ACNS &MM

We report the effect of carboxyl functionalization of graphene in pacifying its strong hydrophobic interaction with cells and associated toxic effects. Pristine graphene was found to accumulate on the cell membrane causing high oxidative stress leading to apoptosis, whereas carboxyl functionalized hydrophilic graphene was internalized by the cells without causing any toxicity.We report the effect of carboxyl functionalization of graphene in pacifying its strong hydrophobic interaction with cells and associated toxic effects. Pristine graphene was found to accumulate on the cell membrane causing high oxidative stress leading to apoptosis, whereas carboxyl functionalized hydrophilic graphene was internalized by the cells without causing any toxicity. Electronic supplementary information (ESI) available: Experimental details, video files of contact angle measurement, cellular uptake and flow cytogram of ROS. See DOI: 10.1039/c1nr10172b

The specific role of size scale, surface capping, and aspect ratio of zinc oxide (ZnO) particles on toxicity toward prokaryotic and eukaryotic cells was investigated. ZnO nano and microparticles of controlled size and morphology were synthesized by wet chemical methods. Cytotoxicity toward mammalian cells was studied using a human osteoblast cancer cell line and antibacterial activity using Gram-negative bacteria (Escherichia coli) as well as using Gram-positive bacteria (Staphylococcus aureus). Scanning electron microscopy (SEM) was conducted to characterize any visual features of the biocidal action of ZnO. We observed that antibacterial activity increased with reduction in particle size. Toxicity toward the human cancer cell line was considerably higher than previously observed by other researchers on the corresponding primary cells, suggesting selective toxicity of the ZnO to cancer cells. Surface capping was also found to profoundly influence the toxicity of ZnO nanoparticles toward the cancer cell line, with the toxicity of starch-capped ZnO being the lowest. Our results are found to be consistent with a membrane-related mechanism for nanoparticle toxicity toward microbes.

The microenvironment of cancer plays a very critical role in the survival, proliferation and drug resistance of solid tumors. Here, we report an interesting, acidic cancer microenvironment-mediated dissolution-induced preferential toxicity of ZnO nanocrystals (NCs) against cancer cells while leaving primary cells unaffected. Irrespective of the size-scale (5 and 200 nm) and surface chemistry differences (silica, starch or polyethylene glycol coating), ZnO NCs exhibited multiple stress mechanisms against cancer cell lines (IC50 ~150 μM) while normal human primary cells (human dermal fibroblast, lymphocytes, human umbilical vein endothelial cells) remain less affected. Flow cytometry and confocal microscopy studies revealed that ZnO NCs undergo rapid preferential dissolution in acidic (pH ~5-6) cancer microenvironment causing elevated ROS stress, mitochondrial superoxide formation, depolarization of mitochondrial membrane, and cell cycle arrest at S/G2 phase leading to apoptosis. In effect, by elucidating the unique toxicity mechanism of ZnO NCs, we show that ZnO NCs can destabilize cancer cells by utilizing its own hostile acidic microenvironment, which is otherwise critical for its survival.The microenvironment of cancer plays a very critical role in the survival, proliferation and drug resistance of solid tumors. Here, we report an interesting, acidic cancer microenvironment-mediated dissolution-induced preferential toxicity of ZnO nanocrystals (NCs) against cancer cells while leaving primary cells unaffected. Irrespective of the size-scale (5 and 200 nm) and surface chemistry differences (silica, starch or polyethylene glycol coating), ZnO NCs exhibited multiple stress mechanisms against cancer cell lines (IC50 ~150 μM) while normal human primary cells (human dermal fibroblast, lymphocytes, human umbilical vein endothelial cells) remain less affected. Flow cytometry and confocal microscopy studies revealed that ZnO NCs undergo rapid preferential dissolution in acidic (pH ~5-6) cancer microenvironment causing elevated ROS stress, mitochondrial superoxide formation, depolarization of mitochondrial membrane, and cell cycle arrest at S/G2 phase leading to apoptosis. In effect, by elucidating the unique toxicity mechanism of ZnO NCs, we show that ZnO NCs can destabilize cancer cells by utilizing its own hostile acidic microenvironment, which is otherwise critical for its survival. Electronic supplementary information (ESI) available: FTIR data, MTT assay and zinc ion release. See DOI: 10.1039/c1nr10272a

Membrane associated folate receptors (FR) is gaining importance in cancer research. Understanding the FR density, distribution, and the strength of its interaction with ligands is crucial in cancer diagnostics and therapeutics. Here we reported the enhanced phase contrast image of FR by scanning with properly functionalized atomic force microscope (AFM) tips over live cell lines. The choice of the ligand was made for better interaction of tip with FR, expressed in the cell lines. The selectively enhanced force of interaction at the receptor molecule produced a considerable enhancement in the phase contrast between a receptor site and a nonreceptor site.

We report the development of a novel magnetic nano-contrast agent (nano-CA) based on Gd3+ doped amorphous TiO2 of size ~25 nm, exhibiting enhanced longitudinal relaxivity (r1) and magnetic resonance (MR) contrasting together with excellent biocompatibility. Quantitative T1 mapping of phantom samples using a 1.5 T clinical MR imaging system revealed that the amorphous phase of doped titania has the highest r1 relaxivity which is ~2.5 fold higher than the commercially used CA Magnevist™. The crystalline (anatase) samples formed by air annealing at 250 °C and 500 °C showed significant reduction in r1 values and MR contrast, which is attributed to the loss of proton-exchange contribution from the adsorbed water and atomic re-arrangement of Gd3+ ions in the crystalline host lattice. Nanotoxicity studies including cell viability, plasma membrane integrity, reactive oxygen stress and expression of pro-inflammatory cytokines, performed on human primary endothelial cells (HUVEC), human blood derived peripheral blood mononuclear cells (PBMC) and nasopharyngeal epidermoid carcinoma (KB) cell line showed excellent biocompatibility up to relatively higher doses of 200 μg ml-1. The potential of this nano-CA to cause hemolysis, platelet aggregation and plasma coagulation were studied using human peripheral blood samples and found no adverse effects, illustrating the possibility of the safe intravenous administration of these agents for human applications. Furthermore, the ability of these agents to specifically detect cancer cells by targeting molecular receptors on the cell membrane was demonstrated on folate receptor (FR) positive oral carcinoma (KB) cells, where the folic acid conjugated nano-CA showed receptor specific accumulation on cell membrane while leaving the normal fibroblast cells (L929) unstained. This study reveals that the Gd3+ doped amorphous TiO2 nanoparticles having enhanced magnetic resonance contrast and high biocompatibility is a promising candidate for molecular receptor targeted MR imaging.We report the development of a novel magnetic nano-contrast agent (nano-CA) based on Gd3+ doped amorphous TiO2 of size ~25 nm, exhibiting enhanced longitudinal relaxivity (r1) and magnetic resonance (MR) contrasting together with excellent biocompatibility. Quantitative T1 mapping of phantom samples using a 1.5 T clinical MR imaging system revealed that the amorphous phase of doped titania has the highest r1 relaxivity which is ~2.5 fold higher than the commercially used CA Magnevist™. The crystalline (anatase) samples formed by air annealing at 250 °C and 500 °C showed significant reduction in r1 values and MR contrast, which is attributed to the loss of proton-exchange contribution from the adsorbed water and atomic re-arrangement of Gd3+ ions in the crystalline host lattice. Nanotoxicity studies including cell viability, plasma membrane integrity, reactive oxygen stress and expression of pro-inflammatory cytokines, performed on human primary endothelial cells (HUVEC), human blood derived peripheral blood mononuclear cells (PBMC) and nasopharyngeal epidermoid carcinoma (KB) cell line showed excellent biocompatibility up to relatively higher doses of 200 μg ml-1. The potential of this nano-CA to cause hemolysis, platelet aggregation and plasma coagulation were studied using human peripheral blood samples and found no adverse effects, illustrating the possibility of the safe intravenous administration of these agents for human applications. Furthermore, the ability of these agents to specifically detect cancer cells by targeting molecular receptors on the cell membrane was demonstrated on folate receptor (FR) positive oral carcinoma (KB) cells, where the folic acid conjugated nano-CA showed receptor specific accumulation on cell membrane while leaving the normal fibroblast cells (L929) unstained. This study reveals that the Gd3+ doped amorphous TiO2 nanoparticles having enhanced magnetic resonance contrast and high biocompatibility is a promising candidate for molecular receptor targeted MR imaging. Electronic supplementary information (ESI) available: FTIR data GTN-RT and GTN-500. See DOI: 10.1039/c1nr10591d

TGF-β (transforming growth factor-beta) plays a key role in osteoblast differentiation and bone development. While the ability of TGF-β to inhibit the expression of osteoblast differentiation genes has been well documented, the mechanism of this inhibition is not yet completely characterized. Runx2, a transcription factor necessary for expression of osteoblast differentiation genes is a central target of inhibition by TGF-β. In this study, we found that TGF-β1 inhibits expression of osteoblast differentiation genes without altering expression of Runx2. Transient transfection experiments determined that TGF-β1 inhibited osteocalcin promoter activity and this effect is mediated through Runx2. We further identified that there was no change in protein expression, cellular localization, or DNA binding affinity of Runx2 after TGF-β1-treatment of osteoblasts, suggesting that Runx2 undergoes post-translational modifications following TGF-β1 treatment. Co-immunoprecipitation experiments identified increased phosphorylation of Runx2 when differentiating osteoblasts were treated with TGF-β1. Mitogen activated protein kinase (MAPK) inhibitors relieved the TGF-β1-inhibitory effect of Runx2-mediated osteocalcin expression. Thus, our results suggest that TGF-β1-inhibition of osteoblast differentiation is dependent on the MAPK pathway and this effect is most likely mediated by post-translational modification of Runx2 such as phosphorylation rather than other regulatory mechanisms. J. Cell. Biochem. 106: 161–169, 2009. © 2008 Wiley-Liss, Inc.