Determination of vasoactive intestinal peptide in rat brain by high-performance capillary electrophoresis

Analytical methods for brain targeted delivery system in vivo: perspectives on imaging modalities and microdialysis

Since the introduction of microdialysis in 1974, the semi-invasive analytical method has grown exponentially. Microdialysis is one of the most potential analysis technologies of pharmacological drug delivery to the brain. In recent decades, analysis of chemicals targeting the brain has led to many improvements. It seems likely that fluorescence imaging was limited to ex vivo and in vitro applications with the exception of several intravital microscopy and photographic imaging approaches. X-ray computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) have been commonly utilized for visualization of distribution and therapeutic effects of drugs. The efficient analytical methods for studies of brain-targeting delivery system is a major challenge in detecting the disposition as well as the variances of the factors that regulate the substances delivery into the brain. In this review, we highlight some of the ongoing trends in imaging modalities and the most recent developments in the field of microdialysis of live animals and present insights into exploiting brain disease for therapeutic and diagnostics purpose.

Review of recent advances in analytical techniques for the determination of neurotransmitters

Methods and advances for monitoring neurotransmitters in vivo or for tissue analysis of neurotransmitters over the last five years are reviewed. The review is organized primarily by neurotransmitter type. Transmitter and related compounds may be monitored by either in vivo sampling coupled to analytical methods or implanted sensors. Sampling is primarily performed using microdialysis, but low-flow push-pull perfusion may offer advantages of spatial resolution while minimizing the tissue disruption associated with higher flow rates. Analytical techniques coupled to these sampling methods include liquid chromatography, capillary electrophoresis, enzyme assays, sensors, and mass spectrometry. Methods for the detection of amino acid, monoamine, neuropeptide, acetylcholine, nucleoside, and soluble gas neurotransmitters have been developed and improved upon. Advances in the speed and sensitivity of these methods have enabled improvements in temporal resolution and increased the number of compounds detectable. Similar advances have enabled improved detection at tissue samples, with a substantial emphasis on single cell and other small samples. Sensors provide excellent temporal and spatial resolution for in vivo monitoring. Advances in application to catecholamines, indoleamines, and amino acids have been prominent. Improvements in stability, sensitivity, and selectivity of the sensors have been of paramount interest.

Determination of binding constants of vasoactive intestinal peptide to poly(amidoamine) dendrimers designed for drug delivery using ACE

The purpose of the present paper was to study at physiological pH the affinity between vasoactive intestinal peptide (VIP) and four poly(amidoamine) dendrimers (PAMAMs) designed for drug delivery. Therefore, a fast and reproducible CE method was first developed to analyze the strongly basic peptide. To allow an accurate determination of binding constant (K) values, the ability to suppress peptide adsorption onto the silica capillary of nonpermanent coatings (poly(ethylene oxide) (PEO), low and medium relative molecular masses poly(diallyldimethylammonium chloride) (PDDA)) or poly(acrylamide) permanent coating (PAA) was evaluated. Very good intraday repeatability of VIP migration times and peak areas (0.1-0.6 and 2.9-4.9% RSD, respectively) was obtained using two of the investigated coatings (PEO and PDDA with medium molecular mass). ACE combined with these dynamic coatings was then employed to evaluate K between VIP and two amine-terminated PAMAM dendrimers of generation 2 and 5 (G2.NH2, G5.NH2) and two carboxyl-terminated PAMAM derivatives of generation 2 and 5 (G2.COOH, G5.COOH). Binding constant of (6.7 +/- 1.1) x 10(4)/M could be determined for the couple VIP/G5.NH2, while no affinity was evidenced between VIP and all other dendrimers investigated. These results suggest that G5.NH2 might be an interesting carrier for the delivery of VIP.

Separation and determination of enkephalin-related peptides using capillary electrophoresis

CZE with UV-absorption detection has been used for the separation and determination of enkephalin-related peptides. The experimental conditions, such as pH and concentration of running buffer, applied voltage, injection method, and time, were investigated in detail. Excellent separation efficiency could be obtained for ten enkephalin-related peptides with a 50 microm (ID) x 58 cm capillary using sodium dihydrogen phosphate as the running buffer (pH 3.11) when 20 kV of applied voltage was used. The concentration detection limits were found to be in the range of 0.31-1.94 microg/mL (defined as S/N = 3). The proposed method has been applied to analyze the spiked cerebrospinal fluid (CSF) sample, and the results showed that CZE is a powerful technique for separation and detection of the above biological peptides.

Recent advances in the application of capillary electrophoresis to neuroscience

With fast separation times (seconds to minutes), minimal sample requirements (nanoliters to femtoliters), and excellent mass detection limits (femtomole to zeptomole), capillary electrophoresis (CE) is ideally suited for in vitro and in vivo sampling of neurological samples with a high degree of spatial resolution. Advances in extracellular fluid analysis employing improved microdialysis and push-pull perfusion sampling methodologies has enabled the resolution of neurotransmitters present in limited amounts using CE. Great progress has been made to resolve complex neuropeptides, amino acids, and biogenic amines in tissue and cell cultures. Finally, owing largely to the small volume sampling abilities of CE, investigations of single nerve cells, both invertebrate and mammalian, have been accomplished. These applications of CE to the advancement of neuroscience are presented.

Analysis of compounds containing carboxyl groups in biological fluids by capillary electrophoresis

Capillary electrophoresis (CE) is one of the suitable separation techniques used to analyze drugs or metabolites in complicated sample matrices such as plasma, serum and urine. It sometimes requires only a simple process of sample pretreatment, deproteinization, dilution or extraction for biological fluids, otherwise no pretreatment is necessary. Various metabolic disorders concerning the compounds which possess carboxyl groups such as organic acids have been monitored by CE. Drug metabolism in the body can be monitored by the same technique. Recent publications suggest the feasibility of an automated system for diagnosis based on CE technique.

Behavior of peptides in capillary electrophoresis: effect of peptide charge, mass and structure

In the last decade the large potential of capillary electrophoresis as a technique for separation and characterization of peptides has been demonstrated extensively. In this field, a large number of chemical structures has to be taken into consideration, for which very often no data or even standards are available. As a result, there has been a strong desire to relate electrophoretic behavior to molecular properties and structure of the compounds. The activities in that direction, in the area of capillary zone electrophoresis, are critically reviewed. Special attention is paid to peptide charge, mass, hydrophobicity and structure, and their influence on the selectivity of the separation. Also, some complexation phenomena are discussed.

Development of a capillary zone electrophoresis assay to examine the disposition of [D-pen2,5]enkephalin in rats

A novel capillary zone electrophoresis (CZE) assay method was developed to evaluate the systemic disposition of [D-pen2,5]enkephalin (DPDPE) in rats. DPDPE was recovered from serum samples (200 microliters) by solid-phase extraction. Complete resolution of DPDPE and the internal standard ([D-ser2]leucine-enkephalin; DSLET) from other serum components was achieved within 15 min on a 50-microns I.D. capillary column with borate buffer (25 mM, pH 8.3). The peak-height ratio (DPDPE to DSLET) was linear through 100 micrograms/ml, with a detection limit of 250 ng/ml in serum, when absorbance of the column eluent was monitored at 210 nm. Serum samples obtained from rats after a 10 mg/kg intravenous bolus dose of DPDPE were analyzed with the present CZE method. The results suggest that CZE is a useful technique for quantitating therapeutic peptides in biological matrices.

Capillary zone electrophoresis and micellar electrokinetic chromatography, with taurodeoxycholate as micellar agent, of protein kinase A peptide substrates

The separation of protein kinase A peptide substrates with the general formula -X-Arg-Arg-Ala-Ser-Y-, where X and Y may be the same or different amino acids, was studied by capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC). Taurodeoxycholate (TDC) was used as the micellar agent. CZE was effective in separating a peptide series differing in the number of amino acids, but not for a series with a difference in the terminating amino acid. For the latter series, MEKC generally gave a higher selectivity, but some of the peptide pairs were more easily separated by CZE, demonstrating the complementary character of the two techniques. The efficiency of the MEKC system was typically < 50% of that of CZE, but its higher selectivity generally outbalanced the lower efficiency regarding resolution. The distribution of the peptides to the micelles was studied by determination of retention factors. Electrostatic and hydrophobic forces were found to be determining factors in the distribution; the most highly charged basic peptides were most heavily distributed, and for peptides with the same charge those containing more hydrophobic amino acids were more strongly distributed. The contribution of some structural features to the distribution degree was also determined.

Clinical and forensic applications of capillary electrophoresis

This survey is aimed at giving the readers a short overview of the present state of the art of clinical and forensic applications of capillary electrophoresis. First, the principles associated with electrokinetic capillary separations and instrumentation, sample preparation and solute quantitation are briefly discussed. This is followed by chapters describing the determination of endogenous and exogenous compounds in body fluids and tissue extracts. Finally, a survey of major achievements including reference to fully developed electrokinetic capillary assays is provided. The paper concludes with a brief outlook.

Detection of neurotensin in tissues by capillary zone electrophoresis

An electrophoretic method for detecting neurotensin in tissues was developed. Homogenates of rat duodenum and adrenal glands were first extracted by solid-phase extraction and purified by reversed-phase high-performance liquid chromatography. The neurotensin-rich fraction was further analyzed by capillary zone electrophoresis (CZE) using a commercial instrument with UV detection. A minor peak was detected as neurotensin and its identity was further confirmed by performing several CZE analyses at different pH values. Such an approach could be used to analyze with good molecular specificity the neuropeptides in some human tissues.

Characterization of metallothionein isoforms. Comparison of capillary zone electrophoresis with reversed-phase high-performance liquid chromatography

The purpose of this study was to compare and contrast the separation of metallothionein (MT) isoforms by reversed-phase high-performance liquid chromatography (RP-HPLC) with capillary zone electrophoresis (CZE). RP-HPLC was performed on a Vydac C8 column eluted with a linear acetonitrile gradient. CZE was performed in a 57 cm x 75 microns I.D. fused-silica tube at an operating voltage of 30 kV. Phosphate buffer (10 mM) at pH 2.5, 7.0 and 11.0 was used for both separations. CZE at pH 2.5 resolved three distinct peaks of rabbit liver MT which were incompletely resolved at pH 7.0 or 11.0. RP-HPLC at pH 2.5 gave two peaks and the resolution was not as good as with CZE at the same pH. At pH 7.0 or 11.0, RP-HPLC of rabbit liver MT gave a single predominant peak of unresolved MT-1 and MT-2. Purified rabbit liver MT-1 and MT-2 were used to verify the identity of these peaks. In contrast, MT from horse kidney demonstrated three predominant peaks which were best resolved by CZE at pH 11.0, whereas RP-HPLC resolved only two peaks at pH 11.0 and 7.0. At pH 2.5, RP-HPLC of horse kidney MT gave three peaks, though two of the peaks were incompletely separated. We conclude that pH has a considerable impact on the resolution of MT isoforms by CZE and RP-HPLC and that it is possible to exploit changes in pH to optimize the separation of isoforms for a particular species of MT. When samples of human and sheep liver MT-1, both of which exhibit microheterogeneity, were subjected to CZE, a single predominant peak was observed at each pH value. RP-HPLC of human liver MT-1 at pH 2.5 yielded two peaks that were incompletely resolved. Purified chick liver MT and rat liver MT-1 and MT-2 gave a single predominant peak at all pH values on CZE. In contrast, pig liver MT-1 and MT-2 each exhibited multiple peaks when subjected to CZE, the number of which depended on the pH used to separate the MT. In conclusion, CZE, with its orthogonal selectivity, and RP-HPLC make an excellent combination for the separation and characterization of MT isoforms. Because CZE is rapid (run times typically < 10 min) and requires little sample (< 100 nl), MT samples can readily be analyzed by CZE in conjunction with RP-HPLC or other techniques in order to maximize the information obtained about the individual isoforms.