TAPP analogs containing ß3 -homo-amino acids: synthesis and receptor binding.

ß-Amino acids containing α,ß-hybrid peptides show great potential as peptidomimetics. In this paper, we describe the synthesis and affinity to µ-opioid and δ-opioid receptors of α,ß-hybrids, analogs of the tetrapeptide Tyr- d-Ala-Phe-Phe-NH(2) (TAPP). Each amino acid was replaced with an l- or d-ß(3) -h-amino acid. All α,ß-hybrids of TAPP analogs were synthesized in solution and tested for affinity to µ-opioid and δ-opioid receptors. The analog Tyr-ß(3) h- d-Ala-Phe-PheNH(2) was found to be as active as the native tetrapeptide.

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.

Effect of recombinant Lactococcus lactis producing myelin peptides on neuroimmunological changes in rats with experimental allergic encephalomyelitis.

Multiple sclerosis (MS) is a human autoimmune neurodegenerative disease with an unknown etiology. Despite various therapies, there is no effective cure for MS. Since the mechanism of the disease is based on autoreactive T-cell responses directed against myelin antigens, oral tolerance is a promising approach for the MS treatment. Here, the experiments were performed to assess the impact of oral administration of recombinant Lactococcus lactis producing encephalogenic fragments of three myelin proteins: myelin basic protein, proteolipid protein, and myelin oligodendrocyte glycoprotein, on neuroimmunological changes in rats with experimental allergic encephalomyelitis (EAE) - an animal model of MS. Lactococcus lactis whole-cell lysates were administered intragastrically at two doses (103 and 106 colony forming units) in a twenty-fold feeding regimen to Lewis rats with EAE. Spinal cord slices were subjected to histopathological analysis and morphometric evaluation, and serum levels of cytokines (IL-1b, IL-10, TNF-α and IFN-γ) were measured. Results showed that administration of the L. lactis preparations at the tested doses to rats with EAE, diminished the histopathological changes observed in EAE rats and reduced the levels of serum IL-1b, IL-10 and TNF-α, previously increased by evoking EAE. This suggests that oral delivery of L. lactis producing myelin peptide fragments could be an alternative strategy to induce oral tolerance for the treatment of MS.

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.

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.

Peptides as receptor selectivity modulators of opiate pharmacophores.

In an effort to investigate whether "address" segments of endogenous opioid peptides, which are responsible for modulating receptor selectivity, also could modulate the selectivity of opioid alkaloid pharmacophores, we have synthesized analogues of leucine-enkephalin and dynorphin in which the N-terminal dipeptide "message" sequence has been replaced by oxymorphone or naltrexone. A hydrazone group was employed as a linkage between the alkaloids and peptides. The binding data for mu, kappa, and delta receptors indicate that peptide portions of the analogues can modulate the receptor selectivity of the attached alkaloid pharmacophores. The selectivity for different opioid receptor types depends on a balance between the affinities of the message and address components. In cases where these components have comparable receptor affinities, the address can significantly shift selectivity by increasing affinity to one receptor type while reducing affinity to other types. When the message component has high affinity for a particular receptor type, the modulatory role of the address is expressed mainly by reducing the affinity of the ligand for other opioid receptor types.

Investigation of the structural requirements for the kappa-selective opioid receptor antagonist, 6 beta,6 beta'-[ethylenebis(oxyethyleneimino)]bis[17-(cyclopropylmethyl)- 4,5 alpha-epoxymorphinan-3,14-diol] (TENA).

In an effort to determine whether or not the basic nitrogens in the spacer of the bivalent ligand 6 beta,6 beta'-[ethylenebis(oxyethyleneimino)]bis[17-(cyclopropylmethyl)4,5 alpha-epoxymorphinan-3,14-diol] (TENA, 1) is responsible for its selective kappa opioid antagonist activity, we have synthesized monovalent analogues 2-4 that contain a C-6 side chain with basic nitrogens. Analogue 2 behaved as a potent opioid agonist in the guinea pig ileum preparation (GPI) and possessed no significant kappa opioid antagonist activity (IC50 ratio = 1) relative to TENA (IC50 ratio = 20). The agonist activity of 3 and 4 interfered with the opioid antagonist assay and therefore did not permit evaluation of antagonist activity in a concentration range where TENA is effective. Although the results obtained with 2 are consistent with the requirement of a second opiate pharmacophore (rather than a second basic nitrogen in the spacer) for the kappa antagonist activity of TENA, the potent agonism associated with these monomers do not allow a firm conclusion in this regard.

Binaltorphimine-related bivalent ligands and their kappa opioid receptor antagonist selectivity.

In an effort to develop selective antagonists for kappa opioid receptors, bivalent ligands that contain opioid antagonist pharmacophores derived from naltrexone or other morphinans were synthesized and tested on the guinea pig ileum (GPI) and mouse vas deferens (MVD) preparations. The minimum requirements for kappa selectivity are at least one free phenolic OH group and one N-cyclopropyl or N-ally substituent. Several compounds (3, 8, 10) with kappa selectivity as good as or better than norbinaltorphimine (nor-BNI, 2) were discovered. The structure-activity relationship revealed that the pyrrole ring functions strictly as a spacer and does not contribute to kappa selectivity. The pharmacologic data suggest that only one antagonist pharmacophore may be required for kappa selectivity and that the other morphinan portion of the molecule confers selectivity by interacting with a unique subsite proximal to the antagonist pharmacophore recognition locus.

Design of cyclic deltorphins and dermenkephalins with a disulfide bridge leads to analogues with high selectivity for delta-opioid receptors.

We earlier suggested that the low receptor selectivity observed for previously synthesized constrained analogues of deltorphin I (DT I) was the result of a reduction in the lipophilic surface of the C-terminal of the peptide. To confirm this prediction and to further test a previously proposed conformational model for bioactivity at delta opioid receptors, we have synthesized several new cyclic analogues with the general structure [D-Xaa2,Yaa5]deltorphin I and II in which Xaa2 is D-cysteine or D-penicillamine (D-Pen), and Yaa5 is an L- or D-penicillamine residue. Additional substitutions at positions 4, 6, and 7 also were examined. The analogues were tested for binding to mu- and delta-opioid receptors and in mouse vas deferens and guinea pig ileum biological assays. The introduction of a lipophilic L-Pen in position 5 and D-Cys or D-Pen in position 2 resulted in a highly delta-selective series of analogues, which fully confirmed our prediction. The cyclic analogues formula; see text: DT I are among the most delta-selective analogues described thus far.

Opioid agonist and antagonist activities of peripherally selective derivatives of naltrexamine and oxymorphamine.

A series of beta-naltrexamine and beta-oxymorphamine derivatives that contain ionizable moieties coupled to the 6 beta-amino group were synthesized in an effort to develop antagonists and agonists that have negligible access into the central nervous system (CNS). Among the beta-naltrexamine derivatives 1-7, all displayed partial agonism on the guinea pig ileal longitudinal muscle preparation except for aspartyl derivative 6, which was a full agonist with activity in the range of morphine. The beta-oxymorphamine derivatives 8-12 were all full agonists with potencies ranging from 1.5 to 6.1 times that of morphine. Among the compounds evaluated in mice for antinociceptive or opioid antagonist activities, aspartyl derivative 6 possessed the greatest difference between peripheral (po or iv) and icv equiactive antagonist doses. Compared to naltrexone, 6 was greater than 100 times more potent by the icv route, but 6000-10,000 times less potent when administered po or icv. The present study suggests that zwitterionic groups are highly effective in preventing penetration of ligands into the CNS. Such ligands may be useful pharmacologic tools for investigation of peripheral opioid mechanisms. Moreover, they could find clinical applications when the central actions are unwanted.

Binary drugs: conjugates of purines and a peptide that bind to both adenosine and substance P receptors.

A "functionalized congener" approach to adenosine receptor antagonists has provided a means to synthesize highly potent peptide conjugates of 1,3-dialkylxanthines. The antagonist XAC, such a functionalized xanthine amine congener, has been attached to a segment derived from the neurotransmitter peptide substance P (SP) to form a binary drug that binds to both receptors with Ki values of 35 nM (central A1-adenosine) and 300 nM (striatal SP). Coupling of the functionalized adenosine agonist N6-[p-(carboxymethyl)phenyl]adenosine to an SP C-terminal peptide also resulted in a binary drug that binds to both receptors. The demonstration that the biochemical properties of two unrelated drugs, both of which act through binding at extracellular receptors, may be combined in the same molecule suggests a novel strategy for drug design. In principle, a combined effect of the two different substances that produce the same final effect (e.g., hypotension by adenosine agonists and by SP analogues) might occur in vivo. Adenosine analogues have analgesic properties, and the binary drug derived from substance P and adenosine agonists or antagonists might provide useful tools for probing interrelationships of SP pathways and sites for the antinociceptive action of adenosine.

X-ray crystal structure of the opioid ligand naltrexonazine.

The anti-anti isomer of naltrexonazine (1) was synthesized, and its configuration was confirmed by X-ray crystallography. The syn-anti isomer is readily converted to 1 under acidic conditions. The apparent equal receptor binding of 1 and syn-anti isomer indicates that isomerization of the azine moiety may take place under the conditions of biological evaluation. Two possible explanations for wash-resistant binding of 1 to opioid receptors are presented. The first possibility involves a noncovalent interaction of the ligand with the opioid receptor, and the second considers covalent binding by a receptor-based sulfhydryl group.

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.

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.

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.

Transfer of fatty acyl groups from membrane phosphatides to opiate ligands.

Investigation of the persistent opioid receptor binding of hydrazine-containing opiate ligands to brain membranes has revealed that it is related to conversion of these ligands to fatty acylhydrazone or fatty acylhydrazide derivatives. The fatty acyl group was found to be derived from membrane phosphatides. Persistent binding does not occur when this pool of phosphatides is removed by extensive washing, and it is restored upon addition of phosphatide to the membranes. In washed membranes, synthetically derived fatty acylhydrazones exhibited persistent binding similar to that found when naltrexonazine was incubated with brain membranes. It is suggested that the persistent binding is a consequence of the localization of fatty acylnaltrexazone derived from naltrexonazine in a membrane lipid bilayer that interfaces with the opioid receptor system rather than the persistence of naltrexonazine itself.

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.

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.

The effect of enkephalin dimers on body temperature in mice.

Short-lasting decrease in rectal temperature in mice after intraperitoneal administration of an enkephalin dimer, the so called double-enkephalin--(Tyr-D-Ala-Gly-Phe-NH)2 (D-ENK-O)--at dose 0.1, 0.5, 1, 2.5, 5, 10 and 20 mg/kg of body weight was observed. Another double-enkephalin--Tyr-D-Ala-Gly-Phe-NH-(CH2)3-HN-Phe-Gly-D-Ala-Tyr-- fai led to produce this effect. The hypothermic effect of D-ENK-O was almost completely reduced by naloxone which suggests an involvement of opiate receptors in the D-ENK-O produced hypothermia in mice.

Double-enkephalins--synthesis, activity on guinea-pig ileum, and analgesic effect.

We have synthesized enkephalin analogues in which C-terminal methionine or leucine residues are replaced by a second active fragment of the enkephalin analogue. Synthesis of two compounds is described: in one, two fragments of a D-Ala2-enkephalin analogue are connected by a -NH-NH-bridge, and in the other, three methylene groups are incorporated between the amino groups. The first compound is a very potent inhibitor of electrically induced contractions of guinea-pig ileum and produces a strong analgesia when administered intraperitoneally in mice. The second compound is less active on the ileum and fails to produce analgesia after systemic injection. The double-enkephalins may interact with mu-receptors.