vasoactive-intestinal-peptide and Diabetic-Retinopathy

Diabetic macular edema (DME), characterized by an increase of thickness in the eye macular area, is due to breakdown of the blood-retinal barrier (BRB). Hypoxia plays a key role in the progression of this pathology by activating the hypoxia-inducible factors. In the last years, various studies have put their attention on the role of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) in retinal dysfunction. However, until now, no study has investigated their protective role against the harmful combined effect of both hyperglycemia and hypoxia on outer BRB. Therefore, in the present study, we have analyzed the role of these peptides on permeability, restoration of tight junctions expression and inhibition of hyperglycemia/hypoxia-induced apoptosis, in an experimental in vitro model of outer BRB. Our results have demonstrated that the peptides' treatment have restored the integrity of outer BRB induced by cell exposure to hyperglycemia/hypoxia. Their effect is mediated through the activation of phosphoinositide 3 kinase (PI3K)/Akt and mammalian mitogen activated protein kinase/Erk kinase (MAPK/ERK) signaling pathways. In conclusion, our study further clarifies the mechanism through which PACAP and VIP perform the beneficial effect on retinal damage induced by hyperglycemic/hypoxic insult, responsible of DME progression. J. Cell. Physiol. 232: 1079-1085, 2017. © 2016 Wiley Periodicals, Inc.

Topics: Apoptosis; Blood-Retinal Barrier; Cell Hypoxia; Cell Line; Cell Membrane Permeability; Cell Survival; Diabetic Retinopathy; Electric Impedance; Humans; Hyperglycemia; Macular Edema; Mitogen-Activated Protein Kinase Kinases; Phosphatidylinositol 3-Kinases; Pituitary Adenylate Cyclase-Activating Polypeptide; Proto-Oncogene Proteins c-akt; Signal Transduction; Tight Junctions; Vasoactive Intestinal Peptide; Zonula Occludens-1 Protein

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) exert a protective role against retinal injuries, including diabetic macular edema (DME). The macular damage is induced by hyperglycemia, which damages vessels supplying blood to the retina and induces hypoxia. The microenvironmental changes stimulate the expression of hypoxia-inducible factors (HIFs), which promote the choroidal endothelial cell transmigration across the retinal pigmented epithelium (RPE) into neurosensory retina, where they proliferate into new vessels under stimulation of the vascular endothelial growth factor (VEGF). In the present study, we have investigated whether PACAP and VIP prevent retinal damage by modulating the expression of HIFs, VEGF, and its receptors. In accord to our hypothesis, we have shown that both peptides are able to significantly reduce HIF-1α and increase HIF-3α expression in ARPE-19 cells exposed to hyperglycemic/hypoxic insult. This effect is also related to a reduction of VEGF and its receptors expression. Moreover, both peptides also reduce the activation of p38 mitogen-activated protein kinase (MAPK), a pro-apoptotic signaling pathway, which is activated by VEGFR-1 and 2 receptors. In conclusion, our study has further elucidated the protective role performed by PACAP and VIP, against the harmful combined effect of hyperglycemia/hypoxia characterizing the DME microenvironment. J. Cell. Physiol. 232: 1209-1215, 2017. © 2016 Wiley Periodicals, Inc.

Topics: Apoptosis Regulatory Proteins; Basic Helix-Loop-Helix Transcription Factors; Cell Hypoxia; Cell Line; Diabetic Retinopathy; Enzyme Activation; Humans; Hyperglycemia; Hypoxia-Inducible Factor 1, alpha Subunit; Macular Edema; Models, Biological; p38 Mitogen-Activated Protein Kinases; Pituitary Adenylate Cyclase-Activating Polypeptide; Repressor Proteins; Retinal Pigment Epithelium; Vascular Endothelial Growth Factor Receptor-1; Vascular Endothelial Growth Factor Receptor-2; Vasoactive Intestinal Peptide

Little knowledge exists about how neurotransmitters behave in the diabetic retina. In this study, the authors measured the concentration of two neuropeptides, substance P and vasoactive intestinal polypeptide, in the streptozotocin-induced diabetic rat retina in a time-dependent manner.. The retinas of 1-, 3-, 5-, 8-, and 12-week diabetic rats were processed using a highly sensitive radioimmunoassay for both substance P and vasoactive intestinal polypeptide. Furthermore, the peptide-immunoreactivities were characterized by high-pressure liquid chromatography.. Substance P and vasoactive intestinal polypeptide were found to be significantly reduced with a maximum decrease of 28.6% (+/-6.7) and 64.5% (+/-10.7) after 5 weeks, respectively. The peptide-immunoreactivities were found in a major peak coeluting with the synthetic peptides indicating that the quantitative values measured by radioimmunoassay represent the authentic peptides.. The reduction of substance P and vasoactive intestinal polypeptide is in clear contrast to the amino acid transmitters GABA and glycine, which have been shown to be elevated in this early stage of diabetic retinopathy. This finding is important for three reasons: First, the decrease may result in reduced excitability of inner retinal neurons, as both peptides are known to modulate the excitability of these neurons; second, the decrease may be the consequence of a depressing and/or damaging effect by excitotoxins; and third, it may help explain why neovascularizations do not occur in this animal model, although VEGF is massively upregulated, as substance P is a very potent vascular growth factor.

Topics: Animals; Chromatography, High Pressure Liquid; Diabetes Mellitus, Experimental; Diabetic Retinopathy; Male; Radioimmunoassay; Rats; Rats, Sprague-Dawley; Substance P; Time Factors; Vasoactive Intestinal Peptide

Topics: Diabetes Mellitus; Diabetic Retinopathy; Female; Humans; Male; Neutrophils; Vasoactive Intestinal Peptide