An investigation on the effects of papaverine on neuroinflammation and serum S100B levels in A mouse model for head trauma

Introduction and purpose: Traumatic brain injury is a common problem in today's world and highly associated with death and permanent or temporary disability. There are two mechanisms at play in traumatic brain injury; first one is primary damage that is caused by direct impact. On the other hand secondary brain injury is usually associated with cellular and molecular damage from the onset of trauma to hours or days that follow. Neurotransmitter mediated excitotoxicity, electrolyte imbalance, mitochondrial dysfunction, inflammatory response, apoptosis, vasospasm, focal microvascular occlusion, ischemia resulting from vascular injury are investigated as secondary damage mechanisms. Papaverine is clinically used for its vasodilator effects due to phosphodiesterase inhibition. In neurosurgical practice, it is particularly used in vasospasm associated cerebral and peripheral tissue ischemia after subarachnoid hemorrhage. Papaverine is shown to suppress microglial activation through RAGE receptor and Nf-KB pathway inhibition, both of which are functionaries to apoptosis. It also stimulates apoptosis and inflammation in neuron, astrocytes and microglia at micromolar levels by the S100b RAGE receptor pathway. The aim of this study was to investigate the effects of intraperitoneal papaverine administration on neuroinflammation and neuroprotection at 24 hours of trauma in a mouse head injury model, to evaluate the effects of post-traumatic anxiety and depression on behavioral tests and to investigate the difference in serum S100b levels between groups. Materials and Methods: A total of 28 male Swiss albino mice were used in each group. The subjects were divided into 4 groups as Sham, trauma, trauma and papaverine and papaverine only. Head trauma model was created by dropping 80 g of free weight from a 9 cm height under isoflurane anesthesia. Intraperitoneal saline was administered to the control group half an hour after the trauma and 40 mg / kg papaverine was administered intraperitoneally to the experimental groups. Locomotor activity, open field and tail hanging tests, anxiety and depression status of all groups before sacrification were evaluated. At the end of the 24th hour, vii mice were sacrificed then histopathological, immunohistochemical findings and serum 100b levels were compared between groups. Results: The number of RAGE-labeled cells increased in trauma group compared to the sham group (p: <0.0001). However, this increase is significant compared to the glial cells in the neurons (p <0.0001 - p = 0.0019) on top of that Nf-KB marked total cell count was increased in trauma group, in comparison to sham group. (P <0.0001). However, this increase is more significant in neurons than in glia (p <0.0001 - p: 0.0002) . The total number of RAGE + stained cells were decreased in the post-traumatic papaverine group as to the trauma group. (p = 0, 0016). In contrast, it was found that papaverine achieved its RAGE inhibitory effect on the neurons mainly after trauma (p=0.018). Likewise, significantly reduced NF-kB immunoreactivity was detected in the group treated with papaverine after trauma (P= 0006). This decrease was more significant in stained glia than stained neuron (p = 0.0003 / p = 0.002). The number of microglia labeled with P2RY12 increased after trauma (p <0.0001) and fell to sham group levels after papaverine administration. The number of NeuN-labeled cells in the post-traumatic papaverine group increased compared to the trauma group (p <0.0001). In the papaverine only group, the NF-kB levels in neurons was increased in comparison to the sham group. (p <0.0001). Serum S100B levels were decreased in the papaverine group (p <0.002). Locomotor activity was decreased in trauma group compared to sham group (p = 0.005). the administration of papaverine to the traumatized mice led to an increase in locomotor activity in comparison to the trauma group. However, it was not statistically significant (p = 0.068). Anxiolytic or antidepressant properties of papaverine could not be demonstrated in the evaluated behavioral tests. Histopatologically papaverine significantly reduced the posttraumatic edema. In addition, the number of neurodegenerative cells decreased compared to the trauma group. Conclusion: As a result, RAGE-NF-k B pathway activation was shown immunohistochemically in neuroinflammation after moderate head trauma. Papaverine acts on this pathway and suppresses neuroinflammation. However, this inhibition is particularly on neurons. Papaverine also caused significant microglia inhibition. In addition, the findings showed that papaverine had neuroprotective effects. On the other hand, papaverine was thought to cause increase in locomotor activity. It also contributes to neuroprotection by lowering serum S100B levels. Keywords: Traumatic brain injury, papaverine, S100b, neuroinflammation