Rate-limiting factors in the oxidation of ethanol by isolated rat liver cells

Meijer, Alfred J.; Woerkom, George M. Van; Williamson, John; Tager, J. M.

doi:10.1042/bj1500205

Cited by 108 publications

(33 citation statements)

References 19 publications

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“…The rate of ethanol oxidation by hepatocytes from fasted rats is a reflection of shuttle activities transferring reducing equivalents from NADH in the cytosol to the mitochondrial matrix [ 16]. Table 1 shows that ethanol oxidation was stimulated by epinephrine and that this stimulation persisted when the malateaspartate shuttle was blocked by aminooxyacetate or accelerated by the addition of lactate.…”

Section: Resultsmentioning

confidence: 99%

Catecholamine stimulation of ethanol oxidation by isolated rat hepatocytes

Ochs

Lardy

1981

FEBS Letters

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Section: Resultsmentioning

confidence: 99%

Catecholamine stimulation of ethanol oxidation by isolated rat hepatocytes

Ochs

Lardy

1981

FEBS Letters

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“…g-', which was almost doubled when ethanol was also present ( Table 1). This latter transfer rate is considerably less than the maximal hepatic shuttle capacity [27, 281 and can be accounted for on the basis of the loss of shuttle components by the isolated hepatocytes during their preparation [29].…”

Section: Glycolysis Ethanol Oxidation and Reducing-equivalent Transmentioning

confidence: 99%

“…Whilst isolated hepatocytes provide a very convenient preparation for studying the regulation of metabolic pathways, the cells when freshly prepared are deficient in shuttle components. Thus, although in this unmodified state they are a useful tool for demonstrating the consequences of limitation of shuttle capacity on metabolism [29], they do not accurately reveal the interactions of glycolysis and ethanol oxidation under physiological conditions where shuttle capacity is intact. During incubation the hepatocytes correct this deficiency in shuttle capacity over a period of 20-30 min [30, 361 but it can be rectified from the commencement of the incubation by inclusion of asparagine in the medium, since this restores shuttle capacity to normal [30].…”

Section: The Fate Of Glucose Not Glycolysed In the Presence Of Ethanolmentioning

confidence: 99%

The capacity of reducing‐equivalent shuttles limits glycolysis during ethanol oxidation

Berry

Gregory

Grivell

et al. 1994

European Journal of Biochemistry

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The inhibition of glycolysis during ethanol oxidation has been examined in isolated hepatocytes from fasted rats. Glycolytic flux was measured by determining the rate of release of tritium from [6-3H]glucose. During ethanol oxidation, the rate of glycolysis was inhibited 80% in freshly prepared hepatocytes, in which shuttle intermediates are depleted, but was depressed only about 20% in the presence of asparagine, a condition under which activity of the malate/aspartate shuttle was restored to normal levels. The inhibition of glycolysis was also partially released by addition of pyruvate and when alcohol dehydrogenase activity was depressed by 4-methylpyrazole. Titrations with this inhibitor revealed inverse linear relationships between the rates of glycolysis and ethanol oxidation. For any given rate of ethanol oxidation, glycolytic flux was lowest and the [lactate]/[pyruvate] ratio highest in the presence of aminooxyacetate, an inhibitor of the malatelaspartate shuttle, whereas flux was highest and the ratio lowest in the presence of asparagine. During these titrations with 4-methylpyrazole the inhibition of ethanol oxidation and concomitant restoration of glycolysis were accompanied by a decline in the [lactate]/[pyruvate] ratio, a substantial fall in the rate of reducingequivalent transfer from cytoplasm to mitochondria and an increase in lactate accumulation. These findings imply that the reducing equivalents generated during ethanol oxidation compete with those arising in glycolysis for transfer to the mitochondria. This competition leads to an inhibition of aerobic glycolysis, and at the same time contributes to a rise in cytoplasmic NADH and fall in NAD+ that results in depression of anaerobic glycolysis. Allosteric inhibition of 6-phosphofructo-1-kinase due to a decrease in the concentration of fructose 2,6-bisphosphate did not appear to play a primary role in the inhibition of glycolysis by ethanol. Ethanol oxidation had no effect on glucose phosphorylation as measured with [2-3H]glucose, but induced a substantial increase in cycling between glucose and glucose 6-phosphate.Although the depression of glycolysis associated with ethanol oxidation was reported 20 years ago [l], there remains some uncertainty as to the mechanism of ethanol action [l -41. The prevailing view is that ethanol oxidation brings about an inhibition of glyceraldehyde-3-phosphate dehydrogenase activity, due either to a limitation in the availability of NAD+ or to a direct inhibitory effect of NADH on the enzyme [l, 4, 51. The fall in NAD' and concomitant rise in NADH is considered to be a consequence of the accumulation of reducing equivalents in the cytoplasm as a result of Enzymes. 6-Phosphofructo-1-kinase (EC 2.7

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“…Hepatic ammonia production As shown in Table 1, ethanol also inhibited basal proteolysis, an effect indicating that intralysosomal proteolysis was directly inhibited. Ethanol has long been known to inhibit urea formation in the liver (Field et al, 1963;Meijer et al, 1975), and we considered the possibility that it might alter hepatic ammonia metabolism as well. We tested this possibility preliminarily by measuring the uptake of 125I-asialofetuin, a protein degraded exclusively by lysosomes (Ashwell & Harford, 1982), which has previously been shown to be inhibited by ammonia (Poso et al, 1982a).…”

Section: Results and Discussion Protein Degradationmentioning

confidence: 99%

Inhibition of intracellular protein degradation by ethanol in perfused rat liver

Pösö¹,

Surmacz²,

Mortimore³

1987

Biochemical Journal

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Ethanol (50 mM) inhibited proteolysis in the perfused rat liver during stringent amino acid deprivation and also in the presence of normal and 10 times normal concentrations of plasma amino acids. The concentration-response curve of ethanol reached a plateau after 5 mm in both the presence and the absence of normal plasma amino acids, suggesting inhibition by oxidation products of ethanol. Intracellular glutamine, tyrosine and proline increased in concentration with ethanol, but the increases were too small to explain the observed inhibition of proteolysis. The uptake of 1251-asialofetuin was slightly decreased and the output of ammonia increased in the presence of ethanol. These, together with a significant suppression of basal proteolysis in the presence of amino acids, suggest that lysosomal function was directly affected. Electron-microscopic examination of lysosomal components showed that the aggregate volume of autophagosomes (initial vacuoles) were significantly smaller in livers perfused with ethanol than in controls. However, the equivalent volume of autolysosomes (degradative vacuoles) was the same in both groups. According to these results, ethanol inhibits protein degradation in the liver by two discrete mechanisms: one decreasing the formation of autophagic vacuoles and the other involving lysosomotropic inhibition, possibly via ammonia.

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Rate-limiting factors in the oxidation of ethanol by isolated rat liver cells

Cited by 108 publications

References 19 publications

Catecholamine stimulation of ethanol oxidation by isolated rat hepatocytes

Catecholamine stimulation of ethanol oxidation by isolated rat hepatocytes

The capacity of reducing‐equivalent shuttles limits glycolysis during ethanol oxidation

Inhibition of intracellular protein degradation by ethanol in perfused rat liver

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