Hyperhomocysteinemia and Inflammatory Profile in the Central Nervous System

Abstract

Homocysteine, an intermediate metabolite biosynthesized from the methionine cycle, is a homologue of cysteine. Homocysteine differs from cysteine by an additional methylene group, which makes it more reactive. Elevated homocysteine level is a risk factor for cardiovascular disease and cerebrovascular disease, brain atrophy, neurodegenerative diseases and cognitive dysfunctions. Recent studies suggest a bi-directional relationship between homocysteine levels and immune-inflammatory activation. Our studies sought to determine if hyperhomocysteinemia affects cell infiltrates in the Central Nervous System (CNS). Inflammatory monocytes recruitment into the CNS and microglia proliferation have been shown in several inflammatory models, and Ly-6Chi CCR2+ monocytes have been shown to be the precursor for microglia. Based on these findings, we hypothesized that hyperhomocysteinemia (HHcy) would alter CNS infiltrate composition. We investigated whether HHcy affected the total mononuclear cells composition in the CNS. We also determined whether HHcy altered the inflammatory monocyte subsets composition in the CNS. In order to determine the effects of HHcy in the CNS mononuclear cells composition, we genotyped the mice, and isolated mononuclear cells from the CNS using percoll gradient method. Then we simultaneously stained the cells with three antibodies, PE-labeled anti-mouse CD11b, PE-Cy5-labeled anti-mouse CD45, and FITC-labeled anti-mouse Ly-6C and analyzed the samples by flow cytometry method. HHcy made no difference in the percentage of lymphocytes, infiltrating monocytes and microglia in the total CNS mononuclear cells, but within infiltrating monocytes, HHcy decreased Ly-6Clo and increased Ly-6Chi subsets. These findings demonstrate that HHcy has effects on the CNS mononuclear cell composition. In summary, HHcy decreased Ly-6Clo and increased Ly-6Chi subsets of infiltrating monocytes in the CNS. There is a potential role of HHcy in increasing inflammatory monocytes infiltration.