Activity Of Tannic Acid Research Articles

Tannic Acid Suppresses Ferroptosis Induced by Iron Salophene Complex in Kidney Cells and Prevents Iron Overload-Induced Liver and Kidney Dysfunction in Rats.

Iron toxicity intricately links with ferroptosis, a unique form of cell death, and is significantly influenced by lipid peroxidation. Despite its critical role in various diseases and drug development, the association between iron toxicity and ferroptosis remains relatively unexplored. Accidental iron ingestion has emerged as a growing concern, resulting in a spectrum of symptoms ranging from gastrointestinal discomfort to severe outcomes, including mortality. This research introduces tannic acid (TA), which contains numerous phenol groups, as a powerful antiferroptotic agent. In male Wistar rats, even a modest dose of TA (7.5mg/kg) significantly curtailed thiobarbituric acid reactive substances (TBARS), a well-established indicator of lipid peroxidation, and mitigated iron accumulation induced by ferrous sulfate (FeSO4) in the liver and kidney. The evidence supporting TA's protective function against iron-triggered liver and kidney dysfunction was substantiated by assessing specifically the levels of blood urea nitrogen (BUN) and alanine aminotransferase (ALT). In cell models using ferroptosis inducers such as iron-salophene (FeSP) and RAS-selective lethal 3 (RSL3), tannic acid (TA) exhibited superior protective capabilities compared to the traditional iron chelator, deferoxamine (DFO). Nrf2 and HO-1, regulators of antioxidant defense genes, are implicated in controlling ferroptosis. The expression of Nrf2 and HO-1 increased with TA treatment in the presence of FeSP, indicating their role in reducing lipid ROS levels. Additionally, TA significantly reduced the heightened levels of COX2, a marker associated with ferroptosis. In summary, the remarkable antiferroptosis activity of TA is likely due to its combined iron-chelating and antioxidant properties. With its safety profile for oral consumption, TA may offer benefits in cases of accidental iron ingestion and conditions like hemochromatosis.

Tannic acid as a biphasic modulator of tau protein liquid–liquid phase separation

Tannic acid (TA) is a natural polyphenol that shows great potential in the field of biomedicine due to its anti-inflammatory, anti-oxidant, anti-bacterial, anti-tumor, anti-virus, and neuroprotective activities. Recent studies have revealed that liquid−liquid phase separation (LLPS) is closely associated with protein aggregation. Therefore, modulating LLPS offers new insights into the treatment of neurodegenerative diseases. In this study, we investigated the influence of TA on the LLPS of the Alzheimer's-related protein tau and the underlying mechanism. Our findings indicate that TA affects the LLPS of tau in a biphasic manner, with initial promotion and subsequent suppression as the TA to tau molar ratio increases. TA modulates tau phase separation through a combination of hydrophobic interactions and hydrogen bonds. The balance between TA-tau and tau-tau interactions is found to be relevant to the material properties of TA-induced tau condensates. We further illustrate that the modulatory activity of TA in phase separation is highly dependent on the target proteins. These findings enhance our understanding of the forces driving tau LLPS under different conditions, and may facilitate the identification and optimization of compounds that can rationally modulate protein phase transition in the future.

Alpha-Pinene and Tannic Acid Inhibit Trichomonas vaginalis Protozoan Cells by Inducing Apoptosis.

Trichomoniasis is one of the most common sexually transmitted infections worldwide. The growing concern of drug resistance of this infection has cautioned the need for new drug development. We evaluated the potential antiproliferative and apoptotic effect of α-pinene and tannic acid (TA) on Trichomonas vaginalis cells. In addition, the cytotoxicity of agents on Vero cells was investigated. Trichomonas cells were axenically cultured in TYI-S-33 medium. In vitro antiproliferative activity of α-pinene, TA, and metronidazole was investigated against Trichomonas cells. The assays were carried out in triplicate using microtiter plate and trypan blue staining method. Annexin V/PI staining with flow cytometry was used to evaluate apoptosis induction. In addition, the cytotoxic effect was measured by MTT assay. α-Pinene and TA exhibited significant inhibition of the Trichomonas cells and the lowest IC50 values were 22.9 μg/ml and 140 μg/ml at 48 hours' incubation, respectively. The CC50 was found at 116 μg/ml for α-pinene and 473 μg/ml for TA, after 48 hours of treatment. The flow cytometry study demonstrated that the natural compounds induced apoptosis in Trichomonas cells. After 24 hours of treatment, the induction of apoptosis was 5.2% - 36.6% at concentrations of 3.9 - 62.5 μg/ml for α-pinene and TA induced-apoptosis was 6.1% - 53.8% at concentrations of 125-2000 μg/ml. Although the results show the antiproliferative and apoptotic effect of α-pinene and TA on Trichomonas cells, in vivo studies are needed to further clarify the effects of these compounds.

Type I Collagen-Adhesive and ROS-Scavenging Nanoreactors Enhanced Retinal Ganglion Cell Survival in an Experimental Optic Nerve Crush Model.

Traumatic optic neuropathy (TON) is a severe condition characterized by retinal ganglion cell (RGC) death, often leading to irreversible vision loss, and the death of RGCs is closely associated with oxidative stress. Unfortunately, effective treatment options for TON are lacking. To address this, catalase (CAT) is encapsulated in a tannic acid (TA)/poly(ethylenimine)-crosslinked hollow nanoreactor (CAT@PTP), which exhibited enhanced anchoring in the retina due to TA-collagen adhesion. The antioxidative activity of both CAT and TA synergistically eliminated reactive oxygen species (ROS) to save RGCs in the retina, thereby treating TON. In vitro experiments demonstrated that the nanoreactors preserve the enzymatic activity of CAT and exhibit high adhesion to type I collagen. The combination of CAT and TA-based nanoreactors enhanced ROS elimination while maintaining high biocompatibility. In an optic nerve crush rat model, CAT@PTP is effectively anchored to the retina via TA-collagen adhesion after a single vitreous injection, and RGCs are significantly preserved without adverse events. CAT@PTP exhibited a protective effect on retinal function. Given the abundance of collagen that exists in ocular tissues, these findings may contribute to the further application of this multifunctional nanoreactor in ocular diseases to improve therapeutic efficacy and reduce adverse effects.

Tannic acid, an IL-1β-direct binding compound, ameliorates IL-1β-induced inflammation and cartilage degradation by hindering IL-1β-IL-1R1 interaction.

Interleukin-1β (IL-1β) is one of the most potent pro-inflammatory cytokines implicated in a wide range of autoinflammatory, autoimmune, infectious, and degenerative diseases. Therefore, many researchers have focused on developing therapeutic molecules that inhibit IL-1β-IL-1 receptor 1 (IL-1R1) interaction for the treatment of IL-1-related diseases. Among IL-1-related diseases, osteoarthritis (OA), is characterized by progressive cartilage destruction, chondrocyte inflammation, and extracellular matrix (ECM) degradation. Tannic acid (TA) has been proposed to have multiple beneficial effects, including anti-inflammatory, anti-oxidant, and anti-tumor activities. However, it is unclear whether TA plays a role in anti-IL-1β activity by blocking IL-1β-IL-1R1 interaction in OA. In this study, we report the anti-IL-1β activity of TA in the progression of OA in both in vitro human OA chondrocytes and in vivo rat OA models. Herein, using-ELISA-based screening, natural compound candidates capable of inhibiting the IL-1β-IL-1R1 interaction were identified. Among selected candidates, TA showed hindering IL-1β-IL-1R1 interaction by direct binding to IL-1β using surface plasmon resonance (SPR) assay. In addition, TA inhibited IL-1β bioactivity in HEK-Blue IL-1-dependent reporter cell line. TA also inhibited IL-1β-induced expression of inducible nitric oxide synthase (NOS2), cyclooxygenase-2 (COX-2), IL-6, tumor necrosis factor-alpha (TNF-α), nitric oxide (NO), and prostaglandin E2 (PGE2) in human OA chondrocytes. Moreover, TA downregulated IL-1β-stimulated matrix metalloproteinase (MMP)3, MMP13, ADAM metallopeptidase with thrombospondin type 1 motif (ADAMTS)4, and ADAMTS5, while upregulating collagen type II (COL2A1) and aggrecan (ACAN). Mechanistically, we confirmed that TA suppressed IL-1β-induced MAPK and NF-κB activation. The protective effects of TA were also observed in a monosodium iodoacetamide (MIA)-induced rat OA model by reducing pain and cartilage degradation and inhibiting IL-1β-mediated inflammation. Collectively, our results provide evidence that TA plays a potential role in OA and IL-1β-related diseases by hindering IL-1β-IL-1R1 interaction and suppressing IL-1β bioactivity.

A dual-cross-linked hydrogel based on hyaluronic acid/gelatin tethered via tannic acid: mechanical properties’ enhancement and stability control

Extracellular matrix (ECM) as a network is mainly composed of glycosaminoglycans and proteins. Among these glycosaminoglycans and proteins that naturally occur in ECM, hyaluronic acid (HA) and gelatin attract more attentions. In this work, a chemically cross-linked HA/gelatin hydrogel (HG hydrogel) was firstly fabricated, and then, tannic acid (TA) was introduced as a physical cross-linker, to form a dual-cross-linked network (HG-TAx hydrogels). The strong hydrogen bonding between TA and HG hydrogel resulted in lower swelling ratio, decreasing from 220% (pristine HG hydrogels) to 7.5% (HG-TA25 hydrogels) and stronger mechanical properties increasing from 6 kPa (HG hydrogel) to 160 kPa (HG-TA25 hydrogel). The hydrogel stability in enzyme was significantly improved, attributing to the hyaluronidase inhibition activity of TA. The degradation time significantly increased along with the addition of TA (from 7 up to 21 days). Furthermore, the HG-TAx hydrogels exhibited good cleavage ability to reactive oxygen species (ROS) that could be generated in human tissues, and the antioxidant capacity increased up to 24.2 mg/mL of L-ascorbic acid standard. The improved mechanical properties, prolonged degradation time, and potential antioxidant ability of the HG-TAx hydrogels could pave the way for the design of biomaterials. Furthermore, TA has shown potential biological functions properties and brought the great potential of the HG-TAx hydrogels for implant applications.

Tannic acid enhanced the physical and oxidative stability of chitin particles stabilized oil in water emulsion

In this work, the stability of CP-TA complex stabilized emulsion was first characterized. It was found that the peak thickness, Turbiscan Stability Index (TSI) and droplet size of CP-TA complex stabilized emulsion gradually decreased with increasing content of TA, indicating the gradually enhanced physical stability of emulsion, which was attributed to the gradually decreased interfacial tension, zeta potential and increased viscosity of CP-TA complex. Moreover, the oxidative stability of CP-TA complex stabilized emulsion gradually enhanced with increasing of TA content due to the antioxidant activity of TA. XRD and FTIR results suggested that the interaction between CP and TA gradually enhanced with increasing content of TA in CP-TA complex, leading to the formation of larger CP-TA clusters shown in AFM results. In conclusion, the presence of tannic acid (TA) enhanced the physical and oxidative stability of chitin particles-tannic acid (CP-TA) complex stabilized oil in water emulsion.

Proteomic analysis deciphers the multi-targeting antivirulence activity of tannic acid in modulating the expression of MrpA, FlhD, UreR, HpmA and Nrp system in Proteus mirabilis

In the present study, the multi-targeting antivirulence activity of tannic acid (TA) was explored against Proteus mirabilis through MS-based proteomic approach. The in vitro biofilm biomass quantification assay and microscopic analysis demonstrated the antibiofilm activity of TA against P. mirabilis in which, minimum biofilm inhibitory concentration (MBIC) of TA was found to be 200 μg/mL concentration. Moreover, the nanoscale liquid chromatography coupled to tandem mass spectrometry (nano LC-MS/MS) analysis revealed that TA (at MBIC) differentially regulated the proteins involved in fimbrial adhesion, flagellar motility, iron acquisition, Fe-S cluster assembly, heat shock response, virulence enzymes, and toxin secretion. Further, the transcriptomic analysis validated the outcomes of proteomic analysis in which, the expression level of virulence genes responsible for MR/P fimbrial adhesion (mrpA), flagellar transcriptional activation (flhD), biosynthesis of urease (ureR), hemolysin (hpmA), non-ribosomal peptide siderophore system (Nrp), oxidative stress responsible enzymes and fitness factors proteins were down-regulated in TA exposed P. mirabilis. These observations were also in correspondence with the in vitro bioassays. Thus, this study reports the feasibility of TA to act as a promising therapeutic agent against multifactorial P. mirabilis infections.

Anti quorum sensing and anti virulence activity of tannic acid and it's potential to breach resistance in Salmonella enterica Typhi / Paratyphi A clinical isolates

Salmonella enterica Typhi and Paratyphi A are food borne pathogens causing typhoid, which is one of the most important food borne disease in the developing world. S. Typhi and S. Paratyphi A are of much concern as multi drug resistance has been on the rise. The current study is aimed to screen phytochemicals for anti quorum sensing (QS) activity against S. Typhi and S. Paratyphi A. Upon screening with swarming assay, tannic acid (TA) showed highest anti-QS activity with minimal concentration of 400μg/ml. The anti-QS activity of TA was confirmed with C. violaceum ATCC 12,472. TA showed 38–43% and 35–50% of inhibition in cell surface hydrophobicity and EPS production respectively. Through FTIR analysis, it has been observed that EPS of treated cells has a considerable change in protein and peptide. TA has also exhibited drastic reduction in the surfactant production as high as 85–90%. Blood sensitivity and antibiotic sensitivity assay revealed that TA significantly sensitizes the S. Typhi and S. Paratyphi A cells to immune components in human blood and antibiotics. It has reduced the resistance of S. Typhi and S. Paratyphi A cells against amikacin, ampicillin, ciprofloxacin, azithromycin, chloramphenicol and gentamycin, thus revitalized the usage of these antibiotics against drug resistant S. Typhi and S. Paratyphi A infections. The consistency of anti-QS potential of TA was further evaluated and established with another eight clinical isolates of S. Typhi and S. Paratyphi A. Thus TA has been proved as a promising anti QS agent that can be developed as a therapeutic combination against S. Typhi and S. Paratyphi A.

Synthesis of morphology-tunable electroactive biomass/graphene composites using metal ions for supercapacitors.

Tannic acid (TA) is a natural polyphenolic biomass, which shows high electro-activity and can be considered for supercapacitor applications. However, the negligible electronic conductivity of TA hinders its direct use as an electrode. In order to achieve the electrochemical activity of TA, herein, a three-dimensional porous TA/graphene composite (TAG) is prepared by mixing TA with graphene oxide (GO) via hydrothermal assembly, and various structural composites are realized by adding metal ions into the system before hydrothermal treatment. Metal ions can chelate with TA molecules and coordinate with GO via electrostatic interactions. As a result, a uniform and well-defined three-dimensional porous network (TAGNi), a regularly arranged scale-like microstructure (TAGCu) and a flower-like structure (TAGFe) are achieved by introducing Ni2+, Cu2+ and Fe3+, respectively. The as-prepared TAG, TAGNi, TAGCu and TAGFe electrodes exhibit a high specific capacitance of 373.6, 412.4, 460.4 and 429.4 F g-1 at 1 A g-1, respectively, and excellent cycling stability. The TAG, TAGNi, TAGCu and TAGFe assembled symmetric supercapacitors display a favorable energy density of 14.76, 16.76, 19.13 and 17.6 W h kg-1 at 300 W kg-1, respectively. The morphology-tunable TA/graphene composites with excellent electrochemical performance are promising for renewable energy storage device applications.

Preparation, Characterization and Antioxidant Evaluation of Cu(II) and Zn(II) Tannates

Introduction: The interest in the antioxidant materials increased due to their free radical scavenging properties avoiding various pathologies. Tannic Acid (TA) is known to have high free radical scavenging activity, but its application is still limited. This paper had the objective of synthesis, characterization and evaluation of free radical scavenging activity of TA associated with Cu (II) and Zn (II) ions, in a buffered aqueous medium. Methods and Materials: Techniques of FTIR, simultaneous TG-DSC characterized the obtained compounds, and the evaluation of free radical scavenging activity was made using 2,2–diphenyl–1–picrylhydrazyl (DPPH) radical. The FTIR analysis of the compounds showed significant displacement of the main bands in the TA spectrum (νC=O, δO-H, σO-H), suggesting an association of metal ions with the oxygen of the hydroxyl group of TA. TG-DSC curves showed information about the thermal stability, stoichiometry, hydration water, and residues formation. Results and Conclusion: The TA association with the metal ions Cu(II) and Zn(II) decreased the antioxidant activity of the molecule significantly, showing that these compounds could be potentially used as pro-oxidant agents.

Tannic acid, a novel histone acetyltransferase inhibitor, prevents non-alcoholic fatty liver disease both in vivo and in vitro model

ObjectiveWe examined the potential of tannic acid (TA) as a novel histone acetyltransferase inhibitor (HATi) and demonstrated that TA prevents non-alcoholic fatty liver disease (NAFLD) by inhibiting HAT activity. MethodsThe anti-HAT activity of TA was examined using HAT activity assays. An in vitro NAFLD model was generated by treating HepG2 cells with oleic and palmitic acids. Male C57BL/6J mice were fed a control diet (CD) or Western diet (WD) with or without supplementation with either 1% or 3% TA (w/w) for 12 weeks. Finally, the possibility of interacting p300 and TA was simulated. ResultsTA suppressed HAT activity both in vitro and in vivo. Interestingly, TA abrogated occupancy of p300 on the sterol regulatory element in the fatty acid synthase and ATP-citrate lyase promoters, eventually inducing hypoacetylation of H3K9 and H3K36. Furthermore, TA decreased acetylation at lysine residues 9 and 36 of histone H3 protein and that of total proteins. Consequently, TA decreased the mRNA expression of lipogenesis-related genes and attenuated lipid accumulation in vivo. We observed that NAFLD features, including body weight, liver mass, fat mass, and lipid profile in serum, were improved by TA supplementation in vivo. Finally, we demonstrated the possibility that TA directly binds to p300 through docking simulation between ligand and protein. ConclusionsOur findings demonstrate that TA, a novel HATi, has potential application for the prevention of NAFLD.

Tannic acid attenuated irradiation-induced apoptosis in megakaryocytes

Ionizing radiation (IR) triggers the generation of reactive oxygen species (ROS), which shows potential roles in damaging the DNA and proteins at the nucleus, and eventually results in apoptosis and even cell death. Antioxidant agents can inhibit the generation of ROS after IR exposure. Tannic acid (TA), has an antioxidant activity involving in preventing cardiovascular and cerebrovascular diseases. However, little is known about the effects of TA on irradiation-induced apoptosis in megakaryocytes. Here, we evaluated the anti-radiation activity of TA in megakaryocytes. Our results showed that TA protected megakaryocytes from apoptosis induced by IR, attenuated IR-induced increases in the production of ROS, and inhibited the changes of mitochondrial membrane potential (MMP). Moreover, TA down-regulated NAPDH oxidase 1 (Nox1) expression, and decreased the phosphorylated levels of JNK and p38. Furthermore, JNK inhibitor could reduce apoptosis induced by X-irradiation in M07e cells. In vivo experiments confirmed that TA could promote the platelet recovery, reduce the percentage of apoptosis CD41+ megakaryocytes in bone marrow and raise survival during 30 days in mice by total body irradiation. In conclusion, TA can protecte the megakaryocytes from apoptosis caused by IR through inhibiting Nox1 expression to reduce ROS generation and repressing JNK/p38 MAPK pathway activation.

Enhancement of bio-stability and mechanical properties of hyaluronic acid hydrogels by tannic acid treatment

Hyaluronic acid (HA) has been widely investigated because of its excellent biocompatibility and its ability to form hydrogels with various chemical modifications. However, HA hydrogels undergo rapid degradation and exhibit poor mechanical stability under physiological conditions. Tannic acid (TA), a naturally occurring polyphenol found in plants and fruits, has recently attracted interest as a crosslinking agent because of its abundant hydroxyl groups. In this study, we prepared HA hydrogels chemically crosslinked by polyethylene glycol diglycidyl ether (PEGDE) and treated with TA in an attempt to enhance the physical properties of HA hydrogels. TA acts as a physical crosslinker owing to the strong hydrogen bonding between TA and PEGDE, resulting in improved mechanical properties that support both cell attachment and proliferation without any sign of cytotoxicity. The enzymatic stability of the HA–TA hydrogels was significantly enhanced with the addition of TA, which was attributed to the hyaluronidase inhibition activity of TA. Additionally, the antioxidant potential of TA resulted in good resistance to degradation by reactive oxygen species, which can be generated in human tissues.

Electrospun Polymer Nanofibers Reinforced by Tannic Acid/Fe+++ Complexes.

We report the successful preparation of reinforced electrospun nanofibers and fibrous mats of polyvinyl alcohol (PVA) via a simple and inexpensive method using stable tannic acid (TA) and ferric ion (Fe+++) assemblies formed by solution mixing and pH adjustment. Changes in solution pH change the number of TA galloyl groups attached to the Fe+++ from one (pH < 2) to two (3 < pH < 6) to three (pH < 7.4) and affect the interactions between PVA and TA. At pH ~ 5.5, the morphology and fiber diameter size (FDS) examined by SEM are determinant for the mechanical properties of the fibrous mats and depend on the PVA content. At an optimal 8 wt % concentration, PVA becomes fully entangled and forms uniform nanofibers with smaller FDS (p < 0.05) and improved mechanical properties when compared to mats of PVA alone and of PVA with TA (p < 0.05). Changes in solution pH lead to beads formation, more irregular FDS and poorer mechanical properties (p < 0.05). The Fe+++ inclusion does not alter the oxidation activity of TA (p > 0.05) suggesting the potential of TA-Fe+++ assemblies to reinforce polymer nanofibers with high functionality for use in diverse applications including food, biomedical and pharmaceutical.

Comparative evaluation of tannic acid inhibiting α-glucosidase and trypsin

In this work, the inhibitory effects of tannic acid on the α-glucosidase and trypsin were systematically evaluated by comparing with the clinical diabetes healer acarbose and the soybean-derived trypsin inhibitor using fluorescence spectroscopy and enzymatic kinetics methods. We showed that the anti-α-glucosidase activity of tannic acid (IC50=0.44μg/mL) was higher than that of acarbose (IC50>0.60μg/mL), while its anti-trypsin activity (IC50=0.79mg/mL) was significantly lower than that of the trypsin inhibitor from soybean (IC50<0.20mg/mL). Enzymatic kinetics measurements confirmed that the inhibitory pattern of tannic acid toward two tested enzymes was a mixed competitive and noncompetitive inhibition. Tannic acid could bind the enzymes to form new complexes, presenting a strong static fluorescence quenching. The presence of tannic acid led to the hypsochromic shift of the maximum fluorescence in trypsin, but not in α-glucosidase. The thermodynamic parameters indicated that the main driving force between tannic acid and both the enzymes was the hydrophobic interaction followed by the electrostatic interaction. Our work suggests that tannic acid is a strong anti-α-glucosidase natural inhibitor with a low inhibitory activity for trypsin, thus its roles in functional food and medicinal plants should be re-recognized.

Tannic acid-induced apoptosis and -enhanced sensitivity to arsenic trioxide in human leukemia HL-60 cells

Tannic acid (TA), a glucoside of gallic acid polymer, has been shown to possess anti-bacterial, anti-enzymatic, anti-tumor and astringent properties. However, the anti-cancer activity of TA in leukemia is still obscure. In this study, we showed TA-induced apoptotic death in acute myeloid leukemia (AML) HL-60 cells via dose- and time-dependent manner as well as increase of sub-G1 fraction, chromosome condensation, and DNA fragmentation. Further analysis demonstrated the involvement of activation of caspase cascade, cleavage of poly (ADP-ribose) polymerase (PARP), disruption of mitochondrial membrane potential, and release of Cytochrome C, in TA-induced apoptosis. These effects were probably associated with the increase of intracellular superoxide in mitochondrial signaling pathway which attributed to the down-regulation of superoxide dismutase (SOD). Notably, a low dose of TA is sufficient to aggravate arsenic trioxide (As 2O 3)-induced cytotoxicity in HL-60 cells. Altogether, this study suggested the effects of TA to induce apoptosis in HL-60 and therapeutic potential in AML by being an adjunct to As 2O 3.

Analysis of condensed and hydrolysable tannins from commercial plant extracts

High performance liquid chromatography (HPLC)/DAD and MS qualitative and quantitative analyses of polyphenols, hydrolysable and condensed tannins from Pinus maritima L. and tannic acid (TA) extracts were performed using normal and reverse phase. Normal-phase HPLC was more suitable for pine bark (PBE) and tannic acid extracts analysis. The chromatographic profile revealed that P. maritima L. extract was mainly composed by polymeric flavanols (containing from two to seven units) and tannic acid (characterized by a mixture of glucose gallates containing from three to seven units of gallic acid). Concerning their antimycotic properties, P. maritima L. extract exhibited a broad activity towards yeast strains of the genera Candida, Cryptococcus, Filobasidiella, Issatchenkia, Saccharomyces: MICs from 200 to 4000 μg/ml (corresponding to 140–2800 μg/ml of active polyphenols) were determined. Conversely, no activity of tannic acid was observed over the same target microorganisms. Taken into consideration the above results of HPLC analysis and on the basis of the current literature, we may conclude that only 70.2% of polyphenols (recognized as condensed tannins) occurring in P. maritima L. extract can be apparently considered responsible for its antimycotic activity.

The antioxidant effect of tannic acid on the in vitro copper-mediated formation of free radicals

Tannic acid (TA) has well-described antimutagenic and antioxidant activities. The antioxidant activity of TA has been previously attributed to its capacity to form a complex with iron ions, interfering with the Fenton reaction [Biochim. Biophys. Acta 1472, 1999, 142]. In this work, we observed that TA inhibits, in the micromolar range, in vitro Cu(II) plus ascorbate-mediated hydroxyl radical ( OH) formation (determined as 2-deoxyribose degradation) and oxygen uptake, as well as copper-mediated ascorbate oxidation and ascorbate radical formation (quantified in EPR studies). The effect of TA against 2-deoxyribose degradation was three orders of magnitude higher than classic OH scavengers, but was similar to several other metal chelators. Moreover, the inhibitory effectiveness of TA, by the four techniques used herein, was inversely proportional to the Cu(II) concentration in the media. These results and the observation of copper-induced changes in the UV spectra of TA are indications that the antioxidant activity of TA relates to its copper chelating ability. Thus, copper ions complexed to TA are less capable of inducing ascorbate oxidation, inhibiting the sequence of reactions that lead to 2-deoxyribose degradation. On the other hand, the efficiency of TA against 2-deoxyribose degradation declined considerably with increasing concentrations of the OH detector molecule, 2-deoxyribose, suggesting that the copper–TA complex also possesses an OH trapping activity.

Polyphenol tannic acid inhibits hydroxyl radical formation from Fenton reaction by complexing ferrous ions

Tannic acid (TA), a plant polyphenol, has been described as having antimutagenic, anticarcinogenic and antioxidant activities. Since it is a potent chelator of iron ions, we decided to examine if the antioxidant activity of TA is related to its ability to chelate iron ions. The degradation of 2-deoxyribose induced by 6 μM Fe(II) plus 100 μM H 2O 2 was inhibited by TA, with an I 50 value of 13 μM. Tannic acid was over three orders of magnitude more efficient in protecting against 2-deoxyribose degradation than classical ⋅OH scavengers. The antioxidant potency of TA was inversely proportional to Fe(II) concentration, demonstrating a competition between H 2O 2 and AT for reaction with Fe(II). On the other hand, the efficiency of TA was nearly unchanged with increasing concentrations of the ⋅OH detector molecule, 2-deoxyribose. These results indicate that the antioxidant activity of TA is mainly due to iron chelation rather than ⋅OH scavenging. TA also inhibited 2-deoxyribose degradation mediated by Fe(III)-EDTA (iron=50 μM) plus ascorbate. The protective action of TA was significantly higher with 50 μM EDTA than with 500 μM EDTA, suggesting that TA removes Fe(III) from EDTA and forms a complex with iron that cannot induce ⋅OH formation. We also provided evidence that TA forms a stable complex with Fe(II), since excess ferrozine (14 mM) recovered 95–96% of the Fe(II) from 10 μM TA even after a 30-min exposure to 100–500 μM H 2O 2. Addition of Fe(III) to samples containing TA caused the formation of Fe(II) n –TA, complexes, as determined by ferrozine assays, indicating that TA is also capable of reducing Fe(III) ions. We propose that when Fe(II) is complexed to TA, it is unable to participate in Fenton reactions and mediate ⋅OH formation. The antimutagenic and anticarcinogenic activity of TA, described elsewhere, may be explained (at least in part) by its capacity to prevent Fenton reactions.