Metabolic Control Analysis

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Summary: Metabolic control analysis is the formal application of kinetics and thermodynamics to determine the extent to which the control of flux through a metabolic pathway is determined by a particular enzymatic step in that pathway. Reviews of the central energy producing pathway, the citric acid cycle, and of mitochondrial bioenergetics have been published. What is found by performing a formal metabolic control analysis is that, in contrast to the widely held view that there is a 'rate controlling step', control of flux in a pathway is distributed across many enzymatic steps in a pathway and varies depending upon conditions. It is this change in flux in a metabolic pathway which often defines the phenotype of a disease process. Further, these insights suggest that a drug or gene therapy directed at a single enzymatic step may not correct a disease phenotype, but rather a number of steps in a single or in several linked pathways would have to be altered in a disease phenotype. This lead to an investigation of several degenerative neurological and cardiac diseases which might be treated by alteration of the substrate provided, among them were Alzheimer's and Parkinson's disease, type I and II diabetes and heart failure. The possibility of treating Parkinson's disease with mild ketosis has been strengthened by subsequent work in outside laboratories where MPTP induced death in hippocampal neurons in C57 black mice was reduced by Na D-?O-hydroxybutyrate. Feeding a hyperketogenic diet to a small group of Parkinsonian patients resulted in an approximately 60% reduction of symptoms in a preliminary trail. These concepts were discussed in two meetings sponsored by the NIH Office of Rare Diseases and the disease phenotype targets more fully outlined. Among the fatal diseases for which there is no current effective therapy is Duchenne's muscular dystrophy affecting 1/3000 male births in the United States. Work done in this laboratory and in the laboratory of Professor Kieran Clarke in Oxford have found that lack of dystrophin in the MDX mouse, the rodent analogue of Duchenne's, results in a failure of insulin to induce translocation the insulin responsive GLUT4 to the plasma membrane. As such, these patients fall into the disease phenotype potentially treatable by ketosis. We have been examining the degree to which mild ketosis can improve the hydraulic efficiency of the isolated working perfused MDX mouse heart, a technically difficult preparation which is unique to this laboratory. This material has been the subject of 2 meetings sponsored by the NIH Office of Rare Disease over the past 2 years. More recently, we have examined the effects of the use of ketone bodies on altering the survival of hippocampal neurons exposed to hypoxia in culture. We found that acute cell death in hippocampal cells could be prevented during 2 hours of hypoxia and that apoptotic cell death could also be decreased for a long period of time. This raises the possibility of the use of ketones in the treatment of acute stroke or cerebral hemorrhage or in the treatment of traumatic brain injury. We currently are scheduled to develop oral preparations of D-?O-hydroxybutyrate for use in military applications. There is no provision in this project for the use of these materials in disease states. It is hoped that various relevant institutes within the NIH may wish to consider the use of these materials in clinical trials of human subjects. Of particular relevance here would be the possible treatment of Parkinson's disease in the light of the recent publications from other labs following our work in this area. Likewise the possible treatment of Duchenne's muscular dystrophy should be considered in view of the absence of any currently effective therapy. Significance to the Programs of this Institute The research reported in this section, by applying a rigorous metabolic control analysis, allows the definition of disease phenotypes which may be ammenable to new therapeutic approaches in a variety of common and rare diseases, which share a common pathophysiological basis. This approach defines a new way of approaching therapy which aims at changing interlinked and interdependent metabolic pathways rather that attempting to define one key "rate limiting step" as causative in a disease state.