Sepsis induces brain mitochondrial dysfunction Joana da Costa P. d’Avila, MS; Ana Paula S. A. Santiago, MS; Rodrigo T. Amâncio, MD; Antonio Galina, PhD; Marcus F. Oliveira, PhD; Fernando A. Bozza, MD, PhD T he evolution to multiorgan dys- function syndrome is a critical determinant of mortality in sep- tic patients, and the mecha- nisms by which sepsis leads to organ dys- function remain to be established. Tissue hypoxia has long been considered the pu- tative mechanism of multiorgan dysfunc- tion syndrome (1). In recent decades, there has been an intense controversy about the benefits of tissue oxygen delivery strategies during sepsis (2– 4), and recently, it has been shown that early intervention aimed at increasing tissue oxygen delivery im- proves the outcome of septic patients (5). Although the determinants of tissue metabolic demands in early sepsis are not completely known, there is strong evi- dence indicating that mitochondrial function is affected during sepsis (6, 7). The functional changes in mitochondria may be, ultimately, a consequence of ei- ther electron transport chain impairment or loss of the membrane potential, which may contribute to organ injury and cell death (8 –12). During sepsis, the brain is one of the first organs to be affected, and sepsis- associated encephalopathy is frequent but infrequently recognized (13, 14). An en- cephalopathy of variable severity has been found to occur in 9% to 71% of septic patients and is associated with higher in- hospital mortality (15, 16). In addition, post mortem analysis of septic patients revealed a high frequency of brain lesions (17). In animal models of polymicrobial sepsis, acute encephalopathy takes place, and survivors present with cognitive im- pairment that could be secondary to cen- tral nervous system damage (18). There is evidence suggesting that short-term oxi- dative damage in brains of rats subjected to cecal ligation and perforation (CLP) could contribute to the development of central nervous system symptoms during the progression of sepsis (19). In fact, brain tissues have unique characteristics that make them especially susceptible to damage during sepsis, such as their high oxygen consumption rate and low levels of antioxidant defenses (20). Thus, in the present work, we investi- gated mitochondrial function in the Objective: Mitochondrial dysfunctions have been associated with the pathogenesis of sepsis. A systematic survey of mito- chondrial function in brain tissues during sepsis is lacking. In the present work, we investigate brain mitochondrial function in a septic mouse model. Design: Prospective animal study. Setting: University research laboratory. Subjects: Male Swiss mice, aged 6 – 8 wks. Interventions: Mice were subjected to cecal ligation and per- foration (sepsis group) with saline resuscitation or to sham op- eration (control group). Measurements and Main Results: Oxygen consumption was measured polarographically in an oximeter. Brain homogenates from septic animals presented higher oxygen consumption in the absence of adenosine 5'-diphosphate (state 4) compared with control animals. The increase in state 4 respiration in animals in the cecal ligation and perforation group resulted in a drastic decrease in both respiratory control and adenosine 5'-diphos- phate/oxygen ratios, indicating a reduction in the oxidative phos- phorylation efficiency. Septic animals presented a significant increase in the recovery time of mitochondrial membrane poten- tial on adenosine 5'-diphosphate addition compared with control animals, suggesting a proton leak through the inner mitochondrial membrane. The septic group presented a general reduction in the content of cytochromes. Moreover, the activity of cytochrome c oxidase was specifically and significantly decreased in the brain during sepsis. Hydrogen peroxide generation by brain mitochon- dria from septic mice did not respond to substrates of electron transport chain or to adenosine 5'-diphosphate, showing that mitochondrial function may be compromised in a critical level in the brain during sepsis. Conclusions: The mitochondrial dysfunctions demonstrated here indicate that uncoupling of oxidative phosphorylation takes place in the brain of septic mice, compromising tissue bioener- getic efficiency. (Crit Care Med 2008; 36:1925–1932) KEY WORDS: energy metabolism; MODS; mitochondria; sepsis; brain; oxidative stress From the Laboratório de Bioquímica Redox, Pro- grama de Biologia Molecular e Biotecnologia (JdCPdA, MFO), Laboratório de Bioenergética Adaptativa, Programa de Biofísica e Bioquímica Celular (APSAS, AG), Instituto de Bioquímica Médica, Universidade Federal do Rio de Ja- neiro, Cidade Universitária, Rio de Janeiro, Brazil; and the Instituto de Pesquisa Clínica Evandro Chagas and Labo- ratório de Imunofarmacologia, Instituto Oswaldo Cruz, Fiocruz, Rio de Janeiro, Brazil (RTA, FAB). The authors have not disclosed any potential con- flicts of interest. Supported, in part, by grants from Conselho Na- cional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil) and DECIT/Ministério da Saúde (MS) through Edital Acidentes e Trauma 2004, CNPq through Edital Universal 2003 and 2006, Fundação Universitáriã José Bonifácio (FUJB, Brazil) through Prêmio Antônio Luiz Vianna 2004 and Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ, Brazil) through APQ-1 and Fundação Os- waldo Cruz - PAPES IV (Brazil). Drs. Oliveira and Galina are research scholars from CNPq. Drs. Oliveira and Bozza contributed equally to this work. For information regarding this article, E-mail: maroli@bioqmed.ufrj.br or fbozza@hucff.ufrj.br Copyright © 2008 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins DOI: 10.1097/CCM.0b013e3181760c4b 1925 Crit Care Med 2008 Vol. 36, No. 6