Structure-activity Relationship Analysis Of Six Dietary 5,7-Dihydroxyflavones On Regulating Inflammation And Lipid Metabolism

Lipid metabolism in adipose tissue,including lipogenesis,browning and related inflammation,plays an important role in regulating obesity and related metabolic diseases.Many dietary flavonoids are shown to have anti-inflammatory activity,antiobesity activity as well as potentiality to improve energy metabolism.Luteolin(LU),apigenin(AP),chrysin(CH),quercetin(QU),myricetin(MY)and kaempferol(KA)are the most common flavonoids and flavonols in food respectively,and they are all 5,7-dihydroxyflavone analogs.However,the difference in the activities of these six flavonoids in regulating inflammation and lipid metabolism and their possible structure-activity relationship remains unclear.In the present study,we evaluated the differences in the activity of the above six 5,7-dihydroxyflavones based on the three in vitro models of inflammatory polarization in macrophages,adipogenic and browning in adipocytes,and delineated the structural determinants involved in their activity.The inhibition effects of six 5,7-dihydroxyflavones on M1 polarization were studied in RAW264.7 and bone marrow derived macrophages stimulated by LPS.Flow cytometry analysis suggested that all the six flavonoids showed inhibition effects on the expression of CD274 and CD38,of which the effects of three flavones were significantly stronger than that of three flavonols.Among the three flavones,the antiinflammatory activity was ranked as follows: LU > AP > CH,while among the three flavonols,QU showed the strongest inhibitory activity,indicating that hydroxylation at position 3 on ring C is not conducive to its anti-inflammatory activity while the hydroxylations at positions 3’ and 4’ on the B ring are beneficial to enhance its activity.In the aspect of lipogenesis,3T3-L1 and subcutaneous primary adipocytes of mice were used as the model of adipocyte differentiation.Lipid deposition was detected by oil red staining.Adipogenic gene expressions was detected by RT-PCR.The results showed that the inhibitory effect of six 5,7-dihydroxyflavones on adipogenesis was ranked as follows: LU > QU/MY > AP/KA > CH,indicating that hydroxylations at positions 3’ and 4’ on the B ring are beneficial to enhance its activity while hydroxylation at position 3 on ring C is not conducive to its activity.In the aspect of browning,subcutaneous primary adipocytes of mice were differentiated to brown adipocytes,which was used as the model of adipocyte browning.The effects of six 5,7-dihydroxyflavones on the expression of thermogenic genes and beige cell markers were detected by RT-PCR,and the expression levels of AMPK/PGC1α pathway proteins were detected by Western blot.The result showed that LU has significant effect in promoting browning,indicating hydroxylations at positions 3’ and 4’ on the B ring are beneficial to enhance its activity.In summary,the structure-activity relationship of six 5,7-dihydroxyflavones on regulating inflammation and lipid metabolism was summarized and discussed in this paper,providing ideas for further utilization of dietary flavonoids.