Effect of ascorbic acid on hydroxylase activity. I. Stimulation of tyrosine hydroxylase and tryptophan-5-hydroxylase activities by ascorbic acid

Ascorbic acid-independent synthesis of collagen in mice

The mouse has become the most important model organism for the study of human physiology and disease. However, until the recent generation of mice lacking the enzyme gulanolactone oxidase (Gulo), the final enzyme in the ascorbic acid biosynthesis pathway, examination of the role of ascorbic acid in various biochemical processes using this model organism has not been possible. In the mouse, similar to most mammals but unlike humans who carry a mutant copy of this gene, Gulo produces ascorbic acid from glucose. We report here that, although ascorbic acid is essential for survival, its absence does not lead to measurable changes in proline hydroxylation. Vitamin C deficiency had no significant effect on the hydroxylation of proline and collagen production during tumor growth or in angiogenesis associated with tumor or mammary gland growth. This suggests that factors other than ascorbic acid can support proline hydroxylation and collagen synthesis in vivo. Furthermore, the failure of Gulo-/- mice to thrive on a vitamin C-deficient diet therefore suggests that ascorbic acid plays a critical role in survival other than the maintenance of the vasculature.

Changes of gene expression profiles during neuronal differentiation of central nervous system precursors treated with ascorbic acid

Ascorbic acid (AA) has been shown to increase the yield of dopaminergic (DA) neurons derived from basic fibroblast growth factor (bFGF)-expanded mesencephalic precursors. To understand the molecular mechanisms underlying this phenomenon, we used cDNA microarray analysis to examine differential expression of neuronal genes following AA treatment. The putative precursor cells were isolated from E13 rat ventral mesencephalons and expanded in the presence of bFGF. Cells were incubated in mitogen-free media supplemented with 200 microM AA or were left untreated as a control, and total RNA was isolated at different time points (expansion stage and 1, 3, and 6 days after induction of differentiation) and subjected to cDNA microarray analysis. Differentiation was evaluated by Western blot analysis and immunocytochemistry of neuron-specific markers. AA treatment of the mesencephalic precursors increased the expression of neuronal (MAP2) and astrocytic (glial fibrillary acidic protein) markers and the percentage of tyrosine hydroxylase (TH)-positive cells. The microarray analysis revealed that 12 known genes were up-regulated and 20 known genes were down-regulated in expansion-stage AA-treated cells. Six days after the induction of differentiation, AA-treated cells showed up-regulation of 48 known genes and down-regulation of 5 known genes. Our results identified several proteins, such as transferrin, S-100, and somatostatin, as being differentially regulated in AA-treated mesencephalic precursors. This novel result may lead to a better understanding of the molecular mechanisms underlying the AA-induced differentiation of mesencephalic precursors into DA neurons and may form the basis for improved DA neuronal production for treatment of Parkinson's disease patients.

Ascorbic acid increases the yield of dopaminergic neurons derived from basic fibroblast growth factor expanded mesencephalic precursors

CNS precursors derived from E12 rat mesencephalon proliferate in the presence of basic fibroblast growth factor and differentiate in vitro into functional dopaminergic neurons, which upon transplantation alleviate behavioral symptoms in a rat model of Parkinson's disease. Here we show that the efficiency of dopaminergic differentiation decreases in the mesencephalic precursors that were proliferated or passaged for extended periods in vitro. Ascorbic acid treatment restored dopaminergic differentiation in these precursors and led to a greater than 10-fold increase in dopamine neuron yield compared with untreated cultures. The effect of ascorbic acid was stereospecific and could not be mimicked by any other antioxidants. The expression of sodium-dependent vitamin C transporter, a recently identified stereospecific ascorbic acid transporter, was maintained in mesencephalic precursors for extended in vitro periods. Pre-treatment of in vitro expanded mesencephalic precursors with ascorbic acid might facilitate the large-scale generation of dopaminergic neurons for clinical transplantation.

Vitamin C deficiency facilitates 5-S-cysteinyldopamine formation in guinea pig striatum

Being a catechol, dopamine (DA) is easily autoxidized in solution to a semiquinone and then further to a quinone. These quinones and by-products, as reduced forms of oxygen, are all cytotoxic. By quantifying quinone metabolites, such as 5-S-cysteinyl adducts of DA, 3,4-dihydroxyphenylalanine (DOPA), and 3,4-dihydroxyphenylacetic acid (DOPAC), an indirect measure of catechol autoxidation is available. Ascorbic acid (AA) has an important role as an antioxidant in the organism. A group of guinea pigs (Dunkin-Hartley) received an AA-free diet for 37 days, whereas a control group was fed an AA-containing diet (1,400 mg/kg of pellets). To one group of AA-deprived animals a single dose of AA (500 mg/kg, i.p.) was administered 2 h before death, whereas another group received two doses 9 and 24 h before death. The striatal levels of 5-S-cysteinyl adducts, DA, noradrenaline, and DOPAC and the cerebellar and the limbic levels of AA were determined. A significant increase in 5-S-cysteinyl-DA content was found in the striatum of AA-deficient animals (143 +/- 12% of control values). A further increase was found 2 h after an AA injection (177 +/- 16% of control values), which was significant compared with both controls and AA-deficient animals. An elevation in 5-S-cysteinyl-DA content was still observed following two AA injections during a 24-h period (153 +/- 7% of control values). The 5-S-cysteinyl-DOPAC content increased significantly (134 +/- 14% of control values) in the AA-deficient animals given AA acutely (2 h), both compared with controls and with the AA-deficient group.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationships between dietary ascorbic acid status and deficiency, weight gain and brain neurotransmitter levels in juvenile rainbow trout,Salmo gairdneri

A study was conducted to determine the interrelationships between dietary ascorbic acid (AA) concentrations, brain neurotransmitter levels and weight gain in juvenile rainbow trout. At the end of 4 weeks and until the end of 12 weeks of feeding test diets of varying AA concentrations (0-320 mg AA/kg diet), increased weight gain was noted in fish fed the AA-free diet. However, by the end of 13 weeks and until the end of the experiment this phenomenon was no longer evident; instead the fish showed the more classical deficiency signs of anorexia and decreased weight gain. After 12 and 24 weeks, there were no significant differences in brain serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE) or dopamine (DA) between fish reared on the different test diets. However, after 12 weeks of feeding the test diets, brain 5-HT, brain AA and weight gain were significantly correlated with one another. No such relationships were found for brain NE or brain DA. After 24 weeks of feeding the diets, the relationships between brain 5-HT, brain AA and weight gain were no longer apparent. Similarly, after 24 weeks brain NE and DA were also unrelated to brain AA and weight gain. These results provide evidence that in very young rainbow trout, AA deficiency, brain 5-HT levels and weight gain were related. However in fish reared on the diets for 24 weeks these relationships were no longer evident.

The deafferentation syndrome in the rat: effects of intraventricular apomorphine

A deafferentation syndrome, produced in rats by dorsal root ganglionectomies, is expressed as scratching of partially deafferented limb areas and/or biting of anesthetic limb areas. This self-mutilation may be objective evidence of dysesthesias, thus serving as an experimental model to study chronic dysesthesias and/or pain from deafferentation in man. This study included behavioral observations of the syndrome and the effects of intraventricular apomorphine, a dopamine agonist, on its expression. Thirty-eight female Sprague-Dawley rats underwent unilateral C5-T2 dorsal root ganglionectomies followed immediately by stereotactically guided cannulation of the right lateral ventricle in 20 of the rats. For 2 weeks continuously via an osmotic minipump, 10 rats received apomorphine (5 micrograms/h) and 10 others received L-ascorbate (the vehicle). Rats with ganglionectomies only, as well as those receiving L-ascorbate, demonstrated early onset, more severe and later onset, less severe biting groups (P less than 0.05 Mann-Whitney U). Animals receiving apomorphine exhibited low autotomy scores irrespective of time of bite onset. Among the control groups, but not the experimental animals, the earlier the onset of biting, the more severe was the autotomy. The rats receiving vehicle via the minipump had earlier bite onsets than the rats in the ganglionectomy only group. This may indicate that the presence of the minipump is a stress which can accelerate the onset of biting. Intraventricular apomorphine can affect the deafferentation syndrome in the rat; it seems to decrease the level of autotomy and disrupt the relationship of bite onset with degree of biting.

Ascorbic acid: the concept of optimum requirements

Experiments with enzymes in situ that are dependent on ascorbic acid for maximum activity will provide critical information about ascorbic acid requirements. Our work with chromaffin tissue as a model system eventually will result in the determination of two dose-response curves for norepinephrine biosynthesis, representing cytosolic ascorbic acid and intragranular ascorbic acid (Fig. 11). These curves for norepinephrine biosynthesis can be combined with curves for other enzymatic events that are also dependent on ascorbic acid for maximal activity. These dose-response curves (Fig. 2) will allow determination of optimum ascorbic acid requirements based on specific product formation and minimum toxicity. These principles are adaptable to other vitamins as well as ascorbic acid, and could form the basis for a new approach to vitamin requirements.

Modulation of neostriatal activity by iontophoresis of ascorbic acid

Iontophoresis (20-80 nA) of ascorbic acid (AA) accelerated the firing rate of approximately one-third of the neurons tested in the anteromedial neostriatum of anesthetized rats. When administered to neostriatal neurons that were activated by the simultaneous ejection of glutamic acid (GLU), AA excited more than two-thirds of the cells examined, including many that were not excited by AA alone. At ejection currents above 80 nA, AA further increased the activity of some GLU-activated neurons, but suppressed the firing rate of others. Electrochemical quantification of AA ejection during iontophoresis indicated that the concentration of AA at the tip of the recording electrode was within reasonable physiological limits. It is concluded that endogenous AA may modulate neuronal activity in the neostriatum.

Effect of ascorbate on the toxicity of morphine in mice

The effects of ascorbic acid on the toxicity of morphine in mice were investigated. An intraperitoneal dose of sodium ascorbate (1 G/kg) injected 10 min prior to morphine (500 mg/kg, i.p.) was found to provide significant protection against mortality due to respiratory depression, while having no effect on the lethality of the pentobarbital. Pretreatment with ascorbate had no effect on the distribution of morphine in brain tissue, nor did it alter the pH of the plasma. Administration of ascorbate in vivo also produced no inactivation of binding to opioid receptors. It is postulated that ascorbate antagonizes the lethality of morphine by selectively affecting neuronal activity.

Dietary ascorbic acid deficiency in guinea pigs: no effect on ethanol preference, spiroperidol binding, or monoamine oxidase activity

Ascorbic acid levels are commonly reported to be decreased in alcoholics. Although this deficiency could be due to dietary factors, there is evidence that ascorbic acid may be involved in the metabolism and acute effects of ethanol, possibly related to the pathogenesis of alcoholism. Therefore, we examined ethanol preference in guinea pigs receiving an ascorbate deficient vs a normal diet. Brain and spleen ascorbic acid levels were dramatically decreased, but ethanol preference was not altered by the acute dietary deficiency of this vitamin. In addition, an acute stressor (cold water swim), alone or in combination with ascorbate deficiency, had no effect on ethanol preference. At termination of the experiment, two measures of brain aminergic function (MAO activity and 3H-spiroperidol binding), purportedly altered by ethanol or ascorbic acid or both, were not associated with tissue ascorbate levels.

Ascorbate blocks amphetamine-induced turning behavior in rats with unilateral nigro-striatal lesions

Unilateral nigro-striatal lesions were produced in rats using 6-hydroxydopamine. Intraperitoneal injections of amphetamine induced circling behavior in these rats due to release of striatal dopamine contralateral to the lesion. Intraperitoneal injections of 1 g/kg of ascorbic acid elevated brain ascorbate. Ascorbate, like other drugs blocking dopamine receptors, attenuated the amphetamine-induced turning behavior. Thus, ascorbic acid might have a role in regulating dopaminergic transmission and could be of therapeutic value in disorders involving functional dopamine excess.

Regulation of tyrosine hydroxylase activity by prostaglandin E1 in guinea pig adrenal gland

The action of prostaglandin E1 on tyrosine hydroxylase activity in adrenal slices of guinea pig was studied. The activity of tyrosine hydroxylase and was decreased by the incubation of adrenal slices with prostaglandin E1 at concentrations beyond 2 mug per ml for 2 hours. The activity of tyrosine hydroxylase was stimulated by dibutyryl adenosine 3',5'-monophosphate in slices of guinea pig adrenal glands. Incubation of adrenal slices wtth the combination of PGE1 and DBc-AMP lead to a tyrosine hydroxylase activity higher than that with PGE1 alone, but not as great as DBc-AMP alone. It was suggested that PGE1 inhibited the enzyme activity independently of the cyclic AMP level. Other prostaglandins such as PGA1 and PGB1 were deficient to the extent that the tyrosine hydroxylase activity was decreased. PGE1 inhibited the enzyme activity much to the same extent seen with protein synthesis inhibitors such as cycloheximide and actinomycin D. However, PGE1 did not influence the incorporation of L-leucine-14C into acid insoluble protein. The studies reported here showed that PGE1 inhibited the synthesis of tyrosine hydroxylase.

Collagen metabolism in folic acid deficiency

1. The effect of folic acid deficiency on collagen formation, with respect to the level of collagen-protein synthesis and the extent of collagen-proline hydroxylation, has been studied. A folic acid-free diet containing 10 g sulphasuxidine/kg was used to induce folate deficiency in young male rats. Animals were judged folic acid-deficient on the grounds of retardation of growth, characteristic haematological changes and the urinary excretion of formimino-L-glutamic acid.

2. From isotope incorporation studies it was found that folic acid deficiency caused a marked impairment in collagen synthesis. It was shown, however, from the use of pair-fed control animals, that this was due in part to a reduced food intake accompanying the vitamin deficiency. The further reduction in synthesis in addition to that attributable to inanition was considered to arise from an involvement of folic acid in general protein synthesis, since it was found that the synthesis of elastin and non-collagenous skin proteins was similarly impaired.

3. Reduced synthesis of collagen was not considered attributable to lack of hydroxylation of peptidyl proline that may occur in ascorbic acid deficiency. Hydroxylation of collagen- and elastin-proline was only very slightly impaired in folic acid deficiency. It was concluded that, at least when ascorbic acid is present, folic acid is not directly essential for the hydroxylation, in vivo, of peptidyl proline. The results support the view that ascorbic acid participates direct, in vivo, in this hydroxylation rather than indirect by simply maintaining an adequate level of reduced folates. They do not, however, exclude the possibility, arising from the known ability of tetrahydrofolate to participate in the hydroxylation of collagen proline in vitro, that when both ascorbate and folate are present, the latter may, in some measure, share in the role of reducing agent in the hydroxylation of peptidyl proline in vivo.

The effect of L-ascorbate on catecholamine biosynthesis

l-Ascorbate stimulates the enzymic hydroxylation of phenylalanine in vitro by recycling tetrahydrobiopterin, which reduces O(2) utilized in the reaction. It is suggested that ascorbate might have a similar function in vivo; this would explain the apparent regulation of tyrosine hydroxylase and tryptophan hydroxylase activities by this vitamin.