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  • Author or Editor: Aij-Lie Kwan x
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Tomikatsu Toyoda, Aij-Lie Kwan, Murad Bavbek, Neal F. Kassell, John E. Wanebo and Kevin S. Lee

Object. Monophosphoryl lipid A (MPL) and diphosphoryl lipid (DPL) are derivatives of the lipopolysaccharide (endotoxin) of Salmonella minnesota strain R595. Monophosphoryl lipid A is relatively nontoxic and can stimulate the natural defense or immune system. Diphosphoryl lipid is relatively toxic; however, at higher concentrations, it can also stimulate an immune response. The purpose of the present study was to determine the effects of these endotoxin analogs on cerebral vasospasm after the onset of subarachnoid hemorrhage (SAH) in rabbits.

Methods. Intrathecal administration of MPL or DPL (5 µg/kg) was performed immediately before and 24 hours after induction of SAH in New Zealand White rabbits. Forty-eight hours after induction of SAH, the animals were killed by perfusion fixation for morphometric analyses of vessels or perfused with saline and assayed for superoxide dismutase (SOD) activity. Additional rabbits were administered MPL or DPL and killed 24 hours later for assessment of SOD activity; no SAH was induced in these animals.

Experimental SAH elicited spasm of the basilar arteries in each group. Vasospasm was markedly attenuated in animals treated with MPL (p < 0.01 compared with vehicle-treated animals), but not in animals treated with DPL. A substantial reduction in SOD activity in the basilar artery accompanied the vasospasm; this loss of activity was significantly blocked by treatment with MPL, but not DPL. In animals that were not subjected to experimental SAH, MPL elicited a significant increase in SOD activity over basal levels, whereas DPL was ineffective.

Conclusions. These data provide evidence of a marked protective effect of the endotoxin analog MPL against vasospasm. Although the mechanism(s) responsible for the protective effect of MPL remains to be verified, an enhancement of basal antioxidant activity and an inhibition of SAH-induced loss of this activity are attractive candidates. An MPL-based therapy could represent a useful addition to current therapies for SAH-induced cerebral injury.

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Aij-Lie Kwan, Murad Bavbek, Arco Y. Jeng, Wieslawa Maniara, Tomikatsu Toyoda, Rodney W. Lappe, Neal F. Kassell and Kevin S. Lee

✓ Delayed cerebral ischemia due to cerebral vasospasm is a major cause of morbidity and mortality in patients with aneurysmal subarachnoid hemorrhage (SAH). Increasing evidence implicates the potent vasoconstrictor peptide endothelin (ET) in the pathophysiology of cerebral vasospasm. In the present study the authors examined the therapeutic value of blocking the production of ET-1 by inhibiting the conversion of its relatively inactive precursor, Big ET-1, to a physiologically active form. An inhibitor of ET-converting enzyme (ECE), CGS 26303, was injected intravenously after inducing SAH in New Zealand white rabbits. Injections of CGS 26303 were initiated either 1 hour after SAH (prevention protocol) or 24 hours after SAH (reversal protocol). One of three concentrations (3, 10, or 30 mg/kg) of CGS 26303 was injected twice daily, and all animals were killed by perfusion fixation 48 hours after SAH occurred. Basilar arteries were removed and sectioned, and their cross-sectional areas were measured in a blind manner by using computer-assisted videomicroscopy.

Treatment with CGS 26303 attenuated arterial narrowing after SAH in both the prevention and reversal protocols. The protective effect of CGS 26303 achieved statistical significance at all dosages in the prevention protocol and at 30 mg/kg in the reversal protocol. These findings demonstrate that inhibiting the conversion of Big ET-1 to ET-1 via intravenous administration of an ECE inhibitor can be an effective strategy for limiting angiographic vasospasm after SAH. Moreover, the results demonstrate that treatment with the ECE inhibitor is capable of reducing vasospasm even when initiated after the process of arterial narrowing has begun. Finally, the results provide further support for the role of ET in the establishment of cerebral vasospasm. The ECE inhibitor CGS 26303 thus represents a promising therapeutic agent for the treatment of cerebral vasospasm following aneurysmal SAH.