Flavonoids are substances that have been studied in-depth and at length in traditional Chinese medicine. They exist widely throughout the kingdom Plantae. Many studies have been absorbed on the abilities of flavonoids to reduce blood lipid levels, inhibit lipid peroxidation, relieve coughs, eliminate phlegm and asthma, and exert anti-tumor, anti-hepatotoxicity, anti-inflammatory, analgesic, antibacterial, and antispasmodic effects. Substances known to reduce UA include quercetin, luteolin, apigenin, puerarin, catechins, and dyestuffs, but there have been few studies into the UA-lowering activities of aspen and daidzein.
In this experiment, extensive targeted metabolomics methods were used to compare the flavonoids present in the fruit of two varieties of Actinidia arguta Sieb.Zucc. cultivated in Northern China. Nine classes and 125 kinds of flavonoids were detected in the fruits of the two varieties; these included 39 kinds of differentially accumulated flavonoids, accounting for 31.2% of the total flavonoids detected. This proved that there was a remarkable distinction in flavonoid composition and accumulation between different varieties. The types and proportions of different flavonoids found in the fruits were as follows: 51.2% flavonols, 14.4% flavonoids, 9.6% dihydroflavonoids, 9.6% flavonols, 1.6% chalcones, 2.4% flavone carboglycosides, 4.8% dihydroflavonols, 0.8% isoflavones, and 5.6% procyanidins. The relative flavonoid content in the fruits of variety Qssg was higher (1.13×) than in LC variety fruits. These data provide a valuable theoretical and practical basis for breeding new varieties of Actinidia arguta Sieb.Zucc. and developing food and drug homologous functional foods.
The flavonoids rutin, populin, and daidzein were isolated from the fruit of the main variety of Actinidia arguta Sieb. Zucc. cultivated in Northern China and tested for their UA-reducing activity. The results showed that populin (flavone1), rutin (flavone2), and daidzein (flavone3) could reduce serum levels of UA, BUN, Cr, and GAPDH in mice to varying degrees. We, therefore, speculate that UA production in mice (in response to purine-rich food ingestion or catabolism of substances such as nuclear proteins and nucleic acids) may be inhibited by reducing the activities of ADA and/or XO. Increases in liver glycogen content in mice may be due to inhibition of glycolysis by flavonoids through the promotion of gluconeogenesis, reduction of free glucose in the blood, promotion of the remedial synthesis pathway of nucleotides, and decreases in serum UA content. This study, therefore, has strong practical significance for the prevention and control of human Hua through the comprehensive development of Actinidia arguta Sieb. Zucc.. as a treatment.
Through pathway enrichment analysis of flavonoids in Actinidia arguta Sieb. Zucc.., we found that the 125 flavonoids identified in the fruits were mainly distributed in three metabolic pathways: the flavonoid and flavonol BP, the flavonoid BP, and the secondary metabolite BP. This finding provides a strong basis for the observed enrichment of flavonoids in Actinidia arguta Sieb. Zucc.
There are two general types of genes bound up with the biosynthesis of plant flavonoids . The first category is structural genes, which encode enzymes that catalyze the biosynthesis of different flavonoids; the second category is regulatory genes, which control the transcription of structural genes [33,35]. Through transcriptome analysis, 43,686 genes were identified as related to flavonoid biosynthesis in the fruits of two main varieties of Actinidia arguta Sieb. Zucc, including 11,650 differentially expressed genes. These genes regulate metabolism, cellular processes, genetic information processing, environmental information, and tissue systems in the fruits of Actinidia arguta Sieb. Zucc. Through KEGG enrichment analysis and gene functional annotation, 41 DEGs encoding enzymes known to be involved in flavonoid biosynthesis were identified (containing CsUGT134, LOC, AT2, CHS, CHI, C4Ha, HCT, CCoAOMT, F3H, CFOL, DFR, LAR2, LSAT, and GSCOC). Among these DEGs, three CsUGT 134 genes, one LAR2, one C4Ha, two CFOL, one CHI, nine LOC, one GSCOC, one CCoAOMT, one DFR, and two AT2 genes are crucial to flavonoid biosynthesis.
A correlation analysis between transcriptome and metabolome profiles showed that expression levels of some structural genes were closely bound up with the accumulation of specific flavonoids, demonstrating that expression of these flavonoid biosynthesis genes promoted flavonoid accumulation during fruit ripening of the two main varieties of Actinidia arguta Sieb. Zucc. CHS, CHI, F3H, cfol, LOC, LSAT, fnsi, DFR, F3'H, FLS, and Hidh may play structural or regulatory roles in the BPs of the flavonoid compounds aspen (flavone1), rutin (flavone2), and/or daidzein (flavone3). DFR, F3'H, and FLS compete with the substrate dihydrokaempferol (DHK); FLS expression was relatively high, and the encoded enzyme activity was high, which ultimately promotes rutin accumulation. LOC expression was relatively low, as were the relative levels of populin and daidzein.
In conclusion, these results expand our understanding of Hua prevention and control by flavonoids. The results also demonstrate the mechanisms of flavonoid biosynthesis and accumulation in Actinidia arguta Sieb. Zucc.. In total, these data provide precious information for the future development of novel food and drug homologous functional foods using Actinidia arguta Sieb. Zucc..