title: Impaired cardiac anti-oxidant activity in diabetes: human and correlative experimental studies.
abstract: Increased reactive oxygen species (ROS) are traditionally viewed as arising from the metabolic flux of diabetes, although reduction in the activity of anti-oxidant systems has also been implicated. Among the latter is the major thiol reducing thioredoxin system, the activity of which may be diminished by high glucose-induced expression of its endogenous inhibitor, thioredoxin interacting protein (TxnIP). We assessed TxnIP mRNA/protein expression along with thioredoxin activity in human right atrial biopsy specimens from subjects with and without diabetes undergoing coronary artery grafting. In correlative experimental studies, we examined TxnIP expression in both type 1 and type 2 rodent models of diabetic cardiomyopathy. Finally, we used in vitro gene silencing to determine the contribution of changes in TxnIP abundance to the high glucose-induced reduction in thioredoxin activity. In human right atrial biopsies, diabetes was associated with a >30-fold increase in TxnIP gene expression and a 17 % increase in TxnIP protein expression (both p < 0.05). This was associated with a 21 % reduction in thioredoxin activity when compared to human non-diabetic cardiac biopsy samples (all p < 0.05). In correlative animal studies, both type 1 and type 2 diabetic rats demonstrated a significant increase in TxnIP mRNA and reduction in thioredoxin activity when compared to non-diabetic animals (all p < 0.05). This was associated with a significant increase in ROS (p < 0.05 when compared with control). In cultured cardiac myocytes, high glucose increased ROS and TxnIP mRNA expression, in association with a reduction in thioredoxin activity (p < 0.01). These findings were abrogated by TxnIP small interfering RNA (siRNA). Scrambled siRNA had no effect upon ROS or TxnIP expression. High glucose reduces thioredoxin activity and increases ROS via TxnIP overexpression. These findings suggest that impaired thiol reductive capacity, through altered TxnIP expression, contributes to increased ROS in the diabetic heart.
authors.affiliation: Keenan Research Centre for Biomedical Science, St. Michael's Hospital, 30 Bond St, 209 Victoria Street, Room 7-052, Toronto, ON, M5B 1W8, Canada, connellyk@smh.ca.
authors.forename: Kim A
authors.initials: KA
authors.lastname: Connelly
authors.forename: Andrew
authors.initials: A
authors.lastname: Advani
authors.forename: Suzanne L
authors.initials: SL
authors.lastname: Advani
authors.forename: Yuan
authors.initials: Y
authors.lastname: Zhang
authors.forename: Young M
authors.initials: YM
authors.lastname: Kim
authors.forename: Vanessa
authors.initials: V
authors.lastname: Shen
authors.forename: Kerri
authors.initials: K
authors.lastname: Thai
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Kelly
authors.forename: Richard E
authors.initials: RE
authors.lastname: Gilbert
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D003920:Diabetes Mellitus / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D013879:Thioredoxins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D017382:Reactive Oxygen Species; C491203:TXN protein, human; C486715:TXNIP protein, human; C493796:TXNIP protein, rat; C495697:Txn1 protein, rat; D013879:Thioredoxins