Download Making basic science clinically relevant for learners: the biochemistry example Eric Niederhoffer

Making basic science clinically
relevant for learners: the
biochemistry example
Eric Niederhoffer
SIU-SOM
Considerations
• Wants and needs
Curriculum design, objectives, goals; USMLE
• Biochemistry as a foreign language
Web lessons, resource pages, animations
• Resource sessions
Complement self-directed learning
Applied to patient case
Start simple, discuss difficult
Big picture, relevant details
Overlap and redundancy
Build upon previous knowledge
• Clinical probes for content and
concepts
Self-assessment questions, examinations
• Glucose metabolism as an example
Red Blood Cell Biochemistry
A 4-year-old African boy presents with a 2-day history
of painful extremities.
RBC Structure - size, spectrin, channels
Metabolism - glycolysis (2,3-BPG), pentose
phosphate pathway (G6PDH, NADPH), glutathione
Hemoglobin - Genes, heme, Mb/Hb (normal), O2 binding,
HbS (defect), fibers (sickling and inflammation)
Students’ Notes
Red Blood Cell Biochemistry
RBC Structure - size, spectrin, channels
Metabolism - glycolysis (2,3-BPG), pentose
phosphate pathway (G6PDH , NADPH),
glutathione
Hemoglobin - Genes, heme, Mb/Hb (normal), O2 binding,
HbS (defect), fibers (sickling and inflammation)
Eric Niederhoffer
SIU-SOM
Devlin, T. M. (ed.). 2006. Textbook of biochemistry with clinical correlations, 6th ed. John Wiley & Sons, Inc., New
York. This is very good for most of what you need.
Mehta, A. B., and A. V. Hoffbrand. 2000. Haematology at a glance, Blackwell Science, Malden, Mass.
Salway, J. G. 2006. Medical biochemistry at a glance, 2nd ed. Blackwell Science, Malden, Mass. This is very good
for general principles and topics, and metabolic pathways and regulation. Good focused clinical correlations.
RBC Metabolic Pathways
GSH
Glc
G6P
NADP+ + H+
PGI
GSSG
GR
F6P
PFK
NADPH
F16BP
aldolase
DHAP
G3P
G3PDH
BPG mutase
1,3-BPG
PGK
2,3-BPG
3PG
G6PDH
lactonase
6PGDH
CO2
6PG
PPP
PGM
2,3-BPG phosphatase
2PG
enolase
PEP
Lactate
No O2
LDH
H2O
GP
HK
Glycolysis
H2O2
PK
Pyr
3-7 C metabolites
(R5P, F6P, G3P)
Students’
Notes
RBC Metabolic Pathways
H2O2
GSH
Glc
GP
HK
G6P
NADP + + H+
GSSG
PGI
GR
F6P
PFK
Glycolysis
H2 O
NADPH
F16BP
aldolase
DHAP
G6PDH
lactonase
6PGDH
G3P
G3PDH
BPG mutase
1,3-BPG
PGK
2,3-BPG
CO2
6PG
PPP
3PG
PGM
2,3-BPG phosphatase
2PG
3-7 C metabolites
(R5P, F6P, G3P)
enolase
PEP
Lactate
Glc: glucose
No O2
LDH
PK
Pyr
HK: hexokinase G6P: glucose-6-phosphate
G6PDH: glucose-6-phosphate dehydrogenase
PGI: phosphoglucose isomerase
PFK: phosphofructokinase
DHAP: dihydroxyacetonephosphate
BPG: bisphophoglycerate
PEP: phosphoenolpyruvate
Pyr: pyruvate
NADP+/NADPH: nicotinamide adenine dinucleotide
R5P: ribulose-5-phosphate
G3P: glyceraldehyde-3-phosphate GSH: reduced glutathione (GSH = Glu-Cys-Gly)
PK: pyruvate kinase (2 genes, 4 isozymes)
F6P: fructose-6-phosphate
GSSH: oxidized glutathione
LDH: lactate dehydrogenase
PPP: pentose phosphate pathway 6PGDH: 6-phosphogluconate dehydrogenase
GR: glutathione reductase
GP: glutathione peroxidase
3PG: 3-phosphoglycerate
6PG: 6-phosphogluconate
Defect in HK, PGI, aldolase, or BPG mutase/2,3-BPG phosphatase  decreased [2,3-BPG]; defect in PK  increased [2,3-BPG]
BPG mutase(or synthase)/2,3-BPG phosphatase is a bifunctional enzyme (one protein, two activities), regulated by hypoxia and T3
MIultiple inositol polyphosphate phosphatase acts on 2,3-BPG to give 2-PG
Fetal Hb - lower affinity for 2,3-BPG compared with adult Hb; 2,3-BPG binds to and stabilizes deoxyHb; it is easily displaced from oxyHb
Common deficiencies:
G6PDH - X-linked
PGI - autosomal recessive
Sodium fluoride inhibits enolase, used to preserve blood samples for glucose determinations.
PK - autosomal recessive
Hemoglobin Structure Changes
http://www.mfi.ku.dk/PPaulev/chapter8/images/8-3.jpg
Factors Affecting Binding of O2
Depends on pH ([H+]), CO2, BPG (DPG), Temp
pH 
BPG or T _; left shift
pH _
BPG or T ; right shift
Review Questions
• What metabolic pathways are used in
erythrocytes?
• What clinical observations would you make
concerning patients with SCD?
Metabolism in Skeletal Muscle
and Nervous Tissue
•
Metabolism in skeletal muscle
•
Pathways overview
•
Regulation in skeletal muscle
•
Metabolism in nervous tissue
•
Pathways overview
•
Clinical aspects
•
Clinical aspects
•
Clinical/laboratory findings
•
GSD, PDHCD
•
Glycogen storage disease type VII
•
Pyruvate dehydrogenase complex deficiency
•
Inborn errors of metabolism
Metabolism in Skeletal Muscle
A 21-year-old woman comes to the physician with pain in her right mid-arm.
A 5-year-old boy is brought to the physician to have sutures removed.
• Glycolysis
• Glycogenolysis
 -oxidation (ketone bodies)
• Krebs (tricarboxylic acid) cycle
• Branched-chain amino acids
• Electron transport chain
• Calcium regulation
• Key enzyme regulation
Pathways Overview
Ketone
bodies
Fatty acids
Glucose
Glycogen
Glycolysis
Glycogenolysis
Ca2+
PKa
Lactate
No O2
BCAA
Ile, Leu, Val
G6P
Pyruvate
Krebs
cycle
-Oxidation
Ca2+
PDH
Acetyl-CoA
Ca2+
ISDH, aKGDH
Production of ATP
Electron
Transport
Chain
Regulation in Skeletal Muscle
Ep
AR
Glc
Glycolysis
ATP
Citrate
AC
cAMP
PKA
ATP
Ca2+
PKa
G6P
F6P
PP
PFK-2
PFK-1
Pi
IMP
AMP
NH4+
AMP
Pi
F16BP
Glycogen
Glycogenolysis
PEP
PK
PDHP
Ca2+
PDHP
PDHK
PDH
F26BP
Pyr
PDH
Acetyl-CoA
Metabolism in Nervous Tissue
A 21-year-old woman comes to the physician with pain in her right mid-arm.
A 19-year-old man is brought to the emergency department after a diving accident.
A 63-year-old woman is brought to the physician for her “parkinsonism.”
• Glycolysis
• Glycogenolysis (stress)
 -oxidation (ketone bodies)
• Krebs (tricarboxylic acid) cycle
• Branched-chain amino acids
• Electron transport chain
Pathways Overview
Glucose
Glycogen
Glycolysis
Glycogenolysis
Lactate
(glial)
Lactate
No O2
BCAA
Ile, Leu, Val
Fatty
acids
Ketone
bodies
-oxidation
G6P
Pyruvate
Acetyl-CoA
Krebs
cycle
Production of ATP
Electron
Transport
Chain
Clinical Aspects for Inborn Errors of
Metabolism in Muscles
Toxic accumulation disorders
•
Protein metabolism disorders (amino acidopathies, organic acidopathies, urea
cycle defects)
•
Carbohydrate/intolerance disorders
•
Lysosomal storage disorders
Energy production/utilization disorders
•
Fatty acid oxidation defects
•
Carbohydrate utilization, production disorders (glycogen storage,
gluconeogenesis, and glycogenolysis disorders)
•
Mitochondrial disorders
•
Peroxisomal disorders
•
Metabolic acidosis (elevated anion gap)
•
Hypoglycemia
•
Hyperammonemia
Clinical Aspects for Inborn Errors of
Metabolism in Nervous Tissue
Evidence of familial coincidence
Progressive decline in nervous functioning
Appearance and progression of unmistakable neurologic signs
General symptoms
•
State of consciousness, awareness, reaction to stimuli
•
Tone of limbs, trunk (postural mechanisms)
•
Certain motor automatisms
•
Myotatic and cutaneous reflexes
•
Spontaneous ocular movements, fixation, pursuit; visual function
•
Respiration and circulation
•
Appetite
•
Seizures
Clinical/Laboratory Findings
Clinical findings
AA
OA
UCD
CD
GSD
FAD
LSD
PD
MD
Episodic decompensation
X
+
++
+
X
+
-
-
X
Poor feeding, vomiting, failure to
thrive
X
+
++
+
X
X
+
+
+
Dysmorphic features and/or skeletal
or organ malformations
X
X
-
-
X
X
+
X
X
Abnormal hair and/or dermatitis
-
X
X
-
-
-
-
-
-
Cardiomegaly and/or arrhythmias
-
X
-
-
X
X
+
-
X
Hepatosplenomegaly and/or
splenomegaly
X
+
+
+
+
+
+
X
X
Developmental delay +/neuroregression
+
+
+
X
X
X
++
+
+
Lethargy or coma
X
++
++
+
X
++
-
-
X
Seizures
X
X
+
X
X
X
+
+
X
Hypotonia or hypertonia
+
+
+
+
X
+
X
+
X
Ataxia
-
X
+
X
-
X
X
-
-
Abnormal odor
X
+
X
-
-
-
-
-
-
Primary metabolic acidosis
X
++
+
+
X
+
-
-
X
Primary respiratory alkalosis
-
-
+
-
-
-
-
-
-
Hyperammonemia
X
+
++
X
-
+
-
-
X
Hypoglycemia
X
X
-
+
X
+
-
-
X
Liver dysfunction
X
X
X
+
X
+
X
X
X
Reducing substances
X
-
-
+
-
-
-
-
-
Ketones
A
H
A
A
L/A
L
A
A
H/A
Laboratory Findings*
Glycogen Storage Disease
Pyruvate Dehydrogenase Complex Deficiency
Glucose
Glycogen
Glycogenolysis
Glycogenesis
G6P
Pentose Phosphate
Pathway
R5P
nucleotides
Glycolysis
F6P
PFK
Tarui disease
Glycogen Storage Disease Type VII
F16BP
Pyruvate
PDH complex deficiency
PDH
Acetyl-CoA
Krebs
cycle
Glycogen Storage Disease Type VII (Tarui Disease)
Classic, infantile onset, Late onset
Exercise intolerance, fatigue, myoglobinuria
Phosphofructokinase
•
Tetramer of three subunits (M, L, P)
•
Muscle/heart/brain - M4; liver/kidneys - L4; erythrocytes - M4, L4, ML3, M2L2, M3L
General symptoms of classic form
•
Muscle weakness, pronounced following exercise
•
Fixed limb weakness
•
Muscle contractures
•
Jaundice
•
Joint pain
Laboratory studies
•
Increased serum creatine kinase levels
•
No increase in lactic acid levels after exercise
•
Bilirubin levels may increase
•
Increased reticulocyte count and reticulocyte distribution width
•
Myoglobinuria after exercise
•
Ischemic forearm test - no lactate increase with ammonia increase
Pyruvate Dehydrogenase Complex Deficiency
Neonatal, infantile, childhood onset
Abnormal lactate buildup (mitochondrial disease)
Pyruvate dehydrogenase complex
•
E1 - a (thiamine dependent) and  subunits, a22 tetramer
•
E2 - monomer (lipoate dependent)
•
E3 - dimer (riboflavin dependent) common to aKGDH and BCAKDH
•
X protein - lipoate dependent
•
Pyruvate dehydrogenase phosphatase
Nonspecific symptoms (especially with stress, illness, high carbohydrate intake)
•
Severe lethargy, poor feeding, tachypnea
•
Key feature is gray matter degeneration with foci of necrosis and capillary proliferation in the brainstem (Leigh syndrome)
•
Infants with less than 15% PDH activity generally die
Developmental nonspecific signs
•
Mental delays
•
Psychomotor delays
•
Growth retardation
Laboratory studies
•
High blood and cerebrospinal fluid lactate and pyruvate levels
•
Elevated serum and urine alanine levels
•
If E2 deficient, elevated serum AAs and hyperammonemia
•
If E3 deficient, elevated BCAA in serum, aKG in serum and urine
Inborn Errors of Metabolism
Carbohydrates (Glycogen storage diseases)
Amino acids (Maple syrup urine disease)
Organic acids (Alkaptonuria)
Mitochondrial function (Pyruvate dehydrogenase deficiency)
Purines and pyrimidines (Lesch-Nyhan disease)
Lipids (Familial hypercholesterolemia)
Porphyrins (Crigler-Najjar syndromes)
Metals (Hereditary hemochromatosis)
Peroxisomes (X-linked adrenoleukodystrophy)
Lysosomes (GM2 gangliosidoses - Tay Sachs disease)
Hormones (hyperthyroidism)
Blood (Sickle cell disease)
Connective tissue (Marfan syndrome)
Kidney (Alport syndrome)
Lung (a1-antitrypsin deficiency)
Skin (Albinism)
Review Questions
• How does muscle produce ATP (carbohydrates, fatty
acids, ketone bodies, branched-chain amino acids)?
• How is skeletal muscle phosphofructokinase-1 regulated?
• What are the key Ca2+ regulated steps?
• How does nervous tissue (neurons and glial cells)
produce ATP (carbohydrates, fatty acids, ketone bodies,
branched-chain amino acids)?
• How do glial cells (astrocytes) assist neurons?
• What are some key clinical features (history, physical,
laboratory test results) associated with defects in
metabolism that affect muscles and nervous tissue?
Carbohydrate Metabolism in Diabetes
A 59-year-old man is brought to the emergency department for
evaluation of his semiconsciousness and minimal responsiveness
• For the third example taken from the ERG Unit,
what would you choose for the resource session?
Carbohydrate Metabolism in Diabetes
• Regulation of glycolysis, glycogenesis, glycogenolysis,
gluconeogenesis by insulin/glucagon
PFK-2 (PKA, AMP-dependent PK)
PK (PKA)
PDH
GS (PKA, PPK, GSK-3, PP-1)
GP (PKA, PPK, PP)
PEPCK (glucagon)
G6Pase (glucagon)
• Regulatory differences among tissues
Liver
Muscle
Cardiac muscle
• Key clinical features (history, physical, laboratory test results)
associated with carbohydrate metabolism that occur in diabetes
Summary
• Remember curriculum wants and needs
• Practice new language skills
• Use resource sessions effectively
Complement self-directed learning
Applied to patient case
Start simple, discuss difficult
Big picture, relevant details
Overlap and redundancy
Build upon previous knowledge
• Clinical probes for content and
concepts