Homocysteine induces DNA damage and alterations in proliferative capacity of T-lymphocytes: a model for immunosenescence?

Abstract

Homocysteine (Hcy) appears to exert different effects on immune functions possibly contributing to age-related pathological states, including vascular diseases, immune dysfunction, and Alzheimer's disease. However, molecular mechanisms underlying Hcy toxicity need to be better characterized. Since T cells are a suitable model to address the possible role of replicative senescence during the in vivo aging, we investigated the effects of high Hcy concentrations on mitogen-activated lymphocytes, with regard to evaluation of DNA damage and cell cycle alterations. Cultured human peripheral blood lymphocytes were stimulated with mitogenic concanavalin A (5 microg/ml) for 48 h in the presence or absence of Hcy (1 mM). Both flow cytometric analysis and caspase-3 activity assay showed an increased rate of apoptosis in Hcy-treated lymphocyte cultures compared to controls. Further, Hcy exposure caused DNA fragmentation as evaluated by single cell gel electrophoresis showing the occurrence of comets. Cytokinesis-block micronucleus assay, performed after addition of cytochalasin B (5 microg/ml) and incubation up to 72 h, revealed a significantly higher frequency of micronucleated/binucleated cells in Hcy-treated cultures compared to controls (P < 0.001). Hcy also reduced cyclin B expression in comparison to control cultures, while cyclin D levels were not significantly affected. Cell cycle alterations, such as the inability of cells to enter into mitosis, could be related with DNA damage. These findings provided a link between perturbation of lymphocyte proliferation homeostasis and commitment towards apoptosis. Our results suggest the involvement of Hcy in the altered immune function associated with age and disease pathology.

Chronic hyperhomocysteinemia alters antioxidant defenses and increases DNA damage in brain and blood of rats: Protective effect of folic acid

“…Picerno et al (2007) showed that Hcy-treated human peripheral blood lymphocytes in culture presented increase in DNA damage and in micronucleus frequency, altering immune function. However, we did not discard other ways of action, considering that DNA strand breakage could be caused by nucleases activated by Ca 2+ and/or by ROS, mainly OH formed by reaction of H 2 O 2 with DNA-bound metal ions (Darley-Usmar and Halliwell, 1996).…”

Histopathology of central nervous system lesions in Behçet's disease

“…It is therefore most likely that neurons undergoing apoptosis might form binucleated neurons. It has been shown that various factors cause apoptosis and binucleation in a variety of cells through the cytokinesis-blocking [13,14]. It is therefore suggested that some inflammatory assault might cause apoptosis and binucleation of neurons in NB.…”

Homocysteine metabolism, growth performance, and immune responses in suckling and weanling piglets1

“…In previous studies, it has been reported that human peripheral blood monocytes exposed to Hcy were unable to enter into mitosis (Picerno et al 2007). The mechanism is still not elucidated but it is known that high levels of the previously mentioned precursor of Hcy, S-adenosyl-L-Hcy can block phosphatidylinositol kinase, an enzyme responsible for second messenger signaling in cellular activation (Pike and DeMeester, 1988).…”