The widespread use of nanomaterials in biomedicine (for example, in gene delivery, cellular imaging and tumour therapy) has been accompanied by an increasing interest in understanding their interactions with tissues, cells and biomolecules, as well as how they might affect the integrity of cell membranes and proteins which is critical for designing safer biomedical applications. Recently, graphene (a two-dimensional nanomaterial) was shown to have antibacterial activity on E. coli, but its underlying molecular mechanisms remain unknown.
In this project, we show experimentally and theoretically that graphene nanosheets can insert/cut through the cell membranes of E. coli and vigorously extract large amounts of phospholipids from the membranes. Our experiments show that this process causes degradation of E. coli membranes and reduces bacteria viability. Molecular dynamics simulations reveal atomic details on how graphene and graphene oxide interact with the inner and outer membranes of E. coli. To the best of our knowledge, such a destructive extraction of phospholipids by graphene has not been reported previously, and the findings may offer insights for the better design of graphene-based antibiotics or other biomedical applications.
B. Endohedral Metallofullerenol Gd@C82(OH)22 and Pancreatic Cancer
Pancreatic adenocarcinoma is the most lethal of the solid tumors and the fourth most common cause of cancer-related death in North America. Inhibition of matrix metalloproteinases (MMPs) has long been viewed as a potential anticancer therapy because of MMP's seminal roles in both angiogenesis and extracellular matrix (ECM) degradation. These two processes are related to tumor survival and invasion. However, the questions of both the ability to selectively inhibit MMPs and the mechanism by which inhibition occurs remain unanswered.
In this project, we investigated the inhibition capability and underlying molecular mechanism of Gd@C82(OH)22 using a combination of in vivo, in vitro, and in silico approaches. Our nude mouse model clearly shows that Gd@C82(OH)22 effectively blocks tumor growth in human pancreatic cancer xenografts. Our in vitro assays have shown that Gd@C82(OH)22 not only depresses expressions of MMPs but also reduces their activities. Meanwhile, our molecular-dynamics simulations have revealed detailed inhibition dynamics and molecular mechanism behind the Gd@C82(OH)22 - MMP-9 interaction. Our findings provide insights for de novo design of nanomedicine for fatal diseases such as pancreatic cancer, and also imply that the pharmacokinetic action of nanoparticles could be markedly different from the traditional target-based molecular drugs.
C. Potential Nanomedicine for AD
The rapid increase of Alzheimer’s disease (AD) concurrent with the aging population worldwide has posed a significant challenge to today’s health care systems. Current therapies for AD, such as small-molecule-based inhibitors, provide a moderate symptomatic reduction or delay at various stages of the disease, but do not arrest the disease progression. As such, novel approaches, including nanomaterial-based nanodrugs or nanotherapies, are in urgent need. Inspired by our recent work on graphene antibacterial activity (Zhou and coworkers, Nature Nanotech 8, 894-601, 2013), where graphene nanosheets can penetrate into cell membranes and also extract large amounts of phospholipids directly from the lipid bilayer, we wonder whether graphene nanosheets could also dissociate and break down the preformed mature amyloid aggregates associated with AD.
In this study, we show, both experimentally and theoretically, that pristine graphene and graphene-oxide nanosheets can not only inhibit the Aβ peptide monomer fibrillation, but also break down mature amyloid fibrils. This provides great promise in reducing the progress of peptide aggregation, a critical step in the AD pathogenesis. Our molecular dynamics simulations first reveal that graphene nanosheets can both penetrate into and extract large amounts of peptides from the preformed amyloid fibrils, due to the exceptionally strong dispersion interactions between graphene and peptides. These interactions are further enhanced by strong π-π stacking between the aromatic residues of the Aβ peptide and graphene once extracted. Atomic force microscopy images then confirm these predictions by showing that mature amyloid fibrils can be cut into pieces by graphene oxides. Thioflavin fluorescence assays further illustrate the detailed dynamic processes of graphene-induced inhibition and dissociation starting from both monomer peptides and mature amyloid fibrils. These findings provide new insights to the underlying molecular mechanism of this important graphene-amyloid interaction, and will promote the development of novel nanotherapies for Alzheimer’s and other related protein conformational diseases.
Related Publications:
Y. Tu, M. Lv, P. Xiu, T. Huynh, M. Zhang, M. Castelli, Z. R. Liu, Q. Huang, C. H. Fan, H. P. Fang, and R. H. Zhou,
Destructive Extraction of Phospholipids from E. Coli Membrane by a Graphene Nanosheet,
Nature Nanotech. 8, 594-601, 2013
S. G. Kang, G. Q. Zhou, P. Yang, Y. Liu, B. Y. Sun, T. Huynh, H. Meng, L. Zhao, G. M. Xing, C. Y. Chen, Y. L. Zhao, R. H. Zhou,
Molecular Mechanism of Pancreatic Tumor Metastases Inhibition by Metallofullerenol Gd@C82(OH)22: Implication for de novo Design of Nanomedicine,
Proc. Natl. Acad. Sci., 109, 15431-15436, 2012 (featured article)
Zaixing Yang, Cuicui Ge, Jiajia Liu, Yu Chong, Zonglin Gu, Camilo A. Jimenez-Cruz, Zhifang Chai, R. H. Zhou,
Destruction of amyloid fibrils by graphene through penetration and extraction of peptides,
Nanoscale 7, 18725-18737, 2015
