Quantitative Metabolomic Analysis of Urinary Citrulline and Calcitroic Acid in Mice after Exposure to Various Types of Ionizing Radiation

With the safety of existing nuclear power plants being brought into question after the Fukushima disaster and the increased level of concern over terrorism-sponsored use of improvised nuclear devices, it is more crucial to develop well-defined radiation injury markers in easily accessible biofluids to help emergency-responders with injury assessment during patient triage. Here, we focused on utilizing ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) to identify and quantitate the unique changes in the urinary excretion of two metabolite markers, calcitroic acid and citrulline, in mice induced by different forms of irradiation; external γ irradiation at a low dose rate (LDR) of 3.0 mGy/min and a high dose rate (HDR) of 1.1 Gy/min, and internal exposure to Cesium-137 ((137)Cs) and Strontium-90 ((90)Sr). The multiple reaction monitoring analysis showed that, while exposure to (137)Cs and (90)Sr induced a statistically significant and persistent decrease, similar doses of external γ beam at the HDR had the opposite effect, and the LDR had no effect on the urinary levels of these two metabolites. This suggests that the source of exposure and the dose rate strongly modulate the in vivo metabolomic injury responses, which may have utility in clinical biodosimetry assays for the assessment of exposure in an affected population. This study complements our previous investigations into the metabolomic profile of urine from mice internally exposed to (90)Sr and (137)Cs and to external γ beam radiation.

In vitro RABiT measurement of dose rate effects on radiation induction of micronuclei in human peripheral blood lymphocytes

Developing new methods for radiation biodosimetry has been identified as a high-priority need in case of a radiological accident or nuclear terrorist attacks. A large-scale radiological incident would result in an immediate critical need to assess the radiation doses received by thousands of individuals. Casualties will be exposed to different doses and dose rates due to their geographical position and sheltering conditions, and dose rate is one of the principal factors that determine the biological consequences of a given absorbed dose. In these scenarios, high-throughput platforms are required to identify the biological dose in a large number of exposed individuals for clinical monitoring and medical treatment. The Rapid Automated Biodosimetry Tool (RABiT) is designed to be completely automated from the input of blood sample into the machine to the output of a dose estimate. The primary goal of this paper was to quantify the dose rate effects for RABiT-measured micronuclei in vitro in human lymphocytes. Blood samples from healthy volunteers were exposed in vitro to different doses of X-rays to acute and protracted doses over a period up to 24 h. The acute dose was delivered at ~1.03 Gy/min and the low dose rate exposure at ~0.31 Gy/min. The results showed that the yield of micronuclei decreases with decreasing dose rate starting at 2 Gy, whereas response was indistinguishable from that of acute exposure in the low dose region, up to 0.5 Gy. The results showed a linear-quadratic dose-response relationship for the occurrence of micronuclei for the acute exposure and a linear dose-response relationship for the low dose rate exposure.

207-nm UV Light-A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. II: In-Vivo Safety Studies

BACKGROUND

UVC light generated by conventional germicidal lamps is a well-established anti-microbial modality, effective against both bacteria and viruses. However, it is a human health hazard, being both carcinogenic and cataractogenic. Earlier studies showed that single-wavelength far-UVC light (207 nm) generated by excimer lamps kills bacteria without apparent harm to human skin tissue in vitro. The biophysical explanation is that, due to its extremely short range in biological material, 207 nm UV light cannot penetrate the human stratum corneum (the outer dead-cell skin layer, thickness 5-20 μm) nor even the cytoplasm of individual human cells. By contrast, 207 nm UV light can penetrate bacteria and viruses because these cells are physically much smaller.

AIMS

To test the biophysically-based hypothesis that 207 nm UV light is not cytotoxic to exposed mammalian skin in vivo.

METHODS

Hairless mice were exposed to a bactericidal UV fluence of 157 mJ/cm2 delivered by a filtered Kr-Br excimer lamp producing monoenergetic 207-nm UV light, or delivered by a conventional 254-nm UV germicidal lamp. Sham irradiations constituted the negative control. Eight relevant cellular and molecular damage endpoints including epidermal hyperplasia, pre-mutagenic UV-associated DNA lesions, skin inflammation, and normal cell proliferation and differentiation were evaluated in mice dorsal skin harvested 48 h after UV exposure.

RESULTS

While conventional germicidal UV (254 nm) exposure produced significant effects for all the studied skin damage endpoints, the same fluence of 207 nm UV light produced results that were not statistically distinguishable from the zero exposure controls.

CONCLUSIONS

As predicted by biophysical considerations and in agreement with earlier in vitro studies, 207-nm light does not appear to be significantly cytotoxic to mouse skin. These results suggest that excimer-based far-UVC light could potentially be used for its anti-microbial properties, but without the associated hazards to skin of conventional germicidal UV lamps.

A microfluidic approach to parallelized transcriptional profiling of single cells

The ability to correlate single-cell genetic information with cellular phenotypes is of great importance to biology and medicine, as it holds the potential to gain insight into disease pathways that is unavailable from ensemble measurements. We present a microfluidic approach to parallelized, rapid, quantitative analysis of messenger RNA from single cells via RT-qPCR. The approach leverages an array of single-cell RT-qPCR analysis units formed by a set of parallel microchannels concurrently controlled by elastomeric pneumatic valves, thereby enabling parallelized handling and processing of single cells in a drastically simplified operation procedure using a relatively small number of microvalves. All steps for single-cell RT-qPCR, including cell isolation and immobilization, cell lysis, mRNA purification, reverse transcription and qPCR, are integrated on a single chip, eliminating the need for off-chip manual cell and reagent transfer and qPCR amplification as commonly used in existing approaches. Additionally, the approach incorporates optically transparent microfluidic components to allow monitoring of single-cell trapping without the need for molecular labeling that can potentially alter the targeted gene expression and utilizes a polycarbonate film as a barrier against evaporation to minimize the loss of reagents at elevated temperatures during the analysis. We demonstrate the utility of the approach by the transcriptional profiling for the induction of the cyclin-dependent kinase inhibitor 1a and the glyceraldehyde 3-phosphate dehydrogenase in single cells from the MCF-7 breast cancer cell line. Furthermore, the methyl methanesulfonate is employed to allow measurement of the expression of the genes in individual cells responding to a genotoxic stress.

Accelerator-Based Biological Irradiation Facility Simulating Neutron Exposure from an Improvised Nuclear Device

We describe here an accelerator-based neutron irradiation facility, intended to expose blood or small animals to neutron fields mimicking those from an improvised nuclear device at relevant distances from the epicenter. Neutrons are generated by a mixed proton/deuteron beam on a thick beryllium target, generating a broad spectrum of neutron energies that match those estimated for the Hiroshima bomb at 1.5 km from ground zero. This spectrum, dominated by neutron energies between 0.2 and 9 MeV, is significantly different from the standard reactor fission spectrum, as the initial bomb spectrum changes when the neutrons are transported through air. The neutron and gamma dose rates were measured using a custom tissue-equivalent gas ionization chamber and a compensated Geiger-Mueller dosimeter, respectively. Neutron spectra were evaluated by unfolding measurements using a proton-recoil proportional counter and a liquid scintillator detector. As an illustration of the potential use of this facility we present micronucleus yields in single divided, cytokinesis-blocked human peripheral lymphocytes up to 1.5 Gy demonstrating 3- to 5-fold enhancement over equivalent X-ray doses. This facility is currently in routine use, irradiating both mice and human blood samples for evaluation of neutron-specific biodosimetry assays. Future studies will focus on dose reconstruction in realistic mixed neutron/photon fields.

Defining AML and MDS second cancer risk dynamics after diagnoses of first cancers treated or not with radiation

Risks of acute myeloid leukemia (AML) and/or myelodysplastic syndromes (MDS) are known to increase after cancer treatments. Their rise-and-fall dynamics and their associations with radiation have, however, not been fully characterized. To improve risk definition we developed SEERaBomb R software for Surveillance, Epidemiology and End Results second cancer analyses. Resulting high-resolution relative risk (RR) time courses were compared, where possible, to results of A-bomb survivor analyses. We found: (1) persons with prostate cancer receiving radiation therapy have increased RR of AML and MDS that peak in 1.5-2.5 years; (2) persons with non-Hodgkin lymphoma (NHL), lung and breast first cancers have the highest RR for AML and MDS over the next 1-12 years. These increased RR are radiation specific for lung and breast cancer but not for NHL; (3) AML latencies were brief compared to those of A-bomb survivors; and (4) there was a marked excess risk of acute promyelocytic leukemia in persons receiving radiation therapy. Knowing the type of first cancer, if it was treated with radiation, the interval from first cancer diagnosis to developing AML or MDS, and the type of AML, can improve estimates of whether AML or MDS cases developing in this setting are due to background versus other processes.

Broad Energy Range Neutron Spectroscopy using a Liquid Scintillator and a Proportional Counter: Application to a Neutron Spectrum Similar to that from an Improvised Nuclear Device

A novel neutron irradiation facility at the Radiological Research Accelerator Facility (RARAF) has been developed to mimic the neutron radiation from an Improvised Nuclear Device (IND) at relevant distances (e.g. 1.5 km) from the epicenter. The neutron spectrum of this IND-like neutron irradiator was designed according to estimations of the Hiroshima neutron spectrum at 1.5 km. It is significantly different from a standard reactor fission spectrum, because the spectrum changes as the neutrons are transported through air, and it is dominated by neutron energies from 100 keV up to 9 MeV. To verify such wide energy range neutron spectrum, detailed here is the development of a combined spectroscopy system. Both a liquid scintillator detector and a gas proportional counter were used for the recoil spectra measurements, with the individual response functions estimated from a series of Monte Carlo simulations. These normalized individual response functions were formed into a single response matrix for the unfolding process. Several accelerator-based quasi-monoenergetic neutron source spectra were measured and unfolded to test this spectroscopy system. These reference neutrons were produced from two reactions: T(p,n)3He and D(d,n)3He, generating neutron energies in the range between 0.2 and 8 MeV. The unfolded quasi-monoenergetic neutron spectra indicated that the detection system can provide good neutron spectroscopy results in this energy range. A broad-energy neutron spectrum from the 9Be(d,n) reaction using a 5 MeV deuteron beam, measured at 60 degrees to the incident beam was measured and unfolded with the evaluated response matrix. The unfolded broad neutron spectrum is comparable with published time-of-flight results. Finally, the pair of detectors were used to measure the neutron spectrum generated at the RARAF IND-like neutron facility and a comparison is made to the neutron spectrum of Hiroshima.

Microbeam-coupled capillary electrophoresis

Within the first few microseconds following a charged particle traversal of a cell, numerous oxygen and nitrogen radicals are formed along the track. Presented here is a method, using capillary electrophoresis, for simultaneous measurement, within an individual cell, of specific reactive oxygen species, such as the superoxide radical ([Formula: see text]) as well as the native and oxidised forms of glutathione, an ubiquitous anti-oxidant that assists the cell in coping with these species. Preliminary data are presented as well as plans for integrating this system into the charged particle microbeam at Columbia University.

New Insight into Quantitative Modeling of DNA Double-Strand Break Rejoining

Accurate and mechanistically plausible mathematical models of DNA double-strand break (DSB) rejoining kinetics are needed to correctly estimate the dependence of cell death and transformation on linear energy transfer, radiation dose and time. When integrated into more comprehensive risk estimation approaches, such models are potentially valuable tools in applications such as treatment planning for radiotherapy. In this study, we compared 10 DSB rejoining models based on data collected from 61 mammalian cell lines after high-dose-rate photon or heavy ion irradiation. The set of models included formalisms with: 1. one, two or three discrete first-order rejoining rates; 2. continuously distributed first-order rejoining rates; and 3. second-order rejoining rates. The Akaike information criterion was used to quantify the relative support for each model from the data, accounting for goodness of fit and model complexity. The best performance was exhibited by a bi-exponential model with two discrete rejoining rates and a model with gamma-distribution rejoining rates. Models with more than three free parameters overfitted the data and models with single DSB rejoining rates or with an inflexible distribution of rejoining rates lacked accuracy. Of special note is that the analyzed data provide little support for models that rely on pairwise interactions to describe DSB rejoining kinetics. Consequently, kinetic cell survival models reflecting bi-exponential DSB rejoining might be preferable to models based on the kinetics of intra- and inter-lesion rejoining.

Serum Dyslipidemia Is Induced by Internal Exposure to Strontium-90 in Mice, Lipidomic Profiling Using a Data-Independent Liquid Chromatography-Mass Spectrometry Approach

Despite considerable research into the environmental risks and biological effects of exposure to external beam γ rays, incorporation of radionuclides has largely been understudied. This dosimetry and exposure risk assessment is challenging for first responders in the field during a nuclear or radiological event. Therefore, we have developed a workflow for assessing injury responses in easily obtainable biofluids, such as urine and serum, as the result of exposure to internal emitters cesium-137 ((137)Cs) and strontium-90 ((90)Sr) in mice. Here we report on the results of the untargeted lipidomic profiling of serum from mice exposed to (90)Sr. We also compared these results to those from previously published (137)Cs exposure to determine any differences in cellular responses based on exposure type. The results of this study conclude that there is a gross increase in the serum abundance of triacylglycerides and cholesterol esters, while phostaphatidylcholines and lysophosphatidylcholines displayed decreases in their serum levels postexposure at study days 4, 7, 9, 25, and 30, with corresponding average cumulative skeleton doses ranging from 1.2 ± 0.1 to 5.2 ± 0.73 Gy. The results show significant perturbations in serum lipidome as early as 2 days postexposure persisting until the end of the study (day 30).

Development of a High-Throughput and Miniaturized Cytokinesis-Block Micronucleus Assay for Use as a Biological Dosimetry Population Triage Tool

Biodosimetry is an essential tool for providing timely assessments of radiation exposure. For a large mass-casualty event involving exposure to ionizing radiation, it is of utmost importance to rapidly provide dose information for medical treatment. The well-established cytokinesis-block micronucleus (CBMN) assay is a validated method for biodosimetry. However, the need for an accelerated sample processing is required for the CBMN assay to be a suitable population triage tool. We report here on the development of a high-throughput and miniaturized version of the CMBN assay for accelerated sample processing.

An automated imaging system for radiation biodosimetry

We describe here an automated imaging system developed at the Center for High Throughput Minimally Invasive Radiation Biodosimetry. The imaging system is built around a fast, sensitive sCMOS camera and rapid switchable LED light source. It features complete automation of all the steps of the imaging process and contains built-in feedback loops to ensure proper operation. The imaging system is intended as a back end to the RABiT-a robotic platform for radiation biodosimetry. It is intended to automate image acquisition and analysis for four biodosimetry assays for which we have developed automated protocols: The Cytokinesis Blocked Micronucleus assay, the γ-H2AX assay, the Dicentric assay (using PNA or FISH probes) and the RABiT-BAND assay.

A Comprehensive Metabolomic Investigation in Urine of Mice Exposed to Strontium-90

Internal emitters such as Strontium-90 ((90)Sr) pose a substantial health risk during and immediately after a nuclear disaster or detonation of an improvised device. The environmental persistency and potency of (90)Sr calls for urgent development of high-throughput tests to establish levels of exposure and to help triage potentially exposed individuals who were in the immediate area of the disaster. In response to these concerns, our team focused on developing a robust metabolomic profile for (90)Sr exposure in urine using a mouse model. The sensitivity of modern time-of-flight mass spectrometry (TOFMS) combined with the separation power of ultra performance liquid chromatography (UPLC) was used to determine perturbations in the urinary metabolome of mice exposed to (90)Sr. The recently developed statistical suite, MetaboLyzer, was used to explore the mass spectrometry data. The results indicated a significant change in the urinary abundances of metabolites pertaining to butanoate metabolism, vitamin B metabolism, glutamate and fatty acid oxidation. All of these pathways are either directly or indirectly connected to the central energy production pathway, the tricarboxylic acid (TCA) cycle. To our knowledge, this is the first in vivo metabolomics to evaluate the effects of exposure to (90)Sr using the easily accessible biofluid, urine.

Construction of mouse phantoms from segmented CT scan data for radiation dosimetry studies

We present the complete construction methodology for an anatomically accurate mouse phantom made using materials which mimic the characteristics of tissue, lung, and bone for radiation dosimetry studies. Phantoms were constructed using 2 mm thick slices of tissue equivalent material which was precision machined to clear regions for insertion of lung and bone equivalent material where appropriate. Images obtained using a 3D computed tomography (CT) scan clearly indicate regions of tissue, lung, and bone that match their position within the original mouse CT scan. Additionally, radiographic films are used with the phantom to demonstrate dose mapping capabilities. The construction methodology presented here can be quickly and easily adapted to create a phantom of any specific small animal given a segmented CT scan of the animal. These physical phantoms are a useful tool to examine individual organ dose and dosimetry within mouse systems that are complicated by density inhomogeneity due to bone and lung regions.

High throughput measurement of γH2AX DSB repair kinetics in a healthy human population

The Columbia University RABiT (Rapid Automated Biodosimetry Tool) quantifies DNA damage using fingerstick volumes of blood. One RABiT protocol quantifies the total γ-H2AX fluorescence per nucleus, a measure of DNA double strand breaks (DSB) by an immunofluorescent assay at a single time point. Using the recently extended RABiT system, that assays the γ-H2AX repair kinetics at multiple time points, the present small scale study followed its kinetics post irradiation at 0.5 h, 2 h, 4 h, 7 h and 24 h in lymphocytes from 94 healthy adults. The lymphocytes were irradiated ex vivo with 4 Gy γ rays using an external Cs-137 source. The effect of age, gender, race, ethnicity, alcohol use on the endogenous and post irradiation total γ-H2AX protein yields at various time points were statistically analyzed. The endogenous γ-H2AX levels were influenced by age, race and alcohol use within Hispanics. In response to radiation, induction of γ-H2AX yields at 0.5 h and peak formation at 2 h were independent of age, gender, ethnicity except for race and alcohol use that delayed the peak to 4 h time point. Despite the shift in the peak observed, the γ-H2AX yields reached close to baseline at 24 h for all groups. Age and race affected the rate of progression of the DSB repair soon after the yields reached maximum. Finally we show a positive correlation between endogenous γ-H2AX levels with radiation induced γ-H2AX yields (RIY) (r=0.257, P=0.02) and a negative correlation with residuals (r=-0.521, P=<0.0001). A positive correlation was also observed between RIY and DNA repair rate (r=0.634, P<0.0001). Our findings suggest age, race, ethnicity and alcohol use influence DSB γ-H2AX repair kinetics as measured by RABiT immunofluorescent assay.

Effect of dose rate on residual γ-H2AX levels and frequency of micronuclei in X-irradiated mouse lymphocytes

The biological risks associated with low-dose-rate (LDR) radiation exposures are not yet well defined. To assess the risk related to DNA damage, we compared the yields of two established biodosimetry end points, γ-H2AX and micronuclei (MNi), in peripheral mouse blood lymphocytes after prolonged in vivo exposure to LDR X rays (0.31 cGy/min) vs. acute high-dose-rate (HDR) exposure (1.03 Gy/min). C57BL/6 mice were total-body irradiated with 320 kVP X rays with doses of 0, 1.1, 2.2 and 4.45 Gy. Residual levels of total γ-H2AX fluorescence in lymphocytes isolated 24 h after the start of irradiation were assessed using indirect immunofluorescence methods. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to determine apoptotic cell frequency in lymphocytes sampled at 24 h. Curve fitting analysis suggested that the dose response for γ-H2AX yields after acute exposures could be described by a linear dependence. In contrast, a linear-quadratic dose-response shape was more appropriate for LDR exposure (perhaps reflecting differences in repair time after different LDR doses). Dose-rate sparing effects (P < 0.05) were observed at doses ≤2.2 Gy, such that the acute dose γ-H2AX and TUNEL-positive cell yields were significantly larger than the equivalent LDR yields. At the 4.45 Gy dose there was no difference in γ-H2AX expression between the two dose rates, whereas there was a two- to threefold increase in apoptosis in the LDR samples compared to the equivalent 4.45 Gy acute dose. Micronuclei yields were measured at 24 h and 7 days using the in vitro cytokinesis-blocked micronucleus (CBMN) assay. The results showed that MNi yields increased up to 2.2 Gy with no further increase at 4.45 Gy and with no detectable dose-rate effect across the dose range 24 h or 7 days post exposure. In conclusion, the γ-H2AX biomarker showed higher sensitivity to measure dose-rate effects after low-dose LDR X rays compared to MNi formation; however, confounding factors such as variable repair times post exposure, increased cell killing and cell cycle block likely contributed to the yields of MNi with accumulating doses of ionizing radiation.

Pilot study for the establishment of biomarkers for radiation damage after computed tomography in children

Computed tomography (CT) is an imaging modality that exposes patients to ionizing radiation (IR). We review and report findings from our pilot study evaluating whether blood markers are altered in 17 children undergoing medically indicated CT scans. Blood was drawn before ('pre-CT') and 1 hour after ('post-CT' CT scans. Plasma carotenoids, tocopherols, Q10, ascorbic acid (AA) and uric acid (UA) were analyzed by RP-HPLC with diode-array and electrochemical detection. Dehydroascorbic acid (DHAA) was calculated by subtraction from total AA. Total antioxidant capacity (TAC) was measured using the ORAC assay. Cytokines were quantified using a multiplex immunoassay. γ-H2AX foci were visualized using immunofluorescence. Mean pre- and post-CT changes were compared using t-tests; P-levels < .05 indicated significance. All major plasma lipid soluble antioxidant levels were lower post- vs pre-CT (P < .05) possibly from the scavenging of free radicals formed by CT-induced IR. Average AA levels increased (134%) while DHAA levels were decreased (29%) post-CT, probably due to intracellular recycling of AA from DHAA. TAC levels in lipophilic and hydrophilic extracts were unchanged, suggesting that other antioxidants may have assisted in free radical quenching, which would corroborate their lower concentrations post-CT. Cytokine levels were unchanged and dose-dependent increases in γ-H2AX foci, a measure of double strand DNA breaks, were observed (P = .046, n = 3 children). Our results suggest that CT-derived IR can influence the antioxidant system and may elicit detrimental responses on the cellular level of young children. When possible and if appropriate non-IR based techniques such as ultrasound or magnetic resonance imaging should be used.

Metabolic oxygen consumption measurement with a single-cell biosensor after particle microbeam irradiation

A noninvasive, self-referencing biosensor/probe system has been integrated into the Columbia University Radiological Research Accelerator Facility Microbeam II end station. A single-cell oxygen consumption measurement has been conducted with this type of oxygen probe in 37° C Krebs-Ringer Bicarbonate buffer immediately before and after a single-cell microbeam irradiation. It is the first such measurement made for a microbeam irradiation, and a six fold increment of oxygen flux induced during a 15-s period of time has been observed following radiation exposure. The experimental procedure and the results are discussed.

A Bead-Based Microfluidic Approach to Integrated Single-Cell Gene Expression Analysis by Quantitative RT-PCR

Gene expression analysis at the single-cell level is critical to understanding variations among cells in heterogeneous populations. Microfluidic reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) is well suited to gene expression assays of single cells. We present a microfluidic approach that integrates all functional steps for RT-qPCR of a single cell, including isolation and lysis of the cell, as well as purification, reverse transcription and quantitative real-time PCR of messenger RNA in the cell lysate. In this approach, all reactions in the multi-step assay of a single lysed cell can be completed on microbeads, thereby simplifying the design, fabrication and operation of the microfluidic device, as well as facilitating the minimization of sample loss or contamination. In the microfluidic device, a single cell is isolated and lysed; mRNA in the cell lysate is then analyzed by RT-qPCR using primers immobilized on microbeads in a single microchamber whose temperature is controlled in closed loop via an integrated heater and temperature sensor. The utility of the approach was demonstrated by the analysis of the effects of the drug (methyl methanesulfonate, MMS) on the induction of the cyclin-dependent kinase inhibitor 1a (CDKN1A) in single human cancer cells (MCF-7), demonstrating the potential of our approach for efficient, integrated single-cell RT-qPCR for gene expression analysis.

Metabolomic and lipidomic analysis of serum from mice exposed to an internal emitter, cesium-137, using a shotgun LC-MS(E) approach

In this study ultra performance liquid chromatography (UPLC) coupled to time-of-flight mass spectrometry in the MS^E mode was used for rapid and comprehensive analysis of metabolites in the serum of mice exposed to internal exposure by Cesium-137 (¹³⁷Cs). The effects of exposure to ¹³⁷Cs were studied at several time points after injection of ¹³⁷CsCl in mice. Over 1800 spectral features were detected in the serum of mice in positive and negative electrospray ionization modes combined. Detailed statistical analysis revealed that several metabolites associated with amino acid metabolism, fatty acid metabolism, and the TCA cycle were significantly perturbed in the serum of ¹³⁷Cs-exposed mice compared with that of control mice. While metabolites associated with the TCA cycle and glycolysis increased in their serum abundances, fatty acids such as linoleic acid and palmitic acid were detected at lower levels in serum after ¹³⁷Cs exposure. Furthermore, phosphatidylcholines (PCs) were among the most perturbed ions in the serum of ¹³⁷Cs-exposed mice. This is the first study on the effects of exposure by an internal emitter in serum using a UPLC–MS^E approach. The results have put forth a panel of metabolites, which may serve as potential serum markers to ¹³⁷Cs exposure.

The effect of low dose rate on metabolomic response to radiation in mice

Metabolomics has been shown to have utility in assessing responses to exposure by ionizing radiation (IR) in easily accessible biofluids such as urine. Most studies to date from our laboratory and others have employed γ-irradiation at relatively high dose rates (HDR), but many environmental exposure scenarios will probably be at relatively low dose rates (LDR). There are well-documented differences in the biologic responses to LDR compared to HDR, so an important question is to assess LDR effects at the metabolomics level. Our study took advantage of a modern mass spectrometry approach in exploring the effects of dose rate on the urinary excretion levels of metabolites 2 days after IR in mice. A wide variety of statistical tools were employed to further focus on metabolites, which showed responses to LDR IR exposure (0.00309 Gy/min) distinguishable from those of HDR. From a total of 709 detected spectral features, more than 100 were determined to be statistically significant when comparing urine from mice irradiated with 1.1 or 4.45 Gy to that of sham-irradiated mice 2 days post-exposure. The results of this study show that LDR and HDR exposures perturb many of the same pathways such as TCA cycle and fatty acid metabolism, which also have been implicated in our previous IR studies. However, it is important to note that dose rate did affect the levels of particular metabolites. Differences in urinary excretion levels of such metabolites could potentially be used to assess an individual's exposure in a radiobiological event and thus would have utility for both triage and injury assessment.

γ-H2AX foci are increased in lymphocytes in vivo in young children 1 h after very low-dose X-irradiation: a pilot study

BACKGROUND

Computed tomography (CT) is an imaging modality involving ionizing radiation. The presence of γ-H2AX foci after low to moderate ionizing radiation exposure has been demonstrated; however it is unknown whether very low ionizing radiation exposure doses from CT exams can induce γ-H2AX formation in vivo in young children.

OBJECTIVE

To test whether very low ionizing radiation doses from CT exams can induce lymphocytic γ-H2AX foci (phosphorylated histones used as a marker of DNA damage) formation in vivo in young children.

MATERIALS AND METHODS

Parents of participating children signed a consent form. Blood samples from three children (ages 3-21 months) undergoing CT exams involving very low blood ionizing radiation exposure doses (blood doses of 0.22-1.22 mGy) were collected immediately before and 1 h post CT exams. Isolated lymphocytes were quantified for γ-H2AX foci by a technician blinded to the radiation status and dose of the patients. Paired t-tests and regression analyses were performed with significance levels set at P < 0.05.

RESULTS

We observed a dose-dependent increase in γ-H2AX foci post-CT exams (P = 0.046) among the three children. Ionizing radiation exposure doses led to a linear increase of foci per cell in post-CT samples (102% between lowest and highest dose).

CONCLUSION

We found a significant induction of γ-H2AX foci in lymphocytes from post-CT samples of three very young children. When possible, CT exams should be limited or avoided by possibly applying non-ionizing radiation exposure techniques such as US or MRI.

Approaches to enhancing radiation safety in cardiovascular imaging: a scientific statement from the American Heart Association

Education, justification, and optimization are the cornerstones to enhancing the radiation safety of medical imaging. Education regarding the benefits and risks of imaging and the principles of radiation safety is required for all clinicians in order for them to be able to use imaging optimally. Empowering patients with knowledge of the benefits and risks of imaging will facilitate their meaningful participation in decisions related to their health care, which is necessary to achieve patient-centered care. Limiting the use of imaging to appropriate clinical indications can ensure that the benefits of imaging outweigh any potential risks. Finally, the continually expanding repertoire of techniques that allow high-quality imaging with lower radiation exposure should be used when available to achieve safer imaging. The implementation of these strategies in practice is necessary to achieve high-quality, patient-centered imaging and will require a shared effort and investment by all stakeholders, including physicians, patients, national scientific and educational organizations, politicians, and industry.

Multicolour FISH analysis of ionising radiation induced micronucleus formation in human lymphocytes

Micronucleation of chromosomal DNA is an effective indicator of DNA damage and micronucleus (MN) analysis is a valuable tool for radiation biodosimetry studies. To gain a comprehensive knowledge of micronucleation process after ionising radiation (IR) exposure, whole genome-wide chromosome analysis is desirable. With this objective, multicolour fluorescence in situ hybridization (M-FISH) technique was utilised in the present study to characterise the chromosome content of spontaneous and IR-induced micronuclei in three human donors. M-FISH analysis revealed a radiation dose-dependant increase in the number of micronuclei with multi-chromosome material above 2 Gy and as many as 3-6 multicolour signals were detected in micronuclei after high γ-rays radiation doses (5-10 Gy). Involvement of each human chromosome material was more frequently detected in multicoloured micronuclei than in single-coloured micronuclei at high radiation doses (>2 Gy). Observation of dose-dependant increase in the MN frequency with multi-chromosome material may be due to misrepair of DNA double-strand breaks involving multiple chromosomes leading to asymmetric dicentric or ring chromosomes and acentric fragments. Chromosomes belonging to groups A (1, 2 and 3) and B (4 and 5) were frequently detected in 35-45% of the total micronuclei either as single entities or in combination with other chromosomes. Among the A and B groups, chromosome 1 material was consistently detected at high MN frequencies after radiation exposure in all the donors. Additionally, chromosomes 13 and 19 were more frequently observed in micronuclei than the expected frequency based on DNA content. Our whole genome approach utilising the M-FISH technique revealed that MN formation at high radiation doses might be complex involving multiple chromosome fragments. Understanding the fate and biological consequences of these multi-chromosome-containing micronuclei may provide key molecular insights for some aspects of IR-induced genomic instability and cancer development processes.

Advances in the use of radiotherapy to reduce second breast cancers

David Brenner* speaks to Ruth Williamson, Commissioning Editor of Breast Cancer Management: David Brenner focuses on developing mechanistic models for the effects of ionizing radiation on living systems, dividing his research between the effects of high doses of ionizing radiation (relating to radiation therapy) and the effects of low doses of radiation (relating to medical, environmental and occupational exposures). In the field of medical imaging, he has focused on the risk–benefit balance of higher-dose imaging techniques; and in the field of radiotherapy, he has focused on optimizing fractionation schemes for different tumor types, to maximize tumor killing and minimize serious side effects. As well as being Director of the Center for Radiological Research (Columbia University, CO, USA), Brenner is the Director of the Radiological Research Accelerator Facility (Columbia University) and principal investigator of the Center for High-Throughput Minimally-Invasive Radiation Biodosimetry (Columbia University).

What we know and what we don't know about cancer risks associated with radiation doses from radiological imaging

Quantifying radiation-induced cancer risks associated with radiological examinations is not easy, which has resulted in much controversy. We can clarify the situation by distinguishing between higher dose examinations, such as CT, positron emission tomography-CT or fluoroscopically guided interventions, and lower dose "conventional" X-ray examinations. For higher dose examinations, the epidemiological data, from atomic bomb survivors exposed to low doses and from direct epidemiological studies of paediatric CT, are reasonably consistent, suggesting that we do have a reasonable quantitative understanding of the individual risks: in summary, very small but unlikely to be zero. For lower dose examinations, we have very little data, and the situation is much less certain, however, the collective dose from these lower dose examinations is comparatively unimportant from a public health perspective.

Next generation platforms for high-throughput biodosimetry

Here the general concept of the combined use of plates and tubes in racks compatible with the American National Standards Institute/the Society for Laboratory Automation and Screening microplate formats as the next generation platforms for increasing the throughput of biodosimetry assays was described. These platforms can be used at different stages of biodosimetry assays starting from blood collection into microtubes organised in standardised racks and ending with the cytogenetic analysis of samples in standardised multiwell and multichannel plates. Robotically friendly platforms can be used for different biodosimetry assays in minimally equipped laboratories and on cost-effective automated universal biotech systems.

Potential for adult-based epidemiological studies to characterize overall cancer risks associated with a lifetime of CT scans

Recent epidemiological studies have suggested that radiation exposure from pediatric CT scanning is associated with small excess cancer risks. However, the majority of CT scans are performed on adults, and most radiation-induced cancers appear during middle or old age, in the same age range as background cancers. Consequently, a logical next step is to investigate the effects of CT scanning in adulthood on lifetime cancer risks by conducting adult-based, appropriately designed epidemiological studies. Here we estimate the sample size required for such studies to detect CT-associated risks. This was achieved by incorporating different age-, sex-, time- and cancer type-dependent models of radiation carcinogenesis into an in silico simulation of a population-based cohort study. This approach simulated individual histories of chest and abdominal CT exposures, deaths and cancer diagnoses. The resultant sample sizes suggest that epidemiological studies of realistically sized cohorts can detect excess lifetime cancer risks from adult CT exposures. For example, retrospective analysis of CT exposure and cancer incidence data from a population-based cohort of 0.4 to 1.3 million (depending on the carcinogenic model) CT-exposed UK adults, aged 25-65 in 1980 and followed until 2015, provides 80% power for detecting cancer risks from chest and abdominal CT scans.

The RABiT: high-throughput technology for assessing global DSB repair

At the Center for High-Throughput Minimally Invasive Radiation Biodosimetry, we have developed a rapid automated biodosimetry tool (RABiT); this is a completely automated, ultra-high-throughput robotically based biodosimetry workstation designed for use following a large-scale radiological event, to perform radiation biodosimetry measurements based on a fingerstick blood sample. High throughput is achieved through purpose built robotics, sample handling in filter-bottomed multi-well plates and innovations in high-speed imaging and analysis. Currently, we are adapting the RABiT technologies for use in laboratory settings, for applications in epidemiological and clinical studies. Our overall goal is to extend the RABiT system to directly measure the kinetics of DNA repair proteins. The design of the kinetic/time-dependent studies is based on repeated, automated sampling of lymphocytes from a central reservoir of cells housed in the RABiT incubator as a function of time after the irradiation challenge. In the present study, we have characterized the DNA repair kinetics of the following repair proteins: γ-H2AX, 53-BP1, ATM kinase, MDC1 at multiple times (0.5, 2, 4, 7 and 24 h) after irradiation with 4 Gy γ rays. In order to provide a consistent dose exposure at time zero, we have developed an automated capillary irradiator to introduce DNA DSBs into fingerstick-size blood samples within the RABiT. To demonstrate the scalability of the laboratory-based RABiT system, we have initiated a population study using γ-H2AX as a biomarker.

Development of a metabolomic radiation signature in urine from patients undergoing total body irradiation

The emergence of the threat of radiological terrorism and other radiological incidents has led to the need for development of fast, accurate and noninvasive methods for detection of radiation exposure. The purpose of this study was to extend radiation metabolomic biomarker discovery to humans, as previous studies have focused on mice. Urine was collected from patients undergoing total body irradiation at Memorial Sloan-Kettering Cancer Center prior to hematopoietic stem cell transplantation at 4-6 h postirradiation (a single dose of 1.25 Gy) and 24 h (three fractions of 1.25 Gy each). Global metabolomic profiling was obtained through analysis with ultra performance liquid chromatography coupled to time-of-flight mass spectrometry (TOFMS). Prior to further analyses, each sample was normalized to its respective creatinine level. Statistical analysis was conducted by the nonparametric Kolmogorov-Smirnov test and the Fisher's exact test and markers were validated against pure standards. Seven markers showed distinct differences between pre- and post-exposure samples. Of those, trimethyl-l-lysine and the carnitine conjugates acetylcarnitine, decanoylcarnitine and octanoylcarnitine play an important role in the transportation of fatty acids across mitochondria for subsequent fatty acid β-oxidation. The remaining metabolites, hypoxanthine, xanthine and uric acid are the final products of the purine catabolism pathway, and high levels of excretion have been associated with increased oxidative stress and radiation induced DNA damage. Further analysis revealed sex differences in the patterns of excretion of the markers, demonstrating that generation of a sex-specific metabolomic signature will be informative and can provide a quick and reliable assessment of individuals in a radiological scenario. This is the first radiation metabolomics study in human urine laying the foundation for the use of metabolomics in biodosimetry and providing confidence in biomarker identification based on the overlap between animal models and humans.

The tumor radiobiology of SRS and SBRT: are more than the 5 Rs involved?

Stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT), also known as stereotactic ablative radiation therapy (SABR), are rapidly becoming accepted practice for the radiation therapy of certain tumors. Typically, SRS and SBRT involve the delivery of 1 or a few large-dose fractions of 8 to 30 Gy per fraction: a major paradigm shift from radiation therapy practice over the past 90 years, when, with relatively large amounts of normal tissues receiving high doses, the goal was to maximize tumor response for an acceptable level of normal tissue injury. The development of SRS and SBRT have come about because of technologic advances in image guidance and treatment delivery techniques that enable the delivery of large doses to tumors with reduced margins and high gradients outside the target, thereby minimizing doses to surrounding normal tissues. Because the results obtained with SRS and SBRT have been impressive, they have raised the question whether classic radiobiological modeling, and the linear-quadratic (LQ) model, are appropriate for large doses per fraction. In addition to objections to the LQ model, the possibility of additional biological effects resulting from endothelial cell damage, enhanced tumor immunity, or both have been raised to account for the success of SRS and SBRT. In this review, we conclude that the available preclinical and clinical data do not support a need to change the LQ model or to invoke phenomena over and above the classic 5 Rs of radiobiology and radiation therapy, with the likely exception that for some tumors high doses of irradiation may produce enhanced antitumor immunity. Thus, we suggest that for most tumors, the standard radiobiology concepts of the 5 Rs are sufficient to explain the clinical data, and the excellent results obtained from clinical studies are the result of the much larger biologically effective doses that are delivered with SRS and SBRT.

Fast image analysis for the micronucleus assay in a fully automated high-throughput biodosimetry system

The development of, and results from an image analysis system are presented for automated detection and scoring of micronuclei in human peripheral blood lymphocytes. The system is part of the Rapid Automated Biodosimetry Tool, which was developed at the Center for High-Throughput Minimally Invasive Radiation Biodosimetry for rapid radiation dose assessment of many individuals based on single fingerstick samples of blood. Blood lymphocytes were subjected to the cytokinesis-block micronucleus assay and the images of cell cytoplasm and nuclei are analyzed to estimate the frequency of micronuclei in binucleated cells. We describe an algorithm that is based on dual fluorescent labeling of lymphocytes with separate analysis of images of cytoplasm and nuclei. To evaluate the performance of the system, blood samples of seven healthy donors were irradiated in vitro with doses from 0-10 Gy and dose-response curves of micronuclei frequencies were generated. To establish the applicability of the system to the detection of high doses, the ratios of mononucleated cells to binucleated cells were determined for three of the donors. All of the dose-response curves generated automatically showed clear dose dependence and good correlation (R(2) from 0.914-0.998) with the results of manual scoring.

Development of urinary biomarkers for internal exposure by cesium-137 using a metabolomics approach in mice

Cesium-137 is a fission product of uranium and plutonium in nuclear reactors and is released in large quantities during nuclear explosions or detonation of an improvised device containing this isotope. This environmentally persistent radionuclide undergoes radioactive decay with the emission of beta particles as well as gamma radiation. Exposure to (137)Cs at high doses can cause acute radiation sickness and increase risk for cancer and death. The serious health risks associated with (137)Cs exposure makes it critical to understand how it affects human metabolism and whether minimally invasive and easily accessible samples such as urine and serum can be used to triage patients in case of a nuclear disaster or a radiologic event. In this study, we have focused on establishing a time-dependent metabolomic profile for urine collected from mice injected with (137)CsCl. The samples were collected from control and exposed mice on days 2, 5, 20 and 30 after injection. The samples were then analyzed by ultra-performance liquid chromatography coupled to time-of-flight mass spectrometry (UPLC/TOFMS) and processed by an array of informatics and statistical tools. A total of 1,412 features were identified in ESI(+) and ESI(-) modes from which 200 were determined to contribute significantly to the separation of metabolomic profiles of controls from those of the different treatment time points. The results of this study highlight the ease of use of the UPLC/TOFMS platform in finding urinary biomarkers for (137)Cs exposure. Pathway analysis of the statistically significant metabolites suggests perturbations in several amino acid and fatty acid metabolism pathways. The results also indicate that (137)Cs exposure causes: similar changes in the urinary excretion levels of taurine and citrate as seen with external-beam gamma radiation; causes no attenuation in the levels of hexanoylglycine and N-acetylspermidine; and has unique effects on the levels of isovalerylglycine and tiglylglycine.

Integrated interdisciplinary training in the radiological sciences

The radiation sciences are increasingly interdisciplinary, both from the research and the clinical perspectives. Beyond clinical and research issues, there are very real issues of communication between scientists from different disciplines. It follows that there is an increasing need for interdisciplinary training courses in the radiological sciences. Training courses are common in biomedical academic and clinical environments, but are typically targeted to scientists in specific technical fields. In the era of multidisciplinary biomedical science, there is a need for highly integrated multidisciplinary training courses that are designed for, and are useful to, scientists who are from a mix of very different academic fields and backgrounds. We briefly describe our experiences running such an integrated training course for researchers in the field of biomedical radiation microbeams, and draw some conclusions about how such interdisciplinary training courses can best function. These conclusions should be applicable to many other areas of the radiological sciences. In summary, we found that it is highly beneficial to keep the scientists from the different disciplines together. In practice, this means not segregating the training course into sections specifically for biologists and sections specifically for physicists and engineers, but rather keeping the students together to attend the same lectures and hands-on studies throughout the course. This structure added value to the learning experience not only in terms of the cross fertilization of information and ideas between scientists from the different disciplines, but also in terms of reinforcing some basic concepts for scientists in their own discipline.

Potential reduction of contralateral second breast-cancer risks by prophylactic mammary irradiation: validation in a breast-cancer-prone mouse model

Background

Long-term breast-cancer survivors have a highly elevated risk (1 in 6 at 20 years) of contralateral second breast cancer. This high risk is associated with the presence of multiple pre-malignant cell clones in the contralateral breast at the time of primary breast cancer diagnosis. Mechanistic analyses suggest that a moderate dose of X-rays to the contralateral breast can kill these pre-malignant clones such that, at an appropriate Prophylactic Mammary Irradiation (PMI) dose, the long-term contralateral breast cancer risk in breast cancer survivors would be considerably decreased.

Aims

To test the predicted relationship between PMI dose and cancer risk in mammary glands that have a high risk of developing malignancies.

Methods

We tested the PMI concept using MMTV-PyVT mammary-tumor-prone mice. Mammary glands on one side of each mouse were irradiated with X-rays, while those on the other side were shielded from radiation. The unshielded mammary glands received doses of 0, 4, 8, 12 and 16Gy in 4-Gy fractions.

Results

In high-risk mammary glands exposed to radiation doses designed for PMI (12 and 16 Gy), tumor incidence rates were respectively decreased by a factor of 2.2 (95% CI, 1.1-5.0) at 12 Gy, and a factor of 3.1 (95% CI, 1.3-8.3) at 16 Gy, compared to those in the shielded glands that were exposed to very low radiation doses. The same pattern was seen for PMI-exposed mammary glands relative to zero-dose controls.

Conclusions

The pattern of cancer risk reduction by PMI was consistent with mechanistic predictions. Contralateral breast PMI may thus have promise as a spatially targeted breast-conserving option for reducing the current high risk of contralateral second breast cancers. For estrogen-receptor positive primary tumors, PMI might optimally be used concomitantly with systemically delivered chemopreventive drugs such as tamoxifen or aromatase inhibitors, while for estrogen-receptor negative tumors, PMI might be used alone.

Single-cell responses to ionizing radiation

While gene expression studies have proved extremely important in understanding cellular processes, it is becoming more apparent that there may be differences in individual cells that are missed by studying the population as a whole. We have developed a qRT-PCR protocol that allows us to assay multiple gene products in small samples, starting at 100 cells and going down to a single cell, and have used it to study radiation responses at the single-cell level. Since the accuracy of qRT-PCR depends greatly on the choice of "housekeeping" genes used for normalization, initial studies concentrated on determining the optimal panel of such genes. Using an endogenous control array, it was found that for IMR90 cells, common housekeeping genes tend to fall into one of two categories-those that are relatively stably expressed regardless of the number of cells in the sample, e.g., B2M, PPIA, and GAPDH, and those that are more variable (again regardless of the size of the population), e.g., YWHAZ, 18S, TBP, and HPRT1. Further, expression levels in commonly studied radiation-response genes, such as ATF3, CDKN1A, GADD45A, and MDM2, were assayed in 100, 10, and single-cell samples. It is here that the value of single-cell analyses becomes apparent. It was observed that the expression of some genes such as FGF2 and MDM2 was relatively constant over all irradiated cells, while that of others such as FAS was considerably more variable. It was clear that almost all cells respond to ionizing radiation but the individual responses were considerably varied. The analyses of single cells indicate that responses in individual cells are not uniform and suggest that responses observed in populations are not indicative of identical patterns in all cells. This in turn points to the value of single-cell analyses.

Microbeam irradiation of C. elegans nematode in microfluidic channels

To perform high-throughput studies on the biological effects of ionizing radiation in vivo, we have implemented a microfluidic tool for microbeam irradiation of Caenorhabditis elegans. The device allows the immobilization of worms with minimal stress for a rapid and controlled microbeam irradiation of multiple samples in parallel. Adapted from an established design, our microfluidic clamp consists of 16 tapered channels with 10-μm-thin bottoms to ensure charged particle traversal. Worms are introduced into the microfluidic device through liquid flow between an inlet and an outlet, and the size of each microchannel guarantees that young adult worms are immobilized within minutes without the use of anesthesia. After site-specific irradiation with the microbeam, the worms can be released by reversing the flow direction in the clamp and collected for analysis of biological endpoints such as repair of radiation-induced DNA damage. For such studies, minimal sample manipulation and reduced use of drugs such as anesthetics that might interfere with normal physiological processes are preferable. By using our microfluidic device that allows simultaneous immobilization and imaging for irradiation of several whole living samples on a single clamp, here we show that 4.5-MeV proton microbeam irradiation induced DNA damage in wild-type C. elegans, as assessed by the formation of Rad51 foci that are essential for homologous repair of radiation-induced DNA damage.

UV microspot irradiator at Columbia University

The Radiological Research Accelerator Facility at Columbia University has recently added a UV microspot irradiator to a microbeam irradiation platform. This UV microspot irradiator applies multiphoton excitation at the focal point of an incident laser as the source for cell damage, and with this approach, a single cell within a 3D sample can be targeted and exposed to damaging UV. The UV microspot's ability to impart cellular damage within 3D is an advantage over all other microbeam techniques, which instead impart damage to numerous cells along microbeam tracks. This short communication is an overview, and a description of the UV microspot including the following applications and demonstrations of selective damage to live single cell targets: DNA damage foci formation, patterned irradiation, photoactivation, targeting of mitochondria, and targeting of individual cardiomyocytes in a live zebrafish embryo.

Simultaneous immersion Mirau interferometry

A novel technique for label-free imaging of live biological cells in aqueous medium that is insensitive to ambient vibrations is presented. This technique is a spin-off from previously developed immersion Mirau interferometry. Both approaches utilize a modified Mirau interferometric attachment for a microscope objective that can be used both in air and in immersion mode, when the device is submerged in cell medium and has its internal space filled with liquid. While immersion Mirau interferometry involves first capturing a series of images, the resulting images are potentially distorted by ambient vibrations. Overcoming these serial-acquisition challenges, simultaneous immersion Mirau interferometry incorporates polarizing elements into the optics to allow simultaneous acquisition of two interferograms. The system design and production are described and images produced with the developed techniques are presented.

A simple add-on microfluidic appliance for accurately sorting small populations of cells with high fidelity

Current advances in single cell sequencing, gene expression and proteomics require the isolation of single cells, frequently from a very small source population. In this work we describe the design and characterization of a manually operated microfluidic cell sorter that 1) can accurately sort single or small groups of cells from very small cell populations with minimal losses, 2) that is easy to operate and that can be used in any laboratory that has a basic fluorescent microscope and syringe pump, 3) that can be assembled within minutes, 4) that can sort cells in very short time (minutes) with minimum cell stress, 5) that is cheap and reusable. This microfluidic sorter is made from hard plastic material (PMMA) into which microchannels are directly milled with hydraulic diameter of 70 μm. Inlet and outlet reservoirs are drilled through the chip. Sorting occurs through hydrodynamic switching ensuring low hydrodynamic shear stresses, which were modeled or experimentally confirmed to be below the cell damage threshold. Manually operated, the maximum sorting frequencies were approximately 10 cells per minute. Experiments verified that cell sorting operations could be achieved in as little as 15 minutes, including the assembly and testing of the sorter. In only one out of 10 sorting experiments the sorted cells were contaminated with another cell type. This microfluidic cell sorter represents an important capability for protocols requiring fast isolation of single cells from small number of rare cell populations.

Optofluidic cell manipulation for a biological microbeam

This paper describes the fabrication and integration of light-induced dielectrophoresis for cellular manipulation in biological microbeams. An optoelectronic tweezers (OET) cellular manipulation platform was designed, fabricated, and tested at Columbia University's Radiological Research Accelerator Facility (RARAF). The platform involves a light induced dielectrophoretic surface and a microfluidic chamber with channels for easy input and output of cells. The electrical conductivity of the particle-laden medium was optimized to maximize the dielectrophoretic force. To experimentally validate the operation of the OET device, we demonstrate UV-microspot irradiation of cells containing green fluorescent protein (GFP) tagged DNA single-strand break repair protein, targeted in suspension. We demonstrate the optofluidic control of single cells and groups of cells before, during, and after irradiation. The integration of optofluidic cellular manipulation into a biological microbeam enhances the facility's ability to handle non-adherent cells such as lymphocytes. To the best of our knowledge, this is the first time that OET cell handling is successfully implemented in a biological microbeam.