Lash - Hematopoiesis Flashcards
INTRODUCTION:
• General:
- Various drugs, hormonal growth factors, vitamins and minerals can affect the blood or blood-forming organs
- Blood cells have relatively short life-spans, so you need continuous replacement of cells by hematopoiesis
Anemia:
- Significant reduction in functional red cells mass with consequent reduction in O2 carrying capacity
- Causes include:
o Blood loss
o Reduced red cell production
o Production of abnormal red cells or precursors
Process of Hematopoiesis:
Pluripotent Stem Cell –>
Lymphocyte progenitor –>
CFU-GEMM –>
CFU-GM –>
Pluripotent Stem Cell –> Variety of different precursor cells
Lymphocyte progenitor –> B cells, T cells, NK cells
CFU-GEMM –>CFU-E/BFU-E and CFU-GM
–>CFU-E/BFU-E –> RBCs
CFU-GM –>Granulocytes (PMNs, Eosinophils, Basophils) and Monocytes
Erythropoietin:
Synthesis
Function
Absence
Synthesis:
o Proximal tubular cells of the kidney (primarily)
o Liver (small amount)
- Structure:
o Primary gene product 193 amino acid protein
o First 27 residues cleave during secretion
o Glycosylated (not essential for function but prolongs half-life)
Function:
o Most important regulator of:
Proliferation of committed progenitors (CFU-E)
Maturation of erythroblasts
Release of reticulocytes into circulation
Synergy with IL-3 and GM-CSF to expand BFU-E population
BFU-E mature to CFU-E, which then mature further into reticulocytes (released)
Acts by binding specific membrane receptors on the surface of bone marrow cells that are committed towards synthesis of RBCs
Absence: invariably results in anemia
Diseases/Agents Affecting Production of Erythropoietin:
In General:
Anemia or hypoxia cause a RAPID increase (~100 fold) in the renal synthesis and secretion of erythropoietin
Disease State
Increase EPO (Kindeys, liver, brain, lung)
Decrease EPO
Increase EPO Production
- Kidney (HTN, carcinoma, sarcoma, renal artery stenosis etc.)
- Liver (carcinoma)
- Brain (hemangioblastoma)
- Lung (pulmonary insufficiency, emphysema, carcinoma, fibrosis)
Decrease EPO Production
–
Pharm agents that increases EPO
- Cobalt (↓ tissue O2 use)
- Thyroxine
- Growth Hormone
- Prolactin
- ACTH (decreases renal blood flow)
- Serotonin
- Vasopressin
- Testosterone
Pharm agents that decrease EPO
- Mercurial diuretics
- Estrogens
- Beta2 blockers
- Adenosine A1 agonist
- Calcium ionophores
- Ca++ channel blockers (chronic use)
- Phorbol esters
- Alkylating agents
- Diacylglycerol
EPO Signaling Pathways that Regulate Expression:
Hypoxia
Detection
What changes after detection?
Hypoxia (due to anemia, ischemia, cobalt etc.) is detected by either:
- Oxygen sensing cell
- EPO producing cell itself
Detection occurs by changes in signaling molecules (ie. adenosine, prostaglandins etc.)
Once cell detects hypoxia, change in the cAMP pathway results in the activation of various proteins that stimulate the production and secretion of EPO
Myeloid (CSFs):
General:
Synthesis
General
Glycoproteins that stimulate proliferation and differentiation of several types of hematopoietic precursor cells AND enhance function of mature leukocytes
Synthesis:
o GM-CSF and IL-3: T lymphocytes
o GM-CSF, G-CSF and M-CSF: monocytes, fibroblasts, endothelial cells
Function of Interleukin-3 (IL-3): (4)
Stimulates colony formation of most cell lines
Synergy with GM-CSF to increase number of PMNs, monocytes and eosinophils in the blood
Synergy with EPO to expand BFU-E compartment to stimulate CFU-E proliferation
Influences the function of eosinophils and basophils
Function of Granulocyte/Macrophage CSF (GM-CSF): (5)
Synergy with IL-3 to stimulate colony formation/proliferation of granulocytes, monocytes/macrophages, and megakaryocytes
Synergy with EPO to promote formation of BFU-E
Increases phagocytic and cytotoxic potential of mature granulocytes
Reduces motility and clearance from circulation of mature granulocytes
Increases cytotoxicity of eosinophils and leukotriene synthesis
Function of Granulocyte CSF (G-CSF): (5)
Stimulates granulocyte colony formation and production of PMNs
Synergy with GM-CSF to stimulate granulocyte/macrophage colonies
Synergy with IL-3 to induce formation of IL-3
Induces release of granulocytes from marrow
Increases phagocytic and cytotoxic potential of mature granulocytes
Function of Macrophage CSF (M-CSF/CSF-1):
Stimulates monocyte/macrophage colony formation (both alone and in synergy with GM-CSF and IL-3)
Induces synthesis of G-CSF and IL-1
Enhances production of IFN and TNF
Enhances functions of monocytes and macrophages
EPO
Therapeutic Use
Administration
Pharmacokinetics
Toxicity
Therapeutic Uses:
Treatment of anemia resulting from chronic renal failure
Transfusion-dependent patients undergoing hemodialysis
Alleviated requirement for transfusions after several weeks
Eventually normalized hematocrit
Also corrects anemia in patients who do not require dialysis
o Treatment of anemia associated with AIDS patients of AZT
o Treatment of anemia associated with cancer chemotherapy
o Preoperative increase in red cell production to allow storage of larger volumes of blood for autologous transfusion
Administration: o Parenterally (IV or SubQ)
Pharmacokinetics:
o Need to titrate dose
Avoid rapid increase in hematocrit early in therapy
Avoid a rise in hematocrit to >36% during maintenance therapy
o Proper response to EPO requires adequate iron stores
May need to co-administer oral iron supplement in those with iron deficiency
Toxicities and Side Effects:
o Increase in red cell mass (most common)
Associated with HTN and thrombotic phenomena
Minimized by raisin hematocrit slowly (titrating dose; monitor BP closely)
o Allergic responses infrequent and mild
Myeloid Growth Factors (CSFs):
- Therapeutic Uses:
Stimulation of hematopoiesis in primary bone marrow failure: (3)
Correction of insufficient Hematopoiesis:
Anemia
Prevention of chemotherapy induced neutropenia
Possibility of dose intensification of chemotherapy
Autologous bone marrow transplant
Stimulation of hematopoiesis in primary bone marrow failure:
Aplastic anemia
Congenital neutropenia
Idiopathic cytopenias
CSF use in:
Treatment of leukemias (types)
Expansion and recruitment of circulating progenitor cells:
Activation of effector cell function (4)
o Treatment of leukemias:
AML
Myelodysplastic syndromes
Expansion and recruitment of circulating progenitor cells:
Peripheral blood stem cell transplantation
Activation of effector cell function:
Infections
Leukocyte function disorders
AIDS
Tumor cytotoxicity
Treatment of sickle cell
Treatment:
• Supportive treatment includes analgesics, antibiotics, pneumococcal vaccination, and
blood transfusions.
• The cancer chemotherapeutic drug hydroxyurea (hydroxycarbamide) reduces venoocclusive
events. It is approved in the United States for treatment of adults with recurrent
sickle cell crises and approved in Europe in adults and children with recurrent vasoocclusive
events.
• In the treatment of sickle cell disease, hydroxyurea acts through poorly defined pathways
to increase the production of fetal hemoglobin (HbF), which interferes with the
polymerization of HbS.
• Clinical trials have shown that hydroxyurea decreases painful crises in adults and
children with severe sickle cell disease.
• Adverse effects include: hematopoietic depression, gastrointestinal effects, and
teratogenicity in pregnant women.
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• Myeloid Growth Factors (CSFs):
Toxicities and side effects:
Common?
Dose-limiting side effects of GM-CSF include:
Less side effects with G-CSF:
By themselves, growth factor:
Toxicities:
Relatively common with GM-CSF (dose-dependent):
Local induration after SC injection
Thrombophlebitis at site of infusion
Fever
Myalgias
Fatigue
Skin rashs
GI distress
Bone pain
Dose-limiting side effects of GM-CSF include:
Pericarditis
Pleuritis
Pleural effusions
Pulmonary emboli
Less side effects with G-CSF:
Bone pain
Vasculitis
Worsening of psoriasis
By themselves, growth factor may have oncogenic potential!
IRON DEFICIENCY:
Basics:
Causes:
Consequences:
What else does iron deficiency affect?
Diagnosis: presence of or?
Basics: most common cause of nutritional anemia in humans
Causes:
- Dietary intake of iron not adequate
- Blood loss (GI tract, menstruation; most common cause in the US)
- Some interference with iron absorption
Consequences:
- Severe Cases: microcytic hypochromic anemia secondary to reduced synthesis of Hb
- Does not only affect RBCs: alters muscle metabolism INDEPENDENT of effect on O2 delivery via blood
• Diagnosis:
- Presence of microcytic anemia, OR
- Quantitation of:
o Transferrin saturation
o Red cell protoporphyrin
o Plasma ferritin content
Iron Stores in the Body:
Two Forms:
Gender Differences:
Location:
Iron Stores in the Body:
Two Forms:
Essential iron-containing compounds
Excess iron (storage form)
Gender Differences: males have higher stores/kg of body mass than females
Locations of Iron Sources:
Most: Hb in RBCs
The Rest:
Myoglobin in muscle
Storage form bound to ferritin
Cytochromes and other iron-containing enzymes (trace amounts)
Transport form bound to transferrin
Ferritin: protein of iron storage
Apoferritin:
Hemosiderin:
Locations:
Apoferritin: not bound to iron; composed of 24 polypeptide chains that form an outer shell with a storage cavity for iron inside (can bind up to 4000 atoms of Fe)
Hemosiderin: aggregated ferritin
Location: predominantly in reticuloendothelial system and liver; small amount in muscle
Transferrin:
Function
Plasma glycoprotein for iron transport
Internal exchange of iron: has 2 binding sites for ferric ion; delivers iron to intracellular sites by binding specific transferrin receptors on cellular plasma membranes.
Iron is delivered from transferrin to intracellular sites by specific transferrin receptors
Synthesis of Ferritin/Trasnferrin Receptors in Response to Iron Supply:
Excess Iron:
Low Iron:
Excess Iron: reduce synthesis of transferrin R; increased synthesis of ferritin
Low Iron: increased expression of transferrin R; decreased synthesis of ferritin
Iron Requirements and Dietary Availability:
Varies by:
High iron foods:
Low iron foods:
Bioavailability of iron:
Absorption of non-heme iron facilitated by:
Form complex with:
Varies by age, gender and other factors:
o Highest for pregnant women (up to 4x increase in daily requirement)
o Menstruating females (blood loss) and infants (rapid growth) also have high requirements
High Iron Foods: organ meats, brewer’s yeast, wheat germ, egg yolks, oysters, some dried beans and fruits
Low Iron Foods: milk products, non-green vegetables
Bioavailability of Iron:
o Heme Iron: most bioavailable form, but dietary iron is mostly non-heme iron
o Absorption of Non-Heme Iron: facilitated by ascorbate
Forms complex with iron, OR
Reduces ferric –> ferrous iron
Treatment of Iron Deficiency:
Oral Therapy:
Duration:
Adverse effects:
Overcome by:
Ferrous Sulfate: treatment of choice (~25% of oral iron given in this form is absorbed)
Duration: usually 3-6 months
Adverse Effects: nausea, epigastric discomfort, abdominal cramps, constipation, diarrhea
- Dose-related
- Overcome by lowering dose or taking tablets with meals
Treatment of iron deficiency
Parenteral Thearpy:
Who?
Compare to oral:
Use:
Patients who can’t tolerate or absorb oral iron
Patients with chronic blood loss
Repletion of iron stores: more rapid than by oral therapy
Interrelationship Between Vitamin B12 and Folic Acid:
Methionine Synthesis:
Purine Synthesis:
DNa synthesis:
Deficiency of either B12 or folate:
Methionine Synthesis: MeFH4 + B12 methylcobalamin, which then acts as methyl donor produce methionine
Purine Synthesis: requires folate derivatives
DNA Synthesis: requires folate derivatives to methylate dUMP dTMP (required precursor)
Deficiency of Either B12 or Folate:
o Decreased synthesis of methionine and S-adenosylmethionine
o Interference with protein synthesis
o Interference with numerous methylation reactions
o Redirection of methylation reactions away from nucleic acid synthesis (compromises production of new cells)
Vitamin B12
Metabolism:
Combines with:
Excess stored in:
Sources:
Daily Requirment:
Metabolism:
o Combines with intrinsic factor in stomach and duodenum (secreted by parietal cells of gastric mucosa)
o Requires IF for absorption in the distal ileum (specific receptor-mediated transport)
o Once absorbed, transported to cells of the body bound to plasma glycoprotein (transcobalamin II)
o Excess stored in the liver or excreted in the urine
Sources:
o Cannot be synthesized so needs to be obtained in the diet
o Only original source in nature is microorganisms
o Animal liver is excellent source (primary storage site)
Daily Requirements:
o Small daily requirement
o Daily turnover of liver vitamin B12 is small and therefore deficiency would not develop for 3-4 years
B12 Deficiency
Affects what systems?
DNA effects
Most profound effects on what type of cell?
Most due to:
- Deficiency
o Affects both hematopoietic AND nervous systems:
Sensitivity of hematopoietic system relates to high rate of cell turnover (requires high rates of DNA synthesis)
Not enough B12 leads to highly abnormal DNA synthesis
Results in morphologically abnormal cells or cells that die during maturation
Most profound effect on RBCs (abnormally large)- megaloblastic anemia
o Nutritional B12 deficiencies are rare:
Most due to malabsorption (NOT insufficient intake)
Deficiency in IF (pernicious anemia, gastrectomy)
Defects in absorption of B12-IF complex by distal ileum
B12 Deficiency
Diagnosis
Treatment
- Diagnosis:
o Measurement of B12 in the serum
o Measurement of methylmalonic acid in the serum - Treatment:
o Most are not curable: require lifelong treatment with B12 injections (important to diagnose underlying cause so proper treatment can occur)
Folic Acid:
Metabolism: absorption (requires) and transport (as)
Sources:
Deficiency:
Therapy:
• Folic Acid:
- Metabolism:
o Taken in via the diet: as reduced polyglutamates
Absorption:
Requires transport and a pteroyl-γ-glutamyl carboxypeptidase associated with the intestinal mucosal membrane
Most occurs in duodenum and upper jejunum (have high activities of dihydrofolate reductase and methylating activities)
Transport to Tissues:
Mostly transported to tissues as MeFH4
Bind plasma proteins
Taken up into cells by receptor-mediated endocytosis - Sources:
o Diet: almost all foods rich in folate (especially leafy green vegetables, liver, yeast, some fruit)
Important point: cooking can destroy most of the folate content of these foods - Daily Requirements:
o Most people take in much more folate than the minimum daily requirement - Deficiency:
o Often caused by inadequate dietary intake:
Elderly or the poor (lack vegetables, eggs, meat in diet)
Prolonged cooking of folate rich foods
Alcoholics and patients with liver disease (poor diet and diminished capacity of the liver to store folates)
o Also causes megaloblastic anemia: difficult to distinguish from B12 deficiency
-Therapy:
o Diagnosis important: potential for mistreating patients with B12 deficiency with folates
Will relieve megaloblastic anemia but will NOT help the neurological defects seen due to B12 deficiency
Cobalt
Deficiency:
Historical Significance:
Deficiency: has not been reported in man
Historical Significance: used to be administered to treat anemia
o No benefit and aplastic anemia
o Beneficial to patients with pure red-cell aplasia (inhibition of enzymes in oxidative metabolism tissue hypoxia increase in secretion of EPO)
o Note: large amounts of Co DEPRESS erythropoiesis
Intoxication in children can cause cyanosis, coma and death
Pyridoxine (Vitamin B6):
Oral Therapy effects:
Anemia is characterized by:
Therapy effective for anemia due to certain drugs:
• Pyridoxine (Vitamin B6):
Oral Therapy: can increase hematopoiesis in patients with hereditary or acquired sideroblastic anemia
Anemia characterized by impaired Hb synthesis and accumulation of Fe in mitochondria of erythroid precurosor cells
Hereditary form is X-linked recessive with variable penetrance and expression
Idiopathic forms associated with use of certain drugs, inflammatory states, neoplastic disorders and preleukemic syndromes
Therapy effective for anemia due to certain drugs (isoniazid, pyrazinamide) but not for others
May interfere with beneficial action of other drugs causing the anemia
Riboflavin:
Deficiency
Therapy with is beneficial to:
Riboflavin:
Deficiency:
o Spontaneous red-cell aplasia (rare)
o Induced hypoproliferative anemia
Therapy with Riboflavin:
o Beneficial to patients with red-cell aplasia due to protein depletion
