title: Homocysteine metabolism in peripheral blood mononuclear cells: evidence for cystathionine beta-synthase activity in resting state.
abstract: Activated peripheral blood mononuclear cells (PBMC) release homocysteine and possess cystathionine β-synthase (CBS) activity; however, it was thought that there is no CBS in resting state. Previously, we found that nickel decreased intracellular homocysteine concentration in un-stimulated (e.g. resting) PBMC, suggesting that resting PBMC might also have active homocysteine metabolism. Here, we demonstrated that un-stimulated PBMC synthesize (incorporate L-[methyl-14C]methionine to DNA, lipids and proteins), release (increase extracellular homocysteine), and metabolize homocysteine. Intracellular homocysteine concentration varied with incubation time, depending on extracellular concentrations of methionine, homocysteine, and glutathione. Methionine synthase activity was constant and independent of thiol concentrations. In Western blot, CBS protein was clearly identified in freshly isolated PBMC. CBS protein level and activity increased with incubation time, upon stimulation, and similar to intracellular homocysteine, depending on intra- and extracellular homocysteine and glutathione concentrations. According to our knowledge, this is the first evidence that certifies homocysteine metabolism and regulatory role of CBS activity to keep balanced intracellular homocysteine level in resting PBMC. Homocysteine, released by PBMC, in turn can modulate its functions contributing to the development of hyperhomocysteinemia-induced diseases.
authors.affiliation: First Department of Medicine, Medical and Health Science Center, University of Debrecen, Nagyerdei krt. 98, H-4012, Debrecen, P.O. Box 19, Hungary.
authors.forename: Monika
authors.initials: M
authors.lastname: Katko
authors.forename: Erzsebet
authors.initials: E
authors.lastname: Zavaczki
authors.forename: Viktoria
authors.initials: V
authors.lastname: Jeney
authors.forename: Gyorgy
authors.initials: G
authors.lastname: Paragh
authors.forename: Jozsef
authors.initials: J
authors.lastname: Balla
authors.forename: Zsuzsa
authors.initials: Z
authors.lastname: Varga
mesh_terms: D003541:Cystathionine beta-Synthase / Q000235:genetics / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006710:Homocysteine / Q000378:metabolism*; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000201:enzymology / Q000378:metabolism*; D008715:Methionine / Q000378:metabolism
chemical_list: D006710:Homocysteine; D008715:Methionine; D003541:Cystathionine beta-Synthase; D005978:Glutathione