Mitochondrial responses to organelle-specific drug delivering nanoparticles composed of polypeptide and peptide complexes

Aims: The mechanistic study of the drug carrier-target interactions of mitochondria-unique nanoparticles composed of polypeptide-peptide complexes (mPoP-NPs). Materials & methods: The isolated organelles were employed to address the direct effects of mPoP-NPs on dynamic structure and functional wellbeing of mitochondria. Mitochondria morphology, respiration, membrane potential, reactive oxygen species generation, were examined by confocal microscopy, flow cytometry and oxygraphy. Lonidamine-encapsulated formulation was assessed to evaluate the drug delivery capacity of the naive nanoparticles. Results: The mPoP-NPs do not alter mitochondria structure and performance upon docking to organelles, while successfully delivering drug that causes organelle dysfunction. Conclusion: The study gives insight into interactions of mPoP-NPs with mitochondria and provides substantial support for consideration of designed nanoparticles as biocompatible and efficient mitochondria-targeted platforms.

Mitochondria membrane transformations in colon and prostate cancer and their biological implications

Mitochondria have emerged as important determinants in cancer progression and malignancy. However, the role of mitochondrial membranes in cancer onset and progression has not been thoroughly investigated. This study compares the structural and functional properties of mitochondrial membranes in prostate and colon cancer cells in comparison to normal mitochondria, and possible therapeutic implications of these membrane changes. Specifically, isolation of cell mitochondria and preparation of inverted sub-mitochondrial particles (SMPs) illuminated significant cancer-induced modulations of membrane lipid compositions, fluidity, and activity of cytochrome c oxidase, one of the key mitochondrial enzymes. The experimental data further show that cancer-associated membrane transformations may account for mitochondria targeting by betulinic acid and resveratrol, known anti-cancer molecules. Overall, this study probes the relationship between cancer and mitochondrial membrane transformations, underlying a potential therapeutic significance for mitochondrial membrane targeting in cancer.

Malate-aspartate shuttle promotes l-lactate oxidation in mitochondria

Metabolism in cancer cells is rewired to generate sufficient energy equivalents and anabolic precursors to support high proliferative activity. Within the context of these competing drives aerobic glycolysis is inefficient for the cancer cellular energy economy. Therefore, many cancer types, including colon cancer, reprogram mitochondria-dependent processes to fulfill their elevated energy demands. Elevated glycolysis underlying the Warburg effect is an established signature of cancer metabolism. However, there are a growing number of studies that show that mitochondria remain highly oxidative under glycolytic conditions. We hypothesized that activities of glycolysis and oxidative phosphorylation are coordinated to maintain redox compartmentalization. We investigated the role of mitochondria-associated malate-aspartate and lactate shuttles in colon cancer cells as potential regulators that couple aerobic glycolysis and oxidative phosphorylation. We demonstrated that the malate-aspartate shuttle exerts control over NAD⁺ /NADH homeostasis to maintain activity of mitochondrial lactate dehydrogenase and to enable aerobic oxidation of glycolytic l-lactate in mitochondria. The elevated glycolysis in cancer cells is proposed to be one of the mechanisms acquired to accelerate oxidative phosphorylation.

Respirometric reserve capacity of cumulus cell mitochondria correlates with oocyte maturity

PURPOSE

Oocyte competence is critical in success of assisted reproduction. Metabolic signaling between oocyte and cumulus cells within the cumulus-oocyte complex procure oocyte development. This study evaluated the relationship between respirometric activity of cumulus cells and maturity of corresponding oocytes.

METHODS

In prospective cohort study, 20 women of age 28-42 undergoing IVF procedure were involved. To evaluate oocyte maturity, the cumulus cells from individual oocytes were assessed flow cytometrically by double labeling of cells with mitochondria specific dyes. The respirometric stress analysis using ATPase inhibitor oligomycin was applied to assess mitochondria metabolic abnormalities.

RESULTS

The cumulus cells from each of 327 oocytes were analyzed. The respirometric index of cumulus cells (O'_R) strongly correlates with maternal ovarian reserve, showing to be higher in patients with higher AMH (p < 0.0017). Cumulus cells from immature oocytes had severe mitochondria deficiency, i.e., low O'_R, than those from mature oocytes (p < 0.02). No significant difference in respirometric capacity was found between cumulus cells associated with good vs poor-quality embryos.

CONCLUSIONS

The oocyte maturity is potentially related to the mitochondria activity of cumulus cells.

Rapamycin increases oxidative metabolism and enhances metabolic flexibility in human cardiac fibroblasts

Inhibition of mTOR signaling using rapamycin has been shown to increase lifespan and healthspan in multiple model organisms; however, the precise mechanisms for the beneficial effects of rapamycin remain uncertain. We have previously reported that rapamycin delays senescence in human cells and that enhanced mitochondrial biogenesis and protection from mitochondrial stress is one component of the benefit provided by rapamycin treatment. Here, using two models of senescence, replicative senescence and senescence induced by the presence of the Hutchinson-Gilford progeria lamin A mutation, we report that senescence is accompanied by elevated glycolysis and increased oxidative phosphorylation, which are both reduced by rapamycin. Measurements of mitochondrial function indicate that direct mitochondria targets of rapamycin are succinate dehydrogenase and matrix alanine aminotransferase. Elevated activity of these enzymes could be part of complex mechanisms that enable mitochondria to resume their optimal oxidative phosphorylation and resist senescence. This interpretation is supported by the fact that rapamycin-treated cultures do not undergo a premature senescence in response to the replacement of glucose with galactose in the culture medium, which forces a greater reliance on oxidative phosphorylation. Additionally, long-term treatment with rapamycin increases expression of the mitochondrial carrier protein UCP2, which facilitates the movement of metabolic intermediates across the mitochondrial membrane. The results suggest that rapamycin impacts mitochondrial function both through direct interaction with the mitochondria and through altered gene expression of mitochondrial carrier proteins.

Artefactual formation of pyruvate from in-source conversion of lactate

RATIONALE

Lactate and pyruvate are high abundance products of glucose metabolism. Analysis of both molecules as part of metabolomics studies in cellular metabolism and physiology have been aided by advances in liquid chromatography-mass spectrometry (LC-MS).

METHODS

We used ion pairing-chromatography and negative ion mode ESI on an QExactive HF to perform stable isotope assisted metabolomics profiling of lactate and pyruvate metabolism.

RESULTS

Using an LC-MS method for polar metabolite analysis we discovered an artefactual formation of pyruvate from in-source fragmentation of lactate. Surprisingly, this in-source fragmentation has not been previously described, thus we report this identification to warn other investigators. This artefact was detected by baseline chromatographic resolution of lactate and pyruvate by LC with confirmation of this artefact by stable isotope labeling of lactate and pyruvate.

CONCLUSIONS

These findings have immediate implications for metabolomics studies by LC-MS and direct infusion MS, especially in negative ion mode, whereby users should resolve lactate from pyruvate or robustly quantify the potential formation of pyruvate from higher abundance lactate in their assays.

Perfusion double-channel micropipette probes for oxygen flux mapping with single-cell resolution

Measuring cellular respiration with single-cell spatial resolution is a significant challenge, even with modern tools and techniques. Here, a double-channel micropipette is proposed and investigated as a probe to achieve this goal by sampling fluid near the point of interest. A finite element model (FEM) of this perfusion probe is validated by comparing simulation results with experimental results of hydrodynamically confined fluorescent molecule diffusion. The FEM is then used to investigate the dependence of the oxygen concentration variation and the measurement signal on system parameters, including the pipette's shape, perfusion velocity, position of the oxygen sensors within the pipette, and proximity of the pipette to the substrate. The work demonstrates that the use of perfusion double-barrel micropipette probes enables the detection of oxygen consumption signals with micrometer spatial resolution, while amplifying the signal, as compared to sensors without the perfusion system. In certain flow velocity ranges (depending on pipette geometry and configuration), the perfusion flow increases oxygen concentration gradients formed due to cellular oxygen consumption. An optimal perfusion velocity for respiratory measurements on single cells can be determined for different system parameters (e.g., proximity of the pipette to the substrate). The optimum perfusion velocities calculated in this paper range from 1.9 to 12.5 μm/s. Finally, the FEM model is used to show that the spatial resolution of the probe may be varied by adjusting the pipette tip diameter, which may allow oxygen consumption mapping of cells within tissue, as well as individual cells at subcellular resolution.

Determination of mitochondrial metabolic phenotype through investigation of the intrinsic inhibition of succinate dehydrogenase

Many diseases are accompanied by systemic or organ metabolic abnormalities. Therefore, investigation of the roles of mitochondrial dysfunction in the pathogenesis of major diseases requires a methodology that reflects the characteristics of mitochondrial metabolism particular for the organ of origin. We provide evidence that for brain and heart mitochondria the intrinsic inhibition of succinate dehydrogenase (SDH) is a key mechanism for attenuation of mitochondrial respiration and energy production in response to the organ's energy needs. This mechanism also serves to minimize the production of reactive oxygen species when the organ is at rest. Changes in the organ's workloads are accompanied by changes in metabolites that are used by mitochondria as substrates and for modification of energy production at the SDH level. Measurement of the respiratory activity of mitochondria with various substrates and substrate mixtures and use of bovine serum albumin as an SDH inhibitor will be useful for evaluation of metabolic phenotype at the mitochondrial level.

Danazol alters mitochondria metabolism of fibrocystic breast Mcf10A cells

Fibrocystic Breast Disease (FBD) or Fibrocystic change (FC) affects about 60% of women at some time during their life. Although usually benign, it is often associated with pain and tenderness (mastalgia). The synthetic steroid danazol has been shown to be effective in reducing the pain associated with FBD, but the cellular and molecular mechanisms for its action have not been elucidated. We investigated the hypothesis that danazol acts by affecting energy metabolism. Effects of danazol on Mcf10A cells homeostasis, including mechanisms of oxidative phosphorylation, cytosolic calcium signaling and oxidative stress, were assessed by high-resolution respirometry and flow cytometry. In addition to fast physiological responses the associated genomic modulations were evaluated by Affimetrix microarray analysis. The alterations of mitochondria membrane potential and respiratory activity, downregulation of energy metabolism transcripts result in suppression of energy homeostasis and arrest of Mcf10A cells growth. The data obtained in this study impacts the recognition of direct control of mitochondria by cellular mechanisms associated with altered energy metabolism genes governing the breast tissue susceptibility and response to medication by danazol.

Metabolic and structural integrity of magnetic nanoparticle-loaded primary endothelial cells for targeted cell therapy

AIM

To successfully translate magnetically mediated cell targeting from bench to bedside, there is a need to systematically assess the potential adverse effects of magnetic nanoparticles (MNPs) interacting with 'therapeutic' cells. Here, we examined in detail the effects of internalized polymeric MNPs on primary rat endothelial cells' structural intactness, metabolic integrity and proliferation potential.

MATERIALS & METHODS

The intactness of cytoskeleton and organelles was studied by fluorescent confocal microscopy, flow cytometry and high-resolution respirometry.

RESULTS

MNP-loaded primary endothelial cells preserve intact cytoskeleton and organelles, maintain normal rate of proliferation, calcium signaling and mitochondria energy metabolism.

CONCLUSION

This study provides supportive evidence that MNPs at doses necessary for targeting did not induce significant adverse effects on structural integrity and functionality of primary endothelial cells - potential cell therapy vectors.

Abstract B07: Tumor promoting activity of SLC13A3 in metastatic prostate cells

Solute carriers are membrane proteins that play an important role in cancer homeostasis by supplying cancer cells with essential building blocks and signaling molecules. Different types of membrane transporters were shown to be overexpressed in tumors in support of tumor growth and survival. Due to high affinity interaction with anticancer drugs they can also significantly contribute to the rapid chemoresistance. There is a limited number of studies on the role of solute carriers in reprogramming of cancer metabolism and signaling, especially in metastatic prostate cancer.

Our study enabled us to establish the identity of the prostate cancer solute carrier that supports uptake of succinate and possibly similar energy rich metabolites from tumor microenvironment to promote an elevated energy metabolism of cancer cells. We demonstrated that prostate metastatic DU145 cells acquire Na+-dependent dycarboxylic acid carrier SLC13A3 but normal prostate PrEC cells do not express this protein. An important finding was that only at acidic pH 6.8 prostate cancer cells are capable of consuming exogenous succinate, while physiological pH 7.4 was not favorable for this process. Importantly, succinate transported by SLC13A3 not only accelerates the oxidative phosphorylation of prostate cancer mitochondria but it is also known to stabilize onco-factor HIF-1α. The HIF-involved signaling pathways have been linked to prostate tumorigenesis and chemoresistance and therefore, targeting these pathways by inhibiting cancer specific SLC13A3 has great potential for clinical benefit. In addition, the mechanism of succinate influx via SLC13A3 transporter in metastatic prostate cancer cells could also yield a novel metabolic onco-marker and has the potential to be used for imaging-based diagnostics to detect non-glycolytic tumors.

Citation Format: Aigul Zhunussova, Zhanar Irgebayeva, Bhaswati Sen, Leah Friedman, Saniya Ossikbayeva, Sultan Tuleukhanov, Ari Brooks, Richard Sensenig, Zulfiya Orynbayeva. Tumor promoting activity of SLC13A3 in metastatic prostate cells. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr B07.

Knockout of cyclophilin D in Ppif⁻/⁻ mice increases stability of brain mitochondria against Ca²⁺ stress

The mitochondrial peptidyl prolyl isomerase cyclophilin D (CypD) activates permeability transition (PT). To study the role of CypD in this process we compared the functions of brain mitochondria isolated from wild type (BMWT) and CypD knockout (Ppif(-/-)) mice (BMKO) with and without CypD inhibitor Cyclosporin A (CsA) under normal and Ca(2+) stress conditions. Our data demonstrate that BMKO are characterized by higher rates of glutamate/malate-dependent oxidative phosphorylation, higher membrane potential and higher resistance to detrimental Ca(2+) effects than BMWT. Under the elevated Ca(2+) and correspondingly decreased membrane potential the dose response in BMKO shifts to higher Ca(2+) concentrations as compared to BMWT. However, significantly high Ca(2+) levels result in complete loss of membrane potential in BMKO, too. CsA diminishes the loss of membrane potential in BMWT but has no protecting effect in BMKO. The results are in line with the assumption that PT is regulated by CypD under the control of matrix Ca(2+). Due to missing of CypD the BMKO can favor PT only at high Ca(2+) concentrations. It is concluded that CypD sensitizes the brain mitochondria to PT, and its inhibition by CsA or CypD absence improves the complex I-related mitochondrial function and increases mitochondria stability against Ca(2+) stress.

Tumor microenvironment promotes dicarboxylic acid carrier-mediated transport of succinate to fuel prostate cancer mitochondria

Prostate cancer cells reprogram their metabolism, so that they support their elevated oxidative phosphorylation and promote a cancer friendly microenvironment. This work aimed to explore the mechanisms that cancer cells employ for fueling themselves with energy rich metabolites available in interstitial fluids. The mitochondria oxidative phosphorylation in metastatic prostate cancer DU145 cells and normal prostate epithelial PrEC cells were studied by high-resolution respirometry. An important finding was that prostate cancer cells at acidic pH 6.8 are capable of consuming exogenous succinate, while physiological pH 7.4 was not favorable for this process. Using specific inhibitors, it was demonstrated that succinate is transported in cancer cells by the mechanism of plasma membrane Na(+)-dependent dycarboxylic acid transporter NaDC3 (SLC13A3 gene). Although the level of expression of SLC13A3 was not significantly altered when maintaining cells in the medium with lower pH, the respirometric activity of cells under acidic condition was elevated in the presence of succinate. In contrast, normal prostate cells while expressing NaDC3 mRNA do not produce NaDC3 protein. The mechanism of succinate influx via NaDC3 in metastatic prostate cancer cells could yield a novel target for anti-cancer therapy and has the potential to be used for imaging-based diagnostics to detect non-glycolytic tumors.

The anti-cancer peptide, PNC-27, induces tumor cell necrosis of a poorly differentiated non-solid tissue human leukemia cell line that depends on expression of HDM-2 in the plasma membrane of these cells

GOALS

We have developed the anti-cancer peptide, PNC-27, which is a membrane-active peptide that binds to the HDM-2 protein expressed in the cancer cell membranes of solid tissue tumor cells and induces transmembrane pore formation in cancer, but not in normal cells, resulting in tumor cell necrosis that is independent of p53 activity in these cells. We now extend our study to non-solid tissue tumor cells, in this case, a primitive, possible stem cell human leukemia cell line (K562) that is also p53-homozygously deleted. Our purpose was twofold: to investigate if these cells likewise express HDM-2 in their plasma membranes and to determine if our anti-cancer peptide induces tumor cell necrosis in these non-solid tissue tumor cells in a manner that depends on the interaction between the peptide and membrane-bound HDM-2.

PROCEDURES

The anti-cancer activity and mechanism of PNC-27, which carries a p53 aa12-26-leader sequence connected on its carboxyl terminal end to a trans-membrane-penetrating sequence or membrane residency peptide (MRP), was studied against p53-null K562 leukemia cells. Murine leukocytes were used as a non-cancer cell control. Necrosis was determined by measuring the lactate dehydrogenase (LDH) release and apoptosis was determined by the detection of Caspases 3 and 7. Membrane colocalization of PNC-27 with HDM-2 was analyzed microscopically using fluorescently labeled antibodies against HDM-2 and PNC-27 peptides.

RESULTS

We found that K562 cells strongly express HDM-2 protein in their membranes and that PNC-27 co-localizes with this protein in the membranes of these cells. PNC-27, but not the negative control peptide PNC-29, is selectively cytotoxic to K562 cells, inducing nearly 100 percent cell killing with LDH release. In contrast, this peptide had no effect on the lymphocyte control cells.

CONCLUSIONS

The results suggest that HDM-2 is expressed in the membranes of non-solid tissue tumor cells in addition to the membranes of solid tissue tumor cells. Since K-562 cells appear to be in the stem cell family, the results suggest that early developing tumor cells also express HDM-2 protein in their membranes. Since PNC-27 induces necrosis of K-562 leukemia cells and co-localizes with HDM-2 in the tumor cell membrane as an early event, we conclude that the association of PNC-27 with HDM-2 in the cancer cell membrane results in trans-membrane pore formation which results in cancer cell death, as previously discovered in a number of different solid tissue tumor cells. Since K562 cells lack p53 expression, these effects of PNC-27 on this leukemia cell line occur by a p53-independent pathway.

One-dimensional nanoprobes for single-cell studies

Owing to variation of individual cells within a population, single-cell studies are of great interest to researchers. Recent developments in nanofabrication technology have made this area increasingly attractive as one-dimensional (1D) nanoscale probes can be manufactured with increasing accuracy. Here, we provide an overview and description of the major designs that have been reported to date. For more details of what applications could be realized and how, based on the probe shapes and designs, we summarize the most recently reported performances of 1D single-cell probes with their advantages and limitations. Minimally invasive probes are required for long-term experiments on single cells. Carbon nanotubes with their unique properties and structure are excellent candidates for multitask robotic intracellular probes. Carbon nanotube-tipped cellular endoscopes are less invasive compared with pipettes or cantilever tips. Advances in nanofabrication techniques have made it possible to produce more consistent nanoscale cellular probes that can capture a variety of information from optical, electrical and chemical signals. In addition, these tools can transfer tiny amounts of fluids and molecular materials in a highly localized fashion for the purpose of analyzing or stimulating a variety of responses at the level of individual cells and even cellular organelles. We conclude with a critical analysis of the current state of the field as well as the major obstacles for further probe development of minimally invasive probes and their widespread use in cell biology.

Bioenergetic and antiapoptotic properties of mitochondria from cultured human prostate cancer cell lines PC-3, DU145 and LNCaP

The purpose of this work was to reveal the metabolic features of mitochondria that might be essential for inhibition of apoptotic potential in prostate cancer cells. We studied mitochondria isolated from normal prostate epithelial cells (PrEC), metastatic prostate cancer cell lines LNCaP, PC-3, DU145; and non-prostate cancer cells - human fibrosarcoma HT1080 cells; and normal human lymphoblastoid cells. PrEC cells contained 2 to 4 times less mitochondria per gram of cells than the three PC cell lines. Respiratory activities of PrEC cell mitochondria were 5-20-fold lower than PC mitochondria, depending on substrates and the metabolic state, due to lower content and lower activity of the respiratory enzyme complexes. Mitochondria from the three metastatic prostate cancer cell lines revealed several features that are distinctive only to these cells: low affinity of Complex I for NADH, 20-30 mV higher electrical membrane potential (ΔΨ). Unprotected with cyclosporine A (CsA) the PC-3 mitochondria required 4 times more Ca²⁺ to open the permeability transition pore (mPTP) when compared with the PrEC mitochondria, and they did not undergo swelling even in the presence of alamethicin, a large pore forming antibiotic. In the presence of CsA, the PC-3 mitochondria did not open spontaneously the mPTP. We conclude that the low apoptotic potential of the metastatic PC cells may arise from inhibition of the Ca²⁺-dependent permeability transition due to a very high ΔΨ and higher capacity to sequester Ca²⁺. We suggest that due to the high ΔΨ, mitochondrial metabolism of the metastatic prostate cancer cells is predominantly based on utilization of glutamate and glutamine, which may promote development of cachexia.

The control of brain mitochondrial energization by cytosolic calcium: the mitochondrial gas pedal

This review focuses on problems of the intracellular regulation of mitochondrial function in the brain via the (i) supply of mitochondria with ADP by means of ADP shuttles and channels and (ii) the Ca(2+) control of mitochondrial substrate supply. The permeability of the mitochondrial outer membrane for adenine nucleotides is low. Therefore rate dependent concentration gradients exist between the mitochondrial intermembrane space and the cytosol. The existence of dynamic ADP gradients is an important precondition for the functioning of ADP shuttles, for example CrP-shuttle. Cr at mM concentrations instead of ADP diffuses from the cytosol through the porin pores into the intermembrane space. The CrP-shuttle isoenzymes work in different directions which requires different metabolite concentrations mainly caused by dynamic ADP compartmentation. The ADP shuttle mechanisms alone cannot explain the load dependent changes in mitochondrial energization, and a complete model of mitochondrial regulation have to account the Ca(2+) -dependent substrate supply too. According to the old paradigmatic view, Ca(2+) (cyt) taken up by the mitochondrial Ca(2+) uniporter activates dehydrogenases within the matrix. However, recently it was found that Ca(2+) (cyt) at low nM concentrations exclusively activates the state 3 respiration via aralar, the mitochondrial glutamate/aspartate carrier. At higher Ca(2+) (cyt) (> 500 nM), brain mitochondria take up Ca(2+) for activation of substrate oxidation rates. Since brain mitochondrial pyruvate oxidation is only slightly influenced by Ca(2+) (cyt) , it was proposed that the cytosolic formation of pyruvate from its precursors is tightly controlled by the Ca(2+) dependent malate/aspartate shuttle. At low (50-100 nM) Ca(2+) (cyt) the pyruvate formation is suppressed, providing a substrate limitation control in neurons. This so called "gas pedal" mechanism explains why the energy metabolism of neurons in the nucleus suprachiasmaticus could be down-regulated at night but activated at day as a basis for the circadian changes in Ca(2+) (cyt) . It also could explain the energetic disadvantages caused by altered Ca(2+) (cyt) at mitochondrial diseases and neurodegeneration.

Physiological validation of cell health upon probing with carbon nanotube endoscope and its benefit for single-cell interrogation

New-generation nanoscale devices for single-cell study are intensively being developed. As has been shown, nanodevices are minimally invasive because of their order-of-magnitude smaller size in comparison to conventional glass pipettes. However, in most studies the evaluation of the nanodevice impact on cell health has not extended to their effects on cell metabolic integrity. In this work we evaluated the degree to which the insertion of a carbon-based nanotube endoscope into a cell induces mechanical and biochemical stress, and affects cellular key metabolic systems. The effects of insertion of the nanotube endoscope on cell morphological and physiological modulations were monitored and compared to those of glass micropipettes. We report that nanotube endoscope insertion does not significantly modulate the plasma membrane and actin network. The cell metabolic mechanisms such as energy production and inositol 1,4,5-trisphosphate-dependent calcium signaling remain preserved for prolonged endoscope presence within a cell.

FROM THE CLINICAL EDITOR

In this basic science study, the effects of insertion of carbon nanotube endoscope on cell morphological and physiological modulations were monitored and compared to those of glass micropipettes. Nanotube endoscope insertion is truly minimally invasive: it does not significantly modulate the plasma membrane and actin network; the energy production and inositol 1,4,5-trisphosphate-dependent calcium signaling also remain preserved during prolonged endoscope presence within a cell.

Multifunctional carbon-nanotube cellular endoscopes

Glass micropipettes, atomic force microscope tips and nanoneedles can be used to interrogate cells, but these devices either have conical geometries that can damage cells during penetration or are incapable of continuous fluid handling. Here, we report a carbon-nanotube-based endoscope for interrogating cells, transporting fluids and performing optical and electrochemical diagnostics at the single organelle level. The endoscope, which is made by placing a multiwalled carbon nanotube (length, 50-60 µm) at the tip of a glass pipette, can probe the intracellular environment with a spatial resolution of ∼100 nm and can also access organelles without disrupting the cell. When the nanotube is filled with magnetic nanoparticles, the endoscope can be remotely manoeuvered to transport nanoparticles and attolitre volumes of fluids to and from precise locations. Because they are mounted on conventional glass micropipettes, the endoscopes readily fit standard instruments, creating a broad range of opportunities for minimally invasive intracellular probing, drug delivery and single-cell surgery.

Surface-enhanced Raman spectroscopy as a tool for detecting Ca2+ mobilizing second messengers in cell extracts

Understanding of calcium signaling pathways in cells is essential for elucidating the mechanisms of both normal cell function and cancer development. Calcium messengers play the crucial role for intracellular Ca(2+) release. We propose a new approach to detecting the calcium second messenger nicotinic acid adenine dinucleotide phosphate (NAADP) in cell extracts using surface-enhanced Raman spectroscopy (SERS). Currently available radioreceptor binding and enzymatic assays require extensive sample preparation and take more than 12 h. With a SERS sensor, NAADP can be detected in less than 1 min without any special sample preparation. To the best of our knowledge, this is the first demonstration of using SERS for calcium signaling applications.

Small diameter carbon nanopipettes

Nanoscale multifunctional carbon probes facilitate cellular studies due to their small size, which makes it possible to interrogate organelles within living cells in a minimally invasive fashion. However, connecting nanotubes to macroscopic devices and constructing an integrated system for the purpose of fluid and electrical signal transfer is challenging, as is often the case with nanoscale components. We describe a non-catalytic chemical vapor deposition based method for batch fabrication of integrated multifunctional carbon nanopipettes (CNPs) with tip diameters much smaller (10-30 nm) than previously reported (200 nm and above) and approaching those observed for multiwalled carbon nanotubes. This eliminates the need for complicated attachment/assembly of nanotubes into nanofluidic devices. Variable tip geometries and structures were obtained by controlled deposition of carbon inside and outside quartz pipettes. We have shown that the capillary length and gas flow rate have a marked effect on the carbon deposition. This gives us a flexible protocol, useful for growing carbon layers of different thicknesses at selective locations on a glass pipette to yield a large variety of cellular probes in bulk quantities. The CNPs possess an open channel for fluid transfer with the carbon deposited inside at 875 degrees C behaving like an amorphous semiconductor. Vacuum annealing of the CNP tips at temperatures up to 2000 degrees C yields graphitic carbon structures with an increase in conductivity of two orders of magnitude. Penetration of the integrated carbon nanoprobes into cells was shown to produce minimal Ca(2+) signals, fast recovery of basal Ca(2+) levels and no adverse activation of the cellular metabolism during interrogation times as long as 0.5-1 h.

In situ intracellular spectroscopy with surface enhanced Raman spectroscopy (SERS)-enabled nanopipettes

We report on a new analytical approach to intracellular chemical sensing that utilizes a surface-enhanced Raman spectroscopy (SERS)-enabled nanopipette. The probe is comprised of a glass capillary with a 100-500 nm tip coated with gold nanoparticles. The fixed geometry of the gold nanoparticles allows us to overcome the limitations of the traditional approach for intracellular SERS using metal colloids. We demonstrate that the SERS-enabled nanopipettes can be used for in situ analysis of living cell function in real time. In addition, SERS functionality of these probes allows tracking of their localization in a cell. The developed probes can also be applied for highly sensitive chemical analysis of nanoliter volumes of chemicals in a variety of environmental and analytical applications.

Screening membrane interactions of pesticides by cells decorated with chromatic polymer nanopatches

Elucidating the factors contributing to the cell toxicity of pesticides and other environmentally sensitive small molecules is critical for evaluation of their health impacts and for understanding the biological processes that they affect. Disruption and permeation of the plasma membrane, which constitutes the critical interface between the cell and its environment, are recognized initiators of cytotoxicity. We present a new approach for predicting pesticide cytotoxicity through rapid screening of membrane interactions of pesticides using a recently developed live-cell chromatic sensor. The sensing platform comprises living mammalian cells labeled with polydiacetylene (PDA), a chromatic polymer that undergoes intense fluorescence transformations induced by structural perturbations of the membrane bilayer. Within a short time after the addition of membrane-interacting tested compounds to the labeled cells, the PDA patches emit high fluorescence, which can be monitored by conventional spectroscopy and microscopy apparatuses. The chromatic technology facilitates rapid evaluation of membrane activity of pesticide compounds and is capable of distinguishing between toxic effects associated with membrane interactions vs intracellular mechanisms.

Membrane processes and biophysical characterization of living cells decorated with chromatic polydiacetylene vesicles

The structural complexity of the cell membrane makes analysis of membrane processes in living cells, as compared to model membrane systems, highly challenging. Living cells decorated with surface-attached colorimetric/fluorescent polydiacetylene patches might constitute an effective platform for analysis and visualization of membrane processes in situ. This work examines the biological and chemical consequences of plasma membrane labeling of promyelocytic leukemia cells with polydiacetylene. We show that the extent of fusion between incubated lipid/diacetylene vesicles and the plasma membrane is closely dependent upon the lipid composition of both vesicles and cell membrane. In particular, we find that cholesterol presence increased bilayer fusion between the chromatic vesicles and the plasma membrane, suggesting that membrane organization plays a significant role in the fusion process. Spectroscopic data and physiological assays show that decorating the cell membrane with the lipid/diacetylene patches reduces the overall lateral diffusion within the membrane bilayer, however polydiacetylene labeling does not adversely affect important cellular metabolic pathways. Overall, the experimental data indicate that the viability and physiological integrity of the surface-engineered cells are retained, making possible utilization of the platform for studying membrane processes in living cells. We demonstrate the use of the polydiacetylene-labeled cells for visualizing and discriminating among different membrane interaction mechanisms of pharmaceutical compounds.

Vaccinia virus interactions with the cell membrane studied by new chromatic vesicle and cell sensor assays

The potential danger of cross-species viral infection points to the significance of understanding the contributions of nonspecific membrane interactions with the viral envelope compared to receptor-mediated uptake as a factor in virus internalization and infection. We present a detailed investigation of the interactions of vaccinia virus particles with lipid bilayers and with epithelial cell membranes using newly developed chromatic biomimetic membrane assays. This analytical platform comprises vesicular particles containing lipids interspersed within reporter polymer units that emit intense fluorescence following viral interactions with the lipid domains. The chromatic vesicles were employed as membrane models in cell-free solutions and were also incorporated into the membranes of epithelial cells, thereby functioning as localized membrane sensors on the cell surface. These experiments provide important insight into membrane interactions with and fusion of virions and the kinetic profiles of these processes. In particular, the data emphasize the significance of cholesterol/sphingomyelin domains (lipid rafts) as a crucial factor promoting bilayer insertion of the viral particles. Our analysis of virus interactions with polymer-labeled living cells exposed the significant role of the epidermal growth factor receptor in vaccinia virus infectivity; however, the data also demonstrated the existence of additional non-receptor-mediated mechanisms contributing to attachment of the virus to the cell surface and its internalization.