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Nakanishi Ikuo - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Reaction Environments on Radical-Scavenging Mechanisms of Ascorbic Acid
    'The Society for Free Radical Research Japan', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Fukuhara Kiyoshi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    The effect of reaction environment on the radical-scavenging mechanism of ascorbic acid (AscH2) was investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by beta-cyclodextrin (beta-CD) in water to use DPPH in phosphate buffer solutions. The DPPH-scavenging rate of AscH2 in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0), where AscH2 undergoes deprotonation to produced ascorbate anion (AscH-). An organic soluble 5,6-isopropylidene-L-ascorbic acid (iAscH2) was also used to compare the DPPH-scavenging reactivity in MeOH and acetonitrile (MeCN). iAscH2 scavenged DPPH much slower in MeCN than in MeOH. In MeOH, Mg(ClO4)2 significantly decelerated the DPPH-scavenging reaction by AscH2 and iAscH2, while no effect of Mg(ClO4)2 on the rate of the reaction of iAscH2 with DPPH was observed in MeCN. On the other hand, Mg(ClO4)2 significantly accelerated the reaction between AscH2 and beta-CD-solubilized DPPH (DPPH/beta-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO4)2 to the AscH2-DPPH/beta-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, DPPH-scavenging reaction by iAscH2 in MeCN may proceed via a one-step hydrogen-atom transfer as the rate-determining step, while an electron transfer pathway is partly involved in the reaction between AscH2 and DPPH/beta-CD in phosphate buffer solution, although the detailed mechanism for the deceleration effect of Mg(ClO4)2 in MeOH is under investigation. These results demonstrate that the DPPH-scavenging mechanism by AscH2 are affected by the reaction environments

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrzyl Radical by Ascorbic Acid
    'Elsevier BV', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrazy Radical by Ascorbic Acid
    2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media.20th Biennial Meeting of SFRR International (SFRR-I 2021

  • Reaction of Glutathione and Bio-Related Thiols with 2,2-Diphenyl-1-picrylhydrazyl Radical Solubilized by beta-Cyclodextrin in Water
    2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ueno Megumi, Ozawa Toshihiko, Sekine-suzuki Emiko, Matsumoto Ken-ichiro
    Abstract:

    Glutathione (GSH) is known to act as a redox regulator. However, the radical scavenging mechanism of GSH has yet to be fully clarified. Recently, we have succeeded in solubilizing water-insoluble 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in water using beta-cyclodextrin. In this study, the scavenging mechanism of the water-solubilized DPPH radical by GSH was investigated using the stopped-flow technique.Upon mixing of GSH with the DPPH radical in phosphate buffer (0.05 M, pH 7.4), the absorption band at 527 nm due to the DPPH radical decreased gradually. The pseudo-first order rated constants (kobs), determined from the decay of the absorbance at 527 nm, increased with increasing the GSH concentration and reached a constant value. Furthermore, the higher pH was, the larger the kobs values became. When H2O of the phosphate buffer was replaced with D2O, little change was observed for the kobs values. Thiol compounds with smaller pKa values than GSH, such as L-cysteine, showed higher scavenging activity than GSH under the same experimental conditions. These results suggest that the DPPH radical-scavenging reaction by GSH may proceed via deprotonation of GSH to produce the corresponding thiolate anion, GS-, followed by an electron transfer from GS- to the DPPH radical.19th Biennial Meeting of Society for Free Radical Research International (SFRRI 2018

  • Evaluation of the Radical-Scavenging Activity of Antioxidants in Water Using a Water-Solubilized 2,2-Dipheny-1-picrylhydrazyl Radical
    2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Matsumoto Ken-ichiro
    Abstract:

    2,2-Diphenyl-1-picrylhydrazyl radical (DPPH•), a relatively stable radical, has been used to evaluate the activity of antioxidants as a reactivity model of reactive oxygen species (ROS) for 60 years [1]. However, the insolubility of DPPH• in water has precluded its use in aqueous media without cosolvents such as, ethanol. The pH of the reaction media of antioxidants is of great importance, because antioxidant molecules have one or more ionizable OH groups and their ionization state largely influence the reactivity of antioxidants. However, the pH of the reaction media is not precisely controlled in the presence of the cosolvents. Recently, we have reported that DPPH• is successfully solubilized in water using β-cyclodextrin (β-CD) [2,3]. In this study, we introduce a novel technique to evaluate the kinetic radical-scavenging activity of antioxidants using the β-CD-solubilized DPPH• in physiological concentrations of buffer solutions.25 mL of boiling water (Milli-Q) was added to the solid mixture of DPPH• (0.15 mmol) and β-CD (0.70 mmol). The suspension was stirred until it reached room temperature and filtered with a membrane filter (pore size: 0.22 µm). The as-obtained filtrate showed an absorption band at 527 nm, which is diagnostic of DPPH•. The concentration of DPPH• was estimated by using the ε value of 11000 M–1 cm–1 determined for DPPH• in a 1:1 ethanol–buffer solution [4]. Upon mixing of Trolox, a water-soluble analog of α-tocopherol (vitamin E), with the β-CD-solubilized DPPH• in phosphate buffer solution (0.1 M, pH 7.4) at 298 K, the absorption band at 527 nm decreased immediately. The decay of the absorbance at 527 nm monitored by a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer obeyed pseudo-first-order kinetics, when the concentration of Trolox was maintained at more than a 10-fold excess of DPPH• concentration. The pseudo-first-order rate constants (kobs) linearly increased with increasing the Trolox concentration. From the slope of the linear plot, the second-order rate constant (k) for the scavenging of DPPH• by Trolox was determined to be 1.8 × 104 M–1 s–1. The k value of the reaction between Trolox and DPPH• in methanol at 298 K was determined in the same manner to be 2.3 × 102 M–1 s–1, which is about 80-fold smaller than that in phosphate buffer solution (0.1 M, pH 7.4). Ascorbic acid (AscH2) scavenged the β-CD-solubilized DPPH• with the k value of 7.2 × 103 M–1 s–1 in phosphate buffer solution (0.1 M, pH 7.4) at 298 K. Because the pKa value of AscH2 is known to be 4.1, AscH2 undergoes deprotonation and exists in its anionic form, AscH– in phosphate buffer solution (0.1 M, pH 7.4). Thus, the actual species that scavenged DPPH• is AscH–. On the other hand, in methanol, the kobs value for the DPPH•-scavenging reaction by AscH2 was much smaller than that in phosphate buffer solution (0.1 M, pH 7.4) and constant with the change in the AscH2 concentration used in excess. This suggests that little AscH– was produced by the deprotonation of AscH2 in methanol. Thus, the radical-scavenging activity of antioxidants is largely affected by the nature of solvents. The solubilization of DPPH• in water by β-CD enables us to evaluate the radical-scavenging activity of antioxidants with use of the same probe, DPPH•, as that has been used in organic solvents for 60 years.\nREFERENCES[1] M.S. Blois, Nature 181 (1958) 1199[2] I. Nakanishi, K. Ohkubo, K. Imai, M. Kamibayashi, Y. Yoshihashi, K. Matsumoto, K. Fukuhara, K. Terada, S. Itoh, T. Ozawa, S. Fukuzumi, Chem. Commun. 51 (2015) 8311[3] I. Nakanishi, K. Ohkubo, M. Kamibayashi, Y. Ogawa, T. Ozawa, K. Matsumoto, S. Fukuzumi, ChemistrySelect 1 (2016) 3367[4] O. Friaa, D. Brault, Org. Biomol. Chem. 4 (2006) 2417International Conference 2018 Modern Trends in Natural Sciences and Advanced Technologies in Science Educatio

Ken-ichiro Matsumoto - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Reaction Environments on Radical-Scavenging Mechanisms of Ascorbic Acid
    'The Society for Free Radical Research Japan', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Fukuhara Kiyoshi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    The effect of reaction environment on the radical-scavenging mechanism of ascorbic acid (AscH2) was investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by beta-cyclodextrin (beta-CD) in water to use DPPH in phosphate buffer solutions. The DPPH-scavenging rate of AscH2 in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0), where AscH2 undergoes deprotonation to produced ascorbate anion (AscH-). An organic soluble 5,6-isopropylidene-L-ascorbic acid (iAscH2) was also used to compare the DPPH-scavenging reactivity in MeOH and acetonitrile (MeCN). iAscH2 scavenged DPPH much slower in MeCN than in MeOH. In MeOH, Mg(ClO4)2 significantly decelerated the DPPH-scavenging reaction by AscH2 and iAscH2, while no effect of Mg(ClO4)2 on the rate of the reaction of iAscH2 with DPPH was observed in MeCN. On the other hand, Mg(ClO4)2 significantly accelerated the reaction between AscH2 and beta-CD-solubilized DPPH (DPPH/beta-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO4)2 to the AscH2-DPPH/beta-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, DPPH-scavenging reaction by iAscH2 in MeCN may proceed via a one-step hydrogen-atom transfer as the rate-determining step, while an electron transfer pathway is partly involved in the reaction between AscH2 and DPPH/beta-CD in phosphate buffer solution, although the detailed mechanism for the deceleration effect of Mg(ClO4)2 in MeOH is under investigation. These results demonstrate that the DPPH-scavenging mechanism by AscH2 are affected by the reaction environments

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrzyl Radical by Ascorbic Acid
    'Elsevier BV', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrazy Radical by Ascorbic Acid
    2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media.20th Biennial Meeting of SFRR International (SFRR-I 2021

  • EVALUATION OF THE RADICAL-SCAVENGING ACTIVITY OF ANTIOXIDANTS IN WATER USING A WATER-SOLUBILIZED 2,2-DIPHENYL-1-PICRYLHYDRAZYL RADICAL
    National University of Mongolia Printing House, 2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Ken-ichiro Matsumoto
    Abstract:

    A 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical is relatively stable at room temperature and has been used as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media without organic cosolvents, such as ethanol. Recently, we have succeeded in solubilizing the DPPH radical in water using beta-cyclodextrin. This enables us to evaluate the radical-scavenging activity of water-soluble antioxidants in aqueous media, particularly in physiological concentrations of buffer solutions, with use of the same probe, the DPPH radical as that has been used in organic solvents for 60 years

  • Kinetic Isotope Effect in the Reaction of Water-Soluble Antioxidants with Water-Solubilized 2,2-Diphenyl-1-picrylhydrazyl Radical in Aqueous Buffer Solutions
    'Elsevier BV', 2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto
    Abstract:

    The radical-scavenging activity and mechanism of antioxidants are of considerable importance to develop drugs for oxidative stress-associated diseases. 2,2-Dipheny-1-picrylhydrazyl (DPPH) radical has been frequently used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen radicals. However, the insolubility of the DPPH radical in water has precluded the its use in aqueous solutions without cosolvents. Recently, we have succeeded in solubilizing the DPPH radical in using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous solutions. We report herein the kinetic isotope effect in the reaction of three water-soluble antioxidants, which are ascorbic acid (AscH(2)), Trolox, and (+)-catechin, with the β-CD-solubilized DPPH radical in aqueous buffer solutions.Upon mixing of the β-CD-solubilized DPPH radical in water (Milli-Q) with a phosphate buffer solution (0.1 M, pH 7.0) of AscH(2) at a volumetric ratio of 1:1 on a UNISOKU RSP-1000-02NM stopped-flow spectrophotometer at 298 K, the absorption band at 527 nm due to the DPPH radical immediately decreased. From the kinetic analysis for the decay of the absorbance at 527 nm, the second-order rate constant (k(H)) was in phosphate buffer (0.05 M, pH 7.0) determined to be 7.9 x 10(3) M(-1) s(-1). When H(2)O was replaced by D(2)O to prepare the phosphate buffer solutions, the second-order rate constant (k(D)) for the reaction between AscH(2) and the β-CD-solubilized DPPH radical was significantly smaller than the corresponding k(H) value (k(D) = 1.5 x 10(3) M(-1) s(-1)). Thus, the kinetic isotope effect (k(H)/k(D)) was calculated to be 5.2. The k(H)/k(D) values for Trolox and (+)-catechin were also determined in the same manner to be 7.3 and 6.5, respectively. Based on these results, the scavenging mechanism of the DPPH radical by these antioxidants will be discussed

Ohkubo Kei - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Reaction Environments on Radical-Scavenging Mechanisms of Ascorbic Acid
    'The Society for Free Radical Research Japan', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Fukuhara Kiyoshi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    The effect of reaction environment on the radical-scavenging mechanism of ascorbic acid (AscH2) was investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by beta-cyclodextrin (beta-CD) in water to use DPPH in phosphate buffer solutions. The DPPH-scavenging rate of AscH2 in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0), where AscH2 undergoes deprotonation to produced ascorbate anion (AscH-). An organic soluble 5,6-isopropylidene-L-ascorbic acid (iAscH2) was also used to compare the DPPH-scavenging reactivity in MeOH and acetonitrile (MeCN). iAscH2 scavenged DPPH much slower in MeCN than in MeOH. In MeOH, Mg(ClO4)2 significantly decelerated the DPPH-scavenging reaction by AscH2 and iAscH2, while no effect of Mg(ClO4)2 on the rate of the reaction of iAscH2 with DPPH was observed in MeCN. On the other hand, Mg(ClO4)2 significantly accelerated the reaction between AscH2 and beta-CD-solubilized DPPH (DPPH/beta-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO4)2 to the AscH2-DPPH/beta-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, DPPH-scavenging reaction by iAscH2 in MeCN may proceed via a one-step hydrogen-atom transfer as the rate-determining step, while an electron transfer pathway is partly involved in the reaction between AscH2 and DPPH/beta-CD in phosphate buffer solution, although the detailed mechanism for the deceleration effect of Mg(ClO4)2 in MeOH is under investigation. These results demonstrate that the DPPH-scavenging mechanism by AscH2 are affected by the reaction environments

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrzyl Radical by Ascorbic Acid
    'Elsevier BV', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrazy Radical by Ascorbic Acid
    2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media.20th Biennial Meeting of SFRR International (SFRR-I 2021

  • Reaction of Glutathione and Bio-Related Thiols with 2,2-Diphenyl-1-picrylhydrazyl Radical Solubilized by beta-Cyclodextrin in Water
    2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ueno Megumi, Ozawa Toshihiko, Sekine-suzuki Emiko, Matsumoto Ken-ichiro
    Abstract:

    Glutathione (GSH) is known to act as a redox regulator. However, the radical scavenging mechanism of GSH has yet to be fully clarified. Recently, we have succeeded in solubilizing water-insoluble 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in water using beta-cyclodextrin. In this study, the scavenging mechanism of the water-solubilized DPPH radical by GSH was investigated using the stopped-flow technique.Upon mixing of GSH with the DPPH radical in phosphate buffer (0.05 M, pH 7.4), the absorption band at 527 nm due to the DPPH radical decreased gradually. The pseudo-first order rated constants (kobs), determined from the decay of the absorbance at 527 nm, increased with increasing the GSH concentration and reached a constant value. Furthermore, the higher pH was, the larger the kobs values became. When H2O of the phosphate buffer was replaced with D2O, little change was observed for the kobs values. Thiol compounds with smaller pKa values than GSH, such as L-cysteine, showed higher scavenging activity than GSH under the same experimental conditions. These results suggest that the DPPH radical-scavenging reaction by GSH may proceed via deprotonation of GSH to produce the corresponding thiolate anion, GS-, followed by an electron transfer from GS- to the DPPH radical.19th Biennial Meeting of Society for Free Radical Research International (SFRRI 2018

  • Evaluation of the Radical-Scavenging Activity of Antioxidants in Water Using a Water-Solubilized 2,2-Dipheny-1-picrylhydrazyl Radical
    2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Matsumoto Ken-ichiro
    Abstract:

    2,2-Diphenyl-1-picrylhydrazyl radical (DPPH•), a relatively stable radical, has been used to evaluate the activity of antioxidants as a reactivity model of reactive oxygen species (ROS) for 60 years [1]. However, the insolubility of DPPH• in water has precluded its use in aqueous media without cosolvents such as, ethanol. The pH of the reaction media of antioxidants is of great importance, because antioxidant molecules have one or more ionizable OH groups and their ionization state largely influence the reactivity of antioxidants. However, the pH of the reaction media is not precisely controlled in the presence of the cosolvents. Recently, we have reported that DPPH• is successfully solubilized in water using β-cyclodextrin (β-CD) [2,3]. In this study, we introduce a novel technique to evaluate the kinetic radical-scavenging activity of antioxidants using the β-CD-solubilized DPPH• in physiological concentrations of buffer solutions.25 mL of boiling water (Milli-Q) was added to the solid mixture of DPPH• (0.15 mmol) and β-CD (0.70 mmol). The suspension was stirred until it reached room temperature and filtered with a membrane filter (pore size: 0.22 µm). The as-obtained filtrate showed an absorption band at 527 nm, which is diagnostic of DPPH•. The concentration of DPPH• was estimated by using the ε value of 11000 M–1 cm–1 determined for DPPH• in a 1:1 ethanol–buffer solution [4]. Upon mixing of Trolox, a water-soluble analog of α-tocopherol (vitamin E), with the β-CD-solubilized DPPH• in phosphate buffer solution (0.1 M, pH 7.4) at 298 K, the absorption band at 527 nm decreased immediately. The decay of the absorbance at 527 nm monitored by a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer obeyed pseudo-first-order kinetics, when the concentration of Trolox was maintained at more than a 10-fold excess of DPPH• concentration. The pseudo-first-order rate constants (kobs) linearly increased with increasing the Trolox concentration. From the slope of the linear plot, the second-order rate constant (k) for the scavenging of DPPH• by Trolox was determined to be 1.8 × 104 M–1 s–1. The k value of the reaction between Trolox and DPPH• in methanol at 298 K was determined in the same manner to be 2.3 × 102 M–1 s–1, which is about 80-fold smaller than that in phosphate buffer solution (0.1 M, pH 7.4). Ascorbic acid (AscH2) scavenged the β-CD-solubilized DPPH• with the k value of 7.2 × 103 M–1 s–1 in phosphate buffer solution (0.1 M, pH 7.4) at 298 K. Because the pKa value of AscH2 is known to be 4.1, AscH2 undergoes deprotonation and exists in its anionic form, AscH– in phosphate buffer solution (0.1 M, pH 7.4). Thus, the actual species that scavenged DPPH• is AscH–. On the other hand, in methanol, the kobs value for the DPPH•-scavenging reaction by AscH2 was much smaller than that in phosphate buffer solution (0.1 M, pH 7.4) and constant with the change in the AscH2 concentration used in excess. This suggests that little AscH– was produced by the deprotonation of AscH2 in methanol. Thus, the radical-scavenging activity of antioxidants is largely affected by the nature of solvents. The solubilization of DPPH• in water by β-CD enables us to evaluate the radical-scavenging activity of antioxidants with use of the same probe, DPPH•, as that has been used in organic solvents for 60 years.\nREFERENCES[1] M.S. Blois, Nature 181 (1958) 1199[2] I. Nakanishi, K. Ohkubo, K. Imai, M. Kamibayashi, Y. Yoshihashi, K. Matsumoto, K. Fukuhara, K. Terada, S. Itoh, T. Ozawa, S. Fukuzumi, Chem. Commun. 51 (2015) 8311[3] I. Nakanishi, K. Ohkubo, M. Kamibayashi, Y. Ogawa, T. Ozawa, K. Matsumoto, S. Fukuzumi, ChemistrySelect 1 (2016) 3367[4] O. Friaa, D. Brault, Org. Biomol. Chem. 4 (2006) 2417International Conference 2018 Modern Trends in Natural Sciences and Advanced Technologies in Science Educatio

Ozawa Toshihiko - One of the best experts on this subject based on the ideXlab platform.

  • Effects of Reaction Environments on Radical-Scavenging Mechanisms of Ascorbic Acid
    'The Society for Free Radical Research Japan', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Fukuhara Kiyoshi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    The effect of reaction environment on the radical-scavenging mechanism of ascorbic acid (AscH2) was investigated using 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) as a reactivity model of reactive oxygen species. Water-insoluble DPPH was solubilized by beta-cyclodextrin (beta-CD) in water to use DPPH in phosphate buffer solutions. The DPPH-scavenging rate of AscH2 in methanol (MeOH) was much slower than that in phosphate buffer (0.05 M, pH 7.0), where AscH2 undergoes deprotonation to produced ascorbate anion (AscH-). An organic soluble 5,6-isopropylidene-L-ascorbic acid (iAscH2) was also used to compare the DPPH-scavenging reactivity in MeOH and acetonitrile (MeCN). iAscH2 scavenged DPPH much slower in MeCN than in MeOH. In MeOH, Mg(ClO4)2 significantly decelerated the DPPH-scavenging reaction by AscH2 and iAscH2, while no effect of Mg(ClO4)2 on the rate of the reaction of iAscH2 with DPPH was observed in MeCN. On the other hand, Mg(ClO4)2 significantly accelerated the reaction between AscH2 and beta-CD-solubilized DPPH (DPPH/beta-CD) in phosphate buffer (0.05 M, pH 6.5), although the addition of 0.05 M Mg(ClO4)2 to the AscH2-DPPH/beta-CD system in phosphate buffer (0.05 M, pH 7.0) resulted in the change in pH of the phosphate buffer to be 6.5. Thus, DPPH-scavenging reaction by iAscH2 in MeCN may proceed via a one-step hydrogen-atom transfer as the rate-determining step, while an electron transfer pathway is partly involved in the reaction between AscH2 and DPPH/beta-CD in phosphate buffer solution, although the detailed mechanism for the deceleration effect of Mg(ClO4)2 in MeOH is under investigation. These results demonstrate that the DPPH-scavenging mechanism by AscH2 are affected by the reaction environments

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrzyl Radical by Ascorbic Acid
    'Elsevier BV', 2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media

  • Effect of Reaction Media on the Scavenging Reaction of Water-Solubilized 2,2-Diphenyl-1-picrylhydrazy Radical by Ascorbic Acid
    2021
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Shoji Yoshimi, Ken-ichiro Matsumoto, Fukuzumi Shunichi
    Abstract:

    Background: The radical-scavenging reaction of antioxidants is known to be significantly affected by pH, solvents, and metal ions. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical has been used to evaluate the radical-scavenging activity of antioxidants as a reactivity model of reactive oxygen species. However, the insolubility of the DPPH radical in water has precluded its use in aqueous media. Recently, we have succeeded in solubilizing the DPPH radical in water using β-cyclodextrin (β-CD). This enables us to evaluate the scavenging activity of the DPPH radical by antioxidants in aqueous media. We report herein the effect of reaction media on the scavenging reaction of the DPPH radical by ascorbic acid, a representative water-soluble antioxidant.Methods: 25 mL of boiling water (Milli-Q) was added to the mixture containing the DPPH radical (0.15 mmol) and β-CD (0.70 mmol), and the suspension was cooled to room temperature. The filtration of the suspension by a membrane filter (pore size: 0.22 µm) gave a deep violet solution of the DPPH radical. The rates of the scavenging reaction of the DPPH radical were determined by monitoring the absorbance change due to the DPPH radical using a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer.Results: The second-order rate constant (k) of the reaction between ascorbic acid and the β-CD-solubilized DPPH radical was determined to be 5.4 × 103 M–1 s–1 in phosphate buffer (0.05 M, pH 7.0) at 25 °C. The k value increased with increasing the pH value. Furthermore, magnesium perchlorate significantly accelerated this reaction. On the other hand, when water was replaced by deuterium oxide to prepare the phosphate buffer (0.05 M, pD 7.0), the k value significantly decreased to be 1.5 × 103 M–1 s–1.Conclusion: The scavenging reaction of the DPPH radical by ascorbic acid is significantly affected by reaction media.20th Biennial Meeting of SFRR International (SFRR-I 2021

  • Reaction of Glutathione and Bio-Related Thiols with 2,2-Diphenyl-1-picrylhydrazyl Radical Solubilized by beta-Cyclodextrin in Water
    2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ueno Megumi, Ozawa Toshihiko, Sekine-suzuki Emiko, Matsumoto Ken-ichiro
    Abstract:

    Glutathione (GSH) is known to act as a redox regulator. However, the radical scavenging mechanism of GSH has yet to be fully clarified. Recently, we have succeeded in solubilizing water-insoluble 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in water using beta-cyclodextrin. In this study, the scavenging mechanism of the water-solubilized DPPH radical by GSH was investigated using the stopped-flow technique.Upon mixing of GSH with the DPPH radical in phosphate buffer (0.05 M, pH 7.4), the absorption band at 527 nm due to the DPPH radical decreased gradually. The pseudo-first order rated constants (kobs), determined from the decay of the absorbance at 527 nm, increased with increasing the GSH concentration and reached a constant value. Furthermore, the higher pH was, the larger the kobs values became. When H2O of the phosphate buffer was replaced with D2O, little change was observed for the kobs values. Thiol compounds with smaller pKa values than GSH, such as L-cysteine, showed higher scavenging activity than GSH under the same experimental conditions. These results suggest that the DPPH radical-scavenging reaction by GSH may proceed via deprotonation of GSH to produce the corresponding thiolate anion, GS-, followed by an electron transfer from GS- to the DPPH radical.19th Biennial Meeting of Society for Free Radical Research International (SFRRI 2018

  • Evaluation of the Radical-Scavenging Activity of Antioxidants in Water Using a Water-Solubilized 2,2-Dipheny-1-picrylhydrazyl Radical
    2019
    Co-Authors: Nakanishi Ikuo, Ohkubo Kei, Ozawa Toshihiko, Matsumoto Ken-ichiro
    Abstract:

    2,2-Diphenyl-1-picrylhydrazyl radical (DPPH•), a relatively stable radical, has been used to evaluate the activity of antioxidants as a reactivity model of reactive oxygen species (ROS) for 60 years [1]. However, the insolubility of DPPH• in water has precluded its use in aqueous media without cosolvents such as, ethanol. The pH of the reaction media of antioxidants is of great importance, because antioxidant molecules have one or more ionizable OH groups and their ionization state largely influence the reactivity of antioxidants. However, the pH of the reaction media is not precisely controlled in the presence of the cosolvents. Recently, we have reported that DPPH• is successfully solubilized in water using β-cyclodextrin (β-CD) [2,3]. In this study, we introduce a novel technique to evaluate the kinetic radical-scavenging activity of antioxidants using the β-CD-solubilized DPPH• in physiological concentrations of buffer solutions.25 mL of boiling water (Milli-Q) was added to the solid mixture of DPPH• (0.15 mmol) and β-CD (0.70 mmol). The suspension was stirred until it reached room temperature and filtered with a membrane filter (pore size: 0.22 µm). The as-obtained filtrate showed an absorption band at 527 nm, which is diagnostic of DPPH•. The concentration of DPPH• was estimated by using the ε value of 11000 M–1 cm–1 determined for DPPH• in a 1:1 ethanol–buffer solution [4]. Upon mixing of Trolox, a water-soluble analog of α-tocopherol (vitamin E), with the β-CD-solubilized DPPH• in phosphate buffer solution (0.1 M, pH 7.4) at 298 K, the absorption band at 527 nm decreased immediately. The decay of the absorbance at 527 nm monitored by a stopped-flow technique on a UNISOKU RSP-1000-02NM spectrophotometer obeyed pseudo-first-order kinetics, when the concentration of Trolox was maintained at more than a 10-fold excess of DPPH• concentration. The pseudo-first-order rate constants (kobs) linearly increased with increasing the Trolox concentration. From the slope of the linear plot, the second-order rate constant (k) for the scavenging of DPPH• by Trolox was determined to be 1.8 × 104 M–1 s–1. The k value of the reaction between Trolox and DPPH• in methanol at 298 K was determined in the same manner to be 2.3 × 102 M–1 s–1, which is about 80-fold smaller than that in phosphate buffer solution (0.1 M, pH 7.4). Ascorbic acid (AscH2) scavenged the β-CD-solubilized DPPH• with the k value of 7.2 × 103 M–1 s–1 in phosphate buffer solution (0.1 M, pH 7.4) at 298 K. Because the pKa value of AscH2 is known to be 4.1, AscH2 undergoes deprotonation and exists in its anionic form, AscH– in phosphate buffer solution (0.1 M, pH 7.4). Thus, the actual species that scavenged DPPH• is AscH–. On the other hand, in methanol, the kobs value for the DPPH•-scavenging reaction by AscH2 was much smaller than that in phosphate buffer solution (0.1 M, pH 7.4) and constant with the change in the AscH2 concentration used in excess. This suggests that little AscH– was produced by the deprotonation of AscH2 in methanol. Thus, the radical-scavenging activity of antioxidants is largely affected by the nature of solvents. The solubilization of DPPH• in water by β-CD enables us to evaluate the radical-scavenging activity of antioxidants with use of the same probe, DPPH•, as that has been used in organic solvents for 60 years.\nREFERENCES[1] M.S. Blois, Nature 181 (1958) 1199[2] I. Nakanishi, K. Ohkubo, K. Imai, M. Kamibayashi, Y. Yoshihashi, K. Matsumoto, K. Fukuhara, K. Terada, S. Itoh, T. Ozawa, S. Fukuzumi, Chem. Commun. 51 (2015) 8311[3] I. Nakanishi, K. Ohkubo, M. Kamibayashi, Y. Ogawa, T. Ozawa, K. Matsumoto, S. Fukuzumi, ChemistrySelect 1 (2016) 3367[4] O. Friaa, D. Brault, Org. Biomol. Chem. 4 (2006) 2417International Conference 2018 Modern Trends in Natural Sciences and Advanced Technologies in Science Educatio

Annemarie Lambeir - One of the best experts on this subject based on the ideXlab platform.

  • dpp8 dpp9 inhibition elicits canonical nlrp1b inflammasome hallmarks in murine macrophages
    ISSN: 2575-1077, 2019
    Co-Authors: Nathalia Moraes De Vasconcelos, Gwendolyn Vliegen, Ruth Geissfriedlander, Amanda Goncalves, Emilie De Hert, Rosa Martinperez, Nina Van Opdenbosch, Anvesh Jallapally, Annemarie Lambeir
    Abstract:

    Activating germline mutations in the human inflammasome sensor NLRP1 causes palmoplantar dyskeratosis and susceptibility to Mendelian autoinflammatory diseases. Recent studies have shown that the cytosolic serine dipeptidyl peptidases DPP8 and DPP9 suppress inflammasome activation upstream of NLRP1 and CARD8 in human keratinocytes and peripheral blood mononuclear cells. Moreover, pharmacological inhibition of DPP8/DPP9 protease activity was shown to induce pyroptosis in murine C57BL/6 macrophages without eliciting other inflammasome hallmark responses. Here, we show that DPP8/DPP9 inhibition in macrophages that express a Bacillus anthracis lethal toxin (LeTx)–sensitive Nlrp1b allele triggered significantly accelerated pyroptosis concomitant with caspase-1 maturation, ASC speck assembly, and secretion of mature IL-1β and IL-18. Genetic ablation of ASC prevented DPP8/DPP9 inhibition-induced caspase-1 maturation and partially hampered pyroptosis and inflammasome-dependent cytokine release, whereas deletion of caspase-1 or gasdermin D triggered apoptosis in the absence of IL-1β and IL-18 secretion. In conclusion, blockade of DPP8/DPP9 protease activity triggers rapid pyroptosis and canonical inflammasome hallmarks in primary macrophages that express a LeTx-responsive Nlrp1b allele.

  • structure activity relationship studies on isoindoline inhibitors of dipeptidyl peptidases 8 and 9 dpp8 dpp9 is dpp8 selectivity an attainable goal
    Journal of Medicinal Chemistry, 2011
    Co-Authors: Sebastiaan Van Goethem, Veerle Matheeussen, Koen Augustyns, Ingrid De Meester, Xin Chen, Annemarie Lambeir, Jurgen Joossens, Achiel Haemers, Pieter Van Der Veken
    Abstract:

    This work represents the first directed study to identify modification points in the topology of a representative DPP8/9-inhibitor, capable of rendering selectivity for DPP8 over DPP9. The availability of a DPP8-selective compound would be highly instrumental for studying and untwining the biological roles of DPP8 and DPP9 and for the disambiguation of biological effects of nonselective DPP-inhibitors that have mainly been ascribed to blocking of DPPIV's action. The cell-permeable DPP8/9-inhibitor 7 was selected as a lead and dissected into several substructures that were modified separately for evaluating their potential to contribute to selectivity. The obtained results, together with earlier work from our group, clearly narrow down the most probable DPP8-selectivity imparting modification points in DPP8/9 inhibitors to parts of space that are topologically equivalent to the piperazine ring system in 7. This information can be considered of high value for future design of compounds with maximal DPP8 selectivity.