Dysfunction of Mitochondrial Respiratory Chain in Rostral Ventrolateral Medulla During Experimental Endotoxemia Sepsis is a complex pathophysiologic state resulting from an exaggerated whole-body inflammatory response to infection or injury. Metabolic disturbances, abnormal regulation of blood flow and diminished utilization of oxygen at the cellular level may account for tissue damage and lead to multiple organ failure and death. As the primary site of cellular energy generation is the mitochondrion, it presents itself as an important target for the septic cascade. In this regard, the notion that bioenergetic failure due to mitochondrial dysfunction contributes to organ failure during sepsis has received attention. We established the low frequency fluctuations in the systemic arterial pressure signals are related to the sympathetic neurogenic vasomotor tone, and reflect the functional integrity of the brain stem. Their origin is subsequently traced to the premotor sympathetic neurons at the rostral ventrolateral medulla (RVLM), whose neuronal activity is intimately related to the ¡§life-and-death¡¨ process. Based on a rat model of experimental endotoxemia that provides continuous information on changes in neuronal activity in the RVLM, the present study was undertaken to evaluate whether changes in mitochondrial respiratory functions are associated with death arising from sepsis. We also evaluated the efficacy of a new water-soluble coenzyme Q10 (CoQ10, ubiquinone) formula in the protection against fatality during endotoxemia by microinjection into bilateral RVLM. Dysfunction of Mitochondrial Respiratory Chain in Rostral Ventrolateral Medulla During Experimental Endotoxemia in the Rat We investigated the functional changes in mitochondrial respiratory chain at the RVLM in an experimental model of endotoxemia that mimics systemic inflammatory response syndrome. Experiments were carried out in adult male Sprague-Dawley rats that were maintained under propofol anesthesia. Intravenous administration of E. coli lipopolysaccharide (LPS; 30 mg/kg) induced progressive hypotension, with death ensued within 4 hours. The sequence of cardiovascular events during this LPS-induced endotoxemia can be divided into a reduction (Phase I), followed by an augmentation (Phase II; ¡§pro-life¡¨ phase) and a secondary decrease (Phase III; ¡§pro-death¡¨ phase) in the power density of the vasomotor components (0-0.8 Hz) of systemic arterial pressure (SAP) signals. Enzyme assay revealed significant decrease of the activity of NADH cytochrome c reductase (Complex I+III) and cytochrome c oxidase (Complex IV) in the RVLM during all 3 phases of endotoxemia. On the other hand, the activity of succinate cytochrome c reductase (Complex II+III) remained unaltered. Neuroprotective Effects of Coenzyme Q10 at Rostral ventrolateral Medulla Against Fatality During Experimental Endotoxemia in the Rat CoQ10 is a highly mobile electron carrier in the mitochondrial respiratory chain that also acts as an antioxidant. We evaluated the neuroprotective efficacy of CoQ10 against fatality in an experimental model of endotoxemia, using a novel water-soluble formulation of this quinone derivative. In Sprague-Dawley rats maintained under propofol anesthesia, intravenous administration of E. coli LPS (30 mg/kg) induced experimental endotoxemia. Pretreatment by microinjection bilaterally of CoQ10 (1 or 2 mg) into RVLM significantly diminished mortality, prolonged survival time, and reduced the slope or magnitude of the LPS-induced hypotension. CoQ10 pretreatment also significantly prolonged the duration of Phase II endotoxemia and augmented the total power density of the vasomotor components of SAP signals in Phase II endotoxemia. The increase in superoxide anion production induced by LPS at the RVLM during Phases II and III endotoxemia was also significantly blunted. Conclusion The present study revealed that selective dysfunction of respiratory enzyme Complexes I and IV in the mitochondrial respiratory chain at the RVLM is closely associated with fatal endotoxemia. CoQ10 provides neuroprotection against fatality during endotoxemia by acting on the RVLM. We further found that a reduction in superoxide anion produced during endotoxemia at the RVLM may be one of the mechanisms that underlie the elicited neuroprotection of CoQ10. These findings therefore open a new direction for future development of therapeutic strategy in this critical, complicated and highly fatal condition known as sepsis.

京都大学 / 新制・課程博士 / 博士(薬科学) / 甲第24555号 / 薬科博第172号 / 新制||薬科||19(附属図書館) / 京都大学大学院薬学研究科医薬創成情報科学専攻 / (主査)教授 大野 浩章, 教授 小野 正博, 教授 掛谷 秀昭 / 学位規則第4条第1項該当 / Doctor of Pharmaceutical Sciences / Kyoto University / DFAM