Cardioprotective potential of lithium and role of fractalkine in euthymic patients with bipolar disorder

OBJECTIVE

Over a half century, lithium has been used as the first-line medication to treat bipolar disorder. Emerging clinical and laboratory studies suggest that lithium may exhibit cardioprotective effects in addition to neuroprotective actions. Fractalkine (CX3CL1) is a unique chemokine associated with the pathogenesis of mood disorders and cardiovascular diseases. Herein we aimed to ascertain whether lithium treatment is associated with favorable cardiac structure and function in relation to the reduced CX3CL1 among patients with bipolar disorder.

METHODS

We recruited 100 euthymic patients with bipolar I disorder aged over 20 years to undergo echocardiographic study and measurement of plasma CX3CL1. Associations between lithium treatment, cardiac structure and function and peripheral CX3CL1 were analyzed according to the cardiovascular risk. The high cardiovascular risk was defined as (1) age ⩾ 45 years in men or ⩾ 55 years in women or (2) presence of concurrent cardiometabolic diseases.

RESULTS

In the high cardiovascular risk group (n = 61), patients who received lithium as the maintenance treatment had significantly lower mean values of left ventricular internal diameters at end-diastole (Cohen's d = 0.65, p = 0.001) and end-systole (Cohen's d = 0.60, p = 0.004), higher mean values of mitral valve E/A ratio (Cohen's d = 0.51, p = 0.019) and superior performance of global longitudinal strain (Cohen's d = 0.51, p = 0.037) than those without lithium treatment. In addition, mean plasma levels of CX3CL1 in the high cardiovascular risk group were significantly lower among patients with lithium therapy compared with those without lithium treatment (p = 0.029). Multiple regression models showed that the association between lithium treatment and mitral value E/A ratio was contributed by CX3CL1.

CONCLUSION

Data from this largest sample size study of the association between lithium treatment and echocardiographic measures suggest that lithium may protect cardiac structure and function in patients with bipolar disorder. Reduction of CX3CL1 may mediate the cardioprotective effects of lithium.

Echocardiographic study of cardiac structure and function in people with bipolar disorder after midlife

BACKGROUND

Heart failure is the leading cause of mortality in older people with bipolar disorder (BD). Studies examining cardiac structure and function in middle-aged patients with BD by using echocardiography and cardiac strain imaging are scant.

METHODS

We recruited 48 patients with bipolar I disorder (BD-I) older than 45 years to undergo conventional and tissue speckle tracking echocardiography. Data of 31 mentally healthy adults older than 45 years were randomly retrieved from the echocardiographic dataset and compared with the data of BD patients.

RESULTS

Patients with BD-I had significantly higher mean values of interventricular septal thickness (Cohen's d = 0.83, p = 0.001) and left ventricular internal diameter (Cohen's d = 0.90, p = 0.001) at end-diastole relative to controls. Additionally, BD-I patients exhibited significantly lower mean values of mitral valve E/A ratio (Cohen's d = 0.67, p = 0.007) and a more reduced global longitudinal strain (Cohen's d = 0.72, p = 0.029) than controls. Multiple linear regression revealed that body mass index was negatively correlated with the mitral valve E/A ratio (adjustment R² = 0.363, p = 0.043) in patients with BD-I.

LIMITATIONS

A relatively small sample size may limit generalization.

CONCLUSIONS

After midlife, BD patients exhibit cardiac diastolic (low mitral valve E/A ratio) and systolic (reduced global longitudinal strain) dysfunction. High body mass index may play a role in the unfavorable cardiac function in aging patients with BD.

The association between carotid atherosclerosis and treatment with lithium and antipsychotics in patients with bipolar disorder

OBJECTIVES

Patients with bipolar disorder are at high risk of cardiovascular diseases. Among cardiovascular diseases, coronary heart disease and stroke are the leading causes of premature death and both share the pathogenesis of arterial atherosclerosis. Increased carotid intima-media thickness is sensitive for detecting early atherosclerosis and a practical index for predicting cardiovascular diseases. However, few studies investigated carotid intima-media thickness in adults with bipolar disorder. We attempted to determine the factors associated with carotid intima-media thickness in adults with bipolar disorder.

METHODS

The euthymic out-patients with bipolar I disorder aged over 20 years were recruited to measure the carotid intima-media thickness value through B-mode carotid ultrasound. Those with any psychiatric disorder, acute or life-threatening medical condition were excluded. All clinical information was obtained by reviewing medical records and directly interviewing patients with reliable others.

RESULTS

Of the 106 participants with a mean age of 44.5 years, 40.6% (N = 43) had concurrent cardiovascular/endocrine/metabolic diseases. A multivariate regression indicated that higher assumed daily lithium dosage was significantly associated with a decreased carotid intima-media thickness in the whole sample. In the young subgroup (⩽45 years old, N = 63), higher current daily lithium dosage and lower body mass index were associated with lower carotid intima-media thickness. In those without concurrent cardiovascular/endocrine/metabolic diseases, higher ratio of first-generation antipsychotics exposure in relation to illness chronicity was associated with higher carotid intima-media thickness, after controlling for body mass index or age.

CONCLUSION

Lithium treatment may be associated with less progression in carotid intima-media thickness and the reduced risk for atherosclerosis in adults with bipolar disorder, including those with high cardiovascular disease risk. In addition to age and body mass index, antipsychotics may increase carotid intima-media thickness even in the low cardiovascular disease-risk patients.

Inhibition of luminol-enhanced chemiluminescence by reduced pterins

Luminol-enhanced chemiluminescence, initially induced by exogenous H2O2 or enzymatic reactions which generate reactive oxygen species in situ, is inhibited by reduced pterins. Except dihydroneopterin which is as effective as tetrahydroneopterin, all tetrahydropterins are more effective than dihydropterins, which in turn is more effective than oxidized pterins in removing reactive oxygen species such as O2-. and H2O2. The antioxidant efficacy of some reduced pterins is better than ascorbic acid and L-glutathione. Reduced pterins may act as physiological scavengers for reactive oxygen species, and play an important role in cellular defense against oxidative damage.

Antioxidation activity of tetrahydrobiopterin in pheochromocytoma PC 12 cells

Rat pheochromocytoma PC 12 cells are susceptible to the oxidative toxicity caused by H2O2, nitrofurantoin, dopamine, and xanthine/xanthine oxidase reaction. The cytotoxicities of these agents are greatly reduced by the simultaneous presence of 0.1 mM tetrahydrobiopterin (BH4), 3 units/ml horseradish peroxidase, 0.2 mM NADH, and 0.1 units/ml sheep liver dihydropteridine reductase (DHPR). Individually, BH4, NADH and DHPR have no protection against H2O2 toxicity in PC 12 cells. Peroxidase alone offers 58% of protection if cells are incubated in the medium but only 3% in Dulbecco's phosphate buffered saline. The efficiency of the BH4-mediated antioxidation system in PC 12 cells is equal to or better than ascorbic acid and catalase, depending on the source of the reactive O2 species (ROS). The reactions responsible for the BH4-antioxidation system may consist of the non-enzymatic and the peroxidase-catalyzed reduction of H2O2 to H2O by BH4 and the regeneration of BH4 by DHPR using NADH as the cofactor. The components of this defence mechanism against ROS are all normal cellular constituents and are ubiquitous in nature. This DHPR-catalyzed redox cycling of BH4 may constitute an as yet little-known antioxidation system in mammalian cells.

Inhibition of dopamine autoxidation by tetrahydrobiopterin and NADH in the presence of dihydropteridine reductase

Dihydropteridine reductase (DHPR) catalyzes the regeneration of tetrahydrobiopterin (BH4) from quinonoid dihydrobiopterin by using NADH as a hydrogen donor. This enzymatic reaction has been found to serve as an antioxidation system during dopamine autoxidation in oxygenated Dulbecco's phosphate buffered saline (pH 7.5) at 37 degrees C. BH4 or NADH by itself has little or no inhibitory effect on dopamine autoxidation. The presence of DHPR, in addition to BH4 and NADH, greatly prolongs the lag period, which increases with increasing concentrations of each of BH4, NADH and DHPR. This BH4/DHPR-mediated antioxidation system is as effective as other antioxidation agents such as ascorbic acid, cysteine and reduced glutathione. Since BH4, NADH and DHPR are ubiquitous in mammalian tissues, this system may play an important role in the reduction of the oxidation products of catecholamines.

Isolation, characterization, and application of monoclonal antibodies to rat tyrosine hydroxylase

Tyrosine hydroxylase (TH, tyrosine 3-monooxygenase; EC 1.14.16.2) activity in crude extracts of rat pheochromocytoma, rat brain, and bovine adrenal medulla can be immunoprecipitated in an indirect assay by monoclonal antibodies prepared against partially purified rat pheochromocytoma TH. One of these monoclonal antibodies, TH-2D8-2, can be used for immunocytochemical localization of TH in cell bodies, dendrites, and axons in catecholaminergic neurons (e.g., cells in the substantia nigra) of rat brain and in the cell body, neurites, and growth cones of rat pheochromocytoma cells after treatment with nerve growth factor. When linked to Affi-gel 10, this monoclonal antibody can also be used for immunoaffinity purification of rat and bovine TH. These results suggest that TH-2D8-2 is a valuable reagent with which to investigate the localization, physiological regulation, and function of this important enzyme.

Human liver GTP cyclohydrolase I: purification and some properties

Human liver guanosine triphosphate (GTP) cyclohydrolase I has been purified more than 1,700-fold to what appears to be homogeneity. The active enzyme complex has an estimated molecular weight of 453,000 +/- 11,500 by gel filtration chromatography. It consists of a polypeptide of 149,000 +/- 4,000 mol wt by SDS-polyacrylamide gel electrophoresis. The activity of the enzyme is heat stable and is inhibited by di- and trivalent cations. The enzyme has an optimum pH of 7.7 in sodium phosphate buffer. It uses GTP as a sole substrate, with a Km of 116 microM.

Regulation of GTP cyclohydrolase I and dihydropteridine reductase in rat pheochromocytoma PC 12 cells

The addition of 8-bromo cyclic AMP, forskolin, theophylline, and 3-isobutyl-1-methylxanthine to the medium of PC 12 cells resulted in an increase in GTP cyclohydrolase I activity, but had no effect on dihydropteridine reductase activity, except theophylline which caused a decrease in dihydropteridine reductase activity at 96 h. GTP cyclohydrolase I activity peaked at 24 h and returned to normal 96 h after drug treatment. Cycloheximide decreased GTP cyclohydrolase I activity at 48 and 96 h, but had little effect on dihydropteridine reductase activity. The addition of reserpine selectively increased only GTP cyclohydrolase I activity. The addition of tetrahydrobiopterin and sepiapterin, however, coordinately inhibited both GTP cyclohydrolase I and dihydropteridine reductase activities. It appears that GTP cyclohydrolase I activity in PC 12 cells is regulated by cyclic AMP stimulation and by end-product inhibition, whereas dihydropteridine reductase activity is only subject to pterin inhibition.

Inhibition of GTP cyclohydrolase I by pterins

Pterins inhibit rat liver GTP cyclohydrolase I activity noncompetitively. Reduced pterins, such as 7,8-dihydro-D-neopterin, (6R,S)-5,6,7,8-tetrahydro-D-neopterin, 7,8-dihydro-L-biopterin, (6R)-5,6,7,8-tetrahydro-L-biopterin, L-sepiapterin, and DL-6-methyl-5,6,7,8-tetrahydropterin are approximately 12-times more potent as inhibitors than are oxidized pterins, such as D-neopterin, L-biopterin, and isoxanthopterin. They are also 12-times more potent than folates, such as folic acid, dihydrofolic acid, (+/-)-L-tetrahydrofolic acid, and aminopterin. The Ki values for 7,8-dihydro-D-neopterin, 7,8-dihydro-L-biopterin, and (6R)-5,6,7,8-tetrahydro-L-biopterin are 12.7 microM, 14.4 microM, and 15.7 microM, respectively. These results suggest that mammalian GTP cyclohydrolase I may be regulated by its metabolic end products.

MPTP metabolites inhibit rat brain glutathione S-transferases

1-Methyl-4-phenyl-2,3-dihydropyridinium and 1-methyl-4-phenyl-pyridinium species, metabolites of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, non-competitively inhibit glutathione S-transferases of rat brain in vitro. The Ki values for 1-methyl-4-phenyl-2,3-dihydropyridinium bromide and 1-methyl-4-phenyl-pyridinium bromide are 0.67 and 0.3 mM, respectively. Inhibition of these enzymes may lead to impairment of cellular defense mechanisms.

An enzyme immunoassay for the quantitation of dihydropteridine reductase

A competitive, enzyme-linked immunosorbent assay for the quantitative determination of dihydropteridine reductase (DHPR) is described. This highly sensitive method can determine the content of DHPR protein in tissue preparations independently of the enzymatic activity of the protein molecule. The method involves initial incubation of samples containing soluble enzyme in microtiter plates coated with purified goat antibodies to rat DHPR and further incubation with DHPR conjugated to alkaline phosphatase. The assay is used to study the ontogeny of DHPR in rat liver.

Rat striatal synaptosomes as a model system for studying the inhibition of dihydropteridine reductase activity

The distribution of dihydropteridine reductase between soluble and particulate fractions in synaptosomes parallels that of lactate dehydrogenase, but not monoamine oxidase. Ki and I50 values for inhibitors obtained with the enzyme-rich P2 fraction and its twice-washed fraction (P2W2) were essentially the same, and were similar to those obtained with highly purified human liver enzyme. Dihydropteridine reductase inhibitory potency of multi-ring compounds containing a catechol-moiety was greater than that of single ring catecholic compounds, which in turn was greater than that of p-hydroxy-phenolic compounds. The P2 fraction of rat striatal synaptosomal preparations may serve as a convenient source of dihydropteridine reductase for studying the inhibition of this enzyme.

A simplified 14CO2-trapping microassay for tyrosine hydroxylase activity

This 14CO2-trapping microassay for tyrosine hydroxylase activity uses microtest tubes (1.5 or 2.0 ml) with pierceable caps for injecting the reaction mixture. A folded filter paper strip (1 X 4 cm) impregnated with Protosol is placed directly inside the top of the tube prior to capping in order to trap liberated 14CO2. The effects of several variables and components involved in the assay have been systematically studied. The tyrosine hydroxylation reaction may be optimized by incubating 300 micrograms protein with 150 microM L-Tyr, 0.8 mM 6MPH4, 1 mM FeSO4, and 0.12 M Tris-acetate buffer (pH 5.8) for 10 min at 37 degrees C. The DOPA decarboxylation reaction may be optimized by continual incubation of the tyrosine hydroxylation medium with 175 micrograms hog kidney aromatic-L-amino acid decarboxylase, 6.25 mM 3-iodotyrosine, and 0.125 M potassium phosphate buffer (pH 8.0) for 30 min at 37 degrees C. Under these conditions, the radioactivity of 14CO2 recovered after 1 h at 37 degrees C may reach 14,000 dpm, whereas the blank only has 300 dpm (less than 3% of test value). This microassay is fast (less than 2 h to complete all reactions) and convenient for performing a large number of determinations.

Serotonergic conversion of MPTP and dopaminergic accumulation of MPP+

[3H]MPP+ had lower Km and higher Vmax values for its accumulation in rat brain synaptosomes than did [3H]MPTP. The kinetic parameters favored the uptake of [3H]MPP+ in the striatum to that in hypothalamus, whereas they were equally favorable for the uptake of [3H]MPTP in both regions. Hypothalamic uptake of [3H]MPTP and [3H]MPP+ was inhibited by desipramine, imipramine, norepinephrine, and serotonin. Striatal uptake of [3H]MPP+ and [3H]MPTP was blocked by nomifensine and dopamine. These results support the concept that MPTP accumulates in serotonergic neurons where it is oxidized by monoamine oxidase B to MPP+, which is released and then is selectively accumulated in dopaminergic neurons via the dopamine uptake system.

Further insight into the mode of action of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Chemical reactions of MPDP+, a recognized intermediate in the metabolic conversion of the neurotoxin MPTP by monoamine oxidase B into its major metabolite MPP+, were studied. Addition of cyanide to MPDP+ bromide in aqueous solutions afforded cyano-compound 5 which isomerized in the presence of silica gel into compound 6. Both 5 and 6 when heated yielded a third isomer 7. MPDP+ bromide disproportionated into MPTP and MPP+ in aqueous solution near neutral or slightly alkaline pH, a reaction which also occurred when MPDP+ bromide was treated with an amine in dichloromethane solution. Disproportionation of MPDP+ at physiological pH may be of biochemical significance, since formation of MPP+ from MPDP+ can occur non-enzymatically. MPTP, MPDP+, and MPP+ inhibited dopamine uptake in rat synaptosomal preparations with I50 values of 30, 37, and 3.4 microM, respectively. The competition of these compounds with dopamine for uptake sites in the membrane may contribute in part to the reduced levels of dopamine observed in animals treated with MPTP.

Inhibition of dihydropteridine reductase in rat striatal synaptosomes and from human liver by metabolites of biogenic amines

Catecholamines are potent noncompetitive inhibitors of dihydropteridine reductase in rat striatal synaptosomal preparations or purified from human liver. Their metabolites, except homovanillic acid, also inhibit the enzyme from both sources. The inhibitory potency of these compounds depends on the presence of the catechol or the 4-hydroxyphenyl structure, but may be modified by the 2-carbon side chain and its substituents. Indoleamines which have a hydroxylated aromatic nucleus (5-hydroxytryptamine and 5,6-dihydroxytryptamine) are equally inhibitory to the enzyme. These results suggest that biogenic amines themselves rather than their metabolites may serve as physiological inhibitors of dihydropteridine reductase in rat brain.

Selected testicular enzymes as biochemical markers for procarbazine-induced testicular toxicity

Single doses of procarbazine (MIH) were injected IP at 0, 50, 100, 200, and 400 mg/kg body weight to CD-1 male mice. Activities of hyaluronidase, lactate dehydrogenase isoenzyme-X, and the dehydrogenases of sorbitol, alpha-glycerophosphate, glucose-6-phosphate, malate, isocitrate, and glyceraldehyde-3-phosphate in the testes of the mice were determined and correlated with changes in spermatogenic cell types in seminiferous tubules. All enzyme activities were higher than controls or remained unchanged on days 10-20 after drug treatment. Activities of hyaluronidase, sorbitol dehydrogenase, and lactate dehydrogenase isoenzyme-X decreased significantly to below normal levels on day 30 after drug treatment for all doses, whereas those of the other five dehydrogenases remained significantly higher than controls. All enzyme activities approached control levels with the concomitant recovery of spermatogenesis by day 60 after drug treatment. Histological examination of seminiferous tubules revealed that premeiotic spermatocytes were significantly reduced on days 10-20 but reappeared on day 30 after MIH treatment (400 mg/kg). The postmeiotic spermatogenic cells were unaffected at the time of MIH treatment, but had disappeared completely on day 30 after drug treatment. MIH, at the highest dosage, selectively destroyed spermatogonia and premeiotic spermatocytes; however spermatozoa and elongated spermatides were unaffected. This study demonstrated that the cytotoxic effect of MIH on spermatogenesis could be evaluated via changes in testicular enzyme activities. The present studies demonstrated that hyaluronidase, sorbitol dehydrogenase, and lactate dehydrogenase isoenzyme-X could serve as useful biochemical markers for assessing testicular toxicity induced by drugs and chemicals.

Inhibition of dihydropteridine reductase from human liver and rat striatal synaptosomes by apomorphine and its analogs

Dihydropteridine reductase from human liver and rat striatal synaptosomes is noncompetitively inhibited by apomorphine and its analogs. The Ki or I50 values are in the range of 0.6 to 2.9 microM for R-(-)-apomorphine, R-(-)-and S-(+)-2, 10, 11-trihydroxyaporphine, R-(-)-norapomorphine, R-(-)-N-hydroxyethylnorapomorphine, R-(-)-2,10,11-trihydroxy-N-n-propylnoraporphine, R-(-)- and S-(+)-N-n-propylnorapomorphine, and R-(-)-N-chloroethylnorapomorphine; and 13 to 151 microM for R-(-)-2,11-dihydroxy- 10-methoxyaporphine, R-(-)-apocodeine, and S-(+)-bulbocapnine. Structure-activity studies reveal that 10,11-dihydroxy substitution of the D ring of apomorphine is required for the inhibitory effectiveness of these aporphines. Methylation of the 10-hydroxy group reduces, whereas the 2-hydroxyl substitution of the A ring enhances, their inhibitory potency. N-Alkylation variably affects the inhibitory potency of aporphines. In addition, S-(+)-enantiomers of aporphines and dopaminergic antagonists are equally potent as inhibitors of this enzyme, as compared to the corresponding R-(-)-enantiomers and other aporphine agonists. Haloperidol (0.1 to 10 microM) failed to reverse the enzyme inhibitory effectiveness of apomorphine when it was incubated with intact rat striatal synaptosomes prior to or after the addition of apomorphine (0.5 to 1 microM). These results suggest that the inhibitory effects of apomorphine and its analogs against this enzyme are not mediated by their stimulation of dopamine autoreceptors. Since dihydropteridine reductase is required in vivo for the hydroxylation of tyrosine, the inhibition of this enzyme by apomorphine may represent one of several mechanisms by which apomorphine inhibits catecholamine synthesis.

Effects of nomifensine and its metabolites on dihydropteridine reductase

Nomifensine and three of its metabolites were studied as potential inhibitors of dihydropteridine reductase. Purified enzyme preparations from human liver and the P2 fraction of rat striatal synaptosomes were used as enzyme sources. Nomifensine and its 3'-hydroxyl derivative inhibit this enzyme from both sources at 1.3 to 3.5 X 10(-4)M (150 values). 4'-Hydroxylated nomifensines, however, non-competitively inhibited this enzyme with Ki values of 2.8 to 4.4 X 10(-5)M. Dihydropteridine reductase regenerates tetrahydrobiopterin, the required cofactor for the hydroxylation of tyrosine and tryptophan, from quinonoid dihydrobiopterin. Inhibition of this enzyme could reduce the availability of the biopterin cofactor for the synthesis of dopamine and 5-hydroxytryptamine.

Inhibition of dihydropteridine reductase by novel 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine analogs

Hydroxylated derivatives of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a nigrostriatal neurotoxin in humans and primates, noncompetitively inhibited dihydropteridine reductase from human liver and rat striatal synaptosomes in vitro at micromolar concentrations. In contrast, MPTP and its chloro- and norderivatives did not inhibit this enzyme at lower than millimolar concentrations. Dihydropteridine reductase converts dihydrobiopterin to tetrahydrobiopterin, the required cofactor for the hydroxylation of aromatic amino acids during the synthesis of dopamine and serotonin.

Potent inhibitory effects of tyrosine metabolites on dihydropteridine reductase from human and sheep liver

L-Phenylalanine and its metabolites, such as phenylpyruvate, phenylacetate and L-phenyllactate, do not significantly inhibit dihydropteridine reductase purified from human and sheep liver (I50 greater than or equal to 5 mM). However, L-tyrosine and its metabolites, such as L-DOPA, tyramine, p-hydroxyphenylpyruvate, p-hydroxyphenylacetate, and p-hydroxyphenylacetate, are potent noncompetitive inhibitors of this enzyme, with Ki values in the range 4-260 microM. These results suggest that tyrosine metabolites can potentially regulate levels of tetrahydrobiopterin, the required cofactor for the hydroxylation of aromatic amino acids.

Evaluation of the PaT Stat Kinetic UV Test set for the determination of phenylalanine and tyrosine in serum or plasma

We have evaluated the PaT Stat Kinetic UV Test Kit for the simultaneous determination of phenylalanine (Phe) and tyrosine (Tyr) in plasma or serum. The Phe and Tyr concentrations measured with the kit show a coefficient of variation of about 15% for both within- and between-day determinations. The assays for both Phe and Tyr are linear to concentrations of at least 18 mg/dL without predilution of the specimen. Concentration differences of as little as 0.5 mg/dL are distinguishable. No significant interference was found from either phenylpyruvate or phenyllactate at levels up to 0.5 mM, nor from bilirubin, haemoglobin, or triglycerides at levels well above those generally found in clinical specimens. A comparative study of 70 clinical specimens, using the kit method and an amino acid analyzer (AAA) showed a linear relationship. Least-squares analysis of the data yielded the following parameters (AAA as reference): slope = 0.93 to 1.00, intercept = 0.04 to 0.21, correlation coefficient = 0.97 to 0.98. We conclude that the kit is suitable for the determination of Phe and Tyr in plasma or serum and can enable any laboratory equipped with a recording UV-spectrophotometer to assay these two amino acids for the dietary management of PKU.

Inhibition of dihydropteridine reductase by catecholamines and related compounds

Catecholamines and related compounds, such as dopamine, 5- or 6-hydroxydopamine, N-methyldopamine, tyramine, octopamine, norepinephrine and epinephrine, inhibit human liver dihydropteridine reductase (NADH:6,7-dihydropteridine oxidoreductase, EC 1.6.99.10) noncompetitively with Ki values ranging from 7.0 X 10(-6) - 1.9 X 10(-4)M (I50 values = 2.0 X 10(-5) - 2.0 X 10(-4)M). The tyrosine analogs alpha-methyltyrosine and 3-iodotyrosine are weak inhibitors of this enzyme (I50 greater than 10(-3)M). The inhibitory effect of catecholamines is slightly decreased by O-methylation of one hydroxyl group, but is essentially abolished by total methylation. The inhibitory strength of the catecholamines and related compounds tested against this enzyme can be arranged in the following order: dopamine, 6-hydroxydopamine, 5-hydroxydopamine, N-methyldopamine greater than tyramine, 3-O-methyldopamine, 4-O-methyldopamine much greater than epinephrine, 3-O-methylepinephrine, norepinephrine, octopamine less than tyrosine much less than alpha-methyltyrosine, 3-iodotyrosine much less than homoveratrylamine. These results suggest that dopamine, norepinephrine and epinephrine may serve as physiological regulators of mammalian dihydropteridine reductase.

Inhibition of dihydropteridine reductase by catechol estrogens

Catechol estrogens, such as 2-hydroxyestriol, 2-hydroxyestradiol, and 2-hydroxyestrone, inhibit human liver dihydropteridine reductase noncompetitively with Ki values ranging from 1.5 to 4.6 X 10(-6)M. Catechol estrogens lose approximately half of their inhibitory potency if the C-2 hydroxyl groups are methylated. Thus, 2-methoxyestrogens have inhibitory potencies equivalent to those of their parent estrogens--estriol, estradiol, and estrone. Aromatization of ring B or stereoisomerism at C-17 does not affect the inhibitory potency of estrogens, although stereoisomerism at C-16 enhances the inhibitory potency of estriol. These results support the hypothesis that catechol estrogens may interfere with catecholamine metabolism by acting as inhibitors of enzymes involved in catecholamine metabolism, such as dihydropteridine reductase.

Screening for PKU heterozygosity in bipolar affectively ill patients

There were no significant differences noted between bipolar manic-depressive patients and normal controls for plasma phenylalanine or tyrosine following an L-phenylalanine loading test given to determine if some affective illness may be related to the heterozygous phenotypic expression of phenylketonuria (reduced liver phenylalanine hydroxylase). The test was able to distinguish known PKU heterozygotes from the other subjects. It is possible that other heterozygous states may be implicated in the development of some psychiatric disorders.

Biochemical properties and immunogenicity of L-phenylalanine ammonia-lyase: effects on tumor-bearing mice

L-Phenylalanine ammonia-lyase (PAL) from yeast was used to deplete plasma L-phenylalanine and L-tyrosine in an attempt to achieve inhibition of tumor growth in mice. Plasma L-phenylalanine and L-tyrosine were reduced to nondetectable levels when circulating PAL activity was maintained at greater than or equal to 0.06 unit/ml. Repeated administration resulted in the appearance of anti-PAL antibodies. A radioimmunoassay based on the method of Farr was developed to determine quantitatively the presence of anti-PAL. Sublethal total-body irradiation temporarily suppressed the immunologic response of the host. Long-term specific immunosuppression to PAL was achieved with cyclophosphamide (CPA). A single dose of 180 mg/kg of CPA administered ip to mice 24 hours before, simultaneously with, or 24 hours after 100 units/kg of PAL induced tolerance for 450 days (20 injections of enzyme). The plasma half-life of PAL in CPA-treated mice remained essentially the same as that found after a single injection (25 hours), and anti-PAL probably will require specific immunosuppression of the host to repeated injections of the enzyme.

Phenylketonuria: a new method for the simultaneous determination of plasma phenylalanine and tyrosine

This quantitative spectrophotometric method is based on the conversion of phenylalanine and tyrosine by phenylalanine ammonia-lyase to trans-cinnamic acid and trans-coumaric acid, respectively. Neither deproteinization nor prior incubation of the sample is required, and the entire procedure can be performed in 20 minutes. The method is sensitive to 1-micromolar concentrations of the two compounds, and only 20 microliters of plasma or serum is required to determine both phenylalanine and tyrosine simultaneously. These amino acids were determined between molar ratios (phenylalanine to tyrosine) of 0.1 to 40 in the serum or plasma of healthy individuals and plasma of phenylketonuric patients.

Clearance of phenylalanine ammonia-lyase from normal and tumor-bearing mice

Yeast phenylalanine ammonia-lyase was administered i.p. to normal and tumor-bearing mice, and its clearance from plasma was studied. Single and multiple weekly injections at dosages of 10,20,50 and 100 units/kg were administered to C57BL female, C57BL X DBA/2F1 male, and A/J female mice. L5178Y murine lymphoblastic leukemia, B16 melanoma, BW10232 adenocarcinoma, and 15091A anaplastic carcinoma were implanted 7 to 11 days prior to enzyme injection in the appropriate host. After a single injection, the average plasma half-lives of phenylalanine ammonia-lyase were 18 to 24 hr in all groups studied. While the other tumors had no effect on the plasma level of phenylalanine ammonia-lyase after a single injection, L5178Y murine lymphoblastic leukemia and 15091A anaplastic carcinoma significantly depressed the maximal level of phenylalanine ammonia-lyase attained in the plasma. After repeated injections of phenylalanine ammonia-lyase, the initial plasma enzyme level was significantly reduced when 20 units/kg were administered, and the clearance of the enzyme from the plasma was greatly accelerated regardless of the amount administered. Furthermore, in tumor-bearing mice, the rate of clearance was significantly more rapid than in the appropriate non-tumor-bearing control.

Developmental patterns of enzymes in mouse testis

Study of the activities of hyaluronidase, lactate dehydrogenase isoenzyme-X and the dehydrogenases of sorbitol, alpha-glycerophosphate, glucose-6-phosphate, malate, glyceraldehyde-3-phosphate and isocitrate in the testes of mice of different ages showed that the changes were correlated with the stages of spermatogenic cell differentiation. The first 4 enzymes had activities which were low in newborn mice and high in adults; this pattern was reversed for the other enzymes.