Hypoxia mediated release of endothelial microparticles and increased association of S100A12 with circulating neutrophils

Abstract

Microparticles are released from the endothelium under normal homeostatic conditions and have been shown elevated in disease states, most notably those characterised by endothelial dysfunction. The endothelium is sensitive to oxidative stress/status and vascular cell adhesion molecule-1 (VCAM-1) expression is upregulated upon activated endothelium, furthermore the presence of VCAM-1 on microparticles is known. S100A12, a calcium binding protein part of the S100 family, is shown to be present on circulating leukocytes and is thought a sensitive marker to local inflammatory process, which may be driven by oxidative stress. Eight healthy males were subjected to breathing hypoxic air (15% O(2), approximately equivalent to 3000 metres altitude) for 80 minutes in a temperature controlled laboratory and venous blood samples were processed immediately for VCAM-1 microparticles (VCAM-1 MP) and S100A12 association with leukocytes by flow cytometry. A pre-hypoxic blood sample was used for comparison. Both VCAM-1 MP and S100A12 association with neutrophils were significantly elevated post hypoxic breathing later declining to levels observed in the pre-test samples. A similar trend was observed in both cases and a correlation may exist between these two markers in response to hypoxia. These data offer evidence using novel markers of endothelial and circulating blood responses to hypoxia.

Keywords: RAGE; S100A12; VCAM-1; endothelium; hypoxia; microparticles; oxidative stress.

Figure 1

Time dependent profile for VCAM⁺ MP and TBARS before and after hypoxic breathing. The data are represented as the mean and standard error of the mean (n = 8). HB = time during which subjects breathed hypoxic air.

Figure 2

Typical flow cytometry profiles showing (top) forward scatter/side scatter with Netrophils and monocytes gated accordingly and (bottom) fluorescence profiles showing gated (black) neutrophils and (grey) monocytes incubated with either (filled) goat serum or (line) anti-human EN-RAGE.

Figure 3

Time dependent profile for S100A12 expression on monocytes and neutrophils before and after hypoxic breathing. The data are represented as the mean and standard error of the mean (n = 8). HB = time during which subjects breathed hypoxic air.