Murder or Medical Mishap?
Death on the Metabolic Ward
by
Nancy M. Boury
Department of Animal Science
Iowa State University, Ames, IA
1
Background
You have been chosen for a very competitive paid undergraduate clinical internship position (uCLIP). You spent
your first weeks becoming a certified nurse assistant
(CNA). You will be paid to work as a CNA at St.
Visintainer’s, assisting the nurses on the suspected
metabolic disorder’s acute-care floor.
As part of your internship, you will also be allowed to
follow Dr. Saccharo as he sees clinic patients. The
doctor is an expert in enzyme deficiency disorders
relating to glycolysis. Because you hope to become a
family physician, you’re excited about the opportunity to
learn about these rare metabolic disorders. To prepare
for your first day on the metabolic ward, Dr. Saccharo
requests that you research normal sugar metabolism,
particularly glycolysis.
2
Monday Morning at the
Metabolic Disorders Clinic
After working all weekend on Dr. Saccharo’s
assignment, you feel ready for anything –
including Monday morning. As you ride up the
elevator with your mentor and fellow interns, Dr.
Saccharo asks a few questions to determine
how prepared you are for this morning’s clinic
hours.
3
Please get into your groups of
four and take out your clickers
4
CQ#1: Which of the following enzymes
catalyzes a reaction that produces ATP
during glycolysis?
A. Hexokinase (HK)
B. Phosphoglucose isomerase (PGI)
C. Phosphofructokinase (PFK)
D. Triosephophate isomerase (TPI)
E. Pyruvate Kinase (PK)
5
CQ#2: Which of the following enzymes
breaks one 6-carbon sugar into two 3carbon sugars?
A. Hexokinase (HK)
B. Phosphoglucoisomerase (PGI)
C. Phosphofructokinase (PFK)
D. Aldolase
E. Enolase
6
Dr. Saccharo’s
Review of Glycolysis
Glucose is an important source of
chemical energy, but this energy must be
converted from a large denomination of
energy (~680 kilocalories per mole of
glucose) to more usable forms, such as
ATP (~7.3 kilocalories per mole). Imagine
standing in front of a vending machine with
a $100 bill vs a $1 bill.
7
Dr. Saccharo’s
Review of Glucose Homeostasis
• Your body (particularly your brain) needs glucose as fuel for
cell processes. When you eat, your blood glucose levels
will temporarily rise, signaling the pancreas to release
insulin. When you have gone without food for several
hours, your pancreas will release glucagon, which triggers
the liver to release glucose from glycogen stores.
• If your blood sugars are too high, your blood vessels are
damaged and the organs they supply with blood are
damaged as well. Consistently high levels of blood sugars
lead to kidney, heart, liver, and brain injury over time.
• If your blood sugars are too low, your brain will starve for
energy. As a result, you could pass out, enter a coma, and
potentially die in a matter of hours.
8
Fed – Blood
Glucose
Levels High
FastingGlucose
Levels Low
Pancreas
Releases
Glucagon
Pancreas
Releases
Insulin
Liver
Glucagon
Receptors
Liver
Releases
Glucose into
the Blood
Body Cells
have Insulin
Receptors
Glucose
Levels
Normal
Body Cells
Take Up
Glucose from
the Blood
9
Dr. Saccharo’s
Review of Glucose Homeostasis
• Diabetics either have cells that don’t respond to
insulin properly (Type II diabetes, or late-onset)
or don’t have functional insulin produced (Type I
diabetes, or juvenile).
• This sugar balance, however, isn’t the only thing
we worry about here in the metabolic disorder’s
ward. There are genetic disorders where a
person is missing an enzyme required to break
down the glucose (or other sugar) once it gets
into its target cell.
10
• Once glucose enters the cell, hexokinase
will add a phosphate group to the glucose.
This gives the glucose a negative charge
and traps it within the cell.
• This addition of a phosphate group is the
beginning of glycolysis, which is also
known as the Embden Myerhof pathway.
11
Please trade papers within your groups
and check each other’s homework
12
Embden-Myerhof Pathway
13
Clicker Survey: How many mistakes
were in the paper you graded?
A. 0-1
B. 2-3
C. 4-5
D. More than 5
What was the most common mistake
made within your group?
14
Jamie, one of your fellow interns, is
bothered because he knows the clinic
frequently treats people with enzyme
deficiency disorders. He asks Dr. Saccharo:
If glycolysis is needed to use glucose,
how can a person live without all the
enzymes needed for glycolysis?
15
One reaction – many different
enzymes
• Isoenzymes use the same reactants to
produce the same products.
• They may have:
– Different genes
– Different tissue expression
– Different developmental timing of expression
• They will likely have slightly different
affinities for their substrates.
16
Phosphofructokinase as an example
• Three different forms & three different genes:
– PFK – L is expressed in the liver; the gene for this
isoenzyme is found on chromosome 21
– PFK – M is expressed in the muscle; the gene is found
on chromosome 12
– PFK – P is expressed in platelets; the gene is found on
chromosome 10
• Looking at the homework – this is the same reaction
– Adds a 2nd phosphate to fructose-6-phophate to form
fructose-1,6-bisphosphate
17
CQ#3: If a person would be deficient in
all 3 forms of PFK, this person would __.
A. Have lower than normal glycogen
stores.
B. Have more mitochondrial activity than
normal.
C. Be dead.
D. Produce more energy per glucose
molecule because glycolysis would
be unregulated.
18
Time for the clinic to open…
Dr. Saccharo asks the
interns, “Any questions
before we get started
seeing patients?”
Please keep your
corrected homework on
your desk to use as a
reference as we discuss
the patients.
19
Patient #1: Ann is a teenager and avid golfer who was
referred to the clinic after being refused at the blood drive and
tiring easily on the high school golf course during practice.
Levels (+ = normal, - = decreased levels, ++ = increased levels)
Blood Metabolic Panel
Blood Glucose
+
Glucose-6-phosphate
++
Fructose-6-phosphate
++
Fructose-1,6,bisphosphate
++
Glyceraldehyde-3-phosphate
++
1,3-bisphosphoglycerate
++
Phosphoenolpyruvate
++
Pyruvate
-
ATP
-
Red Blood Cell Concentration
-
20
CQ#4: Assuming that Dr. Saccharo is
correctly assuming that Ann has a defect in
glycolysis, what is the most likely defect
based on the blood metabolic profile?
A. Hexokinase
B. Phosphofructokinase
C. Triosephosphate Isomerase
D. Pyruvate kinase
E. Aldolase
21
Patient #2: Marie is a 32-year-old mother of three
complaining of fatigue and muscle cramps with
exercise. She had always blamed her intolerance
to exercise on her sedentary lifestyle. However,
she recently joined a gym and, after a week of
aerobics classes, went to her physician who
ordered a series of blood tests. The blood work
came back with abnormal results, leading to her
muscle biopsy and referral to the metabolic clinic.
22
Marie’s Blood Test Results
Levels (+ = normal, - = decreased levels, ++ = increased levels)
Blood Metabolic Panel
Blood Glucose
+
Glucose-6-phosphate
++
Fructose-6-phosphate
++
Fructose-1,6,bisphosphate
-
Glyceraldehyde-3-phosphate
-
1,3-bisphosphoglycerate
-
Pyruvate
-
ATP
-
Red Blood Cell Concentration
23
CQ#5: The muscle biopsy showed an
excess of glycogen in the muscle tissues.
What is the most likely enzyme deficiency?
A. Pyruvate kinase
B. Hexokinase
C. Phosphofructokinase
D. Triosephosphate Isomerase
E. Aldolase
24
CQ#6: If you wanted to test red blood cells
for their ability to complete glycolysis,
what compound would you try to detect?
A. Fructose-6-phosphate
B. Aldolase
C. Pyruvate
D. Phosphofructokinase
E. Dihydroxyacetone phosphate
25
CQ#7: If you had some of Ann’s red blood
cells in a test tube, what compound could
you add to enable these cells to produce
pyruvate?
A. Glucose
B. Fructose-1,6,bisphosphate
C. Insulin
D. Glucagon
E. Fructose-6-phosphate
26
Patient #3: Leo is a 25-year-old accountant. He is
not anemic, has perfect teeth, and experienced two
fainting spells recently. One happened after
accidentally drinking a non-diet soda, the other after
eating “naturally sweetened” fruit salad. His dentist
referred him to Dr. Saccharo’s clinic. Dr. Saccharo
suspected Leo may have hereditary fructose
intolerance (HFI) and recommended a closely
monitored fructose tolerance test. Leo was
scheduled for the test and an observation bed at the
local hospital the next day.
27
Hereditary Fructose Intolerance
• HFI is a recessive disorder where individuals with HFI lack a
functional copy of Aldolase B.
• Individuals with HFI normally become symptomatic with
weaning – as babies switch from breast-milk with lactose to
formula with sucrose or sorbitol. The HFI may go undetected
until adulthood, with adults self-regulating their diet to be low
in sugars.
• They are able to metabolize glucose, because they have
Aldolase A and C. However, in the liver, it is Aldolase B that
breaks down fructose-1-phosphate, sending
dihydroxyacetone phosphate and glyceraldehyde-3
phosphate to glycolytic pathway. Since HFI patients lack
Aldolase B, they are unable to break down fructose.
28
Fructose metabolism
– In the liver
Inside the
cell
Fructose 1Phosphate
Inhibits
Glycogen
phsphorylase
Blood stream
Glycogen
Fructokinase
Fructose
Aldolase B
DHAP
G3P
Glucose-6phosphate
Dihydroxyacetone
phosphate
(DHAP)
Glyceraldehyde-3phosphate
(G3P)
29
CQ#8: Glycogen phosphorylase is an
enzyme required to release the glucose
stored as glycogen. A person with HFI who
ingested fructose would have:
A.
B.
C.
D.
E.
High levels of blood fructose.
High levels of blood fructose-1-phosphate.
High levels of blood glucose.
Low levels of blood fructose.
Low levels of blood glucose.
30
Regulation of glycolysis
• Glycolysis is reversible. Most of the enzymes can work to
break down glucose (gycolysis) or build more glucose
(gluconeogenesis).
• Products of a particular enzymatic reaction will generally
inhibit that enzyme.
• Several points of control exist. For example:
– Hexokinase is inhibited by glucose-6-phosphate and
activity is boosted by free phosphate.
– Phosphfructokinase is inhibited by ATP and fructose1,6,-bisphosphate
– Pyruvate kinase is inhibited by ATP, but activated by
fructose-1,6,bisphosphate and phosphoenolpyruvate.
31
Tuesday at the Hospital
When you arrive at the nurse’s station to
start your shift the next day, you
discover that Leo was found dead in his
room shortly after lunch. “What
happened?!?” you almost shout at Leo’s
nurse.
32
Leo’s Last Morning
Leo’s nurse is occupied with the charge
nurse and security guard. You overhear her
saying, “Just an hour ago, he was fine. He
told me the fructose tolerance test was
exhausting. He planned to nap until lunch.
When I went to check his vitals, I saw him
lying in his bed, dead.”
You see Dr. Saccharo behind the desk,
where he is reviewing Leo’s test results.
33
Fructose Tolerance Test Blood
Glucose Levels
100
Glucose (mg/dL serum)
90
80
70
60
50
40
0
15
30
45
60
Time After Fructose (250 mg/kg) Injection
(Minutes)
34
CQ#9: What was the effect of giving Leo
intravenous fructose?
A. A rise in blood glucose levels.
B. A decrease in blood glucose levels.
C. An increase in glycogen stores.
D. A rapid drop in blood pressure.
35
Explanation of Test Results
• The lack of Aldolase B causes a build-up of
fructose-1-phosphate.
– This will trap phosphate in the liver.
– Fructose-1-phosphate will inhibit glycogen
phosphorylase.
• Glycogen phosphorylase is required for the
liver to break glycogen into glucose-6phosphate.
36
CQ#10: If Leo had been given too much
fructose, he would be at serious risk of
coma or death. If caught in time, what
treatment would you recommend to rescue
him?
A. Insulin
B. Glucagon
C. Glucose
D. Fructose
E. Phosphofructokinase
37
So what happened to Leo
AFTER the test?
38
A few drops of blood were found in the
sink and a syringe was found in the
biohazard trash instead of the Sharps
disposal bin.
Dr. Saccharo is curious about the blood
and the syringe.
39
While the hospital awaits the results of the
DNA analysis of the blood and the
chemical analysis of the syringe, Dr.
Saccharo reserves a small sample of the
blood to test for metabolic activity.
40
Dr. Saccharo’s blood test results
Levels (+ = normal, - = decreased or absent levels, ++ = increased levels)
Compound
Patient 1
(Ann)
Patient 2
(Marie)
Patient 3
(Leo)
Sample
(From Sink)
Blood Glucose
+
+
-
+
Glucose-6-phosphate
+
++
+
-
Fructose-6-phosphate
+
++
+
-
Fructose-1,6,bisphosphate
+
-
+
-
Glyceraldehyde-3phosphate
+
-
+
-
1,3-bisphosphoglycerate
+
-
+
-
Phosphoenolpyruvate
++
-
+
-
Pyruvate
-
-
+
-
Red Blood Cell
Concentration
-
-
+
- (+++ preRBCs)
41
CQ#11: If the syringe in the medical waste in
Leo’s room contained ___, there would be
cause for a full-scale investigation.
A. Insulin
B. Glucagon
C. Fructose
D. Aldolase
E. Glucose
42
CQ#12: Dr. Saccharo reports his lab results
to the police, saying in his expert opinion
that they should look for someone with ___.
A. Pyruvate kinase deficiency
B. Type I diabetes
C. Phosphofructokinase deficiency
D. Glycogen storage disease
E. Hexokinase deficiency
43
Did Dr. Saccharo’s tip
solve the case?
Later that week, you pick up the newspaper and
read that police arrested an individual for Leo’s
murder. It seems that the murderer had some
questionable business practices that Leo noticed
during tax season. The murderer was also a
patient at the clinic. He saw Leo walking into the
clinic and overheard the nurse scheduling Leo’s
fructose test. He knew the test was dangerous and
thought his actions would be considered an
unfortunate complication or medical accident.
44