Exploring enzyme inhibition and comprehensive mechanisms of antioxidant/prooxidative activity of natural furanocoumarin derivatives: A comparative kinetic DFT study

This study aimed to explore the antioxidant and prooxidative activity of two natural furanocoumarin derivatives, Bergaptol (4-Hydroxy-7H-furo [3,2-g] [1]benzopyran-7-one, BER) and Xanthotoxol (9-Hydroxy-7H-furo [3,2-g] [1]benzopyran-7-one, XAN). The collected thermodynamic and kinetic data demonstrate that both compounds possess substantial antiradical activity against HO• and CCl3OO• radicals in physiological conditions. BER exhibited better antiradical activity in comparison to XAN, which can be attributed to the enhanced deprotonation caused by the positioning of the -OH group on the psoralen ring. In contrast to highly reactive radical species, newly formed radical species BER• and XAN• exhibited negligible reactivity towards the chosen constitutive elements of macromolecules (fatty acids, amino acids, nucleobases). Furthermore, in the presence of O2•─, the ability to regenerate newly formed radicals BER• and XAN• was observed. Conversely, in physiological conditions in the presence of Cu(II) ions, both compounds exhibit prooxidative activity. Nevertheless, the prooxidative activity of both compounds is less prominent than their antioxidant activity. Furthermore, it has been demonstrated that anionic species can engage in the creation of a chelate complex, which restricts the reduction of metal ions when reducing agents are present (O2•─ and Asc─). Moreover, studies have demonstrated that these chelating complexes can be coupled with other radical species, hence enhancing their ability to inactivate radicals. Both compounds exhibited substantial inhibitory effects against enzymes involved in the direct or indirect generation of ROS: Xanthine Oxidase (XOD), Lipoxygenase (LOX), Myeloperoxidase (MPO), NADPH oxidase (NOX).

Stability of Coumarins and Determination of the Net Iron Oxidation State of Iron-Coumarin Complexes: Implications for Examining Plant Iron Acquisition Mechanisms

Coumarins are exuded into the soil environment by plant roots in response to iron (Fe) deficiency. Previous studies have shown that coumarins can increase the Fe solubility upon interaction with sparsely soluble Fe(III) (hydr)oxide. However, the chemical mechanisms of Fe(III) (hydr)oxide dissolution by coumarins remain unclear. The high redox instability of dissolved coumarins and the interference of coumarins in determining the Fe redox state hinder the quantitative and mechanistic investigation of coumarin-induced Fe mobilization. In this study, we investigated the oxidative stability of three coumarins that have been found in root exudates, esculetin, scopoletin, and fraxetin, over a broad pH range under oxic and anoxic conditions. Our results show that the oxidation of coumarins is irreversible under oxic conditions and that oxidative degradation rates increased with increasing pH under both oxic and anoxic conditions. However, the complexation of Fe protects coumarins from degradation in the circumneutral pH range even under oxic conditions. Furthermore, we observed that Ferrozine, which is commonly used for establishing Fe redox speciation, can facilitate the reduction of Fe(III) complexed by coumarins, even at circumneutral pH. Reduction rates increased with decreasing pH and were larger for fraxetin than for scopoletin and esculetin. Based on these observations, we optimized the Ferrozine method for determining the redox state of Fe complexed by coumarins. Understanding the stability of dissolved coumarins and using a precise analytical method to determine the redox state of Fe in the presence of coumarins are critical for investigating the mechanisms by which coumarins enhance the availability of Fe in the rhizosphere.

Theoretical Insights into the Oxidative Stress-Relieving Properties of Pinocembrin─An Isolated Flavonoid from Honey and Propolis

Bee products are a valuable group of substances that have a wide range of applications for humans. They contain a high level of polyphenolic compounds, which have been shown to combat radicals and effectively reduce oxidative stress. In this study, density functional theory was utilized to determine the anti-OOH activity, sequestration of free Cu(II) and Fe(III) ions, the potential pro-oxidative activity of the formed complexes, and the repairing capabilities toward essential biomolecules. The kinetic constants for scavenging of hydroperoxide radical were found to be low, with an order of magnitude not exceeding 10-3 M-1 s-1. Chelating properties showed slightly more satisfactory outcomes, although most complexes exhibited pro-oxidant activity. Pinocembrin, however, proved effective in repairing oxidatively damaged biological compounds and restoring their original functionality. The study found that whilst the system displays limited type I and type II antioxidant activity, it may support the role of physiological reductants already present in the biological matrix.

The chemical ecology of coumarins and phenazines affects iron acquisition by pseudomonads

Secondary metabolites are important facilitators of plant-microbe interactions in the rhizosphere, contributing to communication, competition, and nutrient acquisition. However, at first glance, the rhizosphere seems full of metabolites with overlapping functions, and we have a limited understanding of basic principles governing metabolite use. Increasing access to the essential nutrient iron is one important, but seemingly redundant role performed by both plant and microbial Redox-Active Metabolites (RAMs). We used coumarins, RAMs made by the model plant Arabidopsis thaliana, and phenazines, RAMs made by soil-dwelling pseudomonads, to ask whether plant and microbial RAMs might each have distinct functions under different environmental conditions. We show that variations in oxygen and pH lead to predictable differences in the capacity of coumarins vs phenazines to increase the growth of iron-limited pseudomonads and that these effects depend on whether pseudomonads are grown on glucose, succinate, or pyruvate: carbon sources commonly found in root exudates. Our results are explained by the chemical reactivities of these metabolites and the redox state of phenazines as altered by microbial metabolism. This work shows that variations in the chemical microenvironment can profoundly affect secondary metabolite function and suggests plants may tune the utility of microbial secondary metabolites by altering the carbon released in root exudates. Together, these findings suggest that RAM diversity may be less overwhelming when viewed through a chemical ecological lens: Distinct molecules can be expected to be more or less important to certain ecosystem functions, such as iron acquisition, depending on the local chemical microenvironments in which they reside.

Quantum-mechanical characteristics of apigenin: Antiradical, metal chelation and inhibitory properties in physiologically relevant media

Density functional theory was used to examine the antioxidant activity of apigenin. All protonated species that are present in a non-negligible population at physiological pH were considered in the study. The ability to scavenge the hydroperoxide radical was evaluated in lipid and aqueous environments. The capacity to halt the Fenton reaction by chelating Fe(III) and Cu(II) ions was also investigated, as was the ability to inhibit xanthine oxidase. The results indicate that these activities may be particularly important in describing the beneficial effects of apigenin, especially because of its lower anti-•OOH potential than Trolox or vitamin C. The findings underscore the significant role of dianion in the antiradical and chelating properties, despite its presence in much lower molar fractions than other ions.

Post-autotomy regeneration of respiratory tree in sea cucumber Holothuria parva

The respiratory trees present only in the class Holothuroidea and the rest of the echinoderms lack it. Only some holothurian species have the ability to regenerate their respiratory trees after autotomy. Therefore, respiratory trees could be considered as a suitable model to assess the regeneration mechanisms in animals. In the present study, the respiratory tree regeneration after posterior evisceration were examined in Holothuria parva during 75 days. Since autotomy reduces antioxidant defense in the organisms, in the present study alterations of antioxidant enzymes were also evaluated during the experiment. H. parva is the dominant intertidal species distributed in the north of the Persian Gulf. In the present study, H. parva ejected the left respiratory tree, the digestive tract and supportive mesenteries from the anus, about 1-2 min after potassium chloride injection. The closure of the opening at the posterior ends of the body was the first reaction to the injury. Seven days after evisceration, the small bud formed on the dorsal side of the cloaca which was covered with the coelomic epithelium of cloaca. The coelomic epithelium started to proliferate to undifferentiated cells on the apex of the buds. The primary respiratory tree consisted of the luminal cuboidal epithelium and thin connective tissue surrounded by the slender coelomic epithelium. This preliminary organ was observed at the apex of the buds, 13 days after evisceration. Gradually, myoepithelial cells arranged around a longitudinal axis and formed a circular muscle. The primitive branches of primary respiratory tree started to form 18 days after evisceration. Forty days after evisceration, the luminal epithelium of the respiratory tree had the same appearance as the intact luminal epithelium. The regenerated respiratory tree was histomorphologically very similar to an intact respiratory tree 56 days postevisceration, but unlike that, it was not yet wrapped around the intestine and was completely separate from it. Despite the development of the regenerating respiratory tree, no wrapping around the intestine was observed until the end of the experiment. According to the results, the activity of the catalase (CAT) and superoxide dismutase (SOD) in the muscle homogenate was significantly higher than the control 5 days after evisceration. The CAT and SOD levels gradually decreased in eviscerated animals. The lipid peroxidation level followed a decreasing trend in the eviscerated animals during the experiment. However, its value reduced to the control level at the end of the experiment.

New insights into the competition between antioxidant activities and pro-oxidant risks of rosmarinic acid

Direct and indirect antioxidant activities of rosmarinic acid (RA) based on HOO˙/CH3OO˙ radical scavenging and Fe(iii)/Fe(ii) ion chelation were theoretically studied using density functional theory at the M05-2X/6-311++G(2df,2p) level of theory. First, four antioxidant mechanisms including hydrogen atom transfer (HAT), radical adduct formation (RAF), proton loss (PL) and single electron transfer (SET) were investigated in water and pentyl ethanoate (PEA) phases. Regarding the free radical scavenging mechanism, HAT plays a decisive role with overall rate coefficients of 1.84 × 103 M-1 s-1 (HOO˙) and 4.49 × 103 M-1 s-1 (CH3OO˙) in water. In contrast to PL, RAF and especially SET processes, the HAT reaction in PEA is slightly more favorable than that in water. Second, the [Fe(iii)(H2O)6]3+ and [Fe(ii)(H2O)6]2+ ion chelating processes in an aqueous phase are both favorable and spontaneous especially at the O5, site-1, and site-2 positions with large negative Δr G 0 values and great formation constant K f. Finally, the pro-oxidant risk of RA- was also considered via the Fe(iii)-to-Fe(ii) complex reduction process, which may initiate Fenton-like reactions forming reactive HO˙ radicals. As a result, RA- does not enhance the reduction process when ascorbate anions are present as reducing agents, whereas the pro-oxidant risk becomes remarkable when superoxide anions are found. The results encourage further attempts to verify the speculation using more powerful research implementations of the antioxidant activities of rosmarinic acid in relationship with its possible pro-oxidant risks.

The hydroperoxyl and superoxide anion radical scavenging activity of anthocyanidins in physiological environments: Theoretical insights into mechanisms and kinetics

The HOO^• and O₂^•- scavenging activities of 12 natural anthocyanidins were investigated in physiological environments by using DFT calculations. The results suggest high HOO^• scavenging activity in aqueous medium with overall rate constants in the range of k_overall = 1.58 × 10⁸ - 7.59 × 10⁹ M^-1 s^-1, whereas in lipid medium only weak activity is predicted. O₂^•- scavenging is also fast in water with k_app = ∼10⁹ M^-1 s^-1. Like in the case of many other antioxidants that contain acidic moieties, the anion states (H₃A^- and H₂A^2-) and the single electron transfer mechanism play a dominant role in the HOO^• scavenging activity of anthocyanidins in water at pH = 7.4. Analysis of the mechanism suggests that the O₂^•- and HOO^• radical scavenging can occur as a regeneration cycle that might increase the protective efficiency of anthocyanidins against oxidative stress.

Preparation of Fraxetin Long Circulating Liposome and Its Anti-enteritis Effect

This study sought to improve the oral bioavailability and enhance the anti-enteritis effect of fraxetin by incorporating it into long circulating liposomes (F-LC-Lipo). The optimal formulation of F-LC-Lipo was obtained via orthogonal design. The particle size, morphology, encapsulation efficiency, stability, and anti-enteritis effect of F-LC-Lipo were evaluated. The particle size of F-LC-Lipo was 166.65 ± 8.75 nm with entrapment efficiency (EE) of 92.18 ± 0.17%. The release rate in different dissolution media (pH 1.2 HCl, DDW, and pH 7.4 PBS) was significantly higher than that of fraxetin solution. Compared with the free fraxetin solution, F-LC-Lipo increased oral bioavailability of fraxetin by 4.43 times (443%). More importantly, F-LC-Lipo could improve the levels of interleukin-1 beta (IL-1β), IL-6, malondialdehyde (MDA), superoxide dismutase (SOD), tumor necrosis factor-alpha (TNF-α), C-reactive protein (CRP), prostaglandin E2 (PEG2), and IL-10 in rats with enteritis. Overall, these results suggested that LC-Lipo may serve as a potential carrier for improving the solubility and oral bioavailability of fraxetin as well as improving its enteritis effect.

An Overview of Coumarin as a Versatile and Readily Accessible Scaffold with Broad-Ranging Biological Activities

Privileged structures have been widely used as an effective template for the research and discovery of high value chemicals. Coumarin is a simple scaffold widespread in Nature and it can be found in a considerable number of plants as well as in some fungi and bacteria. In the last years, these natural compounds have been gaining an increasing attention from the scientific community for their wide range of biological activities, mainly due to their ability to interact with diverse enzymes and receptors in living organisms. In addition, coumarin nucleus has proved to be easily synthetized and decorated, giving the possibility of designing new coumarin-based compounds and investigating their potential in the treatment of various diseases. The versatility of coumarin scaffold finds applications not only in medicinal chemistry but also in the agrochemical field as well as in the cosmetic and fragrances industry. This review is intended to be a critical overview on coumarins, comprehensive of natural sources, metabolites, biological evaluations and synthetic approaches.

Isolation and Purification of Bioactive Compounds from the Stem Bark of Jatropha podagrica

This paper reports the successive isolation and purification of bioactive compounds from the stem bark of Jatropha podagrica, a widely known medicinal plant. The ethyl acetate extract of the stem bark exhibited the strongest antioxidant activity assessed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, and ferric reducing antioxidant power (FRAP) assays (IC₅₀ = 46.7, 66.0, and 492.6, respectively). By column chromatography (CC) with elution of hexane and ethyl acetate at 8:2, 7:3, and 6:4 ratios, the isolation of this active extract yielded five fractions (C1–C5). Chemical structures of the constituents included in C1–C5 were elucidated by gas chromatography-mass spectrometry (GC-MS), electrospray ionization-mass spectrometry (ESI-MS), and nuclear magnetic resonance (NMR) and resolved as methyl gallate (C1, C2, C3, C4), gallic acid (C1, C2), fraxetin (C2, C3, C4, C5), and tomentin (C3). Mixture C2 (IC₅₀ DPPH and ABTS = 2.5 µg/mL) and C3 (IC₅₀ FRAP = 381 µg/mL) showed the highest antioxidant properties. Among the isolated fractions, C4 was the most potential agent in growth inhibition of six bacterial strains including Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Listeria monocytogenes,Bacillus subtilis, and Proteus mirabilis (MIC = 5, 20, 30, 20, 25, and 20 mg/mL, respectively). All identified constituents exerted an inhibitory activity on the growth of Lactuca sativa, of which the mixture C3 performed the maximal inhibition on shoot (IC₅₀ = 49.4 µg/mL) and root (IC₅₀ = 47.1 µg/mL) growth. Findings of this study suggest that gallic acid, methyl gallate, fraxetin, and tomentin isolated from J. podagrica possessed antioxidant, antibacterial, and growth inhibitory potentials.

Comprehensive Investigation of the Antioxidant and Pro-oxidant Effects of Phenolic Compounds: A Double-Edged Sword in the Context of Oxidative Stress?

Oxidative stress (OS) is a health-threatening process that is involved, at least partially, in the development of several diseases. Although antioxidants can be used as a chemical defense against OS, they might also exhibit pro-oxidant effects, depending on environmental conditions. In this work, such a dual behavior was investigated for phenolic compounds (PhCs) within the framework of the density functional theory and based on kinetic data. Multiple reaction mechanisms were considered in both cases. The presence of redox metals, the pH, and the possibility that PhCs might be transformed into benzoquinones were identified as key aspects in the antioxidant versus pro-oxidant effects of these compounds. The main virtues of PhCs as antioxidants are their radical trapping activity, their regeneration under physiological conditions, and their behavior as OH-inactivating ligands. The main risks of PhCs as pro-oxidants are predicted to be the role of phenolate ions in the reduction of metal ions, which can promote Fenton-like reactions, and the formation of benzoquinones that might cause protein arylation at cysteine sites. Although the benefits seem to overcome the hazards, to properly design chemical strategies against OS using PhCs, it is highly recommended to carefully explore their duality in this context.

Coumarins improved type 2 diabetes induced by high-fat diet and streptozotocin in mice via antioxidation

Coumarins extensively exist in plants and are utilized against diabetes in some folk medicines. Recent studies have demonstrated that oxidative stress plays a crucial role in the etiology and pathogenesis of diabetes mellitus. We investigated the antioxidant ability of 3 coumarins (osthole, esculin, and fraxetin) in type 2 diabetes. After being fed a high-fat diet, ICR mice were exposed to low doses of streptozotocin and then treated with experimental coumarins for 5 weeks. We found osthole, esculin, and metformin significantly lowered fasting blood glucose, HOMA-IR, and 3 blood lipids (total cholesterol, total triglyceride, free fatty acids), and increased insulin levels, while fraxetin only enhanced insulin levels and lessened free fatty acids. Both osthole and esculin had antioxidative effects in pancreas through elevating the activities of glutathione peroxidase, catalase, and superoxide dismutase; fraxetin, however, merely heightened catalase activity. By contrast, 3 coumarins significantly increased those antioxidase activities in liver. Hematoxylin and eosin staining revealed 3 coumarins, especially osthole, attenuated cellular derangement, blurry fringes of hepatic sinusoid and extensive vacuolization due to hepatocellular lipid accumulation, and lessened inflammatory infiltration in pancreas. The glomerular and islet structure of diabetic mice were improved, with reduced mesangial matrix and glomerular basement membrane thickening. Therefore, our study supports that coumarins could be promising candidates against type 2 diabetes through antioxidative mechanisms.

Coumarins as potential antidiabetic agents

OBJECTIVES

Even with great advances in modern medicine and therapeutic agent development, the search for effective antidiabetic drugs remains challenging. Coumarins are secondary metabolites found widely in nature plants and used mainly in anticoagulation and antithrombotic therapy. Over the past two decades, however, there has been an increasing body of literatures related to the effects of coumarins and their derivatives on diabetes and its complications. This review aimed to focus on research findings concerning the effects of coumarins against diabetes and its complications using in-vitro and in-vivo animal models, and also to discuss cellular and molecular mechanisms underlying these effects.

KEY FINDINGS

The search for new coumarins against diabetes and it complications, either isolated from traditional medicine or chemically synthesized, has been constantly expanding. The cellular and molecular mechanisms involved include protecting pancreatic beta cells from damage, improving abnormal insulin signalling, reducing oxidative stress/inflammation, activating AMP-activated protein kinase (AMPK), inhibiting α-glucosidases and ameliorating diabetic complications.

CONCLUSIONS

The effects and mechanisms of coumarins and their derivatives upon diabetes and its complications are discussed in current review. Further investigations remain to be carried out to develop a promising antidiabetic agent based on coumarin cores.

Regeneration of tert-butylhydroquinone by tea polyphenols

To study the antioxidant capacity (AC) regeneration of tert-butylhydroquinone (TBHQ) by tea polyphenols (TPs), a separable system has been designed for its evaluation. The AC values of three natural food matrices (liquorice, oat, and ginger) and TBHQ regenerated by TPs were all higher than their controls, and similar to the initial values (p<0.05). The average regeneration efficiency (RE) value was 1.49 for these three natural food matrices, and 0.82 for TBHQ. Electron paramagnetic resonance spectroscopy analysis has revealed the synergistic effect of TBHQ and TPs, which arose from the regeneration of TBHQ by TPs. The RE value of TBHQ regeneration by TPs embedded in a gelatine membrane was 0.51. The results demonstrated that TPs showed a capacity for regenerating TBHQ, indicating a potential application in regenerative packaging, whereby one antioxidant would be added to the food matrix, with another one as the regenerator incorporated into the packaging material.

Reactions of hydroxyl radicals with benzoic acid and benzoate

Density functional theory was used to study the mechanism and kinetics of benzoic acid with hydroxyl radicals in both gas and aqueous phases as well as benzoate with hydroxyl radicals in the aqueous phase at the M06-2X/6-311+G(d,p) level of theory.

Phenolic Melatonin-Related Compounds: Their Role as Chemical Protectors against Oxidative Stress

There is currently no doubt about the serious threat that oxidative stress (OS) poses to human health. Therefore, a crucial strategy to maintain a good health status is to identify molecules capable of offering protection against OS through chemical routes. Based on the known efficiency of the phenolic and melatonin (MLT) families of compounds as antioxidants, it is logical to assume that phenolic MLT-related compounds should be (at least) equally efficient. Unfortunately, they have been less investigated than phenols, MLT and its non-phenolic metabolites in this context. The evidence reviewed here strongly suggests that MLT phenolic derivatives can act as both primary and secondary antioxidants, exerting their protection through diverse chemical routes. They all seem to be better free radical scavengers than MLT and Trolox, while some of them also surpass ascorbic acid and resveratrol. However, there are still many aspects that deserve further investigations for this kind of compounds.

Simultaneous determination of fraxin and its metabolite, fraxetin, in rat plasma by liquid chromatography-tandem mass spectrometry and its application in a pharmacokinetic study

For the first time, a rapid and sensitive high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of fraxin and its metabolite, fraxetin, in rat plasma, using esculin as the internal standard (IS). The plasma samples were precipitated with methanol before separation on an Nova-Pak C18 column (150mm×3.9mm, 3μm) using a mobile phase consisting of 0.1% formic acid and methanol (55:45) at a flow rate of 0.8mL/min. The analytes were detected by multiple reaction monitoring in the negative ion mode with the mass transitions at m/z 368.9→ m/z 191.9 (fraxin), m/z 206.9→ m/z 191.8 (fraxetin) and m/z 339.0→ m/z 176.9 (esculin, IS). The results demonstrated that the calibration curves for both analytes have good linearity (r≥0.995) over a concentration range of 5.00-3000ng/mL. The assay was validated according to the regulatory bioanalytical guidelines and proved acceptable. The intra- and inter-day precisions (R.S.D.%) were within 10.9% for both analytes, whereas the deviation of assay accuracies (R.E.%) ranged from -5.3 to 1.0%. The method was successfully applied to a pharmacokinetic study after a single oral dose of fraxin at 50mg/kg to rats.

Potential hepatoprotective effects of fullerenol nanoparticles on alcohol-induced oxidative stress by ROS

The free radical scavenging ability of fullerenols is their most exploited property in biomedical studies.

Computational-aided design of melatonin analogues with outstanding multifunctional antioxidant capacity

The IIcD melatonin-analogue was identified as the most promising multifunctional antioxidant from a set of 19, and better for that purpose than the parent molecule and Trolox.

Assessing the Protective Activity of a Recently Discovered Phenolic Compound against Oxidative Stress Using Computational Chemistry

The protection exerted by 3,5-dihydroxy-4-methoxybenzyl alcohol (DHMBA), a phenolic compound recently isolated from the Pacific oyster, against oxidative stress (OS) is investigated using the density functional theory. Our results indicate that DHMBA is an outstanding peroxyl radical scavenger, being about 15 times and 4 orders of magnitude better than Trolox for that purpose in lipid and aqueous media, respectively. It was also found to react faster with HOO(•) than other known antioxidants such as resveratrol and ascorbic acid. DHMBA is also predicted to be able to sequester Cu(II) ions, consequently inhibiting the OS induced by Cu(II)-ascorbate mixtures and downgrading the (•)OH production via the Haber-Weiss reaction. However, it is proposed that DHMBA is more efficient as a primary antioxidant (free radical scavenger), than as a secondary antioxidant (metal ion chelator). In addition, it was found that DHMBA can be efficiently regenerated in aqueous solution, at physiological pH. Such regeneration is expected to contribute to increase the antioxidant protection exerted by DHMBA. These results suggest that probably synthetic routes for this compound should be pursued, because albeit its abundance in nature is rather low, its antioxidant activity is exceptional.

Adrenaline and noradrenaline: protectors against oxidative stress or molecular targets?

Density functional theory was used to investigate the potential role of neurotransmitters adrenaline and noradrenaline regarding oxidative stress. It is predicted that they can be efficient as free radical scavengers both in lipid and aqueous media, with the main reaction mechanism being the hydrogen transfer and the sequential proton loss electron transfer, respectively. Despite the polarity of the environment, adrenaline and noradrenaline react with (•)OOH faster than Trolox, which suggests that they are better peroxyl radical scavengers than the reference compound. Both catecholamines are also proposed to be capable of efficiently inhibiting the oxidative stress induced by copper(II)-ascorbate mixtures, and the (•)OH production via Haber-Weiss reaction, albeit the effects on the later are only partial. They exert such beneficial effects by sequestering Cu(II) ions. In summary, these catecholamines can be capable of reducing oxidative stress, by scavenging free radicals and by sequestering metal ions. However, at the same time they might lose their functions in the process due to the associated structural modifications. Consequently, adrenaline and noradrenaline can be considered as both protectors and molecular targets of oxidative stress. Fortunately, under the proper conditions, both catecholamines can be regenerated to their original form so their functions are restored.

Antioxidant vs. prooxidant action of phenothiazine in a biological environment in the presence of hydroxyl and hydroperoxyl radicals: a quantum chemistry study

In aqueous solution, phenothiazine regenerates and acts as an excellent antioxidant while in lipid media, it behaves as a prooxidant.