Mara Massimi

Chitosan-coated PLGA nanoparticles: a sustained drug release strategy for cell cultures.

A recently patented one-step methodology was used for the formulation of chitosan (CS) coated polylactic-co-glycolic acid (PLGA) nanoparticles containing dexamethasone (DXM) as a model drug. SEM investigations showed that nanoparticles (NPs) were spherical in shape with smooth surface. CS coating switched NPs ζ-potential from negative to positive, without modifying particle size distribution. Moreover, CS coating allowed a significant modulation of in vitro drug release, providing a sustained drug delivery in cultured cells. The uptake of fluorescent CS-coated PLGA NPs by hepatocytes (C3A) and fibroblasts (3T6) as well as the fate of internalized NPs were investigated by confocal microscopy. 3T6 and C3A cells were treated with DXM-loaded NPs and experiments were addressed to analyze the specific cell response to DXM, in order to evaluate its functional efficiency in comparison with conventional addition to culture medium. CS-coating of DXM loaded PLGA NPs allowed their uptake by cultured cells without inducing cytotoxicity.

Effects of resveratrol on HepG2 cells as revealed by 1H-NMR based metabolic profiling

BACKGROUND Resveratrol, a polyphenol found in plant products, has been shown to regulate many cellular processes and to display multiple protective and therapeutic effects. Several in vitro and in vivo studies have demonstrated the influence of resveratrol on multiple intracellular targets that may regulate metabolic homeostasis. METHODS We analysed the metabolic modifications induced by resveratrol treatment in a human hepatoblastoma line, HepG2 cells, using a (1)H-NMR spectroscopy-based metabolomics approach that allows the simultaneous screening of multiple metabolic pathways. RESULTS Results demonstrated that cells cultured in the presence or absence of resveratrol displayed different metabolic profiles: the treatment induced a decreased utilisation of glucose and amino acids for purposes of energy production and synthesis associated to a decreased release of lactate in the culture medium and an increase in succinate utilisation. At the same time, resveratrol treatment slowed the cell cycle in the S phase without inducing apoptosis, and increased Sirt1 expression, also affecting its intracellular localisation. CONCLUSIONS Our results show that the metabolomic analysis of the exometabolome of resveratrol-treated HepG2 cells indicates a metabolic switch from glucose and amino acid utilisation to fat utilisation for the production of energy, and seem in agreement with an effect mediated via AMPK- and Sirt1-activation. GENERAL SIGNIFICANCE NMR-based metabolomics has been applied in a hepatocyte cell culture model in relation to resveratrol treatment; such an approach could be transferred to evaluate the effects of nutritional compounds with health impact.

Rapid prototyping of chitosan-coated alginate scaffolds through the use of a 3D fiber deposition technique†

Three dimensional, periodic scaffolds of chitosan-coated alginate are fabricated in a layer-by-layer fashion by rapid prototyping. A novel dispensing system based on two coaxial needles delivers simultaneously alginate and calcium chloride solutions permitting the direct deposition of alginate fibers according to any designed pattern. Coating of the alginate fiber with chitosan and subsequent cross-linking with EDC and genipin assured the endurance of the scaffold in the culture environment for a prolonged period of time. The cross-linking protocol adopted imparted to the scaffold a hierarchical chemical structure as evidenced by Confocal Laser Microscopy and FTIR spectroscopy. The core of the fibers making up the scaffold is represented by alginate chains cross-linked by ester bonds only, the periphery of the fiber is constituted by an inter-polyelectrolyte complex of alginate and chitosan cross-linked in all pair combinations. Fibers belonging to adjacent layers are glued together by the chitosan coating. Mechanical behavior of the scaffolds characterized by different layouts of deposition was determined revealing anisotropic properties. The biocompatibility and capability of the scaffolds to sustain hepatocyte (HepaRG) cultures were demonstrated. Typical hepatic functions such as albumin and urea secretion and induction of CYP3A4 enzyme activity following drug administration were excellent, thus proving the potential of these constructs in monitoring the liver specific function.

A biomimetic porous hydrogel of gelatin and glycosaminoglycans cross-linked with transglutaminase and its application in the culture of hepatocytes

The development of blended gelatin and glycosaminoglycan (GAG) scaffolds can potentially be used in many soft tissue engineering applications since these scaffolds mimic the structure and biological function of native extracellular matrix (ECM). In this study, we were able to obtain a gelatin-GAG scaffold by using a concentrated emulsion templating technique known as high internal phase emulsion (HIPE), in which a prevailing in volume organic phase is dispersed in the form of discrete droplets inside an aqueous solution of three biopolymers represented by gelatin, hyaluronic acid (HA) and chondroitin sulfate (CS) in the presence of a suitable surfactant. In order to preserve the bioactive potential of the biopolymers employed, the cross-linking procedure involved the use of transglutaminase (MTGase) that catalyzes the formation of covalent N-ε-(γ-glutamyl) lysine amide bonds. Since neither HA nor CS possess the necessary primary amino groups toward which MTGase is active, they were functionalized with the dipeptide glycine-lysine (GK). In this way the introduction of foreign cross-linking bridging units with an unpredictable biocompatibility was avoided. These enzymatic cross-linked gelatin-GAG scaffolds were tested in the culture of primary rat and C3A hepatocytes. Results underlined the good performance of this novel support in maintaining and promoting hepatocyte functions in vitro.

Retinoic acid modulates gap junctional intercellular communication in hepatocytes and hepatoma cells

Abstract. Gap junctional communication permits the direct exchange of small molecules and ions and has been implicated in tissue homeostasis/metabolite exchange. The lack of gap junctional intercellular communication (GJIC) plays important roles in the promotion and progression of carcinogenesis. In the present study, we demonstrate that treatment of human hepatoma Hep G2 cells with retinoic acid (RA) results in increased amounts and phosphorylation of connexins, their stabilisation in plasma membrane plaques and enhanced GJIC. In cultured fetal hepatocytes, which represent a non-transformed, proliferating and incompletely differentiated liver system, the effects of RA are limited to the establishment of connexin in areas of cell-cell contact and the improvement of GJIC. This suggests that modulation of cell-cell channel communication by RA occurs differently in these two experimental models: while RA is able to revert cell transformation in Hep G2 cells, in fetal hepatocytes it may induce the expression of a more differentiated phenotype.

Emodin Prevents Intrahepatic Fat Accumulation, Inflammation and Redox Status Imbalance During Diet-Induced Hepatosteatosis in Rats

High-fat and/or high-carbohydrate diets may predispose to several metabolic disturbances including liver fatty infiltration (hepatosteatosis) or be associated with necro-inflammation and fibrosis (steatohepatitis). Several studies have emphasized the hepatoprotective effect of some natural agents. In this study, we investigated the potential therapeutic effects of the treatment with emodin, an anthraquinone derivative with anti-oxidant and anti-cancer abilities, in rats developing diet-induced hepatosteatosis and steatohepatitis. Sprague-Dawley rats were fed a standard diet (SD) for 15 weeks, or a high-fat/high-fructose diet (HFD/HF). After 5 weeks, emodin was added to the drinking water of some of the SD and HFD/HF rats. The experiment ended after an additional 10 weeks. Emodin-treated HFD/HF rats were protected from hepatosteatosis and metabolic derangements usually observed in HFD/HF animals. Furthermore, emodin exerted anti-inflammatory activity by inhibiting the HFD/HF-induced increase of tumor necrosis factor (TNF)-α. Emodin also affected the hepatocytes glutathione homeostasis and levels of the HFD/HF-induced increase of glutathionylated/phosphorylated phosphatase and tensin homolog (PTEN). In conclusion, we demonstrated that a natural agent such as emodin can prevent hepatosteatosis, preserving liver from pro-inflammatory and pro-oxidant damage caused by HFD/HF diet. These findings are promising, proposing emodin as a possible hindrance to progression of hepatosteatosis into steatohepatitis.

Redox homeostasis and posttranslational modifications/activity of phosphatase and tensin homolog in hepatocytes from rats with diet-induced hepatosteatosis ☆

High-fat and high-carbohydrate diets may predispose to simple steatosis, alone or associated with necroinflammation and fibrosis (steatohepatitis). However, there are few reports about the real effect of these nutrients on hepatocyte redox homeostasis and consequent molecular derangement. Here, we investigated whether different diets would induce oxidative damage in primary rat hepatocytes and thereby affect the activity of phosphatase and tensin homolog (PTEN). We used Sprague-Dawley rats fed, for 14 weeks, a standard diet (SD), a high-fat/low-carbohydrate diet (HFD-LC), a normal-fat/high-fructose diet (NFD-HF), or a high-fat/high-fructose diet (HFD-HF). Metabolic and histological parameters were analyzed in blood and liver samples, while oxidative stress markers and related posttranscriptional modification of PTEN were analyzed in isolated hepatocytes. Our results indicate that different dietetic hypercaloric regimens caused liver damage and a significant increase of body and liver weight, as well as elevated plasma levels of alanine aminotransferase, triglycerides and insulin. Hepatocytes from NFD-HF and HFD-HF rats displayed a decrement of cell viability and proliferation rate. Hepatocytes from animals treated with hypercaloric regimens also exhibited oxidative stress greater than SD hepatocytes. Finally, NFD-HF and HFD-HF hepatocytes showed an increased PTEN phosphorylation and decreased PTEN activity, which seem strongly correlated to an increased glutathionylation of the protein. In conclusion, we demonstrate that fructose-enriched diets cause a tissue and hepatocyte damage that might exacerbate those observed in the presence of high-fat alone and might render, via redox homeostasis imbalance, the hepatocytes more prone to posttranslational modifications and activity alteration of PTEN.

Synthesis and characterization of a novel poly(vinyl alcohol) 3D platform for the evaluation of hepatocytes' response to drug administration

Many whole cell-based assays in use today rely on flat, two-dimensional (2D) glass or plastic substrates that may not produce results characteristic of in vivo conditions. In this study, a three-dimensional (3D) cell-based assay scaffold was fabricated using a gas-in-foam templating technique. The scaffold was made of poly(vinyl alcohol), a water-soluble synthetic polymer with excellent film-forming, emulsifying, and biocompatible properties widely used in the biomedical field. The preliminary rheological studies on the solution of PVA and surfactant permitted us to disclose the significant physical parameters that influence the morphology of the ensuing materials. The scaffolds obtained were subjected to detailed analysis by light microscopy, Scanning Electron Microscopy (SEM), computed X-ray microtomography (μCT), infrared spectroscopy, and mechanical testing. Morphological investigations showed that the produced scaffolds are characterised by average void and interconnect diameters lying in the range of 200-300 and 30-150 μm, respectively, suitable for cell infiltration. Two different cross-linking procedures were adopted in order to modulate the mechanical properties of the PVA scaffolds. One made use of a bi-epoxide (PEGDGE), the other was based on glutaraldehyde (GA). The efficiency in terms of cross-linking density of the two procedures resulted in very different mechanical properties. Furthermore, in this article it is demonstrated how PVA foams can be processed into uniform, porous films suitable to be integrated with multi-well 2D culture plates in order to create a 3D analogue. The PEGDGE cross-linked scaffold was tested on C3A cells, a human hepatocyte cell line, representing an appropriate model for liver toxicity studies. Proliferation and cytotoxicity assays indicated good cell viability throughout the culture time, which was also confirmed by SEM analysis. Typical hepatic functions such as albumin and urea production and induction of Cyp3A4 enzyme activity following drug administration were satisfactory, thus proving the efficiency of this construct in maintaining specific liver functions.

Adhesion to the extracellular matrix is positively regulated by retinoic acid in HepG2 cells

Aims: In this work, we aimed to investigate the possible modulation of cell–matrix interactions by retinoic acid (RA), in view of the well‐known role of the extracellular matrix (ECM) and integrins in hepatocyte differentiation and proliferation. For this purpose, we analysed the adhesion ability of HepG2 cells on different substrates in the presence and absence of RA evaluating both the expression and cellular localisation of major proteins involved in focal contacts, using Western blot and confocal microscopy.

Influence of Retinoic Acid on Adhesion Complexes in Human Hepatoma Cells: A Clue to Its Antiproliferative Effects

Retinoic acid exerts antiproliferative and differentiative effects in normal and transformed in vitro hepatocytes. In order to verify whether these effects are related to a modulation of adhesion molecules, we used Western blot analysis and immunofluorescence microscopy to investigate the E-cadherin/β-catenin complex, the main system of adherens junctions, and the occludin/ZO-1 complex present in the tight junctions in HepG2 cells cultured in the presence or absence of retinoic acid. Results showed that retinoic acid treatment increases the amount of β-catenin bound to E-cadherin by decreasing its tyrosine-phosphorylation level. Similar results were obtained with the tight junction system, in which the amount of occludin/ZO-1 complex is increased by a similar mechanism that reduced the level of ZO-1 phosphorylation on tyrosine. Immunofluorescence images also confirm these results, showing the localization on the cell surface of both adhesion complexes. Their insertion into the plasma membrane could be suggestive of an optimal reassembly and function of adherens and tight junctions in hepatoma cells, indicating that retinoic acid, besides inhibiting cell proliferation, improves cell-cell adhesion, sustaining or inducing the expression of a more differentiated phenotype.