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Biomedical subjects

M Fridkin

Publications and source records attributed to M Fridkin.

At least 145 records · Page 8Linked to original sources
PubMed1989

Vasoactive intestinal peptide potentiates sexual behavior: inhibition by novel antagonist.

Vasoactive intestinal peptide (VIP) has been suggested as a neurotransmitter mediating penile erection. We now show that VIP can stimulate sexual behavior in rats with reduced masculine potential due to pituitary grafting or castration. This effect was attenuated in the presence of a novel VIP antagonist, devised by a hybrid peptide strategy. Thus, we have synthesized a molecule combining a portion of VIP with a portion of neurotensin, peptides of opposite pharmacological action on cAMP formation and smooth muscle relaxation. The hybrid peptide markedly inhibited VIP's effect on sexual behavior. This inhibition was manifested by a significant increase in the mean interval between copulatory events (greater than 3-fold change) coupled with a blockade of VIP-stimulated ejaculation. Other putative VIP antagonists were not as effective in blocking these activities. Thus, our results imply that VIP is not only associated with penile erection, but is involved in sexual behavior as well. Furthermore, the hybrid antagonist was shown to inhibit VIP binding in glial cell cultures. The availability of highly potent VIP antagonists may offer a route to study the possible multiple VIP receptors as well as help delineate other biological activities attributable to VIP.

Amino Acid Sequence↗
PubMed1989

Tuftsin: its chemistry, biology, and clinical potential.

Tuftsin is a tetrapeptide, Thr-Lys-Pro-Arg, which resides in the Fc-domain of the heavy chain of immunoglobulin G. The peptide originates from a specific fraction of the parent protein through enzymatic processing. Tuftsin possesses a broad spectrum of activities related primarily to the immune system function and exerts on phagocytic cells, notably on macrophages. These include potentiation of various cell functions such as phagocytosis, motility, immunogenic response, and bactericidal and tumoricidal activities. The features of tuftsin, coupled with its low toxicity, make the peptide an attractive candidate for immunotherapy. Tuftsin's capacity to augment cellular activation is mediated by specific receptors that were identified, characterized, and recently isolated from rabbit peritoneal granulocytes. Tuftsin has been chemically synthesized by a variety of techniques, some of which are adequate for large-scale preparations. A multitude of analogs have also been synthesized and extensively studied for structure-function relationships.

Adult↗
PubMed1989

Tuftsin stimulates IL-1 production by human mononuclear cells, human spleen cells and mouse spleen cells in vitro.

Human peripheral adherent cells from splenectomized subjects, human spleen cells and mouse spleen cells were tested for IL-1 production in vitro in presence or absence of synthetic tuftsin (Thr-Lys-Pro-Arg). Application of synthetic tuftsin to peripheral blood adherent cells from normal donors as well as from splenectomized subjects induces IL-1 production. In splenectomized subjects the extent of induction was more evident than in controls. In human splenic cells tuftsin stimulates IL-1 production without KLH or LPS. In mouse spleen cells tuftsin alone did not stimulate the IL-1 secretion. However, addition of tuftsin to mouse spleen cells incubated with KLH augmented significantly the IL-1 secretion. As removal of the spleen leads to tuftsin deficiency, our present findings may perhaps explain the fulminant nature of the postplenectomy sepsis and some immune disturbances described in the postplenectomy state.

Animals↗
PubMed1988

C-reactive protein decreases protein phosphorylation in stimulated human neutrophils.

Treatment of human neutrophils with C-reactive protein (CRP) causes a concentration-dependent in the extent of activation of superoxide production and of granule secretion, induced by phorbol-12-myristate-13-acetate (PMA) or N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLF). The same treatment also causes a significant reduction in the degree of PMA- and fMLF-stimulated phosphorylation of several cell proteins. These include the proteins of 43-47 kDa, whose extent of phosphorylation correlates with the activation of superoxide production and of secretion. Contrary to the effects exerted on protein phosphorylation, CRP does not affect the fMLF-elicited increase in neutrophil cytosolic Ca2+.

Blood Proteins↗
PubMed1988

Growth hormone releasing factor and somatostatin concentrations in the milk of lactating women.

The concentrations of growth hormone releasing factor (GRF) and somatostatin, two hypothalamic neuropeptides involved in the regulation of growth hormone secretion, were measured in human milk samples. The study was performed in healthy women within 48 h of delivery or during established lactation (between 1 and 64 weeks post delivery). No statistically significant correlation was found between the levels in milk of either of the neuropeptides and the gestational age at birth. However, lower values of GRF (23 +/- 4.7 pg/ml vs. 40.5 +/- 4.9 pg/ml) were found in milk obtained during established lactation than in milk obtained close to delivery. A positive correlation was observed between somatostatin and GRF concentrations in milk. The possible involvement of milk neuropeptides in the control of growth hormone secretion in the neonate, as well as in the regulation of other physiological processes, are evaluated.

Adolescent↗
PubMed1988

Antigen-tuftsin conjugate signals interleukin-1 synthesis and secretion.

The immunoglobulin heavy chain derived tetrapeptide, tuftsin (Thr-Lys-Pro-Arg), known for its phagocytosis-stimulating activity, was found to augment the antigen-presenting capacity of macrophages in culture, when applied simultaneously with antigen. Injection of antigens or antigens admixed with tuftsin had no immunogenic effect in vivo. On the other hand, antigen-tuftsin covalent conjugates, injected in aqueous solution intramuscularly or intravenously, significantly augmented antibody production. Studying the mechanism underlying these immunogenic effects, we demonstrate that tuftsin, when applied to macrophages together with, or conjugated to, antigens, signals de novo synthesis of mRNA encoding for interleukin-1 (IL-1), and induces secretion of IL-1 from the cells. We suggest that triggering the immunogenic processes by tuftsin conjugates is a consequence of up-regulation of IL-1 synthesis and secretion.

Animals↗
PubMed1987

Modulation of human neutrophil function by C-reactive protein.

Investigation of the effect of C-reactive protein (CRP), an acute-phase reactant, on the functional capacities of human neutrophils was carried out as the basis for elucidating the biological function of C-reactive protein. An initial stimulation at low concentrations, followed by inhibition of superoxide production, and secretion of vitamin-B12-binding protein in the presence of two stimulants, phorbol myristate acetate and concanavalin A, and of neutrophil chemotaxis with increasing concentration of CRP was observed. Correlation between modulation of cell function, at least at relatively high CRP concentrations (greater than 50 micrograms/ml) and an increase in the intracellular level of cAMP is suggested. CRP was also found to enhance neutrophil phagocytosis of particles not containing phosphorylcholine, the native CRP ligand. The proposed role of CRP in neutrophil function is one of regulation and as a negative feedback for potential cytotoxic neutrophil functions.

Bacterial Outer Membrane Proteins↗
PubMed1987

Binding of C-reactive protein to human neutrophils.

The binding of radiolabelled 125I-CRP to human neutrophils has been characterised according to pH, temperature and time dependence. The binding of 125I-CRP was saturable, very fast (less than 2 min at 22 C), and the labelled protein was displaced by unlabelled CRP and aggregated human IgG. The dissociation constant was 3.2 X 10(-8) M at pH 7.4, 22 degrees C and 8.8 X 10(-8) M at pH 6.0, 22 degrees C. The calculated number of binding sites was 5-20 X 10(4) per cell at pH 7.4, 22 degrees C. An association with an Fc-type receptor is suggested, since aggregated IgG was able to displace specifically CRP.

Binding, Competitive↗
PubMed1987

Synthesis of modified tuftsins containing monosaccharides or monosaccharide derivatives.

Synthesis of some modified tuftsins is described in which a monosaccharide or a monosaccharide derivative was incorporated in the molecule. Acylation of H-Thr-Lys(Z)-Pro-Arg(NO2)-OBzl with D(+)-gluco-1,5-lactone followed by catalytic hydrogenation gave N alpha-gluconyl-tuftsin. Glycosylation of the carboxyl function of the C-terminal arginine has been achieved by reacting, through the mixed anhydride procedure, Boc-Thr-Lys(Z)-Pro-OH with 2-deoxy-2-(NG-nitroargininamido)-D-glucopyranose followed by catalytic hydrogenation and trifluoroacetic acid treatment. O-Glucosyl-tuftsin has been prepared by reacting o-nitrophenyl N-benzyloxycarbonyl-O-[(alpha + beta) 2,3,4,6-tetra-O-benzyl-D-glucopyranosyl]-threoninate with H-Lys(Z)-Pro-Arg(NO2)-OBzl in the presence of 1-hydroxybenzotriazole. Flash chromatography on silica gel allowed a partial separation of the diastereoisomers, one of which has been isolated in a reasonable yield. The single diastereoisomer and the alpha + beta anomeric mixture were separately deblocked by catalytic hydrogenation and purified by RP-HPLC.

Carbohydrates↗
PubMed1987

Synthesis and biological activity of tuftsin and rigin derivatives containing monosaccharides or monosaccharide derivatives.

Synthesis of some modified rigins is described in which either D-gluconic acid or 2-amino-2-deoxy-beta-D-glucopyranose have been linked to the parent molecule through amide bonds involving the alpha-amino function, alpha-carboxyl function or the gamma-amide function of glutamine in position 2. Glu2-rigin and D-gluconyl-Glu2-rigin have also been synthesized. Binding and phagocytosis assays have been carried out on the rigin derivatives and on some glycosylated tuftsin derivatives as well. Of all the tested peptides only rigin enhanced the phagocytic capacity of mouse peritoneal macrophages to the same extent as tuftsin. The peptides H-Thr-Lys-Pro-Arg-NH-Glc and N alpha-gluconyl-Gly-Glu-Pro-Arg-OH slightly enhanced phagocytosis. H-Thr[(alpha + beta)-O-glucosyl]-Lys-Pro-Arg-OH was found to displace 3H-tuftsin even better than tuftsin but lacked the ability to stimulate phagocytosis.

Animals↗
PubMed1987

Tuftsin and tuftsin conjugates potentiate immunogenic processes: effects and possible mechanisms.

The immunoglobulin heavy chain associated tetrapeptide, tuftsin (Thr-Lys-Pro-Arg), known for its phagocytosis-stimulating activity was found to augment the antigen presenting capacity of macrophages in culture when applied simultaneously with the antigen. To study the immunogenic effect of tuftsin in vivo the peptide was coupled covalently to keyhole limpet hemocyanin (KLH) and bovine serum albumin (BSA) antigens to form stable entities. Tuftsin-antigen conjugates were found to be very potent immunogens as tested by their capacity to increase antigen presentation in culture in primary and secondary responses. Thus, monolayers of macrophages pulsed in vitro with KLH-tuftsin conjugates exerted a stronger immunogenic effect than KLH alone. BSA, which by itself was not immunogenic, when applied to macrophages as tuftsin conjugate evoked a high lymphoproliferative immune response. In vivo, BSA conjugated to tuftsin, when injected in aqueous solutions, augmented significantly antibody production, whereas administration of BSA alone or BSA admixed with tuftsin had no immunogenic effect. Studies conducted to elucidate the mechanisms underlying the activation of the immunogenic function of macrophages by the peptide revealed that treatment of cells with antigen and tuftsin increases secretion of interleukin-1 and expression of cell surface Ia encoded antigens. The effect of tuftsin on increasing the immunogenic capacity of antigens may at least partly be attributed to these effects.

Adjuvants, Immunologic↗
PubMed1986

Growth hormone releasing factor-like immunoreactivity in human milk.

The presence of immunoreactive growth hormone-releasing factor (GRF) in human milk has been demonstrated. By using sequential high performance liquid chromatography, it has been shown that most of the immunoreactivity co-elutes with the synthetic, hypothalamic-like, GRF (1-40). The concentrations of GRF detected (between 152 and 432 pg GRF/ml milk) exceed several fold its values in plasma.

Chromatography, High Pressure Liquid↗
PubMed1986

Mapping of the cAMP-dependent phosphorylation sites on the acetylcholine receptor.

We have synthesized a tetradecapeptide corresponding to residues 354-367 of the delta-subunit of Torpedo acetylcholine receptor. This peptide contains the sequence Arg-Arg-Ser-Ser which has been proposed as the site for phosphorylation of the acetylcholine receptor (AChR) by an endogenous cAMP-dependent protein kinase. We have shown that the synthetic peptide can be phosphorylated by the catalytic subunit of bovine heart cAMP-dependent protein kinase. Antibodies elicited against peptide 354-367 were shown to cross-react with native AChR and to bind specifically to the delta- and gamma-subunit as detected by immunoblotting. Furthermore, antipeptide antibodies were shown to inhibit specifically the cAMP-dependent phosphorylation of both the delta- and gamma-subunits. This suggests that the phosphorylation sites in the delta- and gamma-subunits are highly cross-reactive, and is in agreement with the demonstration that an endogenous cAMP-dependent kinase phosphorylates these two subunits, probably on homologous sequences. Tryptic digestion of the delta-subunit isolated from phosphorylated AChR yields a single 25-kd phosphorylated fragment. Immunoblotting experiments allowed us to map peptide 354-367 within this phosphorylated fragment.

Amino Acid Sequence↗
PubMed1986

Structure and expression of the vasoactive intestinal peptide (VIP) gene in a human tumor.

To identify the VIP biosynthetic pathways, we have isolated the human VIP gene, using synthetic oligodeoxynucleotides. These specific hybridization probes were constructed according to the neuroblastoma VIP-cDNA sequence and contained up to 39 bases. The gene structure was deduced by direct chemical nucleotide sequencing. Six exons were thus far discovered; among them two short exons, one encoding VIP and the second encoding PHM-27 (a peptide having a N-terminal histidine and C-terminal methionine amide, closely related in sequence and activity to VIP). As a model system for VIP gene expression, we used a human buccal tumor producing elevated amounts of VIP. In these cells, a major transcript of the VIP-gene was identified as a long RNA containing intron sequences. The occurrence of elevated quantities of a high molecular weight, intron containing, gene transcript which is not processed directly into mature RNA suggests that VIP gene expression may be regulated at the RNA processing level.

Base Sequence↗
PubMed1986

Tuftsin analogues: synthesis, structure-function relationships, and implications for specificity of tuftsin's bioactivity.

Thirteen analogues of the natural macrophage activator peptide tuftsin, ten of which are novel, were synthesized with the aim of exploring the relation between their biological potency and their capacity to attach specifically to cellular tuftsin's receptors. The analogues representing modifications and chain extensions at various parts of the parent tuftsin molecule can be classified as N-terminal analogues, C-terminal analogues, "within-chain" derivatives, or dimers of tuftsin and retrotuftsin. The various synthetic routes employed to prepare the analogues are described. A direct correlation was found between the ability of analogues to inhibit [3H-Arg4]tuftsin specific binding to mice peritoneal macrophages and their capacity to enhance phagocytosis or to inhibit tuftsin-mediated phagocytosis by the cells and to potentiate the cell's immune response.

Animals↗
PubMed1986

Analysis of ligand binding to the synthetic dodecapeptide 185-196 of the acetylcholine receptor alpha subunit.

A synthetic dodecapeptide corresponding to residues 185-196 of the Torpedo acetylcholine receptor alpha subunit, which contains the adjacent cysteine residues at positions 192 and 193, was recently shown by us to contain the essential elements for alpha-bungarotoxin binding. In the present study, we have used Sepharose-linked peptides for quantitative analysis of the cholinergic binding properties of this and other synthetic peptides. Sepharose-linked peptides corresponding to residues 1-20, 126-143, 143-158, 169-181, 185-196, 193-210, and 394-409 of the alpha subunit of Torpedo acetylcholine receptor, as well as a peptide corresponding to residues 185-196 of the alpha subunit of human acetylcholine receptor, were tested for their toxin-binding capacity. Of these immobilized peptides, only peptide 185-196 of the Torpedo acetylcholine receptor bound toxin significantly, thus verifying that this synthetic peptide contains essential components of the receptor toxin-binding site. Analysis of toxin binding to the peptide yielded a dissociation constant of 3.5 X 10(-5) M. This binding was inhibited by various cholinergic ligands. The inhibition potency obtained was alpha-bungarotoxin greater than Naja naja siamensis toxin greater than d-tubocurarine greater than decamethonium greater than acetylcholine greater than carbamoylcholine. This pharmacological profile resembles that of the nicotinic acetylcholine receptor and therefore suggests that the synthetic dodecapeptide also includes the neurotransmitter binding site. Reduction and carboxymethylation of the cysteine residues on peptide 185-196 inhibit its capacity to bind toxin, demonstrating that an intact disulfide is required for toxin binding. A decrease in toxin binding was also obtained following chemical modification of the tryptophan residue at position 187, thus implying its possible involvement in toxin binding. The failure to detect binding of toxin to the corresponding human sequence 185-196, in which the tryptophan residue is replaced by serine, supports this hypothesis.

Binding Sites↗
PubMed1986

Peptides related to the calcium binding domains II and III of calmodulin. Synthesis and calmodulin-like features.

Three hexadecapeptides which correspond to the putative Ca2+ binding domains II and III of calmodulin were synthesized employing solid phase methodology. One of the peptides contained an internal cystine bridge which was formed while the corresponding linear peptide was still attached to the polymeric carrier. The interaction of the synthetic peptides with calcium ions was investigated using Tb3+-mediated fluorescence. Binding was of the order Ca12 greater than Ca13 greater than Ca13C (Fig. 1) with binding constants KTb3+ = 0.68 X 10(-5), 0.54 X 10(-5), and 0.21 X 10(-5) M-1 respectively. Biological activity of the compounds was assessed by measuring their stimulatory effect on erythrocyte membrane (Ca2+ + Mg2+)-ATPase activity. For 50% activity as compared with CaM, the concentration of peptides required was for Ca12, Ca13 and Ca13C, 50, 100 and 167 times higher than CaM, respectively. The results suggest that the three synthetic peptides possess certain calmodulin-like features.

Binding Sites↗