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Victor J Hruby

Publications and source records attributed to Victor J Hruby.

80 records · Page 5Linked to original sources
PubMed2002

Interaction of enkephalin peptides with anionic model membranes.

According to the model for passive transport across the membranes, the total flow of permeant molecules is related to the product of the water-membrane partition coefficient and the diffusion coefficient, and to the water-membrane interfacial barrier. The effect of membrane surface charge on the permeability and interaction of analgesic peptide ligands with model membranes was investigated. A mixture of zwitterionic phospholipids with cholesterol was used as a model membrane. The lipid membrane charge density was controlled by the addition of anionic 1-palmitoyl-2-oleoylphosphatidylserine. Two classes of highly potent analgesic peptides were studied, c[D-Pen(2),D-Pen(5)]enkephalin (DPDPE) and biphalin, a dimeric analog of enkephalin. The effect of increased surface charge on the permeability of the zwitterionic DPDPE is a relatively modest decrease, that appears to be due to a diminished partition coefficient. On the other hand the binding of the dicationic biphalin ligands to membranes increases proportionally with increased negative surface charge. This effect translates into a significant reduction of biphalin permeability by reducing the diffusion of the peptide across the bilayer. These experiments show the importance of electrostatic effects on the peptide-membrane interactions and suggest that the negative charge naturally present in cell membranes may hamper the membrane transport of some peptide drugs, especially cationic ones, unless there are cationic transporters present.

Analgesics↗
PubMed2002

Designing peptide receptor agonists and antagonists.

The most ubiquitous mode for controlling and modulating cellular function, intercellular communication, immune response and information-transduction pathways is through peptide-protein non-covalent interactions. Hormones, neurotransmitters, antigens, cytokines and growth factors represent key classes of such peptide ligands. These ligands might either be processed fragments of larger precursor proteins or surface segments of larger proteins. Although there are numerous exceptions, such as insulin, oxytocin and calcitonin, most ligands are not used directly as drugs, and often the most useful ligands for therapy would be analogues that act as antagonists of the native ligands. A search for systematic structure-based or ligand-based approaches to designing such ligands has been an important concern. Today, a robust strategy has been developed for the design of peptides as drugs, drug candidates and biological tools. This strategy includes structural, conformational, dynamic and topographical considerations.

Animals↗
PubMed2002

Assessment of the role of interstitial glucagon in the acute glucose secretory responsiveness of in situ pancreatic beta-cells.

Glucagon is a potent stimulator of insulin release in the presence of a permissive glucose concentration, activating beta-cells in vitro via both glucagon- and glucagon-like peptide-1 (GLP-1)-receptors. It is still unclear whether locally released glucagon amplifies the secretory responsiveness of neighboring beta-cells in the intact pancreas. The present study investigates this question in the perfused pancreas by examining the effects of antagonists for glucagon receptors ([des-His(1),des-Phe(6),Glu(9)]glucagon-NH(2), 10 micromol/l) and GLP-1-receptors [exendin-(9-39)-NH(2), 1 micromol/l] on the insulin secretory response to glucose. The specificity of both antagonists was demonstrated by their selective interaction with glucagon-receptor signaling in rat hepatocytes and GLP-1-receptor signaling in Chinese hamster lung (CHL) fibroblasts. In purified rat beta-cells, the glucagon-receptor antagonist (10 micromol/l) inhibited the effect of 1 nmol/l glucagon upon glucose-induced insulin release by 78 plus minus 6%. In the perfused rat pancreas, neither of these antagonists inhibited the potent secretory response to 20 mmol/l glucose, although they effectively suppressed the potentiating effect of, respectively, an infusion of glucagon (1 nmol/l) or GLP-1 (1 nmol/l) on insulin release. When endogenous glucagon release was enhanced by isoproterenol (100 nmol/l), no amplification was seen in the simultaneous or subsequent insulin secretory response to glucose. It is concluded that, at least under the present selected conditions, the glucose-induced insulin release by the perfused rat pancreas seems to occur independent of an amplifying glucagon signal from neighboring alpha-cells.

Animals↗
PubMed1995

Characterization of supraspinal antinociceptive actions of opioid delta agonists in the rat.

Supraspinally mediated antinociception has been clearly established for agonists acting via both micro- and delta-opioid receptors. The present experiments were undertaken to further characterize the role of supraspinal opioid delta receptors in the mediation of antinociception in rats and to examine the possible role of putative delta1- and delta2-opioid receptors in the antinociceptive effect. Cannulae directed at the right lateral ventricle, the periaqueductal gray (PAG), or the medullary reticular formation (MRF) were implanted in adult male, Sprague-Dawley rats for the microinjection of [D-Ala2,Glu4]deltorphin (delta2 agonist), [D-Pen2,D-Pen5]enkephalin (DPDPE, delta1 agonist), [D-Ser2,Leu5,Thr6]enkephalin (DSLET, mixed delta/micro agonist) or morphine (reference micro-opioid). Pretreatments (24 h prior to agonist microinjection) were made with the putative delta1 and delta2 antagonists, [D-Ala2,Leu5,Cys6]enkephalin (DALCE) and [D-Ala2,Cys4]deltorphin (Cys-DELT) and antinociception was measured in the 55 degrees C hot plate (HP) and 52 degrees C and 55 degrees C (low and high intensity) warm-water tail-flick (TF) tests. Data were converted to percent maximal possible effect (%MPE). Intracerebroventricular (i.c.v.) administration of DPDPE produced less than a 50%MPE in the HP test whereas [d-Ala2,Glu4]deltorphin produced Cys-DELT sensitive antinociception of up to 92% MPE. Neither i.c.v. agonist was effective in the TF assays, and both agonists were without effect in the PAG. [D-Ala2,Glu4]deltorphin microinjected into the MRF produced Cys-DELT sensitive antinociception of 60 and 47% MPE in the HP and low-intensity TF tests, respectively, but was not effective in the 55 degrees C TF test; DPDPE did not produce antinociception when microinjected at this site. Microinjection of DSLET in the MRF produced significant antinociception in all three assays. Morphine produced antinociception following i.c.v. administration or microinjection into the PAG in all tests. Microinjection of morphine into the MRF produced antinociception in the HP and 52 degrees C, but not 55 degrees C, TF tests. Morphine anticociception was not antagonized by either DALCE or Cys-DELT. These data demonstrate that supraspinal delta-opioid receptors can be activated to elicit antinociception in the rat and that opioid delta2 receptors predominate in this effect. Further, these effects may occur predominately via inhibition of supraspinally organized behavior without activation of descending systems such as those mediating the TF response in the rat.

Animals↗
PubMedDate not supplied

Rigid linkers for bioactive peptides.

Rigid linkers of variable length were used to connect two high-affinity Nle4-D-Phe7-alpha-melanocyte stimulating hormone (NDP-alpha-MSH) or two low-affinity MSH(4) ligands. The linked peptides were synthesized by solid-phase methods. Control experiments indicate there is little or no effect of these linkers on NDP-alpha-MSH or MSH(4) binding to the human melanocortin 4 receptor (hMC4R). Tethering two high-affinity ligands gave no binding enhancement, while tethering two low-affinity ligands resulted in binding enhancement that decreased with increased linker length. Furthermore, for the low-affinity ligands, the enhancement of affinity is inversely proportional to the estimated molecular moments of inertia. These results are consistent with a model wherein binding is enhanced when the rate of ligand reattachment to the receptor is fast relative to the rate of ligand diffusion.

Cell Line↗