Critical sample pretreatment in monitoring dried blood spot citrulline

Urea Cycle Related Amino Acids Measured in Dried Bloodspots Enable Long-Term In Vivo Monitoring and Therapeutic Adjustment

BACKGROUND

Dried bloodspots are easy to collect and to transport to assess various metabolites, such as amino acids. Dried bloodspots are routinely used for diagnosis and monitoring of some inherited metabolic diseases.

METHODS

Measurement of amino acids from dried blood spots by liquid chromatography-tandem mass spectrometry.

RESULTS

We describe a novel rapid method to measure underivatised urea cycle related amino acids. Application of this method enabled accurate monitoring of these amino acids to assess the efficacy of therapies in argininosuccinate lyase deficient mice and monitoring of these metabolites in patients with urea cycle defects.

CONCLUSION

Measuring urea cycle related amino acids in urea cycle defects from dried blood spots is a reliable tool in animal research and will be of benefit in the clinic, facilitating optimisation of protein-restricted diet and preventing amino acid deprivation.

The use of mass spectrometry to analyze dried blood spots

Dried blood spots (DBS) typically consist in the deposition of small volumes of capillary blood onto dedicated paper cards. Comparatively to whole blood or plasma samples, their benefits rely in the fact that sample collection is easier and that logistic aspects related to sample storage and shipment can be relatively limited, respectively, without the need of a refrigerator or dry ice. Originally, this approach has been developed in the sixties to support the analysis of phenylalanine for the detection of phenylketonuria in newborns using bacterial inhibition test. In the nineties tandem mass spectrometry was established as the detection technique for phenylalanine and tyrosine. DBS became rapidly recognized for their clinical value: they were widely implemented in pediatric settings with mass spectrometric detection, and were closely associated to the debut of newborn screening (NBS) programs, as a part of public health policies. Since then, sample collection on paper cards has been explored with various analytical techniques in other areas more or less successfully regarding large-scale applications. Moreover, in the last 5 years a regain of interest for DBS was observed and originated from the bioanalytical community to support drug development (e.g., PK studies) or therapeutic drug monitoring mainly. Those recent applications were essentially driven by improved sensitivity of triple quadrupole mass spectrometers. This review presents an overall view of all instrumental and methodological developments for DBS analysis with mass spectrometric detection, with and without separation techniques. A general introduction to DBS will describe their advantages and historical aspects of their emergence. A second section will focus on blood collection, with a strong emphasis on specific parameters that can impact quantitative analysis, including chromatographic effects, hematocrit effects, blood effects, and analyte stability. A third part of the review is dedicated to sample preparation and will consider off-line and on-line extractions; in particular, instrumental designs that have been developed so far for DBS extraction will be detailed. Flow injection analysis and applications will be discussed in section IV. The application of surface analysis mass spectrometry (DESI, paper spray, DART, APTDCI, MALDI, LDTD-APCI, and ICP) to DBS is described in section V, while applications based on separation techniques (e.g., liquid or gas chromatography) are presented in section VI. To conclude this review, the current status of DBS analysis is summarized, and future perspectives are provided.

Citrulline concentration in routinely collected neonatal dried blood spots cannot be used to predict necrotising enterocolitis

AIM

Low citrulline concentration is a marker of low functional enterocyte mass, which may predispose neonates to necrotising enterocolitis (NEC). We hypothesised that citrulline could be used to assess the NEC risk that could not be accounted for by gestational age and birthweight. This study investigated whether citrulline concentrations routinely measured in neonatal dried blood spots (DBS) could predict NEC.

METHODS

We used national Danish registries to retrospectively identify all 361 babies born between 2003 and 2009 who were diagnosed with NEC and had a valid citrulline concentration measured from a DBS sample. The control group comprised 1083 healthy newborns, with three controls for every newborn with NEC, matched for birthweight and gestational age.

RESULTS

Neonatal dried blood spots were collected between 2 and 21 days of life, with a median of 8 days. The results showed that NEC was not associated with low citrulline concentration, either in a direct comparison between the NEC and control groups or in a multivariate logistic regression (p = 0.73).

CONCLUSION

The findings of this study show that the citrulline concentrations found in routine DBS samples between 2003 and 2009 did not predict NEC in newborn babies.

Citrulline levels in a paediatric age group: does measurement on dried blood spots have additional value?

BACKGROUND

Citrulline is considered to be a marker of absorptive enterocyte mass. Citrulline levels can be measured in plasma or dried blood spot (DBS) samples. The purpose of this study is to calculate reference intervals for plasma and DBS citrulline concentrations in children and to examine the effect of age and gender.

METHODS

In 151 healthy subjects ranging from 1 month to 20 years of age, plasma and DBS citrulline concentration were determined by using Liquid Chromatography-tandem Mass Spectrometry. Citrulline concentrations were examined in relation to age and gender. Reference values were calculated according to the guidelines of the International Federation of Clinical Chemistry and the National Committee on Clinical Laboratory Standards.

RESULTS

No significant influence of age and gender could be discerned on plasma or DBS citrulline concentration. In children, the reference intervals for citrulline bounded by the 2.5 and 97.5 percentiles are 13.31-69.05 μmol/L and 23.70-49.04 μmol/L for plasma and DBS samples respectively.

CONCLUSIONS

The reference intervals for citrulline levels in healthy children are widely dispersed. Measuring citrulline concentrations in dried blood spots delivers no additional value to plasma measurements for the calculation of reference intervals in children.

Simultaneous determination of l-citrulline and l-arginine in plasma by high performance liquid chromatography

OBJECTIVE

To develop a method for simultaneously determining l-citrulline and L-arginine levels in plasma using RP-HPLC with ultraviolet detection.

DESIGN AND METHODS

Plasma samples were deproteinized by trichloroacetic acid and heat. Phenyl-isothiocyanate (PITC) solution was used as derivatization reagent and a gradient elution was carried out.

RESULTS

The linearity for L-citrulline and L-arginine ranged from 0 to at least 1000 micromol/L. R(2) values were above 0.9999 for both. LODs for L-citrulline and L-arginine were 0.0201 micromol/L and 0.0476 micromol/L, respectively, while LOQs were 0.240 micromol/L and 0.448 micromol/L, respectively. Intra- and inter-day CVs were less than 3.40% and 7.2%, respectively. The average recovery was from 86.22% to 118.9%. L-citrulline and L-arginine concentrations in healthy controls were 60.77+/-9.18 micromol/L and 58.19+/-16.43 micromol/L, respectively.

CONCLUSION

This approach offers a reliable, efficient analytical platform for the simultaneous determination of citrulline and arginine levels in plasma.

Plasma citrulline measurement using UPLC tandem mass-spectrometry to determine small intestinal enterocyte pathology

Citrulline is a nonessential free amino acid, detectable in various biological fluids such as plasma, urine and cerebrospinal fluid. The plasma citrulline concentration is increasingly considered to be a reliable biomarker of enterocyte function. Current analysis usually involves lengthy HPLC separations as a part of classical amino acid profiling, or mass spectrometry usually in combination with derivatization. We employed UPLC-HILIC-tandem mass-spectrometry (MS/MS) of acetonitrile-derived supernatants from plasma samples of control subjects and of patients who had received myeloablative chemotherapy. Detection was achieved by the selected reaction monitoring of transitions: m/z 176-->70 and 180-->74 (for the deuterated standard), respectively. The method was precise and accurate with inter-day CV<3.9% (n=30), recoveries ranging from 98.0 to 100.3% and high linearity from 0.3 to at least 2,000 micromol/L. The results for 202 plasma samples agreed well with those obtained by the classical HPLC-fluorescence method. By a simple protein precipitation/extraction step and the UPLC separation the result can be available within 30 min of receipt with a capacity of at least 12 assays per hour. Citrulline in blood and plasma or serum was stable for at least 2 days at room temperature which would permit postal transport to the laboratory. The UPLC-MS/MS method for measuring plasma citrulline concentrations is fast and robust and is therefore an ideal tool for monitoring the intestinal enterocyte capacity of patients with various pathological conditions.