Analysis of Catecholamine and Their Metabolites in Mice Brain by Liquid Chromatography-Mass Spectrometry Using Sulfonated Mixed-mode Copolymer Column

In this study, a simultaneous assay for catecholamines and their metabolites in the brain was established using liquid chromatography-mass spectrometry (LC-MS). To achieve complete separation, a cation-exchange/reversed-phase mixed-mode copolymer resin column containing 0.81 wt% sulfo groups was used for the simultaneous LC-MS assay. The analyzed catecholamines were dopamine (DA), norepinephrine (NE), and epinephrine (E), while the metabolites lacking amino groups were 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 3-methoxy-4-hydroxyphenylglycol (MHPG). The metabolites were separated and detected using LC-MS, on columns with and without sulfo groups. However, we could not achieve adequate separation of catecholamines on both columns using a gradient elution of 0 - 50 (v/v)% methanol containing 0.1 (v/v)% formic acid (FA). When volatile ion-pairing reagents were added to the mobile phase, they improved the retention and detection of catecholamines on the sulfonated mixed-mode column. Under optimized elution conditions, which involved a linear gradient elution of water containing 0.1 (v/v)% FA to 50 (v/v)% acetonitrile in 50 mM ammonium formate at 40°C and a 0.20 mL/min rate, all six target molecules were simultaneously detected within 25 min, when using negative mode LC-MS on a sulfonated mixed-mode column. The limits of detection (LODs) for DA, NE, E, DOPCA, HVA, and MHPG were determined to be 20.7, 12.6, 74.6, 1110, 18.7, and 3196 nM, respectively. Moreover, the established LC-MS assay allowed the detection of endogenous DA, NE, and HVA, in normal mouse brain samples at concentrations higher than 20, 9, and 4 pmol/mg, respectively.

Biogenic amines and their metabolites in mouse brain tissue: development, optimization and validation of an analytical HPLC method

A simple and fast HPLC method based on an isocratic, reversed-phased ion-pair with amperometric end-point detection for simultaneous measurement of noradrenergic (MHPG/NA and A), dopaminergic (DOPAC, HVA/DA) and serotonergic (5-HIAA/5-HT) compounds in mouse brain tissue was developed. In order to improve the chromatographic resolution (Rs) with an acceptable total analysis time, experimental designs for multivariate optimization of the experimental conditions were applied. The optimal conditions for the separation of the eight neurotransmitters and metabolites, as well as two internal standards, i.e., DHBA and 5-HMT, were obtained using a mixture of methanol-phosphate-citric buffer (pH 3.2, 50 mM) (9:91, v/v) containing 2 mM OSA as mobile phase at 32°C on a microbore ALF-115 column (150 mm × 1.0 mm, 3 μm particle size) filled with porous C(18) silica stationary phase. In this study, a two-level fractional factorial experimental design (½ 2(K)) was employed to optimize the separation and capacity factor (k') of each molecule, leading to a good separation of all biogenic amines and their metabolites in brain tissue. A simple method for the preparation of different bio-analytical samples in phosphate-citric buffer was also developed. Results show that all molecules of interest were stabilized for at least 24 h in the matrix conditions without any antioxidants. The method was fully validated according to the requirements of SFSTP (Société Française des Sciences et Techniques Pharmaceutiques). The acceptance limits were set at ±15% of the nominal concentration. The method was found accurate over a concentration range of 4-2000 ng/ml for MHPG, 1-450 ng/ml for NA, 1-700 ng/ml for A, 1-300 ng/ml for DOPAC, 1-300 ng/ml for 5-HIAA, 1-700 ng/ml for DA, 4-2800 ng/ml for HVA and 1-350 ng/ml for 5-HT. The assay limits of detection for MHPG, NA, A, DOPAC, 5-HIAA, DA, HVA and 5-HT were 2.6, 2.8, 4.1, 0.7, 0.6, 0.8, 4.2 and 1.4 pg, respectively. It was found that the mean inter- and intra-assay relative standard deviations (RSDs) over the range of standard curve were less than 3%, the absolute and the relative recoveries were around 100%, demonstrating the high precision and accuracy, and reliability of the analytical method described to apply in routine analysis of biogenic amines and their metabolites in brain tissue.

An assay for determination of rat adrenal catechol-O-methyltransferase activity: comparison of spontaneously hypertensive rats and Wistar?Kyoto rats

A method has been developed for measurement of catechol-O-methyltransferase (COMT) activity in the rat adrenal gland. Epinephrine, synthesized in the adrenal gland, was used as substrate, and its enzymatic product, metanephrine, was quantified by high-performance liquid chromatography (HPLC) with fluorescence detection. The method has sufficient precision and accuracy. Soluble (S) and membrane-bound (MB) COMT activity in Wistar-Kyoto (WKY) rats was 20.7 +/- 3.5 and 18.6 +/- 3.4 pmol min(-1) mg(-1) protein (n = 5), respectively. To clarify the role of adrenal COMT in blood-pressure regulation, S and MB COMT activity in spontaneously hypertensive rats were determined. Respective activity was 18.6 +/- 3.4 and 17.0 +/- 1.1 pmol min(-1) mg(-1) (n = 5), which is similar to that in WKY rats. This finding suggests that COMT in the adrenal gland might not be related to blood pressure regulation.