Inherited disorders of brain neurotransmitters: pathogenesis and diagnostic approach

Neurotransmitters (NTs) play a central role in the efficient communication between neurons necessary for normal functioning of the nervous system. NTs can be divided into two groups: small molecule NTs and larger neuropeptide NTs. Inherited disorders of NTs result from a primary disturbance of NTs metabolism or transport. This group of disorders requires sophisticated diagnostic procedures. In this review we discuss disturbances in the metabolism of tetrahydrobiopterin, biogenic amines, γ-aminobutyric acid, foliate, pyridoxine-dependent enzymes, and also the glycine-dependent encephalopathy. We point to pathologic alterations of proteins involved in synaptic neurotransmission that may cause neurological and psychiatric symptoms. We postulate that synaptic receptors and transporter proteins for neurotransmitters should be investigated in unresolved cases. Patients with inherited neurotransmitters disorders present various clinical presentations such as mental retardation, refractory seizures, pyramidal and extrapyramidal syndromes, impaired locomotor patterns, and progressive encephalopathy. Every patient with suspected inherited neurotransmitter disorder should undergo a structured interview and a careful examination including neurological, biochemical, and imaging.

New treatment paradigms in neonatal metabolic epilepsies

Neonatal seizures represent a major challenge among the epilepsies vis-à-vis seizure classification, electroclinical correlation, inherent excitability of neocortex, ontogenic characteristics of neurotransmitter receptors, and responsiveness to standard antiepileptic drugs. Each of these factors renders neonatal seizures more difficult to treat, and therapy has been a vexing area for recent advances in this seizure category. Conversely, specific metabolic disorders have very special therapeutic considerations in the clinical setting of neonatal seizures which require a high index of clinical suspicion and rapid intervention for a successful outcome. The prototype is pyridoxine dependency, although pyridoxal 5'-phosphate dependency is a recently recognized but treatable neonatal epilepsy that deserves earmarked distinction. Clinicians must remain vigilant for these possibilities, including atypical cases where apparent seizure-free intervals may occur. Folinic acid-dependent seizures are allelic with pyridoxine dependency. Serine-dependent seizures and glucose transporter deficiency may present with neonatal seizures and have specific therapy. A vital potassium channel regulated by serum ATP/ADP ratios in the pancreas and brain may be mutated with a resultant neuroendocrinopathy characterized by development delay, epilepsy, and neonatal diabetes (DEND). This requires oral hypoglycaemic therapy, and not insulin, for neurological responsiveness. The startle syndrome of hyperekplexia, which mimics neonatal epilepsy, has been associated with laryngospasm and sudden death but is treated with benzodiazepines.

Prevalence of pyridoxine dependent seizures in south Indian children with early onset intractable epilepsy: A hospital based prospective study

OBJECTIVES

Determine the prevalence of pyridoxine dependent seizures in children less than 16 years of age attending a teaching hospital in south India with early onset (before 3 years) intractable epilepsy of unknown aetiology, using the criteria proposed by Baxter.

METHOD

A cohort of 81 children, fulfilling the above criteria, was given 15 mg/kg/day of oral pyridoxine for 7 days. Non-responders were given a further 7-day trial of 30 mg/kg/day. Diagnosis of pyridoxine dependent seizures was made according to the criteria proposed by Baxter.

RESULT

Six children (7.4%; four boys and two girls) were identified as definite cases and were continued on B6, without recurrence of seizures. Median age of seizure onset and diagnosis were 2.5 months and 2 year 9 months, respectively. No significant complications were observed with B6 therapy.

CONCLUSION

Chance of identifying PDS is not low in a subpopulation of children with intractable early onset cryptogenic epilepsy using the criteria proposed by Baxter, which warrants a therapeutic trial with B6 in them.

Clinical aspects of the disorders of GABA metabolism in children

PURPOSE OF REVIEW

There has been increased recognition of the pediatric neurotransmitter disorders. This review focuses on the clinical disorders of GABA metabolism.

RECENT FINDINGS

The known clinical disorders of GABA metabolism are pyridoxine dependent epilepsy, GABA-transaminase deficiency, SSADH deficiency, and homocarnosinosis. Pyridoxine dependent epilepsy is diagnosed clinically but potentially more common presentations, with later and atypical features, widen the spectrum. No gene locus has been confirmed; the pathophysiology may involve alterations in PLP transport, binding to GAD, or other PLP-dependent pathways. SSADH deficiency is associated with developmental delay, prominent language deficits, hypotonia, ataxia, hyporeflexia, and seizures. Increased detection is reported when specific ion monitoring is used for GHB on urine organic acids. The most consistent MRI abnormality is increased signal in the globus pallidus. MR spectroscopy has demonstrated the first example of increased endogenous GABA in human brain parenchyma in this disorder. GABA-transaminase deficiency and homocarnosinosis appear to be very rare but require CSF for detection, thus allowing for the possibility that these entities, as in the other pediatric neurotransmitter disorders, are underrecognized.

SUMMARY

The disorders of GABA metabolism require an increased index of clinical suspicion. Pyridoxine dependent epilepsy is a treatable condition with a potentially widening clinical spectrum, but with a prognosis dependent on early intervention. SSADH deficiency has a heterogeneous spectrum and requires careful urine organic acid testing for screening, followed by enzymatic confirmation allowing appropriate prognostic and genetic counseling.

[Pyridoxine dependence: the importance of the clinical diagnosis and early treatment]

OBJECTIVE

We described the electroclinical features, evolution and family history of two patients with definitive diagnosis of pyridoxine dependency.

CASE REPORTS

The first patient is a 15-month-old girl who at 1 month of age started with seizures and irritability. At two months of age, pyridoxine was prescribed with a good control of seizures. At five months of age withdrawal response provoked 7 days after seizures recurrence. Pyridoxine was reintroduced and seizures disappeared. Her sister, at two months of age, started with refractory seizures. This sister also had mental retardation and at four years, she died. Her brother, 16 years old, presents mental retardation, refractory epilepsy and progressive motor and cognitive impairment. At 3 months of age, he started with seizures and at 15 years of age, pyridoxine was prescribed with a significative improvement the number of seizures and a better visual connection. The second patient is a 4-month-old girl who started with clonic seizures at 3 days of age and she had a good response to pyridoxine. Withdrawal response provoked seizure recurrence at 48 hours. Pyridoxine was introduced immediately with total control of seizures. She had two cousins with seizures who died at 3 months and 3 years of age respectively.

CONCLUSION

When dealing with an infant with refractory seizures which start in the first two years of life and without etiology, we should consider the diagnosis of pyridoxine dependency. Early diagnosis and treatment with pyridoxine is crucial to avoid high risk morbidity and mortality. All infants in the two first years of life with refractory seizures without etiology must be prescribed oral pyridoxine (50-200 mg per day).

Rabbit aortic endothelial dysfunction by low-density lipoprotein is attenuated by L-arginine, L-ascorbate and pyridoxine

1. We investigated the relative effectiveness of L-arginine, L-ascorbate and pyridoxine in preventing the impairment of endothelium-mediated vasorelaxation induced by native low-density lipoprotein (nLDL) from healthy subjects, oxidised LDL (oxLDL, formed by oxidation of nLDL) or nLDL from type II diabetic patients (dLDL). 2. Rabbit aortic rings were exposed to nLDL, dLDL or oxLDL (50-200 mg protein l-1), or corresponding vehicle, following which they were constricted with noradrenaline 10(-6) M; concentration-relaxation curves were determined to acetylcholine (ACh), A23187, or sodium nitroprusside (NP), in the absence or presence of L-arginine (10(-5)-10(-3) M), L-ascorbate (10(-5)-10(-3) M) and pyridoxine (0.5-2.0 mM). 3. nLDL, dLDL and oxLDL all inhibited relaxant responses to ACh and A23187, but not to NP, in a concentration-dependent manner (oxLDL>dLDL>nLDL). 4. In the presence of all LDL preparations, L-arginine, L-ascorbate or pyridoxine each improved ACh and A23187 responses, although none completely normalised endothelium-dependent relaxations. The maximal effect of L-arginine occurred at 10(-4) M. The combination of L-arginine 10(-4) M, L-ascorbate 10(-5) M and pyridoxine 2.0 mM was equally effective as L-arginine 10(-4) M alone. 5. Our results confirm that nLDL, dLDL and oxLDL exert inhibitory effects on endothelium dependent, but not endothelium independent, relaxation of rabbit aorta. ACh and A23187 responses in the presence of any LDL species can be ameliorated by supplementation with L-arginine, L-ascorbate or pyridoxine, either singly or in combination, with no agent or combination proving superior to L-arginine alone. Nevertheless, ACh and A23187 responses are not completely normalised with such supplements, suggesting that there also exists a component of LDL-induced inhibition of endothelium-mediated vasorelaxation that is independent of the nitric oxide system.

The inherited epilepsies

Our knowledge regarding the genetic bases of the human epilepsies is in a state of rapid flux. For some forms of epilepsy, epidemiologists are still trying to determine whether there is any familial (hereditary) predisposition. Other forms of epilepsy are known to run in families, but the mode of inheritance and degree of penetrance of the trait are still in doubt. Three forms of epilepsy have been tentatively localized to specific chromosomes, and several others are being analyzed with linkage analyses. In no case, has the gene responsible for any human epilepsy been isolated or characterized and we are not yet close to understanding how any specific genetically controlled biochemical or physiological parameter is responsible for the development of an epilepsy syndrome or of any specific epileptogenic increase in brain excitability. However, an extensive animal literature indicates that the mechanisms will be complex as a common phenotype can be the expression of multiple genes, and a single gene can be associated with several phenotypes (Buchhalter, 1993).

Effect of physical activity on thiamine, riboflavin, and vitamin B-6 requirements

Because exercise stresses metabolic pathways that depend on thiamine, riboflavin, and vitamin B-6, the requirements for these vitamins may be increased in athletes and active individuals. Theoretically, exercise could increase the need for these micronutrients in several ways: through decreased absorption of the nutrients; by increased turnover, metabolism, or loss of the nutrients; through biochemical adaptation as a result of training that increases nutrient needs; by an increase in mitochondrial enzymes that require the nutrients; or through an increased need for the nutrients for tissue maintenance and repair. Biochemical evidence of deficiencies in some of these vitamins in active individuals has been reported, but studies examining these issues are limited and equivocal. On the basis of metabolic studies, the riboflavin status of young and older women who exercise moderately (2.5-5 h/wk) appears to be poorer in periods of exercise, dieting, and dieting plus exercise than during control periods. Exercise also increases the loss of vitamin B-6 as 4-pyridoxic acid. These losses are small and concomitant decreases in blood vitamin B-6 measures have not been documented. There are no metabolic studies that have compared thiamine status in active and sedentary persons. Exercise appears to decrease nutrient status even further in active individuals with preexisting marginal vitamin intakes or marginal body stores. Thus, active individuals who restrict their energy intake or make poor dietary choices are at greatest risk for poor thiamine, riboflavin, and vitamin B-6 status.

Effects of vitamin B-6 on (n-3) polyunsaturated fatty acid metabolism

To investigate interactions between vitamin B-6 and fatty acid metabolism, male Wistar rats were fed a vitamin B-6 (B-6)-deficient diet consisting of 70% vitamin-free casein and 10% perilla oil [approximately 63% alpha-linolenic acid, (n-3)] for 5 wk. The amounts of linoleic acid (n-6) and arachidonic acid (n-6) in the B-6-deficient group changed only slightly compared with those in a pair-fed control group. The amount of linoleic acid increased and arachidonic acid decreased in the plasma total lipid fraction, and the ratios of both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the B-6-deficient group were significantly lower than for the controls. The ratios of alpha-linolenic acid and EPA were higher, and DHA lower, in the B-6-deficient group than in the pair-fed control group in the total lipid as well as phospholipid fractions in liver microsomes. The activity of delta6-desaturase was significantly lower in the B-6-deficient group than in the pair-fed control group (approximately 64%), and acyl-CoA oxidase activity, an initial enzyme of the peroxisomal beta-oxidation pathway, was reduced by approximately 80% in the B-6-deficient group. These data suggest that B-6 deficiencies impair the metabolism of (n-3) PUFA from alpha-linolenic acid to EPA and DHA with the most pronounced reduction in the production of DHA.

[Vitamin B6]

1934, vitamin B6 was discovered by P. György. Vitamin B6 consists of 3 closely related pyrimidine derivatives: pyridoxine, pyridoxal and pyridoxamine and their phosphate esters. The tumor-specific compound has been recently found to be as a new B6 derivatives. The active form of vitamin B6 is pyridoxal phosphate (PLP) which is produced by multi-metabolizing enzymes including pyridoxine kinase and PNP/PMP oxidase. PLP functions as the coenzymes of many enzymes which catalyze biochemical reactions such as transamination and decarboxylation. A novel physiological function of PLP which is the negative modulator of the steroid-dependent gene expression and the albumin gene expression has been also revealed.

Pyridoxine dependent epilepsy: a suggestive electroclinical pattern

AIMS

To determine if there is an electroencephalographic pattern suggestive of pyridoxine dependent epilepsy that could be used to improve the chances of early diagnosis.

METHODS

A retrospective study was made of all the clinical records and electroencephalograms of neonates identified with pyridoxine dependent seizures between 1983 and 1994, at this hospital. Neonates whose seizures began after more than 28 days of life were excluded; in all, five patients from four families were studied. Follow up ranged from 2 to 10 years.

RESULTS

A history of miscarriage and neonatal death during an epileptic seizure had occurred in the siblings of two families. One mother reported rhythmic movements of her child during the last month of pregnancy. At birth, all babies were hypotonic; four had decreased visual alertness. All babies were agitated, irritable, jittery, hyperalert, and exhibited sleeplessness and a startle reaction to touch and sound. Age of onset of seizures varied from 30 minutes to 3 days. Seizures of various types were recorded in all cases on EEG tracings, including spasms, myoclonic seizures, partial clonic, and secondary generalised seizures. Burst-suppression patterns occurred in three cases, and a combination of continuous and discontinuous patterns in two others. Bilateral high voltage delta slow wave activity was observed in four patients. Psychomotor delay was severe in three patients, moderate in one, and mild in one.

CONCLUSIONS

There is an identifiable EEG pattern that is highly suggestive of pyridoxine dependent epilepsy. Pyridoxine dependent epilepsy is probably underdiagnosed.

Current knowledge concerning optimum nutritional status of riboflavin, niacin and pyridoxine

The term 'optimum nutrition' has evolved from a perceived need to base recommendations for nutrient intakes firmly in the context of function. It follows that 'optimum nutritional status' for individual nutrients should be defined in terms of biochemical or physiological markers having some functional value but also showing an appropriate relationship to nutrient intake. The present short review considers the current position regarding such markers for riboflavin, pyridoxine and niacin. It is concluded that whilst there are several biochemical measures which respond to changes in intake of each of these vitamins, no single measure is wholly satisfactory as a marker of optimum status.

Vitamin B status in patients with chronic fatigue syndrome

Some patients with chronic fatigue syndrome say they benefit from taking vitamin supplements. We assessed functional status for the B vitamins pyridoxine, riboflavin and thiamine in 12 vitamin-untreated CFS patients and in 18 healthy controls matched for age and sex. Vitamin-dependent activities--aspartate aminotransferase (AST) for pyridoxine, glutathione reductase (GTR) for riboflavin, transketolase (TK) for thiamine--were measured in erythrocyte haemolysates before and after in-vitro addition of the relevant vitamin. For all three enzymes basal activity (U/g Hb) was lower in CFS patients than in controls: AST 2.84 (SD 0.62) vs 4.61 (1.43), P < 0.001; GTR 6.13 (1.89) vs 7.42 (1.25), P < 0.04; TK 0.50 (0.13) vs 0.60 (0.07), P < 0.04. This was also true of activated values: AST 4.91 (0.54) vs 7.89 (2.11), P < 0.001; GTR 8.29 (1.60) vs 10.0 (1.80), P < 0.001; TK 0.56 (0.19) vs 0.66 (0.08), P < 0.07. The activation ratios, however, did not differ between the groups. These data provide preliminary evidence of reduced functional B vitamin status, particularly of pyridoxine, in CFS patients.

B vitamins and homocysteine in cardiovascular disease and aging

The sulfur-containing amino acid, homocysteine, is formed from the essential amino acid methionine, and a number of B vitamins are involved in methionine metabolism. Pyridoxine, vitamin B6, is a cofactor for cystathionine beta synthase, which mediates the transformation of homocysteine to cystathionine, the initial step in the transsulfuration pathway and the urinary excretion of sulfur. In a normal diet there is conservation of the carbon skeleton, and about 50% of the homocysteine formed is remethylated to methionine via steps that require folic acid and vitamin B12. A deficiency of any of these three vitamins leads to modest homocyst(e)ine elevation, as does diminished renal function, both of which are common in the elderly. It is also established that homocyst(e)ine elevation of this order is associated with increased cardiovascular risk but is also associated with most established risk factors, although it is thought to be an independent contributor. In the inborn error of metabolism homocystinuria due to cystathionine beta synthase deficiency there is greatly increased circulating homocyst(e)ine and a clear association with precocious vascular disease. In about 50% of these patients there is a vascular event before the age of 30 years. The homocysteine-induced adverse vascular changes appear to result from endothelial and smooth muscle cell effects and increased thrombogenesis. We have documented a highly significant reduction in the occurrence of vascular events during 539 patient years of treatment in 32 patients with cystathionine beta synthase deficiency (mean age 30 years, range 9-66 years) by aggressive homocyst(e)ine lowering with pyridoxine, folic acid, and B12 (p = 0.0001). The 15 pyridoxine nonresponsive patients also received oral betaine. Although a cause and effect relationship is postulated for the increased cardiovascular risk associated with mild homocysteine elevation, a common cause of this elevation is the methylenetetrahydrofolate reductase C677T mutation. Homozygotes occur in about 11% of Caucasian populations. However, the mutation is not associated with increased coronary risk. Since mild homocysteine elevation is easily normalized by B vitamin supplementation, usually with folic acid, it remains for controlled clinical trials of this inexpensive therapy to determine whether normalizing mild homocyst(e)ine elevation reduces cardiovascular risk.

Mutation and polymorphic marker analyses of 65K- and 67K-glutamate decarboxylase genes in two families with pyridoxine-dependent epilepsy

Pyridoxine-dependent epilepsy is a disease inherited as an autosomal recessive trait, characterized by rapid response to pharmacological dosages of pyridoxine. The defect has been suggested to reside in glutamate decarboxylase (GAD), since a mutant GAD with an abnormally high Km for a cofactor, pyridoxal phosphate, could not synthesize an adequate amount of gamma-amino butyric acid [Scriver and Whelan (1969) Ann NY Acad Sci 166: 83]. To test this hypothesis, we studied two affected families by screening for mutations in the GAD mRNA and by analyzing a polymorphic marker in the GAD gene. Since two forms of GAD, GAD65 and GAD67, have been identified in human brain, we analyzed both forms. To overcome the limited accessibility of brain tissues, we utilized the minute amounts of GAD mRNAs ectopically transcribed in lymphoblasts. The ectopic GAD transcripts were amplified by reverse-transcription-mediated, nested polymerase chain reaction for mutation analysis. Two and three base substitutions were found in GAD65 and GAD67 cDNAs, respectively. All of them were, however, polymorphisms that were also found in control subjects. We then examined a (CA) repeat polymorphism in the GAD65 gene and found that different maternal alleles were transmitted to two affected sibs in one family. Thus, an etiological mechanism other than a K(m) mutant GAD is responsible for pyridoxine-dependent epilepsy.

The role of homocysteine, folate and other B-vitamins in the development of atherosclerosis

Recently, elevated homocysteine blood concentrations have been identified as an independent risk factor for the development of atherosclerotic lesions. The amino acid homocysteine is metabolized in the human body involving the vitamins folic acid, B12 and B6 as essential cofactors and coenzymes, respectively. There is an inverse relationship between the status of the relevant B-vitamins and the homocysteine blood concentration. Supplementation of these vitamins results in a significant reduction of the homocysteine level. Nutritive amounts seem to be sufficient to obtain this reduction, even in the case of elevated homocysteine levels.

[The importance of vitamin B 6 for development of the infant. Human medical and animal experiment studies]

Vitamin B-6 is an important coenzyme in the biosynthesis of the neurotransmitters GABA, dopamine and serotonin and is therefore required for the normal perinatal development of the central nervous system. In rat studies, biochemical and morphological abnormalities (decreased dendritic arborization and reduced numbers of myelinated axons and synapses) in the brains of pups from vitamin B-6 deficient dams were associated with behavioral changes such as epileptiform seizures and movement disorders. In severely vitamin B-6 deficient human infants, similar behavioral abnormalities have been described. Marginally deficient neonates were found to have a lower birthweight and to display less mature reactive and adaptive behavior in the Brazleton Neonatal Assessment Scale than well-fed infants. While it is not yet possible to define the exact amount of vitamin B-6 required to support optimal brain development, pregnant and lactating women should be encouraged to consume a diet that is rich in vitamin B-6.

Relations of vitamin B-12, vitamin B-6, folate, and homocysteine to cognitive performance in the Normative Aging Study

We investigated the relations between plasma concentrations of homocysteine and vitamins B-12 and B-6 and folate, and scores from a battery of cognitive tests for 70 male subjects, aged 54-81 y, in the Normative Aging Study. Lower concentrations of vitamin B-12 (P=0.04) and folate (P=0.003) and higher concentrations of homocysteine (P=0.0009 ) were associated with poorer spatial copying skills. Plasma homocysteine was a stronger predictor of spatial copying performance than either vitamin B-12 or folate. The association of homocysteine with spatial copying performance was not explained by clinical diagnoses of vascular disease. Higher concentrations of vitamin B-6 were related to better performance on two measures of memory (P=0.03 and P=0.05). The results suggest that vitamins (and homocysteine) may have differential effects on cognitive abilities. Individual vitamins and homocysteine should be explored further as determinants of patterns of cognitive impairment.

Homocysteine and coronary atherosclerosis

Homocysteine is increasingly recognized as a risk factor for coronary artery disease. An understanding of its metabolism and of the importance of vitamins B6 and B12 and folate as well as enzyme levels in its regulation will aid the development of therapeutic strategies that, by lowering circulating concentrations, may also lower risk. Possible mechanisms by which elevated homocysteine levels lead to the development and progression of vascular disease include effects on platelets, clotting factors and endothelium. This review presents the clinical and basic scientific evidence supporting the risk and mechanisms of vascular disease associated with elevated homocysteine concentrations as well as the results of preliminary therapeutic trials.

Vitamin dependent erythrocyte enzymes in newborns in relation to gestational age and birth weight

In order to search for any difference in riboflavin and pyridoxine nutrition between term appropriate for gestational age (TAGA), term small for gestational age (TSGA) and preterm appropriate for gestational age (PTAGA) newborns, cord blood from 23, 19 and 20 infants, respectively, were studied, and red cell glutathione reductase (riboflavin-dependent) and glutamic oxaloacetic transaminase (pyridoxine-dependent) activities were measured, as well as their respective activity coefficients (GRase AC and GOT AC). Red cell enzymes were assayed according to BEUTLER [4] in a Gilford recording spectrophotometer model 2451 at 37 degrees C. Values of 1.42, 1.39 and 1.32 of GRase AC and values of 1.17, 1.02 and 1.08 GOT AC, respectively were obtained. These data indicate that there is no significant difference between the three categories of newborns with regard to riboflavin and pyridoxine nutrition, and suggest that neither maturity nor adequacy of intrauterine growth were related to differences in the availability of these vitamins. All groups demonstrate a uniform mild deficiency of riboflavin and an adequate level of pyridoxine, probably the effect of maternal diet.

Vitamin B6 modulates expression of albumin gene by inactivating tissue-specific DNA-binding protein in rat liver

The level of albumin mRNA in the liver of vitamin B6-deficient rats was found to be 7-fold higher than that of control rats. Since the transcriptional activity of the albumin gene, as measured by a nuclear run-on assay, was increased 5-fold in vitamin B6 deficiency, the higher concentration of albumin mRNA in the liver of vitamin-deficient rats could be attributed to the enhanced rate of transcription. The promoter proximal sequences of the albumin gene interact with a number of tissue-specific transcription factors including HNF-1 and C/EBP. We determined the binding activities of liver nuclear extracts to the HNF-1- and C/EBP-binding sites by gel mobility-shift assay and found that the activities of the extract prepared from liver of vitamin B6-deficient rats were greater than those of controls. As the concentrations of C/EBP in nuclear extracts from control and vitamin-deficient rats, estimated by Western-blot analysis, were essentially the same, the lower binding activity of the extract from control liver is probably due to inactivation of tissue-specific factors by pyridoxal phosphate and/or its analogues. We therefore examined the effect of pyridoxal phosphate and its analogues on the binding activity of nuclear extract in vitro and found that only pyridoxal phosphate effectively inhibited the binding. These observations indicate that vitamin B6 modulates albumin gene expression through a novel mechanism that involves inactivation of tissue-specific transcription factors by direct interaction with pyridoxal phosphate.

Vitamin B6 and cancer: adenosine-N6-diethylthioether N1-pyridoximine 5'-PO4, a circulating human tumor marker

Studies in my laboratory on the metabolism and utilization of labeled vitamin B6 by tumor-bearing animals and tumor cells in culture have shown the production and presence in the circulation of a novel pyridoxal 5'-phosphate conjugate metabolite (1-5). Using specific radiolabeling and analytical tests, its structure was tentatively identified (now confirmed) as adenosine-N6-diethylthioether-N1-pyridoximine 5'-phosphate (4-6). The novel vitamin conjugate was isolated from the plasma of patients and control subjects following extraction with perchloric acid and separation by pair-ion HPLC. This communication reports the chromatographic separation of the novel compound and its plasma levels in control subjects, cancer patients and patients with other ailments. The results show that the novel metabolite is a circulating human tumor marker with levels of up to 4x or greater seen in cancer patients compared to controls and to subjects with other ailments. The results indicate strongly that the novel circulating vitamin B6 conjugate compound can be successfully used for the detection of different malignancies in humans by evaluating its level in circulation.

Vitamin nutrition status and homocysteine: an atherogenic risk factor

In an epidemiologic survey, a marginal status of folic acid, vitamin B12, and vitamin B6 was shown to be associated with hyperhomocysteinemia. In a case-control study, a low plasma folate concentration was associated with increased coronary heart disease risk. This phenomenon appears to be mediated by folate's effect on homocysteine metabolism. Both studies offer further perspectives on homocysteine as an atherogenic risk factor.

New perspectives on function of vitamins

Newer aspects of vitamin function are reviewed from a biochemical perspective. Specifically, six themes are developed that include 1) mechanisms and biochemical functions important to oxidant defense, 2) new functions associated with the actions of vitamin D, 3) vitamin K and calcium homeostasis, 4) folic acid and the methylation of DNA, 5) beta-carotene and cellular communication, and 6) newly identified roles for vitamin B6. A decade ago, it was considered highly speculative to propose approaches to disease prevention that involved vitamin supplementation. Nutrition paradigms important to vitamin function, however, have now shifted to include more focus on disease prevention and consideration of supplements. Considerable work has also evolved to provide basic biochemical and physiological mechanisms as bases for the interaction between vitamin status and health.

Immunotoxicity of the colour additive caramel colour III; a review on complicated issues in the safety evaluation of a food additive

Food additives can be regarded as the safest constituents of our daily food. Nevertheless, complicated issues with respect to their safety evaluation do also occur. In this review paper, some of these issues are illustrated by the description and evaluation of the research on the immunotoxicity of the food additive Caramel Colour III. Caramel Colour III is commonly used as a color additive in many products for human consumption. Toxicity studies conducted in the seventies demonstrated that administration of Caramel Colour III can cause a reduction in total white blood cell counts in rats, due to reduced lymphocyte counts. Studies reviewed in this paper demonstrated several other effects of Caramel Colour III on the immune system of rodents, including disturbed immune functions and changed resistance in infection models. In addition, studies in rats demonstrated that most of the effects occur only when the animals are fed a diet low in vitamin B6. The imidazole derivative 2-acetyl-4(5)-(1,2,3,4-tetrahydroxy-butyl)-imidazole (THI) was found to be responsible for the immunotoxicity. Issues such as the mechanism of action of THI and the role of vitamin B6 are discussed. Finally, the results of a human intervention study and the observed effect levels of THI in rats are discussed in terms of safety of the use of Caramel Colour III in our daily food supply.

4-Deoxypyridoxine inhibits chronic granuloma formation induced by potassium permanganate in vivo

4-Deoxypyridoxine (4-DPD) is a potent antagonist of Vitamin B6 coenzyme which inhibits IL-1, lymphocyte proliferation and has demonstrated that tolerance to skin grafts can be induced by administering splenic cells to pyridoxine-deficient mice. Chronic inflammation induced by dorsal injections of 200 microliters of a 1:40 saturated crystal solution of potassium permanganate (KMnO4) in mice treated or untreated with 4-DPD (400 micrograms/dose), has been investigated. After 7 days all mice developed a subcutaneous granulomatous tissue indicative of a chronic inflammatory response, at the site of injection. KMnO4-treated mice injected intraperitoneally with 4-DPD (400 micrograms/dose) on 5 consecutive days (the first at the same time of induction of the granuloma) show a significant decrease in size and weight of granuloma when compared to mice not treated with 4-DPD (Controls). In addition, in all mice treated with 4-DPD there was a strong inhibition of TNF alpha in serum (P < 0.01) and in supernatant fluids (P < 0.05) from minced granuloma, while IL-6 was inhibited in the supernatant fluids (P < 0.05) of minced granulomas but was not detected in the serum of treated and untreated mice. In this study we show for the first time the antiinflammatory effect of 4-DPD on chronic inflammation and the inhibitory effect of TNF and IL-6 generation in supernatant fluids from minced granulomas.

A critical review of minimal vitamin B6 requirements for growth in various species with a proposed method of calculation

We conclude that vitamin B6 is efficiently conserved by the tissues and that the major dietary requirement is to meet physiological stresses such as growth, pregnancy, lactation, vigorous exercise, and/or disease. A reasonable approximation of the minimal requirement for growth in most species can be obtained by assuming 15 nmol vitamin B6 for each g gain in body weight. For birds and fish, which can achieve 1 g gain/g feed, the vitamin B6 content would need to be about 15 mumol (3 mg)/kg feed. Such an intake is achievable with a variety of natural diets and would also be adequate for most mammalian species, which have lower feed efficiencies. Although well-balanced natural diets are usually adequate, supplementation with 5-10 mumol (1-2 mg)/kg diet is inexpensive and would provide a safety factor to allow for variations in feed composition and physiological stresses such as pregnancy, disease, parasites, and so on. At this time, whether the metabolic changes associated with increases in vitamin B6 intake above the minimum confer long-term health benefits on the organisms is not clear. Excessive vitamin B6 intake can be toxic. Fish and prawn seem to be particularly sensitive to this toxicity. Additional work is needed to clarify the interactions between vitamin B6 requirements and protein intake.

Vitamin B6 and immune competence

Animal and human studies suggest that vitamin B6 deficiency affects both humoral and cell-mediated immune responses. Lymphocyte differentiation and maturation are altered by deficiency, delayed-type hypersensitivity responses are reduced, and antibody production may be indirectly impaired. Although repletion of the vitamin restores these functions, megadoses do not produce benefits beyond those observed with moderate supplementation. Additional human studies indicate that vitamin B6 status may influence tumor growth and disease processes. Deficiency of the vitamin has been associated with immunological changes observed in the elderly, persons infected with human immunodeficiency virus (HIV), and those with uremia or rheumatoid arthritis. Future research efforts should focus on establishing the mechanism underlying the effects of vitamin B6 on immunity and should attempt to establish safe intake levels that optimize immune response.

[Vitamin B6 dependency syndrome]

Many enzymes that require pyridoxal 5'-phosphate (PLP), a coenzyme from a vitamin B6, are involved in amino acid metabolism. B6 dependency syndromes are defined as a group of metabolic disorders which are prevented or alleviated by non-physiologically large doses of vitamin B6, and, hence, they are tacitly accounted for by some structural alteration in a responsible B6-dependent enzyme such as a decrease on the affinity for PLP as compared to the normal. In this article, the mode of binding the coenzyme is exemplified by the case of aspartate aminotransferase, a typical B6-dependent enzyme whose three-dimensional structure is known, and, several B6 dependency syndromes are briefly reviewed. Among these syndromes, the molecular basis of only gyrate atrophy has recently been defined by the identification of a mutation in the relevant enzyme, ornithine aminotransferase.

Vitamin B6 and immune function in the elderly and HIV-seropositive subjects

Vitamin B6 plays an important role in immune response. A recent investigation of healthy elderly subjects in a vitamin B6 depletion-repletion study indicates that B6 deficiency impairs interleukin-2 production and lymphocyte proliferation. Another study in HIV-1-infected patients found impaired immune responsiveness in patients with compromised vitamin B6 status.

Vitamin B6 modulates transcriptional activation by multiple members of the steroid hormone receptor superfamily

Recent studies have shown that vitamin B6 modulates transcriptional activation by the human glucocorticoid receptor in HeLa S3 cells. We have now examined the possibility that vitamin B6 might similarly influence transcriptional activation by the glucocorticoid receptor in other cell types, as well as gene expression mediated by other members of the steroid hormone receptor superfamily. We show that elevated vitamin B6 concentrations suppress by 40-65% the level of transcription mediated through the endogenous murine L cell glucocorticoid receptor, as well as the human receptor transfected into E8.2 and T47D cells. In contrast, glucocorticoid receptor-mediated transcription was enhanced 60-110% in mild vitamin deficiency. The level of hormone-independent constitutive gene expression was not affected by these same alterations in vitamin B6 concentration. These studies indicated that the transcriptional modulatory effects of the vitamin were neither restricted to specific cell types nor limited to the human form of the glucocorticoid receptor. We next determined if hormone-induced transcription by several other steroid receptors (androgen, progesterone, and estrogen receptors) was analogously affected by alterations in vitamin B6 concentration. Analysis of gene expression mediated through the mouse mammary tumor virus promoter revealed that transcriptional activation of both the androgen and progesterone receptors was reduced by 35-40% under conditions of elevated vitamin B6 and enhanced by 60-90% in deficiency, again under conditions where constitutive expression was unaffected. Using a different promoter, the estrogen-regulated vitellogenin promoter, we found that transcriptional activation of the estrogen receptor was similarly affected. Estrogen-induced gene expression was reduced by 30% under conditions of elevated intracellular vitamin B6 and enhanced by 85% in vitamin deficiency. Thus, vitamin B6 modulates transcriptional activation by multiple classes of steroid hormone receptors. The similarities in vitamin B6 effects on transcription mediated through different promoters, the mouse mammary tumor virus and vitellogenin promoters, suggest that this vitamin may modulate the expression of a diverse array of hormonally responsive genes. These observations together support the hypothesis that vitamin B6 represents a physiological modulator of steroid hormone action.

Morphological abnormalities in vitamin B6 deficient tarsometatarsal chick cartilage

The aim of this study was to test the hypothesis that deficiency of vitamin B6 would produce morphological characteristics of osteochondral lathyrism. To accomplish this goal, morphological characteristics of chick cartilage in which lathyrism was produced by two separate dietary regimens was compared to morphological changes encountered in vitamin B6 deficiency. Vitamin B6 deficiency should reduce activity of lysyloxidase needed for producing intermolecular cross-links. The question to be addressed was: would this latter deficiency impair collagen morphological features and secondarily other structures indirectly by reducing collagen molecular assembly? Failure of cross-linking of collagen in the positive controls was related to a lack of functional aldehyde cross-link intermediates which are blocked by homocysteine and aminoacetonitrile. Day-old-male Lohmann chicks were fed adequate (6 mg/kg) or vitamin B6-deficient diets. Cross-link defects were induced by homocysteine-rich diets (0.6% w/w) or a diet containing aminoacetonitrile (0.1% w/w). Animals were sacrificed at 6 weeks of age and Ossa tarsalia articular cartilage specimens, as well as the proximal end of tarsometatarsus were dissected from the tibial metatarsal joint, a major weight-bearing site. Light microscopic observations revealed reduction of subarticular trabecular bone formation, concurrent with overexpansion of the hypertrophic cell zone. Ultrastructural electron microscopy observation of articular fibro-cartilage indicated significant thickening of collagen fibers in vitamin B6 deficient birds, as well as the positive controls in comparison to that of cage-matched control birds. It was concluded that vitamin B6 deficient cross-linking may be responsible for the observed delay in bone development and aforementioned cartilage histological alterations.

Vitamin B6 in clinical neurology

Many conditions in clinical neurology may be responsive to pyridoxine as a therapeutic agent. The current difficulty is in trying to isolate the conditions that are most likely to respond. Treating seizures is a major part of a neurologic practice. Our current therapeutic agents are only partially successful and limited by multiple side effects. One problem is that patients often have to take these agents for an entire lifetime, further raising the risk of toxicity. If pyridoxine supplementation can improve the efficacy of currently used medications, it will be gladly accepted into our therapeutic arsenal. Headache, chronic pain, and depression all appear to run together in many of our patients. The observations that serotonin deficiency is a common thread between them and that pyridoxine can raise serotonin levels open a wide range of therapeutic options. Small studies have been carried out with mixed success. Comparison with amitriptyline in the treatment of headache appears to show about equal efficacy, although side effects would be expected to be more of a problem with the amitriptyline. Behavioral disorders are relatively common and continue to be a major problem, disrupting the lives of the patients and their families. Current treatments are not acceptable to most people because of the risk of side effects with long-term usage. If, as Dr. Feingold suggests, many of these problems are caused by "toxic" exposures to chemicals that are pyridoxine antagonists, supplementation at early ages may reduce the incidence of hyperactivity and aggressive behavior. This raises the question of safety. Is pyridoxine safe for long-term use in large segments of the population, including children? The studies on children with Down's syndrome and autism, utilizing much higher doses than are used for other therapeutic purposes, seem to indicate relative safety if carefully monitored. Studies involving large population groups with carpal tunnel syndrome, all adults, using 100-150 mg/day have shown minimal or no toxicity in five- to 10-year studies. Women self-medicating for PMS taking 500 to 5000 mg/day have shown peripheral neuropathy within one to three years. It would appear from this retrospective analysis that pyridoxine is safe at doses of 100 mg/day or less in adults. In children there is not enough data to make any sort of suggestion. Because the major neurologic complication is a peripheral neuropathy and the causes of this condition are myriad, pyridoxine may cause neuropathy only in patients with a pre-existing susceptibility to this condition.

The influence of vitamin B6 on the structure and function of the glucocorticoid receptor

Pyridoxal phosphate influences several properties of steroid hormone receptors in vitro, but its role in vivo has not been clearly established. In an effort to address this issue, we have investigated the in vivo effects of vitamin B6 on the physical properties and biological function of the human glucocorticoid receptor. We demonstrate that vitamin B6 treatment of whole cells in culture produces an alteration in the isoelectric point of the receptor, as well as changes in the steroid and DNA binding capacities. Furthermore, glucocorticoid dependent transcriptional activation properties of the receptor are also altered by modulation of the vitamin B6 status. High concentrations of vitamin B6 suppress activation of transcription, while vitamin deficiency enhances responsiveness to steroid hormone. Together, these studies imply a physiological role for vitamin B6 in glucocorticoid hormone action.

Effects of maternal restriction in vitamin B-6 on neocortex development in rats: neuron differentiation and synaptogenesis

Effects of maternal restrictions in vitamin B-6 on neuron differentiation and synaptogenesis in developing neocortex were examined. Rats were fed ad libitum a vitamin B-6-free diet supplemented with 0.0 or 0.6 mg pyridoxine hydrochloride (PN.HCl)/kg diet during gestation followed by a control level of 7.0 mg/kg diet during lactation, or they were fed the vitamin B-6-free diet supplemented with 0.6 or 7.0 mg PN.HCl/kg diet throughout gestation and lactation. Neocortices of the offspring were examined at 30 d of age by light and electron microscopy. All maternal restrictions in vitamin B-6 reduced the number of higher order dendrites on stellate neurons in layer II and on pyramidal neurons in layer V of the neocortex and decreased synaptic density in the neuropil of the neocortex. The findings indicated that vitamin B-6 restriction during gestation, either marginal or severe, was the critical treatment factor that adversely affected synaptogenesis and at least one event in neuron differentiation in the neocortex, the arborization of dendrites.

In vivo evidence for a vitamin B-6 requirement in carnitine synthesis

The purpose of this study was to determine whether there is a requirement for vitamin B-6 (B6) in carnitine synthesis. Rats were fed a B6-deficient (-B6) (0.04 mg pyridoxine [PN]/kg) diet (ad libitum or meal-fed) or a control (+B6) (5.7 mg PN/kg) diet (ad libitum or pair-fed). These diets were fed for 6 wk, then some of the rats were repleted with the +B6 diet for 2 wk. Total acid-soluble carnitine (TCN) and free carnitine (FCN) levels were compared in the plasma, liver, skeletal muscle, heart muscle and urine and rats fed +B6 or -B6 diets. In -B6 rats vs. +B6 rats, TCN levels were significantly lower (P less than 0.05) in the plasma, skeletal muscle, heart muscle and urine, but not in the liver. However, if rats were fasted for 3 d, liver TCN concentration of -B6 rats was significantly lower than that of +B6 rats. After B6-deficient rats were repleted with the +B6 diet, the TCN level in the plasma, liver, skeletal muscle, heart muscle and urine returned to the levels of control rats. Thus, the decrease in TCN and FCN levels with a B6-deficient diet and the increase of these levels after B6 repletion provides evidence for the B6 requirement in the biosynthesis of carnitine.

Evaluation of vitamin B-6 status and function of rats fed excess pyridoxine

We compared the vitamin B-6 status of 12-wk-old rats (n = 12) fed excess (1400 mg/kg diet) or the recommended level (7 mg/kg diet, control) of pyridoxine (PN) hydrochloride to test if excess vitamin B-6 would cause tissue depletion of pyridoxal phosphate (PLP), the active coenzyme form of vitamin B-6. Plasma PLP, tryptophan-load test results, food intake, and tissue and body weights were not different at wk 6. Red blood cell endogenous alanine aminotransferase activity and PLP concentration were elevated (P less than 0.01) in rats fed 1400 mg PN.HCl/kg diet. In contrast, PLP concentration in muscle was significantly lower (P = 0.01) in rats fed excess vitamin B-6 (9.7 +/- 0.8 nmol/g, mean +/- SEM) than in controls (14.9 +/- 1.4). PLP concentration in other tissues, including plasma, was not affected. In rats fed excess vitamin B-6, pyridoxal was increased in all tissues examined (P less than 0.05), and total vitamin B-6 was increased in plasma, red blood cells and kidneys (P less than 0.05). Total glycogen phosphorylase (a + b) activity in the gastrocnemius was not affected, but phosphorylase a activity was increased in rats fed excess vitamin B-6 (P = 0.025). Concentrations of dopamine and metabolites in the caudate nucleus of the basal ganglia were not affected. A transient, but significant, elevation in acoustic startle response, a central nervous system reflex, was observed in rats fed excess vitamin B-6. The depletion in muscle PLP could not hae been predicted by either plasma or red blood cell PLP concentration, although the latter did reflect vitamin B-6 intake.(ABSTRACT TRUNCATED AT 250 WORDS)