Cerebral artery pharmacology (2) Pharmacology Objectives • List stroke measuring scales • Discuss strengths / limitations of animal models of stroke • Discuss characteristics of drugs to be used in clinical trials for stroke • Explain biological effects of inflammatory markers involved in stroke Scale NIH Stroke Scale Description Range Favorable score Meaning Stroke assessment scales Neurological deficits on 42 point scale with 11 categories (paralysis, speech, visual etc 0-42 (lower is better) <1 0=normal 1=mild facial paralysis >22= severe symptoms 25=one sided paralysis with other losses Barthel Ability to perform daily activities (walking, eating, bathroom use, bathing etc) 0-100 (higher is better) 95-100 100= perform all normal activities independently Modified Rankin Overall assessment 0-5 (lower is better) 0 or 1 0=no symptoms 5= severe disabilities Glasgow Outcome Scale Global assessment from good to vegetative to death 0-5 (lower is better) 1 1=good recovery 2=moderately disabled 3=severe disability 4=vegetative state 5=death Clinical Trails Phase iv:Surveillance APPROVAL Phase IIa: Dose/safety Phase I: Toxicity Lab Studies Phase IIb: Chance of efficacy Phase III: Confirm efficacy Ideal animal model.. • • • • • • • • • • • • Focal ischemia in species with cerebral circulation homologous to humans Reversible arterial occlusion to produce submaximal lesion more sensitive to treatment Use physiologic monitoring and optimize experimental design to avoid hypoxemia, hyperglycemia etc Avoid artifact introduced by fluctuations in brain temperature Use adequate sample size and replication of experiments Use controls matched for surgical manipulation anesthesia, drug administration etc Perform studies in multiple species to demonstrate cross-species benefit Administer drug by route that will be used in humans Define optimal time for administration of drug within 3 to 6 hours after reperfusion Determine whether serum level of drug producing therapeutic benefit in animal can be achieved in humans Couple measurement of infarct volume with assessments of cognitive or motor performance to confirm that preservation of tissue correlates with meaningful neurologic function Conduct pilot studies in aged animals and others with comorbid disorders encountered in humans (e.g., hypertension and diabetes) Ideal characteristics… • May be given under field conditions • Effective in wide range of stroke subtypes and severity • Effective over a broad therapeutic window (period after symptom onset) • Well tolerated by young or old patients with diverse comorbidities (e.g. cardiac disease) • Simplicity of administration (oral or intravenous route preferred) • Does not preclude subsequent use of tissue plasminogen activator, anti-coagulants, or antiplatelet drugs • Low cost For a therapy to proceed to clinical trails… • • • • • • • • • • • Adequate dose–response plus serum concentrations measured, thereby defining minimally and maximally effective doses Time window studies confirming efficacy. Time and duration of drug administration appropriate to the mechanism of action and appropriate to the proposed clinical protocol Physiological monitoring of animals undertaken Randomized, blinded studies; reproducible effects (one independent) Infarct volume measured, compound provides sub-cortical as well as cortical protection. Histological protection of >70% in both transient and permanent focal ischaemia when drug is given 15–30 min after occlusion Attenuates white matter damage in brain Functional tests used, short and long term assessment Small rodent studied with permanent middle cerebral artery occlusion (MCAO). Must show efficacy in permanent MCAO models; compound is efficacious as monotherapy Larger species used for novel, first-in-class compound Studies published in peer-reviewed journal Animal Studies--Pros • • • • • • Made it possible to understand the ischemic penumbra Ethics (Placebo group etc) Greater control of variables Mechanistic studies for therapeutic targeting Animal models have uniform ischemic insult Can measure infarct volume / molecular markers at various time points • Most animal models have MCA occlusion: similar to majority of human strokes. • Transient MCA occlusion: mimics ischemia and reperfusion Animal studies--cons • • • • Young, healthy animals (no co-morbidities, risk factors) Different cerebral anatomy Lab animals are genetically homogenous Animal studies lack clinically important outcomes—e.g. recovery from disability, behavioral effects, speech etc. • Animals treated before / at time of ischemic onset • Some anesthetics used in animal surgery are neuroprotective Neuronal death Events after cerebral ischemia Leukocyte s Neutrophils, monocytes Release pro-inflammatory and cytotoxic mediators, stimulates lipid peroxidation, post-ischemic edema, BBB breakdown, generates ROS, release proteolytic enzymes Cytokines IL-1b BBB breakdown, Ca in neurons, edema, leukocyte adhesion to endothelium, endogenous pyrogen TNF-a glutamate uptake, Ca in neurons, endothelial apoptosis, BBB breakdown, edema,  leukocyte adhesion to endothelium Free radicals ROS, NO Lipid peroxidation, stimulation of inflammation, disrupts protein biochemistry, Matrix metalloproeinases MMP-9 BBB breakdown,  leukocyte adhesion to endothelium , edema Adhesion molecules Selectins, ICAM, VCAM, integrins Slow down neutrophils and monocytes,  platelet adhesion neutrophils and monocytes, stronger attachment of leukocytes to endothelium, Endothelial cells BBB BBB breakdown, permeability to macromolecules, intracranial pressure,  inflammatory mediators,  adhesion molecules Neuroprotection • What is it? Neuroprotective drugs for stroke initiated in 1980s and are still in development . The basic aim of neuroprotection is to interfere with the events of the ischemic cascade by focusing on one or more of mechanisms of damage, blocking the pathological processes, and preventing the death of vulnerable nerve cells in the ischemic penumbra . This concept involves inhibition of the pathological molecular events which eventually lead to the influx of calcium, activation of free radicals and neuronal death. That excludes reperfusion modalities or drugs aimed to reduce the vasogenic edema surrounding the infarct . Neuroprotection