Introduction: 

Stroke is the first cause of morbidity in the European Union. The only approved acute therapy is stimulation of reperfusion by treatment with tissue-type plasminogen activator. The ischemic cascade comprises, among others, excitotoxic effects, neuroinflammation and cell death by necrosis or apoptosis. The inflammatory response may contribute to injury and can exacerbate tissue damage. Insulin-like growth factor (IGF)-I is a pleiotropic factor that stimulates the proliferation and differentiation of oligodendrocytes, myelinisation, synaptogenesis and the survival of neurons and glial cells. In addition, IGF-I may be neuroprotective in animal models of focal cerebral ischemia. Since IGF-I modulates cytokine expression in the immune system, it could thus also be possible that IGF-I influences inflammatory responses in the brain. For successful translation to clinical studies the Stroke Therapy Academic Industry Round Table (STAIR)-criteria are essential. Two important criteria are testing of drugs in conscious animals with a co morbidity factor such as hypertension.

Aims: 

To study the mechanisms by which IGF-I exerts its neuroprotective effects, a preclinical relevant rat model will be used. Optimisation of the Et-1 model was necessary to study the effects of IGF-I in conscious Spontaneous Hypertensive Rats (SHRs) and in their controls, the Wistar Kyoto (WKY) rats. A second study addresses the effects of IGF-I in a lipopolysaccharide (LPS) rat model for neuroinflammation and the in vitro effects of IGF-I on cytokine production by astrocytes.

Material and methods: 

Using a stereotactic frame, Et-1 was applied in the vicinity of the middle cerebral artery of control and SHRs. A dose-range finding study was carried out applying 120–240 pmol Et-1. Motor/sensory functions were measured 1, 6 and 24 hours after the insult using the Neurological Deficit Score. The infarct size was assessed by cresylviolet staining. LPS was administered in the striatum of Wistar CRL rats. For these studies, the activation of microglia and astrocytes in the striatum was investigated by immunohistochemistry using antibodies directed against ED-1 and glial fibrillary acidic protein (GFAP). The effects on IL 8 secretion were determined in vitro using ELISA.

Results: 

A dose of 120 pmol Et-1 had no effect in WKY rats; doses of 180 and 200 pmol induced an appropriate infarct size and motor/sensory deficits but only a dose of 200 pmol produced an infarct in both striatum and cortex. The dose of 240 pmol showed a high mortality rate. For the SHRs there was a significant increase in infarct size using a dose of 180 (33%, p < 0.01) and 200 (26%, p < 0.05) pmol Et-1 compared to the WKY rats. In the LPS model preliminary experiments showed that IGF-I increased the number of activated microglia (ED-1⁺ cells), but not to a significant degree. In vitro IGF-I stimulated the secretion of IL-8 by astrocytes.

Conclusion: 

Using a dose of 200 pmol Et-1 in SHR rats we will further investigate the possibility to use IGF-I as a neuroprotective agent in stroke, and the possible role of immunomodulatory effects of IGF-I in neuroprotection.