Influence of hemodialysis on total and free malondialdehyde measured by a new HPLC method

Accurate evaluation of oxidative stress is needed for patients on chronic hemodialysis (HD), as cardiovascular risk level seems related to it. Oxidative stress is often evaluated by measuring an end product of lipoperoxidation named malondialdehyde (MDA). However, the most common technique for measuring MDA, the Thio Barbituric Acid Reactive Substances method (TBARS), is known to be sensitive but poorly specific. We measured true total and free plasma MDA in fifty-four unselected patients on long-term HD, before and after HD sessions, by a new, highly specific HPLC method. Total and free MDA were higher before than after dialysis. Essentially, free MDA was decreased by HD but its fractional decrease was lower than that of urea or creatinine. This confirms that, in fact, free MDA is more or less bound to low molecular weight compounds and/or suggests that MDA may be produced mainly during HD sessions. We propose this new tool to further explore the relationship between oxidative stress, HD and true MDA.