Let’s take a look at causes
of megaloblastic anemia.
Now, once we have completed
discussion of megaloblastic,
I’m going to mention some
of these non-megaloblasts.
Megaloblastic anemia, now, I’m
going to set this up for you
and this is an important side, a lot
of things that are occurring here.
First, let’s take a look at
the peripheral blood smear.
And what do you end up seeing there?
Our megaloblasts, look
how large they are.
Highly nucleated and lack
of proper maturation.
Those are RBCs.
Can you believe that those are RBCs?
Or in other words, it’s primitive cells.
And you should never have an RBC
that looks like that, right?
I mean, the nucleus
shouldn’t be there.
It should be central pallor, so on and
so forth, but that isn’t occurring.
Now let me set this up, I’m going
to slow down here a little bit
and make sure that you’re very, very
familiar with these two pictures.
And I’m going to tell you as
to how to use these, okay?
The top picture, for the most part,
we’re going to go from the diet
and we’re going to consume,
let’s say, folate.
And we’re going to then interact with B12.
And when we interact with B12,
then I’m going to walk you through
what’s known as tetrahydrofolate
and then have you --
Really, take a look that
first picture here.
The objective is to convert
your dUMP into dTMP, right?
What does that mean to you?
Well you know from genetics, once again,
that if you want to form
DNA, you can’t have UMP.
You can’t have uracil.
You need to convert that U into what?
Good, your thymidine.
And so therefore, this is the objective.
And what we are going to do here is we’re
going to interplay both B12 and folate
so we can form dTMP.
Is that clear?
So that’s the first picture and
then on the second picture,
I will elucidate that further.
Okay, let’s begin at the top.
You are now consuming folate.
What you’re taking in is going to
be that form that you see there,
at least pay attention
to the methyl, please.
The F stands for folate.
H stands for tetra.
So there you go, tetrahydrofolate
attached with the methyl.
We don’t need methyl in order for
proper action and functioning.
So we need to find a way to remove that
methyl and give it to an acceptor.
And so, it will donate the methyl.
Something is going to accept
it and you will see this now.
So what is this acceptor of the methyl?
Because if you don’t accept the methyl,
then you basically have inactive folate.
Do you understand that?
And where are you getting this from?
Okay, so let it be greens
and so on and so forth.
So you’ve taken in the
you’re going to then donate
the methyl to the B12.
Look at the B12 there.
It says methyl B12.
So we have to have B12
communicating or interacting with the
folate so that it can accept the methyl.
Now, what are you going to do?
Now the B12 is going to donate
that methyl to the homocysteine
and the enzyme there is
called methionine synthase.
How appropriate is that?
So the methyl will be donated with
the help of methionine synthase,
will then convert homocysteine
into methionine, stop there.
Clinically, you as a clinician, what
are you going to look for in the urine
to help you suspect or even perhaps
confirm megaloblastic anemia
being caused by B12 or folate.
Now, what I must bring to attention is that
you’re going to find hyperhomocysteinemia
in both folate and B12.
Say that three times fast.
Ready? It’s quite fun.
So now you have tons of
homocystein in the urine,
but all that it's told you now is
that I have megaloblastic anemia
being caused only by B12?
Only by folate?
So all of this tells you that
your megaloblastic anemia
being caused by
either B12 or folate.
But you don’t know which one.
if you’re not taking your methyl, right?
From the diet.
If you’re not taking your
how could you possibly convert
your homocysteine into methionine?
So in folate deficiency, please listen.
You do have hyperhomocysteinemia and
you will have hyperhomocysteinuria.
Number two, what if you didn’t have B12?
If you didn’t have B12,
first it wouldn’t
accept the methyl.
Secondly, methionine synthase
really wouldn’t be working.
You should know that B12 is a
co-factor for methionine synthase.
So if that enzyme isn’t working
and is not accepting methyl,
B12 deficiency results in?
All it tells you is
Now, hyperhomocysteinemia from biochemistry
should know about other things
including your ornithine
and stuff like that,
but cystathionine synthase and I’m not
going to bring all that here though.
Biochem, look up cystathionine.
Next, all right, now if
everything goes well,
the methyl comes in, taken up by
B12 and it's properly handled.
You're left with tetrahydrofolate.
Now what will you do?
Well that tetrahydrofolate, if I were
you, I would know some of this co-factors
and this include your serine and glycine.
And you’re going to then form what’s
known as methylenetetrahydrofolate.
This is a useable form, pay attention here.
We have an interesting enzyme here.
It’s called thymidylate synthase.
Thymidylate synthase is then going
to take that tetrahydrofolate,
accept two of them.
Well, you have four, right?
it will take up two.
And so take up the two folate
and convert the dUMP to dTMP.
You must know the enzyme,
I'll tell you in one second,
many of you already know.
So now, what are you left with?
You’re left with dihydrofolate.
I know you’ve heard of
And what are you going to do in
biochemistry with dihydrofolate?
You’re going to reduce it, aren’t you?
When you have a reduction type
of formula or calculation
in biochemistry it actually
you’re going to increase it.
So anyhow, you’re going to reduce this
dihydrofolate with the help of what enzyme?
You all know about
There it is, look.
We reduced it with reductase.
So now, you took the dihydrofolate
and you converted tetrahydrofolate.
"Dr. Raj, is all this necessary?"
More than you can imagine.
So, my topic is B12 and
We’re going to put in the drugs here.
We’re going to put in some pathology here.
And then once we’re done with this picture,
we’re going to move to another one.
And I’m not going to bring that up
now though, but it’s important.
Say that your patient has
And you’re thinking about giving them an
antineoplastic drug called methotrexate.
Take a look at MTX,
identify it here.
MTX is methotrexate.
High dose of methotrexate has been given.
It’s mechanism of action is to
inhibit the hydrofolate reductase.
In what kind of cells?
Yeah, cancer cells, right?
And if you inhibit this enzyme,
you can’t properly what?
Recycle your folate.
So therefore, you can’t form dTMP.
What happens to this cancer cell?
Is it possible that methotrexate
might bleed over into a normal cell?
You already know this as well.
What’s the name of that rescue?
What’s the name of that folate?
Called folinic acid.
All this come together?
I hope so.
So here’s methotrexate inhibits the
enzyme dihydrofolate reductase.
I can’t properly reduce
For all intent and purposes,
you are folate deficient.
If this bleeds into a normal
human cell, eukaryotic,
then you know that
you’re folate deficient.
What does this result in, please?
If it’s high dose,
what are you going to give this
patient to then replenish the folate
in the human cells only without
affecting the cancer cells?
It’s called folinic acid.
Give me the technical name or give
me the, I guess, the trade name?
That’s leucovorin or
Drug number one.
Who are we trying to combat here?
This is an antibiotic.
Here’s the antibiotic that you’re giving.
You’ve heard of cotrimoxazole, haven't you?
That’s sulfamethoxazole plus your?
So you have cotrimoxazole.
So this is a drug that you’re going
to give to kill off bacteria
and inhibits dihydrofolate
reductase in that bacteria.
It kills off the bacteria.
Unfortunately, may also cause human
cells to die for the same reason.
Is that clear?
So both of these result in
what kind of deficiency?
What kind of anemia is your
patient going to suffer from?
That’s your megaloblastic anemia.
What do you want to
do with this patient?
Either, well as we said, leucovorin
or remove the drug if need be.
All right, change the
drug, so on and so forth.
Two down with drugs.
Let’s talk about the third one.
Here is my thymidylate synthase.
You see it?
That converts your dUMP to dTMP
and it takes up two
of your folates.
So they form dihydrofolate.
The name of this enzyme is 5-FU.
And by FU, I mean fluorouracil.
Hope I didn’t offend anyone,
I’m sorry if I did.
So 5-FU is 5-fluorouracil.
That’s a drug also, antineoplastic.
It inhibits the enzyme
Here once again, for all
intent and purposes,
please know that you’re going to
then become folate deficient.
The only thing that I wish to bring to
your attention, current day practice,
that if you use FU,
you don’t have to
In fact, if you give FU,
it’s just the opposite.
It is going to then
enhance the activity,
enhance the activity.
Keep that in mind.
And so therefore,
there is no such thing as giving this patient
leucovorin to save the overdose of 5-FU.
Keep that in mind
especially when you’re dealing with
drugs later on in pharmacology.
You’re trying to treat a patient
with colorectal cancer.
That’s a big one.
Don’t forget that please.
We’ll have discussions more and we have
talked about this neoplasia as well.
So those were the big drugs, those were
the inhibitions, know those enzymes.
There is interplay between folate and
B12 and that’s the first picture.
In the second picture,
this entire biochemical pathway has
nothing to do with these drugs.
It has nothing to do with
really dietary issue.
And what it really deals with
only is true B12 deficiency.
You tell me about a patient clinically
that is presenting a B12 deficiency,
in which a fully deficient
patient will never present with.
What happens here?
Walking wide stance,
close my eyes.
I don’t know where I am.
And I have upper
motor neuron lesion.
All right, what the
heck is all this?
It’s called subacute
Let’s go step by step.
I’m walking towards you but
wide ataxia, ataxic gait.
So what organ in your brain
controls your coordination?
And so therefore, your spinocerebellar
tract is knocked out, number one.
Another one, I said I close my eyes and
I’m moving, I’m swaying and vibrating.
Not vibrating, I can’t vibrate.
And this is what?
So I don’t have --
loss of touch, loss
I’m doing positive Romberg, right?
I closed my eyes but I’ve lost all spatial
and, you know, I just
can’t stand still.
Stability has been lost.
Which column is that?
Dorsal column, two down.
And what’s this?
Like rigidity almost.
That’s upper motor lesion,
That is going to be?
Lateral corticospinal tract.
All three tracts, you must know.
What’s this called?
three tracts; lateral corticospinal,
spinocerebellar and dorsal column degeneration.
What’s degenerating in those
columns or in those tracts.
The myelin, right?
You only find that in B12 deficiency.
You'll never find that in folate.
What about this demyelinating disorder?
Keep that in mind.
If you don’t give a simple injection of
B12 in your butt, meaning intramuscular,
then understand you go through irreversible
deterioration of your patient.
That’s your patient.
Let’s take a look at the biochemistry.
Identify the B12.
So here, the B12 is also a co-factor for
second enzyme beginning with the letter M.
This is called
"What was the other one, Dr. Raj?"
You tell me.
That was called methionine synthase.
If methionine synthase
was knocked out,
your patient with B12 results
This is methylmalonyl-CoA
So what are you going to
find here in this patient
that you will never find
in folate deficient?
Methylmalonic aciduria, right?
How would you ever find
this in folate deficiency?
There is nothing, please.
Take a look at this.
There is nothing in this formula
here that has folate in it, okay?
Now, so what’s causing demyelination?
Whenever you knock out an enzyme,
would you tell me what happens to
the proximal substrate always?
Yeah, it increases.
Keep going back.
So we talked about MMA, which
is methylmalonyl-CoA aciduria.
And then keep going back.
Are you going to
Of course you are.
Okay. What you need to
properly myelinate your nerve?
Take a look at that what’s in bold here.
You need acetyl-CoA for
normal myelin synthesis.
Now you have too much propionyl-CoA.
It replaces the acetyl-CoA
and you demyelinate.
What are the tracts?
Spinocerebellar, ataxic gait.
Upper motor neuron lesion, that’s
your lateral corticospinal tract.
And positive Romberg and no vibration
or touch, that is you dorsal column.
Now the only thing that I’ll make sure
that we’re clear here from biochemistry
is that you are going to take
up propionyl-CoA pathway.
If everything is perfectly normal
and you had enough of your,
what’s known as your biotin,
and you had enough of your
B12 and you kept going,
then you go into your TCA,
tricyclic, or Krebs cycle, right?
But what kind of fat
would you be taking up?
It’s called odd-chain fatty acids.
Just keep that in mind because the boards
love those questions about odd-chain.
You’ve heard of long chain and short chain
and medium chain, especially medium chain.
They love that one.
But keep in mind though,
that it’s odd-chain fatty acids
that you’re going to take up.
Now, I only have a little thing that I
wish to bring to your attention here.
It’s a nice little figure.
It really is because it
integrates a lot of stuff.
It is that anytime that
you find a carboxylase
in biochemistry, any pathway,
the co-factor here is biotin.
Is that clear?
So they say that if I am able to
consume, on a personal note --
if I am able to consume enough biotin and
I rev up my biotin levels in my body,
I’m supposed to
have hair growth.
You're yet to see that, right?
So anyhow biotin is rather interesting.
Know that is being one of those
co-factors for carboxylase.
Here however, if you
have B12 deficiency,
you undergo demyelination and you would never
find methylmalonic aciduria in folate.
We spend a lot of time on this figures.
A lot of questions come from this
and a lot of integration
as you can see here,
Ultimately, what are
we dealing with?
Macrocytic, greater than 100 MCV.
Megaloblastic or non-megaloblastic?