When carbohydrate metabolism is impaired, fatty acid metabolism is activated. Excess acetyl-coenzyme A (CoA) is generated from fatty acids by β-oxidation and is used for the formation of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) and subsequently for acetoacetate. High levels of secreted ketone bodies (acetoacetate and 3β-hydroxybutyrate) lower the pH of blood and urine, resulting in ketoacidosis. HMG-CoA lyase in hepatic cells is a rate-limiting enzyme catalyzing the cleavage of HMG-CoA to acetoacetate, and thus inhibition of this enzyme results in reduced acetoacetate production, in other words, impaired ketoacidosis. Inhibition of HMG-CoA lyase activity possibly prevents ketoacidosis and should be the therapeutic target. Polyphenols are common and abundant dietary constituents with beneficial effects on human health. We examined the inhibitory effects of dietary polyphenols on HMG-CoA lyase activity in cellular extracts of human hepatoma HepG2 cells. Of the nine representative dietary polyphenols tested, ( )-epigallocatechin (EGC), ( )-epigallocatechin gallate (EGCG), and gallic acid (GA) effectively inhibited HMG-CoA lyase activity. LineweaverBurk analysis revealed that EGC and EGCG are likely to be mixed-type noncompetitive inhibitors. Pyrogallol with the gallyl structure also inhibited HMG-CoA lyase activity, suggesting that the gallyl moiety of polyphenols is important for the inhibition of HMG-CoA lyase activity.Key words 3-hydroxy-3-methylglutaryl-CoA lyase; ketoacidosis; polyphenol; inhibition; (−)-epigallocatechin gallate Under normal conditions, glucose serves as the primary energy source in most human tissues. It is converted via glycolysis to pyruvate and then to acetyl-coenzyme A (CoA), which feeds into the tricarboxylic acid cycle to produce energy. During fasting and starvation on the other hand, ketone bodies converted from fatty acids are readily utilized as an energy source in the brain and muscular tissues. However, in patients with diabetes or soft drink ketosis-so-called "PET bottle syndrome"-which is caused by consuming excessive amounts of soft drinks in summer and/or after exercise, ketone bodies are overproduced due to impaired glucose metabolism.1-3) Long-term impairment of glucose metabolism induces ketoacidosis, which itself can induce a coma.
4)Fatty acid metabolism is activated when carbohydrate metabolism is impaired. Excess acetyl-CoA is generated from fatty acids by β-oxidation and is used for the formation of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) and subsequently acetoacetate. Some of the acetoacetate is converted to 3β-hydroxybutyrate through a reaction catalyzed by 3β-hydroxybutyrate dehydrogenase. In addition, acetoacetate is spontaneously converted into acetone by decarboxylation, albeit in small quantities. Acetoacetate, 3β-hydroxybutyrate, and acetone are ketone bodies, which in high levels lower the pH of blood and urine, resulting in ketoacidosis. Polyphenols are common and abundant dietary constituents with beneficial effects on human health. Recent research strongly...