Analysis of mitochondria isolated from single cells

Etiologies of sperm DNA damage and its impact on male infertility

Male factor is responsible for up to 50% of infertility cases in the world. Semen analysis is considered the cornerstone of laboratory evaluation of male infertility, but it has its own drawbacks and fails to predict the male fertility potential with high sensitivity and specificity. Different etiologies have been linked with male infertility, of which sperm DNA damage has gained significant attention with extensive research on sperm function tests. The associations between sperm DNA damage and a variety of disorders such as varicocele, obesity, cancer, radiation and lifestyle factors are explored in this review. Furthermore, we discuss the mechanisms of DNA damage as well as its impact in different scenarios of male infertility, associated with spontaneous and assisted reproduction. Finally, we review the clinical applicability of sperm DNA fragmentation testing in the management of male infertility.

Separation of subcellular fluorescent microspheres by capillary electrophoresis

Fluorescent microspheres (FMs) are widely employed in diagnostics and life sciences research; here, we investigated the effect of capillary coating, polymer concentration, electric field strength, and sample concentration on the separation performance of 1.0 μm FMs in hydroxyethyl cellulose (HEC) by capillary electrophoresis (CE). Results showed that (1) capillary coating could enhance the fluorescence signal. (2) For HEC with the same molecular weight, the higher HEC concentration is, the later the first peak appears in the electropherogram. (3) When FMs are diluted, increasing the electric field strength can enhance the migration speed and reduce the aggregation of FMs. (4) The number of FMs calculated is close to the theoretical value when it is diluted 10,000 times. The optimum conditions for CE were as follows: 6 cm/8 cm of effective length and total length of the coated capillary, 0.3% HEC (1300 k), and 300 V/cm of electric field strength. Such a study is helpful for the development of a FM counting system. Graphical abstract.

Exploring the Fundamental Structures of Life: Non-Targeted, Chemical Analysis of Single Cells and Subcellular Structures

Cells are a basic functional and structural unit of living organisms. Both unicellular communities and multicellular species produce an astonishing chemical diversity, enabling a wide range of divergent functions, yet each cell shares numerous aspects that are common to all living organisms. While there are many approaches for studying this chemical diversity, only a few are non-targeted and capable of analyzing hundreds of different chemicals at cellular resolution. Here, we review the non-targeted approaches used to perform comprehensive chemical analyses, provide chemical imaging information, or obtain high-throughput single-cell profiling data. Single-cell measurement capabilities are rapidly increasing in terms of throughput, limits of detection, and completeness of the chemical analyses; these improvements enable their application to understand ever more complex physiological phenomena, such as learning, memory, and behavior.

Deterministic Absolute Negative Mobility for Micro- and Submicrometer Particles Induced in a Microfluidic Device

Efficient separations of particles with micron and submicron dimensions are extremely useful in preparation and analysis of materials for nanotechnological and biological applications. Here, we demonstrate a nonintuitive, yet efficient, separation mechanism for μm and subμm colloidal particles and organelles, taking advantage of particle transport in a nonlinear post array in a microfluidic device under the periodic action of electrokinetic and dielectrophoretic forces. We reveal regimes in which deterministic particle migration opposite to the average applied force occurs for a larger particle, a typical signature of deterministic absolute negative mobility (dANM), whereas normal response is obtained for smaller particles. The coexistence of dANM and normal migration was characterized and optimized in numerical modeling and subsequently implemented in a microfluidic device demonstrating at least 2 orders of magnitude higher migration speeds as compared to previous ANM systems. We also induce dANM for mouse liver mitochondria and envision that the separation mechanisms described here provide size selectivity required in future separations of organelles, nanoparticles, and protein nanocrystals.

Nanohole Array-Directed Trapping of Mammalian Mitochondria Enabling Single Organelle Analysis

We present periodic nanohole arrays fabricated in free-standing metal-coated nitride films as a platform for trapping and analyzing single organelles. When a microliter-scale droplet containing mitochondria is dispensed above the nanohole array, the combination of evaporation and capillary flow directs individual mitochondria to the nanoholes. Mammalian mitochondria arrays were rapidly formed on chip using this technique without any surface modification steps, microfluidic interconnects, or external power sources. The trapped mitochondria were depolarized on chip using an ionophore with results showing that the organelle viability and behavior were preserved during the on-chip assembly process. Fluorescence signal related to mitochondrial membrane potential was obtained from single mitochondria trapped in individual nanoholes revealing statistical differences between the behavior of polarized vs depolarized mammalian mitochondria. This technique provides a fast and stable route for droplet-based directed localization of organelles-on-a-chip with minimal limitations and complexity, as well as promotes integration with other optical or electrochemical detection techniques.

Desalting by crystallization: detection of attomole biomolecules in picoliter buffers by mass spectrometry

Sensitive detection of biomolecules in small-volume samples by mass spectrometry is, in many cases, challenging because of the use of buffers to maintain the biological activities of proteins and cells. Here, we report a highly effective desalting method for picoliter samples. It was based on the spontaneous separation of biomolecules from salts during crystallization of the salts. After desalting, the biomolecules were deposited in the tip of the quartz pipet because of the evaporation of the solvent. Subsequent detection of the separated biomolecules was achieved using solvent assisted electric field induced desorption/ionization (SAEFIDI) coupled with mass spectrometry. It allowed for direct desorption/ionization of the biomolecules in situ from the tip of the pipet. The organic component in the assistant solvent inhibited the desorption/ionization of salts, thus assured successful detection of biomolecules. Proteins and peptides down to 50 amol were successfully detected using our method even if there were 3 × 10(5) folds more amount of salts in the sample. The concentration and ion species of the salts had little influence on the detection results.

Patch clamp electrophysiology and capillary electrophoresis-mass spectrometry metabolomics for single cell characterization

The visual selection of specific cells within an ex vivo brain slice, combined with whole-cell patch clamp recording and capillary electrophoresis (CE)–mass spectrometry (MS)-based metabolomics, yields high chemical information on the selected cells. By providing access to a cell’s intracellular environment, the whole-cell patch clamp technique allows one to record the cell’s physiological activity. A patch clamp pipet is used to withdraw ∼3 pL of cytoplasm for metabolomic analysis using CE–MS. Sampling the cytoplasm, rather than an intact isolated neuron, ensures that the sample arises from the cell of interest and that structures such as presynaptic terminals from surrounding, nontargeted neurons are not sampled. We sampled the rat thalamus, a well-defined system containing gamma-aminobutyric acid (GABA)-ergic and glutamatergic neurons. The approach was validated by recording and sampling from glutamatergic thalamocortical neurons, which receive major synaptic input from GABAergic thalamic reticular nucleus neurons, as well as neurons and astrocytes from the ventral basal nucleus and the dorsal lateral geniculate nucleus. From the analysis of the cytoplasm of glutamatergic cells, approximately 60 metabolites were detected, none of which corresponded to the compound GABA. However, GABA was successfully detected when sampling the cytoplasm of GABAergic neurons, demonstrating the exclusive nature of our cytoplasmic sampling approach. The combination of whole-cell patch clamp with single cell cytoplasm metabolomics provides the ability to link the physiological activity of neurons and astrocytes with their neurochemical state. The observed differences in the metabolome of these neurons underscore the striking cell to cell heterogeneity in the brain.

Insulator-based dielectrophoresis of mitochondria

Isolated mitochondria display a wide range of sizes plausibly resulting from the coexistence of subpopulations, some of which may be associated with disease or aging. Strategies to separate subpopulations are needed to study the importance of these organelles in cellular functions. Here, insulator-based dielectrophoresis (iDEP) was exploited to provide a new dimension of organelle separation. The dielectrophoretic properties of isolated Fischer 344 (F344) rat semimembranosus muscle mitochondria and C57BL/6 mouse hepatic mitochondria in low conductivity buffer (0.025-0.030 S/m) at physiological pH (7.2-7.4) were studied using polydimethylsiloxane (PDMS) microfluidic devices. First, direct current (DC) and alternating current (AC) of 0-50 kHz with potentials of 0-3000 V applied over a channel length of 1 cm were separately employed to generate inhomogeneous electric fields and establish that mitochondria exhibit negative DEP (nDEP). DEP trapping potential thresholds at 0-50 kHz were also determined to be weakly dependent on applied frequency and were generally above 200 V. Second, we demonstrated a separation scheme using DC potentials <100 V to perform the first size-based iDEP sorting of mitochondria. Samples of isolated mitochondria with heterogeneous sizes (150 nm-2 μm diameters) were successfully separated into sub-micron fractions, indicating the ability to isolate mitochondria into populations based on their size.

High sensitivity capillary zone electrophoresis-electrospray ionization-tandem mass spectrometry for the rapid analysis of complex proteomes

The vast majority of bottom-up proteomic studies employ reversed-phase separation of tryptic digests coupled with electrospray ionization tandem mass spectrometry. These studies are remarkably successful for the analysis of samples containing micrograms of protein. However, liquid chromatography tends to perform poorly for samples containing nanogram amounts of protein, presumably due to loss of trace-level peptides within the chromatographic system. Capillary zone electrophoresis provides a much simpler flow system and would appear to be an attractive alternative to liquid chromatography for separation of small peptide samples before electrospray ionization and mass spectrometry detection. However, capillary zone electrophoresis has received very little attention as a tool for analysis of complex proteomes. In 2012, we reported the use of capillary zone electrophoresis for the analysis of the secretome of Mycobacterium marinum, a model system for tuberculosis. Roughly 400 peptides and over 100 proteins were identified from this medium-complexity proteome; this identification required analysis of a set of 11 fractions and occupied three hours of mass spectrometer time. We have recently employed an improved capillary zone electrophoresis system for the analysis of 100 ng of the Escherichia coli proteome and observed over 1300 peptides and nearly 350 proteins in a single separation. More interestingly, analysis of 1 ng of the E. coli proteome yielded over 600 peptide and 140 protein groups. This sample size approaches that of a large eukaryotic cell, suggesting that capillary zone electrophoresis may ultimately be a useful tool for chemical cytometry.

Nanofluidic platform for single mitochondria analysis using fluorescence microscopy

Using nanofluidic channels in PDMS of cross section 500 nm × 2 μm, we demonstrate the trapping and interrogation of individual, isolated mitochondria. Fluorescence labeling demonstrates the immobilization of mitochondria at discrete locations along the channel. Interrogation of mitochondrial membrane potential with different potential sensitive dyes (JC-1 and TMRM) indicates the trapped mitochondria are vital in the respiration buffer. Fluctuations of the membrane potential can be observed at the single mitochondrial level. A variety of chemical challenges can be delivered to each individual mitochondrion in the nanofluidic system. As sample demonstrations, increases in the membrane potential are seen upon introduction of OXPHOS substrates into the nanofluidic channel. Introduction of Ca(2+) into the nanochannels induces mitochondrial membrane permeabilization (MMP), leading to depolarization, observed at the single mitochondrial level. A variety of applications in cancer biology, stem cell biology, apoptosis studies, and high throughput functional metabolomics studies can be envisioned using this technology.

Monitoring metabolic responses of single mitochondria within poly(dimethylsiloxane) wells: study of their endogenous reduced nicotinamide adenine dinucleotide evolution

It is now demonstrated that mitochondria individually function differently because of specific energetic needs in cell compartments but also because of the genetic heterogeneity within the mitochondrial pool-network of a cell. Consequently, understanding mitochondrial functioning at the single organelle level is of high interest for biomedical research, therefore being a target for analyticians. In this context, we developed easy-to-build platforms of milli- to microwells for fluorescence microscopy of single isolated mitochondria. Poly(dimethylsiloxane) (PDMS) was determined to be an excellent material for mitochondrial deposition and observation of their NADH content. Because of NADH autofluorescence, the metabolic status of each mitochondrion was analyzed following addition of a respiratory substrate (stage 2), ethanol herein, and a respiratory inhibitor (stage 3), Antimycin A. Mean levels of mitochondrial NADH were increased by 32% and 62% under stages 2 and 3, respectively. Statistical studies of NADH value distributions evidenced different types of responses, at least three, to ethanol and Antimycin A within the mitochondrial population. In addition, we showed that mitochondrial ability to generate high levels of NADH, that is its metabolic performance, is not correlated either to the initial energetic state or to the respective size of each mitochondrion.

Review on recent advances in the analysis of isolated organelles

The analysis of isolated organelles is one of the pillars of modern bioanalytical chemistry. This review describes recent developments on the isolation and characterization of isolated organelles both from living organisms and cell cultures. Salient reports on methods to release organelles focused on reproducibility and yield, membrane isolation, and integrated devices for organelle release. New developments on organelle fractionation after their isolation were on the topics of centrifugation, immunocapture, free flow electrophoresis, flow field-flow fractionation, fluorescence activated organelle sorting, laser capture microdissection, and dielectrophoresis. New concepts on characterization of isolated organelles included atomic force microscopy, optical tweezers combined with Raman spectroscopy, organelle sensors, flow cytometry, capillary electrophoresis, and microfluidic devices.

A hyphenated optical trap capillary electrophoresis laser induced native fluorescence system for single-cell chemical analysis

Single-cell measurements allow a unique glimpse into cell-to-cell heterogeneity; even small changes in selected cells can have a profound impact on an organism's physiology. Here an integrated approach to single-cell chemical sampling and assay are described. Capillary electrophoresis (CE) with laser-induced native fluorescence (LINF) has the sensitivity to characterize natively fluorescent indoles and catechols within individual cells. While the separation and detection approaches are well established, the sampling and injection of individually selected cells requires new approaches. We describe an optimized system that interfaces a single-beam optical trap with CE and multichannel LINF detection. A cell is localized within the trap and then the capillary inlet is positioned near the cell using a computer-controlled micromanipulator. Hydrodynamic injection allows cell lysis to occur within the capillary inlet, followed by the CE separation and LINF detection. The use of multiple emission wavelengths allows improved analyte identification based on differences in analyte fluorescence emission profiles and migration time. The system enables injections of individual rat pinealocytes and quantification of their endogenous indoles, including serotonin, N-acetyl-serotonin, 5-hydroxyindole-3-acetic acid, tryptophol and others. The amounts detected in individual cells incubated in 5-hydroxytryptophan ranged from 10(-14) mol to 10(-16) mol, an order of magnitude higher than observed in untreated pinealocytes.

Sampling techniques for single-cell electrophoresis

Cells are extraordinarily complex, containing thousands of different analytes with concentrations spanning at least nine orders of magnitude. Analyzing single cells instead of tissue homogenates provides unique insights into cell-to-cell heterogeneity and aids in distinguishing normal cells from pathological ones. The high sensitivity and low sample consumption of capillary and on-chip electrophoresis, when integrated with fluorescence, electrochemical, and mass spectrometric detection methods, offer an ideal toolset for examining single cells and even subcellular organelles; however, the isolation and loading of such small samples into these devices is challenging. Recent advances have addressed this issue by interfacing a variety of enhanced mechanical, microfluidic, and optical sampling techniques to capillary and on-chip electrophoresis instruments for single-cell analyses.

The subcellular distribution of small molecules: from pharmacokinetics to synthetic biology

The systemic pharmacokinetics and pharmacodynamics of small molecules are determined by subcellular transport phenomena. Although approaches used to study the subcellular distribution of small molecules have gradually evolved over the past several decades, experimental analysis and prediction of cellular pharmacokinetics remains a challenge. In this review, we survey the progress of subcellular distribution research since the 1960s, with a focus on the advantages, disadvantages and limitations of the various experimental techniques. Critical review of the existing body of knowledge points to many opportunities to advance the rational design of organelle-targeted chemical agents. These opportunities include (1) development of quantitative, non-fluorescence-based, whole cell methods and techniques to measure the subcellular distribution of chemical agents in multiple compartments; (2) exploratory experimentation with nonspecific transport probes that have not been enriched with putative, organelle-targeting features; (3) elaboration of hypothesis-driven, mechanistic and modeling-based approaches to guide experiments aimed at elucidating subcellular distribution and transport; and (4) introduction of revolutionary conceptual approaches borrowed from the field of synthetic biology combined with cutting edge experimental strategies. In our laboratory, state-of-the-art subcellular transport studies are now being aimed at understanding the formation of new intracellular membrane structures in response to drug therapy, exploring the function of drug-membrane complexes as intracellular drug depots, and synthesizing new organelles with extraordinary physical and chemical properties.

Electrochemical probes for detection and analysis of exocytosis and vesicles

Unraveling the mechanistic details of neurotransmitter exocytosis is arguably among the most important molecular problems in neuroscience today. Investigations at single cells, particularly with electrochemical methods, have given unique chemical and biological insight into this process at the fundamental level. The rapid response time (submillisecond) of microelectrodes makes them well suited for monitoring the dynamic process of exocytosis. We review here recent developments in electrochemical techniques to spatially and simultaneously detect exocytosis across a single cell and to measure the transmitter content of single vesicles removed from cells. The former method is used to demonstrate dynamic heterogeneity in release across a cell, and in the latter work comparison is made between vesicle content and release to conclude that only a fraction of the transmitter is released during full exocytosis.

Hybrid capillary-microfluidic device for the separation, lysis, and electrochemical detection of vesicles

The primary method for neuronal communication involves the extracellular release of small molecules that are packaged in secretory vesicles. We have developed a platform to separate, lyse, and electrochemically measure the contents of single vesicles using a hybrid capillary-microfluidic device. This device incorporates a sheath-flow design at the outlet of the capillary for chemical lysis of vesicles and subsequent electrochemical detection. The effect of sheath-flow on analyte dispersion was characterized using confocal fluorescence microscopy and electrochemical detection. At increased flow rates, dispersion was minimized, leading to higher separation efficiencies but lower detected amounts. Large unilamellar vesicles (diameter approximately 200 nm), a model for secretory vesicles, were prepared by extrusion and loaded with an electroactive molecule. They were then separated and detected using the hybrid capillary-microfluidic device. Determination of size from internalized analyte concentration provides a method to characterize the liposomal suspension. These results were compared to an orthogonal size measurement using dynamic light scattering to validate the detection platform.

Separation of DNA-containing organelles from Toxoplasma gondii by CZE

Toxoplasma gondii and other members of the family Apicomplexa have two organelles, in addition to the nucleus, that contain DNA. Herein is reported the separation of the DNA-carrying organelles from T. gondii tachyzoites, i.e. the mitochondrion and the apicoplast, by CZE. The cells were stained with SYTO9, a dye that exhibit fluorescence when interacting with double stranded nucleic acids (e.g. DNA) and disrupted by nitrogen cavitation. Following careful removal of the heavier cellular material, the remaining lysate was injected on a CE instrument and the DNA-containing organelles were detected by LIF. The mitochondrion had longer migration time than the apicoplast, and the migration times were comparable in the replicates. This method should potentially also work for other members of the Apicomplexa including Plasmodium falciparum.

Analytical approaches to investigate transmitter content and release from single secretory vesicles

The vesicle serves as the primary intracellular unit for the highly efficient storage and release of chemical messengers triggered during signaling processes in the nervous system. This review highlights conventional and emerging analytical methods that have used microscopy, electrochemistry, and spectroscopy to resolve the location, time course, and quantal content characteristics of neurotransmitter release. Particular focus is on the investigation of the synaptic vesicle and its involvement in the fundamental molecular mechanisms of cell communication.

Detection of heteroplasmy in individual mitochondrial particles

Mitochondrial DNA (mtDNA) mutations have been associated with disease and aging. Since each cell has thousands of mtDNA copies, clustered into nucleoids of five to ten mtDNA molecules each, determining the effects of a given mtDNA mutation and their connection with disease phenotype is not straightforward. It has been postulated that heteroplasmy (coexistence of mutated and wild-type DNA) follows simple probability rules dictated by the random distribution of mtDNA molecules at the nucleoid level. This model has been used to explain how mutation levels correlate with the onset of disease phenotype and loss of cellular function. Nonetheless, experimental evidence of heteroplasmy at the nucleoid level is scarce. Here, we report a new method to determine heteroplasmy of individual mitochondrial particles containing one or more nucleoids. The method uses capillary cytometry with laser-induced fluorescence detection to detect individual mitochondrial particles stained with PicoGreen, which makes it possible to quantify the mtDNA copy number of each particle. After detection, one or more particles are collected into polymerase chain reaction (PCR) wells and then subjected to real-time multiplexed PCR amplification. This PCR strategy is suitable to obtain the relative abundance of mutated and wild-type mtDNA. The results obtained here indicate that individual mitochondrial particles and nucleoids contained within these particles are not heteroplasmic. The results presented here suggest that current models of mtDNA segregation and distribution (i.e., heteroplasmic nucleoids) need further consideration.

Continuous intact cell detection and viability determination by CE with dual-wavelength detection

We introduce here a method for continuous intact cell detection and viability determination of individual trypan blue stained cells by CE with ultraviolet-visible dual-wavelength detection. To avoid cell aggregation or damage during electrophoresis, cells after staining were fixed with 4% formaldehyde and were continuously introduced into the capillary by EOF. The absorbance of a cell at 590 nm was used to determine its viability. An absorbance of two milli-absorbance unit at 590 nm was the clear cut-off point for living and dead Hela cells in our experiments. Good viability correlation between the conventional trypan blue staining assay and our established CE method (correlation coefficient, R(2)=0.9623) was demonstrated by analysis of cell mixtures with varying proportions of living and dead cells. The CE method was also used to analyze the cytotoxicity of methylmercury, and the results were in good agreement with the trypan blue staining assay and 3-(4,5-dimethyl-2-thiazyl)-2,5-diphenyl-2H-tetrazolium bromide methods. Compared with the 3-(4,5-dimethyl-2-thiazyl)-2,5-diphenyl-2H-tetrazolium bromide method, our established CE method can be easily automated to report cell viability based on the state of individual cells. Tedious manual cell counting and human error due to investigator bias can be avoided by using this method.

Estimation of migration-time and mobility distributions in organelle capillary electrophoresis with statistical-overlap theory

The separation of organelles by capillary electrophoresis (CE) produces large numbers of narrow peaks, which commonly are assumed to originate from single particles. In this paper, we show this is not always true. Here, we use established methods to partition simulated and real organelle CEs into regions of constant peak density and then use statistical-overlap theory to calculate the number of peaks (single particles) in each region. The only required measurements are the number of observed peaks (maxima) and peak standard deviation in the regions and the durations of the regions. Theory is developed for the precision of the estimated peak number and the threshold saturation above which the calculation is not advisable due to fluctuation of peak numbers. Theory shows that the relative precision is good when the saturation lies between 0.2 and 1.0 and is optimal when the saturation is slightly greater than 0.5. It also shows the threshold saturation depends on the peak standard deviation divided by the region's duration. The accuracy and precision of peak numbers estimated in different regions of organelle CEs are verified by computer simulations having both constant and nonuniform peak densities. The estimates are accurate to 6%. The estimated peak numbers in different regions are used to calculate migration-time and electrophoretic-mobility distributions. These distributions are less biased by peak overlap than ones determined by counting maxima and provide more correct measures of the organelle properties. The procedure is applied to a mitochondrial CE, in which over 20% of peaks are hidden by peak overlap.

Capillary electrophoresis with electrospray ionization mass spectrometric detection for single-cell metabolomics

A method that enables metabolomic profiling of single cells and subcellular structures is described using capillary electrophoresis coupled to electrospray ionization time-of-flight mass spectrometry. A nebulizer-free coaxial sheath-flow interface completes the circuit and provides a stable electrospray, yielding a signal with a relative standard deviation of under 5% for the total ion electropherogram. Detection limits are in the low nanomolar range (i.e., <50 nM (<300 amol)) for a number of cell-to-cell signaling molecules, including acetylcholine (ACh), histamine, dopamine, and serotonin. The instrument also yields high-efficiency separations, e.g., approximately 600,000 for eluting ACh bands. The utility of this setup for single-cell metabolomic profiling is demonstrated with identified neurons from Aplysia californica--the R2 neuron and metacerebral cell (MCC). Single-cell electropherograms are reproducible, with a large number of metabolites detected; more than 100 compounds yield signals of over 10(4) counts from the injection of only 0.1% of the total content from a single MCC. Expected neurotransmitters are detected within the cells (ACh in R2 and serotonin in MCC), as are compounds that have molecular masses consistent with all of the naturally occurring amino acids (except cysteine). Tandem MS using a quadrupole time-of-flight tandem mass spectrometer distinguishes ACh from isobaric compounds in the R2 neuron and demonstrates the ability of this method to characterize and identify metabolites present within single cells.

Mobile phone radiation induces reactive oxygen species production and DNA damage in human spermatozoa in vitro

Background

In recent times there has been some controversy over the impact of electromagnetic radiation on human health. The significance of mobile phone radiation on male reproduction is a key element of this debate since several studies have suggested a relationship between mobile phone use and semen quality. The potential mechanisms involved have not been established, however, human spermatozoa are known to be particularly vulnerable to oxidative stress by virtue of the abundant availability of substrates for free radical attack and the lack of cytoplasmic space to accommodate antioxidant enzymes. Moreover, the induction of oxidative stress in these cells not only perturbs their capacity for fertilization but also contributes to sperm DNA damage. The latter has, in turn, been linked with poor fertility, an increased incidence of miscarriage and morbidity in the offspring, including childhood cancer. In light of these associations, we have analyzed the influence of RF-EMR on the cell biology of human spermatozoa in vitro.

Principal Findings

Purified human spermatozoa were exposed to radio-frequency electromagnetic radiation (RF-EMR) tuned to 1.8 GHz and covering a range of specific absorption rates (SAR) from 0.4 W/kg to 27.5 W/kg. In step with increasing SAR, motility and vitality were significantly reduced after RF-EMR exposure, while the mitochondrial generation of reactive oxygen species and DNA fragmentation were significantly elevated (P<0.001). Furthermore, we also observed highly significant relationships between SAR, the oxidative DNA damage bio-marker, 8-OH-dG, and DNA fragmentation after RF-EMR exposure.

Conclusions

RF-EMR in both the power density and frequency range of mobile phones enhances mitochondrial reactive oxygen species generation by human spermatozoa, decreasing the motility and vitality of these cells while stimulating DNA base adduct formation and, ultimately DNA fragmentation. These findings have clear implications for the safety of extensive mobile phone use by males of reproductive age, potentially affecting both their fertility and the health and wellbeing of their offspring.

Determining biological noise via single cell analysis

Single cell analysis techniques describe the cellular heterogeneity that originates from fundamental stochastic variations in each of the molecular processes underlying cell function. The quantitative description of this set of variations is called biological noise and includes intrinsic and extrinsic noise. The former refers to stochastic variations directly involved with a given process, while the latter is due to environmental factors associated with other processes. Mathematical models are successful in predicting noise trends in simple biological systems, but it takes single cell techniques such as flow cytometry and time lapse microscopy to determine and dissect biological noise. This review describes several approaches that have been successfully used to describe biological noise.

Determining under- and oversampling of individual particle distributions in microfluidic electrophoresis with orthogonal laser-induced fluorescence detection

This report investigates the effects of sample size on the separation and analysis of individual biological particles using microfluidic devices equipped with an orthogonal LIF detector. A detection limit of 17 +/- 1 molecules of fluorophore is obtained using this orthogonal LIF detector under a constant flow of fluorescein, which is a significant improvement over epifluorescence, the most common LIF detection scheme used with microfluidic devices. Mitochondria from rat liver tissue and cultured 143B osteosarcoma cells are used as model biological particles. Quantile-quantile (q-q) plots were used to investigate changes in the distributions. When the number of detected mitochondrial events became too large (>72 for rat liver and >98 for 143B mitochondria), oversampling occurs. Statistical overlap theory is used to suggest that the cause of oversampling is that separation power of the microfluidic device presented is not enough to adequately separate large numbers of individual mitochondrial events. Fortunately, q-q plots make it possible to identify and exclude these distributions from data analysis. Additionally, when the number of detected events became too small (<55 for rat liver and <81 for 143B mitochondria) there were not enough events to obtain a statistically relevant mobility distribution, but these distributions can be combined to obtain a statistically relevant electrophoretic mobility distribution.

Recent advances in the analysis of biological particles by capillary electrophoresis

This review covers research papers published in the years 2005-2007 that describe the application of capillary electrophoresis to the analysis of biological particles such as whole cells, subcellular organelles, viruses and microorganisms.

Chemical analysis of single cells

Chemical analysis of single cells requires methods for quickly and quantitatively detecting a diverse array of analytes from extremely small volumes (femtoliters to nanoliters) with very high sensitivity and selectivity. Microelectrophoretic separations, using both traditional capillary electrophoresis and emerging microfluidic methods, are well suited for handling the unique size of single cells and limited numbers of intracellular molecules. Numerous analytes, ranging from small molecules such as amino acids and neurotransmitters to large proteins and subcellular organelles, have been quantified in single cells using microelectrophoretic separation techniques. Microseparation techniques, coupled to varying detection schemes including absorbance and fluorescence detection, electrochemical detection, and mass spectrometry, have allowed researchers to examine a number of processes inside single cells. This review also touches on a promising direction in single cell cytometry: the development of microfluidics for integrated cellular manipulation, chemical processing, and separation of cellular contents.

Chemical cytometry: fluorescence-based single-cell analysis

Cytometry deals with the analysis of the composition of single cells. Flow and image cytometry employ antibody-based stains to characterize a handful of components in single cells. Chemical cytometry, in contrast, employs a suite of powerful analytical tools to characterize a large number of components. Tools have been developed to characterize nucleic acids, proteins, and metabolites in single cells. Whereas nucleic acid analysis employs powerful polymerase chain reaction-based amplification techniques, protein and metabolite analysis tends to employ capillary electrophoresis separation and ultrasensitive laser-induced fluorescence detection. It is now possible to detect yoctomole amounts of many analytes in single cells.

Contributions of capillary electrophoresis to neuroscience

Capillary electrophoresis (CE) is a small-volume separation approach amenable to the analysis of complex samples for their small molecule, peptide and protein content. A number of the features of CE make it a method of choice for addressing questions related to neurochemistry. The figures of merit inherent to CE that make it well suited for studying cell-to-cell and intracellular signaling include small sample volumes, high separation efficiency, the ability for online analyte concentration, and compatibility with sensitive and high-information content detection methods. A variety of instrumental aspects are detailed, including detection methods and sampling techniques that are particularly useful for the analysis of signaling molecules. Studies that have used these techniques to increase our understanding of neurobiology are emphasized throughout. One notable application is single neuron chemical analysis, a research area that has been greatly advanced by CE.

CE analysis of the acidic organelles of a single cell

The properties of organelles within a cell have been shown to be highly heterogeneous. Until now, it has been unclear just how much of this heterogeneity is endemic to the organelle subpopulations themselves and how much is actually due to stochastic cellular noise. An attractive approach for investigating the origins of heterogeneity among the organelles of a single cell is CE with LIF detection (CE-LIF). As a proof of principle, in this report we optimize and use a single cell CE-LIF method to investigate the properties of endocytic (acidic) organelles. Our results show that the properties of individual acidic organelles containing Alexa Fluor 488 Dextran suggest that there are two groups of CCRF-CEM cells: a group with a high dextran content per cell, and a group with a low dextran content per cell. Furthermore, the individual organelle measurements of the single cells allow us to compare in each group the distributions of doxorubicin content per acidic organelle and electrophoretic mobilities of these organelles.

Absolute quantitation of a heteroplasmic mitochondrial DNA deletion using a multiplex three-primer real-time PCR assay

Quantitation of wild-type and deleted mitochondrial DNA (mtDNA) coexisting within the same cell (a.k.a., heteroplasmy) is important in mitochondrial disease and aging. We report the development of a multiplex three-primer PCR assay that is capable of absolute quantitation of wild-type and deleted mtDNA simultaneously. Molecular beacons were designed to hybridize with either type of mtDNA molecule, allowing real-time detection during PCR amplification. The assay is specific and can detect down to six copies of mtDNA, making it suitable for single-cell analyses. The relative standard deviation in the threshold cycle number is approximately 0.6%. Heteroplasmy was quantitated in individual cytoplasmic hybrid cells (cybrids), containing a large mtDNA deletion, and bulk cell samples. Individual cybrid cells contained 100-2600 copies of wild-type mtDNA and 950-4700 copies of deleted mtDNA, and the percentage of heteroplasmy ranged from 43+/-16 to 95+/-16%. The average amount of total mtDNA was 3800+/-1600 copies/cybrid cell, and the average percentage of heteroplasmy correlated well with the bulk cell sample. The single-cell analysis also revealed that heteroplasmy in individual cells is highly heterogeneous. This assay will be useful for monitoring clonal expansions of mtDNA deletions and investigating the role of heteroplasmy in cell-to-cell heterogeneity in cellular models of mitochondrial disease and aging.