Capillary electrophoresis with contactless conductivity detection for the determination of carnitine and acylcarnitines in clinical samples

Application of capillary electrophoresis with capacitively contactless conductivity detection for biomedical analysis

The coupling of capillary electrophoresis (CE) with capacitively coupled contactless conductivity detection (C4 D) has become convenient analytical method for determination of small molecules that do not possess chromogenic or fluorogenic group. The implementations of CE with C4 D in the determination of inorganic and organic ions and amino acids in biomedical field are demonstrated. Attention on background electrolyte composition, sample treatment procedures, and the utilize of multi-detection systems are described. A number of tables summarizing highly developed CE-C4 D methods and the figures of merit attained are involved. Lastly, concluding remarks and perspectives are argued.

Green synthesis of naphthyl derivative as an optical sensor for the detection of l-carnitine in food samples

An economical and green approach to the synthesis of naphthyl derivative for detection of l-carnitine (3-hydroxy-4-N-trimethyl-aminobutyrate) is practically important. We developed a naphthyl derivative as a probe showing 'turn-on' response towards l-carnitine selectively at pH 7.2 through ICT mechanism with a good limit of detection (LOD) of 0.126 μM. Using Job's plot for determining the binding stoichiometry, it was found that probe could form a more stable complex (1:1) with carnitine. The binding constant (K) between probe and carnitine was calculated as 8 × 10⁷  M^-1 using the Benesi-Hildebrand plot. The binding interaction of the probe with l-carnitine was confirmed by nuclear magnetic resonance titrations, Fourier-transform infrared spectroscopy, photo physical studies and density functional theory calculations. Meanwhile, the probe can be used to quantitatively detect carnitine in food samples.

Laboratory analysis of acylcarnitines, 2020 update: a technical standard of the American College of Medical Genetics and Genomics (ACMG)

Acylcarnitine analysis is a useful test for identifying patients with inborn errors of mitochondrial fatty acid β-oxidation and certain organic acidemias. Plasma is routinely used in the diagnostic workup of symptomatic patients. Urine analysis of targeted acylcarnitine species may be helpful in the diagnosis of glutaric acidemia type I and other disorders in which polar acylcarnitine species accumulate. For newborn screening applications, dried blood spot acylcarnitine analysis can be performed as a multiplex assay with other analytes, including amino acids, succinylacetone, guanidinoacetate, creatine, and lysophosphatidylcholines. Tandem mass spectrometric methodology, established more than 30 years ago, remains a valid approach for acylcarnitine analysis. The method involves flow-injection analysis of esterified or underivatized acylcarnitines species and detection using a precursor-ion scan. Alternative methods utilize liquid chromatographic separation of isomeric and isobaric species and/or detection by selected reaction monitoring. These technical standards were developed as a resource for diagnostic laboratory practices in acylcarnitine analysis, interpretation, and reporting.

Function, Detection and Alteration of Acylcarnitine Metabolism in Hepatocellular Carcinoma

Acylcarnitines play an essential role in regulating the balance of intracellular sugar and lipid metabolism. They serve as carriers to transport activated long-chain fatty acids into mitochondria for β-oxidation as a major source of energy for cell activities. The liver is the most important organ for endogenous carnitine synthesis and metabolism. Hepatocellular carcinoma (HCC), a primary malignancy of the live with poor prognosis, may strongly influence the level of acylcarnitines. In this paper, the function, detection and alteration of acylcarnitine metabolism in HCC were briefly reviewed. An overview was provided to introduce the metabolic roles of acylcarnitines involved in fatty acid β-oxidation. Then different analytical platforms and methodologies were also briefly summarised. The relationship between HCC and acylcarnitine metabolism was described. Many of the studies reported that short, medium and long-chain acylcarnitines were altered in HCC patients. These findings presented current evidence in support of acylcarnitines as new candidate biomarkers for studies on the pathogenesis and development of HCC. Finally we discussed the challenges and perspectives of exploiting acylcarnitine metabolism and its related metabolic pathways as a target for HCC diagnosis and prognosis.

Dynamic monitoring of plasma amino acids and carnitine during chemotherapy of patients with alimentary canal malignancies and its clinical value

OBJECTIVE

The aim of this study was to observe the plasma amino acid and carnitine characteristics in patients with metastatic gastrointestinal malignancies during chemotherapy and to identify markers for the early diagnosis and evaluation of adverse reactions and prognosis of the digestive tract malignant tumor patients.

METHODS

Blood samples of 30 patients with metastatic gastrointestinal malignancies were collected at four time points: before chemotherapy, the first day after chemotherapy (+1 day), bone marrow depression period (+14 days), and hematopoietic recovery period (+21 days). The plasma amino acids and carnitine from those 30 patients were determined by high-performance liquid chromatography-tandem mass spectrometry method. Simultaneously, the levels of 21 amino acids were detected in 30 healthy individuals, who were considered as control. Biochemical indexes were also detected at four time points, adverse reactions were recorded during the chemotherapy process, and patients were followed up for 1 year to observe time to progression (TTP) and progression-free survival (PFS).

RESULTS

Compared to healthy people in the control group, patients with malignancies showed significantly increased levels of plasma amino acids such as Arg, Asp, Cit, Gly, Orn, Tyr, Val, and carnitine (such as C2). The levels of compounds such as C3, Asn, Leu, Lys, Pip, Pro, C0, C5:1 decreased significantly before chemotherapy. The levels of Cit, Cys, Lys, Pro, Tyr, Val, C0, and C2 decreased significantly on the second day of chemotherapy (+1 day), whereas the level of C3 increased significantly. During myelosuppression (+14 days), the levels of Asp, Cit, Met, and Orn were observed to still decrease significantly, whereas the level of Val appeared to increase significantly. The levels of Asp, Glu, and Met were clearly different among patients with gastric carcinoma, rectal cancer, and colon cancer. Compared to the control group, aspartate amino transferase and alanine aminotransferase were found to be higher in eight patients with hypocarnitinemia, yet TTP, PFS, and RR (response rate) were lower. No significant difference was observed for adverse reactions. The indexes in 12 patients with citrullinemia showed no difference compared with control group. All the results showed statistically significant differences (P<0.05).

CONCLUSION

Real-time monitoring of plasma amino acids and carnitine in patients with metastatic gastrointestinal malignancies can directly reflect the body's metabolism and nutritional status. The results provide a reference for nutrition therapy or support for patients with alimentary canal malignancies. Hypocarnitinemia is a risk factor for gastrointestinal cancer patients and affects TTP, PFS, and RR by liver function. This study shows that tandem mass spectrometry can be used to detect blood amino acids and carnitine spectrum may be used for an early diagnosis and evaluation of adverse reactions and prognosis of the digestive tract malignant tumor patients.

Micro-injector for capillary electrophoresis

A novel micro-injector for capillary electrophoresis for the handling of samples with volumes down to as little as 300 nL was designed and built in our laboratory for analyses in which the available volume is a limitation. The sample is placed into a small cavity located directly in front of the separation capillary, and the injection is then carried out automatically by controlled pressurization of the chamber with compressed air. The system also allows automated flushing of the injection chamber as well as of the capillary. In a trial with a capillary electrophoresis system with contactless conductivity detector, employing a capillary of 25 μm diameter, the results showed good stability of migration times and peak areas. To illustrate the technique, the fast separation of five inorganic cations (Na(+) , K(+) , NH4 (+) , Ca(2+) , and Mg(2+) ) was set up. This could be achieved in less than 3 min, with good limits of detection (10 μM) and linear ranges (between about 10 and 1000 μM). The system was demonstrated for the determination of the inorganic cations in porewater samples of a lake sediment core.

Single-breath analysis using a novel simple sampler and capillary electrophoresis with contactless conductometric detection

The analysis of ionic content of exhaled breath condensate (EBC) from one single breath by CE with C(4) D is demonstrated for the first time. A miniature sampler made from a 2-mL syringe and an aluminum cooling cylinder for collection of EBC was developed. Various parameters of the sampler that influence its collection efficiency, repeatability, and effect of respiratory patterns were studied in detail. Efficient procedures for the cleanup of the miniature sampler were also developed and resulted in significant improvement of sampling repeatability. Analysis of EBC was performed by CE-C(4) D in a 60 mM MES/l-histidine BGE with 30 μM CTAB and 2 mM 18-crown-6 at pH 6 and excellent repeatability of migration times (RSD < 1.3% (n = 7)) and peak areas (RSD < 7% (n = 7)) of 12 inorganic anions, cations, and organic acids was obtained. It has been shown that the breathing pattern has a significant impact on the concentration of the analytes in the collected EBC. As the ventilatory pattern can be easily controlled during single exhalation, the developed collection system and method provides a highly reproducible and fast way of collecting EBC with applicability in point-of-care diagnostics.

Graphene-based biomimetic materials targeting urine metabolite as potential cancer biomarker: application over different conductive materials for potentiometric transduction

This works presents a novel surface Smart Polymer Antibody Material (SPAM) for Carnitine (CRT, a potential biomarker of ovarian cancer), tested for the first time as ionophore in potentiometric electrodes of unconventional configuration. The SPAM material consisted of a 3D polymeric network created by surface imprinting on graphene layers. The polymer was obtained by radical polymerization of (vinylbenzyl)trimethylammonium chloride and 4-styrenesulfonic acid (signaling the binding sites), and vinyl pivalate and ethylene glycol dimethacrylate (surroundings). Non-imprinted material (NIM) was prepared as control, by excluding the template from the procedure. These materials were then used to produce several plasticized PVC membranes, testing the relevance of including the SPAM as ionophore, and the need for a charged lipophilic additive. The membranes were casted over solid conductive supports of graphite or ITO/FTO. The effect of pH upon the potentiometric response was evaluated for different pHs (2-9) with different buffer compositions. Overall, the best performance was achieved for membranes with SPAM ionophore, having a cationic lipophilic additive and tested in HEPES (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) buffer, pH 5.1. Better slopes were achieved when the membrane was casted on conductive glass (-57.4mV/decade), while the best detection limits were obtained for graphite-based conductive supports (3.6×10-5mol/L). Good selectivity was observed against BSA, ascorbic acid, glucose, creatinine and urea, tested for concentrations up to their normal physiologic levels in urine. The application of the devices to the analysis of spiked samples showed recoveries ranging from 91% (± 6.8%) to 118% (± 11.2%). Overall, the combination of the SPAM sensory material with a suitable selective membrane composition and electrode design has lead to a promising tool for point-of-care applications.

Separation of carnitine and acylcarnitines in biological samples: a review

Carnitine and its acylesters are a family of compounds that can be used in the early diagnosis of many diseases. Carnitine and acylcarnitines have a crucial role in fatty acid transportation. The increased level of free carnitine, total carnitine, or the acylesters can act as biomarkers for many metabolic disorders, including diabetes, encephalopathy and cardiomyopathy. The determination of these compounds is difficult owing to the simple aliphatic structure, the chiral center and the permanent positive charge. Although MS detection can be enough to differentiate between some carnitine derivatives, closely related structural isomers of the acylcarnitines must be separated before detection because they form the same base peak and second most abundant ion peak. Different separation methods are discussed in this review, including reversed-phase, hydrophilic interaction, ion exchange, ion pairing, mixed mode liquid chromatography, gas chromatography and electrophoresis. Representative example chromatograms are shown. The sample preparation and the different derivatization reactions are also covered. A table that summarizes the most important analytical methods by detailing the analyte mixture, the sample matrix, the separation mode and the detection method is provided.

Electrochemical methods in conjunction with capillary and microchip electrophoresis

Electromigrative techniques such as capillary and microchip electrophoresis (CE and MCE) are inherently associated with various electrochemical phenomena. The electrolytic processes occurring in the buffer reservoirs have to be considered for a proper design of miniaturized electrophoretic systems and a suitable selection of buffer composition. In addition, the control of the electroosmotic flow plays a crucial role for the optimization of CE/MCE separations. Electroanalytical methods have significant importance in the field of detection in conjunction with CE/MCE. At present, amperometric detection and contactless conductivity detection are the predominating electrochemical detection methods for CE/MCE. This paper reviews the most recent trends in the field of electrochemical detection coupled to CE/MCE. The emphasis is on methodical developments and new applications that have been published over the past five years. A rather new way for the implementation of electrochemical methods into CE systems is the concept of electrochemically assisted injection which involves the electrochemical conversions of analytes during the injection step. This approach is particularly attractive in hyphenation to mass spectrometry (MS) as it widens the range of CE-MS applications. An overview of recent developments of electrochemically assisted injection coupled to CE is presented.

Recent advances in applications of capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D): an update

Capillary electrophoresis with a capacitively contactless conductivity detector (CE-C⁴D) is becoming a significant useful technique for the analysis of analytes in various fields such as pharmaceutical, biomedical, food and environmental. This review is an update describing the recent developments in the application of CE with a C⁴D detector.