Glucose oscillations, more than constant high glucose, induce p53 activation and a metabolic memory in human endothelial cells

Abstract

Aims/hypothesis Damage persists in HUVECs exposed to a constant high glucose concentration long after glucose normalisation, a phenomenon termed 'metabolic memory'. Evaluation of the effects of exposure of HUVECs to oscillating high glucose on the induction of markers of oxidative stress and DNA damage (phospho-γ-histone H2AX and PKCδ) and onset of metabolic memory, and the possible role of the tumour suppressor transcriptional factor p53 is of pivotal interest. Methods HUVECs were incubated for 3 weeks in 5 or 25 mmol/l glucose or oscillating glucose (24 h in 5 mmol/l glucose followed by 24 h in 25 mmol/l glucose) or for 1 week in constant 5 mmol/l glucose after being exposed for 2 weeks to continuous 25 mmol/l high glucose or oscillating glucose. Transcriptional activity of p53 was also evaluated in the first 24 h after high glucose exposure. Results High constant glucose upregulated phospho-γ-histone H2AX and protein kinase C (PKC)δ compared with control. Oscillating glucose was even more effective than both normal and constant high glucose. Both constant and oscillating glucose resulted in a memory effect, which was more pronounced in the oscillating condition. Transcriptional activity of p53 peaked 6 h after glucose exposure, showing a predicted oscillatory behaviour. Conclusions/interpretation Exposure to oscillating glucose was more deleterious than constant high glucose and induced a metabolic memory after glucose normalisation. Hyperactivation of p53 during glucose oscillation might be due to the absence of consistent feedback inhibition during each glucose spike and might account for the worse outcome of this condition.

Association of the Arg72Pro Polymorphism in p53 with Progression of Diabetic Nephropathy in T2DM Subjects

“…Hyperglycaemia also activates p53 in human endothelial cells [19]. Interestingly, oscillating glucose is more effective in p53 activation than constant high glucose [19] supporting the view of high glucose variability as an additional cellular stressor. Altogether, however, data elucidating the role of p53 in metabolic diseases like diabetes mellitus and its consequences are scarce so far.…”

“…Hyperglycaemia has been shown to induce mobilization of p53 to the mitochondrial membrane with subsequent changes in mitochondrial membrane potential [18]. Hyperglycaemia also activates p53 in human endothelial cells [19]. Interestingly, oscillating glucose is more effective in p53 activation than constant high glucose [19] supporting the view of high glucose variability as an additional cellular stressor.…”

Effect of Vildagliptin, Compared to Sitagliptin, on the Onset of Hyperglycemia-Induced Metabolic Memory in Human Umbilical Vein Endothelial Cells

“…Overall, under conditions of OM and HM, the changes persisted and were similar to those observed under OG and HG, despite the 7 days of growth in the presence of NG levels, confirming the occurrence of the metabolic memory phenomenon induced by both OG and HG. Overall, treatment with vildagliptin could revert these changes and the effect was more evident than upon sitagliptin, suggesting anti-oxidant and anti-apoptotic properties that can, at least in part, counteract the effects observed under HG-induced metabolic memory [5,16,37].…”

“…Hyperglycemia induces oxidative stress [1][2][3][4][5], and increased levels of Reactive Oxygen Species (ROS) exert a detrimental effect on cellular functions by damaging lipid membranes, enzymes and nucleic acids, and by triggering apoptosis [6]. In addition to continuous hyperglycemia, post-prandial oscillations of glucose levels, like those experienced daily by diabetic patients, have been suggested as an independent risk factor for both microvascular and macrovascular complications [7][8][9].…”

“…Moreover, it has been shown that normalization of the extracellular glucose level does not switch off the intracellular pro-oxidant environment, suggesting a role for ROS in the onset of cellular memory [16]. Of great interest is the observation that glucose fluctuations also produce a memory in Human Umbilical Vein Endothelial Cells (HUVECs), likely through the generation of oxidative stress [5]. Therefore, from a clinical point of view, agents able to counteract the phenomenon of metabolic memory in endothelial cells may help preventing vascular complications that negatively affect the outcome of diabetic patients.…”