Steady-State Metabolism of Ethanol in Perfused Rat Livers Treated with Cyanamide: Quantitative Analysis of Acetaldehyde Effects on the Metabolic Flux Rates

17 de abril de 20154min
  1. Chung-Tay Yao1,2,*,
  2. Ching-Long Lai3 and
  3. Shih-Jiun Yin4

Article first published online: 1 APR 2015

DOI: 10.1111/acer.12701

http://onlinelibrary.wiley.com/doi/10.1111/acer.12701/abstract?campaign=woletoc&dmmsmid=93331&dmmspid=21805070&dmmsuid=2433555

 

Keywords:

  • Alcohol Dehydrogenase and Aldehyde Dehydrogenase;
  • Hepatic Influx and Efflux Rates;
  • Ethanol/Acetaldehyde/Acetate;
  • Steady-State Metabolic Rate;
  • Metabolic Flux Control

Background

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are principal enzymes responsible for metabolism of ethanol in mammals. The steady-state metabolic flux of ethanol has been poorly understood.

Methods

We investigated flux rates of the individual steps of ethanol metabolism in perfused rat livers treated with ALDH inactivator cyanamide as an attempt to mimic human ALDH2 deficiency commonly seen in East Asians. The net rates of ethanol oxidation, acetaldehyde oxidation, and acetate activation were determined with a set of defined equations, based on the set influx rates of ethanol and the measured efflux rates of ethanol, acetaldehyde, and acetate.

Results

After intraperitoneal injections of 0.2 and 1.5 mg/kg cyanamide, hepatic activities of mitochondrial ALDH2 and cytoplasmic ALDH1A1 decreased to a similar degree, that is, 51 to 57% and 69 to 74%, compared with the corresponding controls, respectively, whereas cytoplasmic ADH1 activity remained unchanged. At infusing 2 mM ethanol, acetaldehyde oxidation rate well matched (99%) the net ethanol oxidation rate in control liver. Both the ethanol and acetaldehyde oxidation rates were significantly decreased after cyanamide treatments. At 10 mM ethanol, the efflux acetaldehyde was significantly higher than that infusing 2 mM ethanol in both control and cyanamide groups. Seventy-eight percent of the oxidized ethanol released as efflux acetate. At 2 mM ethanol, the apparent flux control coefficients of ADH1 were assessed to be 0.78, 0.54, and 0.39, respectively, in control, low, and high cyanamide-treated livers. Kinetic simulations revealed that inhibition by acetaldehyde may largely account for the observed reduction of ADH1 oxidation rates after cyanamide treatment.

Conclusions

Our results provide the first flux evidence that ADH and ALDH are steps influencing steady-state metabolism of ethanol in rat livers with inactivated ALDHs.


Sobre a UNIAD

A Unidade de Pesquisa em álcool e Drogas (UNIAD) foi fundada em 1994 pelo Prof. Dr. Ronaldo Laranjeira e John Dunn, recém-chegados da Inglaterra. A criação contou, na época, com o apoio do Departamento de Psiquiatria da UNIFESP. Inicialmente (1994-1996) funcionou dentro do Complexo Hospital São Paulo, com o objetivo de atender funcionários dependentes.



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