A phenomenon called the mitochondrial permeability transition (MPT) plays an important role in both necrotic and apoptotic cell death. Increases of mitochondrial free Ca2+, formation of reactive oxygen species, and oxidation of mitochondrial pyridine nucleotides and glutathione promote the MPT that, in turn, leads to mitochondrial depolarization and uncoupling of oxidative phosphorylation. Our studies show that the MPT induces either necrotic cell death or apoptosis in models of reperfusion injury, oxidative stress, excitotoxicity, calcium ionophore-induced toxicity, Reye-related drug toxicity, exposure to tumor necrosis factor-alpha (TNFa) and Fas ligation. Inhibitors of the MPT, like cyclosporin A and trifluoperazine, decrease or abolish cell killing in these models. Progression to apoptosis or necrosis after the MPT depends on the presence or absence, respectively, of ATP. Often, features of both apoptotic and necrotic cell death develop after death signals and toxic stresses. We introduce the term ''necrapoptosis'' to emphasize the shared pathways leading to both forms of cell death. These findings offer new strategies to rescue cells and tissues from irreversible toxic and ischemic injury.

t-BuOOH Increases Mitochondrial Hydroperoxide Generation

We are also studying reperfusion injury to livers stored for transplantation surgery. Following periods of storage associated with graft failure after transplantation, we showed that reperfusion causes sinusoidal endothelial cells to lose viability and Kupffer cells (hepatic macrophages) to become activated. Based on these findings, we developed a new solution, Carolina rinse solution, whose use during reperfusion reduces lethal endothelial injury greatly and improves graft survival dramatically. This solution is now in clinical trials. Similarly, we are developing rinse solutions to decrease reperfusion-induced myocardial infarction. We are further pursuing mechanisms of Kupffer cell activation caused by ischemia/reperfusion, endotoxin and traumatic stress, particularly the roles played by calcium, endocytosis, adenosine receptors and protein kinases. More recently, we are characterizing ischemic preconditioning as a strategy of decreasing graft failure from preservation injury, especially in grafts harvested from non-heart beating cadaver donors.

Ruthenium Red Inhibition of Mitochondrial Calcium Transients

A final project addresses the regulation of mitochondrial free calcium in cardiac myocytes. Recently, we showed by laser scanning confocal microscopy that rapid transients of mitochondrial free calcium occur during the excitation-contraction cycle. These transients may regulate mitochondrial metabolism to match ATP production to ATP demand during changes in cardiac work.

Lemasters, J.J. (2001) Hypoxic, ischemic and reperfusion injury to liver. In The Liver. Biology and Pathobiology, 4th Ed., I.M. Arias, J.L. Boyer, N. Fausto, W.B. Jakoby, D. Schachter, and D.A. Shafritz (Eds.), Raven Press, New York, in press.

Lemasters, J.J. and A.-L. Nieminen, Eds. (2001) Mitochondria in Pathogenesis, Kluwer Academic/Plenum Publishers, New York, 529 pages.

Lemasters, J.J., H. Bunzendahl, and R.G. Thurman (2001) Preservation of the liver. In Transplantation of the Liver, Third Edition, W.C. Maddrey, E.R. Schiff, and M.F. Sorrell, Eds., Lippincott Williams & Wilkins, Philadelphia, pp. 251-273.

Elmore, S.P., T. Qian, S.F. Grissom and J.J. Lemasters (2001) The mitochondrial permeability transition initiates autophagy in rat hepatocytes. FASEB Journal 10, 1096/fj.01-0206fje.

Nishimura, Y., and J.J. Lemasters (2001) Glycine blocks opening of a death channel in cultured hepatic sinusoidal endothelial cells during chemical hypoxia. Cell Death and Differentiation 8, 850-858.

Trollinger, D.R., W.E. Cascio and J.J. Lemasters (2000) Mitochondrial calcium transients in adult rabbit cardiac myocytes: inhibition by ruthenium red and artifacts caused by lysosomal loading of Ca2+-indicating fluorophores. Biophysical Journal 79, 39-50.

Arai, M., R.G. Thurman and J.J. Lemasters (2000) Contribution of adenosine A2 receptors and cAMP to protective ischemic preconditioning of sinusoidal endothelial cells against storage/reperfusion injury in rat livers. Hepatology 32, 297-302.