Stable labeled microspheres to measure perfusion: validation of a neutron activation assay technique

Neutron activation is an accurate analytic method in which trace quantities of isotopes of interest in a sample are activated and the emitted radiation is measured with high-resolution detection equipment. This study demonstrates the application of neutron activation for the measurement of myocardial perfusion using stable isotopically labeled microspheres. Stable labeled and standard radiolabeled microspheres (15 microm) were coinjected in an in vivo rabbit model of myocardial ischemia and reperfusion. Radiolabeled microspheres were detected with a standard gamma-well counter, and stable labeled microspheres were detected with a high-resolution Ge detection after neutron activation of the myocardial and reference blood samples. Regional myocardial blood flow was calculated from the deposition of radiolabeled and stable labeled microspheres. Both sets of microspheres gave similar measurements of regional myocardial blood flow over a wide range of flow with a high linear correlation (r = 0.95-0.99). Neutron activation is capable of detecting a single microsphere in an intact myocardial sample while providing simultaneous quantitative measurements of multiple isotope labels. This high sensitivity and capability for measuring perfusion in intact tissue are advantages over other techniques, such as optical detection of microspheres. Neutron activation also can provide an effective method for reducing the production of low-level radioactive waste generated from biomedical research. Further applications of neutron activation offer the potential for measuring other stable labeled compounds, such as fatty acids and growth factors, in conjunction with microsphere measured flow, providing the capability for simultaneous measurement of regional metabolism and perfusion.     

Measuring Ascending Aortic Stiffness In Vivo in Mice Using Ultrasound

We present a protocol for measuring in vivo aortic stiffness in mice using high-resolution ultrasound imaging. Aortic diameter is measured by ultrasound and aortic blood pressure is measured invasively with a solid-state pressure catheter. Blood pressure is raised then lowered incrementally by intravenous infusion of vasoactive drugs phenylephrine and sodium nitroprusside. Aortic diameter is measured for each pressure step to characterize the pressure-diameter relationship of the ascending aorta. Stiffness indices derived from the pressure-diameter relationship can be calculated from the data collected. Calculation of arterial compliance is described in this protocol.This technique can be used to investigate mechanisms underlying increased aortic stiffness associated with cardiovascular disease and aging. The technique produces a physiologically relevant measure of stiffness compared to ex vivo approaches because physiological influences on aortic stiffness are incorporated in the measurement. The primary limitation of this technique is the measurement error introduced from the movement of the aorta during the cardiac cycle. This motion can be compensated by adjusting the location of the probe with the aortic movement as well as making multiple measurements of the aortic pressure-diameter relationship and expanding the experimental group size.     

Picture series table for marker classification of the structure of erythrocyte marginal bands on specially prepared blood smears

A phase-contrast microscopic procedure of evaluation, measurement and classification which can be simply performed on erythrocyte marginal zones (ERZ) of particularly prepared and coloured smears is described. Classification is made with the help of a classification table and a picture series table after measuring the erythrocyte marginal zones with an ocular measuring plate or with a measuring screw ocular respectively. The same preparing and colouring technique also enables erythrocyte marginal zones to be evaluated with an automatic picture analysis and with the scanning electron microscope. With the help of this technique, which can be applied in human erythrocytes as well as in those of dogs, rats and fish, changes of erythrocyte margin zones which may be caused by haematological, immunological and toxicological processes may be determined in quantity. The mode of action of this preparation technique is dealt with in the discussion.     

Measurement of single macromolecule orientation by total internal reflection fluorescence polarization microscopy

A new approach is presented for measuring the three-dimensional orientation of individual macromolecules using single molecule fluorescence polarization (SMFP) microscopy. The technique uses the unique polarizations of evanescent waves generated by total internal reflection to excite the dipole moment of individual fluorophores. To evaluate the new SMFP technique, single molecule orientation measurements from sparsely labeled F-actin are compared to ensemble-averaged orientation data from similarly prepared densely labeled F-actin. Standard deviations of the SMFP measurements taken at 40 ms time intervals indicate that the uncertainty for individual measurements of axial and azimuthal angles is approximately 10 degrees at 40 ms time resolution. Comparison with ensemble data shows there are no substantial systematic errors associated with the single molecule measurements. In addition to evaluating the technique, the data also provide a new measurement of the torsional rigidity of F-actin. These measurements support the smaller of two values of the torsional rigidity of F-actin previously reported.     

Fluorescence labeling of carbon nanotubes and visualization of a nanotube-protein hybrid under fluorescence microscope

Biological applications of carbon nanotubes have been hampered by the inability to visualize them using conventional optical microscope, which is the most common tool for the observation and measurement of biological processes. Recently, a number of fluorescence labeling methods for biomolecules and various fluorescence probes have been developed and widely utilized in biological fields. Therefore, labeling carbon nanotubes with such fluorophores under physiological conditions will be highly useful in their biological applications. In this Article, we present a method to fluorescently label nanotubes by combining a detergent and a fluorophore commonly used in biological experiments. Fluorophores carrying an amino group (Texas Red hydrazide or BODIPY FL-hydrazide) were covalently attached to the hydroxyl groups of Tween 20 using carbonyldiimidazole. Fluorescence microscopy demonstrated that nanotubes were efficiently solubilized and labeled by this fluorescently labeled detergent. By using this technique, we also demonstrated multicolor fluorescence imaging of a nanotube-protein hybrid.     

基于单分子量子相干调制的细胞温度成像技术

目的 细胞温度成像可以帮助科学家研究和理解细胞内部的温度分布,揭示细胞代谢和生物化学过程的关键信息。目前,基于荧光温度探针的细胞温度成像技术存在低温度分辨率和有限测量范围等限制。本文旨在利用单分子量子相干过程依赖温度的特性,开发一种单细胞温度成像和实时检测技术。方法 基于飞秒脉冲激光制备延时和相位可调的飞秒脉冲对,调制的脉冲对通过显微系统激发细胞内标记的荧光单分子,之后收集并记录每个荧光光子的到达时间。利用单分子相干过程与周围环境温度的关系,定义单分子量子相干可视度（V）,建立V与环境温度的对应关系。通过调制解调荧光光子的到达时间,获取单分子周围环境温度,结合扫描成像,实现细胞的温度成像和实时检测。结果 该方法可以实现高精度（温度分辨率<0.1℃）和大范围温度（10～50℃）的温度成像和测量,并观测到了单个细胞代谢相关的温度变化。结论 该研究有助于深入了解细胞代谢、蛋白质功能和疾病机制,为生物医学研究提供重要工具。     

Isothermal microcalorimetry, a new tool to monitor drug action against Trypanosoma brucei and Plasmodium falciparum

Isothermal microcalorimetry is an established tool to measure heat flow of physical, chemical or biological processes. The metabolism of viable cells produces heat, and if sufficient cells are present, their heat production can be assessed by this method. In this study, we investigated the heat flow of two medically important protozoans, Trypanosoma brucei rhodesiense and Plasmodium falciparum. Heat flow signals obtained for these pathogens allowed us to monitor parasite growth on a real-time basis as the signals correlated with the number of viable cells. To showcase the potential of microcalorimetry for measuring drug action on pathogenic organisms, we tested the method with three antitrypanosomal drugs, melarsoprol, suramin and pentamidine and three antiplasmodial drugs, chloroquine, artemether and dihydroartemisinin, each at two concentrations on the respective parasite. With the real time measurement, inhibition was observed immediately by a reduced heat flow compared to that in untreated control samples. The onset of drug action, the degree of inhibition and the time to death of the parasite culture could conveniently be monitored over several days. Microcalorimetry is a valuable element to be added to the toolbox for drug discovery for protozoal diseases such as human African trypanosomiasis and malaria. The method could probably be adapted to other protozoan parasites, especially those growing extracellularly.     

Determination of adipocyte size by computer image analysis

Methods that allow rapid and accurate determination of adipocyte size are important to studies of energy and glucose metabolism. The direct measurement of adipocyte size by microscopy is widely used, although the method is tedious and time consuming. Computer-assisted image analysis can overcome most of the disadvantages associated with this technique. We report a new method for determining adipocyte size by measuring the cross-sectional area of adipocytes with computer image analysis. This method allows a large number of adipocytes to be measured rapidly with computer hardware and software that are readily available.     

A High-throughput Method for Measurement of Glomerular Filtration Rate in Conscious Mice

The measurement of glomerular filtration rate (GFR) is the gold standard in kidney function assessment. Currently, investigators determine GFR by measuring the level of the endogenous biomarker creatinine or exogenously applied radioactive labeled inulin (³H or ¹⁴C). Creatinine has the substantial drawback that proximal tubular secretion accounts for ~50% of total renal creatinine excretion and therefore creatinine is not a reliable GFR marker. Depending on the experiment performed, inulin clearance can be determined by an intravenous single bolus injection or continuous infusion (intravenous or osmotic minipump). Both approaches require the collection of plasma or plasma and urine, respectively. Other drawbacks of radioactive labeled inulin include usage of isotopes, time consuming surgical preparation of the animals, and the requirement of a terminal experiment. Here we describe a method which uses a single bolus injection of fluorescein isothiocyanate-(FITC) labeled inulin and the measurement of its fluorescence in 1-2 μl of diluted plasma. By applying a two-compartment model, with 8 blood collections per mouse, it is possible to measure GFR in up to 24 mice per day using a special work-flow protocol. This method only requires brief isoflurane anesthesia with all the blood samples being collected in a non-restrained and awake mouse. Another advantage is that it is possible to follow mice over a period of several months and treatments (i.e. doing paired experiments with dietary changes or drug applications). We hope that this technique of measuring GFR is useful to other investigators studying mouse kidney function and will replace less accurate methods of estimating kidney function, such as plasma creatinine and blood urea nitrogen.     

High resolution deuterium NMR studies of bacterial metabolism

High resolution deuterium NMR spectra were obtained from suspensions of five bacterial strains: Escherichia coli, Clostridium perfringens, Klebsiella pneumoniae, Proteus mirabilis, and Staphylococcus aureus. Deuterium-labeled D-glucose at C-1, C-2, and C-6 was used to monitor dynamically anaerobic metabolism. The flux of glucose through the various bacterial metabolic pathways could be determined by following the disappearance of glucose and the appearance of the major end products in the 2H NMR spectrum. The presence of both labeled and unlabeled metabolites could be detected using 1H NMR spectroscopy since the proton resonances in the labeled species are shifted upfield due to an isotopic chemical shift effect. The 1H-1H scalar coupling observed in both the 2H and 1H NMR spectra was used to assign definitively the resonances of labeled species. An increase in the intensity of natural abundance deuterium signal of water can be used to monitor pathways in which a deuteron is lost from the labeled metabolite. The steps in which label loss can occur are outlined, and the influence these processes have on the ability of 2H NMR spectroscopy to monitor metabolism are assessed.     

Stable isotope methodology in the pharmacokinetic studies of androgenic steroids in humans

The use of stable isotopically labeled steroids combined with gas chromatography/mass spectrometry (GC/MS) has found a broad application in pharmacologic studies. Initially, stable isotopically labeled steroids served as the ideal analytic internal standard for GC/MS analysis; however, their in vivo use has expanded and has proven to be a powerful pharmacokinetic tool. We have successfully used stable isotope methodology to study the pharmacokinetic/bioavailability of androgens. The primary advantage of the technique is that endogenous and exogenous steroids with the same basic structure can be differentiated by using stable isotopically labeled analogs. The method was used to examine the pharmacokinetics of testosterone and testosterone propionate, and to clarify the influence of endogenous testosterone. Another advantage of the isotope methods is that steroidal drugs can be administered concomitantly in two formulations (e.g., solution and solid dosage). A single set of blood samples serves to describe the time course of the formulations being compared. This stable isotope coadministration technique was used to estimate the relative bioavailability of 17 alpha-methyltestosterone.     

Protein phosphorylation analysis by site-specific arginine-mimic labeling in gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Although recent advances in gel electrophoresis and mass spectrometry have greatly facilitated separation, purification, and identification of proteins, significant challenges remain in relation to phosphoprotein analysis. Here we introduce a powerful method for analysis of protein phosphorylation in which phosphorylation sites are labeled with guanidinoethanethiol (GET) by beta-elimination/Michael addition prior to proteolysis and mass spectrometry (MS) analysis. This technique is especially useful in conjunction with gel-based technology in that all of the processes involved, including GET labeling, washing, and phosphospecific enzymatic hydrolysis, can be carried out in excised gel slices, thereby minimizing sample loss and contamination. The novel GET tag, which has a highly basic guanidine group, increases the peak intensities for the GET-labeled tryptic peptides by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS. In addition, phosphospecific proteolytic cleavage occurs at guanidinoethylcysteine (Gec) residue, which is arginine-mimic formed by GET tagging of phosphorylated serine residues. Thus, GET tagging is especially useful in analysis of long tryptic phosphopeptides. To illustrate the utility of the in-gel GET tagging and digestion approach, we used it to precisely analyze the phosphorylation sites of human glutathione S-transferase P1 (GSTP1), an enzyme involved in phase II metabolism of many carcinogens and anticancer drugs. The in-gel GET tagging/digestion technique significantly enhances the analytical potential of gel electrophoresis/MS in studies of proteome phosphorylation.     

Simplified assay for lysyl oxidase activity.

A simplified method for the assay of lysyl oxidase activity was developed. The method is based on the measurement of tritiated water released by enzyme action from labeled protein-bound lysine and hydroxylysine. Trichloroacetic acid (TCA) supernates of the incubation mixtures are passed through small Dowex 50 (H⁺) columns and the effluents are counted. For rapid screening purposes an indication of the presence of enzyme activity in enzyme preparations can be obtained by measuring the radioactivity present in aliquots of the TCA supernates as such and by measuring the radioactivity after drying at 60°C, taking the difference between the two as a measurement of enzyme activity.     

Measurement of DNA damage in unlabeled mammalian cells analyzed by alkaline elution and a fluorometric DNA assay

A fluorometric procedure is described that can be used in the alkaline elution technique for the measurement of DNA damage in cells whose DNA is not, or cannot be, radioactively labeled. The procedure can be used for the measurement of DNA single-strand breaks, DNA-protein crosslinking, and DNA interstrand crosslinking, and possibly other DNA lesions produced in unlabeled cells. Although developed for the measurement of DNA damage in tissue-cultured cells, the technique is applicable to the measurement of DNA damage in cells isolated from tissues exposed to DNA damaging agents in vivo.     

Laser scanning cytometer-based assays for measuring host cell attachment and invasion by the human pathogen Toxoplasma gondii.

BACKGROUND: Toxoplasma gondii is among the most common protozoan parasites of humans. Both attachment to and invasion of host cells by T. gondii are necessary for infection, yet little is known about the molecular mechanisms underlying these processes. T. gondii's etiological importance and its role as a model organism for studying invasion in related parasites necessitate a means to quantitatively assay host cell attachment and invasion. METHODS: We present here Laser Scanning Cytometer (LSC)-based assays of T. gondii invasion and attachment. The invasion assay involves automated counting of invaded and non-invaded parasites, differentially labeled with distinct fluorochromes. The attachment assay compares the relative binding of differentially labeled parasites. The assays were evaluated using treatments known to decrease invasion or attachment. RESULTS: The LSC-based assays are robust and reproducible, remove operator bias, and significantly increase the sample size that can be feasibly counted compared to other currently available microscope-based methods. In the first application of the new assays, we have shown that parasites attach to fixed and unfixed host cells using different mechanisms. CONCLUSIONS: The LSC-based assays represent useful new methods for quantitatively measuring attachment and invasion by T. gondii, and can be readily adapted to study similar processes in other host-pathogen systems.     

Sensitivity enhancement in fluorescence correlation spectroscopy of multiple species using time-gated detection

Fluorescence correlation spectroscopy (FCS) is a powerful technique to measure chemical reaction rates and diffusion coefficients of molecules in thermal equilibrium. The capabilities of FCS can be enhanced by measuring the energy, polarization, or delay time between absorption and emission of the collected fluorescence photons in addition to their arrival times. This information can be used to change the relative intensities of multiple fluorescent species in FCS measurements and, thus, the amplitude of the intensity autocorrelation function. Here we demonstrate this strategy using lifetime gating in FCS experiments. Using pulsed laser excitation and laser-synchronized gating in the detection channel, we suppress photons emitted within a certain time interval after excitation. Three applications of the gating technique are presented: suppression of background fluorescence, simplification of FCS reaction studies, and investigation of lifetime heterogeneity of fluorescently labeled biomolecules. The usefulness of this technique for measuring forward and backward rates of protein fluctuations in equilibrium and for distinguishing between static and dynamic heterogeneity makes it a promising tool in the investigation of chemical reactions and conformational fluctuations in biomolecules.     

Fast axonal transport: Effect of antimitotic drugs and inhibitors of energy metabolism on the rate and amount of transported protein in frog sciatic nerves

Mitosis inhibitors, drugs affecting the energy metabolism, heavy water and ouabain were used to partially inhibit fast axonal transport in frog sciatic nerves. Effects on the rate and on the amount of pulse labeled protein could be separated. The pulse of labeled protein, released after a cold-block, rapidly reached a maximum height which indicated that the transport system was saturated in the nerve segment occupied by the pulse. Both the rate and the amount were reduced by the mitosis inhibitors colchicine, vinblastine, and griseofulvin. Colchicine had a differential effect and reduced the rate of material migrating in the advancing front of the pulse less than the rate of that moving in the peak. Preincubation at low temperature potentiated the effects of colchicine. Two inhibitors of energy metabolism, NaCN and IAA, reduced the amount of labeled material in the pulse. The slope of the pulse was markedly reduced and multiple peaks appeared. The distance covered by the migrating pulse was largely unaffected, but some retardation of late components might have occurred. In contrast, 2.4-DNP reduced the rate without any effects on the amount of migrating material. Heavy water uniformly reduced the rate of the migrating pulse, whereas the main effect of ouabain was a diminished amount and multiple peaks as with NaCN and IAA. All drugs were tested for their effects on the electrical activity of sciatic nerves. The compound action potential was not affected by the mitosis inhibitors and heavy water, but was depressed by the inhibitors of energy metabolism and abolished by ouabain. The results indicate that the effects of various transport inhibitory drugs can be differentiated if both the rate and the amount are considered.     

Imaging Barriers to Diffusion by Pair Correlation Functions

Molecular diffusion and transport are fundamental processes in physical, chemical, biochemical, and biological systems. However, current approaches to measure molecular transport in cells and tissues based on perturbation methods such as fluorescence recovery after photobleaching are invasive, fluctuation correlation methods are local, and single-particle tracking requires the observation of isolated particles for relatively long periods of time. We propose to detect molecular transport by measuring the time cross-correlation of fluctuations at a pair of locations in the sample. When the points are farther apart than two times the size of the point spread function, the maximum of the correlation is proportional to the average time a molecule takes to move from a specific location to another. We demonstrate the method by simulations, using beads in solution, and by measuring the diffusion of molecules in cellular membranes. The spatial pair cross-correlation method detects barriers to diffusion and heterogeneity of diffusion because the time of the correlation maximum is delayed in the presence of diffusion barriers. This noninvasive, sensitive technique follows the same molecule over a large area, thereby producing a map of molecular flow. It does not require isolated molecules, and thus many molecules can be labeled at the same time and within the point spread function.     

Quantitative analysis of mononucleotides by isotopic labeling surface-enhanced Raman scattering spectroscopy

A novel surface-enhanced Raman scattering (SERS) approach for accurate quantification of mononucleotides of deoxyribonucleic acid (DNA) is described. Reproducible SERS measurement was achieved by using isotopically labeled internal standard. By measuring the SERS spectra of mononucleotides and its isotope internal standard in combination with multivariate data analysis, the method was successfully applied to quantify mononucleotides. The independent validation of analyte concentrations gave a standard deviation of within 2%, which is comparable to HPLC result. Finally, a mixture of four mononucleotides of DNA was prepared to explore the possibility of quantifying the concentration of label-free, sequence-specific DNA strands by this approach. As compared to liquid chromatography/mass spectrometry (LC/MS), our method can be similarly precise but the SERS measurement is simple, rapid and potentially cheap.