Prolonged exposure to homocysteine results in diminished but reversible pancreatic beta-cell responsiveness to insulinotropic agents.
BACKGROUND
Plasma homocysteine levels may be elevated in poorly controlled diabetes with pre-existing vascular complications and/or nephropathy. Since homocysteine has detrimental effects on a wide diversity of cell types, the present study examined the effects of long-term homocysteine exposure on the secretory function of clonal BRIN-BD11 beta-cells.


METHODS
Acute insulin secretory function, cellular insulin content and viability of BRIN-BD11 cells were assessed following long-term (18 h) exposure to homocysteine in culture. RT-PCR and Western blot analysis were used to determine the expression of key beta-cell genes and proteins. Cells were cultured for a further 18 h without homocysteine to determine any long-lasting effects.


RESULTS
Homocysteine (250-1000 micromol/L) exposure reduced insulin secretion at both moderate (5.6 mmol/L) and stimulatory (16.7 mmol/L) glucose by 48-63%. Similarly, insulin secretory responsiveness to stimulatory concentrations of alanine, arginine, 2-ketoisocaproate, tolbutamide, KCl, elevated Ca2+, forskolin and PMA, GLP-1, GIP and CCK-8 were reduced by 11-62% following culture with 100-250 micromol/L homocysteine. These inhibitory effects could not simply be attributed to changes in cellular insulin content, cell viability, H2O2 generation or any obvious alterations of gene/protein expression for insulin, glucokinase, GLUT2, VDCC, or Kir6.2 and SUR1. Additional culture for 18 h in standard culture media after homocysteine exposure restored secretory responsiveness to all agents tested.


CONCLUSIONS
These findings suggest that long-term exposure to high homocysteine levels causes a reversible impairment of pancreatic beta-cell insulinotropic pathways. The in vivo actions of hyperhomocysteinaemia on islet cell function merit investigation.
Patterson
Steven
S
Diabetes Research Group, School of Biomedical Sciences, University of Ulster, Coleraine, N Ireland, UK. s.patterson@ulster.ac.uk
Scullion
Siobhan M J
SM
McCluskey
Jane T
JT
Flatt
Peter R
PR
McClenaghan
Neville H
NH
D000818:Animals; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects; D005947:Glucose / Q000008:administration & dosage / Q000494:pharmacology; D006710:Homocysteine / Q000008:administration & dosage / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects* / Q000378:metabolism*; D051381:Rats; D013268:Stimulation, Chemical; D013997:Time Factors
D007328:Insulin; D006710:Homocysteine; D005947:Glucose