A natural protective mechanism against hyperglycaemia in vascular endothelial and smooth-muscle cells: role of glucose and 12-hydroxyeicosatetraenoic acid

Abstract

Bovine aortic endothelial and smooth-muscle cells down-regulate the rate of glucose transport in the face of hyperglycaemia, thus providing protection against deleterious effects of increased intracellular glucose levels. When exposed to high glucose concentrations these cells reduced the mRNA and protein content of their typical glucose transporter, GLUT-1, as well as its plasma-membrane abundance. Inhibition of the lipoxygenase (LO) pathway, and particularly 12-LO, reversed this glucose-induced down-regulatory process and restored the rate of hexose transport to the level seen in vascular cells exposed to normal glucose levels. This reversal was accompanied by increased levels of GLUT-1 mRNA and protein, as well as of its plasma-membrane content. Exposure of the vascular cells to elevated glucose concentrations increased by 2-3-fold the levels of cell-associated and secreted 12-hydroxyeicosatetraenoic acid (12-HETE), the product of 12-LO. Inhibition of 15- and 5-LO, cyclo-oxygenases 1 and 2, and eicosanoid-producing cytochrome P450 did not modify the hexose-transport system in vascular cells. These results suggest a role for HETEs in the autoregulation of hexose transport in vascular cells. 8-Iso prostaglandin F(2alpha), a non-enzymic oxidation product of arachidonic acid, had no effect on the hexose-transport system in vascular cells exposed to hyperglycaemic conditions. Taken together, these findings show that hyperglycaemia increases the production rate of 12-HETE, which in turn mediates the down-regulation of GLUT-1 expression and the glucose-transport system in vascular endothelial and smooth-muscle cells.

Characterisation of glucose transporters in the intact coronary artery endothelium in rats: GLUT-2 upregulated by long-term hyperglycaemia

“…Hyperglycaemia had profound effects on all of the GLUTs, significantly reducing the number of labelled voxels for all except GLUT-2, which was dramatically increased. The decrease in GLUT-1 staining is consistent with reports indicating that the expression of this transporter is downregulated both in rat heart endothelium following STZ-induced diabetes [31], and in bovine aortic endothelial cells exposed to hyperglycaemia for 48 h [57]. The latter was associated with an enhanced production of 12-hydroxyeicosatetraenoic acid (12-HETE), which may downregulate the production of GLUT-1 and may decrease its maximal velocity.…”

Delayed autoregulation of glucose transport in vascular endothelial cells

“…American Radiolabelled Chemicals (St. Louis, MO, USA) supplied 2- [1,[2][3] Vascular cell cultures Primary cultures of bovine aortic endothelial and smooth muscle cells were prepared and characterised as described previously [5].…”

“…Western blot analysis of GLUT-1 was performed as described [5]. Western blot analysis of 12-LO was performed using rabbit polyclonal antibody against a synthetic 24-amino acid polypeptide designed from the exon 4 domain of human platelet-type 12-LO, as described [6].…”

“…Extraction of hydroxyeicosatetraenoic acids from culture medium and high-performance liquid chromatography analysis Cell culture media were collected from three culture plates for each data point (2 ml/well), pooled, extracted and analysed for 12-HETE by high-performance liquid chromatography (HPLC), as described previously [5]. The yield and retention time of 12-HETE were 93% and 11.4 min, respectively.…”

“…Other investigators suggest that VEC are particularly susceptible to the deleterious effects of high glucose levels due to an unregulated glucose transport system [3,4]. We recently reported that VEC that had been exposed to high glucose levels for 48 h downregulated the rate of glucose transport by reducing glucose transporter-1 (GLUT-1) mRNA and protein expression, as well as GLUT-1 plasma membrane localisation [5]. The present study was undertaken to characterise the development of the autoregulatory response in VEC and its relationship to 12-lipoxygenase (12-LO) induction and function.…”