Simultaneous quantification of monoamine neurotransmitters and their biogenic metabolites intracellularly and extracellularly in primary neuronal cell cultures and in sub-regions of guinea pig brain

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.

A Long-Term Energy-Rich Diet Increases Prefrontal BDNF in Sprague-Dawley Rats

Findings of the effect of high-fat feeding including “Cafeteria Diets” (CAF) on brain-derived neurotrophic factor (BDNF) in the hippocampus (HIP) and prefrontal cortex (PFC) in rodents are conflicting. CAF is a non-standardized, highly palatable energy-rich diet composed by everyday food items for human consumption and is known to induce metabolic syndrome and obesity in rats. However, the highly palatable nature of CAF may counteract a negative effect of chronic stress on anticipatory behavior and synaptic plasticity in the hippocampus, hence represent a confounding factor (e.g., when evaluating functional effects on the brain). This study investigated the effects of a chronic, restricted access to CAF on BDNF, monoamine neurotransmitters, and redox imbalance in HIP and PFC in male rats. Our results show that CAF induced BDNF and its receptor TrkB in PFC compared to the controls (p < 0.0005). No differences in monoamine neurotransmitters were detected in either PFC or HIP. CAF increased dehydroascorbic acid and decreased malondialdehyde in PFC (p < 0.05), suggesting an early redox imbalance insufficient to induce lipid peroxidation. This study supports that a chronic CAF on a restricted schedule increases BDNF levels in the PFC of rats, highlighting that this may be a suboptimal feeding regime when investigating the effects of diet-induced obesity in the brain and emphasizing this as a point of attention when comparing the findings.

Polymorphisms in the serotonin transporter gene and circulating concentrations of neurotransmitters in Cavalier King Charles Spaniels with myxomatous mitral valve disease

Background

The neurotransmitter serotonin (5‐HT) affects valvular degeneration and dogs with myxomatous mitral valve disease (MMVD) exhibit alterations in 5‐HT signaling. In Maltese dogs, 3 single nucleotide polymorphisms (SNPs) in the 5‐HT transporter (SERT) gene are suggested to associate with MMVD.

Hypothesis/Objectives

Determine the association of SERT polymorphisms on MMVD severity and serum 5‐HT concentration in Cavalier King Charles Spaniels (CKCS). Additionally, investigate the association between selected clinical and hematologic variables and serum 5‐HT and assess the correlation between HPLC and ELISA measurements of serum 5‐HT.

Animals

Seventy‐one CKCS (42 females and 29 males; 7.8 [4.7;9.9] years (median [Q1;Q3])) in different MMVD stages.

Methods

This prospective study used TaqMan genotyping assays to assess SERT gene polymorphisms. Neurotransmitter concentrations were assessed by HPLC and ELISA.

Results

TaqMan analyses identified none of the selected SERT polymorphisms in any of the CKCS examined. Serum 5‐HT was associated with platelet count (P < .001) but not MMVD severity, age or medical therapy and did not correlate with serum concentration of the 5‐HT metabolite, 5‐hydroxyindoleacetic acid. The ELISA serum 5‐HT correlated with HPLC measurements (ρ = .87; P < .0001) but was lower (mean difference = −22 ng/mL; P = .02) independent of serum 5‐HT concentration (P = .2).

Conclusions and Clinical Importance

Selected SERT SNPs associated with MMVD in Maltese dogs were not found in CKCS and only platelet count influenced serum 5‐HT concentration. These SNPs are unlikely to be associated with MMVD pathophysiology or serum 5‐HT concentration in CKCS. HPLC and ELISA serum 5‐HT demonstrated good correlation but ELISA systematically underestimated 5‐HT.

Intravenous administration of sodium propionate induces antidepressant or prodepressant effect in a dose dependent manner

Propionate has been reported to exert antidepressant effects, but high-dose propionate may induce autism-like symptoms in experimental animals through induction of dysbiosis of neurotransmitters. The bi-directional effects of propionate seem to be dose-dependent. However, due to the pathological discrepancies between depression and autism, conclusions drawn from autism may not be simply transferable to depression. The effect and underlying action mechanisms of high-dose propionate on depression remains undetermined. To investigate the effects of propionate on depression, propionate dose gradients were intravenously administrated to rats exposed to chronic unpredictable mild stress (CUMS) for 1 week. Results of these behavioral tests demonstrate that low-dose propionate (2 mg/kg body weight/day) induces antidepressant effect through bodyweight recovery, elevated reward-seeking behaviors, and reduced depression-like behaviors, while high-dose propionate (200 mg/kg body weight/day) induces prodepressant effects opposite of those of low-dose propionate. A comprehensive profiling of neurotransmitters in the hippocampus demonstrated that CUMS induces reduction of NE (Norepinephrine), DA (Dopamine). GABA (γ-aminobutyric acid) was recovered by low-dose propionate, while high-dose propionate exerted more complicated effects on neurotransmitters, including reduction of NE, DA, 5-Hydroxytryptamine and Tryptophan, and increase of GABA, Kynurenine, Homovanillic acid, 3-hydroxyanthranilic acid, 3-hydroxykynurenine, 3,4-dihydroxyphenylacetic acid, and 3-methoxytyramine. The neurotransmitters disturbed by high-dose propionate suggest metabolic disorders in the hippocampus, which were confirmed by the clear group separation in PCA of metabolomic profiling. The results of this study demonstrate the double-edged dose-dependent effects of propionate on depression and suggest potential cumulative toxicity of propionate as a food additive to mood disorders.

The lipid homeostasis regulation study of arenobufagin in zebrafish HepG2 xenograft model and HepG2 cells using integrated lipidomics-proteomics approach

ETHNOPHARMACOLOGICAL RELEVANCE

Arenobufagin (ArBu) is an important anti-tumor ingredient of Chan'su which has long been used as traditional Chinese medicine in clinic for tumor therapy in China.

AIM OF THE STUDY

The purpose of our study is to investigate the lipid homeostasis regulation effects of ArBu on zebrafish model of liver cancer and hepatoma cells, and to provide a reference for further clarifying its active mechanisms.

MATERIALS AND METHODS

The zebrafish xenograft model was established by injecting HepG2 cells stained with CM-Dil red fluorescent dye. Both the xenograft model and HepG2 cells were used to evaluate the anti-hepatoma activity of ArBu. High performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was the main method to study lipidomics, proteomics and the semiquantification of endogenous metabolites. Bioinformatics was used as an assistant tool to further explore the antitumor mechanism of ArBu.

RESULTS

The lipidomics analysis revealed that ArBu caused differential lipids changes in a dose-dependent manner, including PCs, PEs, TGs, SMs, DGs, Cer and PA. PCs, PEs, SMs and TGs were markedly altered in both two models. The influence of glycerophospholipid metabolism was the major and commonly affected pathway. Notably, DGs and Cer were significantly changed only in HepG2 cells. Furthermore, the proteomics research in HepG2 cells fished the target proteins related to lipid homeostasis abnormalities and tumor suppression. ArBu reduced the expression of 65 differential proteins associated with the lipid metabolism, apoptosis and autophagy, such as LCLAT1, STAT3, TSPO and RPS27. Meanwhile, 7 amino acids of 29 determined metabolites were significantly changed, including tyrosine, glutamate, glutamine, leucine, threonine, arginine and isoleucine.

CONCLUSION

ArBu has a significant anti-hepatoma effect in vitro and a therapeutic effect on zebrafish xenograft model. It regulated the lipid homeostasis. Activated SM synthase and arginine deiminase, inhibited sphingomyelinase, amino acid supply and JAK-STAT3 signaling pathway, and the affected glycerophospholipid metabolism might explain these results.

The counterregulatory response to hypoglycaemia in the pig

The domestic pig is commonly used as animal model in the pharmaceutical development of new therapeutics for treatment of diabetes. Since a formal definition of hypoglycaemia only exists in humans, the purpose of this study was to assess the counterregulatory response in the domestic pig at glucose levels known to induce symptoms of hypoglycaemia in humans. Six pigs were included in hyperinsulinaemic glucose clamps with plasma glucose targets of 2, 3 and 5 mmol/L in a cross-over design, and the associated glucose counterregulatory response was assessed by measuring glucose kinetics and levels of glucagon, c-peptide, catecholamines, cortisol and growth hormone. Results showed that the 2 and 3 vs 5 mmol/L clamps significantly decreased and increased the secretion of c-peptide and glucagon, respectively (P < .05). This finding was associated with increased rate of glucose appearance (R_a ) and decreased rate of glucose disappearance (R_d ) (P < .001). No marked differences in the catecholamine, growth hormone or cortisol response were observed. Consequently, like humans, pigs respond to hypoglycaemia by decreasing the pancreatic output of insulin while increasing that of glucagon, with increased glucose mobilization and decreased glucose disposal as a result. The hypoglycaemic clamps did not result in a marked secretion of the other counterregulatory hormones.

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.

Altered gut metabolome contributes to depression-like behaviors in rats exposed to chronic unpredictable mild stress

The gut microbiota has been increasingly correlated with depressive disorder. It was recently shown that the transplantation of the gut microbiota from depressed patients to animals can produce depressive-like behaviors, suggesting that the gut microbiota plays a causal role in the development of depression. In addition, metabolic disorder, which is strongly associated with depression, is exacerbated by changes in the composition of the gut microbiota and is alleviated by treatment with antidepressants. However, the key players and pathways that link the gut microbiota to the pathogenesis of depression remain largely unknown. To evaluate the relationships between depression and metabolic disorders in feces and plasma, we monitored changes in fecal and plasma metabolomes during the development of depressive-like behaviors in rats exposed to chronic unpredictable mild stress (CUMS). In these animals, the fecal metabolome was altered first and subjected to changes in the plasma metabolome. Changes in the abundance of fecal metabolites were associated with depressive-like behaviors and with altered levels of neurotransmitters in the hippocampus. Furthermore, the analysis of the fecal metabolome and the fecal microbiota in CUMS rats demonstrated consistent changes in the levels of several amino acids, including L-threonine, isoleucine, alanine, serine, tyrosine, and oxidized proline. Finally, we observed significant correlations between these amino acids and the altered fecal microbiota. The results of this study suggest that changes in amino acid metabolism by the gut microbiota contribute to changes in circulating amino acids and are associated with the behavior indices of depression.

Integrated Proteomics and Lipidomics Investigation of the Mechanism Underlying the Neuroprotective Effect of N-benzylhexadecanamide

Macamides are very important secondary metabolites produced by Lepidium meyenii Walp, which possess multiple bioactivities, especially in the neuronal system. In a previous study, we observed that macamides exhibited excellent effects in the recovery of injured nerves after 1-methyl-4-phenylpyridinium (MPP⁺)-induced dopaminergic neuronal damage in zebrafish. However, the mechanism underlying this effect remains unclear. In the present study, we observed that N-benzylhexadecanamide (XA), which is a typical constituent of macamides, improved the survival rate of neurons in vitro. We determined the concentration of neurotransmitters in MN9D cells and used it in conjunction with an integrated proteomics and lipidomics approach to investigate the mechanism underlying the neuroprotective effects of XA in an MPP⁺-induced neurodegeneration cell model using QqQ MS, Q-TOF MS, and Orbitrap MS. The statistical analysis of the results led to the identification of differentially-expressed biomarkers, including 11 proteins and 22 lipids, which may be responsible for the neuron-related activities of XA. All these potential biomarkers were closely related to the pathogenesis of neurodegenerative diseases, and their levels approached those in the normal group after treatment with XA. Furthermore, seven lipids, including five phosphatidylcholines, one lysophosphatidylcholine, and one phosphatidylethanolamine, were verified by a relative quantitative approach. Moreover, four proteins (Scarb2, Csnk2a2, Vti1b, and Bnip2) were validated by ELISA. The neurotransmitters taurine and norepinephrine, and the cholinergic constituents, correlated closely with the neuroprotective effects of XA. Finally, the protein–lipid interaction network was analyzed. Based on our results, the regulation of sphingolipid metabolism and mitochondrial function were determined to be the main mechanisms underlying the neuroprotective effect of XA. The present study should help us to better understand the multiple effects of macamides and their use in neurodegenerative diseases.

Spatial Memory Dysfunction Induced by Vitamin C Deficiency Is Associated with Changes in Monoaminergic Neurotransmitters and Aberrant Synapse Formation

Vitamin C (vitC) is important in the developing brain, acting both as an essential antioxidant and as co-factor in the synthesis and metabolism of monoaminergic neurotransmitters. In guinea pigs, vitC deficiency results in increased oxidative stress, reduced hippocampal volume and neuronal numbers, and deficits in spatial memory. This study investigated the effects of 8 weeks of either sufficient (923 mg vitC/kg feed) or deficient (100 mg vitC/kg feed) levels of dietary vitC on hippocampal monoaminergic neurotransmitters and markers of synapse formation in young guinea pigs with spatial memory deficits. Western blotting and high performance liquid chromatography (HPLC) were used to quantify the selected markers. VitC deficiency resulted in significantly reduced protein levels of synaptophysin (p = 0.016) and a decrease in 5-hydroxyindoleacetic acid/5-hydroxytryptamine ratio (p = 0.0093). Protein expression of the N-methyl-d-aspartate receptor subunit 1 and monoamine oxidase A were reduced, albeit not reaching statistical significance (p = 0.0898 and p = 0.067, respectively). Our findings suggest that vitC deficiency induced spatial memory deficits might be mediated by impairments in neurotransmission and synaptic development.