Cerebral nitric oxide and mitochondrial function in patients suffering aneurysmal subarachnoid hemorrhage—a translational approach

Abstract

Background Cerebral ischemia and neuroinflammation following aneurysmal subarachnoid hemorrhage (SAH) are major contributors to poor neurological outcome. Our study set out to investigate in an exploratory approach the interaction between NO and energy metabolism following SAH as both hypoxia and inflammation are known to affect nitric oxide (NO) metabolism and NO in turn affects mitochondria. Methods In seven patients under continuous multimodality neuromonitoring suffering poor-grade aneurysmal SAH, cerebral metabolism and NO levels (determined as a sum of nitrite plus nitrate) were determined in cerebral microdialysate for 14 days following SAH. In additional ex vivo experiments, rat cortex homogenate was subjected to the NO concentrations determined in SAH patients to test whether these NO concentrations impair mitochondrial function (determined by means of high-resolution respirometry). Results NO levels showed biphasic kinetics with drastically increased levels during the first 7 days (74.5 ± 29.9 μM) and significantly lower levels thereafter (47.5 ± 18.7 μM; p = 0.02). Only during the first 7 days, NO levels showed a strong negative correlation with brain tissue oxygen tension (r = − 0.78; p < 0.001) and a positive correlation with cerebral lactate (r = 0.79; p < 0.001), pyruvate (r = 0.68; p < 0.001), glutamate (r = 0.65; p < 0.001), as well as the lactate-pyruvate ratio (r = 0.48; p = 0.01), suggesting mitochondrial dysfunction. Ex vivo experiments confirmed that the increase in NO levels determined in patients during the acute phase is sufficient to impair mitochondrial function (p < 0.001). Mitochondrial respiration was inhibited irrespectively of whether glutamate (substrate of complex I) or succinate (substrate of complex II) was used as mitochondrial substrate suggesting the inhibition of mitochondrial complex IV. The latter was confirmed by direct determination of complex IV activity. Conclusions Exploratory analysis of our data suggests that during the acute phase of SAH, NO plays a key role in the neuronal damage impairing mitochondrial function and facilitating accumulation of mitochondrial substrate; further studies are required to understand mechanisms underlying this observation.

Oxoglutarate dehydrogenase complex controls glutamate-mediated neuronal death

“…Correlation between brain NO, glutamate levels and clinical outcome in SAH patients. In our previous studies, we have shown an increase in NO metabolites in preclinical model of acute traumatic brain injury [ 9 ] and in patients during the acute phase of SAH [ 10 ]. In the current study we explore the pathophysiological consequences of these observations.…”

“…Our previous work [ 10 ] has demonstrated a positive correlation between glutamate and NO metabolites in the brain. Combined with the current data this lead us to an assumption that elevated NO levels impair glutamate metabolism and that elevated glutamate levels were associated with the negative clinical outcome.…”

“…The total amount of NO metabolites (nitrite plus nitrate) in patients with acute brain injury (first 7 days) can be determined by means of microdialysis from affected parts of the brain. NO has been found at levels of approximately 100 μM [ 10 ] declining below 40 μM after the completion of the acute phase of brain injury. These concentrations are still substantially higher than corresponding concentrations of NO metabolites in the blood, which are approximately 15 μM [ 11 ].…”

“…It has been shown that elevated NO levels correlate with increased extracellular glutamate levels [ 10 ]. Thisis associated with the activation of glutamate receptors [ 12 ], and causes excitotoxicity and neuronal death [ 13 ].…”

New Mechanisms and Targets of Subarachnoid Hemorrhage: A Focus on Mitochondria

“…Moreover, mitochondrial dynamics and mitophagy are critical for maintaining cellular function and homeostasis [ 62 , 63 ]. Abundance of evidence has revealed the occurrence of mitochondrial dysfunction after SAH, which was found to be associated with EBI and neurological outcome [ 64 - 68 ]. The relationship between mitochondria and EBI after SAH needs to be further established.…”