Highly sensitive and selective measurement of underivatized methylmalonic acid in serum and plasma by liquid chromatography-tandem mass spectrometry

Simultaneous determination of total homocysteine, methionine, methylmalonic acid and 2-methylcitric acid in dried blood spots by ultra-performance liquid chromatography-tandem mass spectrometry

Homocysteine, methionine, methylmalonic acid and 2-methylcitric acid are clinically relevant markers in the methionine, propionate, and cobalamin metabolism. This study aimed to develop and validate an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method for simultaneously determining total homocysteine, methionine, methylmalonic acid and 2-methylcitric acid in dried blood spots. Three 3.2 mm discs were punched from each calibrator, quality control, and sample dried blood spot into a 96-well U-plate. Each sample was spiked with internal standards and extracted. Then the supernatant was transferred to another 96-well U-plate. After nitrogen drying, the dried residues were reconstituted, centrifuged, and the resulting supernatant was transferred to another 96-well plate for analysis. The method was performed using UPLC-MS/MS within 3 min, validated according to guidance documents, and applied to 72 samples from confirmed patients with methionine, propionate, and cobalamin metabolism disorders. The UPLC-MS/MS method provided satisfactory separation of the four analytes. The R2 values were ≥ 0.9937 for all analytes. The recoveries ranged from 94.17 to 114.29 %, and the coefficients of variation for intraday and interday precision were 0.19 % to 5.23 % and 1.02 % to 6.89 %, respectively. No significant carry-over was detected for the four analytes, and most of confirmed samples exhibited biomarker patterns characteristic of the relevant disorders. A simple and fast UPLC-MS/MS method was successfully developed, validated, and applied to clinical samples for the simultaneous determination of total homocysteine, methionine, methylmalonic acid, and 2-methylcitric acid in dried blood spots.

A Rapid, Simple, Trace, Cost-Effective, and High-Throughput Stable Isotope-Dilution Liquid Chromatography-Tandem Mass Spectrometry Method for Serum Methylmalonic Acid Quantification and Its Clinical Applications

Background: Methylmalonic acid (MMA) is an essential indicator of vitamin B12 (VB12) deficiency and inherited metabolic disorders (IMDs). The increasing number of requests for MMA testing call for higher requirements for convenient MMA testing methods. This study aims to develop a convenient quantification method for serum MMA. Methods: The method was established based on the stable isotope-dilution liquid chromatography−tandem mass spectroscopy (ID-LC-MS/MS) technique. The LC-MS/MS parameters and sample preparation were optimized. Specificity, sensitivity, robustness, accuracy, and clinical applicability were validated according to CLSI C62-A guidelines. MMA levels in VB12-sufficient subjects and VB12-deficient subjects were measured. Results: MMA and its intrinsic isomer, i.e., succinic acid (SA), were completely separated. The average slope, intercept, and correlation relationship (R) with 95% confidence intervals, during the two months, were 0.992 (0.926−1.059), −0.004 (−0.012−0.004), and 0.997 (0.995−0.999), respectively. The limit of detection and quantification were <0.058 μmol/L and 0.085 μmol/L, respectively. Intra-run, inter-run, and total imprecisions were 1.42−2.69%, 3.09−5.27%, and 3.22−5.47%, respectively. The mean spiked recoveries at the three levels were 101.51%, 92.40%, and 105.95%, respectively. The IS-corrected matrix effects were small. The VB12-deficient subjects showed higher MMA levels than VB12-sufficient subjects. Conclusions: A convenient LC-MS/MS method for serum MMA measurement was developed and validated, which could be suitable for large-scale MMA testing and evaluating MMA levels in VB12-deficient patients.

LC-MS/MS Method for High-Throughput Analysis of Methylmalonic Acid in Serum, Plasma, and Urine: Method for Analyzing Isomers Without Chromatographic Separation

Measurement of methylmalonic acid (MMA) plays an important role in the diagnosis of vitamin B₁₂ deficiency. Vitamin B₁₂ is an essential cofactor for the enzymatic carbon rearrangement of methylmalonyl-CoA (MMA-CoA) to succinyl-CoA (SA-CoA), and the lack of vitamin B₁₂ leads to elevated concentrations of MMA. Measurement of MMA in biological samples is complicated because of the presence of succinic acid (SA), isomer of MMA. We developed a liquid chromatography tandem mass spectrometry (LC-MS/MS) method for MMA. The method utilizes derivatization and positive ion mode ionization, which is specific to polycarboxylic acids (MMA and SA are dicarboxylic acids), while derivatives of monocarboxylic acids at these conditions are not ionizable and not detectable. The only organic acid, other than MMA, that is detected in this method is SA. The described method does not require chromatographic resolution of the peaks of MMA and SA; quantitative measurement of MMA is performed using a deconvolution algorithm, which mathematically resolves signal corresponding to MMA, from the combined signal of MMA/SA. Because of the high selectivity of detection, this method utilizes isocratic chromatographic separation; reconditioning and re-equilibration of the chromatographic column between injections is unnecessary. The above features allow high-throughput analysis of MMA with injection-to-injection cycle time of approximately 1 minute.

Biomarker profiling of vitamin responsive seizures: a potential tool to detect pediatric seizures of unknown aetiology

Aim: Certain rare inborn errors of metabolism clinically present with intractable seizures that readily respond to vitamin therapy. If identified early, brain damage due to seizures can be prevented. Methodology: A LC-MS method was developed and validated for the simultaneous quantification of the biomarkers in selected vitamin responsive pediatric seizures from dried blood spots. Results: Application of the validated method to a seizure cohort of 46 patients indicated strong agreement of the method for clinical validity. Reference intervals for these biomarkers in dried blood spots were also determined for the population, after screening 956 neonates. Conclusion: The developed method was seen to be sensitive, linear, accurate and precise for testing vitamin responsive pediatric seizures.

Novel HILIC-ESI-MS method for urinary profiling of MSUD and methylmalonic aciduria biomarkers

Methyl malonic acid and branched-chain keto acids are important biomarkers for the diagnosis of cobalamin deficiencies and maple syrup urine disease. We report the development and validation of a HILIC-ESI-MS2 method for the quantification of these organic acids from neonatal urine. The samples were 100 times diluted and analyzed on a ZIC-HILIC column with 25-mM formic acid in water: 25-mM formic acid in acetonitrile (45:55) at a flow rate of 0.8 mL/min with a runtime of only 6 minutes. The method demonstrated a lower limit of detection of 10 ng/mL, Limit of Quantification (LOQ) of 50 ng/mL, linearity of r2 ≥ 0.990 and recoveries of 87-105% for all analytes. The intraday and interday precision CV's were <10% and 12%, respectively. Extensive stability studies demonstrated the analytes to be stable in stock and in matrix with a percent change within ±15%. The Bland-Altman analysis of the developed method with the gold standard GCMS method demonstrated a bias of 0.44, 0.11, 0.009 and -0.19 for methyl malonic acid, 3-methyl-2-oxovaleric acid, 2-hydroxy-3methylbutyric acid and 4-methyl-2-oxovaleric acid, respectively, proving the methods are comparable. The newly developed method involves no derivatization and has a simple sample preparation and a low runtime, enabling it to be easily automated with a high sample throughput in a cost-effective manner.

Rapid Underivatized Method for Quantitative Methylmalonic Acid by Liquid Chromatography-Tandem Mass Spectrometry

BACKGROUND

Increased methylmalonic acid (MMA) levels can aid in assessing vitamin B12 deficiency or abnormal propionate metabolism. MMA analysis by LC-MS/MS is challenging because of both the nanomolar reference range and potential interference from succinic acid, an endogenous isomer. We show that ultrafiltration followed by gradient chromatography permits rapid, sensitive, and selective quantification that is essentially devoid of matrix effects.

METHODS

Fifty microliters of serum or plasma were mixed with 50 μL of MMA-d3 and deproteinized by ultrafiltration. Filtrates were analyzed by reversed-phase LC-MS/MS. The clinical performance of the MMA assay was validated using guidelines from both the College of American Pathologists and the Clinical and Laboratory Standards Institute. Matrix effects were examined by postcolumn infusion, phospholipid analysis, and peak area comparisons.

RESULTS

The analytical measurement range was 0.05 to 100 μmol/L. The resolution between physiological succinic acid and MMA was >2.3. Recovery of MMA averaged 92%, and MMA eluted away from ion suppressants. Direct correlation with our earlier method and with consensus data from external proficiency testing yielded an R2 ≥ 0.9409 and average biases less than ±5%. In the production environment, ongoing correlation with external proficiency testing yielded an R2 of 0.9980 and a mean bias of 0.36%. Over 1.7 years, the imprecision of 2 quality control levels was <6.4%.

CONCLUSIONS

We combined ultrafiltration, a simple sample extraction method, with gradient chromatography to exclude matrix effects to accurately and precisely quantify MMA.

Methylmalonic Acid Levels and their Relation with Cobalamin Supplementation in Spanish Vegetarians

Cobalamin deficiency represents a health issue for vegetarians, especially vegans, if supplements are not consumed. Vitamin B12 serum levels, traditionally used to assess the vitamin B12 status, can be normal under functional deficiency conditions. In this regard, methylmalonic acid (MMA) has proven to be a more specific marker to detect subclinical vitamin B12 deficiency. In this study, we present for the first time the cobalamin status of Spanish vegetarians using both vitamin B12 and MMA markers, and the effects of the plant-based diet and the intake of vitamin B12 supplements. Healthy adults were recruited (n = 103, 52% vegans). Dietary preferences and use of supplements were assessed by questionnaires and serum samples were collected and stored. Vitamin B12 was measured by chemiluminiscence and MMA by liquid chromatography tandem mass spectrometry (LC-MS/MS) using solid phase extraction for sample preparation. Obtained values, median (IQR), were: vitamin B12, 278.9 (160.2) pmol/l and MMA, 140.2 (78.9) nmol/l. No significant differences between lacto-ovo vegetarians and vegans were observed. Considering these two markers, 10% of the participants were mild vitamin B12 deficient. Supplementation (75% of the participants) was associated with higher vitamin B12 (p < 0.001) and lower MMA (p = 0.012). In conclusion, Spanish vegetarians have low risk of vitamin B12 deficiency due to vitamin B12 supplementation and the MMA determination is useful to detect mild deficiency.

Quantifying MMA by SLE LC-MS/MS: Unexpected challenges in assay development

OBJECTIVES

Analysis of serum/plasma methylmalonic acid (MMA) is important for the diagnosis and management of methylmalonic acidemia in pediatric populations. This work focuses on developing and validating a liquid chromatography tandem mass spectrometry (LC-MS/MS) method to monitor methylmalonic acidemia using a simple method preparation.

DESIGN AND METHODS

MMA and stable isotope labeled d3-MMA was extracted using supported liquid extraction (SLE). Assay imprecision, bias, linearity, recovery and carryover were determined. The relationship between MMA and propionyl acylcarnitine (C3-acylcarnitine) was also evaluated using historical paired results from 51 unique individuals.

RESULTS

Baseline separation between MMA and succinic acid was completed in 7min. The assay was linear from 0.1 to 500μM. The intra-day and inter-day imprecision CV ranged from 4.1 to 13.2% (0.3 to 526μM) and 5.0 to 15.7% (0.3 to 233μM), respectively. Recovery ranged from 93 to 125%. The correlation with a national reference laboratory LC-MS/MS assay showed a Deming regression of 1.026 and intercept of -1.335. Carryover was determined to be <0.04%. Patient-specific correlation was observed between MMA and C3-acylcarnitine.

CONCLUSION

This report describes the first LC-MS/MS method using SLE for MMA extraction. In addition, we illustrate the challenges encountered during this method development that should be assessed and resolved by any laboratory implementing a SLE LC-MS/MS assay designed to quantify analytes across several orders of magnitude.

Methylmalonic acid and neutrophil morphometric index in laboratory diagnosis of cobalamin deficiency without macrocytosis

INTRODUCTION

This study aimed to investigate the utility of methylmalonic acid (MMA) and neutrophil Cell Population Data, available on the Beckman Coulter LH750 Analyser (Miami, FL, USA), in laboratory assessment of cobalamin status in patients at risk of cobalamin deficiency, without macrocytosis and inflammation.

METHODS

The study group included 189 patients. Neutrophil Cell Population Data along with vitamin B12 and homocysteine were assessed in regard to MMA tertile groups.

RESULTS

Statistically significant differences were between lower and upper MMA tertile in serum B12 (P ˂ 0.001), homocysteine (P = 0.001) and neutrophil morphometric index, NeS-DW (P = 0.029). Also, serum B12 concentrations were significantly different between lower and middle MMA tertile, P = 0.005. Receiver operating characteristic analysis of NeS-DW ability to detect MMA˃367 nmol/L revealed a significant area under the curve AUC = 0.761 P ˂ 0.001 95% CI 0.693-0.830. Optimal cut-off value was NeS-DW˃3.51% with sensitivity of 74.19% and specificity of 68.87%.

CONCLUSION

In patients at risk of cobalamin deficiency and normal MCV, classification according to MMA revealed cobalamin status differences. Neutrophil morphometric index may be an indicator of early changes in neutrophil nucleus morphology caused by impaired cobalamin status.

High-Throughput Analysis of Methylmalonic Acid in Serum, Plasma, and Urine by LC-MS/MS. Method for Analyzing Isomers Without Chromatographic Separation

Measurement of methylmalonic acid (MMA) plays an important role in the diagnosis of vitamin B12 deficiency. Vitamin B12 is an essential cofactor for the enzymatic carbon rearrangement of methylmalonyl-CoA (MMA-CoA) to succinyl-CoA (SA-CoA), and the lack of vitamin B12 leads to elevated concentrations of MMA. Presence of succinic acid (SA) complicates the analysis because mass spectra of MMA and SA are indistinguishable, when analyzed in negative ion mode and the peaks are difficult to resolve chromatographically. We developed a method for the selective analysis of MMA that exploits the significant difference in fragmentation patterns of di-butyl derivatives of the isomers MMA and SA in a tandem mass spectrometer when analyzed in positive ion mode. Tandem mass spectra of di-butyl derivatives of MMA and SA are very distinct; this allows selective analysis of MMA in the presence of SA. The instrumental analysis is performed using liquid chromatography-tandem mass spectrometry (LC-MS/MS) in positive ion mode, which is, in combination with selective extraction of acidic compounds, is highly selective for organic acids with multiple carboxyl groups (dicarboxylic, tricarboxylic, etc.). In this method organic acids with a single carboxyl group are virtually undetectable in the mass spectrometer; the only organic acid, other than MMA, that is detected by this method is its isomer, SA. Quantitative measurement of MMA in this method is performed using a deconvolution algorithm, which mathematically resolves the signal corresponding to MMA and does not require chromatographic resolution of the MMA and SA peaks. Because of its high selectivity, the method utilizes isocratic chromatographic separation; reconditioning and re-equilibration of the chromatographic column between injections is unnecessary. The above features of the method allow high-throughput analysis of MMA with analysis cycle time of 1 min.

An LC-MS/MS method for serum methylmalonic acid suitable for monitoring vitamin B12 status in population surveys

Methylmalonic acid (MMA), a functional indicator of vitamin B12 insufficiency, was measured in the US population in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2004 using a GC/MS procedure that required 275 μL of sample and had a low throughput (36 samples/run). Our objective was to introduce a more efficient yet highly accurate LC-MS/MS method for NHANES 2011-2014. We adapted the sample preparation with some modifications from a published isotope-dilution LC-MS/MS procedure. The procedure utilized liquid-liquid extraction and generation of MMA dibutyl ester. Reversed-phase chromatography with isocratic elution allowed baseline resolution of MMA from its naturally occurring structural isomer succinic acid within 4.5 min. Our new method afforded an increased throughput (≤160 samples/run) and measured serum MMA with high sensitivity (LOD = 22.1 nmol/L) in only 75 μL of sample. Mean (±SD) recovery of MMA spiked into serum (2 d, 4 levels, 2 replicates each) was 94 % ± 5.5 %. Total imprecision (41 d, 2 replicates each) for three serum quality control pools was 4.9 %-7.9 % (97.1-548 nmol/L). The LC-MS/MS method showed excellent correlation (n = 326, r = 0.99) and no bias (Deming regression, Bland-Altman analysis) compared to the previous GC/MS method. Both methods produced virtually identical mean (±SD) MMA concentrations [LC-MS/MS: 18.47 ± 0.71 ng/mL (n = 17), GC/MS: 18.18 ± 0.67 ng/mL (n = 11)] on a future plasma reference material compared with a GC/MS method procedure from the National Institute of Standards and Technology [18.41 ± 0.70 ng/mL (n = 15)]. No adjustment will be necessary to compare previous (1999-2004) to future (2011-2014) NHANES MMA data.

Long-term intermittent hypoxia elevates cobalt levels in the brain and injures white matter in adult mice

STUDY OBJECTIVES

Exposure to the variable oxygenation patterns in obstructive sleep apnea (OSA) causes oxidative stress within the brain. We hypothesized that this stress is associated with increased levels of redox-active metals and white matter injury.

DESIGN

Participants were randomly allocated to a control or experimental group (single independent variable).

SETTING

University animal house.

PARTICIPANTS

Adult male C57BL/6J mice.

INTERVENTIONS

To model OSA, mice were exposed to long-term intermittent hypoxia (LTIH) for 10 hours/day for 8 weeks or sham intermittent hypoxia (SIH).

MEASUREMENTS AND RESULTS

Laser ablation-inductively coupled plasma-mass spectrometry was used to quantitatively map the distribution of the trace elements cobalt, copper, iron, and zinc in forebrain sections. Control mice contained 62 ± 7 ng cobalt/g wet weight, whereas LTIH mice contained 5600 ± 600 ng cobalt/g wet weight (P < 0.0001). Other elements were unchanged between conditions. Cobalt was concentrated within white matter regions of the brain, including the corpus callosum. Compared to that of control mice, the corpus callosum of LTIH mice had significantly more endoplasmic reticulum stress, fewer myelin-associated proteins, disorganized myelin sheaths, and more degenerated axon profiles. Because cobalt is an essential component of vitamin B12, serum methylmalonic acid (MMA) levels were measured. LTIH mice had low MMA levels (P < 0.0001), indicative of increased B12 activity.

CONCLUSIONS

Long-term intermittent hypoxia increases brain cobalt, predominantly in the white matter. The increased cobalt is associated with endoplasmic reticulum stress, myelin loss, and axonal injury. Low plasma methylmalonic acid levels are associated with white matter injury in long-term intermittent hypoxia and possibly in obstructive sleep apnea.

The transcobalamin receptor knockout mouse: a model for vitamin B12 deficiency in the central nervous system

The membrane receptor (TCblR/CD320) for transcobalamin (TC)-bound cobalamin (Cbl) facilitates the cellular uptake of Cbl. A genetically modified mouse model involving ablation of the CD320 gene was generated to study the effects on cobalamin homeostasis. The nonlethal nature of this knockout and the lack of systemic cobalamin deficiency point to other mechanisms for cellular Cbl uptake in the mouse. However, severe cobalamin depletion in the central nervous system (CNS) after birth (P<0.01) indicates that TCblR is the only receptor responsible for Cbl uptake in the CNS. Metabolic Cbl deficiency in the brain was evident from the increased methylmalonic acid (P<0.01-0.04), homocysteine (P<0.01), cystathionine (P<0.01), and the decreased S-adenosylmethionine/S-adenosyl homocysteine ratio (P<0.01). The CNS pathology of Cbl deficiency seen in humans may not manifest in this mouse model; however, it does provide a model with which to evaluate metabolic pathways and genes affected.