Repair and Regeneration of the Wounded Cell Membrane

Membrane stabilization versus perturbation by aromatic monoamine-modified γ-PGA for cryopreservation of human RBCs with high intracellular trehalose

As a nonreducing disaccharide, trehalose can be used as a biocompatible cryoprotectant for solvent-free cell cryopreservation, but the membrane-impermeability limits its cryoprotective efficiency. Herein, a series of aromatic monoamines with a 1-4 methylene spacer were grafted onto γ-poly(glutamic acid) (γ-PGA) for promoting intracellular trehalose uptake in human red blood cells (hRBCs) via membrane perturbation. The self-assembled nanoparticles of the obtained amphiphilic γ-PGA could be adsorbed on the cell membrane by the hydrophobic interaction to disturb the lipid arrangement and increase the membrane permeability of trehalose under hypertonic conditions. Results suggested that the intracellular trehalose could be enhanced progressively with the methylene spacer length, significantly increasing to 75.1 ± 0.7 mM by incubating hRBCs in 0.8 M trehalose containing phenylbutylamine-grafted γ-PGA at 4 °C for 24 h. Meanwhile, the other three polymers exhibited membrane stabilization in addition to improved intracellular trehalose, maintaining the membrane integrity during cryopreservation to achieve high cryosurvival. Molecular dynamics simulation further confirmed that defects could be formed by interaction of the above four amphiphilic polymers on the modeled phospholipid bilayer. It was believed that glycerol-free cryopreservation of human cells could be realized by using trehalose as the biocompatible cryoprotectant, and membrane stabilization can be a compensatory approach to membrane perturbation during impermeable biomolecule delivery.

The reversal of drug resistance by two-dimensional titanium carbide Ti2 C (2D Ti2C) in non-small-cell lung cancer via the depletion of intracellular antioxidant reserves

Background

Chemoresistance is a major barrier limiting the therapeutic efficacy of late stage non‐small cell lung cancer (NSCLC). In this study, we sought to use two‐dimensional titanium carbide (2D Ti₂C) to reverse cisplatin resistance in NSCLC.

Methods

We first achieved favorable properties as a potential anti‐tumor agent. We then compared cell viability and cisplatin uptake in chemoresistant NSCLC cells before and after the use of 2D Ti₂C. Afterwards, we explored the effects of 2D Ti₂C on intracellular antioxidant reserves, followed by evaluating the subsequent changes in the expression of core drug resistance genes. Finally, we confirmed the tumor inhibitory effect and bio‐safety of 2D Ti₂C in a drug‐resistant lung cancer model in nude mice.

Results

Due to the properties of thin layer, large specific surface area, and abundant reactive groups on the surface, 2D Ti₂C can deplete the antioxidant reserve systems such as the glutathione redox buffer system, γ‐glutamylcysteine synthetase (γ‐GCS), glutathione peroxidase (GPx), glutathione‐S‐transferase‐Pi (GST‐π), and metallothionein (MT), thereby increasing the intracellular accumulation of cisplatin and decreasing the expression of drug resistance genes.

Conclusions

2D Ti₂C can reverse NSCLC chemoresistance both in vitro and in vivo, suggesting that it may potentially become a novel and effective means to treat chemoresistant NSCLC in the clinic.

Serum Protects Cells and Increases Intracellular Delivery of Molecules by Nanoparticle-Mediated Photoporation

Introduction

Intracellular delivery of molecules is central to applications in biotechnology, medicine, and basic research. Nanoparticle-mediated photoporation using carbon black nanoparticles exposed to pulsed, near-infrared laser irradiation offers a physical route to create transient cell membrane pores, enabling intracellular delivery. However, nanoparticle-mediated photoporation, like other physical intracellular delivery technologies, necessitates a trade-off between achieving efficient uptake of exogenous molecules and maintaining high cell viability.

Methods

In this study, we sought to shift this balance by adding serum to cells during nanoparticle-mediated photoporation as a viability protectant. DU-145 prostate cancer cells and human dermal fibroblasts were exposed to laser irradiation in the presence of carbon black (CB) nanoparticles and other formulation additives, including fetal bovine serum (FBS) and polymers.

Results

Our studies showed that FBS can protect cells from viability loss, even at high-fluence laser irradiation conditions that lead to high levels of intracellular delivery in two different mammalian cell types. Further studies revealed that full FBS was not needed: viability protection was achieved with denatured FBS, with just the high molecular weight fraction of FBS (>30 kDa), or even with individual proteins like albumin or hemoglobin. Finally, we found that viability protection was also obtained using certain neutral water-soluble polymers, including Pluronic F127, polyvinylpyrrolidone, poly(2-ethyl-2-oxazoline), and polyethylene glycol, which were more effective at increased concentration, molecular weight, or hydrophobicity.

Conclusion

Altogether, these findings suggest an interaction between amphiphilic domains of polymers with the cell membrane to help cells maintain viability, possibly by facilitating transmembrane pore closure. In this way, serum components or synthetic polymers can be used to increase intracellular delivery by nanoparticle-mediated photoporation while maintaining high cell viability.

No Direct Postconditioning Effect of Poloxamer 188 on Mitochondrial Function after Ischemia Reperfusion Injury in Rat Isolated Hearts

Myocardial infarction is a leading cause for morbidity and mortality worldwide. The only viable treatment for the ischemic insult is timely reperfusion, which further exacerbates myocardial injury. Maintaining mitochondrial function is crucial in preserving cardiomyocyte function in ischemia reperfusion (IR) injury. Poloxamer (P) 188 has been shown to improve cardiac IR injury by improving cellular and mitochondrial function. The aim of this study was to show if P188 postconditioning has direct protective effects on mitochondrial function in the heart. Langendorff prepared rat hearts were subjected to IR injury ex-vivo and reperfused for 10 min with 1 mM P188 vs. vehicle. Cardiac mitochondria were isolated with 1 mM P188 vs. 1 mM polyethylene glycol (PEG) vs. vehicle by differential centrifugation. Mitochondrial function was assessed by adenosine triphosphate synthesis, oxygen consumption, and calcium retention capacity. Mitochondrial function decreased significantly after ischemia and showed mild improvement with reperfusion. P188 did not improve mitochondrial function in the ex-vivo heart, and neither further P188 nor PEG induced direct mitochondrial protection after IR injury in this model.

Evaluation of In Vitro Neuronal Protection by Postconditioning with Poloxamer 188 Following Simulated Traumatic Brain Injury

Traumatic brain injury (TBI) leads to morbidity and mortality worldwide. Reperfusion after ischemia adds detrimental injury to cells. Ischemia/reperfusion (I/R) injures cells in a variety of ways including cell membrane disruption. Hence, methods to improve endogenous membrane resealing capacity are crucial. Poloxamer (P) 188, an amphiphilic triblock copolymer, was found to be effective against I/R and mechanical injury in various experimental settings. The aim of this study was to establish an in vitro mouse neuronal TBI model and, further, to investigate if postconditioning with P188 directly interacts with neurons after compression and simulated I/R injury, when administered at the start of reoxygenation. Cellular function was assessed by cell number/viability, mitochondrial viability, membrane damage by lactated dehydrogenase (LDH) release and FM1-43 incorporation as well as apoptosis-activation by Caspase 3. Five hours hypoxia ± compression with 2 h reoxygenation proved to be a suitable model for TBI. Compared to normoxic cells not exposed to compression, cell number and mitochondrial viability decreased, whereas membrane injury by LDH release/FM1-43 dye incorporation and Caspase 3 activity increased in cells exposed to hypoxic conditions with compression followed by reoxygenation. P188 did not protect neurons from simulated I/R and/or compression injury. Future research is indicated.

Potential Effects of Poloxamer 188 on Rat Isolated Brain Mitochondria after Oxidative Stress In Vivo and In Vitro

Outcome after cerebral ischemia is often dismal. Reperfusion adds significantly to the ischemic injury itself. Therefore, new strategies targeting ischemia/reperfusion (I/R) injury are critically needed. Poloxamer (P)188, an amphiphilic triblock copolymer, is a highly promising pharmacological therapeutic as its capability to insert into injured cell membranes has been reported to protect against I/R injury in various models. Although mitochondrial function particularly profits from P188 treatment after I/R, it remains unclear if this beneficial effect occurs directly or indirectly. Here, rat isolated brain mitochondria underwent oxidative stress in vivo by asphyxial cardiac arrest or in vitro by the addition of hydrogen peroxide (H₂O₂) after isolation. Mitochondrial function was assessed by adenosine triphosphate synthesis, oxygen consumption, and calcium retention capacity. Both asphyxia and H₂O₂ exposure significantly impaired mitochondrial function. P188 did not preserve mitochondrial function after either injury mechanism. Further research is indicated.

Dynamics of Cell Membrane Permeabilization by Saponins Using Terahertz Attenuated Total Reflection

Understanding the relevant parameters of the formation of pores during permeabilization is very challenging for medical applications. Several components are involved: the arrival of the permeabilizing molecules to the membrane, the efficiency of formation of the pores and their specific dynamics, and the flux of molecules through the plasma membrane. Using attenuated total reflection in the terahertz domain, we studied the dynamics of Madine-Darby canine kidney cells after permeabilization by saponin molecules. We developed an analytical model taking into account saponin molecule diffusion, cell geometry, cytosol molecule diffusion, and pore dynamics. We also studied the effect of possible pore overlapping on the cell membrane, introducing a dimensionless quantity that is the ratio between overlapping and diffusive effects. Pores are found to be static within 1 h after their creation, hinting that the diffusion of the saponin molecules to the membrane is the limiting factor in our experiments.

Multiple poloxamers increase plasma membrane repair capacity in muscle and nonmuscle cells

Various previous studies established that the amphiphilic tri-block copolymer known as poloxamer 188 (P188) or Pluronic-F68 can stabilize the plasma membrane following a variety of injuries to multiple mammalian cell types. This characteristic led to proposals for the use of P188 as a therapeutic treatment for various disease states, including muscular dystrophy. Previous studies suggest that P188 increases plasma membrane integrity by resealing plasma membrane disruptions through its affinity for the hydrophobic lipid chains on the lipid bilayer. P188 is one of a large family of copolymers that share the same basic tri-block structure consisting of a middle hydrophobic propylene oxide segment flanked by two hydrophilic ethylene oxide moieties [poly(ethylene oxide)80-poly(propylene oxide)27-poly(ethylene oxide)80]. Despite the similarities of P188 to the other poloxamers in this chemical family, there has been little investigation into the membrane-resealing properties of these other poloxamers. In this study we assessed the resealing properties of poloxamers P181, P124, P182, P234, P108, P407, and P338 on human embryonic kidney 293 (HEK293) cells and isolated muscle from the mdx mouse model of Duchenne muscular dystrophy. Cell membrane injuries from glass bead wounding and multiphoton laser injury show that the majority of poloxamers in our panel improved the plasma membrane resealing of both HEK293 cells and dystrophic muscle fibers. These findings indicate that many tri-block copolymers share characteristics that can increase plasma membrane resealing and that identification of these shared characteristics could help guide design of future therapeutic approaches.

Would antioxidant-loaded nanoparticles present an effective treatment for ischemic stroke?

Ischemic stroke is a leading cause of death and disability worldwide and is in urgent need of new treatment options. The only approved treatment for stroke restores blood flow to the brain, but much of the tissue damage occurs during the subsequent reperfusion. Antioxidant therapies that directly address ischemia-reperfusion injury have shown promise in preclinical results. In this review, we discuss that reformulating antioxidant therapies as nanomedicine can potentially overcome the barriers that have kept these therapies from succeeding in the clinic. We begin by reviewing the pathophysiology of ischemic stroke with a focus on the effects of reperfusion injury. Next, we review nanotherapeutic systems designed to treat the disease with a focus on those addressing reperfusion injury. Mechanisms of passive and active transport required to traverse a blood–brain barrier are discussed. Finally, we conclude by outlining design parameters for potentially successful nanomedicines as front-line therapeutics for ischemic stroke.

Characterization of Cell Membrane Permeability In Vitro Part I: Transport Behavior Induced by Single-Pulse Electric Fields

Most experimental studies of electroporation focus on permeabilization of the outer cell membrane. Some experiments address delivery of ions and molecules into cells that should survive; others focus on efficient killing of the cells with minimal temperature rise. A basic method for quantifying electroporation effectiveness is measuring the membrane's diffusive permeability. More specifically, comparisons of membrane permeability between electroporation protocols often rely on relative fluorescence measurements, which are not able to be directly connected to theoretical calculations and complicate comparisons between studies. Here we present part I of a 2-part study: a research method for quantitatively determining the membrane diffusive permeability for individual cells using fluorescence microscopy. We determine diffusive permeabilities of cell membranes to propidium for electric field pulses with durations of 1 to 1000 μs and strengths of 170 to 400 kV/m and show that diffusive permeabilities can reach 1.3±0.4×10-8 m/s. This leads to a correlation between increased membrane permeability and eventual propidium uptake. We also identify a subpopulation of cells that exhibit a delayed and significant propidium uptake for relatively small single pulses. Our results provide evidence that cells, especially those that uptake propidium more slowly, can achieve large permeabilities with a single electrical pulse that may be quantitatively measured using standard fluorescence microscopy equipment and techniques.