Evidence of a coupled mechanism between monoamine oxidase and peroxidase in the metabolism of tyramine by rat intestinal mitochondria

Amelioration of Alzheimer's Disease by Gut-Pancreas-Liver-Brain Interaction in an App Knock-In Mouse Model

In this study, we observed disease progression, changes in the gut microbiota, and interactions among the brain, liver, pancreas, and intestine in a mouse model of Alzheimer's disease (AD), in addition to attempting to inhibit disease progression through the dietary supplementation of L-arginine and limonoids. Wild-type mice (WC) and AD mice were fed a normal diet (AC), a diet supplemented with L-arginine and limonoids (ALA), or a diet containing only limonoids (AL) for 12-64 weeks. The normal diet-fed WC and AC mice showed a decrease in the diversity of the gut microbiota, with an increase in the Firmicutes/Bacteroidetes ratio, and bacterial translocation. Considerable bacterial translocation to the pancreas and intense inflammation of the pancreas, liver, brain, and intestinal tissues were observed in the AC mice from alterations in the gut microbiota. The ALA diet or AL diet-fed mice showed increased diversity of the bacterial flora and suppressed oxidative stress and inflammatory responses in hepatocytes and pancreatic cells, bacterial translocation, and neurodegeneration of the brain. These findings suggest that L-arginine and limonoids help in maintaining the homeostasis of the gut microbiota, pancreas, liver, brain, and gut in AD mice.

Tyramine and Amyloid Beta 42: A Toxic Synergy

Implicated in various diseases including Parkinson's disease, Huntington's disease, migraines, schizophrenia and increased blood pressure, tyramine plays a crucial role as a neurotransmitter in the synaptic cleft by reducing serotonergic and dopaminergic signaling through a trace amine-associated receptor (TAAR1). There appear to be no studies investigating a connection of tyramine to Alzheimer's disease. This study aimed to examine whether tyramine could be involved in AD pathology by using Saccharomyces cerevisiae expressing Aβ42. S. cerevisiae cells producing native Aβ42 were treated with different concentrations of tyramine, and the production of reactive oxygen species (ROS) was evaluated using flow cytometric cell analysis. There was dose-dependent ROS generation in wild-type yeast cells with tyramine. In yeast producing Aβ42, ROS levels generated were significantly higher than in controls, suggesting a synergistic toxicity of Aβ42 and tyramine. The addition of exogenous reduced glutathione (GSH) was found to rescue the cells with increased ROS, indicating depletion of intracellular GSH due to tyramine and Aβ42. Additionally, tyramine inhibited the respiratory growth of yeast cells producing GFP-Aβ42, while there was no growth inhibition when cells were producing GFP. Tyramine was also demonstrated to cause increased mitochondrial DNA damage, resulting in the formation of petite mutants that lack respiratory function. These findings indicate that there can be a detrimental synergy between Aβ42 and tyramine, which could be considered in Alzheimer's disease. This work also demonstrates the utility of yeast as a model for studying toxic agents such as Aβ42, tyramine, and agents that might exacerbate AD pathology.

Food sources and biomolecular targets of tyramine

Tyramine is a biogenic trace amine that is generated via the decarboxylation of the amino acid tyrosine. At pico- to nanomolar concentrations, it can influence a multitude of physiological mechanisms, exhibiting neuromodulatory properties as well as cardiovascular and immunological effects. In humans, the diet is the primary source of physiologically relevant tyramine concentrations, which are influenced by a large number of intrinsic and extrinsic factors. Among these factors are the availability of tyrosine in food, the presence of tyramine-producing bacteria, the environmental pH, and the salt content of food. The process of fermentation provides a particularly good source of tyramine in human nutrition. Here, the potential impact of dietary tyramine on human health was assessed by compiling quantitative data on the tyramine content in a variety of foods and then conducting a brief review of the literature on the physiological, cellular, and systemic effects of tyramine. Together, the data sets presented here may allow both the assessment of tyramine concentrations in food and the extrapolation of these concentrations to gauge the physiological and systemic effects in the context of human nutrition.

Chlorogenic acid ameliorates intestinal mitochondrial injury by increasing antioxidant effects and activity of respiratory complexes

Dietary polyphenols are thought to be beneficial for human health by acting as antioxidants. Chlorogenic acid (CGA) is abundant in plant-based foods as an ester of caffeic acid and quinic acid. In this study, we investigated the effects of CGA on mitochondrial protection. Our results demonstrated that pretreatment with CGA ameliorated the intestinal mitochondrial injury induced by H2O2; membrane potential was increased, mitochondrial swelling, levels of reactive oxygen species, contents of 8-hydroxy-2-deoxyguanosine, and cytochrome c released were decreased. The beneficial effects of CGA were accompanied by an increase in antioxidant and respiratory-chain complex I, IV, and V activities. In trinitrobenzene-sulfonic acid-induced colitic rats indicated that CGA supplementation improved mitochondria ultrastructure and decreased mitochondrial injury. Our results suggest a promising role for CGA as a mitochondria-targeted antioxidant in combating intestinal oxidative injury. Daily intake of diets containing CGA, such as coffee and honeysuckle, may be useful for prevention of intestinal diseases.

Chlorogenic acid decreased intestinal permeability and ameliorated intestinal injury in rats via amelioration of mitochondrial respiratory chain dysfunction

Chlorogenic acid (CGA), an abundant polyphenol compound in plants, exhibits anti-oxidant effects. The protective effect of CGA in the rat intestine with endotoxin infusion was evaluated. CGA administration ameliorated endotoxin-induced intestinal injury, and decreased the ratio of lactulose/mannitol, the ileum pathological grade, the myeloperoxidase activity in the ileum, and the malondialdehyde content in the ileum and in ileum mitochondria. The small intestine weight, activities of alkaline phosphatase and superoxide dismutase in the ileum, and β-nicotinamide adenine dinucleotide reduce form (NADH) dehydrogenase and succinate dehydrogenase activities in ileum mitochondria were increased. Intestinal permeability was positively correlated with intestinal mitochondrial injury indicated as the level of malondialdehyde in ileum mitochondria, and negatively correlated with NADH dehydrogenase activity. Dietary administration of CGA protected against increased intestinal permeability caused by endotoxin infusion. The protective effect of CGA was probably associated with a decrease in mitochondrial lipid peroxidation levels and an increase in NADH dehydrogenase activity.

Selective nanomolar detection of dopamine using a boron-doped diamond electrode modified with an electropolymerized sulfobutylether-beta-cyclodextrin-doped poly(N-acetyltyramine) and polypyrrole composite film

N-acetyltyramine was synthesized and electropolymerized together with a negatively charged sulfobutylether-beta-cyclodextrin on a boron-doped diamond (BDD) electrode followed by the electropolymerization of pyrrole to form a stable and permselective film for selective dopamine detection. The selectivity and sensitivity of the formed layer-by-layer film was governed by the sequence of deposition and the applied potential. Raman results showed a decrease in the peak intensity at 1329 cm(-1) (sp(3)), the main feature of BDD, upon each electrodeposition step. Such a decrease was correlated well with the change of the charge-transfer resistance derived from impedance data, i.e., reflecting the formation of the layer-by-layer film. The polycrystalline BDD surface became more even with lower surface roughness as revealed by scanning electron and atomic force microscopy. The modified BDD electrode exhibited rapid response to dopamine within 1.5-2 s and a low detection limit of 4-5 nM with excellent reproducibility. Electroactive interferences caused by 4-dihydroxyphenylalanine, 3,4-dihydroxyphenylacetic acid, ascorbic acid, and uric acid were completely eliminated, whereas the signal response of epinephrine and norepinephrine was significantly suppressed by the permselective film.

Tyramine oxidation by copper/TPQ amine oxidase and peroxidase from Euphorbia characias latex

Tyramine, an important plant intermediate, was found to be a substrate for two proteins, a copper amine oxidase and a peroxidase from Euphorbia characias latex. The oxidation of tyramine took place by two different mechanisms: oxidative deamination to p-hydroxyphenylacetaldehyde by the amine oxidase and formation of di-tyramine by the peroxidase. The di-tyramine was further oxidized at the two amino groups by the amino oxidase, whereas p-hydroxyphenylacetaldehyde was transformed to di-p-hydroxyphenylacetaldehyde by the peroxidase. Data obtained in this study indicate a new interesting scenario in the metabolism of tyramine.

Characterization of the serotoninergic system in the C57BL/6 mouse skin

We showed expression of the tryptophan hydroxylase gene and of tryptophan hydroxylase protein immunoreactivity in mouse skin and skin cells. Extracts from skin and melanocyte samples acetylated serotonin to N-acetylserotonin and tryptamine to N-acetyltryptamine. A different enzyme from arylalkylamine N-acetyltransferase mediated this reaction, as this gene was defective in the C57BL6 mouse, coding predominantly for a protein without enzymatic activity. Serotonin (but not tryptamine) acetylation varied according to hair cycle phase and anatomic location. Serotonin was also metabolized to 5-hydroxytryptophol and 5-hydroxyindole acetic acid, probably through stepwise transformation catalyzed by monoamine oxidase, aldehyde dehydrogenase and aldehyde reductase. Activity of the melatonin-forming enzyme hydroxyindole-O-methyltransferase was notably below detectable levels in all samples of mouse corporal skin, although it was detectable at low levels in the ears and in Cloudman melanoma (derived from the DBA/2 J mouse strain). In conclusion, mouse skin has the molecular and biochemical apparatus necessary to produce and metabolize serotonin and N-acetylserotonin, and its activity is determined by topography, physiological status of the skin, cell type and mouse strain.

Synthesis and biological evaluation of MAO-A selective 1,4-disubstituted-1,2,3,6-tetrahydropyridinyl substrates

Many mammalian tissues express both the A and B forms of monoamine oxidase (MAO), flavoenzymes that catalyze the oxidative deamination of a variety of endogenous and exogenous amines and the ring alpha-carbon oxidative bioactivation of neurotoxic 1,4-disubstituted-1,2,3,6-tetrahydropyridinyl derivatives. Substrates selective for MAO-A that display good kinetic and spectroscopic properties would be of value for developing quantitative assays for MAO-A in tissues that express both the A and B forms of the enzyme. This paper describes the synthesis of several 1-substituted-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridinyl derivatives. Kinetic parameters and MAO-A selectivity indicate that 1-allyl- and 1-propyl-4-(1-methylpyrrol-2-yl)-1,2,3,6-tetrahydropyridine should be good candidates to develop a robust spectrophotometric-based assay that is selective for MAO-A.