Title: BV2 / BV2 - 2 / Modul 7 / Well-fed and fasting states

Q: Which organs are involved in the regulatory network of 4 key organs=
A: There are 4 that play a major role
- Liver
- Adipose tissue
- Muscle
- Brain

Q: What might the 4 key organs do?
A: They might use substrates produced by other tissues

Q: On which 3 levels does regulation take place?
A: he regulation takes place at 3 different levels
- Endocrine - hormones - glukagon/insulin
- Neurocrine with epinephrine and norepinephrine
- Availability of various circulating substrates

Q: What can be said about the enzymatic properties of each organ?
A: Each organ contains a unique combination of enzymes

Q: What do the 4 key tissues in the metabolic regulatory network contain?
A: These tissues contain unique sets of enzymes that are involved in the generation, usage or storage of specific fuels

Q: When does the body store energy?
A: The body stores energy when food is abundant, to be used during fasting and survival situations, such as starvation, trauma or stress

Q: What is triggered when glucose levels are high?
A: When glucose is high it triggers the secretion of insulin

Q: What will the glucose be used by?
A: The glucose will be  used by the fat, muscle, brain, liver

Q: How will the liver respond to high glucose levels?
A: The liver will respond by increasing glycogenesis and lipid synthesis, while decreasing gluconeogenesis

Q: What is the point of the processes activated at high glucose levels?
A: To normalize the blood glucose levels

Q: What will low glucose levels trigger
A: Low blood glucose levels will trigger the synthesis and secretion of glucagon from the pancreas

Q: What will happen in the peripheral tissues at low glucose levels?
A: In the peripheral tissues there will be a breakdown of glycogen and fat storages

Q: What will happen in the liver at low glucose levels?
A: In the liver glycogen breakdown will increase, there will be an increase in hepatic glucose production (gluconeogenesis), there will also be lipid mobilization and ketone body production

Q: What is the point of the processes initiated at low glucose levels?
A: All to restore the blood glucose levels

Q: What is the absorptive/WF state characterized by?
A: This state is characterised by the increase in plasma Glu, AAs and TAG

Q: What happens in our body after a meal?
A: After a meal we get a peak in blood glucose as well as an increase of the secretion of insulin in the blood and a decrease in the secretion of glucagon

Q: What does the pancreas do in response to high glucose and GI secreted incretin?
A: Secrete more insulin and less glucagon

Q: What is the metabolic response of the body to high glucose levels dominated by?
A: The metabolic response of the body is dominated by changes in the metabolism of liver, adipose tissue, skeletal muscle and brain

Q: How long after a meal is the absorptive state reached?
A: 2-4h after food

Q: What regulatory mechanisms are there regarding nutrients and their metabolism?
A: 1. Availability of substrates
2. Allosteric effectors
3. Covalent modifications
4. Transcription regulation - induction or supression of the synthesis of enzymes

Q: How long does it take for availability of substrates to have a regulatory effect?
A: Minutes

Q: How long does it take for allosteric effectors to have a regulatory effect?
A: Minutes

Q: How long does it take for Covalent modifications to have a regulatory effect?
A: Minutes to hours

Q: How long does it take for transcription regulation to have a regulatory effect?
A: Hours to days

Q: What do the regualtory mechanisms ensure during the WF state?
A: During the well-fed state the mechanisms ensure that nutrients are captured as glycogen, TAG and proteins

Q: What do the regualtory mechanisms ensure during the fasting state?
A: The mechanisms ensure that nutrients from storages will be made available and used

Q: What is meant by covalent modification?
A: Phosphorylation

Q: In which state are the principal regulatory mechanisms used?
A: The regulatory mechanisms in both states, well-fed as well as fasting, are the same

Q: Which nutrients does the liver absorb?
A: - Carbohydrates (glucose)
- Lipids (chylomicron remnent)
- Amino acids

Q: What happens to the nutrients in the liver?
A: There the nutrients are metabolized, stores or forwarded to other tissues

Q: What is the anatomical position of the liver?
A: The liver is situated in the central part of the body and receives blood from different organs such as the spleen, pancreas gallbladder, GI tract through the portal vein

Q: How is glucose taken upp in the liver?
A: Glucose uptake by insulin-independent GLUT-2

Q: What happens in the liver at high blood glucose levels?
A: 1. Glucose uptake by insulin-independent GLU-2
2. The rise in glucose allows phosphorylation by glucokinase, which has a high Km for glucose
3. Glycogen synthase is activated covalently (dephosphorylated) and allosterically, by glucose-6-phosphate
4. Glucose-6-P availability stimulates the pentose phosphate pathway, providing NADPH for fatty acid synthesis
5. Activation of pyruvate dehydrogenase favours acetyl-CoA production
6. TCA cycle inhibition at isocitrate dehydrogenase allows use of acetyl-CoA in fatty acid synthesis
7. Glycolysis provides the glycerol backbone for TAG synthesis
8. Acetyl-CoA carboxylase is activated covalently (dephosphorlated) and allosterically by citrate

Q: Which processes connected to glucose metabolsim take place in the liver at high glucose levels?
A: 1. Active glukokinase
2. Glycogen synthase active
3. Active HMP-shunt (PPP)
4. PDH active, acetyl-CoA is formed

Q: Which processes connected to lipid metabolsim take place in the liver at high glucose levels?
A: 5. TCA inhibited -> more acetyl-CoA goes to fatty acid synthesis
6. TAGs -> VLDL export

Q: Which processes connected to protein metabolsim take place in the liver at high glucose levels?
A: Amino acids, high uptake -> protein synthesis

Q: What happens to branched amino acids?
A: The branched chain aa pass through the liver and will not be uptaken here, instead they will be uptaken in the muscles

Q: What can be said about the liver's relation to glucose?
A: The liver is more of a glucose producing organ rather than a glucose user

Q: Which transporter is used to uptake glucose in the liver?
A: Glucose is uptaken to the level through the GLUT-2 transporter

Q: What can be said about GLUT-2's affinity in relation to GLUT-4?
A: GLUT-2 has a slightly higher Michaelis constant (Km) than
GLUT-4

Q: What does carbohydrate metabolism in the liver look like after a meal containing carbs?
A: 1. Increase in Glucose-P
2. Increased glycogenesis
3. Increased PPP activity
4. Increased glycolysis
5. Decreased glucose production

Q: How will there be an increase in glucose-P in the liver after a carb rich meal?
A: Due to glucokinase

Q: How will there be an increase in glycogenesis in the liver after a carb rich meal?
A: Glu-6P -> glycogen is favoured by activation of glycogen synthase

Q: How will there be an increase in the PPP in the liver after a carb rich meal?
A: Glu-6P and active use of NADPH

Q: How will there be an increase in glycolysis in the liver after a carb rich meal?
A: - Ins/glucagon ratio + Glucose conversion to pyruvate due to upreglation of key enzymes (glucokinase, PFK-1, Pyruvate kinase)
- PDH converts pyruvate to acetyl-CoA that is then used in:
- FA synthesis
- Oxidised for energy in TCA cycle

Q: How will there be an decrease in glucose production in the liver after a carb rich meal?
A: Decreased gluconeogenesis and/or glycogenolysis avoiding hyerglycemia
- As acetyl-CoA is used to generate FA, pyruvate carboxylase is mostly inactive
- HIgh ins/glucagon ratio favours inhibition of gluconeogenic enzymes, such as 1,6-bisphosphatase
- Glycogenolysis is inhibited by glycogen phosphorylase and glycogen phosphorylase Kinase

Q: What is glycogenolysis inhibited by?
A: Glycogenolysis is inhibited by glycogen phosphorylase and glycogen phosphorylase Kinase

Q: In what state is ACC active?
A: ACC is active when dephosphorylated

Q: Which processes connected to lipid metabolism will take place in the liver during the WF state?
A: - Increased FA synthesis
- Increased TAG synthesis

Q: What is FA synthesis a source of?
A: - Source of cytosolic acetyl-CoA
- Additional source of NADPH

Q: What is the pirmary site in the body of de novo FA synthesis?
A: The liver

Q: What happens in the liver at a WF state regarding FA synthesis?
A: De novo FA synthesis is favoured by presence of  acetyl-CoA and NADPH and is activated by ACC, which catalyses the formation of malonyl CoA from acetyl-CoA

Q: What happens when the TCA is active?
A: When the TCA is active more ATP is produced, citrate accumulates, leaves the mitochondria and goes to the cytosol where it is cleaved producing Acetyl-CoA

Q: When is additional NADPH formed?
A: Is formed when OAA is reduced to malate and then oxidated to pyruvate via malic enzyme

Q: What is increased TAG synthesis favoured by during the WF state?
A: - Favored by the increase of fatty acyl CoA, from de novo synthesis and from TAG from the chylomicron remnants
- Glycerol-3-P (backbone of TAG) is provided by glycolysis
- Endogenous TAG is packed in VLDL particles and secretetd to the blood to be used by other tissues

Q: Where does fatty acyl CoA come from?
A: from de novo synthesis and from TAG from the chylomicron remnants

Q: What is increased AA degradation a result of?
A: Increased AA degradation is due to the fact that there are more AAs in the liver than what's really needed

Q: What happens to the processes of amino acid metabolism in the liver during the WF state?
A: - Increased AA degradation
- Increased protein synthesis

Q: Why does AA degradation increase in the liver during the WF state?
A: There are more aa there than needed and since aas are not stored they are either released to the blood to be used by other organs via deamination, while the crabon skeletons will be degraded to pyruvate, acetyl-CoA or TCA cycle intermediates
- These metabolites can be oxidised for energy or in FA synthesis

Q: Which amino acids are branched?
A: - Leucine
- Isoleucine
- Valine

Q: Where are branched amino acids being metabolized in the body?
A: In the muscles

Q: What happens to protein synthesis during the WF state?
A: In the WF state, hepatic protein synthesis increases, replacing degraded proteins during previous fasting - there is no protein store in our bodies to produce energy (as glycogen or TAG)

Q: Which processes occur in adipose tissue during the WF state?
A: 1. Increased glucose transport
2. Increased glycolysis
3. Increase in PPP activity -> NADPH
4. Lipogenesis from Acetyl-CoA
5. Exogenous FA from chylomicrons (diet) and endogenous FA ffrom VLDL (liver)
6. TAG syntesis

Q: Which processes regarding carbohydrate metabolism occur in adipose tissue during the WF state?
A: - Increased glucose transport
- Increased glycolysis
- Increase in PPP activity -> NADPH

Q: Which processes regarding lipid metabolism occur in adipose tissue during the WF state?
A: - Lipogenesis from acetyl-CoA
- Exogenous FA from chylomicrons (diet) and endogenous FA from VLDL (liver)
- Tag synthesis

Q: What is LPL regulated by?
A: Insulin

Q: What does high insulin and glucose result in in the WF state in adipocytes?
A: IN the WF state high Glucose + high Insulin -> storage of TAG

Q: What does insulin favour in the adipocytes?
A: Favors the dephosphorylation of HSL (inactive), inhibiting lipolysis of the stored TAG

Q: How much of the total body mass do skeletal muscles constitue?
A: 40%

Q: What do muscles use as fuel?
A: AA, Glu, FA, KB

Q: Which processes occur in in skeletal muscles at rest in the WF state?
A: 1. Increased glucose transport by GLUT4 (for energy and protein synthesis)
2. Increased glycogenesis
3. Increased BCAAs uptake
4. Increased protein synthesis

Q: How is glucose transported into the muscles?
A: By GLUT4

Q: Which fuel is the primary source in muscles at rest in the WF state?
A: In WF at rest FA are secondary, while glucose is the primary source of energy

Q: Which fuel is the primary source in cardiac muscle at rest in the WF state?
A: In cardiac muscle LPL is always secreted and FA constitutes 50-60% of the fuel used but can increase to +-90% in a fasting state

Q: What is the primary source of fuel in cardiac muscle?
A: Fatty acids (50-60% at rest at WF)

Q: What is consumption of O2 at rest in WF of skeletal muscle?
A: 25%

Q: What is consumption of O2 during high physical activity in WF of skeletal muscle?
A: +- 90%

Q: Which type of glucose transporter does skeletal muscle contain?
A: Muscle contains insulin-sensitive GLUT4

Q: Why is there increased protein synthesis after a meal at WF in skeletal muscle?
A: After a protein rich meal, more AAs are uptaken, and protein synthesis can then replace degraded proteins

Q: What happens in the renal medulla regarding metabolism?
A: Metabolism is limited due to relatively low oxygen supply (anaerobic environment) and anaerobic glycolysis dominates
- Glucose -> lactate

Q: What happens in the renal cortex regarding metabolism?
A: The cortex is an aerobic environment in which glucose, FA, and lactate can be converted into acetyl-CoA that enters the TCA

Q: How much of the basal O2 consumption occurs in the brain at rest?
A: 20%

Q: What is needed of substrates that provide energy to the brain?
A: Substrates should cross BBB to provide energy

Q: What does the brain use as fuel in the WF state?
A: At WF the brain only uses glucose as fuel

Q: Which glucose transporter exists in the brain?
A: GLUT-1 transporter, which is insulin-independent and with a low Km

Q: Are there glycogen storages in the brain?
A: No

Q: What happens if glu levels are <50mg/dl?
A: Cerebral function is impaired

Q: Are there TAG and FA storages in the brain?
A: No

Q: What does the brain do with glucose?
A: The brain completely oxidises glucose to carbon dioxide and water

Q: How much of the basal glucose consumption occurs i the brain?
A: 20% of the basal glucose consumption of the body takes place in the brain

Q: In which of the 4 key regulating organs is glucose taken up?
A: Glucose is uptaken in all the organs: liver, adipocyte, brain, muscle

Q: In which organ are lipids mostly absorbed?
A: Fat is mostly absorbed in the adipocyte and in the liver which makes VLDL which go to the adipose

Q: Where will FA be metabolized?
A: FA will be metabolised in the liver and muscles

Q: What is the definition of the fasting or postabsorptive state?
A: Fasting starts after the absorptive period - around 4h after the last meal

Q: Which 2 categories can fasting be divided into?
A: Can be both voluntary (diet) or involuntary (lack of food)

Q: How is the Wf state and fasting state connected?
A: In the well-fed state the body has an energy storage that is ready to be used in the fasting state

Q: Which components does the energy storage consist of?
A: - Fat
- Protein
- Glycogen

Q: For how long does the fat storage last?
A: 15kg=135000 kcal = 2 months

Q: How much fat do we have stored?
A: 15kg

Q: How much protein do we have stored?
A: 6kg

Q: How much glycerol do we have stored?
A: 0.2kg - 800 kcal

Q: What happens to the levels of nutrients in the blood during the fasting state?
A: During this period there is a decrease in plasma levels of glucose, TAG and aa

Q: What will there be a decrease in during the fasting state?
A: - Decrease in plasma levels of glu, TA and AA
- Decrease in insulin (I) secretion
- Decrease in I/crh ratio - circulating substrate

Q: What will there be an increase in during the fasting state?
A: Increase in glucoagon secretion, epinephrine and cortisol (crh= counter regulatory hormones)

Q: What happens during the catabolic period?
A: Degradation of TAG, glycogen and proteins

Q: What is there an exchange between in the fasting state?
A: As in the WF state, there is an important exchange of substrates among liver, adipose tissue, skeletal muscle, and the brain

Q: What are the body's priorities in the fasting state?
A: To keep an adequate level of circulating glucose to maintain energy levels in critical organs (Brain, RBC) and peripheral requirements as well as to generate ketone bodies to spare proteins

Q: What are the enzymatic changes during the fasting period?
A: The flow of intermediates between organs is controlled in the same way as in the WF state by 4 mechanisms
- Availability of substrates
- Allosteric regulation of enzymes
- Covalent changes of enzymes
- Induction or repression of enzyme synthesis

Q: What are most of the enzymes in the WF state?
A: Active when dephosphorylated

Q: What are most of the enzymes in the fasting state?
A: Activated when phosphorylated

Q: Which 3 enzymes are activated when phosphorylated in the fasting state?
A: - HSL
- Glycogen phosphorylase
- Glycogen phosphorylase kinase

Q: Which processes do the substrates come from in the fasting state?
A: - Glycogenolysis
- Lipolysis
- Proteolysis

Q: What is the main goal of the liver during fasting?
A: Main goal is to ensure:
- Blood glucose via glycogenolysis adn synthesis of new glucose via gluconeogenesis
- Synthesis of ketone bodies

Q: What happens in the liver during fasting?
A: 1. Glycogen phosphorylase and phosphorylase kinase are phosphorylated and active
2. Activation of fructose-2,6-bisphosphatase favors gluconeogenesis
2. NADH from beta-oxidation inhibits the TCA cycle, pushing acetyl-CoA to ketogenesis
2. Glucose-6-phosphatase generates free glucose
3. Low malonyl CoA levels allows for beta-oxidation. The acetyl-CoA product activates pyruvate carboxylase adn inhibits pyruvate dehydrogenase, thereby pushing pyruvate to gluconeogenesis
4. Liver lacks thiophorase, preventing use of ketone bodies

Q: Which processes occur in the liver during fasting, regarding carbohydrate metabolism?
A: - Increased glycogenolysis
- Increased gluconeogenesis

Q: What can be said about the increased glycogenolysis in the liver during fasting?
A: I/Glucagon ratio - decrease
- Activation of glycogen phosphorykinase and glycogen phosphorylase

Q: When is glycogenolysis favored?
A: During shorter periods of fasting between meals

Q: When is gluconeogenesis favored?
A: During longer periods of fasting, like over night

Q: What is key in the liver during fasting periods?
A: Hepatic glucose synthesis (gluconeogenesis) is key during short and long periods of fasting

Q: From what are the carbon skeletons for gluconeogenesis derived?
A: from glucogenic AA and lactate from muscle and glycerol from adipose tissue

Q: Which processes occur in the liver during fasting, regarding lipid metabolism?
A: - Increased FA oxidation
- Increased synthesis of ketone bodies - ketogenesis

Q: From where does the major source of energy for the liver come from?
A: The oxidation of FA from TAG degradation in adipocytes

Q: What does acetyl-CoA do in the fasting state?
A: Acetyl-CoA activates PC and inhibits PDH favoring use of pyruvate in gluconeogenesis

Q: What supplies the energy for gluconeogenesis?
A: Oxidation of NADH and FADH2 with oxidative phosphorylation

Q: Where are KBs used?
A: KBs is the fuel for many tissues, important for the brain

Q: When does ketogenesis start?
A: Ketogenesis starts in the first days of fasting and it reduces the need for gluconeogenesis from AA skeletons (preserving essential proteins)

Q: What happens in the liver during fasting, summary?
A: 1. Glycogen phosphorylase is active and glycogen is broken down into glucose-6-phosphate
2. Glucose-6-phosphatase converts glucose-6-Phosphate into free glucose for export
3. Low levels of malonyl CoA allows for B-oxidation
4. Inhibition of TCA, due to NADH, favours ketone body formation

Q: How is glucose intake to adipocytesreduced during fasting?
A: Glucose intake via GLUT4 is reduced due to low levels of insulin - decreased TAG synthesis

Q: Which processes are favored in the adipocytes during fasting?
A: 1. Increased lipolysis
2. Increased FA release
3. Decreased FA uptake

Q: Why does lipolysis increase in adipose during fasting?
A: There will be an increase in catecolamines (NE;E) which leads to the activation of HSL

Q: Why will there be a decrease in FA uptake to the adipocytes during fasting?
A: Low uptake of circulating FA due to low LPL activity in fasting - FA will move to other organs

Q: What occurs in resting skeletal muscles during fasting regarding carb metabolism?
A: There will be a low hepatic glucose uptake (GLUT4)

Q: What occurs in resting skeletal muscles during early fasting regarding lipid metabolism?
A: Usage of FA from adipose tissue and KB from the liver

Q: What occurs in resting skeletal muscles during long fasting regarding lipid metabolism?
A: Decrease in usage of KB (spared for the brain) - E's effect on LPL expression

Q: What occurs in resting skeletal muscles during early fasting regarding amino acid metabolism?
A: Quick proteolysis providing AA (Alanine, Glutamine) to liver

Q: What is proteolysis initiated by in the early fasting state?
A: Proteolysis in initiated by a decrease in insulin and increase in glucocorticoids

Q: What occurs in resting skeletal muscles during long fasting regarding AA metabolism?
A: Muscle proteolysis is reduced to spare muscle tissue

Q: What is used as fuel in skeletal muscle during exercise?
A: - Creatine phosphate
- Glycogen storages

Q: What occurs in the brain during early fasting regarding carb metabolism?
A: The brain uses only glucose as fuel, blood glucose levels are ensured by hepatic gluconeogenesis

Q: What occurs in the brain during prolonged fasting regarding carb metabolism?
A: Circulating KB increase, replacing glucose as the primary fuel for the brain

Q: What does prolonged fasting count as?
A: 2-3 weeks

Q: During which feeding state does the kidney have an important role?
A: The kidney has a very important role during long periods of fasting

Q: What happens in the kidney during long periods of fasting?
A: In the acidic environment due to KB, the kidney takes up the glutamine released by the muscle metabolism (BCAA) and transforms it to a-ketoglutarate (substrate for gluconeogenesis) plus ammonia (NH3)
NH3 picks up at proton from KB degradation and ammonium (NH4) is formed and eliminated via the urine

Q: How much of the gluconeogenesis in the body occurs in the kidney in the later stage of fasting?
A: 50%

Q: What happens in the renal cortex during fasting?
A: FA and KB are converted into acetyl CoA -> TCA

Q: What can low blood glucose affect in the brain?
A: There are effects on the hypothalamus and regulatory centres, e.g. the ANS

Q: What are some processes that insulin inhibits?
A: - Glycogenolysis
- Gluconeogenesis
- Ketogenesis
- Lipolysis

Q: What are some processes that glucagon and epinephrine stimulate/activate?
A: + Glycogenolysis
+ Gluconeogenesis
+ Ketogenesis
+ Lipolysis

Q: What is meant by protein turnover?
A: Most proteins in the body are constantely synthesized and then degraded

Q: What happens in the liver regarding protein turnover during the WF state?
A: In the WF state the liver regenerates proteins that have been degraded during the previous cycle

Q: What happens to protein turnover during fasting?
A: During fasting the body attempts to avoid destruction of proteins (structural proteins)

Q: How does protein degradation work, 2 ways?
A: 1. The ATP-dependent ubiquitin (Ub) - proteasome system of the cytosol degrades damaged or short-lived proteins
2. The ATP-dependent degradative enzyme system of the lysosomes degrades intracellular proteins (autophagy) and extracellular proteins (heterophagy) that are taken into the cell by endocytosis

Q: What does the Ubiquitin-proteasome system do?
A: The ATP-dependent ubiquitin (Ub) - proteasome system of the cytosol degrades damaged or short-lived proteins

Q: How does the lysosome degrade proteins?
A: The ATP-dependent degradative enzyme system of the lysosomes degrades intracellular proteins (autophagy) and extracellular proteins (heterophagy) that are taken into the cell by endocytosis

Q: How does protein degratation with Ub-proteasomes work?
A: 1. Protein selected for degradation is tagged with molecules of ubiquitin (an ATP-dependent process)
2. Ubiquitinated proteins are recognized by the cytosolic proteasome, which unfolds, de-ubiquitinates and transports the protein to its proteolytic core (also an ATP-dependent process)
3. Peptide fragments produced by the proteasome are degraded to amino acids in the cytosol

Q: What can metabolic conditions be affected by?
A: - Genetics
- Microbiota
- Time of the day
- Diseases
- Cancer
- Diabetes
- Lifestyle
- Alcohol