title: Effects of diabetes and insulin on betaine-homocysteine S-methyltransferase expression in rat liver.
abstract: Elevation of plasma homocysteine levels has been recognized as an independent risk factor for the development of cardiovascular disease, a major complication of diabetes. Plasma homocysteine reflects a balance between its synthesis via S-adenosyl-L-methionine-dependent methylation reactions and its removal through the transmethylation and the transsulfuration pathways. Betaine-homocysteine methyltransferase (BHMT, EC 2.1.1.5) is one of the enzymes involved in the remethylation pathway. BHMT, a major zinc metalloenzyme in the liver, catalyzes the transfer of methyl groups from betaine to homocysteine to form dimethylglycine and methionine. We have previously shown that plasma homocysteine levels and the transsulfuration pathway are affected by diabetes. In the present study, we found increased BHMT activity and mRNA levels in livers from streptozotocin-diabetic rats. In the rat hepatoma cell line (H4IIE cells), glucocorticoids (triamcinolone) increased the level and rate of BHMT mRNA synthesis. In the same cell line, insulin decreased the abundance of BHMT mRNA and the rate of de novo mRNA transcription of the gene. Thus the decreased plasma homocysteine in various models of diabetes could be due to enhanced homocysteine removal brought about by a combination of increased transsulfuration of homocysteine to cysteine and increased remethylation of homocysteine to methionine by BHMT.
authors.affiliation: Dept. of Biochemistry, Memorial University of Newfoundland, St. John's, NF, Canada, A1B 3X9.
authors.forename: Shobhitha
authors.initials: S
authors.lastname: Ratnam
authors.forename: Enoka P
authors.initials: EP
authors.lastname: Wijekoon
authors.forename: Beatrice
authors.initials: B
authors.lastname: Hall
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Garrow
authors.forename: Margaret E
authors.initials: ME
authors.lastname: Brosnan
authors.forename: John T
authors.initials: JT
authors.lastname: Brosnan
mesh_terms: D000818:Animals; D050940:Betaine-Homocysteine S-Methyltransferase / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D050545:Choline Dehydrogenase / Q000378:metabolism; D003921:Diabetes Mellitus, Experimental / Q000503:physiopathology*; D015870:Gene Expression / Q000187:drug effects; D005938:Glucocorticoids / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012435:S-Adenosylhomocysteine / Q000378:metabolism; D012436:S-Adenosylmethionine / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014221:Triamcinolone / Q000494:pharmacology
chemical_list: D005938:Glucocorticoids; D007328:Insulin; D012333:RNA, Messenger; D014221:Triamcinolone; D012436:S-Adenosylmethionine; D012435:S-Adenosylhomocysteine; D050545:Choline Dehydrogenase; D050940:Betaine-Homocysteine S-Methyltransferase