Ultrastructural and biochemical changes induced by progressive lipid peroxidation on isolated microsomes and rat liver endoplasmic reticulum.

Ultrastructural and biochemical alterations induced by progressive lipid peroxidation on rat liver endoplasmic reticulum and on isolated microsomes have been studied. Lipid peroxidation was followed by measuring the content of malonaldehyde and similar thiobarbituric acid-reacting substances in the control specimens and in specimens in which lipid peroxidation was stimulated by CCl4 or other prooxidant systems. Lipid peroxidation induced a remarkable decrease in aminopyrine demethylase activity and in the cytochrome P-450 content both in vivo and in vitro. Parallel to these observations, alterations in the assembly of the membranes of isolated rat liver microsomes and of in situ endoplasmic reticulum were followed by electron spin resonance and electron microscopy. Electron spin resonance revealed changes in the resonance spectra interpreted as solubilization of cytochrome P-450 from the membrane. Electron microscopy on fixed and sectioned, negatively stained and freeze-fractured specimens revealed membrane alterations that were progressive with time of peroxidation. These alterations consisted of: (1) increased membrane deformability; (2) local and progressive breakages on the membranes; and (3) loss of intramembranous particles on both fracture faces of the membranes. The results obtained with the different techniques are compared and discussed in light of the importance of the lipid environment for the structure and function of biologic membranes.