Homocysteinemia control by cysteine in cerebral vascular patients after methionine loading test: evidences in physiological and pathological conditions in cerebro-vascular and multiple sclerosis patients.

The toxicity risk of hyperhomocysteinemia is prevented through thiol drug administration which reduces plasma total homocysteine (tHcy) concentrations by activating thiol exchange reactions. Assuming that cysteine (Cys) is a homocysteinemia regulator, the hypothesis was verified in healthy and pathological individuals after the methionine loading test (MLT). The plasma variations of redox species of Cys, Hcy, cysteinylglycine, glutathione and albumin (reduced, HS-ALB, and at mixed disulfide, XSS-ALB) were compared in patients with cerebral small vessels disease (CSVD) (n = 11), multiple sclerosis (MS) (n = 12) and healthy controls (n = 11) at 2-4-6 h after MLT. In MLT-treated subjects, the activation of thiol exchange reactions provoked significant changes over time in redox species concentrations of Cys, Hcy, and albumin. Significant differences between controls and pathological groups were also observed. In non-methionine-treated subjects, total Cys concentrations, tHcy and thiol-protein mixed disulfides (CSS-ALB, HSS-ALB) of CSVD patients were higher than controls. After MLT, all groups displayed significant cystine (CSSC) increases and CSS-ALB decreases, that in pathological groups were significantly higher than controls. These data would confirm the Cys regulatory role on the homocysteinemia; they also explain that the Cys-Hcy mixed disulfide excretion is an important point of hyperhomocysteinemia control. Moreover, in all groups after MLT, significant increases in albumin concentrations, named total albumin (tALB) and measured as sum of HS-ALB (spectrophometric), and XSS-ALB (assayed at HPLC) were observed. tALB increases, more pronounced in healthy than in the pathological subjects, could indicate alterations of albumin equilibria between plasma and other extracellular spaces, whose toxicological consequences deserve further studies.