Lecture 16 Alcohol I

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Lecture 16 Alcohol I
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Alcohol

• Chemically Ethanol (EtOH) Ethyl alcohol
• Energy contribution 29kJ/g (7kcal/g)
• no other nutrients with alcohol
• metabolized mainly in LIVER
• NO DIGESTION in SI
• absorbed intact, by simple diffusion
• 100 absorbed

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Structure of Alcohol molecule

• H H
• H C C OH
• H H
• Ethanol is the hydrocarbon in beer, wine
  spirits

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Metabolism

• EtOH distributed to aqueous (fluid) parts of body
• moves easily through cell membranes
• but denatures proteins in cell membranes
• damage of LIVER
• from protein denaturation of cell membranes
• GI cells have shorter ½ life ? turnover more
  quickly ? effectively less damage

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Metabolism

• Main ENZYME in EtOH metabolism Alcohol
  dehydrogenase (ADH)
• gender differences
• males have ADH in gastric mucosa (stomach lining)
• females have minimal ADH in gastric mucosa
• ? females have higher amount of alcohol reaching
  bloodstream liver c.f. males

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Metabolism

• Factors inhibiting ADH activity
• 1. antihistimine drugs
• more EtOH reaches brain due to ?EtOH breakdown
  (inhibited ADH activity)
• ? drunker quicker
• not worth taking antihistimines B4 drinking (to
  prevent hangover)

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Metabolism

• 2. chronic EtOH abuse
• includes binge drinking
• ? ADH activity
• alcoholics get more drunk than non-alcoholics
• CANNOT build tolerance to EtOH
• 3. Ageing
• ? age, ? ADH activity
• ? drunker quicker

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Metabolism

• Most EtOH consumed metabolised in liver
• small excreted via lungs, urine, sweat
• ? breathalyzer measures EtOH excreted through
  lungs
• estimation of blood EtOH
• directly quantitatively related

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Metabolism

• Rate of EtOH metabolism
• An example
• wt 70kg, male
• metabolises b/w 7-14g EtOH per hour
• ? 0.7-1.5 standard drinks/hour
• ? 100-200mg EtOH/kg body weight/hour
• a standard alcoholic drink

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Rate of alcohol metabolism

• when RATE EtOH consumption gt liver metabolic
  capacity
• ? blood alcohol
• intoxication symptoms appear as brain becomes
  exposed to ? EtOH

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Metabolism

• EtOH CANNOT be stored in the body
• EtOH 1st priority as a fuel source
• 3-pathways for EtOH metabolism
• a) alcohol dehydrogenase (ADH) pathway
• b) microsomal ethanol oxidising system (MEOS)
  excess EtOH metabolism pathway
• c) catalase (minor pathway)

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Metabolism

• 3-pathways of EtOH metabolism
• ADH in stomach (males) ADH MEOS in liver
  (males females)
• Catalse in liver (males females)

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Metabolism

• NOTE
• MEOS also involved in hepatic DRUG metabolism
• if MEOS mainly occupied with excess EtOH
  metabolism
• less MEOS available for drug metabolism
• if co-consumption of EtOH recreational drugs
  (eg. THC, Ecstasy), then ?? prolonged effect
  of the drugs ? potential drug overdose

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Metabolism

• product of EtOH metabolism
• ACETALDEHYDE
• (hangover)
• Alcohol dehydrogenase
• EtOH Acetaldehyde
• NAD NADH H
• (Vitamin B3 co-enzyme)

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Metabolism

• CoA
• Acetaldehyde ? Acetic Acid ? AcetylCoA
• NAD ?
• NADH H Krebs Cycle
• ?
• ATP synthesis

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Metabolism

• Is alcohol converted into FAT in the body?
• ? NADH may promote Fatty Acid synthesis, but most
  NADH is recycled to NAD
• because EtOH is converted directly to Acetyl CoA,
  C-atoms of alcohol not available
• ? cannot be converted into CHO or FAT
• BUT
• ? EtOH consumption ? fat oxidation
• ME FIRST oxidation

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Metabolism

• Euphoria
• the feelings of well-being associated with EtOH
  consumption
• binding of EtOH molecules to Endorphin receptors
  in brain
• EtOH binding with endorphin receptors stimulates
  release of Dopamine in brain cells
• Dopamine neurotransmitter ? euphoria

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Recommended Reading

• 1. Whitney Rolfes
• Understanding Nutrition
• Chapter 7. Highlight. Alcohol and Nutrition. pp
  240-249
• 2. German, J.B. Walzem, R.L. (2000)
• The Health Benefits of Wine
• Ann. Rev. Nutr. 20, 561-93