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Inhibition of brain glycolysis by aluminum
Abstract:
Aluminum inhibited both the cytosolic and mitochondrial hexokinase activities in rat brain. The IC50 values were between 4 and 9 microM. Aluminum was effective at mildly acidic (pH 6.8) or slightly alkaline (pH 7.2-7.5) pH, in the presence of a physiological level of magnesium (0.5 mM). However, saturating (8 mM) magnesium antagonized the effect of aluminum on both forms of hexokinase activity. Other enzymes examined were considerably less sensitive to inhibition by aluminum. The IC50 of aluminum for phosphofructokinase was 1.8 mM and for lactate dehydrogenase 0.4 mM. At 10-600 microM, aluminum actually stimulated pyruvate kinase. Aluminum also inhibited lactate production by rat brain extracts: this effect was much more marked with glucose as substrate than with glucose-6-phosphate. However, the IC50 for inhibiting lactate production using glucose as substrate was 280 microM, higher than that required to inhibit hexokinase. This concentration of aluminum is comparable to those reportedly found in the brains of patients who had died with dialysis dementia and in the brains of some of the patients who had died with Alzheimer disease. Inhibition of carbohydrate utilization may be one of the mechanisms by which aluminum can act as a neurotoxin.
Insights
Aluminum inhibits key enzymes in rat brain energy metabolism, particularly hexokinase. This neurotoxic effect may contribute to conditions like Alzheimer disease.
Area of Science:
- Neurochemistry
- Toxicology
- Biochemistry
Background:
- Aluminum is a metal found in the environment and implicated in neurodegenerative diseases.
- Understanding aluminum's biochemical effects is crucial for elucidating its neurotoxicity.
Purpose of the Study:
- To investigate the inhibitory effects of aluminum on key enzymes involved in carbohydrate metabolism in the rat brain.
- To compare the sensitivity of hexokinase to aluminum inhibition with other glycolytic enzymes.
Main Methods:
- Enzyme activity assays were performed on rat brain cytosolic and mitochondrial fractions.
- Inhibition kinetics were determined for hexokinase, phosphofructokinase, lactate dehydrogenase, and pyruvate kinase.
- Lactate production was measured in rat brain extracts with varying substrates.
Main Results:
- Aluminum significantly inhibited both cytosolic and mitochondrial hexokinase with IC50 values between 4-9 microM.
- Magnesium ions at physiological concentrations (0.5 mM) did not prevent inhibition, but saturating levels (8 mM) antagonized the effect.
- Other enzymes like phosphofructokinase and lactate dehydrogenase were less sensitive to aluminum.
- Aluminum inhibited lactate production from glucose more effectively than from glucose-6-phosphate, with an IC50 of 280 microM.
Conclusions:
- Hexokinase is a primary target for aluminum inhibition in the rat brain.
- The observed inhibition of carbohydrate metabolism by aluminum is consistent with concentrations found in neurodegenerative disease patients.
- Inhibition of carbohydrate utilization represents a potential mechanism for aluminum-induced neurotoxicity.