The metabolism of L-phenylalanine and L-tyrosine by liver cells isolated from adrenalectomized rats and from streptozotocin-diabetic rats

Synaptic and cellular plasticity in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disease, which causes a tremendous socioeconomic burden. PD patients are suffering from debilitating motor and nonmotor symptoms. Cardinal motor symptoms of PD, including akinesia, bradykinesia, resting tremor, and rigidity, are caused by the degeneration of dopaminergic neurons in the substantia nigra pars compacta. In addition, decreased amounts of dopamine (DA) level in the basal ganglia induces numerous adaptive changes at the cellular and synaptic levels in the basal ganglia circuits. These cellular and synaptic adaptations are believed to underlie the emergence and propagation of correlated, rhythmic pattern of activity throughout the interconnected cortico-basal ganglia-thalamocortical network. The widespread pathological pattern of brain activity is closely linked to the devastating motor symptoms of PD. Accumulating evidence suggests that both dopaminergic degeneration and the associated abnormal cellular and circuit activity in the basal ganglia drive the motor symptoms of PD. In this short review I summarize the recent advances in our understanding of synaptic and cellular alterations in two basal ganglia nuclei (i.e. the striatum and the subthalamic nucleus) following a complete loss of DA, and in our conceptual understanding of the cellular and circuit bases for the pathological pattern of brain activity in parkinsonian state.

2-Hydrazinoquinoline as a Derivatization Agent for LC-MS-Based Metabolomic Investigation of Diabetic Ketoacidosis

Short-chain carboxylic acids, aldehydes and ketones are products and regulators of many important metabolic pathways. Their levels in biofluids and tissues reflect the status of specific metabolic reactions, the homeostasis of the whole metabolic system and the wellbeing of a biological entity. In this study, the use of 2-hydrazinoquinoline (HQ) as a novel derivatization agent was explored and optimized for simultaneous liquid chromatography-mass spectrometry (LC-MS) analysis of carboxylic acids, aldehydes and ketones in biological samples. The formation of carboxylic acid derivative is attributed to the esterification reaction between HQ and a carboxyl group, while the production of aldehyde and ketone derivatives is through the formation of Schiff bases between HQ and a carbonyl group. The compatibility of HQ with biological samples was demonstrated by derivatizing urine, serum and liver extract samples. Using this HQ-based approach, the kinetics of type 1 diabetes-induced metabolic changes was characterized by the LC-MS-based metabolomic analysis of urine samples from streptozotocin (STZ)-treated mice. Subsequently, carboxylic acid, aldehyde and ketone metabolites associated with STZ-elicited disruption of nutrient and energy metabolism were conveniently identified and elucidated. Overall, HQ derivatization of carboxylic acids, aldehydes and ketones could serve as a useful tool for the LC-MS-based metabolomic investigation of endogenous metabolism.

An integrated approach for the analysis of biological pathways using mixed models

Gene class, ontology, or pathway testing analysis has become increasingly popular in microarray data analysis. Such approaches allow the integration of gene annotation databases, such as Gene Ontology and KEGG Pathway, to formally test for subtle but coordinated changes at a system level. Higher power in gene class testing is gained by combining weak signals from a number of individual genes in each pathway. We propose an alternative approach for gene-class testing based on mixed models, a class of statistical models that:

In microarray data analysis, when statistical testing is applied to each gene individually, one is often left with too many significant genes that are difficult to interpret or too few genes after a multiple comparison adjustment. Gene-class, or pathway-level testing, integrates gene annotation data such as Gene Ontology and tests for coordinated changes at the system level. These approaches can both increase power for detecting differential expression and allow for better understanding of the underlying biological processes associated with variations in outcome. We propose an alternative pathway analysis method based on mixed models, and show this method provides useful inferences beyond those available in currently popular methods, with improved power and the ability to handle complex experimental designs.

TLC of some free amino acids from sanguine plasma

This research presents the results obtained from analysis by thin layer chromatography (TLC) of some free amino acids from sanguine plasma samples in the different degree progress in maladies: diabetes, renal syndrome and hepatic cirrhosis. The chromatograms were evaluated with a Shimadzu CS-9000 dual-wavelength flying-spot scanner. Better results were obtained in the case of hepatic cirrhosis.

Disturbances in dexamethasone suppression test and lower availability of L-tryptophan and tyrosine in early puerperium and in women under contraceptive therapy

This study investigates the function of the hypothalamic-pituitary-adrenal (HPA)-axis and the availability of L-tryptophan and tyrosine to the brain in postpartum women and in women taking long-term oral contraceptives. To this end, we have measured the following parameters in 50 women (i.e. 9 normal controls, 10 women taking oral contraceptives, and 31 postpartum females): plasma cortisol, L-tryptophan, tyrosine and the amino acids (CAA) known to compete with them for transport through the blood-brain barrier. We have determined the effects of 1 mg of dexamethasone on the above-mentioned biological markers in postpartum females. Plasma cortisol and tyrosine were significantly higher and lower, respectively, in puerperium and in women under contraceptive therapy as opposed to normal controls. L-Tryptophan was significantly lower in postpartum females, whilst the L-tryptophan/CAA ratio did not differ across the three study groups. Postpartum females revealed a significant negative relationship between the availability of L-tryptophan to the brain and postpartum mood, as measured by Zung's Depression and Anxiety Scales and State Anxiety Inventory. Dexamethasone had a significant suppressive effect on L-tryptophan/CAA and tyrosine/CAA ratios, with cortisol nonsuppression appearing in 82% of the postpartum females.

The effects of glucocorticoids on the availability of L-tryptophan and tyrosine in the plasma of depressed patients

There is evidence that a functional deficit of serotonin/noradrenaline and/or of their precursors L-tryptophan (L-TRP)/tyrosine and disorders in the hypothalamic-pituitary-adrenal (HPA) axis are linked to the pathophysiology of severe depressions. Several reports suggest a reciprocal relationship between these neurotransmitters and HPA axis activity. In order to investigate the effect of glucocorticoid excess on the availability of L-TRP and tyrosine to the brain, we measured urinary cortisol (UC) excretion in 24-h urine, and the availability of both amino acids before and after treatment with 1 mg dexamethasone in 26 depressed patients. We found no relationship between UC excretion and the availability of either amino acid. Dexamethasone significantly suppressed the availability of L-TRP (P less than 10(-5] and of tyrosine (P = 0.005). Major depressed patients with melancholia exhibited a significantly lower availability of L-TRP than minor depressives (P = 0.007).

Suppressant effects of dexamethasone on the availability of plasma L-tryptophan and tyrosine in healthy controls and in depressed patients

Formation in the brain of serotonin from L-tryptophan (L-TRP) and noradrenaline from tyrosine are pathways related to the pathophysiology of major depression and to the regulation of the hypothalamic-pituitary-adrenal (HPA) axis. In the past, decrements in L-TRP availability and disorders in the HPA axis have repeatedly been observed in major depressed patients; both factors were shown to be inversely correlated. In order to investigate the relationships between glucocorticosteroid activity and the availability of L-TRP and tyrosine, the authors measured L-TRP, tyrosine, valine, leucine, isoleucine and phenylalanine in baseline conditions and after treatment with 1 mg dexamethasone in 16 healthy controls and in 50 depressed patients. The ratios between L-TRP and tyrosine and the sums of the amino acids known to compete with them during transport across the blood-brain barrier were computed as an index of (respectively) the serotonin and noradrenaline synthesis in the brain. We found significantly decreased plasma L-TRP and tyrosine levels after treatment with dexamethasone compared with basal levels. Accordingly, the plasma ratios between L-TRP and tyrosine and the sum of the competing amino acids were significantly reduced by dexamethasone administration. It was hypothesized that through these actions of dexamethasone on peripheral amino acids, the central noradrenaline and serotonin control over the HPA-axis could be altered.

The effect of streptozotocin-induced diabetes on phenylalanine hydroxylase expression in rat liver

The impact of experimentally induced diabetes on the expression of rat liver phenylalanine hydroxylase has been investigated. A significant elevation in maximal enzymic activity was observed in diabetes. This was associated with significant increases in the amount of enzyme, the phenylalanine hydroxylase-specific translational activity of hepatic RNA and the abundance of phenylalanine hydroxylase-specific mRNA. These changes in phenylalanine hydroxylase expression were not observed when diabetes was controlled by daily injections of insulin. These results are discussed in relation to the hormonal control of phenylalanine hydroxylase gene expression.

Effects of experimental diabetes on rat hepatic phenylalanine hydroxylase in vivo

1. The stimulated levels of phenylanine hydroxylase activity in liver extracts from streptozotocin-induced diabetic rats (Donlon and Beirne, 1982) have been correlated with an increased rate of phenylalanine catabolism in vivo. 2. The levels of hepatic phenylalanine hydroxylase protein in diabetic rats become elevated. This effect is not seen in diabetic animals concurrently treated with insulin. 3. The rate of synthesis of liver phenylalanine hydroxylase in 5-day diabetics is 260% that of control animals. 4. These observations are discussed with reference to the regulation of hepatic phenylalanine hydroxylase and phenylanine metabolism in rats.

The role of insulin in the modulation of glucagon-dependent control of phenylalanine hydroxylation in isolated liver cells

The stimulation of phenylalanine hydroxylation in isolated liver cells by sub-maximally effective concentrations of glucagon (less than 0.1 microM) is antagonized by insulin (0.1 nM-0.1 microM). This phenomenon is a consequence of a decrease in the glucagon-stimulated phosphorylation of phenylalanine hydroxylase from liver cells incubated in the presence of insulin. The impact of insulin on the phosphorylation state and activity of the hydroxylase is mimicked by incubation of liver cells in the presence of orthovanadate (10 microM). A series of cyclic AMP and cyclic GMP analogues enhanced phenylalanine hydroxylation: in each case insulin diminished the stimulation of flux. These results are discussed in the light of the characteristics of insulin action on other metabolic processes.

Control of phenylalanine and tyrosine metabolism by phosphorylation mechanisms

A system for the parallel determination of enzyme phosphorylation and expressed activity in rat liver cells, and its application to studies of phenylalanine hydroxylase and tyrosine aminotransferase, is described. Phenylalanine hydroxylase is phosphorylated by agents which stimulate cyclic AMP- and Ca2+-dependent protein kinase activity. The phosphorylation site(s) appear to be the same for both kinases. Phosphorylation is accompanied by increased metabolic flux at low, physiologically relevant, substrate concentrations. Insulin and spermine both inhibit the phosphorylation of the enzyme, possibly by increasing dephosphorylation. Tyrosine aminotransferase is phosphorylated in liver cell incubations but the rate is slow and insensitive to additions to the medium. No parallel changes in flux could be detected. Both enzymes are subject to complex regulatory mechanisms, short- and long-term. Their activities may be coordinated in vivo by control exerted at the level of the plasma membrane where both amino acids share the same transport processes. Determination of the control coefficients for the several components indicates that membrane transport may be a major limitation on flux.