Quantitative determination of endogenous sorbitol and fructose in human nerve tissues by atmospheric-pressure chemical ionization liquid chromatography/tandem mass spectrometry

Advancement in Analytical Strategies for Quantification of Biomarkers with a Special Emphasis on Surrogate Approaches

Accurate quantification of biomarkers has always been a challenge for many bioanalytical scientists due to their endogenous nature and low concentration in biological matrices. Different analytical approaches have been developed for quantifying biomarkers including enzyme-linked immunosorbent assay, immunohistochemistry, western blotting, and chromatographic techniques assisted with mass spectrometry. Liquid chromatography-tandem mass spectrometry-based quantification of biomarkers has gained more attention over other traditional techniques due to its higher sensitivity and selectivity. However, the primary challenge lies with this technique includes the unavailability of a blank matrix for method development. To overcome this challenge, different analytical approaches are being developed including surrogate analyte and surrogate matrix approach. Such approaches include quantification of biomarkers in a surrogate matrix or quantification of an isotopically labeled surrogate analyte in an authentic matrix. To demonstrate the authenticity of the surrogate approach, it is mandatory to establish quantitative parallelism through validation employing respective surrogate analytes and surrogate matrices. In this review, different bioanalytical approaches for biomarker quantification and recent advancements in the field aiming for improvement in the specificity of the techniques have been discussed. Liquid chromatography-tandem mass spectrometry-based surrogate approaches for biomarker quantification and significance of parallelism establishment in both surrogate matrix and surrogate analyte-based approaches have been critically discussed. In addition, different methods for demonstrating parallelism in the surrogate method have been explained.

Bioengineered Polymer/Composites as Advanced Biological Detection of Sorbitol: An Application in Healthcare Sector

Bioengineered polymers and nanomaterials have emerged as promising and advanced materials for the fabrication and development of novel biosensors. Nanotechnology-enabled biosensor methods have high sensitivity, selectivity and more rapid detection of an analyte. Biosensor based methods are more rapid and simple with higher sensitivity and selectivity and can be developed for point-of-care diagnostic testing. Development of a simple, sensitive and rapid method for sorbitol detection is of considerable significance to efficient monitoring of diabetes-associated disorders like cataract, neuropathy, and nephropathy at initial stages. This issue encourages us to write a review that highlights recent advancements in the field of sorbitol detection as no such reports have been published till the date. The first section of this review will be dedicated to the conventional approaches or methods that had been playing a role in detection. The second part focused on the emerging field i.e. biosensors with optical, electrochemical, piezoelectric, etc. approaches for sorbitol detection and the importance of its detection in healthcare application. It is expected that this review will be very helpful for readers to know the different conventional and recent detection techniques for sorbitol at a glance.

Characterization of the fragmentation behaviors of protonated α-cyclodextrin generated by electrospray ionization

RATIONALE

Electrospray ionization (ESI) of an aqueous solution of α-cyclodextrin (α-CD) gave a protonated molecule, [α-CD + H]⁺ . The fragmentation behavior of the protonated molecule, including direct decomposition and ring cleavage, was investigated by varying the source fragmentor voltage. The possible chemical structures of the product ions were also examined using electronic structure calculations.

METHODS

An aqueous α-CD solution was ionized by ESI and the source fragmentor voltage was varied to examine changes of the product ions depending on collision energy. The structures and energies of the precursor and product ions were obtained by electronic structure calculations using Spartan'10 and Gaussian09.

RESULTS

The major product ions were [M + H - 162m]⁺ (where m = 1-5), with the most abundant being [M + H - 162 × 4]⁺ . The product ions had two chemical structures of the cationic site in the ether linkage ([DPDn - OH]⁺ ) and in the terminal oxonium ion ([DPn - OH]⁺ ) formed by direct decomposition of [α-CD + H]⁺ and fragmentation of the open structure ([DP6 - OH]⁺ ), respectively. The [DP6 - OH]⁺ ion is more stable than the [α-CD + H]⁺ ion.

CONCLUSIONS

The fragmentation behavior of protonated α-CD was characterized by two pathways: direct decomposition of [α-CD + H]⁺ and decomposition of the [DP6 - OH]⁺ open structure. Differences in the relative abundances of product ions were explained by the different fragmentation pathways of [α-CD + H]⁺ and [DP6 - OH]⁺ .

Development and validation of a quantitative ultra performance LC® hydrophilic interaction liquid chromatography MS/MS method to measure fructose and sorbitol in human plasma

AIM

Fructose and sorbitol are utilized as biomarkers for nonalcoholic steatohepatitis. Measurement of fructose and sorbitol levels helps understanding disease progression, drug response and underlying mechanism.

MATERIALS & METHODS

Stable isotope-labeled fructose and sorbitol were used as surrogate standards and internal standards. Human plasma samples were processed and analyzed by ultra performance LC^®-MS/MS via chromatographic separation on a hydrophilic interaction liquid chromatography analytical column without derivatization. Assay was validated with biomarker fit-for-purpose concept.

RESULTS

A 12-min ultra performance LC^®-MS/MS method was developed and validated to directly measure fructose and sorbitol in human plasma with acceptable intra- and inter-assay precision and accuracy.

CONCLUSION

This sensitive, selective, and high-throughput assay with suitable dynamic ranges was successfully applied to clinical studies to provide reliable fructose and sorbitol biomarker data.

Quantification of eicosanoids and their metabolites in biological matrices: a review

The quantification of eicosanoids and their metabolites in biological samples remain an analytical challenge, even though a number of methodologies/techniques have been developed. The major difficulties encountered are related to the oxidation of eicosanoids and their low quantities in biological matrices. Among the known methodologies, liquid chromatography-mass spectrometry (LC-MS/MS) is the standard method for eicosanoid quantification in biological samples. Recently advances have improved the ability to identify and simultaneous quantitate eicosanoids in biological matrices. The present article reviews the quantitative analysis of eicosanoids in different biological matrices by LC and ultra performance liquid chromatography (UPLC)-MS/MS and discusses important aspects to be considered during the collection, sample preparation and the generation of calibration curves required for eicosanoid analysis.

Accurate quantification of PGE2 in the polyposis in rat colon (Pirc) model by surrogate analyte-based UPLC-MS/MS

An accurate and reliable UPLC-MS/MS method is reported for the quantification of endogenous Prostaglandin E2 (PGE₂) in rat colonic mucosa and polyps. This method adopted the "surrogate analyte plus authentic bio-matrix" approach, using two different stable isotopic labeled analogs - PGE₂-d9 as the surrogate analyte and PGE₂-d4 as the internal standard. A quantitative standard curve was constructed with the surrogate analyte in colonic mucosa homogenate, and the method was successfully validated with the authentic bio-matrix. Concentrations of endogenous PGE₂ in both normal and inflammatory tissue homogenates were back-calculated based on the regression equation. Because of no endogenous interference on the surrogate analyte determination, the specificity was particularly good. By using authentic bio-matrix for validation, the matrix effect and exaction recovery are identically same for the quantitative standard curve and actual samples - this notably increased the assay accuracy. The method is easy, fast, robust and reliable for colon PGE₂ determination. This "surrogate analyte" approach was applied to measure the Pirc (an Apc-mutant rat kindred that models human FAP) mucosa and polyps PGE₂, one of the strong biomarkers of colorectal cancer. A similar concept could be applied to endogenous biomarkers in other tissues.

Performance comparison of electrospray ionization and atmospheric pressure chemical ionization in untargeted and targeted liquid chromatography/mass spectrometry based metabolomics analysis of grapeberry metabolites

RATIONALE

Electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) are both used to generate ions for the analysis of metabolites by liquid chromatography/mass spectrometry (LC/MS). We compared the performance of these methods for the analysis of Corvina grapevine berry methanolic extracts, which are complex mixtures of diverse metabolites.

METHODS

Corvina berries representing three ripening stages (veraison, early-ripening and full-ripening) were collected during two growing seasons, powdered and extracted with methanol. Untargeted metabolomic analysis was carried out by LC/ESI-MS and LC/APCI-MS. Processed data files were assembled into a data matrix for multivariate statistical analysis. The limits of detection (LODs), limits of quantification (LOQs), linear ranges, and matrix effects were investigated for strongly polar metabolites such as sucrose and tartaric acid and for moderately polar metabolites such as caftaric acid, epicatechin and quercetin 3-O-glucoside.

RESULTS

Multivariate statistical analysis of the 608 features revealed that APCI was particularly suitable for the ionization of strongly polar metabolites such as sugars and organic acids, whereas ESI was more suitable for moderately polar metabolites such as flavanols, flavones and both glycosylated and acylated anthocyanins. APCI generated more fragment ions whereas ESI generated more adducts. ESI achieved lower LODs and LOQs for sucrose and tartaric acid but featured narrower linear ranges and greater matrix effects.

CONCLUSIONS

ESI and APCI are not complementary ion sources. Indeed, ESI can be exploited to analyze moderately polar metabolites, whereas APCI can be used to investigate weakly polar/non-polar metabolites and, as demonstrated by our results, also strongly polar metabolites. ESI and APCI can be used in parallel, exploiting their strengths to cover the plant metabolome more broadly than either method alone. Copyright © 2016 John Wiley & Sons, Ltd.

Ranirestat has a stronger inhibitory activity on aldose reductase and suppresses inflammatory reactions in high glucose-exposed endothelial cells

OBJECTIVE

Under diabetic conditions, glucose is converted to sorbitol via aldose reductase, whose process could contribute to diabetic vascular complications. However, effects of aldose reductase inhibitors are modest in diabetic patients. This may be attributed to weak inhibitory activity of aldose reductase inhibitors. We compared effects of ranirestat on endothelial cell damage with those of epalrestat.

MATERIALS AND METHODS

Intracellular formations of sorbitol and superoxide were measured by liquid chromatography-mass spectrometry-mass spectrometry and dihydroethidium staining, respectively. Vascular cell adhesion molecule-1 gene expression was analysed by reverse transcription polymerase chain reaction. THP-1 cell adhesion to human umbilical vein endothelial cells was evaluated using a fluorescent probe.

RESULTS

High glucose significantly increased sorbitol levels, superoxide generation and vascular cell adhesion molecule-1 mRNA levels in, and THP-1 cell adhesion to, human umbilical vein endothelial cells, all of which were prevented by 500 nM ranirestat, but not epalrestat except for superoxide production.

CONCLUSION

Our present results suggest that ranirestat has a stronger inhibitory activity on aldose reductase than epalrestat and suppresses inflammatory reactions in high glucose-exposed human umbilical vein endothelial cells.

Formation of deaminated dimer species of amino acids by atmospheric pressure chemical ionization

RATIONALE

Interactions of biological molecules to form cluster species play a key role in biological processes and investigation of non-covalent complexes is one of the research fields using mass spectrometry. Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) is a useful method for the investigation of cluster formation of amino acids (AAs) by ion-molecule reactions.

METHODS

A mixture of 20 protein AAs was ionized by APCI and the product ions were analyzed. The ionization was performed in the positive and negative ion modes. Formation of the homo- and heterocluster ions of AAs was investigated. Mechanism for the formation of AA homo- and heterocluster ions was examined using hydrogen/deuterium (H/D)-exchange experiments.

RESULTS

In the positive ion mode, of the dimer species only the [2Pro+H](+) ion was detected. In the negative ion mode, the [2M - H](-) ions of His, Val, Ser, and Gln were observed. The deaminated dimers such as the [2Gln - H - NH3](-) and [His + Gln - H - NH3](-) ions were also observed. In the negative ion mass spectra of the His/Arg, His/Asn, and His/Lys binary mixture solutions, the [His + AA - H - NH3](-) ions of Asn, Arg, and Lys were also detected.

CONCLUSIONS

The number and abundances of the negative product ions were much greater than those of the positive ones. Mechanism for the formation of [2Gln - H - NH3](-) and [His+AA - H - NH3](-) was examined by deuterium replacement of the amine and hydroxide groups to distinguish the deamination and dehydration reactions with a single quadrupole mass spectrometer. The [His + AA - H - NH3](-) ion is formed by ion-molecule reaction between the [His-H](-) ion and a neutral AA.

Application of a liquid chromatography-electrospray mass spectrometry (LC/MS) method to the biodistribution and excretion studies of novel 5'-chloro-2, 3-didehydroindolo (2', 3': 2, 3) betulinic acid (DRF-4012) in tumour-bearing mice

Novel betulinic acid derivative 5'-chloro-2, 3-didehydroindolo [2', 3': 2, 3] betulinic acid (DRF-4012) is a new effective lupane type triterpenes with greater anticancer activity and efficacy than betulinic acid and currently under advanced preclinical investigation phase. In this study, a sensitive and rapid liquid chromatography-electrospray mass spectrometric (LC/MS) method has been developed for the determination of DRF-4012 in tumour-bearing mice plasma, urine, feces and tissues (liver, brain, lungs, heart, spleen, stomach, thigh muscle, kidneys, urinary bladder, small intestine and tumour). Biodistribution and excretion studies were performed for DRF-4012 nanoparticle (30 mg/kg body weight) after intravenous (i.v.) injection in tumour-bearing mice. DRF-4012 rapidly distributed throughout the body. After 0.5 h, tumour showed the second highest concentration, which was nearly half of the liver. After 4 and 24 h, the highest concentration of DRF-4012 was found in tumour indicating its retention in tumour site for a longer time. Excretion studies revealed that very low amount of unchanged DRF-4012 was observed in urine and primarily excreted through fecal route. This study may be useful to explain the manner in which DRF-4012 can inhibit tumour growth without apparent toxicity and preclinical/clinical evaluation of this potential antitumour agent.

Differentiation of underivatized monosaccharides by atmospheric pressure chemical ionization quadrupole time-of-flight mass spectrometry

RATIONALE

Differentiation of underivatized monosaccharides is essential in the structural elucidation of oligosaccharides which are closely involved in many life processes. So far, such differentiation has been usually achieved by electrospray ionization mass spectrometry (ESI-MS). As an alternative to ESI-MS, atmospheric pressure chemical ionization mass spectrometry (APCI-MS) should provide complementary results.

METHODS

A quadrupole time-of-flight (QTOF) mass spectrometer with accurate mass measurement ability was used with an APCI heated nebulizer ion source because we believe that a recently published article using a single quadrupole mass spectrometer assigned incorrect identities for APCI ions from hexoses. Using APCI-QTOF, the MS(2) and pseudo-MS(3) mass spectra of 11 underivatized monosaccharides were obtained under various collision voltages. The mass spectra were carefully interpreted after accurate mass measurement.

RESULTS

Differentiation of three hexoses was achieved by different MS(2) spectra of their [M + NH(4)](+) and [M - H](-) ions. The MS(2) spectra of the [M + NH(4)](+) ions were also used to distinguish methyl α-D-glucose and methyl β-D-glucose, while the pseudo-MS(3) spectra of the [M + H](+) ions were utilized to differentiate the three hexosamine and N-acetylhexosamine stereoisomers. Unique [M + O(2)](-) ions were observed and their distinctive fragmentation patterns were utilized to differentiate the three hexosamine stereoisomers.

CONCLUSIONS

Although ESI coupled with single or triple quadrupole and ion trap mass spectrometers has been widely utilized in the differentiation of monosaccharides, this report demonstrated that APCI-QTOF-MS had its own advantages in achieving the same goal.

Critical topics in ensuring data quality in bioanalytical LC–MS method development

The use of LC–MS for bioanalysis of pharmaceuticals is entering its third decade and may be considered to be a mature technology. In many respects this is true, considering the advances made in such areas as instrument performance, electronics, software and automation of use. However, there remain instrumental and noninstrumental areas that require significant attention to ensure data quality. Increasing regulatory focus on analytical method performance and unaddressed method issues require the bioanalyst to understand those areas that most greatly impact data quality. This review will focus on instrumental and noninstrumental areas that can influence data quality, including reference standard and internal standard quality and physicochemical properties, matrix effects, stability in matrix, sample preparation, LC and MS.

Atmospheric pressure chemical ionization and fragmentation of aminomonosaccharides in H2O and D2O

Aminomonosaccharides (glucosamine, galactosamine, and mannosamine) in H2O and D2O were ionized by atmospheric pressure chemical ionization (APCI) and their fragmentation patterns were investigated to identify them. All the aminomonosaccharides showed the same fragment ions but their relative ion intensities were different. Major product ions generated in H2O were [M + H]+, [M + H - H2O]+, and [2M + H - 3H2O]+, while in D2O were [M(D6) + D]+, [M(D6) + D - D2O]+, and [2M(D6) + D - D2O - 2HDO]+. At a high fragmentor voltage above 120 V, the relative ion intensities of the major product ions showed different trends according to the aminomonosaccharides. For the use of H2O as solvent and eluent, the order of the ion intensity ratio of [M + H - H2O]+/[2M + H - 3H2O]+ was galactosamine > mannosamine > glucosamine. When using D2O as solvent and eluent, the order of the ion intensity ratios of [M(D6) + D - D2O]+/[MD6 + D]+ and [2M(D6) + D - D2O - 2HDO]+/[M(D6) + D]+ was mannosamine > galactosamine > glucosamine. It was found that glucosamine, galactosamine, and mannosamine could be distinguished by the specific trends of the major product ion ratios in H2O and D2O.

Liquid chromatography/mass spectrometry determination of endogenous plasma acetyl and palmitoyl carnitines as potential biomarkers of beta-oxidation in mice

A robust bioanalytical method capable of measuring acetyl and palmitoyl carnitines was developed and validated. Application of hydrophilic interaction chromatography (HILIC) enabled retention of these highly polar and difficult to analyze compounds on a silica HPLC column. The chromatography was conducted with a high percentage of an organic component in the mobile phase, allowing high sensitivity for the pre-existing positively charged quaternary ammonium ions by electrospray ionization mass spectrometry. Successful application of the method to reliably quantify naturally occurring acyl carnitines in mouse plasma depended on the use of corresponding deuterated analogues. The specificity of the method, achieved through the use of stable isotope labeled compounds in combination with a mass spectral multiple reaction monitoring technique, permitted a non-invasive assessment of the overall change in the levels of these acyl carnitines in the plasma of intact animals administered peroxisome proliferator activated receptor (PPAR) agents. These acyl carnitines, as carriers of the corresponding long-chain fatty acids for transport into mitochondria, can be employed as potential biomarkers for significant alteration in the beta-oxidation process in an intact animal.

Systematic and comprehensive strategy for reducing matrix effects in LC/MS/MS analyses

A systematic, comprehensive strategy that optimizes sample preparation and chromatography to minimize matrix effects in bioanalytical LC/MS/MS assays was developed. Comparisons were made among several sample preparation methods, including protein precipitation (PPT), liquid-liquid extraction (LLE), pure cation exchange solid-phase extraction (SPE), reversed-phase SPE and mixed-mode SPE. The influence of mobile phase pH and gradient duration on the selectivity and sensitivity for both matrix components and basic analytes was investigated. Matrix effects and overall sensitivity and resolution between UPLC technology and HPLC were compared. The amount of specific matrix components, or class of matrix components, was measured in the sample preparation extracts by LC/MS/MS with electrospray ionization (ESI) using both precursor ion scanning mode and multiple reaction monitoring (MRM). PPT is the least effective sample preparation technique, often resulting in significant matrix effects due to the presence of many residual matrix components. Reversed-phase and pure cation exchange SPE methods resulted in cleaner extracts and reduced matrix effects compared to PPT. The cleanest extracts, however, were produced with polymeric mixed-mode SPE (both reversed-phase and ion exchange retention mechanisms). These mixed-mode sorbents dramatically reduced the levels of residual matrix components from biological samples, leading to significant reduction in matrix effects. LLE also provided clean final extracts. However, analyte recovery, particularly for polar analytes, was very low. Mobile phase pH was manipulated to alter the retention of basic compounds relative to phospholipids, whose retention tends to be relatively independent of pH. In addition to the expected resolution, speed and sensitivity benefits of UPLC technology, a paired t-test demonstrated a statistically significant improvement with respect to matrix effects when this technology was chosen over traditional HPLC. The combination of polymeric mixed-mode SPE, the appropriate mobile phase pH and UPLC technology provides significant advantages for reducing matrix effects resulting from plasma matrix components and in improving the ruggedness and sensitivity of bioanalytical methods.

Analysis of sugars and sugar polyols in atmospheric aerosols by chloride attachment in liquid chromatography/negative ion electrospray mass spectrometry

Sugars and sugar polyols are relatively abundant groups of water-soluble constituents in atmospheric aerosols. This paper describes a method that uses liquid chromatography-mass spectrometry (LC-MS) to analyze sugars and sugar polyols in atmospheric aerosols, ranging from C3 sugar alcohols to trisaccharides. Postcolumn addition of chloroform in acetonitrile was found to greatly enhance ionization of these compounds by forming chloride adduct ions in the negative-ion mode using electrospray ionization. A gradient elution program starting at 5%:95% H20/acetonitrile and ending at 30%:70% H2O/acetonitrile provides baseline separations of the sugars and sugar polyols on an amino-based carbohydrate column. The detection limits based on quantification of [M + 35Cl]- adduct ions were in the order of 0.1 microM. By eliminating the need for derivatization, this LC-MS based method provides a simpler alternative method to the commonly used and more laborious gas-chromatography based methods. It also has an additional advantage of being able to quantify trisaccharide sugars. The method was applied to analyze 30 ambient samples of fine particulate matter collected at a site away from urban centers in Hong Kong. The sugar compounds positively identified and detected in the ambient samples included four sugar alcohols (glycerol, erythritol, xylitol, and mannitol), three monosacchride sugars (xylose, fructose, and glucose), two disaccharides (sucrose, trehalose), two trisaccharides (melezitose, raffinose), and one anhydrosugar (levoglucosan). The sum of these sugar and sugar polyol compounds ranged from 38 to 1316 ng m(-3), accounting for an average of 1.3% organic carbon mass. Through the use of a principal component analysis of the ambient measurements, the mono- to trisactharide sugars and C3-C5 sugar polyols were identified to be mainly associated with soil/soil microbiota while the anhydrosugar (levoglucosan) was associated with biomass burning.