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Studies of the structure-antioxidant activity relationships and antioxidant activity mechanism of iridoid valepotriates and their degradation products.

ABSTRACT: Oxidative stress has been associated with diverse diseases, including obesity, cancer and neurodegeneration. In fact, Valeriana jatamansi Jones (valerian) and its extracts possess strong antioxidant activities that extend their application in clinical practice to the treatment of these illnesses, even though the underlying mechanisms are not well understood. Iridoid valepotriate, a characteristic iridoid ester in valerian with poor chemical stability, possesses considerable antioxidant components. The original compounds and their degradation products have been found to exhibit strong antioxidant activities. However, the relationship between their structure and antioxidant effects and the mechanism underlying their oxidation resistance remain unclear. A forced degradation study using three iridoid valepotriates (valtrate, acevaltrate and 1-β acevaltrate) was performed in this work, and the structures of their degradation products were estimated by TLC-MS and LC-MS. Comparison of the antioxidant activities of the iridoid valepotriates before and after forced degradation revealed that degradation reduced the activities of the iridoid valepotriates in free radical scavenging and cytotoxic and cell apoptosis tests. The results suggested that the oxirane nucleus is important for defining the antioxidant profile of iridoid valepotriate. We uncovered possible mechanisms that could explain the antioxidant activities, including the generation of two hydroxyl groups through intramolecular transfer of an H• from an oxirane ring and a reduction in ROS levels through interactions with GABAergic signalling pathways.

SUBMITTER: Wang F

PROVIDER: S-EPMC5726618 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Isoflavonoids such as genistein (GE) are well known antioxidants. The predictive biological activity of structurally new compounds such as thiogenistein (TGE)-a new analogue of GE-becomes an interesting way to design new drug candidates with promising properties. Two oxidation strategies were used to characterize TGE oxidation products: the first in solution and the second on the 2D surface of the Au electrode as a self-assembling TGE monolayer. The structure elucidation of products generated by different oxidation strategies was performed. The electrospray ionization mass spectrometry (ESI-MS) was used for identifying the product of electrochemical and hydrogen peroxide oxidation in the solution. Fourier transform infrared spectroscopy (FT-IR) with the ATR mode was used to identify a product after hydrogen peroxide treatment of TGE on the 2D surface. The density functional theory was used to support the experimental results for the estimation of antioxidant activity of TGE as well as for the molecular modeling of oxidation products. The biological studies were performed simultaneously to assess the suitability of TGE for antioxidant and antitumor properties. It was found that TGE was characterized by a high cytotoxic activity toward human breast cancer cells. The research was also carried out on mice macrophages, disclosing that TGE neutralized the production of the LPS-induced reactive oxygen species (ROS) and exhibits ABTS (2,2'-azino-bis-3-(ethylbenzothiazoline-6-sulphonic acid) radical scavenging ability. In the presented study, we identified the main oxidation products of TGE generated under different environmental conditions. The electroactive centers of TGE were identified and its oxidation mechanisms were proposed. TGE redox properties can be related to its various pharmacological activities. Our new thiolated analogue of genistein neutralizes the LPS-induced ROS production better than GE. Additionally, TGE shows a high cytotoxic activity against human breast cancer cells. The viability of MCF-7 (estrogen-positive cells) drops two times after a 72-h incubation with 12.5 μM TGE (viability 53.86%) compared to genistein (viability 94.46%).

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Studies of the structure-antioxidant activity relationships and antioxidant activity mechanism of iridoid valepotriates and their degradation products.

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