28 research outputs found
Correction to âFluorescent Carbon Quantum Dots with Intrinsic Nucleolus-Targeting Capability for Nucleolus Imaging and Enhanced Cytosolic and Nuclear Drug Deliveryâ
Correction
to âFluorescent Carbon Quantum Dots with Intrinsic Nucleolus-Targeting
Capability for Nucleolus Imaging and Enhanced Cytosolic and Nuclear
Drug Delivery
Fluorescent Carbon Quantum Dots with Intrinsic Nucleolus-Targeting Capability for Nucleolus Imaging and Enhanced Cytosolic and Nuclear Drug Delivery
Nucleolus tracking and nucleus-targeted
photodynamic therapy are
attracting increasing attention due to the importance of nucleolus
and the sensitivity of nucleus to various therapeutic stimuli. Herein,
a new class of multifunctional fluorescent carbon quantum dots (or
carbon dots, CDs) synthesized via the one-pot hydrothermal reaction
of <i>m</i>-phenylenediamine and l-cysteine was
reported to effectively target nucleolus. The as-prepared CDs possess
superior properties, such as low-cost and facile synthesis, good water
dispersibility, various surface groups for further modifications,
prominent photostability, excellent compatibility, and rapid/convenient/wash-free
staining procedures. Besides, as compared with SYTO RNASelect (a commonly
used commercial dye for nucleolus imaging) that can only image nucleolus
in fixed cells, the CDs can realize high-quality nucleolus imaging
in not only fixed cells but also living cells, allowing the real-time
tracking of nucleolus-related biological behaviors. Furthermore, after
conjugating with protoporphyrin IX (PpIX), a commonly used photosensitizer,
the resultant CDâPpIX nanomissiles showed remarkably increased
cellular uptake and nucleus-targeting properties and achieved greatly
enhanced phototherapeutic efficiency because the nuclei show poor
tolerance to reactive oxygen species produced during the photodynamic
therapy. The in vivo experiments revealed that the negatively charged
CDâPpIX nanomissiles could rapidly and specifically target
a tumor site after intravenous injection and cause efficient tumor
ablation with no toxic side effects after laser irradiation. It is
believed that the present CD-based nanosystem will hold great potential
in nucleolus imaging and nucleus-targeted drug delivery and cancer
therapy
Interaction of Polyethylenimine with Model Cell Membranes Studied by Linear and Nonlinear Spectroscopic Techniques
Polyethylenimine
(PEI) has been widely used as a transfection agent for gene delivery,
but it is cytotoxic and can lead to cell apoptosis. Although several
apoptotic mechanisms have been proposed, a molecular level understanding
of PEI/cell membrane interaction can help develop further insight
into such cytotoxicity. We combined sum frequency generation (SFG)
vibrational spectroscopy and attenuated total-internal reflection
Fourier transform infrared (ATR-FTIR) spectroscopy to study the effect
of PEI on lipid transbilayer movement in supported bilayers (serving
as model cell membranes) as a function of lipid composition, PEI concentration,
and temperature. For both dipalmitoylphosphatidylglycerol (DPPG) and
distearoylphosphatidylcholine (DSPC) bilayers, PEI molecules showed
no significant effect on lipid translocation at room temperature (21
°C).
In contrast, significant lipid translocation was observed near the
physiological temperature (39 °C), indicating the ability of
PEI to induce lipid translocation in both negatively charged and zwitterionic
lipid bilayers, without the assistance of membrane proteins. Furthermore,
results showed that PEI had strong interactions with negatively charged
DPPG and weak interactions with zwitterionic DSPC. Concentration-dependent
studies indicated that the lipid translocation rate had a linear dependence
on the PEI concentration in the subphase. The effects of branched
and linear PEIs were compared in the study, showing that branched
PEI had a greater effect on the lipid translocation rate due to the
higher charge density, which might be a possible indication of higher
toxicity. ATR-FTIR spectroscopy verified that the results observed
in SFG were mainly caused by lipid translocation, not bilayer damage
or removal from the substrate. The combined SFG and ATR-FTIR study
provides a powerful method to examine molecular interactions between
lipid bilayers and polyelectrolytes at a molecular level. The results
can help to develop further understanding on PEIâs cytotoxicity
in biological systems
Folding Behaviors of Protein (Lysozyme) Confined in Polyelectrolyte Complex Micelle
The folding/unfolding
behavior of proteins (enzymes) in confined
space is important for their properties and functions, but such a
behavior remains largely unexplored. In this article, we reported
our finding that lysozyme and a double hydrophilic block copolymer,
methoxyÂpolyÂ(ethylene glycol)<sub>5K</sub>-<i>block</i>-polyÂ(l-aspartic acid sodium salt)<sub>10</sub> (mPEG<sub>5K</sub>-<i>b</i>-PLD<sub>10</sub>), can form a polyelectrolyte
complex micelle with a particle size of âŒ30 nm, as verified
by dynamic light scattering and transmission electron microscopy.
The unfolding and refolding behaviors of lysozyme molecules in the
presence of the copolymer were studied by microcalorimetry and circular
dichroism spectroscopy. Upon complex formation with mPEG<sub>5K</sub>-<i>b</i>-PLD<sub>10</sub>, lysozyme changed from its initial
native state to a new partially unfolded state. Compared with its
native state, this copolymer-complexed new folding state of lysozyme
has different secondary and tertiary structures, a decreased thermostability,
and significantly altered unfolding/refolding behaviors. It was found
that the native lysozyme exhibited reversible unfolding and refolding
upon heating and subsequent cooling, while lysozyme in the new folding
state (complexed with the oppositely charged PLD segments of the polymer)
could unfold upon heating but could not refold upon subsequent cooling.
By employing the heatingâcoolingâreheating procedure,
the prevention of complex formation between lysozyme and polymer due
to the salt screening effect was observed, and the resulting uncomplexed
lysozyme regained its proper unfolding and refolding abilities upon
heating and subsequent cooling. Besides, we also pointed out the important
role the length of the PLD segment played during the formation of
micelles and the monodispersity of the formed micelles. Furthermore,
the lysozymeâmPEG<sub>5K</sub>-<i>b</i>-PLD<sub>10</sub> mixtures prepared in this work were all transparent, without the
formation of large aggregates or precipitates in solution as frequently
observed in other proteinâpolyelectrolyte systems. Hence, the
present proteinâPEGylated polyÂ(amino acid) mixture provides
an ideal water-soluble model system to study the important role of
electrostatic interaction in the complexation between proteins and
polymers, leading to important new knowledge on the proteinâpolymer
interactions. Moreover, the polyelectrolyte complex micelle formed
between protein and PEGylated polymer may provide a good drug delivery
vehicle for therapeutic proteins
Cholesterol-Assisted Bacterial Cell Surface Engineering for Photodynamic Inactivation of Gram-Positive and Gram-Negative Bacteria
Antibacterial photodynamic therapy
(PDT), which enables effective killing of regular and multidrug-resistant
(MDR) bacteria, is a promising treatment modality for bacterial infection.
However, because most photosensitizer (PS) molecules fail to strongly
interact with the surface of Gram-negative bacteria, this technique
is suitable for treating only Gram-positive bacterial infection, which
largely hampers its practical applications. Herein, we reveal for
the first time that cholesterol could significantly facilitate the
hydrophobic binding of PSs to the bacterial surface, achieving the
hydrophobic interaction-based bacterial cell surface engineering that
could effectively photoinactivate both Gram-negative and Gram-positive
bacteria. An amphiphilic polymer composed of a polyethylene glycol
(PEG) segment terminated with protoporphyrin IX (PpIX, an anionic
PS) and cholesterol was constructed (abbreviated Chol-PEG-PpIX), which
could self-assemble into micelle-like nanoparticles (NPs) in aqueous
solution. When encountering the Gram-negative Escherichia
coli cells, the Chol-PEG-PpIX NPs would disassemble
and the PpIX moieties could effectively bind to the bacterial surface
with the help of the cholesterol moieties, resulting in the significantly
enhanced fluorescence emission of the bacterial surface. Under white
light irradiation, the light-triggered singlet oxygen (<sup>1</sup>O<sub>2</sub>) generation of the membrane-bound PpIX could not only
severely damage the outer membrane but also facilitate the entry of
external Chol-PEG-PpIX into the bacteria, achieving >99.99% bactericidal
efficiency. Besides, as expected, the Chol-PEG-PpIX NPs also exhibited
excellent antibacterial performance against the Gram-positive Staphylococcus aureus. We also verified that this
nanoagent possesses negligible dark cytotoxicity toward mammalian
cells and good hemocompatibility. To the best of our knowledge, this
study demonstrates for the first time the feasibility of constructing
a fully hydrophobic interaction-based and outer membrane-anchored
antibacterial PDT nanoagent
Enhanced Fluorescence Emission and Singlet Oxygen Generation of Photosensitizers Embedded in Injectable Hydrogels for Imaging-Guided Photodynamic Cancer Therapy
Benefiting from their inherent localized
and controlled release
properties, hydrogels are ideal delivery systems for therapeutic drugs
or nanoparticles. In particular, applications of hydrogels for the
delivery and release of photoresponsive drugs or nanoparticles are
receiving increasing attention. However, the effect of the hydrogel
matrix on the fluorescence emission and singlet oxygen generation
efficiency of the embedded photosensitizers (PSs) has not been clarified.
Herein, meso-tetrakisÂ(1-methylpyridinium-4-yl)Âporphyrin (TMPyP) as
a water-soluble PS was encapsulated into an injectable hydrogel formed
by glycol chitosan and dibenzaldehyde-terminated telechelic polyÂ(ethylene
glycol). Compared to free TMPyP solution, the TMPyP encapsulated in
the hydrogel exhibits three distinct advantages: (1) more singlet
oxygen was generated under the same laser irradiation condition; (2)
much longer tumor retention was observed due to the low fluidity of
the hydrogel; and (3) the fluorescence intensity of TMPyP was significantly
enhanced in the hydrogel due to its decreased self-quenching effect.
These excellent characteristics lead to remarkable anticancer efficacy
and superior fluorescence emission property of the TMPyPâhydrogel
system, promoting the development of imaging-guided photodynamic therapy
Subcellular Fate of a Fluorescent Cholesterol-Poly(ethylene glycol) Conjugate: An Excellent Plasma Membrane Imaging Reagent
Cholesterol-containing
molecules or nanoparticles play a significant role in achieving favorable
plasma membrane imaging and efficient cellular uptake of drugs by
the excellent membrane anchoring capability of the cholesterol moiety.
By linking cholesterol to a water-soluble component (such as polyÂ(ethylene
glycol), PEG), the resulting cholesterol-PEG conjugate can form micelles
in aqueous solution through self-assembly, and such a micellar structure
represents an important drug delivery vehicle in which hydrophobic
drugs can be encapsulated. However, the understanding of the subcellular
fate and cytotoxicity of cholesterol-PEG conjugates themselves remains
elusive. Herein, by using cholesterol-PEG2000-fluorescein isothiocyanate
(Chol-PEG-FITC) as a model system, we found that the Chol-PEG-FITC
molecules could attach to the plasma membranes of mammalian cells
within 10 min and such a firm membrane attachment could last at least
1 h, displaying excellent plasma membrane staining performance that
surpassed that of commonly used commercial membrane dyes such as DiD
and CellMask. Besides, we systematically studied the endocytosis pathway
and intracellular distribution of Chol-PEG-FITC and found that the
cell surface adsorption and endocytosis processes of Chol-PEG-FITC
molecules were lipid-raft-dependent. After internalization, the Chol-PEG-FITC
molecules gradually reached many organelles with membrane structures.
At 5 h, they were mainly distributed in lysosomes and the Golgi apparatus,
with some in the endoplasmic reticulum (ER) and very few in the mitochondrion.
At 12 h, the Chol-PEG-FITC molecules mostly aggregated in the Golgi
apparatus and ER close to the nucleus. Finally, we demonstrated that
Chol-PEG-FITC was toxic to mammalian cells only at concentrations
above 50 ÎŒM. In summary, Chol-PEG-FITC can be a promising plasma
membrane imaging reagent to avoid the fast cellular internalization
and quick membrane detachment problems faced by commercial membrane
dyes. We believe that the investigation of the dynamic subcellular
fate of Chol-PEG-FITC can provide important knowledge to facilitate
the use of cholesterolâPEG conjugates in fields such as cell
surface engineering and drug delivery
Complexation of Lysozyme with Sodium Poly(styrenesulfonate) via the Two-State and Non-Two-State Unfoldings of Lysozyme
To
provide an in-depth understanding of the complexation mechanism
of protein and polyelectrolyte, a heatingâcoolingâreheating
protocol was employed to study the unfolding and refolding behaviors
of a model protein, lysozyme, in the presence of a negatively charged
polyelectrolyte, sodium polyÂ(styrenesulfonate) (PSS). It was found
that, with elevated PSS concentration, a new state (state I) was first
formed via a âtwo-stateâ conversion process and this
state could further convert to a completely unfolded state (state
II) via a ânon-two-stateâ conversion. This non-two-state
conversion process occurs without the coexistence of states I and
II but involves the formation of various intermediate unfolded protein
structures. Different from the pure lysozyme that exhibited refolding
upon cooling from its heat-denatured state, lysozyme in state I could
undergo unfolding upon heating but no refolding upon cooling, while
lysozyme in state II did not undergo unfolding or refolding upon thermal
treatments. In addition, the effects of ionic strength and molecular
weight of polyelectrolyte on the unfolding and refolding behaviors
of lysozyme were also investigated. The present work provides a better
understanding of the principles governing proteinâpolyelectrolyte
interactions and may have implications for the fabrication of biocolloids
and biofilms
Long-Time Plasma Membrane Imaging Based on a Two-Step Synergistic Cell Surface Modification Strategy
Long-time
stable plasma membrane imaging is difficult due to the
fast cellular internalization of fluorescent dyes and the quick detachment
of the dyes from the membrane. In this study, we developed a two-step
synergistic cell surface modification and labeling strategy to realize
long-time plasma membrane imaging. Initially, a multisite plasma membrane
anchoring reagent, glycol chitosanâ10% PEG2000 cholesterolâ10%
biotin (abbreviated as âGC-Chol-Biotinâ), was incubated
with cells to modify the plasma membranes with biotin groups with
the assistance of the membrane anchoring ability of cholesterol moieties.
Fluorescein isothiocyanate (FITC)-conjugated avidin was then introduced
to achieve the fluorescence-labeled plasma membranes based on the
supramolecular recognition between biotin and avidin. This strategy
achieved stable plasma membrane imaging for up to 8 h without substantial
internalization of the dyes, and avoided the quick fluorescence loss
caused by the detachment of dyes from plasma membranes. We have also
demonstrated that the imaging performance of our staining strategy
far surpassed that of current commercial plasma membrane imaging reagents
such as DiD and CellMask. Furthermore, the photodynamic damage of
plasma membranes caused by a photosensitizer, Chlorin e6 (Ce6), was
tracked in real time for 5 h during continuous laser irradiation.
Plasma membrane behaviors including cell shrinkage, membrane blebbing,
and plasma membrane vesiculation could be dynamically recorded. Therefore,
the imaging strategy developed in this work may provide a novel platform
to investigate plasma membrane behaviors over a relatively long time
period
Hyperthemia-Promoted Cytosolic and Nuclear Delivery of Copper/Carbon Quantum Dot-Crosslinked Nanosheets: Multimodal Imaging-Guided Photothermal Cancer Therapy
Copper-containing nanomaterials have
been applied in various fields because of their appealing physical,
chemical, and biomedical properties/functions. Herein, for the first
time, a facile, room-temperature, and one-pot method of simply mixing
copper ions and sulfur-doped carbon dots (CDs) is developed for the
synthesis of copper/carbon quantum dot (or CD)-crosslinked nanosheets
(CuCD NSs). The thus-obtained CuCD NSs with the size of 20â30
nm had a high photothermal conversion efficiency of 41.3% and good
photothermal stability. Especially, after coating with thiol-polyethylene
glycol and fluorescent molecules, the resultant CuCD NSs could selectively
target tumor tissues and realize multimodal (photoacoustic, photothermal,
and fluorescence) imaging-guided cancer therapy. More importantly,
our CuCD NSs exhibited laser-triggered cytosolic delivery, lysosomal
escape, and nuclear-targeting properties, which greatly enhanced their
therapeutic efficacy. The significantly enhanced tumor accumulation
of CuCD NSs after in situ tumor-site laser irradiation was also observed
in in vivo experiments. These in vitro and in vivo events occurring
during the continuous laser irradiation have not been observed. Overall,
this work develops a CD-assisted synthetic method of photothermal
nanoagents for triple-modal imaging-guided phototherapy and deepens
our understanding of the action mechanism of photothermal therapy,
which will promote the development of nanomedicine and beyond