Protective Pleiotropic Effect of Flavonoids on NAD+ Levels in Endothelial Cells Exposed to High Glucose

NAD+ is important for oxidative metabolism by serving as an electron transporter. Hyperglycemia decreases NAD+ levels by activation of the polyol pathway and by overactivation of poly(ADP-ribose)-polymerase (PARP). We examined the protective role of three structurally related flavonoids (rutin, quercetin, and flavone) during high glucose conditions in an in vitro model using human umbilical vein endothelial cells (HUVECs). Additionally we assessed the ability of these flavonoids to inhibit aldose reductase enzyme activity. We have previously shown that flavonoids can inhibit PARP activation. Extending these studies, we here provide evidence that flavonoids are also able to protect endothelial cells against a high glucose induced decrease in NAD+. In addition, we established that flavonoids are able to inhibit aldose reductase, the key enzyme in the polyol pathway. We conclude that this protective effect of flavonoids on NAD+ levels is a combination of the flavonoids ability to inhibit both PARP activation and aldose reductase enzyme activity. This study shows that flavonoids, by a combination of effects, maintain the redox state of the cell during hyperglycemia. This mode of action enables flavonoids to ameliorate diabetic complications

Accelerated Aging during Chronic Oxidative Stress: A Role for PARP-1

Oxidative stress plays a major role in the pathophysiology of chronic inflammatory disease and it has also been linked to accelerated telomere shortening. Telomeres are specialized structures at the ends of linear chromosomes that protect these ends from degradation and fusion. Telomeres shorten with each cell division eventually leading to cellular senescence. Research has shown that poly(ADP-ribose) polymerase-1 (PARP-1) and subtelomeric methylation play a role in telomere stability. We hypothesized that PARP-1 plays a role in accelerated aging in chronic inflammatory diseases due to its role as coactivator of NF-κb and AP-1. Therefore we evaluated the effect of chronic PARP-1 inhibition (by fisetin and minocycline) in human fibroblasts (HF) cultured under normal conditions and under conditions of chronic oxidative stress, induced by tert-butyl hydroperoxide (t-BHP). Results showed that PARP-1 inhibition under normal culturing conditions accelerated the rate of telomere shortening. However, under conditions of chronic oxidative stress, PARP-1 inhibition did not show accelerated telomere shortening. We also observed a strong correlation between telomere length and subtelomeric methylation status of HF cells. We conclude that chronic PARP-1 inhibition appears to be beneficial in conditions of chronic oxidative stress but may be detrimental under relatively normal conditions

Effect on eicosanoid concentrations.

<p>Effect of pre/co incubation with 5 mM erythritol (ERT) on HUVECS cultured in normal glucose (NG, 7 mM) or high glucose (HG, 30 mM) for 24 hours on eicosanoid concentrations in cell pellets (A) and culture medium (B). Data are expressed as means ± standard error of three independent experiments. * = p<0.05 compared to NG; ** = p<0.05 compared to HG; # = p<0.1 compared to HG.</p

Heat map of transcriptomic analysis.

<p>Heat map reflecting the mean gene expression values in the four different treatment groups: From left to right: high glucose (HG, 30 mM), normal glucose and 5 mM erythritol (NGERT), normal glucose (NG), high glucose and 5 mM erythritol (HGERT). Cluster analysis shows that the expression profile in the HG group differs from the other three treatment group that form a separate cluster.</p

Altered transcripts with a link to endothelial function.

<p>Altered transcripts with a link to endothelial function.</p

Transcripts changed in citric acid cycle and electron transport system.

<p>Transcripts changed in citric acid cycle and electron transport system.</p

Effect on oxidative stress parameters.

<p>Effect of pre/co incubation with 5 mM erythritol (ERT) on HUVECS cultured in normal glucose (NG, 7 mM) or high glucose (HG, 30 mM) for 24 hours on malondialdehyde (A), carbonyl (B) and 8-OHdG (C) content. Data are expressed as means ± standard error of three independent experiments. # = p<0.1 compared to HG.</p

Altered transcripts with a link to apoptosis.

<p>Altered transcripts with a link to apoptosis.</p