Browsing by Author "Zhang, Haolin"

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    Amination of Flavonoids Possessing a Pyrogallol Group in Cell Culture Medium at 37◦C
    (Wiley, 2025-02-18) Zhang, Haolin; Zhang, Jingjing; Cao, Hui; Högger, Petra; Arroo, Randolph; Farag, Mohamed A.; Shpigelman, Avi; Xiao, Jianbo; Li, Chunlin
    A class of flavonoid aminated derivatives that had been consistently overlooked in literaturewas shown to be formed as artefacts in cell culturemedium. In this study, 34 flavonoids from different subclasses were incubated in Dulbecco’s modified Eagle’sMedium (DMEM) at 37◦C for 2 h to identify the reaction mechanism behind aminated derivatives formation from flavonoids. Baicalein, scutellarein, dihydromyricetin, (−)-gallocatechin (GC), (−)-epigallocatechin (EGC), (−)-GC gallate, and (−)-EGC gallate were found to yield corresponding nitrogenous derivatives in both DMEM and amino acid solution. The nitrogen source of these seven flavonoid -aminated derivatives was revealed to be amino acids in DMEM. The pyrogallol group of the flavonoids was a key structural motif, being first oxidized into quinone and then further reacting with amino acids (Strecker degradation) to yield aminated flavonoids and corresponding aldehydes. A slightly alkaline environment accelerated the amination of flavonoids, possibly via the formation of flavonoid quinone. These results provide the mechanistic evidence for the in vitro generation of flavonoid -aminated derivatives, yet to be tested using in vivo assays.
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    Stability and antioxidant capacity of epigallocatechin gallate in Dulbecco’s modified eagle medium.
    (Elsevier, 2021-07-05) Wang, Minglong; Zhang, Haolin; Yi, Lunzhao; Högger, Petra; Arroo, R. R. J.; Bajpal, Vivek K.; Prieto, Miguel-Angel; Simel-Gandara, Jesus; Wang, Shengpeng; Cao, Hui
    Though the instability of polyphenols in cell culture experiment has been investigated previously, the underlying mechanism is not completely clear yet. Therefore, in this study, the stability of epigallocatechin gallate (EGCG) in cell culture medium DMEM was investigated at 4 ◦C and 37 ◦C via UPLC-MS-MS analysis followed by determination of the antioxidant capacity of EGCG. EGCG was instable in DMEM and formed various degradation products derived from its dimer with increasing incubation time with many isomers being formed at both temperatures. The dimer products were more stable at 4 ◦C than at 37 ◦C. The structure and formation mechanism of five products were analyzed with four unidentified. Ascorbic acid significantly improved the stability of EGCG by protecting EGCG from auto-oxidation in DMEM, particularly at 4 ◦C. The antioxidative activity of EGCG in DMEM was determined by DPPH, ABTS and FRAP assay. The antioxidative properties of EGCG continuously decreased over 8 h in DMEM, which was consistent with its course of degradation.