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  • By Author: Kassell, Neal F. x
  • By Author: Takenaka, Katsunobu x
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Satoshi Suzuki, Katsunobu Takenaka, Neal F. Kassell and Kevin S. Lee

✓ The roles of hemoglobin (Hb) in the pathogenesis of cerebral vasospasm remain a matter of discussion. Hemoglobin is known to be released from extravasated red blood cells in a variety of pathological conditions, including subarachnoid hemorrhage. These conditions are often accompanied by infiltration of inflammatory cells and an associated release of multiple cytokines. Certain of these cytokines, including interleukin-1β (IL-1β), are capable of increasing nitric oxide (NO) production via the inducible form of nitric oxide synthase (NOS), and excessive NO production under these conditions may contribute to cellular dysfunction. This study further examines these questions by investigating the effects of Hb on the induction of NOS by IL-1β.

The effects of Hb on IL-1β-induced NO production were examined in cultured smooth-muscle cells of rat aorta (RA-SMC's). Production of NO was estimated from the accumulation of nitrite, an oxidative product of NO, in the culture medium. The synthesis of NO was induced by IL-1β in a concentration-dependent manner. This activation of NO production was inhibited by: 1) a general inhibitor of NOS (Nω-nitro-L-arginine); 2) a protein synthesis inhibitor (cycloheximide); and 3) two selective inhibitors of the inducible form of NOS (hydrocortisone and aminoguanidine). These results suggest that IL-1β promotes the expression of the inducible form of NOS in RA-SMC's. The effects of Hb on NO production were tested by adding purified human Hb to the culture medium of the cells in both the presence and absence of IL-1β. Nitrite accumulation was slightly but significantly increased by Hb in the absence of IL-1β. In contrast, Hb markedly augmented nitrite accumulation induced by IL-1β. This augmentation persisted even after the removal of Hb from the culture medium. The number of cells was not affected by Hb or IL-1β.

The findings demonstrate that Hb can modify cytokine-induced production of NO in RA-SMC's by increasing the inducible form of NOS. These observations suggest that Hb can also modify the action of inflammatory cells by facilitating NO production in target cells.

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Toshiki Aoki, Katsunobu Takenaka, Satoshi Suzuki, Neal F. Kassell, Oren Sagher and Kevin S. Lee

✓ The importance of factors within hemolysate in modulating oxyhemoglobin (oxyHb)-induced contraction was examined in an in vitro model of rabbit basilar arteries. When the basilar arteries were exposed to purified oxyHb alone, the contractile response observed was significantly weaker than that seen in arteries exposed to hemolysate containing an equal concentration of oxyHb. In order to delineate the nature of the factors within hemolysate that facilitate contraction, hemolysate was fractionated, and various components were tested individually for their ability to elicit this effect. A low-molecular-weight fraction of hemolysate, ranging from 0.5 to 2.0 kD, elicited only a mild contraction. However, when this fraction was combined with purified oxyHb, the contractile response was comparable in magnitude to that of unfractionated hemolysate. These studies confirm that purified oxyHb is capable of inducing contraction in vitro. The data also demonstrate that oxyHb elicits a significantly weaker contraction than does hemolysate. In addition, the results suggest that low-molecular-weight components in hemolysate (in the 0.5- to 2.0-kD range), while incapable of inducing a potent contraction alone, may act in concert with oxyHb to elicit the vasoconstriction seen following subarachnoid hemorrhage.

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Patricia L. Foley, Katsunobu Takenaka, Neal F. Kassell and Kevin S. Lee

✓ The release of intracellular products from lysed blood cells is believed to play a critical role in the etiology of vascular pathology following intracerebral hemorrhage. The present studies investigated the effects of a mixture of blood and cerebrospinal fluid (CSF) on bovine intracranial endothelial cells maintained in culture. The incorporation of 3H-leucine into endothelial cells was used as an index of cellular viability. Cerebrospinal fluid alone did not alter the incorporation of 3H-leucine into the cells. In contrast, CSF preincubated with blood for 3 days or longer prior to treatment elicited significant reductions in leucine incorporation. Treatment with CSF preincubated with blood for 5 to 7 days resulted in the rapid deterioration of the culture, with large numbers of cells detaching almost immediately. Concentrations of hemoglobin were elevated profoundly in mixtures of blood and CSF preincubated for periods longer than 3 days. The increases in hemoglobin concentration were related temporally to increases in the cytotoxic impact of the bloody CSF.

These findings suggest that factors released during the breakdown of blood exert a deleterious effect on intracranial endothelial cells. The time course of this effect is closely related to the development of vasospasm in humans following subarachnoid hemorrhage. Taken together, these observations are consistent with the hypothesis that intracellular blood products, particularly hemoglobin, contribute to vasospasm by directly compromising endothelial function.