1
Q
Hemoglobin structure?
A
- consists of 4 polypeptides (proteins), called globins
- two types of globins, alpha and beta
- each molecule has 2 alphabeta dimers (tetramer) in hemoglobin (held together by ionic bonds for flexibility between the dimers)
- has 4 heme prosthetic groups, prosthetic group is not a polypeptide, but forms part of a functional part of protein
- each globin chain binds on heme, and each heme can bind one molecule of O2
- globin chains within dimers held together by hydrophobic bonds
2
Q
Globin chains?
A
- heme binds in crevice between two helices of each globin
- 2 alpha types (zeta, alpha)
- 4 beta types (epsilon, gamma, delta, beta)
- developmental regulation controlled by differentiation specific transcription factors
- genes transcribed only in a narrow stage of development in 5-7 days from pro erythroblast to enucleation
- mRNAs very stable, translation continues after enucleation
3
Q
globin genes? (6)
A
- alpha genes on chromosome 16
- beta genes on chromosome 11
- combining them, different forms of hemoglobin
- Hb gower expressed in embryonic yolk sac
- Hb F expressed in fetus from first trimester until 6 months after birth
- Hb A2 found throughout life
- HbA normal adult form
4
Q
developmental regulation of globin chains? (7)
A
- alpha globin begins with zeta, then drops
- alpha picks up and is throughout life
- 6 months after birth, entirely beta chains
- different properties in each type
- F has higher affinity for O2 than A
5
Q
Hemoglobin F (Hb F, alpha2gamma2)?
A
- gamma globin not expressed after 6 months of age
- less than 1% total Hb in adults
- found in small number of RBC called F cells
- HbF has higher affinity for O2 than HbA
- therapy goals for sickle cell anemia when there is a problem with beta globin chain, is to increase number of F cells
6
Q
Hemoglobin A1c?
A
- under physiological conditions, Hb is slowly non enzymatically glycated (added glucose)
- extent of glycation depends on plasma concentration of glucose
- measured in diabetics (information about blood glucose levels over the 120 day lifespan of RBC)
7
Q
How many different types of globin chains are there?
A
-6 (2 alpha, 4 beta), each encoded by a different gene
8
Q
What is the major adult form of hemoglobin?
A
- has 2 alpha globin chains and 2 beta chains
- it is called HbA or HbA1 (alpha2beta2)
9
Q
Sickle cell disease as it relates to globin chains? therapy?
A
- there is a mutation in the beta globin chain
- goal of therapy is to increase number of F cells, which still express some HbF, because they have higher affinity for O2
10
Q
Heme structure?
A
- heme is a prosthetic group also found in other proteins including cytochromes (ETC, cytochrome p450), catalase, peroxidases
- largely planar molecule, consisting of tetrapyrrole ring (protoporyphyrin IX) with one ferrous ion (Fe 2+) in its center
- Fe 2+ does not fit perfectly in the plane, but puckers out to one side as it binds to the 4 N atoms of 4 pyrrole groups
11
Q
What is heme if not associated with protein?
A
- lipophilic pro oxidant
- tends to damage membranes, don’t want it to build in tissues
- pathways for synthesis are highly regulated so as to not have too much heme
12
Q
What are the conjugated double bonds responsible for on heme?
A
- color
- oxygenated is red
- deoxygenated is blue (cyanosis)
13
Q
Oxidation state of iron in heme?
A
- Fe 2+ can only bind O2 (protoporyphrin IX)
- if oxidized to 3+ form, cannot bind O2 (met-hemoglobin)
14
Q
How much heme binds each globin chain?
A
- one heme per globin chain
- 4 heme total
15
Q
What does iron bind to in heme?
A
- 4 N in porphyrin rings
- a histidine AA on globin protein
- free to also bind O2
16
Q
What happens under normal conditions to the ferrous ion?
A
- iron becomes oxygenated, it binds O2
- it is not oxidized
17
Q
Proximal histidine? (12)
A
-a bond is formed between the Fe2+ of heme and a histidine AA in the F helix of the globin chain
18
Q
Distal histidine? (12)
A
- histidine on the E helix is in close proximity helps to stabilize the interaction with O2
- also prevents oxidation of Fe2+ to Fe3+
- reduces Hb affinity for CO
19
Q
Sources of iron?
A
- Fe absorbed in small intestine as heme or free Fe
- absorption of free Fe is less efficient and affected by diet
- increased by Vit C, acidic pH
- decreased by tannates (tea), carbonates, phosphates - transfer of Fe from mucosal cell to capillary is regulated by Fe requirement
- Hepcidin produced by liver when Fe levels are high, inhibits transport from mucosal cells - Fe binds apotransferrin (transferrin after binding) in capillary, carried to Fe consuming tissues, especially bone marrow, liver
- no physiological path for excretion of Fe
- lost by bleeding, sloughed off cells, urine, feces
20
Q
Transferrin?
A
- two binding sites for Fe3+
- carries Fe in blood, delivers to cells by receptor mediated endocytosis
- presence of unbound sites protects against infection by Fe dependent pathogens
- level of saturation changes with Fe availability
- usually only 33% saturated
- TIBC (transferring iron binding capacity) increases in Fe deficient states
21
Q
Ferritin?
A
- 24 subunits (apoferritin) surround a core of 3-4000 Fe3+
- stores iron
- mostly in tissues, but small amount in blood, indicator of Fe reserves
- hemosiderin- microscopic aggregates of partially degraded ferritin (and iron) in lysosomes, increases in iron overload
22
Q
Regulation of iron absorption?(16)
A
- absorb iron in diet in form of heme iron or free Fe
- heme is transported into cell and heme oxygenase breaks it apart
- free iron is reduced to get through DMT1 by ferrireductase, it is then broken down
- there can be competition for DMT1 with other metals - iron leaves cell through ferroportin 1 where it is oxidized to Fe3+ by ferrioxidase
- some extra iron is stored in ferritin, can be mobilized if needed, or is shed with epithelial cells - it is picked up by transferrin and transported to bone marrow and liver
- regulation:
- increased by ascorbic acid, citric acid
- decreased by tannates (tea), carbonates, phosphates
- hepcidin is increased by Fe or IL-6 (inflammatory) to block ferroportin (anemia of chronic disease) so that iron does not leave cell into blood stream
- transfer of iron from mucosal cell to capillary bed is regulated by iron requirement and synthesis of storage protein (apoferritin)
23
Q
How are synthesis of ferritin and transferrin receptor regulated by Fe levels? (17)
A
- iron low: don’t need to make ferritin to store Fe, but need to make receptor to bring Fe into cell
- iron high: express more ferritin to store Fe, limit expression of receptor
- ferritin is regulated at translational level by iron response element (IRE) in the 5’ untranslated region, translation is inhibited when iron levels are low
- transferrin receptor mRNA has an IRE in 3’ untranslated region, when iron is high the mRNA is degraded quickly
- when iron is low, IRE is bound by IRE-BP and mRNA is stabilized so more receptor is made
24
Q
Where is the major site of absorption of iron?
A
in mucosal cells of the proximal duodenum
25
What does ferrireductase do?
- reduces free Fe3+ to Fe2+ in intestinal mucosal cells so that it can enter DMT1
- reductase activity is increased by acidic pH and by reducing substances such as Vit C
- it is inhibited by tannates (tea), carbonates, phosphates
26
Why can Fe have a difficult time entering the cells by DMT1 (divalent metal transporter)
-there is competition from other metals such as calcium
27
Function of ferriportin?
- transports Fe2+ out of the mucosal cell
- since apotransferrin binds only Fe3+, ferriportin is coupled ferroxidase, hephaestin, ceruloplasmin
- ceruloplasmin is also a transport protein for copper in blood
28
Function of hepcidin? what increases its synthesis?
- small circulating peptide, synthesized and released from the liver in response to increased intrahepatic levels of Fe
- inhibits transfer of Fe from the enterocyte to plasma by binding ferriportin and causing it to endocytosed and degraded
- hepcidin synthesis is increased by IL-6 (inflammatory), contributes to anemia of chronic diseases
29
hematochromatosis?
- condition of iron overload in which there is abnormally increased iron absorption
- it is associated with decreased hepcidin activity
- iron accumulates in various organs and can lead to cirrhosis, liver tumors, diabetes, cardiac failure
30
What is the most common cause of iron deficiency anemia in children?
- excess consumption of cows milk
- causes inflammation and damage to intestinal lining, leading to blood loss and decreased iron absorption
31
Where does heme synthesis take place?
- most heme is made in bone marrow and liver, but some is made in all cells because all cells have cytochromes
- first reaction and last 3 take place in mitochondria
32
substrates for heme synthesis?
- glycine AA
- succinyl CoA from TCA
- organic portion of heme is derived entirely from eight molecules each of the above
33
Heme synthesis process? (20)
1. succinyl CoA and glycine turn into ALA by ALA synthase in the mitochondria
- this is the rate limiting step
2. ALA converts to porphobilinogen (first of 4 rings) by ALA dehydratase
- inhibited by lead
3. goes on to make other intermediates to get protoporyphyrin IX
4. Fe2+ is added to make heme by ferrochetolase
- ferrochetolase is inhibited by lead
- underlined reactions are in mitochondria, the rest is in cytosol
- the first reaction is inhibited by the product, heme (feedback inhibitor)
34
ALA synthase reaction? (21)
- occurs in mitochondrial matrix
- first step, rate limiting
- substrates: glycine and succinyl CoA
- cofactor: pyridoxal phosphate (Vit B6)
- product: alpha aminolevulinic acid (ALA)
- inhibited by heme
35
ALA dehydrates reaction? (21)
- occurs in cytosol
- second step
- product: porphobilinogen (PBG)
- inhibited by heavy metals such as lead
36
Ferrochetolase reaction? (22)
- final reaction
- occurs in mitochondria
- catalyzes insertion of Fe2+ into protoporyphryin IX
- inhibited by heavy metals such as lead
37
Regulation of heme synthesis?
1. mostly via regulation of ALA synthase
- negative feedback by heme
- induced by Fe in RBC
- other regulation (in liver):
- glucose inhibits
- steroid hormones increase synthesis
- over 100 different drugs increase ALA synthase activity especially those metabolized by the cytochrome p450 monooxygenase system
38
ALA synthase 1 (ALAS 1)? (24)
- one of two isoforms of ALA synthase
- found in liver and other tissues
- short half-life and more regulation
- major regulation by heme (negative feedback):
- inhibits transcription
- increases mRNA degradation (decreases stability of mRNA)
- blocks post transcriptional translocation of ALAS 1 to mitochondria
- induced by steroid hormones (oral contraceptives)
- inhibited by glucose or proximal glycolytic intermediate
- activity increased by certain drugs, especially those that are metabolized by the cytochrome p450 monooxygenase system
39
ALA synthase 2 (ALAS 2)? (25)
- isoform of ALA synthase
- erythroid, bone marrow, makes 85% of daily heme
- makes heme primarily for hemoglobin, which has a long half life, so its response to heme levels is less regulated
- regulated in response to iron levels:
- IRE in 5' UTR regulate translation, inhibited when iron levels are low
- heme (more leisurely) regulates synthesis indirectly by regulating acquisition of Fe from its transport protein transferrin
- may also inhibit translocation to mitochondria
- transcription regulated by erythroid specific promoter and same transcription factors that regulate globin synthesis
40
Coordination of heme and globin synthesis with iron levels?
- heme is lipophilic pro oxidant that can damage a variety of cell components if it accumulates, so its synthesis is regulated in coordination with availability of its apoproteins
1. heme synthesis is coordinated with iron availability:
- ALAS 2 has IRE in 5' UTR
- heme regulates Fe availability
2. heme synthesis coordinated with globin synthesis
- transcription of ALAS 2 is under control of same transcription factors that regulate globin synthesis
- erythorpoeitin increases transcription of ALAS2, alpha and beta globin, and porphobilinogen deaminase (enzyme 3 in heme synthesis)
- heme increases transcription of globes and stabilizes their mRNAs
- low levels of heme activate a kinase that causes inhibition of translation
41
Process of inhibition of translation of globins in erythrocytes by a kinase? (27)
1. when heme is high, it inactivates a protein kinase, no phosphorylation of eIF-2-GDP
- translation is allowed to continue to synthesize globin chains
2. when heme is low, the protein kinase is active to phosphorylate eIF-2-GDP
- translation is inhibited, no need for globin chains
42
Lead poisoning? (31)
- affects heme synthesis path
- lead inhibits ALA dehydratase and ferrochetolase
- anemia due to decreased Hb
- lead competes with Calcium:
- lead accumulates in bone and developing teeth
- neurotoxic effects primarily due to inhibition of neurotransmitters due to disruption of calcium homeostasis
- symptoms are age dependent (greater effect in children) and dose dependent
43
Porphyrias? (31)
- genetic defects in heme synthesis
- rare but possibly under diagnosed
- symptoms are often intermittent and non specific
- classified as erythropoietic or hepatic
- most are dominantly inherited, but with low penetrance:
- 90% of people with genetic trait for acute intermittent porphyria never show symptoms
- precipitating factors may include:
- certain drugs (cytochrome p450)
- alcohol
- fasting/severe diet
- hormones
- stress
44
symptoms and treatment of porphyria?
- symptoms:
- due to accumulation of toxic intermediates
- nervous dysfunction and abdominal pain
- porphyrins or poryphryinogens cause photosensitivity by reaction with sunlight to form reactive O2 species
- depletion of essential cofactors, substrates (Vit B6, Zn, glycine)
- treatment (especially for hepatic forms):
- hematin, a stable derivative of heme
- carb rich diet to slow pathway
- withdrawal of any precipitating drugs
45
porphyria cutanea tarda? (31)
- most common of porphyria
- dominant inheritance
- expressed mainly in patients with alcoholism or liver damage
- no neurologic or abdominal symptoms
- photosensitivity or pigmented urine
- treatment:
- abstain from alcohol
- reduce extra iron
- avoid sunlight
46
Acute intermittent porphyria? (31)
- intermittent attacks:
- acute abdominal pain, constipation, muscle weakness, cardio abnormalities
- neurological dysfunction: agitation, seizures, psychosis
- colored urine and stool
- episodes last few days to several months
- often misdiagnosed
- inheritance is dominant, but low penetrance
- many have no symptoms except with precipitating factors:
- certain drugs
- fasting/dieting
- stress/infection
- anything that increases glucagon and decreases insulin
47
conformational changes in Hb due to O2 binding? process? (36, 37, 38)
- oxygen binds to Fe2+ from opposite side of poryphryin plane
- iron atom, which had been puckered out from poryphryin plane, is pulled into the plane of heme on oxygenation
- proximal histidine residue of globin chain is pulled along with the iron overcoming steric hindrance and resulting in conformational change of hemoglobin molecule
- process:
1. deoxy state (T form):
- Fe is puckered out from center of heme
- heme plane has slight dome shape
- F helix of globin chain is not perpendicular, but at slight angle
2. transition:
- O2 binds Fe2+ from opposite plane from globin
- pulls Fe2+ down into center of plane, creating strain
3. oxygenated state (R form):
- movement of globin chain relieves strain
- these changes are transmitted to the rest of the Hb molecule
- becomes perpendicular
48
How much does hemoglobin rotate during oxygenation of hemoglobin?
-one alphabeta dimer rotates about 15 degrees relative to each other
49
What happens to ionic bonds as Hb transitions from T to R form? (40)
-some ionic bonds are broken in the oxygenated state (R)
50
T form of Hb? (41)
- tight, taut
- deoxygenated
- low affinity for O2
- lots of ionic bonds and H bonds between dimers that constrain the movement of globin chains
51
R form of Hb? (41)
- relaxed
- oxygenated
- high affinity for O2
- fewer bonds between dimers
- binding O2 ruptures some ionic bonds between two dimers, allowing more freedom of movement
- transition from T to R form increases in likelihood as each heme group becomes oxygenated
- less steric hindrance
- affinity of Hb for O2 increases over 300x in R form
- O2 is allosteric activator of Hb binding of O2
52
O2 dissociation curve? (42)
- myoglobin:
- one globin chain and one heme
- not allosterically regulated, not sigmoidal
- in muscle cells, holds iron until needed my exercising muscles
- fully saturated, normal curve
- hemoglobin:
- sigmoidal curve suggests allosteric regulation
- O2 is an allosteric activator
- allosteric inhibitors decreases Hb affinity for O2 in tissues:
1. 2, 3 BPG
2. H+
3. CO2
- none of the allosteric regulators has much effect in lungs, where O2 is really high to overcome inhibitors
- association of globin chains in tetrameric structure in Hb allows for greater O2 delivery than is possible with only one chain, as in myoglobin
53
2,3 bisphosphoglycerate?
- synthesized from an intermediate (1,3 BPG) of glycolysis
- most abundant organic phosphate in RBCs, equimolar with Hb in RBC
- one molecule of 2,3 BPG binds to a pocket formed by the two beta globin chains (positive charge) in the center of deoxyHb tetramer (T form) because of its negative charge
- stabilizes the T form, creates more ionic bonds, only can bind in T form
- decreases O2 affinity of Hb
- shifts oxygen dissociation curve to the right
54
Why HbF has higher affinity for O2 than HbA? (44)
- HbF has alpha2gamma2 chains
- gamma globin chains have fewer positive charges in center pocket (no beta chains)
- HbF has very low affinity for 2, 3 BPG
- has to pick up O2 from mothers HbA, so must have higher affinity in tissues
- HbF curve more to the left, less sigmoidal
55
2, 3 BPG and adaptation to altitude and hypoxia? (45)
1. adaptation to high altitude is complex and takes several weeks to complete
- increased number of RBCs
- increased Hb concentration in RBC
2. within a day there is increased synthesis of 2, 3 BPG
- curve shifts to right
- helps Hb drop off O2 in tissues even when not fully saturated
3. 2, 3 BPG levels are all increased in conditions of hypoxia
- anemia
- cardiopulmonary insufficiency (COPD)
56
The Bohr effect?
- regulation of O2 binding by H+ and CO2
- as Hb is converted from T to R form, protons (H+) are released
Hb (T) + 4O2 \<-\> Hb(O2)4 (R) + nH+
- increasing H+ in tissues pushes equilibrium to the left, helping release O2
- reaction is reversible
57
Role of H+ in releasing O2? (47)
- as pH decreases (H+ increases), O2 affinity decreases
- H+ stabilizes the T form
- shift dissociation curve right
- little effect at high O2
- more lactate means more H+
58
Role of CO2 in releasing O2? (48,49)
- 70-80% CO2 produced in aerobic metabolism is converted to bicarbonate in RBC by carbonic anhydrase
- carbonic acid spontaneously dissociates to bicarbonate and H+
- bicarbonate diffuses out of RBCs and helps buffer blood
- H+ helps to release O2 in tissues
- reverse reaction happens in lungs, CO2 is exhaled
CO2 + H2O H2CO3 HCO3- + H+
- 15-20% of CO2 is transported to the lungs on Hb as carbamino-Hb
- CO2 binds N terminal AA of globin chains
- this reaction produces H+ so binding of CO2 promotes release of O2 from Hb in tissues
- smaller amount of CO2 is transported to lungs as Carbamino-Hb
59
RBC in capillaries of tissues vs lungs? (50)
- RBC:
- as CO2 binds N terminal AA of globin, releases H+ which help to release O2 to tissues
- lungs:
- O2 comes in and release H+, which releases CO2 exhalation
60
what does increasing temperature do to affinity of Hb for O2?
- decreases affinity
- microenvironment of exercising muscle favors efficient release of O2
61
Hemoglobinopathies?
- disorders affecting structure, function or production of globin chains
- over 900 variant forms of Hb identified
- usually codominant inheritance
- especially common where malaria is endemic
- range in severity from asymptomatic abnormalities detected in lab tests, to death in utero
- thalassemias
- sickle cell disease
- acquired methemoglobinemia, CO poisoning
62
Thalassemias?
- most common single gene disorders
- partial or complete absence of one or more globin chains
63
Alpha thalassemia? (56)
- usually cause by deletion of 1 or more of the 4 alpha globin genes, severity depends on how many
- lack of alpha globins cause gamma or beta tetramers to form that don't work as well
- one deleted = silent carrier
- two deleted= mild symptoms
1. Hb Barts syndrome
- all 4 genes deleted
- Hydrops fetalis: abnormal accumulation of interstitial fluid in a fetus or newborn
- Hb Barts- only gamma chains in fetus (gamma 4), forms tetramer
- increased O2 affinity makes it a poor transporter
- usually fatal at or before birth
2. Hb H disease
- 3 alpha genes deleted
- HbH is formed (4 beta globes)
- unstable tetramer found in patients with 3 alpha chains deleted
- moderate to severe disease
64
Beta thalassemia? (57)
- 170 different mutations
- excess alpha chains precipitate, causes destruction of RBC (hemolysis) anemia
1. beta thalassemia minor
- heterozygous
- usually asymptomatic except for mild anemia
2. beta thalassemia major (cooley anemia)
- homozygous
- transfusions for severe anemia
- often suffer from iron overload
65
beta thalassemia leading to iron overload? (58)
1. reduced beta globin, excess alpha
2. insoluble alpha globes make abnormal erythroblast
3. most die in bone marrow (ineffective erythropoiesis)
4. anemia increases iron absorption and iron overload
5. few abnormal RBC leave in circulation, and destroyed by spleen
6. blood transfusion helps anemia but increases iron overload
7. tissue anoxia, marrow expansion, skeletal deformities
66
Sickle cell disease?
- most common structural hemoglobinopathy
- autosomal recessive
- HbS is a missense mutation (glu to val) in beta globin
- decreased solubility, but only the deoxy form is so insoluble that it precipitates in RBC and causes sickling
- usually homozygotes have symptoms:
- hemolytic anemia (shorter life), vasoocclusion leading to infarction, painful crisis, increased risk of stroke
- precipitating factors:
- acidosis
- hypoxia
- infection
- stress
- anything that increases the amount of the deoxy form of Hb increases risk of painful crisis
67
sickle cell trait?
- heterozygous form
- usually no symptoms
- in rare cases, crisis develops under extreme hypoxic conditions, such as intense exercise
- selective advantage for malaria
68
CO poisoning? (61)
- acquired hemoglobinopathies
- most common fatal poisoning in US
- CO competes with O2 for binding to Hb
- CO increases O2 affinity for remaining sites and makes it impossible for Hb to drop off O2 in tissues
- levels of carboxyhemoglobin:
- normal less than 5%
- smoker up to 9%
- toxic over 25%
- fatal over 95%
- treatment: hyperbaric O2 chamber
69
Methemoglobinemia?
- chocolate blood, cyanosis
- certain drugs, anesthetics increase amount of metHb
- infants are especially vulnerable
- death if metHb levels reach over 70%
- treat with **methylene blue** to reduce metHb
- very rare congenital forms:
1. HbM
- mutation in heme binding pocket
- dominant inheritance
2. NADH cytochrome B5 reductase deficiency
- recessive inheritance
- Type 1- only in RBC
- Type 2- all cells
70
Why degrade heme?
- goal is to preserve Fe and convert protoporyphyrin to products that can be safely excreted
- regulated to prevent toxic build up of heme and its breakdown products
- first reaction is rate limiting and subject to regulation
71
How heme is converted to bilirubin in macrophages? (65)
- begins in macrophages of reticuloendothelial (RES) system, with removal of globin chains and conversion of heme to bilirubin
- usually for RBC at end of lifespan
1. heme oxygenase
- cleaves pyrrole ring to produce biliverdin (linear)
- requires O2, NADPH
- releases CO and Fe3+
- rate limiting step
2. Biliverdin reductase
- requires NADPH
- reduced to bilirubin
3. bilirubin leaves macrophage into blood stream to be carried by albumin to liver cells
- bilirubin not soluble in blood and must be carried
72
What is the only physiological source of CO?
- heme oxygenase reaction
- amount of CO exhaled can be measured and used to estimate the amount of heme being broken down
- CO acts a signal molecule in neural tissue, and has vasodilatory, anti inflammatory and cytoprotectant properties
- good in low amounts
73
Conjugation of Bilirubin (Br)? (67)
1. unconjugated Br is carried on albumin to liver
2. in hepatocytes, Br is bound by glutathione S transferase and is conjugated to 2 molecules of UDP-glucuronate by bilirubin glucuronyl transferase
3. conjugated Br (Br diglucuronide) is actively transported by multi drug resistance protein 2 (MRP2) into bile
- now soluble in blood
74
effects of conjugation of bilirubin?
1. increases solubility
2. prevents resorption from intestinal lumen and promotes excretion
75
What happens to conjugated bilirubin? (68)
1. excreted in bile into intestine
2. it is then deconjugated by bacterial hydrolases and is reduced to urobilinogens
- most are oxidized to urobilins and excreted in feces
3. small amount is reabsorbed to the blood where it combines with albumin and is carried to the liver by enterohepatic circulation
4. small amount can be reabsorbed by the terminal ileum and large intestine to blood and excreted in urine
76
summary of bilirubin metabolism? (69)
pic
77
Heme oxygenase (HO-1)?
- expressed constitutively in liver and spleen, inducible in most tissues
- highly inducible by more different stimuli any other known gene (heme, metal ions, hormones, bacterial toxins, starvation, neoplasm)
- associated with cytoprotective responses
- bilirubin though toxic at very high levels, also has antioxidant properties
78
Jaundice and bilirubin?
- caused by deposits of bilirubin in skin and sclerae when levels in blood are increased
- due to increased production or decreased excretion of Br:
1. pre hepatic (hemolysis)
2. hepatic (neonatal hepatitis, genetic)
3. post hepatic (bile duct obstruction)
79
Measurement of bilirubin?
1. direct (conjugated)
- can easily be coupled to diazonium sals (azo dyes) in a direct van den bergh reaction
2. indirect (unconjugated)
- bilirubin in non covalent complex with albumin won't react with dyes until albumin is released by an organic solvent
Total - direct = indirect
80
Pre hepatic jaundice (hemolytic)? (73)
- indirect hyperbilirubinemia
- increased production of Br, exceeding capacity of liver to conjugate
- excess indirect bilirubin in serum
- increased urobilinogen in blood and urine due to increased conjugated Br reaching intestine
- rarely severe unless problem with liver because capacity of liver is high
- mainly unconjugated
81
Intrahepatic (hepatocellular) jaundice? (74)
- impaired hepatic uptake, conjugation, secretion or Br
- direct or indirect hyperbilirubinemia
- indirect- getting bilirubin into hepatocyte, conjugation
- direct- problem getting git out of liver into bile
- conjugated bilirubin in urine
- liver enzymes often increased
82
Hepatitis and other non specific liver diseases without bile duct obstruction?
- both direct and indirect bilirubin are elevated in serum
- urine may be darker due to conjugated Br
- stools may be lighter due to decreased urobilinogens
83
Neonatal jaundice? (75)
- common, usually self limited
- more common in premature infants
- Br glucuronyl transferase (conjugates Br) is developmentally expressed (adult levels reached 4 weeks after birth)
- heme doesnt need to be conjugated in utero due to using mothers O2
- the enzyme increases close to birth, Br increases at birth and then decreases
- premature infants enzyme increases slower leading to increases Br in blood at birth, could be toxic
- if Br levels exceed binding capacity of albumin, Br can accumulate in basal ganglia and cause toxic encephalopathy called kernicterus
84
Other factors that contribute to neonatal jaundice? (76)
1. ineffective conjugation
2. increased RBC lysis immediately after birth, increased unconjugated Br
3. albumin synthesis is low in premature infants
- if not feeding properly, albumin can breakdown into AA for energy
4. blood brain barrier more permeable in newborns
- kernicterus
85
How to treat neonatal jaundice?
- phototherapy converts Br to more soluble isoforms that can be excreted into bile without conjugation
- best light is blue light but wouldnt be able to tell if baby is cyanotic
- white light is used and eye patches
- mild cases baby goes out in sunshine
86
genetic conditions causing intrahepatic jaundice?
1. crigler najjar syndrome
- rare deficiency Br glucuronyl transferase
- type 1- total deficiency
- type 2- less severe
2. gilbert syndrome
- common, benign mild elevation indirect Br
- mutation in promoter of Br glucuronyl transferase gene, decreased expression
3. dubin johnson syndrome
- defective transport of conjugated Br out of hepatocytes
- rare mutation in MRP2
87
Post hepatic jaundice (obstructive)? (79)
- bile duct obstruction that prevents excretion of conjugated Br
- direct hyperbilirubinemia
- bile acids may also accumulate in plasma
- stool pale
- conjugated Br in urine, dark
- no urobilinogens in stool
- prolonged obstruction can lead to liver damage and increased unconjugated (indirect) Br
88
Haptoglobin? (82)
- bind alphabeta dimers in blood, produces a complex too large to be filtered by renal glomerulus
- delivers dimers to macrophages via specific receptor
- serum haptoglobin concentration reflects degree of intravascular hemolysis
- levels decline with sustained hemolysis
- haptoglobin is an acute phase reactant, so levels may increase during inflammation or infection
- basically removes complexes in normal path to not clog kidney and lose iron in urine
89
hemopexin? (82)
- free Hb not bound by haptoglobin is oxidized to metHb, which dissociates to globin and met-heme
- hemopexin binds met-heme, delivers it to the liver
- delivery of heme to hepatocytes induces heme oxygenase
- hemopexin and its receptor are recycled, but may be depleted with prolonged hemolysis
- basically removes complexes in normal path to not clog kidney and lose iron in urine
90
Met-hemoglobin?
- oxidized Hb (Fe 3+)
- cant bind O2
91
Hemoglobin loading vs unloading?
Unloading- lungs to tissues
Loading- tissues to lungs
92
Importance of sigmoidal curve?
- small decrease in lung function doesn't have major effect on tissue oxygenation
- larger effect in middle of curve allows more efficient unloading in tissues
MBM
flashcards
Decks in class (24)
# Cards
-
DNA Replication110
-
RNA and Protein Synthesis98
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Regulation of Gene Expression133
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DNA Repair79
-
Genetics 1165
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Genetics 217
-
Proteins83
-
Hormones 161
-
Hormones 263
-
Energy Production and Utilization88
-
ATP Synthesis78
-
Carbohydrates 182
-
Carbohydrates 225
-
Glycogen42
-
Gluconeogenesis/Ketogenesis49
-
Lipids138
-
Fatty Acid Oxidation62
-
Fatty Acid Synthesis47
-
Lipoproteins65
-
Dietary Proteins 180
-
Dietary Proteins 246
-
Hemoglobin92
-
Hemostasis63
-
Nutrition38
