Aluminum induced encephalopathy in the rat.

Aluminum tartrate (AlT) but not sodium tartrate (NaT) produces a progressive encephalopathy when injected intracerebroventricularly in the rat. This syndrome, lethal within 30-35 days, is characterized by progressively deranged behavior. An early startle reaction (day 14), later joined by locomotor discoordination (day 19) is followed by locomotor and electrocorticographic (ECoG) seizures (day 21) in chronically instrumented AlT rats. There is early dissociation between ECoG and locomotor aspects. When tested in the shuttlebox for estimation of learning and memory function 7-8 days after AlT injection, marked impairment of both active and passive avoidance was observed. Glucose uptake capacity of synaptosomes from brain areas of AlT and NaT animals was indexed by the 2-deoxy-D-glucose method. Striatal and cortical synaptosomes showed reduced uptake activity 7 days following AlT injection. By day 14, hypothalamic areas also became affected, striatal uptake was further inhibited, and cortical uptake was reduced to 57% of control. The ECoG background rhythm remained unchanged until days 20-23, when the mean peak frequency was reduced. The model may be useful in the study of central aluminum toxicity and may have predictive validity in the testing of procedures to counter aluminum-associated encephalopathies in man.

Studies of aluminum in rat brain.

The effects of high aluminum concentrations in rat brain were studied using(14)C autoradiography to measure the uptake of [(14)C]2deoxy-D-glucose ([(14)C]2DG) and microbeam proteon-induced X-ray emission (microPIXE) with a 20-µm resolution to measure concentrations of magnesium, aluminum, potassium, and calcium. The aluminum was introduced intracisternally in the form of aluminum tartrate (Al-T), and control animals were given sodium tartrate (Na-T). The(14)C was administered intravenously. The animals receiving Al-T developed seizure disorders and had pathological changes, which included cerebral cortical atrophy. The results showed that there was a decreased uptake of [(14)C]2DG in cortical regions in which increased aluminum levels were measured, i.e., there was a correlation between the aluminum in the rat brain and decreased brain glucose metabolism. A minimum detection limit of about 16 ppm (mass fraction) or 3×10(9) Al atoms was obtained for Al under the conditions employed.

Stimulation of glucose uptake by transforming growth factor beta: evidence for the requirement of epidermal growth factor-receptor activation.

Transforming growth factor beta (TGF-beta), derived from human platelets, stimulates the uptake of 2-deoxy-glucose by cultured cell monolayers 2- to 4-fold. Stimulation can be detected as early as 30 min with as little as 0.1 ng of TGF-beta per ml and maximal effects can be obtained at 2 hr with 1 ng of the growth factor per ml. TGF-beta-induced stimulation of sugar uptake is enhanced by the co-addition of platelet-derived growth factor (10 ng/ml) or epidermal growth factor (EGF, 1 ng/ml). The NR-6 variant of mouse 3T3 cells, which lack EGF receptors, is not stimulated by TGF-beta. Antisera to EGF receptors that block 125I-labeled EGF binding also inhibit TGF-beta stimulation of 2-deoxyglucose uptake, although 125I-labeled TGF-beta binding remains unimpaired. In contrast, anti-sera to the EGF receptor, which do not block EGF binding, have no measurable effect on the TGF-beta-stimulated uptake of 2-deoxyglucose. We confirm that the receptor for TGF-beta is distinct from the receptor for EGF and we conclude that TGF-beta stimulation of 2-deoxyglucose uptake requires the co-activation of the EGF receptor kinase system.

Proton-dependent inhibition of yeast and brain hexokinases by aluminum in ATP preparations.

The aluminum present as a contaminant in ATP preparations can cause strong inhibition of yeast hexokinase P-II activity at pH 7.0 or below but has little or no inhibitory effect at a pH of 7.5 or greater. The inhibition is reversed by citrate, 3-phosphoglycerate, malate, phosphate, and catecholamines, all of which have previously been described as activators of hexokinase at low pH. We suggest that these agents activate the enzyme only by virtue of their ability to coordinate with aluminum present in the assay system. The presence of aluminum is also responsible for the "negative cooperativity" observed at low pH with respect to Mg . ATP concentration--i.e., the inhibition by aluminum is uncompetitive at low Mg . ATP concentrations but becomes competitive at high Mg . ATP concentrations. The inhibition is thought to be due to formation of a complex of Al . ATP with the enzyme, with a dissociation constant (Ki) of 0.1 microM. Yeast hexokinase P-I is somewhat less sensitive to A1 than is hexokinase P-II, and yeast glucokinase is not detectably affected. The hexokinase in rat brain (type I) shows a pH-dependent inhibition by Al similar to that observed with the yeast hexokinases, whereas the rat muscle (type II) enzyme is less sensitive, suggesting a possible relationship to aluminum encephalopathy in man.

The increase in hexokinase activity in hereditary avian muscular dystrophy.

Hexokinase activity was found to be increased in both the more severely affected red (thigh) muscle of dystrophic chickens. The increase in activity was largely associated with the particulate fraction. These findings may indicate early events in the pathogenesis of avian muscular dystrophy.

Inhibition of sugar uptake in adenosine-treated 3T3 cells.

Addition of 5 to 250 micromolar adenosine to the culture medium resulted in a 30-80% inhibition of the rate of uptake of 2-deoxyglucose or 3-0-methylglucose by sparse or confluent 3T3 cells within three hours. The inhibition of deoxyglucose uptake could be reversed partially by changing the cells to medium without adenosine for two hours and could be prevented completely by the addition of persantin, an inhibitor of nucleoside uptake. The adenosine effect is not due to inhibition of pyrimidine synthesis, since it is not prevented by uridine. It is not seen in 3T6 cells lacking adenosine kinase. The inhibition could be observed on confluent cells whose deoxyglucose uptake was stimulated by insulin, epidermal growth factor (EGF), calf serum or calcium phosphate. Although the percentage stimulation over control by these factors varied, the percentage inhibition by addition of adenosine of the stimulated rates, as well as the unstimulated rate, was relatively constant. EGF, insulin and calcium phosphate caused little or no stimulation of deoxyglucose uptake by sparse cells, whether adenosine treated or untreated. The results suggest that adenosine acts intracellularly after phosphorylation to regulate sugar uptake through a mechanism which is independent of the regulation by hormones and cell density.

Stimulation of sugar uptake and thymidine incorporation in mouse 3T3 cells by calcium phosphate and other extracellular particles.

Evidence is presented that the marked stimulation of sugar uptake and thymidine incorporation by addition of extra Ca2+ to stationary phase mouse 3T3 cells in culture is phosphate dependent and due to the action of the calcium phosphate precipitate formed in the medium. The cells are similarly stimulated by a variety of particulate materials, including calcium pyrophosphate, barium sulfate, kaolin, and polystrene beads. The precipitate effects on sugar uptake are of the same magnitude as those seen with certain hormones (insulin, epidermal growth factor) or with fresh 10% calf serum. The effect of barium sulfate on thymidine incorporation is also of the same magnitude as seen with these hormones, but much less than half that found with fresh calf serum. The stimulation by barium sulfate or hormones of thymidine incorporation is not phosphate dependent.

Stimulation of sugar uptake in cultured fibroblasts by epidermal growth factor (EGF) and EGF-binding arginine esterase.

Mouse epidermal growth factor causes a rapid increase in 2-deoxyglucose uptake in stationary phase mouse (3T3) cells or human fibroblasts. Maximum effect is approximately two fold over control levels for 3T3 cells and about 50% over controls for human fibroblasts. Maximum effect on 3T3 cells is seen about two hours after addition of 10 ng/ml EGF to the culture medium. Stimulation is easily measureable within the first fifteen minutes after addition of the hormone and may be detected at hormone concentrations as low as 0.1 ng/ml. The EGF-binding arginine esterase found associated with EGF in the mouse submaxillary gland causes an enhancement of the EGF effect. In serum-free medium, the EGF effect is still readily observed, but no enhancement by the esterase is seen. SV40 virus-transformed 3T3 cells show no effect on deoxyglucose uptake after addition of 10 ng/ml EGF to the culture medium, but a response may be demonstrated after these cells are incubated for 12 hours or more in serumless medium. EFG stimulates transport of 3-O-methylglucose in stationary phase 3T3 and human fibroblasts but no EGF stimulation of alpha-amino-isobutyrate uptake in 3T3 cells is seen under conditions is reproted to inhibit intracellular degradation of human EGF by human fibroblasts, does not diminish the EGF effect on deoxyglucose uptake in human fibroblasts.