Lipid peroxidation is an important part of the pathological pathway of membrane damage in membranes that have high levels of polyunsaturated fatty acids such as linoleic, linolenic, arachidonic, and docosahexaenoic acids. Neural membranes are particularly rich in polyunsaturated acids and such damage is implicated in neurological diseases, such as Alzheimer's disease. To obtain a bilayer model that represents the property of susceptibility to lipid peroxidation, we carried out molecular dynamics (MD) simulations of a bilayer of 1-palmitoyl-2-linoleyl-sn-glycero-3-phosphatidylcholine (PLPC). Parameters for the torsional potentials of the cis,cis-Delta(9,12) bis-allylic region of the linoleate chain were fitted to the results of high-level ab initio calculations on model compounds. The MD simulations of the bilayer provided the structural properties of the system and show that the unsaturation induces disorder and affects the physical properties of the membrane.

A molecular dynamics simulation of melittin in a hydrated dipalmitoylphosphatidylcholine (DPPC) bilayer was performed. The 19,000-atom system included a 72-DPPC phospholipid bilayer, a 26-amino acid peptide, and more than 3000 water molecules. The N-terminus of the peptide was protonated and embedded in the membrane in a transbilayer orientation perpendicular to the surface. The simulation results show that the peptide affects the lower (intracellular) layer of the bilayer more strongly than the upper (extracellular) layer. The simulation results can be interpreted as indicating an increased level of disorder and structural deformation for lower-layer phospholipids in the immediate vicinity of the peptide. This conclusion is supported by the calculated deuterium order parameters, the observed deformation at the intracellular interface, and an increase in fractional free volume. The upper layer was less affected by the embedded peptide, except for an acquired tilt relative to the bilayer normal. The effect of melittin on the surrounding membrane is localized to its immediate vicinity, and its asymmetry with respect to the two layers may result from the fact that it is not fully transmembranal. Melittin's hydrophilic C-terminus anchors it at the extracellular interface, leaving the N-terminus "loose" in the lower layer of the membrane. In general, the simulation supports a role for local deformation and water penetration in melittin-induced lysis. As for the peptide, like other membrane-embedded polypeptides, melittin adopts a significant 25o tilt relative to the membrane normal. This tilt is correlated with a comparable tilt of the lipids in the upper membrane layer. The peptide itself retains an overall helical structure throughout the simulation (with the exception of the three N-terminal residues), adopting a 30o intrahelical bend angle.

Melittin, a small peptide found in bee venom, is known to induce membrane lysis. A molecular dynamics simulation of melittin embedded in a hydrated dipalmitoylphosphatidylcholine bilayer is analyzed in order to study the peptide’s effect on water molecules at the membrane/water interface. The peptide, with a protonated N-terminus, was embedded in a trans-bilayer orientation. The simulation highlights the microscopic mechanism by which melittin induces the formation of transmembrane water “pores,” leading to membrane lysis. It was found that melittin has a profound effect on the behavior of the water molecules at the membrane/water interface. It modifies the orientation of the water dipoles and induces water penetration into the bilayer. In fact, melittin’s residue Lys-7 and its protonated N-terminus facilitate the formation of transmembrane water pores by steering water penetration from both sides of the bilayer. The initial step towards pore formation takes about 200 ps, and the process relays on melittin’s bent conformation and tilted orientation. A large body of experimental observations supports the simulation results and the suggested microscopic mechanism.

Stearyl-Nle-VIP (SNV) is a novel agonist of vasoactive intestinal peptide (VIP) exhibiting a 100-fold greater potency than the parent molecule and specificity for a receptor associated with neuronal survival. Here, the developmental and protective effects of SNV were investigated in vivo using two models of developmental retardation, hypoxia and cholinergic blockade. In both cases chronic administration of SNV during development provided protective effects. Water maze experiments on the weaned animals have demonstrated a prophylactic action for SNV and enhancement of spatial memory in animals exposed to a cholinotoxin. SNV may act by providing neuroprotection, thereby improving cognitive functions. This work is dedicated to Prof. R.J. Wurtman whose inspiration and leadership in the field of neuroscience and cognition is beyond comparison.

Stearyl-Nle17-VIP (SNV) is a novel agonist of vasoactive intestinal peptide (VIP) exhibiting a 100-fold greater potency than the parent molecule and specificity for a receptor associated with neuronal survival. SNV protected neurons against the β-amyloid peptide, Alzheimer associated neurotoxicity in vitro, and against memory impairments induced by cholinergic deficiencies in vivo. To further test the breadth of neuroprotection offered by SNV, mice deficient in apolipoprotein E (apoE), a molecule associated with the etiology of Alzheimer’s disease, served as a model to investigate the developmental effects of SNV. In comparison to control animals, the deficient mice exhibited: 1) reduced amounts of VIP mRNA; 2) decreased cholinergic activity (decreased activity of choline acetyl-transferase); 3) significant retardation in the acquisition of developmental milestones: forelimb placing behavior and cliff avoidance behavior; and 4) impairments in learning and memory. Daily injections of SNV to apoE-deficient new-born pups resulted in increased cholinergic activity and marked improvements in the acquisition of behavioral milestones, with peptide-treated animals developing as fast as control animals. Furthermore, SNV-treated apoE-deficient animals exhibited marked improvements in their learning abilities observed after cessation of peptide treatment. Specificity was demonstrated in that treatment with pituitary adenylate cyclase activating peptide (PACAP, a VIP-related peptide) produced only limited amelioration. The neuroprotective effects of VIP and its derivative VIP required the presence of glial cells in the culture. We have recently isolated a novel femtomolar-acting neuroprotective protein (with stress protein sequences) secreted from glial cells in the presence of VIP. The novel protein was named activity-dependent neurotrophic factor (ADNF) as it protected neurons from death mediated by electrical blockade. Neutralizing antibodies to ADNF indicated the existence of endogenous ADNF-like protein in the cerebral cortex, secreted in the presence of VIP. Thus, the protective efects of VIP and SNV may be mediated via endogenous glial derived molecules such as ADNF. SNV and ADNF may provide lead compounds in the design and synthesis of growth-factor-based Alzheimer’s disease therapeutics. Furthermore, as certain genotypes of apolipoprotein E increase the probability of Alzheimer’s disease, early counseling and preventive treatments may now offer an important route for therapeutics design.

Stearyl-Nle17-VIP (SNV) is a novel agonist of vasoactive intestinal peptide (VIP) exhibiting a 100-fold greater potency than the parent molecule and specificity for a receptor associated with neuronal survival. Here, mice deficient in apolipoprotein E (ApoE), a molecule associated with the etiology of Alzheimer's disease, served as a model to investigate the developmental and protective effects of SNV. In comparison to control animals, the deficient mice exhibited (a) reduced amounts of VIP messenger RNA; (b) decreased cholinergic activity (c) significant retardation in the acquisition of developmental milestones: forelimb placing behavior and cliff avoidance behavior; and (d) learning and memory impairments. Daily injections of SNV to ApoE-deficient newborn pups resulted in increased cholinergic activity and marked improvements in the time of acquisition of behavioral milestones, with peptide-treated animals developing as fast as control animals and exhibiting improved cognitive functions after cessation of peptide treatment. Specificity was demonstrated in that treatment with a related peptide (PACAP), pituitary adenylate cyclase-activating peptide, produced only limited amelioration. As certain genotypes of ApoE increase the probability of Alzheimer's disease, early counseling and preventive treatments may now offer an important route for therapeutics design.

The effects of pituitary adenylate cyclase activating polypeptide (PACAP) hybrid, a synthetic antagonist, was investigated on NIH/3T3 cells containing PACAP receptor (R) splice variants (SVs). PACAPhybrid inhibited 125I-PACAP-27 binding to NIH/3T3 cells stably expressing PACAP-R basic, SV-1, SV-2 or SV-3 with an IC50 of 1000 nM. PACAPhybrid antagonized the ability of PACAP-27 to elevate cAMP regardless of the PACAP-R SV used. PACAP was more efficacious at increasing cytosolic Ca2+ in NIH/3T3 cells containing PACAP-R SV-2 than PACAP-R basic, SV-1 or SV-3. PACAPhybrid antagonized the increase in cytosolic Ca2+ caused by PACAP-27 regardless of the PACAP-R SV used. PACAP was more potent at elevating c-fos mRNA using NIH/3T3 cells transfected with PACAP-R SV-2 than PACAP-R basic, SV-1 or SV-3. PACAPhybrid antagonized the increase in c-fos mRNA caused by PACAP-27. These data suggest that PACAPhybrid is a useful PACAP receptor antagonist for PACAP-R SVs.