Potential inhibitors of tyrosine hydroxylase and dopamine-beta-hydroxylase

A series of methyl-substituted 1,2,3,4-tetrahydrocarbazoles was synthesized and screened for in vitro activity against tyrosine hydroxylase and dopamine-beta-hydroxylase. The most potent compounds were evaluated for inhibition of norepinephrine biosynthesis in rats. The results indicated no significant decrease in norepinephrine levels at three dosage levels.     

Biosynthesis of phenylalanine and tyrosine in claviceps

Some enzymes of the terminal steps of phenylalanine and tyrosine biosyntheses were investigated in various alkaloid-forming ergot strains. All strains studied utilize both arogenate and phenylpyruvate as an intermediate in L-phenylalanine synthesis. L-Tyrosine is preferentially or exclusively synthesized via the arogenate pathway. No feedback inhibition of arogenate pathway enzymes by aromatic amino acids was observed.     

Behavioural and biochemical effects of tryptophan,tyrosine and phenylalanine in mice

Behaviour was observed in mice given L-tryptophan, L-tyrosine or L-phenylalanine and then placed either in an open field or in water in a narrow cylinder. Animals placed in water (swim test) soon assume a characteristic immobile posture. Most antidepressants, including pharmacologically atypical ones, decrease immobility in the swim test while many decrease or do not affect activity in the open field test. Tryptophan increased immobility in the swim test, but did not affect open field activity and thus did not exhibit the normal profile of activity for an antidepressant. Tyrosine decreased immobility in the swim test and markedly increased activity in the open field test, an action similar to the psychostimulants amphetamine and caffeine. Phenylalanine decreased immobility in the swim test, but did not affect open field activity. Thus, its behavioural effects are similar to those of an antidepressant. As expected, tryptophan increased brain tryptophan and serotonin in a dose-related fashion. Tyrosine did not alter dopamine or noradrenaline levels, while phenylalanine lowered dopamine, noradrenaline and serotonin. These biochemical data do not fully explain the behavioural results.     

Effects of rapid depletion of phenylalanine and tyrosine on sleep and behavior

The effects of fluctuations of free amino acid concentrations in plasma on sleep patterns and operant behavior in the squirrel monkey were studied. Plasma phenylalanine (PHE) and tyrosine (TYR) were rapidly lowered to trace levels within 4 hr by intraperitoneal administration of phenylalanine ammonia-lyase (PAL), an enzyme which specifically deaminates both PHE and TYR to inactive products. Significant alterations in sleep patterns and in performance on a chained operant task involving hold and reaction time components were found, but no significant effect on the performance of a simple operant task was observed. Administration of saline or trans-p-cinnamic acid and trans-p-coumaric acid, the products of PHE and TYR deamination, produced no changes in behavior or sleep patterns. The reduction of plasma PHE and TYR resulted in a significant decrease in PHE and TYR levels in whole rat brain. Brain serotonin levels were increased within 4 hr after PAL administration, whereas, dopamine and norepinephrine levels were decreased subsequently (within 8 hr). These studies suggest that circulating levels of PHE and TYR are involved directly or indirectly in the modulation of certain parameters of brain function.     

Behavioural effects of acute phenylalanine and tyrosine depletion in healthy male volunteers

Acute phenylalanine and tyrosine depletion (APTD) studies have been used to assess the role of the cathecholaminergic system in various aspects of human behaviour. In this study we conducted a randomized, double-blind, controlled and cross-over comparison to evaluate the effects of APTD on memory, attention and mood in normal subjects. Twelve healthy male volunteers were included in this study. The subjects ingested a nutritionally balanced mixture (B) or a similar mixture deficient in phenylalanine and tyrosine (PT-). Before and 5 h after ingestion of the drink, volunteers underwent tests on mood, memory and attention. Results of the memory tests showed that PT- mixture impaired word recall as measured in Rey's test (p = 0.016). The assessment of changes in mood showed that the balanced mixture improved scores of as alertness (VAMS factor I, p = 0.037) and the PT- mixture induces an opposite effect, increased scores of anxiety (Profiles of Mental State composed-anxious dimension, p = 0.022). These results suggest that tyrosine plasma levels and cathecholamines may be important factors in regulating mood and memory.     

Syntheses of halogen derivatives of L‐tryptophan,L‐tyrosine and L‐phenylalanine labeled with hydrogen isotopes

Halogenated, labeled with tritium and doubly with deuterium and tritium, derivatives of L ‐tryptophan, i.e. 5′‐bromo‐[2‐³H]‐, 5′‐bromo‐[2‐²H/³H]‐, 5′‐fluoro‐[2‐³H]‐5′‐fluoro‐[2‐²H/³H]‐, 6′‐fluoro‐[2‐³H]‐, 6′‐fluoro‐[2‐²H/³H]‐L ‐tryptophan, as well as, L ‐tyrosine, i.e. 3′‐fluoro‐[2‐³H]‐, 3′‐fluoro‐[2‐²H/³H]‐, 3′‐chloro‐[2‐³H]‐, and 3′‐chloro‐[2‐²H/³H]‐L ‐tyrosine, and also L ‐phenylalanine, i.e. 2′‐fluoro‐[(3S)‐³H]‐, 2′‐fluoro‐[(3S)‐²H/³H]‐, 2′‐chloro‐[(3S)‐³H]‐, 2′‐chloro‐[(3S)‐²H/³H]‐, 4′‐chloro‐[(3S)‐³H]‐, and 4′‐chloro‐[(3S)‐²H/³H]‐L ‐phenylalanine were synthesized using enzymatic methods. Isotopomers of L ‐tryptophan were synthesized by coupling of halogenated indoles with S‐methyl‐L ‐cysteine carried out in deuteriated or tritiated incubation media. Labeled halogenated derivatives of L ‐tyrosine were obtained by the enzymatically supported exchange between halogenated L ‐tyrosine and isotopic water. Labeled halogenated isotopologues of L ‐Phe were synthesized by the enzymatic addition of ammonia to halogenated cinnamic acid. As a source of hydrogen tritiated water (HTO) and heavy water (D₂O) with addition of HTO were used.     

Effects of dietary tyrosine, phenylalanine, and tryptophan on aggression in mice

Dietary amino acid regimens designed to enhance catecholaminergic and serotonergic functioning were found to differentially affect territorial-induced attacks in mice. Male albino mice were maintained on a semi-synthetic 12% casein protein diet for 2 weeks, then switched to diets modified by the addition of a 4% L-amino acid supplement, or 4% casein (control). Measures of aggressive behavior and open-field locomotor activity were obtained before and after the dietary supplements were administered. Resident mice fed supplements of L-tyrosine displayed a marked increase in the number of attacks on intruders and shorter attack latencies, but their locomotor activity was unaffected. L-phenylalanine supplements alone or in combination with L-tyrosine reduced the latency to attack and increased motility but did not affect the number of attacks. As a whole, the group of animals fed L-tryptophan showed no changes in aggression or motility.     

Brain phenylalanine and tyrosine levels and hepatic encephalopathy induced by CCl4 in rats

The correlation between the levels of brain aromatic amino acids and hepatic encephalopathy induced by CCl4 was investigated in rats. CCl4 (1.0 ml/kg three times per week for over 10 weeks) caused hyperammonemia and hepatic encephalopathy in rats. The brain levels of aromatic amino acids, especially tyrosine (Tyr) and phenylalanine (Phe) in rats with hepatic encephalopathy were increased by 605% and 255% respectively from that of the corresponding controls. Furthermore, a single intraperitoneal injection of 2,4-dinitrophenol (DNP; 30 mg/kg) in CCl4-treated rats (1.0 ml/kg three times per week for 7 weeks) showed hyperammonemia and hepatic encephalopathy (loss of consciousness) elicited a marked increase of Tyr and Phe levels in the brain. In addition, the blood levels of Tyr and Phe in all rats with hepatic encephalopathy were greatly elevated as compared to controls. On the other hand, continuous injection of ammonium chloride (20 mg N/ml) into the jugular vein for 1 h caused severe hyperammonemia without loss of consciousness. The brain levels of Tyr and Phe showed no change from the corresponding controls. These results suggest that the increase of aromatic amino acids, such as Tyr and Phe, in brain produced by hyperammonemia and high blood levels of Tyr and Phe may be a critical event to the development of hepatic encephalopathy.     

Use of a dietary manipulation to deplete plasma tyrosine and phenylalanine in healthy subjects

The aim of the present study was to lower plasma concentrations of tyrosine, the amino acid precursor of noradrenaline and to determine whether this manipulation impaired noradrenergic function as measured by the evening rise in concentrations of plasma melatonin. Eight healthy volunteers received three drinks: (i) an essential amino acid load with tyrosine, (ii) the same load without tyrosine and its precursor, phenylalanine and (iii) tap water. The tyrosine- and phenylalanine-deficient drink lowered plasma tyrosine by approximately 50% over 5 h. However, this did not alter the evening plasma melatonin levels compared to the other two drinks. The results suggest that amino acid loading produces a modest decline in plasma tyrosine levels but this does not lower noradrenergic neurotransmission in the pineal gland.     

苯丙氨酸、酪氨酸对槐米愈伤组织中总黄酮含量的影响

为了提高愈伤组织中总黄酮的含量 ,实现其商业化价值 ,本文研究了苯丙氨酸 ( phenylalanine,Phe.)、酪氨酸 ( tyrosine,Tyr.)对槐米组织培养中黄酮类化合物含量的影响。结果表明 :添加酪氨酸的效果较添加苯丙氨酸更好     

Effect of tyrosine on the potentiation by aspartame and phenylalanine of metrazol-induced convulsions in rats

Male rats were treated by oral intubation with tyrosine (Tyr), at doses of 0.5 and 1.0 g/kg body weight, alone or together with 1 g aspartame (APM)/kg body weight, or an equivalent dose of phenylalanine (Phe; 0.5 g/kg body weight); the effects on seizures induced by an effective dose of metrazol (ED₅₀) were observed. Tyr (0.5 g/kg body weight) had a protective effect against the Phe-potentiation of metrazol-induced clonic-tonic convulsions. At the same dose Tyr had no effect on the seizure-promoting activity of APM, but at 1 g/kg it reduced the proconvulsant potential of the sweetener. Analysis of the brain and plasma amino acid concentrations indicated that the Tyr to Phe ratio tended to be enhanced in Tyr-Phe treated rats compared with those treated with Phe alone. This ratio remained essentially constant in the brain of APM-treated rats, compared with those treated with APM plus 1 g Tyr/kg body weight, whereas an increase in this ratio in the plasma was observed. These results confirm that Tyr antagonizes the proconvulsant effect of Phe and APM and they further suggest that no simple relationship exists between the relative brain concentrations of the two amino acids and the response to metrazol convulsions.     

Catecholamine formation in brain from phenylalanine and tyrosine— effects of psychotropic drugs and other agents

The present report is a comparative study of phenylalanine and tyrosine as the precursors of cerebral catecholamines. Subcellular fractions of brain regions were incubated with a mixture of (¹⁴C)phenylalanine and (³H)tyrosine for the studies in vitro; the labeled amino acids in solution were injected into the lateral ventricle of rat brain for the experiments in vivo. After the experiments, the ratio of ¹⁴C to ³H (¹⁴C dis./min/³H dis./min × 100) in the isolated catecholamines [R(CA)] and tyrosine [R(TY)] was determined. The ratio R(CA)/R(TY) was taken as a measure of the divergence between the isotope ratio in tyrosine and that in the catecholamines. The experiments in vitro indicate that the rate of phenylalanine hydroxylation, the R(CA) value and the R(CA)/R(TY) value may be characteristic properties of specific brain regions. Several physical or chemical agents were found to have profound effects not only on the hydroxylation of phenylalanine but also on the R(CA) and R(CA)/R(TY) values. Lowering the incubation temperature from 37° to 0° decreased the hydroxylation of both the amino acids but favored the relative formation of (¹⁴C)catecholamines. Lower incubation temperature also favored the formation of the consecutive hydroxylation product (¹⁴C)catecholamines and very little (¹⁴C)tyrosine was present in the incubation mixture. Pretreatment of the synaptosomal-mitochondrial enzyme source with any one of several detergents or with hypotonic sucrose almost completely inhibited the hydroxylation of both the substrates. The residual activity of such preparations favors the formation of (³H)catecholamines. Time studies at 37° and at 0° indicate that the ratio R(CA)/R(TY) is always greater than unity within the time range of 5–60 min. After incubation of the particulate fraction at 0°, the R(CA) value continues to increase up to 60 min, at which time the formation of (¹⁴C)catecholamines is about 1·4 times that of (³H)catecholamines. The results of incubations at various phenylalanine substrate concentrations show that the value of R(CA)/R(TY) is relatively insensitive to changes in phenylalanine concentration in the presence of a constant level of tyrosine and the values were larger than unity. In vivo, several psychotropic drugs—chlorpromazine, amphetamine, apomorphine and morphine—were observed to either stimulate or inhibit the formation of catecholamines from (¹⁴C)phenylalanine. In conclusion, our results suggest that: (1) the tyrosine that is formed in vitro from phenylalanine in brain tissue is not freely miscible with the endogenous free tyrosine; (2) the hydroxylation characteristics of the phenylalanine-derived tyrosine may be distinctly different from that of the free endogenous tyrosine; and (3) phenylalanine hydroxylation may be sensitive to some psychotropic drugs in vitro.     

The phenylalanine and tyrosine contnet of maternal and fetal body fluids from rabbits fed aspartame.

The methyl ester of aspartylphenylalanine (aspartame; SC-18862; 3-amino-N-(α-carboxyphenethyl)-succinamic acid, methyl ester) is a sweetening agent which organoleptically has about 180 times the sweetness of sugar. Since this compounds is a food additive its metabolism in pregnancy has been evaluated. Pregnant female rabbits were fed aspartame at a level of 6% in the diet beginning on day 6 of pregnancy. Maternal plasma samples taken at days 6, 9, 16, and 20 were analyzed for phenylalanine and tyrosine. Fetal amniotic fluids were similarly analyzed on days 16 and 20 as were fetal plasma samples at day 20. Maternal plasma phenylalanine and tyrosine increased as a result of the treatment, reaching a peak on day 9. These values returned toward normal levels by day 20. The ratios of fetal/maternal plasma phenylalanine and tyrosine concentrations were unaffected by the treatment. No evidence of substrate inhibition of phenylalanine hydroxylase was seen in maternal or fetal plasma analyses or in in vitro studies of maternal liver homogenates. Tyrosine concentrations in maternal and fetal plasma rose higher with treatment than phenylalanine concentrations. Both amino acids accumulated in the amniotic fluid in amounts greater than, but proportional to, plasma concentrations.