3. Physiology II Flashcards
1
Q
Metabolic Functions of the Liver: Carbohydrate Metabolism Summary: • Glucose buffer function: • Storage of \_\_\_\_. • \_\_\_\_.
- Conversion of other dietary sugars to ____.
- Formation of biosynthetic compounds from metabolites of the ____ metabolism.• Liver is central organ in carb metbaolism
○ Also lipid metabolism - impt steps > listed on the slide
A
glycogen
gluconeogenesis
glucose
carbohydrate
2
Q
- Summary:
- Use of fatty acids to supply energy for other physiological functions: ____.
- Synthesis of cholesterol, phospholipids, and most lipoproteins.
- 80% of synthesized cholesterol is converted into ____.
- Synthesis of lipids from proteins and carbohydrates.• Metabolism of proteins, inc formation of urea in the urea cycle
A
b-oxidation
bile salts
3
Q
Metabolic functions of the liver: protein metabolism
• Summary:
• Deamination of amino acids into keto-acids:
• Required for energy, conversion into lipids or
____ (gluconeogenesis).
- Formation of urea for the removal of ammonia from body fluids.
- Ammonia derives from deamination and ____ in the GI.
- Formation of plasma proteins.
- Except ____ (antibodies).
- 90% of ____ proteins.
- Amino acid interconversion and synthesis of compounds derived from amino acids.
- Biosynthesis of ALL ____.
A
carbohydrates bacterial metabolism gamma-globulins plasma non-essential amino acids
4
Q
Detoxification Functions of the Liver: Xenobiotics Metabolism
- Xenobiotics - foreign compounds:
- Possibly ____: poisons, plant alkaloids, pharmacologic molecules (e.g. drugs).
- Usually introduced as ____: e.g. plant natural products.
• Elimination of xenobiotics: ____.
• Increase in the rate of inactivation and excretion of xenobiotics.
• Conversion from ____ molecules (easy absorption and retention in the body) to
____ molecules (excretion in the urine or bile).
• Multiple enzymes primarily in the ____.
• It can also activate xenobiotics to more ____ forms.
• It is essential in the pharmacokinetics of many ____.
- Phases:
- Phase I: Introduction of ____ groups (OH, COOH).
- Phase II: ____ (glucuronic acid, glycine, taurine, sulfate).
A
toxic food biotransformation lipophilic hydrophilic liver toxic drugs
polar
conjugation
5
Q
Detoxification Functions of the Liver: Xenobiotics Metabolism
• Xenobiotics ○ Not part of our nutrition, \_\_\_\_ molecules ○ Obtain in diet as part of collection natural products (plants produce for own reasons> \_\_\_\_ involved in defense, \_\_\_\_ that help avoid predation) ○ Our body has always been in contact with these § Have a biological effect on our body > usually \_\_\_\_ • Evolved pathways involved in elim of XB > biotransformation ○ Tries to detoxify the bio effect of these molecules by inc rate of inactivation > efficient \_\_\_\_ of molecules OR \_\_\_\_ intermediates ○ Lipophilic molecule > easily absorbed, and cross membranes of cell > retained at high rate § Hydrophilic (converted to be more polar, or electrical charges) § Retention is then impaired > excretion through urine or bile ○ Main system involved in biotransformatino is the one in \_\_\_\_, but other organs have detox systems as well • BT pathways have evolved to protect body from natural products, but enzymes evolved to carry out function are blind > by carrying out a specific rxn that may inc hydrophilicity of a molecule > it's now more \_\_\_\_ than the original one ○ However, ability to modify molecules > making more biologically active precursors > used in \_\_\_\_ of many drugs ○ Some drugs are in inactive form, and then become \_\_\_\_ by undergoing detoxification
A
small
alkaloids
poisons
bad excretion inactivate liver toxic
development
activated
6
Q
Xenobiotics Metabolism
____ microsomal enzymes (oxidation, conjugation)
Hepatic ____ enzymes (oxidation, conjugation)
Hepatic ____ enzymes
(acetylation, sulfation,GSH,
alcohol/aldehyde dehydrogenase, hydrolysis, ox/red)
A
extrahepatic
microsomal
non-microsomal
7
Q
Detoxification Functions of the Liver: Xenobiotics Metabolism
• Phase I reactions:
• ____, reduction and oxidation, exposing or
introducing a ____ group (-OH, -NH2, -SH or
–COOH).
• Increase ____.
• Slightly increase ____.
• Enzymes mostly locate in the ____ (some in
the cytoplasm, e.g. ____ detoxification).
- Phase II reactions:
- ____, sulfation, ____, methylation, conjugation with glutathione, and conjugation with amino acids (glycine, taurine and glutamic acid).
- Strongly increase ____.• Phase I
○ Series of enzymes either oxidize, reduce, hydroxylate, hydrolysis or exposing a new functional group > molecule will have inc hydrophilicity
○ Presence of -OH > more polar, less lipophilic
• Phase II
○ In general, addition of big, ____, chemical groups (as big as the introduction of AA, or monosaccharides)
§ Sulfate
§ Glucoronic acid (monosaccharide)
A
hydrolysis functional reactivity hydrophilicity smooth ER alcohol
glucuronidation
acetylation
hydrophilicity
bulky
8
Q
Phase I Reactions: Cytochrome P450 Enzymes
• Microsomal monooxygenase cytochrome P450 enzymes:
• Oxidation/reduction enzymes.
• Most important in biotransformation due to catalytic versatility and number of xenobiotics metabolized.
• 400 isozymes in 36 families.
• ____-containing proteins: ____ ring with Fe atom.
• Abundant in ____ (microsomal vesicles).
• Biosynthesis or catabolism of steroid hormones, bile
acids, lipophilic vitamins, fatty acids and eicosanoids.
• Nomenclature: • CYP (\_\_\_\_) + \_\_\_\_ + individual \_\_\_\_: • CYP1A2: metabolizes \_\_\_\_. • CYP3A4: most \_\_\_\_ CYP with \_\_\_\_ substrate specificity. • CYP2E1: metabolizes \_\_\_\_ and ethanol.
• Most impt enzymes: CP450 enzymes ○ Located in microsomal vesicles (in the SER) ○ Contain as active site > heme w/ iron § Exactly like heme group in \_\_\_\_ and those cytochromes in the ox phos chain ○ 450 > for the \_\_\_\_ of light as which these enzymes absorb the most • CYP (gene family) > P450 enzymes; first number is a subfamily, and then the individual enzyme • Some enzymes have a wide specturm of action > can modify via ox/red a lot of subtrates; other enzymes are more restricted in their range of substrate specificity
A
heme pyrrole liver smooth ER gene family subfamily gene caffeine abundant broad acetaminophen
Hb
wavelength
9
Q
Phase I Reactions: P450-mediated Redox Reactions
In the drug-oxidizing reaction, one atom of ____ is used to form a hydroxylated metabolite of a drug.
The hydroxylated metabolite may be the end product of the ____ or serve as an ____ that leads to the formation of another metabolite.
Mechanism of reaction:
1. Drug/metabolite substrate binds to ____ (i.e., Fe3+)
P450.
2. ____ of the drug/P450 complex by CYP reductase,
using electrons donated by the reduced form of ____.
3. The drug/reduced (i.e., Fe2+) P450 complex interacts
with ____.
4. ____ drug/metabolite and water are produced.
• Redox > will go over cycles of oxidation of reaction (themselves, substates, and cofactors) 1. Drug substrate > will bind to P450 cytochrome molecule which is in an oxidized state (iron atoms in the heme group are in the +3 balance) 2. Through redox reaction with another enzyme CP450 reductase (+flavoprotein), the CP450 will get reduced (has obtained electrons from the oxidation of NADPH to NADP+, reduced flavoprotein will now reduce the CP450) 3. Enzyme will interact with molecules of O2 > formation of complex bound to O2 4. O2 oxidizes the drug and oxidizes the CP450 back to its original form > new intermediate metabolites that in a more oxidized form i. A metabolite that's more oxidized is less \_\_\_\_
A
oxygen reaction intermediate oxidized reduction NADPH oxygen oxidized
lipophilic
10
Q
Participation of CYP Enzymes in the Metabolism of Clinically Important Drugs
CYP Enzyme
Examples of substrates
1A1
Caffeine, Testosterone, R-Warfarin
1A2
Acetaminophen, Caffeine, Phenacetin, R-Warfarin
2A6
17-Estradiol, Testosterone
2B6
Cyclophosphamide, Erythromycin, Testosterone
2C-family
Acetaminophen, Tolbutamide (2C9); Hexobarbital, S- Warfarin (2C9,19); Phenytoin, Testosterone, R- Warfarin, Zidovudine (2C8,9,19);
2E1
Acetaminophen, Caffeine, Chlorzoxazone, Halothane
2D6
Acetaminophen, Codeine, Debrisoquine
3A4
Acetaminophen, Caffeine, Carbamazepine, Codeine, Cortisol, Erythromycin, Cyclophosphamide, S- and R- Warfarin, Phenytoin, Testosterone, Halothane, Zidovudine
• Wide range of substrates for \_\_\_\_ • Others are even wider in their spectrum ○ 2C does well done \_\_\_\_ • Same molecule can be modified by different enzymes ○ Modifications are different > oxred reactions, but may not be the same modifications
A
1A1
drugs
11
Q
Phase I Reactions: P450-mediated Redox Reactions
- Mechanisms of Biotransformation:
- Formation of an inactive polar metabolite:
- ____
- Formation of an active metabolite:
- ____, caffeine
- Formation of a toxic metabolite:
- ____ – NAPQI• Enzymes are blind, will modify a molecule bc that molecule fits into their active site, and the enzymes don’t know if the product that results is going to be inactive, more active or toxic
○ 3 possibilites:
§ Formation of an inactive polar metabolite (goal of the pathway)
§ But, since the enzymes are blind > can act on metabolite to make them active
§ Or, the modification of an inactive metabolite results in a toxic product (worst case)
A
phenobarbital
clopidogrel
aceaminophen
12
Q
P450-mediated Biotransformations: Formation of an Inactive Polar Metabolite
• Example: Phenobarbital
• Barbituric acid derivative: ____-inducing and
antiepileptic.
• Hydrophobic: penetrates the ____,
slow renal elimination.
• Excretion: 75% in the form of ____ metabolites.
• ____ not a good substrate for conjugation
reactions:
• Phase I: P450s add a polar ____ group to the aromatic ring.
• Phase II: conjugation with ____ or
sulfate.
• He wants us to get what can happen from each of these slides • Modification of phenobarbital > fits the goal of the pathway perfectly ○ Active molecule > initially modified > results in an inactive metabolite ○ \_\_\_\_ (active) > retained in the body • First reaction > highlight in red > P450 enzymes add a -OH to the original active PB metabolite (on aromatic group), the original PB is not a good substrate for the phase II enzymes > this modification makes the metabolite inactive, but more easily conjugated by phase II enzymes (add sulfate or GA)
A
sleep blood brain barrier conjugated phenobarbital hydroxyl (OH) glucuronic acid
hydrophobic
13
Q
P450-mediated Biotransformations: Formation of an Active Metabolite
- Example: Clopidogrel (Plavix, Iscover, Clopilet, Ceruvin).
- Irreversible inhibitor of the platelet P2Y12 ADP receptor.
- Functions:
- ____ drug.
- ____ agent.
- ____ pro-drug with no pharmacological activity.
• Active metabolite:
• ____ derivative.
• Formed in the liver in two ____-mediated
steps.
• Clopidogrel ○ The active agent of plavix is not active at all ○ First must be absorbed by intestine > during absorption by intestine > clopidogrel can be the substrate for a family of enzymes > esterases § 85% of CD that is reaching the intestine is directly inactivated by the esterases > the \_\_\_\_ group is lost § 15% of the CD escapes inactivation of this step > via two sets of P450 enzymes (2C19) the end result > \_\_\_\_ metabolite (has the functions of the drug, NOT THE ONE GIVEN TO THE PATIENT) ○ Took advantages of CP450 enzymes
A
antiplatelet
fibrinolytic
inactive
thiol
P450
methyl
active
14
Q
P450-mediated Biotransformations: Formation of a Toxic Metabolite
• Example: Acetaminophen (paracetamol).
• ____, anti-inflammatory.
• Inhibitor of cyclooxigenases (mainly ____).
• P450 metabolism in the liver forms ____ (N-acetyl-p-benzoquinone imine), an ____ agent.
• NAPQI is primarily responsible for the toxic effects
of paracetamol: acetaminophen overdose.
• Treatment with ____.
• At usual doses, NAPQI is quickly detoxified by
conjugation with ____.
• Sometimes the actions of the enzymes make things worse > formation of metabolite that's toxic • During detoxicaition > follow the blue lines ○ PA can be directly by phase II enzymes > add sulfate or GA > these metabolites are ianctive (ok) • Some CP450 enzymes can recognize the PA and then they modify in such a way > NAPQI (red path) ○ Toxic > alkylating agent > can react with macromolecules in the cell (\_\_\_\_ and \_\_\_\_ of NA > activating NA and enzymatic activities) ○ Accumulation of this > responsible for the toxic effects of PA > acetaminophen overdose ○ Only to inactive > allow \_\_\_\_ reaction > conjugation of molecule with glutathione ◦This is induced by treatment with N-acetyl-cysteine, which is a \_\_\_\_ molecule that reduces glutathione so that it can be attached
A
analgesic COX-2 NAPQI alkylating N-acetyl-cysteine glutathione proteins bases phase II reduced
15
Q
P450s Also Metabolize Endogenous Metabolites
• CP450 enzymes are involved in many reactions that have nothing to with detox: ○ Synthesis of \_\_\_\_ ○ Synthesis of \_\_\_\_ hormones from cholesterol § Testosterone and its derivatives § Enzyme that regulated by negative feedback by bile acids in hepatocytes > cytochrome P450 enzyme Therefore, some P450 enzymes are involved in the \_\_\_\_, some are a part of the general \_\_\_\_ of the cell
A
FA
steroid
detoxification
metabolism
16
Q
Phase II reactions: Conjugation • Phase II reactions: • Major conjugation reactions • Glucuronidation - \_\_\_\_ capacity. • Sulfation - \_\_\_\_ capacity. • Acetylation - \_\_\_\_ capacity.
- Other Conjugation Reactions: ____, S- methylation, ____ conjugation (glycine, taurine).
- Adding large chemical groups to a metabolite > conjugation reactions
A
high low variable O-methylation amino acid
17
Q
Conjugation Reactions: Glucuronidation
• Example: Morphine.
• Morphine is conjugated to form ____.
• M6G is the major ____ metabolite of morphine.
• Responsible for pharmacological effects of morphine and ____.
• Morphine is not an active molecule ○ M6G (morphine + GA) is the active metabolite of morphine ○ Phase II conjugation reaction
A
morphine-6-glucuronide (M6G)
active
heroine
18
Q
Conjugation Reactions: Sulfation
• Example: Minoxidil. • Trade name: Rogaine. • \_\_\_\_ channel opener. • Antihypertensive \_\_\_\_ medication. • Slows hair loss and promotes hair regrowth in patients with \_\_\_\_ (male baldness). • \_\_\_\_ is the active metabolite.
• Minoxidil > present in rogaine (anti-baldness medicine) ○ Minoxidil sulfate is the active metabolite
A
potassium
vasodilator
adronergic alopecia
minoxidil sulfate
19
Q
Detoxification and Recycling Functions of the Liver: Heme and Iron Metabolism
- Iron is an essential nutrient:
- ____ O2 binding proteins:
- Hemoglobin.
- Myoglobin.
- Metabolic enzymes:
- ____ – e.g. cytochrome c, P450s (CYPs).
- ____ enzymes – e.g. aconitase.
• Immunity – pathogen-killing ____.
- But potentially toxic:
- Highly reactive with ____ – tissue toxicity:
- ____.
- ____ cirrhosis.
- ____ abnormalities.• Heme group is a problem to dispose of during destruction of old RBC, but iron (atom at the center of the heme) > important ion in the body
○ Not only is it an essential nutrient, but its also potentially toxic > high levels can react with O2
○ Metabolism of rion is highly ____
○ Since of use of iron in the heme group and the destruction of Hb > are massive in terms of the amount of Hb and cytochromes and iron that’s recycled > the homeostatic mechanisms that maintain the leevls of iron are really tight
A
reversible
cytochromes
iron sulfur
free radical
O2
cardiomyopathy
liver
endocrine
regulated
20
Q
Detoxification and Recycling Functions of the Liver: Heme and Iron Metabolism
• Systemic iron levels are tightly controlled:
• integrative mechanism that involves iron absorption, storage, and recycling.
• Hepatic regulation of iron homeostasis:
1. Major site for production of proteins that maintain systemic iron balance – e.g.
____.
2. Storage site for excess iron – e.g. as ____ stores.
3. Critical for the mobilization of iron from hepatocytes to the circulation to meet metabolic requirements.
1. Transferrin, a transporter protein a. Produced by \_\_\_\_ 3. Liver has to be able to mobilize the stored iron depending on the metabolic requirement of the body A. If there is an increase in the formation of \_\_\_\_, iron has to be mobilized from liver to bone marrow.
A
transferrin
ferritin-bound
hepatocytes
RBCs
21
Q
• Shows levels of iron that we have in the body
○ Most of the iron is used by the ____ for the synthesis of myoglobin (O2 storage molecule), or in the ____ for the production of RBC
○ Most of the storage of iron is in ____, and transiently in the ____ comprising the reticuloendothelial system
§ Also in:
□ ____ cells (in liver)
□ ____ organ (in the spleen)
A
muscles
BM
hepatocytes
macrophages
kupffer
lymphatic
22
Q
Daily Iron Requirements
Between ____ mg/d has to be absorbed in order to compensate for the amount we lose in the feces.
Don’t have to memorize these numbers
Again, the system has to be in balance (goes back to slide 24). If there is a deficiency in your dietary iron, it means that eventually the iron level will drop and cause ____.
A
1.0-1.5
anemia
23
Q
Iron absorption, transport & storage
There are 2 sources of iron: ____ and ____
There are many places where you can see oxidation and reduction of iron atom.
Then goes on to say “the metabolism of iron is important and a lot of studies have been done on it, but it’s a complete mess. It’s such a mess that some of these oxidation states of the iron atom are not completely clear.
The first rule to understand this slide and learn the basics, forget about the oxidation state of the iron. For instance, in
this slide/the place where I took this slide, it says here on the left side that these steps 5 through 8 involved reduced iron.
Well, I look into the literature and actually to me it looks like it involves oxidized iron. I couldn't make this situation clear, so I made the rule for this module is forget about oxidation state." • He won't be asking questions on oxidation/reduction of iron (Fe2+ vs Fe3+)
A
diet
recycling
24
Q
Iron absorption, transport and storage
• Iron ingest in the food can be reduced or oxidized (usually oxidized) in the ____ environment of the stomach.
• Through the presence of reducing molecules like ____, cystiene, and ascribe acid, it will get reduced to ____.
• What is important here is that the stomach produces a protein that was originally know as ____.
◦ Gastroferrin turns out to be just ____, one of the molecules that make up the mucous layer of stomach that has a high affinity for iron.
◦ Therefore it is used as a ____ of iron from the stomach all the way to the small intestines
• Iron binds to gastroferrin/mucin, which protects iron from precipitating in an ____ way.
• In the small intestines, gastroferrin releases the iron lets the ____ to absorb it.
A
acidic
glutathione
Fe2+
gastroferrin mucin transporter uncontrolled enterocyte
25
Enteric Iron Absorption
• Dietary iron is absorbed by duodenal enterocytes:
• Reduction of Fe+3 to Fe+2 by the____ (DcytB).
• Internalization via the apical iron transporter, ____ (DMT1).
• Iron is either stored bound to ____ or exported by the
____ (FPN), located on the
basolateral side.
* Following export:
* Re-oxidation back to ____.
* Binding to ____ (a β-globulin) to form ____ (Tf) and circulation in the plasma.
What happens in the enterocyte?
• There is a cytochrome that ensures that the absorbed iron is the reduced form (points to duodenal
cytochrome b/DcytB)
• At the apical level of the enterocyte, there is an atom specific transporter. It can actually transport any divalent
metal (points to DMT1). The most common is iron in the reduced form, but it can also be used to absorb, for
instance, ____.
• Inside the cell, iron is bound to a protein called ferritin.
◦ Therefore, some iron (iron bound to ferritin) can be stored ____ in the enterocyte
◦ Or can be exported to the bloodstream into the portal circulation through the basal domain through a
channel molecule/iron transporter known as ferroportin.
‣ Ferroportin is a molecule you will need to remember, because this is one of the places that is
highly ____ in its action in terms of maintaining constant iron homeostasis.
• Then, if the iron is exported ("there is a change in the oxidation state but whatever"), iron has reached the
portal circulation.
duodenal cytochrome b
divalent metal transporter-1
ferritin
iron exporter ferroportin
Fe3+
apotransferrin
transferrin
zinc
transiently
regulated
26
Iron absorption, transport & storage
Iron usually does not travel through the bloodstream in free form. In the bloodstream, iron is bound to a protein
known as ____. The ____ complex is the one that reaches the liver through the portal circulation.
transferrin
| transferrin-iron
27
Transferrin Receptor-Mediated Endocytosis at the Hepatocyte
• Major mechanism for iron uptake.
• As the pH of the endocytic vesicle drops:
• Fe3+ is released from ____.
• Fe3+ is reduced to ____ by an endocytic reductase.
• Exported to the cytoplasm by
____.
```
• Cytoplasm:
• Some free ____ .
• Combination with apoferritin
to form ____ – majority.
• Hemosiderin: insoluble
complex of degraded ferritin and large ferric ____ chains – iron overload, not ____.
```
In the liver, hepatocytes absorb these irons. The mechanism by which these liver cells absorb the iron is ____.
Receptor mediated endocytosis
• Specific receptors present on hepatocytes are able to recognize the transferrin molecule bound to ____ atoms of
iron.
• The binding of transferrin-iron to the receptor will induce the invagination of plasma membrane, and the
formation of ____-coated pits that are characteristic of the first stage in the formation of the endocytic vesicles.
• In the endocytic vesicles (aka endosomes) during receptor mediated endocytosis, there is a change in pH in
endocytic vesicles. Eventually becomes very ____ (~pH 5.5)
• This change in pH will induce the release of iron out of transferrin.
• Then the iron is simply pumped out from the endosome into the cytoplasm of the liver cell using the same
____ (DMT1) at the apical domain of the enterocyte.
• Both the ____ for transferrin and ____ itself get recycled to the surface of the cell, and transferrin goes
into circulation to bind more iron
Tf
Fe2+
DMT1 iron transporter
Fe2+
ferritin
hydroxide
mobilizable
```
recetpro mediated endocytosis
2
clathrin
acidic
divalent metal transporter
receptor
transferrin
```
28
Iron absorption, transport and storage
• Demand for iron In periphery > liver works in ____ > binding iron to transferrin in BS > reaches destination > like BM to product Hb
○ Fate of iron that's ingested in diet
• Once reach BS and liver
○ Two sources of iron: tiny amount of ____, and most of iron that comes from ____ of RBC and turnover of other cells containing enzymes that have iron
§ Macrophages in RES (endothelial system) > break down old ____ > liberate around 18 mg of iron per day; whereas we ingest only 1-2 mg per day and lose about the same amount
§ Big chunk of irion is coming from ____ of rpoteins containing iron
```
reverse
diet
recycling
RBC
turnover
```
29
Fe from ____
(1 mg/day)
>
____ in bone marrow produce hemoglobin (18 mg Fe/day)
>
```
____ in spleen remove and break down
senescent RBCs (18 mg Fe/day)
```
>
Transferrin in plasma carries Fe back to ____
(17 mg/day) (to erythyroid)
OR
____ (1 mg Fe/day)
```
intestine
erythyroid precursor
macrophages
bone marrow
losses
```
30
Red Blood Cell Recycling and Hepatic Iron Metabolism
* RBCs last ≈120 days.
* Degraded by ____ (RE) system:
* ____ macrophages
* ____ macrophages - Kupffer cells.
• Human adult, 1-2×108 RBCs destroyed per hour = 6 g of
hemoglobin per day.
* Hemoglobin degradation:
* Globin → ____ for reuse.
* Heme:
* Iron → iron ____ and reuse.
* Porphyrin ring → ____ pigments.
• Most heme from RBCs (85%) - rest from turnover of
____, P450s, immature erythrocytes
* Most important: Hb coming from ____
* 6g of Hb is hydrolyzed every day by the cells in the RES (reticulo)
```
reticuloendothelial
spleen
liver
amino acids
bile
cytochromes
RBC
```
31
* Molecule of Hb > formed by ____ chains of ____ different kinds of globin proteins > at the center there is the ____ group (ring of carbon atoms [pyrolle ring] at which the center there isa. Single atom of iron) for each molecule of Hb we have ____ iron atoms
* After macrophages destroy RBC and liberate the Hb > the globin part (4 chains) are easily disposed of (they're ____ thatre hydrolyzed by the proteinases) > releasing the ____ > will be reduced like we saw in FS
* Leaves us with what happens with heme > it's destroyed by a different set of enzymes that will liberate the iron, and produce a series of substances that derive from the pyrolle ring known as the ____
4
two
heme
4
proteins
AA
bile pigments
32
Red Blood Cell Recycling and Hepatic Iron Metabolism
* Iron is recovered from the degradation of hemoglobin and heme by ____ in the phagocytic vesicles and ____.
* Iron is exported to the bloodstream through the basolateral iron transporter ____.
* Macrophage from the RES that phagocytosed a RBC > using hydrolytic proteases in the phago vesicles > degrade the Hb and a specific enzyme (heme oxygenase I) will break the heme group to liberate iron
* This iron can be exported into the BS thorugh the same iron transporter (ferroportin I) that we saw in the enterocytes, which also happens to be ____
* Iron from Hb > circulation > binds transferrin, and added to big pool of circulating iron > either into ____, or into the liver into ____ (____ to produce more Hb)
hydrolytic enzymes
heme-oxygenase I
ferroportin
hepatocytes
storage
BM
reduced
33
Hepatic Control of Iron Metabolism
* Hepcidin – major iron metabolism hormone:
* 25-aa peptide.
* Also has an ____ function.
• Hepcidin induction:
• Iron loading:
• Inhibition of duodenal ____ - decrease in duodenal ____ absorption to normalize iron levels.
• Inhibition of ____ FPN – decrease in Fe transport from recycling from RBC
recycling.
• Inflammation:
• Restriction of blood Fe levels during an infection → inhibition of ____.
• Hepcidin repression:
• Iron deficiency:
• ____ of duodenal FPN - more Fe to be transported from the enterocyte to the bloodstream.
• ____ of macrophage FPN - decrease in Fe transport from recycling from RBC
recycling.
• Hypoxia.
• ____.
• Big pool of iron (dietary and recycled iron) > regulated in terms of levels by the liver
○ One liver hormone > hepcidin > major hormone regulating metbaolism of iron
§ Small molecule, 25 aa peptide; iron metbaolism hormone, and has an antimicrobial function
```
antimicrobial
FPN
Fe
macrophages
bacterial growth
```
de-repression
de-repression
erythropoiesis
34
Hepatic Control of Iron Metabolism
• ____ produces hepcidin
○ In cases with high levels of iron in body (high iron loading) > the hepatocytes induced to prodcue hepcidin > the target can be the ____ cells themselves, the ____ in the RES, or the ____ in the SI
• Hepcidin inhibits the ability of ferroportin to transport iron
○ High levels of irion > hepcidin inhibits ferrorportin in hepatocytes > will be less iron going from hepatic stores into the BS
○ Will also inhibit FP in macro's that are digesting RBC > will not be able to export iron
○ FP in the enterocyte, therefore iron from the diet will not be re-xported from the BS > response to high levels of iron in the body > shut down all the export mechanisms
§ Repressing the action of FP
• Similar situation happens in inflammation due to bacterial infection
○ Hepcidin has antimicrobial function
○ Iron is also an essential element for the growth of bacteria > have their own cytochromes and they use iron
§ In cases of inflam and the body is fighting a pathogen > presence fo inflam increases level of hepcidin > repressing ferroportin and lowers level of circulating iron in the BS > starving the bacteria of irion
• When demand of iron is high > like in ____, which induces erythropoiesis > the formatino of RBC requires Hb and iron
○ The production of hepcidin is inhibited in these situations > low levels of hepcidin will depress levels of FP on liver, macros and enterocytes > higher export of iron from these three sources > inc concentration of iron in the BS
```
liver
liver
macrophages
enterocytes
hypoxia
```
35
Heme Metabolism: Formation of Bile Pigments
* Bilirubin Metabolism:
* Bilirubin formation in the ____.
* Transport of bilirubin in ____.
* Hepatic bilirubin metabolism:
* ____.
* Conjugation
* ____ excretion
* Intestinal excretion.
* Formation of bile pigments involves all these steps
* Macros, liver, and intestines are involved
macrophages
plasma
uptake
biliary
36
Bile Pigment Metabolism: Bilirubin Formation
Heme oxygenase (HO) catalyzes the degradation of heme, producing ____, ____, and ____.
* During degradation of Hb > globins are degraded by proteases, and the porphyrin/pyrolle ring is first attacked by heme oxygenase > catalyzes degrad of heme group by removing one carbon (arrows), and combined with an oxidation of resulting molecule
* From ring, we have a ____ molecule
* Reaction produces free iron (exported by the macro's), and CO (form in which the carbons that closed the circle has been eliminated/released)
* Molecule resulting from the HO > is biliverdin
biliverdin
Fe2+
carbon monoxide
linear
37
Bile Pigment Metabolism: Bilirubin Formation
• Biliverdin is the subtrate fort a second enzyme > ____ > catalyzes the reduction of biliverdin into ____
○ Only ____ modification (arrow), and reorganization of ____
biliverdin reductase
bilirubin
chemical
double bonds
38
Bile Pigment Metabolism: Bilirubin Formation
• CO
○ Usually associated with a poison (respiratory poison)
○ Metabolism of Hb, whereas CO2 can ____ bind Hb (can bind and release), CO binds Hb ____ > inactivating that oxygen transporter (Hb)
• Dumb idea for body to degrade heme groups and forming CO
○ The only enzymes capable of catalyzing can only produce CO (evolution couldn’t find alternative pathway)
• Small % of Hb is bound to a poison bound by CO; the CO comes from this step
○ Gas, freely diffuses into BS and other RBC > ____ Hb
○ Always have a background level of inactivated Hb due to produciton of CO during recycling of RBC
§ Small level
§ ____, and behind tractor trailer > poisoned more
○ Body has used the poison, and reconverted into a molecule that can be involved in othe processes:
§ Can be used as a ____ molecule
□ CO has functions that are ____, opposite and sometimes the same as NO
□ Some of the CO ends up poisoning a little bit of myoglobin
reversibly
irreversibly
inactivating
smokers
signaling
complimentary
39
Bile Pigment Metabolism: Bilirubin Transport in Plasma
• Bilirubin (unconjugated) is lipid-soluble: exported from ____ into the circulation.
• Excessive production of ____ bilirubin from excessive destruction of RBCs
leads to ____.
• Transported in plasma as a complex with serum ____:
• Complex too ____ to be excreted in the urine.
• Complex is ____-soluble.
• Prevents entry of bilirubin in most ____, avoiding damage.
Albumin + free Bilirubin Bilirubin ~ Albumin Complex
• Unconjugated > free bilirubin
○ ____ soluble
○ Would cross PM easily
• Hemolytic jaundice > arrives form hemolysis of degrad of ____
• Bilrubin is transported as a complex > albumin
• Accumulation of bilirubin is toxic
○ Immediately binds albumin to form the complex
○ How it travels in the blood
```
macrophages
unconjugated
hemolytic jaundice
albumin
large
water
tissues
```
lipid
RBCs
40
* Certain drugs such as ____ and ____ compete with bilirubin for albumin binding and displace bilirubin.
* Bilirubin may enter into the brain in neonates and may cause ____ (a type of brain damage that can cause ____ and hearing loss).
• Formation of bilirubin-albumin complex is subjected to ____ equilibrium law
◦If there is enough ____, there will be formation of bilirubin-albumin complex
• Drugs that complete with bilirubin in albumin > preventing formation of the complex > inc in cxn of free bilirubin > allowing the entry of bilirubin across PM
sulfonamides
salicylates
kernicterus
cerebral palsy
chemical
albumin
41
Bile Pigment Metabolism: Hepatic Conjugation
* The ALB:UCB complex reaches the ____, where UCB is liberated.
* At the hepatocyte surface, UCB enters the cell by both ____ transport (BT) and ____.
* In the cytoplasm, UCB binds to ____ (GST, a.k.a. ligandin) and is transported to the ____.
* UCB is ____ by bilirubin-UDP- glucuronosyltransferase (UGT1A1) to mono- and diglucuronides.
* BMG and DMG are ____-soluble and actively transported by ____ across the canalicular membrane into the bile.
• Complex (ALB-UCB) it will reach the portal circulation (hepatic sinusoids in the vicinity of the hepatocytes) > can cross the endo and will reach the space of Disse > sinuosid in the vicinty of the hepatocytes that's separated from venous sinusoids
○ Bilirubin is liberated here > lipid soluble > enters the cell mostly thorugh free diffusion but there's indication that there may be a xporter
○ Unconj bilirubin enters the cyto of the hepatocyte > binds another carrier protein > GST > carrier protein was identified by ability to bind bilirubin > ligandin
○ Bilirubin+GST > xported to the ER > where GST is liberated, and the unconj bili is conjugated > one or two GA groups will be added to biliruibin
§ Produces intermediate that contains one or two GA (mono or di)
○ Two molecules comprise the conjugated bilirubin > water-soluble
§ The hepatocyte exports the conj bilirubin into the bile canaliculus (actively pumped)
§ Same way that the hepatocyte pumps out bile acid
□ This is same active transporter (MRP2)
○ Conj bili is now part of the ____ > that will reach the SI
```
space of Disse
facilitated
simple diffusion
glutathione-S-transferases
ER
```
conjugated
water
MRP2
bile
42
Bile pigment metabolism: hepatic phase - conjugation
Unconjugated bilirubin:
Bilirubin not conjugated with ____.
Also called ____, indirect bilirubin.
“Indirect” because it is bound to serum ____, and must be released by an ____ solvent before it can react and be assayed.
Conjugated bilirubin:
Bilirubin modified with ____. Also called ____, direct bilirubin.
• Left side - bilirubin mono GA, and on the right bilirubin di GA
○ Making the conjugated bilirubin
• In the clinical lab > measurement of bilirubin is really important
○ Distinguish between indirect and direct
§ Indirect: hemobilirubin is the unconjugated bilirubin, bc in the BS unconj bili travels associated with albumin
□ So to measure the total cxn of bilirubin > liberate albumin from bili using an organic solvent - it's an indirect measurement
§ Direct: conj bili, if any is present in BS > doesn't travel assoc with albumin > can be directly ____
□ Hepatic bilirubin; only place where conjugation can take place is in the ____
• [EXPLANATION AT END???]
glucuronic acid
hemobilirubin
albumin
organic
glucuronic acid
hepatic bilirubin
measured
hepatocytes
43
EXPLANATION
Answer: if you need to measure the levels of bilirubin in the blood because you suspect that something is
wrong (for instances, someone has jaundice), you do two measurements
• one is direct measurement.
◦Without treating blood sample with any organic solvents, there are methods to measure bilirubin directly. But this direct bilirubin you can measure is only the one that is not associated with albumin. Therefore, it’s ____. If there is high levels of conjugated bilirubin in the blood, it
means that conjugated bilirubin produced in the hepatocytes is not being excreted efficiently or
something is wrong with metabolism of hepatocytes such as that conjugated bilirubin ends up back
into circulation where there shouldn’t be any.
◦If you find direct bilirubin level is too high, it’s an indication of ____ mechanism problem
• If, however, after doing an indirect bilirubin measurement, which first you have to release the unconjugated bilirubin from the albumin, then you see that the high level of bilirubin in the blood is because you have high levels of indirect, meaning ____, it means that there can be, for
instance, excessive activity of those ____ eliminating red blood cells, case of histolytic jaundice due to high level of red blood cells being degraded. Therefore, there is a lot of bilirubin circulation
• Each direct and indirect indicate different kind of problem
• Indirect does not necessarily indicate there is anything wrong with ____
conjugated
hepatic
unconjugated
macrophages
liver
44
Bile Pigment Metabolism: Hepatic Phase – Bile Secretion
• Conjugated bilirubin is released into the ____.
• ____ transport against concentration gradient by
____, requires ATP.
• Mutations in the MRP2 gene cause ____, an autosomal ____ disorder of conjugated hyperbilirubinemia.
• ____ bilirubin is normally not excreted.
• DJ syndrome
○ Bc the exporter is mutated > the hepacoytes are not good at dumping conj bili in bile, so some of it ends up in the ____
§ Usuaully unconj is not excreted, but conj is
```
bile canaliculi
active
MRP2
dubin-johnson syndrome
recessive
unconjugated
```
circulation
45
• IN blood, would expect to see most bili is ____, very tiny bits of conj bili would be present
• IN hepatocytes > ____ and ____
○ Conj derives form unconj
• Bile duct > canaliculus > most of the bili is ____
unconj
conj
unconj
conj
46
• Major source of bile pigment is destruction of RBC > macros breakdown cells > liberate heme groups and form ____ bili > taken up by liver > conj with GA > produce conj bilirubin > since produced in liver > secreted as part of ____ > reach the SI with the rest of the bile components
• In intestine, the conj GA that the liver used to tag will be removed by ____ > produce unconj bili; another rmodification: further modification of bili into another moelcule > ____ > produced by intestinal bacteria, several things can happen: some of the UB can be reabsorbed by the intestine, enter the portal circulation and end up in liver to be rexcreted as part of ____ (enterohepatic circ > refers to EH UB cycle), so it comes back as UB to the SI
○ Some of the UB (since part of circ) can bypass liver completely and end up in the ____ > UB is transformed (chemically) into a diff molecule > ____ > it's yellow > gives the ____ color to urine > excreted out of body in the urine; the bulk of UB in the SI eventually is excreted in the feces (via LI), after subjecting to another xform > oxidized by intestinal bacteria to a different moleule > ____ (brown) > gives color to the feces
unconj
bile
intestinal bacteria
urobilinogen
bile
kidney
urobilin
yellow
stercobilin
47
Bile Pigment Metabolism: Intestinal Phase
• Formation of urobilins in the intestine:
• ____ is deconjugated and reduced by intestinal bacteria to urobilinogen, a ____ compound.
• Most urobilinogen in the feces is oxidized by bacteria to
____, which gives stools their color.
• Some urobilinogen is reabsorbed from the gut into the portal blood and transported to the kidney, where it is converted to the yellow ____ and excreted, giving urine its color. (enterohepatic circulation of bilinogens)
BDG
colorless
stercobilin
urobilin
