Free radicals and superoxide dismutase in blood of patients with Alzheimer's disease and vascular dementia.

We measured hydroxyl radical (.OH) levels in blood, superoxide dismutase (SOD) activity in red blood cells (RBC) relative to both total protein (RBC-SOD/P) and Cu,Zn-SOD protein (RBC-SOD/SOD), SOD activity in plasma (plasma-SOD), and Cu,Zn-SOD protein relative to total RBC protein (Cu,Zn-SOD/P) in 22 patients with probable dementia of the Alzheimer type (DAT group, mean age 74.8+/-9.4 years), 16 with probable vascular dementia (VAD group, mean age 76.9+/-6.7 years) and 19 non-demented controls (control group, mean age 73.5+/-6.2 years). Levels of .OH in the DAT and VAD groups were significantly (P<0.01 and P<0.001, respectively) higher, whereas the values of RBC-SOD/P and RBC-SOD/SOD in these two groups (both P<0.001) and Cu,Zn-SOD/P in the DAT group (P<0.001) were significantly lower than the corresponding control values. Members of the VAD group with risk factors for stroke (RF+ group) showed significantly higher .OH levels than members of the VAD group without risk factors (RF- group; P<0.01) and the control group (P<0.001). RBC-SOD/P and RBC-SOD/SOD values in the RF+ group were significantly (both P<0.01) lower than the corresponding control values. There were no significant differences among the VAD, RF+ and control groups with respect to Cu,Zn-SOD/P values, or between the RF- and control groups for any measured parameter. We conclude that oxidative stress plays a role in the brain damage seen in both DAT and VAD, and that the causes of decreased SOD activity in RBC differ between DAT and VAD patients.