Fluorescent Lipid Nanoparticles as Biomembrane Models for Exploring Emerging Contaminant Bioavailability Supported by Density Functional Theory Calculations

Multiplicity of solvent environments in lipid bilayer revealed by DAS deconvolution of twin probes: Comparative method of Laurdan and Prodan

Laurdan and Prodan were designed for the evaluation of the surrounding hydration state. When inserted into lipid bilayer systems, both probes are located at different positions and their fluorescence properties are drastically varied, depending on their surrounding environment. In this study, a novel method using the above fluorescence probes was proposed on the basis of fluorescence lifetime (τ) and emission peak (λ), called as τ vs. λ plot, determined by global analysis of their multiple fluorescence decays and deconvolution of these decay-associated spectra. According to the evaluation of τ vs. λ plot, the existence of multiple fluorescence components in the membrane was revealed. In addition, their fluorescence distribution properties, described on τ vs. λ plot, of each probe tended to correspond to the phase state and vertical direction of the lipid membrane. To assess the contribution of environmental effect to each distribution, we defined the region in the τ vs. λ plot, which was modeled from a series of solvent mixtures (hexane, acetone, ethanol and water) to emulate the complex environment in the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer system. The distributions of fluorescence components of Laurdan and Prodan in lipid membranes were classified into each solvent species, and Prodan partition into bulk water was distinguished. The sensitivity of Prodan to the phase pretransition of the 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer system was also observed in increasing the temperature. Noticeably, most of the fluorescence components was assigned to the solvent model, except for a single component that has longer lifetime and shorter emission wavelength. This component was dominant in solid-ordered phase; hence, it is assumed to be a specific component in lipid membranes that cannot be represented by solvents. Although these are still qualitative analytical methods, the unique approach proposed in this study provides novel insights into the multi-focal property of the membrane.

Analytical probing of membranotropic effects of antimicrobial copper nanoparticles on lipid vesicles as membrane models

Copper nanoparticles (CuNPs) are antimicrobial agents that are increasingly being used in several real-life goods. However, concerns are arising about their potential toxicity and thus, appropriate legislation is being issued in various countries. In vitro exploration of the permeability and the distribution of nanoparticles in cell membranes should be explored as the first step towards the investigation of the toxicity mechanisms of metal nanoantimicrobials. In this work, phosphatidylcholine-based large unilamellar vesicles have been explored as mimics of cellular membranes to investigate the effect of ultra-small CuNPs on the physicochemical features of phospholipid membranes. 4 nm-sized CuNPs were synthesized by a wet-chemical route that involves glutathione as a stabilizer, with further characterization by UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. Two fluorescent membrane probes bearing naphthalene moieties (laurdan and prodan) were used to monitor the bilayer structure and dynamics, as well as to demonstrate the strong membranotropic effects of CuNPs. The fluorescence spectroscopic studies were supported by dynamic light scattering (DLS) measurements and the calcein leakage assay. Additionally, the degree of perturbation of the phospholipid bilayer by CuNPs was compared against that of Cu2+ ions, the latter resulting in negligible effects. The findings suggested that CuNPs are able to damage the phospholipid membranes, leading to their agglomeration or disruption.

Biomimetic Dispersive Solid-Phase Microextraction: A Novel Concept for High-Throughput Estimation of Human Oral Absorption of Organic Compounds

There is a quest for a novel in vitro analytical methodology that is properly validated for the prediction of human oral absorption and bioaccumulation of organic compounds with no need of animal models. The traditional log P parameter might not serve to predict bioparameters accurately inasmuch as it merely accounts for the hydrophobicity of the compound, but the actual interaction with the components of eukaryotic cells is neglected. This contribution proposes for the first time a novel biomimetic microextraction approach capitalized on immobilized phosphatidylcholine as a plasma membrane surrogate onto organic polymeric sorptive phases for the estimation of human intestinal effective permeability of a number of pharmaceuticals that are also deemed contaminants of emerging concern in environmental settings. A comprehensive exploration of the conformation of the lipid structure onto the surfaces is undertaken so as to discriminate the generation of either lipid monolayers or bilayers or the attachment of lipid nanovesicles. The experimentally obtained biomimetic extraction data is proven to be a superb parameter against other molecular descriptors for the development of reliable prediction models of human jejunum permeability with R2 = 0.76, but the incorporation of log D and the number of aromatic rings in multiple linear regression equations enabled improved correlations up to R2 = 0.88. This work is expected to open new avenues for expeditious in vitro screening methods for oral absorption of organic contaminants of emerging concern in human exposomics.

Quantitative Analysis of the Interactions of Metal Complexes and Amphiphilic Systems: Calorimetric, Spectroscopic and Theoretical Aspects

Metals and metal-based compounds have many implications in biological systems. They are involved in cellular functions, employed in the formation of metal-based drugs and present as pollutants in aqueous systems, with toxic effects for living organisms. Amphiphilic molecules also play important roles in the above bio-related fields as models of membranes, nanocarriers for drug delivery and bioremediating agents. Despite the interest in complex systems involving both metal species and surfactant aggregates, there is still insufficient knowledge regarding the quantitative aspects at the basis of their binding interactions, which are crucial for extensive comprehension of their behavior in solution. Only a few papers have reported quantitative analyses of the thermodynamic, kinetic, speciation and binding features of metal-based compounds and amphiphilic aggregates, and no literature review has yet addressed the quantitative study of these complexes. Here, we summarize and critically discuss the recent contributions to the quantitative investigation of the interactions of metal-based systems with assemblies made of amphiphilic molecules by calorimetric, spectrophotometric and computational techniques, emphasizing the unique picture and parameters that such an analytical approach may provide, to support a deep understanding and beneficial use of these systems for several applications.

In-vitro prediction of the membranotropic action of emerging organic contaminants using a liposome-based multidisciplinary approach

According to ISO 17402:2008 more knowledge is needed on processes controlling bioavailability of organic species so as to close the still existing gap between chemical measurements and biological effects. The bioavailability concept encompasses the investigation of the degree of penetration of target species across biological membranes. In addition, REACH (Registration, Evaluation, Authorisation and restriction of Chemicals) guidelines promote the use of in-vitro methods against conventional ecotoxicological tests because of the ethical controversy of in-vivo tests. This work is aimed at filling the gap by proposing a multidisciplinary approach based on high-resolution and low-resolution empirical techniques, and theoretical quantum mechanics for the in-vitro investigation of the bioavailability and membranotropic effects of organic emerging contaminants, including bioaccumulation, via passive diffusion across lipid bilayers. Phosphatidylcholine (PC) liposomes are selected as biomembrane surrogates, and contaminant effects are explored by (i) fluorescence anisotropy and generalized polarization assays using membrane fluorescence probes (laurdan and prodan) and UV-Vis spectroscopy, (ii) ¹H NMR measurements to ascertain supramolecular interactions with PC and (iii) molecular dynamics simulations. In particular, un-regulated model compounds with distinct physico-chemical properties that are representative of three different classes of emerging contaminants in environmental compartments are chosen for validation of the holistic approach: (i) diclofenac as a model of anti-inflammatory drug; (ii) triclosan as an anti-microbial agent; and (iii) bisphenol A as a plastic-borne compound, and compared with chlorpyrifos as a legacy insecticide. Laurdan anisotropic measurements are in good agreement with ¹H NMR data and both approaches pinpoint that triclosan and chlorpyrifos are highly bioaccumulative in membranes. Molecular dynamic studies indicate that the lateral diffusion of the lipid bilayer is much lower with the incorporation of either triclosan or chlorpyrifos into the bilayer. The theoretical simulations also allowed estimating absolute bioavailability data under passive diffusion (<0.1%, 63%, 73% and 89% for diclofenac, bisphenol A, triclosan and chlorpyrifos, respectively) given as the percentage of time that a given species is located in the region of the fatty acyl chains. Our findings indicate that PC-based liposome assays serve as a fast and cost-effective in-vitro approach, notwithstanding its low resolution features, for environmental bioavailability studies of emerging contaminants for which insufficient or inconsistent ecotoxicological data are identified in the literature.

Ecotoxicological equilibria of triclosan in Microtox, XenoScreen YES/YAS, Caco2, HEPG2 and liposomal systems are affected by the occurrence of other pharmaceutical and personal care emerging contaminants

Contaminants of emerging concern may be considered as any chemicals or factors whose unintended continuous release and persistence in the environment may lead to any observable undesirable response of living beings. Still not much is known on reciprocal toxicological impact of given chemicals when present in binary or more complex mixtures. In this work, an attempt was thus undertaken to study the impact of butylparaben, methylparaben and diclofenac on toxicological behavior and properties of triclosan (at varying concentration levels) with respect to Microtox, XenoScreen YES/YAS, Caco-2, HEPG2, and liposomal systems. Having performed analytical and biological studies modeling was done using two modeling approaches, viz., concentration addition (CA) and independent action (IA) at three concentration levels of each chemical studied. The effect of the highest concentration of triclosan studied was impacted by even small amounts of methylparaben and butylparaben in Microtox while diclofenac preferably affected triclosan activity at its lowest concentration level (with CA model). Estrogenic agonistic properties of triclosan were severely impacted by both parabens in an antagonistic way; diclofenac showed in all cases underestimation or synergy at the lowest triclosan concentration studied. Estrogenic antagonistic activity of triclosan was also slightly affected by parabens and by diclofenac in binary mixtures, showing overestimation and antagonist effects. HepG2 cells appeared to be the most resistant to the toxic effect of the mixtures at the concentrations tested and no significant proof of synergy or antagonism could be detected with the MTT assay. The liposome assays on the mixtures followed the same trends obtained with the MTT assay with Caco-2 cells, confirming the validity of the in vitro model used in this research. As studies on emerging contaminants mixtures toxicity are still scarce, research presented here constitute an important part in confirming utility and versatility of emerging contaminants modeling in environmental toxicology.