Presence of glutamine:fructose-6-phosphate amidotransferase for glucosamine-6-phosphate synthesis in endothelial cells: effects of hyperglycaemia and glutamine.
OBJECTIVE
Recent studies show that glucosamine infusion impairs endothelium-dependent blood flow in normoglycaemic rats. The pathophysiological relevance of this finding, however, depends on whether de novo glucosamine synthesis occurs in endothelial cells. The aim of this study was to test the hypothesis of whether glutamine:fructose-6-phosphate amidotransferase (the first and key regulatory enzyme in hexosamine synthesis) is present for endothelial glucosamine synthesis.


METHODS
Bovine venular, bovine aortic, human microvascular, human umbilical vein, and rat coronary microvascular endothelial cells were used to measure glutamine:fructose-6-phosphate amidotransferase activity. To determine glucosamine-6-phosphate synthesis in intact cells, they were incubated for 1 h in Krebs bicarbonate buffer containing 5, 15 or 30 mmol/l [U-14C]glucose and 0.5, 2 or 4 mmol/l glutamine. The [14C]Glucosamine-6-phosphate and its end products ([14C]UDP-N-acetylglucosamine and [14C]UDP-Nacetylgalactosamine) were separated by HPLC.


RESULTS
There were high glutamine:fructose-6-phosphate amidotransferase activities in all endothelial cells studied. Exposure of cells to 15 to 30 mmol/l glucose or 2 to 4 mmol/l glutamine increased enzyme activity. Glucosamine-6-phosphate, UDP-N-acetylglucosamine and UDP-N-acetylgalactosamine syntheses increased with increasing extracellular concentrations of glucose from 5 to 30 mmol/l or of glutamine from 0.5 to 4 mmol/l.


CONCLUSIONS
Our results show the presence of glutamine:fructose-6-phosphate amidotransferase for de novo glucosamine synthesis in endothelial cells and the modulation of this pathway by hyperglycaemia and glutamine. As glucosamine inhibits endothelial nitric oxide synthesis, these findings could have important implications for impaired endothelium-dependent relaxation and vascular dysfunction in diabetes mellitus.
Department of Animal Science and Faculty of Nutrition, Texas A & M University, College Station 77843-2471, USA.
G
G
Wu
T E
TE
Haynes
W
W
Yan
C J
CJ
Meininger
D000818:Animals; D001011:Aorta; D002417:Cattle; D002478:Cells, Cultured; D003331:Coronary Vessels; D004730:Endothelium, Vascular / Q000187:drug effects / Q000201:enzymology*; D005944:Glucosamine / Q000031:analogs & derivatives / Q000096:biosynthesis*; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives / Q000096:biosynthesis*; D005973:Glutamine / Q000494:pharmacology*; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing) / Q000032:analysis*; D006801:Humans; D006943:Hyperglycemia / Q000201:enzymology*; D007328:Insulin / Q000494:pharmacology; D008833:Microcirculation / Q000201:enzymology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013152:Splanchnic Circulation; D014471:Umbilical Veins; D014536:Uridine Diphosphate N-Acetylgalactosamine / Q000096:biosynthesis; D014537:Uridine Diphosphate N-Acetylglucosamine / Q000096:biosynthesis; D014699:Venules
D007328:Insulin; D005973:Glutamine; C001293:glucosamine 6-phosphate; D014537:Uridine Diphosphate N-Acetylglucosamine; D019298:Glucose-6-Phosphate; D014536:Uridine Diphosphate N-Acetylgalactosamine; D005945:Glutamine-Fructose-6-Phosphate Transaminase (Isomerizing); D005944:Glucosamine