Protective effects of vasoactive intestinal peptide against delayed glutamate neurotoxicity in cultured retina

Retinal VIP-amacrine cells: their development, structure, and function

Amacrine cells (ACs) are the most structurally and functionally diverse neuron type in the retina. Different ACs have distinct functions, such as neuropeptide secretion and inhibitory connection. Vasoactive intestinal peptide (VIP) -ergic -ACs are retina gamma-aminobutyric acid (GABA) -ergic -ACs that were discovered long ago. They secrete VIP and form connections with bipolar cells (BCs), other ACs, and retinal ganglion cells (RGCs). They have a specific structure, density, distribution, and function. They play an important role in myopia, light stimulated responses, retinal vascular disease and other ocular diseases. Their significance in the study of refractive development and disease is increasing daily. However, a systematic review of the structure and function of retinal VIP-ACs is lacking. We discussed the detailed characteristics of VIP-ACs from every aspect across species and providing systematic knowledge base for future studies. Our review led to the main conclusion that retinal VIP-ACs develop early, and although their morphology and distribution across species are not the same, they have similar functions in a wide range of ocular diseases based on their function of secreting neuropeptides and forming inhibitory connections with other cells.

Mesenchymal Stem Cell Secretome Enhancement by Nicotinamide and Vasoactive Intestinal Peptide: A New Therapeutic Approach for Retinal Degenerative Diseases

Mesenchymal stem cells (MSC) secrete neuroprotective molecules that may be useful as an alternative to cell transplantation itself. Our purpose was to develop different pharmaceutical compositions based on conditioned medium (CM) of adipose MSC (aMSC) stimulated by and/or combined with nicotinamide (NIC), vasoactive intestinal peptide (VIP), or both factors; and to evaluate in vitro their proliferative and neuroprotective potential. Nine pharmaceutical compositions were developed from 3 experimental approaches: (1) unstimulated aMSC-CM collected and combined with NIC, VIP, or both factors (NIC+VIP), referred to as the aMSC-CM combined composition; (2) aMSC-CM collected just after stimulation with the mentioned factors and containing them, referred to as the aMSC-CM stimulated-combined composition; and (3) aMSC-CM previously stimulated with the factors, referred to as the aMSC stimulated composition. The potential of the pharmaceutical compositions to increase cell proliferation under oxidative stress and neuroprotection were evaluated in vitro by using a subacute oxidative stress model of retinal pigment epithelium cells (line ARPE-19) and spontaneous degenerative neuroretina model. Results showed that oxidatively stressed ARPE-19 cells exposed to aMSC-CM stimulated and stimulated-combined with NIC or NIC+VIP tended to have better recovery from the oxidative stress status. Neuroretinal explants cultured with aMSC-CM stimulated-combined with NIC+VIP had better preservation of the neuroretinal morphology, mainly photoreceptors, and a lower degree of glial cell activation. In conclusion, aMSC-CM stimulated-combined with NIC+VIP contributed to improving the proliferative and neuroprotective properties of the aMSC secretome. Further studies are necessary to evaluate higher concentrations of the drugs and to characterize specifically the aMSC-secreted factors related to neuroprotection. However, this study supports the possibility of improving the potential of new effective pharmaceutical compositions based on the secretome of MSC plus exogenous factors or drugs without the need to inject cells into the eye, which can be very useful in retinal pathologies.

Neuroprotective Peptides in Retinal Disease

In the pathogenesis of many disorders, neuronal death plays a key role. It is now assumed that neurodegeneration is caused by multiple and somewhat converging/overlapping death mechanisms, and that neurons are sensitive to unique death styles. In this respect, major advances in the knowledge of different types, mechanisms, and roles of neurodegeneration are crucial to restore the neuronal functions involved in neuroprotection. Several novel concepts have emerged recently, suggesting that the modulation of the neuropeptide system may provide an entirely new set of pharmacological approaches. Neuropeptides and their receptors are expressed widely in mammalian retinas, where they exert neuromodulatory functions including the processing of visual information. In multiple models of retinal diseases, different peptidergic substances play neuroprotective actions. Herein, we describe the novel advances on the protective roles of neuropeptides in the retina. In particular, we focus on the mechanisms by which peptides affect neuronal death/survival and the vascular lesions commonly associated with retinal neurodegenerative pathologies. The goal is to highlight the therapeutic potential of neuropeptide systems as neuroprotectants in retinal diseases.

Retinoprotective Effects of TAT-Bound Vasoactive Intestinal Peptide and Pituitary Adenylate Cyclase Activating Polypeptide

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) belong to the same peptide family and exert a variety of biological functions. Both PACAP and VIP have protective effects in several tissues. While PACAP is known to be a stronger retinoprotective peptide, VIP has very potent anti-inflammatory effects. The need for a non-invasive therapeutic approach has emerged and PACAP has been shown to be retinoprotective when administered in the form of eye drops as well. The cell penetrating peptide TAT is composed of 11 amino acids and tagging of TAT at the C-terminus of neuropeptides PACAP/VIP can enhance the traversing ability of the peptides through the biological barriers. We hypothesized that TAT-bound PACAP and VIP could be more effective in exerting retinoprotective effects when given in eye drops, by increasing the traversing efficacy and enhancing the activation of the PAC1 receptor. Rats were subjected to bilateral carotid artery occlusion (BCCAO), and retinas were processed for histological analysis 14 days later. The efficiency of the TAT-bound peptides to reach the retina was assessed as well as their cAMP increasing ability. Our present study provides evidence, for the first time, that topically administered PACAP and VIP derivatives (PACAP-TAT and VIP-TAT) attenuate ischemic retinal degeneration via the PAC1 receptor presumably due to a multifactorial protective mechanism.

Retinoprotective Effects of TAT-Bound Vasoactive Intestinal Peptide and Pituitary Adenylate Cyclase Activating Polypeptide

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) belong to the same peptide family and exert a variety of biological functions. Both PACAP and VIP have protective effects in several tissues. While PACAP is known to be a stronger retinoprotective peptide, VIP has very potent anti-inflammatory effects. The need for a non-invasive therapeutic approach has emerged and PACAP has been shown to be retinoprotective when administered in the form of eye drops as well. The cell penetrating peptide TAT is composed of 11 amino acids and tagging of TAT at the C-terminus of neuropeptides PACAP/VIP can enhance the traversing ability of the peptides through the biological barriers. We hypothesized that TAT-bound PACAP and VIP could be more effective in exerting retinoprotective effects when given in eye drops, by increasing the traversing efficacy and enhancing the activation of the PAC1 receptor. Rats were subjected to bilateral carotid artery occlusion (BCCAO), and retinas were processed for histological analysis 14 days later. The efficiency of the TAT-bound peptides to reach the retina was assessed as well as their cAMP increasing ability. Our present study provides evidence, for the first time, that topically administered PACAP and VIP derivatives (PACAP-TAT and VIP-TAT) attenuate ischemic retinal degeneration via the PAC1 receptor presumably due to a multifactorial protective mechanism.

Vinpocetine and Vasoactive Intestinal Peptide Attenuate Manganese-Induced Toxicity in NE-4C Cells

Increased concentration of manganese (Mn) in the brain is known to be associated with excitotoxicity and neuroinflammation. Vinpocetine, an alkaloid derived from the plant Vinca minor L., basically shows its effect via phosphodiesterase inhibition and voltage-dependent Na⁺ channels. Vasoactive intestinal peptide (VIP) has gastrointestinal, vasomotor, muscular, and neuroprotective effects. The aim of this study was to examine the potential protective effects of vinpocetine and VIP against Mn toxicity in NE-4C neural stem cells (NSCs). VIP treatment at 1 μM and vinpocetine treatment at 2 μM concentrations were sufficient to yield maximum protection, and these concentrations were adopted in the following experiments. In this study, Mn treatment significantly increased lactate dehydrogenase (LDH) leakage, reactive oxygen species (ROS) production, and triggered cell death in NE-4C cultures. However, significant reduction in LDH release was observed following vinpocetine or VIP treatments when compared with control. Similar to these findings, vinpocetine or VIP treatments significantly reduced membrane degradation induced by Mn (p < 0.001). Moreover, vinpocetine attenuated Mn-induced decrease of mitochondrial membrane potential. Similarly, proapoptotic protein bax and ROS production significantly decreased in cells after incubation with vinpocetine (p = 0.01) or VIP in the presence of Mn (p < 0.001). Our study provides the evidence that both vinpocetine and VIP may exert protective effects via modulating oxidative stress and apoptosis in Mn-induced neurodegeneration in NE-4C cells.

The Protective Role of PAC1-Receptor Agonist Maxadilan in BCCAO-Induced Retinal Degeneration

A number of studies have proven that pituitary adenylate cyclase activating polypeptide (PACAP) is protective in neurodegenerative diseases. Permanent bilateral common carotid artery occlusion (BCCAO) causes severe degeneration in the rat retina. In our previous studies, protective effects were observed with PACAP1-38, PACAP1-27, and VIP but not with their related peptides, glucagon, or secretin in BCCAO. All three PACAP receptors (PAC1, VPAC1, VPAC2) appear in the retina. Molecular and immunohistochemical analysis demonstrated that the retinoprotective effects are most probably mainly mediated by the PAC1 receptor. The aim of the present study was to investigate the retinoprotective effects of a selective PAC1-receptor agonist maxadilan in BCCAO-induced retinopathy. Wistar rats were used in the experiment. After performing BCCAO, the right eye was treated with intravitreal maxadilan (0.1 or 1 μM), while the left eye was injected with vehicle. Sham-operated rats received the same treatment. Two weeks after the operation, retinas were processed for standard morphometric and molecular analysis. Intravitreal injection of 0.1 or 1 μM maxadilan caused significant protection in the thickness of most retinal layers and the number of cells in the GCL compared to the BCCAO-operated eyes. In addition, 1 μM maxadilan application was more effective than 0.1 μM maxadilan treatment in the ONL, INL, IPL, and the entire retina (OLM-ILM). Maxadilan treatment significantly decreased cytokine expression (CINC-1, IL-1α, and L-selectin) in ischemia. In summary, our histological and molecular analysis showed that maxadilan, a selective PAC1 receptor agonist, has a protective role in BCCAO-induced retinal degeneration, further supporting the role of PAC1 receptor conveying the retinoprotective effects of PACAP.

Intrahypothalamic pituitary adenylate cyclase-activating polypeptide regulates energy balance via site-specific actions on feeding and metabolism

Numerous studies have demonstrated that both the hypothalamic paraventricular nuclei (PVN) and ventromedial nuclei (VMN) regulate energy homeostasis through behavioral and metabolic mechanisms. Receptors for pituitary adenylate cyclase-activating polypeptide (PACAP) are abundantly expressed in these nuclei, suggesting PACAP may be critical for the regulation of feeding behavior and body weight. To characterize the unique behavioral and physiological responses attributed to select hypothalamic cell groups, PACAP was site-specifically injected into the PVN or VMN. Overall food intake was significantly reduced by PACAP at both sites; however, meal pattern analysis revealed that only injections into the PVN produced significant reductions in meal size, duration, and total time spent eating. PACAP-mediated hypophagia in both the PVN and VMN was abolished by PAC1R antagonism, whereas pretreatment with a VPACR antagonist had no effect. PACAP injections into the VMN produced unique changes in metabolic parameters, including significant increases in core body temperature and spontaneous locomotor activity that was PAC1R dependent whereas, PVN injections of PACAP had no effect. Finally, PACAP-containing afferents were identified using the neuronal tracer cholera toxin subunit B (CTB) injected unilaterally into the PVN or VMN. CTB signal from PVN injections was colocalized with PACAP mRNA in the medial anterior bed nucleus of the stria terminalis, VMN, and lateral parabrachial nucleus (LPB), whereas CTB signal from VMN injections was highly colocalized with PACAP mRNA in the medial amygdala and LPB. These brain regions are known to influence energy homeostasis perhaps, in part, through PACAP projections to the PVN and VMN.

VIP, PACAP-38, BDNF and ADNP in NMDA-induced excitotoxicity in the rat retina

PURPOSE

To evaluate the effect of intravitreal injection of N-methyl-D-aspartate (NMDA) on brain-derived neurotrophic factor (BDNF), pituitary adenylate cyclase-activating peptide-38 (PACAP-38), vasoactive intestinal peptide (VIP) and the VIP-associated glial protein activity-dependent neuroprotective protein (ADNP) in the rat retina. These elements have well-documented neuroprotective properties and may thus be integrated in endogenous neuroprotective mechanisms in the retina which break down in NMDA excitotoxicity.

METHODS

A volume of 2 μl of 100 nmol NMDA was intravitreally injected into one eye of rats, the untreated eye served as a control. Time-dependent effects of NMDA on VIP, PACAP-38 and BDNF were detected by radioimmunoassay and ELISA, and the effect on the expression of VIP, PACAP-38 and ADNP was evaluated by quantitative RT-PCR 20 days after NMDA injection. Topical flunarizine served to find out whether the effect of NMDA is counteracted.

RESULTS

Compared to PACAP-38, VIP levels significantly decreased on days 1, 7, 14, 28 and 56 after NMDA injection indicating that VIPergic cells are more vulnerable than PACAP-38-expressing cells. The expression of VIP and ADNP but not of PACAP-38 was found to be reduced, and application of topical flunarizine counteracted the decrease of VIP. BDNF levels significantly increased after days 1 and 3.

CONCLUSION

The early upregulation of BDNF seems to act neuroprotectively and leads to a delay of ganglion cell loss. Although there is no direct evidence, the decrease of VIP and ADNP - the consequence of the presence of NMDA receptors on these peptide-expressing cells - might contribute to the breakdown of endogenous neuroprotective mechanisms given that the decrease of the VIP-related ADNP runs in parallel with the decrease of VIP. Activating and maintaining these mechanisms must be the primary aim in the therapy of diseases with retinal neuronal degeneration.

Pituitary adenylate cyclase activating polypeptide in the retina: focus on the retinoprotective effects

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neurotrophic and neuroprotective peptide that has been shown to exert protective effects against different neuronal injuries, such as traumatic brain and spinal cord injury, models of neurodegenerative diseases, and cerebral ischemia. PACAP and its receptors are present in the retina. In this study, we summarize the current knowledge on retinal PACAP with focus on the retinoprotective effects. Results of histological, immunohistochemical, and molecular biological analysis are reviewed. In vitro, PACAP shows protection against glutamate, thapsigargin, anisomycin, and anoxia. In vivo, the protective effects of intravitreal PACAP treatment have been shown in the following models of retinal degeneration in rats: excitotoxic injury induced by glutamate and kainate, ischemic injury, degeneration caused by UV-A light, optic nerve transection, and streptozotocin-induced diabetic retinopathy. Studying the molecular mechanism has revealed that PACAP acts by activating antiapoptotic and inhibiting proapoptotic signaling pathways in the retina in vivo. These studies strongly suggest that PACAP is an excellent candidate retinoprotective agent that could be a potential therapeutic substance in various retinal diseases.

Gamma-glutamyl 16-diaminopropane derivative of vasoactive intestinal peptide: a potent anti-oxidative agent for human epidermoid cancer cells

We previously demonstrated that the gamma-glutamyl 16 amine derivative of vasoactive intestinal peptide (VIP) acts as structural VIP agonist with affinity and potency higher than VIP. Herein, we have evaluated the effects of VIP and gamma-Gln16-diaminopropane derivative of VIP (VIP-DAP3) on the proliferation and protection from oxidative stress induced by hydrogen peroxide (H2O2) on epidermoid carcinoma cell lines. We have found that 10(-11) M VIP-DAP3 completely antagonized the inhibition induced by H2O2 on both cell proliferation and S-phase distribution while these effects were only partially antagonized by equimolar concentrations of VIP. Moreover, both oxidative stress and intracellular lipid oxidation induced by H2O2 were reduced by VIP and completely antagonized by VIP-DAP3. Thereafter, we have found that H2O2 increased p38 kinase activity and both HSP70 and HSP27 expression. VIP and VIP-DAP3 again antagonized these effects partially or totally, respectively. H2O2 reduced the activity of extracellular signal-regulated kinases Erk-1/2 and Akt, signalling proteins involved in proliferation/survival pathways. Again VIP restored the activity of both kinases while VIP-DAP3 caused indeed an increase of their activity as compared to untreated cells. These data suggest that VIP-DAP3 has a stronger anti-oxidative activity as compared to VIP likely based on its super-agonistic binding on the putative receptor.

Secretoneurin and the tachykinins substance P and neurokinin-A/B in NMDA-induced excitotoxicity in the rat retina

In a recent investigation using the NMDA-excitotoxicity model in the rat retina, we found that, whereas, following intravitreal injection of NMDA, a time-dependent decrease of the levels of a neuropeptide, namely vasoactive intestinal polypeptide (VIP), was fully counteracted by topical treatment with flunarizine eye drops, the levels of pituitary adenylate-cyclase activating peptide-38 (PACAP-38), another neuropeptide, remained unchanged. The aim of the present study was to find out if NMDA causes reduction in the levels of other neuropeptides such as secretoneurin (SN), neurokinin-A/B (NKA/NKB) and substance P (SP), and if so, whether flunarizine has the ability to counteract this effect or prevent such reduction. The reduction of the levels of SN and NKA/NKB 14 days after intravitreal injection of 2 μl of 100 nmol NMDA into one eye was more pronounced than after 7 days; topical flunarizine had a slight counteracting effect, but could not prevent the decrease in the levels of these peptides. Reduction in SP levels after 28 and 56 days was fully counteracted by flunarizine. By enabling a pronounced influx of Ca²+ ions into peptide-expressing cells, NMDA leads to cell death. Since each of these peptides exerts neuroprotective properties in the central nervous system, the drop in their levels caused by acute insult (e.g. NMDA excitotoxicity) or chronic insult (e.g. glaucoma) may cause a breakdown of endogenous neuroprotection in the retina given that these peptides feature neuroprotective properties in the retina as well.

VIP Immunoreactivity in Human Aqueous Humor

PURPOSE

To demonstrate the presence of vasoactive intestinal pep-tide (VIP)-immunoreactive molecule in the human aqueous humor collected from eyes undergoing either cataract or glaucoma surgeries and to identify them asses of molecules responsible for the VIP immunoreactivity.

METHODS

Aqueous humor specimens were collected by parencentesis from nine cataract patients and also from eight patients undergoing glaucoma surgery following the creation of the limbal based conjunctival flap, partial dissection of the scleral flap, and application of mitomycin-C. The aqueous humor specimens were analyzed by radioimmunoassay to determine the level of VIP immunoreactivity. Specimens from 10 other cataract patients were pooled and analyzed for VIP immunoreactivity by Western blot analysis.

RESULTS

Levels of VIP immunoreactivity in aqueous humor of cataract and glaucoma patients were significantly different and were 610 +/- 160 and 260 +/- 64 pg VIP/ml, respectively (p = 0.03), while there was no correlation between the donor age and the level of VIP immunoreactivity. VIP immunoreactivity was detected as a single molecule with a molecular weight of 9000.

CONCLUSIONS

The disease status and the treatments of the eye that led to surgery and procedures applied to the eye immediately before aqueous humor collection, but not the age of the patients, affected the level of VIP immunoreactivity in the aqueous humor. The relationship between the 9000 Da VIP-immunoreactive molecule and the authentic (3326 Da) VIP remains to be studied.

Pituitary adenylate cyclase activating polypeptide is protective in bilateral carotid occlusion-induced retinal lesion in rats

Pituitary adenylate cyclase activating popypeptide (PACAP) is a pleiotropic neuropeptide, exerting neurotrophic and neuroprotective effects in numerous models of in vitro and in vivo nervous injuries. The aim of the present study was to investigate whether PACAP is neuroprotective in ischemic retinal damage. Adult male Wistar rats underwent bilateral carotid occlusion and PACAP was administered unilaterally into the vitreous body immediately following carotid occlusion. Retinas were analyzed three weeks after the injury. It was found that bilateral carotid occlusion led to a severe degeneration of all retinal layers. PACAP treatment significantly ameliorated the carotid occlusion-induced retinal damage: the overall thickness of the retina was significantly more than in control carotid occluded animals and the morphological characteristics of the photoreceptors showed nearly normal appearance. The outer plexiform layer remained discernible and the inner and outer nuclear layers were significantly thicker than in control animals. In summary, our present study provides evidence, for the first time, that PACAP attenuates ischemic retinal degeneration.

Neuroprotective effects of pituitary adenylate cyclase–activating polypeptide (PACAP) in MPP+-induced alteration of translational control in Neuro-2a neuroblastoma cells

Parkinson's disease (PD) and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity are both associated with dopaminergic neuron death in the substantia nigra. Although a variety of evidence has shown that degenerative cells have apoptotic features, the role of apoptosis in disease pathology remains controversial. The 1-methyl-4-phenylpyridinium ion (MPP(+)), a metabolite of MPTP, was recently shown to alter the expression of proteins involved in translational control. The initiation step of translational control is regulated by a cascade of phosphorylation affecting proteins of the antiapoptotic way controlled by mammalian target of rapamycin (mTOR) and of the proapoptotic way controlled by double-stranded RNA protein-dependent kinase (PKR). A study showed that MPP(+) induced an increase in eIF2alpha phosphorylation, leading to inhibition of protein synthesis.

THE AIMS OF OUR STUDY WERE

(1) to assess the effects of MPP(+) toxicity on molecular factors of PKR and mTOR signaling pathways in murine neuroblastoma cells, and (2) to examine the ability of VIP and PACAP peptides to counteract the MPP(+) toxicity. Our findings showed that MPP(+) induced phosphorylation of eIF2alpha and significantly reduced the expression of phosphorylated mTOR, p70S6K, eIF4E, and 4E-BP1, suggesting its toxicity in controlling protein synthesis. Furthermore, the VIP peptide had no effect on either the PKR or the mTOR signaling pathway. On the contrary, the PACAP 27 neuropeptide prevented MPP(+)-induced eIF2alpha phosphorylation and blocked MPP(+) toxicity in molecular factors of the mTOR pathway. And last, PACAP 27 seemed to protect Neuro-2a cells from the apoptotic process as assessed by the decreased nuclear condensation after DAPI staining. These results could open new paths of research of PACAP in PD.

Vasoactive intestinal peptide modulates luteinizing hormone subunit gene expression in the anterior pituitary in female rat

The direct monosynaptic pathway which exists between vasoactive intestinal peptide (VIP) and GnRH neurons in the hypothalamic preoptic area provides a neuroanatomical background for the modulatory effects of VIP exerted on GnRH neurons activity. Though central microinjection of VIP revealed its involvement in the modulation of LH release pattern, there is a lack of data concerning a possible VIP influence on the alpha and LHbeta subunit gene expression in the pituitary gland. Using a model based on intracerebroventricular pulsatile peptide(s) microinjections (1 pulse/h [10 microl/5 min] over 5 h) the effect of exogenous VIP (5 nM dose) microinjection on subunits mRNA content in ovariectomized/oestrogen-pretreated rats was studied. Subsequently, to obtain data concerning the involvement of GnRH and VIP receptor(s) in the regulation of alpha and LHbeta subunit mRNA expression, OVX/estrogen-primed rats received a pulsatile microinjections of 5 nM VIP with 3 nM antide (GnRH receptor antagonist) or 5 nM VIP with 15 nM VIP 6-28 (VIP receptor antagonist). In this case, substances were given separately with a 30 min lag according to which each antagonist pulse preceded a VIP pulse. Northern-blot analysis revealed that VIP microinjection resulted in a decreased alpha and LHbeta mRNA content in pituitary gland and this effect was dependent on GnRH receptor activity. Moreover, obtained results indicated that centrally administered VIP might operate through its own receptor(s) because a receptor antagonist, VIP 6-28, blocked the inhibitory effect of VIP exerted on both LH subunit mRNA content and LH release.

Neuroprotection by cAMP: Another brick in the wall

Programmed cell death occurs in the nervous system both in normal development as well as in pathologic conditions, and is a key issue related to both brain repair and neurodegenerative diseases. Modulation of cell death in the nervous system may involve neurotrophic factors and other peptides, neurotransmitters and neuromodulators, that activate various signal transduction pathways, which in turn interact with the cell death execution machinery. Here we discuss the role of the second messenger cyclic adenosine 3'5'-monophosphate (cAMP) in cell death, and summarize current evidence that cAMP is a nodal point of neuroprotective signaling pathways.

Neuroprotection of Cerebrolysin in tissue culture models of brain ischemia: post lesion application indicates a wide therapeutic window

All attempts to reduce neuronal damage after acute brain ischemia by the use of neuroprotective compounds have failed to prove efficacy in clinical trials so far. One of the main reasons might be the relatively narrow time window for intervention. In this study 2 different tissue culture models of ischemia, excitotoxic lesion by the use of glutamate and oxygen-glucose deprivation (OGD), were used to investigate the effects of delayed application of Cerebrolysin (Cere) on neuronal survival. This drug consists of low molecular weight peptides with neuroprotective and neurotrophic properties similar to naturally occurring growth factors. After both types of lesion, acute as well as delayed treatment with Cere resulted in a dose dependent and significant rescue of neurons. In the model of excitotoxic cell death significant drug effects were found even when the treatment started with a delay of 96 hours after addition of glutamate. In the OGD model pronounced effects were found after 48 hours delay of treatment, and even after 72 hours a small but significant rescue of neurons was detected. The neuroprotective effects of a single addition of Cerebrolysin to the culture medium resulted in significant protection until end of the experiments which was up to 2 weeks after the initial lesion. A shift of the efficacious dosages from low to high concentrations indicates that most likely active compounds are used up, indicating that multiple dosing might even increase the effect size. In conclusion the results indicate that Cere displays a relatively wide therapeutic time window which might be explained by a combination of acute neuroprotective properties and neurotrophic efficacy.

Degree of damage compensation by various PACAP treatments in monosodium glutamate-induced retinal degeneration

Pituitary adenylate cyclase activating polypeptide (PACAP) has been shown to be neuroprotective in retinal ischemia and monosodium L-glutamate (MSG)-induced retinal degeneration. Here we describe how different MSG treatments (1x and 3x application) cause retinal damage and finally lead to the destruction of the entire inner retina and how PACAP attenuates this effect. Newborn rats from both sexes were injected subcutaneously with 2 mg/g bodyweight MSG on postnatal days 1, 5 and 9. The left eye was left intact while we injected 5 microl PACAP38 solution (100 pmol) into the vitreous of the right eye with a Hamilton syringe at the time of (i) the first, (ii) the first two or (iii) all three MSG injections. Histological analysis has shown that the above described MSG treatment caused the entire inner plexiform layer (IPL) to degenerate, and the inner nuclear (INL) and ganglion cell layers (GCL) seemed fused. One time PACAP38 treatment at the first MSG application did not change the degenerative capacity of MSG. However, if animals received PACAP38 into the vitreous of the eye at the first 2 or all 3 times, a substantial protective effect could be observed. The IPL remained well discernible, the INL retained 2-3 cell rows and the number of cells in the GCL was substantially higher than in the MSG-treated retinas, and was not significantly different from that observed in the control tissue. We conclude that (i) 2 or 3 times PACAP treatment attenuates retinal degeneration; (ii) one PACAP treatment does not provide protection against repeated excitotoxic insults, and (iii) repeated application of PACAP under these experimental conditions may lead to a primed state in which further neurotoxic insults are ineffective.

Control of programmed cell death by neurotransmitters and neuropeptides in the developing mammalian retina

It has long been known that a barrage of signals from neighboring and connecting cells, as well as components of the extracellular matrix, control cell survival. Given the extensive repertoire of retinal neurotransmitters, neuromodulators and neurotrophic factors, and the exhuberant interconnectivity of retinal interneurons, it is likely that various classes of released neuroactive substances may be involved in the control of sensitivity to retinal cell death. The aim of this article is to review evidence that neurotransmitters and neuropeptides control the sensitivity to programmed cell death in the developing retina. Whereas the best understood mechanism of execution of cell death is that of caspase-mediated apoptosis, current evidence shows that not only there are many parallel pathways to apoptotic cell death, but non-apoptotic programs of execution of cell death are also available, and may be triggered either in isolation or combined with apoptosis. The experimental data show that many upstream signaling pathways can modulate cell death, including those dependent on the second messengers cAMP-PKA, calcium and nitric oxide. Evidence for anterograde neurotrophic control is provided by a variety of models of the central nervous system, and the data reviewed here indicate that an early function of certain neurotransmitters, such as glutamate and dopamine, as well as neuropeptides such as pituitary adenylyl cyclase-activating polypeptide and vasoactive intestinal peptide is the trophic support of cell populations in the developing retina. This may have implications both regarding the mechanisms of retinal organogenesis, as well as pathological conditions leading to retinal dystrophies and to dysfunctional cellular behavior.

Vasoactive intestinal peptide and pituitary adenylate cyclase-activating polypeptide attenuate the cigarette smoke extract-induced apoptotic death of rat alveolar L2 cells

Chronic obstructive pulmonary disease is a major clinical disorder usually associated with cigarette smoking. A central feature of chronic obstructive pulmonary disease is inflammation coexisting with an abnormal protease/antiprotease balance, leading to apoptosis and elastolysis. In an in vitro study of rat lung alveolar L2 cells, cigarette smoke extract (CSE) induced apoptotic cell death. Exposure of L2 cells to CSE at a concentration of 0.25% resulted in a 50% increase of caspase-3 and matrix metalloproteinase (MMP) activities. Specific inhibitors for caspases and MMPs attenuated the cytotoxicity of CSE. RT-PCR amplification identified VPAC2 receptors in L2 cells. A radioligand-binding assay with (125)I-labeled vasoactive intestinal peptide (VIP) found high affinity and saturable (125)I-labeled VIP-binding sites in L2 cells. VIP and pituitary adenylate cyclase-activating polypeptide (PACAP27) were approximately equipotent for both VIP receptor binding and stimulation of cAMP production in L2 cells. Both neuropeptides, at concentrations higher than 10(-13) m, produced a concentration-dependent inhibition of CSE-induced cell death in L2 cells. VIP, at 10(-7) m, reduced CSE-stimulated MMP activity and caspase-3 activation. The present study has shown that VIP and PACAP27 significantly attenuate the cytotoxicity of CSE through the activation of VPAC2 receptor, and the protective effect of VIP may partly be the result of a reduction in the CSE-induced stimulation of MMPs and caspases.

Glucagon-like peptide 1 modulates calcium responses to glutamate and membrane depolarization in hippocampal neurons

Glucagon-like peptide 1 (GLP-1) activates receptors coupled to cAMP production and calcium influx in pancreatic cells, resulting in enhanced glucose sensitivity and insulin secretion. Despite evidence that the GLP-1 receptor is present and active in neurons, little is known of the roles of GLP-1 in neuronal physiology. As GLP-1 modulates calcium homeostasis in pancreatic beta cells, and because calcium plays important roles in neuronal plasticity and neurodegenerative processes, we examined the effects of GLP-1 on calcium regulation in cultured rat hippocampal neurons. When neurons were pre-treated with GLP-1, calcium responses to glutamate and membrane depolarization were attenuated. Whole-cell patch clamp analyses showed that glutamate-induced currents and currents through voltage-dependent calcium channels were significantly decreased in neurons pre-treated with GLP-1. Pre-treatment of neurons with GLP-1 significantly decreased their vulnerability to death induced by glutamate. Acute application of GLP-1 resulted in a transient elevation of intracellular calcium levels, consistent with the established effects of GLP-1 on cAMP production and activation of cAMP response element-binding protein. Collectively, our findings suggest that, by modulating calcium responses to glutamate and membrane depolarization, GLP-1 may play important roles in regulating neuronal plasticity and cell survival.

Complex array of cytokines released by vasoactive intestinal peptide

A complex mixture of five cytokines has been shown to be released by vasoactive intestinal peptide (VIP). Cytokines were measured in paired samples of culture medium and astroglial cytosol by capillary electrophoresis. This is the first description of VIP-mediated release for TNF-alpha, IL-3, G-CSF and M-CSF from astrocyte cultures. Kinetic studies after VIP treatment demonstrated a gradual but incomplete depletion of cytosolic cytokine levels, with differences observed among the cytokines. Significant increases in release were apparent within 15-30 min for all cytokines. As the recognized VIP receptors (VPAC1 and VPAC2) are linked to adenylate cyclase and also interact with pituitary adenylate cyclase activating polypeptide-38 (PACAP-38), both this homologous peptide and 8-bromo cAMP were investigated and compared to VIP-mediated release. Treatment with 1 mM 8-bromo cAMP produced cytokine release similar in amount to 0.1 nM PACAP-38, but significantly less (<50%) in comparison to 0.1 nM VIP. PACAP-38 and VIP exhibited similar EC(50)'s for the release of G-CSF and TNF-alpha; however, the maximal release was 4-6 times greater for VIP than for PACAP-38. This similarity in potency suggested a VPAC-like receptor; however, the greater efficacy for VIP in comparison to PACAP-38, combined with a lack of cAMP production at subnanomolar concentrations of VIP, suggested a mechanism not currently associated with VPAC receptors. For M-CSF, IL-3 and IL-6, the EC(50)'s of VIP were 3-30 times more potent than those of PACAP-38 in producing release. These studies suggested that multiple mechanisms mediate cytokine release in astrocytes: (1) a low efficacy release produced by PACAP-38 that is cAMP-mediated and (2) a high efficacy, VIP-preferring mechanism that was not linked to cAMP. In summary, subnanomolar concentrations of VIP released a complex array of cytokines from astrocytes that may contribute to the mitogenic and neurotrophic properties of this neuropeptide in the central nervous system.

Isolation of total-RNA from formalin-fixed rat retina

The aim of this project was to establish a method for the purification of total-RNA from fixed rat-retina. Two different established methods were used for RNA purification, and successful isolation was verified with RT-PCR for amplification of beta-actin (two different product-lengths) and subsequent gel-electrophoresis. Total-RNA was successfully isolated from fixed rat-retina. The house keeping gene, beta-actin could be detected after fixing the retina either with 1% formalin or with 4% paraformaldehyde (PFA). Hexamer-primer based RT-PCR gave better results than the oligo-d(T)-primer based RT-PCR method. Both the 698 and 225 bp beta-actin-fragments could be successfully amplified, where amplification of the latter was more efficient. This approach shows that tissue fixation prior to RNA-isolation facilitates the rapid isolation of undamaged RNAs in tissues such as the retina, which are known to yield low levels of RNA and are vulnerable to RNases.

The neuropeptide PACAP attenuates beta-amyloid (1-42)-induced toxicity in PC12 cells

Pituitary adenylate cyclase activating polypeptide (PACAP) modulates neurotransmission in the central and peripheral nervous systems. In vitro and in vivo studies have shown the protective effects of PACAP against neuronal damage induced by ischemia and agonists of NMDA-type glutamate receptors. Here, we demonstrated that PACAP also protected against neuronal toxicity induced by beta-amyloid (Abeta) peptide, aggregation of which is a causative factor for Alzheimer's disease. PACAP (10(-9)M) rescued 80% of decreased cell viability and 50% of elevated caspase-3 activity that resulted from exposure of PC12 cells to Abeta. PACAP was at least 10(4)-fold more effective than other neuropeptides including vasoactive intestinal peptide (VIP) and humanin, which correlated with the level of cAMP accumulation. Thus, our results suggested that PACAP attenuates Abeta-induced cell death in PC12 cells through an increase in cAMP and that caspase-3 deactivation by PACAP is involved in the signaling pathway for this neuroprotection.

Pituitary adenylate cyclase-activating polypeptide and vasoactive intestinal peptide attenuate glutamate-induced nNOS activation and cytotoxicity

Both vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) act as neurotransmitters in the central and peripheral nervous systems. Attention has been focused on these neuropeptides because among their numerous biological activities, they have been confirmed to show neuroprotective effects against ischemia and glutamate-induced cytotoxicity. It is well established that glutamate has excitatory effects on neuronal cells, and that excessive glutamate shows potent neurotoxicity, especially in neuronal nitric oxide synthase-containing neurons. Glutamate stimulates the production of nitric oxide (NO) in neurons, and the NO generated is tightly associated with the delayed death of neurons. We examined the effects of these neuropeptides on the glutamate-induced neural actions using PC12 cells, and we confirmed the important activities of PACAP/VIP on the production of NO as well as the delayed cell death stimulated by glutamate.

PACAP protects neuronal PC12 cells from the cytotoxicity of human prion protein fragment 106-126

Misfolding of the prion protein yields amyloidogenic isoforms, and it shows exacerbating neuronal damage in neurodegenerative disorders including prion diseases. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) potently stimulate neuritogenesis and survival of neuronal cells in the central nervous system. Here, we tested these neuropeptides on neurotoxicity in PC12 cells induced by the prion protein fragment 106-126 [PrP (106-126)]. Concomitant application of neuropeptide with PrP(106-126) (5x10(-5) M) inhibited the delayed death of neuron-like PC12 cells. In particular, PACAP27 inhibited the neurotoxicity of PrP(106-126) at low concentrations (>10(-15) M), characterized by the deactivation of PrP(106-126)-stimulated caspase-3. The neuroprotective effect of PACAP27 was antagonized by the selective PKA inhibitor, H89, or the MAP kinase inhibitor, U0126. These results suggest that PACAP27 attenuates PrP(106-126)-induced delayed neurotoxicity in PC12 cells by activating both PKA and MAP kinases mediated by PAC1 receptor.

Existence of ionotropic glutamate receptor subtypes in cultured rat retinal ganglion cells obtained by the magnetic cell sorter method and inhibitory effects of 20-hydroxyecdysone, a neurosteroid, on the glutamate response

Glutamate and neurosteroids are known to exist in retinal ganglion cells (RGC). Therefore, patch clamp studies using the whole-cell recording method were performed to determine whether or not ionotropic glutamate receptor subtypes, i.e., N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate receptors, were present on RGC obtained by the magnetic cell sorter (MACS) method and cultures. In addition, the effects of 20-hydroxyecdysone (20-HE), a neurosteroid, on inward currents induced by NMDA, AMPA and kainate were examined at a holding potential of -60 mV. The current-voltage relationship for NMDA in the presence of glycine and Mg2+-free, as well as those for AMPA and kainate were linear, with a reversal potential of around 0 mV. NMDA-induced currents were blocked by MK-801, while both AMPA- and kainate-induced currents were blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Application of 20-HE in the bath resulted in significant inhibitions on NMDA-, AMPA- and kainate-induced currents. Thus, NMDA, AMPA and kainate receptors were confirmed to exist on MACS-separated cultured RGC. Moreover, 20-HE inhibited NMDA receptor-mediated currents most prominently and AMPA- and kainate-mediated currents moderately, suggesting that neurosteroids may be playing a role in modulating glutamate-mediated transmission in RGC, and 20-HE might be useful for preventing glutamate neurotoxicity.

VIP stimulation of cAMP production in corneal endothelial cells in tissue and organ cultures

PURPOSE

To demonstrate that vasoactive intestinal peptide (VIP), an immunosuppressive factor found in the aqueous humor, is a modulator of the corneal endothelium (CE) stimulating its intracellular cAMP production.

METHODS

Rabbit CE cells in cell culture and CE cells in cornea cup organ cultures established from bovine and human donor eyes were treated with VIP at varying concentrations (0, 10(-11)-10(-6) mol/L) for a constant time (4 minutes) or varying times (1, 3.25, 10, 15 minutes) at a constant concentration (1 x 10(-6) mol/L). Intracellular cAMP was extracted and its concentrations were determined by radioimmunoassay. Agonists that are known to modulate the intracellular cAMP concentrations of target cells were allowed to react with cultured rabbit CE cells at 1 x 10(-6) mol/L for 4 minutes.

RESULTS

Vasoactive intestinal peptide stimulated the intracellular cAMP production in CE cells in a dose- and time-dependent manner. At concentrations lower than 10(-9) mol/L, VIP showed little effect. Treatment with 10(-8), 10(-7), and 10(-6) mol/L VIP for 4 minutes, however, increased the intracellular cAMP by 5.7-, 12.3-, and 9.5-fold, respectively, compared with the basal level in rabbit CE cell cultures, and by 19.5-, 38.7-, and 23.3-fold, respectively, in CE cells in bovine cornea cups. The effect of VIP was confirmed in two pairs of donor human corneas in which an average of 2.7-fold stimulation by 5 x 10(-7) mol/L was observed. Treatment of rabbit CE cells with 1 x 10(-6) mol//L VIP for 1 to 15 minutes elevated the intracellular cAMP level by six- to 69-fold. Among the agonists tested, alpha-melanocyte-stimulating hormone and glucagon were not effective, whereas l-isoproterenol and prostaglandin E1 were capable of stimulating the intracellular cAMP levels in rabbit CE cells.

CONCLUSIONS

The current study demonstrated that VIP stimulated cAMP production in CE cells, similar to that shown previously in trabecular meshwork and nonpigmented ciliary epithelial cells. Tissues bathed in the aqueous humor are thus responsive to VIP modulation.

Attenuation by PACAP of glutamate-induced neurotoxicity in cultured retinal neurons

The effects of pituitary adenylate cyclase activating polypeptides (PACAPs: PACAP27, PACAP38) on glutamate-induced neurotoxicity were examined using cultured retinal neurons obtained from 3- to 5-day old Wistar rats. Cell viability was evaluated by double staining with fluorescein diacetate and propidium iodide. Effects of PACAPs on the increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) in retinal neurons was investigated using the Ca(2+) image analyzing system with fura-2. The cAMP contents and the mitogen-activated protein (MAP) kinase activity in retinal cultures were measured by radioimmunoassay. Concomitant application of PACAPs (10 nM-1 microM) with glutamate (1 mM) for 10 min inhibited the delayed death of retinal neurons, which was observed 24 h after glutamate (1 mM) treatment in a dose-dependent manner. Protection by PACAPs (100 nM) against glutamate-induced neurotoxicity was antagonized by PACAP6-38 (1 microM), a PACAP antagonist, and H-89 (1 microM), a protein kinase A (PKA) inhibitor. However, PACAPs did not affect the glutamate-induced increase in [Ca(2+)](i), but PACAPs (1-100 nM) increased the cAMP levels in a dose-dependent manner. In addition, activation of MAP kinase by PACAP38 (1 microM) was inhibited by simultaneous application with H-89 (1 microM). These findings suggest that PACAPs attenuate glutamate-induced delayed neurotoxicity in cultured retinal neurons by activating MAP kinase through the activation of cAMP-stimulated PKA.

Rat retinal ganglion cells culture enriched with the magnetic cell sorter

The magnetic cell sorter (MACS) technique was applied to isolate retinal ganglion cells (RGCs) for culture. RGCs were labeled retrogradely with 1.1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Dil). Subsequently retinal cell suspensions were incubated with biotinylated anti-rat Thy-1 antibody and MACS Streptavidin MicroBeads, and then applied onto the column in the magnetic fields. Cells attached on the column were flashed out without magnetism and plated on glass cover slips. RGCs were enriched to 31.0% of all cells with MACS from 0.55% before applying onto the magnetic column. Mean diameters of Dil-labeled cells were significantly larger than those of unlabeled cells. All cells with soma diameter over 11 microm were labeled. The number of viable RGCs were counted in the 10 fields of six cultures at a magnification of x200; the mean numbers on the 2nd, 7th and 14th culture-day were 53+/-3, 24+/-2 and 21+/-3, respectively (mean +/- SEM, n = 6). Thus, the MACS technique was confirmed to be useful for enrichment of RGCs and long-term study of cultured RGCs.