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at the blood-brain barrier of the rat
1 Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Sciences Center, Amarillo, Texas 79106; 2 Institute of Physiology, Philipps University, 35033 Marburg; and 3 Department of Pediatric Pneumology and Immunology and 4 Neuroscience Research Center, Charité, Humboldt University, 10117 Berlin, Germany
The transport mechanism
mediating brain uptake of tumor necrosis factor (TNF)-
has been
studied. When 125I-labeled rat TNF-
was used in internal
carotid artery perfusions in rats, the cytokine showed transcytosis
through the blood-brain barrier in intact form (permeability-surface
area product 0.34 ± 0.13 µl · min
1 · g
1).
Uptake was inhibited by low nanomolar concentrations of unlabeled rat
TNF-
. Human TNF-
, which does not interact with the p80 TNF receptor in rodents, showed no brain uptake. mRNA expression of both
p60 and p80 receptors could be demonstrated in native brain microvessel
preparations. These transcripts increased to 149% (p60) and 127%
(p80) of control 4 h after a systemic immune stimulation (2 mg/kg
bacterial endotoxin ip). Lipopolysaccharide treatment did not alter the
rate of brain uptake of TNF-
measured between 4 and 24 h later.
In conclusion, a receptor-mediated mechanism is responsible for the
transcytosis of TNF-
. Saturable transport, requiring the p80
receptor, occurs at concentrations encountered under pathophysiological
conditions and therefore constitutes a relevant mechanism of
communication between the immune system and the brain.
brain perfusion; Northern blot; lipopolysaccharide
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