Interactions of dietary polyphenols with epithelial lipids: advances from membrane and cell models in the study of polyphenol absorption, transport and delivery to the epithelium

Classic Phytochemical Antioxidant and Lipoxygenase Inhibitor, Nordihydroguaiaretic Acid, Activates Phospholipase D through Oxidant Signaling and Tyrosine Phosphorylation Leading to Cytotoxicity in Lung Vascular Endothelial Cells

Nordihydroguaiaretic acid (NDGA), a dicatechol and phytochemical polyphenolic antioxidant and an established inhibitor of human arachidonic acid (AA) 5-lipoxygenase (LOX) and 15-LOX, is widely used to ascertain the role of LOXs in vascular endothelial cell (EC) function. As the modulatory effect of NDGA on phospholipase D (PLD), an important lipid signaling enzyme in ECs, thus far has not been reported, here we have investigated the modulation of PLD activity and its regulation by NDGA in the bovine pulmonary artery ECs (BPAECs). NDGA induced the activation of PLD (phosphatidic acid formation) in cells in a dose- and time-dependent fashion that was significantly attenuated by iron chelator and antioxidants. NDGA induced the formation of reactive oxygen species (ROS) in cells in a dose- and time-dependent manner as evidenced from fluorescence microscopy and fluorimetry of ROS and electron paramagnetic resonance spectroscopy of oxygen radicals. Also, NDGA caused a dose-dependent loss of intracellular glutathione (GSH) in BPAECs. Protein tyrosine kinase (PTyK)-specific inhibitors significantly attenuated NDGA-induced PLD activation in BPAECs. NDGA also induced a dose- and time-dependent phosphorylation of tyrosine in proteins in cells. NDGA caused in situ translocation and relocalization of both PLD₁ and PLD₂ isoforms, in a time-dependent fashion. Cyclooxygenase (COX) inhibitors were ineffective in attenuating NDGA-induced PLD activation in BPAECs, thus ruling out the activation of COXs by NDGA. NDGA inhibited the AA-LOX activity and leukotriene C₄ (LTC₄) formation in cells. On the other hand, the 5-LOX-specific inhibitors, 5, 8, 11, 14-eicosatetraynoic acid and kaempferol, were ineffective in activating PLD in BPAECs. Antioxidants and PTyK-specific inhibitors effectively attenuated NDGA cytotoxicity in BPAECs. The PLD-specific inhibitor, 5-fluoro-2-indolyl deschlorohalopemide (FIPI), significantly attenuated and protected against the NDGA-induced PLD activation and cytotoxicity in BPAECs. For the first time, these results demonstrated that NDGA, the classic phytochemical polyphenolic antioxidant and LOX inhibitor, activated PLD causing cytotoxicity in ECs through upstream oxidant signaling and protein tyrosine phosphorylation.

Evaluation of the Astragalus exscapus L. subsp. transsilvanicus Roots' Chemical Profile, Phenolic Composition and Biological Activities

Novel and natural molecules for pharmaceutical applications are a contemporary preoccupation in science which prompts research in underexplored environments. Astragalus exscapus ssp. transsilvanicus (Schur) Nyár. (ASTRA) is a plant species endemic to Transylvania, having a very similar root system with that of A. membranaceus (Fisch.) Bunge, known for its health promoting properties. The present study endeavored to perform basic characterization of the ASTRA roots by proximate analysis, to investigate the fatty acid profile of the lipids extracted from the ASTRA roots, to examine the phenolic composition of the root extracts by liquid chromatography, and to evaluate the biological activities through determination of the antioxidant, antimicrobial and cytotoxic capacities of the extracts. The primary compounds found in the ASTRA roots were carbohydrates and lipids, and the fatty acid composition determined by GC-MS showed linoleic acid as preponderant compound with 31.10%, followed by palmitic, oleic and α-linolenic acids with 17.30%, 15.61% and 14.21%, respectively. The methanol extract of the ASTRA roots presented highest phenolic content, Astragaloside IV being the predominant compound with 425.32 ± 0.06 µg/g DW. The antimicrobial assay showed remarkable antimicrobial potential of the extract at a concentration of 0.356 and 0.703 mg ASTRA root powder (DW)/mL, highlighting its efficacy to inhibit S. aureus and S. epidermidis bacterial strains. Furthermore, the cell proliferation assessment showed the noteworthy proficiency of the treatment in inhibiting the proliferation of B16F10 melanoma cells.

Insights into Polyphenol-Lipid Interactions: Chemical Methods, Molecular Aspects and Their Effects on Membrane Structures

Plant polyphenols have many potential applications, for example, in the fields of chemical ecology and human and animal health and nutrition. These biological benefits are related to their bioavailability, bioaccessibility and interactions with other biomolecules, such as proteins, lipids, fibers and amino acids. Polyphenol-protein interactions are well-studied, but less is known about their interactions with lipids and cell membranes. However, the affinity of polyphenols for lipid bilayers partially determines their biological activity and is also important from the usability perspective. The polyphenol-lipid interactions can be studied with several chemical tools including, among others, partition coefficient measurements, calorimetric methods, spectroscopic techniques and molecular dynamics simulation. Polyphenols can variably interact with and penetrate lipid bilayers depending on the structures and concentrations of the polyphenols, the compositions of the lipids and the ambient conditions and factors. Polyphenol penetrating the lipid bilayer can perturb and cause changes in its structure and biophysical properties. The current studies have used structurally different polyphenols, diverse model lipids and various measuring techniques. This approach provides detailed information on polyphenol-lipid interactions, but there is much variability, and the results may even be contradictory, for example, in relation to the locations and orientations of the polyphenols in the lipid bilayers. Nevertheless, by using well-characterized model polyphenols and lipids systematically and combining the results obtained with several techniques within a study, it is possible to create a good overall picture of these fascinating interactions.

Plant-Based Polyphenols: Anti-Helicobacter pylori Effect and Improvement of Gut Microbiota

Helicobacter pylori (H. pylori) infection affects more than half of the world’s population, and thus, about 10 to 20% of people with H. pylori suffer from peptic ulcers, which may ultimately lead to gastric cancer. The increase in antibiotic resistance and susceptibility has encouraged the search for new alternative therapies to eradicate this pathogen. Several plant species are essential sources of polyphenols, and these bioactive compounds have demonstrated health-promoting properties, such as the gut microbiota stimulation, inflammation reduction, and bactericidal effect. Therefore, this review aims to discuss the potential effect of plant-based polyphenols against H. pylori and their role in the gut microbiota improvement.

A Comprehensive Review on the Interaction of Milk Protein Concentrates with Plant-Based Polyphenolics

Functional properties and biological activities of plant-derived polyphenolic compounds have gained great interest due to their epidemiologically proven health benefits and diverse industrial applications in the food and pharmaceutical industry. Moreover, the food processing conditions and certain chemical reactions such as pigmentation, acylation, hydroxylation, and glycosylation can also cause alteration in the stability, antioxidant activity, and structural characteristics of the polyphenolic compounds. Since the (poly)phenols are highly reactive, to overcome these problems, the formulation of a complex of polyphenolic compounds with natural biopolymers is an effective approach. Besides, to increase the bioavailability and bioaccessibility of polyphenolic compounds, milk proteins such as whey protein concentrate, sodium caseinate, and milk protein concentrate act as natural vehicles, due to their specific structural and functional properties with high nutritional value. Therefore, milk proteins are suitable for the delivery of polyphenols to parts of the gastrointestinal tract. Therefore, this review reports on types of (poly)phenols, methods for the analysis of binding interactions between (poly)phenols-milk proteins, and structural changes that occur during the interaction.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

Curcumin increases heat shock protein 70 expression via different signaling pathways in intestinal epithelial cells

Intestinal inflammation is associated with the integrity of the intestinal epithelium, which forms a physical barrier against noxious luminal substances. Heat shock 70 kDa protein 1A (HSP70), a molecular chaperon that exerts a cytoprotective effect, regulates intestinal integrity. This study investigated the modulation of HSP70 expression by dietary polyphenols, with particular reference to curcumin, in human intestinal Caco-2 cells. Immunoblot analysis demonstrated that among the 21 different polyphenols tested, curcumin most potently increased HSP70 levels in Caco-2 cells without affecting cell viability. Curcumin also increased the phosphorylation of heat shock factor 1 (HSF1), a well-known transcription factor of HSP70. Promoter and qRT-PCR assays indicated that curcumin upregulated Hspa1a levels via transcriptional activation. Pharmacological inhibition of MEK, a mechanistic target of rapamycin, p38 mitogen-activated protein kinase, and phosphatidyl 3-inositol kinase suppressed curcumin-mediated HSP70 expression, whereas HSF1 phosphorylation was sensitive only to MEK inhibition. Taken together, curcumin increases the expression of HSP70 in intestinal Caco-2 cells via transcriptional activation, possibly enhancing cell integrity. The effects exerted by curcumin are regulated by various signaling pathways. Our findings will expectedly contribute to a deeper understanding of the regulation of intestinal HSP70 by dietary components.