Open Access

Nobiletin, a citrus flavonoid, activates vasodilator-stimulated phosphoprotein in human platelets through non-cyclic nucleotide-related mechanisms

  • Authors:
    • Thanasekaran Jayakumar
    • Kao-Chang Lin
    • Wan-Jung Lu
    • Chia-Ying Lin
    • Geraldine Pitchairaj
    • Jiun-Yi Li
    • Joen-Rong Sheu
  • View Affiliations

  • Published online on: December 7, 2016     https://doi.org/10.3892/ijmm.2016.2822
  • Pages:174-182
  • Copyright: © Jayakumar et al. This is an open access article distributed under the terms of Creative Commons Attribution License.

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Abstract

Nobiletin, a bioactive polymethoxylated flavone, has been described to possess a diversity of biological effects through its antioxidant and anti-inflammatory properties. Vasodilator-stimulated phosphoprotein (VASP) is a common substrate for cyclic AMP and cyclic GMP-regulated protein kinases [i.e., cyclic AMP-dependent protein kinase (PKA; also known as protein kinase A) and cyclic GMP-dependent protein kinase (PKG; also known as protein kinase G)] and it has been shown to be directly phosphorylated by protein kinase C (PKC). In the present study, we demonstrate that VASP is phosphorylated by nobiletin in human platelets via a non-cyclic nucleotide-related mechanism. This was confirmed by the use of inhibitors of adenylate cyclase (SQ22536) and guanylate cyclase [1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ)], since they prevented VASP phosphorylation induced by nobiletin. Furthormore, this event was also not affected by specific inhibitors of PKA (H-89), PKG (KT5823) and PKC (Ro318220), representing cyclic nucleotide-dependent pathways upon nobiletin-induced VASP phosphorylation. Similarly, inhibitors of p38 mitogen-activated protein kinase (MAPK; SB203580), extracellular signal-regulated kinase 2 (ERK2; PD98059), c-Jun N-terminal kinase 1 (JNK1; SP600125), Akt (LY294002) and nuclear factor-κB (NF-κB; Bay11-7082) did not affect nobiletin‑induced VASP phosphorylation. Moreover, electron spin resonance, dichlorofluorescein fluorescence and western blotting techniques revealed that nobiletin did not affect hydroxyl radicals (OH•), intracellular reactive oxygen species (ROS) and on protein carbonylation, respectively. Furthermore, the nobiletin‑induced VASP phosphorylation was surprisingly reversed by the intracellular antioxidant, N-acetylcysteine (NAC), but not by the inhibitor of NADPH oxidase, diphenyleneiodonium chloride (DPI). It was surprising to observe the differential effects of nobiletin and NAC on VASP phosphorylation in human platelets, since they both have been reported to have antioxidant properties. The likely explanation for this discrepancy is that NAC may bind to allosteric sites on the receptor different from those that nobiletin binds to in human platelets. Taken together, our findings suggest that nobiletin induces VASP phosphorylation in human platelets through non-cyclic nucleotide-related mechanisms. Nevertheless, the exact mechanisms responsible for these effects need to be further confirmed in future studies.

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January 2017
Volume 39 Issue 1

Print ISSN: 1107-3756
Online ISSN:1791-244X

2015 Impact Factor: 2.348
Ranked #22/123 Medicine Research and Experimental
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APA
Jayakumar, T., Lin, K., Lu, W., Lin, C., Pitchairaj, G., Li, J., & Sheu, J. (2017). Nobiletin, a citrus flavonoid, activates vasodilator-stimulated phosphoprotein in human platelets through non-cyclic nucleotide-related mechanisms. International Journal of Molecular Medicine, 39, 174-182. https://doi.org/10.3892/ijmm.2016.2822
MLA
Jayakumar, T., Lin, K., Lu, W., Lin, C., Pitchairaj, G., Li, J., Sheu, J."Nobiletin, a citrus flavonoid, activates vasodilator-stimulated phosphoprotein in human platelets through non-cyclic nucleotide-related mechanisms". International Journal of Molecular Medicine 39.1 (2017): 174-182.
Chicago
Jayakumar, T., Lin, K., Lu, W., Lin, C., Pitchairaj, G., Li, J., Sheu, J."Nobiletin, a citrus flavonoid, activates vasodilator-stimulated phosphoprotein in human platelets through non-cyclic nucleotide-related mechanisms". International Journal of Molecular Medicine 39, no. 1 (2017): 174-182. https://doi.org/10.3892/ijmm.2016.2822