Structure-activity relationship of antioxidants for inhibitors of linoleic acid hydroperoxide-induced toxicity in cultured human umbilical vein endothelial cells

Unmasking the Antifungal Activity of Anacardium occidentale Leaf Extract against Candida albicans

Invasive fungal disease causes high morbidity and mortality among immunocompromised patients. Resistance to conventional antifungal drugs and the toxicity associated with high doses highlight the need for effective antifungal therapies. In this study, the antifungal potential of the ethanolic extract of Anacardium occidentale (Cashew Leaf) leaves were evaluated against Candida albicans and C. auris. The antifungal activity was tested by the broth microdilution method and growth kinetic test. To further explore its antifungal action mode, spectrofluorophotometry, confocal microscopy and scanning and transmission electron microscopy were performed. Additionally, heterozygous knockout strains associated with resistance to oxidative stress were included in the study. We found that A. occidentale could inhibit the proliferation and growth of C. albicans at concentrations of 62.5 and 125 μg/mL. The doubling time was also drastically affected, going from 2.8 h to 22.5 h, which was also observed in C. auris. The extract induced the accumulation of intracellular reactive oxygen species (ROS), resulting in endoplasmic reticulum stress and mitochondrial dysfunction, while it did not show cytotoxicity or hemolytic activity at the concentrations evaluated. Our work preliminarily elucidated the potential mechanisms of A. occidentale against C. albicans on a cellular level, and might provide a promising option for the design of a new treatment for invasive candidiasis.

Therapeutic efficacy of mitochondria-targeted esculetin in the improvement of NAFLD-NASH via modulating AMPK-SIRT1 axis

Mitochondrial dysfunction due to deregulated production of mitochondria-derived ROS is implicated in the development and progression of non-alcoholic fatty liver disease (NAFLD) to non-alcoholic steatohepatitis (NASH). Recently, we synthesized a novel mitochondria-targeted esculetin (Mito-Esc) and investigated its dose-response therapeutic efficacy in mitigating high-fat diet (HFD)-induced NAFLD and NASH in Apoe-/- mice. Mito-Esc administration, compared to simvastatin and pioglitazone, dose-dependently caused a significant reduction in body weight, improved lipid profile, glucose homeostasis, and pro-inflammatory cytokines level. Mito-Esc administration reduced adipose tissue hypertrophy and lipid accumulation presumably by regulating the levels of CD36, PPAR-γ, EBP-α, and their target genes. Mechanistically, Mito-Esc-induced activation of the AMPK1α-SIRT1 axis inhibited pre-adipocyte differentiation. Conversely, Mito-Esc failed to regulate pre-adipocyte differentiation under AMPK/SIRT1 depleted conditions. In parallel, Mito-Esc administration ameliorated HFD-induced steatosis, fibrosis of the liver, and NAFLD-associated atheromatous plaque formation in the aorta. Importantly, Mito-Esc administration inhibited HFD-induced infiltration of macrophages, a marker of steatohepatitis, in the adipose and liver tissues. The results of the in vitro studies showed that Mito-Esc treatment significantly inhibits TGF-β-induced hepatic stellate cell differentiation as well as the fibrotic markers. Consistent with the above observations, Mito-Esc treatment by activating the AMPK-SIRT1 pathway markedly reversed palmitate-induced mitochondrial superoxide production, depolarization of mitochondrial membrane potential, and lipid accumulation in HepG2 cells. Together, the therapeutic efficacy of Mito-Esc in the mitigation of HFD-induced lipotoxicity, and the associated NASH is in part, mediated by potentiating the AMPK-SIRT1 axis.

Improvement effects of esculetin on the formation and development of atherosclerosis

Atherosclerosis is one of the potential causes of death in patients with cardiovascular disease. With the discovery of new anti atherosclerotic drugs becoming the pursuit of the pharmaceutical industry, natural products have attracted more and more attention because of their unique efficacy in the treatment of atherosclerosis. More and more studies have shown that esculetin, a coumarin mainly found in cortex fraxini, can improve atherosclerosis by participating in cellular antioxidant responses and reducing inflammation related pathogenesis. This paper summarizes the researches of esculetin on anti-atherosclerosis in the past two decades. Esculetin plays an anti atherosclerotic role through reducing blood triglyceride level, preventing the proliferation of vascular smooth muscle cells (VSMC) and the production of matrix metallopeptidase 9 (MMP-9), inhibiting the oxidation of low density lipoprotein (LDL) and the secretion of adhesion factors and chemokines, and increasing the outflow level of high density lipoprotein cholesterol (HDL-C). Esculetin is safe and reliable, easy to be absorbed by the body and can be synthesized in a variety of ways. Although there are still few clinical studies on anti-atherosclerosis, in vivo experiments have proved that esculetin has high bioavailability. From the current research, the anti-atherosclerotic effect of esculetin is positive and encouraging. However, much work remains to be done to clarify the molecular mechanism of esculetin in the treatment of atherosclerosis.

AMPK, Mitochondrial Function, and Cardiovascular Disease

Adenosine monophosphate-activated protein kinase (AMPK) is in charge of numerous catabolic and anabolic signaling pathways to sustain appropriate intracellular adenosine triphosphate levels in response to energetic and/or cellular stress. In addition to its conventional roles as an intracellular energy switch or fuel gauge, emerging research has shown that AMPK is also a redox sensor and modulator, playing pivotal roles in maintaining cardiovascular processes and inhibiting disease progression. Pharmacological reagents, including statins, metformin, berberine, polyphenol, and resveratrol, all of which are widely used therapeutics for cardiovascular disorders, appear to deliver their protective/therapeutic effects partially via AMPK signaling modulation. The functions of AMPK during health and disease are far from clear. Accumulating studies have demonstrated crosstalk between AMPK and mitochondria, such as AMPK regulation of mitochondrial homeostasis and mitochondrial dysfunction causing abnormal AMPK activity. In this review, we begin with the description of AMPK structure and regulation, and then focus on the recent advances toward understanding how mitochondrial dysfunction controls AMPK and how AMPK, as a central mediator of the cellular response to energetic stress, maintains mitochondrial homeostasis. Finally, we systemically review how dysfunctional AMPK contributes to the initiation and progression of cardiovascular diseases via the impact on mitochondrial function.

Relationship between the Physiochemical Properties of Cocoa Procyanidins and Their Ability to Inhibit Lipid Oxidation in Liposomes

The aim of this paper is to evaluate the effects of cocoa polyphenols and procyanidins with different degrees of polymerization that are encapsulated in liposome delivery systems on the inhibition of lipid oxidation at pH 3.0 and 5.0. In general, liposomes at pH 3.0 and 5.0 were physically stable in the presence of polyphenols and procyanidins with mean particle sizes of 56.56 ± 12.29 and 77.45 ± 8.67 nm and ζ-potentials of -33.50 ± 3.16 and -20.44 ± 1.98 mV at pH 3.0 and 5.0, respectively. At both pH 3.0 and pH 5.0, all the polyphenols and procyanidins inhibited lipid hydroperoxide and hexanal formation, and antioxidant activities increased with increasing polymer-chain sizes. The greater antioxidant activities of the isolated procyanidins were likely due to their increased metal-chelating capacities, as determined by ferric-reducing-ability (FRAP) assays, and their greater levels of partitioning into the lipids, as determined by their log K_ow values and encapsulation efficiencies. The crude extract had the greatest antioxidant activity, which could be because other antioxidants were present, or combinations of the different polyphenols and procyanidins inhibited lipid oxidation synergistically.

Mitochondria-targeted esculetin alleviates mitochondrial dysfunction by AMPK-mediated nitric oxide and SIRT3 regulation in endothelial cells: potential implications in atherosclerosis

Mitochondria-targeted compounds are emerging as a new class of drugs that can potentially alter the pathophysiology of those diseases where mitochondrial dysfunction plays a critical role. We have synthesized a novel mitochondria-targeted esculetin (Mito-Esc) with an aim to investigate its effect during oxidative stress-induced endothelial cell death and angiotensin (Ang)-II-induced atherosclerosis in ApoE^−/− mice. Mito-Esc but not natural esculetin treatment significantly inhibited H2O2- and Ang-II-induced cell death in human aortic endothelial cells by enhancing NO production via AMPK-mediated eNOS phosphorylation. While L-NAME (NOS inhibitor) significantly abrogated Mito-Esc-mediated protective effects, Compound c (inhibitor of AMPK) significantly decreased Mito-Esc-mediated increase in NO production. Notably, Mito-Esc promoted mitochondrial biogenesis by enhancing SIRT3 expression through AMPK activation; and restored H2O2-induced inhibition of mitochondrial respiration. siSIRT3 treatment not only completely reversed Mito-Esc-mediated mitochondrial biogenetic marker expressions but also caused endothelial cell death. Furthermore, Mito-Esc administration to ApoE^−/− mice greatly alleviated Ang-II-induced atheromatous plaque formation, monocyte infiltration and serum pro-inflammatory cytokines levels. We conclude that Mito-Esc is preferentially taken up by the mitochondria and preserves endothelial cell survival during oxidative stress by modulating NO generation via AMPK. Also, Mito-Esc-induced SIRT3 plays a pivotal role in mediating mitochondrial biogenesis and perhaps contributes to its anti-atherogenic effects.

Aggregation induced emission from α-napthoflavone microstructures and its cyto-toxicity

α-Napthoflavone (ANF) microstructures of various morphologies were synthesized using reprecipitation method. Sodium Dodecyl Sulfate (SDS) was used as morphology directing agent. The morphologies of the particles were characterized using optical and scanning electron microscopy (SEM). Single crystal data of ANF suggests that the aromatic units of ANF are in parallel slipped conformation in its aggregated form. Photophysical properties of aggregated ANF hydrosol were studied using UV-Vis absorption, steady state and time resolved spectroscopy. Red shift and broadening of UV-Vis spectra of ANF hydrosol are explained due to strong π-π and H-π interactions among the neighboring ANF molecules within the aggregated microstructures. Though ANF is non-luminescent in good solvent, a strong emission is observed in its aggregated state. This aggregation induced emission (AIE) has been explained due to restriction of intramoleculer rotation and large amplitude vibrational modes of ANF in its aggregated state. Our Photophysical study also reveals that AIE effect decreases after an optimum concentration of ANF and this has been explained due to softening of crystal lattice. Cytotoxicity of ANF hydrosol was examined to get an idea of the toxic level of this hydrosol toward cultured normal human cells. It is observed that ANF hydrosol may draw beneficial effect in biological application as it has no higher toxic activity but has antioxidant property.

An inelastic neutron scattering study of dietary phenolic acids

The conformational preferences and hydrogen-bonding motifs of several potential chemopreventive hydroxycinnamic derivatives were determined by inelastic neutron scattering spectroscopy. The aim is to understand their recognized beneficial activity and establish reliable structure-activity relationships for these types of dietary phytochemicals. A series of phenolic acids with different hydroxyl/methoxyl ring substitution patterns were studied: trans-cinnamic, p-coumaric, m-coumaric, trans-caffeic and ferulic acids. Their INS spectra were completely assigned by theoretical calculations performed at the Density Functional Theory level, for the isolated molecule, dimeric centrosymmetric species and the solid (using plane-wave expansion approaches). Access to the low energy vibrational region of the spectra enabled the identification of particular modes associated with intermolecular hydrogen-bonding interactions, which are the determinants of the main conformational preferences and antioxidant capacity of these systems.

Protective Effect of Epigallocatechin Gallate and Esculetin on Oxidative DNA Damage Induced by Psoralen Plus Ultraviolet-A Therapy

We examined antioxidants exhibiting no effects on DNA cross-linking, which is the basis of psoralen and ultraviolet-A therapy for skin diseases, and suppressing oxidative DNA damage incidental to the therapy. Epigallocatechin gallate and esculetin effectively suppressed oxidative DNA damage with little effect on the formation of DNA cross-linking. These antioxidants might be useful in suppressing the adverse reaction induced by this therapy.

Cerumen of Australian stingless bees (Tetragonula carbonaria): gas chromatography-mass spectrometry fingerprints and potential anti-inflammatory properties

Cerumen, or propolis, is a mixture of plant resins enriched with bee secretions. In Australia, stingless bees are important pollinators that use cerumen for nest construction and possibly for colony's health. While extensive research attests to the therapeutic properties of honeybee (Apis mellifera) propolis, the biological and medicinal properties of Australian stingless bee cerumen are largely unknown. In this study, the chemical and biological properties of polar extracts of cerumen from Tetragonula carbonaria in South East Queensland, Australia were investigated using gas chromatography-mass spectrometry (GC-MS) analyses and in vitro 5-lipoxygenase (5-LOX) cell-free assays. Extracts were tested against comparative (commercial tincture of A. mellifera propolis) and positive controls (Trolox and gallic acid). Distinct GC-MS fingerprints of a mixed diterpenic profile typical of native bee cerumen were obtained with pimaric acid (6.31 ± 0.97%, w/w), isopimaric acid (12.23 ± 3.03%, w/w), and gallic acid (5.79 ± 0.81%, w/w) tentatively identified as useful chemical markers. Characteristic flavonoids and prenylated phenolics found in honeybee propolis were absent. Cerumen extracts from T. carbonaria inhibited activity of 5-LOX, an enzyme known to catalyse production of proinflammatory mediators (IC₅₀ 19.97 ± 2.67 μg/ml, mean ± SEM, n = 4). Extracts had similar potency to Trolox (IC₅₀ 12.78 ± 1.82 μg/ml), but were less potent than honeybee propolis (IC₅₀ 5.90 ± 0.62 g/ml) or gallic acid (IC₅₀ 5.62 ± 0.35 μg/ml, P < 0.001). These findings warrant further investigation of the ecological and medicinal properties of this stingless bee cerumen, which may herald a commercial potential for the Australian beekeeping industry.

Epigallocatechin-3-gallate (EGCG) affects the antioxidant and immune defense of the rainbow trout, Oncorhynchus mykiss

Epigallocatechin-3-gallate (EGCG), a very potent antioxidant derived from green tea, was compared with vitamin E in terms of its effects on antioxidant defense and immune response of rainbow trout, by means of a feeding trial of eight weeks. Two of the experimental diets were supplemented with EGCG at either 20 or 100 mg kg(-1) diet (which contained only 30% of the intended levels) and the third was provided with 100 mg kg(-1) vitamin E but not EGCG. The control diet was not supplemented with the test components. Observation of tissue levels indicated that the high amount of EGCG helped to increase the availability of the lipid-soluble antioxidant vitamin E. The lower levels of lipid hydroperoxide in the liver of fish fed the higher amount of EGCG suggested that it was an effective antioxidant. Considering the immune indices, EGCG and vitamin E at 100 mg (actual amounts 31.9 and 94.1 mg kg(-1) diet, respectively) had identical capabilities in improving phagocytic activity and controlling hydrogen peroxide production by leucocytes. However, EGCG could possibly be more effective at enhancing serum lysozyme activity and the alternative complement activity. This work revealed the potential of EGCG as an antioxidant and an immunostimulant for rainbow trout, at least at the inclusion level of 32 mg kg(-1) diet.

Pretreatment with natural flavones and neuronal cell survival after oxidative stress: a structure-activity relationship study

Quercetin shows structural features that have been related to the antioxidant potency of flavonoids and also shows neuroprotection in different models of oxidative death. Because only a few studies have focused on the flavonoid structural requirements for neuroprotection, this work evaluated the protective capacity of 13 flavones structurally related to quercetin, isolated from Kenyan plants, to rescue primary cerebellar granule neurons from death induced by a treatment with 24 h of hydrogen peroxide (150 microM). Each flavone (0-100 microM) was applied 24 h prior to the oxidative insult, and neuronal viability was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Results suggest that the o-dihydroxy substitution in the B-ring is not necessary to afford neuroprotection and could be partly responsible for neurotoxic effects. Furthermore, the hydroxy substitutions in the positions C3 (C-ring) in C5 and C7 (A-ring) would be important for neuroprotection in this model.

Cytotoxicity of flavonoids toward cultured normal human cells

The cytotoxicity of flavonoids, including apigenin, eriodictyol, 3-hydroxyflavone, kaempherol, luteolin, naringenin, quercetin, rutin, and taxifolin, toward cultured human normal cells, i.e., human lung embryonic fibroblasts (TIG-1) and human umbilical vein endothelial (HUVE) cells, was examined. When these normal human cells were incubated with each flavonoid in culture medium for 24 h, some of the flavonoids showed considerable cytotoxicity at relatively high concentrations and in a dose-dependent manner. 3-Hydroxyflavone, luteolin, and apigenin were more toxic toward TIG-1 cells than the other flavonoids, and luteolin, 3-hydroxyflavone, and quercetin were more toxic toward HUVE cells. HUVE cells were more vulnerable to flavonoid cytotoxicity than TIG-1 cells. Using 2',7'-dichlorofluorescin diacetate (DCF-DA), the intracellular reactive oxygen species (ROS) level of flavonoid-treated TIG-1 cells was examined. The ROS level increased significantly in the presence of the flavone apigenin or luteolin or the flavonol 3-hydroxyflavone, quercetin, or kaempherol. These results suggest that these flavones and flavonols exert cytotoxicity through increasing intracellular ROS levels. Further, the incorporation of apigenin, 3-hydroxyflavone, luteolin, and quercetin, which are more toxic, into TIG-1 cells during 24-h incubation was examined. These flavonoids were incorporated into them and the order of their incorporation efficiency was similar to that of their cytotoxicity. In conclusion, some flavonoids are cytotoxic at higher concentrations toward human normal cells. Further, it is suggested that they are incorporated into cells, increase intracellular ROS levels, and then exert cytotoxicity.

Protective effects of flavonoids on the cytotoxicity of linoleic acid hydroperoxide toward rat pheochromocytoma PC12 cells

The protective effects of nine flavonoids, including apigenin, eriodictyol, 3-hydroxyflavone, kaempherol, luteolin, quercetin, rutin, and taxifolin (Table 1), on the cytotoxicity of linoleic acid hydroperoxide (LOOH) toward rat pheochromocytoma PC12 cells were examined. The cytotoxicity was assessed by the trypan blue exclusion test and so-called MTT assay. When cells were preincubated with each flavonoid prior to LOOH exposure, quercetin, 3-hydroxyflavone, or luteolin decreased LOOH cytotoxicity toward undifferentiated cells, while only luteolin decreased efficiently LOOH cytotoxicity toward differentiated cells. On the other hand, when cells were coincubated with each flavonoid and LOOH, kaempherol, eriodictyol, quercetin, 3-hydroxyflavone, luteolin, or taxifolin decreased LOOH cytotoxicity toward undifferentiated and differentiated cells. On both preincubation prior to LOOH exposure and coincubation with LOOH, luteolin acted as the most efficiently protective agent against LOOH cytotoxicity. Further, these flavonoids showed protective effects on coincubation rather than preincubation. Flow cytometry using the fluorescence probe 2',7'-dichlorofluorescin diacetate revealed that LOOH increases the intracellular level of reactive oxygen species in undifferentiated cells in a dose-dependent manner, and that desferrioxamine mesylate suppresses the LOOH-induced increase in the level. These flavonoids suppress the LOOH-induced increase. Further, the protective effect of flavonoids on LOOH cytotoxicity correlates with the suppression of the LOOH-induced increase. These results suggest that such flavonoids are beneficial for neuronal cells under oxidative stress.

Flavonoids suppress the cytotoxicity of linoleic acid hydroperoxide toward PC12 cells

The suppressive effect of flavonoids on the cytotoxicity of linoleic acid hydroperoxide (LOOH) toward rat phenochromocytoma PC12 cells was examined. The extent of cytotoxicity was shown on the basis of % survival determined by the trypan blue exclusion test. On preincubation of cells with either 3-hydroxyflavone, quercetin, or luteolin prior to LOOH exposure, the cytotoxicity was considerably suppressed. In contrast, on coincubation of cells with either eriodictyol, quercetin, kaempherol, luteolin, or 3-hydroxyflavone and LOOH, it was markedly suppressed. Regardless of incubation conditions, quercetin, 3-hydroxyflavone, and luteolin were thus more effective as protective agents against the cytotoxicity than the other flavonoids. These flavonoids further showed a suppressive effect on coincubation rather than on preincubation. These results suggest that such flavonoids are beneficial for cells under oxidative stress.

Effect of quercetin and its conjugated metabolite on the hydrogen peroxide-induced intracellular production of reactive oxygen species in mouse fibroblasts

To clarify the antioxidative role of quercetin metabolites in cellular oxidative stress, we measured the inhibitory effects of the quercetin aglycon and quercetin 3-O-beta-D-glucuronide (Q3GA), which is one of the quercetin metabolites in the blood after an intake of quercetin-rich food, on the production of hydrogen peroxide (H2O2)-induced intracellular reactive oxygen species in mouse fibroblast 3T3 cultured cells. When the cells were exposed to H2O2 in the presence of quercetin or Q3GA, Q3GA was found to be less effective than quercetin. In the case of a pretreatment with quercetin or Q3GA before the exposure, Q3GA, but not the quercetin aglycon, exerted an inhibitory effect, although its cellular uptake was unlikely. The quercetin aglycon appeared to fail in its antioxidative effect due to metabolic conversion into isorhamnetin conjugates, with substantial oxidative degradation resulting from the pretreatment. It is, therefore, suggested that quercetin metabolites take part in the protection of intracellular oxidative stress induced by the extraneous attack of H2O2.