Avaliação do efeito neuroprotetor do propofol e do etomidato em ratos submetidos ao trauma medular espinal

Abstract

Therapeutic intervention in the acute phase of spinal cord injury (SCI) aims to control the secondary neurotoxic process and to interrupt its progression. Thus, general anesthetics became target of diverse studies, since they can modulate proteins related to nervous system transmission, which are altered after spinal injury. Due to the importance of a standardized model of spinal cord injury and the promissing results of injectable anesthetics in central nervous system injuries, this work intended to standardize a spinal cord injury device and to evaluate the neuroprotective effects of propofol and etomidate in rats submitted to contusive spinal cord injury. Therefore, two experiments were conducted. In the first one, 15 male rats were distributed in three groups: negative control (CTR), laminectomy (LMT), and trauma (TRM). Animals from group CTR were only submitted to general anesthesia and liquor collection. For the groups LMT and TRM, the animals were submitted to dorsal laminectomy of the twelfth thoracic vertebra (T12), being TRM animals submitted to SCI caused by the dropping of a 10g metallic rod from a 15mm height right above the exposed dura mater. In order to evaluate the effect of the spinal injury, glutamate concentration in the liquor was measured in CTR group, 50 minutes after the surgical procedure, and seven days later. For the second experiment, 48 adult male rats were equally distributed in four groups: sham (CON-), positive control (CON+), propofol (PRO), and etomidate (ETO). After anesthesia with ketamine and xylazine, T12 laminectomy was performed in all animals, while only the animals from groups CON+, PRO, and ETO were submitted to SCI. One hour after the spinal injury, animals from groups CON+, PRO, and ETO received, intraperitoneally, a single dose of saline solution (1.5 mL/kg), propofol (30 mg/kg), and etomidate (3 mg/kg), according to the group. Neurological deficits of the animals was observed during seven days, using the BBB locomotor scale, and after that period, the animals were euthanized, and the spinal cord was collected for evaluation of neuronal viability, DNA fragmentation, and expression of apoptosis indicators, Bax, Bcl-XI, Caspase-9, and Caspase-3. The study was conducted following a completely randomized design, and the statistics comparisons were performed through SNK, Kruskal Wallis, and Friedman tests (p<0.05). For glutamate concentration, higher concentration of this excitatory neurotransmiter in groups LMT and TRM than CTL, showed that the surgical procedure caused such increase. Nevertheless, the higher concentration of glutamate in TRM group, compared to LMT group 50 minutes after trauma, evidenced an acute excitotoxicity process caused by the SCI, standardizing therefore the spinal cord injury device. In experiment II, for the BBB test, earlier neurological improvement was observed for ETO group, pointing to a better modulation of the SCI secondary lesion. For the evaluation of apoptosis indicators, there was under-expression of Bax gene and fewer apoptotic bodies for ETO and PRO groups, as well as under-expression of Caspase-3 gene for PRO group when compared to CON+, indicating the neuroprotective effect of these drugs. Concluding, the SCI was able to cause standardized SCI, characterized by excitotoxicity. In addition to that, this study showed that propofol and etomidate have neuroprotective effect by the seventh day after spinal cord injury, when administered in the acute phase of the spinal lesion by the inhibition of the apoptosis pathway.