Inhibition of murine embryonic growth by human immunodeficiency virus envelope protein and its prevention by vasoactive intestinal peptide and activity-dependent neurotrophic factor

Targeting VIP and PACAP receptor signalling: new therapeutic strategies in multiple sclerosis

MS (multiple sclerosis) is a chronic autoimmune and neurodegenerative pathology of the CNS (central nervous system) affecting approx. 2.5 million people worldwide. Current and emerging DMDs (disease-modifying drugs) predominantly target the immune system. These therapeutic agents slow progression and reduce severity at early stages of MS, but show little activity on the neurodegenerative component of the disease. As the latter determines permanent disability, there is a critical need to pursue alternative modalities. VIP (vasoactive intestinal peptide) and PACAP (pituitary adenylate cyclase-activating peptide) have potent anti-inflammatory and neuroprotective actions, and have shown significant activity in animal inflammatory disease models including the EAE (experimental autoimmune encephalomyelitis) MS model. Thus, their receptors have become candidate targets for inflammatory diseases. Here, we will discuss the immunomodulatory and neuroprotective actions of VIP and PACAP and their signalling pathways, and then extensively review the structure–activity relationship data and biophysical interaction studies of these peptides with their cognate receptors.

VIP, from gene to behavior and back: summarizing my 25 years of research

Vasoactive intestinal peptide (VIP) is an interesting example of a 28-amino acid neuropeptide that is abundantly expressed in discrete brain regions/neurons and hence may contribute to brain function. This short review summarizes my own point of view and encompasses 25 years of work and over 100 publications targeting the understanding of VIP production and biological activity. The review starts with our original cloning of the VIP gene, it then continues to discoveries of regulation of VIP synthesis and the establishment of the first VIP transgenic mice. The review ends with the identification of novel VIP analogs that helped decipher VIP's important role during development, in regulation of the biological clock(s) and diurnal rhythms, sexual activity, learning and memory as well as social behavior, and cancer. This review cites only articles that I have coauthored and gives my own perspective of this exciting ever-growing field.

Regardless of genotype, offspring of VIP-deficient female mice exhibit developmental delays and deficits in social behavior

Pharmacological studies indicate that vasoactive intestinal peptide (VIP) may be necessary for normal embryonic development in the mouse. For example, VIP antagonist treatment before embryonic day 11 resulted in developmental delays, growth restriction, modified adult brain chemistry and reduced social behavior. Here, developmental milestones, growth, and social behaviors of neonates of VIP-deficient mothers (VIP +/-) mated to VIP +/- males were compared with the offspring of wild type mothers (VIP +/+) mated to VIP +/+ and +/- males, to assess the contributions of both maternal and offspring VIP genotype. Regardless of their own genotype, all offsprings of VIP-deficient mothers exhibited developmental delays. No delays were seen in the offspring of wild type mothers, regardless of their own genotype. Body weights were significantly reduced in offspring of VIP-deficient mothers, with VIP null (-/-) the most affected. Regardless of genotype, all offspring of VIP-deficient mothers expressed reduced maternal affiliation compared with wild type offspring of wild type mothers; +/- offspring of wild type mothers did not differ in maternal affiliation from their wild type littermates. Play behavior was significantly reduced in all offsprings of VIP-deficient mothers. Maternal behavior did not differ between wild type and VIP-deficient mothers, and cross-fostering of litters did not change offspring development, indicating that offspring deficits were induced prenatally. This study illustrated that the VIP status of a pregnant mouse had a greater influence on the growth, development and behavior of her offspring than the VIP genotype of the offspring themselves. Deficiencies were apparent in +/+, +/- and -/- offspring born to VIP-deficient mothers; no deficiencies were apparent in +/- offspring born to normal mothers. These results underscore the significant contribution of the uterine environment to normal development and indicate a potential usefulness of the VIP knockout mouse in furthering the understanding of neurodevelopmental disorders with social behavior deficits such as autism.

Clinical Outcomes Improve with Highly Active Antiretroviral Therapy in Vertically HIV Type‐1–Infected Children

Background. Use of antiretroviral therapy has resulted in a decrease in morbidity and mortality rates in human immunodeficiency virus type 1 (HIV-1)-infected children.Methods. We performed a retrospective study involving 427 children to determine the effectiveness of different antiretroviral therapy protocols on clinical outcome. The follow-up period was divided into 5 calendar periods (CPs): CP1 (1980-1989), before antiretroviral therapy was administered; CP2 (1990-1993), when monotherapy was administered; CP3 (1994-1996), when combined therapy was administered; CP4 (1997-1998), when </=50% of children were receiving highly active antiretroviral therapy (HAART); and CP5 (1999-2003), when >/=60% of children were receiving HAART.Results. Children experienced a progressive increase in the CD4(+) cell count and decrease in the viral load from 1997 onwards. A lower number of AIDS cases and deaths occurred during CP5 than during the other CPs (P<.01), with a relative risk of an absence of AIDS of >20 and a relative risk of survival of >30. The AIDS rate was >50% in CP1; we observed a very strong decrease to 14% in CP2, to 16% in CP3, to 7% in CP4, and to 2% in CP5. The mortality rates in CP2 and CP3 were >6% and thereafter decreased to 0.5% in CP5. The relative risks for no hospital admission in CP4 and CP5 were >3.5. The total rates of hospital admission in CP1, CP2, and CP3 were >30%; we observed a decrease in CP4 and CP5. The duration of hospitalization decreased during the follow-up period, and it was higher in CP1 (~30 days) than in the other periods.Conclusions. We observed that HAART produces a decrease in adverse clinical outcomes (i.e., hospital admission, AIDS, and death) in children with vertical HIV-1 infection in Madrid, Spain.

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Effects of pituitary adenylate cyclase activating polypeptide in a rat model of traumatic brain injury

Pituitary adenylate cyclase activating polypeptide (PACAP) is a widely distributed neuropeptide that has numerous different actions. Recent studies have shown that PACAP exerts neuroprotective effects not only in vitro but also in vivo, in animal models of global and focal cerebral ischemia, Parkinson's disease and axonal injuries. Traumatic brain injury has an increasing mortality and morbidity and it evokes diffuse axonal injury which further contributes to its damaging effects. The aim of the present study was to examine the possible neuroprotective effect of PACAP in a rat model of diffuse axonal injury induced by impact acceleration. Axonal damage was assessed by immunohistochemistry using an antiserum against beta-amyloid precursor protein, a marker of altered axoplasmic transport considered as key feature in axonal injury. In these experiments, we have established the dose response curves for PACAP administration in traumatic axonal injury, demonstrating that a single post-injury intracerebroventricular injection of 100 microg PACAP significantly reduced the density of damaged, beta-amyloid precursor protein-immunoreactive axons in the corticospinal tract.

VIP as a trophic factor in the CNS and cancer cells

The effects of vasoactive intestinal peptide (VIP) on the proliferation of central nervous system (CNS) and cancer cells were investigated. VIP has important actions during CNS development. During neurogenesis, VIP stimulates the proliferation and differentiation of brain neurons. Addition of VIP to embryonic mouse spinal cord cultures increases neuronal survival and activity dependent neurotrophic factor (ADNF) secretion from astroglial cells. VIP is an integrative regulator of brain growth and development during neurogenesis and embryogenesis. Also, VIP causes increased proliferation of human breast and lung cancer cells in vitro. VIP binds with high affinity to cancer cells, elevates the cAMP and increases gene expression of c-fos, c-jun, c-myc and vascular endothelial cell growth factor. The effects of VIP on cancer cells are reversed by VIPhybrid, a synthetic VPAC(1) receptor antagonist. VIPhyb inhibits the basal growth of lung cancer cells in vitro and tumors in vivo and potentiates the ability of chemotherapeutic drugs to kill cancer cells. Due to the high density of VPAC(1) receptors in cancer cells, VIP has been radiolabeled with 123I, 18F and 99mTc to image tumors. It remains to be determined if radiolabeled VIP analogs will be useful agents for early detection of cancer in patients.

Vasoactive intestinal peptide regulation of nerve growth factor in the embryonic mouse

Vasoactive intestinal peptide (VIP), a regulator of embryonic growth, increased the concentration of nerve growth factor (NGF)-like immunoreactivity in the conditioned medium of cultured explanted embryonic day (E) 9.5 neural tube preparations compared to control preparations. VIP treatment also induced an increase of NGF-like immunoreactivity (NGF-IR) within the neural tube preparation tissue. A 60 kDa isoform was the primary form of NGF detected. VIP is shown to be a regulator of NGF in the E9.5 embryonic mouse and stimulates the release of a high molecular weight isoform of NGF.

Impact of antiretroviral protocols on dynamics of AIDS progression markers

AIMS

To assess the "real life" effectiveness of different antiretroviral therapies (ART).

METHODS

A retrospective multicentre observational study in 150 HIV-1 vertically infected children on the progression to AIDS (study A), and in 61 HIV-1 infected children on the evolution of the most relevant markers of progression (study B). All children were categorised into four groups: untreated (NT); on monotherapy (MT); on combination therapy (dual-ART); and on potent ART (HAART).

RESULTS

No child in the HAART group progressed to AIDS, whereas 14 children in the NT and seven in the MT groups progressed to AIDS, respectively, the differences being statistically significant. There was a mean increase of 8 units of %CD4+ per year; this was greater in the HAART group than in the other groups. The mean decrease in viral load was 0.65 log(10) copies/ml per year; this was greater in the HAART group than in the NT and MT groups. The HAART group had the lowest probability of returning to baseline %CD4+ and viral load.

CONCLUSION

Potent ART had the greatest protective effect against progression to AIDS in this observational study.

IGF-I as a mediator of VIP/activity-dependent neurotrophic factor-stimulated embryonic growth

IGF-I and the IGF-I receptor are necessary for normal embryonic growth. VIP is an important regulator of early postimplantation growth and acts indirectly through the release of other factors, including activity-dependent neurotrophic factor. The relationship of IGF-I growth regulation to VIP/activity-dependent neurotrophic factor-stimulated growth was examined with whole cultured embryonic d 9.5 mouse embryos. Somite numbers and DNA and protein contents were measured in embryos treated with IGF-I, anti-IGF-I, VIP, activity-dependent neurotrophic factor, and anti-activity-dependent neurotrophic factor-14 (antiserum to an activity-dependent neurotrophic factor agonist). IGF-I mRNA content was measured after incubation with and without VIP for 30 and 60 min using competitive RT-PCR. IGF-I induced a significant, dose-dependent increase in growth as measured by somite number, DNA levels, and protein content. Furthermore, anti-IGF-I inhibited embryonic growth and also prevented exogenous IGF-mediated growth. Both VIP- and activity-dependent neurotrophic factor-stimulated growth were blocked by anti-IGF-I, whereas anti-activity-dependent neurotrophic factor-14 had no detectable effect on IGF-I-induced growth. Treatment with VIP resulted in a 2-fold increase in embryonic IGF-I mRNA. These data suggest that IGF-I is a downstream mediator of VIP and activity-dependent neurotrophic factor in a regulatory pathway coordinating embryonic growth and that VIP may function as a regulator of IGF-I gene expression in the embryo.

Pharmacologically distinct vasoactive intestinal peptide binding sites: CNS localization and role in embryonic growth

In vitro autoradiography with [125I]vasoactive intestinal peptide revealed that the vasoactive intestinal peptide analogue, stearyl-norleucine17 vasoactive intestinal peptide, reported to be inactive at adenylyl cyclase-linked receptors in astrocytes, displaced a subset of vasoactive intestinal peptide binding sites on rat brain sections. These sites were widespread in adult rat brains and enriched in the olfactory bulb and thalamus, and corresponded to previously demonstrated GTP-insensitive vasoactive intestinal peptide binding sites. Stearyl-norleucine17 vasoactive intestinal peptide also identified receptors in rat lung and liver. In the adult brain, the stearyl-norleucine analog displaced only GTP-insensitive vasoactive intestinal peptide binding sites. In contrast, stearyl-norleucine17 vasoactive intestinal peptide-displaceable sites in the embryonic day 9 mouse appeared to include both GTP-sensitive and GTP-insensitive binding sites. This observation suggested the presence of an embryonic vasoactive intestinal peptide receptor with distinct pharmacological properties. Treatment of whole cultured mouse embryos with stearyl-norleucine17 vasoactive intestinal peptide resulted in stimulation of embryonic growth, with the stearyl-norleucine analog equipotent to vasoactive intestinal peptide, but less efficacious at higher concentrations (10(-7) M). Embryonic growth was inhibited by pituitary adenylyl cyclase-activating peptide and 8-bromoadenosine 3',5'-cyclic monophosphate. In addition, 8-bromoadenosine 3',5'-cyclic monophosphate inhibited stearyl-norleucine17 vasoactive intestinal peptide-stimulated growth. The results of the current study support the hypothesis that vasoactive intestinal peptide regulation of early postimplantation embryonic growth occurs, at least in part, independently of adenylyl cyclase stimulation.

The effects of steroid hormones in HIV-related neurotoxicity: a mini review

This review examines the interaction of steroid hormones, glucocorticoids and estrogen, and gp120, a possible causal agent of acquired immune deficiency syndrome-related dementia complex. The first part of the review examines the data and mechanisms by which gp120 may cause neurotoxicity and by which these steroid hormones effect cell death in general. The second part of the review summarizes recent experiments that show how these steroid hormones can modulate the toxic effects of gp120 and glucocorticoids exacerbating toxicity, and estrogen decreasing it. We then examine the limited in vivo and clinical data relating acquired immune deficiency syndrome-related dementia complex and steroid hormones and speculate on the possible clinical significance of these findings with respect to acquired immune deficiency syndrome-related dementia complex.

Inhibition of natural killer cell cytotoxicity and interferon gamma production by the envelope protein of HIV and prevention by vasoactive intestinal peptide

Natural killer (NK) cell dysfunction is common in human immunodeficiency virus (HIV)-infected subjects, although its mechanisms are poorly understood. A direct effect of HIV envelope glycoprotein gp120 may be involved. We investigated the in vitro effects of gp120 on the major NK cell effector functions, natural cytotoxicity and cytokine production. In addition, the ability of the vasoactive intestinal peptide (VIP) to modulate these effects was investigated. Our results indicated that gp120 inhibits NK natural cytotoxicity and showed, for the first time, that the inhibition affects also the production of the proinflammatory cytokine interferon-gamma (IFN-gamma). Interestingly, the inhibitory effect on NK cell functions was obtained with gp120 at concentrations within the range measured in the serum of HIV-infected subjects. Furthermore, we showed that the inhibitory activity of gp120 can be prevented by coincubation with VIP, even if VIP has no stimulatory activity by itself. Taken together these data suggest that (1) an inhibitory effect of gp120 may account for the NK cell dysfunction in HIV-infected subjects; (2) the gp120-mediated decrease in IFN-gamma production by NK cells may contribute to the cytokine imbalance observed in HIV infection; and (3) VIP counteracts the inhibitory effect of gp120 on NK cell functions.

Vasoactive intestinal peptide regulates embryonic growth through the action of activity-dependent neurotrophic factor

Activity-dependent neurotrophic factor is a potent, neuroprotective protein released from astroglia by VIP and accounts in part for the neuroprotective properties of this neuropeptide. The growth-regulatory actions of VIP during embryogenesis may also occur indirectly through the release of activity-dependent neurotrophic factor. Whole cultured day-9 mouse embryos treated with activity-dependent neurotrophic factor (10(-13) M) for 4 hr grew 3.1 somites, compared with 1.6 somites in control embryos. Treated embryos appeared morphologically normal and exhibited significant increases in cross-sectional area, protein, and DNA content and bromodeoxyuridine incorporation. Anti-activity-dependent neurotrophic factor significantly inhibited growth. Co-treatment of embryos with anti-activity-dependent neurotrophic factor inhibited VIP-stimulated growth; however, anti-VIP did not inhibit activity-dependent neurotrophic factor-induced growth. These data indicate that an activity-dependent neurotrophic factor-like substance is an endogenous embryonic growth factor and that VIP-regulated growth occurs, at least in part, through activity-dependent neurotrophic factor.

VIP neuroprotection against excitotoxic lesions of the developing mouse brain

Intracerebral administration of the excitotoxin ibotenate to new-born mice induced white-matter lesions mimicking the periventricular leukomalacia occurring in human premature babies. In this model, co-injection of vasoactive intestinal peptide (VIP) prevented white-matter lesions. VIP did not prevent the initial appearance of white-matter lesion, but promoted a secondary repair with axonal regrowth. Co-administration of ibotenate, VIP, and transduction inhibitors showed that protein kinase C (PKC) and mitogen-associated protein kinase (MAPK) pathways were critical for neuroprotection. The combination of in vitro and in vivo studies suggested the following model: VIP activates PKC in astrocytes, which release soluble factors; these released factors activate neuronal MAPK and PKC, which will permit axonal regrowth. Previous studies had shown that VIP-treated cultured astrocytes release growth factors including activity-dependent neurotrophic factor (ADNF) and that a 14-amino-acid peptide derived from ADNF protected the developing white matter against ibotenate. However, co-treatment with ibotenate, VIP, and anti-ADNF antibodies did not abolish VIP-induced protection, suggesting that ADNF does not mediate VIP protective properties in the present model.

A new concept in the pharmacology of neuroprotection

Vasoactive intestinal peptide (VIP), originally discovered in the intestine as a peptide of 28 amino acids, was later found to be a major brain peptide having neuroprotective activities. To exert neuroprotective activity, VIP requires glial cells secreting neuroprotective proteins. Activity-dependent neurotrophic factor (ADNF) is a recently isolated factor secreted by glial cells under the action of VIP. This protein, isolated by sequential chromatographic methods, was named activity-dependent neurotrophic factor since it protected neurons from death associated with blockade of electrical activity. A fourteen-amino-acid fragment of ADNF (ADNF-14) and the more potent, nine-amino-acid derivative (ADNF-9), exhibit activity that surpasses that of the parent protein with regard to potency and a broader range of effective concentration. Furthermore, the peptides exhibit protective activity in Alzheimer's disease-related systems (e.g., beta-amyloid toxicity and apolipoprotein E deficiencies, genes that have been associated with Alzheimer's disease onset and progression). ADNP is another glial mediator of VIP-associated neuroprotection. NAP, an eight-amino-acid peptide derived from ADNP (sharing structural and functional similarities with ADNF-9), was identified as the most potent neuroprotectant described to-date in an animal model of apolipoprotein E-deficiency (knock-out mice). These femtomolar-acting peptides form a basis for a new concept in pharmacology: femtomolar neuroprotection.

Activity-dependent neurotrophic factor peptide (ADNF9) protects neurons against oxidative stress-induced death

Activity-dependent neurotrophic factor (ADNF) and a 14-amino acid fragment of this peptide (sequence VLGGGSALLRSIPA) protect neurons from death associated with an array of toxic conditions, including amyloid beta-peptide, N-methyl-D-aspartate, tetrodotoxin, and the neurotoxic HIV envelope coat protein gp120. We report that an even smaller, nine-amino acid fragment (ADNF9) with the sequence SALLRSIPA potently protects cultured embryonic day 18 rat hippocampal neurons from oxidative injury and neuronal apoptosis induced by FeSO4 and trophic factor withdrawal. Among the characteristics of this protection are maintenance of mitochondrial function and a reduction in accumulation of intracellular reactive oxygen species.

Transferrin trojan horses as a rational approach for the biological delivery of therapeutic peptide domains

One novel approach for the biological delivery of peptide drugs is to incorporate the sequence of the peptide into the structure of a natural transport protein, such as human serum transferrin. To examine whether this is feasible, a peptide sequence cleavable by the human immunodeficiency virus type 1 protease (VSQNYPIVL) was inserted into various regions of human serum transferrin, and the resultant proteins were tested for function. Experimentally, molecular modeling was used to identify five candidate insertion sites in surface exposed loops of human serum transferrin that were distant from biologically active domains. These insertions were cloned using polymerase chain reaction mutagenesis, and the proteins were expressed using a baculovirus expression vector system. Analysis of the mutant proteins provided a number of important findings: (a) they retained native human serum transferrin function, (b) the inserted peptide sequence was surface exposed, and most importantly, (c) two of these mutants could be cleaved by human immunodeficiency virus-1 protease. In conclusion, this investigation has validated the use of human serum transferrin as a carrier protein for functional peptide domains introduced into its structure using protein engineering. These findings will be useful for developing a novel class of therapeutic agents for a broad spectrum of diseases.

Maternal regulation of embryonic growth: the role of vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) is an important growth regulator of the embryonic day (E)9-E11 mouse. In comparably aged rat embryos, VIP messenger RNA (mRNA) is not detectable; however, peak concentrations of VIP in maternal rat serum indicate a nonembryonic source. In the current study, mouse maternal and embryonic tissues were examined from E6-E12. Although RT-PCR revealed VIP mRNA in E6-E7 conceptuses, by E8 (when extraembryonic tissues could be separated from the embryo), VIP mRNA was detected only in the decidua/trophoblast. Decidual/trophoblastic VIP mRNA decreased until E10, after which it was not detectable. VIP mRNA was not apparent in the embryo until E11-E12. At E9, VIP immunoreactivity was localized to abundant, diffuse cells in the decidua basalis, which were also immunoreactive for T cell markers. VIP binding sites were dense in the decidua/trophoblast at E6, but gradually decreased until E10, after which they were not apparent. VIP binding sites were detected in embryonic neuroepithelium by E9. The transient presence of VIP binding sites and mRNA in the decidua/trophoblast correlate with the critical period of VIP growth regulation, when VIP mRNA is absent in the embryo. These findings suggest that maternal lymphocytes are the source of VIP's regulating early postimplantation embryonic growth.

The identification of secreted heat shock 60 -like protein from rat glial cells and a human neuroblastoma cell line

The intracellular stress-induced proteins provide protection against toxic insults. Here, a 60,000-Da heat shock 60 (hsp60)-like protein was detected, with five different antibodies, in conditioned media derived from rat cortical astrocytes and a human neuroblastoma cell line. Extracellular neuroblastoma hsp60-like immunoreactivity was increased 3-fold in the presence of the neuropeptide vasoactive intestinal peptide (VIP) and was augmented 2-fold after temperature elevation. Intracellular hsp60 immunoreactivity was reduced 2-3-fold in the presence of VIP; this reduction was attenuated in the presence of brefeldin A, an inhibitor of protein secretion. In contrast, the activity of lactate dehydrogenase (LDH), an intracellular marker, did not change in the presence of VIP. Essentially no extracellular LDH activity was detected, indicating no cellular damage. A novel aspect for stress proteins having extracellular protective roles is suggested.