpha particles show that the optimum alpha particle energies are in the range of 24–27 MeV, giving 102 MBq/μA/h of 43Sc radioactivity which creates the opportunity to produce several GBq of 43Sc. The separation experiments performed indicate that, as with 44Sc, due to the simplicity of the operations and because of the chemical purity of the 43Sc obtained, the best separation process is when UTEVA resin is used. The DOTATATE conjugate was labeled by the obtained 43Sc with a yield >98 % at elevated temperature. Conclusions: Tens of GBq activities of 43Sc of high radionuclidic purity can be obtainable for clinical applications by irradiation of natural calcium with an alpha beam

Rational engineering of a human anti-dengue antibody through experimentally validated computational docking

Antibodies play an increasing pivotal role in both basic research and the biopharmaceutical sector, therefore technology for characterizing and improving their properties through rational engineering is desirable. This is a difficult task thought to require high-resolution x-ray structures, which are not always available. We, instead, use a combination of solution NMR epitope mapping and computational docking to investigate the structure of a human antibody in complex with the four Dengue virus serotypes. Analysis of the resulting models allows us to design several antibody mutants altering its properties in a predictable manner, changing its binding selectivity and ultimately improving its ability to neutralize the virus by up to 40 fold. The successful rational design of antibody mutants is a testament to the accuracy achievable by combining experimental NMR epitope mapping with computational docking and to the possibility of applying it to study antibody/pathogen interactions

Preventive exercise and physical rehabilitation promote long-term potentiation-like plasticity expression in patients with multiple sclerosis

Background and purpose: Loss of long-term potentiation (LTP) expression has been associated with a worse disease course in relapsing-remitting multiple sclerosis (RR-MS) and represents a pathophysiological hallmark of progressive multiple sclerosis (PMS). Exercise and physical rehabilitation are the most prominent therapeutic approaches to promote synaptic plasticity. We aimed to explore whether physical exercise is able to improve the expression of LTP-like plasticity in patients with multiple sclerosis (MS). Methods: In 46 newly diagnosed RR-MS patients, we explored the impact of preventive exercise on LTP-like plasticity as assessed by intermittent theta-burst stimulation. Patients were divided into sedentary or active, based on physical activity performed during the 6 months prior to diagnosis. Furthermore, in 18 patients with PMS, we evaluated the impact of an 8-week inpatient neurorehabilitation program on clinical scores and LTP-like plasticity explored using paired associative stimulation (PAS). Synaptic plasticity expression was compared in patients and healthy subjects. Results: Reduced LTP expression was found in RR-MS patients compared with controls. Exercising RR-MS patients showed a greater amount of LTP expression compared with sedentary patients. In PMS patients, LTP expression was reduced compared with controls and increased after 8 weeks of rehabilitation. In this group of patients, LTP magnitude at baseline predicted the improvement in hand dexterity. Conclusions: Both preventive exercise and physical rehabilitation may enhance the expression of LTP-like synaptic plasticity in MS, with potential beneficial effects on disability accumulation

Itinerant electrons, local moments, and magnetic correlations in the pnictide superconductors CeFeAsO 1 − x F x and Sr(Fe 1 − x Co x ) 2 As 2

A direct and element-specific measurement of the local Fe spin moment has been provided by analyzing the Fe 3$s$ core level photoemission spectra in the parent and optimally doped CeFeAsO{}_{1\ensuremath{-}x}F${}_{x}$ ($x$ $=$ 0, 0.11) and Sr(Fe{}_{1\ensuremath{-}x}Co${}_{x}$)${}_{2}$As${}_{2}$ ($x$ $=$ 0, 0.10) pnictides. The rapid time scales of the photoemission process allowed the detection of large local spin moments fluctuating on a 10{}^{\ensuremath{-}15} s time scale in the paramagnetic, antiferromagnetic, and superconducting phases, indicative of the occurrence of ubiquitous strong Hund's magnetic correlations. The magnitude of the spin moment is found to vary significantly among different families, 1.3{\ensuremath{\mu}}_{B} in CeFeAsO and 2.1{\ensuremath{\mu}}_{B} in SrFe${}_{2}$As${}_{2}$. Surprisingly, the spin moment is found to decrease considerably in the optimally doped samples, 0.9{\ensuremath{\mu}}_{B} in CeFeAsO${}_{0.89}$F${}_{0.11}$ and 1.3{\ensuremath{\mu}}_{B} in Sr(Fe${}_{0.9}$Co${}_{0.1}$)${}_{2}$As${}_{2}$. The strong variation of the spin moment against doping and material type indicates that the spin moments and the motion of itinerant electrons are influenced reciprocally in a self-consistent fashion, reflecting the strong competition between the antiferromagnetic superexchange interaction among the spin moments and the kinetic energy gain of the itinerant electrons in the presence of a strong Hund's coupling. By describing the evolution of the magnetic correlations concomitant with the appearance of superconductivity, these results constitute a fundamental step toward attaining a correct description of the microscopic mechanisms shaping the electronic properties in the pnictides, including magnetism and high-temperature superconductivity