Biochem 7 Flashcards
1
Q
classes of lipids
A
- free fatty acid (nonsterified fatty acid)- carboxylic acid group and acyl chain
- can have one or more double bond but they are always cis
- triglyceride- 3 fatty acid attached to glycerol (3 carbons) via ester bonds
- cholesterol- hydrophobic and free hydroxyl group that gives it polarity
- if you conjugate the hydroxyl with a fatty acid -> forms a cholesteryl ester
- cholesteryl ester- highly hydrophobic (loses polarity)
2
Q
fatty acid nomenclature
A
- carboxylic acid chain is the first carbon
- alpha carbon- second carbon
- beta carbon- third carbon
- gamma carbon- fourth carbon
- omega carbon- last carbon
- if there is a double bond three carbons away from the omega end -> omega 3 fatty acid
3
Q
adipose tissue
A
- major storage site for lipids:- triglycerides
- adipocytes- major cell type of adipose tissue (lipid storage)
- *endocrine organ- regulate metabolism, inflammation, energy balance
- releases hormones- leptin
- white bc they are filled with fats- lipid droplet
4
Q
fasting state
A
- high glucagon
- high glycogenolysis
- high gluconeogenesis
- high fatty acid oxidation
- low glycolysis in liver
- low glycogenesis
- low fatty acid biosynthesis
5
Q
fed state
A
- high insulin
- high glycolysis
- high glycogenesis
- high fatty acid biosynthesis
- low glycogenolysis
- low gluconeogenesis
- low fatty acid oxidation
6
Q
control of food intake (satiety/hunger)
A
- why are we hungry?
- low blood sugar
- empty stomach
- hormonal control:
- ghrelin
- leptin
7
Q
ghrelin
A
- peptide hormone released by stomach
- travel in the blood to the hypothalamus of the brain to stimulate food intake
- before a meal ghrelin levels rise
- after a meal ghrelin levels fall and then increase
8
Q
leptin
A
- hormone released predominantly by adipose tissue
- acts in the hypothalamus of the brain to reduce feeding
- tell us we are full
- chronically elevated in people who are obese
- theory of leptin resistance- obese become desensitized to effects of leptin due to chronically elevated leptin levels
9
Q
leptin deficiency
A
- obesity
- after being treated with leptin -> body weight returns to normal
10
Q
lipid digestion: small intestine
A
- primarily small intestine
- dietary triglycerides are metabolized to monoglycerides and free fatty acids
- free fatty acids, monoglycerides, and cholesterol is absorbed by intestinal cells
11
Q
triglycerides
A
- highly hydrophobic
- pack into large lipids globules
- acyl chains face out -> hydrophobic
- no polar or charged surfaces
- makes it hard to digest -> bile salts
12
Q
bile salts emulsify lipids
A
- synthesized by liver
- stored in gall bladder
- released into the small intestine
- aids in lipid digestion
- makes triglyceride globules smaller and increases SA -> enzymes act on this
- bile salts are derivatives of cholesterol and have highly charged groups
- amphipathic
13
Q
triglyceride hydrolysis by pancreatic lipase
A
- pancreatic lipase enzyme is secreted by the pancreas
- hydrolyzes triglycerides into 2 fatty acids and 2 monoacylglycerol (MAG) in the small intestine
- cleaves triglyceride at the 1 and 3 position
14
Q
summary of triglyceride metabolism and absorption
A
- consume fats -> globules
- mix will bile salts to form smaller globules -> increase SA
- pancreatic lipase can hydrolyze easier -> releases monoacylglycerols and fatty acids
- absorbed by the intestinal cells
15
Q
what happens if you inhibits pancreatic lipase
A
- you cant absorb triglycerides if you cant cleave them
- drugs have targeted this to induce weight loss -> but if we cant absorbs fats -> oily stools
16
Q
intestinal cells
A
- fatty acids and monoglycerides are resynthesized back into triglycerides after absorption
- triglycerides and cholesterol is packaged into chylomicrons and shipped into blood
17
Q
triglycerides and cholesterol ester synthesis in intestinal cells
A
- monoacylglycerol is converted back to triglyceride by adding fatty acids back to the 1 and 3 position
- cholesterol that was absorbed is converted to cholesteryl esters (hydrophobic!)
18
Q
chylomicron synthesis
A
- chylomicrons allow large quantities of hydrophobics like cholesteryl esters and triglycerides in intestinal cells to be transported through blood
- triglycerides are packaged alongside cholesterol and cholesteryl esters into chylomicrons
- densely packed core of triglycerides and cholesteryl esters (highly hydrophobic) -> these are then surrounded by a phospholipid monolayer
- phospholipid monolayer- one layer of phospholipid with the head groups (charged, soluble) are on the outside and the tail (hydrophobic) are in the inside
- shields from the aqueous environment -> solubilized
- allows hydrophobics to be soluble in water
- free cholesterol is embedded in the phospholipid monolayer -> free cholesterol has a free charged hydroxyl group that allows this
- proteins coating the surface of the chylomicrons
19
Q
two fates of chylomicrons
A
- chylomicrons have two fates in the blood: use energy immediately or store it
- within the blood stream chylomicrons will be acted upon by a lipoprotein lipase protein
- lipoprotein lipase is embedded in capillaries that are surrounded adipose, fat or muscle tissue
- lipoprotein lipase will cleave triglycerides within the chylomicron back into monoglycerides and fatty acids -> taken up my muscle tissue for energy use or lipocytes for energy storage
20
Q
lipoprotein lipase (LPL)
A
- enzyme that lines the endothelium (lumen) of capillaries surrounding adipose and muscle tissue
- enzyme is never free floating -> its is localized and tethered to walls
- cleaves the triglycerides within the chylomicrons in the blood
- cleaves triglycerides within chylomicrons at the 1 and 3 positions to generate free fatty acids (FFA) and 2-monoacylglycerols
- free fatty acids and monoglycerides are taken up my muscle tissue for energy or by adipose tissue for storage
21
Q
GPIHBP1 anchors lipoprotein lipase
A
- GPIHBP1 is a binding partner for lipoprotein lipase
- it is tethered to the capillary wall
- has an acidic domain that interacts with lipoprotein lipase and the chylomicron
- the chylomicron and the LPL dock next to each other -> starts to cleave the triglycerides of the chylomicron
- GPIHBP1 anchors lipoprotein lipase to the endothelium of capillaries surrounding adipose and muscle tissue
- enzyme is never free floating -> it is localized
22
Q
chylomicron remnants are taken up by the liver
A
- chylomicrons are filled with triglycerides and cholesteryl esters -> LPL cleaves triglycerides -> monoglycerides and fatty acids
- adipose tissue take up for storage
- muscle tissue takes up for energy use
- LPL doesnt cleave cholesteryl esters -> make up the chylomicron remnants (some triglycerides too)
- liver takes up chylomicron remnants (cholesteryl esters)
23
Q
what would you expect to occur in individuals deficient in lipoprotein lipase
A
- chylomicrons build up
- lipoprotein lipase deficiency
- rare- 1-2 cases/million
- elevated chylomicrons -> elevated triglycerides and cholesterol
- causes abdominal pain (colic in infancy), loss of appetite, nausea, vomiting
- glyberia treatment
24
Q
fatty acids and cholesterol are stored in intracellular lipid droplets
A
- triglycerides are rebuilt again and stored in lipid droplets in adipose tissue
- lipid droplets are in every cell but are prominent in adipose tissue
- *lipid droplets are similar structurally to chylomicrons -> inner core of cholesteryl esters and triglycerides, surrounded by phospholipid monolayer with acyl chains facing inward and charged heads outward, free cholesterol and proteins are embedded in the monolayer
- they are different in that the lipid droplets are inside cells (intracellular) and are a storage site for excess fat
- storage depots for cellular lipids (triglycerides and cholesteryl esters)
- during times of energy need triglycerides are hydrolyzed back into free fatty acids for tissue
25
Q
lipid droplets are dynamic
A
- they grow and shrink depending upon the rate of lipid turnover
- as you consume/store more fat lipid droplet grow and diffuse with each other -> form large lipid globules
- this happens are you gain weight
- as you use the lipid they will shrink
26
Q
fasting state: dipping into the fat/energy storage in adipose tissue: lipolysis
A
- highly regulated
- we dont want to be using stored fats right after a meal
- process of hydrolyzing lipid droplets stored in adipose tissue into free fatty acids -> released into blood -> used by muscles
- glucagon (fasting) and epinephrine/adrenaline (fight or flight) stimulate this
27
Q
enzymatic conversion of triglycerides into fatty acids
A
- triglyceride in lipid droplets is cleaved by adipocyte triglyceride lipase (ATGL, specific to triglyceride)
- ATGL cleaves at the 1 position and generates a diglyceride
- then hormone sensitive lipase (HSL) cleaves the diglyceride into a monoacylglyceride
- monoacylglycerol lipase then cleaves
- 3 fatty acid and glycerol product
- occurs during times of energy need (from storage)
28
Q
regulation of lipolysis
A
- protein kinase A (PKA) phosphorylates proteins involved in lipolysis
- glucagon (or epinephrine) is released from pancreas when you are hungry -> activates a receptor that is present on the adipocyte
- when glucagon activates -> it activates protein kinase A (PKA)
- PKA is a major regulator of lipolysis
- PKA phosphorylates to 2 proteins: perilipin-1 and ABHD5 (and hormone sensitive lipase)
- perilipin-1 and ABHD5 are tethered to each other are in a complex on a lipid droplet surface
- when they are phosphorylated by PKA they dissociate -> ABHD5 can then fully dock onto the lipid droplet surface
- ABHD5 recruits adipocyte triglyceride lipase (ATGL) to the lipid droplet (when phosphorylated) -> ATGL initiates lipolysis
- phosphorylation of hormone sensitive lipase allows it to be recruited to lipid droplet surface -> increase activity
- ATGL and HSL are highly regulated while MAGL isnt
29
Q
chanarin-dorfman syndrome
A
- rare autosomal recessive neutral lipid storage disease
- mutation resulting in nonfunctional ABHD5
- ABHD5 deficiency
- means you cannot recruit ATGL to lipid droplets -> store too many fats
- cannot cleave triglycerides in lipid droplets
- patients have hepatomegaly
- hepatocyte triglyceride lipase, hormone sensitive lipase, monoacylglyceride lipase are also in the liver with similar function -> liver can store some lipids
- patients accumulate fats
30
Q
glycerol is converted into glycolytic intermediates
A
- glycerol is released from adipose tissue
- glycerol is taken up by liver and used for gluconeogenesis
- free fatty acids (released by adipose tissue) are in blood and taken up by other tissue to be used for beta-oxidation
- beta-oxidation- fatty acids are converted to acetyl CoA and NADH, FADH
31
Q
beta-oxidation
A
- mechanism through which cells utilize energy stored in fatty acids (carbons of fatty acyl chains)
- series of enzymatic rxns within the mitochondrial matrix:
- fatty acids -> acetyl CoA
- palmitate (fatty acid)- 16 carbon fatty acid -> 8 acetyl CoA
- acyl-CoA -> acetyl-CoA
32
Q
acyl-CoA synthetase enzyme (ACS)
A
- convert fatty acids into acyl-CoAs
- molecule of Coenzyme A is attached to fatty acid molecule
- these enzymes are in the cytoplasm (membrane enzymes that are cytoplasmically oriented)
- activate fatty acids
- forms a acyladenylate intermediate
- 2 ATP equivalents used (breakage of 2 high energy bonds)
- requires ATP for activation of the fatty acid
- rate limiting
33
Q
activation of fatty acids mechanism
A
- fatty acid -> acyl CoA
- fatty acid comes in the active site of acyl-CoA synthetase and attacks the alpha phosphate of ATP
- breaks the phosphodiester bond
- produces pyrophosphate and fatty acid is attached to alpha phosphate of the adenosine monophosphate (AMP)
- molecule of CoA comes in -> the sulfur of CoA attacks the fatty acid carbon of the acyladenylate mixed anhydride intermediate
- breaks the bond -> fatty acid becomes transferred to Coenzyme A
- yields Acyl-CoA and AMP
- what drives this rxn forward is the cleavage of the high energy bond between the beta and gamma phosphate during hydrolysis of the pyrophosphate
- this rxn breaks 2 high energy bonds: between alpha and beta phosphate and beta and gamma phosphate -> uses 2 ATP equivalents
34
Q
transport of long chain fatty acids into mitochondria
A
- inner mitochondria membrane is not permeable to long chain acyl-CoA
- carnitine palmitoytransferase (CPT) AKA carnitine acyltransferase
- carnitine is a rate limiting carrier
- there are 2 CPT’s: CPT1
- CPT1- enzyme on the outer mitochondrial membrane facing the cytosol
- CPT1 takes the activated acyl-CoA and transfers the fatty acid group to a molecule of carnitine in the cytoplasm -> converts carnitine into acyl carnitine (permeable)
- transporter can transport acyl carnitine in to the matrix of mitochondria (translocase)
- coenzyme A is liberated and returned to cytosol
- CPT2- enzyme on the inner mitochondrial membrane facing the matrix
- CPT2 catalyzes the reverse rxn -> transfer the fatty acid from the acyl carnitine back to the CoA -> regenerates acyl CoA in the matrix
- carnitine is transported back to cytosol
- rate limiting
35
Q
beta oxidation: acyl CoA is converted into acetyl CoA, NADH, FADH2
A
- energy in the carbon bonds are used for energy
- 1 NADH, 1 FADH2, 1 acetyl-CoA with each cycle (2 carbons at a time and repeat)
36
Q
step 1: beta oxidation
A
- aceyl-CoA dehydrogenase (AD)
- formation of trans-alpha-beta double bond through dehydrogenase by acyl-CoA dehydrogenase
- glutamate extracts proton from alpha carbon
- hydride ion (H+) from beta carbon is transferred to FAD -> FADH2
- mitochondria possess 4 acyl-CoA dehydrogenases with different chain link specificities:
- VLCAD- very long chain acyl-CoA DH (12-20C)
- LCAD- long chain acyl-CoA DH (8-20C)
- MCAD- medium chain acyl-CoA DH (6-10C)
- SCAD- short chain acyl-CoA DH (4C)
37
Q
step 2: beta oxidation
A
- enoyl-CoA hydratase
- hydrates the alpha-beta-trans double bond by adding water to the beta carbon
- water is coordinated by 2 glu
- double bond is reduced
- multiple forms for different chain lengths
- beta carbon takes OH and alpha carbon takes 1 H
- no energy generated
38
Q
step 3: beta oxidation
A
- NAD+-dependent dehydrogenation
- 3-L-hydroxyacyl-CoA dehydrogenase (HAD)
- oxidizes a 2ndary alcohol using NAD+
- creates a ketone on the beta carbon
- transfer electrons onto NAD -> NADH
39
Q
step 4: beta oxidation
A
- alpha carbon - beta carbon cleavage in a thiolysis rxn
- thiolase (KT)
- generates acetyl-CoA and a acyl-CoA the is 2C shorter
- cleaves the bond between alpha and beta carbon
- molecule of coenzyme A comes in and sulfur attacks -> attacked to beta carbon
- yields acetyl-CoA and fatty acyl-CoA (2C shorter)
- new fatty acyl-CoA can go back into the cycle
- 8 carbons -> 3 rounds
- 4 carbons -> 1 round
40
Q
products of beta-oxidation are shuttled to the citric acid cycle and oxidative phosphorylation
A
- acetyl-CoA, NADH, FADH2
- generates ATP
41
Q
palmitate (16:0) requires 7 rounds of beta-oxidation
A
- 16C fatty acid
- 7 rounds of beta oxidation
- generates 8 acetyl CoA, 7 FADH2, 7 NADH
- 1 FADH2 generates about 1.5 ATP -> 10.5 ATP
- 1 NADH generates about 2.5 ATP -> 17.5 ATP
- 8 acetyl-CoA generates 10 ATP -> 80 ATP
- 108 ATP molecules per palmitate
- however 2 ATP are used to activate the fatty acid (convert to acyl-CoA)
- net of 106 ATP per palmitate
42
Q
genetic disorders of beta oxidation
A
- new borns
- acyl-CoA dehydrognase:
- VLCAD- cardiomyopathy and muscle weakness
- LCAD- pulmonary surfactant dysfunction
- MCAD- most common beta-oxidation defect (1:15000) -> hypoketotic hypoglycemia with lethargy that develop into coma
- SCAD- relatively mild -> leads to elevated levels of butyrate
- HAD:
- lethal cardiomyopathy -> infant form (lethargy) or peripheral neuropathy
- 10% of sudden infant death
- infants feed on milk from mother which has fatty acids -> if they dont have HAD then the heart will die
- there are screening tests for these disorders
43
Q
beta oxidation of unsaturated fatty acids
A
- oleic acid (oils)
- linoleic acid
- presence of double bonds can be problematic for the second enzyme (enoyl-CoA hydratase (EH))
- if there is double bond at the beta and gamma position -> not a substrate for the EH enzyme
- enoyl-CoA isomerase shifts the double bond from the beta gamma position to the alpha beta trans position -> EH proceeds
- there is another problem bc EH cannot react if there is double bond at 4,5 position as well
- 2,4-dienoyl CoA reductase reduces the 2 double bonds into a single double bond in the trans position BUT it puts it in the beta gamma position (problem again!)
- enoyl-CoA isomerase reacts again and takes the beta gamma double bond and puts it between alpha beta position
44
Q
beta-oxidation of odd chain fatty acids
A
- 15C fatty acid (for example)
- goes through 6 rounds of beta-oxidation
- at the end we generate a 3 carbon fatty acyl-CoA -> propionyl-CoA
- propionyl-CoA is not a substrate for AD
- cells convert propionyl-CoA into succinyl-CoA
- succinyl-CoA can enter the citric acid cycle as an intermediate
45
Q
fatty acids and the brain
A
- fatty acids do not readily diffuse into the brain
- during fasting, the brain cannot use fatty acids released by adipose tissue as source of energy
- alternate source is needed to transfer energy stored in fatty acids (i.e. in adipose tissue or liver) to the brain
- during starvation glucagon levels rise -> fatty acids are released from adipose tissue -> muscle tissue -> converted to acetyl-CoA
- blood brain barrier- cells lining the blood vessels forming tight junctions which causes many molecules to be unable to enter (fatty acids)
46
Q
ketone bodies
A
- 4C molecules -> result from condensation of 2 acetyl-CoAs
- ketone on beta carbon
- 2 ketone bodies:
- D-beta-hydroxybutyrate and acetoacetate
- acetone is breakdown product of these ketone bodies (no energy)
- generated from acetyl-CoA in the liver
- only in liver mitochondria
- released into blood stream by liver
- used for energy during fasting/low blood glucose
- can diffuse into brain
- during starvation the liver will take up a significant portion of fatty acids as well and converts them into acetyl-CoA
- build up of acetyl-CoA is funneled into synthesis of ketone bodies by the liver -> released into circulation and taken up by the brain -> converted back to acetyl-CoA
- ketone bodies are produced from acetyl-CoA
- produced at low levels under normal conditions
- ketone bodies increase when blood fatty acid concentration is high -> high fat diet, starvation conditions, intreated diabetes
47
Q
why do untreated diabetics have high ketone levels
A
- insulin response -> insufficient
- glucose isnt taken up by cells
- cells are starving
- blood sugar is elevated but the cells cant take it up
- mobilizing fatty acids bc it thinks it starving -> converted to ketones
48
Q
energy use by the brain
A
- brain comprises 2% of body weight but uses 20% of glucose
- brain (neurons) is heavily reliant on glucose metabolism (supplemented by ketone bodies during starvation)
- during prolonged fasting/starvation, it is imperative that the brain continues to receive glucose as an energy source -> liver and muscle shift to fatty acid metabolism to preserve glucose
- glucose is preserved for brain
49
Q
products of beta oxidation inhibit glycolysis in liver and muscle
A
- liver and muscle shift to fatty acid metabolism to preserve
- fats are taken up from the circulation from adipose tissue -> liver converts to acetyl-CoA
- build up of acetyl-CoA and NADH -> inhibit pyruvate dehydrogenase
- as you develop higher energy state from the liver it can feedback and inhibit the breakdown of glucose (glycolysis) in the liver
- acetyl-CoA is stimulating pyruvate carboxylase at the same time -> increase gluconeogenesis in the liver
- as you metabolize fatty acids in the liver -> inhibit glycolysis, activate gluconeogenesis, and excess sugar is released to the brain for energy
50
Q
ketogenesis
A
- in the liver mitochondrial matrix
- reverse beta-oxidation
- input of 3 acetyl-CoA and 1 is regenerated
- 2 acetyl-CoAs are conjugated to each other
- reversal of beta oxidation
- 2 acetyl CoAs
- thiolase (acetyl-CoA acetyltransferase) conjugates 2 carbons from an acetyl-CoA to another acetyl-CoA to generates -> 4 carbon acetoacetyl-CoA
- another acetyl-CoA comes in and attacks -> generates beta-hydroxy-beta-methylglutaryl-CoA (HMG-CoA) (6 carbons fused to CoA)
- hydroxymethylgutaryl-CoA lyase (HMG-CoA lyase)- liver enzyme* and also expressed in the liver mitochondrial matrix*
- only in the matrix of the mitochondria will HMG-CoA lyase enzyme cleave and regenerate an acetyl-CoA and acetoacetate (ketone)
51
Q
ketones
A
- released into the blood stream
- taken up by other tissues (brain, heart, sometimes muscle)
- converted back to acetyl-CoA to use for energy
- ketone bodies provide energy to other tissues -> provide a way to transport acetyl-CoA between tissues
- lower demand for glucose by brain during starvation
- reduce amount of protein (i.e. amino acids) that must be broken down for gluconeogenesis
- liver is shifting towards fatty acid metabolism and away from glucose
52
Q
excess of ketone bodies: diabetic ketoacidosis
A
- tissues unable to take up and utilize glucose
- excess ketone body production
- acetone can be smelled in breath
- ketones are acids -> low blood pH
- this will kill you if prolonged
53
Q
excess of ketone bodies: alcoholic ketoacidosis
A
- found in alcoholics
- high (NADH), depletion of oxaloacetate required for gluconeogenesis
- elevated ketone body production
- low blood pH
- this will kill you if prolonged
54
Q
Glut1 deficiency and the ketogenic diet
A
- consume low levels of sugar and high levels of fat
- shift glucose metabolism to fat metabolism
- Glut1 is a glucose transporter at the blood brain barrier
- mutation in Glut1 reduce glucose uptake by the brain
- children with Glut1 deficiency (heterozygous) frequently develop seizures that are poorly controlled by anti-epileptic medications
- seizures bc low glucose to the brain -> and brain is highly reliant on glucose
- ketogenic diet reduces seizures in these patients
- amount of ketones produced are sufficient to use as excess energy to brain if glucose transporter is at 50% compacity -> Reduce seizures
- fatty acid oxidation- important for generation energy
55
Q
lipids
A
- excess energy is stored in the form of lipids (fatty acids) -> converted to triglycerides
- vast majority for the carbon source of fatty acids -> glucose
- under high energy states the carbon from acetyl-CoA comes out of the matrix to convert to citrate -> citrate is converted back to acetyl-CoA -> used for fatty acid biosynthesis
56
Q
fatty acid synthesis and beta oxidation
A
- beta oxidation is the mitochondrial matrix and help generate energy
- fatty acid biosynthesis requires energy -> cytosol
- these rxns will therefore be spatially separated
- regulated separately
57
Q
fatty acid biosynthesis shares chemical similarities to beta-oxidation
A
- however fatty acid biosynthesis is in the cytoplasm
- input of energy for fatty acid biosynthesis and NADPH
- biosynthesis occurs in a high energy state
- oxidation under a lower energy state
58
Q
Fed state
A
- store energy for energy use
- high energy state
- increased insulin
- increase glycolysis
- increased glycogenesis
- increase fatty acid biosynthesis
- decrease glycogenolysis
- decrease gluconeogenesis
- decrease fatty acid oxidation
59
Q
tricarboxylate transport system
A
- acetyl-CoA is transported out of the matrix into the cytosol
- in the high energy state -> high abundance of acetyl-CoA
- acetyl-CoA cannot diffuse out -> it is converted into citrate -> citrate transporter -> cytosol
- acetyl-CoA is the precursor for fatty acid biosynthesis
- acetyl-CoA generated in the mitochondrial matrix in the liver
- acetyl-CoA is conjugated to oxaloacetate via citrate synthase-> forms citrate
- tricarboxylate transport system- transport citrate across the inner mitochondrial membrane
- citrate is now the substrate for ATP-citrate lyase in the cytosol
- transfer these carbons from the citrate onto a CoA -> generates a cytosolic pool of acetyl-CoA -> precursor of fatty acid biosynthesis
- in the cytoplasm oxaloacetate is converted to malate -> pyruvate -> generates a pool of NADH
- this NADPH is used for fatty acid biosynthesis
60
Q
citrate
A
- high concentration of citrate in the cytosol of the liver is a marker of high energy state
- increases the rate of fatty acid biosythesis
61
Q
overview of fatty acid biosythesis
A
- occurs primarily in the liver but also in other tissues (adipose tissue)
- major precursor of acetyl-CoA in the liver is sugar (glucose)
- reverse of beta oxidation
- conjugation of 2 carbon units (acetyl-CoA/malonyl-CoA) to produce palmitate (16 carbon fatty acid)
- each cycle is adding two carbons to the carbon fatty acid chain until we generate palmitate
62
Q
key enzymes in fatty acid biosynthesis
A
- both in the cytoplasm
- acetyl-CoA carboxylase (ACC)- converts acetyl-CoA to malonyl-CoA
- malonyl-CoA- 3 carbon compound
- this conversion is committed step to fatty acid biosynthesis
- fatty acid synthase (FAS/FASN)- converts malonyl-CoA to palmitate
- an acetyl-CoA + 7 malonyl-CoAs to generate palmitate via FAS
63
Q
biosynthesis of malonyl-CoA
A
- cytoplasmic
- committed step to fatty acid biosynthesis
- heavily regulated
- entry point of acetyl-CoA
- acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA
- biotin cofactor
- bicarbonate (CO2) is attached to biotin factor
- takes acetyl-CoA and attach bicarbonate to the methyl group of acetyl-CoA -> generate a 3 carbon malonyl-CoA
- ATP is used
- Acetyl-CoA + HCO3- + ATP -> malonyl-CoA + ADP + Pi
64
Q
acetyl-CoA carboxylase
A
- very large
- many domains
- domains are far apart
- substrate have to be shuttled from one domain to the next
- biotin carboxylase side- biotin group comes in and becomes attached CO2
- once this occurs biotin has to swing between 40-80A to the CT (transcarboxylase) site -> acetyl-CoA comes in and CO2 is transferred
- large movements
- same for FAS
65
Q
acetyl-CoA carboxylase activation
A
- high cytosolic citrate concentration -> high energy state
- abundance of energy and acetyl-CoA
- cytosolic citrate activates ACC (committed step)
- citrate induces polymerization of ACC
- forms long polymers -> large increase in activity -> commits
66
Q
how do cells ensure that fatty acid biosynthesis and beta-oxidation do not occur simultaneously (vicious cycle)
A
- regulate this with malonyl-CoA
- in a high energy state acetyl-CoA is converted to malonyl-CoA (committed)
- in the cytosol malonyl-CoA inhibits beta-oxidation of fatty acids by inhibiting the CPT1 enzyme (faces cytosol)
- CPT1 converts acyl-CoA into acyl carnitines -> allows fatty acids to be transported into the matrix for beta oxidation
67
Q
fatty acid synthase (FAS)
A
- upregulated in cancer and obesity
- acetyl-CoA and malonyl-CoA are used to generate palmitate
- multifunctional enzyme that catalyzes fatty acid biosynthesis
- acetyl-CoA (malonyl-CoA) -> palmitate (C16:0)
- adds 2 carbons to growing fatty acid chain per cycle
- has many domains: catalytic
- has acyl carrier protein (ACP)
- 6 enzymatic activities, 7 cycles of C2 elongation
1. MAT- malonyl/acetyl CoA ACP transferase
2. KS- keto synthase
3. ER- enoyl reductase
4. KR- keto reductase
5. DH- hydroxylacyl dehydrogenase
6. TE- palmitol thioesterase
68
Q
fatty acid synthase mechanism
A
- acetyl-CoA comes in
- 2 acetyl groups are transferred to the enzyme
- all the next cycles the malonyl-CoA comes in (3C)
- with each cycle the chain grows by 2 carbons and CO2 (from malonyl-CoA) leave
- grows in the opposite direction of beta oxidation
69
Q
fatty acid synthase structure
A
- dimeric- symmetry
- large
- many domains: SD, KR, ER, ER, KR, SD, DH, DH, MAT, KS, KS, MAT
- dynamic
70
Q
acyl carrier protein (ACP)
A
- tethered to the growing fatty acid chain
- apart of FAS enzyme
- transports the fatty acid chain to each domain of fatty acid synthase as it is growing
- ensures that the fatty acid chain is never released from the enzyme
- structurally similar to CoA
- has a sulfhydryl on the end (SH)
- ACP is covalently tethered to the enzyme (FAS) -> this is different from CoA (free floating)
71
Q
fatty acid biosynthesis preview
A
- in the first cycle acetyl-CoA will come into the MIT site of FAS
- acyl carrier protein will be docked at the MAT site
- acetyl group is transferred onto the ACP to generate acetyl-ACP (CoA floats away)
- ACP with the acetyl group will migrate over to the KS site and transfer the acetyl group to a cystine on the enzyme
- ACP group is liberated and goes back to MAT site to start bringing in malonyl groups
- same process happens with malonyl -> malonyl goes to KS site and conjugates with the acetyl group that was attached there previously (from acetyl-CoA) -> forms acetoacetyl group attached to ACP (4C with a beta ketone)
- then beta oxidation in reverse (many steps here) -> butyryl-ACP (4C molecule)
- this group goes back to the KS site and repeat (keeping adding malonyl-ACP)
72
Q
fatty acid biosynthesis pt. 2: reverse beta oxidation
A
- ACP on the acetoacetyl-ACP swing it into the KR site
- beta ketone becomes a hydroxyl (reverse beta oxidation) via beta-ketoacyl-ACP reductase (KR) -> forms D-beta-hydroxybutyryl-ACP
- KR uses NADPH
- ACP swing this into the DH site
- beta-hydroxyacyl-ACP dehydrase (DH) removes the hydroxyl and proton -> water leaves -> generates a alpha-beta trans double bond (reverse beta oxidation)
- ACP swings this into ER site
- enoyl-ACP reductase (ER) reduces the double bond between the alpha and beta carbon -> generates a fully saturated 4C fatty acid -> butyryl-ACP
- ER uses NADPH
- butyryl will go back to KS site and transfer the 4C fatty acid to the cysteine of KS and the ACP will go back to MAT to bring another malonyl-CoA
- repeat until we get 16C unit -> palmitate
73
Q
last steps of the cycle: palmitoyl-ACP
A
- after 7 cycles butyryl-ACP forms palmitoyl-ACP (16C)
- ACP docks to TE -> water comes in and attacks -> ACP is released -> goes back to MAT to get acetyl group
- palmitoyl thioesterase (TE) converts palmitoyl-ACP to palmitate
- only goes to TE once we have a 16C fatty acid chain
74
Q
balanced rxn for synthesis of palmitate
A
8 acetyl-CoA (1 acetyl-CoA + 7 malonyl-CoA) + 14 NADPH + 7 ATP -> palmitate + 14 NADP+ + 8 CoA + 7 ADP + 7 Pi + 6 H2O
- NADPH is used by ER and and KR
- ATP is used by acetyl-CoA carboxylase -> when we synthesized acetyl-CoA from malonyl-CoA
75
Q
bigger fatty acids: fatty acid desaturation and elongation
A
- cytoplasm
- once you have a 16C fatty acid it can be extended to 18C, 20C, so forth
- desaturases enzymes -> create double bonds
- humans lack desaturase that can extend beyond the 9th carbon
- bc of this there are fatty acids that essential to us bc we cant make them (diet)
- ex. linoleic acid
76
Q
lipid biosynthesis in the liver
A
- cytosol
- glucose provides the major source for the precursors for fatty acid biosynthesis (after we eat)
- high glucose is not good for you because it pools a large portion of fatty acid biosynthesis -> obesity
- (recall) chylomicron remnants that are taken up by the liver have dietary triglycerides -> broken back down into fatty acids
- dietary fatty acids + fatty acids from acetyl-CoA -> used to resynthesize triglycerides
- these remade triglycerides + cholesterol and cholesterol esters -> are stored in lipid droplets in liver BUT more importantly they are shipped out into the circulation in the lipoproteins called very low density lipoprotein (VLDL) -> other tissues
- tissues are getting dietary fatty acids from chylomicrons and VLDL
77
Q
very low density lipoprotein (VLDL)
A
- in the liver triglycerides (from acetyl-CoA and from chylomicron remnants) and cholesterol/cholesteryl esters are incorporated into VLDL
- lipoproteins that are released into the bloodstream
- triglycerides and cholesteryl esters are packed in the hydrophobic lipoprotein interior while cholesterol is confined to the phospholipid monolayer
- VLDL is analogous to chylomicrons
78
Q
triglyceride release from the liver in VLDL
A
- shipped into the bloodstream
- just like chylomicrons -> triglycerides will be substrates for lipoprotein lipase
- lipoprotein lipase cleaves triglycerides in VLDL to generate fatty acids that can be taken up by adipose or muscle tissue
- deliver for storage (adipose tissue)
- if return back to a low energy state -> glucagon levels rise -> triglycerides will be cleaved in the adipose tissue -> delivered back to liver to make ketones or muscle tissue for energy
- VLDL -> LDL
79
Q
regulation of fatty acid biosynthesis
A
- malonyl-CoA will inhibit CPT1 (commits to biosynthesis)
- regulated by insulin (promotes) and glucagon and epinephrine (inhibits)
- majority of regulation is at acetyl-CoA carboxylase step (committed step)
- high energy state- insulin rising
- low energy state- glucagon levels are rising
80
Q
AMP-activated protein kinase (AMPK)
A
- activated by AMP (an low ATP) -> therefore when its in a low energy state
- AMPK phosphorylates and inactivates acetyl-CoA carboxylase (ACC) (committed step)
- no malonyl-CoA is synthesized -> relieves inhibition of CPT1 -> fatty acid oxidation is activated
- fatty acid biosynthesis occurs under high energy states, necessitating the inactivation of AMPK
- Low energy state -> high AMP -> inhibit ACC -> decrease malonyl concentration -> relieve inhibition of CPT1 -> increase beta oxidation
- many hormones regulate AMPK activity
- high energy state- insulin rising -> AMPK inactivated -> fatty acid biosynthesis
- low energy state- glucagon levels are rising -> AMPK activated -> beta oxidation
81
Q
phosphorylation of ACC reduced polymerization
A
- formation of filaments increases ACC activity >20-fold
- in the presence of citrate ACC forms filaments -> activates ACC -> more malonyl-CoA
- citrate induces abnormal filament formation when ACC is phosphorylated by AMPK -> even in the presence of citrate ACC is still inhibited by AMPK
82
Q
fatty acid biosynthesis in human diseases
A
- acetyl-CoA carboxylase and cancer
- ACC and FAS are important drivers of cancer/tumor growth
- cells use fatty acids for energy, to build membranes, and division
- ACC expression is elevated in cancer cells
- fatty acid promote cancer cell proliferation
- cancer cells lacking acetyl-CoA carboxylase (ACC1KO) -> tumors grow smaller
- FAS overexpression also promotes prostate cancer metastasis -> tumors are larger
- FAS is upregulated in many cancers including prostate cancer
83
Q
functions of cholesterol
A
- essential component of membranes: modulates fluidity and permeability (40%)
- precursor for bile salts (liver): natural detergents in gut
- digest triglycerides
- precursor for steroid hormones (estrogen & testosterone)
- regulates the activity of proteins
- signaling functions
- free hydroxyl on one end and hydrophobic on the other end -> hydrophobic molecule but has a polar group
- has 27C
84
Q
sources of cholesterol
A
- endogenous sources:
- liver (majority)- synthesizes 1g of cholesterol daily
- accounts 70% of all cholesterol needed by the body
- dietary sources:
- account for the other 30% of cholesterol
- 1 large egg= 190mg of cholesterol
- big mac= 80 mg of cholesterol
- clinically used drugs reduce cholesterol levels by targeting both of these processes (dietary and endogenous)
- endogenous drugs are more effective bc the liver makes majority of cholesterol
85
Q
cholesterol is a precursor to bile salts
A
- accounts for the only route of cholesterol out of our bodies
- through the GI (intestines)
86
Q
overview of cholesterol biosynthesis
A
- occurs predominantly in the liver
- increased by insulin and reduced glucagon
- high energy state
- cholesterol biosynthetic enzymes are found in the cytoplasm -> *bc it allows you to spatially segregate energy producing functions in the matrix and biosynthetic rxns in the cytoplasm
- utilizes acetyl-CoA as the major carbon donor (same source of fatty acid biosynthesis)
- precursor is acetyl-CoA
- very similar to fatty acid biosynthesis!
87
Q
major regulatory step in cholesterol biosynthesis
A
-HMG-CoA reductase
88
Q
cholesterol biosynthesis: four stages
A
- acetyl-CoA to HMG-CoA to mevalonate (C5)
- conversion of mevalonate to 2 activated isoprenes
- condensation of 6 activated isoprenes to make squalene (30C)
- cyclization of squalene to make lanosterol and conversion of lanosterol into cholesterol
89
Q
source of acetyl-CoA for cholesterol biosynthesis
A
- acetyl-CoA + oxaloacetate is converted to citrate via citrate synthase
- citrate is transported from matrix to the cytoplasm via tricarboxylate transport system
- citrate is converted back to oxaloacetate in the cytoplasm -> generates acetyl-CoA
- all of this is the same from fatty acid biosynthesis
90
Q
acetyl-CoA is convert to isoprene
A
- acetyl-CoA is converted to isopentenyl-pyrophosphate (isoprene)
- 4C chain with a methyl group on 2 -> 5C
91
Q
cholesterol biosynthesis: stage 1: pt.1
A
- HMG-CoA is made from 3 molecules of acetyl-CoA
- all the cytosolic isozymes for making ketone bodies (matrix) are in the cytosol (use the same enzymes)
- thiolase (acetyl-CoA acetyltransferase) combines 2 acetyl-CoAs and forms acetoacetyl-CoA (4C)
- HMG-CoA synthase brings in another acetyl-CoA (2C) -> forms HMG-CoA (6C)
- this product is diverted towards cholesterol biosynthesis (instead of ketone)
- HMG-CoA becomes the substrate for HMG-CoA reductase
92
Q
why cant we make ketones in the cytoplasm?
A
- HMG-CoA lyase is not found in the cytoplasm
- we are left with the product HMG-CoA -> diverted to cholesterol biosynthesis
- this also makes sense bc when we are in a high energy state we are synthesizing cholesterol -> we dont want to make ketones (made during low energy)
93
Q
cholesterol biosynthesis: stage 1: pt.2
A
- rate limiting enzyme in cholesterol biosynthesis
- major regulatory site
- major drug target to reduce cholesterol levels
- HMG-CoA is converted to mevalonate via HMG-CoA reductase
- uses 2 NADPH
- reduces C=O and releases CoA
94
Q
cholesterol biosynthesis: stage 2
A
- mevalonates is converted to 2 isoprenes
- mevalonate is a substrate for mevalonate-5-phosphotransferase -> produces phosphomevalonate
- we use ATP -> ADP
- transfers the phosphate from ATP to mevalonate
- phosphomevalonate kinase then converts phosphomevalonate to 5-pyrophosphomevalonate
- adds another phosphate via ATP
- there are now 2 phosphate groups attached
- pyrophosphomevalonate decarboxylase converts 5-pyrophosphomealonate to isopentenyl pyrophosphate
- decarboxylates and dehydrates to produce the isoprene unit
- uses ATP
- releases CO2
- forms a double bond
- 5C unit with 2 phosphates attached
95
Q
isopentenyl pyrophosphate isomerase rxn * dont need to know
A
- isopentenyl pyrophosphate is converted to dimethylallyl pyrophosphate via isopentenyl pyrophosphate isomerase
- double bond is shifted
- resonance stabilization
- 5C units with 2 phosphates attached
96
Q
cholesterol biosynthesis: stage 3 * dont need to know
A
- condensation of 6 activated isoprenes to make squalene (30C)
- dimethylallyl pyrophosphate and isopentenyl pyrophosphate -> conjugated to each other -> forms 10C unit -> geranyl pyrophosphate
- pyrophosphate leaves
- geranyl pyrophosphate (10C) is coupled to another 5C -> forms farnesyl pyrophosphate (15C)
- conjugate 2 farnesyl pyrophosphates and form -> 30C squalene
97
Q
cholesterol biosynthesis: stage 4 * dont need to know
A
- cyclization of squalene to make lanosterol and conversion of lanosterol into cholesterol
- ring formations
98
Q
lanosterol
A
- lanosterol (30C) is the ultimate precursor to cholesterol
- step before (in reality its about 19 steps)
- we lose 3 carbons in the process (removal of 3 methyl groups)
- one reduction
- 27C cholesterol
99
Q
major site of regulation of cholesterol synthesis pathway
A
- two regulation pathways
- both are regulated at HMG-CoA reductase
- rapid and long-term
- drug target of statins
100
Q
rapid regulation of cholesterol
A
- phosphorylation by AMP-activated protein kinase (AMPK) inactivates HMG-CoA reductase
- AMPK is activated in low energy states -> inhibits HMG-CoA -> cholesterol is not produced
- this is controlled by energy state: high AMP -> high AMPK -> general biosynthetic pathways decrease
- regulates rate limiting step
101
Q
long term regulation of cholesterol
A
- regulation of HMG-CoA reductase transcription (mRNA)
- regulates rate limiting step
- this is the major pathway for regulation
- decreased cholesterol induces transcription of mRNA for HMG-CoA reductase
- when there is excess cholesterol the liver knows not to make more
- 3 proteins (complex) in the liver: SREBP, SCAP, INSIG
- these proteins are in the ER
- when cholesterol is high the complex remains
- when cholesterol drops -> SREBP and SCAP complex dissociates from INSIG
- SREBP and SCAP move from the ER to the Golgi apparatus
- site 1 protease (S1P) and site 2 protease (S2P) in the Golgi
- S1P recognizes SREBP and clips it into 2 -> these pieces become substrate for S2P
- S2P clips it ag and the head floats away into the cytosol
- the head group is a transcription factor -> translocates into the nucleus -> binds to promoter for HMG-CoA reductase -> increase mRNA levels of HMG-CoA reductase
- more HMG-CoA reductase protein to make cholesterol
- same process controls to the expression of the LDL receptor
102
Q
SREBP
A
-sterol regulatory element binding protein
103
Q
SCAP
A
- SREBP cleavage-activating protein
- contains sterol-sensing domain
104
Q
fate of choelsterols
A
- liver packs dietary and endogenously synthesized cholesterol/cholesterol ester and triglycerides from chylomicron remnants into lipoproteins: VLDL
- shipped out from liver into circulation
- triglycerides that stayed in the liver are deposited into adipose tissue for storage
- triglycerides in the VLDL are substrates for lipoprotein lipase -> stored in adipose tissue
- this VLDL becomes triglycerides poor (they are cleaved and taken up) and cholesterol rich -> LDL
- lipoprotein lipase cleaves triglycerides in VLDL (very low density lipoprotein) to generate LDL (low density lipoprotein)
- LDL is taken up by other tissues and uses the cholesterol
105
Q
VLDL
A
- rich in triglycerides, cholesterols, cholesteryl esters
- very low density lipoprotein
106
Q
LDL
A
- triglyceride poor
- rich in cholesterols and cholesteryl esters
- low density lipoprotein
- has a protein B100 on its surface
- B100 allows your cells to take up LDL from the blood and internalize it
- not permeable to blood brain barrier like fatty acids -> cholesterol produced in the liver doesnt enter the brain
- brain has its own machinery to make its own cholesterol (very low rate)
- turnover of brain cholesterol is very slow
- bad cholesterol
107
Q
LDL is taken up by peripheral tissues
A
- endocytosis
- cells have LDL receptor on the plasma membrane
- LDL receptor will recognize B100 protein on the surface of the LDL
- LDL receptors recognize and bind to apolipoprotein B100 on LDL
- all the proteins become hydrolyzed within the cell by lysosomes
108
Q
excess cholesterol in tissues
A
- cholesterol is sent back to the liver via HDL (high density lipoprotein)
- reduce high levels of cholesterol in the tissue by increasing reverse transport to liver -> excreted through bile salts
109
Q
HDL (high density lipoprotein)
A
- transports cholesterol from peripheral tissues to the liver for excretion
- uses protein ABCA1 to transport the excess cholesterol out of the peripheral cell
- cholesterol is assembled together into HDL
- more HDL you have the more ability you have to transport cholesterol back to liver to excrete as bile salts -> lowers cholesterol
- good cholesterol
110
Q
atherosclerosis and coronary heart disease
A
- caused by deposition of lipid (cholesterol) within arteries
- results in hardening and thickening of arteries and restricted blood flow
- leading cause of death in the US
- greater risk with increasing blood cholesterol (LDL) levels
- deposition of cholesterol -> narrower lumen of arteries
111
Q
atherosclerosis is a progressive disease
A
- high LDL levels
- initiated by deposition of LDL in walls of large blood vessels (typically arteries)
- LDL is oxidized -> induces infiltration of macrophages (immune cells), which take up oxidized LDL and become lipid rich foam cells (fat immune cells)
- foam cells release proteases and factors that damage artery walls
- damage to endothelial lining and cell death results in the formation of necrotic core, calcification (hardening) and thickening of arteries, and reduced blood flow
- plaque rupture exposes necrotic core to blood, resulting in the formation of a thrombus (platelet clot) that significantly restricts blood flow as it grows
- reduced blood flow causes ischemia (death) of tissue (myocardium) and heart attack
- thrombus can detach and lodge in smaller vessels and obstruct blood flow, also leading to heart attack
112
Q
reducing blood cholesterol levels
A
- diet -> reduce intake of sugar and cholesterol
- drugs -> this is better bc most cholesterol is made endogenously
- HMG-CoA reductase inhibitors: statins are used
113
Q
HMG-CoA reductase inhibitors: statins
A
- statins inhibit HMG-CoA reductase (rate limiting)
- structurally similar to the substrate HMG-CoA
- as cholesterols level drop from statins -> SREBP system upregulates the expression AND the expression of the LDL receptor* -> more LDL is taken up by cells and taken out of blood stream
- this reduces the chance of cholesterol embedding into the arteries
114
Q
ezetimibe (zetia)
A
- inhibits intestinal cholesterol absorption
- cholesterol passes through you
- less effective than statins bc its targeting dietary cholesterol (less percentage)
115
Q
PCSK9 inhibitors lower LDL levels (Reptha)
A
- PCSK9 is secreted by the liver
- binds to the LDL receptor and enhances its degradation by lysosome within cells
- PCSK9 inhibitors (reptha) block PCKS9 function -> reduce LDL receptor degradation -> allows it to be recycled to the plasma membrane to take up additional LDL
116
Q
bioactive lipids
A
- lipids are derivative of lipids that have biological activity
- you want these to be low when your healthy
- in addition to providing energy for cellular metabolic needs, some fatty acids are also converted into potent signaling molecules
- there are many classes:
- prostaglandins
- prostacyclin
- endocannabinoids
- leukotrienes
- resolvins
- sphingolipids
- etc.
117
Q
inflammation
A
- acute inflammation is a protective response to tissue injury and infection
- pain
- fever -> infection
- swelling
- many features of inflammation are regulated by signaling lipids
118
Q
arachidonic acid (AA)
A
- precursors to numerous signaling lipids
- this one fatty acid (inert) can be converted to dozens of specialized signaling lipids
- normally inert -> can be converted to many classes of signaling lipids
- 20C fatty acid
- 4 double bonds
119
Q
AA is converted into prostaglandins
A
- AA (arachidonic acid) -> PGE2 (prostaglandin E2)
- intermediate PGH2 (prostaglandin H2)
- COX-1 and COX-2 (cyclooxygenase-1 and 2) convert AA to PGH2
- PGES1 (prostaglandin E synthase 1) converts PGH2 to PGE2
- PGE2 is a major mediator of pain, inflammation, fever -> you dont want this to be elevated if youre not sick
- these enzymes (COX-2 and PGES1) will increase during sickness
120
Q
cyclooxygenase (COX) enzymes
A
- COX-1 is expressed in most tissues (constant)
- COX-2 expression increases during inflammation
- COX-2 upregulation during inflammation*
- convert arachidonic acid into prostaglandin H2 (PGH2)
- PGH2 has no biological activity as an intermediate (but its converted to many different prostaglandins)
- PGH2 is subsequently converted into multiple prostaglandins
121
Q
COX-2
A
- membrane protein
- has no transmembrane domains
- has 2 regions (alpha helices) that anchor it to the phospholipid bilayer
- embedded in the bilayer
- arachidonic acid enters the enzymes active site from the lipid bilayer
- dimeric
- converts AA to prostaglandin H2 (PGH2)
- upregulated during inflammation
122
Q
COX-2 upregulation is self limiting
A
- nature has evolved COX-2
- COX-1 is normally expressed at constant level
- has a 20 amino acid cassette (COX-1 doesnt) -> ensures COX-2 has a very short half life
- stable for only short amount of time -> makes the prostaglandin needed -> degraded
- limits upregulated so were not always inflamed
123
Q
prostaglandin E2 (PGE2)
A
- synthesized by the enzyme prostaglandin E synthase (PGES1) from PGH2
- multiple functions during inflammation/sickness:
- increase pain
- increase swelling/edema (increase vascular permeability)
- fever (major and one of the only ones)
- appetite suppression
124
Q
PGES1 expressions increases during inflammation
A
- just like COX-2
- upregulation
125
Q
How does PGE2 regulate pain, fever, appetite…etc.
A
- PGE2 activates 4 receptors: EP1, EP2, EP4, EP3
- EP1-4 are highly specific for PGE2
- EP2 and EP4 activate protein kinase A -> activates the cell
- when PGE2 activate EP3 receptor is reduces PKA -> inhibit the target cell
- PGE2 binds to EP3 within the protein itself (not on top or bottom) -> conformational change
126
Q
flu
A
- flu has fever and chills, aches and pains, weakness and fatigue, low appetite
- PGE2 regulates this
127
Q
inflammation enhances pain
A
- specialized nerves that project to skin and muscles (normally not active) -> nociceptors
- nociceptors are specialized nerves that transmit painful stimuli from site of inflammation to spinal cord
- inflammation sensitizes nociceptors and enhances pain -> activate nociceptors
- inflammation will sensitize nociceptors and activate them -> send message to spinal cord -> brain -> pain
- high levels of PGE2 activate EP2/EP4 -> activates target cell (increase activity of pain sensing neurons) -> sensitizes nociceptors
128
Q
PGE2 produces fever
A
- central* mediator of fever (the only one)
- cytokines (IL-1, IL-6, TNFalpha) increase the expression of COX-2 and PGES1 in endothelium lining the brain (hypothalamus)
- PGE2 increase thermostat in the hypothalamus of the brain by activating the EP3 receptor
129
Q
activation of EP3 by PGE2 produces fever
A
- specialized neurons in the spinal cord promote shivering and vasoconstriction (constantly want to produce fever) but are inhibited by specialized neurons from the hypothalamus that express the EP3 receptor
- EP3 is expressed in adipocytes
- EP3 receptor is the inhibitory receptor -> inhibits the inhibitory cells in the hypothalamus
- activation of EP3 by PGE2 inhibits the neurons in the hypothalamus -> reduces their inhibition of spinal cord neurons -> fever
130
Q
PGE2 suppresses appetite
A
- PGE2 reduces ghrelin (stimulates feeding) secretion in the stomach
- PGE2 activate EP4 receptor in the hypothalamus
- EP4 is excitatory -> stimulates POMC neurons that suppress feeding
- PGE2 activates POMC neurons to reduce the hunger drive
131
Q
therapeutics targeting the COX-prostaglandin axis
A
- COX inhibitors
- COX-2 inhibitors
- reduce pains, inflammation, appetite, fever
132
Q
COX inhibitors
A
- prostaglandins are synthesized by COX-1 and COX-2* during inflammation/sickness
- prostaglandins contribute to: pain, fever
- inhibition of COX enzymes reduces pain, inflammation, and fever
- aspirin (acetylsalicylic acid)
- ibuprofen- nonsteroidal anti-inflammatory drug (advil)
133
Q
side effects of COX inhibitors
A
- chronic use of COX inhibitor drugs -> develop gastrointestinal ulcers
- COX-1 (constant) -> produces prostaglandins that protect the gastric mucosa (stomach and intestine) from gastric acid
- when you inhibit COX-1 and 2 -> you inhibit fever, inflammation, pain but you also inhibit protection of gastric mucosa by COX-1
- we can avoid this by designing inhibitors that only target COX-2 and not COX-1
- volume of COX-2 active site is larger and its smaller in COX-1 -> to make drug specific to COX-2 -> make larger drugs
134
Q
COX-2 inhibitors
A
- rofecoxib (vioxx)
- celecoxib (celebrex)
- vioxx taken off market in 2004 due to unexpected side effects (heart attacks)
- super drug but heart attack side effect
- celebrex is used sparingly still
- COX-2 produces prostacyclin (PGI2) in lining endothelial cells of vasculature (blood vessels) -> potent vasodilator and inhibitor of platelet aggregation
- COX-1 produces thromboxane A2 (TXA2) in platelets -> vasoconstrictor and stimulates platelet aggregation
- inhibition of COX-2 causes a decrease in PGI2 and allows TXA2 produced by COX-1 to predominate -> thrombus (platelet plugs) form
- clots occludes blood flow -> tissues die -> heart stops
135
Q
PGES1 as a therapeutic target
A
- selective inhibition of PGES1 reduces PGE2 levels without affecting prostacyclin biosynthesis
- currently working on this
136
Q
cannabinoids receptors
A
- marijuana and a derivative of arachidonic acid (AA)
- humans express 2 cannabinoid receptors (CB1 and CB2)
- CB1 and CB2 are activated by THC and 2-AG and anadamide (AA derivatives/endocannabinoid)
- CB1/CB2 are inhibitory -> their activation inhibits the target cell
- cannabinoid receptors are activated by:
- delta-tetrahydrocannabinol (THC), the major psychoactive constituent of marijuana
- 2-arachidonoylglycerol (2-AG), an endocannabinoid
- anadamide, an endocannabinoid
137
Q
endocannabinoids
A
- 2-AG -> 2-arachidonoylglycerol
- anadamide
- arachidonic derivatives
- produced by the body
- activation of CB1/CB2 receptors modulates:
- pain
- reduce anxiety/stress responses
- increase appetite
- reproduction/fertility
- cognition
- development
- major interest in developing drugs targeting the endocannabinoid system
138
Q
2-arachidonoylglycerol (2-AG)
A
- arachidonic acid is attached at the 2 position
- glycerol
- 2-monoacyl glycerol
139
Q
2-AG is hydrolyzed and inactivated by MAGL
A
- you dont want 2-AG to be constantly activating cannabinoid receptors
- you want it to be made when needed and then degraded
- monoacylglycerol lipase (MAGL)- cleaves the ester bonds of monoglycerides at the 2 position -> generates glycerol and a fatty acid (arachidonic acid)
- MAGL terminates the signaling of 2-AG
- MAGL inhibition elevates 2-AG levels -> increased activation of cannabinoid receptors
140
Q
MAGL inhibition elevates 2-AG levels, resulting in CB1/2 activation and reduction in pain
A
- MAGL inhibition -> same effect as marijuana
- elevate 2-AG levels by inhibiting MAGL -> activate cannabinoid receptors -> inhibit pain neurons
- same cells are regulated by PGE2 to increase pain
141
Q
MAGL inhibition reduces arachidonic acid levels and prostaglandin biosynthesis
A
- 2-AG is broken down by MAGL -> generates arachidonic acid
- if you inhibit MAGL -> it increase 2-AG levels and reduce arachidonic acid levels -> therefore reduces prostaglandins
- now arachidonic acid is the intermediate
- arachidonic acid controls levels of prostaglandins
- MAGL is the same enzyme that is used in adipose tissue, brain, etc. to control activity of this potent signaling molecule
142
Q
summary
A
- arachidonic acid is a precursor to numerous bioactive lipids including prostaglandins
- prostaglandins play prominent roles in the modulation of pain and inflammation
- endocannabinoids are derivatives of arachidonic acid that activate cannabinoid receptors
- modulation of bioactive lipid signaling holds therapeutic promise for the treatment of diverse disorders
143
Q
beta-oxidation
A
-multiple isoforms for different lengths
144
Q
fasting state/ketone
A
- low glucose
- acetyl-CoA -> ketone bodies
- liver -> brain
- glycogen is used first and when that is low we use ketones
- beta-oxidation products inhibit pyruvate dehydrogenase -> glycolysis (inhibits fatty acid biosynthesis and cholesterol synthesis)
- beta-oxidation increases ketones
- mutation in acyl-CoA dehydrogenase -> no acetyl-CoA -> no ketones
145
Q
date rape drug (GHB)
A
-shifting OH of D-beta-hydroxybutyrate to the left
