Centre for Pharmaceutical Nanotechnology, Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research-NIPER, SAS Nagar-Mohali Punjab, India 160062.
Chem Res Toxicol. 2012 Oct 15;25(10):2127-37. doi: 10.1021/tx300228d. Epub 2012 Oct 1.
The present study investigates the effect of functionalization density on the toxicity and cellular uptake of oxidized multiwalled carbon nanotubes (f-MWCNTs) in vitro. The toxicity of f-MWCNTs at varying degrees of carboxylation was assessed in a murine macrophage RAW 264.7 cell line, a model for liver Kupffer cells. In vitro cytotoxicity of oxidized MWCNTs was directly proportional to their functionalization density. The increased cytotoxicity was associated with a concurrent increase in the number of apoptotic cells and production of reactive nitrogen species (RNS). In contrast, reactive oxygen species (ROS) generation was the highest in the case of pristine MWCNTs and decreased with increased functionalization density. Quantitative cellular uptake studies indicated that endogenous ROS production was independent of the concentration of CNTs internalized by a specific cell population and was directly proportional to their surface hydrophobicity. Mechanistic studies suggested that cellular uptake of CNTs was critically charge-dependent and mediated through scavenger receptors, albeit the involvement of nonscavenger receptor mechanisms at low CNT concentrations and their saturation at the experimental concentration cannot be ruled out. A mathematical model was established to correlate between the cellular uptake of CNTs with their length and zeta potential. In an attempt to correlate the results of in vitro toxicity experiments with those of the in vivo toxicity in the mouse model, we found that the toxicity trends in vitro and in vivo are rather opposing. The apparent anomaly was explained on the basis of different experimental conditions and doses associated with cells under in vivo and in vitro culture conditions.
本研究考察了功能化密度对体外氧化多壁碳纳米管（f-MWCNTs）毒性和细胞摄取的影响。通过体外培养的肝枯否细胞模型——鼠源巨噬细胞 RAW 264.7 系，评估了不同羧化程度的 f-MWCNTs 的毒性。氧化 MWCNTs 的体外细胞毒性与其功能化密度直接相关。细胞毒性的增加与凋亡细胞数量的增加和活性氮物种（RNS）的产生同时相关。相比之下，在原始 MWCNTs 的情况下，活性氧物种（ROS）的生成最高，并且随着功能化密度的增加而降低。定量细胞摄取研究表明，内源性 ROS 生成与特定细胞群内化的 CNT 浓度无关，而是与它们的表面疏水性直接相关。机制研究表明，CNTs 的细胞摄取与它们的电荷密切相关，并通过清道夫受体介导，尽管不能排除在低 CNT 浓度下涉及非清道夫受体机制及其在实验浓度下的饱和。建立了一个数学模型来关联 CNT 的细胞摄取与其长度和 ζ 电位之间的关系。为了尝试将体外毒性实验的结果与小鼠模型体内毒性的结果相关联，我们发现体外和体内的毒性趋势相反。这种明显的反常现象是基于不同的实验条件和与体内和体外培养条件下细胞相关的剂量来解释的。
