Mechanisms of lipid peroxidation in postischemic and traumatized rat liver: The evolution of a new hypothesis
Abstract
Lipid peroxidation has long been known to occur in tissues undergoing oxidative stress from trauma or from ischemia followed by reoxygenation. The exact initiator of lipid peroxidation has been hotly debated. To study the initiators of lipid peroxidation in vitro, a short term tissue culture model was designed to subject rat liver slices to 1 hr ischemia followed by 30-60 min reoxygenation. Malondialdehyde-like materials (MDA-LM) increased after ischemia in an oxygen dependent manner; however, no postischemic "burst" of hydrogen peroxide was detected in hepatocytes using a sensitive cytochemical method. The effects of ischemia, trauma, calcium, and iron on MDA-LM generation in hepatocytes were also investigated. MDA-LM production was always enhanced by prior ischemia and reoxygenation and by tissue trauma. Elimination of calcium from incubation and buffer significantly reduced MDA-LM production; whereas the addition of the calcium ionophore A23187 (10 $\mu$M) increased MDA-LM production. In non-ischemic, traumatized tissues, the iron chelators deferoxamine and CGP-46,700A (1,2-diethyl-3-hydroxypyrid-4-one) quenched MDA-LM production. In vitro the addition of 100 $\mu$M ferric iron to 30 mM linoleate suspensions at pH 7.4 produced time dependent lipid peroxidation, measured as conjugated diene formation. Complexes of 100 $\mu$M ferric iron and 600 $\mu$M pentanoate also initiated formation of conjugated dienes in linoleate suspensions and formation of MDA-LM in rat liver slices. A histochemical stain for free fatty acids revealed positive reactions within cell membranes in traumatized regions of rat liver tissue that underwent compression injury followed by thirty minutes of blood perfusion, but not in non-traumatized control regions. The diaminobenzidine - H$\sb2$O$\sb2$ histochemical reaction for iron revealed increased levels of redox cyclable iron in the membranes and the cytoplasm of traumatized hepatocytes. The author proposes that traumatic injury initiates cascades leading to liberation of iron from storage proteins and free fatty acids from membranes, which combine, distribute to the lipid domains of cell membranes, and directly initiate lipid peroxidation.
Degree
Ph.D.
Advisors
Voorhees, Purdue University.
Subject Area
Anatomy & physiology|Animals|Pathology
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