Multistationary and Oscillatory Modes of Free Radicals Generation by the Mitochondrial Respiratory Chain Revealed by a Bifurcation Analysis

The mitochondrial electron transport chain transforms energy satisfying cellular demand and generates reactive oxygen species (ROS) that act as metabolic signals or destructive factors. Therefore, knowledge of the possible modes and bifurcations of electron transport that affect ROS signaling provides insight into the interrelationship of mitochondrial respiration with cellular metabolism. Here, a bifurcation analysis of a sequence of the electron transport chain models of increasing complexity was used to analyze the contribution of individual components to the modes of respiratory chain behavior. Our algorithm constructed models as large systems of ordinary differential equations describing the time evolution of the distribution of redox states of the respiratory complexes. The most complete model of the respiratory chain and linked metabolic reactions predicted that condensed mitochondria produce more ROS at low succinate concentration and less ROS at high succinate levels than swelled mitochondria. This prediction was validated by measuring ROS production under various swelling conditions. A numerical bifurcation analysis revealed qualitatively different types of multistationary behavior and sustained oscillations in the parameter space near a region that was previously found to describe the behavior of isolated mitochondria. The oscillations in transmembrane potential and ROS generation, observed in living cells were reproduced in the model that includes interaction of respiratory complexes with the reactions of TCA cycle. Whereas multistationarity is an internal characteristic of the respiratory chain, the functional link of respiration with central metabolism creates oscillations, which can be understood as a means of auto-regulation of cell metabolism. © 2012 Selivanov et al

Evaluation of the western immunoblot as a detection method for brucella abortus exposure in elk

Brucella abortus has been an important wildlife disease issue for most of the last century, especially because wildlife species are considered to be important disease reservoirs for cattle. Diagnostic uncertainty, caused in part by cross-reactions of antibodies to environmental pathogens such as Yersinia enterocolitica O:9 on standard Brucella serology, has exacerbated the challenges of managing the disease and has highlighted the need for test validation in wildlife species. The western immunoblot was evaluated for use in detecting B. abortus exposure in elk (Cervas elaphus) and for ruling out exposure to cross-reacting bacteria. Samples collected from 2003 to 2006, including 54 female and immature elk from four different elk herds, were tested using standard Brucella serologic methods (card, rapid automated presumptive [RAP], and rivanol tests), as well as the western immunoblot. Samples (n=28) from animals known to be naturally infected with B. abortus biovar 1 served as positive controls. For presumed negative samples, sera (n=26) were collected from two elk herds in which negative serologic tests, and the absence of clinical signs of disease such as abortions, supported Brucella-riegative classification. In addition to these study samples, serologic data from 12 tule elk (Cervus elaphus nannodes) were provided from the California Department of Fish and Game in order to illustrate a field application of the western blot. The western immunoblot had the highest sensitivity (1.0;% 0.899-1.0) and specificity (1.0; 0.891-1.0) among all tests used in the study. The Kappa statistic for agreement between the western blot and the card, rivanol, and RAP tests were 0.701,0.808, and 0.921, respectively, showing good to excellent agreement with the standard diagnostic tests currently in use. Although the western immunoblot is more expensive and time intensive than other tests, in this limited study, it was shown to be reliable for establishing and confirming B. abortus disease status in elk. In addition to this study, subsequent applications of the western blot assay have been successful in detecting Yersinia sp. exposure in elk after their antibodies cross-reacted on standard Brucella serology. © Wildlife Disease Association 2010