Tetrahydrobiopterin metabolism in the temporal lobe of patients dying with senile dementia of Alzheimer type

There is a defect in tetrahydrobiopterin metabolism in brains from subjects with senile dementia of Alzheimer type compared to age-matched controls. This defect results in lowered total biopterin concentrations in brain. Brains from subjects with senile dementia of Alzheimer type retain their ability to synthesis neopterin and have normal dihydropteridine reductase activity, indicating a specific loss of ability to convert dihydroneopterin triphosphate to tetrahydrobiopterin.

Blood spots on Guthrie cards can be used for inherited tetrahydrobiopterin deficiency screening in hyperphenylalaninaemic infants

We describe a method of screening for dihydropteridine reductase deficiency and dihydrobiopterin synthesis deficiency--the two inherited defects that cause tetrahydrobiopterin deficiency--using blood spots on Guthrie cards. Dihydropteridine reductase deficiency may be identified positively, and a biopterin value of less than 6.0 micrograms/l in the presence of hyperphenylalaninaemia indicates further investigation for dihydrobiopterin synthesis deficiency.

Effects of phenobarbitone and phenytoin on folate catabolism in the rat

The effects of phenobarbitone and phenytoin on the catabolism of oral [2-14C] and [3',5',7,9-3H] folic acid were investigated. Normal rats were found to excrete an excess of 3H-labelled compounds into the urine and 14C-labelled compounds into the faeces. Phenytoin abolished this urinary 3H imbalance and also delayed and prolonged the overall excretion of radioactive material. Phenobarbitone appeared to increase the amounts of urinary scission products in the first 24 hr but over the 0-72 hr period both anticonvulsants decreased folate polyglutamate catabolism. As the anticonvulsants used in these experiments decreased folate catabolism in the rat it is unlikely that the megaloblastic anaemia caused by chronic anticonvulsant therapy is due to induction of the enzymes responsible for folate breakdown in vivo.

Tetrahydrobiopterin metabolism in senile dementia of Alzheimer type

Tetrahydrobiopterin metabolism was shown to be disturbed in 18 patients with senile dementia of Alzheimer type. This may have a bearing on the pathogenesis of the disease.

Investigations of tissue folates in normal and malignant tissues

The folates present in liver, gut and tumour tissue were examined before and after autolysis. Before autolysis 10-formylfolate tetraglutamate (10-CHOFA(glu)4), 5-methyltetrahydrofolate triglutamate (5-CH3THF(glu)3) and possibly tetrahydrofolate polyglutamate(s) (THF(glu)n) were detected. Liver contained all 3 species whereas no 5-CH3THF(glu)3 was present in the tumours; gut showed an intermediate situation. After autolysis the predominant monoglutamates formed were 5-CH3THF in the liver, 10-formylfolates in the gut and possibly tetrahydrofolate (THF) in the tumour extracts. These differences illustrate changes in tissue folates with the proliferation rate of the tissue and suggest an explanation for the methionine auxotrophy of Walker 256 carcinosarcoma cells.

The effect of inhibitors of folic acid absorption on the transfer rate constants in the rat everted proximal jejunum: a method for their evaluation from a three-compartment model

When solute transfer through the intestinal in vitro everted sac preparation is described by a three-compartment system, solute transfer rate constants can be derived for the mucosal and serosal permeability barriers. A catenary variant has been presented as well as a mammillary one where paracellular movement of solute is additionally allowed for. The first order differential rate equations governing the change in solute concentration in all three compartments with respect to time have been solved and the explicit analytical solutions provided. Since these solutions are cumbersome to use in the estimation of the required rate constants, a least squares procedure has been applied directly to the differential form of the rate equations in order to derive the rate constants without recourse to the analytical solutions. Verification of the solutions and of the estimated rate constants was by substitution of the latter into the former to test the goodness of fit for folic acid absorption data. Both variants take into account the simultaneous fluid movement which occurs during absorption experiments and which complicates the interpretation of absorption data. The mammillary model showed that only 10% of folic acid movement could pass directly through the paracellular pathways and that the bulk of folate movement is probably through the epithelial cells. However the catenary model without paracellular movement gave just as good fit to the data and was used subsequently. Experiments investigating the effect of substances implicated in folate malabsorption were analyzed in terms of the catenary model for folic acid absorption, in order to investigate their effects on the transfer rate constants free from the complicating effects on fluid movement. When pronounced inhibition took place, as with methotrexate, the mucosal rate constants were reduced, whereas the serosal rate constants were elevated. Also, the forward (k12) mucosal rate constant correlated significantly with the overall folate transfer in contrast to the other rate constants. These observations are consonant with the concept of a mucosally sited entry step exerting a controlling influence over the transfer rate of folic acid rather than a serosally sited exit process and with the conclusion that this may be the site of action of substances causing folate malabsorption.

Altered jejunal surface pH in coeliac disease: its effect on propranolol and folic acid absorption

1. Propranolol and folic acid absorption were studied separately in healthy subjects, non-coeliac patients and patients with treated and untreated coeliac disease. 2. The surface pH of jejunal biopsy samples was measured with a pH electrode. 3. When compared with values found in healthy subjects, plasma propranolol levels were elevated in coeliac disease and, in contrast, serum folic acid levels were depressed after oral administration of the drug. Jejunal surface pH was more alkaline in the coeliac groups than in the healthy and non-coeliac subjects. 4. Pharmacokinetic analysis of the plasma drug levels allowed evaluation of the rate constants associated with absorption and elimination. The absorption rate constant was decreased for folic acid in the coeliac group, but increased for propranolol. These changes correlated with variation in surface pH. 5. Although the changes in drug disposition in treated and untreated coeliac disease are the result of several factors, it is suggested that jejunal surface pH may affect the rate of absorption and therefore the plasma concentration-time profile of drugs which undergo dissociation.

Folate metabolism in man: the effect of malignant disease

The metabolism of [2-14C]+[3', 5', 7, 9-3H] folic acid and [214C]+[3', 5', 7, 9-3H] 10-formylfolate was studied in hospital inpatients. Metabolites detected in the urine after folic acid feeding included the unchanged compound, other folates and a number of breakdown products, such as p-acetamidobenzoyl-L-glutamate and p-acetamidobenzoate. This confirms the existence of a folate catabolic pathway in man. Patients with malignant disease excreted less of the dose in urine, incorporated more into the reduced folate pool, and showed decreased catabolism of folate, when compared to controls. 10-Formylfolate was excreted largely unchanged, and appears not to be reduced by man. Also 10-formylfolate interfered with the reduction of folic acid given simultaneously.

The metabolism of 5-methyltetrahydropteroyl-L-glutamic acid and its oxidation products in the rat

Folate metabolism in the rat was investigated using radiolabelled 5-methyltetrahydropteroylglutamate (5-CH3-H4PteGlu) and its oxidation products. 5-CH3-H4PteGlu is absorbed completely from the intestine, although in some preparations it is an equimolecular mixture of C-6 epimers, only one of which is naturally present in biological systems. The methyl group is incorporated into non-folate compounds, including methionine and creatine. No evidence was observed for the oxidation of the methyl group of 5-CH3-H4PteGlu to form other folate types. The tetrahydrofolate moiety of 5-CH3-H4PteGlu is metabolized in a similar manner to folic acid, forming formyl folates and tissue polyglutamates, and is catabolized by scission. The triazine oxidation product of 5-CH3-H4PteGlu is not metabolized by the rat or its gut microflora. 5-Methyl-5,6-dihydropteroylglutamate, however, is assimilated into the folate pool, but is substantially broken down by passage through the gut. The possible implication of this in scorbutic diets is discussed.

Serum dihydrobiopterin levels in patients on tricyclic antidepressants

Serum levels of 7, 8-dihydrobiopterin were significantly raised in female patients with depressive illness who were being treated with tricyclic antidepressants.

Folate catabolism in tumour-bearing rats and rats treated with methotrexate

The metabolism of (2-14C) + (3',5',7,9-3H) folic acid was studied in normal rats, tumour-bearing rats and rats treated with methotrexate (MTX). The experiments were designed to investigate changes in the catabolism and folate. The breakdown of folate to scission products was again demonstrated to be a normal phenomenon. Catabolites excreted included p-acetamidobenzoate, p-acetamidobenzoyl-L-glutamate, 3H2O, urea and a number of pterins. The catabolic process was decreased in the presence of a tumour and increased by the administration of MTX. MTX also led to the excretion of 4 additional radioactive pterins not found in normal urine. The possible mechanisms of folate breakdown are discussed with reference to the point of action of MTX.

Intestinal folic acid absorption and the acid microclimate. The effects of compounds relevant to folate malabsorption

The effect s of various substances and circumstances on folic acid absorption and surface pH were investigated in vitro in rat proximal jejunum. Prior consumption of alcohol and libitum, phenytoin and in vitro methotrexate had no effect on folate absorption. In contrast, ethanol in vitro, low sodium ion containing buffers in vitro and oral methotrexate given prior to experiment reduced absorption. Folate absorption did not correlate with water movement since methotrexate decreased folate but enhanced fluid absorption, ruling out direct coupling. Surface pH was elevated by the low sodium ion containing buffers, ethanol in vitro and oral methotrexate, correlating inversely with folate absorption. The parallelisms between absorption and changes in surface pH support the microclimate hypothesis of folic acid absorption where the rate of transport is largely determined by the surface pH of the proximal jejunum.

Inhibition of dihydropteridine reductase by dopamine

Dihydropteridine reductase has been purified 900-fold from rat liver. Dopamine inhibited the enzyme up to 50% at a concentration of 0.11mm. In the presence of dopamine the enzyme gave non-hyperbolic v-against-[S] plots. This enzyme may have a role in control of dopamine biosynthesis.

The effects of pathological and normal physiological processes on biopterin derivative levels in man

Mean serum biopterin derivative levels in adult males and females were 1.75 microgram/l and 1.53 microgram/l respectively, increased with age and followed a cyclic pattern during menstruation. Foetal brain and liver levels at 16 weeks approximated adult concentrations. Wide distribution in adult tissues and variation in concentration independent of serum levels demonstrated local synthesis. Serum levels were significantly decreased in senile dementia, lead poisoning, coeliac disease and malignant carcinoid disease. Abnormal metabolism of phenylalanine in senile dementia suggest lowered levels of tetrahydrobiopterin in tissue. Methotrexate increased serum biopterin levels by inhibition of dihydropteridine reductase; a saturation effect was noted.