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Colleagues-
I need tap the collective knowledge of this diverse newsgroup. Our
bioanalytical group is considering the development and validation of
a method for determination of an analyte in human cerebrospinal fluid
(CSF). We already have a validated method for determination of the
analyte in human plasma, which is quite solid and well behaved.
Because of the scarcity and unreliable supply of CSF of consistent
quality, we are considering the possibility of using synthetic CSF as
the matrix for calibration standards and possibly some of the QCs.
Of course, the viability of this or any similar approach will need to
be assessed carefully. So in order to evaluate this approach
further, we need to prepare synthetic CSF.
1. Does anyone have a reference that either has a preparation for
synthetic CSF or a reference that describes its composition and might
serve as a starting point for preparation of synthetic CSF?
2. Can anyone share any past experience with such an approach?
Tom
Thomas L. Tarnowski, Ph. D.
Associate Director, Bioanalytical Development
Elan Pharmaceuticals
800 Gateway Blvd.
South San Francisco, CA 94080
thomas.tarnowski.aaa.elan.com
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The following message was posted to: PharmPK
Dear Tom,
I am not sure that preparation of synthetic CSF is the best idea. CSF
composition is highly variable
and it criticaly depends on two things: blood composition and the
state of blood-CSF barrier. Of
course, function of cells like astrocytes, oligodendrocytes etc.
physical properties like molecular
weight and ionisation of solutes and so on make significant impact on
its composition, also. Not to
mention that cytosol components of the cells that degrade extremely
fast in CSF (in a matter of
minutes) could significantly change the composition of the CSF.
You havent said why you need to monitor drug concentration in CSF but
I presume you will need to
analyze samples from ill subjects at some point of your
investigation. If these patients have some
neurologic disease, especially infective or autoimmune disease or
head contusion I highly doubt that
your synthetic CSF can simulate their CSF composition. If you
exclusively deal with healthy subjects
with intact BBB (blood-brain-barrier, this is not the best term for
our purpose but it is frequently
used) I would suggest you to use simple physiological solution (0.9%
NaCl) or phosphate buffered
saline. Normal CSF has content of electrolytes (osmolality) similar
to plasma and, if you make
careful preparation of CSF samples you will remove intact cells and
proteins (I also presume that
your analyte is not protein). Possible interfering substances that
you are probably interested in
could be still present in samples prepared from CSF but detailed
knowledge of analyte structure is
needed for their identification. I think that you could do more by
careful sample preparation and/or
chromatographic separation and/or MS adjustments than with the
synthetic CSF preparation.
I am not aware of reference dealing with synthetic CSF but I suggest
you to consult some of the
textbooks of clinical chemistry like: Clinical Diagnosis and
Management by Laboratory Methods by
J.B. Henry, Clinical Laboratory Diagnostics by L. Thomas or Tietz
Textbook of Clinical Chemistry
which do contain information related to composition of normal CSF and
its changes caused by
different diseases.
Hope this helps.
Zeljko Debeljak, PhD student
Medicinal Biochemistry Specialist
Clinical Hospital Osijek
CROATIA
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The following message was posted to: PharmPK
Dear all,
If CSF composition is highly variable, this would also be a reason
not to use CSF. Perhaps a more pragmatic way is to cross-validate the
method with drug analysis in plasma. For example: mix 100 ul of CSF
to be analyzed with 200 ul of blank plasma and treat as plasma sample
and use a calibration curve in plasma.
Cheers and happy holidays,
Rob ter Heine
--
Rob ter Heine, MSc, PharmD
Department of Pharmacology, Slotervaart Hospital
Amsterdam, The Netherlands
E: aprth.-at-.slz.nl
T: +31-20-5124737
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