Reduced cellular glucose transport confers natural protection against dextrose-induced superoxide generation and endoplasmic reticulum stress in domestic hen

Abstract

Normal blood glucose levels in avian species are two to fourfold higher than that in humans and the higher blood glucose levels in birds do not cause adverse effects. Endothelial cells isolated from the aorta of the domestic hen (Gallus gallus domesticus) and chicken aortic smooth muscle cells (CAOSMC) were compared to human coronary artery endothelial cells (HCAEC) and human primary aortic smooth muscle cells (HASMC). Superoxide (SO) generation was measured using a superoxide-reactive probe. ER stress was measured using the placental alkaline phosphatase assay (ES-TRAP). Glucose transport kinetics were determined using the ³ H-2-deoxyglucose tracer. Dextrose-induced SO generation and ER stress were significantly blunted in avian endothelial cells compared to human cells. The Vmax of glucose uptake (in nmoles/mg protein/min) in avian endothelial cells (0.0018 ± 0.0001) and smooth muscle cells (0.0015 ± 0.0007) was approximately 18-25 fold lower compared to the Vmax in HCAEC (0.033 ± 0.0025) and HASMC (0.038 ± 0.004) (all p < 0.0001). The Michaelis-Menten constant (Km) of transport was also significantly different (p < 0.0001) in avian species. The relative resistance of avian cells to dextrose-induced oxidative stress and ER stress is mostly the result of reduced cellular dextrose transport.

Keywords: chicken aortic endothelial cells; endoplasmic reticulum stress; glucose transport; human coronary artery endothelial cell; oxidative stress.

FIGURE 1

The effect of varying concentrations of dextrose on (a) superoxide (SO) generation and (b) endoplasmic reticulum (ER) stress in human coronary artery endothelial cells (HCAEC) and avian aortic endothelial cells. ER stress is the reverse of secreted alkaline phosphatase (SAP) activity. (N = 6 cell cultures for each figure) *, p < 0.05 relative to cells exposed to 5.5 mM dextrose. All results are expressed as mean ± S.D. Analysis of variance (ANOVA) followed by the Neuman–Keuls procedure for subgroup analysis was carried out using Statistica

FIGURE 2

Kinetics of glucose uptake in human and avian endothelial (a) and smooth muscle cells (b). Glucose uptake was measured and Vmax (nmoles/mg protein/min) and Km (mM) were determined. Endothelial cells were obtained from human coronary arteries and avian aortae. Smooth muscle cells, purchased from ATCC, were obtained from human and avian coronary arteries and avian aortae, respectively. Vmax = maximal velocity of cellular glucose uptake; Km = Michaelis‐Menten constant of glucose transport. Glucose uptake was significantly more efficient in human endothelial and smooth muscle cells relative to avian endothelial and smooth muscle cells (p < 0.05), (N = 6 cell cultures for each data point). All results are expressed as mean ± S.D. Analysis of variance (ANOVA) followed by the Neuman–Keuls procedure for subgroup analysis was carried out using Statistica