Properties of flavonoids influencing the binding to bilitranslocase investigated by neural network modelling

Challenges of Protein-Protein Docking of the Membrane Proteins

Despite the recent advances in the determination of high-resolution membrane protein (MP) structures, the structural and functional characterization of MPs remains extremely challenging, mainly due to the hydrophobic nature, low abundance, poor expression, purification, and crystallization difficulties associated with MPs. Whereby the major challenges/hurdles for MP structure determination are associated with the expression, purification, and crystallization procedures. Although there have been significant advances in the experimental determination of MP structures, only a limited number of MP structures (approximately less than 1% of all) are available in the Protein Data Bank (PDB). Therefore, the structures of a large number of MPs still remain unresolved, which leads to the availability of widely unplumbed structural and functional information related to MPs. As a result, recent developments in the drug discovery realm and the significant biological contemplation have led to the development of several novel, low-cost, and time-efficient computational methods that overcome the limitations of experimental approaches, supplement experiments, and provide alternatives for the characterization of MPs. Whereby the fine tuning and optimizations of these computational approaches remains an ongoing endeavor.Computational methods offer a potential way for the elucidation of structural features and the augmentation of currently available MP information. However, the use of computational modeling can be extremely challenging for MPs mainly due to insufficient knowledge of (or gaps in) atomic structures of MPs. Despite the availability of numerous in silico methods for 3D structure determination the applicability of these methods to MPs remains relatively low since all methods are not well-suited or adequate for MPs. However, sophisticated methods for MP structure predictions are constantly being developed and updated to integrate the modifications required for MPs. Currently, different computational methods for (1) MP structure prediction, (2) stability analysis of MPs through molecular dynamics simulations, (3) modeling of MP complexes through docking, (4) prediction of interactions between MPs, and (5) MP interactions with its soluble partner are extensively used. Towards this end, MP docking is widely used. It is notable that the MP docking methods yet few in number might show greater potential in terms of filling the knowledge gap. In this chapter, MP docking methods and associated challenges have been reviewed to improve the applicability, accuracy, and the ability to model macromolecular complexes.

Structural Analysis and Dynamic Processes of the Transmembrane Segment Inside Different Micellar Environments-Implications for the TM4 Fragment of the Bilitranslocase Protein

The transmembrane (TM) proteins are gateways for molecular transport across the cell membrane that are often selected as potential targets for drug design. The bilitranslocase (BTL) protein facilitates the uptake of various anions, such as bilirubin, from the blood into the liver cells. As previously established, there are four hydrophobic transmembrane segments (TM1-TM4), which constitute the structure of the transmembrane channel of the BTL protein. In our previous studies, the 3D high-resolution structure of the TM2 and TM3 transmembrane fragments of the BTL in sodium dodecyl sulfate (SDS) micellar media were solved using Nuclear Magnetic Resonance (NMR) spectroscopy and molecular dynamics simulations (MD). The high-resolution 3D structure of the fourth transmembrane region (TM4) of the BTL was evaluated using NMR spectroscopy in two different micellar media, anionic SDS and zwitterionic DPC (dodecylphosphocholine). The presented experimental data revealed the existence of an α -helical conformation in the central part of the TM4 in both micellar media. In the case of SDS surfactant, the α -helical conformation is observed for the Pro258-Asn269 region. The use of the zwitterionic DPC micelle leads to the formation of an amphipathic α -helix, which is characterized by the extension of the central α -helix in the TM4 fragment to Phe257-Thr271. The complex character of the dynamic processes in the TM4 peptide within both surfactants was analyzed based on the relaxation data acquired on 15 N and 31 P isotopes. Contrary to previously published and present observations in the SDS micelle, the zwitterionic DPC environment leads to intensive low-frequency molecular dynamic processes in the TM4 fragment.

An In Silico Approach for Assessment of the Membrane Transporter Activities of Phenols: A Case Study Based on Computational Models of Transport Activity for the Transporter Bilitranslocase

Phenols are the most abundant naturally accessible antioxidants present in a human normal diet. Since numerous beneficial applications of phenols as preventive agents in various diseases were revealed, the evaluation of phenols bioavailability is of high interest of researchers, consumers and drug manufacturers. The hydrophilic nature of phenols makes a cell membrane penetration difficult, which imply an alternative way of uptake via membrane transporters. However, the structural and functional data of membrane transporters are limited, thus the in silico modelling is really challenging and urgent tool in elucidation of transporter ligands. Focus of this research was a particular transporter bilitranslocase (BTL). BTL has a broad tissue expression (vascular endothelium, absorptive and excretory epithelia) and can transport wide variety of poly-aromatic compounds. With available BTL data (pKi [mmol/L] for 120 organic compounds) a robust and reliable QSAR models for BTL transport activity were developed and extrapolated on 300 phenolic compounds. For all compounds the transporter profiles were assessed and results show that dietary phenols and some drug candidates are likely to interact with BTL. Moreover, synopsis of predictions from BTL models and hits/predictions of 20 transporters from Metrabase and Chembench platforms were revealed. With such joint transporter analyses a new insights for elucidation of BTL functional role were acquired. Regarding limitation of models for virtual profiling of transporter interactions the computational approach reported in this study could be applied for further development of reliable in silico models for any transporter, if in vitro experimental data are available.

Membrane Transporters for Bilirubin and Its Conjugates: A Systematic Review

Background: Bilirubin is a highly-hydrophobic tetrapyrrole which binds to plasma albumin. It is conjugated in the liver to glucuronic acid, and the water-soluble glucuronides are excreted in urine and bile. The membrane transporters of bilirubin diglucuronide are well-known. Still undefined are however the transporters performing the uptake of bilirubin from the blood into the liver, a process known to be fast and not rate-limited. The biological importance of this process may be appraised by considering that in normal adults 200–300 mg of bilirubin are produced daily, as a result of the physiologic turnover of hemoglobin and cellular cytochromes. Nevertheless, research in this field has yielded controversial and contradicting results. We have undertaken a systematic review of the literature, believing in its utility to improve the existing knowledge and promote further advancements.

Methods: We have sourced the PubMed database until 30 June 2017 by applying 5 sequential searches. Screening and eligibility criteria were applied to retain research articles reporting results obtained by using bilirubin molecules in membrane transport assays in vitro or by assessing serum bilirubin levels in in vivo experiments.

Results: We have identified 311 articles, retaining 44, reporting data on experimental models having 6 incremental increases of complexity (isolated proteins, membrane vesicles, cells, organ fragments, in vivo rodents, and human studies), demonstrating the function of 19 membrane transporters, encoded by either SLCO or ABC genes. Three other bilirubin transporters have no gene, though one, i.e., bilitranslocase, is annotated in the Transporter Classification Database.

Conclusions: This is the first review that has systematically examined the membrane transporters for bilirubin and its conjugates. Paradoxically, the remarkable advancements in the field of membrane transport of bilirubin have pointed to the elusive mechanism(s) enabling bilirubin to diffuse into the liver as if no cellular boundary existed.

Anti‑inflammatory effect of quercetin and galangin in LPS‑stimulated RAW264.7 macrophages and DNCB‑induced atopic dermatitis animal models

Flavonols are compounds that have been shown to possess potent anti-inflammatory effects in cellular and animal models of inflammation. In the present study, the anti-inflammatory effects and mechanisms of two natural flavonols, quercetin and galangin, in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages were investigated. It was identified that quercetin and galangin markedly reduced the production of nitric oxide (NO), inducible NO synthase and interleukin-6, and the nuclear translocation of nuclear factor-κB (NF-κB). In addition, LPS-induced activation of extracellular signal-regulated kinase 1/2 (Erk1/2) and c-Jun N-terminal kinase (JNK) was suppressed by quercetin and galangin. Taken together, these data implied that NF-κB, Erk1/2 and JNK may be potential molecular targets of quercetin and galangin in an LPS-induced inflammatory response. Subsequently, the effects of oral administration of quercetin or galangin, either alone or in combination, in a 2,4-dinitrochlorobenzene-induced atopic dermatitis (AD) mouse model were investigated. As a result, measurements of ear thickness and the levels of serum immunoglobulin E, and histological analysis revealed that the two flavonols led to a decrease in inflammation, whereas, in combination, they were even more effective. These results suggested that quercetin and galangin may be promising therapeutic agents for AD. Additionally, their combination may be a novel therapeutic strategy for the prevention of AD.

Computational Approaches for Revealing the Structure of Membrane Transporters: Case Study on Bilitranslocase

The structural and functional details of transmembrane proteins are vastly underexplored, mostly due to experimental difficulties regarding their solubility and stability. Currently, the majority of transmembrane protein structures are still unknown and this present a huge experimental and computational challenge. Nowadays, thanks to X-ray crystallography or NMR spectroscopy over 3000 structures of membrane proteins have been solved, among them only a few hundred unique ones. Due to the vast biological and pharmaceutical interest in the elucidation of the structure and the functional mechanisms of transmembrane proteins, several computational methods have been developed to overcome the experimental gap. If combined with experimental data the computational information enables rapid, low cost and successful predictions of the molecular structure of unsolved proteins. The reliability of the predictions depends on the availability and accuracy of experimental data associated with structural information. In this review, the following methods are proposed for in silico structure elucidation: sequence-dependent predictions of transmembrane regions, predictions of transmembrane helix–helix interactions, helix arrangements in membrane models, and testing their stability with molecular dynamics simulations. We also demonstrate the usage of the computational methods listed above by proposing a model for the molecular structure of the transmembrane protein bilitranslocase. Bilitranslocase is bilirubin membrane transporter, which shares similar tissue distribution and functional properties with some of the members of the Organic Anion Transporter family and is the only member classified in the Bilirubin Transporter Family. Regarding its unique properties, bilitranslocase is a potentially interesting drug target.

Structural Model of the Bilitranslocase Transmembrane Domain Supported by NMR and FRET Data

We present a 3D model of the four transmembrane (TM) helical regions of bilitranslocase (BTL), a structurally uncharacterized protein that transports organic anions across the cell membrane. The model was computed by considering helix-helix interactions as primary constraints, using Monte Carlo simulations. The interactions between the TM2 and TM3 segments have been confirmed by Förster resonance energy transfer (FRET) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy, increasing our confidence in the model. Several insights into the BTL transport mechanism were obtained by analyzing the model. For example, the observed cis-trans Leu-Pro peptide bond isomerization in the TM3 fragment may indicate a key conformational change during anion transport by BTL. Our structural model of BTL may facilitate further studies, including drug discovery.

Chemometrics approach for the prediction of structure-activity relationship for membrane transporter bilitranslocase

Membrane transport proteins are essential for cellular uptake of numerous salts, nutrients and drugs. Bilitranslocase is a transporter, specific for water-soluble organic anions, and is the only known carrier of nucleotides and nucleotide-like compounds. Experimental data of bilitranslocase ligand specificity for 120 compounds were used to construct classification models using counter-propagation artificial neural networks (CP-ANNs) and support vector machines (SVMs). A subset of active compounds with experimentally determined transport rates was used to build predictive QSAR models for estimation of transport rates of unknown compounds. Several modelling methods and techniques were applied, i.e. CP-ANN, genetic algorithm, self-organizing mapping and multiple linear regression method. The best predictions were achieved using CP-ANN coupled with a genetic algorithm, with the external validation parameter QV(2) of 0.96. The applicability domains of the models were defined to determine the chemical space in which reliable predictions can be obtained. The models were applied for the estimation of bilitranslocase transport activity for two sets of pharmaceutically interesting compounds, antioxidants and antiprions. We found that the relative planarity and a high potential for hydrogen bond formation are the common structural features of anticipated substrates of bilitranslocase. These features may serve as guidelines in the design of new pharmaceuticals transported by bilitranslocase.

Involvement of mammalian bilitranslocase-like protein(s) in chlorophyll catabolism of Pisum sativum L. tissues

Putative pea bilin and cyclic tetrapyrrole transporter proteins were identified by means of an antibody raised against a bilirubin-interacting aminoacidic sequence of mammalian bilitranslocase (TC No. 2.A.65.1.1). The immunochemical approach showed the presence of several proteins mostly in leaf microsomal, chloroplast and tonoplast vesicles. In these membrane fractions, electrogenic bromosulfalein transport activity was also monitored, being specifically inhibited by anti-bilitranslocase sequence antibody. Moreover, the inhibition of transport activity in pea leaf chloroplast vesicles, by both the synthetic cyclic tetrapyrrole chlorophyllin and the heme catabolite biliverdin, supports the involvement of some of these proteins in the transport of linear/cyclic tetrapyrroles during chlorophyll metabolism. Immunochemical localization in chloroplast sub-compartments revealed that these putative bilitranslocase-like transporters are restricted to the thylakoids only, suggesting their preferential implication in the uptake of cyclic tetrapyrrolic intermediates from the stroma during chlorophyll biosynthesis. Finally, the presence of a conserved bilin-binding sequence in different proteins (enzymes and transporters) from divergent species is discussed in an evolutionary context.

Overview of metabolism and bioavailability enhancement of polyphenols

A proper diet is one of major factors contributing to good health and is directly related to general condition of the organism. Phenolic compounds are abundant in foods and beverages (fresh and processed fruits and vegetables, leguminous plants, cereals, herbs, spices, tea, coffee, wine, beer) and their pleiotropic biological activities result in numerous health beneficial effects. On the other hand, high reactivity and very large diversity in terms of structure and molecular weight renders polyphenols one of the most difficult groups of compounds to investigate, as evidenced by ambiguous and sometimes contradictory results of many studies. Furthermore, phenolics undergo metabolic transformations, which significantly change their biological activities. Here, we discuss some aspects of metabolism and absorption of phenolic compounds. On the basis of information reported in the literature as well as in summaries of clinical trials and patent applications, we also give an overview of strategies for enhancing their bioavailability.

Prenylation enhances quercetin uptake and reduces efflux in Caco-2 cells and enhances tissue accumulation in mice fed long-term

Prenyl flavonoids are widely distributed in plant foods and have attracted appreciable attention in relation to their potential benefits for human health. Prenylation may enhance the biological functions of flavonoids by introducing hydrophobic properties in their basic structures. Previously, we found that 8-prenyl naringenin exerted a greater preventive effect on muscle atrophy than nonprenylated naringenin in a mouse model. Here, we aimed to estimate the effect of prenylation on the bioavailability of dietary quercetin (Q). The cellular uptake of 8-prenyl quercetin (PQ) and Q in Caco-2 cells and C2C12 myotube cells was examined. Prenylation significantly enhanced the cellular uptake by increasing the lipophilicity in both cell types. In Caco-2 cells, efflux of PQ to the basolateral side was <15% of that of Q, suggesting that prenylation attenuates transport from the intestine to the circulation. After intragastric administration of PQ or Q to mice or rats, the area under the concentration-time curve for PQ in plasma and lymph was 52.5% and 37.5% lower than that of Q, respectively. PQ and its O-methylated form (MePQ) accumulated at much higher amounts than Q and O-methylated Q in the liver (Q: 3400%; MePQ: 7570%) and kidney (Q: 385%; MePQ: 736%) of mice after 18 d of feeding. These data suggest that prenylation enhances the accumulation of Q in tissues during long-term feeding, even though prenylation per se lowers its intestinal absorption from the diet.

In vivo investigation on the potential of galangin, kaempferol and myricetin for protection of D-galactose-induced cognitive impairment

The potential of three natural flavonols (galangin, kaempferol and myricetin) to protect against D-galactose-induced cognitive impairment in mice was investigated. After 8 weeks treatment, the mice were assessed by behavioural tests. The levels of oxidative stress, the amount of Na(+),K(+)-ATPase and extracellular signal-regulated kinases (ERK)-cyclic AMP response element binding protein (CREB) signaling pathway in hippocampus were also analysed. It was found that all the three dietary flavonols could ameliorate the oxidative stress, enhance the activity of Na(+),K(+)-ATPase and regulate the expression of ERK-CREB pathway in mice. However, only kaempferol and myricetin could significantly improve the learning and memory capability when compared with D-galactose model. Our results suggest that the presence of hydroxyl groups in the B ring of flavonols may have contribution to the neuroprotective activity.

Structural analysis of a peptide fragment of transmembrane transporter protein bilitranslocase

Using a combination of genomic and post-genomic approaches is rapidly altering the number of identified human influx carriers. A transmembrane protein bilitranslocase (TCDB 2.A.65) has long attracted attention because of its function as an organic anion carrier. It has also been identified as a potential membrane transporter for cellular uptake of several drugs and due to its implication in drug uptake, it is extremely important to advance the knowledge about its structure. However, at present, only the primary structure of bilitranslocase is known. In our work, transmembrane subunits of bilitranslocase were predicted by a previously developed chemometrics model and the stability of these polypeptide chains were studied by molecular dynamics (MD) simulation. Furthermore, sodium dodecyl sulfate (SDS) micelles were used as a model of cell membrane and herein we present a high-resolution 3D structure of an 18 amino acid residues long peptide corresponding to the third transmembrane part of bilitranslocase obtained by use of multidimensional NMR spectroscopy. It has been experimentally confirmed that one of the transmembrane segments of bilitranslocase has alpha helical structure with hydrophilic amino acid residues oriented towards one side, thus capable of forming a channel in the membrane.

Transport and bioactivity of cyanidin 3-glucoside into the vascular endothelium

Flavonoids are dietary components involved in decreasing oxidative stress in the vascular endothelium and thus the risk of endothelial dysfunction. However, their very low concentrations in plasma place this role in doubt. Thus, a relationship between the effective intracellular concentration of flavonoids and their bioactivity needs to be assessed. This study examined the uptake of physiological concentrations of cyanidin 3-glucoside, a widespread dietary flavonoid, into human vascular endothelial cells. Furthermore, the involvement of the membrane transporter bilitranslocase (TC No. 2.A.65.1.1) as the key underlying molecular mechanism for membrane transport was investigated by using purified anti-sequence antibodies binding at the extracellular domain of the protein. The experimental observations were carried out in isolated plasma membrane vesicles and intact endothelial cells from human endothelial cells (EA.hy926) and on an ischemia-reperfusion model in isolated rat hearts. Cyanidin 3-glucoside was transported via bilitranslocase into endothelial cells, where it acted as a powerful intracellular antioxidant and a cardioprotective agent in the reperfusion phase after ischemia. These findings suggest that dietary flavonoids, despite their limited oral bioavailability and very low postabsorption plasma concentrations, may provide protection against oxidative stress-based cardiovascular diseases. Bilitranslocase, by mediating the cellular uptake of some flavonoids, is thus a key factor in their protective activity on endothelial function.

Expression of bilitranslocase in the vascular endothelium and its function as a flavonoid transporter

AIMS

Ingestion of flavonoid-rich beverages acutely affects endothelial function, causing vasodilation. This effect might be dependent on flavonoid transport into the endothelium. We investigated flavonoid uptake into vascular endothelial cells and whether this was mediated by bilitranslocase (TC 2.A.65.1.1), a bilirubin-specific membrane carrier that also transports various dietary flavonoids.

METHODS AND RESULTS

Human and rat aortic primary endothelial cells as well as Ea.hy 926 cells were found to express bilitranslocase, as assessed by immunocytochemistry and immunoblotting analysis using anti-sequence bilitranslocase antibodies targeting two distinct extracellular epitopes of the carrier. Bilitranslocase function was tested by measuring the rate of bromosulfophthalein (a standard bilitranslocase transport substrate) uptake into endothelial cells and was inhibited not only by bilitranslocase antibodies but also by quercetin (a flavonol). Similarly, uptake of both quercetin and malvidin 3-glucoside (an anthocyanin) were also found to be antibody-inhibited. Quercetin uptake into cells was inhibited by bilirubin, suggesting flavonoid uptake via a membrane pathway shared with bilirubin.

CONCLUSION

The uptake of some flavonoids into the vascular endothelium occurs via the bilirubin-specific membrane transporter bilitranslocase. This offers new insights into the vascular effects of both flavonoids and bilirubin.

Electrogenic bromosulfalein transport in isolated membrane vesicles: implementation in both animal and plant preparations for the study of flavonoid transporters

Bromosulfalein is an organic anion dye used in the study of a variety of membrane carriers expressed in animal tissues and involved in transport of drugs and metabolites. The spectrophotometric assay of electrogenic bromosulfalein transport in membrane vesicles, isolated from various mammalian organs or tissues, enables to specifically measure the transport activity of bilitranslocase (TCDB 2.A.65.1.1). The latter is a bilirubin- and flavonoid-specific transporter expressed in rat liver, the organ where its function has been best characterized. The spectrophotometric assay of electrogenic bromosulfalein transport requires minimal volumes of membrane vesicles, is completed within 1 min, and, therefore, is a useful tool to screen the transporter spectrum of potential substrates, by testing them as reversible inhibitors of bromosulfalein transport kinetics. Furthermore, the assay enables to study the progress of time-dependent inactivation of bromosulfalein transport, caused by different protein-specific reagents, including specific anti-sequence antibodies. Inactivation can be retarded by the presence of substrates in a concentration-dependent manner, enabling to derive the dissociation constants of the transporter-substrate complex and thus to gain further insight into the transporter structure-function relationship. This assay, implemented in membrane vesicles isolated from plant organs, has paved the way to the discovery of homologues of bilitranslocase in plants.

Identification and localization of the bilitranslocase homologue in white grape berries (Vitis vinifera L.) during ripening

A homologue of the mammalian bilirubin transporter bilitranslocase (BTL) (TCDB 2.A.65.1.1), able to perform an apparent secondary active transport of flavonoids, has previously been found in carnation petals and red grape berries. In the present work, a BTL homologue was also shown in white berries from Vitis vinifera L. cv. Tocai/Friulano, using anti-sequence antibodies specific for rat liver BTL. This transporter, similarly to what found in red grape, was localized in the first layers of the epidermal tissue and in the vascular bundle cells of the mesocarp. In addition, a strong immunochemical reaction was detected in the placental tissue and particularly in peripheral integuments of the seed. The protein was expressed during the last maturation stages in both skin and pulp tissues and exhibited an apparent molecular mass of c. 31 kDa. Furthermore, the transport activity of such a carrier, measured as bromosulphophthalein (BSP) uptake, was detected in berry pulp microsomes, where it was inhibited by specific anti-BTL antibodies. The BTL homologue activity exhibited higher values, for both K(m) and V(max), than those found in the red cultivar. Moreover, two non-pigmented flavonoids, such as quercetin (a flavonol) and eriodictyol (a flavanone), inhibited the uptake of BSP in an uncompetitive manner. Such results strengthen the hypothesis that this BTL homologue acts as a carrier involved also in the membrane transport of colourless flavonoids and demonstrate the presence of such a carrier in different organs and tissues.

Uptake of grape anthocyanins into the rat kidney and the involvement of bilitranslocase

Anthocyanins are among the most common flavonoids in the human diet. In spite of their very low bioavailability, anthocyanins are indicated as active in preventing the progress of cardiovascular and neurodegenerative diseases, obesity, inflammation, and cancer. Any piece of knowledge concerning absorption, tissue distribution, metabolism, and excretion of dietary anthocyanins is expected to help understanding the apparent paradox between their low concentrations in cells and their bioactivity. The aim of this work was to investigate the renal uptake of dietary anthocyanins and the underlying molecular mechanism. A solution containing anthocyanins extracted from grape (Vitis vinifera) was introduced into the isolated stomach of anesthetized rats; after both 10 and 30 min, plasma, liver, and kidney were analyzed for their anthocyanin contents. While anthocyanins in the liver were at apparent equilibrium with plasma both after 10 and 30 min, kidney anthocyanins were 3- and 2.3-fold higher than in plasma, after 10 and 30 min, respectively. Since the transport activity of the bilitranslocase in kidney basolateral membrane vesicles was competitively inhibited by malvidin 3-glucoside (K(i) = 4.8 +/- 0.2 microM), the anthocyanin uptake from blood into kidney tubular cells is likely to be mediated by the kidney isoform of this organic anion membrane transporter.

Copper complexes of nicotinic-aromatic carboxylic acids as superoxide dismutase mimetics

Nicotinic acid (also known as vitamin B3) is a dietary element essential for physiological and antihyperlipidemic functions. This study reports the synthesis of novel mixed ligand complexes of copper with nicotinic and other select carboxylic acids (phthalic, salicylic and anthranilic acids). The tested copper complexes exhibited superoxide dismutase (SOD) mimetic activity and antimicrobial activity against Bacillus subtilis ATCC 6633, with a minimum inhibition concentration of 256 microg/mL. Copper complex of nicotinic-phthalic acids (CuNA/Ph) was the most potent with a SOD mimetic activity of IC(50) 34.42 microM. The SOD activities were observed to correlate well with the theoretical parameters as calculated using density functional theory (DFT) at the B3LYP/LANL2DZ level of theory. Interestingly, the SOD activity of the copper complex CuNA/Ph was positively correlated with the electron affinity (EA) value. The two quantum chemical parameters, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), were shown to be appropriate for understanding the mechanism of the metal complexes as their calculated energies show good correlation with the SOD activity. Moreover, copper complex with the highest SOD activity were shown to possess the lowest HOMO energy. These findings demonstrate a great potential for the development of value-added metallovitamin-based therapeutics.

QSAR modeling for lipid peroxidation inhibition potential of flavonoids using topological and structural parameters

In the present study, Quantitative Structure-Activity Relationship (QSAR) modeling has been carried out for lipid peroxidation (LPO)-inhibition potential of a set of 27 flavonoids, using structural and topological parameters. For the development of models, three methods were used: (1) stepwise regression, (2) factor analysis followed by multiple linear regressions (FA-MLR) and (3) partial least squares (PLS) analysis. The best equation was obtained from stepwise regression analysis (Q2 = 0.626) considering the leave-oneout prediction statistics.

Evidence for a putative flavonoid translocator similar to mammalian bilitranslocase in grape berries (Vitis vinifera L.) during ripening

During maturation, Vitis vinifera berries accumulate a large amount of several anthocyanins in the epidermal tissue, whereas their precursors and intermediates are ubiquitously synthesized within the fruit. Up to date, several mechanisms of flavonoid transport at subcellular level have been hypothesized, but it is not possible to identify a general model applicable in every plant tissue and organ. Recently, a putative anthocyanin carrier, homologue to mammalian bilitranslocase (BTL) (TC 2.A.65.1.1), was found in Dianthus caryophyllus petal microsomes. In the present paper, an immunohistochemical and immunochemical analysis, using an antibody raised against a BTL epitope, evidences the expression and function of such a transporter in V. vinifera berries (cv. Merlot). Specific localisations of the putative carrier within berry tissues together with expression changes during different developmental stages are shown. Water stress induces an increase in protein expression in both skin and pulp samples. A bromosulfalein (BSP) uptake activity, inhibitable by the BTL antibody, is detected in berry mesocarp microsomes, with K (m) = 2.39 microM BSP and V (max) = 0.29 micromol BSP min(-1) mg(-1) protein. This BSP uptake is also competitively inhibited by quercetin (K (i) = 4 microM). A putative role for this carrier is discussed in relation to the membrane transport of secondary metabolites.

QSAR modeling of antiradical and antioxidant activities of flavonoids using electrotopological state (E-State) atom parameters

In the present paper QSAR modeling using electrotopological state atom (E-state) parameters has been attempted to determine the antiradical and the antioxidant activities of flavonoids in two model systems reported by Burda et al. (2001). The antiradical property of a methanolic solution of 1, 1-diphenyl-2-picrylhydrazyl (DPPH) and the antioxidant activity of flavonoids in a β-carotenelinoleic acid were the two model systems studied. Different statistical tools used in this communication are stepwise regression analysis, multiple linear regressions with factor analysis as the preprocessing step for variable selection (FA-MLR) and partial least squares analysis (PLS). In both the activities the best equation is obtained from stepwise regression analysis, considering, both equation statistics and predictive ability (antiradical activity: R 2 = 0.927, Q2 = 0.871 and antioxidant activity: R 2 = 0.901, Q2 = 0.841).