Analytical Method Validation for Estimation of Neurotransmitters (Biogenic Monoamines) from Cerebrospinal Fluid Using High Performance Liquid Chromatography

Bioanalytical validation and clinical application of a liquid chromatography-tandem mass spectrometry method for the quantification of 3-orthomethyldopa, 5-hydroxytryptophan, 5-hydroxyindolacetic acid and homovanillic acid in human cerebrospinal fluid

Inherited disorders of monoamine neurotransmitters are a subset of inborn errors of metabolism affecting biochemical pathways of catecholamines, serotonin or their enzymatic cofactors. Usually, their clinical presentation is similar to those of other common neurological syndromes. For this reason, they are frequently under-recognized and misdiagnosed. Because cerebrospinal fluid concentration of catecholamine metabolites (3-orthomethyldopa and homovanillic acid) and serotonin metabolites (5-hydroxytryptophan and 5-hydroxyindolacetic acid) presents a direct correlation with their brain levels, analysis of this group of compounds is critical to reach an accurate diagnosis. Although there are several published liquid chromatography-based bioanalytical methods for the quantification of these compounds, most of them present disadvantages, making their application difficult to implement in routine clinical practice. In this study, a rapid and simple UHPLC-MS/MS method for simultaneous quantification of 3-orthomethyldopa, 5-hydroxytryptophan, 5-hydroxyindolacetic acid and homovanillic acid in human cerebrospinal fluid was validated. All the evaluated performance parameters, including linearity, carryover, accuracy and precision (within and between-day), lower limit of quantitation, recovery, matrix effect and stability under different conditions met the acceptance criteria from international guidelines. Additionally, 10 human cerebrospinal fluid samples collected via lumbar puncture from 10 pediatric patients were quantified using the validated method to assess its clinical application and diagnostic utility for inherited monoamine neurotransmitter metabolism.

UHPLC-MS/MS combined with microdialysis for simultaneous determination of nicotine and neurotransmitter metabolites in the rat hippocampal brain region: application to pharmacokinetic and pharmacodynamic study

Nicotine crosses the blood-brain barrier and interacts with nicotinic acetylcholine receptors, initiating a cascade of neurotransmitter effects with potential therapeutic implications for neurodegenerative conditions such as Alzheimer's and Parkinson's disease. The hippocampus, pivotal for cognitive processes, plays a crucial role in nicotine-mediated cognitive enhancement due to its abundant expression of nicotinic acetylcholine receptors, particularly the α7 subtype, which is heavily implicated in hippocampus-related behavioral functions and dysfunctions. However, the intricate process of nicotine metabolism within the hippocampus remains poorly understood, impeding our comprehension of how nicotine and its metabolites modulate neurotransmitter dynamics. To address this gap, we have developed and validated a novel methodology combining microdialysis with UHPLC-MS/MS, enabling simultaneous detection of 12 neurotransmitters, nicotine, and its seven metabolites within the rat hippocampus. The linearity range of the targeted compounds is satisfactory (R2 > 0.9970), with intra-day and inter-day precision not exceeding 12.7%, and accuracy ranging from -12.4% to 13.7%. Our findings reveal differential pharmacokinetics of nicotine and its metabolites in the α7KO group compared to the control group, characterized by heightened nicotine absorption and slower elimination and distribution in the former. Notably, the pharmacokinetic parameters of cotinine exhibit similarity across both groups. Studies investigating the impact of nicotine on monoamine neurotransmitters have elucidated its capacity to augment the release of dopamine, serotonin, norepinephrine, glutamate, and acetylcholine in the rat hippocampus. This integrated approach facilitates a comprehensive analysis of neurotransmitter alterations within the hippocampal region following nicotine administration, thereby providing robust technical support and scientific rationale for understanding the neurochemical effects of nicotine and its metabolites. Further exploration into the pharmacokinetics and pharmacodynamics of nicotine holds promise for uncovering novel therapeutic avenues in the management of neurodegenerative diseases such as Alzheimer's.

The High-Precision Liquid Chromatography with Electrochemical Detection (HPLC-ECD) for Monoamines Neurotransmitters and Their Metabolites: A Review

This review highlights the advantages of high-precision liquid chromatography with an electrochemical detector (HPLC-ECD) in detecting and quantifying biological samples obtained through intracerebral microdialysis, specifically the serotonergic and dopaminergic systems: Serotonin (5-HT), 5-hydroxyindolacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), dopamine (DA), 3-metoxytryptamin (3-MT) and homovanillic acid (HVA). Recognized for its speed and selectivity, HPLC enables direct analysis of intracerebral microdialysis samples without complex derivatization. Various chromatographic methods, including reverse phase (RP), are explored for neurotransmitters (NTs) and metabolites separation. Electrochemical detector (ECD), particularly with glassy carbon (GC) electrodes, is emphasized for its simplicity and sensitivity, aimed at enhancing reproducibility through optimization strategies such as modified electrode materials. This paper underscores the determination of limits of detection (LOD) and quantification (LOQ) and the linear range (L.R.) showcasing the potential for real-time monitoring of compounds concentrations. A non-exhaustive compilation of literature values for LOD, LOQ, and L.R. from recent publications is included.

Cerebrospinal Fluid Biogenic Monoamine Analysis for Diagnosis of Primary Neurotransmitter Disorders

Biogenic amine neurotransmitters metabolism is a multistep pathway with pterin and pyridoxal phosphate (vitamin B6) as cofactors. A defect in biogenic amine and cofactor metabolism and vesicular transporters result in a primary neurotransmitter disorders. These are a well-recognized groups of inherited disorders and often present with features overlapping with other neurological conditions. Their diagnosis is made by analysis of biogenic amine metabolites in cerebrospinal fluid (CSF) and other body fluids and respective enzyme assays. Many of these disorders are treatable and deficits can be reverted by timely intervention. CSF biogenic amine or cofactor metabolite analysis is one of the primary indicators of a neurotransmitter disorder. In this paper, 3 cases are reported-2 of cofactor deficiency and 1 with enzyme deficiency wherein biogenic amine estimation has assisted in diagnosis.