Acetylcarnitine inhibits alcohol dehydrogenase

Area of Science:

• Biochemistry
• Nutritional Science
• Pharmacology

Background:

• Carnitine and acetyl-L-carnitine are widely used as dietary supplements and therapeutic agents.
• While carnitine affects ethanol metabolism in vivo, its in vitro effects on key metabolic enzymes are minimal.
• Previous observations suggested acetyl-L-carnitine might play a more significant role in ethanol metabolism than carnitine.

Purpose of the Study:

• To investigate the in vitro effects of acetyl-L-carnitine on enzymes involved in ethanol metabolism, specifically alcohol dehydrogenase (ADH) and the microsomal ethanol oxidizing system (MEOS).
• To elucidate the mechanism by which acetyl-L-carnitine influences ethanol oxidation.
• To identify potential interactions between acetyl-L-carnitine and other nutrients, such as niacin.

Main Methods:

• Isolated rat liver enzymes (ADH and MEOS) were assayed for activity in the presence and absence of acetyl-L-carnitine.
• Enzyme kinetics were analyzed to determine the nature of inhibition and calculate inhibition constants (Ki).
• The ratio of NAD to acetyl-L-carnitine was varied to assess concentration-dependent effects.

Main Results:

• Acetyl-L-carnitine significantly inhibited the activity of alcohol dehydrogenase (ADH), but not MEOS.
• The inhibition of ADH by acetyl-L-carnitine was found to be competitive with respect to NAD+.
• A competitive inhibition constant (Ki) of 135 mumol.L-1 was determined for acetyl-L-carnitine's interaction with ADH.

Conclusions:

• Acetyl-L-carnitine acts as a competitive inhibitor of alcohol dehydrogenase (ADH).
• This study reports a novel function for acetyl-L-carnitine, demonstrating its direct interaction with a key enzyme in ethanol metabolism.
• The findings highlight a unique nutritional interaction between acetyl-L-carnitine and niacin, impacting ethanol processing.