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

<div><p>Oxidative stress has been associated with diverse diseases, including obesity, cancer and neurodegeneration. In fact, <i>Valeriana jatamansi</i> 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-<i>β</i> 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.</p></div

Proposed mechanism for the DPPH^• reaction.

<p>Proposed mechanism for the DPPH^• reaction.</p

Structural formulas of V, AV and BAV.

<p>Structural formulas of V, AV and BAV.</p

MS and MS/MS spectroscopic data for the iridoid valepotriates and their degradation products.

<p>MS and MS/MS spectroscopic data for the iridoid valepotriates and their degradation products.</p

Antioxidant effect of the iridoid valepotriates assessed through ABTS and DPPT^• assays.

<p>Antioxidant effect of the iridoid valepotriates assessed through ABTS and DPPT^• assays.</p

Effect of V, AV, BAV and their degradation products on ROS in HepG2 cells.

<p>ROS in the cells was labelled with DCFH-DA and measured by flow cytometry. (A—G) Results for the (A) control, (B) V (-20°C), (C) V (25°C for 7 days), (D) AV (-20°C), (E) AV (25°C for 7 days), (F) BAV (-20°C) and (G) BAV (25°C for 7 days) groups. (H) The data are presented as the means ± SDs from three separate experiments (* <i>p</i> < 0.05).</p

Proposed interactions between valepotriates and the GABAergic signalling pathway.

<p>Proposed interactions between valepotriates and the GABAergic signalling pathway.</p

DataSheet1_SLC2A9 rs16890979 reduces uric acid absorption by kidney organoids.docx

Introduction: The excretion and absorption of uric acid (UA) by the kidneys helps regulate serum UA levels. GLUT9, encoded by SLC2A9, is mainly expressed in the renal tubules responsible for UA absorption. SLC2A9 polymorphisms are associated with different serum UA levels. However, the lack of proper in vitro models has stalled research on the mechanisms of single nucleotide polymorphisms (SNPs) that affect UA metabolism in human urate transporters.Methods: In this study, we constructed a gene-edited human embryonic stem cells-9 (ESC-H9) derived kidney organoid bearing rs16890979, an SLC2A9 missense mutation with undetermined associations with hyperuricemia or hypouricemia. Kidney organoids derived from ESC-H9 with genetical overexpression (OE) and low expression (shRNA) of SLC2A9 to serve as controls to study the function of SLC2A9. The function of rs16890979 on UA metabolism was evaluated after placing the organoids to urate-containing medium and following histopathological analysis.Results: The kidney organoids with heterozygous or homozygous rs16890979 mutations showed normal SLC2A9 expression levels and histological distribution, phenotypically similar to the wild-type controls. However, reduced absorption of UA by the kidney organoids with rs16890979 mutants was observed. This finding together with the observation that UA absorption is increased in organoids with SLC2A9 overexpression and decreased in those with SLC2A9 knockdown, suggest that GLUT9 is responsible for UA absorption, and the rs16890979 SNP may compromise this functionality. Moreover, epithelial-mesenchymal transition (EMT) was detected in organoids after UA treatment, especially in the kidney organoid carrying GLUT9OE, suggesting the cytobiological mechanism explaining the pathological features in hyperuricosuria-related renal injury.Discussion: This study showing the transitional value of kidney organoid modeling the function of SNPs on UA metabolism. With a defined genetic background and a confirmed UA absorption function should be useful for studies on renal histological, cellular, and molecular mechanisms with this organoid model.</p