Six-hour window of opportunity for calpain inhibition in focal cerebral ischemia in rats.
OBJECTIVE
Stroke patients often experience a significant temporal delay between the onset of ischemia and the time to initiation of therapy. Thus, there is a need for neuroprotectants with a long therapeutic window of opportunity. The efficacy of a potent, central nervous system-penetrating calpain inhibitor (MDL 28,170) was evaluated in a temporary model of focal cerebral ischemia to determine the window of opportunity for intracellular protease inhibition.


METHODS
An ex vivo brain protease inhibition assay established pharmacodynamic dosing parameters for MDL 28,170. Middle cerebral artery (MCA) occlusion was accomplished by advancing a monofilament through the internal carotid artery to the origin of the MCA. Postmortem infarct volumes were determined by quantitative image analysis of triphenyltetrazolium-stained brain sections.


RESULTS
Maximal inhibition of brain protease activity was observed 30 minutes after injection of MDL 28,170 with an estimated pharmacodynamic half-life of 2 hours. MDL 28,170 caused a dose-dependent reduction in infarct volume when administered 30 minutes after MCA occlusion. A window of opportunity study was conducted to determine the maximal delay between the onset of ischemia and the initiation of efficacious therapy. MDL 28,170 reduced infarct volume when therapy was delayed for 0.5, 3, 4, and 6 hours after the initiation of ischemia. The protective effect of MDL 28,170 was lost after an 8-hour delay.


CONCLUSIONS
These data indicate that the therapeutic window of opportunity for calpain inhibition is at least 6 hours in a reversible focal cerebral ischemia model. This protection is observed despite the lethal hypoxic and excitotoxic challenge, suggesting that calpain activation may be an obligatory, downstream event in the ischemic cell death cascade.
Markgraf
C G
CG
Hoechst Marion Roussel, Inc, Cincinnati, Ohio 45215-6300, USA.
Velayo
N L
NL
Johnson
M P
MP
McCarty
D R
DR
Medhi
S
S
Koehl
J R
JR
Chmielewski
P A
PA
Linnik
M D
MD
D000818:Animals; D001921:Brain / Q000201:enzymology; D002154:Calpain / Q000037:antagonists & inhibitors*; D002343:Carotid Artery, Internal; D016923:Cell Death; D002539:Cerebral Arterial Diseases / Q000150:complications; D002544:Cerebral Infarction / Q000188:drug therapy / Q000201:enzymology / Q000209:etiology / Q000473:pathology; D004396:Coloring Agents; D015853:Cysteine Proteinase Inhibitors / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D004151:Dipeptides / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D006207:Half-Life; D000860:Hypoxia / Q000209:etiology; D007091:Image Processing, Computer-Assisted; D002546:Ischemic Attack, Transient / Q000188:drug therapy* / Q000201:enzymology / Q000209:etiology / Q000473:pathology; D008297:Male; D018696:Neuroprotective Agents / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000627:therapeutic use*; D009498:Neurotoxins / Q000009:adverse effects; D051381:Rats; D017208:Rats, Wistar; D013778:Tetrazolium Salts; D013997:Time Factors
D004396:Coloring Agents; D015853:Cysteine Proteinase Inhibitors; D004151:Dipeptides; D018696:Neuroprotective Agents; D009498:Neurotoxins; D013778:Tetrazolium Salts; C009591:triphenyltetrazolium; D002154:Calpain; C058076:calpain inhibitor III