Abstract
Citric acid is recognized and utilized as a dietary supplement for its ability to eliminate fatigue. However, the molecular and cellular mechanism underlying this effect has not been elucidated. This study investigated the effect of intragastric citric acid administration on the energy metabolism and gene expression in the skeletal muscles of mice that had been fasted without exercise, using biochemical analyses of metabolic indicators and DNA microarrays. Expression of the genes involved in the glycolysis, tricarboxylic acid cycle and β-oxidation of fatty acids were not affected by citric acid administration. However, citric acid increased the level of blood glucose and expression of the phosphoenolpyruvate carboxykinase gene. These results indicate that citric acid ingestion may eliminate fatigue by promoting gluconeogenesis.
Highlights
Citric acid has long been recognized for its ability to relieve physical fatigue
One hypothesized mechanism argues that citric acid ingestion suppresses lactic acid accumulation by inhibiting phosphofructokinase (Pfk), a rate-limiting enzyme of the glycolytic pathway, thereby limiting the accumulation of pyruvic acid, and, in turn, the accumulation of lactic acid [4,6]
This hypothesis is based on a report that phosphofructokinase genes (Pfk) activity is suppressed when citric acid, produced in the TCA cycle, moves from the mitochondria to the cytoplasm [4]
Summary
Citric acid has long been recognized for its ability to relieve physical fatigue. citric acid is growing in popularity as a supplement in sports nutrition. Intake of citric acid from lemons (2.7 g/day, 28 days) was determined to be effective for the reduction of lassitude, stress, and boredom in one investigation [1]. Sodium citrate ingestion (0.4 g/kg body weight) has been reported to improve muscle performance, as determined by an ergometer, during exercise in humans [2]. Oöpik et al have suggested that the ingestion of 0.5 g of sodium citrate/kg body mass shortly before a 5 km running time trial improves performance in well trained college runners [3]. Several hypotheses have been proposed to explain the anti-fatigue effects of citric acid, including: 1) that it suppresses the accumulation of lactic acid in the blood; 2) that it increases ATP production; 3) that it suppresses the production of ketone bodies, a fatigue factor, by curtailing fatty acid β-oxidation; 4) that it stimulates glycolgenesis.
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