Fatty acid analysis of blood plasma of patients with Alzheimer's disease, other types of dementia, and cognitive impairment

Fatty acid differences, including docosahexaenoic acid (DHA; 22:6n-3) have been shown in the brains of Alzheimer's patients (AD) as compared with norm al age-matched individuals. Furthermore, low serum DHA is a significant ris k factor for the development of AD. The relative concentration of DHA and o ther fatty acids, however, in the plasma of AD patients compared with patie nts with other kinds of dementias (other dementias; OD), patients who are c ognitively impaired but nondemented (CIND), or normal patients is not known . In this study we analyzed the total phospholipid, phosphatidylcholine (PC ), phosphatidylethanolamine (PE), and lysophosphatidylcholine (lysoPC) frac tions of plasma from patients diagnosed with AD, OD, or CIND and compared t hem with a group of elderly control subjects with normal cognitive function ing. Plasma phospholipid and PC levels of 20:5n-3, DHA, total n-3 fatty aci ds, and the n-3/n-6 ratio were lower in the AD, OD, and CIND groups. Plasma phospholipid 24:0 was lower in the AD, OD, and CIND groups as compared wit h the group of control patients, and total n-6 fatty acid levels were highe r in the AD and CIND groups only. in the plasma PE fraction, levels of 20:5 n-3, DHA, and the total n-3 fatty acid levels were significantly lower in t he AD, OD, and CIND groups. DHA levels were lower in the lysoPC fraction of CIND individuals only. There were no other differences in the fatty acid c ompositions of the different phospholipid fractions. Therefore, in AD, OD, and CIND individuals, low levels of n-3 fatty acids in the plasma may be a risk factor for cognitive impairment and/or dementia. Interestingly, a decr eased level of plasma DHA was not limited to the AD patients but appears to be common in cognitive impairment with aging.