Published online before print August 2, 2007, doi: 10.1161/STROKEAHA.107.481853
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(Stroke. 2007;38:e89.)
© 2007 American Heart Association, Inc.
Letters to the Editor |
Significance of Experimental Infarct Size as an Indicator of Therapeutic Efficacy in Humans
KAT National Hospital, New Psychiko, Greece
To the Editor:
We would like to make a comment not in particular to the article by Shimamura et al1 but to the use of infarct size in animal experiments as a guide to human cerebrovascular research. Many human studies of treatments with neuroprotective agents for acute ischemic stroke, which had good experimental potential, had disappointing clinical results. This failure can be attributed to many factors.2 One of the main problems is that reliance on infarct size measurement alone in animals can be misleading as an indicator of therapeutic efficacy in humans.3
We know for example that nitric oxide synthase (NOS) inhibitors have provided significant neuroprotection in experimental animals subjected to focal ischemia.4,5 Tirilazad mesylate is a potent inhibitor of lipid peroxidation caused by suppression of inducible NOS.6 Most studies have shown a significant reduction of infarct volume in focal ischemia models.7–13 On the other hand, a multicenter, randomized, placebo-controlled study of tirilazad in patients with acute ischemic stroke was halted prematurely because of a lack of benefit.14 There was in reality a trend toward a worse clinical outcome. A possible explanation for the result is that NOS participates in DNA repair.15
Moreover, some compounds (eg, basic fibroblast growth factor, osteogenic protein-1) have been associated with functional improvement without affecting infarct size in animals.16,17
It is also obvious that histological end points cannot tell whether surviving neurons are functional or dysfunctional or will go on to die in a delayed fashion, and they are less predictive of long-term histology than early behavioral assessments.18
We would like to add an alternative hypothesis in the problem of experimental infarct size and its clinical implications. Many studies are based on the supposition that proinflammatory agents are detrimental for the brain and that their elevated appearance after ischemia must be somehow diminished. The offered proof is the increased infarct size, which they usually produce in experimental animals. On the other hand, we can suppose that these agents just help confine and finally clear the damaged brain area. In such a case, the infarct size would be increased, but the chances for the rest of the brain would be conceivably better. Increased intracranial pressure could make the problem more complex, but the main idea remains: it is easier to suppose that what the human body does should be supported rather than to think that it should be reversed.
Let us take the example of tumor necrosis factor-
(TNF-). Its action in ischemia is described as both detrimental and neuroprotective, depending on the experimental conditions. Elevated serum level of TNF- is observed after severe head injury and trauma.19 TNF- mRNA is elevated, especially in the first 5 days.20 Intraventricular injection of TNF- one day before middle cerebral artery occlusion exacerbates tissue injury and is reversed by anti–TNF-.21 On the other hand, transgenic animals lacking TNF- receptors develop significantly larger damage to neurons after focal cerebral ischemia or epileptic seizures.22 TNF- pretreatment of cultured endothelial cells, astrocytes or neurons protects them to the same degree as hypoxic preconditioning. Importantly, if necrosis is attenuated by therapy (ie, by reperfusion or antiexcitotoxic agents), then apoptosis may be unmasked or even promoted.23
These experimental data can be considered consistent under our hypothesis. Therefore, assessment of therapeutic efficacy in preclinical studies should require, in addition to infarct size, demonstration of benefit on functional measures of motor, sensory, or cognitive deficits.24,25 Examples include tests of limb placing, beam walking, grid walking, Rotorod performance, grip strength, balance beam–inclined plane performance, prehensile traction, and cognition (eg, Morris water maze, radial maze, 1-trial passive avoidance, T-maze retention test).18,24,26
Our conclusion is that experimental infarct size cannot serve by itself as a prognostic indicator in human studies, especially when pro- or antiinflammatory agents are tried.
Acknowledgments
Disclosures
None.
References
1. Shimamura N, Matchett G, Yatsushige H, Calvert JW, Ohkuma H, Zhang J. Inhibition of integrin avß3 ameliorates focal cerebral ischemic damage in the rat middle cerebral artery model. Stroke. 2006; 37: 1902–1909.
2. Kidwell CS, Liebeskind DS, Starkman S, Saver JL. Trends in acute ischemic stroke trials through the 20th century. Stroke. 2001; 32: 1349.
3. Gladstone DJ, Black SE, Hakim AM. Toward wisdom from failure lessons from neuroprotective stroke trials and new therapeutic directions. Stroke. 2002; 33: 2123.
4. Coert BA, Anderson RE, Meyer FB. A comparative study of the effects of two nitric oxide synthase inhibitors and two nitric oxide donors on temporary focal cerebral ischemia in the Wistar rat. J Neurosurg. 1999; 90: 332–338.[Medline] [Order article via Infotrieve]
5. Spinnewyn B, Cornet S, Auguet M, Auvin S, Cornet S, Demerlé-Pallardy C, Guilmard-Favre Ch, Marin JG, Pignol B, Gillard-Roubert V, Roussillot-Charnet Ch, Schulz J, Viossat I, Bigg D, Moncada S. Synergistic protective effects of antioxidant and nitric oxide synthase inhibitor in transient focal ischemia. J Cereb Blood Flow Metab. 1999; 19: 139–143.[CrossRef][Medline] [Order article via Infotrieve]
6. del Pilar Fernandez M, Meizoso MZ, Lodeiro MZ, Belmonte A. Effect of desmethyl tirilazad, dizocilpine maleate and nimodipine on brain nitric oxide synthase and cyclic guanosine monophosphate during cerebral ischemia in rats. Pharmacology. 1998; 57: 174–179.[CrossRef][Medline] [Order article via Infotrieve]
7. Schmid-Elsaesser R, Zausinger S, Hungerhuber E, Baethmann A, Reulen HJ. Neuroprotective effects of combination therapy with tirilazad and magnesium in rats subjected to reversible focal cerebral ischemia. Neurosurgery. 1999; 44: 163–171.[CrossRef][Medline] [Order article via Infotrieve]
8. Karki A, Westergren I, Widner H, Johansson B. Tirilazad reduces brain edema after middle cerebral artery ligation in hypertensive rats. Acta Neurochir Suppl (Wien). 1994; 60: 310–313.[Medline] [Order article via Infotrieve]
9. Wilson JT, Bednar MM, McAuliffe TL, Raymond S, Gross CE. The effect of the 21-aminosteroid U74006F in a rabbit model of thromboembolic stroke. Neurosurgery. 1992; 31: 929–933.[Medline] [Order article via Infotrieve]
10. Young W, Wojak JC, DeCrescito V. 21-aminosteroid reduces ion shifts and edema in the rat middle cerebral artery occlusion model of regional ischemia. Stroke. 1988; 19: 1013–1019.
11. Schmid-Elsaesser R, Zausinger S, Hungerhuber E, Baethmann A, Reulen HJ. Monotherapy with dextromethorphan or tirilazad –but not a combination of both- improves outcome after transient focal cerebral ischemia in rats. Exp Brain Res. 1998; 122: 121–127.[CrossRef][Medline] [Order article via Infotrieve]
12. Clark WM, Hotan T, Lauten JD, Coull BM. Therapeutic efficacy of tirilazad in experimental multiple cerebral emboli: a randomized, controlled trial. Crit Care Med. 1994; 22: 1161–1166.[Medline] [Order article via Infotrieve]
13. Hellstrom HO, Wanhainen A, Valtysson J, Persson L, Hillered L. Effect of tirilazad mesylate given after permanent middle cerebral artery occlusion in rat. Acta Neurochir (Wien). 1994; 129: 188–192.[CrossRef][Medline] [Order article via Infotrieve]
14. RANTTAS Investigators. A randomized trial of tirilazad mesylate in patients with acute stroke. Stroke. 1996; 27: 1453–1458.
15. Xu W, Liu LZ, Loizidou M, Ahmed M, Charles IG. The role of nitric oxide in cancer. Cell Res. 2002; 12: 311–320.[CrossRef][Medline] [Order article via Infotrieve]
16. Kawamata T, Alexis NE, Dietrich WD, Finklestein SP. Intracisternal basic fibroblast growth factor (bFGF) enhances behavioral recovery following focal cerebral infarction in the rat. J Cereb Blood Flow Metab. 1996; 16: 542–547.[CrossRef][Medline] [Order article via Infotrieve]
17. Kawamata T, Ren J, Chan TCK, Charette M, Finklestein SP. Intracisternal osteogenic protein-1 enhances functional recovery following focal stroke. Neuroreport. 1998; 9: 1441–1445.[Medline] [Order article via Infotrieve]
18. Corbett D, Nurse S. The problem of assessing effective neuroprotection in experimental cerebral ischemia. Prog Neurobiol. 1998; 54: 531–548.[CrossRef][Medline] [Order article via Infotrieve]
19. Goodman JC, Robertson CS, Grossman RG, Narayan RK. Elevation of tumor necrosis factor in head injury. J Neuroimmunol. 1990; 30: 213–217.[CrossRef][Medline] [Order article via Infotrieve]
20. Buttini M, Appel K, Sauter A, Gehicke-Haerter PJ, Boddeke HW. Expression of tumor necrosis factor alpha after focal cerebral ischemia in the rat. Neuroscience. 1996; 71: 1–16.[CrossRef][Medline] [Order article via Infotrieve]
21. Barone FC, Arvin B, White RF, Miller A, Webb CL, Willete RN, Lysko PG, Feuerstein GZ. Tumor necrosis factor alpha: a mediator of focal ischemic brain injury. Stroke. 1997; 28: 1233–1244.
22. Bruce AJ, Boling W, Kindy MS, Peschon J, Kraemer PJ, Karpenter PK, Holtsberg FW, Mattson MP. Altered neuronal and microglial responses to excitotoxic and ischemic brain injury in mice lacking TNF receptors. Nature Medicine. 1996; 2: 788–794.[CrossRef][Medline] [Order article via Infotrieve]
23. Ginis I, Schweizer U, Brenner M, Liu J, Azzam N, Spatz M, Hallenbeck JM. TNF-alpha pretreatment prevents subsequent activation of cultured brain cells with TNF-alpha and hypoxia via ceramide. Am J Physiol. 1999; 276: C1171–C1183.[Medline] [Order article via Infotrieve]
24. Hunter AJ, Mackay KB, Rogers DC. To what extent have functional studies of ischaemia in animals been useful in the assessment of potential neuroprotective agents? Trends Pharmacol Sci. 1998; 19: 59–66.[CrossRef][Medline] [Order article via Infotrieve]
25. Hudzik TJBA, Bialobok P, Widzowski D, Sydserff S, Howell A, Gendron P, Corbett D, Miller J, Palmer GC. Long-term functional end points following middle cerebral artery occlusion in the rat. Pharmacol Biochem Behav. 2000; 65: 553–562.[CrossRef][Medline] [Order article via Infotrieve]
26. Hunter AJ, Hatcher J, Virley D, Nelson P, Irving E, Hadingham SJ, Parsons AA. Functional assessments in mice and rats after focal stroke. Neuropharmacology. 2000; 39: 806–816.[CrossRef][Medline] [Order article via Infotrieve]
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