A new endocytic model based on the co-rotational grid method

Endocytosis plays important roles in many cellular physiological processes, such as metabolism and immune. Many theoretical models have been proposed to study the endocytic process, but little has considered the tensile deformation of the membrane and the actin forces. In this paper, a new endocytic model is proposed based on the co-rotational grid method. Our model gives a direct estimation of the in-plane strain of the plasma membrane and provides a basis for the calculation of further scission process of the vesicle. The results fit well with experimental data in the literature. Moreover, it is suggested that the active forces of actin at the endocytic site is the main mechanism driving the invagination of the plasma membrane.     

包膜颗粒的表面磷脂重排对细胞内吞的影响

在纳米颗粒表面包裹生物膜可以增强体系的生物相容性、靶向性、内含物释放的可控性，但包膜颗粒与细胞膜作用的机制仍不清楚.在本研究中，我们考察了不同侧向流动性的负电性磷脂膜包裹的多孔硅纳米颗粒的体外细胞内吞行为.发现，高流动的液态磷脂包被产生了较高的内吞效率，并且它的内吞方式也与低流动的凝胶态磷脂包被情况存在差异.Derjaguin-Landau-Verway-Overbeek理论分析表明，前者的磷脂空间重排能够促进生物膜与细胞膜的融合与粒子内吞，而后者在膜融合过程中存在高能量势垒，因此只能以胞饮的方式被动地进入细胞.我们的研究深化了包膜粒子内吞过程的认识，为后续设计复杂的纳米载药体提供了新的思路和参考.     

Effect of surface charge of magnetite nanoparticles on their internalization into breast cancer and umbilical vein endothelial cells

Internalization of magnetite nanoparticles with diameter of approximately 40 nm into normal and cancer cells was examined by microscopic observation and flow cytometry. Magnetite nanoparticles were synthesized by hydrolysis in an aqueous solution containing ferrous chloride with organic amines as a base. It was demonstrated that the difference in surface charge of magnetite nanoparticles brought about the difference in uptake efficiency. The nanoparticles with positive charge showed higher internalization into human breast cancer cells than the nanoparticles with negative charge, while the degree of internalization of the positively- and negatively-charged nanoparticles into human umbilical vein endothelial cells (HUVEC) was almost the same.     

胶体介孔二氧化硅增强抗癌药物治疗效果的研究

胶体介孔Si O_2(CMS)是一种具有良好生物相容性、高稳定性和高负载量的药物载体。本文采用带正电荷的CMS作为药物载体负载抗癌药物5F用来抑制鼻咽癌细胞CNE2的生长。实验结果表明,CMS本身对于细胞是无毒的,可通过细胞的内吞作用进入并在细胞中分布。相对于单独的5F,CMS@5F诱导鼻咽癌细胞凋亡的效果明显增强,说明CMS能将5F有效携带至细胞中使其局部浓度增大,促进5F抑制癌细胞生长的效果。     

Delivering quantum dots into cells: strategies,progress and remaining issues

The use of semiconductor quantum dots (QDs) in biological sensing and labeling continues to grow with each year. Current and projected applications include use as fluorescent labels for cellular labeling, intracellular sensors, deep-tissue and tumor imaging agents, sensitizers for photodynamic therapy, and more recently interest has been sparked in using them as vectors for studying nanoparticle-mediated drug delivery. Many of these applications will ultimately require the QDs to undergo targeted intracellular delivery, not only to specific cells, but also to a variety of subcellular compartments and organelles. It is apparent that this issue will be critical in determining the efficacy of using QDs, and indeed a variety of other nanoparticles, for these types of applications. In this review, we provide an overview of the current methods for delivering QDs into cells. Methods that are covered include facilitated techniques such as those that utilize specific peptide sequences or polymer delivery reagents and active methods such as electroporation and microinjection. We critically examine the benefits and liabilities of each strategy and illustrate them with selected examples from the literature. Several important related issues such as QD size and surface coating, methods for QD biofunctionalization, cellular physiology and toxicity are also discussed. Finally, we conclude by providing a perspective of how this field can be expected to develop in the future.     

Light scattering based analyses of the effects of bovine serum proteins on interactions of magnetite spherical particles with cells

Cellular uptake of magnetite spherical particles (MSPs) were increased with incubation time and were decreased in the presence of medium serum proteins. Results also showed the cell internalized MSPs induced the cellular autophagosome accumulation.     

Real-time measurement of endosomal acidification by a novel genetically encoded biosensor

Genetically encoded fluorescent proteins are optimal reporters when used to monitor cellular processes as they can be targeted to any subcellular region by fusion to a protein of interest. Here, we present the pH-sensitive fluorescent protein E¹GFP which is ideally suited to monitor pH changes in dynamic intracellular structures in real time with high spatio temporal resolution. E¹GFP is a ratiometric pH indicator by emission with a pK close to 6.0. We describe an application of this novel pH reporter in the measurement of pH changes along the endo-lysosomal pathway. By fusing E¹GFP to the HIV-Tat protein which is endowed with cell-penetrating properties, we were able to monitor multi-step endocytosis from the initial cell-surface binding through to the intracellular endocytic network in real time. This represents a framework for the application of E¹GFP to the in situ detection of pH changes involved in dynamic biological phenomena. Figure The green fluorecent protein variant, E1GFP, is a ratiometric pH-indicator by emission with a pK close to 6.0 and is therefore particularly suitable for pH detection below neutrality. Upon excitation of the neutral state of the chromophore (~400-410 nm), E1GFP emission properties are strongly dependent on the environmental pH. We describe an application of this novel pH-reporter in the measurement of pH changes along the endo-lysosomal pathway. By fusing E1GFP to the HIV-Tat protein, which is endowed with cell-penetrating properties, we were able to monitor in real-time multi-step endocytosis from the initial cell-surface binding through to the intracellular endocytic network. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Understanding nanoparticle cellular entry: A physicochemical perspective

Understanding interactions between nanoparticles (NPs) with biological matter, particularly cells, is becoming increasingly important due to their growing application in medicine and materials, and consequent biological and environmental exposure. For NPs to be utilised to their full potential, it is important to correlate their functional characteristics with their physical properties, which may also be used to predict any adverse cellular responses. A key mechanism for NPs to impart toxicity is to gain cellular entry directly. Many parameters affect the behaviour of nanomaterials in a cellular environment particularly their interactions with cell membranes, including their size, shape and surface chemistry as well as factors such as the cell type, location and external environment (e.g. other surrounding materials, temperature, pH and pressure). Aside from in vitro and in vivo experiments, model cell membrane systems have been used in both computer simulations and physicochemical experiments to elucidate the mechanisms for NP cellular entry. Here we present a brief overview of the effects of NPs physical parameters on their cellular uptake, with focuses on 1) related research using model membrane systems and physicochemical methodologies; and 2) proposed physical mechanisms for NP cellular entrance, with implications to their nanotoxicity. We conclude with a suggestion that the energetic process of NP cellular entry can be evaluated by studying the effects of NPs on lipid mesophase transitions, as the molecular deformations and thus the elastic energy cost are analogous between such transitions and endocytosis. This presents an opportunity for contributions to understanding nanotoxicity from a physicochemical perspective.     

Challenges in quantum dot-neuron active interfacing

Semiconductor nanocrystal quantum dots (qdots) are now being explored in applications requiring active cellular interfaces, such as biosensing and therapeutics in which information is passed from the qdot to the biological system, or vice versa, to perform a function. These applications may require surface coating chemistry that is different from what is commonly employed for passive interface applications like labeling (i.e., thick polymer coatings such as poly(ethylene glycol) (PEG)), in which the only concern is nonspecific sticking to cells and biocompatibility. The thick insulating coatings that are generally needed for labeling are generally not suitable for active qdot-cell interface applications. There is currently little data regarding the interactions between viable cells and qdots under physiological conditions. Our initial investigations using mercaptoacetic acid-coated CdS and CdTe qdots as a simple model to interface with neuron cell surface receptors under physiological conditions uncovered two significant technological hurdles: nonspecific binding and endocytosis. Nonspecific binding can be extensive and in general there appears to be greater nonspecific binding for larger particle sizes, but this also depends sensitively on the particle surface characteristics and the type of neuron, possibly indicating a detailed relationship between particle-cell affinity and cell membrane chemistry. More importantly, qdot endocytosis occurs rapidly at physiological temperature for the different nerve cell types studied, within the first five minutes of exposure to both CdS and CdTe qdots, regardless of whether the molecular coatings specifically recognize cell surface receptors or not. As a consequence, new strategies for tagging cell surface recognition groups for long-term active interfacing with cells under physiological conditions are needed, which requires more sophisticated ligands than MAA but also the absence of thick insulating coatings.