Antiradical activity of avarol:theoretical and experimental approach

Avarol je sekundarni metabolit izolovan iz morskog sunđera Dysidea avara. Smatra se da hidrohinonski segment molekula avarola ima ključnu ulogu u njegovoj biološkoj aktivnosti, dok je uloga terpenoidnog dela manje značajna. Avarol ima nisku toksičnost i širok dijapazon bioloških aktivnosti, između ostalog antioksidativnu, antiinflamatornu, antitumorsku, antipsorijatičnu i anti-HIV. Imajući u vidu ove činjenice, kao i to da avarol može proći kroz krvno-moždanu barijeru, on predstavlja dobrog kandidata za razvoj novih terapija za neurodegenerativne bolesti, posebno Alchajmerovu bolest. Međutim, problem primene avarola u terapijske svrhe ogleda se u njegovoj nerastvorljivosti u vodi. Pošto se smatra da su jedan od uzročnika Alchajmerove bolesti slobodni radikali, potrebno je detaljno ispitati prirodu interakcija avarola sa njima. U ovoj doktorskoj disertaciji, interakcije avarola sa slobodnim radikalima proučavane su primenom metoda teorijske hemije i elektronske paramagnetne rezonantne (EPR) spektroskopije. Zbog kompleksnosti sistema, kod teorijskih proračuna upotrebljen je hidrohinon kao model molekul. Osim toga, primenom ciklične voltametrije i ultraljubičaste i vidljive spektroskopije ispitana je interakcija avarola sa L-dopom, prekursorom kateholaminskih neurotransmitera. Teorijskim proračunima zasnovanim na teoriji funkcionala gustine (DFT), odnosno kvantnoj teoriji atoma u molekulima (QTAIM), ispitano je do kakvih interakcija dolazi između hidrohinona i tri radikala: hidroksilnog, hidroperoksilnog i metoksi radikala. Na osnovu rezultata teorijskih proračuna, ustanovljeno je da je energijska barijera za reakciju hidrohinona sa hidroperoksilnim radikalom znatno viša od barijere za reakciju hidrohinona sa hidroksilnim radikalom. Sem toga, reakcija apstrakcije vodonikovog atoma sa hidroksilne grupe hidrohinona od strane sva tri posmatrana radikala odvija se mehanizmom poznatim kao PCET (spregnuti prenos protona i elektrona, od eng. proton-coupled electron transfer). Takođe, primenom modela implicitnog rastvarača, ustanovljeno je i da (u slučaju hidroksilnog i hidroperoksilnog radikala) prisustvo rastvarača ne utiče na mehanizam po kom se apstrakcija atoma vodonika odvija...avara. The hydroquinone moiety of avarol is supposed to play a key role in its biological activity, while the role of its terpenoid moiety is merely marginal. Avarol is known for its low toxicity and a wide range of biological activities, antioxidative, antiinflamatoric, antitumour, antipsoriatic and anti-HIV being some of the most important ones. Having this in mind, as well as the fact that avarol can cross through the blood-brain barrier, it could serve as a good candidate for the development of the new therapies for neurodegenerative diseases, principally Alzheimer’s disease. However, its poor solubility in water hampers its application in therapeutical purposes. Since free radicals are presumed to be one of the causes of Alzheimer’s disease, the nature of interactions of avarol with these species should be explored more elaborately. In this doctoral dissertation, interactios of avarol with free radicals have been studied by the means of computational chemistry and electron paramagnetic resonance (EPR) spectroscopy. Due to the complexity of the systems, hydroquinone was used as a model molecule for computational studies. The interaction of avarol with L-dopa (precursor for catecholamine neurotransmitters) was studied using cyclic voltammetry and ultraviolet-visible spectroscopy. Theoretical computations based on density functional theory (DFT), and quantum theory of atoms in molecules (QTAIM) were employed in order to study interactions between hydroquinone and three radical species: hydroxyl, hydroperoxyl and metoxy radicals. Based on the results of theoretical computations, it was found that the energy barrier for the reaction of hydroquinone with hydroperoxyl radical is significantly higher compared to its reaction with hydroxyl radical. The reaction of hydrogen atom abstraction from the hydroxyl group of hydroquinone by all three radicals follows PCET (proton coupled electron transfer) mechanism. By using the implicite solvent method, it was determined that (in the reactions with hydroxyl and hydroperoxyl radical), the presence of solvent does not affect the mechanism of hydrogen atom transfer..

ANTIRADICAL ACTIVITY OF NEW STRAWBERRY CULTIVAR EXTRACTS INCORPORATED INTO LIPOSOMES – AN EPR STUDY

Strawberries are rich in various health-promoting compounds. A particularly high yield of these molecules could be extracted using methanol which is unfortunately harmful to living beings. To surpass the problem of solvent toxicity, in this paper, we have incorporated methanol extracts of two novel strawberry cultivars into liposomes. Our results show that both extracts possess significant antiradical activity towards hydroxyl and DPPH radicals, unaltered by lipids from liposome membranes. These results indicate that otherwise toxic extracts could easily be turned into a promising pharmaceutical product

Rich in Phenolics—Strong Antioxidant Fruit? Comparative Study of 25 Strawberry Cultivars

Phenolic compounds of 25 newly introduced strawberry cultivars were profiled using spectrophotometry, electron paramagnetic resonance (EPR) spectroscopy, and high-performance liquid chromatography-mass spectrometry. Total phenolic and anthocyanin content (TPC and TACY, respectively), as well as vitamin C, and concentrations of individual phenolic compounds in fruits were evaluated to identify the most promising cultivars according to their phenolic profile. The highest values of TPC, TACY, and vitamin C were recorded in ´Premy´ (1.53 mg eq GA g-1 FW), ´Sandra´ (30.60 mg eq Pg-3-g 100 g-1 FW) and ´Laetitia´ (56.32 mg 100 g-1 FW), respectively. The DPPH and •OH radicals scavenging activity of fruit methanolic extracts was estimated using EPR spectroscopy. All cultivars are almost uniformly effective in the scavenging of •OH radical, while ´Tea´, ´Premy´, and ´Joly´ were marked as highly potent cultivars (over 70%) in terms of DPPH-antiradical activity. Specific peroxidase activities were the highest in ´Garda´, ´Federica´, and ´Rumba´ (0.11, 0.08, and 0.06 U mg-1 prot, respectively). ´Laetitia´, ´Joly´, ´Arianna´, ´Tea´, and ´Mila´ cultivars were distinguished from others as the richest concerning almost all flavonoids and phenolic acids, including some other parameters of bioactivity. These cultivars could be recommended to consumers in terms of fruit as a functional food

Using Density Functional Theory To Study Neutral and Ionized Stacked Thymine Dimers

Stacking interactions in thymine dimers are studied with density functional theory. According to our calculations, six dimers of comparable stability can be prepared at low temperature, but dimerization is impossible at room temperature due to the large entropy contribution that accompanies it. Analysis of vibrational anharmonic coupling terms shows that each of the dimers exhibits distinct vibrational dynamics. Properties of electron density in the intermolecular region are used to analyze neutral stacked species and their ionized forms. Bond paths and critical points in the intermolecular region are identified, but a simple relationship between binding energy and total electron density in the intermolecular critical points could not be found due to an uneven electron distribution in the binding region. The reduced density gradient was confirmed to be a useful tool for analysis of weak stacking interactions. Those interactions also affect vertical and adiabatic ionization energies, which are computed to be slightly lower for the dimers compared to the monomer

The Release of a Highly Cytotoxic Paullone Bearing a TEMPO Free Radical from the HSA Hydrogel: An EPR Spectroscopic Characterization

This study shows the potential of a thermally induced human serum albumin (HSA) hydrogel to serve as a drug depot for sustained release of a highly cytotoxic modified paullone ligand bearing a TEMPO free radical (HL). The binding of HL to HSA was studied by electron paramagnetic resonance (EPR) spectroscopy and imaging. The EPR protocol was also implemented for the study of matrix degradation, and ligand diffusion rate, in two additional spin-labeled hydrogels, containing 5-doxylstearate and 3-carbamoyl-proxyl. The results showed that the hydrogel is an efficient HL reservoir as it retained 60% of the ligand during 11 days of dialysis in physiological saline. Furthermore, upon incubation with Colo 205 human colon adenocarcinoma cells for 3 days, the HL/HSA hydrogel did not exhibit cytotoxic activity, demonstrating that it is also an efficient ligand depot in the presence of living cells. It was observed that the percentage of HL release is independent of its initial concentration in the hydrogel, suggesting that HSA possesses a specific binding site for the ligand, most likely Sudlow site 2, as predicted by molecular docking. The intrinsic property of albumin to bind and transport various substances, including hydrophobic drugs, may be fine- tuned by appropriate physical/chemical hydrogel preparation procedures, providing optimal drug delivery

Electrochemical and spectroscopic study of l‑dopa interaction with avarol

The electrochemistry of catecholamine neurotransmitters and their precursor l-dopa has been widely studied due to their relevance as biologically important compounds. The detection of these compounds from aqueous solution is hindered by the coexistence of quinone or hydroquinone. However, it was suggested that quinones adsorbed on the electrode surface can enhance catechol detection. In order to estimate the degree of interaction between quinones and l-dopa, cyclic voltammetry and UV-Vis spectroscopic study was performed. A sesquiterpenoid hydroquinone, isolated from the marine sponge Dysidea avara (avarol), has been used in this study. The change of apparent heterogeneous rate constant with different avarol/l-dopa ratio indicated that charge transfer could be enhanced at some extent. In addition to this, the obtained results for avarol and hydroquinone (its structural element) were compared. UV-Vis spectroscopic analysis confirmed interaction between l-dopa and avarol or hydroquinone. Taken all together, the interaction of l-dopa was stronger with hydroquinone than with avarol, presumably reflecting the conformational restrains of avarol caused by its terpenoid moiety

Mechanism of Antiradical Activity of Coumarin-Trihydroxybenzohydrazide Derivatives: A Comprehensive Kinetic DFT Study

As part of this study, the mechanisms of the antioxidant activity of previously synthesized coumarin–trihydrobenzohydrazine derivatives were investigated: (E)-2,4-dioxo-3-(1-(2-(2″,3″,4″-trihydroxybenzoyl)hydrazineyl)ethylidene)chroman-7-yl acetate (1) and (E)-2,4-dioxo-3-(1-(2-(3″,4″,5″-trihydroxybenzoyl)hydrazineyl)ethylidene)chroman-7-yl acetate (2). The capacity of the compounds to neutralize HO• was assessed by EPR spectroscopy. The standard mechanisms of antioxidant action, Hydrogen Atom Transfer (HAT), Sequential Proton Loss followed by Electron Transfer (SPLET), Single-Electron Transfer followed by Proton Transfer (SET-PT), and Radical Adduct/Coupling Formation (RAF/RCF) were examined using the QM-ORSA methodology. It was estimated that the newly synthesized compounds, under physiological conditions, exhibited antiradical activity via SPLET and RCF mechanisms. Based on the estimated overall rate constants (koverall), it can be concluded that 2 exhibited a greater antiradical capacity. The obtained values indicated a good correlation with the EPR spectroscopy results. Both compounds exhibit approximately 1.5 times more activity in comparison to the precursor compound used in the synthesis (gallic acid)

Chemical Composition, Antioxidant Potential, and Nutritional Evaluation of Cultivated Sorghum Grains: A Combined Experimental, Theoretical, and Multivariate Analysis

Sorghum grain (Sorghum bicolor L. Moench) is a gluten-free cereal with excellent nutritional value and is a good source of antioxidants, including polyphenols, as well as minerals with proven health benefits. Herein, the phenolic composition, elemental profile, and antioxidant activity of sixteen food-grade sorghum grains (S1–S16) grown under agroecological conditions in Serbia were determined. Nine phenolic compounds characteristic of sorghum grains, such as luteolinidin, 5-methoxyluteolinidin, luteolidin derivative, luteolidin glucoside, apigeninidin, 7-methoxyapigeninidin, apigeninidin glucoside, and cyanidin derivative, were quantified. The antioxidant potential of the analyzed sorghum grains was evaluated by UV/Vis (DPPH, ABTS, and FRAP) and Electron Paramagnetic Resonance spectroscopy (hydroxyl and ascorbyl radical scavenging assays). The content of macro- and microelements was determined by Inductively Coupled Plasma Optical Emission spectroscopy. Theoretical daily intakes of selected major and trace elements were assessed and compared with the Recommended Daily Allowance or Adequate Intake. Sample S8 had the highest amount of phenolic compounds, while S4, S6, and S8 exhibited the strongest antioxidative potential. The sorghum studied could completely satisfy the daily needs of macro- (K, Mg, and P) and microelements (Se, Zn, Fe). Pattern recognition techniques confirmed the discrimination of samples based on phenolic profile and elemental analysis and recognized the main markers responsible for differences between the investigated samples. The reaction between hydroxyl radicals and luteolinidin/apigeninidin was investigated by Density Functional Theory and thermodynamically preferred mechanism was determined

The Release of a Highly Cytotoxic Paullone Bearing a TEMPO Free Radical from the HSA Hydrogel: An EPR Spectroscopic Characterization

This study shows the potential of a thermally induced human serum albumin (HSA) hydrogel to serve as a drug depot for sustained release of a highly cytotoxic modified paullone ligand bearing a TEMPO free radical (HL). The binding of HL to HSA was studied by electron paramagnetic resonance (EPR) spectroscopy and imaging. The EPR protocol was also implemented for the study of matrix degradation, and ligand diffusion rate, in two additional spin-labeled hydrogels, containing 5-doxylstearate and 3-carbamoyl-proxyl. The results showed that the hydrogel is an efficient HL reservoir as it retained 60% of the ligand during 11 days of dialysis in physiological saline. Furthermore, upon incubation with Colo 205 human colon adenocarcinoma cells for 3 days, the HL/HSA hydrogel did not exhibit cytotoxic activity, demonstrating that it is also an efficient ligand depot in the presence of living cells. It was observed that the percentage of HL release is independent of its initial concentration in the hydrogel, suggesting that HSA possesses a specific binding site for the ligand, most likely Sudlow site 2, as predicted by molecular docking. The intrinsic property of albumin to bind and transport various substances, including hydrophobic drugs, may be fine-tuned by appropriate physical/chemical hydrogel preparation procedures, providing optimal drug delivery