The measurement of lipid peroxidation in vivo

Tissue damage due to free radical activity may be a common mediator in pathology [Kehrer, Crit. Rev. Toxicol. 23 (1993) 21-48]. The confirmation that free radicals have a role in the disease process is hampered by the difficulty of their measurement, as free radicals are transient species present at low concentrations in tissue. Direct measurement of free radicals is confined to electron spin resonance, a specialised methodology not available in our laboratory. We have evaluated several indirect measures, namely, changes in antioxidant status, hydroxyl radical trapping assays and monitoring breakdown products of free radical attack. Here we describe a method from the latter category, monitoring lipid peroxidation. The measurement of lipid peroxidation has been favoured as the indicator of free radical activity in previous ex vivo and in vitro studies of oxidative stress, in particular by the measurement of malondialdehyde (MDA). There is an absence of reported measurements of MDA from in vivo preparations especially where samples are collected in situ. The method describes the combination of microdialysis sampling with high performance liquid chromatography coupled to ultraviolet spectroscopy, to measure MDA from in vivo preparations of rat brain. The methodology could equally be applied to other tissues.