Role of Betaine-Homocysteine S-Methyltransferase in Homocysteine Methylation
Strakova, Jana
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Permalink
https://hdl.handle.net/2142/83711
Description
Title
Role of Betaine-Homocysteine S-Methyltransferase in Homocysteine Methylation
Author(s)
Strakova, Jana
Issue Date
2008
Doctoral Committee Chair(s)
Nakamura, Manabu T.
Department of Study
Food Science and Human Nutrition
Discipline
Food Science and Human Nutrition
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Biochemistry
Language
eng
Abstract
In mouse liver homogenates, 1000 mumol/L D,L-CBHcy did not inhibit methionine synthase, CBS and cystathionase activities but 5 mumol/L D,L-CBHcy completely inhibited BHMT activity indicating, that D,L-CBHcy was a specific inhibitor of BHMT. To address whether BHMT inhibition caused hyperhomocysteinemia, mice were injected with 1mg of D,L-CBHcy. This reduced BHMT activity (87%) and elevated total plasma Hcy (tHcy, 2.7-fold) for 8 hours. Repeated intraperitoneal injections of D,L-CBHcy (6 doses) additionally reduced the liver S-adenosylmethionine-to-S-adenosylhomocysteine ratio (65%). To assess whether BHMT inhibition affected liver and plasma amino acids, rats were fed 5mg D,L-CBHcy (9 doses). Plasma methionine and serine decreased (23 and 17%, respectively), while histidine, Hcy and glycine increased (35, 311 and 24% respectively). There were no changes in liver methionine and Hcy, but liver taurine, serine, and glutamate decreased (74, 50 and 46%, respectively). Increased plasma betaine (1465%) confirmed that BHMT was functionally inhibited in vivo. Interestingly, liver CBS activity and protein levels decreased (56 and 26%, respectively). To assess whether BHMT inhibition affected glutathione levels and/or caused fatty liver, rats were fed either an adequate (4.5g/kg methionine, 3.7g/kg cystine); cystine-devoid (4.5g/kg methionine, 0g/kg cystine) or a methionine-deficient diet (1.5g/kg methionine, 3.7g/kg cystine) alone or in combination with L-CBHcy for 3, 7 or 14 days. L-CBHcy treatment reduced liver glutathione in rats fed the adequate and cysteine-devoid diets. All animals fed the methionine-deficient diet with L-CBHcy developed fatty liver. L-CBHcy treatment decreased liver CBS activity (15--74%) and the effect was exacerbated with time. We conclude that BHMT activity is required for normal levels of plasma Hcy and methionine, liver SAM and glutathione, and CBS activity.
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