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Biomedical subjects

J Horvat

Publications and source records attributed to J Horvat.

At least 19 recordsLinked to original sources
PubMed1999

Circular dichroism study of the carbohydrate-modified opioid peptides.

The conformational preferences of enkephalins and the related glycoconjugates in which free or protected carbohydrate moieties were linked to the opioid peptides through an ether, ester or amide bond were investigated by circular dichroism spectroscopy in water, trifluoroethanol and water-trifluoroethanol mixtures. The analysis of the spectra revealed that the conformation of the enkephalin molecule is very sensitive to slight changes in the peptide structure around the C-terminal region. It was found that the type II beta-turn structures are populated in N-terminal tetrapeptide enkephalin fragment, while leucine-enkephalin amide feature a type I (III) beta-turn structure in solution. Incorporation of the sugar moiety into opioid peptide compound did not significantly influence the overall conformation of the peptide backbone, although minor intensity changes may reflect shifts in the population of the different turn systems. These small structural alterations can be responsible for the receptor-subtype selectivity of the various carbohydrate-modified enkephalin analogs.

Carbohydrate Conformation↗
PubMed1999

Synthesis of hexose-related imidazolidinones: novel glycation products in the Maillard reaction.

Carbohydrate-peptide esters which mimic the reactivity of sugar 6-phosphates in nonenzymatic glycations were used as model compounds for the study of the Maillard reaction in vitro. We found that intramolecular cyclization of the monosaccharide ester in which the sugar moiety (D-glucose or D-galactose) is linked, through the C-6 hydroxy group, to the C-terminal carboxy group of the endogenous opioid pentapeptide leucine-enkephalin, in methanol as the solvent, resulted in the formation of imidazolidinone diastereoisomers having cis or trans relative geometry of the substituents at the imidazolidinone ring moiety. The diastereoisomeric imidazolidinones were separated and each transformed by hydrolysis into the corresponding D-gluco- and D-galacto-related imidazolidinone products of leucine-enkephalin. Along with the previous evidence that, from the same sugar-peptide esters by changing the reaction conditions Amadori rearrangement products could be obtained [Horvat et al. (1998) J Chem Soc Perkin Trans 1:909-13], the presented results point to the possibility that similar carbohydrate-related imidazolidinones may also be generated in the early stage of the Maillard reaction in vivo.

Chromatography, High Pressure Liquid↗
PubMed1994

Correlation of structure and retention behaviour in reversed-phase high-performance liquid chromatography. II. Methionine-enkephalin-related glycoconjugates.

Reversed-phase high-performance liquid chromatographic elution data for methionine-enkephalin-related glycoconjugates were analysed as a function of the identity and position of the sugar-peptide linkage. It was shown that binding to the column could be correlated with the degree of sugar moiety protection. Replacement of either the phenylalanine or methionine residue in the peptide backbone of the glycoconjugates with its D-enantiomer leads to a considerably stronger retention on a reversed-phase column. The dependence of retention times on the methanol concentration in the mobile phase suggested that, under the conditions studied, there are different retention mechanisms for glycopeptides containing unprotected sugar moieties in the molecule.

Amino Acid Sequence↗
PubMed1994

Acetylated glucopyranosyl esters of enkephalins.

Acetylated D-glucopyranosyl esters of enkephalins were prepared by two different fragment condensation procedures involving direct participation of imidazole in the ester linkage formation. By both methods anomeric mixtures of D-glucosyl esters were obtained and resolved by column chromatography. Depending on coupling conditions, racemization of either the C-terminal or the penultimate amino acid residue of the enkephalin molecule occurred. The glucoconjugates with inverted stereochemistry were quantitated and separated from the main product by reversed-phase high-performance liquid chromatography. The opioid agonist potencies of the synthesized glucopyranosyl esters of enkephalins on electrically stimulated guinea pig ileum and mouse vas deferens preparations were determined in comparison with [Leu5]enkephalin.

Acetylation↗
PubMed1993

Methionine-enkephalin related glycoconjugates. Synthesis and biological activity.

A series of glycoconjugates, in which [Met5]enkephalin or [D-Ala2,Met5]enkephalin have been linked through an ester bond to the HO-6 of various D-glycopyranose moieties, were synthesized by classical solution methods. The biological activities of these compounds were determined on selective pharmacological preparations: guinea pig ileum and mouse vas deferens for opioid activity, and two mouse cell lines, fibroblasts L929 and melanoma B16BL6, to study the influence on growth processes. The results reported in this study demonstrate the differential effect of the carbohydrate part in enkephalin-related glycoconjugates on receptor recognition. In addition, synthesized neo-glycopeptides stimulate growth of the examined mouse cell lines, whereas parent peptide demonstrated some growth inhibitory properties. Full growth curves showed a dose-dependent effect at concentrations of 10(-7) to 10(-10) M.

Amino Acid Sequence↗
PubMed1991

Effect of dopamine, L-dopa, carbidopa and L-dopa/carbidopa on arthus and delayed hypersensitivity skin reactions in the rat.

This study deals with the effects of dopamine (DA), L-dopa, carbidopa and L-dopa/carbidopa on immuno-inflammatory skin reactions in the rat. For this purpose, male Wistar rats immunized with bovine serum albumin in Freund's adjuvant were treated subcutaneously with different doses of DA, L-dopa, carbidopa and L-dopa/carbidopa, for a period of 14 consecutive days or 3 days before skin-testing with BSA. An additional group of rats received 1 injection of a dopamine-related drug 4 hours before and 1 injection 4 hours after skin-testing. Corresponding controls were treated with saline. Arthus and delayed hypersensitivity skin reactions were read at 4 and 24 hours respectively. The results showed that repeated injections of DA, L-dopa and L-dopa/carbidopa significantly suppressed Arthus and delayed reactions. The highest suppression was recorded in rats treated with L-dopa plus carbidopa. Concerning the dose required for immunosuppression it appears that DA was the most effective. Carbidopa did not affect hypersensitivity skin reactions. These results suggest the in vivo relationship between dopamine-related compounds (L-dopa and DA) and immuno-inflammatory reactions. Most probably, L-dopa when is given alone converts into DA and this increase of DA content in periphery depresses immune reactions. However, L-dopa given together with carbidopa (an enzyme which prevents decarboxylation of L-dopa into DA, and enables the penetration of L-dopa into CNS) augments the content of DA in the brain and thus affects immune responses. It appears, therefore, that L-dopa and DA act both peripherally and centrally on immune responsiveness.

Animals↗
PubMed1991

Brain-associated autoimmune features in heroin addicts: correlation to HIV infection and dementia.

We report here on brain associated autoimmune features in opiate-dependent subjects. This study includes 107 (37 HIV + and 70 HIV -) hospitalized heroin-addicted subjects on a methadone maintenance program, and 45 healthy individuals. Human brain S100 protein, neuron specific enolase (NSE), myelin basic protein (MBF), and old tuberculin (OT) were used as antigens in the study. Serum autoantibodies to brain antigens S100, NSE and MBP were detected by ELISA, whereas delayed hypersensitivity skin reactions were evaluated after intradermal injection of S100, NSE, MBP and OT (control brain-irrelevant antigen). In drug-dependent subjects, 68.2% produced anti-S100, 56.1% anti-NSE and 20.5% anti-MBP autoantibodies, while the incidence of autoantibodies in control healthy individuals was 4.4%, 2.2% and 0%, respectively. Occurrence and amount of anti-S100 and anti-NSE autoantibodies were much higher in HIV + than in HIV - heroin-abusing adults. In drug abusers, the incidence of positive delayed hypersensitivity skin reactions were as follows: 67.2% to S100, 51.4% to NSE, 14.9% to MBP, and 94.3% to OT. In control subjects, the occurrence of hypersensitivity reactions to brain antigens was insignificant. Cutaneous reactions were more frequent in HIV - addicts. The incidence of both autoantibodies and delayed skin responses was positively related to the duration of drug abuse, worsening of HIV infection, and dementia. The high incidence of autoantibodies and delayed hypersensitivity skin reactions to S100 and NSE human brain antigens in heroin-abusers indicates that heroin dependence, as well as HIV infection, are associated with a hyperergy towards brain-related autoimmune phenomena. It has been suggested that the brain-associated autoimmune phenomena in HIV + heroin-addicts represent a hyperimmune phase which precedes immunodeficiency that occurs in the further development of HIV infection.

Adult↗
PubMed1988

The validity of radiolabeled anti fibrin antibody for deep vein thrombosis imaging.

Having previously established the specificity of a newly developed radiolabeled polyclonal anti fibrin antibody (AFA) for tagging fibrin depositions, clinical experiments for validation of this agent for imaging deep vein thromboses (DVT) were carried out in comparison with labeled human serum albumin (HSA) and labeled platelets. Patients with DVT were studied with dual tracers on a computerized scintillation camera, four with simultaneous application of 131I-AFA and 99mTc-HSA, and eight with 131I-AFA and 111In-platelets. The results showed that: a) Labeled AFA predominantly delineated thrombi while labeled HSA prevailingly delineated blood pool within a particular vein. b) Labeled AFA was found to be superior in both ways to labeled platelets for DVT imaging, i.e. by imaging effect and by semiquantitative "thrombus:blood pool" (obtained in counts/pixel) ratio index (RI). Average RI with SD obtained with labeled AFA (9 patients) was 2.44 +/- 0.48 and 1.55 +/- 0.27 with labeled platelets (7 patients). The results indicate that a monoclonal AFA, if labeled with 99mTc, 111In or 123I, might have potential for an optimum agent for DVT imaging.

Adult↗
PubMed1988

Synthesis and biological activity of [Leu5]enkephalin derivatives containing D-glucose.

The synthesis of some [Leu5]enkephalin derivatives is described in which D-glucose has been linked to the opioid pentapeptide through the ester bond involving the carboxyl function at the C-terminal with C-1 or C-6 of the D-glucopyranose moiety. Enkephalin derivatives were assayed for opioid activity and found to be full agonists in bioassays based on inhibition of electrically evoked contractions of the guinea pig ileum (GPI) and of the mouse vas deferens (MVD). The obtained results suggest that the opioid activity of the tested glucoconjugates depend upon the ester bond position in the molecule. Whereas 1-O conjugate 5 was somewhat more potent than [Leu5]enkephalin in the GPI assay, the 6-O conjugates, with the exception of 1-O-benzyl derivative 11, were considerably less potent. All enkephalin derivatives were delta-receptor selective; in particular, the acetylated analog 8 was three times more delta-receptor selective than [Leu5]enkephalin.

Animals↗
PubMed1982

Delayed skin hypersensitivity reactions to human brain S-100 protein in psychiatric patients.

To confirm and extend previous observations concerning the correlation between cell-mediated immunity and psychiatric diseases, 511 patients with schizophrenia, cerebral atrophy, dementia, and mental retardation, and 32 control subjects and 27 control patients were skin-tested with human brain S-100 protein and human liver protein: 70.2-93.1% of tested psychiatric patients developed positive skin hypersensitivity reactions to S-100 protein, while 2.8-20.7% of patients reacted to liver protein. Of control subjects, 6.2-7.4% responded to S-100 protein, and 7.4-9.4% to liver protein. The findings indicate that cell-mediated immune processes may be involved in brain mechanisms underlying cerebral atrophy, depression, dementia, schizophrenia, and mental retardation.

Adolescent↗
PubMed1982

Hypersensitivity to human brain S-100 protein in chronic alcoholics.

We have studied hypersensitivity to neurotissue in alcoholics. Fifty-four male chronic alcoholics with signs of mental deterioration, and 30 age-matched healthy male subjects were skin tested with human S-100 brain protein and liver protein, and protein purified derivate of tuberculin (PPD). The local Arthus and delayed sensitivity reactions were read at 4 hr and 24-48 hr respectively. Alcoholics and non-alcoholics exhibited a similar capacity to develop Arthus and delayed hypersensitivity to PPD. However, of all patients, 98.1% developed positive Arthus and 96.3% delayed skin reactions to S-100 protein, whereas 27.7% developed Arthus and 43.3% delayed reactions to liver protein. In non-alcoholics, the frequency of hypersensitivity reactions to S-100 protein and liver protein was low. The very high incidence of Arthus and delayed hypersensitivity reactions to a brain antigen in chronic alcoholics suggests that both humoral and cell-mediated immunity are involved in the pathogenesis of alcohol-induced brain damage.

Adult↗
PubMed1980

Schizophrenia and other psychiatric diseases: evidence for neurotissue hypersensitivity.

Psychiatric patients (208 with cerebral atrophy, 46 with dementia, 82 with depression and 481 with schizophrenia) with control subjects (56 normal individuals and patients with neurosis) were skin-tested with human S-100 brain protein, soluble fraction from the brain and liver protein. The local Arthus and delayed hypersensitivity reactions were read at 4-6 hr and at 24 hr respectively. The great majority of tested psychiatric patients developed positive Arthus and delayed skin reactions to S-100 protein and soluble brain protein fraction. A small number of control subjects responded to those antigens. The results obtained suggest that there is a correlation between local cutaneous sensitivity to neurotissue antigens and psychiatric diseases, and that both humoral and cell-mediated immunity are involved in the pathogenesis and development of cerebral atrophy, dementia, depression and schizophrenia.

Adult↗
PubMed1977

Antigenic correlation between rat thymus and superior cervical ganglion.

By using rabbit anti-rat thymocyte and anti-rat superior cervical ganglion sera in cytotoxicity, immunofluorescence and absorption assays, it has been shown that surface membranes of rat thymocytes and cervical ganglion cells (i.e. peripheral nervous tissue cells) contain common antigenic determinants.

Animals↗