Upregulation of PEDF expression by PARP inhibition contributes to the decrease in hyperglycemia-induced apoptosis in HUVECs

Poly (ADP-Ribose) Polymerase-1 (PARP-1) Inhibitors in Diabetic Retinopathy: An Attractive but Elusive Choice for Drug Development

Owing to its promiscuous roles, poly (ADP-ribose) polymerase-1 (PARP-1) is involved in various neurological disorders including several retinal pathologies. Diabetic retinopathy (DR) is the most common microvascular complication of diabetes mellitus affecting the retina. In the present review, we highlight the importance of PARP-1 participation in pathophysiology of DR and discuss promising potential inhibitors for treatment. A high glucose level enhances PARP-1 expression; PARP inhibitors have gained attention due to their potential therapeutic effects in DR. They target different checkpoints (blocking nuclear transcription factor (NF-κB) activation; oxidative stress protection, influence on vascular endothelial growth factor (VEGF) expression, impacting neovascularization). Nowadays, there are several improved clinical PARP-1 inhibitors with different allosteric effects. Combining PARP-1 inhibitors with other compounds is another promising option in DR treatments. Besides pharmacological inhibition, genetic disruption of the PARP-1 gene is another approach in PARP-1-initiated therapies. In terms of future treatments, the limitations of single-target approaches shift the focus onto combined therapies. We emphasize the importance of multi-targeted therapies, which could be effective not only in DR, but also in other ischemic conditions.

Pigment epithelium-derived factor (PEDF) ameliorates arsenic-induced vascular endothelial dysfunction in rats and toxicity in endothelial EA.hy926 cells

Although the harmful effects of arsenic exposure on the cardiovascular system have received great attention, there is still no effective treatment. Vascular endothelial dysfunction (VED) is the initial step of cardiovascular diseases, where pigment epithelium-derived factor (PEDF) plays an important role in maintaining endothelial function. Here, we explored the protective role of PEDF in VED induced by arsenic, and its underlying molecular mechanism, designing an in vivo rat model of arsenic exposure recovery and in vitro endothelial EA. hy926 cell-based assays. The edema of aortic endothelial cells in rats significantly improved during recovery from arsenite exposure compared with rats exposed to 10 and 50 mg/L arsenite continuously. In addition, serum levels of nitric oxide (NO), von Willebrand factor, and nitric oxide synthase (inducible and total activities) in rats, which were greatly affected by arsenite exposure, returned to levels similar to those in the control group after recovery with distilled water. The recovery from arsenite exposure was associated with increased levels of PEDF; decreased protein levels of Fas, FasL, P53, and phospho-p38; and inhibited apoptosis in aortic endothelial cells in vivo. Recombinant human PEDF treatment (100 nM) prevented the toxic effects of arsenite (50 μM) on endothelial cells in vitro by increasing NO content, decreasing reactive oxygen species (ROS) levels, and inhibiting apoptosis, as well as increasing cell viability and decreasing levels of P53 and phospho-p38. Our findings suggest that PEDF protects endothelial cells from arsenic-induced VED by increasing NO release and inhibiting apoptosis, where P53 and p38MAPK are its main targets.

Pigment Epithelium-Derived Factor Declines in Response to an Oral Glucose Load and Is Correlated with Vitamin D and BMI but Not Diabetes Status in Children and Young Adults

BACKGROUND

Pigment epithelium-derived factor (PEDF) is associated with obesity and diabetes complications in adults, yet little is known about PEDF in younger individuals. We investigated the relationship between PEDF and various metabolic biomarkers in young healthy volunteers (HV) and similar-aged patients with diabetes (type 1 and type 2).

METHODS

A fasting blood sample was collected in 48 HV, 11 patients with type 1 diabetes (T1D), and 11 patients with type 2 diabetes (T2D) 12-25 years of age. In 9 healthy subjects, PEDF was also serially measured during a frequently sampled oral glucose tolerance test (OGTT).

RESULTS

PEDF was positively correlated with BMI and systolic blood pressure and negatively correlated with vitamin D. Upon multivariable analysis, BMI and vitamin D were independent predictors of PEDF. Prior to adjustment, PEDF was highest in T2D patients (7,168.9 ± 4417.4 ng/mL) and lowest in individuals with T1D (2,967.7 ± 947.1 ng/mL) but did not differ by diagnosis when adjusted for BMI and vitamin D. Among volunteers who underwent an OGTT, PEDF declined by ∼20% in response to an oral glucose load.

CONCLUSION

PEDF was acutely regulated by a glucose load and was correlated with BMI but not with diabetes. The negative correlation with vitamin D, independent of BMI, raises the question whether PEDF plays a compensatory role in bone matrix mineralization.

Neuropeptides, trophic factors, and other substances providing morphofunctional and metabolic protection in experimental models of diabetic retinopathy

Vision is the most important sensory modality for many species, including humans. Damage to the retina results in vision loss or even blindness. One of the most serious complications of diabetes, a disease that has seen a worldwide increase in prevalence, is diabetic retinopathy. This condition stems from consequences of pathological metabolism and develops in 75% of patients with type 1 and 50% with type 2 diabetes. The development of novel protective drugs is essential. In this review we provide a description of the disease and conclude that type 1 diabetes and type 2 diabetes lead to the same retinopathy. We evaluate existing experimental models and recent developments in finding effective compounds against this disorder. In our opinion, the best models are the long-term streptozotocin-induced diabetes and Otsuka Long-Evans Tokushima Fatty and spontaneously diabetic Torii rats, while the most promising substances are topically administered somatostatin and pigment epithelium-derived factor analogs, antivasculogenic substances, and systemic antioxidants. Future drug development should focus on these.

Sirtuin 1-mediated cellular metabolic memory of high glucose via the LKB1/AMPK/ROS pathway and therapeutic effects of metformin

Cellular metabolic memory occurs in diabetic microvascular and macrovascular complications, but the underlying mechanisms remain unclear. Here, we investigate the role of sirtuin 1 (SIRT1) and metformin in this phenomenon. In bovine retinal capillary endothelial cells (BRECs) and retinas of diabetic rats, the inflammatory gene, nuclear factor-κB (NF-κB), and the proapoptotic gene, Bax, induced by hyperglycemia, remained elevated after returning to normoglycemia. BRECs with small interfering RNA-mediated SIRT1 knockdown had increased sensitivity to hyperglycemia stress, whereas SIRT1 overexpression or activation by metformin inhibited the increase of mitochondrial reactive oxygen species-mediated glyceraldehyde-3-phosphate dehydrogenase by poly (ADP-ribose) polymerase (PARP) activity through the upregulation of liver kinase B1/AMP-activated protein kinase (LKB1/AMPK), ultimately suppressing NF-κB and Bax expression. Furthermore, we showed that hyperglycemia led to PARP activation, which in turn may have downregulated SIRT1. Of importance, this study also demonstrated that metformin suppressed the "memory" of hyperglycemia stress in the diabetic retinas, which may be involved in the SIRT1/LKB1/AMPK pathway. Our data suggest that SIRT1 is a potential therapeutic target for the treatment of the cellular metabolic memory, and the use of metformin specifically for such therapy may be a new avenue of investigation in the diabetes field.

Pigment epithelium-derived factor and its phosphomimetic mutant induce JNK-dependent apoptosis and p38-mediated migration arrest

Pigment epithelium-derived factor (PEDF) is a potent endogenous inhibitor of angiogenesis and a promising anticancer agent. We have previously shown that PEDF can be phosphorylated and that distinct phosphorylations differentially regulate its physiological functions. We also demonstrated that triple phosphomimetic mutant (EEE-PEDF), has significantly increased antiangiogenic activity and is much more efficient than WT-PEDF in inhibiting neovascularization and tumor growth. The enhanced antiangiogenic effect was associated with a direct ability to facilitate apoptosis of tumor-residing endothelial cells (ECs), and subsequently, disruption of intratumoral vascularization. In the present report, we elucidated the molecular mechanism by which EEE-PEDF exerts more profound effects at the cellular level. We found that EEE-PEDF suppresses EC proliferation due to caspase-3-dependent apoptosis and also inhibits migration of the EC much better than WT-PEDF. Although WT-PEDF and EEE-PEDF did not affect proliferation and did not induce apoptosis of cancer cells, these agents efficiently inhibited cancer cell motility, with EEE-PEDF showing a stronger effect. The stronger activity of EEE-PEDF was correlated with a better binding to laminin receptors. Furthermore, the proapoptotic and antimigratory activities of WT-PEDF and EEE-PEDF were found regulated by differential activation of two distinct MAPK pathways, namely JNK and p38, respectively. We show that JNK and p38 phosphorylation is much higher in cells treated with EEE-PEDF. JNK leads to apoptosis of ECs, whereas p38 leads to anti-migratory effect in both EC and cancer cells. These results reveal the molecular signaling mechanism by which the phosphorylated PEDF exerts its stronger antiangiogenic, antitumor activities.

Improvement of retinal vascular injury in diabetic rats by statins is associated with the inhibition of mitochondrial reactive oxygen species pathway mediated by peroxisome proliferator-activated receptor gamma coactivator 1alpha

OBJECTIVE

Mitochondrial reactive oxygen species (ROS) plays a key role in diabetic retinopathy (DR) pathogenesis. However, whether simvastatin decreases diabetes-induced mitochondrial ROS production remains uncertain. The aim of this study was to clarify the beneficial effects and mechanism of action of simvastatin against diabetes-induced retinal vascular damage.

RESEARCH DESIGN AND METHODS

Diabetic rats and control animals were randomly assigned to receive simvastatin or vehicle for 24 weeks, and bovine retinal capillary endothelial cells (BRECs) were incubated with normal or high glucose with or without simvastatin. Vascular endothelial growth factor (VEGF) and peroxisome proliferator-activated receptor gamma coactivator 1alpha (PGC-1alpha) in the rat retinas or BRECs were examined by Western blotting and real-time RT-PCR, and poly (ADP-ribose) polymerase (PARP), and p38 MAPK were examined by Western blotting. Mitochondrial membrane potential (Deltapsim) and ROS production were assayed using the potentiometric dye 5,5',6,6'- Tetrachloro1,1',3,3'-tetraethyl-benzimidazolylcarbocyanine iodide (JC-1) or CM-H(2)DCFDA fluorescent probes.

RESULTS

Simvastatin significantly upregulated PGC-1alpha (P < 0.01), subsequently decreased Deltapsim (P < 0.05) and ROS generation (P < 0.01), inhibited PARP activation (P < 0.01), and further reduced VEGF expression (P < 0.01) and p38 MAPK activity (P < 0.01). Those changes were associated with the decrease of retinal vascular permeability, retinal capillary cells apoptosis, and formation of acellular capillaries.

CONCLUSIONS

Simvastatin decreases diabetes-induced mitochondrial ROS production and exerts protective effects against early retinal vascular damage in diabetic rats in association with the inhibition of mitochondrial ROS/PARP pathway mediated by PGC-1alpha. The understanding of the mechanisms of action of statins has important implications in the prevention and treatment of mitochondrial oxidative stress-related illness such as DR.

Pigment epithelium-derived factor as a new marker of metabolic syndrome in Caucasian population

Authors present that serum pigment epithelium derived factor (PEDF) is an independent marker of metabolic syndrome in Caucasianpopulation. PEDF was measured with new ELISA sandwich test. J. Clin. Lab. Anal. 24:17-19, 2010. (c) 2010 Wiley-Liss, Inc.

Potential biological role of poly (ADP-ribose) polymerase (PARP) in male gametes

Maintaining the integrity of sperm DNA is vital to reproduction and male fertility. Sperm contain a number of molecules and pathways for the repair of base excision, base mismatches and DNA strand breaks. The presence of Poly (ADP-ribose) polymerase (PARP), a DNA repair enzyme, and its homologues has recently been shown in male germ cells, specifically during stage VII of spermatogenesis. High PARP expression has been reported in mature spermatozoa and in proven fertile men. Whenever there are strand breaks in sperm DNA due to oxidative stress, chromatin remodeling or cell death, PARP is activated. However, the cleavage of PARP by caspase-3 inactivates it and inhibits PARP's DNA-repairing abilities. Therefore, cleaved PARP (cPARP) may be considered a marker of apoptosis. The presence of higher levels of cPARP in sperm of infertile men adds a new proof for the correlation between apoptosis and male infertility. This review describes the possible biological significance of PARP in mammalian cells with the focus on male reproduction. The review elaborates on the role played by PARP during spermatogenesis, sperm maturation in ejaculated spermatozoa and the potential role of PARP as new marker of sperm damage. PARP could provide new strategies to preserve fertility in cancer patients subjected to genotoxic stresses and may be a key to better male reproductive health.

Protective effect of perindopril on diabetic retinopathy is associated with decreased vascular endothelial growth factor-to-pigment epithelium-derived factor ratio: involvement of a mitochondria-reactive oxygen species pathway

OBJECTIVE

This study aimed to verify whether the decreased vascular endothelial growth factor (VEGF)-to-pigment epithelium-derived factor (PEDF) ratio can serve as an indicator for the protective effect of angiotensin-converting enzyme inhibitors (ACEIs) on diabetic retinopathy (DR) and to investigate the role of mitochondrial reactive oxygen species (ROS) in the downregulated VEGF-to-PEDF ratio.

RESEARCH DESIGN AND METHODS

Diabetic rats and control animals were randomly assigned to receive perindopril or vehicle for 24 weeks, and bovine retinal capillary endothelial cells (BRECs) were incubated with normal or high glucose with or without perindopril. VEGF, PEDF, PPARgamma, and uncoupling protein-2 (UCP-2) in the rat retinas or BREC extracts were examined by Western blotting and real-time RT-PCR. The levels of VEGF and PEDF in cell culture media were examined by ELISA. Mitochondrial membrane potential (Deltapsim) and ROS production were assayed using JC-1 or CM-H2DCFDA.

RESULTS

The VEGF-to-PEDF ratio was increased in the retina of diabetic rats; perindopril lowered the increased VEGF-to-PEDF ratio in diabetic rats and ameliorated the retinal damage. In BRECs, perindopril lowered the hyperglycemia-induced elevation of VEGF-to-PEDF ratio by reducing mitochondrial ROS. We found the decreased ROS production was a result of perindopril-induced upregulation of PPARgamma and UCP-2 expression and the subsequent decrease of Deltapsim.

CONCLUSIONS

It is concluded that the protective effect of ACEI on DR is associated with a decreased VEGF-to-PEDF ratio, which involves the mitochondria-ROS pathway through PPARgamma-mediated changes of UCP-2. This study paves a way for future application of ACEI in treatment of DR.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.

Role of nitrosative stress in the pathogenesis of diabetic vascular dysfunction

Here we overview the role of reactive nitrogen species (nitrosative stress) and associated pathways in the pathogenesis of diabetic vascular complications. Increased extracellular glucose concentration, a principal feature of diabetes mellitus, induces a dysregulation of reactive oxygen and nitrogen generating pathways. These processes lead to a loss of the vascular endothelium to produce biologically active nitric oxide (NO), which impairs vascular relaxations. Mitochondria play a crucial role in this process: endothelial cells placed in increase extracellular glucose respond with a marked increase in mitochondrial superoxide formation. Superoxide, when combining with NO generated by the endothelial cells (produced by the endothelial isoform of NO synthase), leads to the formation of peroxynitrite, a cytotoxic oxidant. Reactive oxygen and nitrogen species trigger endothelial cell dysfunction through a multitude of mechanisms including substrate depletion and uncoupling of endothelial isoform of NO synthase. Another pathomechanism involves DNA strand breakage and activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP). PARP-mediated poly(ADP-ribosyl)ation and inhibition of glyceraldehyde-3-phosphate dehydrogenase importantly contributes to the development of diabetic vascular complications: it induces activation of multiple pathways of injury including activation of nuclear factor kappa B, activation of protein kinase C and generation of intracellular advanced glycation end products. Reactive species generation and PARP play key roles in the pathogenesis of 'glucose memory' and in the development of injury in endothelial cells exposed to alternating high/low glucose concentrations.