Microdialysis-immunoaffinity capillary electrophoresis studies on neuropeptide-induced lymphocyte secretion

Capillary electrophoresis-based immunoassay and aptamer assay: A review

Over the last two decades, the group of techniques called affinity probe CE has been widely used for the detection and the determination of several types of biomolecules with high sensitivity. These techniques combine the low sample consumption and high separation power of CE with the selectivity of the probe to the target molecule. The assays can be defined according to the type of probe used: CE immunoassays, with an antibody as the probe, or aptamer-based CE, with an aptamer as the probe. Immunoassays are generally divided into homogeneous and heterogeneous groups, and homogeneous variant can be further performed in competitive or noncompetitive formats. Interacting partners are free in solution at homogeneous assay, as opposed to heterogeneous analyses, where one of them is immobilized onto a solid support. Highly sensitive fluorescence, chemiluminescence or electrochemical detections were typically used in this type of study. The use of the aptamers as probes has several advantages over antibodies such as shorter generation time, higher thermal stability, lower price, and lower variability. The aptamer-based CE technique was in practice utilized for the determination of proteins in biological fluids and environmentally or clinically important small molecules. Both techniques were also transferred to microchip. This review is focused on theoretical principles of these techniques and a summary of their applications in research.

Cytokine analysis by immunoaffinity capillary electrophoresis

Immunoaffinity capillary electrophoresis (ICE) is a powerful tool used to detect and quantify target proteins of interest in complex biological fluids. The target analyte is captured and bound to antibodies immobilized onto the wall of a capillary, labeled in situ with a fluorescent dye, eluted and detected online using laser-induced fluorescence following electrophoretic separation. Here, we illustrate how to construct an immunoaffinity capillary and utilize it to run ICE in order to capture and quantify target cytokines and chemokines from a clinical sample.

Analysis of neurotrophins in human serum by immunoaffinity capillary electrophoresis (ICE) following traumatic head injury

Neurotrophins, including brain-derived neurotrophic factor (BDNF), ciliary neurotrophic factor (CNTF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), and beta-nerve growth factor (beta-NGF), play an active role in the development, maintenance and survival of cells of the central nervous system (CNS). Previous research has indicated that a decrease in concentrations of these neurotrophins is often associated with cell death and ultimately patient demise. However, much of the research conducted analyses of samples taken directly from the CNS, i.e., of samples that are not readily available in clinical trauma centers. In an attempt to obtain a method for evaluating neurotrophins in a more readily accessible matrix, i.e., serum, a precise and accurate immunoaffinity capillary electrophoresis (ICE) method was developed and applied to measure neurotrophins in serum from patients with various degrees of head injury. The five neurotrophins of interest were extracted and concentrated by specific immunochemically immobilized antibodies, bound directly to the capillary wall, and eluted and separated in approximately 10min. NT-3, BDNF, CNTF and beta-NGF showed a marked decrease in concentration as the severity of the head injury increased: mild versus severe: 91% decrease for NT-3; 93 % decrease for BDNF; 93 % decrease for CNTF; and a 87 % decrease for beta-NGF. This decrease in concentration is consistent with the neuro-protective roles that neurotrophins play in the maintenance and survival of neuronal cells. The results obtained by the ICE method were closely comparable with those generated by a commercially available ELISA method.

Application of immunoaffinity capillary electrophoresis to the measurements of secreted cytokines by cultured astrocytes

The ability of the central nervous system (CNS) to act in conjunction with the immune system has been of great interest to both neurobiologists and immunologists. Previous studies have shown that astrocytes can be stimulated, by various peptides, to act as immune regulators within the CNS and release cytokines and chemokines. However, the regulatory mechanism of astrocytes is still poorly understood. Our present study describes a micro-device capable of monitoring the growth and stimulation of 20 astrocytes by vasoactive intestinal peptide. A microdialysis needle was used to collect the secretion by products, which were analyzed by immunoaffinity capillary electrophoresis (ICE) for the secretion of pro-inflammatory cytokines, IL-1alpha, IL-1beta, IL-6, and tumor necrosis factor (TNF)-alpha; hemopoietic cytokines, IL-3, granulocyte colony-stimulating factor (G-CSF), macrophage colony-stimulating factor (M-CSF), granulocyte/macrophage colony-stimulating factor (GM-CSF); and chemokines; regulated upon activation normal T-cell expression sequence (RANTES), macrophage inflammatory protein (MIP)-1alpha and MIP-1beta. Vasoactive intestinal peptide stimulated astrocytes showed an almost immediate release of pro-inflammatory cytokines and chemokines, with an increase over baseline ranging from 3 to 15 fold, while no substantial increase over baseline was observed for hemopoietic cytokines. This system demonstrates the ability to isolate individual cells in a closely controlled environment and identify and quantify their analytes.

Immunoaffinity capillary electrophoresis as a powerful strategy for the quantification of low-abundance biomarkers, drugs, and metabolites in biological matrices

In the last few years, there has been a greater appreciation by the scientific community of how separation science has contributed to the advancement of biomedical research. Despite past contributions in facilitating several biomedical breakthroughs, separation sciences still urgently need the development of improved methods for the separation and detection of biological and chemical substances. In particular, the challenging task of quantifying small molecules and biomolecules, found in low abundance in complex matrices (e.g., serum), is a particular area in need of new high-efficiency techniques. The tandem or on-line coupling of highly selective antibody capture agents with the high-resolving power of CE is being recognized as a powerful analytical tool for the enrichment and quantification of ultra-low abundance analytes in complex matrices. This development will have a significant impact on the identification and characterization of many putative biomarkers and on biomedical research in general. Immunoaffinity CE (IACE) technology is rapidly emerging as the most promising method for the analysis of low-abundance biomarkers; its power comes from a three-step procedure: (i) bioselective adsorption and (ii) subsequent recovery of compounds from an immobilized affinity ligand followed by (iii) separation of the enriched compounds. This technology is highly suited to automation and can be engineered to as a multiplex instrument capable of routinely performing hundreds of assays per day. Furthermore, a significant enhancement in sensitivity can be achieved for the purified and enriched affinity targeted analytes. Thus, a compound that exists in a complex biological matrix at a concentration far below its LOD is easily brought to well within its range of quantification. The present review summarizes several applications of IACE, as well as a chronological description of the improvements made in the fabrication of the analyte concentrator-microreactor device leading to the development of a multidimensional biomarker analyzer.

Microscale immunoaffinity SPE and MEKC in fast determination of testosterone in male urine

Conventional methods for the determination of testosterone in body fluids typically suffer from poor recovery, lack of specificity, complex sample pretreatment, or the need for derivatization. Here, a simple, specific, and fast analysis method for testosterone was developed, with a methodology based on testosterone-specific immunoaffinity SPE (IA-SPE) and subsequent analysis by partial filling MEKC (PF-MEKC). An immunosorbent consisting of a recombinant antitestosterone Fab fragment covalently attached to activated Sepharose was prepared. IA-SPE and PF-MEKC were set up in hyphenated and off-line constructions, and the applicability of the two constructions in analysis of testosterone in male urine was investigated. The results obtained with the hyphenated construction proved to be only indicative of the presence of testosterone. The off-line IA-SPE and PF-MEKC construction, however, was successfully used in the determination of free testosterone in male urine samples after enzymatic hydrolysis of the glucuronide conjugates. Except for the hydrolysis reaction, no sample pretreatment was required. After hydrolysis, the overall analysis time per sample was only 14 min. The off-line IA-SPE and PF-MEKC method proved to be robust, sensitive (LOQ 35 mug/L), and specific, enabling separation of testosterone from four related steroids. Thus, it provides attractive features when compared to traditional methods for determination of testosterone in male urine.

Immunoaffinity CE in clinical analysis of body fluids and tissues

This paper reviews immunoaffinity CE procedures developed since 1998 for drug, hormone, and disease marker analyses of body fluids and tissues. Immunoaffinity CE and related techniques are described. Examples of clinical applications are included.

Microdialysis for monitoring inflammation: efficient recovery of cytokines and anaphylotoxins provided optimal catheter pore size and fluid velocity conditions

Microdialysis emerges as a useful tool to evaluate tissue inflammation in a number of clinical conditions, like sepsis and transplant rejection, but systematic methodological studies are missing. This study was undertaken to determine the recovery of relevant inflammatory mediators using the microdialysis system, comparing microdialysis membranes with two different molecular weight cut-offs at different flow rates. Twenty and 100 kDa pore sizes CMA microdialysis catheters were investigated using velocities of 0.3, 1.0 and 5.0 microl/min. Reference preparations for cytokines [tumour necrosis factor (TNF)-alpha, interleukin (IL)-1beta, IL-6 and IL-10; m.w. 17-28 kDa] and chemokines (IL-8, MCP-1, IP-10 and MIG; m.w. 7-11 kDa) were prepared from plasma after incubating human whole blood with lipopolysaccharide. Reference preparation for complement anaphylatoxins (C3a, C4a, C5a; m.w. 9-11 kDa) was prepared by incubating human plasma with heat-aggregated immunoglobulin G. The reference preparations were quantified for the respective inflammatory molecules and used as medium for the microdialysis procedure. Through the 20 kDa filter only the four chemokines passed, but with low recovery (3-7%) and limited to the 1.0 microl/min velocity. The recovery with the 100 kDa filter was as follows: IL-1beta = 75%, MCP-1 = 55%, MIG = 50%, IL-8 = 38%, C4a = 28%, IP-10 = 22%, C5a = 20%, C3a = 16%, IL-6 = 11, IL-10 = 8% and TNF-alpha = 4%. The highest recovery for all chemokines and anaphylatoxins were consistently at velocity 1.0 microl/min, whereas IL-1beta and IL-10 recovered most efficiently at 0.3 microl/min. Thus, microdialysis using catheters with a cut-off of 100 kDa is a reliable method to detect inflammation as judged by a defined panel of inflammatory markers. These findings may have important implications for future clinical studies.

Multiplexed cytokine detection in microliter microdialysis samples obtained from activated cultured macrophages

Microdialysis sampling probes were used to collect cytokine samples from lipopolysaccharide (LPS)-stimulated macrophages. The probes were immersed into cell culture wells containing either RAW 264.7 or isolated peritoneal macrophages. Dialysates (15 microL) from these wells were subjected to a multiplexed cytokine sandwich immunoassay platform analyzed by flow cytometry that measures up to six separate cytokines, interleukin-6 (IL-6), interleukin-10 (IL-10), interleukin-12p70 (IL-12p70), interferon-gamma (IFN-gamma), macrophage chemoattractant protein-1 (MCP-1), and tumor necrosis factor-alpha (TNF-alpha) in a single 15-muL sample. In vitro microdialysis sampling relative recovery experiments showed that only IFN-gamma, IL-6, MCP-1, and TNF-alpha could be recovered across a commercially-available 100-kDa MWCO microdialysis membrane. Eleven hours after LPS addition (1 microg/mL), RAW 264.7 macrophages secreted greater than 8000 pg/mL of TNF-alpha and greater than 1000 pg/mL MCP-1. With the peritoneal macrophages, greater than 6000 pg/mL of IL-6, MCP-1, and TNF-alpha were obtained. The maximum dialysate concentrations obtained from the RAW macrophages were 1300 pg/mL for TNF-alpha and 55 pg/mL for MCP-1. Maximum cytokine concentrations from peritoneal macrophage dialysates reached approximately 2000 pg/mL, 1100 pg/mL and 500 pg/mL for TNF-alpha, MCP-1 and IL-6, respectively. Microdialysis sampling allowed for 20-min samples to be collected during the cytokine release from the activated macrophages. These results demonstrate that microdialysis sampling can be used for collection of selected cytokines with improved temporal resolution.

In vivo microdialysis sampling of cytokines produced in mice given bacterial lipopolysaccharide

Cytokines are proteins that mediate communication between cells of the immune system as well as certain other non-immune host cells. These proteins are produced by many cell types and they mediate immune and inflammatory responses. However, the direct site analysis of these critical proteins is hampered by the lack of site-specific tools available for such direct measurements. In this study, both in vitro and in vivo microdialysis sampling of different cytokines (tumor necrosis factor-alpha [TNF-alpha], interferon-gamma [IFN-gamma], interleukin-6 [IL-6], IL-12p70, and macrophage chemoattractant protein-1 [MCP-1]) was performed. A mouse model of bacterial lipopolysaccharide (LPS) administration and response pattern was used for in vivo studies. Three cytokines, TNF-alpha, IL-6, and MCP-1 were quantified in the serum from mice given LPS. In vivo studies demonstrated the ability to monitor increasing levels of these cytokines (TNF-alpha, IL-6, and MCP-1) via microdialysis probes placed in the peritoneal cavity of mice given LPS. All three cytokines were quantified simultaneously in 15 muL of dialysate using a multiplexed bead-based immunoassay for flow cytometry. The detected dialysate cytokine concentrations varied between 200 pg/mL and 1500 pg/mL for TNF-alpha, between 600 pg/mL and 3000 pg/mL for MCP-1, and between 2700 pg/mL and more than 5000 pg/mL for IL-6. The detected serum cytokine concentrations ranged from 5700 pg/mL to 35,000 pg/mL for TNF-alpha, from 40,000 pg/mL to 65,000 pg/mL for MCP-1, and greater than than 100,000 pg/mL for IL-6. This work demonstrates that microdialysis sampling can be used in vivo to collect temporal profiles of cytokine production.

Immunoaffinity solid-phase extraction for pharmaceutical and biomedical trace-analysis—coupling with HPLC and CE—perspectives

Immunoaffinity solid-phase extraction (SPE) technique is based upon a molecular recognition mechanism. The high affinity and the high selectivity of the antigen-antibody interactions allow the specific extraction and the concentration of the analytes of interest in one step. In pharmaceutical and biological fields, where most often matrices are complex and analytes at trace-levels, this approach constitutes a unique tool for fast and solvent-free sample preparation. This review presents a general description of this extraction technique and gives numerous examples of its applications in pharmaceutical and biomedical fields. It emphasizes the on-line coupling with chromatographic and electrophoretic separation techniques and introduces new developments. The future directions, especially with regards to the current development of analytical microsystems, are discussed.

Dietary magnesium intake influences circulating pro-inflammatory neuropeptide levels and loss of myocardial tolerance to postischemic stress

Severe dietary Mg restriction (Mg(9), 9% of recommended daily allowance [RDA], plasma Mg = 0.25 mM) induces a pro-inflammatory neurogenic response in rats (substance P [SP]), and the associated increases in oxidative stress in vivo and cardiac susceptibility to ischemia/reperfusion (I/R) injury were previously shown to be attenuated by SP receptor blockade and antioxidant treatment. The present study assessed if less severe dietary Mg restriction modulates the extent of both the neurogenic/oxidative responses in vivo and I/R injury in vitro. Male Sprague-Dawley rats maintained on Mg(40) (40% RDA, plasma Mg = 0.6 mM) or Mg(100) (100% RDA, plasma Mg = 0.8 mM) diets were assessed for plasma SP levels (CHEM-ELISA) during the first 3 weeks and were compared with the Mg(9) group; red blood cell (RBC) glutathione and plasma malondialdehyde levels were compared at 3 weeks in Mg(9), Mg(20) (plasma Mg = 0.4 mM), Mg(40), and Mg(100) rats; and 40-min global ischemia/30-min reperfusion hearts from 7-week-old Mg(20), Mg(40), and Mg(100) rats were compared with respect to functional recovery (cardiac work, and diastolic, systolic, and developed pressures), tissue LDH release, and free radical production (ESR spectroscopy and alpha-phenyl-N-tert butylnitrone [PBN; 3 mM] spin trapping). The Mg(40) diet induced smaller elevations in plasma SP (50% lower) compared with Mg(9), but with a nearly identical time course. RBC glutathione and plasma malondialdehyde levels revealed a direct relationship between the severity of oxidative stress and hypomagnesemia. The dominant lipid free radical species detected in all I/R groups was the alkoxyl radical (PBN/alkoxyl: alpha(H) = 1.93 G, alpha(N) = 13.63 G); however, Mg(40) and Mg(20) hearts exhibited 2.7- and 3.9-fold higher alkoxyl levels, 40% and 65% greater LDH release, and lower functional recovery (Mg(20) < Mg(40)) compared with Mg(100). Our data suggest that varying dietary Mg intake directly influences the magnitude of the neurogenic/oxidative responses in vivo and the resultant myocardial tolerance to I/R stress.

Specific up-regulation of CRH or AVP secretion by acetylcholine or lipopolysaccharide in inflammatory susceptible Lewis rat fetal hypothalamic cells

Lewis (LEW/N) rats, compared to Fischer (F344/N) rats, are susceptible to inflammatory/autoimmune diseases, in part, as a result of their blunted hypothalamic-pituitary-adrenal (HPA) axis responses. We examined regulation of LEW/N and F344/N fetal hypothalamic cell secretion of corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP), two major HPA axis mediators, by inflammatory and neurotransmitter stimuli. Interleukin-1beta (IL-1beta), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha), and protein kinase A (PKA) and protein kinase C (PKC) activators did not affect LEW/N basal secretion. Compared to F344/N, LEW/N cells were hyporesponsive to lipopolysaccharide (LPS), serotonin (5-HT), and acetylcholine chloride (ACh). However, LPS-induced AVP release and ACh-evoked CRH secretion in LEW/N were comparable with those of F344/N. Our findings suggest that the blunted LEW/N neuropeptide response was more likely related to components of second messenger systems, rather than to any one specific stimulus.

Analysis of single-cell cultures by immunoaffinity capillary electrophoresis with laser-induced fluorescence detection

Neuropeptide regulation of immunological activity is becoming an important issue in both basic and clinical sciences, necessitating the need for analysis to be performed at the single-cell level. A microsampling procedure has been developed for studying secretion of biologically important peptides from neuropeptide-stimulated lymphocytes, based on microdialysis sampling coupled to immunoaffinity capillary electrophoresis (ICE), with laser-induced fluorescence (LIF) detection using a fibre-optic spectrometer and diode laser excitation. The system demonstrated a limit of detection in the high attomole (10(-18) mol/L) range with pure standards and was capable of monitoring secretion from a single cell over time. Using this system it was possible to differentiate the effects of four neuropeptides on both T and B cell release of regulatory cytokines. CD4(+) lymphocytes demonstrated a 7.5-fold increase in cytokine secretion over baseline following stimulation with substance P (SP) and calcitonin gene-related peptide (CGRP). B cells responded to CGRP and vasoactive intestinal peptide (VIP) stimulation (5.5-fold increase), but not to SP. These changes took place 12--20 h post-stimulation and, once the peak secretion had been reached, remained at that level for the duration of the experiment. This system demonstrates the ability to perform high sensitivity measurements on microsamples of biological fluids.

Transient isotachophoresis for sensitivity enhancement in capillary electrophoresis-mass spectrometry for peptide analysis

Transient isotachophoresic (ITP) focusing was used for the on-line analysis of peptides by capillary zone electrophoresis-mass spectrometry (CZE-MS), allowing injection volumes of up to 0.9 microL. A sheath liquid electrospray interface was used with a single quadrupole mass analyzer. First, the technique was applied to the qualitative analysis of a tryptic digest of cytochrome c, resulting in low-background, high-quality spectra. Second, the linear range was investigated by selected ion monitoring (SIM) for a peptidomimetic direct thrombin inhibitor melagatran (Mr 429.5) and two endogenous peptides, substance P (Mr 1348) and calcitonin gene-related peptide (alpha-CGRP; Mr 3806).

In vivo microdialysis sampling: theory and applications

During the last two decades, a number of methods have been developed for in vivo collection, separation and characterization of biological samples and analytes. The capability and reliability of the microdialysis technique for measuring endogenous substances (such as neurotransmitters and their metabolites) as well as exogenous therapeutic agents in various tissue systems have brought it to the forefront of the in vivo tissue sampling methods. The usability of this technique is demonstrated by its application as reported in almost 3600 scientific papers (as of January 1998). This paper describes the general aspects and various applications of this fast growing technique. Emphasis has been given to analytical considerations with regards to microdialysis probe recovery and newer HPLC techniques.

Analysis of recombinant cytokines in human body fluids by immunoaffinity capillary electrophoresis

An immunoaffinity capillary electrophoresis (ICE) system for rapidly quantifying recombinant cytokines in human body fluids has been developed. Cytokines within biological fluids were labeled with a red light emitting fluorochrome and injected into the capillary. Selected cytokines were captured by immobilized antibodies on the internal surface of the capillary, and held while unbound materials were purged. The cytokines were then eluted electrophoretically in acidic buffer. Individual cytokine peaks were detected by on-line laser-induced fluorescence detection coupled to a computerized fiber-optic spectrometer, and analyzed by integration of the eluted peaks. The comparison of the results of ICE to routine assays used for these cytokines demonstrates that ICE provides a fast and accurate procedure for defining these cytokines in complex biological samples. Immunoaffinity separations can be used for any material to which a specific antibody can be raised, making this procedure applicable to a wide range of molecules of biomedical interest.

Assessment of pharmacodynamic and pharmacokinetic characteristics of drugs using microdialysis sampling and capillary electrophoresis

Microdialysis sampling combined with capillary electrophoresis is emerging as a new approach in drug studies. It allows the continuous monitoring, in vivo or in vitro, of changes in free endogenous compounds as well as in drug substances, following the administration of pharmacological agents. The low volume requirement of capillary electrophoresis for injection allows the collection of dialysates during short sampling times, leading to a precise temporal description of drug-induced biochemical changes or pharmacokinetics. Various protocols can be used for analyzing endogenous compounds and drug substances in microdialysis samples. Capillary electrophoresis with laser-induced fluorescence detection often affords the high sensitivity level which is needed in most studies. Furthermore, the direct on-line coupling of microdialysis, derivatization of samples, and electrophoretic analysis now brings a separation-based biosensor, allowing a real-time description of chemical events with a high molecular specificity. Microdialysis sampling combined with capillary electrophoresis has recently been used to assess pharmacodynamic and pharmacokinetic characteristics of various drugs in animal studies; it may also represent a new approach in clinical pharmacology in the near future.

Neonatal cytokines and coagulation factors in children with cerebral palsy

We explored the association of inflammatory mediators and markers of autoimmune and coagulation disorders with cerebral palsy (CP), examining 53 analytes in dried neonatal blood of 31 children with spastic CP, most born at term, and 65 control children. Ultramicroanalysis was performed by recycling immunoaffinity chromatography coupled with laser-enhanced fluorescence and chemiluminescence detection. Reactive antibodies to lupus anticoagulant, anticardiolipin, antithrombin III, and the translational product of the factor V Leiden mutation were isolated by recycling immunoaffinity chromatography and measured by capillary electrophoresis with chemiluminescence-enhanced immunoassay. Higher concentrations of interleukins (ILs) 1, 8, 9, tumor necrosis factor-alpha, and RANTES were observed in these children with CP than in any control child. There were also substantial elevations of IL-6, 11, 13, and other chemokines and colony-stimulating factors in children with CP. Antiphospholipid antibody was present in a titer of 1:100 or greater in 4 children with CP and no control child. Using cuts empirically chosen by recursive partitioning, we found higher concentrations of antibody to antithrombin III, to a translational product of factor V Leiden mutation, and to proteins C and S in children with CP than in controls. We conclude that inflammation and these coagulation abnormalities, which have interacting pathways, are important in the etiology of CP.

Recycling immunoaffinity chromatography for multiple analyte analysis in biological samples

The ability to isolate and measure multiple complex analytes in a single biological sample holds great potential in many biomedical fields, especially immunology and diagnostic clinical chemistry. We have developed a procedure involving recycling immunoaffinity chromatography for the simultaneous measurement of a number of analytes in a single sample. The procedure is based on the passage of a fluorochrome-labelled sample through a battery of small immunoaffinity columns, each column extracting a single analyte. Detection is achieved by acid elution of the bound analytes and laser-induced fluorescence. We have applied this system to a number of different biological fluids and found that it is capable of reliably isolating and measuring up to ten different cytokines in a 25-microl sample of human body fluid.