Flow injection ionization-tandem mass spectrometry-based estimation of a panel of lysophosphatidylcholines in dried blood spots for screening of X-linked adrenoleukodystrophy

Total analysis system for the determination of uremic toxins in human plasma based on bead injection solid phase extraction hyphenated to mass spectrometry

Indoxyl sulfate (INDS) and p-cresol sulfate (pCS) are two of the most relevant uremic toxins that are recognized to have an essential role in chronic kidney disease (CKD) progression and associated cardiovascular risk. Thus, it is crucial to accurately assess their circulating levels in the body. Aiming at establishing an analytical strategy for quantification of INDS and pCS in human plasma, an automatic on-line micro-solid-phase extraction (μSPE) procedure hyphenated to tandem mass spectrometry (MS/MS) detection without previous chromatographic separation was herein developed. The bead injection (BI) concept was used to implement the μSPE procedure in the lab-on-valve (LOV) format. After studying the extraction conditions, the anion-exchange OASIS WAX sorbent beads (10 mg) and 99% ACN-H2O (15:85, v/v)-1% (v/v) NH4OH were chosen as sorbent and eluent, respectively, as they provided the highest analyte recoveries. Subsequently, the μSPE-BI-LOV system was hyphenated on-line to a MS/MS detector and the full analytical cycle, comprising sample preparation and analytes detection, was completed in <20 min. The developed μSPE-BI-LOV-MS methodology presented good linearity (r2 > 0.999) for quantification of the target analytes at concentrations ranging from 18 to 360 μg mL-1 in plasma. LOQ values were 2 μg mL-1 for INDS and 7 μg mL-1 for pCS in plasma. Human plasma samples from healthy subjects and individuals with CKD were successfully analyzed using the developed approach. The proposed automatic methodology can be described as an eco-friendly strategy, with a favorable score of 0.64 after greenness evaluation using the AGREE metric.

Age and gender-specific reference intervals for a panel of lysophosphatidylcholines estimated by tandem mass spectrometry in dried blood spots

Background and objectives

Very long-chain fatty acyl-lysophosphatidylcholines (VLCFA-LysoPCs) are measured in dried blood spots (DBS) for identifying X-linked adrenoleukodystrophy (X-ALD) and other inherited peroxisomal disorders. Our study aimed to establish age- and gender-specific reference intervals for a panel of LysoPCs measured by tandem mass spectrometry in DBS.

Methods

LysoPCs (26:0-, 24:0-, 22:0- and 20:0-LysoPCs) were estimated by flow injection analysis-tandem mass spectrometry (FIA-MS/MS) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods in 3.2 mm blood spots of 2689 anonymized, putative normal subjects (1375 males, and 1314 females) aged between 2 days and 65 years. Samples were divided into groups: Neonates (0-1month), Infants (>1m-1year), Children and Adolescents (>1-18years), and Adults (>18years). Reference intervals were determined using the percentile approach and represented as the median with the 1^st and 99^th percentile lower and upper limits.

Results

The percentage coefficient of variation (CV) for repeatability assays of internal and external quality control samples were within acceptable limits. Significant differences (P <0.0001, P <0.01) were observed in the concentrations of 26:0-, 24:0-, 22:0- and 20:0-LysoPCs and their ratios, 26:0/22:0-, 24:0/22:0-, 26:0/20:0-and 24:0/20:0-LysoPC in neonates and infants when compared to children, adolescents, and adults. Levels of 26:0-, 24:0- and 22:0-LysoPCs decreased, whereas 20:0-LysoPC increased with age. There were no significant gender-based differences in the concentration of LysoPCs.

Conclusion

We established age- and gender-specific reference intervals for a panel of LysoPCs in DBS. These reference values would be helpful when interpreting LysoPC values in DBS during screening for X-ALD and other peroxisomal disorders.

Newborn Screening for X-Linked Adrenoleukodystrophy: Review of Data and Outcomes in Pennsylvania

X-linked adrenoleukodystrophy (X-ALD) is the most common peroxisomal disorder. It results from pathogenic variants in ABCD1, which encodes the peroxisomal very-long-chain fatty acid transporter, causing a spectrum of neurodegenerative phenotypes. The childhood cerebral form of the disease is particularly devastating. Early diagnosis and intervention improve outcomes. Because newborn screening facilitates identification of at-risk individuals during their asymptomatic period, X-ALD was added to the Pennsylvania newborn screening program in 2017. We analyzed outcomes from the first four years of X-ALD newborn screening, which employed a two-tier approach and reflexive ABCD1 sequencing. There were 51 positive screens with elevated C26:0-lysophosphatidylcholine on second-tier screening. ABCD1 sequencing identified 21 hemizygous males and 24 heterozygous females, and clinical follow up identified four patients with peroxisomal biogenesis disorders. There were two false-positive cases and one false-negative case. Three unscreened individuals, two of whom were symptomatic, were diagnosed following their young siblings' newborn screening results. Combined with experiences from six other states, this suggests a U.S. incidence of roughly 1 in 10,500, higher than had been previously reported. Many of these infants lack a known family history of X-ALD. Together, these data highlight both the achievements and challenges of newborn screening for X-ALD.

Development, validation, and clinical application of an FIA-MS/MS method for the quantification of lysophosphatidylcholines in dried blood spots

Background

Lysophosphatidylcholine (LPC) plays pivotal roles in several physiological processes and their disturbances are closely associated with various disorders. In this study, we described the development and validation of a reliable and simple flow injection analysis–tandem mass spectrometry (FIA‐MS/MS)‐based method using dried blood spots (DBS) for quantification of four individual LPC (C20:0, C22:0, C24:0, and C26:0).

Methods

Lysophosphatidylcholines were extracted from 3.2 mm DBS with 85% methanol containing 60 ng/ml internal standard using a rapid (30 min) and simple procedure. The analytes and the internal standard were directly measured by triple quadrupole tandem mass spectrometry in multiple reactions monitoring mode via positive electrospray ionization.

Results

Method validation results showed good linearity ranging from 50 to 2000 ng/ml for each LPC. Intra‐ and inter‐day precision and accuracy were within the acceptable limits at four quality control levels. Recovery was from 70.5% to 107.0%, and all analytes in DBS were stable under assay conditions (24 h at room temperature and 72 h in autosampler). The validated method was successfully applied to assessment of C20:0‐C26:0LPCs in 1900 Chinese neonates. C26:0‐LPC levels in this study were consistent with previously published values.

Conclusion

We propose a simple FIA‐MS/MS method for analyzing C20:0‐C26:0LPCs in DBS, which can be used for first‐tier screening.

LC-MS Based Platform Simplifies Access to Metabolomics for Peroxisomal Disorders

Peroxisomes are central hubs for cell metabolism and their dysfunction is linked to devastating human disorders, such as peroxisomal biogenesis disorders and single peroxisomal enzyme/protein deficiencies. For decades, biochemical diagnostics have been carried out using classical markers such as very long-chain fatty acids (VLCFA), which can be inconspicuous in milder and atypical cases. Holistic metabolomics studies revealed several potentially new biomarkers for peroxisomal disorders for advanced laboratory diagnostics including atypical cases. However, establishing these new markers is a major challenge in routine diagnostic laboratories. We therefore investigated whether the commercially available AbsoluteIDQ p180 kit (Biocrates Lifesciences), which utilizes flow injection and liquid chromatography mass spectrometry, may be used to reproduce some key results from previous global metabolomics studies. We applied it to serum samples from patients with mutations in peroxisomal target genes PEX1, ABCD1, and the HSD17B4 gene. Here we found various changes in sphingomyelins and lysophosphatidylcholines. In conclusion, this kit can be used to carry out extended diagnostics for peroxisomal disorders in routine laboratories, even without access to a metabolomics unit.

Evaluation of a panel of very long-chain lysophosphatidylcholines and acylcarnitines for screening of X-linked adrenoleukodystrophy in China

BACKGROUND

Elevated blood C24:0- and C26:0-carnitines and lysophosphatidylcholines (LPCs) were reported as diagnostic biomarkers for X-linked adrenoleukodystrophy (X-ALD). Our aim was to establish the reference intervals of very long-chain (VLC) acylcarnitines (C20-C26) and LPCs in Chinese population, and evaluate valuable biomarkers and develop panel for screening X-ALD in China.

METHODS

The method of FIA-MS/MS-based quantification of VLC acylcarnitines and LPCs was validated in order to determine their concentrations in dried blood spots from 7 X-ALD boys, 396 age-matched healthy controls, and 3078 putative normal newborns. Screening performance of these metabolites for X-ALD was clinically evaluated.

RESULTS

The reference intervals of VLC acylcarnitines, LPCs and their ratios were established in Chinese population, and for some metabolites like C26 and C26:0-LPC, the reference intervals were found to be significantly different between children and newborns. C24 and C26, C26:0-LPC, C24/C22 and C26/C22 ratios were found to have better performance than other analytes to identify X-ALD boys from normal children.

CONCLUSION

C26:0-LPC, C24 and C26 are three most valuable biomarkers for screening of X-ALD in children group. The information of age-related variations in concentration of some biomarkers is helpful for accurate screening of X-ALD.