The role of physiological oxygen partial pressures in lipid peroxidation. Theoretical considerations and experimental evidence.

The oxidative breakdown of membrane lipids, i.e. lipid peroxidation, is considered to be decisively involved in a number of toxicological and pathological processes including liver injury caused by iron overload and halogenated alkanes such as CCl4. Within the physiological oxygen partial pressure (PO2) range, i.e. at PO2 between 1 and 100 mmHg, lipid peroxidation depends on O2 in a complex manner. For instance, CCl4-induced lipid peroxidation exhibits a distinct maximum at PO2 of around 7 mmHg, and iron-induced lipid peroxidation shows marked differences in its O2 dependence between an early lag phase and a later phase of self-accelerating propagation. The O2 dependence of lipid peroxidation is either determined by the O2 dependence of initiation or the O2 dependence of propagation. Factors decisive for this are presented and the underlying alterations in the pattern of the peroxidation-related reactions delineated.