Zinc Oxide Nanoparticles Synthesized Using Coffee Leaf Extract Assisted With Ultrasound As Nanocarriers For Mangiferin And The Anticancer Activity

Zinc oxide nanoparticles(ZnO NPs)are function as usually anticancer drugs and drug delivery carriers.The traditional physical and chemical methods used to synthesize ZnO NPs have several drawbacks such as serious pollution,high energy consumption,and harm for human health;however the green synthesis of ZnO NPs using plant extract has the advantages of high efficiency,environmental friendly,nontoxicity,and low cost.Ultrasound-assisted synthesis of ZnO NPs can accelerate the reaction rate,reduce particle size,and improve yield.As a low-value by-product of coffee tree,coffee leaves are rich in polyphenolic compounds,sugars,and proteins,which can provide a large amount of reductants,stabilizing agents,chelating agents,and capping agents for green synthesis of ZnO NPs.Mangiferin(MGF)is a polyphenolic substance with anticancer and anti-inflammatory activities;however,its low solubility and bioavailability affect its biological activity.In this paper,we investigated the conditions of ultrasound-assisted green synthesis of ZnO NPs using coffee leaf extract and analyzed the characteristics of as-synthesized ZnO NPs.Thereafter,mangiferin was loaded on the as-synthesized ZnO NPs and the inhibitory effects on cancer cells,including Hep G2 and Caco-2 were investigated.The main findings of this paper are as follows:(1)One factor at a time experimental design was used to screen the synthesis conditions with the highest yield of ZnO NPs,which include: p H value,8;mass ratio of coffee leaf to zinc acetate,1.71 : 1;ultrasound time,10 min;ultrasound frequency,28/40 k Hz;ultrasound power,180 W;and synthesis temperature,30 ℃.The yield of ZnO NPs synthesized under this condition(43.59%)was significantly higher than that of the control group non-ultrasound-assisted synthesis(41.45%)and chemical synthesis methods(24.79%).Therefore,ultrasound-assisted green synthesis of ZnO NPs using coffee leaf extract can not only shorten the synthesis time and reduce the synthesis temperature,but also improve the synthesis yield.(2)By comparing the total phenolic content(TPC)in the two reaction systems with and without ultrasound treatment,it was found that TPC decreased by 98.16% in the ultrasound-assisted synthesis system,and the degree of decrease was significantly higher than that in the non-ultrasound-assisted synthesis system(97.10%).Further analysis of phytochemical components found that polyphenolic compounds including mangiferin,rutin,and chlorogenic acid were reduced by 95.29%-100% in these two reaction systems,while the content of trigonelline and caffeine was only reduced by18.47%-36.06%,indicating that polyphenols,especially 5-caffeoylquinic acid(5-CQA),were the main reductants and chelating agents for the synthesis of ZnO NPs.The study also found that the contents of 5-CQA,trigonelline,and caffeine in the ultrasoundassisted synthesis system were significantly(P < 0.05)lower than that in the nonultrasound-assisted synthesis system.After characterization of ZnO NPs synthesized in these three reaction systems using UV-Vis,SEM,EDX,TEM,FTIR,XRD,and Zeta potential,it was found that the average particle size of the ultrasound-assisted synthesized ZnO NPs was 8.29 nm,which was significantly smaller than ZnO NPs synthesized by the non-ultrasound-assisted(10.48 nm)and chemical methods(17.15nm).The ZnO NPs synthesized by the three methods were all spherical-like in shape,with hexagonal wurtzite structure,good crystallinity,and high purity.(3)The drug loading and encapsulation efficiency of MGF-ZnO NPs were 3.66%and 19.01%,respectively,and the in vitro cumulative release of MGF after 132 h was96.24%.MGF-ZnO NPs significantly reduced the viability of Hep G2 and Caco-2 cells;decreased the intracellular p H;increased the cell membrane permeability,thereby increasing the release of lactate dehydrogenase(LDH);increased the intracellular reactive oxygen species(ROS)level and then leading to the oxidative stress in cells;promoted cellular chromatin condensation and nuclear lysis;increased the overall apoptotic ratio of cells and induced cell cycle arrest in G2/M phase and S phase in Hep G2 and Caco-2 cells,respectively.Therefore,MGF-ZnO NPs can enhance the inhibitory effect on cancer cells,therefore,they are considered promising anticancer drugs.