Aluminium administered in drinking water but not in the diet influences biopterin metabolism in the rodent

To investigate the neurotoxic effects of aluminium (Al) Al was administered: 1) in the diet of the rat (30 mg Al/kg body weight for 6 weeks); 2) as a suspension of aluminium acetate in drinking water of the rat for 3 months and 3) in a long-term study in the mouse in which aluminosilicates were incorporated into a pelleted diet (1035 mg/kg of food over 23 months). In the latter treatment, increased Al was combined with a reduction in calcium and magnesium; a treatment designed to increase absorption of Al into the body. Administration of Al in the drinking water significantly reduced total brain biopterins and BH4 synthesis. However, no significant affect of Al in the diet on total biopterins or BH4 synthesis was found either in the rat or in the long-term study in the mouse. In addition, in the mouse no significant effects of the Al diet on levels of noradrenaline, serotonin, dopamine, 5-HIAA or CAT could be demonstrated. Hence, the occurrence of brain alterations may depend on the Al species present and the method of administration. Al salts in drinking water may increase brain tissue levels compared with the administration of a more insoluble species. Since alterations in biopterin metabolism are also a feature of Alzheimer's disease (AD) these results support the hypothesis that Al in the water supply may be a factor in AD.

Defective gallium-transferrin binding in Alzheimer disease and Down syndrome: possible mechanism for accumulation of aluminium in brain

The plasma distribution of gallium (as an analogue of aluminium) was investigated in patients with Alzheimer disease, Down syndrome, or stroke dementia, in subjects on haemodialysis for chronic renal failure, and in healthy controls. Gallium-transferrin binding was significantly lower in the Alzheimer (mean [SEM] 7.9 [1.1]%) and Down syndrome groups (6.9 [0.7]%) than in the controls (17.1 [1.6]%), whereas stroke dementia and haemodialysis patients had normal binding. There were no differences among the groups in plasma citrate concentration. The plasma transferrin concentration was slightly lower in the Alzheimer and Down syndrome groups than in the controls, but even lower in stroke dementia patients (1.74 [0.14] g/l vs 2.98 [0.18] g/l in controls). Transferrin iron saturation was higher in the Alzheimer (58.9%) and Down syndrome groups (81.6%) than in the controls (39.0%) or stroke dementia patients (33.4%). This deficiency of gallium/aluminium binding would leave more unbound aluminium which could move readily into the brain, where it has neurotoxic effects.

Neopterin: biopterin ratios in Down's syndrome

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Tetrahydrobiopterin metabolism in the streptozotocin induced diabetic state in rats

Streptozotocin induced diabetes has been shown to have associated changes in the metabolism of tetrahydrobiopterin. De novo biosynthesis of tetrahydrobiopterin in the brain was reduced as was dihydropteridine reductase activity. Consequently there is a shift from fully reduced biopterins to more oxidised species. Both can cause reduced levels in the cofactor pool and may cause reduced levels of the associated neurotransmitters and neurological deficits.

Depression and tetrahydrobiopterin: the folate connection

Total biopterin, neopterin and creatinine were measured in spot urine samples from affective disorder patients on lithium therapy and control subjects. Folic acid was also measured in plasma in a sample of the patients. The mean neopterin: biopterin ratio was significantly higher in the 76 patients (3.2 +/- 0.5) than in the 61 controls (1.8 +/- 0.1). In female patients biopterin levels were significantly lower than in controls. In the control groups there was a significant correlation between the molar concentration of neopterin and biopterin. No such correlation was found in the patients. These data indicate that tetrahydrobiopterin (BH4) biosynthesis is reduced in this group. A significant positive correlation was found between plasma folate and urinary biopterin. It is suggested that folate deficiency may impair the synthesis of BH4, a cofactor essential for the synthesis of 5-HT and other monoamines that are involved in the pathogenesis of affective disorders.

Inhibition of monocyte luminol-dependent chemiluminescence by tetrahydrobiopterin, and the free radical oxidation of tetrahydrobiopterin, dihydrobiopterin and dihydroneopterin

Luminol-dependent chemiluminescence of normal human monocytes activated by zymosan is demonstrated to be inhibited by tetrahydrobiopterin in a concentration-dependent manner. The reduced pterins tetrahydrobiopterin, dihydrobiopterin, and dihydroneopterin are all shown to be readily oxidized by the hydroxyl radical. The susceptibility of reduced pterins to free radical attack may explain the inhibition of chemiluminescence observed and an additional role of reduced pterins as free radical scavengers in tissues is considered.

Tissue distribution of gallium following administration of the gallium-maltol complex in the rat: a model for an aluminium-maltol complex of neurotoxicological interest

The intestinal absorption and subsequent tissue distribution of aluminium-maltol, a potentially neurotoxic complex found in foods, was investigated using gallium as a marker for aluminium. Gallium or gallium-maltol labelled with 67Ga was administered orally to rats. The amount of gallium in 'blood-free' tissues was measured by correcting for gallium in residual blood and an estimate of intestinal absorption was then made by summing the values for all tissues examined. In both the test (gallium-maltol dosed) and control (gallium only dosed) experiments absorption of gallium was significantly increased in the fasted state when compared with that of the fed animals. In fasted but not in fed animals, administration of gallium-maltol doubled the amount of gallium absorbed when compared with administration of gallium alone.

Visual evoked potentials and neopterin: biopterin ratios in urine show a high correlation in Alzheimer's disease

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The effect of lead on tetrahydrobiopterin metabolism. A possible mechanism for neurotoxicity

The use of low levels of lead in vivo in rats has been found to inhibit dihydropteridine reductase and cause an apparent increase in tetrahydrobiopterin biosynthesis. At higher dose levels inhibition of tetrahydrobiopterin biosynthesis has been observed. At low levels the disruption of tetrahydrobiopterin metabolism has been found to give an increase in the total level of biopterin derivatives but a movement away from the fully reduced form to the oxidised species in a manner consistent with dihydropteridine reductase inhibition. Lead has been found to inhibit dihydropteridine reductase in man.

The effect of tetrahydrofolate on tetrahydrobiopterin metabolism

5-Methyltetrahydrofolate and vitamin B12 appear to be required for the biosynthesis of tetrahydrobiopterin. A deficiency of either could be sufficient to bring about neurological change which can be corrected by reversing the deficiency. Patients with senile dementia could possibly be benefited by the administration of 5-methyltetrahydrofolate.

Intestinal surface acid microclimate in vitro and in vivo in the rat

The presence of the intestinal surface acid microclimate (ISAM) has long been suggested. Controversy, however, still exists as to the existence, general characteristics, and requirements of this microclimate. We examined the existence and distribution of the ISAM along the rat small intestine and colon and determined its general characteristics. The results clearly demonstrate the existence of the ISAM in vitro and in vivo. Glucose and sodium in the incubation medium, as well as normal intracellular metabolism, are essential requirements for the formation and maintenance of the ISAM. We conclude that the ISAM is a normal physiologic phenomenon of the luminal surface of the intestine.

Effects of meals and meal times on uptake of lead from the gastrointestinal tract in humans

Twenty three adults ingested 203Pb as lead acetate on the 12th hour of a 19 h fast. Retention measured 7 days later in a whole-body counter was 61% and whole-body turnover rates suggested that initial uptake had been considerably greater. Balanced meals eaten with 203Pb reduced lead uptake to 4% and the influence of the food lasted for up to 3 h. The effects of phytate, ethylene-diaminetetra acetate (EDTA), caffeine, alcohol, glucose, a liquid meal and a light snack were tested separately with intermediate results. The effect of a meal was probably largely due to its content of calcium and phosphate salts but lead uptake was probably further reduced by phytate which is plentiful in whole cereals and it was probably increased by a factor in milk. Uptake with skimmed milk was the same as with whole milk and we suggested that the factor was not fat. Comestibles with low mineral and phytate contents reduced lead uptake by intermediate amounts, possibly by stimulation of digestive secretions. The avid uptake of lead during a fast, the large reduction of lead uptake with meals and the likelihood of variations in gastric-emptying rates and dietary habits may be major causes of variation in body burdens of lead in the population.