Aims/hypothesis A long-term 'memory' of hyperglycaemic stress, even when glycaemia is normalised, has been previously reported in endothelial cells. In this report we sought to duplicate and extend this finding. Materials and methods HUVECs and ARPE-19 retinal cells were incubated in 5 or in 30 mmol/l glucose for 3 weeks or subjected to 1 week of normal glucose after being exposed for 2 weeks to continuous high glucose. HUVECs were also treated in this last condition with several antioxidants. Similarly, four groups of rats were studied for 3 weeks: (1) normal rats; (2) diabetic rats not treated with insulin; (3) diabetic rats treated with insulin during the last week; and (4) diabetic rats treated with insulin plus α-lipoic acid in the last week. Results In human endothelial cells and ARPE-19 retinal cells in culture, as well as in the retina of diabetic rats, levels of the following markers of high glucose stress remained induced for 1 week after levels of glucose had normalised: protein kinase C-β, NAD(P)H oxidase subunit p47phox, BCL-2-associated X protein, 3-nitrotyrosine, fibronectin, poly(ADPribose) Blockade of reactive species using different approaches, i.e. the mitochondrial antioxidant α-lipoic acid, overexpression of uncoupling protein 2, oxypurinol, apocynin and the poly(ADP-ribose) polymerase inhibitor PJ34, interrupted the induction both of high glucose stress markers and of the fluorescent reactive oxygen species (ROS) probe CM-H 2 DCFDA in human endothelial cells. Similar results were obtained in the retina of diabetic rats with α-lipoic acid added to the last week of normalised glucose. Conclusions/interpretation These results provide proofof-principle of a ROS-mediated cellular persistence of vascular stress after glucose normalisation.

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Trivalent inorganic arsenic (arsenite, arsenic trioxide, As(III)) is a primary contaminant of groundwater supplies worldwide. As(III), marketed as trisenox, is also an FDA-approved agent to treat cancer It has been previously shown by our laboratory that As(III) administered at doses lower than a therapeutic anticancer dose results in an increase in tumor formation and blood vessel density of tumors. In this work it was found that chronic administration of As(III) approaching the EPA action level of 10 ppb, given in the drinking water of mice 5 weeks prior to B16-F10 melanoma implantation, increased the growth rate of primary tumors and the number of metastases to the lung. Further, levels of arsenic in the tumor and lung were found to be much greater than those in the blood and similar to pro-angiogenic As(III) doses. Levels of hypoxia inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) surrounding the blood vessels in the tumors of the As(III)-treated mice were also found to be increased. Exposure of isolated B16-F10 tumor cells to chronic (3 or 7 day) but not acute (4 h) low-dose As(III) was found to increase HIF-1alpha expression and secretion of VEGF. Finally, coadministration of an inhibitor of HIF (YC-1) or a VEGFR-2 kinase inhibitor (SU5416) was found to antagonize the pro-angiogenic effects of low-dose As(III). Together, these results suggest that chronic exposure to low-dose As(III) could stimulate growth of tumors through a HIF-dependent stimulation of angiogenesis.

The mechanisms of action of drinking water arsenic in the lung and the threshold for biologic effects remain controversial. Our study utilizes Affymetrix 22,690 transcript oligonucleotide microarrays to assess the long-term effects of increasing doses of drinking water arsenic on expression levels in the mouse lung. Mice were exposed at levels commonly found in contaminated drinking water wells in the United States (0, 0.1, 1 ppb), as well as the 50 ppb former maximum contaminant level, for 5 weeks. The expression profiles revealed modification of a number of important signaling pathways, many with corroborating evidence of arsenic responsiveness. We observed statistically significant expression changes for transcripts involved in angiogenesis, lipid metabolism, oxygen transport, apoptosis, cell cycle, and immune response. Validation by reverse transcription-PCR and immunoblot assays confirmed expression changes for a subset of transcripts. These data identify arsenic-modified signaling pathways that will help guide investigations into mechanisms of arsenic's health effects and clarify the threshold for biologic effects and potential disease risk.