Relation of Plasma Homocysteine to Plasma Amyloid Beta Levels

Background Elevated plasma homocysteine and amyloid β (Aβ) have been associated with Alzheimer’s disease (AD). We investigated the cross-sectional association between these biomarkers. Methods We used linear regression to relate plasma homocysteine and Aβ adjusting for age, gender, creatinine, APOE-ε4, and ethnic group in 327 persons aged 78 ± 6.6 years. Results Plasma homocysteine correlated with age, serum creatinine, plasma Aβ40 and Aβ42, and was inversely correlated with serum vitamin B12, and folate. Aβ42, but not Aβ40, was related to later development of dementia. Homocysteine was related to higher Aβ40 levels (coefficient = 2.0; P < 0.0001) and this association was attenuated after adjustment for creatinine (coefficient = 1.0; P < 0.0001). The crude association between homocysteine and Aβ42 was weaker (coefficient = 0.5; P = 0.01) and became non-significant after adjustment for creatinine (coefficient = 0.4; P = 0.06). These associations were unrelated to ethnicity, the presence of APOE-ε4 or dementia. Analyses by quartiles of homocysteine showed that these association were driven primarily by the fourth quartile. Conclusions Plasma homocysteine is directly related to Aβ40. The association with Aβ42 is not significant. These results seem to indicate that homocysteine is related to aging but not specifically to AD. Special issue dedicated to John P. Blass.