Tyrosine depletion lowers in vivo DOPA synthesis in ventral hippocampus

A Preclinical Study of Casein Glycomacropeptide as a Dietary Intervention for Acute Mania

BACKGROUND

Casein glycomacropeptide is a peptide that lacks phenylalanine, tyrosine, and tryptophan. This profile may enable it to deplete phenylalanine, tyrosine, and tryptophan, and subsequently the synthesis of dopamine and serotonin in the brain. Dopamine- and serotonin-depleting amino acid mixtures have shown promise as acute antimanic treatments. In this study, we explore the depleting effects on amino acids, dopamine and serotonin as well as its actions on manic-like and other behavior in rats.

METHODS

Casein glycomacropeptide and a selection of amino acid mixtures were administered orally at 2, 4, or 8 h or for 1 week chronically. Amino acid and monoamine levels were measured in plasma and brain and behavior was assessed in the amphetamine-hyperlocomotion, forced swim, prepulse inhibition, and elevated plus maze tests.

RESULTS

Casein glycomacropeptide induced a time-dependent reduction in tyrosine, tryptophan, and phenylalanine in brain and plasma which was augmented by supplementing with leucine. Casein glycomacropeptide +leucine reduced dopamine in the frontal cortex and serotonin in the hippocampus, frontal cortex, and striatum after 2 and 4 h. Casein glycomacropeptide+leucine also had antimanic activity in the amphetamine-induced hyperlocomotion test at 2 h after a single acute treatment and after 1 week of chronic treatment.

CONCLUSIONS

Casein glycomacropeptide-based treatments and a branched-chain amino acid mixture affected total tissue levels of dopamine in the frontal cortex and striatum and serotonin in the frontal cortex, striatum, and hippocampus of rats in a time-dependent fashion and displayed antimanic efficacy in a behavioral assay of mania.

L-Tyrosine availability affects basal and stimulated catecholamine indices in prefrontal cortex and striatum of the rat

We previously found that L-tyrosine (L-TYR) but not D-TYR administered by reverse dialysis elevated catecholamine synthesis in vivo in medial prefrontal cortex (MPFC) and striatum of the rat (Brodnik et al., 2012). We now report L-TYR effects on extracellular levels of catecholamines and their metabolites. In MPFC, reverse dialysis of L-TYR elevated in vivo levels of dihydroxyphenylacetic acid (DOPAC) (L-TYR 250-1000 μM), homovanillic acid (HVA) (L-TYR 1000 μM) and 3-methoxy-4-hydroxyphenylglycol (MHPG) (L-TYR 500-1000 μM). In striatum L-TYR 250 μM elevated DOPAC. We also examined L-TYR effects on extracellular dopamine (DA) and norepinephrine (NE) levels during two 30 min pulses (P2 and P1) of K+ (37.5 mM) separated by t = 2.0 h. L-TYR significantly elevated the ratio P2/P1 for DA (L-TYR 125 μM) and NE (L-TYR 125-250 μM) in MPFC but lowered P2/P1 for DA (L-TYR 250 μM) in striatum. Finally, we measured DA levels in brain slices using ex-vivo voltammetry. Perfusion with L-TYR (12.5-50 μM) dose-dependently elevated stimulated DA levels in striatum. In all the above studies, D-TYR had no effect. We conclude that acute increases within the physiological range of L-TYR levels can increase catecholamine metabolism and efflux in MPFC and striatum. Chronically, such repeated increases in L-TYR availability could induce adaptive changes in catecholamine transmission while amplifying the metabolic cost of catecholamine synthesis and degradation. This has implications for neuropsychiatric conditions in which neurotoxicity and/or disordered L-TYR transport have been implicated.

Reduction in Pain and Inflammation Associated With Chronic Low Back Pain With the Use of the Medical Food Theramine

Management of chronic back pain is a challenge for physicians. Although standard treatments exert a modest effect, they are associated with narcotic addiction and serious side effects from nonsteroidal antiinflammatory agents. Moreover, neurotransmitter depletion from both the pain syndrome and therapy may contribute to a poor treatment outcome. Neurotransmitter deficiency may be related both to increased turnover rate and inadequate neurotransmitter precursors from the diet, particularly for essential and semi-essential amino acids. Theramine, an amino acid blend 68405-1 (AAB), is a physician-prescribed only medical food. It contains neurotransmitter precursors and systems for increasing production and preventing attenuation of neurotransmitters. A double-blind controlled study of AAB, low-dose ibuprofen, and the coadministration of the 2 agents were performed. The primary end points included the Roland Morris index and Oswestry disability scale. The cohort included 122 patients aged between 18 and 75 years. The patients were randomized to 1 of 3 groups: AAB alone, ibuprofen alone, and the coadministration of the 2 agents. In addition, C-reactive protein, interleukin 6, and plasma amino acid concentrations were measured at baseline and 28 days time points. After treatment, the Oswestry Disability Index worsened by 4.52% in the ibuprofen group, improved 41.91% in the AAB group, and improved 62.15% in the combination group. The Roland Morris Index worsened by 0.73% in the ibuprofen group, improved by 50.3% in the AAB group, and improved 63.1% in the combination group. C-reactive protein in the ibuprofen group increased by 60.1%, decreased by 47.1% in the AAB group, and decreased by 36% in the combination group. Similar changes were seen in interleukin 6. Arginine, serine, histidine, and tryptophan levels were substantially reduced before treatment in the chronic pain syndrome and increased toward normal during treatment. There was a direct correlation between improvement in amino acid concentration and treatment response. Treatment with amino acid precursors was associated with substantial improvement in chronic back pain, reduction in inflammation, and improvement in back pain correlated with increased amino acid precursors to neurotransmitters in blood.

Simplified dietary acute tryptophan depletion: effects of a novel amino acid mixture on the neurochemistry of C57BL/6J mice

BACKGROUND

Diet and nutrition can impact on the biological processes underpinning neuropsychiatric disorders. Amino acid (AA) mixtures lacking a specific neurotransmitter precursor can change the levels of brain serotonin (5-HT) or dopamine (DA) in the central nervous system. The availability of these substances within the brain is determined by the blood-brain barrier (BBB) that restricts the access of peripheral AA into the brain. AA mixtures lacking tryptophan (TRP) compete with endogenous TRP for uptake into the brain across the BBB, which in turn leads to a decrease in central nervous 5-HT synthesis.

OBJECTIVE

The present study compared the effects of a simplified acute tryptophan depletion (SATD) mixture in mice on blood and brain serotonergic and dopaminergic metabolites to those of a commonly used acute tryptophan depletion mixture (ATD Moja-De) and its TRP-balanced control (BAL).

DESIGN

The SATD formula is composed of only three large neutral AAs: phenylalanine (PHE), leucine (LEU), and isoleucine (ILE). BAL, ATD Moja-De, or SATD formulas were delivered to adult male C57BL/6J mice by gavage. TRP, monoamines, and their metabolites were quantified in blood and brain regions (hippocampus, frontal cortex, amygdala, caudate putamen, and nucleus accumbens).

RESULTS

Both ATD Moja-De and SATD significantly decreased levels of serum and brain TRP, as well as brain 5-HIAA and 5-HT compared with BAL. SATD reduced HVA levels in caudate but did not alter total DA levels or DOPAC. SATD decreased TRP and serotonergic metabolites comparably to ATD Moja-De administration.

CONCLUSION

A simplified and more palatable combination of AAs can manipulate serotonergic function and might be useful to reveal underlying monoamine-related mechanisms contributing to different neuropsychiatric disorders.

A simplified method to quantify dysregulated tyrosine transport in schizophrenia

BACKGROUND

Schizophrenia is associated with altered tyrosine transport across plasma membranes. This is typically demonstrated by measuring the uptake of radiolabeled tyrosine in cultured human fibroblasts. Our primary goal was to determine whether tyrosine uptake could be characterized using unlabeled tyrosine. A secondary goal was to assess the effect of antipsychotic drugs added during the incubation.

METHOD

Epithelium-derived fibroblast cultures were generated from patients with schizophrenia (n=6) and age-matched controls (n=6). Cells between cycles 8-12 were exposed to an amino acid free medium for 60min and then for 1min to media containing tyrosine (0.008-1.0mM). Amino acid levels were measured and Michaelis-Menten parameters determined. Uptake of tyrosine (0.5mM) was also measured in control cells after antipsychotic drugs were introduced during the depletion or uptake phases.

RESULTS

Tyrosine uptake was sodium-independent. The maximal transport velocity (Vmax) was significantly lower in patients with schizophrenia than in controls (p<0.01). The transporter affinity (Km) did not differ between the groups. Tyrosine uptake was differentially affected (p<0.001) by inclusion of 10(-4)M haloperidol, chlorpromazine or clozapine during different periods of incubation.

CONCLUSION

Dysregulated tyrosine kinetics in schizophrenia can be readily studied without the use of radiolabeled tracers. The data also indicate that tyrosine uptake may be subject to complex pharmacological effects.

Dietary manipulation of serotonergic and dopaminergic function in C57BL/6J mice with amino acid depletion mixtures

Amino acid (AA) depletion techniques have been used to decrease serotonin (5-HT) and/or dopamine (DA) synthesis after administration of a tryptophan (acute tryptophan depletion, ATD) or phenylalanine/tyrosine-free (phenylalanine-tyrosine depletion, PTD) AA formula and are useful as neurochemical challenge procedures to study the impact of DA and 5-HT in patients with neuropsychiatric disorders. We recently demonstrated that the refined Moja-De ATD paradigm decreases brain 5-HT synthesis in humans and mice and lowers brain 5-HT turnover. In the present study we validated the neurochemical effects of three developed AA formulas on brain 5-HT and DA function in mice. To distinguish the direct and indirect effects of such mixtures on 5-HT and DA and to determine whether additive depletion of both could be obtained simultaneously, we compared the effects of ATD for 5-HT, PTD for DA, and a combined monoamine depletion mixture (CMD) compared to a control condition consisting of a balanced amino acid mixture. Food-deprived male C57BL/6J mice were gavaged with AA mixtures. Serum and brain samples were collected and analyzed for determination of tryptophan (Trp), tyrosine (Tyr), 5-HT, 5-HIAA, DA, DOPAC and HVA levels. ATD was the most effective at decreasing Trp, 5-HT and 5-HIAA. In contrast, PTD reduced Tyr globally but HVA only in certain brain regions. Although CMD affected both 5-HT and DA synthesis, it was less effective when compared with ATD or PTD alone. The present results demonstrate that two newly developed PTD and CMD formulas differentially impact brain 5-HT and DA synthesis relative to 5-HT-specific ATD Moja-De. Different effects on 5-HT and DA function by these mixtures suggest that the exact composition may be a critical determinant for effectiveness with respect to the administered challenge procedure.

Presynaptic regulation of extracellular dopamine levels in the medial prefrontal cortex and striatum during tyrosine depletion

RATIONALE

Available neurochemical probes that lower brain dopamine (DA) levels in man are limited by their tolerability and efficacy. For instance, the acute lowering of brain tyrosine is well tolerated, but only modestly lowers brain DA levels. Modification of tyrosine depletion to robustly lower DA levels would provide a superior research probe.

OBJECTIVES

The objective of this study was to determine whether the subthreshold stimulation of presynaptic DA receptors would potentiate tyrosine depletion-induced effects on extracellular DA levels in the medial prefrontal cortex (MPFC) and striatum of the rat.

METHODS

We administered quinpirole, a predominantly DA type 2 (D2R) receptor agonist, into the MPFC and striatum by reverse dialysis. A tyrosine- and phenylalanine-free neutral amino acid mixture [NAA(-)] IP was used to lower brain tyrosine levels. DA levels in the microdialysate were measured by HPLC with electrochemical detection.

RESULTS

Quinpirole dose-dependently lowered DA levels in MPFC as well as in the striatum. NAA(-) alone transiently lowered DA levels (80 % baseline) in the striatum, but had no effect in MPFC. The co-administration of NAA(-) and a subthreshold concentration of quinpirole (6.25 nM) lowered DA levels (50 % baseline) in both the MPFC and striatum. This effect was blocked by the mixed D2R/D3R antagonist haloperidol at IP doses that on their own did not affect DA levels (10.0 nmol/kg in the MPFC and 0.10 nmol/kg in the striatum).

CONCLUSIONS

Pharmacological stimulation of inhibitory D2R receptors during tyrosine depletion markedly lowers the extracellular DA levels in the MPFC and striatum. The data suggest that combining tyrosine depletion with a low dose of a DA agonist should robustly lower brain regional DA levels in man.