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.

Pathophysiological Concepts in Multiple Sclerosis and the Therapeutic Effects of Hydrogen Sulfide

“…In the present study, it was observed that CBS knockout in PBMNCs decreased cell transmigration across EC. Indeed, CBS is known to be upregulated in activated PBMNCs ( Katko et al, 2012 ). Surprisingly, serotonin treatment of CBS knockout PBMNCs further increased transmigration compared to serotonin-treated control cells.…”

Lean Body Mass Harbors Sensing Mechanisms that Allow Safeguarding of Methionine Homeostasis

“…Taken together, these clinical morbidities cover almost all LBM tissues and account for nearly all the total body REE. Despite apparent disparity, all LBM organs possess the same enzymatic equipment to complete TS and RM processes (taking the brain [ 79 ], gastrointestinal tract [ 80 ], and white blood cells [ 81 ], as examples). We postulate that any LBM component submitted to any stress disorder (e.g., sepsis, trauma, burns, neoplasia) undergoes depletion of its N stores and Met pool size, which might endanger defense and repair systems.…”

Bridging the Gap in Cancer Research: Sulfur Metabolism of Leukemic Cells with a Focus on L-Cysteine Metabolism and Hydrogen Sulfide-Producing Enzymes

“…They reported a mean CBS activity of 0.99 ± 0.32 mU/mg protein, ranging from 0.6 to 1.59 mU/mg protein. The study found that CBS protein levels and activity increased with incubation time and upon stimulation, influenced by intra-and extracellular changes in homocysteine and GSH concentrations, both in vitro and in vivo [39].…”

“…Later studies identified CBS mRNA in resting lymphocytes, suggesting potential trace cellular activity [38]. A significant advancement was made by Katko et al [39], who demonstrated CBS expression and activity in resting PMCs from eight healthy donors. They reported a mean CBS activity of 0.99 ± 0.32 mU/mg protein, ranging from 0.6 to 1.59 mU/mg protein.…”