Ketone Bodies

KETONE BODIES

• Ketone bodies refers to three compounds acetoacetate, β- hydroxybutyrate, acetone.
• Ketone bodies produced in liver from acetyl CoA.
• Ketone Body Synthesis (Ketogenesis)-
•  Ketogenesis occurs when there is a high rate of fatty acid oxidation in liver which provides excessive acetyl CoA.
• Acetoacetyl CoA is the starting material from Beta oxidation.
• HMG CoA Synthase is the rate limiting step.

• HMG- CoA serves as the immediate precursor for acetoacetate.
• Acetoacetate is the primary ketone body.

Utilization of Ketone Bodies–

• Ketone bodies serve as fuel for extrahepatic tissues.
• Utilization of Ketone Bodies with the exception of Liver and RBCs.
• Acetoacetate and β-hydroxybutyrate are used in preference to glucose as energy source by certain tissues, e.g. heart, muscle and renal cortex.
• Brain also switches to using predominatly acetoacetate in starvation.
• In extrahepatic tissues, acetoacetate is activated to acetoacetyl-CoA by succinyl-CoA-acetoacetate CoA transferase or Thiophorase. (First step in ketone body utilization)

• Factors that inhibit lipolysis also ketogenesis.
• Ketogenic Hormone– Glucagon, glucocorticoids, growth hormone.
• Anti-Ketogenic hormone– Insulin 

Test for Ketone Bodies in Urine-

• Gerhardt’s Ferric Chloride- Acetoacetate
• Rothera’s Nitroprusside Test- Acetoacetate and Acetone

• Ketogenesis is usually associated with excessive fatty acid oxidation in starvation and Type I diabetes Mellitus.

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