Brown and beige fats thermogenesis

FNN200

Types of fat depots in humans

• White adipose tissue

  • Subcutaneous and visceral

• Brown Adipose

  • thermogenesis

• Beige fats

  • White fat that converts to brown under thermogenic stimuli 

  • also thermogenesis

White adipose tissue

• Subcutaneous

  • under the skin

• Visceral

  • around internal organs

    • more pro-inflammatory and assocaited with insulin resistance)

• Energy storage, endocrine organ, thermal insulation

Beige adipose 

• white fat that converts to brown under specific thermogenic stimuli (cold, sympathetic nervous activation)

• thermogenesis 

Components of energy expenditure

• Basal metabolic rate

• thermic effect of food 

• energy expenditure of physical activity 

• thermoregulation 

Brown adipose tissue - BAT

• lots in newborns, hibernating animals 

  • heat generation because newborns cannot shiver 

• Decreased in adults 

  • F have more than M

• Associated with 

  • Improved glucose metabolism

  • insulin sensitivity

  • lower prevalence of cardiometabolic diseases 

  • lower overal adiposity (lower overall fats)

Makeup of White adipocyte 

• LD morphology

  • Unicellular (one big lipid)

• Mitochondrial density

  • low

• UCP1 Expression

  • Negative (does not have the uncoupling protein)

Brown adipocyte make up

• LD morphology

  • Multilocular → many lipids 

• Mitochondrial density 

  • High 

• UPC1 expression 

  • Positive 

Beige adipocyte makeup 

• LD morphology 

  • Multilocular

• Mitochondrial density 

  • Medium 

• UPC1 expression 

  • positive 

Thermogenesis of brown fats

• heat production

• Stimuli 

  • Cold exposure → signal through sympathetic nervous system 

  • diet induced 

    • 5-15% of daily energy expenditure 

    • SNS activation → epinephrine 

  • Exercise

    • conflicing evidence

uncoupling protein (UCP1) and thermogenesis

• goes through the electron transport chain but hydrogen cannoy go throguh the atp-synthase so instead it goes throguh the UPC1 and makes heat 

• relies on lipids 

• mobilizes and oxidizes lipids (circulating TGs and fatty acids) to produce heat instead of storage of heat

Characteristics of individuals with more brown adipose tissues

• reduced prevalence of cardiometabolic disease 

  • T2DM, coronary artery disease, CVD and hypertension 

• better lipid profile

  • lower TG 

  • higher HDL

• Lower blood glucose

• Effects are more pronounced in individuals who are overweight or obese 

Alcohol metabolism

• Ethanol is a structure that resembles CHO but is metabolized more similar to a lipid 

• Enzyme 

  • Alcohol dehydrogenase (ADH) system 

• goes from ethanol to acetaldehyde 

  • breaks down small amounds of alcohol 

• Large amounts of alcohol 

  • goes throguh microsomal ethanol oxidizing system

  • this would be the system in alcoholics but we dont talk about this here

Liver alcohol and liver fat storage

IN CYTOSOL

• Ethanol → Alcohol dehydrogenase → Acetaldehyde

  • goes to mitochondria for oxidation

  • becoes acetyl CoA whcih can either go to become Fat or to TCA cycle for energy

• The process creates NADH

Alcohol and NADH

• High NADH ratio inhibits the TCA cycle

  • creates a buildup of Acetyl CoA → fatty acid synthesis → creates fatty liver

Impact of alcohol on metabolism

• Moderate

  • Increased HDL

  • decreased

    • LDL oxidation, blood clotting, platelet aggregation, homocysteine, cell aggregation 

  • Overall beneficial 

• Excessive 

  • INcreased

    • Aceraldehyde, oxidative stress, triglycerides, cell aggregation, reactive species

  • decreased HDL

  • OVerall detrimental to health

Canadian guidelines on alcohol and health

• 0 drinks is no risk

• 1-2 is low risk 

• 3-6 is moderate risk 

  • cancer risk increased 

• 7+ 

  • heart and stroke risk increased 

  • each additional drink increases the risk of alcohol related consequences