Enterostatin (VPDPR) Has Anti-analgesic and Anti-amnesic Activites

Enterostatin (VPDPR), an anorexigenic peptide derived from the amino terminus of procolipase, significantly inhibited analgesia induced by the mu-opioid agonist morphine (5 mg/kg, s.c.) after i.c.v. administration to mice at a dose of 100 nmol. On the other hand, VPDPR (approximately 200 nmol, i.c.v.) did not attenuate analgesia induced by the kappa-opioid agonist D-Phe-D-Phe-D-Nle-D-Arg-NH2 (100 microg/mouse, i.c.v.) or delta-opioid agonist DTLET (4 nmol/mouse, i.c.v.). VPDPR (100 nmol, i.c.v.) significantly improved amnesia induced by scopolamine (0.2 mg/kg, i.p.) in mice. However, VPDPR did not enhance memory in normal mice at the same dose.

Protective effects of TRH and its analogues against various cytotoxic agents in retinoic acid (RA)-differentiated human neuroblastoma SH-SY5Y cells

TRH (thyroliberin) and its analogues were reported to possess neuroprotective effects in cellular and animal experimental models of acute and chronic neurodegenerative diseases. In the present study we evaluated effects of TRH and its three stable analogues, montirelin (CG-3703), RGH-2202 and Z-TRH (N-(carbobenzyloxy)-pGlutamyl-Histydyl-Proline) on the neuronally differentiated human neuroblastoma SH-SY5Y cell line, which is widely accepted for studying potential neuroprotectants. We found that TRH and all the tested analogues at concentrations 0.1-50 μM attenuated cell damage induced by MPP(+) (2 mM), 3-nitropropionate (10 mM), hydrogen peroxide (0.5 mM), homocysteine (250 μM) and beta-amyloid (20μM) in retinoic acid differentiated SH-SY5Y cells. Furthermore, we demonstrated that TRH and its analogues decreased the staurosporine (0.5 μM)-induced LDH release, caspase-3 activity and DNA fragmentation, which indicate the anti-apoptotic proprieties of these peptides. The neuroprotective effects of TRH (10 μM) and RGH-2202 (10 μM) on St-induced cell death was attenuated by inhibitors of PI3-K pathway (wortmannin and LY294002), but not MAPK/ERK1/2 (PD98059 and U0126). Moreover, TRH and its analogues at neuroprotective concentrations (1 and 10 μM) increased expression of Bcl-2 protein, as confirmed by Western blot analysis. All in all, these results extend data on neuroprotective properties of TRH and its analogues and provide evidence that mechanism of anti-apoptotic effects of these peptides in SH-SY5Y cell line involves induction of PI3K/Akt pathway and Bcl-2. Furthermore, the data obtained on human cell line with a dopaminergic phenotype suggest potential utility of TRH and its analogues in the treatment of some neurodegenerative diseases including Parkinson's disease.

NG2 positive cells of rat spinal cord activated during experimental autoimmune encephalomyelitis are spatially associated with radially oriented astroglia and express p75 receptor: a role for nerve growth factor in oligodendrocyte progenitor migration?

Data have been provided from several studies that support the proposal that the adult oligodendrocyte progenitors migrate into the lesioned areas under conditions of experimental autoimmune encephalomyelitis (EAE). However, the routes of migration of these cells and the governing mechanisms are not clear. In the present studies, we have examined the effect of EAE upon activation of endogenous oligodendroglia progenitors and their spatial distribution in the spinal cord of Lewis rats using immunocytochemical procedures. Antibodies against the marker chondroitin sulfate proteoglycan NG2, are used for identification of oligodendroglia progenitors. We find that the activated elongated subpopulation of NG2 positive oligodendroglia progenitors of white matter is spatially associated with the radially-oriented astroglia during the acute phase of EAE. The latter re-expressed the phenotypic embryonic marker nestin while still expressing the mature astroglial marker GFAP. The elongated oligodendroglia progenitors express p75 receptor. In addition, colocalization of NG2 and p75 is observed also in ependymal neural cells of the central canal and the subventricular zone. This raises the possibility that the activated NG2+/p75+ parenchymal cell pool may also be recruited from multipotent neural cells of the germination areas. Our data suggest that, under EAE conditions, the radially oriented astroglia of juvenile phenotype may serve as scaffolding for migrating activated endogenous oligodendroglia progenitors just like radial glia provide a path for neuronal and oligodendroglia progenitor cells in embryonic stage. The expression of p75 receptor in oligodendroglia progenitors associated with radially oriented astroglia during EAE may implicate a role for NGF in the regulation of migration of oligodendroglia progenitors.

Effects of TRH and its analogues on primary cortical neuronal cell damage induced by various excitotoxic, necrotic and apoptotic agents

The tripeptide thyrotropin-releasing hormone (TRH, pGlu-His-Pro-NH2) has been shown to possess neuroprotective activity in in vitro and in vivo models. Since its potential utility is limited by relatively rapid metabolism, metabolically stabilized analogues have been constructed. In the present study we investigated the influence of TRH and its three stable analogues: Montirelin (MON, CG-3703), RGH-2202 (L-6-keto-piperidine-2carbonyl-l-leucyl-l-prolinamide) and Z-TRH (N-carbobenzyloxy-pGlutamyl-Histydyl-Proline) in various models of mouse cortical neuronal cell injury. Twenty four hour pre-treatment with TRH and its analogues in low micromolar concentrations attenuated the neuronal cell death evoked by excitatory amino acids (EAAs: glutamate, NMDA, kainate, quisqualate) and hydrogen peroxide. All the peptides showed neuroprotective action on staurosporine (St)-evoked apoptotic neuronal cell death, but this effect was caspase-3 independent. Interestingly, in mixed neuronal-glial cell preparations only MON decreased St- and glutamate-evoked neurotoxicity. None of the peptides inhibited the doxorubicin- and lactacystin-induced neuronal cortical cell death, agents acting via activation of death receptor (FAS) or inhibition of proteasome function, respectively. Furthermore, we found that neither inhibitors of PI3-K (wortmannin, LY 294002) nor MAPK/ERK1/2 (PD 098059, U 0126) were able to inhibit neuroprotective properties of TRH and MON in St model of apoptosis. The protection mediated by TRH and MON it that model was also not connected with influence of peptides on the pro-apoptotic GSK-3beta and JNK protein kinase expression and activity. Further studies showed that calpains, calcium-activated proteases were induced by Glu, but not by St in cortical neurons. Moreover, the Glu-evoked increase in spectrin alpha II cleavage product induced by calpains was blocked by TRH. The obtained data showed that the potency of TRH and its analogues in inhibiting EAAs- and H(2)O(2)-induced neuronal cell death from the highest to lowest activity was: MON>TRH>Z-TRH>RHG. Interestingly, all peptides were active against St-induced apoptosis, however, on concentration basis MON was far more potent than the other peptides. None of the peptides inhibited Dox- and LC-evoked apoptotic cell death. Additionally, the data exclude potential role of pro-survival (PI3-K/Akt and MAPK/ERK1/2) and pro-apoptotic (GSK-3beta and JNK) pathways in neuroprotective effects of TRH and its analogues on St-induced neuronal apoptosis. Moreover, the results point to involvement of the inhibition of calpains in the TRH neuroprotective effect in Glu model of neuronal cell death.

Adjuvant vaccination with melanoma antigen pulsed dendritic cells (DCs) in stage III melanoma patients

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Background: This is a pilot study evaluating of high-risk melanoma patients (pts) treated with peptide-DC vaccine after lymphadenectomy (LND). DC vaccination was designed to induce the immune response against melanoma antigens in melanoma pts who remain at high risk of dissemination after LND. Methods: DCs were generated from the bone marrow with the use GM-CSF, SCF, FLT3-L and TNFa or from peripheral blood adherent monocytes with GM-CSF and IL-4. DCs pulsed with HLA-A2-binding TYR, MART-1 and gp100 peptides and/or HLA-A1-binding MAGE-1, MAGE-3 peptides, tumor lysate if available, or with tracer antigen keyhole limpet hemocyanin (KLH), were injected sc 9 times within 8 months (mos). Boost injections were performed after 12 and 24 mos. Vaccinated pts were matched to unvaccinated controls (22 of 587) by sex, number of metastatic lymph nodes, extracapsular involvement, completion or therapeutic LND, Breslow stage (T), and ulceration. Results: HLA-A2+, -A1+ or -A3+ melanoma pts (n=22), stage III, N1b-N3, enrolled between Sept. 2002 and Apr. 2004, received 5–16 vaccinations (median: 11) within 2 yrs. Cutaneous delayed type hypersensitivity (DTH) to melanoma peptides was induced in 12 of 22 pts. Peptide-specific IFNg producing CD8+ cells were detected in peripheral blood of 13 of 19 pts after vaccination. At least one of these responses to melanoma antigens was elicited in 17 of 22 pts. DTH to KLH was positive in 15 of 22 pts. Nine vaccinated pts are free of disease, and 1 is stable by Dec. 2008 (follow up is 58–76 mos after LND). Survival analysis for vaccinated pts and matched controls is presented in the Table . Conclusions: The DC/peptide vaccine elicited immune responses to melanoma antigens. Vaccinated pts had clinically substantially longer overall survival (OS) and disease free survival (DFS) than matched control. OS was associated with the immune responsiveness to melanoma antigens and to KLH.

[Table: see text]

No significant financial relationships to disclose.

Synthesis and biological evaluation of constrained analogues of the opioid peptide H-Tyr-D-Ala-Phe-Gly-NH2 using the 4-amino-2-benzazepin-3-one scaffold

The synthesis of conformationally restricted dipeptidic moieties 4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Aba)-Gly ([(4S)-amino-3-oxo-1,2,4,5-tetrahydro-1H-2-benzazepin-2-yl]-acetic acid) and 8-hydroxy-4-amino-1,2,4,5-tetrahydro-2-benzazepin-3-one (Hba)-D-Ala ([(4S)-amino-8-hydroxy-3-oxo-1,2,4,5-tetrahydro-benzo[c]azepin-2-yl]-propionic acid) was based on a synthetic strategy that uses an oxazolidinone as an N-acyliminium precursor. Introducing these Aba scaffolds into the N-terminal tetrapeptide of dermorphin (H-Tyr-D-Ala-Phe-Gly-Tyr-Pro-Ser-NH2)-induced remarkable shifts in affinity and selectivity towards the opioid mu- and delta-receptors. This paper provides the synthesis and biological in vitro and in vivo evaluation of constricted analogues of the N-terminal tetrapeptide H-Tyr-D-Ala-Phe-Gly-NH2, which is the minimal subunit of dermorphin needed for dermorphin-like opiate activity.

The biological consequences of replacing hydrophobic amino acids in deltorphin I with amphiphilic alpha-hydroxymethylamino acids

New analogues of deltorphin I (DT I), in which the Phe residue in position 3, and the Val residue in position 5 or 6 are replaced with respective amphiphilic alpha-hydroxymethylamino acid residues (HmAA), were synthesized and tested for receptor affinity and selectivity to mu and delta opioid receptors. The analogue with (R)-HmPhe at position 3 lost receptor selectivity, as a result of a partial decrease of affinity to delta and a significant increase of affinity to mu receptors. In contrast, an analogue with (S)-HmPhe in the same position, was very potent and more specific to delta receptors than parent DT I. The analogue with (R)-HmVal at position 5 expressed higher delta affinity and selectivity than parent DT I. The analogue with other possible isomer (S)-HmVal was less selective for delta opioid receptors, as a result of decreasing affinity to delta and increasing affinity to mu receptors. The analogues with (R)- or (S)-HmVal in position 6 expressed equally low receptor affinity and selectivity. The data obtained support a previously proposed model of active conformation of deltorphins.

Effect of peptide conformation on membrane permeability

The effect of peptide conformational constraint on the peptide permeation across the model membranes was examined by determining the permeability of pairs of cyclic and acyclic peptides related to c[d-Pen2, d-Pen5] enkephalin (DPDPE). The peptides were cyclized by formation of an intramolecular disulfide bridge between the second and fifth residues composed of either d-penicillamine or cysteine. In each case the acyclic peptide was three to seven times more permeable than corresponding cyclic peptide. The possibility that the differences in permeability of cyclic and acyclic peptides is based on the greater conformational freedom of the acyclic peptides in the presence of membrane was examined in more detail by isothermal titration calorimetric studies of Trp6-DPDPE and its acyclic analog. The membrane binding of the acyclic peptide is a more exothermic process than binding of its cyclic Trp6-DPDPE. The transfer of acyclic peptide from water to membrane is an enthalpy driven process, whereas the transfer of the cyclic peptide is driven by entropy.

Anti-analgesic activity of enterostatin (VPDPR) is mediated by corticosterone

Although enterostatin (VPDPR) inhibited morphine-induced analgesia, it had no affinity for mu-opioid receptors. VPDPR administration was reported to elevate serum corticosterone levels. We found that corticosterone exhibited a similar anti-analgesic effect selective for mu-opioid. Furthermore, the anti-analgesic effect of VPDPR was inhibited by RU486, an antagonist for the glucocorticoid receptor. The anti-analgesic effect of VPDPR was not observed in adrenalectomized mice. These results suggest that the anti-analgesic activity of VPDPR is mediated by corticosterone released from the adrenal cortex.

Antinociceptive effects of hydromorphone, bupivacaine and biphalin released from PLGA polymer after intrathecal implantation in rats

Intraspinal drug delivery, based on the concept of controlling pain by delivering drug to a nociceptive target rich in opioid and other relevant receptors is increasingly used clinically. The therapeutic ratio for opioids or other centrally acting agents is potentially greater if they are administered intrathecally (i.t.) than outside the central nervous system (CNS). The present study was designed with the ultimate goal of formulating a controlled release system for intrathecal analgesia characterized by effectiveness, rapid onset and few side effects for chronic pain control. A biodegradable copolymer poly(L-lactide-co-glycolide) (PLGA) was used to prepare a rod-shaped drug delivery system containing hydromorphone (HM), bupivacaine (BP), both HM and BP, or biphalin (BI). In vitro drug release kinetics of these systems showed a zero-order release rate for HM and BP from PLGA (85:15) rods. Drug-loaded rods were implanted i.t. Control groups received only placebo implants. Measurement of analgesic efficacy was carried out with tail flick and paw-withdrawal tests. In vivo studies showed potent, prolonged analgesia in comparison to controls for all active treatments. Analgesic synergy was observed with HM and BP. With further refinements of drug release rate, these rods may offer a clinically relevant alternative for intrathecal analgesia.

High-affinity NGF receptor in the rat spinal cord during acute and chronic phases of experimental autoimmune encephalomyelitis: a possible functional significance

The biological effects of Nerve Growth Factor (NGF) are primarily mediated via its high affinity receptor-TrkA. In the present study, we examined the effect of experimental autoimmune encephalomyelitis (EAE) upon the expression of TrkA in neuronal and non-neuronal cells of the spinal cord of Lewis rats during the acute (14 days postimmunization) and chronic (12 months postimmunization) phases of the disease. In the normal spinal cord, both of mature and aged rats, we found TrkA immunoreaction (TrkA-IR) in the motoneurons of the Rexed lamina IX and in both oligo- and astroglia cells. In the acute phase of the disease, we found a reduction of TrkA immunoreactivity in motoneurons and its up-regulation in oligodendroglia, mainly in the white matter. We also confirmed our previous findings concerning the up-regulation of TrkA-IR in astroglia. Both neuronal and non-neuronal changes of TrkA immunoreactivity had a transient character: they were not seen in the chronic phase of the disease. Our results suggest that both neuronal and glial TrkA expression changes depend on inflammation. Moreover, our data indicate that, during the acute phase of EAE, the glial cells become more receptive to NGF, pointing to glia as an important target for pharmacological manipulations, particularly for exogenously administered NGF.

Synthesis and binding properties of deltorphin I analogues containing (R) and (S)-alpha-hydroxymethylnaphtylalanine

New analogues of deltorphin I (DT I), in which the phenylalanine residue in position 3 is substituted with amphiphilic alpha,alpha-disubstituted amino acid enantiomers, (R) and (S)-alpha-hydroxymethylnaphtylalanine, were synthesized and tested for mu and delta opioid receptor affinity and selectivity. Although both analogues have lower affinity to delta receptors than DT I, they both expressed specificity to delta receptors.

Crystal structure of biphalin sulfate: a multireceptor opioid peptide

Biphalin is a dimeric opioid peptide, composed of two tetrapeptides connected 'tail-to-tail', that exhibits a high affinity for all three opioid receptor types (i.e. mu, delta and kappa). This study presents the X-ray crystal structure of biphalin sulfate and compares it to other opioids that interact with the same biological targets. Both halves of the molecule have a folded backbone conformation but differ significantly from one another. Residues 1-4 in biphalin, which compare well with the delta selective opioid peptide DADLE, fold into a random coil. Residues 5-8, which can be fit to the mu selective peptide D-TIPP-NH2, exhibit a fairly normal type III' beta bend. Biphalin also exhibits structural similarities with two naltrexone analogs, naltrexonazine and norbinaltorphamine, that are specific to mu and kappa receptor sites.

Synthesis and binding properties of deltorphin I analogues containing (R) and (S)-alpha-hydroxymethylnaphtylalanine

New analogues of deltorphin I (DT I), in which the phenylalanine residue in position 3 is substituted with amphiphilic alpha,alpha-disubstituted amino acid enantiomers, (R) and (S)-alpha-hydroxymethylnaphtylalanine, were synthesized and tested for mu and delta opioid receptor affinity and selectivity. Although both analogues have lower affinity to delta receptors than DT I, they both expressed specificity to delta receptors.

Rubiscolin, a delta selective opioid peptide derived from plant Rubisco

We found that the sequences YPLDL and YPLDLF in the large subunit of spinach D-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) met the structure YP-aliphatic amino acid which might have opioid activity. We then synthesized these peptides to test their opioid activity. The IC(50) of these peptides in mouse vas deferens assay were 51.0 microM and 24.4 microM, respectively, and those in delta receptor binding assay using [(3)H]deltorphin II as radioligand were 2.09 microM and 0.93 microM, respectively. Both peptides were selective for delta receptor. We named them rubiscolin-5 and -6, respectively. Rubiscolin-5 and -6 have antinociceptive activity in mice after i.c.v. or oral administration. The enzymatic conditions to release rubiscolin were investigated using both spinach Rubisco and synthetic fragment peptides. This is the first example of bioactive peptides derived from plant Rubisco.

Peptide analog of fibronectin that inhibits cell migration and ERK 1/2 activity

Two analogs of the peptide mimicking the 1977-1991 C- terminal part of fibronectin have been synthesized and tested. AWLI simulated human fibronectin fragment 1977-1991, whereas AWLII hybridized to both RGD and 1977-1991 fragments. AWLI and AWLII peptides inhibited the migration of the ovarian carcinoma cell line OVP10 regardless of the presence RGD. AWLI peptide inhibited spontaneous and fibronectin-activated cell migration and ERK1/2 activity. Neither AWLI nor fibronectin induced changes in FAK proteins, as could be judged from Western blots. In conclusion, it seems that the C-terminal fragment of fibronectin inhibits ERK1/2-dependent (random) migration of ovarian carcinoma cells.

Possible reverse transport of beta-amyloid peptide across the blood-brain barrier

Our experiments were performed to test the hypothesis that human beta-amyloid peptide 42 (beta A) is able to enter and exit the brain parenchyma through the blood-brain barrier. In an effort to determine the effect of beta A in an animal model, we have injected beta A i.v. into rats following single and repeated brain ischemia. Rats were sacrificed at 3 and 12 months after injection and beta A was localized by monoclonal antibody (mAb) 4G8. The present observations revealed an abundant presence of beta A in the extracellular space of the brain, which appeared to be dilated, and a vigorous uptake of beta A into the cytoplasm of endothelial and ependymal cells, pericytes, astrocytes and neurons. Some of the beta A deposits were associated and/or had migrated to the vessels and to the ventricles, and by 3 months a significant amount of beta A was directly associated with the vessels and was observed inside the ventricular space. Virtually no soluble and aggregating beta A was found in brain tissue 1 year later. This suggests that phagocytic pericytes and astrocytes take up exogenous beta A in an attempt to clear the peptide from the brain extracellular space and deliver it to the circulation. Further, direct removal of beta A from the ventricles by the bloodstream is also possible. These observations suggest that a reverse transport of beta A across endothelial cells of microvessels represents one of the possible mechanisms responsible for removal of extravasated beta A. The findings of the present study indicate that in normal conditions beta A is rapidly cleared from the cerebrospinal fluid and brain parenchyma, suggesting that irreversible changes in the physico-chemical properties of the cerebrovascular endothelial cell surface are involved in beta A deposition in the brain in Alzheimer's disease (AD).

The opioid peptide analogue biphalin induces less physical dependence than morphine

We compared the physical dependence liability of biphalin, a dimeric enkephalin analogue that possesses high antinociceptive activity, with that of morphine in equipotent intravenous doses. Naloxone challenge produced severe withdrawal signs after a 5-day infusion of morphine but only minor withdrawal signs after a 5-day biphalin infusion. In a cross-dependence study, biphalin did not suppress body weight loss after morphine withdrawal, but successfully suppressed weight loss after pentazocine withdrawal. These data support consideration of biphalin as a new analgesic with a novel pharmacological profile and minimum dependence liability.

Effects of endomorphin-2 on arterial blood pressure and pain threshold in spontaneously hypertensive rats and modification of these effects by beta-funaltrexamine and nor-binaltorphimine

The effects of intracerebroventricular (icv) administration of endomorphin-2 (E2) on arterial blood pressure and pain threshold in spontaneously hypertensive rats (SHR) and modification of these effects by K [OP2] and mu [OP3] opioid receptors antagonists were investigated. Endomorphin-2 administrated icv in doses of 8, 16 and 32 mcg produced dose-dependent analgesic and hypotensive effect. In SHR decrease in blood pressure amounted 2.667, 4.0 and 6.534 kPa, respectively. Pain threshold increased by 1.7, 3.6 and 8.9 (g x 10). In Wistar Kyoto (WKY) strain, being the normotensive controls, E2 in doses of 8 and 16 mcg decrease in blood pressure was less pronounced and amounted 1.200 and 1.467 kPa, respectively, whereas the pain threshold increased by 7.2 and 10.4 (g x 10), respectively. Both E2 effects were antagonized by equimolar icv doses of beta-funaltrexamine (beta-FNA). Equimolar doses of nor-binaltorphimine (nor-BNI) attenuated analgesic action of E2, but were without hypotensive action produced by E2. A strong correlation between drop in blood pressure and increase in pain threshold observed in the SHR and WKY strains after icv administration of E2, indicate close interaction between systems responsible for pain perception and blood pressure control.

Biological properties of Phe(o)-opioid peptide analogues

Biological properties of new analogues, which represent Phe(o)-propeptides of a variety of opioid peptides, are described. All Phe(o)-opioid analogues expressed both receptor binding affinities and in vitro biological activities at least at the level of the primary opioid peptides. Surprisingly, some of the propeptides expressed slightly higher activity than the primary opioid peptides. Nevertheless, no significant shift in receptor selectivity was observed, which indicate that these Phe(o)-analogues undoubtedly are propeptides. The possible role of membrane proteolytic enzymes associated with opioid receptors in transformation of propeptides is discussed.

Kappa-opioid receptors and relapse-like drinking in long-term ethanol-experienced rats

RATIONALE

The role of the dynorphin/kappa-opioid receptor system in ethanol reinforcement is unclear.

OBJECTIVE

Examination of the effects of the highly selective kappa-opioid receptor agonist CI-977 (enadoline) and of the long-acting selective kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI) on relapse-like drinking measured by the alcohol deprivation effect (ADE) in long-term ethanol-experienced rats.

METHODS

Rats were either implanted with mini-osmotic pumps delivering 0 or 0.01 mg/kg per h CI-977 or received two injections (12 h apart) of nor-BNI (0 or 5 mg/kg i.p.) before representation of alcohol after 2 weeks of alcohol deprivation in a four-bottle home cage drinking paradigm. In a second experiment, long-term ethanol-experienced rats trained in an operant ethanol self-administration paradigm received either acute CI-977 treatment (0, 0.003-0.1 mg/kg i.p.) or two injections (12 h apart) of nor-BNI (0 or 5 mg/kg i.p.) before a 23-h session.

RESULTS

Chronic CI-977 potentiated ethanol intake and preference during the ADE. Acute CI-977 dose-dependently reduced total lever pressing activity demonstrating an unspecific sedative effect, except for the lowest dose (0.003 mg/kg), which selectively increased lever pressing for ethanol during basal drinking. Nor-BNI did not affect relapse-like drinking at all.

CONCLUSIONS

Stimulation of kappa-opioid receptors can increase ethanol intake, at least in long-term ethanol-experienced rats. Since kappa-opioid receptor agonists have aversive motivational consequences, increased ethanol drinking might be an attempt to counteract the aversive effects of this treatment. On the other hand, the nor-BNI experiments indicate that endogenous kappa-opioid receptor stimulation does not seem to be involved in relapse-like drinking after protracted abstinence.

Inhibition of morphine tolerance development by a substance P-opioid peptide chimera

The neuropeptide substance P (SP), apart from its traditional role in spinal nociceptive processing, is an important regulatory effector of opioid-dependent analgesic processes. The present study stems from our original findings indicating that 1) pharmacologically administered SP mediates a strong inhibitory activity on the development of morphine tolerance in rats, and that 2) a novel SP-opioid peptide chimera YPFFGLM-NH(2), designated ESP7, produces opioid-dependent analgesia without tolerance development. To further examine the effects of simultaneous activation of two distinct opposing spinal systems on opioid tolerance and the mechanisms underlying chimeric peptide function, a second SP-opioid chimera was synthesized. This chimera, designated ESP6 (YPFFPLM-NH(2)), contains overlapping domains of endomorphin-2 and SP, respectively. ESP6 is distinguished from ESP7 by a glycine to proline substitution at position 5. Intrathecal administration of morphine sulfate (MS) with ESP6 leads to a prolongation of MS analgesia over a 5-day period. The analgesia produced by ESP6 and MS is opioid receptor-dependent, due to the ability of naltrexone to block the analgesic response. Furthermore, when ESP6 and MS are administered with concurrent NK-1 receptor blockade, a decay in analgesic potency similar to that seen with MS alone results. The presence of a proline in ESP6 appears to reduce its conformational flexibility, limit its potency at the micro-opioid receptor, and hinder its analgesic effectiveness alone. However, ESP6 represents a novel adjuvant for the maintenance of opioid analgesia over time and provides a means to predict the pharmacological properties of a chimera from its structure.

A substance P-opioid chimeric peptide as a unique nontolerance-forming analgesic

To elucidate mechanisms of acute and chronic pain, it is important to understand how spinal excitatory systems influence opioid analgesia. The tachykinin substance P (SP) represents the prototypic spinal excitatory peptide neurotransmitter/neuromodulator, acting in concert with endogenous opioid systems to regulate analgesic responses to nociceptive stimuli. We have synthesized and pharmacologically characterized a chimeric peptide containing overlapping NH(2)- and COOH-terminal functional domains of the endogenous opioid endomorphin-2 (EM-2) and the tachykinin SP, respectively. Repeated administration of the chimeric molecule YPFFGLM-NH(2), designated ESP7, into the rat spinal cord produces opioid-dependent analgesia without loss of potency over 5 days. In contrast, repeated administration of ESP7 with concurrent SP receptor (SPR) blockade results in a progressive loss of analgesic potency, consistent with the development of tolerance. Furthermore, tolerant animals completely regain opioid sensitivity after post hoc administration of ESP7 alone, suggesting that coactivation of SPRs is essential to maintaining opioid responsiveness. Radioligand binding and signaling assays, using recombinant receptors, confirm that ESP7 can coactivate mu-opioid receptors (MOR) and SPRs in vitro. We hypothesize that coincidental activation of the MOR- and SPR-expressing systems in the spinal cord mimics an ongoing state of reciprocal excitation and inhibition, which is normally encountered in nociceptive processing. Due to the ability of ESP7 to interact with both MOR and SPRs, it represents a unique prototypic, anti-tolerance-forming analgesic with future therapeutic potential.

Modulation of glutamine uptake and phosphate-activated glutaminase activity in rat brain mitochondria by amino acids and their synthetic analogues

Uptake of L-[14C]Gln and phosphate-activated glutaminase (PAG) activity were measured in nonsynaptic mitochondria isolated from rat cerebral hemispheres, in the presence of protein and nonprotein amino acids and their synthetic structural analogues and derivatives. The uptake was inhibited by > 50% in the presence of a 10-fold excess of His, homocysteine (Hcy), Trp, Leu, Tyr, Ile, Thr, Ala, Phe, Met, Ser, by > 20% in the presence of a 10-fold excess of Val, Arg, Glu, and was not affected by a 10-fold excess of Orn, alpha-ketoglutarate, Tau and Pro. Uptake of L-[14C] Leu differed from Gln uptake by its resistance to Arg, Glu, and a relatively high sensitivity to the reference inhibitor of the plasma membrane transport of large neutral amino acids (L-system)--BCH (2-aminobicyclo[2.2.1]heptane-2-carboxylic acid), and a number of natural L-system substrates. A newly synthesized alanine analogue, 2'-cyano-(biphenyl) alanine, referred to as MRC01, was the only compound tested that inhibited Gln uptake more strongly than Leu uptake. The strongest Gln uptake inhibitors: MRC01, His, Hcy and Leu, inhibited PAG activity by > 50% when added at the inhibitor/Gln concentration ratio of 1:2. PAG activity was not affected by Tau, Lys or Pro, compounds which did affect Gln uptake. The results suggest that a number of natural amino acids function as common endogenous modulators of cerebral mitochondrial Gln uptake and its degradation. MRC01, because of its inhibitory potency towards both mitochondrial Gln uptake and PAG activity, may become a convenient tool in studying the role of Gln transport in its mitochondrial metabolism in intact CNS cell and tissues.

Protein hydrolysates for oral tolerance

To induce oral tolerance in multiple sclerosis treatment, we proposed to use the predigested protein of pig spinal cord. The most biologically active composition was obtained from the hydrolysis of an undenaturated homogenate of proteins digested with pepsin. Feeding the rats with our preparation, before or after immunization with MS antigens, strongly reduced development of the experimental autoimmune encephalomyelitis (EAE). The biological results obtained in animals suggest that the developed method of induction of the oral tolerance should be effective in human treatment, at least as a support mechanism in combination with other treatment methods.

Ischemic rats as a model in the study of the neurobiological role of human beta-amyloid peptide. Time-dependent disappearing diffuse amyloid plaques in brain

Brains from patients with Alzheimer's disease contain diffuse and senile amyloid plaques. Using an experimental model, we have addressed the issue whether diffuse plaques of amyloid persist, develop with time, or both, in rats injected with human beta-amyloid-(1-42)-peptide for 3 and 12 mon after brain ischemia. Rats receiving beta-amyloid peptide for 3 months after brain ischemia demonstrated widespread diffuse amyloid plaques in hippocampus and cerebral cortex. Neuronal, glial, ependymal, endothelial and pericyte cell bodies were observed filled with beta-amyloid peptide. No staining was observed in control brains. In the group alive 1 year no deposition of human beta-amyloid peptide was observed, too. Direct evidence that diffuse amyloid plaques can disappear in the brain is thus provided for the first time.

Biological activity of fragments and analogues of the potent dimeric opioid peptide, biphalin

The synthesis and biological activity of two fragments of the very potent opioid peptide biphalin, showed that Tyr-D-Ala-Gly-Phe-NH-NH<-Phe is the minimal fragment necessary to express equal affinities and the same biological activity profile as the parent biphalin. The replacement of N'-Phe with other L- or D- lipophilic amino acids showed the possibility of modification of receptor efficacy of the analogues.

Ultrastructural changes in the central and peripheral nervous system in the rat with experimental allergic encephalomyelitis

The aim of the study was the evaluation of ultrastructural changes in rats central and peripheral nervous system after the introduction of experimental allergic encephalomyelitis (EAE) and after the treatment with spinal cord protein hydrolysate. Reduced structural disturbances in myelin were found after oral treatment with hydrolysate. In addition, the indications of remyelinization processes have been observed.

Inhibitory effect of biphalin and AZT on murine Friend leukemia virus infection in vitro

Biphalin is a bivalent opioid analogue containing two tyrosine residues. We have examined the effect of biphalin's anti-retroviral potency in vitro using a murine model. Biphalin, in non-cytotoxic concentrations, suppressed in a dose-dependent fashion the replication of Friend leukemia virus (FLV) in Mus dunni cells as determined using a focus forming assay. FLV replication was substantially reduced by biphalin at 10(-4) M concentration. When biphalin was combined with 3'-azido-3'-deoxythymidine (AZT) the two acted synergistically in inhibiting FLV replication compared to either used alone. Using a reverse transcriptase (RT) assay, FLV RT levels also were noted to be reduced in the presence of biphalin. These observations indicate that biphalin possesses anti-retroviral activity in vitro, suggesting that this opioid peptide should be examined further in vivo to determine if it is a candidate for combined therapy with AZT and possibly other drugs for retrovirus infections including the human immunodeficiency virus (HIV).

Binding of SPXK- and APXK-peptide motifs to AT-rich DNA. Experimental and theoretical studies

The binding properties of the SPXK- and APXK-type peptides to the AT-rich DNA fragments of different length were studied by measuring the competition of peptides with Hoechst 33258 dye for DNA binding and by the gel shift assay analysis. In parallel to the experimental studies, molecular modeling techniques were used to analyze possible binding modes of the SPXZ and APXK motifs to the AT-rich DNA. The results of the competition measurements and gel shift assays suggest that serine at the i-1 position (i is proline) can be replaced by alanine without affecting the binding properties of the motif. Thus, the presence of the conserved serine in this motif in many DNA-binding proteins is probably not dictated by structural requirements. Based on the results of molecular modeling studies we propose that the binding mode of the SPXK-type motifs to the AT-rich DNA resembles closely that between the N-terminal arm of the homeodomain and DNA. This model confirms that serine in the SPXK motifs is not essential for the DNA binding. The model also indicates that if X in the motif is glutamic acid, this residue is probably protonated in the complex with DNA.

[125I-Tyr1]biphalin binding to opioid receptors of rat brain and NG108-15 cell membranes

Mono iodinated analogues of biphalin [(Tyr-D-Ala-Gly-Phe-NH-)2], both nonradioactive [I-Tyr1]biphalin and radioactive [125I-Tyr1]biphalin have been synthesized. The radioligand binding profiles of these compounds for two types of tissues, rat brain membranes, and NG108-15 cell membranes were identical to the parent biphalin. This is additional evidence for the hypothesis that biphalin behaves like a monomeric ligand and that only one intact tyrosine is necessary for high biological activity. The second tyrosine could be used for successful radioiodination which may greatly simplify biochemical and pharmacological studies of biphalin. The results of receptor binding studies show that the binding of both biphalin and [I-Tyr1]biphalin to the delta and mu opioid receptors are not independent. [125I-Tyr1]Biphalin binds to delta receptors as shown in NG108-15 cell membranes. Nevertheless, [125I]biphalin binding to delta receptors in rat brain membranes was hardly evident and mu receptor binding predominated or at least was much more readily detectable in this preparation.

Binding of SPXK- and APXK-peptide motifs to AT-rich DNA. Experimental and theoretical studies

The binding properties of the SPXK- and APXK-type peptides to the AT-rich DNA fragments of different length were studied by measuring the competition of peptides with Hoechst 33258 dye for DNA binding and by the gel shift assay analysis. In parallel to the experimental studies, molecular modeling techniques were used to analyze possible binding modes of the SPXZ and APXK motifs to the AT-rich DNA. The results of the competition measurements and gel shift assays suggest that serine at the i-1 position (i is proline) can be replaced by alanine without affecting the binding properties of the motif. Thus, the presence of the conserved serine in this motif in many DNA-binding proteins is probably not dictated by structural requirements. Based on the results of molecular modeling studies we propose that the binding mode of the SPXK-type motifs to the AT-rich DNA resembles closely that between the N-terminal arm of the homeodomain and DNA. This model confirms that serine in the SPXK motifs is not essential for the DNA binding. The model also indicates that if X in the motif is glutamic acid, this residue is probably protonated in the complex with DNA.

Modifications of the 4,4'-residues and SAR studies of Biphalin, a highly potent opioid receptor active peptide

Modifications of 4,4' residues of Biphalin have resulted in greater binding selectivity and biological potency for the mu opioid receptor. A higher partition coefficient across the phospholipid bilayer membrane has been achieved by using a beta-branched unusual amino acids.

Decreased hypotensive responsiveness to nitric oxide donor S-nitroso N-acetyl-DL-penicillamine (SNAP) in spontaneously hypertensive (SHR) rats

The aim of the study was to compare hemodynamic effects of intravenously (i.v.) applied nitric oxide (NO) donor S-nitroso N-acetyl-DL-Penicillamine (SNAP) in conscious spontaneously hypertensive (SHR) to those observed in normotensive Wistar Kyoto (WKY) rats. The study was performed on 7 SHR and 8 WKY instrumented with polyethylene catheters inserted to the abdominal aorta and vena cava for blood pressure (MAP) and heart rate period (HRp) monitoring, and for i.v. administration of SNAP (0.05, 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, 20.0, 40.0 and 75.0 microM/kg of body weight). The following differences were found between SHR and WKY rats: 1) the threshold dose of SNAP, eliciting significant decrease of MAP was markedly higher in SHR (1.0 microM/kg b.w.) than in WKY (0.2 microM/kg b.w.), 2) SHR responded with significantly smaller maximum decreases of MAP to administration of 1.0, 2.0, 5.0 and 10.0 microM/kg b.w. of SNAP and with smaller heart rate acceleration to administration of 10.0, 40.0 and 75.0 microM/kg b.w. of SNAP, 3) in SHR MAP decreased progressively, the greatest decline being observed after administration of the highest dose (75 microM/kg b.w.) of SNAP while in WKY the log dose/delta MAP response curve reached plateau beginning with 2 microM/kg b.w. of SNAP, 4) the slopes and intercepts of the regression lines describing relationship between MAP and HRp after administration of SNAP were significantly different in SHR and WKY rats (P < 0.01). The results indicate that SHR are significantly less sensitive to hypotensive effects of NO generated from moderate doses of SNAP.

Transport of human beta-amyloid peptide through the rat blood-brain barrier after global cerebral ischemia

In an attempt to produce an animal model of the Alzheimer's disease (AD), beta-amyloid-(1-42)-peptide (beta A1-42) was injected into the femoral vein in rats after single and repeated cardiac arrest (CA). After survival of 3.5 months, the brains immunoreactivity was evaluated using light microscopic immunocytochemistry of monoclonal beta-amyloid peptide (beta A) antibody 4G8 (mAb 4G8). Rats receiving beta A1-42 after CA demonstrated multifocal and widespread extravasation of beta A1-42 in extra- and intracellular space. The permeability to beta A1-42 was significantly higher in rats after repeated cerebral ischemia. As in AD, there were irregular diffuse amyloid plaque-like deposits and neuronal loss with reactive gliosis. Our data in ischemic rats with beta A1-42 represent a novel animal model of Alzheimer's pathology.

Interaction of a highly potent dimeric enkephalin analog, biphalin, with model membranes

Biphalin, (Tyr-D-Ala-Gly-Phe-NH)2, is a highly potent dimeric analog of enkephalin. Its analgesic efficacy is due in part to its ability to permeate the blood-brain barrier. To aid in understanding the mechanism of the transmembrane movement we determined and analyzed the permeability and partition coefficients of biphalin and a series of analogues where F, Cl, I, NO2, or NH2 were placed in the para position of the aromatic rings of Phe4,4'. Liposomes composed of neutral phospholipids and cholesterol were used as the model membrane. The overall good correlation between permeability and water-membrane partition coefficients suggests that the movement of biphalins across the model membrane is controlled by diffusion and depends on the water-membrane partition coefficient. To explain the observed correlation between permeability and the electron withdrawing/donating character of the substituents in the phenylalanine ring, we examined various folding patterns of Leu-enkephalin, an endogenous pentapeptide that exhibits affinities toward the same classes of opioid receptors (delta and mu). The observed permeabilities and partition coefficients of biphalin and analogues, as well as the tyrosine side chain accessibility, are consistent with the presence of the type of folding where the tyrosine and phenylalanine side chains are in a close contact. We propose that the aromatic ring interaction can promote the peptide permeability by stabilizing a more compact structure of biphalin that would minimize the number of hydrogen bonds with water and therefore enhances partitioning into the model membrane.

Structure-activity relationship of biphalin. The synthesis and biological activities of new analogues with modifications in positions 3 and 4

New analogues of biphalin [(Tyr-D-Ala-Gly-Phe-NH-)2] with modifications of amino acid residues in positions 3,3' and 4,4' have been synthesized. The potency and selectivity of these analogues were evaluated by competitive radioreceptor binding assay in the rat brain using [3H]CTOP (mu ligand) and [3H][p-Cl-Phe4]DPDPE (delta ligand) as ligands, and by bioassay in the mouse vas deferens (MVD, delta receptor assay) and guinea pig ileum (GPI, mu receptor assay). The symmetrical substitution of phenylalanine in positions 4 and 4' with p-fluorophenylalanine or p-nitrophenylalanine resulted in an enhancement of the affinity at both delta and mu receptors, with some increase of the selectivity for delta opioid receptors. The analogue containing p-chlorophenylalanine in positions 4 and 4' is the most selective to the delta receptors in this series, with a selectivity ratio about 5. The symmetrical substitution of the glycine-3 residue with phenylalanine resulted in a decrease of binding affinities and biological potencies at both mu & delta receptors.

Lipid membrane permeability of modified c[D-Pen2, D-Pen5]enkephalin peptides

Permeability coefficients of a series of analogues of a potent opioid peptide, c[D-Pen2, D-Pen5]enkephalin, were measured in a model membrane system. The analogues included hydrophobic amino acid substitutions on position 3. Liposomes of a mixed composition consisting of zwitterionic lipids and cholesterol served as the model membranes. The obtained permeability coefficients range between 0.38 x 10(-12) and 2.9 x 10(-12) cm/s. These data were correlated with the hydrophobicity scale of Nozaki and Tanford (J. Biol. Chem. 246, 1971, 2211-2217) (correlation coefficient = 0.9933) and with determinations of lipid order perturbation by differential scanning calorimetry (correlation coefficient = -0.9779). The reasonably good correlation obtained within the family of analogues substituted on position 3 (Gly, Ala, Leu, Phe) indicates that changes in permeabilities are primarily related to increases in the partition coefficient of the peptide. However, Phe residue added on the N-terminal end of the peptide (position 0) does not appear to follow the observed trend, showing stronger lipid perturbation and lower permeability compared to the Phe3 analog. This observation demonstrates that each class of peptide modifications requires a new basis of permeability analysis and predictions.

Enkephalin analog prodrugs: assessment of in vitro conversion, enzyme cleavage characterization and blood-brain barrier permeability

To improve the blood-brain barrier penetration of the delta-opioid receptor peptides [D-Pen2, D-Pen5]enkephalin (DPDPE) and [D-Pen2, L-Cys5]enkephalin (DPLCE), various prodrug forms were synthesized to increase lipophilicity and drug delivery to the brain. The aims of this study were 3-fold, 1) to assess the metabolic conversion of various DPDPE and DPLCE prodrugs in vitro using mouse brain homogenate and mouse serum, 2)to characterize the proteolytic enzymes responsible for cleaving prodrugs to the parent compounds using select peptidase inhibitors and 3)to assess the blood-brain barrier permeability of prodrugs, compared with their parent compounds, using the in vitro bovine brain microvessel endothelial cell culture model. The prodrugs with carboxyl-terminal phenylalanine residues (DPDPE-Phe and DPLCE-Phe) had significantly longer metabolic conversion times in both mouse serum and brain homogenates than did the prodrugs with amino-terminal phenylalanine residues. Inhibition of leucine aminopeptidase with bestatin in the serum increased the conversion time of Phe0-DPDPE from 6.8 min to 92.2 min. Inhibition of aminopeptidase M with amastatin in the brain homogenate increased the conversion time of Phe0-DPDPE from 3.9 min to > 450 min. The long half-life of DPLCE-Arg-Pro-Ala in serum (317 min) vs. brain (9.2 min) can be explained by the high levels of the degradative endopeptidase 24.15 (EC 3.4.24.15) in the central nervous system but not in plasma. The data also showed that, for specific prodrugs of DPDPE such as Phe0-DPDPE and DPDPE-Arg-Gly, the prodrug shows a significant improvement in permeability, compared with the parent compound. Therefore, these data provide evidence that prodrugs or prodrug-enzyme inhibitor combinations may optimize the delivery of peptide and/or protein drugs to the central nervous system.

Evidence of blood-brain barrier permeability/leakage for circulating human Alzheimer's beta-amyloid-(1-42)-peptide

Brains from patients with Alzheimer's disease contain amyloid plaques which are composed of beta-amyloid peptide and are considered to play a causal role in the neuropathology of this disease. The origin of beta-amyloid peptide in brain parenchyma and vessels of Alzheimer's disease patients is not known. This study examined the permeability of the blood-brain barrier to beta-amyloid peptide in rats subjected to single or repeated episodes of global cerebral ischaemia followed by i.v. injections of human synthetic beta-amyloid-(1-42)-peptide. Rats receiving beta-amyloid peptide after ischaemia demonstrated multifocal and widespread accumulation of beta-amyloid peptide in hippocampus, cerebral cortex and occasionally in white matter. beta-Amyloid peptide penetration involved arterioles, veins and venules. Neuronal, glial and pericyte bodies were observed filled with beta-amyloid peptide. Direct evidence that soluble human beta-amyloid-(1-42)-peptide crosses the blood-brain barrier and enters the brain from the circulation is thus provided for the first time.

Blood-to-central nervous system entry and stability of biphalin, a unique double-enkephalin analog, and its halogenated derivatives

Biphalin (Tyr-D-Ala-Gly-Phe-NH)2 is a unique opioid peptide analog that contains two active enkephalin pharmacophores and is more potent than morphine and etorphine in eliciting analgesia after intrathecal administration. After systemic administration, only a small amount was detected in the brain, but analgesia was observed. Because halogenation of enkephalin analogs has been shown to increase the brain uptake after systemic administration, our research group synthesized both p-[Cl-Phe4,4']biphalin and p-[F-Phe4,4']biphalin. The aim of the present study was to characterize and compare the blood-to-central nervous system (CNS) pharmacokinetics and biological stability of biphalin and related halogenated analogs. The initial screening used an in vitro blood-brain barrier model and identified p-[Cl-Phe4,4')biphalin as the enkephalin analog with the best potential for greater CNS entry. The CNS uptake and stability of biphalin and p-[Cl-Phe4,4']biphalin was examined further using an in situ brain perfusion technique coupled to high-performance liquid chromatography analysis. Both biphalin and its chlorohalogenated analog, were found to significantly enter the CNS through both the blood-brain and blood-cerebrospinal fluid barriers. Chlorohalogenation of biphalin was shown to both improve CNS entry, most likely through an enhancement in lipophilicity, and increase biological stability. This study suggests that incorporation of chlorohalogens at the p-Phe4,4' position is a promising structural modification in the development of biphalin as a successful opioid drug for the clinic.

Synthesis and biological properties of gamma-glutamyl-dermorphin, a prodrug

The possibility of using the gamma-glutamyl-transpeptidase system for transformation of inactive propeptide, gamma-glutamyl-neuropeptides into active neuropeptides has been tested on dermorphin and its gamma-glutamyl analogue. Gamma-glutamyl-dermorphin 2 showed little affinity for opioid receptors. Nonetheless, systemic (intraperitoneal (i.p.), or intravenous (i.v.)) application of this compound induced significant antinociceptive effects, although ten to twenty-fold higher doses were required compared to the parent dermorphin 1. On the other hand, the analogue 2 showed high, antinociceptive activity when injected intrathecally (i.t.). When compared to dermorphin, 2 was one third as potent, but did show a significant prolonged duration of the effect. These results suggest that in the periphery, the peptidase metabolism which results in degradation of bioactivity, is offset by gamma-glutamyl-transpeptidase (GGTP) activity that liberates bioactive peptide 2. On the other hand, in the central nervous system, the activity of gamma-glutamyl-transpeptidase system seems to be more effective than other peptidase systems, resulting in formation of active peptide 2 in a significant amount. These data suggests that gamma-glutamyl analogues of neuropeptides can be considered as potential prodrugs, especially for synthetic analogues which themselves are resistant to peptidase action.