Quartz crystal microbalance measurements of mitochondrial depolarization predicting chemically induced toxicity of vascular cells and macrophages.

Quartz crystal microbalances (QCMs) measure mass on the nanogram (ng) scale. We built novel QCMs as toxicity biosensors incorporating living cells. Human endothelial cells or canine macrophages were equilibrated on QCM crystal surfaces until stable oscillation frequencies occurred. Vehicle or sodium azide (NaN3) (25-100 mM) was added to these QCMs while continuously collecting crystal oscillation frequency data. At these doses, NaN3 alters mitochondrial membrane permeability and causes mitochondrial swelling and intrinsic apoptosis. Our studies demonstrated no frequency change in QCMs with untreated cells or without cells but NaN3. If NaN3 was added to either cell type within QCMs, 5 to 8 min later increases in oscillation frequency (Δf) occurred (400-1600 Hz) that correlated with dose. All frequency changes reverted to baseline by 15 min. In parallel, during the first 30 min, no change in cell or nuclear areas, or in actin or microtubule distributions, was detected. Yet, mitochondrial size and membrane permeability increased significantly during, but not after, 5 to 8 min. Viability studies confirmed dose-dependent toxicity that was predicted and proportionate to the 5- to 8-min Δf. These studies confirm that cell-based QCMs can detect early events in intrinsic apoptosis and reveal unique kinetic information about events occurring within subcellular structures in response to toxins.

Understanding and correcting for carbon nanotube interferences with a commercial LDH cytotoxicity assay.

The lactate dehydrogenase (LDH) assay accurately quantifies cytotoxicity of chemicals via the measurement of LDH released from damaged cells. In the assay, LDH catalyzes formation of a reporter chromophore that can be quantified spectrophotometrically at its 490 nm peak, a standard assay, and related to the released LDH concentration. However, certain engineered nanomaterials have been reported to produce aberrant values, resulting in inaccurate assessment of toxicity as measured by LDH levels in media. We studied this effect spectroscopically by measuring unexpected changes in the complete visible spectrum of the product chromophore resulting from using either purified LDH or LDH from lysed cells in the presence of varying concentrations of single walled carbon nanotubes (SWCNTs) or carbon nanohorns (SWCNH-oxs). Basically, at constant LDH concentrations, the 490 nm product peak decreased with increasing carbon nanotube concentration, while the 580 nm peak increased to a lesser extent and the maximum absorbing wavelength increased. The product chromophore spectrum was altered in different ways by potential interactions with a number of components in the reaction mixture including: BSA, LDH, SWCNTs, SWCNT-oxs, or various combinations of these species. We propose to improve the accuracy of the LDH assay when evaluated in the presence of varying concentrations of these carbon nanostructures by use of both the 490 and 580 nm peak absorbances combined via regression analysis. Our results indicate that molecular probes of cytotoxicity must be assessed individually for accuracy in the presence of engineered nanomaterials.

Dynamic cell adhesion and viscoelastic signatures distinguish normal from malignant human mammary cells using quartz crystal microbalance.

During transformation of a normal cell to a cell capable of forming a cancerous growth, cellular morphology, the cytoskeleton, and focal contacts undergo significant changes. These changes should be capable of being characterized via real-time monitoring of the dynamic cell adhesion process and viscoelastic properties of cells. Here, we describe use of the quartz crystal microbalance (QCM) to distinguish the dynamic cell adhesion signatures of human normal (HMEC) versus malignant (MCF-7) mammary epithelial cells. The significantly reduced QCM responses (changes in frequency [Δf] and motional resistance ΔR) of MCF-7 cells compared with those of HMECs mirror the cancer cells' morphological features as observed via optical microscope. We analyzed the initial 2-h cell adhesion kinetics, suggesting cell-cell cooperativity for HMECs and no or weak cell-cell interactions for MCF-7 cells. We propose that changes of the ΔR/Δf ratio, which we term the cell viscoelastic index (CVI), reflect the establishment of cytoskeleton structure and dynamic viscoelastic properties of living cells. The CVI decreases significantly on initiation of cell to surface interactions as cells establish their cytoskeletal structures. During the cell adhesion process, MCF-7 cells were consistently softer, exhibiting up to a 2.5-fold smaller CVI when compared with HMECs.

Herceptin-directed nanoparticles activated by an alternating magnetic field selectively kill HER-2 positive human breast cells in vitro via hyperthermia.

PURPOSE: HER-2 is in the EGF tyrosine kinase receptor family, overexpressed by many human cancers and minimally expressed by normal adult tissues. HER-2 expression in human cancers is correlated with reduced survival, increased metastasis, reduced apoptosis and increased proliferation. Herceptin is a humanised mouse antibody that targets and inactivates HER-2. In the present study, Herceptin was used to deliver ferric oxide-enriched nanoparticles to HER-2(+) cancer cells. If exposed to alternating magnetic field (AMF), the nanoparticles heat. We tested the ability of AMF-activated Herceptin-directed nanoparticles to selectively kill HER-2(+) human cancer cells. METHODS: Herceptin-conjugated nanoparticles were incubated with normal human mammary epithelial cells (HMEC)(HER-2(-)) or malignant human mammary epithelial cells (SK-BR-3)(HER-2(+)). Cells were stained to detect Herceptin or iron and the kinetics of binding quantified. Once conditions were optimised for binding, cells were exposed to either antibody-directed or non-antibody-conjugated nanoparticles, washed and sham-treated or exposed to AMF and cell death quantified. RESULTS: SK-BR-3 cells bound Herceptin-directed nanoparticles in increasing amounts over 3 h but did not retain non-antibody conjugated nanoparticles. HMECs did not retain either nanoparticles. SK-BR-3 cells with bound Herceptin-directed-nanoparticles, exposed to AMF, died by apoptosis, quantifiable by Live/Dead and nuclear morphology assays and released LDH. Sham-treated SK-BR-3 cells with Herceptin-directed nanoparticles, HMECs with either nanoparticles, with or without AMF treatment, exhibited no increase in toxicity above baseline cell death using these three assays. CONCLUSIONS: These studies demonstrate Herceptin-directed nanoparticles can selectively kill HER-2(+) cancer cells via hyperthermia after AMF activation.

A living cell quartz crystal microbalance biosensor for continuous monitoring of cytotoxic responses of macrophages to single-walled carbon nanotubes.

BACKGROUND: Numerous engineered nanomaterials (ENMs) exist and new ENMs are being developed. A challenge to nanotoxicology and environmental health and safety is evaluating toxicity of ENMs before they become widely utilized. Cellular assays remain the predominant test platform yet these methods are limited by using discrete time endpoints and reliance on organic dyes, vulnerable to interference from ENMs. Label-free, continuous, rapid response systems with biologically meaningful endpoints are needed. We have developed a device to detect and monitor in real time responses of living cells to ENMs. The device, a living cell quartz crystal microbalance biosensor (QCMB), uses macrophages adherent to a quartz crystal. The communal response of macrophages to treatments is monitored continuously as changes in crystal oscillation frequency (Δf). We report the ability of this QCMB to distinguish benign from toxic exposures and reveal unique kinetic information about cellular responses to varying doses of single-walled carbon nanotubes (SWCNTs). RESULTS: We analyzed macrophage responses to additions of Zymosan A, polystyrene beads (PBs) (benign substances) or SWCNT (3-150 µg/ml) in the QCMB over 18 hrs. In parallel, toxicity was monitored over 24/48 hrs using conventional viability assays and histological stains to detect apoptosis. In the QCMB, a stable unchanging oscillation frequency occurred when cells alone, Zymosan A alone, PBs alone or SWCNTs without cells at the highest dose alone were used. With living cells in the QCMB, when Zymosan A, PBs or SWCNTs were added, a significant decrease in frequency occurred from 1-6 hrs. For SWCNTs, this Δf was dose-dependent. From 6-18 hrs, benign substances or low dose SWCNT (3-30 µg/ml) treatments showed a reversal of the decrease of oscillation frequency, returning to or exceeding pre-treatment levels. Cell recovery was confirmed in conventional assays. The lag time to see the Δf reversal in QCMB plots was linearly SWCNT-dose dependent. Lastly, the frequency never reversed at high dose SWCNT (100-150 µg/ml), and apoptosis/necrosis was documented in conventional 24 and 48 hr-assays. CONCLUSION: These data suggest that the new QCMB detects and provides unique information about peak, sub-lethal and toxic exposures of living cells to ENMs before they are detected using conventional cell assays.

Extracellular matrix-derived products modulate endothelial and progenitor cell migration and proliferation in vitro and stimulate regenerative healing in vivo.

Most adult mammals heal without restorative replacement of lost tissue and instead form scar tissue at an injury site. One exception is the adult MRL/MpJ mouse that can regenerate ear and cardiac tissue after wounding with little evidence of scar tissue formation. Following production of a MRL mouse ear hole, 2mm in diameter, a structure rapidly forms at the injury site that resembles the amphibian blastema at a limb amputation site during limb regeneration. We have isolated MRL blastemal cells (MRL-B) from this structure and adapted them to culture. We demonstrate by RT-PCR that even after continuous culturing of these cells they maintain expression of several progenitor cell markers, including DLK (Pref-1), and Msx-1. We have isolated the underlying extracellular matrix (ECM) produced by these MRL-B cells using a new non-proteolytic method and studied the biological activities of this cell-free ECM. Multiplex microELISA analysis of MRL-B cell-free ECM vs. cells revealed selective enrichment of growth factors such as bFGF, HGF and KGF in the matrix compartment. The cell-free ECM, degraded by mild enzyme treatment, was active in promoting migration and proliferation of progenitor cells in vitro and accelerating wound closure in a mouse full thickness cutaneous wound assay in vivo. In vivo, a single application of MRL-B cell matrix-derived products to full thickness cutaneous wounds in non-regenerative mice, B6, induced re-growth of pigmented hair, dermis and epidermis at the wound site whereas scar tissue replaced these tissues at wound sites in mice treated with vehicle alone. These studies suggest that matrix-derived products can stimulate regenerative healing and avert scar tissue formation in adult mammals.

BioDome regenerative sleeve for biochemical and biophysical stimulation of tissue regeneration.

Previous research on vertebrate limb regeneration indicates there are several mediating factors involved during the re-growth process. These factors are both biochemical and biophysical. While the phenomenon of adult limb regeneration does not occur naturally in mammalian species, prior research has focused mainly on biochemical modes of stimulating tissue growth and regeneration. The BioDome was aimed at developing a new experimental tool to permit the more systematic study of the impact of biophysical and biochemical factors on mammalian tissue regeneration. The BioDome is a multi-component sleeve assembly that encompasses the wound site of an amputated murine digit and provides an environment conducive to tissue regeneration. The studies showed that the BioDome was effective in supporting early stages of murine digit tip regeneration when combined with a porcine urinary bladder matrix (UBM) pepsin digest and electrical stimulation. The hydrated inner environment of the BioDome influenced regeneration, with additional effects seen with the application of electrical stimulation and pharmacological treatments.

Degradation products of extracellular matrix affect cell migration and proliferation.

Biologic scaffolds composed of extracellular matrix (ECM) are utilized in numerous regenerative medicine applications to facilitate the constructive remodeling of tissues and organs. The mechanisms by which the host remodeling response occurs are not fully understood, but recent studies suggest that both constituent growth factors and biologically active degradation products derived from ECM play important roles. The objective of the present study was to determine if degradation of ECM scaffold materials in vitro by methods that are biochemically and physiologically relevant can yield products that possess chemotactic and/or mitogenic activities for fully differentiated mammalian endothelial cells and undifferentiated multipotential progenitor cells. ECM harvested from porcine urinary bladder was degraded enzymatically with pepsin/hydrochloric acid or papain. The ECM degradation products were tested for chemoattractant properties utilizing either 48-well chemotaxis filter migration microchambers or fluorescence-based filter migration assays, and were tested for mitogenic properties in cell proliferation assays. Results showed that ECM degradation products possessed chemotactic and mitogenic activities for multipotential progenitor cells and that the same degradation products inhibited both chemotaxis and proliferation of differentiated endothelial cells. These findings support the concept that degradation products of ECM bioscaffolds are important modulators of the recruitment and proliferation of appropriate cell types during the process of ECM scaffold remodeling.