Intrathecal substance P-saporin in the dog: distribution, safety, and spinal neurokinin-1 receptor ablation.
BACKGROUND
Neurokinin-1 receptors (NK1-rs) located on superficial dorsal horn neurons are essential for integration of nociceptive input. Intrathecal injection of substance P-saporin (SP-SAP) leads to local loss of spinal NK1-r (+) neurons suggesting its potential as a therapeutic agent for chronic pain. The authors determined, in a canine model, effects of lumbar intrathecal SP-SAP.


METHODS
Distribution of SP-SAP and Saporin was determined in plasma, lumbar cerebrospinal fluid, and tissue. Safety of intrathecal SP-SAP was determined in four groups (six dogs each) administered 0 (0.9% saline), 1.5, 15, or 150 µg SP-SAP through lumbar intrathecal catheters. Behavioral, physiologic, and biochemical variables were assessed. Spinal tissues were collected at 7 and approximately 90 days, or earlier if significant morbidity developed, and analyzed for NK1-r (+) neuron loss and histopathology.


RESULTS
SP-SAP and Saporin were detectable in lumbar cerebrospinal fluid for up to 4 and 24 h, respectively. Animals receiving intrathecal saline, 1.5, or 15 µg of SP-SAP showed no persistent neurologic deficits. Three animals receiving 150 µg of SP-SAP developed pelvic limb paraparesis and were euthanized prematurely. Immunohistochemistry and in situ hybridization cell counts confirmed a significant reduction in NK1-r (+) in superficial dorsal horn neurons from lumbar spinal cord after intrathecal administration of 15 and 150 µg of SP-SAP. A significant loss of NK1-r neurons in the lumbar ventral horn occurred only with 150-µg SP-SAP.


CONCLUSIONS
Intrathecal 15-µg SP-SAP reduced dorsal, but not ventral, NK1-r (+) neurons at the spinal level of delivery with minimal side effects, whereas 150-µg SP-SAP resulted in motor neuron toxicity.
* Research Fellow, † Staff Research Associate, # Postdoctoral Fellow, §§ Professor of Anesthesiology and Pharmacology, Department of Anesthesiology, University of California, San Diego, California. ‡ President, Tox Path Specialists, LLC, Frederick, Maryland. § Director, Campus Veterinary Medicine, ‖ Associate Director, Diagnostic Laboratory, Office of Animal Research, University of California. ** Vice President, †† President/CSO, ‡‡ Research Scientist, Advanced Targeting Systems, San Diego, California.
Ashley J
AJ
Wiese
Michael
M
Rathbun
Mark T
MT
Butt
Shelle A
SA
Malkmus
Philip J
PJ
Richter
Kent G
KG
Osborn
Qinghao
Q
Xu
Samantha L
SL
Veesart
Joanne J
JJ
Steinauer
Denise
D
Higgins
Douglas A
DA
Lappi
Brian
B
Russell
Tony L
TL
Yaksh
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001794:Blood Pressure / Q000187:drug effects; D001831:Body Temperature / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D004285:Dogs; D004797:Enzyme-Linked Immunosorbent Assay; D005455:Fluorescent Antibody Technique; D017403:In Situ Hybridization; D007278:Injections, Spinal; D064729:Neurokinin-1 Receptor Antagonists; D009460:Neurologic Examination; D020258:Neurotoxicity Syndromes / Q000473:pathology; D009887:Ophthalmoscopy; D010641:Phenotype; D018040:Receptors, Neurokinin-1 / Q000378:metabolism; D054789:Ribosome Inactivating Proteins, Type 1 / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000633:toxicity; D000076985:Saporins; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism*; D013373:Substance P / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology / Q000633:toxicity; D014018:Tissue Distribution
D064729:Neurokinin-1 Receptor Antagonists; D018040:Receptors, Neurokinin-1; D054789:Ribosome Inactivating Proteins, Type 1; C468274:substance P-saporin; D013373:Substance P; D000076985:Saporins