Measurement of plasma 5-hydroxyindole acetic acid by liquid chromatography tandem mass spectrometry—Comparison with HPLC methodology

Plasma or serum 5-hydroxyindoleacetic acid can be used interchangeably in patients with neuroendocrine tumours

5-hydroxyindole acetic acid, a metabolite of serotonin, is used in the diagnosis and monitoring of patients with neuroendocrine tumours, in particular patients with small intestinal neuroendocrine tumours associated with the carcinoid syndrome. Analysis of 5-hydroxyindole acetic acid was commonly performed in urine, but blood-based assays are now becoming available. The objective of this study was to assess how 5-hydroxyindole acetic acid compares in plasma and serum as a biochemical marker of neuroendocrine tumours. Twenty-four-hour urine, plasma and serum samples were obtained from 80 patients with neuroendocrine tumours and 30 healthy volunteers. We developed a liquid chromatography tandem mass spectrometry assay for plasma and serum 5-hydroxyindole acetic acid. Comparison was made between them, and their cut-off was determined using a receiver-operating characteristic curve. A close correlation was shown between plasma and serum 5-hydroxyindole acetic acid. At a cut-off of 135 nmol/l, a sensitivity of 91.2% with a specificity of 61.9% was obtained for both compared to the urinary assay. A statistically significant agreement was shown when plasma and serum 5-hydroxyindole acetic acid were compared with the currently used urine assay in patients with neuroendocrine tumours; κ = 0.675 (95% CI 0.49 to 0.86), p < 0.001 and healthy volunteers; 0.967 (95% CI 0.828 to 0.999), p = <0.001. In conclusion, 5-hydroxyindole acetic acid in plasma and serum were comparable, hence either sample type can be used interchangeably.

Analysis and enhancement of the energy utilization efficiency of corn stover using strain Lsc-8 in a bioelectrochemical system

The strain Lsc-8 can produce a current density of 33.08 µA cm^-2 using carboxymethylcellulose (CMC) as a carbon source in a three-electrode configuration. A co-culture system of strain Lsc-8 and Geobacter sulfurreducens PCA was used to efficiently convert cellulose into electricity to improve the electricity generation capability of microbial fuel cells (MFCs). The maximum current density achieved by the co-culture with CMC was 559 μA cm^-2, which was much higher than that of strain Lsc-8 using CMC as the carbon source. The maximum power density reached 492.05 ± 52.63 mW cm^-2, which is much higher than that previously reported. Interaction mechanism studies showed that strain Lsc-8 had the ability to secrete riboflavin and convert cellulose into acetic acid, which might be the reason for the high electrical production performance of the co-culture system. In addition, to the best of our knowledge, a co-culture or single bacteria system using agricultural straw as the carbon source to generate electricity has not been reported. In this study, the maximum current density of the three-electrode system inoculated with strain Lsc-8 was 14.56 μA cm^-2 with raw corn stover as the sole carbon source. Raw corn stover as a carbon source was also investigated for use in a co-culture system. The maximum current density achieved by the co-culture was 592 μA cm^-2. The co-culture system showed a similar electricity generation capability when using raw corn stover and when using CMC. This research shows for the first time that a co-culture or single bacteria system can realize both waste biomass treatment and waste power generation.

Quantification of serotonin and eight of its metabolites in plasma of healthy volunteers by mass spectrometry

Serotonin is transformed into melatonin under the control of the light/dark cycle, representing a cornerstone of circadian rhythmicity. Serotonin also undergoes extensive metabolism to produce 5-hydroxyindoleacetic acid (5-HIAA), a biomarker for the diagnosis and monitoring of serotonin secreting neuroendocrine tumors (NETs). While serotonin, melatonin and their metabolites are part of an integrated comprehensive system, human observations about their respective plasma concentrations are still limited. We report here for the first time a multiplex UHPLC-MS/MS assay for the quantification of serotonin, 5-HIAA, 5-hydroxytryptophol (5-HTPL), N-acetyl-serotonin (NAS), Mel, 6-OH-Mel, 5-methoxytryptamine (5-MT), 5-methoxytryptophol (5-MTPL), and 5-methoxyindoleacetic acid (5-MIAA) in human plasma. Analytes were extracted by protein precipitation and solid phase extraction. Plasma concentrations for these analytes were determined in 102 healthy volunteers. The LLOQ of the assay ranges from 2.2 nM for serotonin to 1.0 pM for 6-OH-Mel. This sensitivity enables the quantification of circulating serotonin, 5-HIAA, NAS, Mel, and 5-MIAA, even at their lowest diurnal concentrations. This assay will enable specific, precise and accurate measurement of serotonin, Mel and their metabolites to draw a detailed picture of this complex pineal metabolism, allowing a dynamic understanding of these pathways and providing promising biomarkers and a metabolic signature for serotonin-secreting NETs.

Quantification of 5-Hydroxyindoleacetic Acid in Urine by Ultra-performance Liquid Chromatography Tandem Mass Spectrometry

Serotonin (5-hydroxytryptamine) is a neurotransmitter produced in excess by carcinoid tumors, which develop from enterochromaffin cells. 5-Hydroxyindoleacetic acid (5-HIAA) is the primary urinary metabolite of serotonin, making measurement of 5-HIAA useful in the diagnosis and management of carcinoid tumors. Here we describe a simple, inexpensive, and fast method for the detection and quantification of 5-HIAA in urine. Samples are prepared by simple 1:1 dilution. The instrumental analysis is performed by chromatographic separation on a reverse-phase analytical column followed by detection using a triple quadrupole mass spectrometer with electrospray ionization in positive ion mode. Data are acquired by multiple reaction monitoring (MRM).

Full-Color Long-Lived Room Temperature Phosphorescence in Aqueous Environment

Long-lived room temperature phosphorescence (RTP) materials are widely utilized in the field of biological and chemical sensing, due to their unique characteristics of long-lived luminescence and no background autofluorescence. However, the realization of full-color RTP in aqueous solution still remains a great challenge. Herein, a feasible strategy for achieving high stability and full-color RTP of carbon dots (CDs)-based composite materials in aqueous environment is reported by constructing a rigid hydrogen bonds' network. The obtained m,p-CDs@CA composite materials exhibit deep-blue RTP with phosphorescence quantum yield of 23.2% and lifetime of 1.74 s, and the afterglow can last for over 12 s. More importantly, the m,p-CDs@CA composite materials are desirable in the detection of biomarkers, because of excellent stability, dispersion, and long-lived RTP properties. The m,p-CDs@CA suspension also displays excellent sensitivity, and a limitation of detection as low as 5.61 and 550 nm for biomarkers 5-hydroxyindole-3-acetic acid (HIAA) and serotonin (5-hydroxytryptamine, HT), respectively. Meanwhile, the sensing performance exhibits excellent selectivity even in the presence of other competitive species in blood plasma and urine. With superior selectivity, the long-lived phosphorescence probe based on m,p-CDs@CA suspension can be as an effective biomarker for carcinoid identification, which has potential application in clinical analysis.

Electrochemical sensor based on MIP for highly sensitive detection of 5-hydroxyindole-3-acetic acid carcinoid cancer biomarker in human biological fluids

An electrochemically synthetized nano-sensor based on molecularly imprinted polypyrrole (MIPPy) was successfully developed for the detection of 5-hydroxyindole-3-acetic acid (5-HIAA) in human biological fluids namely serum, urine, and plasma. The imprinted glassy carbon electrode was prepared by electropolymerisation of pyrrole via cyclic voltammetry (C.V). After completely leaching the imprinted molecules from the polymeric network, complementary cavities are created. The developed MIPPy sensor, under optimized conditions, shows a high sensitivity towards the target molecule (LOQ = 5 × 10^-11 M). Moreover, it presents a wide linear response in the range of 5 × 10^-11 - 5 × 10^-5 M (R² > 0.999) with a detection limit of 15 × 10^-12 M. In order to evaluate the selectivity of the MIPPy film, several structural analogues and compounds forming the real matrices were tested. The obtained results show an excellent recovery rate (between 98.86 and 101.52%) proving the promising application of the proposed nano-sensor in the detection of 5-HIAA in human biological fluids without any significant interference recorded.

A rapid liquid chromatography-tandem mass spectrometry method for the analysis of urinary 5-hydroxyindoleacetic acid (5-HIAA) that incorporates a 13C-labelled internal standard

BACKGROUND

Urinary 5-hydroxyindoleacetic acid (5-HIAA) is a first-line investigation for gastrointestinal neuroendocrine tumours that secrete serotonin. It also has clinical utility for monitoring disease progression and therapeutic response.

AIM

To develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for urinary 5-hydroxyindoleacetic acid that incorporates a supported liquid extraction and ¹³C-labelled internal standard.

METHODS

Samples were diluted in ammonium acetate containing a ¹³C-labelled internal standard (5-hydroxyindole-3a,4,5,6,7,7a-¹³C₆-3-acetic acid). Supported liquid extraction was performed followed by chromatographic separation using the 2.1 × 30 mm CORTECS® UPLC® T3 column. Mass spectrometry detection (Waters Xevo TQ-XS) was performed in electrospray positive mode using the transitions 192.3 > 146.4 m/z (quantifier) and 192.3 > 118.4 m/z (qualifier) for 5-hydroxyindoleacetic acid and 198.2 > 152.4 m/z for ¹³C-5-HIAA.

RESULTS

A well-defined 5-hydroxyindoleacetic acid peak was observed at 0.8 min with a run time of 2.4 min. The assay was linear (r² > 0.99) to 382 µmol/L, with a lower limit of quantification of 5.3 µmol/L (CV <15%). Analysis of 29 external quality assurance samples showed good agreement between our method and the UKNEQAS method mean (4.7% positive bias). The intra- and inter-assay precision was within acceptable limits, and the assay was stable up to 96 h postextraction with minimal carryover.

CONCLUSION

We have developed a robust LC-MS/MS method with semi-automated extraction that offers an improved run time and performance over the existing, labour-intensive, HPLC method. The method was quick, precise, showed good agreement with UKNEQAS external quality assurance material and is in routine service for clinical samples.

Comparison of Serum and Urinary 5-Hydroxyindoleacetic Acid as Biomarker for Neuroendocrine Neoplasms

CONTEXT

Patients with serotonin-secreting neuroendocrine neoplasms (NENs) have increased serum 5-hydroxyindoleacetic acid (5HIAA) concentrations. Serum 5HIAA thus serves as a biomarker in NEN.

OBJECTIVE

To evaluate an improved tandem mass spectrometric serum 5HIAA assay for diagnosis and follow-up of NEN in a clinical cohort.

DESIGN

A retrospective study during 2016-2018 at the Diagnostic Center and Department of Endocrinology at Helsinki University Hospital, Finland.

METHODS

Detailed patient data was obtained from 116 patients. Serum 5HIAA was analyzed by 2 different liquid chromatography with tandem mass spectrometry (LC-MS/MS) assays with samples prepared either by protein precipitation or solid phase extraction. Twenty-four-hour urine 5HIAA samples (n = 33) were analyzed by amperometric LC, and the results were compared. Specificity and sensitivity were calculated by receiver operating characteristic (ROC) analysis.

RESULTS

We achieved 5 to10 000 nmol/L linearity and ≤2.5% variation with our new serum 5HIAA assay. In ROC analysis, the area under curve was 85% by serum assays [upper reference limit (URL) value 123 nmol/L] and 88% by the 24-h urine 5HIAA assay (URL value of 47.1 µmol), respectively. A difference (P < 0.001) between patients with active NEN and patients in remission was found by all 5HIAA assays.

CONCLUSION

Serum 5HIAA by LC-MS/MS after protein precipitation performs equally well for the diagnosis of NEN as urinary 5HIAA LC assay. The outcome and sensitivity for serum and 24-h urine assays are convergent. Due to much more reliable and convenient sampling, we recommend serum instead of 24-h urine 5HIAA for diagnosis and follow-up of NEN patients.

Ultrafast LC-MS/MS analysis of 5-hydroxyindoleacetic acid (5-HIAA) in serum

A very quick and easy LC-MS/MS analysis method for 5-HIAA (5-hydoxyindoleacetic acid) has been developed. The method was fully validated and proved to work well in a clinical setting. Precision at the upper reference limit 123 nmol/L was 3,3% CV. Accuracy ranged from 96% at low levels (50-100 nmol/L) to 99.7% at high levels (500 nmol/L). A previously reported reference interval of 35-123 nmol/L was confirmed as valid based on analysis of 40 samples from voluntary blood donors.

Plasmatic and Urinary 5-Hydroxyindolacetic Acid Measurements in Patients With Midgut Neuroendocrine Tumors: A GTE Study

CONTEXT

Although 24-hour urinary 5-hydroxyindolacetic acid (24u5HIAA) is a key biomarker in midgut neuroendocrine tumors (NETs), it may be inaccurate and inconvenient.

OBJECTIVE

We compared the diagnostic performances of 24u5HIAA, overnight urinary 5HIAA (Ou5HIAA), and plasmatic 5HIAA (p5HIAA) in midgut NETs.

METHODS

This prospective, multicenter study included 80 patients with metastatic midgut NETs and 17 control patients with irritable bowel syndrome. 24u5HIAA, Ou5HIAA, and p5HIAA were measured in urine and plasma collected on 2 consecutive days following a specific recommended diet. Reproducibility of the biomarkers was evaluated by the Spearman test. Diagnostic performance was assessed by the area under the receiver operating characteristic curve (AUROC). Correlations with the main clinical features and declared observance to the specific diet were assessed using AUROC and logistic regression models.

RESULTS

The reproducibility of 24u5HIAA, Ou5HIAA, and p5HIAA were excellent (ρ = 0.916; 0.897; 0.978, respectively, P < .001) with significant discrimination between patients and controls (AUROC = 0.795, P < .001; 0.757, P = .001; 0.717, P = .005, respectively). All 3 markers were correlated with the presence of carcinoid syndrome (AUROC = 0.702, P = .006; 0.701, P = .006; 0.697, P = .007, respectively), carcinoid heart disease (AUROC = 0.896; 0.887; 0.923, P < .001, respectively, P < .001), and liver metastatic involvement greater than 30% (AUROC = 0.827; 0.807; 0.849, P < .001, respectively, P < .001), independent from other traditional prognostic factors. Biomarker levels were similar between patients with optimal or suboptimal diet observance.

CONCLUSION

Ou5HIAA and p5HIAA could be used as more convenient alternatives to 24u5HIAA in patients with metastatic midgut NETs. Prospective long-term studies with repeated dosages are needed.

Serotonin pathway in carcinoid syndrome: Clinical, diagnostic, prognostic and therapeutic implications

Carcinoid syndrome represents the most common functional syndrome that affects patients with neuroendocrine neoplasms. Its clinical presentation is really heterogeneous, ranging from mild and often misdiagnosed symptoms to severe manifestations, that significantly worsen the patient's quality of life, such as difficult-to-control diarrhoea and fibrotic complications. Serotonin pathway alteration plays a central role in the pathophysiology of carcinoid syndrome, accounting for most clinical manifestations and providing diagnostic tools. Serotonin pathway is complex, resulting in production of biologically active molecules such as serotonin and melatonin, as well as of different intermediate molecules and final metabolites. These activities require site- and tissue-specific catalytic enzymes. Variable expression and activities of these enzymes result in different clinical pictures, according to primary site of origin of the tumour. At the same time, the biochemical diagnosis of carcinoid syndrome could be difficult even in case of typical symptoms. Therefore, the accuracy of the diagnostic methods of assessment should be improved, also attenuating the impact of confounding factors and maybe considering new serotonin precursors or metabolites as diagnostic markers. Finally, the prognostic role of serotonin markers has been only evaluated for its metabolite 5-hydroxyindole acetic acid but, due to heterogeneous and biased study designs, no definitive conclusions have been achieved. The most recent progress is represented by the new therapeutic agent telotristat, an inhibitor of the enzyme tryptophan hydroxylase, which blocks the conversion of tryptophan in 5-hydroxy-tryptophan. The present review investigates the clinical significance of serotonin pathway in carcinoid syndrome, considering its role in the pathogenesis, diagnosis, prognosis and therapy.

Specific urinary metabolites in canine mammary gland tumors

The identification of biomarkers that distinguish diseased from healthy individuals is of great interest in human and veterinary fields. In this research area, a metabolomic approach and its related statistical analyses can be useful for biomarker determination and allow non-invasive discrimination of healthy volunteers from breast cancer patients. In this study, we focused on the most common canine neoplasm, mammary gland tumor, and herein, we describe a simple method using ultra-high-performance liquid chromatography to determine the levels of tyrosine and its metabolites (epinephrine, 3,4-dihydroxy-L-phenylalanine, 3,4-dihydroxyphenylacetic acid, and vanillylmandelic acid), tryptophan and its metabolites (5-hydroxyindolacetic acid, indoxyl sulfate, serotonin, and kynurenic acid) in canine mammary cancer urine samples. Our results indicated significantly increased concentrations of three tryptophan metabolites, 5-hydroxyindolacetic acid (p < 0.001), serotonin, indoxyl sulfate (p < 0.01), and kynurenic acid (p < 0.05), and 2 tyrosine metabolites, 3,4-dihydroxy-L-phenylalanine (p < 0.001), and epinephrine (p < 0.05) in urine samples from the mammary gland tumor group compared to concentrations in urine samples from the healthy group. The results indicate that select urinary tyrosine and tryptophan metabolites may be useful as non-invasive diagnostic markers as well as in developing a therapeutic strategy for canine mammary gland tumors.

Quantitative Profiling of Platelet-Rich Plasma Indole Markers by Direct-Matrix Derivatization Combined with LC-MS/MS in Patients with Neuroendocrine Tumors

BACKGROUND

Currently, several indole markers are measured separately to support diagnosis and follow-up of patients with neuroendocrine tumors (NETs). We have developed a sensitive mass spectrometry method that simultaneously quantifies all relevant tryptophan-related indoles (tryptophan, 5-hydroxytryptophan, serotonin, 5-hydroxyindoleacetic acid) in platelet-rich plasma. Direct-matrix derivatization was used to make the chemical properties of the indoles uniform and to improve the analytical sensitivity and specificity of the assay.

METHODS

In situ derivatization was performed directly in platelet-rich plasma with propionic anhydride at an ambient temperature. The derivatized indoles were extracted by online solid-phase extraction and eluted to the analytical column for separation followed by mass spectrometric detection. The method was validated according to international guidelines. Platelet-rich plasma samples from 68 healthy individuals and 40 NET patients were analyzed for tryptophan, 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid.

RESULTS

The method reproducibly quantified relevant indoles in 8.5 min, including online sample cleanup. Intra- and interassay imprecision, evaluated at 3 different concentrations, ranged from 2.0% to 12% and 1.9% to 13%, respectively. The limit of quantification was sufficient to measure endogenous concentrations of all 4 indoles. Healthy individuals and NET patients had different concentrations of 5-hydroxytryptophan, serotonin, and 5-hydroxyindoleacetic acid, but tryptophan concentrations were the same.

CONCLUSIONS

Direct-matrix derivatization in combination with LC-MS/MS is a powerful tool for the simultaneous quantification of all tryptophan-related indoles in platelet-rich plasma. Simultaneous profiling of relevant indoles improves the biochemical characterization and follow-up of NETs.

The role of 5-hydroxyindoleacetic acid in neuroendocrine tumors: the journey so far

5-Hydroxyindole acetic acid (5-HIAA) is a surrogate marker for serotonin measurement and one of the first biochemical markers used in neuroendocrine tumors. In this review, we give a brief history of 5-HIAA and its precursor serotonin. We discuss its clinical utility and diagnostic performance in small intestinal neuroendocrine tumor and describe the challenges encountered during its analysis, historically performed in urine. The introduction of blood-based assays will help overcome some of the issues associated with its measurement in urine. The diagnostic performance of serum and plasma 5-HIAA has been shown to be comparable to that of urine 5-HIAA. Thus, analysis in either serum or plasma will provide a practical and convenient alternative to urine.

Measurement of urinary 5-HIAA: correlation between spot versus 24-h urine collection

BACKGROUND

The 24-h urinary output of 5-hydroxyindoleacetic acid (5-HIAA) is used to monitor disease progression and treatment responses of neuroendocrine neoplasms (NENs). Several conditions are required for 5-HIAA assay, involving urine collection/preservation and food/drug restrictions.

AIM

To evaluate the correlation between 5-HIAA concentration in a spot urine sample and the output in a 24-h urine collection, and whether spot urine specimens can replace 24-h collection.

METHODS

Patients with NENs or symptoms suggestive of NENs were asked to provide a separate spot urine at the end of the 24-h urine collection for 5-HIAA assessment. The upper reference limit for 24-h urinary 5-HIAA was 40 µmol/24 h. 5-HIAA measurements in spot urine samples were corrected for variation in urine flow rate by expressing results as a ratio to creatinine concentration.

RESULTS

We included 136 paired urinary samples for 5-HIAA assessment from 111 patients (100 NENs). The correlation between 5-HIAA values measured in 24-h and spot urines was r = +0.863 (P < 0.001) and r = +0.840 (P < 0.001) including only NEN patients. Using the 24-h urinary 5-HIAA as reference method, the AUC on ROC analysis for spot urinary 5-HIAA was 0.948 (95% CI, 0.914-0.983; P < 0.001), attaining a sensitivity of 83% and specificity of 95% using 5.3 mol/mmol as cut-off for the spot urine. The AUC among NEN patients alone was 0.945 (95% CI, 0.904-0.987; P < 0.001).

CONCLUSIONS

The ratio of 5-HIAA to creatinine in a spot urine could replace the measurement of 5-HIAA output in a 24-h urine collection, especially for follow-up of patients with known elevated 5-HIAA levels.

Specific Urinary Metabolites in Malignant Melanoma

Background and objectives: Melanin, which has a confirmed role in melanoma cell behaviour, is formed in the process of melanogenesis and is synthesized from tryptophan, L-tyrosine and their metabolites. All these metabolites are easily detectable by chromatography in urine. Materials and Methods: Urine samples of 133 individuals (82 malignant melanoma patients and 51 healthy controls) were analysed by reversed-phase high-performance liquid chromatography (RP-HPLC). The diagnosis of malignant melanoma was confirmed histologically. Results: Chromatograms of melanoma patients showed increased levels of 5,6-dihydroxyindole-2-carboxylic acid, vanilmandelic acid, homovanilic acid, tryptophan, 5-hydroxyindole-3-acetic acid, and indoxyl sulphate compared to healthy controls. Concentration of indoxyl sulphate, homovanilic acid and tryptophan were significantly increased even in the low clinical stage 0 of the disease (indoxyl sulphate, homovanilic acid and tryptophan in patients with clinical stage 0 vs. controls expressed as medium/ interquartile range in µmol/mmol creatinine: 28.37/15.30 vs. 5.00/6.91; 47.97/33.08 vs. 7.33/21.25; and 16.38/15.98 vs. 3.46/6.22, respectively). Conclusions: HPLC detection of metabolites of L-tyrosine and tryptophan in the urine of melanoma patients may play a significant role in diagnostics as well as a therapeutic strategy of melanoma cancer.

Recent Trends in the Quantification of Biogenic Amines in Biofluids as Biomarkers of Various Disorders: A Review

Biogenic amines (BAs) are bioactive endogenous compounds which play a significant physiological role in many cell processes like cell proliferation and differentiation, signal transduction and membrane stability. Likewise, they are important in the regulation of body temperature, the increase/decrease of blood pressure or intake of nutrition, as well as in the synthesis of nucleic acids and proteins, hormones and alkaloids. Additionally, it was confirmed that these compounds can be considered as useful biomarkers for the diagnosis, therapy and prognosis of several neuroendocrine and cardiovascular disorders, including neuroendocrine tumours (NET), schizophrenia and Parkinson's Disease. Due to the fact that BAs are chemically unstable, light-sensitive and possess a high tendency for spontaneous oxidation and decomposition at high pH values, their determination is a real challenge. Moreover, their concentrations in biological matrices are extremely low. These issues make the measurement of BA levels in biological matrices problematic and the application of reliable bioanalytical methods for the extraction and determination of these molecules is needed. This article presents an overview of the most recent trends in the quantification of BAs in human samples with a special focus on liquid chromatography (LC), gas chromatography (GC) and capillary electrophoresis (CE) techniques. Thus, new approaches and technical possibilities applied in these methodologies for the assessment of BA profiles in human samples and the priorities for future research are reported and critically discussed. Moreover, the most important applications of LC, GC and CE in pharmacology, psychology, oncology and clinical endocrinology in the area of the analysis of BAs for the diagnosis, follow-up and monitoring of the therapy of various health disorders are presented and critically evaluated.

Urinary sampling for 5HIAA and metanephrines determination: revisiting the recommendations

CONTEXT

Biogenic amines such as 5-hydroxy-indole acetic acid (5HIAA) the main metabolite of serotonin or metanephrines (catecholamines metabolites) are used as biomarkers of neuroendocrine tumours.

OBJECTIVE

To re-evaluate the recommendations for urinary sampling (preservatives, diet, drugs, etc.) as many of the reported analytical interferences supporting these recommendations are related to obsolete assays.

METHODS

Bibliographic analysis of old and modern assays concerning preservation, extraction, assay and interferences.

RESULTS

5HIAA may degrade as soon as urine is excreted. Thus, acids as preservatives (hydrochloric or acetic acid) have to be immediately added. Care should be taken not to decrease the pH under 2. Urine preservative for metanephrine assays is not mandatory. Diets including serotonin-, tryptophan- and dopamine-rich foods have to be avoided depending on the biomarkers investigated (bananas, plantain, nuts, etc.). Tryptophan-rich over-the-counter formulas have to be prohibited when 5HIAA has to be assayed. Acetaminophen may interfere with electrochemical detection depending on high-pressure liquid chromatography (HPLC) parameters. No interference is known with mass spectrometric assays but with the one described for metanephrines determination. Some drugs interfere however with serotonin and catecholamines secretion and/or metabolism (monoamine oxidase inhibitors, serotonin or dopamine recapture inhibitors, etc.).

CONCLUSION

Revisited recommendations are provided for the diet, the drugs and the preservatives before HPLC coupled with electrochemical and mass spectrometry assays.

Exogenous sample contamination. Sources and interference

Clinical laboratory medicine is involved in the vast majority of patient care pathways. It has been estimated that pathology results inform 60-70% of critical patient care decisions. The primary goal of the laboratory is to produce precise and accurate results which reflect the true situation in vivo. It is not surprising that interference occurs in laboratory analysis given the complexity of some of the assays used to perform them. Interference is defined as "the effect of a substance upon any step in the determination of the concentration or catalytic activity of the metabolite". Exogenous interferences are defined as those that derive from outside of the body and are therefore not normally found in a specimen and can cause either a positive or negative bias in analytical results. Interferences in analysis can come from various sources and can be classified as endogenous or exogenous. Exogenous substances could be introduced at any point in the sample journey. The laboratory must take responsibility for the quality of results produced. It has a responsibility to have processes in place to identify and minimise the occurrence and effect contamination and interference. To do this well the laboratory needs to work with clinicians and manufacturers. Failure to identify an erroneous result could have an impact on patient care, patient safety and also on hospital budgets. However it is not always easy to recognise interferences. This review summarises the types and sources of exogenous interference and some steps to minimise the impact they have.

Determination of urinary 5-hydroxyindoleacetic acid by combining Dμ-SPE using carbon coated TiO2 nanotubes and LC–MS/MS

Background: In this article, carbon coated titanium dioxide nanotubes (TiO2-NT@C) are employed for the determination of 5-hydroxyindole-3-acetic acid in urine by LC–MS/MS. Results: All the variables involved in the extraction have been studied and optimized in depth. The method has been analytically characterized on the basis of its linearity, accuracy, sensitivity and precision. The LOD is 155.8 μg/l while the repeatability and the reproducibility, expressed as RSD, are better than 5.42 and 5.25%, respectively. The obtained relative recovery is 115%. Conclusion: TiO2-NT@C permit the efficient extraction of 5-hydroxyindole-3-acetic acid from complex biological samples such as urine allowing its sensitive determination by LC–MS/MS.

Serum and plasma 5-hydroxyindoleacetic acid as an alternative to 24-h urine 5-hydroxyindoleacetic acid measurement

BACKGROUND

Neuroendocrine tumours are slow growing tumours known to secrete a variety of vasoactive peptides which give rise to symptoms of the carcinoid syndrome. The diagnosis and monitoring of patients with neuroendocrine tumours is undertaken in many centres using 24 h urinary measurement of 5-hydroxyindoleacetic acid. However, 5-hydroxyindoleacetic acid can also be quantified in plasma and serum.

METHODS

We measured 5-hydroxyindoleacetic acid concentration in 134 paired EDTA plasma and urine samples from 108 patients with known neuroendocrine tumours and 26 healthy volunteers. We also compared 5-hydroxyindoleacetic acid concentrations in paired serum and plasma samples (n = 63), then analysed paired urine and serum samples (n = 97). Furthermore, we examined the impact of renal impairment on serum 5-hydroxyindoleacetic acid by analysing 5-hydroxyindoleacetic acid in patients without neuroendocrine tumours in different stages of chronic kidney disease, as indicated by the estimated glomerular filtration rate.

RESULTS

Plasma and urine 5-hydroxyindoleacetic acid had very similar diagnostic sensitivities and specificities, with areas under the curve on ROC analysis of 0.917 and 0.920, respectively. Serum and plasma 5-hydroxyindoleacetic acid values showed good correlation but serum results demonstrated a positive bias, indicating the necessity for different serum and plasma reference intervals. There was an inverse correlation between estimated glomerular filtration rate and serum 5-hydroxyindoleacetic acid concentration, with 5-hydroxyindoleacetic acid increasing once the estimated glomerular filtration rate falls below 60 mL/min/1.73 m(2).

CONCLUSION

The measurement of both serum and plasma 5-hydroxyindoleacetic acid can be used for the diagnosis and monitoring of patients with neuroendocrine tumours. Provided renal function is taken into consideration, either of these tests should be incorporated into standard practice as an alternative assay to urinary 5-hydroxyindoleacetic acid.

Development of a nucleotide sugar purification method using a mixed mode column & mass spectrometry detection

Analysis of nucleotide sugars, nucleoside di- and triphosphates and sugar-phosphates is an essential step in the process of understanding enzymatic pathways. A facile and rapid separation method was developed to analyze these compounds present in an enzymatic reaction mixture utilized to produce nucleotide sugars. The Primesep SB column explored in this study utilizes hydrophobic interactions as well as electrostatic interactions with the phosphoric portion of the nucleotide sugars. Ammonium formate buffer was selected due to its compatibility with mass spectrometry. Negative ion mode mass spectrometry was adopted for detection of the sugar phosphate (fucose-1-phophate), as the compound is not amenable to UV detection. Various mobile phase conditions such as pH, buffer concentration and organic modifier were explored. The semi-preparative separation method was developed to prepare 30mg of the nucleotide sugar. (19)F NMR was utilized to determine purity of the purified fluorinated nucleotide sugar. The collected nucleotide sugar was found to be 99% pure.

Circulating tumor markers in patients with neuroendocrine tumors – a clinical perspective

Abstract: 

Neuroendocrine tumors (NETs) are uncommon malignancies with a very diverse presentation and prognosis. Patients with NETs frequently have circulating tumor biomarkers that may aid in the diagnosis and help with prognostication. The most commonly used and best studied marker is chromogranin A, which appears to reflect the tumor burden and is useful at the time of diagnosis, and to monitor for recurrence after resection as well as to assess response to systemic therapy. Despite being the best studied marker, chromogranin A has significant limitations. Multiple other biomarkers are in use, but most have not been studied well and need further validation before being recommended for clinical practice. We review both established and novel circulating biomarkers, and highlight some of the limitations of tumor marker use in patients with NETs.

Transient elevation of serum 5-HIAA by dietary serotonin and distribution of 5-HIAA in serum protein fractions

Introduction

Dietary serotonin increases urinary secretion of 5-HIAA. A falsely elevated 5-HIAA may lead to incorrect suspicion of a neuroendocrine tumour. Therefore, we determined the effect and duration of dietary serotonin on serum 5-HIAA concentration. We also studied the distribution of 5-HIAA in serum fractions.

Methods

We used serum samples from healthy volunteers (31 women and four men). All test subjects avoided serotonin-containing foods for three days before sample collection. They then ate either pineapple, banana, kiwi fruit, tomato or walnuts and additional blood samples were taken after 2, 4, 6, 24, 48 and 72 h. To study the distribution of 5-HIAA in serum, samples from a healthy individual, a test person who had ingested walnuts, and from a neuroendocrine tumour patient were fractionated by gel filtration chromatography. The fractions were analysed for 5-HIAA.

Results

Serum 5-HIAA concentration increased significantly ( P ≤ 0.001) within 2 h after ingestion of serotonin-containing food. After 2 h, 5-HIAA concentration started to decrease and reached the baseline concentration within 24 h. A calculated half-life of 5-HIAA in circulation was 1.3 h. In fractionated serum, 5-HIAA was found not only in free form but also in the albumin and α2-globulin fractions.

Conclusions

The increase of serum 5-HIAA caused by dietary serotonin is significant but transient. Therefore, serotonin-containing foods should be avoided for one day before blood sampling. In serum, 5-HIAA is free and apparently bound to albumin. Minor amounts were also found in the α2-globulin fraction. Our liquid chromatography tandem mass spectrometry assay measures free 5-HIAA in serum.

Serial surveillance of carcinoid heart disease: factors associated with echocardiographic progression and mortality

Background:

Carcinoid heart disease is a complication of metastatic neuroendocrine tumours (NETs). We sought to identify factors associated with echocardiographic progression of carcinoid heart disease and death in patients with metastatic NETs.

Methods:

Patients with advanced non-pancreatic NETs and documented liver metastases and/or carcinoid syndrome underwent prospective serial clinical, biochemical, echocardiographic and radiological assessment. Patients were categorised as carcinoid heart disease progressors, non-progressors or deceased. Multinomial regression was used to assess the univariate association between variables and carcinoid heart disease progression.

Results:

One hundred and thirty-seven patients were included. Thirteen patients (9%) were progressors, 95 (69%) non-progressors and 29 (21%) patients deceased. Baseline median levels of serum N-terminal pro-brain natriuretic peptide (NT-proBNP) and plasma 5-hydroxyindoleacetic acid (5-HIAA) were significantly higher in the progressors. Every 100 nmol l⁻¹ increase in 5-HIAA yielded a 5% greater odds of disease progression (OR 1.05, 95% CI: 1.01, 1.09; P=0.012) and a 7% greater odds of death (OR 1.07, 95% CI: 1.03, 1.10; P=0.001). A 100 ng l⁻¹ increase in NT-proBNP did not increase the risk of progression, but did increase the risk of death by 11%.

Conclusions:

The biochemical burden of disease, in particular baseline plasma 5-HIAA concentration, is independently associated with carcinoid heart disease progression and death. Clinical and radiological factors are less useful prognostic indicators of carcinoid heart disease progression and/or death.

Determination of the optimal echocardiographic scoring system to quantify carcinoid heart disease

BACKGROUND

Carcinoid heart disease (CHD) is an important complication of metastatic neuroendocrine disease, requiring regular monitoring to enable intervention prior to right heart failure. We aimed to identify the most appropriate echocardiographic scoring systems for the quantitative assessment of CHD.

METHODS

In this prospective study conducted between April and October 2012 in two European Neuroendocrine Tumor Society (ENETS) Centres of Excellence, patients with neuroendocrine tumours with liver metastases and/or carcinoid syndrome underwent transthoracic echocardiography and blood sampling for serum N-terminal pro-brain natriuretic peptide (NT-proBNP) and plasma 5-hydroxyindoleacetic acid (5-HIAA). Each patient was assessed according to six echocardiographic scoring systems. The individual scoring systems' feasibility, observer variability, sensitivity, specificity and correlation with the concentration biomarkers were determined.

RESULTS

100 patients were included; 21% had echocardiographic evidence of CHD. All scores discriminated highly between those with/without CHD, with no single score performing significantly better than another. The severity, determined using all of the scoring systems, correlated with the concentration of both biomarkers, but the strongest correlations were seen between the Bhattacharyya score and serum NT-proBNP.

CONCLUSION

All scoring systems are comparable in terms of sensitivity and specificity for the detection of CHD. There is a variation in the feasibility of the scoring systems due to varying complexity of the score components. All scores correlate with NT-proBNP and plasma 5-HIAA. The Westberg score appears to be the most optimal scoring system for use in screening of CHD whereas the more complex scoring systems are more suited to the patient with established disease who may require surgical intervention.

The association of a panel of biomarkers with the presence and severity of carcinoid heart disease: a cross-sectional study

Purpose

Metastatic neuroendocrine tumors secrete serotonin and other vasoactive substances that are responsible for carcinoid syndrome and carcinoid heart disease. We sought to evaluate the discriminatory utility of diagnostic biomarkers in determining the presence and severity of carcinoid heart disease in patients with metastatic neuroendocrine tumors.

Patients and methods

A cross-sectional study of patients with neuroendocrine tumors with documented liver metastases and/or carcinoid syndrome between April 2009–October 2012 in 5 tertiary referral centers. Serum was analyzed for Chromogranin A, Chromogranin B and N-terminal pro Brain Natriuretic Peptide (NT-proBNP). Plasma was analyzed for Neurokinin A and 5-Hydroxyindoleacetic acid (5HIAA). Echocardiography was used to determine the presence and severity of carcinoid heart disease. Non-parametric receiver operating characteristic curves were constructed for biomarkers, and the area under the curve determined. The severity of cardiac involvement was correlated with the concentration of each biomarker.

Results

A total of 187 patients were identified of whom 37 (20%) had carcinoid heart disease. Significantly higher median values of all biomarkers were found in the patients with cardiac involvement. NT-proBNP and plasma 5HIAA had the highest areas under the curve for the prediction of carcinoid heart disease [NT-proBNP 0.82 (95% confidence interval 0.74–0.90, p<0.0001) and 5HIAA 0.85 (95% confidence interval 0.78–0.92, p<0.0001]. NT-proBNP was moderately correlated (r = 0.48, p<0.001) whereas plasma 5HIAA was only weakly correlated (r = 0.34, p<0.001) with the echocardiographic severity score.

Conclusion

NT-proBNP and plasma 5HIAA are both sensitive and specific biomarkers for the presence of carcinoid heart disease whereas only NT-proBNP is moderately correlated with disease severity.

Circulating serotonin and bone density, structure, and turnover in carcinoid syndrome

CONTEXT

Gut-derived serotonin has been proposed as a regulator of bone formation, and inhibition of gut serotonin synthesis increases bone formation in rodents. Carcinoid neuroendocrine tumors can produce very high levels of circulating serotonin and so offer a model of serotonin excess in humans.

OBJECTIVES

The objective of the study was to determine whether patients with carcinoid syndrome have lower bone formation markers, lower bone density, or poor bone structure compared with healthy controls.

DESIGN

We conducted a cross-sectional study of 25 patients with carcinoid syndrome and 25 healthy controls, individually matched to carcinoid patients by gender, age, height, and body mass index.

OUTCOME MEASURES

We measured circulating serotonin in blood and plasma and 5-hydroxyindoleacetic acid (5HIAA) in plasma and urine. We measured lumbar spine and hip bone mineral density by dual-energy x-ray absorptiometry, the distal radius and tibia with high-resolution peripheral quantitative computed tomography, and bone turnover with serum osteocalcin, amino-terminal propeptide of type I procollagen (PINP) and C-terminal telopeptide of type I collagen (CTX).

RESULTS

All measures of serotonin and 5HIAA were higher in carcinoid patients than in controls. No measures of bone density or bone structure differed significantly between cases and controls. Osteocalcin was higher in the cases than controls (26.0 vs 21.1 ng/mL, P = .02). PINP and CTX did not differ between cases and controls. In patients with carcinoid syndrome, plasma 5HIAA was positively correlated with osteocalcin. In controls, whole-blood serotonin was positively correlated with osteocalcin, PINP, and CTX (R values = 0.40-0.47, all P < .05.).

CONCLUSIONS

High circulating serotonin in carcinoid syndrome is not associated with clinically significant lower bone density, poorer bone structure, or lower bone formation markers.

A single fasting plasma 5-HIAA value correlates with 24-hour urinary 5-HIAA values and other biomarkers in midgut neuroendocrine tumors (NETs)

OBJECTIVES

5-Hydroxyindoleacetic acid (5-HIAA) is used for the evaluation of neuroendocrine tumors (NETs) but currently requires a 24-hour urine collection.

METHODS

We developed a gas chromatography mass spectroscopy-based plasma 5-HIAA assay. We compared 24-hour urine 5-HIAA values against plasma 5-HIAA values in 115 mixed-variety patients with NETs and in a subset of 72 patients with only small bowel NETs. We also compared the information gained from urinary and plasma 5-HIAA values with other biomarkers of midgut NET activity to determine the plasma assay's clinical implications.

RESULTS

In a group of 115 patients with all types of NETS, in a subset of patients with midgut NET and in a subgroup of midgut NETS with liver metastasis, the correlation between the urine and fasting plasma 5-HIAA values were statistically significant (P ≤ 0.0001). Comparison of the proportion of normal or abnormal urinary and plasma 5-HIAA values to the proportion of chromogranin, serotonin, neurokinin, or pancreastatin values that were in the normal or abnormal range yielded essentially identical information.

CONCLUSIONS

Plasma fasting 5-HIAA values are proportional to urinary 5-HIAA values and yielded identical clinical correlation with other biomarkers.

The role and mechanism of action of activin A in neurite outgrowth of chicken embryonic dorsal root ganglia

Activin A, a member of the transforming growth factor β (TGFβ) superfamily, plays an essential role in neuron survival as a neurotrophic and neuroprotective factor in the central nervous system. However, the effects and mechanisms of action of activin A on the neurite outgrowth of dorsal root ganglia (DRG) remain unclear. In the present study, we found that activin A is expressed in DRG collected from chicken embryos on embryonic day 8 (E8). Moreover, activin A induced neurite outgrowth of the primary cultured DRG and maintained the survival of monolayer-cultured DRG neurons throughout the observation period of ten days. Follistatin (FS), an activin-binding protein, significantly inhibited activin A-induced neurite outgrowth of DRG, but failed to influence the effect of nerve growth factor (NGF) on DRG neurite outgrowth. Furthermore, the results showed that activin A significantly upregulated mRNA expression of activin receptor type IIA (ActRIIA) and calcitonin gene-related peptide (CGRP) in DRG, and stimulated serotonin (5-HT) production from DRG, indicating that activin A might induce DRG neurite outgrowth by promoting CGRP expression and stimulating 5-HT release. These data suggest that activin A plays an important role in the development of DRG in an autocrine or paracrine manner.

Development of an LC-MS/MS method for the analysis of serotonin and related compounds in urine and the identification of a potential biomarker for attention deficit hyperactivity/hyperkinetic disorder

Serotonin is a major neurotransmitter and affects various functions both in the brain and in the rest of the body. It has been demonstrated that altered serotinergic function is implicated in various psychiatric disorders including depression and schizophrenia. Serotonin has also been implicated along with dopamine in attention deficit-hyperkinetic disorder (AD-HKD). This study provides a versatile validated method for the analysis of serotonin, hydroxyindole acetic acid and dopamine in urine using LC-MS/MS. This method was then used to quantify these analytes in a test group of 17 children diagnosed with severe AD-HKD. This group was compared to a matched control group to investigate the possibility that one of these compounds may be a potential biomarker for this condition. The developed method provided good linear calibration curves for the multiplex assay of analytes in urine (0.05-3.27 nmol/L; R(2) ≥ 0.9977). Acceptable inter-day repeatability was achieved for all analytes with RSD values (n = 9) ranging from 1.1% to 9.3% over a concentration range of 0.11-3.27 μmol/L in urine. Excellent limits of detection (LOD) and limits of quantitation (LOQ) were achieved with LODs of 8.8-18.2 nmol/L and the LOQs of 29.4-55.7 nmol/L for analytes in urine. Recoveries were in the ranges of 98-104%, 100-106% and 91-107% for serotonin, 5-HIAA and dopamine, respectively. An appropriate sample clean-up procedure for urine was developed to ensure efficient recovery and reproducibility on analysis. Evaluation of matrix effects was also carried out and the influence of ion suppression on analytical results reported. Confirmatory analysis was carried out on a linear trap quadrupole-Orbitrap mass spectrometer to obtain high mass accuracy data of the target analytes in the clinical samples.

Modern laboratory evaluation of peptide and amines: a continuing role for radioimmunoassay?

Modern medicine, and specifically clinical diagnosis, relies, among other diagnostic procedures, on the measurements of the biogenic analytes for elucidation and correlation of specific neuroendocrine markers. Tremendous advances have been made in imaging and radioactive uptake procedures to elucidate tumor presence and characterization. However, such advances only partially provide the fundamental degree of tumor activity and clinical confirmational validity. The author points out in some detail the problems that may arise when the methodological differences presented by each investigational study and investigators are not standardized. This variation causes a concern with the specific objectives of the investigator and the specific aims of the research project at hand, and ultimately for the validity of the published results.