Experimental studies on lipid peroxide formed in the isolated rat liver mitochondria

Lipid peroxide formed in a cell has been known to have a deleterious effect to the cellular metabolism. To find a biological effect of lipid peroxide to the cellular plasma-membrane, the isolated mitochondria prepared from rat liver was used as a source of material. The isolated mitochondrial suspension was exposed to ultraviolet light (UV), for producing a lipid peroxide in mitochondria. In the UV-exposed mitochondria, the following biochemical changes were observed. The oxygen consumption of state 4 in mitochondrial respiration increased gradually, the ADP/O ratio and RCR (respiratory control ratio) were decreased with an increasing dose of radiant energy. Swelling of isolated mitochondria and lipid peroxide formation were induced by UV irradiation. Fatty acid uptake of mitochondria was deminished by UV exposure. But, fatty acid component in the isolated mitochondria did not find any significant difference between the nonexposed control and UV exposed mitochondria. With this general review of mitochondrial damage by exposure, the direct deleterious action of lipid peroxide was determined by using a photoxidation product of linoleic acid (18 : 2). Methyl linoleate (18 : 2) dissolved in petroleum ether was exposed under ultraviolet light irradiation. The lipid peroxide content formed in methyl linoleate was increased with a dose of radiant energy. When the intact mitochondria was incubated with the UV-exposed linoleate, mitochondria showed the similar respiratory disorders as found in the UV-exposed mitochondria. The 20% of lipid peroxide formed in UV-exposed linoleate was found to be soluble in water phase. The nature of water soluble compound was determined by method of gas chromatography and mass spectrum, but a definite molecular structure was not determined yet. (author)