Introduction
The role of NO produced by inducible nitric oxide synthase (iNOS) following traumatic brain injury (TBI) remains a subject of debate. Deletion of iNOS and treatment with iNOS inhibitors could be either beneficial or detrimental suggesting a dual role for iNOS in TBI1, 2, 3 – 4. The aim of the present study was to clarify whether iNOS could be a therapeutic target in TBI. Therefore, the effect of three iNOS inhibitors was evaluated on cerebral edema formation and functional outcome in a rat model of TBI.
Methods
Fluid percussion brain injury was performed on male Sprague-Dawley rat anesthetized with chloral hydrate (400 mg/kg, i. p.) 3 . In order to design an appropriate treatment protocol, kinetics of brain water content (BWC) and neurological score were studied. In the first treatment protocol, a single administration of vehicle (NaCl 0.9%) or iNOS inhibitor, aminoguanidine (AG) (100 mg/kg, i.p.), L-N-iminoethyl-lysine (L-NIL) (20 mg/kg, i.p.), or N-[3-(aminomethyl)benzyl]acetamide (1400W)(20 mg/kg, s.c.) was started at 6 h post-TBI. In the second treatment protocol, 1400W (20 mg/kg, s.c.) was administered at 5 min, 8 and 16 h post-TBI. Cerebral edema and neurological score were evaluated at 24 h.
Results
Trauma caused a significant increase in BWC at 6 h (81. 8 ± 0.6 %, vs 79.1 ± 0.4 % in corresponding sham-operated rats, P<0.001) and 24 h (82.2 ± 0.9 % vs 79.9 ± 0.1 %, P<0.01) following TBI. The neurological score of naive rats was 9 and was reduced after TBI with a minimum at 24 h (4.5 ± 0.3, P<0.01). In the first treatment protocol, the neurological score was improved by AG (6.4 ± 0.3 vs 5.6 ± 0.3 in vehicle-treated rats, P<0.01), L-NIL (6.6 ± 0.4 vs 5.0 ± 0.4, P<0.01), and 1400W (6.2 ± 0.3 vs 5.3 ± 0.3, P<0.05). However, only AG was able to significantly reduce the post-traumatic increase in BWC (80.3 ± 0.2% vs 81.6 ± 0.5, P<0.01). In the second treatment protocol, 1400W administered even early improved the neurological score (6.0 ± 0.2 vs 4.5 ± 0.3, P<0.001), with still no effect on the cerebral edema.
Conclusion
Our results provide evidence that the three iNOS inhibitors improve the post-traumatic neurological function and therefore strengthen the notion that an early induction of iNOS is detrimental to functional outcome following TBI. The fact that only AG was able to reduce the cerebral edema suggests that the anti-edematous effect 1) is not the origin of the functional improvement and 2) does not related to the inhibition of iNOS. In conclusion, iNOS inhibitors are able to reduce the post-traumatic neurological deficit without reducing the cerebral edema. The large therapeutic window of iNOS inhibitors could allow their use in the treatment of functional deficit following TBI.