Alpha-cyano-4-hydroxycinnamate decreases both glucose and lactate metabolism in neurons and astrocytes: implications for lactate as an energy substrate for neurons.
The rates of uptake and oxidation of [U-(14)C]lactate and [U-(14)C]glucose were determined in primary cultures of astrocytes and neurons from rat brain, in the presence and absence of the monocarboxylic acid transport inhibitor alpha-cyano-4-hydroxycinnamate (4-CIN). The rates of uptake for 1 mM lactate and glucose were 7.45 +/- 1.35 and 8.80 +/- 1.0 nmol/30 sec/mg protein in astrocytes and 2.36 +/- 0.19 and 1.93 +/- 0.16 nmol/30 sec/mg protein in neuron cultures, respectively. Lactate transport into both astrocytes and neurons was significantly decreased by 0.25-1.0 mM 4-CIN; however, glucose uptake was not affected. The rates of (14)CO(2) formation from 1 mM lactate and glucose were 12.49 +/- 0.77 and 3.42 +/- 0.67 nmol/hr/mg protein in astrocytes and 29.32 +/- 2.81 and 10.04 +/- 1.79 nmol/hr/mg protein in neurons, respectively. Incubation with 0.25 mM 4-CIN decreased the oxidation of lactate and glucose to 57.1% and 54.1% of control values in astrocytes and to 13.2% and 41.6% of the control rates in neurons, respectively. Preincubation with 4-CIN further decreased the oxidation of both glucose and lactate. Studies with glucose specifically labeled in the one and six positions demonstrated that 4-CIN decreased mitochondrial glucose oxidation but did not impair the metabolism of glucose via the pentose phosphate pathway in the cytosol. The lack of effect of 4-CIN on glutamate oxidation demonstrated that overall mitochondrial metabolism was not impaired. These findings suggest that the impaired neuronal function and tissue damage in the presence of 4-CIN observed in other studies may be due in part to decreased uptake of lactate; however, the effects of 4-CIN on mitochondrial transport would significantly decrease the oxidative metabolism of pyruvate derived from both glucose and lactate.
McKenna
M C
MC
Department of Pediatrics, University of Maryland School of Medicine, 10-035 BRB, 655 W. Baltimore Street, Baltimore, MD 21201, USA. mmckenna@umaryland.edu
Hopkins
I B
IB
Carey
A
A
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001921:Brain / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D003373:Coumaric Acids / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology; D005260:Female; D005333:Fetus; D005947:Glucose / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism*; D009004:Monosaccharide Transport Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D011247:Pregnancy; D019289:Pyruvic Acid / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats
D002250:Carbon Radioisotopes; D003373:Coumaric Acids; D009004:Monosaccharide Transport Proteins; D002245:Carbon Dioxide; C007175:alpha-cyano-4-hydroxycinnamate; D019344:Lactic Acid; D019289:Pyruvic Acid; D005947:Glucose