Study On The Cytotoxicity Of Gold And Silver Nanoparticles Modified By Gallic Acid

Gallic acid (GA), or3,4,5-trihydroxybenzoic acid, is found in many fruits andplants either as a free molecule or as part of tannic acid molecule. It is well knownfor its natural antioxidative, antiallergic, antimutagenic, anticarcinogenic, antiviral,anti-bacterial and anti-inflammatory abilities. It has also been found to selectivelyinduce apoptosis in some tumor cell lines and plays an important role in preventingmalignant transformation and cancer development.Nanomaterials must have at least one dimension between1and100nanometers.Nanomaterials often have unique optical, electronic or mechanical properties due tothe effects of the small size and large surface area. Nanomaterials are increasinglypenetrated into the nature of biological and medical fields and provide moresensitive and reliable methods for the development of modern biological imaging,medical diagnosis and treatment. Precious metals such as gold and silvernanoparticles alone or as the structure units of nanomaterials occupy very importantpositions on the applications of optics, catalysis, biological and medical engineering.GA has been coated onto gold nanoparticles (GA-AuNPs) for somebio-analytical applications, but the influences of GA-AuNPs on human cell lineshave not been studied before. In this study, we synthesized GA-AuNPs using amodified method, in which GAwas served as both the reducer and the stabilizer. Wefirstly characterized the size and the absorption spectrum of GA-AuNPs using atransmission electron microscope (TEM) and a UV-vis-NIR spectrophotometer,respectively. Then, we determined the proportions of GA that combined onto theGA-AuNPs by comparing the absorption peaks of GA before and after the syntheticreaction. Finally, we compared the biochemical effects, such as the cytotoxicity and induction of apoptosis of the GA-AuNPs to that of free GA at the concentrations of0.065,0.13,0.26,0.52and0.65mM on a human hepatocyte cell line (HL-7702).The results indicated that GA-AuNPs contained lower cytotoxicity and were lesslikely to induce apoptosis in HL-7702cells. There were two phenolic hydroxylsoxidation of GA to their quinine forms during the synthesis of the GA-AuNPs,which was the only chemical change in GA. So the different cytotoxicity betweenfree GAand GA-AuNPs suggested that these phenolic hydroxyls were necessary forthe bioactivity of GA. This study might also reveal an easier and new way toilluminate that the phenolic hydroxyls were very important for the cytocidal andcytopathic effects of GAon cells.Antibiotic resistance of the microorganisms brings new challenges fordeveloping drugs to overcome infections. Silver nanoparticles (AgNPs) areattractive alternatives to antibiotics for containing broad-spectrum antimicrobialactivities. We synthesized GA coated silver nanoparticles (GA-AgNPs) using agreen method at room temperature, in which GA acted as both the reducer andstabilizer. The size, morphology and absorption spectrum of GA-AgNPs weredetermined using dynamic light scattering (DLS), transmission electron microscopy(TEM) and UV-vis spectroscopy, respectively. We used the microdilution method toinvestigate the antimicrobial activitiesof GA-AgNPs against Escherichia coli (E.coli), Staphylococcus aureus (S. aureus) and Candida albicans (C. albicans), theminimum inhibitory concentrations (MICs) of which were6,30and24μg/mL,respectively. Then, we used the MTT and Calcein-AM/PI staining assays to studythe cytotoxicity of GA-AgNPs at the concentrations of6,12,18and30μg/mL tohuman cervical carcinoma (HeLa) and HL-7702cells, the results of whichdemonstrated that GA-AgNPs had fewer toxic effects on HL-7702cells than that onHeLa cells. We also studied the influences of GA-AgNPs on the apoptosis of abovecell lines using Annexin-V/PI binding and Hoechst33342staining assays. Theresults showed that there were more proportions of both early and late apoptotic cells in the groups of HeLa cells. Then, we investigated the mitochondrialmembrane potential (MMP) and reactive oxygen species (ROS) of the two cell linesafter the treatment, which might be involved in the cytotoxicity and apoptosisinduced by GA-AgNPs. It was found that GA-AgNPs induced more MMP loss andintracellular ROS generation in HeLa than that in HL-7702cells. The results in thisstudy indicated that GA-AgNPs with good biocompatibility could be a potentialcandidate for fighting infections caused by microorganisms and be used inpharmaceutical applications.