In metastatic bone cancer,
pain does not simply
come from a single source.
Various stresses, be they
mechanical or chemical,
layer upon each other
to create a severe
and unmanageable neuropathy.
Owing to the plasticity
of neurons, pathological
changes soon extend from here
to the central nervous system.
And, to think that
all this starts
with a few cells.
Monday, November 30, 2009
SEGMENT 6 SCENE 1 - CONCLUSION
SEGMENT 5 SCENE 2 - ACIDOSIS
In the low pH,
acid-sensing ion channels
cause nerves
to readily depolarize.
Constant activation of these channels
lead to gradient imbalances,
priming neurons for spontaneous firing.
With the hypersensitization
of these nociceptors,
chronic pain settles in.
Approximate run time: 22 seconds
This section also needs some expansion.
UPDATE 09/12/11
Currently, I have the acid ions binding to the ASIC receptors (not yet labelled - will be labelled immediately under each structure). Then I have the neuron changing colours to represent the gradient imbalance. This is where I would love to get some feedback. Is it effective? Or not?
The reason I did not show ions passing through the bilayer is that I had already established/introduced H+, which for the purpose of clarity, has been blown up by a lot. To now introduce other ions at that scale would be difficult because they wouldn't be able to flow through all that easily (they would fit through channel). And now, suppose that we make them small dots of light flowing through the channel, then we have a discontinuity between ions and H+.
Also... How exactly does H+ bind or activate ASICs...?
SEGMENT 5 SCENE 1 - OSTEOCLASTS
Like macrophages,
osteoclasts release acids.
They do so in order
to dissolve the
minerals in the bone.
Therefore, osteoclast hyperactivity
aside from resorbing bone,
creates a highly
acidic environment as well.
SEGMENT 4 SCENE 2 - INFLAMMATORY NOCICEPTION
And caught in the crossfire
is a sea of nerve endings,
whose surface is littered
by an abundance of receptors
and channels.
Their overstimulation
leads to the inflammatory
pain associated with so
many pathologies.
But, in our case, we have
some cells further
complicating the situation.
SEGMENT 4 SCENE 1 - INFLAMMATORY SOUP
As the tumour progresses,nerves become exposedto an ever-increasingmixture of nociceptive agents.This inflammatory soup containsa host of factorsnot limited to cytokines,*protons, interleukins,**prostaglandins, growth-factors,***released by both tumour and immune cells.And so, as cells fight,and as cells die,debris accumulates.****
*On screen, TNF-alpha released by tumour cell.**H+ by macrophage, IL-2 & IL-10 by T-cell.***PGE2 and NGF by tumour again.****ATP from apoptotic cell.
SEGMENT 3 SCENE 2 - TUMOUR GROWTH & MECHANICAL COMPRESSION
Where the metastasis is
of mammary origins,
there is a great increase
in osteoclastogenesis.
Despite increased osteoblast
hypertrophy and activation,
osteoclast hyperplasia results
in net resorption.
The bone thins,
and its rich
neurovasculature is exposed.
Within the confines
of the marrow cavity,
the tumour expands and
mechanically compresses
the vulnerable vessels.
This is when pain
first settles in.
SEGMENT 3 SCENE 1 - OSTEOCLASTOGENESIS
During the cross-talk,
parathyroid hormone-related protein
is released by cancer cells.
It hyperactivates stromal cells
and osteoblasts,
causing them to increase
surface expression of
the RANK ligand,
which when bound to the
RANK receptor,
causes monocytes
to fuse together
to form multinucleated cells.
With continued exposure
to the RANK ligand,
these cells mature
into osteoclasts.
SEGMENT 2 SCENE 2 - OSTEOID MICROENVIRONMENT
In absence of
circulatory turbulence,
breast neoplasms
can flourish
in the fertile
osteoid microenvironment.
An intimate relationship forms
between local and invasive cells.
The former nurtures
the progression and expansion
of the tumour,
and the latter encourages
the activation and proliferation
of local cells.
This vicious cycle
of uncontrolled growth
is what we know as
metastatic bone cancer.
SEGMENT 2 SCENE 1 - INTRODUCTION
Before the pain,
there are but a small
number of malignant cells.
Here, in a sinusoidal vessel,
the slow flow of blood,
lets them nest and settle.
This foothold,
marks the beginnings
of our chronic pathology.
SEGMENT 1 SCENE 1 - PROLOGUE
Of the most excruciating pains,
the one induced by bone-colonizing
cancers rank among the top.
This experience may start
with a single cancer cell,
that breaks away from its origin,
enters the circulation,
and travels to a distant site.
This cell, like many others,
does not make it. But,
inevitably, some will,
such as these cells
traveling as an embolus,
as they so often do.
And, arriving at their destination,
initiate a series of events
that lead to a pain
that is as difficult to manage
as it is to endure.
Approximate run time: 44 seconds
This prologue section does not count towards the 5 minute limit. This will be completed separately as a side-project for one of my courses. The rest of the script will be confined to the 5 minute limit.